Countdown to Earth Day: Regenerative braking 102

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rav4 ev driving

When is regenerative braking not regenerative braking? Pretty much all the time, it turns out.

Take the Toyota Prius, which has what's called blended braking, which implies that both the friction brake (which all standard cars use to slow down) and the motor work together to reduce speed. In reality, though, you don't often use the friction brake in a Prius. Instead, the computer controlling this process is saying "we're still below my maximum friction brake threshold. I'm going to increase the regenerative effort to match the same level you're feeling on the pedal. As soon as you exceed that threshold, you want to stop faster than I can regenerate power, now I'm going to apply the friction brakes." Thus, any energy (heat) generated by the Prius' friction brakes does not go into the battery pack. (More details available here.)

That's how Sheldon Brown, executive program manager for the Toyota Technical Center, explained things to AutoblogGreen recently. We were talking about the prototype version of the RAV4 EV, which has some pretty serious brake grab when you release your foot from the accelerator. It doesn't feel anything like driving a Prius, and Brown said this was done entirely on purpose.

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[Source: Toyota]

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Countdown to Earth Day: Regenerative braking 102 originally appeared on Autoblog Green on Tue, 19 Apr 2011 20:02:00 EST. Please see our terms for use of feeds.

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