System and method for enhancing the operation of a continuously variable transmission of a work vehicle

In one aspect, a computer-implemented method for enhancing the performance of a continuously variable transmission of a work vehicle may include engaging a range clutch of the continuously variable transmission, cycling a directional clutch of the continuously variable transmission between an engaged state and a disengaged state while the range clutch is engaged and controlling a position of a swash plate of the continuously variable transmission such that a ground speed of the work vehicle is maintained substantially at zero while the directional clutch is cycled between the engaged and disengaged states.

FIELD OF THE INVENTION

The present subject matter relates generally to continuously variable transmissions (CVTs) utilized within work vehicles and, more particularly, to a system and method for enhancing the operation of a work vehicle CVT.

BACKGROUND OF THE INVENTION

Transmissions with hydraulically operated clutches (e.g., continuously variable transmissions (CVTs)) are well known in the art. When operating such transmissions, it is important to accurately control clutch engagement in order to provide the desired vehicle performance. However, due to tolerances within the clutch valve and errors associated with the controller's ability to command the correct current, the pressure needed to move the clutch's actuator (e.g., a hydraulically actuated piston) to the point at which the clutch plates touch and the clutch begins to transmit torque can vary significantly. As a result, it is often necessary to calibrate transmission clutches to ensure that the proper clutch pressures are being supplied for engaging each clutch.

When performing a clutch calibration, the accuracy of the calibration process may often be impacted by imperfections, inconsistencies and/or other mechanical and relates issues within the transmission. For example, air bubbles/pockets trapped within the hydraulic system can cause a clutch to calibrate to a different current value than the value that will be required once the trapped air has been removed. Similarly, mechanical issues, such as friction between one or more of the clutch components, shifting of one or more of the clutch components at start-up, the lack of or excessive seal wear, burrs on metal components and/or the like, may also result in inaccuracies within clutch calibration values.

Accordingly, a system and method that enhances the operation of a CVT, such as by allowing more accurate clutch calibrations to be performed, would be welcomed in the technology.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, the present subject matter is directed to a computer-implemented method for enhancing the performance of a continuously variable transmission of a work vehicle. The method may generally include engaging a range clutch of the continuously variable transmission, cycling a directional clutch of the continuously variable transmission between an engaged state and a disengaged state while the range clutch is engaged and controlling a position of a swash plate of the continuously variable transmission such that a ground speed of the work vehicle is maintained substantially at zero while the directional clutch is cycled between the engaged and disengaged states.

In another aspect, the present subject matter is directed to a computer-implemented method for enhancing the performance of a continuously variable transmission of a work vehicle. The method may generally include engaging a directional clutch of the continuously variable transmission, cycling a range clutch of the continuously variable transmission between an engaged state and a disengaged state while the directional clutch is engaged and controlling a position of a swash plate of the continuously variable transmission such that a ground speed of the work vehicle is maintained substantially at zero while the range clutch is cycled between the engaged and disengaged states.

In a further aspect, the present subject matter is directed to a system for enhancing the performance of a work vehicle. The system may include a continuously variable transmission having a first directional clutch, a second directional clutch and a plurality of range clutches. The transmission may also include a hydrostatic power unit having a pump in fluid communication with a motor. The pump may include a swash plate. The system may also include a controller communicatively coupled to the first directional clutch, the second directional clutch, the plurality of range clutches and the hydrostatic power unit. The controller may be configured to engage one of the plurality of range clutches, cycle the first directional clutch between an engaged state and a disengaged state while the range clutch is engaged and control a position of the swash plate such that a ground speed of the work vehicle is maintained substantially at zero while the first directional clutch is cycled between the engaged and disengaged states.

DETAILED DESCRIPTION OF THE INVENTION

In general, the present subject matter is directed to a system and method for enhancing the operation of a continuously variable transmission (CVT) of a work vehicle. Specifically, in several embodiments, the disclosed system and method may provide a means for automatically and repeatedly cycling one or more clutches of the CVT between engaged and disengaged states, which may allow for the CVT to be broken-in and/or warmed-up prior to operation of the work vehicle and/or prior to the performance of a maintenance operation on the CVT. For instance, for both new and old work vehicles, various system inconsistencies, imperfections and/or other issues may be present due to non-use, wear, manufacturing tolerances and/or the like. Such issues may, for example, include, but are not limited to, air bubbles/pockets trapped in the fluid lines and/or other components of the hydraulic system, friction between one or more of the clutch components, shifting of one or more of the clutch components at start-up, the lack of or excessive seal wear, burrs on metal components and/or the like. By cycling one or more of the transmission clutches in accordance with aspects of the present subject matter, such issues may be eliminated or, at the very least, their impact on the overall performance of the transmission may be reduced.

