Abstract:
A vehicle steering wheel comprises a steering wheel rim having a skeleton, whereon several predetermined deformation zones with predetermined deformation directions are defined. A rigid wood casing surrounds the skeleton. The wood casing has an inner side facing the skeleton, and a deformation space is provided in deformation direction between the inner side of the wood casing facing the skeleton and the skeleton in the predetermined deformation zones. The deformation space is greater than a space of the inner side of the wood casing to the skeleton in radial direction in other zones.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a vehicle steering wheel.  
         BACKGROUND OF THE INVENTION  
         [0002]    Steering wheel rims cased in wood give a vehicle steering wheel a high-quality appearance and a comfortable feel. In addition to steering wheels with a foam casing which is covered by a thin wood veneer layer, steering wheels are also known which have a rigid, solid wood casing consisting for example of two shell parts. This solid wood casing can be formed for example from laminated wood layers, the outer surface of the shells consisting of a veneer layer and of a corresponding lacquering.  
           [0003]    If in the case of an accident a vehicle occupant strikes onto the steering wheel, it can happen that the skeleton of the steering wheel suffers a plastic deformation. A three-spoked steering wheel deforms for example in three main deformation zones, namely at the uppermost point of the steering wheel rim (in a position incorporated in the vehicle, hereinafter also designated as “12 o&#39;clock position”), and at the two sections of the steering wheel rim situated furthest laterally (hereinafter also named “3 o&#39;clock” and “9 o&#39;clock” position). At the 12 o&#39;clock position, the steering wheel rim will yield radially inwards, whereas at the 3 o&#39;clock and 9 o&#39;clock positions the skeleton of the steering wheel rim will widen radially outwards. It is important now, with such a deformation of the steering wheel rim, to avoid a destruction of the wood casing.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    It is an object of the invention to present a steering wheel in which this can be achieved in a simple and favourably-priced manner.  
           [0005]    This takes place in a vehicle steering wheel comprising a steering wheel rim having a skeleton, where several predetermined deformation zones with predetermined deformation directions are defined on the skeleton. A rigid wood casing surrounds the skeleton. The wood casing has an inner side facing the skeleton, and a deformation space is provided in deformation direction between the inner side of the wood casing facing the skeleton and the skeleton in the predetermined deformation zones. The deformation space is greater than a space of the inner side of the wood casing to the skeleton in radial direction in other zones.  
           [0006]    In other words, larger deformation areas are made available to the skeleton of the steering wheel rim in the interior of the wood casing only at discrete sites, so that in the case of an impact, the wood casing does not have to take part in the full plastic deformation of the steering wheel rim. The deformation space is only provided in the known deformation zones. In the other regions, the space between the skeleton of the steering wheel rim and the wood casing can be restricted to the space necessary for the equalization of the different expansion coefficients at different temperature and humidity conditions of the skeleton and the wood casing. The wood casing can partially also lie directly against the skeleton.  
           [0007]    The deformation space between the outer side of the skeleton and the inner side of the wood casing preferably amounts to between 1 and 8 mm.  
           [0008]    Preferably the wood casing surrounds a ring-shaped chamber in which the skeleton is arranged.  
           [0009]    In a first preferred embodiment of the invention, the ring-shaped chamber has an oval, especially elliptical, periphery perpendicular to a rotational axis of the steering wheel. The long axis of the oval or the ellipse, respectively, is arranged here in the direction of the 3 o&#39;clock to 9 o&#39;clock position (in relation to a steering wheel which is positioned for running straight ahead), so that a deformation of the steering wheel rim is easily able to be equalized in all three deformation directions.  
           [0010]    In another preferred embodiment of the invention, provision is made that the center point of the ring-shaped chamber is staggered by a deformation space with respect to the center point of the steering wheel rim. Also through this step, the necessary deformation spaces can be provided.  
           [0011]    Perpendicular to a rotational axis of the steering wheel the ring-shaped chamber and the steering wheel rim can each have the form of a circular ring and can each be defined by an imaginary circle located at their respective radial mid-point, the imaginary circles having equal circle radii and the center points of the imaginary circles being staggered by a deformation space. The “radial mid-point” is to be understood here as the mid-point of a line between the radial inward and the radial outward periphery of the ring-shaped chamber or the steering wheel rim, respectively. The diameter of the ring-shaped chamber in radial direction has of course to be chosen suitably and is smaller than the diameter of the steering wheel rim.  
           [0012]    According to a third preferred embodiment of the invention, the diameter of the ring-shaped chamber, measured in radial direction of the steering wheel, varies along the periphery of the wood casing situated perpendicular to a rotational axis of the steering wheel. Advantageously, the diameter is greatest in the deformation zones, in order to provide the necessary deformation spaces. With this embodiment, the ring-shaped chamber or the wood casing can be optimally adapted to the respective skeleton.  
           [0013]    The ring-shaped chamber is preferably constructed so that the spacing between the inner side of the wood casing and the skeleton to the side of the wood casing lying in deformation direction is greater than to the oppositely directed side.  
