DIRECTIONAL STABILITY IMPROVEMENTS WITH COUPLING FORCE CONTROL ON TRACTOR/SEMI-TRAILER COMBINATIONS
In a tractor/semi-trailer combination the tractor is usually equipped with anti lock device and the semi-trailer is less maintained than the tractor. Since sensing couplers are available from manufacturers, a well-adapted control algorithm can eliminate jack-knifing and high peaks in coupling force during braking. In order to improve the stability and reduce the forces on the kingpin, a three dimensional non-linear mathematical model has been developed for digital simulation. The model includes the following properties: - non-linear characteristics of road-tyre interface, - vehicle units regarded as rigid bodies, - suspensions with non-linear spring and damping behaviour, - detailed description of the brake system. Special efforts were made to use appropriate characteristic curve for the elements in the brake system and these results were validated to experimental measurements. Though the study is limited to the examination of the behavior of the vehicle during braking in a turning maneuver, several test runs were made to reach the best dynamical performance and the minimum number of sensors. Test results are compared in conventional and controlled case.