ZF Introduces Intelligent Wheel Dynamics

TECHNOLOGY FOCUSZF Introduces Intelligent Wheel DynamicsFRANKFURT, GERMANY (Sept. 23, 2007) - In modern passenger cars, innovations to components and systems can increase safety, driving/riding comfort and driving dynamics. These properties can be further reinforced when multiple systems are used in designing control networks. Intelligent power distribution instead of braking intervention One example for such a network is the Intelligent Wheel Dynamics (IWD) concept by ZF Group, wherein active systems in the driveline, steering system, and chassis are networked and controlled in unison. Thus, an intelligent vehicle emerges that supports, rather than thwarts the driver. Critical driving situations can be efficiently handled, on-road as well as off-road. In this regard, networking also generates an increase in safety which, literally, does not have a braking effect in driving dynamics. The IWD networking approach even exceeds these basic networking principles because it also integrates engine and brake controls. Here, the effect of the IWD aims at reducing the number of braking interventions (such as usually effected with traditional stabilization systems). Thus, conflicting aims of autonomous individual systems are remedied. The vehicle becomes more comfortable, safer, and more dynamic - in parallel! With its networking approach, ZF further underscores its off-road vehicle expertise. In the case of such a drive, variable distribution of input torque across the entire driveline is enabled. Longitudinally, this distribution is effected via an intelligent Torque-on-Demand system and, most recently, also transversally via the newly developed ZF-Vector-Drive axle transmission.A holistic approach

The ZF Vector Drive rear axle transmission distributes power in a targeted manner instead of just braking, to make critical situations less terrifying.
Photo - ZF

The target of all active control systems is achieving optimum road contact for all tires, in any given driving situation. ZF has achieved this with its new Vector Drive rear axle transmission, which allows lateral distribution of input torque. The input torque is dosed by the transmission and individually distributed by means of torque vectoring among the wheels. The steering system pre-determines the wheel setting and the individual tire contact force is modified by the chassis, the damping, or the level-control system, as well as by the Active Roll Stabilization system.

But ZF even takes another step ahead: The company combines those control systems, which are utterly important for the tire force potential, in an intelligent network. With the IWD concept, the Torque Vectoring driveline is networked with the Active Steering System, the Electronic Damping System's active suspension components) and the Active Roll Stabilization (ARS) system.

The Torque Vectoring rear axle drive system distributes the drive torque individually to the rear axle wheels, generating a yaw moment around the vertical axis of the vehicle, which can be used both to improve agility and stabilize the vehicle, especially during cornering. The innovation provides better handling in critical situations, enabling it to be stabilized in the event of quick swerving maneuvers without having to brake. The steering system responds more directly - with less effort and fewer required corrections, thereby icreasing safety without restricting driving dynamics.

Examples of the dynamics afforded by Torque Vectoring include:

* When driving straight, the Torque Vectoring rear axle drive acts like an ordinary transmission with an open differential: The drive torque is distributed equally among the drive shafts of the wheels. The torque is only distributed individually among both drive shafts during cornering. It is controlled by the electromechanically actuated multi-disk brake of the superimposed axle drive.

* The Torque Vectoring axle drive also generates a wheel differential torque independently of the drive torque, i.e. also when cornering downhill without additional acceleration; in this case, in the bend the outer wheel receives more drive than the inner wheel. This is achieved by one superimposed axle drive in a planetary design on both sides of the axle drive, respectively.The system, which is based on a planetary design - unlike a high-ratio transmission design - is more efficient. The gears of the planetary gear set do not turn when driving straight on. Therefore, the system power losses are limited to oil shearing in the released multi-disk brake and the churning of the planetary gear set rotating without relative gear rotation.

* The new rear axle drive also features the familiar benefits of locking differentials, as the torque can be targeted to the wheel with the higher friction locking potential. Thus, drive wheel spin can be avoided, in particular when both wheels of the drive axle are on different road surfaces when starting off. This leads to improved vehicle propulsion; moreover, fewer and less intense brake interventions to reduce wheel spin are required. There is less wear on the brakes and also a positive effect on fuel consumption.

IWD almost completely solves the conflict of aims between agile driving behavior and a high level of driving stability. The result is added value for the driver. A higher safety reserve at the same level of dynamics is achieved, critical situations can be managed more confidently by the driver and stress can be kept in check.

(Source: ZF Group)