Year 2 Competition Story

On May 17, 2010, 16 schools across North America tested vehicles on the General Motors Desert Proving Grounds at Yuma, AZ. During the past two years, each school has designed and built a powertrain of the future (fuel cell, hybrid electric, 100% electric) into each of their GM donated vehicles as part of EcoCAR: The NeXt Challenge. As part of the challenge for Year 2, the student teams only had 6 months from the time when the GM donated vehicle was delivered to the time of competition at Yuma, AZ to install their Year 1 designed powertrain. Not every team was able to bring a 100% functioning vehicle to competition. When NC State arrived on May 17, we had just started to make the electric motor drive the vehicle with full power, the diesel engine-generator had never been ran before, and controls strategies still needed to be programed for the engine-generator.

NC State’s EcoCAR team has designed a vehicle, similar in concept to the Chevy Volt, that uses a GM donated front-wheel drive electric motor capable of 148 hp running off of a 21 kWh lithium-ion battery pack from A123 Systems. There is an engine on-board; this one is a 1.3L compact B20 biodiesel engine that spins a permanent-magnet generator. Like in the Volt (which has a small gasoline engine-generator), NC State’s EcoCAR engine does not propel the wheels. Its sole purpose is to charge the lithium-ion battery for long road trips. The driver can choose to run on short trips during the day
with 100% electricity, and charge the battery overnight by using a plug-in charger, driving the car on a daily basis without fuel. You would only fuel up the vehicle for long trips (a weekend out, a beach trip, etc.).

The competition span at Yuma was 5 days; 2 days of passing rigorous safety inspections and then 3 days to compete in some on-road testing by GM drivers to evaluate the vehicle’s performance. Getting through the first 2 days was the biggest hurdle. We had a coolant leak with our diesel engine that took a while to fix and we had to correct a few details here and there during safety inspection (such as re-installing a fuel filter to a more correct position, and buttoning up a few wires just to make sure everything was safe). We had ran out of time to try turning the engine over, but we were excited to see how our electric drive system would perform. After we passed safety inspection and we thought we were in the clear, we weighed in a little too heavy and had to remove a few non-essential vehicle parts on the spot (such as the rear seats).

“As a grad student leader, I was amazed at how the undergrad students lead themselves well in solving the little issues that turned up so quickly. To me, NC State students are leaders themselves, and our success this year is because of the amazing students” states Student Team Leader Ali Seyam.

Our car was tested for 0-60 mph acceleration in 10.8 sec, 50-70 mph acceleration in 6 seconds, and rapid lane change speed at 47 mph. For vehicle handling, GM drivers performed an autocross lap with the NC State car scoring the second best overall time on the lap. Without the diesel engine running, our range test at Yuma indicates that we have a nearly 50 mile 100% electric range, that’s higher than the Chevy Volt’s published 40 mile 100% electric range. To be able to work with new generation batteries and electric motor from industry is exciting. To test endurance during towing, our vehicle was tested by pulling a towing dolly (simulating 1680 kg on a 3.5% slope with its drag) while a GM driver behind the wheel cruised at 45 mph. The powertrain had to be able to tow the dolly for at least half an hour without any breakdowns, and our car did that no sweat.

We also had tests on the quality of the vehicle’s drive (how smoothly it accelerated, decelerated, the feeling of its steering, etc.). We learned tips on how to improve our electric motor controls strategies so that our combination of acceleration and regenerative braking requests to the motor would make the best driver experience possible.

We entered the competition with some uncertainty, but left proud and victorious. In one year alone, the NC State EcoCAR team has improved its rank from 16th overall (students are scored on design reports throughout the first two years) to 7th overall because of how well our vehicle ran through all events. At the awards ceremony in San Diego, CA, the NC State team was hailed as the most improved team of the year.

It’s not over yet, this final third year of the competition is all about making the vehicle’s appearance showroom ready, and also engineer solutions to make the vehicle perform better, with the Yuma results as the benchmark. We will acquire data with the current vehicle to understand the shortcomings and design improvements for the vehicle. For example, we weighed in heavier than expected, and our 12-volt loads are a little higher as well. We will make improvements to the vehicle’s mass by designing lighter parts, or coming up with ways to support the 12-v system besides drawing off of the high-voltage system. It will also be interesting to see in the next couple of months what our full range will be with the diesel engine charging the batteries. Through this competition we saw that engineering students in EcoCAR today are becoming engineers of tomorrow that will bring the automotive industry into a greener future.

Written by Ali Seyam

Edited by Erik Schettig