HYDRAULIC SHIFT CONTROL SYSTEM

A work vehicle that includes a hydraulic system. The hydraulic system includes a hydraulic motor that generates rotational power for one or more wheels on the work vehicle. A hydraulic pump couples to the hydraulic motor. The hydraulic pump pumps hydraulic fluid to the hydraulic motor. A hydraulic shift control system controls shifting of the hydraulic system. The hydraulic shift control system includes a controller that controls a hydraulic motor volume of the hydraulic motor and a fluid volume pumped by the hydraulic pump to gradually change a speed of the work vehicle during a shift.

BACKGROUND

Hydraulic systems may be used on various pieces of equipment, such as on agricultural vehicles and implements. These hydraulic systems use a pressurized hydraulic fluid generated by a hydraulic pump to perform various tasks. In operation, the hydraulic pump pressurizes hydraulic fluid received from a hydraulic fluid source. Some work vehicles use this pressurized hydraulic fluid to actuate hydraulic motors that generate rotational power. The rotational power may then be used to drive wheels on a work vehicle. In some situations, the wheels may rotate tracks that are coupled to the wheels, such as on a skid steer. Unfortunately, shifting between speeds may cause the vehicle to lurch or jerk in response to rapid changes in motor volume with no change in hydraulic fluid flow delivered by the pump.

BRIEF DESCRIPTION

In one example, a work vehicle that includes a hydraulic system. The hydraulic system includes a hydraulic motor that generates rotational power for one or more wheels on the work vehicle. A hydraulic pump couples to the hydraulic motor. The hydraulic pump pumps hydraulic fluid to the hydraulic motor. A hydraulic shift control system controls shifting of the hydraulic system. The hydraulic shift control system includes a controller that controls a hydraulic motor volume of the hydraulic motor and a fluid volume pumped by the hydraulic pump to gradually change a speed of the work vehicle during a shift.

In another example, a hydraulic shift control system that includes a controller with a processor that executes computer executable instructions on a computer-readable medium. The controller gradually changes a speed of a work vehicle from a first speed to a second speed by gradually changing a hydraulic motor volume and a hydraulic pump volume. The controller receives a shift command and in response to the shift command shifts the work vehicle from the first speed to the second speed.

DETAILED DESCRIPTION

As used herein, the term “coupled” or “coupled to” may indicate establishing either a direct or indirect connection, and is not limited to either unless expressly referenced as such. The term “set” may refer to one or more items. Wherever possible, like or identical reference numerals are used in the figures to identify common or the same elements. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale for purposes of clarification.

Agricultural or work vehicles may include one or more hydraulic systems that provide power to complete various tasks. These tasks may include loading, lifting, pushing, rotating, dozing, and even moving the work vehicle. For example, a work vehicle may include a hydraulic system that includes hydraulic motors that drive the wheels of the work vehicle. The wheels in turn couple to tracks which enable the work vehicle to traverse various types of terrain. Depending on the terrain and/or job, the operator may desire to drive the vehicle at different speeds. To change how fast the work vehicle travels, the operator may shift up or shift down. In response to a shifting command, the hydraulic system will either increase or decrease the motor volume and because the oil flow from the pump is unchanged this will cause the motor speed to either rapidly decrease or increase to allow the same oil flow through the new volume. This rapid change in the hydraulic motor volume can cause the vehicle to lurch or jerk as the hydraulic motor responds to the shift command. In order to reduce abrupt changes in hydraulic motor speeds from changing hydraulic motor volumes, the disclosure below describes a hydraulic shift control system. The hydraulic shift control system controls one or more hydraulic pumps to control the flow of hydraulic fluid to one or more hydraulic motors as the hydraulic motor volumes change, which reduces the lurching of the vehicle during the shift.

