Abstract:
A relay has a driving device that includes a magnet portion, two electromagnets, a yoke portion fixed to the above elements, and a rocking armature. The magnet portion includes a ferrite permanent magnet polarized in a direction perpendicular to the yoke portion and a bearing surface facing way from the yoke portion. Each electromagnet includes an iron core fixed to the yoke portion and a coil wound thereon. The two iron cores are arranged at opposite sides of the magnet portion. The rocking armature includes two arms connected to each other with an included angle formed therebetween and a convex joint of the two arms. The convex joint abuts against the bearing surface and the rocking armature pivots about the convex joint between a first position and a second position in which the rocking armature contacts a respective one of the iron cores.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201210051723.5 filed in The People&#39;s Republic of China on Mar. 1, 2012. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to driving devices and in particular, relates to an electromagnetic driving device used in a relay. 
       BACKGROUND OF THE INVENTION 
       [0003]    A driving device for a bistable relay includes a substantially v-shaped rocking plate and two electromagnets arranged on opposite sides of the rocking plate. The rocking plate is made of magnetic material and is rotatably fixed at the center thereof, so that the rocking plate can rotate about its center. When one of the two electromagnets is energized, it generates a magnetic field to attract an end of the rocking plate. When the other electromagnet is energized, the other end of the rocking plate is attracted to this electromagnet, causing the rocking plate to swing. In this way, a movable contact of the relay that is connected to the rocking plate is driven to contact or separate from a static contact, thereby the relay stays in an on or off state. However, in whichever state, one of the electromagnets of the relay has to be fed with power. This makes the relay high electricity-consuming. 
         [0004]    There is a desire for a relay with a driving device having a lower power consumption. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, in one aspect thereof, the present invention provides a driving device comprising: a yoke portion; a magnet portion fixed to the yoke portion and comprising a ferrite permanent magnet polarized along a direction substantially perpendicular to the yoke portion and a bearing surface facing way from the yoke portion; two electromagnets each comprising a iron core fixed to the yoke portion and a coil wound thereon, the two iron cores being arranged at two opposite sides of the magnet portion; and a rocking armature comprising two arms connected to each other with an included angle formed there between and a convex joint of the two arms, the convex joint abutting against the bearing surface so that the rocking armature is capable of pivoting about the convex joint between a first position and a second position to contact a respective iron core. 
         [0006]    According to a second aspect, the present invention provides a relay comprising: a static contact piece comprising a static contact; a movable contact piece comprising a movable contact; the driving device for moving the movable contact, a housing that houses the static contact, the movable contact, and the driving device; and a push rod connected to the movable contact and arranged to move the movable contact between an ‘off’ position where the movable contact is separated from the static contact and an ‘on’ position where the movable contact bears against the static contact, wherein the driving device comprises: a yoke portion; a magnet portion fixed to the yoke portion and comprising a ferrite permanent magnet polarized along a direction substantially perpendicular to the yoke portion and a bearing surface facing way from the yoke portion; two electromagnets each comprising a iron core fixed to the yoke portion and a coil wound thereon, the two iron cores being arranged at two opposite sides of the magnet portion; and a rocking armature comprising two arms connected to each other with an included angle formed there between and a convex joint of the two arms, the convex joint abutting against the bearing surface so that the rocking armature is capable of pivoting about the convex joint between a first position and a second position to contact a respective iron core, the rocking armature being connected to the push rod to drive the push rod. 
         [0007]    Preferably, the push rod is slidably moved along a groove in the housing by the rocking armature. 
         [0008]    Preferably, the rocking armature further comprises a ridge at the convex joint, and the magnet portion comprises a groove in the bearing surface that receives the ridge of the rocking armature. 
         [0009]    Preferably, the ridge comprises a outer surface that contacts the bottom surface of the groove, the outer surface of the ridged and the bottom surface of the groove are arcuate. 
         [0010]    Preferably, each iron core comprises a holding surface facing away from the yoke portion; in the first or second position, the corresponding arm contacts the corresponding holding surface and a part of the bearing surface. 
         [0011]    Preferably, the magnet portion further comprises a armature plate, the permanent magnet is sandwiched between the yoke portion and the armature plate, the groove is formed in the armature plate. 
         [0012]    Preferably, each iron core has a rectangular cross-section, with a long side of thereof arranged close to the permanent magnet while the other long side is remote from the permanent magnet. 
         [0013]    Preferably, the two coils of the electromagnets are wound in opposite directions and are connected together in series. 
         [0014]    Preferably, the rocking armature further comprises a concave joint of the two arms and a position slot at the concave joint, the housing further comprises a locating part partially received in the position slot. 
