Auxiliary Axles - An Axle Manufacturers Perspective 2001-01-2781
Auxiliary non-driven axles are sometimes added to heavy duty trucks, tractors and trailers in order to increase vehicle load capacity (load bearing) or to meet bridge law regulations (load sharing). The number of auxiliary axle installations, done either at the Original Equipment Manufacturers (OEM) level or in the aftermarket, is on the rise. When properly engineered and used, the performance, durability and reliability can all be satisfactory. When misapplied or misused, the results can be serious. Proper consideration must always be given to the load carrying capacity of the primary steer and primary drive axles, especially if the auxiliary axle is of the liftable variety. A thorough system evaluation of the vehicle must go beyond a simple Gross Vehicle Weight (GVW) summation of the rating of the individual axles. It must account for all possible loading conditions on all of the axles. To avoid axle overloading, the plated GVW may need to be less than the GVW rating summation of the axles. While the deployment or retraction of a liftable axle is always the responsibility of the driver, more specific training and certification is required. Typical driver training programs provide insufficient exposure to auxiliary axles and lack sufficient detailed instruction to better acquaint the driver with the added responsibilities associated with vehicles equipped with an auxiliary axle.
This paper looks at each of the mentioned issues for auxiliary axles from the perspective of an axle designer, manufacturer, and tier one supplier to all the major heavy duty truck OEMs. In addition, the paper discusses typical axle design and validation methods and describes various types of vehicle and axle configurations. Load changes imposed on the primary axles as a consequence of axle placement are examined and analyzed. Finally, the paper makes recommendations to ensure that the proper implementation and usage of auxiliary axles are fully understood.