Circuit breaker

Abstract: A circuit breaker includes, a cylindrical portion having a gunpowder and a exploding unit for exploding the gunpowder by application of electric power to the gunpowder, the cylindrical portion being provided with an opening at at least one end; a base material securing the cylindrical portion, at least the surface of which is made of insulating material; a conductor fixed to the base material and having a break portion located at a position opposite to the opening of the cylindrical portion, the break portion being broken by explosive force of the gunpowder; a first metallic cover portion covering the cylindrical portion and the break portion; and a second metallic cover portion covering the base material from an opposite side to the cylindrical portion, wherein the first and second cover portions are fixed to the base material by directly connecting the first and second cover portions each other.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit breaker according to claim 1. 2. Description of the Related Art From US-A-3,873,786 a severing device is known, which is provided for severing a mechanical element such as a strip, bar or the like using pure shear forces generated by ignition of an explosive charge having an energy per unit of mass of more than 1000 joule/gram and a detonation speed of over 3000 ms. In a first ultra-high speed high amperage circuit breaker embodiment of this known device, the mechanical element comprises a cylindrical portion and an annular portion, which extends outwardly therefrom, the internal diameter of the annular portion being approximately equal to that of the cylindrical portion and a fracture initiator in the form of opposed groves having the same diameter is located in the area joining the two portions: The explosive charge, along with a firing unit therefore, is located in a recess in the cylindrical portion of the element to be severed. From DE 83 03 559 U a pyrotechnical circuit breaker is known which comprises an exploding means and an ignition means therefore. The circuit breaker includes short circuit wires extending transversely to gas channels provided within the ignition means. In general, in the electric circuit incorporated into an automobile, it is common to use a fuse or fusible link as a means for quickly shutting off the electric circuit when an overcurrent or a short circuit current flows in the electric circuit. Basically, these fuse and fusible link are composed in such a manner that a fusible conductor is arranged in a case and that a terminal for connection is arranged on the outside of this case. In many cases, these fuse and fusible link are put into practical use being connected with an electric connection box. However, the above fuse and fusible link are fused for the first time when an overcurrent flows in the electric circuit and the electric circuit is shut off. Therefore, it is impossible to forcibly shut off the electric circuit at an arbitrary time. Accordingly, in case of emergency, for example, when an automobile accident has occurred, it becomes necessary to forcibly shut off an electric circuit for the purpose of safety even if no overcurrent flows in the electric circuit. Therefore, instead of the above fuse and fusible link, or in addition to the above fuse and fusible link, it is necessary to provide a circuit breaker for forcibly shutting off the electric circuit by operation conducted from the outside. In order to provide the above circuit breaker, as disclosed in Japanese Examined Patent Publication No. 5847809, it is possible to use a circuit breaker by which a conductor incorporated into the circuit is broken by explosive force of gunpowder. This circuit breaker is composed as follows. An output fuse, gunpowder and filament to heat the gunpowder are enclosed in a single sealed glass case, and an input terminal connected with the filament is led outside the sealed glass case in-such a manner that the input terminal penetrates the sealed glass case. A surface of this sealed glass case is covered with an explosion-proof coat. According to the above circuit breaker, when the input terminal is given an electric current or voltage, the intensity of which is not lower than a predetermined value, and the filament is heated, the gunpowder is exploded by the heat generated in the filament. Therefore, it is possible to forcibly break the conductor by the explosive force. Accordingly, in case of emergency, for example, when an automobile accident has occurred, it is possible to shut off the circuit at any time by controlling an input current or input voltage given to the input terminal. However, according to the circuit breaker disclosed in the above patent publication, the explosive power of gunpowder is dispersed in the sealed glass case in all directions, and only one portion of the explosive power acts on the output fuse. Therefore, a considerably high intensity of explosive power is required for breaking the fuse positively. However, when the intensity of explosive power is enhanced by increasing a quantity of gunpowder, the inside of the sealed glass case is given a high intensity of explosive force. Therefore, the sealed glass case must have a strong structure so that it can withstand the high intensity of explosive power. Further the sealed glass case must be made of expensive material or it must be subjected to a special treatment for enhancing the mechanical strength. Accordingly, the manufacturing cost is inevitably increased. On the other hand, a great task to be accomplished is the prevention of dispersion of broken pieces of the inner structure including the conductor. Further, Japanese Unexamined Patent Publication No. 10-55742 discloses a related circuit breaker. The circuit breaker disclosed in the above patent publication is described as follows. A conductor for composing a circuit is arranged in a case, and an explosion unit for exploding gunpowder is arranged below the conductor. In the case of emergency, the explosion unit is operated, so that the conductor is exploded. Due to the foregoing, the circuit can be quickly and forcibly shut