Patent Publication Number: US-8534413-B2

Title: Primary clutch electronic CVT

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 61/547,485, titled “Primary Clutch Electronic CVT,” filed Oct. 14, 2011, the disclosure of which is expressly incorporated by reference herein. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to electronically controlled transmissions, and more particularly to an electronically controlled continuously variable transmission (CVT) for recreational and utility vehicles. 
     BACKGROUND AND SUMMARY 
     Some recreational vehicles, such as all-terrain vehicles (ATV&#39;s), utility vehicles, motorcycles, etc., include a continuously variable transmission (CVT). In these vehicles, an actuator adjusts the position of one of the primary and secondary clutches of the CVT. The thrust requirement of the actuator for moving the clutch is generally dependent on the sliding friction between the movable sheave and the sliding coupling. 
     Available space is often limited around the CVT for placing the components of the actuator assembly. As such, actuator components having a large package size are often difficult to place in close proximity to the CVT. Further, the removal of some or all of the actuator components is often required when replacing the CVT belt. 
     A starting clutch is sometimes used to engage the CVT. The starting clutch is positioned at the driven or secondary clutch of the CVT to engage the secondary clutch when the CVT is in a low gear ratio condition. Due to the low speeds and high torques of the secondary clutch when the starting clutch engages the secondary clutch, the starting clutch is generally large in size. 
     In some recreational vehicles with CVT&#39;s, such as snowmobiles, the electrical system does not include a battery. As such, the rotational motion of the engine is used to generate power for the vehicle. In these vehicles, or in vehicles that experience a sudden power loss, the clutch assembly of the CVT may require a manual reset to a home position prior to starting the vehicle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary vehicle incorporating the electronic CVT of the present disclosure; 
         FIG. 2  is a perspective view of an exemplary drive system of the vehicle of  FIG. 1  including a continuously variable transmission (CVT); 
         FIGS. 3   a  and  3   b  are diagrammatic views of the CVT of  FIG. 2  according to one embodiment; 
         FIG. 4  is a front perspective view of an exemplary CVT of the vehicle of  FIG. 1  according to one embodiment including a housing with a cover and a mounting bracket; 
         FIG. 5  is a front perspective view of the CVT of  FIG. 4  with the cover removed from the mounting bracket; 
         FIG. 6  is a side view of a primary clutch of the CVT of  FIG. 4 ; 
         FIG. 7  is a rear perspective view of the CVT of  FIG. 4  illustrating an actuator assembly; 
         FIG. 8  is a front perspective view of the CVT of  FIG. 4  illustrating a moveable sheave of the primary clutch in an open position; 
         FIG. 9  is a front perspective view of the CVT of  FIG. 4  illustrating the moveable sheave of the primary clutch in a closed position; 
         FIG. 10  is an exploded front perspective view of the actuator assembly of  FIG. 7  with the mounting bracket partially cut away; 
         FIG. 11  is an exploded rear perspective view of the actuator assembly of  FIG. 7  with the mounting bracket partially cut away; 
         FIG. 12  is an exploded front perspective view of the primary clutch of  FIG. 6  and a launch clutch; 
         FIG. 13  is an exploded rear perspective view of the primary clutch of  FIG. 6  and the launch clutch of  FIG. 12 ; 
         FIG. 14  is a cross-sectional view of the primary clutch of  FIG. 6  taken along line  14 - 14  of  FIG. 8 ; 
         FIG. 15  is a cross-sectional view of the primary clutch of  FIG. 6  taken along line  15 - 15  of  FIG. 9 ; 
         FIG. 16  is a perspective view of the primary clutch of  FIG. 14  illustrating the cross-section taken along line  14 - 14  of  FIG. 8 ; 
         FIG. 17  is a perspective view of the primary clutch of  FIG. 6  partially cut away illustrating a sliding interface of the moveable sheave; 
         FIG. 18  is a partially exploded front perspective view of the primary clutch and the launch clutch of  FIG. 12 ; 
         FIG. 19  is a partially exploded rear perspective view of the primary clutch and the launch clutch of  FIG. 12 ; 
         FIG. 20  is a diagrammatic view of an exemplary electro-hydraulic circuit for controlling the CVT of  FIG. 2  according to one embodiment; 
         FIG. 21  is a block diagram illustrating an exemplary control strategy for moving a clutch of the CVT of  FIG. 2  to a home position; 
         FIG. 22  is a diagrammatic view of an exemplary control system of the vehicle of  FIG. 1  without a system battery; and 
         FIG. 23  is a block diagram illustrating an exemplary control strategy of the control system of  FIG. 22  for moving a clutch of the CVT of  FIG. 2  to a home position. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The embodiments disclosed herein are not intended to be exhaustive or limit the disclosure to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may utilize their teachings. 
     Referring initially to  FIG. 1 , an exemplary vehicle  10  having an electronically controlled CVT is illustrated. Vehicle  10  is illustratively a side-by-side ATV  10  including a front end  12 , a rear end  14 , and a frame or chassis  15  that is supported above the ground surface by a pair of front tires  22   a  and wheels  24   a  and a pair of rear tires  22   b  and wheels  24   b . ATV  10  includes a pair of laterally spaced-apart bucket seats  18   a ,  18   b , although a bench style seat or any other style of seating structure may be used. Seats  18   a ,  18   b  are positioned within a cab  17  of ATV  10 . A protective cage  16  extends over cab  17  to reduce the likelihood of injury to passengers of ATV  10  from passing branches or tree limbs and to act as a support in the event of a vehicle rollover. Cab  17  also includes front console  31 , adjustable steering wheel  28 , and shift lever  29 . Front console  31  may include a tachometer, speedometer, or any other suitable instrument. 
     Front end  12  of ATV  10  includes a hood  32  and a front suspension assembly  26 . Front suspension assembly  26  pivotally couples front wheels  24  to ATV  10 . Rear end  14  of ATV  10  includes an engine cover  19  which extends over an engine and transmission assembly (see  FIG. 2 ). Rear end  14  further includes a rear suspension assembly (not shown) pivotally coupling rear wheels  24  to ATV  10 . Other suitable vehicles may be provided that incorporate the CVT of the present disclosure, such as a snowmobile, a straddle-seat vehicle, a utility vehicle, a motorcycle, and other recreational and non-recreational vehicles. 
     Referring to  FIG. 2 , an exemplary drive system  40  of vehicle  10  of  FIG. 1  is illustrated including an engine  42  and a CVT  48 . CVT  48  includes a primary or drive clutch  50  and a secondary or driven clutch  52 . An endless, variable speed belt  54  is coupled to the primary and secondary clutches  50 ,  52 . Engine  42  includes an engine case or housing  43  and an output shaft  44  configured to drive primary clutch  50  of the CVT  48 . Rotation of primary clutch  50  is transferred to secondary clutch  52  via belt  54 . An output shaft  46  of secondary clutch  52  is coupled to and drives a sub-transmission  56  which is coupled to the final drive  58  for driving wheels  24  (see  FIG. 1 ). In one embodiment, sub-transmission  56  is geared to provide a high gear, a low gear, a reverse gear, and a park configuration for vehicle  10  of  FIG. 1 . Fewer or additional gears may be provided with sub-transmission  56 . 
