Operating assist device for vehicle clutch

A clutch mechanism includes a friction clutch with a clutch spring, a clutch lever connected to the friction clutch via clutch wires and being manually operable against the urging force of the clutch spring, and a clutch assisting device. The clutch assist device has an assist mechanism having an auxiliary force member (e.g., a spring) that urges the clutch wires in such a direction as to disengage the friction clutch while the clutch lever is moved from a disengage start position, where the clutch lever receives the reactive force of the clutch spring, to a disengaged position, where the disengagement of the friction clutch is completed. The assist mechanism maintains the urging force of the auxiliary spring applied to the clutch wires within a fixed range while the clutch lever is shifted from the midpoint between the disengage start position and the disengaged position to the disengage position. The clutch assist device reduces the manual force required to operate the clutch while preserving the operational feel of the clutch lever when moving the lever from a released position to a half clutched position, to a full clutch position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119(a)-(d) to Japanese Patent Application No. 2005-128069, filed Apr. 26, 2005, and to Japanese Patent Application No. 2005-002872, filed Jan. 7, 2005, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a clutch assist device which can reduce the force necessary to operate a friction clutch to engage and disengage a transmission of a vehicle.

2. Description of the Related Art

An engine unit of a vehicle, for example a motorcycle, is often equipped with a friction clutch that operates to engage and disengage a transmission. With the clutch engaged, the transmission transfers torque from the engine crankshaft to one or more wheels of the motorcycle and, with the clutch disengaged, the transmission is decoupled from the engine so as not transfer a driving torque to the wheel(s). The friction clutch typically has friction plates and clutch plates laid alternately next to one another. A clutch spring presses the friction plates against the clutch plates and biases the friction plates into this state so as to transmit torque.

The clutch has a clutch release mechanism. The clutch release mechanism, which is used to release the pressure against the friction plates caused by the clutch spring, is coupled to a clutch operating lever via a clutch wire. A Bowden-wire cable is often used as the clutch wire and includes an inner wire that slides relative to an outer sheath. The clutch operating lever is usually disposed on the handlebars of the motorcycle. When the rider squeezes the clutch operating lever, the friction plates are separated from the clutch plates, against the urging force of the clutch spring, to disengage the clutch and, hence, the transmission from the engine.

With a friction clutch used in a high-power, high-revolution engine, it is desired to set the biasing load of the clutch spring to a high value to increase the torque capacity of the clutch. However, since the clutch operating lever is operated manually, it often is difficult for at least some riders to operate the clutch operating lever when the biasing load of the clutch spring is increased.

A clutch assist mechanism has been previously proposed to reduce the force necessary to actuate the clutch operating lever. See Japanese Patent Publication No. Hei 7-132872. The clutch assist device disclosed in this patent publication is incorporated in a clutch release mechanism to which the clutch wire is connected.

The conventional assist mechanism has an arm rotatable together with a push lever of the clutch release mechanism and a spring unit disposed between an end of the arm and the engine. The spring unit has a spring holder which can expand and contract in its axial direction and a compression coil spring for urging the spring holder in the direction in which the spring holder expands. The spring holder has a first end rotatably connected to the end of the arm and a second end rotatably connected to a bracket extending from the engine.

In the conventional assist mechanism, the center of rotation of the arm and the first and second ends of the spring holder are aligned on one straight line when the clutch operating lever is operated by a distance corresponding to its free play (i.e., movement of the clutch operating lever before disengagement of the clutch start). Therefore, the urging force of the compression coil spring acts in such a direction as to compress the arm and does not act as a force (moment) to rotate the arm.

However, when the clutch lever is rotated beyond the free play range, the joint between the end of the arm and the first end of the spring holder is offset from the straight line connecting the center of rotation of the arm and the second end of the spring holder. Therefore, the urging force of the compression coil spring acts in such a direction as to rotate the arm, and the arm is forcibly rotated in such a direction to disengage the friction clutch. As a result, the urging force of the compression coil spring is added to the force applied to operate the clutch lever and the force necessary to operate the clutch lever to disengage the friction clutch is reduced.

According to the clutch operating device disclosed in the above-noted Japanese patent publication, when the clutch lever is rotated to a disengage start position at the end of the free play range, the urging force of the clutch spring is applied to the clutch lever. The compression coil spring of the assist mechanism expands to cancel the urging force of the clutch spring in synchronization with the operation of the clutch lever in such a direction as to disengage the friction clutch after the clutch lever has passed the disengage start position.

In the clutch operating device, however, the compression coil spring of the assist mechanism can freely expand after the clutch lever has passed the disengage start position. Therefore, the urging force of the compression coil spring applied from the arm to the push lever is not controlled. That is, since an end of the spring holder is directly connected to an end of the arm and the spring unit rotates in the same manner as the arm, the magnitude of the urging force applied to the push lever is left uncontrolled.

Thus, it is not possible to prevent the clutch lever from suddenly becoming light as it gets close to a disengage position where the friction clutch is disengaged while the clutch lever is moved to disengage the friction clutch. Therefore, the operating feel of the clutch lever is unnatural, and there is still room for improvement in terms of the operability of the clutch lever.

When the clutch lever is moved to disengage the friction clutch, the force necessary to operate the clutch lever is preferably small especially in the first half between the disengage start position and the disengage position (the half on the side of the disengage start position). That is, it is preferable to reduce the force necessary to operate the clutch lever in the initial stage of what is called half-clutch operation. However, with the conventional clutch operation device, a large force is necessary in the first stage of the half-clutch operation. Therefore, there is also room for improvement in terms of the operability of the clutch lever in this respect.

A need therefore exists for a clutch operation assisting device with which the operation of the operating element when disengaging the clutch does not feel awkward and which can improve the operability of the assist mechanism.

SUMMARY OF THE INVENTION

An aspect of the present invention involves a clutch mechanism for a vehicle comprising a clutch assist device operating between a clutch and a clutch operator. The clutch operator is connected to the clutch by a transmitting component. The clutch includes a clutch element, which is biased toward an engaged position and is movable by the clutch operator and the transmitting component from the engaged position to a disengaged position. A clutch assist device operates between the clutch an the transmitting component. The clutch assist device comprises an auxiliary force member, which is disposed relative to the transmitting component, at least when the clutch operator is moved to disengage the clutch element, to apply an assist force to the transmitting component. The assist force is applied in such a direction as to assist disengaging the clutch element while the clutch operator is moved from a disengage start position, at which point the clutch operator works against the bias of the clutch spring, to a disengaged position where the clutch element is in the disengaged position. The assist force of the auxiliary force member, which is applied to the transmitting component, is maintained within a fixed range while the clutch operator is moved from an intermediate position, lying between the disengage start position and the disengaged position, to the disengage position.

Accordingly, when the clutch operator is operated in such a direction as to disengage the clutch, the urging force of the auxiliary force member is added to the force applied by the clutch operator. Therefore, the clutch lever is more easily operated.

In addition, the urging force of the auxiliary force member applied to the transmitting component does not increase over a fixed range even when the clutch operator gets close to the disengaged position. Consequently, the manual force operating operator lever is prevented from suddenly becoming light as the operator nears the disengaged position. The clutch assist device thus reduces the manual force required to operate the clutch while preserving the operational feel of the clutch operator when moving the operator from a released position to a half clutched position, to a full clutch position.

