Electromagnetic relay

Abstract: The object of this invention is to provide an electromagnetic relay which would comprise a smaller number of components and would be shorter than its predecessors. A movable block (60) and a contact mechanism in a conventional relay are arrayed in a linear fashion, which tends to increase the length of the relay. This relay, however, has a movable block (60) placed on a electromagnetic block (40), and a drive rod extending from the movable block drives a contact mechanism (30) which is installed on one side of the electromagnetic block (40) to shorten the length of the relay.

Description: Field Of The Invention This invention concerns an electromagnetic relay, and more specifically, the drive mechanism which makes and breaks the contacts of the relay. Background of The Invention An example of an electromagnetic relay belonging to the prior art is shown in Figure 16. This relay comprises electromagnetic block 1, which is formed by wrapping coil 1c around two facing L-shaped cores, 1a and 1b; H-electrode 2b, which rotates shaft 2a on its axis in response to the presence or absence of excitation in electromagnetic block 1; transmission mechanism 3, which travels back and forth with the rotation of H electrode 2b; and contact mechanism 6, in which the movement of transmission mechanism 3 causes movable contacts 4a on members 4 to come in contact with or move away from fixed contacts 5a on members 5. 7 is a spring mounted on support 8 to return mechanism 3 to its original position. In the electromagnetic relay which we have been discussing, contact mechanism 6 is driven by H electrode 2b and transmission mechanism 3, a scheme which requires a large number of components. This entails a large number of assembly processes and increases the likelihood that the precision with which the components are assembled, and hence the operating characteristics, will vary. Also, in this relay electromagnetic block 1, H electrode 2b and contact mechanism 6 are arrayed in a linear fashion, which tends to increase the length of the relay. Since the length of contact mechanism 6 will increase with the number of circuits, it will be impossible to produce a short electromagnetic relay if there are a large number of circuits to make and break. An electromagnetic relay according to the preamble of claim 1 is known from DE 32 24 070 A. Summary Of The Invention The objective of this invention is to provide an electromagnetic relay with fewer components so that it can be made shorter. In the relay described above, H electrode and transmission mechanism are discrete components which are not assembled as a single piece and do not operate as a single component. For this reason they are liable to vary in assembly precision and operating characteristics, which will adversely affect the repeatability of their response. In light of these difficulties, another objective of this invention is to provide an electromagnetic relay whose assembly precision and operating characteristics will not vary and which will have a good response characteristic. In order to achieve the objectives outlined above, the electromagnetic relay of this invention is as defined in claim 1. The aforesaid electromagnetic and movable blocks are enclosed in a box-shaped base block comprising two bases on whose exteriors are mounted the aforesaid contact mechanisms. The aforesaid bases should be identical in shape. The positions of the aforesaid electromagnetic and movable blocks should be adjustable within the aforesaid box-shaped base block in the axial direction of the aforesaid core so that the operating characteristics of the aforesaid contact mechanisms can be adjusted. The aforesaid contact mechanism comprises a number of pairs of movable and fixed contacts fitted into grooves in the exterior walls of the aforesaid box-shaped base. These contacts should act as partitions which touch the interior walls of the cover fitted onto the aforesaid base so that the walls are partitioned by each set of movable and fixed contacts. On the interior walls of the aforesaid cover there should be ribs which adjoin the aforesaid partitions. The aforesaid movable block engages with a member which is mounted on a card from which at least one drive rod protrudes to one side to drive the aforesaid contact mechanisms. The aforesaid movable block should comprise a permanent magnet sandwiched between two movable iron members. Two cut-away portions on the side of the aforesaid lower member should engage with two bosses on the internal surface of the aforesaid card. The aforesaid permanent magnet should engage between a pair of bosses on the internal surface of the aforesaid card. The cut-away portions on the movable member on the upper end of the magnet should engage with tangs extending upward from the upper edge of the aforesaid card. Alternatively, the aforesaid movable block may be supported by two springs which engage with the ends of the card in such a way that the block is free to move back and forth in a course which is parallel to the axis of the aforesaid core. The exterior front edges of the card which come in contact with the inward-facing surfaces of the aforesaid supporting springs may be different distances from the center line of the card. Brief Description Of The Invention Figure 1 is an exploded perspective drawing of an electromagnetic relay which is an ideal