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Eccentric radial piston pump and eccentric radial piston motor

Eccentric radial piston pump and eccentric radial piston motor description/claims

The present invention relates to an eccentric radial piston pump and an eccentric radial piston motor.

In an eccentric radial piston pump or an eccentric radial piston motor, the center of an eccentric cam ring and the rotation center of the casing in a radial piston pump or an eccentric radial piston motor are made eccentric, and by changing this eccentric amount, the stroke amount of the piston in a cylinder block is changed. By changing the stroke amount of the piston, displacement volume of pressure oil by the piston is changed so that the volume of the eccentric radial piston pump or the eccentric radial piston motor can be variably controlled.

An eccentric radial piston pump having a structure as disclosed in Patent Document 1 has been employed conventionally. In the eccentric radial piston pump disclosed in Patent Document 1, the arrangement relationship of a control piston for driving an eccentric cam ring and a servo control valve is specified, so that the occupancy space in the radial direction is attempted to be reduced.

A cross-sectional shape of the eccentric radial piston pump described in Patent Document 1 is shown in FIG. 13 as a prior art example in the present invention. Respective pistons 41 are disposed in respective cylinder bores of a cylinder block 40. Respective connecting rods 42 having respective piston shoes 42a are rotatably coupled with the respective pistons 41. The piston shoe 42a slides along the inner peripheral surface of an eccentric cam ring 43 disposed in the outer periphery side of the cylinder block 40.

A pintle 44 having an intake port and a discharge port is disposed at the center of the cylinder block 40, and the center of the pintle 44 and the center of the eccentric cam ring 43 can be disposed such that they are eccentric. The eccentric cam ring 43 can eccentrically move while maintaining a parallel condition with respect to the center axis line of the cylinder block 40.

The eccentric amount of the eccentric cam ring 43 is controlled by control pistons 46, 47. The respective ends of the control pistons 46, 47 make contact with the eccentric cam ring 43 and press the eccentric cam ring 43 from the both sides by the urging force of springs 48, 49. The eccentric cam ring 43 can be eccentric with respect to the center axis of the pintle 44 by pressure oil that acts on the control piston 46.

Pressure oil supplied to the control piston 46 is controlled by a servo control valve 50 disposed to be tilted in a circumferential direction of a casing 45.

In the eccentric radial piston pump or the eccentric radial piston motor, the eccentric amount of the center of the eccentric cam ring and the rotation center of the casing in the radial piston pump or the eccentric radial piston motor is controlled by the movement amount of the eccentric cam ring. Thrust force generated by the piston is supported by the inner peripheral surface of the eccentric cam ring. Thus, the entire thrust force from the piston is supported in such a way that a concentrated load is supported on the lower surface of the eccentric cam ring.

Accordingly, when rigidity of the eccentric cam ring is small, and for example, when the thickness of the eccentric cam ring is thin, the eccentric cam ring is deformed to be a triangular shape by a thrust force from the piston. That is, as shown in FIG. 14, the eccentric cam ring which is circular in an unloaded condition receives a thrust force (indicated by arrows in FIG. 15) from the pistons whose cylinder bores' insides are at high pressure, so that the eccentric cam ring receives a deformation stress from the inside thereof to be deformed. Thus, the eccentric cam ring, while being circular in an unloaded condition as shown in FIG. 14, is deformed to be a triangular shape by receiving the deforming stress as shown in FIG. 15.

In the case where deformation occurs in the eccentric cam ring, the cylindrical surface of the piston shoe sliding along the inner peripheral surface of the eccentric cam ring is not in complete contact with the inner peripheral surface of the deformed eccentric cam ring along their whole surfaces, so that a gap is generated. Due to this gap, the contact of the piston shoe against the inner peripheral surface of the eccentric cam ring becomes nonuniform.

For example, while the piston shoe is sliding along the inner peripheral surface of the eccentric cam ring, when it reaches a place where the outer diameter on the cylindrical surface of the piston shoe is larger than the inner diameter of the eccentric cam ring, only both end edge sides in the circumferential direction of the piston shoe slide on the inner diameter of the eccentric cam ring, so that a large surface pressure is applied to the both end edge sides. By the large surface pressure applied to the both end edge sides in the circumferential direction of the piston shoe, bending stress is generated in the piston shoe. Further, when it reaches a place where the outer diameter on the cylindrical surface of the piston shoe is smaller than the inner diameter of the eccentric cam ring, the contact of the piston shoe becomes less, so that it is likely to float.

With respect to Patent Document 1, as shown in FIG. 13, in the conventional eccentric radial piston pump or the eccentric radial piston motor, the thickness of the eccentric cam ring is configured to be thick in order to prevent the eccentric cam ring from being deformed.

However, in the case where the thickness of the eccentric cam ring is configured to be thick, a problem arises in that the outside dimension in the radial direction in the eccentric radial piston pump or the eccentric radial piston motor becomes large. Specifically, in the eccentric radial piston pump or the eccentric radial piston motor, while the outside dimension in the radial direction is required to be constructed as small as possible, making the outside dimension in the radial direction large runs counter to the requirement.

An object of the present invention is to solve the problems in the prior art and to provide an eccentric radial piston pump and an eccentric radial piston motor by which the rigidity of an eccentric cam ring can be increased even when the thickness of the eccentric cam ring is not configured to be thick, and the outside dimension in the radial direction can be configured to be small.

Objects of the present invention can be achieved by respective inventions described in claims 1 to 10.

That is, in the first present invention, an eccentric radial piston pump in which a displacement volume of pressure oil is changed in accordance with an eccentric amount of an eccentric cam ring is most mainly characterized in that a rib protruded in a radial direction is provided on an inner peripheral surface of an end portion on a discharge side of the eccentric cam ring over a prescribed range.

In the second present invention, the shape of the rib is defined, and that is the main characteristic.

• Provisional Patent
• Utility Patent

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