GM's Volt EREV

Chevy Volt Topview
The Chevy Volt – In Showrooms by November 2010?

The Chevy Volt is an integral part of GM’s strategy to “take the car out of the environmental equation,” according to GM Vice Chairman Bob Lutz.

Only 67 weeks ago GM announced the Volt concept car, and if all goes according to plan, in only 138 weeks this revolutionary vehicle will be in dealer showrooms. Is this for real? Will they be ready?

Last week, GM hosted about 80 journalists from around the world to provide an on-site update on the progress of the Volt, guiding us through several venues at their Technical Center in Warren, Michigan.

The significance of GM’s Chevy Volt is not easily overstated. Referred to as an “EREV” (extended range electric vehicle), the Volt has an all-electric drive train, can travel up to 40 miles on plug-in battery power only, but has an onboard gasoline engine turning a generator in order to extend the range up to 440 miles if necessary. Because the Volt is designed to operate on gasoline power only, it will not end up being underpowered once the battery is largely depleted, which can happen with conventional hybrids. And since typical commutes are under 40 miles, most of the time the gasoline engine will never be turned on.

The Chevy Volt is intended to provide the best of all worlds – the zero-gas and zero-emission function of a pure EV, along with the range and versatility of a standard high-mileage gasoline powered car. It is also likely the EREV will eventually cost less than a conventional hybrid – unlike the standard hybrid which has an incredibly complex transmission, the EREV requires no transmission at all. Most other components are common to both designs.

This revolutionary design for an EREV has also been called a “series hybrid,” because the gas engine turns the generator which powers the electric motor in a series configuration, whereas by this logic conventional “parallel” hybrids have both the gasoline engine and the electric motor involved to provide traction. The EREV has also been referred to as a member of GM’s “E-Flex” family of vehicles, since eventually the same design could accomodate, for example, a fuel cell to provide electricity instead of an onboard gasoline engine and an electric generator. With E-Flex, as GM’s VP of Global Program Management Jon Lauckner put it, “the only thing we’re ruling out is steam.”

Jon Laukner Portrait
Jon Lauckner
GM VP Global Program Mgmt.
“The only thing we’re
ruling out is steam.”

So will GM deliver the first EREV designed for mass production? According to Frank Weber, GM’s Chief Engineer for E-Flex Systems, “we are working with incredible speed, and this is the number one priority project we have at GM.” Weber went on to say “all project plans we have now are targeting November 2010. We’ve never before had a technology program and a vehicle program moving forward simultaneously.”

During the day-long guided tour of GM’s research facilities, it appeared most if not all of the top engineers and managers involved with the Volt program were available to speak with the journalists. And after a brief initial briefing on the morning of April 3rd, not one of the venues we visited was a standard press briefing room. Everywhere we went, we were taken to actual work areas where we could see work in progress on the Volt.

During one of our first stops, we sat in an engineering visualization studio where, using 3-D glasses relied on by GM’s engineers, the Volt was built for us one component at a time, starting with the battery and stopping just short of the final exterior shell. Many technical specifications were revealed for the first time.

The Volt’s battery will hold 12 kWh of charge; it will weigh 170 kilograms and be 1.8 meters long. The bottom of the battery is strengthened to improve the overall strength of the car, and is designed to be integrated with GM’s standard next generation compact car underbody. The gas tank will have a special unit to reprocess evaporation, something important to manage since the gas in many cases will rarely be used.

The battery pack was designed to allow the Volt to do zero to sixty MPH in 8.5 seconds, have passing capability, deliver a 40 mile range in city driving, have a cycle life of 150,000 miles (in mixed 100% EV and “charge sustaining” mode), and last 10 years. The Volt will have no transmission, and will have a top speed of 100 miles per hour. The engineers would not comment on the top RPM of the electric motor, nor would they reveal the reduction gear ratio. They would disclose that the electric motor-generator that will provide traction for the Volt will deliver 120 kilowatts of peak power and 370 newton meters of torque.

