Brake discs and their manufacturing methods, vehicles

Abstract

A brake disc and its manufacturing method, and a vehicle, are disclosed. The brake disc includes a substrate and a friction layer. The friction layer includes a first surface and a second surface facing away from each other. The first surface is connected to the substrate, and the crack density of the second surface is less than that of the first surface. By setting the crack density on the second surface of the friction layer facing away from the substrate to be less than that on the first surface connected to the substrate, material peeling off from the friction layer on the second surface facing away from the substrate is prevented.

Description

[0001] This application is a divisional application of the parent application with application number "202410844929.6", application date June 27, 2024, and invention title "Brake disc and method of manufacturing thereof, vehicle". Technical Field

[0002] This application relates to the field of brake disc technology, specifically to a brake disc and its manufacturing method, and a vehicle. Background Technology

[0003] Current carbon-ceramic brake discs, due to the requirements of high friction coefficient and long service life, mostly have a silicon carbide friction layer loaded on the brake disc substrate. However, during the firing process of carbon-ceramic brake discs, due to the mismatch in thermal expansion coefficients between silicon carbide and the substrate, a large number of cracks are generated in the friction layer. Too many cracks will cause the friction layer to peel off, while too few cracks require a large amount of silicon carbide, increasing the manufacturing cost of the brake pads. Therefore, solving the problem of excessive crack density on the friction layer surface and reducing friction layer peeling has become crucial. Summary of the Invention

[0004] The purpose of this application is to provide a brake disc, its manufacturing method, and a vehicle, thereby solving the problem of friction layer peeling off the surface of the brake disc.

[0005] To achieve the objectives of this application, the following technical solution is provided: In a first aspect, the present invention provides a brake disc, comprising a substrate and a friction layer, wherein the friction layer comprises a first side and a second side facing away from each other, the first side being connected to the substrate, and the crack density of the second side being less than the crack density of the first side.

[0006] In one embodiment, the friction layer includes a first friction layer and a second friction layer. The first friction layer is disposed on the substrate, and the second friction layer is disposed on the side of the first friction layer facing away from the substrate. The first side is the side of the first friction layer facing away from the second friction layer, and the second side is the side of the second friction layer facing away from the first friction layer. The crack density of the second friction layer is less than the crack density of the first friction layer.

[0007] In one embodiment, the first friction layer includes first silicon carbide particles, and the second friction layer includes second silicon carbide particles, wherein the particle size of the second silicon carbide particles is larger than the particle size of the first silicon carbide particles.

[0008] In one embodiment, the particle size of the first silicon carbide particle is 0.3 μm to 50 μm, and the particle size of the second silicon carbide particle is 50 μm to 200 μm.

[0009] In one embodiment, the first friction layer includes first silicon carbide particles, the second friction layer includes second silicon carbide particles, and the mass percentage of the second silicon carbide particles in the second friction layer is greater than the mass percentage of the first silicon carbide particles in the first friction layer.

[0010] In one embodiment, the first silicon carbide particles account for 50% to 80% of the mass of the first friction layer, and the second silicon carbide particles account for 70% to 95% of the mass of the second friction layer.

[0011] In one embodiment, the average crack spacing λ at the first surface f1 The diameter is 2mm to 9mm.

[0012] In one embodiment, the λ f1 Satisfying the relation: ; The content of the first silicon carbide particles in the first friction layer is α, and the crack spacing of the first friction layer is α, which ranges from 0.3 mm to 0.7 mm.

[0013] In one embodiment, the average crack spacing λ at the second surface f2 The thickness ranges from 3mm to 14mm.

[0014] In one embodiment, the λ f2 Satisfying the relation: ; The content of the second silicon carbide particles in the second friction layer. The base number of the crack spacing in the second friction layer, the The value range is 0.36mm to 1mm.

[0015] In one embodiment, the crack width in the first friction layer is 2μm to 30μm, and the crack width in the second friction layer is 10μm to 80μm.

[0016] In one embodiment, the thickness of the first friction layer is 0.1 mm to 0.5 mm, and the thickness of the second friction layer is 0.3 mm to 5 mm.

[0017] In one embodiment, the first surface includes multiple first cracks, which divide the first surface to form multiple first crack patch areas; the second surface includes multiple second cracks, which divide the second surface to form multiple second crack patch areas; at least a portion of the area of ​​the first crack patch areas is smaller than the area of ​​the second crack patch areas.

[0018] In one embodiment, the area of ​​the first crack patch region is 4 mm.2 ~90mm 2 The area of ​​the second crack patch is 9 mm. 2 ~220mm 2 .

[0019] In one embodiment, the crack density of the first surface is 3 to 20 cracks / cm, and the crack density of the second surface is 2 to 18 cracks / cm.

[0020] In a second aspect, the present invention provides a method for manufacturing a brake disc, comprising: preparing a precursor material of a friction layer into a slurry, applying the slurry onto a preform; and obtaining the brake pad by curing and sintering the slurry on the preform; wherein the precursor material of the friction layer is transformed into a friction layer, the preform is transformed into a substrate, and the crack density on the side of the friction layer facing away from the substrate is less than the crack density at the junction of the friction layer and the substrate.

[0021] In one embodiment, the process of preparing the slurry from the precursor material of the friction layer and applying the slurry onto the preform includes: preparing a first slurry from first silicon carbide particles, applying the first slurry onto the preform and drying it to obtain a first layer; preparing a second slurry from second silicon carbide particles, applying the second slurry onto the first layer and drying it to obtain a second layer.

[0022] Thirdly, the present invention provides a vehicle including a brake disc as described in the first aspect.

