Hydraulic hybrid powertrain system

1. A hydraulic hybrid powertrain system comprising:

a power plant generating a high pressure fluid at an output;

at least one drive motor responsive to said high pressure fluid for generating rotary motion at an output;

a mode selection means connected to said power plant output and said at least one drive motor for selecting a mode of operation from a plurality of modes of operation of said at least one drive motor including at least two of a drive mode, a neutral mode, a reverse mode and a park mode;

a control means connected to said power plant and said at least one drive motor for controlling operation of said at least one drive motor in said plurality of modes of operation;

a selectively actuated brake means for interrupting a flow of the high pressure fluid to said at least one drive motor; and

a check valve bridge circuit for connecting said at least one drive motor to a low pressure fluid source when said brake means is actuated.

2. The system according to claim 1 wherein said power plant includes an engine driving a hydraulic pump/motor to generate said high pressure fluid.

3. The system according to claim 1 wherein said mode selection means includes a mode select valve for connecting said at least one drive motor between said power plant output and a low pressure fluid source in said drive mode and said reverse mode, disconnecting said at least one drive motor from said power plant output and connecting to said low pressure fluid source in said neutral mode, and disconnecting said at least one drive motor from said power plant output and said low pressure fluid source in said park mode.

4. The system according to claim 3 wherein said mode selection means includes a brake override means normally connecting said at least one drive motor between said power plant and said low pressure source and upon actuation by a brake disconnecting said at least one drive motor from said power plant and said low pressure source.

5. The system according to claim 1 wherein said at least one drive motor is a variable displacement pump/motor and said control means selectively varies a displacement of said pump/motor.

6. The system according to claim 5 wherein said control means includes a displacement control valve and a hydraulic actuator connected to said power plant output and said low pressure source, said hydraulic actuator being connected to said at least one drive motor for varying the displacement.

7. The system according to claim 6 wherein said displacement control valve has an acceleration position, a hold position and a deceleration position causing said at least one drive motor to speed up, maintain speed and slow down respectively.

8. A hydraulic hybrid powertrain system comprising:

a power plant generating a high pressure fluid at an output;

at least one variable displacement drive motor responsive to said high pressure fluid for generating rotary motion at an output;

a mode selection means connected to said power plant output and said at least one drive motor for selecting a mode of operation of said at least one drive motor;

a control means connected to said power plant and said at least one drive motor for controlling a displacement of said at least one drive motor in response to an accelerator input and a brake input to said control means; and

a selectively actuated brake means for interrupting a flow of the high pressure fluid from said power plant to said at least one drive motor.

9. The system according to claim 8 including a check valve bridge circuit for connecting said at least one drive motor to a low pressure fluid source when said brake means is actuated.

10. The system according to claim 8 wherein said mode selection means includes a mode select valve for connecting said at least one drive motor between said power plant output and a low pressure fluid source in a drive mode and a reverse mode, disconnecting said at least one drive motor from said power plant output and connecting to said low pressure fluid source in a neutral mode, and disconnecting said at least one drive motor from said power plant output and said low pressure fluid source in a park mode.

11. The system according to claim 10 wherein said mode selection means includes a brake override means normally connecting said at least one drive motor between said power plant and said low pressure source and upon actuation by a brake disconnecting said at least one drive motor from said power plant and said low pressure source.

12. The system according to claim 8 wherein said control means includes a displacement control valve and a hydraulic actuator connected to said power plant output and a low pressure source, said hydraulic actuator being connected to said at least one drive motor for varying the displacement.

13. The system according to claim 12 wherein said displacement control valve has an acceleration position, a hold position and a deceleration position causing said at least one drive motor to speed up, maintain speed and slow down respectively.

14. The system according to claim 12 including a feedback connector connected between said displacement control valve and said hydraulic actuator.

15. A hydraulic hybrid powertrain system, comprising:

a power plant including an engine driving a pump connected to a low pressure fluid source to generate high pressure fluid at an output;

at least one variable displacement pump/motor responsive to said high pressure fluid for generating rotary motion at an output;

a mode selection means connected for fluid communication between said power plant output and said at least one pump/motor;

a control means connected to said power plant outlet and said at least one pump/motor for selectively controlling a displacement of said at least one pump/motor in response to accelerator and brake inputs;

a brake override means connected between said mode selection means and said at least one pump/motor, said brake override means being responsive to said brake input for preventing a flow of said high pressure fluid to said at least one pump/motor.

16. The system according to claim 15 including a check valve bridge circuit for connecting said at least one pump/motor for fluid flow from said low pressure fluid source to said power plant output when said brake means is actuated.

17. The system according to claim 15 wherein said control means includes a displacement control valve and a hydraulic actuator connected to said power plant output and said low pressure source, said hydraulic actuator being connected to said at least one drive motor for varying the displacement.

18. The system according to claim 17 wherein said displacement control valve has an acceleration position, a hold position and a deceleration position causing said at least one drive motor to speed up, maintain speed and slow down respectively.

19. The system according to claim 18 including a feedback connector connected between said displacement control valve and said hydraulic actuator.

20. A hydraulic hybrid powertrain system comprising;

a power plant generating a high pressure fluid at an output;

at least one drive motor responsive to said high pressure fluid for generating rotary motion at an output;

a mode selection means connected to said power plant output and said at least one drive motor for selecting a mode of operation of said at least one drive motor;

a control means connected to said power plant and said at least one drive motor for controlling operation of said at least one drive motor in said mode of operation; and

a check valve bridge circuit for connecting said at least one drive motor to a low pressure fluid source when a brake means is actuated.

21. The system according to claim 20 wherein said brake means is selectively actuated for interrupting a flow of the high pressure fluid to said at least one drive motor.

22. The system according to claim 20 wherein said power plant includes an engine driving a hydraulic pump/motor to generate said high pressure fluid.

23. The system according to claim 20 wherein said mode selection means includes a mode select valve for connecting said at least one drive motor between said power plant output and a low pressure fluid source in said drive mode and said reverse mode, disconnecting said at least one drive motor from said power plant output and connecting to said low pressure fluid source in said neutral mode, and disconnecting said at least one drive motor from said power plant output and said low pressure fluid source in said park mode.

24. The system according to claim 23 wherein said mode selection means includes a brake override means normally connecting said at least one drive motor between said power plant and said low pressure source and upon actuation by a brake disconnecting said at least one drive motor from said power plant and said low pressure source.

25. The system according to claim 20 wherein said at least one drive motor is a variable displacement pump/motor and said control means selectively varies a displacement of said pump/motor.

26. The system according to claim 25 wherein said control means includes a displacement control valve and a hydraulic actuator connected to said power plant output and said low pressure source, said hydraulic actuator being connected to said at least one drive motor for varying the displacement.

27. The system according to claim 26 wherein said displacement control valve has an acceleration position, a hold position and a deceleration position causing said at least one drive motor to speed up, maintain speed and slow down respectively.