The present invention relates to a bicycle accessory.

More specifically the bicycle accessory relates to a tool to put a chain that fell off the gearwheels back onto the gearwheels .

The accessory chiefly applies to mountain bikes and racing bikes that are provided with derailleur gears.

A derailleur is a mechanism that can move the chain from one gearwheel to another gearwheel while cycling.

By providing several gearwheels and changing between them the gear ratio can be changed while cycling. A distinction can be made a between a rear and a front derailleur. With the help of a handlebar control the derailleur can be switched.

A rear derailleur is located near the gearwheel group provided on the back wheel and can be moved left and right in relation to the longitudinal direction of the bicycle. This rear derailleur practically always has two pulley wheels over which the chain is led. All this is spring-mounted so that the position of the wheels in relation to each other can be modified but whereby the tension on the chain is retained. These wheels are indeed pushed to the back by the spring mechanism such that the chain when changing gear between the different combinations is constantly under tension. The rear derailleur therefore not only moves the chain to a desired gearwheel, but it also regulates the tension of the chain .

The front derailleur allows the chain to change from the chainrings or front gearwheels mounted on the crank shaft. The front derailleur is a guiding bracket which in relation to the longitudinal direction of the bicycle can be moved left and right.

It is not necessary to keep the chain under tension here, because the rear derailleur already takes care of that. It is known that the chain can fall off the gearwheels.

In the described gear groups the chain mostly falls off the gearwheels located at the front and more specifically toward the frame of the bicycle.

When a chain has fallen off the gearwheels, the cyclist usually has to get off the bicycle and manually put the chain back on the gearwheels. It goes without saying that your hands get very dirty doing this .

In a race it is mainly the time loss that is an issue. The present invention relates to an accessory of a bicycle that aims to prevent having to get off the bike and manually put on a fallen off chain again. To this end, the invention relates to an accessory for a bicycle which at least comprises a cam or stop which cam or stop are provided near the gearwheel located in the front that is closest to the frame of the bicycle, further referred to as the smallest chainring, and which cam or stop near that smallest chainring is directly or indirectly connected with the frame of the bicycle and which cam or stop reaches to near the bottom pitch circle of the smallest chainring. The bottom pitch radius is the radius of the bottom pitch circle, and this is the circle which describes the most centrally located part of the chain. In other words, the radius of the circle that describes the bottom of the chai .

The accessory for a bicycle according to the invention ensures there is no free passage or space, at least not along the entire 360° periphery around the crank shaft, between the smallest chainring and the frame of the bicycle, such that the chain is prevented from falling between that smallest chainring and the parts of the frame leaning against it.

Indeed, a chain can get significantly stuck here and possibly cause a lot of damage to the bicycle. According to a preferred embodiment variant the cam or the stop, when seen from the extension of the axis of the crank shaft, reaches to near the bottom pitch circle of the smallest chainring.

In other words, the distance measured from the axis of the crank shaft and perpendicular thereto to the part of the cam or stop furthest removed from this axis essentially corresponds with the bottom pitch radius.

On the other hand, according to a preferred embodiment variant the cam or stop there, i.e. on the level of the part of the cam or stop furthest removed from this axis, reaches to near the surface of the smallest chainring.

However, the cam or stop is provided at a limited distance of that plane. This distance is, on the one hand, not too small such that unwanted contact of the cam or stop with the smallest chainring and/or with the chain is prevented and, on the other hand, this distance is not too big such that the chain under normal use cannot end up between that smallest chainring and the cam or stop.

Account needs to be taken of the fact that the smallest chainring does not always form a plane perpendicular to the crank shaft.

This implies that the distance between the smallest chainring and the cam or stop with every revolution can be practically sinusoidal with maximum stroke equal to the amplitude of the curve. The adjustment and/or the positioning of the cam or stop needs to allow for that, as well as for the distance by which the chain reaches next to the plane of the smallest chainring .