An additional aspect of the present invention involves a clutch assist device for incorporation into a clutch mechanism. The clutch mechanism includes a friction clutch with a clutch spring, a transmitting component connected to the friction clutch, and a clutch operator which is connected to the transmitting component and which changes the engagement state of the friction clutch when operated against the urging force of the clutch spring. The clutch assist device comprises a movable member that is movable in synchronization with the clutch operator and a rotatable member. An auxiliary elastic member for applying an urging force to rotate the rotatable member, is pivotal through a fixed path with movement of the movable member. A cam mechanism is interposed between the movable member and the rotatable member for transmitting the urging force applied to the rotatable member to the movable member. When the clutch operator is operated in such a direction as to disengage the friction clutch, the auxiliary elastic member applies an urging force to move the movable member in such a direction as to assist disengaging the friction clutch while the clutch operator is moved from a disengage start position, at which point the clutch operator works against the bias of the clutch spring, to a disengaged position where the clutch element is in the disengaged position.

In a preferred mode, the rotatable member and the cam mechanism are interposed between the auxiliary elastic member and the movable member. Since the auxiliary elastic member oscillates through the fixed path, the direction of the urging force can be freely changed. Therefore, the urging force can be always applied in a desired direction, and the loss of the urging force applied to the movable member can be reduced although a cam mechanism is interposed between the auxiliary elastic member and the movable member. In addition, the wear of the components in the clutch assist device can be reduced, and the service life and reliability of the clutch assist device can be improved.

Also, since the cam mechanism is interposed between the auxiliary elastic member and the movable member, the relation between the auxiliary elastic member and the movement of the movable member can be freely set. Therefore, the variation characteristics of the urging force applied to the movable member (in other words, the variation characteristics of the urging force at the time when the clutch operator is operated) can be easily set according to the application and performance criteria. Therefore, the operability of the clutch lever can be further improved by, for example, reducing the force necessary to operate the clutch lever immediately after the disengagement of the friction clutch has started.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following describes two examples of embodiments that the present clutch assist device can take with reference to the drawings. In the following embodiments, a clutch operating device and a clutch assist device, which are configured in accordance with aspects of the present invention, are applied to a motorcycle. The clutch operating device and the clutch assist device, however, are applicable to other types of vehicles, including other types of straddle-type vehicles, including, without limitation, to scooters, ATVs, snowmobiles and the like.

For the purpose of describing the embodiments below, several terms of orientations are used to describe the motorcycle, the clutch assist device, and the components of the motorcycle with which the clutch assist device operates. Terms such as, for example, “up,” “down,” “left,” “right,” “vertical,” “horizontal,” “higher,” “upper,” “lower,” “front,” and “back” are used from the perspective of the motorcycle orientation shown inFIG. 1and in manner consistent with the ordinary meaning of these terms; however, the clutch assist device and the associated components of the motorcycle can assume different orientations than those illustrated in the embodiments. Hence, it is not intended that such terms of orientation limit the invention.

First Embodiment

With initial reference toFIGS. 1 and 2, a motorcycle, which includes the present clutch assist device, has a frame2. The frame2includes a steering head pipe3, a main frame member4and a down tube5. The steering head pipe3supports a front fork6. To the upper end of the front fork6is secured a handlebar8for steering a front wheel7. A clutch lever9is attached to the left end of the handlebar8. The clutch lever9is one example of the type of clutch operator with which the present clutch assist device can be used. While the clutch operator is manually operated by hand in this embodiment, the clutch operator can be operated by foot or otherwise by the vehicle's rider.

The main frame member4extends backward from the steering head pipe3. The main frame member4supports a fuel tank10and a seat11. The down tube5has a first portion5aextending downward from the front end of the main frame member4and a second portion5bextending backward from the lower end of the first portion5a.

The frame2supports an engine, preferably a V-twin cylinder engine13. In the illustrated embodiment, the engine13has a crankcase14, a front cylinder15and a rear cylinder16. The front cylinder15and the rear cylinder16protrude from an upper surface of the crankcase14toward the fuel tank10above the crankcase14.

The down tube5of the frame2preferably holds the engine13. The first portion5aof the down tube5extends vertically, directly in front of the engine13, and the second portion5bof the down tube5extends longitudinally under the crankcase14.

As shown inFIGS. 1 and 2, the crankcase14preferably houses a crankshaft17and a wet multi-plate friction clutch18. The crankshaft17is disposed horizontally in the vehicle width direction, and a speed reduction small gear19is secured to the left end of the crankshaft17. The friction clutch18is located behind the speed reduction small gear19and at the left end in the crankcase14. The friction clutch18is covered with a clutch cover20attached to the left side of the crankcase14.

The friction clutch18is used to engage or disengage the transmission of torque from the crankshaft17to an input shaft21of a transmission and is manually operated when the rider squeezes the clutch lever9with a hand. As shown inFIG. 2, the friction clutch18has a clutch housing23, a clutch boss24, a plurality of friction plates25, a plurality of clutch plates26, a clutch spring27and a clutch release mechanism28.

The clutch housing23is rotatably supported on the left end of the input shaft21via a bearing30. A speed reduction large gear31is coaxially connected to an end of the clutch housing23. The speed reduction large gear31meshes with the speed reduction small gear19. This engagement allows the torque from the crankshaft17to be transmitted to the clutch housing23.

The clutch boss24is secured to the left end of the input shaft21so as to rotate with the input shaft21. The clutch boss24is surrounded by the clutch housing23and has a plurality of boss parts32(only one of which is shown inFIG. 2) protruding toward the clutch cover20.

The friction plates25are supported on the outer periphery of the clutch housing23. The friction plates25are rotatable together with the clutch housing23and are arranged coaxially in the axial direction of the input shaft21with intervals therebetween.

The clutch plates26are supported on the outer periphery of the clutch boss24. The clutch plates26are rotatable together with the clutch boss24, and each of the clutch plates26extends between adjacent friction plates25. Therefore, the friction plates25and the clutch plates26are arranged alternately in the clutch housing23.

In this embodiment, a diaphragm spring is used as the clutch spring27. The clutch spring27is located on the left side of the clutch housing23and the clutch boss24and supported on the ends of the boss parts32. The clutch spring27constantly presses the friction plates25against the clutch plates26via a pressure plate33. A frictional force is thereby generated between the friction plates25and the clutch plates26and maintains the frictional clutch18in an engaged state capable of transmitting torque.

The clutch release mechanism28is used to release the pressure on the friction plates25caused by the clutch spring27. In this embodiment, the clutch release mechanism28is a rack and pinion type. The clutch release mechanism28has a push rod37having a rack36, and a push lever shaft39having a pinion38.

The push rod37is rotatably supported at the center of the pressure plate33by a bearing35and is located coaxially with the input shaft21. The push rod37is also supported by a clutch cover20for sliding movement in directions toward and away from the input shaft21.

The push lever shaft39is rotatably supported by the clutch cover20. The push lever shaft39extends in a vertical direction and perpendicular to the push rod37, and the pinion38of the push lever shaft39meshes with the rack36of the push rod37. The upper end of the push lever shaft39protrudes upward from the clutch cover20. One end of a push lever40is secured to the upper end of the push lever shaft39. The push lever40extends horizontally from the upper end of the push lever shaft39and has a wire connecting part41at its other end.

The wire connecting part41of the push lever40is connected to the clutch lever9via a clutch wire43(seeFIG. 1). When the rider squeezes the clutch lever9with a hand, the other end of the push lever40is pulled via the clutch wire43to rotate the push lever shaft39. The rotation of the push lever shaft39is converted to linear motion through the meshing of the pinion38with the rack36. Therefore, the pressure plate33is slid in a direction away from the friction plates25against the biasing force of the clutch spring27to release the pressure contact between the friction plates25and the clutch plates26. As a result, the friction clutch18is shifted to a disengaged state in which the transmission of torque is ceased. The push lever shaft39, the push lever40, the clutch wire43and so on constitute a transmitter for transmitting the operating force applied to the clutch lever9to the frictional clutch18.

