Brooks was the only other journalist so far besides CNBC’s Phil Lebeau to test drive the Volt in generator or charge-sustaining mode and has written about it.

His brief article entitled Life After 40 tells us what we’ve been waiting to hear, but maybe not exactly what we wanted to.

Brooks writes:

Like other reporters, I had already driven Volt prototypes in the battery-powered mode, and they were predictably smooth and silent. But for eventual Volt owners, a crucial — and so far unanswered — question is how the car will perform when the battery’s charge is depleted and all electricity is provided by an onboard generator, driven by a gasoline engine, that has no mechanical connection to the wheels.

Then as he runs the car’s electric range meter dramatically down to the zero mark, the moment we’ve all been waiting for occurs:

With the dashboard icon signaling my final mile of range, I point the Volt toward a hill and wait for the sound and feel of the generator engine’s four pistons to chime in. But I completely miss it; the engine’s initial engagement is inaudible and seamless. I’m impressed.

Good so far.  He finds that as he pushed the accelerator, the sound of the engine didn’t change.

But later as he’s accelerating around the test track he gets a little shock that he calls disconcerting.

A few hundred yards later, as we snake through the track’s infield section, the engine r.p.m. rises sharply. The accompanying mechanical roar reminds me of a missed shift in a manual-transmission car. For a moment the sound is disconcerting; without a tachometer, I guess that it peaked around 3,000 r.p.m.

He asks GM’s Tony Posawatz driving with him what just happened.

“The system sensed that it’s dipped below its state of charge and is trying to recover quickly,” apologizes Posawatz. “The charge-sustaining mode is clearly not where we want it to be yet.”

Huh?

He goes on to write:

Immediately the engine sound disappeared, although it was still spinning the generator. A few times later in our test, the generator behaved in similar fashion — too loud and too unruly for production — but there is time for the programmers to find solutions.

So there we have it, the first reporter in history to write about the Volt’s operation in generator mode, and its a bit of a mixed picture.

It seem to go on flawlessly but throughout driving apparently has spikes of on/off engine roars that he finds disconcerting and unruly.

Though not exactly a happy report, he concludes:

Throughout my test, the prototype behaves admirably. At its current state of development, the Volt is an extremely refined vehicle.

Looks like GM has a little more work to do.  But then again the experience may be a bit subjecttive.  We’ll wait to see what others have to say.

Source (New York Times)

Volt in 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.

NEW: Discuss this story in the GM-Volt Forum

Chevy Volt Powertrain

The design of the electric motor, is there a separate generator or does the motor itself just turn the other way and act as a generator?

Very interesting question. There are two motors. One is considered the traction motor and the other one is the generator. However, and they are two motors, the traction motor is  higher-powered and designed specifically to meet the traction requirements.  The generator is designed to efficiently couple to the engine to generate what we need and match the efficiency band of the engine as much as possible in all the operating modes. So we look at that motor as coupled with the engine in system and then we also have a traction motor.

Some of the interesting pieces though of this are, for example, in EV operation I have two motors on board and I typically use the traction motor only to drive the vehicle. However, I do have some mechanisms to couple those motors and in some points of operation these two motors can be coupled and have a more efficient state.

Does that produce more power if they’re coupled?

It’s actually not additive for power, it’s actually the way it’s architected, and a lot of this is proprietary so I can’t get into the full architecture, but what it does is optimize the rotating speed and the losses of the motors so in certain states its better to operate both to propel the vehicle and in some states its better to utilize more of the generator and less of the traction motor. In some states its more efficient to use more of the generator and have more of the traction motor actually be a generator. That would be for example in coast down situation often we use our traction motor as a generator on regen.

We do have the ability to utilize both motors in propulsion mode.

The issue is and the direct answer to your question is we do have a primary traction motor and a primary generator motor and they are designed specifically for those levels of operation. However, we have a little bit of flexibility in exactly how we use them.

Just as vehicle line director Tony Posawatz was asked by Fox the other day, Lutz was also asked what the Chevy Volt’s MPG will be when it is running in charge-sustaining mode, after the first 40 all-electric miles have been driven.

As someone who has followed this Volt story since day one, along with many of you, I have found that Bob Lutz cannot help but be honest.  GM has never officially acknowledged this number though at the time of the initial concept revelation they mentioned 50 MPG was the goal.  However, in those days the generator was to be a 1 L turbocharged 3 Cylinder, and not the normally aspired 1.4L 4 cylinder it turned out to be.

When now asked what the Volt’s fuel economy would be in charge sustaining mode, Lutz replied as follows:

We haven’t published it and it’s not finalized.  Once it’s running on pure gasoline it will be like a highly economical vehicle in that size class. It will be exceptionally good mileage but it obviously won’t be comparable to what it is when it runs on electric.

The vehicle is conceived primarily for urban or suburban use. It’s for that 80 percent of Americans who travel 40 miles or less per day; they will never use a drop of fuel.  If you have a 60 mile commute, you’ll have 40 miles purely electric, the remainder of the mileage on very good gasoline mileage, and your average fuel economy will be somewhere between 120 and 150 miles per gallon.

So let’s do the math.

On a 60 mile commute, the first 40 miles are electric and the next 20 are on gasoline.  At an average of 120 mpg, that would mean 0.5 gallons are used in those 20 miles (40 mpg).  At 150 mpg, it would mean 0.4 gallons are used in those 20 miles (50 mpg).

Thus the Volt will average between 40 and 50 mpg in charge sustaining mode.  Good enough for me, how about you?

