Electromagnetic relay with a flat armature

An electromagnetic relay has a flat armature which is normally biased away from a pole plate by a bearing spring attached to the armature which is mounted in a recess in a yoke plate, and is clamped thereto. A particularly low friction mounting is achieved by specific selection of the ratio of the distance between the bearing point of the armature and the clamping point of the bearing spring, to the distance between the point of attachment of the bearing spring to the armature and the bearing point.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to electromagnetic relays, and in particular 
to electromagnetic relays having a flat armature mounted with a bearing 
edge which is rolled on a yoke plate and is connected to the yoke by a 
bearing spring for normally biasing the armature away from a pole plate. 
2. Description of the Prior Art 
Electromagnetic relays employing flat armatures having a bearing spring 
have long been in use in many relay magnet systems, such as, for example 
as is disclosed in U.S. Pat. No. 3,505,629. If, in such systems, the 
bearing spring acts on that side of the armature which faces away from the 
yoke plate, an undesireably high degree of friction occurs between the 
bearing edge of the armature and the yoke plate. Although this friction 
can be avoided by arranging the bearing spring directly on the yoke 
between the yoke surface and the armature, as is disclosed in U.S. Pat. 
No. 3,701,066, a bearing spring arranged in this manner frequently 
prevents direct contact between the armature and the yoke, so that the 
magnetic circuit is not optimally closed. If such magnetic systems are 
used in relays having relatively large dimensions, such impairment of the 
magnetic circuit may be compensated by an appropriate dimensioning of the 
overall magnet system. This approach, however, cannot be employed in 
miniaturized relays. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an electromagnetic 
relay with a flat armature which is mounted so as to be substantially free 
of friction, and simultaneously insuring an optimum transition of flux 
between the individual components of the magnetic circuit, in particular 
between the yoke and the armature. 
The above object is inventively achieved in an electromagnetic relay having 
a flat armature with a bearing edge which is biased by a bearing spring, 
the bearing edge of the armature being disposed in a recess in the yoke 
plate and the spring being connected to the armature at a specific 
distance from the bearing edge. 
In this inventive structure, the armature is mounted on the yoke in such a 
manner that during the switching movements the bearing edge rolls 
substantially on the same imaginary line of the yoke plate, and thus moves 
in substantially friction free fashion. The bearing spring determines not 
only the bearing force on the armature, but also the armature resetting 
force as well as a rest contact force for the contact springs which are to 
be actuated by movement of the armature. 
It is preferable that the clamping point of the bearing spring in the relay 
is in the same plane as the bearing surface between the armature and the 
yoke, and that in the region of the bearing edge of the armature the 
bearing spring is bent into the yoke recess. This can be achieved, for 
example, by means of two bends in opposite directions which are selected 
to establish the desired forces acting upon the armature. 
The armature bearing is subject to particularly low friction when a 
specific length ratio of the distance between the clamping point of the 
bearing spring and the bearing edge of the armature, to the distance 
between the attachment point of the bearing spring to the armature and the 
bearing point is utilized. This length ratio is selected such that the 
tangent at the attachment point of the bearing spring at the two end 
positions of the armature passes through the bearing position. In a 
preferred embodiment of the invention, this length ratio is selected such 
that the distance between the bearing point of the armature and the 
attachment point of the bearing spring to the armature is double the 
distance from the bearing point of the armature to the clamping point of 
the bearing spring.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A portion of an electromagnetic relay is shown in section in FIG. 1 having 
a yoke plate 1 and a pole plate 2 disposed in substantially the same 
plane. Portions of the relay not essential to the inventive concept 
disclosed herein have been omitted. A flat armature 3, which forms an 
operating air gap h with the pole plate 2, is mounted on the yoke plate 1. 
