How Active Bonnet detects and protects pedestrians
Content
The driver and passengers in a modern car are reliably protected by passive safety systems. This is a strong power frame of the body, crushable zones outside this cage, devices for holding a person and softening blows. Active means of preventing accidents also work.
With pedestrians, everything is much worse, they do not have any protective equipment. Part of the cause can be helped by measures to finalize the most dangerous front area of the car body, the so-called active hoods.
What is the system
The device anticipates a collision with a pedestrian, preparing the hood of the car to the optimal meeting angle for safety. It will not be able to prevent a collision, there are other means of active safety for this, but the technical equipment will be able to fix the inevitable collision.
The system includes typical devices for any automation:
- sensors for recognizing a dangerous proximity to a person on the road;
- a high-speed electronic device that processes their signals and makes a decision;
- mechanisms and components that move the hood to the position of minimal harm;
- sometimes inflatable pillows for a pedestrian flying through the hood into the windshield;
- restraint system, a person falling on the asphalt can get no less dangerous injuries than from hitting a car.
The work of electronics and the mechanics associated with it is complemented by simpler shock mitigation measures. Small-sized and sharp-edged trim and decor details are excluded, all external elements are made as pliable as possible.
Their task is to accept the inevitable deformation upon contact with themselves, causing minimal injury. This applies to the hood, front bumper, grilles and radiator frames, windshield wipers. The windshield cannot be soft, but the angle of its location plays an equally important role.
Principle of operation
Non-contact, and sometimes contact sensors determine the presence of a person in the danger zone. This can work as an element of active safety, and passive.
In the first case, only measures will be taken to display a pedestrian on the screen or emergency braking if the driver does not have time to react. In the second, protection mechanisms are triggered.
The electronic unit must distinguish one situation from another. To do this, radar or visible sensors analyze the speeds and accelerations of people in the field of view at high speed, and continuously have information about the speed, its changes and the direction of the car. In a hopeless situation, a team is developed to minimize the consequences.
The main element of mechanical safety is the hood. He must raise his trailing edge to a certain height so that part of the impact energy is absorbed by his subsequent downward movement under the weight of the fallen person.
To do this, the rear hood mounting brackets are equipped with squibs, a spring device and guides. After actuation of the squibs, the hood is set to the desired position.
By itself, this body part can only slow down the collision. Pedestrian airbags, if provided, will work more effectively. Airbags are also equipped with squibs that trigger gas generators. Pillows inflate in a few tens of milliseconds, completely covering the windshield.
The pedestrian will be accepted with an acceptable level of deceleration. The necessary conditions for opening the pillows are laid down in the algorithm of the electronic unit. Usually this is the minimum collision speed, opening a pedestrian airbag at a lower level is impractical.
How is pedestrian recognition performed?
The vision system in the front of the vehicle, with its radar and video sensors, creates in the memory of the electronic unit an image of the surrounding space to a depth of several tens of meters. All objects that fall into this field are tracked by size, speed and direction.
The identification of an object as a pedestrian occurs by comparison with its typical image stored in memory. There are also criteria for determining the danger. If they are exceeded, a command is generated for the actions of braking systems or preparing the car for an impact.
For reliability, signals from several independent cameras and sensors are compared. Difficulties arise precisely in choosing the line between false positives and skipping a real danger, all automakers and specialized companies are working on this.
Common system malfunctions
The system itself is no less reliable than other safety elements in a car, but sometimes problems arise precisely because of false positives. This can happen, in particular, when driving on rough roads.
You have to replace disposable squib assemblies. It is easier on those vehicles where the drive for lifting the hood is spring-loaded or with the help of servo drives on electric motors. They can be reset a limited number of times at the dealer.
Sometimes the system fails without triggering. In these cases, a malfunction is detected by self-diagnosis, an active hood failure signal appears on the dashboard.
If resetting the error by the scanner does not help, then you have to analyze the circuits for an open or short circuit with the repair of the failed section.
Usually the cause is oxidation of contacts and wiring connectors, as well as sensors damaged by corrosion. After reestablishing connections or replacing sensors, the error must be reset systemically.
