GM-VOLT : Chevy Volt Electric Car Site

As was reported on Friday October 9, GM completed building the last of a total of 74 pre-production Chevy Volts, which were built in the modest-sized pre-production operations facility in GM’s Warren campus. I had the chance to discuss with Volt vehicle line engineer Tony Posawatz what happens now.

Now that these cars are finished what happens next?
Interestingly enough this is probably where the intense work begins. From a build perspective, we won’t build again until early next year in Hamtramck. What we do now is we take the production intent designs that were built up in the integration vehicles and we test the living daylights out of them and continue to do iterations and iterations. A lot of it is software. A lot of it is taking some of the crudeness in fit in the body fits and tighten them up. Although we do it on math, variations occur and flushness and fit come out a little differently then they do on paper.

So we’re now tuning it. And between that time from October of this year and March of next year, we test the vehicle to confirm the production design works, tweak and fix things, and as we tweak and fix things those changes have to be incorporated in the production tooling and those things typically have a longer lead time.

Then the production tooling is in place. Those are the big heavy expensive dyes to stamp the sheet metal. Those are more significant molds and cavities and processes to manufacture plastic parts in high volume. That’s kind of what happens right now. Right now is the testing, problem-solving, refining and putting all that learning into the production tools. Come the March timeframe and we’re running Volts with production tools. And that is still an iteration process or learning process to refine it for what’s going to happen later in the year.

Are you beginning to put hardware into the Hamtramck plant?
Oh yeah, the Hamtramck plant and the battery plant are on a project plan to upgrade themselves to be ready to build in the early 2010 timeframe. So right now there are tools in toolshops being produced and as we find out, we need this or that, we’ll change it on a production tool. That’s the process we’re in.

When you first start building in March what are those vehicles called?
We call them PPVs, pre-production vehicles or validations. We have a couple more “flavors” but those are all flavors of production vehicle that we work through. This is fairly state of the industry, our terminology is a little different, but every manufacturer does these iterations or flavors of vehicles that have the next phase of software.

At some point in time for example the interior parts have a certain graining to them that you do as one of the last things. You put in a little grain into the tool, but once the tool is grained and they have this nice little texture to the plastic parts it’s very hard to change the tool if you have any functional dimensional changes. Later in the Spring we’ll actually grain the parts so that they really look like production and piece the cars together.

Right now things are actually going pretty well.   We have certainly a lot of issues but that’s standard for this type of project and where we are at in the program. Issues are actually a good thing. We know no one is that good to get it spot-on or if the issues don’t properly surface they somehow surface later. If you have a lot of variation in some of the parts, and you don’t see it early enough to try to control it, to get thefir finsihs and execution elements perfect.

PPVs are not saleable?
No, they’re not saleable yet.

So you will build a few hundred of those?
No we build in the two to three thousand range. We’re finalizing that number right now. A lot of that is practicing the processing of that. Ultimately their will be a line rate of many jobs per hour when we do this so you want to get the guys actually practicing in the production environment.

Alex Cattelan is head of the Volt propulsion engineering team.  I had the chance to discuss the current state of Chevy Volt development from her perspective.

What is your role in the Volt program?
I head up the team that does all of the propulsion systems for the Volt. That includes motors, power electronics, we don’t do the battery but we work extensively with the battery team to do the integration of the battery, and the EV propulsion system

Are you only working on the Volt?
I am dedicated to the Volt and I heave a team of people that are dedicated to the Volt and I’m extremely enthusiastic about the Volt. We have segregated a team of people that are working on the Volt and the Volt only.

What are you doing now?
The specific stage of the program that we are in, for powertrain, is building on our third level of hardware which is integrated in the the vehicles. We’re doing all of our validation testing on that level of hardware; we’ve got past development where the architecture needs to be, through two generations of hardware we’ve confirmed all of our performance requirements with that architecture.

There are three major areas I’m focused on right now. Making sure that all of our hardware that has been built to date, that third level of hardware is in testing. We are validating all of our parameters for it; durability, that’s the hugest piece, the reliability, making minor fixed to areas that we’d like to improve.

The other major area that we’re focused on is the calibration of the system which is huge, because it’s a very complex system from the perspective of the torque generators we have, the engine, the motors, the power electronics. So we’re tuning all of those systems to make the vehicle fun to drive, to meet all of our efficiency requirements, our drivability requirements, noise vibration and harshness requirements, and we are now entering the phase of program where we will do all of the development for certification. So that’s fuel economy label certification, and that will continue for some months now. We’re going to test per the procedures that are being developed for this program and verify that all of our calibration is tuned in for optimization of the driving experience along with the efficiency of the vehicles. And that’s really the stage that were tuning into now.

