Abstract:
An auxiliary electrical heating device for a motor vehicle includes a heating block that includes parallel layers of at least one heat emitting element and at least one heat generating element. The heating block is held in a housing having oppositely situated housing openings. In order to permit the electrical heating device to be operated safely even at high operating voltages, a contact protection of an insulating material covers the respective housing openings.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an electrical heating device, in particular to a heating device as auxiliary heating for a motor vehicle, with a heating block that has parallel layers of at least one heat emitting and one heat generating element, which layers are enclosed by a housing that has oppositely situated housing openings formed therein. 
         [0003]    2. Description of the Related Art 
         [0004]    An electrical heating device of this nature is known for example from EP 1 768 459 A1 which originates from the applicant. A generic electrical heating device of the above-mentioned type normally has a heat generating element with at least one PTC element, on the oppositely situated lateral faces of which electrically conducting sheet metal bands abut, through which the PTC element is supplied with electrical current. This electrical supply is normally provided at 12 volts. This operating voltage is harmless, so that normally no special measures need to be taken to prevent unintentional contact with the heating block. Normally, heat emitting elements, which are supplied electrically with the same polarity as the sheet metal bands, are situated externally on oppositely situated sides on the heat generating elements. In this respect the heat emitting elements, which are irradiated by the medium to be heated and which lie exposed in the frame openings, carry electrical current. 
         [0005]    From the previously mentioned state of the art it is known how to provide an insulating layer between the heat emitting elements and the sheet metal bands, in particular for higher operating voltages. Accordingly the strip conductors to the PTC element or elements and the heat emitting elements, i.e. the radiator layers of the heating block, are electrically insulated. This electrical insulation however also causes a certain thermal insulation by means of which the efficiency of the PTC elements is impaired. These PTC elements have self-regulating properties so that operation of the PTC elements with good efficiency gives the most possible undisturbed dissipation of the heat generated by the PTC elements. 
       SUMMARY OF THE INVENTION 
       [0006]    The object of the present invention is to provide an electrical heating device of the type mentioned in the introduction, which can be operated safely even at high operating voltages. 
         [0007]    To resolve this problem with the present invention, the previously mentioned electrical heating device is further formed by at least one contact protection of an insulating material covering the respective housing opening. According to the present invention a housing opening, in particular the front housing opening in the direction of flow, i.e. the housing opening through which the air flowing through the heating device initially flows, is provided with contact protection. Preferably, both of the mutually oppositely situated housing openings which normally enclose the planar heating block are covered by contact protection. The contact protection covers in particular the current-carrying parts of the heating block. The contact protection is selected to be so fine meshed that a user cannot touch the heating block by inserting his fingers through the frame opening. Preferably, the contact protection is equipped such that also tools normally used for repair purposes cannot access the heating block through the frame opening. A relatively finely meshed plastic mesh is particularly considered here. The plastic mesh should be formed from a relatively temperature-resistant plastic, in particular nylon or Teflon. The plastic mesh can here also be considered to be formed in a grid shape. In this respect finely meshed means preferably that the mesh size is specified between 0.7 and 1.0 mm, preferably between 0.8 and 0.9 mm. The objective should be the prevention of the insertion of a test wire with a diameter of 1.0 mm with a force of 1 N into the heating block, i.e. through the contact protection. With regard to the best possible flow through the contact protection the open area for flow through the contact protection should be selected with about 75 to 90%, preferably with 85 and 90%. 
         [0008]    With the present invention safe contact protection is provided so that it is no longer necessary to provide an insulating layer between the heat generating elements and the heat emitting elements. The efficiency of the heating device according to the invention is therefore improved compared to the prior art of EP 1 768 459 A1, particularly if a multi-layered redundant insulating layer is formed which has relatively poor thermal conductivity. 
         [0009]    From EP 1 621 378 A1 an electrical heating device of the generic type is known in which oppositely situated housing openings are covered with flow-resistant grids. The flow-resistant grids however are used to provide a suitable adjustment of a flow resistance through the housing at those points where elements of the heating block are missing. The suggestion according to the invention differs from this in that the contact protection is positioned in the direction of flow directly before or after the active elements of the heating block, i.e. after the at least one heat emitting element and/or the at least one heat generating element. A corresponding situation applies to EP 1 173 340 A1, which discloses at least one placeholder element in the housing which is located adjacent to an element of the heating block. 
