Chevy Bolt 200 Mile EV Battery Cooling and Gearbox Details

2 years ago by George Bower 106

2017 Chevrolet Bolt EV - 0 -30 mph in 2.9 Seconds (InsideEVs/Tom Moloughney)

2017 Chevrolet Bolt EV (full specs/gallery here) – 0 -30 mph in 2.9 Seconds (InsideEVs/Tom Moloughney)

Keep it Simple is the rule of the day

Battery Cooling

GM’s Volt, and Tesla’s Model S both use an active liquid battery cooling system. Tesla snakes a flattened cooling tube thru their cylindrical cells resulting in a very simple cooling scheme with very few points for leakage.

Tesla Battery uses a simple flattened tube which snakes thru the cylindrical cells

Tesla Battery uses a simple flattened tube which snakes thru the cylindrical cells

GM Volt and Spark EV use thin prismatic shaped cooling plates in between the cells with the liquid coolant circulating thru the plate.

GM Volt uses active cooling plates between the prismatic cells: Courtesy General Motors

GM Volt uses active cooling plates between the prismatic cells: Courtesy General Motors

The BMW i3 cools the bottom of the battery case with refrigerant eliminating the liquid coolant entirely.

The Volt cooling scheme is very effective from a cooling point of view but it is complicated. The cells are encased in multiple plastic frames.

GM Volt uses multiple repeating frames stacked together: photo courtesy Karl Reque, Composites World

GM Volt uses multiple repeating frames stacked together: photo courtesy Karl Reque, Composites World

These frames repeat and are then stacked longitudinally to form the whole pack. The main feed line for the liquid coolant runs along the bottom edges of the pack. This main coolant passage is cast into each plastic frame and as the frames are stacked lengthwise the coolant passage is formed. Each inter cell cooling plate is fed off this main feed line.

The problem with this scheme is there are multiple potential points where leaks can develop since there needs to be a seal between each plate but we must point out that there doesn’t seem to be a lot of problems reported in production Volts. Tesla’s system is simpler and less prone to leaks since each battery module has one continuous cooling tube.

This “repeating frame” cooling system seems to have been abandoned in the Bolt. Here is an excellent video animation of the Bolt EV battery pack and power train:

At 1:04 minutes into the video we can see one three cell group being removed from the pack. The active inter cell cooling plates that were used in the Volt are totally absent . Instead we a see a passive plate which is wrapped around each cell. Keep it simple.

Bolt EV appears to use simpler passive inter cell cooling

Bolt EV appears to use simpler passive inter cell cooling

Where does the liquid coolant go? It does not appear to be between the cells as used in both the Volt and the Tesla.

Consider this high resolution slide of the Bolt battery pack.

Bolt battery pack cutaway: Courtesy General Motors

Bolt battery pack cutaway: Courtesy General Motors

Now look at a close up view .

bltbattrygearbox slide 6In this photo we can see what appears to be liquid coolant connection fitting on the front of the pack. Inside the pack we can see liquid coolant tubes. We know they are liquid and not refrigerant tubes because GM has told us so in the early spec release.

Bolt EV Specs Via General Motors

Bolt EV Specs Via General Motors

 

The following “bottom cold plate description” is not directly from GM but is based on the author’s inferences from GM’s high resolution photo of the Bolt’s battery pack.

We can also see that the liquid coolant tube drops down to the bottom of the pack into a flat black plate. The authors believe this is a bottom cooling plate. Bottom cooling plates for battery cooling are not unprecedented. The BMW i3 uses it and GM had just such a system in the Spark EV when A123 was  the supplier of the Sparks battery. This Spark bottom cooling plate was abandoned however when LG Chem was chosen as the battery supplier for the 2015 Spark in favor of the cooling scheme used in the Volt.

Searching the web we find that the same supplier of the Volt’s inter cell active cooling plates also makes bottom cooling plates. These bottom cooling plates can be dimpled or channeled to take the liquid coolant. The ingenious part is that the cooling bottom plate can also be used as a structural member of the battery pack. The cooling plate could also double as the structural battery tray.

Dana bottom cooling plate: Courtesy Dana Corp

Dana bottom cooling plate: Courtesy Dana Corp

 

Simpler, lower cost and less prone to leaks.

Gearbox

The Chevy Spark EV uses a very compact gearbox arrangement called a co-axial gearbox. It is co-axial because the centerline of the electric motor is also the center line of the axle shafts. Another unique part of the Spark co axial gearbox was the planetary gear reduction set.

Chevy Spark co-axial gearbox is compact (via GM)

Chevy Spark co-axial gearbox is compact (via GM)

 

Bolt EV gearbox is still co-axial

Bolt EV gearbox is still co-axial

 

Tesla Model S, and BMW i3 however use simple parallel-helical single speed gear reduction gear sets. What do we see in the Bolts Gearbox?

It is still a co-axial gearbox. The drive shafts are on the same axis as the motor.

 

However, the gear reduction set is now a simple parallel-helical gear set like Tesla and BMW i3.

