Mechanics of Brake Steering Pull on Heavy Trucks 2015-36-0024
Heavy trucks with solid front axles commonly use steering systems that have left to right asymmetry. The asymmetry creates the potential to cause steering pulls during brake application which are by their nature undesirable since they require an input in the steering wheel by the driver to maintain the correct path of the vehicle. Brake forces acting in the tire contact patches create toe-out moments around the kingpin axes that are resisted by the steering linkages. However asymmetry of the linkage allows unbalanced toe-out steer angle deviations at the wheels resulting in a path deviation of the truck that is perceived as brake steering pull.
The factors influencing steering pull include the compliance properties of the steering linkages, road wheel geometry, drag link geometry and spring windup properties. The mechanics of the brake force interactions with these steering and suspension properties are explained here.
Simulation provides an excellent tool to examine and quantify these interactions. The truck simulation model, TruckSim®, is used to show the importance of linkage compliance as a primary variable and the interactions with other steering and suspension properties. It will be shown that jounce steer and/or brake windup steer can be used to compensate for the unbalanced effects arising from the linkage asymmetry.