By on November 23, 2009

(courtesy: photobucket/emawk)

The Chevrolet Volt can very nearly be boiled down to a single a function: range extension. The Volt’s gasoline range-extender is the car’s major technological advantage over other electric vehicles like Nissan’s Leaf, promising consumers freedom from the terror of range anxiety. But how does it actually work? TTAC’s Volt Birth Watch has long asked the question, and GM has assiduously prevented journalists from describing the Volt’s transition from initial EV range to “generator mode.” Until now. The NY Times‘ Lindsay Brooke recently took a pre-production Volt for a spin at the Milford Proving Grounds, and files this report on the generator mode experience:

It takes a few laps of Milford’s twisty, undulating 3.7-mile road course to deplete the remaining eight miles of battery charge. 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. G.M. had not previously made test drives of the Volt in its extended-range mode available to reporters, but I can see that in this development car, at least, the engineers got it right.

Or did they?

I push the accelerator and the engine sound does not change; the “gas pedal” controls only the flow of battery power to the electric drive motor. The pedal has no connection to the generator, which is programmed to run at constant, preset speeds. This characteristic will take some getting used to by a public accustomed to vroom-vroom feedback.

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.

I asked what was going on.

“The system sensed that it’s dipped below its state of charge and is trying to recover quickly,” [Volt vehicle line director Tony Posawatz] said. “The charge-sustaining mode is clearly not where we want it to be yet.”

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. Volt engineers are revising the car’s control software, which will have the effect of “feathering” the transition from the nearly silent all-electric mode to the charge-sustaining mode, when the generator will be operating.

Oops! Brooke was a guest of GM, driving a much-fettled prototype on its home track. Surely GM was aware that “disconcerting” sounds accompanying the switch to generator mode would be noted with disapproval. GM’s answer?

“We’re designing a software set of rules, which will just require more seat time for the engineers to finish,” Mr. Posawatz said. “We have nine months to work this out.”

Brooke concludes by calling the Volt “an extremely refined vehicle,” giving GM’s engineers the benefit of the doubt on their attempts to smooth over the generator mode switch. When production vehicles roll out, Posawatz and company better hope the software codes are up to snuff. After all, the Volt’s range-extender is one of those technologies that doesn’t offer much marginal advantage to consumers in the typical EV early-adopter profile. It’s an attempt to make the Volt a potential replacement for a “real” ICE-powered car, making it an option for (well-heeled) mainstream consumers who might envision using it as a primary vehicle rather than a dedicated commuter. That mainstream appeal is a tough enough sale without weird engine-room thrashing. GM has got to sweat this detail.

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39 Comments on “Volt Birth Watch 173: Generator Mode Revealed...”

  • avatar

    At leat they’re getting some outside feedback. Without it it would be easier for them to convince themselves that the current iteration is okay.

    • 0 avatar

      Old GM would have released the car as is (8-6-4 style) and called it a perception problem “once the consumer knows what to expect…” or something like that.

      New GM admits it is not where they want it yet and allows a reporter to drive it knowing that she will report it.

      Don’t know if they will make it, but there are signs that the atmosphere is changing.

    • 0 avatar

      I know, the whole Volt development has been rather ‘open’ for a GM product. Hopefully this outside input helps them create the car that will save GM and bring it back from the brink.

  • avatar

    Show me a project that’s over budget and/or behind schedule and I’ll show you a project that has a software problem.  

  • avatar

    I hope that GM has a plan for firmware updates….

  • avatar

    I’m less concerned about the noises the car makes as I am with the attitude displayed by Posawatz.  Why is he so defensive about the Volt making unique noises, why does he want the Volt to seem like a normal car?  IT ISN’T A NORMAL CAR!  That’s the whole point!  That’s the reason people *might* be interested in buying one!
    The Volt has to be about efficiency, taking advantage of its unique opportunities as a series hybrid to optimize  Watt*Hours/Gallon.  If GM spends all its time & effort trying to make the Volt feel and sound like a normal car, I’m worried they will succeed – and the whole reason the Volt exists will have been undermined.  Instead of worrying about how the Volt sounds when the engine is on, GM’s #1 priority must be to beat the Prius MPG when in Charge-Sustaining mode.  That’s the only way they’ll get credibility amongst the crowd the Volt is targeted at.
    Why do they think that making another “normal” car will salvage their image?  The more normal they make it, the less people will notice it.

