Paradigm Shift in Thinking on Four-wheel Drives
Vehicles with four-wheel drives have lower fuel efficiency than models with two-wheel drives? Magna Powertrain shakes up this dogmatic way of thinking with an electric transfer case. It greatly increases fuel efficiency and lowers emissions, increasing driving dynamics of vehicles in the top-end segment.
Walter Sackl, Director Product Management, Global – Driveline Systems, Magna Powertrain
Issue: #December 2017
The significance of all-wheel drive (AWD) vehicles is growing, as SUVs are gaining in popularity, which is also one of the fastest growing vehicle segments. In addition, cars are becoming more powerful, and market researchers expect to see upticks in torque, acceleration, braking path, and many other parameters – some even substantial leaps – by the mid-2020s. This changes the requirements for AWDs. Once, traction on snow and ice had been the focus of improvements; now safety and driving dynamics are increasingly overtaking those past needs, enabling sports cars, for example, to benefit from greater traversal traction and faster cornering properties.
However, the AWD trend has one downside: Providing power to four wheels means more weight, more friction, lower fuel efficiency, and higher emissions. The first generation of powertrain systems for AWD vehicles consumed 14 percent more fuel in comparison to two-wheel drive models. Now advances in technology have trimmed this figure down to five percent. Manufacturers are now using disconnect systems, which interrupt the transmission of power to one axle when allwheel drive is not necessary, like when coasting in the city or highway driving. The Flex4 by Magna Powertrain is one example of a solution for actively disconnecting from the secondary axle.
Systems that enable a distribution of the torque between the front and rear axle are also now the standard in vehicles in the top-end segment. However, they do not cover all possibilities in torque distribution. For example, the rear axle is always engaged and the front axle only ever receives approximately 60 percent or less of the entire available torque, often quite less, in particular with faster acceleration. This fact is unsatisfactory when faced with increasing torques.
And all of these systems do not solve the fundamental problem: Compared to twowheel drive systems, there is still the issue of lower fuel efficiency, and there are limitations to a free distribution of the torque between the front and rear axle. Magna Powertrain is developing a novel concept that will finally decouple the driving dynamics–fuel efficiency incongruity. The concept improves the fuel efficiency of a four-wheel drive (4WD) vehicle, surpassing that of a two-wheel drive. The electric transfer case is the remarkable innovation that makes it possible.
Magna Powertrain’s Product Development Center in Lannach, Austria, is developing the transfer case and expects the concept to reach maturity by 2019. It is suitable for vehicle classes with higher performance needs and longitudinally mounted engine and rear-wheel drive. It is located in the P3 position, attached right onto the gearbox output itself. The electric transfer case consists of the following components, in addition to two reduction gears (planetary gear and chain drive):