Abstract:
According to the invention a switching device ( 11 ) for an electric heating device is provided with a rod-shaped temperature sensor ( 15 ) formed by a ceramic rod ( 17 ) and an extension tube ( 16 ). The temperature sensor ( 16 ) operates a snap-action switch ( 22 ) located in a base ( 12 ) by means of an actuator separate from the said switch, which has at least one actuating part ( 41 ), which is loaded in the actuating direction by a leaf spring ( 34 ), the actuating part ( 41 ) and leaf spring ( 34 ) being in one piece. In a further development of the invention the leaf spring ( 34 ) or actuating part ( 41 ) can be a receptacle for an adjusting device, preferably an adjusting screw ( 38 ).

Description:
FIELD OF APPLICATION AND PRIOR ART 
     The invention relates to a switching device for an electric heating device with a substantially rod-shaped temperature sensor, which comprises a tube and a longitudinal element located therein, the tube and the longitudinal element having different thermal expansion coefficients, and with at least one switch located in a base and operated by the temperature sensor and which is provided with a switch spring, particularly a catch spring, the temperature sensor tripping the switch by means of an actuator separate from the switch spring, the actuator having at least one actuating part, which is loaded by a spring element in or counter to the actuating direction. 
     A switching device of the aforementioned type is e.g. known from DE-OS 28 39 161. The latter has as an actuator a unilaterally mounted lever through which is guided a rod-like longitudinal element. Fixing takes place by means of a helical spring supported on the base and which presses the lever against a nut guided by means of a screw thread at the end of the rod. The nut running on the rod screw thread serves as an adjusting device. In the lever are inserted two actuating pins, which in each case point in opposite directions and operate two switches. 
     PROBLEM AND SOLUTION 
     The problem of the invention is to provide such a switching device, which obviates the disadvantages of the prior art and in particular reduces assembly costs and permits reliable operation. 
     This problem is solved by the features of claim  1 . Advantageous developments of the invention form the subject matter of the subclaims. 
     An inventive, one-part construction of the at least one actuating part with the spring element in particular facilitates assembly, but other advantages can also result therefrom. As a result of the one-part nature it is possible to save at least one fixing or mounting means, particularly for at least one actuating part. A fixed association or connection between the actuating part and the spring element increases the mechanical reliability of the switching device, because a disadjustment is avoided. 
     An actuator can be supported in leaf spring-like manner on the base, particularly with both end regions for increasing the spring action. The longitudinal element can act on the actuator, which preferably has at least one actuating part for bearing on the switch. 
     Preferably the spring element and the at least one actuating part and/or the actuator are rough-worked from a single material piece. A particularly simple construction can be rough-worked from a flat material and correspondingly shaped by bending. Another possibility is e.g. a fixed connection by bonding or welding and optionally also by extrusion. This in particular covers a one-part configuration allowing the objects in the fitted state to act as a single part, in which the individual parts have in at least one other direction than the assembly direction a positive engagement. 
     The spring element is preferably constructed as a compression spring in order to ensure precise working. The spring element is preferably leaf spring-like. A leaf spring is advantageously mounted with both end regions or ends in the base, particularly by engagement on engagement areas brought about by spring tension. A leaf spring advantageously runs substantially at right angles to the extension direction of the temperature sensor, so that it is possible to avoid undesired shear forces or the like. 
     In a particularly preferred manner the temperature sensor engages or bears roughly centrally on the leaf spring, so that there is a uniform loading thereof. The actuating part advantageously runs in the vicinity of the temperature sensor and is in particular positioned roughly centrally on the leaf spring. 
     The actuating part advantageously has two legs projecting from the spring element for bearing on the switch and it is in particular roughly U-shaped. The U-shaped legs are preferably twisted by approximately 90° to the longitudinal extension of the leaf spring. The legs can in each case be led to different switches, but preferably engage on the same switch. The temperature sensors can directly point into or run into the U-shape. 
     Preferably a mechanical connection between the temperature sensor and the actuator is an adjustable transfer means, particularly an adjusting device. The adjusting device advantageously engages on the temperature sensor, particularly on the end thereof. The adjusting device preferably engages on the longitudinal element, which can project over the tube. 
     A preferred bearing possibility for the adjusting device is on the actuator and is in particular fixed thereto. In one construction possibility it can engage on or be received in the centre of a U-shaped actuating part. As another advantageous possibility the spring element has a receptacle for the adjusting device, particularly in the case of a one-piece construction of spring element and actuating part. 
     A receptacle for the adjusting device can be a thread for an adjusting screw, which preferably runs in the direction of the longitudinal element and/or in the actuating direction of the switch. The adjustment precision can be varied by modifying the pitch of the adjusting screw. 
     The transfer of the actuating force can be through the switch and/or switch spring, particularly through a corresponding opening, which for stability reasons should not be open to the rim. As a function of the assembly type the longitudinal element can pass through one side or the adjusting device or screw on the other. 