The E-Flex Extended Range Electric Vehicle Operation Modes
Chevy Volt Operation Modes Chart
From 100% battery power, to using the gas generator, to recharge.

The Volt’s power consumption profile is a good way to see just how brilliant – and practical – the EREV (using an onboard gasoline engine turning an electric generator) design really is: As the table indicates, in the pure electric vehicle mode, the battery charge is gradually depleted as the car runs on power exclusively from the battery. The upward spikes on the overall downward slope represent energy returned to the battery by the dual-mode motor-generator whenever the car brakes or deaccelerates. Once the battery is depleted to a certain minimum – not the absolute minimum because by keeping charge in the battery a buffer resource for surge power is maintained, and the battery life is prolonged by not being totally depleted each cycle – the gasoline engine is turned on. In this state, the battery’s state of charge alternates between a minimum level and a somewhat higher level created by the gasoline engine’s generator power delivering more electricity than the electric traction motor requires, wherein at a certain point the gasoline engine shuts down again to let the battery drain back to the minimum. This cycle repeats itself until the duty cycle of the vehicle is over, and the vehicle is parked and plugged in. This third mode, of course, is the charging mode, where the vehicle is shut down and the battery is recharged from a stationary source.

Volt Battery Testing in a Lab
Volt production design battery packs in testing.

The next stop for us on the tour was the battery testing lab, where production versions of the final battery packs for the Volt were being subjected to a variety of tests – essentially designed to simulate ten years of wear into a two year testing cycle. The batteries were subjected to cycle, calendar, temperature, vibration, longevity, road conditions; all conceivable forms of abuse and normal wear were being simulated in this lab.

Possibly the most unforgettable sight on this tour was in the back of the lab, where one of the Volt battery packs was on display next to a battery pack from the legendary EV-1. The comparison was dramatic – both battery packs store 12 kilowatt-hours of charge, but the Volt battery pack weighed 400 pounds (170 kg), and the EV-1 battery pack weighed 1,200 pounds. Both battery packs were in the shape of a “T” – where the long center portion forms the spine of the vehicle, and the somewhat shorter top section ran from side to side in the rear of the vehicle. But the EV-1′s battery pack dimensions were 2.35 meters (7’8″) by 1.38 meters (4’6″), compared to the Volt’s battery pack dimensions of only 1.63 meters (5’4″) by .83 meters (2’9″).

These recent improvements in battery technology cannot be overemphasized, because it is the reason the series hybrid – or EREV – technology wasn’t viable sooner. As John Lauckner patiently explained, the comparison between batteries using lithium ion chemistry (used in the Volt), nickel metal hydride (used in conventional hybrids), and lead acid (used ten years ago in the EV-1) is a best explained by the ratio 3:2:1, i.e., for the same amount of stored energy, the battery pack in the Volt has 1/3rd the volume and mass of the battery pack used in the EV-1, and 1/2 the volume and mass of typical battery packs used in conventional hybrids. Moreover, the ability of the lithium ion battery to provide surge power is significantly higher than that of the nickel metal hydride batteries, and this is the only way the gasoline engine can be disconnected from the drive-train, while still enabling a car to display normal acceleration while in all-electric mode. Based on their current progress and projections, it is possible that GM and their partners have the most advanced lithium ion battery packs in the world today for automotive applications.

Also present at GM’s battery lab was an intact – and very polished – EV-1, one of the few remaining. It was inspiring to view this legendary vehicle, an engineering feat that was not ready for mass production but nonetheless an icon that will never be forgetten. GM learned a great deal from the EV-1 program that they are applying to their Volt program, increasing the likelyhood that the Volt will be a breakthrough, rather than a footnote, in the pages of automotive history.

Chevy Volt Cross-Section
Volt cross-section. Electric traction motor & gasoline motor for the
generator are all under the front hood. The battery runs down the spine
and to each side behind the rear seats. The gas tank is in the rear.

