HYDROSTATIC DRIVE SYSTEM

• US 20140260221A1
• Filed: 03/14/2013
• Published: 09/18/2014
• Est. Priority Date: 03/14/2013
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Metzger, Rustin G., Storer, Corwin E., Moberg, Carl, Dvorak, Paul A.
• Granted Patent: US 9,347,554 B2
• Time in Patent Office: Days
• US Class Current: 60/327
• CPC Class Codes: F16H 61/421 Motor capacity control by electro-hydraulic control means, e.g. using solenoid valves
• CPC Class Codes: F16H 61/431 Pump capacity control by electro-hydraulic control means, e.g. using solenoid valves
• CPC Class Codes: F16H 61/46 Automatic regulation in accordance with output requirements
• CPC Class Codes: F16H 61/47 for achieving a target output speed

Abstract

A hydrostatic drive system for a machine is disclosed. The hydrostatic drive system includes a pump, a hydraulic motor configured to receive a pressurized fluid from the pump and a controller operably connected to the pump and the hydraulic motor. The controller is configured to receive an input signal indicative of a current machine speed and a desired machine speed. Further, the controller is configured to output a motor displacement command signal and a pump displacement command signal to adjust a displacement of the hydraulic motor and the pump respectively based on the input signal to maintain at least one of constant machine speed or constant acceleration or constant deceleration during adjustment of the pump displacement and the motor displacement.

Claims

1. A hydrostatic drive system for a machine comprising:

a pump;

a hydraulic motor configured to receive a pressurized fluid from the pump; and

a controller operably connected to the pump and the hydraulic motor, the controller configured to;

receive an input signal indicative of a current machine speed and a desired machine speed; and

output a motor displacement command signal and a pump displacement command signal to selectively adjust a motor displacement of the hydraulic motor and a pump displacement of the pump based on the input signal to maintain at least one of constant machine speed or constant acceleration or constant deceleration during adjustment of the pump displacement and the motor displacement.

2. The hydrostatic drive system of claim 1, wherein the hydraulic pump is a variable displacement pump.

3. The hydrostatic drive system of claim 1, wherein the hydraulic motor is a two-speed motor.

4. The hydrostatic drive system of claim 1, wherein the controller is configured to determine an acceleration mode, during the acceleration mode desired machine speed is greater than the current machine speed.

5. The hydraulic drive system of claim 4, wherein during the acceleration mode, the controller is configured to:

output the motor displacement command signal to decrease the displacement of a motor swash plate of the hydraulic motor corresponding to the desired machine speed; and

output the pump displacement command signal to decrease the displacement of a pump swash plate of the pump to maintain the current machine speed while decreasing the displacement of the motor swash plate of the hydraulic motor to maintain the constant machine speed.

6. The hydraulic drive system of claim 5, wherein the controller is further configured to output the pump displacement command signal to increase the displacement of the pump swash plate of the pump to achieve the desired machine speed to maintain the constant acceleration.

7. The hydrostatic drive system of claim 1, wherein the controller is configured to determine a deceleration mode, during the deceleration mode the desired machine speed is less than the current machine speed.

8. The hydrostatic drive system of claim 7, wherein during the deceleration mode, the controller is configured to output the pump displacement command signal to decrease the displacement of a pump swash plate of the pump to achieve the desired machine speed.

9. The hydrostatic drive system of claim 8, wherein the controller is further configured to:

output the motor displacement command signal to increase the displacement of a motor swash plate of the hydraulic motor corresponding to the desired machine speed; and

output the pump displacement command signal to increase the displacement of the pump swash plate of the pump to maintain the desired machine speed while increasing the displacement of the motor swash plate of the hydraulic motor to maintain the constant deceleration.

10. A machine comprising:

at least one ground engaging member;

a hydrostatic drive system configured to power the ground engaging member, the hydrostatic drive system comprising;

a power source;

a pump configured to be driven by the power source;

a hydraulic motor configured to receive a pressurized fluid from the hydraulic pump; and

a controller electrically connected to the pump and the hydraulic motor, the controller configured to;

receive an input signal indicative of a current machine speed and a desired machine speed; and

output a motor displacement command signal and a pump displacement command signal to selectively adjust a motor displacement of the hydraulic motor and a pump displacement of the pump based on the input signal to maintain at least one of constant machine speed or constant acceleration or constant deceleration during adjustment of the pump displacement and the motor displacement.

11. The machine of claim 10, wherein the hydraulic pump is a variable displacement pump and the hydraulic motor is a two-speed motor.

12. The machine of claim 10, wherein the controller is configured to determine an acceleration mode, during the acceleration mode desired machine speed is greater than the current machine speed.

13. The machine of claim 12, wherein during the acceleration mode, the controller is configured to:

output the motor displacement command signal to decrease the displacement of a motor swash plate of the hydraulic motor corresponding to the desired machine speed; and

output the pump displacement command signal to decrease the displacement of a pump swash plate of the pump to maintain the current machine speed while decreasing the displacement of the motor swash plate of the hydraulic motor to maintain the constant machine speed.

14. The machine of claim 13, wherein the controller is further configured to output the pump displacement command signal to increase the displacement of the pump swash plate of the pump to achieve the desired machine speed to maintain the constant acceleration.

15. The machine of claim 10, wherein the controller is configured to determine a deceleration mode, during the deceleration mode the desired machine speed is less than the current machine speed.

16. The machine of claim 15, wherein during the deceleration mode, the controller is configured to output the pump displacement command signal to decrease the displacement of a pump swash plate of the pump to achieve the desired machine speed.

17. The machine of claim 16, wherein the controller is further configured to:

output the motor displacement command signal to increase the displacement of a motor swash plate of the hydraulic motor corresponding to the desired machine speed; and

output the pump displacement command signal to increase the displacement of the pump swash plate of the pump to maintain the desired machine speed while increasing the displacement of the motor swash plate of the hydraulic motor to maintain the constant deceleration.

18. A method for operating a hydrostatic drive system of a machine, hydrostatic drive system having a hydraulic motor receiving a pressurized fluid from a pump, the method comprising:

determining a current machine speed;

determining a desired machine speed; and

adjusting a displacement of the pump while maintaining at least one of constant machine speed or constant acceleration or constant deceleration during adjusting a displacement of the hydraulic motor based on the current machine speed and the desired machine speed.

19. The method of claim 18, wherein adjusting the displacement of the pump including decreasing the displacement of the pump while upshifting the hydraulic motor.

20. The method of claim 18, wherein adjusting the displacement of the pump including increasing the displacement of the pump while downshifting the hydraulic motor.