Electromagnetic tripping device

An electromagnetic tripping device for protecting a printed circuit card by opening an electrical circuit of the card in response to an overcurrent of the circuit. The device includes contacts and an energizing coil which are connected in series with the circuit to be opened. When the contacts of the device are closed and the circuit current is normal, a magnetic holding flux provided by a bar magnet holds a plate in contact with two spaced and parallel side-walls between which is located the bar magnet. When an overcurrent occurs, the energizing coil produces a breaking flux which reduces the holding flux sufficiently so that the plate may be moved from the side-walls by a return spring, thereby opening the contacts and the circuit. When the plate is moved from the side-walls, an actuating rod which passes through an opening in the plate is projected out of the device housing to indicate the opening of the circuit. An axial force applied to the projecting end of the actuating rod allows the plate to be reset in contact with the side-walls by an auxiliary spring to reset the device with a like amount of force each time.

BACKGROUND OF THE INVENTION 
The present invention relates to and has essentially for its object an 
electromagnetic tripping device, forming for example a relay, circuit 
breaker or like current interrupting means, designed to meet more 
particularly two categories of new requirements, i.e., on the one hand, 
miniaturization of such devices, and on the other hand, the suitability of 
such miniaturized devices for their most currently contemplated use, 
namely, their mounting on printed-circuit cards as any other electronic 
components. 
Accidents with catastrophic consequences have recently occured in certain 
data processing centers and telephone exchanges using important digital 
processing installations. In such cases, whole cabinets full of 
printed-circuit cards plugged side by side into connectors arranged in 
rows are enclosed in a same room. The printed-circuit cards are usually 
arranged vertically in order to facilitate ventilation and the spacing 
between the cards in a same row is practically standardized to correspond 
to the maximum width of the largest electronic components used. A complete 
installation of this kind using several cabinets full of electronic 
components is obviously very expensive. On the other hand, the risks of 
failure of the installation are not inconsiderable in view of the number 
of components. It has happened that a fault in just one printed-circuit 
card resulting in a short circuit has started a fire which has destroyed 
the whole installation. Designers have therefore recognized the necessity 
for equipping each printed-circuit card with one or several individual 
circuit breakers designed to immediately cut out at least part of the card 
on occurence of an abnormal current at the card, e.g. in the 
direct-current supply. The needed next type of circuit breaker was 
therefore a miniature circuit breaker with the following mutually 
conflicting characteristics: 
it had to be miniaturized in the extreme in order to be of a size 
compatible with the mean size of the electronic components mounted on the 
printed-circuit cards of present-day digital processing systems, 
in particular, it must have a minimum base area in order not to be too 
difficult to be mounted on the printed-circuit card, and its height must 
be greater than the usually adopted spacing between the cards arranged 
vertically within a common cabinet, 
its sensitivity must be increased so as to be compatible with the usual 
orders of magnitude of the supply currents for such printed-circuit cards, 
lastly and above all, the tripping knob must be arranged on the side of the 
circuit-breaker housing so that when the housing is adequately mounted on 
the card the said knob is readily accessible and does not prevent other 
components being mounted in immediate proximity to the circuit breaker. 
Devices meeting such requirements in association with those of 
miniaturization proper (reduced number of members, accurate assembly, 
etc.) are practically unavailable on the market. The present invention is 
the result of extensive research with a view to making all such 
requirements compatible with one another. Otherwise stated, the shape and 
arrangement of the components of the device according to the invention as 
well as its external appearance have been conceived essentially for its 
contemplated application. However, the same basic structure may be quite 
easily reutilized to develop an electromagnetic relay with quite as 
interesting performances. 
SUMMARY OF THE INVENTION 
To this end, the invention relates to an electromagnetic tripping device 
characterized in that it comprises: 
two substantially flat flux-conductive side-walls or cheeks spaced in 
substantially parallel relationship to one another, 
a bar magnet forming a cross-tie between the said side walls, the direction 
of magnetization of the said bar magnet being perpendicular to the 
mutually confronting surfaces of the said side walls, 
an energizing or tripping coil wound around a flux-conductive core forming 
between the said side walls a cross-tie parallel with the direction of 
magnetization of the said bar magnet, 
an actuating rod carrying a transverse, magnetic-circuit closing plate, the 
said rod and the said plate being guided in translation in a common 
direction perpendicular to the said direction of magnetization, the said 
plate being movable into engagement with the respective coplanar edges of 
the said side walls, and 
a return spring bearing against the assembly of the said actuating rod and 
said plate, in a direction tending to move the plate away from the said 
coplanar edges. 
