Abstract:
A continuously variable transmission for a vehicle comprises a primary pulley, a secondary pulley, and a belt entrained around both pulleys in an opposite manner between the fixed and movable sheaves thereof. One pulley carries a selectively deployable stop that may be placed into position to mechanically limit the range of motion between the fixed and movable sheaves. This establishes an actual maximum transmission ratio that is larger than the nominal minimum transmission ratio but smaller than the nominal maximum transmission ratio achievable by the transmission during normal operation thereof. When such a transmission is used on a utility vehicle attached to a substance dispensing applicator operatively driven by the vehicle&#39;s engine, the application rate stays substantially constant despite changes in engine speed when the user keeps the transmission upshifted to the actual maximum transmission ratio set by the position of the deployed stop.

Description:
TECHNICAL FIELD 
     This invention relates to a utility vehicle used for outdoor work purposes such as ground or turf grooming operations, construction activities, farm or ranch tasks, and the like. More particularly, this invention relates to a utility vehicle that has a traction drive train which includes a continuously variable transmission. 
     BACKGROUND OF THE INVENTION 
     Utility vehicles are small, open vehicles designed for carrying a driver and a passenger in a side-by-side configuration at the front of the vehicle with a load carrying dump box being situated behind them. When used in the ground or turf grooming industry, the vehicle dump box might carry a pile of dirt or sand, or a plurality of rolls of sod, or many other things that are typically used for establishing, grooming or repairing ground or turf surfaces, such as the grass or sand traps found on a golf course. In addition to their basic load carrying and transportation functions, utility vehicles are often used as a platform for directly carrying or for towing various other ground or turf working implements. The Workman® utility vehicles manufactured and sold by The Toro Company, the assignee of this invention, are typical utility vehicles of the type being described here. 
     Utility vehicles can be converted to sprayers by removing the dump box and by mounting a sprayer in its place. The sprayer includes a tank for holding a liquid, e.g., a liquid fertilizer, herbicide, pesticide or combination thereof, that is to be sprayed atop the ground or turf surface. The tank occupies much of the space that had previously been filled by the dump box. One or more spray booms are carried at the rear of the vehicle with the booms themselves carrying a plurality of laterally spaced, downwardly facing spray nozzles. A spray pump is coupled to a drive shaft of the engine of the vehicle for pumping the liquid out of the tank and through the nozzles on the booms for application to the ground or turf surface as the vehicle is driven over such surface. Since the rotational speed of the spray pump is governed by the rotational speed of the engine, the application rate of the spray liquid is proportional to the rotational speed of the engine. 
     The use of a belt type continuously variable transmission (CVT) in the drive train of a utility vehicle is documented in US Patent Application Publication 2005/0079937. The use of a CVT provides various advantages over the gear-shift based manual standard transmissions which have been more commonly used in utility vehicles. For one thing, a CVT is an automatic transmission that requires no manual shifting by the operator. Moreover, a CVT is able to provide smooth uninterrupted power without the shift steps and the resulting jerk of standard transmissions. 
     When a utility vehicle is used as a sprayer as described above, a desired application rate of the sprayed liquid, defined by the amount of spray per unit of area, can be achieved by calibrating and establishing a fixed rate of flow through the spray nozzles relative to the fixed gear ratio of the standard transmission when the utility vehicle is operated in a selected gear of the standard transmission. Then, when the vehicle is driven in the selected gear and since the spray pump and standard transmission are both directly driven by the engine, the application rate is insensitive to vehicle ground speed and will remain substantially constant whether the vehicle is on flat ground, or is going up a hill, or is going down a hill. For example, if going up a hill, the vehicle may slow down through engine lug, but the rotational speed of the spray pump will correspondingly slow down as it is also being driven by the engine. When going down a hill, the vehicle may speed up with the engine speed also increasing, but again the rotational speed of the spray pump will correspondingly increase. In either case, the application rate remains constant. 
