Centrifugal multi-plate friction clutch and vehicle equipped with the same

According to some preferred embodiments, a clutch housing (46) of a clutch (2) has a bottom portion (46a) in a closed-end cylindrical shape, a plurality of arms (46d) extending along an axial direction from the bottom portion (46a) and provided along a circumferential direction centering on an axial center (C) of the clutch shaft (33), and a plurality of gaps (46e) formed between adjacent arms (46d). Off-springs (71) are arranged in the gaps and extend along the axial direction.

This application claims priority to Japanese Patent Application No. 2008-264598 filed on Oct. 10, 2008, the entire disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention

The preferred embodiments of the present invention relate, inter alia, to a centrifugal multi-plate friction clutch and a vehicle equipped with the clutch.

2. Description of the Related Art

Multi-plate friction clutches are conventionally known. A multi-plate friction clutch has clutch plates and friction plates arranged alternately along the axis of a clutch shaft, and a pressure plate for making the clutch plates and the friction plates come in contact with each other. A multi-plate friction clutch having a clutch release mechanism for moving the pressure plate is also known. A multi-plate friction clutch equipped with centrifugal weights is also known. Hereinafter, this type of clutch is referred to as a “centrifugal multi-plate friction clutch.” The centrifugal weights rotate around the clutch shaft together with a clutch housing. At this time, receiving centrifugal force, the centrifugal weights move away from the clutch shaft. The centrifugal multi-plate friction clutch has elastic bodies for adjusting the force for pressing the pressure plate against the clutch plates and the friction plates. Adjusting the aforementioned force enables adjustment of the point of the clutch engagement/disengagement, i.e., the so-called “meet point.”

U.S. Pat. No. 7,140,480 (Patent Document 1) discloses a centrifugal multi-plate friction clutch having elastic bodies arranged axially outward of an end of a clutch shaft.

The clutch disclosed in Patent Document 1 has a problem that the length of the clutch along its axis needs to be longer if a longer elastic body is desired. As a consequence, it is often difficult to select an appropriate size of the elastic body because it is necessary to prevent the clutch from increasing in size.

The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. For example, certain features of the preferred embodiments of the invention may be capable of overcoming certain disadvantages and/or providing certain advantages, such as, e.g., disadvantages and/or advantages discussed herein, while retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.

SUMMARY

The preferred embodiments of the present invention have been developed in view of the above-mentioned and/or other problems in the related art. The preferred embodiments of the present invention can significantly improve upon existing methods and/or apparatuses.

Among other potential advantages, some embodiments can provide a centrifugal multi-plate friction clutch capable of using a relatively long elastic body.

Among other potential advantages, some embodiments can provide a vehicle equipped with a centrifugal multi-plate friction clutch capable of using a relatively long elastic body.

According to a first aspect preferred embodiment of the present invention, a centrifugal multi-plate friction clutch comprises: a clutch shaft; a clutch boss attached to the clutch shaft; a clutch housing including a bottom portion in a closed-end cylindrical shape surrounding the clutch boss, a plurality of arms extending along an axial direction of the clutch shaft from the bottom portion and provided along a circumferential direction centering on the axial center of the clutch shaft, and a plurality of gaps each formed between the arms that are adjacent to each other along the circumferential direction, the clutch housing being configured to rotate in the circumferential direction; a plurality of first plates attached to the clutch boss and arranged along the axial direction; a plurality of second plates attached to the clutch housing and arranged along the axial direction alternately with the plurality of first plates; centrifugal weights configured to receive centrifugal force by rotating with the clutch housing and move in a direction away from the axial center of the clutch shaft; a cam mechanism for converting the centrifugal force into a force in the axial direction by contacting with the centrifugal weights; a pressure plate configured to move toward one side in the axial direction by receiving the force in the axial direction to make the first plates and the second plates come into contact with one another; a clutch release mechanism for moving the pressure plate toward the other side in the axial direction; a clutch operator for operating the clutch release mechanism; and a plurality of elastic bodies, arranged in the gaps of the clutch housing, for urging the pressure plate toward the other side in the axial direction.

According to a second aspect preferred embodiment of the present invention, a vehicle is equipped with the aforementioned centrifugal multi-plate friction clutch.

