Drive creep mode for a utility vehicle

Abstract

A utility vehicle with a creep drive control system. The utility vehicle includes an engine, a hydrostatic transmission, an operator interface controller, a control valve, and a hydraulic control module. The hydrostatic transmission includes one or more drive pumps. Each of the one or more drive pumps includes a hydraulic control system. The operator interface controller includes at least one actuator. The control valve is configured to output hydraulic fluid to the hydraulic control system of the one or more drive pumps. The hydraulic control module is coupled to the operator interface controller and the control valve. The at least one actuator initiates a creep mode of operation in which the control valve regulates a pressure of hydraulic fluid flowing to the hydraulic control system of the one or more drive pumps to reduce a speed of the utility vehicle.

Description

DRIVE CREEP MODE FOR A UTILITY VEHICLERELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 63 / 489,723, filed March 10, 2023, entitled “Drive Creep Mode for a Utility Vehicle,” the entire contents of which are incorporated herein by reference for all purposes.BACKGROUND

[0002] Utility vehicles, such as loaders, telehandlers, forklifts, and the like, commonly have hydrostatic transmissions. Conventional hydrostatic transmissions can include a high-speed range and a low-speed range within which operators have infinitely variable speed control. In some forms, the conventional high-speed and low-speed ranges do not provide the level of precision operation desired by the operator in certain applications. Also, in some applications, when the operator encounters a heavy or quickly increasing load while operating a working attachment, the engine can stall. Accordingly, an improved utility vehicle and hydrostatic transmission are desired.SUMMARY

[0003] Some embodiments provide a utility vehicle with a creep drive control system. The utility vehicle includes an engine, a hydrostatic transmission, an operator interface controller, a control valve, and a hydraulic control module. The hydrostatic transmission includes one or more drive pumps. Each of the one or more drive pumps includes a hydraulic control system. The operator interface controller includes at least one actuator. The control valve is configured to output hydraulic fluid to the hydraulic control system of the one or more drive pumps. The hydraulic control module is coupled to the operator interface controller and the control valve. The at least one actuator initiates a creep mode of operation in which the control valve regulates a pressure of hydraulic fluid flowing to the hydraulic control system of the one or more drive pumps to reduce a speed of the utility vehicle.

[0004] In some forms, the control valve is a proportional solenoid valve, and the control valve receives hydraulic fluid from at least the charge pump. The utility vehicle can include a plurality of creep mode settings in which the control valve reduces the pressure of hydraulic fluid flowingto the hydraulic control system, and each of the plurality of creep mode settings reduces the pressure of hydraulic fluid flowing to the hydraulic control system by a different percentage of a standard hydraulic pressure with respect to the others of the plurality of creep mode settings. The plurality of creep mode settings can include a first creep mode setting corresponding to a first electric current output value and a second creep mode setting corresponding to a second electric output value lower than the first electric current output value. When the creep mode of operation is changed from the first creep mode setting to the second creep mode setting, the hydraulic control module applies a third electric current output value to the control valve that is less than the second electric output value before applying the second electric output value to the control valve. The creep mode of operation can include an open loop control that is not modulated in response to a detected vehicle speed or a detected hydraulic control system pilot pressure. The utility vehicle can further include a low-speed setting and a high-speed setting, and a temperature sensor configured to sense a temperature of the hydraulic fluid. The creep mode of operation can be inhibited when one or more of the high-speed setting is active, the temperature of the hydraulic fluid is above a threshold temperature value, or a control valve fault is detected.

[0005] In some forms, the utility vehicle can further include an engine control unit configured to control an engine speed, and an engine speed sensor. The hydraulic control module can be coupled to the engine control unit and the engine speed sensor. The hydraulic control module can initiate a droop assist function to actuate the control valve and reduce the pressure of hydraulic fluid flowing to the hydraulic control system of the one or more drive pumps based on a difference value between a requested engine speed value and an actual engine speed value sensed by the engine speed sensor, and the droop assist function can be configured to override the creep mode of operation. The utility vehicle can include at least one drive motor driven by the one or more drive pumps, wherein a vehicle speed sensor coupled to the hydraulic control module is configured to measure a speed of the drive motor. The hydraulic control module can adjust an electric current delivered to the control valve in response to the speed of the drive motor detected by the vehicle speed sensor.

[0006] Some embodiments provide a utility vehicle including an engine, a hydrostatic transmission including one or more drive pumps, at least one actuator, a foot pedal, and a control valve configured to output hydraulic fluid to the hydraulic control system of the one or more drivepumps. Each of the one or more drive pumps includes a hydraulic control system. The at least one actuator initiates a creep mode of operation in which the control valve reduces a pressure of hydraulic fluid flowing to the hydraulic control system and actuation of the foot pedal increases the pressure of hydraulic fluid flowing to the hydraulic control system.

[0007] In some forms, the creep mode of operation includes a plurality of creep mode settings in which the control valve reduces the pressure of hydraulic fluid flowing to the hydraulic control system. Each of the plurality of creep mode settings can reduce the pressure of hydraulic fluid flowing to the hydraulic control system by a different percentage of a standard hydraulic pressure with respect to the others of the plurality of creep mode settings. Each of the plurality of creep mode settings can correspond to an electric current output value that is applied to the control valve. The at least one actuator can be configured to modify a selected creep mode setting in response to user input to the at least one actuator. A degree to which the foot pedal is actuated can correspond to an increase in the electric current output value applied to the control valve. The plurality of creep mode settings can include a first creep mode setting corresponding to a first electric current output value and a second creep mode setting corresponding to a second electric current output value. Fully actuating the foot pedal can increase the electric current output value from the first electric current output value up to the second electric current output value. The foot pedal can be configured to increase an engine speed by an engine speed boost value during both the creep mode of operation and a standard mode of operation. The engine speed boost value can depend on an engine speed set during the standard mode of operation. During the creep mode of operation, the foot pedal can increase the engine speed to exceed a high idle engine speed of the standard mode of operation.