Therefore, the clutch lever9is rotatable between a return or fully released position where the friction clutch18is maintained in the engaged state and a disengaged position where the frictional clutch18is in the disengaged state. Since the clutch lever9has some degree of free play (for example,10to15mm from the return position as measured at the end of the clutch lever9), the engaged state is maintained even when the clutch lever9is squeezed within this range. The clutch wire43is pulled only slightly and the urging force of the clutch spring27is not transmitted to the clutch lever9when the clutch lever9is operated within this free play range. The position where the free play of the clutch lever9ends is a disengage start position (seeFIG. 15). When the clutch lever9is in the disengage start position, the biasing force of the clutch spring27acts on the clutch lever9via the clutch wire43.

FIG. 15shows the relation between the stroke amount of the clutch wire43and the wire load at the time when the clutch lever9is moved from the fully released position to the disengaged position. InFIG. 15, curve X shows the change of the load applied to the push lever40via the clutch spring27.

As can be understood from curve X, when the clutch lever9reaches the disengage start position from the return position, a load (reactive force) is applied to the push lever40by the clutch spring27. The load rapidly increases with the increase in the stroke amount of the clutch wire43, and keeps a generally constant value after the clutch lever9has passed the midpoint between the disengage start position and the disengaged position. In this embodiment, the point where the load applied to the push lever40becomes generally constant is the midpoint between the disengage start position and the disengaged position. However, the point where the load becomes generally constant may be a point between the disengage start position and the disengaged position other than the midpoint depending on the setting conditions of the push lever40, the type of the friction clutch18, etc. The point where the load becomes generally constant is not limited to the midpoint. The load applied to the push lever40is transmitted to the clutch lever9via the clutch wire43. Therefore, when the biasing load of the clutch spring27is set to a high value to increase the torque capacity of the friction clutch18, the clutch lever9will be stiff to operate.

In this embodiment, a clutch assist device50is installed at an intermediate point of the clutch wire43to reduce the manual load required to operate the clutch lever9. In other words, the clutch wire43has a first clutch wire43aconnected to the clutch lever9and a second clutch wire43bconnected to the push lever40, and the first clutch wire43aand the second clutch wire43bare connected to each other via the clutch assist device50.

As shown inFIG. 4, each of the first clutch wire43aand the second clutch wire43bpreferably has a metal inner wire and a synthetic resin outer tube or sheath45surrounding the inner wire44. The inner wires44are slidably in contact with the outer tubes45, and the both ends of the inner wires44protrude from both ends of the outer tubes45.

As shown inFIG. 3toFIG. 7, the clutch assist device50has an exterior case51and an assist mechanism52housed in the exterior case51. The exterior case51preferably is made of a metal material such as an aluminum alloy. The outer surfaces of the exterior case51can be plated to improve the appearance of the exterior case51. The outer surfaces of the exterior case51may alternatively be painted.

The exterior case51has a case body53and a case cover54. The case body53has a dish-like shape opening toward the left of the engine13and is supported on the first portion5aof the down tube5via a bracket (not shown). The case cover54is fixed to the case body53by a plurality of bolts55and covers the open end of the case body53. The exterior case51is positioned at generally the same height as the push lever40when the motorcycle1is viewed from its left side.

As shown inFIG. 4toFIG. 9, the assist mechanism52in the present embodiment includes the first rotatable member57, a second rotatable member58and a spring unit59. The first rotatable member57preferably is formed of metal by stamping, for example. The first rotatable member57has a pivot part60, a wire connecting part61and a lever part62.

In the illustrated embodiment, the pivot part60is located between the wire connecting part61and the lever part62, and is rotatably supported by a boss part64of the case body53via a first pivot shaft63(seeFIG. 6andFIG. 9). The end of the first pivot shaft63opposite the boss part64is supported by a bearing part65of the case cover54.

As shown inFIG. 4, the wire connecting part61of the first rotatable member57is located in the front half space (in the left half inFIG. 4) in the case body53. The wire connecting part61has a lower edge67. The lower edge67is curved in an arc around the first pivot shaft63. The lower edge67of the wire connecting part61has an engaging groove68(seeFIG. 8) and an engaging hole69. The engaging groove68receives the inner wire44of the first clutch wire43aand the inner wire44of the second clutch wire43band opens at the outer peripheral surface of the edge67. The engaging hole69is a slot elongated along the circumferential direction of the lower edge67. The engaging hole69opens at the outer peripheral surface of the lower edge67and at the engaging groove68. Engaging elements70, which have cylindrical shapes and are secured to the respective ends of the inner wires44, are engaged with the opening edge of the engaging hole69.

Therefore, the inner wire44of the first clutch wire43aand the inner wire44of the second clutch wire43bare integrally connected to each other via the first rotatable member57. This connection allows the inner wire44of the first clutch wire43aand the inner wire44of the second clutch wire43bto move together through the same distance.

The lever part62is located on the rear side in the rear half space in the case body53. The lever part62has a cam groove71. As shown inFIG. 4, the cam groove71is an arcuate slot and curved in a direction opposite that of the lower edge67of the wire connecting part61.

The second rotatable member58has a link plate72and a link lever73. The link plate72and the link lever73preferably are each formed of metal, by a stamping process for example, and are disposed parallel to each other with the lever part62of the first rotatable member57interposed therebetween. The link plate72is rotatably supported by a boss part75of the case body53(seeFIG. 6) via a second pivot shaft74(seeFIG. 5). The link lever73is rotatably supported by a bearing part77of the case cover54via a third pivot shaft76(seeFIG. 4). The second pivot shaft74and the third pivot shaft76are disposed coaxially with each other.

The link plate72and the link lever73are integrally joined to each other via first and second pins78aand78b. The first pin78aextends through the cam groove71of the first rotatable member57. A cam follower79, such as a roller, is rotatably supported by the first pin78a. The cam follower79is located in the cam groove71and in contact with the inner surface of the cam groove71.

Therefore, the cam groove71and the cam follower79can transmit the motion of the first rotatable member57to the second rotatable member58and vice versa. The cam groove71and the cam follower79constitute a cam mechanism.

In the illustrated embodiment, the spring unit59constitutes an auxiliary force member to provide an assist force when operating the clutch lever9. The auxiliary force member, however, can take other forms, as explain below. As shown inFIG. 5, the spring unit59has a spring holder81and an auxiliary spring82. The spring holder81has an inner cylinder83and an outer cylinder84. The inner cylinder83is slidably fitted on the outer cylinder84, which allows the spring holder81to expand and contract.

The inner cylinder83has a spring receiver85and a pivot end86. The spring receiver85extends in a flange-like manner from an outer peripheral surface at one end of the inner cylinder83. The pivot end86is located at one end of the inner cylinder83and is rotatably supported on a mounting seat87formed on a front end inside the case body53.

The outer cylinder84has a spring receiver88and a connecting end89. The spring receiver88extends in a flange-like manner from an outer peripheral surface at one end of the outer cylinder84. The connecting end89is located at one end of the outer cylinder84and is rotatably connected to the link plate72of the second rotatable member58via a pin90. Therefore, the spring holder81connects to a front end of the case body53and to the link plate72and extends generally in the longitudinal direction of the case body53.

The auxiliary spring82preferably is a compression coil spring and is interposed between the spring receiver85of the inner cylinder83and the spring receiver88of the outer cylinder84in a compressed state. Therefore, the spring holder81is constantly biased in the direction in which it expands. When the clutch lever9is in the disengage start position, the pivot end86and the connecting end89of the spring holder81, and the second and third pivot shafts74and76as the center of rotation of the second rotatable member58are positioned on a straight line S1as shown inFIG. 11.

