Theory: Use EV mode just before home...

How does lithium ion (Li-Ion) compare?

 

Note that a high SOC can also be obtained through regenerative braking...

 

At one point in the distant past I thought as the OP does: "I'm going to be charging the battery when the ICE starts in the morning so running down the battery getting into the driveway is a good thing since I'll use less gas getting home."

However, Rokeby's analysis squares 100% with what I have seen. The car will use MUCH more Electric momentum than ICE when the engine is first started. You do yourself no good running the ICE harder in the morning because you have drawn the battery down so far the car won't use it for propulsion or even far enough down that you drop to 2 bars right off the bat. For you newbies (WELCOME!), notice how fast the bars drop on a given 'from home' start when the engine is cold vs already warmed up. It is REALLY noticeable if you start at 4 bars. I would NEVER force it down to 2 unless you are out on the road and facing a LONG downhill, possibly 'B' mode plus brake pedal route that will push to 8 green and force the ICE to run to dump watts out of the battery. I personally never let it go below 4 in EV.

For those living on the hill, while you MIGHT be able to get up the hill in EV, you won't make much distance on the current battery. And remember: The ICE (at least in the Gen II) will run for almost a full minute ANY time you start it even if the engine is already warm enough that the car puts itself into auto-EV for propulsion. So while you might be braking to hold speed down the hill in the morning regenning all the way, the ICE is running and wasting gas. I agree with Rokeby on the use of EV to come down the hill in the morning: Don't let the ICE start until you get off the hill UNLESS the road at the bottom is high speed (ie NOT something the car can handle in normal ICE warm-up with a lot of EV initially). BETTER to let the ICE warm up gently, it is one of the reasons it will last longer than the ICE in a traditional vehicle. Also remember, if you push the battery down to 2 bars, you can't force EV anyway. Better to drive the car normally up the hill and end up with 4-6 bars at night.

 

Thanks, bruceha_2000, for adding this.

For that very purpose then (leaving home in the morning), wouldn't it be nice if we could recharge the battery during the night? I know it is not possible - just a hypothesis. What do you think?

 

ZTrekus,

You have made a very astute observation.

My answer: If the car is properly managed to achieve high FE/MPGs, a
SOC level of high-5 or 6 bars at the end of the day represents many
little energy savings or scavengings achieved by the HSD and not
inefficient use of fuel by the driver.

Some general stuff to back this up follows. All this applies during the
day before those last few hundred yards as you arrive back at home.
It most definitely determines how much SOC you then have and can
decide to use or save for the next morning.

Fact: Ultimately, all the energy resident in the car comes from having
burned gas from the tank. This would include:
* Kinetic Energy - energy from the vehicle being in motion, =mv^2
(mass times velocity squared)
* Potential Energy - energy possesed by a vehicle as the result as its
being at a height higher (+), or lower (-) than some reference, most
typically where the car is at the beginning of the day. Rolling down a
hill in a "no arrows" glide is using this energy.
* Chemical energy - energy stored in the HV and 12v batteries.

Consequence: You have to burn gasoline to do anything useful with the
car. Tough beans, acccept it, move on. But this isn't the real issue.
The real issue is how can the use the HSD to achieve the highest
system efficiency.

Fact: At any given point in time when the HSD has control either the
ICE or electrical power system may be used inefficiently. But taken
together it is most probable that within the prioritized protections
listed earlier the HSD is operating the combination of the two more
efficiently than the driver can.

Consequence: Whether the driver likes it or not, the HSD is making
many, probably thousands per second, adjustments to the
ICE/electrical power mix. You can see this by running the car on a flat
section of road and setting the Cruis Control, CC -- the speed doesn't
matter. Now watch the screen on the MFD with the arrows (this for the
Gen II. Sorry, I'm keeping up with the minutia of the Gen III displays.)
At what appears to be a steady state, there are flickering yellow
arrows (electricity from the battery) and sometimes the orange
arrows (ICE power either directly or indirectly via generated power
that does not go through the battery). This is the HSD being very
selective in using its available resources in a highly efficient manner.