FIG. 1is a side view of an embodiment of a work vehicle10(e.g., a skid steer). The work vehicle10may include wheels11and tracks12that enable the work vehicle10to move. The work vehicle10includes an engine14that provides power to a hydraulic system16. The hydraulic system16in turn powers the wheels11which then rotate the tracks12. The hydraulic system16may also power other systems on the work vehicle10. For example, the hydraulic system16may provide power to hydraulic actuators18(e.g., hydraulic cylinders) that control operation of one or more arms20(e.g., booms). The arms20couple to tools22that enable the work vehicle to perform various tasks. For example, forks, buckets, plows, blades, among others may be attached to the arms20. Each of these tools enable the work vehicle10to perform one or more tasks such as loading, dozing, etc. The hydraulic system16may also include one or more hydraulic pumps and one or more hydraulic motors that provide power to the wheels11on the work vehicle10. In order to reduce or block lurching of the work vehicle10as it shifts, the work vehicle10includes a hydraulic shift control system24. As will be explained below, the hydraulic shift control system24controls operation of one or more hydraulic pumps and one or more hydraulic motors on the work vehicle10to reduce abrupt changes in speed of the work vehicle10while shifting.

FIG. 2is a schematic of an embodiment of a hydraulic system50and hydraulic shift control system52that may be used in a work vehicle (e.g., work vehicle ofFIG. 1). The hydraulic system50may include a first hydraulic pump54and a second hydraulic pump56that receives hydraulic fluid from a hydraulic accumulator or source58. The first pump54and the second pump56supply hydraulic fluid to respective first and second hydraulic motors60,62. The hydraulic motors60,62have discrete volumes associated with respective discrete speed shifts (e.g., two speed shifts). As the first and second hydraulic motors60,62receive hydraulic fluid they drive rotation of respective first and second wheels64,66. The wheels64,66in turn may couple to and rotate first and second vehicle tracks68and70enabling the work vehicle to move. It should be understood, that the hydraulic system50may include a different number of pumps, hydraulic motors, wheels, and/or tracks (e.g., 1, 2, 3, 4, or more).

In order to reduce or block lurching or jerking of the work vehicle as it shifts, the hydraulic shift control system52couples to the hydraulic system50. More specifically, the hydraulic shift control system52couples to and controls operation of the first and second pumps54,56and the first and second hydraulic motors60,62. The hydraulic shift control system52controls operation of the hydraulic pumps54,56and the hydraulic motors60,62to reduce abrupt changes in the speed of the work vehicle. In other words, the hydraulic shift control system52enables a gradual increase and decrease in the speed of the work vehicle in response to a shift signal. The hydraulic shift control system52includes a controller72that receives a shift signal from an input74. The input74may be a joystick, touchscreen, lever, button(s), among others. The controller72receives and processes this signal from the input74and executes instructions stored on a memory78to control operation of the pumps54,56and the hydraulic motors60,62. For example, the controller52may increase or decrease the flow rate of hydraulic fluid produced by the pumps54,56and/or control the change in volume of the hydraulic motors60,62to change the speed of the work vehicle in response to the shift signal.

The processor76may be a microprocessor that executes software that enables control of the hydraulic system50. The processor76may include multiple microprocessors, one or more “general-purpose” microprocessors, one or more special-purpose microprocessors, and/or one or more application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or some combination thereof. For example, the processor76may include one or more reduced instruction set computer (RISC) processors.

The memory78may include a volatile memory, such as random access memory (RAM), and/or a nonvolatile memory, such as read-only memory (ROM). The memory78may store a variety of information and may be used for various purposes. For example, the memory78may store processor executable instructions, such as firmware or software, for the processor76to execute. The memory78may include ROM, flash memory, a hard drive, or any other suitable optical, magnetic, or solid-state storage medium or a combination thereof. The memory78may store data, instructions, and any other suitable data.

FIG. 3illustrates graphs98of the hydraulic shift control system controlling an upshift. As illustrated, there are four graphs100,102,104, and106. The graphs98illustrate different input or responses with respect to time, x-axis108. The first graph100illustrates an input command (e.g., joystick command) relative to time. The first graph100includes a y-axis110for the input command (e.g., joystick command) and the x-axis108for time. The second graph102illustrates change in the speed of the work vehicle relative to time. The second graph102includes a y-axis112for speed and an x-axis108for time. The third graph104illustrates changes in volume of the hydraulic motor relative to time. The third graph104includes a y-axis114for the motor volume and an x-axis108for time. The fourth graph106illustrates a change in the volume of hydraulic fluid pumped relative to time. The fourth graph106includes a y-axis116for the pump volume and an x-axis108for time.

