Motorcycle automatic clutch with manual release

A motorcycle clutch having a drive portion including a clutch basket assembly, and a driven portion including a clutch hub. A plurality of drive clutch plates are driven by the clutch basket assembly and a plurality of driven clutch plates are driven by the clutch hub. A pressure plate is coupled for rotation with the drive portion and is capable of axial movement from at least a first position to a second position. A release plate is capable of axial movement from at least a first position to a second position. The pressure plate and release plate are arranged on opposing sides of an alternating arrangement of the frictional and metal clutch plates. A plurality of engagement balls are placed between the clutch basket assembly and the pressure plate. The clutch basket assembly includes a plurality of ramped surfaces configured such that radial movement of the engagement balls results in axial movement of the pressure plate from its second position to its first position to automatically engage the clutch. The release plate is movable between a first and second position to manually disengage the clutch.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to motorcycle clutches. More particularly, the present invention relates to clutches for off-road racing motorcycle applications.

2. Description of the Related Art

Off-road racing motorcycles intended for older, and often more experienced, riders often utilize a manually controlled clutch and a multiple speed transmission, offering up to five or six different gear ratios. Conversely, most off-road motorcycles for riders of four to nine years in age utilize an automatically engaging clutch and single-speed transmission.

Eliminating the need to shift gears and control the engagement of the clutch reduces learning time for younger, or inexperienced, riders. An automatically engaging clutch also improves safety by allowing inexperienced riders to fully concentrate on maneuvering the motorcycle. Furthermore, in off-road motorcycle competitions (e.g., motocross races), riders in certain age groups and/or engine displacement categories, are required to ride a single speed motorcycle equipped with an automatically engaging clutch.

However, the clutch is not only used by motorcycle riders and racers when shifting the transmission, but is also used to control the overall speed and power delivery of the motorcycle by interrupting engine torque from reaching the rear wheel. For example, the rider may slow the overall speed of the motorcycle while negotiating a corner by briefly disengaging the clutch, instead of altering the throttle position. This method keeps engine speed high in order to have substantial engine torque available immediately upon subsequent re-engagement of the clutch. Experienced off-road motorcycle riders also use a manual clutch to produce a “burst” of acceleration, irrespective of shifting the transmission.

A rider of a motorcycle having an automatically engaging clutch must reduce the position of the throttle to slow the speed of the motorcycle in order to negotiate a corner. Upon exiting the corner, as the rider increases the throttle position, there is a delay in engine torque reaching the rear wheel of the motorcycle due to the time that is necessary for the automatic clutch to re-engage. While this condition may be tolerable for recreational or novice riders, it presents a disadvantage to experienced riders, and racers, of motorcycles having an automatic clutch.

Therefore, a need exists for an improved automatically engaging clutch that may be disengaged without having a delay in torque transfer upon subsequent re-engagement.

SUMMARY OF THE INVENTION

It is therefore an object of a preferred embodiment to provide a motorcycle clutch utilizing engagement balls capable of radial movement upon ramped surfaces, at engine speeds above a predetermined threshold, in order to automatically engage the clutch and pass engine-produced torque through the clutch to the transmission and, eventually, to the rear wheel of the motorcycle. The clutch additionally includes a release plate is provided for permitting manual disengagement of the clutch while in its automatically engaged mode.

As a related object, ball detents are provided to allow the engine velocity required for engagement of the clutch to be altered by selection of the diameter of ball detents.

According to another object, the angle of the ramped surfaces provided for directing the engagement balls may be changed so as to alter the portion of force distributed axially to engage the clutch.

