In our article discussing some of the confusing information surrounding the upcoming 2014 Chevy Spark EV, we discussed how the 400lb-ft of torque isn’t the motor rating, but the final torque after gear multiplication is factored in.
InsideEVs had a lively discussion going and it attracted the attention of GM’s General Director for Electric Drives and Electrification Systems Engineering, Peter Savagian. He joined the conversation and stated:
I need to disabuse you of the mistaken notion that this motor has less than 400 ftlb of Torque. The Spark EV motor is designed and manufactured by GM. This motor makes 540 Nm (402 ftlbf) of Torque at stall and out to about 2000 rpm. This is not gear- multiplied axle torque, but actual motor shaft torque.
Mr. Savagian went on to explain how GM managed that torque-rating, as well as why their EPA ratings are so high:
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 3.18 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 extraordinary 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. This is the highest in the industry, and that is one of the reasons why the Spark EV sets the benchmark for most efficient car.