Probably most significantly, in GM’s battery lab for some tests were two “mules,” prototype Volts that had Volt components installed and running, yet each of them used a 2005 Malibu shell for their bodies. According to GM’s Mickey Bly, Director of Hybrid Vehicle Integration and Controls, this month the first lithium ion battery packs will come off of the testing floor and go into the mules. These prototypes, the first EREV’s ever built, have already been on the track, where GM engineers reported they were “a great handling, spirited car.” Bly stated there would be three more prototypes on the track by summer, using “production intent design” batteries.

Another unforgettable moment was the tour of GM’s wind tunnel, directed by Ken Carbon, GM’s Chief “Aerodynamicist.” One of the largest in the world, GM’s wind tunnel operates 24 hours per day, five days per week, testing every vehicle GM makes as well as many vehicles manufactured by competitors. In the testing section of the wind tunnel, a 1/3rd scale version of the Volt was standing – with tape covering much of the body in order to avoid revealing design details. The wind tunnel has two turntables; the smaller one that the 1/3rd scale model sat on was able to rotate 360 degrees, in order to allow the engineers to evaluate the aerodynamic profile of the vehicle from all angles. The larger turntable was much larger, about 25 feet in diameter. Not only did this turntable rotate 360 degrees, but embedded in the turntable were four smaller turntables, approximately five feet in diameter each, that also had full rotation. Embedded on each of these four smaller turntables was a scale – itself able to rotate. The purpose of all these adjustable turntables is to allow a vehicle of any size to sit with each tire resting on one of the scales, wherein the vehicle can be subjected to wind from any angle, with the the effect of the wind on the weight displacement of the vehicle precisely measured.

General Motors' Wind Tunnel
GM’s Wind Tunnel Rotor – 43′ diameter, six blades of laminated spruce.

After assuring us that the motor could not be accidently activated, Carbon escorted our group around two turns – filled with huge curved vertical “turning vanes” that provided for smooth airflow – of the circular wind tunnel to view the fan. Built in 1980, this almost unreal rotor is 43 feet in diameter, with six blades constructed from laminated Spruce. Until surprisingly recently, Spruce was the best choice for a fan of this size. The material has a high strength to weight ratio and is very durable. Unlike virtually all materials short of recently developed composites, it is not subject to hardening or fatigue. The rotors had balsa tips to absorb impacts from any objects that conceivably could make it through the many screens covering turns one and two in the tunnel and hit one of the tips. The orange center nacelle, 18 feet in diameter, almost the size of a blimp, was designed to smooth the flow of air over the rotor and protect the motor. The 4,500 horsepower DC electric motor has an RPM of 270 and is able to bring the airspeed up to 400 MPH. Once this the air travels around turns three and four to enter the testing section, it can still reach a maximum of 138 MPH.

Chief Engineer Frank Weber would not reveal the aerodynamic drag coefficient of the Volt; he would only say they are targeting under .295. He also noted the Volt has been spending a lot of time in the wind tunnel as the body contours undergo their final refinements. The EV-1 had a drag of .19, which remains the lowest in history for a production vehicle.

Aerodynamic drag is referred to as counts by Bob Boniface, director of both exterior and interior design for the Volt. “Computer Artists” can direct specifications into simulations of aerodynamics, then scale models are milled using a Taurus SC-67 3-axis computer guided milling machine cutting into a clay covered wood and styrofoam armature. Clay can be added later if a particular edge needs to be higher, and the drill can precisely re-render the edge.

“We can go from a foam armature to a finished car in two days, said Boniface, but a car’s exterior only begins there. The many interactions between Boniface’s exterior designers and the wind tunnel tests created a language – every .01 degree change in the vehicles drag coefficient equates to ten “counts” of drag. To shave just a few counts of drag off a vehicle, designers will send a new model into the tunnel, with, for example, the cross-section of the side mirrors reduced slightly. We only saw a glimpse of one corner of the front and rear of the latest exterior version of the Volt, and Boniface had added a special heavier underlayer of covering onto the design prototype in order to prevent a “wardrobe malfunction.”

