Advice on accelerating

<div class='quotetop'>QUOTE(ucsbgaucho @ Feb 7 2007, 04:38 PM) [snapback]386623[/snapback]</div>

I'm a little confused because your profile shows you driving a non-hybrid. But apparently you do have one.

You should read up on the pulse-and-glide technique, but in general, you don't want to run off of the battery. That gets charged from the gas engine (either directly or by recovering kinetic energy), so it adds a layer of energy loss to the equation. The advantage of the batteries is primarily that it helps with acceleration when you need it, so Toyota can put in a smaller, more efficient engine (but too weak for Americans by itself).

That said, you know the engine will charge up the battery anyway when first starting, until it gets warm, so when you're getting close to your destination you can try to use up some of the battery power. Some might argue for other special cases, but in general, don't try to use the battery. Accelerate moderately quickly, not a jack-rabbit start, not a slow creep. You instantaneous mpg will drop, but it's unavoidable. You'll make it up when you get up to speed and can glide or coast.

 

The theory goes something like this (at least for non-hybrid powertrains utilizing Otto-cycle gasoline internal combustion engines):

Since gasoline engines have higher pumping losses at small throttle openings, accelerate with the engine rpm held at the speed where the engine generates peak torque, and hold it there until you reach your target speed. This will normally be brisk acceleration, quicker than most people accelerate away from stoplights, but for a shorter duration.

That's the theory. As to whether this results in highest mpg in practice, all I can say is that the difference between theory and practice is greater in practice than it is in theory. It's also contrary to the oft-told advice of "driving as though there were an egg between your foot and the gas pedal".

 

Nerfer's advise is exactly what I do, and it seems to be working better and better for me as time goes by. I am a part-time driver of our Prius, so I don't get a whole lot of opportunity. I get 25 MPG for the first 5 minutes, no matter what I do. Then, I get between 48 and 99 MPG! after that, with an occassional 38 to 43, just to make things less than completely fantastic. I think my average 12 mile trip is about 62 MPG, but for other obsessive reasons, I don't reset the trip counters, and the average my husband gets pulls mine down, since he drives 80 to 120 miles per day. He gets 43.8 to 50, depending on the weather and the length of his commute. He is the regular driver of the Prius.

Anyway, I just wanted to agree with what has been said, and to reassure you that, in the end, this technique just becomes obvious and easy. Just enjoy and it will all come out fine in a few months.

 

<div class='quotetop'>QUOTE(priusenvy @ Feb 7 2007, 04:15 PM) [snapback]386693[/snapback]</div>

Well that's totally retarded because if you hold the engine speed you aren't accelerating, at least in a non-CVT equipped car. What I meant to write is that you shift to the next higher gear when your engine is at the RPM where it produces peak torque. And the throttle is supposed to be wide open to minimize pumping losses.

One real-world factor that prevents this from being an MPG maximizing strategy is that you actually end up driving at a higher average speed this way. So maybe it's only MPG maximizing if you also reduce your top speed so that your average speed matches that of a strategy with gentler acceleration.

 

<div class='quotetop'>QUOTE(nerfer @ Feb 7 2007, 06:29 PM) [snapback]386663[/snapback]</div>

I'm in agreement with everything posted so far. Accelerating slowly in electric mode reduces your gas mileage. Nerfer gave a lucid explanation of the value of the electric motor under heavy load situations. Here's how I understand the theory of this, for use of the electric motor under light-load situations.

1) Gas engines operate efficiently only if loaded fairly heavily. A lightly loaded gas engine wastes gas.
2) Using the electric motor wastes 20%+ of the incoming energy.
3) All energy to charge the battery comes from running the ICE.
4) (Assume you charge the battery when the engine is running at peak efficiency).
5) Given that, when is it more efficient to run the electric motor only?
6) Answer: only try to use the electric motor when it displaces a light-load situation where the ICE would be running 20% or more below peak efficiency.

Upshot: Putting that another way, if you can load the ICE fully, do so. Only if you can't, try to use the electric motor instead. Use the electric motor for unavoidable light-load situations.

In practice, that means trying to shut down the ICE when (e.g.) cruising a parking lot at low speed, running at constant moderate speed, and mainly, using it to extend the "glide" portion of some moderate "pulse and glide" driving.

Others on this board are more expert than I am, and there are entire threads you can search for here devoted to mileage, but I belive there's general agreement that the typical efficient cycle for urban/suburban driving consists of acceleration to speed using the ICE (how fast is a matter of debate), flick off the gas for a second to shut down the ICE, then glide under electric until demand requires restarting the ICE.