Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Multiple contact type
Patent
1989-03-24
1991-01-22
Broome, H.
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Multiple contact type
335131, H01H 6702
Patent
active
049873962
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an electromagnetic switch for starting devices of internal combustion engines. It is already known in the case of such a switch to provide primary current contacts with inclined flat contact surfaces and the contact bridge with correspondingly bent-off ends as contact sections. On closing of the contacts, the contact bridge and primary current contacts should lie against each other over a relatively large area. In this arrangement, it is of disadvantage that in plan view, a rectangular contact bridge requires an anti-rotation means, as otherwise no parallel contact making is possible. Such anti-rotation means is known, for example, in the form of ribs or walls in the cap which carries the primary current contacts and surrounds the switching space. Such anti-rotation means have, however, the disadvantage that, under harsh operational conditions of motor vehicles, vibrations can cause damage by in the cap because of notches therein and/or damage of the contact bridge or its insulating bearing parts, to which additionally the recoil force of the cap wall can contribute. In addition, with the relatively large level contact surfaces, it is of disadvantage that, with a view to a cost-effective mass production, the contact surfaces cannot be made so flat and/or kept so parallel to each other that contact making always takes place in the centre of the contact surfaces. As a result, no uniform heat dissipation is possible, so that the welding tendency of the contact parts increases in an undesired way. The friction on contact making of the contact surfaces inclined with respect to the switching direction can admittedly have the effect that corrosion deposits on the contact surfaces are dislodged and pushed away to a certain extent. With the relatively large contact surfaces, nevertheless it happens again and again that the contact making takes place at poorly conducting or otherwise unfavourable points, because the self-cleaning effect cannot become sufficiently effective here and the, in itself, desired high contact force can, with contact surfaces arranged obliquely to the switching movement, press the impurities into the contact surfaces.
SUMMARY OF THE INVENTION
The object of the invention is to provide an electromagnetic switch, in particular for starting devices of internal-combustion engines, the primary current contacts and contact bridge of which switch are designed in such a way that the disadventages of the known solutions are avoided and, as a result, the service life of the contact parts with, at the same time, increased requirements on their performance and a greater security against welding of the contact parts are achieved.
It is in this case of advantage that, with higher contact force, reduced bouncing tendency and good self-cleaning effect, it is made possible, by the shape of the contact surfaces, in a cost-effective way, always to achieve contact making at virtually the same point of the contact surfaces, even in the case of dimensional deviations, whereby a reliable contact making and a good heat dissipation is ensured without contact welding. It is to be regarded as a further advantage that the round contact bridge no longer requires lateral guidance, which likewise contributes to the increasing of the service life of the switch.
It is particularly advantageous that the primary current contacts are designed as screws with polygonal head, so that no anti-rotation means are required, since they can be fixed in their position in the cap in a simple way. In addition, the service life of the primary current contacts is increased due to the multiplicity of formed-on contact surfaces, by multiple using of the primary current contacts. With an angle of inclination of the contact surfaces to the switching movement of 45.degree., the most favourable relationship between contact force, bouncing tendency and self-cleaning is made possible. In a cost-effective way, the primary current contacts may be used (sic) not only of expensive copper but also
REFERENCES:
patent: 3569649 (1971-03-01), Collins
patent: 4203084 (1980-03-01), Yamaguchi et al.
patent: 4293835 (1987-10-01), Davis et al.
Broome H.
Donovan Lincoln
Robert & Bosch GmbH
Striker Michael J.
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