Power system and work machine using same

• US 7,197,871 B2
• Filed: 11/14/2003
• Issued: 04/03/2007
• Est. Priority Date: 11/14/2003
• Status: Expired due to Fees

• Current Assignee: Caterpillar Sarl (Caterpillar Incorporated)
• Original Assignee: Caterpillar Incorporated, Shin Caterpillar Mitsubishi Ltd. (Caterpillar Incorporated)
• Inventors: Yoshino, Kazunori
• Primary Examiner(s): LOPEZ, FRANK D
• Application Number:
  US10/714,171
• Publication Number:
  US 20050103006A1
• Time in Patent Office: 1,236 Days
• Field of Search: 604/14
• US Class Current: 60/414
• CPC Class Codes: E02F 9/2207 for reducing or compensating oscillations
• CPC Class Codes: E02F 9/2217 with energy recovery arrangements, e.g. using accumulators, flywheels
• CPC Class Codes: E02F 9/2296 Systems with a variable displacement pump
• CPC Class Codes: F15B 11/006 Hydraulic "Wheatstone bridge" circuits, i.e. with four nodes, P-A-T-B, and on-off or proportional valves in each link
• CPC Class Codes: F15B 21/14 Energy-recuperation means
• CPC Class Codes: F15B 2211/20515 Electric motor
• CPC Class Codes: F15B 2211/20546 variable capacity
• CPC Class Codes: F15B 2211/26 Power control functions
• CPC Class Codes: F15B 2211/30575 in a Wheatstone Bridge arrangement (also half bridges)
• CPC Class Codes: F15B 2211/31576 having a single pressure source and a single output member
• CPC Class Codes: F15B 2211/327 electrically or electronically
• CPC Class Codes: F15B 2211/45 Control of bleed-off flow, e.g. control of bypass flow to the return line
• CPC Class Codes: F15B 2211/63 Electronic controllers
• CPC Class Codes: F15B 2211/6346 representing a state of input means, e.g. joystick position
• CPC Class Codes: F15B 2211/6651 Control of the prime mover, e.g. control of the output torque or rotational speed
• CPC Class Codes: F15B 2211/7053 Double-acting output members
• CPC Class Codes: F15B 2211/88 Control measures for saving energy

Abstract

Engineers are constantly seeking methods to reduce undesirable emissions, noise, and vibrations created by power systems. In the present invention, a power system includes at least one hydraulic cylinder that defines a first fluid volume and a second fluid volume separated from one another via a moveable plunger. Hydraulic power created within the hydraulic cylinder is converted to mechanical energy by a variable displacement hydraulic motor that is fluidly connected to at least the first fluid volume. A generator is attached to the variable displacement hydraulic motor, and produces electrical power that is stored in a power storage system. The stored power can be supplied to an electric motor that is operable to power a hydraulic pump. The hydraulic pump supplies hydraulic fluid to the hydraulic cylinder. The power system of the present invention is a relatively efficient alternative to a power system including a diesel engine that can be a source of undesirable emissions, noise and vibrations.

Claims

1. A power system comprising:

an electric motor being operable to power a hydraulic pump;

at least one hydraulic cylinder being fluidly connected to the hydraulic pump and defining a first fluid volume and a second fluid volume separated from one another via a moveable plunger;

a variable displacement hydraulic motor being fluidly connected directly to the first fluid volume defined by the hydraulic cylinder, with no intervening valve, and being operable to power a generator; and

a power storage system operably coupling the generator to the electric motor.

2. The power system of claim 1 wherein the power storage system includes a fuel cell, an electrolysis device and a hydrogen storage device.

3. A work machine comprising a work machine body;

and the power system of claim 1 being attached to the work machine body.

4. The work machine of claim 3 including an implement attached to the work machine body;

and

the at least one hydraulic cylinder being operably coupled to move the implement.

5. A power system comprising:

means for converting hydraulic power produced within at least one hydraulic cylinder to mechanical power via a variable displacement hydraulic motor fluidly connected directly to the fluid volume of the hydraulic cylinder, with no intervening valve;

means for converting the mechanical power to electrical power;

means for storing the electrical power;

means for supplying an electric motor coupled to a hydraulic pump with the stored electrical power; and

means for supplying hydraulic fluid, via the hydraulic pump, to the at least one hydraulic cylinder.

6. The power system of claim 5 wherein the means for storing electrical power includes a fuel cell, an electrolysis device and a hydrogen storage device.

7. The power system of claim 5 wherein the at least one hydraulic cylinder being operably coupled to move a work machine implement.

8. A method of operating an electrical power system, comprising the steps of:

powering a generator, at least in part, by converting hydraulic power produced within a hydraulic cylinder to mechanical power via a variable displacement hydraulic motor fluidly connected directly to the first fluid volume of the hydraulic cylinder, with no intervening valve;

storing electrical power created by the generator within a power storage system;

powering a hydraulic pump, at least in part, by supplying electrical power from the power storage system to an electric motor coupled to the hydraulic pump; and

supplying hydraulic fluid to the hydraulic cylinder, at least in part, by operating the hydraulic pump.

9. The method of claim 8 wherein the step of powering the generator includes a step of producing hydraulic power by retracting a plunger, which separates the first fluid volume from the second fluid volume, within the hydraulic cylinder.

10. The method of claim 9 wherein the step of producing hydraulic power includes a step of controlling a speed of the retracting plunger, at least in part, by varying the displacement of the motor.

11. The method of claim 8 wherein the step of storing includes a step of producing hydrogen within a reformer.

12. The method of claim 8 wherein the step of storing includes a step of creating hydrogen and oxygen within an electrolysis device from electrical power generated by the generator.

13. The method of claim 12 wherein the step of storing includes a step of absorbing the hydrogen in a hydrogen storage device.

14. The method of claim 13 includes a step of powering a hydraulic pump includes a step of re-producing electrical power, at least in part, by combining the hydrogen with oxygen in a fuel cell.

15. A power system comprising:

a variable displacement hydraulic motor being configured to power a generator;

a power storage system being configured to store electrical power produced by the generator;

an electric motor being configured to power a hydraulic pump with the electrical power from the power storage system; and

a hydraulic cylinder being configured to receive hydraulic fluid from the hydraulic pump and to produce hydraulic power that drives the variable displacement hydraulic motor, which is fluidly connected directly to the first fluid volume of the hydraulic cylinder, with no intervening valve.

16. The power system of claim 15 wherein the power system includes a fuel cell, an electrolysis device and a hydrogen storage device.

17. The power system of claim 15 wherein the at least one hydraulic cylinder being operably coupled to move a work machine implement.