Electromagnetic contactor

Abstract: An electromagnetic contactor has a case (1, 26) including an electromagnet, a movable armature (90), and contact means (11, 12) adapted to close and open in response to a motion of the armature. The electromagnet comprises a substantially U-shaped iron core (30) composed of a first and a second core part (25, 24) defining a main leg and a yoke (25B), and a coil (8) wound on a coil bobbin (27), said main leg extending through an opening of said coil bobbin and said main leg and said yoke each defining a respective pole face adapted to cooperate with said armature. The first core part (25) is substantially U-shaped and has an upper arm (25A) inserted into said opening of the coil bobbin (27), and a lower arm (25B) forming said yoke. The second core part (24) has a first leg which is also inserted into said opening and held in contact with said upper arm therein, and a bent second leg which forms the pole face of said main leg. This structure allows an easy manufacturing of an iron core (30) having sufficiently large areas of both the cross-section of the main leg and the pole face of the main leg.

Description: The present invention relates to an electromagnetic contactor, and in particular, to an iron core for the electromagnet of such contactor. An electromagnetic contactor is a widely used component generally composed of an electromagnet, a movable armature arranged to be driven by the electromagnet, and one or more switch contacts which are opened or closed in response to the armature moving from one position to another one. With reference to Figures 11 and 12 one example of a conventional electromagnetic contactor will be explained in more detail below. Figure 11 is a cross-sectional view of the contactor while Figure 12 is an exploded perspective view of its electromagnet and its armature. The electromagnet comprises an iron core 3 and a coil 8. The iron core 3 comprises a main leg 5 and a yoke 4. The coil 8 is wound around the main leg 5 on a coil bobbin 6. The electromagnet and the armature 9 are housed in a lower case 1 with the yoke 4 disposed on the bottom 1A of the lower case 1. A laterally movable holder 10 is housed in an upper case 2. The holder is biased to the left by a return spring 7 disposed between the holder and a side wall of the upper case 2. The holder 10 carries movable contacts 11 via contact springs 13. Fixed contacts 12 are fixed to the upper case 2. Each pair of movable contact and fixed contact forms a switch contact. A respective contact piece 12A is attached to each fixed contact 12 so as to oppose a respective one of contact pieces 11A attached to the movable contacts 11 so that the contacts can connect and disconnect via their contact pieces. The movable and the fixed contacts 11 and 12 are connected to an external main circuit via terminals (not shown). An engaging section 9A of a movable iron piece forming the armature 9 is fitted in a fitting section 10A of the holder 10 as shown in Figure 11. The armature 9 extends from the inside the lower case 1 to the inside of the upper case 2. The armature is disposed adjacent to the left end surfaces of the main leg 5 and the yoke 4 and pivotally supported on the bottom 1A of the lower case 1. The upper and the lower cases 2 and 1 are connected. A shown in Figure 12 the iron core 3 comprises the bar-like main leg 5 and the L-shaped yoke 4 which together form a U-like shape. The main leg 5 is inserted and fitted in a rectangular through-opening 6A formed in the coil bobbin 6. The armature 9 is located in front of and to the left of the coil bobbin 6, and has at its top the engaging section 9A with a width significantly reduced compared to the remaining part of the armature. Returning to Figure 11, when the coil 8 is energized, the armature 9 is attracted to the iron core 3 and rotates clockwise. Thus, the engaging section 9A of the armature 9 pushes, via the fitting section 10A, the movable holder 10 to the right against the force of the return spring 7. As a result of this motion the contact pieces 11A contact the contact pieces 12A, respectively. Under this condition, the contact springs 13 push the respective movable contacts 11 against the respective fixed contacts 12, thereby providing the contact pressure required for a good contact between the contact pieces 11A and 12A. When the coil 8 is deenergized so that the attractive force of the iron core 3 is removed, the force of the return spring 7 predominates, causing the holder 10 to return to the left while rotating the armature 9 counterclockwise. As a result of this return motion the contact pieces 11A and 12A disconnect from each other. The switch contacts (11, 12) shown in Figure 11 are A contacts (normally open contacts) that are closed when the coil 8 is energized. Instead of or in addition to such A contacts such contactor may include B contacts that are normally closed but are opened when the coil 8 is energized. Conventional contactors such as that described above require an expensive cutter for cutting the iron core from a plate, as well as a large number of processing steps. That is, to ensure that the iron core develops sufficient attractive force, the main leg must have a large cross-sectional area and the end face of the main leg must have a large pole surface. Thus, a thick iron plate is used as the material for the main leg 5 such as shown in Figure 12. With a thick iron plate, the cut surface sags when a general press machine operating at a normal speed is used, resulting in a reduced pole face area with inappropriate