[0023] This invention provides a friction layer on the surface of the brake disc substrate, and ensures that the crack density on the second side of the friction layer facing away from the substrate is less than the crack density on the first side connected to the substrate. This prevents material peeling from the friction layer on the second side facing away from the substrate. Furthermore, since the first side is the inner layer of the friction layer (connected to the substrate), even if there are many cracks on the first side, the material on the first side will not peel off, thereby reducing the excessive use of material on the first side and lowering the manufacturing cost of the brake pads. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 This is a cross-sectional schematic diagram of a brake disc according to one embodiment; Figure 2This is a schematic diagram of the cross-sectional dimensions of a brake disc according to one embodiment; Figure 3 This is a schematic diagram of a first crack patch region and a second crack patch region in one embodiment; Figure 4 This is a flowchart illustrating the manufacturing process of a brake disc in one implementation method. Figure 5 This is a flowchart of step S10 of one implementation method; Figure 6 A flowchart of step S20 of one implementation method; Figure 7 This is a schematic diagram showing the damage caused by patches falling off the second surface of the brake disc.

[0026] Explanation of reference numerals in the attached drawings: 10-substrate, 20-friction layer, 21-first friction layer, 22-second friction layer, 201-first surface, 202-second surface, 203-first crack, 204-second crack, 205-first crack patch area, 206-second crack patch area. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] It should be noted that when a component is said to be "fixed" to another component, it can be directly on the other component or it can be in a middle component. When a component is said to be "connected" to another component, it can be directly connected to the other component or it may be in a middle component.

[0029] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items.

[0030] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0031] This invention provides a brake disc, specifically a carbon-ceramic brake disc. Please refer to [reference needed]. Figure 1The brake disc includes a base 10 and a friction layer 20. The friction layer 20 includes a first surface 201 and a second surface 202 that are opposite to each other. The first surface 201 is connected to the base 10. Both the first surface 201 and the second surface 202 have cracks. The crack density of the second surface 202 is less than that of the first surface 201.

[0032] Specifically, the substrate 10 is made of carbon ceramic. By setting a friction layer 20 on the surface of the carbon ceramic substrate 10, the friction coefficient of the carbon ceramic brake disc can be improved to achieve the requirement of long service life. The friction layer 20 may include silicon carbide and silicon, with silicon carbide as the main component.

[0033] Since the friction layer 20 is disposed on the surface of the substrate 10 to form a coating structure, the friction layer 20 may include a first surface 201 and a second surface 202 facing away from the substrate 10, wherein the first surface 201 is connected to the substrate 10, and the second surface 202 faces away from the substrate 10. It is understood that the second surface 202 is the outward-facing side, and the braking effect is mainly achieved by rubbing the second surface 202. The crack density at the second surface 202 is less than the crack density at the first surface 201.

[0034] It needs to be explained that during the firing process of carbon-ceramic brake discs, due to the mismatch in the coefficients of thermal expansion between silicon carbide and the substrate 10, cracks will be generated in the friction layer 20. These cracks will extend from the interior of the friction layer 20 to its surface (i.e., the first surface 201 and the second surface 202), thus forming cracks on both surfaces. If the cracks on the upper surface of the friction layer 20 (i.e., the second surface 202) are too dense, it will lead to a decrease in the bonding ability between the friction layer 20 and the substrate 10, making it easy for small pieces to peel off during operation. Conversely, if the crack density on the upper surface (i.e., the second surface 202) is low, it often means that the silicon carbide content in the friction layer 20 is insufficient, resulting in a lower coefficient of friction for the brake disc.

[0035] It should be noted that the substrate 10 is annular, comprising two large, opposing surfaces, on which a friction layer 20 needs to be provided. Furthermore, the structural parameters of the friction layers 20 on both large surfaces are identical; that is, the friction layers 20 on both sides of the brake disc are distributed symmetrically with respect to the substrate. Therefore, for ease of description, the following text will only use one of the large surfaces as an example, i.e., one large surface connected to the first surface 201; and... Figure 1 The cross-sectional diagram of the brake disc shown is only a cross-section of the brake disc portion (one of the large faces).

[0036] This invention provides a friction layer 20 on the surface of the base 10 of the brake disc, and sets the crack density on the second side 202 of the friction layer 20 facing away from the base 10 to be less than the crack density on the first side 201 connected to the base 10, in order to prevent the material in the friction layer 20 on the second side 202 facing away from the base 10 from peeling off. At the same time, since the first side 201 is the inner layer structure of the friction layer 20 (connected to the base 10), even if there are many cracks on the first side 201, the material on the first side 201 will not peel off, thereby reducing the excessive use of material on the first side 201 and reducing the manufacturing cost of the brake pad.

[0037] In one implementation method, please refer to Figure 1 The friction layer 20 includes a first friction layer 21 and a second friction layer 22. The first friction layer 21 is disposed on the substrate 10. The first surface 201 is the side of the first friction layer 21 facing away from the second friction layer 22. The second friction layer 22 is disposed on the side of the first friction layer 21 facing away from the substrate 10. The second surface 202 is the side of the second friction layer 22 facing away from the first friction layer 21. The crack density of the second friction layer 22 is less than the crack density of the first friction layer 21.

[0038] Specifically, the friction layer 20 consists of two layers: a first friction layer 21 and a second friction layer 22. The first friction layer 21 is connected to the substrate 10, and the second friction layer 22 is connected to the first friction layer 21. The first friction layer 21 includes a first surface 201, and the second friction layer 22 includes a second surface 202. In a specific embodiment, the first friction layer 21 and the second friction layer 22 can be fabricated separately. That is, a precursor layer of the first friction layer 21 is first fabricated on the substrate 10, and then a precursor layer of the second friction layer 22 is fabricated on the first friction layer 21. After co-sintering, a complete friction layer 20 is obtained.

[0039] Understandably, since the first friction layer 21 and the second friction layer 22 are manufactured separately, the crack density in the formed first friction layer 21 and the second friction layer 22 can be controlled by configuring the silicon carbide parameters (including particle size and content). The crack density in the first friction layer 21 includes the crack density at the first surface 201, and the crack density in the second friction layer 22 includes the crack density at the second surface 202.

[0040] In one embodiment, the first friction layer 21 includes first silicon carbide particles, and the second friction layer 22 includes second silicon carbide particles, wherein the particle size of the second silicon carbide particles is larger than that of the first silicon carbide particles. Specifically, both the first friction layer 21 and the second friction layer 22 include silicon carbide particles, wherein the first friction layer 21 contains first silicon carbide particles, and the second friction layer 22 contains second silicon carbide particles.

