Title of Invention	A BELT TYPE CONTINUOUSLY VARIABLE TRANSMISSION AND A STRADDLE TYPE VEHICLE
Abstract	A belt type continuously variable transmission 30 includes a primary sheave 71 to which driving force from an engine 29 is transmitted, a secondary sheave 72, and a V-belt 73 wound around the primary sheave 71 and the secondary sheave 72 and formed with a resin block belt. A sheave surface of the primary sheave 71 is plated with chrome. The secondary sheave 72 is made of stainless steel and a sheave surface thereof is not plated with chrome. The sheave surface hardness of the secondary sheave 72 is lower than the sheave surface hardness of the primary sheave 71.

Title of Invention

A BELT TYPE CONTINUOUSLY VARIABLE TRANSMISSION AND A STRADDLE TYPE VEHICLE

Abstract

A belt type continuously variable transmission 30 includes a primary sheave 71 to which driving force from an engine 29 is transmitted, a secondary sheave 72, and a V-belt 73 wound around the primary sheave 71 and the secondary sheave 72 and formed with a resin block belt. A sheave surface of the primary sheave 71 is plated with chrome. The secondary sheave 72 is made of stainless steel and a sheave surface thereof is not plated with chrome. The sheave surface hardness of the secondary sheave 72 is lower than the sheave surface hardness of the primary sheave 71.

