GB2409886A - Ventilated disc brake rotor - Google Patents

Abstract

A ventilated disc brake rotor 1 has an inner flange portion 4 containing a plural number N of axial fixing holes 5. This flange portion 4 extends radially outwards into an integral annular braking portion having axially opposed friction surfaces 6. The rotor contains at least 6N ventilation channels 7a, 7b passing between its inner periphery 2 and outer periphery 3, the axial widths of these channels not exceeding one quarter of the axial thickness of the annular braking porion. The inner ends of the channels are preferably arranged to meet in groups of six or more at air collection recesses 8. The high ventilated surface area of the rotors results in a particularly high heat transfer coefficient combined with good mechanical strength and structural integrity.

Description

- 1 2409886 Improvements in or relating to ventilated disc brake rotors

The present invention relates to brake rotors for use in disc brake systems, more particularly to ventilated disc brake rotors exhibiting improved air cooling, for example during repeated and/or high energy braking.

As is well known, braking systems normally operate through dissipation of kinetic energy of a moving object, predominantly through conversion to heat.

Provision should desirably be made for removal of heat so generated, since excessive temperature rises may lead to reduced braking efficiency and/or to undue wear, degradation or distortion of brake components. This is especially the case with brake systems intended for frequent and repetitive use, for example disc brakes for motor vehicles, particularly for high performance motor vehicles such as sports or racing cars.

A common technique for cooling disc brake systems is to employ ventilated brake rotors. These are typically made from conventional materials such as metals (e.g. cast iron or steel) and usually consist of two parallel circular discs or rings, the outer faces of which form the friction surfaces. The discs or rings are spaced at a distance from each other by a series of studs or vanes; straight or curved air channels are thereby formed within the space between the friction surfaces. Air is forced through the channels as the rotor rotates, thereby removing excess heat from the rotor and cooling the brake assembly. Such ventilated metal discs are typically prefabricated by casting or welding.

Examples of representative ventilated metal disc brake rotors of this type are described in US Patents Nos. 5,109,960; 5,492,205; 5,544,726 and 5,626,211. - 2

Other designs include single metal discs having ventilation channels running radially from the inner periphery to the outside circumferential surface (see, for example, US Patent No. 6,321,885) or axially from one friction face to the other (see, for example, US Patent No. 6,422,358).

Interest has also been shown in the use of alternative materials such as carbon, graphite, carbon- carbon fibre composites, silicon carbide-carbon fibre composites, metal matrix composites (e.g. aluminium alloy matrix composite materials, for example with particulate silicon carbide reinforcement), ceramic- carbon fibre composites and combinations thereof, since this may permit the manufacture of disc brake rotors combining lower weight with greater mechanical strength and improved friction and wear properties. It will be appreciated that such materials may require different fabrication techniques from methods such as casting and welding typically used in the manufacture of conventional metal rotors.

Carbon-carbon fibre composite materials, optionally containing additives such as ceramics, have attracted particular attention by virtue of their low weight, high strength and ability to maintain their physical and frictional properties at high temperatures. At temperatures in excess of 500 C, however, such materials become increasingly susceptible to oxidation; at around 800 C the rate of oxidation is limited only by the rate of diffusion of oxygen through the gas surrounding the material. Excessive thermal stress may also cause brake rotors made from such composites to crack or warp. It is therefore generally necessary to provide for cooling of such rotors, since energy dissipation on braking can result in temperature rises of over 1000 C in uncooled systems.

One design of ventilated composite disc brake rotor used by Porsche comprises a silicon carbide--carbon fibre composite rotor having a number of relatively large ventilation slots passing approximately radially through the rotor. A plurality of small axial perforations pass from the friction surfaces of the rotor into each slot.

It will be appreciated that the manufacture of such slotted and drilled rotors is necessarily somewhat complex.

