Range-Extending Engines For EV Makers Driving Innovation

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Although Nissan claims production of the new Leaf all-EV car has been sold out for 2011 already, a recent survey by Accenture covered in a car tech blog called cnet.com found that among the key 34- to 55-year-old buying segment, anxiety over the range of all-EV cars is the main obstacle to higher sales. The blog reported that if they had to choose between a plug-in hybrid or a pure electric vehicle, 71 percent of the responders favored the more conservative plug-in hybrid vehicle, and only 29 percent would prefer an all-electric car. Range anxiety, limited charging infrastructure, and convenience of the dual-propulsion power train were cited as the main preference for hybrid cars, even though the average driving range for survey participants was only 32 miles per day. Respondents were looking for an average EV range of 271 miles on a single charge, according to Accenture’s survey data.

So while there is room for all shapes, sizes and approaches to the clean-tech car market, the mainstream is likely to be dominated by those manufacturers that are to supplement the all-electric component of their products’ propulsion with a range extending supplementary power source in some way, suggesting that GM’s Volt at least has the concept right, whether you like the execution or not.

Interestingly, this opens up the supply market for externally designed and produced range-extender internal combustion engines, designed to run within a narrow yet highly efficient range to provide electric current to the batteries. The motors are designed to be separate from the drive train of the automobile and hence can be configured in any way the OEM car maker desires. The engineer magazine recently ran an article focused on the UK’s Lotus, which has just brought to market a 1.3-liter three-cylinder motor running at speeds from 1,500 to 3,500 rpm with a simple, low-cost, reliable 2 valves per cylinder design. Lotus intends to offer the motor in two power ratings, 35 kW and a supercharged 50 kW, both able to run on methanol, ethanol or gasoline. Range extenders of this type are said by Lotus to enable an EV with just a 30-35 mile range to achieve up to 350 miles on par with regular petrol engine cars. By supplying the range extender as a standalone component, all kinds of assemblers can get into the EV auto market; economies of scale will still count, but while the market is still in its infancy, even the global auto makers don’t have much of a scale advantage yet — sales are just not up there with gasoline engine models.

The choice of two power options is the result of feedback from major OEM car-makers. At the luxury-car end of the market, OEM’s have said it is not acceptable to have their EV models restricted to, say, 50 mph when running on a charge-sustaining mode; their clients will expect a minimum 80 mph capability, particularly in Europe where German drivers have no speed limits on autobahns. Traveling at 50 mph in a small car on a German autobahn is particularly unnerving when passing traffic can be traveling well over 100 mph.

Until such time as inductive charging is built into urban streets, allowing EVs to charge while they drive, some form of additional power source is likely to be required to overcome range anxiety. Although Lotus appears to have a viable product offering, the idea has far to run and it will be intriguing to see how compact, powerful and efficient these little range-extending motors can become it can only benefit engine design and technology.

–Stuart Burns

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