The present invention relates to electric switches, and more particularly to ignition starter switches having fixed contacts which may be electrically connected by a tappet-controlled movable bridging contact.
Prior-art German specification DE-AS No. 1 908 799 discloses an ignition starter switch for motor vehicles comprising fixed contacts fastened to a base plate which contacts can electrically be connected by a movable bridging contact. These bridging contacts are formed as leaf springs producing the contact closing pressure. Such a switch is not appropriate for currents higher than 50 A, because the resilient qualities of the leaf springs decrease due to the heat produced at such high currents. This degrades the contact closing pressure and the resistance between the contacts.
The switch disclosed in prior-art German specification DE-AS No. 1 908 799 has a rotatable operating member which carries operating cams on its front face. The cams act on a tappet, one end of which is attached to the bridging contact or leaf spring. The other end of the tappet lies on the operating cam. When the operating member rotates, forces act circumferentially on the tappet. These forces are transmitted to the bridging contact because of the secure attachment of the tappet to the bridging contact. This may increase the contact resistance.
The object of this invention is to improve the switch disclosed in the prior-art German specification DE-AS No. 1 908 799 so that it may be used for higher currents.
According to the invention this object is achieved by confining the tappet in a guide sleeve disposed in parallel to the axis of rotation of the operating member and attached to a guide plate. This configuration eliminates transmission to the bridging contact of side forces through the tappet. When the operating member is rotated, the rotation is transformed exclusively into a shifting movement of the tappet in parallel to the axis of rotation of the operating member. Hence, canting of the bridging contact is impossible.
The tappet may be advantageously formed as a separate part that is not attached to the bridging contact. Thus, even if the tappet becomes loose within the guide sleeve due to wear, transmission of the side forces to the bridging contact remains impossible.
In addition, the tappet may be advantageously disposed such that it acts on the bridging contact only by means of one of its free front faces. The bridging contact is preferably guided in parallel to the axis of rotation of the operating member via guide walls extending perpendicularly to the base plate. By providing means for guiding the bridging contact which are independent from the tappet guide means, the direction of movement of the bridging contact is not influenced by errors in the direction of the tappet guide sleeve.
In a switch with these features, no forces deviating from the desired direction of movement act on the bridging contact. Thus, a rigid bridging contact may be used, with sufficient contact closing pressure provided by a separate spring. The bridging contact may then be optimized for low resistance and good heat dissipation without affecting the contact closing pressure since that pressure is produced by a separate spring.
In typical ignition starter switch applications, different consumers must be connected with the same pole of a voltage source in different switching positions. To accommodate this requirement, a switch according to the invention may be constructed comprising several bridging contacts located in parallel. On one side, the bridging contacts are electrically connected to one single fixed contact. On the other side, each bridging contact acts in combination with one separate fixed contact. Preferably The fixed contact which all bridging contacts have in common integrally comprises at least two contact arms for connecting one electric cable each. This eliminates the need for special cables with a larger-than-ordinary cross section even for highly-loaded switches. In such a switch, each bridging contact is preferably operated by a separate tappet, and the guide sleeves for all tappets are located along a straight line in the guide plate. This allows the corresponding operating cams of the operating member to be placed on concentric circles with different radii. As a result, small switching angles may be used, and the switch assembly may be made compact.