Title of Invention

COOLING SYSTEM FOR WATER-COOLED ENGINE

Abstract

PROBLEM TO BE SLOVED:To enchance an air-bleeding property in a rising passage while elimitin an air -bleeding bolt and the like to avoid increase of the number of part items,in a cooler for an engine provided with a thermostst for switching a cooling water flowing passage in response to a temperature of cooling water in a midway of the rising passage for making the cooling water flow. SOLUTION: A wax case 87 of which the upper end is faced to a water chamber 90 communicated to a by-pass passage 81 and formed inside a housing 86A is made slidable in response to expansion/shrinkage of wax 89 in the housing 86A,the case 87 is engagged to communicate the water chamber 90 with an upper side passage portion 78 when the wax 89 is shrinked,an inlet hole 102 communicated with passage portion 77 of the rising passage 76 and an outlet hole 103 communciated with the upper side passage portion 78 of the passage 76 are provided in the housing 86A to be blocked by the wax case 87 when the wax is shrinked,and the inlet hole 102 is communicated with the water chamber 90 via an air-bleeding passage 105

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10] "COOLING SYSTEM FOR WATER-COOLED ENGINE" HONDA GIKEN KOGYO KABUSHIKI KAISHA, a corporation of Japan, having a place of business at 1-1, Minamiaoyama 2-chome, Minato-ku, Tokyo, Japan, The following specification particularly describes the nature of the invention and the manner in which it is to be performed:- [Detailed Description of the Invention] [Technical Field to which the Invention Pertains] The present invention relates to a cooling system for a water-cooled engine and more particularly to a cooling system for a water-cooled engine wherein a thermostat for switching a cooling water flowing path from one to another state according to the temperature of the cooling water is disposed halfway of a rise passage which permits the cooling water to flow upward. 2 [Prior Art] Heretofore such a cooling system has already been known, for example, in Japanese Utility Model Laid-open No. 75129/1992. According to this known cooling system, an inlet hole communicating with a lower passage portion of a rise passage is formed in a lower portion of a thermostat housing, an outlet hole communicating with an upper passage portion of the rise passage is formed in an intermediate portion of the housing, a bypass hole communicating with a bypass passage is formed in an upper portion of the housing, and a wax case is received within the housing so as to be slidable between a lower position in which the bypass hole is communicated with the outlet hole when wax contracts and an upper position in which the inlet hole is communicated with the outlet hole when the wax expands. [Problem to be Solved by the Invention] At the time of pouring cooling water into a cooling system it is necessary to extract air from both main and sub circulation circuits, but in the above conventional cooling system using a thermostat, there arises a difference in height between inlet and outlet holes in the thermostat disposed at an intermediate position of 3 the rise passage and the cooling water passage in the thermostat is crank-like. Therefore, when the cooling system must be constructed compactly in the vertical direction so as to be carried on a motorcycle for example, it is necessary that the angle of inclination of the rise passage be set small, that is, it takes time to extract air. To avoid such an inconvenience it is necessary that an air vent bolt or the like be mounted to the rise passage. In the view of the foregoing, the present invention has been made, and an object of the present invention is to provide a cooling system for a water-cooled engine wherein a thermostat is disposed halfway of a rise passage which causes cooling water to flow upward, and the air venting performance from the rise passage is improved while eliminating the need of using an air vent bolt or the like and thereby avoiding an increase in the number of components used. [Means for Solving the Problem] For achieving the above-mentioned object, according to the invention defined in claim 1 there is provided a cooling system for a water-cooled engine including a main 4 circulation circuit which, with a rise passage permitting upward flow of cooling water as a partial passage, connects a water jacket in an engine body, a radiator, a water pump and the water jacket successively in this order, a sub circulation passage made up of by a bypass passage which bypasses the radiator and a part of the main circulation circuit, and a thermostat disposed halfway of the rise passage so as to switch over according to the temperature of the cooling water between a state in which the rise passage is blocked, allowing the cooling water to flow and circulate through the sub circulation circuit, and a state in which the bypass passage is blocked, allowing the cooling water to flow and circulate through the main circulation