Method of manufacturing an electromagnetic relay

An electromagnetic relay comprises a coil bobbin of plastic material defining a protective tube, a contact chamber and a magnet chamber which together form a space that extends the entire length of the bobbin and is initially open at both ends. A permanent magnet is disposed in the magnet chamber, serving to seal one end of the space. This magnet has a surface exposed to the contact chamber and is made of a material activatable as a getter. A contact actuator is mounted to extend along the protective tube with a free end extending into the contact chamber. A pair of pole shoes each have a first end in proximity to the permanent magnet and a second end extending into the contact chamber. These second ends form fixed contacts for cooperating with the free end of the contact actuator. After assembly of these parts the space is subjected to a vacuum and an elevated temperature to drive off moisture and activate the getter. The vacuum is then replaced with an atmosphere of a protective gas, and the other end of the space is sealed with a closure.

The present invention relates to an electromagnetic relay and a method of 
manufacture thereof. 
More specifically the invention relates to a relay of the type comprising 
an actuator arranged within a protective tube formed in a coil bobbin. A 
pair of pole shoes have inner ends arranged in a contact chamber also 
formed in the bobbin and connected with the protective tube, the 
arrangement being such that these ends of the pole shoes are disposed on 
opposite sides of said actuator. The pole shoes also have outer ends 
disposed in the proximity of a permanent magnet arranged in a magnet 
chamber also formed in the bobbin, which latter is open at both ends. 
For the purpose of protecting the contacts of this type of relay, the 
terminals extending therefrom are embedded in insulating material. In 
order to ensure maximum reliability of the contacts and the maintenance of 
accurately predetermined contact resistance values, the contact chamber, 
prior to final assembly, is cleaned in an ultrasonic cleaning bath, 
degassed in a vacuum in the presence of heat and finally closed by means 
of a specially designed housing can. As it is relatively difficult to 
obtain access to the contact chamber, it is necessary to exercise special 
care in the cleaning with an ultrasonic cleaning bath. The necessity to 
close the contact chamber before the embedding operation tends to increase 
the cost of manufacture. Another economic disadvantage is to be found in 
the necessity of using electroplated contacts in view of the fact that, 
due to the manufacturing methods employed, surfaces to be gold- or 
rhodium-plated would have to be much larger than would be necessary for 
satisfactory operation of the contacts. 
Another disadvantage of the known relay resides in the fact that a 
relatively large distance between the ends of the pole shoes and the 
adjacent end of the coil chamber tends to promote the occurrence of stray 
losses which cause the efficiency of the relay to be reduced. While it is 
known to increase the efficiency of the magnet system of a relay by using 
larger pole surfaces, the use of larger pole surfaces tends to introduce 
adjustment difficulties or to shorten the creep paths at those ends of the 
current-carrying pole shoes which are adjacent the respective terminals. 
It is the object of the present invention to provide a relay in which the 
contact system is particularly easily accessible for cleaning purposes and 
which is capable of being manufactured on a mass-production scale without 
using potting compound, while being perfectly sealed from its environment 
in an economical manner. 
This object is achieved by providing according to the invention an 
electromagnetic relay comprising (a) a bobbin of plastic material defining 
therein a protective tube, a contact chamber and a magnet chamber that 
together form a space which extends the entire length of the bobbin and is 
open at both ends, (b) a permanent magnet disposed in the magnet chamber 
to seal one end of said space, (c) a contact actuator mounted to extend 
along the protective tube with a free end extending into the contact 
chamber, (d) a pair of pole shoes each having a first end disposed in 
proximity to the permanent magnet and a second end extending into said 
contact chamber, said second ends forming fixed contacts for cooperation 
with said free end of the contact actuator, (e) a coil mounted on the 
bobbin, (f) means activatable as a getter and disposed in said space, and 
(g) a closure sealing the other end of said space opposite said permanent 
magnet. 
The invention also resides in a method of manufacturing an electromagnetic 
relay comprising (a) assembling (i) a bobbin of plastic material defining 
therein a protective tube, a contact chamber and a magnet chamber that 
together form a space which extends the entire length of the bobbin and is 
open at both ends, (ii) a contact actuator mounted to extend along the 
protective tube with a free end extending into the contact chamber, (iii) 
a coil on the bobbin, (iv) a permanent magnet made of a material 
activatable as a getter and disposed in the magnet chamber to seal one end 
of said space while having a surface exposed to the contact chamber, and 
(v) a pair of pole shoes each having an outer end in the magnet chamber in 
proximity to the permanent magnet and an inner end extending into the 
contact chamber to form a fixed contact for cooperation with said free end 
of the actuator, (b) subjecting the space to a vacuum and an elevated 
temperature to drive off moisture and activate the getter, (c) replacing 
the vacuum with an atmosphere of a protective gas, (d) and sealing the 
other end of the space with a closure. 
