GM-VOLT : Chevy Volt Electric Car Site

It seems very likely that the GM patent application “Output Split Electrically-Variable Transmission with Electric Propulsion Using One or Two Motors” describes the Chevrolet Volt transmission (which GM has called the Electric Drive Unit). The file is a pdf and you’ll need the free Adobe reader to view it:

http://www.freepatentsonline.com/20090082171.pdf

Here is a snapshot of the title page:

I will apologize in advance to those of you who are less technically inclined. This posting contains a lot of engineer speak. I’ve tried to keep it as straightforward as possible, but this is a complex device. If you want help understanding how a planetary gearset works here is a link to help:

http://auto.howstuffworks.com/automatic-transmission2.htm

Figure 1 of the patent application is here:

It shows the internal combustion Engine connected via clutch C3 to Motor/Generator A which connects via clutch C2 to the Ring gear (labeled C) of a planetary gearset . The Ring gear also connects via clutch C1 to a stationary member of the transmission case. Motor/Generator B is connected to the Sun gear (labeled A) of the planetary gearset. The planet Carrier (labeled B) of the planetary gearset is connected to the Final Drive which, though this is not shown, is connected through the differential to the drive wheels of the car. (Don’t worry about the second, dashed, copies of Engine and M/G A, they just show an optional alternative configuration without clutch C3.)

The nature of a planetary gearset is that when the speeds of any two of the Ring, planet Carrier, and Sun gears are known the speed of the third is determined.

Figure 3a of the patent application is here:

It shows a truth table defining the available operating modes of the transmission. In the first three columns C1, C2, and C3 there is an X when that clutch is engaged or a blank when that clutch is disengaged. The rows of the table define six operating modes (plus a seventh, transition, mode).

In mode 1: 1 Motor Electric-only the Ring is held stationary and there is a fixed gear ratio from M/G B to the Final Drive.

In mode 2: Series we still have the fixed gear ratio from M/G B to the Final Drive. In addition, the Engine is connected to M/G A so that M/G A can start the Engine and the Engine can then drive M/G A to generate electricity for the battery and/or M/G B.

In mode 3: Output Split the Engine and M/G A work in unison to drive the Ring gear. This torque is blended with that from M/G B to the Final Drive. (This mode is just like the Toyota Prius’s Hybrid Synergy Drive.) Note that GM seems to have stated that the Volt never mechanically couples the Engine to the wheels. That would imply that mode 3 is never selected in the Volt, even though it could be. I don’t know what GM has really done in the Volt. We will presumably find out by the time the first Volts are delivered to dealers.

In mode 4: Neutral the Final Drive receives no torque since the Sun gear can spin freely.

In mode 5: Neutral / Battery Charge the Final Drive receives no torque, but the Engine is attached to M/G A and can drive M/G A to generate electricity for the battery.

In mode 6: 2 Motor Electric-only M/G A and M/G B are driven simultaneously and their torque is blended for delivery to the Final Drive. The combination of speeds of M/G A and M/G B determines the speed of the Final Drive. Alternately put, the speed of M/G A determines the gear ratio from M/G B to the Final Drive. This is the Electrically Variable Transmission (EVT).

You may ask how these six modes relate to the Charge Depleting (CD or Electric) mode of the Volt and to its Charge Sustaining (CS or Extended Range) mode. Here is my take:

In CD mode the 1 Motor Electric-only and 2 Motor Electric-only modes are used to optimize the electrical efficiency of M/G A and / or M/G B at the required road speeds. It is all about using the EVT to get the most miles of All Electric Range from the charge available from the battery. No gas is used.

In CS mode the Series mode is used to have the Engine, over time, drive M/G A to generate just enough electricity to keep the battery state of charge within the buffer range while M/G B is driving the wheels through the fixed gear ratio when the Ring gear is held stationary. As I said earlier, the Output Split mode could be used in CS but GM may have chosen not to do this for some reason.

