Abstract:
An electric appliance is described which has a casing composed of two identically built casing shells. A spring locking hook for the snap-on mount on a mounting rail is integrated into each of the casing shells, which are assembled in mirror inversion to one another, yielding a simple, inexpensive and easy-to-assemble design composed of only a few parts.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an electric appliance having a casing composed of two identically designed casing half shells mounted in mirror inversion to one another. 
     BACKGROUND INFORMATION 
     An electric appliance composed of two identically designed casing half shells is. 
     An appliance according to the definition of the species is described in from German Utility Model 296 06 759 U1, which describes a multipart casing in modular design to accommodate a circuit board. This is intended for a multipart casing for low-voltage switchgear, such as time relays, thermistor protective gear, for accommodating a circuit board. The casing here is divided into upper and lower casing parts parallel to the mounting plane. The circuit board is designed with stair-step gradations along two opposite edges and is equipped with cable connectors for connecting screw-type terminals designed in block form in the area of the stair-step gradations. In addition to contact pins, the cable connectors also have mounting pins, optionally designed as hook-shaped locking mounting pins. 
     German Patent 30 26 247 C2 describes a casing that can be lined up for mounting on a mounting rail. A circuit board having electric connecting elements arranged on its edges can be inserted into the casing. The connecting elements project partially out of the openings in the casing. The casing here is divided perpendicular to the mounting direction in the longitudinal direction of the casing. 
     SUMMARY 
     An object of the present invention is to provide an electric appliance of the type described above by creating a casing having a simple, inexpensive design that is easy to assemble and has only a few parts parts, with the mounting accomplished by snap-on attachment without any impairment due to the usual distortion of the casing shells. This object is achieved in that the casing is composed of two identically built casing shells mounted in mirror inversion to one another. The separation joint formed by the two casing shells here does not pass through the integrally molded parts provided for the snap-on mount, so that distortion of the casing shells does not cause any problems in assembly. 
     An especially advantageous refinement of the present invention is achieved when the two casing shells are joined together by integrally molded catch elements. 
     An especially simple embodiment minimizing the number of details is achieved by implementing the snap-on mount by two spring locking hooks, one of which is integrated into each of the casing shells. 
     The embodiment having two identically designed casing shells that can be mounted in mirror inversion to one another can be achieved when the two casing shells in the mounted state form a separation joint which passes through the axes of symmetry of two opposing side walls and outside the spring locking hook. 
     An especially advantageous embodiment of the terminals, in particular their connection, is achieved when a circuit board having at least two terminal insulators is mounted in the interior of the casing, the terminal insulators being snapped into the circuit board and their terminal lugs belonging to the terminals being electrically connected to the circuit board by soldering. 
     In addition, it is advantageous when terminals are integrated into the electric appliance and when, for adding additional terminals for expansion, a terminal block can be locked onto in each case one side wall of the two casing shells, the terminal block having terminals into which slide the terminal lugs of terminal insulators projecting out of the casing when locked together. 
     Another advantageous embodiment of the present invention is achieved when the switchgear has on the front side at least one turning knob as an adjusting element having an adjusting security device, where a mechanically coded plate can be locked onto the turning knob, with the mechanical coding of the plate corresponding to a certain position of the turning knob. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing a casing composed of two identically built casing shells. 
     FIG. 2 is a perspective view of an electric appliance according to the present invention in a partially opened state. 
     FIG. 3 is a perspective view of a terminal insulator. 
     FIG. 4 is a side view of the terminal insulator according to FIG.  3 . 
     FIG. 5 is a perspective view of a plate used as the adjusting security device. 
