Study Shows Chevy Volt Can Burn Less Gas Than Any Other PHEV

For everyone who likes to say the Chevrolet Volt is just one more plug-in hybrid, a GM study presented to the Society of Automotive Engineers shows it stands to burn radically less gasoline and emit much less smog-forming gases than competitive PHEVs.

The engineering analysis also projects the new 2016 Volt due in a couple of months will significantly outperform the 2011-2014 specification Volts studied.

Why? The short answer is the Volt has a battery twice to four-times larger and is rated at least double the all-electric range of any conventional plug-in hybrid. For daily driving, this plus unique system architecture and higher top EV speed means the engine stays off longer and the study says the Volt can provide 40-times or more all-electric trips.

By contrast PHEVs – such as by Toyota, Honda and Ford – have batteries one-half to one-quarter the Volt’s size, lower top speeds, and the gas can come on more often.

Prius Plug-in Hybrid, AKA "PHEV A.

Prius Plug-in Hybrid, AKA “PHEV A.

Of course these roomier competitors are midsized and Volt is compact. Also, prices vary, styles do too, and there are myriad other trade-offs besides in a full comparison, but the paper isn’t about any of that. Rather, it drills down solely on the Volt’s number-one virtue: powertrain and daily driving efficiency.

Titled “Chevrolet Volt Electric Utilization,” and citing SAE precedent to justify its assertions, the paper distinguishes between an “extended-range electric vehicle” (“E-REV”) and generic “plug-in hybrid electric vehicle” (PHEV).

Honda Accord PHEV, AKA "PHEV B."

Honda Accord PHEV, AKA “PHEV B.”

For the past four years Volt critics have decried the “E-REV” moniker as mere marketing verbiage by GM, but the paper written by GM engineers and presented to the SAE offers separate definitions for each.

E-REV: “A vehicle that functions as full-performance battery electric vehicle when energy is available from an onboard RESS [rechargeable energy storage system] and having an auxiliary energy supply that is only engaged when the RESS energy is not available.”

PHEV: “A hybrid vehicle with the ability to store and use off-board electrical energy in the RESS.”

Ford Fusion Energi shares powertrain with C-Max Energi. One of these is likely "PHEV C."

Ford Fusion Energi shares powertrain with C-Max Energi. One of these is likely “PHEV C.”

If one takes the fact the Volt uses two power sources, then by a looser definition it is also a plug-in hybrid, but the SAE makes a finer distinction in how the car actually functions next to other competitive PHEVs.

The study is based on real-world data from more than 60,000 2011-2014 Volts. The data was anonymously collected via GM’s OnStar telematics service by cooperating owners from October 2013 through September 2014. This was to ensure all four seasons were represented. For the PHEVs other data samples were used including from 621 vehicles monitored by the Southern California Association of Governments, plus data from the National Renewable Energy Lab, Idaho National Laboratory, and more.

Volt Really Is An EV With Gas Backup

The Volt is able to run gas-free far more than conventional vehicles and even PHEVs because of its system architecture and how it works.

The study found “trip initial engine starts” for the generation-one Volts were reduced by 70 percent compared to conventional vehicles under the same conditions.

"RTS" data refers to Southern California Regional Travel Survey (RTS) data.

“RTS” data refers to Southern California Regional Travel Survey (RTS) data.

“These Volt drivers were able to travel 74 percent of their total miles in EV [mode] without turning the engine on,” said the paper.

By comparison also, the paper observed “a PHEV’s lack of full-performance all-electric capability results in engine operation under everyday speed and/or load conditions, regardless of available battery energy.”

Figure 9 shows the percentage of days that could be completed entirely on electricity as predicted from the RTS data set when considering all three propulsion system constraints for the example PHEVs and the Volt E-REVs.

Figure 9 shows the percentage of days that could be completed entirely on electricity as predicted from the RTS data set when considering all three propulsion system constraints for the example PHEVs and the Volt E-REVs.

“The dominant factor in EV trip capability of a PHEV is determined to be the amount of power available from the battery or electric motor before an engine start is required,” continued the paper. “With full vehicle performance capability as an EV, a 35 mile E-REV is found to provide up to 40-times more all-electric trips than a PHEV over the same data set.”

A “35-mile E-REV” would be none other than 2011-2012 Volts. The 2013 and 2014 Volt models increased to 38 miles rated range with an increase from 16.0 kilowatt-hours for 2011-2012s to 16.5 kilowatt-hours for 2013-2014s. Not studied were 2015s which have 17.1-kwh batteries.

Unidentified, but "A" is most likely Prius PHEV; B is Honda Accord Hybrid; C is C-Max or Fusion Energi.

Unidentified, but “A” is most likely Prius PHEV; B is Honda Accord PHEV; C is C-Max or Fusion Energi PHEV. NOTE: The BMW i3 REx is not counted likely because its not a full-range PHEV. Its small-gas-tank-equipped 2-cylinder range extender means it’s more of an EV with short-distance backup according to BMW. Nor is it in a direct price/performance/market position class against the Volt to the degree that the others are.

As mentioned, the “PHEVs” in question almost certainly are the Prius PHEV, limited-market Accord PHEV, and a C-Max or Fusion Energi PHEV. We say this because they are identified by their top EV-mode speeds and all-electric ranges of 6 miles, 13 miles and 21 miles respectively – note Ford has since been downgraded to 19 miles, but was 21.

2016 Volt Should Do Better

Based on the first-generation Volt’s “in-use operating data,” the paper projects the second-generation Volt will be able to complete 80 percent of total miles driven using electricity.

