Operation principle of safety belt

Today, the seat belt system is the minimum in the passive and indispensable safety system in cars. When you think of a seatbelt, you will ask: how can only with silk bandage save lives? How do their principles work? In this article we study the technology of seat belts to know why they are one of the most important technologies on any car.

Ideas for collisions

The basic working principle of a seat belt is simple: It holds you tight so you don't let you fly forward and hit the windshield or bump into the dashboard when the car suddenly stops. But why does this happen? It can be summarized that: due to inertial forces. So what is inertia?

Inertia is a tendency of an object to retain its movement when there is anything against this movement. In other words, inertia is the object's resistance to changing speed and direction of movement. Everything wants to keep their movements naturally.

If a car has a speed of 50 km / h, inertia will always want to keep them moving at 50 km / hour in that direction. The resistance of the air and friction to the road surface causes it to slow down, but the power from the car engine compensates for the loss of energy to overcome the friction of the road surface and air resistance.

Anything on the car, including the driver and passengers, has its own inertia, according to the car's inertia. The car increases the driver's speed according to its speed. Imagine that you are going at a steady speed of 50 km / h. Your speed and vehicle speed are almost equal, so you feel yourself and the car is moving like a single block.

If suddenly the car crashed into a telephone pole, it will immediately show you that your inertia and the car are completely independent of each other. The force of the telephone pole on the vehicle suddenly stops, but your speed remains the same. If you do not have a seatbelt, you will be ' thrown ' into the handlebar or fly up and hit the windshield door at a speed of 50 km / hour. Just like the phone pole makes the car stand still, the dashboard, windshield or road surface will stop you by holding you back with a tremendous force.

The task of seat belts

In the previous section, you learned that when a car suddenly stopped, passengers were suddenly stopped. The work of the seatbelt is to distribute that stopping force into the healthy part of the body to minimize the danger.

The traditional seatbelt type is lapbelt (usually pulled over your hips) or shoulder belt (pulled over the shoulder). These two types of seat belts are fastened to the body of the vehicle to hold the body tightly tied to their seats.

When the seatbelt is correctly fastened, they will provide the full force to stop in the chest or pelvic area, which are the strongest areas of the body. Because the seat belt acts on a wide band that is equal to the human body, the stopping force does not focus on a small area that is dispersed, so there is no major danger. Moreover, seat belts are made of more flexible materials than watch panels and windshields. They can stretch a little, meaning the stop will not be too sudden. So if you happen to collide, you can only move a little bit, and of course still do not leave your chair.

In addition to the seat belt system, people also let the car have areas that absorb energy collisions. These areas are very ' soft ', located in front and behind the vehicle. When being stabbed from the front or rear, the car's head or tail will be pulled back. Instead of the whole car being stopped abruptly when crashing into an obstacle, it absorbs a part of the impact force on the collapsed part of the impacted area, like you squeeze a can of empty soda. The car's cabin is more rigid, not collapsed and so we avoid the situation of ' squeezing orange '. If at that time, the car has not stopped, the first part of the car will be crumbling obstacles to obstacles. However, the crumpled areas will only protect you when you are in the car cabin, and of course if you buckle up.

The simplest type of seatbelt, seen in thrilling games at amusement parks. It consists of a thin string attached to the body. These cords always hold you firmly into the chair, which is very safe but makes you uncomfortable.

The seat belts have very good elasticity. You can lean back while the rope is still in a tight state. But if there is a collision, the seat belt will suddenly hold you tighter to the seat.

Stretching and contraction: Two prerequisites

In a normal seatbelt system, a strip of fabric is connected to a string tensioner. The central element of the rope tension mechanism is a rotating tube attached to the end of the rope. Inside of the tensioner is a spring that provides a force to rotate the rotating tube. As a result, the spool immediately rolls the rope up whenever the cord is attached.

When you pull the cord to tie it to the body, the rotating tube will rotate counterclockwise and it will turn the revolving spring to the same direction. In fact, the swivel tube works to release the spring tension. The spring always wanted to retain its shape at the beginning, so it resisted twisting movements. If you release the rope, the spring will tighten, rotate the rotating tube clockwise until the seat belt reaches a certain tension. The tensioner has a locking mechanism that prevents the spool from being rotated when the vehicle collides. Currently, there are two common locking systems:

- The system is activated by the movement of the vehicle.

- The system is activated by movement of seat belts.

The first system locks the spool when the vehicle decelerates suddenly (when hitting an obstacle, for example). The diagram below shows the simplest type of this design. The central working factor of this structure is a weight. When the car stopped abruptly, the weight of the inertia caused it to shake forward. A lug is located at the other end of the heavy object immediately inserted into the teeth of the gear connected to the swivel tube. Because of the orange grip, the gear cannot rotate in an anti-clockwise direction so it cannot be rotated. When the seat belt is loosened after the collision, the gear rotates with the clockwise and the orange lug is released from the gear.

The second system locks the swivel tube when something tugs at the rope. The main working element of this design is a centrifugal clutch - the lever (1) has a swing pin installed with the swivel tube. When the tube rotates slowly, the lever does not rotate around its axis. A spring keeps it in place. However, if the safety belt is suddenly jerked, rotate the swivel tube vigorously, centrifugal force causes the heavy end of the lever to shoot out. The lever lays out an orange lug (5) into a space of the tension mechanism. This cam is connected to a latch by a slide in the small slot (4). When the orange moves to the left, the latch moves along the groove of the brake. This pulled the latch into a toad gear (2) that fits with the swivel tube. The brake pin immediately locks the teeth of the ratchet so that it does not rotate counterclockwise, holding the swivel tube to prevent the cord from overlapping.

On some newer seatbelt mechanisms, the pre-collision tensioner - pretensioner also has a working structure to tighten the belt, but it is slightly different from the above two designs. The following is the working principle of this structure.

The idea of ​​this mechanism is to tighten the seatbelt whenever it is loose in the event of a collision. In contrast to the conventional locking mechanism in a tensioner, the cord is always tight in all situations, the pretensioner only really pulls the cord when necessary. This force makes us have the most appropriate position when a collision occurs. Pretensioner always works with normal lock structure, not replacing them.

There are a number of different pretensioner systems on the market. Some types pull the whole tensioner structure back, some just rotate the reel. Typically, pretensioner is connected to the central control processor with airbag control. The processor will monitor all signals from a mechanical or electronic sensor when a sudden deceleration of a collision is detected. When a collision is detected, the processor activates the tensioners then activates the air bag.

Pretensioner set

Some pretensioner sets are designed to use electric motors or electric coils, but most common current designs use fire particles to stretch seat belts. The diagram below shows a typical pattern of this design.

The central element of this pretensioner kit is a closed chamber containing combustion gas. Inside this closed chamber there is a small space containing explosive particles. This detonator is controlled by two wires connected from that combustion chamber to the central processor. When the processor detects a collision, it immediately provides an electrical current through the two poles of the ignition to generate the combustion gas of the combustion gas that is available. High pressure combustion gas pushes piston up high with great speed. A gear bar mechanism connected with piston makes rotating gears and swivel tubes. The speed of the large tooth bar should make the tube rotate very hard, stretching the whole belt.

For years, seat belts have proved to be the most important safety device on cars. However, it does not mean that they guarantee 100% safety for us. With a growing scientific level, advanced technologies will allow safety devices to become more intelligent and accurate. In the future, cars will be provided with seat belts and better airbags with completely new safety technologies. However, the government will have to focus on the bigger issue, which is forcing people to use safety devices when using the vehicle.

Ngoc Hai