WO2023166240A1

WO2023166240A1 - Toothed gear for bicycles or other systems having a similar transmission

Info

Publication number: WO2023166240A1
Application number: PCT/ES2023/070120
Authority: WO
Inventors: Roland Baides Martinez
Original assignee: Gemini Composites, S.L.
Priority date: 2022-03-03
Filing date: 2023-03-03
Publication date: 2023-09-07
Also published as: ES1289256U; ES1289256Y

Abstract

Disclosed is a toothed gear for bicycles or other systems having a similar transmission in which same is an essential element for transmitting the movement. The toothed gear is formed by a circular part (1) provided radially with a plurality of teeth (1a), wherein the part (1) is made of a discontinuous fibre-reinforced composite (DFC) material produced by compression moulding. Preferably, the part (1) is produced from a portion of composite material (5) formed by a binding, thermostable or thermoplastic polymer matrix (2) and fibre reinforcement consisting of discontinuous and disordered threads (3). Once the part (1) has been produced, the threads (3) are arranged mostly randomly in the centre thereof and in the outer area continuously and concentrically towards each of the teeth (1a).

Description

TOOTH GEAR FOR BICYCLES OR OTHER SIMILAR TRANSMISSION SYSTEMS

DESCRIPTIVE MEMORY

OBJECT OF THE INVENTION

The invention, as expressed in the statement of this descriptive report, refers to a toothed gear for bicycles or other similar transmission systems that contributes, to the function for which it is intended, advantages and characteristics, which are described in detail later. .

The object of the present invention falls on a toothed gear for bicycles or other similar transmission systems in which it is constituted as an essential element of said movement transmission, which presents the innovative characteristic of being made of discontinuous carbon fiber, or other composite materials. with discontinuous fibers, known as "Discontinous Fiber Composites" (DFC), providing said gear with the advantages of a better structural distribution and, therefore, greater resistance, especially in the area of the teeth, compared to carbon fiber gears. conventional (or other composite materials with fibers) that are currently used, and less light than their metallic precedents.

FIELD OF APPLICATION OF THE INVENTION

The field of application of the present invention falls within the field of transmission systems that include toothed gears.

BACKGROUND OF THE INVENTION

As is known, bicycles currently incorporate many innovations that make them much more competitive. In this sense, the weight of the parts or its elements is an essential factor, however, the necessary resistance must be guaranteed to fulfill its intended function.

For this reason, carbon fiber, which is a lightweight and highly resistant material, is used in various structural and mechanical parts of a bicycle. The manufacturing processes for carbon fiber parts currently used are based on the use of compounds from sheets that contain continuous, woven or unidirectional fibers. (See Figures 2-A and 2-B).

As is known, epoxy-based carbon fiber is a composite material (composite). Like all "composites", it is made from a binder matrix and a reinforcing fiber. Since its structural distribution depends on the directionality of the fibers that reinforce it, and they are usually found in a specific order, it is an anisotropic material. (See Figures 1).

Epoxy-based carbon fiber composite is a material that must go through a curing process during the manufacturing process of a part. There are different types of raw material that can be purchased depending on each need and supplier.

The mechanical properties of this anisotropic composite material depend on the directionality of the fibers that reinforce it, in this case, the carbon fiber (reinforcement). These fibers have the capacity to withstand large axial tensile stresses, with very little deformation, which makes the composite a very rigid and resistant material.

On the contrary, the fibers do not present a good behavior to other stresses such as compression, bending or shear axial stresses. In these cases, the structural behavior of the fiber decreases and it is the matrix (epoxy resin) that absorbs a large part of the stresses, generating cracks, breaks or breaks in the composite material. It is for this reason that, for a correct manufacturing of a carbon fiber part, it is important to anticipate how the fibers will be directed, especially in the critical areas of the part where it may suffer more pronounced stresses.

The critical stresses to which a toothed gear is usually subjected are located at the end of the teeth, generated by other elements of the transmission system such as a chain, in a tangential direction to the circular movement of the gear itself. and in the opposite direction of its rotation.

Therefore, so that during the most critical phase of the operation of a carbon fiber toothed gear, the structure of the fibers works optimally, the ideal orientation and distribution of said fibers must be concentric to the geometry, as shown in the figure. figure 4. Otherwise, any other orientation of the fiber will prevent it from working in traction, subjecting it to greater bending, compression and shear stresses, and therefore, compromising it to be non-optimal.

