Energy regeneration system for machines

1. An energy regeneration system for machinery comprising:

a fluid pressure actuator adapted to operate by being supplied or discharging fluid;

a first displacement variable regenerating fluid pressure motor in a discharge flow path for fluid discharged from the fluid pressure actuator such that controlling the displacement of the first regenerating fluid pressure motor allows the flow rate of discharge fluid from the fluid pressure actuator as well as the pressure of the discharge flow path to be controlled;

first energy regeneration device for regenerating the energy of discharge fluid as electrical energy, at least in part by rotating the first regenerating fluid pressure motor;

the displacement of the first regenerating fluid pressure motor is controlled so that the flow rate of discharge fluid from the fluid pressure actuator varies from zero to a predetermined maximum value

a relief flow path connected to a supply flow path for fluid to be supplied to the fluid pressure actuator between an intermediate part of the supply flow path and a fluid tank;

a second displacement variable regenerating fluid pressure motor in the relief flow path such that controlling the displacement of the second regenerating fluid pressure motor allows the pressure of the supply flow path to the fluid pressure actuator to be controlled; and

a second regeneration device for regenerating the rotational energy of fluid in the relief flow path as electrical energy, at least in part by rotating the second regenerating fluid pressure motor.

2. The energy regeneration system for machinery according to claim 1 , including:

a pressure sensor in the supply path;

a controller in communication with the pressure sensor, and being operable to generate a pressure relief control command responsive to a sensed pressure in excess of a predetermined relief pressure; and

a pressure relief device in communication with the controller and operable to open the relief path connected to the supply path responsive to the pressure relief control command.

3. The energy regeneration system for machinery according to claim 1 , wherein the pressure control of the discharge flow path and/or the supply flow path performed by the first and second regenerating fluid pressure motors is a relief control in which fluid in the discharge flow path and/or the supply flow path is to be relieved when the pressure of the discharge flow path and/or the supply flow path reaches a predetermined relief pressure.

4. The energy regeneration system for machinery according to claim 1 , wherein the flow rate of supply fluid to the fluid pressure actuator is controlled by a supplying flow rate control valve; and

the relief path being connected to the supply path between the supplying flow rate control valve and the fluid pressure actuator.

5. The energy regeneration system for machinery according to claim 1 , wherein:

the fluid pressure actuator is a bi-directional rotary fluid pressure motor having two fluid ports; and

each of the first and second regenerating fluid pressure motors is a displacement variable fluid pressure motor provided in a discharge flow path for fluid discharged from one of the fluid ports, respectively.

6. The energy regeneration system for machinery according to claim 5 wherein:

the relief flow path is adapted to function as a discharge flow path for fluid discharged from the one of the two fluid ports.

7. The energy regeneration system for machinery according to claim 6 , wherein the machinery is equipped with a controller operable to receive an operation signal from a fluid pressure actuator operation tool, a detection signal from a pressure detection means for detecting the pressure of the discharge flow path and/or the supply flow path of the fluid pressure actuator, said controller further being operable to output a control command to a displacement control means for the first and second regenerating fluid pressure motor based on the operation and detection signals.

8. The energy regeneration system for machinery according to claim 5 , wherein the energy regeneration device comprises:

a power generating means which generates electric power due to the rotational driving of the first and second regenerating fluid pressure motor;

a power storage means for storing electric power generated by the power generating means; and

an inverter for converting electric power stored in the power storage means into AC power.

9. The energy regeneration system for machinery according to claim 1 , wherein electrical energy obtained by the energy regeneration device is used as a power supply source for a motor for driving a pump adapted to supply pressurized fluid to the fluid pressure motor.

10. The energy regeneration system for machinery according to claim 9 , wherein the motor is used as an auxiliary power source for the pump.

11. A machine comprising:

a hydraulic actuator having first and second supply/discharge ports;

a flow rate control circuit including first and second flow rate control lines connecting with said first and second supply/discharge ports, respectively;

at least one displacement variable hydraulic motor within said flow rate control circuit;

at least one pressure sensing means disposed within said flow rate control circuit between said at least one displacement variable hydraulic motor and said hydraulic actuator;

an energy regeneration device coupled with said displacement variable hydraulic motor for regenerating at least a portion of an energy of discharge fluid of said hydraulic actuator as electrical energy;

said first and second flow rate control lines each comprise a supply/discharge line connected with said first and second supply/discharge ports of said hydraulic actuator, respectively;

said at least one displacement variable hydraulic motor comprises a first and a second displacement variable hydraulic motor disposed one within each of said first and second supply/discharge lines.

12. The work machine of claim 11 wherein said hydraulic actuator is a bi-directional rotatable hydraulic motor.

13. The work machine of claim 12 wherein said at least one pressure sensing means comprises a first pressure sensor disposed within said first supply/discharge line and a second pressure sensor disposed within said second supply/discharge line.

14. The work machine of claim 13 further comprising:

a displacement control means coupled with each of said first and second displacement variable hydraulic motors;

an electronic controller operably coupled with each of said first and second pressure sensors and with each said displacement control means, said electronic controller configured to receive a pressure signal from one of said pressure sensors and responsively output a displacement control signal to the corresponding displacement variable hydraulic motor.

15. A method of operating a hydraulic system comprising the steps of:

supplying hydraulic fluid to a hydraulic actuator;

diverting a portion of fluid away from the hydraulic actuator into a relief path if a pressure of the supplying hydraulic fluid exceeds a predetermined relief pressure;

controlling at least one of flow rate and hydraulic Pressure in a discharge flow path of the hydraulic actuator at least in part by adjusting a displacement of a hydraulic energy regeneration motor in a hydraulic control circuit of the system; and recovering energy from fluid flowing in the relief path.

16. The method of claim 15 wherein the controlling step comprises adjusting the displacement of the motor responsively to a determined fluid pressure in the hydraulic control circuit in at least one of an upstream and a downstream position relative to the hydraulic actuator.

17. The method of claim 16 wherein the hydraulic actuator is a bi-directional hydraulic motor, the controlling step further comprising controlling rotational motion of the hydraulic actuator.