DESCRIPTION

Field of the invention

The present invention relates to a bottom bracket shell and a bicycle frame having such bottom bracket shell.

Bicycle frames are formed from a plurality of tubes, made of metal or composite materials, which are welded or otherwise joined together. Particularly, a bicycle frame usually comprises a head tube, which pivotally engages a front fork, a top tube and a down tube which extend from the head tube, a vertical tube (or seat tube) extending between the top tube and the down tube, and two rear forks constrained to the vertical tube. The frame further comprises a case, known as bottom bracket shell, which houses the bottom bracket. The bottom bracket has the purpose of allowing the force applied to the pedals by the rider to be converted into a rotary motion of the driving wheel (usually the rear wheel) of the bicycle. The bottom bracket shell also acts as an element for connection of the seat tube, the down tube and the chainstays of the rear fork (the tubes that form the rear forks).

Discussion of the related art

During the last decades, a growing awareness in environment and health issues has increased commercial interest in bicycles, thereby creating the conditions to enhance research and development efforts in this field. The intended function of each particular bicycle model is being increasingly specialized. Therefore, several bicycle models have been conceived and developed, such as city bikes, mountain bikes, racing bikes, BMX bikes, folding bikes, children's bikes, electric bicycles, and others. In response to such diversification requirement engineers have been considering new frame shapes, the use of new materials and the development of novel technical solutions to address and solve existing problems. These include drive transmission to the driving wheel, which has been traditionally performed by the chain, and has been reconsidered and studied, leading to belt drive solutions. This kind of drive has the advantage of not producing noise when pedaling and shifting, due to the lack of metal parts in mutual sliding contact (belts are usually made of polymeric materials). This arrangement, in addition to a precise form-fit in the belt-and-pulley system, leads to high drive performance. Furthermore, and especially, a belt drive system has virtually no maintenance requirements, as compared with chain drive systems.

The drawbacks of belt drive systems substantially consist in the nature of the belt itself. Particularly, an important drawback as compared with chain drives consists in that the belt is a closed-loop element which cannot be opened, whereas the chain may be opened at any link thereof. Since the belt (like the chain) must extend between the exterior of the rear fork (to engage the crankset) and the interior of the rear fork (to engage the pinion on the drive wheel), and since the rear fork forms a closed loop (on the seat tube and the bottom bracket shell), the use of a drive belt involves the problem of inserting the belt into the operating position.

This problem was solved in the prior art by allowing the rear fork to be opened at one of its tubes to allow insertion of the belt. Particularly, the seatstay (tube) which starts from the chainstay of the rear form and is connected to the seat tube was made out of two halves having respective mutually facing free ends. The free ends have connecting members, allowing to rigidly join the two halves together once the belt has been inserted. These connecting members include, for example, two overlapping appendices, which are joined together by bolts. Alternatively, the rear fork can be opened at the junction between the chainstay and the seatstay. Here, the two ends of the stays are equipped with connectors that are designed to be fastened together by bolts.

While the prior art arrangements as briefly discussed above are effective in allowing insertion of the belt into the operating position, they are still affected by the drawback of introducing a weakened and flexible portion in the rear fork, at the opening area thereof. Such flexibility greatly affects the performances of the bicycle, especially when the bicycle is a high- performance bicycle. Furthermore, the rear fork is exposed to high mechanical stresses, as it is required to transfer the driving torque of the rear wheel to the entire frame and to absorb the shocks caused by ruggedness of the road. Therefore, the fork opening area and the corresponding closing members are exposed to heavy loads. These loads are applied to small-section areas (the stays of the rear fork have diameters ranging from 15 to 22 mm and wall thicknesses of the order of one millimeter), involving apparent structural failure risks.

Also, the above mentioned flexible area is usually found on one side of the rear fork

(usually the side that faces the pinion), which causes an asymmetric response of the rear fork. This will result in a generally poor behavior of the whole frame.

Also, the prior art is known to include the contents of documents EP 1 980 480 Al, DE 10 2014 003625 Al, US 2008/048410 Al, US 547 990, US 5 482 306 A, US 5 967 537 A and JP S54 23457 U. Such contents will be briefly discussed herein.

As used in the present description and in the accompanying claims, the term "tube" is intended to designate a structural member of the frame, having an elongate shape and any section (e.g. a circular or elliptical section) and formed of any material (e.g. aluminum, steel or composite materials).

As used in the present description and in the accompanying claims, the term

"constrained", referring to a tube, is intended to relate to a rigid, stable and inseparable coupling between the relevant tube and the element constrained thereto. Such coupling may be obtained by welding, bonding or appropriate junction elements, such as collars or the like, according to the material that constitutes the tube. In other words, any connection that can be disassembled will not fall within the definition of "constrained" as used in the present application.