embodiment of this invention. Figure 2 is an exploded perspective drawing of the relay shown in Figure 1 when it is partly assembled. Figure 3 is a frontal view of the electromagnetic and movable blocks installed in the base. Figure 4 is a perspective drawing showing how the cover is mounted on the base block. Figure 5 is a frontal cut-away view of the relay in Figure 1 when the cover has been installed on the base block enclosing the electromagnetic and movable blocks. Figure 6 is a magnified perspective drawing of the base units which comprise the base block. Figure 7 is an exploded perspective drawing showing how the contact mechanisms are installed in the base. Figure 8 shows one of the base units. (a) is a perspective drawing of the unit viewed from within; (b) is a drawing of the same unit viewed from without. Figure 9 is a perspective drawing of the electromagnetic block. Figure 10 is an exploded perspective drawing of the electromagnetic block. Figure 11 shows one of the support springs pictured in Figure 10. (a) is a frontal view of the spring before it is bent. (b) is a frontal view of the spring after it is bent. (c) is a view from the left side. (d) is a view from the rear. (e) is a perspective drawing of the spring viewed from below. Figure 12 is an exploded perspective drawing of the movable block. Figure 13 shows the card for the movable block. (a) is a planar view. (b) is a magnified view of an essential part of the block. (c) is a perspective drawing of a cross section of the block. (d) is a cross section viewed from the front. Figure 14 is a perspective drawing which shows the movable block mounted on the electromagnetic block. Figure 15 shows the electromagnetic and movable blocks from Figure 14. (a) is a frontal view and (b) is a simplified frontal view. Figure 16 is a cross section of an electromagnetic relay belonging to the prior art, viewed from the front. Detailed Description of The Invention We shall next discuss an ideal embodiment of this invention with reference to the appended drawings in Figures 1 through 15. The electromagnetic relay shown in Figure 1 is an embodiment of this invention. It comprises primarily of base block 10, electromagnetic block 40, movable block 60 and case cover 80. Base block 10 is shaped roughly like a box and comprises of two halves, base unit 20 and base unit 21 (See Figure 6). Contact mechanisms 30 are installed on the exterior surfaces of the aforesaid base units 20 and 21. Since base units 20 and 21 are identical in shape, we shall omit a detailed explanation of base unit 20 for the sake of brevity. As can be seen in Figures 7 and 8, the exterior surface of base unit 21 is divided by partitions 22a and 22b into three parallel niches, 23a, 23b and 23c. Drive rods 65, 66 and 67 in movable block 60, which is shown in Figure 12 and will be discussed shortly, extend all the way to the innermost portions of niches 23a, 23b and 23c. Apertures 24a, 24b and 24c, which allow the drive rods to travel back and forth, are cut into the lateral surface of the base unit. At the lower ends of niches 23a, 23b and 23c are three pairs of slits, 25a through 25f, which communicate with the aforesaid niches 23a, 23b and 23c. Two indentations, 26a and 26b, are provided on the upper portion of niche 23b. Two disconnected positioning ribs, 27a and 27b, divide each of the aforesaid niches 23a, 23b and 23c down their center lines. Next to the aforesaid niches 23a and 23c are two through holes, 28a and 28b, which are to be used for caulking. On the ends of the aforesaid base unit 21 are cut-away portions 28c, which form apertures 11, to be discussed later. In the lower left and right corners of the outer surface of the aforesaid base unit 21 are bosses 28d, which engage with the case. In the upper left and right corners of the inner surface of the aforesaid base unit 21, the surface which engages with its counterpart, are peg 28e and hole 28f. Terminals 31a through 36a, on fixed contact elements 31, 33 and 36 and movable contact elements 32, 34 and 35, are pressed into slits 25a through 25f in base unit 21. In this way fixed contact elements 31, 33 and 36 come in contact with and are held in position by ribs 27a and 27b on base unit 21; and their fixed contacts, 31b, 33b and 36b, are brought face to face with movable contacts 32b, 34b and 35b so that they can make or break contact with them. Because the positions of fixed contact elements 31, 33 and 36 are stabilized by the aforesaid ribs 27a and 27b in this embodiment, the contacts may be separated by force even if contact welding should occur. Furthermore, the three aforesaid pairs of ribs 27a and 27b are interposed between fixed contact elements 31, 33 and 36 and their respective movable contact elements 32, 34 and 35. This arrangement improves the isolation characteristic of the relay. Also, in this embodiment fixed contact elements 31, 33 and 36 and movable contact elements 32, 34 and 35 can be pressed into various positions. This arrangement is convenient in that it allows the user to realize any of a number of different electromagnetic relays with various contact specifications. Since base units 20 and 21 have the same shape, there are fewer components to manage, a single mold will suffice, and economies can be realized in production costs. Electromagnetic block 40 is pictured in Figures 9 and 10. Coil 44 is wrapped around the central portion