Hydraulic hybrid propel circuit with hydrostatic option and method of operation

1. A hydraulic system for a mobile work vehicle, the hydraulic system configurable in a hybrid mode and a hydrostatic mode, the hydraulic system comprising:

a pump/motor adapted to exchange power with a drive train of the mobile work vehicle;

a propel circuit adapted to exchange hydraulic fluid power with the pump/motor;

a pump adapted to transfer power from a prime mover of the mobile work vehicle to the propel circuit;

a hydraulic accumulator adapted to exchange hydraulic fluid power via an accumulator isolation valve with the propel circuit when the hydraulic system is configured in the hybrid mode; and

an accessory circuit adapted to receive hydraulic fluid power from the hydraulic accumulator and is adapted to receive hydraulic fluid power from the propel circuit at least when the hydraulic system is configured in the hydrostatic mode and the accumulator isolation valve is closed.

2. The hydraulic system of claim 1 , wherein the pump/motor is a first variable displacement pump/motor and the pump is a second variable displacement pump/motor.

3. The hydraulic system of claim 1 , wherein at least one of the pump/motor and the pump is a variable displacement pump/motor with a displacement controller and an actuator, wherein the actuator is adapted to set a position of the displacement controller and thereby set a displacement of the variable displacement pump/motor, and wherein the accessory circuit hydraulically powers the actuator.

4. The hydraulic system of claim 3 , wherein the displacement controller is an adjustable bearing plate, the actuator is a bearing plate actuator, and the position is a bearing plate angle.

5. The hydraulic system of claim 3 , wherein the displacement controller is a swash plate, the actuator is a swash plate actuator, and the position is a swash plate angle.

6. The hydraulic system of claim 1 , wherein the accessory circuit is a steering circuit.

7. The hydraulic system of claim 1 , wherein the accessory circuit is a brake circuit.

8. The hydraulic system of claim 1 , wherein the accessory circuit is configured to operate at a first pressure, wherein the hydraulic accumulator is configured to operate above a second pressure, and wherein the first pressure is less than the second pressure.

9. The hydraulic system of claim 1 , wherein the hydraulic accumulator is configured to be charged and discharged via the accumulator isolation valve when the hydraulic system is in the hybrid mode and wherein the hydraulic accumulator is configured to be charged via a flow restrictor when the hydraulic system is in the hydrostatic mode.

10. The hydraulic system of claim 9 , wherein the propel circuit is substantially at a same pressure as the accumulator when the hydraulic system is in the hybrid mode and wherein the propel circuit is at an independent pressure from the accumulator when the hydraulic system is in the hydrostatic mode.

11. A hydraulic system for a mobile work vehicle, the hydraulic system adapted to capture inertial energy of the mobile work vehicle, convert the inertial energy into potential energy stored within a hydraulic accumulator, and power at least one actuator of the mobile work vehicle by releasing at least some of the potential energy from the hydraulic accumulator when in a hybrid mode, the hydraulic system further adapted to operate in a hydrostatic mode, the hydraulic system comprising:

the hydraulic accumulator;

a variable displacement pump/motor with a swash plate and a swash plate actuator, the swash plate actuator adapted to set a swash plate angle of the swash plate and thereby set a displacement of the variable displacement pump/motor; and

a hydraulic circuit between the hydraulic accumulator and the swash plate actuator, the hydraulic circuit adapted to hydraulically power the swash plate actuator with the potential energy stored within the hydraulic accumulator.

12. The hydraulic system of claim 11 , wherein the variable displacement pump/motor is operably connected to a prime mover of the mobile work vehicle.

13. The hydraulic system of claim 11 , wherein the variable displacement pump/motor is operably connected to a drive train of the mobile work vehicle.

14. The hydraulic system of claim 11 , further comprising a second variable displacement pump/motor with a second swash plate and a second swash plate actuator, the second swash plate actuator adapted to set a second swash plate angle of the second swash plate and thereby set a second displacement of the second variable displacement pump/motor, wherein the hydraulic circuit is also between the hydraulic accumulator and the second swash plate actuator, and wherein the hydraulic circuit is also adapted to hydraulically power the second swash plate actuator with the potential energy stored within the hydraulic accumulator.

15. The hydraulic system of claim 14 , further comprising an accumulator isolation valve for selectively isolating the hydraulic accumulator from a propel circuit, wherein when the hydraulic system is configured in the hybrid mode energy may be transferred between the hydraulic accumulator and a drive train of the mobile work vehicle via the accumulator isolation valve, the propel circuit, and the variable displacement pump/motor, and wherein when the hydraulic system is configured in the hydrostatic mode energy may be transferred between a prime mover of the mobile work vehicle and the drive train via the second variable displacement pump/motor, the propel circuit, and the variable displacement pump/motor.