Bolt EV uses simple parallel helical gears like Tesla and BMW (via GM)

Bolt EV uses simple parallel helical gears like Tesla and BMW (via GM)

 

Simple and lower cost than a planetary reduction set that was used in the Spark.

GM followed the “keep it simple” principal in the Bolt without sacrificing performance. This is essential if we want lower cost EV’s for the masses that are also fun to drive.

About the authors: George Bower is a retired mechanical engineer with over 20 years experience in gas turbine power systems.

Co-Author of the piece, Keith Ritter is a mechanical engineer, and licensed professional engineer with over 35 years of experience in heating ventilation and air conditioning systems.

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106 responses to "Chevy Bolt 200 Mile EV Battery Cooling and Gearbox Details"

  1. Breezy says:

    Thanks George and Keith. Simple is beautiful.

    1. jerryd says:

      Yes an excellent report.
      A couple notes, bottom plate cooling isn’t that effective as heat rises,
      not falls.
      And such a high weight at 3600lbs I see why they need such a large battery.
      I was expecting a 45kwhr battery and 2600lbs or so would have been a much cheaper, better performing way to get 200 mile range.
      And after all that they said they were doing to lower weight!!

      1. David D. Nelson says:

        @jerryd: “A couple notes, bottom plate cooling isn’t that effective as heat rises,
        not falls.”

        This statement is patently false! Every year I would prove this to my Physics students through demonstration. Heat flows any direction equally well regardless of gravitational forces.

        Now, where convection can occur and buoyancy exists then the warmer fluid will rise due to it being less dense than the cooler fluid. So many people leave off the very critical words and say “heat rises” rather than “Hot/warm air/water rises.” A very important distinction that has caused many to misunderstand a very basic characteristic of the world around them.

        1. Bill Howland says:

          Mr. Nelson, please don’t confuse the issue with the truth. As, an example, Apparently some here don’t understand that Compressors work only on GAS, since liquids are mostly incompressible, and its only a small amount of miscible oil that tags along.

          As far as the whole article goes, I’m assuming the somewhat simplified battery heating/cooling is due to the developmental progress of car batteries in that they can now handle greater temperature excursions without meaningful degredation, unlike the early Nissan Leafs. The water/glycol mix has a reasonably high specific heat, the batteries as time goes on have lower and lower equivalent series resistance compared to their capacity, therefore generating less heat to begin with, and, like the VOlt and ELR, can use simple fan cooling of the water in moderate weather, saving refrigerated cooling for those extreme days – that is just so compelling a feature that I’m sure they re-used it.

          1. David D. Nelson says:

            Bill,

            I’m not confusing the issue with the truth. What I said is the truth and I regularly demonstrated such to my Physics students. I was responding to the inaccurate statement that “heat rises.” Heat doesn’t just rise. It goes in any direction and that is what I have demonstrated multiple times in my physics classes. People mistakenly think that heat rises because a warm fluid will rise in the presence of a cooler fluid when in a non-zero gravity situation. Last I checked solids don’t fall under the category of fluids. You then go on to talk about compressors using a gas. What does that have to do with what I said? Nothing.

            Go back and re-read what I wrote. It is not false, it is not confusing any issues with truth, it is fact.

            1. Bill Howland says:

              A bit too much starch in your shirt David. I was making a joke, in that I was agreeing with you completely.

              The compressor reference was due to a truly silly discussion elsewhere, that I just mentioned to frame the joke.

        2. jerryd says:

          That depends on thermal conductivity of the cells David. If charging, discharging fast temps could be well different top to
          bottom.
          Nor does it cool the top above the cells. Basic physics.
          Now if they have a heat sink compounded to the cooling plate running up the cells you’d be right but they don’t mention that.

          1. Open-Mind says:

            Since we’re primarily talking about heat conduction, not heat convection, the “heat rises” rules does not apply. Heat conduction is not affected by orientation.

          2. David D. Nelson says:

            Jerry,

            I know basic physics…and some not so basic physics. It was just one of the requirements go get my diploma. 😉

            I was addressing the inaccurate statement that “heat rises.” This statement is incomplete. The context in which it was used doesn’t apply since we are dealing with heat conduction within the battery. They could have just as well put the cooling plate on top of the pack and it would have worked exactly the same only the bottom of the pack would have been warmer.

      2. Mint says:

        Range isn’t proportional to weight. Highway range is much more important (who is going to do 100+ miles a day at 20mph?), and there you have more drag from air resistance (which goes up with frontal area) than rolling resistance (which goes up with mass).

        If the Bolt was 1000lbs lighter but still the same size (i.e. frontal area and volume), it would still need maybe 54kWh to have the same range. That’s maybe $1500 saved on the cells+pack, but thousands more to make such a light structure and keep it safe.

        (FYI, energy used to accelerate is largely recuperated during regenerated braking, so while heavier cars still waste more energy when starting and stopping, it’s less of a factor with EVs than with gas cars.)

        1. mr. M says:

          If seen figures around 30% of regenerative engery reused for accelerating. I wouldn’t call it a largely portion, but it is better than 0% of the ICE.

          Thats the reason why no regen (sailing) and foresighted driving is way better (energy wise) at the highway.