Full Text	BELT TYPE CONTINOUSLY VARIABLE TRANSMISSION AND STRADDLE TYPE VEHICLE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a belt type continuously variable transmission and a straddle type vehicle having the belt type continuously variable transmission. 2. Description of the Related Art Conventionally, straddle type vehicles having the belt type continuously variable transmission are known. The belt type continuously variable transmission has a primary sheave to which the driving force from an engine is transmitted and a secondary sheave to which the driving force is transmitted from the primary sheave via a V-belt. In the belt type continuously variable transmission, a speed reduction ratio varies in accordance with respective changes of a winding radius of the belt in the primary sheave and a winding radius of the V-belt in the secondary sheave. In the meantime, if the V-belt is made of rubber, the V-belt is likely to wear to reduce durability. Also, due to heat generation following deformation of the V-belt, there can be another problem such that the V-belt is likely to deteriorate. Therefore, an idea in which a resin block belt made of coupled multiple resin blocks is used as the belt type continuously 1 variable transmission is proposed (See JP-A-2002-147553, for example). In the belt type continuously variable transmission having the resin block belt, the belt itself hardly wear. However there arises, to the contrary, another problem such that surfaces of the sheaves are likely to wear. Thus, JP-A-2002-147553 (see Page 2, the right column, lines 34 to 38) proposes that the respective surfaces of the primary sheave and the secondary sheave are plated with chrome. The resin block belt has some extent of strength. However, it was revealed that, if the respective surfaces of the primary sheave and the secondary sheave are plated with chrome, wear of the resin block belt increases. As thus discussed, it was difficult, according to the conventional art, to highly compatibly ensure both of the prevention of wear of the V-belt and the prevention of wear of the sheaves. SUMMARY OF THE INVENTION The present invention is made under the circumstances, and an object of the present invention is to highly compatibly ensure both of prevention of wear of a V-belt and prevention of wear of sheaves. The inventors made every effort in their researches to achieve the object and paid attention to a difference between contact pressures (sheave thrust/ contact area) of the sheave 2 surfaces of the primary sheave and the secondary sheave. That is, in consideration of the primary sheave first, as shown in FIG. 10 (a) , if an engine speed is low (in other words, if a rotational speed of the primary sheave 71 is low), the speed reduction ratio of the belt type continuously variable transmission becomes large and a winding radius rl of the V-belt 73 in the primary sheave 71 becomes relatively small. Accordingly, a contact area S1 between the primary sheave 71 and the V-belt 73 also becomes relatively small. Meanwhile, if the engine speed is low, the driving force (= sheave thrust) transmitted from the primary sheave 71 to the V-belt 73 is relatively small. Thus, the contact pressure of the sheave surface of the primary sheave 71 is not so large. On the other hand, if the engine speed is high, the driving force transmitted from the primary sheave 71 to the V-belt 73 is relatively large. However, as shown in FIG. 10 (b) , if the engine speed is high, the speed reduction ratio becomes small and the winding radius rl of the V-belt 73 in the primary sheave 71 becomes relatively large. Accordingly, the contact area SI between the primary sheave 71 and the V-belt 73 becomes relatively large. Therefore, even though the engine speed is high, the contact pressure of the sheave surface of the primary sheave 71 is not so large. To the contrary, the secondary sheave may have the following situations. That is, as shown in FIG. 10 (a) , if the 3 engine speed is low, the speed reduction ratio becomes large and a winding radius r2 of the V-belt 73 in the secondary sheave 72 becomes relatively large. Accordingly, a contact area S2 between the secondary sheave 72 and the V-belt 73 also becomes relatively large. Meanwhile, if the engine speed is low, the driving force transmitted from the V-belt 73 to the secondary sheave 72 becomes relatively small. Thus, the contact pressure of the sheave surface of the secondary sheave 72 becomes relatively small. On the other hand, as shown in FIG. 10(b), if the engine speed is high, the speed reduction ratio becomes small and the winding radius r2 of the V-belt 73 in the secondary sheave 72 becomes relatively small. Accordingly, the contact area S2 between the secondary sheave 72 and the V-belt 73 also becomes relatively small. Meanwhile, if the engine speed is high, the driving force transmitted from the V-belt 73 to the secondary sheave 72 becomes relatively large. Thus, if the engine speed is high, the contact pressure of the sheave surface of the secondary sheave 72 becomes relatively large. That is, in the primary sheave, the contact pressure does not become so large even though the engine speed varies. To the contrary, it is conceivable that, in the secondary sheave, the contact pressure becomes very large under the condition that the engine speed is large (i.e., at the so-called top speed). From such analyses, the inventors realize that it is 4 important to prevent wear of the belt in the secondary sheave at the top speed. Also, the inventors realize the following facts as different points between the primary sheave and the secondary sheave. That is, because the primary sheave transmits the driving force from the engine to the V-belt, the primary sheave is likely to be affected by fluctuations of the engine speed. To the contrary, the driving force from the engine is transmitted to the secondary sheave via the V-belt. Therefore, the secondary sheave is hardly affected by the fluctuations of the engine speed in comparison with the primary sheave. From such analyses, the inventors realize that both of prevention of wear of the belt and prevention of wear of the sheaves are highly compatibly ensured by making the surface hardness of the secondary sheave less than the surface hardness of the primary sheave. The inventors, thus, made the following invention. That is, the belt type continuously variable transmission according to the present invention includes a primary sheave to which the driving force from an engine is transmitted, a secondary sheave, and a V-belt wound around the primary sheave and the secondary sheave, the V-belt having a contact part contacting with the primary sheave and the secondary sheave, and at least a portion of the contact part being made of resin. The surface hardness of the contact part of the secondary sheave 5 contacting with the V-belt is lower than the surface hardness of a contact part of the primary sheave contacting with the V-belt. According to the above belt type continuously variable transmission, the surface hardness of the contact portion of the secondary sheave is relatively low. Even though the belt type continuously variable transmission is at the top speed where the contact pressure becomes large, the V-belt in the secondary sheave can be prevented from wearing. Meanwhile, because the secondary sheave is hardly affected by the fluctuations, the secondary sheave does not remarkably wear in comparison with the primary sheave even the surface hardness of the secondary sheave is relatively low. Accordingly, both of the prevention of the wear of the V-belt and the prevention of the wear of the sheaves can be highly compatibly ensured. As thus discussed, according to the present invention, in the belt type continuously variable transmission, both of the prevention of the wear of the V-belt and the prevention of the wear of the sheaves can be highly compatibly ensured. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a motorcycle according to an embodiment; FIG. 2 is a top plan view, showing relationships among positions of a vehicle frame, a leg shield, an engine unit and 6 so forth; FIG. 3 is a right elevational view of the engine unit; FIG. 4 is a left elevational view of the engine unit; FIG. 5 is a cross sectional view, showing a mount condition of the engine unit; FIG. 6 is a cross sectional view, showing an internal structure of the engine unit; FIG. 7 is a cross sectional view, showing a part of the internal structure of the engine unit; FIG. 8 is a side elevational view of a V-belt; FIG. 9 is a cross sectional view, taken along the line IX-IX of FIG. 8; FIG. 10 is an illustration, showing a winding condition of the V-belt, and (a) shows a condition at a low speed and (b) shows a condition at the top speed; FIG. 11 is an illustration, showing a sheave surface of a primary sheave according to Embodiment 2, (a) is a front elevational view, and (b) a cross sectional view; FIG. 12 is an illustration, showing a sheave surface of a secondary sheave according to Embodiment 2, and (a) is a front elevational view, and (b) a cross sectional view; FIG. 13 is a front elevational view of the sheave surface according to a variation; FIG. 14 is a graph, showing test data; and FIG. 15 is a graph, showing other test data. 7 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereunder, an embodiment of the present invention will be described based upon the accompanying drawings. As shown in FIG. 1, a straddle type vehicle according to this embodiment is a motorcycle 10. The motorcycle 10 has a vehicle frame 11 forming a framework and a seat 16 on which a rider sits. The motorcycle 10 is the so-called moped type motorcycle. However, the straddle type vehicle according to the present invention can be motorcycles other than the moped type (such as, for example, motorcycle type and scooter type motorcycles) or straddle type vehicles other than motorcycles (such as, for example, ATVs). In the following descriptions, the fore to aft and lateral directions mean directions which the rider sitting on the seat 16 perceives. The vehicle frame 11 includes a steering head pipe 12, a single main frame 13 extending obliquely downward rearward from the steering head pipe 12, a left and right pair of seat rails 14L (see FIG. 2) , 14R extending obliquely upward rearward from a mid portion of the main frame 13, and left and right seat pillar tubes 15L, 15R connected to a rear end portion of the main frame 13 and mid portions of the seat rails 14L, 14R. A vehicle cover 21 covers top and lateral sides of the 8 vehicle frame 11. A space 17 recessed downward in the side elevational view is defined above the vehicle cover 21 and in front of the seat 16. Also, a center tunnel lla through which the main frame 13 extends is defined under the vehicle cover 21. The steering head pipe 12 supports a front wheel 19 via a front fork 18. The seat rails 14L, 14R support a fuel tank 20 and the seat 16 thereabove. The seat 16 extends from an upper location of the fuel tank 20 toward rear ends of the seat rails 14L, 14R. The fuel tank 20 is disposed above top surfaces of respective front half portions of the seat rails 14L, 14R and is covered with the vehicle cover 21 and the seat 16. A first pair of left and right engine brackets 22L, 22R (see FIGs. 3 and 4) protrude downward from the mid portion of the main frame 13. The rear end portion of the main frame 13 has a second pair of left and right engine brackets 23L, 23R (see FIG. 5) and a pair of left and right rear arm brackets 24L, 24R (see FIGs. 3 and 4). The rear arm brackets 24L, 24R protrude downward from the rear end portion of the main frame 13. The rear arm brackets 24L, 24R have a pivot shaft 38. As shown in FIG. 1, the pivot shaft 38 pivotally carries a front end portion of a rear arm 25. A rear end portion of the rear arm 25 supports a rear wheel 26. The vehicle frame 11 suspends the rear half of the rear arm 25 via cushion units 27. 9 As shown in FIG. 5, the second paired brackets 23L, 23R protrude downward from the rear end portion of the main frame 13. The second pair of left and right engine brackets 23L, 23R are spaced apart from each other and oppose each other in a width direction of the vehicle. As shown in FIG. 1, the vehicle frame 11 supports an engine unit 28 driving the rear wheel 26. Specifically, as shown in FIG. 4, the engine unit 28 includes a crankcase 35, a cylinder 43 and a cylinder head 44 . The crankcase 35 has first and second engine mount sections 36, 37. The respective first engine mount sections 36 protrude upward from a top side of a front end portion of the crankcase 35 and are supported by the first engine brackets 22L, 22R. The respective engine mount sections 37 protrude obliquely upward rearward from a top side of a rear end portion of the crankcase 35 and are supported by the second paired engine brackets 23L, 23R (see FIG. 5 also) . The crankcase 35 thus depends from the main frame 13. The engine unit 28 includes an engine 29 and a belt type continuously variable transmission (hereunder, called CVT) 30 (see FIG. 6), details of which will be described later. Although the engine 2 9 is not limited to any types, the engine 29 in this embodiment is a four-stroke, single cylinder engine. As shown in FIG. 1, the motorcycle 10 includes a front fender 31 covering a top side and a rear side of the front wheel 19 and a rear fender 32 covering a portion of the rear wheel 10 28 between top and rear sides thereof. Also, the motorcycle 10 includes a front cowling 33 and lateral leg shields 34L, 34R (see FIG. 2) in addition to the vehicle cover 21. As shown in FIG. 2, footrests 85L, 85R made of rubber or the like are disposed on the left and right sides of the engine unit 28. The crankcase 35 of the engine unit 28 supports the left and right footrests 85L, 85R via a coupling bar 87 made of metal and an attaching plate 88 (see FIGs. 3 and 4) fixed to the coupling bar 87. As shown in FIGs. 1 and 2, a brake pedal 84 is disposed in front of the footrest 85R on the right side. The brake pedal 84 extends below a transmission case 53 and projects obliquely forward on the right side. The brake pedal 84 also extends obliquely upward forwardly on the right side of the transmission case 53. As shown in FIG. 2, when the motorcycle 10 runs, the right foot 62a of the rider is positioned next to the transmission case 53 in the width direction of the vehicle. Next, an internal structure of the engine unit 28 will be described. As shown in FIG. 6, the engine unit 28 includes the engine 29, the CVT 30, a centrifugal clutch 41 and a reduction gear mechanism 42. The engine 29 includes the crankcase 35, the cylinder 43 coupled with the crankcase 35 and the cylinder head 44 coupled with the cylinder 43. The crankcase 35 has divided two case 11 blocks, i.e., a first case block 35a positioned on the left side and a second case block 35b positioned on the right side. The first case block 35a and the second case block 35b oppose each other in the width direction of the vehicle. The crankcase 35 contains a crankshaft 4 6 therein. The crankshaft 4 6 extends in the width direction of the vehicle to be disposed horizontally. The crankshaft 46 is journaled by the first case block 35a via a bearing 47 and the second case block 35b via a bearing 48. A piston 50 is slidably disposed within the cylinder 43. One end of a connecting rod 51 is coupled with the piston 50. A crank pin 59 is disposed between a left side crank arm 46a and a right side crank arm 4 6b. The other end of the connecting rod 51 is coupled with the crank pin 59. A recessed portion 44a and intake ports (not shown) and exhaust ports (not shown) both communicating with the recessed portion 44a are defined in the cylinder head 44. An ignition plug 55 is inserted into the recessed portion 44a of the cylinder head 44. As shown in FIG. 3, intake pipes 52a are connected to the intake ports, while exhaust pipes 52 are connected to the exhaust ports. As shown in FIGs. 1 and 2, the exhaust pipes 52 extend from the cylinder head 44 rearward and obliquely downward on the right side and further extend rearward below the transmission case 53. The exhaust pipes 52 are then