Patent Description:
Hereinafter, the spatial indications, such as in particular those of radial, axial and circumferential direction, will be given with reference to the rotation axis of the rear wheel of the bicycle, which coincides with the axis of the cogset, of the sprocket-carrying body, of the hub of the wheel and in general of all of the elements that rotate with the wheel. Moreover, the axial direction will be indicated as towards the outside if directed away from the longitudinal mid-plane of the bicycle or away from the hub of the wheel, and vice-versa as towards the inside if directed towards such a mid-plane or towards the hub. Moreover, in the radial direction, an orientation away from the rotation axis will be indicated as peripheral and vice-versa an orientation towards the rotation axis will be indicated as inner.

In order to mount a cogset on the hub of a bicycle rear wheel a so-called sprocket-carrying body is normally used, which on one side is made to rotate as a unit with the sprockets through shape coupling, and on the other side is made to rotate as a unit - but in a unidirectional manner - with the hub through a set of ratchets or similar, commonly called free wheel. In this way, the transmission chain engaged with the various sprockets is capable of transmitting a torque to the hub in the advancing direction of the bicycle.

The sprocket-carrying body essentially consists of a tubular body, which is mechanically coupled at the radially peripheral surface thereof with central mounting openings made in the sprockets. The radially peripheral surface of the sprocket-carrying body is shaped with substantially axial ribs and grooves, alternating in the circumferential direction, adapted for allowing the aforementioned shape coupling. For this purpose, the central mounting openings of the sprockets are provided with radially inner extensions or projections, i.e. directed towards the rotation axis, which couple with the grooves present on the sprocket-carrying body.

The sprockets are thus mounted axially on the sprocket-carrying body in succession, from the sprocket having the largest diameter, so that when the sprocket-carrying body is mounted on the hub of the wheel of the bicycle the sprockets having the largest diameter are located towards the inside, i.e. close to the rear wheel, whereas the sprockets having the smallest diameter are located towards the outside.

In most modern bicycle gearshifts, particularly for bicycles intended for competition, there is a well-known trend to increase the number of sprockets. When a cogset reaches <NUM>, <NUM> or even more sprockets, it may be possible to do without the front gearshift; this simplifies and lightens the bicycle, which is undoubtedly appreciated by the cyclist provided that it is not accompanied by a penalization in the availability of gear ratios.

In order to allow this result, it is necessary to have a small sprocket with a very low number of teeth, for example <NUM> or <NUM>, in the cogset. The reduced number of teeth, however, is clearly accompanied by a reduced diameter, which can end up being too small to allow it to be mounted on normal sprocket-carrying bodies.

Cogsets have thus become appreciated in which the smallest sprockets are made fixedly connected to one another to form a monolithic set (also called doublet, triplet or quadruplet, precisely because it groups together two, three or four sprockets), and the central opening for mounting on the sprocket-carrying body extends axially only at the largest sprockets of the set; the smallest sprockets extend more towards the rotation axis, but do not engage directly with the sprocket-carrying body, since it is ensured that they are set in motion by the fact that they are fixedly connected to the largest sprockets of the set. In this way, the smallest sprocket of the set can have <NUM> teeth or even less; on the other hand, the largest sprocket of the set must have at least <NUM> teeth, to be able to engage with the sprocket-carrying body.

There are thus constraints that reflect on the real possibilities of manufacturing. For example, with a doublet (monolithic set of two sprockets) it is necessary to have a first sprocket with <NUM> teeth (and not <NUM> or less), or accept a difference in teeth between the first and the second sprocket equal to <NUM> or more; however, this condition is not liked by cyclists who are normally accustomed to differences of a single tooth between the smallest adjacent sprockets.

In some cases, in order to try to manage the constraints imposed by the particular conditions, shape couplings with projections or teeth extending in the axial direction, between the largest sprocket of the monolithic set and the sprocket-carrying body, or couplings through threaded portions variously engaged between the monolithic set and the sprocket-carrying body are used. These couplings, however, do not ensure the same solidity of the shape coupling with grooved profiles.

<CIT> discloses a cogset according to the preamble of claim <NUM> in which the three smallest sprockets are made in a single piece, mounted on the sprocket carrying body by a threaded coupling.

There is thus a need to be able to have greater flexibility in the selection of the number of teeth of the smallest sprockets of the cogset.

Consequently, the present invention is a cogset according to claim <NUM>; in a second aspect thereof, the invention relates to a sub-assembly according to claim <NUM>. Preferred features of the cogset and of the sub-assembly are given in the dependent claims.