As shown inFIG. 3andFIG. 7, the case cover54preferably has a pair of first wire introduction port95aand95band a second wire introduction port96. The first and second introduction ports95a,95band96open into the exterior case51. The first wire introduction port95aprotrudes upward from an upper part of the front end the case cover54. The other first wire introduction port95bprotrudes obliquely upward from an intermediate part of the front end of the case cover54. The second wire introduction port96protrudes backward from a lower part of the rear end of the case cover54.

In this embodiment, the first clutch wire43ais inserted into the first wire introduction port95a. The inner wire44of the first clutch wire43aextends into the exterior case51and is connected to the first rotatable member57. The first clutch wire43aextends upward along the first portion5aof the down tube5from a front end of the exterior case51(seeFIG. 1).

The first wire introduction port95bis used to change the direction in which the clutch wire43aextends from the exterior case51. The first wire introduction port95bis preferably closed by a dust-proof cap (not shown) to prevent entrance of dust or foreign objects into the exterior case51when it is not used.

The second clutch wire43bis inserted into the second wire introduction port96. The inner wire44of the second clutch wire43bextends into the exterior case51and is connected to the first rotatable member57. The second clutch wire43bextends backward from a rear end of the exterior case51along the left side of the engine13and linearly connects the first rotatable member57of the assist mechanism52and the push lever40(seeFIG. 1).

FIG. 4andFIG. 5show the state of the assist mechanism52at the time when the clutch lever9is in the fully released position. When the clutch operating lever9is in the fully released position, the second pivot shaft74of the link plate72and the third pivot shaft76of the link lever73are positioned below the straight line S1connecting the pivot end86and the connecting end89of the spring holder81. Also, the spring unit59is inclined such that the connecting end89of the spring holder81is positioned higher than the pivot end86. In addition, the cam groove71of the link plate72extends in the longitudinal direction of the case body53and is maintained in a convex upward position.

When the rider moves the clutch operating lever9from the fully released position toward the disengage start position, the first rotatable member57is pulled upward via the first clutch wire43aand is rotated in the clockwise direction as indicated by the arrows inFIG. 10andFIG. 11. The rotation of the rotatable member57causes the lever part62having the cam groove71to move downward. Therefore, the cam follower79, which is in contact with the cam groove71, receives a force; this force urges the cam follower79toward the front of the case body53, and the link plate72and the link lever73are rotated in the counterclockwise direction. As a result, the spring unit59is rotated downward about the pivot end86.

When the clutch operating lever9reaches the disengage start position, the second and third pivot shafts74,76are positioned on the straight line S1as shown inFIG. 11. Therefore, although the urging force of the auxiliary spring82is being applied to the link plate72and the link lever73, the link plate72and the link lever73are not rotated by the urging force.

When the clutch operating lever9is moved from the disengage start position toward the disengage position, the first rotatable member57is further rotated in the clockwise direction. The rotation of the first rotatable member57causes the lever part62having the cam groove71to move downward, and the cam groove71is brought to an upright position. Therefore, the cam follower79in contact with the cam groove71receives a force which urges it obliquely downward toward the front of the case body53, and the link plate72and the link lever73are rotated in the counterclockwise direction.

In this embodiment, when the clutch operating lever9is shifted from the disengage start position to the disengaged position, the spring unit59is rotated downward about the pivot end86and the straight line SI is offset to a position below the center of rotation of the link plate72and the link lever73.

Therefore, the spring holder81, which receives the urging force of the auxiliary spring82, expands and the urging force of the auxiliary spring82acts to rotate the link plate72and the link lever73. Thus, when the clutch operating lever9is moved toward the disengaged position from the disengage start position, the link plate72and the link lever73are forcibly rotated in the counterclockwise direction by the auxiliary spring82. Therefore, the urging force of the auxiliary spring82is added to the operating force the rider applies to squeeze the clutch operating lever9. Thus, less force is required by the rider to operate the clutch operating lever9.

According to this embodiment, the cam groove71determines the timing at which the link plate72and the link lever73receive an urging force from the spring unit59and starts moving in the counterclockwise direction. More specifically, the cam groove71is of such a shape as to maintain the urging force of the auxiliary spring82applied from the link plate72and the link lever73to the first rotatable member57within a fixed range when the clutch lever9is moved from the midpoint between the disengage start position and the disengaged position toward the disengaged position. In other words, the cam groove71is of such a shape as to permit the movement of the link plate72and the link lever73while the clutch operating lever9is moved from the disengage start position to the midpoint and as to restrict the movement of the link plate72and the link lever73to prevent the auxiliary spring82from expanding freely while the clutch lever9is moved from the midpoint to the disengaged position. Therefore, in this embodiment, the cam mechanism, which is comprised of the cam groove71and the cam follower79, controls the urging force of the auxiliary spring82applied to the first rotatable member57.

InFIG. 15, curve designated as Y shows the change of the load applied to the clutch operating lever9when the clutch operating lever9is moved in such a direction as to disengage the friction clutch18. As can be understood from curve Y, the load applied to the clutch lever9is always smaller than the load of the clutch spring27applied to the push lever40while the clutch lever9is shifted to the disengaged position from the disengage start position. This is because, when the link plate72is rotated in the counterclockwise direction by the force transmitted through the first clutch wire43a, the urging force of the auxiliary spring82, which forcibly urges the link plate72to rotate in the counterclockwise direction, is added.

In addition, in this embodiment, since the shape of the cam groove71is determined as described before, the load applied to the clutch operating lever9can be maintained generally constant while the clutch operating lever9is moved from the midpoint to the disengaged position. As a result, the load applied to the push lever40and the load applied to the clutch lever9change with similar characteristics with respect to the wire stroke amount as shown inFIG. 15.

As described before, when the clutch operating lever9is in the fully released position (i.e., the return position), the second pivot shaft74of the link plate72and the third pivot shaft76of the link lever73are positioned below the straight line S1, as shown inFIG. 4andFIG. 5. Therefore, the link plate72and the link lever73are urged in the clockwise direction; that is, in a direction opposite the direction to disconnect the friction clutch18, by the urging force of the auxiliary spring82.

The force urging the link plate72in the clockwise direction serves as a counter assist force against the force to rotate the clutch lever9from the fully released position to the disengage start position. As a result, the initial input load necessary to squeeze the clutch lever9first is increased and the operability of the clutch lever9is adversely affected.

Therefore, in the clutch assist device50of this embodiment, a canceling spring unit100is incorporated in the case body53of the exterior case51. As shown inFIG. 4andFIG. 14, the case body53has a housing part101for housing the canceling spring unit100. The housing part101is positioned at a lower part of the rear end of the case body53and is located on one side of the second wire introduction port96.

As shown inFIG. 14, the housing part101has a cylinder102extending vertically. At the upper end of the cylinder102is formed an opening102aopening into the exterior case51. The opening102ais opposed to a lock pin103secured to the link plate72. The lock pin103is located at a position opposite the connecting end89where the link plate72is connected to the spring unit59with respect to the second pivot shaft74.

As shown inFIG. 14, the canceling spring unit100has a pressing pin104and a canceling spring105. The pressing pin104has a hollow shape with a closed upper end, and a flange-like stopper106is formed at the lower end of the pressing pin104. The pressing pin104is slidably inserted into the cylinder102from below the housing part101.

A spring receiver108is secured to the lower end of the housing part101via a circlip107. The spring receiver108is located below the cylinder102.

The canceling spring105preferably is a compression coil spring and is interposed between the upper inner surface of the pressing pin104and the spring receiver108in a compressed state. The canceling spring105constantly urges the pressing pin104upward. The urging force of the canceling spring105is set to a level slightly lower than that of the counter assist force caused by the auxiliary spring82.