           [0014]    Between the skeleton and the wood casing at least one element of a compressible or elastic material can be arranged. Here, this can be a conventional foaming around of the skeleton. The compressible material can be arranged over the entire periphery of the skeleton, but it is also possible to only cover partial sections of the skeleton.  
           [0015]    The wood casing can be composed of at least two shell parts, as is already known for example from the DE 101 33 324 A1.  
           [0016]    Preferably, the shell parts of the wood casing are solid, and the ring-shaped chamber taking up the skeleton is formed by a milling out in the shell parts. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 shows a diagrammatic view of a steering wheel according to the invention;  
         [0018]    [0018]FIG. 2 shows a diagrammatic sectional view of a steering wheel according to the invention in accordance with a first embodiment;  
         [0019]    [0019]FIG. 3 shows a diagrammatic sectional view of the wood casing of FIG. 2;  
         [0020]    [0020]FIG. 4 shows a diagrammatic sectional view of a steering wheel according to the invention in accordance with a second embodiment;  
         [0021]    [0021]FIG. 5 shows a diagrammatic sectional view of a steering wheel according to the invention in accordance with a third embodiment; and  
         [0022]    [0022]FIG. 6 shows a diagrammatic section through the steering wheel rim of FIG. 4 at the 3 o&#39;clock position.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]    In FIG. 1 a steering wheel  10  is illustrated, with a steering wheel rim  12  and three spokes  14  and a hub region  16 , which is connected by the spokes  14  with the steering wheel rim  12 .  
         [0024]    The steering wheel rim has as outermost layer a solid wood casing  20 . The wood casing  20  is composed here of two shell parts (see FIG. 6), of which in the following figures respectively only one is illustrated. The wood casing  20  is in itself substantially rigid. It can consist of solid wood, a laminate or another suitable wood material. The surface can be covered with a wood veneer. The invention is, however, independent of the exact design of the wood casing.  
         [0025]    In the wood casing  20 , a chamber  22  describing a closed ring is formed by milling a groove respectively into the two shell parts, which receives an metal skeleton  24  of the steering wheel rim  12  forming a closed ring. When the wood casing  20  is closed by connecting the shell parts, the skeleton  24  in the form of a circular ring is completely surrounded by the wood casing  20 .  
         [0026]    The ring-shaped chamber  22  and the skeleton  24  lie in a plane perpendicular to the rotational axis A Rot  of the steering wheel  10 .  
         [0027]    The steering wheel  10  is illustrated in the Figures in a position which it also assumes in its basic position used in the vehicle (running straight ahead). Two of the spokes  14  lie here approximately horizontally, whereas the third spoke  14  runs downwards to the lowest point of the steering wheel  10 .  
         [0028]    If at all, then the driver of the vehicle is likely to strike onto the zone designated by X on the steering wheel rim  12 . Such an impact results in a deformation of the skeleton  24  in this deformation zone  18  (which corresponds to a “12 o&#39;clock position”) by a radially inwardly directed deformation path in direction V y  (see arrow). The deformation zones  18  are indicated diagrammatically in FIG. 1. At the same time, the skeleton  24  deforms in two further deformation zones  18  at the two points of the steering wheel rim  12  (“3 o&#39;clock-” or “9 o&#39;clock position”) situated furthest laterally, in a deformation direction V x  by a deformation path radially outwards. The deformation paths can amount to up to 15 mm. The deformation paths on the lateral deformation zones are generally somewhat smaller than the deformation path at X.  
         [0029]    The elasticity of the wood casing  20  only permits a fraction of such a deformation. According to the invention, therefore, deformation chambers (cavities) are hollowed out in the wood casing  20  on the discrete zones associated with the deformation zones  18 , in which deformation chambers, between the outer side of the skeleton  24  and an inner side  26  of the wood casing  20 , a deformation space d x , d y  is provided, which is necessary for equalizing the deformation of the skeleton  24 . The deformation space d x , d y  preferably corresponds to the difference between the deformation path of the skeleton  24  and the elastic deformability of the wood casing  20 . After completion of the deformation, the outer side of the skeleton  24  can lie against the inner side  26  of the wood casing  20 . However, on no account does a fracture of the wood casing  20  occur through the deformation of the skeleton  24 . Outside the discrete zones  18 , either distinctly smaller spaces are provided between the skeleton  24  and the inner side  26  of the wood casing  20 , or no spacing at all is present, both in order to avoid play.  
         [0030]    In the first embodiment of the invention illustrated in FIG. 2, the steering wheel rim  12  and its skeleton  24  have a circular shape in the plane perpendicular to the rotational axis A Rot , whereas in the same plane the ring-shaped chamber  22  has an oval circumference, the long axis of the oval being aligned from the 3 o&#39;clock- to the 9 o&#39;clock position.  
         [0031]    The eccentricity of the ring-shaped chamber  22  and the arrangement of the long axis of the ring-shaped chamber  22  are selected so that in the three previously-mentioned deformation zones  18 , respectively the deformation space d x , d y  is available for the skeleton  24  in deformation direction V x , V y . In the other zones, in which such a deformation space is not necessary, the space between skeleton  24  and inner side  26  of the wood casing  20  is mostly smaller. Owing to the symmetry relationships, also at the lowest point of the steering wheel  10 , a space corresponding to d y  is formed. This space is, however, unimportant for the function of the steering wheel  10 .  
