Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Reexamination Certificate
1998-09-29
2001-06-05
Walberg, Teresa (Department: 3742)
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
C417S212000, C060S426000
Reexamination Certificate
active
06241482
ABSTRACT:
TECHNICAL FIELD
This invention relates to a hydraulic pilot circuit having a plurality of pilot valves which control a plurality of hydraulic directional control valves by pilot oil.
BACKGROUND ART
A hydraulic excavator having a plurality of hydraulic actuators, for example, comprises a hydraulic cylinder for implements, a hydraulic swing motor for an upper swing body, a hydraulic travel motor for a lower travel body and the like as typical actuators. These hydraulic actuators are made to operate by that discharged oil from an actuator pump driven by an engine is supplied to the hydraulic actuators due to control by the hydraulic directional control valves.
As a typical operating means to control the hydraulic directional control valve, a so-called pilot operation is conducted in which pilot oil is supplied to the end portion of a valve spool of the hydraulic directional control valve by a pilot valve to operate the valve spool. This pilot operation is widely utilized for hydraulic excavators, truck cranes and the like, since pilot operation of the hydraulic directional control valve instead of its manual and direct operation reduces operating effort, and enables remote control of the hydraulic directional control valve. Structure of this hydraulic pilot circuit for hydraulic pilot operation will be described below.
(1) The pilot oil is produced and discharged by an engine driven pilot pump with fixed displacement, for example, a gear pump, other than an actuator pump.
(2) The pressure of the discharged pilot oil is set and remained by a relief valve at the pilot pressure necessary for operating the hydraulic directional control valve and the like.
(3) There are provided a plurality of hydraulic directional control valves corresponding to each of the plurality of hydraulic actuators, and a plurality of pilot valves are provided corresponding to each of the plurality of hydraulic directional control valves. When an attachment and the like having the hydraulic actuators are added, the hydraulic directional control valves and the pilot valves for the added hydraulic actuators are additionally mounted.
(4) Regarding the displacement capacity of the pilot pump, the pilot pump with the possible larger displacement capacity is adopted so that the quantity of the pilot oil which is supplied to the pilot valve does not become insufficient, when the plurality of pilot valves are operated at the same time and/or the pilot valves are operated at various speeds. However, it should be noted that when the pilot valves are additionally mounted and increased in number, it causes insufficiency, and therefore changing to a pump with larger discharge may be necessary.
DISCLOSURE OF THE INVENTION
A conventional hydraulic pilot circuit of the structure described above bears the following problems to be solved.
(1) When a pilot valve is not operated, all pilot oil is returned to a tank via a relief valve. Accordingly, the pilot oil with pressure energy generates heat, and the temperature of hydraulic oil is raised. When the pilot oil flow is increased by changing to a pilot pump with larger displacement capacity in order to increase the number of hydraulic actuators and improve the response of the hydraulic actuators, the heating of the hydraulic oil further increases, and thus an oil cooler for cooling the hydraulic oil is further burdened. Furthermore, fuel consumption by an engine which drives a pilot pump increases.
(2) If a hydraulic directional control valve(s) is(are) added to additionally mount attachment and the like, chances and/or frequency of the operation of the plurality of hydraulic directional control valves at the same time increase, whereby the pilot oil which flows into each of the hydraulic directional control valves from the pilot valves runs short if the conventional pilot pump is used. As a result, operability (response) of the hydraulic directional control valves worsens.
The present invention has been accomplished in the light of the foregoing facts, and its technical object is to provide a hydraulic pilot circuit:
(1) in which the heating of the hydraulic oil is reduced, and
(2) in which the pilot oil is supplied to the pilot valves sufficiently so as not to damage the controllability even if the pilot valves are additionally mounted and plurality of them are operated at the same time.
In the present invention, to solve the foregoing technical problems, the hydraulic pilot circuit has the following structures.
(1) A variable displacement pump is adopted as the pilot pump.
(2) Operating condition of the hydraulic pilot valves is detected by an operation detecting means, then from the operating condition, the quantity of the oil to be discharged from the pilot pump which is necessary to operate the hydraulic directional control valves is computed by a controller, and the pilot pump discharges the oil of only the minimum necessary quantity.
That is, according to the present invention, as a hydraulic pilot circuit for solving the foregoing technical problems, there is provided a hydraulic pilot circuit characterized in that it has a pilot pump which discharges pilot oil and a plurality of pilot valves which control a plurality of hydraulic directional control valves by supplying the pilot oil with control, wherein the pilot pump is formed of a variable displacement pump.
In a preferred embodiment, the hydraulic pilot circuit is provided with an operation detecting means which detects the operating condition of each of the plurality of pilot valves, and a controller which computes the necessary pilot oil flow based on a detecting signal from the operation detecting means to output a signal to the variable displacement pump as a capacity directing signal. The operation detecting means preferably detects the operation angle of operation levers of the pilot valves.
In the hydraulic pilot circuit of the present invention,
(1) The operating condition of the plurality of pilot valves (number of the operated pilot valves, the extent of opening of the operated pilot valves) is detected by the operation detecting means.
(2) The necessary pilot oil flow is computed by the controller, and the necessary discharge is directed to the variable displacement mechanism of the pilot pump.
(3) The variable displacement mechanism of the pilot pump works, and the directed oil flow is discharged from the pilot pump. Therefore, the minimum necessary pilot oil flow is maintained, thus heating of the hydraulic oil and the increase of the fuel consumption by the engine is controlled, and the operability (response) can be improved.
REFERENCES:
patent: 3847061 (1974-11-01), Ifield
patent: 3952509 (1976-04-01), Coleman
patent: 4726186 (1988-02-01), Tatsumi et al.
patent: 4986071 (1991-01-01), Voss et al.
patent: 5048293 (1991-09-01), Aoyagi
patent: 5048294 (1991-09-01), Oshina et al.
patent: 5056312 (1991-10-01), Hirata et al.
patent: 533958 (1992-04-01), None
patent: 593782 (1993-04-01), None
patent: 50-160671 (1975-12-01), None
patent: 63-186005 (1988-08-01), None
patent: 4-140330 (1992-05-01), None
Abstract of JP 4-140330.
Abstract of JP 63-186005.
Campbell Thor
Millen White Zelano & Branigan P.C.
Shin Caterpillar Mitsubishi Ltd.
Walberg Teresa
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