More in particular, according to the first aspect of the invention, a cogset comprises a plurality of <NUM> to <NUM> axially adjacent sprockets between a first sprocket having minimum number of teeth and a last sprocket having maximum number of teeth, wherein the first n sprockets with <NUM> ≥ n ≥ <NUM> are fixedly connected to one another so as to form a monolithic set, and in which the monolithic set is adapted for being directly in shape engagement on a coupling profile formed on the radially peripheral surface of the sprocket-carrying body through a coupling profile formed on the radially inner surface of at least the largest sprocket of the monolithic set, said coupling profile comprising - at the largest sprocket of the monolithic set - projections facing radially inwards, to constitute an inner shape coupling profile formed on the radially inner surface of the largest sprocket (26a; 126a, 126b), wherein the coupling profile formed by the projections (<NUM>) has a shape corresponding to the shape of a coupling profile formed by grooves (<NUM>) on the radially peripheral surface of the sprocket-carrying body <NUM>, wherein the monolithic set (<NUM>; <NUM>) is apt to be mounted partially slotted onto the sprocket-carrying body (<NUM>), with the projections (<NUM>) engaging in the grooves (<NUM>), whereas the smallest sprockets (26a; 126a, 126b) of the monolithic set (<NUM>; <NUM>) remain axially canti-levered.

Having at least three sprockets grouped in the monolithic set makes it possible to have a sprocket with <NUM> teeth suitable for direct engagement on the sprocket-carrying body and two or more smaller sprockets canti-levered; therefore, the first sprocket may have as few as <NUM> teeth (or less), without it being necessary to accept a difference greater than <NUM> between the number of teeth of the adjacent smallest sprockets. Moreover, the fact that a direct shape coupling is provided between the largest sprocket of the monolithic set and the sprocket-carrying body, and the fact that this direct coupling is made between the radially peripheral surface of the sprocket-carrying body and the radially inner surface of the largest sprocket (or of the largest sprockets) of the monolithic set, makes it possible to have very high solidity and rigidity of coupling, so as to ensure the maximum precision of actuation of the gearshift that uses the sub-assembly, comparable to the precision of a gearshift in which the sprockets of the cogset are all individually and directly mounted so as to rotate as a unit on the sprocket-carrying body.

Preferably, the first sprocket has <NUM>, <NUM> or even <NUM> teeth. It is thus possible to achieve very long gear ratios of the gearshift.

Preferably, the number n of sprockets of the monolithic set is equal to <NUM>, <NUM>, <NUM> or even <NUM>. The greater this number n, the greater the flexibility in the selection of the number of teeth of each of them and thus of the gear ratios.

In the case in which there are <NUM> sprockets of the monolithic set, the coupling profile between the monolithic set and the sprocket-carrying body is preferably formed on the radially inner surface of the two largest sprockets of the monolithic set.

In the case in which there are <NUM> sprockets of the monolithic set, the coupling profile between the monolithic set and the sprocket-carrying body is preferably formed on the radially inner surface of the three largest sprockets of the monolithic set.

These features make it possible to keep the solidity and the rigidity of the coupling between the sprockets of the monolithic set and the sprocket-carrying body high, even when the number n of sprockets of the monolithic set is relatively high.

The cogset comprises <NUM>, <NUM> or even <NUM> sprockets. The invention is indeed particularly interesting when the number of sprockets is high, greater than <NUM>.

According to the second aspect of the invention, a sub-assembly comprises a sprocket-carrying body and a cogset mounted coaxially on the sprocket-carrying body, wherein the cogset comprises a plurality of axially adjacent sprockets between a first sprocket having minimum number of teeth and a last sprocket having maximum number of teeth, wherein the first n sprockets with <NUM> ≥ n ≥ <NUM> are fixedly connected to one another so as to form a monolithic set, and wherein the monolithic set is directly in shape engagement on a coupling profile formed on the radially peripheral surface of the sprocket-carrying body through a coupling profile formed on the radially inner surface of at least the largest sprocket of the monolithic set.

Preferably, the monolithic set comprises an axial abutment surface in abutting engagement against a corresponding outer axial abutment surface of the sprocket-carrying body. This allows a precise and stable axial positioning of the monolithic set with respect to the sprocket-carrying body.

Preferably, the sprocket-carrying body comprises a radially inner threaded portion.

Preferably, the sub-assembly further comprises a ring nut with a threaded portion screwed into the radially inner threaded portion of the sprocket-carrying body.

