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IAV Showcases Hybrid Rear Axle

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. The system is on display at the SAE World Congress in Detroit.

The axle unit incorporates two 30kW motors (one for each wheel) with rated torque of 350 Nm (258 lb-ft) each. The prototype, based on the rear axle unit of the BMW X5, permits higher-cornering speeds by active torque vectoring to optimize driving safety and dynamics.

With the addition of a battery pack and control unit, it can also provide the basis for a parallel hybrid system. The integrated motors can recuperate the braking energy.

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.

IAV also has on display a urea SCR aftertreatment system targeted at US Tier 2 Bin 5 light duty diesel applications.



It's about time. For any of the FWD-based AWD vehicles, this setup would be more than sufficient to meet their AWD needs. There is simply no reason to run that transaxle down the middle of the vehicle. Combined with a GM BAS-like system for the rest of the powertrain, you'd probably get 80% of the hybrid benefit at half the cost, and still have an AWD vehicle.


On a side-note, I wonder how this differs from the setup in the rear of an RX400h? Just having the 2 motors that allow torque vectoring?


Doesn't the Toyota Highlander Hybrid already use such a system (they call it "4WD-i")?


I have thought of rear drives for CRV, RAV4 and other AWD small crossover SUVs. The FWD models could be fitted with this kind of drive at a fairly low cost. This is one way the car makers can start making hybrids without a lot of new design.


pictue this.. chevy impala with this in the rear with enough ultracaps to rocket it to 30-35 mph.(faster than a big block v8). use the 48v bas to keep the ultracaps ready to fire all the time. then downsize the ice to 2 liter I4.


I think this is a poor plan.
This won't allow for effective regenerative braking, as the front brakes get the VAST majority of braking load (~90%). It also won't take any significant load off of the brakes to increase thier lifespan.

Also, it can't be adjusted so that rear wheels take the load for regen, as this would make the vehicle incredibly unstable at speed.

Waste of money and effort w/o regen from front wheels.

John Ard

Or put it on the front end of a light truck (4cyl Tacoma, Colorado, etc) for a more efficient 4WD, or maybe a city-driving mode.

Mark A

I disagree with Ash, in that I think it would be an excellent design for the rear axle, in that it would generate significant regen power. Regenerative braking does not take the place of regular brakes. In this application, every time the "acceleration" stops, the regen application could take effect with brakes doing the final stopping.

I personally try to coast as much as I can, under idle, before using the brakes to stop. This axle would be perfect for my driving style and conditions. Of course not everyone is able to drive in my driving conditions to take advantage of this, fully.

But back to the article, it would be nice to see pictures and more specs for this axle.

Rafael Seidl

Ash -

putting the motors in the rear has the advantage of improving weight distribution, greater available space and not having to fit a transmission that incorporates both hybrid and transaxle functions.

Recuperative braking is anyhow limited mostly by the charge rate of the batteries, so at higher speeds the regular brakes have to engage in addition to recuperation.



I like your thinking. I think this could even appease the enthusiast. Rather than have that Impala with the 5.3 V8/4speed auto and rely solely on FWD, how about the new 3.6 V6/6speed auto with this in the rear? You'd have better F/R weight distribution, and I'd bet the performance off the line would be even better with the low-end torque of the electric motors. The extra space created by moving from the V8 to the V6 could theoretically make room for the BAS. Assuming that V6 could employ the Active Fuel Management and even DI, this setup could be very fuel efficient.


I see that as more of a complementary hybrid technology. Why do so many people dismiss advancements when they don't, by themselves, solve all of the world's problems?

Thomas Pedersen

Mark A,

most modern cars switch off the gas completely when coasting in gear (with the foot completely off the gas), resulting in zero gas consumption as opposed to the idle consumption when coasting in neutral.

I do the same as you do, except I stay in 5th gear where there's very little engine brake. Especially as you approach idle revs, but once you get there, the idle regulator kicks in, so disengage the clutch when that happens.


Under light deceleration couldn't the rear axel be responsible for braking the vehicle?


How about a 2L 4 cylinder diesel and this part in the rear ?
Use Ecaps for regen braking if required.


