Background Art Current structural solutions of folding bicycles do not allow spring mounting of wheels which are overhung on swing arms.

According to the U. S. Patent Nr. 5,125,678, the bicycle is folded in such a way that the rear wheel which is not spring mounted is dismantled, then the seat support and finally the chain support is disconnected, the latter being released and turned around the axis of the central assembly towards the front fork. Taking into account that further assemblies must be dismantled when folding the bicycle, the folding procedure is time consuming, and the folded bicycle assumes large dimensions.

The U. S. Patent Nr. 4,634,138 solves the rear wheel folding of a classical type bicycle by turning the chain support together with the wheel around the axis of the central assembly towards the front wheel, whereby the overall length of the bicycle is shortened, and by tipping the seat and the handlebars also the height of the bicycle decreases. The folded bicycle has large dimensions and the folding is time consuming.

Springing of the rear wheel has been solved for the folding bicycle which is described in the patent DE 4313832 Al, where the rear springed wheel can be folded and is springing in a joint of a clamped fork. This joint is located off the axis of the central assembly, whereby both at springing and at folding the bicycle a considerable length difference arises between the central assembly axis and the wheel rotation axis.

A disadvantage of this solution consists in large dimensions of the folded bicycle, and in that the distance between the chain wheels changes at springing.

A disadvantage of the bicycles described so far is the fact, that the folding method requires rather expert knowledge, the chain is not covered and it presents problems when folding the bicycle, the size of the folded bicycles, even if using small wheels, is relatively large, and the time required to fold the bicycle is relatively long.

The joints used so far do not allow to fold a bicycle to a size corresponding to the size of the wheel diameter.

Folding a bicycle is comprehensively solved for a universal type of a folding bicycle, described in PV 1621-99, the nature of which consists in that the front arm and the front swing arm are coupled by means of a joint and telescopic springing of the front wheel or by means of a front wheel spring mounting on which the front wheel is one-sidedly freely clamped and the rear swing arm together with the rear wheel is coupled by means of a joint with the telescopic springing of the rear wheel or with the spring mounting of the rear wheel. Structural solution of the bicycle allows to fold various types of bicycles, those from a bicycle for sportsmen to a bicycle for children, to a size of 667 x 667 x 160 mm.

The aim of the present invention is to provide such solution of the joints of the wheel swing arms which allows to fold in a very simple way a universal type bicycle, for example, to a size of a front or rear wheel with the mudguard.

Disclosure of Invention This aim is fulfilled by a universal joint of a wheel swing arm consisting of a bearing and a journal, the nature of which consists in that the journal which is equipped with a bearing is a hollow journal, the bearing axis being concurrent or coaxial with the axis of the hollow journal. If the bearing axis and the journal axis are concurrent, they may include an angle from 2 to 7°, preferably from 3 to 4.5°.

The bearing may be equipped with at least one tooth and the journal with at least one skew helical slot; in that case the bearing axis is coaxial with the journal axis.

The tooth width is smaller then the slot width, but sufficiently large to allow smooth sliding of the tooth.

The bearing and the hollow journal may be radial and cylindrical, and the bearing may be a sliding bearing ; preferably, the bearing may be cylindrically radially sliding and the hollow journal may be cylindrically radial. If the bearing is equipped with a tooth and the hollow journal with a skew slot, the bearing and the hollow journal are stepped.

An advantage of the joint according to the present invention is its versatility. It can be used to clamp the wheel arms for bicycles as well as for motorcycles. hi the case of folding bicycles the joint according to the present invention allows to clamp the front and the rear wheel one-sidedly on the swing arm. By the present joint it will be achieved that the axis of the radial cylindrical bearing or the axis of the radial sliding cylindrical stepped bearing with a tooth, and the axis of the hollow cylindrical radial stepped journal with a skew slot in which the tooth slides, are perpendicular to the bicycle axis and to the radial face of the wheel. Such solution of the joint allows to fold the rear wheel by turning it around the axis of the central structure to the centre of the bicycle frame. If the stepped bearing is equipped with a tooth, a stepped journal together with the swing arm and with the rear wheel is axially thrown out by sliding in the skew helical slot.

Constructional solution of the joint according to the present invention is suitable for all types of folding bicycles, those from bicycles for children to bicycles for adults, and from mountain bikes to road bicycles. The constructional solution makes possible to fold bicycles of the above types to a size of 667 x 667 x 160 mm within a short time interval. The technique of folding the bicycle is simple and requires no expert knowledge.

Short description of the figures in the drawing Examples of embodiments of the invention are schematically shown in the Figures. Figure 1 shows a horizontal sectional view of the central assembly of the bicycle located in the hollow cylindrical journal with a radial cylindrical bearing.

Figure 2 shows a horizontal sectional view of the bicycle frame at the axis of the radial stepped cylindrical bearing with a tooth, and of the hollow radial cylindrical stepped journal with the skew slot.

Examples of Embodiments The universal joint of the wheel swing arm, as shown in Fig. 1, has an axis of the radial cylindrical sliding bearing 1\'which includes an angle of 4° with the axis of the hollow cylindrical radial journal 2\'. To understand better the joint function the figure shows clamping of the radial cylindrical sliding bearing 1 on the bicycle frame 5 and of the hollow cylindrical radial journal 2 with the wheel swing arm 6.

This joint construction makes possible to clamp the wheel on the swing arm 6, thus allowing, when folding the rear wheel, for example, to tun1 it around the central assembly into the centre of the bicycle frame 5.

Figure 2 shows a joint, the radial cylindrical sliding stepped bearing 1 of which is equipped with a tooth 3, and the hollow stepped journal 2 is provided with a skew slot 4. The axis of the radial cylindrical sliding stepped bearing 1\'is coaxial with the axis of the hollow cylindrical radial stepped journal 2\'.

When folding the bicycle, sliding of the tooth 3 in the skew slot 4 is throwing out the hollow cylindrical radial stepped journal 2 together with the swing arm 6 which turns around the axis of the radial cylindrical sliding stepped bearing 1\'towards the bicycle frame 5.

Industrial Applicability A universal joint according to the present invention can be utilised in the production of folding bicycles of various types, those from bicycles for sportsmen to bicycles for children, having wheels one-sidedly clamped on swing arms, as well as in clamping the wheels of motorcycles.