Chief Powertrain Engineer Pleased With Chevy Volt’s Charge-Sustaining Mode

[admin]

I had the following discussion with Alex Cattelan who is the Chevy Volt’s chief powertrain engineer. She has a very deep understanding of how the car operates and recently drove in a fleet of integration Volt prototypes through rugged mountains of Knoxville Tennessee.

Do you feel the charge-sustaining (CS mode) experience is now pretty solid and are you pleased with it?
We are definitely pleased with the level of progression we’re at. We are right on track to where we need to be in terms of the next stages of development we need to do to meet our target. Is it commercial right now, no, but that’s why were taking the time to get it to be commercial. Does it have the capability of being commercial, absolutely. We’ve proven that to ourselves.


We just took our leadership through a test drive in Warren (Michigan) and comments are that they cant tell when the engine is coming on or off. Those are the kind of things we like to hear.


You drove the IVs around the mountains of Tennessee. What about those big hills and the generator. It sounded like it drove very briskly powerfully and effortless is that true?
Yes, absolutely. Some of our control capability to utilize the battery, the engine, and the motors and to be able to optimize for high load and low load situations we’ve been working on developing that stuff for the last year and half an I couldn’t tell you how happy I was when I was in Knoxville because that’s when I had the opportunity to see it all come together. A lot of those bits of software all came together on one trip and it was a joy to drive.


So you took it up some steep hills and mountains?
Absolutely. We were in the Cherokee area taking it up through those hills and a lot of situations following it. It was a very touristy area. Following the speed of traffic, absolutely no problem, and where I had opportunities I certainly like to push the limits of the vehicle, and we did on those mountains, and I could not get it to degrade in performance.


That’s in charge sustaining mode?
Certainly in charge depleting, we have no issues because we have battery power, I’ve got it all at my fingertips. Now in charge sustaining we know that the engine power is slightly less than the peak vehicle power but we have controls ways to manage that and to utilize the engine in conjunction with the battery to get a little bit of extra power when we need it, and replenish it back when we don’t.


I know the battery runs down to roughly the 30% level before for the engine comes on. Is that 30% itself the whole potential buffer band?
We certainly don’t utilize the full 30% but there’s a portion of that that we utilize as a buffer.


You wouldn’t go to zero ever?
No. When the engine cannot meet peak load requirements we’ll suck a little bit out of that buffer and as soon as we have a situation when we can, we’ll put it right back in. All the controls that we work do that to optimize not only the driveability but the efficiency as we’re doing it, NVH (noise vibration harshness) as we’re doing it, the total driving experience as well as to protect the battery from a life experience. This is what allows us to give really good warranty life on our batteries as we’re doing I all in a controlled fashion.

[omnimoeish]

Cool Lyle. Thanks for posting it in the forum. Some of the more gearheaded individuals like to discuss and speculate and try to read between the lines when we get thrown a bone like this and the home page is a little bit crowded for anything meaningful to flow.

[Texas]

Nice interview Lyle.

There has been a lot of discussion lately about how the Volt will act in CS mode on the highway but you didn't ask those sticky questions. This area of questioning is probably the toughest to talk about but inquiring minds want to know! Do we have to wait until the Volt is delivered to get these important questions answered?

Perhaps Alex can clear up the confusion she stirred up the last time she tried to explain it.


Alex, No need to dumb it down for us. Give us the full engineering explanation and then we can chew on it. Specifically:

1) Is there a mechanical connection of ANY form between the ICE and the wheels? Even a HHSE-like simple connection?

2) Are there any fancy magnetic or electrical coupling mechanisms used to improve the highway (steady state at CS mode for hours of driving) mpg numbers?

3) Yes, we realize that the generator will have a direct electrical connection to the motor (to bypass the electrical conversions) but is there more than? Again, fancy coupling system?

4) What mpg do you think you might be able to achieve for highway driving at 70 mpg at CS mode for long drive in normal conditions (30's, 40's, 50's)?


OK, we know some of the tricks are proprietary and that there is a whole year of software tweaks that need to happen that should allow you to squeeze out more efficiency. However, can you at this point change any of the actual hardware (add new power controls, power supplies, generator or traction motors, etc.)? Is what you have now locked? Is the team now limited to software changes only and the components are set in stone?

Anyway, this is a fascinating topic for some of us and we wonder how the serial hybrid configuration will be able to overcome the "Mechanical - Electrical - Mechanical" energy conversion where the normal car or the Prius stays "Mechanical" for the whole time (ICE powered, CS mode). Energy conversions are never 100 percent efficient. Every dash I typed in is another conversion where the Prius has none. Can software tricks overcome these inherent efficiently losses? Do we have to wait another year to get your thoughts?

P.S. I am personally not worried about the losses because most Volt drivers will be city-centric drivers (if you drive many miles on the highway, get a diesel car). However, I just want people to be prepared should the numbers not be as fantastic as many people here on GM-Volt.com think the Volt might deliver. Thank you, in advance, for your detailed response.

[Jean-Charles Jacquemin]

Thanks Texas to have taken the time to write those questions I had them in my head but I was not resolved to write them down and phrase them corectly.

Regards,

JC