For example, clutch calibrations are often performed on brand new vehicles at the manufacturing plant by plant technicians. When performing such a calibration on a newly manufactured vehicle, it is often the case that small bubbles or pockets of air may be trapped within one or more of the components of the hydraulic system (e.g., within the valve, fluid lines and/or the clutch actuator), which leads to inaccuracies in the resulting clutch calibration values. For instance, while the air is trapped within the system, it may be determined during the calibration that a specific current command is needed to properly engage a given clutch. However, when the air is no longer within the system (e.g., after several hours of operation), the current command resulting from the calibration may no longer be adequate to achieve the required clutch torque. Similarly, for work vehicles that have been operating in the field for an extended period of time, mechanical issues and/or imperfections (e.g., friction, metal burrs, shifting components, uneven seal wear, etc.) may be present that can lead to similar inaccuracies in subsequent clutch calibrations performed by service technicians. Thus, in accordance with aspects of the present subject matter, one or more of the clutches of a CVT may be cycled immediately prior to the performance of a clutch calibration to flush out any trapped air and/or to eliminate any mechanical or other issues. As a result, the accuracy of the subsequent clutch calibration may be significantly improved, thereby allow for the overall operation of the CVT to be enhanced.

Referring now to the drawings,FIG. 1illustrates a side view of one embodiment of a work vehicle10. As shown, the work vehicle10is configured as an agricultural tractor. However, in other embodiments, the work vehicle10may be configured as any other suitable work vehicle known in the art, such as various other agricultural vehicles, earth-moving vehicles, loaders and/or various other off-road vehicles.

As shown inFIG. 1, the work vehicle10includes a pair of front wheels12, a pair or rear wheels14and a chassis16coupled to and supported by the wheels12,14. An operator's cab18may be supported by a portion of the chassis16and may house various control or input devices20,21,22(e.g., levers, pedals, control panels, buttons and/or the like) for permitting an operator to control the operation of the work vehicle10. For instance, as shown inFIG. 1, the work vehicle10may include a Forward-Neutral-Reverse-Park (FNRP) lever20and a clutch pedal21. In addition, the work vehicle10may include a display panel22for displaying message windows and/or alerts to the operator and/or for allowing the operator to interface with the vehicle's controller. For instance, in one embodiment, the display panel22may include a touch screen and/or associated buttons or other input devices that allow the operator to provide user inputs to the controller.

Moreover, the work vehicle10may include an engine23and a transmission24mounted on the chassis16. The transmission24may be operably coupled to the engine23and may provide variably adjusted gear ratios for transferring engine power to the wheels14via an axle/differential26. The engine23, transmission24, and axle/differential26may collectively define a drivetrain28of the work vehicle10.

It should be appreciated that the configuration of the work vehicle10described above and shown inFIG. 1is provided only to place the present subject matter in an exemplary field of use. Thus, it should be appreciated that the present subject matter may be readily adaptable to any manner of work vehicle configuration10. For example, in an alternative embodiment, a separate frame or chassis may be provided to which the engine23, transmission24, and differential26are coupled, a configuration common in smaller tractors. Still other configurations may use an articulated chassis to steer the work vehicle10, or rely on tracks in lieu of the wheels12,14. Additionally, although not shown, the work vehicle10may also be configured to be operably coupled to any suitable type of work implement, such as a trailer, spray boom, manure tank, feed grinder, plow and/or the like.

Referring now toFIG. 2, a schematic diagram of one embodiment of a continuously variable transmission24suitable for use with the work vehicle10described above is illustrated in accordance with aspects of the present subject matter. As shown, the transmission24may include a hydrostatic power unit30and a planetary power unit32. The hydrostatic power unit30and the planetary power unit32may be coupled to a driveline including a range gear set34and may also be coupled to a load L. For example, in one embodiment, the load L may correspond to the drive wheels of the work vehicle10(e.g., the front and/or rear wheels12,14of the work vehicle10). Alternatively, the hydrostatic power unit30and the planetary power unit32may be coupled to any other suitable load L, such as loads that include a track drive or a separate operating system of the work vehicle10.

