Utility vehicle with a continuously variable transmission having a system for selectively establishing a fixed maximum transmission ratio

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'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.

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.

DETAILED DESCRIPTION

One embodiment of a utility vehicle which could advantageously use this invention is illustrated inFIG. 1generally as2. Vehicle2includes a frame4that is supported for rolling over the ground by a pair of front wheels6and a pair of rear wheels8. Vehicle2also includes a drive train, illustrated generally as10inFIGS. 2 and 3, for powering front wheels6and rear wheels8in a four wheel drive (4WD) configuration to cause vehicle2to be self-propelled. Vehicle2shown inFIG. 1is 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 compartment12is provided on frame4for carrying a driver and a passenger in side-by-side seats14. A hydraulically actuated, pivotal dump box16is carried on frame4and extends from behind front compartment12to the rear end of vehicle2. Front wheels6of vehicle2are steerable by the driver using a steering wheel18in advance of driver's seat14. A center console20between seats14carries various operational controls for drive train10and dump box16. One of the drive train controls, which will be discussed in detail hereafter, is newly added to console20as part of this invention.

Referring now toFIGS. 2 and 3, drive train10includes an internal combustion engine22that is mounted in any suitable manner on frame4beneath dump box16. Engine22has a crankshaft24with a forwardly projecting front end (not shown) and a rearwardly projecting rear end26that is visible inFIG. 3. The front and rear ends of engine crankshaft24serve as power take off (PTO) shafts. This allows the power of engine22to be used by the remaining components of drive train10for traction drive purposes via connection of such components to the front end of engine crankshaft24. This also allows engine22to power various auxiliary components via connection to rear end26of engine crankshaft24. 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 box16through a hydraulic cylinder and/or an additional fluid pump used when vehicle2is 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 end26of crankshaft24rather than being indirectly hydraulically driven through the additional fluid pump.

Returning to the remaining components of drive train10, the front end of engine crankshaft24is coupled to the input shaft of a belt type continuously variable transmission (CVT) illustrated generally as28inFIGS. 2 and 3. Various shrouds or covers for CVT28have been removed in the figures of this application for the purpose of better illustrating CVT28. The output shaft of CVT28is the input to a gearbox30that provides the driver with the ability to select a high or low speed range or reverse. Gearbox30has two output shafts which drive a front differential32and a rear differential34through conventional connecting shafts36often referred to as propeller shafts or Cardan shafts. Front differential32is an automatically engaging differential that drives front wheels6of vehicle2. Rear differential34similarly drives rear wheels8of vehicle2but can be electrically locked when actuated by the driver when so desired for increased traction.

The belt type CVT28as used in vehicle2is itself generally well known in the vehicle art with the exception of various modifications to the cover of the primary clutch of CVT28as 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 CVT28will now be set forth to allow the reader to better understand the improvements made to CVT28by this invention.

Referring now toFIG. 4, CVT28includes a primary clutch38and a secondary clutch40that are connected to one another by a rubber belt42. Each clutch38,40has a central shaft44that carries a first sheave46that is fixed to central shaft44, referred to herein as fixed sheave46, and a second sheave48that is rotatively coupled to but is also axially slidable on central shaft44, referred to herein as movable sheave48. During operation of CVT28, movable sheave48of primary clutch38axially slides towards and away from fixed sheave46to vary the axial distance therebetween. Central shaft44of primary clutch38is rotatively coupled to the first end of engine crankshaft24. Central shaft44of secondary clutch40is rotatively coupled to the input shaft of gearbox30.

Movable sheave48of primary clutch38has a plurality of circumferentially spaced posts50that extend parallel to central shaft44of movable sheave48from a backside of the tapered belt engaging face of movable sheave48. A cover52is secured to posts50by a plurality of bolts (not shown) such that posts50and cover52form a cage like structure projecting to one side of movable sheave48. The cage like structure is, in effect, part of movable sheave48in terms of rotary and axial motion of movable sheave48. In addition, movable sheave48also includes a plurality of flyweights54that are pivotally secured between selected pairs of posts50for pivotal motion about a substantially horizontal axis. A portion of one flyweight54is visible inFIG. 4.

The cage like structure of movable sheave48of primary clutch38surrounds a spider56that is secured to central shaft44for rotation with central shaft44. Each arm58of spider56carries a laterally extending pin60with one arm58of spider56and one pin60being visible inFIG. 4. There are as many arms58and pins60on spider56as there are flyweights54on movable sheave48. Each 60 pin on spider56has one flyweight54adjacent thereto with a contoured body of flyweight54underlying pin60.

