Monday, September 7, 2009

Lotus Land

Interesting new tech from the lads at Lotus. It's a speculative project they've developed as a "range extender" for hybrids which would normally be a yawn but this is Lotus after all. It's a 1.2L three cylinder engine integrated with a high efficiency generator. It's a highly optimised rig as befits a company with the engineering credentials of Lotus. It's max output is a seeminly mild 47HP but it is developed at a mere 3500rpm which is extremely good for such a small un-blown unit with only one overhead cam and two valves per cylinder. This 47HP peak results in a generator output of 35 kilowatts which is plenty for cruising a small vehicle at probably 90mph or maybe better. This unit is intended to be used as the primary mover of a vehicle by directly powering the electric motors that move the wheels and not as part of a weighty complex parallel hybrid design such as the Prius. This architecture is actually similar to the Chevy Volt but without the need for a huge heavy insanely expensive lithium battery.

It's intended for use with a relatively small battery for acceleration assistance and energy recovery. This setup may well be ultimately more efficient than an equivalent small conventional powertrain because of the energy recovery capability which is one of the few advantages of hybrids. What is interesting here is the engine which is a very simple light "monoblock" design with crankcase, head, and exhaust manifold all in one casting. The whole integrated engine/generator unit only weighs 123lbs--absurdly light but that's Lotus. The design is specifically designed in all its particulars to run most efficiently at an rpm range that matches the output curve of the generator. This is the sort of approach lacking in almost all other efforts which have adapted off-the-shelf gear to do the job.

It certainly makes sense to go this way rather than the current style which has to be horribly complex, and heavy, to blend electric motor and direct engine power. I've wondered a lot whether the direct generation approach would have any advantage over a conventional direct drivetrain setup and with the use of a small battery for energy recovery it just might. If battery weight could be kept at a reasonable level, say a hundred pounds or so, an awful lot of mechanical weight could be eliminated, several hundred pounds at least. Such a setup would use the strengths of both ICE and electric tecnologies to their best effect which is an approach lacking in the current atmosphere of feckless gee-whiz excitement over pure electrics. As always optimization is the key and the engineers at Lotus are unmatched in this regard.

I can see this unit being used in a 2000lb vehicle that might well get 50mpg plus in town and 60-70 on the highway with a huge range capability--and no plug-in silliness. If wheel motors ever become commercially available efficiency should go up even more. A not inconsiderable bonus of wheel motors in terms of bad weather safety and handling would be the relatively simple, low cost, and light weight implementation of traction control combined with all-wheel-drive.

This setup would also address the major, and so far intractable, issue of pure electrics which is battery cost. A battery properly sized for use with the Lotus unit could be far smaller, lighter, and cheaper than even the smallest hybrid battery in use now. Even a lithium version should cost no more than a thousand dollars in such an application which is around one fifteenth of the cost of the battery in the upcoming Chevy Volt and one fifth of the battery used in the Prius. With a complete optimazation of the powertrain and the overall vehicle an extremely useful, delightfully agile, and small slippery coupe could approach the magical realm of 100 miles per gallon--for about half the price of a Volt.

What's disturbing is that the great-leap-forward techno-crack of pure electrics threatens to eclipse elegantly optimized "serial hybrid" designs which are wildly more practical, far cheaper to implement, and pose no threat to the electrical grid. See my August 18th post for further ruminations on this subject.


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