According to a preferred embodiment, a motorcycle clutch assembly comprises a drive portion, which acts as an input of the clutch and is configured to be driven by an output of a motorcycle engine. A driven portion of the clutch acts as the output of the clutch and is configured to drive a secondary gear of a transmission of a motorcycle. A pressure plate is coupled for rotation with the drive portion and is capable of axial movement from at least a first position to a second position. A release plate is coupled for rotation with the driven portion and is capable of axial movement from at least a first position to a second position. A plurality of drive clutch plates coupled for rotation with the drive portion and a plurality of driven clutch plates coupled for rotation with the driven portion are arranged, in an alternating manner, between the pressure plate and the release plate. The clutch has at least a first mode wherein the pressure plate is in its second position and no engine torque is transferable from the drive portion to the driven portion. The clutch has at least a second mode wherein the pressure plate is in its first position, the release plate is in its first position and engine torque is transferable from the drive portion to the driven portion. The clutch additionally has at least a third mode wherein the pressure plate is in its first position and the release plate is in its second position wherein no engine torque is transferable from the drive portion to the driven portion.

A clutch configured in this manner provides at least three advantageous modes of operation. In the first mode, the pressure plate is not exerting pressure on the plurality of clutch plates and relative rotation is allowed between the drive clutch plates and driven clutch plates. Therefore, no torque is transferred between the engine and transmission. In a second mode, the pressure plate has moved to its first position and the drive clutch plates and driven clutch plates are coupled between the pressure plate and release plate. In this mode, engine torque is passed through the clutch assembly to the transmission, and eventually the rear wheel of the motorcycle. In a third mode, the pressure plate is, again, in its first position, however, the release plate is axially displaced away from the assembly of clutch plates, to its second position, once again permitting relative rotation between the drive and driven clutch plates. In this mode, no torque is passed through the clutch assembly. Thus, no engine-produced torque reaches the transmission and, subsequently, the rear wheel of the motorcycle.

Advantageously, a clutch configured substantially as described above is capable of automatic engagement at engine speeds above a predetermined threshold. In addition, the clutch may be manually disengaged and subsequently re-engaged without a delay in torque transfer.

According to a preferred embodiment, a motorcycle comprises a frame and an engine, having an output shaft, is connected to the frame. A transmission, having a transmission input shaft, is fixed relative to the engine. A clutch is provided, including a drive portion coupled for rotation with the engine output shaft. A driven portion is coupled for rotation with the transmission input shaft. The clutch has a first mode wherein the drive portion and the driven portion are not coupled when the engine is below a predetermined engine speed. The clutch also has a second mode wherein the drive portion and the driven portion are coupled when the engine is above the predetermined engine speed. The clutch has a third mode wherein the drive portion and the driven portion are not coupled when the engine is above the predetermined engine speed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference toFIG. 1, a motorcycle11including a clutch (not shown) constructed in accordance with a preferred embodiment is illustrated. The motorcycle has a frame13with an engine15mounted therein. The engine15preferably operates on a two-cycle, crankcase compression principal and has a displacement of approximately fifty cubic centimeters. However, a clutch constructed according to a preferred embodiment may be utilized in a motorcycle having an engine which operates according to alternative operating principles (i.e., four-cycle) or is of different engine displacements.

A transmission17is fixed relative to the engine15and, when engaged, transfers engine-produced torque to the rear wheel25of the motorcycle11, preferably through a chain and sprocket drive27. Of course, other drive arrangements (e.g., belt drive or shaft drive) may also be used.

The motorcycle11also includes a handlebar assembly19connected to the frame13and operable to steer the motorcycle11. One or more rider controls may be mounted on the handlebar assembly19, including a control lever21and a throttle23. The control lever21is operable to manually disengage the clutch (FIG. 2) of the motorcycle11typically located generally adjacent a crankcase (not shown) of the engine15, as is well known to those of skill in the art. The throttle23is configured to adjust a throttle valve (not shown), thereby adjusting the engine speed of the engine15, as is well known in the art.

With reference toFIGS. 2 and 3, a clutch10is shown in an exploded assembly view and in the motorcycle11, respectively. The clutch10is comprised primarily of the clutch basket assembly12, a set of engagement balls14, a pressure plate16, a release plate18, a clutch hub20and a series of drive clutch plates22,22aand driven clutch plates24. The clutch basket assembly12is comprised of a basket26and a base28secured thereto by a plurality of clutch basket bolts30.

