A SWITCH ARRANGEMENT AND METHOD FOR MOUNTING THE SAME

Abstract: A switch arrangement (37) comprises a plunger device (21), a solenoid (40) and a body (39). The plunger device comprises a plunger insulator (22), a fixed plunger element (25), a movable plunger element (23), and an elastic means (26), which is adapted to bias the movable plunger element (23) in the direction away from the fixed plunger element (25), the movable plunger element (23) moving in the direction of the fixed plunger element (25) when the plunger device (21) is activated. The plunger insulator (22), the fixed plunger element (25), the movable plunger element (23) and the elastic means (26) together form a self-contained unit, which is easy to mount in a body in a solenoid device since the body and the plunger insulator have matching engagement means (45, 47), which allow introduction of the plunger device into the body and releasable mounting of the plunger device by turning the same. A method for mounting the plunger device (22) in the switch arrangement is also disclosed.

Description: A SWITCH ARRANGEMENT AND METHOD FOR MOUNTING THE SAME Field of the Invention The present invention relates to a switch arrange¬ ment comprising a plunger device, a solenoid and a body, said plunger device being adapted to extend through the solenoid and be supported at its ends in said body and comprising a fixed plunger element, a movable plunger element, which moves in a first direction in relation to the fixed plunger element when the plunger device is actuated, an elastic means, which is adapted to bias the movable plunger element in a second direction in relation to the fixed plunger element, and a plunger insulator, which essentially surrounds and keeps the fixed plunger element, the movable plunger element and the elastic means together so as to form a self-contained unit. The invention also concerns a method for mounting such a switch arrangement. The switch arrangement can be used in various elec¬ tric apparatus for opening, closing or changing an elec¬ tric circuit, but is especially intended for mini circuit breakers. Background Art Safety switches are used to quickly interrupt the current in an electric circuit, to which the switch is connected, when too great a current arises in the elec- trie circuit. The switch opens in two different cases. One case is when the current has exceeded a certain value for a predetermined relatively long time. The other case is immediately when an extremely great current, such as a short-circuit current, arises in the electric circuit in which the switch is included. For interruption in the latter case, use is made of a switch arrangement which comprises a plunger device and a solenoid device. Fig. 1, which is a longitudinal section, shows sche¬ matically the composition of a switch arrangement 1 which is intended for a safety switch and is available on the market. The switch arrangement 1 comprises a solenoid device 2 and a plunger device 3. The solenoid device 2 comprises a solenoid 4 which is part of the current path in the electric apparatus and which surrounds the plunger device 3. The solenoid 4 has a first connection point 5 and a second connection point 6. The first connection point 5 is connected to an output pole 50. The second connection point 6 is fixed in a solenoid body 7, which surrounds the solenoid 4 and which serves to conduct a magnetic field which is created when current flows in the solenoid and to support the plunger device 3. A stop lug 8 is further fixed to the body 7. The current flows through the switch arrangement 1 from a contact 51 which is fixed to the body and connected to the other parts of the safety switch, to the second connection point 6, through the solenoid 4 and via the first connection point 5 to the output pole 50. The plunger device 3 mainly consists of five parts: a plunger insulator 9, a movable plunger element 10, a spring 11, a fixed anchor element 12 and a push rod 13. The insulator 9 constitutes the surface of the plunger device 3 and insulates the interior parts thereof from the solenoid 4. The fixed plunger element 12 is fixed in the solenoid body 7 and is in metallic contact with this in order to improve the magnetic coupling. Between the fixed 12 and the movable plunger element 10 the spring 11 is arranged, which during normal function biases the movable plunger element 10 to an end position which is defined by the stop lug 8. The push rod 13 is applied against the movable plunger element 10 at its one end and extends through a longitudinal hole 15 in the fixed plunger element 12. The solenoid body 7 is, adjacent to the fixed plunger element 12, formed with a hole 16, through which the other end of the push rod 13 can pro¬ trude. In the vicinity of the solenoid device 2 in front of the other end of the push rod 13 there is a locking arm 