Of course, there is no proof that the Volt’s transmission is what this patent application describes, but the timing (filed September 10, 2007) is right and it fits the statement by GM public relations guy Rob Peterson that the Volt has a planetary gearset and a number of clutches. It also fits the statements Volt powertrain engineer Alex Cattelan made in her interviews with Lyle last November: http://gm-volt.com/2009/11/09/engineering-design-of-the-chevy-volts-two-electric-motors/ . And there is NASAman’s statement from Bob Lutz that “the Volt will have a transmission like no other” In addition, several people who’ve ordered Volts have posted the following description from the myvolt.com order tracking site:

“Powertrain
TRANSMISSION AUTOMATIC, ELECTRONIC RATIO SELECT, GM, STRONG HYB RID, EVT, PLUG IN
ENGINE FLEXIBLE FUEL, (GAS/ALC), 4 CYL, 1.4L, MFI, DOHC E-FLEX, FAM 0″

In conclusion, if the patent application does describe the Volt’s transmission it means that the Volt is NOT a single speed only transmission. It is an Electrically Variable Transmission (EVT). In addition, if the clutches C2 and C3 are engaged simultaneously there is a mechanical power path from the engine to the wheels. It may be that GM has chosen to never engage C2 and C3 simultaneously, but they could if they wanted to. (I don’t know if that would be an infringement of Toyota’s Hybrid Synergy Drive patents; I’m an engineer, not a patent lawyer.)

For more discussion of this patent see the following thread in the Engineering forum:

http://gm-volt.com/forum/showthread.php?p=43109#post43109

Lyle tells me GM has said it plans to publicly unveil this system soon after the cars are out there, so we should get a definite resolution of all these questions by then. In the meantime it sure is fun to speculate.

We can’t always just focus on the Volt, and once in a while its good to look at exciting developments in the rest of the electric car universe.

One feat most certainly worth noting is a new world’s record land speed in an electric vehicle achieved on Wednesday. 307.7 miles per hour to be exact which was set by a vehicle called the Buckeye 2.5 created by engineering students from the Center for Automotive Research at Ohio State University.

The rocket on wheels is powered by a massive 600 kw peak power lithium-ion battery pack composed of highly potent A123 Systems cells.

The previous record was a paltry 245 mph set in 1999 by White Lightning.

The record was achieved on a 12 mile run over the fastest place on earth, the Bonneville Salt Flats in Utah. It was the average over two runs.

The team is sponsored by the French EV maker Venturi.

The 307.7 mph record has not yet been certified and thus made official by the Federation Internationale de l’Automobile (FIA) which is the worldwide motor sports governing agency, though approval is widely expected it may take a few weeks.

“We’ve been at this for 16 years now and have our newest lithium-ion powered vehicle out,” team manager David Cooke told the AP. “Our vehicle was capable of going much faster.”

The Buckeye Bullet 2 was powered by a hydrogen fuel cell when it set the record for those vehicles at 302.8 MPH in 2009. The Ohio State team spent the previous year removing the fuel cell system and replacing it with over 1600 pure lithium cells in total.

The team was hoping to do one more trial run on the flats to top the 307.7 but had to call it off when the clutch failed.

Hats off to Ohio State. Electric vehicles aren’t just golf carts anymore.

Source (AP)

Pike’s Peak has been a cornerstone of advanced Chevy Volt developmental engineering. The road is so important to Volt development because it represents a continuous long grade uphill. This driving condition would be expected to put a maximum load on the Volt’s engine-generator while in charge sustaining mode. After the battery reserve is depleted, the roughly 3500 pound car has to rely solely on its 53 kw (71 hp) engine to deliver power for the continuous climb, sustained velocity, and any acceleration. Since the car will thus be at its performance limits, engineers can try to tweak the system to keep performance acceptably nimble. Indeed this scenario is exactly why the Mountain Mode was created; to give drivers an extra large battery buffer to dip into when an uphill grade arrives.

Every time GM has gone to Pike’s Peak we’ve been told the Volts perform well. Yet they keep going back, as refinement continues.

