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Winner: The Smart Hybrid

Flip a switch, and DaimlerChrysler's plug-in hybrid electric van will become an electric vehicle

11 min read

When it comes to our cars and the environment, we are all slightly sociopathic--even those movie stars in their Toyota Priuses. It's just a matter of degree.

If you commute 25 km each way to work in a mid-sized car, you make an annual contribution to the Earth's atmosphere of about 5500 kg of carbon dioxide and 1300 grams of the pollutant brew known as smog, according to a study by the Electric Power Research Institute in Palo Alto, Calif. A comparable conventional hybrid vehicle, such as the justly venerated Prius, will cut those emissions by roughly 25 percent and 15 percent, respectively, EPRI says.

Now add an electrical outlet plug to that hybrid, a bigger battery, and a few other modest changes, and a remarkable thing happens. "What you get is this very efficient vehicle on gasoline that can also be an electric vehicle, which is even more efficient," says Mark Duvall, an expert on hybrid vehicles at EPRI.

In round numbers, the total amount of energy you use to travel in your car, week in and week out, is cut by as much as 50 percent, depending on the efficiency of your local utility's generating plants. And you don't have to give up the slightest bit of performance, comfort, or range. Need to take a 1000-km trip that crosses mountainous terrain? No problem. You can travel in air-conditioned comfort, smug as a Prius-driving film star in the knowledge that over the long haul, you are cutting emissions of carbon dioxide and smog by at least 50 percent, according to EPRI's figures. Best of all, dependence on petroleum comes down by a whopping 75 percent, on average, in the United States.

That, in a nutshell, is the promise of the plug-in hybrid electric vehicle, and it is about to be demonstrated in a US $1.5 million pilot program based at a facility of DaimlerChrysler AG in Mannheim, Germany. Several U.S. organizations are helping fund the project; they include EPRI, California's South Coast Air Quality Management District, the utility colossus Southern California Edison Co., and the Metropolitan Energy Center of Kansas City, Mo.

Under the project, DaimlerChrysler is putting together three commercial vehicles--two light-duty utility trucks slated for California and a public transit van for Kansas City--all based on the company's rugged Sprinter truck. But instead of the Sprinter's standard 156-horsepower (115-KW) diesel engine, the utility vans are going to be outfitted with a hybrid gasoline-electric propulsion system and a beefy battery pack that can be recharged by plugging it in.

Winner: Plug-In Sprinter Van

Goal

Build three hybrid gasoline-electric service trucks whose batteries can also be charged overnight

Why It'S A Winner

Hybrid cars are poised for steady growth, and plug-ins improve upon ordinary hybrids because they can cruise in a pure-electric mode

Organizations

DaimlerChrysler, EPRI, Southern California Edison Co., South Coast Air Quality Management District, Metropolitan Energy Center

Center Of Gravity

DaimlerChrysler facility in Mannheim, Germany

Number Of People On The Project

Approximately 15

Budget

US $1 525 000 (total project cost)

The resulting trucks will be able to travel at least 32 km between rechargings in a pure-electric mode. For longer trips, the vehicle will respond to the dwindling charge on the batteries by automatically firing up the truck's combustion engine, which will begin recharging the batteries and spinning the wheels, extending the range indefinitely.

Daimler has no firm plans now to produce a plug-in passenger car, but that could change. "I am convinced we can commercialize this technology," says Ferdinand Panik, an alternative-vehicle expert and retired Daimler senior official who now consults for various organizations, including EPRI. "First for the delivery van, and then for passenger cars as well." The plug, he and other proponents believe, has the potential to transform the burgeoning hybrid-electric vehicle market, in which Japanese automakers, led by Toyota and the surprisingly successful Prius, have established an early and commanding lead over their U.S. and European counterparts.

Cars that both plug in and fuel up? How about a switch on your dashboard that turns your car into an electric vehicle? For plug-in technology to succeed in passenger cars, one of the tricks will be finding a way to avoid befuddling a general public conditioned to do little more than turn a key, step on an accelerator, and buy copious quantities of gasoline.

