Abstract:
The invention relates to a thermal link ( 1 ) for electrical appliances, comprising an insulating part ( 10 ) with electrical terminals ( 11 ) and contact springs ( 12 ) for providing electrical contact between said terminals ( 11 ), a fusible material insert ( 15 ) that acts as the thermal trip element and a transmission pin ( 13 ), which is displaceably mounted in the insulting part ( 10 ), one end of which engaging with the fusible material insert ( 15 ) and the other end with the contact springs ( 12 ). Said link is characterised in that the fusible material insert ( 15 ) is situated in a casing ( 141 ) that is configured as one piece with the heat transfer plate ( 14 ). The invention also relates to a method for producing a thermal link ( 1 ) comprising the following steps: the casing ( 141 ) for housing the fusible material insert ( 15 ) and the casings ( 144 ) that connect the heat transfer plate ( 14 ) to the insulating part ( 10 ) are drawn from the heat transfer plate ( 14 ); the fusible material insert ( 15 ) is inserted into the casing ( 141 ) and formed; the insulating part ( 10 ) is placed on the heat transfer plate ( 14 ) and connected in a positive fit to the graduated inner sections ( 107 ) of the inner cavities ( 108 ) by means of the casings ( 144 ).

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The present invention relates to a thermal link for electrical appliances, comprising an insulating part with electrical terminals and contact springs for producing an electric current path, a heat transfer plate, a fusible material insert as a thermal trip and a transmission pin of insulating material, which is displaceably mounted in the insulating part and engages at its one end with the fusible material insert and at its other end with a contact spring, and the biased contact spring pressing the pin downward after melting of the fusible material and thereby separating a contact of the contact spring. The present invention also relates to a method for producing such a thermal link. 
     Thermal links are known from the prior art, for example from DE 2826205 A1, where a fusible material is arranged inside a casing that is open at the top and bottom and is arranged on the heat transfer plate and in a recess of the insulating part. However, the many individual parts of such thermal links, comprising a heat transfer plate, a casing, a fusible material, an insulating part with a corresponding recess and a transmission pin, require a considerable assembly effort. Furthermore, when various fusible solders come into contact with oxygen, oxidation may cause their melting point to change. 
     The object of the present invention is therefore to provide a thermal link which overcomes the disadvantages of the prior art and can be produced at low cost with little assembly effort, the object of the present invention also being to provide a reliable method for producing a thermal link that is also suitable for large-scale production. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is achieved by the features of the invention. Advantageous embodiments are mentioned in the features of the description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawing: 
         FIG. 1   a  shows a schematic side view of a thermal link according to the invention as provided by one embodiment of the present invention; 
         FIG. 1   b  shows the thermal link from  FIG. 1   a  from above; 
         FIG. 1   c  shows a schematic section through the thermal link from  FIGS. 1   a  and  b  along the line A-A from  FIG. 1   b;    
         FIG. 1   d  shows a schematic plan view of a partial detail of a heat transfer plate of a thermal link from  FIGS. 1   a  and  b.    
         FIG. 2  shows a perspective exploded representation of a thermal link as provided by a further embodiment of the present invention; 
         FIGS. 3   a, b  and  c  show the heat transfer plate with the insert of fusible solder of the thermal link from  FIG. 2 ; 
         FIGS. 4   a  and  b  show the heat transfer plate with the fusible solder and the insulating part of the thermal link from  FIG. 2 ; 
         FIGS. 5   a  and  b  show the heat transfer plate with the mounted insulating part and with the transmission pin  13  of the thermal link from  FIG. 2 ; 
         FIGS. 6   a  and  b  show a suitable first terminal with a contact spring for a thermal link as shown in  FIG. 2 ; 
         FIGS. 7   a  and  b  show a suitable second terminal for a thermal link as shown in  FIG. 2 ; 
         FIG. 8   a  shows a perspective representation of a mounted thermal link from  FIG. 2  and  FIG. 8   b  shows a section through the thermal link from  FIG. 8   a;    
         FIG. 9  shows a perspective representation of a common heat transfer plate according to the invention for the link from  FIG. 1  and a temperature controller; 
         FIG. 10  shows a plan view of a thermal link and a temperature controller mounted on the heat transfer plate from  FIG. 9 ; and 
         FIG. 11  shows a modification of the embodiment of the insulating part from  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A thermal link according to the invention for electrical appliances comprises in particular an insulating part with electrical terminals and a contact spring for providing an electrical connection between the terminals, a fusible material insert as a thermal trip and a transmission pin, which is displaceably mounted in the insulating part and engages at its one end with the fusible material insert and at its other end with the contact springs, the fusible material insert being arranged in a casing that is in one piece with the heat transfer plate. The one-piece form of the casing and heat transfer plate according to the invention makes it possible for the thermal link to be assembled and produced at particularly low cost, the individual parts to be assembled for the final assembly of the thermal link being reduced considerably in comparison with the prior art. In particular, the casing can be drawn from the heat transfer plate during the production of the heat transfer plate and the fusible material can subsequently be pressed into the casing created, it being ensured that the fusible material has particularly effective thermal contact with the heat transfer plate and is only exposed in the upward direction. 