The presence of a coil bobbin which is open at both ends makes it possible 
in a particularly easy and efficient manner to clean or degas the contact 
chamber and the interior of the protective tube. Such a cleaning operation 
will be necessary regardless of the type of relay involved in order to 
remove any contamination of the contacts such as organic deposits 
consisting of adhesives or substances evaporated from the coil bobbin 
during manufacturing operations. Such a cleaning operation is usually 
performed immediately prior to hermetic sealing of the contact chamber, 
for example by the insertion of the permanent magnet, and this cleaning 
operation is of considerable importance as regards the properties of the 
contacts. 
In order to ensure the development of large contact forces, the second ends 
of the pole shoes extend into the contact chamber where the stray flux is 
at a minimum, these ends of the pole shoes forming fixed contacts 
extending parallel to the actuator. It is, however, unnecessary to adjust 
the pole shoes, since they can be positively held in position by being 
embedded in the coil bobbin. To achieve this result, in a preferred 
embodiment, the first ends of the pole shoes are connected to respective 
terminals and are embedded in the walls of the magnet chamber in such a 
manner that each pole shoe has exposed portions on opposite sides thereof, 
the pole shoes being surrounded on both sides by the material of the coil 
bobbin, and the exposed portions being arranged in the magnet chamber in 
the vicinity of the respective end faces of the coil bobbin.

The relay shown in FIGS. 1-4 comprises a single-piece coil bobbin 1 made of 
a plastic material, a central cavity of such bobbin forming a protective 
tube 2 in which is arranged an actuator 3. Embedded in a right-hand bobbin 
flange 33 is a contact carrier 40 (FIG. 3) forming a terminal of a central 
contact. The contact carrier 40 comprises an end portion extending at an 
angle to its main portion, such end portion having exposed portions 41, 
41' (FIG. 4) to which root end portions 42, 42' (FIG. 1) of the actuator 3 
are secured as by spot welding. Another bobbin flange 33' has fixedly 
embedded therein two pole shoes 6 and 7 having inner portions which extend 
towards a central plane of the relay. Innermost end portions 18, 19 of 
these pole shoes extend parallel to one another and to the longitudinal 
axis of the bobbin 1 and are provided on their surfaces with a contact 
material 20 rolled into or onto said end portions. 
The protective tube 2, a contact chamber 8 and a magnet chamber 12 
initially form a continuous space extending the entire length of the 
bobbin, i.e., between its end faces 14 and 15, such space being open at 
these ends so that the contacts 20 and all the inner wall surfaces of the 
inner space are accessible for an efficient cleaning operation, which may 
be performed, for example, in an ultrasonic cleaning bath. The contact 
chamber 8 is closed and sealed by a permanent magnet 13 which is arranged 
within the bobbin flange 33' in abutment against a supporting surface 16 
to which the permanent magnet 13 is preferably connected by means of a 
piece of foil material 28 coated on both sides with an adhesive and shaped 
in such a manner that it extends substantially only over peripheral 
portions 29 of the permanent magnet 13. 
The pole shoes 6, 7 embedded in the bobbin flange 33' are located on 
opposite sides thereof with exposed portions 21, 22, 23, 24 which, as seen 
in FIG. 3 are offset in relation to one another in the longitudinal 
direction by a distance a. These exposed portions and the longitudinal 
spacing a are necessary accurately to define the transverse distance 
between the inner end portions 18, 19 of the pole shoes 6, 7 which are 
also provided with contact material 20 during the embedding thereof in the 
plastic material of the bobbin 1 which is manufactured by an injection 
moulding, pressing or injection pressing operation. During the embedding 
operation, the exposed portions 21, 23 of the pole shoes 6, 7 are engaged 
by laterally arranged slide members of a manufacturing tool via the 
exposed portions 22, 24 and 18, 19 of the pole shoes 6, 7, the result 
being that the respective portions are forced against a punch member 
inserted into the manufacturing tool from one end thereof, such punch 
member being adapted to determine with sufficient accuracy the profile of 
the contact chamber 8 and the magnet chamber 12 and hence the distance 
between the inner end portions 18, 19 of the pole shoes 6, 7 contributing 
to the attainment of the correct contact spacing. 
