Abstract:
The present invention provides a means in which contact between contacts in a “double-break (or double-make) contact structure” occurs in two places in the same state as much as possible. A contact structure includes two fixed members ( 110,112 ) each of which has a fixed contact ( 116,118 ) and a movable member ( 102 ) containing a movable contact ( 106 ) which contacts or separates from the fixed contact of each of the fixed members. The movable member is in the form of a strip as a whole, its one end is supported so as to allow the above mentioned contact and separation of the movable member, and the other end of the movable member has the movable contact, and the movable member has a narrowed section between its two ends.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a double-break (or a double-make) contact structure used in a switch such as a relay, a circuit breaker, and the like, and a circuit protection device comprising such a contact structure. 
     BACKGROUND OF THE INVENTION 
     In a switch such as a relay, and the like, various types of contacts are used. Among those contacts, a double-break (or a double-make) contact structure is extensively used. As used herein, the “double-break (or double-make) contact structure” means a contact structure which has a function wherein a contact provided on a section functioning as a movable terminal of one movable member (i.e. a movable contact) mechanically contacts with a contact provided on a section functioning as a fixed terminal (i.e. a fixed contact) in each of two fixed members to form two electric connections (i.e. a double-make part), thereby closing an electric circuit between the movable member and the fixed members; and also has a function wherein, from the above mentioned contacting state of the contacts, the contact of the movable member is separated from the contacts of the fixed members to form two electric non-connections (i.e. double-break parts), thereby opening the electric circuit between the movable member and the fixed members. That is, a contact structure in which there are two contact pairs which can take reversibly the contacting state or the non-contacting state is called as the double-break (or double-make) contact structure. 
     It is noted that such contacts as mentioned above may be in any suitable forms provided on sections which function as terminals of the movable member and the fixed member, usually on their end portions. For example, they may be in various forms of protruding portions, flat plates or portions of such flat plates. In one embodiment, the contact provided on the fixed member is a protrusion, for example, a portion of a sphere (for example, a hemispherical protrusion), and the contact provided on the movable member is a flat plate. In other embodiment, the contact provided on the fixed member may be a flat plate, and the contact provided on the movable member may be a protrusion. It is noted that when the contact is a flat plate, it is possible that no separate plate is provided, but the terminal itself has a function as a contact. It is noted that the contact provided on the movable member may be in a single form which is integrally connected to the movable member by means of an electrically conductive material, and in particular, the contact may be in the form of an elongated and flat strip provided on the movable member. Furthermore, the strip may be provided with a protrusion(s). 
     In such “double-break (or double-make) contact structure”, a length of its air-gap is doubled in comparison with that of the air-gap of a single-break contact structure having one contact pair. Therefore, such contact structure is said to have an advantage of causing less fusion likelihood between the contacts because energy of arc which is generated when a circuit is opened is dispersed into two air-gaps. Thus, such contact structure is extensively used. 
     For example, WO 2009/128535 proposes a circuit protection device which uses the above mentioned “double-break (or double-make) contact structure”. This device comprises a circuit switching member having a bimetal component as a circuit switching element and a movable contact as well as a PTC member. This circuit protection device is constructed such that, in a state wherein each of two movable contacts and each of two fixed contacts are in contact respectively (i.e. the double-make state) and a current is flowing through a circuit, when an excess current flows through the circuit, for example, due to occurrence of some abnormal state and a temperature of the bimetal component exceeds its threshold temperature, a state wherein the movable contacts are displaced to be separated from the fixed contacts (i.e. a double-break state) by the deformation of the bimetal component, thereby opening the circuit to protect the circuit and/or an electrical apparatus incorporated into the circuit. Then, when the abnormal state is resolved, the temperature of the bimetal component is decreased to return to its original shape, so that the movable contacts and the fixed contacts are in contact at two positions to flow the current through the circuit again. 
     In order that such a circuit protection device adequately provides a circuit protection function, it is necessary to allow contact and separation between the contacts to sufficiently and surely arise at two positions by the deformation of the bimetal component. 
