Method and system for controlling a hydrostatic drive system of an agricultural vehicle

1. A method for braking a work vehicle comprising an engine and a hydrostatic drive system, the hydrostatic drive system comprising a hydraulic pump configured to be rotationally driven by the engine and a hydraulic motor fluidly coupled with the hydraulic pump through a closed hydraulic loop of the hydrostatic drive system, the hydraulic pump configured to fluidly drive the hydraulic motor, the method comprising:

receiving, with one or more computing devices, an operator request to reduce a ground speed of the work vehicle;

monitoring, with the one or more computing devices, a fluid temperature of a hydraulic fluid associated with the closed hydraulic loop;

automatically controlling, with the one or more computing devices, at least one of a pump displacement of the hydraulic pump or a motor displacement of the hydraulic motor based on the operator request and the monitored fluid temperature to adjust hydrostatic braking of the work vehicle and thereby reduce the ground speed of the work vehicle; and

automatically adjusting a control valve to adjust a discharge flow of hydraulic fluid out of the closed hydraulic loop and a charge flow of hydraulic fluid into the closed hydraulic loop based on the monitored fluid temperature to reduce the fluid temperature of the hydraulic fluid associated with the closed hydraulic loop.

2. The method of claim 1 , further comprising:

comparing the monitored fluid temperature with a first predetermined temperature threshold; and

when the monitored fluid temperature exceeds the first temperature threshold, automatically adjusting the control valve to increase the discharge flow and charge flow to reduce the fluid temperature of the hydraulic fluid;

comparing the monitored fluid temperature with a second predetermined temperature threshold, the second predetermined temperature threshold being greater than the first predetermined temperature threshold; and

when the monitored fluid temperature exceeds the second temperature threshold for at least a predetermined time period, automatically adjusting the control valve to increase the discharge flow and charge flow to reduce the fluid temperature of the hydraulic fluid.

3. The method of claim 1 , further comprising:

sensing an engine speed of the engine;

comparing the engine speed with a predetermined engine speed threshold; and

when the engine speed threshold exceeds the predetermined engine speed threshold, adjusting at least one of the pump displacement or the motor displacement.

4. The method of claim 1 , wherein automatically controlling the at least one of the pump displacement or the motor displacement comprises:

sensing an engine speed of the engine;

determining an over-speeding scaling factor based on the sensed engine speed; and

controlling the at least one of the pump displacement or the motor displacement based on the over-speeding scaling factor.

5. The method of claim 1 , further comprising:

determining an upper pump displacement limit and a lower pump displacement limit;

wherein automatically controlling at least one of the pump displacement of the hydraulic pump or the motor displacement of the hydraulic motor comprises adjusting the pump displacement between the upper pump displacement limit and the lower pump displacement limit.

6. The method of claim 1 , wherein automatically controlling the at least one of the pump displacement or the motor displacement comprises:

determining an over-heating scaling factor based on the monitored fluid temperature; and

controlling the at least one of the pump displacement or the motor displacement based on the over-heating scaling factor.

7. The method of claim 1 , further comprising:

monitoring a motor speed of the hydraulic motor; and

adjusting the motor displacement based on the monitored motor speed.

8. The method of claim 1 , further comprising:

monitoring a hydraulic fluid pressure associated with the closed hydraulic loop;

determining whether the hydraulic fluid pressure is greater than a predetermined relief valve pressure; and

when it is determined that the hydraulic fluid pressure is greater than the predetermined relief valve pressure, adjusting the pump displacement between an upper limit and a lower limit, the lower limit being greater than a zero displacement position.

9. A method for braking a work vehicle comprising an engine and a hydrostatic drive system, the hydrostatic drive system comprising a hydraulic pump configured to be rotationally driven by the engine and a hydraulic motor fluidly coupled with the hydraulic pump through a closed hydraulic loop of the hydrostatic drive system, the hydraulic pump configured to fluidly drive the hydraulic motor, the method comprising:

monitoring, with one or more computing devices, a fluid temperature of a hydraulic fluid associated with the closed hydraulic loop;

automatically controlling, with the one or more computing devices, at least one of a pump displacement of the hydraulic pump or a motor displacement of the hydraulic motor to provide hydrostatic braking for the work vehicle; and

automatically adjusting, with the one or more computing devices, a control valve to adjust a discharge flow of hydraulic fluid out of the closed hydraulic loop and a charge flow of hydraulic fluid into the closed hydraulic loop based on the monitored fluid temperature to reduce the fluid temperature of the hydraulic fluid.

