Influence of Steering System Imperfections on Truck Steering Feel | a driving simulator study

Abstract

Road safety is a prime concern in modern society. Statistics on traffic accidents show that articulated vehicles are overrepresented in fatal accidents. A third of all accidents happen during a vehicle maneuver with small lateral displacements: on-center handling. Stable guidance and handling behavior of the vehicle is mainly determined by its chassis, the vehicle dynamics and the steering system which needs to be reliable, predictable and to give the driver good steering feel. Defining steering feel is difficult because it is a subjective matter, but it is clear that good steering feel is necessary for safe vehicle control and an important element to driver experience. Next to the steering system mechanism and architecture the steering system parameters are important for truck driver steering feel. Mechanical systems will degrade over the life time of usage. Steering system imperfections are defined as the steering system parameters that change over lifetime. This study has been a first attempt to investigate the influence of the steering system imperfections on truck drivers steering feel during a simulation study. The first time used Mobile Truck Driving Simulator (MTDS) is validated by using earlier research, interviewing truck drivers, recording truck rides from the view of the driver, measuring dimensions, using employment guides and let professional drivers run test drives on the simulator. The study started with an explorative research on six steering system parameters that show a large degree of degradation: column bearing friction, bevel box friction, hydraulic cylinder friction, king pin friction, free play in the system and the tie rod stiffness. Professional truck drivers were asked to track the moment when the system does not show realistic steering feel anymore. During every test run one of the six steering system parameters is constantly changed using a predefined threshold tracking method resulting in general feedback and mean values of that particular parameter. The experiment resulted in three parameters which were varied in the main experiment: column friction, king pin friction and free play. The first objective of the main experiment was to find out how the three different steering system imperfections affect the steering feel of professional truck drivers. Steering feel is approached by a combination of four elements: general experience of handling, steering system, realism and steering system acceptance scale (SAS) based on the usefulness and satisfaction of the system. Professional truck drivers drove different test runs and completed a questionnaire. The increase of column friction, king pin friction and free play significantly influenced the evaluation of steering feel by the subjects. The second objective was to find out how the three steering system imperfections affect the objective driving indicators of professional truck drivers. Increasing the column friction results in an proportional increase of steering effort and driver burden. The increase of king pin friction to the first value results in an increase of steering effort, driver burden and steer jerk an increase of free play resulted in different steering reversal rate, an increase of steering business, steer rate, steer jerk and steering steadiness. This study shows the large impact of degradation of steering systems on driver experience and driver workload. No conclusion can be drawn on the driving performance regarding driving an articulated vehicle with a degraded steering system.