GB2525931A

GB2525931A - Disc wheel

Info

Publication number: GB2525931A
Application number: GB1408259.8A
Authority: GB
Inventors: Simon Smart; Robert Neumann
Original assignee: Smart Aero Technology Ltd
Current assignee: Smart Aero Technology Ltd
Priority date: 2014-05-09
Filing date: 2014-05-09
Publication date: 2015-11-11
Anticipated expiration: 2034-05-09
Also published as: GB2525931A8; GB2525931B; GB201408259D0

Abstract

A disc wheel comprises a central hub shell (4), a circumferential rim (7), first and second side walls (6) that extend from the hub shell to the rim and define a void between the side walls, and a plurality of reinforcing ribs (8) located within the void. Each rib (8) comprises a web of reinforcing material that extends across the void and interconnects the side walls (6) on opposite sides of the void. Each rib (8) extends outwards from an inner end located adjacent the hub shell (4) to an outer end located adjacent the rim (7).

Description

DISC WHEEL

The present inventiirn relates to a disc wheel and in particular but not cxc] usivey to a disc *hcei for a bicycle. in a preferred embodiment the invention relates to a bicycle wheel that is suitable for racing purposes.

A traditional bicycle wheel includes a steel or aluminium rim, a central huh and a plurality of wire spokes that connect the rim to the hub.

In recent years. there has been a move with racing bicycles to replace spoked wheels with disc wheels, in which the rim and the huh are connected by a pair oF diseshaped side walls. These disc wheels can provide improved aerodynamic efficiency over spoked wheels. The sid' vails are Frequently made from a composite material, for example a carbon fibre reinforced polymer, for strength and light wcight. The void between the side wails may be empty or it may be wholly or partially filled with a structural foam material.

US 473242 describes bicycle wheel formed from two aluminium or caithon fibre half shells with a hollow interior.

US 2004/0135424A describes a bicycle wheel having a pair of carbon fibre side surfaces, wherein the interior of die wheel is filled with a honeycomb type core, Disc wheels having carbon fibre side walls have therefore been used for some time. Such wheels can he extremely light and aerodynamically efficient, hut need to he stiffbned against latcral hcnding forces (the tcrm "lateral bending force' as uscd herein means a force thai tends to deform die wheel so that part of the wheel no longer lies in a plane that is perpendteu]ar to its axis of rotation). In use, bicycle wheels can he subjected to lateral bending forces when the rider tilts the bicycle from one side to the other as pressure is applied alternately to the pedals. If the wheel does not have sufficient lateral rigidity this can interfere with operation of the brakes and can result in poor power transfer through the wheel to the ground.

It is known to increase the stitThess of a disc wheel either by injecting rigid structural foam into the void between the side walls, or by increasing the thickness of the side walls.

However, these solutions both increase the weight of the wheel. In addition, both solutions tend to increase the radial rigidity of the wheel as well as the lateral rigidity. As a result the wheel may transmit vibrations from the ground to the rider, producing a very harsh ride. These vibrations can cause fatigue and poor power transmission to the ground. for example if it causes the wheel to skip over the ground surface.

There is therefore a need for a disc wheel that has good lateral rigidity hut a reasonable amount of radial compliance (that is, limited radial rigidity), but without a substantially increased weight.

IS According to one aspect of the present invention there is provided a disc wheel comprising a central hub shell, a circumferential rim, first and second side walls that extend from the hub shell to the rim and define a void between the side walls, and a plurality of reinforcing ribs located within the void, wherein each rib comprises a web of reinforcing material that extends across the void and interconnects the side walls on opposite sides of the void, and wherein each rib extends outwards from an inner end located adjacent the hub shell to an outer end located adjacent the rim.

Thc radial ribs provided in the void extend across the void and connect the side walls to one another. This helps to prevent flexing of the side walls, which usually consists of highly flexible carbon fibre skins, and greatly increases the lateral strength of the wheel, but without significantly increasing its radial stiffness. Therefore, the wheel transmits power well and also provides a more comfortable ride, producing less fatigue for the rider.

The wheel can also be very light and aerodynamically efficient.

Advantageously, the side walls and/or the ribs are made of composite materials, for example carbon fibre reinforced polymer materials, Preferably, the ribs arc made of a composite material that includes a woven fibre reinforcing thbric, for bi-axial strength and stiffliess. Preferably, each side wall includes unidirectional reinforcing fibres, which arc prefcrably arranged substantially radially, for high radial strength. The rim preferably includes a woven fibre reinforcing fabric for increased radial and tangential strength, allowing it to sustain high stresses resulting from contact with the road and the action of the brakes.

Advantageously, the inner ends of the ribs are connected to the hub shell, for increased strength. Advantageously, the outer ends of the ribs are connected to the rim, also for increased strength. However, it is not essential that the ribs extend through the full radial extend of the wheel.

Advantageously, the rim includes at least one cylindrical flange that is provided on an inner surface of at least one of the side walls, the rim preferably forming a unitary constniction with the side wall.

