Clutch device

The clutch device includes, a right pressure flange that brings clutch discs provided on a clutch outer and clutch plates provided on a clutch inner into pressure contact with one another. A pressure ring that moves the right pressure flange with an external force and a clutch spring transmits the force toward a clutch connected position, from the pressure ring to the right pressure flange. Further, a return spring between the clutch inner and the right pressure flange urges the right pressure flange toward a clutch disconnected position. The clutch spring and the return spring are disposed parallel to a clutch axial direction, their respective positions overlapping each other in the clutch axial direction.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Japanese Application No. 2011-149090, filed Jul. 5, 2011, the entire contents of which are herein incorporated by reference.

TECHNICAL FIELD

The present invention relates to a clutch device for switching between the transmission and non-transmission of power by pressing friction plates in a clutch axial direction or releasing the pressure.

BACKGROUND ART OF THE INVENTION

There is a known structure in which a clutch release mechanism moves a clutch piston away from a clutch inner (moves it to a clutch disconnected position), thereby disconnecting a clutch. The clutch piston is urged toward the clutch inner (toward a clutch connected position) by a disc spring. When the clutch release mechanism is out of operation, the clutch is brought into a connected state by the urging force of the disc spring.

With this structure, the relationship between the moving distance and clutch capacity of a member for moving the clutch piston can be set to be linear, and therefore the clutch capacity can be easily controlled by the moving distance of the member. See JP-A No. 2005-249083.

SUMMARY OF INVENTION

Meanwhile, also in a clutch device that is brought into a clutch connected state by input from the outside and into a clutch disconnected state by cancelling the input, there is a need for a structure that permits easy clutch capacity control and is of a small size so as to be suitable for small vehicles.

Accordingly, it is to achieve easy clutch capacity control and downsizing in a clutch device that is brought into a clutch connected state by input from the outside.

A feature of the invention described herein is that there is provided a clutch device including: a clutch outer and a clutch inner coaxially supported on a rotating shaft; outer friction plates held by engagement with the clutch outer; and inner friction plates held by engagement with the clutch inner, for switching between transmission and non-transmission of power between the clutch outer and the clutch inner by bringing the outer and inner friction plates into pressure contact with one another in a clutch axial direction or releasing the pressure contact.

The clutch device includes: a clutch piston (that is supported movably in the clutch axial direction by the clutch inner and brings the outer and inner friction plates into pressure contact with one another in cooperation with a supporting portion of the clutch inner; an input portion that moves the clutch piston with a force toward a clutch connected position input from an external force mechanism to bring the outer and inner friction plates into pressure contact with one another; a clutch spring that is disposed between the input portion and the clutch piston and transmits to the clutch piston the force toward the clutch connected position input to the input portion from the external force mechanism; and a return spring that is disposed between the clutch inner and the clutch piston and urges the clutch piston toward a clutch disconnected position with a force smaller than that of the clutch spring. The clutch spring and the return spring are disposed parallel to the clutch axial direction. A plane perpendicular to an axis of the clutch passes through the clutch spring and the return spring.

An additional feature of the disclosure is that the input portion fits movably in the clutch axial direction in an inner periphery of the clutch piston.

Another feature of the disclosure is that the clutch spring and the return spring include plural clutch springs and plural return springs, respectively. The plural clutch and return springs are alternately arranged in a clutch rotation direction.

An additional feature of the disclosure is that the clutch inner has a cylindrical wall that supports the inner friction plates. The cylindrical wall is provided with a notch serving as a receiving portion of the return spring.

Another feature of the disclosure is that the clutch piston is provided with a detent that engages in a non-relatively-rotatable manner an end of the notch on a side on which the clutch piston is located.

Still another feature of the disclosure is that the clutch piston has an inner supporting portion that protrudes coaxially toward the clutch inner. The inner supporting portion has: an outer cylindrical wall that extends toward the clutch inner from the clutch piston; a bottom wall that extends toward a clutch inner periphery from an end of the outer cylindrical wall on a side on which the clutch inner is located; and an inner cylindrical wall that rises from an inner peripheral edge of the bottom wall toward the clutch piston. An inner periphery of the inner cylindrical wall is fitted and supported on an outer periphery of a hub of the clutch inner. Also, the clutch spring has one end supported by the input portion and the other end supported by a folded-back portion of the clutch piston. The folded-back portion is surrounded by the outer cylindrical wall, the bottom wall, and the inner cylindrical wall.

Also another feature of the disclosure is that the clutch inner is formed with a feed oil passage, the feed oil passage opening toward the folded-back portion of the clutch piston.

