Abstract:
An electric heating device that provides additional heating for motor vehicles includes several heating elements assembled to form a heating block, and a controller for controlling the heating elements. The controller forms a constructional unit together with the heating block. Contact and/or cooler elements extending between the controller and the heating block. The controller is held at a control means support. Between the controller support and a heating block housing accommodating the heating block, sealing elements are provided through which the contact or cooler elements project and which are sealed by clamping between the controller support and the heating block housing.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an electric heating device for heating air which is in particular suited to be employed as additional electric heating in motor vehicles. 
         [0003]    2. Description of the Related Art 
         [0004]    For the employment in motor vehicles, in particular those with engines of which the consumption is optimized, electric heating devices are used to heat the passenger compartment and/or the engine. An additional electric heating is in particular required after the starting of the engine as long as the internal combustion engine does not yet provide sufficient thermal energy. Internal combustion engines of which the consumption is optimized even principally require the use of an additional electric heating. 
         [0005]    However, the use of such heating devices is not restricted to the field of motor vehicles; they are also suited for a plurality of other applications, for example in the field of domestic installations (room air conditioning), industrial plants and the like. 
         [0006]    An electric heating device for motor vehicles is known from EP-A1-1 395 098. The described heating device comprises several heating elements assembled to a heating block. The heating block is held in a common frame together with a control means for controlling the heating elements. The control means thus forms a constructional unit together with the heating block held in the frame. The control means comprises power electronics with electronic switches which are provided each with a heat sink. The control means is arranged such that a portion of the air flow to be heated flows against the control means, in particular the cooler elements for cooling the electronic switches. 
         [0007]    The electronic switches, in particular in the form of power transistors which control the current that is supplied to the heating elements, are mounted directly on a printed circuit board with one side. To dissipate the thermal loss generated by the power transistors, a cooler element is provided on the opposite side of the printed circuit board. Such a cooler element which directly contacts the power transistor can dissipate the thermal loss of the power transistor in a simple manner and in a sufficient amount. 
         [0008]    In the above-mentioned prior art, a U-shaped heat sink with cooling fins or fingers, respectively, which project from a base, is employed. A pin is provided at the bottom side of the heat sink and can be inserted in the printed circuit board to contact the power transistor. However, a cooler element in the sense of the present invention can be any component which is suited to dissipate heat from the power transistors by heat conduction and emit it effectively to the air flowing around it by heat transfer. To this end, the cooler element is exposed to the air which is to be heated by the electric heating device, i.e. which flows in a channel leading to the electric heating device. However, it cannot be excluded that moisture collects in the channel which is either directly introduced with the inflowing air or is condensed from the air that has flowed in. 
       OBJECT OF THE INVENTION 
       [0009]    It is therefore the object of the present invention to further develop an electric heating device of the type mentioned in the beginning, so that the same can be easily manufactured and the control means of the electric heating device can be reliably protected from penetrating moisture. 
         [0010]    To achieve this object, an electric heating device having the features of claim  1  is provided with the present invention. It differs from the generic prior art in that the control means is held at a control means support and that between the control means support and a heating block housing accommodating the heating block sealing elements are provided through which the contact or cooler elements project and which are sealed by clamping between the control means support and the heating block housing. 
         [0011]    In the electric heating device according to the invention, the constructional unit is provided in that the control means support is connected to the heating block housing. The contact elements which take care of the supply of the heating block with electric current as well as the cooler elements effecting the cooling of the electronic switches extend between the control means support and the heating block housing. The contact or cooler elements, respectively, project through at least one sealing element. The tightness of the sealing element is provided in that the sealing element is clamped between the control means support and the heating block housing. This permits to first mount the sealing elements without stresses and to clamp the respective sealing elements to achieve a sealing contact not before the constructional unit of the control means and the heating block is created, i.e. when the control means support is connected to the heating block housing. The electric heating device according to the invention can thereby be manufactured in a simple manner without having to dispense with a reliable sealing of the control means. 
