Hydraulic Drive System for Construction Machine

• US 20150330415A1
• Filed: 11/15/2013
• Published: 11/19/2015
• Est. Priority Date: 01/25/2013
• 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: TAKAHASHI, Kiwamu, KISHIMOTO, Shingo, TAKEBAYASHI, Yoshifumi, MORI, Kazushige, NAKAMURA, Natsuki
• Granted Patent: US 9,835,180 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: E02F 9/2232 using one or more variable displacement pumps
• CPC Class Codes: E02F 9/2253 Controlling the travelling speed of vehicles, e.g. adjusting travelling speed according to implement loads, control of hydrostatic transmission
• CPC Class Codes: E02F 9/2285 Pilot-operated systems
• CPC Class Codes: E02F 9/2296 Systems with a variable displacement pump
• 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 11/165 for adjusting the pump output or bypass in response to demand
• 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 13/026 Pressure compensating valves
• CPC Class Codes: F15B 2211/20553 with pilot circuit, e.g. for controlling a swash plate
• CPC Class Codes: F15B 2211/253 Pressure margin control, e.g. pump pressure in relation to load pressure
• 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 2211/40515 with variable throttles or orifices
• CPC Class Codes: F15B 2211/428 actuated by fluid pressure
• CPC Class Codes: F15B 2211/50536 using unloading valves controlling the supply pressure by diverting fluid to the return line
• CPC Class Codes: F15B 2211/6058 with isolator valves
• CPC Class Codes: F15B 2211/6355 having valve means
• CPC Class Codes: F15B 2211/67 Methods for controlling pilot pressure
• CPC Class Codes: F15B 2211/7135 Combinations of output members of different types, e.g. single-acting cylinders with rotary motors

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 6d and 6e 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 Pa3 when the travel lever is fully operated. In a first half of a spool stroke, the travel flow control valves 6d and 6e have an opening area approximate to an opening area of comparative example 1.

Claims

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.