According to the disclosure, when a force toward the clutch connected position is input to the input portion of the clutch device from the external force mechanism, the input portion and the clutch piston move toward the clutch connected position while elastically deforming the return spring earlier than the clutch spring, so that the clutch piston abuts on either of the friction plates (the connection of the clutch device is started).

Thereafter, when the input portion moves further toward the clutch connected position, the clutch spring starts to be elastically deformed following the return spring, causing the clutch connection state in which the friction plates are brought into pressure contact with one another by the spring force thereof.

In other words, the spring force of the clutch spring brings the friction plates into pressure contact with one another, and consequently, the moving distance of the input portion is proportional to the clutch capacity, thereby allowing precise clutch capacity control.

Furthermore, the clutch spring and the return spring are disposed parallel to each other along the clutch axial direction. A plane perpendicular to an axis of the clutch passes through the clutch spring and the return spring. Thus, the clutch device can be reduced in axial size, as compared with the case where the clutch spring and the return spring are axially aligned.

Further, the clutch piston and the input portion can be compactly disposed in the clutch axial direction.

According to the disclosure, a well-balanced and efficient arrangement of the springs is possible.

Still further, the return spring can be disposed immediately on the inner peripheral side of the friction plates, thereby allowing a reduction in radial size of the clutch device.

Additionally, the relative rotation between the clutch inner and the clutch piston can be efficiently restricted by using the notch for receiving the return spring.

Still further, positioning of the clutch spring can be facilitated, and the clutch spring can be disposed in a stretchable manner.

Moreover, oil can be efficiently supplied to the fitting portion between the clutch inner and the clutch piston.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. It is to be noted that, unless otherwise stated, references to directions such as front, rear, left and right in the following description are made based on the directions of a vehicle described below. It is also to be noted that, in the drawings used in the following description, there are suitably shown arrow FR indicating the front of the vehicle, arrow LH indicating the left of the vehicle, and arrow UP indicating the upper side of the vehicle.

In a motorcycle (a saddle-ride type vehicle)1shown inFIG. 1, an upper portion of a front fork3that journals a front wheel2is steerably pivotally supported through a steering stem4by a head pipe6at a front end of a body frame5. A main frame7extends obliquely downward and rearward from the head pipe6. An upper end of a pivot frame8is connected to a rear end of the main frame7. A front end of a swing arm9is pivotally supported in a vertically swingable manner by a vertically intermediate portion of the pivot frame8. A rear wheel11is journaled to a rear end of the swing arm9. A cushion unit12is interposed between a front portion of the swing arm9and a rear portion of the body frame5. It is to be noted that reference sign27in the drawing denotes a pivot shaft that serves as a swing shaft of the swing arm9;7a, a down frame that extends obliquely downward and rearward from the lower side of a front portion of the main frame7; and7b, a hanger bracket attached to a leading end of the down frame7a.

A power unit10, serving as a power mechanism of the motorcycle1, is mounted on the body frame5.

Referring also toFIG. 2, the power unit10integrally has an air-cooled single-cylinder engine (hereinafter referred to simply as “engine”)13that constitutes a front portion thereof, and a twin-clutch transmission (hereinafter referred to simply as “transmission”)23that is continuous with the rear of the engine13.

The engine13has a basic construction in which a cylinder15is provided in an upstanding position tilting forward in a vertical direction on a crankcase (a power unit case)14thereof. It is to be noted that reference sip C1in the drawing denotes a cylinder axis parallel to the upstanding direction of the cylinder15. The power unit10is fixedly supported on the body frame5with the top and bottom of the front end of the crankcase14respectively attached to lower ends of the down frame7aand the hanger bracket7bby bolting or the like, and the top and bottom of the rear end of the crankcase14attached to the top and bottom, respectively, of the pivot frame8by bolting or the like. It is to be noted that reference signs M1and M2in the drawing denote front frame fixing portions at the top and bottom of the front end of the crankcase14; and M3and M4denote rear frame fixing portions at the top and bottom of the rear end of the crankcase14.

The cylinder15has, in order from the side thereof on which the crankcase14is located, a cylinder body16, a cylinder head17, and a head cover (not shown). An intake system component and an exhaust system component (which are not shown) are respectively connected to a rear portion (an intake side) and a front portion (an exhaust side) of the cylinder head17.

A piston18that reciprocates along the cylinder axis C1is fitted within the cylinder body16. The reciprocating motion of the piston18is converted into the rotary motion of a crankshaft21through a connecting rod19.