of spool 43, which is linearly symmetric. On either end of spool 43 are flanges 41 and 42. The ends of the coil which are drawn out are tied and soldered to coil terminals 45 on flange 41. Core 50 is inserted into center hole 46 of the aforesaid spool 43. Magnetic isolation plate 51, core support 52 and spring 53 are fitted, one after the other, onto one protruding end of the core and caulked in place. Core support 54, magnetic isolation plate 51 and spring 53 are fitted, one after the other, onto the other end of the core and caulked in place. In this embodiment, then, springs 53 are fixed directly to electromagnetic block 40. This insures that the relay can be assembled with precision so that its operating characteristics will not vary. Magnetic isolation plate 51 and spring 53 are also secured at the same time that core support 52 is caulked in place. This reduces the number of assembly processes required. Magnetic isolation plate 51 comprises a thin plate of spring material in which hole 51a, which is to be used for caulking, has been punched. Its lower edge is bent at a right angle to form positioning stop 51b. Stop 51b engages with the lower surface of core support 52 to ensure that this support is mounted securely. Core supports 52 and 54 have a cross-shaped frontal surface. Arms 52a and 54a, which are used in the caulking process, project to either side of each support. The upper ends of the respective supports serve as magnetic poles 52b and 54b. Holes 52c and 54c, also used for caulking, are in the centers of the lower portions of the two supports. Support springs 53, which can be seen in Figure 11, are stamped from a thin spring material which is then bent into shape. When the lower end of the spring is bent upward and folded upon itself, tab 53b, which will lock the bottom of the spring in position, projects beyond the lower edge of hole 53a, and caulking hole 53c is left open. Support springs 53 have two indentations 53e on their sides to allow them to engage with the other components. The aforesaid tab 53b comes in contact with the lower edge of hole 53a, which is near the line 53d marking the angle created by bending the spring. Thus the upper half of each spring 53 rotates on the axis of line 53d. There is no possibility that the bearing will slip, and the operating characteristics will remain stable. Movable block 60, which is shown in Figure 12, is formed by mounting on card 61, successively, L-shaped movable iron member 70 (first movable member), permanent magnet 71, which has the shape of a rectangular prism, and C-shaped movable iron member 72 (second movable member). Card 61, which is pictured in Figure 13, has two parallel side walls 62. On the inner surface of each wall is a pair of L-shaped projections, 63a and 63b. Tabs 64a and 64b project from the upper edges of both of the aforesaid walls 62. On the outer surface of each wall 62 are three drive rods, 65, 66 and 67, to drive the aforesaid movable contact elements 32, 34 and 35. Drive rods 65, 66 and 67 have, respectively, slits 65a, 66a and 67a, into which the movable contact elements can be pressed. Arms 68 extend in parallel from the ends of the aforesaid side walls 62. Ridges 69a and 69b, which traverse the ends of the card, come in contact with the aforesaid support springs 53. Recesses 68a face each other on the inner surfaces of the aforesaid arms 68. A cross section of one of the aforesaid ridges 69a and 69b would make linear contact with one of the aforesaid support springs 53. The inner edges of ridges 69a and 69b are equidistant form the center line of card 61. However, the loads on the two support springs 53 will vary when their angles of rotation vary, so the outer edges of ridges 69a and 69b will be different distances from the center line of card 61. As shown in Figure 12, first movable member 70 has two recesses 70c on its lateral edges between its two extremities, 70a and 70b. Permanent magnet 71 is of a length which allows it to fit in region 63c between the aforesaid projections 63a and 63b as shown in Figures 13 (c) and (d). Second movable member 72, as shown in Figure 12, has a projection 72c on the lateral surface of each of its ends. Between projections 72c it has two indentations, 72d and 72e, on its lateral surface. Thus when first movable member 70 is placed from above between side walls 62 on card 60, its recesses 70c engage with projections 63a and 63b on the inner surfaces of walls 62 to lock the member in place with respect to both its length and breadth. When permanent magnet 71 is fitted into the region between the aforesaid adjacent projections 63a and 63b, it is also immobilized with respect to its length and breadth. Projections 72c on second movable member 72 engage in recesses 68a on card 61. When indentations 72d and 72e engage with tabs 64a and 64b on side walls 62, second movable member 72 is immobilized with respect to its length and height. This completes the assembly of movable block 60. This embodiment offers the advantage that permanent magnet 71 is securely fixed to card 61. When support springs 53 in electromagnetic block 40 are extended, the ends of arms 68 of movable block 60 engage in recesses 53e on the springs. In this way ridges 69a and 69b on card 61 make contact with the inner surfaces of support springs 53 along a single line, and movable block 60 is supported in such a way that it can travel back