NL2015673B1 - An off-centre type carbon-fibre rim for a bicycle wheel having a symmetrical outside profile shape and an asymmetrical inside profile shape. - Google Patents

Abstract

An off-centre type carbon-fibre rim 1 for a bicycle wheel wherein outer, inner and flange wall parts are manufactured out of carbon-fibre material which wall parts together form a profile enclosing a space 7. The left and right flange wall parts 3, 4 lie symmetric at opposing sides of a central plane 12. The profile’s outside that is directed away from the enclosed space is symmetrical relative to the central plane. The profile’s inside that is directed towards the enclosed space is asymmetrical relative to the central plane, at least in that the inner wall part’s inside is asymmetrical relative to the central plane such that its average wall thickness is greater sideways of the central plane where off-centre spoke mounting apertures 15 are provided, than sideways of the central plane where the spoke mounting apertures are not provided.

Description

Title: An off-centre type carbon-fibre rim for a bicycle wheel having a symmetrical outside profile shape and an asymmetrical inside profile shape.

The invention relates to a carbon-fibre rim for a bicycle wheel of the off-centre type with spoke mounting apertures provided lateral off-centre in a radially inner rim wall part at one side of a central plane of the rim.

Over the years drivetrain cassettes of rear bicycle wheels have become wider because of extra gears added thereto. This however had the disadvantage that a hub flange adjacent this cassette got shifted more towards a centre of the rear wheel hub. The other hub flange kept its place near the free end of the hub. For bicycle wheel rim designs with centre-drilled spoke mounting apertures this shifting made it necessary to use shorter spokes between the rim and the so-called drive-side (DS) hub flange than between the rim and the so-called non-drive side (NDS) hub flange. The shifting furthermore resulted in a smaller angle at which the DS-spokes got to extend towards their DS-hub flange compared to the NDS-spokes extending towards their NDS-hub flange. In order to keep the rear bicycle wheel sufficiently lateral stiff, this angle change made it necessary to substantially increase the tension of the DS-spokes compared to the tension of the NDS-spokes. This however appeared to have a negative effect on the lifespan of the wheel.

In order to overcome those disadvantages, rims were developed of the off-centre type. In this type of rim, the spokes no longer connected to a centre of the rim, but instead the spoke connections with the rim were shifted slightly towards the NDS. This made it possible to use substantially evenly long spokes both at the DS and NDS, while at the same time keeping their angles relative to the radial direction substantially the same. This made it possible to tension those DS- and NDS-spokes more evenly, which helped to improve the strength and stiffness of the wheel and in particular keep its rim sufficiently strong against lateral loads. Also it gave the wheel a longer durability.

This off-centre positioning of the spoke mounting apertures got known for extruded metal alloy rims, see for example US 5,228,756, as well as for moulded carbon-fibre rims, see for example US 2014/0292061. The off-centre type extruded metal alloy rims were cheaper to manufacture compared to the off-centre type moulded carbon-fibre rims, but had the important disadvantage that their aerodynamic behaviour left to be desired.

The off-centre type carbon-fibre rim as is shown in fig. 4b, 5b, 6b and 7b of US 2014/0292061 for four differently dimensioned variants correspond to the off-centre type carbon-fibre rim according to the preamble of claim 1. Each of those known rim variants have cross-sectional profiles with an annular radially outer wall part that forms a tire bed. An imaginary central plane extends in a radial direction through the middle of this tire bed. The outer wall part connects to a left NDS and a right DS annular flange wall part. The right DS flange wall part extends gradually convexly curved inwardly, whereas the left NDS flange wall part extends more radially orientated. Between the NDS and DS flange wall parts a spoke face with spoke mounting apertures is foreseen. The spoke face is formed by a radially inner wall part with an increased wall thickness relative to adjacent thinner sections of the flange wall parts. The aimed positions for the spoke mounting apertures is off-centre at the NDS relative to the central plane. A disadvantage of those known off-centre type carbon-fibre rim variants is that they are relative difficult and expensive to manufacture, particularly because of their fully asymmetric cross-sectional shape with sharp edged inner wall parts at the transitions with the left and right flange wall parts. Furthermore the aerodynamic characteristics of those known variants leave to be desired, and the spoke mounting apertures are difficult to make in the inner wall part.

The present invention aims to overcome those disadvantages at least partly or to provide a useable alternative. In particular the inventions aims to provide a user-friendly bicycle wheel rim having a more optimized combination of strength, rigidity and aerodynamic behaviour.