The armature 3 has a bearing edge 4 which rolls on the yoke plate 1, and 
the armature 3 is both held and biased by a bearing spring 5. The bearing 
spring 5 is connected to the yoke plate 1 at a clamping position 6 and 
bears the armature 3 at an attachment point 7. In the embodiment shown in 
FIG. 1, the bearing spring 5 is attached to the armature 3 by a rivet, 
however, it will be apparent that other conventional means of attachment 
such as welding or screwing can also be employed without departing from 
the inventive concept disclosed herein. 
The armature 3 operates self-biased spring contacts 9 and 10 via a slide 8 
to make and break contact with a fixed central contact 11. The central 
contact 11 is secured in an insulating carrier 12 together with the pole 
plate 2, and the contacts 9 and 10 together with the yoke plate 1 and the 
bearing spring 6 are supported by an insulating layer 13 or other 
insulating body. 
FIG. 1 illustrates the magnetic relay system in a rest state. In this 
state, the bearing spring 5 produces a bearing force P.sub.2, a specific 
armature resetting force P.sub.3, and, for the self-biasing contact 
arrangement, an actuating force P.sub.4 which acts against the contact 
spring 11. These forces are schematically represented by the arrows in 
FIG. 1 in the direction of the forces. 
The same armature is shown in an operating state in FIG. 2, wherein a 
bearing force P.sub.5, a magnetic force P.sub.6 and an actuating force 
P.sub.7 are present and act on the relay in the direction shown by the 
respective arrows. 
In order that, during operation, the armature 3 can rest flat on the pole 
plate 2 and the yoke plate 1, the bearing spring 5 is disposed in a groove 
or recess 14 in the yoke plate 1. The bearing spring 5 is bent into the 
recess 14 by two bends. These bends are selected in such a manner that the 
desired forces are generated in the particular switching state employed. 
Specific distances l.sub.1 and l.sub.2 are selected between the clamping 
point 6 of the bearing spring and the bearing edge 4 of the armature, and 
between the bearing edge 4 and the attachment point 7 of the spring 5 to 
the armature 3. The ratio of the distances l.sub.1 and l.sub.2 is selected 
such that when the armature 3 is actuated, the bearing edge 4 exerts 
virtually no friction on the yoke plate 1. 
The calculation of an optimum length ratio of l.sub.2 to l.sub.1 is 
explained with reference to the graph shown in FIG. 3. FIG. 3 
schematically illustrates the bearing spring 5, the armature 3 and the 
yoke plate 1. The bearing spring 5 is clamped at a point C and is 
deflected at a point B. For simplicity, it will be assumed that simply a 
force P acts on the spring 5 at the deflection point B. The bearing point 
of the armature 3 on the yoke plate 1 is designated at A. 
If a spring having a length l is biased by an amount f.sub.1, the angle of 
inclination .alpha..sub.1 occurs at the deflection point B. If the spring 
is further deflected by an amount .DELTA.f, an angle of inclination 
.alpha..sub.2 occurs at the deflection point B. 
These two angles of inclination which arise by differing deflections of the 
spring are governed by the following equation: 
##EQU1## 
so that 
EQU tan .alpha..sub.2 -tan .alpha..sub.1 =3.DELTA.f/2l. 
The following geometric equation is obtained from FIG. 3; 
EQU tan .alpha..sub.1 =f.sub.1 /l.sub.2 ; tan .alpha..sub.2 =(f.sub.1 
+.DELTA.f)/l.sub.2, 
and by substitution 
##EQU2## 
or 
EQU .DELTA.f/l.sub.2 =3.DELTA.f/2l, so that 1/l.sub.2 =3/2l 
Because l=l.sub.1 +l.sub.2, then l.sub.1 /l.sub.2, then l.sub.1 /l.sub.2 
=1/2. 
By adhering approximately to the length ratio of 1:2 for the bearing 
position of the armature 3, an armature bearing is obtained which is 
substantially free of friction when a force P acts at the deflection 
point. If a number of different forces act upon the armature or on the 
spring, the corresponding length ratio between l.sub.1 and l.sub.2 can be 
determined by known mathematical methods similar to that employed above. 
Although 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.