          1. But as discussed on another thread recently, “sailing” on the highway (i.e. coasting in neutral) brings with it certain safety risks that IMO outweigh any potential efficiency gains one might achieve. I’m all for hypermiling, but please place your safety above energy efficiency.

            1. David S. says:

              What safety risks?

        2. jerryd says:

          Mint,
          Drag is proportional to weight in an EV that is always there either fast or slow.
          Now airdrag becomes equal between 30-45mph and above.
          So low speed range, under 45mph is directly proportional to weight.
          So yes 70% of range is proportional to weight given the same kwhr.
          Your regen numbers are way off.
          I do composites for a living and could easily built a much stronger version in just 1800/2k lbs.
          As both light and aero would only need 150wthrs/mile so would only need 35kwhrs to do 200 miles and much easier to fast charge at 1.8x’s fast because it needs less.
          The Toyota 1/x and GM UltraLite, the cop car in Demolition Man are examples of the body, chassis.

          1. Ziv says:

            jerry, I have seen articles stating that regen can recover anywhere from 50% to 65% of the energy used to accelerate the car to a given speed. That seems to be fairly decent, though not as high as most of us would wish, admittedly.

            1. Djoni says:

              I doubt those number.
              First, regeneration is limited by the C factor of the battery.
              In a Leaf for example, C factor is low and it goes to none when the battery is colder than -5c°, so that’s a lot you won’t recover.
              But even if you drive in ideal climate, the efficiency of the electric drive chain is about 75%. If those are the same in regeneration or power mode this would give you a 75% x 75% in and out efficiency of 56%.
              And as we all know, perfect condition aren’t always there, so it’s 56% in the best case scenario.

      3. Raymondjram says:

        Heat “rises” only if it flows in an open fluid (air and water) using convection. The Bolt EV system uses heat conduction though solid metal (as done in spacecraft) which does not depend on position or gravity, amd moves from the source of heat (cells) to the sink (plate). So a bottom cooling plate will work just as well as a top plate. BTW, the heat extraction is done from the plate to the radiator up front and expelled to the atmosphere.

        1. Fredrick says:

          That makes sense. Thanks.

      4. Fredrick says:

        I was thinking the same thing. Maybe a circulating fan somewhere. Something to circulate it anyway.

    2. Anderlan says:

      Maybe they’re copying Tesla’s approach of “Screw it, swap out the entire drive unit (motor, controller, and gearbox) and get the customer on the road. We can learn what went wrong later.” It only works if the entire drive train is as simple, small, and cheap as possible.

    3. Bubby Valentino says:

      Fascinating and informative discussion. Thanks

      1. pjwood1 says:

        ..and elegant, for those of us who’ve gone in with both hands on traditional engines. It is amazing how simple people will cling to the internal combustion engine for many years, yet.

        EV’s are so “technical”. No, they’re not 😉

  2. Aaron says:

    Excellent analysis, gents. Since there is 6.9 liters of glycol coolant, does that mean Bolt EV owners can go to AutoZone for a “6.9L” badge for the side of their car?

    1. Steven says:

      In some neighborhoods, they probably will.

      You know the ones, where Honda Civics get stick on port-holes on the front quarterpanels…

  3. scott franco says:

    Good job on this article, thanks.

  4. Larry4pyro says:

    I recall electronics packages in fighter jets having circuit boards bonded to a solid aluminum cold plate. Heat was conducted to the bottom of the cold plate where it was evacuated by chilled air running across fins. One module was only about a quarter of an inch thick and included two circuit boards and the cooling plate. What I thought was really cool was the modules provided the structure for the unit by simply bonding them together with a threaded bar at each corner. This arrangement was strong enough to withstand sustained 9G turns.

    Couldn’t this concept be adapted for EVs? That is, two battery pouches bonded to a single cold plate. Bonded batter modules provides the structure for the battery pack. Chilled air from the A/C to cool and heated air from a resistive heater or ICE if there is one, to manage the temperature of the battery. The use of air instead of liquid to conduct heat eliminates the plumbing which as you point out is complex and expensive.

    1. Pushmi-Pullyu says:

      Air is actually a very poor conductor of heat, which is why insulation typically has lots of bubbles of air in it. Also, being a gas, air has comparatively little thermal mass, so can’t absorb much heat per unit of volume. Contrariwise, water has a very high specific heat, and therefore high thermal mass, so can absorb a lot of heat. In addition, in its liquid form, water conducts heat pretty well.

      That’s why very nearly every production ICEV automobile uses a water jacket for cooling the engine. Note that even the VW Beetle, which in its classic form famously used an air-cooled engine, used a water-cooled engine in more modern versions.

      (Yes, I realize the article is about battery pack cooling, not gasoline engine cooling, but the basic engineering principles are the same.)

      Air cooling is much more practical in an airplane, where a high volume of fast-moving air will be available as the plane flies thru the air; no extra energy required to move that “coolant”. Also, the weight savings from avoiding a heavy water jacket around the engine is much more important for an airplane than it is for a ground vehicle.