squareness and flatness. Consequently, a special fast cutter is used to cut the main leg 5. Although the above problem could be solved by cutting the material at high speed, fast cutters are more expensive than general press machines due to their better performance. Thus, use of a general press machine is preferably to avoid an increase in manufacturing costs. In addition, in Figure 12, since the end face 5A of the main leg 5 and the end face 4A of the yoke 4 constitute pole faces, these surfaces must be polished so as to be coplanar, and this increases the number of processing steps. Furthermore, the main leg 5 and the yoke 4 are joined together by means of resistance welding, and such welding increases the number of processing steps further. It is an object of this invention to provide a high performance electromagnetic contactor having an iron core which can be cut by means of a press machine operating at a normal cutting speed, and which can be manufactured with a relatively small number of processing steps. This object is achieved with an electromagnetic contactor as claimed in claim 1. Preferred embodiments of the invention are subject-matter of the dependent claims. According to the invention, since the main leg is composed of two members, when the two members together have a total thickness equal to that of the main leg in the prior art they provide the same cross-sectional area but the thickness of each member is substantially smaller than that of the main leg in the prior art. Thus, the iron core can be manufactured from a correspondingly thin plate using a press machine operating at a normal cutting speed. In addition, because the two members, once they are assembled, are held together by the coil bobbin through which they both extend, no welding or other technique for joining is required. By giving the second core part a shape like an L or a T of which one leg forms a pole face, the pole area of the main leg and the attractive force exerted by it can be easily increased compared to those of the conventional contactor. The upper arm of the first core part may be shorter than its lower arm. In this case, the end face of the lower arm of the first core part and a surface of the second core part constitute the pole faces. These surfaces may be easily disposed to be coplanar during the assembly of the iron core. This eliminates the need for polishing to make the end faces of the U-shaped first core part coplanar. In addition, the first and the second core parts may each be gripped by ribs protruding inside the case. Such ribs allow the core parts to be fixed and reliably positioned. As a result, the pole face forming end face of the lower arm of the first core part and the pole face forming surface of the second core part may be easily disposed so as to be coplanar. The width of the portion of the upper arm of the first core part that penetrates the opening in the coil bobbin may be larger than the width of the corresponding portion of the second core part, while stages that make the inner width of the upper part of the opening smaller than that of the lower part may be formed on the side walls of the opening. This allows the stages to serve as guides when the first core part is inserted into the lower part of the opening first and the second core part is inserted into the upper part of the opening subsequently, thereby enabling the iron core to be incorporated easily. To ensure an intimate contact between the first and second core parts protruding portions that press one of the core parts against the other one are preferably formed on an inner wall of the opening in the coil bobbin and/or on the surface of one or both core parts adjacent to an inner wall of the opening. Preferred embodiments of the invention will be described hereinafter with reference to the drawings, in which: Fig. 1 is a cross-sectional view showing a first embodiment of this invention, Fig. 2 is a cross-sectional view of a lower case in Figure 1, Fig. 3 is a plan view of the lower case in Figure 1, Fig. 4 is a perspective view of the lower case in Figure 1, Fig. 5 is an exploded perspective view of the components forming the electromagnet and the armature, Fig. 6 is a cross-sectional view showing the electromagnet incorporated in the lower case in Figure 2, Fig. 7(A) is a cross-sectional view taken along line A-A in Fig. 6 showing the configuration of the coil bobbin without the main leg inserted, Fig. 7(B) is the same view as in Fig. 7(A) but with the main leg inserted, Fig. 8 is a cross-sectional view showing a second embodiment of this invention, Fig. 9 is a perspective view showing the configuration of the second core part in Figure 8, Fig. 10 is a cross-sectional view showing a third embodiment of this invention, Fig. 11 is a cross-sectional view showing a conventional electromagnetic contactor, and Fig. 12 is an exploded perspective view of the components forming the electromagnet and the armature in Figure 11. Throughout the drawings like reference numerals denote like elements. Figure 1 is a cross-sectional view showing a first embodiment of this invention in a view similar to that of Figure 11. The contactor of this first embodiment differs from that shown in Fig. 11 and explained above in that the iron core 3 is replaced by an iron core 30 which comprises a first substantially U-shaped core part 25 with an upper arm 25A and a lower arm 25B, and a second substantially L-shaped core part 24 with a core leg 24a and a pole leg 24b. The left-side surfaces (as viewed in Figure 1) of the two core parts 25 and 24 