     An actuator assembly  80  is configured to control primary clutch  50 , as described herein. Actuator assembly  80  includes a motor  76  controlled by a clutch controller  36 . In one embodiment, motor  76  is an electrical stepper motor, although motor  76  may alternatively be a brushed motor or other suitable electrical or hydraulic motor. In an alternative embodiment, controller  36  and actuator assembly  80  control secondary clutch  52  of CVT  48 . Controller  36  includes a processor  38  and a memory  39  accessible by processor  38  that contains software with instructions for controlling CVT  48 . In one embodiment, controller  36  is part of an engine control unit (ECU) configured to control engine  42 . In this embodiment, a throttle operator  116  including a position sensor is coupled to controller  36 , and controller  36  electronically controls the throttle position of engine  42  based on the detected position of throttle operator  116 . In one embodiment, controller  36  communicates with sensors/devices of vehicle  10  and/or other vehicle controllers via controller area network (CAN) communication. 
     In the illustrated embodiment, secondary clutch  52  is a mechanically controlled clutch  52  and includes a stationary sheave and a moveable sheave (not shown). Secondary clutch  52  is configured to control the tension of belt  54  of CVT  48  as primary clutch  50  is adjusted. In one embodiment, secondary clutch  52  includes a spring and a torque-sensing helix (not shown). The helix applies a clamping force on belt  54  proportional to the torque on secondary clutch  52 . The spring applies a load proportional to the displacement of the moveable sheave. In one embodiment, secondary clutch  52  provides mechanical load feedback for CVT  48 . 
     As illustrated in  FIGS. 3A and 3B , primary clutch  50  is coupled to and rotates with a shaft  70 , and secondary clutch  52  is coupled to and rotates with a shaft  72 . Shaft  70  is driven by the output shaft  44  of engine  42  (see  FIG. 2 ). Shaft  72  of secondary clutch  52  drives sub-transmission  56  (see  FIG. 2 ). Belt  54  wraps around the primary and secondary clutches  50 ,  52  and transfers rotational motion of primary clutch  50  to secondary clutch  52 . 
     Referring to  FIG. 4 , a housing  60  for CVT  48  is illustrated with a cover  61  coupled to a back plate or mounting bracket  62 . Flanged portions  64   a ,  64   b  of mounting bracket  62  and cover  61 , respectively, are illustratively configured to receive fasteners  74  (see  FIG. 7 ) to couple cover  61  to mounting bracket  62 . Fasteners  74  are illustratively bolts or screws, although other suitable fasteners  74  may be used. Cover  61  includes a pipe portion  68  forming an opening  69  to provide access to belt  54  of CVT  48 . For example, opening  69  may be used to visually inspect belt  54  and/or secondary clutch  52  (see  FIG. 2 ) or to check the tension of belt  54 . Mounting bracket  62  includes a vent structure  66  including a pair of vents  67   a ,  67   b  extending into the interior of housing  60  (see  FIG. 5 ). Vents  67   a ,  67   b  and opening  69  cooperate to provide airflow to CVT  48  to reduce the likelihood of the components of CVT  48  overheating. Vent structure  66  is illustratively coupled to mounting bracket  62  via fasteners  75  (see  FIG. 7 ), although vent structure  66  may alternatively be integrally formed with mounting bracket  62  or cover  61 . Cover  61  is removable from mounting bracket  62  upon removing fasteners  74  from flanged portions  64   a ,  64   b . As illustrated in  FIG. 5 , cover  61  is adapted to be pulled away from mounting bracket  62  in a direction substantially perpendicular to the surface of mounting bracket  62 . 
     Referring to  FIG. 5 , primary clutch  50  of CVT  48  is secured to mounting bracket  62  via a bracket  90 . Bracket  90  includes flanged portions  94  each adapted to receive a fastener (not shown) to couple bracket  90  to mounting bracket  62 . Bracket  90  illustratively includes an end wall  96  and a curved wall  98  (see  FIG. 10 ) that extends perpendicularly between end wall  96  and mounting bracket  62 . In the illustrated embodiment, curved wall  98  extends partially around the outer circumference of primary clutch  50 . A pair of posts  92  further support bracket  90  between end wall  96  and mounting bracket  62 . Posts  92  are illustratively press fit between flanged portions  99  of end wall  96  and mounting bracket  62 , although posts  92  may alternatively be coupled to end wall  96  and/or mounting bracket  62  with fasteners. A position sensor  114  is coupled to a flange  115  (see  FIG. 11 ) of bracket  90  for detecting the axial location of a moveable sheave  102  of primary clutch  50 . In one embodiment, position sensor  114  is a rotary sensor with a bell crank, although a linear sensor or other suitable sensor may be provided. Sensor  114  provides position feedback to controller  36  ( FIG. 2 ). 
     As illustrated in  FIG. 5 , primary clutch  50  includes a pair of sheaves  100 ,  102  that are supported by and rotate with shaft  70 . Sheaves  100 ,  102  cooperate to define a pulley or slot  104  within which belt  54  (see  FIG. 2 ) rides. As illustrated in  FIG. 6 , slot  104  is substantially V-shaped due to slanted inner surfaces  110 ,  112  of respective sheaves  100 ,  102 . Accordingly, belt  54  has a substantially V-shaped cross-section to cooperate with inner surfaces  110 ,  112  of the sheaves  100 ,  102 . Primary clutch  50  further includes a screw assembly including an outer screw assembly  120  and an inner screw assembly  122  positioned between outer screw assembly  120  and moveable sheave  102 . 
     In the illustrated embodiment, sheave  100  is stationary axially in a direction parallel to the axis of shaft  70 , and sheave  102  is movable axially in a direction parallel to the axis of shaft  70 . In particular, sheave  102  is configured to slide along shaft  70  to a plurality of positions between a fully extended or open position (see  FIGS. 8 and 14 ) and a fully closed or retracted position (see  FIGS. 9 and 15 ). With moveable sheave  102  in a fully extended or open position, slot  104  is at a maximum axial width, and belt  54  rides near the radial center of primary clutch  50 , as illustrated in  FIG. 14 . In the illustrated embodiment, belt  54  does not contact a tube portion  216  of a sliding support  200  of primary clutch  50  when moveable sheave  102  is at the fully open position of  FIG. 14 . With moveable sheave  102  in a fully retracted or closed position, slot  104  is at a minimum axial width, and belt  54  rides near the outer periphery of primary clutch  50 , as illustrated in  FIG. 15 . Secondary clutch  52  (see  FIG. 2 ) is similarly configured with a pair of sheaves (not shown) supported by and rotatable with shaft  72 . One sheave of secondary clutch  52  is axially movable, and the other sheave is axially stationary. In one embodiment, secondary clutch  52  is configured to control the tension of belt  54 . For purposes of illustrating primary clutch  50 , secondary clutch  52  and belt  54  are not shown in  FIGS. 5 ,  8 , and  9 . 