     International Publication No. WO 2009/128535 is a prior patent reference. 
     SUMMARY OF THE INVENTION 
     In the above mentioned “double-break (or double-make) contact structure”, the movable contact is usually provided on an end portion of a metal strip as a movable member which portion functions as a movable terminal. When the circuit protection device is intended to be made more compact, it is desired that the distance between the fixed terminals (or the fixed contacts) is shortened as much as possible. In this case, a width of the movable member shortens at the same time. As the result, there is a possibility that contacts between the contacts are not sufficiently or surely formed at two positions, that is, a so-called “partial contact (or one side contact)” state can arise. In this case, there is a problem of being able to increase a contact resistance between the contacts at one position. 
     Therefore, a problem to be solved by the present invention is to provide a means with which contacting states between contacts are formed at two positions in the same states as much as possible in the “double-break (or double-make) contact structure”. 
     In a first aspect, the present invention provides a contact structure (in particular, a double-break (or double-make) contact structure) comprising two fixed members, each of which has a fixed contact, and a movable member comprising a movable contact which contacts or separates from the fixed contact of each of the fixed members, characterized in that 
     the movable member is in the form of a strip as a whole, its one end portion is supported so as to allow the movable member to contact or separate as mentioned above, and the other end portion of the movable member has the movable contact, and 
     the movable member has a narrowed (or constricted) section between the both of the two end portions, 
     such contact structure is able to be used in a circuit protection device. 
     As used herein, the term “in the form of a strip” means a form of a rectangle shape, preferably an elongated rectangle shape, and its thickness is less than the other dimensions (length and width), usually negligible. Therefore, in the specification of the present application, the thickness of the movable member is ignored as to the description of the present invention. Though the form of the strip means, for example, an elongated rectangle shape, sides which define this shape are not necessarily straight lines, and it is sufficient that they only have to provide an elongated rectangle shape in a macroscopic appearance. For example, the sides defining this shape may be a combination of a straight line and a curve line. It is noted that the elongated rectangle shape means in which a length of a long side of the rectangle is at least double length that of a short side of the rectangle. 
     The term “(be) in the form of a strip as a whole” means that, when it is assumed that the narrowed section is ignored or the narrowed section is absent, the movable member is in the form of a strip as mentioned above. The term “narrowed section” means that a section of which dimension perpendicular to a long side which defines the strip under the above mentioned assumption (i.e. a short side of the strip), that is, its width is smaller than the long side length. It is noted that the narrowed section is present between the both ends of the strip shape, not at the end. Such narrowed section is preferably formed such that the width of the strip recedes (or dents) by the same distance from the both edges (i.e. the long sides) at a predetermined position in direction of the length of the strip. 
     One embodiment of a movable member  10  constructing the contact structure of the present invention is schematically shown in a plan view in  FIG. 1 . As illustrated, there is a narrowed section  16  between two ends  12  and  14  of the movable member. If this movable member  10  had no narrowed section  16 , that is, when parts shown by dotted lines  18  and  20  are assumed to be portions of the outer edges of the movable member, the movable member  10  has an elongated shape, for example, the movable member  10  is in the form of an elongated rectangle shape or a rectangle shape. Therefore, the movable member  10  is in the form of a strip as a whole. 
     The narrowed section  16  has a dimension perpendicular to a long side  22  of the strip (i.e. a dimension in direction of a short side  24  of the strip), that is, a width “a”. The width “a” is smaller than a width “b” of a section other than the narrowed section. In other words, the narrowed section is formed by indenting a portion of each of the opposite long sides of the strip form, that is, by forming concave portions  26 . The shape of the concave portion  26  (including the portion of the dotted line here) may be in any suitable form, and for example, as illustrated, may be in the form of a rectangle or a square. Alternatively, it may be in the form of a triangle, a semicircle or a trapezium, and the lines constituting these shapes may be a straight line(s) as illustrated or a curved line(s). Furthermore, in other embodiment, the shape of the concave portion  26  may be any combination of the various shapes as described above. In one embodiment of the present invention, the shape of the concave portion is preferably a rectangle, a trapezium, a triangle, or a semicircle. 
