PATENT ABSTRACT
A magnetic latching relay of a parallel type magnetic circuit, forming two parallel permanent magnetic circuits on the permanent magnetic circuit of a relay; one of the permanent magnetic circuits is used to provide adequate attraction to an armature, so that permanent magnetic attraction can achieve a balance of applied forces with the counter-force provided by a movable spring, so as to realize relay bistability or state transition more stably.

PATENT DESCRIPTION
TECHNICAL FIELD 
     The present disclosure generally relates to a relay, and more particularly, to a magnetic latching relay with a parallel-type magnetic circuit. 
     BACKGROUND 
     A relay is an automatic switch device having isolation function, widely applied in communication, automobiles, automatic control, household appliances and other fields, and is one of the most important control devices. 
     Due to demands in energy preservation and environment protection, magnetic latching relays are applied to ever wide areas. Common relays require to be developed with magnetic latching features. Generally, for a typical clap-type relay, an iron core (or an iron yoke) is divided into two parts. A permanent magnet is connected between the two parts, to form a series-type magnetic circuit. Upon excitation of a coil, the magnetic circuit is closed, and a magnetic force generated by the permanent magnet can keep an armature in closed state.  FIG. 1  is a schematic structural diagram of a magnetic circuit of a magnetic-latching-type electromagnet relay in the prior art. As shown in  FIG. 1 , the magnetic circuit of the electromagnet relay includes a spring sheet  101  (which can form a part of an output circuit of the relay), an armature  102 , an iron yoke  103 , an iron core  104 , a coil  105  and a permanent magnet  106 . The iron core  104  passes through the coil  105 . The permanent magnet  106  is fixed between the iron core  104  and the iron yoke  103 . The armature  102  and the spring sheet  101  are riveted together in advance, and riveted onto the iron yoke  103 . The permanent magnet  106  generates a permanent magnetic circuit which starts from an N pole of the permanent magnet, passes through the iron core  104 , an air gap, the armature  102 , the iron yoke  103 , reaches an S pole of the permanent magnet. Upon excitation, the coil  105  generates a magnetic field which passes through the iron core  104 , the air gap, the armature  102 , the iron yoke  103  and the S-N of the permanent magnet. When the permanent magnet filed and the magnetic field generated by the coil is in the same direction, the magnetic forces will add to each other to form a force which overcomes the counter force of the spring sheet  101 , so as to cause the armature  102  and the iron core  104  to attract each other. After the excitation of the coil  105  stops, the magnetic field generated by the coil will disappear, and the permanent magnetic field will provide a retention force to keep the armature  102  and the iron core  104  in the attracted state. When a reverse current flows through the coil, the coil  105  generates a magnetic field which passes through the iron core  104 , the N-S of the permanent magnet, the iron yoke  103  and the armature  102 . Thus, the magnetic field generated by the coil is opposite to the direction of the permanent magnetic field, and weakens the permanent magnetic force. Under the “cooperation” of the counter force of the spring sheet  101 , the spring sheet  101  brings the armature  102  to be reset. 
     Such a series-type magnetic circuit has the following defects. 
     1. The permanent magnet always causes the armature to be attracted to the iron core, and even though the spring sheet has a large counter force, but a pressure on the contact point at a normal-close terminal of the product is relatively small. Therefore, load capability of the fixed closed terminal is poor, and the product relay has a poor resistance against impact and vibration. 
     2. After the coil is excited for reset, the magnetic force of the permanent magnet still generates a strong attraction force to the armature. Therefore, it requires a large reset force to reset the armature to reset to a released state. If the magnetic force does not match the reset force, the coil may require a small setting voltage and a large resetting voltage, or the coil may fail to be reset. 
     SUMMARY 
     The objective of the present disclosure is to overcome the deficiency in the related art. In one aspect, the objective is to provide a magnetic latching relay with a parallel-type magnetic circuit in which two parallel permanent magnetic paths are formed, one of the paths is for providing a suitable attraction force to the armature, so as to keep balance with a counter force provided by a movable spring sheet and to achieve bistability or state switching more stably. 
     In another aspect, the objective of the present disclosure is to provide a magnetic latching relay with a parallel type magnetic circuit in which a magnetic isolation recess is provided on the iron yoke and a cut is provided on the pole shoe of the iron core, to adjust the retention force generated by the iron core to the armature at the position of the armature, thus keeping balance between the magnitudes of resetting voltage and the setting voltage of the magnetic latching relay as much as possible. 
     In still another aspect, the objective of the present disclosure is to improve the structure of the coil rack and the pole shoe of the iron core. Thus, on one hand, it can increase the creepage distance between the iron core and the fixed spring sheet, preventing electrical accidents caused by unwanted conduction of the movable contact point and the fixed contact point due to accumulation of metal spatters of the contact points. On the other hand, it can significantly improve the impact resistance of the relay. 