     Suitably formed around the casing in the heat transfer plate is an annular depression, which can likewise be provided in one operation with the drawing of the casing from the heat transfer plate. The annular depression surrounding the casing is particularly advantageous for receiving melted fusible material from the casing, so that it is ensured that, when the thermal link is tripped, no fusible material escapes to the outside or even gets to the contact springs and impairs the function of the thermal link or the electrical appliance. 
     One embodiment of the present invention provides that a thermal link according to the invention may suitably comprise an insulating part with two lateral foot parts in contact with the heat transfer plate, the bottom being at a distance from the heat transfer plate. The pin is suitably arranged in a through-hole of the insulating part and a circular recess is formed on the bottom of the insulating part, within which recess the hole is formed. The distance of the bottom from the heat transfer plate and the circular recess on the bottom of the insulating part in the area around the through-hole are suitably formed in a way corresponding to the casing such that the casing corresponds with its upper rim approximately to the recess in the bottom of the insulating part. This additionally provides space for any melted fusible material. 
     The inside diameter of the casing suitably corresponds approximately to the diameter of the transmission pin, so that the fusible material is largely enclosed, and protected from contact with oxygen and consequently protected from oxidation, not only by the casing and the heat transfer plate but also at the top by the transmission pin. 
     A further advantageous embodiment of the present invention provides that a thermal link according to the invention may also suitably comprise furthermore an insulating part with at least one further recess with an inner graduation, which corresponds to a casing drawn from the base plate, the upper rim of the casing engaging around the inner graduation in such a way that the heat transfer plate is firmly connected to the insulating part. Here, the heat transfer plate and the insulating housing are formed particularly advantageously in such a way that the heat transfer plate can be fitted with the insulating housing and the fusible solder from above, and the insulating housing can be fitted with the transmission pin and the terminals likewise from above. 
     The heat transfer plate of a thermal link according to the invention may also be advantageously formed in one piece with the base plate and/or the heat transfer plate of at least one other thermal link and/or a temperature switch, which provides further simplifications and cost advantages in assembly, including in the electrical appliance, and also has the advantageous effect of providing a sensing location for the temperature to be monitored that is the same for the link and the temperature switch. 
     A method according to the invention for producing a thermal link comprises in particular a heat transfer plate from which a casing receiving a fusible material insert and also at least one further casing for connecting the heat transfer plate to an insulating part are drawn, so that a heat transfer plate that can be fitted with components from above is provided. The heat transfer plate corresponds to an insulating part in which suitable recesses are provided, corresponding to the casing for receiving the fusible material insert and the casings for connecting the heat transfer plate to the insulating part. The fusible material insert is inserted into the casing for receiving it and, after that, the insulating part is placed onto the heat transfer plate and is connected to the insulating part with a form fit by way of the casings. After that, a transmission pin is inserted from above into the insulating housing, and the insulating housing is fitted with suitable terminals, likewise from above. The method according to the invention for producing a thermal link, with the heat transfer plate and the insulating part formed in a particularly advantageous manner such that the heat transfer plate and the insulating part can merely be provided with components from above, comprises just a few simple production steps and therefore is, in particular, also particularly inexpensive. 
