Electrical transmission or interconnection systems – Vehicle mounted systems – Automobile
Patent
1998-02-11
1999-08-31
Elms, Richard T.
Electrical transmission or interconnection systems
Vehicle mounted systems
Automobile
307104, 34031007, H01F 2742
Patent
active
059457449
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an arrangement for contactless signal transmission between a stationary vehicle part and one that is rotationally mounted with respect thereto, chiefly between a steering wheel fitted with an airbag and a control switch arranged on the chassis, the arrangement being comprised of a transformer whose primary and secondary windings are situated in separate pot-type cores, which rotate, relative to each other, about the rotational axis of the movable vehicle part, the pot-type cores having an L-profile and fitting with each other such that, in each case, the front end of the short limb of one L-profile faces the inner side of the long limb of the other L-profile and, in this context, air gaps arise which the magnetic flux intersects radially to the rotational axis.
In a rotary transformer known from the prospectus of the Eaton company, "Lebow, Torque, and Force Transducer," 1993, the pot-type cores containing the primary and the secondary windings are comprised of rotationally symmetric U-profiles, which are arranged axially one behind the other such that the openings of the U-profiles face each other. In this way, an air gap is formed running transversely to the rotational axis of the transformer, said air gap being intersected by the magnetic flux in the direction of the rotational axis. In this arrangement of the pot-type cores, an axial displacement of the steering wheel on the steering column directly affects the size of the air gap and, as a result, the degree of coupling between the primary and secondary windings. A transmitted signal would therefore be influenced to a great extent by an axial displacement between the transformer's pot-type cores. This known rotary transformer acts both to transmit firing pulses from a control device fixed to the chassis to an airbag arranged in the steering wheel, as well as, in the reverse direction, to transmit diagnostic signals of the airbag firing pellet resistor to the control device. A diagnostic signal of the firing pellet resistor, transmitted to the control device, could thus, as a result of the change in the air gap, deliver incorrect information concerning the operativeness of the airbag.
In contrast to U-profile pot-type cores, if the pot-type cores, as indicated in the introduction, are formed in an L-profile, savings in both cost and weight are possible. Such a rotary transformer having L-profile pot-type cores is known from German Patent No. 19 20 890 and German Patent No. 30 34 735. In axial displacements of the two L-shaped pot-type cores, in relation to each other, the path for the magnetic flux is lengthened, which in turn can lead to interference with a bridging signal from the transformer.
Thus the object underlying the present invention is to indicate an arrangement of the species indicated above, in which an axial displacement between a stationary and a movable vehicle part exerts as little influence as possible on a signal transmitted, without contact, between the two parts.
SUMMARY OF THE INVENTION
In accordance with the present invention, the pot-type cores have an L-profile, said pot-type cores fitting with each other such that, in each case, the front end of the short limb of an L-profile faces the inner side of the long limb of the other L-profile. In this context, the inner sides, in each case, of the long limbs of the L-profile and/or the front ends of the short limbs are beveled in relation to each other such that in an axial displacement of the two pot-type cores, in relation to each other, the air gap between the long and short limbs decreases. In an axial displacement of the two pot-type cores, their air gaps decrease and in so doing compensate for the longer path of the magnetic flux through the pot-type cores. Axial displacement tolerances and fitting tolerances, for instance of a steering wheel on which one of the two pot-type cores is mounted, therefore have only a slight influence on the transmitted signals. To reduce the weight of the transformer, it is expedient that
REFERENCES:
patent: 5498911 (1996-03-01), Bossler et al.
patent: 5515399 (1996-05-01), Swart
patent: 5636863 (1997-06-01), Reid et al.
Eaton Sales Prospectus "Lebow Torque and Force Transducers" (1993).
Dobler Klaus
Dukart Anton
Zabler Erich
Elms Richard T.
Robert & Bosch GmbH
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