As shown inFIGS. 2 and 3, the crankshaft21, serving as a power shaft of the power unit10, is housed within a front portion of the crankcase14. The crankshaft21has: a pair of left and right crank webs21bthat support a crankpin21a; left and right journal portions21cthat protrude laterally outward from the left and right crank webs21b, respectively; and left and right support shafts21dthat extend further laterally outward from the left and right journal portions21c, respectively. The left support shaft21dintegrally rotatably supports an alternator rotor not shown. The right support shaft21dintegrally rotatably supports a primary drive gear22for power transmission to the transmission23.

It is to be noted that reference sign C2inFIG. 3denotes a rotation axis (a crank axis) of the crankshaft21(the left and right journal portions2c) which is parallel to a left-right direction;24, left and right radial ball bearings that rotatably support the left and right journal portions21c, respectively, on left and right side walls14aof the crankcase14;25, an oil pump drive gear that is supported between the left crank web21band the left journal portion21cso as to be rotatable integrally therewith; and26, a cam drive sprocket that is supported between the right journal portion21cand the primary drive gear22so as to be rotatable integrally therewith.

Also, reference shin27inFIG. 2denotes the pivot shaft parallel to the left-right direction which supports a front end of the swing arm9; C7, a swing axis (a pivot axis) of the pivot shaft27which is parallel to the left-right direction;28, an oil pump that is disposed below the crankshaft21within the crankcase14; and29, a starter motor that is attached to the lower side of a front end of the crankcase14.

Referring toFIG. 2, within a rear portion of the crankcase14, there are housed the transmission23that is provided in a power transmission path between the engine13and the drive wheel, and a change mechanism51that shifts the shift position of the transmission23. The rotative power of the crankshaft21is outputted to the rear left side of the crankcase14through the transmission23, and then transmitted to the rear wheel11, for example, through a chain transmission mechanism.

Referring also toFIGS. 3 and 4, the transmission23has: first and second main shafts31and32that extend along the left-right direction parallel to and separately from each other; first and second clutches33and34that are coaxially supported on tight ends of the main shafts31and32, respectively; a single countershaft35that extends along the left-right direction parallel to and separately from the main shafts31and32; a first gear group36provided extending across the first main shaft31and the countershaft35; and a second gear group37provided extending across the second main shaft32and the countershaft35. The first gear group36is composed of plural gear trains (gear pairs) for odd-numbered shift positions. The second gear group37is composed of plural gear trains (gear pairs) for even-numbered shift positions. It is to be noted that reference signs C3, C4, and C5denote rotation axes (namely, a first main shaft axis, a second main shaft axis, and a countershaft axis, respectively) of the main shafts31and32and the countershaft35which are parallel to the left-right direction.

The transmission23allows power transmission selectively using any one of the above-described gear trains. During normal operation in which the shift position is constant, the transmission23brings one of the clutches33and34into a connected state and the other into a disconnected state to perform power transmission using any one of the gear trains coupled to the clutch being in the connected state and create the state where power transmission using a gear train preliminarily selected from among the gear trains coupled to the clutch being in the disconnected state can be performed. In this state, the clutch being in the connected state is disconnected, and the clutch being in the disconnected state is connected (i.e., switching between the clutches33and34is performed), thereby shifting the shift position between the odd-numbered and even-numbered shift positions.

Referring toFIGS. 3 and 4, each of the clutches33and34is a wet multiplate clutch having plural axially alternately overlapping clutch plates41, and housed within a right side portion of the crankcase14(within a clutch chamber14c). It is to be noted that reference sign14bin each drawing denotes a clutch cover that covers the clutch chamber14c(each of the clutches33and34) from the right side and the periphery (front, rear, left, and right) thereof.

The clutches33and34are of mechanical types in which the clutch plates41are brought into frictional engagement by the pressure from their respective clutch drive mechanisms (not shown).

It should be noted that the motorcycle1includes the so-called AMT (Automatic Manual Transmission), and is designed to allow the clutches33and34to be connected and disconnected in accordance with an operation of a shift operating element or a predetermined shift timing by using the driving force of a clutch actuator such as an electric motor.

The transmission23is of a constant-mesh type in which a drive gear and a driven gear corresponding to each shift position are in constant mesh. The gears are broadly classified into free gears that are relatively rotatable with respect to their respective support shafts, and slide gears that are spline-fitted to the shafts. By axially moving any slide gear with the operation of the change mechanism51, the gears are shifted so that power transmission using the gear tram corresponding to any one of the shift positions is performed.

