Seoul 2000 FISITA World Automotive Congress F2000G362 June 12-15, 2000, Seoul, Korea

The Technology of the A2 – A New Innovative Automobile Concept in the Class

Dipl.-Ing. (FH) Dietrich Engelhart1) * Dr.-Ing. Ernst Lindner2)

1)Audi AG, D-85045 Ingolstadt, 2)Audi AG, D-85045 Ingolstadt, Germany

The Audi A2 signals the advent of a new model line in the compact car class. The vehicle concept is based on the Audi (ASF). The use of a body with a basic structure made entirely of aluminium, in this particular case for a compact car, is unique in volume production. Production methods which permit a high degree of automation had to be developed for this model. As part of an overall technical concept, the Audi Space Frame brings about a significant reduction in the vehicle's weight. The Audi Space Frame moreover provides the ideal basis for an outstanding package and an appropriate safety concept. The car's low aerodynamic drag is made possible by the low cD value. The low weight of the A2 combined with the high efficient spark-ignition and Diesel is resulting in an very agile and fuel- economic car.

Keywords: Audi Space Frame, aluminium car body, weight reduction, fuel economy, CO2 emission reduction

INTRODUCTION The upward weight spiral can only be broken by first reducing the weight of the vehicle's principal components, At the start of the 21st century, the car remains the most namely the body and the suspension. A reduced body important and most popular means of transport. In weight as part of an overall technical concept then makes addition to its primary function as a form of transport, it possible to exploit secondary scope for weight the car also embodies the individual's rising expectations reduction, through measures affecting the , in respect of freedom and mobility. These values are , package and tank, ultimately reversing the becoming ever more pronounced, above all in societies weight spiral. that are becoming increasingly leisure-oriented and where greater emphasis is being placed on the individual. The use of aluminium for suspension components, e.g. subframe, axle support and control arms, is already the The car is therefore increasingly having to satisfy high state of the art. On the other hand, the Audi A2, Fig. 1, expectations in respect of comfort and equipment, which is the first high volume-production car whose body is of go hand in hand with rising standards of passive safety aluminium. and higher overall operating distances. This ultimately leads to a higher gross , with the result that the engine, suspension and body rigidity need to be modified accordingly, thus adding further to the vehicle's weight. This mechanism, known as the upward weight spiral [1], ultimately means that despite the significant improvement in engine efficiency over recent years, there has been no appreciable reduction in fuel consumption. In the light of repeated international calls to reduce the CO2 emissions in order to protect the environment and climate [2], the desired degree of progress with regard to the contribution of the road traffic is therefore not achieved sufficiently so far. Fig. 1: The Audi A2 is the first high volume production The overall energy consumption of a vehicle is in car with the Audi Space Frame. proportion to its overall resistance to motion, which is defined as the sum of rolling, accelerating, aerodynamic resistance and resistance of grade. As all these forms of The Audi A2 is not merely the first high volume resistance to motion apart from aerodynamic resistance aluminium car; more importantly, it signals the are influenced by the vehicle's , a significant establishment of an entirely new vehicle segment. A very reduction in resistance to motion and therefore energy lightweight but rigid car, it offers outstanding interior consumption can be achieved by reducing the weight. dimensions inside a body that is impressively compact. * [email protected] 1 Its standards of soundproofing, seating comfort and On the A2, the use of the ASF body means that the equipment moreover satisfy the high expectations of weight is over 40 % lower than that of a comparable steel present-day and future customers [3]. body. The reduction of the body weight as part of an overall technical concept also makes it possible to exploit secondary scope for reducing the weight of the engine, AUDI SPACE FRAME ASF® transmission, suspension and tank. The A2 1.4 l TDI, for example, is around 230 kg lighter than the average of vehicles with comparable interior dimensions, Fig. 3. The Audi Space Frame of the A2, Fig. 2, is a light alloy body, which consists of 22% aluminium castings, 18% aluminium profiles and 60% aluminium panels. 1400

