Where once they were the preserve of agricultural and all-terrain vehicles only, all-wheel-drive (AWD) transmission systems are now becoming common on upper segment family cars. Apart from the obvious advantages in slippery conditions, one of the motivations for the wider adoption of AWD is the ability to influence the driving dynamics of the vehicle in positive ways. Often, the stated goal of luxury and executive car makers is to adopt AWD in order to make a large vehicle more nimble and to mimic the driving experience found in smaller cars while maintaining luxury and comfort. This article presents a novel approach to the control of modern torque-vectoring differentials based on the concept of beta-angle minimization. Three case studies include two variants of a base case model; with three open differentials, a 70/30-30/70 switchable centre differential with open front and rear and a fully left-to-right vectoring front and rear differential capable of any ratio of torque distribution (the centre differential is left open). All three are examined as they progress through an ISO double-lane change manoeuvre. Beta-angle control was chosen because one attribute of a nimble car is its ability to accelerate through a double-lane change manoeuvre without excessive magnitude or oscillation (so-called fish-tailing) in vehicle beta-angle. Each increase in the complexity of torque vectoring demonstrated a significant reduction in the magnitude of beta-angle witnessed during the manoeuvre. As torque vectoring can also be employed to enhance yaw dynamics, the simulations were performed in such a manner as to produce nearly identical path between the three models; this allowed the direct affect on beta-angle to be understood without the added complexity of considering active yaw control influences. The results have shown that the more complex torque-vectoring differentials can produce a significant improvement in a perceived vehicle's agility and nimbleness. Peak beta-angles were reduced to around 40% of the base case simulations, and fewer high-frequency steer inputs were required to maintain the desired path. In summary, this research shows a method of applying modern advanced transmissions to small executive passenger car to provide the driver with a more enjoyable ride and feel to the vehicle. It has also been shown that by adjusting the control of the transmission, the vehicle dynamics can be altered and could potentially be tuned to the driver's style or mood in real time.
Study of torque vectoring for all-wheel-drive vehicles
Untersuchung von Drehmoment-Vektorumlenkung für Allradantriebsfahrzeuge
2006
8 Seiten, 5 Bilder, 7 Quellen
Conference paper
English
Study of torque vectoring for all-wheel-drive vehicles
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