Friction brake body, friction brake, and method for producing a friction brake body

Abstract

A friction brake body, in particular a brake disc, for a friction brake of a motor vehicle is disclosed. The friction brake body has a main part with at least one wear protection layer on at least one frictional contact region of the main part. The wear protection layer forms a frictional contact surface on the wear protection layer face facing away from the main part. The degree of hardness of the wear protection layer increases incrementally or continuously from the main part to the frictional contact surface.

Claims

1. A friction brake body for a friction brake of a motor vehicle, comprising: a main part; a first wear protection layer located on the main part and comprising a carbon content of less than 0.1% by weight, a first degree of hardness of the first wear protection layer is greater than a degree of hardness of the main part; a second wear protection layer arranged on the first wear protection layer and comprising a carbon content from 0.1% by weight to 1.0% by weight, a second degree of hardness of the second wear protection layer is greater than the first degree of hardness of the first wear protection layer; and a third wear protection layer arranged on the second wear protection layer and comprising a carbon content greater 1.0% by weight, a third degree of hardness of the third wear protection layer is greater than the second degree of hardness of the second wear protection layer, wherein the third wear protection layer is configured to form a frictional contact surface facing away from the main part.

2. The friction brake body according to claim 1, wherein: the first wear protection layer has a first proportion of carbide-forming elements and carbon, the second wear protection layer has a second proportion of carbide-forming elements and carbon that is greater than the first proportion, and the third wear protection layer has a third proportion of carbide-forming elements and carbon that is greater than the second proportion.

3. The friction brake body according to claim 2, wherein a ratio of the carbide-forming elements and the carbon is selected such that carbon atoms are completely, or nearly completely, bound in carbides formed from the carbide-forming elements.

4. The friction brake body according to claim 2, wherein; when chromium is used in an alloy forming the first, second, and third wear protection layers, other carbide-forming elements are included in the alloy, and the other carbide-forming elements have a higher carbon affinity than chromium.

5. The friction brake body according to claim 2, wherein vanadium, niobium, tungsten, titanium and/or chromium are the carbide-forming elements.

6. A friction brake for a motor vehicle, comprising: at least one friction brake body according to claim 1; and at least one brake pad assigned to the at least one friction brake body, the at least one brake pad displaceable relative to the at least one friction brake body.

7. A method for producing a friction brake body according to claim 1, for a friction brake of a motor vehicle, comprising: producing the friction brake body from a main part having at least one wear protection layer on at least one frictional contact region of the main part, in such a way that the at least one wear protection layer forms a frictional contact surface on the wear protection layer facing away from the main part, wherein the at least one wear protection layer is produced with a degree of hardness that increases incrementally or continuously from the main part to the frictional contact surface.

8. The friction brake body according to claim 1, wherein the friction brake body is a brake disc.

9. The friction brake body according to claim 1, wherein the first wear protection layer is a ductile buffer layer.

10. The friction brake body according to claim 1, wherein the second wear protection layer is configured to reduce thermomechanical stresses in the first wear protection layer and the third wear protection layer.

11. The friction brake body according to claim 1, wherein the carbon content in the first, second, and third wear protection layers increases degressively from the main part to the frictional contact surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and preferred features and combinations of features result in particular from the previously described features and from the claims. The disclosure will be explained in more detail below with reference to the drawings, in which:

(2) FIG. 1 shows an advantageous friction brake body in a perspective view, and

(3) FIG. 2 shows a schematic sectional illustration of the friction brake body to explain the advantageous design of the friction brake body and of an advantageous production method.

DETAILED DESCRIPTION

(4) FIG. 1 shows a simplified perspective illustration of a friction brake body designed as a brake disc 1 of a friction brake 2 of a motor vehicle, which is not shown in greater detail here. The brake disc 1 is designed in the shape of a circular ring, and serves to work together with a movable brake pad of the friction brake, which can be pressed against at least one of the end faces of the brake disc 1. An optionally-present brake disc drum is not shown in FIG. 1.

(5) The brake disc 1 has a main part 3 with a circular ring shape, which on both of its end faces has a frictional contact surface 4 that is formed by a wear protection layer 5 on the main part 3. The main part 3 is preferably made of grey cast iron, and the wear protection layer 5 extends at least over a frictional contact surface of both of the end faces of the main part 3. The wear protection layer is produced on the main part 3 by a laser deposition welding method, for example.

