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Seats can also save lives - On car seat head and neck protection systems

By, CoolMotor

• 2023-11-16
• 45 View

Regarding seats in cars, leather seats, electric adjustment, massage, ventilation and heating, etc., these configurations often appear in front of consumers as the selling points of a new car. As consumers gain a deeper understanding of safety, seat head restraints that can protect the occupant's head and neck in rear-end collisions should gradually become the focus of consumers' consideration.

The headrests in car seats can protect the head and neck to a certain extent in collision accidents. The following figure shows the effects of two different headrest designs on the head and neck of a collision dummy in a simulated rear-end collision. It can be seen that in the first working condition, due to the insufficient support of the headrest for the dummy's head, the neck bent back to a large extent, causing injury.

There are many organizations that evaluate the safety of car seat head restraints, such as the Insurance Institute for Highway Safety IIHS in the United States, Thatcham in the United Kingdom, NCAP (E-NCAP, C-NCAP, J-NCAP, K-NCAP), etc. , after various agencies issued relevant test rules, each OEM also launched its own head and neck protection system through its own research to meet the requirements, such as Saab's SAHR system, Volvo's WHIPS system, Toyota's WIL system, and Volkswagen's WOKS system and Mercedes-Benz's NECK-PRO system, etc. These configurations have also become selling points promoted by various manufacturers in the early days. But in fact, how effective are they in protecting the occupant's head and neck in a rear-end collision accident?

First, let’s first understand how to provide better and more complete occupant head and neck protection, mainly focusing on two aspects:

The first is the control of the distance between the passenger's head and the headrest. Under normal driving conditions, we always hope to reserve a certain distance between the head and the headrest, so that the head can have a certain degree of freedom of movement and maximum comfort. sex, but in the event of a collision, we hope that this distance is the minimum value, because this distance is crucial to preventing injuries to the cervical spine area and enabling the head to be supported at the first time. The following figure shows the IIHS’s distance behind the head and Head restraint height requirements;

The second is the support shape and related structural design technology of the headrest and seat itself. For example, the headrests of Volvo cars, which are well-known for their safety, all have the following shape. The shape of the headrests fits the shape of the head better and can provide better support when the head is tilted back. In addition, the seat frame and headrests The stiffness, width and dimensions of the frame also need to be considered. It must be able to withstand the energy from the impact of the human body during a rear-end collision, and it must also allow the human backrest enough space to move backward so that the acceleration difference between the backrest and the head is not excessive. Of course, the shape, density and hardness of the foam cover also need to be considered in the design.

According to these two major demands, the current mainstream head and neck protection measures for seats and seat headrests can be roughly divided into four categories: RHR, PAHR, RAS, and PAS:

1. RHR (Reactive Head Restraint), which is an inductive head restraint. In a collision accident, the protective device is activated on the seat through the weight of the passenger, and the head restraint automatically moves forward and upward. The principle of this type is to use the lever principle. In a rear-end collision, the passenger's backrest will act on the trigger mechanism ①, and the headrest will automatically move forward and upward to reduce the gap behind the head immediately after the collision ② and protect the head. A typical application is Saab SAHR (SAAB Active Head Resistant);

Typical design cases are as follows:

In a rear-end collision, the passenger's backrest will act on the trigger mechanism ④, exerting pressure on it;

When the pressure is greater than the maximum tension that the tension spring ③ can withstand;

The trigger mechanism drives the headrest bracket ⑤ to move forward through the rotation axis point ①②, thus driving the headrest;

2. PAHR (Pro-Active Head Restraint), that is, active head restraint. Within 50 milliseconds after a rear collision, the sensing system of the active head restraint device automatically detects and determines when the preset collision intensity is reached. The preload spring built into the headrest automatically pops up, pushing the headrest forward and upward, and the head and neck support system is activated and in place, providing real-time protection to the front and passenger seat occupants and effectively preventing excessive cervical spine bending in a collision. A typical application is Mercedes-Benz's NECK- PRO system;

3. RAS (Reactive Seat), which is an induction seat. This device absorbs rear collision energy through the integrated design of the seat and headrest. A typical application is Volvo's Whips system.

In a rear-end collision, the seat back will tilt backwards along with the occupant to absorb energy. The entire back of the occupant and the seat back will be securely close together. The backward tilt of the backrest can minimize the force of the head being thrown forward. The backrest and headrest of the seat will move backward horizontally, so that the upper part of the body and head can be gently and evenly supported and protected, thereby reducing the impact on the spine and neck, and preventing the head from being thrown backward. the harm caused;

4. PAS (Passive Seat), that is, passive seat, refers to this kind of seat that uses passive foam technology to absorb collision energy to ensure that the occupant's headrest plays a role in preventing the neck from twisting. Typical applications are Toyota's WIL system (Whiplash Injury Lessening) and Volkswagen's WOKS system;

As for the effectiveness of these types of head and neck protection in actual tests, I counted the data published on the E-NCAP official website (the data range is from 2008 to 2013. After 2015, E-NCAP has canceled the classification description of head restraints. Unable to know the type of headrest), a total of 208 seats were tested, of which 11 were equipped with active headrests, 38 were equipped with inductive headrests, 6 were equipped with inductive seats, and the rest were passive seats.

Judging from the above test results, except for Volvo's standard Whips system, which is relatively stable in terms of head and neck protection performance, other types of protection systems will have high scores and low scores. Therefore, it is not possible to achieve high results with a head and neck protection system. Good protection effects, such as inductive headrests and active headrests, may cause additional damage due to the forward action of the headrest. It is recommended that you refer to the crash test results of each collision agency for the vehicle model when purchasing, so that you can Know the safety performance of the car you choose.