GB2103737A

GB2103737A - Disc brake pad lining wear sensor

Info

Publication number: GB2103737A
Application number: GB08124303A
Authority: GB
Inventors: Robert Beilleau; Pedro Alvarez
Original assignee: General Motors France SA
Current assignee: General Motors France SA
Priority date: 1981-08-08
Filing date: 1981-08-08
Publication date: 1983-02-23
Also published as: NL8203127A; IT8248954A0; IT1149045B; FR2511101A1; ES284843Y; GB2103737B; SE441543B; ES284843U; SE8204504L; FR2511101B1; SE8204504D0; DE3229787A1

Abstract

A disc brake pad lining wear sensor 24 comprises a sheet metal shim 26 which is retained in contact with a surface of a disc brake pad 14 remote from the surface of the pad carrying a brake lining 16, the brake pad 14 being suspended upon guide pins passing through aligned apertures 34 in the brake pad 14 and apertures 28 in the sheet metal shim 26. The sheet metal shim 26 has at least one finger-like portion 30 extending from an edge thereof, which finger-like portion 30 is bent over relative to the plane of the sheet metal shim 26 so that the free end 32 of the finger-like portion 30 lies in a plane extending at an obtuse angle to the plane of the sheet metal shim 26 and will make contact with a brake disc when the lining 16 thereof is worn down to a thickness at which it should be replaced, to cause the portion 30 and shim 26 to vibrate to produce a distinctive warning noise. <IMAGE>

Description

SPECIFICATION Disc brake pad lining wear sensor This invention relates to disc brake pad lining wear sensors for disc brake assemblies, in particular disc brake pad lining wear sensors for disc brake assemblies having two opposed brake pads, each carrying mounted thereon a brake lining arranged to engage a respective side of a brake disc on a motor vehicle wheel upon movement of said brake pads towards said disc.

Disc brake pad lining wear sensors are known in disc brake assemblies wherein one of the disc brake pads has a projection on the backing plate thereof directed towards the brake disc, the height of the projection being such that contact between the projection and the brake disc will occur when the brake pad lining has worn to a thickness at which it should be replaced. When contact is made between the projection and the disc, this becomes apparent to the driver of the vehicle due to the creation of a loud squealing or screeching noise from the brake assembly when the vehicle brakes are applied. Such noise generating sensors, although effective in use, are not simple to manufacture so as to obtain the maximum of generated noise with minimal damage to the brake disc as a result of the frictional contact between the projection and the brake disc during generation of the noise.

A disc brake pad lining wear sensor according to the present invention, for a disc brake assembly having two opposed brake pads, each carrying mounted thereon a brake lining arranged to engage a respective side of a brake disc on a motor vehicle wheel upon movement of said brake pads towards said disc, said brake pads being moveably suspended either side of said disc upon guide pins extending across the rim of said disc and through respective aligned apertures in said pads and said assembly, comprises a sheet metal shim having apertures therein corresponding to the guide pin apertures in said brake pad, and at least one finger-like portion extending from an edge of said shim and being bent over from the plane of said shim to occupy a position in which a free end of the bent over portion lies in a plane extending at an obtuse angle to the plane of said shim so that, when said sensor is installed in said brake assembly, said shim is placed in contact with a surface of one of the brake pads opposite the surface carrying the lining thereon, with said guide pins extending through said shim apertures, and said free end extending alongside an edge of the respective lining towards said disc for a predetermined distance corresponding to the thickness of the respective lining remaining when the respective lining needs replacement.

The finger-like portion of the shim forming the sensor of the invention, being of a thin crosssection, will act in the manner of a vibrating reed when the free end thereof comes into contact with the rotating disc during brake application. The vibration set up in the finger-like portion is transmitted through the shim to the assembly as a very pronounced characteristic noise, easily discernible above other engine noise by the driver of the vehicle.