The hydrostatic power unit30of the transmission10may generally include a fluid pump36coupled by fluid conduits38in a closed loop to a fluid motor40. The motor40may be coupled to the engine23via an input gear N6. Specifically, as shown inFIG. 2, power may be transmitted to the hydrostatic power unit30by a driven gear N4mounted on a forward shaft42of the transmission10and engaged with the input gear N6. In addition, an output gear N10for the hydrostatic power unit30may be connected to a ring gear NR of the planetary power unit32via gears N11and N12. A power take off (PTO) of the vehicle10may also be coupled to the engine23through the forward shaft42(e.g., by coupling a PTO gear reduction N26to the forward shaft42, which is coupled to the engine23via gears N5and N1.

In general, the pump36may comprise any suitable electronically controlled pump known in the art, such as an electronically controlled variable displacement hydraulic pump. As such, operation of the pump36may be automatically controlled using an electronic controller44of the work machine10. For example, as shown inFIG. 2, the controller44may be communicatively coupled to the pump36via a suitable communicative link46so that the angle of a swash plate of the pump36(the swash plate being denoted by a diagonal arrow48through pump36) may be adjusted through a range of positions, thereby adjusting the transmission ratio of the transmission24.

It should be appreciated the controller44may generally comprise any suitable processor-based device known in the art. Thus, in several embodiments, the controller44may include one or more processor(s) and associated memory device(s) configured to perform a variety of computer-implemented functions. As used herein, the term “processor” refers not only to integrated circuits referred to in the art as being included in a computer, but also refers to a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application specific integrated circuit, and other programmable circuits. Additionally, the memory device(s) of the controller44may generally comprise memory element(s) including, but are not limited to, computer readable medium (e.g., random access memory (RAM)), computer readable non-volatile medium (e.g., a flash memory), a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD) and/or other suitable memory elements. Such memory device(s) may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s), configure the controller44to perform various computer-implemented functions, such as the method600described below with reference toFIG. 6. In addition, the controller44may also include various other suitable components, such as a communications circuit or module, one or more input/output channels, a data/control bus and/or the like.

Referring still toFIG. 2, the planetary power unit32of the transmission24may generally include a primary sun gear NS1mounted on a planetary input shaft50. As shown, the planetary input shaft50may be coupled to the engine23via a forward directional clutch52or a reverse directional clutch54. In addition, the planetary power unit32may be configured to be selectively coupled to the load L, coupled to the hydrostatic power unit30and selectively coupled to the engine23, all under automatic control of the controller44. For example, for coupling the planetary power unit32to the load L, the transmission24may include an output shaft56coupled to the load L which carries an input gear N18engaged with an output gear N17on a range ½ shaft58of the range gear set34and a gear N22engaged with a gear N19on a range ¾ shaft60of the range gear set34. The range ½ shaft58may, in turn, be coupled to the planetary power unit32via automatic operation of range selectors or clutches R1and R2for power flow through gears N13and N14, or N15and N16, respectively. Similarly, the range ¾ shaft60may be coupled to the planetary power unit32via range selectors or clutches R3and R4for power flow via gears N13and N20, or N15and N21, respectively. The range ½ and ¾ shafts58,60may also be simultaneously coupled to the planetary power unit32to provide dual power flow. It should be appreciated that operation of the various clutches (e.g., the forward directional clutch52, the reverse directional clutch54, and clutches R1, R2, R3and R4) may be automatically controlled by the controller44using suitable actuators62(e.g., hydraulic pistons) communicatively coupled to the controller44via suitable communicative links46.

The controller44may also be communicatively coupled to a swash plate actuator64for automatically controlling the position or angle of the swash plate48of the pump36. For example, the actuator64may be configured to move the swash plate48across a range of angles in response to control signals (e.g., current commands) received from the controller44. In addition, the controller44may be coupled to any number of sensors for monitoring the various operating parameters of the transmission24including, but not limited to, pressure transducers or sensors66for sensing the pressure within the conduits38connecting the pump36to the motor40and/or for sensing the pressure of the hydraulic fluid within the various clutches of the transmission24, speed sensors68for sensing speeds of the various shafts of the transmission24(e.g., by sensing the motor speed of the fluid motor40), temperature sensors for sensing the temperature of one or more fluids within the transmission24and/or any other suitable sensors. Similarly, the controller44may also be connected to the engine23(e.g., a speed governor of the engine23) for receiving engine speed data and other information therefrom.