         [0015]    Preferably, the movable contact piece comprises a fixed plate fixed to the housing, a movable plate having an end to which the movable contact is fixed, and a plurality of elastic arcuate plates connecting the fixed plate to an end of the movable plate remote from the movable contact, the elastic arcuate plates are thinner than both the fixed plate and the movable plate. 
         [0016]    In embodiments of the present invention, power is consumed only when the relay is being switched. This makes the relay more energy efficient. Meanwhile, the magnet is made from ferrite magnet, which is cheaper, to reduce the cost of the relay. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    A preferred embodiment of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
           [0018]      FIG. 1  shows a relay in accordance with a first embodiment of the present invention with part of a housing of the relay removed, the relay is in the off position; 
           [0019]      FIG. 2  shows a driving device of the relay of  FIG. 1 ; 
           [0020]      FIG. 3  is a sectional view taken along line III-III of  FIG. 2 ; 
           [0021]      FIG. 4  is a similar view to  FIG. 1 , with the relay in the on position; 
           [0022]      FIG. 5  is a sectional view of a driving device according to a second embodiment of the present invention; and 
           [0023]      FIG. 6  is a sectional view of a driving device according to a third embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    Referring to  FIG. 1 , a relay  10 , according to a first embodiment of the present invention, includes a housing  20 , a static contact piece  30 , a movable contact piece  40 , a push rod  50 , and a driving device  60 . 
         [0025]    The housing  20  is made of plastic. The static contact piece  30  is fixed to the housing  20 . An end of the contact piece  30  is provided with a static contact  32  and is received in the housing  20 , while the opposite end of the contact piece  30  extends outside the housing for connecting to an external circuit (not shown). 
         [0026]    The movable contact piece  40  includes a movable plate  42 , a fixed plate  44 , and a number of elastic plates  46 . An end of the movable plate  42  is provided with a movable contact  48 . The fixed plate  44  is fixed to the housing  20 . An end of the fixed plate  44  is arranged outside the housing for connecting to the external circuit, while the opposite end is received in the housing  20 . The elastic plates  46  are arc-shaped. Two opposite ends of each elastic plate  46  are respectively connected to an end of the movable plate  42  remote from the movable contact  48  and an end of the fixed plate  44  received in the housing  20 . Each of the elastic plates  46  is thinner than the other part of the movable contact piece  40  to ease the swing of the movable plate  42  while maintaining the rigidity of the movable plate  42  and the fixed plate  44 . The movable contact  48  is arranged opposing the static contact  32 . 
         [0027]    The push rod  50  is fixed to the driving device  60  and the movable contact  48 , and is slidably received in a guiding slot  24  defined in the housing  20 . As such, the driving device  60  moves the push rod  50  along the guiding slot  24  to cause the movable contact  48  to contact or separate from the static contact  32 . 
         [0028]    Referring to  FIGS. 2 and 3 , the driving device  60  is received in the housing  20 , including a yoke portion  62 , a magnet portion  64 , two electromagnets  74 , and a rocking armature  82 . The yoke portion  62  is fixed to the housing  20  and is made from magnetically conductive material, and has two through holes  63  at opposite ends thereof. 
         [0029]    The magnet portion  64  includes a permanent magnet  66  and an armature plate  68 . The permanent magnet  66  is a ferrite magnet, and is fixed to the middle of the yoke portion  62 . The armature plate  68  is made from magnetically conductive material such as iron, and is fixed to an upper surface of the permanent magnet  66 . The armature plate  68  includes a bearing surface  70  that faces away from the yoke portion  62  (upper surface as shown). The armature plate  68  further defines a groove  72  that is substantially perpendicular to a line connecting the center of the two through holes  63 . The bottom surface of the groove  72  is arc-shaped. 
         [0030]    Each electromagnet  74  includes a iron core  76  fixedly received in a respective through hole  63  and a coil  78  wound around the iron core  76 . Each iron core  76  includes a holding surface  80  that faces away from the yoke portion  62 . The two holding surfaces  80  are both coplanar with the bearing surface  70 . 
         [0031]    The rocking armature  82  is made from magnetically conductive material, including a first arm  84  and a second arm  86 . The first arm  84  and the second arm  86  are both flat-shaped and are connected to each other, with an angle included there between. A ridge  88  is arranged at the convex joint of the first and second arms  84 ,  86 , and is received in the groove  72 . The surface of the ridge  88  is shaped to correspond with the bottom surface of the groove  72 . The rocking armature  82  is preferably integrally formed as a monolithic structure. The first arm  84  can be connected to the push rod  50  directly or through a connecting rod  26  (as shown in  FIG. 1 ). 
