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So I have been watching Jack Rickard's shows and his most recent ones covered the topic of regen and does it actually work? You can watch them here Electric 1957 Porsche 356 Speedster EV (http://web.me.com/mjrickard/weeklies.html)

He came up the the conclusion that not only does regen not work it actually hurts.

So that got me thinking that I have seen regen supposedly working in the Prius and I thought it worked. At lest I could see the Ah increase a small amount. I just never measured it to see if it really does help.

Well today I tried an A B A test.

Now the course I ran was 2 miles in length and included 7 stops and all right hand turns. The speed varied from 25MPH to no more than 35MPH. I ran the course 3 times for each A B A test. The elevation change was some what small mostly flat with only a few hills if you could call them that.

I limited my AMP draw on acceleration to about 50A and my regen to about 60A. I did my best to replicate the acceleration and deceleration each time around while keeping the same speed on all parts of the course.

Since you cannot disable regen in the Prius the only way to not use regen is to shift to neutral before you take your foot off the pedal.

The first test was with regen. I started out at 16.50Ah and finished with 12.17Ah for a total Ah use of 4.33Ah. Thats .721Ah per mile.

The second test was with regen disabled by shifting to neutral when I took my foot off the accelerator. I finished with 6.20Ah for a total Ah use of 5.97Ah. Thats .995Ah per mile.

The third test was with regen again. I finished with 1.76Ah remaining for a total Ah use of 4.44Ah. Thats .74Ah per mile.

The CAN-View is what I use to monitor the Ah usage and according to it I have about 15.50Ah in the Hymotion battery I can use.

Now if I done my math right that means with regen I can go about 21 miles in EV mode on that course. If I did not have regen I could only go about 15 miles on that same course.

The engine did not come on at all during this test and I think my A B A test was accurate since I ended up with about the same numbers on the A A sides.

Is my testing and math correct? Do you see anything wrong with my test?

I think I will preform my A B A test again only start with no regen first and see what happens. Hopefully I will have enough energy in the battery to complete the test.

I have sent my results to Jack to see what if anything he says about it.

No question regen improves mileage in both my FEHs. Anytime I loose regen by staying in neutral and apply the brakes it cost me MPG always. If I drive without using the brakes than that is good also. I also see that not being able to store energy when I drive my Explorer seems like a total waste of that energy.

GaryG

Regen improves range, and coasting to a stop improves range more.

Jack Rickard's the fellow who didn't put a neutral position on his throttle, right?

Good or bad? Depends on the situation? (This argument is very analogous to coasting in neutral vs coasting in gear in non-hybrids)

If you need to slow down anyway, regen is good and helps recapture some of the energy that you are throwing away.

If you're cruising down the road and DON'T need to burn off speed, then regen is bad. You only get 30% or so back of what regen took out. If you're P&Ging, feather the throttle to avoid regen on the glides.

Thanks for doing this, Jay! Jack does some good work and finds out some really interesting things but his testing methodology for regen on public roads wasn't rigorous (repeatable) enough to give good data. A closed course with rally style determined speeds, accelerations, and decelerations would be ideal for this testing but it sounds as though you got pretty close to that. :thumbs_up:

Good or bad? Depends on the situation? (This argument is very analogous to coasting in neutral vs coasting in gear in non-hybrids)

If you need to slow down anyway, regen is good and helps recapture some of the energy that you are throwing away.

If you're cruising down the road and DON'T need to burn off speed, then regen is bad. You only get 30% or so back of what regen took out. If you're P&Ging, feather the throttle to avoid regen on the glides.

I agree. I think this is the correct view of assist as I have experienced it in a year of driving an Insight 1. The results of assist will always depend on circumstances and driving style, and will vary between cars and drivers, but it will always be negative in some degree when compared to the "perfect world." (The "perfect world" would be a ultra hyperemiling world in which we would all have cars with very small engines which would always accelerate and cruise at the sweet spot in the BSFC chart. Incidently, the Insight 1 can get pretty close to this standard in my experience.)

Think about it. Regeneration involves the use of momentum which was obtained by the consumption of gasoline. Therefore, it is an energy conversion process and that process is inefficient to some degree. If the driver is frequently going to brake, and throw this energy away as heat, then regen can help that driver in a relative sense, but his results will alway be worse than a hypermiler who drives without brakes and uses no assist to get his car moving. (Incidently, this is IMHO the reason that hybrids show FE improvement in the various test driving cycles - they include braked stops and moderate acceleration.) My physics is a bit rusty 50 years after the class, but the various laws of conservation of energy and momentum seem to dictate that regeneration is inherently a negative process in an absolute sense. Relative to other actions, it can be a positive.