off. In the above circuit breaker, when the case is tightly shielded up, there is a possibility that the pressure in the case is increased too high by the action of gas generated in the explosion of gunpowder, and further it becomes difficult for the temperature in the case to be lowered. For the above reasons, it is preferable to provide vent holes on the case. However, when the vent holes are provided as described above, not only gas but also flames are dispersed from the vent holes to the outside, which has a bad influence on parts arranged in the peripheral portion. According to the related arrangement, in order to prevent the flames from dispersing from the vent holes to the outside, the case must be covered with a sufficiently large cover, the mechanical strength of which is high, or alternatively the size of the case itself must be increased. Therefore, it is difficult to reduce the overall size and weight of the circuit breaker. SUMMARY OF THE INVENTION In view of the above circumstances, the present invention has been accomplished. It is an object of the present invention to provide a circuit breaker, with which the explosive power of gunpowder is made to act on a break portion effectively, and emergency shutoff can be safely and positively conducted by a simple and compact structure of low cost; and dispersion of pieces of the inner structure caused by the explosion can be positively prevented. A first solution of the above object results from claim 1. Improved embodiment of this inventive circuit breaker result from the subclaims 2 to 9. The present invention is based on the following features: (1) A circuit breaker includes: a cylindrical portion having a gunpowder and a exploding means for exploding the gunpowder by application of electric power to the gunpowder, the cylindrical portion being provided with an opening at at least one end; a base material securing the cylindrical portion, at least the surface of which is made of insulating material; a conductor fixed to the base material and having a break portion which crosses a position immediately above the cylindrical portion so as to be located at a position opposite to the opening of the cylindrical portion, the break portion being broken by explosive force of the gunpowder; a first metallic cover portion covering the cylindrical portion and the break portion; and a second metallic cover portion covering the base material from an opposite side to the cylindrical portion, wherein the first and second cover portions are fixed to the base material by directly connecting the first and second cover portions each other. In the above structure, when the exploding unit in the cylindrical portion is operated and gunpowder is exploded, the explosive power concentrates on the break portion of the conductor which is arranged at a position close to the opening of the cylindrical portion. Due to the above structure, the break portion can be positively broken even if a small quantity of gunpowder is used.Since the break portion and the cylindrical portion are covered with the first cover portion made of metal, the mechanical strength of which is relatively high, there is no possibility that pieces of the inner structure are dispersed outside the circuit breaker.On the assumption that the second cover portion is not provided and only the first cover portion is fixed to the base material, the following problems may be encountered. The base material to which the first cover portion is fixed is broken by the above explosive power, and the first cover portion is separated from the base material, that is, the first cover portion is disconnected from the base material. Therefore, even if the mechanical strength of the first cover itself is high, it is difficult to prevent pieces of the inner structure from dispersing. However, according to the structure of the present invention, in addition to the first cover portion, the second cover portion made of the same metal as that of the first cover portion is arranged in such a manner that the second cover portion covers the base material from an opposite side to the cylindrical portion and the break portion. Further, both cover portions are directly connected with each other. In other words, both cover portions are arranged in such a manner that the base material is interposed between both cover portions from the front and the reverse side. Due to the above structure, even if a high intensity of explosive power is given to both cover portions, there is no possibility that both cover portions are disconnected from the base material. Accordingly, pieces of the inner structure can be positively prevented from dispersing. (2) The circuit breaker according to (1), wherein the first and second cover portions are integrally formed. According to the above structure, the number of parts can be decreased, and the cost can be reduced. (3) The circuit breaker according to (2), wherein the first cover portion has a pair of side walls, the second cover portion is composed of a pair of rolling portions extending from the side walls, and the first and second cover portions are fixed to the base material by rolling the rolling portions on the opposite side of the base material so that the rolling portions are lapped each other while interposing the base material. According to the above structure, the first and the second cover portion can be fixed by a simple assembling work. (4) The circuit breaker according to (1), wherein a recess portion accommodating the second cover portion is formed on the base material. According to the above structure, even if both cover portions are made to be members different from each other, the second cover portion is engaged with the recess portion so that the first and the second cover portions are directly connected with each other. Therefore, it is possible to compose the circuit breaker in a compact structure. (5) The circuit breaker according to (1), wherein insulating material is provided on the inside of the first cover portion. The cylindrical portion and the break portion may be covered with only the first cover portion. However, in this