     In yet still another aspect, the objective of the present disclosure is to improve the structure of the bobbin of the coil rack, to effectively isolate the first circle of an enameled wire and the last circle of the enameled wire, avoiding defects in the related art which are caused by placing the first circle of the enameled wire and the last circle of the enameled wire together. 
     The technical solutions of the present disclosure for solving the technical problems are as follows. 
     A clapper relay, including a magnetic circuit portion and a movable spring portion, characterized in that, the magnetic circuit portion includes an iron core, an armature, an iron yoke, a permanent magnet, a magnetic conductor member, a coil and a coil rack; the iron yoke is L shaped, formed by a first yoke parallel to the iron core and a second yoke perpendicular to the iron core; the coil is wound on the coil rack, the iron core passes through the coil rack, a lower end of the iron core is secured to the second yoke; the armature is movably mounted to a hinge portion of the iron yoke, an air gap is formed between one end of the armature and an upper end of the iron core; one end of the magnetic conductor member is connected to the first yoke, the other end of the magnetic conductor member is connected to first yoke through the permanent magnet; the movable spring portion includes a movable spring sheet and a movable contact point, the movable spring sheet formed with a first side and a second side, an elastically bendable angle is formed between the first side and the second side; the armature is secured to the second side, the first yoke is secured to the first side, the armature is flexibly connected to the first yoke via the movable spring sheet; the movable contact point is secured to the second side, wherein the permanent magnet and the magnetic conductor member, the first yoke, the second yoke, the iron core and the armature form two parallel permanent magnetic paths; the coil and the iron core form a control magnetic path, to control the opening and closing of the air gap; the permanent magnetic paths provide a force to maintain the air gap to be closed; the movable spring sheet provides a counter force to maintain the air gap to be opened. 
     According to an embodiment of the present disclosure, at least one magnetic isolation portion is provided on the first yoke which is between a joint of the first yoke and the permanent magnet and a joint of the first yoke and the magnetic conductor member, the magnetic isolation portion is configured to increase a magnetic resistance of the magnetic circuit portion, and to adjust balance between magnitudes of setting voltage and resetting voltage of the relay by adjusting an opening size of a magnetic isolation recess. 
     According to an embodiment of the present disclosure, an upper end of the iron core is provided with a pole shoe, a cut is provided at a side of the pole shoe, a size of the cut and/or the opening size of the magnetic isolation recess can be adjusted to regulate balance between magnitudes of a setting voltage and a resetting voltage of the relay. 
     According to an embodiment of the present disclosure, one end of the magnetic conductor member is provided with a contact surface for contacting the first yoke. 
     According to an embodiment of the present disclosure, the contact surface of the magnetic conductor member is provided with a boss for positioning with the first yoke, the first yoke is provided with a hole for fitting with the boss of the magnetic conductor member; the boss of the magnetic conductor member is fitted in the hole of the first yoke, and secured thereto via rivet or welding. 
     According to an embodiment of the present disclosure, the permanent magnet is secured to the other end of the magnetic conductor member, and the other end of the magnetic conductor member is provided with a bulge for securing the permanent magnet. 
     According to an embodiment of the present disclosure, the relay further includes a fixed spring portion, the fixed spring portion includes a fixed spring sheet and a fixed contact point secured on the fixed spring sheet; an upper end plate of the coil rack extends to a side where a mounting portion is disposed, the fixed spring sheet is mounted in the mounting portion, the movable contact point is mounted at a position in the mounting portion where matches with the position of the fixed contact point; at least one shielding wall is provided on the coil rack and between the through holes and the mounting portion, to separate a pole shoe at the through hole of the coil rack and the fixed spring sheet at the mounting portion. 
     According to an embodiment of the present disclosure, the shielding wall is disposed close to the through hole, and corresponding to the armature secured to the movable spring sheet, a height of the shielding wall is not lower than a bottom of the armature when the relay is reset, in order to prevent the armature from moving to a direction where the movable contact point contacts the fixed contact point. 
     According to an embodiment of the present disclosure, there are provided two shielding walls, and a groove is formed between the two shielding walls for collecting spatters of the contact points, wherein one of the shielding walls is disposed close to the through hole, and corresponding to the armature secured to the movable spring sheet, a height of the shielding wall is not lower than a bottom of the armature when the relay is reset, in order to prevent the armature from moving to a direction where the movable contact point contacts the fixed contact point. 
     According to an embodiment of the present disclosure, the shielding wall is integrated with the coil rack. 
     According to an embodiment of the present disclosure, the coil rack includes a bobbin, one end of the bobbin is connected to a lower terminal plate, the other end of the bobbin is connected to an upper terminal plate, a first pin, a second pin and a third pin are respectively mounted on the lower terminal plate; a groove for guiding an enameled wire is provided at an inner side of the lower terminal plate which is between the bobbin and the second pin, one end of the groove is connected to the bobbin, and the other end of the groove leads to the second pin. 
     According to an embodiment of the present disclosure, a boss is provided at an inner side of the lower terminal plate which extends from the bobbin to the second pin, a support wall is provided at a side of the boss, and the groove for guiding an enameled wire is surrounded and thus formed by the support wall and the boss. 