The basket26includes a cylindrical drive tab32associated with a counter-bore34in the base28at each connection point between the basket26and base28. The drive tabs32provide a larger area in which to disperse the shear forces between the basket26and the base28as compared to the area of the clutch basket bolts30alone. A preferred clutch basket assembly12is connected at four points by four clutch basket bolts30dispersed along a common radius from the center axis of the clutch10at approximately equal angles.

The clutch basket assembly12is rotatably supported on the secondary transmission gear36by the clutch basket bearing38, and is able to rotate with respect to the secondary transmission gear36. The base28of the clutch basket assembly12is the input to the clutch10. The base28has gear teeth40located at a radial distance from the center axis ATof the secondary transmission gear36. The gear teeth40of the clutch basket base28are meshed with gear teeth42of an output gear43mounted on an output shaft44of the engine (not shown). Thus, the clutch basket assembly12is driven by the output of the engine.

The base28of the clutch basket assembly12defines a plurality of engagement ball pockets46operable for retaining a corresponding number of engagement balls14. Each engagement ball pocket46preferably includes a hole, or ball detent48(FIG.5), defined in a radially inward position and a surface50that is ramped toward the basket26when moving radially outward from the center axis AT. The base28of a preferred clutch10is made from H13 heat-treated tool steel to prevent wear from movement of the engagement balls14, however, other types of hardened materials may be used.

The clutch10includes a pressure plate16which is in contact with the engagement balls14opposite the clutch basket base28and is capable of axial movement with respect to the clutch basket assembly12. Both the pressure plate16and clutch basket assembly12have a set of corresponding apertures52,54to allow a set of pressure plate springs56to pass through. The pressure plate springs56are retained by a set of retaining pins58on either end. The retaining pins58rest in retaining pin cavities60,62(FIG. 5) in opposite sides of the pressure plate16and clutch basket assembly12, respectively. Thus, the pressure plate springs56act to oppose the axial movement of the pressure plate16away from the base28due to movement of the engagement balls14. To ensure proper axial movement of the pressure plate16, the clutch10preferably utilizes at least two engagement balls14and two pressure plate springs56. However, more preferably the clutch10uses twelve engagement balls14and four pressure plate springs56.

The pressure plate16and clutch basket assembly12additionally have a second set corresponding apertures64,66relating to a set of pressure plate limit bolts70. The pressure plate limit bolts70are disposed at approximately the same radial distance from the center axis ATas the pressure plate springs56, only rotated approximately45therefrom (FIG.2). The pressure plate limit bolts70advantageously limit the axial travel of the pressure plate16toward the series of frictional22and driven clutch plates24.

FIG. 4illustrates a partial cross-section of the clutch10, taken along a radial plane which bisects one of the pressure plate limit bolts70(FIG.2). As shown, each of the pressure plate limit bolts70is of a typical shoulder bolt variety having a head portion, a shaft portion of smaller diameter than the head portion and an externally threaded portion of generally equivalent diameter to the shaft portion. The aperture64in the pressure plate16is internally threaded and mates with the threaded portion of a pressure plate limit bolt70. A portion of the aperture66defined by the base28of the clutch basket assembly12is of a larger diameter than the head portion of the pressure plate limit bolt70. A portion of the aperture66defined by the basket26of the clutch basket assembly12is of a slightly larger diameter than the shaft portion of the pressure plate limit bolt70, and is sized small enough to prevent the head portion from passing therethrough.

The shaft portion of the pressure plate limit bolt70is disposed within a portion of the aperture66defined by the clutch basket base28and fixes the pressure plate16for rotation with the clutch basket assembly12while allowing axial movement relative thereto. The length of the shaft portion of the limit bolt70may be varied to adjust the distance the pressure plate16may travel in an axial direction. Preferably, at least two pressure plate limit bolts70are used to ensure the pressure plate16remains parallel to the clutch basket base28while moving in an axial direction with respect thereto. More preferably, the clutch10utilizes four pressure plate limit bolts70.

