Communications: electrical – Land vehicle alarms or indicators – Internal alarm or indicator responsive to a condition of the...
Reexamination Certificate
1998-11-03
2001-05-22
Wu, Daniel J. (Department: 2736)
Communications: electrical
Land vehicle alarms or indicators
Internal alarm or indicator responsive to a condition of the...
C340S453000, C340S449000, C188S00111E, C188S00111E, C188S00111E
Reexamination Certificate
active
06236310
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates to a brake shoe assembly having a sensor for determining when the brake lining of the assembly has worn below a critical thickness and when the temperature of the brake lining has exceeded a predetermined temperature threshold.
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. To eliminate time-consuming and costly visual inspections of the brake lining, the prior art has taught several types of brake lining wear sensors for indicating when the brake lining must be replaced.
One type of brake lining wear sensor, sometimes referred to as a wire loop sensor, indicates when the brake lining has worn below a critical thickness. Although prior art wire loop sensors are relatively inexpensive and simple, they do not indicate the temperature of the brake lining. Accordingly, it would be desirable provide an inexpensive and simple sensor for detecting both when the brake lining has worn below a critical thickness and when the temperature of the brake lining has exceeded a predetermined temperature threshold.
SUMMARY OF THE INVENTION
In a disclosed embodiment of this invention, a brake shoe assembly for a vehicle includes a brake lining and a housing. The brake lining has a predetermined thickness which gradually wears away and increases in temperature during a vehicle braking application. The housing is positioned to wear away and increase in temperature concurrently with the brake lining. An electrical wear loop circuit is encapsulated in the housing for directing power from a power source to a remote indicator in response to a wear opening in the loop circuit. A thermally sensitive switching element is encapsulated in the housing and connected in electrical series with the wear loop circuit for directing power from the power source to the remote indicator in response to the temperature of the housing exceeding a predetermined temperature threshold.
The switching element has a first resistance when the temperature of the housing is below the predetermined temperature threshold and a second resistance which approximates an open circuit when the temperature of the housing is above the predetermined temperature threshold. Thus, when the temperature of the housing is above the predetermined temperature threshold, the second resistance of the switching element directs power from the power source to the remote indicator.
In a preferred embodiment of this invention, the switching element is a polymer positive temperature coefficient device and the assembly includes a biasing resistor connected in electrical series with the switching element to bias the predetermined temperature threshold.
These and other features of the present invention will be best understood from the following specification and drawings, the following of which is a brief description.
REFERENCES:
patent: 3902158 (1975-08-01), Dahlkvist
patent: 4606434 (1986-08-01), Vasilow et al.
patent: 5339069 (1994-08-01), Penner et al.
patent: 5419415 (1995-05-01), Lamb et al.
Kramer Dennis A.
Malinowski Mark E.
Carlson & Gaskey & Olds
Meritor Heavy Vehicle Systems LLC
Pham Toan
Wu Daniel J.
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