The maximum distance between the cam or stop and the smallest chainring needs to be smaller than the width of the chain, with an extra margin that takes into account the possible distortion of the cam or stop and/or of the smallest chainring as a result of the forces that may occur. These forces can be particularly significant if the chain is given the chance to place itself in line with or in the extension of the space between both parts. It is clear that the amplitude of said sinusoidal distance between the smallest chainring and the cam or stop cannot be big, certainly when the cam or stop reaches next to the chain . According to a preferred embodiment variant the part of the cam or stop furthest removed from the crank shaft, also referred to as contact area or running area or free end, is located at a distance from the centre or the axis of the crank shaft which is a distance dl greater than the bottom pitch radius of the smallest chainring.

In this way the cam or stop already forms a barrier for the chain when there is a risk it will move from the smallest chainring toward the frame. In other words, this position of the cam or stop limits the chances that the chain will fall off the smallest chainring . This embodiment variant can be more efficient in certain circumstances, but it tolerates a smaller amplitude of said sinusoidal distance between the smallest chainring and cam or stop. At the part furthest removed from the crank shaft, already referred to as the contact area or running area or free end, the cam or stop can, be executed in a slanted way.

In this way the distance of the part furthest removed from the crank shaft can increase or decrease depending on whether this distance is measured closer or further removed from the smallest chainring.

In short this means that the contact area of the cam or stop can form an ascending or elevating barrier or a descending barrier for a chain when it falls off or risks falling off the smallest chainring.

An ascending or elevating barrier forces the chain in the direction of the smallest chainring.

A descending barrier offers the advantage that once the chain has slid off the smallest chainring it will certainly not move between the cam or stop, on the one hand, and the smallest chainring, on the other hand. According to another preferred embodiment variant the part of the cam or stop furthest removed from the crank shaft is at a distance located from the centre or the axis of the crank shaft which is a distance d2 smaller than the bottom pitch radius of the smallest chainring.

In this embodiment the cam or stop reaches less peripherally than the chain such that the advantage is obtained that there is less chance that the cam or stop during normal use make contact with the chain.

It is clear that this embodiment variant tolerates a greater amplitude of said sinusoidal distance between smallest chainring and cam or stop.

On the other hand, the cam or stop can be provided up to a smaller distance of the smallest chainring such that the chance of the chain ending up between the smallest chainring and the cam or the stop is further restricted.

It is clear that the cam or stop can have different functions: preventing the chain from falling off the smallest chainring; guiding the chain back to the smallest chainring when it falls off the smallest chainring; preventing a very difficult point of departure to put the chain back on the smallest chainring. The latter is indeed prevented because the chain at worst remains on the contact area of the cam or stop, or because the chain ends up on the mounting base of the cam or stop.

In other words it comes down to the fact that the invention relates to an accessory for a bicycle which comprises at least a cam or stop, which cam or stop can be provided near the gearwheel located in the front which leans closest to the frame of the bicycle, further referred to as the smallest chainring and which cam or stop is provided more specifically next to that smallest chainring and whereby the part of the cam or stop furthest removed from the crank shaft is located at a distance from the centre of the crank shaft, which essentially corresponds with the bottom pitch radius of the smallest chainring or a distance dl greater or a distance d2 smaller than the bottom pitch radius of the smallest chainring.

According to a preferred embodiment variant the part of the cam or stop furthest removed from the crank shaft is located at a distance from the centre of the crank shaft, which is a distance dl greater than the bottom pitch radius of the smallest chainring, whereby the distance dl is located between 0.1 mm and 12 mm. This position of the cam or stop which is a few millimetres higher, which means a few millimetres further removed from the centre of the crank shaft in relation to the bottom pitch radius, primarily makes sure that the chain falls off the smallest chainring less quickly, but also that when it does occur, the chain can be guided back to its location more quickly.

Guiding it back is possible, for example, by switching back one position in the direction of the bigger chainring. As already said, the front derailleur is a guiding bracket which in relation to the longitudinal direction of the bicycle can be moved left and right.