17, which, when moved, makes the switch open. The switch arrangement 1 operates as follows: A cur¬ rent in the solenoid 4 produces a magnetic field which results in the fixed plunger element 12 and the movable plunger element 10 being attracted to each other. If the force of attraction is greater than the spring force of the spring 11, the movable plunger element 10 moves towards the fixed plunger element 12. In this movement, the movable plunger element 10 brings along the push rod 13, which thus moves forward and hits the locking arm 17 located in front of the solenoid device 2, whereby the locking arm 17 is displaced such that the safety switch opens. The mounting of the plunger device 3 in the sole¬ noid device 2 is carried out as follows. First, the fix¬ ed plunger element 12 is introduced into the solenoid body 7 and, together with the contact 51, is riveted to the body, the fixed plunger element itself forming a rivet. Then the plunger insulator 9 is arranged around the fixed plunger element 12. After that the push rod 13, the spring 11 and the movable plunger element 10 are introduced into the insulator 9. By these three parts being displaceable, they must be held in place manually so as not to fall out from the plunger insulator 9. Finally, the plunger device 2 and its components are fixed by the stop lug 8 being welded to the body. The mounting of the prior-art plunger device is thus a complicated process that is difficult to automate, which results in a high cost of manufacture and long mounting times. Other switch arrangements available on the market are usually composed correspondingly. Sometimes a stop means in the housing of the safety switch is used instead of the stop lug 8. Alternatively, the push rod can be an integrated part of the movable plunger element, the push rod being provided, in its end facing the locking arm, with a collar which limits the movement of the movable plunger element away from the fixed plunger element. Moreover, there are different types of safety switches with different characteristics, which determine their time lag. The time lag determines the time it takes before the safety switch opens at a certain excess cur¬ rent. Only a few parts differ from each other between safety switches having different characteristics, the plunger device being one of these parts. The time lag is in every essential respect a function of the rigidity of the spring: the more rigid the spring, the longer is the time. It is, of course, disadvantageous not to have the possibility of making a late decision regarding the char¬ acteristic of the switch. Prior-art technique makes such a decision difficult, since the components included in the solenoid device and the plunger device are dependent on each other during mounting, which makes the mounting at a late stage considerably more difficult. In the patent literature there are also examples of different safety switches. EP 0 120 422 discloses a switch having a plunger device, in which the parts are kept together by a plunger insulator, at both ends pro¬ vided with hooks extending inwardly in the radial direc¬ tion. These hooks must be bent sideways during mounting of the parts in the plunger insulator, and therefore it is not easy to automate the mounting operation. The plunger device is riveted in traditional manner to the body of the switch, and therefore also this mounting step is not easy to automate. DE 25 31 215 discloses a switch, in which only some of the parts in the plunger device form a unit. During mounting in the body, a spring is applied on the push rod of the plunger device. Then the solenoid is inserted into the body sideways and the plunger device is pushed in through a hole in the end of the body, through the sole¬ noid and into engagement with the other end of the body. This way of mounting is difficult to automate since the loose springs of the plunger device and the solenoid must be kept in place during mounting. EP 0 199 980 discloses a switch with a plunger device, which are held together by radial deformations of the plunger insulator. The plunger device is mounted in the body by means of a loose washer, which is pushed over one end. Also this step of mounting is difficult to automate. Summary of the Invention, In view of that stated above, an object of the pre¬ sent invention therefore is to provide a switch arrange¬ ment which is easy to mount and suited for automatic mounting. This object is achieved by a switch arrangement according to claim 1. A further object of the invention is to indicate a simplified method, which can be automated, for mounting a switch arrangement. This object is achieved by the method according to claim 9. In a switch arrangement according to the invention, the plunger insulator, the movable plunger element, which may comprise a push rod or some other suitable means for mechanically