Brake disk for a motor vehicle, motor vehicle, and method for operating a brake disk for a motor vehicle

Abstract

The invention relates to a brake disk (10) for a motor vehicle, said brake disk having a main body (12) which is coated with a layer system (14), the layer system comprising at least one friction layer (18) which has at least one hard material and which provides a friction region (20), said friction region being provided so as to be brought into contact with a brake lining in order to brake the vehicle when the brake disk (10) is used as intended in the vehicle, wherein the brake disk (10) has at least one cavity (22) extending completely through the brake disk (10) in the axial direction (RA) and opening with its mouth region (26) in the friction region (20) of the brake disk (10) into an end face (28) of the brake disk (10), wherein the brake disk (10) is cold-hardened in at least one region (34) extending annularly around the mouth region (26) of the cavity (22).

Description

[0001] 24-3017

[0002] 1

[0003] brake disc, in particular for a motor vehicle, motor vehicle and method for manufacturing a brake disc for a motor vehicle

[0004] The invention relates to a brake disc for a motor vehicle, a motor vehicle and a method for manufacturing a brake disc for a motor vehicle.

[0005] From DE 10 2006 060293 A1, a brake disc ring is known which has perforated bores perpendicular to the plane of a friction surface. The perforated bores are cylindrical in shape. The brake disc is made of fiber-reinforced ceramic material.

[0006] Furthermore, a brake disc with a friction surface having areas with recesses is known from DE 102012 106 304 A1.

[0007] The object of the present invention is to provide a solution which enables the provision of a particularly durable brake disc, having at least one recess and reinforced with a hard material.

[0008] This problem is solved according to the invention by the subject matter of the independent claims. Further possible embodiments of the invention are disclosed in the dependent claims, the description, and the figures. Features, advantages, and possible embodiments set forth in the description for one of the subject matter of the independent claims are, at least analogously, features, advantages, and possible embodiments of the respective subject matter of the other claim. 24-3017

[0009] 2 independent claims as well as any possible combination of the subject matter of the independent claims, possibly in conjunction with one or more of the dependent claims.

[0010] The invention relates to a brake disc, in particular a motor vehicle, especially a passenger car. The brake disc can be part of a braking system of the motor vehicle, which is a technical device of the motor vehicle designed to decelerate the motor vehicle and thus reduce its speed, in particular until the motor vehicle comes to a standstill. In addition to the brake disc, the braking system can have at least one brake pad, which is to be applied to a friction surface of the brake disc for deceleration of the motor vehicle. For braking of the motor vehicle, the at least one brake pad is thus pressed against the friction surface of the brake disc, whereby the resulting friction between the at least one brake pad and the brake disc decelerates the motor vehicle.The brake disc is arranged in a rotationally fixed manner relative to at least one wheel of the motor vehicle, whereby, as a result of frictional contact between the at least one brake pad and the brake disc, the wheel of the motor vehicle, which is rotationally fixed to this brake disc, is braked. The brake disc is, in particular, designed to be rotationally symmetrical.

[0011] The brake disc is designed to have a base body, which may, for example, comprise gray cast iron. The base body can be made of a gray cast iron alloy or steel. The gray cast iron alloy can be one of the alloys GG15 to GG35. Gray cast iron has a high melting point and particularly good heat storage and damping properties. Furthermore, gray cast iron is particularly easy to cast and machine. The base body is designed in a circular disc shape.

[0012] It is intended that the base body is coated with a layer system comprising at least one friction layer. The friction layer comprises at least one hard material. This hard material is, in particular, a carbide and / or a corundum. Carbides are a group of binary chemical compounds consisting of an element and carbon. Specifically, the 24-3017

[0013] 3

[0014] The friction layer consists of a hard material based on a metallic carbide. This hard material can be tungsten carbide, titanium carbide, iron carbide, silicon carbide, or nickel carbide. Tungsten carbide, titanium carbide, iron carbide, silicon carbide, and nickel carbide exhibit particularly high hardness, making the friction layer especially robust and wear-resistant. Corundum is a relatively common mineral belonging to the oxide and hydroxide mineral class. Corundum is very hard. Specifically, the corundum used as a hard material is aluminum oxide. Aluminum oxide is the oxygen compound of the chemical element aluminum and is also known as electrocorundum in technical fields.