One of the most common typologies for the production of technical parts are the continuous sheets of carbon fiber pre-impregnated with resin or "prepreg". It is a material that is served in sheets, where the fibers are perfectly ordered and arranged according to a certain pattern, which can be unidirectional, or woven together throughout the sheet. The matrix, generally raw epoxy resin, binds the fibers together, forming a joint sheet. (See Figures 2-A and 2-B)

For the manufacture of a piece with continuous carbon sheets, a pattern must be designed for the desired piece, and mold it onto said pre-impregnated sheets. Once the patterns have been obtained, they must be arranged in the mold of the piece, taking into account the directionality of the fiber in each of the layers. Finally, the mold must be closed with a certain pressure to compact the material and subject it to a temperature curing process.

In some cases, the geometry of a part is not obtained only from the laminate, but once a part is cured with excess material, it is partially or totally machined.

Regardless of whether the piece is machined after the fact or not, in order for the structural distribution of a piece to be correct, the different layers of continuous carbon that make up the piece are arranged in a different way between them, with the aim that they always meet. fibers in the optimum orientation in the areas susceptible to critical stresses.

For the manufacture of a toothed gear, or any other geometry with concentric protrusions, the use of sheets of continuous carbon fiber implies that in the protruding areas (teeth) the carbon fibers remain mostly in a non-optimal orientation, and cut, or either by the design of the pattern, or by machining after curing, nullifying the continuous character of the fiber in those areas, compromising its structural behavior. (See Figures 5 and 6).

For this reason, the resulting structure in the teeth of a toothed gear manufactured by the "prepreg" continuous carbon laminate method is not optimal in terms of the structure of the carbon fibers, since the distribution of the fibers would be different in each case. each tooth of the toothed wheel as it is a circular element.

Another, much less common type of manufacturing of carbon fiber parts is DFC (Discontinous Fiber Composites) compression molding. Usually, this group of materials is served as a composite of discontinuous carbon fibers, also pre-impregnated with a binder (matrix), generally Epoxy resin, in sheet format or SMC (Sheet Molding Compund) or in mass format or BMC (Bulk Molding Compound). The carbon fibers in these composites are shorter (depending on the supplier) and are randomly arranged, making a homogeneous and non-ordered mixture, with a structural distribution more similar to that of an isotropic material. (See Figures 2-C and 2-D)

Manufacturing using discontinuous fiber composites (DFC) is carried out with a specific mould, fitted with a heating system, activated by a press. Said mold essentially has two elements, the cavity half and the force or punch half which, due to their characteristics, exert a certain pressure on the material, allowing it to conform to the geometry of the desired part.

In DFC compression molding, a charge of raw material, of given mass and volume, is placed in the middle of the mold cavity. The mold's heating system allows the binder resin in the compound to become viscous with temperature. Using a press, half the force of the mold or punch is introduced into half the cavity, transmitting high pressure to the material and, thanks to the distribution and size of the discontinuous fibers, the composite material is distributed along the entire geometry. of the mold, being able to fill complex geometries. (See Figures 3-A, 3-B and 3-C)

The objective of the present invention is, therefore, to provide the market with a toothed gear with the advantages of carbon fiber produced by DFC compression molding, improving the behavior of this material in critical areas of the part, such as the of the teeth.

On the other hand, and as a reference to the current state of the art, at least by the applicant, the existence of any other carbon toothed gear for bicycles is unknown, nor any other invention of similar application, which presents technical characteristics, and constitutive equal or similar to those presented by the one claimed here. EXPLANATION OF THE INVENTION

The toothed gear that the invention proposes is configured as the ideal solution to the aforementioned objective, with the characteristic details that make it possible and that distinguish it conveniently included in the final claims that accompany this description.

Specifically, what the invention proposes, as previously noted, is a toothed gear for bicycles or other similar transmission systems, which is distinguished by being manufactured by compression molding of discontinuous fiber composite materials also known as DFC, preferably discontinuous carbon fiber.

More specifically, said part is suitable for constituting a toothed gear thanks to the fact that the carbon fiber material, instead of being laminated layer by layer and made up of layers of continuous fibers with carbon threads arranged unidirectionally and/or woven, as It would be usual, it is made by compression molding a compound of discontinuous fibers together, where the fibers are dragged, by the pressure exerted inside the mold, up to the interior cavity of each one of the gear teeth.

