Abstract:
The present invention relates to a method of manufacturing an electric heating device, comprising a housing in which a heating block is held with the pretensioning force of at least one spring element located approximately at the same level as the heating block in its post assembly position and which defines opposite housing apertures between which the heating block is exposed, wherein the heating block is introduced into a housing part and the heating block is enclosed in the housing by another housing part. The spring element is brought into its assembled position and pretensioned when the housing is being closed to enclose the heating block. The present invention further relates to an electric heating device which can be employed in the method according to the invention and which can be relatively easily manufactured by injection molding.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a method of manufacturing an electric heating device which is in particular employed as auxiliary heater in a motor vehicle. The electric heating device comprises a housing in which a heating block is held with pretensioning force of at least one spring element located approximately at the same level as the heating block in its post assembly position. The housing furthermore embodies opposite housing openings between which the heating block is exposed. 
         [0003]    2. Description of the Related Art 
         [0004]    Such an auxiliary heater for air-conditioning the passenger compartment of a motor vehicle is known, for example, from EP 1 564 503. In the prior method of manufacturing the electric heating device, the elements forming the heating block are introduced into a housing part. Furthermore, the spring element is introduced into the housing part. Then, the housing is closed by placing another housing part onto the first housing part. According to the teaching of EP 1 564 503, the spring element is not pretensioned before the housing is closed, the pretensioning being effected by displacement elements which are formed at the other housing part and which pretension the spring element. These displacement elements form an inclined plane past which the spring element slides with its upper exposed limb and is in the process pivoted towards the heating block about a bearing within the first housing part and is finally pretensioned for generating a tension force. 
         [0005]    The heating block of the generic electric heating device usually comprises several parallel layers of heat-dissipating and heat generating elements. The heat generating elements of the heating block comprise several PTC heating elements, which are provided overlapping in one plane and are arranged between printed conductors, which are normally formed by sheet metal bands. These printed conductors carry current with different polarities. The PTC elements can be glued to these printed conductors. It is also possible for the printed conductors to contact the PTC heating elements under tension. In any case it must be ensured that for extracting the heat produced by the PTC heating elements and for feeding current, good contact between the printed conductors and the PTC heating elements exists. 
         [0006]    One or more heat generating elements can be provided as part of the heating block. The heat produced by the heat generating elements is dissipated through heat dissipating elements to the medium to be heated, i.e. the air. It flows through the housing through the two frame openings, which accommodate the flat heating block. The frame openings here lie normally parallel to one another on oppositely situated sides of an essentially flat, frame-shaped housing. With regard to the most economical manufacture of the electrical heating device, the heat dissipating elements are generally formed from meander-type bent sheet strips, which form corrugated ribs. These corrugated ribs contact heat dissipating elements on one or both sides. Consequently, the heating block comprises several layers of heat dissipating and heat generating elements, wherein it must also be ensured with regard to the thermal emission that the heat dissipating elements have a good contact to the heat generating elements. Also in this respect, the heat dissipating elements can be permanently joined to the heat generating elements and/or contact them under tension through at least one spring element accommodated in the housing. 
         [0007]    Instead of a meander-type sheet metal band, the heat dissipating element can also be formed by an extruded aluminium profile, which forms ridges, which extend essentially at right angles to the layers of the layer structure comprising the heat dissipating and the heat generating elements. In a case of this nature the printed conductor, i.e. the generally flat locating face, for the PTC heating element can be formed by the outer surface of an extruded aluminium profile of this nature. With both alternatives, corrugated rib element or extruded profile, the locating face for the PTC heating elements is formed electrically conducting and is electrically connected to contacts which are normally mounted insulated from one another. In the first case the contacts are generally formed by the exposed ends of the sheet metal bands. 
         [0008]    The layered heating block consisting of parallel heat dissipating and heat generating elements, optionally with one or more additional spring elements extending parallel to it, is preferably mounted in a housing with a U-shaped cross-section. When the layer structure is subjected to the pressure of a spring, the frame has to be dimensioned such that the spring force can be continuously maintained even at increased temperatures. Here it should be noted that the insulating frame is nowadays manufactured as an injection moulded part, due partially to economical reasons. Normal housings nowadays consist of a housing lower part and a housing upper part. The housing lower part here forms a receptacle for the individual elements of the heating block and, where required, of the spring element. The individual elements of the heating block are arranged in this housing lower part. Then the heating block is enclosed in the housing by joining the housing upper part and the housing lower part. To achieve this, edges which surround the frame openings can partially cover the heating block so that the heating block is enclosed between the frame openings and mounted in the housing. The two housing parts are then joined together, for example using a latching connection. 
         [0009]    With this type of assembly there is the problem that the individual layers of the heating block must be arranged at a predetermined point in the housing. Since not every heat generating element is assigned its own contacts, the electrical conditions within the heating block must also be considered during assembly. However to minimise the manufacturing costs, there is also the desire to form the parts of the heating block as standardised as possible, so that identical components can be used for different layers of the heating block. 
         [0010]    Furthermore, the housing itself should be able to be manufactured as simply as possible with regard to an economical manufacture of the electrical heating device. Here however, the particular requirements for the practical installation of one or more spring elements in the housing have to be followed when on joining the housing parts the heating block is already subjected to prestressing in the frame so that joining has to take place against this prestressing. 
         [0011]    With regard to the previously discussed problems, in EP 1 564 503 an electrical heating device of the generic type has already been suggested in which the layers of the heating block including a spring element are first mounted in a housing lower part initially free of tension. A housing upper part, which can be connected to it, forms an oblique sliding surface which extends over the end of the spring element protruding up from the housing lower part in relation to the outer side of the heating block. When joining the housing upper part and housing lower part, the spring element is accordingly compressed in the direction of the heating block and contacts it prestressed. 
         [0012]    This prior suggestion leads to a certain simplification during assembly, which however requires that the elements of the heating block, as also the spring element, are brought into the correct positions in the housing lower part. Furthermore, the housing implemented with this electrical heating device has various oblique surfaces, which are required for stressing and enclosing the spring element when joining the housing parts. Moreover, the embodiment of the spring element has to be relatively complex to fulfill the task. 
         [0013]    The present invention is based on the problem to provide a method of manufacturing an electric heating device, which allows a more simple assembly of the elements of the electric heating device. Furthermore, the present invention wishes to provide an electric heating device for carrying out the method which can be produced in a simpler and thus cheaper manner. 
