Expansible chamber devices – Rotating cylinder – Plural cylinders
Patent
1996-12-23
1999-04-06
Thorpe, Timothy
Expansible chamber devices
Rotating cylinder
Plural cylinders
417269, 91499, 91486, 92 71, 921701, 74 60, F04B 120
Patent
active
058904123
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a control plate of a hydraulic machine, having a core, which at least on its upper side lying in operation against a cylinder drum is covered with a layer of a friction-reducing plastics material and which has at least two control openings.
The control openings are generally in the form of control "kidneys", which are optionally divided into different sections separate from one another.
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 plate in order to keep the transition from the cylinders to the control 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 A) to arrange between the control 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 plate. In particular, there is a danger that hydraulic fluid under pressure will get between the plastics material layer and the control 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 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 plate disc. Here, however, it is difficult to keep the control plate and the end face of the cylinder body close enough to one another, so that considerable leakage can occur here.
Furthermore, the non-prior-published German patent application 43 01 133 discloses a hydraulic piston machine having a control plate which is provided with a plastics material layer. The plastics material layer is produced by an injection-moulding process. In one embodiment it sheathes the core of the control plate completely, that is, it is also taken right through the control kidneys. A lateral movement of the plastics material layer in relation to the core can largely be prevented by that measure.
It has now been discovered, however, that with control plates of this kind a certain problem arises when air becomes trapped between the core and plastics material as the plastics material layer is being applied to the core, or when the plastics material does not lie completely tightly against the core for other reasons. The core provided with the plastics material is in fact normally machined after application of the plastics material, in which case it is often only the plastics material layer, or more accurately, the surface thereof, that requires machining. The surface machining can be effected, for example, by milling. At the locations where the plastics material is separated from the core by air or other inclusions, the core not only no longer lies against the plastics material, it also no longer adheres to the plastics material there. In injection-moulding there is normally a kind
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Hansen Ove Thorb.o slashed.l
Martensen Lars
Danfoss A/S
Gartenberg Ehud
Thorpe Timothy
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