[0041] Smaller silicon carbide particles are used as the raw material for the first friction layer 21. Because these smaller particles have better toughness than the larger particles, cracks initiating at the interface between the first friction layer 21 and the substrate 10 are deflected on the surface of the first silicon carbide particles. Through this effect, the cracks converge, and the cracks gradually decrease in size along the direction from the first friction layer 21 to the second friction layer 22. When extending to the second friction layer 22, due to the influence of the second silicon carbide particles, the second friction layer 22 has poorer toughness, and the cracks no longer deflect but instead penetrate the second silicon carbide particles and extend in a straight line to the second surface 202, ultimately forming the required crack distribution density. Furthermore, the second silicon carbide particles have a high coefficient of friction and good wear resistance, and the formation of appropriately sized cracks greatly improves the working stability and service life of the brake disc.

[0042] In one embodiment, the particle size of the first silicon carbide particle is 0.3 μm to 50 μm, and the particle size of the second silicon carbide particle is 50 μm to 200 μm. Optionally, the particle size of the first silicon carbide particle can be 0.3 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm; and the particle size of the second silicon carbide particle can be 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 140 μm, 160 μm, 180 μm, or 200 μm.

[0043] In one embodiment, the first friction layer 21 includes first silicon carbide particles, and the second friction layer 22 includes second silicon carbide particles, wherein the mass percentage of the second silicon carbide particles in the second friction layer 22 is greater than the mass percentage of the first silicon carbide particles in the first friction layer 21.

[0044] The content of first silicon carbide particles in the first friction layer 21 is set to be less than the content of second silicon carbide particles in the second friction layer 22. This is so that when a crack that originates at the interface between the first friction layer 21 and the substrate 10 extends to the second friction layer 22, due to the influence of the content of second silicon carbide particles, the crack no longer deflects but extends straight through the second silicon carbide particles to the second surface 202, and finally forms the required crack distribution density.

[0045] In one embodiment, the first silicon carbide particles account for 50% to 80% of the mass of the first friction layer 21, and the second silicon carbide particles account for 70% to 95% of the mass of the second friction layer 22. Optionally, the first silicon carbide particles account for 50%, 55%, 60%, 65%, 70%, 75%, or 80% of the mass of the first friction layer 21; and the second silicon carbide particles account for 70%, 75%, 80%, 85%, 90%, or 95% of the mass of the second friction layer 22. By satisfying the above-mentioned range of the mass percentage of the first silicon carbide particles in the first friction layer 21, the content of the first silicon carbide is controlled within a suitable range, which can control the crack density in the first friction layer 21, avoiding excessive crack density or insufficient addition of the first silicon carbide particles that would reduce the performance of the friction layer 20.

[0046] In one embodiment, the thickness of the first friction layer 21 is 0.1 mm to 0.5 mm, and the thickness of the second friction layer 22 is 0.3 mm to 5 mm. Optionally, the thickness of the first friction layer 21 can be 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, or 0.5 mm; and the thickness of the second friction layer 22 can be 0.3 mm, 0.5 mm, 0.8 mm, 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm. By ensuring the thickness of the first friction layer 21 is within the above range, it is possible to avoid the friction layer being too thick or too thin overall. Furthermore, it can be coordinated with the particle size of the first silicon carbide particles, because an excessively thin first friction layer 21 would result in an insufficient content of first silicon carbide particles, while a thicker first friction layer 21 would result in an excessive content of first silicon carbide particles.

[0047] In one embodiment, the crack width in the first friction layer 21 is 2μm to 30μm, and the crack width in the second friction layer 22 is 10μm to 80μm. Optionally, the crack width in the first friction layer 21 can be 2μm, 5μm, 10μm, 15μm, 20μm, 25μm, or 30μm; and the crack width in the second friction layer 22 can be 10μm, 20μm, 30μm, 40μm, 50μm, 60μm, 70μm, or 80μm. Ensuring that the crack widths in the first friction layer 21 and the second friction layer 22 are within the above ranges is to avoid damage to the overall friction layer and to control the amount of silicon carbide particles added to ensure that the friction layer 20 functions effectively. If the crack width in the first friction layer 21 and the second friction layer 22 is too narrow, it indicates that the amount of silicon carbide particles added is too small, so that the friction layer 20 cannot play its corresponding role; if the crack width is too wide, it will lead to poor stability of the friction layer 20, more defects on the friction layer 20, and limited service life of the friction layer 20.

[0048] In one embodiment, the average crack spacing λ at the first surface 201 f1The crack spacing is 2mm to 9mm. The average crack spacing λ on the surface of the second friction layer 22 is... f2 The diameter ranges from 3mm to 14mm. Optional, λ. f1 It can be 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, or 9mm; λ f2 The crack diameter can be 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, or 14mm. It must satisfy the average crack spacing λ at point 201 on the first surface. f1 The average crack spacing λ at the second surface is 202. f2 Within the aforementioned range, the key is to ensure the crack spacing in the first friction layer 21 and the second friction layer 22. This is to avoid excessive crack density due to cracks being too close together, and to control the amount of silicon carbide particles added to ensure that the friction layer 20 functions effectively. When the average crack spacing in both the first friction layer 21 and the second friction layer 22 is too close, it indicates an increased crack density, decreased stability of the friction layer 20, more defects on the friction layer 20, and a limited service life. Conversely, when the average crack spacing in both the first friction layer 21 and the second friction layer 22 is too far, it indicates that the amount of silicon carbide particles added is too small, preventing the friction layer 20 from fulfilling its intended function.

[0049] In one embodiment, the average crack spacing λ at the first surface 201 f1 Satisfying the relation: ; α represents the content of the first silicon carbide particles in the first friction layer 21, and α represents the basic value of the crack spacing in the first friction layer 21, with a value ranging from 0.3 mm to 0.7 mm.

