Abstract:
A heater ( 30 ) is designed for a motor vehicle air conditioning system ( 10 ) and has at least one heat exchanger tube ( 58 ) which produces a heat conducting connection ( 54 ) between a heat generator ( 52 ) and at least one heat releaser via a medium which vaporizes and condenses in the heat exchanger tube. In order to be able to produce the heater ( 30 ) more economically, the heat generator ( 52 ) is made with an extruded profile ( 62, 84 ) to which at least one heat exchanger tube ( 58 ) is coupled by a heat conducting connection.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a heater for a motor vehicle air conditioning system with at least one heat exchanger tube which produces a heat conducting connection between a heat generating means with a heating element and at least one heat releasing means via a medium which vaporizes and condenses in the heat exchanger tube. Furthermore, the invention relates to an air conditioning system for a vehicle with such a heater, a motor vehicle with such an air conditioning system, and a process for producing a heater for such a motor vehicle air conditioning system.  
           [0003]    2. Field of the Invention  
           [0004]    Heaters of the initially mentioned type are used in motor vehicle air conditioning systems in order to be able to heat a liquid or gaseous heat transfer medium independently of the internal combustion engine of the motor vehicle. With the heated heat transfer medium, for example, ambient air, the passenger compartment of the motor vehicle can be heated up relatively quickly and especially the windows of the vehicle can be defrosted. These are so-called defrosters.  
           [0005]    In an electrical heater, as is known from published European Patent Application No. EP 0 243 077 A2, in its heat exchanger, there are PTC heating elements and radiator elements with ribs arranged in layers. The PTC heating elements heat the radiator elements in their immediate vicinity through which ambient air flows. On one edge of the heater, electrical contacts for the PTC heating elements are formed.  
           [0006]    These heaters automatically limit their output, when a certain threshold temperature is reached, by the rise of the resistance of the PTC heating elements. If a high enough voltage is applied to the PTC ceramic so that the ceramic is heated up by the current flow, an equilibrium state occurs between the supplied electrical power and the delivered thermal power. The ceramic cannot assume just any high temperatures. The resistance increases in super proportion due to the special resistance temperature characteristic of the PTC ceramic and the electrical current and output are limited.  
           [0007]    The described property of the PTC ceramic can be ideally used for heating applications. PTC heating elements can be used as self-regulating dynamic heating elements. Therefore, with PTC heating elements, the requirement of the vehicle manufacturer can be satisfied that the electrical heater with the outlet flaps closed and with full heat output due to the danger of melting and fire may not exceed a threshold temperature from roughly 150° C. to 165° C.  
           [0008]    However, known electrical heaters have disadvantages with respect to their construction. Thus, long electrical feed lines for high currents are necessary for the PTC heating elements which are distributed in the heat exchanger of the heater. Furthermore, the division of the heat output in the form of the PTC heating elements results in the problem that the heat output cannot be optionally distributed uniformly over the heat exchanger of the heater. Rather, unoccupied PTC locations, as necessarily form due to the high resistance tolerance of +/−35% of the PTC heating elements, lead to cold spots on the surface of the heater. These cold spots can be pulled as cold air plumes through the air channels of the air conditioning system.  
           [0009]    Integration of the PTC heating elements into the heat exchanger also leads to the heat exchanger being not homogeneous, but being composed of several materials. These materials, for example, aluminum, plastic and ceramic, can only be separated from the heat exchanger and recycled with difficulty after the service life of the heater has expired.  
           [0010]    Furthermore, the use of PTC heating elements leads to high specific heating costs. PTC ceramic is an expensive material with high specific weight. For reliable contact-making, complex mechanical structures in the form of steel frames or the like are necessary on the edge of the heater.  
           [0011]    Electrical headers are also known in which heating elements are electronically controlled. For control purposes, control transistors with a strength of the control currents of roughly 70 to 140 amperes are used. These control transistors produce exhaust heat of roughly 70 watts which is advantageously also fed into the heat exchanger of the heater. However, the delivery of heat requires high structural effort. Therefore, in general, control transistors are used which have a power loss as low as possible. The control currents of high intensity must be switched with repetition rates of, for example, 30 Hz and 100 Hz. This leads to considerable problems with respect to the electromagnetic compatibility of the heater within the vehicle.  