       OBJECT OF THE INVENTION 
       [0014]    To solve the problem as concerns the method, the present invention proposes a method with the features of claim  1 . This method differs from the generic prior art in that the spring element is brought into its post assembly position and pretensioned when the housing is being closed to enclose the heating block. Accordingly, the spring element is initially not in its post assembly position. The spring element is rather entrained and brought into its post assembly position when the housing is being closed, i.e. during a relative movement of the two housing parts with respect to each other. During this introduction movement, the spring element is tensioned to generate the required pretensioning force. The spring element can accordingly be initially brought to a preliminary position in which the spring element partially or completely projects from the heating block and/or the one housing part. The spring element is shifted to its post assembly position and pretensioned only upon cooperation with the other housing part to enclose the heating block. The spring element tensioned when being pushed into the plane of the heating block. 
         [0015]    According to a preferred procedure step, the spring element is first introduced into the housing such that a longitudinal section of the spring element projects from the plane taken by the heating block. In this starting position, however, a partial section of the spring element is preferably already located at the same level with the heating block and thus in a position corresponding to the position to the individual parallel heat-dissipating and heat generating elements. Before the other housing part is placed onto the first housing part, the position of the spring element within the housing is substantially predetermined, at least within one plane extending transversely to the joining direction of the two housing parts. The longitudinal section projecting from the heating block is, in the preferred further development of the invention, not pressed into the post assembly position by an external tool, but by the other housing part, and the other housing part acts against the corresponding longitudinal section in the process and pushes the spring element into its post assembly position during the joining movement. 
         [0016]    To facilitate the joining movement of the housing parts and to better guide the spring element when it is being placed in the plane of the heating block, it is proposed according to a further preferred embodiment of the present invention that the housing parts are guided at each other when the housing is being closed. Guide elements of the two housing parts provided to this end are engaged before a force pressing the spring element into its post assembly position is generated. With this force, usually the tension force of the spring is also generated and only becomes effective when the spring is brought into the plane of the heating block. With an increasing tensioning of the spring, the overlap of the spring elements and accordingly a secure guidance of the joining movement of the two housing parts are increasing. Moreover, this method permits to position the longitudinal section at the other housing part in a predetermined manner, thus promoting the defined introduction of the spring element into the housing. 
         [0017]    According to a further preferred embodiment of the present invention which improves a precise positioning of the spring element when it is brought into the plane of the heating block, the spring element is guided, during its introduction into the housing but before this spring element pretensions the heating block and generates a corresponding force, at one of the housing parts by a housing element which at least linearly cooperates with a flat segment of the spring element. This flat planar segment usually extends in parallel to the introduction direction. In the same manner, the corresponding guiding surface of the housing part extends in parallel to the introduction direction and lies against the segment of the spring element. The spring element and the movement path of the spring element when the same is being introduced into the housing part, however, are designed such that in case of a spring force that is building up, the spring element is pressed towards the heating block and away from the housing element, at least far enough for the spring element to be unobstructedly deformed elastically by any interaction between the segment and the housing element initially guiding the same, which interaction should be avoided. Usually, the spring element is, with the progressive introduction movement, finally guided by the outer side of the heating block against which the spring element acts. 
         [0018]    According to a further development of the present invention, at least one spring limb of the spring element is pretensioned by one of the housing parts when the spring element is being introduced into the housing. With a progressive introduction movement, however, it is pretensioned by another one of the housing parts. This offers the possibility of first somewhat pretensioning the spring element by the first acting housing part, and of generating the final spring force for exerting a pressure on the heating block altogether by the other housing part. By this, movement paths of the housing parts during the joining process as well as of the spring element during its introduction into the housing part as well as the dimensioning of the housing parts can be correspondingly adapted. In particular, the initially acting housing part can have relatively thin walls and not be very rigid as the same only has to be able to generate a slight spring force. 
         [0019]    According to a further preferred embodiment of the present invention, the housing parts are connected with each other in a form-closed manner after the spring element has been brought into its post assembly position. This offers the possibility of only linearly joining the housing parts and in the process simultaneously bringing about a connection of the housing parts at the end of the joining movement. The preferred further development therefore in particular permits an easy assembly of the electric heating device. 
         [0020]    The electric heating device proposed with the independent aspect of the present invention to solve the problem as concerns the device is given in claim  8 . This heating device differs from the above mentioned generic prior art of EP 1 564 503 in that the spring element comprises at least one spring limb defining an inclined sliding surface for an element of one of the housing parts, and which is pretensioned by a supporting surface of one of the housing parts when the housing is being closed by joining the housing parts, the supporting surface extending in parallel to the joining direction of the housing parts. Such an embodiment is in particular preferable in view of a simple manufacture of the housing parts by injection molding, wherein the functional, contour and limiting surfaces of the housing parts, including those functional surfaces which form the support surface for the spring element or spring elements, extend exclusively in parallel or at right angles to the mold joint of the injection molding die. Such injection molding dies, i.e. the surfaces forming the mold cavity of the injection molding die, can be manufactured, while abandoning complex injection molding dies with a spark eroded surface forming the mold cavity, just by milling machining, for example with a face cutter, and thus they can be manufactured inexpensively and without special production know how. 
         [0021]    As spring element in the sense of the invention, in particular a spring element is meant which presses the individual layers of the heating block against each other such that these layers of the heating block, which are usually well connected to each other, are lying against each other so as to conduct heat as well as current. The latter criterion is important because electric heating devices of the generic type are normally operated in a motor vehicle at an operating voltage of 12 V, so that with the desired heating powers of several 100, if not even several 1000 W, a considerable amount of current flows at the phase interfaces of individual layers, which only do not lead to wear if there is no increased transition resistance at the phase interface of not firmly connected parts. The at least one spring element has to take care of this problem. Here, in particular a reliable transmission of electric current at the phase interface between two sheet metal strips and a PTC heating element arranged there between is important. According to experience, the spring has to apply, for example over a length of 200 mm, a spring force in the range of 500 N to 1000 N. Higher spring forces are possible, but in view of the desired heat output and current input they are normally not necessary. 
         [0022]    With the present invention, an electric heating device is proposed in which, by a special embodiment of individual heat generating elements by forming individual fitting elements with matching fitting element receptacles on the housing side, an assignment of individual heat generating elements to special positions within the heating block is predetermined. The individual heat generating elements of the heating block can correspondingly not be installed at any position in the housing. While the position or the positions of certain heat generating elements with corresponding fitting elements is/are predetermined within the housing, the heat-emitting elements can for example each have an identical design, preferably as sheet metal strips bent in a meandering manner and having an identical extension transversely to the layers of the layered structure. 
