Time to collision
The time to collision period between 10 seconds and the human reaction time of roughly one second, constitutes the warning and assistance phase which features optic, acoustic and/or haptic warning. The warning transforms into active assistance under one second.
In a haptic warning system, the active accelerator starts to develop an increasingly stronger force during the warning phase - indicating the need for corrective measures. This is followed by breaking assistance and ultimately by autonomous braking in order to prevent the vehicle from running down a pedestrian.
In a pre-crash system, suitable actuators will take active and autonomous safety measures during the last second before the collision in order to reduce the impact of the crash. Two kinds of intervening measures achieve this goal:
- Reducing the crash kinetic energy through autonomous or semi-autonomous (i.e. amplified) braking.
- Using applications (which become relevant less than 500 milliseconds before the impact) which take advantage of reversible structural actuators such as controllable bumpers, crash boxes and motor hoods. At less than 100 milliseconds before the impact, the so-called pre-fire period could provide the appropriate date and trigger to optimise the protection of reversible restraint systems (e.g. belt-pre-tensioning) in order to reduce the peak deceleration suffered by the collision partners during the crash phase.
Finally, the last 10 milliseconds (the so-called pre-set period) is used to parameterise the electronic control unit of the airbag system, based on the perceptive information about the imminent collision. This will enable the best and appropriate protection to be given to the passengers.