With reference again toFIGS. 2 and 3, the clutch10also includes a clutch hub20. The clutch hub20is fixed for rotation with the secondary gear36of the transmission through a splined aperture along its center axis, the splines68(FIG. 3) of which engage mating splines69on the secondary gear36of the transmission. The clutch hub20is prevented from moving axially relative to the secondary gear36of the transmission with a nut72and is prevented from direct contact with the clutch basket bearing38by a wear washer74.

The clutch10additionally includes a series of drive clutch plates22,22aand driven clutch plates24. The drive clutch plates22are desirably comprised of a base member76and frictional pads78attached to either, or both, sides thereof The base member76is preferably steel or aluminum, while the frictional pads78are a material having a high frictional coefficient. The friction pad material may be of a paper or woven material type common to the automotive and motorcycle industry depending on the frictional and wear characteristics desired. Attachment of the frictional pads78to the base member76may be accomplished with adhesives or by suitable mechanical means, such as riveting or the like. Alternatively, the drive plates22,22amay be formed as an integral unit.

The drive clutch plates22,22ahave a number of tabs80along the radially outermost edge that cooperate with axial slots82in the clutch basket assembly12. The drive clutch plates22,22aare thereby fixed for rotation with the clutch basket12, but are capable of axial movement in relation thereto.

The driven clutch plates24are made from steel or aluminum and have a number of gear teeth84along the radially innermost edge that cooperate with spline teeth86on the radially outermost surface of the clutch hub20. The driven clutch plates24are fixed for rotation with the clutch hub20, but are capable of axial movement in relation thereto.

The series of clutch plates22,22a,24are arranged on the clutch basket member12and clutch hub20, respectively, in an alternating pattern. Preferably, a single-sided drive clutch plate22ais assembled nearest the pressure plate16, having a friction pad78only on the surface opposite the pressure plate16. This allows for a more compact arrangement since there is no relative rotation between the pressure plate16and the single-sided drive clutch plate22a, thus making friction material unnecessary. Preferably, all the other drive clutch plates22have friction pads78on both sides.

As mentioned above, the series of clutch plates22,22a,24are assembled with the single-sided drive clutch plate22aclosest to the pressure plate16and then alternating driven clutch plates24and drive clutch plates22, ending with a frictional clutch plate22. Preferably, the clutch10utilizes a total of five clutch plates arranged in the manner described. However, a greater, or lesser, number of clutch plates22,22a,24may be used.

The clutch10also includes a release plate18, preferably made from steel or aluminum. The release plate18defines a number of cylindrical apertures89(FIG. 2) passing axially therethrough, which are counter-bored to receive a spring pocket member90. The cylindrical apertures are located at a radial distance from the center axis ATof the clutch10so as to be substantially aligned with cylindrical receiving bores91(FIG. 2) in the clutch hub20. Each receiving bore91has an internally threaded aperture extending axially through the clutch hub20from generally the center of the receiving bore91.

The spring pocket members90are preferably made from steel or aluminum. Each of the spring pocket members90has a lip at a first end, which is configured to rest in the counter-bore of the cylindrical apertures89, thereby preventing it from passing through the release plate18. Each of the spring pocket members90also includes an aperture at a second end. The diameter of the aperture is such that it allows a release bolt92to pass through but provides an engagement surface93for a release coil spring94.

The release bolt92is of a typical shoulder-bolt variety with the unthreaded portion of the shoulder-bolt providing a shaft to retain the release spring94and the externally threaded portion cooperating with the internally threaded aperture in the clutch hub20. With such an arrangement, the release plate18is fixed for rotation with the clutch hub20, but is capable of axial movement with respect thereto, subject to the resistive force of the release springs94.

The release springs94may be changed in type, spring rate or number to provide desired resistance to force provided by the pressure plate16. Preferably, the springs94are of a coil-type and five (5) of such springs are utilized.