         [0023]    For the purpose of the present invention fitting elements are taken in particular as parts of the heat generating elements which have no function other than the positioning and/or mounting of these elements in the housing. Fitting elements of this nature with otherwise no function are for example formed from position elements, which hold the PTC heating elements at predetermined places within the heat generating element, particularly by a positional frame made of an insulating material which form adjacently provided receptacles for in each case at least one PTC heating element. The fitting elements are here formed in particular by the ends of the corresponding positional frames. One end or both ends of the positional frames can have a specially shaped head for this, which can be introduced into a correspondingly shaped receptacle on the housing. A positional frame can have identical fitting elements on its respective face-side ends. These can however also vary and in fact such that each heat generating element has fitting elements which differ from the fitting elements of all other heat generating elements. Correspondingly, fitting element receptacles are formed on the housing for this so that a prescribed heat generating element in the housing can only be installed at a predetermined place within the housing. Along with fitting elements, which are formed by the positional frame and have no function other than the holding and positioning of the heat generating elements within the housing, individual sheet metal bands forming the printed conductors can be formed as fitting elements. 
         [0024]    In this respect according to a preferred embodiment of the present invention it is suggested that the heat generating elements comprise sheet metal bands to which the PTC heating elements make electrical contact and which on the face side of the heating block are brought out of the plane of the associated heat generating element by bending and are passed through slots which are cut in the face side of the housing and that the bent sheet metal bands of different heat generating elements and the associated slots are formed such that the heat generating elements cannot be inserted at just any random place in the housing. 
         [0025]    With this preferred embodiment the ends of the selected sheet metal bands, which are located in the heating block on the upper and lower sides of the respective positional frames and which contact the PTC heating elements arranged in the respective positional frame, are bent over on one or both sides on the face-side end of the heating block so that the sheet metal bands leave the plane which is taken up within the heating block by the corresponding heat generating element. At the end of the heating block the sheet metal bands accordingly extend normally at right angles to the layers of the heating block, but after a certain length, i.e. an offset in this lateral direction, are again bent back into their original alignment and passed through a slot, which is cut out on the face side on the housing, i.e. normally extending essentially parallel to the layers of the layer structure. Through the length of the offset, i.e. the distance between the slot and the associated heat generating element, an assignment of predetermined heat dissipating elements to predetermined positions within the housing can be achieved such that the heat generating elements cannot be inserted just at any random position in the housing, but rather at a specific, preferably unambiguous place. 
         [0026]    With the present invention and the previously discussed further developments, assembly faults when arranging the individual layers of the layer structure within the housing before joining the housing parts are avoided. With the electrical heating device according to the invention individual elements of the heating block can only be installed at predetermined positions. The installation of the heat generating elements at a position, which is not admissible in design due to the arrangement and assignment of fitting elements and fitting element receptacles, is completely excluded. The fitting elements and the associated fitting element receptacles are designed with a certain amount of play so that the layers of the layer structure can be easily inserted despite the positive locking fit of the fitting elements in the fitting element receptacles and are generally held with limited movement with respect to the layers of the heating block. The tolerances are however not so large that just any random fitting element receptacle can accommodate any fitting element. 
         [0027]    According to a preferred further development of the present invention the housing comprises a housing lower part, which forms a receptacle for the heating block and a frame surrounding the receptacle as well as the fitting element receptacles, and a housing upper part, which is connected to the housing lower part to enclose the heating block. The fitting element receptacles here are formed such that the fitting elements can be inserted in the housing lower part in a direction transverse to the plane in which the heating block extends. During the assembly of the heating device the individual layers of the heating block are accordingly inserted into the housing lower part, which is open on one side, in the direction of the frame opening formed by this housing lower part, until they reach the bottom of the receptacle. The fitting element receptacles, open in the insertion direction, here specify the easily recognisable position of the corresponding heat generating elements within the heating block. With regard to the unambiguous assignment with this preferred embodiment it is suggested that different fitting element receptacles are formed in the longitudinal direction of the heat generating elements with different lengths and/or in the transverse direction to the heat generating elements with different width. 
         [0028]    The fitting elements of the individual heat generating elements can be widened similar to a hammer head, but be formed relatively short. Other fitting elements can be formed long and narrow in a ridge shape. Long, wide ridges can be provided, which protrude over the heat generating elements on one side. Very different profile shapes are conceivable, the corresponding profile shapes of which are assigned to the fitting element receptacles. For example, the fitting elements can in a plan view be formed round, elliptic, H or U-shaped on the still open housing lower part. The possible cross-sectional shapes previously discussed are normally moulded in one piece on the positional frame and normally joined to a thin ridge which connects the fitting element to the heating block. 
         [0029]    For the further prevention of assembly faults, according to a further preferred embodiment of the present invention, it is suggested that the housing upper part has guide pins, which protrude from the cover of the housing upper part which encloses the heating block, are formed in one piece with said cover and correspondingly engage cut-out pin guides in the housing lower part, wherein the guide pins and the pin guides are formed correspondingly on the two housing parts such that the two housing parts can only be joined together in a certain alignment. This further development takes into account that although the cover can be formed as a type of unspecific cover, with regard to an accurate arrangement of parts of the heating block or of the spring device it is however preferable to form the housing upper part specifically and to provide it in a predetermined arrangement for enclosing the heating block and to form it for the adaptation of the cover to the design of the elements of the heating block and to attach it unambiguously to the housing lower part. 
         [0030]    With regard to easy manufacture of the heating device according to the invention, in particular considering manufacture of the housing injection moulding techniques, according to a preferred aspect of the present invention it is suggested that the functional areas forming the receptacle and the pin guides as well as the contour surfaces of the housing lower part which give the outer contour as well as the functional areas forming the guide pins and the delimiting surfaces of the housing lower part delimiting the cover are exclusively formed such that they run parallel or perpendicular to the plane enclosing the frame opening. This embodiment has the advantage that an injection moulding tool for the manufacture of the housing lower part and housing upper part during the course of injection moulding of thermoplastics has no undercuts and due to the orthogonal alignment of the functional, contour and delimiting surfaces of the tool surfaces forming the housing parts, i.e. the injection moulding tool overall, can be manufactured in a simple manner using a face milling cutter. Breaking away from complicated injection moulding tools with a spark eroded surface forming the mould cavity, the injection moulding tool for the manufacture of the housing of the heating device according to the invention can be economically produced without special knowledge. 
         [0031]    For the purpose of this further development, functional surfaces are taken to be those surfaces of the housing parts which delimit the receptacle for the heating block, facilitate the joining of the housing parts and guide the required relative movement of the housing parts for this. For the purpose of this further development, contour and delimiting surfaces are taken to be those surfaces of the housing parts which define the outer contour of the housing parts and the housing overall. Relatively narrow face sides or edge surfaces at which two plane surfaces meet at a right angle are not regarded as appropriate functional, contour and delimiting surfaces for the purpose of the invention. These face sides and edge surfaces can be rounded off or bevelled. 
         [0032]    In this preferred embodiment the housing is normally formed as a rectangular component which encloses an essentially similarly essentially rectangular receptacle for the heating block and at both its outer sides prescribes in each case a similarly essentially similarly rectangular housing opening. 
