Patent Description:
A toothed pulley with a ring made of an elastically deformable material is disclosed in <CIT> in the form of a sprocket, wherein the cushioning rings serve as cushions between the teeth of the sprocket and the link plates of a roller chain trained engaged with the sprocket. As disclosed therein, the cushioning rings may have an annular or rectangular cross section.

Further toothed pulleys with respective cushioning rings made of an elastically deformable material are disclosed in <CIT> in the form of sprockets of a multi-gear cassette for a rear wheel of a bicycle, wherein the cushioning rings dampen the forces produced by the chain members running from the slack span of the chain onto a sprocket. These cushioning rings have rectangular cross sections.

Document <CIT> shows the preamble of claim <NUM>.

The prior art pulleys have the problem that nevertheless they are relatively noisy and buckling in operation.

Bicycle chains of an unconventional type, so-called flattop chains (or AXS chains), are known in the art, wherein the respective tops of the link plates are straight-lines, which enables a narrower chain construction with increased strength and durability.

If such a chain is used in a bicycle having a derailleur, there may be the problem that such a chain has some difficulties to run low-noise and smoothly through the derailleur. In particular, there would be the problem that the operation is very noisy and buckling. Accordingly, it is an object of the present invention to provide a pulley for a bicycle rear derailleur with silencing characteristics which is very low-noise in operation and runs very smoothly also with flattop chains.

The above object and further objects which will become apparent hereinafter are achieved by a pulley having the features of claim <NUM>.

The present invention also provides for a rear derailleur of a bicycle according to claim <NUM> including the pulley of the invention.

Further advantageous features are set out in the dependent claims.

According to the invention, the pulley is for a bicycle rear derailleur. Such a derailleur usually comprises, as is known in the art, a guide pulley and a tension pulley both being rotatably mounted on a derailleur cage which is movable with respect to the bicycle and adapted to guide and tension a bicycle roller chain in an S-shape feeding to the cassette. The cage can be positioned under the desired sprocket of a multi-gear cassette attached to the hub of a rear wheel of a bicycle by an arm that can swing back and forth under the sprockets. Gear shifting is carried out by moving the arm which transfers the chain from one sprocket to another while pedaling.

Further, according to the invention, the pulley includes an annular channel formed adjacent to each side face to the pulley and opening radially outward, wherein each cushioning ring is supported by the annular channel. In a side view of the pulley, the annular channel forms a polygon, wherein the number of corners of the polygon is equal to the number of teeth of the pulley and wherein the corners of the polygon are angularly offset from the centers of the teeth of the pulley by the half angular distance between adjacent teeth of the pulley.

The cushioning ring is accommodated in the annular channel with a certain tension. The annular channel may be advantageously made in one piece with the pulley. Alternatively, the annular channel may be fixedly joined with the pulley.

Because the corners of the polygon are angularly offset from the center of the teeth of the pulley, the cushioning ring has straight portions, each straight portion extending under one tooth of the pulley and being angularly aligned with the respective tooth of the pulley.

The angular offset of the polygon corners from the teeth is particularly suitable in cases, wherein the derailleur is intended for chains of an unconventional type, wherein tops of the link plates are straight-line which enables a narrower chain construction with increased strength and durability. Such chains are known in the art as AXS or "flattop" chains and are manufactured by the SRAM corporation.

The inventive pulley with polygonal cushioning rings is particularly suited when embodied as a guide pulley of a rear derailleur in conjunction with AXS "flattop" chains devised as mentioned above. In a rear derailleur, the chain is running with the straight tops (flattops) over the guide pulley and the straight tops are perfectly matching the straight portions of the polygonal cushioning ring of the guide pulley. Accordingly, the impact of the chain on the guide pulley is smooth and silent.

While the polygonal cushioning ring according to the invention is particularly advantageous for the guide pulley of a bicycle rear derailleur if used with AXS "flattop" chains, also the tension pulley of a bicycle rear derailleur may advantageously have a polygonal cushioning ring if interacting with the flattop of a "flattop" type chain.

In an embodiment, the annular channel forming a polygon may be limited radially by a polygonal shoulder formed laterally of the pulley, and the annular channel forming a polygon may be defined axially between the side face of the pulley and a polygonal radial extension of the polygonal shoulder, which forms a flange. That is, the cushioning ring is supported radially by the polygonal shoulder and axially between the side face of the pulley and the radial extension of the polygonal shoulder.

The corners of the polygonal shoulder may be rounded. The corners of the polygonal radial extension of the polygonal shoulder may also be rounded.

The polygonal shoulder and the polygonal radial extension may be made in one piece with the pulley. Alternatively, they may be manufactured separately and fixedly joined to the pulley.