1300 The whole body is constructed of curved and straight average value aluminium extruded sections. Within this frame structure, 1200 every element performs an integral, supporting role. The corners and nodes, which have to bear high loads, 1100 - 230 kg incorporate complex diecast elements that are joined to 1000

the extruded sections. As seamless, enclosed hollow Tare weight [kg] profiles, the extruded sections are very rigid. Because the 900 flanges that are commonplace in steel bodies are largely unnecessary here, the space that is freed up can be put to 800 optimum use in varying the cross-section of the profile. 700 By means of ribbed panels and tailored blanks, the rigidity Comparison Vehicles A2 1.4l TDI of the diecast elements is precisely matched to the forces introduced from the engine and suspension mounts. In response to the need for high buckling strength, the Fig. 3: A2 1.4l TDI vehicle tare weight comparison. aluminium walls are thicker than their steel equivalents by a factor of approximately 1.4. In conjunction with the thicker aluminium panels, the aluminium body is extremely strong and exhibits a high energy absorption PRODUCTION capacity when deformed in a collision. With the Aluminium technology was first In the front structure, the longitudinal member comprises implemented on a production vehicle by Audi in 1994 [4]. a vacuum diecast element consisting of two shell halves, The challenge for the A2 was above all to manufacture and an extruded section bolted into it. This easy-to-repair aluminium vehicle bodies on a large scale. In contrast to design is the basis of the car's low insurance the large A8, where manual processes are still used to classification. With integral engine mounts, subframe some extent, automated processes had to be adopted connections and locating points for the car jack, this is a throughout on the A2. Its production facilities are geared multifunctional large-size component. up to an annual output of around 60,000 units. The A2's ASF has undergone further refinement compared with the design used on the A8. In particular, the A2 has a large number of straight profiles and fewer cast nodes, which, however, entail a high degree of integration.

The A2's side section, for example, consists of a single section of deep-drawn sheet aluminium extending from the lower edge of the windscreen to the tail lights. The A- post, on which the hinges of the front doors are mounted, is made from a single section of diecast aluminium. Whereas the B-post on the A8 still comprises six separate sections, much larger diecast components are used on the A2. This brings the obvious advantage that fewer parts need to be handled and joined together in the production process. Further advantages are the greater dimensional accuracy and the absence of joints. A large number of functions can moreover be integrated into the large Fig. 2: The A2 Audi Space Frame ASF. castings, such as reinforcing panels or ribs, which had to be attached in a separate process on the A8.

Thanks to the ASF, the A2 represents a high standard of In order to reduce production time still further, all lightweight design. This means that its static torsional principal extruded sections on the A2 such as the side rigidity in relation to tare weight is high. Through the roof frame are calibrated in a hydroforming plant before functionally optimized use of material, the A2's ASF assembly, significantly reducing the need for bending and achieves torsional rigidity values that are significantly milling operations. In the hydroforming plant, the above the figures for competitor models in this class. The preshaped components are inserted in a two-piece die, dynamic strength of the ASF, again high, guarantees where perfect dimensional accuracy is achieved under outstanding vibrational comfort. high hydraulic pressure. The very low tolerances that can be obtained by means of this technology permit the use of

2 laser , which is much faster and erodes the strength and specific deformation behaviour with a very material less than electric -arc welding. Less auxiliary low weight. material is needed in laser welding than in conventional welding processes, but the resulting welds are stronger In an front offset crash, the Audi Space Frame's front and the vehicle body exhibits greater rigidity. In total longitudinal members absorb the bulk of the deformation around 30 metres of weld seams are produced by this energy, whereas the beam structures behind them form method on every vehicle body. MIG welding is also used the strong passenger cell and barely sustain deformation. to a considerable degree in the production process, in Deformation of the longitudinal member follows a defined particular for the T-joints on the welded platform. Spot pattern, from the front extruded section to the rear welding, on the other hand, is no longer used. Robots join aluminium casting. Energy absorption via the longitudinal together other body sections, such as the rear panel, by members ensures that the passenger cell remains largely means of about 1800 punch rivets. free from deformation, Fig. 5.

PACKAGE AND VARIABILITY

The objective of the package's design was to create an innovative spatial concept allowing passengers to find an comfortable seating position, in conjunction with compact exterior dimensions, Fig. 4.

Its basis was created by the principle and space-saving axle concepts.

Inside, the ergonomics of the A2 are optimized; which means that the position of the front seats conveys a feeling of spaciousness. At the rear, the contour of the car's floor incorporates a recess, the so-called "Space Floor", permitting rear passengers to sit upright in an comfortable seating position. In general the slightly raised position of the front and rear seats also enhances occupant comfort.

Fig. 5: Euro-NCAP 64km/h front offset crash, simulation of structural deformation.