     However, it is the nature of a CVT to provide a continuously changing and varying transmission ratio during operation of the vehicle. For example, when the vehicle is climbing a hill and the vehicle ground speed decreases, a CVT will automatically downshift to a lower transmission ratio. Conversely, when the vehicle is going down a hill and the vehicle ground speed increases, the CVT will automatically upshift to a higher transmission ratio. Transmission ratio is the number of times the output shaft of the CVT revolves for each revolution of the engine, a higher transmission ratio providing more revolutions of the output shaft of the CVT than a lower higher transmission ratio for each revolution of the engine. These constant changes in transmission ratio do not permit one to maintain a constant application rate as the rate of flow through the spray nozzles remains constant despite these variations in the vehicle ground speed. 
     In order to maintain a substantially constant application rate, one could attempt to create a feedback control loop that would change the rate of flow through the spray nozzles in concert with ground speed. However, this is a relatively expensive and complex control system that is not economically suited for the fairly simple spray operations of the type that would be conducted by utility vehicles. A simpler and more cost effective solution is desirable for allowing a CVT equipped utility vehicle to function as an effective sprayer. 
     SUMMARY OF THE INVENTION 
     One aspect of this invention relates to a belt type continuously variable transmission for the traction drive train of a vehicle. The transmission comprises at least one pulley comprising an axially fixed sheave and an axially movable sheave carried on a rotatable shaft. A flexible belt engages between the sheaves. A plurality of movable members are provided that are responsive to centrifugal force for pushing the fixed sheave towards the movable sheave to thereby change the position of the belt between the sheaves to continuously change a transmission ratio provided by the transmission between a nominal minimum transmission ratio and a nominal maximum transmission ratio. A selectively deployable stop is carried on the at least one pulley with the stop being selectively movable relative to the sheaves between a non-deployed position and at least one deployed position. The stop is configured such that in the non-deployed position thereof the stop has no effect on the transmission ratios available from the transmission such that the transmission can continuously shift between its nominal minimum and maximum transmission ratios. The stop is further configured such that in the at least one deployed position thereof the stop is repositioned on the at least one pulley to mechanically limit the relative motion between the fixed and movable sheaves to a range of motion that is smaller than a range of motion provided in normal operation of the transmission but without the stop protruding into the path of or interfering with the operation of the centrifugal force responsive members. Thus, the stop in the at least one deployed position thereof provides an actual maximum transmission ratio that is lower than the nominal maximum transmission ratio but higher than the nominal minimum transmission ratio with the centrifugal force responsive members still being able to operate to continuously shift the transmission between the nominal minimum transmission ratio and the actual maximum transmission ratio set by the position of the stop in the at least one deployed position thereof. 
     Another aspect of this invention relates to a utility vehicle for performing operations on a ground or turf surface. The utility vehicle comprises a frame that is supported for rolling over the ground by a plurality of ground engaging wheels. A prime mover is carried on the frame with the prime mover having a rotatable drive shaft. A drive train is operatively connected to at least one wheel for rotatably driving the at least one wheel for propelling the frame over the ground or turf surface. The drive train includes a belt type continuously variable transmission operatively connected between the drive shaft of the prime mover and the at least one wheel for driving the at least one wheel and thereby the frame at variable ground speeds. The transmission comprises at least one pulley comprising an axially fixed sheave and an axially movable sheave carried on a rotatable shaft, a flexible belt that engages between the sheaves, a plurality of movable members that are responsive to centrifugal force for pushing the fixed sheave towards the movable sheave to thereby change the position of the belt between the sheaves to continuously change a transmission ratio provided by the transmission between a nominal minimum transmission ratio and a nominal maximum transmission ratio, and a selectively deployable stop carried on the at least one pulley with the stop being selectively movable relative to the sheaves between a non-deployed position and at least one deployed position. The stop is configured such that in the non-deployed position thereof the stop has no effect on the transmission ratios available from the transmission such that the transmission can continuously shift between its nominal minimum and maximum transmission ratios. The stop is further configured such that in the at least one deployed position thereof the stop is repositioned on the at least one pulley to mechanically limit the relative motion between the fixed and movable sheaves to a range of motion that is smaller than a range of motion provided in normal operation of the transmission, whereby the stop in the at least one deployed position thereof provides an actual maximum transmission ratio that is lower than the nominal maximum transmission ratio but higher than the nominal minimum transmission ratio to limit a maximum ground speed of the frame. Finally, an applicator is operatively attached to the frame for being propelled over the ground or turf surface by motion of the frame over the ground or turf surface. The applicator is operatively powered directly or indirectly by the drive shaft of the prime mover for dispensing substances onto the ground or turf surface at an application rate that is proportional to the rotational speed of the drive shaft of the prime mover. A desired application rate for such substances can be calculated and set for the ground speed of the frame when the stop of the transmission is in the at least one deployed position thereof establishing the actual maximum transmission ratio. Thus, the application rate of the substance will remain substantially constant when the utility vehicle is operated by the user with the transmission upshifted to the actual maximum transmission ratio established by the at least one deployed position of the stop even though the rotational speed of the drive shaft of the prime mover may vary as the utility vehicle goes up or down hills. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This invention will be described more specifically in the following Detailed Description, when taken in conjunction with the following drawings, in which like reference numerals refer to like elements throughout. 
