Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1989-09-07
1992-01-07
Look, Edward K.
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
60468, F04B 4900, F15B 1100
Patent
active
050779745
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic control system for a hydraulic excavator, and more particularly to a hydraulic control system for a hydraulic excavator which allows operating power and operating speed to be improved as necessary.
Generally, a hydraulic excavator comprises a lower traveling body and a revolving superstructure. The revolving superstructure has an operating machine provided with a boom, an arm, a bucket, and the like. The traveling apparatus, the revolving apparatus, the operating machine, and other apparatus used in a hydraulic excavator are operated by hydraulic actuators that are separately provided therein. In other words, various hydraulic circuits are mounted on a hydraulic excavator. Generally, such hydraulic circuits comprise a main circuit and a pilot circuit. The main circuit includes a hydraulic actuator, a flow-rate control valve, a hydraulic control valve, a direction changeover valve, a servo valve, and other hydraulic devices. The pilot circuit is adapted to provide instructions to the flow-rate control valve, the hydraulic control valve, the direction changeover valve, the servo valve, etc. so that they operate as required. As a pilot system this pilot circuit comprises hydraulic pressure, pneumatic pressure, electrical signals, means for combining them, and other means. Accordingly, so-called hydraulic control circuits generally represent the flow-rate control valve, hydraulic control valve, direction changeover valve, servo valve, etc. of the main circuit, as well as pilot circuits related to them. These pilot circuits control the amount of oil supplied to the hydraulic actuator of the main circuit and the oil pressure thereof.
It has in recent years become the practice to control such a hydraulic control circuit of a hydraulic excavator in such a manner that the hydraulic horsepower is constantly set at a fixed level (hereafter, this control will be referred to as power constant control). This power constant control is conducted with a view to causing the hydraulic horsepower to coincide with the engine output to as practical an extent as possible. By virtue of this control, overall output losses can be reduced. A more advanced type of hydraulic control circuit is generally so arranged as to limit the power constant control when the pressure of the main circuit approaches relief pressure (hereafter, this control will be referred to as cut-off control). Incidentally, the aforementioned relief pressure refers to the maximum hydraulic pressure of the main circuit. When the actuator is subjected to a heavy load or the like, the hydraulic pressure of the main circuit rises, and the relief pressure is provided to limit the extent of this rise in pressure so as to protect the circuit and its component devices from becoming damaged by the hydraulic pressure. This relief pressure is set by the hydraulic control valve (hereafter referred to as the relief valve). Returning to the cut-off control, this control is also designed to reduce output losses. More specifically, when the pressure of the main circuit approaches the relief pressure, the flow rate decreases on the basis of the power constant control. Since the flow rate is still high, this cut-off control is effected to further reduce the flow rate sharply. If this cut-off control is not provided, a large amount of oil would return to the oil sump when the circuit pressure is close to the relief pressure. At this time, output loss would occur due to the rise in oil temperature and the occurrence of relief noise.
Referring now to FIGS. 1 to 3 which illustrate an example of a conventional hydraulic control apparatus for a hydraulic excavator having the above-described arrangement, a detailed explanation will be given of the hydraulic control apparatus. The hydraulic circuit shown in FIG. 1 is an example of a generally adopted hydraulic circuit of this type. It goes without saying that this circuit is provided with a power constant control valve 30 and a cut-off control valve 10. In addition,
REFERENCES:
patent: 3635021 (1972-01-01), McMillen et al.
patent: 4405287 (1983-09-01), Kuchenbecker et al.
patent: 4481770 (1984-11-01), Lohbauer et al.
patent: 4548036 (1985-10-01), Matsuda et al.
patent: 4571941 (1986-02-01), Aoyagi et al.
Kamikawa Nobuhisa
Nishida Kimio
Kabushiki Kaisha Komatsu Setsakusho
Kapsalas George
Look Edward K.
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