BMW i3 Electric Car: Motorcycle Engine Range-Extender For 250 Mile Range

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BMW i3 Coupe concept

BMW i3 Coupe concept

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If you're a fan of electric cars, there's a fair chance BMW's i3 urban electric car is one of the vehicles you're most looking forward to in 2013.

When it goes on sale in the fourth quarter of 2013, it's set to be one of the most advanced vehicles on the road--not least for its lightweight carbon-fiber reinforced plastic chassis.

BMW is also releasing further details on the range-extended option for the i3, allowing drivers just that little extra range for longer trips.

The company hinted a while back that the gasoline-aided version of the i3 would use a twin-cylinder motorcycle engine.

The tiny unit, expected to be an inline-twin of around 600cc, will have no mechanical connection to the wheels, and will be used to turn a generator, extending the car's range once the battery has reached a lower limit.

Automotive News reports the car's range is expected to be around 250 miles, including the 60-90 miles possible on the car's battery pack. It'll lie under the rear deck, in the same compartment as the car's electric drive motor.

If 250 miles doesn't sound like a lot, then that's still more than most owners are likely to need, according to BMW.

"I imagine many buyers will order the range extender to cure their range anxiety, discovering later they need it very seldom," said BMW R&D cheif Herbert Diess.

Drivers of the Chevrolet Volt, another range-extended electric vehicle, will no doubt agree--63 percent of miles traveled by Volt drivers are on electric power alone--despite an all-electric range around the 40-mile mark.

The BMW's range-extender is unlikely to be a straight carry-over from one of the company's motorcycles, however.

Due to strict targets for noise, vibration and harshness, it's likely that BMW will heavily modify the engine for its intended purpose, and optimize it for the constant speeds needed for optimum efficiency.

BMW hasn't yet revealed pricing for the i3 or range-extended i3, but both will appear on sale together at the end of 2013.


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Comments (19)
  1. A range extender used strictly as a generator (series hybrid) is simpler than the Volt series/parallel approach. Why does the Volt need the parallel configuration and the i3 doesn't? Is the i3 so light that acceleration isn't an issue when in range extended mode?

  2. It is NOT the power requirement. It is efficiency.

    You can NOT beat the efficiency from ICE to wheel directly by doing ICE to Generator to Battery to Electric motor to wheel... It only makes sense in some limited case where the "load" characteristic favors the second case.

    I think BMW is trading off efficiency in "extended range" mode for less complexity and "reduced cost and weight". This allows BMW to make the "extender" into an option since it doesn't have the mechanical linkage.

  3. Battery is not involved, it would go from engine to generator to motor (and also charge the battery at the same time).

  4. Well, for "reserve" power during the extended mode operation, it would have to be charging the battery and then release that power during acceleration when the extender can't keep up with the power requirement.

    Sure, it doesn't need to go through battery all the time. But for heavy loading or buffering, it would require it.

  5. Eric, while that's how the REx is set up in the Volt, this does not necessarily mean that BMW will follow the same model. Unless you had more information than the rest of us, I would not go as far as claiming that the battery will not be recharged. If memory serves, I have seen a claim otherwise in an older article, whether right or wrong, I don't know. Personally, if I had to speculate, and knew that a small engine will be selected, I would argue that using the battery as a buffer could be beneficial. Especially in urban driving, when the car is stopped in slow moving traffic or at red lights often.

  6. The answer is that customers are demanding. If they are driving a hybrid, PHEV, or EREV, they expect the performance to be transparent regardless of mode. So, for instance, when the battery charge on the Volt is depleted, the car will operate just fine on the ICE in all situations.

    A low-power range extender would have the capability to extend the range more efficiently than a larger powertrain, but there could be situations where the battery is depleted and the performance of the car significantly deteriorates. That might be acceptable to some buyers, but not to others. So far, manufacturers are unwilling to take the risk, particularly if that lack of performance could put the driver in harm's way.

  7. "when the battery charge on the Volt is depleted, the car will operate just fine on the ICE in all situations."

    Actually, that is NOT true. Unless you are in "Mountain mode", the ICE in the Volt can NOT/will NOT sustain Volt in high speed climbing on some of the mountain terrains. The peak output of the Volt's ICE is less than 80 HP and its main traction motor is 149hp.

    As a Volt owner with over 11,029 miles, I have reached two instances where the Volt's ICE in "normal" mode can NOT keep up with the power requirement.

    But for the most cases, it is fine. That is why Volt designed to have the "Mountain" mode to build up the buffer in the battery.

    I seriously doubt the typical BMW customers would put up with "degraded" performance.

  8. The Volt is in a different category. The i3 is mostly a city car and doesn't need highway speed efficiency which is best handled with a parallel system, hence the Volt hybrid approach.

  9. The i3 won't need to cross the Rocky Mountains in REx mode. I measured about 20 kW energy use when going 87 mph on flat terrain in the LEAF. This type of power is available from existing motorcycle engines. Pay attention to engine type 804: BMW Motorrad, F800 series 85 hp (63 kW) and New F650GS 71 hp (53 kW). I believe that the i3 REx will be a derivative of this design. I would not expect peak power, but it's probably safe to assume that the REx will get between 20 to 30 kW with the engines used in BMW motorcycles today, which should be adequate for freeway driving. It won't be a limp-mobile, as some fear. Since the battery won't be empty, there should be enough power to augment the REx when needed, on hill climbs for example.

  10. I have no interest in the generator, I even told my salesman specifically I do not want the generator when I put down my deposit.

  11. What is the price that your salesman quoted you? I would be interested if it is truly priced "competitively" and has the 250 miles "range"...

  12. My salesman doesn't have the price or specs yet.

  13. Are you in the UK or Europe, I'm trying to arrange to go to BMW Park Lane London to have a look at the car, don't know if i'll be able to afford one though!

  14. They speak of the 60-90 miles range, but no word about the battery pack or other meaningful details. This doesn't sound very serious.
    The I3 is far from reality. This car will never go into production. BMW won't build any production electric car in the next years ahead.
    The price for such a small electric BMW would be above 60K (30K for the car plus 30K for the brand). For that money you can buy the Tesla Model S.

  15. Most likely the reason they haven't released the specs is they know there is a lot riding on getting it right. Given all the articles I've read I'd expect the base price to come in somewhere between 40k to 50k. BMW says they expect to price the i3 just under the base 5-series which starts at $47,800. So maybe it'll be 45k to about 47.

  16. What I'd like to know is what kind of emission system they will put on it. Motorcycle engines put out more emissions than car engines. Great idea all in all.

  17. It will most likely be a derivative of the Rotax engine used in their F650 and F850 bikes. CARB 3-Star certified, this engine has a high power-to-weight ratio and reliability.

  18. just an extended range hybrid without the hybridization. nothing to see here

  19. Thanks for sharing more exciting news about the i3, Antony Ingram! It’s amazing that lightweight materials like CFRP are allowing electric cars to provide a range that is realistic for today’s drivers. New developments like the ability to “process model” long GLASS fiber in Moldflow™ - the precursor to similar processes now being researched by the DOE for carbon fiber injection molded plastics of the future – are allowing for quick and inexpensive carbon fiber mass production in the near future. This means even more lightweight structural parts and larger volume mass production models, without the longer cycle-times in production!

    For more on CFRP car parts, visit:

    Rob Krebs, Market Innovations, ACC

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