This aim is achieved by an off-centre type carbon-fibre rim for a bicycle wheel according to claim 1. This rim has an axis of rotation extending in an axial direction and comprises an annular radially outer wall part forming a tire bed, in which a central plane that lies perpendicular to the axis of rotation extends through a middle of this tire bed. Furthermore the rim comprises an annular radially inner wall part forming a spoke face with spoke mounting apertures extending there through, with which the rim is of the off-centre type in that each of its spoke mounting apertures is provided lateral off-centre in the inner wall part at one side of the central plane. The rim further comprises left and right annular flange wall parts connected to each other by the outer wall part and merging into the inner wall part. The outer, inner and flange wall parts are manufactured out of carbon-fibre material which wall parts together form a profile enclosing a space. According to the inventive thought the left and right flange wall parts lie symmetric at opposing sides of the central plane, such that along at least the flange wall parts and the inner wall part the profile’s outside that is directed away from the enclosed space is symmetrical relative to the central plane, whereas the profile’s inside that is directed towards the enclosed space is asymmetrical relative to the central plane, at least in that the inner wall part is asymmetrical relative to the central plane such that an average wall thickness is greater sideways of the central plane where the off-centre spoke mounting apertures are provided, than sideways of the central plane where the spoke mounting apertures are not provided.

Thus owing to the invention, the off-centre type carbon-fibre rim construction with its symmetric outside and its asymmetric inside now truly combines the advantageous aerodynamics of symmetric rims with the stiffness and strength of asymmetric rims. The carbon-fibre material provides significant freedom in form factor from a designer’s point of view, which advantageously allows for an optimization of the aerodynamic shape of the profile by making crucial parts of its outside shape symmetrical relative to a central plane. Also the lightweight carbon-fibre material makes it possible to keep the weight of the entire rim as low as possible, while its high tensile modulus helps to increase the rim’s stiffness, which reduces power loss when a cyclist transmits energy via the rear cassette to the wheel. If desired, lesser spokes can be used, which also helps to reduce the weight of the wheel, helping the cyclist to use less energy during cycling. The off-centre positioning of the spoke mounting apertures now is possible without causing the profile’s outside to become asymmetric. Instead the off-centre positioning of the spoke mounting apertures can fully be taken care of by strengthening the spoke bed in an asymmetric manner at the inside of the profile. Owing to the off-centre positioning of the spoke mounting apertures the spokes can still be tensioned substantially balanced at its both sides (DS as well as NDS), while at the same time their angles relative to the central plane can be kept substantially equal. Thus the lateral stiffness of a bicycle wheel using the rim according to the invention can be kept substantially equal in both sideways directions. This gives a more compliant and responsive rim behaviour during cycling and a smoother ride for the cyclist. Also it adds to the rider’s safety when cycling at high speed through for example sharp road bends, and it adds to the longevity of a wheel using this type of rim.

In a preferred embodiment the inner wall part can be locally provided with additional carbon-fibre material positioned at the inside. Thus the spoke face area where the spoke mounting apertures for example are to be provided by means of drilling, can locally (off-centre) be reinforced only there where it is deemed necessary, in order to thus prevent the spokes or their nipples to be pulled through during tensioning and/or use.

In a further preferred embodiment the inner wall part’s inside, seen in cross-section, comprises a substantially straight axially extending section and a dented radially inward extending section. The straight axially extending section then provides a proper strengthened supporting face for the spokes or their nipples, whereas the dent helps to save as much weight as possible there where the strengthening is not directly needed.

In an advantageous embodiment the left and right flange wall parts and the inner wall part, seen in cross-section, together form a U-shape, in particular one of which the radial height dimension, also referred to as the depth of the rim, is larger than the axial width dimension, more in particular at least 1.5 times larger. This elongate U-shaped “deep” rim profile helps to increase the rim’s aerodynamic characteristics.

The inner wall part and the flange wall parts preferably gradually merge with each other in such a way that they have a continuous change of curvature along their outside. This also helps to increase the rim’s aerodynamic characteristics, while at the same time helping to increase the rim’s stiffness and rigidity.

In a variant the outer wall part may comprise insertion apertures for the spokes to be inserted via the space into their spoke mounting apertures, which insertion apertures then in particular may be provided lateral off-centre in the outer wall part at the side of the central plane where the spoke mounting apertures are provided. The off-centre positioning of the insertion apertures makes it possible to easily insert and if necessary operate/tension the spokes via the enclosed space, without having to drill truly large holes in the outer wall part which would make it necessary to strengthen it.

In a further embodiment the outer wall part may comprise a concavely curved central section and left and right convexly curved outer sections merging into each other. The advantage hereof is that it provides for a suitably shaped tire bed.

Further preferred embodiments are stated in the dependent subclaims.

The invention also relates to a bicycle wheel comprising an off-centre carbon-fibre rim according to the invention, as well as to a method for manufacturing such an off-centre carbon-fibre rim according to the invention.