connected to a muffler placed on the right side 12 of the rear wheel 26. As shown in FIG. 6, a cam chain chamber 56 is defined in the inside of the cylinder 43 on the left side thereof to connect the inside of the crankcase 35 and the inside of the cylinder head 44. A timing chain 57 is disposed in the cam chain chamber 56. The timing chain 57 is wound around the crankshaft 46 and the camshaft 58. The camshaft 58 rotates with the rotation of the crankshaft 46 to move each of intake valves and exhaust valves, which are not shown, between an open position and a closed position. A generator case 66 containing a generator 63 is detachably mounted to a left side of a front half of the first case block 35a. The transmission case 53 containing the CVT 30 is mounted to a right side of the second case block 35b. An opening is defined in a right side surface of a rear half of the second case block 35b. A clutch cover 60 closes the opening. The clutch cover 60 is detachably fixed to the second case block 35b by bolts 61. The transmission case 53 is formed independently from the crankcase 35. The transmission case 53 includes an inner case 53a covering an inner side (left side) of the CVT 30 in the width direction of the vehicle and an outer case 53b covering an outer side (right side) of the CVT 30 in the width direction of the vehicle. The inner case 53a is attached to a right surface of the crankcase 35, while the outer case 53b is 13 attached to a right surface of the inner case 53a. A belt chamber 67 is defined inside of the inner case 53a and the outer case 53b to contain the CVT 30 therein. As shown in FIG. 6, a right end portion of the crankshaft 46 extends to the belt chamber 67 through the second case block 35b and the inner case 53a. A primary sheave 71 of the CVT 30 is fitted onto the right end portion of the crankshaft 46. The primary sheave 71 thus rotates with the rotation of the crankshaft 46. A right portion of the crankshaft 46 (strictly, a portion positioned on the right side of the bearing 48) forms a primary sheave shaft 4 6c. On the other hand, the left end portion of the crankshaft 46 extends into the generator case 66 through the first case block 35a. The generator 63 is mounted to the left end portion of the crankshaft 46. The generator 63 includes a stator 64 and a rotor opposing the stator 64. The rotor 65 is fixed to a sleeve 74 rotating together with the crankshaft 46. The stator 64 is fixed to the generator case 66. A secondary sheave shaft 62 is disposed in the rear half of the crankcase 35 to extend parallel to the crankshaft 46. As shown in FIG. 7, the clutch cover 60 supports the central portion of the secondary sheave shaft 62 via a bearing 75. The left end portion of the second case block 35b supports a left portion of the secondary sheave shaft 62 via a bearing 76. A right end portion of the secondary sheave shaft 62 extends 14 to the belt chamber 67 through the second case block 35b and the clutch cover 60. A secondary sheave 72 of the CVT 30 is coupled with the right end portion of the secondary sheave shaft 62. As shown in FIG. 6, the CVT 30 includes the primary sheave 71, the secondary sheave 72 and the V-belt 73 wound around the primary sheave 71 and the secondary sheave 72. As described above, the primary sheave 71 is mounted to the right portion of the crankshaft 46. The secondary sheave 72 is coupled with the right portion of the secondary sheave shaft 62. The primary sheave 71 includes a fixed sheave half 71a positioned outside in the width direction of the vehicle, and a movable sheave half 71b positioned inside in the width direction of the vehicle and opposing the fixed sheave half 71a. The fixed sheave half 71a is fixed to the right end portion of the primary sheave shaft 46c and rotates together with the primary sheave shaft 4 6c. The movable sheave half 71b is placed on the left side of the fixed sheave half 71a and is slidably mounted to the primary sheave shaft 4 6c. The movable sheave half 71b thus rotates together with the primary sheave shaft 46c and is also slidable in the axial direction of the primary sheave shaft 4 6c. A belt groove is formed between the fixed sheave half 71a and the movable sheave half 71b. Cooling fans 95 are formed on an outer surface (right side surface in FIG. 6) of the fixed sheave half 71a. A cam surface 15 111 is formed on the left portion of the movable sheave half 71b. A cam plate 112 is disposed on the left side of the cam surface 111. A roller weight 113 is placed between the cam surface 111 of the movable sheave 71b and the cam plate 112. The secondary sheave 72 includes a fixed sheave half 72a positioned inside in the width direction of the vehicle, and a movable sheave half 72b positioned outside in the width direction of the vehicle and opposing the fixed sheave half 72a. The movable sheave half 72b is mounted to the right end portion of the secondary sheave shaft 62. The movable sheave half 72b is rotatable together with the secondary sheave shaft 62 and is slidable on the secondary sheave shaft 62 in the axial direction thereof. A compression coil spring 114 is disposed at the right end of the secondary sheave shaft 62. The movable sheave half 72b receives the leftward urging force of the compression coil spring 114 that is directed leftward. A shaft core portion of the fixed sheave half 72a is a cylindrical slide collar that is fitted on the secondary sheave shaft 62 by spline connection. A speed reduction ratio of the CVT 30 is decided in accordance with relationships between a magnitude of the force with which the roller weight 113 pushes the movable sheave half 71b rightward and a magnitude of the force with which the compression coil spring 114 pushes the movable sheave half 72b of the secondary sheave 72 leftward. 16 That is, upon increase of the rotational speed of the primary sheave shaft 46c, the roller weight 113 receives the centrifugal force and moves outward in the radial direction to push the movable sheave half 71b rightward. Then, the movable sheave half 71b moves rightward and the belt winding radius in the primary sheave 71 becomes larger. Following this operation, the belt winding radius in the secondary sheave 72 becomes smaller. The movable sheave half 72b of the secondary sheave 72 moves rightward against the urging force of the compression coil spring 114. As a result, the winding radius of the V-belt 73 in the primary sheave 71 becomes larger, while the winding radius in the secondary sheave 72 becomes smaller. The speed reduction ratio becomes smaller, accordingly. In the meantime, upon decrease of the rotational speed of the primary sheave shaft 4 6c, the roller weight 113 moves inward in the radial direction along the cam surface 111 of the movable sheave half 71b and the cam plate 112 because the centrifugal force of the roller weight 113 becomes smaller. Therefore, the force with which the roller weight 113 pushes the movable sheave half 71b rightward becomes smaller. Then, the urging force of the compression coil spring 114 becomes larger relative to the above force. The movable sheave half 72b of the secondary sheave 72 moves leftward. In response to this movement, the movable sheave half 71b of the primary sheave 71 also moves leftward. As a result, the belt winding radius 17 in the primary sheave 71 becomes smaller, while the belt winding radius in the secondary sheave 72 becomes larger. The speed reduction ratio becomes larger, accordingly. The fixed sheave half 71a and the movable sheave half 71b of the primary sheave 71 are made of aluminum or an aluminum alloy containing aluminum as a part thereof. Sheave surfaces (surfaces contacting with the V-belt 73) of the fixed sheave half 71a and the movable sheave half 71b of the primary sheave 71 are plated with chrome. Consequently, each sheave surface hardness of the fixed sheave half 71a and the movable sheave half 71b teaches approximately l,000Hv. However, the plating material for coating the sheave surfaces is not limited to the chrome if the material is sufficient to enhance the wear resistance. The fixed sheave half 72a and the movable sheave body 72b of the secondary sheave 72 are made of stainless steel (SUS304) . Additionally, no sheave surfaces of the fixed sheave half 72a and the movable sheave body 72b of the secondary sheave 72 are plated with chrome. Consequently, The respective sheave surface hardness values of the fixed sheave half 72a and the movable sheave half 72b reach approximately 400Hv. A seal groove 68a is formed along a periphery of the inner case 53a on the left side thereof. A periphery of the second case block 35b on the right side thereof is inserted into the seal groove 68a. Additionally, an 0-ring 68 is interposed 18 between the inner case 53a and the second case block 35b in the seal groove 68a. Also, another seal groove 69a is formed along the periphery of the inner case 53a on the right side thereof. A periphery of the outer case 53b is inserted into the seal groove 69a. Another O-ring 69 is interposed between the inner case 53a and the outer case 53b in the seal groove 69a. The outer case 53b and the second case block 35b are coupled with each other by bolts 70 under a condition that the inner case 53a is interposed between the outer case 53b and the second case block 35b. As shown in FIG. 7, the centrifugal clutch 41 is mounted to the left portion of the secondary sheave shaft 62. The centrifugal clutch 41 is a wet type multiple disk clutch and includes a generally cylindrical clutch housing 78 and a clutch boss 77. The clutch housing 78 is fitted onto the secondary sheave shaft 62 by spline connection and rotates in unison with the secondary sheave shaft 62. A plurality of circular clutch disks 79 are attached to the clutch housing 78. The clutch disks 7 9 are spaced apart from each other in the axial direction of the secondary sheave shaft 62. A cylindrical gear 80 is rotatably fitted on and around the left portion of the secondary sheave shaft 62 via two bearings 81a, 81b. The clutch boss 77 is positioned inside relative to the clutch disks 79 in the radial direction and is positioned outside relative to the gear 80 in the radial 19 direction. The clutch boss 77 meshes with the gear 80. The gear 80 thus rotates together with the clutch boss 77. A plurality of circular friction disks 82 are attached to the clutch boss 77 externally in the radial direction. The friction disks 82 are spaced apart from each other in the axial direction of the secondary sheave shaft 62. The respective friction disks 82 are interposed between the neighboring clutch disks 79, 79. A plurality of cam surfaces 83a are formed on the left side of the clutch housing 78. Roller weights 84a are disposed between the cam surfaces 83a and the clutch disk 79 placed at the right-most position and opposing the cam surfaces 83a. The centrifugal clutch 41 is automatically switched between a clutch-in condition (connected condition) and a clutch-out condition (disconnected condition) in accordance with magnitudes of the centrifugal force affected to the roller weights 84a. That is, when a rotational speed of the clutch housing 78 exceeds a preset speed, the centrifugal force moves the roller weights 84a outward in the radial direction. The roller weights 84a thus push the clutch disks 79 leftward. As a result, the clutch disks 79 and the friction disks 82 compressively contact with each other. The centrifugal clutch 41 thus is in the clutch-in condition in which the driving force of the secondary sheave shaft 62 is transmitted through the gear 80 20 and the reduction gear mechanism 42 to the output shaft 85. On the other hand, when the rotational speed of the clutch housing 78 becomes lower than the preset speed, the centrifugal force exerted on the roller weights 84a becomes smaller. The roller weights 84a thus move inward in the radial direction. As a result, the clutch disks 79 and the friction disks 82 are released from the state of compressive contact. The centrifugal clutch 41 thus is brought in the clutch-out condition in which no driving force of the secondary sheave shaft 62 is transmitted through the gear 8 0 and the reduction gear mechanism 42. Additionally, in FIG. 7, the front (upper side in FIG. 7) portion of the centrifugal clutch 41 represents the clutch-out condition, while the rear (lower side in FIG. 7) portion thereof represents the clutch-in condition. The reduction gear mechanism 42 is interposed between the centrifugal clutch 41 and an output shaft 85. The reduction gear mechanism 42 has a shift shaft 100 extending parallel to the secondary sheave shaft 62 and the output shaft 85. The shift shaft 100 is journaled for rotation by the first case block 35a via a bearing 101 and is also journaled for rotation by the second case block 35b via a bearing 102. A first shift gear 103 meshing with the gear 80 is placed at a right end portion of the shift shaft 100. A second shift gear 104 having a diameter smaller than a diameter of the first shift gear 103 is placed at a central 21 portion of the shift shaft 100. A third shift gear 105 meshing with the second shift gear 104 is externally and circumferentially formed at a right end portion of the output shaft 85. The left end portion of the secondary sheave shaft 62 supports an internal circumferential portion of the right end portion of the output shaft 85 via a bearing 106. Accordingly, the secondary sheave shaft 62 journals the output shaft 85 for rotation via the bearing 106. A left end portion of the first case block 35a journals a central portion of the output shaft 85 for rotation via a bearing 107. In the structure described above, the clutch boss 77 and the output shaft 85 are coupled with each other through the gear 80, the first shift gear 103, the shift shaft 100, the second shift gear 104 and the third shift gear 105. The output shaft 85 thus rotates with the rotation of the clutch boss 77. A left end portion of the output shaft 85 extends through the first case block 35a and projects outside of the crankcase 35. A drive sprocket 108 is fixed to the left end portion of the output shaft 85. A chain 109 is engaged with the drive sprocket 108 to transmit the driving force from the output shaft 85 to the rear wheel 26. Additionally, the mechanism for transmitting the driving force to the rear wheel 2 6 is not limited to the chain 109. Other components such as, for example, a transmitting belt, a gear train of plural gears assembled with each other and a drive shaft may be used as the mechanism 22 for transmitting the driving force from the output shaft 85 to the rear wheel 26. Next, a structure of the V-belt 73 will be described. As shown in FIGs. 8 and 9, the V-belt 73 includes a plurality of resin blocks 73a aligned in one direction and a pair of coupling bodies 73b for coupling the resin blocks 73a. As shown in FIG. 9, each resin block 73a is generally formed as a trapezoid to extend along the respective belt grooves of the primary sheave 71 and the secondary sheave 72. Recessed portions 73c recessed inward are formed at respective lateral sides of each resin block 73a. The coupling bodies 73b are endlessly formed. As shown in FIG. 8, the coupling bodies 73b extend in the alignment direction of the resin blocks 73a and are inserted into the recessed portions 73c of the respective resin blocks 73a. Because the coupling bodies 73b are inserted into the recessed portions 73c of the resin blocks 73a as thus described, the plurality of resin blocks 73 are coupled with each other via the paired coupling bodies 73b. Each coupling body 73b is made of rubber. As shown in FIG. 9, a plurality of reinforcing core wires 73d are embedded in each coupling body 73b of rubber. In this V-belt 73, the left and right lateral side surfaces of the resin blocks 73a and the coupling bodies 73b are contact surfaces in contact with the respective sheave surfaces of the primary sheave 71 and the secondary sheave 72. 