Another design of carbon-carbon fibre composite brake disc rotor (manufactured by Brembo of Italy) comprises an array of ventilation holes drilled approximately radially between the inner and outer peripheries of the rotor, the diameters of the holes being approximately one third of the axial thickness of the rotor. The holes are arranged so that their outer ends are uniformly spaced around the circumference of the outer periphery of the rotor, whilst being angled to meet in groups of three at the inner periphery. This arrangement is thought to enhance both mechanical integrity and air catchment. Thus, by grouping the ventilation holes at the inner periphery, it is possible to ensure that they avoid contact with the axial fixing holes which are normally provided in an annular flange portion adjacent the inner periphery of the rotor in order to permit its attachment to a hub assembly, thereby maintaining the structural integrity of the rotor. The areas of the inner periphery at which the grouped inner ends of ventilation holes meet may conveniently be shaped so as to enhance air catchment when the rotor is turned. These areas are typically each positioned so as to be equidistantly spaced between adjacent pairs of the above-mentioned fixing holes; since the ventilation holes meet in groups of three at these areas, a rotor of this type having N fixing holes will contain 3N ventilation holes.

The present invention is based on the finding that air cooling of disc brake rotors having a similar general pattern of ventilation holes or other form of - 4 - ventilation channels may be improved to an unexpectedly advantageous extent by substantially increasing the number of ventilation channels whilst concomitantly reducing their dimensions, e.g. by increasing the number of channels fourfold whilst halving their dimensions.

Thus it has been found that such modifications significantly increase the ventilated surface area available for cooling whilst maintaining the overall rate of air flow through the ventilation channels. In this way the heat transfer coefficient at interfaces between cooling air and the ventilated surfaces to be cooled may be increased without compromising the mechanical and structural integrity of the rotor.

Rotors in accordance with the invention may be manufactured with high precision using simple procedures and may exhibit beneficially high resistance to pressure- and/or heat-induced distortion.

Thus according to one aspect of the invention there is provided a ventilated disc brake rotor having radially opposed inner and outer peripheries and comprising an annular flange portion having a plural number N of axial fixing holes permitting fixable attachment of the rotor to a rotatable hub, said flange portion extending radially outwards into an annular braking portion integral therewith, said braking portion having axially opposed friction surfaces, wherein said rotor contains at least EN ventilation channels passing between said inner and outer peripheries, and wherein the axial widths of said ventilation channels do not exceed one quarter of the axial thickness of the braking portion.

Brake rotors according to the invention may comprise any appropriate structural material including, for example, metals such as iron or steel and materials such as carbon, graphite, inorganic glasses, ceramics, carbon-carbon fibre composites (including carbon- graphite fibre composites), silicon carbide-carbon fibre - 5 - composites, metal matrix composites (e.g. metal containing carbon matrix composites or metal matrix composites reinforced with fibres or particles of ceramic, carbon or metal materials, for example as in aluminium reinforced with alumina fibres), carbon fibre composites, ceramic-carbon fibre composites, ceramic ceramic fibre composites, polymer matrix composites (e.g. comprising an appropriate thermoplastic or thermoses polymer matrix reinforced with ceramic, carbon or metal fibres) or combinations thereof, optionally together with one or more additives serving to enhance friction properties, reduce wear and/or protect against oxidation. The use of low density materials such as carbon-carbon fibre composites is preferred; however, the particularly effective ventilation of brake rotors which may be achieved in accordance with the invention also permits the use of materials with lower temperature stability, for example polymer-, metalor glass-based systems.

In one preferred embodiment of the invention the rotor contains at least ION ventilation channels having axial widths not exceeding one fifth of the axial thickness of the braking portion.

More generally the ventilation channels may, for example, advantageously be arranged in one, two, three or more radial layers wherein the layers are positioned so as to have axial symmetry within the rotor. Thus, for example, the channels may be arranged in a single layer passing through the axial midpoint of the rotor or in two layers respectively positioned equidistantly from their adjacent friction surface (and preferably also from each other).

The ventilation channels may conveniently be parallel to the friction surfaces of the rotor, but may alternatively be inclined to the plane of these surfaces. Thus, for example, in embodiments in which the channels are arranged in two or more layers the - 6 - outer ends of the channels of a particular layer may be further from, or more preferably nearer to, the adjacent friction surface than are the inner ends.