The invention shall be explained in more detail below with reference to the accompanying drawings, in which: - Fig. 1 show a cross-sectional view of preferred embodiment of the rim according to the invention; - Fig. 2 shows the rim of fig. 1 with a NDS-spoke inserted through one of its off-centre spoke mounting apertures; - Fig. 3 shows the rim of fig. 1 with a DS-spoke inserted through its off-centre spoke mounting apertures; and - Fig. 4 shows a schematic side view of a rear bicycle wheel comprising the rim of fig. 1 with DS- and NDS-spokes extending towards the hub flanges.

In fig. 1-4 the rim in its entirety has been indicated with the reference numeral 1. The rim 1 comprises an outer wall part 2, a DS-flange wall part 3, a NDS-flange wall part 4, and an inner wall part 5. The wall parts 2-5 are formed by an assembly of suitably positioned carbon-fibre material layers.

The outer wall part 2, the flange wall parts 3, 4 and the inner wall part 5 together define a profile that circumvents an enclosed space 7. With this the flange wall parts 3, 4 and the inner wall part 5 gradually merge with each other and have an ongoing gradually changing curved shape without sharp edged transitions or the like. Together they here define a U-shape, in which the flange wall parts 3, 4 form the legs of the U which extend substantially in a radial direction.

The flange wall parts 3, 4 are connected to the outer wall part 2 at substantially right angles. Past their connection with the outer wall part 2, the flange wall parts 3, 4 extend further radially outwardly and form edges 10 for engaging a tire. The outer wall part 2 at its outside forms a tire bed against which such a tire can rest. For this the outer wall part 2 comprises a concavely curved central section 2’ and left and right convexly curved outer sections 2” merging into each other. The concavely curved central section 2’ is equipped with a number of spoke insertion apertures 11 that are divided around the rim’s circumference.

In fig. 2 a central plane 12 is indicated with a dashed line. This central plane 12 extends in the radial direction perpendicular to a rotation axis RA of the rim 1 (indicated with a dot in fig. 4). The left and right flange wall parts 3, 4 are constructed fully mirror-symmetrical, both on their inside as well as on their outside, relative to the central pane 12. The inner wall part 5 is constructed with a mirror-symmetrical outside shape relative to the central plane 12. The outer wall part 2 is constructed with a mirror-symmetrical inside and outside shape relative to the central plane 12. As follows from the above, the entire profile’s outside shape is mirror-symmetrical relative to the central plane 12. For the profile’s inside shape this however is not the case, because the inner wall part 5 here is constructed with an asymmetrical inside shape relative to the central plane 12. The inner wall part 5, seen in cross-section has a varying thickness that is asymmetrically distributed relative to the central plane 12. Over part of the width of the rim 1 a larger amount of carbon-fibre material has been provided which forms a local thickening 13. This larger amount of carbon-fibre material extends over the full width of a DS-half of the inner wall part 5 (in fig. 1 the right side half), but merely over a small fraction of the NDS-half of the inner wall part 5 (in fig. 1 the left side half). At the DS-half of the rim 1, a dent 14 is provided in the inner wall part’s inside near the transition towards the DS-flange wall part 3. Because of this, the average wall thickness of the inner wall part 5 and thus here also of the entire rim 1, is greater at the NDS of the central plane 12 than at the DS. This specific inside asymmetric construction of the inner wall part 5, causes the profile’s inside shape to be asymmetrical relative to the central plane 12.

Spoke mounting apertures 15 are provided in the inner wall part’s local thickening 13 at a position of a few millimetres off-centre of the central plane 12. This off-centre position is indicated with OC. Like the insertion apertures 11, the spoke mounting apertures 15 are also divided around the rim’s circumference.

As can be seen in fig. 1 the spoke insertion apertures 11 are provided in the outer wall part 2 at a position which is likewise somewhat off-centre of the central plane 12. In this case however the insertion apertures 11 are a few millimetres less off-centre than the mounting apertures 15.

In fig. 2 and 3 it is shown that NDS-spokes 20 respectively DS-spokes 21 are placed into the apertures 15. A thickened head part 23, for example formed by a nipple that can be tensioned, rests against the inside of the local thickening 13 of the inner wall part 5.

In fig. 4 it Is shown that the rim 1 is connected via those DS- and NDS-spokes 20, 21 to flanges of a hub 25.

The carbon-fibre rim 1 preferably is built up out of a plurality of layers of the carbon-fibre material, and which are laid into a suitably shaped mould. The layers already are or then get impregnated with a suitable resin. Subsequently a curing takes place in the mould. As a final step the spoke insertion and mounting apertures 11 and 15 can then be provided, for example by means of drilling, in the outer and inner wall parts 2, 5.

