BREAKER

Abstract

 [Problems]
Providing a compact breaker which enables to reduce contact resistance and to miniaturization much more by maintaining contact positions of a stationary contact and a movable contact appropriately.
[Means to solve the Problems]
In a breaker comprising a stationary piece 2, a movable piece 3, a bimetal 4 and a case 6, the movable piece 3 has a second elastic portion 35 having an elastic coefficient lower than that of a first elastic portion 34, and is fixed on the case 6 at a fixation portion 33 between the first elastic portion 34 and the second elastic portion 35.

Description

Technical Field

[0001] The present invention relates to a compact breaker which is built in a secondary battery.

Background Art

[0002] Conventionally, a PTC thermistor (which is an electric conductive material that a resistance value thereof suddenly increases in a region above a constant temperature) and a thermal fuse are used as a safety device of a secondary battery such as a compact nickel metal hydride battery, a lithium ion battery or the like, which is installed in a mobile phone or a laptop personal computer. Protection circuits using these respectively have a defect that precision temperature setting is difficult because of a wide bandwidth of an operational temperature, or a defect that 100% inspection is impossible in its manufacturing process because it is unusable in multiple times. Therefore, a safety device based on mechanical action, which enables to set an operating temperature precisely and which can be used in multiple times, is desired replacing with such a conventional protection circuit, and thus, various kinds of technologies are proposed.

[0003] For example, Patent Document 1 discloses a compact breaker that comprises a stationary piece having a stationary contact, a movable piece having a movable contact at a front end thereof, a thermo-reactive element that operates the movable piece so that the movable contact comes away from the stationary contact at a predetermined operation temperature, a PTC element which is connected to the stationary contact, and an insulative flat case that contains these elements. In addition, Patent Document 2 discloses a manufacturing method of a compact breaker.

Prior Art Documents

Patent Documents

[0004] 

Patent Document 1: JP 2005-129471 A

Patent Document 2: JP 2002-83523 A

Disclosure of Invention

Problems that the Invention is going to solve

[0005] Miniaturization of the secondary battery which is used in the mobile phone or the laptop personal computer is advanced much more in recent years, so that more miniaturization is required of the compact breaker built in the secondary battery. However, when dimensions of elements of mechanically functioning products such as the compact breaker become smaller than a constant value, it is difficult to strike a balance between maturity and productivity as long as the elements are simply miniaturized and facilities and methods in existence are applied in manufacture. In particular, in a process of positioning the stationary contact provided on the stationary piece and the movable contact provided on the movable piece of the compact breaker, reduction in size of the elements is accompanied by increase of vulnerability to an error in assembly, so that a contact position of the movable contact on the stationary contact is apt to displace to an improper position.

[0006] Such displacement of the contacts may cause a serious problem for the safety device of an electric appliance that contact resistance becomes unstable, and thus, it becomes an obstacle for reducing defective fraction of the compact breakers. In particular, when dimension of the movable piece reach sub millimeter precision, problems caused by the above mentioned displacement of the contacts become remarkable in assembling processes of all elements including placing the thermo-reactive element or the movable piece and mounting of a cover member. Furthermore, if the compact breaker which is completed and nondefective is roughly treated in installation onto the safety device, there is a fear to give baneful influence upon the contact position of the contacts when a terminal is turned in torsion.

[0007] The present invention is conceived to solve the above mentioned problems and purposed to provide a breaker which enables to reduce contact resistance and to miniaturize much more by means of keeping the contact position of the stationary contact and the movable contact appropriately.

Means to solve the Problems

[0008] In order to achieve the above mentioned purpose, the invention in accordance with claim 1 is a breaker comprising a stationary piece which has a stationary contact, a movable piece which has a movable contact at a front end thereof and presses the movable contact to contact with the stationary contact, a thermo-reactive element which activates the movable piece by deforming with temperature change so that the movable contact comes away from the stationary contact, and a case which contains the stationary piece, the movable piece and the thermo-reactive element, characterized by that the movable piece has a terminal which is protruded outside from the case, a first elastic portion which generates elastic force to press the movable contact to the stationary contact, and a second elastic portion which is formed between the first elastic portion and the terminal and has an elastic coefficient lower than that of the first elastic portion, and the movable piece is fixed on the case in a portion between the first elastic portion and the second elastic portion.

