Abstract:
A brake disc for a vehicle has a wear indicator disposed in a braking surface of the brake disc and embodied such that its appearance in a top view of the braking surface changes across a reducing level of wear. The brake disc further has a reference indicator disposed in the braking surface of the brake disc and is embodied such that its appearance in a top view of the braking surface does not change across the reducing level of wear or changes differently in a specified manner relative to the change in the wear indicator so that wear progression can be discerned from the appearance of the wear indicator in relation to the appearance of the reference indicator.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority of DE 10 2014 03 986.2, filed Mar. 19, 2014, which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to a vehicle brake disc with a wear indicator. 
         [0003]    As a result of high demands on safety-relevant components in vehicles, a brake disc thickness in a vehicle is measured at regular intervals so that the brake disc can be replaced in good time. An inadequate brake disc thickness increases the risk of heat cracks and the risk of severe wear of the brake linings up to failure of the brake disc. In order to avoid premature replacement of the brake disc and unnecessary time in the garage, it is furthermore necessary to be able to ascertain the remaining service life which is still available. In the case of commercial vehicles, this measuring process normally requires a pit or removal of the wheels which is time-consuming. It can also be very difficult for a lay person to carry this out himself or herself. 
         [0004]    It is known from practice to normally use micrometer screws in order to measure the state of wear of the brake disc or the thickness of the brake disc. This is necessary since a ridge is often retained on the outer edge of the brake disc, which ridge does not allow the use of a gauge or a conventional sliding calliper. 
         [0005]    It is furthermore known from the prior art to provide wear features, also referred to below as wear indicators, in the brake disc friction surface in the form of a recess, pocket, groove, bore or chamfer. In this case, different embodiment variants are known which may differ according to three aspects: 
         [0006]    According to a first aspect, variants are known in which the wear features appear with increasing wear and can be seen to their full extent in the case of terminal wear, e.g., EP 1 108 918 B1. Variants are furthermore known in which the wear features disappear with increasing wear and can no longer be seen in the case of terminal wear, e.g., DE 10 2005 032 638 A1. 
         [0007]    According to a second aspect, wear features are known which only mark the terminal state of wear, e.g., U.S. Pat. No. 6,457,566 B1, and wear features which enable a continuous reading off of the state of wear, e.g., US 2013/0299284 A1. The brake disc known from laid-open application US 2013/0299284 A1 has depressions with different diameters which are incorporated in the rear side of the friction ring. With increasing wear, these are covered and can then only be interpreted in terms of brake disc wear with the aid of a measuring gauge. 
         [0008]    According to a third aspect, variants are known in which wear features are distributed over the circumference in order to ensure a better view or in the case of which several features are additionally provided which are distributed radially on the brake disc in order to be able to ascertain a radial or concave oblique wear, e.g., EP 1 108 918 B1. 
         [0009]    The described wear features usually, however, only represent a “black and white” display, i.e., in the event of a complete disappearance of the wear gauge, it can assumed that a defined threshold value has been reached at the corresponding point of the brake disc. Interim states and the continuous progression of wear can, however, as described in US 2013/0299284 A1, only be ascertained with an additional measurement tool as a reference which furthermore requires direct access to the brake disc. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    It is thus an object of the invention to provide a brake disc with an improved wear indicator with which disadvantages of conventional techniques can be avoided. The object of the invention is in particular to provide wear features on brake discs which enable more reliable monitoring of the brake disc wear without having to rely on further aids and without having to remove wheels. Moreover, brake discs with such wear indicators should be produced at low cost. 
         [0011]    The brake disc according to the invention has a visually apparent wear display, comprising a wear indicator which is inserted into a braking surface of the brake disc and is embodied such that its appearance in a top view of the braking surface changes across a reducing level of wear. A reducing level of wear is to be understood as the thickness of the braking surface, also referred to as a friction surface or friction ring, of the brake disc which reduces with increasing wear. 
         [0012]    The brake disc or the visually apparent wear display furthermore comprises a reference indicator which is inserted into the braking surface of the brake disc and is embodied such that its appearance in a top view of the braking surface does not change across the reducing level of wear or changes differently in a specified manner relative to the change in the wear indicator so that wear progression, in particular continuous wear progression, can be read off from the appearance of the wear indicator in relation to the appearance of the reference indicator. 
         [0013]    A particular advantage of the invention lies in the fact that the progression of the wear can be determined on the basis of the relative appearance of the wear indicator and of the reference indicator, which appearance is visible in a top view of the braking surface, without further aids, such as slide gauges, i.e. can be read off visually and without the aid of further measurement devices or the like. 
