Abstract:
Disclosed is a filter device having a filter element disposed in a filter housing and a heater for heating a medium flowing through the filter device. The heater is disposed in the interior of the filter housing and is mounted on the filter element.

Description:
REFERENCE TO FOREIGN PATENT APPLICATION 
       [0001]    This application is based on German Patent Application No. 10 2007 005 771.9 filed 6 Feb. 2007, upon which priority is claimed. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a filter device, in particular a liquid filter, such as a urea filter or fuel filter, having a filter element that is disposed in a filter housing, and having a heater for heating a medium flowing through the filter device. 
         [0004]    2. Description of the Prior Art 
         [0005]    At low operating temperatures, many known filter devices require a heater, since the viscosity of the media to be filtered in them increases at low temperatures, making passage of the medium through the associated filter element more difficult. In diesel fuel filters, for instance, in cold starting of the associated engine, problems can arise if the outdoor temperature is below the so-called CFPP (cold filter plugging point) of the fuel. In urea filters as well, such a heater may be necessary. 
         [0006]    The heaters used are embodied as electrical PTC (positive temperature coefficient) heaters, which have automatic regulation and are especially adapted to the heating situation to be brought about. The PTC elements, however, are comparatively expensive to procure and to process. 
         [0007]    In some applications of filter devices, their installation space is severely limited. For such applications, in the case of fuel filters, which have a filter housing with a housing cup and a housing cap, it is known to embody the heater in the housing cap or as a heating rod that protrudes into the clean side of the filter device. However, both versions are comparatively complex and expensive and make additional adaptations to the components necessary. 
       OBJECT AND SUMMARY OF THE INVENTION 
       [0008]    The object of the invention is to furnish a filter device in which the aforementioned problems are overcome, and in particular in which high heating capacity can be furnished economically. 
         [0009]    According to the invention, a filter device is created, having a filter element that is disposed in a filter housing, and having a heater for heating a medium flowing through the filter device, in which the heater is disposed in the interior of the filter housing and is mounted on the filter element. 
         [0010]    Moreover according to the invention, a filter device, in particular of the type referred to above, is created, having a filter element that is disposed in a filter housing, and having a heater for heating a medium flowing through the filter device, in which the heater is disposed in the interior of the filter housing and is embodied as a component that is separate from the filter housing. 
         [0011]    An important advantage of the embodiments according to the invention is that the heater of the invention in the interior of the filter housing leads to especially uniform distribution of the thermal energy supplied, beyond the surface area of the heater itself. At the same time, the heater of the invention and thus the entire filter device requires especially little installation space, while providing high heating output. At the same time, the temperature sought in all the essential filter regions is in particular attained quite quickly and largely uniformly. Filter housings of known filter devices are as a rule embodied with a housing cup and with a housing cap closing the housing cup. Moreover, the embodiment according to the invention has the advantage that it can furnish heating of the medium for a filter device in the least possible installation space. The embodiment according to the invention, in such filter devices, is suitable both for metal housing cups and plastic housing caps, since the heater is disposed in a separate part inside the housing cup, or in other words independently of the housing cup. 
         [0012]    Preferably, in the filter device of the invention, the heater is embodied with at least one heating track. In contrast to known filter devices, in which the heater is provided with PTC elements, a heating track or heating wire or even a heating coil is preferably provided. This embodiment is in particular more economical, for comparable heating output, than embodiments with PTC elements. 
         [0013]    The heating track of the invention is especially advantageously embodied as a stamped grating, which in a manner similar to known conductor tracks is stamped out from a striplike or sheetlike piece of sheet metal. The stamped grating (especially in the grid portions separate from the actual heater) may also include further electrical functions, such as supplying current to the associated filter device or diverting current from it. The heating track and the stamped grating are preferably injection-molded into a heating track housing. The injection-molding process to be provided can build on extensive knowledge and experience with other components that in the most various kinds of technical equipment are now being injection-molded into housings made in particular from plastic. 
         [0014]    Since the heating track housings according the invention (unlike PTC heating elements) are as a rule not self-regulating, these heating tracks should be provided with their own regulator, in the form of a control device for the controlled delivery of electrical energy to the at least one heating track. This kind of control device may be embodied for instance with pulse width modulation or some other electronic circuit with which overheating of the filter device of the invention is reliably prevented. 
         [0015]    The heating track housing provided according to the invention protects against mechanical damage and moreover maintains a spacing between the heating track and the optionally metal filter housing. 
         [0016]    The transfer of thermal energy to the medium flowing through the filter device of the invention can moreover be improved by providing that the heating track housing is made from a highly thermally conductive plastic. For generating especially good thermal conductivity, this plastic is advantageously embodied with fillings of aluminum oxide and/or magnesium hydroxide. 
         [0017]    These advantages in terms of especially good utilization of the heating energy supplied and the creation of a temperature profile that is especially responsive to need beyond the surface of the filter housing of the invention can moreover be achieved to a particular extent by providing that the at least one heating track is distributed in the form of a loop within the surface of the heating track housing. 