EP 1 980 480 Al discloses a bottom bracket shell comprising first and second halves. The first half is constrained to the first tubes of both rear forks, and the second half is locked to the first half once the pedals have been inserted.

The document DE 10 2014 003625 Al discloses a bicycle whose rear fork is hinged to the rest of the frame. Such frame is equipped with a shock absorber for the rear wheel. Here, the first tubes have mutually connected end portions, closed between the two halves of the bottom bracket shell. As a result, pedals are inserted into a housing defined between the end portions of the first tubes of the rear forks.

US 2008/048410 Al also shows a bicycle frame articulated to allow the installation of a shock absorber between the forks of the rear wheel and the seat post. The hinge between the fork and the tubes of the frame is distinct from the bottom bracket shell. A junction element acts as a connection between the movable fork, the shock absorber and the tubes. The junction element is defined by two halves. In all the illustrated embodiments, the halves are symmetric with respect to the longitudinal plane of the frame, and are designed to be welded together once they have been mounted to the tubes.

US 547 990 A discloses a connection devices for tubes of a bicycle frame. The purpose of this device is to lock the tubes in position during assembly. It shall be noted that the device is permanently locked to the tubes by soldering, and thus becomes an integrated and inseparable part of the frame.

US 5 482 306 A and US 5 967 537 A disclose a bicycle and a "chainless" drive respectively. Such drive is obtained by introducing a rotating shaft into the first tube of the right fork. The bottom bracket shell is defined by a pair of halves, each designed to be connected to a respective first tube of the rear forks. This type of drive does not allow inseparable connection between the right half and the first tube of the right rear fork.

JP S54 23457 U discloses a bottom bracket shell comprising first and second halves. Particularly, the first half is fixed to the first tubes of both rear forks and to the seat tube, and the second half, connected to the transverse tube, is locked to the first half.

SUMMARY OF THE INVENTION

In this context, the technical purpose of the present invention is to provide a bottom bracket shell and a bicycle frame having such bottom bracket shell, that can obviate the above mentioned pri or art drawb acks .

Particularly, the present invention has the object of providing a bottom bracket shell and a bicycle frame having such bottom bracket shell that can allow insertion of the drive belt into its operating position.

A further object of the present invention is to provide a bottom bracket shell and a bicycle frame having such bottom bracket shell that will not affect the structural rigidity of the rear fork of the frame.

The aforementioned technical purpose and objects are substantially fulfilled by a bottom bracket shell and a bicycle frame having such bottom bracket shell, that comprise the technical features as disclosed in one or more of the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will result more clearly from the illustrative, non-limiting description of a preferred, non-exclusive embodiment of a bottom bracket shell and a bicycle frame having such bottom bracket shell as shown in the annexed drawings, in which:

- Figure 1 schematically shows a frame of the present invention;

- Figure 2 shows a detail of the frame of Figure 1;

- Figure 3 shows a bottom bracket shell of the present invention;

- Figures 4 and 5 show certain details of the bottom bracket shell of Figure 3; and

- Figure 6 shows further details of the bottom bracket shell of Figure 3.

DETAILED DESCRIPTION

A bicycle frame of the present invention has been generally designated by numeral 1 in Figure 1.

The frame 1 comprises a head tube 2 which pivotally engages a front fork (not shown), a top tube 3 and a down tube 4 which extend from the head tube 2. The frame further comprises a vertical tube 5 (or seat tube) extending between the top tube 3 and the down tube 4, and two rear forks 6', 6" ( one of which is only shown in Figure 1) constrained to the vertical tube 5. Each of the rear forks 6', 6", i.e. the right rear fork 6' and the left rear fork 6", comprises a substantially horizontal first tube 6a', 6a", and a preferably oblique second tube 6b. Each second tube 6b is constrained to the vertical tube at a first end, and is constrained to the first tube 6a', 6a" of the rear fork 6', 6" at a second end. The frame further comprises a bottom bracket shell 7 which houses a bottom bracket. The bottom bracket has the purpose of allowing the force applied to the pedals by the rider to be converted into a rotary motion of the driving wheel (usually the rear wheel) of the bicycle.

The bottom bracket shell 7 comprises a first half 8 and a second half 9, which are physically separated from each other, wherein the first half 8 is constrained to the first tube 6a' of the right rear fork 6' and the second half is constrained to the first tube of the left rear fork, as shown in Figure 2. Preferably, the second half of the bottom bracket shell 7 is also constrained to the vertical tube 5 of the frame 1. By this arrangement, a closed-loop drive belt may be inserted into the bicycle frame (namely into the rear fork), by passing between the first half and the second half of the bottom bracket shell 7, prior to mutual rigid connection up of the two halves.