     Movement of sheave  102  of primary clutch  50  and movement of the moveable sheave of secondary clutch  52  provides variable effective gear ratios of CVT  48 . In one embodiment, CVT  48  is configured to provide an infinite number of effective gear ratios between minimum and maximum gear ratios based on the positions of the moveable sheaves of the clutches  50 ,  52 . In the configuration illustrated in  FIG. 3A , the moveable sheave  102  (see  FIG. 6 ) of primary clutch  50  is substantially opened, and the moveable sheave (not shown) of secondary clutch  52  is substantially retracted. Accordingly, a low gear ratio is provided by CVT  48  in the configuration of  FIG. 3A  such that shaft  72  of secondary clutch  52  rotates slower than shaft  70  of primary clutch  50 . Similarly, in the configuration illustrated in  FIG. 3B , the moveable sheave  102  (see  FIG. 6 ) of primary clutch  50  is substantially retracted, and the moveable sheave (not shown) of secondary clutch  52  is substantially opened. Accordingly, a high gear ratio is provided by CVT  48  in the configuration of  FIG. 3B  such that shaft  72  of secondary clutch  52  rotates faster than shaft  70  of primary clutch  50 . 
     As illustrated in  FIG. 7 , actuator assembly  80  is coupled to the back of mounting bracket  62 . Actuator assembly  80  is configured to move the moveable sheave  102  (see  FIG. 5 ) of primary clutch  50 , as described herein. In the illustrative embodiment, engine  42  and sub-transmission  56  (see  FIG. 2 ) are configured to be positioned adjacent the back of mounting bracket  62  on either side of actuator assembly  80 . In particular, engine  42  is positioned to the right of actuator assembly  80  (as viewed from  FIG. 7 ), and the output of engine  42  couples to shaft  70  of primary clutch  50  through an opening  82  of mounting bracket  62 . Similarly, sub-transmission  56  is positioned to the left of actuator assembly  80  (as viewed from  FIG. 7 ), and shaft  72  of secondary clutch  52  (see  FIG. 3A ) extends through an opening  84  of mounting bracket  62  to drive sub-transmission  56 . 
     As illustrated in  FIGS. 10 and 11 , actuator assembly  80  includes motor  76  with a geared output shaft  132 , a reduction gear  130  housed within a gear housing  78 , and a main gear drive  86  extending outwardly from the front of mounting bracket  62 . Reduction gear  130  includes first and second gears  134 ,  136  coupled to a shaft  135 . First gear  134  engages geared output shaft  132  of motor  76 , and second gear  136  engages a first gear  106  coupled to an end of a shaft  109  of main gear drive  86 . Main gear drive  86  further includes a second gear  108  coupled to an end of shaft  109  opposite first gear  106 . Second gear  108  engages an outer gear  126  of screw assembly  120  (see  FIG. 6 ) of primary clutch  50 . 
     Gear housing  78  includes flange portions  156  each configured to receive a fastener  158  (see  FIG. 7 ) for coupling gear housing  78  to the back of mounting bracket  62 . Gear housing  78  includes a first portion  150 , a second or intermediate portion  152 , and a third portion  154 . First portion  150  includes an opening  151  (see  FIG. 11 ) that receives output shaft  132  of motor  76 . Second portion  152  includes an opening  153  (see  FIG. 10 ) that receives reduction gear  130 . Reduction gear  130  is supported at one end by second portion  152  and at the other end by a support member  140  mounted on the front face of mounting bracket  62 . Bearings  142 ,  146  are positioned at opposite ends of shaft  135  to facilitate rotation of reduction gear  130  within second portion  152  and support member  140 , respectively. Third portion  154  of housing  78  houses a portion of first gear  106  and supports the end of shaft  109  adjacent first gear  106 . Similarly, end wall  96  of bracket  90  supports the other end of shaft  109  adjacent second gear  108 . As illustrated in  FIG. 11 , bearings  144 ,  148  are coupled at opposite ends of shaft  109  to facilitate rotation of main gear drive  86  relative to gear housing  78  and bracket  90 . In particular, bearing  148  is received within third portion  154  of gear housing  78 , and bearing  144  is received within an opening  95  formed in end wall  96  of bracket  90 . 
     Referring to  FIGS. 12-16 , outer screw assembly  120  of primary clutch  50  includes a neck portion  128  and a threaded screw portion  127 . Neck portion  128  extends through an opening  97  formed in end wall  96  of bracket  90  (see  FIG. 10 ). An outer bearing support  184  is rotatably coupled to neck portion  128  via bearing assembly  183  and is fixedly coupled to an end  71  of shaft  70 . As such, shaft  70  and outer bearing support  184  rotate together independently from outer screw assembly  120 . In the illustrated embodiment, end  71  of shaft  70  is press fit into outer bearing support  184 . End  71  further includes a circumferential channel  73  that engages an inner ridge  189  of outer bearing support  184  (see  FIG. 14 ). End  71  of shaft  70  may also be fastened to outer bearing support  184  with an adhesive or other suitable fastener. 
     Inner screw assembly  122  includes a plate portion  186  and a threaded screw portion  188  positioned radially inwardly from plate portion  186 . An L-shaped wall  185  is illustratively coupled between plate portion  186  and screw portion  188  forming a radial gap  187  between screw portion  188  and wall  185 . Screw portion  188  includes outer threads  196  that mate with inner threads  129  of screw portion  127  of outer screw assembly  120 . Screw portion  127  of outer screw assembly  120  is received within gap  187  formed in inner screw assembly  122  (see  FIGS. 14-16 ). An o-ring seal  192  positioned radially inside of wall  185  is configured to abut screw portion  127  of outer screw assembly  120 . Plate portion  186  of inner screw assembly  122  includes flanges  124  having apertures  125  (see  FIGS. 12 and 13 ) that slidably receive posts  92  of bracket  90  (see  FIGS. 8 and 9 ). Plate portion  186  further includes slots  194  circumferentially spaced near the outer perimeter of plate portion  186 . 
     Still referring to  FIGS. 12-16 , a sliding assembly of primary clutch  50  includes a bushing assembly  172 , a sliding support  200 , and a bearing assembly  190  positioned between bushing assembly  172  and inner screw assembly  122 . Bushing assembly  172  of primary clutch  50  includes a neck portion  176  that receives shaft  70  therethrough and a plurality of flanges  174  that couple to circumferentially spaced seats  202  of moveable sheave  102 . A plurality of fasteners  173 , illustratively screws  173 , are received by corresponding apertures of flanges  174  and seats  202  to couple bushing assembly  172  to sheave  102 . A bushing  178  positioned within neck portion  176  engages shaft  70  and supports the outboard end of moveable sheave  102 . Shaft  70  is configured to rotate inside of bushing  178  at engine idle (when primary clutch  50  is disengaged) and to rotate with bushing  178  when primary clutch  50  is engaged. Bushing  178  is configured to provide a low-friction surface that slides along shaft  70  during movement of sheave  102 . Bushing  178  may alternatively be a needle bearing. 
