Posted by bwilson4web on February 4, 2011, 7:57 am
Hi Bruce,
. . .
> 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.
Not in practice. By doing a 'rolling warm-up,' we're getting the
engine into temperature regions where it can efficiently produce
power. A cold engine has higher internal friction from the oil and
parts. So I don't really have to worry about the traction battery
since within a fairly short distance at constant speed the traction
battery fully recovers. Engine efficiency is the key.
> 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.. . .
I know but there are inefficiencies in today's car including our Prius
that makes this nuts. For example, the NHW11 and NHW20 both have to
use fuel enrichment to prevent excessive, exhaust gas temperatures
from burning out the catalytic converters. The ZVW30 uses cooled,
exhaust gas recirculation but there are other inefficiencies that
happen at high power settings. Another ZVW30 trick is a valve in the
muffler that open under maximum power to reduce back pressure. This
was not an option on the NHW11.
You're starting to see the problem with lack of documentation because
you can only 'estimate' a savings. Without hard numbers, it is easy to
'estimate' the way you want the numbers to be and that isn't mean, it
is just human nature.
It doesn't take much to log the results and on longer test segments,
you'll need a collection of data . . . say five . . . and throw out
the best and worst and average the middle three. But try to keep a
record of winds, directions and temperatures so unusual conditions can
be documented. BTW, be sure and record the start and stop times. It is
very easy to miss-estimate the actual block-to-block speed versus the
equivalent constant speed.
Do you have any type of recording, OBD device? I like to use a laptop
to record critical vehicle parameters and then analyze the data later.
This way I can concentrate on safe driving with my eyes out the
windows instead of trying to be a human data recorder of a ScanGauge.
Thanks,
Bob Wilson
Posted by Bruce Richmond on February 6, 2011, 2:54 am
> Hi Bruce,
> . . .
> > 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.
> Not in practice. By doing a 'rolling warm-up,' we're getting the
> engine into temperature regions where it can efficiently produce
> power. A cold engine has higher internal friction from the oil and
> parts. So I don't really have to worry about the traction battery
> since within a fairly short distance at constant speed the traction
> battery fully recovers. Engine efficiency is the key.
I realize the battery will recover in a short distance at constant
speed. The point was that more fuel will be needed during that
recovery than would have been used to maintain the constant speed
without having to charge the battery. Also since there will be no
load on the engine when it is in "N" won't it take longer for it to
warm up into those more efficient regions? It would be interesting to
see the total fuel used in the first few miles using the different
techniques. BTW I have been trying "N" when cold since reading your
post and it was certainly an eye opener seeing 99+ mpg 100 yards from
my driveway at 9F.
> > 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.. . .
> I know but there are inefficiencies in today's car including our Prius
> that makes this nuts. For example, the NHW11 and NHW20 both have to
> use fuel enrichment to prevent excessive, exhaust gas temperatures
> from burning out the catalytic converters. The ZVW30 uses cooled,
> exhaust gas recirculation but there are other inefficiencies that
> happen at high power settings. Another ZVW30 trick is a valve in the
> muffler that open under maximum power to reduce back pressure. This
> was not an option on the NHW11.
Agreed, I wasn't saying to use WFO for pulse acceleration. On those
old cars the carbs were also re-jetted for a lean mixture when wide
open. Normal jetting is slightly rich at wide open because it makes
more power, and that's what most people want when they hold it wide
open. Just curious, have you done any experimentation to find out
what rate of acceleration during pulses might work best. From what I
have read it doesn't seem to make a whole lot of difference one way or
another.
> You're starting to see the problem with lack of documentation because
> you can only 'estimate' a savings. Without hard numbers, it is easy to
> 'estimate' the way you want the numbers to be and that isn't mean, it
> is just human nature.
> It doesn't take much to log the results and on longer test segments,
> you'll need a collection of data . . . say five . . . and throw out
> the best and worst and average the middle three. But try to keep a
> record of winds, directions and temperatures so unusual conditions can
> be documented. BTW, be sure and record the start and stop times. It is
> very easy to miss-estimate the actual block-to-block speed versus the
> equivalent constant speed.
