See-thru Illusration of Chevy Volt Electric Hybrid
Illustration shows current layout of 1-liter, 3-cylinder engine that drives onboard generator to power the Chevy Volt electric plug-in hybrid. The author believes the design can be improved by someday adapting surge power technology under development for Formula One racing.

Grading Detriot

EV World's European motor racing correspondent grades GM and Ford's first attempts at electric plug-in hybrids.

By Chris Ellis

Just before the Detroit show, Ford announced the Airstream hybrid concept, perhaps in an attempt to steal some of the media attention away from GM's Volt, because the Airstream won't actually appear until the Washington DC auto show on January 23. If so, the move failed, because the Chevrolet Voltis a much more credible hybrid concept, and probably rates a B+, if not an A.

The Volt is certainly on course for an A with its downsized (brutally, by American standards) 1.0 liter E85 engine. From the announcement, it appears the engine may be one of the Biopower series of turbocharged flexible fuel engines with variable boost, which it would need to be in a viable production car, to get maximum fuel efficiency out of both gasoline and E85 or any mix in between. The announcement indicates a peak engine speed of only 3,200 rpm, which limits its peak power, and it is coupled to a generator rated at 53kW, which will presumably also serve as the starter motor for the engine.

When the Volt is on an autobahn or freeway at a steady 70 to 80 mph, well into a long journey, all of the net energy must be coming from the engine and reaching the wheels via the electric motor, which has a continuous maximum output of only 40kW. At this stage, the battery will be functioning as part of a surge power unit, and will be in charge-sustaining mode, with a low SOC. The peak output of the electric motor is 120kW, but the continuous rating is only 53bhp. The only way power can reach the road is through the electric motor, because it's a series hybrid. So the electric motor determines the car's performance, if the generator's continuous rating is adequate for cruising and hill climbing. 0 to to 60 mph in 8.6 seconds is OK, but is 53 bhp from the electric motor enough for a long incline? We can't tell, because the Volt's curb weight is missing from its spec sheet. So it's probably not as light as GM would like us to think. 180kg (398 lb) of battery can't help.

There is no doubt that a series hybrid can at least match a parallel hybrid's fuel consumption in city traffic, but Bob Lutz makes the promise that the Volt should be able to run almost all short and medium length trips on battery power alone. So the engine will normally only be used on long, mainly freeway, trips where a parallel hybrid would generally be more fuel efficient. Of course, by going series, no conventional transmission is required, unlike a parallel hybrid. However, given the objective that all the city activity should be with the engine off, only a very basic, low cost, automatic transmission is required, which GM is selling in hundreds of thousands already. Because this small GM transmission is an automated version of a manual transmission which GM makes in millions, it is very low cost and also very efficient, particularly when cruising, with lower losses than just the generator, leave alone the rest of the system, and it is much less expensive. GM will know very accurately what the efficiency cost is (in terms of mpg lost) between supplying energy to the wheels via a generator, a controller and a motor, and via the AMT at a steady 80 mph, but my guess is that they might be pleased to see a penalty of no more than 5 mpg.

Let's check out an alternative. Let's call it the Volterra, after the ancient Tuscan city, or 'Volt brought down to earth', if it amuses you. The engine remains almost the same, except that it is now allowed to rev to over 6,000 rpm when necessary, yielding peak power of 75kW (100hp) running on E85. The engine is also equipped with a small integrated starter/alternator of about 2kW. The transmission is a version of GM's small AMT. The novelty is that this version of the power unit is small enough to be located under the trunk floor, and it drives the rear wheels when required. Amongst several advantages the most important is a significant reduction in aerodynamic drag, resulting from a sleeker shape with lower hood and roof lines (think Boxster) and a totally smooth underside (look under a Prius for how NOT to do it).

In the city, normally only the front wheels will be driven, by a surge power unit derived from Formula One. In two years time, GM (and anyone else) should be able to buy complete surge power units for their concept cars that weigh less than 40kg (100 lb). Of course, at this stage the prices will be phenomenal, but much less expensive than trying to develop your own - a bit like today's advanced batteries. These racing surge power units will be obliged to use designs and materials that can be developed into road units, and by the time GM can get hold of commercially viable plug-in batteries, prices of advanced surge power units will have reached sensible levels. Let's assume a production surge power unit for a road car the size of the Volta might be rated at 100kW.