         [0010]    With the electrical heating device according to the invention the heating block is circumferentially enclosed by the housing, normally formed from insulating material, in particular plastic, whereas the mutually oppositely situated housing openings left free by the housing are covered by the contact protection, particularly by the plastic grid, such that the medium to be heated, normally air, can pass through the contact protection to the heating block, in particular to the current-carrying components of the heating block situated behind the contact protection in the flow direction, but not however body parts of an installer or service person or a tool used by these persons nor a foreign body which has entered the air passage or optionally has been brought in with the air flow. 
         [0011]    According to a further development of the present invention in which the plastic mesh is mounted on a strut arrangement, the struts of which span the respective housing openings, the plastic mesh is prevented from abutting the surface of the heating block. The strut arrangement can be formed from one or more mutually parallel struts or also a grid arrangement. The individual struts or grid bars of the strut arrangement are preferably formed so rigidly that with normal loads no significant deflection occurs such that the plastic mesh can abut the surface of the heating block exposed towards the housing opening. 
         [0012]    With regard to an economical manufacture, according to a further development of the present invention it is suggested that the plastic mesh is joined to the struts of the strut arrangement by overmoulding of the plastic mesh with a plastic component forming the strut arrangement. Consequently, during the manufacture of the electrical heating device the plastic mesh is placed into an injection mould, which comprises a mould cavity for moulding the strut arrangement. The mould cavity is here preferably formed such that the plastic component for forming the strut arrangement is not only formed on one side of the plastic mesh, but also on the opposite side so that after overmoulding on both sides of the plastic mesh, the plastic mesh is sealed in as a rigid plastic component. The strut or grid arrangement is here preferably formed such that the struts which in each case extend parallel to the heating block layers are located at the same height as the heat generating elements so that the medium to be heated can flow over the heat emitting elements without hindrance. 
         [0013]    According to a preferred further development at least one spacing element is provided between the heating block and the contact protection. This prevents direct contact with the heating block elements occurring through the contact protection even with a certain deflection of the contact protection and optionally also of the strut arrangement due to a conceivable, externally acting application of pressure. The spacing element or elements are selected such that normally a spacing between the contact protection and heating block of between 4 and 8 mm is provided. With conceivable deflections of the contact protection the spacing between the heating block and the contact protection due to suitable dimensioning of the spacing element or elements should be at least 2 mm. The spacing elements can be provided on both sides of the heating block between it and the frame openings covered by the contact protection. 
         [0014]    According to a preferred further development the spacing element is formed by a spacing support protruding over the struts of the strut arrangement on the inside and/or by a spacing web, which protrudes over a positional frame of the heat emitting element, accommodating at least one PTC element, and preferably formed as one part with it. 
         [0015]    In the second case the heat generating element is formed in a manner known per se by at least one PTC element, which is provided between mutually parallel sheet metal bands and which is accommodated in a positional frame of an insulating material. The positional frame normally has a plurality of receptacle openings for accommodating one or more PTC elements. Normally, the positional frame has a thickness which is less than the thickness of the PTC elements. According to the further development, the positional frame however also forms the spacing element, which protrudes over the essentially flat heating block and maintains the spacing of the contact protection, particularly the plastic mesh, with respect to the surface of the heating block. For this purpose the positional frame is normally extended out of the plane of the heating block and protrudes beyond it. 
         [0016]    In the other design case the at least one strut of a strut arrangement penetrating the housing opening is formed as a spacing element. In a manner known per se the struts can extend parallel to the layers of the heat emitting elements and in front of them. Also, cross struts extending at right angles to these struts can be provided with spacing webs. The spacing support can here interact with the spacing web, which is formed by the positional frame, to realize the required spacing between the contact protection and the heating block elements. Thus, the spacing supports and the spacing webs can in each case be formed continuously in the longitudinal direction with the struts or positional frame. In each case, at the intersection of the spacing support and spacing web at least one spacing support or spacing web can have a recess accommodating the other so that there is a certain linking of the two elements. 
         [0017]    According to a preferred further development of the present invention, the strut arrangement is clipped to the housing together with the plastic mesh. This embodiment offers the possibility of retrofitting the contact protection according to the invention to installed electrical heating devices. The clipping is normally realized by latching elements which are formed during injection moulding of the strut arrangement. 