circuit, characterized in that the thermostat is provided with a housing having a slide hole which extends upward across the rise passage halfway of the same passage, also provided with a wax case fitted slidably in the slide hole and whose upper end faces a water chamber formed within the housing in communication with the bypass passage, and further provided with wax contained in the wax case so as to Permit the wax case to slide in accordance with expansion and contraction of the wax caused by a change in temperature of the cooling water, 5 the wax case being fitted in the slide hole so as to permit communication of the water chamber with an upper passage portion of the rise passage when the wax contracts, and an inlet hole which communicates with a lower passage portion of the rise passage and an outlet hole which communicates with the upper passage portion of the rise passage are formed in the housing so as to be open to an inner surface of the slide hole at a position blocked by the wax case when the wax contracts, the inlet hole and the water chamber being communicated with each other through an air vent passage through which air contained in the cooling water is to be directed. According to the above configuration of the invention defined in claim 1, the inlet hole and the outlet hole, which are open to the inner surface of the slide hole for sliding the wax case, are formed in the housing of the thermostat so as to be blocked with the wax case upon contraction of the wax, the inlet hole being in communication with the lower passage portion of the rise passage and the outlet hole being in communication with the upper passage portion of the rise passage. Thus, it is possible to prevent the occurrence of a difference in height in the rise passage at the 6 portions thereof sandwiching the thermostat. Even when the cooling system must be constructed compactly in the vertical direction, it is not necessary that the angle of inclination of the rise passage be set so such a small extent as in the prior art, and air can be allowed to flow rapidly within the rise passage. Besides, since the inlet hole communicates through an air vent passage with the water chamber which is formed in the upper portion of the housing in communication with the bypass passage, the air present in the lower passage portion of the rise passage is discharged quickly to the bypass passage side, whereby the air venting performance can be improved. The invention defined in claim 2 is characterized, in addition to the configuration of the invention defined in claim 1, in that the thermostat is received within the receptacle case in which the housing is fitted, and the air vent passage is formed by both the groove formed in the inner surface of the receptacle case and the outer surface of the housing. According to this configuration, since the air vent passage bypasses the thermostat, the air venting performance can be further improved. The invention defined in claim 3 is characterized, 7 in addition to the configuration of the invention defined in claim 1 or 2, in that the radiator, the water pump and the thermostat are attached to the engine body at approximately the same heights. According to this configuration, the cooling system can be mounted to the engine body compactly in the vertical direction. The subject invention relates to a cooling system for a water-cooled engine including: a main circulation circuit which, with a rise passage permitting upward flow of cooling water as a partial passage, connects a water jacket in an engine body, a radiator, a water pump and the water jacket successively in this order; a sub circulation circuit made up of a bypass passage which bypasses the radiator and a part; of the main circulation circuit; and a thermostat disposed halfway of the rise passage so as to switch over according to the temperature of the cooling water between a state in which the rise passage is blocked, allowing the cooling water to flow and circulate through the sub circulation circuit, and a state in which the bypass passage is blocked, allowing the cooling water to flow and circulate through the main circulation circuit, characterized in that the thermostat is provided with a housing having a slide hole which extends upward across the rise passage halfway of the same passage, also provided with a wax case fitted slidably in the slide hole and whose upper end faces a water chamber formed within the housing in communication with the bypass passage, and further provided with wax contained in the wax case so as to permit the wax case to slide in accordance with expansion and contraction of the wax caused by a change in temperature of the cooling water, the wax case being fitted in the slide hole so as to permit communication of the water chamber with an upper passage portion of the rise passage when the wax contracts; and an inlet hole which communicates with a lower passage portion of the rise passage and an outlet hole which communicates with the upper passage portion