These graphs100,102,104, and106includes various lines that illustrate the response of a hydraulic system to commands that change pump volume and motor volume and how changes in pump volume and motor volume change the speed of a work vehicle during in upshift. The first graph100includes line118that illustrates a command generated by an input device (e.g., touch screen, button, joystick, lever) to increase the speed of the work vehicle. The hydraulic shift control system (e.g., controller) receives this signal and generates a speed command to increase the speed of the work vehicle. This speed command is illustrated by line120. As illustrated, the speed command line120includes a first steady state portion122, a transition portion124, and a second steady state portion126. The first steady state portion122illustrates the previous speed command associated with a previous speed of the work vehicle. Upon receiving a new speed input (e.g., from an input device) the speed command line120increases from the first speed to a second speed (e.g., jumps) along the transition portion124. After changing the speed command, the speed command line120continues with the second steady state portion126associated with the new desired speed of the work vehicle.

In response to the speed command, the hydraulic shift control system generates a motor volume command and a pump volume command. These commands are sent to the respective hydraulic motor(s) and hydraulic pump(s), which change the volume of the hydraulic motor(s) and the volume of hydraulic fluid pumped by the hydraulic pump(s). The motor volume command is illustrated by line128and the pump volume command is illustrated by line130. As illustrated, the motor volume command line128includes a first steady state portion132, a transition portion134, and a second steady state portion136. The first steady state portion132illustrates the previous motor volume that enables the previous speed of the work vehicle. Upon receiving a new speed input (e.g., from an input device) the motor volume command line128decreases from the first volume to a second volume (e.g., jumps) along the transition portion134. The motor volume command line128then continues with the second steady state portion136associated with the new desired motor volume.

The pump volume command line130includes a first steady state portion138, a first transition portion140, a second transition portion142, and a second steady state portion144. The first steady state portion138illustrates the previous pump volume that enables the previous speed of the work vehicle. Upon receiving a new speed input (e.g., from an input device) the motor volume command line130decreases from the first volume to a second volume along the transition portion140. As illustrated, this change may be a rapid change but is not a jump. For example, a rapid linear change from a first pump volume to a second pump volume. After reaching the second pump volume, the pump volume command line130transitions from the second pump volume to the first pump volume along the second transition portion142. The second transition portion142may be a linear signal to increase the pump volume from the second pump volume to the first pump volume. The motor volume command line130then continues with the second steady state portion144associated with the first pump volume.

In some embodiments, there may be a delay between the change in the speed command120(i.e., the transition portion124) and the change in the motor volume command128(i.e., the transition portion134) and the pump volume command130(i.e., the start of the first transition140). The motor wait delay is labeled146and the pump wait delay is labeled148. In some embodiments, the difference between the motor wait delay146and the pump wait delay148may be zero. In other embodiments, there may be a difference between the motor wait delay146and the pump wait delay148depending on the whether the hydraulic motor(s) or the hydraulic pump(s) take longer to respond to the speed command. As will be explained below, simultaneous changes in the motor volume and the pump volume enable a smooth upshift from a first speed to a second speed.

As explained above, the motor volume command and pump volume commands are sent to the respective hydraulic motor(s) and hydraulic pump(s), which change the volume of the hydraulic motor(s) and the volume of hydraulic fluid pumped by the hydraulic pump(s). The changes in the volume of the hydraulic motors and the volume pumped by hydraulic pumps changes the speed of the work vehicle as well as the abruptness of the shift. The graphs inFIG. 3illustrate three speed response lines that occur in response to changes of the motor volume and the pump volume. These speed lines are illustrated with lines150,152, and154.

The first speed line150includes a first steady state portion156, a transition portion158, and a second steady state portion160. The first steady state portion156illustrates the operation of the work vehicle at a first speed. Once the speed command is produced the hydraulic motor(s) and hydraulic pump(s) change operation enabling an increase in the speed of the work vehicle from the first speed illustrated by the first steady state portion156to the second speed illustrated by the second steady state portion160. As illustrated, the transition portion158illustrates the change in speed between the first and second speeds. The transition portion158may linear wherein the speed of the work vehicle gradually increases from the first speed to the second speed. In other words, the work vehicle may not lurch or jerk as it upshifts and transitions from the first speed to the second speed.

