Parking brake circuit for hydraulically driven vehicle

Fluid-pressure and analogous brake systems – With pump – Pressure control

Patent

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Details

303 72, E02F 922

Patent

active

053204190

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION

This invention relates to a parking brake circuit for a hydraulically driven construction vehicle such as, for example, a power shovel, and the like, and more particularly to such a parking brake circuit being adapted to prevent an erroneous operation when the vehicle travels on a downward slope.


BACKGROUND ART OF THE INVENTION

Heretofore, a parking brake circuit as shown in FIG. 1 has been known. This prior art parking brake circuit is constructed such that, in order to introduce hydraulic operating fluid having a high pressure into a conduit 5, first and second main circuits 2, 3 are connected to first and second ports 1a, 1b of a hydraulically driven motor 1 for driving a vehicle, respectively, and further a counterbalance valve 4 is provided between the main circuits 2, 3, and still further one end of the conduit 5 is connected to a pressure receiving chamber 6a of an actuator 6 for actuating a parking brake. The parking brake circuit is adapted to release a parking brake 7 when hydraulic operating fluid is supplied into the pressure receiving chamber 6a of the parking brake actuating actuator 6 and, on the other hand, to operate or apply the parking brake 7 by the action of a compression spring and the like when the hydraulic operating fluid is discharged from the pressure receiving chamber 6a. In addition, in the parking brake circuit when the hydraulically driven motor 1 is driven by supplying hydraulic operating fluid through an operation valve not shown into either one of the first and the second main circuit 2, 3, the parking brake 7 is released. On the other hand, when the rotating operation of the hydraulically driven motor 1 is stopped by interrupting the supply of hydraulic operating fluid into the first and the second main circuits 2, 3, the parking brake 7 is applied or operated.
In the above described parking brake circuit, since the parking brake is released by the utilization of hydraulic operating fluid within either one of the first and the second main circuits 2, 3, which has become a high hydraulic pressure side. When either one of the first and the second main circuits 2, 3, on the side of high hydraulic pressure, becomes a low pressure (i.e., less than such a hydraulic pressure as releases the parking brake) because of a pumping operation of the hydraulically driven motor 1 caused, for example, by the vehicle travelling on a downward slope, the parking brake 7 is rendered operative undesirably so as to stop the rotating operation of the hydraulically driven motor 1.


SUMMARY OF THE INVENTION

The present invention has been made in view of the above-described circumstances, and has for its aim to provide a parking brake circuit for a hydraulically driven vehicle which can prevent the occurrence of an erroneous operation when the vehicle travels on a downward slope.
In order to achieve the above aim, according to one aspect of the present invention, there is provided a parking brake circuit for a hydraulically driven vehicle, comprising: a hydraulically driven motor; first and second main circuits connected to first and second ports, respectively, of the hydraulically driven motor so as to introduce hydaulic operating fluid from a supply source thereof into the motor; a parking brake actuator for rendering a parking brake operative/inoperative, the parking brake being so mounted as to brake a drive shaft of the hydraulically driven motor, the parking brake actuator being adapted to render the parking brake inoperative when hydraulic operating fluid is supplied into a pressure receiving chamber of the actuator and, on the other hand, to render the parking brake operative when the hydraulic operating fluid is discharged from the pressure receiving chamber thereof; a counterbalance valve provided between the first and the second main circuits so as to feed hydraulic operating fluid within either one of the first and the second main circuits which has become a high hydraulic pressure side; and a conduit provided so as to connect an outlet port of the

REFERENCES:
patent: 3743162 (1973-07-01), Gage
patent: 4057298 (1977-11-01), Seegers
patent: 4244276 (1981-01-01), Iwata
patent: 4478318 (1984-10-01), Hayden
patent: 4645271 (1987-02-01), Brearey et al.

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