The IAV differential with integrated motors, prototype (left) and rendering (right). Click each to enlarge.

The unit supports three modes of operation. First, with the motors not activated, it behaves with the properties of an open differential. Torque is balanced between the driven shafts, permitting different speeds.

Click to enlarge.

Second, with the motors enabled but without energy storage, the differential can provide lateral torque vectoring—allocating torque on a wheel-specific basis. Here, one electric machine operates in the generator mode and, through the electrical power split, delivers the appropriate energy to the second machine working in the motor mode. By supporting the generator through the open differential, additional differential torque is built up through the mechanical power split.

This makes it possible to produce a vectoring torque that is approximately twice as high as would be permitted by the limiting torques of an electric machine. This means it is possible, independently of the torque applied to the axle, to achieve an asymmetrical lateral distribution of wheel torque, thereby responding to available grip and meeting the demands of the particular driving situation.

The improvement in traction thereby achieved, particularly in cases where road friction coefficients differ, results in better longitudinal dynamics. The influence on lateral dynamics improves cornering behavior and agility, and makes it possible to actively influence steering which, in turn, enhances vehicle safety.

Third, with the addition of a battery pack and control unit, the unit can also provide the basis for a parallel hybrid system by operating both electric machines in the motor or in the generator mode. Boosting and recuperation take place in direct wheel proximity without increasing the unsprung wheel mass.

As a further benefit to the hybrid application, there is no traction interrupt during shifting.

By topping up with “electric” torque during the traction-interrupting shift pauses occurring in a manual or automated transmission, it is possible to achieve the effect familiar from twin-clutch transmissions.

—IAV

According to IAV, initial simulations under the NEDC test cycle show “a significant potential” to save fuel, depending upon the vehicle, storage system and operating strategy.

The system could serve as the basis for an electric axle, or as the basis for a retrofit 4WD system.

IAV is in discussions with OEMs over a possible future for the axle, but as of now there is no committment. The axle unit has yet to be vehicle tested, although IAV has done a great deal of simulation work with it, not only in terms of longitudinal and lateral dynamics but also in the overall context of the powertrain.