[0015] The friction layer provides a friction area intended to be brought into contact with the brake pad for braking the vehicle when the brake disc is used as intended. The brake disc is designed to have at least one recess extending completely through the disc in the axial direction, with its opening region located within the friction area of ​​the brake disc and terminating in an end face of the brake disc. This termination region is an end region of the recess, encompassing an axial end of the recess. The axial direction runs, in particular, parallel to a longitudinal extension direction of a central axis of the base body or an axis of symmetry of the base body.

[0016] In the opening area, the recess is thus designed to be open to the surrounding environment. At the opening of the recess, a wall of the brake disc, which circumferentially encloses or limits the recess, abuts an end face of the brake disc. The opening area of ​​the recess is therefore the axial end region of the recess, which closes off the recess towards one of the end faces of the brake disc. The recess can be a continuous perforation opening, with its respective ends opening into the surrounding environment at opposite end faces of the brake disc. Alternatively, the recess can be a depression that does not extend from one end face to the other of the brake disc. It is possible that the depression leads into a cooling channel that runs inside the brake disc. This cooling channel can be connected to a 24-3017

[0017] 4

[0018] Cooling fluid, for example air, flows through the cooling channel, allowing the brake disc to be cooled by the fluid flowing through it. The brake disc can have a recess on each of its opposing end faces, and these recesses on the different end faces can be aligned axially with each other or laterally offset from one another.

[0019] The brake disc is designed to be work-hardened in at least one ring-shaped area extending around the opening of the recess. In other words, the wall of the brake disc circumferentially enclosing the recess in the opening area and / or a region of the end face of the brake disc that extends ring-shaped around an inlet opening of the recess—and thus radially enclosing the inlet opening of the recess—is work-hardened, at least partially, and in particular completely. Work hardening can also be referred to as strain hardening. Cold forming is the plastic deformation of metals below a recrystallization temperature. The resulting work hardening increases the material strength. Since plastic deformation in metals increases the dislocation density, the probability that dislocations will restrict and impede each other's movement also increases.As a result, an increase in yield strength and tensile strength is achieved. This work hardening is accompanied by increased brittleness and / or reduced ductility. By cold-working the brake disc in an area surrounding the opening of the recess in a ring-like fashion, the risk of stress cracks forming in the brake disc in the immediate vicinity of the recess, particularly originating from the recess's opening as the crack initiation point, can be effectively avoided. Without this cold-working of the brake disc in the immediate vicinity of the recess, the brake disc could be prone to cracking, especially under maximum braking loads.By cold-working the brake disc, at least in part, in the ring-shaped area around the opening of the recess, a particularly long service life of the brake disc and a particularly good appearance can be achieved, with no or very few stress cracks. 24-3017.

[0020] 5

[0021] In a further possible embodiment of the invention, the at least one recess is provided for in the base body prior to coating it. This means that the at least one recess is first made in the base body, and then the base body is coated with the layer system. This can be recognized on the finished brake disc by the distribution of the respective coatings of the layer system on the base body. Since the base body is not yet coated with the hard-reinforced layer, the at least one recess can be made particularly easily in the brake disc if it is made in the base body before coating it.

[0022] In an alternative embodiment, the at least one recess is provided for in the base body after the base body has been coated with at least one layer of the coating system, in particular after the base body has been coated with the entire coating system. By manufacturing the brake disc in the sequence of first coating the base body with the at least one layer of the coating system, in particular with all layers of the coating system, and then producing the at least one recess in the base body, it can be achieved that the recess can be produced in the base body with a particularly precise and predetermined geometry.On the finished brake disc, it is particularly easy to see from the coating gradient of the at least one coating of the layer system whether the respective layer of the layer system was applied to the base body before or after the introduction of the at least one recess into the base body.