Recently Edmunds captured a fleet of Volts taking the climb and descent and posted the video below. Volt spokespersons Rob Peterson confided Volts have traveled altogether about 800 miles on Pike’s Peak. The path is 38 miles round-trip and the summit is at 14,110 feet. “At this point, our development engineers are focusing on real-world miles, putting the vehicles through their final paces,” said Peterson.

The ride back down form the summit is also interesting because the car can recapture a significant amount of energy via regenerative braking. “By the time the Volts made it off the hill, they had recaptured double-digit miles of energy,” said Peterson.

I asked Volt director Tony Posawatz, what GM is learning from its repeated trials up and down the Peak.

“As you know, we are very serious about the testing we do on our cars, especially the VOLT with it being loaded with so many “technology firsts,” he said. “We try to prove to ourselves that in the most severe and harshest environments that every VOLT will exceed our expectations including on-going “tweaks” as we finalize our software/controls and assure full completion of all of our tests.”

“It is pretty fun to continue to do work on Pikes Peak when you know your car can handle it,” said Posawatz. “Do all other plug-ins tout their prowess on Pikes Peak? I think not.”

“You know our ReGen braking recaptures a lot of electric miles on the way down and records a really low brake pad temp,” he added. Such low temperatures have occurred that a ranger who performs mandatory brake testing seven miles from the summit actually had to check the Volt twice with his laser gun.

Recently there has been a lot of Internet controversey with at least a dozen articles covering a story out of the Telegraph in England. Of course, GM-Volt.com was the first to notice this claim and publish it, all the other sites followed.

The author, Andrew English, claimed the 65% calibration version Ampera/Volt prototype seemed to have a flat torque curve at high velocity. He wrote that an engineer claimed GM was planning to correct this by connecting the gas engine driectly to the drivetrain. I had checked in with Rob Peterson who said the claim was untrue and unfounded, and is not the case. Rob explained to us the Volt uses clutches and a planetary gear system to maximize performance and efficiency.

Despite this, English published a second report called “Volt Shock.”

In this repert he outed his source. “We are considering driving the wheels directly from the petrol engine,” said Andreas Voight, an Opel project engineer. There are a number of different ways we could do it, but the whole thing is subject to some intellectual property rights negotiations so I can’t say any more,” said Voight. “You will see an announcement this autumn.”

While that story may be shocking, it remains untrue. Sam Abuelsamid from Autobloggreen determined Voight is simply a technician whose job (?former) is to simply shuttle cars for journalists and who has no actual knowledge about Volt engineering. Know the type?

Another bad piece of journalism came out fo hybridcars.com, who won’t even publish authors’ names. The anonymous author claimed an “exclusive” interview with Rob Peterson. In that interview Peterson’s comments were taken out of context and distorted to make it seem the Volt would act like a parallel hybrid in range extended mode. Peterson was simply saying it was theoretically possible but the author left out the part where he said it wouldn’t. Anything is possible.

What many authors don’t know is that the Volt has two electric motors that can act either in parallel at times, in other cases one acts as the traction motor to drive the wheels and the other acts as a generator. The system uses 2-mode technology to determine which configuration is optimal for that driving moment. It never, however, includes a direct ICE to wheel configuration. For more deatils see my post with Volt powertrain engineer Alex Cattelan.

Finally to put this all to rest, I asked Volt vehicle line director Tony Posawatz if any of this rumor was true, if the ICE ever drives the wheels.

“No.” said Posawatz. “I don’t know how those folks got so confused.”

Got it?

The Opel Ampera is the identical sister car to the Chevy Volt only sporting Opel design cues.  It will be built side-by-side with the Volt in Michigan for export to Europe where it will go on sale in 2011.

Like the Volt, only a little later, Opel is beginning to allow journalists to test drive an Ampera. Famed British publication Telegraph had its chance at the wheel and author Andrew English has produced an interesting review.  GM has been careful to only allow journalists, myself included, the chance to test drive Volts at modest sub-50 mph speeds, limited to pylon-flanked parking lot impromptu tracks.  English had the chance to take an Ampera out on the highway.

