Expansible chamber devices – Rotating cylinder – Plural cylinders
Patent
1995-06-06
1997-04-22
Denion, Thomas E.
Expansible chamber devices
Rotating cylinder
Plural cylinders
92 71, 91499, 74 60, F01B 1304
Patent
active
056220979
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a hydraulic piston machine with a cylinder body, which comprises at least one cylinder with a piston movable therein, and a control counter-plate which engages the cylinder body by way of a contact surface and, on relative movement between the cylinder body and the control counter-plate parallel to the contact surface, connects the cylinder in dependence upon its position with inlet and outlet channels respectively, the control counter-plate and/or the cylinder body being provided, at least in the region of the contact surface, with a friction-reducing layer of plastics material.
In piston pumps, as known, for example from DE-AS 12 67 985, the cylinder body has to be pressed with a relatively strong pressure against the control counter-plate in order to keep the transition from the cylinders to the control counter-plate as well-sealed as possible. The larger are the unsealed areas in this region, the greater is the leakage, which has an adverse effect on the volumetric efficiency of the machine. Because of the high pressure, considerable frictional forces act on the contact surface and, without supplementary measures, lead relatively quickly to wear and tear or even to destruction of the machine. This phenomenon can be partially counteracted by lubricating the contact surface to reduce friction. The hydraulic fluid is used for that purpose. This presupposes, however, that the hydraulic fluid has satisfactory lubricating properties. This requirement considerably restricts the group of hydraulic fluids that can be used. Fluids which have satisfactory lubricating properties are in many cases harmful from the point of view of their impact on the environment, especially in so far as synthetic oils are concerned.
For that reason, in a machine of the kind mentioned in the introduction, which is intended for use for water, it is known (JP 2-125 979) to arrange between the control counter-plate and the cylinder body a plastics material layer which is adhesively secured to the roughened contact surface. A number of manufacturing steps are required for this, however. It is also not always possible to ensure that the plastics material layer is reliably fixed to the cylinder body or to the control counter-plate. In particular, there is a danger that hydraulic fluid under pressure will get between the plastics material layer and the control counter-plate or cylinder body and detach the layer at least partially. This leads very rapidly to serious damage to the machine.
From DE 16 53 529 B2 it is furthermore known to provide a control control counter-plate disc with inserts of carbon, which are in the form of linear strips, to reduce the friction between the cylinder body and the control counter-plate disc. Here, however, it is difficult to keep the control counter-plate and the end face of the cylinder body close enough to one another, so that considerable leakage can occur here.
The invention is therefore based on the problem of providing a hydraulic piston machine that is inexpensive to manufacture and which can be operated reliably even with hydraulic fluids that have few or no lubricating properties.
This problem is solved in a hydraulic piston machine of the kind mentioned in the introduction in that the friction-reducing layer is in the form of an injection-moulded part.
Injection moulding on the one hand enables relatively thin layers to be achieved which can, on the other hand, be fixed securely to the part carrying them. This simplifies manufacture quite considerably, especially when the layer is produced "in situ", that is, is injected directly onto the cylinder body or the control counter-plate. The function of "lubrication" is transferred to a machine element, namely to the friction-reducing layer, which forms a surface layer in the region of the contact surface. Combinations of materials are known which are able to slide on one another with relatively little friction even under relatively large pressures. Through suitable selection of the material for the layer, taking into account t
REFERENCES:
patent: 4014250 (1977-03-01), Bosch
patent: 4799419 (1989-01-01), Krause
patent: 4911614 (1990-03-01), Kawai et al.
Hansen Ove T.
Martensen Lars
Danfoss A/S
Denion Thomas E.
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