Thanks to Philerup for the tip!

It is this range-extender that make the car so unique. Although the Volt always operates as an EV, once the battery’s state of charge reaches roughly 30% this generator powers on, providing electricity to the motor. Energy is also obtained from regeneration and the battery buffer when power demands are high.

GM has yet to publicly demonstrate the car operating in this charge-sustaining mode, but most accounts indicate it is unnoticeable.

In spite of many months of rampant speculation here, GM’s lead Volt engineer Andrew Farah has finally disclosed some details about the engine’s operation. He said the generator would “operate from 1200 to 4000 RPMs and from a 30% to 100% load.”

Further explanation comes from Volt Powertrain Engineer Alex Cattelan:

“We don’t keep it at a fixed RPM, we have a window of operation that is optimized. We have been able to optimize the engine for a window of efficiency but it is still best to change your power and torque levels within that window as the customer torque request varies.”

“We don’t want to always be operating at one state because really you may be putting too much energy into the battery or drawing too much energy out of the battery. It is still good to vary that engine power and torque. Not to follow exactly what the accelerator pedal does, but to optimize efficiency.”

Finally Volt vehicle line director Tony Posawatz explains it this way:

“In charge sustaining or range extender mode, the Volt will not follow the throttle position. The challenge is to select the right operating points (RPMs) that are 1.) efficient, 2.) pleasing to the driver, and 3.) meet regulatory requirements.”

And he teases us, “we are about ready to expose people to this experience.”

According to Volt vehicle line engineer Tony Posawatz, “the VOLT can run without gas since it is an EV.”

Here’s how he explains it:

We will provide many tips to customers on how they can get the most out of their VOLT as we continue the education process, work our demo programs and train our dealers and customers at the point of sale. For example, we will recommend that they keep some gas in their tank to avoid range anxiety and if they are always driving in EV, we want to make sure that once every month or so, we can perform a maintenance run on the engine (for keeping the engine parts lubricated and the gas from getting stale).

This will be done automatically for the customer because of the intelligence built right into the car. We don’t want to have the customers worry about putting additive in their gas tanks like snowmobilers and boaters have to. If the customer runs primarily in EV mode, we would also suggest that they not keep their tank full. That’s a lot of extra mass to carry around. Prior to a long trip is the right time to gas up at one of our countries 170,000 gas stations.

As to whether the car can run without its battery he says “the VOLT can run with an injured battery but not without a battery in the car.”

Finally Posawatz declares “the VOLT is a very smart car, it will be the smartest device on the smart grid of the future.”

When the Volt concept was first unveiled in January 2007, GM said the car would get 50 MPG average when it was in generator mode based on computer simulations.

We understand the car will get up to 40 miles of pure electric driving from a fully charged battery, and that the average city driver will average 230 miles of cumulative driving on a gallon of gas, but what will the average fuel economy be in charge sustaining mode?

When the battery reaches a roughly 30% state-of-charge, its 1.4 L 4-cylinder engine will fire up, spin a generator, and produce electricity.

That electricity will purely be used to power the 110 kw electric motor, though the battery will still have that 30% hearty buffer and contribute to driving power demands as necessary. Furthermore, any braking, coasting or downhill opportunities will allow the recapture kinetic energy into the battery.

Clearly this series-hybrid design differs considerably then the typical power-split architecture of today’s modern hybrids like the Prius. It is of great interest to see how much fuel economy it can attain.

I recently asked Volt line engineer Tony Posawatz whether the production Volt would still get 50 MPG like the concept was promoted to. He said “that was just the concept,” though he didn’t specify what the real car will get.

Frank Weber when asked the same question said the story would eventually be told, but not right now.

So with this uncertainly why not a little speculation? What will the series hybrid mode fuel economy be? And how important is that number to us?
Note: There is a poll embedded within this post, please visit the site to participate in this post's poll.

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.

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)

They have strictly restricted those driving experiences to the vehicle’s charge depleting mode. Outsiders thus only have the experience of driving the car in pure electric mode without the gas generator running.

And lets face it, that is the main idea. We after all want to drive it only in that mode to limit use of gasoline.  The range extender is there for less than 20% of the public’s driving needs and many people will never use it at all except perhaps in cases of emergency.

However, GM’s insistence on not allowing observation of the generator mode has raised the usual suspicions of the blogosphere.

EV enthusiast Chelsea Sexton, who appeared in the film Who Killed the Electric Car, spent a day recently test driving the Volt in EV mode, and highly praised it. However, because she was on the track all day doing interviews for a new film, she actually accidentally witnessed test Volts passing by while in generator mode.

She writes “in range extended mode- the thing is already Prius quiet.”

“And because the generator operates within certain distinct ‘power bands’ depending on the driver’s right foot,” she writes. “Any detectable sound should directly correlate with attendant ambient and road noise.”

She pressed Volt exec Frank Weber as to why GM wont let anyone outside experience driving the generator mode, and he replied sheepishly “well, when the engine comes on, you can hear it.”

So it is the fear of hearing the engine, not its feeling or performance that GM PR wants to avoid.

However, the reality is the Cruze-mules are not Volt. They may have 80% of the final car’s parts but the lack the refinement, component location, and engine noise shielding the final Volts will have. As such they are likely to be considerably noisier.

GM wants the series hybrid mode to feel as butter smooth and maximally silent as possible.

Since the true Volts are currently being built, it wont be long before myself and the automotive journalism universe get to experience them, likely in the fall, and I sure believe it will be quite quite and quite awesome.

Source (EVChels)