Source: Hybrid Electric Vehicle Working Group

As one U.S. driver told EPRI pollsters: "I'm lazy. I wouldn't be organized enough to remember to plug in."

For those who could remember to plug in, however, the benefits would be considerable. Like most people, you probably travel a set distance to and from work five days a week, and also make intermittent excursions of varied lengths. If you had a plug-in hybrid with a battery big enough to cover your daily commute, you would have, in effect, a pure-electric vehicle five days a week, but one that could burn gasoline whenever you wanted to go on a ski trip, visit your cousin, or drop off the kids at summer camp. You'd go to a gas station maybe six times a year instead of six times a month.

There would be other benefits, too. For example, that dashboard switch--the one that lets the driver put the vehicle into a pure-electric mode--could let the car operate in a crowded, downtown urban area where combustion-engine fumes and noise were unwelcome. And utility executives become visibly excited about the possibility of recharging millions of vehicle batteries at night, when their generating plants would otherwise languish. "Powering up generating plants in the day and then powering them down at night is very inefficient," notes Ed Kjaer, director of electric transportation at Rosemead-based Southern California Edison.

The first glimmerings of that vision are to be seen at Daimler's Kompetenz-center fur Emissionfrei Nutzfahrzeuge, known as KEN, where the plug-in hybrid project is based. KEN already does a modest but steady business converting small trucks, mostly Sprinter vans, to run on compressed or liquefied natural gas, electricity, or hybrid electric drive trains. The group has 7700 square meters tucked away in a cavernous Daimler truck engine factory in Mannheim.

On a rainy October afternoon, a couple of dozen Sprinter vans are scattered around the facility in various stages of conversion, many of them up on lifts. A pair in one corner, one orange and one white, are being outfitted with pure-electric drive trains; a tangled rainbow of harness wires spills out through their open front hoods. One of these Sprinters is destined for the University of Bremen in Germany and the other for Helgoland, a North Sea fishing and resort island where internal combustion engine vehicles are banned.

Across the street from the factory, in a small white conference room, Heinz Jorgensen gives me a status report and reviews the technical challenges. Jorgensen, an electrical engineer, has been corresponding with EPRI's Duvall and leading a team of four other engineers at KEN who are working out the electrical and mechanical details of the van. Precise, wry, sleepy-eyed, the 35-year-old Jorgensen is a study in contrasts: an automotive expert who walks to work and a son of lifelong Volkswagen employees who works for Daimler.

The first of the plug-in hybrid Sprinter vans are due in late 2004, he tells me. Although the team hasn't built any hardware yet, they have worked out the basic design of the drive train--based on specific engines, motor, and batteries--and even simulated the vehicle's performance.

Illustration: Bryan Christie

Special Delivery:

A plug-in hybrid van could put the combustion engine and electric motor in front, along with the electronics for charging the batteries and powering the motor. The battery pack would be installed under the floor of the cargo bay. The plug connects to the conversion electronics, enabling ac wall current to be turned into dc to charge the batteries. This front-wheel-drive configuration shows the main elements clearly, but DaimlerChrysler's Sprinter will be a rear-driven truck.

They plan to stick with proven components, including an ac motor of about 70- or 75-kW output power, which is being produced by ZF Sachs AG of Schweinfurt, Germany.

The 14.4-kWh battery pack will use durable nickel-metal hydride batteries from Varta Automotive GmbH, Hannover, Germany. (The company is 80 percent owned by Johnson Controls Inc. of Milwaukee, Wis.) The vans destined for California will use Daimler's four-cylinder, 2.3-liter M111 gasoline engine; a Kansas City bus will have a 2.1-liter diesel engine.

Of course, there's much more to a hybrid vehicle than motor ratings and battery chemistry. The most fundamental choice in the design of any kind of hybrid is whether the drive train will use the series or parallel configuration. Series hybrids are conceptually very simple: a combustion engine turns a generator that charges a battery that powers an electric motor, which turns the wheels. Only the electric motor can spin the wheels. Parallel hybrids are more complicated; because both the electric motor and the combustion engine are connected to the drive shaft, either one or both can make the wheels turn.