The shafts31,32, and35are arranged in the following order from the crankshaft21to the rear: the first main shaft31, the countershaft35, and the second main shaft32, and located higher with rearward distance from the crankshaft21. A shift drum52of the change mechanism51is disposed above the first main shaft31and forwardly of the second main shaft32.

The change mechanism51has: the shift drum52of a hollow cylindrical shape parallel to the shafts31,32, and35; and four shift forks53ato53dthat engage four lead grooves (not shown) formed on the outer periphery of the shift drum52. In response to the rotation of the shift drum52, the shift forks53ato53dmove individually axially in accordance with the patterns of the respective lead grooves to individually axially move shifters40ato40dof the transmission23which is to be described later. Thus, the gears to be used for power transmission between one of the main shafts31and32and the countershaft35in the transmission23are arbitrarily selected (established as power transmission elements). It is to be noted that reference sign C6denotes a rotation axis (a drum axis) of the shift drum52which is parallel to the left-right direction. A left end of the countershaft35protrudes outwardly of the crankcase14, the protruding portion being provided with a drive portion (a drive sprocket in the drawing)35cof the transmission mechanism.

Referring toFIG. 3, the first main shaft31has a left end rotatably supported by the left sidewall14aof the crankcase14through a left radial needle bearing55a, and a right end rotatably supported by the right sidewall14aof the crankcase14through a right radial ball bearing55b. The first clutch33is coaxially supported at a portion of the first main shaft31which extends rightward of the right radial ball bearing55b.

Referring toFIG. 4, the second main shaft32has a left end rotatably supported by the left sidewall14aof the crankcase14through a left radial needle bearing56a, and a right end rotatably supported by the right sidewall14aof the crankcase14through a right radial ball bearing56b. The second clutch34is coaxially supported at a portion of the second main shaft32which extends rightward of the right radial ball hearing56b.

Referring toFIGS. 2 to 4, rotative power is input to a clutch outer42of the first clutch33from the primary drive gear22(the crankshaft21) through a large-diameter transmission gear45of the first clutch33.

On the other hand, rotative power from the crankshaft21is transmitted to the clutch outer42of the second clutch34through in the following order: the primary drive gear22, the large-diameter transmission gear45of the first clutch33, a small-diameter transmission gear46of the first clutch33, an idle gear47, the small-diameter transmission gear46of the second clutch34, and the large-diameter transmission gear45of the second clutch34.

The gear groups36and37constitute a total of six shift positions.

The first gear group36constitutes first-, third-, and fifth-speed gear trains36a,36c, and36ecorresponding to odd-numbered positions (first, third, and fifth speeds), and is provided in such a manner as to extend between right portions of the first main shaft31and the countershaft35. The first-speed gear train36ais composed of a first-speed drive gear38aand a first-speed driven gear39a. The third-speed gear train36cis composed of a third-speed drive gear38cand a third-speed driven gear39c. The fifth-speed gear train36eis composed of a fifth-speed drive gear38eand a fifth-speed driven gear39e.

On the other hand, the second gear group37constitutes second-, fourth-, and sixth-speed gear trains37b,37d, and37fcorresponding to even-numbered positions (second, fourth, and sixth speeds), and is provided in such a manner as to extend between left portions of the second main shaft32and the countershaft35. The second-speed gear train37bis composed of a second-speed drive gear38band a second-speed driven gear39b. The fourth-speed gear train37dis composed of a fourth-speed drive gear38dand a fourth-speed driven gear39d. The sixth-speed gear train37fis composed of a sixth-speed drive gear38fand a sixth-speed driven gear39f.

Any one of the gear trains of the gear groups36and37is selectively established, so that the rotative power of the crankshaft21which is input to either the main shaft31or32is reduced in speed at a predetermined reduction ratio and then transmitted to the countershaft35.

An ECU (not shown), serving as a controller for the transmission23, controls the operation of the clutches33and34and the shift drum52on the basis of the information detected by various sensors to shift the shift position of the transmission23.

More specifically, the transmission23brings one of the clutches33and34into the connected state to perform power transmission using any one of the gear trains operatively connected to the one of the clutches33and34and preliminarily select a gear train to be established next from among the gear trains operatively connected to the other of the clutches33and34. In this state, disconnection of the one of the clutches33and34and connection of the other one are simultaneously performed, thereby switching to power transmission using the preliminarily selected gear train. Thus, upshifting or downshifting of the transmission23is performed.