         [0012]    The electric heating device according to the invention can be particularly simply and therefore economically manufactured if the cooler element or elements, respectively, is/are embodied as pin or plate-shaped solid bodies which are lead through the printed circuit board for their connection to the electronic switch (e.g. power transistor) and which project over the printed circuit board at the bottom side facing away from the electronic switch. In the contact area with the sealing element, at the cooler element or elements as well as at the contact element/ elements, sealing or contact surfaces for the sealing elements can be provided which differ from a cylindrical and thus the simple shape. Such embodiments are in particular preferred with respect to a radial clamping of the sealing elements against the inside circumference of the contact or cooler elements, respectively. Alternatively, the control means support and/or the heating block housing can comprise conical mountings for the sealing elements which surround the passages for the contact or cooler elements, respectively. To generate a sealing contact of the sealing elements at the inside circumference of the passages on the one hand and the outside circumference of the contact elements or the cooler elements on the other hand, the sealing elements are fixed between the heating block housing and the control means support preferably axially, i.e. in the longitudinal direction of the cooler or contact elements, respectively. When the constructional unit consisting of the heating block housing and the control means support is being completed, the sealing elements through which the contact or cooler elements, respectively, project are compressed in the longitudinal direction of these elements leading to a sealing contact in the radial direction. 
         [0013]    In electric heating devices of the type mentioned above, several electronic switches can be provided. Moreover, usually more than two contact elements for supplying the individual heating elements are provided, which practically project over the heating block housing at the frontal side at which the control means support is located. With respect to an assembly of the electric heating device as simple as possible, it is suggested according to a further preferred embodiment of the present invention to connect the sealing elements with each other to form an integral sealing unit. This integral sealing unit can be, for example, pre-fixed during the assembly in that the sealing unit is shifted onto the contact elements projecting over the heating block housing. In this manner, the sealing elements for the cooler elements at the heating block housing are also brought to a predetermined position corresponding to the position of the cooler elements if the control means support is connected to the heating block housing. The sealing unit can be manufactured as injection-molded part from a heat resisting thermoplastic elastomer. Such an injection-molded part can also be inserted, for example, as an insert into an injection mold which is used to manufacture the control means support or the heating block housing or a housing half of the same. In this manner, the joining steps for the manufacture of the heating device can be reduced. 
         [0014]    If the sealing unit is, however, embodied as insert which is separately mounted, it is preferred to connect the sealing elements with each other by a base section. To increase tightness, it can be preferred to clamp this base section at the edge of the passages between the heating block housing and the control means support in a sealing manner. Thereby, in addition to a possibly existing radial sealing effected by the sealing elements themselves, a sealing acting at right angles to the same is created. To generate clamping forces as high as possible, it is furthermore preferred to provide a projecting collar surrounding the mountings for the sealing elements on the side of the housing. With respect to an embodiment of the heating block housing as simple as possible, it is preferred here to provide this projecting collar at the control means support which should, for the same reason, also comprise the conical mountings for the sealing elements. 
         [0015]    To improve sealing, it is suggested according to a further preferred embodiment of the present invention to embody the sealing element to each of the contact or cooler elements, respectively, with several sealing contact surfaces arranged one after the other in the longitudinal direction with respect to these contact or cooler elements. These are preferably arranged conically stepped with respect to each other and are preferably predetermined by sealing beads arranged one after the other. In the latter preferred embodiment, the sealing beads are situated spaced apart in the longitudinal direction of the contact or cooler elements, respectively, wherein the material of the sealing elements connecting the respective sealing beads with each other preferably forms a kind of film hinge which permits a certain movability of the individual sealing beads with respect to each other in the longitudinal direction of the contact or cooler elements, respectively. This promotes the sealing contact of the individual sealing contact surfaces at the contact or cooler elements and the passages or the conical mountings, respectively. 
