Abstract:
Provided is a method for manufacturing an electrically insulating support for an electromechanical switch. In some embodiments, the presently disclosed method includes manufacturing at least first and second portions of the support with respectively first and second plastics having different temperature heat resistances and manufacturing the support as a single piece by at least one of an overmolding process and a multi-material injection process. In some embodiments, the electrically insulating support is manufactured according to the method for manufacturing an electrically insulating support. Also provided is a method for manufacturing an electromechanical switch, which in some embodiments includes manufacturing an electrically insulating support according to the presently disclosed method for manufacturing an electrically insulating support and attaching electrically conductive elements to different regions thereof. Also provided is an electromechanical switch manufactured according to the presently disclosed method.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of European Patent Application EP15382404, filed Jul. 31, 2015, the disclosure of which is incorporated by reference herein in its entirety 
       TECHNICAL FIELD 
       [0002]    The present invention generally concerns, in a first aspect, to a method for manufacturing an electrically insulating support for an electromechanical switch, comprising manufacturing different portions with plastics having different temperature heat resistances, and more particularly to a method comprising manufacturing the support as a single piece by at least an overmolding process and/or a multi-material injection process. 
         [0003]    A second aspect of the invention concerns to a method for manufacturing an electromechanical switch, comprising manufacturing an electrically insulating support according to the method of the first aspect of the invention and attaching electrically conductive elements to different regions thereof. 
         [0004]    A third aspect of the invention relates to an electrically insulating support manufactured according to the method of the first aspect of the invention. 
         [0005]    A fourth aspect of the invention concerns to an electromechanical switch manufactured according to the method of the third aspect of the invention. 
       BACKGROUND 
       [0006]    Different electrically insulating supports for electromechanical switches and methods for their manufacturing are known in the art. 
         [0007]    Some of them comprises manufacturing the entire body of the support from only one insulating material, generally a plastic, while other combine different types of plastic, such as thermoplastics, into the same support. 
         [0008]    One of said proposals is disclosed in International Application WO9960315, which describes a support comprising two different types of thermoplastics: one of which is electrically insulating and the other one is electrically conductive. 
         [0009]    EP751865B1 discloses a housing for an electrical switch and a method for its manufacturing, where the housing is made from to thermoplastic components which are welded to one another. The thermoplastic components have different transmission and absorption coefficients for the spectrum of a laser beam, in order allow the laser welding. 
         [0010]    Some low and medium voltage applications, such as the ones associated to electrical circuits of a household electrical appliance (such as an oven) require the use of electromechanical switches having electrically insulating supports with portions withstanding different temperatures. These supports are conventionally manufactured from only one material, such as a thermosetting material, selected to withstand the highest possible temperature, thus increasing the cost of such a support. 
         [0011]    None of the above mentioned patent documents discloses selecting the different thermoplastic components to have different temperature heat resistances. 
         [0012]    However, there is a patent document which discloses such a thermoplastics selection based on temperature heat resistance criteria. Said patent document is EP0484747, which discloses a puffer switch, for high voltage applications, comprising a rotor assembly inserted into a shell secured between a pair of stationary contact supports, where depending on the temperature to withstand some parts are made from a high or a low cost thermoplastic or from a thermosetting plastic. 
         [0013]    EP0484747 does not disclose different portions of the same part being formed from different plastics having different temperature heat resistances, nor to manufacture the entire switch support into only one piece made of different plastics having different temperature heat resistances. 
         [0014]    It is, therefore, necessary to provide an alternative to the state of the art which covers the gaps found therein. 
       SUMMARY 
       [0015]    To that end, the present invention relates, in a first aspect, to a method for manufacturing an electrically insulating support for an electromechanical switch, comprising:
       selecting and providing a first plastic having a first temperature heat resistance and a second plastic having a second temperature heat resistance, said first temperature heat resistance being higher than said second temperature heat resistance, wherein at least said second plastic is a thermoplastic; and   manufacturing at least first and second portions of the electrically insulating support with respectively said first and second provided plastics.       
 
         [0018]    Contrary to the known methods, particularly contrary to the method used for manufacturing the high voltage switch support disclosed in EP0484747, the method of the first aspect of the invention comprises, in a characteristic manner, manufacturing the electrically insulating support as a single piece by at least one of:
       an overmolding process, comprising manufacturing at least said first portion and then manufacturing at least said second portion by overmolding at least some regions of said first portion with at least said second plastic, or vice versa; and   a multi-material injection process, comprising simultaneously manufacturing and joining at least said first and second portions, and/or other portions of the electrically insulating support also having different temperature heat resistances.       
