Abstract:
An electrical heating device includes a housing which encloses a circulation chamber through which a medium can flow and in which heating ribs protrude. The heating ribs are in thermally conducting contact with at least one PTC heating element. A control device is provided in a constructional unit with at least one assembled conductor board. The constructional unit is accommodated in a control housing that comprises a control housing cover and a control housing frame. The control housing frame circumferentially surrounds the assembled conductor board and is formed from a metallic material. During the installation of the control housing on the housing, a control element, producing a power loss, is held by the assembled conductor board and is placed in abutment with a cooling element formed on the housing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an electrical heating device, in particular for a motor vehicle, with a housing, which encloses a circulation chamber through which a medium can flow, in which heating ribs protrude, which are in thermally conducting contact with at least one PTC heating element, and with a control device provided in a constructional unit with at least one assembled conductor board, which is accommodated in a control housing. 
         [0003]    2. Description of the Related Art 
         [0004]    An electrical heating device of this nature is known from EP 1 872 986 A1 which originates from the applicant. This prior-art electrical heating device involves a type with a housing, which encloses a circulation chamber through which a medium can flow. In this respect the heating ribs protrude enveloped by heating ribs with in each case a U-shaped recess in the circulation chamber. The U-shaped recesses are provided within the housing and separate the circulation chamber, through which the fluid to be heated can flow, from a connecting chamber in which the power current is passed for the electrical supply of the PTC heating elements. 
         [0005]    However, the present invention is not restricted to electrical heating devices of this nature normally designed for liquid media. Also an electrical heating device for heating air, in particular for heating the interior of a motor vehicle, can be regarded as generic. With this device the heating ribs are normally formed by meander-type bent sheet metal strips, which are exposed to the air flow to be heated and directly abut the PTC heating elements. These PTC heating elements comprise at least one PTC block and on oppositely situated sides of them abutting sheet metal bands, through which the PTC blocks can be supplied with electrical current with different polarity. The housing is normally formed by a frame, frequently of plastic. This frame has a very slight extension in the flow direction of the air to be heated. A generic electrical heating device of this nature with a control device in a constructional unit is for example known from EP 0 901 311 or DE 199 25 757. 
         [0006]    Electrical heating devices of this nature switch high currents. With the usual on-board electrical voltage of 12 volts currents of over 250 amps and with high-voltage applications of 180 to 500 volts currents of over 70 amps are switched in order to obtain the required heating powers. This demands amongst other aspects special contacting of all elements of the electrical heating devices. A good contact resistance must always be ensured on all live connections. Furthermore, with electrical heating devices of this nature there is the problem that switching high currents leads to electromagnetic interference, which admittedly can be reduced with electrical heating devices with a control device in a constructional unit, but not completely eliminated. Thus, EMC problems continue to present an obstacle to a satisfactory electrical heating device producing high thermal outputs. 
       SUMMARY OF THE INVENTION 
       [0007]    The object of the invention is to provide an electrical heating device of the type mentioned in the introduction, which takes into account the EMC problems in an improved manner and can be economically manufactured. Furthermore, the intention of the present invention is to specify an electrical heating device of the type mentioned in the introduction with a control device with an assembled conductor board, which at least bears one control element producing a power loss, with a method by which the electrical control device can be manufactured particularly easily. 
         [0008]    For the solution of the device-related problem the invention suggests an electrical heating device that differs from the generic state of the art in that the control housing comprises a control housing frame and a housing cover, which abuts a face side of the control housing frame. The control housing frame circumferentially surrounds the assembled conductor board and is formed from a metallic material. In a similar way the control housing cover is also preferably formed from a metallic material. In this way in any case a control housing is provided surrounding the assembled conductor board and thus screening the components on the laminated conductor board to the outside. The control housing frame is here preferably formed as a cylindrical component, i.e. it has—apart from face-side boundary surfaces, in particular on the ends of the control housing frame—only walls the surfaces of which extend parallel to one another. Here the control housing frame is formed in aluminium. The housing cover can however be formed from another material, for example from punched steel sheet. 
