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More on the IAV “Hybrid Rear Axle”—An Active Differential with Hybrid Functionality

An example of the IAV active differential integrated in the rear axle of a SUV application. Click to enlarge.

IAV Automotive Engineering has developed a rear-axle differential with integrated motors that can enable a parallel hybrid powertrain without affecting existing engine/transmission configurations. (Earlier post.)

The open differential gearbox incorporates two 30 kW motors with rated torque of 350 Nm (258 lb-ft) each. Each of the two electric machines is assigned directly to one of the driven shafts. Both machines can be operated independently of each other in the motor and generator mode, with the direct flow of electrical power producing an electromechanical superposition.

Iavaxle4 Iavaxle2
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.


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.


Mark A

At last we get to see specifics, from the earlier post, and this appears to be one of the better ideas, and clean designs, I have seen yet, for hybrid. It would be great to be able to retrofit it in older vehicles. I have an older Nissan truck, or a 2 wheel drive Jeep Liberty that I could see would be a great fit in. I wonder what the torque rating for this axle would be?

Bud Johns

Great technology, but retrofit? Come on, the price would be enormous. Let's see if manufacterers buy into this instead of developing thier own technolgy....Toyota doesn't need it but there are many who do.

fred dzlsabe

Isnt one of the "missions" to eliminate power-wasting ring&pinions?

Rafael Seidl

Fred -

no, conical gears are here to stay for RWD/AWD applications because they're actually a lot more efficient and much cheaper than a purely electrical transmission. It is possible to tinker with the fluid dynamics of the oil in the rear gear box but if you really want to save fuel, you buy a FWD vehicle with limited rated power (<250bhp) and lower curb weight.


I want this on my vehicle just for better standing start acceleration...the mild regen and better front to rear balance would be added bonuses.

Winter traction would be better as well.

Kirk Ellis

As a retro-fit, this seems less promising than what PML Flightlink did with the Cooper Mini QED.

Using wheelmotors means you could retrofit to any 2wd vehicle.

Using an axle as shown here means you are limited to fwd vehicles that were designed to have an awd option. Otherwise there simply isn't space in the unibody design to put a rear axle.

James White

UQM integrated motor and differential called the INTETS does everything this does and more.


It has 1700 N-m torque, weighs less and is smaller.

German Engineer

@ James White: Have you heard about Torque Vectoring?

Please read carefully...


I really like this kind of method. I hope more companies do these designs and prove them out. This would be great for traction and handling without all the large and long term redesign of the engine and transmission.


It isn't too difficult to retrofit any FWD vehicle for RWD...AWD is a bit more difficult except this system makes it much easier.

Cut the rear trunk floor pan and reweld it higher to allow for the differential mounting. You can use the stock fuel tank in most cases as you won't have a central drive shaft to get power from up front. Have new rear suspension components to allow rear hubs & axles.

In wheel motors may be easier, but the ruggedness requirements versus a differential mounted motor would mean that they are definitely more expensive. Suspension responsiveness goes down a bit as well with wheel mounted motors vs. differential mounted.


I have thought about taking a RAV4 or other AWD crossover and remove the drive shaft to the rear and put an electric motor on the back. However, it looked like the rear drive was hydraulic, to allow the full time AWD function.

Peter Harper

Fascinating concept. I am new to the electric scene but learning, this seem,s like a good idea, keep me posted.

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