[0008] Some embodiments provide a method including providing a utility vehicle having an engine, a hydrostatic transmission including one or more drive pumps, each of the one or more drive pumps including a hydraulic control system, an actuator, a control valve configured to output hydraulic fluid to the hydraulic control system of the one or more drive pumps, and a hydraulic control module coupled to the actuator and the control valve. The method can further include the steps of activating a creep mode of operation in response to actuation of the actuator, setting a first creep mode setting value from a plurality of creep mode setting values in response to a creep mode setting selection, applying an electric current output value to the control valve, the electric currentoutput value corresponding to the first creep mode setting value, and reducing a pressure of hydraulic fluid flowing to the hydraulic control system in response to the applied electric current output value.

[0009] In some forms, the utility vehicle further comprises a low-speed setting and a highspeed setting, and a temperature sensor configured to sense a temperature of the hydraulic fluid. The creep mode of operation can be inhibited or deactivated when one or more of the low-speed setting is active, the temperature of the hydraulic fluid exceeds a temperature threshold value, or a control valve fault is detected. In some forms, the electric current output value applied to the control valve is not modified in response to a detected vehicle speed or a detected hydraulic control system pilot pressure.

[0010] Some embodiments provide a utility vehicle with a droop assist control system. The utility vehicle includes an engine, a hydrostatic transmission, an engine control unit, at least one engine speed sensor, a control valve, and a hydraulic control module. The hydrostatic transmission includes one or more drive pumps. Each of the one or more drive pumps includes a hydraulic control system. The engine control unit controls a speed of the engine. The control valve is configured to output hydraulic fluid to the hydraulic control system of the one or more drive pumps. The hydraulic control module is coupled to the engine control unit, the engine speed sensor, and the control valve. The hydraulic control module initiates a droop assist function to regulate the pressure of hydraulic fluid flowing to the hydraulic control system of the one or more drive pumps based on a difference value between a requested engine speed value determined by the engine control unit and an actual engine speed value sensed by the engine speed sensor. The hydraulic control module can also initiate the droop assist function to reduce a pressure of hydraulic fluid flowing to the hydraulic control system of the one or more drive pumps based on a measured engine load value.

[0011] In some embodiments, the engine control unit includes one or both of an accelerator pedal and an engine speed actuator of an operator interface controller. The hydraulic control module can cause the control valve to reduce the pressure of hydraulic fluid when the difference value is above a droop threshold value and ramp up the pressure of hydraulic fluid when the difference value is below the droop threshold value. A rate of the hydraulic pressure reduction canbe proportional to one of the actual engine speed value, the requested engine speed value, or a difference between the actual engine speed and the requested engine speed. A rate of the hydraulic fluid pressure reduction can be proportional to a rate at which the difference value is changing. The droop threshold value can be adjustable between a plurality of droop threshold values. The droop threshold value can be proportional to one of the actual engine speed value or the requested engine speed value. An engine load value can also be used to initiate the droop assist function when the engine load value is a certain percentage above a threshold value.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of embodiments of the invention:

[0014] FIG. 1 is a schematic view of a drive system for a utility vehicle according to an embodiment;

[0015] FIG. 2 is a block diagram of a creep mode control system for the utility vehicle according to an embodiment;

[0016] FIG. 3 is a block diagram of a droop assist control system for the utility vehicle according to an embodiment;

[0017] FIG. 4 is a graph of a correlation between the current applied to a control valve of the utility vehicle and the resulting pressure in pilot lines of the utility vehicle according to an embodiment;

[0018] FIG. 5 is a graph of a correlation between vehicle creep mode settings and an electrical current output to the control valve of the utility vehicle according to an embodiment;

[0019] FIG. 6 is a graph of a correlation between an engine speed boost provided as part of a creep boost function with respect to an engine speed set prior to initiating a creep mode of operation according to an embodiment;

[0020] FIG. 7 illustrates a method for the activation, editing, and deactivation of the creep mode of operation according to am embodiment; and

[0021] FIG. 8 is creep selection interface on a visual display unit of the utility vehicle according to an embodiment.DETAILED DESCRIPTION

[0022] The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Accordingly, the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the attached drawings. Thus, embodiments of the invention are not intended to be limited to the embodiments shown but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention.

[0023] As used herein, unless otherwise specified or limited, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, unless otherwise specified or limited, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. For example, the use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof, as well as additional items.

[0024] As used herein, unless otherwise specified or limited, “at least one of A, B, and C,” and similar other phrases, are meant to indicate A, or B, or C, or any combination of A, B, and / or C.As such, this phrase, and similar other phrases can include single or multiple instances of A, B, and / or C, and, in the case that any of A, B, and / or C indicates a category of elements, single or multiple instances of any of the elements of the categories A, B, and / or C.

[0025] As explained above, it would be useful to provide an improved utility vehicle having an improved hydrostatic drive system with precision, high-powered functions and features, and to mitigate engine stall. In general, a utility vehicle according to the embodiments described herein includes a vehicle body, an operator cab, one or more lift arms or booms coupled to the vehicle body, a set of wheels or tracks, and a vehicle drive and control system 100 (see FIG. 1). Various working attachments can be coupled to the one or more lift arms or booms to provide a wide range of functions. For example, the working attachments can be provided in the form of an auger, backhoe, bale mover, blade, boom lift, breaker, broom, bucket, chipper, concrete tool, grader blade, grappler, land leveler, log splitter, material unroller, mower, mulcher, pallet fork, rake, rock wheel, roto tiller, scarifier, scrapper, silage defacer, snow blower, snow push, sod unroller, spreader, stump grinder, stump remover, tree handler, trencher, and the like.

[0026] As illustrated in FIG. 1, the vehicle drive and control system 100 includes a charge pump 110, one or more implement pumps 112a, 112b, a control valve 114, a hydraulic control module 116, a drive joystick, a hydrostatic transmission 130, a right-side traveling unit 150, a leftside traveling unit 160, and a prime mover (not shown). Further, as illustrated in FIGS. 2 and 3, the vehicle drive and control system 100 can also include an operator interface controller 168, a visual display unit 172, an engine control unit 174, and a controller area network (CAN) bus communication network 176. In some embodiments, the vehicle drive and control system 100 can include at least one vehicle speed sensor 178, at least one hydraulic temperature sensor 180, and at least one foot pedal position sensor 182 (see FIG. 2). In some forms, an electronic service tool 186 can be selectively communicatively coupled to the CAN bus network 176 in order to calibrate the control valve 114 or modify various system parameters such as temperature compensation values, acceptable rates of vehicle acceleration, or hydraulic pressure and temperature thresholds in the system.