23 Additionally, any V-belts are sufficient to be the V-belt for the present invention if at least a part of the contact portion thereof contacting with the sheave surfaces is made of resin. That is, the V-belt for the present invention is not limited to the V-belt 73 in which the coupling bodies 73b couple the plurality of resin blocks 73a with each other. As thus described, according to the CVT 30 of this embodiment, the sheave surface hardness of the secondary sheave 72 is lower than the sheave surface hardness of the primary sheave 71. Therefore, the wear of the V-belt 73 in the secondary sheave 72 can be avoided even in the top speed where the contact pressure of the sheave surfaces is high. On the other hand, because the secondary sheave 72 is hardly affected by fluctuations of the engine speed in comparison with the primary sheave 71, the secondary sheave 72 is unlikely to remarkably wear in comparison with the primary sheave 71, even though the sheave surface hardness of the secondary sheave 72 is relatively low. Accordingly, both of the prevention of the wear of the V-belt 73 and the prevention of the wear of the sheaves (the primary sheave 71 and the secondary sheave 72) can be highly compatibly ensured. In this embodiment, the sheave body of the primary sheave 71 (the fixed sheave half 71a and the movable sheave half 71b) is made of aluminum and the sheave surface of the sheave body is coated with chrome. Therefore, the surface hardness of the 24 sheave surface can be raised while the sheave body is lightened. Also, because aluminum has good cooling retaining property, the cooling performance of the primary sheave 71 can be enhanced. Higher performance of the CVT 30 in turn thus can be achieved. On the other hand, the fixed sheave half 72a and the movable sheave half 72b of the secondary sheave 72 are made of stainless steel and the sheave surfaces thereof are not plated with chrome. Accordingly, the CVT 30 can be inexpensively produced to the extent that no plating is necessary for the secondary sheave 72. Further, according to this embodiment, the surface hardness of the sheave surface of the primary sheave 71 can be raised higher than the surface hardness of the sheave surface of the secondary sheave 71 by the relatively simple method or plating process. Additionally, stainless steel has the superior wear resistance. The corrosion resistance of the secondary sheave 72 thus can be maintained in a good state without the sheave surface of the secondary sheave 72 being plated. Because any rust hardly occurs, the ambient air can cool the secondary sheave 72 without requiring any particular measures. Because the secondary sheave 72 in this embodiment is made of stainless steel, the sheave surface hardness of the secondary sheave 72 can be approximately 400Hv. However, the sheave surface hardness of the secondary sheave 72 is only required to be equal to or higher than l00Hv in view of the 25 prevention of the wear of the sheave surface, and thus is not limited to be about 400Hv. In the CVT 30 according to this embodiment, a distance in which the V-belt 73 moves in the radial direction of the secondary sheave 72 while a condition under which the speed reduction ratio is the maximum value (top speed) varies to another condition under which the speed reduction ratio is the minimum value (low speed) is shorter than a distance in which the V-belt 73 moves in the radial direction of the primary sheave 72. Specifically, the distance of the movement of the V-belt 73 in the radial direction of the sheaves is represented by a difference between the belt winding radius at the top speed and the belt winding radius at the low speed. In this embodiment, the difference between the belt winding radius at the top speed and the belt winding radius at the low speed in the primary sheave 71 is approximately 36.5mm, while the difference between the belt winding radius at the top speed and the belt winding radius at the low speed in the secondary sheave 72 is approximately 32.5mm ( As thus discussed, the amount of the movement of the V-belt 73 in the radial direction in the secondary sheave 72 is shorter than that in the primary sheave 71. Therefore, the wear of the secondary sheave 72 can be prevented even though the sheave surface hardness of the secondary sheave 72 is lower than the sheave surface hardness of the primary sheave 71. 26 As shown in FIG. 10(a), in the CVT 30 according to this embodiment, a distance between the primary sheave 71 and the secondary sheave 72 is short in comparison with sizes of the primary sheave 71 and the secondary sheave 72. Specifically, in this embodiment, a distance L between the axis of the primary sheave 71 and the axis of the secondary sheave 72 is less than double the diameter D2 of the secondary sheave 72. Also, both of the primary sheave 71 and the secondary sheave 72 are disposed between the axis of the front wheel 19 and the rear wheel 26 (see FIG. 1) . In this embodiment, therefore, a ratio of the part contacting with the sheave surfaces of the primary sheave 71 and the secondary sheave 72 to the whole length of the V-belt 73 is large. Accordingly, ingoing and outgoing times of the V-belt 73 to and from the sheave grooves are frequent. The CVT 30 thus intrinsically has the structure in which the V-belt 73 is likely to wear. In this embodiment, however, the wear of the V-belt 73 can be prevented as discussed above. Thus, no problem arises even though the distance between the primary sheave 71 and the secondary sheave 72 is short. As shown in FIGs. 11 and 12, a CVT 30 according to Embodiment 2 has a structure in which a spiral groove is formed in each of the sheave surfaces of the primary sheave 71 and the secondary sheave 72 of Embodiment 1. 27 The CVT 30 needs some frictional force between the sheaves 71, 72 and the V-belt 73 to properly transmit the driving force. In the meantime, however, because the V-belt 73 travels between the primary sheave 71 and the secondary sheave 72, respective portions of the V-belt 73, in local views, continuously go into the sheave grooves and go out therefrom. Some extent of slidability (hereunder, "lubrication property" is used) thus is necessary between the V-belt 73 and the respective sheaves 71, 72. This is because, unless the lubrication property is ensured, heat is generated by the friction between the V-belt 73 and the sheaves 71, 72, and the CVT 30 is likely to be under an excessively heated condition. Meanwhile, the CVT 30 is normally used under the circumstances in which no oil, water or the like are allowed to enter the CVT 30 (hereunder, referred to "under the dry circumstances"). No lubricating agent is permissible to be applied between the V-belt 73 and the sheaves 71, 72. Thus, it is conceivable that the lubrication property between the sheaves 71, 72 and the V-belt 73 is brought mainly by powder originating from the V-belt 73 (wear powder) . That is, it is conceivable that the sheaves 71, 72 and the V-belt 73 are slidable with each other while keeping some extent of the friction because the wear powder originating from the V-belt 73 is retained on the sheave surfaces. If, however, the sheave surfaces are smooth, proper 28 retention of the wear powder on the contact portions with the V-belt 73 is difficult. If the retention is difficult, proper keeping of the lubrication property between the sheaves 71, 72 and the V-belt 73 is also difficult. Consequently, irregularities for retaining the wear powder are preferably given to the sheave surfaces (at least the portions in contact with the V-belt 73) . As shown in FIGs. ll(a) and (b), in this embodiment, a groove 91 is formed on the sheave surfaces of the fixed sheave half 71a and the movable sheave half 71b of the primary sheave 71 by turning. Also, as shown in FIGs. 12(a) and (b) , another groove 91 is formed on the sheave surfaces of the fixed sheave half 72a and the movable sheave half 72b of the secondary sheave 72 by turning. The respective grooves 91 of this embodiment are spirally formed around axes 92 of the sheave halves 71a, 71b, 72a, 72b. As shown in FIG. 11(b) and FIG. 12(b), because of having the grooves 91, cross sections of the sheave halves 71a, 71b, 72a, 72b in the radial direction are unevenly formed. Additionally, reference numeral 93 of FIG. 11(b) indicates a chrome plating layer. A pitch [p] of the groove 91 is preferably, for example, 0.10mm. Surface roughness of each sheave surface is preferably, equal to or less than 0.5z, for example. However, the respective grooves on the sheave surfaces are 29 not limited to the spiral grooves 91. For example, as shown in FIG. 13, a plurality of coaxial circular grooves 91a formed on each sheave surface are applicable. In view of properly retaining the wear powder, the grooves of the sheave surfaces are required to be formed in such a manner that the cross sections of the sheave halves 71a, 71b, 72a, 72b in the radial direction are to be uneven. However, as long as the wear powder can be properly retained, configurations of the grooves on the sheave surfaces are not specifically limited. FIGs. 14 and 15 show test results indicating differences as to the belt wear based upon sheave surface hardness of the secondary sheave 72. In FIGs. 14 and 15, each horizontal axis indicates of the running distance of a motorcycle, while each vertical axis indicates the wear of the V-belt 73 in its width direction. In both tests shown in FIGs. 14 and 15, the sheave surface of the primary sheave 71 is plated with chrome. In the embodiments, the secondary sheave 72 is made of stainless steel, i.e., SUS304, and is not coated with any plating material. Therefore, the sheave surface hardness of the secondary sheave 72 is lower than the sheave surface hardness of the primary sheave 71. To the contrary, in the compared examples, the sheave surface of the secondary sheave 72 is plated with chrome. Thus, the sheave surface hardness of the secondary sheave 72 and the sheave surface hardness of the first sheave 71 are equal to each other. 30 FIG. 14 shows examples in which the pitch [p] of the groove is 0.05mm, while FIG. 15 shows examples in which the pitch [p] is 0.10mm. As understood from the figures, the wear of the V-belt 73 in the embodiments is less than in the comparative examples. According to this embodiment, because each of the sheave surfaces of the primary sheave 71 and the secondary sheave 72 has the spiral groove 91, the wear powder of the V-belt 73 can be properly retained on the sheave surfaces. Accordingly, a good lubrication property can be ensured between the sheaves 71, 72 and the V-belt 73 while some extent of the frictional force is kept therebetween. As a result, the heat generation of the V-belt 73 can be prevented. In this point as well, both of the prevention of the wear of the V-belt 73 and the prevention of the wear of the sheaves 71, 72 can be highly compatibly ensured. Also, according to this embodiment, because the wear of the sheaves 71, 72 is prevented, the uneven configuration on each sheave surface is hardly deteriorated with time elapsing. Accordingly, the lubrication property of the V-belt 73 can be maintained for a long period of time. If the sheave surface of the secondary sheave 72 is plated with chrome, the plated chrome of the secondary sheave 72 whose contact pressure is high at the maximum drive speed (top speed) can wear away prior to the primary sheave 71, and excessive 31 amount of the wear powder can be produced from the secondary sheave 72. In this embodiment, however, because the secondary sheave 72 is not plated with chrome, the wear power produced from the secondary sheave 72 does not cause any damage to the primary sheave 71. Also, the wear powder of the plated chrome is only produced from the primary sheave 71 whose contact pressure is low. Therefore, an amount of the wear powder produced from the whole sheaves can be small. In addition, according to this embodiment, the grooves 91 are formed by turning the sheave surfaces of the respective sheaves 71, 72. The grooves 91 thus can be simply and inexpensively realized. As thus described, the present invention is useful with belt type continuously variable transmissions and straddle type vehicles having the same. 32 WHAT IS CLAIMED IS: 1. A belt type continuously variable transmission comprising: a primary sheave to which a driving force from an engine is transmitted; a secondary sheave; and a V-belt wound around the primary sheave and the secondary sheave, the V-belt having a contact part contacting with the primary sheave and the secondary sheave, and at least a portion of the contact part being made of resin, wherein a surface hardness of a contact part of the secondary sheave contacting with the V-belt is lower than a surface hardness of a contact part of the primary sheave contacting with the V-belt. 2. The belt type continuously variable transmission as claimed in Claim 1, wherein: each of the primary sheave and the secondary sheave includes a sheave body made of a predetermined material; at least a surface of a contact part of the sheave body of the primary sheave contacting with the V-belt is coated with a plating material having a hardness higher than a hardness of the sheave body; and a surface of a contact part of the sheave body of the secondary sheave contacting with the V-belt is not coated with 33 the plating material. 3. The belt type continuously variable transmission as claimed in Claim 2, wherein the plating material is a plating material containing chrome as at least a part thereof. 4. The belt type continuously variable transmission as claimed in Claim 3, wherein the material of the sheave body of the primary sheave is aluminum or an alloy containing aluminum. 5. The belt type continuously variable transmission as claimed in Claim 2, wherein material of the sheave body of the primary sheave is aluminum or an alloy containing aluminum, and material of the sheave body of the secondary sheave is stainless steel. 6. The belt type continuously variable transmission as claimed in Claim 1, wherein material of the sheave body of the secondary sheave is stainless steel. 7. The belt type continuously variable transmission as claimed in Claim 1, wherein the surface hardness of the contact part of the secondary sheave is equal to or greater than lOOHv. 34 8. The belt type continuously variable transmission as claimed in Claim 1, wherein a distance in which the V-belt moves in a radial direction of the secondary sheave while a condition under which a speed reduction ratio is the maximum value varies to another condition under which the speed reduction ratio is the minimum value is shorter than a distance in which the V-belt moves in a radial direction of the primary sheave. 9. The belt type continuously variable transmission as claimed in Claim 1, wherein a distance between an axis of the primary sheave and an axis of the secondary sheave is double or less than double the diameter of the secondary sheave. 10. The belt type continuously variable transmission as claimed in Claim 1, wherein at least the contact part of the secondary sheave is machined by turning. 11. The belt type continuously variable transmission as claimed in Claim 1, wherein at least the contact portion of the secondary sheave has a spiral groove or a plurality of coaxial circular grooves. 12. The belt type continuously variable transmission as claimed in Claim 11, wherein a pitch between neighboring grooves is equal to or smaller less than 0.1mm. 35 13. A straddle type vehicle comprising the belt type continuously variable transmission as claimed in Claim 1. 14. The straddle type vehicle as claimed in Claim 13, further comprising: a front wheel and a rear wheel, wherein both of the primary sheave and the secondary sheave are disposed between an axis of the front wheel and an axis of the rear wheel in a fore to aft direction of the vehicle. A belt type continuously variable transmission 30 includes a primary sheave 71 to which driving force from an engine 29 is transmitted, a secondary sheave 72, and a V-belt 73 wound around the primary sheave 71 and the secondary sheave 72 and formed with a resin block belt. A sheave surface of the primary sheave 71 is plated with chrome. The secondary sheave 72 is made of stainless steel and a sheave surface thereof is not plated with chrome. The sheave surface hardness of the secondary sheave 72 is lower than the sheave surface hardness of the primary sheave 71.