[0050] It should be noted that the average crack spacing λ on the first surface 201 f1 The content of the first silicon carbide particles will affect the production of the actual brake disc. In order to control the average crack spacing λ of the first surface 201, the following measures are taken before production: f1 Within the range provided in the above embodiments, the average crack spacing λ of the produced brake disc can be ensured by adjusting the values ​​of the above parameters. f1 Within the required range. Therefore, the present invention aims to provide a method for facilitating the pre-calculation of the average crack spacing λ on the first surface 201. f1 The formula is used to determine the content of the first silicon carbide particles in the first friction layer 21 before manufacturing the brake disc, thereby reducing the manufacturing difficulty of the brake disc and constraining the average crack spacing λ. f1 This helps prevent the actual crack spacing from exceeding the range provided above, thereby improving the yield rate.

[0051] In one embodiment, the average crack spacing λ at the second surface 202 f2Satisfying the relation: ; The content of the second silicon carbide particles in the second friction layer 22. This is the base number for the crack spacing of the second friction layer 22. The value range is 0.36mm to 1mm. Similarly, the average crack spacing λ at point 202 on the second surface is set. f2 The purpose of satisfying the above relationship is also to balance the content of the second silicon carbide particles in the second friction layer 22, so as to control the average crack spacing λ. h2 For details regarding the purposes within the aforementioned scope, please refer to the above explanation; further details will not be elaborated upon here.

[0052] In one embodiment, the average crack spacing λ in the first friction layer 21 h1 The average crack spacing λ in the second friction layer 22 is 2mm~9mm. h2 The crack spacing is 3mm to 14mm. Optionally, the average crack spacing λ in the first friction layer 21 is... h1 The crack spacing λ in the second friction layer 22 can be 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, or 9mm. h2 The crack width can be 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, or 14mm. This satisfies the average crack spacing λ in the first friction layer 21. h1 The average crack spacing λ in the second friction layer 22 h2 The above range is to avoid excessive crack density due to cracks being too close together, and to control the amount of silicon carbide particles added to ensure that the friction layer 20 can fully function. When the average crack spacing in the first friction layer 21 and the second friction layer 22 is too close, it indicates that the crack density is increased, the stability of the friction layer 20 is deteriorated, there are more defects on the friction layer 20, and the service life of the friction layer 20 is limited. When the average crack spacing in the first friction layer 21 and the second friction layer 22 is too far, it indicates that the amount of silicon carbide particles added is too small, so that the friction layer 20 cannot play its corresponding role.

[0053] In one implementation method, please refer to Figure 2 The average crack spacing λ in the first friction layer 21 h1 Satisfying the relation: , h1 < h T .

[0054] Among them, h T h1 is the thickness of the first friction layer 21, h1 is the shortest distance between the crack in the first friction layer 21 and the substrate 10, β is the specific stiffness coefficient of the friction layer 20, and σ is the thickness of the first friction layer 21. maxE represents the residual thermal stress at the junction of the friction layer 20 and the substrate 10. r Δα is the Young's modulus of friction layer 20, L is the reference distance for horizontal deflection of the crack, Δα is the difference in thermal expansion coefficients between friction layer 20 and substrate 10, and ΔT is the difference between silicon diffusion temperature and room temperature.

[0055] Optionally, the thickness h of the first friction layer 21 T The above implementation method can be referred to, and will not be repeated here. It should be explained that this formula is used to calculate the average spacing λ between cracks in the first friction layer 21. h1 h1 is the shortest distance between the crack at the first friction layer 21 and the substrate 10, which needs to be calculated; for example Figure 2 As shown.

[0056] Optionally, the specific stiffness coefficient β of the friction layer 20 refers to the ratio of the elastic modulus of the material to its density, also known as "specific modulus" or "specific elastic modulus".

[0057] It should be noted that the average crack spacing λ of the first friction layer 21 h1 It will be affected by the above parameters, but in reality, it is affected by the material's own properties (such as the material's modulus, content, and the required thickness of the first friction layer 21). Before the actual production of the brake disc, in order to control the average crack spacing λ of the first friction layer 21... h1 Within the range provided in the above embodiments, the average crack spacing λ of the produced brake disc can be ensured by adjusting the values ​​of the above parameters. h1 Within the required range. Furthermore, it is evident from the above relationship that the average crack spacing λ of the first friction layer 21 is... h1 The crack spacing λ of the first friction layer 21 is directly proportional to some parameters and inversely proportional to others. Therefore, by strictly controlling the values ​​of each parameter, the required average crack spacing λ of the first friction layer 21 can be obtained. h1 .

[0058] Therefore, the present invention aims to provide a method for facilitating the pre-calculation of the average crack spacing λ of the first friction layer 21. h1 The formula is used to determine the parameters of the friction layer before manufacturing the brake disc, thereby reducing the manufacturing difficulty of the brake disc and constraining the average crack spacing λ. h1 This helps prevent the actual crack spacing from exceeding the range provided above, thereby improving the yield rate.

[0059] In one implementation method, please refer to Figure 2 The average crack spacing λ in the second friction layer 22 h2 Satisfying the relation: h T ≤h2≤(h T+h S ).

[0060] Among them, h S h1 is the thickness of the second friction layer 22, and h2 is the shortest distance between the crack in the second friction layer 22 and the substrate 10.

[0061] Optionally, the thickness h of the second friction layer 22 S The above implementation method can be referred to, and will not be repeated here. It should be explained that this formula is used to calculate the average spacing λ between cracks in the second friction layer 22. h2 h2 is the shortest distance between the crack at the second friction layer 22 and the substrate 10, which needs to be calculated; for example Figure 2 As shown, this distance should be greater than h1 mentioned above. Similarly, the average crack spacing λ in the second friction layer 22 is set. h2 The purpose of satisfying the above relationship is also to balance the proportions of various parameters in the second friction layer 22, so as to control the average crack spacing λ. h2 For details regarding the purposes within the aforementioned scope, please refer to the above explanation; further details will not be elaborated upon here.

[0062] In one implementation, Where p is the Poisson's ratio of friction layer 20, and E S For Young's modulus of matrix 10, t S The thickness of the substrate is 1 / 2, h R This represents the original thickness of the second friction layer 22 after silicon infiltration.

