Patent Publication Number: US-8123017-B2

Title: Centrifugal clutch with expansion ring assembly

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The Present Application is a continuation application of U.S. patent application Ser. No. 12/787404, filed on May 26, 2010 now U.S. Pat. No. 7,810,624 which claims priority to U.S. Provisional Patent Application No. 61/299225, filed on Jan. 28, 2010, which is hereby incorporated by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to centrifugal clutches for motorcycles, and a method and apparatus for converting a stock manufacturer manual clutch into a centrifugal clutch for a motorcycle. 
     2. Description of the Related Art 
     A typical motorcycle clutch includes a clutch basket, a hub, a cover and clutch plates. A typical motorcycle has two types of plates, a steel plate and a fiber plate (the fiber plate is usually constructed of an aluminum substrate with a fiber material the substrate). A typical motorcycle clutch has eight fiber plates and seven steel plates structured in an alternating manner with a steel plate positioned between each of the fiber plates. The fiber plates typically have twelve tabs that are positioned between fingers of a clutch basket which allow the fiber plates to move with the clutch basket. Each of the steel plates has interior teeth that fit into a spline of an aluminum hub allowing the steel plates to move with the aluminum hub. Each of the steel plates preferably has a thickness of approximately 1.5 millimeters (“mm”) and each of the fiber plates typically has a thickness of 3 mm. The steel plates are 1.5 mm thick because the teeth are forced against the aluminum hub, which can groove quite easily due to the massive amount of force. The exception to this general rule is a KTM rfs motor (no longer in production) which used 1 mm steel plates because the steel plates ran against a steel hub. 
     The clutch basket is connected to a crankshaft, and the hub is connected to the transmission. The only connection between the engine and gear box is the friction caused by the engagement of the fiber plates against the steel plates, and the engagement comes from the force exerted by multiple coil springs. The coil springs hold the engine and transmission together at all times except when the clutch lever is pulled by a rider. When the clutch lever is pulled, a cam or slave is actuated which compresses the coil springs thereby creating gaps between the fiber plates and steel plates so that there is no longer any friction between them. When the clutch lever is pulled, the engine and transmission are two completely separate entities. Usually the coil springs clamp at around 200-300 pounds per square inch, which is more than enough to prevent the clutch from slipping. The clamping of coil spring feels positive on the rider&#39;s hand, and if there is a shock load to the transmission the clutch slips rather than breaking gears, sprockets or chains. For example, a shock load could come from a miscalculated jump. 
     Motorcycle clutches require the generation of sufficient centrifugal force to clamp the clutch plates together without substantial slippage and without utilizing a larger sized case which exceeds the space allowances available in most motorcycles. In the past, a pressure control mechanism was devised which combines the features of an automatic clutch with the performance of a traditional manual clutch so that the clutch engages smoothly without the use of a clutch lever at low speeds but limits the actual force transmitted to the clutch plates by the cam members at higher speeds. At the same time, the pressure control mechanism cooperates with a manual override lever to minimize the hand pressure required to override the cam members and effectively operate as a conventional manual clutch with relatively light feel or manual pressure and yet be capable of operating within the same space limitations as the standard or stock motorcycle clutches. Further, with hydraulic actuated clutches, there is no way of adjusting the hydraulic fluid in order to act on a clutch pack. 
     The prior art discloses various clutch mechanisms for motorcycles. One example is Youngwerth, Jr. et al., U.S. Patent Publication Number 2009/0242351, for an Automatic Clutch employing Expanding Friction Disk And An Adjustable Pressure Plate, which discloses an expanding friction disk assembly that expands under centrifugal force to provide automatic engagement of the clutch. 
     Yet another example is Maimone, U.S. Pat. No. 6,533,056 for a Motorcycle Automatic Clutch With Manual Release which discloses the use of a release plate which is movable between a first and second position to manually disengage the clutch. 
     Yet another example is Youngwerth, U.S. Pat. No. 6,957,730 for a Clutch Apparatus With An Automatic Centrifugal Engagement Of Pressure Plate which discloses a centrifugal pressure plate that moves axially which causes the plates to couple thereby forcing engagement between the engine and the transmission. 
