Method for making a wooden structural element, in particular for a bicycle frame, and structural element thus obtained

Abstract

A method is described for making a wooden structural element (12) for a vehicle frame, in particular a tube of a front triangle (10) of a bicycle frame, the method comprising the steps of: a) providing a pair of wooden half-shells (12a, 12b), each having a respective flat inner face (20a, 20b), at least one respective longitudinal cavity (18a, 18b) open on said flat inner face (20a, 20b) and at least one respective longitudinal seat (30a, 30b) extending adjacent to said at least one longitudinal cavity (18a, 18b) and open on said flat inner face (20a, 20b); b) providing, for each pair of longitudinal seats (30a, 30b) in said two half-shells (12a, 12b), a respective longitudinal blade element (32) having a thickness less than the height of said longitudinal seats (30a, 30b); c) applying glue onto said inner faces (20a, 20b) and in said longitudinal seats (30a, 30b) of said two half- shells (12a, 12b); and d) inserting said longitudinal blade element (32) into the respective pair of longitudinal seats (30a, 30b) and pressing said two half-shells (12a, 12b) against each other, with the inner face (20a) of one half-shell (12a) in contact with the inner face (20b) of the other half-shell (12b).

Description

[0001] METHOD FOR MAKING A WOODEN STRUCTURAL ELEMENT, IN PARTICULAR FOR A BICYCLE FRAME, AND STRUCTURAL ELEMENT THUS OBTAINED

[0002] Technical field

[0003] The present invention relates generally to a method for making a wooden structural element for a vehicle frame structure. More specifically, the present invention relates to a method for making a wooden structural element of a bicycle frame, in particular (though not exclusively) the horizontal tube, the oblique tube or the vertical tube (also referred to as seat tube) of a bicycle frame.

[0004] State of the art

[0005] The use of wood as a material for the construction of vehicle frames, in particular bicycle frames, is well known. With a low specific weight, the wood has high strength and stiffness values, but also high durability. In addition, the wood retains an elastic behaviour even under conditions of high deformation combined with a high internal damping factor and allows to make bicycle frames with significant capability to absorb the roughness of the road, and therefore very comfortable for the cyclist. For this reason, bicycle frames made of wood are beginning to gain popularity.

[0006] Bicycle frames, especially if intended for competitive use or, more generally, if intended for mid- or high-end bicycles, must be as light as possible in order not to penalise the cyclist's performance due to excessive weight. Therefore, in the case of bicycle frames made of wood, it is known to make the main structural elements of the frame, i.e. the horizontal tube, the oblique tube and the vertical tube, by joining two wooden half-shells, so as to obtain a hollow structural element that has mechanical characteristics substantially similar to those of a solid structural element with the same external dimensions, but a significantly lower weight. Typically, the two half-shells are joined by means of gluing at the flat facing surfaces of the two half-shells. However, such a joining method may not be durable. In fact, it must be considered that wood is a living material subject to shrinkage (or expansion), besides in a non-homogeneous manner, and furthermore the bike is subject to severe operating conditions, being also exposed to atmospheric factors. The joints of the shell elements have very small bonding surfaces (with the aim of limiting the weight of the frame) and these surfaces work in traction to prevent detachment between the shell elements, which significantly reduces the strength of the joint, since glues, especially two-component glues, work much better under shear conditions than under traction conditions.

[0007] A method for making wooden structural elements, in particular for bicycle frames, is known, for example, from AU 2015 202 766 A1. According to this known solution, each structural element of the frame is formed by two wooden half-blocks, each of which has a central cavity open towards an inner face of the half-block. The two half-blocks are joined to each other at their respective inner surfaces, and the respective central cavities together form an inner cavity of the structural element.

[0008] Summary of the invention

[0009] It is therefore an object of the present invention to overcome the drawbacks of the prior art discussed above, by providing a method for making a wooden structural element, in particular for a bicycle frame, which ensures greater strength of the joint between the two half-shells, without thereby adversely affecting the mechanical characteristics of the structural element and without increasing the weight of the structural element.

[0010] This and other objects are fully achieved according to the present invention by a method for making a wooden structural element as defined in the attached independent claim 1 A wooden structural element, in particular for a bicycle frame, as defined in the attached independent claim 7, also forms the subject-matter of the present invention.

[0011] Further advantageous aspects of the invention are defined in the dependent claims, the subject-matter of which is to be understood as forming an integral part of the following description.