Full Text

BELT TYPE CONTINOUSLY VARIABLE TRANSMISSION AND STRADDLE TYPE
VEHICLE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a belt type continuously
variable transmission and a straddle type vehicle having the
belt type continuously variable transmission.
2. Description of the Related Art
Conventionally, straddle type vehicles having the belt
type continuously variable transmission are known. The belt
type continuously variable transmission has a primary sheave
to which the driving force from an engine is transmitted and
a secondary sheave to which the driving force is transmitted
from the primary sheave via a V-belt. In the belt type
continuously variable transmission, a speed reduction ratio
varies in accordance with respective changes of a winding
radius of the belt in the primary sheave and a winding radius
of the V-belt in the secondary sheave.
In the meantime, if the V-belt is made of rubber, the V-belt
is likely to wear to reduce durability. Also, due to heat
generation following deformation of the V-belt, there can be
another problem such that the V-belt is likely to deteriorate.
Therefore, an idea in which a resin block belt made of coupled
multiple resin blocks is used as the belt type continuously
1

variable transmission is proposed (See JP-A-2002-147553, for
example).
In the belt type continuously variable transmission having
the resin block belt, the belt itself hardly wear. However
there arises, to the contrary, another problem such that
surfaces of the sheaves are likely to wear. Thus,
JP-A-2002-147553 (see Page 2, the right column, lines 34 to
38) proposes that the respective surfaces of the primary sheave
and the secondary sheave are plated with chrome.
The resin block belt has some extent of strength. However,
it was revealed that, if the respective surfaces of the primary
sheave and the secondary sheave are plated with chrome, wear
of the resin block belt increases. As thus discussed, it was
difficult, according to the conventional art, to highly
compatibly ensure both of the prevention of wear of the V-belt
and the prevention of wear of the sheaves.
SUMMARY OF THE INVENTION
The present invention is made under the circumstances, and
an object of the present invention is to highly compatibly
ensure both of prevention of wear of a V-belt and prevention
of wear of sheaves.
The inventors made every effort in their researches to
achieve the object and paid attention to a difference between
contact pressures (sheave thrust/ contact area) of the sheave
2

surfaces of the primary sheave and the secondary sheave.
That is, in consideration of the primary sheave first, as
shown in FIG. 10 (a) , if an engine speed is low (in other words,
if a rotational speed of the primary sheave 71 is low), the
speed reduction ratio of the belt type continuously variable
transmission becomes large and a winding radius rl of the V-belt
73 in the primary sheave 71 becomes relatively small.
Accordingly, a contact area S1 between the primary sheave 71
and the V-belt 73 also becomes relatively small. Meanwhile,
if the engine speed is low, the driving force (= sheave thrust)
transmitted from the primary sheave 71 to the V-belt 73 is
relatively small. Thus, the contact pressure of the sheave
surface of the primary sheave 71 is not so large.
On the other hand, if the engine speed is high, the driving
force transmitted from the primary sheave 71 to the V-belt 73
is relatively large. However, as shown in FIG. 10 (b) , if the
engine speed is high, the speed reduction ratio becomes small
and the winding radius rl of the V-belt 73 in the primary sheave
71 becomes relatively large. Accordingly, the contact area
SI between the primary sheave 71 and the V-belt 73 becomes
relatively large. Therefore, even though the engine speed is
high, the contact pressure of the sheave surface of the primary
sheave 71 is not so large.
To the contrary, the secondary sheave may have the
following situations. That is, as shown in FIG. 10 (a) , if the
3

engine speed is low, the speed reduction ratio becomes large
and a winding radius r2 of the V-belt 73 in the secondary sheave
72 becomes relatively large. Accordingly, a contact area S2
between the secondary sheave 72 and the V-belt 73 also becomes
relatively large. Meanwhile, if the engine speed is low, the
driving force transmitted from the V-belt 73 to the secondary
sheave 72 becomes relatively small. Thus, the contact
pressure of the sheave surface of the secondary sheave 72
becomes relatively small.
On the other hand, as shown in FIG. 10(b), if the engine
speed is high, the speed reduction ratio becomes small and the
winding radius r2 of the V-belt 73 in the secondary sheave 72
becomes relatively small. Accordingly, the contact area S2
between the secondary sheave 72 and the V-belt 73 also becomes
relatively small. Meanwhile, if the engine speed is high, the
driving force transmitted from the V-belt 73 to the secondary
sheave 72 becomes relatively large. Thus, if the engine speed
is high, the contact pressure of the sheave surface of the
secondary sheave 72 becomes relatively large.
That is, in the primary sheave, the contact pressure does
not become so large even though the engine speed varies. To
the contrary, it is conceivable that, in the secondary sheave,
the contact pressure becomes very large under the condition
that the engine speed is large (i.e., at the so-called top
speed). From such analyses, the inventors realize that it is
4

important to prevent wear of the belt in the secondary sheave
at the top speed.
Also, the inventors realize the following facts as
different points between the primary sheave and the secondary
sheave. That is, because the primary sheave transmits the
driving force from the engine to the V-belt, the primary sheave
is likely to be affected by fluctuations of the engine speed.
To the contrary, the driving force from the engine is
transmitted to the secondary sheave via the V-belt. Therefore,
the secondary sheave is hardly affected by the fluctuations
of the engine speed in comparison with the primary sheave.
From such analyses, the inventors realize that both of
prevention of wear of the belt and prevention of wear of the
sheaves are highly compatibly ensured by making the surface
hardness of the secondary sheave less than the surface hardness
of the primary sheave. The inventors, thus, made the following
invention.
That is, the belt type continuously variable transmission
according to the present invention includes a primary sheave
to which the driving force from an engine is transmitted, a
secondary sheave, and a V-belt wound around the primary sheave
and the secondary sheave, the V-belt having a contact part
contacting with the primary sheave and the secondary sheave,
and at least a portion of the contact part being made of resin.
The surface hardness of the contact part of the secondary sheave
5

contacting with the V-belt is lower than the surface hardness
of a contact part of the primary sheave contacting with the
V-belt.
According to the above belt type continuously variable
transmission, the surface hardness of the contact portion of
the secondary sheave is relatively low. Even though the belt
type continuously variable transmission is at the top speed
where the contact pressure becomes large, the V-belt in the
secondary sheave can be prevented from wearing. Meanwhile,
because the secondary sheave is hardly affected by the
fluctuations, the secondary sheave does not remarkably wear
in comparison with the primary sheave even the surface hardness
of the secondary sheave is relatively low. Accordingly, both
of the prevention of the wear of the V-belt and the prevention
of the wear of the sheaves can be highly compatibly ensured.
As thus discussed, according to the present invention, in
the belt type continuously variable transmission, both of the
prevention of the wear of the V-belt and the prevention of the
wear of the sheaves can be highly compatibly ensured.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a motorcycle according
to an embodiment;
FIG. 2 is a top plan view, showing relationships among
positions of a vehicle frame, a leg shield, an engine unit and
6

so forth;
FIG. 3 is a right elevational view of the engine unit;
FIG. 4 is a left elevational view of the engine unit;
FIG. 5 is a cross sectional view, showing a mount condition
of the engine unit;
FIG. 6 is a cross sectional view, showing an internal
structure of the engine unit;
FIG. 7 is a cross sectional view, showing a part of the
internal structure of the engine unit;
FIG. 8 is a side elevational view of a V-belt;
FIG. 9 is a cross sectional view, taken along the line IX-IX
of FIG. 8;
FIG. 10 is an illustration, showing a winding condition
of the V-belt, and (a) shows a condition at a low speed and
(b) shows a condition at the top speed;
FIG. 11 is an illustration, showing a sheave surface of
a primary sheave according to Embodiment 2, (a) is a front
elevational view, and (b) a cross sectional view;
FIG. 12 is an illustration, showing a sheave surface of
a secondary sheave according to Embodiment 2, and (a) is a front
elevational view, and (b) a cross sectional view;
FIG. 13 is a front elevational view of the sheave surface
according to a variation;
FIG. 14 is a graph, showing test data; and
FIG. 15 is a graph, showing other test data.
7

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereunder, an embodiment of the present invention will be
described based upon the accompanying drawings.
As shown in FIG. 1, a straddle type vehicle according to
this embodiment is a motorcycle 10. The motorcycle 10 has a
vehicle frame 11 forming a framework and a seat 16 on which
a rider sits. The motorcycle 10 is the so-called moped type
motorcycle. However, the straddle type vehicle according to
the present invention can be motorcycles other than the moped
type (such as, for example, motorcycle type and scooter type
motorcycles) or straddle type vehicles other than motorcycles
(such as, for example, ATVs).
In the following descriptions, the fore to aft and lateral
directions mean directions which the rider sitting on the seat
16 perceives. The vehicle frame 11 includes a steering head
pipe 12, a single main frame 13 extending obliquely downward
rearward from the steering head pipe 12, a left and right pair
of seat rails 14L (see FIG. 2) , 14R extending obliquely upward
rearward from a mid portion of the main frame 13, and left and
right seat pillar tubes 15L, 15R connected to a rear end portion
of the main frame 13 and mid portions of the seat rails 14L,
14R.
A vehicle cover 21 covers top and lateral sides of the
8

vehicle frame 11. A space 17 recessed downward in the side
elevational view is defined above the vehicle cover 21 and in
front of the seat 16. Also, a center tunnel lla through which
the main frame 13 extends is defined under the vehicle cover
21.
The steering head pipe 12 supports a front wheel 19 via
a front fork 18. The seat rails 14L, 14R support a fuel tank
20 and the seat 16 thereabove. The seat 16 extends from an
upper location of the fuel tank 20 toward rear ends of the seat
rails 14L, 14R. The fuel tank 20 is disposed above top surfaces
of respective front half portions of the seat rails 14L, 14R
and is covered with the vehicle cover 21 and the seat 16.
A first pair of left and right engine brackets 22L, 22R
(see FIGs. 3 and 4) protrude downward from the mid portion of
the main frame 13. The rear end portion of the main frame 13
has a second pair of left and right engine brackets 23L, 23R
(see FIG. 5) and a pair of left and right rear arm brackets
24L, 24R (see FIGs. 3 and 4).
The rear arm brackets 24L, 24R protrude downward from the
rear end portion of the main frame 13. The rear arm brackets
24L, 24R have a pivot shaft 38. As shown in FIG. 1, the pivot
shaft 38 pivotally carries a front end portion of a rear arm
25. A rear end portion of the rear arm 25 supports a rear wheel
26. The vehicle frame 11 suspends the rear half of the rear
arm 25 via cushion units 27.
9

As shown in FIG. 5, the second paired brackets 23L, 23R
protrude downward from the rear end portion of the main frame
13. The second pair of left and right engine brackets 23L,
23R are spaced apart from each other and oppose each other in
a width direction of the vehicle.
As shown in FIG. 1, the vehicle frame 11 supports an engine
unit 28 driving the rear wheel 26. Specifically, as shown in
FIG. 4, the engine unit 28 includes a crankcase 35, a cylinder
43 and a cylinder head 44 . The crankcase 35 has first and second
engine mount sections 36, 37. The respective first engine
mount sections 36 protrude upward from a top side of a front
end portion of the crankcase 35 and are supported by the first
engine brackets 22L, 22R. The respective engine mount
sections 37 protrude obliquely upward rearward from a top side
of a rear end portion of the crankcase 35 and are supported
by the second paired engine brackets 23L, 23R (see FIG. 5 also) .
The crankcase 35 thus depends from the main frame 13.
The engine unit 28 includes an engine 29 and a belt type
continuously variable transmission (hereunder, called CVT) 30
(see FIG. 6), details of which will be described later.
Although the engine 2 9 is not limited to any types, the engine
29 in this embodiment is a four-stroke, single cylinder engine.
As shown in FIG. 1, the motorcycle 10 includes a front
fender 31 covering a top side and a rear side of the front wheel
19 and a rear fender 32 covering a portion of the rear wheel
10

