Thin film sensor for brake lining pad wear and brake temperature sensing

• US 20060076196A1
• Filed: 10/11/2004
• Published: 04/13/2006
• Est. Priority Date: 10/11/2004
• Status: Active Grant

• Current Assignee: International Truck Intellectual Property Co. LLC (Volkswagen AG)
• Original Assignee: International Truck Intellectual Property Co. LLC (Volkswagen AG)
• Inventors: Palladino, James
• Granted Patent: US 7,165,657 B2
• Time in Patent Office: Days
• US Class Current: 188/1.11W
• CPC Class Codes: F16D 2066/001 Temperature
• CPC Class Codes: F16D 66/026 indicating different degrees of lining wear

Abstract

A modular electrical resistance sensor is positionable in gaps between brake linings for a drum brake. The modular sensor is worn with the brake linings resulting in steadily increasing electrical resistance of the modular sensor. A measurement circuit associated with the modular sensor is programmed to equate electrical resistance to the degree of wear when the sensor has assumed a steady state temperature at or near the ambient temperature. Otherwise, particularly during periods of use of the brakes, resistance and the degree of wear last calculated become arguments into a function for determining brake lining temperature.

Claims

1. A sensor for measuring operating temperature and for use in indicating progressive brake wear of a brake lining, the sensor comprising:

an erodable substrate having a major surface and an upper edge bordering the major surface with the erodable substrate oriented to bring its upper edge into contact with a brake surface;

a thin film of conductive material disposed on the major surface of the substrate and extending downwardly along the major surface from the upper edge;

a pair of conductive rails defining first and second edges of the thin film which are generally perpendicular to the upper edge; and

an encapsulant disposed over the major surface including the thin film and the conductive rails.

2. The sensor according to claim 1, wherein the encapsulant enclosed the sensor to form a modular sensor unit.

3. The sensor according to claim 2, wherein the pair of conductive leads have substantially lower resistance than does the thin film.

4. The sensor according to claim 3, further comprising:

a measurement circuit connected to at least one of the pair of conductive leads for reading resistance of the thin film, the measurement circuit providing means for indicating whether the thin film is at or near ambient temperature, means responsive to an indication that the thin film is at or near ambient temperature for determining degree of wear of a brake lining as a function of resistance, and means responsive to determination of a degree of wear of the brake lining and resistance of the thin film for determining temperature of the sensor.

5. A brake system for a motor vehicle comprising:

a brake drum having an inner surface;

a brake linings for wearing against the inner surface of the brake drum for braking a motor vehicle;

a brake actuator for urging the brake linings into contact against the inner surface;

an electrical resistance sensor mounted on the brake actuator in gaps between the brake linings to exhibit a wear profile conforming to that of the brake linings;

the electrical resistance sensor exhibiting increasing resistance as it is worn down and with increasing temperature; and

a measurement circuit connected to the electrical resistance sensor, the measurement circuit providing means for indicating whether the electrical resistance sensor is at or near ambient temperature, means responsive to an indication that the electrical resistance sensor is at or near ambient temperature for determining a degree of wear of a the brake lining as a function of resistance, and means responsive to a subsequent measurement of resistance of the electrical resistance sensor for determining temperature of the sensor based on the determined degree of wear.

6. A brake system according to claim 5, wherein the electrical resistance sensor further comprises:

a wearable substrate having a major surface perpendicular to a wearing surface of the brake linings and a erodable edge;

a thin film conductive member disposed over a portion off the major surface of the wearable substrate;

a pair of conductive rails disposed on the first major surface defining first and second sides of the thin film conductive member, the thin film conductive member and the conductive rails being oriented so that the thin film conductive member is eroded along an edge running between the conductive rails.

7. A brake system according to claim 6, wherein the substrate, the conductive rails and the thin film are encapsulated in a heat stable thermoplastic to form a sensor module.

8. A brake system according to claim 7, further comprising a vehicle ambient temperature sensor coupled to the measurement circuit.

9. A brake lining wear and temperature measurement system comprising:

an electrically resistive element disposed in proximity to the brake lining, the electrically resistive element comprising an erodable sensor module fitted between a gap in the brake lining with a resistive lead and a ground lead extending from the erodable sensor module;

the electrically resistive element including a major surface and a thin film pad disposed on the major surface oriented to be gradually worn away along an edge thereof in conformance to a wear profile for the brake lining;

first and second electrically conductive rails in contact with the thin film pad and defining first and second sides of the thin film pad, respectively; and

a measurement circuit connected to the resistive lead for measuring the resistance of the thin film pad.

10. A brake lining wear and temperature measurement system according to claim 9, further comprising:

the measurement circuit including a program providing means for determining if brakes for a vehicle are likely to be at ambient temperature and, responsive to an affirmative determination that the brakes are likely to be at ambient temperature, providing means responsive to a measurement of the resistance for equating the measured resistance to a degree of wear of the sensor; and

the program stored on the measurement circuit further providing means responsive to determination that the brakes are likely to be at a temperature elevated compared to the ambient, using the measured resistance and the most recently obtained measurement of wear to determine brake lining temperature.