Power plants – Pressure fluid source and motor – Condition responsive control of pump or motor displacement
Patent
1997-11-17
1999-06-01
Nguyen, Hoang
Power plants
Pressure fluid source and motor
Condition responsive control of pump or motor displacement
60445, F16D 3102
Patent
active
059079525
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for controlling the capacity of a hydraulic motor in a hydraulically driven motor vehicle in which the hydraulic motor of a variable capacity type is rotated by a discharge pressure fluid from a hydraulic pump for driving a traveling body that constitutes the motor vehicle allowed to travel with the hydraulic motor.
BACKGROUND ART
There has hitherto been known a hydraulically driven motor vehicle in which a hydraulic pump is driven by an engine and a hydraulic motor is rotated by a discharge pressure fluid from the hydraulic pump for driving a traveling body that constitutes the motor vehicle caused to travel with the hydraulic motor. In order to allow such a hydraulically driven motor vehicle to be accelerated and decelerated, the hydraulic motor has commonly been designed to be of a variable capacity type in which for the purpose of the vehicle acceleration the hydraulic motor is accelerated by increasing the capacity thereof and for the purpose of the vehicle deceleration the hydraulic motor is decelerated by reducing the capacity thereof.
As disclosed, for example, in Japanese Unexamined Patent Publication No. Sho 62-255658, it has been known that the capacity of a hydraulic pump can be gradually reduced by permitting an operating member for increasing and decreasing the capacity thereof to be operated in a direction in which the capacity is reduced and the capacity of the hydraulic pump can be swiftly increased by permitting the operating member to be operated in a direction in which the capacity is increased, thereby effecting a gradual deceleration of a motor vehicle while enhancing an ability thereof to swiftly accelerate itself.
It has also been known that a hydraulically driven motor vehicle having a hydraulic motor of variable capacity type can be provided with a servo cylinder assembly and a servo valve which are designed to control the capacity thereof in accordance with the pump pressure of a hydraulic pump and the rotation speed of an engine, in which the capacity of the hydraulic motor is reduced when the rotation speed of the engine is increased (when the vehicle is to be accelerated) to increase the rotation rate of the hydraulic motor and the capacity of the hydraulic motor is increased when the rotation rate of the engine is reduced (when the vehicle is to be decelerated) to reduce the rate of rotation of the hydraulic motor.
And, where it is desirable to change the capacity of the hydraulic motor in such a manner, it has been found that as in the case in which the capacity of the hydraulic pump is varied as described previously, not only is the ability to accelerate enhanced but also it is possible to decelerate gradually, by rapidly reducing the capacity of the hydraulic motor when the rotation speed of the engine has been increased whereas by gradually increasing the capacity of the hydraulic motor when the rotation speed of the engine has been reduced.
It has been found, however, that whereas the former system noted previously as disclosed in the Japanese Unexamined Patent Publication Sho No. 62-255658 in which the capacity of the hydraulic pump is controlled without regard to the pump pressure and the engine rotational speed makes it possible to control how to change the capacity variably as regards the directions in which it is increased and reduced, the latter system as described above in which a combination of the servo cylinder assembly and the servo valve is employed to control the capacity in accordance with the pump pressure and the engine rotational speed is not able, as it is, to control how to change the capacity variably with respect to the directions in which it is increased and decreased as in the former system.
For this reason, a measure has typically been taken in the prior art, in which a circuit for interconnecting the servo valve and the servo cylinder chambers is provided with a slow return valve whereby the speed of the servo piston at which it is displaced in a direction in which the capacity is
REFERENCES:
patent: 5070695 (1991-12-01), Metzner
patent: 5184466 (1993-02-01), Schniederjan et al.
patent: 5653107 (1997-08-01), Beck
Akasaka Tosiyuki
Hayashi Seita
Nunotani Sadao
Kananen Ronald P.
Komatsu Ltd.
Nguyen Hoang
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