[0023] In a further possible embodiment of the invention, it is provided that the brake disc, after the application of at least one layer of the coating system, in particular after the application of all layers of the coating system, has been cold-worked in at least one area. In particular, the area comprises the at least one layer of the coating system, whereby it can be recognized from a cold-work effect in the at least one layer of the coating system that the brake disc was cold-worked only after the application of the at least one layer to the base body, in particular after the application of all layers of the coating system to the base body. 24-3017

[0024] 6. Because the brake disc has been cold-worked after the application of at least one layer of the coating system, this layer applied to the base body exhibits particularly high strength in the cold-worked area, thereby minimizing the risk of cracking in this layer, especially in the recess area. This, in turn, significantly reduces the risk of damage to at least one layer of the coating system, and in particular to all layers of the coating system, due to stress cracking. For example, the brake disc can be cold-worked in the at least one area using a rolling tool. Depending on the rolling task, several hardened rollers are arranged in a rolling tool. Simultaneous engagement of several rollers allows for a particularly short processing time.Rolling is a chipless forming process used to produce smooth, dimensionally accurate, and wear-resistant surfaces. Rolling involves the rolling of rollers or cylinders across the brake disc. This process re-forms at least one area of ​​the brake disc, resulting in work hardening in that area.

[0025] In a further possible embodiment of the invention, a wall of the brake disc, which circumferentially delimits the recess, transitions into the respective end faces of the brake disc in the opening area with a chamfer and / or a rounded edge. In other words, the brake disc has the chamfer and / or the rounded edge on the wall that circumferentially delimits the recess in the opening area. The chamfer or rounded edge effectively prevents a sharp edge at the transition from the wall that delimits the recess in the opening area to the next end face of the brake disc. Cracks can form at sharp edges under load. By avoiding such sharp edges, the risk of crack initiation and, consequently, the risk of stress cracks forming during operation can be effectively minimized. The chamfer or rounded edge can define the radial outer boundary of the recess in the opening area.A chamfer is a beveled surface created by machining an edge. The transition from the wall that circumferentially defines the recess in the mouth area to the face of the brake disc can alternatively or additionally be provided by a radius of a predefined shape. This radius prevents the occurrence of 24-3017.

[0026] 7. Mechanical stresses in the brake disc, particularly in the area of ​​the recess, are especially well avoided. This effectively prevents cracking of the brake disc, especially of at least one layer of the coating system, in the area of ​​the recess.

[0027] In this context, it may be particularly suitable for the work-hardened area of ​​the brake disc to encompass the entire chamfer and / or the entire radius. This ensures that the brake disc exhibits particularly high hardness in the chamfer or radius area due to work hardening. The risk of damage to at least one layer of the coating system as a result of stress during normal use of the brake disc, and in particular the risk of crack formation, can be significantly reduced by work hardening in the chamfer or radius area.

[0028] In a further possible embodiment of the invention, the brake disc is cold-worked in all areas that annularly enclose the respective openings of recesses. This significantly reduces the risk of cracking at all entry points of all recesses. The risk of damage to the brake disc during operation due to stress cracking in the area of ​​the respective recesses is also significantly reduced due to the particularly low risk of cracking. Consequently, a particularly long service life of the brake disc can be achieved. By preventing stress cracking, the risk of damage to layers of the coating system is also significantly reduced, resulting in a particularly long service life for the brake disc.

[0029] The invention further relates to a motor vehicle with a brake disc, as already described in connection with the brake disc according to the invention. The brake disc can be used in the motor vehicle in a braking system which, in addition to the brake disc, can have at least one brake pad. In particular, it is provided that the braking system has two brake pads for each brake disc, which can be applied to the brake disc from axially opposite sides for braking the motor vehicle. In particular, the motor vehicle has for each 24-3017

[0030] Each of the eight wheels to be braked is equipped with a brake disc, which is non-rotatably connected to its respective wheel. By applying at least one brake pad to the corresponding brake disc, the wheel of the motor vehicle, which is non-rotatably connected to this brake disc, can be braked. Due to the design of the motor vehicle with at least one brake disc, which exhibits particularly high durability, the motor vehicle can be operated for a particularly long time with very little maintenance, as the brake disc offers exceptional resistance and a particularly long service life. Furthermore, the at least one recess in the brake disc allows for a particularly sporty appearance of the motor vehicle's brake disc.