         [0009]    The control housing frame can be realised as one part with a supporting framework structure which is provided for the positioning and/or fixing of the assembled conductor board. The supporting framework structure is here preferably provided as a lattice structure with relatively thin walls such within the control housing frame that most of the interior space of the control housing frame remains free from the supporting framework structure. 
         [0010]    Taking into account the manufacture of the control housing frame in the course of extrusion, functional surfaces and elements provided as one part on the control housing frame preferably extend between the two face sides of the control housing frame, preferably with the same amount of longitudinal extension which the walls of the control housing frame have. According to a preferred further development of the present invention the supporting framework structure is however manufactured as a separate component and is joined to the control housing frame. For this purpose, it can for example have longitudinal grooves, which are formed on inner wall sections of the control housing and in which hammer-head ends of the supporting framework structure are introduced to retain them at a predetermined position. The supporting framework structure is in this case located preferably with its upper side flush with that free face side of the control housing frame on which the control housing cover abuts. Thus, the control housing cover screwed onto the control housing frame forms an end-stop for the separate element forming the supporting framework structure. 
         [0011]    In the inventive electrical heating device, the supporting framework structure bears a compressible compression element which produces compression force acting against the assembled conductor board. The supporting framework structure is then fixed under compression between the assembled conductor board and the control housing cover. The aspect of clamping the assembled conductor board by an element storing elastic strain components, such as for example a compression element, may in itself be inventive. With an embodiment of this nature, apart from the pre-characterising features of claim  1 , additionally at least a means is provided with which the conductor board is pressed against the housing which encloses a circulation chamber through which the medium to be heated flows, or however against a heat sink, which is arranged in this housing such that it is in thermally conducting contact with the medium to be heated. The compression element can be formed separately or as one part with the supporting framework structure. Also the supporting framework structure can overall form the compression element. It is also conceivable to manufacture the compression element in the course of two-component injection moulding, whereby a compressible more flexible plastic is formed in the vicinity of the assembled conductor board, whereas a harder and stiffer plastic is located in the vicinity of the control housing cover. 
         [0012]    The compression element is preferably formed from a plastic with Shore A hardness between 60 and 80. In particular silicone (Si) or a rubber (EPDM) can be considered as a suitable material. 
         [0013]    The compression element is used for fixing the conductor board against an opposing surface formed on the underside on the housing of the heating device and/or on a housing base. Due to this compressive force the assembled conductor board is then fixed in the height direction of the control housing frame, and in a plane extending transversely to the direction of action of the compression force the assembled conductor board is normally accommodated with slight play between the inner surfaces of the control housing frame and accordingly positioned. 
         [0014]    The transfer of the compression force from the compression element to the assembled conductor board preferably occurs through pillar supports which extend at right angles to the surface of the assembled conductor board. These pillar supports can just rest on the surface of the assembled conductor board situated opposite the supporting framework structure, they can penetrate the conductor board or however protrude over the conductor board and for example be formed thickened by fusion of the free ends of the pillar supports in order to join the conductor board captively to the supporting framework structure. Normally, a plurality of pillar supports are provided, each of which can be formed deviating from one another subject to the above. Generally however, it is sufficient just to abut the pillar supports against the surface of the assembled conductor board facing the supporting framework structure in order to press the assembled conductor board with pressure against the above mentioned opposing surface and then to fix it. 
         [0015]    The compression force caused by the compression element is preferably used to dissipate heat of one or all control elements, which produce a power loss and which are borne by the conductor board, to a cooling element. For this purpose the control element producing the power loss is located on the side of the conductor board facing away from the compression element, and namely preferably between the free end of the pillar support and the cooling element. The pillar support can here directly abut the control element producing the power loss or however with the intermediate positioning of a further element, in particular the assembled conductor board. 
         [0016]    In particular with the formation of the housing in plastic it is preferable to form the cooling element as separate therefrom in a good thermally conducting material, such as for example aluminium or copper and to provide a heat conducting contact with the medium to be heated. Here, the cooling element can be directly exposed in the circulation chamber or however in a region of the electrical heating device separate therefrom and subject to the flow of the medium to be heated. The cooling element can however be formed just as well by a region of the housing, in particular when the housing itself is formed from a good thermally conducting material. 
