AU2002334092A1 - Rotor disc for a disc brake - Google Patents

Description

ROTOR DISC FOR A DISC BRAKE

The present invention relates to a rotor disc, particularly, but not

exclusively for a disc brake and the like.

Traditionally, brake discs have been made of cast iron. Cast iron

exhibits the necessary thermal and strength characteristics for this purpose.

A disadvantage, however, is its weight. In an average motor vehicle with

disc brakes on all four wheels the rotor discs of the brakes may add 40 kg

to the weight of the vehicle. This weight is carried permanently around

with the vehicle, although the brakes may be used relatively infrequently,

thus adding to fuel consumption and emissions. Making discs of other

lighter materials has been proposed but so far a satisfactory solution has not

yet been found. For example, aluminium has been suggested but although

its thermal properties are good they are not as good as those of cast iron.

These poorer thermal characteristics adversely affect the performance of the

material as a rotor disc.

According to the present invention there is provided a composite rotor

disc comprising a substrate made of a thermally conductive material, a first

coating layer on at least one circular face of the disc, the first coating layer

being made of a thermally insulating material and a second coating layer

superposed on the first coating layer, the second coating layer being made

of a wear resistant, thermally conductive material whereby the substrate is

protected from heat generated at the circular surface of the disc. In a preferred embodiment of the invention, the substrate is

advantageously aluminium or other suitable metal or metallic alloy. The first

coating layer may advantageously be Zirconia or other ceramic. The second

coating layer may advantageously be a carbon-silicon carbide composite or

other metallic alloy. The thicknesses of the layers and substrate

advantageously lie in the following ranges. Layers 0.01 to 2.00mm

substrate 5-40mm

In order that the invention may be more clearly understood

embodiments thereof will now be described, by way of example, with

reference to the accompanying drawings, in which:-

Figure 1 shows a cross section through a part of a rotor disc according

. to the invention.

Figure 2 shows a front elevational view of the rotor disc of figure 1 ,

Figure 3 shows a cross-section of a modification of the rotor disc of

figures 1 and 2, and

Figure 4 shows a cross-section of a further modification of the rotor

disc of figures 1 and 2.

Referring to Figures 1 and 2 the rotor disc is indicated generally by

the reference numeral 1 and ~~ .nprises a circular substrate 2 and two

superposed coating layers 3 and 4 disposed on both outer circular faces of

the substrate. The substrate is vented at 5 so that air may circulate through

the substrate to cool the substrate. The substrate 2 is made from a low density but high thermal conductivity material such as aluminium or other

suitable metal or metallic alloy. The outer coating layer 3 is made from a

high thermal conductivity and high wear resistant material such as a carbon-

silicon carbide composite or metallic-type material. The inner coating layer

4 is made from a thermally insulating material such as zirconia or other

ceramic material.

In operation under braking conditions heat is generated on both

surfaces of the disc due to friction between the brake pad shown

diagrammatically at 6 and the rotor disc 1 as the disc 1 rotates causing the

temperature of the disc 1 to rise. Heat is lost from the disc 1 by conduction

convection and radiation. Heat lost by conduction is to the surrounding air

and through the material of-the outer layer 3. to. inner layer 4„an. Jhro.ugh

that layer to the substrate 2 beneath. Heat lost by convection is to the

surrounding air as the air moves relative to all surface of the disc including

those opening to the vent 5. Heat lost by radiation is lost from all hot

surfaces. An exemplary temperature profile through the rotor disc 1 is

shown at 7. The temperature is at its maximum on both outer surfaces of

the disc 1 where the heat is generated through the friction between the disc

brake pad 6 and those surfaces. Heat is conducted relatively easily through

the outer layers 3, which are made of a highly thermally conductive and

wear resistant material, to the inner layers 4, and the fall in temperature

through those layers is correspondingly small. Heat conduction through the inner layers 4, which is made of a thermally insulating material, is restricted

and, as compared with the outer layer there is a greater fall in temperature.

