The structure and principle of operation of the passive safety system SRS
Content
A car is not only a common means of transportation, but also a source of danger. The constantly increasing number of vehicles on the roads of Russia and the world, the growing speed of movement inevitably lead to an increase in the number of accidents. Therefore, the task of the designers is to develop not only a comfortable, but also a safe car. The passive safety system helps to solve this problem.
What does the passive safety system include?
The vehicle passive safety system includes all devices and mechanisms designed to protect the driver and passengers from severe injuries at the time of an accident.
The main components of the system are:
- seat belts with tensioners and limiters;
- airbags;
- safe body structure;
- child restraints;
- emergency battery disconnect switch;
- active head restraints;
- emergency call system;
- other less common devices (for example, rollover protection systems on a convertible).
In modern vehicles, all SRS elements are interconnected and have common electronic controls to ensure the efficiency of most components.
However, the main elements of protection at the time of an accident in the car remain belts and airbags. They are part of the SRS (Supplemental Restraint System), which also includes many more mechanisms and devices.
Evolution of passive safety devices
The very first device created to ensure the passive safety of a person in a car was the seat belt, first patented back in 1903. However, the mass installation of belts in cars began only in the second half of the twentieth century - in 1957. At that time, the devices were installed on the front seats and fixed the driver and passenger in the pelvic area (two-point).
The three-point seat belt was patented in 1958. After another year, the device began to be installed on production vehicles.
In 1980, the design of the belts was significantly improved with the installation of a tensioner that provides the most tight belt fit at the time of a collision.
Airbags appeared in cars much later. Despite the fact that the first patent for such a device was issued in 1953, production cars began to be equipped with pillows only in 1980 in the United States. At first, airbags were installed only for the driver, and later - for the front passenger. In 1994, side impact airbags were introduced in vehicles for the first time.
Today, seat belts and airbags provide the main protection for people in the car. However, it should be remembered that they are only effective when the seat belt is fastened. Otherwise, the deployed airbags can cause additional injury.
Types of blows
According to statistics, more than half (51,1%) of serious accidents with victims are accompanied by a frontal impact to the front of the vehicle. In second place in terms of frequency are side impacts (32%). Finally, a small number of accidents occur as a result of collisions with the rear of the vehicle (14,1%) or rollovers (2,8%).
Depending on the direction of impact, the SRS system determines which devices should be activated.
- In a frontal impact, the seat belt pretensioners are deployed, as well as the driver and passenger front airbags (if the impact is not severe, the SRS system may not activate the airbag).
- In a frontal-diagonal impact, only the belt tensioners can be engaged. If the impact is more severe, the front and / or head and side airbags will need to be deployed.
- In a side impact, the head airbags, side airbags and belt tensioners on the side of the impact can be deployed.
- If the impact is to the rear of the vehicle, the seat belt pretensioner and battery breaker may be triggered.
The logic of triggering the passive safety elements of a car depends on the specific circumstances of the accident (force and direction of impact, speed at the moment of collision, etc.), as well as on the make and model of the car.
Collision timing diagram
The collision of cars happens in an instant. For example, a car traveling at a speed of 56 km / h and colliding with a stationary obstacle comes to a complete stop within 150 milliseconds. For comparison, during the same time, a person can have time to blink his eyes. It is not surprising that neither the driver nor the passengers will have time to take any action to ensure their own safety at the moment of impact. The SRS must do this for them. It activates the belt tensioner and the airbag system.
In a side impact, the side airbags open even faster - in no more than 15 ms. The area between the deformed surface and the human body is very small, so the impact of the driver or passenger on the car body will occur in a shorter period of time.
To protect a person from repeated impact (for example, when a car rolls over or drives into a ditch), the side airbags remain inflated for a longer period of time.
Shock sensors
The performance of the entire system is ensured by shock sensors. These devices detect that a collision has occurred and send a signal to the control unit, which in turn activates the airbags.
Initially, only frontal impact sensors were installed in cars. However, as vehicles began to be equipped with additional pillows, the number of sensors was also increased.
The main task of the sensors is to determine the direction and force of the impact. Thanks to these devices, in the event of an accident, only the necessary airbags will be activated, and not everything that is in the car.
Electromechanical type sensors are traditional. Their design is simple but reliable. The main elements are a ball and a metal spring. Due to the inertia arising from the impact, the ball straightens the spring, closing the contacts, after which the shock sensor sends a pulse to the control unit.
The increased stiffness of the spring does not allow the mechanism to be triggered during sudden braking or a slight impact on an obstacle. If the car is moving at a low speed (up to 20 km / h), then the inertia force is also not enough to act on the spring.
Instead of electromechanical sensors, many modern cars are equipped with electronic devices - acceleration sensors.
In simplified terms, the acceleration sensor is arranged like a capacitor. Some of its plates are rigidly fixed, while others are movable and act like a seismic mass. On collision, this mass moves, changing the capacitance of the capacitor. This information is decoded by the data processing system, sending the received data to the airbag control unit.
Acceleration sensors can be divided into two main types: capacitive and piezoelectric. Each of them consists of a sensing element and an electronic data processing system located in one housing.
The basis of the vehicle's passive safety system is made up of devices that have been successfully demonstrating their effectiveness for many years. Thanks to the constant work of engineers and designers, improving safety systems, motorists and passengers are able to avoid serious injuries at the time of an accident.
