Brakes – With condition indicator – Wear
Reexamination Certificate
1998-11-24
2001-06-26
Butler, Douglas C. (Department: 3613)
Brakes
With condition indicator
Wear
C374S141000, C303S020000, C340S454000
Reexamination Certificate
active
06250430
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates to a system and method for determining the thickness of a brake lining using a temperature detector and a brake actuation system.
Most motor vehicles include a brake system having a set of brake shoe assemblies for retarding the rotation of the wheels of the vehicle when the brakes are applied. Typically, each brake shoe assembly includes a brake lining made of a friction material which gradually wears away during brake applications. After numerous brake applications, the brake lining wears below a critical material thickness and, therefore, should be replaced. As a result, the brake lining must be periodically inspected for excessive wear. Thus, it is desirable to provide an indication when the brake lining thickness is worn 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 must be removed from the vehicle so that the brake lining thickness can 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 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 the brake lining requires replacement without physically measuring the thickness of the brake lining material. However, the use of visual wear indicators can also be cumbersome and time consuming because visual wear indicators require the inspector to visually check each lining while the vehicle is stationary. Thus, it is desirable to have an efficient way to monitor the brake lining thickness during the operation of the vehicle to indicate whether the brake linings require replacement without having to visually inspect each brake lining.
Some prior art systems have monitored brake lining thickness on vehicles by using a brake lining including a single thermistor sensor with the electrical resistance of the thermistor changing with the temperature of the brake lining. Brake lining wear for this system is calculated based on changes in the 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 monitored temperatures to electronically stored standard characteristics for the brake lining. These systems are complicated and vary from lining to lining due to changing characteristics in lining materials and configurations. Thus, it is desirable to have a simple system and method for determining the thickness of a brake lining using a temperature detector and a brake actuation system.
SUMMARY OF THE INVENTION
In a disclosed embodiment of this invention, a system for indicating the amount of material in a brake lining includes a frictional brake surface and a brake lining having a sensor for detecting when the temperature of the brake lining exceeds a predetermined temperature. A brake actuation system actuates the brake lining against the frictional brake surface. A controller counts the number of temperature detections and the number of brake actuations during a predetermined period and produces a first signal when a ratio of the number of temperature detections to the number of brake actuations is greater than a first predetermined value. In a preferred embodiment of this invention, the controller produces a second signal when the ratio of the number of temperature detections to the number of brake actuations is greater than a second predetermined value and less than the first predetermined value.
The invention includes a method for indicating the amount of material in a brake lining in a brake system having a frictional brake surface, a sensor for detecting when the temperature of the brake lining exceeds a predetermined temperature, and an actuation system for actuating the brake lining against the frictional brake surface. The method includes the steps of: counting the number of brake actuations during a predetermined period, counting the number of temperature detections during the predetermined period, and producing a first signal when a ratio of the number of temperature detections to the number of brake actuations is greater than a first predetermined value. A preferred method includes the step of producing a second signal when the ratio of the number of temperature detections to the number of brake actuations is greater than a second predetermined value and less than the first predetermined value.
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Butler Douglas C.
Carlson, Caskey & Olds
Meritor Heavy Vehicle Systems LLC
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