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Technical Paper

On the Impact of the Maximum Available Tire-Road Friction Coefficient Awareness in a Brake-Based Torque Vectoring System

Tire-road interaction is one of the main concerns in the design of control strategies for active/semi-active differentials oriented to improve handling performances of a vehicle. In particular, the knowledge of the friction coefficient at the tire-road interface is crucial for achieving the best performance in any working condition. State observers and estimators have been developed at the purpose, based on the measurements traditionally carried out on board vehicle (steer angle, lateral acceleration, yaw rate, wheels speed). However, until today, the problem of tire-road friction coefficient estimation (and especially of its maximum value) has not completely been solved. Thus, active control systems developed so far rely on a driver manual selection of the road adherence condition (anyway characterized by a rough and imprecise quality) or on a conservative tuning of the control logic in order to ensure vehicle safety among different tire-road friction coefficients.
Technical Paper

Numerical Investigation of the Vertical Dynamics of an Agricultural Vehicle Operating on Deformable Soil

This work focuses on the analysis of the vertical dynamics of an agricultural tractor, investigating the influence of suspensions' parameters on riding comfort and contact forces. The use of lugged tires coupled with the operation over banked, irregular and deformable tracks, determines significant levels of vertical acceleration over several components of the tractor. These operating conditions have a direct effect on the driver, whose alertness and efficiency are undermined by the exposure to high levels of acceleration for a long time. Secondly, variations of the normal and traction forces provided by the tires affect the quality of tillage and other operations. The paper presents a multi-body vehicle model of a tractor interfaced with a tire-soil contact model allowing to take into account soil's deformation and tread pattern design.
Journal Article

Bifurcation Analysis of a Car Model Running on an Even Surface - A Fundamental Study for Addressing Automomous Vehicle Dynamics

The paper deals with the bifurcation analysis of a simple mathematical model describing an automobile running on an even surface. Bifurcation analysis is adopted as the proper procedure for an in-depth understanding of the stability of steady-state motion of cars (either cornering or running straight ahead). The aim of the paper is providing the fundamental information for inspiring further studies on vehicle dynamics with or without a human driver. The considered mechanical model of the car has two degrees of freedom, nonlinear tire characteristics are included. A simple driver model is introduced. Experimental validations of the model are produced. As a first step, bifurcation analysis is performed without driver (fixed control). Ten different combinations of front and rear tire characteristics (featuring understeer or oversteer automobiles) are considered. Steering angle and speed are varied. Many different dynamical behaviors of the model are found.
Technical Paper

Instrumented steering wheel for accurate ADAS development

The knowledge of the forces exerted by each hand of the driver at the steering wheel is useful for a better understanding of the driver steering action. This information is needed while developing haptic steering wheels useful for tuning Advanced Driver Assistance Systems (ADAS). The actual forces applied by the driver’s hands can be measured by means of a new Instrumented Steering Wheel (ISW), that, by using two six axis load cells, can measure the three force components and the three moment components exerted by the two hands, separately. Additionally, the instrumented steering wheel allows to measure the grip force, defined as the holding force applied by each hand on the handle. A full compensation of the inertia forces due to the vehicle acceleration guarantees an extremely high level of accuracy in the measure of the forces exerted by the driver. The resolution is just 0.1 N. The ISW has been already used for a couple of ADAS activities.