Chevy Volt Inside View
Inside the Volt. Center shift lever, concave door interiors.

The interior of the Volt is a good mix of next generation controls and traditional features. The Volt is designed to be driven by someone completely unfamiliar with the Volt, but who knows how to drive a car. In a way, the Volt benefits from coming in after many new standard new interfaces, such as GPS navigation, have already been added. The Volt is adding its uniqueness as an EREV onto a mature grouping of next-generation interfaces. The center spine – where the battery adds a low center of gravity mass and structural strength – also adds spaciousness to the cab, since the four seats are necessarily further apart. This center spine also makes feasible a more spacious driver interface, with plenty of room for a navigation console and a center-placed ignition and shifting lever. The impact of a widened center is countered somewhat with negative (concave) surfaces on the doors to allow the Volt to have a roomy interior while retaining an excellent drag coefficient.

Volt interior designer Tim Greig emphasized how the Volt will incorporate a “human machine interaction” that will take advantage of modern technology along with traditional automotive signals that humans intuitively associate with operating a vehicle. Accordingly, the car will recognize the key from a distance, preparing the car for operation in anticipation of being occupied by the owner – per a user-defined program. “The entire driver experience is being carefully choreographed,” said Greig, “sight, smell, sound, lighting.”

It is clear the Volt design, interior and exterior, is nearly ready to take the next steps towards production. As Boniface put it, “We are starting to freeze surfaces.” Also being finalized is the interior power management system. The Volt’s state of the art systems will be extremely efficient. As Weber puts it, the “baseload electricity budget of the Volt is only about 50% of the typical modern car.” Yet the Volt designers also paid attention to affordability – to get that extra mile of efficiency, for example, they did not go to LED headlights – nor an alumnium frame, for that matter.

Frank Weber Portrait
Frank Weber
GM Chief Engineer E-Flex
“We are working with
incredible speed.”

It is also clear GM isn’t kidding. In response to criticisms that to meet a 2010 launch, production version prototypes should be on the road right now, Frank Weber said “You will not see a final Volt with a final propulsion system until 2009, it isn’t necessary.” The Volt, again, is the first time GM has ever had a technology (EREV) program and a vehicle (Volt) program moving forward simultaneously – but the design and development tools available today make this feasible while ten years ago it might not have been. As GM’s Jon Lauckner put it, “GM is spending a lot of talent and treasure on the Volt.” Is this the most expensive development project GM has ever done? Without answering specifically, Laukner compared the Volt program to the 1979 “X-Car,” which introduced unibody construction and front wheel drive, two revolutionary and enduring innovations.

Can the Volt “take the car out of the environmental discussion?” It certainly appears a car like the Volt could shift primary reliance from gasoline to electricity for most passenger transportation miles, if not more. EREV technology offers affordable cars that can run on cheap electricity, only requiring gasoline for infrequent longer trips. In late 2006, Vice Chairman Lutz instructed VP Global Product Development Jon Laukner to “lead development of a game-changing concept car to announce in January 2007.” With the Chevy Volt EREV, GM delivered the announcement, and at about one-third of the way between announcement and the planned November 2010 launch, GM is still playing for keeps. The Volt’s EREV technology, arriving alongside smart-car features and enhanced safety features – all parts of GM’s “new automotive DNA” – is going to change how we think of cars forever.

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2 Responses to “GM's Volt EREV”
  1. Pete says:

    I want one. I like the idea of using no gas. All cars should be plug-ins.

  2. Anomoly says:

    i would love a PHEV or EREV. it sounds like it will take some time before they are affordable.. or even exist…

    but i will believe it when i see it.


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