In a preferred embodiment of the invention, the sheet metal shim has a finger-like portion extending from each of two opposite edges of the shim such that the free ends of the bent over portions extend, when the sensor is installed in said brake assembly, along opposite edges of the respective lining. Such an arrangement makas the shim of universal application to the brake assemblies concerned, in that it will function equally well when assembled in contact with either one of the brake pads in the disc brake assembly.

Preferably, the sheet metal shim of the wear sensor has each finger-like portion first bent over to extend at an acute angle to the plane of said shim, and then the free end of the finger-like portion is bent back in the opposite direction so that the finger-like portion has a second bend formed therein adjacent a mid-section thereof and the free end of the finger-like portion extends across the edge of the shim. This ensures that the length and the disposition of each finger-like portion are such that the pitch and amplitude of the generated noise is markedly different from noise generated elsewhere in the motor vehicle during movement thereof.

The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, in which: Figure 1 shows a side view of a disc brake assembly with parts broken away to show a disc brake pad lining wear sensor according to the present invention; Figure 2 shows a side view of a disc brake pad lining wear sensor according to the present invention; Figure 3 shows a cross-sectional view of the lining wear sensor shown in Figure 2, taken along the lines 3-3 of Figure 2; Figure 4 shows a view of the lining wear sensor of Figure 2 in position upon a disc brake pad; and Figure 5 shows a cross-sectional view of the disc brake pad and lining wear sensor shown in Figure 4, taken along the line 5-5 of Figure 4.

Figure 1 shows a side view of a disc brake assembly 10 having two opposed brake pads 12, 14, each of which carries mounted thereon a brake lining 16. The disc brake assembly 10 comprises a housing 1 8 incorporating a piston and cylinder arrangement for hydraulic actuation of the brake assembly, and a calliper portion 20 which bridges the disc (not shown) over which the disc brake assembly 10 is mounted. There is an aperture in the calliper portion 20 through which can be inserted the disc brake pads 12, 14 either side of the brake disc. The disc brake pads 12, 14 are moveably suspended upon guide pins 22 which extend across the rim of said disc and through respective aligned apertures in said disc brake pads 12, 14 and in said housing 18 and calliper portion 20.The remaining operating components of the disc brake assembly are conventional ones, and do not require any further description for an understanding of the present invention.

As can be seen in Figure 1, part of the calliper portion 20 is broken away to show a disc brake pad lining wear sensor 24 according to the present invention. As can be seen more clearly in Figures 2 and 3 of the accompanying drawings, the disc brake pad lining wear sensor 24 comprises a sheet metal shim 26 having apertures 28 therein and two finger-like portions 30, each of which extends from a respective edge of said sheet metal shim 26 in a direction substantially parallel to a line joining the axes of the apertures 28 in the sheet metal shim 26. Each finger-like portion 30 is first bent at its root to take up an acute angle with respect to the plane of the sheet metal shim 26.The free end 32 of the finger-like portion 30 is then bent back towards the plane of the sheet metal shim 26 so as to form a bend in the finger-like portion 30 adjacent a mid-section thereof, with the free end 32 of the finger-like portion 30 lying in a plane extending at an obtuse angle close to a right angle to the plane of the sheet metal shim 26 as can be clearly seen in Figure 3 of the accompanying drawings.

The lining wear sensor 24 is assembled in the brake assembly 10 by placing the sheet metal shim 26 in contact with the side of the disc brake pad 14 remote from the side of the pad carrying the lining 1 6, as is indicated in Figure 5 of the drawings. The sheet metal shim 26 is aligned in position upon the disc brake pad 14 so that the apertures 28 in the sheet metal shim coincide with corresponding apertures 34 in the disc brake pad 14. In this position, the free end portions 32 of the finger-like portions 30 take up the positions shown in Figures 4 and 5, in which the free end portions 32 extend along the edges of the lining 1 6 for a predetermined distance that corresponds to the thickness that the lining 1 6 will have at the time that it should be replaced.Once the sheet metal shim 26 is aligned in position upon the disc brake pad 14, the disc brake pad 14 and shim 26 are placed in position within the aperture in the calliper portion 20 and retained therein by threading the respective guide pins 22 through the aligned apertures 28, 34 respectively in the shim 26 and the brake pad 14.