         [0017]    With a view to the best possible thermal conduction, according to a preferred further development of the present invention it is suggested that a control housing base is provided which abuts a face side of the control housing frame which is other than the control housing cover and which at least has one opening in extension of the pillar support. In this way the possibility is obtained of thermally conductively joining the control element producing the power loss to a cooling element which is located outside of the control housing, in particular within the housing of the heating device and which then can also be designated as the heater housing. 
         [0018]    Due to an electrically insulating layer between the element producing the power loss and the cooling element, in particular located in the heater housing, the possibility is obtained of isolating the control device electrically from the heater housing which encloses the circulation chamber. 
         [0019]    On the other hand, considering an easy manufacture and secure fastening of the control housing to the heater housing, the control housing frame has mounting protrusions in the corner areas. These protrusions are preferably formed as a type of eye, through which a threaded rod can be passed so that the threaded rod is held positively locked within the eye. A threaded rod of this nature, which for example can be formed by the shank of a screw, is held in the corresponding mounting protrusions on the control housing frame and is preferably screwed to the housing forming the circulation chamber. Here the cooling element(s) and the face side of the control housing frame which can abut the heater housing and the control element(s) producing the power loss are matched such that with this screwing of the control housing frame onto the heater housing initially a contact is produced between the cooling element and the control element producing the power loss. With increasing screwing a prestressed contact of the control element producing the power loss occurs on the surface of the cooling element until finally, after termination of the assembly, the face side of the control housing contacts the housing and the control element producing the power loss is assembled under contact pressure directly or indirectly—in any case however thermally conducting—against the surface of the cooling element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Further details and advantages of the present invention are given in the following description of an embodiment in conjunction with the drawing. This shows the following: 
           [0021]      FIG. 1  an exploded drawing of a first embodiment; 
           [0022]      FIG. 2  a central longitudinal section through the embodiment illustrated in  FIG. 1 ; 
           [0023]      FIG. 3  a cross-sectional view along the line according to the illustration in  FIG. 2 ; 
           [0024]      FIG. 4  perspective views of the two housings with the covering elements of the previously discussed embodiment provided in between them; 
           [0025]      FIG. 5  an exploded drawing of a second embodiment; 
           [0026]      FIG. 6  a partially cut-away perspective side view of the second embodiment; 
           [0027]      FIG. 7  a longitudinal sectional view of the second embodiment; 
           [0028]      FIG. 8  an enlarged longitudinal sectional view of the control housing of the second embodiment; 
           [0029]      FIG. 9  a partially cut-away perspective side view of the control housing of the second embodiment; 
           [0030]      FIG. 10  a longitudinal sectional view of the control housing of the second embodiment; 
           [0031]      FIG. 11  a plan view of the control housing of the second embodiment; 
           [0032]      FIG. 12  an exploded drawing of a third embodiment; 
           [0033]      FIG. 13  a longitudinal sectional view of the third embodiment; 
           [0034]      FIG. 14  a perspective side view of a fourth embodiment and 
           [0035]      FIG. 15  a longitudinal sectional view of the fourth embodiment illustrated in  FIG. 14 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0036]      FIG. 1  illustrates a perspective exploded drawing of a first embodiment of an electrical heating device. It comprises a first housing  2  and a second housing  4 , formed essentially mirrored to it, which with the intermediate positioning of a covering element  6  are joined together, each being covered on the outside by a housing cover  8 . 
         [0037]    On a common face side of the two housings  2 ,  4  there is a control housing, identified with the reference numeral  10 , of a control device  11 , which has a control housing frame  12 , which accommodates an assembled conductor board  14  and is closed by a control housing cover  16 . 
         [0038]    On their face sides facing the control housing  10 , both housings  2 ,  4  have a housing connection opening  18  which is provided close to the housing cover  8 . In this control housing connection opening  18  in each case a plug housing  20  can be inserted, which is manufactured from an insulating material, for example plastic, and bears a plurality of plug elements  22 , which provide an electrical contact between electrical conductive paths provided in the two housings  2 ,  4  and the conductive paths of the assembled conductor board  14 . 
