2016 Toyota Prius: Racing Improves the Breed, Or the Other Way Around
by Jason Kavanagh, Engineering Editor on June 24, 2016
[Note: Prius not shown above.]
One of the more astounding things about our long-term 2016 Toyota Prius — and its predecessors — is how immune to mistreatment it is despite its enormous technical complexity. This is not to be taken lightly. Toyota has done a masterful job of making the Prius' hybrid powertrain as reliable as the sunrise. This robustness is an industry triumph and one of the keys to the car's widespread acceptance by consumers over the years.
Which is what makes Toyota's loss at the 24 Hours of Le Mans last weekend that much more puzzling.
If you haven't heard, Toyota lost the storied 24-hour endurance race when their leading TS050 Hybrid racecar broke down on the last lap. They'd had a dominant run up to that point and were a single lap from what would have been a historic first-ever Le Mans victory for the company. Seeing the Toyota coast to a halt in front of the pits mere minutes from jubilation was as crushing a sight as I've ever witnessed in motorsport.
The cause was "a technical defect on a connector on the air line between the turbocharger and the intercooler," which I interpret as a broken intercooler coupler. Basically, a tube that holds the boost in sprung a leak. Other outlets are reporting this as a "turbo-related failure." Nope. This is a "charge plumbing-related" or "air intake-related" failure. The turbo actually functioned flawlessly. By the same logical extension, you could say this was an "engine-related failure." But I digress.
This component failure obviously needs attention. However, the situation is worse than merely a bad clamp. The more troubling problem here is that Toyota did not implement adequate fault tolerance into their racecar. Let me explain.
Fault tolerance is a system's ability to cope with component failure. A small issue shouldn't result in a larger one. Neel at Apex Speed Technology, a motorsports calibrator unrelated to this Toyota program, summarizes the fault tolerance he applies to the Porsche 997 race cars he calibrates thusly: "You can unplug almost every sensor on the engine — crank position, coolant temp, mass airflow, throttle position, everything but one cam position sensor — and the car will still run and drive. The idle won't even waver."
Now, a normally aspirated non-hybrid Porsche is certainly less complex than the TS050. But the the TS050 suffered only a relatively minor anomaly and not the loss of nearly every engine sensor. The blown-off intercooler hose resulted in some loss in boost pressure. That's all. A smart engine calibration, upon detecting the loss in boost pressure on that cylinder bank and/or rise in turbo speed (they run turbo speed sensors) would have seamlessly transitioned to an alternate strategy that controlled the engine based primarily on, say, turbo speed and the pressure ratio across the inlet restrictor. No stopping, just a reduction in power. And perhaps not even a significant power reduction, depending on how severe the boost leak was.
Instead, the Toyota ran for about a minute in a limp-home mode (capped to about 6,000 rpm, down from about 9,000), and then ground to a halt. The driver, on the radio with engineers in the pits, shut the car off and stayed parked for nearly a minute before the car began moving again slowly under its own power, presumably after the world's most frantic button-pushing sequence.
Who knows, perhaps even flawless fault tolerance still wouldn't have staved off the hard-charging Porsche during that final lap. And it'd be a stretch to say that the purpose-built TS050 racecar has much to do with a production Prius. But that a relatively minor failure led to total electronic breakdown is completely at odds with the corporate philosophy that resulted in the latter.
Maybe the Prius calibration team should pay a visit to the race shop.
Jason Kavanagh, Engineering Editor