16. A method of powering an accessory circuit of a hydraulic system for a mobile work vehicle, the hydraulic system configurable in a hybrid mode and a hydrostatic mode, the method comprising:

hydraulically connecting the accessory circuit to a hydraulic accumulator at least when the hydraulic system is configured in the hydrostatic mode;

regenerating the hydraulic accumulator with inertial energy of the mobile work vehicle when the hydraulic system is configured in the hybrid mode;

charging and discharging the hydraulic accumulator with a propel circuit of the hydraulic system at substantially an equal pressure in the hydraulic accumulator and the propel circuit when the hydraulic system is configured in the hybrid mode; and

charging the hydraulic accumulator via a flow restrictor from the propel circuit of the hydraulic system with a higher pressure in the propel circuit than in the hydraulic accumulator when the hydraulic system is configured in the hydrostatic mode, wherein the hydraulic accumulator is isolated from the propel circuit when the hydraulic system is configured in the hydrostatic mode.

17. The method of claim 16 , further comprising actuating a displacement controller of a variable displacement pump/motor with the accessory circuit.

18. The method of claim 17 , further comprising maintaining hydraulic pressure within the hydraulic accumulator and thereby maintaining control of the variable displacement pump/motor when the hydraulic system is configured in the hydrostatic mode.

19. The method of claim 17 , wherein the variable displacement pump/motor does not include a hydraulic pump dedicated to supplying control pressure for actuating the displacement controller.

20. The method of claim 16 , further comprising actuating a steering unit of the mobile work vehicle with the accessory circuit.

21. A hydraulic system for a mobile work vehicle, the hydraulic system configurable in a hybrid mode and a hydrostatic mode, the hydraulic system comprising:

a pump/motor adapted to exchange power with a drive train of the mobile work vehicle;

a propel circuit adapted to exchange hydraulic fluid power with the pump/motor;

a pump adapted to transfer power from a prime mover of the mobile work vehicle to the propel circuit, wherein at least one of the pump/motor and the pump is a variable displacement pump/motor with a displacement controller and an actuator, wherein the actuator is adapted to set a position of the displacement controller and thereby set a displacement of the variable displacement pump/motor;

a hydraulic accumulator adapted to exchange hydraulic fluid power via an accumulator isolation valve with the propel circuit when the hydraulic system is configured in the hybrid mode; and

an accessory circuit adapted to receive hydraulic fluid power from the hydraulic accumulator at least when the hydraulic system is configured in the hydrostatic mode and the accumulator isolation valve is closed, wherein the accessory circuit hydraulically powers the actuator.

22. A hydraulic system for a mobile work vehicle, the hydraulic system configurable in a hybrid mode and a hydrostatic mode, the hydraulic system comprising:

a pump/motor adapted to exchange power with a drive train of the mobile work vehicle;

a propel circuit adapted to exchange hydraulic fluid power with the pump/motor;

a pump adapted to transfer power from a prime mover of the mobile work vehicle to the propel circuit;

a hydraulic accumulator adapted to exchange hydraulic fluid power via an accumulator isolation valve with the propel circuit when the hydraulic system is configured in the hybrid mode; and

an accessory circuit adapted to receive hydraulic fluid power from the hydraulic accumulator at least when the hydraulic system is configured in the hydrostatic mode and the accumulator isolation valve is closed, wherein the accessory circuit is configured to operate at a first pressure, wherein the hydraulic accumulator is configured to operate above a second pressure, and wherein the first pressure is less than the second pressure.

23. A hydraulic system for a mobile work vehicle, the hydraulic system configurable in a hybrid mode and a hydrostatic mode, the hydraulic system comprising:

a pump/motor adapted to exchange power with a drive train of the mobile work vehicle;

a propel circuit adapted to exchange hydraulic fluid power with the pump/motor;

a pump adapted to transfer power from a prime mover of the mobile work vehicle to the propel circuit;

a hydraulic accumulator adapted to exchange hydraulic fluid power via an accumulator isolation valve with the propel circuit when the hydraulic system is configured in the hybrid mode, wherein the hydraulic accumulator is configured to be charged and discharged via the accumulator isolation valve when the hydraulic system is in the hybrid mode and wherein the hydraulic accumulator is configured to be charged via a flow restrictor when the hydraulic system is in the hydrostatic mode; and

an accessory circuit adapted to receive hydraulic fluid power from the hydraulic accumulator at least when the hydraulic system is configured in the hydrostatic mode and the accumulator isolation valve is closed.

24. A method of powering an accessory circuit of a hydraulic system for a mobile work vehicle, the hydraulic system configurable in a hybrid mode and a hydrostatic mode, the method comprising:

hydraulically connecting the accessory circuit to a hydraulic accumulator at least when the hydraulic system is configured in the hydrostatic mode;

regenerating the hydraulic accumulator with inertial energy of the mobile work vehicle when the hydraulic system is configured in the hybrid mode;

charging and discharging the hydraulic accumulator with a propel circuit of the hydraulic system at substantially an equal pressure in the hydraulic accumulator and the propel circuit when the hydraulic system is configured in the hybrid mode;

charging the hydraulic accumulator via a flow restrictor from the propel circuit of the hydraulic system with a higher pressure in the propel circuit than in the hydraulic accumulator when the hydraulic system is configured in the hydrostatic mode; and

actuating a displacement controller of a variable displacement pump/motor with the accessory circuit.