     Advantageously the longitudinal element is at least partly constructed as a rod and is in particular completely in the form of a rod. It is possible in the case of a temperature sensor, which covers differently heatable heating areas of a heating device, to associate with in each case one heating area a rod area or a separate rod with characteristics adapted thereto. The rods are then successively placed in the tube, so that their individual extensions can be summated to an overall extension. However, in particularly preferred manner the longitudinal element is constructed as a one-piece rod. Advantageously the longitudinal element has a lower expansion coefficient than the tube and e.g. ceramic or glass can be used as its material. 
     According to an embodiment the at least one actuating part can substantially embrace the rod and preferably engages externally in the end region thereof. It advantageously forms a guide for the rod, particularly for securing the rod against undesired movement transversely to the actuating direction. A positive connection between the actuating part in a plane at right angles to the actuating direction can prevent an undesired, mutual shifting of the parts. A guide can be constructed as an inward curvature of the at least one actuating part towards the rod. The inward curvature is preferably provided with a recess corresponding to the external diameter of the rod in or along which runs said rod. Guidance by an adjusting screw can be in the form of a tubular portion engaging over the rod, e.g. in the form of a bore in the end face of the adjusting screw. 
     An overpressure preventer for the switch can be implemented by the actuating part having a certain elasticity in the actuating direction. This can be obtained by at least one S-shaped or Z-shaped bend, preferably as an inward curvature in the form of a spring bend or elbow, which can be combined with the above-described guide. 
     Preferably the leaf spring in the base is mounted in a reception chamber, which has in particular bearing areas for the leaf spring pointing counter to the actuating direction. The reception chamber can widen in the leaf spring bending direction as from the bearing areas. The leaf spring preferably engages on through base walls, which serve as bearing areas and limit widening. Preferably the widening is roughly symmetrical, particularly symmetrical to a plane running along the actuating direction. A mobility of the leaf spring in the reception chamber can be obtained in that at the point of maximum width the reception chamber exceeds the leaf spring length. Thus, on relaxing, the leaf spring can expand laterally. An insertion of the leaf spring is also simpler if, in the untensioned state, it has a certain clearance in the reception chamber. 
     For thermal, strength and insulating reasons, a ceramic material, e.g. steatite, is suitable as the material for the base. The base can substantially form the casing for the switching device and have all the walls and supports and it is merely necessary to cover it by a simple, substantially flat cover. 
     These and further features can be gathered from the claims, description and drawings and the individual features, either singly or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions for which protection is hereby claimed. The subdivision of the application into individual sections and the subtitles in no way limits the general validity of the statements made thereunder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in greater detail hereinafter relative to two preferred embodiments and the attached drawings, wherein show: 
     FIG. 1 A plan view of a switching device according to the invention with a leaf spring, which has two legs operating a switch as the actuating part. 
     FIG. 2 An oblique view of a variant of the leaf spring of FIG. 1 with legs, which have an inwardly drawn curvature for guiding a rod of the temperature sensor. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIG. 1 shows a switching device  11  according to the invention, which has a base  12 , which contains or carries all the components. 
     The base  12  can be fixed in not shown manner, e.g. by means of twisting tongues and engagement cams, on a sheet metal tray rim  13  (shown in broken line form) of a sheet metal tray containing a radiant heater. A rod-shaped temperature sensor  15  projects in known manner at least partly and preferably completely over the heater. 
     The temperature sensor  15  comprises an outer tube  16  and a rod  17  located therein. In the represented embodiment the rod  17  is made from ceramic material and the outer tube  16  from a metal with a much higher expansion coefficient. The upper end of the outer tube  16  has a transversely projecting collar  18 , to which it is firmly connected and which engages in lateral reception slots  19  in order to fix the tube  16 . In the represented embodiment the rod  17  projects somewhat over the collar  18  of tube  16 . At the not shown end of the temperature sensor  15  the tube  16  is closed, the rod  17  either being applied or fixed to the tube end. 
     In a free space above the rod end  21  is located a snap-action switch  22 , whereof a free end  23  is fixed to a switch support  24 . The subsequently described snap effect of the snap-action switch  22  is brought about by a spring clip  27  running centrally between two spring legs  26  and which is supported on a bearing  28  of the switch support  24 . At its other, free end the snap-action switch  22  carries an upwardly directed switching contact head  30 , which faces a countercontact head  32 , which is fitted to a plug-in connecting lug  37 . The switch support  24  is fixed both by engagement of the area carrying the free end  23  of the snap-action switch  22  in a matching recess of the base  12  and by the path of a connecting lug  31  through a passage in the base  12 . Together with a second connecting lug  40  and a second plug-in connecting lug  43  connected thereto, the connecting lug  31  is used for the electrical contacting of a not shown heating means by means of the connecting lugs. The switch  22  interrupts the connection between the plug-in connecting lug  37  and connecting lug  31 , the interruption state being shown in FIG.  1 . 
