This invention relates to a unique brake lining wear indicator utilizing a temperature sensor assembly embedded in a brake lining of a drum brake assembly.
Drum brakes are widely used in vehicle braking systems. In a typical drum brake, two arcuate brake shoe assemblies are located inside a rotating cylindrical brake drum. Each brake shoe assembly includes a backing plate which carries brake lining friction material presenting a wear surface. A brake actuator moves the brake shoe assemblies toward the rotating brake drum such that the wear surface of the brake lining friction material contacts the inner surface of the drum, thus retarding the rotation of the drum. Over a period of time, the contact between the lining and the drum causes the lining to wear. If the lining becomes too thin, ineffective braking can occur. Thus, it is desirable to provide an indication when brake lining thickness is such that the brake shoes should be changed.
Several problems arise when trying to determine whether the brake linings have sufficiently worn such that they need to be changed. Often the wheel and the brake drum have to be removed from the vehicle for the brake lining thickness to be measured. This is cumbersome and time consuming. Visual brake lining wear indicators, such as notches in the lining or color coded layers in the lining, have been used more effectively to determine when the linings should be changed. When a visual wear indicator is used, an inspector can visually examine each brake lining to determine whether it needs to be changed without having to physically measure the thickness. However, the use of these visual wear indicators can also be cumbersome and time consuming because they require the inspector to visually check each lining while the vehicle is stationary. Thus, it is desirable to have an efficient way to continuously monitor the brake lining thickness during the operation of the vehicle to determine whether the brake linings need to be replaced without having to visually inspect each brake lining.
Some prior art systems have monitored brake lining thickness on vehicles by using a single thermistor sensor in the lining which changes its electrical resistance based on temperature. Brake lining wear for this system is calculated based on changes in measured resistance of the thermistor. Such systems can often be ineffective and produce inaccurate results. Other systems have monitored the temperature of the brake linings to compare these temperatures to electronically stored standard characteristics for the brake lining. These systems are complicated and vary from lining to lining due to varying characteristics in lining materials and configurations.
Thus, it is desirable to have a simple temperature based lining wear indicator which can be used universally on all brake linings and which calculates accurate remaining useful thicknesses of brake lining material.