When engine22is rotating and primary clutch38is spinning, flyweights54will react to centrifugal force and will pivot upwardly to engage against pins60of movable sheave48. The contoured bodies of flyweights54will push against pins60to laterally shift movable sheave48, posts50, cover52and flyweights54as a single unit in a direction towards fixed sheave46to close the gap between the opposed tapered faces of fixed sheave46and movable sheave48. As this gap begins to close, primary clutch38first grips belt42with enough force to cause belt42to begin rotating to thereby transfer power to secondary clutch40. Eventually, as more and more force is exerted by flyweights54as the rotational speed of engine22continues to increase and CVT28continues to upshift, the additional lateral shifting of movable sheave48and the components carried thereby cause belt42to ride upwardly away from central shaft44towards the top of the belt engaging faces of fixed sheave46and movable sheave48as the gap gets progressively narrower. Eventually, at a full shift condition, belt42will have moved upwardly between fixed sheave46and movable sheave48of primary clutch38all the way from the bottom to the top of the sheaves with the diameter of belt42around primary clutch38having changed from a minimum diameter to a maximum diameter during this process.

The opposite action occurs within secondary clutch40of CVT28, which has a larger diameter than that of primary clutch38. As belt42begins to ascend between the faces of fixed sheave46and movable sheave48of primary clutch38and the diameter around primary clutch38increases, belt42gets tighter. The increasing force of belt42on fixed sheave46and movable sheave48of secondary clutch40(as well as any loads experienced by secondary clutch40from gearbox30) progressively forces fixed sheave46and movable sheave48of secondary clutch40apart to widen the gap therebetween to allow belt42to begin to drop down between the belt engaging faces of fixed sheave46and movable sheave48of secondary clutch40. Eventually, at full shift belt42will have its maximum diameter around primary clutch38and its minimum diameter around secondary clutch40.

Thus, CVT28has a nominal minimum transmission ratio when belt42has been gripped enough to begin rotating but with belt42having its minimum diameter around primary clutch38and its maximum diameter around secondary clutch40. Belt42has a nominal maximum transmission ratio when CVT28has upshifted far enough that the reverse belt configuration has occurred, i.e. belt42has its maximum diameter around primary clutch38and its minimum diameter around secondary clutch40. As CVT28responds to engine rpm and load conditions in drive train10, 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 CVT28provided above is true for many known belt type CVT's, including that shown in the '540 patent incorporated by reference herein. No part of this prior description involves the improvement to CVT28that 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 toFIGS. 5 and 6, this invention is directed to a system that allows the driver of vehicle2to selectively establish at least one maximum transmission ratio for CVT28for use when vehicle2is operating that is lower than the nominal maximum transmission ratio for which CVT28was designed. This system has two primary parts: 1.) a selectively deployable stop added to primary clutch38of CVT28to prevent CVT28from fully upshifting during operation of vehicle2, 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 as62inFIG. 5. The actuator is illustrated generally as64inFIG. 6.

In one embodiment as shown inFIG. 5, stop62includes a fluid operated piston stop66that is housed within a first cylinder68that is formed internally within cover52of primary clutch38. Piston stop66comprises a hollow tube70having an outwardly facing closed end72and an inwardly facing open end74. A spring76is inserted into hollow tube70with spring76having an inner end that bears against a portion of CVT28and an outer end that bears against closed end72of hollow tube70. When CVT28is assembled, spring76is normally under compression to thereby bias piston stop66formed by hollow tube70into a retracted position relative to primary clutch38. In the retracted position of piston stop66, closed end72of hollow tube70is brought into a close or abutting engagement with a cross wall78that marks the outer end of first cylinder68in which piston stop66is slidable. Piston stop66is designed to be fluid tight with first cylinder68with various seals (not shown) being provided between the outer diameter of piston stop66and the inner diameter of first cylinder68.

Cover52includes an adjacent second cylinder80that receives a cylindrical body82of a rotary union84. Rotary union84is shown in an exploded form pulled out of cover52inFIG. 5for the purpose of clarity. Second cylinder80containing rotary union84is separated from first cylinder68containing piston stop66by cross wall78. Cross wall78has a circular aperture86to permit fluid that has passed through an internal fluid supply passageway88in rotary union84to be received within first cylinder68to act against closed end72of hollow tube70that forms piston stop66. Fluid supply passageway88in rotary union84is supplied with fluid by a first supply hose90and a fitting92connected to the nipple94of rotary union84. First supply hose90and fitting92remain stationary as other portions of rotary union84rotate along with primary clutch38. Body82of rotary union84will be sealed against leakage with respect to second cylinder80in cover52in which rotary union84is housed.