         [0033]    According to a preferred further development, the spring element defines a planar contact surface at which the heating block is placed with its outer side. This embodiment has the advantage that in case of an embodiment of the heat-dissipating elements in the form of corrugated ribs bent in a meandering manner, the spring element can simultaneously form the contact surface for the bent ends of the corrugated rib. The spring element can correspondingly replace a sheet metal band known from prior art, which is possibly used for feeding current to the heating block, but can otherwise also exclusively form a planar contact surface for the adjacent corrugated rib element. With this preferred further development, the number of components which are required for assembling the electric heating device can be correspondingly reduced. The further development moreover has the advantage that the planar contact surface forms a sliding surface for the heating block which can effect an unobstructed sliding movement between the heating block and the spring element when the latter element is brought into the post assembly position. 
         [0034]    For facilitating the assembly, it is proposed according to another preferred embodiment of the present invention that the spring element comprises a sheet metal band which substantially extends over the whole length of the heating block. For facilitating the manufacture of the spring element by stamping and bending, spring limbs integrally formed at the sheet metal band are provided at this sheet metal strip. In the longitudinal direction of the sheet metal band, several spring limbs are provided successively. The sheet metal strip and the individual spring limbs causing the pretensioning spring force are correspondingly defined as uniform component. 
         [0035]    To reduce the force required for bringing the spring element into its post assembly position, it is proposed according to a further preferred embodiment of the present invention to provide two spring limbs as part of the spring element which limbs are provided in the joining direction at opposite ends and one behind the other. These two spring elements are correspondingly acted upon successively in the joining direction. Moreover, the spring force acting on the heating block in the joined state can be rendered uniform with this embodiment. In this preferred embodiment, each spring limb defines an inclined sliding surface. 
         [0036]    The spring limbs can be pretensioned by a support surface which is assigned to one single housing element when the housing is closed by joining the housing parts. Alternatively, the spring limbs arranged one upon the other can also cooperate by elements of different housing parts. The latter alternative offers the possibility of designing the element of a certain housing part cooperating with the inclined sliding surface less rigid and thus designing the housing part altogether somewhat lighter. 
         [0037]    In the preferred further development with two spring limbs provided one after the other in the joining direction, too, these are preferably pretensioned by a support surface of one of the housing elements, which support surface extends in parallel to the relative movement during the joining process, when the housing is being closed by joining the housing parts. It showed that in this embodiment, those spring forces can also be better controlled which are generated by the at least one spring element when the housing is not yet completely closed. These spring forces can be again supported by the guide elements which guide the guiding movement of the housing parts. Insofar, the probability that force action portions of the spring force which do not strictly act in parallel to the position of the heating block press the heating block or parts thereof out of the housing is reduced. 
         [0038]    According to a further preferred embodiment of the present invention, several spring limbs are provided successively in the longitudinal direction of the spring element. The heating block is correspondingly pretensioned by several spring limbs arranged in parallel to the layers, so that the spring force acting altogether is uniformly distributed. Furthermore, the spring elements or spring limbs can be selectively provided where PTC heating elements are provided within the heating block to cause in particular at these locations a high press-on force between the sheet metal bands feeding current to the PTC heating elements and the PTC heating elements. These spring limbs are connected with each other by means of substantially flat segments of a sheet metal strip which also define the spring limbs formed by stamping and bending. Adjacent spring limbs and the flat segments thus form a uniform component. The flat segments, however, are not only used for connecting adjacent spring limbs. They rather also permit a selective guidance of the spring element when it is introduced into the housing. At least one of the housing parts forms spacers to this end which project from the support surfaces and form a contact surface for the flat segments. These can first be guided by the spacers. Furthermore, the embodiment of the spring with spring limbs only provided on one side of the sheet metal band and a contact surface for the adjacent element of the heating block provided on the opposite side in connection with the embodiment of spacers at the housing lead to the spring element only being installable in the correct orientation with respect to the heating block, i.e. it can only be installed if the planar contact surface is situated adjacent to the heating block. By this embodiment, which can be essential for the invention alone and is independent of the introduction direction of the spring into the heating block or the orientation of the support surface relative to the introduction direction, errors in the assembly of the electric heating device can be avoided. For this, it is also irrelevant whether the spacers define a guide surface for the flat segments. It is only substantial that a contouring is realized in the longitudinal direction at the inner surface of the housing limiting the heating block by the spacers, the contouring fitting to the embodiment of the spring element. Spacers of the contouring projecting inwards correspond to the position of the flat segments of the spring element. 
         [0039]    The embodiment of the spring element with several flat segments, i.e. segments of a normal sheet metal strip with spring limbs arranged there between and projecting from the plane of the flat segments on one side, moreover offers the possibility of winding the sheet material onto a coil after the spring limbs have been stamped and bent and of supplying or storing them in this manner. The preferred spring element of the heating device according to the invention can correspondingly be taken from the strip as endless product and cut off to length which makes the adaptation of the spring to the desired spring force or length relatively easy. 
         [0040]    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: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0041]      FIG. 1  a perspective side view of an embodiment of the electrical heating device; 
           [0042]      FIG. 2  a side view of a housing lower part with an installed heating block from the embodiment illustrated in  FIG. 1 ; 
           [0043]      FIG. 3  an enlarged detail from the illustration according to  FIG. 2 ; 
           [0044]      FIG. 4  a perspective side view of the embodiment illustrated in  FIGS. 1 to 3 ; 
           [0045]      FIG. 5  a perspective side view of the housing upper part of the electrical heating device according to  FIG. 1 ; 
           [0046]      FIG. 6  a perspective exploded view of a heat generating element of the electrical heating device according to  FIG. 1 ; 
           [0047]      FIG. 7  a sectional illustration along the line VII-VII according to the illustration in  FIG. 6  of an assembled heat generating element; 
           [0048]      FIG. 8  a perspective side view of a spring element for prestressing the heating block of the embodiment illustrated in  FIGS. 1 to 7 ; 
           [0049]      FIG. 9  a side view of an end of the example according to  FIG. 1  before joining the housing parts; 
           [0050]      FIG. 10  a sectional view along the line X-X according to the illustration in  FIG. 9 ; 
           [0051]      FIG. 11  an enlarged detail view of the detail A in  FIG. 10  and 
           [0052]      FIGS. 12   a  to  12   e  enlarged detail views similar to the view according to  FIG. 11  in various states during joining the housing parts. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0053]      FIG. 1  shows a perspective side view of an embodiment of the electrical heating device with a housing  2 , consisting of a housing lower part  4  and a housing upper part  6 . Both housing parts  4 ,  6  are joined together positively locked and accommodate a heating block  8 , which consists of several heat generating elements  10  and heat dissipating elements  12  arranged in layers parallel to one another. The heat dissipating elements  12  are formed as corrugated rib elements from meander-type bent sheet metal strips. 