The inner layers 4 therefore operate to protect the substrate from the heat

and high temperatures generated at the outer surfaces of the disc 1 . The

temperature at the interface between the substrate 2 and the inner layers 4

is much less than that between the outer and inner layers 3 and 4 and it

continues to fall across the material of the substrate heat flowing through

the substrate being removed at the surfaces adjoining the vent 5 by

conduction, convection and radiation.

The thickness of the layers 3 and 4 is advantageously in the range

0.05 to 5.00 millimetres, preferably in the range 0.01 to 2.00 millimetres

and in. this-example outer layers 3 are 1 .0 millimetres thick and inner layers ..

4 are 0.5 millimetres thick. The thickness of the substrate lies in the range

5 to 40 millimetres. By appropriately choosing the dimensions of the layers

and substrate and the material from which the layers and substrate are

made the thermal behaviour of the rotor disc may effectively be 'tuned' for

optimum operational performance.

In a modification, a protective layer may be disposed over the outer

cylindrical surface and adjacent the vent of the substrate as shown in figure

3 to protect the substrate against oxidation in all regions not coated by

layers 3 and 4. In this modification parts equivalent to the parts of the

embodiment of figures 1 and 2 bear the same reference numerals. With the above described arrangements heat maybe conducted around the

outer layer(s)3 and lost by convention from the surface thereof. Heat from

the outer layer(s) may also be dissipated by controlled conduction through

the inner layer 4 and through the substrate 3 and lost by convention from

the surfaces adjacent the vent 5 in the substrate.

Although the disc has been described with a vent, the vent may be

dispensed with. Such an arrangement is illustrated in Figure 4. In this

figure parts equivalent to parts in figures 1 to 3 bear the same reference

numerals.

It will be appreciated that the above embodiment has been described

by way of example only and that many variations are possible without

departing from the scope of the invention.

Claims (15)

Claims

1 . A composite rotor disc a composite rotor disc comprising a substrate

made of a thermally conductive material, a first coating layer on at

least one circular face of the disc, the first coating layer being made

of a thermally insulating material and a second coating layer

superposed on the first coating layer, the second coating layer being

made of a wear resistant, thermally conductive material whereby the

substrate is protected from heat generated at the circular surface of

the disc.

2. A composite rotor disc as claimed in claim 1 , in which the substrate

is metal.

3.. A composite, rotor disc as claimed in claim 1 , in which the_m.etal in.

aluminium.

4. A composite rotor disc as claimed in claim 1 , in which the substrate

is a metallic alloy.

5. A composite rotor disc as claimed in any preceding claim, in which

the full coating layer is a ceramic.

6. A composite rotor disc as claimed in claim 5, in which the ceramic is

zirconia.

7. A composite rotor disc as claimed in any preceding claims, in which

the second coating layer is a metallic alloy.

8. A composite rotor disc as claimed in claim 7, in which the metallic alloy is a carbon-silicon carbide composite.

9. A composite rotor disc as claimed in any preceding claim, in which

the thickness of the substrate lies in the range 5 to 40 millimetres.

10. A composite rotor disc as claimed in any preceding claim, in which

the thickness of the layers lies in the range 0.05 to 5.00 millimetres.

1 1 . A composite rotor disc as claimed in any of claims 1 to 9, in which

the thickness of the layers lies in the range 0.01 to 2.00 millimetres.

1 2. A composite rotor disc as claimed in any preceding claims, in which

the first coating layer is 0.5 millimetres thick.

1 3. A composite rotor disc as claimed in any preceding claims, in which

the second coating layer is 1 .00 millimetres thick.

14. A composite- rotor- disc as claimed in any preceding claims, in which

the substrate is vented.

1 5. A composite rotor disc as claimed in any preceding claims, in which a

protective coating is disposed over the outer cylindrical surface.