     Neck portion  176  of bushing assembly  172  is rotatably coupled to screw portion  188  of inner screw assembly  122  via bearing assembly  190  positioned within screw portion  188 . A collar  182  and a toothed lock washer  180  are coupled to neck portion  176  extending through screw portion  188  (see  FIGS. 14-16 ). Lock washer  180  illustratively includes an inner tab  181  (see  FIG. 12 ) that engages a corresponding slot  177  (see  FIG. 12 ) in the outer surface of neck portion  176  such that lock washer  180  rotates with bushing assembly  172 . Collar  182  is threaded onto neck portion  176  and is rotatably fixed in place on neck portion  176  with tabbed lock washer  180 . Accordingly, bushing assembly  172 , sheaves  100 ,  102 , collar  182 , washer  180 , and outer bearing support  184  are configured to rotate with shaft  70 , while outer screw assembly  120  and inner screw assembly  122  do not rotate with shaft  70 . Bushing assembly  172  is configured to slide axially along shaft  70  via bearing  178 . 
     Sliding support  200  is coupled to sheaves  100 ,  102  to provide a sliding interface for moveable sheave  102  relative to stationary sheave  100 . As illustrated in  FIGS. 14-16 , sliding support  200  includes a tube portion  216  and a plate portion  214  coupled to and substantially perpendicular to tube portion  216 . In one embodiment, plate portion  214  and tube portion  216  are molded together, although plate and tube portions  214 ,  216  may be coupled together with a fastener or by other suitable coupling means. Plate and tube portions  214 ,  216  each rotate with sheaves  100 ,  102  and shaft  70 . A pair of seals  220   a ,  220   b  and a clutch  218  positioned between seals  220   a ,  220   b  are coupled between tube portion  216  and shaft  70 . Clutch  218  is illustratively a one-way clutch  218  that free-wheels during vehicle idle and that locks tube portion  216  to shaft  70  during engine braking. As such, one-way clutch  218  acts as a bearing between tube portion  216  and shaft  70  during idling conditions and locks tube portion  216  to shaft  70  when CVT  48  is being driven faster than engine  42  (i.e., when belt  54  and clutch  50  work to overdrive engine  42  of  FIG. 2 ). 
     As illustrated in  FIG. 12 , plate portion  214  includes a plurality of sliding couplers  206  that are circumferentially spaced around the outer diameter of plate portion  214 . In the illustrated embodiment, the outer diameter of plate portion  214  is nearly the same as the outer diameter of moveable sheave  102  such that couplers  206  of plate portion  214  are immediately adjacent an inner cylindrical wall  203  of sheave  102 . Couplers  206  are illustratively clips  206  that are configured to slidingly receive corresponding sliding members or ridges  204  that are circumferentially spaced around inner wall  203  of moveable sheave  102 . Ridges  204  extend radially inward from and substantially perpendicular to cylindrical inner wall  203 . Ridges  204  illustratively include a radial width and a radial height that is substantially greater than the radial width. As illustrated in  FIG. 17 , a low-friction liner  208  is positioned in each clip  206  to engage the sliding surface of ridges  204 . In one embodiment, liner  208  is a low-friction composite or plastic material, such as polyether ether ketone (PEEK), polyimide-based plastic (e.g. Vespel), or nylon, for example, with additives to reduce friction. As illustrated in  FIGS. 14-16 , a cylindrical bearing or bushing  222  and an o-ring seal  224  are positioned between moveable sheave  102  and tube portion  216  to locate sheave  102  radially onto tube portion  216 . Bushing  222  provides a low friction sliding surface for sheave  102  relative to tube portion  216 . In one embodiment, grease is provided in the interfaces between ridges  204  and clips  206  and between bushing  222  and tube portion  216  to reduce sliding friction. 
     Moveable sheave  102  is configured to slide relative to sliding support  200  along ridges  204  of  FIG. 12 . In one embodiment, the sliding friction between sheave  102  and sliding support  200  is minimized with the sliding interface between couplers  206  and ridges  204  being near the outer diameter of moveable sheave  102 . In the illustrated embodiment, the outer diameter of moveable sheave  102  is large relative to the outer diameters of shaft  70  and tube portion  216 . In one embodiment, the outer diameter of moveable sheave  102  is at least three times greater than the outer diameters of shaft  70  and tube portion  216 . 
     As illustrated in  FIGS. 14-16 , bearing assemblies  183  and  190  are each positioned outside of the outer profile of moveable sheave  102 . In particular, referring to  FIG. 14 , bearing assemblies  183 ,  190  are positioned axially outside of the end of sheave  102  lying in plane  198 . As such, bearing assemblies  183 ,  190  are axially spaced apart from the sliding interfaces formed with couplers  206  and ridges  204  and with bushing  222  and tube portion  216 . In one embodiment, bearing assemblies  183 ,  190  include angular contact bearings, although other suitable bearings may be used. Neck portion  176  of bushing assembly  172  is also illustratively positioned outside of the outer profile of moveable sheave  102 , as illustrated in  FIG. 14 . 
     In operation, the actuation of gear drive  86  by motor  76  (see  FIG. 10 ) is configured to modulate the gear ratio provided by primary clutch  50 . Referring to  FIG. 10 , the output of motor  76  is transferred through reduction gear  130  to main gear drive  86  to thereby rotate outer screw assembly  120  (see  FIG. 8 ) of primary clutch  50 . Outer screw assembly  120  is stationary axially and rotates due to the rotation of main gear drive  86  independent of a rotation of shaft  70 . Referring to  FIGS. 8 and 14 , rotation of outer screw assembly  120  in a first direction unscrews threaded screw portion  188  of inner screw assembly  122  from threaded screw portion  127  of outer screw assembly  120 , thereby causing inner screw assembly  122  to slide axially along posts  92  towards stationary sheave  100  while remaining rotationally stationary. 
     Referring to  FIG. 14 , the axial movement of inner screw assembly  122  provides a thrust force against moveable sheave  102  via bushing assembly  172  to move sheave  102  towards stationary sheave  100 . As described herein, bushing assembly  172  rotates within the rotationally stationary inner screw assembly  122  via bearing assembly  190 . As such, the thrust force provided by inner screw assembly  122  is applied to bushing assembly  172  through bearing assembly  190 . Similarly, rotation of outer screw assembly  120  in a second, opposite direction causes inner screw assembly  122  to move axially away from stationary sheave  100  along posts  92  (see  FIG. 8 ) and to apply a pulling force on bushing assembly  172  and moveable sheave  102  through bearing assembly  190 . Bearing assemblies  183 ,  190  provide axial movement of inner screw assembly  122 , bushing assembly  172 , and sheave  102  relative to shaft  70  that is independent from the rotational movement of shaft  70 , sheaves  100 ,  102 , sliding support  200 , and bushing assembly  172 . In the illustrated embodiment, the range of axial motion of inner screw assembly  122  relative to outer screw assembly  120  defines the maximum and minimum gear ratios provided with primary clutch  50 , although other limit stops may be provided. 
     As illustrated in  FIGS. 18 and 19 , a clutch assembly  170  is coupled to shaft  70  to serve as a starting or launch clutch for primary clutch  50 . Clutch assembly  170  is illustratively a dry centrifugal clutch  170  integrated into primary clutch  50 . Clutch assembly  170  is configured to be positioned external to the engine case  43  (see  FIG. 2 ) of engine  42 . As such, clutch assembly  170  is not integrated with the engine case  43  of engine  42  and is therefore not positioned in the engine oil. Rather, clutch assembly  170  is positioned outside of the engine case  43  and is coupled to the output shaft  44  of engine  42  to operate as a dry starting clutch for primary clutch  50 . As such, clutch assembly  170  is removable from engine  42  by pulling the clutch assembly  170  from shaft  44 . 