[0027] Referring further to FIG. 1, the implement pumps 112a, 112b can include a standard flow pump 112a and a high flow pump 112b. The charge pump 110 and the implement pumps112a, 112b, can each be provided in the form of a fixed displacement pump such as a gear pump or a vane pump. The charge pump 110, the implement pumps 112a, 112b, a right-side drive pump 138, and a left-side drive pump 142 are driven by the prime mover, such as an internal combustion engine or an electric motor. The charge pump 110 supplies hydraulic fluid to the drive joystick and the hydraulic circuit generally. The control valve 114 is configured to regulate the pressure and / or flow of hydraulic fluid from the charge pump 110 to a series of actuatable valves 124 associated with the drive joystick, and the control valve 114 is controlled by the hydraulic control module 116 as described in further detail below. In some forms, the control valve 114 is provided in the form of a proportional solenoid valve.

[0028] The drive joystick controls the pressure and flow of hydraulic fluid from the charge pump 110 to the pilot lines for the hydrostatic transmission 130 through the series of actuatable valves 124. In particular, the operator can move the drive joystick, which causes the actuatable valves 124 to selectively open and close. The actuatable valves 124 control the magnitude of hydraulic fluid pressure and flow through the pilot lines of the hydrostatic transmission 130. For example, when the drive joystick is pushed forward, the actuatable valves 124 will open or close to provide a flow of pilot hydraulic fluid to a hydraulic control system of the right-side drive pump 138 and a hydraulic control system of the left-side drive pump 142. The right-side drive pump 138 and the left-side drive pump 142 can be provided in the form of a variable displacement hydraulic pump. The hydraulic control systems can include, for example, a spool that changes the angle of a drive pump swash plate and, thus, the displacement of the corresponding drive pump 138, 142. Based on the magnitude of pressure of the pilot hydraulic fluid and which pilot lines the pressure is applied to, the right-side drive pump 138 and left-side drive pump 142 will pump hydraulic fluid to the right-side traveling unit 150 and the left-side traveling unit 160, respectively, in order to provide forward movement of the utility vehicle. In particular, the right-side traveling unit 150 can include a right-side hydraulic motor 154 that will be rotated in a forward direction, and the leftside traveling unit 160 can include a left-side hydraulic motor 164 that will also be rotated in a forward direction.

[0029] Similarly, when the drive joystick is pulled backward, the actuatable valves 124 will open or close to provide a flow of pilot hydraulic fluid to the hydraulic control system of the rightside drive pump 138 and the hydraulic control system of the left-side drive pump 142 to move theutility vehicle in a reverse direction. Based on the magnitude of pressure of the pilot hydraulic fluid and which pilot lines the pressure is applied to, the right-side drive pump 138 and left-side drive pump 142 will pump hydraulic fluid to the right-side traveling unit 150 and the left-side traveling unit 160, respectively, in order to provide backward movement of the utility vehicle. In particular, the right-side hydraulic motor 154 will be rotated in a backward direction, and the leftside hydraulic motor 164 will also be rotated in a backward direction. To provide right and left turning control when the drive joystick is moved to the right or left, the actuatable valves 124 will provide a flow of pilot hydraulic fluid to the hydraulic control system of the right-side drive pump 138 and the hydraulic control system of the left-side drive pump 142 that causes the right-side hydraulic motor 154 to be rotated in a direction opposite the left-side hydraulic motor 164. For example, when the joystick is moved to the right, the right-side hydraulic motor 154 will be rotated in reverse and the left-side hydraulic motor 164 will be rotated forward, thus causing the utility vehicle to turn right. A similar operation is provided when the joystick is moved to the left. For example, the right-side hydraulic motor 154 will be rotated forward and the left-side hydraulic motor 164 will be rotated in reverse, thus causing the utility vehicle to turn left.

[0030] Additionally, in a standard mode of operation, the utility vehicle can be operated in a low-speed setting or in a high-speed setting. For example, the utility vehicle can include a speed setting actuator that toggles the utility vehicle between the low-speed setting and the high-speed setting. In some embodiments, the actuator that toggles between the low-speed setting and the high-speed setting is provided on the operator interface controller 168, the drive joystick, or both. In some embodiments, the drive joystick can be considered part of the operator interface controller 168. Further, the utility vehicle can include an accelerator pedal and an engine speed actuator, such as a rotary dial, lever, or other type of user-selectable actuator. In the standard mode of operation, the accelerator pedal and the engine speed actuator can each control the speed of the engine independently. For example, as the accelerator pedal is pressed, the engine speed can increase, and as the rotary dial is jogged clockwise, the engine speed can increase and vice-versa.

[0031] FIGS. 2 and 3 illustrate block diagrams of a creep mode control system and a droop assist control system, respectively, and the parts of the utility vehicle that are associated with these functions. In general, both the creep mode control system and the droop assist control system involve controlling the control valve 114 with the hydraulic control module 116 in response toinputs thereto. In some forms, the hydraulic control module 116 can be provided in the form of a microcontroller or other electronic assembly having a processor and a memory, and the hydraulic control module 116 can be configured to receive communications through the CAN bus network 176 from at least the operator interface controller 168, the visual display unit 172, the engine control unit 174, the foot pedal position sensor 182, and / or the electronic service tool 186. The hydraulic control module 116 can also receive communications from the vehicle speed sensor 178 and the hydraulic temperature sensor 180. In some embodiments, the vehicle speed sensor 178 is provided in the form of a hall effect sensor that collects both speed and rotation direction data. In some forms, one or more of the sensor communications can be provided in the form of an analog voltage output, an analog current output, or a frequency output to the hydraulic control module 116. In some forms, one or more of the sensor communications can be provided by way of a CAN bus communication.