         FIG. 1  is a perspective view of a utility vehicle that incorporates the improved CVT of this invention; 
         FIG. 2  is a perspective view a portion of the vehicle of  FIG. 1 , particularly illustrating the drive train components of the vehicle taken from the front of the vehicle of  FIG. 1 ; 
         FIG. 3  is a perspective view similar to  FIG. 2  but taken from the rear of the vehicle of  FIG. 1 ; 
         FIG. 4  is a perspective view of a CVT that is part of the drive train of the vehicle of  FIG. 1 ; 
         FIG. 5  is a cross-sectional, partially exploded view of the cover of the CVT of  FIG. 4 , particularly illustrating the rotary union, the piston stop housed within a cylinder formed in the cover, and the retraction spring that have been added by this invention to the cover of the primary clutch of the CVT for the purpose of preventing full upshift of the CVT when the piston stop is extended by fluid pressure out of the cylinder in which the piston stop is housed in the cover; 
         FIG. 6  is a perspective view of a hand operated fluid cylinder that acts as pump that has been added by this invention to the vehicle for supplying fluid pressure to the cylinder in the cover of the primary clutch of the CVT to extend the piston stop and for withdrawing fluid pressure from the cylinder in the primary clutch of the CVT when the piston stop is to be retracted; and 
         FIGS. 7-9  are similar cross-sectional views of the primary clutch of the CVT illustrating the different gaps or differences in distance between the fixed and movable sheaves of the primary clutch for different operational conditions of the primary clutch and different positions of the piston stop, namely with  FIG. 7  illustrating the primary clutch at neutral with the piston stop fully retracted into the moveable sheave,  FIG. 8  illustrating the primary clutch at full shift with the piston stop fully retracted into the moveable sheave, and  FIG. 9  illustrating the primary clutch at full shift with the piston stop fully extended from the moveable sheave. 
     
    
    
     DETAILED DESCRIPTION 
     One embodiment of a utility vehicle which could advantageously use this invention is illustrated in  FIG. 1  generally as  2 . Vehicle  2  includes a frame  4  that is supported for rolling over the ground by a pair of front wheels  6  and a pair of rear wheels  8 . Vehicle  2  also includes a drive train, illustrated generally as  10  in  FIGS. 2 and 3 , for powering front wheels  6  and rear wheels  8  in a four wheel drive (4WD) configuration to cause vehicle  2  to be self-propelled. Vehicle  2  shown in  FIG. 1  is a utility vehicle from the Workman® line of utility vehicles manufactured and sold by The Toro Company, the assignee of this invention. 
     An open front compartment  12  is provided on frame  4  for carrying a driver and a passenger in side-by-side seats  14 . A hydraulically actuated, pivotal dump box  16  is carried on frame  4  and extends from behind front compartment  12  to the rear end of vehicle  2 . Front wheels  6  of vehicle  2  are steerable by the driver using a steering wheel  18  in advance of driver&#39;s seat  14 . A center console  20  between seats  14  carries various operational controls for drive train  10  and dump box  16 . One of the drive train controls, which will be discussed in detail hereafter, is newly added to console  20  as part of this invention. 