     There is still a need for a mechanism to easily convert a standard motorcycle clutch into a centrifugal clutch. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a novel improvement upon the clutch features discussed in U.S. Pat. Nos. 6,705,446, 6,814,208, 7,014,026 and 7,140,480, which have been assigned to the assignee of the present application and which are all herein incorporated by reference in their entireties. The present invention allows a stock manufacturer manual clutch to be converted into a centrifugal clutch. 
     The main feature of the present invention is a dynamic expansion ring assembly. The dynamic expansion ring assembly preferably fits within a stock motorcycle clutch allowing the stock manufacturer manual clutch to be converted into a centrifugal clutch. In a preferred embodiment, the dynamic expansion ring assembly is substituted for a fiber clutch plate. The dynamic expansion ring assembly can be considered a fiber plate since fiber material is bonded on both sides of the dynamic expansion ring assembly. In an alternative embodiment, one additional fiber plate is removed from a stock manufacturer manual clutch, however, the surface area of the fiber on the dynamic expansion ring assembly is on average that of 1.5 fiber plates. Since the steel plate and fiber plates alternate, losing one fiber plate means losing one steel plate. In this embodiment, the steel plates are machined on one side to the size of the inside diameter of the fiber to create additional space for the dynamic expansion ring assembly. The steel plates are machined down to 1 mm only where the steel plate engages with a fiber plate so as to not change the cross-sectional area of the interior teeth of the steel plate that engage the aluminum hub. 
     The dynamic expansion ring assembly contains ball bearings encompassed in multiple ramps. Six springs holding the two pieces of the dynamic expansion ring assembly together and these springs change the speed at which the engine has to spin before the dynamic expansion ring assembly opens. 
     The present invention allows a change from neutral to gear without using a clutch lever and never stalling because there is a gap within the clutch pack (similar to when a rider pulls a clutch lever on a stock clutch). The gap is created by adjusting a clutch cable or hydraulic fluid of a hydraulic actuate clutch. The tighter the clutch cable (more preload), the bigger the gap. With motorcycles that use a hydraulic clutch there is a slave that preloads the clutch springs. As soon as the engine increases speed above idle, the dynamic expansion ring assembly expands and closes the gap (in order for the dynamic expansion ring assembly to open, the force of the ball bearings must overcome the force of the springs of the dynamic expansion ring assembly. The number of springs is 2, 3, 4 or 6). The faster the engine rotates, the greater the force applied to the clutch pack. The maximum possible force that could be applied to the clutch pack is that of the stock coil springs (approximately 200-300 pounds per square inch (“psi”)). The gap that is required is approximately 0.025 inch. The dynamic expansion ring assembly can open up to 0.100 inch so after the gap closes there is approximately 0.075 inch available (the extended opening of the dynamic expansion ring assembly allows for wear) which would only open up if the force was 200 psi, which only occurs at high rotations per minute (“RPM”). 
     The clutch lever remains and works at all times because the clutch lever has overall more travel than the dynamic expansion ring assembly, so the clutch lever can open the gap at any engine speed similar to a stock clutch. The clutch lever feels positive on the rider&#39;s hand, and if there is a shock load to the transmission it will slip rather than break gears, sprockets or chains, because the maximum force on the pack is approximately 200-300 psi. In a hydraulic actuated clutch, an aspect of the invention is adjusting a reservoir cap on a master cylinder to adjust the gap. 
     The adjustment of the gap is performed externally, without tools in most cases, by loosening of the clutch cable which allows for the return of a stock clutch set up in order to bump start the bike. 
     In a preferred embodiment, the present invention is a centrifugal clutch with a dynamic expansion ring assembly specifically adapted for motorcycles and which is preferably composed of a minimum number of parts which can be retrofit into most standard centrifugal clutches which employ annular clutch plates, commonly referred to as a “clutch pack”. The clutch pack is modified to incorporate a dynamic expansion ring assembly at an intermediate location between the clutch plates, as opposed to being mounted at one end. If a manual override is utilized, the manual override employs a control rod to control a gap between one end of the clutch elements and a spring-loaded cover plate to maintain the clutch elements in the disengaged position at lower speeds as well as enable shifting of the clutch out of clutching engagement at higher speeds with a minimum degree of manual force required. Among other features is the ability to employ the dynamic expansion ring assembly in place of one or more of the standard clutch plates without increasing the total space occupied by the clutch pack, and eliminating a separate pressure plate within the cover at one end of the clutch pack while achieving increased stability and control in engaging and disengaging the multiple clutch plates in the clutch pack. 