           [0012]    A generic heater is known from the Patent Abstracts of Japan 6365752 A. There, a fluid heater is described in which heat can be transported to ribs in a heat accumulator and to ribs in a flow heat exchanger with the heat pipe of the PTC heating element. The PTC heating element is used as a heat generating means from which the heat is transported to the ribs as the heat releasing means via the heat pipe. The object is to store heat in a heat accumulator over a long interval by special techniques. In the latter heater there is the problem that it is relatively expensive to produce. In particular, the configuration of the heat generating means is complex.  
           [0013]    Published German Patent Application DE 197 43 427 A1 discloses a heat exchanger which is made in the classical execution without a heat exchanger tube, with a plurality of flat tubes which are arranged parallel to one another for guiding a cooling medium. The ends of the flat tubes are bent, are placed tightly against one another and are each connected to a connecting pipe piece which is used as the collecting pipe for the cooling medium. The collecting pipe is made in an extrusion process as a profile pipe section. The object is to form a fluid-tight connection between the flat tubes and the collecting pipe here. Heat is conversely not routed via the connection between the flat tube and the collecting pipe.  
           [0014]    German Patent DE 31 43 334 C2 discloses a heat exchanger with a bundle of parallel running pipes which are exposed transversely to air, the pipes being positioned in the manner of heat exchanger tubes between two heat exchanger heads. Within the individual heat exchanger head, between two adjacent pipes, there is a heat exchanger plate which is made as an extruded profile in the form of a double web plate with several channels which run parallel next to one another. The heat exchanger plates extend transversely to the lengthwise direction of the respective heat exchanger head. On the lengthwise sides of each heat exchanger head, there are lengthwise channels which are connected to the channels of the transversely extending heat exchanger plates to carry liquid.  
           [0015]    Published German Patent Application DE 40 14 510 A1 discloses a motor vehicle heating system and a process for its operation in which a heat exchanger tube is used as a connection between a burner as the heat generating means and a heat exchanger as the heat releasing means.  
           [0016]    Published German Patent Application DE 199 11 547 A1 discloses an electrical heating means for a motor vehicle which is composed of several heating elements which are arranged parallel and which have PTC heating elements, and of corrugated ribs which adjoin the heating elements in a heat conducting connection.  
         SUMMARY OF THE INVENTION  
         [0017]    An object of the present invention is to devise a heater of the initially mentioned type that it can be economically produced. In this way, the total production costs of the pertinent air conditioning system of a motor vehicle will be reduced.  
           [0018]    This object is achieved in accordance with the invention with the initially mentioned heater in which the heat generating means is made with an extruded profile to which at least one heat exchanger tube is coupled by heat conduction. Furthermore, the object is achieved with an air conditioning system for a motor vehicle in which such a heater of the invention is incorporated and with a motor vehicle which has such an air conditioning system according to the invention. In addition, a process with the steps of producing a heat conducting connection between at least one heat exchanger tube and an extruded profile, with an opening in its lengthwise direction, and insertion of at least one heat conductor or a PTC heating element into the opening, creates one approach to the object.  
           [0019]    The heat generating means of the heater in accordance with the invention is provided with a housing which is produced as an elongated extruded profile. The extruded profile can be economically produced, meet high dimensional requirements and enable great freedom in the configuration of the profile cross sections. In addition, for extrusion purposes, in particular, aluminum alloys can be used which have high thermal conductivity. The extruded profile of the invention leads to an especially uniform heat distribution on the heat generating means. Therefore, in a heater with several heat exchanger tubes, they are uniformly heated and formation of cold plumes on the heat releasing means of the heater is thus avoided.  
           [0020]    For the profile of the invention, it is especially feasible if it is produced by extrusion in two areas.  
