EXCLUSIVE: 2015 Chevy Spark EV – Final Drive Ratio Moves Up To 3.87 – Battery Capacity Drops To 19 kWh

3 years ago by Eric Loveday 39

2015 Chevy Spark EV

2015 Chevy Spark EV

Drive Unit Design

Drive Unit Design

In a 2013 presentation of the the 2014 Chevy Spark EV to SAE International, General Motors Steven Tarnowsky, Senior Manager of Electrification Systems Engineering, highlighted some mostly unknown facts related to the Spark EV.

Of importance here is that GM had tested two different final drive ratios in the Spark EV.  One, a 3.17 ratio, was eventually adopted for use in the production 2014 Spark EV.  The other, a 3.87 ratio, will come standard on the 2015 Chevy Spark EV.

The switch to the 3.87 ratio is documented in dealer ordering material for the 2015 Chevy Spark EV.  Additional changes for 2015 are detailed above, most of which relate to color choices and minor interior changes.

But that 3.87 ratio for the final drive is a significant alteration.  As the graphic on the right shows, the switch to 3.87 should increase city range for the Spark EV.  However, in announcing that LG Chem will be responsible for the 2015 Spark EV battery (no longer is A123 involved), General Motors suggested that no MPGe or range ratings will change for 2015:

“A newly designed battery system features an overall storage capacity of 19 kWh and uses 192 lithium ion cells. The cells are produced at LG Chem’s plant in Holland, Mich. The battery system weight of 474 lbs. is 86 pounds lighter than the system in the 2014 Spark EV.”

“Changes in battery design will not affect the Spark’s MPGe, or gasoline equivalent, performance compared to the 2014 model. Range will remain at an EPA-rated 82 miles and MPGe will remain at 119.”

In previously discussing the Spark’s torque and final drive ratio, Peter Savagian, General Director for Electric Drives and Electrification Systems Engineering at General Motors, stated:

“The Spark EV motor is designed and manufactured by GM. This motor makes 540 Nm (402 ft lb) of Torque at stall and out to about 2000 rpm. This is not gear- multiplied axle torque, but actual motor shaft torque.”

“The very high torque is motor performance that we are very proud of, and customers will notice the difference: (It has a gear reduction of 3.17 to 1, so the axle torque is the product of these two). This is a very low numerical reduction ratio, which has several great benefits – 1) Feels much better to drive. 3.18:1 is less than half of the reduction of all other EVs. This makes for extraordinarly low driveline inertia, less than 1/5 of the driveline inertia of the Nissan Leaf and 1/4 that of the Fiat 500 EV. Their cars feel like you are driving around in second gear all day long; ours feels like fourth gear. 2) Lower gear mesh, spinning losses, and lower high speed electromagnetic losses mean very high drive unit efficiency. The Spark EV efficiency from DC current to delivered Wheel torque is 85% averaged over the city driving schedule and 92% when averaged over the highway schedule.”

It’s our belief then that by changing the final drive ratio from 3.17 to 3.87, there has to be a change to MPGe and range.  It’s unknown how the new 3.87 ratio will make the Spark EV perform off the line, but the current belief is that General Motors uses some sort of electronic limiter on the current Spark, which deadens its 0 to 60 MPH time.  If that’s the case, GM could probably adjust the performance so the 3.87 ratio may have little no impact on off-the-line zip, but still should provide improved range up to speeds of ~ 55 MPH.

For proof that GM limits the Spark EV’s off-the-line pep, check out this video where a Spark EV owner supposedly found a way to remove or override this electronic limiter.  All those torques are certainly capable of moving the Spark EV swiftly, but for the sake of range (and perhaps to limit driveline abuse) GM wisely limited the Spark’s power output at 0 MPH.

With a whole host of changes set for 2015 (only one year after the Spark EV launched in the US), could it be that GM is readying the electric Spark for a broadened rollout?  We know that LG Chem has the capability to supply the cells that would be needed if GM decided to sell the Spark EV at the nationwide level, so why not give it a shot?

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39 responses to "EXCLUSIVE: 2015 Chevy Spark EV – Final Drive Ratio Moves Up To 3.87 – Battery Capacity Drops To 19 kWh"

  1. Nathan Crawford says:

    A lot will depend on if there are any changes in the motor and other parts of the drive train. I have not heard of any yet.

    Wouldn’t the higher gear ratio make for more torque at the wheel (i.e. more peppy, not less)?

    Also, I am not convinced that the 19kWh number is for the raw battery capacity. I think it is the usable capacity based on other statements in that press release (range and MPGe being identical).

    1. Ted Fredrick says:

      YOu are correct. A higher gear ratio will give you more power off the line. Torque X gear ratio = final torque to wheels

      1. GSP says:

        More axle torque, but the same power.

        GSP

    2. MrEnergyCzar says:

      Perfect size battery for the next Volt….