In addition the third element that we’re working on is tuning in the manufacturing systems. So we’ve been building our production in our manufacturing plant and we’re right now preparing for what we call pre-production level hardware. That before we build saleable parts we’re going to build pre-production parts in the assembly plant so that its ready for volume. Make sure that our suppliers are prepared for that, make sure that our supplier’s tools are prepared for that and tweaked for quality, our manufacturing plant is tweaked for quality. I was just there last week and walked through all of their systems and systems development to make sure there ready for the production phase.

So those are kind of my three major areas of focus right now.

When you mention the production plant are you talking about Detroit-Hamtramck (DHAM)?
No that’s vehicle assembly plant but ahead of that we’re going to our suppliers and their manufacturing plants for individual parts and systems. And in addition, our drive unit and engine have their own manufacturing facilities that we are walking through and making sure they are ready.

Is GM building its own electric motor for the Volt?
The motor is actually supplied to us but we will be integrating that motor in our drive unit so its encased in our drive unit, we provide tooling, rotating components and all of that which is built in a manufacturing plant owned by GM. We are getting ready to do all of that manufacturing , so the housings, for example we take the castings from a supplier we do all the machining of the housings, the bearing the gearing, all of that kind of stuff.

So you get some of the parts from outside but you put them all together?
Exactly, so it’s a manufacturing step that happens and we send that drive unit and that engine to the assembly plant in DHAM for installation into the vehicle.

Have they done anything at DHAM yet to get ready?
There’s a ton of work going on at DHAM to get ready, and we’ve built our what we call our integration vehicle, and we’re towards the end of that phase. That is being built in pre production operations, however the DHAM team has been very integral in those builds. They have been overseeing the builds they’ve been doing slow builds, they’ve been identifying all issues for their production processes. They’re currently working on tooling for the body. There’s a number of things that DHAM’s doing to get engaged and ready. Because the next phase of vehicle, which is not a saleable vehicle yet, but its our next phase of product, will be built in DHAM so they are getting all of their systems tuned, the personnel trained and ready to go.

When will the first vehicle be built at DHAM?
We’re tuned towards first quarter of next year for that date.

After the Chevy Volt has been driven 40 miles on electricity, the gas-powered generator turns on supplying electricity along with a buffer in the battery that the electric motor needs for continued operation.  Though GM has been developing this function for a while they have not shown it publicly.

I had a chance to discuss this extremely important and unique mode of Volt operation with Volt executive Tony Posawatz who explains what functions GM still has to work on.

When the generator goes on will it come on gradually?
We’re still playing with it. The initial transition we like very much, it is almost imperceptible. We want to tune it and exercise it more for production readiness, but we have an algorithm of software that feathers it in so that its almost imperceptible.

To many people it is imperceptible, to those that are a little bit more tuned in…Frank (Weber) says its not quite perfect, he wants it so that no one can hear it.

That transition isn’t handled in most hybrids that well, particularly when you stop at a light an the engine shuts off and you get that shudder. We have this benchmark we set, that we’re going to blow them away.

By the way, our motor is so much bigger than theirs, the power output of the electric motor, that effectively is the starter. We’re in the point of tuning it and it’s a very very complicated tuning exercise if you want to make it perfect.

It’s a balance equation. Here lies the challenge. You will get some feedback from the car about its environment, or the road load. You’re demanding so much power from the car, and you will get some feedback. That’s one input that you have to be able to respond to to deliver the right amount of power. The other aspect that we have to play with is this area of OK when I respond to it, the engine generator will run in different modes or RPMs. How do I transition from mode to mode, a timing issue, do I smooth it, do I try to react immediately to that response? If I act immediately to that response how will customers receive that? such as a wild of swing of RPMs?

There’s the responding to the car’s demands based on the loads number one, then there’s the affect on the customer, we want that to be really pleasant. The transition to charge sustaining, we’ve got that down, it’s the operating in the very different modes we’ve got to figure out. The next leg is making sure the engine is running the most efficiently that it can.

Generators are typically run at a sweet spot that’s very efficient. We could do that. The question is, does the amount of output of power that results from that manage or balance with what the car needs?…hmm how do you do that? That’s another reason we have this battery buffer reserve.

How often do you turn the engine off and on is another question. These are the factors that have to be balanced.

People ask why can’t you show it to me? Because we want it just right.

This requires a lot software. The other interesting challenge is the regulatory issues. Theoretically you could run the engine enough to build a surplus of energy. The regulatory guys are not going to let us do that, it’s a five legged stool.

Is the EPA sitting on a committee while you engineer the car?
This is more CARB than it is EPA. EPA is interested from the perspective that they need to understand how to label it. CARB really doesn’t want you to burn fuel if you don’t have to.

The message on charge sustaining mode is we’ve got a good beat on it, its the four or five things that have to be balanced together and the team needs time to work.