Up till now most of the things I have looked at made big enough
differences so that they stood out with informal testing. Changing
tire pressure by 10 psi makes a big difference, and the fact that it
stays the same from then on tells me that it is a result of the
change, not just some fluke of the day. But I am interested now in
looking at things in finer detail and logging my measurements.
> Do you have any type of recording, OBD device? I like to use a laptop
> to record critical vehicle parameters and then analyze the data later.
> This way I can concentrate on safe driving with my eyes out the
> windows instead of trying to be a human data recorder of a ScanGauge.
> Thanks,
> Bob Wilson
I have a laptop. What hardware/software do I need to go with it?
Bruce
Posted by bwilson4web on February 7, 2011, 12:36 am
> . . . Also since there will be no
> load on the engine when it is in "N" won't it take longer for it to
> warm up into those more efficient regions?
Not that I can tell from my data records:
http://hiwaay.net/~bzwilson/prius/pri_temp.html
All heat comes from combustion and exhaust gas but the area exposed to
these high temperatures remains constant and exposure in the engine
block very limited . . . measured in fractions of a millisecond. Then
the hot exhaust gas passed into the tail pipe and can no longer heat
the block. Only the ZVW30 has an exhaust gas, coolant heater loop.
> . . Just curious, have you done any experimentation to find out
> what rate of acceleration during pulses might work best. . . .
I'm pretty much driven by my measured, brake-specific fuel consumption
graphs but generally speaking:
o 2,400 rpm or less - very good (I believe Hobbit prefers 2,200 rpm or
less . . . )
o 2,400 - 3,200 - Ok, don't make a habit of it
o 3,200 - 4,100 - make it brief
o 4,100 - higher - better be to avoid a traffic issue or 'blowing off
steam'
FYI, I was updating my software this weekend trying to get an ELM 323
($0) to work . . . so far, no joy but I was testing MacOS. It may
work with Windows. I'll test it later this evening.
Bob Wilson
Posted by Elmo P. Shagnasty on February 3, 2011, 2:01 am
> On 2/2/2011 2:12 AM, bwilson4web wrote:
> > Pulse was handled by using "resume" on the cruise control stalk. Glide
> > was handled by shifting into "N". This limited the speed range to
> > 25-42 mph due to the 23 mph lower limit of cruise control memory and
> > upper limit of 41 mph on hybrid mode.
>
> With respect, what effect do you think this sort of repeated, wide speed
> variation (+68% to -41%) has on surrounding drivers and traffic?
He doesn't care.
But I bet he gets REAL cranky when the outside world doesn't cooperate
and let him play his rolling video game according to HIS rules.
It's amazing how many people think they don't have to live in the real
world.
Posted by Neo on February 4, 2011, 11:14 am
> Good testing is based upon holding as many variables constant and only
> changing the one under question. Certainly it is important to document
> the methodology to so others can replicate THE RESULT. Sad to say, we
> get a lot of "Pulse and Glide" methodology and too little test results
> where everything is kept constant except the use of "Pulse and Glide"
> versus say "constant equivalent speed."
> On a single day I conducted a series of runs over the same course,
> both ways, only changing:
> o pulse and glide
> o constant speed
> PROTOCOL
> Pulse was handled by using "resume" on the cruise control stalk. Glide
> was handled by shifting into "N". This limited the speed range to
> 25-42 mph due to the 23 mph lower limit of cruise control memory and
> upper limit of 41 mph on hybrid mode.
> Constant speed was handle by setting cruise control to the equivalent,
> speed over the course of the pulse and glide protocol. Entry to the
> course was at the constant speed equivalent. Exit was at a fixed
> location at least six pulse and glide cycles later.
> RESULTS:
> constant - PnG
> 70 - 78
> 74 - 85
> 76 - 90
> 85 - 93
> 90 - 94
> - - - - - -
> 79 - 88 MPG average
> PnG = 11.4% improvement
> So for the pleasures of changing the speed from 25 mph to 42 mph,
> mileage improved 11.4%. Sad to say, I've only found one other similar
> report, SAE 2009-01-1322. However, it looks like they allowed the
> traction battery SOC to decrease during some of their tests. Still, we
> have two documented tests comparing PnG to constant speed.
