Brakes – Operators – Spring
Patent
1997-06-20
1999-12-28
Oberleitner, Robert L.
Brakes
Operators
Spring
477199, F16D 6524
Patent
active
060068728
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a braking apparatus for a hydraulic motor, which may be a hydraulic motor for turning, used in a hydraulic power shovel or the like.
BACKGROUND ART
A hydraulic motor has, in general, a shaft rotatably supported in a casing. The shaft in turn is coupled to a cylinder block which is rotatable therewith. The cylinder block is formed with a plurality of cylinder bores which are circumferentially spaced apart from one another and in parallel to the shaft. Each of the cylinder bores has a piston slidably inserted therein, thus defining a cylindrical chamber between the piston and an end of the cylinder bore. Also, the above mentioned shaft has a thrust ball coupled thereto, which in turn has a shoe inserted therein so as to be inclined with respect to the shaft by extending along a swash plate. The thrust ball and the shoe are designed to be rotatable with the shaft while being energized towards the above mentioned swash plate by a spring. Further, each of the above mentioned pistons has a front end connected with the shoe via a universal coupling thereto. If the pistons are reciprocated by supplying and draining a pressure fluid from a hydraulic pressure source into and out of a pressure receiving chamber of each cylinder bore the above mentioned swash plate and shoe will guide the pistons circumferentially causing the shaft and the cylinder block to rotate together.
Also, a braking apparatus for the above mentioned hydraulic motor has a plurality of movable side frictional plates and a plurality of fixed side frictional plates mounted to the cylinder block and housing, respectively, so that they are alternately mounted with respect to one another in a direction which is parallel to the above mentioned shaft. Opposite the frictional plates is provided a piston that is adapted to be pushed towards a first side of the frictional plates by a spring and to be pushed towards a second side opposite the first side by a pressure fluid in a piston driving pressure receiving chamber. Using the spring to push the piston causes pressure contact between the fixed side frictional plates and the moveable side frictional plates. As a result, the rotational speed of the cylinder is reduced and is eventually rendered incapable of being rotated. In contrast, supplying the piston driving pressure receiving chamber with a pressure fluid causes the piston to move against the spring. As a result, the fixed side frictional plates and the movable side frictional plates are moved apart from one another. Consequently, braking force is not applied to the cylinder block and thus it is capable of being rotated.
In such a braking apparatus for a hydraulic motor in which the non-braking state is established by supplying the piston driving pressure receiving chamber with the pressure fluid and in which braking force is established by draining the pressure fluid from the piston driving pressure receiving chamber, it can be seen that the time required to switch from the non-braking state to the braking state is determined by the distance and the velocity of movement of the piston (i.e., the time required to drain the pressure fluid from the piston driving pressure receiving chamber).
The time required to drain the pressure fluid from the above mentioned piston driving pressure receiving chamber is determined by a difference between a volume of the fluid in the chamber during the non-braking state and a volume of the fluid in the chamber during the braking state, that is, an effective volume in the piston driving pressure receiving chamber and a velocity of draining the pressure fluid out.
On the other hand, in the case of a hydraulic motor for turning an upper vehicle body in a hydraulic power shovel, it has been observed that after the hydraulic motor is stopped by returning an operating valve to a neutral position the hydraulic motor will continue to rotate a number of times due to an inertia of the upper vehicle body.
For this reason, if the braking apparatus is brought into a braking state
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Komatsu Ltd.
Lipka Pamela J.
Oberleitner Robert L.
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