According to the preferred embodiments of the present invention, it is possible to provide a centrifugal multi-plate friction clutch capable of using a relatively long elastic body for adjusting the pressing force of a pressure plate, and a vehicle equipped with the clutch.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following paragraphs, some preferred embodiments of the invention will be described by way of example and not limitation. It should be understood based on this disclosure that various other modifications can be made by those in the art based on these illustrated embodiments.

Hereinafter, a motorcycle1equipped with a friction clutch according to an embodiment will be described in detail with reference to the drawings. It should be understood, however, that the motorcycle1and a clutch2described below are merely illustrative of the preferred embodiments of the present invention. The vehicle according to the present invention is not limited to the motorcycle1described below. The vehicles according to the present invention are not limited to motorcycles, including the so-called sport-type motorcycle, a moped, and a motor scooter, but can be other types of vehicles, such as, e.g., ATVs (All Terrain Vehicles). In the present invention, the term “motorcycle” refers to a vehicle whose body is to be leaned when taking a turn. The number of wheels of the motorcycle is not limited to two, but can be three or more.

FIG. 1is a left side view of a motorcycle1. In the following description, the front, rear, right and left directions refer to the respective directions seen from the rider sitting on a seat16.

Structure of Motorcycle:

As illustrated inFIG. 1, the motorcycle1includes a vehicle body7, a front wheel14provided in front of the vehicle body7, and a rear wheel19provided at the rear of the vehicle body7. The vehicle body7includes a vehicle body frame10. The vehicle body frame10has a head pipe11. A handle bar12is attached to the upper end of the head pipe11. A front wheel14is attached rotatably to the lower end of the head pipe11via front forks13.

A power unit3is suspended from the vehicle body frame10. A body cover15is attached to the vehicle body frame10. A seat16is arranged behind the central part of the vehicle body7. A fuel tank17is arranged in front of the seat16.

A rear arm18is supported pivotally by the vehicle body frame10. A rear wheel19is attached rotatably to a rear end part of the rear arm18. The rear wheel19is coupled to an engine4(seeFIG. 2) via a power transmission mechanism, which is not illustrated in the drawing. Thereby, the power of the engine4is transmitted to the rear wheel19to rotate the rear wheel19.

An accelerator grip, not shown in the drawing, is provided on the right side of the handle bar12. A left grip29is provided on the left side of the handle bar12. A clutch lever24, which is to be operated for engaging/disengaging a clutch2(seeFIG. 2), is provided in front of the left grip29.

Footrests20are provided on both the left and right sides of the vehicle body7. A shift pedal27, which is to be operated when changing the transmission gear ratio of a transmission device5(seeFIG. 2), is provided in front of the left side footrest20L.

Structure of Power Unit:

As illustrated inFIG. 2, the power unit3is equipped with an engine4, a transmission device5, and a clutch2. The type of the engine4is not particularly limited. In this embodiment, the engine4is a water-cooled, four-stroke parallel four-cylinder engine.

Although not shown in the drawings, the engine4has four cylinders, pistons that reciprocate inside the cylinders, and a crankshaft32coupled to the pistons via connecting rods. The crankshaft32extends along a vehicle width direction. Reference numeral “31” denotes a crankcase.

The crankshaft32is connected to the transmission device5via the clutch2. The transmission device5is equipped with a main shaft33, a drive shaft23, and a gear selection mechanism36. The main shaft33is connected to the crankshaft32via the clutch2. The main shaft33and the drive shaft23are arranged in parallel with the crankshaft32.

A plurality of transmission gears34are attached to the main shaft33. A plurality of transmission gears35corresponding to the plurality of transmission gears34are attached to the drive shaft23. The transmission gears35mesh with the transmission gears34mutually only by a pair of selected gears. At least one of unselected transmission gears34and35is capable of rotating with respect to the main shaft33or the drive shaft23. The power transmission between the main shaft33and the drive shaft23is performed only via the selected transmission gears34and35.

The selection of the transmission gears34and35is performed by the gear selection mechanism36. A plurality of cam grooves37aare formed in the outer circumferential surface of a shift cam37. A shift fork38is attached to each of the cam grooves37a. Each shift fork38is engaged with a predetermined transmission gear34of the main shaft33and a predetermined transmission gear35of the drive shaft23. In response to rotation of the shift cam37, each of the plurality of the shift forks38is guided by the cam groove37a, and moves in an axial direction of the main shaft33. As a result, a pair of mutually engaged gears is selected out of the transmission gears34and35. The gear selection mechanism36is operated by the shift pedal27(seeFIG. 1).

