With the close of the on-track stages barely 12 hours behind them, teams spent the better portion of Wednesday, July 28th loading and transporting their vehicles from Michigan International Speedway to Chrysler’s Proving Grounds in Chelsea, a short distance away. Since then, all vehicles that advanced to the Validation Stage (the last and final hurdle toward the $10 million purse) were put through a Coast Down exercise, which involved test engineers accelerating each vehicle up to approximately 70mph on a 2.25 mile long, level paved roadway and then “coasting” them in neutral until they come to a stop, unassisted by brakes.
The exercise provides a few key metrics that are required for Validation Testing on the chassis dynamometers at Argonne National Lab facilities located just outside Chicago:
· First is aerodynamic resistance, a factor of the vehicle’s shape and footprint that determines how much air the vehicle has to push out of the way as it moves. The more resistance, the more energy has to be expended.
· Second is rolling resistance, a factor of tire design that determines how much energy the vehicle has to use to overcome the resistance caused by the friction between the tires and the road.
· Third is mechanical resistance, a factor of the vehicle’s powertrain and how much energy the vehicle has to use to overcome internal friction to drive the wheels.
Day 1 of Coast Down weather proved less than ideal, so Chrysler test engineers made the best of it by rigging up the vehicles with the needed instrumentation and training Chrysler’s professional drivers to handle the vehicles. Thankfully, the weather on Day 2 proved ideal, and teams RaceAbout Association, Li-Ion Motors, ZAP, and Aptera wrapped up under sunny skies and little wind without incident. All four vehicles were shipped off early the following morning on a hauler to arrive at Argonne National Lab for Validation testing.
Also on the morning of Day 3, Edison2, TW4XP, and X-Tracer hit the proving grounds for their turn through Coast Down. On the straight-away of the test track, Edison2’s Mainstream Class entries, vehicle numbers 97 and 98, were fielded. In both cases, as third party test drivers accelerated the vehicles to speed, a mechanical over-rev condition resulted in engine failures and the tests had to be aborted.
The fact that the Edison2 vehicles employ sequential transmissions may have contributed to the unintended downshift and subsequent mechanical over-rev condition that damaged the engines. In a typical racing configuration, the driver pulls rearword on the shift lever to shift up through the gears. This is opposite the convention used by many US automakers in their semi-automatic transmissions (like Chrysler's AutoStick), where manual upshifting is executed by pushing forward, away from the driver. Further, given that this is a competition vehicle, the automated software that would normally override an unintended downshift at speed or at high RPM is not yet perfected.
Chrysler’s test engineers, working with Oliver Kuttner and Ron Mathis of Edison2, were able to quite literally push their way through this particular setback, however. With the engines of both Edison2 vehicles out of commission, Chrysler, with Kuttner piloting the competition vehicle and Mathis behind the wheel of one of their trucks, put their assist vehicles to work, pushing one of the identical Edison2 vehicles to a speed sufficient to acquire the needed measurements.
Coast Down data was ultimately obtained for the Edison2 vehicles, and the tests were completed successfully. Both X-Tracer and TW4XP successfully completed Coast Down as well.
And so the week ended not without incident, but with a bit of determination and resourcefulness. All of the finalist vehicles have safely arrived at Argonne’s facilities for Validation. Testing began Tuesday, August 3rd, and will continue throughout the month of August.
Since the Edison2 engines require costly repairs due to damage that was no fault of their own, and because the timing of these repairs presents substantial schedule challenges, competition officials have agreed to review objective third-party dynamometer results on Edison2’s vehicles to determine whether the data can be accepted in lieu of Validation Testing at Argonne National Lab. Until this determination is made, Edison2 will be granted a waiver that releases the team from the requirement to present their vehicles at Argonne for Validation Stage testing.
Again, both Edison2 vehicles remain active in the competition, and eligible for the $5 million prize purse. Visit www.progressiveautoxprize.org to follow the progress of the remaining vehicles and track the competition.