10. The method of claim 9 , wherein automatically adjusting the control valve comprises:

comparing the fluid temperature with a first predetermined temperature threshold; and

when the fluid temperature exceeds the first temperature threshold, automatically opening the control valve to increase the discharge flow out of the closed hydraulic loop and charge flow into the closed hydraulic loop.

11. The method of claim 9 , further comprising:

comparing the fluid temperature with a second predetermined temperature threshold, the second predetermined temperature threshold being greater than the first predetermined temperature threshold; and

when the fluid temperature exceeds the second temperature threshold, automatically opening the control valve to increase the discharge flow out of the closed hydraulic loop and charge flow into the closed hydraulic loop.

12. The method of claim 9 , wherein automatically controlling the at least one of the pump displacement or the motor displacement comprises:

sensing an engine speed of the engine;

comparing the engine speed with a predetermined engine speed threshold; and

when the engine speed threshold exceeds the predetermined engine speed threshold, adjusting at least one of the pump displacement or the motor displacement.

13. The method of claim 9 , wherein automatically controlling the at least one of the pump displacement or the motor displacement comprises:

sensing an engine speed of the engine;

determining an over-speeding scaling factor based on the sensed engine speed; and

controlling the at least one of the pump displacement or the motor displacement based on the over-speeding scaling factor.

14. The method of claim 9 , further comprising:

determining an upper pump displacement limit and a lower pump displacement limit;

wherein automatically controlling at least one of the pump displacement of the hydraulic pump or the motor displacement of the hydraulic motor to provide hydrostatic braking for the work vehicle comprises adjusting the pump displacement between the upper pump displacement limit and the lower pump displacement limit.

15. The method of claim 9 , wherein automatically controlling at least one of the pump displacement or the motor displacement comprises:

determining an over-heating scaling factor based on the monitored fluid temperature; and

controlling the at least one of the pump displacement or the motor displacement based on the over-heating scaling factor.

16. The method of claim 9 , further comprising:

monitoring a motor speed of the hydraulic motor; and

adjusting the motor displacement based on the monitored motor speed.

17. The method of claim 9 , further comprising:

monitoring a hydraulic fluid pressure associated with the closed hydraulic loop;

determining whether the hydraulic fluid pressure is greater than a predetermined relief valve pressure; and

when it is determined that the hydraulic fluid pressure is greater than the predetermined relief valve pressure, adjusting the pump displacement between an upper limit and a lower limit, the lower limit being greater than a zero displacement.

18. A method for braking a work vehicle comprising an engine and a hydrostatic drive system, the method comprising:

receiving, with one or more computing devices, an operator request to reduce a ground speed of the work vehicle;

monitoring a temperature of hydraulic fluid in the hydrostatic drive system comprising a closed hydraulic loop; and

automatically distributing, with the one or more computing devices, a kinetic energy of the work vehicle between an engine braking energy component and a heat dissipation energy component based on the received operator request by adjusting an operation of the hydrostatic drive system,

wherein adjusting an operation of the hydrostatic drive system comprises adjusting a control valve to adjust a discharge flow of hydraulic fluid out of the closed hydraulic loop and a charge flow of hydraulic fluid into the closed hydraulic loop based on the monitored temperature of hydraulic fluid in the hydrostatic drive system to reduce the temperature of the hydraulic fluid in the hydrostatic drive system.

19. The method of claim 18 , wherein automatically distributing the kinetic energy comprises sensing an engine speed of an engine, and wherein adjusting an operation of the hydrostatic drive system includes adjusting at least one of a pump displacement of a hydraulic pump or a motor displacement of a hydraulic motor to maintain the engine speed below a predetermined maximum engine speed.