Posted by bwilson4web on March 15, 2011, 10:02 am
I was hoping you might have considered doing a series of tests with
and without P&G to document the differences, the scientific method.
But it sounds like you are still trying to figure out how P&G applies
to your specific environment, the DC area where I and my wife lived
My wife and I used to live on Sherier Place near Arizona and MacArthur
Blvd in DC, also Fairfax, Arlington, and Lanham Maryland. Many of the
routes you've described are familiar but remembering DC traffic, there
may be no opportunity for constant speed benchmarks, much less
testing. It is a lovely area but with that traffic, you have my
In contrast, Huntsville has a 'rush minute' that is easily avoided by
leaving a little early or late, +/-15-30 minutes. I even have base
access to Redstone which provides another set of low-traffic routes.
So when the 1989 tornado blocked the main north-south roads, Redstone
opened up Pershing and everyone got home that night without having to
drive to the river bridges at Decatur or Scottsboro.
Regardless, you are welcome to look over my mileage records:
The cold weather is ending and once temperatures rise to 50F, mileage
Posted by bwilson4web on March 15, 2011, 10:44 am
. . .
One late thought, you'll notice my early records were running two per
week. I would fill-up the car Friday and Sunday evening to separate
the weekly commuting mileage from the longer, weekend errands and
drives. This allowed me to quickly understand what was happening with
the car and how it behaved in different conditions.
With the newer, ZVW30:
I don't drive it that often so we're using refueling normally.
Posted by Bruce Richmond on February 3, 2011, 12:18 pm
Thank you for demonstrating that you don't even know what that term
means. In my first post to this thread where I mention pulse and
glide I wrote "The roads around here are mostly 2 lane, and coasting
down to 20 mph in a 35 zone with traffic behind you isn't really an
So I made it clear from the begining that I didn't condone getting in
the way of others. You are a troll to keep implying that I do.
Posted by bwilson4web on February 3, 2011, 2:15 pm
. . .
All I'm interested in is a comparison of pulse and glide versus the
equivalent constant speed speed. BTW, there is one place I use 'pulse
and glide' without being a traffic hazard . . . a 'rolling warm-up.'
On cold mornings, I cut through my 25 mph posted, neighborhood streets
taking the 'back roads' to let the engine warm-up with a minimum fuel
The characteristics are:
17-25 mph, PnG, 'glide' in "N"
~30-35 MPG, ~1.5 miles
21 mph, constant speed
Because I'm running parallel to the main commuting route, there is
very little traffic 'going my way.' With four cross streets leading to
the main commuting route, the vast majority of traffic turns at the
next intersection to commute to work. In those rare cases were someone
is following, it is because they are going to park at their home in
that block. But about once every four months or so, I pull over to
park at someone's house to let a following vehicle pass . . .
following traffic is very, very rare.
Coasting in "N" minimizes the fuel burned to warm-up the engine to a
rate of ~0.30 gallons per hour. There is no throttle setting that has
an equivalent, consistent, low fuel burn rate measured with my
ScanGauge. Regardless, the goal is to arrive at the commuting route
intersection when the car has warmed enough to enter "stage 4" or
hybrid mode. It is more accurate to call this a 'rolling warm-up'
because I don't use it once the engine coolant reaches 70 C.
I have a somewhat similar protocol leaving work where I can exploit
catalytic converter warm-up. There is a 30-40 second window when the
NHW11 Prius uses traction battery power and idles the engine at
~0.60-0.70 gallons per hour. By parking near the parking lot exit,
this is long enough to reach 35-40 mph before the catalytic converters
light off and normal engine warm-up begins. But at 35-40 mph, I'm
keeping up with traffic and by follow downgrades, can maximize the use
of the low-fuel burn rate, "N" during warm-up. Again, as soon as the
car reaches "stage 4" or normal hybrid mode, I'm back to normal,
constant speed mode.
BTW, in warmer mornings, I often take one of the earlier cross streets
once the engine coolant goes over 60 C. Again, this is a rolling 'warm-
up' using "N" to minimize fuel burn when rolling. In contrast, most
'pulse and glide' advocates claim the engine must be off or throttle
feathered during the glide. My scangauge indicates there is no
feathering with a lower rate of fuel burn than "N".
Posted by Bruce Richmond on February 4, 2011, 4:50 am
Never gave much thought to p&g during the warm up cycle. Doesn't the
battery have to get up to some minimum charge before the engine will
shut off? If you are shifting into "N" it may use less fuel at the
moment, but even out in the long run because it takes longer to get
the battery up to charge so the engine can shut off. I don't know
this, just speculating.
After warm up the idea with p&g is to get the engine to shut off
during the glide. Back in the day, drivers in economy runs would
accelerate at full throttle in high gear, then step on the clutch
while shutting the engine off with the key, then slip into neutral.
They would keep the throttle wide open with the engine off to keep the
accelerator pump from squirting when they stepped on the gas again.
When they had coasted down to their min they would step on the clutch,
slip it back into high gear, turn on the ignition, and let the clutch
out to bump start the engine, still WFO. The whole idea here was to
eliminate the losses due to pulling a vacuume against the throttle
plates. The same applies somewhat to the Prius. During the Pulse the
throttle is open wider than it is during steady state cruising.
During the glide you make the engine shut off so it uses no fuel at
all. Feathering the pedal is to prevent regenerative braking from
kicking in. There are losses every time the battery is charged or
discharged, so we do our best to prevent any charging/discharging. It
would be nice if we could just flick a switch and let the computer do
the feathering for us.
I haven't done much in the way of formal record keeping for p&g vs
steady speed. I know that by using it I have averaged 70-75 mpg for a
40 mile trip on several occasions. That was done on two lane
secondary roads where the speed limit ranged from 35 to 50 mph, so
much of the time I was well below the speed limit, averaging about 35
mph. A steady 35 mph is usually good for 55-60 mpg, so the p&g gives
about a 25% improvement. Over a distance of 40 miles I don't think a
few % on the SOC makes much difference. When I get the chance I will
try to come up with some specific numbers under more controlled
conditions. Right now isn't the best time though since the temp has
been running in mostly in the single digets and teens.