Circuit breaker with overcurrent tripping device

Abstract: An overcurrent tripping device which is included in a circuit breaker is constituted by a pre-assembly unit of a holder (15) with a conductor (2), a fixed core (4) for generating a magnetic attraction force responding to an overcurrent, and a bimetal (5) warping responding to the temperature rise of the conductor, and an operation arm (18) rotatably borne on the holder and having a moving core (10) which is to be attracted to the fixed core by the magnetic attraction force.

Description: The present invention relates to a circuit breaker with an overcurrent tripping device which operates via a time limit tripping by a bimetal and an instantaneous tripping by an electromagnet. A conventional circuit breaker with an overcurrent tripping device, which is, for example, shown in a Gazette of Unexamined Japanese Utility Model Application Hei 3-19236, is described referring to FIG. 4. FIG. 4 is a sectional side view schematically showing the constitution of the conventional circuit breaker, and especially showing the conventional overcurrent tripping device of the circuit breaker. As shown in FIG. 4, the conventional circuit breaker comprises a housing 1 made of a resin. The housing 1 consists of a base member 1a and a cover member 1b. A conductor 2, whereon a load current flows, is fixed on the base member 1. An end 2a of the conductor 2 is connected to a known moving contact mechanism (which is not shown in the figure) and the other end 2b is connected to a terminal member 3. A fixed core 4, which has substantially U-letter shaped section in a plane vertical to the paper sheet of FIG. 4, is provided on the conductor 2 for generating a magnetic force by the load current flowing on the conductor 2. A bimetal 5 is fixed to the conductor 2 on an end 5a thereof. An adjustable screw 6 is provided on the other free end 5b of the bimetal 5 in a manner such that an end 6a of the screw 6 faces to a trip lever 7. The trip lever 7 is rotatably borne by a pivot 8. An operation arm 9 is rotatably borne by another pivot 11 and has a moving core 10 which is fixed on an end 9b and a pushing part 9a which is formed on the other end 9a for pushing the trip lever 7 when the operation arm 9 rotates in clockwise direction in the figure. An extension spring 12 is provided for supplying a rotation force to the operation arm 9 in a direction to make the moving core 10 separate from the fixed core 4. Another adjustable screw 13 is provided on a fixed part 14 for adjusting a gap between the fixed core 4 and the moving core 10. The above-mentioned pivots 8 and 11 and the fixed part 14 are provided on a frame which is not shown in the figure. Tripping operation of the above-mentioned conventional circuit breaker with an overcurrent tripping device is described in the following: When an overload current which is a little larger than a rated current of the conductor 2 flows, the bimetal 5 warps. Thereby, the end 6a of the screw 6 contacts the trip lever 7. As a result, the trip lever 7 rotates in clockwise direction in the figure. When an overload current which is larger than a predetermined value flows on the conductor 2, the fixed core 4 generates a magnetic attraction force, and the moving core 10 is momentarily attracted to the fixed core 4. Thereby, the operation arm 9 rotates in clockwise direction in the figure. When the operation arm 9 rotates, the end 9a of the operation lever 9 pushes the trip lever 7. As a result, the trip lever 7 rotates in clockwise direction in FIG. 4. When the trip lever 7 rotates in clockwise direction in the figure, a latch of a tripping device (which is not shown in the figure) is released. Thereby, the conventional circuit breaker is tripped, and the current is cut off. In the conventional circuit breaker with the overcurrent tripping device configured above, since the fixed core 4 and the moving core 10 are respectively fixed on the independent members such as the base member la and the frame (not shown in the figure), there are dimensional tolerance limits in the mass-produced parts. Therefore, for making the operation arm 9 start to rotate by a current of a predetermined value, the gap between the fixed core 4 and the moving core 10 must be adjusted by provision of the adjustable screw 13. Furthermore, since the fixed core 4, the operation arm 9 and so on are respectively held on different independent members, total size of the overcurrent tripping device becomes larger. Accordingly, a larger space is necessary for containing the overcurrent tripping device in the housing 1 of the circuit breaker. US-A-3 3 317 867 shows a circuit breaker with thermal-magnetic tripping allowing for overtravel of the thermal means. From this known circuit breaker the present invention starts from. According to US-A-3 317 867 there is provided a conductor, an end thereof being connected to a moving contact mechanism and the other end being connected to a terminal member. A fixed