With such a structure, when the engine4is operated after bringing the clutch2in a connected state, the power of the engine4is transmitted to the main shaft33via the clutch2. Via a pair of predetermined transmission gears34and35, the power is transmitted from the main shaft33to the drive shaft23, allowing the drive shaft23to rotate. As the drive shaft23rotates, the power is transmitted to the rear wheel19via a transmission mechanism (not shown), such as, e.g., a chain, connected to the drive shaft23and the rear wheel19. As a result, the rear wheel19rotates.

The vehicle width direction means a lateral direction. The axial direction of the main shaft33also means a lateral direction. Hereinafter, the axial direction of the main shaft33will be referred to simply as “the axial direction.” As illustrated inFIG. 3, since the clutch2is arranged on the right side of the main shaft33, the outside of the vehicle width direction means the right side, and the inside of the vehicle width direction means the left side. In the following description, the outside and inside of the vehicle width direction will be referred to simply as “the right side” and “the left side,” respectively.

Structure of Clutch:

The clutch2is constituted by a wet-type multi-plate friction clutch. The clutch2is a centrifugal clutch that is automatically engaged/disengaged at the time of starting or stopping the motorcycle1. The clutch2is engaged/disengaged by the rider's operation of the clutch lever24. It should be noted, however, that the clutch2can be a dry-type multi-plate friction clutch.

As illustrated inFIG. 3, the clutch2is provided with a clutch housing46. The clutch housing46is manufactured by casting. However, the method for manufacturing the clutch housing46is not limited to casting. A main shaft33penetrates through the clutch housing46. An end part of the main shaft33constitutes the clutch shaft. The axial center of the clutch housing46is in agreement with the axial center C of the main shaft33.

The clutch housing46has a bottom portion46a. The bottom portion46ais in a closed-end cylindrical shape. Thus, the clutch housing46is in a substantially cylindrical shape with one end closed by the bottom portion46a. The main shaft33penetrates through the bottom portion46a. As illustrated inFIGS. 5 and 6, the clutch housing46is provided with a plurality of arms46d. These arms46dare arranged along the circumference direction centering on the axial center C of the main shaft33. Each arm46dextends to the right from the bottom portion46a. Gaps46eare formed between respective two adjacent arms46d.

As illustrated inFIG. 3, a scissors gear45is attached to the clutch housing46. The scissors gear45includes two gears45aand45b, a spring49, and two plates51and52. The gear45aand the gear45bare located between the plates51and52. The gear45aand the gear45bare configured to prevent their relative movements along the axial direction but to allow relative rotation along the circumferential direction.

The gear45ameshes with a gear32a(seeFIG. 2) of the crankshaft32. The gear45ais configured to prevent its relative rotation with respect to the bottom portion46aof the clutch housing46. In response to rotation of the crankshaft32, the gear45aand the clutch housing46rotate integrally.

A needle bearing53and a spacer54, which does not rotate relative to the main shaft33, are arranged between the scissors gear45and the main shaft33. The scissors gear45is capable of rotating relative to the main shaft33via the needle bearing53. In other words, rotation of the scissors gear45is not directly transmitted to the main shaft33.

As illustrated inFIG. 3, a clutch boss48is fixed to the main shaft33with a nut67. The clutch boss48rotates together with the main shaft33. A thrust bearing63is arranged between the clutch boss48and the scissors gear45. Thereby, the scissors gear45, the needle bearing53, and the spacer54are inhibited from coming closer to the clutch boss48more than a predetermined distance. In other words, movements of the scissors gear45, the needle bearing53, and the spacer54toward the clutch boss48are inhibited. The clutch boss48is arranged radially inward of the clutch housing46.

d. Plate Group

A plurality of friction plates64are arranged inside the clutch housing46. The friction plates64are arranged along the axial direction. Each of the friction plates64rotates together with the clutch housing46. Each of the friction plates64can change its position along the axial direction. For this reason, the gap between adjacent friction plates64is variable. Clutch plates65are interleaved between the respective adjacent friction plates64. The clutch plates65face the friction plates64. Each of the clutch plates65rotates together with the clutch boss48. Each of the clutch plates65can change its position along the axial direction, and the gap between adjacent clutch plates65is variable. In this embodiment, a plate group66is constituted by the friction plates64and the clutch plates65.