of the rise passage are formed in the housing so as to be open to an inner surface of the slide hole at positions blocked by the wax case when the wax contracts, the inlet hole and the water chamber being communicated with each other through an air vent passage through which air contained in the cooling water is to be directed the thermostat is received with a receptacle case in which the housing is fitted, wherein the receptacle case forms the water pump. 8 [Brief Description of the Drawings] [Fig. 1] Fig. 1 is an entire side view of a scooter type motorcycle,-[Fig. 2] Fig. 2 is an enlarged sectional view taken on line 2-2 in Fig. 1; [Fig. 3] Fig. 3 is an enlarged view of a principal portion shown in Fig. 2; [Fig. 4] Fig. 4 is a view as seen in the arrowed direction 4-4 in Fig. 2; [Fig. 5] Fig. 5 is a view as seen in the arrowed direction 5-5 in Fig. 1; [Fig. 6] Fig. 6 is an enlarged sectional view taken on line 6-6 in Fig. 2; [Fig. 7] Fig. 7 is a vertical sectional view of a thermostat in a low temperature condition; [Fig. 8] 9 Fig. 8 is a vertical sectional view of the thermostat in a high temperature condition; [Fig. 9] Fig. 9 is a sectional view taken on line 9-9 in Fig 7; [Fig. 10] Fig. 10 is a side view corresponding to Fig. 6 in the second embodiment of the invention; [Fig. 11] Fig. 11 is a vertical sectional view of a thermostat in a low temperature condition; and [Fig. 12] Fig. 12 is a vertical sectional view of the thermostat in a high temperature condition. ] 10 [Mode for Carrying Out the Invention] Hereinafter, the present invention will be described by way of embodiments thereof illustrated in the accompanying drawings. Figs. 1 to 9 illustrate the first embodiment of the present invention, of which Fig. 1 is an entire side view of a scooter type motorcycle, Fig. 2 is an enlarged sectional view taken on line 2-2 in Fig. 1, Fig. 3 is an enlarged view of a principal portion shown in Fig. 2, Fig. 4 is a view as seen in the arrowed direction 4-4 in Fig. 2, Fig. 5 is a view of a power unit as seen in the arrowed direction 5-5 in Fig. 1, Fig. 6 is an enlarged sectional view taken on line 6-6 in Fig. 2, Fig. 7 is a vertical sectional view of a thermostat in a low temperature condition, Fig. 8 is a vertical sectional view of the thermostat in a high temperature condition, 11 and Fig. 9 is a sectional view taken on line 9-9 in Fig. 7. In Fig. 1 there is illustrated a scooter type motorcycle V provided with a front wheel Wf which is steered by a steering handlebar 11 and a rear wheel Wr which is driven by & swing type power unit P. A body frame F of the motorcycle V is divided into three frames - a front frame 12, a center frame 13 and a rear frame 14. The front frame 12 is a cast aluminum alloy frame integrally provided with a head pipe 12a, a down-tube 12b and a step floor support portion 12c. The power unit P is supported vertically swingably by the center frame 13 through a pivot 15. The center frame 13 is a cast aluminum alloy frame and is connected to a rear end of the front frame 12. The rear frame 14, which extends behind and above the power unit P, is constituted by an annular pipe, with a fuel tank 16 being carried thereon. On an upper surface of the center frame 13 is carried a helmet case 17. The helmet case 17 and the fuel tank 16 are covered with a cover 19 so that they can be opened and closed, the cover 19 being integrally provided with a seat 18. 12 The power unit P comprises a water-cooled type single-cylinder four-cycle engine E with the cylinder disposed toward the front side of the vehicle body and a belt type continuously variable transmission T extending backward of the vehicle body from the left-hand side of the engine E, the engine E and the continuously variable transmission T being coupled together integrally. An upper surface of a rear portion of the transmission T is connected to a rear end of the center frame 13 through a rear cushion 20. An air cleaner 21 is carried on the upper surface of the continuously variable transmission T, a muffler 22 is supported on the right-hand side of the transmission T, and a main stand 23 capable of rising and falling is supported on the underside of the engine E. In Figs. 2 to 4, an engine body 24 of the engine E is provided with first and second engine blocks 27, 28 partitioned from each other by a partition surface 26 which extends in the vertical direction along a crankshaft 25. The first engine block 27 constitutes a cylinder block 27a and a crank case half 27b, while the second engine block 28 constitutes the other half of the crank case. A cylinder head 29, which constitutes the engine body 24 together with the first and second engine 13 blocks 27, 28, is connected to a front end of the first engine block 27 and a head cover 30 is connected to a front end of the cylinder head 29. Further, a generator cover 31 is connected to right side faces of the first and second engine blocks 27, 28. The continuously variable transmission T is provided with a right casing 32 and a left casing 