         [0018]    With an alternative embodiment the housing comprises a housing upper part and a housing lower part, whereby each of the housing parts leaves one of the housing openings free. The housing parts are formed from plastic and circumferentially enclose the housing block. They normally have the strut arrangement so that the plastic mesh is directly joined to the associated housing part by overmoulding with the plastic material forming the housing parts. 
         [0019]    According to a further preferred embodiment of the present invention, a creep path of at least 5 mm is in each case formed between the current-carrying components of the heating block and the contact protection. On one hand the spacing elements contribute to this creep path and namely also when they just provide spacing between the heating block and the inner side of the contact protection which is less than the above measure for the creep path. In this case an appropriate creep path is realized by the geometric embodiment of the spacing element or elements. In particular, protrusions extending parallel to the plane of the heating block and which increase the creep path are formed on the spacing element or elements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    Further details and advantages of the invention are given in the following description of embodiments in conjunction with the drawing. This shows the following: 
           [0021]      FIG. 1  a perspective side view of a first embodiment before the contact protection is fitted; 
           [0022]      FIG. 2  a perspective plan view onto the contact protection according to  FIG. 1 ; 
           [0023]      FIG. 3  a perspective plan view of a second embodiment of the present invention; 
           [0024]      FIG. 4  a perspective interior view of a housing part of the second embodiment illustrated in  FIG. 3 ; 
           [0025]      FIG. 5  a cross-sectional view of the second embodiment illustrated in  FIGS. 3 and 4 ; and 
           [0026]      FIG. 6  a perspective interior view according to  FIG. 4  of a housing of a third embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0027]      FIG. 1  illustrates an electrical heating device as auxiliary heating for a motor vehicle with a housing  2  comprising two identically formed housing parts  4 ,  6 , which are joined by clipping, thus enclosing a heating block  8 . The housing parts  4 ,  6  each have a housing opening  10  which is open to the heating block  8  and are joined on their connecting side to a flange  12  which provides access to and holds the electrical plug contacts for the connection of the heating block  8  as well as a controller enclosed by a control housing  14 . 
         [0028]      FIG. 1  shows the embodiment from the flow inlet side. Here, the housing opening  10  of the housing part  4  is penetrated by five cross struts  16 . The longitudinal spars  16  extend at right angles to the parallel layers of the heating block  8 . These layers are formed by heat emitting elements in the form of radiator elements  18  and heat generating elements  20  accommodated between them. 
         [0029]    As emerges particularly from  FIG. 5 , the heat generating elements  20  each consist of a positional frame  22  of an electrically insulating material which has a receptacle opening  24  for the accommodation of a PTC element  26  in each case. The positional frames  22  in turn accommodate electrically conducting sheet metal bands  28  which abut on oppositely situated sides of the PTC element  16  and supply them with electrical current. In the embodiment illustrated in  FIG. 5  insulating layers  30  are provided in each case on the outer side of single sheet metal bands  28 , which insulate the sheet metal bands  28 , which are supplied with electrical current of different polarity, with respect to the metallic radiator elements  18 , so that individual heat generating elements  20  are electrically delimited from one another and can be specifically controlled. Within the heating block  8  different potentials are prevented from being directly opposite one another. Consequently, it is possible for example to operate two heating stages of the heating block using one ground connection. 
         [0030]    Mutually oppositely situated longitudinal spars  32  of the frame-shaped housing  2  have latch openings  34  for the accommodation of latch protrusions  36  of a cover  38  which forms contact protection. This cover  38  consists of an injection moulded covering frame  44  through which frame longitudinal and cross struts  40 ,  42  pass. The cover  38  also comprises a plastic mesh  46 , which is joined on both sides to the plastic material forming the struts  40 ,  42  and the covering frame  44  by means of overmoulding. Accordingly, the struts  40 ,  42  and the covering frame  44  are formed in the flow direction on both sides of the plastic mesh  46 . 
         [0031]    The cover  38  illustrated in  FIGS. 1 and 2  can be detachably joined to the housing  2 . For this purpose the latch protrusions  36  are introduced into the assigned latch openings  34 . 
         [0032]    Latch lugs formed on the latch protrusions  36  latch with respect to the housing  2  so that the cover  38  is retained captively on the housing  2 . 
         [0033]    In the embodiment illustrated in  FIGS. 1 and 2  the plastic mesh  46  has a mesh size such that a piece of wire with a nominal diameter of 1 mm cannot pass through the plastic mesh  46  to the elements  18 ,  20  of the heating block  8 . 