           [0021]    The first area is where the heating element, for example, a heat conductor, can be located within the heat generating means. This first area extends over almost the entire length of the extruded profile. In the extruded profile, elongated cavities can be formed especially advantageously. Such a cavity can be used in the extruded profile to the invention in order to insert and fix the heat conductor in it, for example. Fixing can take place with a heat conducting mass which is added to the cavity between the extruded profile and the heat conductor. In addition, the extruded profile can be pressed. All these arrangements create a combination of the housing and heating elements which can be produced easily and economically as a heat generating means.  
           [0022]    The second area is the interface between the heat generating means and the heat exchanger tube. This interface must conduct heat especially well. This second area can be made on an extruded profile by transverse openings which can be formed easily, and moreover, precisely in the profile. These openings can be punched or drilled, for example, in the extruded profile. The material of the extruded profile can be soldered or pressed with the heat exchanger tubes located in the transverse openings in an economical, and moreover, controlled manner. Alternatively, the heat exchanger tubes can also be inserted in a lengthwise groove of the extruded profile. A combination of the transverse opening and lengthwise groove is also conceivable. In any case, an extruded profile with this shape can be produced easily, economically, and moreover, with high dimensional accuracy.  
           [0023]    In addition, on the extruded profile, there can very easily also be so-called function surfaces for mounting of electronic components. These function surfaces can be formed on the extruded profiles especially well for mounting of transistors.  
           [0024]    Furthermore, extruded profiles can be formed with the same tool almost without added costs in different lengths. There can be systematically or modularly different lengths by which different heater types can be produced using only one tool.  
           [0025]    For known heat exchangers with a liquid heat transfer medium which have no heat exchanger tubes, to some extent extruded profiles have been used, because with them a fluid-tight connection was formed. According to the invention, between the heating element and the heat exchanger tube, there is no fluid-conducting connection so that heat must be transported conductively according to the invention.  
           [0026]    A principle aspect of the invention is, therefore, that several problems can be solved at the same time with an extruded profile. One of the problems is the question of how the heating element can be coupled, a second problem is the mounting of the heat exchanger tubes. In addition, the extruded profile forms the foundation for advantageous developments and different heater types which can be produced especially economically.  
           [0027]    The approach of the invention can be effectively used in heaters with a high power density at the interface between the heat generating means and the heat exchanger tube. As a result of the good thermal conductivity of the extruded profile used, a comparatively small temperature gradient in heat conduction can be achieved in this area. Therefore, the heat generating means according to the invention reacts, for example, especially quickly when the heat releasing means is dammed, by its slowing down.  
           [0028]    In one advantageous development of the invention, in the extruded profile, at least one first opening is formed in its transverse direction for holding one end of the heat exchanger tube. As mentioned above, these openings can be produced economically. The end of the heat exchanger tube is encompassed, in this configuration, by the extruded profile and a comparatively large heat transfer surface is formed. Alternatively, the heat exchanger tube with its end or its base can be soldered onto the heat generating means.  
           [0029]    The aforementioned heat conducting connection between the extruded profile and the heat exchanger tube can be formed especially advantageously by soldering. When soldering, a plurality of heat exchanger tubes can be coupled to the extruded profile in one process. In addition, cavities and gaps between the heat exchanger tube and the extruded profile are filled in soldering and thus good thermal conductivity of the connection is formed.  
           [0030]    Alternatively or additionally, the heat conductive connection between the extruded profile and the heat exchanger tube can be formed by caulking. Caulking offers especially the advantage that high temperatures do not form and accordingly the heat generating means cannot be damaged by high heating. Furthermore, a caulking process is generally very economical, and especially for production of large numbers, it is the process of choice.  
           [0031]    In the lengthwise direction of extruded profile, a second opening is advantageously formed for accommodating at least one PTC heating element or one heat conductor. The second opening can, as mentioned above, be made with great freedom of configuration and therefore can be exactly matched to the shape required for one or more PTC heating elements or a heat conductor.  
           [0032]    A PTC heating element can be pushed into the opening and fixed in it by pressing the extruded profile towards the PTC heating element and optionally electrical contact can be made with it.  