     One aspect of the present invention is a centrifugal clutch for utilization with an engine of a motorcycle. The centrifugal clutch includes a clutch basket, a cover plate, a hub, first clutch plates, second clutch plates and a dynamic expansion ring assembly. The clutch basket includes a base plate with periphery walls spaced apart by teeth engaging slots. The cover plate is mounted on the clutch basket. The cover plate has an undermost portion. The hub has a cylindrical wall with radial slots. The hub extends through a center of the clutch basket. Each of the first clutch plates is positioned within the clutch basket. Each of the first clutch plates has teeth for engaging with a corresponding teeth engaging slot of the teeth engaging slots of the clutch basket. Each of the first clutch plates comprises a non-metal material. Each of the second clutch plates is positioned within the clutch basket. Each of the second clutch plates has radially inwardly extending teeth. Each of the radially inwardly extending teeth engage with a corresponding radial slot of the slots of the cylindrical wall of the hub. Each of the second clutch plates is composed of a metal material. The dynamic expansion ring assembly is positioned substantially in a middle of the clutch basket. The dynamic expansion ring comprises a first cam ring portion, a second cam ring portion and cam members held between the first cam ring portion and the second cam ring portion. The first cam ring portion comprises cam receiving portions, external teeth and cam faces. The second ring portion comprises indented cam faces. Each of the external teeth engage with a corresponding teeth engaging slot of the teeth engaging slots of the clutch basket. The cam members are capable of moving inward and outward in the each of the cam receiving portions. The dynamic expansion ring assembly imparts substantially equal expansion forces in opposite directions away from the dynamic expansion ring assembly and against the first clutch plates and the second clutch plates to urge them into clutching engagement. A gap is present between the cover plate and an end plate of the plurality of first clutch plates when the engine is at an idle speed and each of the cam members is positioned radially inward in the dynamic expansion ring assembly. The gap is not present when the engine is operating faster than idle and each of the cam members is positioned radially outward in the dynamic expansion ring assembly by centrifugal force. 
     Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a view partially in section of one embodiment of a clutch mechanism and schematically illustrating a shift drum for regulating the gear ratio between a transmission shaft and motorcycle, kickstart lever, clutch lever, crankshaft driven off of an engine, and gear drive. 
         FIG. 2  is an exploded view of the clutch housing illustrated in  FIG. 1 . 
         FIG. 3  is a sectional view taken about lines  3 - 3  of  FIG. 2 . 
         FIG. 4  is another sectional view of the clutch housing with the engine at idle speed. 
         FIG. 4   a  is a detailed view taken at  4   a  of  FIG. 4  and illustrating in more detail a gap present at idle speed. 
         FIG. 5  is another cross-sectional view of the clutch housing showing the relationship between parts when a control rod is disengaged. 
         FIG. 5   a  is a detailed view taken at circle  5   a  of  FIG. 5  and illustrating the relationship between parts when the engine is above idle speed. 
         FIG. 6  is a cutaway, enlarged view of the clutch housing. 
         FIG. 7  is an exploded view of the clutch plates and dynamic ring assembly as well as spring-loaded cover plate of the one embodiment. 
         FIG. 8  is an exploded view of the cam ring assembly of the one embodiment. 
         FIG. 9  is a plan view of the cam ring assembly. 
         FIG. 10  is an exploded view in section through lines  10 - 10  of  FIG. 9 . 
         FIG. 11  is a plan view of one of the cam ring tracks of the assembly shown in  FIG. 9 . 
         FIG. 12  is an enlarged cross-sectional view taken about lines  12 - 12  of  FIG. 11 . 
         FIG. 13  is a plan view of another cam track of the cam ring assembly that fits within the cam ring portion shown in  FIGS. 9 to 12 . 
         FIG. 14  is a cross-sectional view taken about lines  14 - 14  of  FIG. 13 . 
