Ładownie danych, proszę czekać.


25 years quattro - Technology
Applying the brakes to all four wheels on a car is old hat in automotive technology. Applying the power of the engine to both axles, on the other hand, was for many years not regarded as the ultimate wisdom and therefore remained a technical concept reserved to offroaders and trucks for quite some time. In other words, this technology was reserved to vehicles required to do their job under extreme driving conditions.

This is quite surprising, considering that the advantages of all-wheel drive are at least as significant for the driver of a passenger car. The only thing needed to really start a significant development, therefore, was a kind of "wow" experience. And precisely this experience became reality on a winter drive through icy Finland, pitching the upcoming 170 bhp Audi 200 with front-wheel drive against all its less powerful models in the range and the Iltis, a 75 bhp, long-legged offroader. Because despite its inferior power, the Iltis was easily able in bends to make up for its lower speed on straights, quickly catching up with the other cars and, indeed, usually leaving them behind on winding, serpentine roads and tracks.

So it did not take long for everybody to realise that only permanent all-wheel drive was able to get superior power and performance on to the road without problems under all conceivable driving conditions. And reaching engine output of 170 bhp, the upcoming Audi 200 was approaching the limits of conventional front-wheel drive. Indeed, engineers back then believed that 200 bhp was the absolute limit for the car's joints and steering. And this was not enough to challenge the two leaders in the luxury segment.

The decision was therefore taken at a very early point in time in developing the Audi quattro: four-wheel drive it had to be, but permanent four-wheel drive. The option to feed power to one of the car's axles on demand was quickly rejected for several reasons, in particular because a variable system offers benefits only on rough terrain and on snowbound surfaces.

On a dry road, by contrast, variable four-wheel drive usually means disadvantages: Due to the absence of an intermediate differential, the entire chassis and suspension would be subject to unpleasant tension in bends and when manoeuvring. And this, in practice, would mean excessive tyre wear as well as extra fuel consumption, with all drive components constantly remaining in operation in this case, even when only one axle is actually conveying engine power.

A further drawback is that the chassis and suspension cannot be aligned and configured in the same way and with the same standard for both conceivable drive variants, the car's handling and driving behaviour changing every time four-wheel drive is activated or deactivated.

With front-wheel drive looking back at a tradition of more than 70 years with Audi, the Company's engineers obviously had some essential points in mind right from the start. Compared with standard drive - that is the engine at the front, the drive wheels at the rear - front-wheel drive offers a number of fundamental benefits acknowledged by the car industry worldwide and honoured by customers the world over for many years. Indeed, back in the early '80s the German Motor Vehicle Registration Office in the city of Flensburg for the first time registered more cars with front-wheel drive than with standard drive.

Enhancing the driving safety of the front-wheel drive system and conveying this extra safety to the even more powerful cars with additional qualities was therefore the essential development automatically leading to permanent all-wheel drive.

At the same time the existing configuration of Audi's models with the engine fitted lengthwise offered ideal conditions for all-wheel-drive technology, avoiding the need for an additional transfer box. The only modification required was to upgrade the manual gearbox by adding an additional differential and providing a driveshaft leading to the rear axle. In practice, this meant fewer components, leading to lower weight and lower frictional losses.

The use of three differentials provided precisely the perfection Audi sought to achieve from the start with its fast-running all-wheel drive allowing dynamic motoring in bends and preventing the chassis tension typically occurring in an offroader: precisely the right qualities are ensured by the front axle differential, an intermediate differential with locking action integrated in the transmission, and the rear axle differential likewise featuring a differential lock. The intermediate differential plays the main role in the quattro concept by ensuring the right kind of motoring comfort and smoothness expected of an upmarket saloon.

Audi's transmission engineer Franz Tengler, a member of Hans Nedvidek's technical team, subsequently invented and built the hollow shaft for the flawless interaction of parts within the most compact spaces and at the lowest conceivable weight: the hollow shaft is a 26.5 cm long connecting shaft serving to smoothen the direct flow of power to the rear axle. A heavy converter transmission was therefore no longer required thanks to the particular function of this hollow shaft, and all technical concerns regarding integrated operation of the rear axle soon became null and void. In this very first quattro concept, engine power of 200 bhp was distributed equally to the two axles.

Comparing the various characteristics of driving dynamics, this gives the quattro driver a number of advantages over rear-wheel and front-wheel drive alike: Whenever drive energy is distributed equally to all four wheels, the wheels and the car itself are able to build up more side power keeping the car on track. This also means that the driver can take bends much more quickly and enjoy superior safety reserves in the process. And should the driver ever misjudge the radius of a bend, quattro will provide important help in correcting the position and behaviour of the car, supporting the driver in rectifying his mistake by way of its docile, forgiving reaction.

The next stage of quattro drive reached the customer in autumn 1986: the self-locking Torsen centre differential operates mechanically, splitting up drive power under ideal conditions at a 50:50 ratio to both axles.

Whenever there is a difference in speed between the two axles on account of external conditions, the Torsen differential automatically and with virtually no distortion feeds more power to the axle able to convey higher forces, in the process allowing up to 75 per cent of engine power to go to one axle alone.

Two years later, the quattro system was significantly upgraded once again through the market launch of the Audi V8 featuring Audi's EDS electronic differential lock. This sophisticated system automatically prevents the wheels from spinning and guides excess power to the wheels for even more traction. Power is conveyed consistently to the wheels as long as the driver keeps his foot on the gas pedal.

This was also the first model to see a combination of quattro drive and an automatic transmission: For the first time, quattro drive came with two integrated locks - an electronically controlled, hydraulically operated multiple-plate lock in the intermediate differential and a self-locking Torsen differential on the rear axle.

In 1994, finally, the Torsen differential was also introduced in the manual gearbox, open differentials controlling the differences in rotation speed with the help of EDS acting on the car's axles.

An ideal feature on a car featuring its engine fitted crosswise was the introduction of the electronically controlled, hydraulic multiple-plate clutch serving as a longitudinal lock on the Audi A3 and the Audi TT. This system is commonly referred as the Haldex clutch.

In their all-out initiative, Audi's engineers seek to perfect the incomparable functionality of Audi quattro drive through the use of appropriate differentials and locks, in the process integrating the most sophisticated electronic control systems. And one thing is for sure: the future of this outstanding drive technology which started 25 years ago has only just begun.

Poprzedni: quattro in Motorsport
Czytaj dalej: Marketing and Markets

Lista artykułów