In order to produce the smooth transition between speeds illustrated by the transition portion158of the speed line150, the hydraulic shift control system rapidly changes the pump volume to counter discrete motor volume transitions. These changes are illustrated by the motor volume line162and the pump volume line164. The motor volume line162illustrates the changes in motor volume in response to the motor volume commands. As illustrated, the motor volume line162includes a first steady state portion166, a transition portion168, and a second steady state portion170. At the first steady state portion166the motor volume is at a first volume (e.g., 100%) which then transitions to a second volume (e.g., 50%) of the second steady state portion170. The transition between these two volumes is illustrated by the transition portion168. As illustrated, the transition portion168(e.g., rate) is gradual enabling a gradual change from the first volume to the second volume.

The pump volume line164illustrates the change in pump volume in response to the pump volume commands. The pump volume line164includes a first steady state portion172, a first transition portion174, a second transition portion176, and a second steady state portion178. In order to block or reduce the rapid increase in the hydraulic motor speed due to the same fluid flow through a smaller hydraulic motor volume, the hydraulic pump may decrease the volume of hydraulic fluid pumped at the same time as the motor volume decreases, illustrated by the first transition portion174(e.g., rate). This simultaneous change reduces or blocks lurching of the work vehicle as the motor transitions from the first volume to the second volume in preparation for increased speed. In some embodiments, the rate of the motor volume change illustrated by the transition portion168is equal to the change in the pump volume rate illustrated by the first transition portion174. After reducing the volume of hydraulic fluid from the first volume to the second volume, the hydraulic pump gradually (e.g., progressively) increases the pump volume from the second pump volume back to the first pump volume, illustrated by the second transition portion176(e.g., rate). In some embodiments, the pump volume rate illustrated by the first transition portion174may be greater than the pump volume rate of the second transition portion176. The increase in pump volume through the reduced motor volume (e.g., second motor volume) increases the speed of the work vehicle illustrated by the transition portion158of the speed line150. In this way, the hydraulic shift control system gradually increases the speed of the work vehicle from a first speed to a second speed without lurching or jerking the work vehicle. It should be understood that the hydraulic shift control system may control the aggressiveness of the upshift by controlling how rapidly the motor volume and pump volumes changes (e.g., the slope of the transition portions168,174, and176).

As explained above, the simultaneous change in the motor volume and pump volume creates a smooth upshift and speed increase. However, if the motor volume and pump volume do not change simultaneously the work vehicle may jerk. For example, if the volume through the hydraulic motor is reduced by half but the hydraulic fluid flow remains unchanged, the hydraulic motor will instantaneously or near instantaneously spin twice as fast. Accordingly, to accommodate the change in motor volume, the hydraulic shift control system changes the amount of fluid pumped by the hydraulic pump or in other words the pump volume in response to changes in the motor volume. The speed line152illustrates a curved portion180where the vehicle rapidly increases in speed before again decreasing in speed. This is caused by a motor volume decreasing before the pump volume decreases. This is illustrated by motor volume line182and pump volume line184. Similarly, the work vehicle may decrease in speed below an initial or first speed during the upshift if the motor volume and pump volume do not change simultaneously. As illustrated, speed line154includes a curved portion186(e.g., dip) where the speed of the work vehicle dips below an initial or first speed. This is caused by the pump volume decreasing before a decrease in the motor volume. A constant flowrate of hydraulic fluid flowing through an increasing hydraulic motor volume decreases the rotational speed of the hydraulic motor. This is illustrated by the motor volume line188and the pump volume line190.

FIG. 4illustrates graphs220of a hydraulic control system controlling a downshift. As illustrated, there are four graphs222,224,226, and228. The graphs220illustrate different input or responses with respect to time, x-axis230. The first graph222illustrates an input command (e.g., joystick command) relative to time. The first graph222includes a y-axis232for the input command (e.g., joystick command) and an x-axis230for time. The second graph224illustrates changes in speed of the work vehicle relative to time. The second graph224includes a y-axis234for speed and an x-axis230for time. The third graph226illustrates changes in volume of the hydraulic motor relative to time. The third graph226includes a y-axis236for the motor volume and an x-axis230for time. The fourth graph228illustrates a change in the volume of hydraulic fluid pumped relative to time. The fourth graph228includes a y-axis238for the pump volume and an x-axis230for time.

