FIELD The embodiments discussed herein are related to an electromagnetic relay. The electromagnetic relay is used for domestic, industrial, and in-vehicle purposes. BACKGROUND In an electromagnetic relay, electric current flows or be interrupted from flowing through an electric circuit by opening and closing a contact. The contact includes a fixed contact and a movable contact. The electromagnetic relay includes a mechanism for moving the movable contact toward or away from the fixed contact. As an example of a mechanism for displacing the movable contact, Patent Document 1 discloses a so-called plunger (moving core) type electromagnetic relay.
[Patent Document 1]: Japanese Patent No. 4078820 US6204742 (B1) discloses a magnetic switch including a switch case, a molded cap fastened to the switch case by crimped portions, two fixed terminals having fixed contact shafts and fixed contacts, and a movable contact, wherein the crimped portions are disposed between the fixed terminals and coil terminal conductors in the vicinity of an open end portion of the molded cap to form four crimped portions engaging the molded cap by crimping at positions radially further inwards than the inside diameter of the switch case. The outside diameter of the molded cap may be equal to or greater than the outside diameter of the switch case. The cross-sectional shape of the fixed contacts is an octagon and two sides thereof are approximately parallel to the outer circumferential surface of the molded cap. JP2003184710 (A) discloses a plurality of slits provided in a tip side of a cover installed on an outer circumference of a rod, elastic pieces are formed between slits in a circumference direction, and engagement parts are provided on outer circumferences of the elastic pieces. The engagement part engages with a collar inserted in a round hole of a plunger to transmit the inertia force of the plunger to a rod when the plunger is energized and pushed back by a return spring. The elastic piece of a cover is elastically deformable in the radial direction of the rod, elastically deforms inward in the radial direction when the rod is inserted in the round hole of the plunger and the engagement part gets over the collar, and expands outward in the radial direction and return to an original state after the engagement part gets over the collar. EP2333803 (A2) discloses a normally-closed electromagnetic relay which may be used in controlling a supply of electric current to an automotive engine starter. The electromagnetic relay is equipped with a resistor and a short circuit. The short circuit is created by closing of relay contacts when a relay coil is energized to establish an electric connection between ends of the resistor to supply the current from a battery to an electric motor without flowing through the resistor and opened by opening of the relay contacts when the relay coil is de-energized to supply the electric current from the battery to the electric motor through the resistor. Document EP 2 093 786 A1 discloses a solenoid switch for controlling power supply to starter motors. The solenoid switch comprises a fixed core disposed on the inner periphery of a magnetic coil and a movable core which is movable in an axial direction and is urged backward by a return spring interposed between the fixed and the movable core. The solenoid switch comprises further fixed contacts and a movable contact coupled to the movable core via a rod, wherein the one end of the rod is embedded in a radially-central blind hole in the movable core. The solenoid switch works as a normally-opened switch. Upon being energized, the solenoid coil makes up an electromagnet together with the fixed core. The electromagnet attracts the movable core to move along with the movable contact in the forward direction, causing the movable contact to connect the fixed contacts. Upon deenergizing the solenoid coil the movable core is returned, by the force of the return spring, to its initial position, thereby causing the movable contact to disconnect the fixed contacts. Document US 2011/080240 A1 discloses an electrical switch, which includes a solenoid, a fixed and movable contact, and an actuator rod that connects the solenoid to the movable contact. The solenoid is configured to move the movable contact between an open and a closed position via the movable core connected to the actuator rod and movable along a central longitudinal axis of the switch. A channel extends through the length of the movable core. The actuator rod has a larger diameter part and extends partially through the channel of the movable core. SUMMARY Problem to be solved by invention In the electromagnetic relay disclosed in