[0063] Optional, Poisson's ratio refers to the ratio of transverse normal strain to axial normal strain when a material is under uniaxial tension or compression. It is also called the transverse deformation coefficient and is an elastic constant reflecting the transverse deformation of the material. The Poisson's ratio of silicon and silicon carbide (the Poisson's ratio of friction layer 20) is around 0.2. Optional, h R The thickness ranges from 1mm to 4mm.

[0064] Furthermore, it should be noted that in calculating the residual thermal stress at the junction of the friction layer 20 and the substrate 10, the thickness of the second friction layer 22 before silicon diffusion and processing needs to be considered. The second friction layer 22 can be processed to different sizes after silicon diffusion, but the residual thermal stress at the junction of the friction layer 20 and the substrate 10 does not change with the size of the processed layer (residual stress is generated during cooling and causes the friction layer 20 to crack). Therefore, the residual stress should be calculated using the thickness of the second friction layer 22 before processing (generally, the processing allowance is 0.5 mm to 1.5 mm, i.e., h). R Compared to h S (0.5mm~1.5mm larger).

[0065] In one embodiment, the residual thermal stress σ at the junction of the friction layer 20 and the substrate 10 max The pressure ranges from 100 MPa to 500 MPa. Optionally, the residual thermal stress σ at the junction of the friction layer 20 and the substrate 10... max It can be 100MPa, 200MPa, 300MPa, 400MPa, or 500MPa.

[0066] The residual thermal stress σ at the junction of friction layer 20 and substrate 10 is satisfied. max Within the aforementioned range, it is to ensure the average crack spacing λ h2 and the average crack spacing λ h1 Within the aforementioned range. It is understandable that, based on the aforementioned average crack spacing λ... h2 and the average crack spacing λ h1 The relationship between residual thermal stress σ max Since the residual thermal stress σ is inversely proportional to both, in order to control the average crack spacing (i.e., crack density), it is necessary to strictly control the residual thermal stress σ. max The range of values ​​for . Furthermore, the residual thermal stress σ max Due to the inherent properties of the matrix 10 and silicon carbide particles, the residual thermal stress σ can be controlled by adjusting the ratio of the parameters of the matrix 10 and silicon carbide particles. max The purpose is to reduce the manufacturing difficulty of brake discs and improve the yield rate through the above relationship.

[0067] In one embodiment, the first friction layer 21 further includes first silicon particles, and the second friction layer 22 further includes second silicon particles. , of which E SiC E represents the Young's modulus of silicon carbide. Si V is the Young's modulus of silicon. TSiC V represents the content of the first silicon carbide particles in the first friction layer 21. TSi V represents the content of the first silicon particles in the first friction layer 21. SSiC V represents the content of the second silicon carbide particles in the second friction layer 22. SSi The content of the second silicon particles in the second friction layer 22.

[0068] Optional, the Young's modulus E of silicon carbide SiC The Young's modulus E of silicon is approximately 300 GPa to 700 GPa. Si The pressure is approximately 90 GPa to 150 GPa. The content V of the first silicon carbide particles in the first friction layer 21 is... TSiC The content V of the second silicon carbide particles in the second friction layer 22 SSiCThe above-described embodiments can be referred to, and will not be repeated here. Since the friction layer 20 only includes silicon carbide and silicon, the content V of the first silicon particles in the first friction layer 21 is... TSi The content V of the second silicon particle can be calculated from the content of the first silicon carbide particle. SSi Similarly.

[0069] In one implementation, , where α SUB The coefficient of thermal expansion of the matrix 10 is taken as 1×10^ -6 / ℃, α Si α is the coefficient of thermal expansion of silicon. SiC is the coefficient of thermal expansion of silicon carbide.

[0070] Optionally, near room temperature (approximately 25°C), the coefficient of thermal expansion α of silicon is... Si Approximately 2.5 × 10^ -6 / ℃~3.0×10^ -6 Within the range of / ℃, the coefficient of thermal expansion α of silicon carbide SiC Approximately 4.4 × 10^ -6 / ℃.

[0071] In one embodiment, the specific stiffness coefficient β of the friction layer 20 is 1500-7000. Optionally, the specific stiffness coefficient β of the friction layer 20 can be 1500, 2000, 3000, 4000, 5000, 6000, or 7000.

[0072] In one embodiment, the reference distance L for the horizontal deflection of the crack is 1mm to 4mm. Optionally, the reference distance L for the horizontal deflection of the crack can be 1mm, 2mm, 3mm, 4mm, or 4mm. Ensuring that the reference distance L for the horizontal deflection of the crack is within the above range is to avoid excessive horizontal deflection of the crack. Excessive crack deflection would cause the crack texture in the friction layer 20 to extend too far, thus affecting the stability of the friction layer 20. Therefore, controlling the above range can improve the structural stability of the friction layer 20.

[0073] In one implementation method, please refer to Figure 3 The crack width on the first surface 201 is smaller than the crack width on the second surface 202.

[0074] Specifically, during the firing process of carbon-ceramic brake discs, due to the mismatch in the coefficients of thermal expansion between silicon carbide and the substrate 10, a large number of cracks are generated in the friction layer 20. Furthermore, the crack widths vary depending on the silicon carbide content. Excessively wide cracks on the upper surface (i.e., the second surface 202) of the friction layer 20 lead to a decrease in the strength and bonding ability of the friction layer 20 itself, making it prone to small pieces peeling off during operation. Conversely, excessively narrow cracks on the upper surface (i.e., the second surface 202) often indicate insufficient silicon carbide content in the friction layer 20, resulting in a lower coefficient of friction for the brake disc.

[0075] It should be explained that in this embodiment, the crack width on the first surface 201 can be referenced to the crack width in the first friction layer 20 in the above embodiment; the crack width on the second surface 202 can be referenced to the crack width in the second friction layer 20 in the above embodiment. However, it should be explained that the first surface 201 is the surface of the first friction layer 20, so the crack width on the first surface 201 can be different from the crack width in the first friction layer 20, or the range of the crack width on the first surface 201 can be different from the range of the crack width in the first friction layer 20; the second surface 202 is the surface of the second friction layer 20, so the crack width on the second surface 202 can be different from the crack width in the second friction layer 20, or the range of the crack width on the second surface 202 can be different from the range of the crack width in the second friction layer 20.