28 between top and rear sides thereof. Also, the motorcycle
10 includes a front cowling 33 and lateral leg shields 34L,
34R (see FIG. 2) in addition to the vehicle cover 21.
As shown in FIG. 2, footrests 85L, 85R made of rubber or
the like are disposed on the left and right sides of the engine
unit 28. The crankcase 35 of the engine unit 28 supports the
left and right footrests 85L, 85R via a coupling bar 87 made
of metal and an attaching plate 88 (see FIGs. 3 and 4) fixed
to the coupling bar 87.
As shown in FIGs. 1 and 2, a brake pedal 84 is disposed
in front of the footrest 85R on the right side. The brake pedal
84 extends below a transmission case 53 and projects obliquely
forward on the right side. The brake pedal 84 also extends
obliquely upward forwardly on the right side of the
transmission case 53. As shown in FIG. 2, when the motorcycle
10 runs, the right foot 62a of the rider is positioned next
to the transmission case 53 in the width direction of the
vehicle.
Next, an internal structure of the engine unit 28 will be
described. As shown in FIG. 6, the engine unit 28 includes
the engine 29, the CVT 30, a centrifugal clutch 41 and a
reduction gear mechanism 42.
The engine 29 includes the crankcase 35, the cylinder 43
coupled with the crankcase 35 and the cylinder head 44 coupled
with the cylinder 43. The crankcase 35 has divided two case
11

blocks, i.e., a first case block 35a positioned on the left
side and a second case block 35b positioned on the right side.
The first case block 35a and the second case block 35b oppose
each other in the width direction of the vehicle.
The crankcase 35 contains a crankshaft 4 6 therein. The
crankshaft 4 6 extends in the width direction of the vehicle
to be disposed horizontally. The crankshaft 46 is journaled
by the first case block 35a via a bearing 47 and the second
case block 35b via a bearing 48.
A piston 50 is slidably disposed within the cylinder 43.
One end of a connecting rod 51 is coupled with the piston 50.
A crank pin 59 is disposed between a left side crank arm 46a
and a right side crank arm 4 6b. The other end of the connecting
rod 51 is coupled with the crank pin 59.
A recessed portion 44a and intake ports (not shown) and
exhaust ports (not shown) both communicating with the recessed
portion 44a are defined in the cylinder head 44. An ignition
plug 55 is inserted into the recessed portion 44a of the
cylinder head 44. As shown in FIG. 3, intake pipes 52a are
connected to the intake ports, while exhaust pipes 52 are
connected to the exhaust ports. As shown in FIGs. 1 and 2,
the exhaust pipes 52 extend from the cylinder head 44 rearward
and obliquely downward on the right side and further extend
rearward below the transmission case 53. The exhaust pipes
52 are then connected to a muffler placed on the right side
12

of the rear wheel 26.
As shown in FIG. 6, a cam chain chamber 56 is defined in
the inside of the cylinder 43 on the left side thereof to connect
the inside of the crankcase 35 and the inside of the cylinder
head 44. A timing chain 57 is disposed in the cam chain chamber
56. The timing chain 57 is wound around the crankshaft 46 and
the camshaft 58. The camshaft 58 rotates with the rotation
of the crankshaft 46 to move each of intake valves and exhaust
valves, which are not shown, between an open position and a
closed position.
A generator case 66 containing a generator 63 is detachably
mounted to a left side of a front half of the first case block
35a. The transmission case 53 containing the CVT 30 is mounted
to a right side of the second case block 35b.
An opening is defined in a right side surface of a rear
half of the second case block 35b. A clutch cover 60 closes
the opening. The clutch cover 60 is detachably fixed to the
second case block 35b by bolts 61.
The transmission case 53 is formed independently from the
crankcase 35. The transmission case 53 includes an inner case
53a covering an inner side (left side) of the CVT 30 in the
width direction of the vehicle and an outer case 53b covering
an outer side (right side) of the CVT 30 in the width direction
of the vehicle. The inner case 53a is attached to a right
surface of the crankcase 35, while the outer case 53b is
13

attached to a right surface of the inner case 53a. A belt
chamber 67 is defined inside of the inner case 53a and the outer
case 53b to contain the CVT 30 therein.
As shown in FIG. 6, a right end portion of the crankshaft
46 extends to the belt chamber 67 through the second case block
35b and the inner case 53a. A primary sheave 71 of the CVT
30 is fitted onto the right end portion of the crankshaft 46.
The primary sheave 71 thus rotates with the rotation of the
crankshaft 46. A right portion of the crankshaft 46 (strictly,
a portion positioned on the right side of the bearing 48) forms
a primary sheave shaft 4 6c.
On the other hand, the left end portion of the crankshaft
46 extends into the generator case 66 through the first case
block 35a. The generator 63 is mounted to the left end portion
of the crankshaft 46. The generator 63 includes a stator 64
and a rotor opposing the stator 64. The rotor 65 is fixed to
a sleeve 74 rotating together with the crankshaft 46. The
stator 64 is fixed to the generator case 66.
A secondary sheave shaft 62 is disposed in the rear half
of the crankcase 35 to extend parallel to the crankshaft 46.
As shown in FIG. 7, the clutch cover 60 supports the central
portion of the secondary sheave shaft 62 via a bearing 75. The
left end portion of the second case block 35b supports a left
portion of the secondary sheave shaft 62 via a bearing 76.
A right end portion of the secondary sheave shaft 62 extends
14

to the belt chamber 67 through the second case block 35b and
the clutch cover 60. A secondary sheave 72 of the CVT 30 is
coupled with the right end portion of the secondary sheave shaft
62.
As shown in FIG. 6, the CVT 30 includes the primary sheave
71, the secondary sheave 72 and the V-belt 73 wound around the
primary sheave 71 and the secondary sheave 72. As described
above, the primary sheave 71 is mounted to the right portion
of the crankshaft 46. The secondary sheave 72 is coupled with
the right portion of the secondary sheave shaft 62.
The primary sheave 71 includes a fixed sheave half 71a
positioned outside in the width direction of the vehicle, and
a movable sheave half 71b positioned inside in the width
direction of the vehicle and opposing the fixed sheave half
71a. The fixed sheave half 71a is fixed to the right end portion
of the primary sheave shaft 46c and rotates together with the
primary sheave shaft 4 6c. The movable sheave half 71b is placed
on the left side of the fixed sheave half 71a and is slidably
mounted to the primary sheave shaft 4 6c. The movable sheave
half 71b thus rotates together with the primary sheave shaft
46c and is also slidable in the axial direction of the primary
sheave shaft 4 6c. A belt groove is formed between the fixed
sheave half 71a and the movable sheave half 71b.
Cooling fans 95 are formed on an outer surface (right side
surface in FIG. 6) of the fixed sheave half 71a. A cam surface
15

111 is formed on the left portion of the movable sheave half
71b. A cam plate 112 is disposed on the left side of the cam
surface 111. A roller weight 113 is placed between the cam
surface 111 of the movable sheave 71b and the cam plate 112.
The secondary sheave 72 includes a fixed sheave half 72a
positioned inside in the width direction of the vehicle, and
a movable sheave half 72b positioned outside in the width
direction of the vehicle and opposing the fixed sheave half
72a. The movable sheave half 72b is mounted to the right end
portion of the secondary sheave shaft 62. The movable sheave
half 72b is rotatable together with the secondary sheave shaft
62 and is slidable on the secondary sheave shaft 62 in the axial
direction thereof. A compression coil spring 114 is disposed
at the right end of the secondary sheave shaft 62. The movable
sheave half 72b receives the leftward urging force of the
compression coil spring 114 that is directed leftward. A shaft
core portion of the fixed sheave half 72a is a cylindrical slide
collar that is fitted on the secondary sheave shaft 62 by spline
connection.
A speed reduction ratio of the CVT 30 is decided in
accordance with relationships between a magnitude of the force
with which the roller weight 113 pushes the movable sheave half
71b rightward and a magnitude of the force with which the
compression coil spring 114 pushes the movable sheave half 72b
of the secondary sheave 72 leftward.
16

That is, upon increase of the rotational speed of the
primary sheave shaft 46c, the roller weight 113 receives the
centrifugal force and moves outward in the radial direction
to push the movable sheave half 71b rightward. Then, the
movable sheave half 71b moves rightward and the belt winding
radius in the primary sheave 71 becomes larger. Following this
operation, the belt winding radius in the secondary sheave 72
becomes smaller. The movable sheave half 72b of the secondary
sheave 72 moves rightward against the urging force of the
compression coil spring 114. As a result, the winding radius
of the V-belt 73 in the primary sheave 71 becomes larger, while
the winding radius in the secondary sheave 72 becomes smaller.
The speed reduction ratio becomes smaller, accordingly.
In the meantime, upon decrease of the rotational speed of
the primary sheave shaft 4 6c, the roller weight 113 moves inward
in the radial direction along the cam surface 111 of the movable
sheave half 71b and the cam plate 112 because the centrifugal
force of the roller weight 113 becomes smaller. Therefore,
the force with which the roller weight 113 pushes the movable
sheave half 71b rightward becomes smaller. Then, the urging
force of the compression coil spring 114 becomes larger
relative to the above force. The movable sheave half 72b of
the secondary sheave 72 moves leftward. In response to this
movement, the movable sheave half 71b of the primary sheave
71 also moves leftward. As a result, the belt winding radius
17

in the primary sheave 71 becomes smaller, while the belt winding
radius in the secondary sheave 72 becomes larger. The speed
reduction ratio becomes larger, accordingly.
The fixed sheave half 71a and the movable sheave half 71b
of the primary sheave 71 are made of aluminum or an aluminum
alloy containing aluminum as a part thereof. Sheave surfaces
(surfaces contacting with the V-belt 73) of the fixed sheave
half 71a and the movable sheave half 71b of the primary sheave
71 are plated with chrome. Consequently, each sheave surface
hardness of the fixed sheave half 71a and the movable sheave
half 71b teaches approximately l,000Hv. However, the plating
material for coating the sheave surfaces is not limited to the
chrome if the material is sufficient to enhance the wear
resistance.
The fixed sheave half 72a and the movable sheave body 72b
of the secondary sheave 72 are made of stainless steel (SUS304) .
Additionally, no sheave surfaces of the fixed sheave half 72a
and the movable sheave body 72b of the secondary sheave 72 are
plated with chrome. Consequently, The respective sheave
surface hardness values of the fixed sheave half 72a and the
movable sheave half 72b reach approximately 400Hv.
A seal groove 68a is formed along a periphery of the inner
case 53a on the left side thereof. A periphery of the second
case block 35b on the right side thereof is inserted into the
seal groove 68a. Additionally, an 0-ring 68 is interposed
18

