The present invention relates to a vehicle wheel rim and to a method for its manufacture.

One of the aims of present day car manufacturing industries is to reduce the total weight of cars, by reducing the weight of car components. This is achieved by optimizing existing constructions, choos¬ ing lighter materials, finding new material combina¬ tions (composites) , or using new manufacturing meth¬ ods. At the same time, the car industry is extremely sensitive with regard to product -design and conse- quently methods which enable design changes without incurring too much expense are often chosen.

Normally, solely steel rims are used as standard on the wheels of private cars. Although these rims can be produced relatively cheaply, they greatly limit design possibilities. In order to satisfy customers who desire a special rim design, special rims made of aluminium or magnesium are available instead. These rims, however, demand a much higher price and are just as heavy as corresponding steel rims. Furthermore, more energy is consumed in the manufacture of magne¬ sium or aluminium rims and the manufacture of such rims creates a dirtier environment than the manufac¬ ture of corresponding steel rims. These special design rims are also susceptible to damage from external mechanical sources and create many problems when attaching balancing weights to the rims.

These problems are solved by means of an inventive wheel rim having the characteristic features set forth in the characterizing clause of the following Claim l and by a method for the manufacture of the wheel rim, in accordance with the characterizing clause of Claim 5. The lightness and mechanical strength of the

inventive wheel rim is achieved in that the rim in¬ cludes an outer hub, an inner hub and a base, wherein the inner hub and the outer hub include respectively male and female type snap coupling means which func- tion to lock the inner hub to the outer hub, and wherein the outer hub and the rim base include respec¬ tively male and female type snap coupling means which function to lock the outer hub to the rim base. The space defined between the inner hub, the outer hub and the rim base is filled with foam and glue, so as to obtain a strong and light sandwich construction.

The invention will now be described in more detail with reference to an exemplifying embodiment thereof and also with reference to the accompanying drawings, in which

Figure 1 is a cross-sectional view of the main compo¬ nents of the inventive wheel rim, prior to assembling said components; Figure 2 is a cross-sectional view of the inventive wheel rim subsequent to assembly;

Figure 3 shows two stages of the rim manufacturing process; and Figure 4 is a cross-sectional view of part of the inventive wheel rim, illustrating the construction and function of the snap coupling means.

Figure 1 is a cross-sectional view of the main compo- * nents of the inventive wheel rim prior to assembly. The inventive rim includes an outer hub 10, an inner hub 12 and a rim base 14. As shown in Figure 1, the outer hub 10 is provided with male-type, first snap coupling means 16 and a male-type second snap coupling means 18. The male-type first snap coupling means 16 is circular and extends in the centre of the hub. The male-type second snap coupling means 18 is also circu¬ lar and is positioned at the outer edge of the outer hub 10. The outer hub 10 also has a flanged abutment means 20 (flange not shown) where the flange is in-

tended to fit into an aperture (not shown) in the inner hub 12 when the wheel rim is assembled. The inner wheel 12 is provided with a circular, female- type snap coupling means 22 which is positioned at the centre of the hub and which is intended to fit into first, male-type snap coupling means 16 on the outer hub. The rim base 14 is provided with a circular, female-type snap coupling means 24 at one outer edge of the rim base 14. This female snap coupling means 24 is intended to fit onto the second, male snap coupling means 18 of the outer hub 10.

Figure 2 is a cross-sectional view of the inventive wheel rim after assembly. Like parts in Figures 1 and 2 have been identified with like reference signs. In assembling the wheel rim, the inner hub 12 has been pressed into the rim base 14 and glued and/or welded thereto. The outer hub 10 is then mounted on the assembly consisting of the inner hub 12 and the rim base 14. When fitting the outer hub 10, the hub is

"snapped" firmly to the inner hub 12 at the centre of the hub, by fitting the first, male snap coupling means 16 into the female snap coupling means 22 of the inner hub, therewith mutually locking the rim halves. When fitting the outer hub 10, the hub is also

"snapped" firmly onto the rim base 14, by fitting the second male snap coupling means 18 on the outer hub into the female snap coupling means 24 on the rim base, therewith locking the outer hub 10 to the wheel base 14. The wheel rim is stiffer, more rigid, at those attachment points where the snap coupling means hold the rim components together, because of the double plates obtained therewith (see also Figure 4). The supportive part of the rim is the inner hub 12, which is glued and welded to the inner surface of the rim base. Glue and foam 34, preferably polyurethane glue and polyurethane foam 34, are injected into the space formed between the outer hub 10, the inner hub 12 and the rim base 14, through a suitable number of

holes. The foam and glue are injected into said space partly to prevent the collection of condensation and dirt and partly to glue together the hub halves and create a firm sandwich construction. It will be seen from Figure 2 that the outer hub abutment means 20 lies against the inner hub 12. Although not evident from Figure 2, the flange of the abutment means 20 is located in holes in the inner hub 12. The inner hub 12 has a construction which affords maximum strength to the hub and is manufactured from steel plate, prefer¬ ably boron steel having a thickness of 1.2 mm for in¬ stance. The rim base 14 is manufactured, e.g. , from 1.2 mm metal plate which is welded to form a cylinder which is then roll-shaped to the correct profile. The outer hub 10, which determines the appearance of the rim, is manufactured from thinner metal plate, e.g. 0.7 mm, to enable small radii to be pressed more readily. This facilitates design possibilities to a modern varied design which simulates cast aluminium rims. The outer hub 10 is preferably manufactured from boron steel, or optionally from aluminium, metal plate or standard steel.