     According to an embodiment of the present disclosure, an inclined plate is provided at an inner side of the lower terminal plate, the inclined plate is gradually inclined in a direction from the bobbin to the second pin; the boss and the support wall are respectively disposed at the middle of the inclined plate and a side of the inclined plate. 
     According to an embodiment of the present disclosure, a first cover plate which can press and seize the enameled wire is mounted at the inner side of the lower terminal plate and between the first pin and the bobbin. 
     According to an embodiment of the present disclosure, neither of an upper surface of the boss and an upper surface of the support wall is higher than an upper surface of the first cover plate. 
     According to an embodiment of the present disclosure, a second cover plate which can press and seize the enameled wire is mounted at the inner side of the lower terminal plate and between the third pin and the bobbin. 
     According to an embodiment of the present disclosure, neither of the upper surface of the boss and the upper surface of the support wall is higher than an upper surface of the second cover plate. 
     It can be seen from the above description of the present disclosure that, compared with related art, the present disclosure has the following advantageous effects. 
     According to an embodiment, due to the effect of the magnetic conductor member, the magnetic flux generated by the permanent magnet is divided into two paths and both of the two paths of magnetic fluxes are adjustable. Thereby, it can solve the problem that in the series-type magnetic circuit, there is only one path which cannot be adjusted, and the permanent magnet in the resetting position will keep a large attraction force to the armature and reduce the pressure on the contact points of the normal-close terminal and weaken the load capability of the fixed closed terminal and the product relay has a poor resistance against impact and vibration. 
     According to an embodiment, the first yoke is provided with a magnetic isolation recess for increasing the magnetic resistance of the magnetic circuit, and a portion of the pole shoe of the iron core is cut off. The size of area of the cut (the portion cut off) can be adjusted to, together with the magnetic isolation recess, regulate the balance between the magnitudes of the setting voltage and resetting voltage of the relay. The size of the magnetic isolation recess of the iron yoke can be adjusted to regulate the balance between the magnitudes of the setting voltage and resetting voltage of the relay. However, the magnetic isolation recess cannot be increased infinitely. That is, the magnetic conduction cross sectional area at either side of the magnetic isolation recess cannot be reduced infinitely. Therefore, the magnitudes of the setting voltage and the resetting voltage of the relay cannot be regulated without limit. For a magnetic latching relay, it is generally desirable to make the resetting voltage to be approximate to the setting voltage as much as possible. Therefore, in order to increase the resetting voltage, in the prevent disclosure, a portion of the pole shoe of the iron core is cut off. According to a magnetic circuit principle, the smaller the area of the pole shoe of the iron core is, the larger the retention force (the magnetic attraction force) on the armature when the armature is at the setting position is, and the larger the resetting voltage required is. Accordingly, the magnitudes of the resetting voltage and the setting voltage can be balanced (to make the resetting voltage to be approximate to the setting voltage in the value) as much as possible. 
     According to an embodiment, a shielding wall is provided on the coil rack between the fixed spring sheet and the iron core. After the movable contact point and the fixed contact point are burned, metal spatters of the movable contact point and the fixed contact point can be blocked by the shielding wall, to prevent the metal spatters from drifting from the contact points to the iron core. A groove formed between the two shielding walls and a region between the shielding wall and the fixed contact point can also be configured to collect the metal spatters of the contact points. Thereby, the creepage distance between the movable contact point and the fixed contact point as well as the dielectric Strength can be improved, and it can effectively prevent electrical accidents caused by unwanted conduction of the movable contact point and the fixed contact point due to accumulation of metal spatters of the contact points. The shielding wall is disposed close to the through hole, and corresponding to the armature which is secured to the movable spring sheet. The height of the shielding wall is not lower than the bottom of the armature when the relay is reset. When the relay is subject to an impact in a length direction, the armature will move toward the contact points. Due to the presence of the shielding wall, the armature is limited in the length direction. Thus, the armature and the movable contact point will not displace from normal positions due to the impact, significantly improving the impact resistance of the relay. 