         [0016]    To precisely fix the sealing elements or the sealing unit during the assembly of the electric heating device, it is suggested according to a further preferred embodiment of the present invention to provide a cross web at the heating block housing which covers window openings formed at the heating block housing, the cross web forming a contact surface for the base section of the sealing element and thereby first improving the sealing. To this end, the cross web practically forms an essentially plane contact surface for the base section. However, the cross web further comprises centering mountings according to a further preferred embodiment of the present invention, in which centering projections formed at the base section are received. These centering projections are preferably located at the bottom side of the base section facing away from the sealing elements. This bottom side is placed on the plane contact surface, whereby, due to the centering mountings, an accurate positioning of the sealing unit is effected which also favors the insertion of the contact or cooler elements during the further assembly of the electric heating device. To this end, the centering mountings preferably surround the passages for the cooler and/or the contact element(s). 
         [0017]    The constructional unit between the control means and the heating block is preferably prepared in that the heating block housing is connected to a control means housing which comprises the control means support. The control means housing has a housing lid which comprises at least one interface for the supply and control of the heating device. The control means housing furthermore surrounds a printed circuit board with cooler elements essentially projecting at right angles therefrom and electronic switches. The control means housing is to effect in particular a certain mechanical protection of the control means. It is not absolutely necessary for this control means housing to seal the control means against liquids. The control means housing is in particular used for the electric connection of the electric heating device as well as possibly the fixing of the control means or the complete heating device. 
         [0018]    To easily manufacture the constructional unit, it is however preferred to press the parts accommodated in the control means housing and electrically connected with each other onto each other in the longitudinal direction of the contact or cooler elements. To this end, the housing lid preferably comprises a contact bar which is electrically connected to at least one of the interfaces as well as to the printed circuit board and is placed onto the printed circuit board, which means that the contact bar extends essentially at right angles to the plane of the printed circuit board. The printed circuit board furthermore comprises flexible tongues cooperating with the contact elements. These flexible tongues are electrically connected to strip conductors of the printed circuit board, the flexible tongues being dimensioned such that the contact elements lying against the flexible tongues are securely electrically connected to the printed circuit board. This connection is usually effected when the contact elements are introduced into the passages recessed at the control means support. The cooler elements firmly mounted to the printed circuit board here project through passages which are recessed at the heating block housing, preferably at the cross web. At the end of this introduction movement, the sealing elements are clamped between the control means support and the heating block housing. 
         [0019]    The thus prepared constructional unit is preferably secured in that the control means support or the control means housing, respectively, is locked with the heating block housing. 
         [0020]    Further advantageous embodiments of the present invention are given in the subclaims. 
         [0021]    The present invention will be described below with reference to an embodiment in connection with the drawing. In the drawing: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0022]      FIG. 1  shows a perspective exploded view of an embodiment of an electric heating device according to the invention; 
           [0023]      FIG. 2  shows a longitudinal section of an embodiment modified compared to  FIG. 1  in an assembled condition; and 
           [0024]      FIG. 3  shows an enlarged detail of the longitudinal section shown in  FIG. 2  at the phase interface between the heating block housing and the control means housing. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0025]    In  FIG. 1 , a perspective exploded drawing is shown essentially in form of a side view of an embodiment of the electric heating device according to the invention. As essential elements, it comprises a heating block housing  1  as well as a control means housing  2 . A sealing unit  3  is provided between the two housings  1 ,  2 . The control means housing  2  surrounds a control means  4 . 
         [0026]    The heating block housing  1  consists of two essentially identical frame halves  10   a ,  10   b  which are embodied in the present case as injection-molded plastic parts and at the surface of which a stiffening grid structure is embodied. A heating block  11  consisting of a plurality of layered or stacked heating elements  12  is arranged between the grid structures of the two frame halves  10   a ,  10   b . Each of the heating elements  12  consists of one or several resistance heating elements, which in the representation according to  FIG. 1  are covered behind the longitudinal struts of the stiffening grid, and of radiators  3  arranged adjacent thereto which are in the present case formed by sheet metal strips folded in a meandering manner. In view of a good heat transfer and contact of the radiators  13  at the resistance heating elements which are preferably formed by so-called PTC elements, a plane sheet metal strip is disposed between the PTC elements and the radiator  13  of a heating element  12 . 
