Title of Invention

TENSIONER

Abstract

A tensioner capable of stably suppressing amplitude even for a strong input vibration load from an engine, the suppression being made over a wide range of engine speed both in advancing operation and retreating operation. A first shaft member (3) and a second shaft member (4) screwed to each other by screw portions (8, 9) and a return spring (5) for rotatingly urging the first shaft member (3) in one direction are received in a case (2). The second shaft member (4) is restrained from rotation, and a rotation urging force by the return spring (5) is converted into a propulsive force of the second shaft member (4). A resisting torque applying mechanism (20) is placed between the first shaft member (3) and the second shaft member (4), and the mechanism constantly produces, both in advancing operation and retreating operation, resisting torque against an external input load inputted in the second shaft member (4), finely and stably suppressing the amplitude of the second shaft member (4).

Full Text

FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See section 10, Rule 13] TENSIONER; NHK SPRING CO., LTD., A CORPORATION ORGANIZED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 10, FUKUURA 3-CHOME, KANAZAWA-KU, YOKOHAMA-SHl, KANAGAWA 236-0004, JAPAN. THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED. 1 TENSIONER Field of the Invention The present invention relates to a tensioner that adjusts and maintains at a constant level the tension of an endless belt or a chain. Background Art of the Invention A tensioner applies pressure of a predetermined level on a timing chain or timing belt (that is used, for example, for an automobile engine), and if the timing chain or timing belt becomes loose or slack, serves to maintain at a constant level the tension of the timing chain or timing belt. Figure 25 is a layout diagram that shows the condition when a tensioner 100 is mounted on an engine block 200 of an automobile. Inside the engine block 200, there are arranged two cam sprockets 210, 210 and a crank sprocket 220, and an endless timing chain 230 encircles the cam sprockets 210, 210 and the crank sprocket 220. The timing chain 230 freely moves on the chain guide 240. An installing face 250 on which the tensioner is to be mounted is formed on the engine block 200, and the tensioner 100 is fastened onto the installing face 250 by bolts 270 that penetrate an installing hole 260 in the installing face 250. Also, the engine block 200 contains lubricating oil (not shown). Figure 26 is a vertical cross-sectional view of a conventional tensioner, and Figure 27 is a dynamic-model diagram that shows how a conventional tensioner maintains a balance between the operative forces. Because the conventional tensioner 100 shown in Figure 26 is already known publicly, a 2 detailed explanation of it will be omitted here. A case 110 accommodates a rotating shaft 120 and a drive shaft 130, which are screwed together by a male screw portion 121 and a female screw portion 131, and a torsion spring 150 that presses the rotating shaft 120 clockwise or counterclockwise, thereby causing it to rotate. The rotation and pressure of the torsion spring 150 is converted into a driving force that moves the drive shaft 130, and rotation of the drive shaft 130 is restrained as described below. A flange 112 of the case 110 is attached to the installing face 250 of the engine block 200 by bolts 270, as shown in Figure 25. In a tensioner 100 that has the above-mentioned structure, both (1) the drive shaft 130, which penetrates a planar bearing 160 that is fixed at a top end in Figure 25 of the case 110 under the condition that the planar bearing 160 is prevented from rotating, and (2) a through-hole 161 in the bearing 160 are formed so as to have noncircular cross-sections, so that the drive shaft 130 is restrained from rotating against the case 110. As a result, the rotating shaft 120 rotates due to the pressure of the torsion spring 150, and this rotation of the rotation shaft 120 is converted into a force that drives forward the drive shaft 130, as a result of which the drive shaft 130 moves forward. Therefore, as shown in Figure 25 and 26, the drive shaft 130 presses the timing chain 230 via a cap 180 and the chain guide 240, so that the drive shaft 130 gives tension to the timing chain 230. Now the function of the tensioner 100 and how it balances the operative forces will be explained with reference to the dynamic-model diagram of Figure 27. A load W that results from the vibration of the engine 200 is transmitted to the drive shaft 130. However, as a reaction force to the load, a balance arises between (1) the spring force K of the torsion spring 150 and (2) the sliding-face friction-resistance M both on the faces of (a) the screws 121, 131 and (b) the bottom faces the rotating shaft 120. When the load is static, the friction coefficient μ. on the sliding faces is large (M = W x μ), and as a result the 3 drive shaft 130 does not perform either a protruding action or a returning action. However, when the received load W, which is caused by the vibration of the engine 200, is transmitted to the drive shaft 130, the friction coefficient \i of the sliding faces decreases due to said friction coefficient's change from static friction to dynamic friction. Thus, the drive shaft 130 moves backwards (downward in Figure 27), the rotating shaft 120 moves (to the right in Figure 27), and the torsion spring 150 is compressed. All these actions take place sequentially but almost simultaneously. Therefore, the drive shaft 130 finally returns to a position where the forces balance each other. Recently, engine performance of both two-wheeled and four-wheeled vehicles has advanced greatly, and the sizes of engines, inside of which the vibration of a cam-chain system is great, are increasing. In an engine that has much vibration, the load W that the tensioner 100 receives via the chain guide 240, as shown in Figure 25, also tends to be large. The received load W is a vibration load that usually varies according to the vibration of an engine, but it also varies according to the protrusion-margin length A (i.e., the length A of the margin of the drive shaft 130's protruding movement) of the drive shaft 130 (see Figures 26 and 27). Figure 28 is a diagram that shows the characteristics of a received load of a tensioner in relation to the rpm (rpm) of a certain engine. In a conventional engine, vibrational load from the engine is generally small, and, as shown by L in Figure 28, the received load W tends not to vary significantly as the rpm changes. However, in a high-performance engine of the type that has been developed recently, the received load W tends to vary significantly as rpm changes, as shown by H in Figure 28. In Figure 28, the upper and lower lines of L and H show the minimum and maximum values, respectively, of the received load W, and the distance between the upper and lower L and H lines shows their respective amplitude. In general, the amplitude of the received load W tends to increase as an engine's rpm increases. However, at the midpoint of the increase, there is a temporary 4 peak in the amplitude. This is regarded as a unique point where resonance and the like take place, as a result of the matching of the inherent vibration frequency of a cam-chain system, including the tensioner, and the engine's rpm. A tensioner's functions must satisfy at least the following two requirements, in a balanced manner, in relation to the cam-chain system, including when the rpm, or the vibration, of the engine is large. (1) Provide optimum chain tension (i.e., ensure that the drive shaft does not protrude too much [too much chain tension] or return too far backward [insufficient chain tension]). (2) Stabilize the chain (i.e., the amplitude between the aforementioned protruding and returning should be small). It is basically desirable that such a tensioner will function as will now be described. When receiving a vibration load from the chain guide 240, the tensioner should cause the drive shaft to return (move backward) when the vibration is large and should cause the drive shaft to protrude (move forward) when the vibration is small. The tensioner should also maintain an optimum protrusion-margin length, so that the tensioner will ensure optimum chain tension. Figure 29 is a diagram that shows the relationship between the received-vibration load W and the friction coefficient u. on the aforementioned sliding faces in a conventional tensioner (as shown in Figures 26 and 27). As the received-vibration load W increases, the friction coefficient u tends to decrease. When the received-vibration load W exceeds a certain limit, the upper face, which normally slides on the lower face, rises and thus loses contact with the lower face, and the friction coefficient u. suddenly decreases, as a result of which the tension condition becomes unstable. Now, the area Q2, where the friction coefficient ji becomes unstable, will be explained with reference to the dynamic model diagram of Figure 27. The sliding-face friction-resistance M approaches 0, and then the 5 received-vibration load W of the input vibration balances with only the spring force K; therefore, the amplitude b of the drive shaft rapidly increases and then the vibration of the drive shaft might diverge. At this time, the protrusion-margin length A of the drive shaft also becomes unsteady and cannot be determined. Under such a circumstance, the tensioner 100 cannot give proper tension to the chain system, resulting in insufficient performance of the tensioner 100. Therefore, when a conventional tensioner 100 is used for an engine that has a high level of vibration, it is necessary that the chain guide 240 be pressed strongly, so that the pressure (amplitude b) of the drive shaft 130 — against the vibration load from the chain guide 240 — is restrained, and so that the operation of the chain guide 240 is stabilized. For this purpose, the following measures are taken: (1) the spring torque of the torsion spring 150 is made large, (2) the screw lead angles of both the male screw portion 121 and the female screw portion 131 — which screw the rotation shaft 120 and the drive shaft 130 together — is made small (for example, 12° is reduced to 9°), and (3) the diameter of the bottom end face of the rotating shaft 120 is made large, so that the contact radius between the rotating shaft 120 and the swivel plate 140 (or the case 110) (see Figure 26) is made large. However, with the above-mentioned structure there is a strong tendency that the drive shaft 130 will move forward. If the drive shaft 130 moves forward more than is required, excessive tension is applied to the chain system and the friction between the chain guide 240 and the chain 230 increases, which undesirably causes the engine to suffer a large loss of output. To cope with the above problems, there is a structure, which has been disclosed recently, wherein (1) a friction plate is installed onto the aforementioned case, (2) a jaw-like friction-face whose surface-contact diameter is large is provided at the place of the rotating shaft that is opposite the position of the friction plate, and (3) the rotating shaft's 6 friction-face is restrained by an auxiliary spring in such a way that the friction-face does not contact the friction plate. With this structure, when the external load applied from the chain guide is small, the friction-face does not contact the friction plate, but when the external input load exceeds a specified value, the friction-face contacts the friction plate, thereby generating a frictional force. Thus, the above-mentioned structures (1) to (3) are not necessary, the engine's output loss can be reduced, and the amplitude of the drive shaft that is cause by the large external input load can also be restrained. (Patent Document 1: Japanese Unexamined Published Patent Application No. 2001-21012) Disclosure of the Invention Problem to be Solved by the Invention As described above, the amplitude of a drive shaft can be. restrained by the structure disclosed in Japanese Unexamined Published Patent Application No. 2001-21012. However, for some types of engines, such as present-day high-performance engines, there is a strong demand for a tensioner that places emphasis on restraining the amplitude of the drive shaft, that is, restraining the protruding and returning movements. The present invention has been made to meet such a requirement. One object of the present invention is to provide a tensioner that can stably restrain the amplitude — over a wide range of revolution speeds of an engine — against a strong input vibration load from the engine, both at the time of a protruding movement and at the time of a returning movement. Means of Solving the Problem For the purpose of achieving the above-mentioned object, the tensioner of the invention 7 described in Claim 1 is a tensioner that: (1) has a structure such that (a) first and second shaft members, which are fastened to each other by screw parts, and a torsion spring, which presses the first shaft member clockwise or counterclockwise, thereby causing it to rotate, are accommodated in a case, and (b) the second shaft member is restrained from rotating so that the rotation and pressure of the tensioner's torsion spring is converted into a force that drives the second shaft, and (2) is characterized such that a resistance-torque-applying mechanism, which always gives reciprocating resistance torque in both the forward and backward directions of the second shaft member, is arranged between said first shaft member and said second shaft member. According to the invention of Claim 1, the resistance-torque-applying mechanism, which is arranged between the first shaft member and the second shaft member, always applies resistance torque in both directions, with the second shaft member moving forward and backward in response to an external input load due to the vibration of the engine. Therefore, the resistance torque generates a damping effect, so that the forward and backward amplitude of the second shaft member can be restrained at a low level. Thus, even when the external input load is large, it is not necessary for the driving force of the second shaft member to be made large by making the spring torque of the torsion spring large or by making the screw lead angle of the screw portions small. As a result, the friction between the chain guide and the chain does not become large, and therefore the loss of engine output can be limited to a low level. This can simultaneously solve the following problems: loss of horsepower due to excessive tension of the tensioner, and insufficient tension of the chain due to over-returning of the second shaft member. The invention of Claim 2 is a tensioner as set forth in Claim 1, but wherein 8 (1) said resistance-torque-applying mechanism comprises (a) at least one third shaft member, which is screwed using the screw portion of said first shaft member, and (b) a first elastic member, which is provided between (i) either said second shaft member or said first shaft member and (ii) the third shaft member; and (2) said third shaft member is restrained — together with the second shaft member — from rotating, but is movable in its axial direction. According to the invention of Claim 2, the third shaft member 21, in addition to having the characteristics of the invention of Claim 1, is a kind of so-called floating screw member that does not directly contact the second shaft member and directly contacts only the first elastic member. That is to say, the third shaft member of the resistance-torque-applying mechanism indirectly contacts either the second-shaft member or the first shaft member via the first elastic member. Therefore, the external input load is not directly received by the third shaft member; only the axial force (compression force) due to the first elastic member acts on the third shaft member. Therefore, the friction coefficient of the screw portion of the resistance-torque-applying mechanism, including the third shaft member, does not decrease due to the magnitude of the external input load. Regardless of the magnitude of the external input load, the resistance-torque-applying mechanism always applies resistance torque so as to control the amplitude of the second shaft member, and therefore that amplitude can be stably restrained. Because the screw portion of the third shaft member is always pressed against the screw portion of either the first shaft member or the second shaft member due to the compression load of the first elastic member, the resistance torque is always applied effectively in a reciprocating manner in the forward and backward directions at the time of the protruding and returning operations, respectively. Here, a simple structure — in which only an elastic member, comprising a compression spring, is provided between the first shaft member and the second shaft member — can be possible. 