Technical field

The present invention relates to a bicycle frame made of an anisotropic material, in particular wood.

State of the art

Bicycle frames must have high torsional stiffness and high strength, but at the same time be very light.

The design specifications of bicycle frames are aimed at optimising the efficiency of the vehicle and the cyclist, while at the same time ensuring adequate comfort for the cyclist to reduce muscular and joint stress.

Cyclist comfort is influenced by the ability of the frame to absorb road bumps without transmitting them to the cyclist. In general, bicycles intended to provide a high level of comfort have mechanical components designed to perform these functions, such as springs and shock absorbers, but these components add weight and complexity to the bicycle frame. Therefore, in the case of high-performance bicycles, where comfort characteristics are of secondary importance compared to the characteristics of torsional stiffness and lightness of the frame, such mechanical components are typically omitted to minimise the overall weight of the bicycle.

Nowadays, bicycle frames, particularly high-performance ones, are predominantly made of carbon fibre, or rather a composite material comprising an epoxy resin matrix reinforced with carbon fibres. This material, in fact, provides a good compromise between torsional stiffness and weight, although it reduces the cyclist's comfort. Alternatively, frames can be made of metallic material such as aluminium or steel. Aluminium frames have good characteristics of lightness and torsional stiffness, which characteristics are however lower than those of carbon fibre frames. Steel frames are preferable for rider comfort, but they have lower torsional stiffness than aluminium or carbon fibre frames.

The use of wooden bicycle frames is also known. A wooden bicycle frame offers a number of advantages over a metal or carbon fibre frame, in that it naturally absorbs shocks and vibrations and is able to withstand the stresses and vibrations typical of any bicycle. However, making a high-performance wooden bicycle frame involves high costs, time and production difficulties, to the extent that the production of this type of frame is difficult to industrialise.

Summary of the invention

The object of the present invention is, in general, to overcome the drawbacks of the prior art.

More specifically, the object of the present invention is to provide a bicycle frame made of an anisotropic material, in particular wood, that offers high performance, but at the same time can be manufactured industrially.

These and other objects are fully achieved according to the present invention by a bicycle frame as defined in the enclosed independent claim 1 , as well as, according to a further aspect of the present invention, by a method for making a bicycle frame as defined in the enclosed independent claim 7.

Further advantageous aspects of the invention are defined in the dependent claims, whose subject-matter is to be regarded as forming an integral part of the present description.

In summary, the invention is based on the idea of making the rear triangle of the frame by joining two monocoque elements, one forming the two seat stays (seat stays) and the other forming the two chain stays (chain stays) of the rear triangle, wherein each of these two monocoque elements is obtained by machining a respective block formed by several layers of anisotropic material (where the expression "several layers of anisotropic material" means both the case where all the layers are formed by the same anisotropic material and the case where the layers are formed by two or more different anisotropic materials) assembled to each other by gluing.

The rear triangle is a crucial part of the structure of a bicycle frame, as it is made of elements with a reduced section that must nevertheless be robust and stable. The solution proposed herein makes it possible to increase the reliability and robustness of the rear triangle by eliminating most of the imponderables linked to the unevenness and defects inevitably present in solid wood blocks. In fact, starting from single layers of material, in particular wood, for the construction of the blocks from which the monocoque elements of the rear triangle are obtained, it is possible to identify immediately, and with a control system that can be implemented in an industrial manufacturing line, the nonconforming layers of material that must therefore be eliminated from the production cycle. This possibility of inspection would not be feasible on blocks with a cross-sectional area equal to that of the final component to be manufactured, as in this case any defects would remain hidden within the block and could only be detected by more complex, timeconsuming and costly inspection methods, such as radiographic and ultrasonic inspections. In addition, in case of detection of a non-conforming block, the entire block would have to be discarded, which would increase the costs related to scraps.

The solution proposed herein therefore makes it possible to optimise the construction of the rear triangle of a bicycle frame made of anisotropic material, in particular wood, thus making the entire frame manufacturing cycle industrialisable.