Fact: At least on the Gen II, the arrows on the Power Screen are only
an approximation of what the HSD is doing with power flows. Some
folks call the Power screen a "mimic," because it doesn't tell the whole
story.

Consequence: There are two electric motors/generators (MG) not one.
There is no way with only one motor depicted to show electrical flow
between them. Also, it is known that all electrical power flows are not
shown, such as the small flow from the battery to the wheels when in
a "no arrows glide."

Fact: The demi-intelligence in the HSD knows nothing about the real
world that the car is operates in. What little it knows is limited to
outside air temp, air density, -- from which can be derived the
atmospheric pressure (altitude is a factor here) -- and the car's
velocity. It has not a clue about what is about to happen;
climb/descend a hill, slow/come to a stop, shut down for the day,
whatever. So the HSD has to maintain its resources in a very
conservative condition to be able to react to anything that might
happen.

Consequence: The driver is the interface/intermediary between the
HSD operating in its near perfect world and the constantly changing
demands of the real world. Fortunately, the algoriths used by the HSD
are not go-no go; they have some fiddle room for the driver to play
with.
As an example, let's examine accelerating up a gentle hill. You just
step on the gas, and up you go, but with a yellow arrow showing
power going into the battery with attendant conversion losses. If you
push down on the on the accelerator ever so little, the yellow arrow
goes away. This would be a more efficient way to use the gas that you
must burn.
Likewise, if you saw a orange arrow going to the front wheels, this
represents power sent by the Power Split Device, PSD, first to MG1 to
be turned into electricty and then sent by the HSD to MG2 to drive the
wheels. Here too there are conversion losses. If you ease off the
accelerator ever so little, the arrow disappears. This to is a more
efficient way to burn your fuel.

Question:What does the accelerator, the "go-pedal" really do?

Answer: When the driver responds to conditions in the real world,
he/she makes an acceleration. Speeding up is an positive acceleration,
slowing down is a negative acceleration. Changing direction, turning, is
also an acceleration. In the Prius all these changes are communicated
over wires. No acceleration control -- accelerator or "go-pedal," brake
pedal, or steering wheel is mechaniclly connected to the thing it
controls. The car is "fly by wire;" all command signals go over wires
to a control computer.

As I understand it, pressing on the go-pedal sends an electronic
request to the appropriate computer to increase torque to the front
wheels. Not very exciting is it? In turn that torque will accelerate the
car to speed up, or hold a contant velocity up a hill, or overcome drag
forces that are acting on the vehicle -- there are many, including; in
the ICE, in the MGs, where the rubber meets the road, and those
created by the air as the car passes through it.

Now, back to the original question:

"a high SOC is obtained because it has burned up your gas supply
to get there. At the end of the day - surely it is better to leave the
energy in the form of gas in the tank as opposed to bars on the dash
representing the SOC in the battery."

As the driver you can most definitely affect how much SOC you have
at the end of the day. I use "affect" intentionally. Because the HSD is
busily working away in the background no matter what you do, you
cannot fully determine what the SOC is. The HSD is going to give and
take as it sees fit.

That said, you can intentionally send little power to the HV battery,
and take little from it. In reality due inevitable regen from necessary
braking on hills, mis-timed traffic signals, interactions with traffic, you
should always put more power into the the battery than you
intentionally use. This is no real problem as if the SOC level gets too
high -- high-7 or 8 green bars -- the HSD will first try to use it in
moving the car, or as a last resort dump it by spinning the ICE without
fuel.

For your convenience, here again is my answer:

If the car is properly managed to achieve high FE/MPGs, a SOC
level of high-5 or 6 bars at the end of the day represents many little
energy savings or scavengings achieved by the HSD and not inefficient
use of fuel by the driver.

 

Just a quick note on something that I haven't seen while reading through the thread:

The reason the Prius favours electric use during warm up is for pollution control, not for efficiency reasons.