     It is noted that the shape of the narrowed section, the position of the narrowed section (a position of a central part of the narrowed section with respect to the length “L” of the movable member in  FIG. 1 ), the width “a” of the narrowed section, the depth “c” of the narrowed section (lengths c 1  and c 2  in  FIG. 1 , which are preferably the same), the length “d” of the narrowed section (see  FIG. 2 , corresponding to the length of the dotted line in  FIG. 1 ), and the like can be appropriately selected depending on the movable member to be used, in particular depending on a material constituting the movable member, the length “L” of the movable member, the width “b” of the movable member, and the like. For example, the width “a” of the narrowed section is preferably 0.3-0.6 times the width “b” of the movable member, and the length “L” of the movable member is preferably 2-4 times the width “b”. 
     In one specifically preferable embodiment, the following narrowed section is preferable: 
     Material of movable member: material having both of a high strength and an excellent springiness (for example, made of a beryllium copper); 
     Length “L” of movable member: 15 mm (±10 mm); 
     Width “b” of movable member: 10 mm (±7 mm); 
     Shape of narrowed section: rectangle or trapezium; 
     Position of narrowed section: it is preferable to be nearer to the movable contact (for example, the movable contact  106  in  FIG. 2 ) (for example, the position, for example, 0.05 L-0.4 L, in particular 0.1 L-0.3 L from the end of the movable member which end functions as the movable terminal of the movable member); 
     Width “a” of narrowed section: it is preferable to be small as much as possible (for example, a:b=about 0.5-2:2-4, for example, a:b=about 1:3); 
     Depth “c” of concave portion (the length “c 1 ” (=“c 2 ”) in  FIG. 1 ): it is selected such that the narrowed section is located in the center of the width direction of the movable member; 
     Length d of the narrowed section: 0.5 mm or more (for example, 0.5 mm-15 mm, preferably 2 mm-12 mm, and more preferably 3-10 mm); and 
     Thickness of movable member: 0.15 mm (±0.05 mm). 
     In further embodiment, the above “L”, “a” and “b” have dimensions as follows: 
     Embodiment (1) L: 16.4 mm, b: 4.4 mm, a: 1.5 mm 
     Embodiment (2) L: 22.0 mm, b: 11.0 mm, a: 8.0 mm 
     Embodiment (3) L: 25.0 mm, b: 11.0 mm, a: 7.0 mm. 
     In a second aspect, the present invention provides a circuit protection device which comprises the contact structure above and below mentioned wherein the device comprises a circuit switching member which comprises a bimetal component as a circuit switching element and a movable terminal having a movable contact as well as and a PTC component, which device is characterized in that 
     (1) the PTC component and the movable terminal are electrically connected in parallel; 
     (2) the circuit switching member is able to interrupt a current flowing through the circuit switching member by moving the movable terminal disposed to pass the current so that the movable contact is separated from the fixed contacts by actuation of the bimetal component at its actuating temperature (Top), and is also able to pass, by resetting of the bimetal component at its reset temperature (Tcl), the current through the circuit switching member by moving the movable terminal disposed to interrupt the current so that the movable contact becomes in contact with the fixed contacts; and 
     (3) the bimetal component is disposed between the PTC component and the movable terminal. 
     In one preferable embodiment of the above mentioned circuit protection device, (4) the actuating temperature (Top) of the bimetal component is at least 20° C. higher than the reset temperature (Tcl); and/or (5) a trip temperature (Ttr) of the PTC component is at least 10° C. higher than the actuating temperature of the bimetal component. 
     Furthermore, the present invention also provides an electrical circuit (having a concept also including an electronic circuit) comprising such circuit protection device, and further provides an electrical apparatus (having a concept also including an electronic apparatus) comprising such electrical circuit. 