         [0039]    Furthermore, in  FIG. 1  heater plate elements  24  are illustrated which are formed slightly wedge-shaped and correspond to those PTC heating elements which are disclosed in the European patent application EP 1 921 896 A1. The disclosure of this European patent publication is included by reference in the disclosed content of this patent application. 
         [0040]    A temperature probe  26  is illustrated in front of the row of heater plate elements/PTC heating elements  24 . 
         [0041]    The installation of these elements into the housings  2 ,  4  can be particularly taken from  FIG. 2 . Accordingly, the housings  2 ,  4  each form two different chambers, namely a connecting chamber  28  and a circulation chamber separated from it by a partition wall  30 . From the partition wall  30  in the circulation chamber  32  U-shaped recesses  34  protrude which extend deep into the circulation chamber  32  and terminate at the same height to the connecting chamber  28  as the partition wall  30 . These recesses  34  are designed such that the heater plate elements  24  with a wedge surrounded by them can be used for heat conduction against the oppositely situated walls of the U-shaped recesses  34 , as comprehensively described by the already mentioned EP 1 821 896 A1. 
         [0042]    The circulation chamber  32  of each single housing  2 ,  4  extends between a connection piece  36  for the connection of a fluid hose and a flow passage aperture  38 . Between these two outputs or end points of the circulation chamber  32  within it a meander-type flow channel  40  is formed within the housing  2  or  4 , the course of which can be particularly taken from  FIG. 3 . The flow channel  40  has flow channel sections  42 , which extend at right angles to the longitudinal extension of the housing  2  or  4  and are each bounded by outer walls of heating ribs  44  forming the U-shaped recesses  34 . These heating ribs  44  are arranged alternately on oppositely situated inner sides  46  of the housings  2 ,  4 . The housing  2  and the heating ribs  44  are here uniformly realised on an aluminium die-cast part. The heating ribs  44  are mounted on the oppositely situated inner sides  46  of the housing  2  or  4  via a ridge  48 . This ridge  48  is less thick than the heating ribs  44 . Thickness in this sense is taken to be the extent of the ridge in a direction at right angles to the flow channel sections  42 , i.e. in the longitudinal direction of the housing  2 . The exposed surfaces of the ridges  48 , exposed to the flow channel  40 , are formed concave, whereby a recess  50  is produced as part of the flow channel  40 . In the flow channel  40  the flowing fluid to be heated can accordingly on one hand flow around the free ends  52  of the heating ribs  44 , but on the other hand it can also in any case flow around a substantial part of the base end  54 , so that the heating ribs  44  can dissipate heat to the fluid to be heated both via their oppositely situated longitudinal sides as well as via their face sides  52 ,  54 . Here, a flow passage  56 , which connects the relevant flow channel sections  42  together, is formed between the free ends  52  and the inner side  46  of the housing. 
         [0043]    The housings  2  illustrated in  FIGS. 1 to 3  are identically formed so that a flow path through two meander-type flow channels  40  is produced between the two connection pieces  36 . The previously described temperature probes  26  are also provided double and namely directly in the region of the opening of the connection pieces  36 . For this purpose temperature probe holes  60  are formed in the relevant housings  2 ,  4  in each case for the accommodation of a temperature probe  26  (cf.  FIG. 4 ). 
         [0044]    Furthermore, as can be seen from  FIG. 4 , tapered ridges  70  are formed on the underside of the heating ribs  44 . All tapered ridges  70  terminate at the same height and form a support level for the covering element  6 . Accordingly, the covering element between the tapered ridges  70  and the supporting counter ridges  71  of the oppositely situated housings  2 ,  4  is clamped for sealing. 
         [0045]    The covering element  6  can for example be formed from a metal sheet, around which a flexible plastic is injection molded around, on one hand to form a circumferential sealing edge  72  and on the other hand however the sealing strips corresponding to the meander-type structure of the tapered ridges  70 , which are illustrated in  FIGS. 1 and 4 , and which abut between the mutually oppositely situated, tapered ridges  70 . The sealing edge  72  is clamped between the mutually oppositely situated face sides of the housings  2 ,  4 . 