     Referring now to  FIGS. 2 and 3 , drive train  10  includes an internal combustion engine  22  that is mounted in any suitable manner on frame  4  beneath dump box  16 . Engine  22  has a crankshaft  24  with a forwardly projecting front end (not shown) and a rearwardly projecting rear end  26  that is visible in  FIG. 3 . The front and rear ends of engine crankshaft  24  serve as power take off (PTO) shafts. This allows the power of engine  22  to be used by the remaining components of drive train  10  for traction drive purposes via connection of such components to the front end of engine crankshaft  24 . This also allows engine  22  to power various auxiliary components via connection to rear end  26  of engine crankshaft  24 . These auxiliary components may comprise a first hydraulic fluid pump used for supplying pressurized hydraulic oil for power steering and/or for lifting and lowering dump box  16  through a hydraulic cylinder and/or an additional fluid pump used when vehicle  2  is converted to or equipped with a sprayer or other hydraulically powered implement. The sprayer or other implement could in some cases be alternatively directly mechanically driven from rear end  26  of crankshaft  24  rather than being indirectly hydraulically driven through the additional fluid pump. 
     Returning to the remaining components of drive train  10 , the front end of engine crankshaft  24  is coupled to the input shaft of a belt type continuously variable transmission (CVT) illustrated generally as  28  in  FIGS. 2 and 3 . Various shrouds or covers for CVT  28  have been removed in the figures of this application for the purpose of better illustrating CVT  28 . The output shaft of CVT  28  is the input to a gearbox  30  that provides the driver with the ability to select a high or low speed range or reverse. Gearbox  30  has two output shafts which drive a front differential  32  and a rear differential  34  through conventional connecting shafts  36  often referred to as propeller shafts or Cardan shafts. Front differential  32  is an automatically engaging differential that drives front wheels  6  of vehicle  2 . Rear differential  34  similarly drives rear wheels  8  of vehicle  2  but can be electrically locked when actuated by the driver when so desired for increased traction. 
     The belt type CVT  28  as used in vehicle  2  is itself generally well known in the vehicle art with the exception of various modifications to the cover of the primary clutch of CVT  28  as will be described in more detail hereafter. U.S. Pat. No. 6,149,540, which is hereby incorporated by reference, contains a useful description of a belt type CVT as used in this invention. However, a brief overall summary of the structure and operation of CVT  28  will now be set forth to allow the reader to better understand the improvements made to CVT  28  by this invention. 
     Referring now to  FIG. 4 , CVT  28  includes a primary clutch  38  and a secondary clutch  40  that are connected to one another by a rubber belt  42 . Each clutch  38 ,  40  has a central shaft  44  that carries a first sheave  46  that is fixed to central shaft  44 , referred to herein as fixed sheave  46 , and a second sheave  48  that is rotatively coupled to but is also axially slidable on central shaft  44 , referred to herein as movable sheave  48 . During operation of CVT  28 , movable sheave  48  of primary clutch  38  axially slides towards and away from fixed sheave  46  to vary the axial distance therebetween. Central shaft  44  of primary clutch  38  is rotatively coupled to the first end of engine crankshaft  24 . Central shaft  44  of secondary clutch  40  is rotatively coupled to the input shaft of gearbox  30 . 
     Movable sheave  48  of primary clutch  38  has a plurality of circumferentially spaced posts  50  that extend parallel to central shaft  44  of movable sheave  48  from a backside of the tapered belt engaging face of movable sheave  48 . A cover  52  is secured to posts  50  by a plurality of bolts (not shown) such that posts  50  and cover  52  form a cage like structure projecting to one side of movable sheave  48 . The cage like structure is, in effect, part of movable sheave  48  in terms of rotary and axial motion of movable sheave  48 . In addition, movable sheave  48  also includes a plurality of flyweights  54  that are pivotally secured between selected pairs of posts  50  for pivotal motion about a substantially horizontal axis. A portion of one flyweight  54  is visible in  FIG. 4 . 
     The cage like structure of movable sheave  48  of primary clutch  38  surrounds a spider  56  that is secured to central shaft  44  for rotation with central shaft  44 . Each arm  58  of spider  56  carries a laterally extending pin  60  with one arm  58  of spider  56  and one pin  60  being visible in  FIG. 4 . There are as many arms  58  and pins  60  on spider  56  as there are flyweights  54  on movable sheave  48 . Each 60 pin on spider  56  has one flyweight  54  adjacent thereto with a contoured body of flyweight  54  underlying pin  60 . 