[0031] The invention further relates to a method for manufacturing a brake disc for a motor vehicle. In this method, a base body is coated with a layer system. The layer system comprises at least one friction layer, which in turn includes at least one hard material. The friction layer provides a friction area intended to come into contact with a brake pad of the motor vehicle during normal use of the brake disc for braking the vehicle. Furthermore, the method provides for at least one recess to be formed in the brake disc, which extends completely through the brake disc in the axial direction and opens into an end face of the brake disc within the friction area.It is possible that the recess is either formed in the base body before it is coated with all layers of the coating system, or that the recess is formed in the base body after it has been coated with at least one layer of the coating system, and in particular with all layers of the coating system. The recess may represent a weak point in the brake disc from which stress cracks could originate under high operating loads. The method further provides for the brake disc to be work-hardened in at least one ring-shaped area extending around the opening of the recess. This ensures that the risk of crack initiation in the brake disc originating from the at least one recess is particularly low.In particular, the process involves the production of a brake disc as described in 24-3017.

[0032] 9 has already been described in connection with the brake disc according to the invention.

[0033] In a possible further development of the method, it is provided that the brake disc is cold-worked in the at least one ring-shaped area extending around the opening of the recess by means of at least one ball and / or at least one roller rolling over this area. The area of ​​the brake disc is thus cold-worked within the framework of a rolling process, which is a type of smooth rolling. By rolling the at least one ball or the at least one roller ring-shaped over the wall of the brake disc that delimits the recess in the opening area, a uniform cold-working of the brake disc can be achieved in the ring-shaped area extending around the opening.

[0034] Uniform cold working significantly reduces the risk of cracking. Furthermore, this rolling process makes cold working particularly easy to implement in the ring-shaped area.

[0035] Further features of the invention may become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures themselves, can be used not only in the combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0036] The drawing shows in:

[0037] Fig. 1 shows a schematic top view, partially showing a brake disc in the area of ​​a recess in the brake disc;

[0038] Fig. 2 shows a schematic sectional view of a section of the brake disc in the area of ​​the recess in a first embodiment; and

[0039] Fig. 3 shows a schematic sectional view of a section of the brake disc in the area of ​​the recess in a second embodiment. 24-3017

[0040] 10

[0041] In the figures, identical and functionally equivalent elements are provided with the same reference symbols.

[0042] Figure 1 shows a partial top view of a brake disc 10 for a motor vehicle. Sectional views of the brake disc 10 along the line marked A:A in Figure 1 are shown in Figures 2 and 3, where the brake disc 10 is depicted in different embodiments. As can be seen particularly well in Figures 2 and 3, the brake disc 10 comprises a base body 12, which in this case is made of gray cast iron. A layer system 14 is applied to the base body 12, which in this case comprises an intermediate layer 16 and a friction layer 18. The intermediate layer 16 is arranged between the friction layer 18 and the base body 12. In this case, the friction layer 18 is reinforced with at least one hard material, such as, in particular, a carbide and / or a corundum.

[0043] Figure 1 shows a top view of a friction area 20 of the brake disc 10. The friction area 20 is designed to come into contact with at least one brake pad of the motor vehicle when the brake disc 10 is used as intended, thus braking the vehicle. As can be clearly seen in Figure 1, the brake disc 10 has at least one recess 22 in this friction area 20. This recess 22 extends completely through the brake disc 10 in the axial direction RA. In the representation shown in Figure 1, the axial direction RA extends into the plane of the image. The recess 22 can also be described as a ventilation opening. In particular, the recess 22 is designed as a perforated bore. In other words, the recess 22 has been created by drilling into the base body 12.

[0044] As can be seen particularly well in Fig. 1, the recess 22 is designed to have an at least substantially circular cross-section in a plane perpendicular to the axial direction RA. Figs. 2 and 3 show particularly well that the recess 22 is circumferentially bounded by a wall 24 of the brake disc 10. The recess 22 has an opening 26 into which the recess 22 connects to an end face 28 of the 24-3017

[0045] 11

[0046] The brake disc 10 opens into the surrounding area. The opening area 26 is thus an end region of the recess 22. In this case, the opening area 26 is an axial longitudinal section of the recess 22. The wall 24 of the brake disc 10, which circumferentially delimits the recess 22 in the opening area 26, transitions into the end face 28 of the brake disc 10 or directly adjoins the end face 28 of the brake disc 10. In this case, it is provided that the brake disc 10 has both a chamfer 30 and a radius 32 in the opening area 26 of the recess 22. The radius 32 is located at a transition from the chamfer 30 to the end face 28 of the brake disc 10. As can be seen in Fig. 1, it is provided that both the chamfer 30 and the rounding 32 extend in a ring shape around the entire recess 22.

