TDI - the pinnacle of economy
Another key aspect of the three-litre A2's low fuel consumption is its modern, ultra-efficient direct-injection turbodiesel 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.
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: it also has an aluminium engine block. The weight saving here is around 16 kilograms compared with a conventional grey cast iron block. Weighing just 100 kilograms, the 1.2-litre TDI is one of the lightest passenger-car diesel engines in existence.
It is also the motor industry's most thermodynamically efficient production engine. A high-pressure direct fuel injection system with pump-injector technology, in conjunction with the turbocharger's variable turbine geometry, makes the decisive contribution to the new TDI's fuel economy. This guarantees an 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 of up to 2050 bar are possible. High pressure results in even higher efficiency, thanks to ultra-fine atomisation of the fuel, its optimum combustion and therefore low emissions and fuel consumption values.
The 1.2-litre TDI's peak torque of 140 Nm is produced at between 1800 and 2400 rpm. Almost 80 percent of the maximum propulsive power is available at just above idle speed, from 1300 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 car's performance leaves nothing to be desired in everyday driving situations: it sprints from 0 to 100 km/h in 14.9 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 electro-hydraulic system takes charge of engaging and disengaging the clutch; no help is needed from the driver's left foot.
There are three gearshift modes to choose from: manual gear selection by tiptronic and two modes in which gear changes are fully automatic - the conventional mode and an "Eco" mode.
The selector lever on the centre console can be moved in two separate gates: in the left-hand gate the driver can actively govern changes of gear by tapping the selector lever as desired. In position E to the right, on the other hand, gears are changed automatically. The electronics always select the optimum shifting points on the basis of the driving situation and the amount of power required.
The "Eco" mode activates a consumption-optimised gearshift program and a start/stop function at a switch on the centre console. The latter cuts the engine if the vehicle is stationary for more than four seconds with the brakes on. As soon as the brake pedal is released, the engine cuts in again fully automatically and instantly.
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, the clutch is automatically engaged again once the engine has reached the necessary speed. The clutch is also engaged when the brakes are applied, for instance when driving downhill, so that the engine's braking effect can be utilised.
The engine consequently only operates when its power is actually needed. As a result, in the "Eco" mode the A2 1.2 TDI uses less than three litres of diesel per 100 kilometres (overall consumption to 1999/100/EC). A theoretical cruising range of over 700 kilometres is thus possible with the 21-litre tank.