         [0054]    Five contact lugs  14 , arranged one over the other in the transverse direction protrude over a face side of the housing  2 . The contact lugs pass through the housing  2  at the cut-out slots  15 , each of which accommodate one contact lug and are mainly formed by the housing lower part  4 , but are complemented on a face side by the housing upper part  6 . 
         [0055]    The housing  2  has two oppositely situated frame openings, of which in  FIG. 1  only the frame opening  16  formed by the housing upper part  6  can be seen. The frame opening formed by the housing lower part  4  can be seen in  FIG. 4  and is identified with the reference numeral  18 . The frame openings  16 ,  18  are each interspersed with struts  20 , which extend at right angles to the layers of the heating block  8  and which join together longitudinal spars oppositely situated to one another on the housing lower part  4  and housing upper part  6 . 
         [0056]      FIG. 2  illustrates details of the heating block  8  and its accommodation in particular in the housing lower part  4  and illustrates the housing lower part  4  in a plan view with the housing upper part removed. The heat dissipating elements  12  are only illustrated incomplete on the respective face side ends of the housing lower part  4 . Accordingly, the illustration in  FIG. 2  provides a view onto the frame opening  18  formed by the housing lower part  4 . 
         [0057]    As can be seen, the illustrated embodiment has four heat generating elements  10 , which are each insulating on the face side and are accommodated with a certain movement transverse to the layers of the layer structure (heating block  8 ) in the housing lower part  4 . The housing lower part  4  has fitting element receptacles  22  for this, which open to a receptacle  24 , which is essentially formed by the housing lower part  4  and accommodates the heating block  8 . In the illustrated embodiment on each face side of the housing lower part  4  two different types of fitting element receptacles  22   a ,  22   b  are provided (cf. also  FIG. 3 ). Corresponding to the geometry of the fitting element receptacles  22 , the heat generating elements  10  have on their face side ends fitting elements  26   a ,  26   b , which each only fit into the appropriate corresponding fitting element receptacle  22   a  or  22   b . Here the corresponding fitting element receptacles  22  are matched to the correspondingly provided fitting elements  26  such that the heat generating elements  10  can move a few tenths of a millimetre transverse to the longitudinal extent of the layers of the heating block  8  in the housing  2 . The outer fitting elements  26   a  are formed as hammer heads and engage appropriately formed fitting element receptacles  22   a . In the longitudinal direction of the heat generating elements  10  these are substantially shorter than the second, centrally provided fitting element receptacles  22   b . The fitting elements  26   b  assigned to these longitudinal fitting element receptacles  22   b  are bar-shaped and less wide than the hammer-head shaped fitting elements  26   a . Due to this special design the central heat generating elements  10  do not fit into the outer positions for heat generating elements  10  on the heating block. In a corresponding manner the outer heat generating elements cannot be arranged in the centre of the heating block, i.e. inserted into the housing  2 . 
         [0058]    Whereas the heat generating elements  10  cannot be inserted at just any random place in housing  2 , the heat dissipating corrugated rib elements  12  are produced non-specifically and initially as longitudinal sections of a meander-type bent sheet metal strip and are then cut to length from this endless material. Each individual heat dissipating element  12  can be inserted at any position for a heat dissipating element within the heating block  8 . 
         [0059]    The fitting elements  26  are formed in one piece on a positional frame  28 , which can be seen in  FIGS. 6 and 7  and are explained in more detail with reference to these figures. The positional frame  28  consists of an insulating material and is used for positioning the PTC heating elements  30 . Here, for each individual PTC heating element  30  a receptacle  32  is cut out in the positional frame  28 , which circumferentially holds and configures this PTC heating element. On both sides of each of the PTC heating elements  30 , which are arranged adjacent to one another on one plane, sheet metal bands  34 ,  36  make contact, which form electrical printed conductors for powering the PTC heating elements  30  and via which the heat produced by the PTC heating elements is passed to the heat dissipating elements  12  by means of thermal conduction. These are located directly on the sheet metal bands  34 ,  36 . 
         [0060]    The face side ends of the positional frames  28  are extended by a fitting element ridge  38  beyond the position of the sheet metal bands  34 ,  36 . At the outer ends of the fitting element ridges  38  there are the respective fitting elements  26  of the positional frame  28 . As illustrated by the cross-sectional view along the line VII-VII drawn in  FIG. 6  (cf.  FIG. 7 ), most of the extent of the positional frame  28  in the width direction is taken up by the respective sheet metal bands  34 ,  36 . In the cross-sectional view at the side next to the sheet metal bands  34 ,  36  the positional frame has retaining ridges  40 , which are provided immediately adjacent to the side edge of the sheet metal bands  34 ,  36  and protrude over the corresponding sheet metal bands  34 ,  36  on the upper side and overlap them at the outside, preferably touching the printed conductors  34 ,  36  and making contact to them. In the illustrated embodiment the retaining ridges  40  are formed as a single part in the course of injection moulding, initially as protrusions extending at right angles to the principal extension direction of the positional frame  28 . The spacing of oppositely situated protrusions is selected such that the sheet metal band  34  or  36  just fits between these protrusions. 
         [0061]    The one-part component manufactured in this way by means of injection moulding is then fitted with the main parts of the heat generating element  10 , i.e. the PTC heating elements  30  are inserted into the corresponding receptacle  32  and surrounded on both sides by the sheet metal bands  34 ,  36 . Thereafter the recesses are plastically deformed inwards, comprehensively forming the printed conductors  34 ,  36 . Here, normally hot forming is applied in which the material forming the retaining ridges  40  is heated locally in the region of the sheet metal bands  34 ,  36  and is thus softened. The means employed in each case can for example locally heat the positional frame  28  by means of hot air or thermal conduction. In the case of heating using thermal conduction the means causing the heating is preferably formed by a tool which simultaneously carries out the shaping of the retaining ridges  40 . 
         [0062]    The retaining ridges  40  are not formed continuously in the longitudinal direction of the heat generating element  10 , but rather are provided in sections  40 . 1  to  40 . 5 . These sections  40 . 1  to  40 . 5  leave a passage  41  free between them which is formed such that in each case a strut  22  fits between the sections  40 . 1 ;  40 . 2 ;  40 . 3 ;  40 . 4  or  40 . 5  in the width direction. The section formed by the passage  41  protrudes with respect to the outer surface of the retaining ridges  40  in each case so far inwards that at least half the thickness of the struts  22  fits between the retaining ridges  40  and is accommodated there. 
         [0063]    However, a positive locking engagement between the struts  22  and the positional frame  28  is missing in a direction transverse to the layers of the heating block  8  so that movement transverse to the layers of the heating block  8  is provided between the struts  22  of the housing parts  4 ,  6 , which can also be designated as the first strut and the retaining ridges  40  which can be designated as the second strut  43 . 