     According to an embodiment, a groove for guiding the enameled wire is surrounded and thus formed by a boss and a support wall. The bottom of the groove is an inclined plate. One end of the groove is connected to the bobbin, one end of the groove leads to the second pin. Thus, in winding the first circle of the outer circles of the enameled wire, the enameled wire is placed on the inclined plate. In winding the last circle of the outer circles of the enameled wire, due to the effect of the boss and the support wall, the last circle of the enameled wire can be held up, to form an air gap between the first circle of the enameled wire and the last circle of the enameled wire, thus avoiding an unfavorable situation of the first circle and the last circle being directly placed together in winding the out circles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic structural diagram of a magnetic circuit portion of a magnetic-latching-type electromagnet relay in the prior art; 
         FIG. 2  is an exploded view of the configuration according to an embodiment of the present disclosure; 
         FIG. 3  is a schematic structural diagram of a magnetic circuit portion according to an embodiment of the present disclosure; 
         FIG. 4  is a schematic structural diagram of an iron yoke of the magnetic circuit portion according to an embodiment of the present disclosure; 
         FIG. 5  is a schematic structural diagram of an iron yoke of the magnetic circuit portion according to an embodiment of the present disclosure, with one portion removed; 
         FIG. 6  is a schematic structural diagram of a magnetic conductor member of the magnetic circuit portion according to an embodiment of the present disclosure; 
         FIG. 7  is a side view of the magnetic conductor member of the magnetic circuit portion according to an embodiment of the present disclosure; 
         FIG. 8  is a schematic structural diagram of an iron core of the magnetic circuit portion according to an embodiment of the present disclosure; 
         FIG. 9  is a top view of an iron core of the magnetic circuit portion according to an embodiment of the present disclosure; 
         FIG. 10  is a schematic circuit diagram of the magnetic circuit portion according to an embodiment of the present disclosure, in a resetting state and when the coil is powered off; 
         FIG. 11  is a schematic circuit diagram of the magnetic circuit portion according to an embodiment of the present disclosure, in a resetting state and when the coil is powered with a setting voltage; 
         FIG. 12  is a schematic circuit diagram of the magnetic circuit portion according to an embodiment of the present disclosure, in a setting state and when the coil is powered off; 
         FIG. 13  is a schematic circuit diagram of the magnetic circuit portion according to an embodiment of the present disclosure, in a setting state and when the coil is powered with a resetting voltage; 
         FIG. 14  is a cross sectional view of an embodiment of the present disclosure; 
         FIG. 15  is a schematic structural diagram of a coil rack according to an embodiment of the present disclosure, mainly showing an upper end plate; 
         FIG. 16  is a top view of the coil rack according to an embodiment of the present disclosure, mainly showing an upper end plate; 
         FIG. 17  is a schematic diagram of the coil rack according to an embodiment of the present disclosure, with an iron core and a fixed spring assembled; 
         FIG. 18  is a partial structural diagram of an armature and contact mechanism according to an embodiment of the present disclosure; 
         FIG. 19  is a perspective diagram of a coil rack according to an embodiment of the present disclosure; 
         FIG. 20  is a schematic diagram of a coil rack when winding inner circles of an enameled wire according to an embodiment of the present disclosure; 
         FIG. 21  is a schematic diagram of a coil rack when winding outer circles of an enameled wire according to an embodiment of the present disclosure; 
         FIG. 22  is a side view of a coil rack when winding outer circles of an enameled wire according to an embodiment of the present disclosure; and 
         FIG. 23  is a schematic diagram of a coil rack when inner circles and outer circles of an enameled wire have been wound according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Representative embodiments showing characteristics and advantages of the present disclosure will be described in detail in the following description. It should be understood that, the present disclosure can be varied with various embodiments without departing from the scope of the present disclosure. The description and the illustration are merely for explanation, rather than for limitation of the present disclosure. 
     Terms representing orientations, such as upper, lower, top, bottom and the like mentioned in the present disclosure are merely for illustrating relative positions between components, and not for limitation of specific assembly orientation of the components in the present disclosure. 
     As shown in  FIGS. 2-9 , an embodiment of the present disclosure provides a magnetic latching relay with a parallel type magnetic circuit, including a magnetic circuit portion  1 , a movable spring portion  2 , a fixed spring portion  3  and a base  4 . Wherein the magnetic circuit portion  1  includes an iron core  11 , an armature  12 , an iron yoke  13 , a permanent magnet  14 , a magnetic conductor member  15 , a coil rack  16  and an enameled wire  17 . The movable spring portion  2  includes a movable spring sheet  21  and a movable contact point  22 . The fixed spring portion  3  includes a fixed spring sheet  31  and a fixed contact point  32 . 
     As shown in  FIGS. 2 and 3 , the iron yoke  13  is L shaped, formed by a first yoke  131  parallel to the iron core and a second yoke  132  perpendicular to the iron core. An upper end of the first yoke  131  forms a hinge portion of the iron yoke  13  (a “hinge portion” refers to a contact portion of the iron yoke contacting with the armature rotating around the iron yoke). The armature  12  can rotate around the hinge portion of the iron yoke. The enameled wire  17  is wound on the coil rack  16 , and the coil rack  16  is mounted on the base  4 . In the present embodiment, the coil rack  16  is integrally formed with the base  4 . The coil rack  16  is provided with a through hole  161  along a vertical direction. The iron core  11  is mounted in the through hole  161  of the coil rack. The iron core  11  is provided at an upper end thereof with a pole shoe  111 , and the iron core  11  is secured to the second yoke  132  at its lower end. The armature  12  is connected to the iron yoke  13  via the movable spring sheet  21 . The movable spring sheet  21  is formed with a first side  211  and a second side  212 . An elastically bendable angle is formed between the first side  211  and the second side  212 . The armature  12  can be secured to the second side  212  through a rivet. The first yoke  131  can be secured to the first side  211  through a rivet. The armature  12  is flexibly connected to the first yoke  131  via the movable spring sheet  21 . The movable contact point can be secured to an end portion of the second side  212  which extends beyond the armature  12 . The second side  212  of the movable spring sheet is secured to the armature  12  and fitted on the upper side of the pole shoe  111  of the iron core, and the armature  12  is thus mounted at the hinge portion of the iron yoke. 
