How to accelerate?

I mostly agree with Evan. Where I disagree is with the suggestion that <1700 RPM is inefficient. Though the theoretical power curves for the Prius ICE suggest such inefficiency, many of us who routinely use lower RPM ranges are getting excellent results. My RPM off the line may be as little as 1200 RPM, assuming following traffic will tolerate it. Recent results are rather respectable.

How, you might wonder, will you know what your RPM is without a tachometer? Good question. Here's a rule of thumb: Watch your instantaneous MPG on your MFD during acceleration, and aim to keep it the same as your speed. That should keep it well within efficient ranges. If you need to push harder due to hills or impatient tailgaters (please do try to avoid inciting road rage), try to keep iMPG above MPH/2. That is the point, over a wide range of vehicle speeds, where RPM increases above ~2300-2400, which most everyone agrees is where a significant dropoff in efficiency begins.

Another small area of disagreement is in the significance of the "dead band" condition that he describes. Though theoretically ideal, it is hard to hit and even harder to maintain during acceleration, especially if hybrid battery SOC (state of charge) is low. If I'm watching the factory display, I focus on the iMPG/MPH relationship.

See this for a thorough discussion of the iMPG/MPH rule of thumb.

 

You will get 10 different answers from 10 different drivers. I don't think any of those methods are wrong. Use what works for you. For me, I like to accelerate on all electric until 40-45 because I believe an ICE is more efficient at higher rpm or speeds (thats why most cars get better economy on highway. The most fuel is used on starting from a standstill. My method is to use all electric to start and stop the vehicle and only use the ICE when cruising at a steady speed.

 

Answer #6 here.

I use moderate acceleration from a stop to 40 MPH and glide. Then anticipate traffic and stops decelerating to regenerate. I usually get >65 MPG doing that and it's almost by feel now without the need to constantly look at that screen.

Bob

 

Understood, I am fairly happy with my 57 mpg, however I will try your method in the next couple tanks. 65-70 mpg is better than 57.

 

Nope, I'm with you. (Whew, glad you won't smite me! ) It seems the Prius ICE actually is rather efficient over a fairly wide range of RPM, as long as we keep it below ~2400. The only issue is how to define "moderate." What is moderate to some might be either gentle or brisk to others. That is why I tried to define an objective rule (the iMPG/MPH ratio) that anyone without added instrumentation can follow.

And I'm in absolute agreement with your advice to TheSpoils.

 

Don't worry. After almost four years, that light bulb still occasionally flickers for me. Just be patient.

Here's an offer: If you ever get down to central VA, I'll be glad to give you a hands-on clinic. Or, I'll be passing through your area on 9/20 on my way to Maryland on business, and I can stop for awhile for a clinic.

 

The dent in the carpet under my accelerator pedal tells the story for me.
I only get 4.3 L/100km on my cross town commute but I enjoy my car too.
3/4 to full throttle until target speed is reached, then lift off and glide. It might not be the most efficient way to drive a Prius but I don't hold up traffic and I raise a few eyebrows when people can't keep up.
My key to economy is maximising glides and lifting off in anticipation of having to stop at red lights. Select a route with steep climbs but gradual descents to limit application of power to short time high climb rates then coast down hills in a no arrows glide as much as you can.

My economy is suffering right now because I am teaching my son to drive in my Prius, hypermiling can wait until he masters the basics.

Don't listen to me, others get much better results. I just added my bit because my priorities are a little different. I hope others see the performance of Prius and it helps them overcome the misconception that Prius is slow.

I also have a theory that if I accelerate slowly and hold one other driver at the lights I caused him/her to sit idling at the light until the next change, then the next car etc until peak hour is over and no one is left waiting for 2 changes of the light. So is a slow take off really saving gas over the whole community?

 

If you figure on the 2010 it has the ECO mode to maximize gas mileage. I don't have a 2010 but I would think in ECO mode going from a stop it would prevent you from making any real fast accelerations, like you can in normal mode, to get up to speed so you can glide. So if that was the ECO intention to get the best mph, it's better to slowly accelerate up to your max speed so you can start gliding. I don't know if that's right or not. I've been accelerating from stops briskly to get up to speed so I can start gliding.

 

I agree with Evan in Post #2 above. Using electric mode is efficient only when certain narrow criteria are met: the battery is near full, speed is constant, and power demand is light. The reasons for this are that energy is lost to inefficiencies when the battery is being charged or drawn down, and this loss is only justified when the battery is so full that some of its charge needs to be used in order to bring it back to the mid-range where it needs to be in order to have both head room to absorb charge and available charge when needed to provide torque for acceleration. A long slow acceleration under electric power will draw it down below this efficient level.

Would-be hypermilers need to pay attention to RPMs and iMPG/MPH ratios and deadband and suchlike, but if your wish is simply to drive the car without being overly inefficient, the answer to the OP's question is: Accelerate moderately, neither extremely gently nor extremely hard. In other words: drive with the normal flow of traffic. This keeps you in the efficient range, and avoids angering the drivers around you.

Note also, that MPGs are affected by weather, road conditions, and length of trip. Not everybody can achieve extreme numbers. Don't be the fellow who drives an extra 20 miles in order to warm the car up enough for MPG bragging rights. I used to live in Fargo, ND, and bought my car in January of 2004. I had a three-mile, ten-minute commute in 20-below-zero weather. My first tank was 29 mpg, if I remember correctly, but I burned far less gas than these hypermilers because of my short commute: I drove very few miles, so the car never warmed up enough for MPG bragging rights, but fewer miles driven also means less gas burned, and a small carbon footprint is far more important than high MPG numbers.

And most importantly of all: drive safely. More time watching the MFD is less time watching the road.

 

Wow... so many rules and differing opinions.

Now that I have a ScanGauge, I am curious about opinions on the "best" acceleration rate for pulse and glide. How hard show I go for the pulse up to ~42 mph. Should I look at iMPG (on the MFD) or gps or TPS or RPMs or IGN? If so, what should they be? How low should I let my speed drop before I pulse again?

My current commute only lets me P & G over a short stretch and the speed limit is only 35 mph, but I'm ok w/staying between 32 to 41 mph. Sadly, I will be relocating to another state very soon and my eventual commute is still unknown.

What about SHM? If I'm trying to maintain 55-67 mph, how aggressive should the pulses/gradual accelerations back up to 65 mph be? What about 46-55 mph? How about accelerating back up to 55?

 

None of these methods are wrong except this one. Using all electric is always less efficient, and it's easy to see why. Evan already did a good job explaining why, and he is correct.

The only place where all electric makes sense is to avoid short cycling of the ICE, as in stop and go traffic, or moving only a short distance.

The general concept of using the ICE at its most efficient is correct. All of the different suggestions relating to that come from the difficulty of knowing exactly when the ICE is at its best. For a simple, non-precise method of efficient acceleration, don't crawl away from a stop, and don't mash the pedal to the floor. Stay somewhere in between, closer to the brisk side, and you will do fine.

Obviously, if you are in stop and go traffic, efficient acceleration is trumped by timing. There is no point to rapid acceleration only to brake to a stop.

Tom

 

For sub-41 MPH glides I try to keep RPM as low as traffic will tolerate, and generally at 1600 or below.

I don't use SHM much; my terrain and driving conditions aren't favorable for it. The SHM gurus primarily use IGN, aiming for 14 during the deceleration phase and 17 or so during acceleration.

A major part of efficient ICE-on conditions, acceleration or steady-state, is keeping the ICE under load. Hobbit has described using injector timing as a surrogate indicator of engine loading. If you have the X-gauge option, you can use that as one of your efficiency indicators. That's my primary efficiency indicator on the highway.

 

So I am doing it wrong then?

Here is something that is right, don't brake for corners. See my avatar.