      1. Michael says:

        Whether it’s coolant or refrigerant, it’s still air cooled through a radiator. The problem isn’t in cooling the batteries per se, but rather offsetting ambient temperature and keeping them within a set operating range. Cooling them when it’s hot, heating them when it’s cold. Engines and electronics can generate a lot of heat but can also work at very high temperatures. So air cooling even at high ambient temperatures is possible. But desert heat might be too much for some batteries. If it’s 40 deg C outside, no amount of airflow is going to “cool” the batteries.

      2. jerryd says:

        Air works fine as a battery coolant as so little heat needs to be moved as they are so efficient.

    2. Raymondjram says:

      According to GM’s video, each cell has metal plates across their wide sides, and these plates contact the coolong plate on the bottom on two long edges. So heat does conduct downward, and removed from that plate with a fluid to the radiator up front.

  5. Tman says:

    Excellent work George and Keith. Very insightful analysis. After dropping the planetary headset, the bolt motor is now more similar to the coaxial motor in the Honda fit EV as seen in this saw article
    http://articles.sae.org/11591/

    And image below

  6. Jeff N says:

    The article sez:
    “The BMW i3 uses it and GM had just such a system in a preliminary development configuration of the Spark EV when A123 was being considered as the supplier of the Sparks battery. This early spark bottom cooling plate was abandoned however when A123 was not selected as the battery supplier for the Spark in favor of the cooling scheme used in the Volt.”

    This is misleading because A123 actually was selected as the battery supplier for the regular production 2014 Chevrolet Spark EV — A123 wasn’t just used in a “preliminary development configuration”.

    GM switched to using LG Chem cells and a different physical battery pack design for the 2015 model year.

    1. Jay Cole says:

      Thanks for the note Jeff, fixed!

  7. shrink says:

    …and Nissan still insists it does not need active cooling of the LEAF battery pack.

    1. ggpa says:

      VW does not have that either, and maybe they put more thought into that than you give them credit for.

      PS: No need to go back to the 2011/2 Nissan batteries, we all know about that, and the evidence suggests the problem has been solved.

      1. Pushmi-Pullyu says:

        No, I would say that if you look at the evidence for a surprisingly low rate of capacity loss in a Tesla Model S (link below), and compare that to the average loss over time for a Leaf battery pack, even the post-2012 Leafs which used improved battery chemistry… I’d say it’s quite clear that Nissan has the inferior technology.

        Now, it’s certainly true that the Leaf outsells every other plug-in EV, worldwide. So perhaps Nissan thinks its tech is good enough for now. But the competition between BEVs is heating up (pardon the pun) quite a bit with the introduction of the Bolt, and with other 200+ mile BEVs coming within a year or two.

        I think the question isn’t whether or not Nissan will eventually move to a liquid cooling system; I think the question is how soon.

        http://evobsession.com/tesla-model-s-battery-degradation-level-5-30000-miles/

        1. ggpa says:

          Answered below by accident …

          You write “compare that to the average loss over time for a Leaf battery pack, even the post-2012 Leafs which used improved battery chemistry”

          Do you have any actual data of lizard batteries losing capacity?

          1. Michael says:

            Jim Francfort at the Idaho National Laboratory looked at the effect of DC fast charging on a handful of 2012 LEAFS.

            http://energy.gov/sites/prod/files/2014/07/f18/vss131_francfort_2014_o.pdf

            Can’t say I’m happy about 25% loss after 80k km. I’m hoping to do better in the temperate Pacific Northwest. I’ve planned for the worst case of 100 km range after three years.

            1. ggpa says:

              2012 … not lizard battery, thanks anyway

            2. Bill Howland says:

              But the Big Experts just got done telling us that fast charging doesn’t degrade batteries.

              SO how long did it take for the 25% range loss to appear?

        2. zzzzzzzzzz says:

          They will move to it if their new battery chemistry will require it. Obviously they will not add it if it will not be mandatory like with NCA chemistry. You don’t add random unnecessary stuff to economy car just to please enthusiasts who imagine they know everything better than actual engineers. It just costs money and adds weight, and adds more points of failure.

        3. mr. M says:

          Yes, Model S battery hold the capacity better, but Nissan Leaf is cheaper. I think when we will reach 300 miles batteries (2025?) a drop of 20% is tolerable over 6 years.

          Bigger batteries will always hold longer, since the cycles are less for the same miles driven.

          The model S is also charging a little bit slower than the Leaf. Compared by c-rate, the higher the c-rate the more stress for the batteries. So we learn bigger batteries can charged faster (in absolute numbers) than small batteries or bigger batteries can be charged slow (<1C) to preserve battery life and still could provide a decent miles added/hour wait time.

          Higher C-rate = faster charging
          C rates compared by model:

          Model S 1.6C (135kW charging a 85kWh batt)
          Leaf 1.7C (40kW charging a 24kWh batt)
          2016 Leaf 1.7C (50kW charging a 30kWh batt)
          Spark EV 2.3C (45kW charging a 19kWh batt)

        4. Sopfu says:

          Comparing Leaf capacity loss to a Tesla is not really fair. You would have to look at cycles since that is the primary driver in capacity loss. Considering the Leaf is cycling at three times the rate of the Tesla, you would have to look at Leafs with 1/3rd the mileage to compare apples to apples.

