Abstract:
A vehicle with a continuously variable transmission (continuously variable transmission) includes a torque responsive clutch having a cam and at least one coupling. The cam has a plurality of projecting surfaces, and a plurality of slots being defined between the projecting surfaces. The slots of the cam are used to direct cam followers that move across the slot surfaces as the vehicle is driven forward or in reverse. As the vehicle adjusts from forward to reverse or vice versa, the cam followers may jump from one side of the slot to the other.

Description:
RELATED APPLICATIONS 
   The present application is related to U.S. patent application Ser. No. 10/327,725 entitled “Methods and Apparatus for Providing Reverse Drive in a Recreational Vehicle” by the same inventor and filed on an even date herewith. The entire disclosure of the above mentioned patent application is hereby incorporated by reference. 

   TECHNICAL FIELD 
   The present invention relates generally to recreational vehicles. More particularly, the present invention relates to drive systems for use with recreational vehicles. 
   BACKGROUND OF THE INVENTION 
   Split sheave continuously variable transmissions (continuously variable transmissions) are used in a variety of recreational type off-road vehicles such as snowmobiles, golf carts, all-terrain vehicles (ATVs), and the like. Continuously variable transmissions, as their name implies, do not require shifting through a series of forward gears, but rather provide a continuously variable gear ratio that automatically adjusts as the vehicle speeds up or slows down, thus providing relatively easy operation for the rider. Typically, continuously variable transmissions are comprised of a drive clutch, a driven clutch, and an endless drive belt disposed about the clutches. The driven clutch includes a pair of opposed sheaves, which together define a generally V-shaped “pulley” within which the drive belt rides. The drive clutch is similarly configured from a pair of opposed sheaves. 
   SUMMARY OF THE INVENTION 
   The invention provides a system and method for dampening a continuously variable transmission by utilizing a cam and at least one coupling with a bore extending there-through. The continuously variable transmission is comprised of a drive clutch, a driven clutch, and an endless drive belt disposed about the drive and driven clutches. Each driven clutch includes a cam, which further includes a plurality of surfaces projecting upward, defining a plurality of slots. Cam followers contact first surfaces of the slots when the continuously variable transmission operates as the off-road vehicle is driven forward. Conversely, the cam followers contact second surfaces of the slots oppositely disposed from the first surfaces when the continuously variable transmission operates in reverse as the off-road vehicle is driven in reverse. The invention helps dampen the sound and impact from a contact between the cam followers and the first or second surfaces of the cam slots, which is a natural occurrence when the vehicle goes from forward to reverse, or vice versa. 
   This dampening can be accomplished by utilizing a two-part cam, whereby the cam includes a first and second member, each having a plurality of surfaces projecting upward, defining a plurality of slots. The first cam member is inserted and held in place by the inner shell of the second cam member, whereby a plurality of couplings are interposed between the bases of both cam members. The combination of the cam members forms a plurality of narrowed slots having first and second slot surfaces. As the two-part cam is utilized in a driven clutch of a continuously variable transmission, a plurality of cam followers are utilized in the two-part cam, whereby a single cam follower is disposed in every other narrowed slot. When the engine is driving the vehicle in the forward direction, the cam followers engage the first slot surfaces of the narrowed cam slots. As the torque applied to the driven pulley increases, the cam followers roll up these first slot surfaces. However, when these off-road vehicles are operated in reverse, the cam followers stop engaging the first slot surfaces, and instead, jump so as to make contact with the second slot surfaces located opposite the first slot surfaces of the narrowed cam slots. When this slamming occurs, the vehicle operator may hear and feel an impact from the cam followers coming into contact with the second slot surfaces of the narrowed cam slots. However, with the couplings located between the first and second cam members, there is a reduced force transfer from the first cam member to the second cam member upon switching between forward and reverse. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a snowmobile including a drive system in accordance with an exemplary embodiment of the present invention. 
