Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-02-26
2001-01-23
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S099000
Reexamination Certificate
active
06177742
ABSTRACT:
PRIOR ART
The invention relates to an electric drive unit useful for a windshield wiper. An electric drive unit is already known (German Patent Disclosure DE 44 19 769 A1) in which a worm wheel is supported on a power takeoff shaft. To set an axial spacing between an armature shaft of the drive motor, the power takeoff shaft is supported in an eccentric bush. The eccentric bush is relatively long, is embodied without graduations, and is retained in the housing in a relatively long, ungraduated cylindrical bore by a press fit. The housing having the bore is typically made by metal casting. Embodying the relatively long bore in the housing, which must be made to precise tolerances so that the eccentric bush can be received in it with a press fit, requires intensive post-machining after the casting operation; but in mass production, this is very expensive.
Further drive units are known for instance from German Patent Disclosures DE 32 20 191 A1, DE 32 35 622 A1, and DE 41 16 100 A1 and from German Patent DE 39 30 144 C2.
Because of the worm gears used, both low rotary speeds of the windshield wiper and at the same time high torques are attainable. To meet the demands made of such drive units for motor vehicle windshield wipers in terms of noise, the gear meshing (torsional flank clearance) must remain constant regardless of production variations. To eliminate or at least minimize production variations, the axial spacing of the power takeoff shaft and the armature shaft must therefore be set very precisely during assembly.
This can be done for instance by means of a slightly canted position of the armature.
Furthermore, in known wiper motors, the spacing between the armature shaft and the power takeoff shaft can also be set by means of interchangeable worm wheels, each having a pitch circle diameter adapted to the axial spacing. Then the particular worm wheel in which an optimal axial spacing is brought about between the armature shaft, with the worm secured to it, and the power takeoff shaft, with the worm wheel secured to it, can be selected from among a plurality of worm wheels of different pitch circle diameters.
In addition, worm wheels with half-global toothing are used, which can be mounted at adjustable heights on the power takeoff shaft by placing one or more shims under them; as a result, the engagement diameter can be varied slightly, and can be set to an exact spacing between the worm and the worm wheel. A problematic aspect, though, is not only that to assemble the power takeoff shaft and the worm wheel, many different parts are needed, such as a plurality of worm wheels of different pitch circle diameter or a plurality of shims, but also that assembling the power takeoff shaft and worm wheel encompasses a very high number of steps and thus is time-consuming.
ADVANTAGES OF THE INVENTION
The electric drive unit according to the invention, has the advantage over the prior art that it can be made more simply and economically. In particular, post-machining of the gearbox, in which the eccentric bush is supported for instance in a power takeoff dome and which is usually a cast metal part, is unnecessary, since because of the graduated embodiment of the outer cylindrical surface of the eccentric bush, which has a smaller diameter on its side toward the worm wheel than on its side remote from the worm wheel, the resultant bores in the gearbox are correspondingly graduated and short, and the gearbox can be produced simply, to close tolerances, in an intended casting operation for making the gearbox, and unmolding of the completed cast gearbox is especially simple.
By means of the provisions recited herein, advantageous refinements of an improvements to the drive unit defined are possible.
One such eccentric bush, that is, a bush whose bore is eccentrically disposed, and which is rotatable to set the axial spacing between the armature shaft and the power takeoff shaft and can be mounted in the rotated state in a manner secured against relative rotation, has the especially great advantage that additional parts, such as additional worm wheels or shims, can be omitted entirely, thus reducing the cost for material, and that moreover very simple and in particular very quick assembly is possible. Setting a desired axial spacing between the power takeoff shaft and the armature shaft requires merely rotating the eccentric bush and the power takeoff shaft supported in it, before the eccentric bush is finally secured in that position.
Even relatively great production variations can be compensated for by the choice of the eccentricity of the inner bore.
Purely in principle, the most various options for rotating the eccentric bush in the gearbox are possible. One advantageous embodiment provides that the eccentric bush is rotatable in infinitely graduated fashion. In this way, an extremely precise setting of the axial spacing between the armature shaft and the power takeoff shaft can be accomplished.
In another advantageous embodiment, it is provided that the eccentric bush has a plurality of detent elements, which are secured to the flange embodied on its face end and which, being offset from one another by equal angles, engage detent elements provided in complementary fashion in the gearbox. Not only do these detent elements enable rotation of the eccentric bush in stages; at the same time the detent elements, engaging one another in a manner fixed against relative rotation in the mounted state also embody a torsion-securing means.
In a preferred embodiment, which meets most requirements, it is provided that the detent elements are each offset from one another by an angle of 30°.
The eccentric bush itself may comprise the most various materials. Particularly with a view to simple production of the eccentric bush, it is preferably provided that the eccentric bush is of plastic.
Thus, by way of example, the eccentric bush can be made in the form of an injection-molded part.
In particular to prevent dirt from getting into the bearing of the power takeoff shaft, it is provided in an advantageous embodiment that a sealing lip is injection-molded onto the flange of the eccentric bush.
To assure good lubrication of the power takeoff shaft in the eccentric bush, it is preferably provided that lubrication grooves are embodied on an inner cylindrical surface of the eccentric bush.
To use particularly over a wide temperature range, which can range for instance from −30° C. to +80° C., and thereby to prevent the eccentric bush from shrinking onto the power takeoff shaft, it may be provided that the eccentric bush is slit over its entire length.
REFERENCES:
patent: 4367660 (1983-01-01), Becker et al.
patent: 4369387 (1983-01-01), Haar et al.
patent: 4944375 (1990-07-01), Ohta et al.
patent: 5053661 (1991-10-01), Kitamura et al.
patent: 5325736 (1994-07-01), Tsujita
patent: 6051899 (2000-04-01), Walther et al.
Fischer Ernst
Herp Juergen
Hurst Richard
Karcher Hansjoerg
Lauk Detlef
Dougherty Thomas M.
Greigg Edwin E.
Greigg Ronald E.
Perez Guillermo
Robert & Bosch GmbH
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