Abstract:
An electrical heating device for a motor vehicle has a layer structure held by a retaining device. The heating device has several heat generating elements and heat dissipating elements between the heat generating elements, and a control device for controlling the heat generating elements. The heating device has a sound deadening housing, which circumferentially encloses the control device and by which sound waves produced by the control device are deadened. Through this measure, disturbing exposure of persons located in the vehicle to structure-borne noise and/or to sound waves borne by the air flowing through the electrical heating device is prevented.

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 layer structure held by a retaining device, comprising several heat generating elements and between these said elements heat dissipating elements and a control device for the control of the heat generating elements. 
         [0003]    2. Description of the Related Art 
         [0004]    An electrical heating device of this nature is for example known from EP 1 691 579 which originates from the applicant. 
         [0005]    The individual layers of the layer structure can with heating devices with corresponding conformity be glued together and/or pressed together under pretension from a spring, in particular when the layer structure is accommodated in an enclosed frame which forms the retaining device. Single electrical heat generating elements are held insulated from one another in the retaining device and generally, on a face side of the layer structure, for example in the longitudinal direction of the layer structure, are provided with electrical contact elements, via which certain heat generating elements can be electrically connected to the vehicle electrical system. 
         [0006]    For forming the heat generating elements normally resistance heating elements, so-called PTC heating elements, are used with which overheating of the heat generating elements can be reliably prevented due to their control characteristic. Each heat generating element usually comprises several PTC heating elements arranged one behind the other in the longitudinal direction of the layer structure. Said heating elements lie flat on an electrically conducting and generally well thermally conducting surface, via which the heat generating elements are supplied with electrical energy and the heat generated is dissipated by thermal conduction. This flat surface is normally formed by the heat dissipating elements, which for this purpose have on their outer side a sheet metal band which contacts a heat generating element and which is connected as a separate component or integrally with heating ribs or plates essentially extending transverse to the layer structure. Where the flat surface is formed by flat sheet metal bands, they are generally assigned to the heat generating elements. The sheet metal bands can in this respect form a prefabricated unit with the PTC heating elements. 
         [0007]    For the open or closed-loop control of the electrical heating device it has a control unit which controls the heat generating elements. The control device can here comprise electronic control elements and/or conventional relays. 
         [0008]    Following the general trend in the automotive industry, the electrical heating devices for motor vehicles are also prepared as modules which often means that the control device is mounted on the retaining device as part of the electrical heating device or is at any rate arranged adjacent to it. Thus, it is known for example from EP 1 157 867 that a control device for the control of the heat generating elements can be arranged within the frame and formed using power transistors, which have cooling fins on the side facing the layer structure. A similar arrangement is known from EP 1 492 384, which can similarly be regarded as forming a generic class and in which the control device is accommodated in the frame and similarly formed by power transistors. Also here there is the necessity of dissipating the heat loss produced by the transistors to the air flowing through the electrical heating device so that the control device is provided within the retaining device. An alternative design solution is known from EP 1 691 579 mentioned in the introduction, in which the control device is accommodated in a separate housing at the side of the frame and is mainly formed from switching relays which do not dissipate any loss. 
         [0009]    The arrangement of the control device in the retaining device or adjacent to the retaining device particularly with mounting of the control device directly on the retaining device has the problem in that noises produced during switching can penetrate relatively easily into the passenger compartment with the conveyed air where they can be heard by the passengers in the motor vehicle. Sounds produced by the control device can however also for example be passed into the interior as structure-borne noise via the walls of the ventilation ducts. In this case even relatively slight acoustic disturbances produced by the control device can be amplified by the walls in the hollow ventilation ducts, so that acoustic disturbance of the occupants of the vehicle is not only to be expected when traditional mechanically switching relays in the control device switch. 
       OBJECT OF THE INVENTION 
       [0010]    The object of the present invention is to reduce the effect of disturbing acoustic noise on the occupants of the vehicle. 
         [0011]    This object is solved according to the invention by an electrical heating device with the features of claim  1 . 
         [0012]    Preferred further developments are given in the dependent claims. 