Patent Document 1, a shaft is inserted in a through-hole provided in a moving core and is temporarily fastened to the moving core with a screw. Then, the moving core and the shaft are integrated by laser welding. However, such temporary fastening for welding the moving core and the shaft increases the number of components and the number of manufacturing steps. This leads to an increase in manufacturing cost. The present invention is defined by the appended independent claims, to which reference should now be made. Specific embodiments are defined in the dependent claims. EFFECT OF INVENTION According to the present invention, manufacturing cost can be reduced by eliminating the need to fix an axial core and a movable core, for example, by welding or using screws, so that cost reduction can be achieved. BRIEF DESCRIPTION OF DRAWINGS - Fig. 1 is a cross section of an electromagnetic relay according to a first embodiment of the present invention taken along a central axis line of a shaft;
- Fig. 2 is a schematic diagram illustrating the coupling of the shaft and a plunger of the electromagnetic relay of the first embodiment;
- Fig. 3 is a schematic diagram illustrating the shaft of the electromagnetic relay of the first embodiment viewed from its radial direction;
- Fig. 4 is a schematic diagram illustrating the coupling of the shaft and a recovering spring of the electromagnetic relay of the first embodiment;
- Fig. 5 is a schematic diagram illustrating an insulating barrier of the electromagnetic relay of the first embodiment;
- Fig. 6 is a schematic diagram illustrating the assembling of a driving part housing and yokes of the electromagnetic relay of the first embodiment;
- Fig. 7 is a schematic diagram illustrating the assembling of a contact housing, a connection housing, and a PWM control circuit of the electromagnetic relay 1 of the first embodiment;
- Fig. 8 is a schematic diagram illustrating the positioning of the PWM control circuit inside a space for installing a fixed contact and a movable contact of the electromagnetic relay of the first embodiment;
- Fig. 9 is a schematic diagram illustrating a configuration of a fixed terminal, the fixed contact, and the movable contact of the electromagnetic relay of the first embodiment; and
- Fig. 10 is a schematic diagram illustrating the coupling of a shaft and a plunger of the electromagnetic relay according to a second embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS In the following, embodiments of the present invention are described with reference to the accompanying drawings. <First embodiment> As illustrated in Fig. 1, the electromagnetic relay 1 of the first embodiment includes a pair of fixed contacts 2, a pair of movable contacts 3 that can be moved relative to the fixed contacts 2 in a contacting/separating direction Xa-Xb, a movable element 4 that supports the movable contacts 3 and moves in the contacting/separating direction Xa-Xb, a shaft (an example of axial core) 5 coupled to the movable element 4, and a plunger (an example of movable core) 6 that is coupled to, and is movable relative in the direction Xa-Xb to, the shaft 5. The electromagnetic relay also includes a driving part 7 that drives the plunger 6 to move in a contacting direction Xa (upward in Fig. 1), a recovery spring (an example of urging part) 8 that urges the shaft 5 in a separating direction Xb (downward in Fig. 1), a constraining part that constrains the movement of the shaft 5 relative to the plunger 6 in the separating direction Xb, and a pressure spring 9 that urges the movable element 4 in the contacting direction Xa. The constraining part of this embodiment includes an opening 6b for inserting an insertion part 5a of the shaft 5 therethrough as illustrated in Fig. 2. The opening 6b is formed with a closed end by perforating a cylindrical plunger 6 from the side of a flange 6a of the plunger 6. The constraining part of this embodiment also includes a bottom 6ba. As illustrated in Fig. 2, the shaft 5 includes a small diameter part 5b for installing the pressure spring 9 provided in the side of the contacting direction Xa of the insertion part 5a. The small diameter part 5b has a diameter smaller than the insertion part 5a as illustrated in Figs. 2 and 3. The shaft 5 also includes a groove 5c formed close to an end of the small diameter part 5b. As illustrated in Fig. 4, the groove 5c extending in a circumferential direction is formed on an end of the shaft 5 (upper end in Fig. 4) in the contacting direction Xa. An E-ring (an example of plate part) 10 is engaged to the groove 5c. The E-ring 10 functions as an engaging part that engages an end of the recovery spring 8 in the separating direction