## First look at all-new Voltec propulsion system for 2G Volt; “the only thing in common is a shipping cap”

##### 29 October 2014
 Cutaway of the new power electronics unit, which is much smaller than in gen 1, and which is now integrated into the drive unit housing. The power electronics and the motors use separate cooling: water for the PE and ol for the motor unit. Click to enlarge.

The second-generation Volt, which makes its world debut in about 10 weeks at the North American International Auto Show in Detroit, features a clean-sheet, all-new Voltec propulsion system—new battery, new electric drive unit, new power electronics and new range-extending engine. At an introductory media briefing on the new powertrain held at the Warren Transmission Plant in Michigan, where the new drive unit will be built, Larry Nitz, GM Executive Director, Transmission and Electrification, noted that the only common part between the gen 1 and gen 2 drive units was a little yellow plastic intra-plant shipping cap for the manual selector.

The battery cells, with a tweaked NMC/LMO chemistry from LG, increase storage capacity by 20% volumetrically when compared to the original cell. The drive unit features a large number of changes: new roles for the two motors, two clutches instead of three, and a smaller power electronics unit integrated into the housing among them. (No more big orange high-voltage cables underneath the hood.) The new direct-injected 1.5 liter engine with cooled EGR features a high compression ratio and is optimized to function in its range extender role.

 The second-generation Voltec propulsion system with range-extending engine and integrated power electronics and battery pack. The high-voltage (orange) cables from battery to drive unit are the only high-voltage cables in the system; there are no cables connecting the power electronics to the motor unit under the hood. Click to enlarge.

Overall the engineering team increased efficiency and reduced weight; the drive unit is up to 12% more efficient in operation—although GM has yet to quantify publicly what that means in terms of range or fuel economy—and 100 lbs (45 kg) lighter. The battery system, with fewer, albeit larger, cells (192 vs. 288) is nearly 30 lbs (13.6 kg) lighter, but offers more capacity (also unspecified at this point) than its predecessor.

The overall goal of the redesign was to give the customers more of what they want, the GM team emphasized over and over: more electric range, better fuel economy, and more power, and lower noise from the engine when it runs.

In a five-year period, I can’t think of any other product that we have that we have gone through a complete, a complete reengineering.

—Larry Nitz

 The second-generation battery pack retains the T shape, but increases capacity and reduces weight with almost 100 fewer cells (192 vs. 288). Click to enlarge.

Battery. Although it maintains the external form factor of its predecessor, the battery pack for the second-generation Volt features a number of significant changes, including revised cell chemistry, developed in conjunction with battery supplier LG Chem, which also provides the current generation cells for the Volt.

The Gen 2 battery was also a clean-sheet design, said Bill Wallace, Director, Battery Systems; there are only 9 carry-over products in the new battery. The cell is still a prismatic pouch, but redesigned. The engineers went to a 3P design instead of a 2P, allowing them to increase individual capacity in cells by slightly more than 50%. There are mechanical changes as well, for a more efficient package.

In terms of chemistry, Wallace said:

We are still NMC and LMO. We changed the ratio a little bit—a little more NMC and a little less LMO. NMC is a high surface area modified product—this is a brand new class of NMC. We’ve changed things like binder materials, electrocoat and ionic conductivity, and we were also able to drive our electrode count down and our coating weights up. That helps us get more energy. We were able to improve volumetic energy density 20% at a cell level.

It’s not a radical change in cell chemistry, but it is absolutely the most modern NMC/LMO material. We also made some changes on the graphite side to improve performance and life.

Wallace noted that approximately 20 million battery cells have been produced for the more than 69,000 Chevrolet Volts on the road today with industry-leading quality levels of less than two problems per million cells produced (2 ppm).

The battery system continues to use the Volt’s active thermal control system that maintains electric range over the Volt’s life.