Full-size airbags for the driver and front passenger and side airbags in the seat backs, Fig. 6, in conjunction with seat belts that are fitted with belt tensioners and force limiting devices, provide added occupant protection. Head airbags (Sideguard system) are available as an optional feature.

Fig. 4: A2 Package.

When the concept was elaborated, considerable importance was also attached to interior variability. The availability of 4- and 5-seater versions reflects the diversity of customer requirements. With the rear seats' multiple folded constellations, including scope for their removal entirely from the car, the A2 offers a wide range of different layouts, with a luggage capacity ranging from 390 to 1140 litres.

THE SAFETY CONCEPT

The safety concept is based substantially on the Audi Fig. 6: Safety concept. Space Frame. The Audi Space Frame is a highly effective three-dimensional beam structure that combines high

3 Within the vehicle concept the sills are relatively high, The range of engines, Table 1, currently includes a 1.4 l with the result that the position of the seats in a side spark-ignition engine and two Diesel engines with impact collision is above the area most commonly displacements of 1.2 l and 1.4 l. These engines are shared affected by intrusion, providing a very high standard of with other cars built by the VW Group, and have been safety. The strong door impact members, in conjunction adopted on the A2 with slight modifications. with the B-post taking the form of a large-size ribbed casting and side airbags fitted as standard, reduce the load on the car's occupants. The structure with a roof frame designed for maximum rigidity in addition affords very good protection in a rollover. 1.4L 55 KW SPARK-IGNITION ENGINE The Audi Space Frame is likewise beneficial in a rear-end crash. The sturdy structure formed by the longitudinal and cross-members at floor level permits effective energy The 1.4 l engine has an output of 55 kW at 5000 rpm and absorption and braces the impact forces in a forward develops a of 126 Nm at 3800 rpm. direction. Energy is absorbed in a highly effective manner thanks to the folding-dent behaviour of the extruded This engine, designed for low weight and fuel sections of the rear longitudinal members. The casting in consumption, has an aluminium diecast crankcase with front of these is designed such that it sustains minimum cast-in grey cast iron liners. The engine is fitted with a deformation, to keep the protected. The shell-type plastic intake manifold and an exhaust system deformation of specifically only the rear section means made entirely from stainless steel. that the passenger cell protects the occupants very effectively in a rear-end collision, too. The two camshafts, which each operate two valves via frictionally-optimized timing gear with roller cam follower, are mounted in the two-piece cylinder head. The engine AERODYNAMICS charge cycle has been designed for an ample torque characteristic. Audi’s new aero-acoustic wind tunnel was used for the aerodynamic testing of this model. With the road surface The frictionally optimized engine is an ideal basis for low moving at the wind speed being simulated, and thanks to fuel consumption. The A2 1.4 l recorded fuel the rotation of the vehicle wheels, the boundary consumption of 6.0 l/100 km over the MVEG II cycle. conditions that prevail in reality can also be simulated, so The low fuel consumption is partly attributable to the low that realistic measurements are obtained. idle speed of 680 min-1. CO2 emissions are only 144 g/km. The EU 4 emission standard is fulfilled in particular The good aerodynamic performance has been achieved thanks to the inclusion of a primary catalytic converter in by defining the vehicle's fundamental characteristics at an the front pipe. early stage:

· Short rounded front structure

· Flat, inclined windscreen that flows continuously into the arched roof

· Relatively high, aerodynamically effective · Optimized exterior rear mirrors

The aerodynamic fine-tuning, such as the measures to the underbody, has produced low cD values. A drag coefficient of cD = 0.28 has been measured for the basic versions with the two 1.4 litre engines, and of cD = 0.25 for the 1.2 l TDI.

The aerodynamic drag, which is proportionally cD * A, is relatively low, particularly on the A2 1.2 l TDI, at 0.544. Unlike other vehicle concepts, Fig 7, the A2's low Fig. 7: Cross-sectional area and cD value comparison. aerodynamic drag is achieved by reducing the drag coefficient, and not the cross-sectional area. The ergonomics of the A2 are consequently much better than for comparison vehicles. 1.4 l 55 kW The following features are making the 1.4l 55 kW TDI ENGINES AND PERFORMANCE Diesel engine particularly suitable for use on the A2: · Inline 3-cylinder engine as a spacesaving, weight- optimized unit for transverse installation,

4 · it fulfils the emission standards currently in force, cylinder engine blocks can be manufactured on the same while maintaining the advantageous fuel consumption production line. of the direct-injection principle, For a high standard of refinement, a balancing shaft is · Low-cost, durable engine concept. driven in conjunction with the oil pump via a chain drive with a hydraulic tensioning element. The balancing shaft is mounted in a diecast aluminium ladder frame bolted to the bearing pedestals in the engine block.