9 However, such a structure has the following problem. Although at the time of the returning operation, said elastic member generates an effective resistance torque between the first shaft member and the second shaft member, at the time of the protruding operation the screw faces of the second shaft member rises from the screw faces of the first shaft member because of the compression force of said elastic member (in this case, the frictional coefficient of the screw face becomes almost 0, and, as a result, the resistance torque due to friction is not necessarily generated in an effective manner. In contrast, according to the present invention, the resistance-torque-applying mechanism, having said third shaft member and the first elastic member, always generates effective resistance torque, not only at the time of a returning operation but also at the time of a protruding operation, as described above. Therefore, the above-mentioned problem can be eliminated. In addition, when the first elastic member is provided between the first shaft member and the third shaft member, the second shaft member and the third shaft member move forward and backward together. Thus, the length of the first elastic member set between the first shaft member and the third shaft member changes, and therefore, the axial load Z due to the first elastic member also changes. At this time, if the difference between the spring torque of the torsion spring and the resistance torque added by the resistance-torque-applying mechanism — which comprises the first elastic member, the third shaft member, and the like — are set to be the same, the driving force (pressure) of the second shaft member can be made constant. As a result, problems such as over-protruding/over-returning of the tensioner, and subsequent abrasion, the loss of engine horsepower, and the like can be prevented over both a wide range of engine-revolution speeds and a wide range of engine-vibration levels, so that both a stable damping effect and durability of the second shaft member can be secured. The invention of Claim 3 is a tensioner as set forth in Claim 1, but wherein (1) said resistance-torque-applying mechanism comprises at least one third shaft 10 member, which is screwed into the screw portion of said second shaft member, and a first elastic member, which is provided between said first shaft member and said third shaft member, and (2) said third shaft member is restrained from rotating against said first shaft member, but is movable in said third shaft member's axial direction. According to the invention of Claim 3, the third shaft member of the resistance-torque-applying mechanism, in addition to having the characteristics of the invention of Claim 1, is indirectly connected with the first shaft member via the first elastic member, and therefore the external input load is not directly received by the third shaft member. Regardless of the magnitude of the external input load, the resistance-torque-applying mechanism always applies the resistance torque so as to control the amplitude of the second shaft member, and therefore said amplitude can be stably restrained. The invention of Claim 4 is a tensioner as set forth in Claim 1, but wherein (1) said resistance-torque-applying mechanism comprises at least (a) one third shaft member, which is screwed with the screw portion of said first shaft member, (b) a first elastic member, which is provided between said first shaft member and said third shaft member, and (c) a second elastic member, which is provided between said first shaft member and said third shaft member, and (2) said third shaft member is restrained — together with the second shaft member — from rotating, but is movable in its axial direction. The invention of Claim 4, in addition to having the characteristics of the invention of Claim 1 or Claim 2, is constituted such that when an external load is input to the second shaft member, the load acts on the second elastic member that is arranged between the first shaft member and the third shaft member. As a result, the second elastic member generates 11 resistance torque against the external input load, and therefore the amplitude of the second shaft member can be reduced even further than aforementioned tensioners. Furthermore, according to the invention of Claim 4, because the second elastic member is arranged between the first shaft member and the third shaft member, when the external load is input, the third shaft member and the first shaft member constantly generate resistance torque due to friction. Accordingly, regardless of the magnitude of the external input load, resistance torque is generated to effectively control the amplitude of the second shaft member, and therefore the amplitude can be finely and stably restrained. The invention of Claim 5 is a tensioner as set forth in any one of Claims 2, 3, or 4, but wherein said first elastic member is a coil spring that (1) is arranged — while it is compressed — between either the second shaft member or the first shaft member and the third shaft member, and (2) generates — independently from any external input load — continuous resistance torque between the first and second shaft members and the third shaft member. According to the invention of Claim 5, the first elastic member is a coil spring, and said coil spring is compressed by (a) either the second shaft member or the first shaft member, and (b) the third shaft member, and it does not directly receive any external input load. Therefore, the amplitude of the second shaft member can be finely and stably restrained, similar to the invention of Claims 2, 3, or 4. Also, by adjusting the axial load of the coil spring, the resistance torque can be increased or decreased and set to an optimum value. An invention of Claim 6 is a tensioner as set forth in Claim 4, but wherein said second elastic member is a coil spring that (1) is arranged — under a compressed condition — between said first shaft member and said third shaft member, and 12 (2), by being compressed by the external input load, generates resistance torque between the first shaft member and the third shaft member. According to the invention of Claim 6, in addition to having the characteristics of the invention of Claim 4, the second elastic member is a coil spring. The coil spring is compressed by the first shaft member and the third shaft member, and a compression force acts due to the external load input to the second shaft member, as a result of which the coil spring is compressed. By this compression, an additional resistance torque due to friction is added between the first shaft member and the third shaft member, and the resistance torque of the entire tensioner increases, and thus rotation of the first shaft member is effectively restrained. That is to say, by receiving the external input load, the second shaft member is pushed inside the case, and therefore the first shaft member rotates in the direction opposite to the direction of the rotation and pressing of the torsion spring. A braking force due to the friction force of the second elastic member — namely the coil spring — acts against this reverse rotation of the first shaft member. Therefore, the amplitude of the second shaft member's forward and backward movements is effectively restrained. In this manner, according to the invention of Claim 6, because the second elastic member, namely the coil spring, is arranged between the first shaft member and the third shaft member, the coil spring always generates resistance torque due to fiction against the first shaft member and the third shaft member. When an external load is input, the coil spring is further compressed so as to strongly restrain the rotation of the first shaft member, and thus the amplitude-restraining effect against the second shaft member is enhanced. The invention of Claim 7 is a tensioner as set forth in any of Claims 2 through 6, but wherein said first and second elastic members are either compression springs, disc springs, rubber moldings, or resin moldings. 13 According to the invention of Claim 7, a disc spring, a rubber molding, or a resin molding is used as the first or second elastic member. Accordingly, in addition to having characteristics similar to those of the inventions of Claims 2 through 6, when, for example, a plate-winding spring is adopted as a torsion spring and disc springs are adopted as first and second elastic members, the tensioner can be reduced in size and made lighter in weight, because the plate-winding spring and disc springs are all compact. The invention of Claim 8 is a tensioner as set forth in any of Claims 1, 2, or 4, but wherein said second shaft member has a tubular member that (1) is connected with a main member, namely a base end that is screwed into the screw portion of the first shaft member, (2) restrains the third shaft member from rotating, but (3) makes the third shaft member movable in said shaft member's axial direction. According to the invention of Claim 8, which has characteristics similar to those of the invention of Claim 1, 2, or 4, the amplitude of the second shaft member can be finely and stably restrained regardless of the magnitude of the external input load. In addition, a separate tubular member, which restrains the direction of rotation of the third shaft member but makes the third shaft member movable in its axial direction, is connected with the main member of the second shaft member, and thus more flexibility is possible in manufacturing and designing a tensioner. The invention of Claim 9 is a tensioner as set forth in any of Claims 1 through 4, but wherein the relationship Tmz According to the invention of Claim 9, in addition to having the characteristics of the 14 inventions of Claims 1 through 4, because the spring torque Tb of the torsion spring is set larger than the resistance torque Tmz that the resistance-torque-applying mechanism applies to the first shaft member, the forward and backward movement of the second shaft member can correspond to the first shaft member favorably, and stable amplitude-restraining operation of the second shaft member can be secured. An invention of Claim 10 is a tensioner as set forth in any one of Claims 1 through 8, but wherein the fluid pressure from a fluid-pressure source is made to act in the direction in which said second shaft member moves. According to the invention of Claim 10, in addition to having characteristics similar to those of the inventions of Claims 1 through 8, because the fluid pressure from a fluid-pressure source is applied in the direction in which said second shaft member moves, a damping effect due to the viscosity resistance of the fluid is added against the operations of the first, second, and third shaft members. Thus, the amplitude of the second shaft member can be restrained even more stably. In addition, because said fluid also serves as a lubricant for these shaft members, said torsion spring, and various elastic members, smooth operation of the tensioner is possible, and abrasion of these shaft members, said torsion spring, and various elastic members is reduced, improving their durability. Effects of the Invention According to the invention of Claim 1, a resistance-torque-applying mechanism applies resistance torque, and thus always produces a damping effect in both of the directions to which a second shaft member moves (forward and backward — reciprocating movements) under an external input load. Thus, the forward and backward amplitude of the second 15 shaft member can be made small. As a result, the following problems can be simultaneously solved: horsepower loss due to over-tensioning of a tensioner; and inefficient chain tension due to over-returning. The invention of Claim 2, in addition to having effects similar to those of the invention of Claim 1, is constituted such that the third shaft member of the resistance-torque-applying mechanism does not directly receive the external input load. As a result, regardless of the magnitude of the external input load, the resistance-torque-applying mechanism always applies resistance torque both at the time of the returning operation and at the time of the protruding operation, so that the amplitude of the second shaft member is controlled. Thus, the amplitude can be stably restrained. Also, when a first elastic member is provided between the first shaft member and the third shaft member, the second shaft member and the third shaft member move forward and backward together, and therefore, the set length — namely the axial force — of the first elastic member changes accordingly. Thus, the following characteristics can be obtained: the difference between (a) the spring torque of the torsion spring and (b) the resistance torque applied by the resistance-torque-applying mechanism — namely the driving force (pressure) of the second shaft [the difference between (a) and (b)] — becomes constant. As a result, over-returning of the tensioner, and subsequent abrasion, loss of engine horsepower, and the like are prevented over a wide range of engine-revolution speeds and over a wide range of engine-vibration levels. Thus, stable damping effect and durability of the second shaft member can be secured. According to the invention of Claim 3, in addition to having effects similar to those of the invention of Claim 1, because the third shaft member of the resistance-torque-applying mechanism is indirectly connected with — via the first elastic member —the first shaft member, the external input load is not directly received by the third shaft member. Thus, 16 regardless of the magnitude of the external input load, the resistance-torque-applying mechanism always applies resistance torque and controls the amplitude of the second shaft member, and the amplitude of that member can be stably restrained. According to the invention of Claim 4, in addition to having effects similar to those of the invention of Claim 1 or Claim 2, because a second elastic member — which receives the external input load via the second shaft member — also generates resistance torque against the first shaft member and the third shaft member, the amplitude of the second shaft member is restrained more effectively, and said amplitude can be finely and stably restrained. According to the invention of Claim 5, the coil spring — which is a first elastic member, and which is compressed by (a) either the second shaft member or the first shaft member and (b) the third shaft member — does not directly receive the external input load, and thus the amplitude of the second shaft member can be finely and stably restrained, in a way similar to that of the invention of Claim 2, Claim 3, or Claim 4. Also, by adjusting the axial load of the coil spring, the resistance torque can be increased or decreased and set to an optimum value. The invention of Claim 6, in addition to having effects similar to those of the invention of Claim 4, is constituted such that the second elastic member (namely a coil spring) is compressed by the first shaft member and the second shaft member when the external load is input onto the second shaft member. Thus, the resistance torque due to friction is added in an overlapping manner between the first shaft member and the third shaft member. Therefore, the resistance torque of the entire tensioner increases, and the rotation of the first shaft member is strongly restrained. Therefore, the effect of restraining the amplitude of the second shaft member can be enhanced. 