     FIG. 6 is a perspective view of an electric appliance having a front cover that can be sealed. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows two identically built casing shells  1  arranged in mirror inversion to one another, assembled by catch elements  3 ,  4  on their edges to form a casing  2  of an electric appliance according to the present invention. Catch elements  3 ,  4  are composed of integrally molded locking hooks  3  and matching recesses  4 . To stabilize assembled casing  2  and to simplify assembly, casing shells  1  have webs  5  on their edges, facilitating assembly because of their guidance function while also having a stabilizing effect because of the overlapping with side walls of in each case the other casing shell  1 . A spring locking hook  6  is integrally molded on each of the side walls of casing shells  1  forming the rear wall of casing  2 . These spring locking hooks are used for snap-on mounting of casing  2  on a mounting rail and permit dismantling without the use of a tool. Spring locking hook  6  which is integrated into casing shell  1  is dimensioned with respect to its force-strain characteristic so that the initial stress in the engaged state is sufficient to securely fix the appliance at defined maximum accelerations with a defined maximum appliance weight. 
     The separation joint of both casing shells  1  in the assembled state passes through the axes of symmetry of two opposing side walls  7  and  8  and on the outside along spring locking hooks  6 . 
     FIG. 2 shows a perspective view of the electric appliance according to the present invention, with one casing shell  1  and a front cover  9  which extends over the two casing shells  1  in the assembled state having been removed. A circuit board  10  belonging to the electric appliance and having a plurality of terminal insulators  11  mounted on its edges has been inserted into casing shell  1  shown here. Terminal insulators  11  are each designed as 3-pin devices, i.e., they each have three terminal lugs  12  having extruded insulation. For assembly, terminal insulators  11  (see also FIGS. 3 and 4) are first snapped into circuit board  10  and then soldered. In assembly of circuit board  10  in casing shells  1 , terminal lugs  12  of terminal insulators  11  contacted with circuit board  10  in this way slide into clamping cages  13 , which are just indicated here and are in turn inserted into suitably designed pockets in casing shells  1 . Terminal lugs  13  of terminal insulators  11  adjacent to spring locking hook  6  project out of casing  2  at the side and can be used for expanding by additional terminals, so that terminal blocks  15  are locked in this area of casing  2 . In this way, the usual 6-pin appliances can be expanded to 12 pins. 
     Casing  2  can be covered by a cover  16  on the front side. After positioning cover  16 , terminal screws (not shown) belonging to terminals on the casing are mounted from the outside through screw holes  17  and secured against loss by integrated catches  18  (not shown here) in the area of screw holes  17 . 
     Terminal insulators  15  are designed symmetrically according to FIGS. 3 and 4, permitting a 180° offset installation in various installation positions on circuit board  10 . Thus, only a single embodiment of a terminal insulator  11  is sufficient to cover all applications. 
     Adjusting elements operated by turning knobs  19  are provided on the front side of the electric appliance according to FIG.  2 . Turning knobs  19  have mechanical codings  20  whose position changes accordingly with the angle of rotation of the respective turning knob  19 . Through appropriately mechanically coded plates  21 , which can lock onto the mechanical codings of turning knobs  19  according to FIG. 5, turning knobs  19  can be protected from unintentional adjustment. The adjustment value or function corresponding to the rotational position is applied in plain text or in graphic symbols to each plate  21 . Due to the mechanical coding between turning knob  19  and plate  21 , a certain plate  21  can be engaged only when turning knob  19  is in the matching position. Thus, it is possible to achieve a coding among several appliance variants through different positions of catches  22 . This implements in a simple and inexpensive manner the pure function setting by turning knobs  19 , with the additional function of securing the adjustment and providing a visible correlation between set value and function in plain text and graphic symbols. 
     The single adjustment of turning knobs  19  can also be performed through a cover, e.g., a transparent injection molded part  23  according to FIG.  6 . Cover  23  can be sealed by a locking part  24  which is hooked in the casing. 
     Although the present invention is explained with reference to the embodiment illustrated in the accompanying drawing, it should be recalled that the intention is not to limit the present invention to only the embodiment illustrated here, but instead all possible revisions, modifications and equivalent arrangements are possible.