> . . . Anyone else?
> Bob Wilson
impressive
my two cents...
Environmental and Experimental Factors that would effect a fuel
efficiency P&G experiment:
1) Type of gas formulation: Winter Fuel Formulation whose distribution
in DC/MD/VA starts about Mid October lower fuel efficiency by about 7
to 15%
summer/spring time gasformulation has more energy in it. In addtion,
if you can get 100% pure gas instead of E10 - the Prius fuel
efficiency -
Mileage would also increase (as would any car). E15 would lower the
MPG results.
2) Cold/Winter operational Temperature/inital warmup stage: During the
first few minutes after initially turning on the Prius the fuel
efficiency drops
( about 24 mpg for the first 5 minutes ) because the ICE needs to
warm up the coolant/catalytic converters - outside temperatures below
45 F
which occure more often in the winter can also cause the ICE to run
more oftent to warm up if it is standing still ( stop and go urban
traffic).
Once the ICE coolant warms up to over 110 degrees F - fuel efficiency
improves dramatically on the Prius ( you can monitor the temperature
with the ScangaugeII FWT Xgauge). This is characteristic of all gas-
electric hybrid. My 2010 Prius III MPG usually doesn't achieve over
50 mpg (AVG) until the ICE is over 140 F degrees(FWT). Grill blocking
can be used to decrease the number of times an ICE
is turned on to warmup the coolant/catalytic converters during the
winter time temperatures in urban driving conditions. Grill Blocking
is less useful for highway driving conditions since the ICE is running
harder and more often in this driving condition. MPG results can
be biased by the car's intial startup/warmup temperature and a low
battery SOC (which could trigger the ICE to run)
3) Tire Pressure - overinflating the tire pressures by about 9 psi
over the door panel recommendations decreases the tire rolling
resistance
and can increase the fuel efficiency by about 3 to 5 mpg - this is
true for all tires/cars to some degree. Increasing the tire pressure
over
the door panel recommendations can lead to a harsher ride with more
road irregularities being transmitted via the tires this is less of
a problem with good roads and very punishing with poorly kept roads.
Increasing the tire pressure over the maximum tire pressure
designated on the side wall can result in a lost of road
traction(increased stopping distance) especially in wet/icy road
conditions.
4) Route selection - selecting a flat driving circuit/road with no
stop signs would optimize P&G fuel efficiency. Traffic lights along
the route
would require a hypermiler also employ DWB techniques. Route
selection can improve fuel efficiency on any vehicle but would improve
fuel efficiency more for a hypermiler using a hybrid.
5) Timing/Traffiic - While higher MPG can be achieved via a longer
P&G where the velocity is allowed to
drop greater than 10 mph between cycles - in heavier traffic a shorter
P&G cycle with a 6 mph range
would be more practical. .
6) Gallon per Hour Monitoring vs Velocity - From what I noticed, the
fuel efficiency of a P&G cycle is dictated more
by the gallon per hour (GPH) peak usage than by speed. Fuel Efficency
(MPG instantaneous) is a trade-off between
instantaneous fuel used (GPH) and the current top velocity (MPH). The
optimum fuel efficent velocity being the
velocity whose kinetic energy translates to the potential energy which
equates to the max distance the vehicle
would coast on the road without braking regeneration if it needed to
come to a full stop. The optimum MPG inst
thus is maximized when the mimumum GPH is used to achieve that max
velocity within this cycle.
HTH
Walter Lee
2010 Toyota Prius III, Blue Ribbon/Dk Grey/ OEM floormats
Washington DC/MD/VA region
Odeometer 7800 miles, 58.0 mpg overall
best tank 66 mpg, worst tank 52 mpg, last tank 52 mpg
(tank = about 9 u.s. gallons of E10, about 500 miles/tank)
Best route MPG (81 mpg/15 miles as measured by a ScangaugeII)
Yokohoma Avid S33 ( 44psi/42psi)
grill blocking top 100% bottom 100%
ScangaugeII (AVG, FWT, GPH, RPM)
XML site map
> 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.