In the transmission23, after an engine start of the motorcycle1and during a stop of the motorcycle1, the clutches33and34are held in the disconnected state, and then, in preparation for startup of the motorcycle1, moved from a neutral position where power transmission using any one of the gear trains is disabled to a first-speed position where a first-speed gear (a startup gear, the first-speed gear train36a) is established. In this state, for example, the engine rotational speed increases to bring the first clutch33into the connected state through a half-clutch state so as to start the motorcycle1.

While the motorcycle1is moving, the transmission23brings one clutch corresponding to a current shift position into the connected state, and at the same time, preliminarily establishes the gear train corresponding to the next shift position from among any one of the gear trains coupled to the other clutch being in the disconnected state, on the basis of vehicle driving conditions or the like.

More specifically, when the current shift position is an odd-numbered position (or an even-numbered position), the next shift position is to be an even-numbered position (or an odd-numbered position). Therefore, the rotative power of the crankshaft21is input to the first main shaft31(or the second main shaft32) through the first clutch33(or the second clutch34) being in the connected state. At this time, since the second clutch34(or the first clutch33) is in the disconnected state, no rotative power of the crankshaft21is input to the second main shaft32(or the first main shaft31).

After that, when the ECU determines that the shift timing is reached, switching to power transmission using the gear train corresponding to the preliminarily established next shift position is performed simply by bringing the first clutch33(or the second clutch34) being in the connected state into the disconnected state, and the second clutch34(or the first clutch33) being in the disconnected state into the connected state. Thus, rapid and smooth transmission without a time lag or interruption of the power transmission during shift transmission is performed.

Referring toFIGS. 3 and 5, the first clutch33has: the clutch outer42that has a bottomed cylindrical shape coaxial with the first main shaft31and opening rightward, and is supported in a relatively rotatable manner by the first main shaft31to constantly perform rotative power transmission between the crankshaft21and the clutch outer42; a clutch inner43that has the same bottom cylindrical shape as the clutch outer42, is coaxially disposed on the inner peripheral side of the clutch outer42and supported in a relatively rotatable manner by the first main shaft31; plural clutch discs41a(the clutch plates41) that are axially stacked on the inner peripheral side of a cylindrical wall42bof the clutch outer42and supported in an integrally rotatable manner and an axially movable manner by the inner periphery of the cylindrical wall42b; plural clutch plates41b(the clutch plates41) that are axially stacked on the outer peripheral side of a cylindrical wall43bof the clutch inner43in an alternating manner between the clutch discs41aand the clutch plates41band supported in an integrally rotatable manner and an axially movable manner by the outer periphery of the cylindrical wall43b; and a pressure unit44that is coaxially disposed on an open side of the clutch inner43to press leftward the plural clutch plates41(hereinafter also referred to as “clutch plate group41”) stacked between the cylindrical walls42band43b.

On the left side of a bottom wall42cof the clutch outer42, there is mounted, through a damper45a, the large-diameter transmission gear (primary driven gear)45having a diameter larger than the bottom wall42c. The large-diameter transmission gear45has a meshing engagement with the primary drive gear22provided on a right end of the crankshaft21.

A cylindrical outer hub45b, which is coaxial with the first main shaft31and in which the first main shaft31is inserted, is integrally formed on the inner peripheral side of the large-diameter transmission gear45. The outer hub45bis rotatably supported through a pair of radial needle bearings45dby the outer periphery of a distance collar45c. The distance collar45cis disposed between the right radial ball bearing55band the clutch inner43to allow insertion of the first main shaft31.

The small-diameter transmission gear46having a relatively small diameter is integrally formed on the left-hand outer periphery of the outer hub45b. The small-diameter transmission gear46has a meshing engagement with the idle gear47rotatably supported by a right end of the countershaft35. The idle gear47also has a meshing engagement with the large-diameter transmission gear45of the second clutch34is to be described later.

A left pressure flange43ais integrally formed on the outer periphery of a bottom wall43cof the clutch inner43. The left pressure flange43ais adjacent to the left side of a left side surface of the clutch plate group41.

A right pressure flange (pressure plate)44aof the pressure unit44is adjacent to the right side of a right side surface of the clutch plate group41. The right pressure flange44ais moved leftward by the operation of the clutch drive mechanism. Thus, the clutch plate group41is pressed in sandwich relation between the left and right pressure flanges43aand44aand brought into integral frictional engagement, causing a clutch connected state in which torque can be transmitted between the clutch outer42and the clutch inner43. On the other hand, the right pressure flange44ais moved rightward to release the friction engagement, causing a clutch disconnected state in which the torque transmission is disabled.