case, when the break portion directly comes into contact with the first cover portion made of metal after explosion, there is a possibility of occurrence of short circuit. According to the above structure, the break portion is not directly contacted with the first cover portion, and the occurrence of short circuit can be positively prevented. (6) The circuit breaker according to (1), wherein an inner surface of the first cover portion is coated with insulating material. According to the above structure, it possible to reduce the number of parts. (7) The circuit breaker according to (1), wherein a cover made of resin is molded so as to cover a connecting portion of the base material with each cover portion. According to the above structure, it is possible to keep the connection in a good condition, and it is possible to positively prevent each cover from being disconnected from the base material. That is, it is possible to more positively prevent pieces of the inner structure from dispersing. Further, the appearance can be enhanced. (8) The circuit breaker according to (1), wherein the base material is made of one of aluminum and aluminum alloy, the surface of which is oxidized to form its oxide layer. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing an electric power supply circuit for automobile use having a circuit breaker of the present invention; Fig. 2 is a cross-sectional front view showing a main body and a cover cap of the circuit breaker of the first embodiment of the present invention; Fig. 3A is a top view of the circuit breaker of the first embodiment; Fig. 3B is a front view of the circuit breaker of Fig. 3A; Fig. 3C is a bottom view of the circuit breaker of Fig. 3A; Fig. 4 is a side view of the circuit breaker of the first embodiment; Fig. 5 is a cross-sectional view taken along line A - A in Fig. 3B; and Fig. 6 is a schematic illustration showing a temperature gradient when a flame is propagated toward a solid wall. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to Figs. 1 to 5, an embodiment of the present invention will be explained below. Fig. 1 is a view showing an example of the electric power supply circuit for automobile use into which the circuit breaker of the present invention is incorporated. In the figure, a negative terminal 10a of the battery 10 is grounded, and a positive terminal lob is connected to each electrical equipment mounted on an automobile via the circuit breaker 12 of the present invention, the fusible link 14 and the fuses 16 of small capacity arranged in parallel with each other. Further, this automobile is provided with harness ECU (harness control unit) 17. This harness ECU outputs a control signal into the above circuit breaker 12 when an air bag signal is inputted into it (when an automobile collision is detected), and this circuit breaker 12 is forcibly shut off. Electric devices for safety use such as a drive circuit for driving a room lamp and a hazard lamp for emergency, a device for releasing a door lock, and another ECU are connected to the battery 10 not via the circuit breaker 12 but via only the fuse 18. Due to the above arrangement, even after-the circuit has been shut off by the above circuit breaker 12, electric power can be supplied to the electric devices:for safety use. Next, a specific structure of the circuit breaker 12 will be explained below referring to Figs. 2 to 5. The circuit breaker 12 shown in the drawing includes a substantially rectangular parallelepiped base material 20 made of in-sulating material. At the center on the upper surface of this base material 20, there is provided a cylindrical portion 22 which is vertically attached to the base material 20 with the bracket 24 made of insulating material. This cylindrical portion 22 is open upward. and houses a predetermined quantity of gunpowder and a filament for heating the gunpowder. This filament is connected to harness ECU 17 via the lead wire 28 and heated when an electric current flows in the filament according to a control signal sent from harness ECU 17. At the center in the lower portion of the base material 20, there is formed a recess portion 20a which is open in the longitudinal direction (in the direction perpendicular to the surface of Fig. 2). In this recess 20a, there is provided a cover bottom plate (second cover portion) 26 made of metal. In this cover bottom plate 26, there are formed a pair of bolt insertion holes 26a which penetrate the cover bottom plate 26 in the longitudinal direction. At the center of the cover bottom plate 26, there is formed a lead wire insertion hole 26b which penetrates the cover bottom plate 26 in the vertical direction. In a portion of the base material 20 immediately above the lead wire insertion hole 26b, there is formed a lead wire insertion hole 20b. The lead wire 28 is led outside the circuit breaker from the cylindrical portion 22 via both lead wire insertion holes 20b, 26b. A conductor 30 composing a portion of the circuit shown in Fig. 1 is fixed onto the base material 20. This conductor 30 includes: a horizontal break portion 31; a pair of vertical wall portions 32 extending downward from both ends of this break portion 31; and connecting terminal portions 33 extending outside from both ends of the vertical wall portions 32. This break portion 31 is designed in this embodiment as follows. Width of this break portion 31 is small. Therefore, even when a low intensity of explosive power is given to the conductor 30, the break portion 31 can be broken, and this break portion 32 functions as a fusible link in this embodiment capable of fusing by the heat generated due to electric resistance when an overcurrent flows in the circuit. That is, this conductor 30 is made of the same material as that used for a commonly used fuse. However, it should be noted that the break portion 31 is not necessarily provided with the fuse function. Both connecting terminals 33 are provided with bolt insertion holes 33a. In the same manner, both end portions of the base material 20 are provided with bolt insertion holes 20c penetrating the base material 20 vertically. When bolts 36 are inserted