POLARIZED ELECTROMAGNET DEVICE

Abstract: A polarized electromagnet device is constructed with a mag­ netic block movable within a specially designed yoke in response to the attraction forces of permanent magnets and an electromag­ netic coil. The movable block and yoke designs form magnetic circuits which result in a relatively large permanent magnet attraction forces on the attraction side of the device and rela­ tively small permanent magnet attraction force on the return side such that a spring load on the return side is not required.

Description: The present invention relates to a polarized electromagnet device in which a movable block is driven by the composite attraction force of permanent magnets and an electromagnetic coil. More particularly, the present invention relates to a polarized electromagnetic device which is constructed so that the effect of the attraction force of the permanent magnets is relatively large on the attraction side but sufficiently small on the return side such that it is not necessary to add a new spring load on the return side. From EP-A-0 078 324 a polarized electromagnetic relay is known comprising a pair of U-shaped outer yokes having a central piece and leg pieces extending from the central piece on both sides. Between a pair of inner yokes and said outer yokes there is provided a pair of permanent magnets for moving a pole bar within said pair of inner yokes. Between the inner yoke means is provided a coil to which a voltage is applied, thereby defining a return state when no voltage is applied and an attraction state when a voltage is applied to the coil. In the return state the first end of said pole bar is in contacting relationship with said inner yoke means and in the attraction state the second end is in contacting relationship with said inner yoke means. On each of the respective two ends of said pole bar there is attached a non-magnetic plate for providing a spacing between the respective ends of the pole bar and the outer yoke means. The end of each inner yoke which is contacted in the return state may show a leg portion which is perpendicular to the remainder of its inner yoke. From EP-A-0 186 393 published on July 2, 1986 an electromagnetic relay has been proposed in the art which comprises a pair of outer yoke means, a coil disposed between a pair of inner yoke means, a magnetic pole bar and a pair of permanent magnets disposed between the inner and outer yoke means. The inner yoke means consist of a central portion and a leg portion which extends from the central portion on one side. The magnetic force of the permanent magnets is sufficient to hold the pole bar at either of its extreme positions of travel when no voltage is applied to the coil, i.e. the relay is of the bistable type. Attached to the outer yoke means are residual plate members which provide a spacing for the respective ends of said magnetic pole bar and the outer yoke means. A conventional polarized electromagnet device, as shown in FIG. 1, is of four-magnetic-gap type. In FIG. 1, reference numeral 1 designates two outer yokes which are substantially U-shaped. Each outer yoke 1 is made up of a central piece 1a and leg pieces 1b extending from the central piece 1a on both sides. The central portion of each central piece 1a is in contact with the magnetic pole surface of the north pole of a permanent magnet 2, and the magnetic pole surface of the south pole of each permanent magnet 2 is in turn in contact with the central piece 3a of an inner yoke 3, to form a stationary side. The inner yokes 3 are L-shaped, and made up of a central piece 3a and a leg piece 3b. A magnetic coil 4 is provided inside the inner yokes 3, and is penetrated by a plunger or movable magnetic pole bar 5, as shown in FIG. 1. The ends of the plunger 5 are fixedly secured to the central portions of armatures 6 and 7. Non-magnetic plates 8 are provided on the outer surfaces of the armatures 6 and 7. The plunger, the armatures 6 and 7, and the non-magnetic plates 8 form a movable block which is movable between the legs 1b of the outer yoke 1. FIG. 1 illustrates the configuration of a conventional device in its "return state" when no voltage is applied to the electromagnetic coil 4. In this state the armature 7 and corresponding non-magnetic plate 8 is confronted with the legs 1b of the outer yokes 1. Gaps A, B, and C are formed between the armature 6 and the legs 1b of the outer yokes 1, between the armature 6 and the legs 3b of the inner yokes 3, and between the armature 7 and the end of the central pieces 3a of the inner yokes 3, respectively. When a sufficient voltage is applied to the electromagnetic coil 4 to drive the movable block to an "attraction state" such that armature 6 and corresponding non-magnetic plate 8 is confronted with the legs 1b on the opposite side of the outer yoke 1, gaps B, C, and D are formed. Gap D corresponds to that spacing created between the armature 7 and the legs of the outer yokes 1. The solid line arrows in FIG. 1 represent the direction of the magnetic flux of one of the permanent magnets 2. A similar flux pattern exists for the other permanent magnet 2, but is not shown. The X-Y arrow represents the directions in which the movable block may be driven. FIG. 2 graphically shows the magnetic attraction forces and spring load charcteristics of the conventional polarized electromagnetic device of FIG. 1. In FIG. 2, the horizontal axis represents the stroke of the movable block which corresponds substantially to the length of the magnetic gap A, and the vertical axis represents magnetic attraction forces and spring loads. The composite attraction force P′₁ shown in FIG. 2 with a solid line is the vector composition of the magnetic flux of the permanent magnets 2 and that of the electromagnetic coil 4, acting in the X direction. This composite attraction force P′₁ is provided when a rated voltage is applied to the electromagnetic coil 4. Similarly, a composite attraction force P′₂ is provided when a minimum allowable voltage (70% of the rated voltage in this example) is applied to the electromagnetic coil 4. The reference character P′m in FIG. 2 designates the attraction force of permanent magnets 2. The fact that the attraction force of permanent magnets 2 act in the negative direction on the return side indicates that the movable block is urged in the Y direction. In the conventional device, a spring load P′₃ of a return spring (not shown) is applied to the movable block of FIG. 1 in the Y direction at all times. In addition to the spring load P′₃, a spring load P′₄ provided by a main contact spring and an auxiliary contact spring (both not shown) is also applied to this movable block from the time when the movable block reaches a predetermined position while moving in the X direction. Spring load P′₃ is shown graphically by a broken line in FIG. 2. The cumulative effect of these forces is represented by a composite spring load P′₅ on the attraction side. Spring load P′₅ is shown in FIG. 2 by a one-dot chain line. In order that the conventional polarized electromagnet device will operate effectively as an electromagnetic contactor, the composite spring load P′₅ must be lower than the composite attraction force P′₂. The attraction force P′m of the permanent magnets acts greatly in the negative side, i.e., in the Y direction on the return side. In the device shown in FIG. 1, however, the composite attraction force P′₂ is smaller than the spring load P′₃ of the return spring, and is insufficient to urge the movable block towards the attraction side. Therefore, in the conventional polarized electromagnet device, a spring load P′ X must be added in the operating X direction so that the composite spring load P′₅, as indicated by the one-dot chain line in FIG. 2, will become lower than the composite attraction force P′₂. As is apparent from the above description, the conventional polarized electromagnet device is disadvantageous in that, when used as an electromagnetic contactor, its spring load characteristic is intricate and its construction is unnecessarily complicated. Another disadvantage of the conventional device is that the contact pressure is low. As can be seen from FIG. 2, the attraction force P′m of permanent magnets 2 acts greatly on the negative side, and therefore the composite attraction force P′₂ or P′₁ obtained by adding the attraction force of the electromagnetic coil 4 thereto is small. It is the object of this invention to provide a polarized electromagnetic device that can be used as a contactor with an increased contact pressure and decreased permanent magnet attraction force on the return side. This object is solved by the device comprising the features of claim 1. A preferred embodiment is the subject of the dependent claims. Additional advantages of the present invention will be set forth in part in the description that follows and in part will be obvious from that description or can be learned by practice of the invention. The advantages of the invention can be realized and obtained by the structure particularly pointed out in the appended claims. The accompanying drawings, which are incorporated in and which constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, explain the principles of the invention. FIG. 1 is a sectional view showing the construction of a conventional polarized electromagnet device. FIG. 2 is a