[0012] In summary, the invention is based on the idea of providing, in each wooden half-shell with which the structural element is formed, at least one seat extending parallel to a longitudinal axis of the structural element (i.e. the axis along which the structural element extends), and of inserting into each pair of facing seats formed by the two half-shells, a wooden blade element, so that the glue used for joining the two half-shells also enters these seats, thus causing the opposite faces of each blade element to adhere to the respective opposite faces of each of the two facing seats into which said blade element is inserted. Thanks to such a solution, the adhesion surface between the two half-shells, i.e. the surface on which the glue with which the two half-shells are joined acts, is greatly increased, and this contributes to increasing the strength of the joint, i.e. the resistance of the joint against forces tending to cause the separation of the two half-shells. Furthermore, since the opposite faces of the blade elements, and thus also the opposite faces of the respective seats, extend substantially perpendicular to the main joining plane of the two half-shells, joining planes with an orientation other than that of the main joining plane, in particular joining planes perpendicular to the main joining plane, are created. This allows to greatly increase the strength of the joint, since a force tending to separate the two half-shells produces shear stresses on the layers of glue applied between the faces of the blade elements and the corresponding faces of the respective seats, and the glue typically has much greater resistance to shear stresses than tensile stresses.

[0013] Brief description of the drawings

[0014] Further features and advantages of the present invention will be evident from the following detailed description, given purely by way of non-limiting example with reference to the accompanying drawings, in which:

[0015] - Figure 1 is an exploded view of the front triangle of a bicycle frame whose tubes are made with the method according to the present invention; and

[0016] - Figures 2 and 3 are exploded views, from two different points of view, of the horizontal tube of the front triangle of Figure 1.

[0017] Detailed description

[0018] The present invention has been conceived to be applied to the bicycle sector, and therefore will be described herein with particular reference to its application to the manufacturing of a wooden structural element of a bicycle frame. However, this application is not to be considered as limiting, since the invention is applicable to the manufacturing of wooden structural elements for frame structures of vehicles in general. For example, the present invention could be applied for the manufacturing of frame structures for motorised quadricycles.

[0019] Referring initially to Figure 1 , numeral 10 generally denotes a front triangle of a bicycle frame, which in the present case is a frame with a geometry suitable for a racing bike, a mountain bike or a gravel bike, but which could also be a frame for another type of bicycle, for example a so-called cargo bike.

[0020] The front triangle 10 basically comprises three wooden structural elements, at least one (preferably all three) of which is made with the method according to the present invention. A first structural element, indicated 12, forms the horizontal tube of the front triangle 10, a second structural element, indicated 14, forms the oblique tube of the front triangle 10, and finally a third structural element, indicated 18, forms the vertical tube (or seat tube) of the front triangle 10 The structural elements 12, 14 and 16 are obtained separately from each other and then joined to each other at their ends, by gluing, to form the front triangle 10. In particular, each of the structural elements 12, 14 and 16 is obtained by joining two wooden hollow parts, hereinafter referred to as half-shells, by means of glue. More specifically, the first structural element 12 (horizontal tube) is obtained by joining two half-shells 12a and 12b, the second structural element 14 (oblique tube) is obtained by joining two half-shells 14a and 14b, and the third structural element 16 (vertical tube) is obtained by joining two halfshells 16a and 16b. In the embodiment proposed herein, the two half-shells of each of the structural elements 12, 14 and 16 are substantially symmetrical to each other, but may also exhibit a certain asymmetry.

[0021] Referring now to Figures 2 and 3, which show in detail the first structural element 12 (but similar considerations also apply to the second structural element 14 and the third structural element 16, as will be better explained below), each of the two half-shells 12a, 12b of the structural element 12 has a respective longitudinal cavity 18a, 18b, i.e., a cavity extending along the longitudinal direction of said structural element (that is to say, along the main direction of extension of said structural element). Each of the longitudinal cavities 18a, 18b is open on a respective flat inner face 20a, 20b of the respective halfshell 12a, 12b, in such a manner that, once the two half-shells 12a and 12b are joined together with their respective flat faces 20a and 20b in contact with each other, the two longitudinal cavities 18a and 18b form a closed longitudinal cavity within the structural element 12.