[0032] The hydraulic control module 116 is configured to apply one or more of an electrical current or voltage to the control valve 114. In some embodiments, the electrical current or voltage is applied via pulse width modulation. In some forms, as the electrical current applied to the control valve 114 is increased, the control valve 114 opens to an extent correlated to the applied electrical current to increase the pressure in the pilot lines to the hydrostatic transmission 130 and / or allow a greater flow of hydraulic fluid through the control valve 114. As the electrical current applied to the control valve 114 is decreased, the control valve 114 closes to an extent correlated to the applied electrical current to decrease the pressure in the pilot lines to the hydrostatic transmission 130 and / or restrict the flow of hydraulic fluid to the actuatable valves 124 (see FIG. 4).

[0033] Further, the operator interface controller 168 can be positioned within the operator cab of the utility vehicle and can include one or more creep mode actuators. The creep mode actuators can be provided in the form of buttons, switches, levers, touch screen widgets, knobs, dials, or other user-selectable and actuatable elements. In some forms, the creep mode actuator is provided in the form of a rotary dial that can jog between various creep mode settings. In some embodiments, the same rotary dial that functions as the engine speed actuator can also provide a dual function as one of the creep mode actuators. In some forms, each of the creep mode actuators can correspond to one of a plurality of creep mode settings, which will be described further below. The visual display unit 172 can be provided in the form of a graphic display screen having variousmodules or widgets that can inform an operator of the status of the utility vehicle, such as the engine speed, vehicle speed, hydraulic fluid temperature, engine coolant temperature, service or error conditions, activation statuses of various vehicle components such as the lights, fan, or other auxiliary components, the status of a low-speed or high-speed setting, the status of the creep mode setting, or the status of a droop assist function, which will be described in further detail below.

[0034] As shown in FIG. 3, the engine control unit 174 can receive CAN bus communications from the operator interface controller 168 and can control the speed of the prime mover. The engine control unit 174 can also include an engine speed sensor to detect engine speed and an engine load sensor to sense engine load, such as a manifold absolute pressure sensor. The engine control unit 174 can communicate these values to the operator interface controller 168, the visual display unit 172, and / or the hydraulic control module 116. The at least one vehicle speed sensor 178 (see FIG. 2) can be coupled to the right-side traveling unit 150 and / or the left-side traveling unit 160 and can be configured to detect the actual speed of the right-side hydraulic motor 154 and / or the left-side hydraulic motor 164.

[0035] In one embodiment, a creep mode of operation is disclosed that provides precise vehicle drive speed and vehicle control while also providing high power from the prime mover. First, in the standard mode of operation, prior to activation of the creep mode of operation, the engine can be set to a high idle, or maximum, engine speed such as 2000 RPM or 2500 RPM using the accelerator pedal or the engine speed actuator. For example, the accelerator pedal position sensor 182 or the engine speed actuator can send a signal to the engine control unit 174 to increase and control the speed of the engine by way of increased fuel injection. Next, either the high-speed setting or the low-speed setting is selected by the operator. In some forms, the creep mode of operation is available in both the low-speed setting and the high-speed setting. In some forms, the creep mode of operation only becomes available when the utility vehicle is in the low-speed setting. Once the engine speed is set to the desired RPM, the creep mode actuator can be actuated to activate a particular creep mode setting. Each of the plurality of creep mode settings corresponds to a particular pressure regulation and / or flow restriction setting for the control valve 114. In some forms, each of the plurality of creep mode settings can also correspond to a particular utility vehicle speed and / or the particular set engine speed.

[0036] FIG. 4 illustrates an exemplary graph of a correlation between the electric current applied to the control valve 114 by the hydraulic control module 116 and the resulting pressure in the pilot lines of the hydrostatic transmission 130. As shown in FIG. 4, the current applied to the control valve 114 is proportional to the change in pressure of the pilot hydraulic fluid. Here, a start current and an end current are electrical current values corresponding to the minimum current required to open the control valve 114 at least partially and the current at which the control valve 114 is substantially 100% open and allowing full pilot hydraulic fluid pressure, respectively. In some forms, the start current is about 500mA, and the end current is about 1100mA. During normal operation, the hydraulic control module 116 applies a hold current, which is an even greater electrical current value than the end current, to ensure that the control valve 114 is essentially fully open. In some forms, the hold current is about 1200mA. In each creep mode setting, the current output to the control valve 114 is a current value somewhere within a range between the start current and the end current, causing the control valve 114 to at least partially close. The partial closing of the control valve 114 results in a pressure reduction for the pilot hydraulic fluid flowing to the hydraulic control system of the right-side drive pump 138 and the hydraulic control system of the left- side drive pump 142 and, thus, a reduction in vehicle speed.

[0037] As a non-limiting example, when the start current is applied, the pressure of the pilot hydraulic fluid jumps to about 5.3 bar or about 75 psi, and when the end current is applied, the pressure of the pilot hydraulic fluid is about 21.3 bar or about 310 psi. Accordingly, the resulting pressure of the pilot hydraulic fluid ranges between about 5.3 bar or about 75 psi to about 21.3 bar or about 310 psi depending on the electric current value output to the control valve 114. In some forms, the degree to which the control valve 114 is open is proportional to the change in pressure of the pilot hydraulic fluid and / or the change in vehicle speed. For example, in some forms, when the control valve 114 is about 60% open, the pressure of the pilot hydraulic fluid will be reduced to about 60% of the pressure that would be provided when the control valve 114 is about 100% open and / or the vehicle speed will be reduced to about 60% of the vehicle speed that would otherwise be provided when the control valve 114 is about 100% open.

[0038] The quantitative relationship between the electrical current applied to the control valve 114 and the resulting pilot hydraulic fluid pressure can exist essentially independent of the engine speed. Accordingly, the relationship between the current applied to the control valve 114 and theresulting pilot hydraulic fluid pressure will be substantially always the same regardless of the engine speed setting (provided that the engine speed is high enough to produce the resulting pilot hydraulic pressure). However, because increased engine speed increases the vehicle travel speed of the utility vehicle, each of the creep mode settings produces a different vehicle travel speed based on whether the engine is set to a first engine speed versus a different, second engine speed.