core is provided in the vicinity of said conductor for generating a magnetic attraction force responding to a current value flowing on said conductor. Furthermore provided is a bimetal which warps responding to a current flowing on said conductor for driving a trip member. An operation arm is rotatably borne on a holder and has one end facing said fixed core and an action part for actuating said trip member when said operation arm is rotated in a predetermined direction. The circuit breaker according to US-A-3 317 867 suffers from a couple of disadvantages: Upon a current value above the normal or rated value of the circuit breaker, the bimetal warps in order to move the latch member so that the contact mechanism is released. If due to a whatsoever reason there still flows a current, the bimetal warps further and the latch member reaches a specific position, thereby resting on an apex between two inclined surfaces of the fixed core. Simultaneously notches of the latch member must slide on lugs against the force of the spring. It is this tilting movement of the latch member, which is the core concept of the invention according to US-A-3 317 867. Due to the fact, however, that the latch member only "hangs" with its notches on the lugs and in addition must slide along these lugs in order to reach the specific position, the whole current breaker of US-A-3 317 867 suffers from the disadvantages that there are severe restraints as to the mounting position of the whole circuit breaker in order to not obstruct movement of the notches along the lugs and in order to prevent the latch member falling off the fixed core or its lugs, respectively. The whole circuit breaker is furthermore susceptible to vibrations and shocks and its whole operation characteristics are unreliable and unsafe. A further disadvantage of the circuit breaker according to US-A-3 317 867 is that there is no predetermined gap between the fixed core and the movable core, which is constituted by the latch member itself. Accordingly, in the latched position the gap between this fixed core and the movable core is - after restoring of the latch member - not always constant and accordingly the tripping values of this known circuit breaker cannot be fixed to a given value in a reliable way. In view of this it is an object of the present invention to provide an improved circuit breaker with an overcurrent tripping device wherein any adjustable screw is not necessary for adjusting a gap between a fixed and a moving core and the down-sizing of the circuit breaker can be achieved. Solution of this object is achieved by the measures which are defined in claim 1. According to the present invention the bimetal is carried by the holder; one end of the operation arm facing the fixed core has a moving core for being attracted by the fixed core; and a stopper part is provided at the operation arm for contacting the holder in a manner to keep a predeterminded gap between the fixed core and the moving core when the stopper part contacts the holder, wherein a holder pre-assembly unit is formed by piling up the holder, the fixed core, the conductor, the bimetal and a presser plate in the mentioned order and by fixing them together. While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and contents will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings, in which: FIG. 1 is a sectional side view showing a constitution of a main part of a circuit breaker with overcurrent tripping device in accordance with the present invention; FIG. 2 is a front view showing the constitution of an overcurrent tripping device of the circuit breaker in accordance with the present invention; FIG. 3 is an exploded perspective view showing the constitution of the assembly unit shown in FIG. 2; and FIG. 4 is the sectional side view showing the constitution of the conventional circuit breaker with overcurrent tripping device. It will be recognized that some or all of the Figures are schematic representations for purposes of illustration and do not necessarily depict the actual relative sizes or locations of the elements shown. A preferred embodiment of a circuit breaker with an overcurrent tripping device in accordance with the present invention is described referring to FIGS. 1, 2 and 3. FIG. 1 is a sectional side view showing a constitution of a main part of the circuit breaker with an overcurrent tripping device in accordance with the present invention. FIG.2 is a front view showing the constitution of an overcurrent tripping device of the circuit breaker. FIG.3 is an exploded perspective view showing the constitution of the assembly unit shown in FIG.2. In FIG.1, a housing 1 of the circuit breaker consists of a base member 1a and a cover member 1b. An end 2a of a conductor 2 is connected to a moving contact mechanism which is described in detail below, and the other end 2b of the conductor 2 is connected to a terminal member 3. A fixed core 4, which has substantially U-letter shaped section