         [0014]    In one embodiment, the wear indicator and the reference indicator are embodied such that a position which is visible in a top view of the braking surface, shape, and/or dimension of the wear indicator change relative to a visible position, shape, and/or dimension of the reference indicator across the reducing level of wear in a specified manner. 
         [0015]    According to general perspectives of the invention, the wear indicator is embodied such that, with the reducing feature of the wear, at least one further gauge of the wear indicator in the top view changes and leads to a change in the feature appearance. For example, the wear indicator can be selected such that, for example, a width, a length, a radius and/or an arc length of the wear indicator changes across the reducing level of wear. 
         [0016]    Geometrically, this further gauge thus represents a non-constant function of the level of the wear indicator. These can be shapes such as, e.g., ramps or funnels, the width or length of which changes across the level of wear. Alternatively, a conical recess can be selected in which the radius changes across the level. Another example is helix shapes in which the arc length changes across the level of wear. The derivation of this function and thus the gradient of the changing parameter can be, e.g., linear or parabolic. 
         [0017]    An appearance of the wear indicator in a top view of the braking surface is thus not restricted to a specific shape. The shape in a top view can be e.g. straight or arcuate. 
         [0018]    As mentioned above, it is possible in the context of the invention to embody the reference indicator such that its appearance in a top view of the braking surface does not change across the reducing level of wear, for example, by incorporating a depression in the braking surface with a constant cross-section in the direction of wear. Alternatively, the reference indicator is embodied such that its appearance in a top view of the braking surface changes differently in a specified manner across the reducing level of wear relative to the change in the wear indicator, i.e., the appearance of the reference indicator changes to a different extent than the wear indicator itself. 
         [0019]    In this case, the gauge of a non-constant function of the level of the reference indicator is selected such that the respectively visible position, shape and/or dimension of the reference indicator indicates a proportional reference point or notional zero position, relative to which the visible position, shape and/or dimension of the wear indicator can be compared in order to read off the relative wear progression. 
         [0020]    According to a further aspect, a shape and an orientation of the reference indicator can be embodied such that it corresponds to a shape and orientation of the wear indicator in a top view of the braking surface. In contrast, the length of the wear indicator changes at least in one direction along the braking surface with increasing wear. Moreover, according to this variant, the reference indicator can be arranged adjacent to or in the direct vicinity of the wear indicator. According to this variant, the reference indicator can be formed such that an appearance in a top view of the braking surface is unchanged across a reducing level of wear. 
         [0021]    According to this aspect, the appearance of the wear indicator and reference indicator, in the new state of the brake disc, can be substantially the same, wherein, with increasing wear, only the appearance of the wear indicator changes gradually so that, in each state of wear, a gauge which is visually easy to detect for the progression of the wear process is provided by comparison of the current appearance of the wear indicator with the appearance of the reference indicator. 
         [0022]    According to a further embodiment, the reference indicator can be formed in the shape of an elevation, recess or edge which remains visible across the reducing level of wear. Moreover, the reference indicator according to this variant is arranged at a point of the braking surface at which the reference indicator, in the new state of the brake disc, is located adjacent to or in the direct vicinity of a region, e.g., an end region, of the wear indicator, wherein the region changes its position with a reducing level of wear, i.e., this region defines a visibly migrating wear mark on the braking surface. The respective distance between the migrating end region of the wear indicator and the stationary elevation, recess or edge of the reference indicator thus represents a gauge for the wear progression which is visually easy to detect. 
         [0023]    The reference indicator thus describes by means of its shape and position the starting position of the wear mark which migrates as a result of wear. 
         [0024]    It is particularly advantageous if such an elevation, recess or edge is provided at both end regions of the wear indicator. 
         [0025]    The wear indicator can be formed as a ramp-shaped recess, and the reference indicator can be formed as a groove-shaped recess which runs parallel and adjacent to the ramp-shaped recess. Such a recess is also referred to below as a depression. A depth of the groove-shaped recess in the direction of wear is preferably at least as large as the maximum depth of the groove-shaped recess. This ensures that the reference indicator is also not visible in the maximum state of wear of the wear indicator. According to a further aspect of this embodiment variant, the ramp-shaped recess and the groove-shaped recess, in the new state of the brake disc, begin at an identical starting point and end at an identical end point. A parallel profile of the ramp-shaped and the groove-shaped recess refers, in the case of a curved profile of the recess, to a profile with an identical curvature, e.g., in the case of a circular arc-shaped profile of the ramp-shaped recess, the groove-shaped recess is arranged concentrically thereto. The groove-shaped recess can be embodied in particular with a constant depth. 