Based on a GM study of more than 300 model year 2011 and 2012 Volts in service in California for more than 30 months, many owners are exceeding the EPA-rated label of 35 miles (56 km) of EV range per full charge, with about 15% surpassing 40 miles (64 km) of range. Current generation Volt owners have accumulated more than 600 million EV miles.

EV range estimates will be revealed in January at the North American International Auto Show in Detroit.

GM will manufacture the Volt battery pack at its battery assembly plant in Brownstown, Mich.

 The second-generation Voltec drive unit. Click to enlarge.

Drive unit. Like the battery system, the next-generation Volt’s drive unit was reengineered with a focus on increased efficiency and performance, improved packaging and reduced noise and vibration characteristics. The two-motor drive unit operates approximately 5 to 12% more efficiently and weighs 100 pounds (45 kg) less than the current system.

The gen 1 Volt drive unit comprised two motors—a 111 kW main traction and 63 kW (at 4800 rpm) generator motor (55 kW generator output)—as well as three clutches and a planetary gear set tucked in the end of the traction motor.

Although the gen 2 system also uses two motors, the motors are new (one being rare-earth element free, the other with lower use of rare earth elements) and their roles have changed. Rather than designating Motor A as the generator motor and motor B as the traction motor, the two motors in the gen 2 system share both roles, providing more flexibility. GM has reduced the number of clutches to two from three.

Further, the ability to use both motors helps deliver more than 20% improvement in electric acceleration.

If we do it [provide traction] with two motors rather than one, we can spread the ratio. So now we have a spread torque band that’s actually wider and more responsive with a two-motor configuration. I like to call it a twin torque path. How those motors actually during the EV drive work together to give you that interval response is one of the key characteristics that our experts said really will make this be a better drive feel than we had before.

When you add that [two-motor] flexibility to your system, you increase efficiency—we're up about 12% in some of the driving modes,—but you also make it more responsive. The whole twin torque path spread ratio requires a lot of software and a lot of optimization.

—Tim Grewe, General Director, Electrification

The Traction Power Inverter Module (TPIM), which manages power flow between the battery and the electric drive motors, has been directly built into the drive unit to reduce mass, size and build complexity while further improving efficiency.

 Top: The integrated motor/TPIM drive unit. Bottom: The drive housing being prepared to receive and receiving the TPIM module; the motors are already in place, but hidden by the housing. (The briefing including a hands-on build of two complete drive units.) The high-voltage connectors linking power electronics to motors are seen at the bottom of the housing in both pictures. Click to enlarge.

The two motors are all-new GM motor designs, although they are built for GM by Hitachi. They are bar-wound interior permanent magnet type motors, and feature common tooling but with a reduced total physical size. The motors feature a mass reduction of more than 33 lbs. (15 kg), while offering a greater total power capability of 4% and with peak motor efficiencies increased by 2%.

While the stators are twins, there are differences in the rotors, Savagian noted.

Design for the motors was begun several years back when concerns over rare earth metals pricing were quite high, noted Pete Savagian, General Director, Electric Drive. Accordingly, Motor A uses no rare earth magnets at all, featuring instead a GM multi-barrier Ferrite magnet design. Motor B uses a reduced dysprosium-type grain boundary diffusion magnet technology.

Total rare earth magnet mass reduction in the new system is 60%—from 7 lbs (3.2 kg) to 2.6 lbs (1.2 kg). The reduction of heavy rare earths is more than 80%—from 0.6 lb (282 g) to 0.08 lb (40 g).

New 1.5L range extender. Energy for extended-range operation comes from an all-new, high-efficiency 1.5L 4-cylinder engine. The engine features a direct injection fuel system, high-compression ratio of 12.5:1, cooled exhaust gas recirculation and a variable displacement oil pump. The Voltec range extender also runs on regular unleaded fuel. Its use in the Voltec system is the first production application of the engine in North America, GM said.

