Brake Disc and Method for Producing Same

Abstract

A brake disc, in particular for a motor vehicle, includes a base disc of a first material and a wear-reducing coating of a second material. The first material is a lightweight metal and the second material is an oxide layer.

Claims

1. A brake disc for a motor vehicle, comprising: a base disc including a first material that is a lightweight metal; and a wear-reducing coating including a second material that is an oxide layer.

2. The brake disc as claimed in claim 1, wherein the lightweight metal is aluminum.

3. The brake disc as claimed in claim 1, wherein the lightweight metal is titanium or magnesium.

4. The brake disc as claimed in claim 1, further comprising: a support body on which the first material is disposed, wherein the support body is plastic.

5. The brake disc as claimed in claim 1, further comprising: a support body on which the base disc is mounted.

6. The brake disc as claimed in claim 5, wherein the base disc and/or the support body includes a phase change material.

7. The brake disc as claimed in claim 6, wherein: the base disc and/or the support body includes at least one chamber; and the phase change material is arranged in the at least one chamber.

8. A braking device for a motor vehicle, comprising: a brake disc configured to be connected to a wheel and including a brake caliper, the brake caliper assigned to the brake disc and carrying at least one actuable braking element, the brake disc further including: a base disc including a first material that is a lightweight metal; and a wear-reducing coating including a second material that is an oxide layer.

9. The braking device as claimed in claim 8, further comprising: at least one heat conducting element configured to be brought into direct contact with the brake disc and arranged on the brake caliper.

10. The braking device as claimed in claim 9, wherein the at least one heat conducting element is a contact brush.

11. The braking device as claimed in claim 9, wherein the at least one heat conducting element is a rotatably mounted contact wheel.

12. The braking device as claimed in claim 9, wherein the at least one heat conducting element is thermally connected to a heat sink.

13. A method for producing a brake disc, comprising: forming a base disc comprised of lightweight metal; and producing an oxide layer on a base element by hard anodizing or by plasma electrolytic oxidation.

14. The method as claimed in claim 13, further comprising: manufacturing the base disc from titanium or aluminum.

15. The method as claimed in claim 13, further comprising: mounting the base disc on a support body and/or producing the base disc as a sheet-metal part.

16. The brake device according to claim 8, wherein the brake disc is connected to the wheel.

17. The brake device according to claim 9, wherein the at least one heat conducting element is in direct contact with the brake disc.

Description

[0023] The invention will be explained in greater detail below by means of the drawing, in which:

[0024] FIG. 1 shows a first illustrative embodiment of an advantageous brake disc.

[0025] FIG. 2 shows a detail view of the brake disc,

[0026] FIG. 3 shows a braking device having the brake disc, and

[0027] FIG. 4 shows a second illustrative embodiment of the brake disc.

[0028] FIG. 1 shows a brake disc 1 for a motor vehicle (not shown) in perspective. The brake disc 1 has a brake ring 3, which is formed by a base disc 2. The brake ring 3 has brake surfaces 4 and 5, respectively, on both faces. In the center, the brake disc 1 has a support boss 6 for fastening the brake disc 1 on a wheel bearing or a wheel of the motor vehicle. In terms of materials, the support boss 6 can differ from the brake ring and can be manufactured from aluminum, for example. This reduces the unsprung mass, and more advantageous heat dissipation to the hub and rim is achieved. A plurality of holes for screwed joints for fastening are formed on the support boss 6. The braking surfaces A, b are subject to wear during operation, leading to the necessity of replacing the brake disc 1 at regular intervals. Current brake discs are usually produced from gray cast iron and, in some cases, also from ductile cast iron or are cast from a suitable steel alloy and machined by turning. Brake discs for motorcycles are preferably manufactured from corrosion-resistant steels. In some cases, more wear-resistant ceramic brakes are also employed, although these lead to high costs. For greater braking power, higher wear resistance and better insensitivity to fading combined with low weight, silicon carbide reinforced with carbon fibers and carbon-fiber-reinforced plastic are also used for brake discs in racing and in aircraft construction. Vehicle brake discs can also be punched out of sheet metal.

[0029] The base disc 2 or brake ring 3 has two brake rings 3 and 3, which are arranged spaced apart and each form one of the braking surfaces 4 and 5, respectively. Arranged between the brake rings 3 and 3 are spacers in the form of ribs 1, which form a plurality of cavities between the brake rings 3, 3. In this case, an air flow from the inside to the outside between the brake rings 3, 3 arises from the centrifugal force that occurs during driving, with the result that the brake disc 1 is actively cooled. As an option, ventilation holes can also be formed in the respective brake ring 3, 3 in order to improve the air cooling, with the air flow also passing through the ventilation holes and thereby producing turbulence which optimizes the heat transfer between the brake disc and the air.

[0030] The base disc 2 or brake rings 3, 3 and optionally also the ribs 7 are manufactured from a lightweight metal, in particular titanium, aluminum or magnesium. The braking surfaces 4, 5 are furthermore provided with an oxide layer 8, 9.

[0031] In this regard, FIG. 2 shows an enlarged detail view of the brake disc 1 in a simplified sectional illustration. According to the illustrative embodiment under consideration, both braking surfaces 4, 5 are provided with an oxide layer 8, 9, which, in particular, extends 100 nm to 10 m into the material of the brake rings 3, 3. In particular, the oxide layer is produced by hard anodizing or plasma electrolytic oxidation of the base disc 2 or brake rings 3, 3. If the base disc 2 is manufactured from aluminum, the braking surfaces are converted into an aluminum oxide layer or provided with such a layer by the methods mentioned.