17 According to the invention of Claim 7, a disc spring, a rubber molding, or a resin molding is used as a first or second elastic member. In addition to having characteristics similar to those of the inventions of Claims 2 through 6, when, for example, a plate winding spring is adopted as a torsion spring and disc springs and the like are adopted as the first and second elastic members, flexibility in manufacturing and designing the tensioner — such as reducing the size and weight of the tensioner — can be obtained, because these springs are all compact. The invention of Claim 8, in addition to having effects similar to those of the invention of Claim 1, Claim 2, or Claim 4, is constituted such that separate tubular member — that restrains rotation of the third shaft member, and that enables the third shaft member to move in its axial direction — is connected with the main member of the second shaft member, and thus flexibility in manufacturing and designing the tensioner is enhanced. According to the invention of Claim 9, in addition to having effects similar to the inventions of Claims 1 through 4, because the spring torque Tb of the torsion spring is set higher than the resistance torque Tmz against the first shaft member of the re si stance-torque-applying mechanism, the forward and backward movement of the second shaft member is good, and stable restraint of the amplitude of the second shaft member can be secured. According to the invention of Claim 10, in addition to having effects similar to those of the inventions of Claims 1 through 8, because a damping effect and a lubricating effect — due to the viscosity resistance of a fluid (from a fluid-pressure source) having viscosity, such as a hydraulic oil — are added against the operations of the first shaft member, the second shaft member, and the third shaft member, the effect of stably restraining the amplitude of the second shaft member can be further enhanced, and abrasion of these various members is reduced, improving their durability. 18 Brief Descriptions of the Drawings Figure 1 is a vertical cross-sectional view that shows the tensioner in Embodiment 1 of the present invention. Figure 2 is a cross-sectional view taken along the line F-F of Figure 1. Figure 3 is a partial vertical cross-sectional view that shows the action of the resistance-torque-applying mechanism in Embodiment 1. Figure 4 is a partial cross-sectional, oblique-perspective view that shows the action of the resistance-torque-applying mechanism in Embodiment 1. Figure 5 is a diagram that presents test data comparing the behavior of tensioners with or without the resistance-torque-applying mechanism described in Embodiment 1. Figure 6 is a vertical cross-sectional view that shows the tensioner in Embodiment 2. Figure 7 is a vertical cross-sectional view that shows the tubular member in Embodiment 2. Figure 8 is a plan view of Figure 7. Figure 9 is a vertical cross-sectional view that shows the second shaft member in Embodiment 2. Figure 10 is a plan view of Figure 9. Figure 11 is a vertical cross-sectional view that shows the third shaft member in Embodiment 2. Figure 12 is a plan view of Figure 11. Figure 13 is a vertical cross-sectional view that shows the tensioner according to a modification of Embodiment 2. Figure 14 is a plan view of Figure 13. Figure 15 is a vertical cross-sectional view that shows the tensioner in Embodiment 3. Figure 16 is a cross-sectional view taken along the line H-H of Figure 15. Figure 17 is a vertical cross-sectional view that shows a connecting member in 19 Embodiment 3. Figure 18 is a plan view of Figure 17. Figure 19 is a vertical cross-sectional view that shows a tensioner according to a modification of Embodiment 3. Figure 20 is a vertical cross-sectional view that shows a tensioner according to another modification of Embodiment 3. Figure 21 is a diagram that shows the dynamic characteristics of a tensioner according to another modification of Embodiment 3. Figure 22 is a vertical cross-sectional view that shows the tensioner in Embodiment 4. Figure 23 is a vertical cross-sectional view that shows the tensioner in Embodiment 5. Figure 24 is a vertical cross-sectional view that shows the tensioner in Embodiment 6. Figure 25 is a layout diagram that shows the condition when a tensioner is mounted on an engine block. Figure 26 is a vertical cross-sectional view that shows a conventional tensioner. Figure 27 is a dynamic-model diagram that shows how a conventional tensioner balances the operative forces. Figure 28 is a diagram that shows one example of the received-load characteristics of a tensioner, according to the rpm of a certain engine. Figure 29 is a diagram that shows certain relationships — in a conventional tensioner — between the received-vibration load W and the friction coefficient \x of a sliding face. Figure 30 is a partial cross-sectional view that shows the action of a conventional tensioner. Figure 31 is another diagram that presents test data comparing the behavior of the present invention and that of a conventional tensioner. Figure 32 is another diagram that presents test data comparing the behavior of the present invention and that of a conventional tensioner. 20 Explanations of Numbers and Letters Used in the Drawings 2 Case 2a Shell 2al Shell 2a2 Shell 2b Flange 2bl Flange 2b2 Flange 2c Accommodation hole 2c 1 Accommodation hole 2c2 Accommodation hole 2d Installing hole 2e Jig hole 2f Hook groove 2g Notch groove 2h Bottom face 3 First shaft member 3a Shaft 3b Screw portion 3c Flange 3d Small-diameter portion 3e Slit 3f Top face 3h Top face 3j Top face 4 Second shaft member 4a Base end 21 4b Tubular portion 4f Bottom face 5 Torsion spring 5a Hooking portion 5b Hooking portion 6 Bearing 6a Slide hole 6b Engaging piece 7 Spacer 7a Top end 7b Base end 8 Male screws 8a Female screws 9 Female screws 9a Male screws 10 Cap 10c Elastic member 13 Cover ring 19 Swivel plate 20 Resistance-torque-applying mechanism 21 Third shaft member 21a Top face 21b Bottom face 21c Female screws 21d Parallel cut portion 21e Small-diameter portion 21f Lock groove 22 Coil spring or Disc springs or First elastic member 22 22a Top end 22b Base end 40 Main member 40a Upper face (of large-diameter jaw-like-shaped base-end) 40b Upper face 40c Outer face 40d Parallel cut portion 41 Tubular member 50 Connecting member 51 Base end 52 Shells 52a Hook portion 53 Through-hole 55 Connecting member 56 Top end 56a Ceiling face 57 Shell 60 Coil spring 60a Top end 60b Other end 71 Fluid 72 Flow path 73 Fluid circulation port 74 Fluid-circulation port 75 Fluid-circulation port 76 Blind plug 80 Arrow 100 Tensioner 23 110 Case 112 Flange 120 Rotating shaft 121 Male screw portion 130 Drive shaft 131 Female screw portion 140 Swivel plate 150 Torsion spring 160 Bearing B161 Through-hole 180 Cap 200 Engine 210 Cam sprocket 220 Crank sprocket 230 Timing chain 240 Chain guide 250 Installing face 260 Installing hole 270 Bolt Al Tensioner A2 Tensioner A3 Tensioner A4 Tensioner A5 Tensioner A6 Tensioner W Load Z Axial load Tb Torque Tmz Resistance torque 3i Inside diameter of base-end side shaft 3a 4c Inner face of the base end 4a of the second shaft member 4 4e Unknown, but in Figure 1 (and perhaps other figures) 10a Head part of cap 10b Leg of cap 11 Spring pin 57a Indentation part of shell 57 70 Fluid source A Protrusion-margin length A b Amplitude (forward and backward) of second shaft member 4 b' Amplitude (forward and backward) of conventional tensioner K Spring force of torsion spring H Maximum vibration load L Minimum vibration load M Friction resistance of sliding face Ql Area where the friction coefficient u. is stable Q2 Area where the friction coefficient \i is unstable μ Friction coefficient Best Mode for Carrying Out the Invention Some embodiments of the present invention will now be described in detail. For each embodiment, the same number is used for members that have partially different shapes but that perform the same function. In order to stably restrain the amplitude of a tensioner, which is caused by a strong 25 vibration load input from an engine, a tensioner is constituted by adding a minimum number of parts thereto, in such a way that there is no problem in terms of space for arrangement of the tensioner. Embodiment 1 Figure 1 is a vertical cross-sectional view that shows the tensioner Al in Embodiment 1 of the present invention, and Figure 2 is a cross-sectional view taken along the line F-F of Figure 1. The tensioner Al comprises a case 2, a first shaft member 3, a second shaft member 4, a torsion spring 5, a bearing 6, a spacer 7, and a resistance-torque-applying mechanism 20. The case 2 is formed into a bottomed cylinder having a flange 2b at the middle part of a shell 2a. Inside the shell 2a, an accommodation hole 2c is formed so as to extend toward the top end in Figure 1 of the case in its axial direction (driving direction). The top of the accommodation hole 2c is open, and an assembly consisting of the first and second shaft members 3, 4, the torsion spring 5, the spacer 7 and a resistance-torque-applying mechanism 20 is accommodated therein. Flanges 2b of the case 2 are used to attach said tensioner Al to the engine block. Installing holes 2d, through which bolts (not shown) are screwed to the engine block, are formed in the flanges 2b. When the Tensioner Al is attached to the engine block, the top faces of the flanges 2b contact the installing face 250 of the engine block 200, as is similar to a conventional tensioner 100 shown in Figure 25. A first shaft member 3 is pressed and rotated by a torsion spring 5 (described below), and it is restrained from rotating by a bearing 6 (described below) that is installed onto the case 2. A second shaft member 4 that is movable in its axial direction moves forward from the case 2 due to the rotation of the first shaft member 3. 26 A shaft 3a on the base of the first shaft member 3, and a screw portion 3b on the top side (in the upper part in Figure 1) of the first shaft member 3 are integrally formed in the axial direction of the case 2, and male screws 8 are placed on the outer periphery of the screw portion 3b on the top side of the first shaft member 3. Also, the top of the shaft 3a contacts a swivel plate 19 that is installed in the case 2, so that the rotation of the shaft is supported. A slit 3e, into which is inserted the top of a fastening jig (not shown) that is used for rotating the first shaft member 3, is formed on the base face of the shaft 3a. The slit 3e is connected to a jig hole 2e that is formed on the base face of the shell 2a of the case 2. The top of the fastening jig is inserted in the slit 3e from the jig hole 2e, and the first shaft member 3 is rotated through the slit 3e, making it possible for the torsion spring 5, which is described later, to be wound. The second shaft member 4 is formed with a tubular portion 4b that is open at its axial top end (in the upper part in Figure 1), and female screws 9, which are fastened using male screws 8 of the first shaft member 3, are placed on the inner face of the base end 4a of the second shaft member 4. These shaft members 3 and 4 are inserted into the accommodation hole 2c of the case 2, under the condition that the male screws 8 and the female screws 9 are fastened to each other. A cap 10 is attached to the top of the tubular part 4b of the second shaft member 4. The cap 10 comprises a head portion 10a and a leg 10b. A spring pin 11 is pressure-fitted into the head portion 10a and the leg 10b, under the condition such that the head part 10a covers the top of the tubular part 4b of the second shaft member 4, and such that the leg 10b is engaged with the top of the tubular part 4b. Thus, the cap 10 is affixed to the tubular part 4b and is prevented from coming off. The torsion spring 5 is installed on the shaft 3a of the first shaft member 3. A hooking portion 5a on one end (top end in Figure 1) of the torsion spring 5 is inserted into and fastened to a hook groove 2f that is formed on the case 2, while a hooking portion 5b on 27 the other end (base end) of the torsion spring 5 is inserted into and fastened to the slit 3e that is formed on the base-end face (bottom) of the first shaft member 3. Accordingly, by winding the torsion spring 5 so as to generate torque, the first shaft member 3 can be rotated. The bearing 6 is attached to the top portion of the case 2, and fixed by a cover ring 13. The bearing 6 has a slide hole 6a that the second shaft member 4 penetrates. The inner face of the slide hole 6a of the bearing 6 and the outer face of the second shaft member 4 are both formed — in their respective cross-sections — into corresponding approximately oval shapes, D-like cuts, parallel cuts, or other noncircular shapes, thereby restraining the rotation of the second shaft member 4. The bearing 6 is formed so as to have a flat, plate-like shape of a specified thickness, and, for example, a plurality of engaging pieces 6b are formed on the outer peripheral side of the bearing 6, as is similar to a conventional tensioner. When the engaging pieces 6b are engaged with notch grooves 2g that are formed at the top of the case 2, rotation of the bearing 6 is stopped completely. Because the rotation of the bearing 6 against the case 2 is stopped, the second shaft member 4 that penetrates the bearing 6 is also prevented — via the bearing 6 — from rotating against the case 2. The first shaft member 3 is screwed into the second shaft member 4 via female screws 9 and male screws 8, and the rotation force of the first shaft member 3 that rotates due to the rotation and pressure of the torsion spring 5 is transmitted to the second shaft member 4. However, because the second shaft member 4 is restrained from rotating by the bearing 6, the second shaft member 4 receives a driving force and moves forward and backward in its axial direction against the case 2. The spacer 7 is formed into a tubular shape, and screw portions of the first shaft member 3 28 and the second shaft member 4 are inserted into said tubular part. In this case, a large-diameter flange 3c is formed at the boundary between the shaft 3a on the base-end side of the first shaft member 3 and the screw portion 3b of the first shaft member 3; the base end 7b of the spacer 7 is brought into contact with the flange 3c. The top end 7a of the spacer 7 is adjacent to the bottom face of the bearing 6, and said top end 7a is brought into contact with the bearing 6, so that the first and second shaft members 3 and 4 are prevented from coming off the case 2. In addition, in Embodiment 1, there is provided a resistance-torque-applying mechanism 20 that applies an approximately constant resistance torque to the screw portion 3b of the first shaft member 3. The resistance-torque-applying mechanism 20 comprises (1) a third shaft member 21 that is screwed into the screw portion 3b of the first shaft member 3, and (2) a coil spring 22 that functions as a first elastic member that is installed between the third shaft member 21 and the second shaft member 4. The third shaft member 21 is arranged inside a tubular part 4b that is closer to the top-end side than to the base end 4a