The orientation of the clutch10in the motorcycle11is shown in detail in FIG.3. The engine15of the motorcycle provides two housings or cases: the clutch-side engine case96and the ignition-side engine case98. As noted earlier, the engine of the motorcycle is equipped with an output shaft44having an output gear43and rotatably supported in the clutch-side engine case96. The output gear43includes a number of gear teeth42which are meshed with the gear teeth40of the clutch basket assembly12, thus operable for transferring torque produced by the engine to the clutch10.

The transmission17of the motorcycle is equipped with a secondary gear36, which is supported for rotation by both the clutch-side and ignition-side engine cases96,98, respectively. The secondary gear36is fixed for rotation with the clutch hub20and transfers engine torque from the clutch10to the transmission17. The secondary gear36further is equipped with gear teeth in meshed engagement with gear teeth of the output shaft100of the transmission17.

The output shaft100is supported for rotation by both the clutch-side and ignition-side engine cases96,98and acts as the output of the transmission17to provide engine torque to the rear wheel23of the motorcycle (FIG.1). Torque transfer to the rear wheel is typically by chain and sprocket drive27(FIG.1), but may be of shaft, belt or similar drive type.

The clutch10additionally includes a release shaft102. The release shaft102is housed within a cylindrical aperture extending axially through the secondary gear36. A first end104of the release shaft102is in a position to be engaged by an actuator108and the second end106is in close proximity to the release plate18. The release shaft102is capable of axial movement so as to move the release plate18away from the assembly of frictional22and driven clutch plates24.

The actuator108may be mechanical (e.g. cam-type) or hydraulic and is configured to selectively produce axial movement of the release shaft102. The actuator108is instructed by the control lever21(shown schematically inFIG. 2) to produce movement of the release shaft102or allow its return. The control lever21may act on the actuator108by means of a braided steel cable (i.e., a bowden wire) or a hydraulic line, in the cases of a mechanical or hydraulic actuator, respectively.

A preferred actuator108comprises a cam shaft assembly, having a cam surface in contact with a first end104of the release shaft102, and being configured to translate rotational motion of the assembly into linear motion of the release shaft102. The cable110is preferably a bowden wire assembly and is connected to a lever arm of the cam shaft assembly. Engagement of the control lever21creates a pulling force on the cable110which, in turn, rotates the cam shaft assembly, thereby causing linear movement of the release shaft102.

The clutch10preferably has at least three modes of operation: disengaged, automatically engaged and manually released.FIG. 5is a partial cross-section of the clutch10in a disengaged mode. The clutch10is in a disengaged mode when the engine is not rotating or is at low angular velocities (revolutions per minute).

When the engine15and, thus the output gear43mounted on the output shaft44of the engine15and accordingly, the clutch basket assembly12is operating at a low angular velocity (i.e., below a predetermined engagement speed), radially outward movement of the engagement balls14is resisted by a combination of the pressure plate16and the ball detents48. The pressure plate16applies substantially axial force on the engagement balls14via the pressure plate springs56. This force assists in holding the engagement balls14within the ball detents48.

The slots82in the clutch basket12are of such a depth that when the engagement balls14are within the ball detents48, there is no contact between the pressure plate16and the single-sided frictional clutch plate22a. Thus, the drive clutch plates22,22aand driven clutch plates24are capable of rotation relative to each other and no torque is transmitted therebetween.

FIG. 6illustrates the clutch10in an automatically engaged mode. This mode preferably occurs when the output shaft44of the engine15is rotating the output gear43(which is, in turn, driving the clutch basket assembly12) at or above an angular velocity sufficient to move the engagement balls14radially outward from their position in the ball detents48as a consequence of the rotational force acting upon the engagement balls14(i.e., at engine speeds above the predetermined engagement speed).

As the force created on the engagement balls14move them in a radially outward manner, the ramped surfaces50of the engagement ball pockets46cause a simultaneous axial movement of the engagement balls14against the pressure plate16. The resulting force on the pressure plate16compresses the stack of drive22,22aand driven clutch plates24against the release plate18until a magnitude of force is achieved that prevents relative rotation between the individual drive22,22aand driven clutch plates24. As will be understood by one of skill in the art, the force necessary to couple the clutch plates22,22aand24are related to the total frictional area of the clutch plates22,22a,24and the coefficient of friction therebetween.