Additionally, as shown inFIG. 2, the controller44may also be communicatively coupled to the operator-controlled input device(s)20,21,22positioned within the cab18via a suitable communicative link46. For example, the controller44may be coupled to the FRNP lever20, the clutch pedal21, the display panel22and/or any other suitable input device of the vehicle10(e.g., the speed control lever or pedal, the engine throttle lever, the neutral button and/or any other suitable lever, pedal, button or control panel of the vehicle10).

During operation, the transmission24may be operated to have a combined hydrostatic and mechanical power flow by engaging the reverse directional clutch54to the power planetary power unit32via gears N1, N3, N5and N7, or engaging the forward directional clutch52to power the power planetary power unit32via gears N1, N8, and N2. Alternatively, the transmission44may be operated to have a pure hydrostatic power flow by disengaging both of the directional clutches52,54. Regardless, the transmission24may provide a seamless transition between ranges to provide work/road configurations as desired. In particular, speed changes from zero to the maximum speed within each speed range of the transmission24may be achieved in a smooth and continuous manner by automatically changing the swash plate angle of the pump36via control signals transmitted from the controller44. For each speed range, substantially the full range of travel of the swash plate may be used. For example, in several embodiments, the swash plate may be at one end of its range of travel for zero speed within a specific speed range, may be at the other end of its range of travel for the maximum speed of that speed range and may be at a zero tilt or neutral position within its range of travel for an intermediate speed of that same speed range.

Referring still toFIG. 2, the transmission24may also include a parking brake70operably positioned on the load shaft56. In several embodiments, the parking brake70may be communicatively coupled to the controller44(via a suitable communicative link46) for automatic control thereof. For example, the controller44may be configured to proportionally or gradually engage the parking brake70as well as gradually release or disengage the parking brake70. In such embodiments, the pressure of the hydraulic fluid supplied to the parking brake70may be controlled using an automatic valve (e.g., a proportional pressure reducing valve) configured to be operated via control signals transmitted from the controller44. As is generally understood, the parking brake pressure may be inversely related to the parking brake torque. Thus, contrary to the various clutches of the transmission24, the parking brake70may be designed such that it is engaged when the pressure within the brake70is reduced and disengaged when the pressure within the brake70is increased.

In addition, for operation when the controller44is not powered or is not properly functioning, the parking brake70may also be configured to be engaged using a separate means. For instance, the parking brake70may be spring applied or may include any other suitable biasing means configured to bias the parking brake70into engagement. Alternatively, the parking brake70may include a suitable mechanical means for engaging the brake70when the controller44is not powered or is not properly functioning. Moreover, a means may be provided to store pressurized hydraulic fluid in the event the engine23stalls so that the parking brake70may remain released and/or may be applied and released several times if needed to control the vehicle10until the engine23can be restarted. Additionally, other means (e.g., a hand pump) may be provided to disengage the parking brake70if there is a fault and no stored pressurized hydraulic fluid is left within the system.

It should be appreciated that the configuration of the transmission24shown inFIG. 2simply illustrates one example of a suitable transmission with which the disclosed system and method may be utilized. Thus, one of ordinary skill in the art should appreciate that application of the present subject matter need not be limited to the particular CVT configuration shown inFIG. 2, but, rather, the present subject matter may be advantageously used with various different CVT configurations.

Referring now toFIG. 3, a schematic diagram of one embodiment of a hydraulically operated clutch is illustrated in accordance with aspects of the present subject matter. The clutch is generally representative of a suitable configuration for the directional clutches52and54, and the range clutches R1-R4of the transmission24described above with reference toFIG. 2.

As shown, the hydraulically operated clutch may include an enclosure or can72that contains one or more clutch plates74coupled to an output shaft76and one or more clutch plates78coupled to an input shaft80. In addition, the clutch may include both a clutch spring(s)82configured to hold the clutch plates74,78apart and a fluid operated actuator (e.g., actuator62described above with reference toFIG. 2) configured to press the clutch plates74,78together to engage the clutch.