         [0013]    With the electrical heating device according to the invention the control device is essentially surrounded by a circumferentially closed sound deadening housing. This sound deadening housing can completely or almost completely circumferentially enclose the control device and is formed such that sound waves emanating from the control device are at least partially absorbed. In this respect both those sound waves are preferably absorbed which otherwise propagate as structure-borne noise as well as those which are carried along by the air flowing through the electrical heating device. The sound deadening housing should be formed such that sound waves produced by the control device are preferably absorbed directly at the control device. The electrical heating device according to the invention has proved to be particularly effective with embodiments with which the control device is arranged at the side on the retaining device and is joined to it. In particular with these embodiments there is the problem that sound waves penetrate relatively unhindered to the occupant cell through structure-borne noise and through the air passing through the electrical heating device. 
         [0014]    Further advantages and details of the invention are given in the following description of an embodiment in conjunction with the drawing. This shows the following: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  a perspective side view of the embodiment; 
           [0016]      FIG. 2  a perspective exploded illustration of the housing of the embodiment enclosing the control device; 
           [0017]      FIG. 3  a perspective plan view of a housing element of the housing according to  FIG. 2 ; 
           [0018]      FIG. 4  a perspective plan view of an internal housing of the embodiment illustrated in the  FIGS. 1-3  and 
           [0019]      FIG. 5  a plan view of the inner housing illustrated in  FIG. 4  from the other side. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]      FIG. 1  illustrates the main parts of the electrical heating device. This comprises a two-part plastic housing  2 , in which a layer structure with several heat generating elements and intervening heat dissipating elements are held and pretensioned by a spring device described in more detail in the following. The heat dissipating elements  4  can be seen as meandering, curved sheet metal strips. Between said strips and behind longitudinal struts  6 , which pass through a housing opening  8  formed by the plastic housing  2 , there are heat generating elements running parallel to the longitudinal struts  6  and which cannot be recognized. In the central region of the housing opening  8  the layer structure has been removed and a spring strip  10  can be seen from which spring webs protrude inwardly. The spring strip  10  is introduced through an insertion slot  12  formed on the face side, as is described in EP-A-1 432287 which originates from the applicant. 
         [0021]    On the plastic housing  2  enclosing the layer structure a sound deadening housing  14  is arranged on the face side. The sound deadening housing  14  comprises essentially a second housing element accommodating a control device  16  and a first housing element arranged between it and the plastic housing. The first housing element is labeled with the reference numeral  18 , the second housing element with the reference numeral  20 . The first housing element  18  is joined both to the second housing element  20  and also to the plastic housing  2 . 
         [0022]    The first housing element  18  has on its underside facing the plastic housing flange segments  22  with holes for mounting the embodiment on the ventilation duct of a motor vehicle. Furthermore, the first housing element  18  forms on its underside a circumferential sealing groove  24  which interacts with ridges formed on the ventilation duct in order to seal the plastic housing  2 , which is pushed into the ventilation duct which it transversely passes, to the outside. From the underside of the first housing element  18  single-part, T-shaped latching tongues  26  also protrude down, which are latched with the plastic housing  2 . 
         [0023]    On the upper side facing away from the underside the first housing element  18  forms a single-part housing cover  30  with a rectangular base area ( FIG. 2 ), said housing cover being formed by reinforcing ribs  28  and stiffened opposite the flange segments  22 . 
         [0024]    This housing cover  30  fits between a collar  32  running externally around the second housing element  20  and sound deadening plates  34 , accommodated in the second housing element  20  and protruding from it. Apart from the sound deadening plates  34 , which can be seen in  FIG. 2  and which circumferentially clad the interior of the sound deadening housing  14 , further sound deadening plates can be provided on the inner side of the housing cover  30  or on the bottom of the second housing element  20 . With the illustrated embodiment the bottom of the second housing element  20  is nevertheless not occupied with a deadening plate  34  and has a design which is described below. The housing cover  30  can have a sound deadening plate which is closely located to the face sides of the circumferentially provided sound deadening plates  34 . 
         [0025]    The sound deadening plates  34  are cut from a foam plastic with a relative high density and precisely fitted into the second housing element  20 . In the illustrated embodiment the sound deadening plates  34  have a thickness of between 4 mm and 6 mm, preferably a thickness of 5 mm. As further measures in the sound deadening encapsulation of the interior of the sound deadening housing  14 , a sound deadening layer is provided between the collar  32  and the circumferentially arranged sound deadening plates  34 , for example in the form of an inlaid seal or in the form of a sound deadening element formed by means of two-component injection moulding on the first or second housing element  18 ,  20 , said sound deadening element being provided according to a type of sealing lip preferably on the face side on the housing cover  30  or on a sealing edge  36  of the second housing element  20  which can be seen in  FIG. 3 , surrounded circumferentially by the collar  32 . Through this sound deadening layer, the two housing elements  18 ,  20  are brought together in a soundproof manner. 
