Surprising article on the utility of brake regeneration

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DeaneG

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I saw this article today with an interesting set of data points on the effectiveness or braking regeneration. The testers were very surprised to find a negative benefit from regeneration, which I think everyone agrees should be incorrect but I guess sometimes isn't:

http://green.autoblog.com/2010/07/18/evtv-questions-whether-regenerative-braking-is-worth-the-bother/
 
Regenerative braking has its benefits and its drawbacks. If implemented badly, it can have a negative effect. It also depends on the sort of driving you do.

If you are driving in busy cities, regenerative braking can make a significant improvement on range. If you are taking a long road trip, there is comparatively little benefit - and if your regen is too high when you just have your foot off the throttle, it can actually decrease range.

Bear in mind that this research was carried out on a home built special, created for a few tens of thousands of dollars, not a production car created with a development budget of hundreds of millions of dollars. However, the results are not that surprising to me. If they did another test driving through Los Angeles, or any other big American city, I suspect their results would have been quite a bit different.
 
MikeBoxwell said:
Regenerative braking has its benefits and its drawbacks. If implemented badly, it can have a negative effect. It also depends on the sort of driving you do.

If you are driving in busy cities, regenerative braking can make a significant improvement on range. If you are taking a long road trip, there is comparatively little benefit - and if your regen is too high when you just have your foot off the throttle, it can actually decrease range.

Bear in mind that this research was carried out on a home built special, created for a few tens of thousands of dollars, not a production car created with a development budget of hundreds of millions of dollars. However, the results are not that surprising to me. If they did another test driving through Los Angeles, or any other big American city, I suspect their results would have been quite a bit different.

With no control group. Why does stuff like this get hyped up, it's non-scientific hype.
 
If the Regen comes on automatically when you take your foot off the "go-faster", this Regen can be unwanted, energy-consuming drag, just like the wasteful ICE-engine drag that it "simulates".

So, Auto-Drag (automatic application of regen) is often wasteful of kenetic energy, and thus, a poor (not energy efficient) way to implement regen.
 
DeaneG said:
I saw this article today with an interesting set of data points on the effectiveness or braking regeneration. The testers were very surprised to find a negative benefit from regeneration, which I think everyone agrees should be incorrect but I guess sometimes isn't

Hmm. Well, IIRC the LEAF is supposed to support turning the Regenerative Breaking off. I wonder if this is because although, as many have said, it's great for city driving, it's not so good for highway.
 
Properly utilized, regenerative braking will always add to your range.

The issue comes with the fact that people are generally trained to lift off the gas pedal completely when they want to stop accelerating - whether or not it'd be more appropriate to simply coast with slight pedal pressure. Remember that generative braking never captures 100% of the energy - you lose some due to inefficiencies in charging though the motor, electronics and battery.

Anyone who has attempted to "pulse-and-glide" in a Prius is familiar with this - one method of maximizing fuel economy in the Prius is to alternate acceleration to a set speed, say 40mph, with the engine running at it's most efficient load, then coast until you've dropped to a lower speed, say 30mph. But you can't coast with your foot completely off the gas pedal as this triggers regenerative braking slowing you down faster in addition to incurring the conversion loss of converting kinetic energy back in to electricity. So you have to keep a tiny bit of pressure on the gas pedal while watching the multi-function-display to confirm that you are indeed coasting.

This would be a lot easier if you didn't have to apply the gas a bit to disable the regenerative braking.

Similarly for EVs, it would likely be a lot easier to maximize range if you didn't have to worry about keeping a specific pedal pressure to avoid regenerative braking when conditions permit.

Then when you really need to slow down, the brake pedal would turn on regen until maxed out, then engage friction brakes as needed.
 
I agree 100%.

I am not totally stupid, and it is still quite difficult for me to "glide" (no regen coasting) in my 2010 Prius, especially if I keep my eyes on the road, not on the instruments.

If a manufacturer insists upon using foot-off regen, they could make it a lot easier to "glide":

1. There could be a "flat spot" (small range) in the "go-pedal" response where there is no power or regen, not just a single "spot". Not difficult to do.

2. When in the "glide" mode, a visible indicator, still in the driver's view while looking ahead, could be provided. As simple as an icon, a color change, or a single LED.
 
My ideal would be to have the regen built into the braking system. When applying the brakes, deceleration would be via regen as much as possible before actually engaging the friction brakes. For most driving I want the accelerator to be a "go" pedal, not a "slow" pedal. That's what brakes are for.

Actually if I could make a wish, there would be an option to turn on coasting regen, as this would be useful on long downhills to control speed. And since I'm wishing, have it be variably controlled with something like an airplane's "trim wheel". That would be sweet!
 
I would just have it variably controlled by being a strong regen that you could reduce by by light pressure on the go-pedal. But, yes, a switch is fine with me. That is what I believe a "B" mode, as exists on a Prius, should control. The Leaf "Eco" mode appears to be the same general concept, but it sounds like the regen will be too light for my taste. My goal is to be able to go down a long 6% freeway grade at a constant 60 or 65 MPH without touching the brake pedal.
 
Nubo said:
Actually if I could make a wish, there would be an option to turn on coasting regen, as this would be useful on long downhills to control speed. And since I'm wishing, have it be variably controlled with something like an airplane's "trim wheel". That would be sweet!
Yes - that would be totally awesome!
 
drees said:
Nubo said:
Actually if I could make a wish, there would be an option to turn on coasting regen, as this would be useful on long downhills to control speed. And since I'm wishing, have it be variably controlled with something like an airplane's "trim wheel". That would be sweet!
Yes - that would be totally awesome!

What's the point ? Just turn on the cruise control and it should take care of it...
 
Good point. Cruise control probably should be able to increase regen as necessary (within the limits of what the battery can take). It certainly doesn't do that in our Gen 2 Prius; cruise control downhill is almost like freewheeling. "B" mode sure slows the sucker down, though.
 
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