Electromagnetic relay

Abstract: A bi-stable electromagnetic relay has a U-shaped core (10) carrying between its poles (10a, 10b) an energising coil (12). A magnet (13) makes magnetic contact with a central part of the core (10), and provides at its free end a central fulcrum for an armature (20, 21) which is arranged to cooperate at its ends (20a, 20b) with the respective core poles (10a, 10b). The fulcrum enables a see-saw movement of the armature (20) about a biased neutral position according to the direction of an ener­ gising current supplied to the coil (12), so as to close/­ open alternative moving contacts (221, 223; 231, 233) relative to respective fixed contacts (301, 311; 321, 331). Each moving contact (221, 223; 231, 233) includes a cantilever spring (221, 231) mounted on the armature so as to have a large flexing length when closing on to its associated fixed contact (301, 311; 321, 331), but a much smaller flexing length when moving away from that contact (301, 311; 321, 331). This is achieved by the presence of a cantiliver arm (211) carried on the armature (20, 21) alongside the cantilever spring (221, 231), and reduces the tendancy of the cantilever spring (221, 231) and associated moving contact tip (223, 233) to oscillate when the moving contact (221, 223; 231, 233) is moved away from its associated fixed contact (301, 311; 321, 331].

Description: This invention relates to an electromagnetic relay of a flat configuration which can switch electric contacts by seesaw movement of an armature. As the electromagnetic relays of this type, there have been proposed a structure described in U.S. Patent Application Serial No. 07/198,476 (corresponding to Japanese Patent Application No. 137265/1987) assigned to the same assignee as this invention and a structure disclosed in U.S. Patent Nos. 4,695,813; 4,342,016; and 4,499,442. Each of those relays comprises as shown in FIG. 1, for example, a coil assembly 100 having a U-shaped core 10 wound with a coil 12 and a permanent magnet 13, a box-like plastic base 300 having stationary contact terminals 30, 31, 32 and 33, an armature assembly 200 integrating an armature 20 and movable contact terminals 221 and 231, and a cover (not shown). When this relay is to be assembled, the coil assembly 100 is inserted into the base 300 and fixed with an adhesive material, and a coil terminal 113 and coil lead terminals 34 to 36 are connected by such means as welding or soldering. The armature assembly 200 is mounted by fixing hinge springs 222 and 232 on the ends thereof to common terminals 38 and 39. The cover (not shown) is attached lastly, and a sealant of insulating resin is filled between the lower surface of the base 300 and the periphery of the internal walls of the cover to complete the assembly of the relay. The prior art relays are, however, detrimental in that the assembly is cumbersome as adhesive is used for fixing the coil assembly 200 with the base 300, and, moreover, the assembly dimensions are unstable as the adhesive strength is affected by environmental changes, particularly by high temperature and high humidity to thereby inconveniently fluctuate the operational characteristics of the relay. Easpecially, when the adhesive strength weakens, vibration applied to the relay causes displacement in relative positions among structural elements. For instance, if the coil assembly 100 is displaced downward from a predetermined position, as the effective distance between movable contacts 223, 223 and stationary contacts 301, 311, 321, 331 increases beyond a specific value, the contact force decreases below a satisfactory level. Conversely, if the coil assembly 100 is displaced upward, the gap between movable contacts and stationary contacts on the open-state side decreases less than a specific value to decrease dielectric strength between the contacts. If even a slight vibration is applied in this state to the relay, the movable contact springs vibrate to short-circuit the contacts. Such vibration would also lower precision in relative positions between the coil assembly 100 and the base 300 by a large margin. An object of this invention is, therefore, to provide an electromagnetic relay which is free from the above-mentioned disadvantages and which has stable characteristics free from the influences from fluctuation in environment or under vibration and can secure a high dielectric strength between contacts. Another object of this invention is to provide an electromagnetic relay which can be assembled simply. Still another object of this invention is to provide an electromagnetic relay which has a longer life because of the reduction of the contact erosion caused by arc discharge which occurs when the electric current is cut off. In an arrangement which will be described below an electromagnetic relay includes: a coil assembly having a U-shaped core wound with a coil, a permanent magnet arranged in a manner to cause at least one of the magnetic poles thereof to contact the