between the inner case 53a and the second case block 35b in
the seal groove 68a. Also, another seal groove 69a is formed
along the periphery of the inner case 53a on the right side
thereof. A periphery of the outer case 53b is inserted into
the seal groove 69a. Another O-ring 69 is interposed between
the inner case 53a and the outer case 53b in the seal groove
69a. The outer case 53b and the second case block 35b are
coupled with each other by bolts 70 under a condition that the
inner case 53a is interposed between the outer case 53b and
the second case block 35b.
As shown in FIG. 7, the centrifugal clutch 41 is mounted
to the left portion of the secondary sheave shaft 62. The
centrifugal clutch 41 is a wet type multiple disk clutch and
includes a generally cylindrical clutch housing 78 and a clutch
boss 77. The clutch housing 78 is fitted onto the secondary
sheave shaft 62 by spline connection and rotates in unison with
the secondary sheave shaft 62. A plurality of circular clutch
disks 79 are attached to the clutch housing 78. The clutch
disks 7 9 are spaced apart from each other in the axial direction
of the secondary sheave shaft 62.
A cylindrical gear 80 is rotatably fitted on and around
the left portion of the secondary sheave shaft 62 via two
bearings 81a, 81b. The clutch boss 77 is positioned inside
relative to the clutch disks 79 in the radial direction and
is positioned outside relative to the gear 80 in the radial
19

direction. The clutch boss 77 meshes with the gear 80. The
gear 80 thus rotates together with the clutch boss 77. A
plurality of circular friction disks 82 are attached to the
clutch boss 77 externally in the radial direction. The
friction disks 82 are spaced apart from each other in the axial
direction of the secondary sheave shaft 62. The respective
friction disks 82 are interposed between the neighboring clutch
disks 79, 79.
A plurality of cam surfaces 83a are formed on the left side
of the clutch housing 78. Roller weights 84a are disposed
between the cam surfaces 83a and the clutch disk 79 placed at
the right-most position and opposing the cam surfaces 83a.
The centrifugal clutch 41 is automatically switched
between a clutch-in condition (connected condition) and a
clutch-out condition (disconnected condition) in accordance
with magnitudes of the centrifugal force affected to the roller
weights 84a.
That is, when a rotational speed of the clutch housing 78
exceeds a preset speed, the centrifugal force moves the roller
weights 84a outward in the radial direction. The roller
weights 84a thus push the clutch disks 79 leftward. As a result,
the clutch disks 79 and the friction disks 82 compressively
contact with each other. The centrifugal clutch 41 thus is
in the clutch-in condition in which the driving force of the
secondary sheave shaft 62 is transmitted through the gear 80
20

and the reduction gear mechanism 42 to the output shaft 85.
On the other hand, when the rotational speed of the clutch
housing 78 becomes lower than the preset speed, the centrifugal
force exerted on the roller weights 84a becomes smaller. The
roller weights 84a thus move inward in the radial direction.
As a result, the clutch disks 79 and the friction disks 82 are
released from the state of compressive contact. The
centrifugal clutch 41 thus is brought in the clutch-out
condition in which no driving force of the secondary sheave
shaft 62 is transmitted through the gear 8 0 and the reduction
gear mechanism 42. Additionally, in FIG. 7, the front (upper
side in FIG. 7) portion of the centrifugal clutch 41 represents
the clutch-out condition, while the rear (lower side in FIG.
7) portion thereof represents the clutch-in condition.
The reduction gear mechanism 42 is interposed between the
centrifugal clutch 41 and an output shaft 85. The reduction
gear mechanism 42 has a shift shaft 100 extending parallel to
the secondary sheave shaft 62 and the output shaft 85. The
shift shaft 100 is journaled for rotation by the first case
block 35a via a bearing 101 and is also journaled for rotation
by the second case block 35b via a bearing 102. A first shift
gear 103 meshing with the gear 80 is placed at a right end portion
of the shift shaft 100.
A second shift gear 104 having a diameter smaller than a
diameter of the first shift gear 103 is placed at a central
21

portion of the shift shaft 100. A third shift gear 105 meshing
with the second shift gear 104 is externally and
circumferentially formed at a right end portion of the output
shaft 85. The left end portion of the secondary sheave shaft
62 supports an internal circumferential portion of the right
end portion of the output shaft 85 via a bearing 106.
Accordingly, the secondary sheave shaft 62 journals the output
shaft 85 for rotation via the bearing 106. A left end portion
of the first case block 35a journals a central portion of the
output shaft 85 for rotation via a bearing 107.
In the structure described above, the clutch boss 77 and
the output shaft 85 are coupled with each other through the
gear 80, the first shift gear 103, the shift shaft 100, the
second shift gear 104 and the third shift gear 105. The output
shaft 85 thus rotates with the rotation of the clutch boss 77.
A left end portion of the output shaft 85 extends through
the first case block 35a and projects outside of the crankcase
35. A drive sprocket 108 is fixed to the left end portion of
the output shaft 85. A chain 109 is engaged with the drive
sprocket 108 to transmit the driving force from the output shaft
85 to the rear wheel 26. Additionally, the mechanism for
transmitting the driving force to the rear wheel 2 6 is not
limited to the chain 109. Other components such as, for example,
a transmitting belt, a gear train of plural gears assembled
with each other and a drive shaft may be used as the mechanism
22

for transmitting the driving force from the output shaft 85
to the rear wheel 26.
Next, a structure of the V-belt 73 will be described. As
shown in FIGs. 8 and 9, the V-belt 73 includes a plurality of
resin blocks 73a aligned in one direction and a pair of coupling
bodies 73b for coupling the resin blocks 73a. As shown in FIG.
9, each resin block 73a is generally formed as a trapezoid to
extend along the respective belt grooves of the primary sheave
71 and the secondary sheave 72. Recessed portions 73c recessed
inward are formed at respective lateral sides of each resin
block 73a.
The coupling bodies 73b are endlessly formed. As shown
in FIG. 8, the coupling bodies 73b extend in the alignment
direction of the resin blocks 73a and are inserted into the
recessed portions 73c of the respective resin blocks 73a.
Because the coupling bodies 73b are inserted into the recessed
portions 73c of the resin blocks 73a as thus described, the
plurality of resin blocks 73 are coupled with each other via
the paired coupling bodies 73b. Each coupling body 73b is made
of rubber. As shown in FIG. 9, a plurality of reinforcing core
wires 73d are embedded in each coupling body 73b of rubber.
In this V-belt 73, the left and right lateral side surfaces
of the resin blocks 73a and the coupling bodies 73b are contact
surfaces in contact with the respective sheave surfaces of the
primary sheave 71 and the secondary sheave 72.
23

Additionally, any V-belts are sufficient to be the V-belt
for the present invention if at least a part of the contact
portion thereof contacting with the sheave surfaces is made
of resin. That is, the V-belt for the present invention is
not limited to the V-belt 73 in which the coupling bodies 73b
couple the plurality of resin blocks 73a with each other.
As thus described, according to the CVT 30 of this
embodiment, the sheave surface hardness of the secondary sheave
72 is lower than the sheave surface hardness of the primary
sheave 71. Therefore, the wear of the V-belt 73 in the
secondary sheave 72 can be avoided even in the top speed where
the contact pressure of the sheave surfaces is high. On the
other hand, because the secondary sheave 72 is hardly affected
by fluctuations of the engine speed in comparison with the
primary sheave 71, the secondary sheave 72 is unlikely to
remarkably wear in comparison with the primary sheave 71, even
though the sheave surface hardness of the secondary sheave 72
is relatively low. Accordingly, both of the prevention of the
wear of the V-belt 73 and the prevention of the wear of the
sheaves (the primary sheave 71 and the secondary sheave 72)
can be highly compatibly ensured.
In this embodiment, the sheave body of the primary sheave
71 (the fixed sheave half 71a and the movable sheave half 71b)
is made of aluminum and the sheave surface of the sheave body
is coated with chrome. Therefore, the surface hardness of the
24

sheave surface can be raised while the sheave body is lightened.
Also, because aluminum has good cooling retaining property,
the cooling performance of the primary sheave 71 can be enhanced.
Higher performance of the CVT 30 in turn thus can be achieved.
On the other hand, the fixed sheave half 72a and the movable
sheave half 72b of the secondary sheave 72 are made of stainless
steel and the sheave surfaces thereof are not plated with chrome.
Accordingly, the CVT 30 can be inexpensively produced to the
extent that no plating is necessary for the secondary sheave
72. Further, according to this embodiment, the surface
hardness of the sheave surface of the primary sheave 71 can
be raised higher than the surface hardness of the sheave surface
of the secondary sheave 71 by the relatively simple method or
plating process.
Additionally, stainless steel has the superior wear
resistance. The corrosion resistance of the secondary sheave
72 thus can be maintained in a good state without the sheave
surface of the secondary sheave 72 being plated. Because any
rust hardly occurs, the ambient air can cool the secondary
sheave 72 without requiring any particular measures.
Because the secondary sheave 72 in this embodiment is made
of stainless steel, the sheave surface hardness of the
secondary sheave 72 can be approximately 400Hv. However, the
sheave surface hardness of the secondary sheave 72 is only
required to be equal to or higher than l00Hv in view of the
25

prevention of the wear of the sheave surface, and thus is not
limited to be about 400Hv.
In the CVT 30 according to this embodiment, a distance in
which the V-belt 73 moves in the radial direction of the
secondary sheave 72 while a condition under which the speed
reduction ratio is the maximum value (top speed) varies to
another condition under which the speed reduction ratio is the
minimum value (low speed) is shorter than a distance in which
the V-belt 73 moves in the radial direction of the primary
sheave 72. Specifically, the distance of the movement of the
V-belt 73 in the radial direction of the sheaves is represented
by a difference between the belt winding radius at the top speed
and the belt winding radius at the low speed. In this
embodiment, the difference between the belt winding radius at
the top speed and the belt winding radius at the low speed in
the primary sheave 71 is approximately 36.5mm, while the
difference between the belt winding radius at the top speed
and the belt winding radius at the low speed in the secondary
sheave 72 is approximately 32.5mm ( As thus discussed, the amount of the movement of the V-belt
73 in the radial direction in the secondary sheave 72 is shorter
than that in the primary sheave 71. Therefore, the wear of
the secondary sheave 72 can be prevented even though the sheave
surface hardness of the secondary sheave 72 is lower than the
sheave surface hardness of the primary sheave 71.
26

As shown in FIG. 10(a), in the CVT 30 according to this
embodiment, a distance between the primary sheave 71 and the
secondary sheave 72 is short in comparison with sizes of the
primary sheave 71 and the secondary sheave 72. Specifically,
in this embodiment, a distance L between the axis of the primary
sheave 71 and the axis of the secondary sheave 72 is less than
double the diameter D2 of the secondary sheave 72. Also, both
of the primary sheave 71 and the secondary sheave 72 are
disposed between the axis of the front wheel 19 and the rear
wheel 26 (see FIG. 1) . In this embodiment, therefore, a ratio
of the part contacting with the sheave surfaces of the primary
sheave 71 and the secondary sheave 72 to the whole length of
the V-belt 73 is large. Accordingly, ingoing and outgoing
times of the V-belt 73 to and from the sheave grooves are
frequent. The CVT 30 thus intrinsically has the structure in
which the V-belt 73 is likely to wear. In this embodiment,
however, the wear of the V-belt 73 can be prevented as discussed
above. Thus, no problem arises even though the distance
between the primary sheave 71 and the secondary sheave 72 is
short.