diagram illustrating the magnetic attraction characteristics and spring load characteristics of the polarized electromagnet device shown in Fig. 1. FIGS. 3 and 4 are sectional views showing an embodiment of polarized electromagnet device of the present invention. FIGS. 5 and 6 are sectional views showing one embodiment of a high sensitivity contactor utilizing an embodiment of the polarized electromagnet device of the present invention. FIG. 7 is a diagram illustrating the magnetic attraction characteristics and spring load characteristics of the embodiment shown in Figs. 3 and 4. One embodiment of a polarized electromagnet device of the present invention is shown in FIGS. 3 and 4. This device comprises a first outer magnetic yoke 11 and a second outer magnetic yoke 12. Outer yokes 11 and 12 are, for example, substantially U-shaped, and have central portions 11a and 12a opposite one another. Outer yoke 11 has a first leg 11b and a second leg 11c; outer yoke 12 has a first leg 12b and a second leg 12c. Permanent magnets 9a and 9b are disposed with the north faces of these magnets abutting the interior edge of outer yoke central portions 11a and 12a, respectively. The device of FIGS. 3 and 4 also comprises a first inner magnetic yoke 13 and second inner magnetic yoke 14. Inner yokes 13 and 14 are, for example, substantially L-shaped, having central portions 13a and 14a and legs 13b and 14b, respectively. Inner yoke central portion 13a abuts the south face of permanent magnet 9a such that leg 13b extends from the end of central portion 13a nearest to outer yoke leg 11c and in the same direction as leg 11c. Inner yoke central portion 14a abuts the south face of permanent magnet 9b such that leg 14b extends from the end of central portion 14a nearest to outer yoke leg 12c and in the same direction as leg 12c. In the preferred embodiment, the end of central portions 13a nearest to outer yoke leg 11b is substantially aligned with the end of permanent magnet 9a nearest to leg 11b; the end of central portion 14a nearest to outer yoke leg 12b is substantially aligned with the end of permanent magnet 9b nearest to leg 12b. U-shaped inner yokes 13 can also be formed by using two L-shaped units. Magnetic coil 10 is disposed between inner yokes 13 and 14. A non-magnetic plate 18 is secured to outer yoke legs 11b and 12b on the interior edges of legs 11b and 12b. Another non-magnetic plate 19 is secured to the interior edges of outer yoke legs 11c and 12c. The device of FIGS. 3 and 4 also comprise a block means 20. As embodied herein the block means 20 includes a body that passes through the magnetic coil 10, and is configured so as to be able to operate between a return state wherein one end of the block means is in contact with non-magnetic plate 19 when no voltage is applied to magnetic coil 10 and an attraction state wherein the other end of the block means is in contact with non-magnetic plate 18 when voltage is applied to magnetic coil 10. In the preferred embodiment, block means 20 comprises a plunger or movable magnetic pole bar 15 passing through magnetic coil 10, a first magnetic armature 16 on the end of the bar 15 nearest to the plate 18 and a second magnetic armature 17 on the end of the bar 15 nearest to the plate 19. Movement of the armature 17 is confined to the passageway bounded by the inner yoke legs 13b and 14b on one side and a plate 19 and the outer yoke legs 11c and 12c on the other side. This is unlike the construct of the prior art which has the legs of the inner yokes disposed on the attraction side and which has the return side armature confined only by the outer yoke and the ends of the magnetic coil or the central inner yokes. FIGS. 5 and 6 show one example of a high sensitivity contactor to which the polarized electromagnet device of the present invention is applied. The contactor of FIGS. 5 and 6 is made of a contact mechanism and the polarized electromagnet device of FIGS. 3 and 4 discussed above. The contact mechanism is accommodated in an upper casing 21, and the polarized electromagnet is in a lower casing 22. The contact mechanism and the polarized electromagnet device are coupled through a lever 23 to each other, but partitioned with an insulating plate 24 from each other. The contact mechanism has a supporting member 25 which is coupled to the lever 23. In a contactor having, for example, a main contact with three poles, three movable contacts 26 with corresponding contact springs 27, and one auxilliary movable contact 28 with a contact spring 29, are mounted on the supporting member 25. As shown in FIG. 6, stationary contacts 31, with which movable contacts 26 and 28 are brought into contact, are also provided