Moreover, as shown inFIG. 3, pressurized fluid may be supplied to the actuator62by a proportional solenoid pressure reducing valve84(e.g., via fluid lines86). The valve84may be configured to receive the pressurized fluid from a pump P of the vehicle10and may also be in fluid communication with a fluid tank88of the vehicle10. As is generally understood, operation of the valve84may be automatically controlled by the vehicle controller44through the transmission of suitable control signals via the communication links46. Each control signal may generally correspond to a current command associated with a specific electrical current value, which, in turn, may be directly proportional to the pressure of the hydraulic fluid supplied to the actuator62from the valve84. Thus, by varying the current command, the controller44may directly control the clutch pressure supplied to the actuator62and, thus, control engagement/disengagement of the clutch.

Referring now toFIGS. 4 and 5, simplified graphs providing examples of the change in clutch pressure over time for both clutch engagement (FIG. 4) and clutch disengagement (FIG. 5) are illustrated in accordance with aspects of the present subject matter. As shown inFIG. 4, when engaging a clutch, the clutch pressure may be increase from a reduced pressure to an engagement pressure during a ramp phase (where the current command is ramped up) to ensure that clutch engagement is achieved in a controlled manner. As is generally understood, the initial clutch pressure may correspond to a zero pressure (i.e., when the clutch is fully dumped) or a fill pressure (e.g. a clutch pressure below the pressure at which the clutch plates74,78begin to engage). For instance, in several embodiments, the clutch may be configured to be automatically quick-filled to the fill pressure prior to the ramp phase. Similarly, the engagement pressure may correspond to the clutch pressure at which the clutch is fully engaged (i.e., when there is no slippage across the clutch and the speed differential across the clutch is equal to zero). As is generally understood, the engagement pressure may vary depending on the configuration of the clutch as well as other factors (e.g., component wear, etc.). Additionally, as shown inFIG. 5, when disengaging a clutch, the clutch pressure is reduced from the engagement pressure to a reduced pressure (e.g., a zero pressure) as the hydraulic fluid is dumped from within the clutch.

Referring now toFIG. 6, a flow diagram of one embodiment of method600for enhancing the operation of a continuously variable transmission of a work vehicle is illustrated in accordance with aspects of the present subject matter. In general, the method600will be described with reference to the continuously variable transmission24described above with reference toFIG. 2. However, it should be appreciated by those of ordinary skill in the art that the disclosed method600may generally be utilized to enhance the operation of any CVT having any suitable configuration. In addition, althoughFIG. 6depicts steps performed in a particular order for purposes of illustration and discussion, the methods discussed herein are not limited to any particular order or arrangement. One skilled in the art, using the disclosures provided herein, will appreciate that various steps of the methods disclosed herein can be omitted, rearranged, combined, and/or adapted in various ways without deviating from the scope of the present disclosure.

In general, the method600may allow for the operation of a CVT24to be enhanced by reducing the amount of time required to break-in and/or warm-up the transmission. Specifically, as will be described below, the disclosed method600allows for a computer-implemented clutch cycling routine to be performed in which one or more of the clutches of a CVT24are automatically and quickly cycled on and off (i.e., between engaged and disengaged states) to remove, reduce and/or eliminate any system inconsistencies, imperfections and/or other potential issues that may impact the overall performance and/or maintenance of the CVT24, such as air trapped within the hydraulic system, friction within the clutch springs, plates, piston or valve, shifting of the clutch springs and/or other clutch components (e.g., due to initial wear on the clutch seals), burrs on metal components and/or any other potential issues. For instance, prior to performing a clutch calibration on a CVT24, the disclosed method600may be performed to flush out any air bubbles/pockets contained within the hydraulic system and/or to address any mechanical issues within the transmission24, which may improve the overall accuracy of the resulting clutch calibration. Accordingly, aspects of the present subject matter may be advantageously utilized, for example, by plant workers prior to performing the initial clutch calibration on a CVT24and/or by service technicians prior to performing a routine clutch calibration.

As shown inFIG. 6, at (602), the method600includes receiving a signal associated with initiating a clutch cycling routine. Specifically, in several embodiments, the controller44may be configured to receive a user input command or signal instructing the controller44to cycle one or more of the CVT clutches between engaged and disengaged states. For example, the operator may be provided with a suitable means within the cab18for selecting a clutch cycling mode (e.g., via a button, touch screen or other suitable user input device) within which the disclosed clutch cycling routine is automatically performed by the controller44.