 
         [0021]    Depending on the embodiment, the first plastic is also a thermoplastic or a thermosetting plastic. 
         [0022]    For an embodiment, the cited manufacturing of said portions comprises performing the above mentioned plastics selection and configuring, sizing and arranging said portions with respect to each other, at least by selecting the size and shape of moulds used for said overmolding and/or multi-material injection processes, based on thermal conduction heat transfer criteria. 
         [0023]    For an embodiment, said multi-material injection process is a multi-material co-injection process. 
         [0024]    The method of the first aspect of the invention comprises, for an embodiment, selecting said second plastic to withstand at least the highest temperature value reached at a joining region of the second portion with the first portion, said highest temperature value being calculated using said thermal conduction heat transfer criteria. 
         [0025]    For an embodiment, the method of the first aspect of the invention comprises selecting the first and the second plastics based on chemical bonding affinity criteria. For this embodiment, none of the plastics is a thermosetting plastic, as that kind of plastics cannot be chemically bonded. 
         [0026]    According to an embodiment, the method of the first aspect of the invention comprises chemically bonding and/or mechanically bonding the cited portions of the electrically insulating support. 
         [0027]    For another embodiment, the method of the first aspect comprises selecting and providing a third plastic having a third temperature heat resistance higher than said second temperature heat resistance, and manufacturing the electrically insulating support as a single piece including a third portion made with said third plastic into said overmolding and/or injection process. 
         [0028]    Depending on the embodiment, the third temperature heat resistance of the third plastic is lower, equal or higher than the first temperature heat resistance. 
         [0029]    A second aspect of the invention relates to a method for manufacturing an electromechanical switch, comprising:
       manufacturing an electrically insulating support according to the method of the first aspect of the invention;   providing at least a first, a second and a third electrically conductive elements configured and arranged such that the third electrically conductive element selectively connects the first and second electrically conductive elements; and   attaching the first and the second electrically conductive elements respectively to:
           two separated regions of said first portion, or   one to the first portion and the other to a third portion made of a plastic having a third temperature heat resistance higher than the second temperature heat resistance, said first and third portions being distanced by the second portion.   
               
 
         [0035]    As stated above, depending on the embodiment, the third temperature heat resistance of the third plastic is lower, equal or higher than the first temperature heat resistance. This is useful, for example, for manufacturing a switch where, although both the first and the third portions are attached to respective electrically conductive elements and, therefore, in use, submitted to the heating caused by the circulation of electrical current there through, one of said first and third portions is submitted to a lower ambient temperature than the other one, for example because it is placed in a refrigerating chamber. Thus, said refrigerated portion does not need to withstand the same high temperature than the other one, and can, therefore, be made of a plastic having a lower temperature heat resistance. 
         [0036]    A third aspect of the invention concerns to an electrically insulating support for an electromechanical switch, manufactured as a single piece according to the method of the first aspect of the invention. 
         [0037]    For an embodiment, the electrically insulating support of the third aspect of the invention is manufactured according to the above described embodiment of the method of the first aspect comprising manufacturing the electrically insulating support as a single piece including a third portion made with a third plastic, wherein the first and third portions are distanced by the second portion. 
         [0038]    A fourth aspect of the invention relates to an electromechanical switch manufactured according to the method of the second aspect of the invention. 
         [0039]    For an embodiment, the electromechanical switch of the fourth aspect of the invention is configured, arranged and adapted for low or medium voltage applications. 
         [0040]    According to another embodiment, the electromechanical switch is configured, arranged and adapted for withstanding a high number of switching actions per use of the electrical circuit into which is interconnected. For a variant of said embodiment, said electrical circuit is a thermostat. 
         [0041]    For a further embodiment, the electromechanical switch is configured, arranged and adapted for being connected into an electrical circuit of a household electrical appliance, such as an oven. 
         [0042]    Generally, but not exclusively, the electromechanical switch of the fourth aspect of the invention is a manual switch. 
