Vehicle Dynamics and Control Abstracts

D. J. M. Sampson, Active Roll Control of Articulated Heavy Vehicles, Ph.D. Thesis, University of Cambridge, UK, 2000.

This thesis is concerned with the use of active roll control systems consisting of active anti-roll bars to improve the roll stability of single unit and articulated heavy vehicles.

Chapter 1 reviews previous research into the yaw-roll dynamics of heavy vehicles and into using active roll control systems on trucks, cars and trains.

Chapter 2 details a simplified dynamic model for simulating the handling and roll performance of a torsionally flexible single unit vehicle and a technique for coupling multiple single unit models to enable simulation of any long combination vehicle. A model of the active roll control system hardware is also presented.

Chapter 3 reviews the mechanics of the roll-over process and identifies a mechanism for reducing lateral load transfer by rolling the vehicle body into corners. Functional controllability analysis is used to show that achievable roll stability, even with ideal active anti-roll bars, is ultimately limited by suspension travel. A procedure for identifying critical axles whose lift-off determines the limit of roll stability is presented. The best achievable control objective for maximising roll stability is shown to be balancing the normalised load transfers at all critical axles while taking the largest inward suspension roll angle to the maximum allowable angle.

Chapter 4 proposes an LQR-based method for designing a full-state active roll control system for a single unit vehicle. A more practical partial-state feedback controller, using measurements of suspension roll angles, body roll rate, yaw rate and steering input, is also described. Simulations indicate that a system of active anti-roll bars incorporating moderately priced, low bandwidth hydraulic actuators and servo-valves and relatively simple instrumentation can improve steady-state roll stability of a rigid single unit vehicle by 23% and of a torsionally flexible single unit vehicle by 30%. Improvements in severe transient manoeuvres can be even greater. The effects of actuator bandwidth on system performance are investigated. Active roll control is also shown to increase handling stability, particularly for torsionally flexible vehicles.

Chapter 5 extends the work of chapter 4 to a tractor semi-trailer. Simulations show that active roll control systems can increase the roll-over threshold of a torsionally rigid tractor semi-trailer by 30% and of a torsionally flexible tractor semi-trailer by 35%.

Chapter 6 examines the use of active roll control systems on long combination vehicles, including those with flexible couplings. Simulations show that active roll control can increase the roll-over threshold by 27% for a B-double, by 25% for a truck full-trailer and by 24% for an A-double. The effect of rearward amplification on transient load transfer can be significantly reduced.

Conclusions and recommendations for further work are presented in chapter 7.

The full thesis is available online (PDF, 3384 KB).