     The method according to the invention for producing a thermal link also comprises in particular the stamping of the heat transfer plate to create in it a suitable first casing, receiving a defined volume of fusible material, and at least one further, second casing, forming a cup collar. After that, the fusible material insert is suitably introduced in the form of a ball and pressed into the first casing. After that, the insulating part is connected to the heat transfer plate with a form fit, in that the second casing, and suitably a further casing that likewise forms a cup collar on the heat transfer plate, enter the insulating part and are widened from above by means of a suitable tool, and advantageously a ball stamp, so that the casings come to lie around suitable undercuts of the insulating part. After that, a one-part insulating pin of a predetermined length is suitably introduced to the insulating part in such a way that the insulating pin rests on the fusible material insert of the heat transfer plate. 
     After that, suitable electrical terminals, to be precise firstly the terminal with the switching spring and then the terminal with the fixed contact, are fastened in the insulating part without rivets. This is suitably and advantageously performed by means of legs that are angled away from the terminals and have at their ends suitably formed and advantageously V-shaped clamps. The legs enter the insulating part likewise from above and are widened from the opposite side by a predetermined force and by means of a suitable tool in such a way that the clamps come to lie around undercuts in the insulating part, it advantageously being possible for the tool to be introduced from below through suitable slits in the heat transfer plate. 
     The present invention is described in detail below on the basis of the schematic drawings. 
       FIG. 1   a  shows a schematic side view of a thermal link  1  according to the invention, comprising electrical terminals  11  and an insulating part  10 , which is arranged with both its lateral foot parts  104  on a heat transfer plate  14 , which is formed in one piece with a casing  141  for a fusible material  15 , and  FIG. 1   b  shows the thermal link  1  from above. 
       FIG. 1   c  shows a schematic section through the thermal link  1  from  FIGS. 1   a  and  1   b  along the line A-A from  FIG. 1   b , comprising the insulating part  10 , the electrical terminals  11 , the contact spring  12 , a hole  101 , passing through the insulating part  10 , and the heat transfer plate  14 , with the casing  141  and the fusible material  15  arranged inside the casing, and also the transmission pin  13 , arranged inside the through-hole  101  and engaging at its one end with the fusible material insert  15  and at its other end with the contact spring  12 . Lateral graduations  105 , which correspond to fastening arms  143  extending from the heat transfer plate  14 , are suitably formed on the insulating part  10 , and the fastening arms  143  engage at their ends around the graduations  105 , so that the insulating part is firmly arranged on the heat transfer plate  14 . The insulating part  10  also has two lateral foot parts  104 , which stand on the heat transfer plate  14 , the bottom  102  being at a small distance from the heat transfer plate  14 . On the bottom  102  of the insulating part  10 , a recess  103  that corresponds to the casing  141  is also suitably formed in such a way that the upper rim of the casing  141  is arranged approximately in the recess  103 . 
       FIG. 1   d  shows a schematic plan view of a partial detail of the heat transfer plate  14  with the casing  141  and the annular depression  142 , surrounding the casing  141 , and the fusible material insert  15 , arranged inside the casing  141 . The bottom  102 , the foot parts  104 , the recess  103 , the depression  142  and the casing  141  are suitably. formed in such a way that it is ensured that, when the thermal link trips, no fusible material reaches the contact springs or escapes from the thermal link  1 . 
       FIG. 2  shows a perspective exploded representation of a thermal link as provided by a further embodiment of the present invention, comprising a heat transfer plate  14 , an insulating part  10 , a fusible material insert  15 , a transmission pin  13  and electrical terminals  11 . Formed in the base plate  14  is a casing  141  for receiving the fusible material insert  15 , which corresponds to the casing  141  of the first embodiment of the present invention described above. Also formed in the heat transfer plate  14  is at least one further casing  144 , which corresponds to a suitable recess of the insulating part  10 , which is described in detail below on the basis of  FIG. 5 . 
       FIGS. 3   a, b  and  c  show an enlarged representation of the heat transfer plate  14  with the casing  141  for receiving the fusible material insert  15 , which is suitably arranged midway between two casings  144  for connecting the heat transfer plate to the insulating part  10 . The fusible material insert  15  may be formed as a ball or as a piece of wire and is inserted from above into the casing  141  and stamped. 
     After that, the insulating part  10 , with its inner hole  101 , which corresponds to the fusible material insert  15  arranged in the casing  141 , and with the inner recesses  108 , which correspond to the casings  142 , is placed from above onto the heat transfer plate  14 . Suitable graduations  107  are formed in the inner recesses  108  of the insulating part  10 , so that the heat transfer plate  14  and the insulating part  10  are connected with a form fit, in that a stamp that is introduced into the recesses  108  from above is used to make the casings engage around the graduations  107 , which is best represented by the partial section of  FIG. 4   b.    