of the second shaft member 4, where the female screw 9 of the second shaft member 4 is formed. Furthermore, the coil spring 22 is arranged between (1) the bottom face 21b of the third shaft member 21 in the tubular portion 4b, and (2) the inner face 4c of the base end 4a of the second shaft member 4. A compression spring, both of whose ends are free ends, is used as the coil spring 22, which is (1) brought into contact with the bottom face 21b of the third shaft member 21 on its top end 22a, and (2) brought into contact with the inner face 4c of the base end 4a of the second shaft member 4 on its base end 22b. Such a coil spring 22 is incorporated into the tubular portion 4b under the condition that (1) the two ends 22a and 22b of the coil spring 22 contact the shaft members 21 and 4, respectively, and (2) the coil spring 22 is compressed to a certain extent. As a result, the second shaft member 4 and the third shaft 29 member 21 are always pressed against the male screws 8 of the screw portion 3b of the first shaft member 3 in opposite axial directions (the upper and lower directions in Figure 1) by the compression force of the coil spring 22. For the purpose of preventing entanglement of the coil spring 22 with the screw portion 3b of the first shaft member 3, it is desirable that the winding direction of the coil spring 22 be opposite to the torsion direction of the thread of the screw portion 3b. As shown in Figure 2, the third shaft member 21 is (1) formed into a hexagonal shape, (2) is engaged with the inner face of the tubular portion 4b, whose cross-section also has a hexagonal shape, of the second shaft member 4, (3) is restrained from rotating, but (4) can move in its axial direction. In this case, the cross-sectional shapes of both (a) the inner face of the tubular portion 4b of the second shaft member 4 and (b) the outer face of the third shaft member 21 should be formed in approximately oval shapes, or as D-like cuts, parallel cuts, or other noncircular shapes, so that the inner face of the tubular part 4b and the outer face of the third shaft member 21 fit each other. The third shaft member 21 is (1) screwed into the screw portion 3b of the first shaft member 3, (2) fits with the inner face of the tubular portion 4b, whose cross-sectional shape is noncircular, of the second shaft member 4, (2) is restrained from rotating, but (4) can move in its axial direction. Figure 3 is a partial vertical cross-sectional view that shows the action of the resistance-torque-applying mechanism 20 of the tensioner Al. In the third shaft member 21 that has the above-mentioned structure, female screws 21c, which are formed onto the inside surface of said third shaft member 21, are screwed to the male screws 8 of the screw portion 3b of the first shaft member 3, which rotates in a forward or reverse direction so as to balance the following forces: (1) the external load (received load) input from the engine, (2) the friction resistance (described below) against 30 the first shaft member 3, and (3) the spring force of the torsion spring 5 — under the tight contact condition that the female screws 21c is always pressed in the axial direction of said third shaft member 21 by the compression force (axial load) Z of the coil spring 22. In this way, while the first shaft member 3 rotates in said force-balancing direction, the third shaft member 21 is restrained from rotating and receives a driving force, so that said third shaft member 21 moves forward and backward in its axial direction integrally with the second shaft member 4 and the coil spring 22, always being under the condition that said third shaft member 21 is tightly screwed by the screw portion 3b of the first shaft member 3. Thus, the third shaft member 21 does not directly contact the second shaft member except for the coil spring 22 portion thereof; therefore the third shaft member 21 is a type of so-called floating screw member. That is to say, the axial-positional relationship between the third shaft member 21 and the second shaft member 4 (namely, the set length of the coil spring 22) is maintained constant. At the same time, the third shaft member 21 gives approximately constant resistance torque — which is due to friction — against the rotation of the first shaft member 3, irrespective of whether said rotation is in the forward or reverse rotation. At this time, the external load (received load) input from the engine directly acts — in the axial direction — on the first shaft member 3 that is screwed into the second shaft member 4, but does not directly act on the resistance-torque-applying mechanism 20, including the third shaft member 21. Therefore, the friction coefficient ja of the screw part of the resistance-torque-applying mechanism 20 is not reduced even if the magnitude of the external input load (received load) increases or decreases. As will be described below, this means that the resistance-torque-applying mechanism 20 can give approximately constant resistance torque to the rotation of the first shaft member 3, irrespective of whether that rotation is forward or reverse rotation, and even when the input vibration load from the engine is high. This is a very important point in achieving the object of the present invention, which is to restrain stably the amplitude of a timing chain or timing belt over a wide range of engine rpm. 31 Accordingly, when the load from the engine for pushing the second shaft member 4 is input, the axial force (1) directly acts on the first shaft member 3 that is screwed into the second shaft member 4, and (2) rotates the first shaft member 3. As the first shaft member 3 rotates, the resistance-torque-applying mechanism 20, including the third shaft member 21, and the second shaft member 4 move integrally in their axial direction. During these actions, resistance torque Tmz is generated between (a) the third shaft member 21 and the second shaft member 4, and (b) the first shaft member 3. That is to say, resistance torque Tmz — which is generated due to the compression force (axial load) Z of the coil spring 22 between the third shaft member 21, the second shaft member 4, and the first shaft member 3 — is further added to the friction torque that is generated between the drive shaft 130 and the rotating shaft 120 of said conventional tensioner 100, resulting in an increase of the total resistance torque that presses against the first shaft member 3. As a result, a strong braking force acts against the first shaft member 3, so that rotation of the first shaft member 3 is effectively restrained. Also, the axial load Z of the coil spring 22 is adjusted, so that the resistance torque Tmz can be increased or decreased. As a result, the resistance torque Tmz can be set to an optimum value. The value of the resistance torque Tmz varies slightly according to the vibration load, received from the engine, which acts on the second shaft member 4. According to the structure of Embodiment 1, the following value is generally observed when no load is applied. Tmz « 2»Z«μ»r That is to say, Tmz almost equals 2«Z»μ*r. In said formula, |i is the fiction coefficient of a screw face, and r is the effective radius of the screw portion 3b. The reason that the right side of the above formula is multiplied by the numeral "2" is that there are two friction-faces, into which the third shaft member 21 32 and the second shaft member 4 — which are pressed by the coil spring 22 against the screw portion 3b of the first shaft member 3 — are screwed, as shown in Figure 3. Figure 4 is a partial cross-sectional view that shows the action of the resistance-torque-applying mechanism 20 in Embodiment 1 (Al). Here, the action will be explained in comparison with that of a conventional tensioner 100 shown in Figures 26 and 27. Figure 30 is a partial cross-sectional view that shows the action of the conventional tensioner 100. In Figure 30, the numerals that are used to illustrate Embodiment 1 (Al) of the present invention are also used to illustrate the conventional tensioner 100. As shown in Figures 4 and 30, the rotation and pressure, comprising the torque Tb, of the torsion spring 5, act on the first shaft member 3. When the received-vibration load W from the engine, namely an external load, is input via a chain guide, the second shaft member 4 is pressed into the case 2, and thus the first shaft member 3 rotates in its axial direction against the rotation and pressure (torque Tb) of the torsion spring 5. A conventional tensioner 100, which lacks the resistance-torque-applying mechanism 20, slightly reciprocates (swings or oscillates) and rotates in forward and reverse axial directions due to the rotation torque corresponding to the input of the received-vibration load W, as shown in Figure 30. At this time, the rotation angle of the first shaft member 3 is 0, and the amplitude — corresponding to the angle 0 — of the second shaft member 4 is b. Vibrations from the engine are transmitted sequentially in the following sequence: to the chain guide (see the chain guide 240 in Figure 25), to the cap 10 (see Figure 1) (the received-vibration load W is input), to the second shaft member (drive shaft) 4, to the first shaft member (rotating shaft) 3, to the swivel plate 19, and to the case 2. As resistance elements against the above load, forces balance between (1) the resistance torque due to friction of the screw portion 3b of the first shaft member 3 with the swivel plate 19, and (2) 33 the spring torque Tb of the torsion spring 5. As a result, the first shaft member 3 moves forward and backward at a swing-rotation angle 0, and the second shaft member 4 moves forward and backward at the amplitude b. At this time, the friction coefficient (dynamic-friction coefficient) on the sliding faces of the screw portion 3b and the swivel plate 19 is lower than that under a static condition (static-friction coefficient). When the vibrations from the engine increase (for example, when the received-vibration loads becomes 2W or more, and then 4W or more, and so on), the friction coefficient declines further. At the same time, when the vibrations exceed a certain limit, the fiction coefficient of said sliding faces approaches 0. Under such a condition, as shown in Figure 30, the amplitude of the second shaft member 4 significantly increases (to 2b, then to 4b, and finally the vibration of the second shaft member 4 should be dispersed.), and the protrusion-margin length (the length A of the margin of the drive shaft's protruding movement) becomes very unstable. In contrast, in Embodiment 1 (Al) of the present invention, as shown in Figure 4, the resistance-torque-applying mechanism 20 is arranged between the first shaft member 3 and the second shaft member 4. As the resistance-torque-applying mechanism 20, the second shaft member 4 and the third shaft member 21 are pressed against the faces (upper and lower faces) of the male screws 8 of the screw portion 3b of the first shaft member 3 by the coil spring 22,' and the received-vibration load from the engine hardly acts directly on the third shaft member 21. The axial load Z is always applied between the second shaft member 4 and the third shaft member 21 by the coil spring 22. To rotate the first shaft member 3, a rotation force larger than the resistance torque Tmz is required (see Figure 3). As a result, the resistance torque Tmz always (continuously) serves to brake against both the normal forward and reverse reciprocating and rotating movements of the first shaft member 3, and, as a result, the reciprocating and rotating angle 0' of the first shaft member 3 becomes smaller than the reciprocating and rotating angle 9 of said conventional 34 tensioner. In addition, the forward and backward amplitude b' (see Figure 4) of the second shaft member 4 also becomes smaller than the forward and backward amplitude b (see Figure 30) of the conventional tensioner. Even when the vibrations from the engine become large (received-vibration loads: 2W or more, 4W or more, and so on), the received-vibration load hardly acts directly on the resistance-torque-applying mechanism 20, and therefore the friction coefficient against the first shaft member 3 does not lower and stays almost constant. Thus, as shown in Figure 4, the amplitude (2b' or more, 4b' or more, and so on) of the second shaft member 4 does not significantly increase like the forward and backward amplitude (2b, 4b, and dispersion) of said conventional tensioner. As a result, the protrusion-margin length (the length A of the margin of the drive shaft's protruding movement) of the second shaft member remains very stable; that is to say, the forward and backward amplitude is stably restrained. Figure 5 is a diagram that presents test data comparing the behavior of two types of tensioners (the present tensioner and a conventional one) that include and do not include, respectively, a resistance-torque-applying mechanism. In Figure 5, the horizontal axis shows the frequency (Hz) of various engine rpm, and the vertical axis shows the protrusion-margin length A of the second shaft member (drive shaft). Also in Figure 5, the dense black circles show data for the tensioner A1, which includes the resistance-torque-applying mechanism 20 according to the present invention, and the dispersed white circles show data for the conventional tensioner 100. In the conventional tensioner 100, as is obvious from Figure 5, the range (amplitude) between the maximum value and the minimum value of the protrusion-margin length A is large in a high-frequency band of the engine — namely, in a high-speed-rotation area, which is an area where the vibrations of the engine are large — thereby showing unstable behavior. In contrast, in the case of the tensioner Al of the present invention, the protrusion-margin 35 length A and the range (amplitude) between the maximum value and the minimum value are almost constant, even when the engine's rpm and the subsequent vibrations of the engine are large, arid both the maximum value and the amplitude of the protrusion-margin length A also show smaller values than with the conventional tensioner. This proves that the resistance-torque-applying mechanism 20 restrains the amplitude very effectively and stably. Figures 31 and 32 are diagrams that present test data comparing the behavior of the present and conventional tensioners when they are attached to a high-performance engine that vibrates greatly. Figure 31 shows the maximum value Amax of the protrusion-margin length A according to the rpm of the engine; Figure 32 shows the dynamic characteristic of a received load (external input load) W according to the rpm of the engine. In Figure 31, a conventional tensioner shows the oscillation characteristic where the value Amax is relatively large and varies significantly; a tensioner according to the present invention shows the oscillation characteristic where the value Amax is relatively small and almost constant, with little variation. In Figure 32, the dense black circles in the lower portion show the data for a tensioner according to the present invention, and the dispersed white circles in the upper portion show the data for a conventional tensioner. As is obvious from Figure 32, in a conventional tensioner, the range (amplitude) between the maximum value and the minimum value of the received load W is large in a high-frequency band — namely, when the engine is rotating at a high rpm and the vibrations of the engine are large — and thus, the conventional tensioner shows unstable behavior. In contrast, in the tensioner of the present invention, the received load W and the range (amplitude) between the maximum value and the minimum value are almost constant, even in the area where both the range of rpm and the range of engine vibrations are wide, and 36 both the maximum value and the amplitude of the received load W also are smaller than those of the