         [0064]    The heat generating element  10  is formed as a preassembled component and can thus be handled during assembly without the risk that the printed conductors  34 ,  36  or even the PTC heating elements  30  inserted in the positional frame  28  will be lost. It must however be pointed out that normally the retaining ridges only fix the sheet metal bands  34 ,  36  in the positional frame, but do not contact them with contact pressure against the PTC heating elements  30 , which is sufficient to reliably power the PTC heating elements  30  in operation. With the embodiment discussed within the scope of the present invention this is in any case carried out by a spring element which is explained in more detail with reference to  FIGS. 8 to 10 . 
         [0065]    First however, some features will be dealt with which ensure that parts of the heating block  8  cannot be installed just at any random place within the housing  2 . 
         [0066]    As can be seen, in particular from  FIGS. 3 and 6 , a sheet metal band, i.e. the sheet metal band  34  illustrated in  FIG. 6 , is bent out of the plane of the heat generating element  10 . Consequently, an offset  42  is produced between the plane in which the sheet metal band  34  contacts the PTC heating elements  30  and a free end  44  which extends parallel to the first mentioned principal section of the sheet metal band  34  due to being again bent, but in the opposite direction. As can be seen from  FIG. 3 , this free end  44  is mechanically and electrically connected by a crimping element  46  to the assigned contact lug  14 . 
         [0067]    The upper heat dissipating elements in  FIG. 3  designated with reference numerals  10 . 3  and  10 . 4  have an offset  42 . 3  and  42 . 4  projecting from the upper sheet metal band  34  upwards. The lower heat generating element  10 . 1  has an offset  42 . 1  projecting downwards. The sheet metal bands  34 ,  36  of the heat generating element  10  designated with reference numeral  10 . 2  are bent on both sides to form an offset  42 . 20  or  42 . 21  and each is provided with a contact lug  14 . Due to these differences there is the possibility of preventing interchanging the positions of the heat generating elements  10 . 3  and  10 . 2  within the housing  2 . In this case due to the design of the contact lug receptacles  48 , the embodiment permits interchanging of the two central heat generating elements  10 . 2  and  10 . 3 . An appropriate interchangeability is also given for both outer heat generating elements  10 . 1  and  10 . 4 . 
         [0068]    The slots  15  previously mentioned with reference to  FIG. 1  extend from the outer side of the housing  2  and run into the lug receptacles  48  widened in each case with respect to the slots  15 . Behind this contact lug receptacle  48  a constricted slot  50  is in turn formed, which can accommodate a sheet metal piece shaped by punching and forming the contact lug  14  as well as the free end  44  of the assigned sheet metal band  34 . 
         [0069]    The housing lower part  4  can be formed in an economically manufactured injection mould, because all the surfaces significant for the housing  4  extend parallel or at right angles to the frame opening  18  of the housing lower part  4 . 
         [0070]    Thus, the housing lower part  4  has firstly frame surfaces  52   a - d  which essentially run at right angles to one another, which circumferentially surround the heating block  8  and run at right angles to the plane which contains the frame opening  18 . On the face side, on which the contact lugs  14  are brought out of the housing lower part  4 , the corresponding frame surface  52   b  opens outwards over four fitting element receptacles  54 , the principal walls of which also extend at right angles to the plane which contains the frame opening  18 . Those functional surfaces of the housing lower part  4 , which essentially form the contact lug receptacles  48  as well as the slots  15  or  50  leading to them as well as those walls which delimit the fitting element receptacle  22  and are illustrated in  FIG. 3 , have an appropriate extent. The above described receptacles  15 ,  22 ,  50  and  54  are delimited on the side of the housing lower part  4  by a bottom, which runs parallel to the plane which contains the frame opening  18  of the housing lower part  4 . This receptacle bottom is identified in  FIG. 4  with the reference numeral  56 . This bottom  56  also forms the inner surface of the struts  22  as well as on one hand limit stops  58 ,  60  at the edge for the spring element still to be explained as well as on the other hand the outer heat dissipating element  12  located on the oppositely situated longitudinal side. These limit stops  58  or  60  are in turn parallel to the plane which also contains the frame opening  18 . 
         [0071]    The inner surface of the housing lower part  4 , which is formed on the face side of the face side ends of the walls which form the fitting element receptacles  22  or the contact lug receptacles  48 , runs parallel to this plane. On a longitudinal side this upper edge is formed by spacers  62 , which project over the frame surface  52   c  to the receptacle  24  and its function will be dealt with in the following description of the spring element. Below this upper plane of the inner surface of the housing lower part  4  there are the inner surfaces  63  of the two longitudinal spars  64 ,  66  of the housing lower part  4 , which however project so far beyond the limit stops  58 ,  60  at the edge that the heating block  8  is almost completely circumferentially held, i.e. with more than 70% of its height extent, in the housing lower part  4 . The longitudinal spars  64 ,  66  are interspersed by pin guides  68 ,  70 ,  72 , which extend at right angles to the plane which contains the frame opening  18 . The pin guides  68 ,  70 ,  72  intersperse in sections essentially the whole longitudinal extent of the longitudinal spars  44 ,  66 . 
         [0072]    In the centre of the respective longitudinal spars  64 ,  66  there is a pin guide  70 , which is formed with a relatively short length and opens into a window  74  located on the outside of the housing lower part  4 . 
         [0073]    Adjacent to this central journal guide  70 , journal guide  68  are provided which extend in each case over about ⅓ of the length of the longitudinal spars  64 ,  66 . On the outer end of these pin guides  68  there are in turn pin guides  70  with assigned windows  74 , as described above. On the face side ends of the longitudinal spars  64 ,  66  again relatively small pin guides  72  are formed which extend from the inner surface of the longitudinal spars  64 ,  66  to the outer surface of the housing lower part which also contains the frame opening  18 . 
         [0074]    The functional surfaces forming or delimiting the pin guides  68 ,  70 ,  72  all extend at right angles to the plane which contains the frame opening  18 . Only the face side edges of the corresponding openings  68  to  72  are slightly bevelled or rounded off in order to facilitate the introduction of corresponding guide pins  76  to  80  of the housing upper part  6 . For easier joining of the housing lower part  4  and housing upper part  6 , furthermore the free ends of the walls are also bevelled or rounded off which delimit the spacers  62  as well as the receptacles  22   b ,  15 ,  50 ,  48  at the ends and form the upper ends of the spacers  62 . 