         [0034]    The frame cross struts  42  are aligned with the cross struts  16  of the housing part  4 . Due to the accumulated thickness of the cross struts  16  and the cover  18 , in particular in the region of the frame cross struts  42 , there is a free distance of about 6 mm between the surface of the heating block  8  and the plastic mesh  46 . Due to the frame longitudinal struts  40  the plastic mesh  46  is additionally stiffened, so that a pressure force acting on the plastic mesh  46  does not lead to it being pressed down to the level of the heating block  8 . 
         [0035]    A further embodiment is given in  FIGS. 3 to 5 . The same components are given the same reference numerals compared to the previously discussed embodiment. Whereas the previous embodiment illustrated with reference to  FIGS. 1 and 2  is particularly suitable for retrofitting existing electrical heating devices, the embodiment given in  FIGS. 3 to 5  is produced from the beginning as an electrical heating device according to the invention. Consequently, the plastic mesh  46  is formed as part of the housing part  4  or  6 . 
         [0036]    As shown particularly in  FIG. 4 , also with the second embodiment the plastic mesh  46  is joined by overmoulding to the material forming the housing part  4 . The material forming the cross struts  16  of the housing part  4  is here located on the two sides of the plastic mesh  46  and protrudes over it. In addition, on the inner side cams  48  are formed protruding over the cross struts  16 , delimiting a free space  50 , the height of which (extending in a direction transverse to the layers of the layered heating block) corresponds approximately to the thickness of the heat generating elements  20 , so that they can be accommodated between the cams  48  (cf.  FIG. 5 ). Due to this embodiment the heat generating elements  20  are fixed in their plane. The cams  48  provide an adequate distance between the plastic mesh  46  and the radiator element or elements  18 , even with a certain deflection of the cross struts  16 . 
         [0037]    Although the second embodiment according to  FIGS. 3 to 5  only has cross struts  16 , it is pointed out here that the relevant housing parts  4 ,  6  can have not only a strut arrangement with cross struts  16 , but also such an arrangement as has been described above for the cover  38  and which has cross struts and longitudinal struts. A strut arrangement of this nature leads to a particular stiffening of the housing opening  10  and largely prevents a deflection of the contact protection in the direction of the heating block  8 . 
         [0038]    As particularly emerges from  FIG. 5 , with the embodiment according to  FIGS. 3 to 5  the positional frames  22  are extended beyond the heating block  8 , i.e. in the direction of flow. The positional frames  22  accordingly form spacing webs  52  which protrude on both sides of the heating block  8 . These spacing webs  52  interact with the two housing parts  4 ,  6  and keep the cross struts  16  spaced to the heating block  8 . Due to the plurality of supporting points along the cross struts there is no concern that they will deflect substantially in the direction of the heating block  8 , for example in the case of a pressure force acting on the housing part  4  externally. As emerges from  FIG. 5 , here it should be noted that only the housing part  4  is provided with plastic mesh  46 , whereas the housing part  6  with otherwise an identical embodiment has no corresponding plastic mesh  46 . The two housing parts  4 ,  6  can therefore be formed in injection moulding tools of identical geometry with the difference that in one injection moulding tool for the manufacture of the housing part  4  the plastic mesh  46  is inserted as an inserted part before the moulding of the plastic components. The dimension of the spacing webs  52  at right angles to the plane accommodating the heating block  8  is selected such that a spacing A of between 4 and 8 mm is produced between the surface of the heating block  8  and the contact protection  46 . 
         [0039]      FIG. 6  illustrates a housing part  4  of a further embodiment, which is formed identically to the embodiment previously described with the difference that parallel to the cross struts  16  on the inner side of the housing part  4  there are spacing supports  54 , which extend between the two longitudinal spars  32  continuously at a uniform height and which protrude over the struts  16 ,  40 ,  42  on the inside of the housing  2 . The height of the spacing supports  54  is selected such that the contact protection  46  is maintained at a predetermined distance from the heating block  8 . The contact protection  46  is supported via the spacing support  54  in particular with the face sides of the positional frames  22 . 
         [0040]    It is pointed out that the spacing supports  54  can also be provided in combination with the spacing webs  52  of the positional frames  22  to realize a desired distance between the plastic mesh  46  and the heating block  8  due to the spacing webs  52  and spacing supports  54  essentially crossing at right angles. Here the face sides of the spacing webs  52  and/or the spacing supports  54  can be formed like cams with free spaces between, as has been described above with reference to the second embodiment.