We had the idea in first gen that we would have a full-size battery and a half-size engine. We did all our simulation and analysis, and thought we had the tiny engine that can. But if you drive the car hard, in more strenuous situations, the full-size battery and the half-size engine get behind, and the engine gets loud. It wants to make power, has to make power. But our customers want the quiet EV experience in extended range. So we developed the next gen volt with a 60% size engine. Just a little bit more.

On an average basis, the engine runs at lower speed, delivers more torque, is quieter. So making the engine bigger is actually giving our customers exactly what they want. They want the feel of an electric car even when they get into range extension. And that’s what we’re going to give them.

—Larry Nitz

The 1.5L engine will be manufactured at GM’s Toluca, Mexico engine plant for the first year of production, then shift to the Flint, Mich. engine plant.

GM engineers are in the process of preparing of number of SAE papers on the new Voltec system, getting deeper into design, power flow and the like. These will be presented beginning in February.

The second-generation Volt is due to go on sale in the second half of 2015.

Customer feedback from buyers of BMW i3 range extended version also show that some customers are not happy with the loud noise from the small range extender that needs to work at its peak when the battery is drained and the car is driven hard or at highway speed. In these conditions some even reported that the car can only do 0 to 60 mph in 30 sec! That is a safety hazard.

It was my original hope that PHEVs could be made less costly by using a smaller gas engine. Now I am more convinced you need a full size gas engine for the range extender in order to make a good car that functions as expected in all conditions. That also implies that PHEVs will be more expensive than hybrids that again will be more expensive than plain gassers. I think that the 30,000 to 55,000 USD segment is the one where PHEVs can be less costly than long-range BEVs of similar size and comfort. For now at least. For cars between 20,000 and 35,000 hybrids can compete and for cars below 25,000 the gassers will continue to rule for many years to come.

But no Miller or Atkinson cycle as most of us were expecting?

Henrik,

I agree with you. The problem that you have outlined has engaged my mind since the 1980s when I first studied the performance and whole life cost of BEVs and Hybrids, fitted with generic batteries. I am still waiting for the ‘miracle battery’ that will disrupt the technology of today’s electrified vehicles.

Laszlo

The Volt I pack weighs about 180kgs according to the Volt forums.
So the saving of 13.6 kgs is around 7.5%

Irritatingly they don't give the specific energy , but they have improved the volumetric density by 20%, so making the heroic assumption that the relationship is unchanged then the overall increase in capacity would be around 10%, just about enough to back up GMs claim that every parameter is improved although hardly enough to have the ICE community quaking.

I loved the VOLT 1 design, as he best possible full purpose car compromise for its (small) # 16KHW battery. Its original ICE engine not being just a range extender / electric power generator then, but also being capable to help the electric motors mechanically when more power was required, at high speed on the motorway, or when climbing mountain roads.
Then I was expecting the Volt 2 to benefit from larger batteries, with improved instant power and larger dual electric motors (one per axis with different ratios like new Tesla D), to an extend where it could move to a (Tesla like) 100% ALL ELECTRIC DRIVE TRAIN, means the ICE would have no tracting capability any more, and be used only as an electric power generator, that could then be optimized differently for constant speeds...etc. That would have simplified the cinematic of this drive train big times, saving weight, costs, and space for an even larger battery, still fitting in the expected budget.
What is presented here is not clear.... Seams this improved ICE will retain the capability to tract the car in conjunction with the electric motors, despite battery was improved as well as electric motors... Why needed ?

This marginal increase in battery energy density for PHEVs from one of the leading manufacturers is way less than most of us had hoped, encouraged by endless excited headlines.

We don't know the most important parameter, cost, however.

Lets hope that the very different batteries in a BEV are susceptible to much better improvements.

Toyota with its reservations about battery technology is not sounding too daft just at the moment however.

Anyone remember if GM changed the battery chemistry mix after the highly publicized fire three years ago? I thought I'd recalled that but could not find it in a web search just now. Thicker railings around the battery pack and a programming change to shut it down after a wreck but nothing about a battery change.