  2. Kyle Cuzzort says:

    I think you’ve got the terminology here backwards. 3.17 to 3.87 is moving to a LOWER gear ratio, not a higher one.

    “It’s further believed that the 3.87 ratio will make the Spark EV slightly less peppy off the line”

    Who believes that? Switching to a lower gear is an old hot-rodder trick to make the car faster off the line at the expense of cruising speed/efficiency. With no motor changes I’d expect the Spark EV with the new gearing to accelerate noticeably faster.

    “Their cars feel like you are driving around in second gear all day long; ours feels like fourth gear.”

    I would never, ever want to drive a city car around all day in 4th gear. That sounds dreadful. What kind of marketing statement is that?

    1. GeorgeS says:

      Yeh your right.

      They went from 3.17 to 3.87. Just like the old days going to a 4.11 rear end. So I think the articles wording should be changed. The ratio change should give it MORE pep off the line not less.

      1. GeorgeS says:

        and higher motor RPM for the same vehicle speed.

      2. Spec9 says:

        Has anyone verified this? I find it kinda unlikely that they would make this car even more peppy. I hope that is true but I doubt it.

      3. WopOnTour says:

        George, what this article fails to interpret is that the 2015 Spark’s pack capacity will actually be decreasing from 60Ah (3x20Ah per group or “triplet”) to 45Ah (the LG cells are 15Ah each) So this drop has been compensated for by an equivalent increase in final drive ratio and as such an equivalent increases MGU RPM at any given road speed.- WOT

        1. WopOnTour says:

          Correction: Actually the Spark EV pack is 54Ah using a 2P96S configuration.

  3. Everyone is wondering …
    Will reducing the battery from 21 to 19 kWh have a cost savings that will be passed on to customers?

    The IRS values each kWh at $417, implying a $834 value reduction. Additionally, using the same LG modules as used in the Volt should provide additional volume and logistic related production savings (based on ~60,000 Volts).

    1. pjwood says:

      Beyond 16kwh, the IRS values additional capacity at $0. The tax-credit fully applies and does not roll down, until you get below 16kwh.

    2. protomech says:

      IRS valuations have little to do with how much the battery costs GM. There’s no reduction in tax credit beyond 16 kWh stored.

    3. The IRS value of $417/kWh is just a reference since manufactures have not released EV battery pack pricing. In real money, a kWh of battery could cost between ~$250 to $700. Tesla is expected to have lowest internal costs based on large kWh production and the cheap 18650 production format.

    4. GeorgeS says:

      Not sure if it will be passed on.
      In addition to decreasing kwh to 19 they went to a larger format battery (cell count approx in half). This results in a cost reduction as well (approx 17%) as pointed out in this article I wrote

      http://insideevs.com/argonne-computer-model-and-the-implications-for-the-3rd-generation-tesla/

    5. GeorgeS says:

      @Brian

      These are not the same cells as the current volt. They are larger format cells.

      I think we will see these larger format cells in the Gen2 Volt.

      It also implies that Tesla will go to larger format cells in Gen 3 from the current 18650 format.

    6. Fabian says:

      Doesn’t California require a 24kwh+ battery to get the full $2500 rebate?

      1. Spec9 says:

        No. It just has to be a full ZEV. So this is all full-speed EV cars and fuel cell cars (which is just the Honda FCX).

        So you can actually buy an iMiEV for around $13,000 after the $7500 tax-credit and $2500 California rebate. It is basically a free car if you replace a gas-guzzler with it.

  4. scottf200 says:

    Note the 4G and wi-fi hotspot

  5. ClarksonCote says:

    I would suspect that the EPA range will remain unchanged. If they’re decreasing the battery by 2kWh, and changing this ratio, it’s likely that they are not dipping further into the DOD with the new battery, but using the ratio to account for the lower capacity.

  6. scott franco says:

    “With a whole host of changes set for 2015 (only one year after the Spark EV launched in the US), could it be that GM is readying the electric Spark for a broadened rollout? We know that LG Chem has the capability to supply the cells that would be needed if GM decided to sell the Spark EV at the nationwide level, so why not give it a shot?””

    Guys, the Spark has compliance car written all over it.

    1. Dave R says:

      If it were a compliance car, why would they redesign the pack after just one year of production?

      Two reasons I see:

      1. They were worried about A123 after the bankruptcy.
      2. They are focusing on reducing cost so they can make money on the car when they start selling the car in more markets.

      I do agree with others that it would have been wise of them to apply the weight savings towards more capacity, they would have a 100 mile EV.

    2. evnow says:

      People here argued endlessly before Spark introduction that it greatly hurt Leaf sales ! GM fans refuse to see the writing on the wall.

