Plunger type electromagnetic relay with arc extinguishing structure

An electromagnetic relay is provided which features an arc-extinguishing structure. This electromagnetic relay includes a pair of permanent magnets which are so arranged as to have their magnetic poles oriented diametrically opposite each other across a pair of movable contacts and a pair of stationary contacts for biasing electric arcs produced between the movable and stationary contacts into given spaces defined in a relay housing.

BACKGROUND OF THE INVENTION 
1. Technical Field of the Invention 
The present invention relates generally to an electromagnetic relay, and 
more particularly to an improved arc-extinguishing structure of an 
electromagnetic relay which is designed to bias an electric arc produced 
in a contact gap into a given space defined in a relay housing. 
2. Background Art 
A plunger type electromagnetic relay is known in the art wherein a pair of 
movable contacts is moved by a common movable contact retainer according 
to linear displacement of a plunger of a solenoid assembly. 
Japanese Patent First Publication No. 59-14219, filed on Jul. 16, 1982, 
teaches, in FIGS. 3 and 4, an arc-extinguishing structure of a plunger 
type electromagnetic relay having permanent magnets and pairs of magnetic 
metal strips. The permanent magnets are mounted, opposite a contact gap 
across movable contact retainers, perpendicular to a center line of the 
relay in a direction offset from the center line. The pairs of the 
magnetic metal strips are attached to both ends of the permanent magnets, 
respectively, to work as magnetic poles for producing an arc-extinguishing 
magnetic field across the contact gap. 
The above publication further discloses, in FIGS. 6 and 7, an alternative 
arc-extinguishing structure which has permanent magnets, mounted inside 
movable contact retainers, oriented magnetically in a direction 
perpendicular to the permanent magnets discussed above for producing an 
arc-extinguishing magnetic field across a contact gap. 
The former structure shown in FIGS. 3 and 4 encounters the drawback in that 
the permanent magnets need to be fixed outside the movable contact 
retainers, thus resulting in an increased size of the relay in a 
lengthwise direction. This will lead to a bulk structure of the relay. 
Additionally, it is difficult to mount each pair of the magnetic metal 
strips so as to extend from both sides of the permanent magnet across the 
movable contact retainer and the contact gap. Usually, such small 
component parts are difficult to install in a relay housing using screws 
because it is inconvenient assembling operation in a narrow space. It is 
also infeasible to bond the magnetic metal strips to, for example, 
supports extending from an inner wall of a resin-made housing for the 
inconvenience of assembly and vibration resistance. 
It is, therefore, most useful to form metal strip installation cavities in 
a resin-made housing in dice-casting for ease of securement of the 
magnetic metal strips. It is, however, difficult to form such cavities in 
the resin housing, especially, because it becomes difficult to remove the 
resin housing from a die after casting. Additionally, if the magnetic 
metal strips are not provided on both sides of the permanent magnets, the 
magnetic flux of the permanent magnets will partially act on the contact 
gap, resulting in reduced magnetic field across the contact gap so that an 
arc cannot be extinguished completely. 
Further, the later structure, taught in the above publication, shown in 
FIGS. 6 and 7 has the permanent magnets inserted into the U-shaped movable 
contact retainers, respectively. This arrangement, however, assumes a 
decreased strength of magnetic field equal to that produced by the 
structure shown in FIGS. 3 and 4 from which the magnetic metal strips are 
omitted, thus resulting in greatly decreased arc-extinguishing ability. 
U.S. Pat. No. 4,367,448 (corresponding to Japanese Patent First Publication 
No. 1-45688), file on Jun. 26, 1981, to Nishizako, discloses an 
arc-extinguishing magnetic structure of an electromagnetic contactor which 
has permanent magnets mounted above outer two of three contact retainers 
arranged in parallel to extinguish arcs with the magnetic flux produced by 
the permanent magnets. These permanent magnets are oriented to have 
opposite magnetic poles face each other to establish a magnetic flux for 
extinguishing an arc produced in a contact gap formed between central 
contacts. This arrangement is magnetically identical with that taught in 
the above discussed publication No. 59-14219, but different therefrom in 
that magnetic fluxes produced by the two permanent magnets act on one 
contact only. 
SUMMARY OF THE INVENTION 
It is therefore a principal object of the present invention to avoid the 
disadvantages of the prior art. 
It is another object of the present invention to provide an electromagnetic 
relay with a simple arc-extinguishing structure which is designed to bias 
an electric arc produced in a contact gap into a given space defined in a 
relay housing. 
