Closed-loop hydraulic system having energy recovery

• US 9,151,018 B2
• Filed: 09/30/2011
• Issued: 10/06/2015
• Est. Priority Date: 09/30/2011
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Knussman, Michael L.
• Primary Examiner(s): LESLIE, MICHAEL S
• Application Number:
  US13/250,002
• Publication Number:
  US 20130081383A1
• Time in Patent Office: 1,467 Days
• Field of Search: 604/14, 914/54
• US Class Current: 1/1
• CPC Class Codes: E02F 9/2217 with energy recovery arrangements, e.g. using accumulators, flywheels
• CPC Class Codes: E02F 9/2289 Closed circuit
• CPC Class Codes: E02F 9/2296 Systems with a variable displacement pump
• CPC Class Codes: F15B 11/16 with two or more servomotors
• CPC Class Codes: F15B 15/1476 Special return means
• CPC Class Codes: F15B 2211/20546 variable capacity
• CPC Class Codes: F15B 2211/20561 reversible
• CPC Class Codes: F15B 2211/20569 capable of working as pump and motor
• CPC Class Codes: F15B 2211/255 Flow control functions
• CPC Class Codes: F15B 2211/27 Directional control by means of the pressure source
• CPC Class Codes: F15B 2211/30575 in a Wheatstone Bridge arrangement (also half bridges)
• CPC Class Codes: F15B 2211/327 electrically or electronically
• CPC Class Codes: F15B 2211/351 Flow control by regulating means in feed line, i.e. meter-in control
• CPC Class Codes: F15B 2211/625 Accumulators
• CPC Class Codes: F15B 2211/6346 representing a state of input means, e.g. joystick position
• CPC Class Codes: F15B 2211/665 Methods of control using electronic components
• CPC Class Codes: F15B 2211/6652 Control of the pressure source, e.g. control of the swash plate angle
• CPC Class Codes: F15B 2211/6654 Flow rate control
• CPC Class Codes: F15B 2211/7053 Double-acting output members
• CPC Class Codes: F15B 2211/7107 the output members being mechanically linked
• CPC Class Codes: F15B 2211/7128 : the chambers being connected in parallel
• CPC Class Codes: F15B 2211/88 : Control measures for saving energy

Abstract

A hydraulic system is disclosed. The hydraulic system may have a pump with variable-displacement, a first linear actuator, and a second linear actuator coupled to the first linear actuator to operate in tandem. The first and second linear actuators may be connected to the pump in closed-loop manner, and each of the first and second linear actuators may have a first chamber and a second chamber separated by a piston. The hydraulic system may also have an accumulator in fluid communication with the second chamber of only the second linear actuator.

Claims

1. A hydraulic system, comprising:

a pump having variable-displacement;

a first linear actuator and a second linear actuator coupled to operate in tandem and connected to the pump in closed-loop manner, each of the first and second linear actuators having a first chamber and a second chamber separated by a piston;

an accumulator in fluid communication with the second chamber of only the second linear actuator;

an inlet passage connected to the pump;

a discharge passage connected to the pump;

a first valve disposed between the inlet passage and the first chambers of the first and second linear actuators;

a second valve disposed between the inlet passage and the second chamber of the first linear actuator;

a third valve disposed between the discharge passage and the first chambers of the first and second linear actuators; and

a fourth valve disposed between the discharge passage and the second chamber of the first linear actuator.

2. The hydraulic system of claim 1, wherein the first chambers of the first and second linear actuators are fluidly connectable in parallel to pump.

3. The hydraulic system of claim 2, wherein:

the second chamber of the first linear actuator is connected to pump; and

the second chamber of the second linear actuator is isolated from pump.

4. The hydraulic system of claim 1, wherein each of the first, second, third, and fourth valves is an independent metering valve.

5. The hydraulic system of claim 4, further including a rotary actuator connected to the pump in closed-loop manner, in parallel with the first and second linear actuators.