That said, even after reading the thread, I remain to be convinced whether the OP suggestion would be good or bad, from some empirical evidence.

 

The archives of the Gen II forum have threads about the same do or don't. Some owners actually did the experiment and found the charge depletion at night made for less overall fuel economy. But if someone wants to repeat history.....

Wayne

 

That's one of the all time bogus stats. I think the deep voiced announcer said, "Remember, most accidents happen within 25 miles of home."

DUH! MOST DRIVING OCCURS WITHIN 25 MILES OF HOME!

 

First, let me thank all who participated in this thread. So far it's been the most useful one I've read here.

I have been switching into EV mode about 1/2 mile before home and it does get my MPG's up as I head into the garage. However, I have also noticed that MPGs drop down to the same level they were at before EV mode, when I start it up the next day.

I'm going to stop the practice and just take it slow coming into the neighborhood, and I'll see if it makes any observable difference.

 

dont know where you live, but unless you work next door to your home, your car will already be warmed up and you will be driving (hopefully) in a manner that you will not accidentally run your kid over and you will already be in EV mode anyway.

listen to him, knows of which he speaks

great info, but this is not an option on the 2010. cannot force EV mode if car is not warmed up.

about the same, slightly better. both are rated to drain only a few % of charge over a 30 day period. since you would be unlikely to leave your car sit that long, its a non-issue. i would simply disconect the 12 volt lead acid battery since it provides features that will drain it when the car is off plus, its chemistry does cause it to lose charge MUCH faster

 

Question: I've experimented in the past, and by driving normally home from work, I usually end up with a high SOC, i.e. 8-9 bars, 3/4th of the way home. Does that mean that the last 1/4 of my commute, I'm throwing away energy when I brake? So shouldn't I use EV mode in that last quarter?

That's what I've been doing, with the last 2-3 miles of my commute, I have ample opportunities to feather the gas pedal and keep the engine off (gen 2 w/o EV button). By the time I get home, I shut off the car with 5-7 bars on the SOC.

 

That's my thinking and practice too.

 

I've put it into EV mode to move the car a few feet to find a different parking spot and it does delay ICE starting whether or not it's warmed up. I take it this delay doesn't last too long (or I was under a certain mph)?

 

on the 2009 and down, most installed an EV switch which forces EV mode. so short movements like you speak can be done. at my house, i park both Pri's on the street but to get to my garage, i have to drive around the corner to go thru the alley. i can easily move the SPM that far in forced EV mode (only about 2-3 blocks) and back even when cold.

the 2010 however, will only go into EV mode when warmed up making the EV button much less effective.

but that is really the only time you want to force EV mode, that and when you know you are coming to a very large downhill and the possibility of regen overwhelming the traction batt capacity is an issue

 

Then why am I able to do that on my 2010? I start it up, press the EV button, shift into D and move to a different parking spot, all without starting ICE (even when it's cold). As soon as I press the EV button again to get out of EV mode, the ICE starts up.

 

I do the same. In fact, I make a point of it to keep the engine from turning on as I'm backing out.

EV mode tend to be unavailable to me only if I try to start it after driving down the street a bit.

 

Once a GENIII is started, you've got about 7 seconds to switch it to EV. That's not a guarantee the ICE won't be enabled (if batt is too low for instance). But it works for a short period most of the time. Not a good idea to deplete the battery at start ups, but it can be done if you want a quiet or exhaust-free take off.

 

The EV switch simply requests the control system to use EV if it is possible. At the end of your drive you already have a warm engine and high SOC, so if EV mode is possible your Prius will automatically switch to it. Pressing the EV button won't make much difference, except in some very specific cases where the Prius is fooled into running the ICE, such as stop and go traffic.

Tom

 

i can confirm this. i tried to use this when leaving my parking garage at work. i can start off in EV mode, but as soon as i go any reasonable speed (>10mph or so, don't remember exactly), EV mode shuts off, which makes it quite useless