Differential thermal tripping device with bimetallic strips

Differential thermal tripping device with bimetallic strips for electrical protection appliance such as a circuit breaker. The circuit breaker includes a tripping assembly with two contact strips 30, 40 free to move along the X direction, and for each bimetallic strip, a single adjustment part 15 fixed to a free inclined edge 19 of the bimetallic strip head 13, adjustable along the X direction, in the position obtained after heating of the bimetallic strips for calibration. The assembly 30, 40 may consist of a frame supporting adjustment parts until they are fixed and provided with separable areas 36, 46 to generate two contact strips following cutting.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a differential thermal tripping device for an 
electrical switching appliance, particularly for a circuit breaker, 
comprising tripping assembly with two adjustable contact strips installed 
parallel to each other and associated with a tripping mechanism, and 
several bimetallic strips with opposite faces that come into contact with 
each of the two contact strips through intermediate adjustment elements, 
so that a concomitant or different deflection of the bimetallic strips 
will cause a simultaneous or differential displacement of the contact 
strips. 
2. Description of the Related Art 
This type of tripping device is known and is described in document FR-2 666 
928. This document describes a process for adjusting the tripping 
distances of the bimetallic strips by using a single part for contact 
strips, then by disassociating the connecting areas specific to this part 
at locations determined by measuring the deflection of the bimetallic 
strips that cause tripping. 
Furthermore, another known procedure is to associate adjusting parts with 
contact strips that are moved by bimetallic strips during the tripping 
device calibration operation, the position of the elements being fixed on 
the contact strips in the required position by welding or gluing. 
According to document WO-86 02197, an adjustment part is provided for each 
bimetallic strip, and is housed in a slit that opens up near the end of 
the bimetallic strip. However, positioning the adjustment part in the slit 
causes jamming and does not facilitate welding, particularly when it is 
done by a laser beam. 
SUMMARY OF THE INVENTION 
The purpose of this invention is to provide a simple and in situ adjustment 
of the distance moved by the bimetallic strips in the described type of 
tripping device, avoiding risks of jamming and facilitating the operation 
of attaching adjustment parts. 
According to the invention, before being fixed the adjustment part is 
placed so that it can slide freely on an inclined edge away from the head 
of the bimetallic strip, being held vertically in place on the contact 
strips. Due to the edge inclination, the adjustment part can position 
itself vertically on the edge thus facilitating its attachment, 
particularly by a laser welding beam. 
Preferably, the two contact strips in the tripping assembly are obtained by 
cutting separable areas of an installation frame; and include recesses 
facing each other for adjustment parts, these recesses being laid out to 
keep the adjustment parts in contact with the bimetallic strips in an 
inclined position until they are fixed to the bimetallic strips.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The differential thermal tripping device 10 is designed to be included in 
an electrical protection device such as a circuit breaker-motor, a 
contactor-circuit breaker or a thermal relay for example a three-pole 
relay, in order to protect a load against overcurrents or phase 
unbalances. 
In this case, it includes three bimetallic strips 11a, 11b, 11c formed of 
flat elongated elements of which the stands 12a, b, c are mounted fixed on 
the appliance and in which the heads 13a, b, c are capable of moving along 
a direction X as a function of the temperature rise to which they are 
subjected; this temperature rise results from the current passing through 
the various phase conductors (not shown) or the bimetallic strips 
themselves. The tripping device also contains a tripping assembly 20 
fitted with two contact strips 30, 40 free to move in the X direction and 
acting as devices detecting concomitant or differentiated displacement of 
the bimetallic strips. In the X direction, the contact strip 30 comprises 
stop surfaces 31a, b, c that may be contacted by each of the bimetallic 
strips, these surfaces 31 being placed on arms 32a, b, c, perpendicular to 
a rod 33 on the contact strip oriented along the X direction; similarly, 
the contact strip 40 comprises stop surfaces 41a, b, c, that may be 
contacted by bimetallic strips in the X' direction opposite to X and 
fitted on arms 42a, b, c perpendicular to a rod 43 on the contact strip 
along the X direction. A lever 21 is hinged onto contact strips 30, 40 at 
points 34, 44 and acts on a tripping mechanism 14, for which only the 
control element is shown on the figure. The device that has been described 
above, and its method of operation, is well known to those skilled in the 
art; when the bimetallic strips act in exactly the same way under a 
temperature rise due to an overcurrent, they pull contact strip 30 and 
contact strip 40 through lever 21, but there is no relative displacement 
between contact strip 40 and contact strip 30; when the bimetallic strips 
react differently to applied thermal loads, the motion of the contact 
strip 40 along X is limited by one of the bimetallic strips, such that the 
relative displacement between the contact strips cause an anticipating 
rotation of the lever. 
According to the invention, there is an adjustment part 15a, b, c, at the 
head 13 of each bimetallic strip 11, in this example formed by a disk (see 
figures) but which could also be a needle or another similar element. Each 
disk 15 cooperates through end 16 or 17 with a stop surface 31, 41 of a 
contact strip 30, 40 respectively. 
Before the adjustment operation, the disks are carried by contact strips in 
side recesses 35, 45 formed in the arms 32, 42 of the contact strips, the 
contact strips initially being assembled or formed in a single rectangular 
frame 30, 40, being kept at a small distance h above an upper horizontal 
edge 18 of the head 13 of the bimetallic strips and in contact with a 
vertical or inclined edge 19 of the head 13, so that they can slide freely 
on this edge, to be positioned at a height above it and so that they can 
move laterally without getting jammed. The frame 30, 40 includes weakened 
areas 36, 46 at two opposite corners, which will enable separation by 
cutting after adjustment. During calibration, following a predetermined 
temperature rise in the bimetallic strips, the bimetallic strips will bend 
and their heads will move along the X direction relative to frame 30, 40; 
at the obtained adjustment position, the center O of the disk coincides 
with the average plane P of the bimetallic strip, which is more or less 
offset from this plane (see FIG. 2). Disk 15 is then welded in this 
position, for example using a laser beam L, to edge 19 of the head; this 
edge is preferably inclined and free to move laterally (see FIG. 3) 
firstly so that the disk 15 can be reliably applied by gravity in contact 
with the bimetallic strip at the required welding location, and secondly 
that an inclined laser beam source L can be positioned away from the 
tripping device or the appliance in which the circuit breaker is placed. 
Recesses 35, 45 formed in contact strip arms 32, 42 include inclined edges 
37, 47 to support disks in contact with the inclined edges 19 of the 
bimetallic strips. As soon as the disks have been welded to the bimetallic 
strips, the two contact strips can be separated by cutting weakened areas 
36, 46, for example by laser or by any other means.