1. What are the types of safety belts?
(1) Working at height type
Prevent working at heights Personal protective equipment used to safely suspend workers when a person falls or after a fall. According to the different conditions of use, it can be divided into the following three categories:
1. Safety belts for working around poles
Through the rope around the fixed structure Or a safety belt that binds the human body near a fixed structure so that the operator’s hands can perform other operations.
2. Area restriction safety belts
Safety belts used to limit the range of activities of workers and prevent them from reaching areas where falls may occur.
3. Falling suspension safety belt
Safety belts used to suspend workers when working at heights or climbing high.
(2) Half-body safety belt
According to different operations and wearing types, it can be divided into full-body safety belts and half-body safety belts:
1. Full Body Hasty Harness: The seat belt wraps the whole body and is equipped with multiple suspension points on the waist, chest and back. It can generally be disassembled into a half-body harness and a chest harness. The biggest application of the full-body safety belt is that it allows rescuers to work in a “head-down” manner without having to consider the safety belt slipping. For example, in deep well rescue, rescuers need to go deep “head down” and get close to the trapped people.
2. Half Body Hasty Harness, that is, the seat belt only wraps half of the body (usually the lower body, but like a chest belt, it is used to protect the upper body). Its range of use is narrower than that of the full-body safety belt, and it is generally used for “seat suspension”.
The safety belt parameters are working tension (WS) and blasting tension (BS). According to different standards and manufacturers, the above parameters are also different.
(3) Bungee jumping equipment type
Personal fall protection system is a complete set of products necessary to connect workers to fixed points, which can be completely Prevent falls from heights or completely prevent them from happening. Used alone, these products do not provide protection against falls. However, if these components fit together well, they form a personal fall protection system that is extremely important to both workplace safety and the overall fall protection program. Personal fall protection system products mainly include hanging points, hanging point connectors, intermediate connectors, and full-body safety belts.
(4) Car type
1. Seat belt pre-retractionWhen an accident occurs, the person moves forward and the seat moves backward. If the seat belt is too loose at this time, the safety belt will be tightened. The consequences are likely to be: the occupant slipped out from under the seat belt; or the person has touched the airbag, and at this time the seat belt failed to tighten in time due to the excessive tension margin, that is, the seat belt failed to be tightened as expected. Some of the momentum is lost, but all the burden is handed over to the airbag. Both situations could result in serious injury to the occupants. But the problem is, properly installed seat belts. Where does the slack come from? First, because the occupant’s clothes themselves have a certain thickness, and there is also some room for looseness hidden in the seat belt device. This room cannot be eliminated, but when an accident occurs, it should be eliminated as much as possible. what to do? For this reason, this kind of seat belt pre-tensioner device appears, which is responsible for providing instant tightening of the seat belt.
2. Seat belt tension limiter After the accident, the seat belt has been tightened by the pre-tightening device. But we hope that after the peak force has passed, the tension of the seat belt will be reduced immediately to reduce the force on the occupant. This special task is completed by the seat belt tension limiter: On the seat belt device, there is a The pre-tensioning device has a safety belt wound underneath. Inside the shaft core is a steel torsion rod. When the load reaches a predetermined condition, the torsion bar begins to twist, which relaxes the seat belt to a certain extent and realizes the tension limiting function of the seat belt.
Under the joint action of the seat belt pre-tensioner device and the seat belt tension limiter, the protective ability of the seat belt has almost reached an ideal state. As the saying goes, attention is paid to the details. Advanced safety belts can indeed provide reliable safety protection for the occupants.
3. When the car encounters an emergency braking situation, it can restrain the driver and passengers in the seats to prevent them from rushing forward, thus protecting the driver and passengers from injuries caused by secondary collisions. .
2. Principle and function of car seat belts
According to a research report by the National Highway Traffic Safety Administration (NHTSA), in the United States, seat belts can save an average of 13,000 lives every year. life. At the same time, NHTSA also estimated that 7,000 victims could have survived if they had worn seat belts. While seat belts do cause serious injury or death in some situations, nearly all safety experts agree that wearing a seat belt significantly increases your chances of survival in an accident. NHTSA estimates that seat belts reduce the risk of death for front-seat passengers by 50 percent.
