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The study of vehicle handling behaviour is of fundamental importance in order to improve vehicle safety, especially as concerns the loss of stability in the lateral direction resulting from unexpected lateral disturbances like side wind force, tyre pressure loss, μ-split braking due to different road pavements such as icy, wet, and dry pavement, etc. The interest for vehicle stability has been actually increasing, and consequently the study of the local stability has become a fundamental discipline in the field of vehicle dynamics, being a vehicle a strongly non linear system mainly because of tyres behaviour. The study of the driving stability of a vehicle travelling on a curve in steady state conditions is the first and most important step in order to understand the effects of perturbations inevitably occurring during vehicle motion. Such a study may have a dual application: first of all it can contribute to develop and optimize control logic of the vehicle subsystems; secondly it may be useful to identify the physical quantities affecting stability and to find out their optimal set under this point of view. At this purpose it is fundamental to dispose of suitable stability maps, which typically are constituted by curves in a phase plane delimiting zones in which the system of equations describing the vehicle dynamics admits stable and strongly attractive solutions. Outside of such zones only unstable or marginally stable solutions exist. In the recent years several ways to construct these maps have been proposed. A great number of studies in literature are mainly oriented to the development of control systems strategies aimed to improve vehicle stability and so in such papers the authors proposed methods based on vehicle and tyre models extremely simplified. Typical simplifications consist in considering a bicycle model (i.e. neglecting roll dynamics and the lateral load transfer) and/or in linearising the tyre-road interaction (i.e. underestimating saturation effects in the tyre lateral forces). No studies have been found aimed to find out which vehicle physical characteristics affect significantly its stability and the influence of their variation on stability. This paper pursues precisely this purpose and hence it is necessary to use a sufficiently detailed vehicle model allowing to take into account all the physical parameters on which investigate. The stability of a complete four wheel, two axle, vehicle model will be discussed, Pacejka magic formula will be adopted to model the pure tyre-road interaction, lateral load transfer will also be considered. Two different methods will be presented: a “mathematical” method consisting in the evaluation of the state matrix eigenvalues and a ”geometrical” method inspired to the so called “handling diagram” construction. The influence exerted on the stability zone extension in the phase plane by some vehicle parameters, such as tyre cornering stiffness and front/rear roll stiffness will be evidenced with the aim to suggest solutions able to increase vehicle stability.

The results of an experimental activity carried out with the aim to investigate on the adhesive behaviour of visco-elastic materials in sliding contact with road asperities are presented. Experiments are carried out using a prototype of pin on disk machine in which pin is constituted by a specimen of rubber coming from a commercial tire, while different disks are realized in glass, marble, steel and in abrasive paper of different roughness. Tests are performed in both dry and wet conditions. Roughness of the test surfaces is evaluated by a rugosimeter, while pressure is evaluated, off-line, analysing the extension of the contact patch left by the pin on a sheet of graph paper under known applied loads. Slide velocity is imposed by an inverter controlled motor driving the disk. Basing on well known theoretical hypotheses, adhesive component of friction coefficient is estimated making the specimens slide on surfaces characterized by low values of macro-roughness, in order to underline the differences in rubber behaviour respect to micro-roughness surface variations. The results confirmed adhesion dependence on pressure and sliding velocity in both cases of smooth surfaces, where the main friction mechanism is the adhesive one, and of rough surfaces, where the main friction mechanism is the hysteretic one. Analysing various surfaces roughness it is possible to notice a maximized adhesive contribution on flat surfaces; it reduces with increasing roughness, while hysteretic friction comes over instead of it because of asperities penetration into rubber sliding surface. Moreover in the case of rough surfaces the separation between static and dynamic friction coefficient is evident and the static coefficient is greater than the dynamic one. On the other hand in case of smooth surface the absence of indentation phenomena doesn’t allow to recognize, in the measured force time history, the “classical” peak usually associated to the static friction coefficient. Dry and wet tests performed on different micro-roughness profiles highlighted that friction coefficient in dry conditions is greater on smoother surfaces, while an opposite tendency is shown in wet condition, when asperities are greater enough to break the thin water layer, providing a certain degree of indentation. A proposal for a methodology able to estimate the only adhesive friction component, developed thanks to wet contact tests, is expressed in the end of the paper.

