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Posted today to Autoblog.


http://www.autoblog.com/2016/05/18/2016-chevy-volt-more-ev-range-exclusive/


The second-generation Chevy Volt has 20 percent more power from the gasoline engine and an impressive 40-percent better EV range. With an EPA-rated 53-mile electric range, the Volt can handle most commutes without burning a drop of fuel. Those improvements landed Chevy's plug-in on the 2016 Ward's 10 Best Engine list. And the story of how the Volt earned that accolade dates back to 1990s.


The tale starts with the ill-fated 1990s EV1 effort
The tale starts with the ill-fated 1990s EV1 effort, when GM's Advanced Technology Vehicles team rethought and, in many cases, redesigned virtually every element of the modern automobile. The bullet-shaped (0.19 Cd), 137-hp, two-seat EV1 delivered strong, smooth performance, and respectable ride and handling on narrow tires pumped up to 50 psi. Driven gently in warm temperatures it could manage 50 to 70 miles of real-world range from its nearly 1,200-pound lead-acid battery pack. [Disclaimer: I was a part of the EV1 team.]

GM was aware that EV sales success would depend on advancing battery technology. Emerging nickel-metal hydride (NiMH) batteries could double that range, but at much higher cost. Another promising option, lithium-polymer chemistry being developed by 3M and other companies promised gasoline-competitive size, weight, and cost but never panned out. Just 500 EV1s were built and around 400
leased for the 1997 model year. About the same number of '99 Gen IIs (there was no '98 model) - some with optional NiMH batteries – followed before the program's demise. But while GM's $1 billion-plus EV1 effort was a costly and embarrassing market failure, it did provide a rich body of learning. GM used knowledge and learning from the EV1 to work on fuel-cell EVs, two-mode hybrids, and eventually extended-range EVs like the Volt.



Fast-forward to January 2007, when the Volt EREV concept debuted at Detroit's North American International Auto Show. Unlike any other EV or hybrid of the time, it was designed to run on battery power for the first 38 miles or so, then keep going on electricity from a generator driven by a small gas engine. Thus it was a non-fuel-burning, tailpipe-emissions-free BEV that would morph into a fuel-efficient gas-powered compact when its 16-kWh li-ion pack was depleted, completely eliminating EV range anxiety.

When the production Volt hit the streets four years later, it was named a 2011 "Wards 10 Best Engines" (or in this case, "Powertrains") winner. "A car that revolutionizes mobility," Wards editors called it; "a magnificent achievement that marries the best attributes of all-electric vehicles with those of fun-to-drive, fuel-efficient gasoline cars."

The 2016 Volt is more that just an updated powertrain.
Getting back to the 2016 Volt, it's more that just an updated powertrain. It's also lighter, quicker and more agile, plus the rear seat fits three passengers instead of the previous two. The updated propulsion system marries a 1.5-liter Atkinson-cycle four-cylinder engine to two electric motors through two planetary gearsets and three clutches. A new lighter and more energy dense li-ion battery pack carries 18.4 kWh of energy versus the previous 17.1 kWh. The new Volt's EPA combined fuel economy in range-extending mode is up from 37 to 42 mpg, while its battery-only range improves from 38 to 53 miles.

One significant improvement that enabled the 100 pounds of savings in the drive unit was the capability to use both motors as either motor or generator, at any time, whether in EV or range-extending mode. Another was mounting the power electronics directly on top of the drive unit, which got rid of the first-generation Volt's heavy and expensive orange connecting cables.

Still more mass reduction came from eliminating one of the old Volt drive unit's two oil pumps. "In the first-generation gearbox," says hybrid/electric drive-unit chief engineer Jason Ditman, "we used a high-voltage electric pump when driving electrically and a mechanical pump in extended-range mode. But we had high enough reliability to go with only the electric pump, which saved a significant amount of mass and a lot of real estate inside the gearbox. We also implemented a chain system to transfer torque from the engine to the output drive."