[0032] The brake disc is produced at low cost by virtue of manufacture from a lightweight metal and, by virtue of the advantageous oxide layer, ensures low wear and high temperature stability. The formation of the wear-reducing oxide layer 8, 9 ensures optimum chemical bonding of the protective layer to the base disc 2. Moreover, the oxide layer is produced uniformly and airtightly, thus preventing corrosion of the base disc 2.

[0033] FIG. 3 shows, in a simplified illustration, a braking device 10 which has a brake caliper 11, which has two movably mounted brake pads 12, 13, between which the brake disc 1 is situated, brake pad 12 thus being assigned to braking surface 4 having oxide layer 8, and brake pad 13 being assigned to braking surface 5 having oxide layer 9. If the brake pads 12, 13 are moved toward one another, the brake disc 1 situated therebetween is clamped between them and adhesion occurs between them, exerting a decelerating effect on the rotating brake disc 1, as with conventional braking devices.

[0034] In the present case, the inner brake ring 31 has an annular region 14 which is free from the oxide layer 9. This annular region 14 is assigned a heat conducting element 15, which in the present case is designed as a heat conducting brush 16 and is pressed against the brake disc 1 in the region of region 14 by means of a preloading force by a brush holder 17. The brush 16 is manufactured from metal and serves for heat dissipation. The heat conducting element 15 is furthermore connected to a heat sink 18, to which the heat absorbed by the heat conducting element 15 is dissipated. The heat sink 18 can be a radiator, a heat storage element or a coolant line of a cooling circuit of the motor vehicle, for example.

[0035] Region 14, which in the present case is situated radially to the inside of the oxide layer 9, can also be embodied as a groove in the brake ring 3, thereby making possible improved guidance of the heat conducting element 15. In an alternative embodiment, provision is preferably made for region 14 to be coated with a hard metal. The maximum temperature of the brake disc 1 is thus limited by the design of the direct contact between the heat conducting element 15 and the brake disc 1 and by the thermal heat dissipation to the heat sink 18.

[0036] As an alternative to embodiment as a brush 16, provision is made, according to another illustrative embodiment, for the heat conducting element 15 to be designed as a contact wheel 19 (illustrated in dashed lines), which is mounted rotatably on the brake caliper 11 by means of a bearing 20, in the present case a rolling element bearing. In this case, the bearing 20 is formed in thermal contact with the heat sink 18. Like the alternative brush 16, the contact wheel 19 is in continuous direct contact with the brake ring 3 in order to dissipate heat from the brake disc 1 to the heat sink 18 by means of the direct contact. In this arrangement, the axis of rotation of the contact wheel 19 is aligned radially with respect to the axis of rotation of the brake disc 1.

[0037] FIG. 4 shows another illustrative embodiment of the brake disc 1 in a simplified sectional illustration. In contrast to the previous illustrative embodiments, provision is now made for the brake disc 1 to have a heat storage element 21. The heat storage element 21 is situated between the brake rings 3 and 3 and is connected thermally thereto. In particular, the heat storage element 21 is formed integrally with the brake rings 3, 3 and the ribs 7. In the interior, the heat storage element 21, which thus forms a heat storage ring, has one or more chambers 22, in which a material with a high specific heat capacity, e.g. oil, is arranged or held. As a particular preference, the material 23 is designed as a phase change material, e.g. a paraffin, which stores heat by changing its state of aggregation from solid to liquid, for example. Heat is thereby stored in the brake disc 1 by means of a phase change in accordance with the specific heat capacity of the phase change material, in addition to the increase in temperature, and hence thermal overloading of the brake disc 1, in particular of the brake rings 3 and 3, is avoided.

[0038] It is advantageous if the base disc 2 is manufactured by metal powder injection molding, 3-D printing and/or deep drawing, thus enabling the production of the brake disc 1 to be carried out at low cost and with little effort.

[0039] As an alternative to the illustrative embodiment under consideration, one or more such chambers 22 are formed in the brake rings 3 and 3 themselves, as shown in FIG. 3. It is also conceivable to provide additional chambers 22 in the brake rings 3 and 3 in the illustrative embodiment in FIG. 4. As already described above, the chambers 22 are filled with a material that has a high specific heat capacity and/or a phase change material. As a final step, openings 24 used to fill the chambers are closed, in particular welded.

[0040] The brake disc 1 according to the illustrative embodiments under consideration is in each case of single-part design. According to an alternative embodiment, however, provision is advantageously made for the brake disc to be of multi-part design, wherein the parts are connected to one another by suitable joining technologies, e.g. ultrasonic welding or laser welding. In particular, it is conceivable to produce the brake disc 1 in three parts, wherein parting lines are in each case preferably situated in a central plane of one of the brake rings 3 and 3, as shown by dashed lines in FIG. 3. In this way, it is also possible to produce the chambers 22 at low cost during the manufacturing process.

[0041] In order, in general terms, to improve the decrease in strength at high temperatures and the reduction in weight through the avoidance of metal mass, the maximum temperature is lowered by increasing the heat capacity C. For the same heat energy Q to be stored, this results in a lower temperature difference, i.e. a lower maximum temperature T.sub.max. A reduction in temperature can furthermore be achieved when using phase change materials. This is explained below by means of basic physical equations:

[00001]$.Math..Math.T=\frac{Q}{C}$

[0042] The heat capacity C is influenced by three parameters, the material-dependent, specific heat capacity c, the volume V and the density . The latter can be combined in the weight m, although this should be kept as low as possible:

C=c.Math..Math.V,C=c.Math.m

[0043] To enable as much heat as possible to be stored with a low weight in comparison with gray cast iron brake discs, the primary choice is for a high specific heal capacity. Materials with a phase change, e.g. paraffin, are suitable for this purpose. The additional heat that can be stored in the case of a phase transition is:

Q=m.Math.L

where L is the enthalpy of melting.