Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Reexamination Certificate
1999-07-29
2001-03-20
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
C060S452000
Reexamination Certificate
active
06202411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flow rate control device for use in relief cut-off control in a hydraulic excavator.
2. Description of the Related Art
In a certain hydraulic excavator there is made a control called relief cut-off control in which the discharge flow rate from a pump is decreased when the pump pressure has reached a relief cut-off pressure. Once this relief cut-off control is made, for example when a rock or the like strikes against a bucket during excavating work of the hydraulic excavator and an overload acts on the excavator, it is not only possible to prevent the energy loss of hydraulic oil caused by relief operation but also possible to diminish the relief noise. Besides, there does not occur any shock during relief operation, so it becomes possible to effect smooth operation and it is also possible to improve the heat balance of hydraulic oil and devices.
In the conventional hydraulic excavator, however, the relief cut-off control is made on the basis of only a preset relief pressure of a relief valve. That is, the relief cut-off control is made irrespective of what work and under what conditions the hydraulic excavator is performing.
Generally, it is known that once the relief cut-off control is made, the operator of the hydraulic excavator feels a sense of incongruity or feels as if force were gone, as an inevitable result of decrease in the discharge flow rate from the pump.
In the above conventional hydraulic excavator, the relief cut-off control is made each time the load imposed on a hydraulic actuator increases to a certain degree. Consequently, at every relief cut-off control, a sense of incongruity or an extinct-of-force feeling is given to the operator. As the case may be, it may become impossible to continue operation due to an insufficient pump discharge.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a flow rate control device capable of making the relief cut-off control only where required for various works of different conditions performed by a hydraulic excavator, including excavating, crushing and land readjusting works.
The flow rate control device in a hydraulic excavator according to the present invention comprises a hydraulic pump which is driven rotatively by an engine, a hydraulic actuator which is driven by a hydraulic oil discharged from the hydraulic pump, a control valve which controls the supply of the hydraulic oil to the hydraulic actuator, an operating means which operates the control valve so as to change over the valve from one position to another, a relief valve disposed in a discharge oil path extending from the hydraulic pump to limit the maximum pressure in the discharge oil path, an operational condition detecting means for detecting an operational condition of the hydraulic actuator, a pump pressure detecting means for detecting the discharge pressure of the hydraulic oil discharged from the hydraulic pump, a flow rate adjusting means for adjusting the discharge flow rate of the hydraulic oil discharged from the hydraulic pump, and a control means to which are inputted detection signals from both operational condition detecting means and pump pressure detecting means. When a specific operational condition of the hydraulic actuator is detected and when the discharge pressure is held at a predetermined relief cut-off pressure or higher for a predetermined period of time, the said control means makes control so that the discharge flow rate of the hydraulic oil discharged from the hydraulic pump is decreased to a relief cut-off pressure by the flow rate adjusting means.
In this case, the relief cut-off control can be made only where required for various works of different conditions performed by the hydraulic excavator, including excavating, crushing and land readjusting works. More specifically, even in the case where the discharge pressure is held at a predetermined relief cut-off pressure or higher for a predetermined period of time, it is required, for execution of the relief cut-off control, that the hydraulic actuator be in a specific operational condition.
The specific operational condition of the hydraulic actuator may be at least either a condition such that an attachment to the hydraulic excavator, which is driven by the hydraulic actuator, is a predetermined type attachment or a condition such that the operating means is operated a predetermined amount or more. In this case, for example, the relief cut-off control can be made only when a special attachment such as a crusher is used or only when a full lever operation or an operation close thereto is performed.
The flow rate control device may be further provided with an engine revolution detecting means for detecting the state of engine revolution and outputting a detected signal to the control means. In this case, when the specific operational condition of the hydraulic actuator is detected and the discharge pressure is held at the predetermined relief cut-off pressure or higher for the predetermined period of time, further, when it is detected by the engine revolution detecting means that the number of revolutions of the engine is in a predetermined high revolution condition, the control means may perform a control so that the discharge flow rate of the hydraulic oil discharged from the hydraulic pump is decreased to the relief cut-off flow rate. The predetermined high revolution condition may indicate either a condition such that the engine revolution is held at a predetermined number of revolutions or higher for a predetermined period of time or a condition such that the operational position of a throttle lever for setting the engine speed is set to a high speed side.
The flow rate control device may be further provided with a work mode setting means for setting drive characteristics of the engine, hydraulic pump, etc. as work modes and inputting a set signal to the control means. In this case, when the specific operational condition of the hydraulic actuator is detected and the discharge pressure is held at the predetermined relief cut-off pressure or higher for the predetermined period of time, further, when a predetermined work mode is set by the work mode setting means, the control means may perform a control so that the discharge flow rate of the hydraulic oil discharged from the hydraulic pump is decreased to the relief cut-off flow rate.
Control may be made so as to decrease the discharge flow rate gradually when decreasing the discharge flow rate of the hydraulic pump to the relief cut-off flow rate or so as to increase the discharge flow rate gradually when canceling the relief cut-off state. In this case, when the relief valve performs a relief cut-off operation during operation of the hydraulic excavator, it is possible to eliminate the “sense of incongruity” or “extinct-of-force feeling” of the operator during operation.
REFERENCES:
patent: 4697418 (1987-10-01), Okabe et al.
patent: 5586869 (1996-12-01), Benckert et al.
patent: 5896930 (1999-04-01), Arai
patent: 6-081773 (1994-03-01), None
(Kobe Steel, Ltd.)
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ryznic John E.
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