     In assembly, clutch assembly  170  is positioned in an interior  209  of primary clutch  50  (see  FIG. 19 ). Clutch assembly  170  includes an end plate  232  coupled to shaft  70  and having a plurality of posts  234 . In the illustrated embodiment, shaft  70  and end plate  232  are integrally formed, although shaft  70  may be coupled to end plate  232  using a fastener or press-fit configuration. As illustrated in  FIG. 14 , shaft  70  includes substantially cylindrical outer and inner surfaces  226 ,  228 , respectively. Inner surface  228  forms a hollow interior region  229  of shaft  70 . Outer and inner surfaces  226 ,  228  illustratively taper from end plate  232  towards end  71 . The outer surface of shaft  70  further includes a step  88  such that the diameter of the portion of shaft  70  received by bushing assembly  172  and outer bearing support  184  is smaller than the diameter of the portion of shaft  70  positioned in tube portion  216  of sliding support  200 . In the illustrated embodiment, the output shaft  44  of engine  42  (see  FIG. 2 ) is received by interior region  229  of shaft  70  to drive rotation of clutch assembly  170 . As such, clutch assembly  170  and shaft  70  rotate with engine  42 . 
     Referring to  FIGS. 18 and 19 , clutch assembly  170  further includes shoes or arms  238  pivotally mounted to posts  234  via fasteners  240 . Arms  238  each include an aperture  236  that receives a corresponding post  234  of end plate  232 . Fasteners  240  illustratively include bolts and washers. Each arm  238  includes a friction pad  230  coupled to the outer circumferential surface of each arm  238 . A spring  242  is coupled between adjacent arms  238  at seats  244  to bias arms  238  into spaced relation with each other. 
     In the illustrated embodiment, clutch assembly  170  is disengaged from primary clutch  50  when engine  42  (see  FIG. 2 ) is at or below engine idle speed. As the engine speed and the corresponding rotational speed of clutch assembly  170  increases, the centrifugal force acting on arms  238  overcomes the biasing force of springs  242  and causes ends  246  of arms  238  to swing radially outward, thereby forcing friction pads  230  into engagement with an inner friction surface  210  (see  FIG. 13 ) of stationary sheave  100 . The engagement of clutch assembly  170  with stationary sheave  100  transfers torque to sliding support  200  and moveable sheave  102 . As such, sheaves  100 ,  102 , sliding support  200 , and bushing assembly  172  all rotate with shaft  70 . When the rotational speed of shaft  70  decreases to a threshold speed, the reduced centrifugal force causes arms  238  to move radially inward away from surface  210  of sheave  100 . As such, clutch assembly  170  disengages primary clutch  50 . Stationary sheave  100  illustratively includes a plurality of circumferentially spaced cooling fins  212  configured to reduce the heat generated by the engagement of clutch assembly  170 . 
     In the illustrated embodiment, upon removing cover  61  and bracket  90  from mounting bracket  62  (see  FIG. 5 ), a disengaged centrifugal starting clutch  170  allows primary clutch  50  to be pulled off shaft  70  as one assembled unit. Belt  54  (see  FIG. 2 ) may be removed and/or replaced upon removing primary clutch  50  from shaft  70 . Further, actuator assembly  80  (see  FIGS. 9 and 10 ) remains coupled to mounting bracket  62  when primary clutch  50  is removed from shaft  70  such that the gears of actuator assembly  80  (e.g. reduction gear  130 ) are not required to be removed and reset or recalibrated. In one embodiment, primary clutch  50  and belt  54  are removable from shaft  70  without removing main gear drive  86  (see  FIG. 5 ). 
     Centrifugal starting clutch  170  serves to separate the shifting function of primary clutch  50  from the engagement function of the primary clutch  50 . In particular, the shifting function is performed by the primary clutch  50  via controller  36  (see  FIG. 6 ), while the engagement of primary clutch  50  is controlled by starting clutch  170 . As such, controller  36  is not required to control the engagement of primary clutch  50  because starting clutch  170  automatically engages primary clutch  50  upon reaching a predetermined rotational speed. 
     In an alternative embodiment, primary clutch  50  may be configured to operate without a starting clutch  170 . For example, in this embodiment, primary clutch  50  of CVT  48  is directly coupled to the output of engine  42 . When vehicle  10  is at idle or not running, controller  36  positions moveable sheave  102  away from stationary sheave  100  such that belt  54  is positioned radially inward towards shaft  70 , as illustrated in  FIG. 6 . In one embodiment, controller  36  positions sheave  102  at a maximum open position when engine  42  is idling or not running such that moveable sheave  102  does not contact belt  54 . In one embodiment, sheave  102  is disengaged from belt  54  during shifting of sub-transmission  56  (see  FIG. 2 ). As such, secondary clutch  52  is rotating at a zero or minimal speed upon shifting sub-transmission  56 . Engagement of sheave  102  and belt  54  is initiated upon engine driving torque being requested, e.g. upon throttle request by an operator. In another embodiment, sheave  102  is moved into engagement with belt  54  after sub-transmission  56  is shifted out of neutral and into gear. In another embodiment, moveable sheave  102  is spring-loaded away from belt  54  during engine idle, and the shifting of sub-transmission  56  into gear mechanically causes sheave  102  to move back into engagement with belt  54 . 
     In one embodiment, controller  36  of  FIG. 2  provides a spike load reduction feature configured to automatically shift CVT  48  upon detection of vehicle  10  being airborne. For example, when vehicle  10  of  FIG. 1  is airborne, wheels  24  may accelerate rapidly due to the wheels  24  losing contact with the ground while the throttle operator  116  (see  FIG. 2 ) is still engaged by the operator. When the wheels  24  again make contact with the ground upon vehicle  10  landing, the wheel speed decelerates abruptly, possibly leading to damaged or stressed components of the CVT  48  and other drive train components. Controller  36  initiates spike load control upon detection of vehicle  10  being airborne to slow drive train acceleration of the airborne vehicle  10 . In one embodiment, controller  36  slows the rate at which CVT  48  upshifts during spike load control. In one embodiment, controller  36  stops upshifting of CVT  48  at least momentarily during spike load control or downshifts CVT  48  to a lower gear ratio. As such, the drive train acceleration of vehicle  10  is slowed before vehicle  10  returns to the ground, and the inertial loading on CVT  48  and other drive train components (e.g. sub-transmission  56 , final drive  58 , etc.) upon vehicle  10  landing is reduced or minimized. In one embodiment, controller  36  automatically adjusts the gear ratio of CVT  48  of the airborne vehicle  10  such that the wheel speed upon vehicle  10  returning to the ground is substantially the same as the detected wheel speed immediately prior to vehicle  10  becoming airborne. 
