Electromagnetic relay

Abstract: An electromagnetic relay includes a coil assembly having a permanent magnet arranged so that one of its magnetic poles contacts the centre of a U-shaped core on which a coil is wound, an armature assembly in which the ends of an armature are arranged opposite to respective ends of the core, hinge springs enable the ends of the armature to come into contact with or be separated from the respective ends of the core in a seesaw movement, and movable contact springs cooperate with the seesaw movement of the armature, and in which the armature, the hinge spring and the movable spring are integrally fixed with an insulating moulded member, an insulating base having a box-like shape with an opening on the top thereof, stationary contact terminals having stationary contacts to oppose the movable contacts of the movable contact springs and common terminals for connection to one end of the hinge springs when the coil assembly is placed within the opeing and when the armature assembly is arranged in such a manner that the other magnetic pole of the magnet acts as a supporting point for the seesaw movement of the armature.

Description: BACKGROUND OF THE INVENTION This invention relates to an electromagnetic relay of a flat configuration with a lower height. Description of the Prior Art An example of prior art electromagnetic relays of this type is explained by referring to FIGs. 1A and 1B. The relay comprises an insulating base member 40 serving as a lower coil spool, two exterior lead terminals 43 of a magnetic member having stationary electric contacts 41 and permanent magnets 42 fixed thereon, and a common terminal 44 of a non-magnetic member. The outer lead terminals 43 and the common terminals 44 are fixed on the insulating base member 40. Both ends of the external lead terminals 43 are opposed to both ends of a seesaw-movable armature 45, and a movable contact spring 47 with movable electric contacts 46 is fixed above the armature 45. Two hinge springs 48 of the spring 47 are fixed on the common terminals 44, and an insulating cover 49 serving as an upper coil spool is fixed on the base member 40 to wind a coil 50. An example of relays having the above-mentioned structure is disclosed, for instance in U.S.P. No. 4,342,016. However, the above-described conventional electro-magnetic relay is detrimental in its structure concerning the following points: (1) Since the armature 45 is directly excited by the coil 50, a space is required within the winding portion of the cover 49 for allowing movement of the armature 45, thereby failing to achieve higher coil magnetization efficiency. (2) Since leakage magnetic flux is large and the magnetic flux path is not closed enough, a higher magnetic circuit efficiency cannot be attained. (3) After winding of the coil 50 is completed, there are no other means to adjust sensitivity of the relay than adjustment of magnetization. In European Patent Application No. 118715, published on September 19 1984, and European Patent Application No. 196022, published on October 1 1986, there were proposed polarised relays with rocking armatures. An arrangement which will be described below has as features a relay which is less subject to the above-mentioned problems encountered in the prior art, which can effectively utilize generated magnetic fluxes and improve the coil magnetization efficiency, and which can be driven at higher sensitivity and low power consumption, in addition to having a flat configuration so as to reduce the height in packaging, and providing an electromagnetic relay adjustable in sensitivity such as in spring load adjustment even after it is assembled. Still another object of this invention is to provide an electromagnetic relay having a higher reliability in electric contacts. In an arrangement which will be described below an electromagnetic relay includes: a coil assembly having a permanent magnet placed in a manner to make one of the magnetic poles contact with the center of a U-shaped core which is wound with a coil; an armature assembly including an armature having both ends of oppose both ends of said core, hinge spring for supporting a seesaw movement of the armature as both ends thereof come to contact with or separate from both ends of the core respectively, and movable contact springs cooperating with the seesaw movement of said armature, the armature, the hinge spring and the movable spring being integrally fixed with an insulating molded member; and an insulating base having a box like configuration with an opening on the top thereof and including stationary contact terminals having stationary contacts to oppose movable contacts of said movable contact springs and common terminals to be connected to one end of said hinge springs, when said coil assembly is placed within said opening and when said armature assembly is arranged in a manner so that the other magnetic pole of said magnet acts as a supporting point for the seesaw movement of said armature. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and features of this invention will become clearer from the detailed description when taken in conjunction with the attached drawings in which: FIGs. 1A and 1B are vertical sectional and plane views respectively to show a prior art electromagnetic relay; FIG. 2 is a perspective view to show an embodiment of this invention; FIG. 3 is an exploded view of FIG. 2; FIGs. 4A to 4C are explanatory views of the operation principle of the relay shown in FIG. 2; FIGs. 5A and 5B are views to show the contact state and separation state between the armature and the core end shown in FIG. 3; FIGs. 6A and 6B are a partially cut-out perspective view and a sectional view respectively to show details of the coil spool shown in FIG. 3; FIG. 7 is a perspective view to show another example of the coil spool shown in FIG. 3; FIGs. 8A and 8B are a perspective view and a vertical sectional view respectively to show details of the embodiment of FIG. 3; and FIG. 9 is a perspective view to show another embodiment of the invention. In the drawings, the same reference numerals denote the same structural elements. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGs. 2 and 3, an embodiment of the invention comprises a coil assembly 1, an armature assembly 2, an insulating base 3 and a cover 4. The coil assembly 1 comprises a magnetic iron core 10 of the shape of a letter U, a coil spool 11 formed by insert-molding the core 10, a coil 12 externally wound around the spool 11, and a permanent magnet 13. Projections 101 and 102 are formed on both sides of the two ends of the U-shaped core 10. The magnet 13 is inserted into a hole 112 of a central flange 110 of the spool 11, and one of the magnetic poles (lower end) is fixed at the center of the core 10. Two pairs each of coil terminals 113 are provided on flanges 111 on both ends of the spool 11. The armature assembly 2 comprises an armature 20 having a flat plate form of the magnetic member, an insulating molded member 21 formed by molding the armature 20 at the center thereof, and two electrically conductive spring members 22, 23 respectively provided with movable contact spring sections 221, 231 having movable electric contacts 223 and 233 on both sides and hinge spring sections 222 and 232 of a crank form. Two notches 201, 202 are formed on both ends of the armature 20 in the longitudinal direction so as to correspond to the shapes of the projections 102, 103 of the core 10. The spring members 22, 23 are fixed on both sides of the armature 20 with the molded member 21 made of insulating resin such as a plastic material to hold the armature 20 and spring members 22, 23 integrally. The armature 20 is insulated from the members 22 and 23. The base 3 comprises a flat box-like member with an opening on the top thereof. The base 3 is provided substantially at four corners thereof with four pairs of stationary contact terminals 30 through 33 respectively having electric contacts (stationary contacts) 301, 311, 321, 331, four coil terminals 34 through 37 and two common terminals 38, 39. The coil assembly 1 is fixed to the base 3 internally with a material such as adhesive, while the coil terminals 113 of the spool 11 are fixed to the coil terminals 34 through 37 of the base 3 by soldering, etc. The armature assembly 2 is placed from above so that the center lower surface of the armature 20 comes to contact with the upper magnet pole of the magnet 13. The ends of the hinge spring sections 222 and 232 are mounted by soldering, etc. to the fixing sections 381 and 391 of the common terminals 38 and 39 of the base 3 respectively. When the cover 4 (FIG. 2) is placed from above, the above-mentioned members 1, 2, 3 and 4 form an electromagnetic relay. In this state, the armature 20 can move on the upper end of the magnet 13 upward and downward due to a seesaw action, and the movement is supported with elasticity given by the hinge spring sections 222 and 232 fixed on the common terminals 38, 39 of the base 3 on the ends thereof. The operational principle of the relay will now be described referring to FIGs. 4A through 4C. As described in the foregoing, a permanent magnet 13 is provided at the center of the inside of the iron core 10. On both ends 10a and 10b of the core 10 are positioned ends 20a, 20b of the armature 20 to oppose each other in a manner to allow the seesaw movement. In FIG. 4A showing the state when the coil 12 is not excited, the armature 20 is attracted to the side of the core 10a by the magnetic flux ₁ generated from the magnet 13. In FIG. 4B showing the state when the coil 12 is excited, the magnetic flux ₀ generated on the core 10 by excitation overcomes the magnetic flux ₁ on the side of the armature end 20a while the magnetic flux ₀ is added to the magnetic flux ₂ of the magnet 13 on the other side of the armature end 20b. Therefore, the armature 20 is made to swing clockwise around the upper end of the magnet 13 to cause the armature end 20b and the core 10b to contact each other. At this state, even if the excitation from the coil 12 is suspended as shown in FIG. 4C, the armature 20 becomes attracted toward the core end 10b with the magnetic flux ₂ of the magnet 13. When the