     The magnetic conductor member  15  has one end connected with the first yoke  131 , and the other end connected to the first yoke  131  via the permanent magnet  14 . A magnetic isolation recess  133  is provide between a conjunction of the first yoke  131  and the permanent magnet  14  and the first yoke  131  and the magnetic conductor member  15 . The magnetic isolation recess  133  is for increasing the magnetic resistance of the magnetic circuit, and a size of the magnetic isolation recess  133  can be adjusted to adjust balance between the setting voltage and resetting voltage of the relay. The pole shoe  111  has a side provided with a cut  112 . Combined with the magnetic isolation recess  133 , a size of the cut  112  can be adjusted to adjust the balance between the setting voltage and resetting voltage of the relay. Now the drawing only shows one magnetic isolation recess  133 , however two magnetic isolation recesses  133  can be implemented as long as a cross section area of solid portion of the first yoke  131  can be adjusted. The magnetic isolation recess  133  can be replaced with other magnetic isolation configuration, such as a pillar member or the like. 
     In the present embodiment, the cut  112  of the pole shoe  111  is a full circular shape with one portion cut off (as shown in  FIG. 9 ), the full circular shape being symmetric with respect to the central axis of the iron core. However, alternatively, the cut of the pole shoe can be a full rectangle with one portion cut off, the full rectangle being symmetric with respect to the central axis of the iron core. The cut  112  of the pole shoe  111  is disposed toward a direction in which the movable contact point and the fixed contact point are to be attracted to each other (as shown in  FIG. 2 ). Thereby, a creepage distance between the iron core and the fixed spring sheet can be increased. 
     A creepage distance is a “distance” measured along an insulated surface between two conductive components. 
     As shown in  FIGS. 3, 6 and 7 , the magnetic conductor member  15  is at one end provided with a contact surface  151  for contacting the first yoke  131 . The contact surface  151  of the magnetic conductor member is provided with one or more bosses  152  for positioning of the first yoke. The first yoke  131  is provided thereon with holes  1311  fitted with the bosses of the magnetic conductor member. The bosses  152  of the magnetic conductor member is fitted within the holes  1311  of the first yoke  131 , and secured with them via a rivet or weld. The permanent magnet  14  is secured to the other end of the magnetic conductor member  15 . The magnetic conductor member is provided at the other end with bosses  153  for securing the permanent magnet. 
       FIGS. 10-13  are schematic circuit diagrams of the relay when the relay is respectively powered off, powered with a setting voltage, when the coil is powered with a resetting voltage. Φm1, Φm2 denote magnetic fluxes (referred to as permanent magnet fluxes, generally represented by Φm) generated by the permanent magnet  14 . The paths passed by the permanent magnet fluxes are respectively referred to as a first magnetic path A 1  and a second magnetic path A 2 . Φc1, Φc2 denote magnetic fluxes (referred to as control magnet fluxes, generally represented by Φc) generated by current in the coil, and the path passed by the control magnet fluxes is referred to as a third magnetic path A 3 . Wherein, Φc1 is a magnetic flux generated by current of the coil under a setting voltage, and Φc2 is a magnetic flux generated by current of the coil under a resetting voltage. δ2 denotes an operation air gap, and F2 denotes an electromagnetic attraction force (generally represented by F) applied on the armature at the air gap δ2. The magnetic circuit has two stable states, that is, the armature  12  being at the setting position or at the resetting position. 
     When the armature  12  is in the resetting state (the armature  12  is at an opened position, and the coil is not supplied with current) as shown in  FIG. 10 , due to the effects of the magnetic conductor member  15  and the magnetic isolation recess  133 , the magnetic flux generated by the permanent magnet  14  passes through paths of the first magnetic path A 1  and the second magnetic path A 2  as shown in the figure. The magnetic fluxes denoted by Φm1 and Φm2 are parallel. On the second magnetic path A 2 , due to the influence of the air gap δ2, Φm2 has a small effect. Therefore, at this time, the armature  12  is subject to a weak electromagnetic attraction force F2 under the effect of Φm2, which is smaller than a counter force F1 applied by the movable spring sheet  21  on the armature  12 , that is, F1&gt;F2. Then, under the counter action of the counter force of the movable spring sheet  21 , the armature  12  can be stably maintained at the resetting position (i.e. the opened position). Due to the effects of the magnetic conductor member  15  and the magnetic isolation recess  133 , the magnetic flux generated by the permanent magnet  14  are divided into magnetic fluxes Φm1 and Φm2 of two paths, and the magnitudes of the magnetic fluxes Φm1 and Φm2 can be adjusted. Thereby, it can solve the problem in the series-type magnetic circuit, there is only one path which cannot be adjusted, and the permanent magnet in the resetting position will keep a large attraction force to the armature and reduce the pressure on the contact points of the normal-close terminal and weaken the load capability of the fixed closed terminal and the product relay has a poor resistance against impact and vibration. 