The pressure unit44has the right pressure flange44athat is integrally rotatable with the clutch inner43. An inner supporting portion65of the same bottomed cylindrical shape as the clutch inner43is coaxially disposed on the inner peripheral side of the clutch inner43. The inner supporting portion65has: an outer cylindrical wall65athat extends toward the clutch inner43(leftward) from the right pressure flange44a; a bottom wall65bthat extends toward a clutch inner periphery from an end (a left end) of the outer cylindrical wall65aon the side on which the clutch inner43is located; and an inner cylindrical wall65cthat rises from an inner peripheral edge of the bottom wall65btoward the right pressure flange44a(rightward). A right end (an open end) of the outer cylindrical wall65ais integrally continuous with the right side of the inner periphery of the right pressure flange44a. In other words, the right pressure flange44aand the inner supporting portion65are integrally formed.

Also, the pressure unit44has: a pressure ring44bthat is disposed on the inner peripheral side of the right pressure flange44aand can press leftward the inner supporting portion65(the right pressure flange44a) through a clutch spring48; and a pressure cap44cthat engages in a relatively rotatable manner in an inner periphery of the pressure ring44bthrough a radial ball bearing44dand can press leftward the pressure ring44b. The pressure ring44bcan move axially with respect to the right pressure flange44a, with its outer periphery spline-fitted to the inner periphery of the right pressure flange44a. It is to be noted that reference sign44edenotes a snap ring for restricting the rightward movement of the pressure ring44b.

An input portion of the clutch drive mechanism is disposed on the right side of the pressure cap44c. The input portion presses leftward the right pressure flange44athrough the pressure cap44cand the pressure ring44b, thereby pressing in sandwich relation the clutch plate group41and bringing the clutch plate group41into frictional engagement. On the other hand, when the pressure is released, the right pressure flange44ais moved rightward by the action of a return spring49provided between the right pressure flange44aand the cylindrical wall43bof the clutch inner43, so that the above-described sandwich pressure and frictional engagement are released.

A cylindrical inner hub43d, which is coaxial with the first main shaft31and in which the first main shaft31is inserted, is integrally formed in a manner rising rightward on the inner peripheral side of the bottom wall43cof the clutch inner43. The inner periphery of the inner hub43dis supported by spline-fitting to the outer periphery of the first main shaft31. The inner periphery of the inner cylindrical wall65cof the inner supporting portion65is fitted and supported on the outer periphery of the inner hub43d.

A lock nut43efor fixing the inner hub43d(the clutch inner43) or the like is screwed on a right end of the first main shaft31. The right end of the inner cylindrical wall65cabuts on a lock washer43fheld between the lock nut43eand the inner hub43d. Thus, the rightward movement of the right pressure flange44aunder the urging force of the return spring49is restricted (this position of the right pressure flange44ais its initial position).

In this state, the bottom wall65bof the inner supporting portion65and the bottom wall43cof the clutch inner43are spaced apart in the axial direction to form a clearance66in between. The clearance66allows the inner supporting portion65(the right pressure flange44a) to move leftward, so that the clutch plate group41can be pressed in sandwich relation between the left and right pressure flanges43aand44a.

The clutch spring48is a compression coil spring extending parallel to a clutch axial direction, and includes plural (four) clutch springs48that are arranged with equal spacing in a clutch circumferential direction (seeFIG. 6). The clutch springs48are provided in a compressed state under a predetermined initial load between the left side of the pressure ring44band the right side of the bottom wall65bof the inner supporting portion65. A relatively-shallow right recess67afor fitting a right end of each of the clutch springs48through a guide67bis formed on the left side of the pressure ring44b. A relatively-deep left recess67for fitting a left end of each of the clutch springs48is formed in a left portion of the inner supporting portion65. The left recess67corresponds to a folded-back portion surrounded by a left portion of the outer cylindrical wall65a, the bottom wall65b, and the inner cylindrical wall65c.

The return spring49is a compression coil spring extending parallel to the clutch axial direction (parallel to the clutch springs48), and includes plural (four) return springs49that are arranged with equal spacing in the clutch circumferential direction (seeFIG. 6). The return springs49are located toward a clutch outer periphery relative to the clutch springs48and each arranged in the bisector of the angle between the adjacent clutch springs48. In other words, the clutch springs48and the return springs49are alternately arranged so as to form equal angles in a clutch rotation direction. The return springs49are provided in compressed state under a predetermined initial load between the left end surfaces of slit-like notches68formed in the cylindrical wall43bof the clutch inner43and the right end surfaces of right recesses68aformed on the left side of the inner periphery of the right pressure flange44a.