"Like mass, which comes off by the tenth of a gram, range goes up with every detail." - Tim Grewe
How did they achieve the impressive 40-percent improvement in EV range? "Like mass, which comes off by the tenth of a gram," say Tim Grewe, Chevy's general director of electrification, "range goes up with every detail. Our motors are more efficient, our battery discharge is more efficient, our inverter efficiency is higher and our drive-unit spin losses lower. Yet we also improved [the] fun-to-drive [aspect], with 30-percent better launch and low-end acceleration, because that's a very pleasing feel."

One major challenge was ensuring that the drive-unit-mounted integrated power electronics could survive significant powertrain vibration, especially if the engine misfires. Another was validating the redesigned battery pack. "The battery has to meet life requirements as well as range and environmental requirements," Grewe says, "which involves cell chemistry, the way you mount it, its interconnection, and its cooling."

Besides 20 percent more power and 10 percent more torque versus the previous 1.4-liter engine, the new 1.5-liter four runs on regular gas, providing 101 hp and 103-lb.-ft. "This engine was designed to be most efficient [in the rpm range] where the drive unit and the motors are most efficient," Grewe says. While it shares many parts with the new 1.5-liter in other GM products, the Volt engine's combustion process and calibration are specific to Volt. And the new Volt's drive unit is essentially the
same one used in the 2016 Malibu Hybrid.

There was early controversy around the first-generation Volt's propulsion system because its range-extender engine could help power the wheels under some conditions, which some took to mean that the car was a Prius-like hybrid instead of an
electric car with a generator. That capability is actually enhanced with the new car. "It is most efficient at all times," Grewe explains. "A real-time optimizer senses driver, road load, and environmental demands and continually searches about 100 times a second for the most efficient operating points, which are sometimes in the parallel mode. I think the world has gotten over that being controversial."
 

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Future technological improvements are going to be HUGE. The typical American does not have any clue that a revolution is coming.
When do you expect that revolution to begin?
Anyone observing a revolution from within might not be aware of it until it has effects.

I am of the opinion that we have been 'revolving' for some time now.

My enjoyment of my part is substantially offset by my personal financial strain that accompanies my decision to take part.
There are no financial incentives offered by the Australian government to assist me, as forward thinking as we may appear to the rest of the world here, our leaders sometimes seem very backward.
 

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I really liked reading this discussion...

...and then I thought about GM's marketing department. So sad. Every time I drive by a Chevy dealer, I look for a Volt on the lot and I never see one. You have to wonder how all the Volt engineers feel with their accomplishments going for naught.

Our Tesla Model X will be arriving in a few weeks. We went for a test drive in an X last Friday. Afterward, my wife said she felt embarrassed by me...constantly telling the salesman how the X was lacking in this way or that. Too be fair, I think my wife was only listening to what she wanted to hear, as I did give the X many positive comments. I LOVE their panoramic windshield and seating room, amongst other things. However, our new 2017 Volt already has me so spoiled that the reality of spending (WELL) over twice as much to get slightly better reward provides pause. On the other hand, I think the X auto pilot will quickly become VERY addictive. Nonetheless, I love my Volt...

...and it just makes me so sad that GM cannot figure out how to get the rest of the world to love it as much as I do.
 

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I really liked reading this discussion...

...and then I thought about GM's marketing department. So sad. Every time I drive by a Chevy dealer, I look for a Volt on the lot and I never see one. You have to wonder how all the Volt engineers feel with their accomplishments going for naught.
Haha, I do this too. Have yet to see one behind the endless rows of giant trucks Chevy sells here in Texas.
 

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From the article:

The updated propulsion system marries a 1.5-liter Atkinson-cycle four-cylinder engine to two electric motors through two planetary gearsets and three clutches.
Is the Gen 2 Volt engine actually an Atkinson-cycle? I thought that it had been modified slightly from the regular 1.5 L engine with some additional variable valve cam timing capability that allowed it to achieve some "sort-of" Atkinson-cycle properties when appropriate to improve efficiency, but that it was essentially a standard Otto-cycle engine.
 

