Brakes – With condition indicator – Electrical
Reexamination Certificate
2000-03-17
2001-08-21
Butler, Douglas C. (Department: 3613)
Brakes
With condition indicator
Electrical
C188S00111E, C340S453000, C340S588000
Reexamination Certificate
active
06276495
ABSTRACT:
BACKGROUND OF THE INVENTION
This application relates to a temperature measuring system in a brake shoe assembly that uses a thermally conductive heat pipe to comparatively measure the temperature of the brake lining at the point of the frictionally engaging surface of the brake lining.
Most motor vehicles include a brake system having a set of brake shoe assemblies for slowing rotation of the wheels of the vehicle when the brakes are applied. Typically, each brake shoe assembly includes a brake lining material that frictionally engages a portion of a wheel of the vehicle when the brakes are applied. Such frictional contact results in the generation of heat at the frictionally engaging, or wearable, surface of the brake lining. Of course, some degree of heat generation at the wearable surface of the brake lining is expected and normal. However, an abnormal degree of heat generated is an indication of a fault in the braking mechanism.
An example of an abnormal degree of heat generation occurs in the case of a dragging brake. The brakes are applied and normal frictional engagement between the lining of the brake shoe and the wheels occurs. Once the brakes are no longer applied, the brake shoe assumes an out of service position of non-engagement with the wheel. However, a dragging brake does not fully assume an out of service position and therefore, some frictional engagement continues. Thus, an abnormal generation of heat occurs at the wearable surface of the brake lining.
Another example of an abnormal degree of heat generation may occur when comparing the wearable surface heat of the brake shoe of one wheel to that of its respective mate across the axle of a vehicle. Significant variations on temperature of the brake linings of respective wheel pairs is an indication of unbalanced wheels, or a fault in one of the braking components.
Various methods using temperature to predict lining wear, but not to measure temperature itself are disclosed in co-pending application Ser. No. 09/176,490 filed Oct. 21, 1998, entitled “Packaging A Temperature Sensing Brake Lining Wear Indicator In A Brake Shoe Assembly”.
It would be desirable to provide a temperature measuring system in a brake shoe assembly that can directly measure the temperature of the brake shoe lining at its frictionally engaging, or wearable, surface. It would further be desirable to provide a system to alert a vehicle user of an abnormal temperature reading at the wearable surface of the brake shoe lining.
SUMMARY OF THE INVENTION
In a disclosed embodiment of this invention, a brake shoe assembly includes a backing plate and a brake lining. The brake lining has an interface surface abutting the backing plate and a wearable surface for frictionally engaging a portion of a wheel of a vehicle. A temperature measuring system includes a temperature measuring device which is embedded in the brake lining at a position adjacent the interface surface of the brake lining. The temperature measuring device communicates directly with the frictionally engaging, or wearable, surface of the brake lining by way of a wearable heat pipe that exhibits highly conductive thermal properties.
In one embodiment, the heat may be approximately one eighth of an inch in diameter. Preferably, it is made of copper or brass which are highly conductive materials and provide fast response when transmitting the heat generated on the frictionally engaging surface of the brake lining to the temperature measurement device positioned at a point that is deeper in the brake shoe.
The temperature measurement device is of a known type and may be a thermistor which measures temperature continuously or a poly switch which is actuated when a predetermined temperature is attained. A control receives a signal from the temperature measurement device and determines an abnormal brake condition based on the signal.
The thermally conductive heat pipe may be thermally isolated from the adjacent brake lining material by surrounding the heat pipe with thermally insulative material. The heat pipe may also be thermally insulated from the backing plate of the brake shoe.
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.
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Butler Douglas C.
Carlson & Gaskey & Olds
Meritor Heavy Vehicle Systems LLC
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