       FIG. 2  is a perspective view of a drive system in accordance with an exemplary embodiment of the present invention. 
       FIG. 3  is a plan view of a continuously variable transmission in accordance with an exemplary embodiment of the present invention. 
       FIG. 4  is a perspective view of a drive system in accordance with an additional exemplary embodiment of the present invention. 
       FIG. 5  is a diagrammatic illustration of a drive system in accordance with an additional exemplary embodiment of the present invention. 
       FIG. 6  is a perspective view of a cam in accordance with an additional exemplary embodiment of the present invention. 
       FIG. 7  is an exploded perspective view of a cam in accordance with an exemplary embodiment of the present invention. 
       FIG. 6  is a perspective view of a cam  632  in accordance with an additional exemplary embodiment of the present invention. 
       FIG. 7  is an exploded perspective view of a cam  732  in accordance with an exemplary embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Accordingly, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of components set forth in the following description or illustrated in the drawings. 
     FIG. 1  is a perspective view of a snowmobile  100  including a drive system  102  in accordance with an exemplary embodiment of the present invention. Snowmobile  100  has a chassis  104  defining a tunnel  106 . In the embodiment of  FIG. 1 , a drive track  108  can be seen extending from tunnel  106 . In the embodiment of  FIG. 1 , drive track  108  comprises an endless loop that is supported by a rear suspension. In a preferred embodiment, drive track  108  is operatively connected to an engine by a drivetrain so that drive track  108  may be used to propel snowmobile  100 . In some embodiments of the present invention drive track  108  maybe used to propel snowmobile  100  in both a forward direction and a reverse direction. In  FIG. 1 , it may also be appreciated that snowmobile  100  includes a plurality of skis. Although a snowmobile is illustrated in  FIG. 1 , it is to be appreciated that a drive system in accordance with the present invention may be used in conjunction with various types of vehicles. Examples of such vehicles include ATVs, golf carts and the like. 
     FIG. 2  is a perspective view of a drive system  202  in accordance with an exemplary embodiment of the present invention. Drive system  202  of  FIG. 2  may be used, for example, to propel a snowmobile such as the one illustrated in the previous figure. Drive system  202  includes a drive track  208  that is illustrated using phantom lines in FIG.  2 . Drive track  208  may be driven by two drive sprockets  220  that are fixed to a drive shaft  222 . Drive shaft  222  is preferably adapted to be used to urge motion of drive track  208 , such that drive shaft  222  and drive track  208  propel a vehicle. 
   Drive system  202  of  FIG. 2  also includes a jack shaft  224 . In the embodiment of  FIG. 2 , jack shaft  224  and drive shaft  222  are connected to one another by a speed reduction mechanism  226 . In a preferred embodiment, speed reduction mechanism  226  is configured to provide a desired reduction in rotational velocity. Speed reduction mechanism  226  may comprise various elements without deviating from the spirit and scope of the present invention. Examples of elements which may be suitable in some applications include gears, sprockets, belts and chains. 
   A driven clutch  230  is connected to jack shaft  224  in the embodiment of FIG.  2 . Driven clutch  230  includes a cam  232  that can be seen extending beyond a sheave  236  of driven clutch  230 . Driven clutch  230  is connected to a drive clutch  228  by a drive belt  234 . In the embodiment of  FIG. 2 , drive clutch  228  is fixed to a crankshaft  238  of an engine  240 . Crankshaft  238  is illustrated using dashed lines in FIG.  2 . In a preferred embodiment, engine  240  is capable of rotating crankshaft  238  in both a first rotational direction  242  and a second rotational direction  244 . 
