FIELD OF INVENTION

The field of invention relates to a bicycle chain derailment prevention and retention means.

PRIOR ART

The bicycle is propelled forward by the engagement of the chain with the chain rings. The teeth on the chain ring mesh with the links of the chain, and the chain ring either pulls or gets pulled by the chain, resulting in to chain ring rotation ultimately resulting in forward translation of the bicycle. At times, due to any of the various reasons, the chain climbs over the teeth of the chain ring and manages to fall aside outside of the mesh with the teeth. When this incident happens, the pedalling input provided by the rider can no longer propel the bicycle forward, rendering the bicycle unusable.

This event, chain derailment can pose serious problems to the rider depending on the circumstances. If the rider is incapable of putting the chain back on the chain ring, he/she may get stranded in middle of nowhere. Not to forget, chain re-railing is a tedious process, where the rider often ends up with dirty greasy hands. At times, the chain may just get stuck in crevices near the rear axle and only a mechanic may be able to reclaim the chain. All in all, repeated chain derailments over a period of time can create an aversion to riding bicycles in the mind of the rider.

There are 2 kinds of products that exist in the current scenario as known to the invention and which are illustrated in figures 13 A-F. One set consists of an element fixed to the bicycle frame, generally to the seat tube. This product works by limiting the sway of the chain away from the chain ring either on one side or both the sides. The solution can be utilized for the chain ring as well as freewheel, depending on the kind of attachment design. (Fig. 13A - Fig. 13D). The other set consists of components that are attached to the chain ring and have a chain tensioner or a guide in place to entrain the chain. This set is used only on the chain ring, and is an expensive yet a very effective solution. (Fig. 13E, Fig. 13F).

The disadvantages of this prior art is that it:-

1. Employs roller guides

2. Not adapted to freewheel

3. Wall diameter = Chain ring diameter

4. Spacing from teeth not designed

US20040009835A1 (Fig. 13G) discloses only one guide member on the bottom

US20130217527A1 (Fig. 13H, Fig. 131) This patent discloses, only one wall that rotates, there is an element behind that does not rotate. Both guides are stationary. This is not adapted to freewheel (rear end of the bicycle)

US 20120172164A1 (Fig. 13J, Fig. 13K)

Chain Catcher, but also claims to prevent chain derailment

The differences are 1) No rotating member 2) Applicable only for multi speeds, doesn't work for single speeds 3) Prevents chain from derailing only on inner side 4) Construction is totally different

The advantageous elements of the invention over prior art is as below:

DESCRIPTION OF INVENTION

The chain consists of two types of links alternating in the bush roller chain. The first type is inner links, having two inner plates held together by two sleeves or bushings upon which rotate two rollers. Inner links alternate with the second type, the outer

links, consisting of two outer plates held together by pins passing through the bushings of the inner links. The components are illustrated in (Fig.1 A - Fig.1 E)

Between the inner links and the outer links, there is a little bit of play involved, about 1mm. This together with the small gap between the bush and the roller allows the chain to tolerate a certain amount of offset.

The play and the dimensions discussed above are intrinsic to chain design. (Illustrated in Fig. 2A & Fig.2B). Fig.2A illustrates regular case : (intended use case) inner links equally spaced between outer links. Fig.28 illustrates stretched case : All the inner pins are completely displaced towards one side, touching the outer link.

Constituent Component: Sprocket / Chain ring / Freewheel illustrated in Fig.3 & 4.

Chain slack or Loose chain: (illustrated in Fig.5)

The inner link bushing wears out over a period of time, and a play is introduced between the roller and the inner link bushing. This phenomenon in all the links of the chain cumulatively result in a 2-3% elongation in its length. At times, there may also be a few extra links in the chain as against needed for a particular combination of freewheel and chain ring. The rear axle may also have slid to the end of the dropout nearer to the bottom bracket. This extension in chain length provides the required freedom to the chain to manage to climb to the top of the chain ring.

Stiff links - Occasionally, the chain may have a stiff link i.e. the inner link bushing may be larger in diameter than the acceptable limit. This makes the rotation of the corresponding roller about this bushing difficult. Now at the time of meshing with the chain ring, when the chain links are expected to adapt to the chain ring curvature, the links do not rotate enough and end up climbing over the teeth.

Offset between chain rings (illustrated in Fig.6)

Due to deviances in the assembly or damage during transit, the centre planes of the front and the rear chain ring my end up being offset by an amount which the chain cannot tolerate.

By design, the centre plane of the chain ring and freewheel are supposed to be in the same plane. A offset tolerance of 0.8 mm is built into the assembly, and will be adhered to in the ideal scenario. In a realistic environment, though, the offsets between the two components have been observed to be as high as 10 mm, 12.5x the acceptable limit. The chain can tolerate such an offset under low load conditions, but if the rider tries to put in a higher effort, it gets pulled out of the mesh due to cross pulling. The problem is further aggravated if the slack in the chain is more than the acceptable limit of 4-5 cm

Wobbly teeth, worn out teeth (illustrated in Fig.7)

Worn out tooth can also come in way of the chain meshing with it, and can cause instability during engagement.

