Power plants – Pressure fluid source and motor – Servo-motor having externally operated control valve sets...
Patent
1991-12-04
1994-04-05
Look, Edward K.
Power plants
Pressure fluid source and motor
Servo-motor having externally operated control valve sets...
60465, 60494, F16D 3102
Patent
active
052994210
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for controlling a variable capacity motor incorporated in an industrial vehicle provided with shovel loader etc., and particularly to the device which is effectively incorporated in an infinite variable-speed hydraulic drive vehicle in which the maximum traveling speed of the vehicle should be controlled in response to a working condition.
BACKGROUND TECHNOLOGY
Illustrated in FIG. 12 is a conventional hydraulic circuit of an infinite variable-speed hydraulic drive vehicle which has a variable capacity hydraulic pump 1 and a motor 2. In the same figure, a part of the output of an engine 5 drives a working machine hydraulic pump 4 and acts upon a working machine hydraulic cylinder 52 by way of a working machine hydraulic circuit 51. Remaining output of the engine 5 drives the control pump 3 and a hydraulic pump 1 in which oil pressure is generated. The oil pressure thus generated at the hydraulic pump 1 flows through main circuits 24 and 25, rotates the variable capacity motor 2, thereby forming a driving force.
Designated at 6 is a pump control valve for controlling the capacity of the hydraulic pump 1, 7 is a pump capacity control cylinder, 8, 8 are main relief valves and 10 is a filter. Oil under pressure, which flows from the pump control valve 6 to the motor control oil line 11, is introduced into one end of the motor control valve 14, whereby the oil introduced into the motor control valve 14 operates to introduce the oil under high pressure, which is introduced by a pilot hydraulic piping 16 from the main circuits 24 and 25, into a motor capacity control cylinder 31.
That is, the pump capacity control cylinder 7 and the motor capacity control cylinder 31 are controlled by the pump control valve 6 and the motor control valve 14 so that the capacity of the pump 1 and the capacity of the hydraulic motor 2 are arbitrarily varied, thereby varying the traveling speed of the vehicle.
A graph representing a traveling performance curve of the conventional hydraulic drive vehicle, as explained in FIG. 12, will be described with reference to FIG. 13. As illustrated in the same figure, in the infinite variable-speed hydraulic drive vehicle having the conventional variable capacity hydraulic motor, both the traveling driving force and the traveling speed are continuously varied so that they are automatically and continuously varied without changing operation from the maximum driving force (traveling speed is 0) to the maximum speed. Accordingly, since the driver can control the traveling speed and the driving force, it is possible to travel the vehicle easier than a vehicle provided with a mechanical speed change gear.
The conventional hydraulic drive vehicle has an advantage that the traveling operation is easy. However, in the industrial vehicle provided with a loading apparatus such as a shovel loader, the working machine pump 4 of the loader is also driven by the engine in the same way as the hydraulic drive pump 1. Since the maximum rising speed of the loader is proportional to the engine speed, the rising speed of the loader is also controlled by the travel of the accelerator pedal in the same way as the traveling speed. Accordingly, in case that the hydraulic drive vehicle travels while raising the loader at the working site, the working efficiency is improved, when the loader rises at the maximum speed and the vehicle travels at low speed. However, there was such a serious problem that when the loader rises at the maximum speed, the traveling speed at the same time increases at the maximum. This problem will be described with reference to FIG. 14 which depend on the engine speed of the engine 5. Pst1", . . . Pst5" represent pressures of pilot hydraulic piping 15. The relation between the capacity of the motor (horizontal axis) and the pressure P.sub.H" (vertical axis) in the main hydraulic circuits 24 and 25 is varied by the pilot pressures Pst1" . . . Pst5". In case that the traveling speed is accelerated at full throttle so as to rise the load
REFERENCES:
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patent: 3986358 (1976-10-01), Hoffmann
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patent: 4546847 (1985-10-01), Abels
patent: 4554991 (1985-11-01), Eden
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patent: 5018351 (1991-05-01), Otte
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English translation of claim for Japanese Patent Publication No 62-13543 dated Mar. 27, 1987 (1 page).
Kabushiki Kaisha Komatsu Seisakusho
Komatsu Mec Kabushiki Kaisha
Look Edward K.
Nguyen Hoang
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