Functions of active car head restraints
Car manufacturers spend huge sums to improve the safety of their creations. New designs are invented, perfect systems are developed, and tests are conducted. One such invention is active head restraints. These designs are located at the top of the car seat. To understand the principle of their work, it is necessary to make a small digression and excursion into the physics course. An accident is dangerous not because of the impact, but because of the law of conservation of energy. By inertia, the body continues to move in a given direction, then receives momentum and quickly changes its motion. On its way it meets obstacles. If they are soft, a person is not injured in a collision. Such obstacles are a seat belt and an airbag.
The purpose and usefulness of active head restraints.
When a person’s body receives an impulse about a sudden stop or a sudden change in motion, a powerful impulse travels down the spine. Some of it is lost along the way, but the neck still suffers greatly from the impulse that reaches it. At this point, the active systems of the chair are activated by shifting the body, which actuates the lever. The headrest will move toward the head and take a significant portion of the momentum. A short shift allows the structure to dissipate this energy, after which the head support returns.
What are active head restraints?
The purpose and principle of these systems is understood, but it is still unclear what they are – active head restraints of front seats. They can be a part of a seat, have a shape of an extended backrest. In this case the movement of head and neck is limited, respectively the impact damage is excluded. Other designs are in the form of small cushions. They are fixed on the ends of the backrests and can be adjusted. In this case, you can choose the most comfortable and safe position of the headrests. On the other hand, if not properly adjusted, the safety of the person decreases. Still, such a simplified design is reliable.
What kinds of active headrests there are
Active headrests are divided into two categories depending on the type of actuator used:
- The mechanical actuator is a device that is located inside the design. It senses the movement of the driver’s back, based on which the protective support moves relative to the head. When the load on the spine is reduced, the support returns to its original position.
- The electric actuator is equipped with an electronic control system. It consists of a number of components:
- the shock sensor is located at the rear of the car,
- the control unit,
- the actuator.
When the sensor is activated, a signal is sent to the control unit. This activates the pyro cartridge, which activates the actuator mechanism on the headrests. There are also active headrests that can be installed on the front and rear seats. Such designs greatly increase safety not only for the driver, but also for the passengers.
Problems that can arise
Front active head restraints are definitely a useful invention, which significantly increases human safety when the car is struck. Such designs appeared relatively recently, they continue to improve and change. Unfortunately, there are a lot of problems, connected with active head restraints:
- The mechanism is triggered by even a slight push on the seat, causing the structure to strike the head.
- The rails can press into the back.
- The fixers or knots of the mechanism fail much earlier than they are supposed to. The cause of this trouble are low-quality materials and violations of technology during assembly. Almost no one was able to fix this problem independently. Before the warranty expires, you should demand the replacement of the seat.
It is dangerous to drive the car with defective active head restraints. Not only they won’t help during the accident, but can also aggravate the situation by causing harm.
There is no doubt that active head restraints are a useful invention that protects us in times of danger. But the design is still imperfect and has many problems. We hope that in the near future we will be able to install a better design without any flaws.
One of the first automobile headrests was introduced by Mercedes-Benz in 1960. At first, they were installed at the customer’s request. In the late ’60s, all cars in the Mercedes lineup were produced with headrests. In 1969, the NHTSA approved the significance of the new accessory and recommended its installation to all automakers.
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Active front seat headrests
Although such products are considered to be passive safety, their role and importance in the driver and passenger protection system does not become any less. Their purpose is the exclusion of unacceptable loads on the spine and its cervical section. Most often headrests, especially of front seats, are performed as a structural element, for example, simply as their elongated backrest, which limits movement of passenger’s or driver’s head, thereby protecting it from damage.
In other cases, small pads attached to the ends of the seat backs are used for this purpose, which can be moved up and down, selecting the most comfortable position for the individual. Even in this somewhat simplified form, headrests have significantly improved the protection of passengers in both the rear and front seats.
For the first time such elements of passive protection as part of the standard equipment was used by Mercedes. However, the development of cars, increasing its dynamic characteristics, the increase in overall safety requirements led to the appearance of active head restraints, and among them the most famous versions for cars Tiguan and Mercedes.