These graphs222,224,226, and228include various lines that illustrate the response of a hydraulic system to commands that change pump volume and motor volume and how changes in pump volume and motor volume change the speed of a work vehicle during a downshift. The first graph222includes line240that illustrates a command generated by an input device (e.g., touch screen, button, joystick, lever) to decrease the speed of the work vehicle. The hydraulic shift control system (e.g., controller) receives this signal and generates a speed command to decrease the speed of the work vehicle. This speed command is illustrated by line242. As illustrated, the speed command line242includes a first steady state portion244, a transition portion246, and a second steady state portion248. The first steady state portion244illustrates the previous speed command associated with the previous speed of the work vehicle. Upon receiving a new speed input (e.g., from an input device) the speed command line242decreases from the first speed to a second speed (e.g., jumps) along the transition portion246. After changing the speed command, the speed command line242continues with the second steady state portion248associated with the new desired speed of the work vehicle.

In response to the speed command, the hydraulic shift control system generates a motor volume command and a pump volume command. These commands are sent to the respective hydraulic motor(s) and hydraulic pump(s), which change the volume of the hydraulic motor(s) and the volume of hydraulic fluid pumped by the hydraulic pump(s). The motor volume command is illustrated by line250and the pump volume command is illustrated by line252. As illustrated, the motor volume command250includes a first steady state portion254, a transition portion256, and a second steady state portion258. The first steady state portion254illustrates the previous motor volume that enables the previous speed of the work vehicle. Upon receiving a new speed input (e.g., from an input device) the motor volume command250increases from the first volume to a second volume (e.g., jumps) along the transition portion256. The motor volume command250then continues with the second steady state portion258associated with the new desired motor volume.

The pump volume command line252includes a first steady state portion260, a first transition portion262, a second transition portion264, and a second steady state portion266. The first steady state portion260illustrates the previous pump volume that enables the previous speed of the work vehicle. Upon receiving a new speed input (e.g., from an input device) the pump volume command252increases from the first volume to a second volume along the first transition portion262. As illustrated, this change may be a rapid change but is not a jump. For example, the first transition portion262may be a rapid linear change from a first pump volume to a second pump volume. After reaching the second pump volume, the pump volume command252transitions from the second pump volume to the first pump volume along the second transition portion264. The second transition portion264may be a linear signal to decrease the pump volume from the second pump volume to the first pump volume. The pump volume command252then continues with the second steady state portion266associated with the first pump volume.

In some embodiments, there may be a delay between the change in the speed command242(i.e., the transition portion246) and the change in the motor volume command250(i.e., the transition portion256) and the pump volume command252(i.e., the start of the first transition262). The motor wait delay is labeled268and the pump wait delay is labeled270. In some embodiments, the difference between the motor wait delay268and the pump wait delay270may be zero. In other embodiments, there may be a difference between the motor wait delay268and the pump wait delay270depending on whether the hydraulic motor(s) or the hydraulic pump(s) take longer to respond to the speed command. As will be explained below, simultaneous changes in the motor volume and the pump volume enable a smooth downshift from a first speed to a second speed.

As explained above, the motor volume command and pump volume commands are sent to the respective hydraulic motor(s) and hydraulic pump(s), which change the volume of the hydraulic motor(s) and the volume of hydraulic fluid pumped by the hydraulic pump(s). The changes in the volume of the hydraulic motors and the volume pumped by hydraulic pumps change the speed of the work vehicle and how smoothly it shifts. The graphs220inFIG. 4illustrate a speed response line272, a motor volume line274, and a pump volume line276.