When the drive22,22aclutch plates and driven clutch plates24are rotating as a unit, or coupled, torque is transferred from the clutch basket12to the clutch hub20via the tabs80on the drive clutch plates22,22abeing driven by the clutch basket12and the gear teeth84on the driven clutch plates24driving the clutch hub20. As a result, torque produced by the engine is passed through the clutch10to the transmission17, and ultimately the rear wheel of the motorcycle.

Preferably, the release springs94are of a spring rate so as to provide sufficient force to prohibit relative rotation of the frictional22and driven clutch plates24when they are compressed by the above-described automatic engagement of the pressure plate16. This rate may be adjusted to provide some cushioning effect to the engagement of the clutch10. In addition, the engagement speed of the present invention may be adjusted to suit the individual output characteristics of the engine.

Advantageously, the ball detent48diameter may be adjusted, with respect to the diameter of the engagement balls14, to determine engagement speed. A smaller diameter would allow the engagement balls14to leave the detent48at lower angular velocities, while a larger ball detent48diameter would serve to hold the engagement balls14radially inward until a higher angular velocity is achieved. Desirably, the ball detent48diameter is less than the diameter of the engagement balls14, more preferably, the ball detent diameter48is less than one-half the diameter of the engagement balls14. Most preferably, the ball detent48diameter is approximately four-tenths the diameter of the engagement balls14. Preferably, the ball detent48diameter is approximately 0.2 inches and the engagement balls14have a diameter of approximately 0.5 inches.

In addition to ball detent48diameter, the preload of the pressure plate springs56may be adjusted to prevent movement of the pressure plate16until a sufficient force is created through rotational velocity to overcome the preload. Less preload would allow the engagement balls14to quickly engage, while a higher preload would result in a higher engagement speed.

An angle θ, may be defined between the ramped surfaces50of the engagement ball pockets46and an axis ARperpendicular to the axis of rotation (the center axis AT). Advantageously, the angle θ, or incline, may be increased or decreased to adjust the amount of force distributed to the pressure plate16. The force on the engagement balls14due to rotation acts in a radial manner. The proportion of that radial force which is exerted on the pressure plate16is determined by the angle θ of the surfaces50for any particular angular velocity. The angle θ is desirably between 5° and 75°, more preferably between 10° and 35° and most preferably is approximately 21°.

In addition, the radial force generated by rotation is, in part, determined by the mass of the engagement balls14. Thus, the mass of the engagement ball14may be altered by either changing the diameter or material used. A current version of the clutch10utilizes steel ball bearings.

FIG. 7illustrates the clutch10in a manually released mode. In this mode, the engine15has an angular velocity above its engagement speed, and thus the engagement balls14have caused axial movement of the pressure plate16sufficient to engage the clutch plates22,22a,24. To achieve the manually released mode, a rider of the motorcycle engages the control lever21, which signals the actuator108(FIG. 3) through a cable110to cause linear movement of the release shaft102, along the center axis ATagainst the release plate18. The release shaft102causes axial movement of the release plate18, overcoming the resistance of the release springs94until the frictional22and driven clutch plates24are no longer coupled. At this point, the engine15and transmission17become disengaged.

Upon subsequent release of the control lever21by the rider, the release plate18once again couples the frictional22and driven clutch plates24as a result of release spring94force, passing engine-produced torque through the clutch10and to the transmission17. Advantageously, the torque transfer occurs without the delay associated with automatic engagement of the clutch10by movement of the engagement balls14. This allows manual interruption of torque transfer from the engine15to the rear wheel23to control the speed of the motorcycle11while providing immediate torque transfer upon manual re-engagement of the clutch10.

One skilled in the art will readily recognize from the discussion above, that a preferred embodiment has been disclosed. Accordingly, various changes, modifications and variations can be made without departing from the true spirit and fair scope of the invention.