Coasting and braking

[Pappy]

In my first trial drive my sales agent talked about how the brakes regenerate power to the battery. I see it put this way in other places, as well, with no reference to coasting. But, as far as I can see, braking is part of coasting. So, my question is, if you're coasting, does applying the brakes increase the amount or rate of regeneration? Or, in mpg, for that matter if, say, you're on a downhill slope and you're braking just to moderate speed?

[EricGo]

As you have noticed, coasting (foot off the pedals) is slight braking.

Foot pressing the brake is more regenerative braking up to about 20 kw, and then friction braking.
Very slight pressure on the gas pedal is no braking (no arrows on the screen.

In the beginning this sounds counter-intuitive, but everybody gets used to it easily, and I like not having to move my foot over to the brake for mild deceleration. As Prius history tells it, this design was done to simulate the slowing down inherent in non-hybrids when the gas pedal is completely released.

In a non-hybrid car, the slowing down occurs from engine braking; the Prius generates electricity

[coloradospringsprius]

The answers to your questions are yes and yes. The more slowly you can politely brake, the more energy you'll get back. However, no regeneration occurs below 7 mph. You've probably already noticed how the car seems to "sail" during slow braking when you reach 8 mph - that's the moment that the generator disengages and the brake pads engage. If you're in a position to brake gently all the time - using only the generator from 8 mph up - your brake pads should last just about forever.

As EricGo hints, the Prius uses energy most efficiently when it's coasting - aka "gliding mode," with no arrows heading into or out of the battery. This is because there are always conversion losses when converting kinetic energy to electricity. Therefore, on slight downhills, it's better to roll without losing momentum to battery charging than to charge the battery and then use power to regain your momentum. Of course, if you need to brake a little just to keep from going too fast, you're still way ahead of a conventional car.

(Don't go crazy trying to find gliding mode. A very slight push on the gas pedal will get you close, even if the energy screen shows regeneration or discharge. And some days your Prius just won't feel like gliding, especially if it's not fully warmed up.)

The beauty of gliding mode versus traditional coasting is that you still have control of your car. It will accelerate if you have to punch it - which I had to do once when a guy ran a red light and nearly T-boned me!

[jeneric]

Originally posted by coloradospringsprius@Feb 15 2006, 03:14 PM
(Don't go crazy trying to find gliding mode. A very slight push on the gas pedal will get you close, even if the energy screen shows regeneration or discharge. And some days your Prius just won't feel like gliding, especially if it's not fully warmed up.)

The beauty of gliding mode versus traditional coasting is that you still have control of your car. It will accelerate if you have to punch it - which I had to do once when a guy ran a red light and nearly T-boned me!

[snapback]210120[/snapback]

Any other issues with shifting into N to go into glide mode? As long as you don't brake or hit the gas while in N. I believe if you brake while in N, you'll get no regeneration. Also, any extra energy from the engine wouldn't get stored?

[coloradospringsprius]

Originally posted by jeneric@Feb 15 2006, 06:38 PM
Any other issues with shifting into N to go into glide mode?  As long as you don't brake or hit the gas while in N.  I believe if you brake while in N, you'll get no regeneration.  Also, any extra energy from the engine wouldn't get stored?

[snapback]210135[/snapback]

I've never used N to glide - I only use the standard light-touch-on-the-accelerator method. Some hyper-milers claim better mileage using N, but they tend to live miles from nowhere. Around here, there's just too much traffic to feel safe in N!

[INPrius]

Correct me if I am wrong, but is 'gliding' (with no arrows in or out of battery) is very difficult to achieve at speeds higher than 40mph? I have been 'gliding', when situation permits, at up to 40mph, and found it very difficult to do that above 40mph.

[coloradospringsprius]

Originally posted by INPrius@Feb 16 2006, 05:32 PM
Correct me if I am wrong, but is 'gliding' (with no arrows in or out of battery) is very difficult to achieve at speeds higher than 40mph?  I have been 'gliding', when situation permits, at up to 40mph, and found it very difficult to do that above 40mph.

[snapback]210733[/snapback]

Difficult or even impossible! The ICE always spins when you're going faster than 42 mph. Above that speed, you'll rarely glide for more than a second, and then only while the computer is deciding what to do. But even at higher speeds you can get virtually the same effect the same way - by depressing the gas pedal a teensy bit. Trekkier-minded Prius owners have dubbed it"warp stealth."

[hdrygas]

I would like to jump in here. The differences between "gliding" "stealth" and "dead banding" are more quantity than qualitative differences. I am basing these conclusions on both observations with the ScanGage and the CAN View. Gliding is really more "mini stealth" i.e. power is being expended at a rate of discharge approximately twice that of resting. Stealth is a constant discharge rate 10 times the resting rate depending on the grade, rate of speed and other factors. "Dead Banding" appears to represent rapid oscillation between charging and discharging at a level of 1-8 amps or so. The MFD over simplifies the what is actually happening in the system.