After the bobbin 1 has been provided with an energizing coil 43 and after 
such coil has been connected to coil terminals 5, 5', 5", the actuator 3 
is adjusted in relation to its root portions 42, 42', in such a manner 
that it may assume a rest position on one or other side, or in its 
centered position, depending on the contemplated use of the relay. 
Subsequent to this adjustment, the relay is simultaneously subjected to a 
vacuum of about 10.sup.-5 torr and a temperature between 100.degree. and 
150.degree. C. in order to drive off moisture retained by crystals and at 
the same time to activate as a getter the permanent magnet 13 which is 
made of barium ferrite or one or more rare earths. After this operation 
has been completed, the vacuum is replaced by a protective gas atmosphere 
which is at a normal pressure of about 760 torr, and a sealing cap 34 is 
applied to close the protective tube 2 and the contact chamber 8. Hermetic 
sealing of the bobbin cavity is preferably effected by means of an 
ultrasonic welding process or by means of a process in which a preheated 
plate is used. In order to enhance the effectiveness of the ultrasonic 
welding operation serving to connect the sealing cap 34 to the bobbin 
flange 33, such flange is provided on its side facing away from the 
sealing cap 34 with a peripheral shoulder 59 serving as an abutment for 
the anvil of the ultrasonic welding device. 
For the purpose of providing magnetic screening and of increasing the 
magnetic efficiency of the relay, there is provided a housing can 57 made 
of a ferromagnetic material for enclosing the relay. Such housing can 
being fixed in position by means of a potting compound 58, for example a 
casting resin. This arrangement tends to improve considerably the sealing 
effect and both the mechanical and functional stability of the relay. In 
cases in which the bobbin 1 is made of a thermoplastic material, it is 
convenient to provide recesses 31 surrounding the contact terminals 4, 4', 
4" and the coil terminals 5, 5.dbd., 5", such recesses being at least 
partially filled with potting compound 58, which is dimensionally more 
stable than thermoplastic materials, so that the accuracy with which the 
contact and coil terminals are held in position will not be impaired by 
any higher-than-average heating during soldering operations. 
Bobbin flange 33' has formed therein a space or cavity 60 which extends 
between the coil terminal 5 and the coil terminal 5' and is adapted to 
receive such circuit elements as diodes or resistors. Since in certain 
cases the getter action of the activated permanent magnet 13 may not be 
fully sufficient, and because it is necessary under all circumstances to 
provide a predetermined spacing between the permanent magnet 13 and the 
adjacent pole shoes, there is provided an additional cavity or space 30 
which can receive special type getters or molecular sieves. 
Instead of introducing a separate getter material or employing the 
permanent magnet as the getter, it is also possible to coat the inner 
walls of the bobbin 1, parts of which form the protective tube 2, with a 
getter material prior to insertion of the actuator 3; such a coating may 
be applied in a conventional manner using, for example, the evaporating 
method employed in the manufacture of electronic tubes. Such a coating 
will absorb gases exhaled by the plastic material and will thus enhance 
the dependability of the contacts. 
In the case of the relay diagrammed in FIG. 5 in which the actuator may 
assume two different contact engaging positions or a centered position 
between the two pole shoes 6, 7, the permanent magnet 13 is centrally 
arranged between these pole shoes, there being gaps c for the purpose of 
enhancing the electric insulation of the magnet. In a relay of the type 
shown in FIG. 3, which relay is designed for a rest position of the 
actuator on one side only, which relay can be provided with a normally 
open contact as shown in FIG. 6 or a normally closed contact as shown in 
FIG. 7, the distance b (FIGS. 3 and 6) between the permanent magnet 13 and 
the outer end portion 10 of the pole shoe 7, is larger than the distance 
c. In cases in which a relay is desired that has only a normally open 
contact as shown in FIG. 6, it is convenient to provide the pole surface 
of the inner end portion 19 of the pole shoe 7 with a sheet metal 
separator 27 having a thickness d to maintain the response of the relay 
stable for the entire life of the relay and to reduce adhesion between the 
actuator 3 and the pole shoe 7. In a relay of the type shown in FIG. 7 
having a normally closed contact, the thickness e of the layer of contact 
material is selected along similar lines. 