      2. shrink says:

        I don’t think much thought was put into an extremely low volume car selling about 350/month over the past year.

        It’s anecdotal and a small sample size, but there are mixed reports of lizard battery capacity loss here:

        http://www.mynissanleaf.com/viewtopic.php?f=27&t=20706

        On page 5 of that thread, one owner even writes: ” I am disappointed that my Lizard (with 2,400 less traveled miles in same time frame) is not holding up any better than my other car with original battery.”

        What credible and published evidence exists that Nissan, just 3 years after the first LEAF was manufactured, discovered and put into production a technological battery breakthrough suddenly making EV batteries heat resistant to degradation – other than claims from a since departed auto executive?

        Anyway, back on topic, glad the Bolt engineers were so thoughtful about actively managing battery temps.

    2. Raymondjram says:

      The Fusion and C-Max Hybrid and Energi models also use forced air cooling, but their packs are much smaller.

  8. SJC says:

    The Remy “hairpin” motor can be coaxial.

  9. ggpa says:

    I guess many folks saw the battery swap videos from Tesla when they introduced that program. It was really quick. Does anyone know how they swapped the coolant hoses?

  10. JakeY says:

    I believe it has quick connect couplings for the coolant.

    1. Pushmi-Pullyu says:

      Yes.

      See the photo illustrated post linked below, and note the caption:

      “View of the front two modules showing the coolant loop quick disconnects. Those are spring loaded and the coolant actually seems to be under pressure.”

      http://www.teslamotorsclub.com/showthread.php/34934-Pics-Info-Inside-the-battery-pack

  11. Djoni says:

    Helpfull.
    Question, I thought that planetary gear had less friction and weight than parallel helical.
    Is that true, and by what amount?
    Won’t it make the Bolt more efficient in the long run?

    1. Tman says:

      It appears parallel helical gears are more efficient than planetary gears. Toyota claims a 20% lower mechanical friction by switching from a planetary gear arrangement in the Gen3 Prius to a parallel setup in the Gen4 as outlined here http://www.greencarcongress.com/2015/10/20151013-prius.html

      So the Bolt motor might be more efficient than the One in the Chevy Spark.

      However planetary gearsets have the advantage of greater durability due to even load distribution compared to parallel gearsets which are loaded on one side. But the higher cost and complexity makes a parallel gearset more doable

      1. Bill Howland says:

        You are mixing two issues.. Both here, with the double reduction, and in the Volts with a “CVT” Planetary, they are all Helical style gears.

        There is only one motor here, so there is no way to switch gear ratios as there is in the volt, since they can play games with what device is driving which gear at what time.

        Like the VOlt, I’d expect the ‘off the line’ efficiency would be poor up to around 20 mph unless you use a very light foot. Of course, this also means ‘conservative driving’ should get fantastic mileage. We’ll see..

    2. Pushmi-Pullyu says:

      Djoni said:

      “Question, I thought that planetary gear had less friction and weight than parallel helical.
      Is that true, and by what amount?”

      Hmmm, I recall seeing an apparently authoritative claim that using a planetary gear set for an EV’s reduction gear allows it to fit in a shorter space, but I don’t recall any claim that it weighs less or generates less friction. In fact, it requires more moving parts, so all else being equal I’d expect more friction.

  12. Pushmi-Pullyu says:

    Thank you very much, George and Keith.

    A couple of recent articles here at InsideEVs argued that the Volt 1.0’s cooling system was “better” than Tesla’s because a refrigerant-based system can transfer heat faster, per square inch of transfer surface, than a glycol/water based system.

    I pointed out in several posts that this was looking at only one characteristic of a complex system, and that Tesla’s simpler system might well be better overall, especially if you consider energy used per BTU of heat transferred.

    Looks like GM’s Voltec engineers agree with me, since the Volt 2.0’s cooling system is more like Tesla’s. 😀

    (Kinda hard for the two ends of a two-headed llama to high-five themselves, but we’ll give it a try! 😉 )

    1. Jeff N says:

      Volt 2.0 and the CT6 plugin hybrid use the same full contact cooling fin design in-between adjacent pouch cells that was originally developed for Volt 1.0 and apparently it is also used in the 2015 Spark EV that used LG cells. The fins, shown in the article above, are very thin but contain multiple channels where glycol-based water coolant circulates through.

    2. ModernMarvelFan says:

      “if you consider energy used per BTU of heat transferred. Looks like GM’s Voltec engineers agree with me, since the Volt 2.0’s cooling system is more like Tesla’s. ?”

      I would think they did it for reduction in cost/complexity/packaging rather than BTU.

      If you think about it, the Bolt battery is actually discharging at much lower rate than the Volt.

      60kWh for about 150kW of discharging power vs. Volt’s 18.4kWh for about 111kW. The C rating is much lower in the Bolt thus lower heat generated.

  13. SparkEV says:

    Does co-axial gear configuration have any effect on torque steer? SparkEV is pretty bad, especially when accelerating at full throttle.

    1. Tman says:

      Not really, but it does make for a more compact packaging.