According to one aspect of the present invention, there is provided an 
electromagnetic relay which comprises a movable contact retainer having 
disposed thereon a pair of movable contacts, a stationary contact retainer 
having disposed thereon a pair of stationary contacts at a given interval 
away from the movable contacts, a magnetically driving means for 
selectively driving the stationary contact retainer to bring the 
stationary contacts into engagement with and disengagement from the 
movable contacts, and a pair of permanent magnets having magnetic poles 
oriented opposite each other across the pair of the movable contacts 
retained on the movable contact retainer. 
According to another aspect of the present invention, there is provided an 
electromagnetic relay which comprises a movable contact retainer having 
disposed thereon a pair of movable contacts, a stationary contact retainer 
having disposed thereon a pair of stationary contacts at a given interval 
away from the movable contacts, a magnetically driving means for 
selectively driving the stationary contact retainer to bring the 
stationary contacts into engagement with and disengagement from the 
movable contacts, and a pair of permanent magnets having magnetic poles 
oriented, in alignment with a current flow through the movable contact 
retainer, diametrically opposite each other across the pair of the movable 
contacts retained on the movable contact retainer. 
In the preferred mode of the invention, the magnetically driving means 
includes a solenoid assembly and a plunger. The plunger is connected to 
the movable contact retainer. The solenoid assembly is energized to move 
the plunger to move the movable contacts into engagement with the 
stationary contacts. A housing is further provided which is connected to 
the solenoid assembly and defines therein a working chamber within which 
the movable contact retainer is disposed. 
The solenoid assembly includes a magnetic coil wound in the vicinity of an 
outer peripheral surface of the plunger and a cylindrical yoke, receiving 
therein the magnetic coil, constituting part of a stationary magnetic 
circuit of the solenoid assembly. 
The working chamber has arc spaces to which electric arcs produced between 
the movable and stationary contacts are biased by magnetic forces of the 
permanent magnets, respectively. Each of the .arc spaces is so defined in 
the housing as to extend over a contact gap in a width direction of the 
movable contact retainer. 
The housing is formed with a resin material in cup-shape and has permanent 
magnet storage cavities formed in an end surface of a side wall thereof. 
The movable contact retainer is formed with a strip member which retains 
thereon the movable contacts at a given distance away from each other in a 
lengthwise direction. The movable contact retainer hats side portions 
curved outward from the movable contacts in a direction away from the 
stationary contact retainer. 
The stationary contact retainer is formed with a strip member which retains 
thereon the stationary contacts at a given distance away from each other 
in a lengthwise direction. The stationary contact retainer has side 
portions curved outward from the stationary contacts in a direction away 
from the movable contact retainer. 
An arc-resistant member is further arranged to receive an electric arc, 
produced in the contact gap, biased by the magnetic forces of the 
permanent magnets. The arc-resistant member is made of a ceramic material. 
According to a further aspect of the present invention, there is provided 
an electromagnetic relay which comprises a relay housing, a movable 
contact retainer having disposed thereon a pair of movable contacts, a 
stationary contact retainer having disposed thereon a pair of stationary 
contacts with a given contact gap between itself and the movable contacts, 
a magnetically driving means for selectively driving the stationary 
contact retainer to bring the stationary contacts into engagement with and 
disengagement from the movable contacts, pairs of permanent magnets 
disposed within the relay housing, each pair being arranged to have 
magnetic poles, oriented opposite each other across one of contact pairs 
composed of the movable contacts and the stationary contacts for biasing 
an electric arc produced in the contact gap in a given direction, and an 
arc-resistant member provided in the relay housing for cooling an electric 
arc, produced in the contact gap, biased by the permanent magnets.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Prior to describing an electromagnetic relay of the present invention, a 
comparative example of a plunger type electromagnetic relay will be 
discussed below with reference to FIG. 1 to 4. 
The plunger type electromagnetic relay 100 generally includes a solenoid 
assembly 1 and a switching assembly S mounted on the solenoid assembly. 
The solenoid assembly 1 includes a cup-shaped frame or yoke 11 and an 
electromagnetic coil 13. The yoke 11 has a bracket 10 attached to its 
bottom for mount on an electric automobile, for example. The coil 13 is 
wound around a bobbin 12 disposed coaxially within the yoke 11. 