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What are the functions of a headrest
Such an addition to the car seat is an element of passive safety, not just a component for comfort. It’s all about the behavior of our body in the car seat during a rear impact. The body rushes back, and the head is reclined with great force and speed a little later. This is called the “whiplash effect.” The head restraint stops the head from moving during the impact, preventing possible neck fractures and head damage.
Even with a non-serious but unexpected impact, you can get a serious dislocation or fracture of your cervical vertebrae. Years of observation have shown that this simple design has more than once saved lives and prevented more significant injuries.
This type of injury has been called “whiplash”.
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The design of active head restraints
An active head restraint is a device that has a special lever camouflaged in the back of the seat. In the event of a car impact, the driver’s back presses against the seat back and presses on the lower portion of the lever. The mechanism activates the head restraint and brings it to the driver’s head before the car rolls over. This keeps the impact force to a minimum.
Active head restraints operate at all speeds (low and medium). And in 90% of cases, injuries happen at low speed. A vivid example is the situation, when a car with passengers stands at the crossroads, and another car crashes into it with all its might. This impact creates a “whiplash” effect, which leads to serious injuries. At the end of the collision, the head restraints return to their original position. The main thing is to make the adjustment correctly.
The finer points of adjustment
The problem with fixed head restraints is the need for height adjustment. This means that the devices are useless in frequent passenger changes and will not save you from injury. The active head restraint is more effective.
Passive safety systems are special in that their cervical area is supported by the design of the head restraint and the seat. The design of the active head restraint is better and ensures that it protects the passenger even without pre-setting.
How the active head restraint works
After understanding what an active head restraint is and what it serves, let’s look at its design. According to the type of implementation there are two main types: based on a mechanical drive and based on an electric drive. From the very name it becomes clear that the design and device will be different.
Mechanical active headrest
It is considered the simplest in its design. Such a mechanism consists of levers, springs and transfer mechanisms. The entire principle of operation is based on the laws of physics. On the other hand, such a mechanical active headrest is repairable and does not require additional maintenance.
An electrical active head restraint
Unlike the mechanical headrest, this type is based on electronics. This mechanism includes the shock sensors (usually located on the rear bumper), the electronic control unit, the squib with the electric igniter which activates the whole mechanism. Practice shows that this type of active mechanisms performs its task much better, but there will be more problems with repair. The pyro cartridge is disposable, so after the operation it must be replaced, although it is often necessary to change the sensors and the whole mechanism of the headrest.
Some experts also distinguish two additional types of active headrests: movable and stationary. Moving, also adjustable, can move in any direction. The headrest can be adjusted by pressing a special button on the back of the seat and the headrest can be moved down or up accordingly. Fixed headrests are often made at the same time as the backrest or are made as a cushion, without the possibility of adjustment. In such a case, the adjustment of fixed head restraints should be taken seriously in order to minimize the impact force. The adjustment is often made by tilting the entire seat or the backrest separately. See also a review of the active anti-roll bar.
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What are the tasks of active head restraints
The main purpose of active head restraints is to provide support for your head as quickly as possible, reducing possible spinal and neck injuries in an accident situation to zero. There are two types of active head restraints by their design:
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What is an active car headrest
For the first time the mandatory presence of headrests on the backs of car seats was talked about back in the early 1960s, the inventor was Bela Bareni. Initially the headrests were installed as an option and at the request of car owners. From 1968 onwards Mercedes made head restraints a standard feature, thereby increasing the safety of its cars. In early 1969, the NHTSA recommended that all automobile manufacturers install headrests even as standard equipment.
What is the difference between the active head restraint and the conventional classic head restraint. At first sight there are practically no differences, but the engineers hid the entire cunning of the mechanism in the backrest of the seat. Due to the mobile mechanism and levers, the driver’s back is pressed into the seat back and the lower part of the lever correspondingly presses the lower part of the lever. The upper part of the mechanism, in turn, acts proportionally in reverse, bringing the head restraint closer to the driver’s head, anticipating the moment the head tilts back. Thus, the active head restraint reduces the impact force at medium and low speeds. These are the times when injuries due to the so-called “whiplash effect” most frequently occur.
