TDI engines

The 2.5 TDI V6

Audi's 132 kW (180 bhp) 2.5 V6 turbocharged direct-injection diesel is further evidence of its expertise in TDI technology. This engine made its production début in November 1999 as a fitting source of power for Audi's top model, the A8 saloon, and was offered shortly afterwards in the A6 model line.

Audi's move in making the new 2.5 V6 available in the A4 Avant as the top TDI option is in response to the huge success of its high-performance turbocharged diesels in this model line. TDI drivers, who are already accustomed to the V6's typical combination of substantial torque and smooth, quiet running, will discover another new dimension of excellence in this engine.

The vigorous 132 kW (180 bhp) engine with four valves per cylinder, centrally located injectors, a turbocharger with electronically controlled variable turbine geometry (VTG) and an ultra-modern radial-piston distributor-type injection pump, represents the state of the art in TDI technology.

Engine torque is an ample 370 Nm between 1,500 rpm and 2,500 rpm, an ideal basis for excellent pulling power over a large road-speed range and powerful acceleration even from low engine speeds.

This engine is very similar to the 114 kW (155 bhp) V6 TDI, the capacity of which is also 2.5 liters and which is now also available for the A4 Avant. Its torque of 310 Nm will satisfy even the most demanding performance requirements.

The V6 TDI's response to accelerator pedal pressure, even at very low engine speeds, is also quite amazing. A substantial and immediately usable amount of torque is available even at only 1,000 rpm. The carefully optimized dynamic response characteristic now consigns the term "turbo lag" well and truly to the history books.

Performance on the road speaks for itself: it takes the 2.5 TDI quattro (132 kW) with 6-speed manual gearbox only 8.7 seconds to accelerate from a standstill to 100 km/h and continue briskly up to its maximum speed of 222 km/h. The manual-shift 114 kW version with front-wheel drive takes only marginally longer, at 9.6 seconds from 0 to 100 km/h. Its maximum speed is 219 km/h.

Fuel consumption, on the other hand, is extremely economical: the 132 kW A4 2.5 TDI quattro consumes a mere 7.8 liters of diesel (total figure according to 1999/100/EC) per 100 kilometers, the 114 kW version even less at 6.9 l/100 km. A single tank of fuel is thus sufficient for an operating range of up to 1000 kilometers. Another positive factor is that the Audi A4 TDI 2.5 V6 complies with the EU3 exhaust emission standards.

The 1.9 TDI with pump-injector technology

The new top-of-the-line 1.9-litre four-cylinder TDI is a further highlight in the A4 model line. Even those familiar with TDI engines find the power output of this ultra-modern engine most impressive: 96 kW (130 bhp) at 4,000 rpm.

Yet the torque of this high-tech-TDI is even more impressive: 285 Nm from the 5-speed version of the 1.9 even at 1,750 rpm. The 6-speed version has no less than 310 Nm at 1,900 rpm, a supreme figure for a four-cylinder engine.

The key technical feature of this new engine version is its high-pressure pump-injector fuel supply system, which currently achieves the highest operating pressures of any such system. The technological input is considerable: each cylinder has a separate pump-injector unit controlled by a solenoid valve.

An injection pressure of up to 2050 bar is possible: this is equivalent to the weight of a midsize car being supported on an area the size of a finger nail. Such a pressure permits unparalleled torque values, while further optimizing the already low fuel consumption.

The maximum speed and power output figures are equally impressive: the front-wheel-drive Audi A4 TDI 1.9 with manual gearbox accelerates from 0 to 100 km/h in 10.1 seconds and has a maximum speed of 204 km/h.

Conversely, the fuel consumption of 5.6 liters per 100 km (overall figure acc. to 93/116/EC) is as low as that of many a less powerful diesel engine. This means that the car has an operating range of around 1,250 kilometers on a single tank of fuel. Emissions from the new engine with pump-injection fuel supply are also gratifyingly low. This has earned it a place in the lowest vehicle tax bracket according to the EU3 standard.

Another version of the 1.9-litre inline four-cylinder engine with a power output of 74 kW (100 bhp) at 4,000 rpm is available. This engine reaches its maximum torque of 250 Nm at 1,900 rpm. This is part of the secret of the 5-speed manual-shift A4 Avant 1.9 TDI's inspiring performance: acceleration from 0 to 100 km/h in 12.5 seconds and a maximum speed of 191 km/h. Its economical fuel consumption of just 5.4 liters per 100 kilometers is another plus for the A4 Avant 1.9 TDI.

Stepless perfection: the multitronic

Audi is offering the multitronic, a continuously variable automatic transmission, for the first time in this vehicle category on the new A4 Avant. This transmission is the only one of its kind in the world. The revolutionary multitronic is available for all versions with front-wheel drive.

The multitronic can now transmit torques as high as 310 Nm. Even the most powerful petrol engine in the A4 series, the 3.0-litre V6 with 220 bhp and 300 Nm of torque, can be combined with multitronic.

With its multitronic Audi has developed a continuously variable transmission which avoids the previous drawbacks of this principle and exploits all its advantages by adopting optimum gearshift strategies. The big difference with multitronic is that, for the first time, the gain in convenience is not at the expense of dynamism or operating economy. Quite the opposite, in fact: most of the performance data for an A4 with multitronic are actually superior to an otherwise identical vehicle with 5-speed manual gearbox.

The differences compared with the conventional multi-stage automatic transmission with torque converter are even more impressive, as the latter - despite all the progress that has been made - is prone to transmission losses due to its fundamental concept. A further advantage of multitronic compared with even the most modern torque-converter transmissions is that the gearshifts are entirely jerk-free.

Another significant advantage shouldn't be forgotten either: the multitronic weighs around 15 kilograms less than conventional 5-speed automatic transmissions. The use of magnesium for its casing in particular saves an impressive eight kilograms.

One fundamental advantage of the "variator" in the multitronic is the high spread of ratios. This refers to the difference between the largest to the smallest transmission ratio - 1:2.1 to 1: 12.7. This spread of more than 1 to 6 is almost the ideal gearbox scenario. It permits dynamic, sports-style acceleration thanks to the use of lower ratios, but also fully exploits the engine's economy potential by using the highest ratio.

A further special feature is the ability of the electronics to emulate the functions of a manual gearbox. Audi has opted for six forward speeds, which can be selected by the driver with a single touch of the selector lever in the second gear-shift plane, or activated by pushing a button on the multifunction steering wheel (optional extra).

These six speeds are stored as fixed gear-shift programs. Depending on which gear the driver selects, the controller is supplied with the ratio as a set point, which it establishes at the variator and maintains. Even these manually prompted gearshifts take place with pleasing smoothness and without jerking, satisfying the desire for sports performance thanks to the smooth, jerk-free changes between them.

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