[0009] In this breaker, it is preferable that a cross-sectional area of the second elastic portion perpendicular to an extension direction of the movable piece from the second elastic portion to the movable contact is smaller than that of the first elastic portion.

[0010] In this breaker, it is preferable that a through-hole is formed in the second elastic portion.

[0011] In this breaker, it is preferable that the second elastic portion is formed symmetrical with respect to the extension direction of the movable piece.

[0012] In this breaker, it is preferable that the case has a main body of the case having an opening through which the stationary piece, the movable piece and the thermo-reactive elements are contained, and a cover member to be attached to seal the opening of the main body of the case, the movable piece is fixed by being wedged between the main body of the case and the cover member, and the main body of the case has protruded portions of slant faces that contact edges of the movable piece and are used to position the movable piece.

[0013] In this breaker, it is preferable that the through-hole be circular.

[0014] In this breaker, it is preferable that the case have a main body of the case having an opening through which the stationary piece, the movable piece and the thermo-reactive elements are contained, and a cover member to be attached to seal the opening of the main body of the case, the movable piece is fixed by being wedged between the main body of the case and the cover member, the main body of the case has a protrusion of cylindrical shape that is engaged with the through-hole of the movable piece, and a tapered portion of slant face is formed at a top portion of the protrusion.

[0015] In this breaker, it is preferable that the protruded portions be formed to protrude in semicircular shapes in top view from an end face of the main body of the case.

[0016] In this breaker, it is preferable that the protruded portions have slant faces on sides of the opening.

[0017] In this breaker, it is preferable that the protruded portions be formed in a vicinity of the second elastic portion of the movable piece, and the movable piece has notches corresponding to the slant faces of the protruded portions.

[0018] In this breaker, it is preferable that a ratio of X:Y-X be in a range from 1.5:1 to 1:1.5, hereupon X denotes a dimension of width of the through-hole and Y denotes a dimension of width of the second elastic portion in a widthwise direction of the movable piece perpendicular to the extension direction of the movable piece.

Effects of the Invention

[0019] According to the present invention, since the second elastic portion which has the elastic coefficient lower than that of the first elastic portion is formed in the terminal side outside from a portion of the movable piece fixed by the case, even when an external force or an impact is applied to the terminal of the movable piece in processes of manufacture or conveyance of the breaker or installation into the secondary battery, it is absorbed by the second elastic portion, so that the position of the movable contact is appropriately maintained. Consequently, the contact position of the stationary contact and the movable contact is appropriately maintained, so that contact resistance can be restrained stably and the breaker can be miniaturized much more.

[0020] Furthermore, since it is configured that the cross-sectional area of the second elastic portion perpendicular to the extension direction of the movable piece becomes smaller than that of the first elastic portion, it is possible to form the second elastic portion having the elastic coefficient lower than that of the first elastic portion by forming the movable piece by press working or the like.

[0021] Still furthermore, it is possible to form the second elastic portion having the elastic coefficient lower than that of the first elastic portion by existence of the through-hole. In addition, it is possible to increase the freedom of design of the elastic coefficient of the second elastic portion.

[0022] Still furthermore, since the second elastic portion is formed in symmetry with respect to the extension direction of the movable piece, even when an external force or an impact that twists the terminal of the movable piece is applied in any rotation direction, it can be absorbed by the second elastic portion, similarly. Thereby, the position of the movable contact can be maintained appropriately much more.

[0023] Still furthermore, since the through-hole is formed circularly, it is possible to alleviate concentration of stress occurring in the second elastic portion and to restrain fracture of the movable piece in the second elastic portion.

[0024] Still furthermore, since the dimension of width of the through-hole and the dimension of width of the second elastic portion are appropriate, effects for absorbing impact or the like by the second elastic portion can be increased much more.