           [0033]    Furthermore, on the extruded profile of the invention, there is advantageously at least one function surface for the mechanical, electrical or heat conducting connection of at least one PTC heating element or at least one heat conductor. Such a function surface in accordance with the invention is a free by-product of the extrusion process. A means which is to be located in the heat generating means can be thermally linked using the function surface, electrical contact can be made with it, and moreover, it can be mechanically fixed. A function surface can be provided with an especially smooth surface using an extrusion process, which is advantageous especially for thermal and electrical contact-making. On such a function surface, besides a PTC heating element or a heat conductor, an electrical controller, for example, in the form of a control transistor, can be mounted.  
           [0034]    The indicated second opening can moreover be made as a slot into which especially at least one PTC heating element is pushed in the transverse direction of the extruded profile. Alternatively, heating elements can also be pushed axially into the extruded profile. Generally, in the heater of a motor vehicle air conditioning system there can be a majority up to a plurality of PTC heating elements. This takes place in the described development by simply inserting the individual PTC heating element radially into an axially pointed slot. The resulting short insertion path and high dimensional accuracy on the slot enable economical and moreover controlled production of the heater which has been developed in this way.  
           [0035]    At least one PTC heating element is furthermore advantageously held in the slot by elastic pre-tensioning of the extruded profile. The PTC heating element is pinched in the slot and is mechanically fixed by clamping. Moreover, between the clamped faces of the PTC heating elements and the material of the extruded profile, outstanding heat transfer is formed. The clamping can be produced by elastic expansion of the extruded profile itself. Alternatively or additionally, there can specially be a spring element in order to ensure clamping over the service life of the heater.  
           [0036]    Embodiments of the motor vehicle air conditioning system are explained in detail below using the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]    [0037]FIG. 1 shows a cross section of an air conditioning system in accordance with the invention,  
         [0038]    [0038]FIG. 2 is a perspective view of the heater of the air conditioning system as shown in FIG. 1,  
         [0039]    [0039]FIG. 3 shows a side view of a segment of a partially cutaway heat pipe of the heater as shown in FIG. 2,  
         [0040]    [0040]FIG. 4 is an exploded perspective view of a first embodiment of an extruded profile with a heat generating means in accordance with the invention of the heater shown in FIG. 2,  
         [0041]    [0041]FIG. 5 shows a perspective view of a second embodiment of an extruded profile with a heat generating means of the invention for the heater as shown in FIG. 2,  
         [0042]    [0042]FIG. 6 shows a cross section of a third embodiment of an extruded profile with a heat generating means according to the invention for the heater as shown in FIG. 2,  
         [0043]    [0043]FIG. 7 shows a cross section of a fourth embodiment of an extruded profile with a heat generating means in accordance with the invention of the heater as shown in FIG. 2, and  
         [0044]    [0044]FIG. 8 is a graph which illustrates the relationship between the resistance and temperature of a PTC ceramic. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0045]    [0045]FIG. 1 shows an air conditioning system  10  for a motor vehicle  12  in the form of a passenger car. The air conditioning system  10  is installed in the area of the dashboard  14  of the motor vehicle  12 . it has an air inlet  16  which is located between the hood  18  and the windshield  20  of the vehicle  12 . Underneath the air inlet  16  is a fan  22  which delivers air from the vicinity of the motor vehicle  12  into the air conditioning box  24 . The air conditioning box  24  is a space which is located underneath the windshield  20  and in which there are two heat exchangers  26 ,  28  and a heater  30  in succession.  
         [0046]    Air which has been conveyed by the fan  22  through the heat exchanger  26 ,  28  and the heater  30  and which has been optionally heated, then travels into diverse air channels  32 ,  34 ,  36  which are made in the dashboard  14 . The air travels through the air channels  32 ,  34 ,  36  to the outlet flaps  38 ,  40  and  42  and finally through air outlets  44 ,  46 , and  48  into the passenger compartment  50 .  