33 which are coupled each other. A front right side face of the right casing 32 is connected to left side faces of the first and second engine blocks 27, 28. Further, a casing 34 of a reduction mechanism is connected to a rear right side face of the right casing 32. A piston 36 is slidably fitted within a cylinder 35 provided in the first engine block 27 and is connected to the crankshaft 25 through a connecting rod 37. A camshaft 38 is rotatably supported in the cylinder head 29 and intake and exhaust valves (not shown) provided in the cylinder head 29 are opened and closed by the camshaft 38. A timing chain 40 is disposed within a chain passage 39 which is formed in the first engine block 27. The timing chain 40 is wound around both a driving sprocket 41 mounted on the crankshaft 25 and a driven sprocket 42 14 mounted on the camshaft 38. With the timing chain 40, the camshaft 38 rotates once every time the crankshaft 25 rotates twice. A driving pulley 43 is mounted on the left end of the crankshaft 25 projecting inside the right and left casings 32, 33. The driving pulley 43 comprises a fixed pulley half 44 fixed to the crankshaft 25 and a movable pulley half 45 capable of moving toward and away from the fixed pulley half 44. The movable pulley half 45 is urged in a direction to approach the fixed pulley half 44 by means of a centrifugal weight 46 which moves radially outwards as the number of revolutions of the crankshaft 25 increases. A driven pulley 48 is mounted on an output shaft 47 which is supported between a rear portion of the right casing 32 and the casing 34 of the reduction mechanism. The driven pulley 48 comprises a fixed pulley half 49 mounted on the output shaft 47 in a relatively rotatable manner and a movable pulley half 50 capable of moving toward and away from the fixed pulley half 49. The movable pulley half 50 is urged toward the fixed pulley half 49 by means of a spring 51. Between the fixed pulley 15 half 49 and the output shaft 47 is disposed a centrifugal clutch 52 which assumes a power transfer state as the engine speed exceeds a preset number of revolutions. An endless V belt 53 is wound around the driving pulley 43 and driven pulley 48. An intermediate shaft 54 and an axle 55 are supported between the right casing 32 and the reduction mechanism casing 34 and in parallel with the output shaft 47. A reduction gear train 56 is disposed among the output shaft 47, intermediate shaft 54 and axle 55. The axle 55 projects through the reduction mechanism casing 34 to the right-hand side and the rear wheel Wry which is a driving wheel, is mounted on the right end of the axle. A rotational power of the crankshaft 25 is transmitted to the driving pulley 43, from which it is further transmitted to the rear wheel Wr via V belt 53, driven pulley 48, centrifugal clutch 52 and reduction gear train 56. An AC generator 57 disposed on the right-hand side of the crankshaft 25 is covered with the generator cover 16 31 and a radiator 58 is disposed on the right-hand side of the generator cover 31. For the supply of cooling air to the radiator 58, a cooling fan 59 fixed onto the right end of the crankshaft 25 so as to be positioned between the AC generator 57 and the radiator 58, whereby the heat radiation capacity of the radiator 58 is kept larger than the quantity of heat generated from the engine E. The cooling fan 59 and the radiator 58 are covered with a synthetic resin cover 60 which is clamped to the generator cover 31, and a louver 61 for introducing air from the exterior is provided on an outer side of the louver 60. A water jacket 62 is provided for both the cylinder block 27a of the first engine block 27 and the cylinder head 34. A water pump 63 for the supply of cooling water to a lower portion of the water jacket 62 on the cylinder block 27a side is connected to the right end of the camshaft 38 so as to be substantially equal in height to the radiator 58. A receptacle case 65 is connected to the right-hand side of the cylinder head 34 and a thermostat 64A is 17 received within the receptacle case 65, with the water pump 63 being received within the space surrounded with the cylinder head 34.and the receptacle case 65. Thus, the radiator 58, water pump 63 and thermostat 64A are mounted to the engine body 24 at approximately the same heights. Referring also to Fig. 5, one end of a cooling water conduit 68 is connected to the cylinder head 34 so as to communicate with an upper portion of the water jacket 62, while the opposite end thereof is connected to a filler neck 70 which can close an upper-end opening with a cap 71 openably. The filler neck 70 is clamped to a rear fender 66 which is mounted to the power unit P for swing motion together with the radiator 58 and which covers the rear wheel Wr from above. The filler neck 70 is connected through a water supply conduit 69 having flexibility such as rubber hose to a water supply port 58a formed in a rear upper portion of the radiator 58. The filler neck 70 is provided with an overflow pipe 70a for allowing cooling water to overflow, the overflow pipe 70a being connected to a reservoir tank (not shown). 