    • 0 avatar

      I can’t agree with that.  I believe GM should be striving to make it a ‘normal’ car.
      It will already be abnormal since:

      requiring 2 fuels, special tires, and (probably) daily plug-in for the average commuter
      it needs a special and expensive charger for it
      apartment dwellers can’t own one because it must be plugged in
      it will cost $40k, and for that price, it must be perfect.

      Adding a dissonant engine symphony to the mix will only deter mainstream customers.
      The technology whiz-bang on this car is impressive, but its expression in the product has to satisfy real paying customers, not just technogeeks willing to tolerate its idiosynchracies.  Remember: this is Chevy’s product, not Aptera’s.

  • avatar

    I don’t know that I’d be much bothered by the noises. I would be bothered if the range extender was the power equivalent of driving on a donut.

  • avatar

    I wonder if they would allow the range extender to operate when the vehicle is not otherwise being operated.  Like if you were nearing the end of your 40-mile range, but needed to make a stop at the grocery store.  While you’re in the store, the extender could be running in the low-charge mode, using that time to recharge the batteries.  You get back in and have more charge to get home, or to your next destination, without having to engage the (presumably) more wasteful quick charge mode.
    However, I doubt they’ll allow it to do this.

    • 0 avatar

      Excellent point.  But will the Volt be subject to the same restrictions as cars propelled by internal combustion engines?  That is, in some cities you can be fined for leaving your car idling.  The reasons are usually for safety, reduction of emissions and encourage fuel economy.  

      So… will the nanny state allow a Volt to sit in the parking lot and charge its battery but not allow a Civic to sit idling to keep it cool/warm on the inside?  That should make for a fascinating battle of conflicted interests.  

  • avatar
    Kyle Schellenberg

    It’s interesting to read about their implementation. Once upon a time before GM upgraded it’s mileage rating from 40 to 230mpg, many of us scoffed at how a heavy vehicle with a small 4-pot would be capable of producing 40 MPG. What I’m gleaning from this is an engine that runs at varying sets of constant RPM.
    I know that for my Honda when I doing 50km/hr and the car kicks into 4th gear, I’m running only about 1,100 RPM which should be saving gas. If the Volt engine has a transmission that allows it run constantly at low RPM to feed the generator then perhaps the potential for a more fuel efficient car exists.
    It still seems counterproductive to run a gas motor to generate electricity to drive an electric motor, but assuming the Volt ever makes it to market we’ll see how this all works in the real world (stop-n-go traffic, highway speeds, etc).

    • 0 avatar

      I don’t believe GM ever said 40mpg.  They said 40 miles on a charge.  By the EPA rules for these types of vehicles, it would be 230mpg.  It would get 50 mpg in charge sustaining mode.

  • avatar
    Rod Panhard

    “We have nine months to work this out.”
    If I only had a dollar for every time I’ve heard the software engineers say that at the places I’ve worked. Legions of code warriors, all uttering the same thing. “Yeah, we’ve got this handled. You’ll be telling the board next month how great it’s working now.” Oddly enough, quarters turned into years.
    God help Mr. Posawatz. You’re gonna need it.

  • avatar

    Just a general question …. have any of you ever ridden on a Hybrid Bus??  They are quite common here in Minneapolis, and in the neighborhoods running stop and go they are real quite with the engine just a bit above idle.  HOWEVER ….. get them out on I-35 at 60mph for a few miles and the exact behavior that Lindsay noted in the Volt is quite apparent in the bus.  You are cruising along nice and quite, then the diesel motors on up in the rev range to charge the battery pack.  20 seconds later, it idles back down a bit.  For a 12 mile commute downtown on the X-way, it runs through this cycle about 5 times.  It isn’t annoying, but it is startling if you aren’t accustom to it.  A couple of the passengers I normally ride with noticed the odd behavior and questioned it, but once they understood, it didn’t bother them.  Even with this rev up, rev down behavior, it was much less noisy than the usual diesel rigs they run.  Since the Hybrid Bus is essentially the same technology as the Volt, I don’t find the behavior surprising in the development mules.  The trick will be to keep the variation in engine rpm and the rate at which it accelerates up to that rpm acceptable to “human perceptions”.