Additionally, at (604), the method600includes receiving a signal associated with selecting a forward travel direction or a reverse travel direction for the work vehicle. Specifically, in several embodiments, the operator of the work vehicle10may select which directional clutch52,54is to be cycled by selecting the corresponding forward or reverse travel direction via the FRNP lever20. For example, if it is desired for the forward directional clutch52to be cycled, the operator may be required to select forward using the FNRP lever20, which, in turn, causes the forward directional clutch52to be engaged within the transmission24.

It should be appreciated that, in several embodiments of the present subject matter, the forward or reverse travel direction may selected before or after instructing the controller44to enter into the clutch cycling mode. For instance, when the clutch cycling mode is initiated, a message window may, in one embodiment, be displayed (e.g., via the display panel22) that prompts the operator to select forward or reverse by moving the FNRP lever20to the appropriate position. It should also be appreciated, that in alternative embodiments, any other suitable input device may be utilized by an operator to select the forward or reverse travel direction, such as push buttons, a control panel or any other suitable input device.

Referring still toFIG. 6, at (606), the method600includes engaging the parking brake70of the work vehicle10. Specifically, in several embodiments, the parking brake70may be engaged to prevent vehicle movement while the driveline28is disengaged during cycling of the selected directional clutch52,54. However, in other embodiments, the clutch cycling routine may be performed without engaging the parking brake70. In such instance, the work vehicle10may be allowed to move slightly during the performance of the disclosed method600.

Additionally, at (608), the method600includes engaging a range clutch of the CVT24(e.g., range clutch R1, R2, R3or R4). Specifically, in several embodiments, the disclosed clutch cycling routine may be configured to be performed in a “powered zero” operating mode in which the drivetrain28is engaged while the ground speed of the work vehicle10is maintained at or substantially at zero. In the “powered zero” mode, both a directional clutch52,54and a range clutch R1-R4must be engaged. Thus, when the FRNP lever20is moved to the forward or reverse position and the corresponding directional clutch52,54is engaged within the transmission24, one of the range clutches R1-R4may also be engaged to constrain the planetary gear unit32. For instance, given the configuration of the CVT24described above with reference toFIG. 2, the R1range clutch or the R3range clutch may be engaged together with the selected directional clutch52,54to command the “powered zero” mode. However, with other CVT configurations, any other suitable range clutch(es) may be engaged in combination with the selected directional clutch52,54to command the “powered zero” mode.

Referring still toFIG. 6, (at610), the method600includes cycling the selected directional clutch52,54between an engaged state and a disengaged state while the range clutch R1-R4(and, optionally, the parking brake70) is maintained in engagement. For instance, if the operator selects the forward travel direction, the forward directional clutch52will be engaged. Thereafter, the controller44may be configured to repeatedly cycle the forward directional clutch52between engaged and disengaged states (i.e., by transmitting suitable control signals to the corresponding clutch valve84) in order to remove, reduce, and/or eliminate any issues that may impact the performance of the transmission24, such as air trapped within the hydraulic system and/or any mechanical issues.

As used herein, the term “engaged state” refers to a clutch operating state in which at least some amount of torque is transmitted through the clutch. Thus, to cycle one of the directional clutches52,54to the engaged state, the hydraulic pressure within the clutch may be increased to the appropriate pressure (e.g., the engagement pressure ofFIG. 4) such that the clutch is engaged. In several embodiments, when cycling a clutch to the engaged state, it may be desirable to increase the pressure to the maximum clutch pressure or system pressure so that the clutch is fully engaged (i.e., when the clutch is fully locked up and fully transmitting torque). Similarly, the term “disengaged state” refers to a clutch operating state in which the clutch is fully disengaged (i.e., no torque can be transmitted through the clutch). Thus, to cycle one of the directional clutches52,54to the disengaged state, the hydraulic pressure within the clutch may be reduced to the appropriate pressure such that the clutch is disengaged. For example, in several embodiments, the hydraulic fluid may be fully dumped to a achieve a zero pressure within the clutch when cycling to the disengaged state.