The first half 8 and the second half 9 of the bottom bracket shell 7 are complementary to each other, to form a right prism-shaped body, which is cylindrical in the preferred embodiment of the invention. Such cylindrical body, i.e. the bottom bracket shell, has an inner through opening which extends between opposite, preferably flat end surfaces to receive a bottom bracket whose axis of rotation is substantially parallel to the axis of extension X of the cylindrical body. The first half 8 and the second half 9 of the bottom bracket shell have respective mutually facing mating surfaces 10, 11 (as shown in Figure 3). The mating surface 10, 11 are specially shaped to define a finite number of effective coupling conditions between the first 8 and second 9 halves. In the preferred embodiment of the invention, there is only one effective coupling condition between the first 8 and seconded 9 halves. In other words, the mating surfaces 10, 11 have such a shape that the first and second halves 8, 9 can only mate in one mutual orientation, i.e. the one that imparts a cylindrical shape to the bottom bracket shell 7. Constraint members 12, better explained hereinafter, stably but separably (i.e. removably) retain the first half 8 against the second half 9. It shall be noted that the constraint members 12 con be only actuated when the mating surfaces 10, 11 are in an effective mating condition.

As best shown in Figures 4 and 5, each mating surface 10, 11 extends in a closed loop at one respective end of the first and second halves 8, 9. Each of the mating surfaces 10, 11 comprises portions contained in planes that are not perpendicular to the axis X of extension of the cylindrical body 7 defined by the two halves 8, 9 when coupled together. Each mating surface 10.11 is not contained in a single plane. Preferably, each mating surface comprises a lower portion 10a, 11a and an upper portion 10b, l ib, which extend at different levels, i.e. are situated at difference distances from a plane perpendicular to the axis of extension X of the cylindrical body. The upper and lower portions are connected by ramp portions 10a, 11a which start from the lower portion and reach the upper portion. It shall be noted that the ramp portions 10c, 11c act as shoulders (see Figure 3), when the two halves 8, 9 contact each other, thereby inhibiting the rotation of one half relative to the other about the axis X, regardless of whether the constraint members 12 are actuated or not.

The above mentioned constraint members 12 are operable between the first 8 and second 9 halves to rigidly join them and possibly separate them when needed. Thus, as mentioned above, when the constraint members 12 are not actuated, the drive belt can be inserted into its position within the rear fork. As the constraint members 12 are actuated with the drive belt in the operating position, the bottom bracket shell 7 becomes a single rigid body, which is ready to accommodate the bottom bracket. It shall be noted that, when the constraint members 12 are not actuated, at least one rear fork, and particularly the fork that faces the pinion of the rear wheel, is "open", which means that it does not define a closed-loop structure. Conversely, when the constraint members 12 are actuated, the rear forks are "closed", which means that they define respective closed-loop structures (like in a common bicycle). It shall be also noted that the insertion of the drive belt into its operating position does not require any tube of the rear forks to be broken, opened or divided, whereby all the structural properties of the forks are unaffected.

In the preferred embodiment of the invention, the constraint members 12 are operable on a casing of the cylindrical body, i.e. on the thickness of the cylindrical body that surrounds the inner cavity that is designed to receive the bottom bracket. Preferably, the constraint members 12 comprise a plurality of bolts 12 (one of which is shown in Figure 6), operable in threaded blind holes 14 of the casing. These blind holes 14 are formed both in the first half 8 and in the second half 9 (in the respective casings) and extend in a direction substantially parallel to the axis of extension X of the cylindrical body defined by the bottom bracket shell. Thus, the action of the constraint members 12, i.e. the compression of the first half on the second half (exerted by the bolts) is directed substantially perpendicular to the direction of application of the loads that are typically applied to the bottom bracket shell (i.e. the stresses transferred by the tubes that are constrained thereto and the stresses transferred by the bottom brackets).

The bottom bracket shell 7 comprises, as mentioned above, an inner cavity for receiving the bottom bracket. This cavity comprises at least one threaded portion 15 for engagingly receiving a threaded portion of a bottom bracket. This bottom bracket 15 comprises a first part 15a formed on the first half 8 and a second part 15b formed on the second half (as shown in Figure 6). It shall be noted that the two parts 15a, 15b of the threaded portion 15 are complementary to each other to form threads adapted to receive the threaded part of a bottom bracket. Thus, since the bottom bracket engages both parts 15a, 15b of the threaded portion 15, the bottom bracket assists in holding the first and second halves 8, 9 of the bottom bracket shell 7 together. Preferably, there are two threaded portions 15, at opposite ends of the inner cavity of the bottom bracket shell 7.

The bottom bracket shell and the frame having such bottom bracket shell of the invention are susceptible to many variants, such as the provision of screws instead of bolts as constraint members, without departure from the scope of the invention as described above and claimed below.