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Old 06-22-2016, 04:55 PM   #105 (permalink)
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2016 Toyota Prius

This one was interesting!

The owners of the car are friends (retired professional couple) and the car is brand new (their first hybrid). They seem to be getting a kick out of the learning curve and enjoying the game of getting good fuel economy.

A credit to the Prius and to them: we did two "baseline" laps, and their results (both the same, according to the SG) were the best of any "regular" drivers I've done this with: 59 mpg US / 4.0 L/100 km. And that was with the A/C on all the time. I was afraid my demo & coaching laps wouldn't show much improvement!

(The owner of the previously discussed Lexus 200h had a higher baseline MPG, but he doesn't count - he was already really familiar with hybrid-specific ecodriving techniques.)

The 2016 Prius encourages ecodriving by providing a numeric Eco Score out of 100 and (sometimes) helpful hints after EVERY drive, eg:

Before we even did the drive, I wondered aloud if the car's coach would agree with some of my coaching tips.

It did not. (More on that in a minute.)

"Baseline" techniques that weren't helping:

- First
the good news: Both drivers were very laid back, with no evidence of the typical bad habit of rushing into predictable stops/slowdowns and jumping on the brakes.

- The less good news was they tended to accelerate so gently that the car used EV mode a lot. I explained why that wasn't necessarily a good thing.

- Also, their Toyota salesman had mistakenly told him that using the transmission's "B" gear (equivalent to downshifting or engine braking a conventional car) would regenerate more energy into the battery, so he was using it often approaching stops & slowdowns instead of just braking with the pedal.

Demonstration lap:

I showed them how using the engine under moderate load to get up to speed is OK, provided you have a clear road ahead and then let off the accelerator early to kill the engine when approaching the next stop/slowdown.

So this was another example where driving efficiently doesn't necessarily equal driving slowly: the average speed of my demo lap was 16 mph, vs. 14 mph for each of their baseline laps. Maybe that was traffic or stop light patterns, maybe not. But I used EV mode less and returned to the starting point with a higher state of charge in the hybrid battery.

No "B" mode for normal deceleration

I explained that you can get maximum regen using the regular brake pedal -- "B" mode doesn't give you any extra amps or volts. In fact, B mode is worse from an efficiency standpoint than regular brakes for normal deceleration because it also causes the ICE to spin up (without fuel) to add extra drag, which means you're throwing away some kinetic energy as heat.

B mode is OK for very steep or extended descents (eg. mountain driving).

The "Eco Score" computer didn't like me, but the numbers don't lie

When we used a bit more gas pedal to cause the engine to fire up during acceleration, the Eco Score told us afterward that we were accelerating too briskly (paraphrasing). Yet the MPG was significantly better on the laps where we did just that.

My guess is Toyota's Eco Score programmers erred on the side of caution, deciding they don't want to encourage drivers to accelerate energetically because it's too complicated to explain that it only makes sense when there is NOT a stop or slowdown in your immediate future. (In that case, EV mode makes more sense.)

Anyway, fun car and good results.
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