Advantageously, each reinforcing rib extends substantially radially from the hub shell to IS the rim, or is inclined relative to a radius at an angle not exceeding 15°, preferably no more than 100.

Advantageously, each rib includes a central web and a perpendicular flange on each edge of the web, which is bonded to a respective side wall. The rib may for example have an I-shaped profile or C-shaped or Z-shaped profile.

Advantageously, each reinforcing rib includes one or more apertures for reduced weight, without compromising the strength of the wheel.

Advantageously, the side walls converge in the direction of increasing radius, for increased lateral strengt& Advantageously, the wheel is a bicycle wheel having a diameter of at least 400mm, optionally greater than 550mm, preferably for a racing bicycle.

Advantageously, the weight of the wheel including the hub shell is less than I 000grms, preferably less than SOOgrams, An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is an exploded isometric view ora disc wheel; Figure 2 is a side view of the wheel, showing in broken lines some internal constructional details of the wheel; Figure 3 is a front view of the wheel; Figure 4 is a sectional view on lineAA of Figure 2; Figure 5 is a sectional view on line BB of Figure 2; Figure 6 is a sectional view on line CC of Figure 2, and Figures 7a to 7e illustrate graphically the results of a set of test carried out with a disc according to an embodiment of the invention and a number of comparative conventional disc whccls.

The wheel 2 shown in Figures 1-6 includes a central hub shell 4, two disc-shapcd side walls 6, a rim 7 and a plurality of reinforcing ribs 8 located in a void 10 between the two side walls 6.

The hub shell 4 may for example be made of aluminium alloy, titanium alloy, a composite material or any other suitable material. It includes a cylindrical bore 12 that receives an axle and bearings (not shown) that allow the wheel 2 to rotate about the axle. The spindle and bearings may be conventional and will not therefore be described further. On its outer surface the hub shell 4 carries a pair of radial flanges 14 to which the side walls 6 are attached.

The side walls 6 are disc-shaped (annular) and extend radially from a central hole 15 having an inner diameter that corresponds to the outer diameter of the main body of the hub tell 4, to the circular rim 7 that provides the outer diameter of the wheel 2. The side walls 6 converge in the direction of increasing radius, the separation of the walls being greater near thc hub shell 4 than at the rim 7. This helps to increase thc lateral stiffness of thewheel2.

The side walls 6 may be made of any suitable material, preferably a composite material. In a preferred cmbodimcnt the sidc walls are made of a carbon fibre reinforccd polymer material comprising a mat of carbon fibres in a polymer matrix. Preferably, a unidirectional carbon fibre mat is used for the side waits 6, which is bid in sections so that the fibres extend substanLially radially from the hub shell 4 towards the rim 7 of the wheel 2. The side walls 6 may for example include two plies of T800 grade carbon fibre cloth, providing a wall thickness of approximately 0.5mm.

Each side wall 6 includes at its outer edge a cylindrical flange 16 that extends inwards from the inner lice of the side wall 6. The radius of the flange 16 is slightly less than the radius of the side wall 6 (for example about 5mm less), so that the outermost part 18 of the side wall 6 extends outwards beyond the flange. When the two side walls 6 are joined togcther the edges of the flanges 16 are bonded together providing a channel 20 for receiving a pneumatic tyre (not shown). The outermost parts 18 of the side walls 6 preferably include an additional layer of carbon fibre reinforcing material, for example consisting of woven carbon fibre fabric, to providc additional strength so that the wheel can withstand the stresses applied in use by a braking mechanism.

The reinforcing ribs 8 extend substantially radially from the hub shell 4 to the rim 7 of the wheel 2. In the embodiment shown in the drawings ten ribs 8 are provided, which are spaced apart by an angle of 36°. However, more or fewer ribs may be provided. We have found that the number of ribs 8 is preferably in the rangeS to 25, more preferably 10 to 20.

Also, although in the embodiment the ribs 8 extend exactly radially from the hub shell 4 to the rim 7, they may alternatively be inclined forwards or backwards, for example at an angle of up to 15°.

Each rib 8 is preferably made of a similar composite material to that of the side walls 6, For example, the ribs 8 may be made of a carbon fibre composite material. Preferably, the carbon fibre reinforcing material is a woven carbon fibre fabric, typically a 3K weave.

Each rib 8 extends across the void 10 between the side waIls 6 and is bonded to the inner faces of the side walls 6 to interconnect the side walls. This helps to prevent relative movement of the side walls 6 and greatly increases the lateral stiffness of the wheel 2. In the embodiment shown in the drawings each rib is I-shaped in cross-section and comprises a central web 22 and two peipendicular flanges 24, which are bonded to the side walls 6.

Other proffles are of course possible. For example, the ribs 8 may be C-shaped or Z-shaped in cross-section, or any other suitable profile.

In this embodiment the ribs 8 extend through the full radius of the wheel 2, from the hub shell 4 to the rim 7. Alternatively, the ribs 8 may extend through only part of the radius of the wheel 2. The ribs 8 may also include one or more apertures in the web 22 in order to reduce the weight of the wheel but without significantly reducing its lateral stiffness.