By moving this guiding bracket toward the bigger chainring, the chain will be forced to also move in this direction.

Normally this movement is not feasible when the chain has fallen off the chainring and is lying against the frame. Thanks to the accessory according to the invention this is made possible. Preferably two or more cams or stops are provided at a distance from each other.

Not all parts of the cams or stops that are located most peripherally in user position have to be located at the same distance from the centre of the crank shaft.

With the intention of better showing the characteristics of the invention, a preferred embodiment of an accessory of a bicycle is described hereinafter, by way of an example without any limiting nature, with reference to the accompanying drawings wherein: figure 1 shows a perspective view of part of a bicycle ;

figure 2 shows the same set-up as shown in figure 1 from a different . perspective and created with a computer drawing program;

figure 3 shows the part indicated in figure 2 with F3 on a larger scale; figure 4 shows the part indicated in figure 2 with F4 on a larger scale.

Figures 1 and 2 show the part of a bicycle which comprises the crank shaft 1 and the two gearwheels 2 and 3 located in the front here, the big chainring 2 and the small chainring 3 with the chain 4 fitted thereon.

The crank shaft 1 is provided in the part located at the bottom of the frame 5.

The front derailleur is not shown as it is mounted on the frame 5 on the side of the gearwheels 2 and 3. According to a preferred embodiment variant of the invention two cams 6 are provided here, more specifically a high cam 6A and a low cam 6B, whereby the choice of the name refers to their location on the bicycle when it is positioned in user position.

Figure 3 shows the high cam 6A in more detail and on a larger scale. Similarly, in figure 4 the low cam 6B is shown in more detail and on a larger scale. Each cam 6A, 6B comprises a mounting base 7A, 7B with mounting means which here consist of a groove 8A, 8B with on one of the free ends 9A, 9B a wall 10A, 10B provided perpendicular to the mounting base 7A, 7B with a half-round free end 11A, 11B that serves as contact area 11A, 11B. Indeed, if the chain 4 were to fall off the smallest chainring 3 the chain 4 primarily would make contact with one or both contact areas 11A, 11B of the cams 6A, 6B . The total height of the wall 10A, including the thickness of the mounting base 7A, is such that the part of the wall 10A furthest removed from the centre of the crank shaft 1, in mounted position, is located at a distance from the centre of the crank shaft 1, which here is located 4 millimetres further from the centre of the crank shaft 1 than the bottom pitch circle.

The low cam 6B is built exactly the same and analogously placed and appropriately sized.

Indeed, the total height of the wall 10B, including the thickness of the mounting base 7B, is such that the part of the wall 10B furthest removed from the centre of the crank shaft 1, in mounted position, is located at a distance from the centre of the crank shaft 1, which here is located 4 millimetres further from the centre of the crank shaft 1 than the bottom pitch circle.

The half-round free ends 11A and 11B are the contact areas or running areas 11A and 11B for a chain 4 that has fallen off and prevent the chain 4 from falling further to the frame 5.

In short, we can state that the cams 6A and 6B keep the chain 4 on the small chainring 3 thanks to the preferred but not necessary position of the cams 6A and 6B in relation to the bottom pitch circle of the small chainring 3.

If the chain 4 still falls off the small chainring 3, the chain 4 in terms of circulation or diameter is kept near the small chainring 3 such that a simple lateral move of the chain 4, possibly by suitably switching and moving the front derailleur, makes the intended co-operation of the chain 4 with the small chainring 3 possible again.

Possibly, the chain 4 can also slide off the contact areas or running areas 11A and 11B to then end up on the mounting base 7A and/or on the mounting base 7B. In that case a simple manual action may suffice to get the chain 4 back on the smallest chainring.

It is clear that the adjustable mounting, executed here as a groove 8Ά/8Β, can be realised differently.

Adjustment means may be provided, which make the simple adjustment possible.

The present invention is by no means limited to the embodiment described as an example of an accessory of a bicycle according to the invention, but this accessory can be realised in all kinds of forms and dimensions without departing from the scope of the invention.