direction of the electric current of the coil 12 is reversed, the state is inverted to become that shown in FIG. 4A. The above-mentioned movement indicates a self-holding-type (bistable-type) relay. Since the movable contact springs 221 and 231 are integrally formed with the armature 20 along with the seesaw movement, movable contacts 223 and 233 and stationary contacts 301, 311 (and 321, 331) come to contact with or become separated from each other to switch electric circuits. The displacement of the armature 20 on the end which is remote from the core 10 largely affects dielectric strength between electric contacts. More particularly, the larger the gap between the armature end and the core end, the larger becomes the dielectric strength. However as the gap increases, the magnetic reluctance increases to increase leakage flux on the attraction side of armature 20 when the armature state is about to be inverted. This induces a drastic drop of magnetic attraction force, and the insufficient magnetic attraction reduces the sensitivity of the relay. The problem is solved in this embodiment by the provision of the notches 201, 202 of the armature 20 and the projections 101, 102 of the core 10. More particularly, in the structure of this embodiment, when the armature end 20a is contact with the core end 10a (FIG. 5A), the magnetic flux  passes through the lower side of the end 20a (contact surface) where the magnetic reluctance is minimum while when the armature end 20a is separated from the core end 10a (FIG. 5B), the magnetic flux  is likely to pass from projections 101, 102 to the side of the end 20a. Even when the armature end 20a is separated from the upper surface of the core end 10a (contact surface), the gap x between the side surface of the armature end 20a and the projections 101, 102 which act as side yokes does not change. Therefore, a path of the magnetic flux  is constantly secured to reduce leakage flux, and even if the gap y is large (in other words, the dielectric strength is determined large), the magnetic attraction force is prevented from drastically decreasing when the armature state is inverted. As a result, a relay with higher sensitivity and larger dielectric strength between contacts can be realized. Referring to FIGS. 6A, 6B and 7, details and a modification of the coil spool will be described. In FIGs. 6A and 6B, the iron core 10 which is wound with coil is partially covered with the molded section 114, and partially exposed in the spool 11. Respective flanges 110, 111 and a molded section 114 are formed by insert-molding the core 10. More particularly, the core 10 is substantially formed in the shape of a letter U by bending both ends of a flat plate, and four dents 103 are formed in the section wound with coil by partially pressing four corners of the core 10. The dents 103 are provided in order to facilitate application of resin along the entire length of the core 10 when resin is injected from several injection ports into a metal die used in insert-molding. In the cross section of the core 10, the dents 103 and two side surfaces (shorter sides) are covered by the molded section 114 while two major surfaces (longer sides) are largely exposed. On the major surfaces, the surface area of the molded section 114 is raised higher by the thickness t than the exposed surface of the core 10. The molded section 114 is given the thickness t on the side surfaces of the core 10. When the coil 12 is wound around the spool 11 of the above structure as shown in FIG. 6B, a void space of the depth of t is created between the core 10 and the coil 12 on the major surface to insulate them. The thickness t which is equivalent to the thickness of the wound section can be reduced to about 0.1 millimeters if PBT (polybuthylene terephthalate) is used. Since the area which should be molded is small on the side surface of the core 10, a mold of a smaller thickness t can be formed. In the prior art as the core 10 is entirely molded, the minimum thickness t cannot be reduced to less than about 0.3 millimeters, while in this embodiment the coil 12 and the core 10 can be placed closer to each other, and the number of windings in the same space can be increased so that the coil excitation efficiency (coil constant) can be improved by 40% over the prior art. Therefore, this spool structure contributes to achievement of a relay with higher sensitivity. FIG. 7 shows another example of the spool wherein the permanent magnet 13 is omitted from the structure by forming the central flange 110 with a plastic magnet which is magnetized vertically. The armature assembly 2 will now be described in more detail referring to FIGs. 8A and 8B. The hinge springs 222 and 232 which support the seesaw movement of the armature assembly 2 and the movable contacts 223 and 233 of the movable contact spring members 221 and 231 are electrically communicated, and the hinge springs 222 and 232 can act as common terminals for the transfer switching contacts. As the hinge springs 222 and 232 which are formed in the shape of a crank are exposed before the cover is placed from above, they can be adjusted for optimal loads even after assembly simply by bending them. A window 210 is formed on the lower surface of the molded member 21 to expose the lower central surface of the armature 20. Within the window 210 is formed a supporting projection 203 by press-working the armature 20. The projection 203 encircled by the molded section 21 comes in contact with the magnet 13 to become a supporting point for the movement of the armature 20. The molded member 21 prevents powders which are generated by frictional movement from entering the electric contacts as shown in FIG. 8B. This eliminates an adverse effect on said contacts which may otherwise be caused by the generated powders (insulator) from friction to thereby attain higher reliability in the relay. Although all the embodiments are described as selfholding-type relays in the foregoing statement, this invention can also be readily applied to current-holding-type (monostable-type) relays in a manner described below. The relay can be structured by causing the armature 20 to be attracted to either side of the core when the coil is not excited, a residual plate 204 of a non-magnetic material is fixed on one end 20b of the armature 20 as shown in FIG. 9, and the balance is disturbed by increasing magnetic reluctance from ends of the core 10. Alternatively, hinge springs 222 and 232 in a crank form are bent (224, and 234) to use the spring pressure generated when the ends of these springs 222 and 232 are soldered to the neutral common terminals of the base 3 for contacting the armature end 20a and the core end 10a when the coil is not excited to achieve the same effect. Either method can be used to achieve the same effect.

Claims: An electromagnetic relay including a coil assembly (1) having a permanent magnet (13) so arranged that one of its magnetic poles is able to make contact with the centre of a U-shaped core (10) on which a coil (12) is wound, an armature assembly (2) including an armature (20) having opposite ends which are mounted to oppose the opposite ends of the core (10), hinge springs (22, 23) for supporting the armature (20) and enabling a seesaw movement to occur, wherein each end of the armature (20) either comes into contact with or is separated from its respective opposite end of the core (10), movable contact springs (221, 231) cooperate with the seesaw movement of the armature (20), and the armature (20), the hinge springs (22, 23), and the movable springs (221, 231) are integrally fixed to an insulating moulded member (21), and an insulating base (3), having a box-like shape with an opening on the top thereof, and including stationary contact terminals (30-33) having stationary contacts (301, 311, 321, 331) positioned to oppose movable contacts (223, 233) of the movable contact springs (221, 231), and including common terminals (38, 39) arranged to be connected to one end of the hinge springs (22, 23), when the coil assembly (1) is placed within the opening and when the armature assembly (2) is arranged in such a manner that the other magnetic pole of the magnet acts as a supporting fulcrum for the seesaw movement of the armature (20), characterised in that at each side of the opposite ends of the U-shaped core (10) there is a projection (101, 102) and in that each of the opposite ends of the armature (20) has two notches (201, 202) formed in shapes corresponding to the projections (101, 102) to form an air gap between the side surfaces of the armature ends and each of the projections (101, 102), whereby a path for the magnetic flux is formed by the air gap when each of the armature ends is separated from its respective core end. The electromagnetic relay as claimed in Claim 1 wherein said U-shaped core (10) has dents (103) on corners of the coil wound section having a polygonal cross section and the portion near the dents (103) are molded with resin to form a coil spool, and at least one of the surfaces of said core is exposed, and the surface of said mold is raised higher than the surface of said core on both sides of the exposed core surface. The electromagnetic relay as claimed in Claim 1 wherein the insulating molded member (21) of said armature assembly (2) is formed in a manner to enclose the supporting point contacting the other end of said magnet (13) on the lower central surface of the armature (20). The electromagnetic relay as claimed in Claim 1 wherein said coil assembly (1) includes a coil spool formed by insert-molding said core except for end flanges and central flange thereof, and said permanent magnet (13) is a plastic magnet forming said central flange of said spool. The electromagnetic relay as claimed in Claim 1 wherein the hinge springs (222, 232) of said armature assembly (2) extend from said insulating molded member (21) toward both sides of the armature assembly (2) and is bent in the form of a crank in the intermediate portion thereof.

Inventors: HITACHI HIDEKI, IKEDA MATSUJIRO, YOKOO KIYOTAKA, HITACHI, HIDEKI, IKEDA, MATSUJIRO, YOKOO, KIYOTAKA
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1988
Main classification: H01H51
IPC codes: H01H51