Turning now toFIG. 6, actuator64in one embodiment comprises a hand operated, fluid supply pump96comprising a pump cylinder98that houses an internal pump piston (not shown inFIG. 6). The pump piston has a stem100that extends upwardly through various seals such that an upper end of pump piston stem100is external of pump cylinder98. The lower end of pump cylinder98is pivotally coupled by a lower pivot pin102to various walls104in frame4of vehicle2. The upper end of pump piston stem100is pivotally connected by an upper pivot pin106to one arm of a bell crank108.

Bell crank108is pivotally connected to one wall104in frame4of vehicle2by a pivot shaft110. An elongated handle112is clamped or otherwise secured to the other arm of bell crank108. Handle112extends upwardly and forwardly from bell crank108and terminates in a knob114that is positioned above console20in front compartment12of vehicle2with handle112passing downwardly through a slot116(shown inFIG. 1) in the top of console20to be secured to bell crank108. The driver can pivot handle112and thus bell crank108about the horizontal axis of pivot shaft110of bell crank108by moving the upper portion of handle112and knob114forwardly or rearwardly as shown by the arrows A and B inFIG. 6.

Handle112is shown inFIG. 6in its most forward position. Normally, handle112is laterally canted slightly to the side by a biasing device, such as a laterally acting spring (not shown), to allow handle112to abut against a detent plate118that is part of console20and that underlies slot116in the top of console20. As shown inFIG. 6, detent plate118has a first rather elongated detent d1at the front of detent plate118in which handle112is currently received inFIG. 6. The rear of detent plate118contains a plurality of four shorter, additional detents d2-d5with any one of these additional detents also being capable of holding and retaining handle112in a selected, adjusted position. To move handle112between the various positions afforded by detent plate118, the driver pulls handle112to the side to disengage it from detent plate118and then pivots detent plate118through slot116in console20in the appropriate direction A or B to align handle112with the selected detent. If the operator then releases handle112, the bias of the biasing device will tilt handle112into engagement with the selected detent and hold handle112in that detent.

Pump cylinder98has an upper fluid supply port120and a lower fluid supply port122. Lower fluid supply port122is connected by first supply hose90to rotary union84as previously described. Upper fluid supply port120is connected by a second fluid supply hose124to a reservoir126fixed or attached in some fashion to frame4of vehicle2. Reservoir126contains an incompressible fluid. It is the purpose of pump96to pump fluid to rotary union84in primary clutch38of CVT28when the driver pivots handle112from the position in which it is shown inFIG. 6in the direction of arrow B inFIG. 6. This pivoting motion causes the pump piston to descend within pump cylinder98to afford a pump stroke. The fluid passing into primary clutch38of CVT28is what acts on piston stop66to extend piston stop66inwardly relative to cover52of primary clutch38of CVT28. When the pivoting motion of handle112is reversed with handle112now being moved back in the direction of arrow A inFIG. 6, the pump piston rises upwardly within pump cylinder98in a vacuum stroke to help drain or pull back the fluid that had previously been pumped against piston stop66. This is aided by spring76acting to return piston stop66to its retracted position in first cylinder68in cover52of primary clutch38of CVT28.

When the pump piston has risen to its uppermost position in pump cylinder98, a bypass (not shown) in pump cylinder98is opened between upper port120and lower supply port122to allow any air bubbles that might have accumulated in the fluid being directed to CVT28to escape or be vented to atmosphere through reservoir126. This helps the system of this invention remain properly calibrated so that repeated cycles of operation of pump96provide substantially the same result in how far piston stop66is extended from cover52of primary clutch38of CVT28. An accumulation of air bubbles in the fluid would otherwise eventually lead to an error in how far piston stop66is extended.

FIGS. 7-9illustrate the operation of the system of this invention. For the most part and in many uses of vehicle2, handle112of the pump96will be in the position shown inFIG. 6, namely with handle112against the leading edge of the large front detent d1. In this position, piston stop66is fully retracted into first cylinder68in cover52of primary clutch38of CVT28and has no effect on the operation of CVT28.