An annular plate 14 made of magnetic material is fitted into an opening end 
of the yoke 11 and staked on an upper end of the bobbin 12 coaxially 
therewith. A stationary cylindrical core 15 made of magnetic material is 
inserted into the bobbin 12 in engagement with the bottom of the yoke 11. 
A cylindrical magnetic plunger 17 functioning as an armature is also 
inserted into the bobbin 12 above the core 15. 
Interposed between bobbin 12 and the peripheral surface of the stationary 
core 15 is a return spring 16 which is mounted in shoulder portions formed 
on an upper end portion of the stationary core 15 and a lower end portion 
of the plunger 17. The return spring 16 urges the plunger upward, as 
viewed in the drawing. An insulating bush 18 made of a resin bar is so 
fitted into a recessed portion formed in a central portion of the upper 
surface of the plunger 17 as to extend vertically along the center line of 
the relay 100. 
The switching assembly S includes a resin-made box-like housing 2 and a 
resin-made annular insulator 3. The housing 2 engages through its bottom 
the insulator 3 so that an opening of the housing is shielded by the 
insulator 3 except a central portion thereof. The housing 2 and the 
insulator 3 are, as shown in FIG. 2, fixed on the plate 14 using screws 
20. 
The housing 2 has formed therein a box-like working chamber R into which 
the insulating bush 18 of the solenoid assembly 1 is inserted along the 
center line of the relay 100. The housing 2 also has a cylindrical stopper 
21 extending downward from a central portion of an inner wall. Arranged 
between the stopper 21 and the insulating bush 18 is a movable contact 
retainer 4 which is urged against the stopper 21 by the return spring 16 
through the plunger 17 and the insulating bush 18. 
The movable contact retainer 4 is formed with a strip member made of a good 
conductive material, and oriented horizontally, as viewed in FIG. 1. A 
pair of movable contacts 40 is mounted on a bottom surface of the movable 
contact retainer 4 at a given interval away from each other. The contact 
retainer 4 also has both end portions curved upward with a preselected 
curvature to form arc runners 41. A coil spring 5 is wound around the 
stopper 21 to bias the movable contact retainer 4 downward. 
Formed in the upper surface of the insulator 3 exposed to the working 
chamber R is a pair of recessed portion elongated horizontally into which 
a pair of stationary contact retainers 6 is inserted partially in tight 
engagement therewith. Each of the stationary contact retainers 6 is made 
of a conductive strip member, and has mounted on its end a stationary 
contact 60 in vertical alignment with a corresponding one of the movable 
contacts 40 with a given air gap g (i.e., contact gap). An inner portion 
of the insulator 3, as shown in FIG. 1, projects toward the movable 
contacts 40, on which the end portions of the stationary contact retainers 
6 bearing the stationary contacts 60 are placed. An outer portion of each 
of the stationary contact retainers 6 is bent to form an arc runner 61 
extending horizontally. 
The working chamber R includes contact chambers R1 and R2 and an axial bore 
chamber R3. The contact chambers R1 and R2 have disposed therein two 
contact pairs each composed of the movable contact 40 and the stationary 
contact 60. The axial bore chamber R3 receives therein the insulating bush 
18. Each of the contact chambers R1 and R2 forms recessed portions Rm 
arranged, as can be seen in FIG. 2, opposite each other across the movable 
contact retainer 4 and the fixed contact retainers 6. Each of the recessed 
portion Rm opens downward to define a permanent magnet storage cavity 
within which a permanent magnet 7 is disposed tightly. The permanent 
magnets 7 function as an arc-extinguishing means. 
The permanent magnets 7 are formed with a disc member, and so arranged 
across the contact gap as to orient their poles magnetically opposite each 
other. Specifically, the north poles of the upper side magnets 13, as 
viewed in FIG. 2, face the south poles of the lower side magnets 13. 
The permanent magnets 7 are also physically oriented so that the center 
line C.sub.1 of each of the permanent magnets 7, as shown in FIGS. 1 and 
2, may be offset by a given interval X from the center line C.sub.2 of 
each of the movable contacts 40 and the stationary contacts 60 outward, or 
toward the arc runners 41 and 61. In this comparative example, the center 
line C.sub.1 of each of the permanent magnets 7 extends through the 
outermost portion of the periphery of each of the movable contacts 40. 
Terminals 81 and 82, as shown in FIG. 2, are connected to both ends of the 
coil 13 for power supply, and supported by terminal supports 83 and 84 
which extend upward from the bobbin 12 through bores formed in the 
insulator 3. 
