Abstract:
The invention under consideration relates to an electric heating device for heating a flowing medium with a housing, in which the at least one electric heating element of the electric heating device is held securely and fully shielded from the medium held in the circulation chamber by a separating wall that divides the housing into a heating chamber and a circulation chamber. The circulation chamber has inlet openings and outlet openings for introducing and removing, respectively, the medium. The heating element is preferably a PTC heating element and is held by means of a clamping force in a recess formed by the separating wall, said recess preferably projecting into the circulation chamber. The invention furthermore relates to a recuperator for converting electrical energy into thermal energy, particularly for an electric drive in a vehicle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention under consideration relates to an electric heating device for heating a flowing medium, wherein, in the context of the invention under consideration, a medium is particularly understood as a liquid medium. In particular, the invention under consideration relates to an electric heating device for a motor vehicle, in this case, especially for a motor vehicle that is operated with a drive that gives off almost no process heat or that does not give off any pertinent quantity of process heat. Particularly included in this group are hybrid drives. Accordingly, the invention under consideration is intended to provide a heating device that is particularly suited for generating the heat that is required for the processes running in individual system parts of a motor vehicle, or at least the heat that promotes such processes. The heating device according to the invention should, in particular, be suitable for generating a larger amount of heat in the shortest time, in order to give off this heat within the shortest time to the corresponding system parts within the motor vehicle. At the same time, some of the attention of the invention under consideration should be given to avoiding overheating of the electric heating device caused by control errors. 
     2. Description of the Related Art 
     In the state of the art, it is known to use so-called resistance heating elements or even PTC heating elements in motor vehicles, whereby such heating elements are self-regulating, because these display a greater resistance as the heating increases and consequently allow a lower amount of current through. The PTC heating elements consequently have self-regulating characteristics that prevent these heating elements from overheating. The maximum temperature that a PTC resistor can reach at a given operating voltage can be influenced by certain parameters during the manufacture of the PTC heating elements, which does not have to be explained in more detail here. 
     PTC heating elements are accordingly routinely deployed in radiators, particularly those that serve to heat the passenger compartment in such vehicles whose drive unit in any case gives off insufficient waste heat for climate control in the passenger compartment. 
     From DE 39 07 179, an electric heating device with a housing is known, in which a multitude of PTC heating elements are arranged, whereby the liquid medium (in this case, water) that is to be heated flows directly around these PTC heating elements. The electric connecting elements leading to the electric heating elements accordingly lie freely in the medium to be heated, which does not comply with the safety requirements that should be required and that additionally carries the problem of the corrosion of the metallic parts of the connecting elements. Furthermore, the arrangement of the electric heating elements directly in the flow conduit hinders any maintenance and repair work. 
     OBJECT OF THE INVENTION 
     The object of the invention is to provide an electric heating device that complies with the above requirements, offers adequate safety and avoids the abovementioned problems, 
     To solve this problem, the invention under consideration provides an electric heating device including a housing in which a separating wall is formed that divides the housing into a heating chamber and a circulation chamber that holds a medium through which the medium flows. An inlet opening is provided for feeding the medium into the circulation chamber and an outlet opening is provided for guiding the heated medium out of the circulation chamber. An electric heating element is held in the heating chamber. This differs from the state of the art as given in DE 39 07 179 in that the housing has a separating wall that divides the housing into a heating chamber and a circulation chamber. The medium can circulate in the circulation chamber from an inlet opening to an outlet opening. The circulation chamber is sealed off from the surroundings, i.e., it is accessible only through the inlet and outlet openings. On the side of the separating wall opposite the circulation chamber is located the heating chamber, in which is arranged at least one electric heating element which heats the medium flowing in the circulation chamber. 
     The electric heating device according to the invention offers the advantage that, due to the separating wall, the heat-dissipating medium, for example, water or oil, is reliably separated from the electric heating element. Accordingly, any heat-dissipating medium can be used, including such media as could, in the event of direct contact with the electric heating element, possibly damage this electric heating element and/or cause a short circuit. 
     With consideration to good heat conduction between the electric heating element and the circulation chamber, the housing is formed from a good heat-conducting material, preferably metal. Among the metals, aluminium is particularly preferred. 