     In the contact structure of the present invention, it is facilitated that each part of the movable member located on either side of the narrowed section rotates about the longitudinal axis of the movable member in a direction opposite relatively to each other doe to the presence of the narrowed section. As a result, when a situation arises in which one pair of the movable contact and the fixed contact is in contact, and the other pair of the movable contact and the fixed contact is not in contact (i.e. in the case of the “partial contact” state), the fixed contact of such the contact pair presses the movable contact, and by its pressure, the part of the movable member on which the movable contact is located rotates as mentioned above. In consequence, the movable contact which had not been in contact yet gets close to and eventually contacts the fixed contact. 
     When the narrowed section is present, a force needed for rotating as mentioned above, i.e. a force for moving the movable contact closer to the fixed contact becomes smaller. Therefore, when the “partial contact” state is likely to arise, its occurrence can easily be prevented. As a result, even if the distance between the fixed terminals in the contact structure is reduced, the partial contact can be suppressed as much as possible, thus the circuit protection device can be made more compact. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows schematically as a plan view one embodiment of the movable member constituting the contact structure of the present invention; 
         FIG. 2  shows schematically as a perspective view one embodiment of the contact structure of the present invention; 
         FIG. 3  shows schematically as a cross-section view one embodiment of a circuit protection device of the present invention which comprises the contact structure of the present invention; and 
         FIG. 4  shows schematically as an exploded perspective view the circuit protection device of the present invention shown in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A contact structure  100  of the present invention is shown in  FIG. 2  as a perspective view. A movable member  102  has a movable contact  106  which is disposed on its one end and functions as a movable terminal  104 , and a narrowed section  108  which is disposed posterior to the movable terminal  104 . It is noted that the thickness of the movable member is ignored in the Figure. 
     Two fixed members  110  and  112  are disposed below the movable terminal  104 , and fixed contacts  118  and  120  are disposed on one ends of the respective fixed members respectively which contacts function as fixed terminals  114  and  116 . 
     Each of the respective fixed contacts  118  and  120  can contact the movable contact  106  opposing thereto and also can be separated from such contact state by a force acting on the movable member (i.e. a force acting to move the movable terminal closer to the fixed terminal) and an opposite force thereto, respectively. It is noted that, in the illustrated embodiment, the movable contact is in the form of a single part, and two movable contacts may be provided on the movable terminal so that they are opposite to the fixed contacts, respectively. 
     Essentially, the illustrated movable terminal  104  and the illustrated fixed terminals  114  and  116  are constituted such that when a force acts to make them get closer to each other (for example, when a downward force acts on the movable terminal  104  so that it gets closer to the fixed terminals  114  and  116 ), the contacts provided on the members sufficiently get in contact with each other. However, the sufficient contact cannot always be ensured because of, for example, a force applied during a manufacturing step of the contact structure or its following step in which the structure is handled. 
     Normally, though both contacts are expected to be in contact with each other when it is intended to pass a current from the fixed terminal  110  to the fixed terminal  112  via the movable terminal  104 . However, as illustrated, a situation may occur in which the fixed contact  118  is a little away from the movable contact  106  while the fixed contact  120  is in contact with the movable contact  106 . In this situation, it is impossible to pass the current. 
     However, according to the contact structure of the present invention, after the fixed contact  120  contacts the right side of the movable terminal  106 , when a downward force further acts on the movable terminal  104 , a upward force acts such that the right side of the movable terminal  106  is pushed upward as shown with an arrow “A”. At this time, the movable terminal can easily rotate about the longitudinal axis of the movable member  122  as shown with an arrow “B” due to the presence of the narrowed section  108 . Then, a force which pushes the left side of the movable terminal  106  downward as shown with an arrow “C”. As a result, the left side of the movable terminal  106  contacts the fixed contact  118 . 
     As understood, the longer the length “d” of the narrowed section  108  and the smaller the width “a” of the narrowed section, the smaller the force needed to rotate the movable terminal  104 . However, when the width “a” is excessively small and/or the length “d” is excessively long, the narrowed section  108  cannot strongly and integrally connect the movable member disposed posterior thereto to the movable terminal  104  and hold them. Therefore, as mentioned above, the length “d” and the width “a” of the narrowed section can be appropriately selected depending on the material of the movable member to be used, the length “L” of the movable member, the width “b” of the movable member, the shape and the position of the narrowed section, and a force acting on the movable terminal (for example, the force shown with the arrow “A” in  FIG. 2 ). 
