DE102022211519A1 - Friction disc with wear indicator - Google Patents

Abstract

The invention relates to a friction disk (1) for a vehicle brake (3). This comprises a core material (5) with a wear protection layer (7) applied thereto, wherein at least part of an outer surface (9) of the wear protection layer (7) defines a friction surface (11). At least one wear indicator (14) is provided below the friction surface (11), wherein a raised region (15) of the core material (5) is provided as the wear indicator (13).

Description

The present description relates to a friction disc, in particular a brake disc, for motor vehicle brakes.

As is well known, friction brakes convert kinetic energy into heat energy. This requires a functioning friction lining, and if the friction lining wears down too much, road safety is no longer guaranteed.

To ensure this safety, friction discs can be equipped with wear indicators to show that they need to be replaced. EN 10 2010 013 343 A1 a friction disc made of grey cast iron with a wear protection layer and a wear indicator arranged between them, which takes up part of the friction surface. The wear indicator differs from at least one of the components friction surface and wear protection layer of the friction surface by at least one of the features colour and structure. In practical use of a friction disc acc. EN 10 2010 013 343 A1 As abrasion increases, the wear indicator in the friction surface can be visually recognized from a certain point onwards.

In contrast, it is an object of the present invention to simplify the construction of a friction disc with wear indicator.

This object is solved by the independent claim. Advantageous embodiments result from the features of the dependent claims.

According to one embodiment of the invention, a friction disk and in particular a brake disk is proposed which can be provided for the brake, for example a disk or drum brake, of a motor vehicle. The friction disk, which is in particular flat, comprises a core region or a core material, in particular an axially symmetrical core material, with a wear protection layer applied thereto. At least part of an outer surface of the wear protection layer defines a friction surface, i.e. the part against which the brake pads are pressed during braking.

At least one wear indicator is provided below the friction surface or between the outer surface and the core material. The wear indicator can be detected optically, for example with the naked eye, in order to detect advanced wear of the friction disc and, based on this, to decide whether it needs to be replaced. This can be ensured by a suitable brightness or color contrast between the core material and the wear indicator and the layer material on top of it, for example a wear protection layer or an intermediate layer.

A raised area of the core material is provided as a wear indicator. The wear indicator protrudes axially outwards from the core material towards the friction surface and is made of the same material as the core material. In the said area, the thickness of the wear protection layer is less, so that as the wear progresses, the raised area becomes visible, particularly before the non-raised area. When it becomes visible, it indicates that the brake disc needs to be replaced.

Due to the low layer thickness of the wear protection layer in the range of 100 to 250 µm, the proposed solution is very well suited to easily carrying out a visual inspection for excessive wear in the workshop, as such thin friction surfaces cannot be measured using a caliper. In order to determine how advanced the abrasion or wear is, a micrometer screw or similar would otherwise have to be used, which is avoided with the solution according to the invention, which in turn saves costs.

It is advisable if both sides of the friction disc have a corresponding raised area. For various reasons, the wear on the two sides of a friction disc is not always the same and the visibility of a wear indicator on only one of the two sides is not sufficient to indicate the end of the friction disc's service life.

In one embodiment, an axially symmetrical core material is provided, the roughness R_z of which, viewed in the axial direction, is smaller than the extension E of the raised area measured from the non-raised area or the base level. The extension E can be, for example, two to seven times as large as the roughness R_z. In other words, a part of the core material that protrudes in the direction of the friction surface, with the above formulation the above-mentioned raised area, is provided as a wear indicator, the axial distance A of which from the friction surface is greater than the roughness R_z of the core material. The raised character of the wear indicator is thus independent of the roughness of the core material.

In practice, vehicle brake manufacturers have known correlations between the distance travelled by a vehicle with a specific friction disc and abrasion of the friction disc measured in the axial direction. It is therefore possible to roughly indicate how many micrometers of abrasion correspond to which distance traveled and from this to estimate the expected service life of the friction disc. Accordingly, it is proposed that, given a known correlation between a distance traveled by a (motor) vehicle operated with the friction disc according to the invention and abrasion of the friction disc according to the invention measured in the axial direction for a given material of the wear protection layer, an extension E of the raised area is selected that corresponds to a remaining distance of between 1,000 km and 20,000 km. In other words, after the wear indicator becomes visible, the vehicle can still be driven safely for 1,000 km to 20,000 km before the friction disc has to be replaced.

According to a second embodiment, an intermediate layer is provided between the core material and the wear protection layer and the wear indicator protrudes into the wear protection layer. This means that when the wear indicator becomes visible, the wear protection layer has not yet been completely worn away and the (motor) vehicle can still be driven for a certain distance until this is the case. This circumstance can be used to replace the friction disc before the wear protection layer is completely worn away and the braking behavior is different due to the new friction pairing of brake pad/intermediate layer.

All layers can be applied using laser cladding, laser powder cladding or extreme high-speed laser cladding (EHLA). The intermediate layer can also be colored, which is an additional warning sign of advanced abrasion.

The core material can be gray cast iron and the wear protection layer can be a carbide-containing stainless steel layer, e.g. a stainless steel layer containing tungsten or titanium carbide. An optional intermediate layer can also be a stainless steel layer, for example, whereby the intermediate layer and the wear protection layer can be the same material apart from the carbides. The latter has the advantage that the friction behavior changes only slightly when a vehicle brakes if the friction partner of the brake pad changes from wear protection layer to intermediate layer due to abrasion.

The geometry and number of wear indicators can be freely selected over a wide range, as the wear indicators can be incorporated into the core material using a turning or grinding operation. For example, a (radially) circumferential raised area can be selected, e.g. in the form of a ring, which is a few millimeters wide, e.g. 5 mm, and can therefore be seen through openings in the wheel rim even if the wear protection layer is worn down, preferably with the naked eye or, if necessary, with a mirror. The raised area can either be made up of a number of individual wear indicators that are a certain distance apart from one another, or it can be a full-surface raised area.

The width of the surrounding area can be selected between 1 mm and 6 mm to ensure it can be easily seen by workshop personnel.

• 1 und 2 eine erste Ausführungsform der erfindungsgemäßen Reibscheibe, ohne Zwischenschicht;
• 3 eine zweite Ausführungsform der erfindungsgemäßen Reibscheibe, mit Zwischenschicht;

The invention will be explained in more detail below using an exemplary embodiment. The figures used here are not to scale and show a possible way of implementing the invention, to which the invention is not intended to be limited. The same reference numerals refer to the same objects unless otherwise stated. They show:

• 1 and 2 a first embodiment of the friction disc according to the invention, without intermediate layer;
• 3 a second embodiment of the friction disc according to the invention, with intermediate layer;

In a first embodiment, 1 a part of a vehicle brake 3 designed as a disc brake for a passenger car. The rotationally symmetrical disc brake has a circumferential surface F on which a friction disc 1 is placed, which during braking is the friction partner of the brake pad arranged in the brake calliper (not shown) and positioned on a brake block (not shown), so that the kinetic energy is converted into heat during braking.

2 shows a small section of the friction disc 1 of the 1 , as indicated by the arrow P. It has a core material 5 made of gray cast iron, the surface 19 of which is finely turned flat and has a surface roughness (average roughness depth) R_z of 10 µm. The core material 5 has two raised areas 15, 15' which in practical use function as wear indicators 13, 13'. The raised areas 15, 15` are identical and have an axial extension E of 20 µm, which is therefore greater than the roughness depth R_z. The wear indicators 13, 13' are also made of gray cast iron and are formed in one piece with the core material 5.

The wear protection layer 7 has a layer thickness of 200 µm. As the wear protection layer 7 continues to wear down during use of the friction disk 1, the wear indicators 13, 13' finally become visible when 180 µm of it have been worn away. There is then a reserve of 20 µm of wear protection layer 7 until the brake pads rub directly against the gray cast iron, which corresponds to approximately 20,000 km of the vehicle's remaining range. It goes without saying that the remaining range can be selected largely freely, since a larger or smaller value of the extension E means a larger or smaller remaining range.

For better recognition of the wear indicators 13, 13', they should occupy a sufficiently large area in a plane perpendicular to the axial direction A and preferably fill this area completely, e.g. as an elongated strip or as a circumferential band, e.g. in ring form, in order to enable a visual inspection of the friction disc 1 when the vehicle is stationary without removing the wheel cap.

In a second embodiment according to. 3 the core material 5 has a raised area 15 with an axial extension E of 65 µm. As in the first embodiment, the core material is gray cast iron, which is finely ground here and has a roughness R_z of 10 µm. The wear protection layer 7 has a layer thickness of 150 µm and consists of stainless steel with titanium carbide particles.

Since the thermal expansion coefficients of gray cast iron and stainless steel with titanium carbide are too different, an intermediate layer 17 is located between them. This is made of the same stainless steel as the wear protection layer 7, but without titanium carbide. The intermediate layer 17 has a layer thickness of 50 µm and is quite elastic, so it can compensate for the mechanical stresses between the core material 5 and the wear protection layer 7 when the friction brake 1 heats up as a result of braking. This can prevent cracking, which could otherwise become a safety problem due to subsequent corrosion.

As in 3 As can be seen, the wear indicator 13 protrudes from the surface 19 of the core material 5, through the intermediate layer 17 and 15 µm into the wear protection layer 7. As the wear protection layer continues to wear down during the service life of the friction disc 1, 85 µm of the wear protection layer 7 are initially removed before the intermediate layer 17 is exposed axially outside the raised area 15 in this area. It should be noted, however, that with respect to the friction disc 1, radially outside and inside or into the 2 and 3 left and right, the wear protection layer 7 continues to be abraded, the abrasion of the intermediate layer 17 is only a local event which does not significantly change the braking characteristics of the friction disc 1 as a whole.

After exposing the intermediate layer surface radially outside the raised area 15, 50 µm of intermediate layer material are subsequently removed with further use of the friction brake 1 until the wear indicator 13 is exposed and indicates that the friction disc 1 must be replaced. There are then 15 µm left until a brake pad should rub directly against the gray cast iron, which corresponds to a remaining driving distance of approx. 15,000 km.

Furthermore, embodiments are conceivable in which a multi-layer system is used, i.e. several wear protection layers and/or several intermediate layers are used. This can also be combined with one or more of these layers being colored, which also signals wear, for example with a well-defined remaining driving time, so that there are a number of wear indicators in total that become visible at different mileages. Optical sensors could also detect the exposure of the wear indicator 13 and issue a warning message to the driver, for example via a display in the instrument panel, in order to detect a replacement of the friction brake 1.

List of reference symbols

1

Friction disc

3

Vehicle brake

5

Core material

7

Wear protection layer

9

Exterior surface

11

Friction surface

13

Wear indicator

15

raised area

17

Intermediate layer

19

Surface of the core material/grey cast iron

E

Extension

A

Axial axis

R_z

Roughness (average roughness depth)

P

Arrow

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• DE 102010013343 A1 [0003]

Claims (7)

Friction disc (1) for a vehicle brake (3), comprising a core material (5) with a wear protection layer (7) applied thereto, wherein at least a part of an outer surface (9) of the wear protection layer (7) defines a friction surface (11) and at least one wear indicator (13) is provided below the friction surface (), characterized in that a raised region (15) of the core material (5) is provided as the wear indicator (13). Friction disc after Claim 1 , characterized in that an axially symmetrical core material (5) is provided, the roughness R_z of which, viewed in the axial direction (A), is smaller than the extension (E) of the raised region (15) measured in the axial direction (A) from the non-raised region (15). Friction disc after Claim 2 , characterized in that , given a known correlation between a driving distance of a vehicle operated with the friction disc (1) and abrasion of the friction disc (1) measured in the axial direction for a given material of the wear protection layer (7), an extension (E) is selected which corresponds to a remaining driving distance of between 1000 and 20,000 km. Friction disc according to one or more of the previous Claims 1 until 3 , characterized in that an intermediate layer (17) is provided between the core material (5) and the wear protection layer (13) and the wear indicator (13) projects into the wear protection layer (7). Friction disc according to one or more of the preceding claims, characterized in that a grey cast iron is provided as the core material (5) and a carbide-containing stainless steel layer is provided as the intermediate layer (17). Friction disc according to one or more of the preceding claims, characterized in that a plurality of wear indicators (13) are provided, which are arranged in a circumferential raised region. Friction disc according to one or more of the preceding claims, characterized in that the width of the circumferential region is between 1 mm and 6 mm.

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