A dynamic model for the study of theoretical limitations and effectiveness of active safety systems using internal combustion engine friction

Many scientific researches and huge investments have been addressed towards improving the safety of passenger cars in recent decades. However, about 3,600 people dead and 265,000 people injured because of almost 187,000 road accidents that occurred in Italy during 2012 prove that much still needs to be done. The new opportunities offered by mechatronics push R&D towards active safety systems, such as antilock braking system (ABS), traction control system (TCS), and electronic stability control (ESC). Active safety systems are very interesting because they act before the collision event in order to avoid/limit the accident effects and, therefore, they contribute also to increase the effectiveness of any co-existing passive safety system. This paper presents a dynamical model of the engine–car–brakes system that is used to simulate vehicle deceleration and calculate the risk of injuries. The model is used to quantify the performance of active safety systems during specific collision scenarios in which several vehicle cruising speeds and different values of distance from the obstacle that causes the active system activation are considered. The base system constituted by actual hydraulic brakes with embedded ABS is first compared to the ideal active system. The latter allows for maximum vehicle deceleration owing to ideal operation of hydraulic brakes supported by ABS and also to mechatronic actuation which anticipates the human intervention and eliminates the delay due to reaction time. Then, the model is used to analyse two feasible evolutions of the ideal active safety system. In the first one, the internal combustion engine friction power aids the vehicle speed decrease before the action of brakes. In the second one, specifically devoted to vehicles powered by hybrid electrical–thermal units, the reversible electric motor operates in addition/substitution to the braking action exerted by the engine mechanical friction.