Partial and Full Braking Algorithm According to Time-to-Collision for Both Safety and Ride Comfort in an Autonomous Vehicle

In this study we developed an autonomous braking algorithm to satisfy both safety and ride comfort of a vehicle. The proposed algorithm is composed of two-step braking strategies depending on the value of time-to-collision. The first step is a partial braking strategy to provide not only deceleration but also good ride comfort in a normal braking situation, and the second step is a full braking strategy to avoid forward collisions in an emergency braking situation. Further, the partial braking is divided into a recovery and a release zones. The former is to apply braking pressures for the safe deceleration, whereas the latter is to release the braking pressure smoothly for good ride comfort. To determine the partial braking pressures, the nonlinear characteristics of the tire friction is considered and the linear momentum of a preceding vehicle is calculated based on the extrapolation of its motion. Computer simulations using CarSim were executed combined with MATLAB/Simulink to implement the driving situations, and finally we obtained successful performances satisfying ride comfort as well as safety of the vehicle.