[0076] This invention provides a friction layer 20 on the surface of the brake disc substrate 10, and ensures that the crack width on the first surface 201 is smaller than the crack width on the second surface 202. This ensures that the amount of silicon carbide particles added on the second surface 202 facing away from the substrate 10 can be fully utilized, thus ensuring a higher coefficient of friction on the second surface 202. It also saves on the material used on the first surface 201. Since the first surface 201 is the inner layer structure of the friction layer 20 (connected to the substrate 10), even if the crack width on the first surface 201 is small, the amount of silicon carbide particles added is less, which can reduce the excessive use of material on the first surface 201 and reduce the manufacturing cost of the brake pad.

[0077] In one embodiment, the crack width on the first surface 201 is 0.1 μm to 4 μm, and the crack width on the second surface 202 is 1 μm to 10 μm. Optionally, the crack width on the first surface 201 can be 0.1 μm, 0.4 μm, 0.8 μm, 1.2 μm, 1.6 μm, 2 μm, 2.4 μm, 2.8 μm, 3.2 μm, 3.6 μm, or 4 μm. The crack width on the second surface 202 can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. Ensuring that the crack widths on the first surface 201 and the second surface 202 are within the above ranges is to avoid damage to the overall friction layer 20 and to control the amount of silicon carbide particles added to ensure that the friction layer 20 functions effectively. If the gap width of the cracks on the first surface 201 and the second surface 202 is too narrow, it indicates that the amount of silicon carbide particles added is too small, so that the friction layer 20 cannot play its corresponding role; if the crack width is too wide, it will lead to a decrease in the stability of the friction layer 20, more defects on the friction layer 20, and a limited service life of the friction layer 20.

[0078] In one implementation method, please refer to Figure 3 The first surface 201 includes multiple first cracks 203, which divide the first surface 201 to form multiple first crack patch areas 205; the second surface 202 includes multiple second cracks 204, which divide the second surface 202 to form multiple second crack patch areas 206; at least some of the first crack patch areas 205 have an area smaller than the area of ​​the second crack patch areas 206.

[0079] Specifically, such as Figure 3 As shown in a), the first surface 201 includes multiple intersecting first cracks 203, so the first cracks 203 can divide the first surface 201 into multiple regions of different sizes and shapes. All the regions divided on the first surface 201 are collectively referred to as the first crack patch region 205. Figure 3 As shown in b), the second surface 202 includes multiple intersecting second cracks 204, so the second cracks 204 can divide the second surface 202 into multiple regions of different sizes and shapes. All the regions divided on the second surface 202 are collectively referred to as the second crack patch region 206.

[0080] Understandably, since the crack density on the first surface 201 is different from the crack density on the second surface 202, and the crack density on the second surface 202 is less than that on the first surface 201, there are fewer second crack patch regions 206 on the second surface 202, and more first crack patch regions 205 on the first surface 201. Therefore, when the areas of the first surface 201 and the second surface 202 are the same, the area of ​​the second crack patch region 206 is greater than the area of ​​the first crack patch region 205. Thus, the crack density on the first surface 201 and the crack density on the second surface 202 can be obtained from the number and area of ​​the second crack patch regions 206. The difference in crack density can be visually determined by the area of ​​the first crack patch region 205 and the area of ​​the second crack patch region 206. When the area of ​​the first crack patch region 205 is small and there are many areas, the material at the first surface 201 will not peel off, thereby reducing the excessive use of material at the first surface 201 and reducing the manufacturing cost of the brake pad.

[0081] In one embodiment, the area of ​​the first crack patch region 205 is 4 mm. 2 ~90mm 2 The area of ​​the second crack patch 206 is 9 mm. 2 ~220mm 2 Optionally, the area of ​​the first crack patch region 205 can be 4 mm. 2 10mm 2 20mm 2 30mm 2 40mm 2 50mm 2 60mm 2 70mm 2 80mm 2 90mm 2 The area of ​​the second crack patch 206 is 9 mm. 2 20mm 2 30mm 2 50mm 2 70mm 2 100mm 2 150mm 2 200mm 2 220mm 2 By ensuring that the areas of the first crack patch region 205 and the second crack patch region 206 are within the aforementioned range, it can be ensured that the second crack patch region 206 has a larger area, and it is not easy for the second crack patch region 206 to fall off during long-term use; while the area of ​​the first crack patch region 205 is small, so even if there are many cracks on the first surface 201, the material at the first surface 201 will not peel off.

[0082] In one embodiment, the crack density of the first surface 201 is 3 to 20 cracks / cm, and the crack density of the second surface 202 is 2 to 18 cracks / cm; wherein the crack density of the second surface 202 is 1 to 6 cracks / cm lower than that of the first surface 201.

[0083] Optionally, the crack density of the first surface 201 can be 3 cracks / cm, 4 cracks / cm, 6 cracks / cm, 8 cracks / cm, 10 cracks / cm, 12 cracks / cm, 14 cracks / cm, 16 cracks / cm, 18 cracks / cm, or 20 cracks / cm. The crack density of the second surface 202 can be 2 cracks / cm, 4 cracks / cm, 6 cracks / cm, 8 cracks / cm, 10 cracks / cm, 12 cracks / cm, 14 cracks / cm, 16 cracks / cm, or 18 cracks / cm.

[0084] It is understandable that by setting the crack density on the second surface 202 to be less than the crack density on the first surface 201 connected to the substrate 10, the material in the friction layer 20 on the second surface 202 facing away from the substrate 10 is prevented from peeling off. At the same time, since the first surface 201 is the inner layer structure of the friction layer 20 (connected to the substrate 10), even if there are many cracks on the first surface 201, the material on the first surface 201 will not peel off, thereby reducing the excessive use of material on the first surface 201 and reducing the manufacturing cost of the brake pad.

