Skip Ribbon Commands
Skip to main content

Passive Safety Electronics

The "brain" of the passive safety system

The electronic control unit (ECU) is the brain of the car’s passive safety system. It decides not only if, but also exactly when, the seatbelt pretensioners should be triggered and each airbag system should be deployed. The ECU contains crash sensors and a microprocessor, as well as back-up power in the event the connection to the car's main battery is cut off in the crash. The ECU is located in the middle of the vehicle where it is well protected during a crash.

The ECU also records event data for analysis after an event. 

At what speed do airbags deploy?

Passive safety electronics measure deceleration, since vehicle speed is not an adequate indicator of whether an airbag should be deployed or not.  Airbags and seatbelt pretensioners in frontal and near-frontal collisions are typically designed to deploy when the crash force is comparable to hitting a solid barrier at approximately 12 to 20 km/h (about 8 to 12 mph). This is, roughly speaking, equivalent to striking a parked car of similar size at about 43 km/h (about 27 mph), assuming 100% of the fronts of both vehicles are engaged in the crash.

Unlike most crash tests into barriers, real-world crashes typically occur at angles, and the crash forces usually are not evenly distributed across the front of the vehicle. In addition, the parked car absorbs some of the energy of the crash and is pushed by the striking vehicle. Consequently, the relative speed between a striking and struck vehicle required to deploy the airbag in a real-world crash can be much higher than an equivalent barrier crash.

Satellite Sensors


Satellite sensors are often used to quickly provide the electronic control unit ECU) with acceleration data to enable appropriate deployment of the airbags and seatbelt pretensioners. These sensors are mounted in the door beam, the B-pillar between the doors, the rocker panel, and various locations at the front of the vehicle.   

New Generation ECU

Autoliv has developed the world’s first system that combines the controls of the vehicle’s restraint system with the controls for the vehicle’s brakes that can provide Electronic Stability Control (ESC), Anti-lock Brakes (ABS) and Automatic Traction Control (ATC). This merger of control systems, for which we received the first order in 2011, provides significant savings and enhanced performance.

This technology is the first step in an ongoing fundamental redesign of electronic safety control architecture in vehicles.