     In one embodiment, controller  36  determines that vehicle  10  is airborne upon detection of a sudden acceleration in drive train components. For example, controller  36  may detect the sudden acceleration based on feedback from a wheel speed sensor, engine speed sensor, transmission speed sensor, or other suitable speed sensor on the drive train of vehicle  10 . In the illustrated embodiment, controller  36  continuously monitors the angular acceleration of the drive train by measuring the speed of one of the shafts of CVT  48  or sub-transmission  56  with a speed sensor  59 . Vehicle  10  is determined to be airborne when the acceleration in wheel speed or drive train speed exceeds the design specifications of vehicle  10 . For example, vehicle  10  has a maximum wheel acceleration based on available torque from engine  42 , the frictional force from the ground, the weight of vehicle  10 , and other design limits. When the monitored drive train components accelerate at a faster rate than vehicle  10  is capable under normal operating conditions (i.e., when wheels  24  are in contact with the ground), controller  36  determines that wheels  24  have lost contact with the ground. One or more predetermined acceleration limits are stored at controller  36  that correspond to the design limits of vehicle  10  to trigger the spike load control. 
     In one embodiment, the spike load reduction feature of controller  36  works in conjunction with a drive train protection feature that uses an electronic throttle control system to reduce drive train acceleration (i.e., by reducing the throttle opening, etc.) upon detection of an airborne condition, as described in U.S. patent application Ser. No. 13/153,037, filed on Jun. 3, 2011 and entitled “Electronic Throttle Control,” the disclosure of which is incorporated herein by reference. In some operating conditions, a high or increasing throttle demand is provided with throttle operator  116  while vehicle  10  is airborne. In one embodiment, the engine  42  continues to rev due to the high throttle demand until a rev limit of the engine  42  is reached. In a vehicle  10  having electronic throttle control, airflow to the engine  42  is automatically restricted upon detection of the airborne condition to reduce engine power and to reduce the likelihood of reaching the rev limit. 
     Controller  36  may detect an airborne condition of vehicle  10  using other methods, such as by detecting the compression distance or height of a suspension system (e.g. front suspension assembly  26  of  FIG. 1 ) of vehicle  10  with a suspension height sensor and/or by monitoring engine torque and power, as described in the referenced U.S. patent application Ser. No. 13/153,027. 
     In one embodiment, controller  36  provides a plurality of operating modes for CVT  48 . Exemplary operating modes, illustratively selectable by an operator with operating mode selector  113 , include performance, economy, manual mimic, cruise control, and hydrostatic modes. In one embodiment, the performance and economy modes are selectable for each of the manual mimic, cruise control, and hydrostatic modes. In one embodiment, the operating modes are only selectable when vehicle  10  is moving below a predetermined vehicle speed, such as below 10 mph, for example, although other suitable threshold speeds may be provided. In one embodiment, one or more of the operating modes are selectable only when vehicle  10  is substantially stopped. 
     The performance and economy modes are illustratively automatic modes wherein controller  36  actively controls CVT  48  based on engine speed, the position of throttle operator  116  and/or the throttle valve, and vehicle speed. In the economy mode, primary clutch  50  is adjusted based on engine speed according to a brake specific fuel consumption map stored at memory  39  of controller  36 . In particular, CVT  48  and engine  42  cooperate to provide an improved fuel economy as compared with the performance mode. In a performance mode, primary clutch  50  is adjusted based on engine speed such that peak power is output for a given engine speed and/or other operating condition. As such, the performance mode provides improved vehicle performance as compared with the economy mode. 
     In the cruise control mode, at least one of the engine throttle position and the gear ratio of CVT  48  is held constant to hold the vehicle speed at a predetermined vehicle speed. In one embodiment, the throttle position of engine  42  is locked or held constant to hold the engine torque substantially constant, and the gear ratio of CVT  48  is varied based on vehicle speed feedback to maintain the target vehicle speed. In another embodiment, the gear ratio of CVT  48  is held constant during cruise control while the throttle position of engine  42  is varied to maintain the target vehicle speed. Alternatively, both the throttle position and the gear ratio of CVT  48  may be held substantially constant or may be simultaneously adjusted to control vehicle speed. 
     In the hydrostatic mode, the engine speed and the gear ratio of CVT  48  are controlled independently by an operator. For example, the engine speed is selected (e.g. with throttle operator  116  or another suitable input device) based on a particular use or application, i.e., for powering vehicle implements, for charging system capacity, etc. The gear ratio of CVT  48  is selected by a separate input device, such as a pedal lever, or joystick. In one embodiment, the hydrostatic mode is provided in a controller  36  that also includes electronic throttle control functionality, as described herein, or in a vehicle  10  that includes an engine speed governor. 
     In a manual mimic mode, controller  36  shifts CVT  48  between a plurality of discrete gear ratios to simulate a traditional manual or automatic transmission. In particular, primary clutch  50  is moved to a plurality of predetermined positions during operation that each correspond to a different gear ratio. For example, in a first gear, primary clutch  50  is moved to a first predetermined position providing a first gear ratio. When CVT  48  is shifted to a second gear, primary clutch  50  is moved to a second predetermined position providing a second gear ratio higher than the first gear ratio. Each predetermined position of primary clutch  50  corresponds to a different gear ratio. 
     In one embodiment, an operator inputs a shift command to controller  36  to initiate a gear shift in the manual mimic mode, further simulating operation of a traditional manual or semi-automatic transmission. For example, shift lever  29  (see  FIG. 1 ) of vehicle  10  may be used for the selection of each discrete gear ratio by the operator. Other exemplary shifters include a switch, paddle, or knob. Alternatively, controller  36  shifts CVT  48  automatically between each predefined discrete gear ratio. In one embodiment, primary clutch  50  is moved to five or six predetermined positions across the displacement range of primary clutch  50  to provide five or six discrete gear ratios of CVT  48 , although fewer or additional gear ratios may be provided. In one embodiment, ignition to engine  42  ( FIG. 2 ) is momentarily cut as primary clutch  50  moves between each predetermined position. In particular, one or more spark plugs of engine  42  are cut during the transition between discrete gear ratios to simulate the inertia shift experienced in a vehicle  10  having a traditional manual or automatic transmission. Other torque interruption of engine  42  may be used to simulate traditional transmission shifting. 
     In one embodiment, CVT  48  further includes a planetary gear assembly to provide an infinitely variable transmission system. In one embodiment, the planetary gear assembly consists of a ring gear, several planetary gears coupled to a carrier, and a sun gear. The ring gear is driven directly off the output of engine  42  via a gear or chain. The planetary gears and the carrier are connected to and driven by the secondary clutch  52 . The sun gear serves as the output of CVT  48  connected to the sub-transmission  56 . Based on the gear ratios of the planetary gear assembly, the combined CVT  48  and planetary gear assembly are configured to provide both positive and negative speeds (forward and reverse) by varying the gear ratio of the CVT  48 . In one embodiment, the hydrostatic mode provided with controller  36  and described herein is implemented in a CVT  48  having a planetary gear assembly. 