         [0026]    As can be seen from  FIG. 3 , holders  38  for electrically conducting contact springs  40  protrude from the bottom  52  of the second housing element  20 . Contact lugs electrically connected with the individual heat generating elements engage in these contact springs  40 , said contact lugs being formed regularly by sheet metal bands, which at any rate partially form a locating face for the PTC heating elements and are brought out at the side via the face side of the plastic housing  2 . To achieve this, the first housing element has slot-shaped insertion openings  42 , which are illustrated in  FIG. 2 , to which transversely broken up longitudinal webs  44  are recessed, single part, on the underside of the first housing element  18 , their conically running web edges  46  leading hopper-shaped to the insertion openings  42 , thus easing the introduction of the contact lugs into the insertion openings  42 . As can be seen from the illustration in  FIG. 3 , the holders  38  are formed by slotted tubes  48 , which are stiffened at the base by reinforcing ribs  50  against the bottom  52  of the second housing element  20 . These tubes  48  have a transverse slot  54  which is formed in an extension of the reinforcing ribs  50  and which only partially passes through the slot  48 . Furthermore, the tubes  48  have a cable slot  56  cut out at right angles to this, which extends down to the vicinity of the bottom  52 . 
         [0027]    In the second housing element  20  an inner housing  60  is inserted which is illustrated in more detail in  FIGS. 4 and 5 . The inner housing is preferably formed from a sound deadening material and is for example an injection molded part in a foamed plastic. The inner housing  60  has an inner housing base  62 , which has a cross-section of essentially a U-shape and to which an inner housing cover  64  is supported for swiveling. The inner housing base  62  forms three control element accommodation spaces  68 , separated by partition walls  66 . Each control element accommodation space  68  can have further sound deadening partition walls, which are shown as examples in  FIG. 4  and are identified with reference numeral  70 . The face side of a side wall  72  of the inner housing base  62  forms locating faces  74  for circuit boards  76 , which are protruded beyond by the partition walls  66  extending at right angles to them and are separated from one another by them. On these locating faces  74  the circuit boards  76  are located of which in  FIG. 4  only one circuit board  76  is shown as an example. The other circuit boards have been omitted in the illustration. 
         [0028]    It can be seen that the face side of the partition walls  66  and the upper side of the circuit board  76  are at about the same height. The closed inner housing cover  64  is located on this surface. The circuit board  76  and the inner housing cover  64  protrude beyond the side wall  72 . This protruding part of the circuit board  76  is used for the connection of electrical connecting leads  78 ,  80  and control leads  82 . Control elements, for example relays, which cannot be seen in the figures, protrude from the inner side of the respective circuit boards  76  into the control element accommodation spaces  68 . The control elements for each circuit board  76  are in each case accommodated in a control element accommodation space  68  separated by the partition walls  66  and which is divided by the other partition walls  72 . 
         [0029]    The connecting leads  80  leading to the circuit boards  76  are formed by extensions of a central feeder cable  84 . The further ground leads  86  lead to the inner housing  60 . These ground leads  86  and the connecting leads  78  leaving the circuit boards  76  each have one contact spring  40  at the end in each case, which is electrically connected to the corresponding leads  78 ,  86 . The leads  78 ,  80  connected to the circuit boards  76  initially extend essentially parallel to the side wall  72  and are then passed in front of a further side wall  88  which transversely passes through the housing  14  in the fitted state. 
         [0030]    As can be seen particularly in  FIG. 5 , the circuit boards  76  protrude beyond the respective connecting leads  78 ,  80  at the connection point. Furthermore, the inner housing cover  64  at this point protrudes beyond the inner housing  60  as well as the circuit boards  76 . The embodiment of an inner housing  60  illustrated in  FIG. 5  can be formed as a pre-assembled component. In this respect it is sufficient if the inner housing cover  64  is located on the circuit boards  76 . It is in particular not necessary that the inner housing cover  64  is fixed with respect to the inner housing base  62 . Fixing of this nature can however be realized with the prefabricated component. 