When cycling each directional clutch52,54between the engaged and disengaged states, a slight delay period may be provided to ensure that the clutch is fully engaged or fully disengaged prior to subsequently decreasing or increasing the clutch pressure. For instance, if the hydraulic pressure is being reduced down to zero pressure in order to cycle the clutch to the disengaged state, the controller44may be configured to wait a short time period (e.g., time period90shown inFIGS. 4 and 5) to ensure that the clutch has fully disengaged prior to cycling the clutch back to the engaged state. Once the time period has lapsed, the hydraulic pressure may be increased to the engagement pressure in order to cycle the clutch to the engaged state. Thereafter, the controller44may be configured to wait another short time period (e.g., time period92shown inFIGS. 4 and 5) to ensure that the clutch has fully engaged prior to cycling the clutch back to the disengaged state.

When performing the disclosed clutch cycling routine, the controller44may, in several embodiments, be configured to continuously cycle the selected clutch between the engaged and disengaged states until the routine is cancelled. For instance, the operator may provide a suitable user input (e.g., via a button, touch screen or other suitable user input device) to terminate the clutch cycling. Similarly, the clutch cycling routine may also be cancelled if the operator commands movement of the work vehicle10. For instance, if the operator pushes the speed lever (not shown) forward to increase the speed of the vehicle10, the clutch cycling routine may be cancelled and the appropriate directional clutch engaged to allow the vehicle10to move in the selected direction.

Additionally, the operator may also be allowed to switch from cycling one directional clutch52,54to the other while in the clutch cycling mode. For instance, if the forward directional clutch52is currently being cycled, the operator may select the reverse travel direction for the work vehicle (e.g., by moving the FRNP lever20to the reverse position) to initiate cycling of the reverse directional clutch54. In doing so, the forward directional clutch52may be immediately disengaged. Thereafter, the reverse directional clutch54may be engaged and subsequently cycled between the engaged and disengaged states.

Referring still toFIG. 6, at (612), the method600includes controlling the position of the swash plate48of the CVT24such that the ground speed of the work vehicle10is maintained at or substantially at zero while the directional clutch52,54is being cycled. Specifically, in several embodiments, the swash plate angle may be controlled such that there is no slippage or speed differential across the clutch being cycled, thereby ensuring that ground speed of the work vehicle10is maintained at or substantially at zero. As indicated above, the swash plate angle may be automatically controlled via the controller44by transmitting suitable control signals (e.g., current commands) to the swash plate actuator64of the transmission24.

It should be appreciated that, in several embodiments, the ground speed of a work vehicle10is maintained “substantially at zero” if the ground speed is less than a predetermined speed threshold. For instance, in one embodiment, the speed threshold may correspond to a ground speed of less than 2 kilometers per hour (KPH), such as less than 1.5 KPH or less than 1 KPH. Additionally, a time component may also be combined with the speed threshold to determine whether the ground speed of the work vehicle is maintained “substantially at zero.” For instance, in several embodiments, the ground speed is maintained “substantially at zero” as long as the ground speed does not exceed the predetermined speed threshold for a predetermined time period, such as by exceeding 1.5 KPH for 0.1 seconds or by exceeding 0.8 KPH for 0.2 seconds.

It should also be appreciated that any suitable sensor feedback may be provided to the controller44to ensure that the angle of the swash plate48is properly adjusted in order to maintain the ground speed of the work vehicle10at or substantially at zero. For instance, the controller44may be configured to correlate the current commands transmitted to the swash plate actuator64to a corresponding output speed of the fluid motor40(e.g., by monitoring the motor speed via a speed sensor(s)68). The swash plate angle may then be controlled to ensure that the appropriate motor speed is achieved for maintaining the ground speed at or substantially at zero.

Additionally, it should be appreciated that, although the method600was described above with reference to cycling one or both of the directional clutches52,54, a similar methodology may also be utilized to cycle one or more of the range clutches R1-R4of the transmission24. For instance, when the operator selects the forward or reverse travel direction and the corresponding directional clutch52,54is engaged, one of the range clutches R1-R4may be cycled between engaged and disengaged states while the directional clutch52,54is maintained in engagement and the swash plate angle is controlled in a manner that provides for a ground speed that is at or substantially at zero. For instance, referring to the CVT configuration shown inFIG. 2, while the forward or reverse directional clutch52,54is engaged, the R1or R3range clutch may be cycled between engaged and disengaged states to remove trapped air and/or eliminate mechanical issues associated with the clutch.