Hydraulic drive system for construction machine

Patent metadata

Field	Value
Publication number	US-9835180-B2
Application number	US-201314763000-A
Country	US
Kind code	B2
Filing date	Nov 15, 2013
Priority date	Jan 25, 2013
Publication date	Dec 5, 2017
Grant date	Dec 5, 2017

Abstract

An object of the invention is to achieve a travel speed known in the art during travelling operation, improve energy efficiency by reducing energy loss, and obtain favorable travel operability less susceptible to effects from variations in a travel load and changes in a pump delivery pressure when travelling operation is performed through operation of a travel lever over a half stroke range or less. A variable restrictor valve 80 is disposed in parallel with a flow sensing valve 50 of an engine speed sensing valve unit 13. A travel pilot pressure is adapted to act in an opening direction of the variable restrictor valve 80. The variable restrictor valve 80 is set to have a continuously increasing opening area from a full closure to a maximum with an increasing travel pilot pressure. Travel flow control valves 6 d and 6 e have an opening area that allows a predetermined flow rate QT required for traveling to be obtained even when a target LS differential pressure is decreased to a second specified value Pa 3 when the travel lever is fully operated. In a first half of a spool stroke, the travel flow control valves 6 d and 6 e have an opening area approximate to an opening area of comparative example 1.

First claim

The invention claimed is:

1. A hydraulic drive system for a construction machine, the system comprising:
a variable displacement main pump driven by a prime mover;
a plurality of actuators including travel hydraulic motors and driven by a hydraulic fluid delivered from the main pump;
a plurality of flow control valves including travel flow control valves, that controls flow rates of a hydraulic fluid supplied from the main pump to the plurality of actuators;
a plurality of operating units including travel operating units, that instructs operating directions and operating speeds of the plurality of the actuators and outputs commands for operating the plurality of flow control valves;
a plurality of pressure compensation valves for controlling differential pressures across the plurality of flow control valves; and
a pump control unit for performing load sensing control of a displacement of the main pump such that a delivery pressure of the main pump becomes higher by a target differential pressure than a maximum load pressure of the actuators,
the plurality of pressure compensation valves being configured to control the differential pressures across the respective flow control valves such that the differential pressure across each of the flow control valves is maintained at a differential pressure between the delivery pressure of the main pump and the maximum load pressure of the actuators,
wherein the hydraulic drive system further comprises:
a travel detection unit that detects travelling operation in which the travel hydraulic motors are driven; and
a target differential pressure setting unit that, based on a result of detection by the travel detection unit, sets the target differential pressure of load sensing control at a first specified value at any time other than the travelling operation and sets the target differential pressure of load sensing control at a second specified value smaller than the first specified value during the travelling operation, wherein
the travel flow control valves each has such an opening area characteristic that an opening area at a spool stroke when the corresponding travel operating unit is fully operated is large enough to obtain a predetermined flow rate required for traveling when the target differential pressure of load sensing control is set at the second specified value, and an opening area in a spool stroke range when the corresponding travel operating unit is finely operated is approximate to an opening area of a travel flow control valve having a maximum opening area that can obtain a predetermined flow rate required for traveling when the target differential pressure of load sensing control is set at the first specified value.

2. The hydraulic drive system for a construction machine according to claim 1 , wherein
the target differential pressure setting unit comprises:
a pilot pump driven by the prime mover;
a prime mover speed sensing valve unit including: a flow sensing valve disposed in a line through which a hydraulic fluid delivered from the pilot pump flows, for varying a differential pressure across the flow sensing valve in accordance with a delivery flow rate of the pilot pump; and a differential pressure reducing valve that generates the differential pressure across the flow sensing valve as an absolute pressure and outputs the absolute pressure as the target differential pressure of load sensing control; and
a variable restrictor valve disposed in parallel with the flow sensing valve in a line through which the hydraulic fluid delivered from the pilot pump flows, wherein
the variable restrictor valve is in a fully closed position at any time other than the travelling operation and is in a restricting position during the travelling operation and continuously increases an opening area thereof from a full closure up to a maximum as an input amount of the travel operating unit increases from a minimum to a maximum.

Assignees

• Hitachi Construction Machinery Tierra Co Ltd
• Hitachi Construction Machinery Tierra Co Ltd

Inventors

• Takahashi Kiwamu
• Kishimoto Shingo
• Takebayashi Yoshifumi
• Mori Kazushige
• Nakamura Natsuki

Classifications

• F15B13/026

  Pressure compensating valves · CPC title

• E02F9/2285

  Pilot-operated systems · CPC title

• E02F9/2253

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

• F15B2211/7135

  Combinations of output members of different types, e.g. single-acting cylinders with rotary motors · CPC title

• F15B2211/67

  Methods for controlling pilot pressure · CPC title