in the upper casing 21. In this embodiment, the movable block is urged in the X direction through supporting member 25 and the lever 23 by a return spring 30 at all times. A load in the X direction is added to this spring load by the three contact springs 27 and the auxilliary contact spring 29, as supporting member 25 is moved in the X direction. The operation of the high sensitivity contactor utilizing the polarized electromagnet device of the present invention will be described with reference to FIGS. 3 and 4. FIG 3. illustrates the preferred embodiment in the return state, and FIG. 4 illustrates the preferred embodiment in the attraction state. As shown in these figures, magnetic gaps E, F, and G are formed between the block means 20 and the inner and outer yokes. More specifically, magnetic gap E is provided between armature 16 and outer yoke legs 11b and 12b, magnetic gap F is provided between armature 17 and inner yoke legs 13b and 14b, and magnetic gap G is provided between armature 17 and outer yoke legs 11c and 12c. As discussed above, FIG. 3 shows a return state of the device in which no voltage is applied to electromagnetic coil 10. In this state, the magnetic attraction force produced by, for example, the magnetic flux of permanent magnet 9b is indicated by the solid line arrows. For convenience, the magnetic attraction force produced by the magnetic flux of permanent magnet 9a is omitted. FIG. 7 indicates the magnetic attraction force and spring load characteristics of the high-sensitivity contactor according to this embodiment of the invention. In the return state shown in FIG. 3, the attraction force Pm of permanent magnet 9b is provided by a magnetic circuit forming a loop between permanent magnet 9b, outer yoke 12, magnetic gap E, movable block 20, and magnetic gap F and by a second magnetic circuit forming a loop between permanent magnet 9b, outer yoke 12, magnetic gap G, and inner yoke 14. In this configuration, the attraction force Pm of permanent magnets 9a and 9b can be represented by the equation Pm = P E + P F - P G , where P E , P F , and P G are the attraction forces provided in the magnetic gaps E, F, and G, respectively. As shown in FIG. 7, the attraction force Pm acts slightly in the Y direction. Reference characters P₁ and P₂ correspond to P'₁ and P'₂ of FIG. 2, respectively. The composite spring load P₅ is the sum of the spring load P₃ of the return spring 30, the spring load P₄₁ of the three contact springs 27, and the spring load P₄₂ of the auxilliary contact spring 29. When energized, the electromagnetic coil 10 forms magnetic flux such that the composite attraction force P₂ (or P₁) of the permanent magnets 9a and 9b and the electromagnetic coil 10 becomes larger than the composite spring load P₅. Accordingly, the polarized electromagnet device is placed in the attraction state as shown in FIG. 4. In the attraction state of FIG. 4, in addition the magnetic circuits shown in FIG. 3 there is an additional magnetic circuit forming a loop between outer yoke 12, magnetic gap E, movable block 20, and magnetic gap G, as shown by the broken line arrows. For convenience, only the magnetic flow in the bottom half of the device is shown. The composite attraction force P₂ (or P₁) is the composition of the attraction forces P' E , P' F , and P' G (P' E P E , P' F P F , and P' G P G ) provided respectively in the magnetic gaps E, F, and G. That is, P₂ = P' E + P' F - P' G . As is apparent from FIG. 7, when compared with the characteristic of the attraction force P'm of the permanent magnets in the conventional polarized electromagnet device, the characteristic of the attraction force Pm of the permanent magnets of the present invention is such that the attraction force is large on the attraction side but small on the return side. This is due, in part, to the presence of the inner yoke legs 13b and 14b on the return side of the device. Accordingly, in the device of the present invention, unlike the conventional device, it is unnecessary to add spring load P x on the return side. This greatly simplifies the construction of the device. Furthermore, in the device of the present invention, the permanent magnet attraction force is increased on the attraction side, and accordingly the composite attraction force characteristic P₂ is greatly increased on the attraction side, to provide a high contact pressure. The invention in its broader aspects is, therefore, not limited to the specific details and illustrated examples shown and described. Accordingly, it is intended that the present invention cover such modifications and variations, provided that they fall within the scope of the appended claims and their equivalents.