affecting a locking arm, the fixed plunger element and an elastic means together form a self-con¬ tained unit, the plunger insulator having the holding- together function. Thus, the parts stick together by themselves and can be assembled to a unit before mounting in the solenoid device. Since the parts in the plunger device need not be held together during the actual mount¬ ing in the solenoid device, the mounting is simplified to a considerable extent and can be automated. The design as a premountable unit also permits separate manufacture and testing of plunger devices. The possibility of separately testing plunger devices is, of course, a great advantage since it is then guaranteed that they are always perfect once they are mounted in a safety switch. Besides, there will be possibilities of separate storing and mounting even when the manufacturing process for safety switches has proceeded far. In the inventive switch arrangement, the plunger device and the body have matching engagement means, which allow insertion of the plunger device into the body and releasable mounting of the plunger device by turning thereof. The self-contained plunger device and the match¬ ing engagement means thus result in the possibility of the plunger device being mounted in the body by only a linear movement followed by a turning motion. Therefore the mounting is suited for automation. A further advan¬ tage is that the plunger device in a safety switch can easily be replaced if, for instance, another character¬ istic is desired. The matching engagement means are conveniently a lug and a matching recess. The lug may be arranged on the plunger insulator and preferably constitutes a part thereof, and the recess may be formed in the body or vice versa. The recess in the body can be produced by a simple punching operation. A simple technique of manufacturing the plunger insulator is injection moulding of plastic in one piece. The engagement means of the plunger insulator will then be particularly easy to manufacture. The plunger insulator advantageously has a grip por¬ tion at one end. In automatic mounting, the grip portion can be used by a mounting machine. Suitably the plunger insulator further has a stop means which defines an end position for the movable plunger element in a first direction, preferably away from the fixed plunger element. The stop means can be designed in various ways and either be an integrated part of the plunger insulator or be attached thereto. For instance, it may comprise a stop bar which extends across one end of the insulator. The stop means has several functions. It holds the movable plunger element in place in the plunger insula- tor. It also contributes to orienting the plunger device as this is introduced into the solenoid body. The stop means can also advantageously serve as a gripping por¬ tion. The fixed plunger element can have retaining means which serve to retain the fixed plunger element in the plunger insulator in a reliable manner without the aid of the solenoid body and without deformations of the plunger insulator. The plunger insulator may then have the essen- tial form of a cylinder which is easy to injection mould. The retaining means can suitably be grooves which are formed on the outside of the fixed plunger element. The forward movement of the movable plunger element towards the fixed plunger element is a quick procedure which causes an air cushion between the two plunger ele¬ ments. With a view to releasing this air cushion in an effective manner, the plunger insulator preferably com¬ prises one or more air outlets essentially in that part of the circumferential surface which is located between the movable plunger element and the fixed plunger ele¬ ment, while that part of the plunger insulator which surrounds the fixed and the movable plunger element has essentially no air outlet. The size of the air outlets can easily be optimised for the application in question. Usually, as rapid an evacuation as possible is desired. However, the technique also affords other possibilities. By arranging, for example, air outlets spaced apart from the fixed plunger element, a braking action is achieved since the air cushion is evacuated more rapidly at the beginning of the movement of the movable plunger element and more slowly at the end thereof. If the plunger insu¬ lator is injection moulded, the air outlets will be par¬ ticularly easy to arrange. When mounting the plunger device in the solenoid device, the plunger device is, as mentioned above, assembled to a unit outside the solenoid device. Subse¬ quently, the plunger unit can easily be inserted into the body of the solenoid device by the matching engage¬ ment means being aligned with each other, and be fixed by the plunger unit being turned such that the engagement means are no longer aligned with each other. Brief Description