      The length of the half shafts and the king pin axis on the wheel carrier are the biggest determinants of torque steer.

      equal half shafts is ideal, unequal lengths less so. Most FWD cars use unequal length half shafts for packaging reasons. The 2006 Pontiac grand Prix GXP used equal length half shafts to tame the 438NM/323lbft of torque to the front wheels.

      All Audi FWD cars based on the MLB architecture underpinning the A4-A8 also use equal lengths.

      Wider kingpin axis can also reduce torque steer as done in the Cadillac ELR, the ELR uses a hyper strut front suspension instead of a conventional McPherson strut. That’s why it can handle more torque than the volt, but the trick suspension is cost prohibitive to use in a car like the Spark or Bolt EV.

    2. Pushmi-Pullyu says:

      Another recent article here at InsideEVs quoted a GM engineer as saying the Volt 2.0 is engineered to automatically compensate for torque steer, and that it was pretty bad if it wasn’t compensated for.

      1. Jeff N says:

        That may have been Bolt chief engineer Josh Tavel since he recently said something like that in a YouTube video.

  14. ggpa says:

    You write “compare that to the average loss over time for a Leaf battery pack, even the post-2012 Leafs which used improved battery chemistry”

    Do you have any actual data of lizard batteries losing capacity?

  15. Pajda says:

    I was thinking why GM did not release the third dimension of LG cells used in Bolt? So there is no possibility to calculate volumetric energy density of these pouch cells. And so what progress was achieved by LG in modern pouch cell technology.

    1. JakeY says:

      I’m waiting for that number too to do a cell based equivalency estimate. Hopefully when it nears production, GM will release it.

  16. Tech01x says:

    One of the concerns for this design is actually the effectiveness when under high charge rates and the effectiveness for heating, especially when it is extremely cold outside. It would seem that this design would be make the Bolt less effective in winter.

    1. Seems unlikely that battery heating in the winter will be a problem. The Leaf only kicks on a heater at like -20C. It has never come on in my car, even when ambient temps approached -20C, because using/charging the battery creates heat.

      1. Tech01x says:

        That is precisely why the Leaf has much worse degradation of range in winter conditions than, say, a Model S.

    2. Bone says:

      I don’t see any reason why bottom plate heating would be less efficient in cold weather as long as there is proper insulation layer below the bottom plate.

    3. Raymondjram says:

      Just like in the Volt, the Bolt EV’s battery pack will have excellent thermal insulation (and I expect a strong cover underneath) to keep all the cells at a constatnt temperature. Only if the pack was exposed to many days of very cold will I expect it to be affected. If the Bolt EV is charged and driven every day, it will never get cold in winter.

  17. ClarksonCote says:

    Why are bottom cooling plates used if heat rises?? Seems like a top coolant plate would make more sense?

    1. Jake Brake says:

      Because conduction and condensation.

    2. Tman says:

      @Clarksoncote “Why are bottom cooling plates used if heat rises?? Seems like a top coolant plate would make more sense?”

      Heated “Air” rises aka “Convection”, but “Conduction” which occurs in solids is not influenced by gravity.

      1. AlphaEdge says:

        Thank you for that. The bottom cooler was bugging me, but now it doesn’t.

      2. ClarksonCote says:

        Good point, and obviously makes sense. Thanks!

    3. Bill Howland says:

      Heat doesn’t ‘rise’ unless it is being carried by something. Who told you that? Sensible heat (the kind you can feel, and measured by a dry-bulb thermometer, goes from hot to cold, in proportion to the temperature gradient at the time.

      Who told you heat rises? It can go down just as easily as up if nothing is moving. And I hope the only thing moving in the battery assembly is within the stationary hosing.

      1. ClarksonCote says:

        Hot air rises Bill, like hot air balloons.

        I was thinking in terms of convection and not conduction. Obviously the latter is what is occurring here, and the placement is completely logical given that.

        1. Bill Howland says:

          Well, not so obviously since you missed it.

          Hot air rises? Really?

          You’d think someone would take that revelation and invent a Chimney.

          There’s 2 things going on here and as a result of buoyancy it goes up, the 3rd thing. But its not a basic principle – take the following example:

          Hot water doesn’t always rise, since Lakes freeze from the TOP.

          But water is special.

          1. ClarksonCote says:

            I really don’t understand why you make such big issues out of small ones. Do you disagree that hot air rises? If you do, you seem to either be focusing on corner cases or lack a fundamental understanding of air density.

            I swear you just look for things to argue about most of the time, just for the heck of it.

            “Hey, someone here said something, and I’ll twist it to mean something else, and try to make them look foolish.”

            Yes, I am human, and can make a mistake and misinterpret and incorrectly infer something when reading it quickly.

            1. Bill Howland says:

              I correct factual errors in your text, since that is what previously you’ve stated you will only respond to. For instance, stating things as a basic principle when they are not.

              Or numerical errors such as stating Brian’s Leaf tops out at 16 amps when he has said it is 18. Which we proved at a Dual chargePoint with comparison with my car, as a for instance.

              But, there has been lately an uncharacteristic snooty-ness and thin-skinned responses from you, now that you mention it. I guess the ‘real you’ comes out now that I’ve sold my Roadster. I mean anyone can test drive an ELR anywhere.