The outer ends of the ventilation channels within any individual layer as described above are preferably uniformly spaced around the circumference of the outer periphery of the rotor. Where the channels are arranged in two or more layers, the outer ends of the channels within a particular layer may advantageously be circumferentially staggered relative to the outer ends of the channels within the adjacent layer or layers, since this may enhance uniformity of cooling.

It is preferred that the inner ends of the ventilation channels meet in groups of 6, 8, 9, 12, 15, 18 or more at air collection recesses formed in or adjacent to the inner periphery of the rotor. Such recesses may advantageously be shaped to enhance air catchment when the rotor is turned and are preferably symmetrically positioned between the axial fixing holes within the flange portion of the rotor.

Where the ventilation channels are arranged in a plurality of radial layers it is preferred that each air collection recess meets with grouped inner ends of channels from all such layers.

The ventilation channels advantageously all have the same dimensions, since this simplifies fabrication of the rotors and thereby keeps costs to a minimum. In some embodiments of the invention the channels may, however, be of differing dimensions; when this is the case the larger channels will preferably be positioned nearer to the centre of the axial thickness of the rotor while the smaller channels will preferably be nearer to the friction surfaces.

For ease of manufacture it is preferred that the ventilation channels have circular cross-section, since such channels may be formed by simple drilling operations. Other forms of ventilation channel, for example having oval, rectangular or square cross- - sections may, however, be produced, e.g. using appropriate machining or moulding procedures.

It may be advantageous to coat one or more exposed surfaces of a disc brake rotor according to the invention with an oxidation-reducing coating. This is particularly the case where the rotor comprises a carbon-carbon fibre composite material since, as noted above, such materials become increasingly susceptible to oxidation at temperatures in excess of 500 C. Such coatings may act to prevent or at least reduce the oxidative effect of atmospheric oxygen contacting the rotor and/or to inhibit penetration of oxygen into the rotor, e.g. by diffusion or by permeation through cracks and/or pores within the structure of the rotor.

In general coatings may be continuous or non- continuous and may be sacrificial or non-sacrificial.

Thus, for example, they may act as a scavenger for reactive gases such as oxygen or carbon dioxide, as an anticatalyst or poisoner of oxidation reactions, or as a barrier with low permeability to reactive gases such as oxygen or carbon dioxide. It will be appreciated that a coating may be unreactive with the structural material of a rotor or may react with one or more components of the structural material, for example with a matrix material and/or with an infiltrate or reinforcement (e.g. in fibre form) therewithin.

Coatings may, for example, be applied by methods such as impregnation, dipping, painting, chemical vapour deposition, chemical vapour infiltration or chemical vapour reaction and may, for example, include materials such as silicon carbide, boron, boron carbide or boron nitride. Such coatings may advantageously be applied to all exposed surfaces of the rotor, optionally apart from the friction surfaces (i.e. including the surfaces of the ventilation channels). It will be appreciated that the coating material(s) should not adversely react with - 8 or catalyse reactions with the structural material of the rotor.

Representative coatings include melting glazes containing boron or phosphorus, e.g. mixed with powders such as silica alumina or silicon carbide. These may be applied as a paint or dip coating and may provide oxidation protection at temperatures up to about 1000 C.

Another form of coating comprises finely divided powder of materials such as boron, silicon or silicon carbide dispersed in a thermosetting resin and cured under high temperature oxidising conditions, whereby the powdered material is oxidised to form a glaze. This glaze may block cracks and/or pores at exposed surfaces of the rotor so as to inhibit oxygen permeation.

Antioxidant paints of this type are available from, for example, Dunlop Aviation Braking Systems (e.g. as product DMS745) and have been found to give good protection following application of a single coating (e.g. using a flexible foam or flexible fibre-covered wire brush to ensure thin, even covering of the surfaces of the ventilation channels) and high temperature curing (e.g. at a temperature of about 340 C).

Carbon-carbon fibre composites may also be protected against oxidation by impregnation with phosphates, for example as described in US Patent No.

5,853,821 or the prior art referred to therein.

