GB2047827A - Wear indicating - Google Patents

Abstract

In order to provide a visual indication of the wear of a brake pad for a vehicle wheel, it is proposed that beyond a predetermined extent of use the pad produces dust deposited as a distinct film on the wheel. As shown, the pad has a layer 8 so constituted that as it becomes worn in use it produces a dust of a colour different from that produced by the wear of the outer layer 6 of the pad. Layer 8 may be red e.g. of iron oxide. Different coloured intermediate layer(s) may be provided. <IMAGE>

Description

SPECIFICATION Brake pad for automobiles for giving visual indication of wear The invention relates to brake pad for automobiles forgiving visual indication of wear.

It is known to produce brake pads in a plurality of layers of material with the innermost layer of different colour from the outermost layer or layers with the object that the pad may show a different visual appearance when it is worn down to the innermost layer. However, the arrangement suffers from the disadvantage that the appearance of the pad can normally only be seen when the vehicle to which the pad is fitted is jacked up and the pad is not normally apparent to the driver of the vehicle when it is on the road.

It has also been proposed to provide a brake pad with an inner layer comprising a material which emits a characteristic odour when the brake is applied after the pad is worn down to that layer, but it is believed that the odour would in practice be quickly dissipated and would not reliably give an adequate warning of brake wear.

It is therefore an object of the invention to provide a brake pad such that the driver of a vehicle of which the brakes comprise the pad may more readily ascertain when the brake has worn down to a predetermined level.

The invention stems from the finding that in many automobiles the wheels are so constructed that dust formed by the abrasion of brake material in wear permeates to, and deposits as a film on, the outside of the wheels, and such wheels are referred to in this specification and the claims as wheels of the type aforesaid.

According to the invention there is provided a brake pad for a vehicle wheel of the type aforesaid which pad in use beyond a predetermined extent of use forms a dust capable of depositing as a distinct film on the outside of said wheel.

Preferably the pad is so constituted that the dust film is distinctive as to colour.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, of which the single figure shows in perspective a brake pad for a motor car disc brake.

As shown in the figure the pad comprises a mounting plate 2 to one face of which is secured a block 4 of brake material. The block 4 comprises an outermost layer 6 of conventional brake material of which the predominant colour is black, and a thinner layer 8 of a distinctive colour which in this embodiment is red but in other embodiments may have other colours.

The material of which layer 8 is formed is such as to give substantially similar braking performance as the major and outer layer6 in orderthatwhen the outer layer 6 has become worn away in use the remaining layer 8 provides effective braking. This is particularly important inasmuch as brakes tend to wear unevenly and it would be dangerous for the effective braking surface to consist of areas of dissimilar braking efficiency.

The composition of the layer 8 is such as to form dust particles by the abrasion caused in use of the brake, the particles being coloured as the layer itself and being of such a size that they are capable of permeating through apertures which are conven tionallyfound in motor car wheels. Having permeated through the apertures the dust particles settle on the outer surface ofthe wheel where they form a flim, distinctive as to colour. When the film has built up to a substantial thickness the colour may be readily seen by observation by the driver for example prior to getting into the vehicle at the start of a journey. Even when the layer is only thin, the characteristic colour may be observed by wiping a finger over the outer surface of the wheel whereupon the dust is transferred to the finger and again its distinctive colour is noticable.

It is preferable to use inorganic ratherthan organic pigments for the coloration of the layer 8 because of their better heat tolerance and in the embodiment described the pigment is in the form of iron oxide known as "Turkey Red".

In other embodiments of the invention an intermediate layer or layers are formed between the outer layer 6 and the layer 8. The or each immediate layer is coloured differently from the outer layer 6 and the layer 8 and produces a correspondingly coloured dust by which the wheel outer surface is coated when the brake pad is worn down to that layer. By this means the driver of the vehicle is given a warning that the brake has worn substantially but not quite to the level represented by the layer 8 which can be arranged to represent a pad worn to a dangerous level and in need of urgent replacement.

1. A brake pad for a vehicle wheel of the type aforesaid which pad in use beyond a predetermined extent of use forms a dust capable of depositing as a distinct film on the outside of said wheel.

2. A brake pad according to claim 1 so consti tutedthatthe dust film is distinctive as to colour.

3. A brake pad according to claim 2 wherein the colour is given to the dust by incorporation of inorganic pigment.

4. A brake pad according to Claim 3 wherein the pigment is an oxide of iron.

5. A brake pad according to any preceding claim comprising two or more layers.

6. A brake pad for a vehicle wheel of the type aforesaid substantially as described with reference to the drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Brake pad for automobiles for giving visual indication of wear The invention relates to brake pad for automobiles forgiving visual indication of wear. It is known to produce brake pads in a plurality of layers of material with the innermost layer of different colour from the outermost layer or layers with the object that the pad may show a different visual appearance when it is worn down to the innermost layer. However, the arrangement suffers from the disadvantage that the appearance of the pad can normally only be seen when the vehicle to which the pad is fitted is jacked up and the pad is not normally apparent to the driver of the vehicle when it is on the road. It has also been proposed to provide a brake pad with an inner layer comprising a material which emits a characteristic odour when the brake is applied after the pad is worn down to that layer, but it is believed that the odour would in practice be quickly dissipated and would not reliably give an adequate warning of brake wear. It is therefore an object of the invention to provide a brake pad such that the driver of a vehicle of which the brakes comprise the pad may more readily ascertain when the brake has worn down to a predetermined level. The invention stems from the finding that in many automobiles the wheels are so constructed that dust formed by the abrasion of brake material in wear permeates to, and deposits as a film on, the outside of the wheels, and such wheels are referred to in this specification and the claims as wheels of the type aforesaid. According to the invention there is provided a brake pad for a vehicle wheel of the type aforesaid which pad in use beyond a predetermined extent of use forms a dust capable of depositing as a distinct film on the outside of said wheel. Preferably the pad is so constituted that the dust film is distinctive as to colour. Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, of which the single figure shows in perspective a brake pad for a motor car disc brake. As shown in the figure the pad comprises a mounting plate 2 to one face of which is secured a block 4 of brake material. The block 4 comprises an outermost layer 6 of conventional brake material of which the predominant colour is black, and a thinner layer 8 of a distinctive colour which in this embodiment is red but in other embodiments may have other colours. The material of which layer 8 is formed is such as to give substantially similar braking performance as the major and outer layer6 in orderthatwhen the outer layer 6 has become worn away in use the remaining layer 8 provides effective braking. This is particularly important inasmuch as brakes tend to wear unevenly and it would be dangerous for the effective braking surface to consist of areas of dissimilar braking efficiency. The composition of the layer 8 is such as to form dust particles by the abrasion caused in use of the brake, the particles being coloured as the layer itself and being of such a size that they are capable of permeating through apertures which are conven tionallyfound in motor car wheels. Having permeated through the apertures the dust particles settle on the outer surface ofthe wheel where they form a flim, distinctive as to colour. When the film has built up to a substantial thickness the colour may be readily seen by observation by the driver for example prior to getting into the vehicle at the start of a journey. Even when the layer is only thin, the characteristic colour may be observed by wiping a finger over the outer surface of the wheel whereupon the dust is transferred to the finger and again its distinctive colour is noticable. It is preferable to use inorganic ratherthan organic pigments for the coloration of the layer 8 because of their better heat tolerance and in the embodiment described the pigment is in the form of iron oxide known as "Turkey Red". In other embodiments of the invention an intermediate layer or layers are formed between the outer layer 6 and the layer 8. The or each immediate layer is coloured differently from the outer layer 6 and the layer 8 and produces a correspondingly coloured dust by which the wheel outer surface is coated when the brake pad is worn down to that layer. By this means the driver of the vehicle is given a warning that the brake has worn substantially but not quite to the level represented by the layer 8 which can be arranged to represent a pad worn to a dangerous level and in need of urgent replacement. CLAIMS

1. A brake pad for a vehicle wheel of the type aforesaid which pad in use beyond a predetermined extent of use forms a dust capable of depositing as a distinct film on the outside of said wheel.

2. A brake pad according to claim 1 so consti tutedthatthe dust film is distinctive as to colour.

3. A brake pad according to claim 2 wherein the colour is given to the dust by incorporation of inorganic pigment.

4. A brake pad according to Claim 3 wherein the pigment is an oxide of iron.

5. A brake pad according to any preceding claim comprising two or more layers.

6. A brake pad for a vehicle wheel of the type aforesaid substantially as described with reference to the drawing.