Will the engine rev higher when you step on the accelerator?
Yes, but the question is, if I have a little battery reserve at that time, do I turn the engine on right away to follow that or is it a smoothing function?

Also lets say you just went up a monster hill and the engine feathered up a little to support you and you get to the top of the hill and hit a light. Should the engine keep on running to allow you to recover or do you turn off the engine because the customer expects it too because they’re stopped at a light?

Technically are these difficult challenges? No. Its hard development work balancing the calibration of a lot of software.

Greg Ceisel is the Chevy Volt Program manager and has integral knowledge about the car’s engineering.

He recently shed some light on how the battery pack detects and reacts if there are any problems.

“The reliability of the Chevy Volt and its battery are essential to the success of this technology,” he said. “Our battery design includes multiple computers that run hundreds of tests to monitor the cells and the overall battery to confirm everything is working correctly.”

He explains that all of this testing is continuous and automatic and that the system is designed to respond in case of trouble.

“If any of these tests identify an issue a diagnostic trouble code (DTC) is set to identify the specific issue and an indicator light on the instrument panel will light informing the driver that service is needed,” said Ceisel.

Ceisel also notes GM’s satellite system OnStar can help out both the driver and the mechanic in this situation.

“If the driver wants immediate feedback, OnStar can access these codes to provide more information,” he said. “These codes will also provide the dealer technician with specific information on the repair required.”

He explains how the battery cells are configured both in parallel and series and how the failure of some cells wont take down the car. If need be, the generator can also be used to help out.

“If a diagnostic issue is detected the control system will adapt to use available battery power and, if needed, the gas engine/generator to maintain propulsion until the vehicle can be serviced,” he said.

Source (GM)

Lithium-ion batteries degrade over time. There’s no getting around this fact. GM is going out of its way to pamper the Volt’s pack so as to guarantee up to 40 miles of pure electric range even at 10 years or 150,000 miles of driving. But what happens beyond that?

Most experts believe the Volt’s battery will have anywhere from 50% to 75% of its original capacity after 10 years. Since 8kwh of energy are required to deliver 40 miles of driving, when the battery drops below 8 kwh of storage potential, the range should reduce.

GM’s Director of Hybrids and EVs, Bob Kruse, predicts the Volt will continue to function successfully even after 10 years. “People will continue to use them well after that period of time,” he says. “That’s the beauty of the Voltec system. As the battery begins to age it will eventually have less capacity but it still will provide some capacity and some amount of electric range.”

Asked if the software and controls could dysfunction if there is less than 8kwh of energy left Kruse promises, “the software and the control system will be there to allow the customer to utilize what battery capacity if left.”

I asked him about is whether the system will continue to operate within a 50% band of the now smaller total capacity.

“I’m not going to talk about that because it is highly prized intellectual property,” said Kruse. “That whole notion of how you make this successful, how you use the battery, how you treat the battery, how you charge and discharge it is all central to our promise and how we do that and what we are going to do, as open as we are, I’m not interested in telling my competitors things that I don’t want them to know at this point in time.”

I don’t blame him.

It is known that no one outside GM at this point has been allowed to witness the Chevy Volt prototypes running in generator mode.

Previously it was reported that the reason for this is that the car isn’t soundproofed and GM doesn’t want people to hear the engine. Jon Lauckner has also told me the reason is that the mules were designed to evaluate performance and not man-machine interface and therefore aren’t meant for public consumption. GM would rather wait for reporters to experience the real cars not a subpar mule.

John McElroy of Autoline, has either conjectured or discovered another intriguing reason.

He reports that the way the generator is configured it will snap on at 4500 RPM should the car be going uphill or at highway speed at the time. This would then cause the driver to be “suddenly assaulted by the sound of a roaring engine.”

He further writes that GM engineers figured an easy solution to this was to have the generator go on sooner at a lower RPM at a higher battery state of charge.

Those people claim, he reports, that the EPA “frowns on this idea” because they would like to see the car get the highest fuel efficiency estimate possible. If the car were to spend more time than necessary converting gas to electricity those estimates would be lower.

Thus GM engineers he says are still “playing around with calibration strategies” to maximize efficiency while minimizing engine noise and thus the generator mode is still not ready for primetime display.

GM sources have not confirmed this to GM-Volt.com, characterizing the report as “inaccurate”.

GM writes on the Volt media site “the battery will continue to generate some power and work together with the engine-generator to provide peak performance when it’s required, such as driving up a steep incline or for high acceleration maneuvers.”

McElroy has the idea the generator would have to power on independently (and at 4500 RPM) if the battery were “drained.” We know it never really is drained though.  If the 30% SOC is hit at a point of peak power demand, the battery will continue to contribute energy along with the generator making lower RPMs possible.

What do you think?

Source (Autoline)