[0022] Preferably, each of the two half-shells 12a, 12b of the structural element 12 also has, in a forward end region 22a, 22b thereof, a semicylindrical cavity 24a, 24b with a vertical axis, which is also open on the inner face 20a, 20b of the respective half-shell 12a, 12b. In this way, once the two half-shells 12a and 12b are joined together, the two semicylindrical cavities 24a and 24b form a cylindrical cavity, open at the top and bottom, through which a fork tube (not shown) of the bicycle can be passed.

[0023] Furthermore, in the embodiment proposed herein, a rear end region 26a, 26b of each of the two half-shells 12a, 12b of the structural element 12 is preferably provided with a comb-like formation 28a, 28b configured to engage with a corresponding comb-like formation (not shown) provided at an upper end of the third structural element 16. The use of such comb-like formations for joining the various structural elements, in the present case for joining the first structural element 12 and the third structural element 14, makes it possible to increase the surface to which the glue is applied for joining these two elements, and hence to increase the strength of the joint. However, the presence of such a comb-like formation is not necessary for the purposes of the present invention.

[0024] The two half-shells 12a and 12b of the structural element 12 are joined to each other by gluing at the respective inner faces 20a and 20b. In other words, the two half-shells 12a and 12b of the structural element 12 are joined to each other by applying glue on the respective inner faces 20a and 20b. In the assembled condition of the structural element 12, the inner faces 20a and 20b of the two half-shells 12a and 12b lie therefore in the same plane, hereinafter referred to as the main joining plane. In the embodiment proposed herein, in which the two half-shells 12a and 12b are symmetrical to each other, preferably the main joining plane coincides with the plane of symmetry of the structural element 12.

[0025] In order to increase the strength of the joint between the two half-shells 12a and 12b of the structural element 12, i.e. the ability of the structural element 12 to withstand forces tending to cause the separation of the two half-shells 12a and 12b, according to the invention blade elements are used, which are inserted into special seats provided in both half-shells.

[0026] More specifically, again with reference to Figures 2 and 3, each of the two half-shells 12a, 12b of the structural element 12 has a respective longitudinal seat 30a, 30b, i.e. a seat extending along the longitudinal direction of said structural element, next to the respective longitudinal cavity 18a, 18b. In the example proposed herein, a longitudinal seat 30a, 30b is provided in each half-shell 12a, 12b and is arranged above the respective longitudinal cavity 18a, 18b, but depending on the specific application of the structural element this longitudinal seat might also be arranged below the longitudinal cavity of the respective half-shell. Alternatively, each half-shell 12a, 12b might have two longitudinal seats above and below the respective longitudinal cavity 18a, 18b, respectively. Each of the longitudinal seats 30a, 30b is open on the inner face 20a, 20b of the respective half-shell 12a, 12b, in such a manner that, once the two half-shells 12a and 12b are joined together, the two longitudinal seats 30a and 30b form a closed longitudinal seat within the structural element 12.

[0027] The longitudinal seats 30a and 30b extend substantially in a plane, having a height (which may be approximately 1 mm, or even less) that is much smaller than their length and width. Preferably, this plane extends substantially perpendicular to the inner faces 20a and 20b of the two half-shells 12a and 12b, i.e. - in the assembled condition of the structural element 12 - substantially perpendicular to the main joining plane of said element. A longitudinal blade element 32, also preferably made of wood (which may be the same type of wood of which the two half-shells 12a and 12b are made or a different type of wood), is inserted into the longitudinal seats 30a and 30b. In this way, once the two halfshells 12a and 12b have been joined to each other, the longitudinal blade element 32 remains closed within the closed longitudinal seat formed by the longitudinal seats 30a and 30b of the two half-shells. The longitudinal blade element 32 has a thickness slightly less than the height of the longitudinal seats 30a and 30b, so that between the opposite flat faces of the longitudinal blade element 32 and the opposite flat faces of each of the longitudinal seats 30a and 30b there is a certain clearance for the insertion of a layer of glue between the opposite flat faces of the longitudinal blade element 32 and the opposite flat faces of the longitudinal seats 30a and 30b. Of course, in case an additional longitudinal seat is provided in each half-shell 12a, 12b below the longitudinal cavity 18a, 18b, an additional longitudinal blade element inserted into these additional longitudinal seats will also be provided.