         [0032]    During operation, assume that the rocking armature  82  is in a first position, namely, the second arm  86  is touching the iron core  76  remote from the push rod  50  (the right iron core in  FIG. 3 ). In this first position, the second arm  86  contacts the holding surface  80  of the right iron core  76  and the right half of the bearing surface  70  in  FIG. 3 . As the armature plate  68 , the rocking armature  82 , the iron core  76 , and the yoke portion  62  are all magnetically permeable, the flow of magnetic flux of the permanent magnet  66  is as shown by dashed lines with arrows in  FIG. 3 . As can be clearly seen, magnetic force caused by the permanent magnet  66  between the second arm  86  and the right iron core  76  is much greater than that between the first arm  84  and the left iron core  76 . As such, the rocking armature  82  remains in the first position without applying power to the relay  10 . In this case, the push rod  50  is in a high position as shown in  FIG. 1 , forcing the movable contact  48  to separate from the static contact  32 . Thus the relay is in the off state. 
         [0033]    When there is a need to switch the relay  10 , a pulse is applied to the right electromagnet  74  through a leg  28  of the relay  10 , for example, the positive leg on the right of  FIG. 1 . The right electromagnet  74  then generates a magnetic field whose flow is shown by the solid line with arrows in  FIG. 3 . In this case, the magnetic field generated by the right electromagnet  74  weakens or even counteracts the magnetic field generated by the permanent magnet  66  between the right iron core  76  and the second arm  86 . While at the same time, the magnetic field generated by the right electromagnet  74  overlaps with the magnetic field generated by the permanent magnet  66  between the left iron core  76  and the first arm  84 . As such, the magnetic force between the left iron core  76  and the first arm  84  is greater than that of the right iron core  76  and the second arm  86  and thus the first arm  84  is moved to contact the left iron core  76  so that the rocking armature  82  is switched to a second position, the ‘on’ position, as shown in  FIG. 4 . 
         [0034]    In the second position, the first arm  84  contacts the holding surface of the left iron core  76  and the left half of the bearing surface  70 . The push rod  50  is moved to a low position as shown in  FIG. 4 , forcing the movable contact  48  to contact the static contact  32 . When the relay  10  has to be switched again, a pulse is applied to the left electromagnet  74  via another leg  28 . The principle of this pulse is similar to that described above and will not be described again here. 
         [0035]    In the present embodiment, the permanent magnet  66  is a ferrite magnet, which is cheaper than rare earth magnets such as NdFeB magnet, to reduce the cost of the relay  10 . Preferably, considering that the magnetism of ferrite magnetic is lower than that of rare earth magnets, the iron core  76  is shaped as a rectangle, with the short side shown in  FIG. 3 . That is, a long side of the iron core  76  is arranged close to the permanent magnet while the other long side is away from it. In this way, comparing to a relay employing square or circular iron cores, more room is left between the two electromagnets  74  for the permanent magnet  66  while the magnetism of the electromagnets remain the same. 
         [0036]    It should be understood that the magnetic poles of the permanent magnet  66  can be reversed. In the above embodiment, the two electromagnets  74  are electrically separate from each other so that only one of them is energized when switching the relay  10 . However, in other embodiments, the coils  78  of the two electromagnets  74  can be wound in opposite directions and connected together in series, as shown schematically in  FIG. 5 . In this way, when switching the relay, both electromagnets  74  can be applied with the same pulses to generate opposite magnetic fields to enhance the switching magnetic force. 
         [0037]    Preferably, the housing  20  further includes a locating part  22 , as shown in  FIG. 1 . The rocking armature  82  further defines a position slot  90  at the concave joint  94  of the first and second arms  84 ,  86 , opposite to the ridge  88 . A distal end of the locating part  22  is received in the position slot  90  to locate the rocking armature  82 . 
         [0038]    The arrangement of the groove  72  and the ridge  88  not only facilitates the pivoting of the rocking armature  82 , but also lowers the magnetic reluctance between the rocking armature  82  and the iron cores  76  and the armature plates  68  as it ensures contact between the rocking armature  82  and the bearing surface  70  and the holding surfaces  80  in the first and second positions, with virtually no air gap. 
         [0039]    The armature plate  68  allows most of the magnetic field of the N pole of the permanent magnet  66  to go to the arm of the rocking armature  82  that is in contact with a corresponding iron core  76 , which is schematically demonstrated by dashed line  52  in  FIG. 3 . Compared to relays without an armature plate  68 , the magnetic force between the arm and iron core when in contact is relatively high. However, it should be understood that without the armature plate  68 , the relay can still work properly. In this situation, the groove  72  is defined in the permanent magnet  66 , as shown in  FIG. 5 . 
         [0040]    In other embodiments, the ridge  88  may be eliminated from the convex joint  92  of the two arms  84 ,  86 , as shown in  FIG. 6 . In this case, still no air gap exists between contacting arm and iron core, just like the first embodiment. The position slot  90  is preferably formed at the concave joint  94  of the two arms  84 ,  86  to receive the locating part  22 . 
         [0041]    In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items. 
         [0042]    Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow.