Theory: Use EV mode just before home...

[V8Cobrakid]

hmm... interesting theory.. i see it only working for people around gentle hills who have EV mode.

Otherwise... you're draining "warm up" electricity.. since the car relies heavily on the battery for the 1st half mile or so. (i live on a hill, and i use EV to park the car.. but mileage is not the factor) so.. you drain the battery parking the car.. and now it gets even more depleted because the car is using it to reduce load on the ICE during startup... . so... now you have a potentially low battery and extremely poor mpg for the next couple mins of the warm up process.

[ZTrekus]

Originally Posted by V8Cobrakid

hmm... interesting theory.. i see it only working for people around gentle hills who have EV mode.

Otherwise... you're draining "warm up" electricity.. since the car relies heavily on the battery for the 1st half mile or so. (i live on a hill, and i use EV to park the car.. but mileage is not the factor) so.. you drain the battery parking the car.. and now it gets even more depleted because the car is using it to reduce load on the ICE during startup... . so... now you have a potentially low battery and extremely poor mpg for the next couple mins of the warm up process.

I really don't understand this concept. If the car needs the ICE in the morning to "warm up", then shouldn't you have an empty battery to capture whatever electricity is generated as a result anyway? I mean the generation of electricity is going to be a side-effect of the ICE being on no matter how hot or cold it is. So an empty battery goes hand-in-hand with that. Seems like you will be simply wasting energy whenever the batter is full and the ICE needs to be on - like every start-up for instance. Another reason why one ought to use EV mode just before shutdown etc...

[CivicQc]

Originally Posted by royrose

I am in the exact same situation, almost identical distance and slope. Mine is a little curvy as well. I can't go very fast up the hill, so the speed limit of EV would not be a problem.

So, I wonder if the electric motor, with it's plenty of torque, would be more efficient going up the hill vs the ICE. In fact, I assume the electric motor would be assisting the ICE going up the hill in normal mode.

Have you tried going up the hill in EV mode?

Originally Posted by royrose

One of the posts criticizes using regen on startup, but with my hill, breaking is necessary down the hill, so why not get regen going down and therefore, why not use EV going up? I assume that poster was responding to the first post, not your uphill/downhill question.

Yes, that is what I assume. I guess he meant regen through the ICE, which is not efficient when the engine is cold.

In your situation however, you would not be able to brake-regen as much energy as you use when going up. Can you tell me how much energy is regenerated when going down your 400 m hill?

[V8Cobrakid]

when your car starts up.. it uses electricity to lighten the load on the ICE.. so you don't fill it back up.. you drain it more.. then you fill.

the golden rule to this car and gas mileage is to NOT use the battery because when you use electricity, you take on the energy losses of having to make more energy.

i used to question things just like you... then i stopped... because it's about efficiency losses.. i'd rather keep my battery level... and have the ICE warm up so the engine can shut off quicker.

if you have stop lights, you don't want to sit there and watch your mpg drop like a bomb because the hybrid system requires more power before shutting off the ICE...

[royrose]

Originally Posted by CivicQc

Have you tried going up the hill in EV mode?

Can you tell me how much energy is regenerated when going down your 400 m hill?

My car is still on order. I expect to get it in about 6 weeks. I'll post my experience when I get it.

[Rokeby]

I'm not at all positive that I can shed light on this matter. Nonetheless,
I'm foolish enough to try. Here goes...

There are a number of issues, some non-intuitive, mixed up into a
thick gurry here. They include:
* Hybrid Synergy Drive, HSD, Control Algorithms
* ICE and HV battery use at start-up
* Most efficient use of the infamous EV mode/switch
* Short term vs. long term efficiency.

Lest the message get lost in the following flood of words, here it is up-
front:

It is most unlikely that starting a new day with a cold Internal
Combustion Engine, ICE, and only red bars for HV battery State of
Charge, SOC will yield the highest day's end Fuel Efficiency, FE.

Why? Well, because what is know about how the HSD control
algorithms control energy flow to and from the HV battery say,
"Sorry boys, it ain't so. Never has been. Never will be."

OK, some general stuff:

First off, the HSD works with control algorithms prioritized in this
order:
1. Protect the mechanical and electrical systems from damage.
2. Operate the the mechanical and electrical systems to generate the
least possible pollution.
3. Operate the mechanical and electrical systems to maximize fuel
efficiency.

Fact: The HSD is least intrusive when the SOC is at high 5 bar or 6 bar
levels.

Consequence: Whenever SOC is out of this range the HSD will quietly,
ever so sneakily, but inevitably work behind whatever the driver is
trying to do to get SOC to this range.
* At 2 greens bars, the HSD will happily use SOC to spin the ICE to
burn off charge, that is to waste energy. In accordance with its first
priority, it has to do this to have room for more charge if necessary,
* At one or two red bars, the car will refuse access to EV mode, keep
the ICE turning over when otherwise you would expect 0 RPM, and
through the Power Split Device, PSD, divert ICE power to Motor-
Generator 1, MG1, to build up the SOC.

Fact: At start-up, the HSD runs the ICE with a rich fuel mixture to
quickly heat the Catalytic Converter, CC. I does this to get pollution
super low ASAP.

Consequences:
* When cold and running on rich mixtures, the ICE has greatly
reduced torque.
* For the first few minutes after start-up the HSD uses huge amounts
of SOC to accelerate/move the car as requested by the driver via the
go-pedal.

Fact: Using the ICE to burn gasoline to generate power and then
sending that power to the HV battery for storage, and then using that
power to move the car involves huge conversion losses. I've seen
figures here between 58 and 80% losses.

Consequence: The best way to use an EV switch is hardly at all: very
short runs to set up a down hill situation to get the power used back
thru regen, etc.

Fact: Just because the ICE is turning over, it doesn't mean the HSD is
diverting power through the PSD to generate electrical power.

Consequence: At start-up the HSD is taking power out of the HV
battery to help move the car.

Back to the original question: Is it most efficient to end the day with
very low SOC? Answer: Most likely, no.

At start-up the HSD will be using power to move the car. This will
reduce SOC. If you're down in the red bars range, to protect the HV
battery the HSD may not take power from the HV battery and the car
will be very sluggish. Until the ICE and CC get fully warmed up the car
runs at lower FE, somewere ~30-35MPG. When the ICE/CC are fully
warmed up, the HSD will divert power to charge the HV battery vice
move the car. FE will be less than maximum. The ICE may be
operating efficiently, but the overall HSD is not.

What to do?
Recognize that high 5 bar, 6 bar SOC is a desirable condition. Don't
use EV mode excessively, ever, for any reason.

Possible exception:
* If you live at the top a hill of sufficient length and declivity to
increase SOC from red bars to green bars during the roll-down,
AND
* You have an EV switch and get into EV mode before the ICE starts,
AND
* Air temps are above 32 degF so you can get into EV mode,
AND
* You limit speeds down the hill to 34 MPH to stay in EV mode and
suppress the inefficient ICE start-up sequence...

Then, and only then, is it possible that starting a day with red bars on
the SOC will yield long term high FE/MPGs.

Hope this helps.

[CivicQc]

Thank you very much, Rokeby, for that very interesting info. I never owned a hybrid, so I dont have any experience and very little knowledge. Your message contains valuable information to me!

[CivicQc]

Originally Posted by royrose

My car is still on order. I expect to get it in about 6 weeks. I'll post my experience when I get it.

Oops - just seen it - sorry. Yes, please do not hesitate to post your experience on this thread - I am eager to read it!

[royrose]

Rokeby,

I also thank you for your thorough response. It sounds like CivicQc and I just may be in a position to benefit. Time will tell. I will get a baseline and get familiar with my Prius and then experiment.

[qbee42]

Originally Posted by ZTrekus

I really don't understand this concept. If the car needs the ICE in the morning to "warm up", then shouldn't you have an empty battery to capture whatever electricity is generated as a result anyway? I mean the generation of electricity is going to be a side-effect of the ICE being on no matter how hot or cold it is. So an empty battery goes hand-in-hand with that. Seems like you will be simply wasting energy whenever the batter is full and the ICE needs to be on - like every start-up for instance. Another reason why one ought to use EV mode just before shutdown etc...

When the Prius warms up the ICE, it does so in a manner that burns gas to make heat but not much power. You can force it to deliver power, but it isn't happy about it and does so in a less efficient manner. On the surface of it, your thoughts make sense, but once you understand the finer details of the entire Prius drive system you realize why it doesn't work that way.

Tom