GM Unveils Second Propulsion System for Chevrolet Volt: A Fuel Cell Variant
19 April 2007
|Cutaway drawing of the Volt fuel cell variant. Click to enlarge.|
At the Shanghai Auto Show, GM unveiled a second propulsion system for the Volt concept under the aegis of the E-Flex electric drive family: a hydrogen fuel cell variant that uses GM’s new fifth-generation fuel cell system as its primary power source.
This second variant of the E-Flex system combines the new 80 kW fuel cell stack with an 8 kWh (50 kW peak power) lithium-ion battery to provide up to 300 miles (483 km) of petroleum- and emissions-free electric driving. The Volt fuel cell variant is plug-in capable, adding up to 20 additional miles (34 km) of range each time it is charged.
|The two Volts, battery-dominant with ICE range extender on the left, fuel-cell centric on the right. Click to enlarge.|
Unlike the first Volt propulsion system, which is battery-dominant with a small combustion engine range extender, the second system is fuel-cell centric, and uses a blended operating strategy to augment its range and power with a battery pack that is half the size of that in the first Volt.
A different configuration under E-Flex in which a smaller fuel cell would function as the range extender to a larger battery pack is also possible. (This is the approach Ford took with its HySeries concept. Earlier post.) However, this is not the design that GM implemented in the second variant of the Volt.
The E-Flex system is a flexible all-electric production vehicle architecture that can be configured to run on electricity from a number of sources. It was first shown in January at the North American International Auto Show in the Chevrolet Volt concept vehicle. The first Volt concept is a plug-in series hybrid electric vehicle that has a 40 mile all electric range and uses a small bio-fuel engine with a generator to extend its range to 640 miles (1,030 km). (Earlier post.)
We think electrically driven vehicles are really going to be a big part of the solution to the energy and environmental challenges that our vehicles face. We’re talking about purely electrically driven vehicles, not a hybrid, not mechanically driven. And this really sets the stage for diverse energy sources in simpler vehicles.
When we talk about electrically driven vehicles, we're really talking about what GM calls E-flex. It has a common drive architecture, electric drive component, and electric drive architecture.
The key is to be able to create and store electricity onboard the vehicle, and you can store electricity obviously by plugging the car in and storing electricity in a battery. And you can create electricity by running an engine generator or by using a fuel cell. So the key enabling technologies here are engines and generators and batteries and fuel cells and hydrogen storage and the plug in capability that they offer. And then because electricity and hydrogen can be generated from a range of energy sources, we can have all that diversity with a very simple, common E-flex electric drive architecture, so that really helps from a business standpoint.—Larry Burns, GM Vice President Research & Development and Strategic Planning
The fuel cell variant shares many parts with the first version of the Volt, such as the front electric drive component.
|The 5th generation fuel cell system in the Volt. Click to enlarge.|
GM’s fifth-generation fuel cell system is half the size of its predecessor, and provides the same power and performance. The fourth-generation system currently powers the Chevrolet Sequel concept vehicle. To double the specific output of the fourth-generation system, GM worked with different material sets and then improved efficiency and improved yield from each square inch of material inside the cells.
Our improvements are in management of all of those gasses and the water flows, [and] the selection of the materials to make that whole membrane electrode assembly center. It’s a system. The real key is in the controls.—Larry Burns
The Sequel stores 8 kg of hydrogen and delivers a range of 300 miles (483 km). The fuel cell Volt—a lighter vehicle—will also deliver a range of 300 miles, but with only 4.0 kg of hydrogen (75 miles/kg) stored at 10,000 psi in two Type IV tanks.
The front drive motor offers a maximum 70 kW of power, with 250 Nm (184 lb-ft) of torque. The Volt fuel cell variant also showcases GM’s two third-generation wheel hub motors, packaged inside the rear wheels to add torque for all-wheel electric drive capability. The new motor technology reduces mass and produces more power (25 kw and 500 Nm /368 lb-ft per motor) compared to the first generation shown in 2003.
The fuel-cell Volt accelerates from 0 to 60 in 8 to 8.5 seconds, and has a burst top speed of 120 mph, with a continuous top speed of 100 mph.
A variety of other technological advancements and lightweight materials contribute to the efficiency of the Volt. With an estimated curb weight of 3,500 pounds (1,588 kg), it weighs 30% less than the Sequel. The fuel cell propulsion system is packaged entirely under the hood and is equivalent in size to a four-cylinder engine with automatic transmission.
The Volt also features molded GE plastic panels on the fenders, window glazings, instrument panel and steering wheel, which offer between 30% and 50% weight reduction per part. The car is fitted with low rolling resistance tires.
The global economy is going to grow 3% or 4% per year, and there’s a correlation with that economic growth to the demand for energy growing at about 2% per year.
You know you compound 2% over 10 years, that’s 25%. That puts you right in the range of the efficiency gains that you get from a hybrid, right in the range of what it would be energy efficient-wise versus a gas engine, and right in the range of what most people think can be teased out of the internal combustion engine going forward. So we really need to look at alternatives in addition to just efficiency improvements to solve this problem.
So we really think now is the time to face the reality. We have to find solutions to the energy and environmental challenges that automobiles face. We have to do it in General Motors simply as a matter of business. If we don’t, there are real concerns about the growth of our industry being capped and that’s not a good thing for our industry.
And at General Motors, our strategy is pretty simple. We want to displace petroleum, displace oil, reduce the amount of oil that’s being consumed, and we think the key to doing that is through energy diversity. By having a wide variety of energy pathways made available for automobiles, we can grow our business and we have the chance of growing our business sustainably going forward.
We’ve become increasingly confident that we can meet the automotive competitive targets that we've set for the [hydrogen fuel cell] technology, $50 per kilowatt, 150,000-mile life, with a 300-mile range. But before this technology can be made widely available, governments, energy suppliers and infrastructure companies around the world need to collaborate with GM and the auto industry to develop a market for fuel cell vehicles and hydrogen fuel.—Larry Burns
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