Each of the friction plates64has substantially an annular shape (seeFIGS. 7 and 8). Each of the friction plates64has a plurality of claws64c. The claws64cextend radially outwardly. Each of the friction plates64is attached to the clutch housing46by fitting the claws64cinto respective ones of the gaps46eof the clutch housing46. Thereby, each of the friction plate64rotates together with the clutch housing46as described above.

e. Pressure Plate

As illustrated inFIG. 3, a pressure plate77is arranged on the right side of the main shaft33. The pressure plate77is formed in a substantially disk shape. A sub-clutch100is arranged in a center portion of the pressure plate77. The radially outward end of the pressure plate77is attached to the arms46d. The pressure plate77rotates together with the clutch housing46.

A pressing part77bprojecting toward the plate group66side is formed in a radially outward portion of the pressure plate77. This pressing part77bfaces the friction plate64located on the rightmost side of the plate group66. When the pressure plate77moves to the left, the pressing part77bpresses the plate group66to the left. As a result, the friction plates64and the clutch plates65in the plate group66are brought into pressure contact with each other.

On the other hand, a cam face81, which supports roller weights41, is formed on the surface of the radially outward portion of the pressure plate77that is opposite to the plate group66. A plurality of the cam faces81and the roller weights41are formed along the circumferential direction. The plurality of cam faces81are arranged radially from the axial center C of the main shaft33. Each of the cam faces81is inclined to the right as it advances toward the radially outward edge thereof.

A roller retainer78is arranged on the right of the pressure plate77. The roller retainer78faces the cam faces81of the pressure plate77. As a result, a space82is formed by and between each cam face81and the roller retainer78. The space82becomes narrower in width as it advances toward the radially outward edge of the main shaft33.

Like the pressure plate77, the radially outward end of the roller retainer78is attached to the plurality of arms46d. Accordingly, the roller retainer78rotates together with the clutch housing46. On the other hand, the roller retainer78can change its position along the axial direction with respect to the clutch housing46.

The roller retainer78is urged to the left by a disc spring83serving as an urging member. The roller retainer78and the disc spring83constitute a touching member70for pushing the roller weights41against the cam faces81.

The roller weights41are arranged respectively in a plurality of the spaces82. The roller weights41whirl around in accordance with the rotation of the clutch housing46, and move radially outwardly on the cam faces81by the centrifugal force produced at the time of the rotation. When the centrifugal force exceeds a predetermined value, the roller weights41receive a reaction force from the touching member70, pressing the pressure plate77toward the plate group66. In the clutch2, at least the touching member70and the cam faces81constitute a cam mechanism. The direction in which the roller weights41move in response to the centrifugal force is changed by the cam faces81. When the roller weights41move radially outwardly in response to the centrifugal force, they come into contact with the touching member70and the cam faces81, and the centrifugal force of the roller weights41is converted into a force along the lateral direction.

When the rotation speed of the crankshaft32is slower than a predetermined value, the rotation speed of the clutch housing46is also slower. For this reason, the centrifugal force that acts on the roller weights41is relatively small, and the roller weights41will sit relatively inward. Later-described off-springs71urge the pressure plate77in a direction opposite to the direction in which the plate group66is pressure-contacted. Therefore, when the roller weights41sit relatively inward, the resultant force of the force with which the roller weights41push the pressure plate77to the left and the urging force of the off-springs71will be substantially zero. As a result, the plate group66will be in a non pressure-contact state in which practically it is not pushed by the pressure plate77. When in the non pressure-contact state, the torque of the clutch housing46will not be transmitted to the clutch boss48, so the clutch2will be in a disengaged state.

On the other hand, when the rotation speed of the crankshaft32becomes relatively fast, the rotation speed of the clutch housing46will be also relatively fast accordingly. As the rotation speed of the clutch housing46increases, the centrifugal force acting on the roller weights41increases. When the centrifugal force acting on the roller weights41exceeds a predetermined value, the roller weights41move radially outward. As a result, the pressure plate77is pressed to the left by the roller weights41, and moves toward the plate group66. At this time, the urging force of the off-springs71becomes weaker than the force with which the roller weights41push the pressure plate77to the left. As a result, the plate group66is pressure-contacted, and thus, the clutch2will be in an engaged state.