     When engine  22  is rotating and primary clutch  38  is spinning, flyweights  54  will react to centrifugal force and will pivot upwardly to engage against pins  60  of movable sheave  48 . The contoured bodies of flyweights  54  will push against pins  60  to laterally shift movable sheave  48 , posts  50 , cover  52  and flyweights  54  as a single unit in a direction towards fixed sheave  46  to close the gap between the opposed tapered faces of fixed sheave  46  and movable sheave  48 . As this gap begins to close, primary clutch  38  first grips belt  42  with enough force to cause belt  42  to begin rotating to thereby transfer power to secondary clutch  40 . Eventually, as more and more force is exerted by flyweights  54  as the rotational speed of engine  22  continues to increase and CVT  28  continues to upshift, the additional lateral shifting of movable sheave  48  and the components carried thereby cause belt  42  to ride upwardly away from central shaft  44  towards the top of the belt engaging faces of fixed sheave  46  and movable sheave  48  as the gap gets progressively narrower. Eventually, at a full shift condition, belt  42  will have moved upwardly between fixed sheave  46  and movable sheave  48  of primary clutch  38  all the way from the bottom to the top of the sheaves with the diameter of belt  42  around primary clutch  38  having changed from a minimum diameter to a maximum diameter during this process. 
     The opposite action occurs within secondary clutch  40  of CVT  28 , which has a larger diameter than that of primary clutch  38 . As belt  42  begins to ascend between the faces of fixed sheave  46  and movable sheave  48  of primary clutch  38  and the diameter around primary clutch  38  increases, belt  42  gets tighter. The increasing force of belt  42  on fixed sheave  46  and movable sheave  48  of secondary clutch  40  (as well as any loads experienced by secondary clutch  40  from gearbox  30 ) progressively forces fixed sheave  46  and movable sheave  48  of secondary clutch  40  apart to widen the gap therebetween to allow belt  42  to begin to drop down between the belt engaging faces of fixed sheave  46  and movable sheave  48  of secondary clutch  40 . Eventually, at full shift belt  42  will have its maximum diameter around primary clutch  38  and its minimum diameter around secondary clutch  40 . 
     Thus, CVT  28  has a nominal minimum transmission ratio when belt  42  has been gripped enough to begin rotating but with belt  42  having its minimum diameter around primary clutch  38  and its maximum diameter around secondary clutch  40 . Belt  42  has a nominal maximum transmission ratio when CVT  28  has upshifted far enough that the reverse belt configuration has occurred, i.e. belt  42  has its maximum diameter around primary clutch  38  and its minimum diameter around secondary clutch  40 . As CVT  28  responds to engine rpm and load conditions in drive train  10 , it is able to smoothly vary the transmission ratio between these minimum and maximum ratios in a continuously or infinitely variable manner rather than in a stepwise manner. 
     The description of the structure and operation of CVT  28  provided above is true for many known belt type CVT&#39;s, including that shown in the &#39;540 patent incorporated by reference herein. No part of this prior description involves the improvement to CVT  28  that is involved in the embodiment of the invention under consideration here. That improvement and the reasons for it will now be described. 
     Referring now first to  FIGS. 5 and 6 , this invention is directed to a system that allows the driver of vehicle  2  to selectively establish at least one maximum transmission ratio for CVT  28  for use when vehicle  2  is operating that is lower than the nominal maximum transmission ratio for which CVT  28  was designed. This system has two primary parts: 1.) a selectively deployable stop added to primary clutch  38  of CVT  28  to prevent CVT  28  from fully upshifting during operation of vehicle  2 , and 2.) an actuator accessible to the driver to allow the driver to selectively deploy or not the stop as may be desired. The selectively deployable stop is illustrated generally as  62  in  FIG. 5 . The actuator is illustrated generally as  64  in  FIG. 6 . 
     In one embodiment as shown in  FIG. 5 , stop  62  includes a fluid operated piston stop  66  that is housed within a first cylinder  68  that is formed internally within cover  52  of primary clutch  38 . Piston stop  66  comprises a hollow tube  70  having an outwardly facing closed end  72  and an inwardly facing open end  74 . A spring  76  is inserted into hollow tube  70  with spring  76  having an inner end that bears against a portion of CVT  28  and an outer end that bears against closed end  72  of hollow tube  70 . When CVT  28  is assembled, spring  76  is normally under compression to thereby bias piston stop  66  formed by hollow tube  70  into a retracted position relative to primary clutch  38 . In the retracted position of piston stop  66 , closed end  72  of hollow tube  70  is brought into a close or abutting engagement with a cross wall  78  that marks the outer end of first cylinder  68  in which piston stop  66  is slidable. Piston stop  66  is designed to be fluid tight with first cylinder  68  with various seals (not shown) being provided between the outer diameter of piston stop  66  and the inner diameter of first cylinder  68 . 
