2015 Chevy Spark EV
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?