conventional tensioner. This, too, is because the resistance-torque-applying mechanism 20 restrains the amplitude very effectively and stably. In said Embodiment 1 (Al), the resistance-torque-applying mechanism 20 is arranged between the first shaft member 3 and the second shaft member 4. Thus, the resistance-torque-applying mechanism 20 — under almost no influence from the external input load (received load) W, and in both forward and backward directions of the second shaft member 4 — always applies resistance torque to the first shaft member 3. Accordingly, regardless of the magnitude of the external input load W, the amplitude of the second shaft member 4 can be restrained finely and stably. Moreover, regardless of the magnitude of the external input load (received load) W, the resistance torque also acts in the forward (protruding) direction of the second shaft member 4, and thus the resistance-torque-applying mechanism 20 can restrain the amplitude in the forward (protruding) direction. Due to these effects, a tensioner according to the present invention can suitably vary according to the vibrations of the engine, and it can cope with a wide range of modern high-performance engines that vibrate greatly. Also, unlike a conventional tensioner 100, even when the external input load W is large, there is no need to increase the spring torque of the torsion spring 5 so as to restrain the amplitude of the second shaft member 4, or to decrease the lead angle of the screws (8, 9) so as to increase the driving force of the second shaft member 4. Therefore, friction between the chain guide and the chain does not become excessive, and thus the engine's loss of output can be restrained at a low level. Embodiment 2 Figure 6 is a vertical cross-sectional view of the tensioner A2 in Embodiment 2 of the present invention. In Embodiment 2 (A2), the tubular part 4b is separated from the base 37 end 4a of the second shaft member 4 of Embodiment 1 (Al) so as to form a separate tubular member 41, although other features are identical to those in Embodiment 1 (Al). That is to say, the second shaft member 4 in Embodiment 2 (A2) is constituted so as to have a main member 40, which corresponds to the base end 4a of the second shaft member 4 in Embodiment 1, and a tubular member 41 [Embodiment 2 (A2) that corresponds to the invention of Claim 8]. Figure 7 is a vertical cross-sectional view that shows the tubular member 41, and Figure 8 is a plan view thereof. As shown in Figure 8, the tubular member 41 is molded into a noncircular shape having parallel cut parts 41c, 41 d on both its inner face and outer face. The inner and outer faces of the tubular member 41 can be molded into approximately oval shapes, D-cut shapes, or other noncircular shapes. This is because the inner face of the tubular member 41 is meant to restrain the rotation of a third shaft member 21 (described below), whose outer face is similarly molded into a noncircular shape, and to guide the member movably in its axial direction. In addition, the outer face of the tubular member 41 is to be restrained from rotating against the inner face of the slide hole 6a — which is similarly molded into a noncircular shape — of the bearing 6, and is to be guided movably in the axial direction. Also, a cap 10 is engaged with, and attached to, the top end 41b of the tubular member 41. Two through-holes 41e — into which spring pins (not shown) are pressure-fitted — are formed at the top end 41b so as to be opposite each other (see Figures 6 and 7). Figure 9 is a vertical cross-sectional view that shows the main member 40, and Figure 10 is a plan view thereof. The main member 40 is formed into a circular jaw-like shape having a stepped jaw portion. Female screws 9 —- into which male screws 8 of the first shaft member 3 are screwed — 38 are formed on the inner face of the main member 40. The first and second shaft members 3, 4 and a shaft member 21 (described below) are inserted in accommodation holes 2c of the case 2, under the condition that the female screws 9 and 21c, respectively, are engaged with male screws 8 in a similar manner to that in Embodiment 1, as shown in Figure 6. In the main member 40, a small-diameter stepped portion (upper face 40b) is formed so as to be opposite the upper face 40a of the large-diameter jaw-like-shaped base-end. As shown in Figure 10, the outer face 40c of the small-diameter stepped portion is molded into a noncircular shape, having, for example, a parallel cut portion 40d, so that the outer face 40c can be fitted to the inner face of the base end 41a of the tubular member 41. The base ends 41a of the tubular member 41 are connected and fitted — by caulking, so that the base ends 41a cannot come off— with both the base-end upper face 41a and the small-diameter stepped-portion outer face 40c, in order to constitute a second shaft member 4 (see Figure 6). Furthermore, a small-diameter part 40e is formed to be opposite the upper face 40b of the small-diameter stepped portion. The base end 22b of the coil spring 22 is placed on both the upper face 40b and the small-diameter portion 40e. In this manner, in Embodiment 2 (A2), because the second shaft member 4 is individually connected with the tubular member 41 and the main member 40, the manufacture, assembly, or disassembly of the tensioner can be facilitated, and flexibility in manufacturing and designing is enhanced. Figure 11 is a vertical cross-sectional view that shows a third shaft member 21, and Figure 12 is a plan view thereof. The third shaft member 21 is formed into a circular jaw-like shape. Female screws 21c — 39 into which the male screws 8 of the first shaft member 3 is screwed — are formed in the inner face of the third shaft member 21. As shown in Figure 12, the outer faces (top face 21a, bottom face 21b) (see Figure 11) of the jaw portion are molded into a noncircular shape having, for example, a parallel cut portion 21d, in order to be fitted with the inner face of the tubular member 41. The third shaft member 21 is screwed into the screw portion 3b of the first shaft member 3, and is fitted to the inner face of the tubular part 41 — which is molded into a noncircular shape — of the second shaft member 4, so that the third shaft member 21 is restrained from rotating but is movable in its axial direction. Furthermore, a small-diameter portion 21e is formed so as to be opposite the jaw portion bottom face 21b. The top end 22a of the coil spring 22 is placed on both the bottom face 21b and the small-diameter portion 21e. As is similar to Embodiment 1, a first elastic member, namely the coil spring 22, is compressed and arranged between the second shaft member 3 and the third shaft member 21. Also, it is similarly desirable that the winding direction of the coil spring 22 be opposite to the torsion direction of the thread of the screw portion 3b of the first shaft member 3, so as to prevent entanglement of the coil spring 22 with the screw portion 3b of the first shaft member 3. Furthermore, for the purpose of restraining radial-direction movement of the coil spring 22, both ends 22b, 22a of the coil spring 22 are placed, respectively, on the small-diameter stepped-portion top face 40b and the small-diameter portion 40e, and the jaw-portion bottom face 21b and the small-diameter portion 21e, all four of which (40b, 40e, 21b, and 21e) serve as bearing surfaces for both the main member 40 and the coil spring 22 of the third shaft member 21. It is also possible that the outside diameter of the coil spring 22 is made close to that of the inner face of the tubular member 41 or that of the parallel-cut portion 4 Id, so as to prevent the aforementioned entanglement 40 (see Figures 6, 9, 11, and 12). Figure 13 is a vertical cross-sectional view that shows a tensioner A2a according to a modification of Embodiment 2 (A2), and Figure 14 is a plan view thereof. In the embodiment of Figure 13 (A2a), although the constituent members are slightly different in shape to those of the embodiment (A2) in Figure 6, their functions and constitutions are essentially similar to them. For example, the case 2 is molded into an approximately conical shape such that the corner of the shell 2a is rounded, and the flange 2b is also molded into such a shape that the periphery of the installing holes 2d are made slim. The flange 3c of the first shaft member 3 is formed so as to have a stepped small-diameter portion 3d at its top portion, and the base end 7b of the spacer 7 is stably fitted into the small-diameter portion 3d. Also, the torsion spring 5 covers the outer face of the spacer 7 in such a way that the torsion spring 5 covers the proximity area of the top end 7a, and the hooking portion 5a is inserted in and hooked to the hook groove 2f that is formed adjacent to the bottom face of the bearing 6 at the top end of the case 2. Therefore, the torsion spring 5 is guided by the outer face of the spacer 7 so that the torsion spring 5 can be prevented from displacement in the radial direction and can be maintained in a stable condition. Also, because the attachment length of the torsion spring 5 can be long, the winding number of the spring can be made large, so that the protruding stroke of the second shaft member 4 can be made long as well. A more important point is that the rate of change of the spring torque Tb in relation to the protruding stroke can be set to be gradual. As a result, a stable damping operation can be secured. 41 The bearing 6 is formed into a cap-like shape such that the slide hole 6a is enlarged toward the top -end face of the case 2. The top end 7a of the spacer 7 is directed adjacent to the bottom face of the slide hole 6a to the cap-like peak of the bearing 6, and it is brought into contact with the bottom face of the slide hole 6a, so that the first and second shaft members 3,4 are prevented from coming off the case 2. Thus, Embodiment (A2a), shown in Figure 13, in addition to having effects similar to those of Embodiment 1 (Al) and Embodiment 2 (A2) of Figure 6, achieves the above-mentioned benefits as well. Also, as described above, the tensioner has a small and slim constitution, so that it can be made compact and light in weight. Embodiment 3 Figure 15 is a vertical cross-sectional view that shows the tensioner A3 of Embodiment 3 of the present invention, and Figure 16 is a cross-sectional view taken along the line H-H of Figure 15. As shown in Figure 15, in the tensioner A3 of this embodiment, only the arrangement of the resistance-torque-applying mechanism 20 is different — the arrangement of the second shaft member 4 and the third shaft member 21 is made upside down — while other constituents are essentially identical to those of the above-mentioned embodiment. That is to say, the resistance-torque-applying mechanism 20 has a constitution such that a third shaft member 21 that is screwed into the screw portion 3b of the first shaft member 3 is arranged below the base end of the second shaft member 4, and is connected with the second shaft member 4 by a connecting member 50 via the coil spring 22. 42 Figure 17 is a vertical cross-sectional view that shows the connecting member 50 of Embodiment 3 (A3), and Figure 18 is a plan view thereof. As shown in Figures 17 and 18, the connecting member 50 is formed approximately into a shape such that four top-side portions of a bottomed cylinder are cut at equal intervals. A through-hole 53 that has a diameter slightly larger than the outside diameter of the screw portion 3b for inserting the screw portion 3b of the first shaft member 3 is provided on the bottom face of the base end 51 of the connecting member 50. On the top side there are four shells 52 that are placed on the base end 51 and that are provided with hook portions 52a, each of whose tip is bent like a hook. In addition, as shown in Figure 15, four hook parts 52a of the connecting member 50 are inserted into and locked onto the outer periphery of the base end 4a of the second shaft member 4, and four lock grooves 4c are provided for restraining the rotation of the connecting member 50. Also, as shown in Figure 16, four lock grooves 21 e — which restrain the connecting member 50 from rotating, and into which the four shells 52 of the connecting member 50 are inserted from the outside — are provided on the outer periphery of the third shaft member 21. The top end 22a of the coil spring 22, which is a compression spring, contacts the bottom face 21a of the third shaft member 21, and its base end 22b contacts the bottom face (inner face) of the base end 51 of the connecting member 50. Such a coil spring 22 is incorporated in the tensioner under the condition that (1) the two ends 22a, 22b of the coil spring 22 contact the third shaft member 21 and the connecting member 50, respectively, and (2) the coil spring 22 is compressed to a certain extent. As a result, the second shaft 43 member 4 and the third shaft member 21 always press against the male screws 8 of the screw portion 3b of the first shaft member 3 — via the coil spring 22 and the connecting member 50 — in mutually opposite axial directions (the upper and lower directions in Figure 17) due to the compression force of the coil spring 22. As described above, the tensioner A3 of Embodiment 3, which includes the resistance-torque-applying mechanism 20, which is composed of the third shaft member 21, the coil spring 22, the connecting member 50, and the like, has the benefit that the resistance-torque-applying mechanism 20 can be incorporated between the first shaft member 3 and the second shaft member 4 very easily— in addition to having effects similar to those of the above-mentioned embodiment. Figure 19 is a vertical cross-sectional view that shows the tensioner A3a in a modification of Embodiment 3. Comparing the embodiment of Figure 19 (A3a) with Embodiment 3 of Figure 17 (A3), only the arrangement of the resistance-torque-applying mechanism 20 of A3a is different, in that in the embodiment of Figure 19 (A3a) the coil spring 22 is arranged between the second shaft member 4 and the third shaft member 21, and in that the connection member 50 also serves the same function as does the spacer 7 in the embodiment of Figure 13 (A2), while the other features of A3a are basically identical to those of the above-mentioned embodiments. The top end 22a of the coil spring 22, which is a compression spring, contacts the bottom face 4f of the base end 4a of the second shaft member 4, and its base end 22b contacts the top face 21a of the third shaft member 21. Such a coil spring 22 is incorporated into the tensioner under the condition that (1) the two ends 22a and 22b of the coil spring 22 contact the shaft members 4 and 21, respectively, and that (2) the coil spring 22 is 44 compressed to a certain extent. As a result, the second shaft member 4 and the third shaft member 21 always press against the male screws 8 of the screw portion 3b of the first shaft member 3 in mutually opposite axial directions (upper and lower directions in Figure 19) due to the compression force of the coil spring 22. The base end 50b of the connecting member 50 is fitted, in a rotatable manner, onto the small-diameter portion 3d, which is the upper portion of 3c, which has a stepped shape, of the first shaft member 3. Also, the top end 50a of the connecting member 50 is adjacent to the bottom face of the slide hole 6a at the cap-like peak of the bearing 6, and said top end 50a is brought into contact with the bottom face of the slide hole 6a, so that the first and second shaft members 3, 4 are prevented from coming off the case 2. Also, the present embodiment has a function such that the outer face of the connecting member 50 serves as a guide for the torsion spring 5 in a way that is similar to that function of the spacer 7 in the above-mentioned embodiment. In addition, the inner face of the connecting member 50 is molded into a noncircular