The pressing pin104is elastically movable between a first position where its upper end largely protrudes from the opening102aof the cylinder102and a second position where its upper end slightly protrudes from the opening102aof the cylinder102. When the pressing pin104is in the first position, the stopper106of the pressing pin104abuts against the lower end of the cylinder102to restrict the position of the pressing pin104. When the pressing pin104is in the second position, the stopper106of the pressing pin104abuts against the spring receiver108to restrict the position of the pressing pin104.

While the clutch lever9is moved from the fully released position to the disengage start position, the upper end of the pressing pin104abuts against the lock pin103of the link plate72from below, as shown inFIG. 5andFIG. 11. Therefore, the link plate72receives the urging force of the canceling spring105via the lock pin103. As a result, the total of the urging force of the auxiliary spring82and the urging force of canceling spring105applied to the link plate72is almost zero and the link plate72is restricted from rotating in the clockwise direction when the clutch lever9is in the range of the free play.

When the clutch lever9approaches the disengaged position from the disengage start position, the lock pin103of the link plate72is separated from the upper end of the pressing pin104, as shown inFIG. 13. As a result, the pressing pin104is maintained in the first position by the urging force of the canceling spring105, and the link plate72and the link lever73are forcibly rotated in the counterclockwise direction by the urging force of the auxiliary spring82.

As shown inFIG. 3,FIG. 6andFIG. 7, the case cover54of the exterior case51has a circular opening110. The opening110is opposed to the wire connecting part61of the first rotatable member57, and the engaging groove68and the engaging hole69of the wire connecting part61are exposed to the outside of the exterior case51through the opening110. In other words, fingers or a tool can be inserted through the opening110to engage the inner wires44into the engaging groove68of the wire connecting part61or to engage the engaging elements70at the ends of the inner wires44into the engaging hole69. Therefore, the inner wires44can be connected to the first rotatable member57with the case cover54secured to the case body53.

The case cover54has a support wall111extending from the opening edge of the opening10to the center of the opening110. The support wall111is located at a position which does not interfere with the wire connecting part61of the first rotatable member57and has a boss part113with a screw hole112at its end. The position of the screw hole112preferably coincides with the center of the opening110.

The opening110is covered with a disk-like lid114(seeFIG. 1). The lid114is removably fitted in the opening110and fixed to the support wall111by a bolt115(seeFIG. 6). The bolt115extends through the center of the lid114and is threaded into the screw hole112of the boss part113.

As shown inFIG. 3andFIG. 9, the wire connecting part61of the first rotatable member57has a hexagonal insertion hole118. The insertion hole118is located in the area of the opening110, and is at a position which corresponds to a positioning recess119of the case body53when the clutch lever9is in the correct disengage start position. Therefore, by inserting a tool such as a hexagonal wrench into the insertion hole118through the opening110and engaging the tip of the tool into the recess119, the first rotatable member57can be held in the position shown inFIG. 10.

Thus, the position of the first rotatable member57at the time when the clutch lever9is in the correct disengage start position can be determined, and, in this state, adjustment of the free play of the clutch wire43and connection of the inner wires44can be carried out.

According to this embodiment, the assist mechanism52installed at an intermediate point of the clutch wire43maintains the urging force of the auxiliary spring82applied to the clutch wire43via the first rotatable member57within a fixed range while the clutch lever9is moved from the midpoint between the disengage start position and the disengaged position to the disengaged position.

Therefore, the load applied from the clutch spring27to the push lever40of the clutch release mechanism28and the actual load applied to the clutch lever9thorough the assist mechanism52change with similar characteristics with respect to the wire stroke amount.

As a result, the clutch lever9can be prevented from becoming suddenly light when it gets close to the disengaged position in disengaging the frictional clutch18although the urging force of the auxiliary spring82is applied to the clutch wire43. Thus, the force necessary to operate the clutch lever9is reduced, and the clutch lever9can be operated with the same operating feel as in operating a conventional clutch lever. The operation of the clutch lever9does not cause any uncomfortable feeling, and the operability of the clutch lever9can be improved.

In addition, according to this embodiment, the first clutch wire43aand the second clutch wire43bare moved with a one-to-one relationship between them being maintained. Therefore, the assist mechanism52can be installed in the length of clutch cable, through which the motion of the clutch lever9is transmitted to the push lever40, without changing the construction of the friction clutch18.

Furthermore, the assist mechanism52of this embodiment has the canceling spring unit100, which abuts against the lock pin103of the link plate72from below when the clutch operating lever9is in the fuilly released position. The canceling spring105of the canceling spring unit100acts to cancel the counter assist force caused by the auxiliary spring82and prevents the rotation of the link plate72in such a direction as to engage the friction clutch18based on the counter assist force. Therefore, the initial input load necessary to squeeze the clutch lever9first is not increased to ease the operation and feel of the clutch lever9.

Second Embodiment

In the second embodiment, the clutch assist device50according to the first embodiment is modified as shown inFIG. 16toFIG. 25. The clutch assist device50of the first embodiment is further decreased in size in accordance with the second embodiment of a clutch assist device. In the following description, those parts corresponding to the components of the first embodiments are identified with the same reference numerals.

As shown inFIG. 16toFIG. 18, the second embodiment of the clutch assist device50also preferably has an exterior case51and an assist mechanism52. The exterior case51has a case body53and a case cover54. In the second embodiment, the areas of the case body53and the case cover54as viewed from a side are smaller than those in the first embodiment.

As shown inFIG. 16andFIG. 18, each of the case body53and the case cover54has first, second and third fastening parts151,152and153, each having a bolt hole. The case body53and the case cover54are secured to each other at the fastening parts151,152and153by bolts115.

As shown inFIG. 18, the assist mechanism52has a first rotatable member57, a second rotatable member58, a spring unit59, and a canceling spring unit100.

The first rotatable member57has a pivot part60and a wire connecting part61. As shown inFIG. 4, the first rotatable member57of the first embodiment has a lever part62having the cam groove71in addition to the wire connecting part61. The rotatable member57of the second embodiment, however, does not have the lever part62and the wire connecting part61has a cam groove71, as shown inFIG. 18. In this embodiment, since the lever part62is omitted, the area of the first rotatable member57is smaller. The first rotatable member57is generally in the form of a sector with a central angle of smaller than 120° as viewed along the axial direction of the first pivot shaft63. The shape of the first rotatable member57is not specifically limited, though. The first rotatable member57may have other shape as well, such as, for example, be triangular. The first rotatable member57may be made even smaller in size in some applications. For example, the first rotatable member57, in the illustrated embodiment, is generally in the form of a sector with a central angle of less than 90°.

As shown inFIG. 24, the pivot part60is rotatably supported by a boss part64of the case body53via the first pivot shaft63. The end of the first pivot shaft63opposite the boss part64is supported by a bearing part65of the case cover54.

As shown inFIG. 18andFIG. 25, the wire connecting part61has a first engaging groove68aand a first engaging hole69aat one end of its lower edge. The wire connecting part61has a second engaging groove68band a second engaging hole69bat the other end of its lower edge.

The inner wire44of the first clutch wire43ais received in the first engaging groove68a. The first engaging grooves68aopens at the outer peripheral surface of the lower edge. The first engaging hole69ais of a circular shape. The first engaging hole69aopens at the outer peripheral surface of the lower edge and in the first engaging groove68a. An engaging element70awith a cylindrical shape is attached to an end of the inner wire44of the first clutch wire43a. The engaging element70ais engaged with the opening edge of the first engaging hole69a. The inner wire44of the first clutch wire43ais thereby engaged with the wire connecting part61.