18 An output port 58b formed in a front lower portion of the radiator 58 and the receptacle case 65 are connected with each other through a cooling water conduit 72. The cooling water conduit 72 is connected to a suction port of the water pump 63 through the thermostat 64A received within the receptacle case 65. The receptacle case 65 and the water jacket 62 in the first engine block 27 are connected with each other through a cooling water conduit 73. Thus, the water jacket 62, radiator 58 and water pump 63 are connected with one another through the cooling water conduit 68, filler neck 70, water supply-conduit 69 and cooling water conduits 72, 73 and constitute a main circulation circuit 75. In the main circulation circuit 75, cooling water discharged from the water pump 63 flows through the water jacket 62 and the radiator 58 and returns to the water pump 63, and thus the cooling water flows circulatively. In the main circulation circuit 75, as shown in Fig. 6, the outlet port 58b formed in the front lower portion of the radiator 58 and the suction port of the water pump 63 are connected together through a rise passage 76 which 19 causes cooling water to flow upward from the outlet port 58b located at a lower position up to the suction port located at an upper position. The rise passage 7 6 is made up of a lower passage portion 77 which comprises the cooling water conduit 72 and a passage portion formed within the receptacle case 5 and contiguous to the cooling water conduit 72 and an upper passage portion 78 formed within the receptacle case 65 and communicating with the suction port of the water pump 63. The thermostat 64A is received within the receptacle case 65 so as to be positioned between both passage portions 77 and 78. One end of a bypass conduit 7 9 which bypasses the radiator 58 is connected to the cylinder head 34 at a position adjacent to the cooling water conduit 68 so as to communicate with the upper portion of the water jacket 62, while the opposite end of the bypass conduit 79 is connected to a lid member 80 which is clamped to an upper portion of the receptacle case 65. The bypass conduit 79 can communicate through the thermostat 64A in the receptacle case 64 with the upper passage portion 78 which communicates with the suction portion of the water pump 63. 20 In the main circulation circuit 75, the portion between the water pump 63 and the water jacket 62, the portion between the thermostat 64A and the water pump 63, as well as a bypass passage 81 formed between the lid member 80 and the cylinder head 34, including the bypass conduit 74, constitute a sub circulation circuit 82. The thermostat 64A is disposed between the lower and upper passage portions 77, 78 of the rise passage 76 so as to switch over according to the temperature of cooling water between a state in which the rise passage 76 is blocked and the bypass passage 81 is opened, allowing cooling water to flow and circulate in the sub circulation circuit 82, and a state in which the rise passage 76 is opened and the bypass passage 81 is blocked, allowing cooling water to flow and circulate in the main circulation circuit 75. According to the temperature of cooling water the thermostat 64A switches over in which of the main and sub circulation circuits 75, 82 the cooling water is to flow and circulate. Referring also to Figs. 7 and 8, the thermostat 64A extends vertically across the lower and upper passage portions 77, 78 of the rise passage 76 in the main 21 circulation circuit 75 and is provided with a bottomed cylinder-like housing 86A having a bottomed slide hole 85 with a lower end closed, a wax case 87 fitted slidably into the slide hole 85, a spring 88 disposed in a compressed state between the housing 86A and the wax case 87, and wax 89 which is contained in the wax case 87 so as to cause the wax case to slide in accordance with expansion and contraction of the wax caused by a change in temperature of the cooling water. The wax case 87 is slidably fitted in the slide hole 85 so that an upper end thereof faces a water chamber 90 formed within the housing 86A. The housing 86A is fitted in a bottomed mounting hole 91 formed in the receptacle case 85 and is received and fixed into the receptacle case 85 so as to be held between a closed end of the mounting hole 91 and the lid member 80 when an open end of the mounting hole 91 is closed with the lid member 80. At one end of the housing 86A is mounted a bottomed cylinder-like seal member 92 of an elastic material so as to cover the one end of the housing. The one end of the 22 housing 86A is exposed as a tip reinforcing portion 84 to a central part of an inner surface of a closed end of the seal member 92. An open upper end of the housing 86A is in abutment against the lid member 80 and a retaining ring 93 is fitted in an inner surface on the upper end side of the housing 86A. The wax case 87 is made