A combination of these above 4 factors can lead to the chain getting derailed. The concept of understanding of detailed phenomenon is pasted below Chain design a) Interplay between links b) Dimensions of individual chain elements Sprocket tooth profile a) Height b) Addendum diameter Understanding of the failure phenomenon and factors contributing to failure Principal reason:

Chain Slack combined with any of the below reasons Worn out components Damaged components Manufacturing tolerances, deviances Based on two components involved and identifying the principal failure mode

Evaluate feasibility and effectiveness of fixing root cause

Evaluate feasibility and effectiveness of fixing the symptom at the occurrence site

Resolution: Prevent the chain from swaying by a certain distance from the chain ring centre plane

Distance calculated based on maximum play in chain, and observation of not letting the chain mount addendum

Technology : Based on observations, we have established that the chain elements never really jump above the tooth height, they only hike to the top based on failure conditions. Allthe chain jumping happens between the front and tear chain ring, not on the chain ring. This is described in the illustration (Fig. 8),

The chain position captured in the yellow ellipse is as high as the chain jumps. This is also the height the chain has to hike to get to the top surface of the tooth. It is in this position that the possibility of the chain derailment creeps in. The illustration in Fig. 9 describes the minimum condition required for the chain to derail.

In Fig. 9, if the chain manages to hike to the top surface, i.e. above the magenta line in the image below, it is then and only then that the chain is free to go all the way over to the other side, that is de-rail. If any portion of the chain is below the magenta line, the tooth functions as a barrier that prevents the chain from slipping, or derailing over to the other side.

From this observation, it is understood that if a barricade is provided at a certain distance from the chain ring centre plane, the barricade can effectively function as a means of preventing chain derailment. To distance the barricade has to be away from the centre plane is derived from the understanding of the chain and tooth cross sectional profile.

The principle underlying wall profile and tolerances is illustrated in Fig.10A& Fig.tOB and Fig.lOH illustrates resultant wall profile from derived equations.

With reference to Fig.lOA & Fig. 10H a : Gap between two inner links

b : width of each plate ( = d )

c : play between inner and outer links

e : pin length extruding out of the bush

r: curved profile of the wall following the curvature of tooth With reference to Fig.lOB & Fig. 10C, which define the principle identifying wall profile and tolerances.

x: Gap b/w tooth centre plane, guide wall;

y: Width at any cross section of tooth;

yt: Width of tooth base

From the dimensions described above, then, the locus of a point on the inner boundary of the wall is dictated by the following inequality, EQ1.

With this, chain derailment can be eliminated completely on both scales of the tooth if the inner profile (i.e. side facing the tooth) of the wall is constructed in the region defined by the above equation.

This inequality gives how the profile of the wall should be, at any point relative to the tooth. Fig 10D - Fig. 10G illustrate the regions M and N, wherein Region M is defined by and Region N is defined by
The wall can take any profile in this defined region. The following illustration explains the minimum height of the wall required over and above the tooth top surface to effective arrest the chain derailment.

Principle for determining the guide wall height above tooth is illustrated in figs. 11A - 11C.

h: height coverage above top surface;

t: height of tooth;

J: Maximum observed chain jump

The amount J the chain jumps is constrained by the equation

Ja+b+d-^

wherein a : Gap between two inner links b : width of each plate (= d) x: Gap b/to tooth centre plane, guide wall; y: Width at any cross section of tooth yt: Width of tooth base the said profile of the wall characterised in that on both sides of the tooth, derailment of the chain is arrested.

6. The bicycle chain derailment prevention and retention means as claimed in claim 1-4, wherein the predetermined profile distance of the locus of a point on inner surface of the wall from the said chain ring centre is further calculated to be in the region defined by

x a + b + d + c-Z and

x>a+fc+d+c-y wherein c : play between inner and outer links

7. The bicycle chain derailment prevention and retention means as claimed in claim 1-5, wherein the predetermined profile distance of the locus of a point ofi inner surface of the wall from the said chain ring centre is further calculated to be in the region defined by

x a + b + c + d + e- ^ and

Vt x > a + fc + c + d + e-y-

wherein e : pin length extruding out of the bush

8. The bicycle chain derailment prevention and retention means as claimed in claim 1 - 6, wherein the optimal predetermined height of the wall over and above the tooth top surface is calculated to be in the range defined by

*e[(H).(M)] and

but any height h in the inequality below will suffice

h = height coverage above tooth top surface s = maximum height of the chain p = diameter of the pin

the said height of the wall characterised in that it provides a barrier to the chain anywhere on the pin surface to arrest the lateral sway.

9. The bicycle chain derailment prevention and retention means as claimed in claim 1-7 wherein the preferred height of the wall over and above the tooth top surface is such that the wall may start at any point below "h" but not beyond it.

10. The bicycle chain derailment prevention and retention means as claimed in claim 1 wherein the said wall is a profiled annular ring.

11. The bicycle chain derailment prevention and retention means as claimed in claim 9 wherein the said annular ring is attached to the chain ring or free wheel of the bicycle.