Audi A 6 safety

au t h o r s

Dipl.-Ing. (FH) Michael Broscheit

is Properties Developer for Front-end Protection within the area of Vehicle Safety at AUDI AG in Ingolstadt (Germany).

Dipl.-Ing. Jose David Martin Rodriguez

is Properties Developer for Side Protection within the area of Vehicle Safety at AUDI AG in Ingolstadt (Germany).

Protective system to a high standard

The new Audi A6 offers highest level of safety among the current Audi fleet. Yet compliance with current legislation and consumer tests, in which the new A6 will position itself among the leaders in the ratings, accounts for only a small proportion of the extensive safety requirements. The focus of attention in developing passive safety for the A6 was its protective potential in a real-life accident. Key components of passive safety were transferred from the Audi A8 to the A6 within the framework of the modular longitudinal platform and developed further, 1. They are an essential part of the integral safety of the Audi A6.

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Klaus Semmler

Dipl.-Ing. (BA) Christian HeSS

is Properties Developer for Rear-end Impact Protection within the area of Vehicle Safety at AUDI AG in Ingolstadt (Germany).

is Properties Developer for Pedestrian Protection within the area of Vehicle Safety at AUDI AG in Ingolstadt (Germany).

Development objectives

With regard to the safety aspects of ­vehicle design, Audi uses scientific findings obtained from actual accidents and their consequences. For this purpose, the AARU (Audi Accident Research Unit) examines accidents involving vehicles from the company and also evaluates ­relevant accident databases. The task of the research team is to analyse and reconstruct accidents and determine potential for improvement. The development team, made up of members from a range of disciplines, evaluates various design models, construction and package versions and subsequently establishes the most important parameters for the body structure, the interior and the restraint

systems. Findings obtained in this way are used to develop guidelines for design and safety functions for all crash-relevant components. In addition to the electronic safety functions that have already become standard such as fuel shut-off, battery disconnect feature, door unlocking or hazard warning lights activation following a crash, the objective of vehicle development at Audi remains to produce a very rigid passenger cell so that the restraint systems can provide full protective action in the event of an impact. As early as the concept phase of the new Audi A6 care was taken to ensure that the car body, seatbelts and airbags would work together optimally in the event of an accident, 2. Vehicle defor-

Passive safety The new Audi A6 offers the highest standard of passive safety. As early as the concept phase of the new Audi A6, care was taken to ensure that car body and safety systems such as belts and airbags work optimally together in the event of an impact. The deformation behaviour of the vehicle was deliberately influenced so that the systems could provide the best possible protection during a collision. The sporty, flat design of the new A6 was conceived by way of extremely efficient safety measures so that the consequences for pedestrians would be substantially reduced in the event of an accident.

mation behaviour was deliberately influenced in order to provide the best pos­ sible protection for vehicle occupants during a crash. In addition to the safety components of body and restraint systems, all package components such as air conditioning, cockpit elements, trims and ancillary units in the engine compartment were

designed and positioned with a view to safety. Here at a very early stage, simulations were able to show the correct way forward in terms of concept-specific decisions. From the concept phase to series maturity, more than 4000 crash simulations were carried out using virtual prototypes, which created the basis for the reallife vehicle’s superior crash behaviour.

Robustness analyses with the aid of stochastic simulation methods were increasingly used and all safety-related vehicle components examined and optimised in terms of crash behaviour. Close networking of the design, simulation and testing departments from the very beginning of the project led to reliable crash results, even with the initial A6 prototypes. Excel-

1 Overview of passive safety January 2011

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lent teamwork facilitated interdisciplinary collaboration and thus made a valuable contribution towards the integral safety of the new Audi A6. Front-end protection

Protection of occupants in a frontal impact particularly depends on the interplay of the vehicle structure with a restraint system that is ideally adapted to the occupants. Great importance was attached to both during the development of frontal impact protection. First of all, the objective was to further develop the modular longitudinal platform in terms of crash behaviour. Design of front structure

The bumper system, the side members and the front subframe in particular were adapted to meet the high requirements of a vehicle from the executive class. Here materials, geometric design and joining technology are chosen so that, in the event

2 Airbags and protective components at the front end

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of a frontal impact, as much impact energy as possible is absorbed by deformation and optimum use is made of the available deformation distance. In addition, the targeted use of hot-formed, high-strength steels for the sills, centre tunnel and bulkhead cross-member ensures that the passenger cell offers occupants a safe survival space during a more severe accident. The footwell area, with defined areas of low deformation, together with special crash foam, offers a high level of protection for the legs and feet in a frontal crash. The pedals on the driver’s side also play their part. In the event of a serious crash, the pedals are deliberately detached from the vehicle structure to minimise the load on the driver’s legs and feet. The restraint system is supplemented on the driver’s side by a safety steering column, which can increase the driver’s forward displacement during impact by 80 mm. The steering column features a force/ travel characteristic, which offers optimum restraint regardless of the stature of the occupants.