         [0075]    The housing upper part  6  shown in perspective illustration in  FIG. 5  also has exclusively functional or delimiting surfaces aligned orthogonal or parallel to the corresponding housing opening  16 . As functional surfaces in particular the guide areas of the previously mentioned guide pins  76 ,  78 ,  80  are provided which can be introduced into the corresponding pin guides  68 ,  70 ,  72 . The guide pins  78  are moulded as notched pins and form latching ridges  82 , over which on the upper side a thickened head of the notched pin  78  protrudes, which form a latching surface  86  which extends parallel to the plane which also contains the frame opening  16 . The latching ridges  82  extend from the upper side of a cover  88 , which is formed essentially as a flat component and produces the frame opening  16  and furthermore contains the outer surface of the struts  22 . The cover  88  is formed frame-shaped as a cover for the housing lower part  4 . Accordingly, the guide pins  76  to  80  extend from the inner side of the cover  88  at right angles. A recess  90  is provided for the latching ridges  82 . In the region of the recess  90  the edge surface of the cover  88  is drawn inwards so that the flat, even side surface of the latching ridge  82  extends parallel to the guide surfaces of the guide pins  76  or  80 , but is located inward to the respective outer guide surface of these guide pins  76 ,  80 . The inner surfaces of the corresponding guide pins  78  to  80  facing the heating block  8  nevertheless lie in one plane. 
         [0076]    On one face side of the housing upper part  6 , on the inner wall of the cover  88 , five recesses are formed corresponding to the five contact lug receptacles  48  which form part of the slots  15  and also comprise an upper margin region of the contact lugs  14  after the assembly of the heating block in the closed housing. On the oppositely situated face side a further guide pin  92  is provided, which interacts with a corresponding further guide receptacle cut out on the housing lower part  4 , but does not fit into the fitting element receptacles  22  or the contact lug receptacles  48 , so that it is ensured that the housing upper part  6  is placed on the housing lower part  4  and joined to it in a predetermined and unambiguous manner. Also the walls enclosing the further pin guide  94  and forming the guide pin  92  extend at right angles to the plane located on the frame opening  16  or  18 . 
         [0077]      FIG. 8  illustrates a perspective side view of a spring element  96 , which contacts the heating block  8  at the edge and is located in its installation position at the level of the heating block  8 . The front side of the spring element  96  in  FIG. 8  forms a flat locating face  98  to which the adjacent, the uppermost in  FIG. 3 , heat dissipating element contacts with its vanes. Put more accurately, the face side bent ends of more meandering vanes of the corrugated rib band  12  contact this locating face  98 . The locating face  98  is formed by an initially flat sheet metal band, on which transversely protruding spring limbs  100  have been formed by punching on both sides, which lie initially within the plane of the locating face  98  and after punching have been brought into the shape recognisable in  FIGS. 8 ,  10 ,  11  and  12  by bending. Two spring limbs  100   o ,  100   u  lie overlapping in the width direction, i.e. transverse to the longitudinal extent of the flat locating face  98  and thus in the insertion direction of the spring element  96  during assembly. Each individual spring limb  100   o ,  100   u  forms the sloping sliding surface  102   a ,  102   b ,  102   c , which in each case includes an angle of between 35 and 55°, preferably about 45°, between it and the flat locating face. Between the pairs of spring limbs  100  provided one behind the other in the longitudinal direction of the spring element  96  there are flat segments  104  in which the spring element  96  is formed as a rectangular flat sheet metal band. 
         [0078]    The spring element  96  illustrated in  FIG. 8  has pairs of spring limbs  100   o ,  100   u  corresponding to the number of intervening spaces between the individual spacers  62  on the longitudinal spar  64  (cf.  FIG. 4 ). Each pair of spring limbs  100   o ,  100   u  lies in the installation position of the spring element  96  between these spacers  62 . The flat segment  104  spans the width of the spacers  62  and joins together adjacent pairs of spring limbs  100   o ,  100   u . The correspondingly manufactured spring can thus be introduced as a one-part component into the housing  2 , in particular into the housing lower part  4 , which simplifies the manufacture of the electrical heating device. The wall sections of the frame surface  42   c  provided between adjacent spacers  62  accordingly form a supporting surface  106  for the respective pairs of spring limbs  100 . Due to the matching of the spring element  100 , in particular of the embodiment of the flat segments  104  between the pairs of overlapping spring limbs  100 , it is not possible to introduce the spring element  96  into the housing lower part  4  in the incorrect alignment. The spring element  96  can then only be pushed into its installation position, in which the spring element is accommodated at the level of the heating block  8  in the housing  2  when the flat locating face  98  is aligned to the heating block. Furthermore, the heating block is held by the spacers  62  at a distance to the supporting surfaces  106  so that the spring element  96  can contact these surfaces at any time on introduction into the housing lower part  4  and without hindrance by the heating block  8 . 
         [0079]    With a continuing insertion movement of the spring element  96  in the direction of the heating block  8 , i.e. with continuing insertion into the heating block, the spring element  96  is then forced in the direction of the heating block  8  due to the spring force from the lower spring limb  100   u , so that the layers  10 ,  12  of the heating block are compressed. The flat locating face  98  with the adjacent heat dissipating element  12  already has a covering such that with a continuing insertion movement the spring element  96  is sufficiently guided in the insertion direction between the heating block  8  and the housing lower part  4 . Finally, with continued insertion the lower spring limb  100   u  is elastically compressed. The counter force on the housing side is here formed by an upper edge  108 , which is formed between the supporting surface  106  and the inner surface of the longitudinal spar  64  by the meeting point of the two surfaces. This edge  108  initially forces the lower spring limb  100   u  inwards on the introduction of the spring element  96 . With a continued introduction movement the upper spring limb  100   o  is finally forced inwards by the interaction of the free end of the corresponding spring limb  100   o  which is bevelled inwards and bent. 
         [0080]    As can be seen from  FIGS. 10 ,  11  and  12 , the housing  2  has a further housing element which interacts with the spring element  96 . This further housing element is formed by an edge  110  of the housing upper part  6 , which is formed between the inner surface of the cover  88  and a bottom  112  of the housing upper part  6 , and in fact by the joining edge of an outer edge  113  delimiting the bottom  112  of the housing upper part with the inner surface of the cover  88 . The height offset between this bottom  112  and the inner surface of the cover  88  takes into account that the heating block  8  protrudes over the surface  63  formed by the longitudinal spars  64 ,  66 , and in fact approximately with the same length as the spacers  62  protrude over the inner surface  63  of the longitudinal spars  64 ,  66 . The edge  110  contacts a sloping sliding surface  102   a  of the spring element  96  which is formed by the upper spring limb  100   o . As emerges from  FIGS. 10 and 12   a , the upper end of the spring element  96  is in a state essentially free of contact pressure with spacing to the bottom  112  of the housing upper part  6 . 
         [0081]    For the description of the assembly reference is made in the following to  FIGS. 12   a  to  12   e . First the individual layers  10 ,  12  are introduced into the housing lower part  4 . Then the spring element  96  is manually inserted part way into the housing lower part, in each case so far until the layers of the heating block  8  are located against one another and the spring element  96  is placed sufficiently deeply between the heating block  6  and the frame surface  52   c.    