At first glance, at least, the series option seems better suited for a plug-in hybrid. A series hybrid must have an electric motor that can supply, all by itself, enough rotational force, or torque, to accelerate the car briskly. As it happens, you want such a powerful motor for a plug-in hybrid, too, so that when you're in pure-electric mode, the car's acceleration won't be sluggish.

"As soon as you want significant range and performance on batteries alone, you're going to want a series [configuration]," argues Alan Cocconi, a San Dimas, Calif., electrical drive consultant whose company, AC Propulsion Inc., builds high-performance electric and hybrid cars.

Cocconi built one of the handful of plug-in hybrids now on the road; he did it by pulling the gas-powered guts out of a Volkswagen Jetta and replacing them with a 120-kW electric motor and 8.7 kWh's worth of lead-acid batteries, which are charged by a four-cylinder, 1.4-liter internal combustion engine scavenged from a Volkswagen Lupo. He and I hit the road on a brilliantly sunny October afternoon, cruising among multimillion-dollar mansions in the foothills of southern California's San Gabriel mountains.

The Jetta is a joy to drive. The acceleration, particularly at low speeds, is strong and silky smooth, and Cocconi is happy to explain why. Series hybrids, like pure electrics, can fully exploit the most endearing feature of an electric motor: its relatively flat curve of torque versus revolutions per minute. What a driver feels as acceleration is a function of torque. And in a gasoline engine, not much torque is available at low RPM; maximum torque is available only when the engine is spinning at roughly three-fourths of its red-line RPM, or, say, 4000-5000 RPM. That's why a combustion engine vehicle needs a transmission--to let the engine spin fast enough, even at low vehicle speeds, so that it can generate enough torque to move the car.

An electric motor, on the other hand, delivers maximum torque pretty much the instant the rotor starts spinning. Thus, an electric motor with no transmission whatsoever delivers torque in a manner that is almost ideally suited to the demands of accelerating a car from a standstill. It's the main reason why electrically powered cars are so much fun to drive.

Still, series hybrids have their drawbacks. The long chain of components from the engine to the drive shaft leaves lots of places for power to leak out, lowering the overall efficiency. But perhaps the biggest problem with series hybrids is the fact that they are regarded as a leap for a global automotive industry that has grown quite comfortable converting combustion directly and mechanically into propulsion.

That comfort factor weighed heavily on the plug-in Sprinter design team. "We don't want to change the normal drive train too much," explains Jorgensen, the Daimler team's technical leader. "If you make something totally new, there's more chance of failure."

So the team has decided to go with the parallel option. That leaves them two fundamental technical challenges, Jorgensen notes. One is specifying the configuration and placement of the major drive-train elements--engine, motor, starter motor (if any), clutches, gearboxes, transmission, and so on. The other is working out the details of the control strategy that will determine when the vehicle is being powered by electricity, the combustion engine, or some combination of the two.

There are several different basic configurations of a parallel hybrid. The Daimler team has chosen one of the most common, in which there is a clutch in between the engine and the electric motor and also a separate, smaller starter motor to start the engine. It's an apt choice for a plug-in hybrid because, crucially, it can operate in a pure-electric mode: with the clutch open, the engine is decoupled from the drive train and you are running on electrons only. Of course, with the clutch open, it's also possible to operate on the engine alone.

Yet another nice feature of this arrangement is the ability to use the vehicle as a mobile generator of electricity. You start the combustion engine, put the gear shift in neutral, and close the clutch, and you can use the motor to generate up to 40 kW--enough to supply a small home.

The challenge with this configuration is figuring out a way to start the combustion engine when you are cruising in the pure-electric mode. Remember, both the engine and the motor connect to the drive shaft. With the motor spinning the drive shaft, starting and engaging the engine demands a bit of choreography: start the engine with the starter motor; bring the engine up to the same rotational speed as the spinning drive shaft; and close the clutch to engage the engine. It could all be done in a fraction of a second, Jorgensen says, and timed so that the driver wouldn't notice the minute discontinuity in torque.