  7. It seems reasonable the overall performance will be similar between 2014 & 2015 Spark EV models.

    1) 86 lb weight reduction will improve acceleration, and range slightly

    2) 3.87 vs. 3.18 will lower RPM ~20% for same speed
    – from Transmission Loss curve above, this would imply a 1000 RPM will become 800 RPM (20% lower), resulting in 80-120 W less energy use (~450-800 kWh over an hour driving depending on speed). *note: graph stops at 1300 and doesn’t include data for 1500-3000 RPM which would be a common operating range (eg: 504 Nm torque was recorded at 2000 RPM)

    3) since the motor will be spinning at lower RPMs for all speeds, the Power Inverter (creating AC drive power from DC in the battery) will be cycling its circuits less, thus operating at a higher efficiency.

    There may be a small differences in MPGe, (range), but it will be less than the effect of using heat, or A/C during a drive.

    1. Mark C says:

      With lower gearing {higher numerical}, it should require less torque to move the car with the 3.87 ratio, if all else were equal. Motor RPM going down the road will also be higher, but I don’t know how that affects current draw. The slightly lighter weight will help with acceleration and range as well.

      As for the smaller battery pack, I agree with that commercial on TV where in the end all the children agree, more is better.

    2. Mint says:

      You got it backwards. The motor will be spinning at a higher RPM for the same vehicle speed.

      It’s unlikely that there will be any noticeable efficiency difference. Unlike an ICE, electric motors have very good efficiency across a wide RPM and throttle range.

      Performance should slightly improve.

  8. Anon says:

    Let the Sparks fly…

  9. Suprise Cat says:

    EPA range is counted until battery empty warning pops on or until it car gets into turtle mode?
    With the smaller battery, I would guess it’s now going less far with turtle mode.

    1. Dave R says:

      EPA counts range until the car is no longer able to maintain the required speed on the test circuit.

  10. Dr. Kenneth Noisewater says:

    Interesting point about GM’s gimping in software, perhaps the taller gear won’t affect acceleration as much if GM lightens up on the software gimping, much like the reduction in battery could make no difference if they couple that with a decrease in reserve percentage.

    Still, I would like the choice to not be gimped at all.

    1. GeorgeS says:

      Higher numerical=taller gear + higher motor rpm for a given speed = more accel (not less).

      Yes??

      I think the wording in the article should be changed.

      1. Dr. Kenneth Noisewater says:

        Guess so.. Also helpful:

        http://www.badasscars.com/index.cfm/page/ptype=product/product_id=398/category_id=13/mode=prod/prd398.htm

        “Rear end gears (2.79’s, 3.00’s, 3.25’s, etc) are great for freeway driving, bit not good for 0-60 MPH or accelerating from a dead stop. Shorter gears (higher numbers) are much better suited for accelerating, such as 3.55, 3.73, 3.91’s, 4.11’s etc. Always remember, for very “give” there is a “take”. If you take lower gears to accelerate quickly from 0-60, you will give top-end speed.”

    2. GeorgeS says:

      @doc

      Motor RPM= axle RPM X GR

      higher GR=higher Motor RPM

  11. Lad says:

    With 400 ft/lbs available, I can see GM limiting ramp up to save the differential and Planetary gearing.

  12. Ocean Railroader says:

    If only they could have used this new system raise the range of the car. It would have been cool. But now I have feeling that the California air resources board has a GM Executive tied and duck tapped in a back room somewhere saying build us our compliance car or else

  13. an_outsider says:

    With a 30A (7.2kW) or at minimum a 6.6kW AC charger onboard + DC plug + heat pump, I’m on board!

  14. QCO says:

    The motor controller settings will determine the maximum torque, which will be based on what the rest of the driveline components can take.

    In this case they have geared up the motor speed, mainly to reduce current losses (higher speed motor means lower current), but reprogrammed the contoller to keep the same max torque spec.

    The consequences are slightly higher efficiency due to lower currents/losses, but also a lower top speed, which is limited by centrifugal forces in the motor. In this case I suspect the motor already had the headroom to meet the specified vehicle top speed, so no changes there either. There’s a slight increase in windage and bearing loss, but they’ve factored that into this optimization.

    The end result is better efficiency with the same vehicle specification. However they decided to use that incremental efficiency (along with other battery improvements) to reduce battery costs rather than increase range. That’s the main point worth debating here.

    BTW, this is all basic stuff EEs learn in their second year motor lab. The rest of the confusion is created by non-EEs, like the authors….

    1. Foo says:

      Oh no EE didn’t!

  15. Nozferatu says:

    It’s hard to determine if any modification has been done to that Spark EV in the video…it’s not very difficult to make a FWD car do that especially if your wheels are turned.

    I, for one, want more torque and rid the top speed limiter of 90MPH…this thing pulls like a train and I’ve shocked some drivers in some seriously fast cars in midrange…this is where this car really shines.

    It could do with a better suspension and tire setup too.