         FIG. 15  is a plan view of the inner surface of the cam track shown in  FIG. 13 . 
         FIG. 16  is an enlarged sectional view taken about lines  16 - 16  of  FIG. 15 . 
         FIG. 17  is a plan view of a clutch plate. 
         FIG. 18  is a cross-sectional view taken about lines  18 - 18  of  FIG. 17 . 
         FIG. 19  is a plan view of a modified form of cam track of the cam ring assembly. 
         FIG. 20  is a cross-sectional view taken about lines  20 - 20  of  FIG. 19 . 
         FIG. 21  is a plan view of the modified form of cam ring assembly shown in  FIGS. 19 and 20 . 
         FIG. 22  is a cross-sectional view taken about lines  22 - 22  of  FIG. 21 . 
         FIG. 23  is an enlarged cross-sectional view taken about lines  23 - 23  of  FIG. 21 . 
         FIG. 24  is a cross-sectional view taken about lines  24 - 24  of  FIG. 21 . 
         FIG. 25  is a plan view of the outer surface of the modified cam assembly shown in  FIG. 21 . 
         FIG. 26  is a plan view of another cam track which fits into the cam ring portion illustrated in  FIG. 21 . 
         FIG. 27  is a cross-sectional view taken about lines  27 - 27  of  FIG. 26 . 
         FIG. 28  is a plan view of the inner surface of the cam portion shown in  FIG. 26 . 
         FIG. 29  is a cross-sectional view taken about lines  29 - 29  of  FIG. 28 . and 
         FIG. 30  is a cross-sectional view taken about lines  30 - 30  of  FIG. 28 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A preferred embodiment of a centrifugal clutch is shown in  FIGS. 1 to 19  in which a clutch  10  is specifically adaptable for use in a motorcycle, not shown. As specifically shown in  FIG. 1 , a crankshaft C is driven by an engine, not shown, to impart rotation to a power input side of the clutch  10  via a gear drive N or other standard drive means. The gear drive N imparts rotation to a first sprocket S at one end of a clutch housing H which is broadly made up of outer walls and base of a clutch basket  12  and a cover plate  28  to be hereinafter described in more detail. A transmission shaft  14  is secured at one end by a nut  15  within the clutch housing H and is rotated by a hub  16  within the clutch housing H when the first plurality of clutch plates  18  and the second plurality of clutch plates  20  are engaged by a dynamic expansion ring assembly  22 ; and through speed reduction gearing P, are operative to rotate the standard drive means, not shown, off of an output sprocket S′ to the rear wheel of the motorcycle. A shift drum D controls the gear ratio of the gearing P, and a kickstart lever K operates in a well-known manner through gears L 1 , L 2  and L 3  through the crankshaft C to start the engine. 
     When a manual override is utilized, a control rod  26  extends into the clutch housing H in spaced inner concentric relation to the hollow transmission shaft  14  and is manually controlled by a hand lever L typically mounted on the handle bar of the motorcycle and which operates through a control cable A to force the cover plate  28  axially to form a gap G between the cover plate  28  and an end plate of the first clutch plates  18  as shown in  FIGS. 4 and 4A . When the clutch lever L is squeezed by the operator, the control rod  26  acts through the clutch plate lifter to lift the cover plate  28  for a distance greater than the dynamic expansion ring assembly  22  is capable of expanding and the gap G is thereby created to disengage the drive irrespective of the speed of the motorcycle. 
     As shown in more detail in  FIGS. 2 to 8 , the clutch basket  12  includes an annular base plate  30  with upstanding circumferentially spaced periphery walls  32  which are spaced apart to define teeth-engaging slots  33  at uniformly spaced intervals. The periphery walls  32  are affixed to and extend upwardly from the outer periphery of the base plate  30 , and inturned ledges  34  are located at the free ends of each of the periphery walls  32 . The clutch basket  12  is preferably of standard construction and one example is a model manufactured by Kawasaki (Part No. 13095-0052). A hub  16  is mounted within the hollow interior of the clutch housing H and includes a hollow cylindrical portion  37  extending upwardly from an annular base plate  38  with a thrust bearing  31  interposed between the base plate  30  and the lower end of the cylindrical portion  37 . A base plate  38  is disposed in adjacent spaced relation to and above the base plate  30  and terminates in an outer circular wall  39  in inner spaced concentric relation to the spaced walls  32  of the clutch basket  12 . 