Figure 3 illustrates two stages in the manufacture of the wheel rim. As will be seen from Figure 3, glue 26 is applied to the rim base 14 and also to the inner hub 12. The inner hub 12 is glued to the rim base 14, as shown to the left of Figure 3, and also welded thereto. Glue 26 is then applied to the rim base 14 and also to the inner hub 12, whereafter the outer hub 10 is fitted in position. The outer hub 10 is thus secured with the aid of glue and also with the aid of the aforesaid snap coupling means.

Figure 4 is a cross-sectional view which illustrates part of the inventive wheel rim and which is intended to illustrate the construction and working method of the snap coupling means. Figure 4 illustrates part of the view shown in Figure 2 on a larger scale. The

mutually relative positions of the outer hub 10, the inner hub 12 and the rim base 14 in the assembled state of the wheel rim can be clearly seen from Figure 4. The reference numeral 32 identifies the centre hole of the wheel rim and reference numeral 28 identifies a hole intended for a wheel bolt 30, a suitable number, for instance four, of such holes being provided. Also shown is a cover plate which is fitted to the outer hub 10 and covers the rim centre hole 32 and the wheel bolts 30. This cover plate is lockable and renders stealing of the tyres difficult to achieve, besides preventing the ingress of dirt. The manner in which the male and female snap coupling means 18, 24 lock the outer hub 10 to the rim base 14, and how the male and female snap coupling means 16, 17 lock the inner hub 12 to the outer hub 10 can be readily seen from Figure 4. This locking effect is obtained because the shape of the second male snap coupling means 18 of the outer hub corresponds to the shape to the female snap coupling means 24 of the rim base, although the sizes of respective means are different (the diameters). This size difference creates a space problem when pressing the outer hub 10 and the rim base 14 togeth¬ er. The female snap coupling means 24 of the rim base are first forced apart and then return to their origi¬ nal form when the snap coupling means 24 of the rim base grips around the second male snap coupling means 18 of the outer hub. The first male snap coupling means 16 of the outer hub and the female snap coupling means 22 of the inner hub function in a corresponding manner, even though their cross-sectional shape is different to that of the snap coupling means 18, 24. The snap coupling means 16, 22 of the Figure 4 embodi¬ ment have a cross-sectional shape which corresponds generally to two mutually U-shaped grooves which extend around the centre hole 32. The rim becomes stiffer because of the double plates obtained at the snap coupling means 16, 18, 22, 24, therewith enabling the outer hub 10, the inner hub 12 and the rim base 14

to be made of relatively thin metal plate, so as to keep down the total weight of the wheel rim.

A description of the method of manufacture of the inventive wheel rim will now follow. The inner hub 12 containing a female snap coupling means is first pressed from boron steel plate for instance. An outer hub 10 containing a first male snap coupling means 16 and a second male snap coupling means 18 is pressed from thin metal plate, for instance boron steel plate. The rim base 14 is manufactured by roll-shaping the base from, e.g., boron steel plate. Subsequent to cutting, welding the plate together to form a cylin¬ der, the cylinder is roll-shaped to the correct pro- file. The next stage of manufacture involves pressing the inner hub 12 into the rim base 14 and welding the hub and base together to form a sub-assembly, which is then placed in a fixture and heated in a tempering furnace for instance, to the correct temperature. The sub-assembly held in the fixture is then cooled to harden/temper the sub-assembly, this cooling being effected, for instance, by spraying water onto the sub-assembly through spray nozzles. In the next stage of manufacture, the outer hub 10 is fitted and glued to the sub-assembly, so that the female snap coupling means 22 of the inner hub are locked to the first male snap coupling means 16 of the outer hub, and so that the female snap coupling means 24 of the rim base are locked to the second male snap coupling means 18 of the outer hub. Glue and foam, preferably polyurethane glue and polyurethane foam 34, are then injected into the space formed between the inner hub 12, the outer hub 10 and the rim base 14. The glue and foam are injected through appropriate holes on the rear side of the rim, these holes then being plugged. When the injection process has been completed, the finished wheel rim may be removed and the surfaces of the rim treated. The aforesaid glue will preferably be a two- component glue of polyurethane type, which affords

good properties at both high and low temperatures. The glue is also tough and therewith capable of withstand¬ ing external mechanical forces on the rim.

The selection of material and the method of manufac¬ ture provide a wheel rim which is lighter in weight than wheel rims that are made of aluminium, magnesium, and conventional steel wheel rims. The design options are quite comparable with cast wheel rims, although at a much lower cost. The lower total weight of the wheel rim improves vehicle performance, therewith also contributing to a better environment. As a result of the construction of the inventive wheel rim, there is obtained a strong and partially resilient rim which improves road performances. The sandwich construction assists in reducing sound levels, since the poly¬ urethane foam dampens body sound in the wheel rim. The lower energy consumption afforded by the manufacture of the inventive wheel rim and the reduced need of aluminium rims and the reduced manufacturing problems associated therewith also have a favourable effect on the environment.

It will be understood that the illustrated exemplify- ing embodiment of the inventive wheel rim does not limit the scope of the present invention, and that the scope of the invention is limited solely by the scope of the following claims.