In designing front-end protection, stateof-the-art development methods were applied, covering the entire range of vehicle safety from crash simulation and component tests through to tests on the complete vehicle. 3 shows simulation and car crash superimposed. The adaptive restraint system

The seatbelts and both front airbags in the new A6 have been significantly enhanced compared with the predecessor model. They are based on the same technology that is already used in the A8. The tried and tested adaptive restraint system consists of switchable seat belts and multistage front airbags. In the event of a crash, the load is determined based on accident severity, seatbelt usage and seat position. The adaptive seatbelt and airbag systems are then controlled by the airbag control unit in such a way that available forward displacement is ideally utilised. In this way, adaptive restraint systems solve the design conflict arising from

4 Design conflict between various body statures

3 Simulation and vehicle crash superimposed at 0 ms, 20 ms, 40 ms, 60 ms, 80 ms and 100 ms

5 Different forward displacement of occupants using an adaptive restraint system (green) compared with a conventional system (red)

­having occupants of various sizes. 4 gives an overview of the various requirements of restraint systems depending on the stature of the occupants. The adaptive seatbelt system in the new Audi A6 is equipped with a powerful belt tensioner and a switchable belt-force limiter. In its initial condition, the high force limit is always active. At an optimum point for the occupant, it switches to a low belt-force limit. This lessens the restraining effect and reduces the load on the occupant’s chest, en­abling the occupant to move further forward. The adaptive driver’s airbag in the new A6 has a conventional filling volume of 60 l. This airbag volume is utilised completely; if needed, however, the original firmness of

the airbag is reduced by means of an additional venting hole – the airbag has a softer force/travel characteristic, which also reduces the load on smaller occupants. 5 shows a longer forward displacement path for the occupant using an adaptive (green) restraint system compared with a conventional (red) restraint system. The adaptive front passenger airbag also comprises a conventional airbag with a volume of around 120 l. As with the driver’s airbag, the firmness of the airbag can be reduced here too if necessary via an additional venting hole. Different degrees of airbag inflation lead to different forward displacement paths for the occupants. Thanks to these options for con-

January 2011

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trolling the firmness of the seat belts and airbags, the load on passengers of all statures is reduced. Side protection

With an intense focus on simulations in the early phase of the project, safety requirements were fully considered as early as the concept development stage. To bring these concepts reliably to series production with optimised weight, the process of test-related simulations and validations of sub-components in reproducible and load-specific tests was further extended for the A6. Using the complete models validated in this way in the simulation, it was possible to specifically

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develop optimum solutions in terms of weight by means of robustness and stochastic analyses of bodyshell structure and interior components, in order to achieve the highest safety standards in side protection that have become a tradition at Audi. Design of side structure

The design of the side structure poses a major challenge in vehicle development. In comparison with the front end structure, less space is available here to absorb impact energy. When developing the A6, Audi therefore paid particular attention to the stability and deformation characteristics of the load-bearing side wall frame and the doors. Optimum coordination of structural and interior components ensured that the load on occupants in the event of a side impact remains as low as possible. Taking the doors as an example, this means that both high-strength materials and aluminium are used. Care was taken, for instance, to ensure that the doors, by overlapping significantly with the side wall frame, distribute loads evenly and so fulfil the highest structural requirements. In addition, the door trim panels are deformable and designed to dissipate as much impact energy as possible, 6.

Rear impact protection

The integrity of the fuel system and the stability of the passenger cell in a rear-end collision depend in particular on the force paths of the vehicle structure. The focus of attention during the development of rear impact protection for the new A6 was to further enhance the already very good crash characteristics of its predecessor. In the event of the new Audi A6 being involved in a rear-end collision, the load is transferred via the rigid bumper crossbeam and connected deformation elem­ ents to the two rear side members made of high-strength steel. Thanks to this load path the fuel tank – which is already protected by its position – remains outside the deformation area even in the event of a rear-end impact, 8. Occupants are naturally also well protected by the high-strength side members and the chosen load distribution in the

Design of side protection system

Through the interplay of the optimised side body structure with the doors and the interior door trims, fewer intrusions and lower penetration speeds were achieved for the new Audi A6. Other subsystems – the large-volume head airbag system, the side airbags optimally positioned in the seats and the triggering of active seat belt components – have been precisely matched to the crash kinematics. In addition, the seats protect the occupant from extremely local impact thanks to their high level of lateral rigidity, 7. Acceleration sensors in the area of the C-post as well as pressure sensors in the doors ensure prompt activation of the side airbags. In conjunction with information from the central acceleration sensors in the airbag control unit, the restraint systems are activated quickly and adjusted as appropriate for all crash scenarios.

