2009 was a year in which Mercedes-Benz celebrated several anniversaries in the safety field: in August 1939 the safety pioneer Béla Barényi started his work in Sindelfingen. He invented for example the principle of the crumple zone, a trailblazing innovation which entered series production at Mercedes-Benz in 1959. With the help of its in-house accident research function, which was founded in 1969, Mercedes engineers in the following years have developed several groundbreaking innovations in passenger car safety. Now it is time for a look behind the scenes, and in this anniversary year, Mercedes-Benz is using the ESF 2009 research vehicle to reveal what its safety specialists are currently working on – with a time horizon that often extends well into the future.
The ESF 2009 is the first Experimental Safety Vehicle to be built by Mercedes-Benz since 1974. Like its historic predecessors, it illustrates trailblazing innovations in the field of safety and makes the progress achieved clearly visible. These amazing but by no means crazy ideas include inflatable metallic sections which give more stability to structural components within fractions of a second, as well as the so-called “Braking Bag.” This airbag housed within the vehicle floor is deployed when a crash is deemed to be unavoidable, and uses a friction coating to support the vehicle against the road surface. The ESF 2009 was premiered on 15 June 2009, at the Enhanced Safety of Vehicles (ESV) Conference in Stuttgart.
“Safety is a central element of the Mercedes-Benz brand. In this respect we have been setting the pace in the market for almost 70 years. For the benefit of our customers and for road users in general. The ESF 2009 shows that we still have plenty of ideas and the absolute will, to lead the automobile industry in this field even in future,” says Dr. Dieter Zetsche, Chairman of Daimler AG and CEO of Mercedes-Benz Cars.
The ESF 2009 was developed and built completely in the test vehicle workshops in Sindelfingen. This safety research vehicle based on the Mercedes S 400 HYBRID features more than a dozen safety innovations, most of which are fully functioning in demonstration mode. “With the ESF 2009, we have chosen this particular time to clearly demonstrate the innovative strength of Daimler. Anybody examining the ESF 2009 in detail will recognise that more safety and improved energy efficiency are not necessarily a contradiction in terms. We want to make progress in both fields with new, trailblazing ideas,” says Dr. Thomas Weber, the member of the Daimler Executive Board responsible for corporate research and development at Mercedes-Benz Cars.
The following five innovations on the basis of the S 400 Hybrid are among the highlights of the ESF 2009:
- PRE-SAFE Structure: The inflatable metal structures save weight or increase the stability of structural components. When at rest, the metal section is in a folded state to save space. If its protective effect is required, a gas generator builds up an internal pressure of 10 to 20 bar within fractions of a second, causing the section to unfold for significantly more stability.
- Braking Bag: This auxiliary brake accommodated in the vehicle floor is a new type of PRE-SAFE® component. If the sensor system concludes that an impact is unavoidable, the Braking Bag is deployed shortly before the crash and stabilises the car on the road surface by means of a friction coating. The vehicle’s vertical acceleration increases the friction, and helps to decelerate the vehicle before the impact occurs.
- Interactive Vehicle Communication: The ESF 2009 is able to communicate directly with other vehicles, or via relay stations. Using “ad hoc” networks and WLAN radio technology, it is e.g. able to receive and transmit warnings of bad weather or obstacles in the road.
- PRE-SAFE Pulse: This further development of PRE-SAFE® is able to reduce the forces acting on the torsos of the occupants during a lateral collision by around one third. It does this by moving them towards the centre of the vehicle by up to 50 millimetres as a precautionary measure. As an active restraint system, it uses the air chambers in the side bolsters of the seat backrests.
- Spotlight lighting function: This partial LED main beam specifically illuminates potential hazards. If the infrared camera of Night View Assist PLUS e.g. detects deer at the roadside or pedestrians on the road, these can be briefly illuminated beyond the normal area covered by the main beams, as if by a spotlight.
Mercedes-Benz also presented an innovative PRE-SAFE Demonstrator at the 21st ESV Conference. For the first time this simulator uses a linear motor for this purpose, in order to accelerate the vehicle cabin to up to 16 km/h within a distance of four metres before the impact occurs. The linear drive system, which is similar to that used by the Transrapid train, is freely programmable and also works in the opposite direction. This enables various acceleration profiles and also a rear-end collision to be demonstrated. The special feature of this system is that the ‘vehicle occupants’ experience the effect of the PRE-SAFE® functions live, e.g. belt pretensioning, NECK-PRO and the inflatable side bolsters of the seats.
Mercedes-Benz is continuing a longstanding tradition with the ESF 2009: for the ESV Safety Conferences held in 1971 to 1975, the safety experts in Stuttgart built more than 30 experimental vehicles and subjected them to crash tests to satisfy the visionary safety requirements of that time. Four of these ESFs (Experimental Safety Vehicles) were presented to the public, and many of the revolutionary ideas such as ABS or the airbag first entered series production at Mercedes-Benz.
The history of experimental safety vehicles (ESFs)
Safety development milestones
In the early 1970s, Mercedes-Benz built well over 30 experimental vehicles for research on future automotive safety systems as part of the ESV programme alone. 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, airbags 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 experimental safety vehicles were defined. These included an extremely demanding frontal and rear-end impact against a rigid barrier at 80 km/h (50 mph), and a side impact against a mast at 20 km/h (12 mph). The test vehicles also had to withstand minor accidents at 16 km/h (10 mph) 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 Committee (EEVC).
At Mercedes-Benz the challenge of designing even safer vehicles was taken up with great enthusiasm. After all, the company was already able to look back on more than 20 years of ongoing 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 (50 mph). The tests also included frontal and rear-end collisions, side collisions with masts and other vehicles and also drop tests from a height of 0.5 metres (20 in).
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 front and rear bumpers with foam-covered sides, 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 (/8) 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 (50 mph)
- 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 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
- 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 (40 mph)
- 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.”
Safety was now included in the development specifications for new cars as a matter of course, and in rapid succession the ideas first realised as part of the ESF project entered series production. The milestones included:
1978: ABS enters series production
1980: World premiere of the driver airbag and belt tensioner
1995: Belt force limiters and sidebags enter series production