into the bolt insertion holes 33a, 20c and fastened with nuts 38, both connecting terminals 33 are fixed to the base material 20. In the above fixing state, the entire profile of the conductor 30 is set so that the break portion 31 crosses a position immediately above the cylindrical portion 22 as shown in Fig. 2 and 3A. One connecting terminal 33 is electrically connected to the positive terminal 10b of the battery 10 shown in Fig. 1, and the other connecting terminal 33 is electrically connected to the fusible link 14 shown in Fig. 1. There is provided a cylindrical insulating cover 40 outside the conductor 30 so that the conductor 30 can be covered with the cylindrical insulating cover 40. Further, there is provided a cover cap (first cover portion) 42 made of metal outside the cylindrical insulating cover 40. This cover cap 42 includes: an upper wall 44 for covering the cylindrical portion 22 and the break portion 31 from above; and side walls 46 for covering the cylindrical portion 22 and the break portion 31 from the sides. On these upper wall 44 and the side walls 46, there are formed vent holes 47 by which an increase of inner pressure can be prevented in the case of explosion. A pair of extending walls 48 are extended from the side walls 46 located in the front and at the rear. A pair of bolt insertion holes 48a are formed at the lower end of each extending wall 48. A bolt 50 is inserted into each bolt insertion hole 48a and the bolt insertion hole 26a of the cover bottom plate 26 and fastened with a nut 52. Due to the foregoing, the cover cap 42 and the cover bottom plate 26 are directly fastened to each other. As long as the material of the above base material 20 and the insulating cover 40 has the insulating property, any material may be used. For example, ceramics may be used. However, it is preferable to use light synthetic resin which can be easily molded, for example, it is preferable to use heat-resistant and highly strong resin such as polyacetal, nylon resin containing glass and PPS resin. The cover cap 42, which is a cover portion, and the cover bottom plate 26 may be made of metal, the mechanical strength of which is relatively high, however, it is preferable that they are made of stainless steel such as SUS304 and others. Next, operation of this circuit breaker of the first embodiment will be explained as follows. When an air bag signal is made by a collision between automobiles and inputted into harness ECU 17, an electric current is made to flow by harness ECU 17 in the filament arranged in the cylindrical portion 22 via the lead wire 28. Therefore, the filament is heated and explodes gunpowder accommodated in the cylindrical portion 22. This explosive power is concentrated upon the break portion 31 immediately above the cylindrical portion 22. Therefore, even if a quantity of gunpowder is small, it is possible to break the break portion 31. Due to the foregoing, the electric power supply circuit shown in Fig. 1, into which the conductor 30 having the above break portion 31 is incorporated, is forcibly shut off. That is, electric power supply to substantially all electric devices except for some electric devices is shut off at the same time, and safety can be guaranteed after the collision. Here, we assume that the cover bottom plate 26 made of metal is not provided and the cover cap 42 made of metal is only fixed to the base material 20 with bolts. In this case, even if the mechanical strength of the cover cap 42 is high, the mechanical strength of the-base material 20 made of synthetic resin connected to the cover cap 42 is low. Therefore, there is a possibility that pieces of the inner structure (pieces of the break portion 31, which has been broken, and pieces of a portion of the cylindrical portion 22) are dispersed in such a manner that the base material 20 is broken by the explosive power and the cover cap 42 is disconnected from the base material 20. However, when the base material 20 is interposed between the cover cap 42 made of metal and the cover bottom plate 26 made of metal, and also when the cover cap 42 and the cover bottom plate 26 are directly fastened to each other with the bolts 50 as shown in the figure, even if the mechanical strength of the base material 20 is low, the fastening portion, in which the cover cap 42 and the cover bottom plate 26 are directly fastened to each other, is not broken. Therefore, these members are not disconnected from the base material 20, and dispersion of the inner structure can be positively prevented. In this circuit breaker, the base material 20 is provided with a recess portion 20a in which the cover bottom plate 26 is engaged. Therefore, even if two cover members of the cover cap 42 and the cover bottom plate 26 are used, it is possible to make the circuit breakercompact. Since the insulating cover 40 is interposed between the inner conductor 30 and the cover cap 42 and also between the cylindrical portion 22 and the cover cap 42, it is possible to prevent the break portion 31, which has been broken; from coming into contact with the cover cap 42, that is, it is possible to prevent the occurrence of short circuit. Quenching a flame by a solid wall When a solid wall exists at a position to which the flame is propagated as shown in Fig. 6, there is a remarkable difference between the flame temperature and the temperature of the solid surface. Accordingly, a remarkably high gradient of temperature is caused between the flame and the solid wall. A combustion limit flame temperature exists between both temperatures. Accordingly, in a region, the temperature of which is lower than this combustion limit flame temperature, that is, in a region, the distance from the solid surface of which is not more than a predetermined value "d", the flame can not be propagated. Therefore, the flame is quenched in the region. This region is a dead space. Size "d" of this dead space is determined by the combustion condition. Accordingly, when a gap, which is smaller than the size (quenching distance) corresponding to size "d", is formed, it is impossible for the flame to propagate through this gap.