         [0027]    The heating block  11  of the heating elements  12  is held in the frame  10  formed by the two frame halves  10   a ,  10   b . To this end, the frame  10  comprises oblong longitudinal spars  14   a ,  14   b  and lateral spars  15   a ,  15   b  extending at right angles thereto. 
         [0028]    Between the upper lateral spar  15   a  in  FIG. 1  and the heating block  11 , window openings  16  are recessed in the shown embodiment. The longitudinal webs  17  separating adjacent window openings  16  surround a free end of the sheet metal strips arranged between the radiators  13  and the resistance heating elements which are continued outwards to form a contact stud  18 . The contact studs  18  project over the upper edge of the frame  10  in  FIG. 1 . 
         [0029]    The control means housing  2  has an essentially two-piece design with a lower housing part  21  comprising a control means support  20  and a housing lid  22  placed upon it. The lower housing part  21  has an essentially trough-like design and comprises mounting flanges  23  at its respective frontal sides for assembling the electric heating device at the chassis of a motor vehicle. The bottom of the lower housing part  21  forms the control means support  20  of which the surface that points to the inner side of the control means housing  2  is completely plane. The control means support  20  has several slotted first passages  24   a  which are arranged so as to alternate with round passages  24   b  in the longitudinal direction of the control means support  20  one after the other. 
         [0030]    The first passages  24   a  with rectangular cross-sections are formed in the longitudinal and transverse directions of the control means support  20  towards the control means housing  2  in a tapering manner. The second passages  24   b  with a round cross-sectional area are formed so as to taper in the same direction. At the bottom side of the control means support  20  facing away from the interior of the control means housing, first and second collars  25   a ,  25   b  are located, the cross-sectional shape of which corresponds to the shape of the passages  24 . These collars  25   a ,  25   b  form the major portion of internal side walls of tapered mountings  26   a ,  26   b . The control means support  20  is bordered by a double groove  27  opened to the bottom side which is embodied such that the edge of the heating block housing  1  on the frontal side fits inside the double grooves  27 . 
         [0031]    The housing lid  22  forms a plug mounting  28  in which electric control contacts  29  are received. The housing lid  22  furthermore comprises two electric supply interfaces  30   a ,  30   b  which are shielded from each other by upright walls forming supply plug mountings  31   a ,  31   b . The electric supply interface  30   b  is electrically connected to a contact bar  32  which is formed by an electrically conductive sheet metal which comprises several contacts  33  at its frontal side facing the control means support  20 . Analogously, the control contacts  32  are electrically connected to each other with another control contact bar provided so as to be covered behind the contact bar  32 , which control contact bar also embodies contact pins at its frontal side. 
         [0032]    The control means  4  is disposed between the lower housing part  21  and the housing lid  22  and comprises a printed circuit board  34  on the upper side of which four double-acting flexible tongues  35  and four power transistors  36  are arranged in contact with each other in an alternating manner in the longitudinal direction. The power transistors  36  are connected to cylindrical cooler elements  37  which are lead through openings recessed in the printed circuit board  34  and project over the bottom side of the printed circuit board  34 . The cylindrical cooler elements  37  are aligned with the second passages  24   b  and the mountings  26   b  embodied corresponding thereto. 
         [0033]    The sealing unit  3  is formed of a heat resisting elastic material, in the present case of EPOM, as one-piece component, for example by means of injection molding or casting, and it comprises a band-shaped base section  40 . First and second sealing elements  41   a ,  41   b  project over the upper side of this base section, which points to the control means housing  2 . Corresponding to this, the bottom side of the base section  40  comprises centering projections  42 . Each of the sealing elements  41  consists of two first and second sealing beads  43   a ,  43   b  arranged one after the other in the longitudinal direction of the cooler elements  37  or the contact studs  18 . The first sealing beads  43   a  comprise a rectangular base with a recess embodied corresponding thereto, the second sealing beads  43   b  comprise a correspondingly embodied circular basic shape. The lower sealing bead  43 ′ arranged adjacent to the base section  40  has larger dimensions than the sealing bead  43 ″ located thereabove. Each of the sealing beads  43  forms circumferential sealing contact surfaces  44  at its outer circumferential surface which lead, due to the stepped arrangement of the sealing beads  43   a ,  43   b , to a conical embodiment of the outer sealing surface formed by the respective sealing element  41   a ,  41   b  (cf.  FIG. 3 ). The inside circumference of the respective sealing beads  43   a ,  43   b  is essentially constant, so that the internal sealing contact surface  45  formed by the beads  43   a ,  43   b  has a cylindrical extension. 
