Evolving Safety Devices

Safety devices that detect danger on their own, prompt the driver to take evasive action, or in some cases, avoid accidents themselves. The first example of such a system is said to be Mercedes-Benz's “PRE-SAFE,” introduced about 10 years ago. Today, while simple automatic braking is available even in minicars, more advanced systems are continuously being introduced for high-end vehicles.

However, systems of this type are truly effective only once, or perhaps not even once, in the lifetime of a car. In other words, the critical moment rarely comes, but if the system does not operate accurately at that crucial time, there is no point in installing it. Conversely, if it malfunctions when it should not operate, it can lead to another accident. Therefore, safety devices demand extremely high reliability.



Typically, safety devices consist of three components: sensors to detect the vehicle's and its surroundings' conditions, a controller to analyze sensor information and make appropriate judgments, and actuators that receive instructions from the controller to warn the driver or perform evasive maneuvers.

In the context mentioned above, high reliability is required for sensors, controllers, and actuators. Among these, sensors, which form the basis of all operations, demand particularly high precision. This is because "correct information is essential for making correct judgments."

A Two-Tier System of Cameras and Radar

Recently, Mercedes-Benz held a "TecDay Intelligent Drive" near Stuttgart, Germany, where they announced the safety devices planned for the upcoming new "S-Class." Various innovations aimed at improving sensor accuracy were introduced.

For example, the new "S-Class" will be equipped with a stereo camera. While there are Japanese cars that use stereo cameras, which employ two CCD sensors placed at a fixed interval to detect not only the shape and direction of objects but also their distance, similar to human eyes, as sensors for safety devices, this is not a surprising adoption in itself.



However, what is noteworthy is that Mercedes is adopting a stereo camera in addition to the existing short-range and long-range radars. What is the intention behind this? Frank Wernard Mohr, responsible for active safety at Mercedes, explained:

"While radar is convenient for detecting the position and distance of objects, it is not good at detecting their shape. Therefore, radar alone cannot accurately determine whether you are approaching the car ahead or if falling leaves are about to land on the car. However, by combining this with a stereo camera, we can determine what the approaching object is and accurately decide whether to take evasive action."

The current "S-Class" also offers automatic braking. However, since it is not equipped with a stereo camera (though a monocular camera can be fitted), there is a slight possibility of misrecognition regarding object identification. Considering this risk, Mercedes' "Distronic" has historically operated at only about 50% of the brake's full capacity, rather than utilizing its full potential. However, with the improved recognition capabilities of the new "S-Class," if a risk of collision with a pedestrian is detected, the newly installed "PRE-SAFE Brake" will utilize 100% braking power to avoid the accident (at speeds below 50 km/h).

Why is the Stereo Camera Necessary?

The benefits of the stereo camera extend beyond avoiding pedestrian collisions. For instance, the new "S-Class" newly adopts "Brake Assist with Cross-Traffic Assist" to prevent intersection collisions at uncontrolled intersections. When the stereo camera detects a vehicle emerging from behind an obstruction, it immediately applies the brakes to avoid or mitigate a collision.

Features such as "Distronic Plus with Steering Assist," which prevents lane departure during cruise control and automatically steers to follow the vehicle ahead, and "Active Lane Keeping Assist," which controls the vehicle's direction using the same principle as ESP when a lane departure could lead to a collision with surrounding vehicles, would not have been possible without the stereo camera.



The "Adaptive Highbeam Assist Plus," which detects the position of preceding or oncoming vehicles and masks the illumination from the headlights in those areas, is an excellent technology that ensures a lighting range comparable to high beams in many situations. Here too, the detection capabilities of the stereo camera contribute to the system's realization.

In essence, the active safety features of the new "S-Class" have been dramatically improved by the adoption of the stereo camera. However, it is important to remember that none of these controls rely solely on the stereo camera; they achieve diverse functions and excellent reliability by working in conjunction with numerous sensors installed in various parts of the body. When we counted the sensors for the safety devices installed in the new "S-Class," including the ultrasonic sensors for "Parktronic," the total came to 26. This number illustrates that the new "S-Class" is equipped with multiple layers of "electronic eyes" watching over safety.

New Features for Seatbelts Too

There are several other safety features debuting in the new "S-Class," but the one I absolutely want to introduce is the "Beltbag." This can be described as a "seatbelt version of an airbag," and in the event of an accident, it inflates by blowing compressed air into the seatbelt worn by the occupant, significantly reducing the impact of the collision.

When inflated, the belt width expands to approximately 15 cm, about three times its normal width, and the risk of occupant injury is halved. Seatbelts are considered the "last line of defense" to minimize occupant injuries, but in an accident, forces many times, or even tens of times, the occupant's body weight are exerted. These immense forces are borne by a seatbelt about 5 cm wide, but if the belt is not positioned correctly, it can cause serious injuries, including internal damage.