Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1990-10-31
1992-12-15
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
91511, 91446, F16D 3102
Patent
active
051706253
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a control system for a hydraulic pump in a hydraulic drive circuit for use in hydraulic machines such as hydraulic excavators and cranes, and more particularly to a control system for a hydraulic pump in a hydraulic drive circuit of load sensing control type which controls a pump delivery rate in such a manner as to hold the delivery pressure of the hydraulic pump higher than the load pressure of a hydraulic actuator, by a fixed value.
BACKGROUND ART
Hydraulic drive circuits for use in hydraulic machines such as hydraulic excavators and cranes each include at least one hydraulic pump, at least one hydraulic actuator driven by a hydraulic fluid delivered from the hydraulic pump, and a flow control valve connected between the hydraulic pump and the actuator for controlling a flow rate of the hydraulic fluid supplied to the actuator. It is known that some of those hydraulic drive circuits employs a technique called load sensing control (LS control) for controlling the delivery rate of the hydraulic pump. The load sensing control is to control the delivery rate of the hydraulic pump such that a delivery pressure of the hydraulic pump is held at a fixed value higher than a load pressure of the hydraulic actuator. This causes the delivery rate of the hydraulic pump to be controlled dependent on the load pressure of the hydraulic actuator, and hence permits economic operation.
Meanwhile, the load sensing control is carried out by detecting a differential pressure (LS pressure) between the delivery pressure and the load pressure, and controlling the displacement volume of the hydraulic pump, or the position (tilting amount) of a swash plate in the case of a swash plate pump, in response to a deviation between the LS differential pressure and a differential pressure target value. Conventionally, the detection of the differential pressure and the control of tilting amount of the swash plate have usually been carried out in a hydraulic manner as disclosed in JP, A, 60-11706, for example. This conventional arrangement will briefly be described below.
A pump control system disclosed in JP, A, 60-11706 comprises a control valve having one end subjected to the delivery pressure of a hydraulic pump and the other end subjected to both the maximum load pressure among a plurality of actuators and the urging force of a spring, and a cylinder unit operation of which is controlled by a hydraulic fluid passing through the control valve for regulating the swash plate position of the hydraulic pump. The spring at one end of the control valve is to set a target value of the LS differential pressure. Depending on the deviation occurred between the LS differential pressure and the target value, the control valve is driven and the cylinder unit is operated to regulate the swash plate position, whereby the pump delivery rate is controlled so that the LS differential pressure is held at the target value. The cylinder unit has a spring built therein to apply an urging force in opposite relation to the direction in which the cylinder unit is driven upon inflow of the hydraulic fluid.
However, the above conventional control system for the hydraulic pump has had problems below.
In the conventional pump control system, the tilting speed of a swash plate of the hydraulic pump is determined dependent on the flow rate of the hydraulic fluid flowing into the cylinder unit, while the flow rate of the hydraulic fluid is determined dependent on both an opening, i.e., a position, of the control valve and setting of the spring in the cylinder unit and, in turn, the position of the control valve is determined by the relationship between the urging force of the LS differential pressure and the spring force for setting the target value. Here, the spring of the control valve and the spring of the cylinder unit each have a fixed spring constant. Accordingly, a control gain for the tilting speed of the swash plate dependent on the deviation between the LS differential pressure and the target value thereo
REFERENCES:
patent: 3579987 (1971-05-01), Busse
patent: 4617854 (1986-10-01), Kropp
patent: 4809504 (1989-03-01), Izumi et al.
patent: 4856278 (1989-08-01), Widmann et al.
patent: 4967557 (1990-11-01), Izumi et al.
Izumi Eiki
Nakamura Shigetaka
Onoue Hiroshi
Tanaka Yasuo
Watanabe Hiroshi
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Nguyen Hoang
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