ACTIVE AND PASSIVE SAFETYthestandardsofactiveandpassivesafetyachievedbytheaudia1gowellbeyondeitherlegalrequire-

mentsorthosecalledforbytestsinconsumermagazines.thedevelopmentobjectivewastocoordinate

theactionoftheoccupantrestraintsystems,thesteeringcolumnandthebodystructureinthemost

effectivepossiblewayandthustoofferthecar’soccupantscomprehensiveprotectioninactualaccident

situations.

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safetY concept

With the A1, Audi adds a new model to the compact class, one that brings a high standard of active and passive safety to this market segment. The A1, like other Audi models, stands for an acknowledged high standard of safety combined with a dynamic driving experience. The dynamic suspension and the latest electronic stabil-isation program (ESP) generation, with settings specially chosen for this car and with an electronic axle-differential lock, reduce the risk of accidents. But if a colli-sion is nonetheless unavoidable, passive safety systems provide the highest pos-sible level of occupant protection.

The development objective was for the occupant restraint systems, the steering column and the body structure to be matched together in an optimal, robust manner. The ratings take Audi’s high in-house safety standards into consideration; these go beyond legal requirements or those called for by tests in consumer maga-zines. The findings reached by the Audi Accident Research Unit (AARU) and the well-founded experience of the manufac-turer’s engineers formed the basis for fur-ther development work on the passive pro-tection systems, with the aim of providing the car’s occupants with comprehensive protection in actual accident situations.

passiVe safetY

A highly rigid body using grades of material and wall thicknesses suitable for the loads that have to be withstood, energy-absorbing zones at the front and rear ends of the car and the specific layout of load paths – these are the factors that form the basis for good occupant protection in the Audi A1. The passive restraint systems take effect accord-ing to the nature of the accident and reduce the forces acting on the occupants. Three-point automatic seat belts with pyrotechnic belt tensioners and belt force limiters ensure that the occupants are held firmly and in a favourable position in their seats at an early stage in the accident.

The potential level of protection is fur-ther increased by careful matching of the seat belt, safety steering column and air-bag. Additional protection for the feet and legs is provided by energy-absorbing foam in the knee area and a safety pedal assem-bly. Seat occupancy sensors emit a speed-

dependent signal to remind the driver and front seat passenger that the seat belts have not been fastened. For rear-seat occupants every change in seat belt status is indi-cated audiovisually.

Seat and head restraint design is also an element in the safety specification. In the event of a rear-end collision, the risk of whip-lash injuries to the spinal vertebrae is reduced by the integral head restraint system.

The head airbag systems integrated into the roof frame and the side airbags install ed in the front seat backs are key elements in side impact protection. These components of the occupant restraint system are closely coordinated with the crash behaviour of the body-in-white and the door trims, and ensure more effective accident protection in such situations by minimising the loads to

Dr. thomas schWarZ isHeadofVehicleSafetyProjects/Process-

esataUDIaGinIngolstadt(Germany).

anDreas tschritter isProjectManagerinVehicleSafetyDevelop-

mentataUDIaGinIngolstadt(Germany).

tobias KÖppel isresponsibleforfrontRestraintSystems

Designforthea0ModelSerieswithinVehicleSafetyDevelopmentataUDIaG

inIngolstadt(Germany).

anDreas meier isresponsibleforfrontStructural

Designforthea0ModelSerieswithinVehicleSafetyDevelopmentataUDIaG

inIngolstadt(Germany).

marKus geiss isresponsibleforSensoralgorithms

Developmentforthea0ModelSerieswithinVehicleSafetyataUDIaGin

Ingolstadt(Germany).

arturo llamaZares isresponsibleforPedestrian

ProtectionfunctionalDesignforthea0ModelSerieswithinVehicleSafety

DevelopmentataUDIaGinIngolstadt(Germany).

aUtHORS

❶Correlationbetweensimulationandtestintheoffsetdeformablebarriercrashtest(ODB)–frontalcrashat40%overlap(timeintervals20ms)

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which the seat occupants are exposed. The safety package is completed by Isofix child seat anchorages at the rear, front passenger airbag deactivation if a child seat is to be used on the front passenger seat and fuel supply shut-off in the event of a crash. The front end of the car is designed to provide pedestrians with the best possible protec-tion if the car collides with them.

The rating and detail coordination of all components was carried out as part of the successful, continuously optimised Audi development process, which involves in -tensive cooperation and interaction be -tween the various specialist departments: Design, Simulation and Testing. Extensive use of numerical simulation methods and the resulting high level of maturity reached by test units, together with a large num ber of component, sled and complete-vehicle tests, enabled the requirements to be sat-isfied with a high standard of quality.

Design for front-enD protection

When the Audi A1 body was under devel-opment, the central focus was on crash safety, ❶. The basic element in this is the strong occupant cell, with reinforcement of specific areas of the sills and A-posts. These are surrounded by deformation zones and their effect enhanced by match-ing occupant protection systems. With the aid of numerical simulation methods, a body structure systematically designed for safety was developed.

By incorporating a load-distributing crash management system, the energy input in an offset crash is partly transmit-ted to the side member on the side farther away from the impact point. The result of this is a more uniform load on the front end of the car. The side members are tuned to ensure that the vehicle is slowed down in the most effective way and the

loads to which the occupants are exposed therefore remain low.

To lower bio-mechanical loads on the lower limbs, great importance was attached during development work to minimum in -trusion into the footwells. This was achiev- ed by means of a form-hardened front frame bulkhead of very high strength and low weight. Protection of the ankles and feet is aided by a crash-optimised pedal assembly and padded areas in the carpet.