[0025] Still furthermore, the movable piece can be fixed by a simple configuration. In addition, it is possible to position the movable piece easily and precisely by the protruded portions of slant faces when installing the movable piece into the main body of the case. Thereby, it is possible to maintain the position of the movable contact appropriately much more with increasing the productivity.

[0026] Still furthermore, since the protruded portions are formed to protrude in a shape of semicircle in top view from an end face of the main body of the case, it is possible to restrain reduction of contacting area of the end face of the main body of the case with the cover member due to providing the protruded portion. Thereby, the main body of the case and the cover member can be welded strongly, so that toughness and sealing performance of the case can be increased and fixation of the movable piece in a portion between the first elastic portion and the second elastic portion can be made strong.

[0027] Still furthermore, since the protruded portions have slant faces on a side of the opening, it is possible to position the movable contact precisely much more. In addition, since an area of the end face of the main body of the case can be made larger in outside of the protruded portions, sealing performance of the case can be increased, and thus, it is possible to reduce the fear of intrusion of undesirable intruder such as moisture, electrolytic solution, and so on into the inside of the case.

[0028] Still furthermore, it is possible to reduce the elastic coefficient of the second elastic portion easily by forming notches corresponding to the protruded portions in the second elastic portion of the movable piece, and thus, it is possible to miniaturize the breaker easily.

Brief Description of Drawings

[0029] 

FIG. 1 is an assembly drawing in a perspective view showing a configuration of a breaker in accordance with an embodiment of the present invention.

FIG. 2 is a perspective view showing a state to install a cover member to a main body of the breaker.

FIG. 3 is a cross sectional view showing a motion of the breaker in a normal electric charge or discharge state.

FIG. 4 is a cross sectional view showing a motion of the breaker in an electric hypercharge state or an abnormal state.

FIG. 5 is an enlarged perspective view showing a movable piece and the main body of the case.

FIG. 6 is an enlarged perspective view showing a modification of the movable piece and the main body of the case.

FIG. 7 is a cross sectional view showing shapes of a protrusion of the main body of the case before assembly.

FIG. 8 is a perspective view showing a modification of the protrusion and protruded portions of the main body of the case before assembly.

Mode for Carrying Out the Invention

[0030] A breaker in accordance with an embodiment of the present invention is described with reference to drawings. FIG. 1 and FIG. 2 show a configuration of the breaker. The breaker 1 is configured of a stationary piece 2 having a stationary contact 21, a movable piece 3 having a movable contact 31 at a front end thereof, a thermo-reactive element 4 which deforms responding to temperature change, a PTC (Positive Temperature Coefficient) thermistor 5, a case 6 which contains the stationary piece 2, the movable piece 3, the thermo-reactive element 4 and the PTC thermistor 5, and so on. The case 6 is configured of a main body 61 of the case, a cover member 62 which is attached to a top face of the main body 61 of the case, and so on.

[0031] The stationary piece 2 is formed by press working of a metal plate which contains phosphor bronze as a chief ingredient (alternatively, metal plates such as copper-titanium alloy, nickel silver, brass), and installed into the main body 61 of the case by insert molding or crimping, or the like. A terminal 22 is formed at an end and the PTC thermistor 5 is disposed at the center portion of the stationary piece 2. The stationary contact 21 is formed by cladding, plating or spreading of a material having good electro-conductivity such as silver, nickel, nickel-silver alloy, copper-silver alloy, gold-silver alloy, and so on, and exposed from a part of an opening 63 formed at an upper portion of the main body 61 of the case. The terminal 22 is protruded outward from an end of the main body 61 of the case.

