Friday, August 18, 2006

The Gran Turismo 4 Virtual Prius Battery-Drain Challenge

Early this week, I was showing my vast collection of GT4 virtual cars to a friend. For some reason, I remembered that the Prius included a wild and wacky engine/battery flow diagram (3rd-party screenshot) that is based on the actual 2nd-generation car. At the time, I was lapping Tsukuba and we watched the batteries drain as I drove (using the standard controller), with its characteristic non-conservative near-digital accelerator modulation. That evening, there were better things to do than stare at a virtual battery guage -- but the seed was planted.

So, I repeated the experiment, but this time on the Circuit de Sarthe II (the old LeMans course, without the chicanes, for even more flat-out acceleration time, and a couple fewer brake/recharge zones). The results were indeed entertaining:
  • First lap: thanks to a couple of brief off-track excursions, this lap took just over 6 minutes, and depleted about 75% of the battery.
  • Second lap: the battery lasted long enough to get me up up to speed on the Mulsanne straight, just as the virtual charge management software swiched to "oh crap, I need to charge the battery some" mode. Because of improved familiarity with the track and the car, despite the diminished acceleration on the latter part of the course, I managed to shave nearly a second off of the fairly pathetic first lap.
  • Third lap: the virtual charge management software refused to let the last bar from the battery go away; complete discharge is apparently not possible -- at least not in a GT4 virtual Prius. Because the battery was not being used to power the motor during hard acceleration, only the gasoline engine was available for almost this entire lap. By the time I hit the straightaway, I had already lost almost 15 seconds, and I finished the lap a full 45 seconds behind the second lap, despite improving my driving lines and braking timing yet again...
Based on this very spurious method of testing, one can only conclude that the combination of endurance racing and ridiculously agressive throttle modulation make for a fantastically bad mix in terms of the classic vehicular dynamics of a Prius.