When the plate group66is compressed and the clutch2is engaged in this way, the torque of the clutch housing46is transmitted to the clutch boss48via the plate group66. As a result, the clutch boss48rotates together with the clutch housing46.

On the other hand, when the rotation speed of the crankshaft32decrease while the clutch2is in an engaged state, the centrifugal force acting on the roller weights41will decrease. This moves the roller weights41radially inward. Thereby, the resultant force of the force with which the roller weights41push the pressure plate77to the left and the urging force of the off-springs71will be substantially zero. In other words, the force with which the pressure plate77presses the plate group66will become substantially zero. At this time, the plate group66is in a non pressure-contact state in which it is not substantially pressed by the pressure plate7, and thus, the clutch2will be disengaged.

As described above, the motorcycle1is equipped with the centrifugal clutch2. Therefore, at the time of starting or stopping the vehicle, the clutch2is automatically engaged/disengaged according to the rotation speed of the engine4. Thus, operation of the clutch lever24is unnecessary. Thus, in the motorcycle1according to this embodiment, the rider's operation burden at the time of starting or stopping can be alleviated.

The clutch2is equipped with the off-springs71. The off-springs71adjust the force for compressing the plate group66by the pressure plate77. In addition, the off-springs71urge the pressure plate77in a direction opposite to the direction in which the pressure plate77is pushed by the roller weights41and the Disc spring83. Adjusting the force of compressing the plate group66by the pressure plate77enables adjustment of the engaged/disengaged point of the clutch2(the so-called meet point of the clutch).

In this embodiment, the clutch2is provided with a plurality of the off-springs71. As illustrated inFIG. 4, the off-springs71are arranged in an outer rim portion46fof the clutch housing46. Specifically, the off-springs71are arranged in the gaps46eof the clutch housing46. The off-springs71extend substantially parallel to the direction in which the arms46dextend. In other words, the off-springs71extend along the axial direction of the main shaft33. The off-springs71are formed, for example, by coil springs. Illustration of the off-springs71is omitted inFIGS. 2 and 3.

As illustrated inFIGS. 5 and 6, some of the arms46dhave a notch portion46k. The notch portion46kis a portion of the arm46dhaving a width narrower than that of the rest of the portion. As illustrated inFIG. 6, a support portion46pextending along the circumferential direction is formed on the proximal end of the arm46dthat has the notch portion46k. The support portion46pis a surface that supports one end of the off-spring71.

As illustrated inFIGS. 7 and 8, the claws64cof the friction plates64are fitted in the respective gaps46eof the clutch housing46. Each of the arms46dand each of the claws64ccome into contact with each other at the time of rotation of the clutch housing46. The clutch housing46rotates in the direction R indicated in the drawings such asFIG. 7. Each of the arms46dcomes into contact with each of the claws64con a contact surface50. A plurality of the contact surfaces50are formed corresponding to the plurality of arms46dand the claws64c. As illustrated inFIG. 8, the support portion46pis adjacent to one of the claws64c. The support portion46pis provided on the opposite side of the contact surface50that is across the claw64c. The support portion46pis arranged on the side of the rotation direction R of the clutch housing46with respect to the claw64c.

As illustrated inFIG. 5, the circumferential widths of the plurality of arms46dare substantially identical in this embodiment. The term the width of the arm46dherein means the width of the proximal part thereof. Likewise, the circumferential widths of the plurality of gaps46eare substantially identical.

As illustrated inFIG. 5, the off-springs71are arranged at constant intervals along the circumferential direction. In other words, the off-springs71are arranged evenly along the circumferential direction. The virtual straight line L is a line that passes through the axial center C of the main shaft33. The off-springs71are arranged symmetrically with respect to the virtual straight line L. The number of the arms46dprovided is 12. The number of the gaps46eprovided is also12. One off-spring71is provided per four arms46d, and three in total are provided. However, the total number of the off-springs71is not limited to three. The number of the off-springs71can be, for example, four, six or twelve. The numbers of the arms46dand the gaps46eare not limited to 12 either. The numbers of the arms46dand the gaps46ecan be eight, for example. In this case, one off-spring71is provided per two arms46d, and the total number thereof is four.