If my memory's better than my web searching skills then this is now part restoration and only part advancement.

@Earle:
I don't think they changed the chemistry, just the design somewhat.

Here is comment in September 2011 after some of the post fire investigation:
'The Volt, which uses different technology, is being investigated after three batteries caught fire since May following government crash tests. The National Highway Traffic Safety Administration’s probe isn’t centered on battery cell chemistry, said Randy Fox, a spokesman for Detroit-based GM.

The probe is focused on pack design and any fix would likely involve the pack, he said in a telephone interview.'

http://www.bloomberg.com/news/2011-12-08/gm-seeks-out-batteries-less-volatile-than-volt-s-for-spark-model.html

And here is comment on alterations by June 2012:

'“The best way to explain what we’ve done at the cell level is to compare it to a cake batter recipe. Sometimes if you use more sugar and less vanilla you get a better tasting cake. We’ve done some work at the cell level to modify the ‘ingredients’ to make a better end result,” said Bill Wallace, GM's director of Global Battery Systems Engineering. “This attention to detail will allow our customers to experience more pure EV range, which is the true benefit of owning a Volt.”'

http://www.dailytech.com/2013+Chevy+Volts+Battery+Range+Boosted+to+38+Miles+Now+Rated+at+98+MPGe+/article24885.htm

That was supposed to be small tweaks to improve performance, with no mention of major change due to the fire.

In re: Atkinson cycle: from Greencarreports:

Finally, GM fits what it calls wide-authority cam phasers, which allow a broader spread of valve timing to allow the engine to operate in a mode close to the Atkinson Cycle, which reduces back pressure by keeping the inlet valves open longer.

This could have been called mini-improved Generation 1.1?

"On an average basis, the engine runs at lower speed, delivers more torque, is quieter."

"The engine features a direct injection fuel system, high-compression ratio of 12.5:1, cooled exhaust gas recirculation..."

This is what I thought would be required for a good EREV, you need torque at lower RPM, direct injection, forced induction and/or displacement will give you that. The engine pulls at 2400 RPM and generates at least 40 kW. That allows charge sustaining and mountain modes.

Would love to see this drive train in a CUV/wagon of some sort.

@Henrik,
>>>>"Now I am more convinced you need a full size gas engine for the range extender in order to make a good car that functions as expected in all conditions. "

Well, GM agrees with you, the engine got a little bigger instead of getting smaller.
However, GM failed to consider the case of a 1-liter-3-cylinder TURBOCHARGED ENGINE that I proposed for Tesla to replace Model III with Model S and X in PHEV form. The 1-liter turbocharged engine runs very quietly due to the muffling effect of the turbocharger, AND rpm can be reduced at higher power due to the torque boost of the turbocharger. No high-pitched whiny sound from an overworked tiny engine when a turbocharger is installed, because a turbocharge will upgrade a small engine into a BIG ENGINE with BIG TORQUE at lower rpm, with twice the displacement in a tiny package.

Another beauty about a turbocharged 1-liter engine is that the turbocharger allows torque to build up significantly with rpm instead of torque to fall at higher rpm. This means that the car can remain in a the same high gear the whole time from speed to its top speed WITHOUT GEAR SHIFTING REQUIRED. This means that only a 2 to 3 speed transmission will be required, while only ONE MOTOR will be needed, having 1/2 of the power of the GM's two motor setup in the next Volt 2nd gen. This will save tons of money for GM, since a 2-3 speed transmission is very cheap in comparison to another electric motor.