[0032] The movable piece 3 is formed by press working of a metal plate equivalent to that of the stationary piece 2. A terminal 32 is formed at an end of the movable piece 32 to protrude outward from the main body 61 of the case, and a movable contact 31 is formed at the other end. The movable contact 31 is formed at a front end of the movable contact 3 by a material and a method equivalent to those of the stationary contact 21. The movable piece 3 has a fixation portion 33, a first elastic portion 34 and a second elastic portion 35 between the movable contact 31 and the terminal 32. The movable piece 3 is fixed at the fixation portion 33 by being wedged between the main body 61 of the case and the cover member 62, and the movable contact 31 formed at the front end thereof is pressed and contacted to the stationary contact 21 by elastic deformation of the first elastic portion 34, so that the stationary piece 2 and the movable piece 3 can be electrically conducted. In addition, the second elastic portion 35 is formed between the fixation portion 33 and the terminal 32. Elastic coefficient of the second elastic portion 35 is set to be lower than that of the first elastic portion 34 by providing a through-hole 36 of a circular shape and notches 37 between the fixation portion 33 and the terminal 32. Hereupon, the elastic coefficient is defined as a rate of change of strain responding to stress, and direction of the stress is not limited in particular. The fact that elastic coefficient of the second elastic portion 35 is set to be lower than that of the first elastic portion 34 means that deformation in the second elastic portion 35 is larger than deformation in the first elastic portion 34 when an external force of degree that does not destroy the movable piece 3 is applied to the terminal 32. Furthermore, in this embodiment, the movable piece 3 is firmly fixed in the fixation portion 33 between the second elastic portion 35 and the first elastic portion 34, so that stress occurring in the second elastic portion 35 is hardly transmitted to the first elastic portion 34, and thus, no deformation occurs in a region between the second elastic portion 35 to the movable contact 31.

[0033] A dimension of width of the fixation portion 33 (a dimension in a direction perpendicular to the extension direction of the movable piece 3) is set to be larger than those of the first elastic portion 34 and the second elastic portion 35. In addition, minute protrusions 38 are formed to face the thermo-reactive element 34 on a lower face of the first elastic portion 34. The minute protrusions 38 always contact with the thermo-reactive element 4, so that deformation of the thermo-reactive element 4 is transmitted to the first elastic portion 34 (see FIG. 3 and FIG. 4). As for a material of the movable piece 3, it is preferable to include phosphor bronze as the chief ingredient. Alternatively, electro-conductive elastic materials such as copper-titanium alloy, nickel silver, brass, or the like can be used. In addition, the movable piece 3 is curved or bent in the first elastic portion 34 by press working. Degree of curving or bending is not limited in particular so far as the thermo-reactive element 4 can be contained, and thus, it should be set appropriately in consideration with elastic forces, pressure of contacts and so on at operating temperature and return temperature.

[0034] The thermo-reactive element 4 has a curved shape like an arc, and consists of a composite material such as a bimetal, a trimetal, and so on. When reaching at an operating temperature by overheat, the curved shape inverts, and when dipping below a return temperature by cooling, it restores itself to the original shape. Since the bimetal is usually used as the thermo-reactive element 4, it is called as bimetal 4, unless there is a limitation in particular, hereinafter. The shape of the bimetal 4 can be formed by press working. As long as the first elastic portion 34 of the movable piece 3 can be pushed up by inverting operation of the bimetal 4 at a predetermined temperature and can be restored to the original shape by elastic force of the first elastic portion 34, materials and shape of the bimetal 4 are not limited in particular, but a rectangle is desirable from the viewpoint of productivity and effectiveness of the inverting operation, and it is desirable to be a rectangle that is almost a square in order to push up the first elastic portion 34 effectively, while it is compact. In addition, as for the materials of the bimetal 4, lamination of two kinds of materials having different thermal expansion coefficients are used in combination according to required condition, for example, consisting of copper-nickel-manganese alloy or nickel-chrome-iron alloy used at high expansion side, and an iron-nickel alloy and other various kinds of alloys including nickel silver, brass, stainless steel used at low expansion side.

[0035] When power distribution between the stationary piece 2 and the movable piece 3 is shut off by the inverting operation of the bimetal 4, a quantity of electric current flowing into the PTC thermistor 5 is increased. As long as the PTC thermistor 5 is a positive characteristic thermistor which restrains an electric current by increasing a value of electric resistance with a temperature rise, it can be selected among various kinds according to requirement such as operating current, operating voltage, operating temperature, restoring temperature, and so on, and the shape of it is not limited in particular unless it may not deteriorate these characteristics.