cross-section shape — having, for example, a parallel cut part (not shown) — so as to fit the outer shapes of the base end 4a of the second shaft member 4 and the third shaft member 21, so that said inner face of the connecting member 50 restrains the rotation — but allows the axial movement — of both of the shaft members 4, 21. As described above, in the embodiment shown in Figure 19 (A3a) — which includes the resistance-torque-applying mechanism 20 that is constituted with the third shaft member 21, the coil spring 22, the connecting member 50, and the like — when the first shaft member 3 rotates in the forward or reverse direction under the external input load, the second shaft member 4, the coil spring 22, and the third shaft member 21 move together in the axial direction (namely, forward or backward) because the rotation of those parts 4, 22, and 21 is restrained. At this time, the connecting member 50 restrains the rotation of the 45 third shaft member 21, and guides the axial movement of the shaft members 4 and 21, under the condition that said connecting member 50 is restrained from rotating and is stopped together with the second shaft member 4. Also, an elastic member 10a, such as rubber with an approximately spherical shape, is mounted on a top end (a head) of a cap 10. The elastic member 10a serves as a buffer material that reduces the vibrations of the external input load W, and said member 10a is especially effective when it is applied to a tensioner for a high-performance engine, such as that mentioned above, that vibrates greatly. As described above, the tensioner A3a of this embodiment has, in addition to having effects similar to those of the above-mentioned embodiment, benefits in terms of cost. That is, because the connecting member 50 also serves as the spacer 7 in the embodiment (A2) of Figure 13, the number of members can be reduced, and the constitution and assembly of the tensioner A3 a can be simplified. Figure 20 is a vertical cross-sectional view that shows the tensioner A3b of another modification of Embodiment 3. In the tensioner A3b of the embodiment shown by Figure 20, the arrangement of the resistance-torque-applying mechanism 20 differs from that of the embodiment (A3) shown by Figure 19 only in that in tensioner A3b the coil spring 22 is arranged between the first shaft member 3 and the third shaft member 21, while other features of its constitution are basically similar to those of the above-mentioned embodiments, including that the connecting member 50 also serves as the spacer 7 in the embodiment (A2) shown by Figure 13. The top end 22a of the coil spring 22, which is a compression spring, contacts the bottom 46 face 21b of the third shaft member 21, and its base end 22b contacts the top face 3f of a small-diameter part 3d, which is the upper, stepped-shape part of the flange 3c of the first shaft member 3. Such a coil spring 22 is incorporated into the tensioner under the condition that (1) both of the ends 22a and 22b of the coil spring 22 contact the third shaft member 21 and the first shaft member 3, and (2) the coil spring 22 is compressed to a certain extent. As a result, the female screws 9 of the third shaft member 21 is always pressed against the male screws 8 of the screw part 3b of the first shaft member 3 in the axial direction and toward the top of the third shaft member 21 due to the compression force of the coil spring 22. Figure 21 is a diagram that shows the dynamic characteristics of the tensioner A3b in this embodiment. In this embodiment (A3b), as the second shaft member 4 moves forward and backward, the third shaft member 21 — which, together with the second shaft member 4, is restrained from rotating by the connecting member 50 — also moves forward and backward. As a result, the set length of the coil spring 22 changes (bends), and therefore the axial force Z, which is due to the coil spring 22, also changes. At this time, when the difference between (1) the spring torque Tb of the torsion spring 5 and (2) the resistance torque Tmz that is applied by the resistance-torque-applying mechanism 20, which consists of the coil spring 22, the third shaft 21, and the like are set to be identical (Tb - Tmz = constant), the driving force (pressure) J for the second shaft member 4 becomes constant. The characteristic-line diagram in Figure 21 shows the relationship between the torques Tb and Tmz and the pressure J in relation to the protrusion-margin length A in this embodiment (A3b). With either a conventional tensioner 100 or the above-mentioned embodiments, the pressure J varies when the forward- and backward-movement position (stroke) of the driving member or a second shaft member 4 changes. According to the embodiment shown 47 in Figure 21 (A3b), however, the pressure J does not change at any forward and backward movement position (stroke) of the second shaft member 4, and this is a unique characteristic. This can prevent such potential problems as over-protruding and over-returning of the tensioner, abrasion of various parts, and loss of engine horsepower over a wide range of engine rpm and over a wide vibration range of the engine. Thus, a stable damping effect and durability of parts can be secured. Embodiment 4 Figure 22 is a vertical cross-sectional view that shows a tensioner A4 in Embodiment 4 of the present invention. In addition to having the features of Embodiment 3 (A3) that is shown in Figure 15, the constitution of the resistance-torque-applying mechanism 20 of the tensioner A4 in this embodiment (A4), as shown in Figure 22, is such that a coil spring 60 is provided as a second elastic member - which is the only difference between the two embodiments. Other features of this embodiment are basically the same as those of the above-mentioned embodiments. The coil spring 60 is arranged between the first shaft member 3 and the third shaft member 21. In this embodiment (A4), the coil spring 60 is arranged between the base end of the screw portion 3b of the first shaft member 3 and the bottom face 21b of the third shaft member 21. That is to say, the resistance-torque-applying mechanism 20 is constituted such that the third shaft member 21 that is screwed in the screw portion 3b of the first shaft member 3 is connected with the second shaft member 4 by the connecting member 50 via the coil spring 22, and that the coil spring 60 is provided between the first shaft member 3 and the third shaft member 21. Also, a compression spring, whose hook parts on its two ends are free ends, is used as the 48 coil spring 60. The top end 60a of the coil spring 60, which is a compression spring, contacts the third shaft member 21, and its base end 60b contacts the first shaft member 3. In this case, the base end 60b contacts the top face 3f of the small-diameter portion 3d that is formed at the upper portion of the flange 3c of the first shaft member 3. Such a coil spring 60 is incorporated into the tensioner under the condition that (1) the two ends 60a, 60b of the coil spring 60 contact the shaft members 21, 3, respectively, and that (2) the coil spring 60 is compressed to a certain extent. Because of the addition of the coil spring 60, the third shaft member 21 is pressed in its axial direction and toward the top end of the screw portion 3b of the first shaft member 3. As a result, resistance torque — due to the total compression force that is obtained by adding the compression force of the coil spring 60 to the compression force of the above-mentioned coil spring 22 — is applied as the resistance torque Tmz to the first shaft member 3 by the resistance-torque-applying mechanism 20. Accordingly, when an external load, which presses the second shaft member 4 inwardly, is input, the first shaft member 3 rotates. As a result, the third shaft member 21, which is restrained by the connecting member 50 from rotating, is also pressed — together with the second shaft member 4 — to the base-end side of the screw portion 3b of the first shaft member 3. Thus, the compression force directly acts on the coil spring 60, whose top end 60a contacts the third shaft member 21, as a result of which the coil spring 60 is compressed. Because the other end 60b of the coil spring 60 contacts the first shaft member 3, frictional resistance torque is applied between the coil spring 60 and the first shaft member 3 due to the compression of the coil spring 60. As a result, the resistance torque — which has already been generated due to the compression force of the coil spring 22 — increases further. As a result, a braking force strongly acts against the first shaft member 3, and rotation of the first shaft member 3 is strongly restrained. Thus, an even stronger and more stable damping function can be secured. 49 A step portion 3g, whose outside diameter corresponds to the inside diameter of the coil spring 60, is further formed between the small-diameter part 3d and the screw portion 3b at the upper portion of the flange 3c of the first shaft member 3. The step portion 3g serves as a seat that supports the base end 60b of the coil spring 60. The step portion 3g is inserted into the base end 60b of the coil spring 60 so as to provide a more stable, supporting condition for the coil spring 60. It is also desirable that a metallic washer be installed as a buffer plate or friction plate (not shown) between the base end 60b of the coil spring 60 and the top face 3f of the small-diameter portion 3d at the upper portion of the flange 3c of the first shaft member 3. In this embodiment (A4), the coil spring 60 is compressed to a certain extent. In this manner, the two ends 60b, 60a of the coil spring 60 are supported by the first and third shaft members 3, 21, respectively, and the two ends 22b, 22a of the coil spring 22 are supported by the second and third shaft members 4, 21, respectively, via the connecting member 50. Therefore, even when the first shaft member 3 repeats reciprocation and rotation, that operation can be smoothly coped with by the tensioner. Thus, a more stable damping operation can be performed. Embodiment 5 Figure 23 is a vertical cross-sectional view that shows the tensioner A5 in Embodiment 5 of the present invention. As shown in Figure 23, the tensioner A5 in this embodiment (which corresponds to the invention of Claim 3) has a structure that reverses the arrangement of the second shaft member 4 and the first shaft member 3 in Embodiment 3 (A3) as shown by Figure 15. Also, a plate-winding spring is used as a torsion spring 5, and laminated disc springs 22 is used 50 as a first elastic member. Although the shapes of many members — such as the case 2 — are different, the function and damping performance of this embodiment as a tensioner are basically similar to those of Embodiment 3 (A3). The case 2 is divided into two parts — a base-end side case and a top-end side case — that are connected with each other by bolt members (not shown) via flanges 2bl and 2b2. The case 2 is molded into a bottomed approximately cylindrical shape having the flange 2b 1 at the top end of a shell 2al. An accommodation hole 2cl that extends to the top end of the shell 2al in the axial direction (driving direction) is formed inside said shell 2al. The top portion of the accommodation hole 2c 1 is open. An assembly of base-end side shafts 3a, 4a of the first and second shaft members 3,4, and the torsion spring 5 is accommodated inside the accommodation hole 2c 1. The top-end side case is molded into an approximately cylindrical shape that includes the flange 2b2 at the base end of a shell 2a2. An accommodation hole 2c2 that penetrates in the axial direction is formed inside the shell 2a2. Both ends of the accommodation hole 2c2 are open, and an assembly of top-side shafts 3b, 4b of the first and second shaft members 3, 4 is accommodated inside the accommodation hole 2c2. The top-end side accommodation hole 2c2 is slightly thinner than the base-end side accommodation hole 2c 1; the reason for this will be mentioned later. The flange 2b2 of the top-end side case is meant for mounting the tensioner to the engine block, and installing holes (not shown) that are penetrated by bolts to be screwed into the engine block, are formed. When mounting the tensioner to the engine block, as is similar to the arrangement of an additional tensioner 100 shown by Figure 25, the top face (upper face in Figure 23) of the flange 2b2 contacts an installing face 250 of the engine block 200. The first shaft member 3 is pressed and rotated by the torsion spring 5, and restrained from 51 rotating by a bearing 6 that is installed on the top-end side case, and the second shaft member 4, which is movable in its axial direction, moves forward from the case 2 due to rotation of the first shaft member 3. The first shaft member 3 is molded into an approximately cylindrical shape with both ends open in such a manner that the base-end side shaft 3a integrally is placed on the top-side shaft 3b in the axial direction, and female screws 8a are formed on the inner face of the top-side shaft 3b. The inside diameter 3i of the base-end side shaft 3a is a clearance-hole diameter that is slightly larger than the outside diameter of male screws 9a of the second shaft member 4. Also, the base end of the base-end side shaft 3a contacts a swivel plate 19 that is installed in the case 2, and thus the rotation of the base-end side shaft 3a is supported. A top-side shaft 4b that extends to the top end of the tensioner A5 in the axial direction is formed to the second shaft member 4, and male screws 9a — that are screwed into female screws 8a "of the first shaft member 3 — are placed on the outer periphery of the base-end side shaft 4a, so as to form a screw part. The first and second shaft members 3, 4 are inserted into the accommodation holes 2cl and 2c2, respectively, of the case 2, under the condition that the female screws 8a and the male screws 9a are screwed together. A cap 10 is attached to the top of the top-side shaft 4b of the second shaft member 4. The torsion spring 5, which is a plate-winding spring, is placed on the base-end side shaft 3a of the first shaft member 3. The outside diameter end 5a (not shown), which is formed like a hook, of the torsion spring 5 is inserted into and locked in a hook groove (not shown) that is formed in the base-end side case of the case 2. Further, the inside diameter end 5b, which is formed like a hook (not shown), is inserted into and locked in a slit (not shown) of the base-end side shaft 3a of the first shaft member 3. Accordingly, by winding the torsion spring 5, torque can be given so as to rotate the first shaft member 3. 