of the Drawings The present invention will now be described by means of preferred embodiments and with reference to the accom¬ panying drawings, in which Fig. 1, as discussed above, is a longitudinal sec- tion of a prior-art switch arrangement, Fig. 2 is a longitudinal section of a plunger device according to a preferred embodiment of the present inven¬ tion, Fig. 3 is a side view of a switch arrangement with a plunger device according to Fig. 2, and Fig. 4 is a rear view of a switch arrangement ac¬ cording to Fig. 3. Description of Preferred Embodiments Below follows a description of a plunger device and a switch arrangement which are intended to be used in a safety switch. Fig. 2 shows an embodiment of a plunger device 21 according to the invention. The plunger device 21 com¬ prises a plunger insulator 22, a movable plunger element 23 with a push rod 24, a fixed plunger element 25 and a spring 26. The plunger insulator 22 encompasses the other parts 23-26 of the plunger device for insulation thereof when the plunger device 21 is mounted in a solenoid device. The insulator 22 is cylindrical and made of an injection- moulded plastic material which is slightly elastic. A stop means 27 is arranged at one end 28 of the insulator 22. The stop means comprises a stop bar 27 extending transversely of one opening 29 of the insulator 22. The stop bar 27 is attached to or comprises preferably a part of the plunger insulator 22. The movable plunger element 23 is movably arranged inside the insulator 22 at one end 28 thereof. The move¬ ment of the movable plunger element 23 towards one open¬ ing 29 of the plunger insulator 22 is limited by the stop bar 27. The fixed plunger element 25 is fixedly arranged at the other end 30 of the insulator 22 by press-fit. This press-fit is made possible by means of grooves 31 which are formed in the surface of the fixed plunger element 25. The plunger insulator 22 is slightly elastic, enabling the grooves 31 to engage therein during the press-fitting. The diameter of the fixed plunger element 25 is larger adjacent to the grooves 31 than the inner diameter of the insulator 22, which provides for good fixing of the fixed plunger element 25. A contact flange 32 is formed at that end portion of the fixed plunger element 25 which faces away from the plunger insulator 22, said flange 32 establishing good magnetic contact when the plunger device 21 is applied against a solenoid body of a solenoid device. The spring 26 is biased between the movable plunger element 23 and the fixed plunger element 25 and extends through a space of motion 33 between the two plunger ele¬ ments. The push rod 24 which is made of injection-moulded plastic, abuts against the movable plunger element 23 in a recess 34 and extends along the longitudinal axis of the insulator 22 through the spring 26 and through a rod recess 35 in the fixed plunger element 25. A plurality of air outlets 36 are arranged in the circumferential surface of the plunger insulator 22 along its circumference. These are located in that part of the circumferential surface which during normal function is located between the movable plunger element 23 and the fixed plunger element 25. The mounting of the self-contained plunger device 23 is carried out as follows. First, the movable plunger element 23 is introduced into the plunger insulator 22 through the insulator opening without a stop bar 27. The end position of the movable plunger element 23 is defined by the stop bar 27. Then the push rod 24 and the spring 26 are introduced into the insulator 22, whereby the push rod 24 comes to be applied against the movable plunger element 23. Finally, the fixed plunger element 25 is press-fitted in place in the plunger insulator, whereupon the plunger device 27 constitutes a self-contained sepa¬ rate unit. Fig. 3 shows a switch arrangement which comprises a plunger device 21 and a solenoid device 38 according to the present invention. The main parts of the solenoid device 38 are a solenoid body 39, a solenoid 40, an out¬ put pole 41 and a fixed contact 42, which, as appears from the Figure, constitutes an integrated part of the body. The output pole 41, the contact 42 and the solenoid 40 constitute a link in the current path of the safety switch. As appears from Fig. 3, the plunger device 21 is arranged inside the solenoid device 38, the solenoid 40 encompassing the major part of the plunger device 21. The solenoid body 39 has, at the end where the contact 42 is arranged, a first hole 43 which allows partial passage of the fixed plunger element 25 of the plunger device 21 and, at the end where the first contact 42 is arranged, a second hole 44 which allows passage of the plunger device 21. The end position of the plunger device 21 adjacent to the hole 43 is defined by the contact flange 32 of the fixed plunger element 25 (see Fig. 2), said