Precrash Safety Systems

by Spencer Mead, Clemson Electrical Engineering Student

Basic Description

One of the newest safety additions to cars are Precrash Safety Systems. These systems vary by manufacturer as to what extent they prepare the car for a crash, but they all make a serious impact towards the safety of drivers. These systems are designed around the concept of giving the driver a warning of a possible crash ahead and then taking various actions to improve the safety of the car if the driver does not prevent the impact. These systems have been shown in real world tests to reduce the force at impact by up to 40%. This is quite a drastic improvement in crash safety and if every vehicle in the United States employed a Precrash Safety System, imagine the amount of saved money, injuries, and lives that are lost in car crashes every year.

Precrash Safety Systems use either radar or laser sensors, which are explained further on, to detect if a crash is imminent in front of the car. If the system detects a possible collision, it will alert the driver with visual and/or audio signals to the impending crash. If the driver still does not make a move to slow the car down or is going to fast to brake in time, the system will pull up the slack in the seatbelts along with applying brake pressure or preparing the brakes for better performance. Some systems, from Audi or Mercedes-Benz for example, will even close the windows and sunroof to further prevent injury. Mercedes-Benz takes it even one step further by inflating the air chambers in the seats, positioning the passenger seat in a more upright and safe position, and also raises the rear headrests of the backseats if installed on the vehicle. Some of these systems are also applied to the rear of the vehicle to help make the vehicle more safe in rear collisions.

These systems use two types of sensors similar to adaptive cruise control. Radar sensors employ microwave signals (typically at 35 or 76 GHz) where as Lidar, or laser, sensors employ a laser diode to produce infrared light signals. Both types of sensors send a signal away from the car and monitor the time required for the signal to reflect off the object ahead. From this time, the system can calculate how far away the vehicle is. Also the system can detect how fast the object in front of the vehicle is moving by taking multiple samples over time. Although laser based systems are significantly lower in cost, they have difficulty detecting or tracking vehicles in adverse weather conditions. They can also have difficulty tracking extremely dirty vehicles. Also laser based systems can have narrower beam trajectories which can create complications in detecting objects. For these reasons radar is generally used in these systems due to higher reliability even if they cost more.

Sensors

Radar or Laser sensors, vehicle speed sensor, yaw sensor, acceleration sensor, accelerator pedal position, brake pedal position

Actuators

Throttle, brakes, window control, power seats, headrest control, seatbelt tensioner

Data Communications

Control Unit Communication: Control Area Network (CAN) or FlexRay

Manufacturers

Audi, Ford, Honda, Infiniti, Lexus, Mercedes-Benz, Toyota, Volkswagen, Volvo

For More Information

[1] Mercedes-Benz Presafe, Mercedes-Benz, Nov. 12, 2008.

[2] Reward 2010-Mercedes Presafe, European New Car Assessment Program, EuroNCAP.com.

[3] Precrash System, Wikipedia.

[4] Development of a Pre-Crash System, National Highway Traffic Safety Administration, nhtsa.dot.gov.

[5] Audi Pre Sense Plus, YouTube, May 16, 2011.

[6] Mercedes-Benz Presafe Braking, YouTube, May 12, 2007.

[7] Honda Collision Mitigation Braking System, YouTube, Sep. 27, 2008.

[8] Toyota Precollision System, YouTube, April 21, 2009.

[9] Volvo Collision Warning with Full Auto Brake, YouTube, Dec. 23, 2008.