Quantitative Pulse and Glide - Page 2

 On 2/3/2011 12:46 AM, Bruce Richmond wrote:

http://groups.google.com/group/alt.autos.toyota.prius/msg/b5b72484521c684d?hl=en

You backpedal well.

 
I'm less interested in what people do in traffic as there are plenty
of 'bad examples' out there. For example, this morning there was an
upscale sedan doing between 40-45 mph on a cross-town, 50 mph, divided
road followed by a service van towing a trailer that was rocking back
and forth. Traffic was backed up behind them and I took advantage to
follow the van. So I got the mileage advantage by exploiting the poor
judgement of two other vehicles . . . sweet. I parked at work with
just over 50 MPG indicated and the temperature was just under 40 F.

What I still don't see posted is anyone else's pulse-and-glide
performance over the same route, same average speed versus the
constant speed equivalent. This test can be conducted late at night,
say after midnight, if nothing else to answer the question:

"What mileage improvement does PnG provide over the equivalent,
constant speed?"

As for the safety aspects, there are enough poor drivers we don't
really need to 'flog our own.' But if someone thinks PnG is so great,
answer the question. Give some quantitative numbers:

a) minimum speed - glide end
b) maximum speed - pulse
c) equivalent constant speed
d) MPG in PnG
e) MPG at constant speed

Several years ago, some folks spent a week in Oklahoma driving section
lines in a Honda Insight endurance test. Using their mileage log,
they'd been driving at a constant speed equivalent of 16-18 mph. This
also corresponds to the maximum speed range of a Prius (and probably
quite a few other hybrids.)

If PnG boosts the equivalent constant speed mileage say by a factor of
two:

20 MPG @40 mph - constant speed
40 MPG @40 mph, 5 to 75 mph - pulse and glide

(40-20)/20 = 100% improvement

This would be a game changer but I never measured more than 12%
improvement. In contrast, the SAE paper claimed some curious numbers:

89.1 MPG @25 mph - constant speed (0.0% SOC decrease)
128.9 MPG @25 mph, 20 to 30 mph - pulse and glide (0.5% SOC decrease)
(128.9 - 89.1)/89.1 = 44.7% improvement

81.0 MPG @35 mph - constant speed (0.0% SOC decrease)
151.5 MPG @35 mph, 30 to 40 mph - pulse and glide (1.5% SOC decrease)
(151.5 - 81.0)/81.0 = 87% improvement

80.9 MPG @35 mph - constant speed (0.0% SOC decrease)
99.9 MPG @35 mph, 30 to 40 mph - pulse and glide (0.5% SOC decrease)
(99.9 - 80.9)/80.9 = 23.5% improvement

What I suspect is many lay reports about how great Pulse and Glide
performs may be just the discharge of the traction battery providing
the additional energy that is not counted in the total energy
picture.

So the challenge remains, the question remains:

What is the payback of Pulse and Glide versus a constant speed?

BTW, a route will hills changes the physics. Climbing can move the
engine into power regions that are fuel inefficient. In reality, any
test should be against a constant ICE power setting and let speed
follow load. But more of this advanced topic later ... if we can stop
bashing poor driving including going the minimum posted speed limit on
an Interstate.

Bob Wilson

 
Most of my daily route is hills with stop lights  at the top or at the
bottom of the hills.  If I know can make the light by speeding up
it sometimes is more fuel efficient to speed up just so I can make
the light. If the light is not visible until I get over a hill - it is
often
more fuel efficent to limit the speed to less than 30 mph for I get
to the top of the hill.  The main challenge is to avoid using fuel
to create kinetic energy that would be wasted if one has to stop.
There are only a few sections of flat road where I can do a classic
P&G but if there isn't any traffic - I can increase my mileage in
those sections by either doing a P&G or doing a SHM if the
SOC has atleast 3 to 5 bars. When the SOC is only 2 bars,
then P&G and DWB are the only options I have. Warp Drive
and SHM take almost no skill.  DWB and P&G require much
more skill, timing, and luck.


The data of your experiment would be even more useful
if the P&G cycle were from 50 mph to 65 mph range because
then it would useful for the highway. Late spring I do
a 600 mile plus trek from DC to Michigan via the super highway.
The last time I did it I experimented with using regular non toll
roads. The 2010 Prius got 5 mpg better mileage on the high speed
toll roads (58 mpg, OH/PA Turnpike) than on the slower speed
regular  non-toll roads ( 53 mpg - via Garmin Nuvi designated
route). The weather was mostly sunny and warm, my tire
pressure was set at the normal 35psi /33 psi - but it surprised
me that the lower speed non-toll roads were less fuel efficient.
This year I will use only  the high speed toll roads (OH/PA turnpike)
but I plan to test out and monitor the use higher tire pressures
44psi/42 psi at these speeds.  I will also have a Scangauge II
to monitor my progress. I also hoping to hone my
P&G skills then.

 . . .

What were the equivalent speeds?