up of a case body 94 whose outer surface is in direct contact with the inner surface of the housing 86A and a cover 95 joined to the case body 94. A peripheral edge portion of a diaphragm 96 is held between the case body 94 and the cover 95. Integral with the case body 94 is a guide cylinder 97 which is slidably fitted in the seal member 92. Wax 89 is contained in the wax case 87 so as to be filled between the diaphragm 96 and the cover 95. The diaphragm 96 is deformed according to expansion and contraction of the wax 89 caused by a change in temperature. On the other hand, into the guide cylinder 97 are slidably fitted a bar-like piston 98, a disc-like plate 99 and a rubber piston 100 in this order from the side opposite to the diaphragm 96. A medium 101 for transmitting the deformation of the diaphragm 96 to the 23 rubber piston 100 is charged into the wax case 87 at the position between the rubber piston 100 and the diaphragm 96. The spring 88, which is for urging the wax case 87 toward the seal member 92, is mounted between the wax case 87 and the retaining ring 93. When the temperature of cooling water is low and the wax is in its contracted state, the wax case 87 is in an abutted position against the seal member 92, as shown in Fig. 7. As the cooling water temperature rises and the wax 89 expands, the diaphragm 96 is deformed so as to deflect downwards in Fig. 8 and the piston 98 is pushed out from the guide cylinder 97, so that the wax case 87 slides away from the seal member 92, i.e., upward, while compressing the spring 88, as shown in Fig. 8. In the housing 86A, an inlet hole 102 communicating with the lower passage portion 77 of the rise passage 76 in the main circulation circuit 75 and an outlet hole 103 communicating with the upper passage portion 78 of the rise passage 76 are formed on a diametrical line of the slide hole 85 so as to be open to an inner surface of the slide hole 85, and a bypass hole 104 for providing 24 communication of the water chamber 90 with the upper passage portion 78 is formed above and adjacent the outlet hole 103. The inlet hole 102 and the outlet hole 103 are formed in the housing 86A in such a manner that when the wax 89 contracts, both holes are closed with the wax case 87 as shown in Fig. 7, while when the wax 89 expands, the wax case 87 slides and both holes are opened to the inner surface of the slide hole 85 at such communicated positions as in Fig. 8. The bypass hole 104 is formed in the housing 86A at a position at which upon contraction of the wax 89 the bypass hole 104 causes the water chamber 90 to communicate with the upper passage portion 78, while when the wax 89 expands and the inlet and outlet holes 102, 102 are opened by a sliding motion of the wax case 87, the bypass hole is blocked by the wax case 87. The water chamber 90 and the inlet hole 102 are in communication with each other through an air vent passage 105 through which the air contained in cooling water is conducted. The air vent passage 105 is formed by both a groove 106 formed in an inner surface of a mounting hole 25 91, the mounting hole 91 being formed in the receptacle case 65, and an outer surface of the housing 86A of the thermostat 64A. The operation of this first embodiment will now be described. Since the inlet and outlet holes 102, 103 are formed in the housing 86A of the thermostat 64A so as to be positioned on a diametrical line of the slide hole 85 which permits a sliding motion of the wax case 87, the inlet hole 102 being in communication with the lower passage portion 77 of the rise passage 76 which is a passage position of the main circulation circuit 75 and the outlet hole 103 being in communication with the upper passage portion 78 of the rise passage 76, it is possible to prevent the occurrence of a difference in height in the rise passage 76 at the portion sandwiching the thermostat 64A. Therefore, even where the cooling system must be constructed compactly in the vertical direction, it is not necessary that the angle of inclination of the rise passage 76 be set so small as in the prior art, but the said angle can be set relatively large so that air can flow quickly through the rise passage 76. Besides, since the inlet hole 102 communicates 26 through the air vent passage 105 with the water chamber 90 which, as a constituent of the bypass passage 81, is formed in an inside upper portion of the housing 86A, the air present in the lower passage portion 77 of the rise passage 76 can be discharged quickly to the bypass passage 81 side. As a result, despite the thermostat 64A being provided halfway of the rise passage 76 which permits cooling water to flow, it is possible to eliminate the need of using an air vent bolt or the like, thereby preventing an increase in the number of components, and improve the air venting performance from the rise passage 76. Since the housing of the thermostat 64A is fitted in the receptacle case 65 and the air vent passage 105 is formed by both the groove 106 formed in the inner surface