[0036]  The main body 61 of the case and the cover member 62 which constitute the case 6 are formed of resin such as polyamide having flame resistance, polyphenylene sulfide (PPS), liquid crystal polymer (LCP), or polybutylene terephthalane (PBT) which is superior to heat-resistance. An opening 63 through which the stationary piece 2, the movable piece 3, the bimetal 4, the PTC thermistor 5 and so on are contained, a cylindrical protrusion 64 and protruded portions 65 of slant faces which are engaged with the movable piece 3 are formed on the main body 61 of the case. The cylindrical projection 64 is engaged with the through-hole 36 of the circular shape, and the protruded portions 65 of the slant faces are engaged with the notches 37. In addition, the movable piece 3, the bimetal 4 and the PTC thermistor 5 built-in the main body 61 of the case are respectively contacted with frames 67, 68 and 69 which are formed in an inside of the opening 63, so that they are guided in the inverting operation of the bimetal 4.

[0037] As shown in FIG. 2, the cover member 62 is attached to the top face of the main body 61 of the case so as to seal the opening 63 of the main body 61 of the case which contains the stationary piece 2, the movable piece 3, the bimetal 4, the PTC thermistor 5 and so on. The main body 61 of case and the cover member 62 are joined by ultrasonic welding. At this time, vertexes of the cylindrical protrusion 64 and the protruded portions 65 of the slant faces are joined with the cover member 62. The cover member 62 may have a metal portion. It is advantageous to have the metal portion for miniaturization from the viewpoint of mechanical strength, and it is possible to supply standby power source to other units of the safety device by providing cover terminals in the metal portion.

[0038] FIG. 3 shows a motion of the breaker 1 in a normal electric charge or discharge state. In the normal electric charge or discharge state, the bimetal 4 has original shape (before inversion), so that the stationary contact 21 and the movable contact 31 are contacted, and both terminals 22 and 23 of the breaker 1 are electrically conducted through the first elastic portion 34 of the movable piece 3 and so on. The first elastic portion 34 of the movable piece 3 and the bimetal 4 are contacted, so that the movable piece 3, the bimetal 4, the PTC thermistor 5 and the stationary piece 2 are conducted as a circuit. However, since electric resistance of the PTC thermistor 5 is much larger than electric resistance of the movable piece 3, electric current flowing into the PTC thermistor 5 is in a degree as little as to be completely negligible in comparison with a quantity of it flowing through the stationary contact 21 and the movable contact 31.

[0039] FIG. 4 shows a motion of the breaker I in an electric hypercharge state or an abnormal state. When it becomes a high temperature state due to electric hypercharge or abnormality, the PTC thermistor 5 is heated and the bimetal 4 reaching the operating temperature inverts, so that the first elastic portion 34 of the movable piece 3 is pushed up, and thus, the movable contact 31 comes away from the stationary contact 21. At this time, an electric current flowing between the stationary contact 21 and the movable contact 31 is shut off, and a slight leakage current flows through the bimetal 4 and the PTC thermistor 5. The PTC thermistor 5 generates heat as long as such a leakage current flows, and suddenly increases electric resistance with keeping the bimetal 4 in the inverted state, so that no electric current flows between the stationary contact 2 and the movable contact 3, and only the above mentioned slight leakage current exists. This leakage current can be appropriated to other functions of the safety device.

[0040] When the electric hypercharge state is removed or the abnormal state is canceled, heat generation in the PTC thermistor 5 is stopped, so that the bimetal 4 is cooled to the return temperature and is restored to its original shape. Subsequently, the movable contact 31 and the stationary contact 21 are contacted again by elastic force of the first elastic portion 34 of the movable piece 3, and the circuit is released from the shut off state and returns to the conductive state as shown in FIG. 3.