To increase the space available for for-ward body movement on the driver’s side, the well-proven energy-absorbing steering column concept was adopted. This defor-mation absorbs additional energy and therefore reduces the risk of the driver being injured. The underside of the steer-ing column has a foam covering and a load distributor to minimise the risk of knee and thigh injuries. Together with its driver’s and front passenger’s airbags, seat belt system and crash-optimised seats, the Audi A1’s front-end occupant restraint system provides the best possible occu-pant restraint at reduced risk of injury.

Although slow and fast crash events result in contradictory demands, it was pos-sible to develop a rear-end structure suitable for all mentioned load situations. It is based on form-hardened side members and, together with the occupant cell itself, is developed in a way that the occupants are provided with a survival zone and that the fuel tank cannot leak.

Design for siDe impact protection

One of the development priorities is the design and rating of effective side impact pro-tection. In the event of such an impact, much less space is available in which to protect the occupants than in the case of a frontal colli-sion. The challenge can only be met by per-fect coordination between the occupant pro-tection systems and a rigid occupant cell.

The high-strength B-post is a key elem ent in the effective dissipation of the loads that occur. In the event of a side impact it diverts energy into the sill and the roof frame. The seat cross-members, which are rated to withstand the severe loads incurred in a col-lision with a post, transmit the energy fur-ther into the floor pan and in this way cre-ate an adequately large survival zone for the car’s occupants. The doors, containing high-strength impact beams, permit force to be ❷Networkingofpassiveoccupantrestraintsystems

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absorbed. This minimises both penetration speed and intrusion depth. In combination with the restraint systems the interior equip-ment and trim, which are matched to the body’s performance potential, keep the probability of occupant injury as low as possible. Standard equipment in the new Audi A1 are thorax/pelvic side airbags and the head protection system known as Audi sideguard. Altogether, effective protection potential is provided in every seated pos-ition the car’s occupants may prefer.

crash sensing anD airbag release

The airbag release system consists of four satellite sensors and a central airbag con-trol unit that is responsible for safety com-ponent networking, ❷.

As early as the concept phase, long before the complete system was expected to demonstrate its merits in the first crash test, the ratings for the airbag release system were determined with the aid of virtual pro-totypes and advanced simulation processes. With the aid of virtual vehicle development the nature, quantity and positioning of the sensors was determined at an early stage, so that the restraint systems (airbags, seat belt tensioners) are triggered off with high preci-sion in the event of a crash. The Audi A1 has an innovative sensor concept that satis-fies the Audi brand’s high standards of occupant safety.

The airbag control unit contains three internal acceleration sensors which are inte-grated but independent of one an other; two

of these sensors operate along the vehicle and one across the vehicle. Alignment of the internal sensors and positioning of the airbag control unit close to the car’s centre of gravity make it possible for the control unit, with the aid of a complex crash algo-rithm, to make the de cision to activate the airbags for all frontal, side or rear crashes. The systematic use of satellite sensors at suitable positions on the car also increases the triggering reliability of the system con-siderably. If a frontal collision occurs, an acceleration sensor in the car’s front-end module permits an early conclusion to be drawn regarding the severity of the crash, so that the restraint devices can be activated reliably and in good time. There are pres-sure sensors for side crash identification in the car’s front doors. If a side collision occurs these sensors measure the increase in air pressure caused by front door defor-mation; this in turn is an indication of the severity of the crash. In addition, a crash sensor mounted level with the C-post in the centre of the vehicle is used for side crash identification; its effect is particularly valu-able if the car’s door is not sufficiently dam-aged in the side crash. It permits restraint devices for the rear passengers to be trig-gered off if there is a side impact at the rear that is unable to cause any pressure increase in the doors. The combination of pressure and acceleration sensors in a side crash calls for extreme accuracy to be main-tained in the release times for the side restraint devices. In addition, the use of dif-ferent physical measuring principles pro-vides a defence against incorrect release. A

rear-end crash is identified and the occu-pant restraints activated by the two acceler-ation sensors in the airbag control unit that respond in a longitudinal direction.

In addition to releasing the protective restraint systems, that is to say the seat belt tensions and the airbags, the airbag release system communicates with other control units in the event of a crash: the hazard warning lights and the interior light are switched on and the fuel pump switched off.

peDestrian protection

In view of its high concept relevance, pedestrian protection was given high prior-ity from the start when designing the front end of the A1. It was a challenge to har-monise the predetermined peripheral tech-nical conditions, i.e. the car’s front-end package, with the requirement for sporty design. Close interaction between the Test-ing and Simulation departments enabled optimal solutions in terms of space require-ments to be found, yet for pedestrian pro-tection to be well above the level laid down by law. ❸ is an example showing the excellent conformity of simulation results in the case of the pedestrian’s head striking the bonnet.

Despite the short body overhang, an efficiently constructed bumper system sig-nificantly reduces leg injuries if a pedes-trian is hit by the car. The aluminium bumper cross-member was specially shaped with this in mind, and the energy-absorbing pedestrian protection foam optimised in its geometry.

The wraparound bonnet is a major A1 design element. Its pedestrian protection and rigidity were optimised at an early stage by the use of simulation. So the head is extremely well protected against injury from the bonnet or striking hard objects in the engine compartment. The very demanding regulations concerning rigidity were also complied with, for example those concerning wind load or torsional rigidity. Two bonnet catches are provided. Attractive design has been achieved by specific design of the hinges, the inner panel and the catch and hinge reinforce-ments. As a result of this development work the new Audi A1 has been homolo-gated according to the new European Directive EG 78/2009 Phase 2 and there-fore already conforms with legal require-ments that will come into force in 2013.

❸Correlationbetweensimulationandtest–pedestrian’sheadstrikingbonnet

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