ZF is presenting its new all-wheel drive system: ECOnnect. Its automatic decoupling function minimizes the extra consumption associated with the operating principle of all-wheel drive vehicles. Fuel consumption can be reduced by up to five percent compared with conventional all-wheel drives. At the same time, vehicle dynamics and driving safety are substantially enhanced by distributing torque to the individual wheels, for example. Furthermore, the front-transverse architecture enables ECOnnect to be combined with ZF's new 9-speed automatic transmission (9HP).
To successfully position all-wheel drive cars with front-transverse drive on the market, the consumption in comparison with two-wheel drive (2WD) vehicles must be kept to a minimum. Currently, vehicles with classic, controllable all-wheel drive (AWD) do not have better fuel consumption than vehicles with permanent all-wheel drive: Even when the second axle is trailing, the entire driveline is moving, which causes churning and friction losses.
ZF has therefore developed two efficient all-wheel drive systems for front-transverse installation that literally shut down the extra consumption resulting from the all-wheel drive design. It relies on the fact that the all-wheel drive is unnecessary in the majority of day-to-day driving situations: For constant straight-ahead driving, powering all four wheels presents no advantages for vehicle dynamics or for handling. But as soon as the terrain or the driving mode changes, there are clear advantages to having two driven axles. All-wheel performance with simultaneously low fuel consumption thus requires strategy-based activation of the all-wheel drive that is imperceptible to the driver, within a few hundred milliseconds. This is the only way to provide the driver with all-wheel drive functionality at the right time, completely and highly efficiently.
Systematic decoupling reduces fuel consumption
All-wheel vehicles with front-transverse drive are excellently suited for ECOnnect, ZF's decouplable AWD system: In the front-operating 2WD, the entire all-wheel driveline comes to a standstill—from the angle drive to the propshaft and the rear axle drive.
The automatic decoupling takes place in front directly after the main transmission and in the rear axle drive by using a side shaft clutch. This multidisk clutch decouples both the directly connected and opposite side shaft. This process exploits the basic characteristic of the differential, which is able to coast at a high speed differential almost free of drag torque and noise as long as it is not under load. The systematic decoupling eliminates the drag losses, which increase fuel consumption, produced on the AWD components; the all-wheel driveline is completely separated. If a driving situation occurs that is favorable for AWD operation, the decoupling elements are closed instantly and imperceptibly to the driver so that all four wheels are in the flow of torque. The fitted multidisk clutch then also allows the input torque to be split between the front and rear axle as required, to ensure optimum all-wheel performance.
The weight-optimized design of the AWD system also has a fuel-saving effect: In all, this results in savings potential of up to five percent. ZF's efficient decouplable AWD system not only benefits the end customer by lowering fuel consumption, but also manufacturers by making it easier to adhere to the increasingly stringent legislation regarding CO₂ emissions being rolled out globally.
Increased agility and safety thanks to torque vectoring
In addition to the version with a multidisk clutch on the rear side shaft, ZF also offers the new ECOnnect AWD system in a variant with two clutches on the rear axle drive. The automatic decoupling takes place in this configuration via a clutch for the left and right wheel respectively.
In addition to the fuel savings through complete decoupling, this solution also has advantages for driving dynamics in particular: The two clutches at the rear axle enable a free transverse distribution of the input torque between the left and right rear wheels. Therefore, through the classic hang-on concept (demand-oriented distribution of torque between front and rear axles), it is also possible to use the effect of torque vectoring: This causes the vehicle's yaw moment to be actively influenced by individual control of each rear wheel. On a changing surface or on bends, traction and driving stability are therefore improved simultaneously.
With both variants of the automatically decouplable front-transverse all-wheel system, ZF shows that CO₂ reductions and improved all-wheel performance are not irreconcilable: The two demands can be united in a single intelligent concept.