Noiseless electromagnet and a contactor using such an electromagnet

The electromagnet comprises a fixed magnetic circuit, a mobile magnetic circuit forming, with the fixed magnetic circuit, at least one air gap and a coil. The distance over which the mobile magnetic circuit travels with respect to the fixed magnetic circuit is limited by at least one working position stop determining the working position, this stop being provided with at least one working position damper.

The present invention relates to an electromagnet whose applications 
require noiseless operation, this electromagnet being able to form part of 
the most diverse devices and, in particular, of a contactor or 
contact-maker. 
Generally, it is known that the regulation of household heating apparatus 
at night as well as devices for controlling a high power electric current 
in operating rooms require the use of noiseless means. Now, it so happens 
that, for these types of use, the controlled power levels and the 
insulation requirements mean that static relays or contactors are not yet 
in a position to replace electromagnetic contactors. 
It is well known that, for such applications, electromagnets fed with 
direct AC current cannot be used because of the closure shocks and 
vibrations in the closed condition which still remain too high. 
So studies have been made on contactors with a DC supply (fed with a 
rectified and filtered AC current) whose drive torque is adapted as well 
as possible to the variations of the resisting torque during closing, 
which limits the increases in drive power and, therefore, closure shocks, 
French Pat. Nos. 2 260 176 and 2 406 885 give two examples of this 
adaptation to the variations of the resistance forces. 
Although very efficient, these solutions are still insufficient because 
more especially of the manufacture tolerances concerning the resistance 
forces and especially because of fluctuations in the supply voltages. 
Thus, arrangements made for guaranteeing operation under unfavourable 
conditions, cause when favourable conditions are present, an increase in 
energy at the end of closure which makes the closure shock sufficiently 
great from the auditive point of view for it to be troublesome. 
The aim of the invention is therefore to overcome these disadvantages by 
providing damping of this energy increase on closure as well as the 
increase in energy for the return. 
It provides therefore an electromagnet with DC supply, of the type 
comprising a fixed magnetic circuit, a magnetic circuit movable in 
translation and forming with the fixed magnetic circuit air gaps of 
variable width. 
This electromagnet is more particularly characterized in that it comprises 
at least two air gaps, and in that one of the faces of the magnetic 
circuits which define each of these two air gaps is provided with a 
damping element made from an amagnetic material serving as working stop, 
which limits the width of each of the air gaps of the electromagnet to a 
minimum value, in the working position. 
According to an advantageous characteristic of the invention, said damping 
elements may be formed from a molded piece made from silicon-coated 
elastomer.

With reference to FIGS. 1 and 2, the contactor has a conventional structure 
of a translation contactor comprising, inside a case 1: 
a fixed magnetic circuit 2, in the form of an E whose web 3 is fixed 
against a bottom plate 4 firmly secured to case 1, 
a mobile magnetic circuit 5, also in the shape of an E whose legs 6, 7 are 
aligned respectively with the legs 8, 9 of fixed magnetic circuit 2, the 
respective ends of legs 6, 7, 8, 9 of these two magnetic circuits being 
mutually facing each other and forming air gaps 10, 11, 
a coil 13 wound on a tubular carcase 14 and disposed in the volume between 
legs 6, 7, 8,9 of the fixed magnetic circuit 2 and of the mobile magnetic 
circuit 5, 
fixing means for fixing the carcase 14 of coil 13 to the fixed magnetic 
circuit 2, 
guide means for guiding the mobile magnetic circuit 5 in said carcase 14. 
a mobile contact holding assembly 15 mounted on the web 16 of the mobile 
magnetic circuit 5, and 
at least one return spring 17 disposed between the upper shoulder 18 of 
carcase 14 of coil 13 and the web 16 of the magnetic circuit 5. 
More precisely, in the example shown, the fixed magnetic circuit is secured 
in coil 13 by means of a cylindrical pin 19. Of course, the invention is 
not limited to such an arrangement. The fixed magnetic circuit 2, could, 
for example, be quite simply force fitted into the carcase 14 of coil 13. 
For guiding it, the mobile magnetic circuit 5 comprises a key 21 
cooperating with an axial groove 22 provided in the carcase 14 of coil 13. 
The shapes of air gaps 10 and 11 are determined at the design stage for 
adapting the law of variation of the drive force to the resistant force. 