The attachment through the ring nut ensures a stable and precise positioning in the axial direction of the entire cogset on the sprocket-carrying body.

Further features and advantages of the invention will become clearer from the following description of a preferred embodiment thereof, made with reference to the attached drawings. In such drawings:.

<FIG> represents a hub <NUM> of a hub assembly <NUM> of a bicycle rear wheel (not shown), mounted coaxially on a pin <NUM>, by means of bearings <NUM>; the hub <NUM> is thus free to rotate on the pin <NUM>, whereas the latter is intended to be mounted fixed on the frame of the bicycle.

The hub <NUM> is coupled with a sprocket-carrying body <NUM>, through a free wheel mechanism (not highlighted) that ensures that the hub <NUM> is set in rotation by the sprocket-carrying body <NUM> only in the direction that determines forward motion of the bicycle, not in the opposite direction. The sprocket-carrying body <NUM> has an approximately tubular shape and is mounted free on the pin <NUM>, by means of bearings <NUM>. The sprocket-carrying body <NUM> is provided on its radially peripheral surface with a coupling profile formed by grooves <NUM> arranged in the axial direction. Moreover, the sprocket-carrying body <NUM> is provided close to its axially inner end with an end stop <NUM>, in the form of teeth projecting in the radial direction from the sprocket-carrying body <NUM>; alternatively instead of the teeth, as end stop <NUM> it is possible to provide a flange, extending along the entire circumference of the sprocket-carrying body <NUM>.

The sprocket-carrying body <NUM> has a substantially annular axial abutment surface <NUM> at the outer axial end thereof.

A cogset <NUM> is mounted on the sprocket-carrying body <NUM>, with formation of a sub-assembly <NUM>. The shown cogset <NUM> comprises <NUM> sprockets organized from the largest to the smallest as follows: the three largest sprockets 21a, 21b, 21c are made fixedly connected to one another to form a monolithic set (or triplet) <NUM>; the next three sprockets 22a, 22b, 22c are made fixedly connected to one another to form a monolithic set (or triplet) <NUM>; the next three sprockets <NUM>, <NUM>, <NUM> are independent from one another; the three smallest sprockets 26a, 26b, 26c are made fixedly connected to one another to form a monolithic set (or triplet) <NUM>. These elements are mounted peripherally on the sprocket-carrying body <NUM>, with the monolithic set <NUM> rested axially at the end stop <NUM>, the monolithic set <NUM> rested axially at the monolithic set <NUM>, the sprocket <NUM> rested axially at the monolithic set <NUM>, the sprocket <NUM> rested axially at the sprocket <NUM>, the sprocket <NUM> rested axially at the sprocket <NUM>, the monolithic set <NUM> rested axially at the sprocket <NUM>.

The monolithic sets <NUM>, <NUM> and the sprockets <NUM>-<NUM> are slotted onto the sprocket-carrying body <NUM>, constrained in rotation to the sprocket-carrying body <NUM> but substantially free in the axial direction; the constraint in rotation is ensured in a per se conventional manner by the grooves <NUM> that engage with corresponding projections (not visible in the figures) on the radially inner surface of the monolithic sets <NUM>, <NUM> and of the sprockets <NUM>-<NUM>.

In the sub-assembly <NUM> formed by the sprocket-carrying body <NUM> and the cogset <NUM>, as stated, <NUM> sprockets are mounted, single or grouped in monolithic sets. In particular, there is a very small sprocket, the sprocket 26c, which has a number of teeth so low as not to be able to be mounted on the sprocket-carrying body <NUM> without the provision of having grouped it in the monolithic set <NUM>. Indeed, if this small sprocket were single, it would be too small to be able to be slotted on the sprocket-carrying body <NUM>; the monolithic set <NUM>, on the other hand, can have an inner axial portion at the sprocket 26a (which has <NUM> teeth) of dimensions such as to be able to engage on the sprocket-carrying body <NUM>.

The monolithic set <NUM>, visible particularly in <FIG>, comprises - at the largest sprocket 26a - a series of projections <NUM> facing radially inwards, which as a whole constitute an inner shape coupling profile formed on the radially inner surface of the sprocket 26a. This coupling profile formed by the projections <NUM> has a shape corresponding to that of the coupling profile formed by the grooves <NUM> on the radially peripheral surface of the sprocket-carrying body <NUM>. In mounting, the monolithic set <NUM> is thus partially slotted onto the sprocket-carrying body <NUM>, with the projections <NUM> that engage in the grooves <NUM>, whereas the smallest sprockets 26b and 26c of the monolithic set <NUM> remain axially canti-levered. This provision, made on the radially peripheral surface of the sprocket-carrying body <NUM>, ensures that the entire monolithic set <NUM> (and therefore all of its sprockets 26a, 26b and 26c) is made to rotate as a unit with the sprocket-carrying body <NUM> in a stable and secure manner; any uncertainty of coupling (i.e. any possibility of angular micro-displacements of the monolithic set <NUM> with respect to the sprocket-carrying body <NUM>), which would make the operation of a gearshift using the sub-assembly <NUM> imprecise, is thus ruled out.