In operation, the supply of dc current to the coil 13 causes a stationary 
magnetic circuit composed of the yoke 11, the plate 14, and the stationary 
core 15 to be magnetized, thereby bringing the plunger 17 into engagement 
with the stationary core 15 against a compression force of the return 
spring 16. The movement of the plunger 17 causes the movable contact 
retainer 4 to be pulled downward with the aid of a spring force of the 
coil spring 5 so that the movable contacts 40 engage the stationary 
contacts 60 for establishing electrical communication between the 
stationary contact retainers 6 and the movable contact retainer 4. 
When the current is withdrawn from the coil 13, it will cause the 
magnetization of the stationary magnetic circuit to disappear, releasing 
the return spring 16 to lift the plunger 17 upward. This causes the 
movable contact retainer 4 to be displaced away from the stationary 
contact retainers 6 against a compression force of the coil spring 5, 
thereby bringing the movable contacts 40 into disengagement from the 
stationary contacts 60 to break both the stationary contact retainers 6 
electrically. The upward movement of the: movable contact retainer 4 is 
restricted by the stopper 21 to maintain the contact gap constant. 
When the movable contacts 40 disengage from the stationary contacts 60, 
electric arcs will be generated therebetween. These arcs are then biased 
outward in a lateral direction, as viewed in FIG. 1, by the activities of 
Lorentz forces produced by magnetic fields of both the permanent magnets 
7. Since intervals between the arc runners 41 and 61 of the movable 
contact retainer 4 and the stationary contact retainers 6 formed outside 
the contact pairs 40 and 60 increase gradually in outward directions, 
spaces in which arc currents, or discharges are generated are increased, 
thereby reducing the density of ions per unit space so that the arcs are 
extinguished quickly according to increases in the intervals between the 
arc runners 41 and 61 caused by the disengagement of the movable contact 
retainer 4 (see FIG. 4). 
Additionally, the centers of the permanent magnets 7 are, as discussed 
above, shifted by the interval X from the centers of the contact pairs 40 
and 60 toward the arc runners 41 and 61. This arrangement provides for 
strong magnetic fields acting on the arcs. In this comparative example, 
each of the permanent magnets 7 is so arranged that the center line 
C.sub.1 may intersect a line extending through an intermediate point 
between the outer end of each of the arc runners 41 and the inner end of 
each of the movable contacts 40. 
The assembling operation of the above electromagnetic relay 100 will be 
discussed below. 
First, the coil 13 wound around the bobbin 12 is disposed within the yoke 
11 mounted on the bracket 10. The stationary core 15, the return spring 
16, and the plunger 17 with the insulating bush 18 are disposed, in 
sequence, inserted into the bobbin 12 and then the plate 14 is staked on 
the yoke 11. 
Subsequently, the insulator 3 having disposed thereon the stationary 
contact retainers 6, the movable contact retainer 4, and the coil spring 5 
are mounted, in sequence, on the yoke 11, and then covered by the housing 
2 having therein the permanent magnets 7. Brackets 22 of the housing 2 and 
outer flange portions 3a of the insulator 3 are, as shown in FIG. 3, fixed 
on outer flange portions 14a of the plate 14 using screws 20 to complete 
the assembly. 
The inner ends of the stationary contact retainers 6, as can be seen in 
FIG. 1, project inside the opening of the insulator 3 for preventing the 
plunger 17 from being dislodged out of the opening of the insulator 3. 
This requires the stationary contact retainers 6 to be assembled after 
installation of the plunger 17. Thus, if the movable contact retainer 4 is 
inseparably secured on the plunger 17 to form a plunger assembly, as found 
in some conventional structures, it is necessary to incorporate the 
stationary contact retainers 6 into the housing 2 from lateral directions, 
respectively. 
In this comparative example, the movable contact retainer 4 is separate 
from the insulating bush 18 attached to the plunger 17 and detachably 
mounted thereon. Thus, the stationary contact retainers 6 may be fitted 
downward into the open grooves of the insulator 3 after installation of 
the plunger 17. Alternatively, the stationary contact retainers 6 
premounted on the insulator 3 may be assembled after installation of the 
plunger 17. The movable contact retainer 4 may subsequently be mounted on 
the insulating bush 18. This assembling process provides for ease of 
assembling operations, and is suitable for automatic assembly. 
Referring to FIGS. 5 and 6, there is shown a plunger type electromagnetic 
relay 200 according to the present invention. 