         [0046]    On the face sides facing the control housing  10  the housings  2 ,  4  have a protrusion formed by milling, through which a cooling element  76  is formed in each case, which constitutes a cooling element contact base  78  extending parallel to the face side and the oppositely situated surface of which is exposed in the circulation chamber in the vicinity of the flow passage aperture  38  (cf.  FIG. 4 ). 
         [0047]    With the embodiment illustrated in  FIGS. 1 to 4  the housing covers  8  are normally formed from punched metal. Also, they can bear a seal in an elastic plastic formed by injection molding around the housing covers  8 . This applies correspondingly to the housing cover  16 . Normally, the housing covers  8  in any case contact the housings  2 ,  4  through screws which also fix and seal the two housings  2 ,  4  together with the intermediate positioning of the covering element  6 . The housings  2 ,  4  are formed identically. The feet  80  visible in  FIGS. 1 and 3  can be separately manufactured and fastened retrospectively to the outer wall of the lower housing  2 . The heating power of the electrical heating device can be increased in that a further package of two housings  2 ,  4  is positioned adjacent to that shown in  FIGS. 1 to 4 . The control of the individual heater plate elements  24  can be realised by a uniform controller with a uniform control housing. 
         [0048]      FIGS. 5 to 11  illustrate a further embodiment of a heating device according to the invention. The same components are identified with the same reference numerals compared to the previously discussed embodiment. The construction of the housings  2 ,  4  of the circulation chambers  32  and the connecting chambers  28  is essentially identical to the previously discussed embodiment. However, the control housing  10  of the control device  11  extends sideward over the two housings  2 ,  4  for mounting a connecting housing  82 , which bears an electrical cable  84  for the power current and an electrical cable  85  for the control signals and leads in a sealed manner into the interior of the connecting housing  82 . In the region of the connection pieces  36  a contact element  86 , contacting the housings  2 ,  4  electrically, is provided in each case, which facilitates a check of the polarity of the two housings  2 ,  4  in order to detect any fault in the electrical isolation of the housing  2  or  4  from the current-carrying paths.  FIG. 5  illustrates in any case the connecting end of this further contact element  86 . The parts of the embodiment omitted in  FIG. 6  clearly show the flow path within the housings  2 ,  4  as well as the embodiment of the heating ribs  44  and of the U-shaped recesses  34  formed in them. 
         [0049]    As can also be seen from  FIG. 6 , the heater plate elements  24  have a widened collar  88 , which rests on the upper side of the partition wall  30 , so that the heater plate elements  24  protrude into the U-shaped recesses  34  with a certain depth. This collar  88  has contact lugs  90  of the heater plate elements  24  protruding over it. These contact lugs  90  are freely cut ends of electrically conducting sheet metal plates, which contact PTC blocks  92  on both sides, can supply current to them with different polarity and are graphically illustrated in  FIG. 7  and are identified with the reference numeral  93 . Four PTC blocks  92  are enveloped one above the other by each heater plate element  24 . As can also be taken from  FIG. 7 , the contact lugs  90  are exposed at the same level within the connecting chamber  28 . At this level the connecting end of the temperature probe  26  is exposed. 
         [0050]    In the connecting chamber  28  there is a connecting conductor board, the representation of which is omitted in  FIG. 7 , but which is identified with the reference numeral  94  in  FIG. 2 . The connecting conductor board  94  extends essentially parallel to the partition wall  30  and rests on the collar  88 . It forms electrical connecting elements for the accommodation of the individual contact lugs  90  and a contact receptacle for the connecting end of the temperature probe  26 . On the face side oppositely situated to the temperature probe  26  the connecting conductor board  94  has electrical connecting recesses for contacting the plug elements  22  exposed in the connecting chamber  28 . The connecting conductor board  94  and the electrical connecting elements of it are here embodied such that all electrical connections to the connecting conductor board  94  are realised when the connecting conductor board  94  is placed on the collars  88 . Thus the electrical plug contacts in the connecting chamber  28  are electrically connected to the plug elements  22 . 