Claims: A polarized electromagnet device comprising: first (11) and second (12) outer magnetic yoke means; first (13) and second (14) inner magnetic yoke means; a first and second permanent magnet (9a,9b) respectively disposed in an abutting relationship between said first and second outer (11,12) and inner (13,14) yoke means; a magnetic coil (10) disposed between said first (13) and second (14) inner yoke means; magnetic block means (20) having a first and second end (16,17) and a magnetic pole bar (15) passing through said magnetic coil (10), a first and second non-magnetic plate (18,19) disposed between said first (11) and second (12) outer yokes, and said block means (20); said block means (20) being operative between a return state wherein said second end (17) of the block means (20) is in a contacting relationship with said second plate (19) when no voltage is applied to said magnetic coil (10) and an attraction state wherein said first end (16) of the block means is in a contacting relationship with said first plate (18) when a voltage is applied to said magnetic coil (10); said first and second inner yoke means (13,14) each having a base portion (13a,14a) abutting said first permanent magnets (9a,9b) and a leg portion (13b,14b), said leg portions (13b,14b) extending substantially perpendicularly from the base portions (13a,14a) of the first and second inner yoke means towards the block means (20); characterized by said leg portions (13b,14b) extending in proximity of the second end (17) of the block means from the ends of the first and second inner yoke means (13,14) whereby in the attraction state, the second end (17) of the block means is adjacent to the leg portions (13b,14b) of the inner yoke means and in the return state there is no magnetic flux between the first end (16) of the block means and the inner yoke means (13,14). A polarized electromagnet device according to claim 1, characterized in that in the return state of the block means (20) there is provided a first magnetic circuit in which the magnetic flux flows from said permanent magnets (9a,9b) in one direction to the outer yoke means (11,12) via a first magnetic gap (E) between the first plate (18) and the first end (16) of said block means (20), a first armature (16), said block means (20), to a second armature (17) and via a second magnetic gap (F) between said leg portions (13b,14b) of said first and second inner yoke means (13,14) and said second end of said block means (20) to the inner yoke means (13,14) and back to the permanent magnets (9a,9b); and a second magnetic circuit in which the magnetic flux flows from said permanent magnets (9a,9b) in the other direction of said outer yoke means (11,12) via a third magnetic gap (G) corresponding to said second magnetic plate (19) to the second armature (17), and via the second magnetic gap (F) and said inner yoke means (13,14) back to said permanent magnets (9a,9b); and in said attraction state of block means there is provided a third magnetic circuit in which a magnetic flux generated by the magnetic coil (10) flows from said block means to the second armature (17), via a third magnetic gap (G) between said second non-magnetic plate (19) and said second end of said block means (20), to the outer yoke means (11,12), and via the first magnetic gap (E) to said first armature (16) back to the block means (20). A polarized electromagnet device according to claims 1 or 2 characterized in that the first (11) and second (12) outer magnetic yoke means each have an interior central portion (11a,12a) bounded in a first direction by a first interior leg edge (11b,12b) and bounded in a second direction by a second interior leg edge (11c,12c), said first and second interior leg edges extending at substantially right angles to said interior central portions (11a,12a). A polarized electromagnet device according to claim 3 characterized by said first non-magnetic plate (18) abutting said first interior leg edges (11b,12b) of said first and second outer yokes (11,12) and said second non-magnetic plate (19) abutting said second interior edges (11c,12c) of said first and second outer yokes (11,12). A polarized electromagnet device according to at least one of claims 1 to 4 characterized in that the first magnetic armature (16) is formed at said first end of the magnetic pole bar (15), and in that the second magnetic armature (17) is formed at said second end of said bar (15) and disposed within the passage way created between said leg portions (13b,14b) of said first and second inner yokes (13,14) and said second plate (19).

Inventors: HIROTA, TAKATO, ICHIKAWA, HARUO
Applicants: FUJI ELECTRIC CO., LTD.
Application year: 1987
Main classification: H01H51
IPC codes: H01H51, H01F7