Thus, in this example, the end of the central leg 9 of the fixed magnetic 
circuit has a V shaped recess 24, in which is engaged the end 25 of the 
central leg 7 of the mobile magnetic circuit 5 which accordingly has a 
substantially complementary convex V shape. These two complementary shapes 
24, 25 define a substantially V shaped air gap 11. 
Similarly, the ends of the two side legs 8 of the fixed magnetic circuit 2 
each comprise an outer chamfered face 26, 27 and the ends of the two side 
legs 6 of the mobile magnetic circuit 5 each comprise an inner chamfered 
face 28, 29, the outer chamfered faces 26, 27 of the fixed magnetic 
circuit 2 cooperating with the inner chamfered faces 28, 29 of the mobile 
magnetic circuit 5 so as to form two lateral air gaps 10 oblique with 
respect to each other. 
These shapes of the air gaps 10, 11 have the advantage of being readily 
reproducible for industrial mass production, because of the adoption of a 
technique for cutting out thin metal sheets assembled together by methods 
which are henceforth traditional (rivetting) for obtaining magnetic 
circuits with AC supply. 
As mentioned above, FIGS. 3 and 4 show the mobile assembly of the 
contactor, in which the mobile magnetic circuit 6 is connected to the 
contact holding assembly 15 by a securing pin 31. The return spring 17 is 
in the totally relaxed state. In the working position, it serves for 
returning the mobile assembly back to the rest position, which position is 
shown in FIGS. 1. 2 in which the upper face of the mobile contact holding 
assembly 15 comes to bear, at the end of travel, on an abutment surface 32 
provided on the upper wall of case 1, while balancing the contact forces 
(opening contact). 
Such as shown in FIG. 5, the fixed magnetic circuit 2 comprises two lateral 
grooves 33 serving for mounting it by snap fitting into the bottom plate 4 
of case 1. This bottom plate has a U shaped section surrounding the lower 
part of the fixed magnetic circuit 2 and whose legs comprise bosses for 
engagement in grooves 33. 
The means for damping the opening and closing shocks comprise: 
on the one hand, a rest position damper 34, made from a shock absorbing 
material for example from a silicon coated elastomer, fixed to the upper 
face of the mobile assembly 15 and which is consequently crushed against 
the abutment surface 32 provided on the upper face of case 1 when the 
mobile assembly returns to the rest position, and 
on the other hand, two working position dampers 35, also made from a 
resilient material, for example from silicon coated elastomer, fixed 
respectively to the two side legs 8 of the fixed magnetic circuit 2 and on 
which come to bear the ends of the side legs 6 of the mobile magnetic 
circuit 5 in the working position. 
These means are completed by bearing elements such as bosses 36, made 
preferably from a thermoplastic material, provided between the web 3 of 
the magnetic circuit 2 and the web of the bottom plate 4, which serve for 
eliminating the play between these two parts and which contribute to 
damping the closure shocks of the contactor. 
Such as shown in FIGS. 8 and 9, the rest position damper 34 is in the form 
of a plate made from a silicon coated elastomer formed in three parts 38, 
39, 40, rectangular in shape and connected together by connecting lugs 41, 
namely a central part 39 and two lateral parts 38, 40. The central part 39 
comprises a central recess 39' for fixing the damper 34 on the upper face 
of the mobile contact holding assembly 15 and two centering side flanges 
42. The side parts 38 and 40 may also each comprise a central centering 
and/or fixing bore 43. 
Of course, the invention is not limited to this particular form of the rest 
position damper 34; obviously, this particular form is only an adaptation 
of the invention to the forms of the mobile contact holding part 15 and 
all shapes of parts used for damping the return shock may be used within 
the scope of the invention. 
FIGS. 10, 11 and 12 show the detail of the working position dampers 35. 
These working position dampers 35, two in number in this example, are each 
formed of a ring having a rectangular section and made from a silicon 
coated elastomer obtained by molding. They are fitted onto two respective 
studs 45 provided on the outer faces of the side legs 8 of the fixed 
magnetic circuit 2, substantially at the base of the chamfered faces 26, 
27. These studs 45 form, with the ends of the side legs 6 of the mobile 
magnetic circuit, small lateral air gaps 10' distinct from the lateral air 
gaps which exist between the surface 6a and surface 45' (FIG. 6). 
These studs 45 are obtained by cutting out magnetic metal sheets at an 
appropriate angle 46 for facilitating the assembly of the rings forming 
dampers 35. 
