Intelligent transportation systems
Today’s vehicles are equipped with many electronically controlled systems, whose integration is rising in complexity with the increasing number of available customer features and technologies. A way to solve the integrationproblem can be the introduction of a hierarchical control structure, where allcontrol commands are computed in parallel in one core algorithm, and wherethe control has to take into account the interactions among the vehiclesubsystems, driver and vehicle.
The key element of integrated vehicle controlis that the behavior of the various vehicle subsystems has to be coordinated,i.e. subsystems has to behave as cooperatively as possible in performing thedesired vehicle functions. Clearly, the fully integrated controller will be morecomplex than the sum of the stand alone ones, but it will guarantee increasedperformance and robustness. Active Safety Systems Integration is one of themain research topics in vehicle control area. In order to maintain safehandling characteristics of the vehicle, several active system technologies(active braking, active steering, active differential, active suspension, etc.) havebeen developed. These devices modify the vehicle dynamics imposing forces ormoments to the vehicle body in different ways and can now make use of smartsensors (for example, the so–called intelligent tires), allowing precise anddistributed measurements from the environment, to increase the performanceof the control action, the vehicle stability, the safety and comfort of the driver.On top of that, hierarchical and hybrid structures guarantee increasedperformance and robustness of control strategies, taking into account theinteractions among vehicle, driver and environment, considered in parallel inone core algorithm.
An important design factor to be considered in thestandalone or integrated controller design is the actuator saturation, whichlimits the maximum obtainable performance. In an integrated controlstructure more power is available for control, thus potentially limiting thesaturation occurrences. In all cases, it is important to manage criticalsituations, whenever actuators are not physically able to apply the requiredinput.
The use of “intelligent” (also called smart) tires with sensors that areembedded in the tread to provide direct tire strain measurements, allowsprecise measurement of friction, forces, load transfer, actual tire-road friction(kinetic friction) and maximum tire-road friction available, and henceincreases significantly the efficiency of active safety systems. Currently, mostof these variables are indirectly estimates using onboard sensors. With a moreaccurate estimation, we could even identify road-surface condition in realtime. It also reduces realization costs, it increases flexibility, and it easesmaintenance, debugging and diagnostics.
The vehicle motion can be in generaldescribed as a rigid body moving in the free space, with 6 degrees of freedom,connected with the ground surface through tires and suspensions. This resultsin a model with high non–linear behavior and high coupling effects. As afurther complication, these new technologies introduce problems regardingwireless communication, e.g., packet losses, fading effects, andsynchronization losses. In this environment, an analytic approach and formalmodels that take into account all non-idealities that are typical of NetworkedControl Systems (NCSs) are needed. For the above reasons, we first addressedthe vehicle control problem in a non-linear setting with ideal communication,and proposed an integrated controller to guarantee vehicle stability/trajectorytracking. We are currently introducing the non-idealities of thecommunication system in the control scheme derived in the ideal case. Inparticular, we are developing self-triggering control strategies that allow totrigger sampling and wireless transmission only when necessary, to preventenergy shortage.