The polygonal shoulder may comprise a number of straight portions equal to the number of teeth of the pulley and angularly aligned with each respective tooth of the pulley. The polygonal radial extension of the polygonal shoulder may comprise a number of straight portions equal to the number of teeth of the pulley, each straight potion being angularly aligned with a respective tooth of the pulley.

Each cushioning ring may advantageously project radially from the annular channel, preferably by at least <NUM>/<NUM> of the total radial height of the cushioning ring and more preferably by at least <NUM>/<NUM> of the total radial height of the cushioning ring.

The straight portions of the polygonal cushioning ring dampen the impact of the chain rollers on the depressions or valleys between consecutive teeth. As known in the art, the depressions or valleys are formed between consecutive teeth of a pulley as seen in the axial direction of the pulley. Advantageously, the straight portions of the cushioning ring prevent, at least during the initial contact of the chain with the pulley, the contact of the chain rollers with the depressions or valleys between consecutive teeth, such that the cushioning ring is contacted only by the link plates of the chain.

While the cushioning rings may have well know cross sections, for example square, rectangular or circular, in a preferred embodiment of the invention each cushioning ring comprises, at least on its side facing the roller chain, a groove extending along its entire perimeter length, which groove, as seen in a cross-sectional view through the cushioning ring, is a recess flanked by two protrusions, wherein the protrusions are adapted and orientated to come in contact with outer and inner link plates, respectively, of a roller chain running over the pulley. This contributes to make the derailleur very silent and smooth running, because by the two protrusions which may be much narrower than the total width of the outer and inner link plates, relatively week dampening forces can be provided.

In said preferred embodiment, in a cross-sectional view through the cushioning ring the protrusions on each cushioning ring may be curved convexly and may be connected contiguously by the recess which is curved concavely, as seen from inside the cushioning ring.

In preferred embodiments, the cross section of each cushioning ring is generally x-shaped. In particular, the cross-sectional profile of each cushioning ring may have the shape of an alphabetic character x whose legs are short with respect to the body of the character and have concave sections between them. Preferably, the ends of the legs are concavely rounded. The legs may also be short with respect to their length and have concavely rounded ends.

In a cross-sectional view through the cushioning ring, the concavely rounded ends of the legs may be four circumferentially distributed and convexly curved protrusions of the respective cushioning ring which are connected contiguously by four circumferentially distributed and concavely curved recesses. Some profiles of this type can be mathematically described as elongated hypotrochoids with reversal points and four peaks, which are continuous and continuously differentiable, but the cross-sectional profile of the cushioning ring is not limited to such special shapes or to continuous and/or continuously differentiable shapes.

The x-shaped cushioning rings according to the preferred embodiment should be mounted to the pulley in a manner and orientation in which two convexly curved protrusions of the respective cushioning ring partially face the outer and inner link plates, respectively, of a roller chain running over the pulley and are able to come in contact therewith.

The invention is suited for a special form of a bicycle rear derailleur wherein the pulleys are rotatably mounted to the cage by mounting means and an interposed radial bearing, wherein the mounting means are arranged so as to be spaced from the center of rotation of the pulleys and are positioned along a circular mounting opening provided in the cage spaced away from the center of rotation of the pulleys, so as to leave a free space in the center of the pulleys in its mounted state, as described in <CIT>. The relevant teaching of <CIT> is herewith incorporated by reference.

The invention is also suited for common bicycle rear derailleurs, wherein, for instance, the pulleys are rotatably mounted between two lateral plates of the cage on central bearings which are fitted on central bolts which connect two lateral plates of the cage to each other.

The elastically deformable material may be natural or synthetic rubber, polymer or elastomer or mixtures of the foregoing materials.

The above and other features of the invention will become apparent from the following description of preferred embodiments, given by way of non-limiting examples with reference to the accompanying drawings, wherein:.

Conventionally, pulleys of a rear derailleur may be rotatably mounted between two lateral plates of a cage on central bearings which are fitted on central bolts which connect two lateral plates of the cage to each other.

Pulleys as shown and described herein may also be mounted by mounting means (and not by central bolts) and an interposed radial bearing, wherein the mounting means are arranged so as to be spaced from the center of rotation of the pulley. The mounting means are positioned along a circular mounting opening provided in the cage spaced away from the center of rotation of the pulley. Such a bearing, which may be a ball bearing, a roller bearing or a slide bearing, may have a much larger radius than conventional bearings of the pulleys of a rear derailleur. The cage can be a single-plate or a two-plate cage. Such a bearing can be arranged so as to leave a free space in the center of the guide pulley in its mounted state, which provides for a free space which works against the accumulation of dirt because rotating pulley structural arms have been eliminated, and the chain guide is easy to clean. In addition, the free space, if provided at least in the center of the tension pulley, provides for a totally new and impressive look of the derailleur. With respect to this, reference is made to the pertinent teachings of a former patent application of the applicant of the present invention having the title "Improved chain guide for a rear derailleur of a bicycle" filed on <CIT>, the content of which is herewith incorporated by reference.