[0039] In some embodiments of the creep mode of operation, the utility vehicle will be configured to move at a vehicle speed that is a certain percentage of the rated vehicle speed that would otherwise be provided in the standard mode of operation while the engine is rotating at a particular engine speed. This is accomplished by the control valve 114 modulating the pressure of the pilot hydraulic fluid flowing to the hydraulic control system of the right-side drive pump 138 and the hydraulic control system of the left-side drive pump 142. In a non-limiting example, if the engine speed is set to 2500 RPM, a first creep mode setting can correspond to a vehicle speed that is about 10% of the vehicle speed that would otherwise be provided in the standard mode of operation when the engine speed is 2500 RPM. If the engine speed is 2500 RPM, a second creep mode setting can correspond to a vehicle speed that is about 50% of the vehicle speed that would otherwise be provided in the standard mode of operation when the engine speed is 2500 RPM. If the engine speed is 2500 RPM, a third creep mode setting can correspond to a vehicle speed that is about 80% of the vehicle speed that would otherwise be provided in the standard mode of operation when the engine is set to 2500 RPM. The relationship between the electric current supplied to the control valve 114, the degree to which the control valve 114 opens based on the electric current supplied, and the vehicle speed produced by the degree to which the control valve 114 opens is known for various engine speeds. Accordingly, each creep mode setting can be programmed to cause a certain electric current to be supplied to the control valve 114 in order to induce known vehicle speeds.

[0040] FIG. 5 illustrates an exemplary graph of a correlation between various creep mode settings and the resulting electrical current output to the control valve 114. In this example, each of the creep mode settings corresponds with a percentage value between l%-99%, in one percent increments, e.g., 1%, 2%, 3% . . . 97%, 98%, 99%. For example, the creep mode actuator can be configured to toggle between individual percentage values in response to inputs to the operator interface controller 168, such as via a rotary dial, touchscreen, or keypad. In response, the hydrauliccontrol module 116 will deliver an electric current output to the control valve 114. In some forms, the creep mode setting value, l%-99%, corresponds to an electrical current value within the range of current values between the start current of about 500mA and the end current of about 1100mA. In some forms, the correlation is proportional, as shown in FIG. 5. However, other correlative relationships between the creep mode setting value and the electrical current output to the control valve 114 are contemplated. In effect, when the creep mode setting value increases, the vehicle speed increases. In some forms, each creep mode setting is provided as an open loop control where the electric current supplied to the control valve 114 is not modulated based on any pilot pressure feedback or vehicle speed feedback.

[0041] FIG. 5 further illustrates a creep boost function and the effect of the creep boost function on the electric current output from the hydraulic control module 116 to the control valve 114. As mentioned above, the accelerator pedal, in the standard mode of operation, functions to increase the engine speed. In some embodiments, the accelerator pedal can also be used to modulate the current delivered to the control valve 114 while the utility vehicle is in the creep mode of operation. In this instance, the accelerator pedal acts as a “boost” for the vehicle speed by further opening the control valve 114 to provide a greater pressure and / or flow of pilot hydraulic fluid. For example, if the creep mode setting is set to 30%, the creep boost function allows the electric current output to the control valve 114 to increase by a creep mode increment up to a maximum boost value, which is the current output that would be provided if the creep mode setting was, as a non-limiting example, 10% higher. In some forms, the maximum boost value can be toggled by the operator on the operator interface controller 168 to correspond to a creep mode increment larger than 10%, such as 20% or 30%. Accordingly, the magnitude of the creep boost function can be adapted to the operator’s preferences.

[0042] In the specific example shown in FIG. 5, the creep mode setting is set to 30%, and the creep mode increment corresponding to the maximum boost value is 10%. When the operator presses on the accelerator pedal, the pedal position sensor 182 will communicate the accelerator pedal position to the hydraulic control module 116 via the CAN bus network 176. As the operator gradually actuates the accelerator pedal, the current output to the control valve 114 will gradually increase from the current output value corresponding to the 30% creep mode setting to the current output value corresponding to the 40% creep mode setting when the accelerator pedal is fullyactuated. Accordingly, the vehicle speed will increase. Here, during the creep mode of operation, the pedal position sensor 182 sends signals to the hydraulic control module 116 rather than to the engine control unit 174.

[0043] It should be known that the control valve 114, when provided in the form of a solenoid valve, can experience hysteresis. Accordingly, for any change in the creep mode setting from a higher setting to a lower setting, or in some instances, when decreasing or deactivating the creep boost function, the hydraulic control module 116 will drop the current output to the control valve 114 below the current output value corresponding to the selected creep mode setting. Then, the hydraulic control module 116 will increase the current output up to the current output value corresponding to the selected creep mode setting. In some forms, the hydraulic control module 116 will overshoot by approximately 5% before raising to the selected creep mode setting. In this way, the creep mode of operation compensates for any hysteresis experienced by the solenoid, resulting in more precise creep mode control.

[0044] In some embodiments, the creep boost function can also include a boost in the engine speed. In this instance, the pedal position sensor 182 will communicate with both the hydraulic control module 116 and the engine control unit 174. Accordingly, as the operator presses on the accelerator pedal, the hydraulic control module 116 will increase the current output to the control valve 114 as described above, and, in addition, the engine control unit 174 will increase the engine speed. In some forms, the maximum engine speed increase allowable with the creep boost function is a static value, such as 30 RPM, 50 RPM, 100 RPM, or 200 RPM. Therefore, as the operator presses on the accelerator pedal, the engine speed will increase from the engine speed value that was set prior to initiating the creep boost function by up to the static value, i.e., 30 RPM, 50 RPM, 100 RPM, or 200 RPM when the accelerator is fully actuated.