         [0047]    The heat exchangers  26 ,  28  are designed for liquid heat transfer media, for example, the coolant of an internal combustion engine of the motor vehicle  12  (not shown). The liquid heat transfer media are delivered by the heating or cooling system of the motor vehicle  12  (not shown) through the heat exchangers  26 ,  28 .  
         [0048]    The heater  30  is made as an electrical heater which heats air from the vicinity of the vehicle  12  if enough heat energy cannot be made available by the remaining heating system of the vehicle  12 . This is the case, for example, when the coolant of the internal combustion engine is cold immediately after the engine starts. Furthermore, an electrical heater can be efficient or necessary when the motor vehicle  12  is provided with a consumption-optimized internal combustion engine which delivers relatively little exhaust heat.  
         [0049]    [0049]FIG. 2 illustrates the basic structure of the electrical heater  30  of the invention.  
         [0050]    The heater  30  has a single, essentially closed heat generating means  52  which is connected to the heat conducting means  54  in the form of heat exchanger tubes. The heat exchanger tubes  58  are connected by thermal conduction to the heat releasing means  56  which are in the form of a plurality of ribs and form with them the heat exchanger of the heater  30 .  
         [0051]    The individual means  52 ,  54 ,  56  within the heater  30  form individual modules which can be combined and matched individually to the ribs depending on the required heat output and desired flow and space conditions. For the heat exchanger tubes  58  in combination with the ribs, a conventional heat exchanger can be used, as is used, for example, in water-air heat exchangers. The ribs can also extend between two heat exchanger tubes  58  as corrugated or zig-zag sheets. One such heat exchanger which is economical to produce is known, for example, from publishe European Patent Application EP 0 775 884 A3. The heat exchanger tubes  58  are round tubes. A configuration as flat tubes is also advantageous. The aforementioned zig-zag ribs can also be coupled especially well to these flat tubes.  
         [0052]    The heat generating means  52  is located, in accordance with the invention, on an edge of the heater  30 . From the heat generating means  52 , several heat exchanger tubes  58  project perpendicularly to and through the plurality of ribs  56  which generally extend spaced parallel to the heat generating means  52 . The heat pipes  58  therefore pass through the ribs  56  essentially normal thereto.  
         [0053]    Connections which are especially heat conductive are formed between the heat generating means  52  and the heat exchanger tubes  58  and between the heat exchanger tubes  58  and the heat releasing ribs  56 .  
         [0054]    The heat tubes  58  provided according to the invention, make it possible for the heating elements of the heater  30  to be concentrated on one edge or at least in one area of its heat exchanger. The generated heat can be distributed uniformly by the invention over the entire surface of the heat exchanger by means of the heat exchanger tubes  58  without formation of cold air plumes.  
         [0055]    [0055]FIG. 3 illustrates the operation of a heat exchanger tube  58  as a heat conducting means  54  within the heater  30 . Such a heat exchanger tube is also called a heat pipe.  
         [0056]    In the heat exchanger tube  58 , which is shown broken-away in FIG. 3, the heat is transported from bottom to top. In the bottom area of the heat exchanger tube  58 , the heat generating means  52  is located as the heat source. The liquid which is located in the heat exchanger tube  58  is vaporized by it. The liquid can be, for example, high-purity water. The vaporized liquid rises at high speed as steam in the heat exchanger tube  58 . This is illustrated with the arrow A.  
         [0057]    The steam travels to points of a hollow cylindrical wall  60  of the heat exchanger tube  58  at which comparatively low temperatures prevail because the heat exchanger tube  58  has been cooled there, for example, by heat conduction to a rib (arrow B). At the colder locations, the steam condenses. The liquified steam flows as a liquid to the bottom area of the heat exchanger tube  58  and back to the heat source located there (arrow C). With re-vaporization of the liquid the described cycle of heat transport begins again.  
         [0058]    The steam condenses on the heat exchanger tube  58  exactly where the colder locations of the wall  60  are located, therefore at the locations where there is a heat demand. The wall  60  of the heat exchanger tube  58  is therefore almost homogeneously heated. A noticeable temperature drop as is known in heat conduction in a solid generally cannot be noted. Large amounts of heat can be transported by the phase transition between liquid and gas. The heat transport capacity of such a heat exchanger tube  58 , as compared to solids with similar dimensions, is roughly 10 to 100 times higher.  
