Chain-rings set for a bicycle power transmission system provided with segmented chain-ring and segmentation method for obtaining it

Method, in a chain-rings set for a power transmission system comprising a chain, a first chain-ring, a second chain-ring having a common axis with the first chain-ring and provided with more teeth than the first chain-ring, wherein a shifting configuration with tensed chain section is defined, wherein the second chain-ring is formed by independent segments, such that each segment is delimited by two segmentation cuts, which comprises axial displacement means of the segments such that they can be moved in an independent manner at least in the direction of the common axis, wherein an up-shift segment, has a first tooth which is the first which is engaged with the chain in the rotation movement, a point of the valley previous to the first tooth corresponding to the point wherein the segmentation of the up-shift segment starts,

• for the determination, to achieve an ideal shift from the first chain-ring to the second chain-ring, of the angular position between the first chain-ring and the second chain-ring and the determination of the valley of the second chain-ring wherein the segmentation starts, which comprises the steps consisting of:
• a. Determine in the first chain-ring an angle interval [−ϑ1/2;
• ϑ1/2] wherein the force between the first chain-ring and the section of tensed chain is transmitted, the extreme angles of this interval being symmetrical with respect to a reference radius (ϑ=0) which is perpendicular to the section of tensed chain, wherein an arc subtended by said interval corresponds to the chain pitch;
• b. Determine in the angle interval [−ϑ1/2;
• ϑ1/2] an optimum angle for shifting from the first chain-ring to the second chain-ring, for which a distance between:
• a first intersection, between the radius corresponding to said optimum angle and a primitive line of the first chain-ring having radius r wherein the center of the roller of the chain must fall and therefore respect thereof the valley of the teeth of the first chain-ring is defined;
• and
• a second intersection, between a straight line passing through the first intersection and which is perpendicular to the reference radius (ϑ=0) and a primitive line of the second chain-ring having radius R, wherein the center of the roller of the chain must fall and therefore respect thereof the valley of the teeth of the second chain-ring is defined, in a rearmost position in the rotation,
• is a multiple of the chain pitch, such that an optimum relative angle between a radius passing through the first intersection and a radius passing through the second intersection is defined;
• c. Arranging the first chain-ring and the second chain-ring with a relative angular position wherein:
• the lowest point of a valley of the first chain-ring is located in a radius forming an optimum angle with the reference radius (ϑ=0);
• and
• the lowest point of a valley of the second chain-ring previous to the first tooth, which is the valley wherein the segmentation of the first segment starts, is located in a radius forming an optimum relative angle between valleys with the radius corresponding to the optimum angle,
• such that the chain can seat in both valleys in the moment for shifting from the first chain-ring to the second chain-ring, with a simultaneous traction on the tensed chain section exerted by the last tooth of the first chain-ring and the first tooth of the second chain-ring.

Method, in a chain-rings set for a power transmission system comprising a chain, a first chain-ring, a second chain-ring having a common axis with the first chain-ring and provided with more teeth than the first chain-ring, wherein a shifting configuration with a tensed chain section is defined, wherein the second chain-ring is formed by independent segments, such that each segment is delimited by two segmentation cuts, which comprises axial displacement means of the segments such that they can be moved in an independent manner at least in the direction of the common axis, wherein a down-shift segment has a last tooth, which is the last tooth engaging with the chain in the rotation movement, a subsequent valley to the last tooth corresponding to the valley wherein the segmentation of the down-shift segment terminates,

• for the determination, to achieve an ideal shift from the second chain-ring to the first chain-ring, of the angular position between the first chain-ring and the second chain-ring and the determination of the subsequent valley to the last tooth of the second chain- ring wherein the segmentation is carried out, which comprises the steps consisting of:
• a. Determine in the first chain-ring an angle interval [−ϑ1/2;
• ϑ1/2] wherein the force between the first chain-ring and the tensed chain section is transmitted, the extreme angles of this interval being symmetrical with respect to a reference radius (ϑ=0) which is perpendicular to the tensed chain section, wherein an arc subtended by said interval corresponds to the chain pitch;
• b. Determine in the angle interval [−ϑ1/2;
• ϑ1/2] an optimum angle for shifting from the second chain-ring to the first chain-ring, for which a distance between:
• a first intersection, between a radius corresponding to said optimum angle and a primitive line of the first chain-ring having radius r;
• and
• a second intersection, between a straight line passing through the first intersection and which is perpendicular to a reference radius and a primitive line of the second chain-ring having radius R in a more advanced position in the rotation,
• is a multiple of the chain pitch, such that an optimum relative angle between the radius passing through the first intersection and a radius passing through the second intersection is defined;
• c. Arranging the first chain-ring and the second chain-ring with a relative angular position wherein:
• the lowest point of a valley of the first chain-ring is located in a radius forming an optimum angle with the reference radius (ϑ=0);
• and
• the lowest point of a valley of the second chain-ring is located in a radius forming an optimum relative angle with the radius corresponding to the optimum angle,
• such that the chain can seat in both valleys in the moment for shifting from the second chain-ring to the first chain-ring and such that a simultaneous traction on the tensed chain section exerted by a last tooth of the second chain-ring and a first tooth of the first chain-ring is obtained.

Bicycle comprising a chain-rings set, the set comprising a chain, a first chain-ring, a second chain-ring having a common axis with the first chain-ring and more teeth than the first chain-ring, the teeth comprising a front flank which is the flank that pushes links of the chain, wherein the second chain-ring is formed by at least two segments, which comprises axial displacement means of the segments such that they can be moved in an independent manner at least in the direction of the common axis, the second chain-ring being segmented in at least:

• an up-shift segment for chain shifting from the first chain-ring to the second chain-ring;
• a down-shift segment for chain shifting from the second chain-ring to the first chain-ring;
• the up-shift segment being angularly arranged with respect to the first chain-ring such that, in a starting configuration for shifting from the first chain-ring to the second chain-ring and in tensed chain conditions in an up-shift section of the chain between both, a last section of chain being tensed between a last tooth of the first chain-ring and a first tooth of the up-shift segment, a front flank for pushing rollers of the chain being defined in the engaged teeth:
• a last engaged tooth of the first chain-ring, is engaged in the up-shift section, with an engaged chain-link of the up-shift section, such that the front flank of the last tooth of the first chain-ring contacts an engaged roller of the engaged chain-link of the up-shift section;
• and
• a first tooth engaged of the up-shift segment, is engaged in the up-shift section, with an engagement chain-link of the up-shift section, such that the front flank of the first tooth of the up-shift segment contacts an engagement roller of the engagement chain-link of the up-shift section;
• the down-shift segment being angularly arranged with respect to the first chain-ring such that, in a starting configuration for shifting from the second chain-ring to the first chain-ring and in tensed chain conditions in a down-shift section of the chain between both, which is the chain section which is tensed between a last tooth of the down-shift segment and a first tooth of the first chain-ring, a front flank for pushing rollers of the chain being defined in the engaged teeth:
• a last engaged tooth of the down-shift segment, is engaged in the down-shift section, with an engaged chain-link of the down-shift section, such that a front flank of the last tooth of the down-shift segment contacts an engaged roller of the engaged chain-link of the down-shift section;
• and
• a first engagement tooth of the first chain-ring, is engaged in the down-shift section, with an engagement chain-link of the down-shift section, such that a front flank of the first tooth of the first chain-ring contacts an engagement roller of the engagement chain-link of the down-shift section.