Table 1: Engine and vehicle data 1.2l 45 kW DIESEL ENGINE The rated output of 55 kW laid down in the specifications is achieved at an engine speed of 4000 rpm. The high- The Diesel engine with two-valve technology has a pressure assures efficient mixture displacement of 1.2 l (bore: 86.4 mm, stroke: 76.5 mm) preparation, with the result that peak torque of 195 Nm is and a compression ratio of 19.5 : 1. An overhead achieved as low down as 2200 rpm. camshaft driven by a toothed belt controls the valves via bucket-type tappets. To reduce free inertial forces, the A key feature of this engine is the new high-pressure fuel three-cylinder engine has a base-mounted balancing shaft injection system, which permits injection pressures of up rotating in the oil sump. Both the cylinder head and the to 2050 bar. A precisely metered, separate pilot injection engine block of this Diesel engine are made from process, which reduces combustion noise and nitrogen aluminium. This measure helps to keep the engine's dry oxide emissions, is achieved with this injection system. weight down to approximately 100 kg.

To reach the objective, the pump-injector units were The key to this engine's high level of efficiency is once incorporated directly into the cylinder head. The pump- again a pump-injector direct fuel injection system. The injector elements are driven by the camshaft via the roller turbine geometry of the exhaust turbocharger with rocker arm by means of additional lifting cams. charge-air cooling is variable, thus further reducing emissions and fuel consumption. In view of the high cylinder pressures, the cylinder crankcase is made from grey cast iron. As the engine The engine achieves its maximum power output of 45 block has the same design features (distance between kW at 4000 rpm. Maximum torque of 140 Nm is available cylinder axes 88 mm; bore 79.5 mm) as the 4-cylinder across an engine speed range of 1800 to 2400 rpm. engine blocks of the new Golf DI engines, the 3- and 4-

5 The A2 1.2l TDI has a stop-start drivetrain management The 1.4l TDI accelerates from 0 to 100 km/h in 12.3 s, system, which switches off the engine when the car is and reaches the same top speed of 173 km/h as with the standing at traffic lights or in a tailback and the footbrake A2 1.4l Thanks to its pump-injector technology, the 1.4l is held down for more than three seconds. As soon as the TDI achieves fuel consumption of only 4.3 litres of brake is released, the engine starts again. Diesel fuel per 100 km. Compared to similar vehicles the A2 1.4l TDI has approximately 13% up to 53% less fuel consumption, Fig. 9. Its CO2 emissions are 116 g/km and it satisfies the EU 3 emission standard.

The 1.2l TDI achieves fuel consumption of only 2.99 TRANSMISSIONS l/100 km for the MVEG cycle, accelerating from 0 to 100 km/h in 14.8 seconds and is reaching a top speed of 168 The transmissions were developed for the specific km/h [5]. requirements of the engines: 160% · A lightweight 5-speed manual gearbox with 150% magnesium casing has been chosen for the 1.4l 55 kW spark-ignition engine. 140% MVEG-cycle [%] 130% · The higher-torque 1.4l 55 kW Diesel engine has a for reinforced 5-speed manual gearbox with a 120% conventional aluminium casing. 110% 4,3 l/100 km

consumption · In view of the engine's high efficiency, the A2 1.2l 100% TDI is supplied with an automised, five-speed fuel mechanical gearbox with aluminium casing. In 90%

Relative conjunction with its Economy program, which 80% 1 2 3 4 5 6 7 8 9 10 consistently strives to establish the lowest possible Comparison Vehicles A2 1,4l TDI shifting speeds, and a high overall ratio for fuel economy, it is able to operate at the best specific fuel Fig. 9: Fuel consumption for the A2 1.4l TDI. consumption in any given situation.

VEHICLE PERFORMANCE / FUEL CONSUMP- TION SERVICE MODULE

After 12.0 seconds the A2 1.4l is accelerated from 0 to The A2 has a new functional feature that also has the 100 km/h. This is an outstanding low value in comparison double role of a design element: the service module, Fig. to similar cars, Fig 8. 10. The conventional radiator grille has been replaced by a folding cover behind which the oil dipstick and the filler openings for engine oil and washer fluid are to be found. 18 It is now no longer necessary to open the engine comparison vehicles compartment lid to check the engine oil level and to top 17 up oil or washer fluid.

16 If more extensive servicing work involving access to the engine compartment is required, the engine cover – 15 known as the "front top" – can easily be removed by releasing the quick-acting couplings. 14

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A2 1,4l TDI 12 A2 1,4l

11 40 45 50 55 60 65 70 75 80

Engine Power [kW]

Fig. 8: Acceleration from 0 to 100 km/h.

The driver gets an agile feeling up to a top speed of 173 km/h. The fuel consumption nevertheless is 6,0 litres per 100 km. The emission standard EU IV is satisfied and the CO2 emissions are 144g/km.

Fig. 10: A2 Service Module.

6 ENVIRONMENT With regard to the more and more eminent air pollution problem, the A2 vehicle concept, Fig. 11, represents an adequate technical solution, because the amount of CO2 In order to achieve also environmental objectives emissions for this vehicle concept is on a very low level. especially such as the reduction of CO2 emissions, it is essential to view the broader context. Therefore it has to The Audi A2 is a sophisticated, progressive and be focused on the entire life-cycle of the car, from its responsible vehicle, which satisfies the rising expectations production, through its operation, to its ultimate recycling. of the individual customer, while meeting the increasingly As the bulk of the energy required throughout the lifetime challenging requirements of society and the legislative. of a vehicle is consumed during its operation, consumption-cutting measures focusing on resistance to motion, such as the reduction of the vehicle's weight, are ACKNOWLEDGMENT particularly significant. On the Audi A2, measures aiming in this direction were implemented systematically through the use of the Audi Space Frame body and the low- We thank the colleagues of the Audi A2 Team, who all consumption engines. The bigger amount of energy supported the success of this sophisticated project. required for the initial Aluminium Space Frame production in comparison to a conventional steel body is The collegues of the plant and of the Aluminium already compensated after a driving distance of Technical Centre in also merit our thanks for approximately 85.000 km. their expertise which provided the very basis for volume production of the Audi A2. The tare weight of the Audi A2 (with 1.4 l, 55 kW spark- ignition engine) is only 895 kg, thanks to the use of modified weightsaving materials such as aluminium, magnesium and plastics. According to the materials classification of VDA guideline 231, the overall proportion of the weightsaving materials aluminium/ magnesium/ polymers is 52%. The proportion of steel and ferrous materials is about 34% by weight. The ASF body's large castings as well as the extruded sections and alloy panels, made from the same alloy, can be cut away completely without undue effort, allowing these special aluminium alloys to be recycled separately. Following their removal, the castings can be used in the production of new cast-alloy components.

Along with the rise in the number of vehicles with a high aluminium content such as the Audi A2, the world's first Fig. 11: The very low CO2 emissions of the A2 are one volume-production car with an all-aluminium body, the of the important technical highlights. supply of secondary aluminium from scrap vehicles will outstrip demand for primary aluminium. In anticipation of future developments in the field of scrap-vehicle recycling, Audi has established the basis for effective REFERENCES recycling of aluminium by providing scope for the segregation of cast and wrought alloys through such [1] Kaiser, M.: Aluminium as a body in white material, 6. techniques as filleting and new cut detection methods. Aachener Kolloquium Fahrzeug- und Motorentechnik, 1997 CONCLUSION [2] Radiative Forcing of Climate Change. The 1994 Report of the Scientific Assessment Working Group of The expertise in aluminium technology that Audi AG has acquired over the past decade was an essential basis for IPCC, 1995. building the world's first aluminium car, the Audi A2, on a large scale. [3] Der neue Audi A2, Special edition ATZ/MTZ, ISSN 0001-2785, March 2000. The use of the ASF aluminium body and the exploiting of secondary weight reduction measures is resulting in a [4] Paefgen,F.-J.; Leitermann, W.: Audi Space Frame lower vehicle weight that is used to the customer's benefit. The low weight of the A2, combined with highly ASF. Ein neues Pkw Rohbaukonzept in Aluminium, VDI efficient engines, results in a particularly agile, low fuel- Report 1134, 1994. consumption vehicle concept. The A2's interior dimensions are nevertheless generous, and its variability [5] Engelhart, D.; Mödl, C.: The Development of the Audi clearly above-average. A2, a new Vehicle Concept in the Compact Car Class, VDI Report Nr. 1505, 1999

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