The total spring force of the return springs49is smaller than that of the clutch springs48. Therefore, when the pressure ring44bmoves leftward, only the return springs49are compressed, while the clutch springs48are not compressed, to cause the inner supporting portion65(the right pressure flange44a) to move leftward.

Thereafter, even when the right pressure flange44aabuts on the right side surface of the clutch plate group41, the pressure ring44bcan move further leftward. This further leftward movement of the pressure ring44binitiates compression of the clutch springs48. And then when the pressure ring44bis fully moved leftward, the clutch plate group41is pressed in sandwich relation between the left and right pressure flanges43aand44aby the spring force of the clutch springs48.

Referring toFIGS. 5 and 7, arc-shaped grooves69are formed on the left side of the inner periphery of the right pressure flange44aso as not to interfere with the leading end (the right end) of the cylindrical wall43bof the clutch inner43. Detents70protruding toward the clutch inner43are formed at portions at the bottom of the arc-shaped grooves69facing the return springs49(the portions forming the right recesses68a). Each of the detents70engages the leading end of the corresponding notch68during the interval that the right pressure flange44amoves from the initial position to a position to press in sandwich relation the clutch plate group41, thereby restricting the relative, rotation about the axis C3between the clutch inner43and the right pressure flange44a.

Referring toFIG. 5, an inner oil groove71athat allows a portion of engine oil in the first main shaft31to circulate therethrough is formed between a left inner periphery of the inner hub43dand an outer periphery of the first main shaft31. An inner oil passage71that allows communication between the inner oil groove71aand the clearance66is formed in the bottom wall43cof the clutch inner43. Through the inner oil passage71, a portion of the engine oil in the first main shaft31is supplied to the fitting portion between the clutch inner43and the right pressure flange44a, the clutch plate group41or the like.

A portion of the engine oil in the first main shaft31is supplied to the needle beating45dthrough an oil gallery72bof the distance collar45c. An outer oil groove72athat allows the engine oil supplied to the needle bearing45dto circulate therethrough is formed between an inner periphery of the outer hub45band an outer periphery of the needle bearing45d. An outer oil passage72that allows communication between the outer oil groove72aand the fitting portion between the clutch outer42and the large-diameter transmission gear45is formed in the outer hub45b. Through the outer oil passage72, a portion of the engine oil in the first main shaft31is supplied to the clutch outer42, the large-diameter transmission gear45or the like.

It should be noted that the second clutch34also has the same construction as the first clutch33(seeFIG. 4). Therefore, the same portion is denoted by the same reference sign, and the detailed description thereof will not be repeated.

Furthermore, the above-described clutch device construction is not limited to twin-clutch transmissions, but also is applicable to general single-clutch transmissions. Also, the above-described clutch device construction is not limited to wet multiplate clutches, but also is applicable to dry or single plate clutches, or alternatively, may be applied to pull type clutches rather than push type clutches.

As described above, the clutches33and34according to the above-described embodiment each include: the clutch outer42and the clutch inner43coaxially supported on each of the main shafts31and32; the clutch discs41aheld by engagement with the clutch outer42; and the clutch plates41bheld by engagement with the clutch inner43, for switching between the transmission and non-transmission of power between the clutch outer42and the clutch inner43by bringing the clutch discs41aand the clutch plates41binto pressure contact with one another in the clutch axial direction or releasing the pressure contact.

Each of the clutches33and34includes: the right pressure flange44athat is supported movably in the clutch axial direction by the clutch inner43and brings the clutch discs41aand the clutch plates41binto pressure contact with one another in cooperation with the left pressure flange43aof the clutch inner43; the pressure ring44bthat moves the right pressure flange44awith the force toward a clutch connected position input from a pressure mechanism59to bring the clutch discs41aand the clutch plates41binto pressure contact with one another; the clutch springs48that are disposed between the pressure ring44band the right pressure flange44aand transmits, to the right pressure flange44a, the force toward the clutch connected position input to the pressure ring44bfrom the pressure mechanism59; and the return springs49that are disposed between the clutch inner43and the right pressure flange44aand urges the right pressure flange44atoward the clutch disconnected position with a force smaller than that of the clutch springs48. The clutch springs48and the return springs49are disposed parallel to the clutch axial direction. A plane perpendicular to an axis of the clutch passes through the clutch spring and the return spring.