FIG. 7illustrates CVT28with piston stop66fully retracted and with CVT28in neutral at an engine idle speed prior to CVT28engaging against belt42with enough force to begin rotation of belt42. In this condition, fixed sheave46and movable sheave48of primary clutch38are 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 inFIG. 7.

As engine rpm increases due to the driver stepping on the accelerator pedal and flyweights54in primary clutch38begin to pivot upwardly under the influence of centrifugal force, CVT28will upshift in its usual manner from its minimum transmission ratio to its maximum transmission ratio.FIG. 8illustrates CVT28at full shift with piston stop66fully retracted as handle112remains in the position ofFIG. 6. In this condition, fixed sheave46and movable sheave48of primary clutch38are 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 toFIG. 7. See the distance g1inFIG. 8and compare to the distance g inFIG. 7. The difference between g1and g is sufficient to cause belt42to have ascended all the way to the top of fixed sheave46and movable sheave48of primary clutch38with belt42correspondingly lowering between fixed sheave46and movable sheave48of secondary clutch40. Inwardly facing end74of hollow tube70that forms the retracted piston stop66remains spaced from hub57of spider56by the small distance x inFIG. 8even at full shift of CVT28as long as piston stop66is fully retracted.

However, look at what happens when handle112of the fluid supply pump is selectively pivoted rearwardly by the driver in the direction of the arrow B inFIG. 6all the way through slot116until handle112is received in detent d2that is farthest to the rear in detent plate118. In this situation and when fluid supply pump96is properly calibrated, the pivoting of handle112causes the pump piston to pump a measured amount of fluid into first cylinder68in cover52of primary clutch38to extend piston stop66out of cover52in an inward direction relative to cover52by a predetermined distance. This is the condition shown inFIG. 9. Note that piston stop66has been extended out of first cylinder68compared to its retracted position as shown inFIGS. 7 and 8. InFIG. 9, piston stop66is in what would be its fully extended position.

Now, with piston stop66in its fully extended position, inwardly facing end74of hollow tube70that forms piston stop66will engage against hub57of spider56during operation of CVT28at some point that is well short of full shift. When such abutment occurs, CVT28becomes locked against further upshifting. This results in fixed sheave46and movable sheave48of CVT28having 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 g2inFIG. 9. Note that g2inFIG. 9is somewhat less than g inFIG. 7meaning the transmission has been able to upshift to a higher transmission ratio from its nominal minimum transmission ratio. However, g2inFIG. 9is considerably greater than g1inFIG. 8meaning that the maximum transmission ratio as established by the position of piston stop66inFIG. 9will be substantially lower than the nominal maximum transmission ratio of CVT28.

Desirably, when vehicle2is 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 vehicle2operating with the CVT continuously upshifted to the lowered maximum transmission ratio that has been chosen by the position of piston stop66even when vehicle2is driving over varying terrain. This then allows the application rate of any spray being put down by vehicle2to remain substantially constant as vehicle2goes 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 CVT28in drive train10of vehicle2, the use of piston stop66to establish a lowered maximum transmission ratio in CVT28while spraying enables more effective use of vehicle2as 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 vehicle2in this situation will be comparable to the performance of a vehicle2that utilizes a gear-shift based manual standard transmission even though vehicle2is equipped with CVT28.

While the above description refers to use of vehicle2as a sprayer, the same rationale for using piston stop66would apply when vehicle2is 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 vehicle2is equipped with CVT28. Such other uses would include, but not be limited to, use of vehicle2as 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 d3-d5allow the driver to set other lower maximum transmission ratios in CVT28that are higher than the lower maximum transmission ratio set when handle112is in detent d2but are lower than the nominal maximum transmission ratio set when handle112is in detent d1. For example, this would make it possible for the driver to conveniently keep vehicle2operating at any one of a plurality of predetermined speeds that are lower than the usual transport speed, e.g. at 3 mph at detent d2, 6 mph at detent d3, and so on. A particular lowered speed may be desirable when vehicle2is 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 vehicle2at a reduced speed by maintaining handle112in one of detents d2-d5.

Various modifications of this invention will be apparent to those skilled in the art. While the use of a fluid operated piston stop66as 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 cover52of primary clutch38of CVT28. Alternatively, rather than controlling moveable sheave48of primary clutch38, the improvements of this invention could be used instead to control moveable sheave48of secondary clutch40in a similar manner as described herein. Thus, this invention is not to be limited to the details of the embodiment thereof as described herein.