Is the Torsen Slip Differential the Key Technology in Audi’s Quattro System?

The Evolution and Innovation of Quattro

The origin of Quattro can be traced back to a forest in Finland, located within the Arctic Circle. During a test drive, Audi’s head of testing was driving a 75 hp Volkswagen Iltis 4WD off-road vehicle, following behind a convoy of front-wheel-drive cars based on the Audi 100, which had 200 horsepower. Due to the significant power difference, the Audi 100 easily outpaced the Volkswagen Iltis on straight roads. However, the situation reversed on bends. This interesting observation led them to conclude that the Volkswagen Iltis’ 4WD system was the reason for its superior performance on bends. They decided to transplant the 4WD system from the Volkswagen Iltis to Audi’s passenger cars. This happened in the year 1977.

However, things were not as simple as imagined. Although the Audi test car, which first showed the 4WD prototype to Volkswagen sales executives in January of the following year, was very ideal, Audi engineers still faced a tricky problem: using the traditional fixed front and rear axle connection structure caused the rear wheels to slip during turns. The standard solution was to use a cumbersome and expensive independent power distributor. However, Audi transmission designer Franz Tengler found an ideal solution: using a hollow shaft to transfer power to the center differential, and then using universal joints to transfer power to the rear wheels, while the hollow shaft was responsible for directing power to the front wheels. This was the first-generation Quattro.

In Italian, “Quattro” means “four.” Audi later established a subsidiary named quattro specifically to develop high-performance models. The Audi S line package, S series, RS series, and even the R8 that we see today are all developed by Audi’s quattro GmbH. As a tribute to rally cars based on Audi Quattro models, the company deliberately changed its name to lowercase “q.”

The Key Technology in Audi's Quattro System

The key technology of Quattro lies in its development of full-time four-wheel drive technology with the Torsen center differential as its core, making it a representative technology known for its rapid response, stability, and reliability.

Relying on the structural characteristics of the Torsen limited-slip differential, power is evenly distributed between the front and rear axles in a 50:50 ratio during straight-line driving, with the planetary gears inside the differential not rotating. When the car accelerates, the Torsen differential automatically allocates more power to the rear wheels due to increased traction, allowing for greater effective traction.

The Torsen differential is a worm gear planetary gear structure that operates purely mechanically, without the need for any electronic system intervention. Its basic principle is to utilize the one-way transmission characteristic of the worm gear, where motion can only be transmitted from the worm to the wheel, and reverse motion results in self-locking. This allows the Torsen differential to adjust front and rear torque distribution more promptly and reliably than electronically controlled central differential systems. Power can smoothly pass through the planetary gears to the front and rear output shafts, thereby driving the front and rear axles.

The power transmission characteristics of the worm gear are opposite to those of a conventional open differential’s straight-toothed planetary gears. The worm gear can automatically distribute power to the output shaft with greater resistance.

Conclusion

Quattro is not a purely mechanical four-wheel drive system. After seven generations of evolution, engineers added the Electronic Differential Lock (EDL) to the Torsen differential. EDL, short for Electronic Differential Lock, is a system that monitors the speed of all four wheels. When a wheel loses traction and starts spinning freely, the EDL applies braking force to that wheel independently using the ABS system. This allows torque to be transferred through the open differential to the other wheel that has traction, preventing slippage.

Is the Torsen Slip Differential the Key Technology in Audi’s Quattro System?

The Evolution and Innovation of Quattro

The Key Technology in Audi's Quattro System

Conclusion

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