Everything in the car (including the driver and passengers) has its own inertia, which is independent of the car’s inertia. A car accelerates its occupants to the speed of the car. Assuming you are traveling at about 80 km/hcruise. Your speed and the speed of the vehicle are nearly equal, so it feels like you and the vehicle are moving as one unit.
But if the car hits a telephone pole, obviously your inertia and the car’s inertia will be completely independent of each other. The resistance of the telephone pole causes the car to stop suddenly, but your speed remains the same. Without a seat belt, you would hit the steering wheel at approximately 80 km/h or fly out of the windshield. Just like a telephone pole slows down a car, a dashboard, windshield, or road surface exerts a strong force on you to slow you down. One thing is certain, no matter what happens in a collision, something needs to be exerting force on you to bring you to a stop. But depending on where and how the force is applied, it can kill you instantly or leave you unscathed. If your head hits the windshield, the force of that stop is concentrated on the most vulnerable part of your body. It will also cause you to stop quickly because the glass surface is hard. But this can easily leave a person seriously injured or killed.
Seat belts apply stopping force to parts of the body that can withstand pressure for longer periods of time. A typical safety belt consists of a lap belt that goes around the pelvis and a shoulder belt that goes across the chest. These two sections of seat belt are tightly attached to the car’s frame to keep the passenger in the seat.
When the seat belt is worn correctly, it applies most of the stopping force to the chest and pelvis, which are relatively strong parts of the body. Because the seat belt spans a wider part of the body, the force is not concentrated on a smaller area and therefore does not cause excessive harm. Additionally, the material used in seat belts is much softer than the dashboard or windshield. It can stretch slightly, which means the stopping process won’t be too sudden. However, the seat belt should not be stretched too far, as this could push you against the steering wheel or side window. The seat belt only allows you to move forward slightly.
Helical springs rotate the spool to keep the belt tight
The crumple zone of a car is an area that actually acts as a cushion. The crumple zone is the area at the front and rear of the car that is relatively easy to crumple. The car doesn’t stop suddenly when it hits an obstacle, but absorbs some of the force of the impact by collapsing (like an empty soda can). The car’s cabin is relatively solid, so it doesn’t crush the passengers. It continues to move briefly, causing the front of the car to crash into the barrier. Of course, the crumple zone only protects you when you’re moving with the car’s cabin (that is, when the belt is holding you in place). The simplest safety harness (the kind used on some roller coasters) consists of a long strap bolted to the body of the car. This type of harness keeps you tightly strapped into the seat, which is secure but not particularly comfortable.
Car seat belts stretch and retract—your body can lean forward easily when the belt is tightened. But in a crash, the seat belt tightens suddenly and holds you tightly in place. In typical securityIn the belt system, the safety belt is connected to a retractor. The core element in the retractor is the reel, which is connected to one end of the safety belt. Inside the retractor, a spring provides the rotational force (or torque) to the spool. It spins the spool to take up any slack in the harness. When you pull out the belt, the spool will rotate counterclockwise and cause the attached spring to rotate in the same direction. In this way, the rotating reel reverses the spring. Because the spring wants to return to its original shape, it resists this twisting motion. If you loosen the belt, the spring tightens and rotates the spool clockwise until the belt is taut. The retractor has a locking mechanism that stops the rotation of the reel in the event of a car collision. Today, there are two commonly used locking systems: those triggered by car movement and those triggered by seat belt movement.
The first system locks the reel when the car decelerates rapidly
The first system locks the reel when the car decelerates rapidly (for example, when the car hits an object) Lock the scroll. The central element in this mechanism is a weighted pendulum. When the car suddenly stops, inertia causes the pendulum to swing forward. A pawl on the other end of the pendulum catches a toothed ratchet fixed to the spool. Because the pawl is stuck on one of the gear teeth, the gear cannot rotate counterclockwise, and the reel connected to it cannot rotate. When the seat belt is released again after the impact, the gear rotates clockwise and separates from the ratchet.