With this, the wall parts 2, 3, 4, 5 advantageously may get to share one or more layers of the carbon-fibre material. For example for the flange wall parts 3, 4 and the inner wall part 5 such shared layers then may get to extend all around the U-shape giving good integrity to the rim there. By placing those shared layers at the outside of the U-shape, a smooth surface is automatically obtained there. Besides those outside layers forming the flange wall parts and inner wall part, one or more additional layers may get locally positioned at the inside of the inner wall part 5 for forming the local thickening 13.

The outer wall part 2 may be formed by a plurality of layers of which the outermost are kept somewhat longer than intermediate ones such that their surplus sections can be used to be angled and laid against layers of the flange wall parts 3, 4. Thus it is automatically obtained there that thickened sections are formed at the transitions of the left and right flange wall parts 3, 4 with the outer wall part 2. This particularly may be advantageous when those transitional sections are destined to be used as breaking surfaces.

Besides the embodiments shown numerous variants are possible. For example the shape and dimensioning of the rim’s cross-section can be changed. Instead of having the tire bed being of the clincher type it is also possible to use the inventive thought for a tubular type tire bed. The inventive rim is not only suitable to be used for rear bicycle wheels. It can also be used for front wheels when an off-centre positioning of the spokes is desired there while at the same time maintaining an asymmetry for the rim’s outside shape. Besides the inner wall part’s inside shape being asymmetrical, it is also possible to make the flange wall part’s insides and/or the outer wall part’s inside or outside asymmetrical if this is deemed necessary for other purposes. Important is that the profile’s outside shape that directly gets in contact with the air during cycling remains as symmetrical as possible in order to keep its aerodynamic behaviour as optimal as possible.

Thus the invention provides a new symmetric/asymmetric rim construction that can easily and quickly be designed and manufactured for all kinds of cycling sports, particularly there where speed, strength and weight are crucial factors.

Claims (11)

A eccentric-type carbon fiber rim for a bicycle wheel, the rim having an axis of rotation, comprising: an annular wall portion located radially outside forming a bed for a tire, a central plane extending perpendicular to the axis of rotation extending through a center of the tire bed; an annular wall part in radial direction forming a spoke surface with spoke mounting recesses extending therethrough, the rim being of the eccentric type in that each of the spoke mounting recesses is provided eccentrically laterally on one side of the central plane in the inner wall part; left and right annular flange wall parts that are connected to each other by the outer wall part and which merge into the inner wall part; wherein the outer wall parts, inner wall parts and flange wall parts are made of carbon fiber material which wall parts together form a profile enclosing a space, characterized in that the left and right flange wall parts lie symmetrically on opposite sides of the central plane, along at least the flange wall parts and along the inner wall part, the outside of the profile, which is directed away from the closed space, is symmetrical with respect to the central plane, and the inside of the profile, which is directed towards the closed space, is asymmetrical with respect to the central plane, at least because the inside of the inner wall part is asymmetrical with respect to the central plane such that its average wall thickness is greater laterally of the central plane where the eccentric spoke mounting recesses are provided, than laterally of the central plane where the spoke mounting recesses are not provided n. Carbon fiber rim of the eccentric type according to claim 1, wherein the inner wall part is locally provided with additional carbon fiber material which is provided on the inside. An eccentric type carbon fiber rim according to any one of the preceding claims, wherein, viewed in cross-section, the inside of the inner wall part comprises a section extending substantially straight in the axial direction and a dented section extending inward in the radial direction. Carbon fiber rim of the eccentric type according to one of the preceding claims, wherein, viewed in cross-section, the left and right flange wall parts and the inner wall part together form a U-shape, in particular a U-shape whose radial height dimension is greater than the axial width dimension, more in particular at least one and a half times larger. 5. An eccentric type carbon fiber rim according to any one of the preceding claims, wherein the interlocking inner wall parts and flange wall parts have a continuous change of curvature along their outer side. 6. Eccentric type carbon fiber rim according to one of the preceding claims, wherein the outer wall part comprises insert recesses for inserting the spokes into their spoke mounting recesses through the space, which insert recesses are in particular laterally eccentrically provided in the outer wall part at the side of the central plane where the spoke mounting recesses are provided. An eccentric type carbon fiber rim according to any one of the preceding claims, wherein the outer wall portion comprises a concave curved central section and left and right convex curved outer sections that merge. An eccentric type carbon fiber rim according to any one of the preceding claims, wherein the left and right flange wall portions extend beyond their connection to the outer wall portion in radial direction further outward to form edges for engaging a tire. An eccentric type carbon fiber rim according to any one of the preceding claims, wherein the left and right flange wall portions have thickened sections at their connections to the outer wall portion. A bicycle wheel comprising an eccentric type carbon fiber rim according to any one of the preceding claims. A method for manufacturing an eccentric type carbon fiber rim according to any one of the preceding claims.