52 As is similar to the above-mentioned embodiments, the bearing 6 is attached to the top portion of the top-end side case of the case 2 — under the condition that said bearing 6 is restrained from rotating — and fastened by a cover ring 13. The bearing 6 has a slide hole 6a, inside which the top-side shaft 4b of the second shaft member 4 penetrates. The cross-section of the inner face of the slide hole 6a of the bearing 6, and the cross-section of the outer face of the top-side shaft 4b of the second shaft member 4 are both formed into approximately oval shapes, D-cut shapes, or parallel-cut shapes, or any other noncircular shapes (not shown), so that the second shaft member 4 is restrained from rotating. The first shaft member 3 is screwed into the second shaft member 4 via the female and male screws 8a, 9a, and the rotation force of the first shaft member 3, which rotates due to the rotation and pressure of the torsion spring 5, is transmitted to the second shaft member 4. However, because the second shaft member 4 is restrained from rotating by the bearing 6, the second shaft member 4 obtains a driving force, and it moves forward and backward in its axial direction against the case 2. In this Embodiment 5 (A5), the spacer 7 that is in Embodiment 3 (A3) is omitted, and the top-end side case of the case 2 also functions as a spacer. That is to say, (1) a large-diameter flange 3c is formed at the boundary of the base-end side shaft 3a and the top-side shaft 3b of the first shaft member 3, and (2) the top face 3h of the flange 3c is adjacent — in a contactable manner — to the bottom face 2h on the inner face 2c2 side (which is a stepped portion that is created because the accommodation hole 2c2 on the top-end side is slightly thinner than the accommodation hole 2cl on the base-end side) of the flange 2b2 of the top-end side case. This contact of the flange 3c of the first shaft member 3 prevents the first and second shaft members 3, 4 from coming off the case 2. In addition, this Embodiment 5 (A5) provides a resistance-torque-applying mechanism 20 53 that applies an almost constant resistance torque to the male screws 9a of the second shaft member 4 and the base end 3a of the first shaft member 3. The resistance-torque-applying mechanism 20 is arranged in the above-mentioned top-end side case, and it comprises (1) the third shaft member 21 that is screwed into the male screws 9a of the second shaft member 4, (2) disc springs 22 as a first elastic member that are provided between the third shaft member 21 and the first shaft member 3, and (3) a connecting member 55 that connects the third shaft member 21 with the second shaft member 4. Disc springs 22 are arranged between (1) the bottom face 21b of the third shaft member 21 in the top-end side case and (2) the top-end face (upper face in Figure 23) 3j of the first shaft member 3. The plural pairs of laminated disc springs 22 that are overlaid on their top and rear faces in pairs, and it is used as a compression spring whose two ends are free ends. The base end 22b of the compression spring, namely the disc springs 22, contacts the base-end face 21b of the third shaft member 3, and the base end 22b contacts the top-end face 3j of the first shaft member 3. Such disc springs 22 are incorporated in the tensioner under the condition that the disc springs 22 contacts the two the shaft members 21, 3 at its two ends 22a, 22b, respectively, and that the disc springs 22 are compressed to a certain extent. As a result, the first shaft member 3 and the third shaft member 21 always press the male screw 8a of the second shaft member 4 in axial directions opposite to each other (upper and lower directions in Figure 23). At the same time, the base end 3a of the first shaft member 3 is always pressed to the swivel plate 19 in the axial direction toward the base end (downward in the figure) by the compression force of the disc springs 22. The connecting member 55 is formed into an approximately cylindrical shape that has a top, as shown in Figure 23. A through-hole 58 for inserting the second shaft member 4 is provided on the ceiling face 56a of the top end 56 of the connecting member 55. A shell 57 54 on the base-end side that is placed on the top end 56 is provided with an indentation part 57a in such a manner that the periphery of the top end that communicates with the ceiling face 56a is inwardly bent like an indentation. In addition, as shown in Figure 23, a lock groove 21f for inserting and locking the indentation part 57a of the connecting member 55 is formed on the outer periphery at the top end of the third shaft member 21. Also, the inner face of the connecting member 55 is molded into a noncircular shape, having, for example, a parallel-cut part (not shown) so as to correspond to outer shapes of the third shaft member 21 and the top end 3b of the first shaft member 3, so that both of the shaft members 21, 3 are restrained from rotating and so that the first shaft member 3 is made movable in the axial direction. As described above, in an embodiment (A5) of Figure 23 having a resistance-torque-applying mechanism 20 that comprises the third shaft member 21, the disc springs 22, the connecting member 55, and the like, when the first shaft member 3 rotates in the forward or reverse direction under an external input load, then (1) the third shaft member 21, which is connected with the first shaft member 3 by the connecting member 55, and (2) the disc springs 22 rotate simultaneously, while the third shaft member 21 and the second shaft member 4 move forward and backward in the axial direction because the bearing 6 prevents the third shaft member 21 and the second shaft member 4 from rotating. As described above, the tensioner A5 in this embodiment has effects similar to those of the above-mentioned Embodiment 3 (A3). Also, because the top-end side case of the case 2 also servers as a spacer 7 in the embodiment shown by Figure 13 (A2), the number of the tensioner's parts can be reduced, and its constitution and assembly can be simplified, 55 resulting in cost benefits. Also, the case 2 is divided into two parts, which are a base-end side case and a top-end side case; therefore, assembly and disassembly of the entire tensioner are facilitated. Furthermore, both the plate-winding spring 5 as a torsion spring and the disc springs 22 as a first elastic member are compact, and thus the tensioner can be small in size and light in weight. Embodiment 6 Figure 24 is a vertical cross-sectional view that shows the tensioner A6 in Embodiment 6 of the present invention. In the tensioner A6 of this embodiment, due to fluid pressure, such as oil hydraulic pressure, fluid 71 from a fluid source 70 is filled in the case 2 — which includes a resistance-torque-applying mechanism 20 comprising first, second, and third shaft members 3, 4, and 21, respectively, of the tensioner in the embodiments mentioned above — and the above-mentioned fluid pressure acts in the driving direction of the second shaft member 4. As one example thereof, the tensioner A6 shown in Figure 24 has a constitution similar to that of the embodiment shown in Figure 13 (A2a). Accordingly, the tensioner A6 of Figure 24 has, in addition to its tension-maintenance and tension-damping functions, which are similar to those of the embodiment of Figure 13 (A2a), a buffer function due to the viscous resistance of the fluid. Thus, the tensioner A6 sufficiently buffers vibrations from the engine, and it has more-stable behavior characteristics than the embodiments mentioned above. The tensioner A6 of Figure 24 has a structure such that the second shaft member 4 is 56 integrally equipped with a cap 10 at the tip of the tubular member 41. The case 2 has a flange 2b on a side face of the shell 2a, and the case is bolted to the engine block via said flange 2b. Because this embodiment's other features — except for its fluid-pressure system, — are similar to those of the embodiment shown in Figure 13 (A2a), a detailed explanation thereof will be omitted here. A flow path 72 of the fluid 71 is provided to the flange 2b on the side face of the shell 2a of the case 2 in such a manner as to connect to the inside (groove 2e) of the case 2 on its top side (upper side in Figure 24). Furthermore, at the base end 7b of the spacer 7 there is provided a fluid-circulation port 73 for the fluid 71, and said fluid-circulation port 73 contains a fluid-flow resistance means, such as an orifice (not shown), for appropriately limiting the flow of the fluid 71. Fluid-circulation ports 74, 75 of the fluid 71 are formed to both (1) the main member 40 at the base end of the second shaft member 4 and (2) the third shaft member 21. Also, a blind plug 76 is screwed into, and tightly seals, a jig hole 2e that is opened on the base-end face of the shell 2a of the case 2. When the second shaft member 4 moves forward in the top-end (protruding direction), the fluid 71 from the fluid source 70 — which is provided in the engine block — flows into the case 2 via the flow path 72, and further flows into the spacer 7 through the fluid-circulation port 73, and then into the second shaft member 4 via the fluid-circulation ports 74, 75, as shown by the arrow-line 80 in Figure 24. When the second shaft member 4 moves in the direction of the base end (returning direction), the fluid 71 in the second shaft member 4 flows in the direction opposite to the 57 arrow-line 80 in Figure 24; the fluid 71 flows out of the case 2 via the flow path 72, and then reversely flows into the fluid-pressure source 70. Furthermore, when the fluid 71 flows into or out of the fluid-circulation port 73, it receives more-effective flow resistance due to the above-mentioned fluid-flow resistance means. By the viscous flow resistance of the fluid 71 that occurs with the forward and backward (protruding and returning) movement of the second shaft member 4, which receives the external input load from the engine, said forward and backward movement is buffered. As a result, the tensioner A6 in Embodiment 6 obtains a buffering effect due to the fluid 71 — in addition to a damping effect due to the above-mentioned resistance-torque-applying mechanism 20 — and as a result it manifests very effective and stable damping characteristics. Furthermore, because the fluid 71 also serves as a lubricant for the above-mentioned shaft members 3,4,21, the torsion spring 5, and the first elastic member 22, the tensioner can be smoothly operated, abrasion of these members can be restrained, and thus their durability can be improved. As explained above, the tensioner of the present invention enables, in addition to the embodiments shown in Figures 1 through 24, optional variations with regard to the shapes or combinations of the case 2, the first, second, and third shaft members 3, 4, 21, and other members. Also, regarding the torsion spring 5, the first and second elastic members 22, and 60, and the dimensions and shapes of the spring members, including their diameters, can be optionally changed, so that the spring torque or resistance torque due to the compression force can be adjusted. Furthermore, the first and second elastic members can optionally be 58 a compression spring, a disc spring, a rubber molding or resin molding; the torsion spring 5 can adopt a coil spring, a plate winding spring, or other type of spring. Industrial Applicability Because with the present invention the resistance-torque-applying mechanism does not directly receive an external input load, resistance torque is always applied — irrespective of the magnitude of the external input load — so as to restrain the amplitude of the second shaft member. Therefore, the amplitude can be stably restrained, and the present invention can be effectively applied as a tensioner for a timing chain or a timing belt of an engine that vibrates greatly, especially a modern high-performance engine. 59 WE CLAIM 1. A tensioner that (1) has a structure such, that (a) first and second shaft members, which are fastened to each other by screw portions, and a torsion spring, which presses the first shaft member clockwise or counterclockwise, thereby causing it to rotate, are accommodated in a case, and (b) the second shaft member is restrained from rotating so that the rotation and pressure of the torsion spring is converted into force that drives the second shaft, and (2) is characterized such that a resistance-torque-applying mechanism, which always gives reciprocating resistance torque in both the forward and backward directions of the second shaft member, is arranged between said first shaft member and said second shaft member. 2. A tensioner as set forth in Claim 1, but wherein (1) said resistance-torque-applying mechanism comprises (a) at least one third shaft member, which is screwed using the screw portion of said first shaft member, and (b) a first elastic member, which is provided between (i) either said second shaft member or said first shaft member and (ii) a third shaft member; and (2) said third shaft member is restrained — together with the second shaft member — from rotating, but is movable in its axial direction. 3. A tensioner as set forth in Claim 1, but wherein (1) said resistance-torque-applying mechanism comprises at least one third shaft member, which is screwed to said first shaft member by the screw portion of said second 60 shaft member, and a first elastic member, which is provided between said first shaft member and said third shaft member, and (2) said third shaft member is restrained from rotating against said first shaft member, but is movable in its axial direction. 4. A tensioner as set forth in Claim 1, but wherein (1) said resistance-torque-applying mechanism comprises at least (a) one third shaft member, which is screwed with the screw portion of said first shaft member, (b) a first elastic member, which is provided between said first shaft member and said third shaft member, and (c) a second elastic member, which is provided between said first shaft member and said third shaft member, and (2) said third shaft member is restrained — together with the second shaft member — from rotating, but is movable in its axial direction. 5. A tensioner as set forth in any one of Claims 2, 3 or 4, but wherein said first elastic member is a coil spring that (1) is arranged — while it is compressed — between either the second shaft member or the first shaft member and the third shaft member, and (2) generates — independently from an external input load — continuous resistance torque between the first and second shaft members and the third shaft member. 6. A tensioner as set forth in Claim 4, but wherein said second elastic member is a coil spring that (1) is arranged — under a compressed condition — between said first shaft member and said third shaft member, and (2), by being compressed by the external input load, generates resistance torque between the first shaft member and the third shaft member. 61 7. A tensioner as set forth in any one of Claims 2 through 6, but wherein said first and second elastic members are either compression springs, disc springs, rubber moldings, or resin moldings. 8. A tensioner as set forth in any of Claims 1, 2, or 4, but wherein said second shaft member has a tubular member that (1) is connected with a main member, namely a base end that is screwed into the screw portion of the first shaft member, (2) restrains the third shaft member from rotating, but (3) makes the third shaft member movable in said shaft member's axial direction. 9. A tensioner as set forth in any one of Claims 1 through 4, but wherein the relationship Tmz resistance-torque-applying mechanism applies to the first shaft member is designated as Tmz, and the spring torque of said torsion spring is designated as Tb. 10. A tensioner as set forth in any one of Claims 1 through 8, but wherein the fluid pressure from a fluid-pressure source is made to act in the direction in which said second shaft member moves. Dated this 2nd day of February, 2006, FOR NHK SPRING CO. LTD. By their Agent (GIRISH VIJAYANAKD SHETH) KRISHNA & SAURASTRI 62 Abstract A tensioner is provided that can stably restrain the amplitude a timing chain or timing belt over a wide range of rpm of an engine both at the time of a protruding operation and a returning operation against a strong input vibration load from the engine. A first shaft member 3 and a second shaft member 4, which are fastened together with screws 8, 9, and a torsion spring 5 that presses the first shaft member clockwise or counterclockwise, thereby causing it to rotate, are accommodated in a case 2. The second shaft member 4 is restrained from rotating, so that the rotation and pressure of the torsion spring 5 are converted into a force that drives the second shaft member 4. A resistance-torque-applying mechanism 20, which always generates resistance torque against an external load input to the second shaft member 4 both at the time of a protruding operation and at the time of a returning operation, is arranged between the first shaft member 3 and the second shaft member 4, so that the amplitude of the second shaft member 4 is finely and stably restrained. 63

