Improving Stability and Controllability of Two-Axial Vehicles with a Connectable Front Axle by Redistributing Torque between the Axles

Abstract

A steering aid system called active steering is evaluated by simulating different driving events. The active steering solution, which is taken from a scientific paper, has been implemented in Matlab/Simulink. A vehicle model, also implemented in Matlab/Simulink, is used to form a total system and to compare the two systems: a conventional vehicle and a controlled vehicle.The input to the vehicle model is the steering wheel angle performed by the driver. Simulations are made for a constant speed and a specific changeable road adhesion coefficient. The control system takes the yaw rate as input and derives a steering angle contribution to be added to the drivers command.The motivation for this work is to understand and characterize the response of a vehicle with a complementary steering system. Specific driving events are considered for the simulations such as a wind force disturbance and a severe double lane change.The response of the controlled vehicle is similar to the response of the conventional vehicle for nominal driving, but the steering aid system reduces the effect of wind force disturbances. Improved stability is obtained for the vehicle during slippery road driving. IntroductionThis master thesis is based on two articles [1][8] with a proposed solution of a control system for the steering of a car. The solution has to be implemented and driving events simulated.There are a lot of research and development in the area of steering and steer-by-wire (SBW).The main reason for this is the aim to improve safety and handling. However it is still difficult to value the improvements. In this thesis one solution is implemented and analysed.An active steering system is a complementary system for a front-steered vehicle that adds or subtracts a component to the steering signal performed by the driver. The steering signal from the driver is an angular movement on the steering wheel. The resulting steering angle is thus composed by the component performed by the driver and the component contributed by the steering system. Problem formulationThe aim of the thesis is to reproduce the work in the articles [1][8] and to make a set of simulations to determine whether the predefined goals are fulfilled. Amongst the simulations that are made, events such as wind force disturbances are analysed and input from real driving experiment such as the ISO-standardized double lane change are analysed. The manoeuvres will be simulated for different speeds and road adhesions. Implementation of the system will be made in Matlab/Simulink. All the simulations will be made in Simulink.The assignment for the master thesis is to implement a steering aid system taking driver action as input. A vehicle model is implemented and the total system including the active steering system is simulated for different driver events. Some focus is laid on the effect of driver reactions due to disturbances.The goals are to:Characterise the difference of the response between the controlled and the uncontrolled vehicle for nominal driving and at th...