Xb (lower side in Fig. 4). For example, a JIS standard E-type retaining ring may be used as the E-ring 10. The E-ring 10 includes an inner peripheral part contacting an outer peripheral surface of the groove 5c and an outer peripheral part contacting the end of the recovery spring 8 in the separating direction Xb. The electromagnetic relay 1 of the first embodiment includes an insulating barrier 15 that ensures insulation between the yokes 11-13 constituting the driving part 7 and an electric coil wiring 14 as illustrated in Fig. 1. Each of the yokes 11-13 constitutes a part of a magnetic circuit. The electromagnetic relay 1 also includes a reel-like bobbin (an example of wound part) 16 around which the electric coil wiring 14 is wound. In this embodiment, target engagement parts 16a are formed in two parts of the bobbin 16 as illustrated in (a) of Fig. 5. The target engagement parts 16a have concave sector shapes to be engaged with the insulating barrier 15 at an outer side thereof in its radial direction. The insulating barrier 15 includes an engagement part that engages the target engagement part 16a. As illustrated in (a) of FIG. 5, the insulating barrier 15 has a hollow sector-pillar shape that is concaved at an inner side thereof in its radial direction and includes a sector surface 15a forming an engagement part with another sector surface 15a on its opposite side. Two insulating barriers 15 are provided for the bobbin 16. A pair of planar constraining parts 15b are arranged in parallel on upper and lower surfaces of each insulating barrier 15, so that the bobbin 16 is constrained from moving in a circumferential direction of the bobbin 16 relative to the yokes 11, 13 having a part extending_in a radial direction of the bobbin 16. The insulating barriers 15 and the bobbin 16 are formed of, for example, a synthetic resin. The pair of sector-shaped target engagement parts 16a are arranged at equal intervals in a circumferential direction of the bobbin 16. When the insulation barriers 15 are engaged to corresponding target engagement parts 16a from the outside in the radial direction, the four constraining parts 15b on the upper side form a configuration that sandwiches the planar yoke 13 (see Fig. 1) therebetween whereas the four constraining parts 15b on the lower side form a configuration that sandwiches the planar U-shaped yoke 11 illustrated in (a) of Fig. 6. The insulation barriers 15 are arranged to be interposed between the electric coil wiring 14 and an area in a circumferential direction of the electromagnetic relay 1 having the yokes 11, 13 extending in this area of the electromagnetic relay 1. The electromagnetic relay 1 of the first embodiment includes a driving part housing 17, a contact housing 18, and a connection housing 19 as illustrated in Fig. 1. The driving part housing 17 may be formed of, for example, a mold resin. As illustrated in (a) of Fig. 6, the driving part housing 17 has a close-ended box-like shape for encasing the driving part 7 therein. The connection housing 19 and the contact housing 18 may also be formed of, for example, mold resin. A cylindrical projection 17a is provided at a bottom of the driving part housing 17. A hole 11a having a diameter greater than the diameter of the projecting part 17a is provided in the U-shaped planar yoke 11. A groove 17b is also provided in the bottom of the driving part housing 17. The groove 17b has a width that is substantially equal to a width W of the yoke 11 and a depth that is less than a thickness T of the yoke 11. In this embodiment, the total dimension of the depth of the groove 17b and the height of the constraining part 15b is adjusted to be less than or equal to the thickness of the yoke 11. When the yoke 11 and the cylindrical yoke 12 are mounted to the housing 17 in the arrow direction illustrated in (a) of Fig. 6, the projecting part 17a is inserted through the hole 11a and then inserted through an inner periphery of the yoke 12. As illustrated in (b) of Fig. 6, the position of the yoke 12 is defined by the projecting part 17 inserted therethrough, and the position of the yoke 11 is defined in a manner sandwiched between both sidewalls of the groove 17. Then, the bobbin 16 being engaged with the insulation barriers 15 as illustrated in (b) of Fig. 5 is inserted into the driving part housing 17 from above in (b) of Fig. 6, and the assembly in which the plunger 6 and the shaft 5 are assembled are inserted into the yoke 12. Then, the yoke 13 including a hole 13a for inserting the shaft 5 therethrough is mounted on the bobbin 16, and the shaft 5 is inserted through the hole 13a. Thereby, the driving part 7 is assembled. Then, a planar connection