This is the classic problem of PnG advocates who consistently report
"MPG" without the "mph." Mileage claims without:

o "mph" for each test, one PnG and the other the equivalent constant
speed
o a record of altitude, temperature and wind effects

If you live within a reasonable distance of an interstate, it would
only take four runs, two with PnG and two with the equivalent steady
speed, to quantify the effect. Many interstates have exits at least 10
miles apart, the perfect distance for doing a compare and contrast.
Then you'll have some data others can use.

BTW, about a year ago, I tried comparing PnG at highway speeds, 45-70
mph, to the equivalent constant speed, only to find a significant loss
of MPG. The test was conducted between 2:00-5:00 AM between Decatur
and Courtland on a divided highway. Given the increased driver load
and poor, high speed results, I can't find any reason to use it.

Good Prius friend Hobbit said it best that the goal is to operate the
engine in efficient modes and that can be easily monitored using
engine rpm. The surest path to higher MPG is to drive slower down to
the 15-18 mph range. Below this speed, the vehicle overhead becomes
the limiting factor.

Bob Wilson

 
I could drive a constant 55 mph on the toll roads for
several hours. but the non-toll roads had stop signs and
traffic lights every 15 minutes to 30 minutes so my
average speed dropped to something closer to 40 mph
on the non toll roads even with light traffic. The non toll
roads were less efficient because of the more frequent
acceleration and deceleration events ( where I would lose
kinetic energy every time I had to stop and and where
I had to spend extra fuel to accelerate to a proper speed)
Also some of the non toll roads were no well maintain
while the toll roads were for the most part well maintained.
So the rolling resistance/drag was significantly more
on the non-toll roads. My Garmin Nuvi generated my
alternate non-toll road route from Maryland to Michigan.
So while I saved a small chunk of change using the
non toll roads - I spent slightly more at the pump ( a
decrease in about 5 mpg)  and had to deal with a
much rougher ride







P&G  works best between 25mph to 35 mph (when wind resistance
is not a big factor) and the terrain is flat or nearly flat.  I use
it  on
several segments of my commute when I have about a 1/2 to 1 mile
segment of flat surfaces or gentle downhill.  While P&G is only
useful in a limited driving environment - it has the advantage
of being independent of the traction battery's SOC


In "ECO" mode, the Prius does not have much torque and
it's heavy curb weight becomes a  liabilty when going
uphill. In Maryland, my testbed road is a stretch of Norbeck
Rd.  Westbound Norbeck Rd (Rt 28) from Georgia Ave
(Rt 97) to Rockville Pike (Rt 355).  Westbound Norbeck from
Muncaster Mill to Baltimore Rd is basically a gentle downhill route
where the Prius FE increases from 35-45 mpg to 50 mpg to
63 mpg. However, going westbound on Norbeck Rd after passing
the Rock  Creek Trail bridge there is a steep uphill climb (about
12 degrees uphill ) to Avery  where the Prius fuel efficiency
can rapidly drop. At the top of the hill at Avery there is a traffic
light which might require a full stop..  My current technic is to
give a initial pulse as I am going downhill to achieve a desired
top speed is upon arriving at the bottom of the hill ( e.g. 45
to 55 mph).  If I think I will have to stop at the traffic light at
the top of the hill my max speed is 46 mph is I think I will
drive through the traffic light at the top of the hill my max
speed at the bottom of the hill is from 50 to 55 mph.
Before the Prius has climb up the next hill, I start
up the gas engines about two seconds  before the Prius
needs to climb up the hill ( I start a bit earlier because my
Prius in "ECO" mode and this compensates for the "
ECO" throttle delay ). I am using  a Scangauge II to
monitor how much gasoline the ICE is burning.- on the uphill
climb I am trying to maintain the initial speed as long as I
can without having the the gasoline burn rate exceed over 1.15
gallons per hour (GPH).  This gasoline consumption rate limit
the ICE to roughly 1200 to 1400 rpm, wrt to the HSI display
the HSI bar will be slighty pass the middle marker ( slightly to the
right of the "C" of the "ECO" indicator).  If I allow the velocity to
drop about 15 mph ( e.g. from 50mph at the bottom of the
hill to 35mph at the top of the hill). then I have minimized
the negative impact of the uphil climb on the route's fuel
efficiency. If I attempt to maintain speed while going uphill
then there is a  signifcant impact (e.g. loss of  7 mpg)
on that segment'  fuel efficiency.  At the bottom of the hill,
before starting uphill, my AVG mpg during the summer is
normally about 58 to 65 mpg. After climbing uphill, if I
try to maintain a speed from the bottom of the hill my
AVG drops to about 52 to 56 mpg.  After I climbig uphill,
if the Prius throttle is restricted to less than 1.15 GPH
and the speed is allow to gradually decrease then the
AVG drops to about 58  to 62 mpg.   Even if the Prius
had an initial speed of 50 mph at the bottom and the
traction battery SOC was at 100% and I have my tires
overinflated to 44psi/42psi --  the Prius electric motors
cannot pull the Prius to the top of this particular hill
without the ICE.  All my number, represent ideal
driving conditions, when the temperature drops - my
fuel efficiency drops significantly.  (9_9)