         [0032]    In the example illustrated here, the diameter of the ring-shaped chamber  22  in a section plane in radial direction R is identical over the entire circumference U of the steering wheel rim  12 . However, it is also conceivable to vary the diameter, as is further described later.  
         [0033]    The skeleton  24  is fastened in the wood casing  20  in a known manner, e.g. by clips or spacers. It is also possible to provide a surrounding foam between the skeleton and the inner side  26  of the wood casing  20 , which surrounds the skeleton  24  and fills the ring-shaped chamber. During a foaming process for the introduction of the surrounding foam in the ring-shaped chamber  22 , the skeleton can be fixed in the desired position by centering pins (not shown) which, for example, engage into the skeleton base. In the finished steering wheel, the fixing of the skeleton can take place solely by means of the surrounding foam which extends between the skeleton  24  and the inner side  26  of the wood casing.  
         [0034]    If a surrounding foam also extends in the deformation zones  18 , it must be constructed so as to be at least compressible there. It is also possible to insert special compressible elements  30  in the deformation zones  18  (indicated in FIG. 2). The elements  30  are compressed in the deformation of the steering wheel rim skeleton  24 . The material of the elements  30  must have such a high stability that in the normal operating of the steering wheel, the skeleton  24  can not move with respect to the wood casing  20 .  
         [0035]    [0035]FIG. 3 shows diagrammatically the ring-shaped chamber  22  in the wood casing  20  in a section perpendicular to the rotational axis A Rot . The ring-shaped chamber  22  shown has an oval, especially elliptical, shape in this plane. The inner sides of the wood casing  20  limiting the ring-shaped chamber  22  also form in this section two ellipses which are oriented concentrically with each other. The longest and shortest diameter of the ellipses along their respective long and short axes (major and minor axis) are designated with A to D. Here applies that the diameters A, B along the long axes in the direction from the 3 o&#39;clock position to the 9 o&#39;clock position are greater than the diameters C, D along the short axes in the direction from the 12 o&#39;clock position to the 6 o&#39;clock position.  
         [0036]    [0036]FIG. 4 shows a second embodiment of the invention, in which the diameter of the ring-shaped chamber  22  in a section in radial direction R varies along the circumference U in the plane perpendicular to the rotational axis A Rot . In the deformation zones  18 , the diameter in the radial direction R is so great that in deformation direction V x , V y  the space between the inner side  26  of the wood casing  20  and the skeleton  24  (indicated by the dashed line) corresponds to the deformation path d x , d y , whereas it is smaller outside the deformation zones  18  (see also FIG. 6). The ring-shaped chamber  22  can have the smallest diameter at the lowermost site of the steering wheel. In the example shown here, the diameter D 1  of the ring-shaped chamber  22  provided at the 12 o&#39;clock position is greater than the diameter D 2  provided at the 3 o&#39;clock- or 9 o&#39;clock position. The diameter D 3  of the ring-shaped chamber  22  is smallest at the 6 o&#39;clock position. According to the given relationships, the diameter D 1  at the 12 o&#39;clock position could also be equal to the diameter D 2  at the 3 o&#39;clock- or 9 o&#39;clock position. Through the adaptation, in line with specific objectives, of the diameter of the ring-shaped chamber  22  along the circumference U, an optimum adaptation of the wood casing  20  to the deformation behaviour of the steering wheel skeleton  24  can be achieved.  
         [0037]    In the third embodiment of the invention shown in FIG. 5, the ring-shaped chamber  22  is constructed in a circular shape in the plane perpendicular to the rotational axis A Rot , the center M 2  of the circle of the ring-shaped chamber  22  being shifted downwards, however, by the deformation space d y  with respect to the center M 1  of the circle of the skeleton  24  (which lies on the rotational axis A Rot  of the steering wheel). Considering an imaginary circle located at the radial mid-points of the ring-shaped chamber  22  and the steering wheel rim  12 , respectively, their circle radii will be equal, whereas their center points M 1 , M 2  will be shifted with respect to each other.  
         [0038]    By the staggering between ring-shaped chamber  22  and skeleton  24 , likewise the necessary deformation spaces d x , d 1  are produced between the inner side  26  of the wood casing  20  and the skeleton  24 .  
         [0039]    Also in this embodiment, at the lower end of the steering wheel a further spacing d y  is formed which, however, is unimportant for the function of the steering wheel.  
         [0040]    The ring-shaped chamber  22  and the skeleton  24  are coordinated with each other in the embodiments according to FIGS. 4 and 5 so that the skeleton  24  lies with its radially inwardly-directed surface in the 6 o&#39;clock zone on the inner side of the ring-shaped chamber  22 .  
         [0041]    All the features described in connection with the various embodiments of the invention can be exchanged for each other or combined with each other as desired, at the discretion of the specialist in the art.