MONOSTABLE TYPE RELAY

Abstract: A monostable relay comprises a bar-like core having a coil, and a yoke connected to the core and extending in paral­ lel therewith. An armature including a permanent magnet is laterally movably disposed between a pair of upstanding legs formed at a free end of the yoke. Movable contacts are opera­ tionally coupled to the armature. The upstanding legs of the yoke have effective areas of magnetic pole differing from each other. Upon energiztion of the coil, the armature is moved toward the upstanding leg having the smaller magnetic pole area to close one of the stationary contacts by overcoming the resilient resistance of the movable contact arm. Upon deenergization, the movable contact is restored to the other stationary contact under the resilient restoring force of the movable contact arm.

Description: This invention relates to a monostable polarized relay. The invention relates particularly but not exclusively to a miniature relay of this type which is suitable for mounting, for example, on a substrate for a printed circuit. Typically a polarized relay comprises an electromagnetic coil assembly, a bar-like iron core inserted in the coil assembly, a movable armature block, and movable contact members, wherein the movable contact members are actuated selectively to either one of two switch positions by means of the movable armature block in response to energization or deenergization of the electromagnetic coil assembly. Figure 1 is an exploded perspective view of a polarized relay according to an earlier proposal; Figure 2(a) is a top plan view showing the polarized relay in the assembled state; Figure 2(b) is a side elevational view of the same; Figure 2(c) is a partially broken end view of the same; Figure 3 is a view for graphically illustrating the operation characteristics of the hitherto known polarized relay; Figure 4 is a view for graphically illustrating operation characteristics of a polarized relay according to an exemplary embodiment of the invention; and Figure 5 is a perspective view showing a structure of the yoke which may be used in the relay according to the invention. By way of background to the present invention, reference will now be made to the polarized relay shown in Figure 1 and disclosed in Japanese U.M. Application No. 104536/1982 (JA-U-9455, published Jan. 21, 1984), in the name of the same assignee as the present application and having not been laid open to public inspection at the moment the present application was filed. A similar polarized electromagnetic relay is the subject-matter of European Patent Application 84302737.6 (EP-A-0127308) bearing the same priority date as the present application and belonging to the same applicant. Japanese unexamined Patent publication No. 57-18816 (Patent Abstract of Japan Vol. 7 No. 36, 15th February 1983, page (E-158)(1181)), discloses an electromagnetic device comprising an E-shaped yoke having three parallel legs of equal length and an excitation coil wound around the central leg. In more detail, the device has a generally U-shaped armature having two parallel legs which are made from soft magnetic material and which are inter-digitally disposed within spaces formed between the legs of the E-shaped yoke. The two parallel legs of the armature are connected by a permanent magnet. Upon excitation of the excitation coil, the magnetic flux so created flows through the yoke and the inter-digitally disposed legs of the armature to form a flux-path assuming a figure of "8" without flowing through the permanent magnet. According to Figure 1 an electromagnetic coil 1 is wound on a spool 3 having a through-hole 3a into which a bar-like iron core 2 is inserted. The iron core 2 has an enlarged end portion which serves as stoppers 2a and 2b. In the state in which the core 2 is inserted completely in the through-hole or bore 3a of the spool 3, the end portion serving as the stoppers 2a and 2b projects outwardly from the end of the spool 3. A yoke 4 is disposed below the electromagnetic coil assembly 1 so as to form a magnetic circuit in cooperation with the iron core 2. The yoke 4 is of a substantially U-shaped configuration and has a pair of bifurcated upstanding legs 4a and 4b formed integrally at the free end. In the assembled state, the enlarged end portion of the core 2 is disposed substantially at a mid point between the upstanding legs 4a and 4b of the yoke 4. A movable armature block is constructed generally U-shaped in section having a pair of legs magnetically polarized in opposite to each other. The armature block is constituted by a permanent magnet 6 which is fixedly sandwiched between pole plates 5a and 5b and held together by means of a frame-like holder 7 as shown in Figure 1. In the assembled state of the polarized relay, the movable armature block is laterally movably between the pair of upstanding legs 4a and 4b of the yoke 4, wherein the enlarged end portion serving as the stoppers 2a and 2b of the core 2 is positioned in a space defined between the pole plates 5a and 5b in opposition to the permanent magnet 6. Air gaps are thus formed between the core 2 and and the pole plates 5a, 5b on one hand and between the upstanding legs 4a, 4b of the yoke 4 and on the other hand between the pole plates 5a, 5b, respectively. The stopper faces 2a and 2b serve to limit the movement of the armature block. The holder 7 has a pair of depending legs 7a and 7b formed with respective guide grooves in which movable contact arms 8′ and 8″ are inserted, respectively, as is shown in Figure 2b. The components 1 to 10 mentioned above are mounted on a base plate 11 which carries connector pins A1, A2, B1, B2, C1 and C2 depending downwardly. The relay, thus assembled, is protected by a cover case 12. In operation, when the electromagnetic coil 1 is electrically energized in one direction, the iron core 2 is magnetized in a corresponding direction, as a result of which there are formed magnetic poles in the upstanding legs 4a and 4b of the yoke 4. In this connection, it is assumed that the permanent magnet 6 is magnetized as indicated by symbols S and N in Figure 1 and that N-pole makes appearance in the upstanding leg 4b of the yoke 4 through the energization mentioned above. On this assumption, the holder 7 holding the