     The electric heating element preferably comprises at least one PTC heating element, due to the merits already described in the preceding. At the same time, with a view to electrical insulation from the housing, the PTC heating element preferably lies against the separating wall with at least one ceramic plate as an intermediate layer. The ceramic plate is formed so that it is very thin, as a result of which the heat conduction from the PTC heating element to the separating wall is essentially not adversely influenced, although the PTC heating element is electrically insulated from the housing. Also possible are embodiments in which the PTC heating elements lie directly on a wall of the housing and the electricity is conducted to a pole of the PTC heating elements by means of a current feed to the housing, whereas another contact of the PTC heating element is electrically insulated from the housing. 
     It has been seen that in the case of one advantageous formation in which the housing is longer than it is wide and the inlet and outlet openings are cut into ends of the housing opposite one another along the length, an adequately large quantity of heat can be transferred from the electric heating elements to the medium. With a view to a uniform and effective delivery of the heat generated by the electric heating element to the medium, in accordance with a preferred further development of the invention under consideration, it is proposed that the separating wall form at least one recess running along the length of the housing in order to hold the at least one electric heating element in the heating chamber, whereby this recess projects into the circulation chamber, is open to the heating chamber and has flowing medium on both sides. With a view to good heat transfer from the electric heating element to the medium, the thickness of the electric heating element preferably roughly corresponds to the width of the recess. Preferably, a number of recesses are arranged along the width of the housing, parallel and one behind the other, by means of which the quantity transferred by the electric heating device can be relevantly increased. The recess preferably has a roughly U-shaped cross-section, whereby the recess&#39;s interior sides, formed by the opposing side pieces, are preferably flat. With a view to the use of identical electric heating elements for simple configuration of a heating device with a high heat output, the U-shaped recesses are formed with essentially the same depth, i.e., the tabs connecting opposing side pieces of the U-shaped recess end at the same height, so that the recesses project into the circulation chamber to the same depth. These recesses preferably end shortly before the bottom of the circulation chamber, whereby this bottom lies opposite the heating chamber. To allow the best-possible use of standard parts when forming the electric heating elements, a multitude of electric heating elements, one behind the other, are held in each of the recesses. The lower end of the heating elements is preferably held at a given level by being in contact with the tab. 
     Particularly when PTC heating elements are used, in view of the self-regulating characteristics of these electric heating elements, a heat transfer to both sides of sheet-like PTC heating elements that is as uniform as possible should be guaranteed. Accordingly, a further preferred development of the invention under consideration proposes that the electric heating element be pressed against the opposing side pieces of the recess in good contact by a pressure element likewise positioned in the recess, with the electric heating element held in the U-shaped recess. Preferably the electric heating elements are fully flat, as are the opposing side pieces, and preferably run slightly towards each other in a slightly conical arrangement, whereby the pressure element should also be formed in a wedge shape, so that the pressure element tightly wedges the heating element in the recess and ensures full-surface contact between the long sides of the U-shaped recess, the heating element and the wedge. The electric heating elements lie against at least one side piece, whereby, with a view to electric insulation from the housing, the electric heating elements do not have to lie directly at the side pieces, but instead are preferably electrically insulated from the housing by means of a thin ceramic plate. Out of consideration for improved protection against short circuit, thin electrically insulating plates are arranged on both sides of the flatly-formed electric heating elements, whereby these thin electrically insulating plates only insignificantly obstruct the heat transfer from the electric heating elements to the separating wall, especially at the opposing side pieces of the U-shaped recess. 
     The pressure element is likewise formed from a good heat-conducting material and preferably lies with its full surface against the heating element, optionally with the electrically insulating plate as an intermediate layer. In this way, good heat conduction to both sides of the electric heating element is guaranteed by the opposing side pieces of the U-shaped recess for transfer to the medium in the circulation chamber. To this end, the pressure element is pressed with a large force into the U-shaped recess, in order to brace the electric heating element in the recess, namely by introducing the pressure element along the length of plate-shaped electric heating elements. The later pressure surfaces of the electric heating element should be level and smooth for this. If the pressing forces are large, it is preferable that the pressure element be slid in against an electrically insulating plate formed by a ceramic plate, whereby the upper surface of this electrically insulating plate opposes the sliding-in motion of the pressure element with a lower frictional resistance. Practical attempts have shown that the insertion force for bringing the pressure element to a heating element amounts to several hundred Newton. Not least due to this reason, it is preferred to arrange a number of electric heating elements along the length of the recess, one behind the other, each one of which is braced in the recess by separate pressure elements. The pressure element preferably has a footprint that corresponds to the footprint of the electric heating element, so that heat generated by the heating element can be conducted transversely into the side pieces without disturbance. 