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6 Side impact

7 Occupant protection systems (simulation/test)

body; passenger cell deformation is minimised by these measures, 9. At higher collision speeds the front seat belt tensioners are also activated in order to ­protect vehicle occupants even more effectively. The whiplash-optimised front seat

Accident research studies show that bumper-to-bumper collisions, in particular at 32 to 50 km/h, cause many injuries to the cervical spine. The front seats in the new A6 were therefore designed with the help of an impact test based on the studies, during which the seat is accelerated to a speed of 16 km/h within 90 ms. FEM simulation, which precisely reproduces these accident constellations, is an important design aid in the early development phase. Here the loads on the ­cervical spine are determined using a

8 Fuel tank outside deformation area

detailed dummy model – the “Biorid II”, ❿. In this so-called whiplash simulation the seat is optimised as a whole in order to keep the load on the cervical spine as low as possible during a crash. To do so, the upper body must sink slightly into the backrest and the head should be cushioned by the head restraint at an early stage. This was solved by way of energy-absorbing foam elements in the backrest, optimised structural rigidity and a solid head restraint. The effectiveness of the system was examined by simulating real-life accidents in tests using a sled system and by means of rear-end crashes. The combination of tests and FEM simulations facilitated more detailed parameter studies and targeted optimisation loops, which ultimately led to an efficient overall system. Comparative tests conducted by wellknown consumer protection groups such as ADAC, Thatcham, IIHS, GdV (German Insurance Association) and Folksam confirm the effectiveness of the head restraint design and thus ensure top ratings for Audi seats.

9 Integrity of passenger cabin

tion, with the result that development work was focused on the entire vehicle front end, including all add-on parts. In order to offer a high level of protective potential in the event of a head impact on the bonnet, all components in the engine compartment are deformable or are positioned low as appropriate. In addition, the energy-absorbing behaviour of the bonnet plays a vital role. Thanks to simulations carried out early on during the concept phase, space-efficient solu-

tions in the front package have been developed. ⓬ shows the impressive predictive capability of the simulation, with an example of a head impact on the bonnet, making contact with the deformable engine design cover. The efficient bumper system made it possible to achieve the high requirements in terms of pedestrian protection and at the same time a short overhang at the front end. The energy-absorbing bumper cover and space-efficient deformation

Pedestrian protection

The sporty, flat design of the new A6 was realised using particularly efficient safety measures in order to substantially reduce the consequences for pedestrians in the event of a collision, ⓫. As early as the concept phase, active and passive pedestrian protection was given high priority with regard to the design of the front secJanuary 2011

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❿ Detailed Biorid II dummy model

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⓫ Overview of active and passive pedestrian protection

new A6 offers passive pedestrian safety that exceeds current statutory regulations and consumer protection requirements. In addition to passive measures, the new A6 features daytime running lights as standard, which ensure that the vehicle is recognised sooner by other road users. The optionally available night vision assistant

DOI: 10.1365/s40111-010-0263-2

foam offer optimum protective potential for the pedestrian in the event of impact on the leg. The vehicle was designed with the aim of achieving the highest standard of protection with regard to passive pedestrian safety, taking into consideration the findings of accident analysis. As a result, the

with highlighting of detected pedestrians and pedestrian warning supports the driver when driving in the dark. Daytime running lights and the night vision assistant make a significant contribution towards preventing accidents involving pedestrians and, together with the passive measures, form an integral pedestrian protection system.

Thanks Also involved in compiling the article were: Dipl.-Ing. Horst Pankalla, Project Manager for the C Model Line within the area of Vehicle Safety at AUDI AG in Ingolstadt (Germany). Dipl.-Ing. Arnaud Freyburger, Properties Developer for Pedestrian Protection within the area of Vehicle Safety at AUDI AG in Ingolstadt (Germany). Dipl.-Ing. (FH) Franz-Xaver Riedl, Properties Developer for Crash Sensor Systems within the area of Vehicle Safety at AUDI AG in Ingolstadt (Germany).

⓬ Acceleration curve for simulation and test, head impact on bonnet with deformable engine design cover

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