[0085] In one embodiment, the present invention also provides a method for manufacturing a brake disc, please refer to [reference needed]. Figure 4 Specifically, it includes: Step S10: Prepare a slurry from the precursor material of the friction layer and apply the slurry onto the preform.

[0086] Step S20: Brake pads are obtained by curing and sintering the slurry on the preform.

[0087] The precursor material of the friction layer is transformed into the friction layer, and the preform is transformed into the matrix. The crack density on the side of the friction layer facing away from the matrix is ​​less than the crack density at the junction of the friction layer and the matrix.

[0088] In one implementation method, please refer to Figure 5 The process of preparing a slurry from the precursor material of the friction layer and applying the slurry onto the preform includes: Step S11: The first silicon carbide particles are made into a first slurry, the first slurry is brushed onto the preform and dried to obtain a first layer.

[0089] Step S12: The second silicon carbide particles are made into a second slurry, the second slurry is coated on the first layer and dried to obtain the second layer.

[0090] Optionally, in step S11, the process of preparing the first silicon carbide particles into a first slurry specifically includes: mixing the first silicon carbide particles, phenolic resin powder, and alcohol, wherein the particle size of the first silicon carbide is 0.3μm to 50μm, the content of the first silicon carbide particles is 40% to 60%, the content of the phenolic resin powder is 10% to 50%, and the content of the alcohol is 30% to 40%, thereby obtaining the first slurry.

[0091] Optionally, in step S11, the first slurry is applied to the preform and dried to obtain the first layer. Specifically, this includes applying the first slurry to the upper and lower surfaces of the preform and placing it in a 60°C oven to completely dry the alcohol to obtain the first layer.

[0092] Optionally, in step S12, the process of preparing the second silicon carbide particles into a second slurry specifically includes: mixing the second silicon carbide particles, phenolic resin powder, and alcohol, wherein the particle size of the second silicon carbide is 50μm to 200μm, the content of the second silicon carbide particles is 30% to 50%, the content of the phenolic resin powder is 10% to 50%, and the content of the alcohol is 30% to 40%, to obtain a first slurry.

[0093] Optionally, in step S12, the second slurry is applied to the first layer and dried to obtain the second layer. Specifically, this includes applying the second slurry to the upper and lower surfaces of the first layer and placing it in a 60°C oven to completely dry the alcohol to obtain the second layer.

[0094] In one implementation method, please refer to Figure 6 Brake pads are obtained by curing and sintering the slurry on the preform, including: Step S21: The preform having the first and second layers is solidified and then placed in a carbonization furnace for carbonization to obtain a carbonized blank.

[0095] Step S22: After processing the carbonized green body, liquid phase silicon infiltration is performed to obtain a carbon ceramic green body.

[0096] Step S23: The surface and sides of the carbon ceramic blank are machined to obtain the brake disc.

[0097] Optionally, in step S21, the preform having the first layer and the second layer is cured, specifically including: placing the preform having the first layer and the second layer at 150°C for curing, and the curing time is 2h~3h.

[0098] Optionally, in step S21, the preform is placed in a carbonization furnace for carbonization, specifically including: the solidified preform is placed in a carbonization furnace for carbonization at a temperature of 1000℃ for 2-4 hours.

[0099] Optionally, in step S22, after processing the carbonized preform, liquid-phase silicon infiltration is performed, and the thickness h of the second friction layer in the resulting carbon-ceramic preform is... RThe thickness is 1mm to 4mm. R The rationale for the value can be found in the above implementation method, and will not be repeated here.

[0100] In one embodiment, the present invention also provides a vehicle including a brake disc as described in the above embodiments.

[0101] The technical solution of the present invention will be described in detail below through specific embodiments, and the data of each embodiment are shown in Table 1.

[0102] Table 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative Example 1 The particle size (μm) of silicon carbide in the first friction layer 100 100 100 100 100 50 200 100 Silicon carbide content (%) in the first friction layer 60% 70% 80% 50% 80% 60% 60% 60% Thickness of the first friction layer (mm) 0.3 0.5 0.7 0.3 0.3 0.3 0.3 0.3 Average crack spacing in the first friction layer 0.963 0.988 1.008 0.921 1.021 1.925 0.700 1.021 The particle size (μm) of silicon carbide in the second friction layer 25 25 25 25 25 0.3 50 100 Silicon carbide content (%) in the second friction layer 80% 85% 90% 70% 95% 80% 80% 60% Thickness (mm) of the second friction layer after silicon infiltration 3.3 3 2.8 3.3 3.3 3.3 3.3 3.3 Thickness of the second friction layer (mm) 1.8 1.5 1.3 1.8 1.8 1.8 1.8 1.8 Average crack spacing in the second friction layer 1.155 1.369 1.650 1.105 1.225 2.750 0.757 0.998 Specific stiffness coefficient β 4000 4000 4000 4000 4000 2000 5500 / Reference distance L for horizontal deflection of the crack 1.8 1.8 1.8 1.8 1.8 1 4 / Half the thickness of the substrate (mm) 17 17 17 17 17 17 17 17 Residual thermal stress (MPa) 392 392 404 370 427 392 392 / <![CDATA[Size of the brake disc falling plaque (cm 2 )]]> 1.4 0.9 0.7 1.5 1.2 0.2 1.9 2.4 Table 1 shows the size of the brake disc chips after use. These chips will appear on the second surface of the brake disc due to cracks. After the chips fall off, holes will form on the second surface (please refer to...). Figure 7 The shaded area in the diagram represents the hole. The "size of the patch" mentioned above refers to the open area of ​​the hole, so the unit is "cm". 2 Based on the data in Table 1, it can be found that the size of the patches that fell off the brake discs provided in Examples 1-7 is smaller than that in Comparative Example 1, which shows that the brake discs provided by the present invention can solve the problem of friction layer peeling.

[0103] In the description of the embodiments of this application, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0104] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A brake disc, characterized in that, The device includes a substrate and a friction layer disposed on the surface of the substrate. The substrate is made of carbon ceramic material, and the friction layer contains silicon carbide and silicon. The friction layer has cracks that extend from the interior of the friction layer to the surface of the friction layer.