     Cover  52  includes an adjacent second cylinder  80  that receives a cylindrical body  82  of a rotary union  84 . Rotary union  84  is shown in an exploded form pulled out of cover  52  in  FIG. 5  for the purpose of clarity. Second cylinder  80  containing rotary union  84  is separated from first cylinder  68  containing piston stop  66  by cross wall  78 . Cross wall  78  has a circular aperture  86  to permit fluid that has passed through an internal fluid supply passageway  88  in rotary union  84  to be received within first cylinder  68  to act against closed end  72  of hollow tube  70  that forms piston stop  66 . Fluid supply passageway  88  in rotary union  84  is supplied with fluid by a first supply hose  90  and a fitting  92  connected to the nipple  94  of rotary union  84 . First supply hose  90  and fitting  92  remain stationary as other portions of rotary union  84  rotate along with primary clutch  38 . Body  82  of rotary union  84  will be sealed against leakage with respect to second cylinder  80  in cover  52  in which rotary union  84  is housed. 
     Turning now to  FIG. 6 , actuator  64  in one embodiment comprises a hand operated, fluid supply pump  96  comprising a pump cylinder  98  that houses an internal pump piston (not shown in  FIG. 6 ). The pump piston has a stem  100  that extends upwardly through various seals such that an upper end of pump piston stem  100  is external of pump cylinder  98 . The lower end of pump cylinder  98  is pivotally coupled by a lower pivot pin  102  to various walls  104  in frame  4  of vehicle  2 . The upper end of pump piston stem  100  is pivotally connected by an upper pivot pin  106  to one arm of a bell crank  108 . 
     Bell crank  108  is pivotally connected to one wall  104  in frame  4  of vehicle  2  by a pivot shaft  110 . An elongated handle  112  is clamped or otherwise secured to the other arm of bell crank  108 . Handle  112  extends upwardly and forwardly from bell crank  108  and terminates in a knob  114  that is positioned above console  20  in front compartment  12  of vehicle  2  with handle  112  passing downwardly through a slot  116  (shown in  FIG. 1 ) in the top of console  20  to be secured to bell crank  108 . The driver can pivot handle  112  and thus bell crank  108  about the horizontal axis of pivot shaft  110  of bell crank  108  by moving the upper portion of handle  112  and knob  114  forwardly or rearwardly as shown by the arrows A and B in  FIG. 6 . 
     Handle  112  is shown in  FIG. 6  in its most forward position. Normally, handle  112  is laterally canted slightly to the side by a biasing device, such as a laterally acting spring (not shown), to allow handle  112  to abut against a detent plate  118  that is part of console  20  and that underlies slot  116  in the top of console  20 . As shown in  FIG. 6 , detent plate  118  has a first rather elongated detent d 1  at the front of detent plate  118  in which handle  112  is currently received in  FIG. 6 . The rear of detent plate  118  contains a plurality of four shorter, additional detents d 2 -d 5  with any one of these additional detents also being capable of holding and retaining handle  112  in a selected, adjusted position. To move handle  112  between the various positions afforded by detent plate  118 , the driver pulls handle  112  to the side to disengage it from detent plate  118  and then pivots detent plate  118  through slot  116  in console  20  in the appropriate direction A or B to align handle  112  with the selected detent. If the operator then releases handle  112 , the bias of the biasing device will tilt handle  112  into engagement with the selected detent and hold handle  112  in that detent. 