The position and the thickness of these dampers 35 against which the end of 
legs 6 of the mobile magnetic circuit 5 come into abutment, in addition to 
the role of damper, also fulfil the anti-remanence function of the air 
gaps 10, 11, the size of these air gaps being determined by the thickness 
which the compressed elastomer assumes when the armature is applied 
thereagainst. The choice of a silicon coated elastomer results from the 
requirements of resistance of the anti-remanent damper to the working 
temperatures of the electromagnet, to the oils used for cutting the metal 
sheets and high mechanical endurance. Moreover, the non adhesion qualities 
(gumming) of such an elastomer are advantageous for guaranteeing in time 
separation of the mobile circuit should a cut off occur in the power 
supply of the electromagnet. It is clear that any magnetic material having 
mechanical damping properties and appropriate for the requirements of 
endurance and resistance to the environmental conditions may be used 
within the scope of the invention. 
FIG. 7 gives the operating laws for a contactor equipped with a damper in 
accordance with the invention. In this Figure which is a force F(N) 
diagram as a function of the travel of the mobile assembly and of the air 
gap 
curve C.sub.1 shows the drive force for the minimum condition guaranteeing 
closure, 
curve C.sub.2 represents the maximum resistance force related to the drive 
force shown in curve C.sub.1, 
curve C'.sub.1 shows the drive force under favourable closure conditions, 
curve C'.sub.2 shows the resistant force related to the drive force 
represented by curve C'.sub.1, 
the vertical of abscissa O corresponds to the end of travel without 
crushing of the dampers, 
the vertical V.sub.1 of abscissa 1 corresponds to closure of the main and 
additional contacts, 
the vertical V.sub.2 of abscissa 2 corresponds to the opening of the basic 
contacts, the additional contacts opening for a travel distance of 
abscissa V'.sub.2 slightly less than 2. 
Under unfavourable closure conditions (maximum resultant forces, minimum 
supply voltage) the difference between the positive energies (movement 
with drive force greater than the resistant force) and negative energies 
(resistant forces greater than the drive force overcome by the kinetic 
energy accumulated by the mobile assembly) is necessarily positive, 
otherwise closure of the contactor could not be guaranteed. 
This difference of the areas between curves 1 and 2, hatched in opposite 
directions depending on whether they are positive or negative, is equal to 
area A at the left of O of the travel distance. Thus, dampers 10, 11 are 
crushed (0.08 mm in this application) while counterbalancing the energy 
increase, which thus allows a resultant zero shock to be obtained. When 
extreme favourable conditions are present (curves C'.sub.1 and C'.sub.2), 
crushing of the working position dampers 10, 11 corresponds to the 
absorption of the energy shown in zone B at the left of O of the travel 
distance. It is obvious that it is necessary to take measures so that the 
variations in crushing dampers 10, 11 do not compromise the qualities of 
the contacts F (closure contacts), nor influence too much the separation 
values of the contactor. 
In this application, these conditions are fulfilled satisfactorily, since 
the overtravel of the contacts (about 1 mm) and of the longitudinal air 
gaps, without crushing the dampers 10, 11 (1 mm) remains large with 
respect to the crushing of the dampers 10, 11 (0.08 mm to 0.35 mm). Thus, 
it is evident that the shapes shown for dampers 10, 11 are only a 
particular application of the invention and that any specific adaptation 
remains within the scope of this latter. 
Thus, the contactor might for example comprise, as shown in FIG. 13 a 
central damper 50, formed from a molded V shaped part, made from a sheet 
of amagnetic resilient material and being engaged in the V shaped concave 
recess 24 of the central leg 9 of the fixed magnetic circuit 2 (or 
possibly, on the convex portion 25 of the central leg 7 of the mobile 
magnetic circuit 5). This solution may be used more especially in the case 
when it is not desirable to have the mechanical bearing surface of the 
mobile and fixed magnetic circuits 5, 2 on the lateral legs 6, 8 of these 
circuits. 
However, it should be noted that more generally three cases arise for 
location of the working position dampers: 
(a) solely in the air gap 11, 
(b) solely in air gap 10 and/or in the side air gaps, 
(c) both in air gap 11 and in air gap 10 and/or air gap 10'. 
Furthermore, in all the cases envisaged, it is always possible to provide, 
between all the slanted parts of armatures 27, 29; 26, 28, 24, 25, gaps 
filled with air or brass for overcoming the remanence effects.