November 28, 1999
Audi A2 1.2 TDI: The three-litre car from Audi
Text and photos courtesy of Audi AG
The latest model in the A2 series, the 1.2 TDI, requires only 2.99 litres of diesel fuel per 100 kilometres. Audi has now become the first manufacturer in the world to supply a four-door "three-litre" car, in other words one with fuel consumption of less than three litres per 100 km. In common with the other members of its model family, the 3-litre A2 1.2 TDI brings together all the characteristic features of a high-quality, ultra-practical car within its compact shape. Its spacious interior is as impressive as its ride comfort and quality character.
Lightweight design as the key
Low weight and outstanding aerodynamics - these, in conjunction with a fuel-optimized engine and minimum rolling resistance, are the main technical requirements to be met by any car that seeks to break through the much-discussed three-litre fuel consumption barrier.
The Audi A2 with 1.4 litre, three-cylinder TDI engine has already clocked up an overall consumption value of only 4.2 litres per 100 kilometres (according to 93/116/EC). An ideal basis for the three-litre version, on which the characteristics of this model series have been further optimized down to the tiniest detail.
Audi's technical experts have systematically reduced the weight of numerous components on the three-litre version, in many cases by using new materials. Compared with the A2 1.4 TDI, the suspension alone is over 80 kilograms lighter. The axle mounting frame, control arms and spring struts are made from aluminium instead of steel. The brake calipers on the front disc brakes and the brake drums at the rear are likewise of this lighter metal.
Lightweight forged aluminium wheels, developed specially with a view to optimizing the overall weight, reduce the unsprung masses.
Even on the car's interior, effective measures have been taken to reduce its weight. The weight of the rear bench seat, for example, was reduced by 19 kilograms by the use of special materials and a sandwich principle. This high-tech process of shedding weight even on the smallest features involved considerable outlay. The reward for all this effort: the weight of the 3-litre A2 1.2 TDI now undercuts that of the "mainstream" 1.4 TDI by 135 kilograms, and weighs in at 825 kilograms.
Progress from the wind tunnel
Audi's engineers have reduced the drag coefficient of the A2 1.2 TDI to a sensationally low cD = 0.25 - making the three-litre version the most aerodynamically efficient of any production passenger car. As when optimizing the weight, this achievement can be expressed as a clear-cut equation: excellent basis + fine-tuning of detail features = Advancement Through Technology.
The body shape of the Audi A2 is characterized by lines tapering to the rear, and is thus reminiscent of one of the most aerodynamically effective shapes, the droplet. The generous amount of space for rear passengers comes as something of a surprise when one considers how sleek the car's exterior is. This is all thanks to a further highlight of the A2 body, the Space Floor Concept. The rear footwells are sunk into the floor and therefore 13 centimetres lower than the front footwells; this allows rear passengers to find an ergonomically good, relaxed seated position, making the rear seats superior even to many a larger, nominally more spacious car.
In order to achieve the three-litre fuel consumption goal, Audi's aerodynamics experts enhanced the properties of the A2's body still further. For example, to reduce drag at the front end, some of the air inlets in the front apron were sealed. This was made possible by the fact that the compact 1.2 litre three-cylinder engine requires only little cooling air.
In addition, special size 145/80 R 14 tyres of a new design not only reduce rolling resistance on the A2 1.2 TDI; they also bring aerodynamic advantages. They are narrower than the standard tyres on the other A2 models, and are aerodynamically optimized by additional fine grooves incorporated into their sidewalls. The wheel arches are narrower, to match the dimension of the tyres; this measure likewise reduces drag.
Even the aerodynamically effective underbody of the A2 has been given an additional aerodynamic undershield on the three-litre version, to deflect the airflow around points where turbulence could otherwise occur. The result is that the three-litre A2's underbody, one of the most aerodynamically problematic zones on a car, generates only little turbulence.
The Audi A2 1.2 TDI's record-breaking drag coefficient of cD = 0.25 extends Audi's lengthy tradition in this field: the 1982 version of the Audi 100 was a record-breaker in its day, achieving drag of cD = 0.30 - at that time a sensationally low value.
TDI - the pinnacle of economy
Another key aspect of the three-litre A2's low fuel consumption is its modern, ultra-efficient turbodiesel direct-injection engine. It, too, extends a long-standing tradition: for over ten years, Audi has repeatedly been redefining the standard for fuel economy - coupled always with outstanding performance and excellent engine refinement - through its developments in the field of TDI technology.
The three-cylinder Audi A2 with 1.4 litre engine, which made its début at the 1999 Frankfurt Motor Show, is already very economical. The engine that is 0.2 litres smaller treats fuel with even greater thrift. The 1.2 litre TDI power unit, developing 45 kW (61 bhp), is at the heart of Audi's concept of a three-litre car.
As with the body, the overriding priority during development of the engine was to keep its weight down. The three-cylinder TDI is the first direct-injection diesel engine to have a light-alloy cylinder head, but that is not all: the engine block, too, is made from aluminium. The weight saving here is around 16 kilograms compared with a conventional grey cast iron engine block. Weighing in at only 100 kilograms, the 1.2 litre TDI is one of the lightest passenger-car diesel engines in existence.