Figure <NUM> is a schematic view of the rear part of a bicycle having a rear derailleur <NUM> which comprises a tension pulley <NUM> and a guide pulley <NUM> mounted at a cage <NUM>. The pulleys <NUM> and <NUM> may optionally each have a free space in their center. The rest of the derailleur <NUM> is shown only schematically. The cassette is shown also schematically at reference number <NUM>.

Pulleys as shown and described herein may be rotatably mounted between two lateral plates of a cage on central bearings which are fitted on central bolts which connect the two lateral plates of the cage to each other, or rotatably mounted on central bearings which are fitted on a single-plated cage.

Pulleys as shown and described herein may also be rotatably mounted between two lateral plates of a cage by mounting means (and not by central bolts) and an interposed radial bearing, wherein the mounting means are arranged so as to be spaced from the center of rotation of the pulley, as it is the case in <CIT>. Also, in this case the cage may be a single-plated cage, as described in <CIT>.

With reference to <FIG>, an embodiment of a pulley of a rear derailleur for a bicycle is described.

As shown therein, a pulley <NUM>, which is shown as a guide pulley but may also be embodied as a tension pulley, has a plurality of teeth <NUM> adapted to come in contact with link members of a roller chain <NUM> running over the pulley <NUM> (as partially shown in <FIG> and <FIG>).

The pulley <NUM> carries on each of its axial side faces a cushioning ring <NUM> made of an elastically deformable material like natural or synthetic rubber, polymer or elastomer or mixtures thereof.

As is best seen in <FIG>, each cushioning ring <NUM> is supported by and accommodated in an annular channel formed adjacent to each side face to the pulley <NUM> and opening radially outward. In a side view of the pulley <NUM>, the annular channel forms a polygon, wherein the number of corners of the polygon is equal to the number of teeth <NUM> of the pulley <NUM>. The corners of the polygon are angularly offset from the centers of the teeth <NUM> of the pulley <NUM> by the half angular distance between adjacent teeth <NUM> of the pulley <NUM>.

The annular channel is limited radially by a polygonal shoulder <NUM> formed laterally of the pulley <NUM> and is defined axially between the side face of pulley <NUM> and a polygonal radial extension <NUM> of the polygonal shoulder <NUM>. The corners of the polygonal shoulder <NUM> and of the polygonal radial extension <NUM> are advantageously a little bit rounded.

The polygonal shoulder <NUM> and the polygonal radial extension <NUM> each comprises a number of straight portions being equal to the number of teeth <NUM> of the pulley <NUM> and being angularly aligned with a respective tooth <NUM>.

Because each cushioning ring <NUM> is mounted with a certain tension around the corresponding polygonal shoulder <NUM> it also adopts a polygonal form.

As seen best in <FIG>, each cushioning ring <NUM> has a cross section which is called herein generally x-shaped. More specifically, the cross-sectional profile of each cushioning ring <NUM> has the shape of an alphabetic character x whose legs are short with respect to the body of the character and have concave sections between them. The legs as such have preferably convex rounded ends which will be discussed later.

Preferably each cushioning ring <NUM> projects radially from the radial extensions <NUM> by at least approximately <NUM>/<NUM> of a total radial height of the cushioning ring <NUM> or by at least <NUM>/<NUM> of a total radial height of the cushioning ring <NUM>. Advantageously, the compressibility and height of the cushioning ring <NUM> has to be chosen so that in operation the link plates of the roller chain <NUM> may contact the cushioning ring <NUM> but not the radial extensions <NUM>.

As seen best in <FIG>, the rounded ends of the legs of each cushioning ring <NUM> are four circumferentially distributed and convexly curved protrusions <NUM> on the respective cushioning ring <NUM> which are connected contiguously by four circumferentially distributed and concavely curved recesses <NUM> in the respective cushioning ring <NUM>.

Each cushioning ring <NUM> is mounted to the pulley <NUM> in a manner and orientation in which two curved protrusions <NUM> and one concavely curved recess <NUM> partially face the outer and inner link plates, respectively, of a roller chain <NUM> running over the pulley <NUM>. The inner protrusion <NUM> is able to contact and dampen the inner link plates, and the outer protrusion <NUM> is able to contact and dampen the outer link plates.

While the x-shape of the cushioning rings <NUM> is advantageous in that one does not have to pay attention to the orientation in which one places them on the cushioning rings <NUM>, it has to be noted that only the two upper curved protrusions <NUM> and the one upper concavely curved recess <NUM> are essential for the function of the cushioning ring <NUM> according to the broadest aspect of the present invention.