     The plurality of first clutch plates  18  alternate[in Position ]with the plurality of second clutch plates  20  within the clutch basket  12 . Each of the plurality of first clutch plates  18  are keyed to the periphery walls  32  of the clutch basket  12  by radially outwardly extending teeth  42  to inter-engage with the teeth-engaging slots  33 . Each of the plurality of second clutch plates  20  are keyed to the outer cylindrical portion  37  of the hub  16  by radial inwardly extending teeth  44  which inter-fit with radial slots in the cylindrical wall  37  of the hub  16 . Each of the plurality of second clutch plates  20  is preferably composed of a relatively hard metal such as steel. Each of the plurality of first clutch plates  18  is preferably composed of a metal such as aluminum, and each has a plurality of circumferentially spaced, generally rectangular fibrous friction pads R. Each rectangular fibrous friction pad[s ]extends radially for the substantial extend of one of the opposed flat surfaces of each of the second clutch plates  20 . However, the opposite surface of each of the plurality of second clutch plates  20  is flat and has a flush engagement with an annular surface portion of a corresponding plurality of first clutch plate  18 . 
     In one embodiment, the dynamic expansion ring assembly  22  is utilized to convert a standard motorcycle manual clutch into a centrifugal clutch. Each of a plurality of first clutch plates  18  are aluminum plates with fibrous friction pads  18 ′ and each of a plurality of second clutch plates  20  comprise steel. Preferably, there are eight first clutch plates  18  and seven second clutch plates  20 . The plurality of first clutch plates  18  ride in the clutch basket  12  with circumferentially spaced tabs  42  that fit between the fingers of the clutch basket  12 . The plurality of second clutch plates  20  ride upon an aluminum hub  16  and each of the plurality of second clutch plates  20  has teeth that fit in a spline of the aluminum hub  16 . The first clutch plates  18  and the second clutch plates  20  alternate with each second clutch plate  20  positioned between a pair of first clutch plates  18 . Typically, each of the plurality of second clutch plates  20  has a thickness of approximately 1.5 mm and each of the plurality of first clutch plates  18  has a thickness of approximately 3 mm. The dynamic expansion ring assembly  22  is preferably positioned in a center position of the clutch basket  12 , typically substituting for a first clutch plate  18  when a standard manual clutch is converted into a centrifugal clutch. For example, as shown in  FIG. 7 , a preferred structure has a first clutch plate  18 , a second clutch plate  20 , a first clutch plate  18 , a second clutch plate  20 , a first clutch plate  18 , a second clutch plate  20 , the dynamic expansion ring assembly  22 , a second clutch plate  20 , a first clutch plate  18 , a second clutch plate  20 , a first clutch plate  18 , a second clutch plate  20  and a first clutch plate  18 . In this preferred structure, the dynamic expansion ring assembly  22  imparts substantially equal force against an equal number of first clutch plates  18  and second clutch plates  20  on each side of the dynamic expansion ring assembly  22 . 
     As shown in  FIGS. 4 ,  5 ,  6  and  7 , the cover plate  28  is mounted on the clutch basket  12  and has a radially outer wall portion  52  overlaying the first clutch plates  18  and the second clutch plates  20  between the periphery walls  32  of the clutch basket. The cover plate  28  also has a radially inner slightly raised solid circular wall portion  54  which is substantially flat and is provided with a central bore to receive a clutch lifter in the form of a cap-like extension  55  of a sleeve member  56  to receive the end of the control rod  26 . The cover plate  28  is preferably of unitary construction, and as shown in  FIGS. 5 and 6 , a series of circumferentially spaced sleeves  58  extend outwardly from the inner wall portion  54 , with each sleeve  58  terminating at its inner end in a radially inwardly extending annular lip  59 . A series of tubular posts  60  project upwardly from the base plate  38  of the hub  16 , with each of the tubular posts  60  preferably adapted for insertion of a shoulder bolt  62  and outer surrounding compression spring member  64 . Specifically, each bolt  62  has an enlarged head  66 , a shoulder portion  67  and a reduced diameter threaded stem portion  68 , the latter being threadedly connected into each tubular post  60  of the hub  16 . In this way, the shoulder  67  bears against the spring  64  which is inserted between each sleeve  58  and tubular post  60  with the opposite end of each tubular post  60  bearing against an annular lip  59 . 