It is also the production engine with the highest thermodynamic efficiency in the car industry. The high-pressure direct fuel injection with pump-injector technology, in conjunction with the turbocharger's variable turbine geometry, supplies the finishing touches to the new TDI's outstanding fuel economy. This fuel delivery system assures agile response, rapid attainment of the optimum boost pressure and low-end torque across a broad engine speed range. The three pump-injector elements (one per cylinder) are located in the cylinder head and are driven directly by the camshaft. This technical principle does not need pressure lines, so extremely high injection pressures in excess of 2,000 bar are possible. High pressure results in even higher efficiency, thanks to ultra-fine atomization of the fuel, its optimum combustion and therefore low emissions and fuel consumption values.
The 1.2 litre TDI's peak torque of 140 Newton-metres is achieved at engine speeds of between 1,800 and 2,400 rpm. Almost 80 percent of the maximum propulsive power is already available just above idle speed, from 1,300 rpm upwards - an excellent basis for high agility and low fuel consumption.
With its low weight, the A2 1.2 TDI is easily able to handle the high torque that is typical of this engine type. The performance leaves nothing to be desired for everyday driving situations: it sprints from 0 to 100 km/h in 14.8 seconds, and touches a top speed of 168 km/h.
Intelligent power transmission
The automatically controlled manual gearbox renders a clutch pedal unnecessary on the A2 1.2 TDI. An intelligent electronic-hydraulic system takes charge of engaging and disengaging the clutch; the driver's left foot need do nothing.
The selector lever on the centre console can be moved in two separate gates: in position E in the right-hand gate, gears are changed automatically. The electronics always select the optimum shifting point on the basis of the driving situation and the amount of power required. In the left-hand gate, on the other hand, the driver can actively govern changes of gear by pressing the selector lever as desired.
A separate switch on the instrument panel in addition activates the fuel-saving "Eco" mode. This driving program means that the shifting points are reached earlier. By means of a start/stop function, the engine cuts out if the vehicle remains stationary for a few seconds and the driver is operating the brake. As soon as the brake pedal is released, the engine cuts in again - entirely automatically, and without any delay. If the driver releases the throttle while on the move, the electronics disengage the clutch and the car freewheels along, with the engine idling. When the driver presses the accelerator again, once the engine has reached the necessary speed the clutch is automatically engaged again. The clutch is likewise engaged when the brakes are applied, for instance when driving downhill, so that the engine's braking effect can be utilized.
The engine consequently only operates when its power is actually needed. As a result, in the "E" mode the A2 1.2 TDI uses precisely 2.99 litres of fuel per 100 kilometres (overall consumption acc. to 93/116/EC). Its 20-litre tank therefore permits a theoretical operating range of 669 kilometres.
Lightweight and safe
In addition to its low weight, the Audi Space Frame of the Audi A2 provides an ideal basis for optimum occupant protection: it is made from high-strength aluminium profiles and surrounds the driver and passenger like a protective cage which dissipates impact energy highly effectively.
The three-litre version is no exception in that it comes with the Audi A2's complete range of safety equipment: the driver, front-passenger and side airbags, the belt tensioners and belt force limiters are of course included as standard. The SIDEGUARD head airbag system is in addition available as an equipment option.
The Audi A2 1.2 TDI's active driving safety features also contribute towards this high standard. The latest generation of anti-lock brake system, in conjunction with electronic brake-force distribution (EBD) and the electronic stability program (ESP), defines the standard in this class.
Audi A2 1.2 TDI - a double saving
Drivers of the three-litre version of the Audi A2 are rewarded not only by exceptionally low fuel consumption: the A2 1.2 TDI complies with the EU III emission regulations throughout Europe; in Germany, it in addition meets the requirements of the even stricter D4 exhaust emission standard. This further reduces the cost of ownership.
In Germany, the vehicle tax saving for this officially recognized three-litre diesel car is DM 1,000, and a further DM 1,200 for complying with the D4 exhaust emission standard. This means that the 3-litre Audi A2 1.2 TDI is exempted from vehicle tax until these tax concessions expire on December 31, 2005.
Responsible through and through
Low fuel consumption and exhaust emissions are not the only things that make a car more environmentally acceptable. Its overall impact, from the raw materials consumed, through the car's operating life, to its ultimate recycling, is of decisive importance. In terms of the accumulated CO2 emissions throughout its product life, the amount of energy it consumes and also the total load of virtually all relevant environmental pollution, the 3-litre Audi A2 1.2 TDI is currently the most progressive production car in the world in its size and performance class.
Audi is the only manufacturer to possess such extensive experience in the development and series production of aluminium cars. The aluminium-bodied Audi A8 has been in production since 1994 at Audi's Neckarsulm plant, where the Audi A2, including the three-litre version, is to go into production at the end of 1999. Audi's Aluminium Centre is the "think-tank" of modern aluminium technology in automotive engineering.