The second system locks the reel when the harness is yanked. Most designs utilize the speed of the reel rotation as activation power. The central element of this design is a centrifugal clutch, a weighted pendulum mounted on a rotating reel. When the reel spins slowly, the pendulum does not swing. A spring keeps it in its original position. But when the belt is yanked hard, the spool spins rapidly, and centrifugal force drives the weighted end of the swing bar outward.
The second system locks the spool when the belt is yanked
The extended swing bar pushes a cam on the retractor housing. The cam is connected to a pivoting pawl via a sliding pin. As the cam moves to the left, the slide pin moves along the notch in the pawl. This pulls the pawl into the rotating ratchet wheel attached to the spool. The pawl locks into the gear teeth and prevents counterclockwise rotation.
In some new seat belt systems, pretensioners are also used to tighten the seat belts. Pretensioners are designed to take up any slack in the seat belt during a crash. The traditional locking mechanism of the retractor prevents the belt from stretching further, while the pretensioner’s job is to pull the belt back. This pullback force moves the passenger into the optimal impact position in the seat. Pretensioners are typically used in conjunction with traditional locking mechanisms, not in place of them.
There are many different pretensioner systems on the market. Some pretensioners pull the entire retractor back, some rotate the spool itself. Typically, the pretensioner is connected to the central control processor that activates the vehicle’s airbags. The processor monitors mechanical or electronic motion sensors, which canSudden deceleration due to impact. When an impact is detected, the processor activates the pretensioners and then the airbags. Some pretensioners use electric motors or solenoids, but most designs today use ignition to pull the belt in. When the gas ignites, the pressure pushes the piston upward, which rotates the retractor.
When the gas ignites, the pressure pushes the piston upward, thereby rotating the retractor
The core element in this pretensioner is a gas chamber . Within the gas chamber, there is also a small combustion chamber containing explosive ignition materials. This small combustion chamber has two electrodes and is connected to the central processor. When the processor detects an impact, it immediately applies an electric current to the electrodes. The spark produced by the electrode will ignite the ignition material, thereby igniting the gas in the gas chamber. The burning gases create a large amount of external thrust. This pressure pushes the piston located in the gas chamber, causing it to move upward at high speed. A rack is fixed to one side of the piston. When the piston springs up, the rack engages a gear connected to the retractor spool. The high-speed rack rotates the reel quickly, thereby winding up the safety belt.
In a severe impact (such as when a car collides with an obstacle at high speed), seat belts can cause serious injuries. As the passenger’s inertial velocity increases, more force is required to stop the passenger. In other words, the faster you are moving at the time of impact, the greater the force the seat belt exerts on you.
Some seat belt systems use load limiters to minimize injuries caused by seat belts. The load limiter is designed to release more of the belt when a large force is applied to it. The simplest load limiter is a folding strap sewn into the harness. When the force applied to the harness reaches a certain level, the stitching holding the folded straps in place will break. When the stitches break, the folded portion of the belt unfolds, allowing the belt to stretch some more.
More advanced load limiters utilize a torsion bar in the retractor. A torsion bar is simply a long metal rod that twists when enough force is applied to it. In a load limiter, one end of the torsion bar is fixed to the locking mechanism and the other end to the rotating spool. In a mild accident, the torsion bar will retain its shape and the reel will lock using the locking mechanism. But when a huge force is applied to the harness (and therefore the reel), the torsion bar will twist slightly. This will make the belt extend a little more.
In a sense, the importance of seat belts surpasses airbags, so most cars now require drivers to wear seat belts. If there is a problem with the seat belt system, the effect of passive safety will be Most of it will be lost, and its importance is self-evident. Of course, true safety cannot rely solely on seat belts. Drivers must also maintain good driving habits.
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