Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1996-09-05
1998-06-02
Nguyen, Hoang
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
60452, F16D 3102
Patent
active
057584990
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic control system equipped on construction machines such as hydraulic excavators and cranes, and more particularly to a hydraulic control system provided with a pump regulator for controlling the displacement of a hydraulic pump in accordance with a status variable of a hydraulic driving system.
BACKGROUND ART
A known hydraulic control system provided with a pump regulator for controlling the displacement of a hydraulic pump in accordance with a status variable of a hydraulic driving system generally comprises a signal pressure generator for generating, as a first hydraulic signal, a pressure depending on the status variable of the hydraulic driving system, a pressure detector for detecting the first hydraulic signal from the signal pressure generator and converting the detected signal into a first electric signal, a control unit for executing an arithmetic operation based on the first electric signal from the pressure detector and outputting a second electric signal, and a pump regulator driven depending on the second electric signal from the control unit for controlling the displacement of a hydraulic pump. One example of such a hydraulic control system is described in JP, U, 5-64506. In this prior art system, a flow control valve of center bypassing type is used as a flow control valve contained in the hydraulic driving system, a throttle is disposed, as the signal pressure generator, in a center bypass line on the downstream side, and a so-called negative control pressure generated by the throttle is detected as the first hydraulic signal by the pressure detector. Furthermore, a solenoid proportional valve for converting a pilot pressure into a second hydraulic signal depending on the second electric signal is disposed between the control unit and the pump regulator, and the pump regulator is driven by the second hydraulic signal from the solenoid proportional valve.
DISCLOSURE OF THE INVENTION
The foregoing prior art system is advantageous in that such a function as compensating the effect of fluid temperature can be easily added, because the displacement of the hydraulic pump is controlled in accordance with the status variable of the hydraulic driving system in an electric manner by using the control unit. In the electric control using the control unit, however, the process after the step of detecting the first hydraulic signal by the pressure detector to the step of driving the solenoid proportional valve by the second electric signal is all carried out using electric signals. If there occurs any trouble in the electric system such as a contact failure of wires and abnormal operation of the control unit, the pump regulator fails to operate normally any longer, resulting in the problem that the hydraulic pump may always deliver a maximum flow rate to exert an excessive load on a hydraulic circuit, or may always deliver a minimum flow rate to pose a difficulty in working. Such a failed condition cannot be overcome unless the electric system is repaired. Also, as well known, it is generally more difficult to troubleshoot the electric system than the mechanical system.
An object of the present invention is to provide a hydraulic control system which can easily hydraulically back up a trouble caused in an electric system, while employing a control unit to utilize the advantage of electric control, when the displacement of a hydraulic pump is controlled in accordance with a status variable of a hydraulic driving system.
To achieve the above object, the present invention is constructed as follows. In a hydraulic control system comprising a hydraulic driving system including a variable displacement hydraulic pump, a hydraulic actuator driven by a hydraulic fluid delivered from the hydraulic pump, a flow control valve for controlling a flow of the hydraulic fluid supplied from the hydraulic pump to the hydraulic actuator, and manipulation means for operating the flow control valve; first signal pressure generating means for generating, as a fi
REFERENCES:
patent: 5085051 (1992-02-01), Hirata
patent: 5447027 (1995-09-01), Ishikawa et al.
patent: 5533867 (1996-07-01), Strenzke
patent: 5575148 (1996-11-01), Hirata et al.
patent: 5586869 (1996-12-01), Benckert et al.
Hirata Toichi
Sugiyama Genroku
Hitachi Construction Machinery Co. Ltd.
Nguyen Hoang
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