[0047] The recess 22 can act as a notch initiation point. To effectively prevent crack formation originating from the recess 22 during the intended use of the brake disc 10 in a motor vehicle, it is provided that the brake disc 10 is cold-worked at least in a ring-shaped area 34 extending around the opening 26 of the recess 22. In particular, the cold-worked area 34 of the brake disc 10 includes the entire chamfer 30 and, in this case, additionally the entire radius 32. For cold work, at least one ball and / or at least one roller is used, which is rolled over the area 34 of the brake disc 10 to be worked. This results in plastic deformation of the brake disc 10 in this area 34.Plastic deformation in metals increases the dislocation density, thereby increasing the probability that dislocations will restrict and impede each other's movement. Consequently, further deformation requires greater stress, which can manifest as an increase in yield strength and tensile strength. This work hardening is accompanied by increased brittleness and / or reduced ductility. This work hardening effect through plastic deformation is used to increase the strength of the brake disc 10, at least in the specified ring-shaped area 34 extending around the recess 22.

[0048] In this case, a roller burnishing process is used for cold forming. This can also be referred to as burnishing. Burnishing is a 24-3017

[0049] 12

[0050] Forming processes for producing mirror-smooth surfaces or those with a defined surface structure. During burnishing, a contact stress is created at the contact point between a rolling element, such as a ball and / or a roller, and the surface of the area of ​​the brake disc 10 to be cold-worked. This stress causes plastic deformation when a material yield strength is exceeded. Roughness peaks are flattened almost perpendicular to the surface, and a material flow lifts roughness valleys from below. The smoothing is thus achieved through the plastic flow of a near-surface material layer.

[0051] It is provided that the brake disc 10 is cold-worked in all areas 34 which annularly enclose the respective opening areas 26 of recesses 22. Because the respective recess 22 extends completely through the brake disc 10 in the axial direction RA, this recess 22 has an opening area 26 at each of its ends opposite each other in the axial direction RA.

[0052] The brake disc 10 is manufactured in several process steps, the sequence of which can be chosen differently. In the first embodiment shown in Fig. 2, the base body 12 is first coated with the layer system 14, and then the recess 22 is formed in the coated base body 12. Subsequently, at least one area 34 of the brake disc 10 is cold-worked. In the second alternative embodiment shown in Fig. 3, the recess 22 is formed in the uncoated base body 12, and then the base body 12 is coated with the layer system 14. In this case, the brake disc 10 can be cold-worked in the at least one predetermined area 34 after application of the intermediate layer 16 and before application of the friction layer 18, and / or after application of the friction layer 18.It is therefore possible to freely choose how often the brake disc 10 is cold-worked in certain areas and whether the brake disc 10 is cold-worked in certain areas before or after the application of the friction layer 18.

[0053] The brake disc 10, provided with the hard material layer - which is the friction layer 18 reinforced with at least one hard material - exhibits particularly low abrasion and wear when used as intended 24-3017

[0054] 13 and a particularly long service life. For the manufacture of the brake disc 10, a coating system 14, in particular one-, two- or three-layer coating system 14, is applied to the base body 12, which is made of a gray cast iron alloy, in this case of system GG15 or GG25 to GG35, particularly using a thermal spraying process. Laser metal deposition (LMD), laser cladding (also known as laser coating), plasma coating, arc welding, cold gas spraying or high-speed flame spraying can be used as coating processes. The coating system 14 applied to the base body 12 is characterized by extreme hardness. Under maximum braking stress, a brake disc 10, which has at least one recess 22, can be prone to cracking, which can negatively affect the service life of the coating system 14 and the visual appearance of the brake disc 10.To avoid this, it is provided that the area 34 of the brake disc 10 radially enclosing the recess 22, in particular the brake disc 10 in the area 34 of the chamfer 30 and / or the rounding 32, is cold-worked by means of a rolling process.

