Electromagnetic relay with solder flux penetration preventing structure

Abstract: An electromagnetic relay has an iron core (1), an armature (2), a coil (12) wound around the iron core (1), a yoke (3), a hinge spring (6), and a joining structure. The yoke (3) is fastened rigidly to the iron core (1) and has an engaging hole (3b) and a fitting portion (3a),3d). To prevent solder flux penetration of the electromagnetic relay, the coil bobbin (4) is formed, integral with or separate from a base block (9), and a venting portion (4c), for allowing air trapped in a center hole in the coil bobbin (4) to be vented therethrough, is formed in an upper flange (4b) of the coil bobbin (4). Therefore, sealing of the base block of the electromagnetic relay with sealant (13) can be performed smoothly and pinhole-free sealing thereof can be provided.

Description: The present invention relates to an electromagnetic relay with a presenting penetration of soldering flux. In the construction of an electromagnetic relay, for example, a coil is wound around an iron core to construct an electromagnet, a yoke as a component to complete a magnetic circuit with it is fastened rigidly to the iron core and an armature is rotatably mounted in such a manner as to bridge between the yoke and the head of the iron core of the electromagnet to construct an electromagnet structure. Then, one end of this electromagnet structure is fixed to the yoke and the other end thereof is made to engage with the armature, the rotatable movement of the armature being supported by a plate-like hinge spring formed from a resilient member. When mounting the prior art electromagnetic relay on a printed circuit board, the printed circuit board is passed through a high-temperature solder bath, for example, and the electromagnetic relay with solder applied to the terminal leads thereof is mounted rigidly on the printed circuit board. At this time, there is a possibility that flux may rise from the solder bath and penetrate into the interior of the electromagnetic relay; to prevent this, the bottom of the electromagnetic relay (base block) is sealed. In constructing an electromagnetic relay having such a flux penetration preventing structure, a liquid sealant is filled into the base of the base block and the liquid sealant is then heated to form the sealing structure. This, however, has entailed the problem that, when the liquid sealant cures after heating, bubbles are trapped in the sealing structure, forming pinholes and defeating the purpose of the dealing. The prior art electromagnetic relay and problems associated with the prior art will be described in detail later with reference to drawings. Document JP4145608 discloses a device according to the preamble of claim 1. According to the present invention, there is provided an electromagnetic relay comprising an iron core having an iron core head; a coil bobbin for winding a coil around the iron core, formed integral with or separate from, a base block; and a venting portion, for allowing air trapped in a center hole in the coil bobbin to be vented therethrough, formed in an upper flange of the coil bobbin and closed by sealant material in the base block. The venting portion may comprise at least one groove formed in the upper flange of the coil bobbin in a position where the upper flange contracts the underside of an iron core head. The venting portion may comprise four grooves. The present invention will be more clearly understood from the description of a preferred embodiment as set forth below with reference to the accompanying drawings, wherein: Figure 1 is a perspective view showing the construction of an electromagnetic relay according to the present invention. Figure 2 is an exploded perspective view showing the entire construction of the electromagnetic relay of Figure 1; Figure 3A is a longitudinal-sectional view showing one example of a prior art electromagnet structure; Figure 3B is a bottom view of the electromagnet shown in Figure 3A; Figure 4A is an exploded perspective view of the electromagnet of Figures 1 and 2; Figure 4B is a perspective view showing the electromagnet of Figure 4A in an assembled condition; Figure 5A is a front sectional view of the electromagnet shown in Figure 4B; and Figure 5B is a bottom view of the electromagnet shown in Figure 5A. In Figures 1 and 2, reference numeral 1 is an iron core, 2 is an armature, 3 is a yoke, 4 is a coil bobbin, 5 is a coil terminal, 6 is a hinge spring, 9 is a base block, 10 is a card, and 12 is a coil. Further, reference numeral 7 is a moveable contact spring, 7a is a movable contact, 8 is a stationary contact spring, 8a is a stationary contract, and 11 is a case. As shown in Figure 2, in the assembly process of the