core, and a coil spool fixing the magnet and the core integrally; an armature assembly including an armature having both ends to oppose both ends of said core, hinge springs for supporting a seesaw movement of both ends of the armature which come to contact or separate from both ends of said core respectively, and movable contact springs cooperating with the seesaw movement of the armature, the armature, the hinge springs and the movable contact springs being integrally fixed with an insulating molded member; an insulating base having a box-like shape with an opening on the top thereof and including stationary contact terminals which have stationary contacts opposed to movable contacts of said movable contact spring and common terminals to be connected to one end of said hinge springs respectively, when said coil assembly is placed within said opening and said armature assembly is arranged so that said permanent magnet becomes a fulcrum of the seesaw movement of said armature, the base having projecting reference blocks to determine the reference positions for engagement of the coil assembly, flanges on both ends of said spool which are cut off in the shape substantially corresponding to the shape of said reference blocks, a cover to be placed from above on said insulating base after it is mounted with said coil assembly and armature assembly, openings of the cover being sealed with sealant. An electromagnetic relay to be described is characterized in that the base is provided on the bottom surface thereof with through holes extending outwardly projections are provided on at least either one of said inner walls of the base or said flanges of said spool for engaging with said base when said coil assembly is inserted from above into said base, and said base and said coil assembly are fixed with a sealant which is poured into the bottom surface of said base to creep through the through holes of said base to contact the lower part of said flanges and with said projections for engagement. Another feature of an electromagnetic relay to be described lies in that it has the relay structure similar to the prior art relay but the insulating molded member of the armature assembly is integrally molded with an arm which projects in the longitudinal direction of said movable contact spring to contact with the surface of the springs on the side where the movable contacts are fixed. The extent of the protection to be conferred hereby is to be determined by the terms of the appended claims, interpreted with the aid of the following description and drawings, which disclose, by way of example, the invention which is characterised in the claims. A known arrangement will now be described, together with arrangements which illustrate the invention by way of example, with reference to the accompanying drawings in which: FIG. 1 is an exploded perspective view to show the structure of a prior art electromagnetic relay; FIG. 2 is a perspective view of an electromagnetic relay; FIG. 3 is an exploded perspective view of FIG. 2; FIGs. 4A to 4C are explanatory views for operational principle of the relay of FIG. 2; FIGs. 5A and 5B are views to show the contact state and separation state between the armature and the ion core end shown in FIG. 3; FIGs. 6A and 6B are a plane view and a cross sectional view along the line VIB of the base shown in FIG. 3, respectively; FIGs. 7A to 7D are a plane view, a cross sectional view along the line VIIB, a cross sectional view along the line VIIC and a cross sectional view along the line VIID of the base and the coil assembly shown in FIG. 2, respectively; FIG. 8 is a perspective view to show the details of the armature assembly shown in FIG. 3; FIGs. 9A and 9B are side views to show the movement of an armature assembly shown in FIG. 8; FIG. 10 is a side view to show the operation of the prior art armature assembly shown in FIG. 1; FIG. 11 is a modification of the engagement construction of the base and the coil assembly shown in FIG. 2; and FIGs. 12A to 12C, 13A and 13B are explanatory views to illustrate the engaged state of respective parts shown in FIG. 11. In the drawings, the same reference numerals denote the same structural elements. Referring to FIGS. 2 and 3, there is shown a relay which includes a coil assembly 1, an armature assembly 2, an insulating base 3 and a cover 4. The coil assembly 1 comprises a magnetic 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 iron 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-like 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 plastic 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 to 33 respectively having electric contacts (stationary contacts) 301, 311, 321,331, four coil terminals 34 to 37 and two common terminals 38, 39. The coil assembly 1 is fixed to the base 3 internally (described in more detail hereinafter), while the coil terminals 113 of the spool 11 are fixed to the coil terminals 34 to 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 