and forth parallel to the center line of core 50 (See Figure 14). In this embodiment, then, the ends of movable block 60 are supported by two springs 53. This arrangement minimizes the effects of friction and so stabilizes the operating characteristics. Furthermore, because the ends of block 60 are supported by two springs 53, the aggregate spring force will not vary even if the spring characteristics of individual springs produced in different lots may vary. Thus there will be no variation of operating characteristics due to variations in the precision with which springs 53 were produced. Once they are assembled as outlined above, electromagnetic block 40 and movable block 60 are mounted on the interior walls of base 20. Movable contact elements 32, 34 and 35 are pressed into slits 65a, 66a and 67a in drive rods 65, 66 and 67 on card 61, which project through windows 24a, 24b and 24c in the base unit. When the aforesaid pegs 28e and holes 28f on base units 20 and 21 engage with each other, movable contact elements 32, 34 and 35 are pressed into slits 65a, 66a and 67a in drive rods 65, 66 and 67, which project from windows 24a, 24b and 24c in base unit 21. When arms 52a and 54a of core supports 52 and 54, which project from through holes 28a and 28b in base units 20 and 21 are caulked, base units 20 and 21 are combined into a single unit and base block 10 is completed. In this embodiment, arms 52a and 54a are able to travel slightly in the dimension of their length in through holes 28a and 28b. Thus if the load on the spring varies as a consequence of changing the combination of normally open and normally closed contacts, we can adjust it by sliding the electromagnetic and movable blocks lengthwise with respect to the base block. This arrangement allows us to realize various electromagnetic relays with different contact specifications using the same set of components. In this embodiment, when cut-away portions 28c in base units 20 and 21 are put together, they form aperture 11, which allows support springs 53 on either end of base block 10 to be adjusted. Thus the user can check the operating characteristics before installing cover 80, which will be discussed shortly. If the characteristics are not suitable, he can change them by adjusting support springs 53. The contacts in contact mechanism 30 are separated by electromagnetic block 40 and movable block 60 with the help of base units 20 and 21. This arrangement insures that the electromagnetic relay will have a superior isolation characteristic. Case cover 80 has the form of a box which engages with base block 10 to enclose electromagnetic block 40 and movable block 60. It has two parallel ribs, 81a and 81b, on its interior surface. Even if cover 80 expands outward, ribs 81a and 81b are still engaged in indentations 26a and 26b in base units 20 and 21, so they will remain in contact with partitions 22a and 22b. For this reason the surface distance between niches 23a, 23b and 23c will increase and the isolation characteristic will improve. 82 are anchoring holes, and 83 are the anchors which go through them. As can be seen in Figure 4, ribs 81a and 81b on cover 80 are pressed into recesses 26a and 26b in base block 10, which encloses electromagnetic block 40 and movable block 60. Bosses 28d on base units 20 and 21 engage in holes 82 in cover 20. At this point the assembly process is completed. In this embodiment, partitions 22a and 22b on base units 20 and 21 and cover 80 are interposed between each pair of fixed and movable contact elements in contact mechanism 30. This arrangement insures that the isolation characteristic will be favorable. We shall next discuss the operation of an electromagnetic relay configured as described above. First, as can be seen in Figure 15 (b), the opposed surface areas of end segment 70b of first movable member 70 and magnetic pole 54b of core support 54 are large, as are the opposed surface areas of end segment 72a of second movable member 72 and magnetic pole 52b of core support 52. This destroys the magnetic balance to left and right. For this reason, when voltage is not being applied to coil 44 in electromagnetic block 40, end segment 70b of first movable member 70 and end segment 72a of second movable member 72 are drawn to the aforesaid magnetic poles 54b and 52b by the magnetic force of permanent magnet 71 in opposition to the spring force of support springs 53. Accordingly, as can be seen in Figure 5, movable contacts 32b and 34b on contact elements 32 and 34 separate from fixed contacts 31b and 33b on elements 31 and 33, and movable contact 35b on contact element 35 moves over and touches fixed contact 36b on element 36. When voltage is applied to coil 44 so as to create magnetic flux in a direction which negates the magnetic flux of the aforesaid permanent magnet 71, end segment 70a on first movable member 70 is drawn toward magnetic pole 52b of core support 52. End segment 72b on second movable member 72 is drawn toward magnetic pole 54b of core support 54. Thus end segment 70b on first movable member 70 separates from pole 54b of core support 54, and segment 72a on second movable member 72 separates from pole 52b of core support 52. As a result, movable block 60 slides toward coil terminals 45 against the magnetic force of magnet 71 and the spring force of springs 53. Movable contact 35b separates from fixed contact 36b, and movable