Power plants – Pressure fluid source and motor – Condition responsive control of motive fluid flow
Patent
1997-12-03
1999-08-03
Nguyen, Hoang
Power plants
Pressure fluid source and motor
Condition responsive control of motive fluid flow
60493, 60494, F16D 3102
Patent
active
059309970
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hydraulic motor driving apparatus that is adapted to rotationally drive a hydraulic motor, especially but not limited to, a traveling purpose hydraulic motor for a hydraulically driven traveling vehicle in construction machines or the like, by supplying the hydraulic motor with a pressure discharge fluid from a hydraulic pump.
BACKGROUND ART
Where a hydraulic motor is used to drive a traveling body, i. e., a hydraulically driven traveling vehicle, such a traveling purpose hydraulic motor is supplied with a pressure fluid. There, one of the parts of the hydraulic motor is supplied with a discharge pressure fluid from a hydraulic pump where the other or one port thereof is in fluid communication with a tank, to cause the hydraulic motor to be rotationally driven in one rotary direction or the other and then to cause a driving hydraulic fluid to be fed to the vehicle to drive the latter.
By the way, where a hydraulically driven traveling vehicle is traveling downhill, it can happen that the vehicle body may be driven to travel by the weight of the traveling vehicle itself to cause the hydraulic motor to be driven reversely by the vehicle body. Such a situation in which the feed of the driving hydraulic fluid is reversed, if continued, is highly dangerous since the hydraulically driven vehicle will then be moved downhill in an accelerated fashion.
Accordingly, there has been proposed, as disclosed, e. g., in Japanese Unexamined Utility Model Publication No. Hei 4-133003 and Japanese Unexamined Patent Publication No. Hei No. 4-50507, a braking valve called a counterbalance valve which can be switched so that the hydraulic motor may not be rotationally driven when it is reversely driven by an external force such as the weight of the vehicle body itself.
This can be illustrated with reference to FIG. 1 of the drawings attached hereto, which shows a drive circuit for a hydraulic motor, as disclosed in these publications. The drive circuit comprises a hydraulic pump 1, a first and a second main circuit 3 and 4 which are connected to the hydraulic pump 1, and a directional control valve 2 disposed between the hydraulic pump 1 and the first and second main circuits 3, 4 for supplying a discharge pressure fluid from the hydraulic pump 1 to the first and second main circuits 3 and 4 which are connected via a first and a second check valve 5 and 6 to a first and a second port 8 and 9 of a hydraulic motor 7, respectively. The drive circuit for the latter is further provided between the first and second main circuits 3 and 4 with a braking valve 11 that is designed to selectively connect and block a return circuit 12 through which a return fluid from the hydraulic motor 7 is passed to communicate with a tank 10.
And, with the directional control valve 2 at its first position a, if the first main circuit 3 is supplied with the pressure fluid from the hydraulic pump 1, the pressure built up therein (i. e., the driving pressure for the hydraulic motor 7) will cause the braking valve 11 to take its first position b to allow the second port 9 of the hydraulic motor 7 to communicate via the return circuit 12, the braking valve 11 and the directional control valve 2 with the tank 10. A return fluid will thereby be allowed to flow out of the hydraulic motor 7 into the tank 10. Thus, the hydraulic motor 7 is permitted to be rotationally driven in a given direction (as shown by the arrow c) to drive the traveling body.
In the state described above, while the vehicle is traveling downhill, if the hydraulic motor 7 tends to be reversely driven by the vehicle body to rotate in the direction of the arrow c in a runaway manner, it will be caused to undergo a pumping action whereby its first port 8 side has a reduced pressure and its second port 9 side has an elevated pressure. As a result, the first main circuit 3 will be reduced in pressure to cause the braking valve 11 to assume its neutral position e by a pair of springs 13. This will cause the return circuit 12 to be blocked and
REFERENCES:
patent: 4694647 (1987-09-01), Yoshida
patent: 5058383 (1991-10-01), Tsunemi et al.
patent: 5062266 (1991-11-01), Yoshimatsu
patent: 5421156 (1995-06-01), Beater et al.
patent: 5709083 (1998-01-01), Sorbel et al.
Akasaka Tosiyuki
Hayashi Seita
Nunotani Sadao
Komatsu Ltd.
Nguyen Hoang
LandOfFree
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