Optimization to Improve Lateral Stability of Tractor Semi-Trailers During Steady State Cornering 2004-01-2690

Decreasing the propensity for rollover during steady state cornering of tractor semi-trailers is a key advantage to the trucking industry. This will be referred to as “increasing the lateral stability during steady state cornering” and may be accomplished by changes in design and loading variables which influence the behavior of a vehicle. To better understand the effects of such changes, a computer program was written to optimize certain design variables and thus maximize the lateral acceleration where an incipient loss of lateral stability occurs.

The vehicle model used in the present investigation extends that developed by Law [1] and presented in Law and Janajreh [2]. The original model included the effects of tire flexibility, nonlinear roll-compliant suspensions, and fifth wheel lash. This model was modified to include (a) additional effects of displacement due to both lateral and vertical tire flexibility, and (b) provisions for determining “off-tracking”. This improved model was used as a basis for an optimization routine that initially maximizes the payload capacity, subject to legal per-axle load constraints, by determining an optimum set of tractor and semi-trailer adjustments in the placement of the fifth wheel and the trailer axles. After this initial step, an optimization routine is implemented which maximizes the rollover indicator, a practical measure of rollover propensity. The rollover indicator is calculated as an average of two components including (a) the minimum acceleration for which there is no valid solution to the equations of equilibrium (or critical lateral acceleration) where rollover is imminent and (b) the acceleration at which inside wheel lift-off first occurs. The rollover indicator is maximized in the optimization routine by the choice of appropriate values of various design variables. These include load placement, tire stiffness, vehicle track, and others.

The tractor semi-trailer considered in the optimization was equipped with new single tires. Michelin Americas Research and Development Corporation provided parameter data for the vehicle.