There are generators for a variety of purposes. There are for instance small local wind power plants, for separate households or a small group of households, another application is for bicycles. Present generators for such seldom operate satisfactorily, as they are mounted for contact with a tyre when light shall be switched on. Often, especially with rain or snow, the friction between the tyre and the driving wheel of the generator is inadequate such that the generator does not operate in the intended way. When a conventional generator for a bicycle operates it exerts a considerable brake action at the wheel, which may be annoying.

The object of the present invention is to provide a generator of the art mentioned introductorily, that does not show the drawbacks, that are typical for generators, hitherto present, that is to say with a great braking action in relationship to effect gained, or else inferior function.

According to the invention, such a generator is characterised primarily in the fact, that magnets are provided, concentric with the coil, turning a first group with alternating N-and S-magnet poles to a first plane, and a second group with alternating N-and S-magnet poles turning to an opposite second plane, whereas a first and a second pole changer are provided to rotate in relationship to the wheel axis, whereas during the rotation one of the pole changers passes relatively close to the first group of magnet poles and the second pole changer passes relatively close to the second group of magnet poles. Further characteristics and features for the generator according to the invention are disclosed in the enclosed dependent claims.

The invention will be described in the following, reference being made to a generator for a bicycle as an example, reference being made to the enclosed schematic figures.

Thus there is shown in figure 1 a generator for a bicycle according to the invention in an axial section, figure 2 a view toward a section perpendicular to figure 1, whilst figure 3 shows an alternative embodiment of a pole changer in an axial section.

The bicycle generator forms part of the wheel nave at an axis 1. The generator is protected by and is enclosed in a casing 2, that is ended by an end plate 3, which is carried by the axis by a ball-bearing 4, engaging a flange 5 at the axis 1. The encapsulation is part of the wheel nave and the casing 2 has an outer flange 19 with holes for the wheel spokes in a conventional wheel design. The other end of the casing is carried via the wheel nave of a corresponding bearing at the axis.

The generator also comprises a portion 17, fixed to the axis, forming a magnet casing. In this there are provided a number of magnets 15,21,22, placed in a circle within the casing 17, and within these a coil 14. The fixed portion also comprises a gear ring 10 with inner cogs, cooperating with a gear wheel 9 to transfer a quick rotating movement to pole changers 12,13, provided at the sides of the magnets and the coil.

An axis 6 is fixed at the end plate 3 of the nave, direct inwards to the generator.

The gear wheel 9 is arranged to rotate freely on the axis 6 on a ball-bearing 8 at the flange 7 of the axis. The gear wheel 9 is engaging the gear ring 10 and also a gear ring 11 that is fixed, via a bearing ring 18, to pole changers 12,13. The bearing ring is arranged to rotate by a ball-bearing on the wheel axis 1.

A number of magnets 15,21,22 are directed parallel to the axis 1, the magnets being provided outside of the coil 14 concentric with and evenly distributed in a ring around the complete circumference of the coil, such that the magnet poles, turned outwards to the pole changers are alternating North-respectively South- poles with the same partition between different arts of poles around the complete ring. The pole changers 12,13 are plane discs and have each of them a number of protruding flanges 26, extending from a central disc of the pole changer in the same plane as the disc outwards to and somewhat above the middle of the magnet poles. Preferably the number of flanges is the same as the number of magnet pole groups of one art of pole and the width b of each flange corresponds approximately to the partition measure d between the magnet poles. The magnet poles are coupled together, magnetically conductive, by the bearing ring 18.

The function of the device may be described as follows. When the wheel rotates around the axis 1 the nave is turned and therewith the casing 2 and the end plate 3 around the axis 1 with the same number of revolutions as that of the wheel, whilst the magnet casing 17, at the inside of the casing 2, is fixed to the axis 1 and remains still in relationship to same. The axis 6 of the gear wheel 9 will then be transferred in relationship to the magnet casing 17 and the gear ring 10, which is part of same, which means, that the gear wheel 9 rotates on the axis 6. The gear wheel 9 will then act upon the gear ring 11 such that this will rotate on the axis 1 and via the bearing ring 18 this rotation will be transferred to the pole changers 12,13, which will then rotate in relationship to the magnets 15,21,22, which stand still in relationship to the axis 1. The gear ratio between the gear ring 10 and the gear wheel 9 and that between the gear wheel 9 and the gear ring 11 will make the pole changers rotate at a much higher speed of rotation than that of the wheel and the wheel nave. Variations in the magnet field, that occur in relationship to the coil 14 will mean, that an electric current is created in the coil and is conducted via the electrical lines 23 and 25 to an electrical circuit, that usually is formed from components, being part of the of the bicycle lightning. In this case, the magnet casing and the wheel axis are used as one conductor, whilst the other conductor 23 is led out through a channel 24 in the axis.

The design disclosed above is such, that the generator only demands a small space, and it is for instance possible to combine it with a brake drum in the same nave. Within the scope of the invention, the design of the generator may be varied in different ways. This is, for example, true for the number of magnets and the location of these inwards our outwards of the coil, with different partitions. The design of the pole changers may also be varied in several ways. In figure 3 it is shown, that the pole changers 26 and 26 are formed as truncated cones with a small axial extension, with recesses, such that flanges are formed.