              You no longer have to be friendly since I have no vehicle you have to solely deal with me, since the only Roadster remotely around Syracuse at the time was one in distant Ithaca. Someone has purchased a used one near where you live, so perhaps you’ve driven his.

              The example of the ‘hot water’ was simply to point out , unlike you who has an engineering background, to nip in the bud clowns and greenhorns’ responses about fluids rising due to heat is a basic principle, when the so-called basic principle is falacious when it comes to lakes, therefore, it is not one.

              1. ClarksonCote says:

                I assure you my frustration lately has nothing to do with what vehicle you own, and everything to do with your responses.

                How ironic to be calling me snooty when referencing a conversation we were having about vehicle max amps, when I was trying to show you we were saying the same thing (and not argue) and you were intent on arguing. Who is being snooty?

                My statement of “heat rises” apparently needs to be taken literally instead of the context of the popular vernacular that references that term, which again, ironically, goes back to your whole “Who knows? NOSE! You’re talking about my nose!” dialogue a while back to suggest I was taking things too literally. Again, a whole bunch of irony.

                I was thinking of that general concept of heat rises and casually posed a question without giving it much thought. I was corrected, admitted my error, and you continue to talk down to me here like I’m a fool. “Seriously? Why doesn’t someone invent a chimney” This, after I admitted my error numerous times and tried to move on. So again, who is being snooty?

                And to bring up the Leaf amperage issue again is quite comical. Here you continue to focus on me saying 16 amps when Brian saw 18 amps, and all I was point out with the 16 amps was that the Leaf, unlike the Volt, would go higher in amperage. But again here, you seem to want to take everything I say, and turn it into an argument.

                So I do think this whole dialogue is quite ironic to call me snooty given all the examples above. And I am frankly disappointed to have you think that any of my frustration here with these last two dialogues could be relegated to something so petty as the current vehicle you own. I assure you, whether you owned an ELR, Roadster, or BMW i8, I would be consistently disappointed with the amount of beraiting you’ve been giving me online lately, for no apparent reason.

                1. ClarksonCote says:

                  And to be clear, to hopefully avoid the risk of additional criticisms pointed in my direction, when I refer to the general idea of “heat rises” I mean if you search for “does heat rise” or similar on Google, you get an explanation of why hot air rises. Because the general population would say “heat rises” just like other generalizations that are not factual but stated in sloppy terms as being true.

                  And no, I haven’t ridden in anyone’s Roaster, nor have I tried to find anyone with a Roadster, or any other vehicle for that matter. The opportunity to try your vehicle was a side benefit of meeting you, not the other way around. However, this assertion is just another disappointing example of how it seems like you keep trying to interpret every message in the worst light possible, and assume that to be the message that I intend to relay.

                2. Bill Howland says:

                  Anytime I make a minor mis-statment of fact, or make a spelling error, I get corrected here. If it is of import, I thank the person for pointing it out to me.

                  1. ClarksonCote says:

                    Which is exactly what I did above…

                    “Good point, and obviously makes sense. Thanks!”

                    LOL

    4. Raymondjram says:

      See my post above. Heat travels by conduction (like electricity) through metal, and doesn’t depend on position or gravity. This is how spacecraft cool in the vacuum of space.

      1. ClarksonCote says:

        Yep, see my posts above as well, thanks.

        I had air cooled batteries on my mind and was thinking more of convection than conduction.

        Just a silly oops moment. I design and work with conduction cooled systems, including space-based systems.

        Seems like I need to not pose questions when I’m over-tired. 😉

  18. DanCar says:

    What is meant by electronic precision shift system?

  19. Master One says:

    So does “liquid active thermal control” mean cooling AND heating of the battery?

    This is something that I find really strange in the LEAF, to leave out active cooling and offer battery heating only optional for cars sold to the northern countries. This is not about battery longevity, but avoiding reduced range and longer charging times in cold climates.

    1. ClarksonCote says:

      Battery heating helps save the range in the winter. Battery cooling saves the long term life of the battery.

      Nissan has apparently taken the American viewpoint of worrying only about short term effects and kicking the can on long term ones.

      The Bolt, on the other hand, will employ active heating AND active cooling.

      1. Master One says:

        Nissan nevertheless is very confident in their battery chemistry, to give 8 years / 160.000 km of warranty on the new battery.

        I am not that much worried about battery life, but living with the central European climate it is quite a PITA to see such reduced range in winter.

        Active battery heating & cooling is definitely the way to go!

        1. Brandon says:

          Question: Let’s say on a 2013 LEAF and newer with the heat pump heating and cooling system, in cold weather, is range lost more because of heating or because the battery doesn’t do as well in the cold?

          1. ClarksonCote says:

            I think heating is more efficient. In the cold, a Lithium Ion battery can lose as much as half of its rated capacity given a 2C discharge rate. In the grand scheme of things, a heater running to bring it up to temperature should consume much less energy than that.

            You also likely risk some damage to the battery if not warmed up. Li-Ion loves to be stored cold, but prefers to be used when warm.