It is understood that in such a structure, where the movement of the 
movable part (actuating rod and transverse plate) takes place 
perpendicularly to the direction of magnetization of the bar magnet and to 
the axis of the coil, both a reduced base area facilitating the mounting 
on the printed-circuit card is obtained and the occupied space in height 
with respect to the plane of the card is minimized since the actuating 
rod, (which, in the case of a circuit breaker, also serves as an actuating 
knob) moves in a parallel direction to the plane of the card.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Shown in the drawings is a miniature electric-circuit breaker or like 
electric current interrupting device comprising essentially two 
half-casings 11 and 12 forming the protective insulating housing of the 
device, two flat metal side-plates or cheeks 13 and 14 in spaced parallel 
relationship to one another, a bar magnet 15, an energizing or tripping 
coil 16 wound around a cylindrical flux-conductive core 17, an actuating 
rod 18 carrying a transverse metal plate 19 serving to close the magnetic 
circuit, and a helical return spring 20. The bar magnet 15 and the core 
17, which are mutually parallel and equal in length, form cross-ties or 
the like between the side plates 13 and 14, as can be seen in FIG. 1. It 
should be noted, however, that this is not indispensable as far as the bar 
magnet 15 is concerned, since a gap may be provided between the bar magnet 
and the side walls 13, 14. The direction of magnitization N-S of the bar 
magnet 15 is perpendicular to the mutually opposite surfaces of the side 
walls 13 and 14. The side walls are positioned and adhesively retained in 
lateral cavities 13.sub.a, 14.sub.a provided in the half-casing 11, so 
that their edges 13.sub.b, 14.sub.b project outwardly of the said 
half-casing. Preferably, after adhesively securing the side walls in the 
half-casing 11, the edges 13.sub.b, 14.sub.b are planed, as by grinding, 
so as to render them rigorously coplanar. Such mounting and machining 
features are important since the edges 13.sub.b and 14.sub.b provide the 
bearing surface for the movable transverse plate 19 when the circuit 
breaker is operative. The plate 19 is provided with a central hole 25 the 
diameter of which corresponds to that of the rod 18 so as to allow for 
relative sliding motion between the rod 18 and the plate 19. Furthermore, 
the rod 18 is provided with a transverse stop collar 26 displaying two 
opposite bearing faces 27 and 28 so that the plate 19 can bear against the 
face 27 whereas the return spring 20 coaxially surrounding the rod 18 
bears against the opposite face 28. The transverse plate 19 is urged 
towards the bearing face 27 by an auxiliary helical spring 30, but this 
auxiliary spring is designed so that the force which it exerts on the 
plate 19 is markedly smaller than that of the return spring 20 applied to 
the face 28 of the stop 26. As the previously mentioned spring, the spring 
30 is arranged coaxially around the rod 18 on the other side of the stop 
26 with respect to the spring 20. 
The actuating rod 18 and the transverse plate 19 are guided in translation 
within the housing in perpendicular relationship to the direction of 
magnetization N-S, this movement being stopped in one direction when the 
plate 19 moves into engagement with the ground coplanar surfaces 13.sub.b, 
14.sub.b. The guiding of the rod 18 is ensured in the simplest manner by 
means of two mutually opposite apertures 31, 32 provided in the 
half-casings 11 and 12, respectively. Furthermore, the end 33 of the rod 
portion carrying the auxiliary spring 30 projects laterally outside the 
housing in at least the open or break position (shown in phantom lines in 
FIG. 2) of the device. The end 33 thus forms the reset knob of the circuit 
breaker. 
The two half-casings 11 and 12 also accomodate a break circuit 35 including 
of course the above-mentioned coil 16. This circuit comprises two plug-in 
pins or access terminals 36, 37 projecting from the base face 38 of the 
housing formed by the two half-casings 11 and 12 assembled together (FIG. 
2). It is therefore seen that in accordance with what has been said 
earlier, the base face 38 and the actuating rod 18 are located as far 
apart as possible, and the actuating rod 18 is adapted to move in a 
parallel direction to the said base face. The break circuit 35 comprises a 
first metallic collecting pole 39 electrically connected (welded) to the 
end 40 of the coil 16, a second metallic collecting pole 41 parallel with 
the first collecting pole and electrically connected to (in fact an 
extension of or prolonged by) the access terminal 36, and a flexible 
metallic contact blade 42, located between the two said poles and secured 
(welded) to the second pole 41 by its curved portion 43. The flexible 
blade 42 carries a contact stud 44 forming with the first pole 39 the 
breaking means proper. The freely movable endmost portion 45 of the 
flexible blade 42 is placed on the path of movement of the transverse 
plate 19 (which path is symbolized by the two endmost positions of plate 
19 shown in FIG. 2 in full lines and interrupted lines, respectively) so 
as to be pushed by the said plate towards the left in FIG. 2, i.e. towards 
the second pole 41, when the device is in its open or break position. On 
the other hand, it should be noted that when the device is not open, i.e. 
when the transverse plate 19 is applied to the coplanar edges 13.sub.b and 
14.sub.b of the side walls 13 and 14, the contact blade 42 is disengaged 
from the transverse plate 19 and applied through its contact stud 44 to 
the first pole 39. 