contacts 32b and 34b make contact with fixed contacts 31b and 33b, thus switching all the contacts. Segment 70a on first movable member 70 is drawn to magnetic pole 52b of core support 52, and segment 72b on second movable member 72 is drawn to pole 54b of core support 54. When this excitation is removed, the spring force of support springs 53 and the magnetic force of permanent magnet 71 cause movable block 60 to slide in the opposite direction and return to its original state. With this embodiment we have been discussing a relay in which the contacts automatically return to their original state. However, by choosing an appropriate spring force for the movable contacts and the support springs and an appropriate magnetic force for the permanent magnet, we could apply the invention in an electromagnetic relay which automatically maintained itself in the switched state. As should be clear from the previous discussion, the electromagnetic relay disclosed in claim 1 of this application has a movable block which fulfills the same function as the H electrode and the transmission mechanism in the example of the prior art. This invention, then, requires fewer components. Fewer production processes are required, and no variation will occur in the precision with which the parts are assembled or the operating characteristics, as was the case with prior art relays. Because the contact mechanism is driven directly by means of the movable block, energy loss is minimized and the energy efficiency of the relay is excellent. The arrangement chosen, whereby the movable block sits atop the electromagnetic block and the contact mechanisms are placed to either side of the electromagnetic block, allows us to achieve a shorter relay. Placing the contact mechanisms on both sides of the electromagnetic block gives the result that the length of the relay does not increase directly with the number of contacts or the length of the contact mechanism, as in prior art relays. The contact mechanism is partitioned by the electromagnetic block and the movable block with the help of the base. This arrangement allows us to achieve an electromagnetic relay with a superior isolation characteristic. The box-shaped base block is formed from two base units. As a result, the mold used to form the aforesaid base has a simpler configuration than would be required to form an entire box-type base block and is easier to construct. With the invention disclosed in claim 2, there is no need to stock two types of base units. This simplifies parts control and allows us to employ a single mold to form the base. The position of the electromagnetic block and the movable block may be adjusted by sliding them along the axial direction of the core. This changes the operating characteristics of the contact mechanism. Thus even if the load on the springs is altered when the combination of movable and fixed contact elements in the mechanism is changed, that load can be adjusted. Thus contact mechanisms with various specifications can be driven by the same electromagnetic block. Since the same components can be put to use for multiple purposes, parts control is simplified. With the invention disclosed in claim 3, the contact mechanism surrounded by the base on which the cover has been installed has a partition between each pair of movable and fixed contact elements. This design results in a contact mechanism with a superior isolation characteristic. With the invention disclosed in claim 4 the ribs on the cover make contact with the partitions on the aforesaid base. This has the effect of creating a longer surface between the neighboring pairs of contact elements already isolated by the base partitions, which further enhances the isolation characteristic of the relay. In the electromagnetic relay disclosed in claim 5, a movable block is installed on a card as one piece with a movable iron member. This movable block travels back and forth with its member in response to the presence or absence of excitation in the electromagnetic block, thus driving the contact mechanism. This arrangement eliminates variation in the precision with which the parts are assembled and the precision with which the relay operates. Also, the response characteristic is superior to that of prior art relays. In the electromagnetic relay disclosed in claim 6, the movable block is polarized to make it easier to achieve an electromagnetic relay with the desired operating specifications. In the electromagnetic relays disclosed in claims 7, 8 and 9, the two movable iron members and the permanent magnet can be mounted on the card easily and with a high degree of precision. In the electromagnetic relay disclosed in claim 10, support springs engage with both ends of the movable block. This allows the block to be supported in such a way that it can travel back and forth. With this arrangement, the aggregate spring force will not vary even if the spring characteristics of two springs produced in different lots does vary. Thus there will be no variation of operating characteristics due to variations in the precision with which the springs were produced. In the electromagnetic relay disclosed in claim 11, changing the shape of a cross section of the ridges on the card which come in contact with the support springs will adjust the angle of rotation of the springs and their force. This increases the freedom inherent in the design.