The inner wire44of the second clutch wire43bis received in the second engaging groove68b. The second engaging grooves68bopens at the outer peripheral surface of the lower edge. The second engaging hole69bis also of a circular shape. The second engaging hole69bopens at the outer peripheral surface of the lower edge and in the second engaging groove68b. An engaging element70bwith a cylindrical shape secured to an end of the inner wire44of the second clutch wire43bis engaged with the opening edge of the second engaging hole69b. The inner wire44of the second clutch wire43bis thereby engaged with the wire connecting part61.

The first engaging groove68aand the second engaging groove68bare each curved in an arc around the first pivot shaft63. The inner wire44of the first clutch wire43aand the inner wire44of the second clutch wire43bare integrally connected to each other via the first rotatable member57. Therefore, the inner wire44of the first clutch wire43aand the inner wire44of the second clutch wire43bcan move together at the same displacement rate. Since the distance from the first pivot shaft63to the engaging element70aand the distance from the first pivot shaft63to the engaging element70bare equal, the inner wires44can move through the same distance.

The cam groove71is located between the first engaging hole69aand the second engaging hole69b. The cam groove71is a curved slot which is concave toward the first engaging hole69a.

The second rotatable member58of the first embodiment has a link plate72and a link lever73(seeFIG. 4). However, in this embodiment, the second rotatable member58is comprised of only a link plate72as shown inFIG. 19. The link plate72is located on the reverse side of the first rotatable member57. The link plate72is rotatably supported by a boss part75(seeFIG. 24) of the case body53via a second pivot shaft74.

A first pin78a, which extends to the front side of the first rotatable member57, is joined to the link plate72. A cam follower79, such as a roller, is rotatably supported by the first pin78a. The cam follower79is located in the cam groove71and in contact with the inner surface of the cam groove71.

Therefore, the cam groove71and the cam follower79can transmit a force from the first rotatable member57to the second rotatable member58or from the second rotatable member58to the first rotatable member57when the first rotatable member57or the second rotatable member58rotates. The cam groove71and the cam follower79comprise a cam mechanism.

The construction of the spring unit59is the same as that of the first embodiment. However, the spring unit59is attached at a different position and in a different posture in this embodiment. As shown inFIG. 21, the mounting seat87for supporting the pivot end86of the spring unit59is disposed at a rear end (at a right-hand end inFIG. 21) in the case body53in this embodiment. The spring unit59extends forward or obliquely forward from a rear end in the case body53(seeFIG. 23).

As shown inFIG. 19, the connecting end89of the spring unit59is rotatably connected to the link plate72of the second rotatable member58via a pin90. When the clutch lever9is in the disengage start position (in the state shown inFIG. 19), the pivot end86and the connecting end89of the spring holder81and the second pivot shaft74as the center of rotation of the second rotatable member58are positioned on a straight line S1.

FIG. 20andFIG. 21show the state of the assist mechanism52at the time when the clutch lever9is in the fully released position. When the clutch lever9is in the fully released position, the second pivot shaft74of the link plate72is positioned above the straight line S1connecting the pivot end86and the connecting end89of the spring holder81, as shown inFIG. 21. The cam follower79is positioned at the left end of the cam groove71.

When the rider moves the clutch lever9from the fully released position toward the disengage start position, the first rotatable member57is pulled upward via the first clutch wire43aand is rotated in the clockwise direction about the first pivot shaft63. The rotation of the first rotatable member57causes the cam groove71to rotate (also in the clockwise direction) about the pivot shaft63and to move upward. Therefore, the cam follower79in contact with the cam groove71receives a force which urges it upward, and the link plate72is rotated in the counterclockwise direction about the second pivot shaft74. As a result, the spring unit59is rotated in the clockwise direction about the pivot end86.

When the clutch lever9reaches the disengage start position, the second pivot shaft74is positioned on the straight line S1connecting the pivot end86and the connecting end89of the spring holder81, as shown inFIG. 19. Therefore, the urging force of the auxiliary spring82does not act to rotate the link plate72at this position.

When the clutch lever9is moved from the disengage start position toward the disengaged position, the first rotatable member57is further rotated in the clockwise direction. The rotation of the first rotatable member57causes the cam groove71to rotate further about the pivot shaft63and move upward. At this time, the cam groove71is brought to a generally horizontal position. As a result, the cam follower79in contact with the cam groove71receives a force which urges it toward the top or front of the case body53, and the link plate72is further rotated in the counterclockwise direction.

When the clutch lever9is moved from the disengage start position to the disengaged position, the spring unit59is further rotated in the clockwise direction about the pivot end86. Then, the straight line SI (connecting the pivot end86and the connecting end89of the spring unit59) is offset upward from the center of rotation of the link plate72(pivot shaft74).

Therefore, the spring holder81receiving the urging force of the auxiliary spring82expands, and the urging force of the auxiliary spring82is transmitted to the link plate72and acts as a force to rotate the link plate72in the counterclockwise direction. Thus, when the clutch lever9is moved toward the disengaged position from the disengage start position, the link plate72is forcibly rotated in the counterclockwise direction by the auxiliary spring82. The urging force of the auxiliary spring82is added to the operating force the rider applies to squeeze the clutch lever9, and the load on the rider in operating the clutch lever9is reduced.

Also in this embodiment, the cam groove71determines the timing at which the link plate72receives an urging force from the spring unit59and starts moving in the counterclockwise direction. The cam groove71is of such a shape as to change the angular velocity ratio, which is the ratio of the angular velocity of the second rotatable member58to the angular velocity of the first rotatable member57, while the clutch lever9is moved from the disengage start position to the disengaged position. The cam groove71is of such a shape that the urging force of the auxiliary spring82transmitted to the first rotatable member57via the link plate72(more specifically, the moment which rotates the first rotatable member57in the clockwise direction) can increase more rapidly than in a conventional device in the initial stage of the process where the clutch lever9is moved from the disengage start position to the midpoint.

FIG. 34contrastively shows the variation characteristics of the urging force Z of the auxiliary spring82and the variation characteristics of the urging force Z0in a conventional device. The gradient at the rising section of the characteristic curve of the urging force Z in this assist mechanism52is greater than that in a conventional device.

Here, the conventional device is a device in which a rotatable member connected to a clutch release mechanism is directly connected to an auxiliary spring and in which the rotatable member and the auxiliary spring rotate at the same speed and the auxiliary spring can freely expand as the rotatable member rotates (for example, the device disclosed in the U.S. Pat. No. 5,495,928).

In this assist mechanism52, the ratio of the angular velocity of the second rotatable member58to the angular velocity of the first rotatable member57is greater when the clutch lever9is in the disengage start position than when the clutch lever9is in the disengaged position. Also, the average of the angular velocity ratio at the time when the clutch lever9is moved from the disengage start position to the midpoint is greater than the average of the angular velocity ratio at the time when the clutch lever9is moved from the midpoint to the disengaged position. The angular velocity ratio may be gradually smaller while the clutch lever9is moved from the disconnect start position to the disengaged position. By properly adjusting the angular velocity ratio, the variation characteristics of the urging force Z of the auxiliary spring82transmitted to the first rotational member57, that is, the variation characteristics of the assist force which the clutch lever9receives, can be advantageously set.

As described above, by properly setting the shape of the cam groove71, the variation characteristics of the assist force can be freely adjusted. As shown in FIG.34, the load X applied to the push lever40of the frictional clutch18varies greatly, immediately after the clutch lever9has passed the disengage start position, and the degree of change is smaller after that. With this assist mechanism52, the gradient of the rising section of the characteristic curve of the urging force Z can be large so that the load Y applied to the clutch lever9can be changed with characteristics almost the same as those of the load X applied to the push lever40of the friction clutch18while the clutch lever9is moved from the disconnect start position to the midpoint. That is, the ratio between the load Y applied to the clutch lever9and the load X applied to the push lever40can be within a fixed range. It is, therefore, possible to reduce the load necessary to operate the clutch lever9and to provide the same operating feel as a conventional clutch lever at half-clutch operation.

