Method for machining the surface of a friction surface of a brake disc and brake disc produced using the method

Abstract

Method for machining the surface of a friction surface (4) of a brake disc (1) for a disc brake of a motor vehicle, wherein a chip direction on the friction surface (4) is arc-shaped, wherein a concave side of the arc-shaped chip direction faces a center of the brake disc (1), wherein the machining is performed with a geometrically undefined cutting edge and the friction surface (4) is ground, wherein a circular tool (6) driven to rotate about its axis, which for machining the surface is inclined with a point of its circumference on the friction surface (4) of the brake disc (1), is inclined towards a center of the brake disc (1), wherein the axes of the tool (6) and the brake disc (1) intersect, and wherein the brake disc (1) is rotated about its axis relative to the tool (6) during the machining, characterized in that the tool is a grinding wheel (6).wherein the inclination of the grinding wheel (6) is selected such that the chip direction runs in the circumferential direction of the brake disc (1), and that the grinding wheel (6) is moved radially with respect to the brake disc (1) during the machining surface finishing.

Description

[0001] The invention relates to a method for machining the surface of a friction surface of a brake disc for a disc brake of a motor vehicle, comprising the features of the preamble of claim 1, and to a brake disc produced by the method comprising the features of the preamble of claim 3. Friction surfaces are defined as the perforated disc-shaped surfaces of a brake disc against which friction brake pads are pressed during braking. State of the art

[0002] Brake discs are known for disc brakes in motor vehicles. They can be installed with unmachined surfaces. It is also known to grind, i.e., machine, the friction surfaces of brake discs before delivery. In this process, a grinding wheel or a cylindrical grinding element is placed perpendicularly onto the friction surface so that the axes of the grinding wheel or grinding element and the brake disc intersect at right angles. During grinding, the grinding wheel or cylindrical grinding element is driven in a rotating motion, and the brake disc is rotated about its axis so that the grinding wheel or cylindrical grinding element moves in a circular path over the friction surface of the brake disc. Instead of rotating the brake disc, the grinding wheel or cylindrical grinding element can also be guided in a circular path over the friction surface of the brake disc.The rotational speeds of the grinding wheel or cylindrical grinding element and the brake disc are selected such that a relative speed is achieved at the circumference of the grinding wheel or cylindrical grinding element with respect to the friction surface of the brake disc, in order to grind the friction surface. Furthermore, the grinding wheel or cylindrical grinding element is moved radially with respect to the brake disc to grind the friction surface of the brake disc across its entire width.

[0003] The grinding wheel or cylindrical grinding element, mounted perpendicularly to the friction surface of the brake disc, creates chip marks tangential to the brake disc. These chip marks are fine grooves left by the abrasive particles of the grinding wheel or cylindrical grinding element during grinding on the friction surface of the brake disc. The chip marks therefore run at an angle to the fine, circular grooves coaxial with the brake disc that friction brake pads create on the friction surfaces of a brake disc during braking. Consequently, the coefficient of friction and the braking behavior of the brake discs change from a new brake disc to a used one.

[0004] Methods for machining the surface of a friction surface of a brake disc are known, for example, from the patent applications DE 23 43 949 A1, US 4 262 452 A, US 5 353 553 A and US 2009 / 0275270 A1. Disclosure of the invention

[0005] The method according to the invention, with the features of the preamble of claim 1, provides for a machining surface finishing of a friction surface of a brake disc. The chip direction is arc-shaped, with a concave side of the arc-shaped chip direction facing the center of the brake disc. The chip direction is the relative movement of one or more cutting edges of a tool to the friction surface of the brake disc. Chip marks, i.e., the fine grooves left by the machining surface finishing in the friction surface of the brake disc, run in the chip direction. Claim 1 provides that the chip direction during the machining surface finishing of the friction surface of the brake disc runs in the circumferential direction of the brake disc.

[0006] The invention has the advantage that chip marks left by the machining of the surface finish in the friction surface of the brake disc run in the same or at least approximately the same direction, namely the circumferential direction of the brake disc, as grooves or marks left by friction brake pads during braking. In any case, the angle between the chip marks and the marks left by the friction brake pads during braking is smaller with the method according to the invention than with a brake disc with tangential chip marks according to the prior art. As a result, the coefficient of friction and the braking behavior of the brake disc change less from a new state to a used state, preferably not noticeably, and the break-in period of the brake disc until a used state in which the coefficient of friction and the braking behavior of the brake disc are stable is shortened.

[0007] The dependent claims relate to advantageous embodiments and further developments of the invention specified in claim 1.