are located to face a movable iron piece forming the armature 90. The first core part 25 is disposed at the bottom of a lower case 26. The remaining part of the configuration is the same as that of the conventional contactor. Figures 2, 3, and 4 are a cross-sectional view, a plan view, and a perspective view of the lower case 26 in Figure 1. In each figure, ribs 26A, 26B, 26C, and 26D protrude inside the lower case 26, and the end surface of the rib 26A adjacent to the bottom is coplanar with the side of the rib 26B. Figure 5 is an exploded perspective view of the core parts 24, 25, the coil 8 and the armature 90. The upper arm 25A and the lower arm 25B of the first core part 25 are formed by bending an iron plate, and the upper arm 25A is inserted into the rectangular through-opening 27A of the coil bobbin 27 from one side and moved in the direction shown by arrow 32. The core leg 24a and the pole leg 24b of the second core part 24 are also formed by bending an iron plate and the core leg 24a is additionally inserted into the opening 27A from the opposite side along the two-dot chain line 31. The armature 90 has notches 90B in its lower part. Their purpose will be explained later. Both the first and the second core parts 25 and 24 shown in Figure 5 are made by first cutting an iron plate to the respective shape and then bending it. Since the main leg of the iron core is composed of two members, that is, the upper arm 25A of the first core part 25 and the core leg 24a of the second core part 24, the thickness of each member is smaller than that of the main leg in the prior art. In other words, in order to obtain a sufficient cross-sectional area of the main leg it is no longer necessary to cut the main leg from a correspondingly thick iron plate. Instead, those two members can be cut from relatively thin plates. Thus, cutting can be carried out by a press machine operating at a normal cutting speed, thereby eliminating the need for an expensive fast cutter. In addition, the first and second core parts 25 and 24 need only be brought together during assembly, thereby eliminating the need for welding. Consequently, fewer processing steps are required than in the case of the conventional contactor. Furthermore, a surface 24C of the pole leg 24b of the second core part 24, which extends vertically (as viewed in Figure 1), constitutes a pole face. The area of this pole face is determined by the length and the width of the pole leg 24b. Therefore, the size of this area can be suitably selected independent from the thickness of the plate so as to optimize the attraction exerted on the armature 90. As shown in Figure 5, the width of the pole leg 24b may be greater than that of the core leg 24a (see portions 24A on both sides of the pole leg 24b). Figure 6 is a cross-sectional view showing the iron core incorporated in the lower case 26 in Figure 2. The first core part 25 is gripped between the ribs 26A and 26D, while the second core part 24 is gripped between the ribs 26B and 26C. The left-side end face of the lower arm 25B of the first core part 25 must be coplanar with the left-side surface 24C of the pole leg 24b of the second core part 24 because they constitute pole faces. The relative positions of the ribs are such that the two ribs 26A and the two ribs 26B are disposed on the left side of the lower case 26 (the side of the armature 90), while the two ribs 26C and the two ribs 26D are disposed on the side wall on the right side of the lower case 26 (the side remote from the armature 90). These ribs fix the first and the second core parts 25 and 24 and secure their positioning. Thus, the pole face of the first core part 25 can easily be made to be in the same plane as the pole face of the second core part 24. The notches 90B in the armature 90 in Figure 5 are formed to prevent the armature from contacting the ribs 26A in the lower case 26 during rotation in Figure 4. In addition, as shown in Figure 6, the upper arm 25A of the first core part 25 is somewhat shorter than its lower arm 25B. The upper and the lower arms 25A and 25B may have the same length, but making the upper arm 25A shorter than the lower arm 25B ensures that the armature 90 constantly contacts the surface 24C of the second core part 24 when the coil 8 is energized. Even though only the pole leg 24b of the second core part 24 is used as the pole face on the main leg side, sufficient attractive force can be obtained because the area of the surface 24C can be adjusted easily. This eliminates the need for polishing to make the left-side end faces of the upper and the lower arms 25A and 25B coplanar, thereby further reducing the number of processing steps required. Figures 7(A) and (B) are a cross-sectional views of Figure 6 taken along line A-A. Figure 7(A) shows only the coil bobbin 6, and Figure 7(B) shows the coil bobbin 27 with the main leg inserted. As shown in Figure 7(A), protrusions 27B are formed on the upper wall of the opening 27A in the coil bobbin 27, and stages 27C are formed on the side walls of the opening 27A. The width of the upper arm 25A of the first core part 25 and that of the core leg 24a of the second core part 24 are such that they can be fitted in the opening with the stages, as shown in Figure 7(B). Since the protrusions 27B press the core leg 24a against the upper arm 25A when they are inserted into the opening 27A, the upper arm 25A and the core leg 24a are forced into intimate contact with each other, thereby reducing the magnetic resistance between them. In addition, when the main leg is inserted into the