The other major challenge--the control strategy that determines when the vehicle is electric, when it is a fossil-fuel burner, and when it is both--is a bit trickier. The goal is to wring every last pure-electric kilometer out of the battery packs. And to be really effective, the strategy must change depending on the length and even the topography of the journey.

To understand why, first consider a 30-km trip in a plug-in hybrid with a 32-km range. That's easy: do the whole thing in pure-electric mode. Run on your battery until it's almost dead. But what about a 320-km trip? For that one, it would be better to start off in pure-electric mode and then use up only, say, two-thirds of the battery's charge. Then fire up the engine for the remaining 300-odd km. That way, you would still have enough battery energy to run like a conventional hybrid for the rest of the trip, using the electric motor mainly to absorb load surges to climb hills and accelerate and keeping the engine running steadily and relatively cleanly at its most efficient rate.

The power of the 16.6 million cars and light trucks sold in the United States in 2003 adds up to Two And A Half Times The Total U.S. Electrical Generating Capacity

And what about that switch, the one that would put the vehicle in pure-electric mode? For fleet vehicles and delivery vans, "it's a must," says DaimlerChrysler's Jorgensen, because it will let them operate in restricted areas, such as some urban centers. But in passenger vehicles, such a switch might merely baffle some drivers.

That fact prompts Kjaer, of Southern California Edison, to wonder aloud, "Do you allow the consumer to have control of the control strategies, or do you let the car's computer have control of the control strategies?" There's no clear answer at the moment.

Kjaer has other things on his mind, anyway. What he really wants to talk about is a pipe dream called V-to-G, for "vehicle to grid." Imagine countless plugged-in vehicles parked in lots and trickling electric power back into the grid during the day. It would greatly help utilities manage peak loads and would give the vehicle owners a break on their utility bills.

Say you have a plug-in hybrid with a 40-km range, and your daily commute starts with a trip to a train station only 6 km away from your home. That train station, happily enough, has receptacles where you can plug in your car.

Now imagine that electrical demand soars that day. With your prior consent, the local utility could use some of the energy from the battery in your car--and many thousands of other cars--but leave enough charge for you to get home. (In fact, even if they drained your battery, you still have a combustion engine to get you wherever you wanted to go.) The electricity would flow through that same plug, in the other direction, of course, and you'd be credited for the transaction on your utility bill.

Kjaer wants to be clear about this. "You could be paid to park your car in an urban center," he says, enunciating clearly and with a defiant smile on his face.

A back-of-the-envelope calculation, at least, suggests that the idea is not all that far-fetched. According to the research firm J.D. Power and Associates in Westlake Village, Calif., 16.6 million new cars and light trucks were sold in the United States in 2003. The power output of all those engines adds up to roughly 2500 GW--or two and a half times the entire electrical generating capacity of the United States.

In the grand scenarios of transportation analysts, plug-in hybrids occupy a box of indefinite length straddling those of conventional hybrids in the very near future and, farther out, fuel-cell cars, which experts predict will begin to dominate in 20, 30, or 40 years ("depending on which liar you believe," says one West Coast transportation expert). Plug-ins will be "an enabling pathway from where we'll be in a few years, with hundreds of thousands of conventional hybrids on the road, to nirvana, with zero- or near-zero-emission vehicles," Kjaer says.

What is the obstacle to getting plug-in hybrids in showrooms? "The main thing is cost," says project leader Jorgensen. With its relatively big battery pack and more powerful motor, a plug-in would be more expensive up front than an ordinary hybrid, although the total cost over the life of the vehicle would be less.

In the meantime, DaimlerChrysler, EPRI, and their partners will take the crucial first step, showing what plug-in hybrids can do not only on the test track but also in real applications, with ordinary drivers, and in actual working conditions. As EPRI consultant Panik puts it, "If you make a vehicle, you will find out the truth."

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