Research shows clean fuel-use for ships off California coast extremely effective in reducing sulfur dioxide pollution
Study finds that combining fluids of highly contrasting viscosity in confined spaces can induce fast mixing

EVO Electric and MAHLE partnering on 2-cylinder range extender engine for EVs

MAHLE-EVO Range Extender (2)
The MAHLE-EVO range extender. Click to enlarge.

MAHLE has selected EVO Electric Ltd., a developer of electric drive solutions for the automotive sector (earlier post), as a partner for the development of its range extender engine for electric-drive vehicles.

The engine is a “clean sheet” design optimized for cost, weight, NVH, package size and installation flexibility. It is a 900cc, twin-cylinder, 4-stroke gasoline unit with an output of 30 kW at 4,000 rpm. An axial flux generator has been fully integrated within the crankcase to provide a compact modular solution. Fuel consumption of the engine is 240 g/kWh minimum, and it meets Euro 6 emission requirements.

Under the agreement, EVO Electric will be responsible for the design and manufacture of generators based on its advanced Axial Flux technology. MAHLE Powertrain will be responsible for engine design, development and manufacture plus the overall system integration and marketing of the concept to vehicle manufacturers and industry observers.

The engine is currently undergoing further development testing at the MAHLE Powertrain headquarters in Northampton, UK prior to being installed in a test vehicle in the coming months.

The MAHLE range extender was designed to optimize fuel efficiency across a range of driving conditions and to minimize cost, volume, weight, noise, vibration and harshness. The range extender engine has been sized to be suitable for a typical C-segment passenger car.

MAHLE analyzed fleet vehicle drive data, using a drive style analysis toolset it developed, to identify the typical daily usage pattern of such passenger cars. A detailed design study then led to the selection of the 900 cc twin cylinder 4-stroke gasoline engine layout and EVO Electric’s Axial Flux generator.

Unlike radial flux motors with a cylindrical rotor turning within a cylindrical stator, axial flux motors use a disc-like rotor sandwiched between two (or facing one) disc-like stator(s). Advantages to this type of motor design include higher torque density; better cooling due to higher contact area; high efficiency due to lower cooling losses; and better overload capacity.

A key feature of the engine is the oil system that enables the engine to be installed vertically or horizontally for increased package flexibility. The entire system (including generator) weighs 70 kg and has a power output of 30 kW, and is already being presented to the industry, including vehicle manufacturers. (Weight is 50 kg without the generator.)

EVO Electric is working with a number of automotive industry partners to bring its advanced Axial Flux motor/generator technology to market. In addition to the MAHLE collaboration, EVO now has confirmed orders and commitments with a number of customers including: Jaguar Land Rover, Lotus and Nissan Motor (as announced previously); two other global car manufacturers; two global bus and truck manufacturers; and three premium electric vehicle manufacturers.



Although NVH is an issue for 2-cyl engines, this appears better than a Wankel engine. The specific fuel consumption is close to that of a "full-size" 4-cylinder engine and you could never achieve this with a Wankel engine.


So that's 320 ml gasoline per kWh, or 11.8 kWh per US gallon.

Given 4 miles per kWh for a typical C-segment car, that's about 47 mpg US if used in range-extending mode.

Toyota's upcoming super-expansion engines will do much better (closer to 15 kWh per US gallon as generator).


It is a range extender, not a main engine, it does not have to be ultra efficient, it has to be small enough and cheap enough to get added to cars and trucks.

It would mean you could "range proof" cars like the Leaf and increase the market share of EVs without everyone having to design their own range extender.

If most of the driving is done on the battery, and most of the charging is done from the mains, the efficiency of the range extender is not critical - you just have to have one.


47mpg isn't bad especially if you're using electricity alone for 2/3 of your driving. PHEVs with a relatively small electric only range of ~10 miles would be low cost and go a long ways toward kicking our oil habit.

Neil Blanchard

At 30kW this genset should be able to extend the range of a car like the Leaf; powering it at highway speed and charge the battery in about 1 hour, correct? If that is right, then the gen set would turn off for about 2 hours or so.

So, the 47MPG applies for the 1 hour while the engine is running, but then the Leaf (in this example) would go back to getting over 100MPGe for the next 2 hours. Or maybe I am not correct?



An axial flux generator

That is a good design, very small, light and powerful.


We have always felt this is a better solution than all the charging stations that are going to be built.

This unit, with a 30kW output, has about twice the power output (and size, and weight, and cost) than is needed. Most battery systems will not handle 30kW of charge. A vast majority of range extending will need less than 10kWh of use, just enough to get home for overnight charging.

But this is definitely a step in the right direction.

Thomas Pedersen


The 30kW is probably based on cruising demand at 75-80 mph plus a little extra for charging for a B-C segment car. It is not intended for charging of a stationary vehicle.

Also, don't forget that best efficiency point is always at lower rpm than rated power, so best efficiency might be 15-20kW at 2800 rpm close to max torque (guessing).


Also a range extender vehicle must be efficient. For example, it has to compete against PHEVs under certain driving conditions. Since a series hybrid is less efficient than a parallel hybrid, it already starts with a handicap. Heavy batteries also give a weight penalty. MIT showed in a study a couple of years ago that a PHEV gives better overall WTW efficiency (electricity and gasoline) than an EREV. Significant improvement of the EREV concept would be necessary to compete. The improvement shown by Mahle is impressive but probably still not enough to equal a PHEV.

A 3-cylinder engine could be a compromise to reduce NVH issues at the cost of slightly higher fuel consumption (but still better than a Wankel engine).