As described in the description of the first embodiment, the assist force applied to the first rotatable member57is maintained within a fixed range when the clutch lever9is moved from the midpoint to the disengaged position. That is, the cam groove71is of such a shape as to maintain the urging force of the auxiliary spring82applied to the first rotatable member57via the link plate72within a fixed range when the clutch lever9is moved from the midpoint toward the disengaged position.

In this embodiment, the housing part101housing the canceling spring unit100is disposed at an upper front end of the case body53of the exterior case51as shown inFIG. 19. The housing part101is aligned with the first wire introduction port95ain the transverse direction (in a direction perpendicular to the plane ofFIG. 19). The internal structure of the canceling spring unit100is the same as that of the canceling spring unit100of the first embodiment.

As shown inFIG. 23, the opening102aof the cylinder102of the canceling spring unit100opens downward. The pressing pin104is elastically movable between a first position where its lower end largely protrudes from the opening102aof the cylinder102and a second position where its lower end slightly protrudes from the opening102aof the cylinder102. When the pressing pin104is in the first position, the stopper106of the pressing pin104abuts against the upper end of the cylinder102to restrict the position of the pressing pin104. When the pressing pin104is in the second position, the stopper106of the pressing pin104abuts against the spring receiver (not shown) to restrict the position of the pressing pin104.

While the clutch lever9is moved from the return position (seeFIG. 21) to the disengage start position (seeFIG. 19), the pressing pin104abuts against the lock pin103of the link plate72from above. Thus, the link plate72receives the urging force of the canceling spring105(not shown inFIG. 21, but seeFIG. 14) via the lock pin103. As a result, when the clutch lever9is in the range of free play, the urging force of the auxiliary spring82applied to the link plate72is cancelled by the urging force of the canceling spring105. Therefore, the force applied to the link plate72is substantially zero and the rotation of the link plate72in the clockwise direction caused by the auxiliary spring82(and thus the return of the clutch lever9) is restricted.

When the clutch lever9gets close to the disengaged position over the disengage start position, the lock pin103of the link plate72is separated from the lower end of the pressing pin104, as shown inFIG. 23. As a result, the pressing pin104is held in the first position by the urging force of the canceling spring105, and the link plate72receives a force which urges it to rotate in the counterclockwise direction from the auxiliary spring82.

As shown inFIG. 17, the case cover54of the exterior case51has a circular opening110. The opening110is opposed to the wire connecting part61of the first rotatable member57, and the engaging grooves68aand68band the engaging holes69aand69bof the wire connecting part61are exposed to the outside of the exterior case51through the opening110. In other words, fingers or a tool can be inserted through the opening110to engage the inner wires44into the engaging grooves68aand68bof the wire connecting part61or to engage the engaging elements70aand70bat the ends of the inner wires44into the engaging holes69aand69b. Therefore, the inner wires44can be connected to the first rotatable member57with the case cover54secured to the case body53.

The case cover54has first and second support walls111aand111bextending from the edge of the opening110toward the center of the opening110. The first support wall111aand the second support wall111bare located at opposite positions with respect to the center of the opening110. Each of the first and second support walls111aand111bhas a boss part113with a screw hole112at its end.

As shown inFIG. 16, the opening110is covered with a disk-like lid114. The lid114is removably attached to the opening110and is secured to the support walls111a,111bby bolts115. The bolts115are threaded into the screw holes112of the boss parts113of the support walls111a,111b.

As shown inFIG. 17, the wire connecting part61of the first rotatable member57has a hexagonal insertion hole118. The insertion hole118is located in the area of the opening110. Therefore, when a tool such as a hexagonal wrench is inserted from the opening110into the insertion hole118, the position of the first rotatably member57can be adjusted. The wire connecting part61of the first rotatable member57has a positioning recess119a. The second support wall111bof the case cover54has a positioning projection119b. The projection119band the recess119aalign with each other when the clutch lever9is in the proper disengage start position. Therefore, by adjusting the amount of free play of the clutch lever9so that the projection119aand the recess119bcan align with each other, the disengage start position can be easily set.

The method of attaching the clutch assist device50to the frame2of the motorcycle1and an example of the mounting structure thereof are next described. The clutch assist device50described below is the same as the clutch assist device50described above except that the position of the third fastening part153is changed from on an upper part of the case body53to on a lower part of the case body53(seeFIG. 26). The other construction is the same as that as described above.

As shown inFIG. 32, the clutch assist device50preferably is attached to the down tube5of the frame2via a first bracket161, a second bracket162, a third bracket163and a mounting plate164. Of course, other locations of the clutch assist device50on the vehicle are also possible, depending upon the type of vehicle and application.

As shown inFIG. 27, in the illustrated embodiment, the first bracket161is secured to the down tube5. The method for securing the first bracket161is not specifically limited. Here, the first bracket161is joined to the down tube5by welding. The first bracket161is, as in the case with the second bracket162, originally attached to the down tube5to support a part of the engine13. That is, the clutch assist device50is attached using the existing brackets161and162. The first bracket161extends along the longitudinal direction of the down tube5. The first bracket161has bolt holes171at its longitudinal ends.

As shown inFIG. 28, the second bracket162is laid on the front side of the first bracket161. The second bracket162is a bent plate member with a generally triangle shape as viewed from a side. The second bracket162has a front half part162a, which extends in a direction inclined from the longitudinal direction of the vehicle along the first bracket161, and a rear half part162b, which is located behind the front half part162aand is bent inward (seeFIG. 32). The front half part162aof the second bracket162has bolt holes172at positions corresponding to the bolt holes171of the first bracket161. The rear half part of the second bracket162also has a bolt hole173. As shown inFIG. 32, a bolt174for fixing a part of the engine13is fitted into the bolt hole173. The part of the engine13is supported by the down tube5via the first bracket161and the second bracket162.

As shown inFIG. 29, the third bracket163is laid on the front side of the second bracket162. The third bracket163is a bent plate configured into a three sections from front to rear, and has a front part163aextending along the front half part162aof the second bracket162, an intermediate part162bextending outward from the front part163a, and a rear part163cextending inward from the intermediate part162b(seeFIG. 32). The front part163ahas bolt holes175at positions corresponding to the bolt holes172of the front half part162aof the second bracket162. The rear part163calso has bolt holes176at its upper and lower end.

As shown inFIG. 32, bolts177are inserted through the bolt holes171of the first bracket161, the bolt holes172of the second bracket162and the bolt holes175of the third bracket163. The second bracket162and the third bracket163are secured together with the first bracket161.

As shown inFIG. 30, the mounting plate164is laid on the front side of the rear part163cof the third bracket163. The mounting plate164is in the form of a flat plate (seeFIG. 32). The mounting plate164has slots178preferably extending in the longitudinal direction at its upper and lower rear ends. The mounting plate164has a hole179having an oval shape at its center. The mounting plate164also has three bolt holes181through which bolts (not shown) for attaching the case body53of the clutch assist device50can be inserted.

Bolts180(seeFIG. 32) are inserted through the bolt holes176of the third bracket163and the slots178of the mounting plate164. The bolts180can be fixed at arbitrary positions in the slots178. Therefore, by sliding the mounting plate164back or forth with the bolts180inserted through the slots178, the longitudinal position of the mounting plate164with respect to the third bracket163can be finely adjusted with ease.