With this, it is advantageously achieved that the gear presents a structural improvement with respect to a gear laminated with continuous fiber, since the orientation and distribution of the fibers, obtained thanks to the pressure that the mold provides, corresponds very similarly to the structural orientation. of ideal fibers described in Figure 4-B, which they must have in order for them to present optimal behavior in the face of the efforts to which a gear is subjected.

DESCRIPTION OF THE DRAWINGS To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, this specification is attached, as an integral part of it, a set of drawings in which, for illustrative and non-limiting, the following has been represented:

Figure number 1 Shows a schematic view of the representation of the parts that make up the material constituting the carbon fiber or other fiber composite material as reinforcement; Figures number 2-A, 2-B, 2-C and 2-D.- Show a schematic representation of the different types of carbon fiber with pre-impregnated resin that can be found commercially; Figures number 3-A, 3-B and 3-C.- Show respective schematic views of the DFC compression molding phases, showing respectively the initial arrangement of the material in the center of the mold and its distributed arrangement throughout the mold after having received pressure; figures number 4-A and 4-B.- Show, respectively, a schematic representation of a toothed gear with the chain, and enlarged detail A of the toothed area showing, by means of double arrow lines, the ideal orientation of the fibers and, by means of a bold arrow, the force exerted by the chain on the teeth; Figures number 5-A and 5-B.- Show respective views, in elevation and section, respectively, of an example of toothed gear, according to a hypothetical embodiment of the gear obtained by rolling; Figures number 6-A, 6-B and 6-C.- Show respective views of the different layers of laminate comprising the gear of Figure 5-B, appreciating the different orientations of the fibers between layers, each of them being unidirectional; Figures number 7-A, 7-B.- Show, respectively, an elevation view of the representation of the initial arrangement of the raw material in the center of the piece to obtain the carbon fiber toothed gear with SMC, according to the invention, and the enlarged detail of said material with disordered short threads in different orientations; and figures number 8-A and 8-B.- They show, respectively, an elevation view of the part obtained that makes up the carbon toothed gear object of the invention, and an enlarged detail of the area of the teeth, where it is shown the orientation of the fibers.

PREFERRED EMBODIMENT OF THE INVENTION

In view of the aforementioned figures, and in accordance with the numbering adopted, it can be seen that what the invention proposes is a toothed gear for bicycles or other similar transmission systems, made from a circular part (1). Radially equipped with a plurality of teeth (1 a), it is distinguished by the fact that said part (1) is made of a composite material with discontinuous reinforcing fibers, known as DFC (discontinuous fiber composite material), preferably discontinuous fibers carbon, obtained by compression molding or compression molding.

Preferably, said piece (1) is obtained from a portion of composite material (5) formed by a binder, thermosetting or thermoplastic polymeric matrix (2), and fiber reinforcement, normally carbon, consisting of discontinuous threads (3). and disordered, whose threads (3), once the part (1) is obtained, are oriented mostly randomly in the center of said part and in a continuous and concentric way towards each of the teeth (1 a). The material is placed in the mold in a random arrangement, and by compressing the mold in the central area, the material continues to remain in this position, providing a quasi-isotropic behavior, but in the area of the teeth, the material is pushed, leaving the fibers concentrically oriented and more continuous with the shape of the teeth.

Considering figure 1, it can be seen, schematically represented, how the carbon fiber with which the toothed gear (1) of the invention is made is a material composed of a binder matrix (2), usually epoxy thermosetting resin, and a structural reinforcement consisting of carbon fiber or threads (3).

Figures 2-A, 2-B, 2-C and 2-D show, schematically, the different types of carbon fiber with pre-impregnated resin that can be found commercially.

Figure 2-A shows how, in an example of a UD (unidirectional) sheet (4), the carbon fiber threads (3) are continuous and are all oriented in the same direction.

Figure 2-B shows how, in another example of sheet (4), the carbon fiber threads (3) are continuous and intertwined in an orderly fashion.

In figure 2-C it can be seen how, in another example of sheet (4) of discontinuous fibers (SMC), the carbon fiber threads (3) are discontinuous, of a determined length and are disordered throughout the entire length of the sheet. leaf.