[0041] FIG. 5 shows an enlarged configuration of the movable piece 3 and the main body 61 of the case. In the movable piece 3 of the present invention, the fixation portion 33 is disposed between the first elastic portion 34 formed in the side of the movable contact 31 and the second elastic portion 35 formed in the side of the terminal 32. In addition, the fixation portion 33 shown by hatching in the figure is firmly fixed by being wedged from above and below by the main body 61 of the case and the cover member 62, and the second elastic portion 35 having an elastic coefficient lower than that of the first elastic portion 34 is formed in the side of the terminal 32 outside thereof, so that even when an external force or an impact is applied to the terminal 32 of the movable piece 3 in processes of manufacture or conveyance of the breaker 1 or installation into the secondary battery, it will be absorbed by the second elastic portion 35, and thus, position of the movable contact 31 is appropriately maintained. Consequently, contact position of the stationary contact 21 and the movable contact 31 is appropriately maintained, so that it is possible to restrain contact resistance stably and to miniaturize the breaker 1 much more.

[0042] In this embodiment, the through-hole 36 and the notches 37 are simultaneously formed in the second elastic portion 35 by punching out a metal plate at the time of forming the movable piece 3 by press working. Thereby, a cross-sectional area of the second elastic portion 35 cut by a plane (ZX plane in the figure) perpendicular to the extension direction of the movable piece 3 from the second elastic portion 35 to the movable contact 31 becomes smaller than that of the first elastic portion 34, so that it is easily possible to form the second elastic portion 35 having the elastic coefficient lower than that of the first elastic portion 34. In particular, when a dimension of width (diameter) of the through-hole 36 is designated by W1 and a dimension of width of the second elastic portion 35 is designated by w2 in a widthwise direction (X direction in the figure) of the movable piece 3, the diameter of the through-hole 36 is set so that a ratio W1:W2-W1 becomes in a range from 1.5:1 to 1:1.5. By setting the diameter of the through-hole 36 as just described, it is possible to enhance the effect of absorbing the impact or the like by the second elastic portion 35 much more. In addition, since the through-hole 36 is formed as the circular shape, it is possible to reduce concentration of stress occurring in the second elastic portion 35, and to restrain the fracture of the movable piece 3 in the second elastic portion 35.

[0043] Furthermore, the second elastic portion 35, the through-hole 36 and the notches 37 are formed in symmetry with respect to the extension direction (Y direction in the figure) of the movable piece. Thereby, even when an external force or an impact which twists the terminal 32 of the movable piece 3 is applied in any rotation direction, it can be absorbed by the second elastic portion 34
similarly, and thus, the position of the movable contact 31 can be maintained more appropriately. In addition, the fixation portion 33 is extended like wings in the widthwise direction of the movable piece 3, so that an elastic coefficient of the fixation portion 33 is increased than that of the first elastic portion 34.

[0044] Still furthermore, the protruded portions 65 of the slant faces which contact edges of the notches 37 of the movable piece 3 and position the movable piece 3 are formed on the main body 61 of the case, so that it is possible to guide and to install the movable piece 3 into the main body 61 of the case easily and precisely by falling down the edges of the notches 37 along the slant faces of the protruded portions 65 and engaging the through-hole 36 with the protrusion 64 at the time of installing the movable piece 3 into the main body 61 of the case. In particular, in this embodiment, a pair of protruded portions 65 is formed at both sides of the cylindrical protrusion 64 which is to be inserted into and engaged with the through-hole 36, so that it is possible to prevent rotation of the movable piece 3 around the protrusion 64 serving as a shaft, and thus, the movable contact 31 with respect to the stationary contact in top view can be positioned precisely. Thereby, it is possible to maintain the position of the movable contact 31 more appropriately with increasing the productivity.

[0045] Still furthermore, the protruded portions 65 of the slant faces are formed to protrude in semicircular shapes in top view from an end face 66 of the main body of the case, so that it is possible to restrain the reduction of contact areas between the end face 66 of the main body of the case and the cover member 62 due to providing of the protruded portions 65 with enjoying the above mentioned effects of the protruded portions 65. Thereby, the main body 61 of the case and the cover member 62 can be welded firmly, so that toughness and sealing performance of the case 6 can be increased and fixation of the movable piece 3 in the fixation portion 33 between the first elastic portion 34 and the second elastic portion 33 can be made strong. In addition, the protruded portions 65 which are protruded in semicircular shapes in top view have good afflux of resin in resin molding of the main body 61 of the case, so that productivity of the breaker 1 may not be inhibited. Moreover, the protruded portions 65 have the slant faces in the side of the opening 63, that is, in the side of the movable contact 31, so that it enables to position the movable contact 31 more precisely. Still furthermore, an area of the end face 66 of the main body of the case in outside region beyond the protruded portions 65 (in the side of the terminal 32) can be made larger, so that sealing performance of the case 6 can be increased, and thus, it is possible to reduce the fear of intrusion of undesirable intruder such as moisture, electrolytic solution, and so on into the inside of the case 6. Still furthermore, the fixation portion 33 having an elastic coefficient larger than that of the first elastic portion 34 engages with the protruded portions 65, so that fixation of the fixation portion 33 can be made more precisely and firmly, and thus, posture of the movable piece 3 becomes stable.