         [0026]    According to an alternative embodiment variant, the wear indicator is formed as a ramp-shaped recess, the reference indicator is formed as a recess which is arranged at an angle between 0° and 180°, e.g., at right angles, and adjacent to the ramp-shaped recess, and the ramp-shaped recess and the recess begin, in the new state of the brake disc, at an identical starting point. For example, the reference feature can thus be arranged T- or L-shaped in relation to the wear feature. According to this embodiment variant, a depth of the recess in the direction of wear can preferably be in turn at least as large as the maximum depth of the ramp-shaped recess, which is, however, not essential. 
         [0027]    According to a further exemplary embodiment, the wear indicator can be embodied as a funnel-shaped recess, and the reference indicator can be embodied by two depressions, for example, in the form of bores. In this case, a depth of the depressions is preferably at least as large as the maximum depth of the funnel-shaped recess. This in turn ensures that the reference indicator is also still visible in the maximum state of wear of the wear indicator. 
         [0028]    Moreover, the elongated hole-shaped depressions, in the new state of the brake disc, are arranged adjacent to or in the direct vicinity of the opposite edge regions of the funnel-shaped recesses. A funnel-shaped recess within the meaning of this invention also refers in particular to a slot-shaped opening on the braking surface which tapers in a funnel shape in the direction of wear. The elongated hole-shaped depressions thus mark the original dimension of the wear indicator in the new state such that the distance which becomes larger with increasing wear from the edge region of the funnel-shaped recess to the elongated hole-shaped depression represents a gauge for wear. 
         [0029]    In particular, the brake disc can be configured such that, if the funnel-shaped depression arranged between the elongated hole-shaped depressions is now barely visible or no longer visible, a maximum state of wear is reached which indicates to the driver or another person that the brake disc should be replaced. 
         [0030]    According to a further embodiment variant, the wear indicator can be embodied as a helical recess, wherein an arc length of the helical recess on the braking surface reduces with a reducing level of wear. The formation of the wear indicator as a helical recess has the advantage that the wear-induced change in the wear indicator enables self-referencing. The original arc length in the new state can be derived, for example, from the current arc length so that the reference indicator can be formed as part of the wear indicator. 
         [0031]    As a result, a feature of the helical recess, which is a gauge for original arc length in the new state, can be used as the reference indicator. An example of this is a radial edge of the helical recess, the position of which is unchanged with a reducing level of wear. Alternatively, the original arc length in the new state (or the arc length projected onto the braking surface in the new state) itself can also be used as the reference indicator if the arc length in the new state is fixedly defined since this can be derived from the current (remaining) arc length. 
         [0032]    Alternatively, the original central angle of the circular arc which is generated by projecting the arc length onto the braking surface can be used. The central angle simultaneously reduces with an arc length of the helical recess which reduces as a result of wear. 
         [0033]    According to a further embodiment, the wear indicator can be embodied as an elevation countersunk in the braking surface, which elevation tapers conically towards the braking surface, and the reference indicator can be an edge of the braking surface concentrically surrounding the countersunk elevation. 
         [0034]    According to this embodiment variant, with a reducing level of wear, the countersunk elevation is gradually removed and shaped into a truncated cone with a reducing level which appears in a top view of the braking surface in the form of a widening circle. The distance from the upper circumferential edge of the truncated cone to the reference indicator reduces gradually and as a result visualizes the state of wear. 
         [0035]    The brake disc and the countersunk elevation can, for example, be configured such that a maximum state of wear is characterized by a complete approximation of the truncated cone to the edge which concentrically surrounds the countersunk elevation (reference indicator). This embodiment variant thus also enables detecting a new state of the brake disc, a maximum state of wear and also the percentage progression of the wear visually and without further measurement means in a simple manner. 
         [0036]    According to a further aspect of the invention, a plurality of wear indicators with one or more assigned reference indicators can be arranged distributed evenly on the brake disc. This has the advantage that the wear indicator can be better seen through the hand holes of the rim irrespective of the wheel position. 
         [0037]    According to a further aspect, the appearance of the reference indicator in a top view of the brake disc can change linearly across a reducing level of wear. This is particularly advantageous for reading off the wear since a linear change, i.e., a constant increase or change in shape of the wear indicator, can be easily interpreted or extrapolated. 