electromagnetic relay, the coil bobbin 4 is placed on the base block 9 made of an insulating material, and the coil 12 is wound around the coil bobbin 4. Further, the iron core 1 is inserted through a center hole 4a in the coil bobbin 4 until the lower end portion 1b of the iron core 1 reaches the bottom of the base block 9. After that, the L-shaped yoke 3 is inserted through a hole 9a in the base block 9 from the underside thereof, and a hole 3c opened through the yoke 2 is fitted onto the lower end portion 1b of the iron core 1 to fix the yoke 3 to the base block 9, so that an electromagnet is constructed. Here, the coil bobbin 4 may be formed integrally with the base block 9 beforehand or may be fabricated as a separate coil component. Thereafter, the hinge spring 6 is assembled to the yoke 6; alternatively, the yoke 6 may be fitted with the hinge spring 6 beforehand. Next, the movable contact spring 7 and the stationary contact spring 8 are inserted in the base block 9 and secured in place, after which the armature 2 is engaged with the free end 6d of the hinge spring 6 so that the armature 2 is held opposite the head 1a of the iron core. Further, the card 10 is fitted in position by engaging it onto the armature 2 and the movable contact spring 7. Here the coil terminals 5 may be attached beforehand by inserting them in the base block 9 during the process of moulding the latter. Finally, the case 11 is mounted to complete the assembly of the electromagnetic relay. As previously described with reference to Figures 2 and 3, in constructing the electromagnet of the electromagnetic relay, for example, the coil 12 is wound around the coil bobbin 4, the iron core 1 is inserted through the center hole 4a in the coil bobbin 4, and the yoke 3, as a component to form a magnetic circuit, is fixed to the iron core 1. Further, the armature 2 is mounted in such a manner as to bridge between the head 1a of the iron core and the other end of the yoke 3, and the armature 2 is rotatably held on the plate-like hinge spring 6 formed from a resilient member, to construct the electromagnet structure. In operation of the electromagnetic relay, when the coil 12 is energized by passing a current through the coil 12, the armature 2 is attracted to the head 1a of the iron core 1, which in turn moves the movable contact spring 7 via the card 10, causing the movable contact 7a to come into contact with the stationary contact 8a. When mounting the electromagnetic relay on a printed circuit board, usually the printed circuit board is passed through a high-temperature solder bath, and the electromagnetic relay with a solder applied to the externally extending terminal leads thereof is mounted rigidly on the printed circuit board. At this time, there is a possibility that flux may rise from the solder bath and penetrate into the interior of the electromagnetic relay. If the flux from the solder bath penetrates into the interior of the electromagnetic relay, the solder may be deposited on the contracts, which can cause contact failures. To prevent the flux from rising from the solder bath and penetrating into the interior of the electromagnetic relay, it has traditionally been practised to seal the externally extending terminal side (for example, coil terminals 5) of the base block 9, that is, the bottom side of the electromagnetic relay (a bottom sealing portion 9b), as shown in Figures 3A and 3B). When constructing the electromagnetic relay having the bottom sealing portion 9b, not only the terminal leads (5) but also the lower end portion 1b of the iron core 1 and the portion of the L-shaped yoke 3 exposed in the bottom sealing portion 9b must be embedded in the sealing. To seal these portions, the electromagnetic relay is turned upside down with the bottom of the coil block 9 facing up, for example, and a liquid sealant 13 is filled into the exposed area to seal the bottom sealing portion 9b of the base block 9. In one known means, this is accomplished by applying the liquid sealant 13 to the exposed area and by curing the sealant by heating. After the sealing, the case 11 is mounted onto the electromagnetic relay structure and fitted into the fitting portion of the base block 9 to secure it in position. In the above securing means, since the head 1a of the iron core 1 is placed in intimate contact with the upper flange 4b of the coil bobbin 4, a gap 14 is formed between the outer circumferential surface of the iron core 1 and the inner circumferential surface of the coil bobbin 4. As a result, when the liquid sealant 13 is filled into the bottom of the base block 9 and heated, the air trapped in the gap 14 expands by heat and air bubbles are formed when the liquid sealant 13 cures after heating. This