And in figure 2-D it can be seen how, in an example of a mass of discontinuous fibers (BMC), the carbon fiber threads (3) are discontinuous, of a determined length and are disordered throughout a mass ( 2) that binds them together, generally Epoxy resin. On the other hand, looking at figures 3-A, 3-B and 3-C, the DFC compression molding phases can be seen schematically, showing respectively the initial arrangement of the material in the center of the mold and the arrangement distributed throughout the mold after receiving pressure.

In this case, to obtain the pieces, said material (5) is placed in the mold (6) in the amount of volume required, and is subjected to high temperature and high tonnage by means of a press, whose pressure force is represented in figure 3-B by arrow (p). The temperature causes the resin to become viscous, and thanks to the distribution and size of these fibers, the composite material (5) allows the pressure (p) to be distributed throughout the geometry of the mold (6).

Looking at figures 4-A and 4-B, it can be seen how, in the case of a toothed gear (1) for a bicycle where the teeth (1 a) will be tensioned by the chain (7), so that the threads (3) receive the most traction forces, their ideal position would be radial in the center of the part and continuously towards each of the teeth (1 a), as shown by the traced line represented in figure 4-B.

Considering figures 5-A and 5-B, a hypothetical embodiment of a laminated carbon toothed gear (1 ') is observed, that is, obtained by laminating several layers, for example, an anterior (a) an intermediate (b ) and a later one (c) of sheets (4) pre-impregnated with carbon fiber with continuous unidirectional threads (3). Figure 5-B shows a sectional view according to section B-B indicated in Figure 5-A. And in figures 6-A, 6-B and 6-C the different expected direction of the wires (3) in each of the layers can be observed.

As can be seen, even if the three layers (a, b, c) are combined, represented in figures 6-A, 6-B and 6-C, the carbon fibers or threads (3) are not distributed as is the case. ideal shown in Figure 4-B, so it is forced to the material to be worked in a non-optimal way. In addition, with the cutting of the sheets at different angles, most of the fibers or threads (3) that remain in the area of the teeth (1 a), which is the critical part of the piece, are cut and lack continuity. with the whole, compromising the structural character of the composite.

Considering figures 7-A to 8-B, it can be seen how, when the toothed gear (1), as is the case of the gear object of the present invention, consists of a piece of composite material obtained by compression molding of DFC , it is achieved that the carbon fibers or threads (3) follow the ideal orientation shown in figure 4-B.

More specifically, as can be seen in figures 7-A and 7-B, in an initial instance, the raw material (5) is arranged in the central part of the mold (6) with the shape of the piece without actually covering the edges where the teeth will form (1 a). It can be seen in the detail of figure 7-B how the carbon wires (3) are short and disordered.

Finally, looking at figures 8-A and 8-B, the toothed gear (1) can be seen, in this case a bicycle chainring, in the final position, once the mold has been closed. It can be seen how the material (5) by pressure moves to the ends of the piece, dragging the short carbon threads (3) into each tooth (1 a), this being the property that makes the toothed gear (1 ) of carbon presents a structural improvement with respect to a laminated gear with sheets of continuous fiber, since the orientation and distribution of the fibers is practically identical to the ideal orientation shown in figure 4-B.

Having sufficiently described the nature of the present invention, as well as the way of putting it into practice, it is not considered necessary to make its explanation more extensive so that any expert in the field understands its scope and the advantages derived from it.

Claims

CLAIMS 1 Toothed gear for bicycles or other similar transmission systems in which it is constituted as an essential element of said movement transmission, which, constituted from a circular part (1) radially equipped with a plurality of teeth (1 a), is characterized by the fact that said piece

(1) is a composite material of discontinuous reinforcing fibers or DFC obtained by compression molding.

2. Toothed gear for bicycles or other similar transmission systems, according to claim 1, characterized in that said part (1) is obtained from a portion of composite material (5) formed by a polymeric matrix.

(2) binder, thermosetting or thermoplastic, and fiber reinforcement consisting of discontinuous and disordered threads (3), whose threads (3), once the piece (1) is obtained, are oriented mostly randomly in the center of said piece and in the outer zone in a continuous and concentric way towards each of the teeth (1 a). .

3. Toothed gear for bicycles or other similar transmission systems, according to claim 1 or 2, characterized in that the discontinuous reinforcing fibers of the composite material of the piece (1) are made of carbon.