         [0038]    A further aspect of the invention relates to a vehicle, in particular a commercial vehicle, with a brake disc according to one of the aspects described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    Further details and advantages of the invention are described below with reference to the enclosed drawings. In these drawings: 
           [0040]      FIGS. 1A to 1C  are a perspective view, a partial cross sectional view, and a magnified view of a brake disc according to a first exemplary embodiment in a first state of wear; 
           [0041]      FIGS. 2A to 2C  are a perspective view, a partial cross sectional view, and a magnified view of a brake disc according to the first exemplary embodiment in a second state of wear; 
           [0042]      FIGS. 3A to 3C  are a perspective view, a partial cross sectional view, and a magnified view of a brake disc according to the first exemplary embodiment in a third state of wear; 
           [0043]      FIGS. 4A to 4C  are a perspective view, a partial cross sectional view, and a magnified view of a brake disc according to the first exemplary embodiment in a fourth state of wear; 
           [0044]      FIGS. 5A and 5B  are a partial cross sectional view and a perspective view of a brake disc according to a second exemplary embodiment in a first state of wear; 
           [0045]      FIGS. 6A and 6B  are a partial cross sectional view and a perspective view of a brake disc according to the second exemplary embodiment in a second state of wear; 
           [0046]      FIGS. 7A and 7B  are a partial cross sectional view and a perspective view of a brake disc according to the second exemplary embodiment in a third state of wear; 
           [0047]      FIG. 8  is a partial sectional view of a brake disc according to a third exemplary embodiment in a first state of wear; 
           [0048]      FIG. 9  is a partial sectional view of a brake disc according to the third exemplary embodiment in a second state of wear; 
           [0049]      FIG. 10  is a partial sectional view of a brake disc according to the third exemplary embodiment in a third state of wear; 
           [0050]      FIG. 11  is a partial sectional view of a brake disc according to a fourth exemplary embodiment in a first state of wear; 
           [0051]      FIG. 12  is a partial sectional view of a brake disc according to the fourth exemplary embodiment in a second state of wear; 
           [0052]      FIG. 13  is a partial sectional view of a brake disc according to the fourth exemplary embodiment in a third state of wear; 
           [0053]      FIG. 14  is a partial sectional view of a brake disc according to the fourth exemplary embodiment in a fourth state of wear; and 
           [0054]      FIGS. 15A and 15B  are partial sectional views schematically showing the insertion of a wear indicator into the brake disc. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0055]      FIG. 1A  shows a perspective view of an internally ventilated brake disc  1  with two brake discs  2 ,  3  which are arranged parallel across webs but spaced apart from one another. Air cooling of brake disc  1  is carried out via gap  5 . 
         [0056]    A visually apparent wear display  6  is provided on at least one braking surface or friction surface  4 . Region A in  FIG. 1A  is represented in an enlarged form in the sectional view of  FIG. 1B  and the perspective view of  FIG. 1C . 
         [0057]    Wear display  6  is formed from a wear indicator in the form of a funnel-shaped recess  8  and a reference indicator, comprising two elongated hole-shaped depressions  7 A and  7 B. The depth of elongated hole-shaped depressions  7 A and  7 B is at least as large as the maximum depth of funnel-shaped depression  8  so that reference indicators  7 A and  7 B are also still visible in a state of maximum wear. 
         [0058]    In a top view, funnel-shaped depression  8  appears as a slot-shaped depression. It is, however, apparent in the cross-sectional view of  FIG. 2B  that the depth of the depression increases towards the middle, i.e., is formed in a funnel shape. 
         [0059]      FIGS. 1A to 1C  show the state of the brake disc in the new state, i.e., without wear. In this state, two elongated hole-shaped depressions  7 A and  7 B are arranged adjacent to both end regions  8 A,  8 B of funnel-shaped depression  8 . If the slot visible in a top view of funnel-shaped depression  8  thus extends up to both elongated hole-shaped depressions  7 A and  7 B, the user can recognise that brake disc  1  is still in the new state. 
         [0060]      FIGS. 2A to 2C  illustrate a first state of wear in which friction surface  4  has already been partially worn by abrasion. As a result, it is apparent in the top view of brake disc  1  that the funnel-shaped depression no longer extends up to elongated hole-shaped depressions  7 A and  7 B. A region  9  of the braking surface without a depression is exposed between the end region of elongated hole-shaped depression  8  and reference indicators  7 A and  7 B. From the size of region  9  or from the distance from end regions  8 A,  8 B of wear indicator  8  from reference indicators  7 A and  7 B, the user can identify the extent to which the wear of the brake disc has already progressed. 
         [0061]      FIGS. 3A to 3C  show a state with a higher degree of wear in comparison to  FIGS. 2A to 2C . This is apparent from the fact that region  9  has become larger in comparison to  FIGS. 2A to 2C  since a further surface layer of braking surface  4  has been removed as a result of wear. It is furthermore apparent in  FIG. 3B  that, as a result of the wear of braking surface  4 , the funnel-shaped depression in the vertical and the horizontal expansion was made even smaller. 
         [0062]    In a comparable manner,  FIGS. 4A to 4C  show a state with a higher level of wear in the case of which the distance from funnel-shaped depression  8  to reference indicators  7 A and  7 B became even larger. 
         [0063]      FIG. 5A  shows a further exemplary embodiment of a brake disc  10  in an enlarged partial sectional view. Visually apparent wear display  11  is, in this exemplary embodiment, formed from a wear indicator which is embodied as a ramp-shaped recess  12  of braking surface  4  and from a groove-shaped recess which is arranged offset parallel to ramp-shaped recess  12 . Groove-shaped recess  15  has a constant depth which corresponds to the maximum depth of ramp-shaped recess  12 . Ramp-shaped recess  12  and groove-shaped recess  15  are, in the new state of the brake disc which is shown in  FIG. 5A , of equal length so that starting point  13  of the ramp-shaped recess lies directly adjacent to starting point  17  of the groove-shaped recess. The same applies to both end points  14 ,  16  of both recesses. 
         [0064]      FIG. 5B  shows the new state in a perspective top view, where it is apparent that the appearance of wear indicator  12  and of reference indicator  15  is identical, from which the user can conclude that the brake disc is in a new state or in an unworn state. 
         [0065]      FIGS. 6A and 6B  shows a state of medium wear. In this state, braking surface  4  is already so worn that already half of ramp-shaped depression  12  has been removed. As a result, it is apparent in a top view of braking surface  4  that edge region  18  of wear indicator  12  has migrated to the centre of reference indicator  15  so that the exposed surface of braking surface without a depression  19  is exposed between original edge region  13  and current edge region  18 . The state of reference indicator  15  is unchanged. 
         [0066]    It is further apparent that the combination of wear indicator  12  and reference indicator  15  enables determining in each case the current state of wear in a simple manner visually without further aids since a comparison of the length along braking surface  4  of remaining wear indicator  12  with the unchanged length of groove-shaped depression  15  shows the progression of wear. 
         [0067]    In the case of the state of wear represented in  FIG. 6B , it can be concluded, for example, from the relative length of remaining wear indicator  12  relative to the length of groove-shaped depression  15  that approximately half of the brake disc is worn. To this end, it is naturally necessary that the brake disc and the depths of the groove- or ramp-shaped recesses are formed so that the relative lengths of the recesses correlate to the respective state of wear with the relative state of wear. 
         [0068]      FIGS. 7A and 7B  represent a third state of wear which shows a state of even greater wear. In particular a state of wear is shown which makes a replacement of the brake disc necessary since the remaining length of the wear feature is small relative to the length of the reference feature. The end region of wear feature  18  has migrated almost to opposite end region  14 . 
         [0069]      FIG. 8  shows a further embodiment variant of a brake disc  20  in an enlarged representation of the region of the braking surface on which the wear indicator and the reference indicator are accommodated. According to this variant, the wear indicator is embodied as a helical recess  21 . Helical recess  21  is delimited at one end by an edge  22  which is arranged in a stationary manner on braking surface  4  and remains visible across all states of wear. 
         [0070]    However, a further edge  23  changes with an increasing state of wear and migrates in a clockwise direction with reducing arc length  25 . Proceeding from edge  23 , a surface  24  extends in a spiral shape in the direction of wear on an incline up to stationary edge  22 . 
         [0071]    This is represented in  FIGS. 9 and 10  which show states with respectively increasing wear. The helical recess forms a self-reference since the progression of the state of wear can be read off from visible arc length  25  or on the basis of the relative position of migrating edge  13  to fixed edge  22 . The state of wear can also be derived from the central angle between edge  23  and edge  22  since the central angle in the new state is almost 360° and becomes smaller with increasing wear. The helical recess can be incorporated, for example, by fixing the inclination of the helix so that edge  23  in the new state of the brake disc is arranged in the position of  FIG. 8 , in the case of 25% wear at the position of  FIG. 9 , in the case 50% wear at the position of  FIG. 10 , etc. 
         [0072]      FIG. 11  shows a further exemplary embodiment of a brake disc  25  in an enlarged representation of the region of the braking surface on which the wear indicator and the reference indicator are fitted. According to this exemplary embodiment, the wear indicator is embodied as a countersunk elevation  26  which is inserted into braking surface  4 . Countersunk elevation  26  tapers conically towards braking surface  4 . In the new state of the brake disc, countersunk elevation  26  forms an upper tip in region  28 . Countersunk elevation  26  is surrounded concentrically by an edge  27  of braking surface  24  which simultaneously serves as a reference indicator which is described below. 
         [0073]      FIG. 12  shows a first state of wear in the case of which a part of braking surface  4  has been removed as a result of wear. As a result, an upper part of elevation  26  was also removed so that the elevation is now in the shape of a truncated cone. The upper tip was removed and appears as a circular surface  28  in a top view. 
         [0074]      FIGS. 13 and 14  represent in each case further states of wear, the state of wear in  FIG. 14  being the most advanced. It is apparent from this that with increasing wear the level of the truncated cone of elevation  26  is reduced and as a result upper circular surface  28  increases in size. As a result, the distance from circumferential edge  29  of the circular surface to reference edge  27  is reduced. Both edges  29  and  27  thus approximate one another with increasing wear. 
         [0075]    The progression of wear can be derived from the comparison of the two radii of edges  29  and  27  or from the distance from circular edge  29  to concentrically arranged circular edge  27 . The smaller the distance from edge  29  to reference edge  27  or the smaller the ratio of the radius of circular edge  29  to the radius of circular edge  27 , the more advanced the state of wear. This embodiment thus also enables a visually simple detection of the new state of the brake disc, of the maximum state of wear and of the progression of the wear on the basis of interim states. 
         [0076]    The embodiment variants described by way of example show that the user can detect the state of wear by comparison of the wear indicator with the reference indicator. The user can in particular not only precisely determine the starting and end state of wear, rather also detect the percentage progression of wear easily and without further aids. In particular, a look through the hand holes of the rim is sufficient in order to determine the state of wear so that no disassembly of the tyre is necessary. 
         [0077]    The variants described above for forming a visually apparent wear display can be produced in a variety of ways. 
         [0078]    The wear indicators and reference indicators can already be accommodated in the casting process. When cutting the molding blank, the indicators are then taken as reference points with regard to which the subsequent machining is aligned. It is particular advantageous here if the wear indicators and reference indicators then also reflect the direct relationship of the distance to the cooling channel friction surface which is relevant in terms of strength and defines the critical gauge more precisely. Alternatively, the wear features can be incorporated by machining, e.g., by boring or milling. 
         [0079]    In a further embodiment of the invention, defined recesses such as pockets  32  or  34  can be provided in brake discs  30 ,  35 , which is represented in  FIGS. 15A  or  15 B. The wear features can be subsequently fixed, for example, pressed-in, welded-on or screwed-in, into pockets  32  or  34 . The wear features themselves can then be produced in a separate process. Alternatively, shaping measures can also be used to incorporate the feature. 
         [0080]    Although the invention has been described with reference to specific exemplary embodiments, a plurality of variants and modifications are possible which also make use of the concept of the invention and thus fall into the scope of protection. As a result, the invention should not be restricted to the disclosed specific exemplary embodiments, rather the invention should encompass all the exemplary embodiments which fall into the scope of the attached claims. 
       LIST OF REFERENCE NUMBERS 
       [0000]    
       
           1 ,  10 ,  20 ,  25 ,  35  Brake disc 
           2 ,  3  Brake disc 
           4  Braking surface 
           5  Gap for cooling 
           6 ,  11  Visually apparent wear display 
           7 A,  7 B Elongated hole-shaped depression 
           8  Funnel-shaped depression 
           9  Region between elongated hole-shaped depression and funnel-shaped depression 
           12  Ramp-shaped depression 
           13  Starting region 
           14  End region 
           15  Groove-shaped depression 
           16  Starting region 
           17  End region 
           18  Migrating end region 
           19  Exposed surface of the braking surface 
           21  Helical recess 
           22  Reference edge 
           23  Migrating edge 
           24  Spiral-shaped surface 
           26  Countersunk elevation 
           27  Reference edge 
           28  Visible elevation 
           29  Circumferential edge of the visible elevation 
           31 ,  33  Wear indicator or reference indicator 
           32 ,  34  Introduction pocket