The history of Mercedes-Benz Experimental Safety Vehicles (ESFs): milestones in safety development

In the early 1970s, alone on the occasion of the ESV programme
Mercedes-Benz built over 30 experimental vehicles for research on future automotive safety systems. These prepared the ground for numerous innovations, some of which only reached series production maturity years later. They include ABS, belt tensioners and belt force limiters, airbag and side impact protection.

In the 1960s it became impossible to ignore a negative aspect of mass motorisation: more and more people were being killed on the roads. In 1968 the US
Department of Transport therefore started a programme for the development of Experimental Safety Vehicles (ESVs), and initiated the international "Technical Conference on the Enhanced Safety of Vehicles". In 1970 the first requirements to be met by ESVs were defined. These included an extremely demanding frontal and rear-end impact against a rigid barrier at 80 km/h, and a side impact against a mast at 20 km/h. The test vehicles also had to withstand minor accidents at 16 km/h without lasting deformations at the front and rear. It was also believed that American consumers would not accept having to actively put on and fasten a seat belt, therefore automatic belt systems were envisaged which would envelop the front occupants when the doors were closed.

The American government also issued an invitation to foreign countries to take part in this safety research. In 1970 this gave rise to the still active European
Enhanced Vehicle Safety Commitee (EEVC).

At Mercedes-Benz the challenge of designing vehicles with even more safety was taken up with great enthusiasm. After all, the company was already able to look back on more than 20 years of continual safety research at the time. And about ten years previously, in 1959, the fundamental basis for all future safety developments had already entered series production at Daimler-Benz: the safety bodyshell with impact energy absorbing crumple zones at the front and rear, and a
rigid passenger compartment between them.
From spring 1971 the ESV project went full-steam ahead in the separate safety research department founded at Mercedes-Benz in Sindelfingen in 1969. All in all, 35 vehicles were built and tested over the four following years. The first test took place on 12 March 1971 with a W 114 from series production, i.e. the medium-class series at the time. The car was subjected to a frontal impact on a rigid wall at 80 km/h. The tests also included frontal and rear-end collisions, lateral collisions with masts and other vehicles, and also drop tests from a height of 0.5 metres.

The development focus was not only on occupant protection during an accident by means of correspondingly improved vehicle structures and innovative
restraint systems, however. Even almost forty years ago, the still valid, comprehensive approach to safety always taken by Mercedes-Benz applied, as an extract from the description of the ESF 13 first presented in May 1972 shows.

This already refers to still current concepts such as driver-fitness safety through seating comfort, climate control and non-intrusive vibration/noise characteristics. Where perceptual safety is concerned, the ESF 13 featured pneumatic beam range control, a headlamp wash/wipe system, a tail light monitoring system in the cockpit, a rear wiper and a safety paint finish with a light colour and contrasting strips. External safety features for the protection of pedestrians and two-wheeled road users included foam-covered front and rear bumpers, rubber drainage channels and rounded door handles. Fire safety was also taken into account: the fuel tank was above the rear axle, well away from the exhaust system. The fuel pump was if necessary deactivated by a mechanism that depended on the engine oil pressure, a valve system prevented any spillage of fuel if the car stood at an unusual angle, the materials used in the interior were fire-retardant and a fire extinguisher was conveniently mounted on the lower front of the driver's seat.

Mercedes-Benz presented the following four ESFs to the public:

ESF 5: developed on the basis of the W 114 (“Strich Acht”) series and
presented at the 2nd International ESV Conference from 26 to 29 October 1971 in Sindelfingen
• Designed for an impact speed of 80 km/h
• Five three-point seat belts, each with three force limiters, front seat belts self-fitting.
• Driver and front passenger airbag, also an airbag in each of the front seat backrests for rear passengers on the outer seats. This increased the weight of the front seats to 63 kg each (standard: 16 kg).
• Extensive structural modifications in the front end and sides
• Kerb weight: 2060 kg (665 kg more than standard)
• Overall length: 5340 mm (655 mm more than standard)
• Wheelbase increased by 100 mm, so as to maintain spaciousness in the rear despite the larger seats
• Front-end extension incl. hydraulic impact absorber: 370 mm
• Experimental V6 engine to gain deformation space at the front
• Dashboard with impact-absorbing metal structure on the front passenger side
• All relevant impact areas in the interior were padded with polyurethane foam, especially the doors, pillars and roof frame
• Doors without quarterlights, power windows
• Headlamp wipers, beam range control, parallel rear window wipers
• Side marker lights, tail lights with standstill relay and control function
• Windscreen and rear window of laminated glass, bonded in place
• Pedals with rounded-off lower section
• ABS brakes

ESF 13: Stylistically revised variant of the ESF 5, presented at the 3rd International ESV Conference from 30 May to 2 June1972 in Washington (USA)
• Restraint systems and other features adopted from the ESF 5
• Kerb weight: 2100 kg (705 kg more than standard)
• Overall length: 5235 mm (550 mm more than standard)
• Front-end extension incl. hydraulic impact absorber: 420 mm
• The changes to the external dimensions were primarily the result of the redesigned front and rear ends. The bumpers were now designed to be underrun, while the deformation path remained the same. The front and rear were extended to reduce the bumper overhang to an acceptable level.

ESF 22: Based on the W 116 series (1971 S-Class) and presented at the 4th International ESV Conference from 13 to 16 March 1973 in Kyoto (Japan)
• Designed for an impact speed of 65 km/h
• Four three-point belts, each with three force limiters and a belt tensioner
• Driver: airbag instead of belt tensioner
• Kerb weight: 2025 kg (287 kg more than standard)
• Overall length: 5240 mm (280 mm more than standard)
• Front-end extension incl. hydraulic impact absorber: 245 mm
• ABS brakes

ESF 24: Modified S-Class (W 116) presented at the 5th International ESV Conference from 4 to 7 June 1974 in London (Great Britain)
• Restraint systems identical to ESF 22
• Kerb weight: 1930 kg (192 kg more than standard)
• Overall length: 5225 mm (265 mm more than standard)
• Front-end extension incl. hydraulic impact absorber: 150 mm
• ABS brakes

The foundations for the current safety level of cars bearing the Mercedes star had therefore been laid. Extract from the summary test report (1975): "The ESF 24 can be regarded as the completion of the project, as this vehicle represents the best possible compromise between the original ESV requirements and our current series production cars."

At Mercedes-Benz safety was included in the development specifications for new cars as a matter of course decades before the ESV programme, and in rapid
succession the ideas first realised as part of the ESF project entered series
production as well.

The milestones included:
1978: premiere of the ABS as an option for the S-Class
1981: driver airbag and belt tensioner available in the S-Class
1995: belt force limiters and sidebags enter series production of the E-Class