     Pump cylinder  98  has an upper fluid supply port  120  and a lower fluid supply port  122 . Lower fluid supply port  122  is connected by first supply hose  90  to rotary union  84  as previously described. Upper fluid supply port  120  is connected by a second fluid supply hose  124  to a reservoir  126  fixed or attached in some fashion to frame  4  of vehicle  2 . Reservoir  126  contains an incompressible fluid. It is the purpose of pump  96  to pump fluid to rotary union  84  in primary clutch  38  of CVT  28  when the driver pivots handle  112  from the position in which it is shown in  FIG. 6  in the direction of arrow B in  FIG. 6 . This pivoting motion causes the pump piston to descend within pump cylinder  98  to afford a pump stroke. The fluid passing into primary clutch  38  of CVT  28  is what acts on piston stop  66  to extend piston stop  66  inwardly relative to cover  52  of primary clutch  38  of CVT  28 . When the pivoting motion of handle  112  is reversed with handle  112  now being moved back in the direction of arrow A in  FIG. 6 , the pump piston rises upwardly within pump cylinder  98  in a vacuum stroke to help drain or pull back the fluid that had previously been pumped against piston stop  66 . This is aided by spring  76  acting to return piston stop  66  to its retracted position in first cylinder  68  in cover  52  of primary clutch  38  of CVT  28 . 
     When the pump piston has risen to its uppermost position in pump cylinder  98 , a bypass (not shown) in pump cylinder  98  is opened between upper port  120  and lower supply port  122  to allow any air bubbles that might have accumulated in the fluid being directed to CVT  28  to escape or be vented to atmosphere through reservoir  126 . This helps the system of this invention remain properly calibrated so that repeated cycles of operation of pump  96  provide substantially the same result in how far piston stop  66  is extended from cover  52  of primary clutch  38  of CVT  28 . An accumulation of air bubbles in the fluid would otherwise eventually lead to an error in how far piston stop  66  is extended. 
       FIGS. 7-9  illustrate the operation of the system of this invention. For the most part and in many uses of vehicle  2 , handle  112  of the pump  96  will be in the position shown in  FIG. 6 , namely with handle  112  against the leading edge of the large front detent d 1 . In this position, piston stop  66  is fully retracted into first cylinder  68  in cover  52  of primary clutch  38  of CVT  28  and has no effect on the operation of CVT  28 . 
       FIG. 7  illustrates CVT  28  with piston stop  66  fully retracted and with CVT  28  in neutral at an engine idle speed prior to CVT  28  engaging against belt  42  with enough force to begin rotation of belt  42 . In this condition, fixed sheave  46  and movable sheave  48  of primary clutch  38  are spaced apart as far as they ever get with a maximum gap or distance being shown between them. This gap or distance is designated g in  FIG. 7 . 
     As engine rpm increases due to the driver stepping on the accelerator pedal and flyweights  54  in primary clutch  38  begin to pivot upwardly under the influence of centrifugal force, CVT  28  will upshift in its usual manner from its minimum transmission ratio to its maximum transmission ratio.  FIG. 8  illustrates CVT  28  at full shift with piston stop  66  fully retracted as handle  112  remains in the position of  FIG. 6 . In this condition, fixed sheave  46  and movable sheave  48  of primary clutch  38  are as close to one another as they ever get with the gap or distance between them having disappeared at the bottom of the sheaves and with the gap or distance being much smaller everywhere else compared to  FIG. 7 . See the distance g 1  in  FIG. 8  and compare to the distance g in  FIG. 7 . The difference between g 1  and g is sufficient to cause belt  42  to have ascended all the way to the top of fixed sheave  46  and movable sheave  48  of primary clutch  38  with belt  42  correspondingly lowering between fixed sheave  46  and movable sheave  48  of secondary clutch  40 . Inwardly facing end  74  of hollow tube  70  that forms the retracted piston stop  66  remains spaced from hub  57  of spider  56  by the small distance x in  FIG. 8  even at full shift of CVT  28  as long as piston stop  66  is fully retracted. 
     However, look at what happens when handle  112  of the fluid supply pump is selectively pivoted rearwardly by the driver in the direction of the arrow B in  FIG. 6  all the way through slot  116  until handle  112  is received in detent d 2  that is farthest to the rear in detent plate  118 . In this situation and when fluid supply pump  96  is properly calibrated, the pivoting of handle  112  causes the pump piston to pump a measured amount of fluid into first cylinder  68  in cover  52  of primary clutch  38  to extend piston stop  66  out of cover  52  in an inward direction relative to cover  52  by a predetermined distance. This is the condition shown in  FIG. 9 . Note that piston stop  66  has been extended out of first cylinder  68  compared to its retracted position as shown in  FIGS. 7 and 8 . In  FIG. 9 , piston stop  66  is in what would be its fully extended position. 