[0046] Still furthermore, the second elastic portion 35 is disposed to be contained in the inside of the case 6 when the cover member 62 is attached to the main body 61 of the case, so that it is possible to restrain the fracture of the movable piece 3 in the second elastic portion 35. In addition, the second elastic portion 35 is formed in the side of the terminal 32 which is laid on outside of the fixation portion 33 to be fixed by being wedged between the main body 61 of the case and the cover member 62, so that an impact applied to the terminal 32 will be absorbed by the second elastic portion 35, and thus, it is possible to reduce the fear that the case 6 is broken.

[0047] Besides, the present invention is not limited to the configuration of the above mentioned embodiment, so that in the breaker 1 having at least the stationary piece 2, the movable piece 3, the bimetal 4 and the case 6, it may be sufficient that the configuration of the movable piece 3 has the second elastic portion 35 having an elastic coefficient lower than that of the first elastic portion 34, and is fixed by the case 6 in the fixation portion 33 between the first elastic portion 34 and the second elastic portion 35. In addition, the present invention can be modified in various manners. For example, FIG. 6 shows another mode of the movable piece 3. In a movable piece 30, no through-hole 36 is provided on the second elastic portion 35, and dimensions of the notches 37 in Y-direction are set to be larger. In this embodiment, a cross-sectional area of the second elastic portion 35 in Z-X plane is reduced, so that the elastic coefficient in the second elastic portion 35 can be lowered below that of the first elastic portion 34. Furthermore, the cross-sectional area of the second elastic portion 35 may be reduced by reducing a dimension in thickness of the second elastic portion by press working, so that the elastic coefficient in the second elastic portion 35 is lowered below that of the first elastic portion 34. Still furthermore, the movable piece 3 and the thermo-reactive element 4 may be formed integrally by forming the movable piece 3 of a bimetal or a trimetal. In this case, a configuration of the breaker can be made much simpler, and it enables the miniaturization much more. Still furthermore, although the protruded portions 65 are most desirable that slant faces are formed in semicircular shape in top view in the sides of the opening 63, they may be permitted to be an ark shape from full circumference to a quarter of a circle in top view. In case of the arc shape of a quarter circle, it is possible to increase the contact areas between the cover member 62 and the end face 66 of the main body of the case in addition to maintaining guide function of the movable piece 3 by the protruded portion 65, and thus, toughness and sealing performance of the case can be increased.

[0048] FIG. 7 shows a cross-section in Z-X plane including the protrusion 64 of the main body 61 of the case before assembling as shown in FIG. 1. The protrusion 64 has a vertex 64a which is to be joined with a rear face of the cover member 62, a side face 64b which is to be engaged with the through-hole 36 of the movable piece 3, and a tapered portion 64c of a slant face which is formed between the vertex 64a and the side face 64b. The tapered portion 64c has a function to position the movable piece 3 with the protruded portions 65 of the slant faces at the time of installing the movable piece 3 into the main body 61 of the case. In other words, by dropping the edge of the through-hole 36 of the movable piece 3 on the slide way along the slant face of the tapered portion 64c, it is possible to guide and to dispose the movable piece 3 to the main body 61 of the case correlatively with the synergistic effects of positioning by the protruded portions 65 of the slant faces. Thereby, it is possible to prevent short time stop of assembly line of the breakers, and thus, it enables to increase the productivity. In addition, the vertex 64a of the protrusion 64 is joined with the rear face of the cover member 62, so that contact areas between the main body 61 of the case and the cover member 62 at the time of ultrasonic welding of them, and thus, strength of the case 6 can be secured much more.