     Between the electrically insulating plates and the at least one PTC heating element arranged between them, preferably electric contact plates are arranged on each side of the PTC heating element and electrically contacted to the PTC heating elements. The contact plates preferably have extension sections formed on the contact plates as a single piece, whereby these extension sections project beyond the electrically insulating plates on diagonally opposing sides of the heating element. As one result of the diagonally offset arrangement of the extension sections it is prevented that these sections are opposed, spaced apart by the thickness of the PTC heating elements only, so that the risk of a short-circuit forming is further reduced and, furthermore, the electrical connection of the extension sections to a power supply is simplified, even while taking into consideration sufficient protection against short-circuit. The size of the surface area of the contact plates arranged between the insulating plates essentially corresponds to the outer surface of the at least one PTC heating element, whereby this outer surface faces the interior side of the insulating plate, with a view to the best possible electrical contacting of the PTC heating elements. Accordingly, each of the PTC heating elements is in contact with the contact plates across the entire surface. In contrast, the insulating plates also form a slightly projecting edge, also with a view to sufficient spacing of the heating elements from the housing along the circumference of the heating elements. The electric heating element can have one or more PTC heating elements. The use of a number of PTC heating elements is preferred particularly when the voltage is more than 230 V, in order to be able to operate these PTC heating elements as parallel resistors. Through this, the resistance realised with the individual PTC heating elements does not have to be unnecessarily reduced, which can lead to a reduced breakdown voltage. When the voltage is &lt;230 V, a single PTC heating element is preferably realized in an electric heating element. 
     As already mentioned in the preceding, the electrical connection of the PTC heating elements is made via the extension sections that project beyond the insulating plates. With a view to the simplest possible connection of each of the extension sections, these extension sections, which are arranged in the recess, are arranged at essentially the same height, and the housing has at least one supporting surface in the area of the extension sections for a printed circuit board, which has contact recesses on its lower side, which faces the extensions, whereby the extension sections can be slid into these recesses. In the case of an arrangement of a number of heating elements, one behind the other, in the recess, according to a preferred further development of the invention under consideration, each of the extension sections can be contacted in a simple manner by means of forming the contact receptacle for several extension sections, arranged in a row, one behind the other, from contact plates that oppose one another and that lie on the extension sections under an initial tension. These contact plates accordingly extend essentially parallel to the extension sections and are pressed against the extension sections with an initial tension when the extension sections have been slid between the contact plates, so that good contacting is guaranteed. The contacting can be accomplished in a simple manner by means of sliding the printed circuit board onto the extension sections along the length of these extension sections, until the printed circuit boards lie directly on the bearing surface of the housing, preferably with an intermediate layer of electrical components or a cooling bar for these components. 
     Particularly when the heating device is used in the engine compartment of a motor vehicle, and for sealing the heating chamber, according to a preferred further development of the invention under consideration it is proposed to provide a cover that has a power and signal terminal and that seals the heating chamber. This cover furthermore has contact elements that act in combination with the plug-in elements on the upper side of the printed circuit board. The contact elements preferably can be slid into one another, forming a contact, when the cover is placed into position, and preferably extend parallel to the extension sections, so that the movement for placing the cover into position along the length of the extension sections not only leads to the contacting of the contact elements that lead to the power and signal terminal, but also to good retention of the extension sections at the opposite side of the printed circuit board. 
     The electric heating device according to the invention is particularly suitable as a heating device for the hybrid drive of a vehicle. Furthermore, the heating device according to the invention is also suitable as a recuperator for dissipating excess energy, which arises due to the generator operation of an electric motor during a regenerative brake application. Such excess electrical energy is initially used for filling an electric storage battery provided on the vehicle. Should this storage battery also have been fully charged, however, electrical energy must be dissipated, and the electric heating device according to the invention, which converts electrical energy into thermal energy, is particularly well-suited for this, whereby it is possible to discharge the thermal energy into the surroundings via, for example, heat exchangers or to use the thermal energy for heating the vehicle interior. 