Claims: A circuit breaker comprising: a cylindrical portion (22) having a gunpowder and an exploding means for exploding the gunpowder by application of electric power to the gunpowder, the cylindrical portion (22) being provided with an opening at at least one end; a base material (20) securing the cylindrical portion (22), at least the surface of which is made of insulating material; a conductor (30) fixed to the base material (20) and having a break portion (31), the break portion (31) being broken by explosive force of the gunpowder, a first metallic cover portion (42) covering the cylindrical portion (22) and the break portion (31); and a second metallic cover portion (26) covering the base material from an opposite side of the cylindrical portion (22), wherein the first and second cover portions (42, 26) are fixed to the base material (20) by directly connecting the first and second cover portions (42, 26) to each other, characterised in that the conductor (30) crosses a position immediately above the cylindrical portion (22) so as to be located opposite to the opening of the cylindrical portion (22) The circuit breaker according to claim 1, wherein the first and second cover portions (42, 26) are integrally formed. The circuit breaker according to claim 2, wherein the first cover portion (42) has a pair of side walls (46), the second cover portion (26) is composed of a pair of rolling portions (59) extending from the side walls (46), and the first and second cover portions (46, 26) are fixed to the base material (20) by rolling the rolling portions (59) on the opposite side of the base material (20) so that the rolling portions (59) are lapped each other while interposing the base material (20). The circuit breaker according to claim 1, wherein a recess portion (20a) accommodating the second cover portion (26) is formed on the base material (20). The circuit breaker according to claim 1, wherein insulating material is provided on the inside of the first cover portion (42). The circuit breaker according to claim 1, wherein an inner surface of the first cover portion (42) is coated with insulating material. The circuit breaker according to claim 1, wherein a cover made of resin is molded so as to cover a connecting portion of the base material (20) with each cover portion (42, 26). The circuit breaker according to claim 1, wherein the base material (20) is made of one of aluminum and aluminum alloy, the surface of which is oxidized to form its oxide layer.

Inventors: AMANO JUNYA, HORI HIROSHI, KIDO MOTONORI, KIMURA AYUMU, KUME MASAHIRO, MATSUMARU AKIO, MIYAZAKI YOSHIYUKI, NISHIDA KENJIRO, TANIGAWA MITSURU, TOYAMA HIDEAKI, YASUKUNI JUN, AMANO, JUNYA, HORI, HIROSHI, KIDO, MOTONORI, KIMURA, AYUMU, KUME, MASAHIRO, MATSUMARU, AKIO, MIYAZAKI, YOSHIYUKI, NISHIDA, KENJIRO, TANIGAWA, MITSURU, TOYAMA, HIDEAKI, YASUKUNI, JUN, Tanigawa, Mitsuru, c/o Sumitomo Wiring Systems, YASUKUNI, JUN, C/O SUMITOMO WIRING SYSTEMS, LTD.
Applicants: AUTONETWORKS TECHNOLOGIES LTD, NIPPON KAYAKU KK, SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO WIRING SYSTEMS, AUTONETWORKS TECHNOLOGIES, LTD., NIPPON KAYAKU KABUSHIKI KAISHA, SUMITOMO ELECTRIC INDUSTRIES, LTD., SUMITOMO WIRING SYSTEMS, LTD.
Application year: 1999
Main classification: H01H39
IPC codes: H01H39