         [0051]    In the following the construction of the control device  11  is described, particularly with reference to the  FIGS. 7 to 11 . On its surface facing away from the housings  2 ,  4  the assembled conductor board  14  bears various electrical or electronic components  96 . On the oppositely situated underside of the assembled conductor board  14 , facing the housings  2 ,  4 , components and control elements  98  producing a power loss, in particular power transistors, are provided. Between these power transistors  98  and the cooling element contact base  78  there is an electrical insulating layer  100 . This insulating layer  100  is located in a recess of a control housing base  102  of a flexible material, in particular in a flexible plastic, which is clamped between the face side of the control housing frame  12  facing the housing  2  or  4  and the face side of the housing  2 ,  4 . This control housing base  102  has receptacles into which the plug housings  20  are introduced. The plug housings  20  have flanges which grasp the control housing base  102  on the uppersides and undersides (cf.  FIGS. 7 ,  9 ). The control housing base  102  protrudes sleeve-like into the control housing connection openings  18 , whereby secure mounting and sealing of the plug housings  20  is realised (cf.  FIG. 7 ). The inside of the control housing  10  is accordingly sealed with respect to the connecting chamber  28 . 
         [0052]    As can be seen, particularly from  FIGS. 9 and 11 , a supporting framework structure  104 , which is manufactured as a separate component, formed from thin ridges  105  forming the supporting framework structure  104 , is located within the control housing frame  12 . The ends of the ridges  105  are enlarged to a hammer head  106  in the vicinity of the control housing frame  12 . The hammer head  106  is held in accommodating slots  108 , which are formed on the inner wall of the control housing frame  12  by the control housing frame. 
         [0053]    Also in the corner regions mounting protrusions in the form of mounting eyes  110 , the longitudinal extension of which corresponds to the height of the control housing frame  12 , are formed on the control housing frame  12 . These eyes are not circumferentially closed, but rather have an open slit towards the inside of the control housing frame  12 . The mounting eyes  110  are used for holding the threaded rods which join the control housing frame  12  to the housings  2 ,  4  with the inclusion of the control housing cover  16 . They are also used however to accommodate threaded rods, which fasten the connecting housing  82  to the control housing frame  12 . 
         [0054]    Between the supporting framework structure  104  and the assembled conductor board  14  a compression element identified with the reference numeral  112  is provided in a flexible plastic. On its face side facing the supporting framework structure  104  this compression element  112  forms U-shaped recesses for the ridges  105  of the supporting framework structure  104 , so that the compression element  112  is held positively locked on the supporting framework structure  104 . The compression element  112  is similarly formed lattice-like, whereby lattice ridges  114  of the compression element  112  have pillar supports  116  of the compression element  112  extending over them, the said supports engaging corresponding recesses formed on the assembled circuit board  14  for this purpose and directly contacting the control components  98  producing the power loss. The pillar supports  116  are provided there where the control components  98  producing the power loss are arranged on the side of the assembled conductor board  14  oppositely situated with respect to the pillar supports  116 . One or a plurality of retaining clamps  117 , which act on the conductor board  14 , protrude from the compression element  112  and/or the lattice ridges  114 . 
         [0055]    As can be seen from  FIG. 11 , the assembled conductor board  14  also has contact element receptacles  118 , which are formed on oppositely situated marginal regions  120  of the assembled conductor board  14 . The contact element receptacles  118  are formed as elongated holes. Also a further contact lug receptacle  122  for the contact element  86  is formed as an elongated hole. All elongated holes have longitudinal axes which are mutually parallel. Plug counter elements  119  are arranged in the contact element receptacles  118 . The assembled conductor board  14  is fixed with a slight play within the control housing frame  12 . In the corner regions of the assembled conductor board  14  cut-outs  124  are provided, whereby the mounting eyes  110  pass right through the plane of the assembled conductor board  14 . 