As illustrated inFIGS. 4 and 6, each of the off-springs71is arranged between a spring holder72and a spring holder73, and extends along the axial direction. As illustrated inFIG. 6, the spring holder72is disposed on the support portion46p. As illustrated inFIG. 4, the spring holder73is disposed on the pressure plate77. The spring holders72and73have a base72cand a base73c, respectively. One end of the off-spring71is supported by the base72c, and the other end is supported by the base73c.

As illustrated inFIG. 3, the sub-clutch100is equipped with a friction plate101, a first pressing plate102that faces a left side surface101a(hereinafter referred to as the “first friction face”) of the friction plate101, and a second pressing plate103that faces a right side surface101b(hereinafter referred to as the “second friction face”) of the friction plate101.

The friction plate101is configured to rotate together with the pressure plate77. The pressure plate77is provided with a slide arm part77c. On the other hand, a gap (not shown) is formed in a radially outward portion of the friction plate101. The slide arm part77cis attached to the gap of the friction plate101. The friction plate101can slide along the axial direction with respect to the pressure plate77.

The first pressing plate102is fixed to a short push rod43a. Accordingly, the first pressing plate102is movable along the axial direction together with the short push rod43a. In addition, the first pressing plate102rotates together with the short push rod43a.

The second pressing plate103is serration-fitted to the short push rod43a. For this reason, the second pressing plate103rotates together with the short push rod43a, but the second pressing plate103is capable of relatively moving along the axial direction with respect to the short push rod43a. The second pressing plate103has a boss portion103athat extends to the right. This boss portion103arotatably supports the pressure plate77via a bearing104. This allows the second pressing plate103and the pressure plate77to rotate relative to each other. The second pressing plate103and the pressure plate77are configured to move integrally along the axial direction.

When the short push rod43amoves to the right, the first pressing plate102also moves to the right. Then, the first pressing plate102presses the friction plate101toward the second pressing plate103. As a result, the friction plate101is sandwiched between the first pressing plate102and the second pressing plate103. Thereby, the torque of the pressure plate77is transmitted to the first pressing plate102and the second pressing plate103via the friction plate101, and the torque is applied to the first pressing plate102and the second pressing plate103.

h. Force Boosting Mechanism

As illustrated inFIG. 3, the clutch2has a force boosting mechanism200. The force boosting mechanism200converts part of the torque of the pressure plate77into the force for disengaging the clutch2. The force boosting mechanism200reduces the rider's force required for disengaging of the clutch2. The force boosting mechanism200according to this embodiment is constructed by the so-called ball cam. The force boosting mechanism200includes a slide shaft201fixed to the second pressing plate103, a first cam plate202(seeFIG. 9C), a second cam plate203(seeFIG. 9A), a ball plate204(seeFIG. 9B), and a coil spring205that urges the second cam plate203in a direction in which the second cam plate203separates from the first cam plate202. A supporting plate250that supports the coil spring205by contacting the right side part of the coil spring205is fixed to one end side of the slide shaft201.

i. Clutch Release Mechanism

The clutch2is provided with a clutch release mechanism86. The clutch release mechanism86forcibly releases the pressure contact state of the plate group66in response to the operation of the clutch lever24by the rider. This clutch release mechanism8enables disengagement of the clutch2by the rider's manual operation.

Operation of Clutch:

Next, the operation of the clutch2will be described. First, the operation for disengaging the clutch2will be described.

When the rider grips the clutch lever24(seeFIG. 1), the internal pressure of an operation chamber92(seeFIG. 10) of a drive mechanism87increases. As a result, a piston91inside a cylinder90moves to the right against the urging force of a spring93, and a long push rod43balso moves to the right. Then, a ball43cand the short push rod43aof a push mechanism43also move to the right, moving the first pressing plate102of the sub-clutch100to the right. Thereby, the friction plate101of the sub-clutch100is sandwiched between the first pressing plate102and the second pressing plate103, causing the sub-clutch100to be in an engaged state. Then, the slide shaft201of the force boosting mechanism200rotates together with the pressure plate77in a predetermined direction.