         [0059]    The condensed liquid can be returned to the heat source also by capillary action in, for example, a fine network on the inside of the heat exchanger tube  58 . The heat exchanger tube  58  can also be operated horizontally.  
         [0060]    [0060]FIG. 4 shows a first embodiment of a heat generating means  52  as is used for the heater  30  of the invention.  
         [0061]    The heat generating means  52  has an extruded profile  62  of aluminum alloy with an essentially cylindrical base body in which a cylindrical lengthwise opening  64  is provided in the lengthwise direction of the extruded profile  62  and three cylindrical transverse openings  66  are formed transversely to the extruded profile.  
         [0062]    The bottom ends of the heat exchanger tubes  58  are inserted and mounted in the transverse openings  66 , being caulked or soldered there to conduct heat.  
         [0063]    The lengthwise opening  64  is used for accommodating an electrical heating element in the form of a heating rod  68 . The heating rod  68  is provided with a cylindrical pipe jacket  70  with a diameter which is matched to the diameter of the lengthwise opening  64 . In the pipe jacket  70 , there is an insulating mass  72 . On the ends, the pipe jacket  70  is sealed by ceramic end sleeves  74  on which a respective electrical terminal  76  is located with a terminal bolt  78 . Between the terminal bolts  78 , a heat conductor  80  is routed through the ceramic end sleeves  74  and the insulating mass  72 . In an embodiment which is not shown, the pipe jacket  70  is omitted and the heat conductor  80  and the insulating mass  72  are inserted directly into the lengthwise opening  64  and fixed in it.  
         [0064]    Using the heat conductor  80 , in the operation of the heater  30  with the heating rod  68 , the extruded profile  62  can be heated. The extruded profile  62  transfers the heat directly to the embedded ends of the heat exchanger tubes  58 . The latter route the heat uniformly and quickly to the ribs which are used as heat releasing means  56 .  
         [0065]    On the extruded profile  62 , finally, a flattened area  82  is formed as a so-called “function surface” by which the extruded profile  62 , and optionally the heat exchanger tubes  58  which are attached to it with their ribs, can be mounted directly on a component of the vehicle  12  or in an outside housing of the heater  30 , which housing is not shown. The flattened area can also be used for mounting a control transistor with which the heat output of the heat conductor  80  is electrically controlled.  
         [0066]    [0066]FIG. 5 shows a second embodiment of the heat generating means  52  with an extruded profile  84  which is used to accommodate the PTC heating elements  86 .  
         [0067]    The extruded profile  84  is made as a cylindrical base body in which a lengthwise slot  88  is formed and three cross openings  90  are formed transversely to the lengthwise slot  88 . The cross openings  90  are used, in turn, to accommodate the ends of the heat exchanger tubes  58 .  
         [0068]    When the heater  30  is installed, the PTC heating elements  86  are pinched in the lengthwise slot  88 . The extruded profile  84  in the area of the lengthwise slot  88  is elastically widened for clamping, the PTC heating elements  86  are pushed in and the lengthwise slot  88  is allowed to elastically taper again.  
         [0069]    Thus, between the extruded profile  84  and the PTC heating elements  86 , a highly heat conductive connection which is, moreover, suited for electrical contact-making is formed. Function surfaces which are (not shown) are provided in the lengthwise slot  88  for this purpose. The PTC heating elements  86  make contact using a contact foil  92  which adjoins one side of the PTC heating element  86  in the lengthwise slot  88  and is electrically insulated against the extruded profile  84  using an insulating foil  94 .  
         [0070]    [0070]FIG. 6 shows another embodiment of a heat generating means  52 . In this embodiment, in the extruded profile  84 , as explained above, at least one cross opening  90  for accommodating one end of the heat exchanger tube  58  is formed.  