to 4C. As described in the foregoing, a permanent magnet 13 is provided at the center of the inside of the 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 232) and stationary contacts 301, 311 (and 321, 331) come to contact with or become separated from each other to switch electric circuits. Above-mentioned operational principle is analogous to that of the relay disclosed in Japanese Patent Disclosure No. 211929/1984 assigned to the same assignee as the present invention. The displacement of the armature 20 on the end which is remote from the core 10 greatly 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 makes 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. Description will now be given to the engagement of the base 3 with the coil assembly 1 referring to FIGs. 6A, 6B, 7A and 7B. As shown in FIGs. 6A and 6B, reference blocks 40a and 40b for positioning the coil assembly 1 are internally provided one each on both longitudinal ends of the bottom of the base 3. On both sides of the reference block 40a are bored one each hole 41a, 41b while on both sides of the reference block 40b are bored one each hole 41c, 41d. These holes 41a, 41b, 41c and 41d are through holes extending beyond the bottom of the base 3. Projections 42a, 42b, 42c and 42d are formed on the internal walls of the base 3 above the respective holes 41a to 41d for engaging and fixing the coil assembly 1. Each of these projections 42a to 42d has a triangle shape which is tapered. The upper tapered portion facilitates assembly of the coil assembly 1 into the base 3 while the lower tapered portion firmly presses the coil assembly 1 onto the base 3. Flanges 111 on both sides of the spool 10 of the coil assembly 1 have cut off portions 114a and 114b corresponding to the shapes of the reference blocks 40a and 40b of the base 3, respectively. On the upper faces of the cut off portions 114a and 114b are formed rail-like projections 115 extended along the upper faces. The projections 115 may be formed on the blocks 40a and 40b. When the coil assembly 1 of this structure is to be inserted into the base 3, tapered portions provided at four positions below both sides of the flanges 111 (i.e., on both sides of cut off portions 114a, 114b) fit neatly with the upper tapered portions of the projections 42a to 42d of the base 3 to allow smooth insertion. When the coil assembly 1 is further pushed in, the four corners of the spool 11 become fitted in with the lower tapered portions of the projections 42a to 42d (see FIGS. 7A and 7B). Simultaneously, the reference blocks 40a and 40b are engaged with the cut off portions 114a and 114b of the spool 10 while the projections 115 become firmly abutted onto the reference blocks 40a and 40b to become deformed and secure the dimensional precision of the coil assembly 1 in vertical direction at target values. Subsequently, the armature assembly 2 is placed in a manner mentioned above, and then the cover 4 is placed from above and a sealant 48 of insulating resin is filled into the gap formed between the bottom of the base 3 and the periphery of the cover 4. The sealant 48 creeps through the holes 41a through 41d into the base 3 to contact the lower ends of the flanges 111. As a result, when the sealant 48 is set, the spool 11 (i.e., the coil assembly 1) is fixed to the base 3 remarkably (see FIGs. 7C and 7D). In this manner, the coil assembly 1 and the base 3 are fixed fully even without the adhesive material mentioned on the prior art relay, because the assembly 1 and the base 3 are fixed by two kinds of forces caused by the sealant 48 and the pressure due to the projections 42a to 42d. As a result, when the coil assembly 1 is inserted unidirectionaly (from above) and sealed in an ordinary manner, the coil assembly 1 is firmly fixed to the base 3 to thereby markedly facilitate the assembly procedure. The armature assembly 2 will now be described in more detail referring to FIG. 8. 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 springs 221 and 231 are electrically connected, 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. 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. A portion of the molded member 21 projects in the longitudinal direction of contact springs 221 and 231 to form arms 211 which contacts the bottom surfaces of the springs 221 and 231 (surfaces on the sides of the electric contacts 223 and 233). As the arms 211 is formed by insert-molding of the armature assembly 2, it does not apply pressure on the contact springs 221 and 231 but it simply stays in contact with them. Therefore, the arms 211 will not influence spring load characteristics thereof and yet can reduce spring vibrations of the springs 221 and 231. Description will now be given to the effect of the arms 211 referring to FIGs. 9A and 9B. FIG. 9A shows the state where contacts are closed. More specifically, the stationary contact 301 and the movable contact 223 are in contact with each other. The contact spring 221 is displaced