     As shown in  FIG. 11 , when a resetting pulse voltage with a certain width is applied on the coil of the relay, a control magnetic flux Φc1 generated by the coil of the relay has a direction as shown by a third magnetic path A 3  in  FIG. 11 . At this time, the magnetic flux Φc1 generated by the coil and the magnetic flux Φm2 generated by the permanent magnet  14  have the same direction (as shown by a second magnetic path A 2  in  FIG. 11 ). This increases a composite magnetic flux at the air gap δ2. Therefore, the armature  12  is subject an increased electromagnetic attraction force F2 due to the effect of the composite magnetic flux of Φc1 and Φm2. When the electromagnetic attraction force F2 subjected by the armature  12  is larger than the counter force F1 applied by the movable spring sheet  21  on the armature  12 , the armature  12  will complete an action moving from the resetting position to the setting position under the composite force of F2 and F1. Afterwards, after the operation current of the coil is powered off, the electromagnetic attraction force F2 generated by the magnetic flux Φm2 of the permanent magnet  14  is larger than the counter force F1 applied by the movable spring sheet  21  on the armature  12 . Then, the armature  12  will be stably maintained in the setting position, as shown in  FIG. 12 . 
     When the relay is at the setting position as shown in  FIG. 12 , a resetting pulse voltage (opposite to the setting voltage) with a certain width is applied to the coil of the relay, a control magnetic flux Φc2 generated by the coil of the relay has a direction as shown in  FIG. 13 . At this time, the magnetic flux Φc2 generated by the coil and the magnetic flux Φm2 generated by the permanent magnet  14  have opposite directions (as shown by the second magnetic path A 2  and the third magnetic path A 3  in  FIG. 13 ). Thereby, the magnetic flux Φm2 generated by the permanent magnet  14  is counteracted. Therefore, at this time, electromagnetic attraction force F2 subjected by the armature  12  is decreased due to the effects of Φc2 and Φm2. When the electromagnetic attraction force F2 subjected by the armature  12  is smaller than the counter force F1 applied by the movable spring sheet  21  on the armature  12 , the armature  12  will complete an action moving from the setting position to the resetting position under the composite force of F2 and F1, and return to the resetting position as shown in  FIG. 10 . 
       FIG. 12  shows magnetic fluxes of the magnetic circuit when the armature is at the setting position and the coil is powered off. The permanent magnet  14  has two paths of magnetic fluxes Φm1 and Φm2. The total flux of the permanent magnet  14  (Φmtotal)=Φm1+Φm2. By adjusting the size of the magnetic isolation recess  133 , a magnetic conduction cross sectional area  1331  at either side of the magnetic isolation recess  133  of the yoke (as shown in  FIG. 5 ) changes and thus a magnetic resistance of the first magnetic path A 1  changes, to form a changed first magnetic fluxe Φm1. Since the total flux(Φmtotal) is substantially constant, and Φm2=(Φmtotal)−Φm1, when (Φm1 changes, Φm2 will change too (in an opposite direction of value variation). When Φm2 changes, the electromagnetic attraction force F2 generated by the permanent magnet  14  through the second magnetic path A 2 , which attracts the armature  12  on the pole shoe of the iron core, will change. That is, the retention force to keep the armature  102  against the pole shoe of the iron core changes, to solve the problem that it is hard to reset in the series-type magnetic circuit. Due to the effect of the magnetic conductor member  15  and the magnetic isolation recess  133 , the magnetic flux generated by the permanent magnet  14  is divided into two paths Φm1 and Φm2, and the magnitudes of Φm1 and Φm2 can be adjusted, to solve the problem that in the series-type magnetic circuit, there is there is only one path which cannot be adjusted, causing difficulty in resetting. 
     When the coil of the relay is applied with a resetting pulse voltage (opposite to the setting voltage) with a certain width, the magnetic flux Φc2 generated by the coil will be counteracted by the magnetic flux Φm2 generated by the permanent magnet  14 . When the composite magnetic flux (Φm2−Φc2) is reduced to a degree that the electromagnetic attraction force F2 generated by composite magnetic flux to the armature  12  is smaller than the counter force F1 applied by the movable spring sheet  21  on the armature  12 , the armature  12  will complete an action moving from the setting position to the resetting position under the composite force of F2 and F1. As discussed above, since the size of the magnetic isolation recess  133  can be provided differently, to form a different Φm2. While the electromagnetic attraction force F2 is generated by the composite magnetic flux (Φm2-Φc2), therefore, under a different Φm2, to reduce the electromagnetic attraction force F2 to a value smaller than the counter force F1, the value of Φc2 should be changed. Since Φc2 is generated by applying a voltage on the coil, changing the size of the magnetic isolation recess  133  will change the magnitude of Φm2, and in turn, change the magnitude of the resetting voltage for resetting the armature. 