housing 19 having a shape for engaging the contact housing 18 as illustrated in (a) of Fig. 7 is mounted on the driving part housing 17. A trapezoidal protrusion 16b that is formed on the upper side of the bobbin 16 (see (a) of Fig. 5) defines the position of the connection housing 19 with respect to the bobbin 16 when mounting the connection housing 19 on the driving part housing 17. Then, the pressure spring 9 is inserted through the small diameter part 5b of the shaft 5 in which a hole 4a of the movable element 4 is engaged with the small diameter part 5b. Then, the E-ring 10 is engaged with the groove 5c that is formed at the end of the small diameter part 5b, and the end of the recovery spring 8 to the side of the separating direction Xb contacts the outer peripheral part of the E-ring 10. As illustrated in Fig. 1, the contact housing 18 fixes a pair of columnar fixed terminals 21 each of which having a fixed contact 2 at its end. The contact housing 18 is inserted into the driving part housing 17 through an opening of the driving part housing 17, and legs 18a of the contact housing 18 are engaged with the driving part housing 17. Thereby, the fixed contacts 2 are arranged facing the movable contacts 3. After the end of the recovery spring 8 to the side of the contacting direction Xa is fixed to an opening 18b provided on the contact housing 18, the contact housing 18 and the driving part housing 17 are hermetically sealed to each other by using an adhesive, welding, or soldering. As illustrated in (b) of Fig. 7, the contact housing 18 includes an installing part 18c for installing a PWM control circuit substrate (drive circuit) 20 that drives the driving part 7. The PWM control circuit 20 is provided in an installing space for installing the fixed contact 2 and the movable contact 3 as illustrated in Fig. 8. In this embodiment, the fixed terminal 21 corresponds to the fixed contact 2 as illustrated in Fig. 9. The fixed contact 2 is only provided on the end of the fixed terminal 21 at the separating direction Xb and an area facing the movable contact 3. The movable element 4 has a planar shape extending in both ways in a radial direction of the shaft 5. One movable contact 3 is provided on both ends of the movable element 4, respectively. The contact 3 has a hexagonal shape formed by cutting two corners of a longitudinal side of a rectangle. The fixed contact 2 has a semi-circular shape that circumscribes the hexagonal contact 3. The electromagnetic relay 1 of the first embodiment is a 1-form-X plunger type relay having a pair of contacts as described above. In the first embodiment, a pair of fixed terminals 21 of Fig. 1 is inserted into any part of a direct current circuit to be connected/disconnected, and a terminal of the electric coil wire of the driving part 7 is connected to an input/output interface of the PWM control circuit 20, so that excitation current can be suitably controlled. In a state where excitation current is not applied to the terminal of the driving part 7, the shaft 5 is exerted downwardly as illustrated in Fig. 1 by the resilient force of the recovery spring 8, so that the fixed contact 2 and the movable contact 3 shift to an open state that are not contacting each other, or the open state is maintained. In the state illustrated in Fig. 1, the end of the insertion part 5a at the separating direction Xb exerts pressure to the bottom 6ba of the plunger 6 in a downward direction in Fig. 1 by the resilient force of the recovery spring 8. By the exerting pressure from the shaft 5, the flange 6a of the plunger 6 contacts a step formed in the bobbin 16, and the bottom 6ba of the plunger 6 maintains a state contacting the end of the insertion part 5a of the shaft 5. When excitation current is applied to the terminal of the driving part 7, an attracting force is generated by the electric coil wire 14 and the yokes 11-13 to attract the plunger 6 in the contacting direction Xa and cause the bottom 6ba of the plunger 6 to exert pressure to the end of the insertion part 5a of the shaft 5. Thereby, the shaft 5 and the movable element 4 are moved upward, so that the fixed contact 2 and the movable contact 3 shift to a closed state that are contacting each other, or the closed state is maintained. With the electromagnetic relay 1 of the first embodiment, the following effects can be attained. Owing to the configuration having the insertion part 5a of the shaft 5 inserted into the close-ended opening 6b of the plunger 6, contact between the bottom 6ba and the end of the insertion part 5a can be ensured by using the resilient force of the recovery spring 8 when excitation current is not applied whereas the contact between the