Prius Coasting

It could be the process of turning that energy into energy to charge the battery back up.

John or someone else more technical know?

 

1 word: Regeneration

 

Rick with his fancy terminology! :lol:

 

It is, indeed, regeneration. You can begin to predict how much braking will be done by the regeneration with time and find that you can slow to a near stop without touching the brake at all.

I have also found that by VERY lightly depressing the accelerator that you can disengage regeneration while still not draining power from the battery to drive the wheels or turning on the ICE. This essentially allows you to free-wheel. I tend to do that on uphill areas where I need to coast to a stop. My options in those cases are to use power to climb or brake hard when I get to the top if I don't free-wheel coast. You don't regen anything, but you don't lose anything either. This takes practice and it really helps to watch the energy screen to help you learn when you've 'hit the sweet spot' b/w regen and powering the wheels.

 

Jerry,
If the car is stopped by regeneration be it by 1 wheel, 2, or 4 all of the available kinetic energy IS recaptured. It would increase the complexity without increasing regeneration. You don't need all 4 wheels to do it. The key is that the friction brakes mustn't engage, and, if I understand it correctly, the friction brakes don't kick in until needed.

 

Ummm, I think you're wrong. The regen braking kicks in any time the accelerator is released completely, and it's not an intelligent regen--that is, it's the same amount if your on the flat, down hill, or up hill. I could be wrong, but that's my take and experience.
--evan

 

Allow me to add to this.

1. Everyone is correct in that the same amount of regen is possible in the Prius whether it be 1, 2 or 4 wheels or motors doing the job. The limiting factors are the max current which the battery can safely accept without reducing it's useful life, and to a lesser degree, the capacity of MG2 to gegen. One additional factor could be wheel lockup, but that could only occur at very low speeds given the current generated in our setup.

2. Regen *is* variable. Allow me to expand:

"Foot off" regen is more or less constant. This is present since the DOT says it's illegal for any car to be allowed to freewheel - some sort of "braking" must occur when the foot is off, whether it be engine or regenerative.
B mode "regen" is also fairly constant to a threshold, before the rest of the energy is directed to MG1 to spin the ICE. At lower speeds, this threshold isn't met, and all power is sent to the HV battery.
Braking regen *is* variable. Depending on pedal pressure, more or less regeneration will be used. Light pressure might be only regen, where as heavier or more sudden pressue, or pressure at higher speeds will cause the friction brakes to apply as well. Again, the limiting factor is the max current that is allowed to the battery. If more stopping force is required, friction must be used. The difference between Prius version 1.x and 2.0 ('04) is the amount of regen used during braking, the '04 using significantly more.

Note - when braking, I've heard, but can't confirm that the rear drums are applied to some degree regardless of front disk status. This could be bad info though.

Only adding additional batteries to increase current input capacity could allow for more regeneration w/ less use of the friction brakes.

Hope this helps,
-Rick

 

On the contrary, I can come down a hill in my city each morning and through stop and go down hill, I'll have the battery top green.

It's significant enough to make it worth while.

The best way to take advantage of regen is to come to slow, controlled, gradual stops. Quick braking kicks in friction brakes, and doesn't allow regen to kick in to recoup the energy for later use.

hope this helps,
-Rick

 

Sorry Rick, I should have been more clear....certainly regen is variable when braking, dramatically so in my experience.

The discussion title, and thus my comments, were about coasting and I was assuming everyone understood that it was foot off brake coasting.

Let me put this to you though, you said "regen is more or less constant" So, is it constant or not...is there some variability based on whether you're going uphill, down or flat, or other variables?

 

I've heard on the classic some pretty extended mileage figures where the driver was still on the original pads in front. I want to say 75-100k miles, but don't quote me on that. The classic Prius archives would have the info if you're willing to search.

Other tests have shown as little as 125 ft., so unless the exact same conditions and methods were used for each test, they're somewhat subjective. Some may get an average, others may take the lowest of a run of 5 stops, and others still may include brake fade in the average which could increase the average stopping distance. Either way, my first suggestion would be that the narrow tires for the weight of the car are the culprit. Some would go as far as suggesting that drums vs. discs in the rear contribute as well, but I'm not personally inclined to agree as the braking load back there isn't substantial as in practice, about 70% of braking occurs up front (and 30% or more of that is handled by regen at max braking). Now if 142 ft. was done after 10 runs to test fade, then the drums could be a limiting factor.

Either way, bigger discs, pads, or swept area has little use if the traction available can easily be exceeded by braking force. It may help with fade, but that's about it.

My thoughts,
-Rick

 

Honestly, in the Prius case, they focus on LRR as well, and because of our continued gripes about classic tire longevity, these may last a bit longer. I'm curious to see too.

In the end, I'd love to have the Euro 16's to see how it affects performance.