         [0043]    For another embodiment, the electromechanical switch of the fourth aspect of the invention is an automatic switch. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    The previous and other advantages and features will be more fully understood from the following detailed description of embodiments, with reference to the attached drawings, which must be considered in an illustrative and non-limiting manner, in which: 
           [0045]      FIGS. 1A and 1B  are respectively a side view and a perspective view of the electrically insulating support of the third aspect of the invention, for an embodiment; 
           [0046]      FIGS. 2A and 2B  are respectively a side view and a perspective view of the electromechanical switch of the fourth aspect of the invention, for an embodiment, including the support of  FIGS. 1A and 1B ; 
           [0047]      FIGS. 3A and 3B  are respectively a side view and a perspective view of the electromechanical switch of the fourth aspect of the invention, for another embodiment, including also the support of  FIGS. 1A and 1B ; 
           [0048]      FIGS. 4A and 4B  are respective top and a bottom perspective views of the electrically insulating support of the third aspect of the invention, for another embodiment; 
           [0049]      FIGS. 5A and 5B  are respective top and a bottom perspective views of the electromechanical switch of the fourth aspect of the invention, for an embodiment, including the support of  FIGS. 4A and 4B ; 
           [0050]      FIGS. 6A and 6B  are respective top and bottom perspective views of the electrically insulating support of the third aspect of the invention, for a further embodiment; 
           [0051]      FIGS. 7A and 7B  are respective top and a bottom perspective views of the electromechanical switch of the fourth aspect of the invention, for an embodiment, including a support similar to the one of  FIGS. 6A and 6B ; 
           [0052]      FIGS. 8A and 8B  are respectively a side view and a perspective view of the electrically insulating support of the third aspect of the invention, for an embodiment which differs from the one shown in  FIGS. 1A and 1B  in that only two plastic portions are included in the support; 
           [0053]      FIG. 9  is a graph showing the temperature distribution of the electrically insulating support of the third aspect of the invention, for an embodiment where the support is made of polyamide; 
           [0054]      FIGS. 10A and 10B  are respectively a side view and a perspective view of the electromechanical switch of the fourth aspect of the invention, for another embodiment, including also the support of  FIGS. 1A and 1B , constituting a toggle actuator switch; 
           [0055]      FIGS. 11A and 11B  are respectively a side view and a perspective view of the electromechanical switch of the fourth aspect of the invention, for another embodiment, including also the support of  FIGS. 1A and 1B  and also constituting a toggle actuator switch, slightly different to the one of  FIGS. 10A and 10B ; 
           [0056]      FIGS. 12A and 12B  are respectively a side view and a perspective view of the electromechanical switch of the fourth aspect of the invention, for another embodiment, similar to the one of  FIGS. 3A and 3B , but for a metallic bridge constituting a flexible switching element; and 
           [0057]      FIGS. 13A and 13B  show a further embodiment of the electromechanical switch of the fourth aspect of the invention, by means of a side view and a perspective view, where the switch constitutes a rocker switch. 
       
    
    
     DETAILED DESCRIPTION 
       [0058]    The appended Figures show different embodiments of the one-piece electrically insulating support and of the electromechanical switch of the present invention, from simple designs to more elaborated ones, as described below. 
         [0059]    Particularly,  FIGS. 1A and 1B  show a simple electrically insulating support comprising three portions: a first portion  2 , a second portion  1 , and a third portion  12 , where the second portion  1  is arranged between the other two portions  2  and  12  and has a lower temperature heat resistance, but high enough to withstand the temperature to be present at the joining regions with portions  2  and  12 , which is estimated based on thermal conduction heat transfer criteria. 
         [0060]      FIGS. 2A, 2B, 3A, and 3B  show two different embodiments of the electromechanical switch of the fourth aspect of the invention, both including the support of  FIGS. 1A and 1B , where two metallic terminals  5   a  and  5   b  are respectively attached to first  2  and third  12  portions, contacting and trapping respective metallic plates  3   a  and  3   b  which are selectively connected to one another through a movable metallic bridge  4 , upon the orthogonal actuation of vertical actuator  7 , for the embodiment of  FIGS. 2A, 2B , or rotatory actuator  6 , for the embodiment of  FIGS. 3A and 3B . For the embodiment of  FIGS. 2A and 2B  only one end of the metallic bridge  4  is movable, particularly that contacting metallic plate  3   b , while for the embodiment of  FIGS. 3A and 3B  both ends of the metallic bridge  4  are movable. 
         [0061]      FIGS. 12A and 12B  show another embodiment of the electromechanical switch of the fourth aspect of the invention, which differs from the one of  FIGS. 3A and 3B  in that metallic plate  3   a  and metallic bridge  4  are two respective portions of the same element or two elements joined by an elastic material, in both cases the metallic bridge  4  being movable with respect to the metallic plate  3   a  in an elastic manner, thus constituting a flexible switching element. 
