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This paper examines how commercial vehicle aerodynamic improvements can be influenced by regulation particularly with respect to size and weight policy. It discusses the potential use of performance based standards (PBS) first introduced to optimize vehicle configurations in terms of vehicle stability and control and compatibility with highway geometry. There are several vehicle treatments that can be used to reduce aerodynamic drag, some of which lengthen or widen the vehicle without increasing cargo capacity. One such solution is referred to as ‘boat tails” consisting of a light weight external extension of the trailer allowing the air flow to remain attached as the vehicle cross section diminishes resulting in a reduction in the area of negative pressure at the end of the vehicle which reduces drag force.

Today, active dynamic control systems for commercial vehicles, offering improved safety, are frequently discussed. Yaw stabilising systems are based on theories from passenger car implementation, yet roll stabilisation - probably introduced in the near future - requires increased knowledge of rollover mechanics. Static analysis, providing steady state rollover threshold (SSRT), is the most common approach. Nevertheless in a rolling vehicle, kinetic energy is always present, deteriorating roll stability, invalidating the analysis. A simple method determining the dynamic rollover threshold (DRT) is therefore introduces in this paper. DRT is the worst case measure of roll instability: the conditions are necessary but not sufficient for rollover.

Active vehicle dynamics control ensures improved safety. So far, yaw instability is mostly associated with transient steering manoeuvres when driving at a constant speed. However, braking related load transfer affects yaw stability. Intense braking at high friction combined with elevated and forwarded CG amplifies this influence on unloaded tractors. Designing a dynamic stability system to enhance active safety requires fresh insight into braking related yaw instability. This investigation covers a theoretical analysis of braking influence on yaw stability on unloaded 4×2 tractors, being applicable to vehicle braking while cornering, including steering induced by other asymmetrical forces, since it focuses essentially on small steering angles.

Steady state non-linear cornering properties, giving the lateral slip to force characteristics of individual axles as result are determined from experimental data. The handling diagram of the vehicle combination facilitates an examination of any unstable steady state yaw response. The method offers a viable alternative to the traditional constant radius test. Axle data is derived using the bicycle model via measurements taken during handling manoeuvring while the magic tire formula is used for adaptation of measured axle data into mathematical representation. The results of axle data evaluation, using a semi-trailer combination, manoeuvring over high friction surface conditions are presented.

A generic articulated heavy vehicle model, applied to a tractor semi trailer combination is modelled on an approach characterised by simplicity. Yet, the handling characteristics accuracy serves well within the frequency domain of interest. Possessing the capacity of performing in real time simulation up to the limits of yaw and roll stability, its simplicity derives advantages offering effective parameter variation possibilities at an elevated educational level. As an example, better understanding of the expected wheel angle deviation from the current wheel spindle angle is achieved through an extension of the model. Validated against field experiments of lane change manoeuvring under high friction conditions up to the limit of roll stability, it also compan?s well against a more complex computer model.