Hydraulic drive system

Patent metadata

Field	Value
Publication number	US-9683585-B2
Application number	US-201214129387-A
Country	US
Kind code	B2
Filing date	Aug 13, 2012
Priority date	Aug 24, 2011
Publication date	Jun 20, 2017
Grant date	Jun 20, 2017

Abstract

A hydraulic driving system includes a hydraulic pump, a driving source, a hydraulic cylinder, a closed circuit hydraulic path between the pump and cylinder, a pump-flow-rate control unit controlling a discharge flow rate of the pump, a flow rate control valve between the pump and the cylinder in the fluid path, a directional control unit, a target flow rate setting unit and a control device. The directional control unit allows a flow of fluid from the pump to the cylinder and prohibits a flow of fluid from the cylinder to the pump when fluid is supplied from the pump to the cylinder via the flow rate control valve. The control device controls fluid flow to the cylinder with the flow rate control valve when the target flow rate is within a prescribed range, and with the pump-flow-rate control unit when the target flow rate is greater than the prescribed range.

First claim

What is claimed is:

1. A hydraulic driving system comprising:
a hydraulic pump;
a driving source configured to drive the hydraulic pump;
a hydraulic cylinder configured to be driven by hydraulic fluid discharged from the hydraulic pump;
a hydraulic fluid path forming a closed circuit between the hydraulic pump and the hydraulic cylinder, the hydraulic fluid path including
an adjustment path supplied with hydraulic fluid from the hydraulic pump,
a pump path connected to the hydraulic pump,
a cylinder path connected to the hydraulic cylinder, and
a pilot path;

a pump-flow-rate control unit configured to control a discharge flow rate of the hydraulic pump in response to a first command signal;
an adjustment flow rate control unit arranged and configured to control a flow rate of hydraulic fluid supplied to the adjustment path from the hydraulic pump, the adjustment flow rate control unit including a pilot port connected to the pilot flow path, the adjustment flow rate control unit being further configured to
allow communication between the pump path and the adjustment path when a differential hydraulic pressure between the pump path and the pilot path is greater than a prescribed set pressure, and
shut off communication between the hydraulic pump and the adjustment path when the differential hydraulic pressure between the pump path and the pilot path is equal to or less than the prescribed set pressure;

a flow rate control valve arranged to provide an adjustable opening degree in the hydraulic fluid path between the hydraulic pump and the hydraulic cylinder, the flow rate control valve being arranged and configured to connect the pump path to the cylinder path and to connect the cylinder path to the pilot path, the flow rate control valve being configured to control a flow rate of hydraulic fluid supplied to the hydraulic cylinder from the hydraulic pump by varying the opening degree of the flow rate control valve in response to a second command signal;
a directional control unit configured to allow a flow of hydraulic fluid from the hydraulic pump to the hydraulic cylinder and prohibit a flow of hydraulic fluid from the hydraulic cylinder to the hydraulic pump when hydraulic fluid is supplied from the hydraulic pump to the hydraulic cylinder via the flow rate control valve; and
a controller configured to control the flow rate of hydraulic fluid supplied to the hydraulic cylinder from the hydraulic pump based on a target flow rate by
controlling the flow rate control valve using the second command signal when the target flow rate is within a prescribed range, and
controlling the pump-flow-rate control unit using the first command signal when the target flow rate is greater than the prescribed range,

the controller being further configured such that when the target flow rate is within the prescribed range, the controller controls the pump-flow-rate control unit to set a discharge flow rate of the hydraulic pump to a flow rate greater than the target flow rate such that hydraulic fluid from the hydraulic pump is divided between the hydraulic cylinder and the adjustment path,
a differential hydraulic pressure between the pump path and the cylinder path being greater than the prescribed set pressure when the target flow rate is within the prescribed range, and
the differential hydraulic pressure between the pump path and the cylinder path being equal to or less than the prescribed set pressure when the target flow rate is greater than the prescribed range.