contact flange abutting against the solenoid body 39 for obtaining a good contact metal-against-metal. The plunger device 21 is at its end with the stop bar 27 attached to the solenoid body 39 by means of two turning lugs 45, which are formed in the surface of the plunger insulator 22, and two matching turning recesses 47, which are form¬ ed in the solenoid body 39. Fig. 3 also shows schematically a locking arm 49 which is included in the safety switch and which is dis¬ placed by the push rod 24 when the switch arrangement is activated. Fig. 4 is a rear view of a solenoid device 38 with an attached plunger device 21. This Figure shows the turning lugs 25 of the plunger device 21 and the recesses 47 in the solenoid body 39. The mounting of a plunger device 21 in a solenoid device 38 will now be described. When the plunger device 21 is introduced into the solenoid device 38 through the second hole 44, the stop bar is held vertically such that the turning lugs 45 and the turning recesses 47 are aligned with each other. The introduction proceeds until the contact flange 32 comes to be applied against the solenoid body 39 and the turning lugs 45 have passed the turning recesses 47, the entire plunger device 21 being moved through a quarter of a turn such that the turning lugs 45 engage the solenoid body 39 and bias the plunger device in the longitudinal direction. After the turning, the plunger device 21 is fixed to the solenoid device 38. The stop bar 27 facilitates this mounting to a consider¬ able extent since on the one hand it serves as engagement portion for a gripping hand or the like, such that the plunger device 21 becomes easy to grip and turn, and, on the other hand, it orients the plunger device 21 during the introduction such that the plunger device 21 will be exactly correctly positioned for the turning. The function of the plunger device 21 will be de- scribed below with reference to the Figs 2 and 3. As described above, the plunger device 21 is acti¬ vated when too great a current arises in the solenoid 40 arranged round the plunger device 21. The current causes a magnetic field which attracts the two plunger elements 23, 25. The distance between the fixed plunger element 25 and the movable plunger element 23 during normal function is maintained by means of the spring 26. When the force of attraction between the two plunger elements 23, 25 is so great that the spring 26 can no longer keep the mov¬ able plunger element 23 back, this moves towards the fixed plunger element 25. In this movement, the movable plunger element 23 takes along the push rod 24, which then extends further through the rod recess 35 so as to finally hit the locking arm 49, which is positioned in front of the end with the fixed plunger element 25 of the plunger device 21. When being hit, the locking arm 49 is displaced and makes the safety switch open. When the movable plunger element 23 moves towards the fixed plunger element 25, an air cushion forms there¬ between. The air cushion is evacuated effectively by means of the air outlets 36 in the circumferential sur- face of the plunger insulator 22. The air outlets 36 and the design of the stop means 27 as a bar provide for a free flow of air on both sides of the movable plunger element 23. Alternative Embodiments Several modifications of the present invention are feasible within the scope thereof. For instance, the stop bar for the movable plunger can be designed in various ways. It need not extend across the opening of the plunger insulator, but only a distance. Other stop means are also possible, such as one or more lugs, or one or more coherent surfaces, with¬ out, however, the varied functionality of the stop bar being achieved. Besides, the air outlets may comprise holes, gaps, air-permeable surface layers, etc. Press-fitting of the fixed plunger element in the plunger insulator is a convenient method in automatic assembly. However, other methods may function as well, such as thermoforming, bayonet catches of different kinds, riveting, gluing, lugs and recesses, etc. Instead of a spring between the two plunger ele¬ ments, use can also be made of other elastic means, such as a piece of rubber or some other elastic material. Instead of the push rod being a separate component as in the embodiment illustrated above, it may comprise an integrated part of the movable plunger, but then it is preferably made of a non-magnetic material. The arrangement of turning lugs and matching turn¬ ing recesses would also be possible for other types of plunger devices and solenoid devices than those described above. It would also be possible that the two plunger ele¬ ments, instead of attracting each other, repel each other in case of too great a current. This would require a dif- ferent mutual positioning of the parts included in the plunger device than the one described above.