structure, therefore, has had the problem that pinholes 13a due to the bubbles are formed in the bottom sealing portion 9b (liquid sealant 13), defeating the purpose of the sealing structure. In view of the above-described problem with the prior art electromagnetic relay, venting grooves are formed in the flange of the coil bobbin so that, when the liquid sealant is cured by heating, if the air trapped in the gap between the outer circumferential surface of the iron core and the inner circumferential surface of the coil bobbin expands, the air is vented through the venting grooves to the exterior of the construction, thus facilitating the sealing. In figures 4A, 4B, 5A and 5B, reference numeral 4 indicates the coil bobbin, 4a the center hole opened through the coil bobbin, 4b the flange of the coil bobbin, and 4c the venting holes of the coil bobbin. The general assembly process of the electromagnetic relay is the same as that described with reference to Figure 2, and a description thereof will not be repeated here. As can be seen from figures 4A and 5A, the base block 9 is provided with the venting grooves 4c formed in the upper flange 4b of the coil bobbin 4. These venting grooves 4c are formed, for example, by molding. The head 1a of the iron core 1 is held firmly on the flange 4b where the venting grooves 4c are formed, with the underside of the head 1a in intimate contact with the flange 4b. The outside edges of the venting grooves 4c extend outside the outer diameter of the head 1a of the iron core, that is, the venting grooves 4c are formed to extend outward of the head 1a of the iron core so that, if the air trapped in the gap 14 between the outer circumferential surface of the iron core 1 and the inner circumferential surface of the coil bobbin 4 expands by heating, the air can be vented outside the coil bobbin 4 through the venting grooves 4c. That is, during assembly, the iron core 1 is fitted in position with gaps provided between the head 1a of the iron core 1 and the venting grooves 9c provided in the base block 9 (the flange 4b of the coil bobbin 4), as show in Figure 5A. This structure serves to prevent pinholes 13a from being formed in the bottom sealing portion 9b (liquid sealant 13) due to air bubbles when the liquid sealant 14 filled into the bottom of the base block 9 is heated. In this way, the coil bobbin 4 formed integrally with the base block 9,or fabricated as a separate component and mounted on the base block 9, is provided with venting grooves 4c in the flange 4b thereof at the inlet of the center hole 4a so that a gap is formed between the head 1a of the iron core 1 and the flange 4b of the coil bobbin 4 when the lower end portion 12b of the iron core 1 is fitted rigidly into the hole 3c in the yoke 3 in such a manner as to clamp the coil bobbin 4 in a sandwich fashion; in this structure, the lower end portion 1b of the iron core 1 and the portion around the hole 3c of the yoke exposed in the bottom sealing portion 9b of the base block 9 are sealed with the liquid sealant 13. That is, when curing the liquid sealant 13 by heating, if the air trapped in the gap 14 between the outer circumferential surface of the iron core 1 and the inner circumferential surface of the coil bobbin 4 expands, the air can be vented outside through the venting grooves 4c formed in the flange 4b of the coil bobbin. This structure facilitates sealing work. With the present invention, work efficiency can be enhanced by smoothly performing sealing work and providing pinhole-free sealing to the bottom sealing portion of the base block of the electromagnetic relay.

Claims: An electromagnetic relay comprising: an iron core (1) having an iron core head (1a); a coil bobbin (4) for winding a coil (12) around said iron core (1), formed integral with or separate from, a base block (9), charaterised in that the relay also comprises a venting portion (4c), allowing air trapped in a center hole in said coil bobbin (4) to be vented therethrough, formed in an upper flange (4b) of said coil bobbin (4), said base block being closed by sealant material (13). An electromagnetic relay, as claimed in claim 1, wherein said venting portion comprises at least one groove (4c) formed in the upper flange (4b) of said coil bobbin (4) in a position where said upper flange (4b) contacts the underside of the iron core head (1a). An electromagnetic relay, as claimed in claim 2, wherein said venting portion comprises four grooves (4c).

Inventors: NAKABAYASHI TAKAHIRO, TAKAHATA MASAKI, TAKANO SATOSHI, YOSHINO KOSEI, NAKABAYASHI, TAKAHIRO, TAKAHATA, MASAKI, TAKANO, SATOSHI, YOSHINO, KOSEI
Applicants: TAKAMISAWA ELECTRIC CO, TAKAMISAWA ELECTRIC CO., LTD.
Application year: 1998
Main classification: H01H50
IPC codes: H01H50