[0028] In the embodiment proposed herein, in which the structural element 12 forms at its front end a cylindrical cavity suitable for accommodating a fork tube, preferably each half-shell 12a, 12b further has a respective vertical seat 34a, 34b extending substantially parallel to the axis of the respective semicylindrical cavity 24a, 24b and in which a vertical blade element 36 is accommodated. The characteristics and function of the vertical seats 34a and 34b and of the vertical blade element 36 are similar to those described above with reference to the longitudinal seats 30a and 30b and the longitudinal blade element 32. The second structural element 14 and the third structural element 16 of the front triangle 10 have a configuration similar to that described above with reference to the first structural element 12. In particular, also for these two structural elements longitudinal blade elements are provided, which are inserted into respective pairs of longitudinal seats extending in the two half-shells on one side and / or on the other side with respect to the longitudinal cavity. More specifically, the two half-shells 14a and 14b of the second structural element 14 have respective longitudinal seats (of which only the seat provided in the half-shell 14a, indicated 38a, can be seen in Figure 1), into which a longitudinal blade element 40 is inserted, while the two half-shells 16a and 16b of the third structural element 16 have respective longitudinal seats (of which only the seat provided in the half-shell 16a, indicated 42a, can be seen in Figure 1), into which a longitudinal blade element 44 is inserted.

[0029] In addition, in the embodiment proposed herein, in which also the second structural element 14 has at its front end a cylindrical cavity which in the assembled condition of the front triangle 10 is aligned with the cylindrical cavity of the first structural element 12, also in the half-shells 14a and 14b of the second structural element 14 there are vertical seats (of which only the seat provided in the half-shell 14a, indicated 46a, can be seen in Figure 1) at the front ends of the two half-shells 14a and 14b. In particular, in the embodiment proposed herein, the vertical seat of each half-shell of the first structural element 12 is connected to the vertical seat of the corresponding half-shell of the second structural element 14, whereby the same vertical blade element 36 of the first structural element 12 is also inserted into the vertical seats of the second structural element 14. Of course, other solutions are possible, so that, for example, separate vertical blade elements may be provided for the two structural elements 12 and 14.

[0030] Referring again to Figures 2 and 3, the method for making the structural element 12 (but the same applies to the other structural elements 14 and 16) initially requires the step of obtaining the two half-shells 12a and 12b, which is done by machining from a wooden board (or a respective wooden block), preferably the same wooden board (or the same wooden block) for the two half-shells 12a and 12b. Said wooden board (or block) may be either made of solid wood or consist of several layers of wood glued together. By machining of the wooden board (or block) the two half-shells 12a and 12b with the respective longitudinal cavities 18a and 18b, the respective longitudinal seats 30a and 30b, the respective semicylindrical cavities 24a and 24b, and the respective vertical seats 34a and 34b, are obtained. In addition, the longitudinal blade element 32 (or the longitudinal blade elements, in case two such blade elements are provided) and the vertical blade elements 36 (or the vertical blade elements, in case two such blade elements are provided), which - as mentioned above - are preferably also made of wood, for example formed of glued layers of birch wood, are also provided.

[0031] At this point, the two half-shells 12a and 12b are joined to each other by gluing. To this end, glue is first applied onto the inner faces 20a and 20b and in the seats 30a, 30b and 34a, 34b of the two half-shells 12a and 12b, then the blade elements 32 and 36 are inserted into the respective seats of one of the two half-shells, for example into the longitudinal seat 30a and the vertical seat 34a of the half-shell 12a, and finally the two half-shells are pressed against each other, with the inner face 20a of the half-shell 12a in contact with the inner face 20b of the half-shell 12b, taking care that the blade elements 32 and 36 are correctly inserted into the seats 30b and 34b of the second half-shell 12b as well. The glue used to join the two half-shells 12a and 12b is therefore applied not only onto the inner faces 20a and 20b of the two half-shells, but also in the free space between the opposite faces of the blade elements 32 and 36 and the opposite faces of the respective seats 30a, 30b and 34a, 34b. In this way, in case of stresses tending to separate the two half-shells 12a and 12b, the glue layer applied onto the inner faces 20a and 20b will work in tension, while the glue layers applied onto the blade elements 32 and 36 will work in shear. Since the glue has a shear strength that is significantly higher than the tensile strength, the glue layers applied onto the blade elements 32 and 36 allow to significantly increase (for example tenfold, for the same glued surface area) the strength of the joint between the two half-shells 12a and 12b.

