Abstract:
The invention relates to a heating element for a part of an automobile which is held, especially the steering wheel. The heating element consists of a textile support with at least one heating resistor. According to the invention, a knitted textile support is used.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a heating element for a graspable part of a motor vehicle, in particular for the steering wheel. 
     DE 29 51 871 A1 discloses a steering wheel cover, to the inner face of which is fastened a fabric lining, into which resistance wires are embedded. The fabric lining is provided with a masking, so that the resistance wires do not rest directly on the steering wheel rim. 
     This steering wheel cover with a heated fabric lining has the disadvantage that fabric is only slightly stretchable, so that the cover can be adapted only incompletely to the three-dimensional steering wheel rim. It is therefore scarcely possible to avoid creases. 
     SUMMARY OF THE INVENTION 
     The object on which the invention is based is to design the heating element in such a way that it can be adapted creaselessly to three-dimensional parts in the motor vehicle which are to be heated. 
     In a heating element for a graspable part of a motor vehicle, in particular for the steering wheel, the heating element consists of a textile support with at least one heating resistor. In an embodiment, a textile support knitted by stitch row or by single stitch is used. Such a support has high elasticity, so that it is adapted to three-dimensional parts without creases being formed. 
     In an embodiment for the steering wheel, the textile support is designed so that the textile support masks the steering wheel rim and the adjoining regions of the spokes. It is expedient to mask part of the spokes, because the driver, when operating the steering wheel, occasionally also grasps the region of the spokes which is contiguous to the steering wheel rim. The support knitted by stitch row or by single stitch is so elastic that it is even laid onto the spokes, without creases being formed. 
     It is expedient that the heating resistor be knitted by stitch row or by single stitch as a thread into the textile support. The elasticity of the textile support is not impaired by the inelastic heating resistor if this type of fastening is adopted. At the same time, the heating resistor is expediently knitted in, so that the heating resistor is masked by the material of the textile support to a lesser extent on one side than on the other side. The heating element is laid with the side masked to the greater extent onto a base, for example onto the steering wheel, while the other side forms the top side having the essentially exposed heating resistor. 
     Preferably, a plurality of threadlike heating resistors are arranged next to one another, and can in particular, follow a meandering course. At the same time, the heating resistors may both lie at a distance from one another at which they do not intermesh and be arranged so as to be nested one in the other, without touching one another. The degree of heating can be influenced by arranging the heating resistors with differing density in this way. 
     In a preferred embodiment, the textile support is designed as a plane band, at the two ends of which the heating resistor ends are connected, in each case via a connection piece, to the commercially available junction leads of the vehicle. In order to avoid a buildup of heat at the connection pieces, it is expedient for connection pieces to be connected to the individual heating resistors at the two ends of the textile support over the entire width of the latter. 
     The textile support may have any desired selected length, so that, for example, a steering wheel rim is masked by the heating element completely or only on selected portions. 
     Although the heat is radiated to the top side to a greater extent as a result of the essential masking of the heating resistors on the underside of the textile support, this effect may be reinforced even further if the textile support is provided on the underside with a reflection layer. 
     The heating element according to the invention can be used in a simple way for heating different parts in the motor vehicle. A heating element which masks the entire steering wheel rim may be arranged on the steering wheel. However, a plurality of shorter heating elements may also be provided, which mask only specific regions of the steering wheel rim, for example the East/West segments on a steering wheel which has to be operated only through 180° to left or right due to the use of an electronic control. Heating is then required only in these segments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in an exemplary embodiment with reference to drawings in which: 
     FIG. 1 shows a top view of a portion of a steering wheel; 
     FIG. 2 shows a top view of a heating element; 
     FIG. 3 shows the detail Z of FIG. 2; 
     FIG. 4 shows a partially sectional perspective view of a heating element; 
     FIG. 5 shows a partially sectional perspective view of a portion of the steering wheel rim. 
    
    
     DETAILED DESCRIPTION 
     A heating element  2  with junction leads  3 ,  4  is arranged in the cover of a steering wheel rim  1 . The heating element  2  has, in the region of the spokes  5  of the steering wheel, protuberances  2   a  which can be laid around the spoke junctions  2   b  to the steering wheel rim, so that even the region of the spokes  5  which adjoins the steering wheel rim can be heated. Since, according to the invention, the textile support  6  of the heating element  2  is knitted by stitch row or by single stitch, said heating element can be laid ceaselessly both around the steering wheel rim  1  and around the spokes  5 . 
     FIG. 2 shows the heating element  2  in the spread-out position. Heating resistors  7 , which extend between the ends  8 ,  9  of the textile support  6 , are knitted into said textile support  6 . The heating resistors follow a meandering course, adjacent heating resistors being arranged at a distance from one another, so that they have no electrical contact. Electrical contact is made only at the ends of the textile support via connection pieces  10 ,  11 . These extend over the entire width of the textile support, so that the ends of the heating resistors are connected separately from one another to the connection pieces. This avoids a buildup of heat at the connection pieces. The connection pieces  10 ,  11  are connected to the junction leads  3  and  4  respectively. 
     FIG. 3 illustrates, in the form of a detail, how an individual heating resistor is connected to the textile support by means of stitches  12 ,  13  of the latter. FIG. 4 shows, in the form of a larger detail, the textile support  6  with two heating resistors  7 . The textile support has an underside  14  which rests on the steering wheel rim  1  and on the spoke junctions  2   b  to the steering wheel rim, while the top side  15  is surrounded by the steering wheel cover  21 . It can be seen that the heating resistors on the top side are not surrounded by every stitch of the textile support. The heating resistors are essentially exposed there, so that the heat can be radiated upward. By contrast, a denser stitchwork  16  extends on the underside  14 , so that less heat is radiated thereto. Unnecessary heating of the steering wheel skeleton is consequently prevented. 
     The construction of the steering wheel rim  1  can be seen from FIG.  5 . This consists, in a known way, of a steering wheel skeleton  17  with a plastic cover  18 . The latter is surrounded, in the embodiment illustrated, by a layer of rubber  19  lacquered in a silver color or by a reflection foil  20 . These two layers are intended to reduce to an even greater extent the heat radiation of the heating element  2  which rests on the reflection foil  20 . The heating element  2  is surrounded by the leather cover  21  which forms the surface of the steering wheel.