Patent Publication Number: US-4924197-A

Title: Electromagnetic relay

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed generally to an electromagnetic relay having a coil which includes a winding applied to a coil member between end flanges thereof and having a core axially arranged within the winding. A yoke is included arranged outside of the winding and connected to one end of the core. An armature is seated at the yoke and forms a working air gap with the free end of the core. At least one switch contact is actuateable by the armature, the switch contact being connected through a power lead element to a terminal element, whereby the power lead element is conducted at least once through the excitation flux circuit formed by the yoke, core, and the armature. 
     2. Description of the Related Art 
     When switching electromagnetic load relays, a problem occurs in specific applications in that the excitation voltage for the winding drops off during the attraction of the armature. As a result, the armature is no longer fully attracted under certain circumstances which causes the armature to undergo a chattering motion. This causes the switch contact to either not close or to undergo repeated interruptions or openings before closing. This problem occurs particularly often in applications where the voltage source for the excitation winding of the relay also simultaneously supplies the current to the load, as is specifically the case in motor vehicles. When certain users or loads, such as lamps or starters, are switched on in a motor vehicle, extremely high turn-on current peaks appear which leads to the reduction of the battery voltage. Thus, reliable operation of the relay is no longer assured. 
     Another, related problem occurs when relays are driven by mechanical switches which have multiply longer bouncing times for the switch elements. As a result of these bouncing impacts, the relay is then also multiply switched on and off until it ultimately closes. Particularly when extremely high turn-on current peaks are required by the load, this leads to great stressing and/or erosion of the relay contacts. In extreme cases, for example, when switching lamp currents, it leads to welding of the contact members. 
     In a relay disclosed in European Published Application 0 231 793 and corresponding U.S. Pat. No. 4,803,589, it is provided to conduct the load current between the coil and yoke so that an auxiliary excitation is induced isodirectionally with the excitation of the winding. Given appropriate dimensioning, a reliable response of the relay is guaranteed in this way even when the excitation voltage drops off during the turn-on event or is interrupted in the interim as a consequence of a bouncing switch. 
     Given a relay of small volume, however, problems arise for guiding the load current around the excitation flux circuit under certain circumstances when there is only an extremely small gap present between the winding and the yoke, so that it is only possible to conduct a power lead element of large cross section therethrough with difficulty. It has thereby also been proposed to conduct a thin plate which occupies essentially the entire length of the winding between the winding and the yoke as the power lead element in order to obtain the required cross section for the load current and still provide an optimally low height. In any case, however, problems derive during assembly and problems derive in view of the insulation between the load circuit and winding in this type of relay. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to improve the relay of the species initially cited so that an auxiliary excitation of the load circuit can be generated isodirectionally with the excitation circuit but so that a modification or interference in the actual winding space is simultaneously avoided and a reliable insulation of the power lead of the load circuit is guaranteed. 
     This and other objects of the invention are achieved in a relay wherein a power lead element has one side connected to the coil with a terminal element and is conducted to the other side of the coil through a transverse bore or opening in a coil flange and is then connected there to a switch contact. 
     The transverse opening in the coil member flange, of course, is situated in the region between the coil core and the yoke so that the desired auxiliary excitation for the relay is generated as the result of current flow through the power lead without having to mount an additional element in the actual winding space. Of course, the direction of the current flow through the power lead must be such that it has an additive effect on the magnetic flux. By guiding the current in the coil flange, it also guarantees a good insulation between the load circuit and the actual excitation circuit. 
     An auxiliary excitation that is generated by the power lead element conducted through the flange holds the relay in its attracted condition once the contact current has been switched on, so that even a brief interruption of the current due to the aforementioned bouncing during turn-on no longer allows the relay to drop off. Moreover, the auxiliary excitation upon turn-on promotes a rapid attraction of the relay armature, so that high contact forces are quickly achieved and any burning off or erosion of the contact material is kept within limits. After the decay of the initial current in the load circuit, for example after the filament of a lamp switch has been heated, the holding effect due to the auxiliary excitation is so slight that a disadvantageous influence on the relay during drop-off hardly occurs. The height of the auxiliary excitation can be defined on the basis of appropriate dimensioning or sizing of the elements. As needed, it is also possible to divide the power supply and to conduct only one part thereof through the transverse in the yoke. 
     The described auxiliary excitation is especially useful in relays wherein the armature and the yoke are traversed by the contact current. To thereby make the auxiliary excitation optimally high, the resistance through the armature and the yoke can thereby also be increased in that, for example, the contact spring is not manufactured of highly conductive material but of a poorly conductive spring material such as, for example, steel. This has an additional advantage than materials having better spring properties and higher fatigue strength for an infinite length of time can be used. These steel materials are also usually more cost beneficial than the highly conductive copper alloys that are otherwise required. The contact current is thereby expediently conducted through a stranded conductor directly welded onto the rivet head of the contact, the stranded conductor passing through the transverse bore in the coil flange. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a relay according to the principals of the present invention; and 
     FIG. 2 is a second perspective view of the inventive relay of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The relay shown in FIGS. 1 and 2 has an inherently known basic structure comprising a coil member 1 as a bearing element on which the winding 4 is applied between two flanges 2 and 3. A core 5 is axially attached inside the coil 1. The core 5 has one end connected to an angular yoke 6, namely connected to the leg 6a thereof which extends vertically, whereas the horizontal leg 6b extends above the coil 1. A flat armature 7 that is secured to the yoke 6 via an armature spring 8 is seated at a free end of the yoke leg 6b. An extension of the armature spring 8 serves as the contact spring 8a and carries the contact piece 9 at its free end which lies opposite a stationary cooperating contact piece 10. The cooperating contact piece 10 is secured to a terminal element 10a that is fashioned as a flat plug. A flat plug 6c fashioned as an extension of the yoke leg 6a serves as a terminal element for the contact piece 9 at the contact spring 8a. 
     Plug elements 11 and 12 are also anchored in a base body as coil terminal elements. 
     As a result of the described structure, thus, the current supplied to the contact 9 ensues via the yoke 6 and the armature 7. In order, however, to offer low resistance for high currents, a stranded conductor 13 is also provided, which is directly connected to the flat plug 6c at one end and has its other end directly welded on the contact piece 9. This copper stranded conductor 13 can, for example, carry up to 90 percent of the current, particularly when the armature spring 8, for instance, is manufactured of a relatively poorly conductive metal such as spring steel. 
     To also be able to generate an auxiliary excitation by the contact current in order to improve the attraction behavior of the relay, the stranded conductor 13 is conducted through a transverse bore 3a in the coil member flange 3. This transverse bore proceeds in a horizontal direction given the normal integration position of the relay, namely between the coil core 5 and the yoke legs 6b. To obtain the initially described promotion of the attractive behavior of the relay by the auxiliary excitation, the polarity when connecting the load circuit must be correspondingly selected so that the auxiliary excitation is added to the coil excitation. 
     Although other modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.