[0032] Finally, with reference again to Figure 1 , it can be envisaged, for the assembly of the front triangle 10, that first the half-shells of each of the two sides (left and right) of the triangle are joined to each other, that is to say, the half-shells 12a, 14a and 16a on the one hand and the half-shells 12b, 14b and 16b on the other, to form two half-triangles, and that the two half-triangles are then joined to each other by gluing, naturally after the blade elements 32, 36, 40 and 44 have been inserted into the respective seats.

[0033] The present invention has been described herein with specific reference to a preferred embodiment thereof, but it is clear that other embodiments may be envisaged that share the same inventive concept with the one described herein, as defined by the appended claims.

[0034] For example, the half-shells of a structural element might each have several separate longitudinal cavities, arranged one after the other or next to each other, instead of a single longitudinal cavity. Furthermore, each longitudinal blade element might be replaced with two or more separate longitudinal blade elements, arranged one after the other.

Claims

CLAIMS1. Method for making a wooden structural element (12) of a vehicle frame structure, the method comprising the steps of: a) providing a pair of wooden half-shells (12a, 12b), each having a respective flat inner face (20a, 20b), at least one respective longitudinal cavity (18a, 18b) which is opens on said flat inner face (20a, 20b) and at least one respective longitudinal seat (30a, 30b) which extends next to said longitudinal cavity (18a, 18b) and is open on said flat inner face (20a, 20b); b) providing, for each pair of longitudinal seats (30a, 30b) of the two half-shells (12a, 12b), a respective longitudinal blade element (32) having a thickness smaller than the height of said longitudinal seats (30a, 30b); c) applying glue onto said inner faces (20a, 20b) and in said longitudinal seats (30a, 30b) of the two half-shells (12a, 12b); and d) inserting said longitudinal blade element (32) into the respective pair of longitudinal seats (30a, 30b) and pressing the two half-shells (12a, 12b) one against the other, with the inner face (20a) of one half-shell (12a) in contact with the inner face (20b) of the other half-shell (12b).

2. Method according to claim 1 , wherein at said step a) the half-shells (12a, 12b) are obtained by machining from a wooden board or block.

3. Method according to claim 2, wherein said wooden board or block is made of solid wood or of a plurality of wooden layers glued together.

4. Method according to any one of the preceding claims, wherein said longitudinal blade element (32) is made of wood, in particular formed by glued layers of birch wood.

5. Method according to any one of the preceding claims, wherein each pair of longitudinal seats (30a, 30b) is configured so that the opposite faces of said longitudinal seats (30a, 30b) are substantially perpendicular to the plane of the inner face (20a, 20b) of the respective half-shell (12a, 12b).

6. Method according to any one of the preceding claims, wherein said structural element (12) is a tube for a bicycle frame.

7. Wooden structural element (12) comprising:- a pair of wooden half-shells (12a, 12b), each having a respective flat inner face (20a, 20b), at least one respective longitudinal cavity (18a, 18b) which is open on said flat innerface (20a, 20b) and at least one respective longitudinal seat (30a, 30b) which extends next to said longitudinal cavity (18a, 18b) and is open on said flat inner face (20a, 20b); and- for each pair of facing longitudinal seats (30a, 30b), a respective longitudinal blade element (32) with a thickness smaller than the height of said longitudinal seats (30a, 30b), said respective longitudinal blade element (32) being inserted into said pair of facing longitudinal seats (30a, 30b); wherein the two half-shells (12a, 12b) are joined to each other by means of glue applied onto said inner faces (20a, 20b) and in said longitudinal seats (30a, 30b) of the two halfshells (12a, 12b).

8. Structural element according to claim 7, wherein said longitudinal blade element (32) is made of wood, in particular formed by glued layers of birch wood.

9. Structural element according to claim 7 or claim 8, wherein each pair of longitudinal seats (30a, 30b) is configured so that the opposite faces of said longitudinal seats (30a, 30b) are substantially perpendicular to the plane of the inner face (20a, 20b) of the respective half-shell (12a, 12b).

10. Vehicle frame structure comprising at least one structural element according to any one of claims 7 to 9.

11. Structure according to claim 10, wherein said structure is a front triangle (10) of a bicycle frame, comprising a horizontal tube (12), an oblique tube (14) and a vertical tube (16), and wherein at least one of said tubes (12, 14, 16) is formed by a structural element according to any one of claims 7 to 9.

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