         [0018]    The object of the invention is also attained with a filter device, in particular of the inventive type described above, having a filter element that is disposed in a filter housing, and having a heater for heating a medium flowing through the filter device, in which the filter housing is embodied hollow-cylindrically, and the heater, likewise embodied hollow-cylindrically, is disposed in the interior of the filter housing. This embodiment is especially expediently usable for automotive applications, and especially advantageously, the filter element is located essentially in the interior of the hollow-cylindrical heater, and/or the hollow-cylindrical heater can be bathed radially on the inside and outside by the medium that is to be heated. These refinements require only little installation space and nevertheless create an advantageous heat transfer between the heater and the medium to be heated. 
         [0019]    The heater of the filter device of the invention is moreover preferably embodied with at least one electrical contact, which is extended out from the material comprising the filter housing. The electrical contacts can then be used in particular for connecting the aforementioned control device, for communication with one or more temperature sensors, and/or for inputting electrical energy. 
         [0020]    In the filter device of the invention, the electrical contact is moreover embodied from a different material from the heating track. In these refinements, the heating track is preferably made from a high-impedance material, and the electrical contact is made from a low-impedance material. Such different materials for the heating track and the electrical contact are adapted to the functions associated with the various elements. Hence as the material for the electrical contacts, CuSn is preferably selected, while conversely the heating track is made especially from a material with high electrical resistance that can be stamped out especially well. The material comprising the electrical contact may be connected to the heating track in particular by means of a clamping, stamping, crimping, or soldering process. These embodiments make it possible in particular for a plug, of the kind already available on the market and as rule standardized, to be connected to the heating track of a heater of a filter device. The aforementioned electrical contacts, which are coupled according to the invention to the heating track and embodied from a different material, can in fact be freely selected not only with regard to their shape and size but also with regard to their material and can be adapted accordingly to the specifications of a standardized plug. 
         [0021]    The electrical contact is advantageously formed by the heater via a clamping connection with a component of the filter housing, on which component an externally accessible electrical terminal is provided. The clamping connection can be embodied economically during assembly of the heater of the invention on the component of the filter housing, in particular on a housing cap of the filter housing. The electrical terminal is preferably embodied in the form of an either directly connected or plugged-in cable, and the cable can be plugged together with plug pins by means of which the aforementioned clamping connection is also embodied. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments, taken in conjunction with the drawings, in which: 
           [0023]      FIG. 1  is an exploded view of one exemplary embodiment of a filter device according to the invention with the following group of components: housing cap, heater, filter element, and housing cup; 
           [0024]      FIG. 2  is a side view of the filter device of  FIG. 1 , with the housing cup shown broken open; 
           [0025]      FIG. 3  is a fragmentary sectional view taken along the line III-III in  FIG. 2 , in perspective; 
           [0026]      FIG. 4  shows the detail IV in  FIG. 3  in a side view; and 
           [0027]      FIG. 5  shows the detail V in  FIG. 3 , in a side view. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    In the drawings, a filter device  10  is show, which as its fundamental components has a filter housing, composed of a housing cup  12  and a housing cap  14 , and a filter element  16  located in the filter housing. 
         [0029]    The housing cup  12  is embodied in its basic shape as a pot or cup, which includes a housing bottom  18  and an annular wall  20  adjoining the bottom on the circumference. The annular wall  20  is embodied essentially cylindrically about a longitudinal axis A. The housing bottom  18  is penetrated centrally by a through opening  22 , which is used for connecting a sensor, not shown. Diametrically opposite, a connection  24  is embodied centrally in the housing cap  14 . In operation of the filter device  10 , a fluid or medium, such as fuel or urea, is introduced through connection  24  and subsequently passes from radially inside radially outward through the filter element  16  and leaves the filter device  10  through a connection  26 . 
         [0030]    So that at especially low operating temperatures at the filter device  10  flaking, in particular, or freezing of the filtered fluid will not occur in or at the filter element  16 , a hollow-cylindrical heater  28  is disposed below the housing cap  14 , in terms of the drawings, between the annular wall  20  of the housing cup  12  and the outer jacket face of the cylindrical filter element  16 . 
         [0031]    In this heater  28 , the heat generation is effected by means of a heating track  30  laid in loops, through which electrical current can be conducted. The loops of the heating track  30  are cut out, in the form of a so-called stamped grating, from a sheet-metal strip by means of a stamping process, and after a bending operation they are insert-molded with a heat-conducting material  32  in the form of a heating track housing. In this way, the overall hollow-cylindrical shape of the heater  28  and of the heating track housing is formed. The heating track  30  is distributed over the jacket face of the hollow cylinder in such a way that a large-area and simultaneously uniform input of thermal energy into the heat-conducting material  32  and thus into the fluid flowing around it occurs. 
         [0032]    In the process of injection-molding the thermally conducting material  32 , two contact points  34  on the heating track  30  have also been extended out of the heat-conducting material  32  in such a way that they are connectable to plug pins  36 . The plug pins  36  are injection-molded in the housing cap  14  and are clamped to the contact points  34  upon mounting of the heater  28  on the housing cap  14 . In the built-in state of the filter device  10 , a control device  38 , shown only highly simplified, for delivering and regulating electrical current to the heating track  30  is then connected to the plug pins  36 . 
         [0033]    The heater  28 , thus preassembled on the housing cap  14 , protrudes in the assembled state from the outside of the filter element  16  into the housing cup  12  and is kept spaced apart from the inside of the housing cup  12  by means of ribs  40 . 
         [0034]    The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.