         [0056]    For assembly normally the control device  11  is first pre-assembled, i.e. the assembled conductor board  14  is arranged within the control housing frame  12 . The plug housings  20  are inserted through the cut-outs in the control housing base  102  and thus connected. Then the pre-assembled control device  10  is pushed onto the housings  2 ,  4  with the intermediate positioning of the insulating layer  100 . Here, the plug housings  20  are introduced for sealing into the housing connection openings  18 . Due to the embodiment of the contact receptacles  118  as elongated holes, the plug elements  22  can in this respect perform a certain compensating movement without the electrical contact between these plug elements  22  and the plug counter elements  119  of the assembled conductor board  14  being lost. Then the control housing frame  12  together with the control housing cover  16  is screwed to the housings  2 ,  4 . Here, first the surfaces of the control components  98  producing the power loss rest on the cooling element contact bases  78 . After the assembly of the control housing  10  on the housings  2 ,  4  the control components  98  producing the power loss abut the cooling elements  76  at the housing end under prestress and are thus connected reliably for thermal conduction. Within the scope of this assembly the pillar supports  116  of the compression elements  112  are in particular elastically compressed, whereby an elastic prestress is stored in the compression element  112 . 
         [0057]      FIGS. 12 and 13  illustrate a further embodiment of an electrical heating device according to the invention. The same components are identified with the same reference numerals compared to the previously discussed embodiment. 
         [0058]    The embodiment according to  FIGS. 12 and 13  has only one housing  2 , which is provided with a covering element  6  for forming the circulation chamber  32  between the covering element  6  and the partition wall  30 . The embodiment also has a housing cover  130  which bears a pump  132  and in any case partially forms a pump housing  134 . Here, the housing cover  130  forms a flow inlet housing part  136  which forms attachment elements  138  for flange-connecting the pump  132  and a hose connection piece  140 . The covering element  6  only has sealing strips  74  suitable to the structure of the tapered ridges  70  on its underside facing the housing  2 . On the oppositely situated upper side, sealing strips  74  are provided running on the covering element  6  suitable for a pump channel  142  formed by the housing cover  130 . This pump channel  142  connects the flow passage aperture  38  to the flow inlet housing part  136 . 
         [0059]    The control housing frame  12  is formed identically to the embodiment discussed with reference to  FIGS. 1 to 4 . However the control housing frame is partially closed by a control housing base cover  144  which forms a bent flange  146  which is screwed onto the upper side of the control housing cover  130 . 
         [0060]    The power supply and the control connection of the pump  132  preferably occurs similarly via the assembled conductor board  12 . With the embodiment illustrated in  FIGS. 12 and 13  this occurs via a cable which connects the control device  11  to the pump  132 . With the embodiment illustrated in  FIGS. 12 and 13  the cable (not illustrated) extends from a lateral face of the control housing frame  12  to the pump  32 . Just as well however, a plug housing  20  can be provided at the level of the pump  132  through which the electrical connection of the pump  132  occurs. 
         [0061]      FIGS. 14 and 15  illustrate a fourth embodiment. The same components are identified with the same reference numerals compared to the previously discussed embodiment. 
         [0062]    As the previously described embodiments, the fourth embodiment comprises a housing  2  which is joined to a housing cover  148  and mounting flanges  150  for mounting the electrical heating device are fitted to its longitudinal sides. On a face side of the housing  2  and the housing cover  148  there is the control housing  10  with the controller which is accommodated in it and which is not detailed in  FIGS. 14 and 15 . This control housing  10  is in the present case formed L-shaped with an overhang  152  protruding slightly over the housing cover  148 , with two cable clamps  154 ,  156  mounted on its face sides for mounting and sealing cables secure against twisting and strain. The cable clamp  154  is used for connecting a connecting cable; the larger cable clamp  156  is used for connecting a cable for the power current. The housing  2  is formed identically to the previously described housings  2 . In this respect reference is made to the above description. 
         [0063]    The housing cover  148  has a bottom plate  158  positioned on the housing  2 , with the said bottom plate interacting with the edge of the housing  2  and the tapered ridge  10  with the inclusion of the covering element  6 , whereby the circulation chamber  32  is sealed in the region of the tapered ridges  70 . In the flow direction behind the flow passage aperture  38 , the housing cover  148  forms a flow passage  160  which communicates with a tube  162  formed as one part on the housing cover  148 , which extends parallel to the connection piece  136  and terminates with it essentially at the same level. 
         [0064]    The embodiment illustrated in  FIGS. 14 and 15  is relatively small and has a thermal output of not more than 3 kW, and normally a thermal output of between 1.5 and 2.8 kW. The embodiment is suitable for example for battery preheating in electric vehicles.