Driving Hills

You are correct about those of us who live in hillier areas getting less gas mileage
then those who live in flat areas like Ohio. It takes energy to get up them and I see
no way to traverse them without expending it! I feel that the gas I save going down
them does not offset the total amount I used to get up :-|

The only tip I have is that when you are going down a hill, try to gently speed up so
you can use that momentum to climb the next hill. I know truckers do it so they do not
end up crawling up the hills.. impeding traffic.

 

Hi Lois, I feel your pain. I live at the bottom of a long hill.

Think of the hill in Pulse-and-Glide terms, since you have two ways: pulse up the steep hill and glide down the longer way. You'll take a hit for the hill, but have more miles on the way down.

 

Wow, i live on a hill with the same characteristics. I have found that going 30 up it, i get about 20-22 MPG

 

It isn't just a feeling, it's the truth.

You can't roll downhill without friction and air resistance, so going downhill has losses. So going downhill never regains all the potential energy the car has at the top of the hill.

That loss is almost nothing compared to the losses in the regeneration system. The car can't regenerate power with 100% efficiency.

 

Luizap, take comfort in the fact that even though you'll burn a little more gas because of the hill than you might if you lived on the flat, you (a) probably live in a more scenic spot than, say, Iowa (no offense to any Iowans out there!), and (b) you will still burn a lot less gas than you would have in that Tahoe you were looking at before you wisely decided to buy the Prius.

 

"They" say regeneration (when you go down the hill) and then subsequent use of that regenerated energy is only about 50% efficient overall. The energy is lost in the generator, inverter, and battery charging, then more is lost when the battery delivers what it got, more in the inverter, and more in the motor. As auricchio said, you also loose to air friction, tire friction, and friction in the drive train. So you are never able to coast back up the hill. However, a "normal" car can't even reuse the 50% we do, they just loose it in brake heat. So take solace in the fact you are still doing much better than any other vehicle.

Slower speeds will loose less energy. It doesn't matter whether you go up a steep or gentle hill, if you go up the same amount. The Prius ICE is more efficient at wider throttle opening/RPM, as long as you aren't changing the RPM rapidly (taken from a Toyota publication on the net). So my guess is the steep hill would be the most efficient up. I haven't thought out the reason in detail, but I would guess the gentle slop down would be most efficient, reducing the amount of regeneration and allowing you to coast for a longer distance.