FIGS. 8 and 9 show the coil bobbin 1 formed as two positively 
interengageable halves 1', 1" capable of being welded together and forming 
part of a relay in which the contact terminals 4, 4', 4" and the coil 
terminals 5, 5', 5" remain connected together by transverse portions 36, 
36' until after embedding of said terminals in their respective bobbin 
halves. Before the bobbin halves 1', 1" are welded together, the 
transverse portions 36, 36' of the respective pre-cut terminal plates 35, 
35' are severed in planes 61, 61' indicated in FIGS. 8 and 9 by dot-dash 
lines. In the present case, the exposed portions 41, 41' serving as 
contact carriers are formed as parts of the contact terminals 4". 
In the plane separating the casing halves, the casing halves, the casing 
half 1" is provided with ridge-like projections 25, whereas the casing 
half 1' is provided with matching grooves 26 adapted to receive said 
projections. The projections 25 are so dimensioned that their cross 
section is smaller than that of the grooves 26. However, the height of the 
projections 25 is greater than the depth of the grooves 26, so that, 
during the operation of connecting the two bobbin halves together by means 
of an ultrasonic welding process, the ensuing deformation of the 
projections 25 will tend to compensate for unavoidable manufacturing 
tolerances of the bobbin halves. At it is of primary importance to 
establish an accurately defined travel s (FIG. 3) of the actuator 3, 
during the welding operation, there is inserted between the inner end 
portion 18 of the pole shoe 6 and the free end 9 of the actuator 3, which 
is in contact with the opposite inner end portion 19 of the pole shoe 7, 
an assembly gauge comprising a tongue having a thickness selected to 
determine the travel s of the actuator 3. In addition to compensating for 
manufacturing tolerances of the bobbin halves 1', 1", this arrangement 
provides for compensation of tolerances or deviations introduced by the 
thickness of the actuator, including the thickness of the contact material 
20. 
FIGS. 10-15 show a relay in which the coil bobbin 1 is formed as a 
so-called dual-in-line relay casing. Relays having their contacts arranged 
in a protective tube and embedded in dual-in-line casings are described, 
for example, in U.S. Pat. No. 3,575,678 issued Apr. 20, 1971 to W. F. 
Barton. In a relay of this type, use is made of a protective tube of glass 
carrying an energizing coil, the relay comprising terminals connected to a 
so-called relay carrier. The entire arrangement is embedded in a plastic 
material having a casing of the "dual-in-line" shape. In known relays of 
this type, it has been impossible to adjust the characteristic parameters 
to obtain a satisfactory cooperation between the energizing field and the 
field of the permanent magnet for the purpose of enabling the relay to be 
economically controlled by pulses, to operate the relay as a monostable or 
a bistable device, to obtain large contact forces with a low level of 
energizing power and to adjust the actuator in a central rest position. 
However, when a bobbin 1 forming a protective tube according to the present 
invention is used in a dual-in-line casing, it is possible to attain 
almost all the parameters or operating characteristics that may be 
required of a relay. In the present case, as shown in FIGS. 10-15, contact 
terminals 4, 4', 4" and coil terminals 5, 5', 5" are led out of the bobbin 
1 in lateral directions at a central plane and, after embedding in the 
bobbin, are all bent to extend in a common direction. This arrangement is 
typical of the "dual-in-line" style of construction. 
In all other respects, the relay of FIGS. 10-15 is designed substantially 
in the same manner as the embodiment shown in FIGS. 1-4. In order to 
permit the ends of the energizing coil 43 to be economically connected to 
the coil terminals 5, 5', 5", such terminals are provided with exposed 
portions 39 on both sides of the bobbin 1 at the points at which they 
extend from the bobbin, this arrangement greatly facilitating the 
establishment of connections by spot welding. In a similar manner, the 
contact carrier 40 is provided with exposed portions 41, 41' (FIG. 12) 
extending from a respective end face of the bobbin 1 and permitting spot 
welding thereto of the root portions 42, 42' of the actuator 3. The 
current-carrying pole shoes 6, 7 which are provided with fixed contacts 20 
are preferably spot welded to their associated contact terminals 4, 4' 
before being embedded in the bobbin 1. For the purpose of protecting the 
energizing coil 43, there are provided two preferably identical shell 
members 44, 44' which are adhesively interconnected or welded together in 
the plane in which the contact terminals and the coil terminals extend 
from the bobbin 1. If the transverse surfaces defining the chamber 
receiving the coil 43 and those on the bobbin flanges 33, 33' are given a 
conical shape, it is also possible to weld the shells 44, 44' to the 
bobbin flanges 33, 33'. The two shells may also be formed in such a manner 
that they cover the exposed portions 39, as shown in FIGS. 12 and 14. As 
an alternative to this arrangement, FIG. 15 shows a differently designed 
shell 62 surrounding the energizing coil 43 and shaped to match the 
external cross section of the bobbin flanges 33, 33' or forming a 
continuous shell surrounding the bobbin 1. In contrast to the embodiment 
of FIGS. 8 and 9, the coil terminals 4, 4', 4" and the contact terminals 
5, 5', 5" forming parts of the respective pre-cut terminal plates are of 
crooked shape along their portions to be embedded, in such a manner that 
they extend, for example, towards the exterior of the protective tube 2 
within the bobbin flange 33, separation of these terminals from the 
pre-cut terminal plates being effected after the bending operation. 