Brief description of the drawings

The features and advantages of the present invention will be evident from the following detailed description, given by way of non-limiting example with reference to the accompanying drawings, wherein:

- Figure 1 is a perspective view of a bicycle frame according to the present invention, in the assembled condition;

- Figure 2 is a perspective view of the frame of Figure 1 , wherein the front triangle is separated from the rear triangle;

- Figure 3 is a perspective view of the two monocoque elements that make up the rear triangle of the frame of Figure 1 ;

- Figure 4 is a view of the rear triangle of Figure 1 , showing in detail the material layers of the two monocoque elements of the rear triangle;

- Figure 5 shows a cross-section of one of the two chain stays of the rear triangle of Figure 4 (section A-A) and a cross-section of one of the two seat stays of the rear triangle of Figure 4 (section B-B);

- Figure 6 is a perspective view similar to Figure 2, wherein the front triangle of the frame is shown disassembled into its various components; and

- Figure 7 shows a wooden plank used for the horizontal element of the front triangle of the frame of Figure 1 .

Detailed description

Referring first to Figures 1 and 2, a bicycle frame according to an embodiment of the present invention is generally indicated 1 and basically comprises a front triangle 7 and a rear triangle 2. Although the accompanying drawings show a frame having a geometry suitable for a racing bike, a mountain bike or a gravel bike, the present invention is applicable to frames for any type of bicycle, including, for example, so-called cargo bikes.

The rear triangle 2 comprises an oblique monocoque element 3 and a horizontal monocoque element 4, which are shown separated from each other in Figure 3. The oblique monocoque element 3 comprises a pair of seat stays 3a and 3b connected to each other at the top via a connecting portion 3c. Likewise, the horizontal monocoque element 4 comprises a pair of chain stays 4a and 4b connected to each other at their front ends via a connecting portion 4c.

The oblique monocoque element 3 and the horizontal monocoque element 4 are joined to each other at the lower ends (denoted 3d) of the seat stays 3a and 3b of the former and at the rear ends (denoted 4d) of the chain stays 4a and 4b. The joining of the two monocoque elements 3 and 4 at the ends 3d and 4d is preferably obtained by gluing using a thermosetting polymer, but in general any other known joining method that is suitable for the purpose can be used.

According to the embodiment proposed herein, the oblique monocoque element 3 forms a fork-shaped portion which protrudes upwardly with respect to the connecting portion 3c and comprises a pair of prongs 3e which extend substantially parallel to each other to form each a kind of extension of the respective seat stay 3a, 3b. This fork-shaped portion serves as a connecting portion for the connection between the oblique monocoque element 3 and the front triangle 7 and, due to its conformation, allows for a large contact surface with the front triangle 7 on which to deposit the adhesive means for joining the oblique monocoque element 3 to the front triangle 7. Likewise, the horizontal monocoque element 4 forms a fork-shaped portion which protrudes frontward with respect to the connecting portion 4c and comprises a pair of prongs 4e which extend substantially parallel to each other to form each a kind of extension of the respective chain stays 4a, 4b. Also in this case, the fork-shaped portion serves as a connecting portion for connection between the horizontal monocoque element 4 and the front triangle 7 and, due to its conformation, allows for a large contact surface with the front triangle 7 on which to deposit the adhesive means for joining the horizontal monocoque element 4 to the front triangle 7.

The rear triangle 2 is made of anisotropic material, in particular wood. More specifically, with reference to Figure 4, both the oblique monocoque element 3 and the horizontal monocoque element 4 of the rear triangle 2 are formed by a plurality of layers of anisotropic material joined to each other by gluing, in particular with the use of a thermosetting polymer, for example an epoxy resin, as gluing means.

Furthermore, in each of the monocoque elements 3 and 4 the different layers may be made of different anisotropic materials, so that, for example, each layer may be made of a material different from that of the adjacent layer.