upward on in the opposite direction of the arm 211 to cause the movable contact 223 to exert the contact force. As there is formed an interspace between the arm 211 and the contact spring 221, the end of the contact spring is fixed at the point A, and there is no significant difference produced in characteristics from the case without the arm 211. FIG. 9B shows the state where the two contacts 223 and 301 are separated. In this state, the vibration of the contact spring 221 is decreased in amplitude as the fulcrum of the vibration is moved to the point B by the arm 211 and at the same time, attenuation time of the vibration is remarkably decreased. As shown in FIG. 10, as the fulcrum of the vibration by the contact spring 221 of the prior art is at the point A during the time transient to the open state, the amplitude and attenuation of the vibration zre usually large. As described in the foregoing statement, according to this invention even if the relay is vibrated, the vibration on the contact springs 221 and 231 can be restricted to thereby keep the gap M between contacts at a large value, and hence maintain the dielectric strength between contacts at a high value. In the prior art structure shown in FIG. 10, in addition to the free vibration occurring on the cantilevered spring, since additional vibration is produced by the impact of the armature 20 on the opposite side against the end of the core 10 (i.e., on the side where contacts are closed), arc discharge produced at the break of current tends to continue to accelerate the wear of contacts. However, in this embodiment, due to the effect of the arm 211, vibration applied on the spring whenever contacts are switched is rapidly attenuated to remarkably prevent the wear on the contact otherwise produced by arc discharge, which greatly contributes to extend life of the relay. Referring to FIG. 11, a modified engagement of the base 3 with the coil assembly 1 is described. In this embodiment, as cut off portion 117 is provided on the lower surfaces of the both sides of the flanges 111 of the spool 10 of the coil assembly 1 to thereby form projections 116, and through holes 43 are bored one each on both sides of the base 3 for engagement with the projections 116. On both sides of the holes 43 are provided reference blocks 44 in a shape corresponding to the cut off portions 117 of the coil assembly 1. In the flange 110 at the center of the coil assembly 1 are formed projections 119 on both sides and cut off portions 118 on the lower surface thereof. The base 3 is provided on the center of the side walls with projections 46 to fit with the projections 119, and projections 47 to fit with the cut off portions 118. The projections 47 have through holes 45 extending to the outside of the base 3 so as to allow the creepage of the sealant 48 therethrough from the bottom of the base 3 to reach the projections 119. This further reinforces the firm engagement of the coil spool 10 (i.e., the coil assembly 1) with the base 3. The effect of fixation with the sealant 48 is similar to the above when it is used for fixing the projection 116 of the coil spool 10 with the hole 43 of the base 3. FIGs. 12A to 12C show the engagement of the coil assembly 1 on the both ends in the longitudinal direction. The upper surface of the reference blocks 44 of the base and the lower surface of the cut off portions 117 of the coil assembly 1 are used as the reference for assembly. By abutting these two surfaces onto each other, the slope of the upper tapered surface 116a provided on the projection 116 may come to contact and engage with the inner walls of the base 3. The projection 116 is tapered at two positions, upper one of which is used for engagement and the lower one of which is used as a guide for insertion in the hole 43. After mounting the cover 4, the sealant 48 is filled in the gap between the periphery of the cover walls and the lower surface of the base 3. The sealant 48 flows into the holes 43 to contact the projections 116, which further enhances the engagement. FIGs. 13A and 13B show engagement of the coil assembly 1 with the base 3 on the center side. The surface of the cut off portion 118 and the upper surface of the projection 47 of the base 3 are used as the reference, and the projections 46 and 119 are abutted against these two surfaces for engagement. In the above arrangements, all the references used are upper surfaces of the reference blocks projected from the bottom of the base 3. This is because it would reinforce the strength of the reference surfaces to further stabilize the dimensional precision. This allows the thickness of the other parts of the base 3 to be reduced and thus greatly contributes to minimization of the relay height. It will be understood that, although the invention has been explained with reference to particular embodiments by way of example, variations and modifications thereof, as well as other embodiments, may be made within the scope of the appended claims.