Coatings on exposed surfaces of the rotor may advantageously be designed to ensure optimum heat transfer from the rotor to surrounding air, for example by using a coating material which has greater thermal conductivity than the structural material of the rotor and/or by selecting a coating thickness which optimisms heat transfer.

In the accompanying drawings, which serve to illustrate the invention without in any way limiting the same, Fig. 1 is a perspective view of a brake rotor suitable for use in a motor vehicle, and Fig. 2 is a - 9 semisectional view of the same rotor.

Referring to the drawings in more detail, rotor 1 has inner periphery 2 and outer periphery 3. Annular flange portion 4 incorporates axial fixing holes 5 which permit the rotor to be attached to a rotatable hub by means of, for example, appropriate bolts, studs or clamping means. Surface 6 is one of the axially opposed friction surfaces of the annular braking portion of the rotor. Circular cross-sectioned ventilation channels are arranged in two axially symmetric layers 7a and 7b, the outer ends of the channels of the two layers respectively being circumferentially staggered as shown.

The inner ends of the channels in each layer meet in groups of six at air collection recesses 8, which are equidistantly positioned around the inner periphery 2 between fixing holes 5; since there are two layers of ventilation channels, each recess 8 meets with the inner ends of a total of twelve channels. - 10

Claims (13)

1. Claims: 1. A ventilated disc brake rotor (1) having radially opposed inner

   and outer peripheries (2, 3) and comprising an annular flange portion (4) having a plural number N of axial fixing holes (5) permitting fixable attachment of the rotor to a rotatable hub, said flange portion (4) extending radially outwards into an annular braking portion integral therewith, said braking portion having axially opposed friction surfaces (6), wherein said rotor contains at least EN ventilation channels (7a, 7b) passing between said inner and outer peripheries (2, 3), and wherein the axial widths of said ventilation channels (7a, 7b) do not exceed one quarter of the axial thickness of the braking portion.
2. 2. A rotor as claimed in claim 1 wherein the rotor (1) contains at least ION ventilation channels (7a, 7b) having axial widths not exceeding one fifth of the axial thickness of the braking portion.
3. 3. A rotor as claimed in claim 1 or claim 2 wherein said ventilation channels (7a, 7b) are arranged in one or more radial layers, said layer or layers being positioned so as to have axial symmetry within the rotor.
4. 4. A rotor as claimed in claim 3 having two layers of ventilation channels (7a, 7b), each of said layers respectively being equidistant from the adjacent friction surface of the braking portion.
5. 5. A rotor as claimed in claim 3 or claim 4 wherein the outer ends of the ventilation channels (7a, 7b) of each said layer are uniformly spaced around the circumference of the outer periphery (3) of the rotor.

   - 11 -
6. 6. A rotor as claimed in claim 5 having at least two layers of ventilation channels (7a, 7b), wherein the outer ends of the ventilation channels of each layer are circumferentially staggered relative to the outer ends of the ventilation channels of the adjacent layer or layers.
7. 7. A rotor as claimed in any of the preceding claims wherein the inner ends of the ventilation channels meet in groups of six or more at air collection recesses (8) in the inner periphery (2) of the rotor (1).
8. 8. A rotor as claimed in claim 7 wherein said recesses (8) are symmetrically positioned between the axial fixing holes (5) of the flange portion.
9. 9. A rotor as claimed in claim 7 or claim 8 wherein each air collection recess (8) meets with grouped inner ends of ventilation channels from two or more radial layers (7a, 7b).
10. 10. A rotor as claimed in any of the preceding claims wherein the ventilation channels have circular cross- section.
11. 11. A rotor as claimed in any of the preceding claims wherein at least one exposed surface of the rotor (1) is at least partially coated with an oxidation-reducing coating.
12. 12. A rotor as claimed in claim 11 wherein all exposed surfaces of the rotor (1) other than the friction surfaces (6) are coated with an oxidation-reducing coating.
13. 13. A rotor as claimed in claim 11 or claim 12 wherein said oxidationreducing coating is such as also to - 12 increase the heat transfer coefficient of said surfaces.