For example, in the case where wood is used as an anisotropic material, woods of different nature and/or quality may be used for the various layers. Furthermore, as shown in the cross-sections A-A and B-B in Figure 5 (i.e., in cross-sections through planes perpendicular to the direction of longitudinal extension of each stay), relating to one of the chain stays 4a, 4b and one of the seat stays 3a, 3b, respectively, preferably each pair of contiguous layers has an opposing orientation of the wood rings, particularly in the case where these layers are made from the same wood, so as to achieve a better balance of the stress directions on the stay.

The rear triangle 2 is obtained from a first and a second block of material, each formed by a plurality of layers of anisotropic material assembled by gluing, in particular with the use of a thermosetting polymer, for example an epoxy resin, as gluing means. As mentioned above, it is possible to provide for two or more contiguous layers to be made of different materials and/or to provide, in the case of the use of wood as an anisotropic material, for contiguous layers of wood to have, in cross-section, an opposing fibre orientation.

Once these two blocks of material have been provided, each of them is subjected to machining, performed in particular with a numerically controlled milling machine, so as to obtain from the first block the oblique monocoque element 3, with the two seat stays 3a and 3b, with the connecting portion 3c connecting the two seat stays 3a and 3b to each other and with the fork-shaped portion comprising the two prongs 3e extending from the connecting portion 3c, and from the second block the horizontal monocoque element 4 with the two chain stays 4a and 4b, with the connecting portion 4c connecting the two chain stays 4a and 4b to each other and with the fork-shaped portion comprising the two prongs 4e extending from the connecting portion 4c.

Finally, the two monocoque elements 3 and 4 are joined at the lower ends 3d of the seat stays 3a and 3b and at the rear ends 4d of the chain stays 4a and 4b, in the manner explained above.

The rear triangle 2 thus created is finally assembled to the front triangle 7 to form the frame 1.

With reference again to Figures 1 and 2, the front triangle 7 comprises a horizontal element (or tube) 7a, an oblique element (or tube) 7b and a vertical element (or tube) 7c. The horizontal element 7a and the oblique element 7b are joined to each other at their respective front ends to form a steering node portion 8. The horizontal element 7a is joined at its rear end to the upper end of the vertical element 7c to form a saddle node portion 9. Finally, the oblique member 7b is joined at its rear end to the lower end of the vertical element 7c to form a bottom bracket casing portion 10. The steering node portion 8 has a through-hole 8a configured to accommodate a fork stem (not shown) of the bicycle. The seat node portion 9 has a through-hole (not shown) configured to accommodate a seat post of the bicycle. The bottom bracket casing portion 10 has a through-hole 10a configured to accommodate a bottom bracket of the bicycle. Such holes are preferably obtained by drilling into the corresponding portions of the frame mentioned above once the frame 1 has been assembled, i.e. , once the front triangle 7 and the rear triangle 2 have been made and joined to each other.

Referring to Figure 6, the horizontal element 7a, the oblique element 7b and the vertical element 7c of the front triangle 7 may each be obtained by joining, in particular by gluing, two specular parts, indicated respectively with 7a' and 7a" for the horizontal element 7a, with 7b' and 7b" for the oblique element 7b and with 7c' and 7c" for the vertical element 7c.

The two parts 7a' and 7a" of the horizontal element 7a, as well as the two parts 7b' and 7b" of the oblique element 7b and the two parts 7c' and 7c" of the vertical element 7c, are obtained by machining from a respective plank (or a respective block) of an anisotropic material, for example wood, namely a plank for the two parts 7a' and 7a" of the horizontal element 7a, another plank for the two parts 7b' and 7b" of the oblique element 7b and yet another plank for the two parts 7c' and 7c" of the vertical element 7c. Such planks need not necessarily consist of several layers glued to each other, but may also be formed each by a respective block of homogeneous material. If, for example, wood is used as an anisotropic material for the front triangle, the planks may also be made of solid wood.

