Expansible chamber devices – Rotating cylinder – Plural cylinders
Patent
1995-06-27
1998-08-18
Denion, Thomas E.
Expansible chamber devices
Rotating cylinder
Plural cylinders
92 71, 92248, 417269, 74 60, F01B 1304
Patent
active
057945136
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a pressure-applying arrangement in a hydraulic axial piston machine, having a pressure plate and a piston that is axially displaceable in a cylinder body, is biased by a force acting in an axial direction with respect to the cylinder body, and acts against the pressure plate.
By means of the pressure plate, slider shoes of work pistons are held in engagement with a slanting plate, which is inclined in known manner with respect to the axis of the cylinder body, so that on rotation of the cylinder body the work piston is moved back and forth. Whereas the slider shoes have no problem engaging the slanting plate during the inward movement of the piston into the cylinder body, during the outward movement of the work piston they have to be held by the pressure plate. The pressure plate therefore always has to remain parallel to the slanting plate, so that as the cylinder body rotates, the pressure plate performs a continuous tilting movement with respect to the cylinder body.
To allow this tilting movement, U.S. Pat. No. 2,733,666 provides a ball between the pressure plate and the piston. The piston is here biased by a spring. Opening into the contact surfaces between the ball and the piston and between the ball and the pressure plate there are channels through which hydraulic fluid is able to penetrate to the contact surfaces in order to reduce by lubrication the friction between the ball and piston and between the ball and the pressure plate. Without such lubrication, friction is relatively high so that this ball-and-socket joint would wear very quickly. In an extreme case, it could even seize up, leading to destruction of a part of the machine.
A hydraulic fluid that has a lubricating action is therefore an essential requirement here. This lubricating action is without exception a property of the hydraulic oils previously used as hydraulic fluids. Such oils are, however, in some cases toxic. From the point of view of their effect on the environment they are being used with increasing reluctance.
SUMMARY OF THE INVENTION
The problem on which the invention is based is to be able to use a pressure-applying arrangement even when hydraulic fluids having little lubricating action or even no lubricating action are to be used, for example, water.
This problem is solved in a pressure-applying device of the kind mentioned in the introduction in that the piston is formed from a high-strength thermoplastic plastics material.
When using such a plastics material, the ball and the pressure plate can continue to be made of metal, as they were previously. Since, however, metal is no longer rubbing on metal but on plastics material, lubrication can largely be eliminated. In most cases, lubrication is not required at all. For the rest, a film of fluid, such as that provided by water, for example, will be sufficient for lubrication.
The plastics material is preferably selected from the group of polyaryl ether ketones, especially polyether ether ketones, polyamides or polyamide imides. Such plastics materials are particularly low-friction in combination with metals, so that when they are used, further lubrication by means of oils or similar substances can be omitted without problems.
The plastics material is preferably reinforced by glass, graphite, polytetrafluoroethylene or carbon in fibre form. This measure enables the piston to be stressed by higher forces. Wear is reduced.
In a preferred construction, a ball is arranged between the piston and the pressure plate. This is admittedly already known per se from U.S. Pat. No. 2,733,666. In combination with the plastics piston, however its use is even better, and also requires no lubrication.
Advantageously the piston has a diameter which is at least 30% larger than the diameter of the ball. Because the plastics material, even when it is high-strength plastics material, does not normally attain the same mechanical strength as a part made of steel or another metal, this sizing ensures that the piston is nevertheless able to tr
REFERENCES:
patent: 3187644 (1965-06-01), Ricketts
patent: 3208395 (1965-09-01), Budzich
patent: 4762468 (1988-08-01), Ikeda et al.
patent: 4800801 (1989-01-01), van Zweeden
patent: 5022313 (1991-06-01), Shontz et al.
Encyclopedia of Plastics pp. 33-34 dated Dec. 1989.
Danfoss A/S
Denion Thomas E.
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