When the slide shaft201rotates in the predetermined direction, the second cam plate203of the force boosting mechanism200will also rotate in the same direction. Then, balls204ain the ball plate204move over from the space between a first cam face202aand a second cam face203a, causing the second cam plate203to be pushed to the right by the balls204a. Thereby, the slide shaft201is also pushed to the right. As a result, the pressure plate77moves to the right because of the force with which the short push rod43apushes the pressure plate77to the right via the first pressing plate102and the friction plate101, and the force with which the slide shaft201pulls the pressure plate77to the right via the second pressing plate103and the bearing104. Thereby, the pressure contact state of the plate group66is released, and the clutch2is disengaged.

The second cam plate203is inhibited from rotating more than a given amount. For this reason, in the condition in which the clutch2is disengaged, the friction plate101rotates with respect to the first pressing plate102and the second pressing plate103. In other words, the friction plate101slips with respect to the first pressing plate102and the second pressing plate103in the condition in which the clutch2is disengaged. However, oil is supplied to the first friction face101aand the second friction face101bof the friction plate101, and therefore, wear of the friction plate101is controlled.

Hereinafter, the operation for engaging the clutch2will be described.

To engage the clutch2, the rider releases the clutch lever24. This reduces the internal pressure of the operation chamber92of the drive mechanism87. This causes the piston91and the long push rod43bto move to the left. Consequently, the ball43cand the short push rod43aalso move to the left, and the first pressing plate102of the sub-clutch100accordingly moves to the left. This causes the first pressing plate102of the sub-clutch100to separate away from the friction plate101. In addition, the second pressing plate103is no longer pushed rightward by the first pressing plate102. Therefore, the rightward force against the slide shaft201is lost, and the second cam plate203that receives the urging force of the coil spring205rotates in the opposite direction, whereby the second cam plate203and the slide shaft201move to the left. As a result, the second pressing plate103also moves to the left.

Moreover, the rightward force by the first pressing plate102is released, the pressure plate77is moved to the left by the urging force of the disc spring83. As a result, the pressure plate77compresses the plate group66, allowing the clutch2to be engaged. In this case, the friction plate101of the sub-clutch100separates away from the second pressing plate103.

The urging force that the pressure plate77receives from the disc spring83and the off-springs71varies depending on the radial positions of the roller weights41. Specifically, when the rotation speed of the pressure plate77is fast, the roller weights41move radially outward. As a result, the roller weights41move to the right, causing the disc spring83to deform greatly. When the roller weights41move to the right, the pressure plate77compresses the plate group66. This contracts the off-springs71. As the off-springs71contract, the urging force thereof increases. Accordingly, the urging force that the pressure plate77receives from the disc spring83becomes relatively large even without making the elastic coefficient of the disc spring83large, because the disc spring83is deformed greatly by the roller weights41and the off-springs71. On the other hand, when the rotation speed of the pressure plate77is slow, the roller weights41move radially inward. As a result, the roller weights41move to the left. At this time, the amount of shrinkage of the off-springs71is small. Therefore, the amount of deformation of the disc spring83is small. For that reason, the urging force that the pressure plate77receives from the disc spring83becomes relatively small.

When the engine rotation speed is high, the plate group66needs to be compressed by the pressure plate77with a large force. In the clutch2according to this embodiment, when the engine rotation speed becomes high, the amount of deformation of the disc spring83will become large in response to the radially outward movement of the roller weights41. For this reason, a sufficient force can be obtained without increasing the elastic constant of the disc spring83. Accordingly, the elastic constant, i.e., the spring capacity, of the disc spring83can be kept relatively small.

When the engine rotation speed is low, the roller weights41move radially inward, and the pressure plate77will not compress the plate group66. In other words, the clutch becomes disengaged. When the engine rotation speed increases from an idle state, the roller weights41eventually move radially outward, causing the pressure plate77to compress the plate group66. In other words, the clutch becomes engaged. However, in the clutch2according to this embodiment, the off-springs71urge the pressure plate77in a direction opposite to the direction in which the pressure plate77compresses the plate group66. At the moment when the clutch is engaged, the engine rotation speed is not so fast and the amount of deformation of the disc spring83is also relatively small, so the force with which the pressure plate77compresses the plate group66is relatively small. Therefore, the plate group66is not compressed abruptly, and the clutch2is engaged smoothly.