         [0062]    The configuration, sizing, and arranging of portions  1 ,  2 , and  12 , with respect to each other, is selected based on thermal conduction heat transfer criteria. In other words, the heat distribution (in magnitude and direction) from the hottest points of portions  2  and  12 , i.e. those in contact with the metallic elements, towards portion  1  is estimated and taken into account in the design stage in order to determine the dimensions (thickness, width, length) and spatial arrangement for each of the portions  1 ,  2 , and  12 . The plastics selection for each of the portions  1 ,  2 , and  12  is also based on said estimated heat distribution. At the end of this section, this design stage is further developed in a generic manner. 
         [0063]    A further embodiment is shown in  FIGS. 4A and 4B  for the electrically insulating support of the third aspect of the invention, which in this case is intended for providing four switchable electrical paths, and where portion  1  includes a central region acting as bridge between portions  2  and  12 , and also a frame region laterally surrounding said portions  2  and  12 . 
         [0064]      FIGS. 5A and 5B  show an embodiment of the electromechanical switch of the fourth aspect of the invention, including the support of  FIGS. 4A and 4B , where four metallic terminals  5   a  are attached to respective slots of first portion  2  forming a row and, opposed thereto, four further metallic terminals  5   b  are attached to respective slots of third portion  12  also forming a row. Terminals  5   a  are selectively connected to terminals  5   b  through respective movable metallic bridges (not shown) upon the rotation of actuation shaft  13  which can be made of a plastic having a high temperature heat resistance. A cover  11  is coupled to the support, preferably made of a high temperature heat resistance material, such as the same than portion  1 . 
         [0065]      FIGS. 6A and 6B  show a further embodiment for the electrically insulating support of the third aspect of the invention, which in this case is intended for providing twelve switchable electrical paths, and where portion  1  includes a central region acting as bridge between portions  2  and  12 , and also two raised end walls abutting on the respective ends of portions  2  and  12 . 
         [0066]      FIGS. 7A and 7B  show an embodiment of the electromechanical switch of the fourth aspect of the invention, including a support similar to the one of  FIGS. 6A and 6B , but in this case intended for providing eight switchable electrical paths, where eight metallic terminals  5   a  are attached to respective slots of first portion  2  forming a row and, opposed thereto, eight further metallic terminals  5   b  are attached to respective slots of third portion  12  also forming a row. Terminals  5   a  are selectively connected to terminals  5   b  through respective movable metallic bridges (not shown) upon the actuation of plastic discs arranged about a horizontal shaft, together forming a cam, guided on the two raised end walls of portion  1  and having a shaft actuation end  13  to rotate the horizontal shaft and thus perform the closing/opening of the electrical paths. 
         [0067]      FIGS. 8A and 8B  show a further embodiment of the electrically insulating support of the third aspect of the invention, for an embodiment which differs from the one shown in  FIGS. 1A and 1B  in that only two plastic portions are included in the support, particularly a first portion  2  and a second portion  1 , where the second portion  1  has a lower temperature heat resistance and is arranged between two separated regions  2   a  and  2   b  of portion  2 . Electromechanical switches similar to the ones of  FIGS. 2A, 2B, 3A, and 3B  are obtained by substituting the support of  FIGS. 1A and 1   b  with the one of  FIGS. 8A and 8B , where the two metallic terminals  5   a  and  5   b  are, in this case, respectively attached to the two separated regions  2   a  and  2   b  of the first portion  2 . 
         [0068]      FIGS. 10A and 10B  show another embodiment of the electromechanical switch of the fourth aspect of the invention, which differs from the one of  FIGS. 3A and 3B  in that it constitutes a toggle actuator switch, where the actuator is a toggle actuator including a rotary actuator  8  with several protrusions distributed in circle along one of its major faces and an actuator lever  9  arranged to move between the protrusions and displace the rotary actuator by pushing a corresponding protrusion. 
         [0069]    The embodiment of  FIGS. 11A and 11B  differs from the one of  FIGS. 10A and 10B  in that only one end of the metallic bridge  4  is movable, particularly that contacting metallic plate  3   b.    
         [0070]    A further embodiment for the electromechanical switch of the fourth aspect of the invention is shown in  FIGS. 13A and 13B , which constitutes a rocker switch, where a lever  10  is pivotable about a shaft  10   a  to actuate a flat metallic bridge  4  through a lower end of the lever  10 . 
         [0071]    Next, the above mentioned design stage based on the heat distribution and relationship with the characteristics of the plastics materials to be selected, is broadly described. 