An electric motor + controller cost around $70 per hp, while a 6-speed transmission costs around$15 per hp while a 3-speed transmission costs around $7-10 per hp. So, replacing a device that costs$70/ hp with another device that costs $7 / hp would make good business sense! The reason that only 1 motor is needed with 1/2 of total electric hp required is due to the torque-boosting effect of the transmission that can double or triple the torque of the electric motor. Thus, acceleration below 60-70 mph is the same with two motors and no gear shift vs. with one motor of 1/2 power when the torque will be tripled in first gear, and then doubled in second gear! For cruise above 70 mph, the engine and turbocharger can kick in to provide additional power for powerful high-speed acceleration to allow fast overtaking in two-lane rural highways. Thus, if well designed, a PHEV can be surprisingly affordable with VERY generous passenger and luggage capacity, with the use of the power train as I've outlined IN COMBINATION WITH TESLA'S UNBEATABLE BATTERY TECHNOLOGY AND PACKAGING. WHAT ARE YOU WAITING FOR, TESLA, BEFORE ADAPTING MY UNBEATABLE PHEV POWER TRAIN DESIGN ON EXISTING MODEL S AND MODEL X, with your unbeatable battery technology? While saving tons of money from NOT developing Model III and the huge GIGA factory that may bankrupt the company! @Lazlo The "miracle battery" that you have been waiting for is already here TODAY. It is known as Tesla's battery. Just kindly approach Mr. Musk to ask him to share it with the rest of the auto MFG's, or ask him to make PHEV versions of Model S and Model X. @Clett, The next Volt will run on Atkinson cycle. But, why bother, when you only need to use the engine only 10- 20% of the time? It is better to have a very powerful but smaller engine with a turbocharger for all the reasons outlined above. Roger, The proposed Tesla X PHEV would end up with a much smaller sized battery pack, using the Panasonic 18650 format cells, currently installed in Tesla S. It would inevitable degrade vehicle performance in the pure electric drive mode. Tesla S has an outstanding performance and range thank to a very large (c. 400 kg) pack as well as very good but not miraculous energy and power density performance at cell level. laszlo @laszlo, With a 16-kWh pack to get the most out of Fed incentive, and at 5.5 C max discharge power that Tesla's NCA chemistry is well capable of, according to independent University testing, the power available should be: 5.5 x 16 = 88 kW, perfect power for the all-electric mode. Adding another 90 kw turbocharged 1-liter engine, and total power would be almost 180 kw, or 241 hp, in a car that is well below 3,500 lbs curb weight. Should be capable of luxury-sport sedan type of performance worthy of a$45,000 price tag.