         [0082]    This initial introductory movement, through which the spring element  96  essentially introduces no spring pressure into the heating block  8 , guides the spring element  96  over the face side surfaces of the spacers  62  facing the heating block  8 , which interact with the flat segments  104  of the spring element  96 . Due to the contacting of the spring element  96  and spacers  62 , the spring element  96  is aligned with its flat locating face  98  parallel to the layers  4 ,  6  of the heating block. After this first assembly step the spring element  96  protrudes over the plane taken up by the heating block  8  by a longitudinal section which is identified with L in  FIG. 12   a . Then the housing upper part  6  is placed on the housing lower part  4 . The guide pins  76 ,  78 ,  80 ,  92  here engage in the corresponding pin guides  68 ,  70 ,  72 ,  94 . In doing this, the spring element  96  remains initially essentially free of stress. In this state sufficient coverage between the guide pins and the corresponding recesses can already be achieved so that both housing parts  4 ,  6  can only be moved in a linear direction relative to one another. Then follows the joining of the housing parts  4 ,  6  with the application of the spring force. 
         [0083]    First, the spring limbs  100   o ,  100   u  are slightly compressed until the bottom  112  of the housing upper part  6  meets the upper end of the spring element  96  (cf.  FIG. 12   b ). The two edges  108  and  100  have here already slid a certain way along the sloping sliding surfaces  102   a  and  102   b . The upper spring limb  100   o  is in this way already bent elastically so far inwards that with increasing insertion movement the free end of the limb  100   o  bent inwards at the centre of the spring element  96 , which forms a further sloping sliding surface  102   c  can reliably pass the edge  108 . Thereafter, a continuing joining movement between the two housing parts  4 ,  6  also leads to the spring element  96  being carried along. Here, initially the edge  108  produces a further elastic stressing of the lower spring limb  100   u . This lower spring limb  100   u  is finally completely accommodated between the supporting surface  106  and the heating block  8  ( FIG. 12   c ). With increasing insertion of the spring element  96  into the housing lower part  4  the upper spring limb  100   o  is finally also elastically deformed by the interaction of the edge  108  with this upper spring limb  100   o  in the direction of the heating block  8  and accordingly produces a spring force. This elastic spring force is mainly produced in that the edge  108  slides down the further sloping sliding surface  102   c  and forces the upper spring limb  100   o  in the direction of the heating block  8  (intermediate step between  FIG. 12   c  and  FIG. 12   d ). The spring element  96  has reached its final position when the two housing parts  4 ,  6  contact one another with their respective surfaces aligned to one another. The spring element  96  is stressed and held in this installation position due to the spring force between the heating block  8  and the frame surface  52   c . If the spring element  96  is pushed from outside by an unintentional force, the limit stop  58  or the bottom  112  of the housing upper part  6  in each case prevents the spring element  96  being forced out of the housing  2 . 
         [0084]    Shortly before the two housing parts  4 ,  6  contact one another, heads  84 , which are guided in the guide channels under slight elastic bending of the latching ridges  82  in the pin guides  70 , are forced outwards, so that their latching surface  86  contacts a latching counter surface  114  or it protrudes beyond it with slight play, so that both housing parts  4 ,  6  are fixed together captively. 
         [0085]    As the above description explains, during the manufacture of the electrical heating device according to the discussed embodiment, on closing the housing by joining the housing lower part and housing upper part, the spring element is brought into its installation position in which the spring element is located at the level of the heating block, i.e. it is arranged in the plane which is also taken up by the heating block. Furthermore, the spring element is only put under spring pressure on introduction and only then when the two housing parts  4 ,  6  are guided relative to one another by the positive locking engagement of the guide pins  76  to  80  in the corresponding pin guides  68 ,  70 ,  72 . The constructive development accordingly offers the possibility of introducing the components of the heating block into the receptacle  24  formed by the housing  2  without tension being applied. It is only thereafter that spring stressing follows and in fact this occurs on making contact and in housing parts  4 ,  6 , limited with respect to one another in position. If thereafter, due to the spring pressure produced, on joining the housing parts  4 ,  6 , displacement of the elements of the heating block  8  or even forcing out of the elements of the heating block  8  from the receptacle  24  occurs, these parts are held by the parts of the housing parts  4 ,  6  enclosing the heating block in the housing  2  and forced back into the desired position on joining the housing parts  4 ,  6 . 
         [0086]    With regard to the constructive development the present invention is not restricted to the embodiment described. Thus, a spring element can for example be provided which has a spring limb which in the installation position is initially essentially free of stress. This spring element is introduced without stress with the heating block into the receptacle  24 . The spring element has a spring limb and the spring limb forms a sliding surface sloping obliquely outwards and downwards in the direction onto the limit stop  58 , and in fact for a pin, which interacts with the spring element and sets the corresponding spring limb during the joining of the housing upper part and housing lower part under spring pressure such that the spring element overall contacts the heating block  8  under spring pressure. With this embodiment the spring element is initially accommodated without stress together with the heating block in the housing lower part and however remains stationary relative to the joining direction on production of the spring pressure. The spring element is just pushed slightly in the plane of the heating block and contacts the heating block. Furthermore, the spring limb or limbs are pivoted to produce the elastic stress. The special development of the heat generating elements  10  facilitates a more simple assembly, because the grid arrangement formed by the first and second struts  20 ,  43  is not a complete part of the housing, but rather the second struts with the positional frames  28  are formed and thus are reliably located where the PTC heating elements  30  come to rest within the heating block  8 . Compared to the prior state of the art in which the grid arrangement is solely formed by the housing parts, housing parts can be accordingly manufactured which are relatively simply formed. Furthermore, higher tolerances can be permitted, because no one-part struts joined to the housing exist which extend parallel to the layers of the heating block  8  and must be provided exactly at the position of the heat generating elements  10 . Through the dimensioning of the struts  20  and the passage  41  and in particular the insertion of the struts  20  between two sections of the retaining ridges  40  there is still the possibility of supporting the first and second struts  20 ,  43  with positive locking with respect to one another and thus of stiffening the housing overall. 
         [0087]    Since the heat dissipating element  12  is prepared as a preassembled unit and furthermore it is ensured by the fitting elements  26  and the associated receptacle  22  that the heat generating elements  12  can only be installed at certain places within the housing  2 , the production of the electrical heating device, in particular the assembly of the individual parts can also be carried out by less skilled personnel. 
         [0088]    The definitive arrangement of the embodiment gives an unambiguous assignment of different components of the electrical heating device. If this unambiguous assignment is not maintained, the components of the electrical heating device cannot be assembled.