The seat belt has remained one of the most integral passenger vehicle safety systems over many years of its existence in the automotive industry. The first four-wheelers were low on speed and had very few requirements to restrain occupants, since no real danger was foreseen in terms of injury as a result of inertia. However, with time vehicles got more refined and powerful, leading to increased speed. In such a scenario, when a vehicle stopped abruptly, the physical forces of inertia made the occupants move towards the dashboard, windshield or the seat in front of them.
The method to address the forward movement of vehicle occupants during sudden braking or collisions was the humble seat belt in the 1940s. The first iteration of the seat belt was literally an additional belt around the waist of the occupants, called lap belt, which would limit forward movements of the body during rapid deceleration. While this lap belt carried out the job satisfactorily to a certain extent, it did not provide restraint from the upper body of occupants moving forward and crashing into the steering wheel or the dashboard. Occupants were still prone to heavy injury and fatal results in case of high-speed crashes, even while using the lap belt.
In the late 1950s, an engineer with the Swedish automotive company Volvo Cars invented the three-point seat belt. The company found that this invention has such high value for the automotive industry that it subsequently opened up patents on its design and manufacturing to the public. And this was rightly done, since the three-point seat belt still happens to be the largest type of seat belt form adopted by the automotive industry globally.
The three-point seat belt has three mounting points when in use – it provides occupant restraints at the waist as well as diagonally across the shoulder to the waist. The diagonal restraint offers good resistance to the upper body from moving forward too much at the time of a sudden halt, thereby ensuring low damage due to injury from banging against a part of the vehicle. The most common type of three-point seat belt is the one having a retraction system, along with pretensioners and restraints to ensure the least amount of movement of the body during a crash. Further, height adjustable seat belts are also gaining prominence in the mass segments, aimed at offering equal levels of safety to occupants of various sizes.
While three-point seat belts have the shoulder belt attached to the vehicle structure, another iteration of the three-point belt is the Belt-in-Seat. This is a seat belt system, where the shoulder belt is attached to the seat itself and not the vehicle structure. The Belt-in-Seat system is more suitable for vehicle models like convertibles and cabriolets that do not have a B-pillar to mount the shoulder belt on. Therefore, it can be seen as adding safety in a design having structural restrictions.
The other types of seat belts developed for the automotive industry include four, five and six-point belts. These seat belts are more suitable for child safety harnesses as well as in racing vehicles, where the rate of speed is much higher and the possibility of crashes has also increased. These seat belts, especially in race vehicles, are mounted on the roll cage of the vehicle for higher performance and increased safety standards.
The evolution of the seat belt has predominantly been to the levels mentioned above, with some next-generation innovations taking place at regular intervals. These technological developments of seat belts have not entered into mainstream products due to the advanced level of innovation that leads it to be expensive as well as much above the regulatory requirements.
One of the more largely exposed modern seat belt innovation is that of the inflatable seatbelt, which carries over some of the features of the airbag. An inflatable seat belt has tubular inflatable bladders that are contained within an outer cover, where the bladder inflates with a gas during a crash, in order to increase the area of the restraint contacting the occupant. While it inflates, the seat belt also shortens the length of the restraint and tightens the belt around the occupant, thereby improving protection further. The inflatable sections could be limited to the shoulder alone or could be even extended to the lap section.
Another important technological innovation in the area of seat belts is active seat belt systems, which make this passive safety technology a semi-active one. These seat belts feature active control retractors and active buckle lifters that work in combination with the vehicle’s other active safety systems. These active seat belt technologies help reduce belt slack in dynamic driving situations and decrease the possibility of occupants being out-of-position.
The active control retractor from a top global automotive component manufacturer is the combination of a reversible, electromechanical pretensioner and a non-reversible, pyrotechnic pretensioner. The reversible, electromechanical pretensioner offers pre-crash activation, comfort functions and haptic feedback. Meanwhile, the second type of pretensioner enables safety in the event of an accident that is past the point of prevention. These active retractors ensure additional occupant safety functions, besides supporting the introduction of automatic emergency braking and emergency steer assist functions through reduced occupant displacement.
The future of the automotive industry is expected to be connected, shared, electric and autonomous, with automated driving vehicles being the final destination as far as technology is concerned. This autonomy trend completely changes the manner in which a vehicle is operated, since a fully-autonomous vehicle will not require a driver to face in a certain manner to navigate the vehicle. This means that autonomous vehicles would allow occupants to face each other in the manner in which a meeting is conducted and carry on their business while on the move. Such a form of transportation would require the seat belt to ensure the safety of occupants, who may or may not be facing the front of the vehicle as in the case of traditional vehicles.
The trends of the automotive industry will require seat belts to become more intelligent and keep up with other systems of the car, and also work in unison with these active safety systems. Seat belts could be developed to offer features such as automatic adjustments as per the size of the occupant, enable adequate slack when required, and provide heating, cooling and ventilation for personalised temperature requirements. Such factors could ensure that individual preferences are met inside the vehicle, even when shared mobility is in effect.
Likewise, the different types of additional safety features embedded into the seat belt could be essential in the autonomous driving environment that is envisioned to be the ultimate future of the automotive industry. The seat belt system could be connected to various collision avoidance systems in the vehicle to offer predictive actions to enhance occupants’ safeness, be it adults or toddlers, whose seats are restrained by seat belts. Such advances could definitely see seat belts becoming an intelligent system, much like that of other electronic components in the vehicle.
It would be appropriate to note that the seat belt, which began its life as a passive, non-intrusive form of safety system, is currently blurring into becoming a light form of active safety system. While seat belt is still being equipped as a basic safety system in the global automotive industry at large, there are numerous developments taking place that could be considered for mass adoption. In terms of whether the seat belt has reached the end of its evolutionary cycle – the answer would definitely be in the negative. There are possibilities in further enhancing seat belt technologies and innovations to offer occupants even more safety.
(Inputs from ZF, Volvo Cars, Nissan Motor Corporation)
TEXT: Naveen Arul