Claims: An electromagnetic relay, comprising: an electromagnetic block (40) formed by winding a coil (44) around a core (50) ; a movable block (60), placed on an upper end of said electromagnetic block (40) and having an iron member (70, 72), which moves back and forth parallel to said core (50) in response to a magnetization and demagnetization of said electromagnetic block (40), said movable block (60) being suspended on said electromagnetic block (40) by support springs (53); and a contact mechanism (30) having a fixed contact (31b, 33b, 36b) and a movable contact (32b, 34b, 35b) driven by a movement of said movable block (60), which is installed on one side of said electromagnetic block (40); characterized by a box-shaped base block (10) enclosing both said electromagnetic block (40) and said movable block (60), on whose exterior said contact mechanism (30) is mounted, said movable block (60) being provided with a drive rod (65, 66, 67) projecting from a window (24a, 24b, 24c) formed in said box-shaped base block (40), said drive rod (65, 66, 67) engaging said movable contact (32b, 34b, 35b) of said contact mechanism. An electromagnetic relay according to claim 1, wherein said box shaped base block (10) comprises a pair of base units (20, 21) having the same shape. An electromagnetic relay according to claim 1, said base block (10) comprising a base unit (20, 21) having a partition to separate a set of two contact elements (31, 32; 33, 34; 35, 36) for said fixed contact (31b, 33b, 36b) and said movable contact (32b, 34b, 35b) from another sets of two contact elements. An electromagnetic relay according to claim 3, wherein said base unit (20, 21) further comprises a rib (27a, 27b) to separate said set of two contact elements. An electromagnetic relay according to claim 1, wherein said movable block (60) comprising a card (61) having a drive rod (65, 66, 67) to drive a contact element (32, 34, 35) for said movable contact (32b, 34b, 35b). An electromagnetic relay according to claim 5, wherein said movable block (60) further comprises: first and second movable members (70, 72) driven by said magnetization of said electromagnetic block (10); and a permanent magnet (71) sandwiched between said first and second movable members (70, 72). An electromagentic relay according to claim 5, wherein a recess (70c) of said first movable member (70) engages with a projection (63a, 63b) on an internal surface of said card (61). An electromagnetic relay according to claim 5, wherein said permanent magnet (71) is immobilized between a pair of projections (63a, 63b) on an internal surface of said card (61). An electromagnetic relay according to claim 5, wherein said movable block (60) further comprises an indentation (72d, 72e) of said second movable member (72) engaging with a tab (64a, 64b) on said card (61). An electromagnetic relay according to claim 5, wherein said support springs (53) engage with ends of said card (61) in such a way that said movable block (60) is free to slide back and forth in a direction parallel to an axis of said core (50) in said electromagnetic block (40). An electromagnetic relay according to claim 10, wherein a distance between a ridge (69a) contacting with one of said support springs (53) and the center of said card (61) is different from a distance between another ridge (69b) contacting with another one of said support springs (53) and said center of said card (61).

Inventors: NOGUCHI TAKASHI, YAMAGUCHI TATSUNORI, NOGUCHI, TAKASHI, YAMAGUCHI, TATSUNORI, Noguchi, Takashi, c/o Omron Corporation, Yamaguchi, Tatsunori, c/o Omron Corporation
Applicants: OMRON TATEISI ELECTRONICS CO, OMRON CORPORATION
Application year: 1997
Main classification: H01H51
IPC codes: H01H51, H01H50