Counter balance valve

Fluid handling – Self-proportioning or correlating systems – Supply and exhaust type

Patent

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Details

91450, 137110, F15B 1302

Patent

active

06068013&

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a counter balance valve provided for a hydraulic circuit arrangement for driving a hydraulic motor used for a travelling apparatus of a construction machine.


BACKGROUND ART

As a hydraulic circuit arrangement for driving a hydraulic motor, there is known a circuit arrangement such as shown in FIG. 1.
In this circuit arrangement, a drain passage la of a hydraulic pump 1 is connected to first and second main circuits 3 and 4 through an operation valve 2, the first and second main circuits 3 and 4 are in turn connected respectively to first and second ports 6.sub.1 and 6.sub.2 of a hydraulic motor 5, and a supply of pressure oil to the first and second main circuits 3 and 4 is controlled by means of the operation valve 2. Furthermore, a counter balance valve 7 is disposed between the first and second main circuits 3 and 4. According to such arrangement, when the operation valve 2 takes its neutral position N, the first and second main circuits 3 and 4 are communicated with each other and the pressure oil flows out therefrom towards a tank 9, and accordingly, the counter balance valve 7 takes its neutral position N and check valves 8, 8 of the first and second main circuits 3 and 4 are closed to thereby block the hydraulic motor 5 side of the hydraulic circuit arrangement to prevent the hydraulic circuit arrangement to prevent the hydraulic motor 5 from being reversely rotated by an external force. On the other hand, when the operation valve 2 is shifted to a first position a or second position b, the pressure oil is supplied to the first or second main circuit 3 or 4, and the check valve 8 thereof is opened to thereby drive the hydraulic motor 5, and at the same time, the counter balance valve 7 is switched to a first position A or second position B by the pressure oil from the first main circuit 3 or second main circuit 4, and the hydraulic oil in the second main circuit 4 or first main circuit 3 is returned to the tank 9 through the counter balance valve 7 and the operation valve 2.
As mentioned above, the counter balance valve 7 provided for such hydraulic circuit arrangement for driving the hydraulic motor is switched in its position to the first position A or second position B by the pressure oil from the first main circuit 3 or second main circuit 4, and when all the pressure oil flows out from these main circuits 3 and 4, the counter balance valve 7 returns to its neutral position N.
Incidentally, when the supply of the pressure oil to the hydraulic motor 5 is stopped for stopping the operation thereof, the hydraulic motor 5 is rotated by the inertia of the travelling vehicle to attain a pumping function.
For this reason, at the time of stopping the hydraulic motor 5 by shifting the operation valve 2 to its neutral position N, when the counter balance valve 7 is shifted to its neutral position N and the check valve 8 is closed, the pressure oil in one of the first and second main circuits 3 and 4, disposed downstream of the check valve 8, exhibits a high pressure, thereby imparting a large shock at the time of stopping the operation of the hydraulic motor.
Such shock imparted at the time of stopping the operation of the hydraulic motor 5 can be reduced by delaying the shifting speed of the counter balance valve from the first or second position A or B to the neutral position N and throttling the flow of the pressure oil by the counter balance valve 7 so as to cause the pressure oil to gradually flow out the pressure oil to the tank 9. For example, as shown in FIG. 1, throttles 11, 11 are arranged in circuits 10, 10 connecting the counter balance valve 7 to the first and second main circuits 3 and 4, and the degree of throttling of these throttles 11, 11 is made small to thereby delay the returning speed of the counter balance valve 7 to the neutral position N from the first or second position.
However, in such arrangement, it will take considerable time for the counter balance valve 7 to return to its neutral position N, resulting in an occurrence of

REFERENCES:
patent: 2837106 (1958-06-01), Bauer
patent: 3980001 (1976-09-01), Cyphelly
patent: 4114516 (1978-09-01), Johnson
patent: 5113894 (1992-05-01), Yoshida

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