The Quattro permanent all-wheel drive system has been one of the central components of Audi’s success since it debuted in the Audi Quattro in 1980. The technology has obviously come a long way since then as it continues to usher in several trailblazing evolutions. Audi replaced the manual-locking centre differential of the first generation Quattro with the Torsen differential in 1986. And in 2005, came the planetary drive that offered asymmetrical, dynamic distribution of the power.
One of many such revolutionary developments of the permanent all-wheel drive system is the crown gear differential. This stage of evolution of Audi’s permanent all-wheel drive system for longitudinal front-mounted engines, i.e. Quattro drive with crown gear differential and torque vectoring, debuted three decades after Quattro’s premiere at the 1980 International Geneva Motor Show.
Inside the centre differential are two crown gears; the rear crown gear drives the prop shaft to the rear-axle differential while the front crown gear drives the output shaft to the front-axle differential. The crown gears are connected with four rotatable pinion gears. Positioned at right angles to one another, they are driven by the differential’s housing – the transmission output shaft. During standard driving conditions, the two crown gears rotate at the same speed as the housing. Their unusual geometry brings about a purposely disproportionate leveraging: 60 per cent of the engine torque is directed to the rear axle and 40 per cent to the front. However, if a shift in torque occurs due to a loss of grip at one axle, different speeds and axial forces develop within the differential and the adjacent plate packages are forced together. The consequent self-locking effect channels most of the torque to the axle with the better traction. And in the opposite sequence of events, i.e. if the rear axle experiences decreased grip, the same happens in reverse, with up to 70 per cent of the torque redirected to the front axle.
With such a wide gamut of torque distribution, the crown gear differential enables unprecedented traction. It ensures constant, steady, and almost immediate redistribution of forces and torques. Furthermore, the system’s mechanical operating principle assures maximum efficiency and prompt responsiveness. Audi combines the crown gear differential with an intelligent brake management software system a.k.a. torque vectoring that can act on each of the four wheels individually. This system makes cornering even more exact and spirited. How does it achieve that? While taking on corners at a high speed, the software uses the driver’s steering input and the fitting acceleration to compute the ideal distribution of propulsive power between all four wheels. And if it observes that the wheels on the inside of the curve, which have a decreased load, are about to enter a slide, it brakes the concerned wheels ever so slightly.
And if you are wondering, the next step in the evolution of the Quattro drive is the electrified Quattro a.k.a. the e-tron Quattro, which promises the combination of efficiency and driving pleasure typical to Audi.
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