Hydraulic drive system for construction machine

Patent metadata

Field	Value
Publication number	US-9963856-B2
Application number	US-201415038179-A
Country	US
Kind code	B2
Filing date	Dec 2, 2014
Priority date	Mar 17, 2014
Publication date	May 8, 2018
Grant date	May 8, 2018

Abstract

An object to achieve favorable operability, in a combined operation that involves a specific actuator and involves a great difference in load pressure and when an operation of an operating unit for the specific actuator is a fine operation, by reducing energy consumption arising from wasted restricting pressure loss of a pressure compensating valve and by flexibly varying a flow rate of a hydraulic fluid supplied to the specific actuator depending on the load pressure. To achieve this object, a boom cylinder ( 3 a ) is provided with an open center type flow control valve ( 6 a ) that controls a hydraulic fluid from a main pump ( 202 ) and a closed center type flow control valve ( 6 i ) that controls a hydraulic fluid from a main pump ( 102 ). The main pump ( 102 ) is subject to load sensing control. The flow control valve ( 6 a ) is opened to control a supply flow rate up to an intermediate zone of an operating range of an operating unit for the boom cylinder ( 3 a ). Both the flow control valves ( 6 a ) and ( 6 i ) are opened to control the supply flow rate after the intermediate zone.

First claim

The invention claimed is:

1. A hydraulic drive system for a construction machine, comprising:
a variable displacement first pump device;
a second pump device;
a plurality of first actuators that are driven by hydraulic fluids delivered from the first pump device;
a plurality of second actuators that are driven by hydraulic fluids delivered from the second pump device;
a plurality of closed center type flow control valves that control flows of hydraulic fluids supplied from the first pump device to the first actuators;
a plurality of open center type flow control valves that control flows of hydraulic fluids supplied from the second pump device to the second actuators;
a plurality of pressure compensating valves that control differential pressures across the respective closed center type flow control valves; and
a first pump control unit including a load sensing control section that controls capacity of the first pump device such that a delivery pressure of the first pump device is higher by a target differential pressure than a maximum load pressure of the first hydraulic actuators, wherein
the first and second actuators include at least one first specific actuator as a common actuator,
the first actuators include a second specific actuator that is used at relatively high frequency in a combined operation with the first specific actuator,
the open center type flow control valves include a first flow control valve that controls a flow of a hydraulic fluid supplied from the second pump device to the first specific actuator,
the closed center type flow control valves include a second flow control valve that controls a flow of a hydraulic fluid supplied from the first pump device to the first specific actuator, and
the first and second flow control valves are set to have an opening area characteristic such that, when an operating unit for the first specific actuator is operated up to an intermediate zone of an operating range, only the first flow control valve opens to supply a hydraulic fluid from the second pump device to the first specific actuator and, when the operating unit is operated further from the intermediate zone, both the first and second flow control valves open to join and supply hydraulic fluids from the first and second pump devices to the first specific actuator.

2. The hydraulic drive system for a construction machine according to claim 1 , wherein
the first flow control valve is set to have the opening area characteristic such that an opening area increases with increase in the spool stroke and reaches a maximum before a maximum spool stroke is reached, and
the second flow control valve is set to have the opening area characteristic such that an opening area remains zero before a spool stroke reaches an intermediate stroke, opens at the intermediate stroke, and then increases with increase in the spool stroke and reaches a maximum opening area before a maximum spool stroke is reached.

3. The hydraulic drive system for a construction machine according to claim 1 , further comprising:
a second pump control unit that controls capacity of the second pump device, wherein
the first pump device includes the load sensing control section and a first torque control section that receives the delivery pressure of the first pump device introduced thereto and controls to limit the capacity of the first hydraulic pump such that, when at least one of the delivery pressure and the capacity of the first hydraulic pump increases and absorption torque of the first pump device increases, the absorption torque of the first hydraulic pump does not exceed a first predetermined value,
the second pump control unit includes a second torque control section that receives a delivery pressure of the second pump device introduced thereto and controls to limit the capacity of the second hydraulic pump such that, when the delivery pressure of the second hydraulic pump increases and absorption torque of the second pump device increases, the capacity of the second pump device is maintained at a maximum when the absorption torque of the second hydraulic pump is equal to or smaller than a second predetermined value and the absorption torque of the second hydraulic pump does not exceed the second predetermined value when the absorption torque of the second hydraulic pump increases up to the second predetermined value, and
the first pump control unit further includes: a reducing valve that receives the delivery pressure of the second pump device introduced thereto and, when the delivery pressure of the second pump device is equal to or lower than a capacity limiting control starting pressure of the second torque control section, outputs the delivery pressure of the second pump device without reduction and, when the delivery pressure of the second pump device increases beyond the capacity limiting control starting pressure of the second torque control section, reduces the delivery pressure of the second pump device to the capacity limiting control starting pressure of the second torque control section and outputs the reduced delivery pressure of the second pump device; and a reducing torque control actuator that receives the output pressure of the reducing valve and reduces the capacity of the first pump device such that the first predetermined value decreases as the output pressure of the reducing valve increases.

4. The hydraulic drive system for a construction machine according to claim 1 , wherein the first specific actuator is a boom cylinder that drives a boom of a hydraulic excavator and the second specific actuator is an arm cylinder that drives an arm of the hydraulic excavator.

5. The hydraulic drive system for a construction machine according to claim 2 , wherein the first specific actuator is a boom cylinder that drives a boom of a hydraulic excavator and the second specific actuator is an arm cylinder that drives an arm of the hydraulic excavator.

6. The hydraulic drive system for a construction machine according to claim 3 , wherein the first specific actuator is a boom cylinder that drives a boom of a hydraulic excavator and the second specific actuator is an arm cylinder that drives an arm of the hydraulic excavator.

Assignees

• Hitachi Construction Machinery Tierra Co Ltd

Inventors

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

Classifications

• E02F9/2292

  Systems with two or more pumps · CPC title

• F15B11/165

  for adjusting the pump output or bypass in response to demand · CPC title

• E02F9/2239

  using two or more pumps with cross-assistance · CPC title

• E02F9/2267

  Valves or distributors (position of valves arrangements on upper-structures E02F9/0875) · CPC title

• E02F3/425

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