of the receptacle case 65 and the outer surface of the housing 86A, the air vent passage 105 bypasses the thermostat 64A and hence the air venting performance can be further improved. Further, since the radiator 58, water pump 63 and 27 thermostat 64A are attached to the engine body 24 at approximately the same heights, the cooling system can be mounted to the engine body 24 compactly in the vertical direction. As in this embodiment, by mounting the cooling system vertically compactly to the engine body 24 of the engine E which constitutes the power unit P together with the continuously variable transmission T and which is supported swingably by the body frame F, it is possible to diminish the required space for swing motion and the installation of the cooling system onto the body frame F can be made advantageous. Figs. 10 to 12 illustrate the second embodiment of the present invention, of which Fig. 10 is a side view corresponding to Fig. 6 in the first embodiment, Fig. 11 is a vertical sectional view of a thermostat which is in a low temperature condition, and Fig. 12 is a vertical sectional view of the thermostat which is in a high temperature condition. In these figures, the portions corresponding to the previous first embodiment are identified by the same reference numerals as in the first embodiment. A thermostat 64B is disposed between a lower 28 passage portion 77 and an upper passage portion 78 of a rise passage 76 which constitutes a part of a main circulation circuit 75. According to the temperature of cooling water the thermostat 64B switches over to which of the main circulation circuit 75 and a sub circulation circuit 82 the cooling water is to flow and circulate. A housing 86B of the thermostat 64A is formed integrally with a cylinder head 29 of an engine body 24 or is clamped to the cylinder head 29. A vertically extending slide hole 85 having a closed lower end is formed in the housing 86B. An upper end of the housing 86B is closed with a lid member 80". [0048] A wax case 87 is slidably fitted in the slide hole 85 and a spring 88 is mounted in a compressed state between the lid member 80" and the wax case 87. The wax case 87 is slidably fitted in the slide hole 85 so that an upper end thereof faces a water chamber 90 formed in the housing 86B. The wax case 87 is slidable in accordance with expansion and contraction of wax 89 contained therein. 29 The wax case 87 is composed of a case body 94 whose outer surface is in direct contact with an inner surface of the housing 86B and a cover 95 joined to the case body 94. A peripheral edge portion of a diaphragm 96 is held between the case body 94 and the cover 95 and wax 89 is filled between the diaphragm 96 and the cover 95. Integral with the case body 94 is a guide cylinder 97. A piston 98, a plate 99 and a rubber piston 100 are slidably fitted into the guide cylinder 97, and a medium 101 is charged into the wax case 87 at the position between the rubber piston 100 and the diaphragm 96. An inlet hole 102" communicating with the lower passage portion 77 of the rise passage 76 in the main circulation circuit 75 and an outlet hole 103" communicating with the upper passage portion 78 of the rise passage 76 are formed in the housing 86B so as to be open to the inner surface of the slide hole 85 on a diametrical line of the slide hole. The inlet hole 102" is tapered so as to be smaller in diameter toward the inner surface of the slide hole 85. The outlet hole 103" is formed in the housing 86B so that a portion incapable of being blocked by the wax case 87 30 upon contraction of the wax 89 remains in its upper portion. The upper portion of the outlet hole 103" functions as a bypass hole 104" which permits the water chamber 90 to communicate with the upper passage portion 78 when the temperature of cooling water is low. Besides, the inlet hole 102" and the water chamber 90 are communicated with each other through an air vent passage 107 through which the air contained in cooling water is directed. The air vent passage 107 is formed like a groove above the tapered inlet hole 102" so as to provide communication of the inlet passage 102" with the water chamber 90 when the wax 89 contracts. Also by this second embodiment there can be attained the same effects as in the previous first embodiment. Particularly, since the wax case 87 is put in direct contact with passages in the cooling system and with the engine body 24, it is possible to prevent the occurrence of hunting or overshooting phenomenon caused by a change in temperature of cooling water and hence possible to further improve the cooling performance. 