6. The hydraulic system of claim 5, further including:

a fifth valve disposed between the inlet passage and the a first side of the rotary actuator;

a sixth valve disposed between the inlet passage and a second side of the rotary actuator;

a seventh valve disposed between the discharge passage and the first side of the rotary actuator; and

a eighth valve disposed between the discharge passage and the second side of the rotary actuator.

7. The hydraulic system of claim 6, wherein:

each of the fifth, sixth, seventh, and eighth valves is an independent metering valve; and

the rotary actuator is a fixed displacement motor.

8. The hydraulic system of claim 7, wherein:

the first, second, third, and fourth valves together are configured to selectively switch a fluid flow direction into the first and second linear actuators; and

the fifth, sixth, seventh, and eighths valves together are configured to selectively switch a fluid flow direction into the rotary actuator.

9. The hydraulic system of claim 5, wherein:

the first and second linear actuators are boom cylinders configured to move a boom of a machine; and

the accumulator is configured to accumulate fluid during lowering of the boom.

10. The hydraulic system of claim 9, wherein the rotary actuator is a travel motor.

11. The hydraulic system of claim 1, wherein each of the second chambers of the first and second linear actuators is a head-end chamber having a pressure area about equal to two times a pressure area of the first chambers of each of the first and second linear actuators.

12. A hydraulic system, comprising:

a pump having variable-displacement;

a first hydraulic cylinder and a second hydraulic cylinder coupled to raise and lower a boom in tandem and connected to the pump in closed-loop manner, each of the first and second hydraulic cylinders having a rod-end chamber fluidly connectable in parallel to the pump and a head-end chamber separated from the rod-end chamber by a piston;

an accumulator in fluid communication with the head-end chamber of only the second hydraulic cylinder, wherein the head-end chamber of the second hydraulic cylinder is isolated from pump;

an inlet passage connected to the pump;

an discharge passage connected to the pump;

a first independent metering valve disposed between the inlet passage and the rod-end chambers of the first and second hydraulic cylinder;

a second independent metering valve disposed between the inlet passage and the head-end chamber of the first hydraulic cylinder;

a third independent metering valve disposed between the discharge passage and the rod-end chambers of the first and second hydraulic cylinders; and

a fourth independent metering valve disposed between the discharge passage and the head-end chamber of the first hydraulic cylinder.

13. The hydraulic system of claim 12, wherein each of the head-end chambers of the first and second hydraulic cylinders is about equal to two times a pressure area of the rod-end chambers of each of the first and second hydraulic cylinders.

14. A method of operating a hydraulic system, comprising:

pressurizing fluid with a pump;

directing fluid pressurized by the pump into first and second linear actuators operating in tandem and returning fluid from the first and second linear actuators to the pump via a closed-loop circuit; and

accumulating fluid from and discharging accumulated fluid into a head-end chamber of only the second linear actuator,

wherein;

directing fluid pressurized by the pump into the first and second linear actuators includes;

directing fluid into rod-end chambers of the first and second linear actuators in parallel; and

directing fluid into the head-end chamber of the first linear actuator simultaneously with accumulated fluid discharging into the head-end chamber of the second linear actuator; and

returning fluid from the first and second linear actuators to the pump includes;

returning fluid from the rod-end chambers of the first and second linear actuators in parallel; and

returning fluid from the head-end chamber of the first linear actuator simultaneously with accumulation of fluid from the head-end chamber of the second linear actuator.

15. The method of claim 14, further including selectively metering the fluid directed into the first and second linear actuators.

16. The method of claim 14, further including directing fluid pressurized by the pump into a rotary actuator in parallel with the first and second linear actuators via the closed-loop circuit.

17. The method of claim 16, further including selectively activating a valve arrangement associated with the first and second linear actuators and a valve arrangement associated with the rotary actuator to switch fluid flow directions into the first and second linear and rotary actuators.