     In the magnetic circuit of the present invention, in order to ensure a certain strength of the components, the magnetic conduction cross sectional area  1331  (as shown in  FIG. 5 ) at either side of the magnetic isolation recess  133  of the yoke cannot be reduced infinitely. Therefore, Φm2 cannot be too large, and generally a small resetting voltage can be applied to obtain an electromagnetic attraction force F2, as generated by the composite magnetic flux (Φm2-Φc2), smaller than the counter force F1, to reset the armature. For a magnetic latching relay, it is desirable to make the resetting voltage to be approximate to the setting voltage as much as possible. Therefore, in order to increase the resetting voltage, in the prevent disclosure, half of the pole shoe of the iron core is cut off (according to a magnetic circuit principle, the smaller the area of the pole shoe of the iron core is, the larger the retention force (the magnetic attraction force F2) on the armature when the armature is at the setting position is, and the larger the resetting voltage required is), so as to balance the resetting voltage and the setting voltage (to make the resetting voltage to be approximate to the setting voltage in the value) as much as possible. 
     An embodiment regarding the coil rack  16  and the fixed spring portion  3  in the relay will be described below. As shown in  FIG. 2  and  FIG. 14 , the fixed spring portion  3  includes the fixed spring sheet  31  and the fixed contact point  32  fixed on the fixed spring sheet  31 . The fixed spring sheet  31  is mounted at a position which allows the movable contact point and the fixed contact point to contact each other. The coil rack  16  includes an upper terminal plate  160 , a bobbin  167  and a lower terminal plate  168 . The upper terminal plate  160  of the coil rack  16  extends to a side, and a mounting portion  162  is disposed at the side. The fixed spring sheet  31  and the fixed contact point  32  are embedded in the mounting portion  162 . The movable contact point  22  is mounted at a position in the mounting portion  162  where matches with the position of the fixed contact point  32  (as shown in  FIGS. 15-17 ). At least one shielding wall  163 ,  164  is provided on the coil rack  16  and between the though hole  161  and the mounting portion  162 . The shielding wall  163 ,  164  is formed as one piece with the coil rack  16 , to separate the pole shoe  11  at the through hole of the coil rack and the fixed spring sheet  31  at the mounting portion. 
     In the present embodiment, as shown in  FIG. 14  and  FIG. 18 , there are two shielding walls  163  and  164 . A groove  165  is formed between the shielding walls  163  and  164  to collect spatters of the contact points. Wherein one shielding wall  163  is disposed close to the through hole  161 , and corresponding to the armature  12  of the movable spring sheet. The height of the shielding wall  163  is not lower than the bottom of the armature  12  when the relay is reset, in order to prevent the armature  12  from moving to the direction where the movable contact point contacts the fixed contact point. 
     There can be provided one shielding wall. When there is only one shielding wall, the shielding wall is disposed close to the through hole, and corresponding to the armature of the movable spring sheet. The height of the shielding wall is not lower than the bottom of the armature when the relay is reset, in order to prevent the armature from moving to the direction where the movable contact point contacts the fixed contact point. 
     A cut  112  is provided at a side of the pole shoe  111  where close to the fixed spring sheet  31 . Thus, the creepage distance between the pole shoe and the fixed spring sheet is increased by a distance of the cut  112 . Thereby, the creepage distance between the pole shoe of the iron core and the fixed spring sheet can be increased. 
     Also referring to  FIGS. 15-17 , shielding walls  163  and  164  are provided on the coil rack and between the fixed spring sheet  31  and the iron core  11 . After the movable contact point and the fixed contact point are burned, metal spatters of the movable contact point and the fixed contact point can be blocked by the shielding wall, to prevent the metal spatters from drifting from the contact points to the iron core. The groove  165  formed between the two shielding walls and a region  166  between the shielding wall  164  and the fixed contact point  32  can also be configured to collect the metal spatters of the contact points. Thereby, the creepage distance between the movable contact point and the fixed contact point as well as the dielectric Strength can be improved, and it can effectively prevent electrical accidents caused by unwanted conduction of the movable contact point and the fixed contact point due to accumulation of metal spatters of the contact points. The shielding wall  163  is disposed close to the through hole  161 , and corresponding to the armature  12  which is secured to the movable spring sheet. The height of the shielding wall  163  is not lower than the bottom of the armature  12  when the relay is reset. When the relay is subject to an impact in a length direction, the armature  12  will move toward the contact points. Due to the presence of the shielding wall  163 , the armature  12  is limited in the length direction. Thus, the armature  12  and the movable contact point  22  will not displace from normal positions due to the impact, significantly improving the impact resistance of the relay. The above configuration can expand the application range of the relay. 
     As shown in  FIGS. 19-23 , an embodiment of the present disclosure provides a coil rack of a double-coil relay. One end of the bobbin  167  is connected to the upper terminal plate  160 , the other end of the bobbin  167  is connected to the lower terminal plate  168 . A first pin  51 , a second pin  52  and a third pin  53  are respectively mounted on the lower terminal plate  168 . The lower terminal plate  168  can be integrated with the base  4 . 