Claims: An electromagnetic relay including a coil assembly (1) having a U-shaped core (10) wound with a coil (12), a permanent magnet (13) arranged in a manner to cause at least one of the magnetic poles thereof to contact the core (10), and a coil spool 11 fixing the magnet 13 and the core (10) integrally, an armature assembly (2) including an armature (20), two ends (10a), (10b) of the core (10), hinge springs (22, 23) for supporting a seesaw movement of the two ends of the core (10) respectively, and movable contact springs (221, 231) cooperating with the seesaw movement of the armature (20), the armature (20), the hinge springs (22, 23) and the movable contact springs (221, 231) being integrally fixed to an insulating molded member (21), an insulating base (3) having a box-like shape with an opening at the top thereof and including stationary contact terminals (30 to 33) which have stationary contacts (301, 311, 321, 331) opposed to movable contacts (223, 233) of the movable contact springs (221, 231) and common terminals (38, 39) respectively, when the coil assembly (11) is placed within the opening, the armature assembly (2) being so arranged that the permanent magnet (13) provides a fulcrum for the seesaw movement of the armature (20), the base (3) having projecting reference blocks (44) to determine the reference positions for the engagement of the coil assembly (1), and flanges (111) being provided on both sides of the spool (11) which are cut off in a shape substantially corresponding to the shape of the reference blocks (44) and a cover (4) to be placed from above on to the insulating base (3) after the coil assembly (1) and the armature assembly (2) are mounted thereon, the opening of the cover (4) being sealed with sealant (48), the relay being characterised in that the hinge springs (22,23), the movable contact springs (221,231) and the insulated member (21) are molded integrally together, such that the respective end portions of the armature (20), the hinge springs (22,23) and the movable contact springs (221,231) extend from the insulating member (21) on substantially the same plane, the box-like base (3) is closed at the bottom thereof to provide a bottom surface having through-holes (43) extending outwardly, in that projections (116) are formed on at least either one of the internal walls of the insulating base (3) and the flanges (111) of the spool (11) for engaging with the base (3) when the coil assembly (1) is inserted from above into the base (3), and in that the base (3) and the coil assembly (1) are fixed with a sealant(48) which is poured into the bottom surface of the base (3) to creep through the through-holes (43) to contact the lower portions of the flanges (111) and the projections (116) for engagement. An electromagnetic relay as claimed in claim 1, wherein the projections (116) for engagement are provided on both flanges (111) of the spool (11), the projections (116) being engaged with the through-holes (43) of the base (30), wherein second projections (119) for engagement are formed on both sides of the central flange (110) in the longitudinal direction, and wherein the base (3) is provided with third projections (46) for engagement with the second projections (119), and bored through second holes (45) extending to the lower surface of base (3), so that the sealant (48) which has crept through the second through-holes (45) may come in contact with the third projections (46) for engagement.

Inventors: YOKOO KIYOTAKA, YOKOO, KIYOTAKA, YOKOO, KIYOTAKA C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1988
Main classification: H01H51
IPC codes: H01H51, H01H1