     In one embodiment, CVT  48  is electro-hydraulically actuated, as illustrated with the exemplary electro-hydraulic circuit  278  of  FIG. 20 . In the illustrated embodiment of  FIG. 20 , primary clutch  50  of CVT  48  is actuated by electro-hydraulic circuit  278  rather than by actuator assembly  80  of  FIGS. 10 and 11 . Circuit  278  may also be configured to control secondary clutch  52 . Electro-hydraulic circuit  278  illustratively includes a hydraulic circuit  282  and an electric circuit  284 . Controller  36  illustratively receives analog inputs  250 , digital inputs  252 , and CAN inputs  254 . Exemplary analog and digital inputs  250 ,  252  include hydraulic system pressure sensors, a clutch position sensor (e.g. sensor  290  of  FIG. 20 ), a servo valve position sensor, and other sensors detecting various parameters of vehicle  10 . Exemplary CAN inputs  254  include an engine speed sensor, throttle position sensor, vehicle speed sensor, vehicle operating mode sensor, and other CAN based sensors that detect various parameters of vehicle  10 . Controller  36  is configured to control an electric motor  262  of electric circuit  284  and a pump  264  and a servo valve  272  of hydraulic circuit  282  based on inputs  250 ,  252 ,  254 . 
     A motor driver  256  is configured to control the power provided to motor  262  based on control signals from controller  36 . Alternatively, a relay may be provided in place of motor driver  256  that is selectively actuated by controller  36  to provide fixed power to motor  262 . Motor  262  may be any motor type suitable for driving pump  264 . In the illustrated embodiment, motor  262  is a DC electric motor. A voltage supply  261 , illustratively 12 VDC, is provided to motor  262 , and the speed of motor  262  is controlled by controller  36  via motor driver  256 . An output  263  of motor  262  drives pump  264 . In the illustrated embodiment, pump  264  is a variable displacement pump  264 . A pump control unit  258  of controller  36  modulates the displacement of pump  264  to control hydraulic pressure of hydraulic circuit  282  based on inputs  250 ,  252 ,  254 . Pump  264  may alternatively be a fixed displacement pump. 
     A hydraulic accumulator  268  stores pressurized hydraulic fluid to assist pump  264  and motor  262  with meeting the pressure demands of hydraulic circuit  282 . For example, accumulator  268  is configured to achieve required pressure demands of hydraulic circuit  282  during peak shift rates of CVT  48 . As such, the likelihood of spike loads being induced on the electric circuit  284  during peak shift rates of CVT  48  is reduced. A pressure relief valve  270  is provided to maintain the pressure on hydraulic line  288  below a predetermined maximum threshold pressure. Pressure relief valve  270 , pump  264 , and servo valve  272  are coupled to a hydraulic return reservoir  280 . 
     Servo valve  272  regulates the flow of hydraulic fluid from line  288  to actuator  274  to adjust the position of moveable sheave  102 . Servo valve  272  is illustratively a three-way electro-hydraulic servo valve  272  controlled by a servo valve driver  260  of controller  36 . Servo valve driver  260  of controller  36  controls servo valve  272  based on inputs  250 ,  252 ,  254 . Actuator  274 , illustratively a linear hydraulic actuator, includes a piston  275  coupled to moveable sheave  102  via a rotary bearing  276 . In one embodiment, rotary bearing  276  is a flanged bearing or a face bearing, although another suitable bearing  276  may be provided. In one embodiment, actuator  274  is coupled to chassis  15  of vehicle  10  (see  FIG. 1 ), and moveable sheave  102  rotates about piston  275  of actuator  274  and moves axially relative to actuator  274  via bearing  276 . Servo valve  272  is coupled to actuator  274  via hydraulic lines  286 . In one embodiment, lines  286  are small diameter, high pressure hydraulic lines  286 . By regulating the fluid flow to actuator  274  with servo valve  272 , linear displacement of actuator  274  is adjusted to cause corresponding axial adjustment of moveable sheave  102 . 
     In one embodiment, electric circuit  284  and hydraulic circuit  282  are positioned on vehicle  10  (see  FIG. 1 ) away from CVT  48 , and actuator  274  is positioned immediately adjacent or within housing  60  (see  FIG. 4 ) of CVT  48 . As such, hydraulic lines  286  are routed from servo valve  272  to the actuator  274  positioned near CVT  48 . For example, electric circuit  284  and hydraulic circuit  282  may be placed beneath hood  32  and/or seats  18   a ,  18   b  (see  FIG. 1 ), and CVT  48  and actuator  274  may be positioned towards the rear end  14  of vehicle  10  beneath engine cover  19  (see  FIG. 1 ). As such, the actuation components (i.e. actuator  274 ) of the moveable sheave(s)  102  of CVT  48  occupy a small space at the location of CVT  48  while some or all of the remaining components of electro-hydraulic circuit  278  are positioned elsewhere on vehicle  10 . 
     In one embodiment, the pressure applied to moveable sheave  102  via actuator  274  is modulated to achieve a desired gear ratio of CVT  48  and/or a desired pinch force on belt  54 . As illustrated in  FIG. 20 , a position sensor  290  is configured to detect the linear position of moveable sheave  102  and provide a corresponding signal to controller  36  with the detected position data. As such, the position of sheave  102  may be monitored during operation. 
     In one embodiment, controller  36  implements a fail-safe mode in the control of moveable sheave  102 . In particular, when a system failure or signal loss is detected by controller  36 , moveable sheave  102  is positioned to a maximum low ratio or open position such that the pinch force on belt  54  is minimized or removed. An exemplary system failure is when no or inadequate hydraulic pressure in hydraulic circuit  282  is detected with inputs  250 ,  252 . 
     The electronically controlled clutch  50 ,  52  of CVT  48  is configured to move to a home position prior to or upon shutting down vehicle  10 . For example, the controlled clutch  50 ,  52  moves to its fully open position (see  FIG. 8 , for example) or to its fully closed position (see  FIG. 9 , for example). In the illustrated embodiment, upon vehicle shutdown, moveable sheave  102  of primary clutch  50  moves to its furthest open position, as illustrated in  FIG. 8 . As such, moveable sheave  102  is positioned away from belt  54  prior to vehicle  10  being started, thereby reducing the likelihood of vehicle  10  taking off upon starting engine  42 . In one embodiment, for an electronically controlled secondary clutch  52 , the moveable sheave (not shown) of secondary clutch  52  moves to its furthest closed position. 
     Referring to  FIG. 2 , vehicle  10  includes a system battery  118  (e.g. 12 VDC) configured to provide power for starting vehicle  10  and to provide peripheral power to vehicle  10  during operation. The system battery  118  provides power to actuator assembly  80  to move moveable sheave  102  to the home position upon vehicle  10  being shutdown or being stopped and shifted into neutral. Primary clutch  50  of CVT  48  is also configured to return to a home position upon vehicle  10  suffering an abrupt power loss, as described herein with reference to  FIGS. 21-23 . 
     In another embodiment, vehicle  10  does not have a system battery  118 . For example, vehicle  10  may include a mechanical rope and recoil assembly that is pulled by an operator to start engine  42 . In particular, the pull of the rope by an operator rotates a power generator that starts engine  42  of vehicle  10 , and the power generator (driven by the rotating engine  42 ) provides peripheral power to the electronic components of vehicle  10  during operation. See, for example, generator  304  of  FIG. 22 . As such, power from a system battery  118  is not available to move primary clutch  50  to its home position while vehicle  10  is shut down. In the illustrated embodiment, primary clutch  50  is moved to its home position prior to shutting down vehicle  10  using the power provided with generator  304 , as described herein. 