[0049] In addition, the slant faces of the tapered portion 64c and the protruded portions 65 are not limited to a constant inclination, and they may be configured to be varied corresponding to height. For example, as shown in FIG. 8, the slant faces of the tapered portion 64c and the protruded portions 65 may be formed as curved convexities. Alternatively, the slant faces of the tapered portion 64c and the protruded portions 65 may be formed as curved concavity. In this way, the tapered portion 64c and the protruded portions 65 of the slant faces are not limited to constant inclination.

Explanation of Marks

[0050] 

1

Breaker

2

Stationary Piece

3

Movable Piece

4

Thermo-reactive Element (Bimetal)

6

Case

21

Stationary Contact

22

Terminal

31

Movable Contact

32

Terminal

33

Fixation portion

34

First Elastic Portion

35

Second Elastic Portion

36

Through-Hole

37

Notch

61

Main Body of the Case

62

Cover Member

63

Opening

64

Protrusion

64c

Tapered Portion

65

Protruded portion

Claims

1. A breaker comprising a stationary piece which has a stationary contact, a movable piece which has a movable contact at a front end thereof and presses the movable contact to contact with the stationary contact, a thermo-reactive element which activates the movable piece by deforming with temperature change so that the movable contact comes away from the stationary contact, and a case which contains the stationary piece, the movable piece and the thermo-reactive element, wherein
the movable piece has a terminal which is protruded outside from the case, a first elastic portion which generates elastic force to press the movable contact to the stationary contact, and a second elastic portion which is formed between the first elastic portion and the terminal and has an elastic coefficient lower than that of the first elastic portion, and
the movable piece is foxed on the case in a portion between the first elastic portion and the second elastic portion.

2. The breaker in accordance with claim 1, wherein a cross-sectional area of the second elastic portion perpendicular to an extension direction of the movable piece from the second elastic portion to the movable contact is smaller than that of the first elastic portion.

3. The breaker in accordance with claim 1 or 2, wherein a through-hole is formed in the second elastic portion.

4. The breaker in accordance with one of claims 1 to 3, wherein the second elastic portion is formed symmetrical with respect to the extension direction of the movable piece.

5. The breaker in accordance with one of claims 1 to 4, wherein the case has a main body of the case having an opening through which the stationary piece, the movable piece and the thermo-reactive elements are contained, and a cover member to be attached to seal the opening of the main body of the case, the movable piece is fixed by being wedged between the main body of the case and the cover member, and
the main body of the case has protruded portions of slant faces that contact edges of the movable piece and are used to position the movable piece.

6. The breaker in accordance with one of claims 3 to 5, wherein the through-hole is circular.

7. The breaker in accordance with claim 6, wherein
the case has a main body of the case having an opening through which the stationary piece, the movable piece and the thermo-reactive elements are contained, and a cover member to be attached to seal the opening of the main body of the case, the movable piece is fixed by being wedged between the main body of the case and the cover member,
the main body of the case has a protrusion of cylindrical shape that is engaged with the through-hole of the movable piece, and
a tapered portion of slant face is formed at a top portion of the protrusion.

8. The breaker in accordance with one of claims 5 to 7, wherein the protruded portions are formed to protrude in semicircular shapes in top view from an end face of the main body of the case.

9. The breaker in accordance with claim 8, wherein the protruded portions have slant faces in sides of the opening.

10. The breaker in accordance with one of claims 7 to 9, wherein the protruded portions are formed in a vicinity of the second elastic portion of the movable piece, and
the movable piece has notches corresponding to the slant faces of the protruded portion.

11. The breaker in accordance with one of claims 3 to 10, wherein, a ratio of X:Y-X is in a range from 1.5:1 to 1:1.5,
hereupon, X denotes a dimension of width of the through-hole and Y denotes a dimension of width of the second elastic portion in a widthwise direction of the movable piece perpendicular to the extension direction of the movable piece.

Drawing