Accelerating briskly from stop compared to slower acceleration...

You can keep it at the top of the ECO bar

When starting on an uphill incline, you can go into the power band.

 

I am no hypermiler by any means but I accelerate the way one person described as "the red bar tickles the far right hand side of the PWR zone". Where I live I have to do this just to keep up with existing traffic and not to impede anyone else's progress.

I have found that I may lose more mpg during the acceleration or pulse phase but gain it back more quickly by getting up to speed quicker and thus gliding more quickly and for longer periods.

You will find a lot of different variations and opinions on this topic, so experiment and pick the one that fits your driving style the best.

 

That is because it takes the same amount of work to accelerate you car to a given speed no matter how fast you accelerate. Your engine is more efficient at relatively high throttle openings.

 

Interesting observation. Would you care to elaborate?

 

Part Load Pumping Losses In A Spark Ignited IC Engine

The Prius minimizes pumping losses in several ways:
Atkinson engine makes less power so throttle is opened wider.
Computer control can open throttle more than needed and save energy to battery
Very light loads (those with the most pumping loss) can be battery driven.

 

Pumping losses, mostly. To a lesser extent heat loss comes into play.

Tom

 

Nice link. Thanks:rockon:

 

If you accelerate "slowly" you might end up using more battery than necessary to compensate for the lower rpms of the ICE, although the computer will likely try to compensate within the torque request of the driver and a myriad of other factors. Battery is better used to glide with ICE off (when below 73km/h), than to move the car swiftly at a traffic light.

 

Ideally you don't want to use the battery during a glide either. Battery power is inefficient power. For gliding you want to use the kinetic energy stored in the moving mass of the car.

Tom

 

Well, if traffic and roads permit. Which is practically never in my case. The flow of traffic is pretty constant on specific roads I drive each day, so if I start gliding with no intervention of the electric motor I end up slowing down traffic. I need to keep a constant speed - I let the Prius decide what to do, I cannot (and I don't like, honestly speaking) pulse & glide...
The only P&G I can do is between traffic lights I know the timing of.
Otherwise my best fuel saver is predicting traffic trying to stop the car as much and as less abruptly as possible.

 

Allowing the Prius to do what is does is almost always the best policy. My reply did not relate to pulse and glide, but it does apply. You will note that the word "pulse" is nowhere mentioned. I was commenting on your statement that you like to glide with the assistance of the electric motor. Gliding is more efficient without using power from the battery.

I suspect you are referring to cruising under electric power, where the motor allows you to maintain the speed of traffic without running the engine at inefficient loads. This mode better fits with your description.

Tom

 

Yes - but that is what I almost never manage to do in my traffic situations... (hence my <50mpg personal average...)

That's what I meant. Is that coasting? or AKA stealth mode?
I think I need to come up with a collection of these names and add them to the Wiki...

 

I would call that stealth or EV mode. I think of coasting and gliding as having zero power consumption, so a gradual reduction in speed is required unless going downhill.

Tom

 

Just as important as the acceleration rate is
whether the Prius must shortly have to stop
and lose all the kinetic energy created by
the acceleration. When the Prius has to stop
frequently and lose its kinetic energy, the Prius
becomes less energy efficient. The amount of
energy loss is roughly indicated by the speed
from which the Prius must make a full stop at
and how often it must stop. Hypermiling minimizes
accelerating at speeds which would require
stopping (lost of kinetic energy). To maximize
the Prius fuel efficiency hypermiling minimize
the lost of kinetic energy by avoiding speeds
which would incur higher energy lost if the vehicle
were required to stop AND minimizing the
number of times the Prius needs to stop.
.

Assuming that the Prius does not have to stop
anytime soon after accelerating from a full stop...
Then fuel efficiency depends on the

A. first 100-500 feet of road that the Prius must travel.
Is it (1) downhill, (2) flat, or (3) uphill.

B. What is the top speed that you are going to
accelerate to? (1) under 25 mph (2) between
25mph to 45 mph (3) over 46 mph.

C. Is your HV battery State of Charge
(1) over 50% (2) under 50%

D. Is your engine coolant temperature
(1) under 160F, the first 50 minutes
of driving a Prius in winter city driving
and the first 25 minutes of winter highway
driving. For summer time divide time in half.
(2) over 160F, after driving the Prius
for over 50 minutes in the winter city
driving or or over 25 minute in winter
highway driving. For the summer time divide
time in half.

IF A.(3) or B(3) or C.(1) or D.(1) THEN
To start immediate press the Accelerator
so that HSI display moves is pass *ECO*
capsule midpoint approximately 3/4 to 5/6
of the way to on the *Eco" bar but not
creating a "red" bar in the power range
the middle of the ECO capsule. This will
put you in the most efficent ICE burn mode
possible while minimizing electricity usage.
It will also warm up the Prius ICE. Only if the
Prius is not able to reach the desired terminal
velocity of X mph B.(3) should you press the
accelerator harder and go into the power
bar section ( > 2.0 GPH, > 2000 RPM ).
Assuming that the Prius must accelerate from
0 mph at the bottom of the hill to a terminal
velocity of X mph and it is desirable to
maintain that speed to the top of the hill.
Once X mph is achieve - throttle back the
HSI to avoid accelerating over X mph.
As you reach near the top of the hill
slowly let go of the accelerator allow momentum
to keep the Prius going.

At very high speeds, its more fuel efficient to use
Driving with Load (DWL) hypermiling technique
which requires the driver fix the power on the
HSI display via the accelerator and allow the speed
of the Prius to drop/slowdown as the Prius climbs
uphill. As the Prius reaches the top of the hill
the foot is off the accelerator and the Prius is
suppose to glide/coast on the crown of the hill.
As the Prius starts to go downhill again, the
accelerator is use to set the initial velocity and
then the Prius is allow to glide (in Neutral ) down
hill or coast downhill(in Drive - while charging the
batteries if the Soc is low or barely using the
electric motors in but not recharging the batteries).

On a Flat road, there is also an option to do
what's called a high speed pulse and glide. It
works best when you have a tail wind and when
the top speed is less than 55 mph.

IF A.(1 or 2) or B.(1 or 2) or C.(1) or D.(2) Then
press the accelerator so that the HSI indicator
is about 1/8 to 3/8 of the way on the "ECo" bar
to the left of the *ECO" capsule on the HSI until the
Prius is between 12mph(flat road) to 25mph(downhill
road). After which press the accelerator down
further so the HSI indicator is 1/2 to 5/8 the
way of the HSI indicator "ECO" bar this is the
most fuel efficient setting to accelerate (1.5kilowatt
power/.80 to 1.10 gallons per hour/1280rPm to
1480rpm) You get the best fuel efficiency when
accelerating downhill.

If A.(3) the downhill is very long and you don't
need to recharge the HV batteries C.(1) then you
can switch the transmissionto N(eutral) when
the Prius reaches X mph - this removes the
internal drag cause by the ICE but doesnot
allow the HV batteris to recharge. before
exiting the downhill put the transmission back
into D(rive).

IF A.(3) the downhill is very long and you need to
recharge the HV batteries C.(2) then keep the Prius
in D(rive) take your foot off the accelerator
completely and the Prius was start recharging
the HV battery pack. As you exit the downhill
put your foot back on the accelerator making
sure that the HSI is now in eco bar area and not
in charge mode.