movable armature block, is moved toward the upstanding leg 4b under magnetic attraction acting between the leg 4b and the permanent magnet 6 as well as under repulsing force acting between the magnet 6 and the leg 4a of the yoke 4. When the force acting on the holer 7 and hence the armature overcomes the spring force or resilient resistance of the movable contact arms 8′ and 8″, the latter are moved toward stationary contacts 10, respectively, resulting in that the contacts of the movable contact arms 8′ and 8″ are closed to the stationary contacts 10. This is because the movable contact arms 8′ and 8″ are operationally coupled to the holder 7 at the depending legs 7a and 7b, respectively, as described above. On the other hand, when the direction of the current flowing through the electromagnetic coil 1 is reversed, the series of operations described above take place in the reverse direction, whereby the contacts carried by the movable contact arms 8′ and 8″ are detached from the stationary contacts 10 to be closed to other stationary contacts 9, respectively. The relay designed to perform the above operation is generally referred to as the latching or bistable type relay. Figure 3 of the accompanying drawings graphically illustrates operation characteristics of such bistable relay and, a broken line curve I, represents intrinsic resilient resistance of the movable contact arms 8′ and 8″ which has to be overcome by the electromagnetic force during switching operation of the relay. This curve I may be referred to as the load characteristic curve. In Figure 3, the stroke of the movable contact arm performed upon switching operation of the relay is taken along the abscissa. The electromagnetic force (actuating force) required to move the movable contact to one of the stationary contacts, e.g. the contact 10, is taken along the lefthand ordinate, while the electromagnetic force (restoring force) required for the restoration of the movable contact 10 to the other stationary contact 9 is taken along the righthand ordinate. Intersection of the load curve I with the abscissa at a point 0.2 means that the movable contact carried by the arm 8 is located at the mid position between the stationary contacts 9 and 10. Solid curves represent, stepwise, the levels of the excitation current of the magnetic coil 1. As will be seen from Figure 3, as long as the movable contact is in the state "closed" to the stationary contact, this state is maintained even in the deenergized state of the magnetic coil (excitation current of 0%), because of the magnetic force of the permanent magnet 6. In order to move the movable contact away from the stationary contact, the excitation current supplied to the coil in the corresponding direction must rise up to the level of more than 20% of the rated value (100%). In this way, in the case of the bistable relay, energization of the coil is required every time the movable contact is changed over from one to the other stationary contact. In practice, however, there are some applications in which the relay of monostable type is to be employed which has only one stable contact state. For example, when the illustrated relay has to be realized in the monostable structure, arrangement must be made such that the movable contact closed to one of the stationary contacts, e.g. the contact 10, upon energization of the magnetic coil is restored to the other stationary contact 9 upon deenergization of the coil. The operation characteristics of the monostable type relay are graphically illustrated in Figure 4. It will be seen that the movable contact is spontaneously restored to the stationary contact when the coil current is 0%. When the monostable relay is to be realized starting from the bistable relay described hereinbefore, effort has heretofore been primarily made to impart a restoring resilliency to the movable contact arm (8′, portion (8a) at which the movable contact arm is mounted on the base plate 11 in consideration of the operating voltage, the voltage level at which the movable contact is restored to the contact of the stable postion and other factors. This adjusting procedure which must be performed for the individual relays is extremely delicate and troublesome, providing a great obstacle in fabricating the monostable type relay on a large scale manufacturing basis. To evade the difficulty, it is conceivable to previously deform the movable contact arm 8 before mounting on the base plate. However, since the terminal pins A1, A2, B1 and B2 are already mounted on the base plate when the terminal pins C1 and C2 which support the movable contact arms 8′ and 8″ are to be secured to the base plate, it is practically impossible to mount the pins C1 and C2 on the base plate from the above. Further, the terminal pins C1 and C2 themselves may be previously bent or deformed so as to impart the desired resilience characteristic to the movable contact arm when mounted on the base plate. However, because of unevenness in thickness and hardness of the pins which brings about unevenness in the deformation of the pins, the subsequent adjustment of the movable contact arms is inevitable. EP-A-74,577 discloses a monostable relay comprising two parallel yoke protions which are located on opposite faces of and polarised by a permanent magnet. An armature is pivotally mounted at one end of one of the yoke portions such that its free end can swing between facing leg portions of the respective yoke portions. These leg portions are unequal length in order to make the relay monostable. FR-A-2,357,051 discloses a somewhat similar construction in which the yoke portions have downwardly-extending leg portions at each end and the armature is pivoted about its mid point such that its ends can swing between the two pairs of facing leg portions of the yoke. Recesses are formed in the inner faces of two diagonally opposite leg portions of the yoke in order to make the relay monostable. In both of the above relays, air-gaps exist at both ends of the yoke. JP 57-188,816 (already referred to) discloses a polarised electromagnetic relay comprising: a bar-like core having an electromagnetic coil mound thereon; a yoke connected to one end of said core and extending in a direction substantially parallel to the core towards the