     The invention under consideration is explained in more detail in the following using an embodiment in connection with the drawing. The figures show: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  a perspective top view of a part of the embodiment with the cover open; 
         FIG. 2  a perspective top view of the bottom part of the housing with the housing base removed; 
         FIG. 3  a view of the longitudinal section through the embodiment shown in  FIG. 1 ; 
         FIG. 4  a perspective top view onto an embodiment of an electric heating element which is used in the heating device according to  FIGS. 1 to 3 ; 
         FIG. 5  two plates to be placed onto the part shown in  FIG. 1 ; 
         FIG. 6  the embodiment according to  FIG. 1  with plates according to  FIG. 5  set onto the part; 
         FIG. 7  the embodiment according to  FIG. 1  with the second printed circuit board placed upon it; and 
         FIG. 8  the embodiment shown in the preceding figures with the cover placed upon it. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows the embodiment of a heating device  2  with an elongated housing  4 , consisting of an essentially cylindrical housing frame  4  and a housing base  4   b  screwed to it. Connecting pieces are arranged on a lateral surface of the housing frame  4   a , on opposite ends of this elongated housing frame  4   a , whereby these connecting pieces surround inlet and outlet openings  6 ,  8 , whereby connection lines can be connected to these connection pieces via hose clips or the like, and whereby these connection lines lead to a circulation chamber  10  that is essentially surrounded by the housing frame  4   a . In  FIG. 1 , the connecting pieces are arranged on the frontal ends of the housing frame  4   a . Another arrangement of the connecting pieces on the opposing ends of the elongated housing frame  4   a  is indicated by dashed lines. This circulation chamber  10  is separated from a heating chamber  14  above it by a separating wall  12 , namely in such a way that the fluid (for example, water) contained in the circulation chamber  10  cannot reach the heating chamber  14 . In other words, the separating wall  12  fluidically separates the circulation chamber  10  and the heating chamber  14  from one another. The separating wall  12  can, for example, be formed on to the housing frame  4   a  as a single piece. 
     As  FIG. 3  illustrates, the separating wall  12  forms a number of recesses  16  arranged one behind the other along the width, whereby these recesses  16  essentially extend across the entire length of the housing  4  (cf.  FIG. 2 ). The separating wall  12  accordingly has a meandering shape with recesses  16  that project deeply into the circulation chamber  10 , which recesses are completely sealed off from the circulation chamber  10  and open to the heating chamber  14 . In other words, the circulation chamber  10  is fluidically isolated from the recesses  16 . The recesses  16  include a closed end opposite an open end that is open to the heating chamber  14 . Because these recesses  16  are preferably manufactured from a material that is a good conductor, particularly metal and, in this case, especially aluminum, manufacturing the separating wall  12  as, for example, a separate component by means of shaping suggests itself. The recesses  16  have a U-shaped cross-section and run along the length of the housing  4 , parallel to one another. 
     Heating elements  18 , which have the design shown in  FIG. 4 , are located in each of the recesses  16 . The exterior side of each of the heating elements  18  is formed by ceramic plates  20 . A number of PTC heating elements  22  are arranged between these ceramic plates here. Contact plates  24  made of an electrically conducting material are, in turn, located between these PTC heating elements  22  and the ceramic plates  20 . Extension sections  26  are formed on to these contact plates  24  as a single piece. The extension sections  26  of the contact plates which lie opposite one another are located on diagonally opposing sides. The extension sections are accordingly spaced apart from one another not only on the basis of the thickness of the PTC heating elements  22  but furthermore also essentially by the width of the heating elements  18 . For reinforcement, the extension sections  26  are doubled by folding the material of the contact plates  24  one time in the thickness. 
     The ceramic plates  20 , the PTC heating elements  22  and the contact plates  24  are preferably combined into one unit by means of gluing. As  FIG. 4  illustrates, the ceramic plates  20  project beyond the PTC heating elements  22  and the contact plates  24  on all sides, forming an edge around the circumference. The heating elements  18  introduced into the recesses  16  lie on a side piece  28  of the U-shaped recess  16  with one of the ceramic plates  20 . Between the opposing side piece  30  and the heating unit  18  is a pressure element  32 , which is introduced into the recess  16  under tension and which is assigned to a single electric heating element  18 . The respective pressure element  32  holds a single heating element  18  in the recess  16  and braces it against the opposing side pieces  28 ,  30  of the recess  16 . The heating element  18  accordingly lies against the opposing side pieces  28 ,  30  with good heat conduction. Furthermore, the heating elements  18  stand up on a tab  34  of the recess  16 , said tab  34  connecting the side pieces  28 ,  30 , so that the heating elements  18  are accordingly fixed with respect to the height. The electric heating element  18  lies, with the lower face sides of the ceramic plates  20 , on the tab  34 , so that the electrically conducting parts of the heating element  18  are spaced at a distance from the metallic tab  34  and consequently insulated. The depth of the recesses  16  is furthermore selected in such a way that the medium in the circulation chamber  16  flows around the heating element  18  at least above the height of the PTC heating elements  22  that are stacked one on top of the other, i.e., the entire electric heating element  18  is held in the recess  16 . 