As shown inFIG. 26, three bolt holes182corresponding to the bolt holes181of the mounting plate164are formed in the reverse side of the case body53of the clutch assist device50. The case body53is so positioned that the bolt holes182overlap the bolt holes181of the mounting plate164and are placed on the front side of the mounting plate164(seeFIG. 32). Then, bolts (not shown) are threaded into the bolt holes181of the mounting plate164and the bolt holes182of the case body53to secure the case body53to the mounting plate164. As described before, since the longitudinal position of the mounting plate164can be finely adjusted with ease, the longitudinal position of the case body53secured to the mounting plate164can be finely adjusted with ease. Therefore, the position of the case body53can be adjusted so that the case body53can be positioned in a desired position if needed after the case body53has been attached to the amounting plate164.

After the mounting plate164has been attached to the case body53, the case cover54is placed on the case body53and bolts are threaded into the bolt holes of the first, second and third fastening parts151,152and153to secure the case cover54to the case body53. Then, the first clutch wire43aand the second clutch wire43bare attached to the first rotatable member57through the opening110of the case cover54.

As shown inFIG. 33, an engaging element200with a cylindrical shape (which is not shown inFIG. 31and so on) is secured to an end of the outer tube45of the second clutch wire43b. The engaging element200may be bonded to the outer tube45or press-fitted over the outer tube45. A block204with a screw hole is fixed in a wire introduction port of the case cover54. A screw201extending in the longitudinal direction (lateral direction ofFIG. 33) is threaded into the screw hole of the block204.

The screw201has a threaded part201aand a large diameter part201bformed on the rear side of the threaded part201a. The engaging element200is rotatably inserted in the large diameter part201b. The large diameter part201bhas a step at its distal end so that the rear end of the engaging element200can be captured on the step and prevented from coming off from the large diameter part201b. Therefore, when the screw201is moved back or forth by rotating it, the outer tube45moves back or forth together with the screw201.

The screw201and the engaging element200have through holes through which the inner tube44can extend. The inner tube44of the second clutch wire43bextends through the through holes of the engaging element200and the screw201and is connected to the first rotatable member57. A cap203is attached over the outer periphery of the large diameter part201bof the screw201. The reference numeral202designates a nut for fixing the position of the screw201.

The screw201is used to adjust the installation positions of the second clutch wire43band the clutch assist device50. That is, after the outer tube45of the second clutch wire43bhas been attached at a predetermined position on the friction clutch18side, the bolts180are inserted into the bolt holes176of the third bracket163and the slots178of the mounting plate164and fastened to the extent that the clutch assist device50can be slid back and forth, as described before. Then, the length of the outer tube45of the second clutch wire43bis so adjusted, by rotating the screw201, that the positioning recess119aof the first rotatable member57and the projection119bof the case cover54align with each other. When the recess119aand the projection119balign with each other, the nut202is tightened to fix the position of the screw201. The outer tube45of the second clutch wire43bcan be thereby set to an appropriate length. After that, the bolts180are tightened to fix the mounting plate164firmly. Then, the lid114is placed over the opening110of the case cover54and is secured to the support walls111a,111bof the case cover54by the bolts115.

Also in this embodiment, a cam mechanism, having the cam groove71and the cam follower79, is interposed between the first rotatable member57and the second rotatable member58. Therefore, by properly determining the curve of the cam groove71, the relation between the pendulum-like oscillation of the spring unit59and the rotation of the first rotatable member57can be freely set and desired operability can be achieved.

When the clutch lever9is moved from the disengage start position to the midpoint, the increasing rate of the urging force of the auxiliary spring82applied to the first rotatable member57can be high in the initial stage immediately after the disengage start position and then reduced. Therefore, since the assist force can be significantly large in the initial stage of the half-clutch operation, the operability can be improved.

Also, when the clutch lever9is moved from the disengage start position to the midpoint, the ratio between the load of the clutch spring27applied to the push lever40of the clutch release mechanism28and the actual load applied to the clutch lever9can be maintained within a fixed range. Therefore, the load applied to the clutch lever9when the clutch lever9is operated is smaller than the load applied to the push lever40and varies with a tendency similar to that of the load from the clutch spring27. Therefore, the load in operating the clutch lever9can be reduced and natural and comfortable operating feel can be provided.

The spring unit59having the auxiliary spring82can oscillate about the pivot end86in a pendulum-like manner. Thus, since the direction in which the urging force of the spring82acts can be freely changed, the urging force can be applied in the appropriate direction. Therefore, although a cam mechanism is interposed between the spring unit59and the first rotatable member57, the loss of the urging force of the auxiliary spring82applied to the first rotatable member57can be reduced. In addition, the wear of the assist mechanism52can be reduced, and the service life and reliability of the clutch assist device50can be improved.

The present invention is not limited to the embodiments described above, and various modifications can be made to the present invention without departing from the scope thereof.

For example, the operating element for operating the frictional clutch is not limited to a clutch lever to be operated by a hand and may be a clutch pedal to be operated by a foot.

In the embodiments described above, the first and second clutch wires43a,43b(more specifically, the inner wires44thereof) as first and second linear members are physically separated from each other. However, the first linear member and the second linear member are not necessarily separated from each other as long as they can be connected to the rotatable member57. The first linear member and the second linear member may be joined together. That is, one side portion and other side portion of one linear member connected to the first rotatable member57may be regarded as the first linear member and the second linear member, respectively. In this case, although the first joint and the second joint may be located in different locations, the linear member may be connected to the first rotatable member57at one point so that the first and second joints can be located at the same position.

Additionally, as noted above, the auxiliary force member for applying an urging force to the first rotatable member57is not limited to the spring unit59having the auxiliary spring82. Moreover, the auxiliary spring82is not limited to a compression spring which can apply an urging force in the direction in which it expands and may be a tension spring or a torsion spring which can apply an urging force in the direction in which it contracts. The canceling elastic member for applying a canceling force to cancel the urging force of the auxiliary spring82when the clutch lever9is between the return position and the disengage start position is not limited to the canceling spring unit100having the canceling spring105. A different type of elastic member, such as an air spring, may be used for the auxiliary elastic member or the canceling elastic member.

In the embodiments described above, the movable member which moves in synchronization with the clutch lever9is the rotatable member57rotatable about a specific rotating shaft (pivot shaft63). Therefore, the clutch assist device50can be simplified in structure and have high ruggedness. The movable member which moves in synchronization with the clutch lever9is not limited to such a rotatable member, though. For example, the movable member may be a slidable member that can be reciprocated along a direction (linearly or in a curve) or the like. When the movable member is a member which can be reciprocated along a direction, the traveling speed of the movable member can be specified as, for example, a velocity in the direction. Therefore, the velocity ratio, which is the ratio of the traveling velocity of the rotatable member to the traveling velocity of the movable member, can be specified, for example, as the ratio between the velocity of the movable member in the above direction and the angular velocity of the rotatable member.

The component for generating the assist force in the assist mechanism52is not limited to an elastic member such as the auxiliary spring82and may be a motor or the like.

In addition, the friction clutch is not limited to a multi-plate wet clutch and may be a single-plate dry clutch. In addition, the clutch release mechanism is not limited to rack-and-pinion type. The present invention can be implemented when the clutch release mechanism is ball screw type or cam type.

In the embodiments described above, the clutch assist device50is supported by the down tube5of the frame2. However, the installation position of the clutch assist device50is not specifically limited. For example, the clutch assist device50may be located below the fuel tank10or the seat11with the first clutch wire43aextending in the longitudinal direction as shown inFIG. 35.

Although not shown, the clutch assist device50may be located in the vicinity of the friction clutch18. The exterior case51of the clutch assist device50may be attached to the clutch cover20.

As shown inFIG. 36andFIG. 37, the second clutch wire43bmay be omitted and a shaft coaxially extending from the push lever shaft39may be used as a pivot shaft63as the rotatable shaft for the first rotatable member57. This configuration can create an effect almost the same as those of the embodiments described above.