other end of the core, said yoke comprising a pair of opposed, spaced-apart legs, said other end of the core being positioned substantially at the mid-point of the space between said legs; a movable armature block generally -shaped in section and having a pair of legs magnetically polarised in opposition to each other and so disposed that one of said polarised legs is positioned in air-gap between one of said legs of the yoke and said core and the other of said polarised legs is positioned in an air gap between the other of said legs of the yoke and said core; and movable contact arms operatively coupled to said movable armature block so as to selectively make contact with stationary contacts. Summary of the Invention The present invention provides a polarised relay of this type (in accordance with JP 57-188,816), characterised in that a bar-like core having an electromagnetic coil mound thereon; a yoke connected to one end of said core and extending in a direction substantially parallel to the core towards the other end of the core, said yoke comprising a pair of opposed, spaced-apart legs, said other end of the core being positioned substantially at the mid-point of the space between said leg; a movable armature block generally - shaped in section and having a pair of legs magnetically polarised in opposition to each other and so disposed that one of said polarised legs is positioned in an air-gap between one of said legs of the yoke and said core and the other of said polarised legs is positioned in an air gap between the other of said legs of the yoke and said core; and movable contact arms operatively coupled to said movable armature block so as to selectively make contact with stationary contacts. Preferred embodiment of the invention are defined in the dependent claims. Description of the preferred Embodiments In the following description, the yoke structure of Figure 1 is replaced by a yoke structure shown in Figure 5. Except for this feature, the remaining structure of the relay according to the invention is same as that of the relay described with reference to Figures 1,2 and 3. Referring to Figure 5, a yoke 13 is of substantially U-like configuration. The yoke 13 has a leg 13c at one end to which the core wound with an electromagnetic coil is fixedly connected. A pair of upstanding legs 13a and 13b are provided at the other end in oppostion to each other with a distance therebetween for accommodating movably the movable armature block constituted by the permanent magnet and others parts as described hereinbefore. It is important to note that the leg 13a is partially cut away in order to reduce the effective area of the magnetic pole when compared with that of the other leg 13b. The yoke 13 is incorporated in the structure of the polarized relay in the same manner as the hitherto known relay. In operation, upon electric energization of the magnetic coil, the movable armature block can be caused to be attracted to the the upstanding leg 13a when the magnetization of the permanent magnet 6 and other factors are correspondingly dimensioned, whereby the movable contacts carried by the resilient contact arms are closed to respective ones of the stationary contacts. On the other hand, upon deenergization of the relay (corresponing to excitation current of 0% shown in Figure 4), the armature is retracted toward the large magnetic pole 13b and thus the movable contacts are restored to the other stationary contact respectively, under the intrinsic restoring resiliency of the movable contact arms which overcomes the sticking force exerted to the small magnetic pole 13a. In this way, the operation characteristics illustrated in Figure 4 can be attained. As will be apparent from the foregoing, a monostable relay can be easily implemented by using a yoke of the structure according to the invention without need for the subsequent adjustment of the load presented by the movable contact arms. Furthermore, a bistable relay can be readily changed or modified to a monostable relay by merely exchanging the yokes, whereby the manufacturing process of the polarized relays of both operation types can be much facilitated and simplified.

Claims: 1. A polarised electromagnetic relay comprising: a bar-like core (2) having an electromagnetic coil wound thereon; a yoke (13) connected to one end of said core and extending in a direction substantially parallel to the core towards the other end of the core, said yoke comprising a pair of opposed, spaced-apart legs (13a, 13b), said other end of the core being positioned substantially at the mid-point of the space between said legs; a movable armature block generally U-shaped in section and having a pair of legs magnetically polarised in opposition to each other and so disposed that one of said polarised legs is positioned in an air-gap between one of said legs (13a, 13b) of the yoke (13) and said core (2) and the other of said polarised legs is positioned in an air gap between the other of said legs (13a, 13b) of the yoke (13) and said core (2); and movable contact arms (8′, 8″) operatively coupled to said movable armature block so as to selectively make contact with stationary contacts (9, 10); characterised in that said spaced-apart legs of said yoke (13) are in the form of upstanding leg portions (13a, 13b) which extend from a region of said yoke which is adjacent said other end of the core (2), in that the effective magnetic pole area in one of said upstanding leg portions (13a) of the yoke (13) is reduced in comparison with the effective magnetic pole area in the other of said upstanding leg portions (13b), and in that said relay is monostable. 2. A monostable type relay according to Claim 1, wherein said movable armature block is composed of a permanent magnet (6) sandwiched between a pair of pole plates (5a, 5b) forming the said pair of legs of the armature block, and wherein the said pole plates are magnetically polarised in opposition to each other. 3. A monostable relay according to Claim 1 or Claim 2, wherein said one upstanding leg (13a) is decreased in size as compared with the other upstanding leg (13b).

Inventors: IMAI, YOSHIKIYO, YASUOKA, YUJI
Applicants: OMRON TATEISI ELECTRONICS CO.
Application year: 1984
Main classification: H01H51
IPC codes: H01H50, H01H51