This $45,000 price tag for the PHEV Model S will be$10,000 higher than the proposed $35,000 price tag for the Model 3, because the car is bigger and more internal capacity and a bigger presence in the roadway, while the profit margin will be much larger than Model 3, with much lower developmental cost that will ensure the rapid growth of Tesla to bring electromobility wide and far into the world! This does not look like a step forward more like a step sideways. Typical GM parlor trick. Volvo using triple electric turbos are getting over 400 horses from a small engine 4 cylinders. Go with 1/2 that and you don't even need the batteries. Then there is the Professor Lee Cronin of the University of Glasgow’s School of Chemistry who has a new way to store hydrogen safely and batteries start to look like a waste of time. Plus the COST and the quality of the Volt, it looks so cheap. I've always favored PHEVs over BEVs and FCEVs, no matter their specific configuration. PHEVs complement, rather than overwhelm utility grids, offer households various incentives to drive less and reduce household energy consumption. The larger the battery pack, the further the average driving distance. I'm more interested in changing the system than entertaining the whims of hapless motorists stuck in traffic yelling at the kids in the back seat, "Don't make me turn this car around," when they whine, "Are we there yet?" It seems to me that the bigger picture is being missed in the discussion of new technology. The most valuable technological advancement of autonomous, self-driving car, for instance, may be strict regulation of accelleration and speed rather than emergency braking and hands-off driving nonsense. Those bitching that it should be a 1-liter, 3-cylinder or a turbo-charged whatever, need to consider that there is more to fuel economy than engine size. What really matters is that the engine is running in an efficient manner with little or no throttling loss and has a relatively high compression ratio. A good example of this was to compare a 6 or 6.2 liter Corvette with the 2 liter Honda S2000 a few years ago. They both got about the same mileage even though the Corvette was considerably larger and much more capable. And, yes, if you tried hard, you could burn considerably more fuel with the Corvette but with similar driving, the Corvette would deliver the same or better mileage. The new Corvette with the ability to run on 4 cylinders would do even better. An even funnier example was when Top Gear ran a comparison between a Prius and a BMW 3 Series. They flogged the Prius around a race course and had the BMW loaf around matching the performance (or lack thereof) of the Prius. Guess which one got the better fuel economy. A clue -- it wasn't the Prius. I also read the article in Car and Driver mentioned in previous post on the 2016 Volt -- http://www.caranddriver.com/news/2016-chevrolet-volt-spy-photos-news The really telling thing was to read the comments by 3 different current owners of the Volt. Everyone was quite pleased with the car and commented on how well the car drove. I know that Jay Leno, who has a warehouse full of exotic cars and could afford to drive anything he pleased, used a Volt as a daily driver and he would not have been doing that had it been a chore to drive it. Bob tasa, I am inclined to disagree with a number of your points. First, the Volt is a battery/gas vehicle. Turbocharging a smaller engine with electric (or conventional) turbo's does not result in stunning MPG. Yes, it's a small help, under some conditions, but BSFC numbers don't improve to the 100MPGe range as it does via efficient battery-electric drive. I also don't understand your "step sideways" comment. It promises to be a more refined drivetrain. What's not to like about refinement? Or more efficient operation, or better battery range? Finally, compared to the cars I drive, the Volt is not/does not look "cheap" or low "quality" in any way. Not all of us can afford expensive vehicles, oozing with hand stitched leather, 40 series tires or other luxuries. Compared to a Yaris, or my little Honda, the Volt is far more car, and far quieter. I should have put in a link for the Top Gear Prius vs BMW https://www.youtube.com/watch?v=JmxUsGiGp3w It is in the 2nd half of the 6 minute clip and the BMW was actually a 400 hp M3 with a 4 liter V8. They got 17 mpg with the 1.5 liter Prius and 19 mpg with the 4 liter BMW. One of the reasons that the Prius normally does so well on fuel economy is that it so under performing that there is little or no incentive to do anything but drive it slowly. The Volt has enough performance and drives well enough in normal driving that it is not an unpleasant car to drive. @sd, For a car that must rely on its engine 100% of the time, a bigger engine would lead to higher durability and lower rpm operation. However, for a car that only needs its engine 20% of the time, then some weight and space saving can be had with the smaller engine. The 1-liter-3cylinder turbocharged engine has other special advantages. 1) First of all, at over 120 hp, the turbocharged engine may have over 30 hp advantage over that of an Atkinson-cycle engine that probably will not make over 85-90 hp, given that the Prius 1.5 liter Atkinson engine makes 76 hp. All in a smaller package. 2) Secondly, the torque of the turbocharged engine matches closely the torque-demand curve of the car from 20-120 mph, meaning that the engine will remain at peak efficiency from slow to high speed all on a single gear. No gear shifting required! When extra torque is needed, the motor can provide the extra torque boost without requiring gear shifting. 3) With this kind of engine, GM can do away with the second motor, hence requiring only a single traction motor of the same size, hence cutting the cost of the electric drive train to half. The reason that a 2-motor arrange is required is that the 2 motors are acting as an electric transmission (e-CVT), in which one motor acts as a generator and the second motor is acting as a traction motor. The non-turbocharged engine has its torque curve drops off at higher rpm range. This means that gear down shifting is required if one needs to cruise at high speeds due to the much higher torque demand at higher cruise speeds. So,a gear-ratio-change transmission is required. The saving of having one motor + inverter of 60-kW power instead of two of those would be ~60kW x$94/kW = ~$5,645 4) A 3-speed automated manual style of transmission or planetary gear sets is still provided in case of prolonged hill climbing to provide the torque needed, but not necessary. How can a single 60-kW motor perform on par with two 60 kW mtor up to 60-70 mph? Answer: Put the motor on second gear most of the time, whereby the torque of the motor can be doubled to be equal to the torque of 2 60-kW motor. For Power Mode, the motor cans start on first gear and goes thru all the gear shifting. Thus, a 3-speed gear transmission may cost$1,000-1,500 and rarely used, to replace a second electric motor/inverter at \$5,500.

