The P&G article says...
"First, Pulse - Getting The Car Up To Speed
When the car needs to get up to speed, gently accelerate. As much as possible, avoid using energy from the large hybrid battery while accelerating."

Ken@Japan

 

My own unscientific experience confirms Ken's thoughts. I accelerate deadband or green arrows to battery ownly as much as possible. It doesn't take many seconds of repeated below 10 mpg during brisk to fast acceleration to bring down the overall mpg for a tank.

 

Keeping that arrow away at low speeds is tough. People around here generally push real hard to get to a stop light then stop, so in most conditions I'm not sure I can accellerate that gradually, unfortunately.

Keeping it away also leads to what sounds like very low RPMs from the gas engine at low speeds, but maybe that's less important than avoiding using that lossy energy from the battery.

 

Well this trick definitely works. I've been able to do 54mpg without it and am working towards 60mpg with it. Thanks for clarifying!

Keeping the arrow away varies in difficulty - sometimes it won't stay away below 15 and sometimes keeping it away below 30mph is near impossible. I'd guess SoC and incline affect it but there seems to be at least one more factor... .

 

So, from all these posts, I gather the following:

The best way to accelerate to maximize the ICE efficiency is to push the ICE just enough so that there are no bars going to or from the battery (is that dead band?) so that the engine does not work on very low RPMs (near about idling), but at the same time, do not push the ICE to its limits that it works at high RPMs thus killing the mileage ..

Is my understanding correct?

 

You're more or less correct kam except that the goal is not to keep the ICE at optimal RPM, but rather, keep the battery out so that you don't waste gas refilling it. In fact, by accellerating slow below 20mph (to avoid the yellow arrow from the battery) the ICE is running below optimal RPM - but what Ken's suggesting is that what's more important is avoiding draining the battery - optimal RPM is a secondary concern. So far, from my testing this method around town, this has proved to be correct - avoiding draining the battery gets better overall MPG than pushing the ICE at low speeds to increase its RPM into an optimal range.

Between 35-42mph, it's possible that accellerating gradually so that there's a green arrow going to the battery may be optimal - avoiding revving the ICE higher than optimal. Ken or Bob will have to let us know. Ken? Bob?

Which reminds me, I have to post a new tank - 57mpg this time.

 

This is something I'll eventually get around to looking at but right now, I'm looking at some other aspects:

1) improved NHW11 warm-up, burning less fuel
2) improved NHW11 transaxle oil, Type WS
3) auto-glide for NHW11 (and some NHW20s)

The first two changes should significantly improve NHW11 performance and in some cases, bring the NHW11 closer to NHW20 performance level. The auto-glide will automate one of the trickier aspects and make high efficiency driving something even untrained drivers can do.

I have looked at ICE efficiency and found keeping the ICE rpm below 2,500 is great. But rpms above 3,500 should be avoided due to higher fuel consumption per hp produced.

http://hiwaay.net/~bzwilson/prius/pri_power.html

Bob Wilson

 

So Soopahman, until what speed do you suggest that we should maintain the operation of Prius in deadband (no yellow arrow coming from the battery .. the car runs completely on ICE)?

I mean, until what speed starting the car from 0 MPH?

 

Well, I was just clarifying Ken's suggestion - I can take no credit for this knowledge :O)

Generally, if you can avoid seeing a yellow arrow coming from the battery anytime above 10mph, your MPG will do better. Based on what Ken's saying and how my MPG is playing out so far, the cost of generating that electricity you're using from the battery is very high. It's also possible that driving on electric at high speeds is super inefficient for the electric motor, but that's based on what I've read about electric motors in general - I'm not sure about the one in the Prius and how it plays out in the HSD.

I'm sure of one more factor in keeping the yellow arrow away: How long the car's been running. The first minute, it's practically impossible to keep the arrow away at low speeds. The first five minutes it's still difficult. After that it's easy sailing.

 

One of the things you learn in engineering is to avoid energy conversions because they are never 100% efficient. The best you can do is convert kinetic energy to potential energy and back (aka. a pendulum.) So I look for upslopes leading to slower speeds so the car can "coast to a stop or turning speed." Although compared to converting kinetic energy to brake-pad heat, regeneration is brilliant, it is not perfect so I avoid it through careful driving.

Bob Wilson