The present invention relates to a gear, especially for bicycles, of the kind in which a pulling chain or tooth belt can be changed between a number of toothed rims of different diameter and number of teeth by means of a chain guide and a chain tighten¬ er.

External chain-shifting gears (derailleur gears) have a number of toothed rims on the rear axle. The bi- cycle can by means of a chain guide and a chain tight¬ ener change from one toothed rim to another. Hereby the chain is generally exposed to a wrong pull, as only one of the toothed rims can be lying on the same level as the crank blade of the bicycle.

The object of the invention is to provide a gear which permits the chain to remain on the same level, which has a lower weight than known gears, which is compact and sturdy, which provides an exact gear shifting, which is simple to repair, and which, contrary to hub gears, can be individually adjusted to bicycles.

This object is obtained by embedding the toothed rims with axial displacement and by adapting a gear chang- in mechanism for carrying out this displacement.

Hereby is obtained that waste and chain wear is re¬ duced and that it is possible to use a symmetric rear- wheel which is considerably more stable than the gen¬ erally used rear-wheels in connection with derailleur- gears.

The gear can according to claim 2 be characterized in

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that a number of toothed rims by means of pins is embedded in a guiding barrel with axial slits and side flanges. By these means a compact gear is ob¬ tained, as the toothed rims, which are not in mesh with the chain or the tooth belt, are packed up at the side flanges of the guiding barrel so that only the toothed rim, which is in mesh, is free.

The gear can according to claim be characterized in that a number of toothed rims by means of round or long holes is embedded on a guiding barrel which consists of two end flanges and a number of round- going stay bolts. This embodiment is insensitive to mud.

The gear can according to claim 4 be characterized in that the gear changing mechanism consists of a sleeve, which is placed coaxially inside the guiding barrel, and which has helical grooves in which the turning-in pins of the toothed rims are in mesh, and that the gear changing mechanism is activated. ^" by a braking of the sleeve and at the same time a forward or backward movement of the pulling chain. This em¬ bodiment is simple and inexpensive.

The gear can according to claim 5 be characterized in that the gear changing mechanism consists of ax¬ ially sliding bolts adapted for moving the toothed rims in axial direction. This embodiment is sturdy and provides an exact gear shifting.

The gear can according to claim β be characterized in that a number of toothed rims is embedded with equidistant intervals on a sleeve with axial dis-

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placement, that the gear changing mechanism consists of a besides generally known shifter fork, and that the toothed rims can be locked by means of a ball catch or the like. This embodiment is simple and very inexpensive to produce, t the same time as the gear fulfils the requirements of most cyclists as the toothed rims in a simple way can be individually adjusted.

The gear can according to claim 7 be characterized in that the chain tightener permits the -application of a back-pedal brake as it, when the chain is mov¬ ing in the opposite direction, holds this in a tight position to such an extent that the braking operat- ion is neither delayed nor reduced. Hereby a consid¬ erable inconvenience is eliminated, which is known from generally known derailleur gears in which the chain is not all the time lying on the same level.

The invention is further elucidated with reference to the drawing ^' in which

Pig. 1 shows components for a gear according to the invention seen in perspective; Fig. 2 a sectional view through a gear which consists of the single components in fig. 1, and Pig. 3 components for the other embodiment of the gear seen in perspective.

A gear according to the invention is shown separated in fig. 1, only the essential components being shown. A toothed rim 1 has -hree internal pins 2, hich can be thrown into mesh with corresponding slits 3 in a guiding barrel 4, which is provided with side flang-

es 5. A sleeve β with three helical grooves 7 corres¬ ponding to the three pins 2 in the toothed rim 1 is placed coaxially inside the guiding barrel. Fig. 2 shows a cross section view of these three components 1 ₃ ^ and β in an assembled condition.

By a relative rotation of the sleeve β in relation to the guiding barrel 4 the toothed rim will be dis¬ placed towards one of the side flanges 5 dependent on the direction of this rotation. At the same time ^■ another, not shown, toothed rim will be led from the other side flange 5 towards the middle of the guiding barrel k where the pulling chain v/ill be twisted on the toothed rim gradually as the chain is twisting off the first toothed rim 1. The guid¬ ance of the chain takes place by means of a general chain guide and a chain tightener, which in this way only has to move on one level.

Pig. 3 shows another embodiment of the gear, in which a guiding barrel 11 consists of two end flanges 12, which are held together by a number of stay bolts 13- Toothed rims 8 provided with round or long holes

9 are embedded on the guiding barrel 11. The toothed rims 8 have like the toothed rims 1 turning-in pins

10 to be thrown into mesh with the grooves 7 in the sleeve 6.

In the shown and described embodiment of the gear the toothed rims are mounted on the rear axle. How¬ ever, toothed rims can also be mounted on the pedal axle, which can be axially displaced. The chain is guided by a steering fork, and the gear shifting takes place by an axial displacement of the pedal

axle .

The invention is not confined to a bicycle gear, as the gear can be used for many other purposes, where general gear constructions are used today. Thus it is obtained that the gear shifting can take place without using a clutch and that the transmission takes place with less waste, since indirect gears are avoided. Besides the gear can be independently placed either on the pulling or on the pulled axle. Furthermore, in the ^" embodiments described the sleeve and the guiding barrel can be interchanged, as the grooves in the sleeve can be changed into through- going slits.