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Mechanical active headrests, device and principle of operation
Mechanical variations of active headrests are arranged quite simply. A lever is built into the seat which is connected to the headrest. During an accident the person’s back is strongly pressed into the seat, so this lever is pressed and the head restraint begins to move towards the head. When the pressure on the back of the seat eases, the spring brings the head restraint back. The more pressure the person’s back puts on the chair, the faster the system will work.
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In modern cars there are headrests with built-in monitor for rear passengers. Such headrests have a DVD player which plays DVDs, CDs, MP3 discs, TV tuner, FM transmitter and can receive signals from external information sources like game consoles, rear view cameras, etc.
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Both passive and active car headrests need to be adjusted. The correct position will have the maximum effect during impact. Also, during long journeys, a comfortable head position will reduce strain on the cervical area.
As a rule, only separate headrests from the seats can be height-adjusted. If it is combined with the seat, you can adjust only the position of the seat. Often there is an inscription “Active” on the mechanism or button. It is enough to follow the prescribed instructions. This process does not cause difficulties.
The correct position of the head and headrest
The optimal position of the support pillow at the back of the passenger’s or driver’s head. It is also recommended by many drivers that you first adjust the position of the seat. The seats are designed for an average body size of approx. 70 kg. If the passenger or driver does not fit into these parameters (low or very tall), it will be difficult to adjust the position of the mechanism.
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Problems that can arise
Despite the benefits they bring, active head restraints can also cause problems. For instance, many drivers complain that the slightest pushing on the backrest triggers a lever mechanism and the headrest hits them on the head. Or the rails of the mechanism are pressed into the back. Almost always dealers admit the defect as a “non-warranty”, arguing that “this is the way it is in all our cars”. Some car owners get used to the delicate nature of the mechanism, while others have to eliminate the defect at their own expense.
Sometimes active headrests cause some discomfort
Another frequent problem is a breakdown of the lock or nodes of the lever mechanism. As a rule, it happens because of the use of low-quality materials or the reason may be the breached technology of assembly. Most likely, you will not be able to cure such a defect. Feel free to demand a replacement of the seat from your dealer, if the car is under warranty, of course. Because the defective active headrests will not only help you in a difficult moment, but may also harm you…
In case the dealer starts waving you off like a pesky fly, hurry up to make a written conclusion about the defect by a good independent expert. Having the paperwork in your hands will make it easier to talk to the dealer.
How to Remove and Install Active Headrests
There are a lot of variations on the removal and installation of active car head restraints, and a lot depends on the brand and model of the car itself. It should be noted right away that removing the active headrest is not as easy as the classic one. It is not enough to press a special button on the seat and just pull out.
Let’s introduce the most common option of removing and installing active car headrests. First of all you need to decide whether you have active or classic headrests in your car. The first thing that distinguishes the active mechanism is the presence of wiring in the headrest pin or a small cable. You can’t remove it like a regular headrest. There are two variants, the first one is disassembly of the head restraint by removing the plastic back part, it is enough to disconnect cable or remove it from the locking mechanism.
It is possible if the back part of head restraint is trimmed at the same time with front part. In this case, it is necessary to remove the back part of the front seat. As a rule, this is not an easy process and requires little repair skills. Most manufacturers put the plastic covers on the backs of the seats on special fasteners. Therefore, it is necessary to remove carefully and without unnecessary movements. Getting to the mechanism, it is necessary to understand how the cable mount or loop wiring (it all depends on the type of active headrests: mechanical or electrical) is arranged and where it is located.
After disconnecting the loop or the cable fastener, carefully remove the headrests, slowly feeding the accompanying elements through the holes in the backrest (the place where the headrest is installed). Install the active headrests in reverse order. Many experts say that you should be careful with electrical active mechanisms, because the contacts require careful connection, otherwise from a bad contact at the time of impact, the mechanism may not work.
So is it worth installing active headrests on car seats. If you doubt it, statistically 33% of accidents involve a rear-end collision. As a result, the neck of the driver and front passenger is most often affected. On average, the cost of installing active headrests will cost about 3 to 5 thousand rubles, in some cases the cost of expensive cars will be about 10 thousand rubles. But if you compare with the consequences and injuries, the price is not so big.
Video overview of the principle of active headrests:
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