Best FE techniques for slight inclines

Hi SomervillePrius,

My comments are within the context of a reasonably charged HV.

A lot of my driving is like yours. I glide down, and deadband (?correct term) up. By that I mean no arrows to or from the battery. I like driving inclines like this, because the incline bleeds off speed when I have to stop for a red light.

The rationale is to use the ICE at an efficient output. P&G is not the best in this case because you would be just putting the battery in the middle of your energy flow without benefit.

Long inclines that are too steep for deadbanding from the beginning, and would bleed the HV battery down too low if I just relied on it for the extra power then entire distance is something I have not figured out to my satisfaction. Lately I have been pulsing up to 5 mph or so greater than the lower speed I can drive, and then deadbanding until pulsing again. If I fail and the SOC runs down, low FE results.

The engineers in the group may have to correct me, but my impression is that ICE deadbanding is not a constant power output level. It seems that a short pulse at high power output allows subsequent deadbanding at a higher power output than would have been possible otherwise. Or maybe I'm just enjoying a shoulder of the rpm/torque topology. Or maybe, I am rambling, and this is nonsense.

 

Deadbanding instantaneous MPG depends on speed. At 35 mph I see FE mid 30's, and at 40 mph, low 40's MPG.

So a good drive gives glide down and 35 - 40 mpg up, or an average of 70 - 80 mpg.

 

The "deadbanding" level of demand [right foot] depends ENTIRELY
on battery SOC. When it's at 60% nominal [six bars], most normal
acceleration doesn't charge or discharge it -- no need, since it's
at the target level already. That's your easy "deadband" with no
arrows to or from the battery. When the SOC gets lower, the system
tends to charge the battery unless you make a much *heavier* demand,
in which case more of the engine's output needs to go to the wheels.
So if you're trying to "deadband" with a low SOC you're going to
carom into the car ahead of you. Conversely, if the SOC is high
then the system is going to give you more out of the battery and
you won't see the "charge arrow" at all until it gets lower.
.
It's not really about SOC. Sure, cranking less energy in and out
of the battery results in better engine-to-wheels efficiency, but
I believe that this is trumped by having the engine run in *its* own
most efficient power-output region. Thus for pure P&G it doesn't
really matter where your SOC *is*, what matters is how much delta
it goes through in the course of you optimally running the engine.
.
These days I tend to use a "slightly augmented" glide, letting the
car tool along on about 10A of battery current [it turns out that
in no-arrows "glide" the system can be drawing up to 5A out of the
battery anyways, so helping it just a little more seems fine], and
then pulsing to greater than 1500 RPM if traffic allows. Increased
following distance gives a much wider window to play in. So at
times I can hold that 10A glide for a long time and the SOC drops,
but this has a mild advantage that my threshold for the next
engine-run is at a lower demand and that makes it easier to "pulse"
in heavier traffic without taking off too fast. I don't worry too
much about battery current flow during pulse; the system is going
to do what it thinks is necessary to get back to 60% target with or
without my help.
.
_H*

 

If I had to go uphill steady I would try for limiting my fuel flow to x gal per hour. That is assuming no traffic stuck behind. It might be 1.5 gal or 2 etc depending on the grade, and how much I felt like slowing. (readout on the can view.)

I would let the battery do some chargeing. When it gets to the set point it will stop.
I would never try to run it down, unless I had a long downhill ahead.

I would try not to discharge the battery going uphill while the engine was running.

I generally use just one can view screen for regular driving showing:

Fuel flow, Amperes, SOC, and Engine Temperature.