The electromagnetic relay 200 has substantially the same construction as 
that of the above discussed electromagnetic relay 100 except for an 
arrangement as discussed below and explanation of the same construction in 
detail will be omitted here. 
The electromagnetic relay 200 includes a pair of permanent magnets 7 which 
are disposed, respectively, within cavities 70 formed in a side wall of a 
housing 2 which are diametrically opposed to each other across a movable 
contact retainer 4 so that the permanent magnets 7 may be arranged outside 
a pair of movable contacts 40 and a pair of stationary contacts 60 mounted 
on stationary contact retainers 6. The permanent magnets 7 are so oriented 
that opposite magnetic poles face each other. Specifically, the north pole 
of the left-hand side magnet 7, as viewed in the drawings, is arranged 
opposite the south pole of the right-hand side magnet 7 along the 
direction of current flow through the movable contact retainer 4. Thus, 
the magnetic flux produced between the north and south poles of the 
permanent magnets 7 acts on both contact gaps between the movable contacts 
4 and the stationary contacts 60, and the magnetic flux produced by each 
of the permanent magnets 7 itself is also exerted on the adjacent contact 
gap. This will produce an arc-extinguishing magnetic flux stronger than 
that produced by an arrangement having permanent magnets, only one for 
each contact gap. With these arrangements, electric arcs, or discharges 
travel from the contact pairs 40 and 60 in a horizontal direction. Thus, 
if the arcs are biased backward by some back current, the surface of an 
insulating bush 18 will not be deteriorated. Particularly, an electric 
automobile is commonly driven by a motor and charged for regeneration. 
During the regenerative charging, the current flows in a reverse direction 
to that during the traveling of the automobile. However, with the above 
mentioned arrangements of the electromagnetic relay 200, arcs are drawn 
somewhere in arc chambers or spaces Ra defined, as shown in FIG. 6, across 
a stopper 21 in the housing 2, even if the current flows through the relay 
200 in any directions. This prevents movable parts of the relay 200 from 
being welded undesirably. The arc spaces Ra are so formed as to extend 
over the contact pairs in a width direction of the movable and stationary 
contact retainers 4 and 6. 
The movable contact retainer 4 and the stationary contact retainers 6 may 
have, as shown in FIG. 7, arc runners 45 and 65. FIG. 7 illustrates cross 
sections of the movable and stationary contact retainers 4 and 6 in width 
directions thereof. The arc runners 45 and 65 are formed by bending both 
side portions of the movable and stationary contact retainers 4 and 6 
outward from the movable and stationary contacts 40 and 60 in opposite 
directions away from each other. This arrangement enhances the 
arc-extinguishing ability. The symmetrical geometry of the arc runners 45 
of the movable contact retainer 4 also serve to keep a dynamic balance of 
the movable contact retainer 4 during operation of the relay. 
FIG. 8 shows a modification of the electromagnetic relay 100 of the 
comparative example as described above with reference to FIGS. 1 to 4, and 
is different from the relay 100 only in an arrangement as discussed below. 
Explanation of the same arrangements in detail will be omitted here. 
The shown electromagnetic relay 300 has arc-resistant plates 99 disposed 
within plate storage cavities 29 in tight engagement therewith. The 
arc-resistant plates 99 are made of a ceramic material. The plate storage 
cavities 29 are so formed in an inner wall of a housing 2 as to orient 
inner surfaces of the arc-resistant plates 99 around the movable contact 
retainer 4 (i.e., a contact gap). The platte storage cavities 29 are 
opened downward, as viewed in the drawing, for facilitating easy removal 
from a die after casting. 
With the above arrangements, arcs biased by the permanent magnets 7 in a 
direction perpendicular to the drawing collide against the arc-resistant 
plates 99 so that they are cooled effectively. This prevents the 
deterioration, carbonization, and reduction in insulation of the 
resin-made housing 2. 
The above discussed arrangements may be used with the electromagnetic relay 
200 of the first embodiment, as shown in FIGS. 5 and 6. In this case, it 
is preferable that the plate storage cavities 29 be formed in an inner 
wall of the housing 2 around the arc chambers Ra. 
While the present invention has been disclosed in terms of the preferred 
embodiment in order to facilitate better understanding thereof it should 
be appreciated that the invention can be embodied in various ways without 
departing from the principle of the invention. Therefore, the invention 
should be understood to include all possible embodiments and modification 
to the shown embodiments which can be embodied without departing from the 
principle of the invention as set forth in the appended claims.