[0045] As shown in FIG. 6, in some instances, the amount of engine speed boost provided as part of the creep boost function can be correlated to the engine speed that was set prior to initiating the creep mode of operation. For example, when the engine speed is set to 1100 RPM prior to initiating the creep mode of operation, the maximum engine speed boost allowable by the creep boost function is 200 RPM, but when the engine speed is set to 2500 RPM, the maximum engine speed boost allowable by the creep boost function is 30 RPM. In an embodiment where high idleis 2500 RPM, the creep boost function can allow the operator to exceed the high idle engine speed, which is otherwise capped during the standard operation. FIG. 6 illustrates a proportional relationship between the maximum RPM provided by the creep boost function and the set engine speed, such that the higher the set engine speed, the less the engine speed can be increased by the pedal boost function.

[0046] The flowchart of FIG. 7 illustrates a method 700 for the activation, editing, and deactivation of the creep mode of operation. For example, in step 710, the creep mode of operation is not active. Next, in some forms, the one or more creep mode actuators can include a creep activation button on the operator interface controller 168. When the creep activation button is pressed, the method 700 moves from step 710 to a creep mode activation step 720, where the creep mode of operation is activated. Upon activation, the creep mode of operation defaults to a default creep mode setting. In some embodiments, the default creep mode setting is 65% for the first activation of the creep mode of operation. As described above, the one or more creep mode actuators can include a rotary dial on the operator interface controller 168 for selecting between different creep mode settings. If the operator either presses the rotary dial, presses the creep activation for less than a threshold period of time (i.e., less than two seconds), or if the operator activates the creep mode of operation for the first time, the method 700 moves from step 720 to a creep mode editing step 730. In step 730, a creep mode selection interface is displayed to the operator on the visual display unit 172, and the operator can use the rotary dial to select a particular creep mode setting value between 1 %-99% (see FIG. 8) as described above.

[0047] When step 730 is activated, an edit mode timer is also activated to countdown from a specific time value, such as 60 seconds, 50 seconds, 40 seconds, 30 seconds, 20 seconds, 10 seconds, etc. If one or more of the edit mode timer expires, the rotary dial is pressed to confirm a creep mode setting selection, the creep activation button is pressed, or another, non-creep mode widget on the operator interface controller 168 is selected, the method 700 moves from step 730 back to step 720 where the creep mode of operation is activated at the creep mode setting selected during step 730 or the default creep mode setting if no creep mode setting was selected. If the creep activation button is pressed for longer than the threshold period of time (i.e., more than two seconds) while the method 700 is at either step 720 or step 730, the method 700 moves back to step 710 where the creep mode of operation is deactivated. It should be noted that if the creepactivation button is then pressed to activate the creep mode of operation again, the creep mode of operation will automatically initiate in the last creep mode setting that was selected, e.g., the default creep setting if it was never altered, or whichever creep mode setting was selected by the operator in the previous step 730.

[0048] In some embodiments, if one or more creep inhibition factors are triggered at any point before, during, or after any point of the method 700, the method 700 will return to, or remain at, step 710 where the creep mode of operation is inactive. The one or more creep mode inhibition factors can include whether the hydraulic temperature sensor 180 detects a hydraulic fluid temperature above a maximum hydraulic temperature threshold value or below a minimum hydraulic temperature threshold value, or if a predetermined fault trigger is detected such as a fault corresponding to the function of the control valve 114. Further, if the hydraulic fluid temperature is outside the acceptable temperature range, the visual display unit 172 can also provide a visual, auditory, and / or message alert to the operator to ensure that the operator is aware of the reason that the creep mode of operation was inhibited. In some forms, the hydraulic temperature thresholds can be modified by the operator via the operator interface controller 168. Also, the creep inhibition factors can include the speed setting of the vehicle being set to the high-speed mode because, as described above, in some forms, the creep mode of operation is only available in the low-speed setting.

[0049] One non-limiting example of the creep mode of operation is explained in the following description. In this example, the operator turns on the vehicle, initiates the engine, sets the vehicle to the low-speed mode, and sets the engine speed to 2500 RPM using the rotary dial of the operator interface controller 168, which acts as the engine speed actuator. In this example, 2500 RPM is the high idle limit for engine speed control during the standard mode of operation. Then, the operator selects the creep activation button of the operator interface controller 168, which activates the creep mode of operation. Upon first activation, the default creep mode setting is set at 65%, and the creep mode editing function is automatically initiated where a creep selection interface is prompted on the visual display unit 172. FIG. 8 illustrates an exemplary creep selection interface, wherein creep mode settings between 1-99 are displayed as a ring widget. The operator then rotates the rotary dial of the operator interface controller 168 to select a 30% creep mode setting and confirms the selection by pressing down on the rotary dial. Once selected, the operator interfacecontroller 168 will send a signal to the hydraulic control module 116 to modulate the control valve 114 to achieve the creep mode setting of 30%. Using FIGS. 4 and 5 as a reference, this means that the electric current output to the control valve 114 will change from the hold current of 1200 mA to an electric current output of 688 mA, which partially closes the control valve 114 and results in a pilot hydraulic fluid pressure of about 10.3 bar or about 150 psi.

[0050] When the operator moves the drive joystick forward to the full extent, the actuatable valves 124 will direct the flow of hydraulic fluid for forward movement of both the right-side hydraulic motor 154 and the left-side hydraulic motor 164, and the utility vehicle will ramp up to the vehicle speed associated with the 30% creep mode setting at 2500 RPM. In this example, no feedback is provided from the vehicle speed sensor 178. During forward movement, the operator may desire a boost in speed, and thus, the operator activates the creep boost function. In this example, the creep boost function is set to have a 10% creep boost increment and allows an increase in the electric current output to the control valve 114 up to the electric current output associated with a 10% increase in the creep mode setting. For example, if the operator actuates the accelerator pedal to the full extent, the electric current output to the control valve 114 will increase from about 688 mA (current output associated with a 30% creep mode setting) to about 750 mA (current output associated with a 40% creep mode setting), as shown in FIG. 5. Accordingly, the pilot hydraulic fluid pressure will increase from about 10.3 bar or about 150 psi to about 11.9 bar or about 173 psi. As a result, the vehicle speed will increase from the vehicle speed associated with the 30% creep mode setting at 2500 RPM to the vehicle speed associated with the 40% creep mode setting at 2500 RPM.