As can be seen clearly in Figure 5, the free ends 32 of the finger-like portions 30 do not contact the edges of the disc brake pad 14 or the lining 16, and, therefore, are free to vibrate if twanged.

When the lining wear sensor 24 is in position in the disc brake assembly 10, and the brake pad linings are relatively unworn, the lining wear sensor 24 remains latent. It does not interfere in any way with the normal actuation of the disc brake assembly 10. When the brake pad lining 1 6 upon brake pad 14 wears down to a thickness at which it should be replaced, application of the disc brake pads 12, 14 to the brake disc will result in the free ends 32 of the finger-like portions 30 of the sensor 24 coming into contact with the rotating disc during braking.The frictional contact between the free ends 32 and the rotating disc is sufficient to set the finger-like portions 30 vibrating at such a rate as to generate a loud, distinctive noise which becomes amplified by the vibrations being transferred to the main body of the sheet metal shim 26, causing it to vibrate between the disc brake pad 14 and the piston of the disc brake assembly 10, thus further amplifying the generated noise. Upon hearing the distinctive noise generated by the vibrating contact of the free ends 32 with the rotating disc, the driver of the vehicle is warned that the disc brake pad linings require replacement.

During replacement of the worn disc brake pad linings with new disc brake pad linings, the wear sensor can be inspected and, if not unduly worn, can be used again, or, if showing distinct signs of wear, can be replaced completely by a fresh wear sensor.

The brake pad lining wear sensor of the present invention is an effective sensor which is economical to make, install and replace in a disc brake assembly. The thickness of the shim and of the length and disposition of the finger-like portions can be predetermined to obtain the desired pitch, amplitude and characteristic sound desired from the sensor. The preferred embodiment of the invention disclosed herein not only is quick and easy to install, but is capable of universal application in the disc brake assembly for which it is designed, in that it could be positioned on either brake pad 12 of brake pad 14, as desired. Moreover, since the overall cost of the sensors is low, a sensor according to the present invention could be installed on each of the brake pads, if this is thought desirable.

Claims

1. A disc brake pad lining wear sensor for a disc brake assembly having two opposed brake pads, each carrying mounted thereon a brake lining arranged to engage a respective side of a brake disc on a motor vehicle wheel upon movement of said brake pads towards said disc, said brake pads being movably suspended either side of said disc upon guide pins extending across the rim of said disc and through respective aligned apertures in said pads and said assembly, said pad lining wear sensor comprising a sheet metal shim having apertures therein corresponding to the guide pin apertures in said brake pad, and at least one finger-like portion extending from an edge of said shim and being bent over from the plane of said shim to occupy a position in which a free end of the bent over portion lies in a plane extending at an obtuse angle to the plane of said shim so that, when said sensor is installed in said brake assembly, said shim is placed in contact with a surface of one of the brake pads opposite the surface carrying the lining thereon, with said guide pins extending through said shim apertures, and said free end extending alongside an edge of the respective lining towards said disc for a predetermined distance corresponding to the thickness of the respective lining remaining when the respective lining needs replacement.

2. A disc brake pad lining wear sensor according to claim 1, in which said sheet metal shim has a finger-like portion extending from each of two opposite edges of the shim such that the free ends of the bent over portions extend, when the sensor is installed in said brake assembly, along opposite edges of the respective lining.

3. A disc brake pad lining wear sensor according to Claim 1 or 2, in which each fingerlike portion is first bent over to extend at an acute angle to the plane of said shim, and then the free end of the finger-like portion is bent back in the opposite direction so that the finger-like portion has a second bend formed therein adjacent a mid section thereof and the free end of the finger-like portion extends across the respective edge of the shim.

4. A disc brake pad lining wear sensor substantially as hereinbefore particularly described and as shown in Figures 1 to 5 of the accompanying drawings.