in a plane vertical to the paper sheet of FIG.1 and generates a magnetic attraction force responding to a current value flowing on the conductor 2, is provided to be fixed on the conductor 2. A bimetal 5 is provided to be fixed on the conductor 2 at an end 5b thereof. An adjustable screw 6 is provided on the other end Sa of the bimetal 5. A trip lever 7 is rotatably borne by a pivot 8. As shown in FIGs. 1,2 and 3, the conductor 2, the fixed core 4, the bimetal 5 and so on are mounted on a holder 15, and these elements constitute a holder pre-assembly unit. As shown in FIG.3, the holder pre-assembly unit is formed by piling-up of the holder 15, the fixed core 4, the conductor 2, the bimetal 5 and a presser plate 16 which has a substantially U-letter shaped section in this order. These elements are fixed by caulking of rivets 17 with the presser plate 16. Furthermore, the holder 15 has through-holes 15a wherethrough the rivets 17 penetrate and protrusions 15b and 15c which are to be engaged with grooves formed on the base member 1a (not shown in the figure). Bracket parts 15d are formed substantially in the center of the holder 15 for bearing an operation arm 18. Stopper parts 15e are formed in the vicinity of the top end for regulating the rotation of the operation arm 18. Furthermore, engaging parts 15f are formed in the vicinity of the top end which is to be engaged with the cover member 1b. The operation arm 18 is borne so as to be rotatable on the above-mentioned holder pre-assembly unit via a shaft 19. A moving core 10 is fixed on an end 18e of the operation arm 18 in a manner to face the fixed core 4. Stopper parts 18a which are to contact the stopper parts 15e of the holder 15 and a pushing part 18b for pushing the trip lever 7 are formed in the vicinity of the other end of the operation arm 18. Furthermore, bearing holes 18c wherethrough the shaft 19 penetrates and a spring engaging part 18d whereby a spring 20 is suspended are formed substantially at the center of the operation arm 18. An operation arm pre-assembly unit consists of the operation arm 18, the moving core 10 and the like. As shown in FIG.3, the spring 20 is configured in a double torsion type. Coil parts 20b of the spring 20 are penetrated and held by the shaft 19. Center arm part 20c of the spring 20 is to be engaged with the spring engaging part 18d of the operation arm 18. As shown in FIG.2, both arms 20a of the spring 20 are respectively engaged with the presser plate 16. As mentioned above, the holder pre-assembly unit, the operation arm pre-assembly unit and the spring 20 are further assembled in one unit, thereby configuring the overcurrent tripping device. As shown in FIG.1, such overcurrent tripping device is put between the base member 1a and the cover member 1b, and thereby, it is contained in the housing 1 of the circuit breaker. Under this condition, the end 2a of the conductor 2 is connected to a flexible conductor 23 of the moving contact mechanism. The other end 2b of the conductor 2 is connected to the terminal member 3. As shown in FIG.1, the moving contact mechanism comprises: a moving contact 21 which is to contact a known stationary contact (not shown in the figure because of being obvious); a moving member 22 which supports the moving contact 21; the flexible conductor 23 which electrically connects the conductor 2 and the moving member 22; a moving contact arm 24 which is rotatably pivoted by a pivot 25; a cross-bar 26 which mechanically connects a plurality of moving contact members and is to be coupled to a known handle (not shown in the figure). FIG.1 shows a tripped condition in that the moving contact 23 is separated from the stationary contact (which is not shown in the figure). In FIG.1, link mechanisms for linking the moving contact mechanism and the trip lever 7, a handle and the like are omitted. In the circuit breaker with the overcurrent tripping device as configured above, the operation arm 18 always receives a rotation force of the spring 20 in a direction to separate the moving core 10 from the fixed core 4. Since the stopper part 18a of the operation arm 18 contacts the stopper parts 15e of the holder 15, a gap between the fixed core 4 and the moving core 10 is maintained within a predetermined dimension tolerance. Under this condition, when an overload current such as a shortcircuited current, which is above a predetermined value, flows on the conductor 2, the fixed core 4 generates a magnetic attraction force, and thereby the moving core 10 is attracted to the fixed core 4 against the force of the spring 20. As a result, the operation arm 18 starts to rotate, and the pushing part 18b of the operation arm 18 pushes and rotates the trip lever 7. When the trip lever 7 is rotated, the circuit breaker turns to the tripping state. On the other hand, when the value of the overload current is relatively small, the bimetal 5 warps responding to the temperature rise of the conductor 2. Thereby, the trip lever 7 is