Documents:

129-MUMNP-2006- AMANDED CLAIMS(18-9-2009).pdf

129-MUMNP-2006-ABSTRACT(1-4-2009).pdf

129-mumnp-2006-abstract(complete)-(2-2-2006).pdf

129-mumnp-2006-abstract(granted)-(16-12-2009).pdf

129-mumnp-2006-abstract.doc

129-mumnp-2006-abstract.pdf

129-MUMNP-2006-CANCELLED PAGES(1-4-2009).pdf

129-MUMNP-2006-CANCELLED PAGES(18-9-2009).pdf

129-MUMNP-2006-CLAIMS(1-4-2009).pdf

129-MUMNP-2006-CLAIMS(29-6-2009).pdf

129-mumnp-2006-claims(complete)-(2-2-2006).pdf

129-mumnp-2006-claims(granted)-(16-12-2009).pdf

129-MUMNP-2006-CLAIMS(MARKED COPY)-(1-4-2009).pdf

129-mumnp-2006-claims.doc

129-mumnp-2006-claims.pdf

129-MUMNP-2006-CORRESPONDENCE(1-4-2009).pdf

129-mumnp-2006-correspondence(12-12-2006).pdf

129-MUMNP-2006-CORRESPONDENCE(18-9-2009).pdf

129-MUMNP-2006-CORRESPONDENCE(29-6-2009).pdf

129-mumnp-2006-correspondence(ipo)-(16-12-2009).pdf

129-MUMNP-2006-CORRESPONDENCE(IPO)-(18-9-2009).pdf

129-MUMNP-2006-CORRESPONDENCE(IPO)-(29-9-2008).pdf

129-mumnp-2006-correspondence-received.pdf

129-mumnp-2006-description (complete).pdf

129-MUMNP-2006-DESCRIPTION(COMPLETE)-(1-4-2009).pdf

129-mumnp-2006-description(complete)-(2-2-2006).pdf

129-mumnp-2006-description(granted)-(16-12-2009).pdf

129-MUMNP-2006-DRAWING(1-4-2009).pdf

129-mumnp-2006-drawing(complete)-(2-2-2006).pdf

129-mumnp-2006-drawing(granted)-(16-12-2009).pdf

129-mumnp-2006-drawings.pdf

129-MUMNP-2006-FORM 1(2-2-2006).pdf

129-mumnp-2006-form 1(21-4-2006).pdf

129-mumnp-2006-form 13(1-4-2009).pdf

129-mumnp-2006-form 13(18-9-2009).pdf

129-mumnp-2006-form 18(12-12-2006).pdf

129-mumnp-2006-form 2(1-4-2009).pdf

129-mumnp-2006-form 2(complete)-(2-2-2006).pdf

129-mumnp-2006-form 2(granted)-(16-12-2009).pdf

129-MUMNP-2006-FORM 2(TITLE PAGE)-(1-4-2009).pdf

129-mumnp-2006-form 2(title page)-(complete)-(2-2-2006).pdf

129-mumnp-2006-form 2(title page)-(granted)-(16-12-2009).pdf

129-MUMNP-2006-FORM 3(1-4-2009).pdf

129-MUMNP-2006-FORM 3(17-4-2006).pdf

129-MUMNP-2006-FORM 3(29-6-2009).pdf

129-mumnp-2006-form-1.pdf

129-mumnp-2006-form-2.doc

129-mumnp-2006-form-2.pdf

129-mumnp-2006-form-3.pdf

129-mumnp-2006-form-5.pdf

129-mumnp-2006-form-pct-ib-301.pdf

129-mumnp-2006-form-pct-ib-304.pdf

129-mumnp-2006-form-pct-ib-308.pdf

129-mumnp-2006-pct-search report.pdf

129-mumnp-2006-power of attorney(23-9-2009).pdf

129-MUMNP-2006-POWER OF ATTORNEY(24-4-2006).pdf

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