opening 27A, the upper arm 25A of the first core part 25 is inserted first and the core leg 24a of the second core part 24 second. Since the stages 27C serve as guides when the upper arm 25A is inserted, the upper arm 25A can be moved along the bottom of the opening 27A, leaving a free space in the upper part of the opening 27A to allow the core leg 24a to be fitted into the opening 27A smoothly. This reduces the number of operations required during the insertion of the main leg. Instead of the protrusions 27B, ribs may be formed on the upper wall of the opening. Figure 8 is a cross-sectional view showing a second embodiment of this invention. The contactor according to this embodiment differs from the one explained above in that the second core part 24' includes protrusions 28. These protrusions are provided on the side of the core leg 24a' remote from the upper arm 25A. Thus, these protrusions 28 serve the same purpose as the protrusions 27B and may be provided instead of or in addition to the latter. As shown in Figure 9 two protrusions 28A are provided on the core leg 24a'. Similar protrusions (not shown) may be provided on the side of the upper arm 25A remote from the core leg 24a' (or 24) in addition to or instead of the protrusions 28 and/or 27B. The remaining parts of the second embodiment are the same as those of the first embodiment. Figure 10 is a cross-sectional view showing a third embodiment of this invention. The contactor according to this embodiment differs from the first and the second embodiment in that the second core part 24" is T-shaped rather than L-shaped, while the remaining parts may be the same as in the first or the second embodiment. A vertical (as viewed in the Figure) pole leg 24b" on the left end of the second core part 24" is formed by, for example, forging. The surface of the pole leg 24b" facing the armature 90 constitutes a pole face and acts like the surface 24C (Figure 5) in the first and the second embodiment. Compared to the L-shape of the second core part in the preceding embodiments, the T-shaped structure allows for a further increase in the area of the pole face on the side of the main leg while maintaining the advantage of not requiring polishing to make the left-side end faces of the upper and the lower arms 25A and 25B of the first core part 25 coplanar.

Claims: An electromagnetic contactor having a case (1, 26) including an electromagnet, a movable armature (90) adapted to be driven by the electromagnet, and contact means (11, 12) adapted to close and open in response to a motion of the armature, said electromagnet comprising a substantially U-shaped iron core (30) having a main leg (25A, 24a; 25A, 24a'; 25A, 24a") and a yoke (25B), and a coil (8) wound on a coil bobbin (27), said main leg extending through an opening (27A) of said coil bobbin and said main leg and said yoke each defining a respective pole face adapted to cooperate with said armature, characterized in that said iron core (30) comprises a substantially U-shaped first core part (25) having an upper arm (25A) inserted into said opening (27A) of the coil bobbin (27), and a lower arm (25B) forming said yoke, and a second core part (24; 24'; 24") having a first leg (24a; 24a'; 24a") which is also inserted into said opening and held in contact with said upper arm therein, and a bent second leg (24b; 24b'; 24b') which forms the pole face of said main leg, wherein means (26A-26D) are provided for fixing said core parts in said case (1, 26). The contactor according to Claim 1, characterized in that said second core part (24; 24') is substantially L-shaped. The contactor according to Claim 1, characterized in that said second core part (24") is substantially T-shaped. The contactor according to any one of Claims 1 to 3, characterized in that the upper arm (25A) of the first core part (25) is shorter than its lower arm (25B). The contactor according to any one of Claims 1 to 4, characterized in that the first and the second core parts (25, 24; 25, 24'; 25, 24") are each gripped and positioned by ribs (26A-26D) protruding inside the case (1, 26). The contactor according to any one of Claims 1 to 5, characterized in that the width of the upper arm (25A) of the first core part (25) is larger than that of the first leg (24a; 24a'; 24a") of the second core part (24; 24'; 24"), that stages (27C) that make the inner width of the upper part of the opening (27A) of the coil bobbin (27) smaller than that of the lower part are formed on the side walls of the opening, and that the upper arm of the first core part (25) is fitted in the lower part of the opening while the first leg of the second core part is fitted in the upper part of the opening. The contactor according to any one of Claims 1 to 6, characterized in that protruding portions (27B) that press one of the core parts (25, 24; 25, 24'; 25, 24") against the other are formed on the inner wall of the opening (27A) in the coil bobbin (27). The contactor according to any one of Claims 1 to 7, characterized in that protruding portions (28) are formed on the side of at least one (24a') of said upper arm (25A) of the first core part and said first leg (24a') of the second core part, which is remote from the other one of the two (25A, 24a').

Inventors: HIRAMATSU ETSUYA, HIROTA TAKATO, KAWASAKI MAKOTO, MACHIDA NORIYOSHI, SHIBATA KATSUMI, HIRAMATSU, ETSUYA, HIROTA, TAKATO, KAWASAKI, MAKOTO, MACHIDA, NORIYOSHI, SHIBATA, KATSUMI
Applicants: FUJI ELECTRIC CO LTD, FUJI ELECTRIC CO. LTD.
Application year: 1997
Main classification: H01H50
IPC codes: H01H50, H01H51