Importance

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Abstract

A solenoid for an electric starting motor housed in a generally cylindrical plastic cup. A pair of diametrically arranged fixed contacts penetrate the end wall, forming binding posts for a load circuit. A magnetic sub-assembly is provided consisting of an armature and wound bobbin surrounded by a hollow magnetic annulus having axial clearance openings. A movable contact sub-assembly includes a conductive disc mounted on an axial plunger which is seated against the armature. The disc has, on its opposite side, a return spring. When control current is applied the armature is sucked into the annulus overcoming the force of the return spring and shifting the conductor disc into seated engagement with the fixed contacts thereby completing the load circuit. The disc and fixed contacts both have substantial axial and radial thickness providing high heat capacity as well as high conductivity for prompt dissipation of heat. The fixed contacts are spaced from the disc at such distance that only a minor portion of the presented area is engaged by the edge portion of the disc to develop high contact pressure per unit area. The disc is freely rotatable with respect to the fixed contacts so that contact occurs in random positions on the disc for constant renewal of the contacting surface.

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First Claim