Claims: CLAIMS 1. A switch arrangement comprising a plunger device (21), a solenoid (40) and a body (39), said plunger device being adapted to extend through the solenoid (40) and be supported at its ends in said body and comprising a fixed plunger element (25), a movable plunger element (23, 24), which moves in a first direction in relation to the fixed plunger element when the plunger device is actuated, an elastic means (26), which is adapted to bias the movable plunger element in a second direction in relation to the fixed plunger element, and a plunger insulator (22), which essentially surrounds and keeps the fixed plunger element, the movable plunger element and the elastic means together so as to form a self- contained unit, c h a r a c t e r i s e d in that the plunger device ( 21 ) and the body ( 39 ) have matching engagement means (45, 47), which permit insertion of the plunger device into said body and releasable mounting of the plunger device by turning the same. 2. A switch arrangement as set forth in claim 1, wherein said engagement means comprise at least one lug (45) and at least one matching recess, said lug (45) being arranged on one of the plunger insulator (22) and the body (39 ) and the recess (47) in the other of the plunger insulator (22) and the body (39). 3. A switch arrangement as set forth in claim 1 or 2, wherein the plunger insulator (22) is injection-mould- ed of plastic in one piece. 4. A switch arrangement as set forth in claim 1, 2 or 3, wherein the plunger insulator (22) comprises a grip portion (27) at its one end. 5. A switch arrangement as set forth in any one of the preceding claims, wherein the plunger insulator (22) comprises a stop means (27), which defines an end posi- tion for the movable plunger element (23, 24) in said first direction (25). 6. A switch arrangement as set forth in claim 5, wherein the stop means comprises a bar (27) extending across one end (28) of the plunger insulator (22). 7. A switch arrangement as set forth in any one of the preceding claims, wherein the fixed plunger element (25) has retaining means (31) serving to retain it in the plunger insulator (22) upon introduction therein. 8. A switch arrangement as set forth in any one of the preceding claims, wherein the plunger insulator has, essentially in that part which is located between the movable plunger element and the fixed plunger element, at least one air outlet (36) but has essentially no air out- let in those parts which surround the fixed plunger ele¬ ment and the movable plunger element. 9. A method of mounting a plunger device, which com¬ prises a plunger insulator (22), a fixed plunger element (25), a movable plunger element (23, 24) and an elastic means (26), in a solenoid device (38), which comprises a solenoid (40) which is fixed in a body (39) having a first and a second hole, which are aligned with the sole¬ noid, c h a r a c t e r i s e d by the steps of mounting the plunger insulator, the fixed plunger element, the movable plunger element and the elastic means to a self-contained plunger device; introducing the plunger device into the solenoid (40) while matching engagement means (45, 47) of the plunger device and the body are kept aligned, such that a first end (30) of the plunger device extends through the first hole and a second end (28) of the plunger device extends through the second hole in the body (39); and fastening the plunger device releasably in the body (39) by turning the plunger device such that the matching engagement means are no longer aligned with each other. 10. A method as set forth in claim 9, wherein the self-contained plunger device is provided by the steps of introducing the movable plunger element (23, 24) into the plunger insulator (22) , so that it comes to occupy an end position defined by the plunger insulator; introducing the elastic means (26) into the plunger insulator ( 22 ) so that it comes to be applied against the movable plunger element (23, 24 ) ; and fastening the fixed plunger element ( 25 ) in the plunger insulator (22), such that the plunger insulator, the movable plunger element, the fixed plunger element and the elastic means together form a self-contained plunger device. 11. A method as set forth in claim 9 or 10, where- in the step of fastening the fixed plunger element in the plunger insulator comprises press-fitting of the fixed plunger element in the plunger insulator. 12. A method as set forth in any one of claims 9-11, wherein the step of introducing the movable plunger ele- ment comprises the introducing of a push rod (24) into the plunger insulator so that it comes to be applied against the movable plunger element.

Inventors: SJOESTEDT LENNART, SOEDERLUND PATRIK, SJOESTEDT, LENNART, SOEDERLUND, PATRIK
Applicants: ENPECE SIGMA AB
Application year: 1997
Main classification: H01H71
IPC codes: H01H71