Brake Disk Comprising A Ceramic Friction Ring

Abstract

The invention relates to a brake disk comprising a ceramic friction ring (4) and a connecting flange (6) that is disposed concentric to the friction ring (4). The friction ring (4) is provided with a fastening ring (8) in an interior area, which encompasses fastening bores (10). The friction ring (4) is joined to the connecting flange (6) at the fastening bores (10) by means of fixing means. The invention is characterized in that the friction ring (4) is provided with relief slots (12) between the fastening bores (10) in the fastening ring (8), said relief slots (12) radially extending from an interior area of the fastening ring (8) in the direction of a friction zone (20) of the friction ring (4).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Advantageous embodiments of the invention will be described in detail in the examples below. They show:

FIG. 1 a top view of a brake disk according to the invention with a friction ring and a connecting flange,

FIG. 2 a perspective view of a friction ring according to the invention with a partial cross-sectional view.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1 a brake disk 2 is shown which features a ceramic friction ring 4 and a connecting flange 6. In a center region the friction ring 4 features a fastening ring 8. The fastening ring 8 features fastening bores 10 and relief slots 12. The relief slots 12 run from a center region of the friction ring 4 radially through the fastening ring 8 to a friction zone 20 of the friction ring 4. The friction zone 20 is depicted by the dashed lines in the friction ring. During brake application brake pads which are not shown here are located in this region. The friction zone 20 is the region of the friction ring which is exposed to the highest thermal loads. The relief slots 12 are designed such that they come as close as possible to the friction zone 20 (inner dashed line 24). As the case may be, the relief slots 12 can also extend into the friction zone 20. In this case calculations of the mechanical stability need to be taken into account, wherefore the relief slots 12 usually end about 1 mm to 5 mm before the beginning of the friction zone 20.

As shown in FIG. 1 the relief slots 12 end in relief bores 14. The relief bores 14 provide for a reduction of the possibly developing mechanical stress concentrations at the ends of the relief slots and prevent notch effects. Usually the relief bores 14 have a diameter between 1 mm and 7 mm.

FIG. 1 also shows a connecting flange 6 which is by means of a screw connection connected to the friction ring 4 in the region of the fastening ring 8. The screw connection is not shown in FIG. 1. Usually the connecting flange 6 consists of an aluminum alloy or steel. The use of these metals depends on the temperatures which develop during operation of the brake disk 2.

In FIG. 1 the connecting flange 6 is shown as additional component, which can be bolted to the hub of a wheel of a vehicle. However, the connecting flange 6 can just as well be constituted by the wheel hub of the vehicle itself. In this embodiment the friction ring 4 is connected directly to the wheel hub of the vehicle.

Through the use of a connecting flange 6 on the basis of aluminum, the weight advantage of the brake disk 2, which is already given by the low specific weight of the friction ring 4, can be significantly improved. In the embodiment of FIG. 1 the friction ring 4 features twelve equidistant relief slots 12. The dashed line 24 marks the inner border of the friction zone 20, which is just about contacted by a brake pad which is not shown here. Basically it is possible to run the relief slots 12 radially outwards up to the line 24.

In FIG. 2 a perspective view of the friction ring 4 according to the invention is shown. The friction ring 4 in FIG. 2 features cooling holes 16 which in the front part of the drawing are shown in a partial cross-sectional view. Also in FIG. 2 it can be seen that the fastening ring 8 and the friction ring 4 feature different thicknesses. This results in a step 22 between the fastening ring 8 and the friction ring 4. The relief slots 12 preferably run so far to the outside that they pass across the step 22 and reach into the friction zone 20.

The fastening ring 8 which is an integral part of the overall friction ring 4, thus consisting of the same material as the friction ring 4, usually features a thickness between 5 mm and 40 mm. In a preferred embodiment the thickness of the fastening ring 8 is 12 mm. A radial dimension of the fastening ring 8 is between 10 mm and 40 mm, usually the radial dimension of the fastening ring 8 is 25 mm. Depending on the design of the cooling holes 16 the thickness of the friction ring 4 in the friction zone 20 is between 20 mm and 40 mm. The diameter of the brake disk 2 is between 250 mm and 400 mm.

For the fabrication of the ceramic friction ring 4 according to the invention usually a mixture of resin and carbon fibers is poured into a pressing mold, pressed and subsequently hardened at elevated temperatures. The result of the hardening is a carbon fiber reinforced plastic (CFRP). Subsequently the CFRP body is carbonized under exclusion of air to a carbon fiber reinforced carbon. In the following the carbon fiber reinforced carbon (CC) is referred to as a preform. The machining of the friction ring is usually done on the preform. In this state generally the relief slots 12 and as the case may be the relief bores 14 are machined. However it is also possible to create the relief slots 12/relief bores 14 during the pressing of the CFRP body by means of an accordingly shaped press form.

The machined preform is subsequently infiltrated or impregnated with silicon under exclusion of air at temperatures about 1600° C. During this infiltration the liquid silicon reacts with the carbon of the preform to silicon carbide. After cooling down the result is a silicon carbide ceramic which is reinforced with carbon fibers and as the case may be contains residual silicon.

The embodiment of the brake disk 2 according to the invention, especially of the friction ring 4, is can be extended to other ceramic materials as friction material. Alternative materials which are suitable for brakes are, for instance, metal matrix composites (MMC) or intermetallic composites. Fundamentally the construction according to the invention is applicable for all materials which are tribologically exceptionally durable but relatively brittle compared to gray cast iron.

Claims

1. A brake disk comprising a ceramic friction ring (4) and a connecting flange (6) in which the connecting flange (6) is concentrically arranged with regard to the friction ring (4), the friction ring (4) in its center region featuring a fastening ring (8) with fastening bores (10) connected at these fastening bores (10) with the connecting flange (6) through fixing means, wherein the friction ring (4) in the fastening ring (8) features relief slots (12) between the fastening bores (10) which run radially from a center region of the fastening ring (8) towards the direction of the friction zone (20) of the friction ring (4).

2. The brake disk according to claim 1, wherein the relief slots (12) feature relief bores (14) at their outer edge.

3. The brake disk according to claim 1, wherein the relief slots (12) are between 2 mm and 30 mm in length.

4. The brake disk according to claim 3, wherein the relief slots (12) are between 10 mm and 20 mm in length.

5. The brake disk according to claim 1, wherein the number of relief slots (12) is between 3 and 20.

6. The brake disk according to claim 5, wherein the number of relief slots (12) is between 10 and 14.

7. The brake disk according to claim 5, wherein the number of relief slots (12) is 6.

8. The brake disk according to claim 1, wherein the friction ring (4) consists of a carbon fiber reinforced silicon carbide ceramic.