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From the article:

Is the Gen 2 Volt engine actually an Atkinson-cycle? I thought that it had been modified slightly from the regular 1.5 L engine with some additional variable valve cam timing capability that allowed it to achieve some "sort-of" Atkinson-cycle properties when appropriate to improve efficiency, but that it was essentially a standard Otto-cycle engine.
No, and none of the modern so-called Atkinson cycle engines are. https://en.wikipedia.org/wiki/Atkinson_cycle

Not mentioned here and most places is that the given compression ratio values for such engines are misleadingly high, for example here: http://www.priups.com/misc/prius-specs.htm

The 13:1 is a mechanical ratio like it would be on a normal engine. But, since for part of the compression upstroke the intake valve is open, the effective c/r is more like 9:1. Also note that, AFIK, all modern A-c engines use direct fuel injection. With port injection or, heaven forbid, carbs, the reverse flow in the intake tract would make accurate fuel metering very difficult. That reverse flow also tends to make these engines sound wheezey, FWIW, though some do a better job of masking that sound than others.
 

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Is the Gen 2 Volt engine actually an Atkinson-cycle? I thought that it had been modified slightly from the regular 1.5 L engine with some additional variable valve cam timing capability that allowed it to achieve some "sort-of" Atkinson-cycle properties when appropriate to improve efficiency, but that it was essentially a standard Otto-cycle engine.
Yes, most modern engines that claim to use the Atkinson cycle are really modified Otto cycle engines. A true Atkinson cycle engine uses a design that allows the physical piston and cylinder to have different expansion and compression ratios, as shown in this diagram from the Wikipedia article:

 

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No, and none of the modern so-called Atkinson cycle engines are. https://en.wikipedia.org/wiki/Atkinson_cycle

Also note that, AFIK, all modern A-c engines use direct fuel injection. With port injection or, heaven forbid, carbs, the reverse flow in the intake tract would make accurate fuel metering very difficult. That reverse flow also tends to make these engines sound wheezey, FWIW, though some do a better job of masking that sound than others.
I hadn't thought about the additional requirement for direct injection, but then, of course it would HAVE to be that way. Thanks for the great clarifications. So really, the practical "Atkinson cycle" engine is actually the result of the miracle of electronics laid onto a conventional Otto cycle engine, with electronic direct fuel injection, electronic intake air flow control, electronic intake valve timing control, electronic ignition control.....

These are "Atkinson-by-wire-and-software" cycle engines.
 

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The truth is most of the 18 mile range is from expanding the usable battery capacity to what, 14 kwh? My 2012 with 9.5 kwh usable would also get near 53 mile rating if it had 14 kwh usable :) The efficiency improvements are nice, but don't do much to stretch the range more than a few miles.
 

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Seems to me like six of one, half dozen of the other. Whether the Atkinson timing is achieved below the piston via crankshaft eccentricities, or via VVT, the end intake/compression/combustion/exhaust result would be much the same. Except that VVT is a lot more tunable.
 

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The truth is most of the 18 mile range is from expanding the usable battery capacity to what, 14 kwh? My 2012 with 9.5 kwh usable would also get near 53 mile rating if it had 14 kwh usable :) The efficiency improvements are nice, but don't do much to stretch the range more than a few miles.
Basically true, but it's important to note they did two things: crammed more capacity into the same T-shaped space (actually the new T is slightly smaller and a bit lighter), and widened the SoC window that is allowed to be used. I roughly estimated each of those were worth about half of the increase in range. Well, maybe more like 45-45, with efficiency improvements being the last 10%.

I still wish they had worked with the Bolt group and just used 1/3 of the Bolt pack in the new Volt... much tighter packaging for more interior space and even greater capacity. Oh well.
 
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