Closed-loop hydraulic system having force modulation

• US 8,973,358 B2
• Filed: 10/21/2011
• Issued: 03/10/2015
• Est. Priority Date: 10/21/2011
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Kuehn, Jeffrey L., Edler, Brad A., Peterson, Jeremy T., Verkuilen, Michael T.
• Primary Examiner(s): Lazo, Thomas E
• Application Number:
  US13/278,788
• Publication Number:
  US 20130098014A1
• Time in Patent Office: 1,236 Days
• Field of Search: 604/20, 604/21, 604/22, 604/84, 604/86, 604/68
• US Class Current: 60/421
• CPC Class Codes: E02F 9/2228 including an electronic controller
• CPC Class Codes: E02F 9/2285 Pilot-operated systems
• CPC Class Codes: E02F 9/2289 Closed circuit
• CPC Class Codes: E02F 9/2292 Systems with two or more pumps
• CPC Class Codes: E02F 9/2296 Systems with a variable displacement pump
• CPC Class Codes: F15B 11/17 using two or more pumps
• CPC Class Codes: F15B 2211/20546 variable capacity
• CPC Class Codes: F15B 2211/20561 reversible
• CPC Class Codes: F15B 2211/265 Control of multiple pressure sources
• CPC Class Codes: F15B 2211/3111 the pump port being closed in the centre position, e.g. so-called closed centre
• CPC Class Codes: F15B 2211/3116 the pump port being open in the centre position, e.g. so-called open centre
• CPC Class Codes: F15B 2211/3144 the positions being continuously variable, e.g. as realised by proportional valves
• CPC Class Codes: F15B 2211/329 actuated by fluid pressure
• CPC Class Codes: F15B 2211/7053 Double-acting output members
• CPC Class Codes: F15B 2211/7058 Rotary output members
• CPC Class Codes: Y02P 80/10 Efficient use of energy, e.g. using compressed air or pressurized fluid as energy carrier

Abstract

A hydraulic system is disclosed. The hydraulic system may have a unidirectional variable displacement first pump, a first actuator connected to the first pump via a closed-loop first circuit, and a first switching valve disposed between the first actuator and the first pump. The first switching valve may be configured to control a fluid flow direction through the first actuator. The hydraulic system may also have a second actuator connected to the first pump in parallel with the first actuator via the first circuit, and a second switching valve disposed between the second actuator and the first pump. The second switching valve may be configured to control a fluid flow direction through the second actuator. The hydraulic system may further have a modulation valve associated with the first circuit and configured to selectively modulate a pressure of the first circuit during actuation of the first or second switching valves.

Claims

1. A hydraulic system, comprising;

a unidirectional variable displacement first pump;

a first actuator connected to the first pump via a closed-loop first circuit;

a first switching valve disposed between the first actuator and the first pump and configured to control a fluid flow direction through the first actuator;

a second actuator connected to the first pump in parallel with the first actuator via the first circuit;

a second switching valve disposed between the second actuator and the first pump and configured to control a fluid flow direction through the second actuator;

a modulation valve associated with the first circuit and configured to selectively modulate a pressure of the first circuit during actuation of the first or second switching valves;

a unidirectional variable displacement second pump;

a third actuator connected to the second pump via a closed-loop second circuit; and

a unidirectional variable displacement third pump selectively connectable in closed-loop manner to the first or second circuits.

2. The hydraulic system of claim 1, wherein the modulation valve is configured to increase the pressure of the first circuit as an operator requests movement of the first or second actuators with greater force.

3. The hydraulic system of claim 2, wherein:

the first actuator is a linear actuator; and

the second actuator is a rotary actuator.

4. The hydraulic system of claim 2, wherein each of the first and second switching valves is a three-position, four-way valve.

5. The hydraulic system of claim 1, further including:

a low-pressure tank;

an unloading valve connected to the low-pressure tank via a return passage; and

a control valve associated with the third pump and configured to control fluid flow from the third pump into the first circuit, the second circuit, or the low-pressure tank via the unloading valve.

6. The hydraulic system of claim 5, wherein the control valve is a variable position, four-way valve.

7. The hydraulic system of claim 1, wherein:

the first circuit is configured to selectively direct fluid to the second and third pumps; and

the second circuit is configured to selectively direct fluid to the first and third pumps.

8. The hydraulic system of claim 7, further including:

a first isolation valve disposed between intakes of the first and third pumps; and

a second isolation valve disposed between intakes of the second and third pumps.

9. The hydraulic system of claim 7, wherein, the third pump is fluidly connected to the low-pressure tank when the first or second circuit directs fluid to the third pump.

10. The hydraulic system of claim 1, further including:

a first check valve disposed between the first pump and the first and second actuators; and

a second check valve disposed between the second pump and the third actuator,

wherein;

the third pump connects to the first circuit at location between the first check valve and the first and second actuators; and

the third pump connects to the second circuit at a location between the second check valve and the third actuator.

11. The hydraulic system of claim 10, wherein the modulation valve is a variable position, two-way valve connected to the discharge passage of the first pump at a location upstream of the first check valve.

12. A hydraulic system, comprising:

a unidirectional variable displacement first pump;

a first actuator connected to the first pump via a closed-loop first circuit;

a first switching valve disposed between the first actuator and the first pump, the first switching valve being movable between a first position at which fluid from the first circuit passes through the first actuator in a first direction, a second position at which fluid flow through the first actuator is substantially blocked, and a third position at which fluid from the first circuit passes through the first actuator in a second direction;

a second actuator connected to the first pump in parallel with the first actuator via the first circuit;

a second switching valve disposed between the second actuator and the first pump, the second switching valve being movable between a first position at which fluid from the first circuit passes through the second actuator in a first direction, a second position at which fluid flow through the second actuator is substantially blocked, and a third position at which fluid from the first circuit passes through the second actuator in a second direction;

a modulation valve associated with the first circuit and configured to selectively increase a pressure of the first circuit as an operator requests movement of the first or second actuators with greater force;

a unidirectional variable displacement second pump;

a third actuator connected to the second pump via a closed-loop second circuit;

a unidirectional variable displacement third pump selectively connectable in closed-loop manner to the first or second circuits; and

a control valve associated with the third pump and configured to control fluid flow from the third pump into the first and second circuits.

13. The hydraulic system of claim 12, wherein;

the first actuator is a boom actuator;

the second actuator is a travel motor; and

the third actuator is a stick actuator.

14. The hydraulic system of claim 12, wherein:

the first and second switching valves are three-position, four-way valves;

the modulation valve is a variable-position valve, two-way valve; and

the control valve is a variable-position, four-way valve.

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

discharging pressurized fluid with a first pump in a single direction;

directing the pressurized fluid to a first linear actuator via a closed-loop first circuit;

selectively switching a fluid flow direction through the first actuator via a first switching valve;

directing the pressurized fluid to a second linear actuator via the closed-loop first circuit;

selectively switching a fluid flow direction through the second actuator via a second switching valve;

selectively adjusting an amount of fluid from the first circuit that bypasses the first or second actuators via a modulation valve during actuation of the first or second switching valves;

discharging pressurized fluid with a second pump in a single directionn;

directing the pressurized fluid from the second pump to a third hydraulic actuator via a closed-loop second circuit;

discharging pressurized fluid with a third pump in a single direction; and

selectively directing the pressurized fluid from the third pump to the first circuit, to the second circuit, or to a low-pressure tank.

16. The method of claim 15, wherein selectively adjusting the amount of fluid bypassing the first or second actuators includes reducing the amount of fluid bypassing the first or second actuators as an operator requests movement of the first or second actuators with greater force.

17. The method of claim 15, wherein selectively directing the pressurized fluid from the third pump to the first circuit, to the second circuit, or to the low-pressure tank includes selectively directing a portion of the pressurized fluid from the third pump to the low-pressure tank and a remaining portion of the pressurized fluid to one of the first and second circuits.

18. The method of claim 15, further including selectively isolating the second pump or the second and third pumps from the first circuit.