Newbie question

Well, if it's inbetween stoplights where you know you don't need to speed up a lot, then running on the battery is best.

The situation you talk about where you can go on battery only for miles you should do the P&G if possible. If you can't do P&G then you should run on battery for a little bit then on the gas engine to charge the battery for a bit, then back to battery. Make sure that you end the segment using the gas engine though, else the battery may run down more than you want it to.

 

<div class='quotetop'>QUOTE(Alexstarfire @ Apr 1 2007, 10:11 AM) [snapback]415695[/snapback]</div>

Newbie here.

Surely the computer would know when the battery charge drops to the level requiring ICE to recharge? Or does the method described above improve MPG?

Cheers

 

Welcome to PriusChat, Bo and Wakdos!

Bo, if you accellerate to the point that the ICE starts, get as much speed out of the ICE as you need and quickly as you can without flooring it. Look at Evan Fusco's The Four Stages of Prius Enlightenment. Much depends on the temperature of the ICE and catalytic converter and the state of HV battery charge. There are a few good suggestions in sticky threads about maximizing MPG.

Wakdos, the computer takes very good care of the HV battery, trying to maintain it at around 60% charged. The battery display on the Energy screen goes from all green (about 80% fully charged battery) to 1 pink or purple bar (about 40% charged). Most people rarely see these extremes. If you go down a long hill and regenerative braking "overcharges" the HV battery, the computer will first switch to hydraulic brakes to keep from taking even more charge, then spin up the ICE without fuel to "burn" the excess charge.

 

<div class='quotetop'>QUOTE(Wakdos @ Mar 31 2007, 10:50 PM) [snapback]415747[/snapback]</div>

It's not that it doesn't, but at least on my '02 Prius you have to watch the battery if you are just coasting on it. The thing is that on my Prius the battery SoC only shows 3 levels, but I don't know what % they stand for. When it drops one level you can still run on the battery, if you don't need too much power from it, but if you do that too long the ICE will want to run just to charge the battery, and you don't want that. When that happens the ICE will run when you are just sitting at stoplights, and that's not too helpful.

I've seen it improve my MPG, but I do know that my situation is different than yours. Around here you can't go half a mile without going up or down a hill. So I'm always charging my battery going up the hills. Provided you don't use too much battery it'll be fine, but it won't be near as good as P&G.

 

<div class='quotetop'>QUOTE(BoHenriksson @ Mar 31 2007, 06:07 PM) [snapback]415665[/snapback]</div>

I am a newbie as well and I was lurking on this forum for a month before I bought my 07 Pii on 3/31. The Pii had 21 miles on the Odometer when I bought it. I've put on 150 miles since with the screen completely OFF. I still managed 42.5 MPG average, using nothing else except what my father taught me when I was 16 yrs old, driving a 1971 Toyota Corolla with a 1.2 liter with a 4 speed manual transmission. Since I used to get low 30's mpg with the 1971 Corolla, which had a peak output of 48 HP, by just "listening" to the engine and select the optimum gear for passing, turning, braking, etc. it wasn't difficult to get low 40's with the help of the HSD and CVT. Just remember, your brain is the smartest computer there is!

Cogito

 

Hi Cogito, welcome to PriusChat! Your brain is the best computer, but it has learned many things that don't apply to the Prius. For example, to accelerate, step on the accelerator pedal; sounds simple enough, but sometimes the ICE will go into high rpm that sounds like the clutch is slipping, so you ease off on the pedal like you would in a '71 Corolla to keep from burning the clutch up, and wonder why the Prius has poor acceleration. Or you judge how fast you must be going from the shift-jerks as the automatic transmission kicks up, and suddenly notice you're doing 80 mph.

The ICE is controlled by the computer, and a high-rev state is taking motive power directly as well as running one motor like a generator so the other motor can contribute power. If you take your foot off the pedal, you're telling the computer you don't want to go so fast, so acceleration slows down. You can't hurt the ICE or HSD with a high-speed rev. The HSD smoothly shifts power, with no gear changes, so you don't waste time or feel the kick of a gear change.

Somethings you have to unlearn. Or learn anew for the Prius.

 

<div class='quotetop'>QUOTE(BoHenriksson @ Apr 5 2007, 04:17 PM) [snapback]418524[/snapback]</div>

I sure wouldn't complain about 59 mpg. You're never going to regain as much on the downhills as you lose on the uphills.

Dave M.

 

Up to a point you are correct about ICE efficiency. They don't get much energy out of the fuel at light throttle/low load. But then there's the Prius. HSD works in such a way that above ~1200RPM or so the engine is always operating at 80% load, which is very efficient. So the truth is that your car takes care of it for you and you don't need to worry about going to wider throttle position to get peak efficiency. In fact you can't because you have no direct control over the throttle.

All I've been doing, which works, is to strive to keep the engine turning at a sufficiently low speed that the intake doesn't drop out of the efficient atkinson profile (~2400RPM is best, ~3,000RPM or so still seems to be fine when you need the power). I used the terrain to pull 59mpg over about 65mi of really nasty New England hills. For the really big ones I made it a point to gain speed on my way down so that I could use that momentum to supplement engine power on the way back up, trading some speed for altitude rather than flogging the engine. For gentler hills I just held speed with the engine turning at whever speed it needed.

How you handle the other side of the hill is important. Since the engine seems to lose efficiency at very low RPM, you don't want it to be turning when you don't need the power. (This is where your understanding of efficiency comes into play.) Rather than letting it idle, try to get some Warp Stealth glide time in (same as a normal glide except you will see battery power to the wheels, no arrows to or from the engine.) If you can maintain speed while gliding, great! If you can't, go into a light P&G to get back your speed once in a while. There's not much you can do but brake if you need to stop yourself from picking up too much speed on a really steep hill, but keep in mind that lighter braking should capture more energy than heavy braking. (Lower current means lower losses.)

All that said, you're doing great! Play around a little more with that terrain if traffic allows and you'll see some improvement. It sounds like you've already figured out at least 90% of what I'm saying.