Hydraulic system for working machine

Patent metadata

Field	Value
Publication number	US-11840825-B2
Application number	US-202217841716-A
Country	US
Kind code	B2
Filing date	Jun 16, 2022
Priority date	Aug 11, 2021
Publication date	Dec 12, 2023
Grant date	Dec 12, 2023

Abstract

A hydraulic system for a working vehicle includes a first hydraulic pump to deliver pilot fluid to a control valve for a hydraulic actuator whose highest load pressure acts on a first fluid passage, and a second hydraulic pump to deliver hydraulic fluid whose pressure acts on a second fluid passage. A hydraulic controller is operable to control a load-sensing (LS) differential pressure between the highest load pressure and a delivery pressure of the hydraulic fluid from the second hydraulic pump. A third fluid passage to which the second hydraulic pump delivers the hydraulic fluid branches to a fourth fluid passage for flow of the pilot fluid. A solenoid valve is operable to change a pilot pressure of the pilot fluid for the hydraulic controller, and a controller is configured or programmed to control the solenoid valve to adjust the pilot pressure to change the LS differential pressure.

First claim

What is claimed is:

1. A hydraulic system for a working machine, the hydraulic system comprising:
a prime mover;
a hydraulic actuator;
a control valve to control activation of the hydraulic actuator;
a first hydraulic pump to be driven by power of the prime mover to deliver pilot fluid to switch the control valve;
a second hydraulic pump to be driven by power of the prime mover to deliver hydraulic fluid to activate the hydraulic actuator, the second hydraulic pump being a variable displacement hydraulic pump;
a first fluid passage to allow a highest load pressure, when the hydraulic actuator is activated, to act thereon;
a second fluid passage to allow a delivery pressure of the hydraulic fluid from the second hydraulic pump to act thereon;
a third fluid passage to which the first hydraulic pump delivers the pilot fluid;
a fourth fluid passage branched from the third fluid passage;
a hydraulic controller operable to control the second hydraulic pump to set a load-sensing (LS) differential pressure, the LS differential pressure being a pressure difference between the delivery pressure of the hydraulic fluid from the second hydraulic pump and the highest load pressure;
the hydraulic controller including a solenoid valve to change a pilot pressure, the pilot pressure being a pressure of the pilot fluid that flows through the fourth fluid passage and acts on the hydraulic controller; and
a controller configured or programmed to control activation of the solenoid valve to adjust the pilot pressure to change the LS differential pressure.

2. The hydraulic system for a working machine according to claim 1 , wherein
the first hydraulic pump includes a fixed-displacement hydraulic pump having a delivery flow rate that varies in accordance with a rotational speed of the prime mover,
the hydraulic controller includes:
the solenoid valve;
a swash-plate variable assembly capable of changing an angle of a swash plate included in the second hydraulic pump;
a flow rate compensation valve connected to the first fluid passage to supply the hydraulic fluid to the swash-plate variable assembly to activate the swash-plate variable assembly; and
an opening adjuster connected to the fourth fluid passage to change an opening of the flow rate compensation valve; and

the controller is configured or programmed to control activation of the solenoid valve to cause the opening adjuster to change the opening of the flow rate compensation valve to change the LS differential pressure.

3. The hydraulic system for a working machine according to claim 2 , wherein
the fourth fluid passage includes a first branch fluid passage and a third branch fluid passage;
the opening adjuster includes a first opening adjuster connected to the first branch fluid passage, and a second opening adjuster connected to the third branch fluid passage;
the hydraulic controller includes one or more solenoid valves including the solenoid valve;
the one or more solenoid valves include a solenoid valve connected to the first opening adjuster and/or the second opening adjuster; and
the controller is configured or programmed to control activation of the solenoid valve connected to the first opening adjuster and/or the second opening adjuster to cause the first opening adjuster and/or the second opening adjuster to change the opening of the flow rate compensation valve to change the LS differential pressure.

4. The hydraulic system for a working machine according to claim 1 , further comprising:
a speedometer to measure an actual rotational speed of the prime mover; wherein
the controller is configured or programmed to change the LS differential pressure, based on the actual rotational speed measured by the speedometer.

5. The hydraulic system for a working machine according to claim 1 , further comprising:
a speedometer to measure an actual rotational speed of the prime mover; wherein
the controller is configured or programmed to change the LS differential pressure, based on a difference between the actual rotational speed measured by the speedometer and a predetermined target rotational speed.

6. The hydraulic system for a working machine according to claim 1 , further comprising:
a speedometer to measure an actual rotational speed of the prime mover; wherein
the controller is configured or programmed to decrease the LS differential pressure in response to the actual rotational speed measured by the speedometer being lower than a predetermined target rotational speed.

7. The hydraulic system for a working machine according to claim 1 , wherein
the prime mover includes an internal combustion engine to be driven by combustion of injected fuel; and
the controller is configured or programmed to change the LS differential pressure, based on an injection amount of fuel to the internal combustion engine or a load factor of the internal combustion engine.

8. The hydraulic system for a working machine according to claim 1 , further comprising:
a command generator to provide a command to change the LS differential pressure; wherein
the controller is configured or programmed to change the LS differential pressure such that the LS differential pressure is increased in response to a command being generated by the command generator to change the LS differential pressure.

9. The hydraulic system for a working machine according to claim 8 , further comprising:
an accelerator capable of setting a rotational speed of the prime mover; wherein
the accelerator also defines the command generator; and
the controller is configured or programmed to determine a set value of the rotational speed of the prime mover in accordance with an operating state of the accelerator, and change the LS differential pressure, based on the determined set value.

10. The hydraulic system for a working machine according to claim 9 , wherein
the accelerator includes a first accelerator and a second accelerator; and
the controller is configured or programmed to change the LS differential pressure, based on a smaller amount of operation among an amount of operation of the first accelerator and an amount of operation of the second accelerator.

11. The hydraulic system for a working machine according to claim 10 , wherein the controller is configured or programmed to determine the set value of the rotational speed of the prime mover, based on a larger amount of operation among the amount of operation of the first accelerator and the amount of operation of the second accelerator, and control driving of the prime mover in accordance with the determined set value.

12. The hydraulic system for a working machine according to claim 1 , further comprising:
a thermometer to measure a temperature of at least one of the hydraulic fluid that flows through a flow path provided in the working machine, cooling water that flows through a water passage provided in the working machine, or oil of the prime mover;
wherein the controller is configured or programmed to change the LS differential pressure, based on the temperature measured by the thermometer.

13. The hydraulic system for a working machine according to claim 1 , wherein
the controller is configured or programmed to execute automatic idle control to control driving of the prime mover to keep a rotational speed of the prime mover low; and
the controller is configured or programmed to set a predetermined pressure as the LS differential pressure, the predetermined pressure being equal to or greater than a pressure corresponding to the rotational speed of the prime mover, if the rotational speed of the prime mover is changed while the controller is executing the aut

Assignees

• Kubota Kk

Inventors

• Fukuda Yuji
• Arii Kazuyoshi
• Takemura Toshihiko

Classifications

• E02F9/2292

  Systems with two or more pumps · CPC title

• E02F9/2285

  Pilot-operated systems · CPC title

• E02F9/2253 Primary

  Controlling the travelling speed of vehicles, e.g. adjusting travelling speed according to implement loads, control of hydrostatic transmission · CPC title

• E02F9/2228 Primary

  including an electronic controller · CPC title

• E02F9/2235

  including an electronic controller · CPC title