The study does not say so, but where a Volt will not do as well is if used on a lengthy trip or with un-charged battery. Here it comes down to mpg ratings and its unique electric-operating advantages do not come into play.

The study does not say so, but where a Volt will not do as well is if used on a lengthy trip or with un-charged battery. Here it comes down to mpg ratings and its unique electric-operating advantages do not come into play.

That means no gas required, and would beat the first-generation Volt by 25 percent assuming the same driving and charging behavior as observed in the study.

The paper points out the 2016 Volt is rated 50 miles EV range and 41 mpg compared to 38 miles and 37 on premium for the 2013-2015 Volt.

“For PHEV operation, there are three constraints that primarily impact vehicle all-electric performance capability,” says the paper. “These include the useable energy in the battery pack, the available electric propulsion power before engine assistance is required, and top speed electric capability. For E-REV operation, only useable energy stored in the battery pack is applicable, as an E-REV is designed to provide full vehicle power and speed performance without starting the engine.”

“For PHEV operation, there are three constraints that primarily impact vehicle all-electric performance capability,” says the paper. “These include the useable energy in the battery pack, the available electric propulsion power before engine assistance is required, and top speed electric capability. For E-REV operation, only useable energy stored in the battery pack is applicable, as an E-REV is designed to provide full vehicle power and speed performance without starting the engine.”

“With 12 additional miles of all-electric range in the second generation Chevrolet Volt, the need to start the ICE would be eliminated on over 5 million additional trips bringing the total percentage of all-electric trips to 77,” says the paper. “Leaving only 23 percent of the conventional vehicle’s initial engine starts translates to a substantial reduction in criteria emissions.”

Opportunity Charging

Part of why the first-generation Volt did so well in the analysis was due to opportunity or intra-day charging. The study found the average Volt owner does charge overnight, and many also plug in during the day to stretch effective daily range beyond EPA limits for a single charge.

“It was found that if a 35-38 mile range was strictly enforced while maintaining observed charge behavior, the all-electric miles would be approximately 66-68 percent,” said the study. “With actual data showing 74 percent miles electrically, this suggests these drivers are achieving ranges that exceed EPA estimates near 45 miles.”

Far Fewer Cold Starts

One factor called out is that when a plug-in hybrid – or a Volt – starts its internal combustion engine, it is a “cold start” where the engine is least efficient and most polluting within the first minute.

“For simplicity, the cold-start emissions are considered as a 25-percent contributor to total smog emissions and running emissions are considered as the remainder of the emissions,” says the paper.

This chart illustrates the separation between E-REV and PHEV by comparing the amount of electric power available as a ratio to the vehicle power demand at full driving performance.

This chart illustrates the separation between E-REV and PHEV by comparing the amount of electric power available as a ratio to the vehicle power demand at full driving performance.

“The distinguishing feature of an E-REV that differentiates it from a PHEV is the capability of full vehicle performance as an EV,” said the study. “The fuel powered engine in an E-REV is primarily intended to be a generator to extend driving range for long trips. Whereas, a PHEV is a hybrid electric vehicle architecture with the addition of plug in charge capability and has limited all-electric performance.”

Air Pollution

According to the paper, EPA Plug-in Hybrid Electric Vehicle labels with a numerical smog score from 1 to 10 meant to grade degree of smog-forming emissions are only so valuable because “less clear for the consumer” is the effect of EV operation to prevent gas-engine startup.

label

"A consumer may not be able to understand the benefit to smog forming emissions of the PHEV or EREV that they are considering by just looking at the label in its present form. The label for the MY13 Volt is shown in Figure 10 (non-CARB) [16], and the smog score rating scale is shown in Figure 11 [15]. Note that the label for California and other states which adhere to the CARB rating system will show a 9 in the Smog Rating section."

“A consumer may not be able to understand the benefit to smog forming emissions of the PHEV or EREV that they are considering by just looking at the label in its present form. The label for the MY13 Volt is shown in Figure 10 (non-CARB) [16], and the smog score rating scale is shown in Figure 11 [15]. Note that the label for California and other states which adhere to the CARB rating system will show a 9 in the Smog Rating section.”

“This rating may vary by state, and typically reflects the smog forming emissions of the base engine without regard for the all-electric capability,” says the paper. “States that modify the label smog score for advanced technology vehicles will change the rating based on a PZEV or AT-PZEV certification, which requires SULEV engine exhaust emissions as a first pre-requisite. Existing smog score label methodology does not reflect the infrequent engine starts on an EREV vehicle.”

The first generation Volt reduces smog forming emissions by 76 percent as compared to a conventional vehicle with the same engine and the second generation Volt reduces smog forming emissions by 82 percent. PHEV A (presumed Toyota), B (presumed Honda), and C (presumed Ford) reduce smog forming emissions by 17 percent, 26 percent, and 31 percent respectively

The first generation Volt reduces smog forming emissions by 76 percent as compared to a conventional vehicle with the same engine and the second generation Volt reduces smog forming emissions by 82 percent. PHEV A (presumed Toyota), B (presumed Honda), and C (presumed Ford) reduce smog forming emissions by 17 percent, 26 percent, and 31 percent respectively

Bottom line, says the paper, the Volt outdoes all others.

“There is significantly less real-world production of smog forming emissions from E-REVs than a conventional vehicle or even a PHEV equivalent, which is not yet accounted for in the smog score rating in many states.”

SAE