     Both the switch support  24  and also the snap-action switch  22  have a covering opening located in the extension of the rod  17 . On either side of said opening the snap-action switch  22  has two switch protuberances  29  produced by inward curvature. 
     The space in which the snap-action switch  22  is located passes outwardly into a reception chamber  33  for a leaf spring  34  as a spring element. 
     Towards the outside an extension  35  is connected to the reception chamber  33  and into it is bent the leaf spring  34 . The widening is approximately triangular, symmetrical to the longitudinal axis of the rod  17  and issues into an opening  36 . 
     An adjusting spring  38  is centrally mounted in the leaf spring  34 , preferably by a thread fitted in said spring  34 . The upper end of the adjusting screw  38  is accessible through the opening  36 , even when the base  12  is closed, for adjusting the switching device  11 . The screw tip  39  engages on the rod end  21  and has a rounded or spherical construction. 
     Alternatively the screw tip  39  can engage somewhat with a tubular portion as a guide over the rod end  21  in order to avoid slipping off. It is also possible to have a pin or peg on the screw tip  39 , which engage in a depression on the face of the rod end  21  and exert the same action. 
     On both sides of the adjusting screw  38  the leaf spring  34  has an outgoing, downwardly bent leg  41  as an actuating part. The lower edge  42  of the legs  41  engage on the switch protuberances  29  of the snap-action switch  22  in the switching state shown. 
     Function 
     The switching device shown in FIG. 1 essentially functions as follows: 
     Through the tensioned leaf spring  34  the adjusting screw  38  presses the rod  17  against the end of the outer tube  16 . When the heating means is in the cold state the bending of the leaf spring  34  is such that the legs  41  or the lower edge  42  are located well above the snap-action switch  22  or the switch protuberance  29 . The free end  23  of the snap-action switch  22  is fixed to the switch support  24  in such a way that the spring legs  26  are above the engagement of the spring clip  27  on the bearing  28  and the switching contact head  30  engages on the countercontact head  32 . 
     If the heating means is now put into operation, it evolves heat through which the outer tube  16  expands much more strongly than the rod  17 , so that the rod end  21  migrates from the leaf spring  34  towards the collar  18 . As a result the leaf spring  34  can relax downwards and the legs  41  move towards the snap-action switch  22 . At a specific settable temperature with a corresponding expansion of the outer tube  16  it is possible to precisely set the point by twisting the adjusting screw  38  at which the legs  41 , by engaging on the switch protuberances  29 , have pressed the spring legs  26  on the bearing  28 , accompanied by the engagement of the spring clip  27 . As this is the switching or snapping over point of the snap-action switch  22 , the spring clip  27  suddenly presses the end with the switching contact head  30  away from the countercontact head  32  in the downwards direction. The switch is consequently tripped at a settable temperature. One application example is an excess temperature preventer for a radiant heating under a glass ceramic hob, which is intended to respond e.g. at a temperature of approximately 650° C. By opening the switch the power supply to the heating device is interrupted and the risk of overheating the glass ceramic is avoided. As a result of the following cooling of the outer tube  16  it contracts again, presses the rod  17  upwards, which once again moves the leaf spring  34  and consequently the legs  41  upwards and away from the switch protuberances  29 , so as to bring about a reclosing of the switch  22 . 
     A variant of the legs  41  of leaf spring  34  is shown in FIG.  2 . The legs  41  emanating from the substantially elongated, rectangular leaf spring  34  have in their path an inward curvature  44 , which is roughly spring elbow-like. Behind the inward curvature  44  the legs  41  move apart again, but with a smaller mutual spacing than upstream of the curvature  44 . Inward curvatures  44  are in particular advantageous in those constructions in which the rod  17  extends between the legs  41 . 
     To the inner edge  45  of the inward curvature  44  is fitted a recess  46 , which is arcuate in the rod direction and in which the rod  16  is guided. In the examples shown the recesses  46  are sufficiently deep for the inner edges  45  of the curvature  44  to approach one another to within half a rod diameter. This permits an adequate embracing of the rod  16 , which secures the rod transversely against a movement with respect to the legs  41 . The recesses  46  can engage with a certain force on the rod  17 , because a relative movement between rod and legs only occurs during the adjustment process. 
     Another advantage of the spring elbow-like inward curvatures  44  is that is possible to have a certain spring action between the adjusting screw  38  or the upper part of the legs  41  connected rigidly thereto in the rod direction and the lower portions of the legs  41  or the lower edges  42 . This can prevent an overpressing of the snap-action switch  22  or at least partly reduce the same. However, in order to ensure a precise switching, spring action must not be too weak. 
     In the centre of the leaf spring  34  is provided a threaded nozzle  48  drawn downwards from the spring and having the reception thread for the adjusting screw  38 .