     The U-shaped recesses  16  have a slightly conically tapered cross-section. The pressure element  32  is likewise formed in a wedge-shape, namely, with a pitch corresponding to the conical progression of the recess  16 . The thickness of the pressure element  32  and the electric heating element  18  essentially corresponds to the width of the respective recess  16 . 
     The pressure element  32  consists of a good thermally conducting material, for example, aluminium, and the thickness of the ceramic plates  20  is selected in such a way that the heat conduction from the heating elements  18  is scarcely interfered with by the material of the side pieces  28 ,  30 . Because of the high degree to which the heating elements  18  are pressed together with the pressure element  32 , the heat dissipation to the two sides of the elongated recesses  16  is virtually symmetrical. 
     As can be seen in  FIG. 1 , the extension sections  34  project beyond the upper side of the separating wall  12  and lie freely in the heating chamber  14 . The plates shown in  FIG. 5 , namely an insulating plate  35  and a first printed circuit board  36 , are slid on to these extension sections  26 . The insulating plate  35  is made from an electrically insulating material and has a hole pattern corresponding to the size and position of the extension sections. The openings cut into the insulating plate  35  for the extension sections  26  serve to guide the extension sections  26  and to ensure insulation. Furthermore, the insulating plate  35  has recesses and receptacles for parts of the first printed circuit board  36  that protrude from the first printed circuit board  36 . 
     The first printed circuit board  36  has two contact receptacles  38  for each recess  16 , whereby said contact receptacles  38  are formed by bent and pre-tensed extension section receptacles  40  that hold the extension sections  26  (cf. particularly  FIG. 3 ). In an alternative development, not shown here, the contact receptacles can also be formed by two opposing contact plates, whose clear spacing is selected in such a way that the extension sections held in the contact receptacles lie against the contact plates with an initial tension. In such a case, a number of extension sections of electrical elements arranged one behind the other are connected in series via the contact plates. In the embodiment shown, the electrical grouping of heating elements  18  is produced by the strip conductors of the first distributor plate  36 , which is accordingly also indicated as a printed circuit board. 
     Six tab elements  41  and a cylindrical connecting element  42  for the positive phase project beyond the first printed circuit board  36  on the upper side facing away from the heating elements  18 , whereby each projection is arranged on the first printed circuit board  36 . The first printed circuit board  36  lies approximately at the height of the supporting surfaces  43  that are provided on the frontal ends of the housing frame  4   a . The first printed circuit board  36  has no electronic components, but instead only strip conductors and the previously mentioned connecting elements  41 ,  42 , and consequently the first printed circuit board  36  serves only to combine individual electric heating elements  18  into groups, with a view to the control of all electric heating elements in a group. 
     The second printed circuit board  37  has six plug-in contact receptacles  44  assigned to the contact stud elements  41 , whereby these plug-in contact receptacles  44  are arranged on the upper side of the second printed circuit board  37 . Furthermore, a negative connecting element  45  is provided on the upper side of the second printed circuit board  37 . On its underside, the second printed circuit board  37  carries electric switching elements, particularly semiconductor switches  46  which project beyond the second printed circuit board  37  frontally or at the end and, with an insulating layer  47  placed in between, lie against the supporting surfaces  43  so that, because of the direct contact created in this way, it is possible to dissipate lost heat generated by the semiconductor switches  46  by conducting it into the housing  4 , seeing that the second printed circuit board  37  is mounted at a distance to the first printed circuit board  36 . The contact stud elements  41  then engage in the corresponding plug-in contact receptacles  44 . The positive connecting element  42  protrudes through a recess cut into the second printed circuit board  37  and projects beyond the second printed circuit board  37 . The subsequent contacting takes place on the two connecting elements  42  and  45  when a housing cover  48  is placed in position. This cover has a power terminal  50  and a signal terminal  52  on its upper side and serves to seal the heating chamber  14  off from the surroundings. 
     The embodiment shown in the drawing has 24 heating elements, each with four PTC heating elements and, surprisingly, it has been seen that this electric heating device can deliver thermal heat output of more than 10 kW. With this output, the energy of an electric drive created by the generator operation that cannot be stored can be converted into thermal energy via the heating device.