31 Although embodiments of the present invention have been described above, the present invention is not limited thereto, but various design modifications may be made without departing from the scope of the invention defined in the claims. [Effect of the Invention] As set forth above, according to the invention defined in claim 1, air can be allowed to flow quickly by setting the angle of inclination of the rise passage at a relatively large value even when the cooling system must be constructed vertically compactly, and the air present in the lower passage portion of the rise passage is discharged quickly to the bypass passage side. Thus, the air venting performance can be improved while avoiding an increase in the number of components used. According to the invention defined in claim 2, since an air vent passage is formed so as to bypass the thermostat, the air venting performance can be further improved. Further, according to the invention defined in claim 3, the cooling system can be mounted to the engine body in a vertically compact form. 32 [Explanation of Reference Numerals] 24 : engine body 58: radiator 62: water jacket 63 : water pump 64A, 64B: thermostats 75: main circulation circuit 76: rise passage 77 : lower passage portion 78: upper passage portion 33 81: bypass passage 82: sub circulation circuit 85: slide hole 86A, 86B: housings 87: wax case 89: wax 90: water chamber 102, 102": inlet holes 103, 103": outlet holes 105, 107: air vent holes 106: groove E: engine 34 We Claim: 1. A cooling system for a water-cooled engine including: a main circulation circuit which, with a rise passage (76) permitting upward flow of cooling water as a partial passage, connects a water jacket (62) in an engine body (24), a radiator (58), a water pump (63) and the water jacket (62) successively in this order; a sub circulation circuit (82) made up of a bypass passage (81) which bypasses the radiator (58) and a part; of the main circulation circuit (75); and a thermostat (64A, 64B) disposed halfway of the rise passage (76) so as to switch over according to the temperature of the cooling water between a state in which the rise passage (76) is blocked, allowing the cooling water to flow and circulate through the sub circulation circuit (82), and a state in which the bypass passage (81) is blocked, allowing the cooling water to flow and circulate through the main circulation circuit (75), the thermostat (64A, 64B) is provided with a housing (86A, 86B) having a slide hole (85) which extends upward across the rise passage (76) halfway of the same passage, also provided with a wax case (87) fitted slidably in the slide hole (85) and whose upper end faces a water chamber (90) formed within the housing (86A, 86B) in communication with the bypass passage (81), and further provided with wax (89) contained in the wax case (87) so as to permit the wax case (87) to slide in accordance with expansion and contraction of the wax caused by a change in temperature of the cooling water, the wax case (87) being fitted in the slide hole (87) so as to permit communication of the water chamber (90) with an upper passage portion (78) of the rise passage (76) when the wax (89) contracts; and an inlet hole (102, 102") which communicates with a lower passage portion (77) of the rise passage (76) and an outlet hole (103, 103") which communicates with the upper passage portion (78) of the rise passage (76) are formed in the housing (86A, 86B) so as to be open to 35 an inner surface of the slide hole (85) at positions blocked by the wax case (87) when the wax (89) contracts, characterized in that the inlet hole (102, 102") and the water chamber (90) being communicated with each other through an air vent passage (105, 107) through which air contained in the cooling water is to be directed the thermostat (64A) is received with a receptacle case (65) in which the housing (86A) is fitted, wherein the receptacle case (65) forms the water pump (63) 2. A cooling system for a water-cooled engine as claimed in claim 1, wherein the air vent passage (105) is formed by both a groove (106) formed in an inner surface of the receptacle case (65) and an outer surface of the housing (86A). 3. A cooling system for a water-cooled engine as claimed in claim 1 or 2, wherein the radiator (58), the water pump (63) and the thermostat (64A, 64B) are attached to the engine body (24) at approximately the same heights. Dated this 21st day of June, 2001 [SHUKADEV KHURAIJAM] OF REMFRY AND SAGAR ATTORNEY FOR THE APPLICANTS

Documents:

580-mum-2001-abstract(21-06-2001).doc

580-mum-2001-abstract(21-06-2001).pdf

580-mum-2001-cancelled pages(21-06-2001).pdf

580-mum-2001-claims (granted)-(21-06-2001).doc

580-mum-2001-claims (granted)-(21-06-2001).pdf

580-mum-2001-correspondence(13-12-2006).pdf

580-mum-2001-correspondence(ipo)-(20-10-2006).pdf

580-mum-2001-drawing(21-06-2001).pdf

580-mum-2001-form 1(21-06-2001).pdf

580-mum-2001-form 18(10-06-2005).pdf

580-mum-2001-form 2(granted)-(21-06-2001).doc

580-mum-2001-form 2(granted)-(21-06-2001).pdf

580-mum-2001-form 3(16-04-2006).pdf

580-mum-2001-form 3(21-06-2001).pdf

580-mum-2001-form 5(21-06-2001).pdf

580-mum-2001-petition under rule 137(16-03-2006).pdf

580-mum-2001-petition under rule 138(16-03-2006).pdf

580-mum-2001-power of authority(16-03-2006).pdf

580-mum-2001-power of authority(21-11-2001).pdf

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