            1. Brandon says:

              Ok. What I’m trying to get at is whether more range is lost in a LEAF because of heating the cabin or because of the battery being cold and not having as much kW to give.

              1. ModernMarvelFan says:

                Both…

                1. Brandon says:

                  Both meaning the same amount? I know they are both a factor, but I’m wondering which one might be affecting the most… lets say in 20 degree weather. I know it’s a hard type of question to answer. Considering it may be difficult to know for sure what is actually happening.

                  1. ModernMarvelFan says:

                    I think that depends on the temperature of the battery at the time (duration in the cold), amount of heat required by the passenger and speed of the car (hwy vs. stop/go)

                    In my PEV (not a LEAF), I would say the range impact is about 60/40 split between heat usage and cold battery temperature.

                    So, if I lose 10 miles of range, 6 miles was caused by the heat usage and 4 miles was due to the cold temperature of the battery.

                    1. Brandon says:

                      Thanks for that useful info!! That’s what I was getting at. What I’m wondering too is if this active cooling and heating system for the Bolt battery will be significantly better than the LEAF’s passive system in terms of how much is lost because of a cold battery. Any thoughts?

                    2. ModernMarvelFan says:

                      I think it will help. But keep in mind that if your EV isn’t plugged in, the power to keep the battery warm still comes from the battery…

                      So, it only makes a difference if the car isn’t park and let it cool down completely. Of course, those are impacted heavily by driving pattern and outside temperature.

      2. Bill Howland says:

        You guys are forgetting one thing that Nissan has remembered, namely viewing as heating is much more important than cooling with battery longevity.

        As an example, my Roadster would not turn on the battery heater if it was self-powered until the temp dropped to -5 deg F.

        But, here’s the point, It wouldn’t attempt charging the battery unless it was +34 deg F.

        So discharging the battery between -5 and +34 was deemed perfectly safe, since the car would ‘start’ immediately. It would only delay turn on at temps under -5.

        But charging at these temps was deemed impossible without ruining the battery. So it makes perfect sense to me that Nissan is more concerned about heating the battery.

        After all, driving the car when the battery is cold will heat the battery, and the more dead it becomes its ESR will increase, making even more heat.

        In the roadster above -5 F, the heater was NEVER turned on while discharging since it wasn’t a concern as mentioned.

        I have no info on the volt, other than it takes longer and takes more kwh to charge my volt when it is very cold outside. I always assumed it was acting just like my roadster, that is, heating the battery up to a safe temperature first. Perhaps Nissan does the same thing.

  20. rashomon says:

    There’s some confusion here in the relationship between energy used in combatting rolling resistance and that used fighting aerodynamic drag. In general, rolling resistance is linear with speed (V), and aerodynamic drag goes up with the cube of speed (V-3). GM has released the Cd and A date for the Bolt, which isn’t particularly good, with an effective frontal area (CdA) of about 0.78 meters squared. It’s about a third less aerodynamic than a Tesla MS which is at about 0.58 meters squared. At 75 mph, the Bolt uses about 5 times more power overcoming aero forces than rolling forces, and at this speed, requires about as much power as a Model S to go down the road, and (if powertrain efficiencies are about the same) will have similar highway range to a Model S60. Go faster and the V-cubed term kills you, and the Bolt won’t do as well as Model S. Drop down to 35mph, and aerodynamic loads and rolling loads are roughly the same, and the lighter Bolt should have greater city range than a Model S60.

  21. ModernMarvelFan says:

    “GM has released the Cd and A date for the Bolt,”

    what is the Cd and A for Bolt?

    1. Jeff N says:

      Car and Driver says the Bolt Cd is .312 and perhaps someone else claimed the frontal area as 25.8 leading to a drag area of 8.05 sq ft. For context, Car and Driver independently measured the LEAF at 7.8 sq ft.

      I have not seen officially published GM sources for these Bolt numbers but they seem reasonable.

      1. ModernMarvelFan says:

        Cd of 0.312 would be pretty poor in my opinion.

        Maybe the rear drag is too big due to its more squarish tail.

        But I haven’t seen any official numbers yet.

  22. ModernMarvelFan says:

    I guess now EV supporters shouldn’t make rush judgement anymore as far as complexity of ICE vs. EV go…

    Just look at Bolt’s “complexity”.

    1. Bill Howland says:

      Doesn’t look too bad to me MMF, although granted they could have perhaps ‘dressed’ the cabling and piping a bit cleaner. Perhaps the next iteration will streamline things a bit.

      Of course, there’s things in every modern car that either the gov’t requires or else people demand as standard equipment, namely, antilock brakes, with the motorized interruptor, vacuum assisted brakes, air conditioning, power steering, and then this car’s economy modes such as the assumed non-refrigeration of the battery during moderate climates, and then the refrigeration of same when it gets really hot, and, then other heating that has to be specifically addressed in BEV’s since there is no engine to provide a convenient source of heat, nor an easy shaft to drive the refrigeration compressor/condensor fan off of.

      So doesn’t look bad to me at all – especially for what they’re charging for a 200+ mile epa rated ‘Mid size Station Wagon’