     The compression springs  64  are mounted under compression concentrically between each shoulder  67  and lip  59  of each post  60  to control the gap G between the flat undersurface of the annular portion  54  of the cover plate  28  and the endmost friction pad-covered surface  51  of an end plate of the first clutch plates  18  in facing relation to the annular portion  52 . Initially, the gap G is created by adjusting the clutch cable mechanism so that as the clutch cable is tightened, the control rod  26  forces the cap-like extension  55  of the sleeve through the central bore. The sleeve member  57  is provided with an external shoulder  57 ′ and bearing  53  against the cover plate  28  to increase the gap G by overcoming the spring force of the compression spring  64 . Gap adjustment is further discussed in greater detail in connection with the operation of the clutch. 
     The dynamic expansion ring assembly  22  is explained in detail in relation to  FIGS. 7 to 10 . The dynamic expansion ring assembly  22  is preferably positioned in the clutch basket  12  intermediately between the first clutch plates  18  and the second clutch plates  20 . 
     The dynamic expansion ring assembly  22  preferably comprises a relatively thick first cam ring portion  82  of a generally L-shaped cross-sectional configuration defined by an outer peripheral circular band  83  and a first cam-receiving portion  85  extending radially inwardly from one edge of the outer peripheral circular band  83 . The first cam ring portion  82  also preferably has indented, circumferentially spaced cam faces  84  on an inner surface  84 ′ and a continuous friction pad layer F on an outer flat surface  85 ′ of the portion  85 , as further shown in  FIGS. 12-16 . The outer peripheral circular band  83  is disposed in surrounding relation to the cam faces  84  and is provided with radially outwardly projecting external teeth  86  which correspond to and are aligned with the external teeth  42  on the first clutch plates  18 . 
     As shown in  FIGS. 13 to 16 , the dynamic expansion ring assembly  22  also has a second cam-receiving portion  90  having a series of indented circumferentially spaced cam faces  89  on an inner surface aligned in opposed facing relation to the cam faces  84 . The second cam-receiving portion  90  is inset within the band  83  and secured to the first ring portion  85  by the screw members  92  as best seen in  FIG. 10 . Each cam face  89  is relatively shallow and flat at W between opposed end surfaces V in comparison with the spherical and inclined surface portions X and Y of each cam face  89 . Another continuous friction pad layer F is joined to the outer surface  74  so that, as best seen in  FIG. 7 , the friction pad layers F are in opposed facing relation to two of the second clutch plates  20  of the clutch basket  12 . A series of three screw members  92  are illustrated in  FIGS. 8 and 9  and are disposed in equally spaced circumferential relation around the ring assembly  22  but the number of screw members  92  may vary in number up to a total of six, as shown in  FIGS. 8 and 9 , depending upon the spring-loading required in resisting the expansion force of the cam members  88 . The cam members  88  are in the form of ball bearings, each cam member being sized to fit between each pair of confronting cam faces  84  and  89  when the second cam-receiving portion  90  bears against the first cam-receiving portion  85  and, under centrifugal force, the cams  88  will undergo a combination of sliding and rolling movement from the deepest spherical portions X of each cam face  84  radially outwardly along the inclined surface portions Y. The distance of travel of the cam members  88  is sufficient to compress the clutch plates together on opposite sides of the cam ring assembly  22  and force the endmost plate  18  of the clutch pack into engagement with the undersurface portion  52  of the cover plate  28 , and the opposite end plate  18  bearing against the base  38  of the hub  16 , for example, as illustrated in  FIGS. 5 and 5A . 
