HYDRAULIC DRIVE SYSTEM FOR CONSTRUCTION MACHINE

• US 20140174068A1
• Filed: 08/28/2012
• Published: 06/26/2014
• Est. Priority Date: 08/31/2011
• Status: Active Grant

• Current Assignee: Hitachi Construction Machinery Tierra Co.,Ltd. (Hitachi Construction Machinery (China) Co., Ltd.)
• Original Assignee: Hitachi Construction Machinery Company Limited (Hitachi, Ltd.)
• Inventors: Mori, Kazushige, Takahashi, Kiwamu, Takebayashi, Yoshifumi, Nakamura, Natsuki
• Granted Patent: US 9,518,593 B2
• Time in Patent Office: Days
• US Class Current: 60/328
• CPC Class Codes: E02F 3/325 Backhoes of the miniature type
• CPC Class Codes: E02F 9/207 of the type electric propulsion units, e.g. electric motors or generators
• CPC Class Codes: E02F 9/2075 of the hybrid type for vehicles in general B60W20/00
• CPC Class Codes: E02F 9/2217 with energy recovery arrangements, e.g. using accumulators, flywheels
• CPC Class Codes: E02F 9/2232 using one or more variable displacement pumps
• CPC Class Codes: E02F 9/2285 Pilot-operated systems
• CPC Class Codes: E02F 9/2296 Systems with a variable displacement pump
• CPC Class Codes: F04B 49/06 Control using electricity regulating by means of floats actuating electric switches F04B49/04
• CPC Class Codes: F15B 11/163 for sharing the pump output equally amongst users or groups of users, e.g. using anti-saturation, pressure compensation
• CPC Class Codes: F15B 11/168 with an isolator valve (duplicating valve), i.e. at least one load sense [LS] pressure is derived from a work port load sense pressure but is not a work port pressure itself
• CPC Class Codes: F15B 15/02 Mechanical layout characterised by the means for converting the movement of the fluid-actuated element into movement of the finally-operated member
• CPC Class Codes: F15B 21/14 Energy-recuperation means
• CPC Class Codes: F15B 2211/20546 variable capacity
• CPC Class Codes: F15B 2211/30535 the pressure compensating valve is arranged between pressure source and directional control valve
• CPC Class Codes: F15B 2211/329 actuated by fluid pressure
• CPC Class Codes: F15B 2211/6058 with isolator valves
• CPC Class Codes: F15B 2211/71 Multiple output members, e.g. multiple hydraulic motors or cylinders

Abstract

A hydraulic motor (52) is arranged in a control hydraulic line (51) connecting a second hydraulic fluid supply line (4a) (for supplying the hydraulic fluid delivered from the main pump (2) to flow control valves (26a to 26h)) to a tank (T). A generator (53) connected with the rotating shaft (52a) of the hydraulic motor (52). Maximum load pressure (PLmax) is detected by a pressure sensor (54). Power generation control of the generator (53) is performed by a second control device (55) so that the hydraulic motor (52) rotates when the delivery pressure of the main pump (2) exceeds target control pressure (Pun) determined by adding a preset value (Pb) to the maximum load pressure (PLmax). AC power generated by the generator (53) is stored in a battery (41).

Claims

1. A hydraulic drive system for a construction machine including a prime mover, a main pump of the variable displacement type driven by the prime mover, a plurality of actuators driven by hydraulic fluid delivered from the main pump, a plurality of flow control valves that respectively control the flow of the hydraulic fluid supplied from the main pump to the actuators, and a pump control device that performs load sensing control for the delivery flow rate of the main pump so that delivery pressure of the main pump becomes higher than maximum load pressure of the actuators by target differential pressure, comprising:

a hydraulic motor arranged in a control hydraulic line connecting a hydraulic fluid supply line for supplying the hydraulic fluid from the main pump to the flow control valves, to a tank, the hydraulic motor being drivable by the hydraulic fluid delivered from the main pump;

a generator connected with the rotating shaft of the hydraulic motor;

a control device that performs power generation control of the generator so that the delivery pressure of the main pump becomes higher than a target control pressure determined by adding a preset value to the maximum load pressure with the rotation of the hydraulic motor; and

an electricity storage device that stores electric power generated by the generator.

2. The hydraulic drive system for a construction machine according to claim 1, further comprising a pressure sensor that detects the maximum load pressure,

wherein the control device calculates the target control pressure by adding the preset value to the maximum load pressure detected by the pressure sensor, calculates power generation torque of the generator having magnitude overcoming a rotating torque of the hydraulic motor caused by the target control pressure, and performs the power generation control of the generator so that the power generation torque is achieved.

3. The hydraulic drive system for a construction machine according to claim 1, further comprising a correction device that corrects the target differential pressure of the load sensing control so that the target differential pressure decreases with the decrease in the revolution speed of the prime mover,

wherein the control device corrects the preset value so that the preset value decreases with the decrease in the revolution speed of the prime mover.

4. The hydraulic drive system for a construction machine according to any one of claim 2, further comprising a correction device that corrects the target differential pressure of the load sensing control so that the target differential pressure decreases with the decrease in the revolution speed of the prime mover,

wherein the control device corrects the preset value so that the preset value decreases with the decrease in the revolution speed of the prime mover.

5. The hydraulic drive system for a construction machine according to claim 1, wherein:

the prime mover includes an electric motor, and

the electricity storage device functions as a power supply for the electric motor.

6. The hydraulic drive system for a construction machine according to claim 2, wherein:

the prime mover includes an electric motor, and

the electricity storage device functions as a power supply for the electric motor.

7. The hydraulic drive system for a construction machine according to claim 3, wherein:

the prime mover includes an electric motor, and

the electricity storage device functions as a power supply for the electric motor.

8. The hydraulic drive system for a construction machine according to claim 4, wherein:

the prime mover includes an electric motor, and

the electricity storage device functions as a power supply for the electric motor.