As an alternative to the embodiments shown in FIGS. 10-15, FIG. 18 shows in 
a cross section similar to FIG. 15 a relay comprising coil and contact 
terminals 5, 5' which, while they do not extend from the relay in a single 
plane, nevertheless for an arrangement typical of a dual-in-line 
structure. In this case, the space available for the magnet system and a 
continuous housing can 57 of ferromagnetic material can be more 
efficiently utilized. In addition, an actuator 3 of greater width may be 
used, such actuator being provided with a centrally located, 
longitudinally extending slot 63 permitting employment of twin contacts. 
For the purpose of positive location of mechanical stabilization and 
securement of the housing can 57, and of more efficient sealing, the 
hollow space between the housing can 57 and the relay body is filled with 
a potting compound 58. 
The relays described may be designed to afford a rest position of the 
actuator on one side or on both sides. When it is desired to obtain a 
relay in which the actuator 3 is capable of assuming a predetermined 
centered position, the arrangement of FIG. 17 can be adopted according to 
which supporting plates 46', 47' are positioned on opposite sides of the 
actuator 3, such supporting plates being urged by adjusting springs 45, 
45' against nose-like projections 48, 48' of opposite walls of a cavity 
containing the adjusting springs. The other ends of the adjusting springs 
45, 45' bear against secondary supporting plates 46, 47 which are in turn 
supported by side walls 49, 49' of the bobbin 1 or by adjusting members, 
such as adjusting screws 51, 51'. It is convenient in the present case, to 
select the thickness f of the nose-like projections 48, 48' slightly to 
exceed the thickness g of the actuator 3. Suitably shaped adjusting 
springs 45, 45' are shown in an isometric view in FIG. 16 and in the 
assembly in FIGS. 10-12. These adjusting springs comprise leaf springs 52, 
52', which are bent to S-shape and which are arranged in the vicinity of 
the free end 9 of the actuator 3. Both ends of each spring 52, 52' are 
provided with flanges 55, 55' extending at right angles in relation to the 
respective ends of each spring and are arranged at right angles in 
relation to one another; these flanges serve the same function as the 
supporting plates 46 and 46' shown in FIG. 17. The side walls 49, 49' of 
the cavity 50 receiving the adjusting springs have formed therein 
groove-like recesses 56, 56' adapted to receive the associated flanges 55 
of the two adjusting springs. An adjusting spring of the type just 
described need only be dropped into the cavity 50, sincel this spring, 
according to FIG. 16, is also laterally supported in relation to the inner 
walls of the bobbin flange 33 and in relation to the permanent magnet 13 
by its rigid flange 55 which is of slightly increased width as compared to 
the width of the flexible part of the spring. 
A force diagram applying to this arrangement is shown in FIG. 19. In FIG. 
19, the force P of the permanent magnet follows the pattern indicated by 
the associated symmetrical curve extending across the gap s in which the 
actuator 3 is disposed, this curve applying to the deenergized condition 
of the relay; the dotted line curve associated with the force P1 
illustrates the total magnetic force obtained with the relay in its 
energized condition. The curve associated with the force P2 indicates the 
force with which the actuator 3 opposes the magnetic force, and the curves 
associated with the force P3 illustrate the forces exerted by the two 
adjusting springs 45, 45'. The length of travel h beyond which the 
adjusting springs come into action is given as the difference between the 
thickness f of the nose-like projections 48, 48' and the thickness g of 
the actuator 3 on the other (h= f-g).