         [0031]    For mounting the inner housing  60  on the second housing element  20  this has a receptacle provided on the bottom  52  into which the protruding edge of the inner housing cover  64  can be fitted as also the ends of the circuit boards  76  on insertion into the housing  14 . In this arrangement illustrated in  FIG. 3  the inner housing cover  64  is located on the assigned sound deadening plate  34 . The pre-assembled inner housing  60  contacts the bottom  62  formed from plastic only via the face side of the inner housing cover  64 , which is formed from a sound deadening material. The sound deadening material is a silicone-free plastic, preferably a relative soft plastic, such as for example polyurethane, which ensures a certain deadening support of the inner housing  60  via the material forming the inner housing  60 . A polyurethane plastic with a hardness of ASHORE A between 50 and 90 has proven practicable. The receptacle is dimensioned such that the inner housing cover  64  fits precisely into the receptacle with the circuit boards  76 . Optionally, with slight compression of the sound deadening material of the inner housing cover  64 , a press fit can also be realized so that the inner housing  60  is fixed to the sound deadening housing  14  via the receptacle. The receptacle can for example be formed by recesses, ribs, webs or similar features on the bottom  52  by means of injection moulding as a single part on the housing  14 . Alternatively, it is possible to form a receptacle by single and/or between single sound deadening plates  34 . 
         [0032]    During the assembly of the embodiment, first the prefabricated component is inserted into the second housing element  20 . Then the contact springs  40  are pushed into the respective transverse slots. While doing so, the connecting leads  78  or the ground leads  86  are pushed into the cable slot  56  where they are accommodated. 
         [0033]    A first cable opening  90  is cut out on the second housing element  20  for bringing out the leads  80  or  86 ; a second cable opening  92  is cut away for the control leads  82 . The two openings  90 ,  92  are each covered on the upper side by the first housing element  18  and thus simplify the insertion of the respective leads  80 ,  82 ,  86 . 
         [0034]    The embodiment presented above has the advantage that the individual circuit boards  76  are accommodated with the associated control elements in separate control element accommodation spaces. The situation is avoided in which a common circuit board for all control elements of the control device is provided which as a resonating body would unnecessarily amplify emitted sounds. Since the inner housing  60  is formed with the associated circuit boards  76  and the leads  78 ,  80 ,  82 ,  86  connected to it as a prefabricated component, this component can first of all be prefabricated and the sensitive control elements sealed by fitting the inner housing cover  64  onto the inner housing base  62 . With the ensuing mounting of the prefabricated component on the sound deadening housing  14  the control elements are thus protected from impact. Also, the circuit board is prevented from becoming contaminated on its sensitive sections. The circuit board  16  is only free at its section protruding from the inner housing base  62 , which has no sensitive electrical or electronic regions. Due to the receptacle formed on the second housing element  20  for inserting the prefabricated inner housing  60 , the inner housing and the sound deadening housing  14  can be easily joined. 
         [0035]    Since the sound emitting control elements are on one hand enclosed by the inner housing and on the other hand supported in a sound deadening manner by the inner housing cover  64  with respect to the sound deadening housing  14  and furthermore are surrounded by the sound deadening plates  34 , the best possible sound insulation is achieved. The propagation of sound is in particular also reduced by an airtight sealing of the housing. In this respect, the flat plug contacts introduced into the housing  14  from the radiator are for example passed through a lip seal formed by means of two-component injection moulding. Using appropriate seals, the openings  90  or  92  can also be provided with sealing for the passage of the leads  80 ,  86 , the said sealing being formed on the housing  14  by means of two-component injection moulding. 
         [0036]    The special design of the tubes  48  facilitates a simple and precisely fitting assembly of the contact springs  40  introduced with the prefabricated component. The design also facilitates automatic insertion of the contact springs  40  into the tubes  48 . 
         [0037]    A subunit of the control device  16  is then accommodated in each of the control element accommodation spaces  68 . Each of these control subunit devices, separately accommodated in the inner housing  60 , is in itself soundproofed. The control subunit devices control by open or closed-loop preferably proportionally the complete heating power of the electrical heating device. With the illustrated embodiment three control subunit devices are provided, which then each control one third of the heating power of the whole heating device. In this way a better adaptation of the electrical energy consumed by the electrical heating device to a generator power of the motor vehicle can be achieved. The electrical heating power can with the illustrated embodiment then be switched to one third, two thirds or three thirds of the maximum heating power. Taking into account the switching capacity of the relays, the heating power of the switching circuits can be designed however different one to the other. The grading of the respective heating powers of a single switching circuit should here be selected such that the whole heating power can be switched in the smallest possible stages, despite the division giving just three switching circuits, using elaborate on/off switching of the individual switching circuits. With the illustrated embodiment only relays are used as the control element.