Are Plug-In Hybrids (PHEVs) Really the Answer?
Getting a PHEV depends on what sort of driving you do.
Plug-in hybrid vehicles—PHEVs—are going to save the auto industry. Oh, and help save the planet, too. Well, that’s the theory. The reality is a little more complicated.
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The recent slowdown in sales of electric vehicles has revealed an awkward truth about the auto business: You can lead consumers to a new technology, but you can’t make them buy it. EVs remain comparatively expensive and, compared with their internal combustion engine counterparts, still somewhat inconvenient to live with. Charging a battery still takes longer than topping up a gas tank, and charging stations are nowhere near as ubiquitous as gas stations. The early adopters may have jumped aboard, but many mainstream car, truck and SUV buyers remain wary.
Automakers who bet big on EVs in the past few years are now rethinking their entire business strategies. Bentley, for example, which four years ago vowed it would be building nothing but EVs by 2030, says it now plans to continue to produce cars and SUVs with internal combustion engines until at least 2035. And like most other automakers making the same hurried pivot away from electrons and back to hydrocarbons, Bentley has made a point of saying those vehicles would be PHEVs.
There’s a compelling logic that underpins the PHEV concept. It can be an EV until the battery runs out of charge. Then the internal combustion engine will fire up and continue to take you where you want to go. Goodbye, range anxiety. Until recently, the EV part of the equation was rather small, with most PHEVs struggling to get 20 miles on pure electric power before they run out of battery. But a new generation of PHEVs equipped with bigger batteries can now travel as much as 60 miles or more without the internal combustion engine starting up.
All-In on Plug-Ins—Why?
Automakers are coalescing around the big-battery PHEV format. Although PHEV powertrains are complex and costly to execute, and add unwelcome mass to a vehicle, the car companies see them as a technology that bridges the gap between traditional internal combustion engine vehicles and EVs, offering consumers the benefits of both with relatively few compromises. And, mostly, they’re right. But if anyone thinks PHEVs are a silver bullet, think again.
Although they’re far from a one-trick pony, the reality is PHEVs make most sense in a singular operating environment, namely urban and suburban areas. Americans on average travel about 42 miles a day, mainly commuting to work, or dropping the kids off at school, or going to sporting events in cities and suburbs. If you can recharge your big-battery PHEV overnight, you could do most of your daily driving chores without waking up the internal combustion engine.
But if you regularly drive longer distances, a PHEV won’t save you much money, as I found after a recent long drive in the Mercedes-Benz C300e. This is the PHEV version of the C-Class that combines a 2.0-liter turbocharged four-cylinder gas engine that develops 201 horsepower and 236 lb-ft of torque with an electric motor that boosts total system output to 308 hp and 406 lb-ft. A 25.4-kWh battery pack gives the car a 62-mile electric range under the WLTP test protocol used in Europe. (For what it’s worth, WLPT figures are often optimistic when compared against EPA testing.)
The C300e started the trip with a full tank of gas and the battery at a 70 percent state of charge. Driven in Hybrid Auto mode, the PHEV Benz traveled 43 miles on pure EV power before the internal combustion engine fired up and the powertrain management system started mixing and matching power sources to maximize overall efficiency. At 88 miles, the trip computer showed the C300e’s e-motor had accounted for 47 percent of the distance traveled, giving an overall fuel economy equivalent to 69 mpg. But at journey’s end, after 327 miles, the indicated overall fuel economy had fallen to just 34 mpg.
For context, the regular C300 sedan sold in the U.S. is rated by the EPA for 35 mpg on the highway. And here’s the kicker: In Germany, the C300e costs 12.2 percent more than an identically equipped C300.
If you do a lot of long-distance driving, trips that take you well past the 60-mile mark, PHEV math starts to look less compelling. Especially as the big-battery PHEVs don’t offer the fast-charging capability of the latest EVs. The C300e can accept a peak charge rate of 55 kW, which means it needs 20 minutes to take the battery from a 10 percent state of charge to 80 percent. That sounds reasonable, until you realize you’ve added barely 40 miles of electric driving range, which doesn’t count for much if you’re halfway between Denver and Des Moines.
Better Alternatives Exist
It might not be popular anymore, but the best, most efficient engine for long-distance mile munching is still a diesel—my 2.0-liter turbodiesel-powered Mercedes E220d wagon, bigger and more luxuriously equipped than the C300e (and, tellingly, about 600 pounds lighter overall), would have returned 42 mpg or better on the same 327-mile round trip. But with diesel being a nonstarter in the U.S., the next best thing for long-distance fuel efficiency looks to be an enhanced mild hybrid like the Audi MHEV+ system fitted to European market versions of the new S5.
MHEV+ is the halfway house to the halfway house, a sophisticated mild hybrid designed to minimize the time the internal combustion engine is operational during driving without the need to plug the car into a charging station. MHEV+ comprises a belt alternator starter, an electric motor mounted adjacent to the engine and transmission that acts on the transmission output shaft, and a water-cooled 1.7-kWh lithium-iron-phosphate battery. The system can provide up to 24 hp and 169 lb-ft of torque on demand and can recoup as much as 25 kW through deceleration and regenerative braking.