(6) The wear protection layer 5 is characterized in that it has a degree of hardness that increases from the main part 3 to the exposed frictional contact surface 4. In particular, the wear protection layer has an incremental or continuous hardening profile in the axial direction and/or in the direction from the main part 3 to the frictional contact surface 4. According to the embodiment of FIG. 1, the wear protection layer 5 is formed in multiple layers, namely two layers, such that the wear protection layer 5 is formed from two layers 5_1 and 5_2, wherein the outer layer 5_1 has a higher degree of hardness than the layer 5_2 positioned between the layer 5_1 and the main part 3. In particular, the different hardness degrees of the two layers 5_1, 5_2 are realized by different proportions of carbide-forming elements and carbon. Due to the fact that the degree of hardness of the wear protection layer increases from the main part 3 to the layer surface on the frictional contact surface 4, an improved crack resistance of the brake disc 1 results. In particular, the advantageous design ensures that crack propagation into the main part 3 is avoided. This is achieved by a graded distribution of carbon and carbide-forming elements, such as vanadium, titanium, niobium or chromium within the wear protection layer 5. During solidification, the reaction of the carbide-forming elements with carbon atoms forms finely distributed metal carbides in the wear protection layer 5, which increase the degree of layer hardness of the given layer 5_1, 5_2 and thus the wear resistance of the wear protection layer 5. The content of carbon and carbide-forming elements increases in the direction of the frictional contact surface 4, wherein, according to the present embodiment of FIG. 1, it increases incrementally from layer 5_2 to layer 5_1. According to an alternative embodiment, the degree of hardness of the wear protection layer 5 and/or the content of carbon and carbide forming elements increases continuously from the main part 3 to the frictional contact surface 4.

(7) The wear protection layer 5 has, in particular, an iron base alloy, the carbon content of which in the wear protection layer 5 gradually increases from the main part to the frictional contact surface 4. This is achieved, for example, by a variation of the coating material. The carbon content in this case preferably increases at least substantially linearly or degressively, wherein a linear increase improves the crack resistance and a degressive increase ensures that the coefficient of friction at the frictional contact surface 4 is maintained as long as possible.

(8) FIG. 2 shows a further embodiment of the brake disc 1, wherein, FIG. 2 shows a longitudinal sectional view of a portion of the brake disc 1. In contrast to the preceding embodiment, the wear protection layer 5 here is designed in three layers, wherein a third layer 5_3 is present between the main part 3 and the layer previously denoted as 5_2. The carbon content varies from layer to layer to ensure an incremental increase in the direction of the frictional contact surface 4.

(9) The first layer 5_3 on the main part 3 serves primarily as a ductile buffer layer without, or with only a low, carbide content, and therefore also has only a low carbon content of preferably less than 0.1% by weight.

(10) The second layer 5_2 represents a transition region to the outer layer 5_1, which forms the frictional contact surface 4. The layer 5_2 not only improves the adhesion between the layers 5_1 and 5_3, but also reduces thermomechanical stresses in the layer system when the brake disc 1 is used for braking. For this purpose, the layer 5_2 has a higher carbon content than the first layer 5_3, preferably between 0.1% by weight and 1.0% by weight.

(11) The third layer 5_1 functions as an actual wear protection layer, and therefore forms the frictional contact surface 4. The third layer 5_1 is characterized by the highest carbon content and thus by the highest degree of layer hardness. The carbon content of the layer 5_1 is thus preferably higher than 1.0% by weight.

(12) Since carbide-forming elements such as vanadium, titanium, niobium or chromium are also used for the formation of metal carbides, as already mentioned above, the content of carbide-forming elements is preferably distributed and/or varied analogously to the carbon content in the layers 5_1 to 5_3. Preferably, the ratio of the carbon content and the carbide-forming metal atoms is selected in such a manner that complete binding of the carbon atoms in carbides occurs in each of the layers 5_1 to 5_3. Furthermore, it is preferred that the alloyed carbide-forming metal atoms have a higher carbon affinity than chromium. In this way, in the event that chromium is additionally used in the alloy, which is advantageous for increasing the corrosion resistance of the wear protection layer, chromium does not function as a carbide former, and is thus available for corrosion protection of the wear protection layer 5.