In the clutch2of this embodiment, the off-springs71are arranged in the gaps46eof the clutch housing46. At least a space equal to the length of the arms46dof the clutch housing46is ensured as the space for disposing the off-springs71. Thus, it is possible to use relatively long off-springs71. Therefore, it is possible to select the off-springs71with an appropriate size for adjusting the pressing force of the pressure plate77.

In this embodiment, the support portions46pfor supporting the off-springs71are provided at the proximal ends of some of the arms46d. The space for accommodating the off-springs71, such as notches, is not provided in the friction plates64. Therefore, there is no risk that the strength of the friction plates64may degrade. The friction plates64do not have a special shape for accommodating the off-springs71. Therefore, the friction plates64may be used for other types of clutches that do not use the off-springs71.

As illustrated inFIG. 8, the support portions46pare formed at positions adjacent to the gaps46e. When casting the clutch housing46, the shape of the mold may be simplified since complicated parts in the mold can be eliminated. Therefore, the clutch housing46can be cast easily. Moreover, even in cases where the arms46dof the clutch housing46are manufactured by a cutting process, the support portions46pcan be formed easily. As a result, the clutch housing46can be manufactured easily.

As illustrated inFIG. 8, the support portions46pare arranged on the rotation direction side of the clutch housing46relative to the claws64cof the friction plates64. The claws64ccome into contact with the arms46don the contact surfaces50, but not with the off-springs71. Therefore, the strength of the clutch housing46is sufficiently ensured.

The widths of the plurality of arms46dare substantially identical, and the widths of the plurality of the gaps46eare substantially identical. A load that each of the arms46dreceives is made uniform, and the strength of the arms46dis ensured sufficiently.

As illustrated inFIG. 5, the off-springs71are arranged at constant intervals along the circumferential direction. Thereby, the off-springs71can urge the pressure plate77in a well-balanced manner.

The number of the arms46dis 12, and that of the off-springs71is 3. Thereby, the pressure plate77can be urged with sufficient balance by the off-springs71, while inhibiting the shape of the clutch housing46from becoming complicated and preventing the parts count from increasing. In this way, it becomes possible to obtain the clutch2that is more suitable.

In this embodiment, the off-springs71are formed by coil springs. The coil spring is a relatively long elastic body; however, the clutch2can employ a relatively long elastic body, as mentioned above, so it can adopt the coil spring. Among well-known springs, a coil spring is simple in structure. By changing the number of coil turns and/or the coil diameter, the urging force of the off-spring71can be varied easily. Thus, selection of the off-springs71is made easy by the clutch2of this embodiment.

Hereinafter, a clutch2of Modified Embodiment 1 will be described. In this modified Embodiment, the support portions46pare arranged on the opposite side of the rotation direction R of the clutch housing46with respect to the claws64c, as illustrated inFIGS. 11 and 12. The claws64cthat are adjacent to the off-springs71are only some of the plurality of claws64c. The number of the claws64cthat are adjacent to the off-springs71is three, and that of the other claws64cis nine. The other claws64care fitted in the gaps46e. As a result, the friction plates64do not move greatly with respect to the clutch housing46. Moreover, sufficient spaces are provided between the off-springs71and the claws64c. For this reason, in this modified Embodiment as well, the off-springs71and the claws64cdo not come in contact with each other.

In this modified Embodiment, each support portion46pis arranged at an intermediate position between two of the adjacent arms46d, as illustrated inFIGS. 13 and 14. The arms46d1and46d2on both sides of each support portion46phave narrower widths than the other arms46d. In other words, the notch portion46kis formed in the central part of the arm46d, and the support portion46pis formed in this notch portion46k. The off-springs71are not adjacent to the claws64cof the friction plates64. For this reason, interference between the off-springs71and the claws64cis prevented reliably.

In this modified Embodiment, some of the claws64chave a notch portion64k, as illustrated inFIG. 15. The notch portion64kis formed substantially at the center of the claw64c. Each of the off-springs71is arranged in a respective one of the notch portions64k, and extends along the axial direction. In the clutch2of this modified Embodiment, the notch portion46kis not formed in the arm46d. This enables the arms46dto have a great strength. As a result, the strength of the clutch housing46can be increased. Therefore, the clutch housing46of this modified Embodiment can be used commonly with the clutch that does not use the off-springs71.

BROAD SCOPE OF THE INVENTION