Modern anti-lock braking systems (ABS) are based on tyre slip observation. Tyre slide conditions are estimated considering, as a rule, a fully stiff carcass. During braking motions, tyre – road forces cause carcass strain and, consequently, slip variation respect to the values estimated with reference to no compliance systems. In this paper, the influence of the “effective slip”, estimated considering carcass compliance, on bus anti-lock braking systems is evaluated. To this aim, a simplified tyre carcass model has been realized. This one, combined with a tyreroad interaction model, allows defining the effective slip. Simulations have been carried out employing a quarter vehicle model and braking performances have been evaluated for an anti-lock system equipped with an algorithm able to estimate the effective slip.

In this paper an experimental test rig aimed to characterize a pneumatic tyre, together with the first experimental results, is presented. The objective is to determine some tyre mechanical characteristics useful to physically model its behaviour; in particular: the normal interaction characteristic, the radial stiffness, the total stiffness and the longitudinal hysteretic cycles. To this aim two different kind of tests have been executed: radial and longitudinal tests. In the radial test the load is statically applied, along the vertical direction, to the tyre by means of an hydraulic press and it is measured together with the consequent radial deformation, so allowing the estimation of the tyre normal interaction characteristic and of its radial stiffness. Different radial tests can be conducted for an assigned tyre varying the inflation pressure. The longitudinal tests are conducted applying, under an assigned constant vertical load, a variable horizontal strain to the tyre by means of a linear actuator, two profile rail guides and a system to transfer the horizontal motion to the contact patch of the tyre, opportunely placed on a moving steel plate placed on the two linear guide rails. During the tests the horizontal load and the resulting deformations are measured and acquired so allowing the estimation of tyre total stiffness and of its longitudinal hysteretic cycles. Longitudinal tests can be conducted varying the assigned vertical load, the horizontal displacement law in terms of frequency and amplitude, the tyre inflation pressure. All the different types of rim can be mounted on the test rig thanks to a universal quick flange.

In this paper the development and the experimental testing of a magnetorheological coupling for a 4WD vehicle are presented. Unlike most of the active devices use multidisc wet clutches as engagement mechanism, this device does not have any sliding contact and is characterized by an electrical actuation mechanism. The coupling performance is obtained by means of the magnetorheological fluid (MRF), able to change its rheological behaviour when a magnetic field is applied. Therefore the supply current control allows to manage the torque transmitted to the rear drive shaft. So this device can be used to bias the drive torque between the front and rear drive shafts of a 4WD vehicle. In particular the magnetorheological fluid (MRF) employment allows to realize an adaptive system able to improve vehicle directional behaviour and traction. An MRF coupling model and its control logic have been developed and are described. The results of the simulations carried on with these models are reported; they have shown the feasibility of this application in terms of torque transmission and biasing. The above simulation models have been implemented in a Software-In-the-Loop (SIL) scheme together with a vehicle dynamics model. The SIL results are reported and they show the MRF coupling effectiveness on the vehicle dynamical behaviour. A test bench has been realized to test an MRF coupling prototype in order to verify the capability to transmit torque.

The design of automotive systems requires the joint knowledge of aspects and problems regarding various subjects such as mechanics, fluid dynamics, hydraulics, electronics, etc. In traditional design approaches the different components are designed separately by different workgroups and the integration of the whole system is executed in the final stage. This certainly implies longer development time and higher costs, at least because of practical interfacing problems. This paper analyses a modern approach to design, develop and set up control systems. The key idea is to get a functional validation of the interaction among the different subsystems using cosimulation before getting to the experimental stage. As an example is illustrated a particular application to one of the most widespread modern vehicle’s control systems: the ABS braking control system, carried on by means of ADAMS-Car – MatLab-Simulink co-simulation.