The new Sport Differential in the Audi S4 - Reflection of the gearbox realization of a torque-vectoring-system for the audi quattro

摘要

The new S4 offers lower fuel consumption combined with enhanced vehicle dynamics compared to its predecessor model. The foundation of the new model's superior vehicle dynamics is the new sport differential in the quattro drive train. The sport differential is an entirely new design of torque-vectoring gearbox capable of delivering asymmetric wheel torques on the rear axle in any driving situation (such as in trailing throttle conditions or when coasting). This system is mechanically realised by adding an overdrive unit with two gear stages on the left and right respectively of the classic rear axle differential, configured for a maximum speed difference between the input (differential housing) and output (wheel drive shaft) of around 10 percent. An electrohydraulic actuator operates a multi-plate clutch running in the oil sump which interconnects the power-transmitting components. When the clutch closes, the drive wheel is accelerated by the overdrive unit and receives an additional driving torque. This torque component is held back from the 50/50 differential split by being tapped via the differential housing and so effects a higher wheel torque on one side. Particular attention was paid to attaining low locking and drag torques, high efficiency, high dynamics and a modular design entailing minimal package impact. The sport differential greatly enhances agility and traction. It prevents understeer on fast cornering, makes steering response much more direct and precise, and stabilises the vehicle in power off situations. As well as delivering much enhanced driving pleasure, higher lateral acceleration can be achieved on cornering and the steering effort required by the driver is significantly reduced. The system does not merely take effect at the stability limit, but is also supporting within the normal customer speed range.