rotated by the warped bimetal 5, after passing a predetermined time from the start of the temperature rise. Furthermore, as shown in FIG.2, the arms 20a-of the spring 20 are respectively engaged with the inner face 16a of the U-letter shaped section of the presser plate 16 (that is, the distance between both arms 20a is kept smaller than the length L1), and the distance is not expanded to the width L2 of the operation arm 18. d Accordingly, the operation arm 18 smoothly moved without any interference of the spring 20. In the above-mentioned embodiment, the double torsion spring is used as the spring 20. However, a tension spring or a compression spring, which is provided between the holder pre-assembly unit and the operation arm pre-assembly unit, can be used for supplying the rotation force of the operation arm pre-assembly unit. Furthermore, when the torsion spring is used as the spring 20, hooking holes are provided on the conductor 2 or the presser plate 16, and the arms 20a of the spring 20 can be engaged with the hooking holes. Thereby, the distance between both arms 20a can be regulated so as not to interfere the motion of the operation arm pre-assembly unit. In the circuit breaker configured above and shown in FIGs. 1, 2 and 3, the fixed core 4 is previously fixed on the holder 15, and the moving core 10 is also previously fixed on the operation arm 18. The operation arm 18 is borne on the holder 15 via the shaft 19 before assembling the overcurrent tripping device. Therefore, the gap between the moving core 10 and the fixed core 4 can be adjusted in the predetermined dimension tolerance during the previous assemblage of the operation arm 18 on the holder 15. As a result, the adjustable screw for adjusting the gap between the fixed core 4 and the moving core 10, which has been necessary in the conventional circuit breaker, is no more need in the circuit breaker in accordance with the present invention. Furthermore, the overcurrent tripping device becomes smaller, and thereby, the total size of the circuit breaker also becomes smaller. Still more, since the main parts of the overcurrent tripping device are united into one unit comprising the conductor 2, the fixed core 4, the bimetal 5, the holder 15, the moving core 10, and the operation arm 18 prior to the over all assemblage, the assemble work of the circuit breaker becomes easy. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the invention.

Claims: A circuit breaker with overcurrent tripping device comprising: a conductor (2), an end thereof being connected to a moving contact mechanism (24) and the other end being connected to a terminal member (3); a fixed core (4) provided in the vicinity of said conductor (2) for generating a magnetic attraction force responding to a current value flowing on said conductor (2); a bimetal (5) which warps responding to a current flowing on said conductor (2) for driving a trip member (7); and an operation arm (18) rotatably borne on a holder (15) and having one end facing said fixed core (4) and an action part (18b) for actuating said trip member (7) when said operation arm (18) is rotated in a predetermined direction, characterized in that said bimetal (5) is carried by said holder (15); said one end of said operation arm (18) facing said fixed core (4) has a moving core (10) for being attracted by said fixed core (4); and a stopper part (18a) is provided at said operation arm (18) for contacting said holder (15) in a manner to keep a predetermined gap between said fixed core (4) and said moving core (10) when said stopper part (18a) contacts said holder (15), wherein a holder pre-assembly unit is formed by piling up said holder (15), said fixed core (4), said conductor (2), said bimetal (5) and a presser plate (16) in the mentioned order and by fixing them together. A circuit breaker according to claim 1, wherein a spring (20) is provided between said holder (15) and said operation arm (18) for supplying a rotation force to said operation arm (18) in a direction to separate said moving core (10) from said fixed core (4). A circuit breaker according to claim 1 or 2, wherein said presser plate (16) has a substantially U-letter shaped section. A circuit breaker according to claim 1, 2 or 3, wherein an operation pre-assembly unit is constituted by said operation arm (18) which'is rotatably borne on said holder pre-assembly unit and said moving core (10) which is fixed on the operation arm (18). A circuit breaker according to anyone of the preceeding claims, wherein said holder (15), said fixed core (4), said conductor (2), said bimetal (5) and said presser plate (16) are fixed together by caulking of rivets (17) with said presser plate (16).

Inventors: KONDA TAKAFUMI, TODA HARUHISA, KONDA, TAKAFUMI, TODA, HARUHISA, KONDA, TAKAFUMI C/O MITSUBISHI DENKI ENJ K.K. H., Toda, Haruhisa, c/o Mitsubishi Denki Enj Kab. K. H
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1993
Main classification: H01H71
IPC codes: H01H73, H01H71