System for driving a boom of a hybrid excavator and a control method thereof

Patent metadata

Field	Value
Publication number	US-9260835-B2
Application number	US-201013517399-A
Country	US
Kind code	B2
Filing date	Dec 23, 2010
Priority date	Dec 23, 2009
Publication date	Feb 16, 2016
Grant date	Feb 16, 2016

Abstract

Disclosed is a system for driving a boom of a hybrid excavator, and a method for controlling the same. The system comprises: an electric motor; a capacitor for storing electricity generated by the electric motor; a hydraulic pump motor driven by the electric motor to supply working oil to a boom; a boom control valve having a closed circuit selectively connecting/disconnecting a discharge line and an inlet line of the hydraulic pump motor to/from a head or a load of the boom; a main pump arranged separately from the motor to supply working oil; a boom-assisting valve connecting discharge lines of the main pump and the hydraulic pump motor to combine discharged working oil; and a control unit controlling the electric motor, the hydraulic pump motor, and the boom control valve. The system minimizes energy loss during excavation, ensures performance of the boom, and recovers regenerative energy from the boom.

First claim

The invention claimed is:

1. A system for driving a boom of a hybrid excavator, comprising:
an electric motor that operates as a motor or an electricity generator;
a capacitor that stores electricity generated by the electric motor;
a hydraulic pump motor that is driven by the electric motor and supplies working fluid to a boom cylinder;
a boom control valve that constitutes a closed circuit selectively connecting/disconnecting a discharge line of the hydraulic pump motor, which connects a discharge side of the hydraulic pump motor with the boom control valve, and an intake line of the hydraulic pump motor, which connects an intake side of the hydraulic pump motor with the boom control valve, to/from a head or a rod of the boom cylinder;
a main pump that is driven by a driving source disposed separately from the electric motor and supplies the working fluid to a bucket, a traveling motor, or an arm;
a boom-assistant valve that allows the working fluid discharged from the main pump and the hydraulic pump motor to meet each other by connecting the discharge line of the main pump to the discharge line of the hydraulic pump motor;
a first control valve that connects the intake line with a tank for the working fluid;
a second control valve that connects the discharge line to tank for the working fluid;
wherein when the boom is descended a flow rate of working fluid from the boom cylinder flows through the boom control valve and the intake line to the intake side of the hydraulic pump motor and from the hydraulic pump motor through the discharge line and the second control valve to tank, and
wherein when the boom is descended and when the flow rate flowing into the hydraulic pump motor from the boom cylinder exceeds available capacity of the hydraulic pump motor or a capacity of the electric motor, the first control valve is connected to tank and drains at least a portion of the flow rate flowing into the hydraulic pump motor from the boom cylinder to tank; and
a control unit that controls the electric motor, the hydraulic pump motor, the boom control valve, the first control valve and the second control valve.

2. The system of claim 1 , wherein when the boom is lifted the first control valve is connected and the second control valve is disconnected.

3. The system of claim 1 , wherein the boom-assistant valve is switched such that a flow rate of the main pump is supplied to the boom cylinder, when a control signal of a boom joystick increases and a flow rate over a flow rate supplied from the hydraulic pump motor or a capacity of the electric motor is necessary.

4. A method of controlling a system for driving a boom of a hybrid excavator, the method comprising:
(a) detecting an amount of operation of a boom joystick;
(b) determining lifting or descending of a boom due to operation of the boom joystick;
(c) opening a first control valve connected to a tank when the boom is lifted to return a flow rate of working fluid from a boom cylinder to tank;
(d) comparing a driving power of the boom according to the amount of operation of the boom joystick with a maximum supply power of an electric motor when the boom is lifted;
(e) comparing a consumed flow rate of the boom cylinder with a maximum flow rate of a hydraulic pump motor when the driving power of the boom is smaller than the maximum supply power of the electric motor;
(f) disconnecting a boom-assistant valve, when the consumed flow rate of the boom cylinder is smaller than the maximum flow rate of the hydraulic pump motor;
(g) connecting the boom-assistant valve when the driving power of the boom is larger than the maximum supply power of the electric motor;
(h) connecting the boom-assistant valve when the consumed flow rate of the boom cylinder is larger than the maximum flow rate of the hydraulic pump motor;
(i) opening a second control valve connected to tank when the boom is descended to return the flow rate of working fluid from the boom cylinder to tank through the hydraulic pump motor to drive the electric motor and through the second control valve;
(j) comparing a recovery power of the boom with a maximum recoverable power of the electric motor;
(k) comparing a recovery flow rate of the boom cylinder with an available flow rate of the hydraulic pump motor, when the recovery power of the boom is smaller than the maximum recoverable power of the electric motor;
(l) disconnecting the first control valve while the boom is descending, when the recovery flow rate of the boom cylinder is smaller than the available flow rate of the hydraulic pump motor to return the flow rate of working fluid from the boom cylinder to tank through the hydraulic pump motor, to drive the electric motor, and through the second control valve;
(m) connecting the first control valve while the boom is descending, when the recovery flow rate of the boom cylinder is larger than the available flow rate of the hydraulic pump motor to return at least a portion of the flow rate of working fluid from the boom cylinder to tank through the first control valve; and
(n) connecting the first control valve while the boom is descending, when the recovery power of the boom is larger than the maximum recoverable power of the electric motor to return at least a portion of the flow rate of working fluid from the boom cylinder to tank through the first control valve.

Assignees

• Kang Byung Il
• Doosan Infracore Co Ltd

Inventors

• Kang Byung Il

Classifications

• E02F3/435 Primary

  for dipper-arms, backhoes or the like · CPC title

• F15B2211/327

  electrically or electronically · CPC title

• E02F9/2292

  Systems with two or more pumps · CPC title

• E02F9/2217

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

• F15B13/044

  operated by electrically-controlled means, e.g. solenoids, torque-motors · CPC title