   With reference to  FIG. 2 , it may be appreciated that rotation of crankshaft  238  is transferred via a drivetrain  246  to drive-shaft  222  so as to cause rotation of drive shaft  222 . In the embodiment of  FIG. 2 , drivetrain  246  comprises drive clutch  228 , drive belt  234 , driven clutch  230 , jack shaft  224 , and speed reduction mechanism  226 . Drive shaft  222  causes movement of drive track  208  such that drive track  208  propels a vehicle. When crankshaft  238  is rotated in a first rotational direction  242  vehicle is propelled in a forward direction  248 . When drive shaft  222  is rotated in a second rotational direction  244 , vehicle is propelled in a reverse direction  250 . 
     FIG. 3  is a plan view of a continuously variable transmission  352  in accordance with an exemplary embodiment of the present invention. Continuously variable transmission  352  includes a drive clutch  328 , a driven clutch  330 , and an endless drive belt  334  disposed about the drive clutch  328  and driven clutch  330 . Driven clutch  330  includes a pair of opposed sheaves which together define a generally V-shaped “pulley” within which drive belt  334  rides. One of the sheaves is axially movable (i.e., movable in the direction parallel to the axis of driven clutch  330 ), and the other sheave is axially stationary. 
   Continuously variable transmission  352  includes a cam  332  that is preferably adapted to urge the sheaves of driven clutch  330  toward one another. In the embodiment of  FIG. 3 , cam  332  comprises a first cam member  354  and a second cam member  356 . In the embodiment of  FIG. 3 , cam  332  comprises a first cam member  354  and a second cam member  356 . As shown in  FIG. 3 , first cam member  354  of cam  332  includes a first cam surface  358  that contacts a cam follower  360  when a crankshaft  338  of continuously variable transmission  352  is turning in a first direction. Also as shown in  FIG. 3 , second cam member  356  of cam  332  includes a second cam surface  362  that contacts cam follower  360  when crankshaft  338  is turning in a second direction. Drive clutch  328  comprises a pair of opposed sheaves, one being axially movable and the other being axially stationary. 
     FIG. 4  is a perspective view of a drive system  402  in accordance with an additional exemplary embodiment of the present invention. Drive system  402  of  FIG. 4  includes an engine  440  and a drive clutch  428  that is fixed to a crankshaft of engine  440 . In a preferred embodiment, engine  440  is capable of rotating the crankshaft in both a first direction and a second direction that is different from the first direction. Various methods and apparatus may be used to rotate the crankshaft in a first direction and a second direction without deviating from the spirit and scope of the present invention. Examples of methods and apparatus that may be suitable in some applications can be found in U.S. Pat. Nos. 5,161,489; 5,782,210; 5,794,574; 5,964,191; 6,039,010; 6,044,807; 6,098,574; 6,234,119; and 6,237,546. The entire disclosure of each of these U.S. Patents is herby incorporated by reference. 
   Drive clutch  428  is connected to a driven clutch  430  by a drive belt  434 . Driven clutch  430  is connected to a drive shaft  422  by a speed reduction mechanism  426 . In a preferred embodiment, speed reduction mechanism  426  is configured to provide a desired reduction in rotational velocity. Speed reduction mechanism  426  may comprise various elements without deviating from the spirit and scope of the present invention. Examples of elements which may be suitable in some applications include gears, sprockets, belts and chains. 
     FIG. 5  is a diagrammatic illustration of a drive system  502  in accordance with an additional exemplary embodiment of the present invention. Drive system  502  includes an engine  540 . In the exemplary embodiment of  FIG. 5 , engine  540  is capable of rotating a crankshaft  538  in a first direction and a second direction. Crankshaft  538  of engine  540  is connected to a drive shaft  522  via a drivetrain  546 . In the embodiment of  FIG. 5 , drivetrain  546  includes a drive clutch  528 , a driven clutch  530 , a cam  532 , and a cam follower  560 . In the embodiment of  FIG. 5 , cam  532  comprises a first cam member  554  and a second cam member  556 . As shown in  FIG. 5 , first cam member of cam  532  includes a first cam surface  558  that contacts a cam follower  560  when cam  532  is turning in a first direction. Also as shown in  FIG. 5 , second cam member  556  of cam  532  includes a second cam surface  562  that contacts cam follower  560  when cam  532  is turning in a second direction. 