The belt alternator starter is used to start the engine and send electrical energy to the battery. Because the e-motor—powertrain generator, in Audi-speak—acts directly on the transmission's output shaft, the power it supplies or recuperates does not have to go through the transmission, allowing it to be used on both front-wheel-drive and all-wheel-drive models. The e-motor can support the internal combustion engine at speeds up to 87 mph.
Although it allows the S5 to drive short distances on electric power at low speeds, the MHEV+ system is designed not to deliver as much electric driving range as possible, but to ensure the battery is emptied and filled in fast cycles. This, Audi says, allows the most energy to be recovered and used efficiently for propulsion. The lithium-iron-phosphate battery is key in all this: Its chemistry allows for thousands of rapid charge and discharge cycles with only a minimal impact on capacity, Audi claims.
Audi says MHEV+ helps the S5 deliver almost 8 percent better fuel economy than its predecessor, the S4, despite having 4 percent more power and 10 percent more torque. On a long highway cruise, the S5 should average close to 32 mpg. No, it’s not as good as a diesel—Audi sold a version of the previous-generation S4 in Europe powered by the 3.0-liter TDI V-6 diesel engine that delivered almost 38 mpg on the highway. But it’s a step in the right direction.
The Best Alternative Is …
But only a step. There is a hybrid powertrain that can truly offer the best of both worlds—ultra-low emissions and low range anxiety—but it’s one the auto industry has, for various reasons, been reluctant to adopt until recently. It’s the series hybrid, a powertrain system that uses an internal combustion engine as a generator that supplies electric power to the motors that drive the car. More popularly known as EREV (for extended-range electric vehicle) systems, Chinese automakers have been rapidly pushing their chips into the middle of the table regarding the tech. The Chevrolet Volt was an early EREV in America (although its engine did drive the wheels in rare scenarios), and Ford, Hyundai, and Stellantis all have big plans for EREVs. Stellantis’ Ram 1500 Ramcharger will be among the first new-generation EREVs for sale here and will offer up to 690 miles of total range. In fact, sales of the Ramcharger were fast-tracked to the first half of this year.
The key advantage of this system is that as the internal combustion engine is decoupled from the task of driving the wheels, it can be tuned to constantly run at its most efficient operating speed; you don’t need to constantly overfuel the engine to allow it to cope with constantly changing torque demands. Emissions are therefore very, very low and easily cleaned. What’s more, an internal combustion engine designed to be used as a generator can be lighter and smaller and made to run on a variety of liquid fuels, including biofuels, for which a large distribution infrastructure already exists.
In the early 1990s, I attended an electric vehicle conference where the star speaker was Howard Wilson, the former Hughes Aircraft Corporation engineer who helped mastermind the solar-powered GM Sunraycer and shepherded GM’s extraordinary EV1 electric vehicle into (low-volume) production. I asked Wilson what, if anything, he would change on the EV1, then arguably the most technically advanced car in the world, if he could. “What I'd really like to do,” he said, “is install a small gas turbine engine that could run at a constant speed to provide the electricity for the motors.” In other words, make it a series hybrid. “Fuel consumption would be low, emissions would be tiny, and you’d be able to drive it much further.”
More than 30 years on, those things are still true.
I can’t remember a time when I wasn’t fascinated by cars. My father was a mechanic, and some of my earliest memories are of handing him wrenches as he worked to turn a succession of down-at-heel secondhand cars into reliable family transportation. Later, when I was about 12, I’d be allowed to back the Valiant station wagon out onto the street and drive it around to the front of the house to wash it. We had the cleanest Valiant in the world.
I got my driver’s license exactly three months after my 16th birthday in a Series II Land Rover, ex-Australian Army with no synchro on first or second and about a million miles on the clock. “Pass your test in that,” said Dad, “and you’ll be able to drive anything.” He was right. Nearly four decades later I’ve driven everything from a Bugatti Veyron to a Volvo 18-wheeler, on roads and tracks all over the world. Very few people get the opportunity to parlay their passion into a career. I’m one of those fortunate few.
I started editing my local car club magazine, partly because no-one else would do it, and partly because I’d sold my rally car to get the deposit for my first house, and wanted to stay involved in the sport. Then one day someone handed me a free local sports paper and said they might want car stuff in it. I rang the editor and to my surprise she said yes. There was no pay, but I did get press passes, which meant I got into the races for free. And meet real automotive journalists in the pressroom. And watch and learn.
It’s been a helluva ride ever since. I’ve written about everything from Formula 1 to Sprint Car racing; from new cars and trucks to wild street machines and multi-million dollar classics; from global industry trends to secondhand car dealers. I’ve done automotive TV shows and radio shows, and helped create automotive websites, iMags and mobile apps. I’ve been the editor-in-chief of leading automotive media brands in Australia, Great Britain, and the United States. And I’ve enjoyed every minute of it. The longer I’m in this business the more astonished I am these fiendishly complicated devices we call automobiles get made at all, and how accomplished they have become at doing what they’re designed to do. I believe all new cars should be great, and I’m disappointed when they’re not. Over the years I’ve come to realize cars are the result of a complex interaction of people, politics and process, which is why they’re all different. And why they continue to fascinate me.Read More
