Rotary expansible chamber devices – Moving cylinder – Rotating
Reexamination Certificate
2000-03-13
2001-08-14
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Moving cylinder
Rotating
C418S112000, C418S113000
Reexamination Certificate
active
06273695
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sickleless internal gear wheel pump for the generating of high pressure according to the generic term of patent claim
1
.
A pump of this category is known from DE 41 04 397 Al.
Internal gear wheel pumps have in general an internally geared hollow wheel with which and externally geared pinion with lower number of teeth meshes, i.e. stands in engagement in driving. Each tooth tip of the hollow wheel has a profile groove. Into this groove a sealing element is inserted. In turning of the pinion this sealing element comes into sliding contact with its tooth tips. In the process there is briefly established a sealing-off, which blocks off the suction space against the pressure space. For the achieving of a certain contact pressure the radial outer ends of the sealing elements are acted upon with springs.
The sealing elements consist, as a rule, of plastic. There it was hitherto assumed that a certain elasticity is necessary in respect to the sealing-off.
In practical operation it has proved that, especially at relatively high operating pressures, there occur manifestations that were hitherto inexplicable. To these there belongs above all a decline of the efficiency of the pump. But also pressure pulsations have set in, which are extremely undesired.
Underlying the invention is the problem of constructing an internal gear wheel pump in such manner that neither a decline of the efficiency nor pressure pulsations manifest themselves.
SUMMARY OF THE INVENTION
The apices of the tooth tips of the pinion lie on different radii. This is conditioned by manufacturing tolerances. This means, for example, that the apex point of the one tooth tip lies on a greater radius than the apex point of the tooth tip of an adjoining tooth. For the sealing elements this means that also their sealing surfaces in the turning of the pinion lie from tooth to tooth on different radii. In a certain sense the sealing elements hereby carry out a dancing movement in radial direction. This leads to a relative movement of the individual sealing elements on the inner surface of the profile groove which is worked into the tooth tip of the hollow wheel.
A further circumstance is involved here: As stated above, the individual sealing element presents a blockade between the suction space and the pressure space. This means that on the sealing element a pressure differential acts, with pressure direction from the suction space to the pressure space. This means further, that the side surface of the sealing element facing the suction space is pressed against the corresponding inside surface of the profile groove. The micro-movement in radial direction mentioned leads, in respect to the pressure differential mentioned, to a grinding process. This results in a wear on the surfaces involved. The sealing is acted on in an extremely undesired manner on the sealing element's one surface. The wearing-down can be so severe that it leads to a tilting of the sealing elements and therewith to disturbances of the tooth engagement. For this reason it was also not possible to ascertain it as a cause for the above-mentioned harmful effects (loss of efficiency, pressure pulsations).
A further inventive insight lies in that, instead of the plastic, metals are altogether well suited for the sealing elements. Steel has proved itself very well, for example ordinary carbon steel, but also wear-proof special steels.
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Arbogast Franz
Peiz Peter
Baker & Daniels
Denion Thomas
Trieu Theresa
Voith Turbo GmbH & Co. KG
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