  • avatar

    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.
    Welcome to the world of the managed powertrain.  Please enjoy your stay.
    If you’ve ever driven a CVT-equipped car (or at least one that hasn’t been tuned to simulate an AT**) you’re probably familiar with this feeling: the RPM is pegged at the most efficient/powerful/whatever point to achieve the required results.  You get used to it very quickly; in fact, stepping back into an AT or (especially) an MT-equipped car after spending time in a CVT makes the jerking “thumps” that accompany a shift very, very apparent.  After four weeks in a CVT Versa I was sure something was “wrong” with my usual car.
    ** which is nothing but pandering to old-school gearheads who don’t like how a CVT “feels”, and costs the transmission efficiency, to boot.

    • 0 avatar

      “nothing but pandering to old-school gearheads who don’t like how a CVT “feels””

      I hate to agree with a post CVT post, but I have to concur with this. If they’re going to do CVT, they should make sure AT “gears” mode is only there to supplement the true CVT mode. On the other hand this, “or (especially) an MT-equipped car after spending time in a CVT makes the jerking “thumps” that accompany a shift very, very apparent” I’d disagree with. Leaving aside the possibility of generally shifting well and not thumping (ahem, the whole point of not getting at AT in the first place), I’d say that my response going from a CVT to manual is relief at the clean* throttle response both up and down the tach.

      *”Clean” is a weak way to describe it, but there it is. You know what I mean. 

  • avatar

    The ICE is too small to power the car and charge the batteries at the same time. Therefore the ICE runs at a much higher RPM that a conventional engine. GM needed to put a larger ICE in to help handle both of these tasks. But that would drive up cost and lower mileage in the extended mode. Therefore they have decided on this compromise. Which will not satisfy most american consumers. The engine rpm’s while on extended range will be much too high and annoying for most americans. This thing will be a real ‘turkey’.  But what else would you expect from GM. They are always over promising and under delivering. What else is new???

  • avatar

    Sounds like a problem that sound deadening materials (like in most Buick’s) and active noise cancelation (like in the ’10 Equinox) could solve fairly easily if they aren’t able to come up with better software.

    Also, I read that EPA requirements are kind of forcing them to do binary steps instead of nice smooth transitions.

  • avatar
    cRacK hEaD aLLeY

    Sounds like Lindsay’s describing how my Honda EM generator works when the eco-throttle function is turned on: lot’s of quietness until there’s a demand… and all the quietness that was kept inside is released, at once.
    If Honda could do it on a $3K generator, GM can do it on a 40K car.

  • avatar
    John Horner

    Forty miles EV range is not enough to cover the round trip commutes of many people here in California. The market for a vehicle which is limited to a 40 mile total range is very, very small. Thus, the Volt architecture is hardly a frill if more than a handful of vehicles are to be sold.
    Several attempts have been made to sell dedicated limited range commuter vehicles. All were flops.

  • avatar
    Kyle Schellenberg

    <i>The ICE is too small to power the car and charge the batteries at the same time.</i>
    I think it’s fairly common knowledge that the ICE in the Volt doesn’t recharge the batteries, it just keeps the car going when the batteries run out.

  • avatar
    Carlson Fan

    I think anyone who purchases a Volt with the intent of  running the generator on a daily basis will be sorely disappointed with it. Please stop comparing it to a Prius.


  • avatar

    alright, i have a question? wouldn’t it make more sense for the volt to be powered by a turbine rather then a piston engine.

    • 0 avatar
      bumpy ii

      Yes it would, except for emissions and that catastrophic failure mode.

    • 0 avatar
      Mark out West

      IIRC, SFC for a gas turbine is worse than a piston engine, particularly diesels.  Remember, turbines idle at 70% of their rated RPM, so if they aren’t working, they’re sucking gas.  Also, start/stop times are excessive for the turbine.  Finally, the cost differences are insane – both purchase and maintenance. 

      But gawd, how I’d love to equip my “green” car with a TPE-331.  People everywhere running in pain covering their ears. 

  • avatar

    Missing from this “drive” are statements of the speeds driven. Once transition was made to petrol-electric did the speed drop, was it maintained and would it accelerate?

  • avatar
    John Horner

    I’m pretty sure the Volt’s generator set has to be configured to recharge the batteries at least somewhat. I don’t think the gen-set on its own puts out enough power to execute a freeway speed fast passing maneuver, some battery energy is going to be needed to do that.  The NYT driving experience description makes me think that the gen-set is indeed charging the battery at least some of the time, otherwise it would not be able to operate with just a few discrete steps. The smartest algorithm would have the gen-set kick in and run at its peak recharging RPM and load, recharge the batteries to some maximum amount and/or temperature limit, then shut down until it is time to do it all over again. The gen-set isn’t connected directly to the wheels at all, so the output has to either be used to charge batteries or be used immediately to supply the main motor.
    Optimizing the algorithms to maximize fuel economy, battery life and driving experience is a very big job. There are a lot of variables to deal with.

    • 0 avatar

      I think you have a problem with how many times you can recharge the batteries if you did it that way.  While the batteries can be charged several thousand times, I don’t know the actual number, but recharging it all the time while driving it isn’t good care for the battery.  Why charge the battery when you need to drive the vehicle?
      From what I have read, it works like this.  Once the battery is depleted (30% charge remaining), the generator kicks in to power the motors.  The generator does not produce as much power as the batteries.  When you need more power, the batteries will give you more power.  When you don’t need the power, the batteries will do nothing.  They will regen from braking.

    • 0 avatar

      GM has always said that the generator will not be used to charge the batteries.

  • avatar

    When this vehicle is released, it will have to behave better than this.  Whether that means having the generator running slightly higher than what it is or allowing more variations with speed, it shouldn’t kick up so high that it is disruptive.

  • avatar

    I think the drive train is one of the few things it’s got right in the last 20 years. It’ far better than the Honda and 3 steps better then the Prius.  Concerning  MPG/ENERGY consumption, reliability, ease of adaptability and the environment Is heads and shoulders better than any thing else out there. Now if they can get the price in a range to make it affordable ?
    Last thing is does GM have the B—s to actually stay with it and not float back to trying to make the big profit on gas guzzlers with oil prices start falling due to the demand for oil dropping.  This would at this lead to their final failure.
    Have a good day   “Skip”
    argin: 0.79in } P { margin-bottom: 0.08in } –>

    • 0 avatar

      @ skipwkk

      I think the drive train is one of the few things it’s got right in the last 20 years. It’ far better than the Honda and 3 steps better then the Prius.  Concerning  MPG/ENERGY consumption, reliability, ease of adaptability and the environment Is heads and shoulders better than any thing else out there.
      I’d be curious as to how you figure that given the Volt hasn’t even hit the market?

      Will it be “3 steps better than Prius” if it can’t hit it’s economy target, or only matches it? Toyota might be further down the road by the time the Volt ever makes it. At a lower price point.

  • avatar
    Jeff Puthuff

    Lindsay considers disconcerting engine noises “extremely refined”? Oooooo-kay.

  • avatar

    GM is betting the house on a flawed, interim technology that will be retired to the dust bin of automotive history – but the bright spot is that maybe an aftermarket kit will become available to replace that stupid lump of an ICE with a bank of ultracapacitors.

  • avatar
    Kyle Schellenberg

    I don’t believe GM ever said 40mpg.

    Jon Lauckner, New GM’s Vice President of Global Program Management: “I think most customers will be surprised at the refinement of the ICE. It will operate at several RPM points (not roaring) and the charge sustaining fuel economy (gas engine on) will be much more than 30 mpg.”
    Yes, we are surprised by the ‘non roaring’ refinement of the engine.

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