Gliding over 42 mph

You could glide safely at any speed as long as you're in "D". If your foot is off the brake and off the gas, I think that is called "cruising", meaning the car is braking but it's a gentle braking. The computer will turn the ICE off in this situation. Whether you should glide downhill or not depend mostly on traffic condition and safety. That's my opinion. I personally glide in neutral going downhill if the hill is not steep. But this is something not safe to do. If you're not careful, you could over-rev the MG1

 

I think the computer knows best, if wanting maxim mpg's
Cruise control will slow you on descents, but unless mph are the problem, why slow? Of course touching the brake adds to the traction battery, but pushing the brake pedal more than 3/4th's of it's travel toward's the floor will actually engage the brakes, so slowing with the brake pedal is actually helping the overall mileage

 

Going down a slope, maintaining speed, with no accelerator and no brake; how would you turn off the ICE? Or how would you turn on the ICE?

The 16 on-board computers control the ICE.

 

When the car sense that you don't need the power, the ICE will be turned off automatically. However, it may still turn depending on how fast you're going. If you're going above 42 mph, the ICE will turn without fuel to keep the MG1 from over revving. If the slope is very steep, you may need to use regen to maintain constant speed.

If for some reason you want the ICE to fire up, just press on the accelerator hard.

 

Going down a slope, maintaining speed, with no accelerator and no brake; the 16 on-board computers control the ICE.

Regen is a part of braking. That does not happen until you apply the brakes.

Sometimes when going down a slope the Prius will gain speed, unless you apply the brakes.

I do not see why you would want to control the ICE to be on or off.

 

Who said I would want to control the ICE? I was describing the ICE.

 

The OP said: "... when going down a hill and slow down or keep the ICE running and ..."

The thread is about going down a slope, and whether to keep the ICE running.

 

Are you saying the HSI was showing that real-time MPG at 100, but you still feel the ICE was running with fuel?

From my experience, if my car hasn't warmed up yet and I was gliding, the ICE would run and my real-time MPG would show 80 or 90, but never at 100. The only time I get 100 is when no fuel going into the ICE.

 

My practice on a down-grade:

• Use "N" if speed build-up is not a problem - shifting into "N" avoids converting some of the potential energy into battery charge, keeping them cooler, but it must be done on a case-by-case basis.
• Use "D" if speed needs moderation and feet remain on floor - the default behavior, always safe. But if you have to use the brake to moderate the speed, use the next gear.
• Use "B" if speed builds up in "D" - this reduces charge heating of the traction battery and allows feet-on-floor descents of the steep hills (aka., 8% grade or better.)

I try to drive with my 'feet on the floor.' So I maximize used of cruise control and shifting between "N", "D", and "B" to management speed and the never ending tradeoffs between energy sources and sinks.

Bob Wilson

 

If accelerating to 42 mph, I coast or regen brake with engine off. If decelerating to 42 mph, I glide with engine on.

The reason is that the engine may continue to run on acceleration even if speeds go below 42 mph due to warm up times. On deceleration, engine is already on.

The only exception on decelerating is if I need to go at or above 42 mph. Regen is a lossy conversion, so it's better to conserve momentum and glide with engine on.

 

My ScanGauge betrays cases where the ICE is still burning fuel, but the car is getting between 100 and 300 MPG. The U.S.-market real time MPG scale doesn't distinguish between this and the no-fuel situation.