Procedure for drive stability enhancement

The invention relates to a method for obtaining the trailer related state variables in a vehicle combination, having sensors only on the towing vehicle unit characterised in that the combination vehicle model's parameters, both of the state estimator and the reference model, which is identical to the model used for state observer and generally understeered negotiating steady turn at low speed, for the tractor and trailer(s) are calculated from the signals measured on the towing vehicle, such as pressure difference between the left and right air bags on the towing vehicle's rear axle, brake cylinder pressures, steering angle, yaw rate and lateral acceleration and the wheel speed of each wheel on the tractor by means of an adaptive algorithm, which is finished when the critical parameters are convergent, and the hitch angle, hitch angle rate are fed into the adaptive controller together with the directly measured signals.