Lateral stability analysis of the tractor/full trailer combination vehicle
This paper presents a linear dynamics model of tractor/full trailer with six degrees of freedom, and a series of simulations are performed on obstacle avoidance manoeuvers in which the combination vehicle moves at a constant forward speed. It is found that the ratio of the peak lateral acceleration of the full trailer's center of gravity (CG) to that of the tractor is 2.3, meanwhile, the articulated angle of the trailer is larger than that of the dolly. This phenomena, defined as the ‘rearward amplification ratio’(RWA), leads vehicle to rollover easily. A larger wheelbase of trailer would be useful to improve the lateral stability of the combination vehicle but it is limited by width of the road. Acting a resistive torque on the turntable can be absolutely effective in improving the dynamics stability of the tractor/full trailer combination vehicle but if acted at hitch point it has little improvement.
Sensitivity of rearward amplication control of a truck/full trailer to tyre cornering stiffness variations
Abstract Highway safety and vehicle performance are two important considerations in the design of a heavy vehicle combination. In this paper a performance measure called the ‘rearward amplification ratio’ (RWA) is used as a control criterion in the design of a vehicle-handling controller. This approach is different to conventional control techniques. The RWA is defined as the ratio of the peak lateral acceleration at the rearmost trailer's centre of gravity (CG) to that of the lead unit during a lane-change manoeuvre. The vehicle under consideration is a six-axle truck/full trailer, which usually exhibits a high level of RWA leading to roll-over during obstacle avoidance manoeuvres. In this study, several control strategies are examined, namely active yaw control at the truck CG, active yaw control at the dolly CG and active yaw control at the trailer CG. These could be employed individually or in combination. The effect of an active control torque applied to various vehicle units is examined by using an optimal linear quadratic regulator approach combined with a simplified four degrees-of-freedom linear vehicle model. The controller performance index parameters are determined for the vehicle based on acceptable RWA target values. The sensitivity of the controller to tyre cornering stiffness variation is further evaluated. Simulation results indicate that the RWA can be reduced without significant change of the uncontrolled vehicle trajectory when active yaw torque is applied to the dolly. The controller can be more effective in improving the dynamic performance and roll stability of this type of commercial vehicle, if applied to the lead unit (truck) or to the last unit (trailer). However, the path of the vehicle will be strongly influenced and driving difficulties can be experienced. For active yaw control at the dolly CG, the optimal controller is found to be most sensitive to the dolly's tyres' cornering stiffness variations and least sensitive to steering axle from the RWA point of view. It is also found that the controller is most sensitive to steering axle parameter variations for path following.
COMPARISON OF THE BEHAVIOR OF ARTICULATED RECREATIONAL VEHICLES WITH EITHER FIXED OR POSITION CONTROL OF STEERING
The use of a subset of the complete equations of motion to determine the lateral stability of an articulated vehicle is considered. It is shown that, with fixed steering, the path of the vehicle diverges from the nominal path even when each eigenvalue associated with the subset of equations has a negative real part. A linear steering law is introduced which is shown to be effective in controlling the path of the vehicle. Critical speed is significantly affected by the addition of steering control. With control, speed can be higher, lower, or about the same as it is without control. Four different articulated vehicles are treated; the powered vehicle in each case represents a mid-size American car, and the towed vehicles represent utility, boat, travel, and horse trailers. Trailer swing oscillations for the controlled system can be more pronounced, less pronounced, or about the same as those for the system with fixed steering.