The seat belt takes a major role in the passive safety. Driver and passengers are restrained in their seats in the event of a collision. Various airbags form supplemental restraint systems.

The seat belt

One click to safety: Simply unreel it, pull it over your hips and upper body and fasten it in the buckle – putting on the seat belt before setting off has become a matter of course for vehicle drivers and passengers alike. Its function is as simple as it is effective: in the event of a collision, standard three-point seat belts secure the pelvis in the seat and restrain the upper body. Consequently, they fulfil a pivotal role within vehicles’ comprehensive passive safety systems. Accidents meant many severe injuries prior to the introduction of the seat belt because the inertia during a collision suddenly propels occupants towards the front or the sides, causing them to potentially hit parts of the vehicle’s interior or body – or simply be ejected from the vehicle. Seat belts significantly improved the situation.

Debut in 1950s supersports car: The seat belt was first introduced at what used to be Daimler-Benz AG in the Mercedes-Benz 300 SL Roadster (W 198). In March 1957 the company launched the open-top supersports car at the Geneva Motor Show and announced the seat belt, which would be optionally available that same year. Back in the day, this item of optional equipment cost DM 110 per seat. In 1957, the restraint system was described as a “belt to buckle up, aircraft design”: it was a two-point lap belt, which we are also familiar with from passenger aircraft. As part of the “33 Extras” series the Mercedes-Benz Museum is showcasing one such specimen made by northern German manufacturer Autoflug.

Pioneers from France: Early automotive inventors already pondered concepts centring on the seat belt. Frenchman Gustave-Désiré Leveau registered his “Bretelles protectrices pour voitures automobiles” as a patent on 11 May 1903, which was granted on 8 October that same year. The patent drawing illustrates complex four-point seat belts, which the driver as well as the passengers in the front and rear are wearing. The restraint system consisted of a lap belt and two criss-crossing shoulder belts each. The depiction of a rapidly moving vehicle in patent application number FR331926 reflects the enthusiasm for this new mode of transport prevailing in France at the time.

Learning from aircraft: Seat belts were developed in the first half of the 20th century, primarily for commercial and military aircraft. Swedish engineer Nils Ivar Bohlin registered the three-point seat belt for vehicles as a patent in 1958. He had also previously worked in the aircraft industry. The German Patent Office quoted the system’s benefits in the translation of Bohlin’s patent application, explaining that it “restrains both the upper and lower body in such a physiologically beneficial way and is easy to engage and disengage”.

Ample range: In 1958, Mercedes-Benz also introduced the two-point seat belt as optional equipment for the entire range of passenger cars with individual seats in the front. For instance, it was priced at DM 120 for a Mercedes-Benz 220 S (W 180 model series) and at DM 150 in the 300 d (W 189) (per seat in each case). By the end of the year lap belts in the rear seats were also optionally available. Konrad Adenauer, the first Chancellor of the Federal Republic of Germany, was also convinced by the system. His official car was equipped with a lap belt in the rear. His last of a total of six Mercedes-Benz 300, known as “Adenauer Mercedes”, is on show at the Mercedes-Benz Museum in the Collection 4 exhibition space: Gallery of Celebrities.

Race and rally: From the 1950s onwards an increasing number of racing cars in motorsport were also fitted with a seat belt. Nowadays competitive vehicles mostly feature four- or six-point seat belts. These are supplemented by links to systems, such as HANS. This head-and-neck support reduces the dangerous acceleration of the head during a collision.

Three points and an automatic mechanism: In the 1960s the three-point seat belt finally became a standard feature in passenger cars. It combines the benefits of a lap belt and shoulder belt – just like Bohlin had described it in 1958. Equipped with a reeling mechanism, the restraint system becomes automatic. Mercedes-Benz introduced this particular version as standard equipment in front seats in 1973, and in 1979 it was also available as standard equipment in rear seats. It is not just the way the seat belt wraps around the body which is critical, but also how it is attached: Mercedes-Benz delivered the R 107 model series SL (introduced in 1971) with a seat belt anchored to the bottom of the seat as standard equipment.

Seat belts become mandatory: Accident research clearly demonstrates the effect of seat belts. For this reason, many countries made them mandatory for newly homologated vehicles. In the US, seat belts became mandatory as of 1966 and in West Germany this was the case from 1974. However, nowhere near all drivers and passengers actually buckled up. For this reason, wearing seat belts was made mandatory  – a decision that initially met with plenty of resistance. Within the German-speaking region, wearing a seat belt became mandatory in 1976 (West Germany and Austria), 1980 (GDR) and 1981 (Switzerland, following the suspension of the requirement to wear seat belts – in 1976 – as a result of protests and a referendum). Respective governments introduced corresponding fines to enforce the requirement to buckle up soon after: in 1981 (Switzerland), 1982 (GDR) and 1984 (West Germany and Austria). Fines for failing to wear a seat belt have been in force across the European Union since 2006.

Research in the interests of safety: Mercedes-Benz has been intensively researching passive safety and thus also restraint systems since the 1950s, e.g. as part of the experimental safety vehicle (ESV) programme. Automatically engaging seat belts for the front seats were trialled back in 1972 in the ESV 13 experimental safety vehicle. ESV 22, developed in 1973, served as a platform to test three-point seat belts featuring three seat belt force limiters and seat belt tensioners as well as the driver airbag. In 1981, the driver airbag in conjunction with a seat belt with a tensioner system celebrated its series-production launch in the 126 model series S-Class. ESV 22 is on show at the Mercedes-Benz Museum in the Legend 5 exhibition space: Visionaries – Safety and Environment.

System concept: Seat belt feeder, seat belt tensioner, airbag and belt airbag – further solutions supplement the system over the years. In this context, seat belts are considered the primary restraint system. For this reason, steering wheels equipped with airbags used to say “SRS”, an acronym for supplemental restraint system. And what if the seat belt and airbag become one? For instance, the belt airbag in the rear of the 222 model series S-Class was introduced in 2013: an inflatable seat belt which significantly increases the seat belt surface that is in contact with the upper body.

Source: Mercedes-Benz Classic