Would you prefer a less efficient engine? If Mahle knows how to make an engine of this size efficient, we should give them credit for that and not try to advocate a less efficient solution.


I figured after the Volt was announced January 2007, we would see gensets being offered to the OEM. The Volt has 16 kWh worth of batteries for several reasons, one of them being the $7500 tax credit.

If the car only needs 8-12 kWh to do what needs to be done and the genset can keep them charged cleanly and quietly then you have what you need. I have thought that having 40 mile range under all electric was the wrong way to look at things in the first place. Make it 20 or 10 miles and use the genset.


The genset/drivetrain we need would be a two cylinder opposed diesel. It would be air-cooled and designed to run at the most efficient, constant speed.

It would have no mechanical connections to the drive wheels.


SJC: the added 6-8kWh capacity in the Volt is to ensure the warranty over 8 years. GM engineers went conservative in limiting SOC to slightly under 50% capacity. This excess capacity will drop in next gen EREVs making them lighter and lower cost.

47 MPG is about 25% improvement on 2011 Volt MPG and would bring EPA overall rating up around 110 MPGe. Very promising.


I said several reasons, warranty and tax credit constitute several.


Buyers should have the option to match the genset with their need:

1. Not necessarily the most efficient but ultra light (15 KW to 30 KW) genset to extend e-range on rare occasions and leave more room for extra batteries. This could be the best choice the small PHEVs.

2. A heavier, more robust, more powerful (30 KW to 60 KW) more efficient genset for PHEV used more often on longer trips. This could be the best choice for mid-size PHEVs.

3. A Volt style very heavy, more powerful (60 KW to 120 Kw) for those who expect the same performance from their PHEV than their current ICE unit. This could be the best choice for large PHEVs.

4. A monster, very powerful (120 KW to 240 KW) for those who need or think they need a 3+ ton PHEV.


I like the EV with optional genset. If an EV does it for you, then fine. If you need a genset, you buy that model. Lighter, stronger, safer EVs with the genset option could be real popular. Buy what you need, not just what they offer.


I favor an EREV genset designed for extreme thermodynamic efficiency, 0.5Kwhr of Capacitor for braking, acceleration and battery life extension, and 10-12Kwhr of battery for running off grid. Between the improved regenerative braking energy capture and the genset only running at optimal efficiency, I think you get 60-65mpg running on gasoline, and 140MPGe.

This would depend on the capacitor having some pretty smart programming to optimally condition power for the batteries, etc.


This is a sensible approach. Batteries alone won't get us out of gasoline for years. Use the newer graphene ultra capacitors (when they come out) to drive an electric motor we might have something. Any car that can do 20 to 40 miles all electric and at a flip of a switch kick this motor on and get the rest of the miles.. I guess thats everyones dream..
Wonder the cost/weight of this motor? Wonder if the 2 cylinder side by side is better?
Just wish there were kits that could retrofit older cars to reduce gas use. I dont think anyone is going to see gas getting a lot cheaper.

Mike Urseth

I'd like to see this as an optional "swap" setup like the battery swap stations. You could rent it when a long trip is in the offing. Return it and lose the weight.


The drop in idea sounds good, but you do not have a drop in fuel tank with any range, nor exhaust, nor cooling system. Connecting up all the air intake, exhaust and other components is not convenient.

Some people might be thinking just drop a Honda generator in there and you are done. Those are 3 kW devices, this is a 30 kW device, so fuel, cooling and exhaust all come into the picture.

When you use a genset, you need less batteries. 24 kWh may be the entry level for an EV, but 8 kWh may do the trick with a genset. Weight and cost are offset and the incremental additional battery pack idea comes back into focus.


This things has 34% efficiency, Toyota is doing 38% with there latest Prius, and above 40% for the next generation models.

If you want drop in why not go with a microturbine? Sure it would be less efficient at around 25-28%, but it will be lighter, won't need a cooling system, and could run on any thing from biodiesel, ethanol, gasoline, natural gas, hydrogen, etc, etc.


Well, it would be difficult - probably impossible - to achieve 40% efficiency in a piston engine of this size. Thus, a PHEV will always be more efficient than an EREV in charge sustaining mode. However, why not make the EREV as efficient as you can. Microturbine? Why? A piston engine can also run on biodiesel, ethanol, gasoline, natural gas, hydrogen, etc, etc… if you want and be more efficient. A Wankel engine is more efficient than a microturbine. If we strive for high efficiency, piston engines are the only (contemporary) options.


"SJC said:

The Volt has 16 kWh worth of batteries for several reasons, one of them being the $7500 tax credit."

Volt came first and then came the $7500 tax credit designed to support it.
GM chose the size to support the magical 40 miles of range and for longevity (15 years), SOC is limited to 65%.
Will the public buy a car that is limited to 80mph?


@ Peter XX,

Last I heard microturbines were hampered by being too expensive, too loud, and apparently the smaller the turbine the less efficient it is.


Herm is correct - Volt SOC is closer to 65% (85% max) with genset starting at 30%. As for sales:

"The latest cumulative U.S. sales totals for the plug-in duo, since launching in late 2010, has the Volt leading the pack with 2,029 units sold, while the Leaf comes in at 1,040." May 2011


It is sort of chicken and the egg. The Volt was announced January 2007 and I think the tax credit came later that year.

16 kWh of batteries is the amount required to get the full $7500 tax credit. There were probably many reasons for that battery size, it was locked in when they could get maximum credit.

There was a GM person quoted as saying they might use less batteries to bring the cost down, but that faded away when the tax credit came out.

The comments to this entry are closed.