Typically, the weight of the wheel 2 including the hub shell 4 is approximately 740grms.

The weight excluding the hub shell 4 is about 69Ogrms.

The wheel 2 is assembled by separately moulding the side walls 6 and the ribs 8. A first one of the side walls 6 is then placed in ajig and the hub shell 4 is located in the centre of the first side wall 6 and is bonded to the side wall 6. The ribs 8 are then positioned on the side wall 6 in the correct locations as defined by the jig and bonded to the inner surface of the side wall 6 and to the hub shell 4 using a suitable adhesive. When all of the ribs 8 have been bonded into position the second side wall 6 is located in position on top of the first side wall, and it is bonded to the ribs 8 and the hub shell 4. The inner edges of the flanges 16 of the first and second side walls are simultaneously bonded to one another. Once the adhesive has cured the assembled wheel 2 is removed from the jig and sent for any required finishing processes.

Test results In order to assess the qualities of a disc wheel according to an embodiment of the invention, a series of quantitative and qualitative test were carried out, comparing the embodiment disc wheel (referred to below as "Smart Disc #5") to a number of leading conventional disc wheels: a HED StingerTM disc wheel, a Zipp Super 9Th1 disc wheel and a LightweightW disc wheel from CarboSports GmbH.

The quantitative measurements involved weighing the wheel and measuring the lateral stillness of the wheel by loading the wheel transversely at its rim and measuring the deflection of the wheel rim at the loading point. The subjective test involved asking a group of experienced cyclist to score the wheels subjectively out of a maximum score of 5 for perceived lateral stiffness, acceleration capability and vertical compliance. The results of these subjective tests were then averaged to provide the scores indicated in table I below, The results of Le quantitative and subjective tests arc shown graphically in Figs. 7a-7c, and in tabular form in Table II below, fable I Quantitative results Stibjeclive score totals Product Weight Drive side Non-drtve Lateral Acceleration Vertical stillness sme stithcss stillness compliance Grains /mm N/mm Max 5 Max 5 Max 5 Max 5 Smart Disc I5 893 62.39 65.71 4.0 4.3 4.8 lIED Stinger 1220 44.21 4421 30 3.0 3.5 Lipp Super 9 1015 48.76 46.14 3.8 3.0 5.0 Lightweight 802 5924 57.85 4.0 4.3 3.3 As can he seen from the quantitative resuLts above, although the embodiment disc wheel (Smart Disc #5) was one of the lightest wheels, on test, it had the greatest lateral stiffness on both the drive side and the non-drive side. This result was confirmed by the subjective test scores., where it achieved an equa top score with [lie Lightweight wheel, The embodiment wheel also achieved an equal top score with the Lightweight wheel in the acceleration test. However, it was ranked higher than any of the other wheels in the vertical compliance test, indicating that it provided the most comfortable ride with least vibration-induced fatigue.

Claims

CLAIMS1. A disc wheel comprising a central hub shell, a circumferential rim, lust and second side walls that extend from the hub shell to the rim and define a void between the side walls, and a plurality of reinforcing ribs located within the void, wherein each rib comprises a web of reinforcing material that extends across the void and interconnects the side walls on opposite sides of the void, and wherein each rib extends outwards from an liner end located adjacent the hub shell to an outer end located adjacent the rim.
2, A disc wheel according to claim I in which the side walls and/or the ribs are made of composite materials.
3. A disc wheel according to claim 2 wherein the ribs are made of a composite material that includes a woven fibre reinforcing fabric.
4. A disc wheel according to claim 2 or claim in which each side wall includes unidirectional reinforcing fibres.
5. A disc wheel according to any one of claims 2 to 4 in which the rim includes a
6. A disc wheel according to any one of the preceding claims in which the inner ends of the ribs are connected to the hub shell,
7. A disc wheel according to any one of the preceding claims in which the outer ends of thc ribs arc connected to the rim.
8. A disc wheel according to any one of the preceding claims in which the rim includes a cylindrical flange provided on an inner surface of at least one of the side walls.
9. A disc wheel according to any one of the preceding claims in which each reinforcing rib extends substantially radially from the 1mb shell to the rim, or is inclined relative lo a radius at an angle not exceeding 15°.
10. A disc wheel according to any one of the preceding claims in which each rib includes a central web arid a perpendicular flange on each edge ol the web, which is bonded to a respective side waLl.11 A disc wheel according to any one of the preceding claims in which each reinforcing rib includes one or more apertures.12. A disc wheel according to any one of the preceding claims, in which the side walls converge in the direction of increasing radius, 13. A disc wheel according to any one of the preceding eainis, wherein the wheel is a bicycle wheel having a diameter of at least 400mm.14. i-\ disc wheel according to any one of the preceding claims, wherein the weight of the wheel including the huh shell is less than I 000grms, preFerably less than SOOgrams.