     The second cam-receiving portion  90  is normally urged against the first cam-receiving portion  85  by the screw members  92  which are inserted in countersunk bores  91  in the cam-receiving portion  90 , and a threaded end  70  of each screw member  92  is threaded into an aligned threaded bore  94 , the bores  93  being located at equally spaced circumferential intervals between the cam faces  84 . In this way, the screw members  92  are spring-loaded by the compression springs  93 , and the spring tension may be regulated to resist radial outward movement of the cam members  88  and expansion of the second ring portion  90  away from the first portion  85  until the clutch reaches a predetermined rotational speed. Most importantly, the dynamic expansion ring assembly  22  imparts substantially equal expansion forces in opposite directions away from the dynamic expansion ring assembly  22  and against the clutch plates  18  and  20  to urge them into clutching engagement. Briefly summarizing from the above, the spherical shape of the cam members  88  and mating faces  84  and  89  minimizes the friction and reduces assembly drag while contributing to a more responsive clutch feel. The position of the dynamic expansion ring assembly  22  in the middle of the clutch basket  12  places the expansion forces closer to the center of mass for the motorcycle clutch and minimizes the likelihood of unbalanced forces otherwise generated in models that are assembled with a pressure plate between one end of a clutch pack and a cover. Further, to minimize wear of the first clutch plates  18  with the friction pads  18 ′, the position of the dynamic expansion ring assembly  22  in the middle of the clutch basket  12  evenly distributes the clutch expansion forces and provides for more uniform disk pack compression. In one embodiment, in order to compensate for the increase in thickness of the dynamic expansion ring assembly  22  which is substituted for a first clutch plate  18 , the remaining first clutch plates  18  are machined to their thickness without altering the effectiveness of the clutch pack. This is achieved with a minimum retrofit and substantially no modifications required to the stock original equipment manufacturer (“OEM”) parts since the dynamic expansion ring assembly  22  is conformable to the existing OEM clutch pack. Further, utilizing the OEM clutch springs  64  and housing mechanism ensures maximum ease of installation and adjustment for use in the field. 
     As described in U.S. Pat. No. 7,014,026, assigned to the assignee of the present application, an important characteristic of the special compression springs  93  is their greatly reduced height or travel for a given amount of resistance and can therefore occupy much less space in an axial direction. Preferably, the springs  93  are SPIRA WAVE® wave springs which are flat wire compression springs manufactured and sold by Smalley Steel Ring Co. of Lake Zurich, Ill. Their spring force is such as to resist the spreading of the cam portions  82  and  90  and provides a method to increase or decrease spring force which in turn allows the rider/operator to easily “fine-tune” the clutch engagement. 
     The maximum clamping force that can be exerted on the first clutch plates  18  and the second clutch plates  20  to assure non-slipping engagement under normal operating conditions is determined by the stock springs  64  of the cover plate  28 . The springs  64  permit the clutch to slip in the event that extreme shock loads are transmitted through the drive train. For example, the first clutch plates  18  and the second clutch plates  20  permit some slippage so as to absorb any shock loading when the rear wheel of the motorcycle is off the ground and spinning, and then suddenly stops. 
     At engine idle, the cover plate  28  normally rides upon the clutch lifter  55  thereby creating the gap G which is finely adjustable (larger and smaller) with the OEM or standard clutch cable adjusters provided with the clutch lever mechanism. The gap G can be reduced to zero in order to return to a stock clutch set up, this might be desirable in order to “bump” start the engine. Further, as the engine is idling the dynamic expansion ring assembly  22  is in the relaxed position and the spacing between the first clutch plates  18  and second clutch plates  20  is present. As soon as the engine revs higher than idle the dynamic expansion ring assembly  22  expands so that the gap G will close at the end of the clutch basket  12  and the first clutch plates  18  and the second clutch plates  20  move into positive engagement with one another. 
     In one alternative embodiment, the dynamic expansion ring assembly  22  fits within a stock clutch basket and takes the place of one fiber plate so as to be within the size limits of the standard clutch housings. The dynamic expansion ring assembly  22  can be considered a fiber plate as it has the fiber material bonded on both sides. As space is an issue, one additional fiber plate is removed, however, the surface area of the fiber on the dynamic expansion ring assembly  22  is on average that of 1.5 clutch plates. As you lose one fiber plate you also lose one steel plate. In order to provide additional space, the steel plates are machined on one side to the size of the inside diameter of the fiber. 