The monolithic set <NUM> has a substantially annular axial abutment surface <NUM>, at the inner shape coupling profile formed by the projections <NUM>. The abutment surface <NUM> goes into abutting engagement against the corresponding axial abutment surface <NUM> of the sprocket-carrying body, thus acting as reference for the axial positioning of the monolithic set <NUM>, preventing the axial sliding thereof.

Towards the inside in the axial direction (i.e. towards the hub <NUM>), the entire cogset <NUM> (i.e. the monolithic sets <NUM>, <NUM> and <NUM> and the sprockets <NUM>-<NUM>) is held by the end stop <NUM>; towards the outside in the axial direction, the cogset <NUM> is held by a ring nut <NUM>, inserted on the pin <NUM> and screwed to the sprocket-carrying body <NUM>, by means of an outer threaded portion <NUM> of the ring nut <NUM> and a radially inner threaded portion <NUM> of the sprocket-carrying body <NUM>. The ring nut <NUM> has a flange <NUM> that goes into abutment axially against the outer face of the monolithic set <NUM>. The clamping of the ring nut <NUM>, with the axial pressure on the cogset <NUM> exerted by the flange <NUM> and by the end stop <NUM>, ensures that the entire cogset <NUM> is locked on the sprocket-carrying body <NUM>.

In use, the coupling of the monolithic set <NUM> with the sprocket-carrying body <NUM> is particularly solid, thanks to the engagement of the projections <NUM> in the grooves <NUM>, and thus ensures high precision of actuation.

The monolithic set <NUM> shown in <FIG>, as stated, comprises the three smallest sprockets 26a, 26b and 26c of the cogset <NUM>. According to the invention, however, the number of sprockets of the monolithic set can also be higher, up to <NUM>. <FIG>, for example, show a monolithic set <NUM> (quadruplet) that groups together the four smallest sprockets 126a, 126b, 126c and 126d, having <NUM>, <NUM>, <NUM> and <NUM> teeth respectively.

Claim 1:
Cogset for a bicycle rear wheel, adapted for being mounted coaxially on a sprocket-carrying body (<NUM>), comprising a total of <NUM>, <NUM> or <NUM> axially adjacent sprockets (21a, 21b, 21c, 22a, 22b, 22c, <NUM>, <NUM>, <NUM>, 26a, 26b, 26c; 126a, 126b, 126c, 126d) arranged from a first sprocket (26c; 126d) having minimum number of teeth to a last sprocket (21a) having maximum number of teeth, wherein the first n sprockets (26c, 26b, 26a; 126d, 126c, 126b, 126a) with <NUM> ≥ n ≥ <NUM> are fixedly connected to one another so as to form a monolithic set (<NUM>; <NUM>), and wherein the monolithic set (<NUM>; <NUM>) is adapted for being directly in shape engagement on a coupling profile (<NUM>) formed on the radially peripheral surface of the sprocket-carrying body (<NUM>) through a coupling profile (<NUM>; <NUM>) formed on the radially inner surface of at least the largest sprocket (26a; 126a, 126b) of the monolithic set (<NUM>), whereas the smallest sprockets (26b, 26c; 126c, 126d) of the monolithic set (<NUM>; <NUM>) remain axially canti-levered, said coupling profile comprising - at the largest sprocket (26a; 126a, 126b) of the monolithic set (<NUM>; <NUM>) - projections (<NUM>) facing radially inwards, to constitute an inner shape coupling profile formed on the radially inner surface of the largest sprocket (26a; 126a, 126b), wherein the coupling profile formed by the projections (<NUM>) has a shape corresponding to the shape of a coupling profile formed by grooves (<NUM>) on the radially peripheral surface of the sprocket-carrying body (<NUM>), characterized in that the monolithic set (<NUM>; <NUM>) is apt to be mounted partially slotted onto the sprocket-carrying body (<NUM>), with the projections (<NUM>) engaging in the grooves (<NUM>).