An Engine/Vehicle Model to Assess the Theoretical Increase of Car Safety by Using the Spark Ignition Engine to Support the Conventional Braking System

Abstract

Introduction of active safety systems has led to a significant increase of passenger car safety. However, statistics on road accidents show that further improvements of active systems would be necessary. 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.