The speed line272includes a first steady state portion278, a transition portion280, and a second steady state portion282. The first steady state portion278illustrates the operation of the work vehicle at the first speed. Once the speed command is produced the hydraulic motor(s) and hydraulic pump(s) change operation enabling a decrease in the speed of the work vehicle from the first speed illustrated in the first steady state portion278to the second speed illustrated by the second steady state portion282. As illustrated, the transition portion280illustrates the change in speed between the first and second speeds. The transition portion280may linear wherein the speed of the work vehicle gradually increases from the first speed to the second speed. In other words, the work vehicle may not lurch or jerk as it downshifts and transitions from the first speed to the second speed.

In order to produce the smooth transition between speeds illustrated by the transition portion280of the speed line272, the hydraulic shift control system gradually (e.g., progressively) changes the pump volume to counter the rapid change in motor volume during the shift. These changes are illustrated by the motor volume line274and the pump volume line276. The motor volume line274illustrates the changes in motor volume in response to the motor volume commands. As illustrated, the motor volume line274includes a first steady state portion282, a transition portion284, and a second steady state portion286. At the first steady state portion282the motor volume is at a first volume (e.g., 50%) and at a second volume (e.g., 100%) at the second steady state portion286. The transition between these two volumes is illustrated by the transition portion284(e.g., rate). As illustrated, the transition portion284may be gradual enabling a gradual change from the first volume to the second volume. By increasing the volume of the hydraulic motor, the hydraulic motor may decrease the speed of the hydraulic motor. However, if this change in not accompanied by a corresponding change in hydraulic fluid flow the decrease in speed may be abrupt or sudden. For example, if the volume of the hydraulic motor is doubled but the hydraulic fluid flow remains unchanged, the hydraulic motor will spin half as fast. Accordingly, to accommodate the change in motor volume, the hydraulic shift control system changes the amount of fluid pumped by the hydraulic pump or in other words the pump volume.

The pump volume line276illustrates the change in pump volume in response to the pump volume commands. The pump volume line276includes a first steady state portion288, a first transition portion290, a second transition portion292, and a second steady state portion294. In order to block or reduce the rapid decrease in rotations by the hydraulic motor as the hydraulic motor increases in volume, the hydraulic pump may increase the volume of hydraulic fluid pumped at the same time the motor volume increases, illustrated by the first transition portion290(e.g., rate). This simultaneous change reduces or blocks lurching of the work vehicle as the hydraulic motor transitions from the first volume to the second volume in preparation for a decrease in speed. In some embodiments, the rate of the motor volume change illustrated by the transition portion284is equal to the change in the pump volume rate illustrated by the first transition portion290. After increasing the volume of hydraulic fluid from the first volume to the second volume, the hydraulic pump gradually (e.g., progressively) decreases the pump volume from the second pump volume back to the first pump volume, illustrated by the second transition portion292(e.g., rate). In some embodiments, the pump volume rate illustrated by the first transition portion290may be greater than the pump volume rate of the second transition portion292. The decrease in pump volume through the increased motor volume (e.g., second motor volume) gradually decreases the speed of the work vehicle illustrated by the transition portion280of the speed line272. In this way, the hydraulic shift control system gradually decreases the speed of the work vehicle from a first speed to a second speed without lurching or jerking the work vehicle. It should be understood that the hydraulic shift control system may control the aggressiveness of the upshift by controlling how rapidly the pump volumes changes. As explained above, the simultaneous change in the motor volume and pump volume neutralizes the shift and then the smooth change in pump volume creates a smooth downshift and speed decrease. However, if the motor volume and pump volume do not change simultaneously the work vehicle may jerk or lurch.

FIG. 5illustrates graphs310of a hydraulic shift control system controlling a downshift. As illustrated, there are four graphs312,314,316, and318. The graphs310illustrate different input or responses with respect to time, x-axis320. The first graph312illustrates an input command (e.g., joystick command) relative to time. The first graph312includes a y-axis322for the input command (e.g., joystick command) and an x-axis320for time. The second graph314illustrates a change in speed of the work vehicle relative to time. The second graph314includes a y-axis324for speed and an x-axis320for time. The third graph316illustrates a change in volume of the hydraulic motor relative to time. The third graph316includes a y-axis326for the motor volume and an x-axis320for time. The fourth graph318illustrates a change in the volume of hydraulic fluid pumped relative to time. The fourth graph318includes a y-axis328for the pump volume and an x-axis320for time.