     In another aspect of the present invention, a method for converting a standard manufacturer manual clutch into a centrifugal clutch begins with positioning a dynamic expansion ring assembly  22  into a clutch basket  12  as a substitute for a first clutch plate  18  comprising fiber. Next, a gap G is set by changing a tension in a clutch cable wherein loosening a cable tension by lengthening the clutch cable results in the increasing of the gap G. Similarly, shortening the length of the clutch cable decreases the gap G and results in the first clutch plates  18  and the second clutch plates  20  in contact with each other thereby permitting a bump start by “popping of the clutch.” 
     A modified form of dynamic expansion ring assembly  22 ′ is illustrated in  FIGS. 19 to 30  wherein like parts are correspondingly enumerated with prime numbers. The modified form comprises multiple staggered rows of cam faces  95  and  96  for cam members  88 ′ and  98  in the cam-receiving portion  85 ′; and cam faces  97  and  98  for the cam-receiving portion  90 ; however, the indented inner radial row  96  of cam faces are shorter only to accommodate a series of smaller cam members or balls  98  and in this relation, two or more staggered concentric rows of ball bearings are employed as set forth and described in U.S. Pat. No. 7,140,480, assigned to the assignee of this application. 
     In use, one or more adjustments may be made in the dynamic expansion ring assembly  22  or  22 ′ including but not limited to changing the number of cam members in a single row, reducing the spring tension of the springs  93  or changing the number of spring-loaded screw members  92  in regulating the resistance to expansion of the dynamic expansion ring assembly  22 . If the number of the spring-loaded screw members  92  is varied it is still important that they be symmetrically spaced about the dynamic expansion ring assembly  22  and apply equal tension or resistance to expansion. When the dynamic expansion ring assembly  22  is expanded in response to displacement of the cam members  88  to lock the first clutch plates  18  and the second clutch plates  20  together, the hub  16  then imparts the rotation of the clutch housing H to the transmission shaft  14 . The spring force of the spring-loaded screw members  92  is such as to resist spreading of the dynamic expansion ring assembly  22  beyond a pre-determined limit which is the maximum pumping force that can be safely exerted on the first clutch plates  18  and the second clutch plates  20  to assure a non-slipping engagement but which will permit the clutch plates  18  and  20  to slip in the event that extreme shock loads are transmitted through the drive train. In order to override the automatic clutch, the control rod  26  is operated by the manual clutch lever L to advance against the clutch lifter and cover plate  28  to form a sufficient clearance space or gap G between cover plate  28  and the end plate of the first clutch plates  18 . 
     In another embodiment, a hydraulic actuated clutch is utilized to preload the gap G of the clutch  10 . The hydraulic actuated clutch comprises a master cylinder that has a body substituted for a stock reservoir cap. The body is bolted to the master cylinder of the hydraulic system. The body preferably has a flat portion for attachment to the master cylinder with a cylindrical portion extending upward from the flat portion and having an aperture. A piston is positioned within the aperture of the cylindrical portion of the body. When the piston is pushed downward within the aperture, fluid is forced through a hydraulic line of the hydraulic system thereby creating a gap G in clutch  10 , as described above in relation to the clutch lever. A cap is placed over the cylindrical portion of the body. The cap preferably threadingly engages the cylindrical portion of the body. The tightening and loosening of the cap on the cylindrical portion adjusts the gap G in the clutch  10 . Tightening the cap increases the size of the gap G, and loosening the cap reduces the size of the gap G. With the hydraulic adjuster arrangement, the gap G is controlled from a zero gap size to an installed gap G size. At a zero gap it is possible to bump start the motorcycle whereas the installed gap G operates as an automatic clutch. 
     From the foregoing it is believed that those skilled in the pertinent art will recognize the meritorious advancement of this invention and will readily understand that while the present invention has been described in association with a preferred embodiment thereof, and other embodiments illustrated in the accompanying drawings, numerous changes modification and substitutions of equivalents may be made therein without departing from the spirit and scope of this invention which is intended to be unlimited by the foregoing except as may appear in the following appended claim. Therefore, the embodiments of the invention in which an exclusive property or privilege is claimed are defined in the following appended claim.