In other words, in the broadest aspect of the invention, each cushioning ring <NUM> comprises, at its side facing the roller chain <NUM>, only one groove extending along its entire perimeter length, which groove, as seen in a cross-sectional view through the cushioning ring <NUM>, is the recess <NUM> flanked by the two protrusions <NUM>, wherein the protrusions <NUM> are adapted and orientated to come in contact with outer and inner link plates, respectively, of the roller chain <NUM> running over the pulley <NUM>. Preferably, a similar additional groove can be provided at the opposite side of the cushioning ring <NUM> facing the polygonal shoulder <NUM>. Further preferably, similar additional grooves can be provided at the lateral faces of the cushioning ring <NUM> facing the polygonal radial extension <NUM> and the pulley <NUM>, respectively.

The number of similar additional grooves may vary between <NUM> and <NUM>, and any combinations of sides are envisaged as preferred alternatives of the invention. The most preferred alternative of the invention includes <NUM> grooves resulting to the above-described x-shape which is advantageous in terms of its insertion, as discussed, and elasticity. In addition, the x-shape is advantageous in terms of manufacturing.

The function of the groove at the side facing the roller chain <NUM> is to dampen the forces produced by chain members running from the slack span of the roller chain <NUM> onto the pulley <NUM> in a smooth and well-defined manner and with fewer losses than cushioning rings having exact annular or rectangular cross sections.

The cushioning rings <NUM> may also have other basic cross sections than shown herein, for example square with three even sides, if each cushioning ring <NUM> comprises, at least on its side facing the roller chain <NUM>, a groove extending along its entire perimeter length, which groove, as seen in a cross-sectional view through the cushioning ring <NUM>, forms a recess <NUM> flanked by two protrusions <NUM>, wherein the protrusions <NUM> are adapted and orientated to come in contact with outer and inner link plates, respectively, of a roller chain <NUM> running over the pulley <NUM>.

The cushioning rings <NUM> may have well known cross sections, for example square or circular.

Essential for the embodiment of <FIG> is that the cushioning rings <NUM> adopt the polygonal form of the polygonal shoulders <NUM>. That is, also each cushioning ring <NUM> comprises a number of straight portions being equal to the number of teeth <NUM> of the pulley <NUM> and being angularly aligned with one respective tooth <NUM>.

Therefore, the embodiment of <FIG> is particularly suited when embodied as a guide pulley of a rear derailleur. Such a rear derailleur would be suited for chains <NUM> of a special type wherein the tops of the link plates are straight-line (flattops) which are known as AXS chains, as mentioned above. In a rear derailleur, the chain <NUM> is running with the straight tops over the guide pulley <NUM>, as seen from <FIG>, and the straight tops are perfectly matching the straight portions of the polygonal cushioning ring <NUM> of the guide pulley <NUM>. Accordingly, the impact of the chain <NUM> on the pulley <NUM> is smooth and silent.

The tension pulley <NUM> of such rear derailleur may be of any known type or may be a similar type as described herein. In operation, the conventional part of the link plates of the AXS chain <NUM> will interact first with the tension pulley <NUM> and subsequently in a reverse orientation over the guide pulley <NUM>, where the straight tops of the link plates of the chain <NUM> will cooperate with the straight portions of the guide pulley <NUM>. Thus, the impact of the chain <NUM> at both pulleys is silent and smooth.

In the embodiment of <FIG>, the pulley <NUM> is of a type having a free space <NUM> in its center, as described in <CIT>. In this case the pulley <NUM> will be mounted by mounting means (not shown) via an interposed roller bearing <NUM> to a single-plated cage of the rear derailleur. However, any conventional guide or tension pulley for a rear derailleur of a bicycle, wherein for instance the pulleys are rotatably mounted between two lateral plates of the cage on central bearings which are fitted on central bolts which connect two lateral plates of the cage to each other are envisaged as to be included in the scope of the present invention, as defined by the appended claims.

The disclosure of the present invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless indicated otherwise herein.

Where technical features mentioned in any claim are followed by reference signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, neither the reference signs nor their absence have any limiting effect on the technical features as described above or on the scope of any claim elements.

Claim 1:
A toothed pulley (<NUM>) for a bicycle rear derailleur (<NUM>), the pulley (<NUM>) carrying on each of its side faces a cushioning ring (<NUM>) made of an elastically deformable material and adapted to come in contact with link plates of a roller chain (<NUM>) running over the pulley (<NUM>), wherein
the pulley (<NUM>) includes an annular channel formed adjacent to each side face to the pulley (<NUM>) and opening radially outward, wherein each cushioning ring (<NUM>) is supported by the annular channel, characterized in that
in a side view of the pulley (<NUM>), the annular channel forms a polygon, wherein the number of corners of the polygon is equal to the number of teeth (<NUM>) of the pulley (<NUM>), and wherein the corners of the polygon are angularly offset from the centers of the teeth (<NUM>) of the pulley (<NUM>) by the half angular distance between adjacent teeth (<NUM>) of the pulley (<NUM>).