Page - 11 - in Maximum Tire-Road Friction Coefficient Estimation

1 Introduction 3) Decision 2) Warning1) Collision prediction 4) Intervention Last point to brake (LPB) Last point to steer (LPS) Figure 1.7.: Activation strategy for ADAS shown for a combined evasive and emergency brakingassistantconsistingofthe fourphasesofcollision detection,warning, decision and intervention, based on [Nie11, p.110] and [Har11] known as the time-to-collision (TTC), is given for steady state motion by TTC= dW ∆vx , (1.2) with the warning distance dW to the obstacle and the relative velocity ∆vx between ve- hicle and obstacle, [Eic11, p.127]. In frontal collisions on dry roads, initiating an evasive manouevre at TTC 0.6 s is not enough to avoid a collision due to the physical limits. The driver’s limit for an intervention is already at aTTC of about 1 s, but this situation is perceived as very risky by non-expert drivers and thus only of theoretical importance. A non-hazardous situation is perceived with a TTC greater than 1.6 s. Depending on the actual friction potentialµ, these activation times for braking manoeuvres have to be increased by 1µ, according to Winner, [Win09a]. Forµ= 0.2, the activation times have to be 5 times higher than for dry roads of aboutµ= 1. For an evasive manoeuvre, the activation times have to be adapted by 1√µ, according to Winner, [Win09a]. The follow- ing sectiondiscusses the requirements for estimating the frictionpotential for theoretical 11