     A cross-section view of one embodiment of a circuit protection device which comprises the contact structure of the present invention, that is, the circuit protection device of the present invention is schematically shown in  FIG. 3 , and additionally, its exploded perspective view is schematically shown in  FIG. 4 . The circuit protection device  200  of the present invention shown in the Figures comprises a circuit switching member which comprises a bimetal component as a circuit switching element and a movable member as well as and a PTC component, which device is characterized in that 
     (1) the PTC component and the circuit switching member are electrically connected in parallel; 
     (2) the circuit switching member is able to interrupt a current flowing through the circuit switching member by moving the movable terminal disposed to pass the current (in particular, the movable contact disposed thereon) so that it is separated from the fixed terminal (in particular, the fixed contacts disposed thereon) by actuation of the bimetal component at its actuating temperature (Top), and is also able to pass the current therethrough by resetting of the bimetal component at its reset temperature (Tcl), that is, is able to pass the current through the circuit switching member by moving the movable terminal disposed to interrupt the current (in particular, the movable contact disposed thereon) so that the movable terminal becomes in contact with the fixed terminal (in particular, the fixed contacts disposed thereon). 
     In the illustrated circuit protection device  200 , a lower side lead  230  and an upper side lead  232  are disposed on a lower side and an upper side of a PTC component  210 , respectively. These are electrically connected by, for example, soldering. Further, fixed members  221  and  220  are electrically connected to these leads  230  and  232 , respectively, by for example, resistance welding or ultrasound welding. One end (a right side section in  FIG. 3 ) of each of the fixed members  220  and  221  is connected to a terminal or the like of a prescribed electric circuit, so that the circuit protection device is disposed in series in the electrical circuit. 
     It is noted that the PTC component used in the circuit protection device may be a conventional PTC component which is itself used as a so-called circuit protection device and generally comprises a laminated electrically conductive PTC element and metal electrodes disposed on its both sides. The electrically conductive PTC element may be made of a ceramic or of a polymer material. A particularly preferable PTC component is a so-called polymeric PTC component, and a PTC component may be suitably used which comprises an electrically conductive polymer element wherein electrically conductive fillers (for example carbon, nickel, nickel-cobalt fillers) are dispersed in a polymer material (for example a polyethylene, a polyvinylidene fluoride, etc.). 
     A base plate  238  is also disposed on the PTC component  210 . In the illustrated embodiment, the base plate  238  has a portion  239  that protrudes upwards; a bimetal component  214 , a spacer  240 , a movable member  216 , and an upper plate  242  are disposed in thus mentioned order over this portion  239 . These are integrated by swaging them with a pin  244  as illustrated. It is noted that the connection between the base plate  238  and the PTC component  210  may be performed by any appropriate method; it may, for example, be performed by a soldering connection. 
     In the illustrated embodiment, the movable member  216  has a strip structure as a whole. Its one end functions as a movable terminal  217 , and the other end functions such that the movable terminal is integrated with other members to support (or fix) it as mentioned above. The movable member  216  has a narrowed section  213  between those ends. The bimetal component  214  changes in its shape (i.e. curves) by heat so as to change the position of its tip  215  upward or downward, thereby the movable member  216  is curved or transforms toward the original shape, and as the result, the position of the movable terminal  217  moves up or down. 
     In the embodiment shown in  FIG. 3 , the bimetal component  214  is in a reset state (i.e. the electrical circuit is functioning normally). The tip  215  of the bimetal component  214  is separated from the movable terminal  216 . It is noted that, in the illustrated embodiment, the movable member  216  is in a state of being trying to return toward its original shape. As a result, the movable contacts  218  and  219  disposed on a tip of the movable member which tip functions as the movable terminal  217  are in contact with contacts  222  and  223  which are disposed on left side ends of the fixed members  220  and  221 , and function as the fixed terminals. Therefore, when the circuit protection device in thus mentioned state is disposed in an electrical circuit (not illustrated) and a current flows through the circuit, the current flows in the order of the fixed member  220 →the fixed contact  222 →the movable contact  219 →the movable contact  218 →the fixed contact  223 →the fixed terminal  221 . 