[0055] Compressive residual stresses introduced by cold working have a positive effect on the crack initiation behavior of the brake disc 10 in the critical stress zone of the recess 22. A rolling tool suitable for the burnishing process can comprise at least one roller and / or at least one ball, which should cover the entire chamfer 30 in the axial direction RA. This ensures that the chamfer 30 is cold worked over its entire height in the axial direction RA. The pressure to be set on the rolling tool can depend on the contact area of ​​the rolling tool on the brake disc 10, but must be set so as not to damage the base body 12.

[0056] Overall, the invention demonstrates how cold working of a bore geometry can be used to prevent stress cracking. 24-3017

[0057] 14

[0058] Reference symbol list

[0059] 10 brake disc

[0060] 12 basic shapes

[0061] 14-shift system

[0062] 16 Intermediate shift

[0063] 18 friction layer

[0064] 20 friction area

[0065] 22 Exclusion

[0066] 24 wall

[0067] 26 Mouth area

[0068] 28 Front

[0069] 30 phase

[0070] 32 rounding

[0071] 34 cold-worked area

[0072] RA axial direction

Claims

24-3017 15 Patent claims 1. Brake disc (10) for a motor vehicle, comprising a base body (12) coated with a layer system (14) comprising at least one friction layer (18) which has at least one hard material and which provides a friction area (20) which is intended to be brought into contact with a brake pad when the brake disc (10) is used as intended in the motor vehicle for braking the motor vehicle, wherein the brake disc (10) has at least one recess (22) extending completely through the brake disc (10) in the axial direction (RA) and opening into an end face (28) of the brake disc (10) with its opening region (26) in the friction area (20) of the brake disc (10), wherein the brake disc (10) is cold-worked in at least one area (34) extending annularly around the opening region (26) of the recess (22).

2. Brake disc (10) according to claim 1, characterized in that the at least one recess (22) has been introduced into the base body (12) prior to coating the base body (12).

3. Brake disc (10) according to claim 1, characterized in that the at least one recess (22) has been introduced into the base body (12) after coating the base body (12) with at least one layer of the coating system (14), in particular after coating the base body (12) with the entire coating system (14).

4. Brake disc (10) according to one of the preceding claims, characterized in that the brake disc (10) has been cold-worked after the application of at least one layer of the coating system (14), in particular after the application of all layers of the coating system (14), in which at least one area (34) has been cold-worked. 24-3017 16 5. Brake disc (10) according to one of the preceding claims, characterized in that a wall (24) of the brake disc (10) circumferentially delimiting the recess (22) transitions in the opening area (26) with a chamfer (30) and / or a rounding (32) into respective end faces (28) of the brake disc (10).

6. Brake disc (10) according to claim 5, characterized in that the cold-worked area (34) of the brake disc (10) comprises the entire chamfer (30) and / or the entire rounding (32).

7. Brake disc (10) according to one of the preceding claims, characterized in that the brake disc (10) is cold-worked in all areas (34) which enclose the respective opening areas (26) of recesses (22) in an annular manner.

8. Motor vehicle with a brake disc (10) according to one of the preceding claims.

9. Method for manufacturing a brake disc (10) for a motor vehicle, in which a base body (12) is coated with a layer system (14) comprising at least one friction layer (18) which has at least one hard material and which provides a friction area (20) which is intended to be brought into contact with a brake pad when the brake disc (10) is used as intended in the motor vehicle for braking the motor vehicle, - at least one recess (22) is provided in the brake disc (10), which extends completely through the brake disc (10) in the axial direction (RA) and opens with its opening area (26) into an end face (28) of the brake disc (10) in the friction area (20) of the brake disc (10), and 17. The brake disc (10) is cold-worked in at least one region (34) extending annularly around the opening region (26) of the recess (22).

10. Method according to claim 9, characterized in that the brake disc (10) is cold-worked in the at least one region (34) extending annularly around the opening region (26) of the recess (22) by means of at least one ball and / or at least one roller rolling over the region (34).

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