Thomas, you better check which gasoline engines you are using. The manufacturers I am familiar with ONLY shutoff injectors when certain criteria are met: Cylinder head temps ~ operating temps, TPS at 0%(0V), and rpm above a set amount. My car will turn off injectors above 2200rpm ONLY...from idle to 2000 rpm the injectors are running and there are more injection events at 2000rpm than there are at idle even if the amount of fuel squirted out is equivalent to idle fueling. Also, even at smallish throttle position opening settings you will get full rich running above a certain RPM (dumping the code on a few ECUs and looking at the fuel tables shows you this quite easily).

Mark A

Back to the axle, and away from the "idle"/shutoff tangent we are on, does anyone have any links to see this axle? Could it be retrofitted in any older cars, or is it just as a model for the new models? It would be nice if any front wheel drive vehicle could have this retrofitted. Imagine a $400 90's model Geo Metro with this axle. Could approach 70-80mpg if fitted properly.


This is bmw as such they have a larger car budget for the engine and trans then most car companies. aThe design is likely well outside the trans budget of most fords or gm cars ans as such entirely useless.
There is a solid reason many cars still use 4 speed trans.. they fit the cars alot,ent for the tranny.
These budgetsare abolute and utterly unyielding limits on what can go into a car.

Warren Heath

This is a great idea for BEV's and series HEV's. They should also make a version for the front axle. Get rid of the stupid differentials for EV's & HEV's without going the more expensive route of wheel motors. Get true all wheel drive and no differential & transmission energy loss, as well as better high speed turning and zero turning radius. I've often wondered why this has not been done before, as Electric Motors of 30 hp can be made less than the diameter of the differential, so there is no reason they can't be axle mounted.

Note that the combined torque of 700 Nm exceeds the 510 Nm maximum torque of the Mercedes-Benz V6 diesel, supposed to have the most torque in its class.

Used in a parallel hybrid, bad idea. That results in maximum inefficiency of battery charging, all battery energy has to go from the engine mostly running well below maximum efficiency, through the mechanical drivetrain, to the wheels, and back from the wheels to the Electric Motors. Why not just install the system in a series hybrid and maximize efficiency & performance?


I would kind of like something like this to convert my 2004 Toyota Sienna to a Hybrid. Replace the rear axle with the hybrid rear axle, use the well in the back of the van to store batteries or ultracaps (or both), and leverage the engine's always-on design to keep the batt/caps charged. Throw in some control electronics to manage acceleration between the ICE/electric motors, and voila!

How much?



Automatic transmission makes better use of fuel injection cut-off than manual, and without any efforts from driver. While coasting, signal from TPS initiates torque converter lock-up to relax, and engine RPM drops lower than corresponding vehicle speed, resulting in less engine braking, but inertia of rolling car keeps engine RPM from falling too low, thus prolonging zero fuel consumption coasting. On most cars I am familiar with AT allows the engine to spin without fuel down to about 1.5 idle RPM, and then seamlessly resumes fuel injection. It is quite easy to determine exact numbers for particular car: simple measurement of oxygen sensor voltage between ground and wire running form oxy sensor to ECU (or from diagnostic connector) by digital voltmeter will tell the picture. In regular closed loop mode voltage dances between 0.4 and 1.0 Volt, and when fuel injection stops it drops to zero.

And yes, engine should be heated up; once I managed to froze the engine to the point when it engaged warming mode when I was caught on deserted mountain road (no cell signal) with almost dry tank, and drove for a 30 miles in most economical mode: gentle acceleration to 50 mph, then coasting back to 30 on downhill.


In order to make the most from rear-wheel electric axle, gasoline engine should be at least micro-hybrid with engine stop on intersections, and preferably with AC electric drive.


The retrofit the minivan idea sounds good, but I am not sure it would have optimal performance. If you were to convert a Sienna, CRV or other vehicle, you would not have quite the mileage of say a Civic hybrid or Prius. It would be a good project for a school to work on though, just to see the results.


Would this work for off road all terrain driving - what would be the best spec for my lovely Range Rover because I know the Lexus SUV cannot go off-road (what are the reasons for this anyway?)

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