Because the surge power unit will take care of the surges of braking and acceleration, the battery can lead a much more sheltered life, probably needing to supply no more than 20kW in any normal urban journey. Consequently, the battery's 'companions' will be a simple 20kW motor (no generation required) and its equally simple, low-cost controller.

With the engine off, the battery and surge power unit in the Volterra can provide a total of 120kW at the front wheels. With the engine running, up to another 75kW can be added through the rear wheels, giving a four-wheel-drive total of 195kW, or over 260bhp, which should deliver adequate performance for a car with only a one liter engine.

To achieve the same engine-off range, the battery can be smaller, lighter and less expensive because the specialized surge power unit will handle the surges of energy in urban traffic more efficiently than any system based on batteries. Battery-based surge power units, such as those in the Toyota Prius and Ford Escape Hybrid require four energy transformations in a full regenerative cycle, each of which causes losses which serially compound to give a typical figure of only 35% efficiency. We can expect the boys and girls of Formula One to lift that figure to well over 60%, which will have a sensational impact on urban fuel consumption. And the power of the new units, starting at 80bhp in 2009 with upward exposure later, will make 'brutal downsizing' a practical possibility, leading to further gains in fuel economy on the highway. Bear in mind that the most powerful hybrid car you can currently buy adds only 49bhp to the engine's power. 'Paradigm shift' is an over-used and over-hyped term, but this should be a significant one, for a change.

If Larry Burns is right, and fuel cell 'engines' (according to Ballard) eventually take over, then the configuration above requires no fundamental change other than the obvious replacement of the IC engine by a fuel cell, etc, and the addition of an electric motor to drive the rear wheels and provide freeway levels of power. Clearly, GM would love a common, flexible platform. This is one also.

After the Chevrolet Volt, the Ford Airstream announcement ( www.evworld.com/view.cfm?page=news&newsid=13844&url= )is rather a sorry tale. Note the 41 mpg gasoline-equivalent combined figure. The Volt can do better than that on E85 alone. Let's assume the 41 mpg is on hydrogen only, because if it's based on any usage of grid electricity, leave alone renewable electricity, the fuel cell is a real bust! Note also that hydrogen starts getting used when the battery still has 40% charge. Presumably, the 40% 'remainder' is to provide (wimpish) surge power. In which case the battery needs to be even larger and more expensive than a 40-mile plug-in battery, to cope with surges of braking and acceleration. I wonder what it weighs.

Now replace the 'hot bits' with a 2.0 liter BioPower(-type - it's Ford, not GM) direct injection engine, a Formula One surge power unit and a Firefly 25-mile battery pack. Do you think the Airstream DR (done right) could match or exceed 41 mpg? And provide performance Ford can only dream of? At a much lower cost? OK, not with a real Formula One surge power unit, but with 'son of'.

For complete nonsense, read this again, from the announcement - 'The architecture could provide a more likely path toward commercialization of fuel-cell-powered vehicles than earlier parallel hybrid fuel cell systems. In a parallel hybrid system, electricity from the fuel cell directly powers the vehicle, rather than recharging the batteries.' And that's a bad thing? No wonder it gets only 41 mpg!

However, if your company is addicted to the idea of the 'hydrogen economy', try replacing the 80kW(?) motor-generator and controller with a surge power unit complete with integrated 40kW MG and controller, reduce the size and cost of your fuel cell and hydrogen tanks and halve the size of the battery, or leave it the same size and go the first 50 miles on electricity alone. You'll also get much better acceleration and lower hydrogen and electricity consumption. That might be a little more credible concept.

So how did they do? Ford clearly failed with the Airstream. With all the talent in its various groups, it should have been able to come up with something more convincing than this. 'Could do much better, see me' was what my headmaster used to write, rather too often. Could apply here, also. For GM, I'm inclined to think 'at last GM is beginning to show real progress. Keep this up, and a place in the top three is assured'.

Times Article Viewed: 18136
Published: 09-Jan-2007


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