2. The brake disc according to claim 1, characterized in that, The friction layer includes a first side and a second side facing away from each other. The first side is connected to the substrate. The crack extends inside the friction layer to the first side and the second side of the friction layer, forming a crack on the first side and the second side.

3. The brake disc according to claim 2, characterized in that, The crack density on the second surface is less than that on the first surface.

4. The brake disc according to claim 2, characterized in that, The friction layer includes a first friction layer and a second friction layer. The first friction layer is disposed on the substrate, and the second friction layer is disposed on the side of the first friction layer that faces away from the substrate. The first side is the side of the first friction layer that faces away from the second friction layer, and the second side is the side of the second friction layer that faces away from the first friction layer.

5. The brake disc according to claim 4, characterized in that, The first friction layer includes a first silicon carbide particle, and a crack that originates at the interface between the first friction layer and the substrate deflects on the surface of the first silicon carbide particle; the second friction layer includes a second silicon carbide particle, and the crack extends along the first friction layer to the second friction layer, and the crack extending to the second friction layer passes through the second silicon carbide particle and extends in a straight line to the second surface.

6. The brake disc according to claim 5, characterized in that, The horizontal deflection reference distance L of the crack on the surface of the first silicon carbide particle is 1 mm to 4 mm.

7. The brake disc according to claim 4, characterized in that, The average crack spacing λ in the first friction layer h1 Smaller than the average crack spacing λ in the second friction layer h2 The average crack spacing λ in the first friction layer h1 The average crack spacing λ in the second friction layer is 0.7 mm to 1.021 mm. h2 The diameter ranges from 0.757 mm to 1.650 mm.

8. The brake disc according to claim 7, characterized in that, The λ h1 Satisfying the relation: ,h1<h T , Among them, h T h1 is the thickness of the first friction layer, h1 is the shortest distance between the crack in the first friction layer and the substrate, β is the specific stiffness coefficient of the friction layer, and the value of β ranges from 1500 to 7000. max The residual thermal stress at the junction of the friction layer and the substrate, σ max The value range is 100 MPa to 500 MPa, E r The value of L is the Young's modulus of the friction layer, L is the reference distance for horizontal deflection of the crack, and the value of L ranges from 1 mm to 4 mm. Δα is the difference in the coefficient of thermal expansion between the friction layer and the substrate, and ΔT is the difference between the silicon diffusion temperature and the room temperature. The λ h2 Satisfying the relation: ,h T ≤h2≤(h T +h S ), Among them, h T h is the thickness of the first friction layer. S h1 is the thickness of the second friction layer, h2 is the shortest distance between the crack in the second friction layer and the substrate, β is the specific stiffness coefficient of the friction layer, and the value of β ranges from 1500 to 7000. max The residual thermal stress at the junction of the friction layer and the substrate, σ max The value range is 100MPa~500MPa, E r Let L be the Young's modulus of the friction layer, L be the reference distance for horizontal deflection of the crack, and L range from 1 mm to 4 mm. Let Δα be the difference in the coefficient of thermal expansion between the friction layer and the substrate, and ΔT be the difference between the silicon diffusion temperature and room temperature.

9. The brake disc according to any one of claims 4 to 8, characterized in that, The crack density of the second friction layer is less than that of the first friction layer.

10. The brake disc according to claim 5, characterized in that, The mass percentage of the second silicon carbide particles in the second friction layer is greater than the mass percentage of the first silicon carbide particles in the first friction layer; the mass percentage of the first silicon carbide particles in the first friction layer is 50%~80%, and the mass percentage of the second silicon carbide particles in the second friction layer is 70%~95%.

11. The brake disc according to claim 4, characterized in that, The crack width in the first friction layer is 2 μm to 30 μm, and the crack width in the second friction layer is 10 μm to 80 μm; the thickness of the first friction layer is 0.1 mm to 0.5 mm, and the thickness of the second friction layer is 0.3 mm to 5 mm.

12. The brake disc according to claim 3, characterized in that, Average crack spacing λ at the first surface f1 Satisfying the relation: The content of the first silicon carbide particles in the first friction layer is α, and the crack spacing of the first friction layer is α, which ranges from 0.3 mm to 0.7 mm. Average crack spacing λ at the second surface f2 Satisfying the relation: The content of the second silicon carbide particles in the second friction layer. The base number of the crack spacing in the second friction layer, the The value ranges from 0.36 mm to 1 mm.

13. The brake disc according to claim 1, characterized in that, The Young's modulus E of the friction layer r Satisfying the relation: Among them, h T h is the thickness of the first friction layer. S E represents the thickness of the second friction layer. SiC E represents the Young's modulus of silicon carbide, within the range of 300 GPa to 700 GPa. Si V represents the Young's modulus of silicon, in the range of 90 GPa to 150 GPa. TSiC V represents the content of the first silicon carbide particles in the first friction layer. TSi V represents the content of the first silicon particles. SSiC V represents the content of the second silicon carbide particles in the second friction layer. SSi The content of the second silicon particle.

14. The brake disc according to claim 2, characterized in that, The first surface includes multiple first cracks, and the second surface includes multiple second cracks. The width of the first crack is 0.1 μm to 4 μm, and the width of the second crack is 1 μm to 10 μm.

15. The brake disc according to claim 14, characterized in that, The density of the first crack is greater than the density of the second crack.

16. The brake disc according to claim 14, characterized in that, The first crack divides the first surface to form a plurality of first crack patch areas, and the second crack divides the second surface to form a plurality of second crack patch areas, wherein at least a portion of the area of ​​the first crack patch areas is smaller than the area of ​​the second crack patch areas.

17. The brake disc according to claim 16, characterized in that, The area of ​​the first crack patch region is 4 mm. 2 ~90 mm 2 The area of ​​the second crack patch region is 9 mm. 2 ~220 mm 2 .

18. The brake disc according to claim 14, characterized in that, The density of the first crack is 3 to 20 cracks / cm, and the density of the second crack is 2 to 18 cracks / cm.

19. A vehicle, characterized in that, Includes the brake disc as described in any one of claims 1-18.

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