   In  FIG. 5 , it may be appreciated that a coupling  564  extends between a coupling portion  566  of first cam member  554  and a coupling portion  568  of second cam member  556 . In some advantageous embodiments of the present invention, coupling  564  is capable of absorbing shock when the rotation of the crankshaft  538  is changed from the first direction to the second direction or from the second direction to the first direction. In the embodiment of  FIG. 5 , coupling  564  comprises a spring  570  and a damper  572 . 
     FIG. 6  is a perspective view of a cam  632  in accordance with an additional exemplary embodiment of the present invention. Cam  632  of  FIG. 6  comprises a first cam member  654  and a second cam member  656 . As shown in  FIG. 6 , first cam member  654  of cam  632  includes a first cam surface  658  that is preferable dimensioned to contact a cam follower when cam  632  is turning in a first direction. Also as shown in  FIG. 6 , second cam member  656  of cam  632  includes a second cam surface  662  that is preferably dimensioned to contact a cam follower when cam  632  is turning in a second direction. 
   In  FIG. 6 , it may be appreciated that cam  632  comprises a plurality of couplings  664 . In the embodiment of  FIG. 6 , each coupling  664  includes a coupling portion  666  of first cam member  654 , a coupling portion  668  of second cam member  656 , and an intermediate member  674 . In the embodiment of  FIG. 6 , intermediate member  674  extends between coupling portion  666  of first cam member  654  and coupling portion  668  of second cam member  656 . In some advantageous embodiments of the present invention, coupling  664  is capable of absorbing shock when the rotation of cam  632  is changed from a first direction to a second direction or from the second direction to the first direction. 
   In some useful embodiments of the present invention, intermediate member  674  comprises a reversibly deformable material. For example, intermediate member  674  may comprise an elastomeric material. The term elastomeric generally refers to a rubberlike material (e.g., a material which can experience about a 7% deformation and return to the undeformed configuration). Examples of elastomeric materials include rubber (e.g., natural rubber, silicone rubber, nitrile rubber, polysulfide rubber, etc.), thermoplastic elastomer (TPE), butyl, polyurethane, and neoprene. 
     FIG. 7  is an exploded perspective view of a cam  732  in accordance with an exemplary embodiment of the present invention. In  FIG. 7 , it may be appreciated that a first coupling portion  766  of first cam member  754  comprises a tang  776 . In  FIG. 7 , it may also be appreciated that a second coupling portion  768  of second cam member  756  comprises a slot  778 . A plurality of intermediate members  774  are visible in FIG.  7 . In the embodiment of  FIG. 7 , first cam member  754  and second cam member  756  are dimensioned so that they can be joined together with intermediate member  774  interposed between first coupling portion  766  of first cam member  754  and second coupling portion  768  of second cam member  756 . 
   A bushing  780  is also visible in FIG.  7 . In the embodiment of  FIG. 7 , bushing  780  comprises of a flange  782  on its upper end and a bore extending there-through. A lower end of the bushing  780  may be inserted mounted into a central bore extending through first cam member  754 . In some embodiments of the present invention, a portion of second cam member  756  may be inserted into the bore defined by bushing  780 . The intermediate member  774  slides around and over tang  776  of coupling portion  766  of the second cam member  756 , such that when the first cam member  754  and the second cam-member  756  are adjoined, the coupling portion  766  of the first cam member  754  slides over and around the outer extent of intermediate member  774 . 
   The complete disclosures of all patents, patent applications, and publications are hereby incorporated by reference as if individually incorporated. Having thus described the various exemplary embodiments of the present invention, those of skill in the an will readily appreciate that yet other embodiments may be made and used within the scope of the claims hereto attached. Thus, it is to be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of parts without exceeding the invention&#39;s scope which is, of course, defined in the language in which the appended claims are expressed.