Types and principle of operation of car headrests
Content
One of the first car head restraints was introduced by Mercedes-Benz in 1960. At first, they were installed at the request of the buyer. In the late 60s, all Mercedes cars were produced with head restraints. In 1969, the safety association NHTSA confirmed the importance of the new accessory and recommended its installation to all car manufacturers.
What functions does the headrest perform?
This addition to the car seat is a passive safety feature, not just a convenience component. It's all about the behavior of our body in a car seat during a rear impact. The body rushes back, and the head leans back with great force and speed a little later. This is called the "whip effect". The headrest stops the movement of the head during an impact, preventing possible neck fractures and head injuries.
Even with a not strong, but unexpected blow, you can get a serious dislocation or fracture of the cervical vertebrae. Years of observation have shown that this simple design has repeatedly saved lives and protected from more significant injuries.
This type of injury is called "whiplash".
Types of headrests
Globally, two groups of head restraints can be distinguished:
- Passive.
- Active.
Passive car headrests are static. They serve as an obstacle to a sharp backward movement of the head. There are different design solutions. You can find head restraints that are an extension of the seat. But most often they are attached separately in the form of a pillow and can be adjusted in height.
Active head restraints are a more modern design solution. Their main task is to provide a fulcrum for the driver's head as quickly as possible during an impact. In turn, active head restraints are divided into two types according to the drive design:
- mechanical;
- electric.
The work of mechanical active systems is based on physics and the laws of kinetic energy. A system of levers, rods and springs is installed in the seat. When the body presses against the back during the impact, the mechanism tilts and holds the head in an earlier position. When the pressure decreases, it returns to its original position. All this happens in a split second.
The design of electrical options is based on:
- Pressure Sensors;
- Control block;
- electrically activated squib;
- drive unit.
During the impact, the body presses on the pressure sensors, which send a signal to the electronic control unit. Then the igniter activates the igniter and the headrest tilts towards the head using the drive. The system takes into account body weight, impact force and pressure to calculate the speed of the mechanism. The whole process takes a split second.
It is believed that the electronic mechanism works faster and more accurately, but its main disadvantage is its disposability. After triggering, the igniter must be replaced, and with it the other components.
Headrest adjustment
Both passive and active car headrests need to be adjusted. Correct position will have maximum impact on impact. Also, during long trips, a comfortable head position will reduce the stress on the cervical spine.
As a rule, only the head restraints separate from the seats can be adjusted in height. If it is combined with the seat, then only the position of the seat can be adjusted. Often, the mechanism or button has the word "Active" on it. It is enough to follow the prescribed instructions. This process does not cause difficulties.
The position of the support cushion at the back of the head of the passenger or driver is considered optimal. Also, many drivers recommend adjusting the seat first. The seats are designed for an average body size of a person weighing about 70 kg. If the passenger or driver does not fit into these parameters (low or very tall), then it will be problematic to adjust the position of the mechanism.
Malfunctions and problems of active head restraints
While the advantages of the mechanism outweigh the disadvantages, there are also disadvantages. Some drivers note the operation of the mechanism even with a slight pressure. At the same time, the pillow rests uncomfortably against the head. This is very annoying. You have to adjust to the mechanism, or repair it at your own expense. If this is a factory defect and the car is under warranty, then you can safely contact the dealer with claims.
Locks and levers of the mechanism may also fail. Poor quality materials or wear and tear may be the reason. All of these breakdowns are related to mechanical active head restraints.
Statistics show that in 30% of accidents with a rear impact, head restraints were the ones that saved head and neck injuries. We can confidently say that such systems are only beneficial.