The other end 46 of the coil 16 is connected (welded) to a third metallic 
collecting pole 47 resting on the bottom wall of the housing and 
electrically connected to (in fact prolonged by or an extension of) the 
other access terminal 37. 
Lastly, another important feature of the invention lies in the fact that a 
metal screen tube 48, e.g. of copper or brass, is interposed between the 
coil 16 and its core 17. When a current flows through the coil the said 
screen tube performs the function of a short-circuit turn through which a 
current induced by the coil passes. This results in retarding core 
induction. By these simple means the circuit breaker is prevented from 
being tripped by false alarms caused by transient current peaks of short 
duration, therefore involving no danger for the installation. 
The operation of the device just described is quite simple and can be 
obviously inferred from the foregoing description. The rod 18 being 
depressed towards the right in FIG. 2, the plate 19 is applied to the 
edges 13.sub.b and 14.sub.b of the side walls 13 and 14. The magnetic 
field of the bar magnet 15 therefore closes through the transverse plate 
19 remaining applied with a certain force to the edges 13.sub.b and 
14.sub.b. This application force is of course greater than the force 
exerted by the spring 20 on the stop 26. If, however, a current flows 
through the coil 16, the flux in the core 17 increases against the flux of 
the bar magnet 15. This aggregately results in a decrease in the force of 
attraction of the plate 19 against the side walls 13 and 14. When the 
current in the coil 16 reaches a definite threshold accurately 
predetermined by appropriately selecting the characteristics of the coil, 
the bar magnet 15 and the spring 20, the force of application of the 
transverse plate 19 becomes smaller than the force exerted by the spring 
20, thus releasing the actuating rod 18 and displacing it towards the left 
in FIG. 2. During this movement the rod 18 drives along with it the 
transverse plate 19 which in its turn repels or moves the flexible contact 
blade 42 thus opening the break circuit 35 and interrupting the flow of 
current between the terminals 36 and 37 of the device. The end 33 of the 
rod 18 then noticeably protrudes from the housing of the device, thus 
showing that the device is in its open position. So, an operator entrusted 
with the supervision of the electronic system diagrammatized in FIG. 3, is 
able to immediately locate any fault that may occur, by checking the 
condition of the circuit breakers mounted on the various printed-circuit 
cards. After eliminating the fault and, if necessary, changing the faulty 
card, the new card may be cut in by simply pressing on the end 33 of the 
rod 18, thus reapplying the transverse plate 19 to the coplanar edges 
13.sub.b and 14.sub.b of the side walls 13 and 14. The plate 19 then 
remains in that position until such time as a further abnormal current is 
detected. In this connection, an important advantage of the resetting 
system just described should be noted. It has indeed been found that the 
tripping threshold of a circuit breaker may vary according to the manner 
in which the operator resets the device subsequent to breaking, more 
particularly in accordance with the force with which he presses on the 
resetting knob. It will be observed that in the arrangement described it 
is not the operator's actuating force that reapplies the transverse plate 
19 onto the edges 13.sub.b, 14.sub.b (this force serving only to move the 
rod 18 against the action of the spring 20) but rather the combined return 
forces of the spring 30 and the flexible contact blade 42. Otherwise 
stated, the resetting pressure on the transverse plate 19 is always the 
same or identical with itself and corresponds to a value selected by the 
manufacturer. It will also be observed that the auxiliary spring 30 is not 
indispensable, for the return travel of the flexible contact blade 42 is 
often sufficient to move the transverse plate to a location very close to 
the edges 13.sub.b and 14.sub.b, where there is a sufficient magnetic 
field to cause the plate 19 to be magnetically attracted towards the 
cheeks 13, 14, thus completing its resetting travel. 
Of course the invention is by no means limited to the form of embodiment 
just described which has been given by way of example only. In particular, 
the same basic system may be used to obtain a relay instead of a circuit 
breaker, in which case the flexible blade 42 becomes useless and can be 
dispensed with. It is then sufficient to add a system of movable contacts 
whose actuation may be, for example, mechanically connected to the motion 
of the rod 18. Instead of a system of contacts there can also be provided 
any suitable mechanical system, in particular the operating member of a 
valve, etc. The invention therefore covers all technical equivalents to 
the means described should the latter be used within the scope of the 
following claims.