Regen while coasting -- why?

[Sailfish11]

It seems like a waste to me. We use precious energy to build up speed; why give it away to coast? If we want to regen we can lightly press on the brakes. I know we can 'feather', but wouldn't it be easier to have the Prius coast in neutral (neither using nor generating energy)?

[icarus]

You need to learn to pay attention to the arrows, and your right foot. You can "coast" without regen by keeping the arrows neutral (neither charging nor discharging.) You regen only when you take your foot far enough off to start the arrows flowing back into the battery. If you watch the arrows you will get the feel of it.

You regen when you really need to slow down or stop, but not when you are cruising. Look at warp/stealth in these boards.

Icarus

[jarrett_gorin]

I am new at Prius driving technique (I just got mine on Sunday), but I also have a question about this. Are you all saying that you should keep your foot slightly on the gas pedal when you coast?

Also, I wanted to find out under what circumstances people use the "B" setting. I understood that you use it to regen when coasting down hills etc. and that it will also help you from building up excessive speed. I have also been using it occasionally as the first stage of stopping when I exit the freeway, since it provides a nice gradual slowing and appears to regenerate electricity doing that. Is this a good idea or not?

Would appreciate input on this.

[qbee42]

<div class='quotetop'>QUOTE(Sailfish11 @ Aug 16 2007, 11:53 AM) [snapback]496924[/snapback]</div>

It seems like a waste to me. We use precious energy to build up speed; why give it away to coast? If we want to regen we can lightly press on the brakes. I know we can 'feather', but wouldn't it be easier to have the Prius coast in neutral (neither using or generating energy)?
[/b]

The regen during coasting is done to simulate engine drag on a normal car. Every effort was made to make the Prius drive and control in a fashion understandable to drivers. It's the same reason the Prius creeps forward when you take your foot off the brake. There is absolutely no reason for this other than that's how it works with a normal automatic transmission, so the Prius control system makes it work that way.

Tom

[Danny Hamilton]

<div class='quotetop'>QUOTE(icarus @ Aug 16 2007, 11:04 AM) [snapback]496935[/snapback]</div>

You can "coast" without regen by keeping the arrows neutral. You regen only when you take your foot far enough off to start the arrows flowing back into the battery.
[/b]

The original poster is already aware of this. His question isn't how to glide. . . .

His question is: Why is the car designed to to regen when I take my foot all the way off?

It seems like a better design for hypermilers would be to design the car to "glide" when you completely remove your foot from the accelerator and not to "regen" until you ever so slightly press the brake.

Of course the car wasn't designed for hypermilers (it just seems that way), it was designed for average drivers.

Perhaps average drivers expect a car to slow down a bit from engine drag when they remove their foot from the pedal?

[Washington1788]

<div class='quotetop'>QUOTE(JG in SB @ Aug 16 2007, 11:21 AM) [snapback]496945[/snapback]</div>

I am new at Prius driving technique (I just got mine on Sunday), but I also have a question about this. Are you all saying that you should keep your foot slightly on the gas pedal when you coast?

Also, I wanted to find out under what circumstances people use the "B" setting. I understood that you use it to regen when coasting down hills etc. and that it will also help you from building up excessive speed. I have also been using it occasionally as the first stage of stopping when I exit the freeway, since it provides a nice gradual slowing and appears to regenerate electricity doing that. Is this a good idea or not?

Would appreciate input on this.
[/b]

B is used primarily for "engine" braking. For instance, if you're coming out of the mountains and all you're doing is coasting, once you build up an all green charge for your battery, you can switch to the B mode so your engine essentially helps slow you down rather than relying on your brakes -- it takes some of the pressure off them. As far as I know, that's really the only situation where you'd use B.

I'm sure someone will correct me if I've missed something.

[tekn0wledg]

Perhaps average drivers expect a car to slow down a bit from engine drag when they remove their foot from the pedal?[/b]

That is correct.

You can feel the drag of letting off the gas pedal in a normal car quite significantly. I believe the regen here was made to feel the same way.

Most people let off the accelerator at driving speeds to avoid having to use the brakes. A good example would be when someone switches into your lane abruptly. It seems stupid to use the brakes if you can just let off gas for a few seconds to gain a reasonable distance from them.

The autoregen at this point is probably used to simulate this type of behavior.

[Danny Hamilton]

<div class='quotetop'>QUOTE(JG in SB @ Aug 16 2007, 11:21 AM) [snapback]496945[/snapback]</div>

Are you all saying that you should keep your foot slightly on the gas pedal when you coast?
[/b]

Yes, if you are trying to maximize your fuel efficiency (mpg) and glide as far as possible while losing as little energy as possible.

<div class='quotetop'>QUOTE(JG in SB @ Aug 16 2007, 11:21 AM) [snapback]496945[/snapback]</div>

Also, I wanted to find out under what circumstances people use the "B" setting.
[/b]

Most of the experts around here will tell you to use "B" when heading down a steep hill for a long distance. ( Like a mountain for instance ). In general it is reccomended to use "B" to keep from wearing down (or overheating) the brake pads when the battery is as charged as the car will allow, or when regen won't slow the car down enough.

It is not intended to be used for charging the battery. When exiting the expressway, using the brake pedal will also "provide a nice gradual slowing and regenerate electricity"

[Godiva]

<div class='quotetop'>QUOTE(Danny Hamilton @ Aug 16 2007, 11:25 AM) [snapback]496949[/snapback]</div>

Why is the car designed to to regen when I take my foot all the way off?
[/b]

Why not?

[icarus]

<div class='quotetop'>QUOTE(JG in SB @ Aug 16 2007, 09:21 AM) [snapback]496945[/snapback]</div>

I am new at Prius driving technique (I just got mine on Sunday), but I also have a question about this. Are you all saying that you should keep your foot slightly on the gas pedal when you coast?

Also, I wanted to find out under what circumstances people use the "B" setting. I understood that you use it to regen when coasting down hills etc. and that it will also help you from building up excessive speed. I have also been using it occasionally as the first stage of stopping when I exit the freeway, since it provides a nice gradual slowing and appears to regenerate electricity doing that. Is this a good idea or not?

Would appreciate input on this.
[/b]

The trick is to use only as much decleration as needed. If you coasting just to maintain speed, or in anticipation of a traffic situation you want to coast without regen. If you need to slow down as for a light, then taking your foot off will start regen and slow you down faster. Using the "B" setting will not add to the regen, and in fact will reduce it. You should only use "B" for coming down a long hill or mountain grade where you would need the brakes, just like shifting down in a regular car. When you get off the freeway, anticipate your deceleration time and allow the car to come to a nice, gentle slow down with as little use of the brakes as possible. (I don't know, but I think the regen comes not from the friction brakes, but from the electric motor charging instead. I think the friction brakes do nothing more than conventional brakes. The advertisment about "regen braking" is (I think) a misnomer,,,correct me if I am wrong).

Get used to the arrows and drive accordingly,

Icarus