         [0072]    Generally in the case of normal operation, the temperatures that occur due to the circulation of current through the global resistance of an elementary switching circuit are within temperatures assumable by normal thermoplastics, such as polyamides, though relatively close to their limits when the ambient temperature of the specific application reaches values up to 150° C. which is, therefore, added to the temperature generated by said current circulation. 
         [0073]    However in certain circumstances certain phenomena can occur which can adversely affect the performance of the switching circuit such as, for example, increases in electrical resistance due, for example, to deficient external connections, or the electrical arc phenomena that occur at the circuit opening times. Arc phenomena are of extraordinary complexity, but always causes high currents of a very short duration, that often cause a cumulative deterioration effect. 
         [0074]    All these effects of potential increase in temperature affect the switch circuit support and must be compensated with the use of suitable support materials. 
         [0075]    In the case of the present invention, at least a bimaterial configuration, and generally a multimaterial configuration, is used, selecting the plastic with a higher temperature heat resistance for the region(s) which must withstand a higher temperature and plastics with a lower temperature heat resistance for the joining regions or in other regions which do not have to withstand with high temperatures. 
         [0076]    For determining the geometry of these zones of different materials, i.e. for the above mentioned different portions  1 ,  2 , and  12  of the support, an analysis has been conducted by the present inventors regarding temperature versus distance to the heat focus in order to know the temperature distribution curve and, therefore, its gradient, which is what finally determines the zones to be occupied by each of the different plastic, i.e. the dimensions of the different portions  1 ,  2 , and  12  and also the boundaries between said zones. 
         [0077]    This temperature distribution analysis has been conducted on a support made of polyamide, and is represented in the graph of  FIG. 9 , where the thicker wave represents the measured values and the thinner wave represents the average profile thereof. 
         [0078]    As shown, the temperature distribution profile responds approximately to a Gaussian curve profile (darker wave), which is to be expected given the analysed distances are relatively short and the support material (polyamide) is completely uniform in its characteristics. 
         [0079]    They have been measured temperatures around 200° C. in cases of normal operation and up to 250° C. in conditions with some abnormality, such as conditions associated to a high number of switching actions and some deterioration of the material surface. 
         [0080]    This temperature distribution gives an approximate gradient of temperature decreasing of about 30° C./mm. This value is used to establish the boundaries of the zones of different material, i.e. the boundaries between portions  1 ,  2 , and  12  in relation to the estimated maximum temperature point. 
         [0081]    In a practical case, assuming that the electrical current will come to the electromechanical switch through electric cables coupled to, for example, Faston connectors connected to the metallic terminals  5   a  and  5   b  attached to portions  2  and  12 , and taking into account also the geometry of said Faston connectors, a distance of ±5 mm from the hottest point, i.e. from the end of the connector  5   a  and  5   b  nailed into the portion  2  and  12 , is adequate for dimensioning said portions  2  and  12 . In other words, if each of the connectors  5   a  and  5   b  is symmetrically attached to the respective portion  2  and  12 , a thickness of 5 mm and a width of 10 mm is determined to be appropriate, where said width refers to the dimension in the direction of the electrical path to be selectively connected between two opposed connectors  5   a  and  5   b . If said distances were lower than the determined as appropriate, then the plastic selected for portions  1  should be selected to withstand a higher temperature, and then its cost would increase. The above appropriate distance values have been confirmed to be valid for all the embodiments of the support illustrated in the appended figures, by means of corresponding empiric tests. 
         [0082]    Regarding the plastics selection, from the above analysis, it has been concluded that for an embodiment of the support of the third aspect of the invention using a bimaterial configuration, Polyamide (PA) standard is perfectly suitable for use in areas of lower temperature requirements, i.e. for second portion  1 , since the softening temperature is, depending on the specific types of Polyamide, of between 200° C. and 250° C., which gives an adequate safety coefficient for normal operation with a reserve sufficient for abnormal operation for a limited time, even for the boundary regions, i.e. even for the joining regions of second portion  1  with first portion  2  or with third portion  12 . For those areas of higher temperature requirements, i.e. for portions  2  and  12 , Poliphtalamide type thermoplastics can be selected, as they have a softening temperature of between around 300° C. and 350° C., depending on the type of Poliphtalamide, which offers excellent performance guarantee in all conditions. 
         [0083]    A person skilled in the art could introduce changes and modifications in the embodiments described without departing from the scope of the invention as it is defined in the attached claims.