     After that, a suitable transmission pin  13  of a suitable insulating material is inserted likewise from above into the hole  101 , which is represented in  FIGS. 5   a  and  5   b.    
       FIG. 6   a  shows a suitable first electrical terminal  11  with a contact spring  12  and suitable fastening legs  111 , which is likewise inserted from above into the insulating part  10 , and  FIG. 6   b  shows the terminal  11  inserted under the biasing of the contact spring  12 , the fastening legs  111  being introduced from above into lateral recesses  109  of the insulating housing and fastening clamps  112  that are formed at the lower end of the legs  111  engaging around graduations that are formed on the lateral recesses  109 . It is clear that the terminal  11  can be suitably provided in mass production by means of pre-punched terminals hanging on a strip, the legs  111  being suitably bent and the contact spring  12  being riveted to the terminal  11 . The contact spring  12  is made of suitable electrically conductive material with a sufficiently constant resilient property up to a temperature of approximately 300° C. and suitably of roll-clad, silver-plated high-grade steel and is fitted in a biased manner, so that it is possible to compensate to the greatest extent for a tolerance of the insulating part  10  suitably consisting of ceramics. The heat transfer plate  14  suitably also comprises a fastening arm  143  and may also comprise suitable recesses for bending up the fastening clamps  112  from below by means of a suitable tool. 
       FIGS. 7   a  and  b  show a second electrical terminal  11 , which is formed in a way analogous to the first electrical terminal  11  and suitably without the contact spring with a fixed contact  16 , and is likewise inserted from above into the insulating part  10  and connected to the insulating part  10  with a form fit in a way analogous to the first electrical terminal  11 . 
       FIG. 8   a  shows a perspective representation of a mounted thermal link  1  according to the embodiment from  FIG. 2  and  FIG. 8   b  shows a section through the thermal link  1  from  FIG. 8   a  with the terminals  11 , the inserting part  10 , the heat transfer plate  14 , the transmission pin  13 , the fusible material insert  15 , the fastening casings  144 , the contact spring  12  and the fixed contact  16 . 
       FIG. 9  shows a perspective representation of a common base plate  14  according to the invention for the thermal link from  FIG. 1  and a further thermal link and/or a temperature switch and, in particular, a temperature switch  2  with a bimetallic element  20 . 
       FIG. 10  shows a plan view of a thermal link  2  and a temperature switch  2  that are mounted on a common heat transfer plate  14 . It is clear that a common heat transfer plate  14  according to the invention may also be formed analogously for a thermal link  1  according to the second embodiment of the present invention from  FIG. 2 . 
       FIG. 11  shows a modification of the embodiment from  FIG. 2  and a perspective exploded representation of a thermal link as provided by a further embodiment of the present invention, comprising a heat transfer plate  14 , an insulating part  10 , a fusible material insert  15 , a transmission pin  13  and electrical terminals  11 . The embodiment from  FIG. 11  corresponds to the embodiment from  FIG. 2 , with the difference that the insulating part  10  comprises lateral webs  109 ″, in which two continuous recesses  109 ′ for securing the legs  111  of the electrical terminals  11  are respectively formed. The embodiment from  FIG. 11  is particularly advantageous, since the legs  111  that are arranged in the recesses  109 ′ are held particularly securely by way of the bent-up clamps  112  on the underside of the webs  109 ″. 
     It is also clear that a thermal link  1  according to the invention may also comprise a combination of the features of the first and second embodiments of the present invention according to  FIGS. 1 and 2  that are described above. 
     LIST OF DESIGNATIONS 
     
         
         Thermal link  1   
         Insulating part  10   
         Hole  101   
         Bottom  102   
         Recess  103   
         Foot part  104   
         Outer graduation  105   
         Inner graduation  107   
         Inner recess  108   
         Lateral recess  109 ,  109 ′ 
         Lateral web  109 ″ 
         Electrical terminals  11   
         Leg  111   
         Clamp  112   
         Contact spring  12   
         Pin  13   
         Heat transfer plate  14   
         Casing  141   
         Depression  142   
         Fastening arm  143   
         Casing  144   
         Fusible material insert  15   
         Fixed contact  16   
         Temperature switch  2   
         Bimetallic element  20