These graphs312,314,316, and318include various lines that illustrate the response of a hydraulic system to commands that change pump volume and motor volume and how changes in pump volume and motor volume change the speed of a work vehicle during a downshift. The first graph312includes line330that illustrates a command generated by an input device (e.g., touch screen, button, joystick, lever) to increase the speed of the work vehicle. The hydraulic shift control system (e.g., controller) receives this signal and generates a speed command to decrease the speed of the work vehicle. This speed command is illustrated by line332. As illustrated, the speed command332includes a first steady state portion334, a transition portion336, and a second steady state portion338. The first steady state portion334illustrates the previous speed command associated with the previous speed of the work vehicle. Upon receiving a new speed input (e.g., from an input device) the speed command332decreases from the first speed to a second speed (e.g., jumps) along the transition portion336. After changing the speed command, the speed command332continues with the second steady state portion338associated with the new desired speed of the work vehicle.

In response to the speed command, the hydraulic shift control system generates a motor volume command and a pump volume command. These commands are sent to the respective hydraulic motor(s) and hydraulic pump(s), which change the volume of the hydraulic motor(s) and the volume of hydraulic fluid pumped by the hydraulic pump(s). The motor volume command is illustrated by line340and the pump volume command is illustrated by line342. As illustrated, the motor volume command340includes a first steady state portion344, a transition portion346, and a second steady state portion348. The first steady state portion344illustrates the previous motor volume that enables the previous speed of the work vehicle. Upon receiving a new speed input (e.g., from an input device) the motor volume command340increases from the first volume to a second volume (e.g., jumps) along the transition portion346. The motor volume command340then continues with the second steady state portion348associated with the new desired motor volume.

The pump volume command line342includes a first steady state portion350, a first transition portion352, a second steady state portion354, a second transition portion356, and a third steady state portion358. The first steady state portion350illustrates the previous pump volume that enables the previous speed of the work vehicle. Upon receiving a new speed input (e.g., from an input device) the pump volume command342decreases from the first volume to a second volume along the first transition portion352(e.g. rate). As illustrated, this change may be a gradual change (e.g., linear). After reaching the second pump volume, the pump volume command342transitions to the second steady state portion354. The pump volume command342then again increases from the second pump volume to the first pump volume along the second transition portion356. The second transition portion356may be a linear signal to increase the pump volume from the second pump volume to the first pump volume. The motor volume command342then continues with the third steady state portion358associated with the second pump volume.

In some embodiments, there may be a delay between the change in the speed command332(i.e., the transition portion336) and the change in the motor volume command340(i.e., the transition portion346) and the pump volume command342(i.e., the end of the first transition352and the start of the second transition356). The motor wait delay is labeled360and the pump wait delay is labeled362. In some embodiments, the difference between the motor wait delay360and the pump wait delay362may be zero. In other embodiments, there may be a difference between the motor wait delay360and the pump wait delay362depending on the whether the hydraulic motor(s) or the hydraulic pump(s) take longer to respond to the speed command. As will be explained below, simultaneous changes in the motor volume and the pump volume enable a smooth downshift from a first speed to a second speed.

As explained above, the motor volume commands and pump volume commands are sent to the respective hydraulic motor(s) and hydraulic pump(s), which change the volume of the hydraulic motor(s) and the volume of hydraulic fluid pumped by the hydraulic pump(s). The changes in the volume of the hydraulic motors and the volume pumped by hydraulic pumps changes the speed of the work vehicle and how it shifts. The graphs310inFIG. 5illustrate a speed response line364, a motor volume line366, and a pump volume line368.

The speed line364includes a first steady state portion370, a transition portion372, and a second steady state portion374. The first steady state portion370illustrates the operation of the work vehicle at a first speed. Once the speed command is produced the hydraulic motor(s) and hydraulic pump(s) change operation enabling a decrease in the speed of the work vehicle from the first speed illustrated in the first steady state portion370to the second speed illustrated by the second steady state portion374. As illustrated, the transition portion372illustrates the change in speed between the first and second speeds. The transition portion372may be linear wherein the speed of the work vehicle gradually decreases from the first speed to the second speed. In other words, the work vehicle may not lurch or jerk as it downshifts and transitions from the first speed to the second speed.