2. The hydraulic drive system according to claim 1 , wherein
the controller fully opens the flow rate control valve to allow communication between the hydraulic pump and the hydraulic cylinder when the target flow rate is greater than the prescribed range.

3. The hydraulic drive system according to claim 1 , wherein
when the target flow rate is greater than the prescribed range,
the pump-flow-rate control unit sets a discharge flow rate of the hydraulic pump to the target flow rate, and
a path between the adjustment path and the hydraulic pump in the hydraulic fluid path is closed.

4. The hydraulic drive system according to claim 1 , wherein
the flow rate control valve is configured to control
a flow rate of hydraulic fluid supplied from the hydraulic pump to the hydraulic cylinder and
a flow rate of hydraulic fluid supplied from the hydraulic pump to the adjustment path.

5. The hydraulic drive system according to claim 4 , wherein
the hydraulic fluid path further includes a pump path connected to the hydraulic pump, and a cylinder path connected to the hydraulic cylinder, and
the flow rate control valve includes a pump port connected to the pump path via the directional control unit, a cylinder port connected to the cylinder path, and an adjustment port connected to the adjustment path.

6. The hydraulic drive system according to claim 5 , further comprising:
a hydraulic fluid tank configured to store the hydraulic fluid, the adjustment path being connected between the hydraulic fluid tank and the pump path, a pressure relief valve being connected between the pump path and the adjustment path.

7. The hydraulic drive system according to claim 1 , further comprising:
a charge pump configured to replenish hydraulic fluid to the hydraulic pump,
the hydraulic fluid path further including a charge path connecting the charge pump and the hydraulic pump, and
the adjustment path being connected to the charge path.

8. The hydraulic drive system according to claim 1 , further comprising:
a charge pump configured to replenish hydraulic fluid to the hydraulic pump,
the hydraulic fluid path further including a charge path connecting the charge pump and the hydraulic pump, and
the flow rate control valve shutting off communication between the pump path and the cylinder path and connecting the pilot path to the charge path in a neutral position state.

9. The hydraulic drive system according to claim 1 , further comprising
an operating member configured to be operated by an operator, wherein
the hydraulic pump is a variable displacement pump,
the pump-flow-rate control unit controls the discharge flow rate of the hydraulic pump by controlling a tilt angle of the hydraulic pump,
the controller sets the target flow rate based on an operation amount of the operating member,
when the operation amount of the operating member is zero, the controller sets the tilt angle of the hydraulic pump to zero, and
when the operation amount of the operating member is within a prescribed operation range corresponding to the prescribed range of the target flow rate, the controller controls the tilt angle of the hydraulic pump so that the discharge flow rate of the hydraulic pump meets or exceeds the target flow rate corresponding to the operation amount of the operating member.

10. The hydraulic drive system according to claim 1 , further comprising
an operating member configured to be operated by an operator, wherein
the pump-flow-rate control unit controls the discharge flow rate of the hydraulic pump by controlling a rotation speed of the hydraulic pump,
the controller sets the target flow rate based on an operation amount of the operating member,
when the operation amount of the operating member is zero, the controller stops rotation of the hydraulic pump, and
when the operation amount of the operating member is within a prescribed operation range corresponding to the prescribed range of the target flow rate, the controller controls the rotation speed of the hydraulic pump so that the discharge flow rate of the hydraulic pump meets or exceeds the target flow rate corresponding to the operation amount of the operating member.

Assignees

• Akiyama Teruo
• Iida Noboru
• Saito Koji
• Watanabe Takayuki
• Yamashita Koji
• Komatsu Mfg Co Ltd

Inventors

• Akiyama Teruo
• Iida Noboru
• Saito Koji
• Watanabe Takayuki
• Yamashita Koji

Classifications

• E02F9/2228

  including an electronic controller · CPC title

• F15B2211/27

  Directional control by means of the pressure source · CPC title

• E02F9/2217 Primary

  with energy recovery arrangements, e.g. using accumulators, flywheels · CPC title

• F15B2211/7053

  Double-acting output members · CPC title

• F15B2211/6346

  representing a state of input means, e.g. joystick position · CPC title