As shown in FIGs. 11 and 12, a CVT 30 according to Embodiment
2 has a structure in which a spiral groove is formed in each
of the sheave surfaces of the primary sheave 71 and the
secondary sheave 72 of Embodiment 1.
27

The CVT 30 needs some frictional force between the sheaves
71, 72 and the V-belt 73 to properly transmit the driving force.
In the meantime, however, because the V-belt 73 travels between
the primary sheave 71 and the secondary sheave 72, respective
portions of the V-belt 73, in local views, continuously go into
the sheave grooves and go out therefrom. Some extent of
slidability (hereunder, "lubrication property" is used) thus
is necessary between the V-belt 73 and the respective sheaves
71, 72. This is because, unless the lubrication property is
ensured, heat is generated by the friction between the V-belt
73 and the sheaves 71, 72, and the CVT 30 is likely to be under
an excessively heated condition.
Meanwhile, the CVT 30 is normally used under the
circumstances in which no oil, water or the like are allowed
to enter the CVT 30 (hereunder, referred to "under the dry
circumstances"). No lubricating agent is permissible to be
applied between the V-belt 73 and the sheaves 71, 72. Thus,
it is conceivable that the lubrication property between the
sheaves 71, 72 and the V-belt 73 is brought mainly by powder
originating from the V-belt 73 (wear powder) . That is, it is
conceivable that the sheaves 71, 72 and the V-belt 73 are
slidable with each other while keeping some extent of the
friction because the wear powder originating from the V-belt
73 is retained on the sheave surfaces.
If, however, the sheave surfaces are smooth, proper
28

retention of the wear powder on the contact portions with the
V-belt 73 is difficult. If the retention is difficult, proper
keeping of the lubrication property between the sheaves 71,
72 and the V-belt 73 is also difficult. Consequently,
irregularities for retaining the wear powder are preferably
given to the sheave surfaces (at least the portions in contact
with the V-belt 73) .
As shown in FIGs. ll(a) and (b), in this embodiment, a
groove 91 is formed on the sheave surfaces of the fixed sheave
half 71a and the movable sheave half 71b of the primary sheave
71 by turning. Also, as shown in FIGs. 12(a) and (b) , another
groove 91 is formed on the sheave surfaces of the fixed sheave
half 72a and the movable sheave half 72b of the secondary sheave
72 by turning.
The respective grooves 91 of this embodiment are spirally
formed around axes 92 of the sheave halves 71a, 71b, 72a, 72b.
As shown in FIG. 11(b) and FIG. 12(b), because of having the
grooves 91, cross sections of the sheave halves 71a, 71b, 72a,
72b in the radial direction are unevenly formed. Additionally,
reference numeral 93 of FIG. 11(b) indicates a chrome plating
layer.
A pitch [p] of the groove 91 is preferably, for example,
0.10mm. Surface roughness of each sheave surface is
preferably, equal to or less than 0.5z, for example.
However, the respective grooves on the sheave surfaces are
29

not limited to the spiral grooves 91. For example, as shown
in FIG. 13, a plurality of coaxial circular grooves 91a formed
on each sheave surface are applicable. In view of properly
retaining the wear powder, the grooves of the sheave surfaces
are required to be formed in such a manner that the cross
sections of the sheave halves 71a, 71b, 72a, 72b in the radial
direction are to be uneven. However, as long as the wear powder
can be properly retained, configurations of the grooves on the
sheave surfaces are not specifically limited.
FIGs. 14 and 15 show test results indicating differences
as to the belt wear based upon sheave surface hardness of the
secondary sheave 72. In FIGs. 14 and 15, each horizontal axis
indicates of the running distance of a motorcycle, while each
vertical axis indicates the wear of the V-belt 73 in its width
direction. In both tests shown in FIGs. 14 and 15, the sheave
surface of the primary sheave 71 is plated with chrome. In
the embodiments, the secondary sheave 72 is made of stainless
steel, i.e., SUS304, and is not coated with any plating material.
Therefore, the sheave surface hardness of the secondary sheave
72 is lower than the sheave surface hardness of the primary
sheave 71. To the contrary, in the compared examples, the
sheave surface of the secondary sheave 72 is plated with chrome.
Thus, the sheave surface hardness of the secondary sheave 72
and the sheave surface hardness of the first sheave 71 are equal
to each other.
30

FIG. 14 shows examples in which the pitch [p] of the groove
is 0.05mm, while FIG. 15 shows examples in which the pitch [p]
is 0.10mm. As understood from the figures, the wear of the
V-belt 73 in the embodiments is less than in the comparative
examples.
According to this embodiment, because each of the sheave
surfaces of the primary sheave 71 and the secondary sheave 72
has the spiral groove 91, the wear powder of the V-belt 73 can
be properly retained on the sheave surfaces. Accordingly, a
good lubrication property can be ensured between the sheaves
71, 72 and the V-belt 73 while some extent of the frictional
force is kept therebetween. As a result, the heat generation
of the V-belt 73 can be prevented. In this point as well, both
of the prevention of the wear of the V-belt 73 and the prevention
of the wear of the sheaves 71, 72 can be highly compatibly
ensured.
Also, according to this embodiment, because the wear of
the sheaves 71, 72 is prevented, the uneven configuration on
each sheave surface is hardly deteriorated with time elapsing.
Accordingly, the lubrication property of the V-belt 73 can be
maintained for a long period of time.
If the sheave surface of the secondary sheave 72 is plated
with chrome, the plated chrome of the secondary sheave 72 whose
contact pressure is high at the maximum drive speed (top speed)
can wear away prior to the primary sheave 71, and excessive
31

amount of the wear powder can be produced from the secondary
sheave 72. In this embodiment, however, because the secondary
sheave 72 is not plated with chrome, the wear power produced
from the secondary sheave 72 does not cause any damage to the
primary sheave 71. Also, the wear powder of the plated chrome
is only produced from the primary sheave 71 whose contact
pressure is low. Therefore, an amount of the wear powder
produced from the whole sheaves can be small.
In addition, according to this embodiment, the grooves 91
are formed by turning the sheave surfaces of the respective
sheaves 71, 72. The grooves 91 thus can be simply and
inexpensively realized.
As thus described, the present invention is useful with
belt type continuously variable transmissions and straddle
type vehicles having the same.
32

WHAT IS CLAIMED IS:
1. A belt type continuously variable transmission
comprising:
a primary sheave to which a driving force from an engine
is transmitted;
a secondary sheave; and
a V-belt wound around the primary sheave and the secondary
sheave, the V-belt having a contact part contacting with the
primary sheave and the secondary sheave, and at least a portion
of the contact part being made of resin,
wherein a surface hardness of a contact part of the
secondary sheave contacting with the V-belt is lower than a
surface hardness of a contact part of the primary sheave
contacting with the V-belt.
2. The belt type continuously variable transmission as
claimed in Claim 1, wherein:
each of the primary sheave and the secondary sheave
includes a sheave body made of a predetermined material;
at least a surface of a contact part of the sheave body
of the primary sheave contacting with the V-belt is coated with
a plating material having a hardness higher than a hardness
of the sheave body; and
a surface of a contact part of the sheave body of the
secondary sheave contacting with the V-belt is not coated with
33

the plating material.
3. The belt type continuously variable transmission as
claimed in Claim 2, wherein the plating material is a plating
material containing chrome as at least a part thereof.
4. The belt type continuously variable transmission as
claimed in Claim 3, wherein the material of the sheave body
of the primary sheave is aluminum or an alloy containing
aluminum.
5. The belt type continuously variable transmission as
claimed in Claim 2, wherein material of the sheave body of the
primary sheave is aluminum or an alloy containing aluminum,
and material of the sheave body of the secondary sheave is
stainless steel.
6. The belt type continuously variable transmission as
claimed in Claim 1, wherein material of the sheave body of the
secondary sheave is stainless steel.
7. The belt type continuously variable transmission as
claimed in Claim 1, wherein the surface hardness of the contact
part of the secondary sheave is equal to or greater than lOOHv.
34

8. The belt type continuously variable transmission as
claimed in Claim 1, wherein a distance in which the V-belt moves
in a radial direction of the secondary sheave while a condition
under which a speed reduction ratio is the maximum value varies
to another condition under which the speed reduction ratio is
the minimum value is shorter than a distance in which the V-belt
moves in a radial direction of the primary sheave.
9. The belt type continuously variable transmission as
claimed in Claim 1, wherein a distance between an axis of the
primary sheave and an axis of the secondary sheave is double
or less than double the diameter of the secondary sheave.
10. The belt type continuously variable transmission as
claimed in Claim 1, wherein at least the contact part of the
secondary sheave is machined by turning.
11. The belt type continuously variable transmission as
claimed in Claim 1, wherein at least the contact portion of
the secondary sheave has a spiral groove or a plurality of
coaxial circular grooves.
12. The belt type continuously variable transmission as
claimed in Claim 11, wherein a pitch between neighboring
grooves is equal to or smaller less than 0.1mm.
35

13. A straddle type vehicle comprising the belt type
continuously variable transmission as claimed in Claim 1.
14. The straddle type vehicle as claimed in Claim 13,
further comprising:
a front wheel and a rear wheel,
wherein both of the primary sheave and the secondary sheave
are disposed between an axis of the front wheel and an axis
of the rear wheel in a fore to aft direction of the vehicle.

A belt type continuously variable transmission 30 includes
a primary sheave 71 to which driving force from an engine 29
is transmitted, a secondary sheave 72, and a V-belt 73 wound
around the primary sheave 71 and the secondary sheave 72 and
formed with a resin block belt. A sheave surface of the primary
sheave 71 is plated with chrome. The secondary sheave 72 is
made of stainless steel and a sheave surface thereof is not
plated with chrome. The sheave surface hardness of the
secondary sheave 72 is lower than the sheave surface hardness
of the primary sheave 71.

A BELT TYPE CONTINUOUSLY VARIABLE TRANSMISSION AND A STRADDLE TYPE VEHICLE

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Inventors:

PCT Conventions: