GB2343720A

GB2343720A - A disc brake wear indicator

Info

Publication number: GB2343720A
Application number: GB9817329A
Authority: GB
Inventors: Kiernan Antony Geary
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1998-08-11
Filing date: 1998-08-11
Publication date: 2000-05-17
Anticipated expiration: 2018-08-11
Also published as: GB9817329D0; GB2343720B

Abstract

A disc brake wear indicator comprises a wear indicating finger 3, attached by clips (11, 12 Figs. 3-5) to the backing plate 2 of a brake pad 20a, the end 10 of the finger, in use, engaging a non-braking surface of a brake disc to cause an audible warning sound when the brakes are worn. As illustrated, the end 10 of the finger is located between non-braking surfaces 8a, 8b of a ventilated brake disc.

Description

BRAKE PAD WEAR INDICATOR This invention relates to a brake pad wear indicating arrangement for disc brakes of a motor vehicle, in particular for use with disc brakes which have ventilated brake discs.

Mechanical brake pad wear indicators conventionally operate against the braking surface of a brake disc.

However, over a period of time, the wear on the brake disc caused by the brake wear indicator can produce an uneven braking surface, which reduces braking efficiency and limits the life of the brake disc.

Accordingly, the present invention provides a brake wear indicating arrangement wherein a brake pad which has a layer of friction material mounted on a backing plate acts against a brake disc with at least one non braking surface that is parallel to the braking surfaces, the arrangement including a wear indicating finger mounted on the pad and extending towards the non braking surface, the finger being adapted to make contact with that surface when the brakes are applied and the brake pad is worn, and to be out of contact otherwise.

Since the wear indicating finger does not contact the braking surface of the brake disc, damage to the braking surface does not occur when the driver of the vehicle fails to replace a worn brake pad immediately.

A warning sound may be produced when the finger makes contact with a non braking surface of the brake disc to alert the driver that a brake pad needs to be replaced.

The warning could be augmented by completing an electrical circuit which activates a buzzer or lights up an indicator on the instrument panel.

However, since an electrical circuit can involve significant cost and is prone to faults, it is preferred that brake pad wear is indicated just by the warning sound which is produced by mechanical vibration when the finger is in contact against the non braking surface of the rotating brake disc.

In a preferred embodiment of the invention, the non braking surface is formed by a side wall of a circumferential groove running around the edge of the brake disc, between the braking surfaces. Such a circumferential groove is commonly found in a ventilated brake disc, the area within the groove being used for ventilation. However, the non braking surface may lie in the same plane as the braking surface.

In order to reach the side wall of the circumferential groove whilst avoiding contact with the outer brake disc surface used for braking, the wear indicating finger may be L-shaped, having a long section extending from the brake pad backing plate in the direction in which the brake pad moves during braking, and a short section extending from the end of the long section and orientated towards the axis of the brake disc, with part or all of the short section residing in the groove.

Such an arrangement is particularly suitable for use with ventilated brake discs where the inner non braking surfaces are often rough, this roughness helping to increase the volume of the warning sound. In addition, the presence of radially aligned ribs on the non braking surfaces, which is an inherent feature in the design of ventilated brake discs, may introduce a repetitive beating noise into the warning signal, making it more noticeable to the driver.

A U-shaped spring may be included between the end of the wear indicating finger and the pad to provide additional flexibility when the end of the finger is riding over the ribs or any other roughness on the non braking surface of the disc brake.

To facilitate fabrication, the U-shaped spring and the finger may be formed integrally from a single piece of spring steel or other resilient material that is sufficiently soft as to avoid undue wear when contact occurs between the finger and the non braking surface of the brake disc.

It may be desirable for the finger to be part of a separate wear indicating unit that can be mounted on to an existing brake pad. Therefore to allow for easy mounting, the wear indicating finger may be attached to the brake pad backing plate by means of spring clips formed integrally with the finger.

Where a pair of brake pads mounted on a brake calliper are operated by a single piston, the wear indicating unit will preferably be mounted on the brake pad directly in contact with the piston, since this brake pad normally wears the fastest. However, it is within the scope of the invention to include a wear indicating unit for each of a pair of brake pads, for example when each pad is operated by an individual piston.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a brake assembly with a brake wear indicating arrangement in accordance with the invention, where the brake pads are in good condition; Figure 2 is a view corresponding to Figure 1, but showing the brake pads in a worn condition; Figure 3 is a view of a wear indicating unit from the direction marked A in Figure 1; Figure 4 is an enlarged view from the direction marked B in Figure 3 of a portion of the brake pad with a wear indicating unit mounted thereon; and Figure 5 is a view from the direction marked B in Figure 3 of a wear indicating unit in the process of being mounted on a brake pad.

In the disc brake assembly of Figures 1 and 2, callipers (not shown) hold brake pads 20a, 20b in place either side of a brake disc 6, in this example a ventilated brake disk. During operation of the brakes, the friction material 5a, 5b of the brake pads 20a, 20b is forced into contact with the brake disc 6 by one or more pistons (not shown). The friction between the brake pads 20 and the rotating brake disc 6 results in the braking action, and also causes wear in the friction material 5, gradually reducing its thickness from that indicated in Figure 1, where the brake pads are in good condition, to that in Figure 2, where they are worn.

Figure 1 shows a wear indicating unit 1 mounted on a brake pad backing plate 2 of the pad 20a. The wear indicating unit 1 comprises an L-shaped finger 3 attached by means of clips 11,12 to the brake pad backing plate 2, with one end of the finger positioned adjacent to the friction material 5a and radially beyond the periphery of the ventilated brake disc 6. The long section 9 of the Lshaped finger 3 extends perpendicularly from the brake pad backing plate 2 and curves to form a short section 10 residing partially in the ventilated area 7 between the two inner brake disc surfaces 8a, 8b, so that the short section 10 of the finger 3 is aligned in a generally radial direction, separated by a distance S from the inner surface 8a, which is a non braking surface.

In the braking action, the brake pads move towards the brake disc 6 in a transverse direction and make contact with the disc 6. Because the finger 3 is connected to the brake pad backing plate 2, transverse displacement of the brake pad when the brakes are applied causes an identical transverse displacement of the short section 10 that extends into the ventilated area 7, between the two inner brake disc surfaces 8.

During normal operation with brake pads in good condition, the finger 3 does not make contact with the rotating brake disc 6. This is achieved by choosing the length of the long section 9 so that when the brakes are applied, as shown in Figure 1, the short section 10 has some separation S from the inner surface 8a. The finger 3 is designed so that releasing the brakes does not cause the short section 10 of the finger 3 to touch the opposite inner surface 8b. This is possible since the displacement of a brake pad during braking is normally less than separation between the two inner surfaces 8.

The separation S between the edge of the short section of the finger 3 and inner surface 8a when the brakes are applied is controlled by the thickness of friction material 5a. Since the thickness of friction material 5a will diminish as it becomes worn, so too will the separation S, eventually resulting in the situation shown in Figure 2, where the friction material 5a is sufficiently worn that application of the brakes causes the finger 3 to make contact with the inner surface 8a of the ventilated disc 6.

Contact of the finger 3 against the surface 8a of the rotating brake disc 6 produces a noise that is used to provide an audible warning to alert the driver of wear in the brake pad.

The friction material thickness at which finger 3 makes contact with surface 8a depends on the length of the long section of the finger, allowing a predetermined minimum safe level of friction material thickness to be set, below which the driver is alerted each time the brakes are applied.

It should be noted that the thickness of friction material 5 on an unworn brake pad is normally less than the spacing between surfaces 8a and 8b, so that the length of the long section 9 can be set to make full use of the available friction material 5.

Figure 3 shows the brake wear indicating unit 1 as viewed from above. The finger 3 lies in a plane perpendicular to the brake pad backing plate and is orientated in a generally radial direction when attached to the backing plate as shown in Figure 4. This allows the finger some flexibility in the direction of rotation of the brake disc, whilst maintaining sufficient rigidity in the radial direction. Additional flexibility in the direction of rotation is provided by a U-shaped spring region 14 joining the finger 3 to the clip 11, the spring region being formed integrally by a U-bend in the sheet metal, positioned towards the base of the finger 3.

The flexibility of the finger in one particular direction provided by the above design allows the finger to tolerate mechanical vibration when making contact against the rotating brake disc inner surface 8a. In particular, the provision of the U-shaped spring region 14 assists the finger in riding over a surface that is not planar, for example, if it contains radially extending ribs, as are found on the inner surfaces of ventilated brake discs.

The mechanical vibration due to the finger rubbing against a rotating inner brake disc surface, especially a ribbed surface, causes vibration in the braking components which generates sufficient audible noise to alert the driver of the vehicle that the brake pad needs to be replaced.

Since immediate replacement of the brake pad may not be possible, the finger 3 is able to tolerate some wear, equivalent to about 2 mm of friction material thickness, which allows normal driving for a further distance of typically 1000 km. To ensure the that the wear occurs predominantly in the finger rather than in the brake disc surface, the finger is formed from spring steel, which is softer than the brake disc material.

The finger 3 is formed integrally with spring clips 11, 12 that allow push-fitting attachment to a standard brake pad backing plate, as indicated in Figure 5, without any modification to the backing plate being required. The clips 11,12 comprise near parallel, inwardly pointing surfaces which grip the short fingers 13 of the backing plate, as shown in Figures 4 and 5. The section 16 joining clips 11 and 12 provides further support for the finger 3 by resting against the back surface of the brake pad, and is shaped with some curvature to follow the contours of that surface.

The short outer side of each clip contains a longitudinal deformation 15 to ensure that these sides of the clips make a line contact with the fingers 13 of the brake pad backing plate 2, in order to minimise damage to the backing plate painted surface and allow the use of an appropriate tool when fitting the brake pad wear indicating unit 1.

The wear indicating unit 1 is formed from a single piece of, initially flat, spring steel.

With the brake wear indicating unit mounted on the brake pad backing plate as described above, the brake pad can be fitted to the brake callipers in the normal way. The brake wear indicating unit can be separate and can be attached to the brake pad immediately before assembly of the brake pads in a vehicle.

Claims

CLAIMS 1 A brake wear indicating arrangement wherein a brake pad which has a layer of friction material mounted on a backing plate acts against a brake disc with at least one non braking surface that is parallel to the braking surfaces, the arrangement including a wear indicating finger mounted on the pad and extending towards the non braking surface, the finger being adapted to make contact with that surface when the brakes are applied and the brake pad is worn, and to be out of contact otherwise.
2 A brake wear indicating arrangement as claimed in Claim 1, wherein the non braking surface is formed by a side wall of a circumferential groove running around the edge of the brake disc, between the braking surfaces.
3 A brake wear indicating arrangement as claimed in Claim 2, wherein the wear indicating finger has a long section extending from the brake pad backing plate in the direction in which the brake pad moves during braking, and a short section extending from the end of the long section and orientated towards the axis of the brake disc, with part or all of the short section residing in the groove.
4 A brake wear indicating arrangement as claimed in any preceding claim, wherein a warning sound is produced when the finger makes contact with a non braking surface of the brake disc.
5 A brake wear indicating arrangement as claimed in any preceding claim, wherein a warning sound is produced by mechanical vibration when the finger is in contact against the non braking surface of the rotating brake disc.
6 A brake wear indicating arrangement as claimed in any preceding claim, wherein a U-shaped spring lies between the end of the wear indicating finger and the pad.
7 A brake wear indicating arrangement as claimed in Claim 6, wherein the U-shaped spring is formed integrally with the finger.
8 A brake wear indicating arrangement as claimed in any preceding claim, wherein the finger is attached to the brake pad backing plate by means of spring clips formed integrally with the finger.
9 A brake wear indicating arrangement as claimed in any preceding claim, wherein the brake disc is a ventilated brake disc.
10 A brake wear indicating arrangement substantially as herein described with reference to the accompanying drawings.