Imperforate bowl: centrifugal separators – Rotatable bowl – Driven by energy of material supplied
Reexamination Certificate
2002-02-06
2003-03-11
Cooley, Charles E. (Department: 1723)
Imperforate bowl: centrifugal separators
Rotatable bowl
Driven by energy of material supplied
C494S083000
Reexamination Certificate
active
06530872
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a free jet centrifuge which has a rotor mounted for rotation in a housing.
Such free jet centrifuges are known. Their construction can be seen, for example, in EP 728 042 B1. An oil centrifuge is disclosed therein, as it is usually employed in the automotive field. It is made of sheet metal and consists of a plurality of sheet metal shells
1
,
7
and
11
(see FIG.
1
), which are attached together by beading. Furthermore, a central tube
2
is provided into which bushings
3
and
4
are pressed, which together with bearings in the housing form a friction suspension. The friction bearing is lubricated by the oil being centrifuged. The centrifuge is driven through bores
8
which are placed in the bottom
7
of the centrifuge rotor.
The centrifuge rotor described is a component which is made by low-cost large series production. For economical considerations in production, however, tolerances occur in the centrifuge rotor which for various reasons limit the maximum achievable speed. The openings
8
, which can be made by drilling or punching, and which form the driving jets, are limited in their efficiency as drives by the imprecision of the openings. A certain friction occurs in the bushed bearings, which is produced mainly by the fact that the bearing bushes are not perfectly in line axially. Furthermore, a certain leakage occurs which leads to an uncentrifuged bypass of lubricant oil. Due to imbalances occurring in the centrifuge rotor the speed must be limited to some extent, since otherwise the stress on the bearings and the vibrations which the rotor applies to the housing increases excessively.
For an effective separation of the material being centrifuged, however, a high speed of the rotor combined with a low volume throughput of the fluid is necessary. Basically, the speed can be increased by providing larger openings
8
, but this would at the same time increase the volumetric throughput, so that in spite of higher rotor speed the particles to be removed have less time to settle on the separating surfaces. Another possibility for optimizing the centrifugation effects consists in providing rolling bearings instead of friction bearings, as is proposed, for example, in DE 10 12 776. This is intended to reduce the bearing friction on the centrifuge rotor, so that higher rotor speeds can be attained. In that case, however, the problem arises that, due to the high pressure difference between the rotor interior and its surroundings (housing interior) a leakage occurs which flows through the rolling bearings. If this leakage should flow unhampered through the gap formed between the inner and outer races of the rolling bearings, not only would the oil losses become excessive, but also the bearing friction would be increased to such an extent that the friction advantage in comparison to friction bearings would be lost. Therefore an additional sealing of this gap must be provided. Encapsulation of ball bearings, however, is not possible, since due to the high pressure difference between the two sides of the bearing would be pressed so greatly on the bearing races that greater friction would be created than in the case of friction bearings.
The rolling bearing proposed in DE 10 12 776 is therefore combined with a friction bearing. The friction bearing provides for a reduction of the leakage and can be designed as a clearance fit so that the leakage simultaneously oils the bearings. During the operation of the centrifuge, however, the interstice between the races of the rolling bearings nevertheless become full of oil, so that the friction losses again increase unnecessarily. Also, the friction losses are increased by the two clearances, so that the resistence to rotation of the centrifuge rotor can be reduced but very little in this manner. Moreover, the solution also constitutes a definite increase in the cost of the centrifuge because the fit of the friction bearings must be achieved and the cost of the rolling bearings used must be dealt with.
SUMMARY OF THE INVENTION
The aim of the invention is to provide a free jet centrifuge which can be produced cost-effectively and will provide optimal results in regard to separation.
This aim is achieved by the invention as described and claimed hereinafter.
ADVANTAGES OF THE INVENTION
The free jet centrifuge according to the invention has a rotor which is journaled in a housing. The housing serves the purpose of protecting the environment from the centrifuged fluid issuing through the drive nozzles. At the same time no special housing bell needs to be provided for the centrifuge rotor. It is also conceivable to include this bell in a housing designed for other components. For example, the crankcase of an internal combustion engine or an oil filter module is a possibility, in which the centrifuge rotor is used as a secondary filter in addition to a mainstream filter element.
One of the bearing locations of the centrifuge rotor is simultaneously configured as an inlet for the fluid being centrifuged. This bearing location, in cooperation with a friction bearing, simultaneously offers a sufficient sealing of the liquid being fed to the housing interior. The other bearing is formed according to the invention by a rolling bearing. A ball bearing is one possibility. It is practical to place both bearing means on the two opposite sides of the top cover surface and the bottom surface, so as to minimize the bearing forces involved.
The bearing socket on the cover surface for the rolling bearing is sealed from the interior of the rotor. This can be accomplished, for example, by making the cover surface of the rotor closed and forming the journal shaft in one piece. In any case the journal shaft must be configured such that the fluid being centrifuged is not able to pass from the rotor interior to the housing interior. This has the important advantage that the rolling bearing is not exposed to any leakage on the centrifuge rotor. In order to lubricate the rolling bearing, the oil mist produced by the driving nozzles of the centrifuge rotor is entirely sufficient and even provides optimal lubricating conditions. The friction of the rolling bearing is therefore extraordinarily low.
In addition, an encapsulated rolling bearing can be used. Thus it can be shielded against contaminants in the fluid being centrifuged and can be lubricated for life before being put into operation. Of course, the frictional sealing point of the encapsulation must not be subjected to the oil pressure prevailing in the interior of the centrifuge since this would cause excessive bearing friction resulting in seizure. A sealed journal shaft on the rotor, in the manner already described, is thus also necessary in this variant.
The journal shaft can consist, for example, of a closed stub shaft which protrudes from the cover surface and is inserted into the inner race of the rolling bearing. Also conceivable is a concentric pocket in the cover surface into which the rolling bearing is inserted with its outer race. The stub shaft transfers the radial forces acting on the centrifuge rotor. If an appropriate selection of the rolling bearing is made, e.g., a ball bearing, the latter can absorb the axial forces which are caused by the oil pressure on the friction bearing, among other things.
An alternative solution of the bearing problem in the centrifuges described above is that at least one friction bearing is provided, the latter comprising a bearing bush and a sleeve bearing. The bearing bush is fastened in the housing. This can be performed by pressing it in, but other possibilities are conceivable, such as cementing or a threaded coupling. The sleeve bearing is inserted into the bearing bush and contacts a bearing journal which is provided on the rotor. The bearing journal simultaneously constitutes the inlet into the rotor for the fluid to be centrifuged. The bearing journal can consist, for example, of a hollow stub shaft which is inserted into the sleeve bearing. Also conceivable is a hole-like socket in the rotor into
Fischer Helmut
Frehland Peter
Cooley Charles E.
Filterwerk Mann & Hummel GmbH
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