As shown in Figure 7, where the plank of material (in this case wood) from which the two parts 7a' and 7a" of the horizontal element 7a are obtained is depicted, such parts are obtained from the plank in such a way as to extend consecutively (i.e., one after the other) along the longitudinal direction of the wood fibres, being at the same time specular with respect to each other. In this way, after the assembly, which, as already stated, is performed by gluing, of each part 7a', 7b' and 7c' with the complementary part 7a", 7b" and 7c", a course of the wood fibres of the two parts is obtained which is specular with respect to the plane in which said parts are joined by gluing. Each of the three planks may be made of an anisotropic material different from that of the other two planks, i.e., the elements 7a, 7b, 7c of the front triangle 7 may be made of different materials from each other, for example different types of wood.

Before joining the pairs of complementary parts to each other to form the various elements 7a, 7b and 7c of the front triangle 7, a cavity may be made within each of the two complementary parts so as to form a half-shell, whereby each of the elements 7a, 7b and 7c is internally hollow, and therefore lighter than a full-section configuration without internal cavity. The solution with a hollow interior is the best one in terms of performance/weight compromise, since the stresses are greatest on the outer skin of the tubes and decrease rapidly going inwards. For this reason, a defect that does not affect the outermost layer, and is therefore not visible from the outside, is not structurally critical.

The elements 7a, 7b and 7c thus obtained are finally assembled to form the front triangle 7. The assembly of these elements is preferably carried out by gluing at complementary formations suitably obtained at the ends of each of these elements, as shown in Figure 6.

At this point, the front triangle 7 is joined to the rear triangle 2 to form the frame 1 , in particular by gluing the fork-shaped portion of the oblique monocoque element 3 of the rear triangle 2 to the saddle node portion 9 of the front triangle 7 and by gluing the forkshaped portion of the horizontal monocoque element 4 of the rear triangle 2 to the bottom bracket casing portion 10 of the front triangle 7.

In this regard, in order to increase the contact surface, on which the adhesive means is to be applied, between the fork-shaped portion of the oblique monocoque element 3 of the rear triangle 2 and the saddle node portion 9 of the front triangle 7, each of the two parts 7a' and 7a" of the horizontal element 7a of the front triangle 7 forms at its rear end a respective abutment surface 12, in particular, a flat face inclined with respect to the longitudinal axis of the horizontal element 7a, against which in the assembled condition of the frame 1 a corresponding face of a respective prong 3e of the fork-shaped portion of the oblique monocoque element 3 is abutting. Furthermore, each of the two portions 7c' and 7c" of the vertical element 7c of the front triangle 7 forms at its rear a respective projection 14 having a respective abutment surface for the connecting portion 3c of the oblique monocoque element 3.

Likewise, in order to increase the contact surface, on which the adhesive means are to be applied, between the fork-shaped portion of the horizontal monocoque element 4 of the rear triangle 2 and the bottom bracket casing portion 10 of the front triangle 7, each of the two parts 7b' and 7b" of the oblique element 7b of the front triangle 7 forms at its lower end a respective abutment surface 16, in particular a horizontal flat face, and furthermore each of the two parts 7c' and 7c" of the vertical element 7c of the front triangle 7 forms at its lower end a respective abutment surface 18, in particular a horizontal flat face, which in the assembled condition of the frame 1 is coplanar with the abutment surface 16. In this manner, in the assembled condition of the frame 1 the surfaces 16 and 18 of each pair of parts 7b', 7c' and 7b", 7c" are in abutment against a corresponding face of a respective prong 4e of the fork-shaped portion of the horizontal monocoque element 4. Such a manner of joining the rear triangle 2 and the front triangle 7 is also applicable to frames in which the rear triangle is made in a different manner than the one illustrated in the present description.

The present invention has been described herein with specific reference to preferred embodiments, but it is clear that other embodiments may be envisaged, which share the same inventive concept as those described herein, as defined by the appended claims.