[0051] In embodiments where the creep boost function also includes an increase in engine speed, as shown in FIG. 6, when the operator actuates the accelerator pedal to the full extent, the electric current output to the control valve 114 will increase to 750 mA, and the engine speed will increase from 2500 RPM to 2530 RPM. As a result, the vehicle speed will increase from the vehicle speed associated with the 30% creep mode setting at 2500 RPM to the vehicle speed associated with the 40% creep mode setting at 2530 RPM. If the operator desires to deactivate the creep mode of operation, the operator can select the creep activation button, and the creep mode of operation will deactivate. Also, if at any point during operation, one or more of the creep inhibition factors are detected, the creep mode of operation will automatically turn off.

[0052] In some embodiments, while the creep mode of operation is active, the hydraulic control module 116 receives input from the vehicle speed sensor 178 in order to achieve a specific vehicle speed corresponding to a particular creep mode setting and the set engine speed. The hydraulic control module 116 modulates the electric current delivered to the control valve 114 in response to the sensed vehicle speed to adjust the pressure of the hydraulic fluid flowing to the actuatable valves 124 and the hydrostatic transmission 130. This changes the stroke of the rightside drive pump 138 and the left-side drive pump 142, and, thus, the speed of the right-side hydraulic motor 154 and the left-side hydraulic motor 164. Accordingly, the intended speed for the particular creep mode vehicle speed is achieved. In some forms, the vehicle speed corresponding to each creep mode setting is a value that is independent of the engine speed. For example, the hydraulic control module 116 can receive feedback from the vehicle speed sensor 178 in order to partially open or partially close the control valve 114 to achieve the vehicle speed of a particular creep mode setting independent of the set, or actual, engine speed.

[0053] The relationship between the milliamps of electric current provided to the control valve 114 and the corresponding vehicle ground speed at various engine speeds can be stored in the memory of the hydraulic control module 116. In some forms, pressure sensors are provided in the pilot lines to the hydrostatic transmission 130, and feedback from the pressure sensors is used by the hydraulic control module 116 to change the electric current to the control valve 114 and achieve various creep mode vehicle speeds.

[0054] In some embodiments, the lowest creep mode setting can prevent the utility vehicle from moving if the engine speed is set too low. Accordingly, hydraulic control module 116 can store a minimum vehicle drive speed that will override the creep mode setting. In a non-limiting example, if (1) the engine speed is set to 1100 RPM, (2) a 5% creep mode setting is selected, and (3) the right and left-side hydraulic motors 154, 164 cannot develop enough torque to move the vehicle, the hydraulic control module 116 will override the 5% creep mode setting and send signals to the control valve 114 to increase the pressure of hydraulic fluid until a minimum drive speed threshold is detected by the vehicle speed sensor 178.

[0055] In some embodiments, a droop assist function is provided. The droop assist function is designed to reduce loading on the prime mover temporarily to avoid engine stalling due tooverload. In some forms, the droop assist function is always activatable, and in some forms, the droop assist function is only activatable in one of the low-speed setting or the high-speed setting. As mentioned above, the engine control unit 174 can detect engine speed and engine load. During operation, the engine control unit 174 sends the detected, actual engine speed value to the hydraulic control module 116, and the hydraulic control module 116 compares the actual engine speed value to the requested engine speed value. The requested engine speed value can be determined by the accelerator pedal position sensor 182 and / or the engine speed actuator. If the difference value between the actual engine speed value and the requested engine speed value exceeds one or more droop threshold values, then the utility vehicle activates the droop assist function. In some embodiments, the droop assist function is activated when an engine load value exceeds an engine load threshold. When the droop assist function is activated, the hydraulic control module 116 ramps down the electric current supplied to the control valve 114 to reduce the drive pilot pressure to the hydrostatic transmission 130. In some forms, the hydraulic control module 116 reduces the electric current according to a proportional curve that is correlated to one or more of the actual engine speed value, the requested engine speed value, or the difference between the two.

[0056] Once the difference value between the actual engine speed value and the requested engine speed value drops back below the droop threshold value, or the engine load no longer exceeds an engine load threshold, the hydraulic control module 116 will ramp up the electric current supplied to the control valve 114 back to the value it would have been prior to activation of the droop assist function. In some embodiments, the hydraulic control module 116 will ramp up the electric current supplied to the control valve 114 according to a proportional curve that is correlated to one or more of the actual engine speed value, the requested engine speed value, or the difference between the two. In some embodiments, the one or more droop threshold values include both an engine load value and a difference value between the actual engine speed value and the requested engine speed value. As is contemplated by this disclosure, the creep mode of operation may be active when the droop assist Junction is activated. In this instance, the droop assist function will override the creep mode of operation, and the hydraulic control module 116 will ramp down the electric current supplied to the control valve 114 according to the disclosure provided above. Once the difference value between the actual engine speed value and the requested engine speed value drops back below the droop threshold value, the hydraulic control module 116will ramp up the electric current supplied to the control valve 114 back to the value corresponding to the current creep mode setting.

[0057] In some forms, the droop assist function includes multiple user- selectable droop threshold values that can be selected via the visual display unit 172. For example, in some forms, a high or firm droop threshold valve may allow a large drop in engine speed, such as 450 RPM, before activating the droop assist function. In some forms, an additional medium droop threshold valve may allow a modest drop in engine speed, such as 375 RPM, before activating the droop assist function. In some forms, a low or soft droop threshold valve may only allow a small drop in engine speed, such as 300 RPM, before activating the droop assist function. Further, each of the droop threshold values may also include a temporal element. For example, the droop assist function may only activate when the difference between the actual engine speed value and the requested engine speed value exceeds the droop threshold value for a certain amount of time, such as 1 , 2, or 3 seconds. Similarly, the droop assist function may only deactivate and ramp the electric current supplied to the control valve 114 back up after the difference between the actual engine speed value and the requested engine speed value drops back below the droop threshold value for a certain amount of time.

