Rotary expansible chamber devices – With mechanical sealing – Axially movable end wall or end wall portion
Patent
1998-12-24
2000-09-26
Vrablik, John J.
Rotary expansible chamber devices
With mechanical sealing
Axially movable end wall or end wall portion
418133, F04C 2344
Patent
active
061235326
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND TO THE INVENTION
The invention relates to a vane pump with movable vanes and more particularly to a pressure plate on the pump.
Vane pumps of the type addressed here are known. They are used, for example, to provide a fluid for a power steering system in a motor vehicle. They have a pump unit which comprises a cam ring and a rotor which is rotatably mounted in the latter. Said rotor is provided with slots which run radially with respect to the axis of rotation and in which vanes are mounted such that they can move in the radial direction. During the rotation of the rotor in the interior of the cam ring, spaces which become larger and smaller are formed by the vanes, so that at least one each of a suction region and a pressure region are produced. Provided on at least one side of the pump unit is a pressure plate, which forms a lateral boundary surface for the suction and pressure regions. When the pump is operating, the pressure plate is pressed against the pump unit, which sharply increases the wear. In order to counteract this, an appropriate clearance between the cam ring and rotor is provided when the pump is being assembled, as a result of which the volumetric efficiency is often not adequate.
U.S. Pat. No. 3,695,791 discloses a vane pump in which a domed pressure plate produced from a bimetal is used. The pressure plate is installed with such a bias that a predetermined spacing remains between the pressure plate and the rotor and such that the pressure plate is clamped flat between the housing and the rotor. The bimetal function of the sealing washer is intended to maintain this spacing during the operation of the pump. Should the pressure plate be bent under a pressure arising during the operation of the pump, then if the fluid to be delivered heats up, the bending is cancelled out, since the bimetal is correspondingly heated and counteracts the deflection caused by the pressure forces, in that the pressure plate snaps back. It has been shown that, in the case of the known pump, an adequate volumetric efficiency cannot be ensured in every case.
SUMMARY OF THE INVENTION
It is therefore the object of the invention to provide a vane pump which does not have this disadvantage.
In order to achieve this object, a vane pump which according to the invention is proposed. The pump is defined in that that surface of the pressure plate which faces the pump unit, that is that side of the pressure plate which faces the rotor, the vanes, the cam ring and the suction and pressure regions, is designed to be concave when there is no pressure in the pump. When the pressure plate is not under load, that is to say at low pressure (for example during straight-ahead travel, when no steering is being carried out), an adequate spacing in relation to the rotor and the vanes is provided, so that at low pressure the oil friction in the gap, and hence the mechanical losses, are low. If then, during the operation of the pump, a higher pressure acts on the pressure plate on the side facing away from the pump unit, said pressure plate will be bent, so that the gap between the vanes, the rotor and the pressure plate is reduced. This therefore results in a very high volumetric efficiency. In addition, the pressure plate rests flat on the lateral surface of the cam ring, so that under high pressure, pressing of the edges and a correspondingly high loading of the pressure plate and of the cam ring, said loading bringing about wear, are avoided.
Preference is given to an exemplary embodiment of the pump which is defined in that a pressure plate, which is correspondingly designed to be concave, is provided on each side of the rotor or of the pump unit, the concave side of the pressure plate facing the pump unit. In the case of a configuration of this type, optimal adaptation of the pressure plates to the operating pressure is possible on both sides. In the event of the pressure plates bending, caused when the pump is operating under high pressure, the gaps between vanes and the two plates are reduced to a minimum, so that
REFERENCES:
patent: 2544988 (1951-03-01), Gardiner et al.
patent: 3019737 (1962-02-01), Prasse
patent: 3096720 (1963-07-01), Younger
patent: 3695791 (1972-10-01), Brundage
patent: 3752609 (1973-08-01), Niemiec et al.
Lauth Hans-Jurgen
Nied-Menninger Thomas
Luk Fahrzeug--Hydraulik GmbH & Co. KG
Vrablik John J.
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