Expansible chamber devices – Displacement control of plural cylinders arranged in... – Parallel cylinders
Patent
1996-12-26
1998-04-14
Nguyen, Hoang
Expansible chamber devices
Displacement control of plural cylinders arranged in...
Parallel cylinders
92 57, 92 71, 417269, F01B 300
Patent
active
057379963
DESCRIPTION:
BRIEF SUMMARY
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, and having a control plate, which on rotation of the cylinder drum and control plate relative to one another connects the cylinder, in dependence on its position, to a fluid inlet and a fluid outlet, a pressure plate being arranged between the cylinder drum and the control plate and having for each cylinder a fluid path between the control plate and the cylinder drum.
The control counter-plate normally has arcuate or kidney-shaped control slots, one of which is connected to the fluid inlet whilst the other is connected to the fluid outlet. The control plate is oriented such that the inlet is located in a region in which the piston moves away from the control plate, whilst the outlet is located in a region in which the piston moves towards the control plate.
The connection between the control plate and the cylinders should be as fluid-tight as possible, at least on the pressure side. Escaping fluid reduces the volumetric efficiency. This tight seal is achieved in that the pressure plate is pressed as firmly as possible against the control plate (U.S. Pat. No. 4,481,867). The connection between the cylinders; and the pressure plate can be effected by bushings or sleeves, which are inserted in the cylinder and bear against the pressure plate or are constructed in one piece therewith.
Movement of the piston in the cylinder creates friction. This friction is not serious provided that a fluid which has lubricating properties is used as hydraulic fluid. Most hydraulic oils, in particular synthetic hydraulic oils, are designed and are suitable for this purpose. On the grounds of environmental pollution, however, such synthetic hydraulic oils, which are often relatively toxic, are being used with increasing reservation. In order for there to be greater freedom in the choice of hydraulic fluids, that is, in order to be able also to use those fluids which have only slight or even no lubricating properties, such as water, for example, the prior German patent application P 43 01 126 proposed the use of bushings made of a plastics material which co-operates with little friction with the material of the piston. Such bushings, however, can be reliably secured in the cylinder drum only with relatively great difficulty. Often, they are loaded not only by the frictional forces of the piston, but also by the changing pressures of the hydraulic fluid within the cylinder enclosed by the bushing.
The invention is based on the problem of being able to operate a hydraulic axial piston machine of the kind mentioned in the introduction even with hydraulic fluids which have slight or even no lubricating properties, for example, with water.
This problem is solved in a hydraulic axial piston machine of the kind mentioned in the introduction in that the cylinder is lined with a bushing of a friction-reducing plastics material which projects from the cylinder drum and is inserted in the pressure plate.
This construction provides several advantages. Firstly, the piston now slides with little friction in the cylinder. This is caused by the bushing's being formed from a plastics material which co-operates with little friction with the piston, which generally consists of a metal, for example, steel. Examples of plastics materials which may be considered for the bushing or for the bushing layer are, in particular, materials from the group of high-strength thermoplastic plastics materials on the basis of polyaryl ether ketones, in particular polyether ether ketones, polyamides, polyacetals, polyaryl ethers, polyethylene terephthalates, polyphenylene sulphides, polysulphones, polyether sulphones, polyether imides, polyamide imide, polyacrylates, phenol resins, such as novolak resins, or similar substances, and as fillers, use can be made of glass, graphite, polytetrafluoroethylene or carbon, in particular in fibre form. When using such materials, it is possible to use even water
REFERENCES:
patent: 2451379 (1948-10-01), Burke
patent: 3169488 (1965-02-01), Galliger
patent: 4620475 (1986-11-01), Watts
patent: 5588347 (1996-12-01), Jepsen
patent: 5678471 (1997-10-01), Ash, Jr. et al.
patent: 5685215 (1997-11-01), Jepsen et al.
Danfoss AS
Nguyen Hoang
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