[0058] In other embodiments, other configurations are possible. For example, those of skill in the art will recognize, according to the principles and concepts disclosed herein, that various combinations, sub-combinations, and substitutions of the components discussed above can provide appropriate protection for the drive creep mode of operation and the droop assist function disclosed herein.

Claims

CLAIMS1. A utility vehicle having a creep drive control system, the utility vehicle comprising: an engine; a hydrostatic transmission including one or more drive pumps, each of the one or more drive pumps including a hydraulic control system; an operator interface controller including at least one actuator; a control valve configured to output hydraulic fluid to the hydraulic control system of the one or more drive pumps; and a hydraulic control module coupled to the operator interface controller and the control valve, wherein the at least one actuator initiates a creep mode of operation in which the control valve regulates a pressure of hydraulic fluid flowing to the hydraulic control system of the one or more drive pumps to reduce a speed of the utility vehicle.

2. The utility vehicle of claim 1, wherein the control valve is a proportional solenoid valve, and the control valve receives hydraulic fluid from at least one charge pump.

3. The utility vehicle of claim 1, wherein the creep mode of operation includes a plurality of creep mode settings in which the control valve reduces the pressure of hydraulic fluid flowing to the hydraulic control system, and each of the plurality of creep mode settings reduces the pressure of hydraulic fluid flowing to the hydraulic control system by a different percentage of a standard hydraulic pressure with respect to the others of the plurality of creep mode settings.

4. The utility vehicle of claim 3, wherein the plurality of creep mode settings includes a first creep mode setting corresponding to a first electric current output value and a second creep mode setting corresponding to a second electric output value lower than the first electric current output value, and when the creep mode of operation is changed from the first creep mode setting to the second creep mode setting, the hydraulic control module applies a third electric current output value to the control valve that is less than the second electric output value before applying the second electric output value to the control valve.

5. The utility vehicle of claim 1 , wherein the creep mode of operation comprises an open loop control that is not modulated in response to a detected vehicle speed or a detected hydraulic control system pilot pressure.

6. The utility vehicle of claim 1 further comprising: a low-speed setting and a high-speed setting; and a temperature sensor configured to sense a temperature of the hydraulic fluid; wherein the creep mode of operation is inhibited when one or more of the high-speed setting is active, the temperature of the hydraulic fluid is above a threshold temperature value, or a control valve fault is detected.

7. The utility vehicle of claim 1, further comprising: an engine control unit configured to control an engine speed; and an engine speed sensor, wherein the hydraulic control module is coupled to the engine control unit and the engine speed sensor, the hydraulic control module initiates a droop assist function to actuate the control valve and reduce the pressure of hydraulic fluid flowing to the hydraulic control system of the one or more drive pumps based on a difference value between a requested engine speed value and an actual engine speed value sensed by the engine speed sensor, and the droop assist function is configured to override the creep mode of operation.

8. A utility vehicle comprising: an engine; a hydrostatic transmission including one or more drive pumps, each of the one or more drive pumps including a hydraulic control system; at least one actuator; a foot pedal; a control valve configured to output hydraulic fluid to the hydraulic control system of the one or more drive pumps; and wherein the at least one actuator initiates a creep mode of operation in which the control valve reduces a pressure of hydraulic fluid flowing to the hydraulic control system and actuation of the foot pedal increases the pressure of hydraulic fluid flowing to the hydraulic control system.

9. The utility vehicle of claim 8, wherein the creep mode of operation includes a plurality of creep mode settings in which the control valve reduces the pressure of hydraulic fluid flowing to the hydraulic control system, and each of the plurality of creep mode settings reduces the pressure of hydraulic fluid flowing to the hydraulic control system by a different percentage of a standard hydraulic pressure with respect to the others of the plurality of creep mode settings.

10. The utility vehicle of claim 9, wherein each of the plurality of creep mode settings corresponds to an electric current output value that is applied to the control valve, and the at least one actuator is configured to modify a selected creep mode setting in response to user input to the at least one actuator.

11. The utility vehicle of claim 10, wherein a degree to which the foot pedal is actuated corresponds to an increase in the electric current output value applied to the control valve.

12. The utility vehicle of claim 11 , wherein the plurality of creep mode settings includes a first creep mode setting corresponding to a first electric current output value and a second creep mode setting corresponding to a second electric current output value.

13. The utility vehicle of claim 12, wherein fully actuating the foot pedal increases the electric current output value from the first electric current output value up to the second electric current output value.

14. The utility vehicle of claim 8, wherein the foot pedal is configured to increase an engine speed by an engine speed boost value during both the creep mode of operation and a standard mode of operation.

15. The utility vehicle of claim 14, wherein the engine speed boost value depends on an engine speed set during the standard mode of operation.

16. The utility vehicle of claim 14, wherein during the creep mode of operation, the foot pedal increases the engine speed to exceed a high idle engine speed of the standard mode of operation.

17. A method comprising: providing a utility vehicle having: an engine, a hydrostatic transmission including one or more drive pumps, each of the one or more drive pumps including a hydraulic control system, an actuator, a control valve configured to output hydraulic fluid to the hydraulic control system of the one or more drive pumps, and a hydraulic control module coupled to the actuator and the control valve; activating a creep mode of operation in response to actuation of the actuator; setting a first creep mode setting value from a plurality of creep mode setting values in response to a creep mode setting selection; applying an electric current output value to the control valve, the electric current output value corresponding to the first creep mode setting value; and reducing a pressure of hydraulic fluid flowing to the hydraulic control system in response to the applied electric current output value.

18. The method of claim 17, wherein the utility vehicle further comprises a low-speed setting and a high-speed setting, and a temperature sensor configured to sense a temperature of the hydraulic fluid.

19. The method of claim 18, wherein the creep mode of operation is inhibited or deactivated when one or more of the low-speed setting is active, the temperature of the hydraulic fluid exceeds a temperature threshold value, or a control valve fault is detected.

20. The method of claim 17, wherein the electric current output value applied to the control valve is not modified in response to a detected vehicle speed or a detected hydraulic control system pilot pressure.

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