         [0071]    Furthermore, in the extruded profile  84 , a slot-shaped opening  96  is formed as a lengthwise opening and is located in the lengthwise direction of the heat exchanger tube  58  underneath its end. The PTC heating elements  86  are inserted in the opening  96  using a contact foil  92  and an insulating foil  94 , as explained above.  
         [0072]    On the sides of the extruded profile  84 , two flattened areas  98 ,  100  are formed, on which the extruded profile  84  has been caulked or pressed in the direction toward the PTC heating elements  86 . By this pressing, the PTC heating elements  86  are fixed mechanically to conduct heat in the opening  96  and electrical contact-making on the contact foil  92  is produced.  
         [0073]    [0073]FIG. 7 shows an embodiment of a heat generating means  52  in which in the extruded profile  84 , underneath and next to the heat exchanger tubes  58 , has two openings  96  for accommodating the PTC heating elements  86 . In this arrangement, especially good heat release from the PTC heating elements  86  to the ends of the heat exchanger tubes  58  is provided. The PTC heating elements  86  are inserted aligned in the openings  96  such that their surfaces which are in direct contact with the extruded profile  84  face toward the lengthwise axis of the heat pipe  58 . In an embodiment which is not shown, the indicated surfaces are each aligned relative to the an end of the heat exchanger tube  58 . Therefore, openings  96  are arranged in a V shape. In addition, the end of the heat exchanger tube  58  can be pressed flat and sealed. The transverse opening  90  can be matched on its base to the shape of the flat-pressed heat exchanger tube  58 . It is likewise V shaped in this area in cross section.  
         [0074]    On the sides of the extruded profile  84 , analogously to the embodiment shown in FIG. 6, flat areas  98 ,  100  are formed. The extruded profile  84  is made stable in the area between the openings  96  such that, essentially it is not deformed during the pressing of the PTC heating elements  86  in this area.  
         [0075]    Alternatively, the extruded profile  84  can be made deformable in a controlled manner in the area between the two openings  96 . The deformation process can be used to compress and seal at least one end of the heat pipe  58  which has been inserted into the cross opening  90  before pressing.  
         [0076]    The PTC heating elements  86  in the electrical heater  30  are components which cause high costs as a result of their complex production and their more expensive material. Therefore, efforts are made to operate the PTC heating element  86  with maximum output P. At a constant supply voltage, due to P=U 2 /R, it means that the minimum resistance should be triggered on the resistance characteristic of the PTC heating elements  86 .  
         [0077]    The initially described equilibrium state between the resistance and temperature on the PTC heating elements  86  and also the temperature of the ceramic which has been reached there depend largely on the heat release to the vicinity. High heat outputs can be achieved only with a favorable heat conducting means  54  and thus an optimized and long-lived heater with PTC ceramic can be formed.  
         [0078]    The combination of PTC heating elements  86  with heat exchanger tubes  58  according to the invention leads to stronger release of heat from the PTC heating elements  86  than in the technologies used in the past. As a result of the better heat conduction the temperature difference between the PTC heating elements  86  and the heat releasing means  56  of the heater  30  decreases. The PTC heating elements  86  cool off. The associated increase of resistance allows the electrical output to drop until a new equilibrium state is reached (see point  1  to point  2  in FIG. 8). The PTC heating elements  86  would therefore work basically at a lower temperature.  
         [0079]    However, a PTC ceramic with an especially low electrical resistance can be used. In this way, the output of the PTC heating elements  86  is increased and thus the temperature rises again to the optimum operating point  86  (see point  2  to point  3  in FIG. 8). At the optimum operating point the PTC heating elements  86  are located in the vicinity of the point of lowest resistance of the PTC ceramic.  
         [0080]    This means that the PTC heating elements  86  have the lowest inherent weight per delivered output. The use of heat exchanger tubes  58  as claimed in the invention therefore offers the possibility of significantly reducing the number and weight of the PTC heating elements  86  together with contact-making at a constant heat output. The heat output can be greatly increased relative to the costs of the PTC heating elements  86 . Moreover, the heat generating means  52  can be made especially compact.