         [0034]    To assemble the embodiment shown in the Figures, for example the heating block housing  1  as well as the control means housing  2  are first completely prepared with the heating and control elements accommodated therein. To join the three essential elements, heating block housing  1 , control means housing  2  and sealing unit  3 , the sealing unit  3  is, for example, pre-assembled on the side of the heating block. To this end, the first sealing elements  41   a  are shifted onto the contact studs  18  until the base section  40  rests on a cross web  46  represented in  FIG. 2  which covers the window openings  16  on the upper side and recesses centering mountings  47   a ,  47   b  for the centering projections  42  as well as passages  48  for the cooler elements  37  leading to the window openings  16 . Then, the preassembled control means housing  2  is connected to the heating block housing  1  to form a constructional unit. The cooler elements  37  are to this end inserted into the associated sealing elements  41   b  so as to be aligned with them until the upper edge of the heating block housing  1  is received in the internal double groove  27 . During this movement, the respective sealing elements  41   a ,  41   b  each enter the respective associated mountings  26   a ,  26   b , are centered due to the conical embodiment and finally compressed in the radial direction as the base section  40  fixes the sealing unit  3  by the contact with the cross web  46 . At the same time, the free ends of the contact studs  18  are shifted through the passages  24   a  into the interior of the control means housing  2  and between the double-acting flexible tongues  35 , whereby an electric contact between the flexible tongues  35  and the contact studs  18  is created. 
         [0035]    At the end of the introduction movement, a radial pressure increasing with the introduction movement has built up and acts on the sealing elements  41   a ,  41   b , which are now in sealing contact with the inside circumference of the mounting  26  on the one hand and with the outside circumference of the contact studs  18  or the cooler elements  37 , respectively. In the shown embodiment, there further is a particularity in that the height of the collars  25   a ,  25   b  is selected such that the collars  25   a ,  25   b  are placed against the base section  40  on the frontal side, which is thus clamped in the longitudinal direction of the cooler elements  37  or the contact studs  18  between the cross web  46  and the frontal sides of the collars  25  in a sealing manner. 
         [0036]    In the constructional unit prepared in this manner, the control contacts  29  are in contact with the printed circuit board  34  by means of the control contact bar, the corresponding strip conductors of which are connected to the power transistors  36 . The contact pins  33  contact contact points provided at the printed circuit board  34  which lead to the power transistors  36  and can be applied to the flexible tongues  35  and thus to the contact studs  18  depending on the switching characteristic of the power transistors  36 . The electric supply interface  30   a  for ground is electrically connected to the heating block housing  1  by means of electric strip conductors formed at the control means housing in the area of the double groove  27 . The cooler elements  37  are located with their front end in the respective window openings  16 . 
         [0037]    The connection between the heating block housing  1  and the control means housing  2  can be secured in various manners, in particular by welding or gluing. The embodiment shown in the Figures is in particular suited for an inexpensive manufacture of the electric heating device as the lower housing part  21  as well as the housing lid  22  of the control means housing  2 , as well as the two housing halves  10   a ,  10   b  can be manufactured by means of injection molding. The sealing unit  3  is connected to the housings  1 ,  2  during the assembly as insert manufactured separately from this housing. 
         [0038]    The embodiment shown in  FIG. 2  only differs from the one shown in  FIG. 1  in that slotted heat conducting plates  49  are provided in the window openings  16  which are clipped to the front end of the cooler elements.