Expansible chamber devices – Displacement control of plural cylinders arranged in... – Parallel cylinders
Patent
1996-12-26
1998-07-14
Nguyen, Hoang
Expansible chamber devices
Displacement control of plural cylinders arranged in...
Parallel cylinders
92 57, 92 71, 417269, F01B 300
Patent
active
057787573
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic axial piston machine having a cylinder drum, which has at least one cylinder in which a piston is arranged to move back and forth, which piston bears by way of a slide shoe against a swash plate, wherein the cylinder drum and the swash plate are rotatable relative to one another, and a pressure plate, which holds the slide shoe in contact with the swash plate, is joined, articulated, to the cylinder drum by way of a ball-and-socket joint having a convexly spherical bearing surface.
In machines of that kind, on rotation of the cylinder body with respect to the swash plate or on rotation of the swash plate with respect to the cylinder body, the piston moves axially. During the pressure stroke, that is, on shortening of the cylinder moved by the piston, the swash plate exerts a pressure on the slide shoe. During the suction stroke on the other hand, the pressure plate has to hold the slide shoe in contact with the swash plate. Corresponding to the axial back and forth movements of the piston, the pressure plate has to tilt back and forth, the tilting angle range extending, for example, from about -15.degree. to about +15.degree.. On each rotation, the pressure plate has to pass through the entire tilting angle range once in the positive direction and once in the negative direction.
A machine of the kind mentioned in the introduction is shown, for example, in DE 39 01 064 A1.
Since the articulated connection between the cylinder body and the pressure plate has to absorb considerable forces, considerable friction occurs here. So that the losses caused by the friction and the wear and tear are not allowed to become too great, it is known to lubricate this articulated connection. For that purpose the oil already present, which serves as hydraulic fluid, is usually used. But this leads to the disadvantage that one is restricted in one's choice of hydraulic fluids to hydraulic oils. Even here, choice is not without restriction since not all oils have the same good lubricating properties. In the past there has therefore been an increasing change-over to the use of synthetic oils, but these are being regarded with increasing criticism from the point of view of their compatibility with the environment.
In order also to be able to use a hydraulic fluid having relatively poor or no lubricating properties, such as water, for example, the prior German patent application P 43 01 121 describes a machine in which an insert of a friction-reducing plastics material is inserted in the pressure plate and is supported radially and axially by the pressure plate. This insert lies against a counterpart, which in turn bears against the cylinder drum. Although this arrangement has proved successful when operated with water as the hydraulic fluid, it requires relatively complicated machining of the pressure plate. The contact surfaces for the insert piece have to be created.
SUMMARY OF THE INVENTION
The invention is based on the problem of simplifying the manufacture of a hydraulic axial piston machine which is intended to be suitable for non-lubricating hydraulic fluids.
This problem is solved in a machine of the kind mentioned in the introduction in that the convexly spherical bearing surface is formed from a friction-reducing plastics material.
Although, here, a pairing of materials between a friction-reducing plastics material and a harder material, of which the pressure plate must consist, for example, iron or steel, still obtains, the low friction that is a condition here for operation with a liquid having no lubricating properties is achieved in this case by the design of the spherically convex bearing surface. It is there that the plastics material that effects the reduction in friction is found. The pressure plate now no longer needs to be machined, that is, no additional contact surfaces have to be produced. On the contrary, the pressure plate can be constructed in the manner known from the state of the art. Moreover, the advantage is gained that machining o
REFERENCES:
patent: 5017095 (1991-05-01), Burgess et al.
patent: 5588347 (1996-12-01), Jepsen
patent: 5622097 (1997-04-01), Martensen et al.
patent: 5660097 (1997-08-01), Nomura et al.
Kristensen Egon
Mamsen Kurt
Danfoss A/S
Nguyen Hoang
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