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An Automatic Tire Inflation System (ATIS) specifically designed for commercial use on trailer axles is currently being installed and utilized successfully by trucking companies, the military and owner/operators throughout the U.S. A need exists for an ATIS specifically designed for the drive axles of Class 8 over-the- road tractors. The addition of an ATIS for drive axles will expand automatic tire monitoring capability to all heavily loaded tires of the over-the-road truck/trailer rig. An ATIS for drive axles has been designed, fabricated and tested. Testing and evaluation of the prototype ATIS drive axle system indicates the system can be successfully installed on a typical tractor rig and operated for an extended period without problems. The testing included a 50,000 mile evaluation of the ATIS installed in a laboratory test fixture. The test fixture used stock axle parts and operated at 65 MPH. Environmental testing was conducted at temperatures ranging from -20 to +200 degrees F.

An Automatic Tire Inflation System (ATIS), specifically designed for use on commercial long haul trailers, requires modification of the axles to direct air to the tires. The ATIS requires a drilled hole through the axle tube for the installation of a pneumatic fitting. The trucking industry expressed concern about the modification and its impact upon the axle structure, and the general durability of the system over a long period. A three-phase test program was developed and conducted to satisfy the concerns of the industry.

For over 30 years, spring brake chambers have been the norm for air brake systems, now the new technology of air- applied, mechanically-held air chambers offers the industry a smaller lighter, more efficient, safer and maintainable actuator. The air applied, mechanically-held air brake system is a system that marries air valves and chambers to achieve a performance level that has a positive effect on many of the important components of the air system and the components of the foundation brakes. The intent of this paper is to outline the functioning of an air-applied, mechanically-held air brake system and to enlighten the reader to the variety of ways this technology benefits the operation and safety of an air brake equipped vehicle. It is assumed that common spring brake technology is readily understood therefore the dynamics and properties of that type of air brake system will not be detailed except where functional comparisons are made to the air-applied, mechanically-held system.