[0008] The surface finishing machining according to the invention is carried out with a geometrically undefined cutting edge. According to the invention, the friction surface of the brake disc is ground. However, the invention does not provide for rotary machining of the friction surface of the brake disc, which refers to the surface finishing machining process with a geometrically defined cutting edge, for example, with a turning tool or with an (indexable) cutting insert. During turning, the chip direction runs as desired in the circumferential direction of the brake disc. For grinding, the invention provides a circular tool, which is a grinding wheel. For surface finishing machining, the circular tool is driven in rotation, placed with one point of its circumference on the friction surface of the brake disc, and arranged at an angle to the center of the brake disc, so that the desired arcuate chip direction is achieved with the concave side facing the center of the brake disc.The inclination of the circular tool to the brake disc and the tool's diameter determine the curvature of the chip direction. This means that by selecting the inclination of the circular tool relative to the brake disc, a chip direction can be achieved that runs circumferentially, or at least approximately circumferentially, to the brake disc. During surface machining, the brake disc is rotated around its axis relative to the tool. The tool can also be guided along a circular path across the friction surface of the brake disc, so that the machining area moves along a circular path across the friction surface. Furthermore, the tool is moved radially relative to the brake disc, ensuring that the friction surface is machined across its entire width.

[0009] Claim 2 provides for the inventive machining of a surface finish on a brake disc whose friction surface has a surface coating. Such surface coatings serve to increase the wear resistance and / or improve the corrosion resistance of the brake disc or its friction surfaces. Such surface coatings are applied, for example, as thermal powder coatings, for instance by arc or flame spraying, to the friction surfaces of brake discs.

[0010] Claim 3 relates to a brake disc whose friction surfaces are machined using the machining surface finishing process described above according to the invention. The friction surfaces of the brake disc have arcuate chip marks, the concave sides of which face the center of the brake disc. In particular, the chip marks, i.e., the fine grooves caused by the machining surface finishing, extend in the circumferential direction of the brake disc. Brief description of the drawing

[0011] The invention is explained in more detail below with reference to embodiments illustrated in the drawing. The drawing shows: Fig. 1 a brake disc according to the invention and manufactured using the inventive method in perspective view; Fig. 2 a side view representation of a method according to the invention; Fig. 3 a top view of the inventive method Fig. 2; and Fig. 4 A side view representation of a method not according to the invention.

[0012] The figures are to be understood as simplified and schematic representations for the purpose of understanding and explaining the invention. embodiment of the invention

[0013] The in Fig. The brake disc 1 shown in Figure 1, according to the invention, has a cup-shaped hub 2 and a circular-drilled brake ring 3, which is integral with the hub 2. The circular-drilled surfaces of the brake ring 3 form friction surfaces 4 of the brake disc 1. For braking, friction brake pads (not shown) are pressed against the friction surfaces 4. The brake ring 3 can also be considered the actual brake disc.

[0014] The brake disc 1 can be made of metal, for example, steel. In the exemplary embodiment, it is made of gray cast iron, i.e., cast iron with lamellar graphite. The friction surfaces 4 are provided with a wear-reducing, friction-enhancing, and corrosion-resistant surface coating by flame spraying. The surface coating has a metallic matrix of, for example, nickel or cobalt, in which carbides, for example, metallic carbides with a metal from the chromium group, such as chromium carbide and / or tungsten carbide, are embedded. The surface coating is not essential for the invention. Strictly speaking, if present, the surface coating or its surfaces form the friction surfaces 4 of the brake disc 1.

[0015] The friction surfaces 4, if present, are machined after the application of the surface coating. This machining process produces fine grooves, referred to here as chip marks 5. According to the invention, the chip marks 5 extend circumferentially around the brake disc 1. The chip marks 5 are therefore arc-shaped, with their convex side facing the center of the brake disc 1. The chip marks 5 are circular arcs or approximately circular arcs and are concentric with the brake disc 1.

[0016] According to a first embodiment of the method according to the invention, the friction surfaces 4 are ground, i.e., the machining of the surface finish of the friction surfaces 4 of the brake disc 1 is a machining operation with geometrically undefined cutting edges. As in Fig. 2 and Fig. As shown in Figure 3, a grinding wheel 6, i.e., a circular tool, is driven to rotate around its axis and its circumference is placed on one and then the other friction surface 4 of the brake disc 1. The brake disc 1 is also driven to rotate around its axis, so that the grinding wheel 6 performs a concentric circular motion on its friction surface 4 relative to the brake disc 1. The rotational speed of the brake disc 1 is a fraction of the rotational speed of the grinding wheel 6; for example, the brake disc 1 rotates approximately 1:100 to 1:1000 slower than the grinding wheel 6. Thus, a relative speed exists between the grinding wheel 6 and the brake disc 1 at the point where the grinding wheel 6 contacts the brake disc 1. This relative speed is necessary for machining. The brake disc 1 and the grinding wheel 6 can be driven in the same direction or in opposite directions.