     Now, with piston stop  66  in its fully extended position, inwardly facing end  74  of hollow tube  70  that forms piston stop  66  will engage against hub  57  of spider  56  during operation of CVT  28  at some point that is well short of full shift. When such abutment occurs, CVT  28  becomes locked against further upshifting. This results in fixed sheave  46  and movable sheave  48  of CVT  28  having been moved towards one another by a distance that is much smaller than at full shift with no further movement towards one another being possible. This is shown by the distance g 2  in  FIG. 9 . Note that g 2  in  FIG. 9  is somewhat less than g in  FIG. 7  meaning the transmission has been able to upshift to a higher transmission ratio from its nominal minimum transmission ratio. However, g 2  in  FIG. 9  is considerably greater than g 1  in  FIG. 8  meaning that the maximum transmission ratio as established by the position of piston stop  66  in  FIG. 9  will be substantially lower than the nominal maximum transmission ratio of CVT  28 . 
     Desirably, when vehicle  2  is equipped with or converted to a sprayer, the substantially lower maximum transmission ratio as compared to the nominal maximum transmission ratio will be set low enough that it will be reached at a fairly low vehicle ground speed on flat ground, e.g. 3 mph or so. By maintaining a reasonably high engine rpm during operation, it will be fairly simple for the driver to keep vehicle  2  operating with the CVT continuously upshifted to the lowered maximum transmission ratio that has been chosen by the position of piston stop  66  even when vehicle  2  is driving over varying terrain. This then allows the application rate of any spray being put down by vehicle  2  to remain substantially constant as vehicle  2  goes from flat ground to uphill or downhill situations as the transmission ratio is being held at the lowered maximum transmission ratio, thereby allowing a computation of how much spray flow is required relative to the lowered maximum transmission ratio to achieve a desired application rate. Accordingly, even with the use of CVT  28  in drive train  10  of vehicle  2 , the use of piston stop  66  to establish a lowered maximum transmission ratio in CVT  28  while spraying enables more effective use of vehicle  2  as a sprayer since the application rate of the spray, again measured by the amount of spray per unit of area, will remain substantially constant. Thus, the performance of vehicle  2  in this situation will be comparable to the performance of a vehicle  2  that utilizes a gear-shift based manual standard transmission even though vehicle  2  is equipped with CVT  28 . 
     While the above description refers to use of vehicle  2  as a sprayer, the same rationale for using piston stop  66  would apply when vehicle  2  is being used for the application of other substances to the ground or turf surface that are desirably applied at a substantially constant application rate even when vehicle  2  is equipped with CVT  28 . Such other uses would include, but not be limited to, use of vehicle  2  as a topdresser which applies a blended soil mixture over the surface of turf grass or as a spreader which applies a dry particulate fertilizer to the ground or turf surface. 
     The other detents d 3 -d 5  allow the driver to set other lower maximum transmission ratios in CVT  28  that are higher than the lower maximum transmission ratio set when handle  112  is in detent d 2  but are lower than the nominal maximum transmission ratio set when handle  112  is in detent d 1 . For example, this would make it possible for the driver to conveniently keep vehicle  2  operating at any one of a plurality of predetermined speeds that are lower than the usual transport speed, e.g. at 3 mph at detent d 2 , 6 mph at detent d 3 , and so on. A particular lowered speed may be desirable when vehicle  2  is equipped with ground working or grooming implements other than a sprayer, such as a top dresser. Or, an inexperienced driver may be required by his or her supervisor to drive vehicle  2  at a reduced speed by maintaining handle  112  in one of detents d 2 -d 5 . 
     Various modifications of this invention will be apparent to those skilled in the art. While the use of a fluid operated piston stop  66  as described herein is preferred for durability reasons, other types of stops including stops that are mechanically moved between their retracted and extended positions could be used on cover  52  of primary clutch  38  of CVT  28 . Alternatively, rather than controlling moveable sheave  48  of primary clutch  38 , the improvements of this invention could be used instead to control moveable sheave  48  of secondary clutch  40  in a similar manner as described herein. Thus, this invention is not to be limited to the details of the embodiment thereof as described herein.