In order to produce the smooth transition between speeds illustrated by the transition portion372of the speed line364, the hydraulic shift control system gradually (e.g., progressively) changes the pump volume prior to the motor shift and then rapidly changes the pump volume during the motor shift to counter the change in motor volume. These changes are illustrated by the motor volume line366and the pump volume line368. The motor volume line366illustrates the changes in motor volume in response to the motor volume commands. As illustrated, the motor volume line366includes a first steady state portion376, a transition portion378, and a second steady state portion380. At the first steady state portion376the motor volume is at a first volume (e.g., 50%) which then transitions to a second volume (e.g., 100%) of the second steady state portion380. The transition between these two volumes is illustrated by the transition portion378(e.g. rate). As illustrated, the transition portion378is gradual (e.g., linear) enabling a gradual change from the first volume to the second volume. By changing the volume of the hydraulic motor, the hydraulic motor may decrease the speed of the hydraulic motor (e.g., rapidly) if the hydraulic fluid flow is not also adjusted. For example, if the volume of the hydraulic motor is doubled but the hydraulic fluid flow remains unchanged, the hydraulic motor will rapidly change to spinning half as fast. Accordingly, to accommodate the change in motor volume, the hydraulic shift control system changes the amount of fluid pumped by the hydraulic pump or in other words the pump volume.

The pump volume line368illustrates the change in pump volume in response to the pump volume command342. The pump volume line368includes a first steady state portion382, a first transition portion384, a second steady state portion386, a second transition portion388, and a third steady state portion390. In order to block or reduce the rapid decrease in the speed of the hydraulic motor as the hydraulic motor increases in volume, the hydraulic pump may first decrease the volume of hydraulic fluid pumped, illustrated by the first transition portion384(e.g., rate). This gradual reduction in flow through the hydraulic motor decreases the speed of the hydraulic motor to reduce or block lurching of the work vehicle. After decreasing the volume of hydraulic fluid from the first volume to the second volume, the hydraulic pump transitions to the second steady state portion386as the hydraulic pumps waits for the motor volume command340to change. After the second steady state portion386, the hydraulic pump receives the command to increase the pump volume. The pump volume increases as illustrated by the second transition portion388. The increase in pump volume occurs as the motor volume increases. In some embodiments, the rate of the motor volume change illustrated by the transition portion378is equal to the change in the pump volume rate illustrated by the second transition portion388. The rotational speed of the hydraulic motor therefore remains unchanged. After reaching the second pump volume, the hydraulic pump maintains constant pump volume illustrated by the third steady state line390. Furthermore, in some embodiments, the pump volume rate illustrated by the first transition portion384may be less than the pump volume rate of the second transition portion388. In this way, the hydraulic shift control system gradually decreases the speed of the work vehicle from a first speed to a second speed without lurching or jerking the work vehicle. It should be understood that the hydraulic shift control system may control the aggressiveness of the downshift by controlling how rapidly the pump volumes changes.

Technical effects of the invention include a hydraulic shift control system that enables a work vehicle to smoothly change speeds as it upshifts or downshifts. The hydraulic shift control system enables the smooth shift by simultaneously controlling the hydraulic fluid flow through a hydraulic pump and a volume of a hydraulic motor.

As used herein, the terms “inner” and “outer”; “up” and “down”; “upper” and “lower”; “upward” and “downward”; “above” and “below”; “inward” and “outward”; and other like terms as used herein refer to relative positions to one another and are not intended to denote a particular direction or spatial orientation. The terms “couple,” “coupled,” “connect,” “connection,” “connected,” “in connection with,” and “connecting” refer to “in direct connection with” or “in connection with via one or more intermediate elements or members.”

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. Moreover, the order in which the elements of the methods described herein are illustrated and described may be re-arranged, and/or two or more elements may occur simultaneously. The embodiments were chosen and described in order to best explain the principals of the disclosure and its practical applications, to thereby enable others skilled in the art to best utilize the disclosure and various embodiments with various modifications as are suited to the particular use contemplated.