bottom 6ba and the end of the insertion part 5a can be ensured by using the electromagnetic force that attracts the plunger 6 in the contacting direction Xa when excitation current is applied. That is, the procedure of securely fixing the shaft 5 and the plunger 6 by welding, using an adhesive, or the like after temporarily fastening the shaft 5 and the plunger 6 can be omitted. Thereby, simplification of the manufacturing process and cost reduction can be achieved. Dynamic coupling between the end of the recovery spring 8 to the side of the separating direction Xb and the end of the shaft 5 to the side of the contacting direction Xa can be easily achieved by engaging the groove 5c of the small diameter part 5b of the shaft 5 to a commonly used E-ring 10. That is, the processing procedures such as changing the shape of the end of the small diameter part 5b of the shaft 5 for coupling with the recovery spring 8 or inserting a pin for receiving the end of the shaft 5 into an opening provided in a radial direction of the small diameter part 5b can be omitted. By placing the insulating barrier 15 along the areas in which the yoke 11 and the yoke 13 extend, the insulating performance between the electric coil wire 14 and the magnetic circuit can be enhanced. That is, even if a sufficient insulating distance cannot be obtained due to downsizing of the electromagnetic relay 1, a reliable insulating property can be attained by placing the insulating barrier 15. Further, the constraining part 15b of the insulating barrier 15 defines the positioning between the bobbin 16 and the driving part housing 17 interposed by the yoke 11 and the positioning between the bobbin 16 and the connection housing 19 interposed by the yoke 13. Because a reliable insulating property can be attained, the PWM control unit 20 can be easily installed in the contact housing 18, and centralization of components can be achieved. By arranging the fixed contact 2 only in a part of the end of the fixed terminal 21 that faces the movable contact 3, the volume of the material used for forming the fixed contact 2 can be reduced to achieve cost reduction. Particularly, cost reduction can be achieved significantly in a case where a noble metal system is used as the fixed contact 2. <Second embodiment> Unlike the constraining part of the electromagnetic relay 1 of the first embodiment, a constraining part of the second embodiment includes a shaft 25 and a through-hole 26b as illustrated in Fig. 10. The shaft 25 includes an insertion part 25a and a large diameter part 25b having a diameter greater than the diameter of the insertion part 25b. The through-hole 26b for inserting the insertion part 25a therethrough is formed by perforating a plunger 26. Similar to the first embodiment, the electromagnetic relay of the second embodiment can ensure contact between an end of the large diameter part 25b toward the separating direction Xb and an surface of the plunger 26 toward the contacting direction Xa by using the resilient force of the recovery spring 8 when excitation current is not applied whereas the contact between the end of the large diameter part 25b and the surface of the plunger 26 can be ensured by using the electromagnetic force that attracts the plunger 26 in the contacting direction Xa when excitation current is applied. That is, similar to the first embodiment, the procedure of securely fixing the shaft 25 and the plunger 26 by welding, using an adhesive, or the like after temporarily fastening the shaft 25 and the plunger 26 can be omitted. Thereby, simplification of the manufacturing process and cost reduction can be achieved. With the second embodiment, the processing of the plunger 26 is easier compared to the processing of the close-ended plunger 6 because the through-hole 26b is formed by simply perforating the plunger 26. Thereby, further cost reduction can be achieved. The electromagnetic relay according to the embodiments of the present invention is suitably used for domestic, industrial, and in-vehicle purposes. Explanation of Reference Numerals - 1
- electromagnetic relay
- 2
- fixed contact
- 3
- movable contact
- 4
- movable element
- 5
- shaft (axial core)
- 6
- plunger (movable core)
- 7
- driving part
- 8
- recovery spring (urging part)
- 9
- pressure spring
- 10
- E-ring (plate part)
- 11
- yoke (planar U-shape)
- 12
- yoke (cylindrical shape)
- 13
- yoke (planar shape)
- 14
- electric coil wiring
- 15
- insulating barrier (sector shape)
- 16
- bobbin (wound part)
- 17
- driving part housing
- 18
- contact housing
- 19
- connection housing
- 20
- PWM control circuit (drive circuit)
- 21
- fixed terminal
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