With this structure, when a force toward the clutch connected position is input to the pressure ring44bof each of the clutches33and34from the pressure mechanism59, the pressure ring44band the right pressure flange44amove toward the clutch connected position while elastically deforming the return springs49earlier than the clutch springs48, so that the right pressure flange44aabuts on either the clutch discs41aor the clutch plates41b(the connection of each of the clutches33and34is started).

Thereafter, when the pressure ring44bmoves further toward the clutch connected position, the clutch springs48start to be elastically deformed following the return springs49, causing the clutch connection state in which the clutch discs41aand the clutch plates41bare brought into pressure contact with one another by the spring force thereof.

In other words, the spring force of the clutch springs48brings the clutch discs41aand the clutch plates41binto pressure contact with one another, and consequently, the moving distance of the pressure ring44bis proportional to the clutch capacity, thereby allowing precise clutch capacity control.

Furthermore, the clutch springs48and the return springs49are disposed parallel to each other along the clutch axial direction. A plane perpendicular to an axis of the clutch passes through the clutch spring and the return spring. Thus, the clutches33and34can be reduced in axial size, as compared with the case where the clutch springs48and the return springs49are axially aligned.

Also, in each of the above-described clutches33and34, the pressure ring44bfits movably in the clutch axial direction in the inner periphery of the right pressure flange44a. Thus, the right pressure flange44aand the pressure ring44bcan be compactly disposed in the clutch axial direction.

Further, each of the above-described clutches33and34is provided with the plural springs48and49, the springs48and49being alternately arranged in the clutch rotation direction, thereby allowing well-balanced and efficient arrangement of the springs48and49.

Moreover, in each of the above-described clutches33and34, the clutch inner43is provided, in the cylindrical wall43bthereof which supports the clutch plates41b, with the notch68serving as a receiving portion of each of the return springs49. Thus, the return springs49can be disposed immediately on the inner peripheral side of the clutch plates41b, thereby allowing reductions in radial size of the clutches33and34.

Also, in each of the above-described clutches33and34, the right pressure flange44ais provided with the detents70that engage in a non-relatively-rotatable manner the leading ends of the notches68on the side on which the right pressure flange44ais located. Thus, the relative rotation between the clutch inner43and the right pressure flange44acan be efficiently restricted by using the notches68for receiving the return springs49.

Also, in each of the above-described clutches33and34, the right pressure flange44ahas the inner supporting portion65that protrudes coaxially toward the clutch inner43. The inner supporting portion65has: the outer cylindrical wall65athat extends toward the clutch inner43from the right pressure flange44a; the bottom wall65bthat extends toward the clutch inner periphery from an end of the outer cylindrical wall65aon the side on which the clutch inner43is located; and the inner cylindrical wall65cthat rises from an inner peripheral edge of the bottom wall65btoward the right pressure flange44a. The inner periphery of the inner cylindrical wall65cis fitted and supported on the outer periphery of the hub43dof the clutch inner43. Also, the clutch springs48, having one end supported by the pressure ring44b, have the other end that is supported by the folded-back portion (the left recess67) of the right pressure flange44awhich is surrounded by the outer cylindrical wall65a, the bottom wall65b, and the inner cylindrical wall65c. Thus, positioning of the clutch springs48can be facilitated, and the clutch springs48can be disposed in a stretchable manner.

Additionally, in each of the above-described clutches33and34, the inner oil passage71formed in the clutch inner43opens toward the folded-back portion (the left recess67) of the right pressure flange44a, thereby allowing efficient supply of oil to the fitting portion between the clutch inner43and the right pressure flange44a.

It should be understood that the present invention is not limited to the foregoing embodiment. Examples of the above-described power unit engine include not only air-cooled single-cylinder engines, but also various types of reciprocating engines such as parallel or V-type multicylinder engines and longitudinal engines with a crankshaft parallel to a vehicle front-rear direction as well as water-cooled engines.

In addition, examples of the saddle-ride type vehicle include general vehicles in which a rider sits astride a vehicle body, and include not only motorcycles (including scooter-type vehicles), but also three-wheeled vehicles (including vehicles having one wheel in front and two in the rear, as well as vehicles having two wheels in front and one in the rear) or four-wheeled vehicles (such as ATVs (All Terrain Vehicles)).

It should be also understood that the construction according to the foregoing embodiment is only illustrative of the present invention, and various changes may be made without departing from the scope of the present invention.

Although a specific form of embodiment of the instant invention has been described above and illustrated in the accompanying drawings in order to be more clearly understood, the above description is made by way of example and not as a limitation to the scope of the instant invention. It is contemplated that various modifications apparent to one of ordinary skill in the art could be made without departing from the scope of the invention which is to be determined by the following claims.