     A groove  1684  is provided at an inner side of the lower terminal plate  168  between the bobbin  167  and the second pin  52 , to guide the enameled wire. One end of the groove  1684  can be connected to the bobbin  167 , and the other end of the groove can lead to the second pin  52 . An inclined plate  1681  is provided at an inner side of the lower terminal plate  168 , and located between the bobbin  167  and the second pin  52 . The inclined plate  1681  is gradually inclined in a direction from the bobbin to the second pin. A boss  1682  extending from the bobbin to the second pin is provided in the middle of the inclined plate  1681 . That is, the boss  1682  is provided on the inclined plate  1681 , and the boss  1682  is a boss with a flat surface. A support wall  1683  is provided at a side of the inclined plate  1681 . The support wall  1683  is also provided on the inclined plate  1681 , and an upper surface of the support wall  1683  is also flat. The groove  1684  for guiding the enameled wire is surrounded and thus formed by the support wall  1683  and the boss  1682 . The bottom of the groove  1684  is an inclined plate. 
     The height of the boss  1682  is the same as the height of the support wall  1683 . However, the height of the boss  1682  can be different from the height of the support wall  1683 . 
     A first cover plate  1685  which can press and seize the enameled wire is mounted at the inner side of the lower terminal plate  168  and between the first pin  51  and the bobbin  167 . That is, the first cover plate  1685  is provided at the inner side of the lower terminal plate  168 , and located between the bobbin  167  and the first pin  51 . 
     In the present embodiment, the upper surface of the first cover plate  1685 , the upper surface of the boss  1682  and the upper surface of the support wall  1683  are in the same horizontal plane. However, the upper surface of the first cover plate  1685  can also be disposed as higher than the upper surface of the boss  1682  and the upper surface of the support wall  1683 . 
     A second cover plate  1686  which can press and seize the enameled wire is mounted at the inner side of the lower terminal plate  168  and between the third pin  53  and the bobbin  167 . That is, the second cover plate  1686  is provided at the inner side of the lower terminal plate  168 , and located between the bobbin  167  and the third pin  53 . 
     In the present embodiment, the upper surface of the second cover plate  1686 , the upper surface of the boss  1682  and the upper surface of the support wall  1683  are in the same horizontal plane. However, the upper surface of the second cover plate  1686  can also be disposed as higher than the upper surface of the boss  1682  and the upper surface of the support wall  1683 . 
     As shown in  FIGS. 20-23 , the present embodiment provides a coil rack of a double-coil relay. To wind the enameled wire, the enameled wire are firstly wound from inner circles. After the enameled wire  17  is firstly wound on the first pin  51 , the enameled wire  17  passes below the first cover plate  1685 . After the enameled wire  17  is wound on the bobbin  167  anticlockwise for a required number of circles, the enameled wire  17  passes through the groove  1684  and leads to the second pin  52 . After the enameled wire  17  is wound on the second pin  52 , winding of the inner circles of the enameled wire  17  is completed. In winding of the outer circles, after the enameled wire  17  is wound on the second pin  52 , a first circle  171  of the enameled wire passes through the groove  1684  and leads to the bobbin  167 . After the enameled wire is wound on the bobbin  167  clockwise for a required number of circles, the last circle  172  of the enameled wire passes through the boss  1682 , the support wall  1683  and leads to the below part of the second cover plate  1686 . After the enameled wire passes through the below part of the second cover plate  1686 , and is wound on the third pin  53 , the winding of the outer circles is completed. The boss  1682  and the support wall  1683  form the groove  1684  which can guide the enameled wire; the bottom of the groove is an inclined plate; one end of the groove is connected to the bobbin; and the other end of the groove leads to the second pin. Thereby, in winding the first circle  171  of the outer circles of the enameled wire, the enameled wire is placed on the inclined plate  1681 . In winding the last circle  172  of the outer circles of the enameled wire, due to the effect of the boss  1682  and the support wall  1683 , the last circle  172  of the enameled wire can be held up, to form an air gap  173  between the first circle  171  of the enameled wire and the last circle  172  of the enameled wire, thus avoiding an unfavorable situation of the first circle and the last circle being directly placed together in winding the out circles. 
     The above is an embodiment of the coil rack  16 , and is not exclusively applied to the above magnetic latching relay with a paralleltype magnetic circuit. The coil rack  16  can also be applied in other types of relays by those skilled in the art. 
     Although the present disclosure has been described with reference to some exemplary embodiments, it should be understood that the terms are not restrictive, but illustrative and exemplary. The present disclosure can be embodied in various forms without departing from the spirit or essence thereof. Therefore, it can be understood that the above embodiment is not limited to the above details, but should be interpreted broadly within the spirit and scope defined by the appending claims. In this regard, all alterations and modifications falling within the claims or their equivalent scope should be covered by the appending claims.