New Mercedes safety feature prepares your ears for a crash

MERCEDES-BENZ HAS always been at the forefront of car safety and technology development. Back in 1939 Mercedes was the first automobile manufacturer to begin passenger-car safety research using a test vehicle.

By 1951 this research led to a patent for the first safety car body with a rigid passenger cell and defined deformation zones, what we now call crumple zones.

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Fast forward half a century and in 2002 Mercedes-Benz had developed Pre-Safe, a groundbreaking system that helps prepare a car’s occupants for an accident before it happens. This safety system ushered in a new era of vehicle safety, bringing to an end the separation of active and passive safety.

Pre-Safe works by using intelligent technology that recognises dangers before they happen. A network of sensors, many of which are already used for other safety systems in the vehicle, detect certain conditions that suggest an accident is about to occur.

For example, Pre-Safe engages when the Electronic Stability Program (ESP) is fully engaged but not restoring control. If the Pre-Safe system senses extreme skidding it can close the windows and sunroof. In the milliseconds before an accident occurs, it is able to activate preventive protection measures like tightening the front seatbelts and adjusting the front head restraints as this optimises the effectiveness of those restraint systems.

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However, if the accident is avoided the seat belts relax and the headrests, windows and sunroof return to their original position and the anticipatory occupant protection system is immediately ready for use again.

In the 14 years since Pre-Safe made its first appearance in passenger vehicles, Mercedes has been constantly developing the safety features and this year a new feature called Pre-Safe Impulse Side made its world debut in the new E-Class.

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This new feature offers enhanced protection against side collisions. If an unavoidable side collision is detected, the system inflates the air chambers in the backrest side bolsters, which pushes the affected occupant sideways, away from the danger zone by increasing the distance between occupant and door.

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But this new feature wasn’t enough for Mercedes who wanted to take a big step into the future with its new E-Class. So, Mercedes developed a feature that, for the first time, made the car’s occupants an integral part of the safety technology.

This new feature is called Pre-Safe Sound and it works by triggering a protective physical reflex that protects the occupants’ ears from the expected noise associated with a collision.

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This protective physical reflex is known as the stapedius reflex. When the ear’s stapedius muscle contracts, the connection between the eardrum and the inner ear is weakened. This means that some of the sound pressure is reflected in the eardrum thus decreasing the transmission of vibrational energy to the cochlea.

Previous research on the stapedius reflex shows that to trigger the reflex there normally needs to be high sound pressures at around 100 decibels. The reflex is contingent on the spectral composition of the sound and as single tones carry energy on a single frequency they have to be transmitted to the ear at a loud volume.

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However, a tone played at 100 decibels is far too loud to play in a car. So Mercedes engineers had to find another way to trigger the reflex in the car. And they did. What they discovered is that if the required energy is spread out across many frequencies it can be transmitted at a much lower volume. And they also discovered that the pink noise frequency spectrum ideally suited this purpose.

Wilfried Bullinger who works on Pre-Safe said that “this finding was the breakthrough”.

Once human trials of the pink noise method ended in 2011, results proved that the concept worked and another major milestone for Mercedes and passenger car safety had been reached.

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From here, Mercedes integrated the pink frequency into a soundchip in the multimedia system and when the Pre-Safe system detects that an impact is about to happen it plays the pink noise at around 80 decibels. The stapedius reflex is then activated and the ear protects itself from the noise that typically accompanies a collision, which is “a very significant level of noise,” explains Rodolfo Schöneburg, Head of Vehicle Safety, Durability and Corrosion Protection at Mercedes-Benz Cars.

“It can lead to temporary impairment of hearing – and this is exactly what Pre-Safe Sound works to counteract. Although the system cannot completely prevent the damage caused by an accident, it can help to reduce it.”

So, for the first time, Mercedes is making human reflexes an integral part of automotive safety engineering and once again pushing the envelope in automotive safety.

This is an exciting time for passenger car safety and Mercedes is leading the R&D of some of the most advanced and futuristic technology. And where Mercedes goes others usually follow and hopefully it won’t be long before we see such life-saving, smart technology not only in luxury vehicles but mainstream passenger cars, too.

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