     In the illustrated embodiment, resilience of an electrically conductive metal material of the movable member  216 , and a force to make to move the movable member  217  downward (a force in the direction opposite to the arrow “A” shown in  FIG. 2 ) are acted wherein the force is generated by being kept the movable member in the illustrated shape which is different from its original shape, that is, the movable member is held as illustrated, though the movable member is trying to return to its original shape. If only one pair of the fixed contact and the movable contact get in contact as shown in  FIG. 2 , a force acts at such contact position in the direction of the arrow “A” shown in  FIG. 2  so that the other pair of the contacts is able to be in contact with each other. 
     In the illustrated embodiment, when an abnormality occurs in the electrical circuit and an excess current flows, a temperature in the proximity of the movable terminal  217  of the movable member  216  rises. Then, the temperature of the movable member  216  rises, while the heat is transferred to the bimetal component  214  so that the bimetal component  214  actuates. As a result, the bimetal component  214  inverts so that its tip  215  bends upward to raise the movable terminal  217 ; and the contact state between the movable contacts  218  and  219  and the fixed contacts  223  and  222  is lost, that is, the electrical connection between the fixed contact  222  and the movable contact  219 , and the electrical connection between the fixed contact  223  and the movable contact  218  are broken. In such a state, when the PTC component  210  is not yet in a tripped state, and its resistance is sufficiently low, the current flows in the order of the fixed member  220 →the upper side lead  232 →the PTC component  210 →the lower side lead  230 →the fixed member  221 , thereby being diverted. 
     When there is no change in the abnormality of the electrical circuit, the excess current flows through the PTC component  210 , whereby the PTC component  210  trips thereafter. As the result, the current flowing through the electrical circuit is substantially interrupted so that the electrical circuit can be protected. It is noted, as can be easily understood from the above mentioned descriptions, that the circuit switching member in the circuit protection device of the present invention is of a non-current carrying type circuit switching member, wherein the current flows through the movable terminal and/or the movable contacts provided thereon and the current does not flow through the bimetal component itself. 
     As shown in  FIG. 3  and  FIG. 4 , it is noted that the above mentioned circuit protection device  200  of the present invention is inserted inside a casing  246  through its opening  248 ; the opening is sealed with an insulating resin  250  and an adhesive  252 . 
     THE ELEMENT REFERENCE NUMERALS ARE 
     
         
           10 —movable member which constitutes contact structure; 
           12 , 14 —end; 
           16 —narrowed section; 
           18 ,  20 —dotted line part; 
           22 —long side; 
           24 —short side; 
           26 —concave portion; 
         “a”—width of narrowed section; 
         “b”—width of movable member; 
         “c”—depth of narrowed section; 
         “d”—length of narrowed section; 
           100 —contact structure; 
           102 —movable member; 
           104 —movable terminal; 
           106 —movable contact; 
           108 —narrowed section; 
           110 ,  112 —fixed member; 
           114 ,  116 —fixed terminal; 
           118 ,  120 —fixed contact; 
           122 —longitudinal axis of movable member; 
           200 —circuit protection device; 
           210 —PTC component; 
           213 —narrowed section; 
           214 —bimetal component; 
           215 —tip of bimetal component; 
           216 —movable member; 
           217 —movable terminal; 
           218 , 219 —movable contact; 
           220 ,  221 —fixed member; 
           222 , 223 —fixed contact; 
           230 —lower side lead; 
           232 —upper side lead, 
           238 —base plate; 
           240 —spacer; 
           242 —upper plate; 
           244 —pin; 
           246 —casing; 
           248 —opening; 
           250 —insulating material; 
           252 —adhesive