Hydraulic hybrid swing drive system for excavators

1. A hybrid swing drive system of a hydraulic machine comprising:

an over center variable displacement hydraulic swing pump/motor operable by a prime mover and configured to be stroked over center to act as a motor;

a hydraulic swing motor for performing a swing function of the machine;

an accumulator;

a controller;

a swing control valve assembly disposed in a first hydraulic path extending from the swing pump/motor to the swing motor, the swing control valve assembly having a first position fluidly connecting the swing pump/motor to a first side of the swing motor and a second position fluidly connecting the swing pump/motor to a second side of the swing motor; and

an accumulator control valve having an open position fluidly connecting the accumulator to the first hydraulic path at an accumulator control valve connection point and a closed position fluidly isolating the accumulator from the first hydraulic path;

wherein, in an operating mode, the controller is configured to direct flow from the hydraulic swing motor to the hydraulic swing pump/motor;

wherein, in a second operating mode, the controller is configured to direct flow from the hydraulic swing motor to the accumulator;

wherein, in a third operating mode, the controller is configured to direct flow from the accumulator to the hydraulic swing motor;

wherein, in a fourth operating mode, the controller is configured to direct flow from the accumulator to the hydraulic swing pump/motor in a first direction through the hydraulic swing pump/motor and the swing pump/motor is stroked over center to act as a motor; and

wherein, in a fifth operating mode, the controller is configured to direct flow from the hydraulic swing pump/motor to the accumulator in a second direction through the hydraulic swing pump/motor that is opposite that of the first direction, and the swing pump/motor is stroked to act as a pump to charge the accumulator.

2. The hybrid swing drive system of claim 1 , wherein the swing control valve assembly includes a first pilot-operated check valve disposed between the swing pump/motor and the first side of the swing motor and facing the swing pump/motor, and a second pilot-operated check valve disposed between the swing pump/motor and the second side of the swing motor and facing the swing pump/motor, and

wherein the hybrid swing drive system further includes a third pilot-operated check valve disposed between the first side of the swing motor and a reservoir and facing the swing motor, and a fourth pilot-operated check valve disposed between the second side of the swing motor and the reservoir and facing the swing motor.

3. The hybrid swing drive system of claim 1 , wherein flow from the swing motor to the swing pump/motor is not metered.

4. The hybrid swing drive system of claim 1 , wherein flow from the swing motor to the accumulator is not metered.

5. The hybrid swing drive system of claim 1 , further comprising a metering dump valve configured to selectively fluidly connect the first hydraulic path to a reservoir port.

6. The hybrid swing drive system of claim 1 , further comprising an isolation valve disposed in the fluid pathway between the accumulator control valve connection point and the swing control valve assembly, the isolation valve having an open position fluidly connecting the swing pump/motor to the swing motor, and a closed position fluidly isolating the accumulator and the swing pump/motor from the swing motor.

7. The hybrid swing drive system of claim 1 , wherein the controller is configured to open the accumulator control valve and to disengage the swing pump/motor.

8. The hybrid swing drive system of claim 1 , wherein the controller is configured to close the accumulator control valve and engage the swing pump/motor for use as a motor, and wherein a system relief valve is configured to allow excess flow to go to tank.

9. The hybrid swing drive system of claim 1 , wherein the controller is configured to open the accumulator control valve, and engage the swing pump/motor for use as a motor.

10. The hybrid swing drive system of claim 9 , wherein the controller is configured to close a dump valve.

11. The hybrid swing drive system of claim 1 , wherein the controller is configured to open the accumulator control valve, close an isolation valve, meter flow through a dump valve, and engage the swing pump/motor for use as a pump.

12. The hybrid swing drive system of claim 1 , wherein the controller is configured to open the accumulator control valve, close an isolation valve, and engage the swing pump/motor for use as a pump, and wherein a system relief valve is configured to allow excess flow to go to tank.

13. The hybrid swing drive system of claim 1 , wherein the controller is configured to open the accumulator control valve, close an isolation valve, meter flow through a dump valve, and engage the swing pump/motor for use as a motor.

14. The hybrid swing drive system of claim 1 , wherein the controller is configured to open the accumulator control valve, close an isolation valve, and engage the swing pump/motor for use as a motor, and wherein a system relief valve is configured to allow excess flow to go to tank.

15. The hybrid swing drive system of claim 1 , wherein the controller is configured to open the accumulator control valve, close an isolation valve, and engage the swing pump/motor for use as a motor.

16. The hybrid swing drive system of claim 1 , wherein the controller is configured to open the accumulator control valve, close an isolation valve, and engage the swing pump/motor for use as a pump.

17. The hybrid swing drive system of claim 1 , wherein the prime mover is an internal combustion engine and the controller is configured to monitor engine speed and torque, compare engine speed and torque with efficiency data, and adjust engine speed and adjust displacement of the hydraulic pump, and thereby engine torque, based on the comparison.

18. The hybrid swing drive system of claim 1 , wherein the controller is configured to turn off an engine during operation of the drive system.

19. The hybrid swing drive system of claim 1 , further comprising a low pressure accumulator disposed between a reservoir and the swing motor and configured to prevent cavitation in the system.

20. The hybrid swing drive system of claim 1 , wherein the swing pump/motor is configured to power other functions when stroked over center to act as a motor.

21. The hybrid swing drive system of claim 1 , wherein the swing pump/motor is configured to supplement the available torque in an engine shaft to power other functions when stroked over center to act as a motor.

22. The hybrid swing drive system of claim 21 , wherein the other functions are one or more of a boom, bucket, and arm.

23. A hybrid swing drive system of a hydraulic machine comprising:

a variable displacement hydraulic swing pump operable by a prime mover;

a hydraulic swing motor for performing a swing function of the machine;

an accumulator;

a controller;

a swing control valve assembly disposed in a first hydraulic path extending from the swing pump to the swing motor, the swing control valve assembly having a first position fluidly connecting the swing pump to a first side of the swing motor and a second position fluidly connecting the swing pump to a second side of the swing motor; and

an accumulator control valve having an open position fluidly connecting the accumulator to the first hydraulic path at an accumulator control valve connection point and a closed position fluidly isolating the accumulator from the first hydraulic path;

wherein the controller is configured to close the accumulator control valve, meter flow through a dump valve, and engage the swing pump for use as a motor.