     Referring to  FIG. 21 , an exemplary control strategy  350  is illustrated for moving primary clutch  50  to its home position in a vehicle  10  not having a system battery  118 . Control strategy  350  is illustratively implemented by controller  36  of  FIG. 2 , although another control unit of vehicle  10  may be used. At block  352 , an indicator (e.g. audible or visual) is provided on vehicle  10  upon moving the vehicle key to the ON position to indicate to the operator if primary clutch  50  is at its home position. In one embodiment, the indicator, such as a light, for example, is powered by a small, low-voltage battery. The indicator may alternatively be mechanically linked to the CVT  48  to detect the position of clutch  50 . If primary clutch  50  is at its home position, engine  42  is started by the operator, as illustrated at blocks  354 ,  356 , and  358 . For example, an operator may start engine  42  via a manual start system, such as a rope/recoil assembly or kick start assembly. In one embodiment, actuation of the manual start system is blocked when primary clutch  50  is not at its home position at block  352 . 
     Upon an operator commanding engine  42  to stop at block  360  (e.g. turning the vehicle key to OFF), primary clutch  50  automatically returns to its home position at block  362  prior to controller  36  allowing engine  42  to power down. In particular, controller  36  executes a shut down sequence at block  362  wherein controller  36  retains engine power despite the operator commanding shutdown, moves sheave  102  of primary clutch  50  to its home position (i.e., with actuator assembly  80 ), and then allows engine  42  to shut down (block  364 ). At block  366 , engine  42  shuts down. Accordingly, primary clutch  50  is at the home position before engine  42  shuts down such that vehicle  10  may be properly started up again at a future time without having to reset clutch  50 . 
     If primary clutch  50  is not at its home position at block  352 , primary clutch  50  must be moved to its home position prior to starting vehicle  10 , as illustrated at blocks  368 ,  370 , and  372 . For example, clutch  50  may require a reset when vehicle  10  abruptly loses power before controller  36  is able to reset clutch  50  to its home position. Primary clutch  50  may be reset manually or automatically. In the manual reset of block  374 , an operator removes cover  61  (see  FIG. 5 ) of CVT  48  and manually resets moveable sheave  102  to its home position by turning outer screw assembly  120  (see  FIG. 5 ). In the automatic reset of block  376 , vehicle  10  includes an auxiliary power connection  330  (see  FIG. 22 ) for connecting vehicle  10  to an external power supply (e.g. 12 VDC). The external power supplied through auxiliary power connection  330  is routed to controller  36 . Upon detecting the presence of external power, controller  36  moves primary clutch  50  to its home position via actuator assembly  80 . In one embodiment, power provided through auxiliary power connection  330  is routed directly to motor  76  of actuator assembly  80  (see  FIG. 2 ), and an operator manually controls actuator assembly  80  with a switch or a diagnostic tool to move primary clutch  50  to the home position. At block  378 , if primary clutch  50  is at the home position, the operator is able to start engine  42  at blocks  354  and  356 . If primary clutch  50  is not at the home position at block  378 , the process returns to block  372  for additional manual or automatic movement of clutch  50 . 
     Referring to  FIG. 22 , an exemplary control system  300  for a vehicle  10  without a system battery  318  ( FIG. 2 ) is illustrated. Control system  300  illustratively includes a microcontroller  302  that controls a switch  320  to selectively route power stored at a capacitor  316  to controller  36 . Microcontroller  302  includes a processor and a memory accessible by the processor and containing software with instructions for monitoring vehicle power  306 , detecting power interruption, and controlling switch  320 . Microcontroller  302  and controller  36  may alternatively be integrated in a single controller. Generator  304 , driven by engine  42  ( FIG. 2 ), provides vehicle power  306  (illustratively 12 VDC) for controller  36 , microcontroller  306 , and other peripheral components and for charging capacitor  316 . Capacitor  316  may alternatively be charged by an external power supply via auxiliary connection  330 . A fuse  308  and a diode  310 , illustratively a Zener diode  310 , are provided in series between vehicle  306  and controllers  302 ,  36  to provide reverse voltage protection. A diode  312 , illustratively a transient voltage suppression diode  312 , is coupled between the output of diode  310  and ground to provide over-voltage protection for controllers  302 ,  36 . A resistor  314  is provided for charging capacitor  316 . 
     Microcontroller  302  is configured to close switch  320  upon detection of a power loss at vehicle power  306 . For example, upon vehicle  10  abruptly losing power, microcontroller  302  senses the drop in vehicle power  306  and closes switch  320 . As a result, power stored at capacitor  316  is routed to controller  36  for moving primary clutch of CVT  48  to the home position. In one embodiment, capacitor  316  is an ultra-capacitor. Capacitor  316  is alternatively a lithium ion battery or another lightweight battery that is smaller than a typical vehicle system battery  318  ( FIG. 2 ). 
     Referring to  FIG. 23 , an exemplary control strategy  400  is illustrated for control system  300  of  FIG. 22 . With engine running at block  402 , an operator signals a vehicle shutdown at block  404 , and the normal shutdown process for vehicle  10  is performed at block  406 . For example, the shutdown process illustrated in blocks  360 ,  362 ,  364 , and  366  of  FIG. 21  and described herein is performed at block  406  of  FIG. 23 . If an abrupt power loss is detected by controller  302  ( FIG. 22 ) at block  410 , controller  302  determines if capacitor  412  is charged and functioning properly. If controller  302  determines capacitor  316  is not functioning properly, switch  320  is not closed and primary clutch  50  is manually moved to its home position at block  418 , as described with block  374  of  FIG. 21 . If capacitor  316  is functioning properly at block  412 , microcontroller  302  closes switch  320  to route power to controller  36  at block  414 . Controller  36  uses the power from capacitor  316  to drive actuator assembly  80  to move primary clutch  50  of CVT  48  to its home position. At block  416 , controller  36  (or microcontroller  302 ) determines if clutch  50  is at its home position based on feedback from a position sensor (e.g. sensor  290  of  FIG. 20 ). If clutch  50  is at its home position, the shutdown of vehicle  10  is determined to be proper at block  408 . If clutch  50  is not at its home position at block  416 , process  400  proceeds to block  418  for a manual reset of clutch  50 , as described herein. In one embodiment, capacitor  316  is sized to contain enough energy for moving clutch  50  to its home position based on a worst set of initial operating conditions where power interruptions could occur. 
     In one embodiment, vehicle  10  includes a mechanical return system for automatically positioning primary clutch  50  at the home position upon system power being removed. For example, a mechanical spring/linkage system is coupled to moveable sheave  102  (see  FIG. 5 ) of primary clutch  50  to position primary clutch  50  in its home position upon vehicle  10  being powered down. When power is returned to vehicle  10 , controller  36  operates normally to control primary clutch  50 , as described herein. 
     While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.