5) In POWER MODE, both the engine and motor will provide power, and the gear will shift thru all 3 speeds in order to maximize the torque for maximum acceleration.

The "secret sauce" here is the enabling small engine with turbocharger without waste gate, for power doubling or even higher power, perhaps power tripling if higher cruise speed is truly desired!

Think of the Honda Civic hybrid layout, instead of a weak 1.3 L with 14 HP motor, you have a 1L direct inject turbo with a 40 HP motor.

Performance would be better, it would be simpler but still get good mileage. Make it FFV so it can run on cellulose E85 to reduce oil imports, clean the air and reduce CO2.

To get improved economy out of a smaller engine, it would have to take a page out of the book of turbodiesels.  The key feature of the turbodiesel is the recycling of exhaust energy to the crankshaft via the turbocharger.  When the intake manifold pressure is higher than the exhaust BP, the pressure on the piston during the intake stroke can be greater than that on the exhaust stroke and the engine reaps pumping gains instead of pumping losses.

It should be possible to turbocharge an Atkinson-cycle engine and achieve a similar cycle.  Reducing the geometric compression reduces the compression work, but the expansion work will be about the same if the air charge is unchanged.  Also, a hybrid is ideally suited for TIGERS, reclaiming any excess exhaust energy via the HV electrical system instead of using a waste gate.

Is it worth the expense?  I don't know.  What I can say is that I've driven a 2-liter turbodiesel cranking out 95 horsepower, and a 2-liter Atkinson probably doing less than that... and the turbodiesel does the job much more quietly and likely more efficiently as well.

Roger Pham

I am not sure what you are trying to say. GM designed the power train assuming that most of the driving would be electric only but that it would be fairly seamless when it was ICE was operating.

Anyway, on engine design issues, engine RPM does not matter. What matters is mean piston speed. Interestingly, most engines run about the same mean piston speed whether they are large ship diesel running 88 RPM or small model airplane engines.

Concerning turbochargers, GM certainly has experience with turbocharged engines as they have been building turbocharged engines for more than 75 years (Allison V-1710) and turbocharged cars for more than 50 years. (I had one of the first, a 1963 Corvair Spyder.) Their current 2 liter turbocharged direct injection engine is one of the more power dense engines available for a street vehicle with 136 hp/liter. However there is detonation limit to how much boost you run with a spark ignition engine. A turbocharger is basically a positive feedback device (more boost generates more exhaust which generates more boost, etc) so you can not run a turbocharger without someway to limit the boost otherwise something will blow up. Yes, GM could run a smaller turbocharged engine and they already have current turbocharged engines that would work but they probably decided the cost was not worth the gain as the engine does not run most of the time.

All these calculations about engine configuration still neglect the bigger picture. All EVs will plug-in to households, specifically complementing utility grids or ultimately overwheming them with high demand, followed by the need to increase decentralized power generation. Battery capacity is the key. Do we want a utility grid to daily recharge 10 (85kwh)Telsa coupes or 170 (5kwh)PHEVs? The smaller PHEV battery pack is also the more ideal match to rooftop solar arrays.

A PHEV more than doubles the 'effective' mileage of a standard hybrid of 50mpg to 110mpg for a plug-in. This economic incentive to drive less is closer to a real solution than any standard drivetrain vehicle without an electric propulsion mode. Drive more than 10-20 miles daily means paying the higher costs of fuel.

You want a sporty car? The EV-1 had a dashboard switch that instantly increased HP from economy mode to performance mode. PHEVs could do that too.

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