[0017] In surface finishing machining, the grinding wheel 6 is inclined towards the center of the brake disc 1, as is particularly common in Fig. Figure 2 shows that the inclination of the grinding wheel 6 relative to the brake disc 1 results in an arc-shaped path along the circumference of the grinding wheel 6 in the plane of the friction surface 4 of the brake disc 1. The radius of this arc depends not only on the inclination of the grinding wheel 6 but also on its diameter. Thus, the radius of the chip marks 5 produced by the grinding wheel 6 on the friction surface 4 of the brake disc 1 can be changed by adjusting the inclination of the grinding wheel 6 relative to the brake disc 1. If the grinding wheel 6 is tilted more steeply, the radius of the chip marks 5 increases; if the grinding wheel 6 is tilted more sharply towards the brake disc 1, the radius of the chip marks 5 decreases. The inclination of the grinding wheel 6 to the brake disc 1 is chosen such that the chip marks 5 run, at least approximately, in circular arcs concentric to the brake disc 1. One chip direction runs in the circumferential direction of the brake disc 1.Chip direction refers to the movement of abrasive particles around the circumference of the grinding wheel 6 at the point where the grinding wheel 6 rests on the friction surface 4 of the brake disc 1. The abrasive particles form geometrically undefined cutting edges on the grinding wheel 6.

[0018] The rotation of the brake disc 1 during the machining process causes the friction surface 4 of the brake disc 1 to be ground over its entire circumference. Fig. Figure 3 shows the movement of the grinding wheel 6 relative to the brake disc 1 along a circular path due to the rotating drive of the brake disc 1, indicated by a dashed circle. To grind or generally machine the entire width of the friction surface 4, the grinding wheel 6 is moved slowly radially to the brake disc 1, as indicated by the double arrow in Figure 3. Fig. 2 and Fig. 3 indicates. The radial movement is so slow that it is negligible compared to a grinding speed, thus not changing the circumferential chip direction and the chip traces 5.

[0019] Fig. Figure 4 shows a machining process by turning, i.e., machining with a geometrically defined cutting edge. The friction surfaces 4 of the brake disc 1 are precision turned, resulting in circular chip marks 5 that are concentric with the brake disc 1. The radial movement of a turning tool 7, indicated by a double arrow, is slow compared to the rotational speed of the brake disc 1, so that any deviation of the chip direction and the chip marks 5 from the circumferential direction of the brake disc 1 is negligible; the chip marks 5 can be interpreted as circles concentric with the brake disc 1.

[0020] Both in Fig. 2 and Fig. 3 as well as in Fig.4. Both friction surfaces 4 of the brake disc 1 are machined one after the other or simultaneously in the manner described.

[0021] The chip direction during the machining of the friction surfaces 4 of the brake disc 1 and the chip traces 5 on the friction surfaces 4 of the brake disc 1 run in the same direction and, at most, with a small angular deviation, like the fine grooves produced by the friction brake pads (not shown) of a disc brake (also not shown) during braking on the friction surfaces 4 of the brake disc 1. The fine grooves produced by the friction brake pads can also be described as traces. Because the chip traces run in the same direction as the traces produced by the friction brake pads during braking, the coefficient of friction and the braking properties of the brake disc 1 hardly change from a new state to a used state, and the break-in period until the brake disc 1 exhibits constant braking properties is shortened.

Claims

[1] Method for machining the surface of a friction surface (4) of a brake disc (1) for a disc brake of a motor vehicle, wherein a chip direction on the friction surface (4) is arc-shaped, wherein a concave side of the arc-shaped chip direction faces a center of the brake disc (1), wherein the machining is performed with a geometrically undefined cutting edge and the friction surface (4) is ground, wherein a circular tool (6) driven to rotate about its axis, which for machining the surface is inclined with a point of its circumference on the friction surface (4) of the brake disc (1), is inclined towards a center of the brake disc (1), wherein the axes of the tool (6) and the brake disc (1) intersect, and wherein the brake disc (1) is rotated about its axis relative to the tool (6) during the machining process. characterized by, that the tool is a grinding wheel (6), wherein an inclination of the grinding wheel (6) is selected such that the chip direction is in the circumferential direction of the brake disc (1), and that the grinding wheel (6) is moved radially with respect to the brake disc (1) during the machining surface finishing. [2] Method according to claim 1, characterized by , that the friction surface (4) of the brake disc (1) has a surface coating. [3] Brake disc for a disc brake of a motor vehicle, wherein a friction surface (4) of the brake disc (1) has a machined surface, wherein chip traces (5) are arcuate, wherein a concave side of the chip traces (5) faces a center of the brake disc (1), characterized by , that the friction surface (4) of the brake disc (1) is machined according to the method according to one of claims 1 to 2.

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