He was pleased with the spacious and attractive interior calling it “comfortable, classy and commodious.”

He found acceleration strong noting the car “charges hard” up to 50 mph. After that he perceived, “the single-speed electric motor’s flat torque curve has begun a nose dive and acceleration at high speeds is poor.” Perhaps this is why GM hasn’t allowed US drives beyond 50 MPH. That was the fastest speed I could hit on a roughly half mile track, though one US reporter was said to take a Volt to 92 MPH at the Warren Tech Center, on a side road.

English suspects the perceived power fade at high speed is because the Volt/Ampera’s top speed is100 mph which is lower than most similar-sized gas sedans which is typically 130 mph.

He claims GM has a solution forthcoming:

General Motors is working on the problem and this autumn plans to unveil a mechanical direct-drive from the engine to the front wheels through the existing twin-clutch planetary gearbox. This would reduce the energy losses of turning petrol power into electricity to drive the car at high speeds, and would also give the Ampera more spritely overtaking performance.

This claim, if true, is rather shocking because it flies in the face of everything GM has said in the past and would mean the gas engine could power on even during the first 40 miles.

I reached out to Volt spokesperson Rob Peterson who with utmost respect for the reporter denies this is the case.  He also notes the Ampera English drove is a 65% calibration build, whereas current Volt test cars are at a much more refined 99%.  This is what Peterson had to say about the powertrain change claim:

This report is inaccurate. First off, the Volt cannot be driven without electric power. It always makes use of electric power within the drive unit.

Secondly, we have no plans to make any mechanical or control strategy changes prior to launch.

The team is in the final stages of validation and durability and have not identified any reason to make any changes. We have a very innovative drive unit that includes a number of clutches and a planetary gear-set which is highly efficient and exists in our pre-production vehicles today. For competitive reasons we won’t provide more details on the operation at this point, but will soon.

Source (Telegraph)

After a long three and a half year watch period we can finally make the following statement “work on the Chevrolet Volt is nearly completed.”

From concept to production design, from battery pack prototype to assembly plant, from Cruze-mule to validation build, the ramp up to production appears to be almost over.

The testing, tweaking, refining and engineering that has been done with the pre-production fleet since last summer is finally completed.

The third quarter begins on July 1st, and with it will come assembly of the last phase of pre-production Chevrolet Volts eventually merging seamlessly into saleable builds that will start in the forth quarter and end in the driveways of America.

Micky Bly who is GM’s director of hybrids and electric vehicles told reporters GM will be holding a large-scale internal event a the end of June to decide if work on the Volt is finally complete. According to GM sources this event is “not a PowerPoint presentation”, but an event in which top executives and decision-makers drive and sample the final refinement of Volt prototypes. If this group gives a thumbs up, then essentially all aspects of the vehicle are frozen into place for retail production.

“Are we done. No. Can we learn more. Yes. But it looks really good right now,” Bly told reporters.

Most of the remaining minimal work involves refining the software that monitors the the car’s electric power system.

This software has to monitor 1000 seperate functions in the extended range electric car propulsion system. Engineers have to decide whether detection of abnormal events are to be displayed on the screens to the driver or recorded for technicians to evaluate at a later point.

There were still some lingering issues on cabin climate control as recently as April which have since been resolved.

Engineers will continue to test not weather behavior throughout July, August, and September. At that point the company will decide exactly when to put the car into production. A day in mid-November remains the intended target.

Cars being built in the assembly plant from now until the first saleable car will be continuously driven in the real world by GM engineers who will attempt to find any flaws thy can.

Test cars are regularly achieving 40 miles or more of pure electric range.

“I see no issues with 40 (miles) at all,” said Bly.
Source (CanadianBusiness)

Also, for those who are interested, you can participate in a live webchat below with Tony Posawatz GM’s Volt director; Richard Lowenthal, CEO of Coulomb Technologies; and Don Korner, CEO of ECOtality who will be discussing the Volt’s free charing station program today at 11AM Eastern: