Glide, yes. Pulse? What's that?

Pulse refers to accelerating with the ICE (internal combustion engine) at a throttle setting yielding no arrows to or from the electrical system.

 

Pulsing can actually be more challenging than gliding (if you're trying to do it right). Basically, the idea is to get the ICE operating at higher revolutions, because it's more effecient there. So you quickly accelerate (don't floor it, thats too high) up to a certain speed, then glide back down... the sweet spot of pulsing is when you have arrows only from the ice to the wheels and the ice to the motor to the wheels, and nothing going to or coming from the battery.

 

It doesn't really matter. Again, the whole "deadband" myth is just
that -- whether the battery charges or not during a pulse is ENTIRELY
dependent upon its current state of charge, always seeking 60%, and
where you happen to have it at any given time is not something you
have a lot of control over. The torque and power curves of this
engine are very forgiving, so exactly how hard you pulse, as long
as you're running under load but not reaming it hard, just doesn't
matter a whole lot. Your best bet is to install a tachometer, and
then you can pulse somewhere in the neighborhood of 1800 RPM [for
the lower speed ranges] which will put you right in the sweet spot.
If you can hear your engine and judge that RPM by earball, go for it.
Otherwise there isn't a whole lot on the MFD that's useful, except
perhaps the instantaneous but what's "optimal" there slides all
over the place depending on wheel speeds.
.
Suggest you get over to http://www.cleanmpg.com/ and read Wayne
Gerdes' excellent "pulse and glide" article, with pictures and all.
.
_H*

 

<div class='quotetop'>QUOTE(hobbit @ Aug 18 2006, 08:11 PM) [snapback]305634[/snapback]</div>

The engine map for our engine that I just saw in a presentation linked by ken1784 indicates that the engine is most efficient around 2300 RPM. Is 1800 RPM more efficient due to the PSD at low speeds? Is it to extend the pulse cycles a bit due to losses with engine start-up and shut-down? I haven't verified the accuracy of the engine map.

 

<div class='quotetop'>QUOTE(TonyPSchaefer @ Aug 18 2006, 09:42 PM) [snapback]305756[/snapback]</div>

And Oolong's ears are flattened, clearly a Pancake Spatial Deformer (PSD).

 

At higher speeds, 2300 rpm is about where I see a vacuum decrease
that I attribute to different valve timing. I call that the high
end of the "sweet spot". At lower speeds this tends to happen less.
I did try to do an A/B/A/B highway test of 2200 vs. 2400 rpm, i.e.
just either side of that transition, and the 2400 tests came in
2-3 mpg under the 2200 ones but it wasn't a huge delta. Still,
higher RPM in general seems to chew more fuel -- the hypermilers
all advocate low RPM, the Miller paper referenced above refers to
"negative split" aka "heretical mode" as "forced engine lugging to
optimize fuel economy" ... and my own observations so far seem to
support all this too. So while the engine may have its *theoretical*
peak efficiency on a dyno at higher RPM, it may be that when the
rubber meets the road several parameters change that shifts that
down. For example, where that vacuum rise falls off at the top
varies pretty significantly with vehicle speed, so something in the
ECUs are taking that into account and modifying the strategy.
.
_H*

 

Efficiency peak doesn't mean that is where engine should be run. Running very efficiently at high power is a waste if the HP you need is less. So running slower and with less power and less efficiency will use less fuel.
The greater the rpm the greater the losses. The efficiency increase is wasted if you don't need the even greater power increase.

At higher rpm the losses in the gears are also increased.

Therefore lowest rpm should always be better economy, as long as the torque is adequate, which the HSD takes care of.

My back up generator works the same way. It is a Yamaha, and the engine rpm varies with the load so it is always running as slow as possible. Makes it far more efficient than a fixed rpm generator always running at it's max efficiency rpm.

Running at extra rpms is kind of like driving a car with a big engine. Say you had a choice of car engines:

1 has 3000 HP and is 90% efficient.

The other has 100 HP and is 30% efficient

Which would you pick to cruise along at 40 mph in order to burn the least fuel?

 

<div class='quotetop'>QUOTE(TonyPSchaefer @ Aug 19 2006, 12:42 AM) [snapback]305756[/snapback]</div>

I think I've got the P&G down....

But...

Dang...no matter what I do, I can't get a pix of Oolong on my MFD....

Does Wayne have any Oolong articles????

I loved the bit you wrote about SOC in relation to P&G in another post, Tony!!

Thanks....I'm printing out the link by WG to read....



terri

 

<div class='quotetop'>QUOTE(tomdeimos @ Aug 19 2006, 10:16 AM) [snapback]305820[/snapback]</div>

I thought we were talking about pulse and glide in this thread.

Hypothetically, is it better to produce 20 bhp at 30% efficiency 30% of the time (0 bhp 70% of the time), or is it better to produce 5 bhp at 15% efficiency all of the time? I'm sure the numbers are off, but I thought this is the idea of pulse and glide versus cruising at a constant speed.

 

<div class='quotetop'>QUOTE(hobbit @ Aug 18 2006, 10:31 PM) [snapback]305768[/snapback]</div>

Listen to Hobbit, he is good he is kind. He is analog. He may be picking up subtle differences, that we in the digital world can not see. At the very lest look at what he is saying.

 

<div class='quotetop'>QUOTE(theorist @ Aug 19 2006, 09:40 PM) [snapback]306033[/snapback]</div>

I was responding to Hobbit's comments implying surprise that lower rpm was better for max mpg when max efficiency is at higher rpm.

True in steady cruising or the pulse of pulse and glide. But with pulse and glide you have to weigh the benefits of more pulse to get longer gliding time. So there is an ideal balance somewhere. It is hard to figure where though and most of these discussions neglect much of the problem by ignoring the drive train losses. We really need a simulator for this.

 

Thank you again, Hobbit.

<div class='quotetop'>QUOTE(tomdeimos @ Aug 19 2006, 10:12 PM) [snapback]306047[/snapback]</div>

Thank you. I guessed the difference might be due to the PSD. I suppose the rest of the drivetrain would play a role as well. The engine map may have excluded the exhaust system as well.

<div class='quotetop'>QUOTE(hdrygas @ Aug 19 2006, 10:01 PM) [snapback]306039[/snapback]</div>

I actually cling eagerly to what Hobbit says. I asked about the RPM difference because I wanted to learn more from him. I also worry that a relatively wide open throttle might cost longevity a bit even if it helps fuel efficiency a bit.

 

<div class='quotetop'>QUOTE(tomdeimos @ Aug 19 2006, 09:16 AM) [snapback]305820[/snapback]</div>

I think this needs to be repeated - efficiency and economy are two different things. Efficiency is getting the most power per unit of fuel, economy is getting the most distance per unit of fuel. Car manufacturers have been improving engine efficiency impressively for decades, but have put it into extra power for more performance, not better economy.

Since a gas engine has the highest efficiency under about 80% of max load (if I recall correctly, might be different for Atkinson engine), it will be accelerating the car at that level, unless it's a weak engine for the size of the car. Since the Prius has the battery to help with acceleration, the engine is comparatively weak, but not that weak. You can't accelerate a car forever, so either you go with lower RPMs, or periodically you glide (coast if necessary). It would be interesting to run a suite of tests on a simulator to see what has the best economy. It seems rather well established that pulse and glide is better than continuous low RPM, but the question here seems to be how strong should the pulse be and is engine efficiency the only variable that needs to be considered. I was hoping there was a definitive answer to that. Now it looks like I have to do my own seat-of-the-pants testing until smarter, more diligent people than I have the spreadsheets filled out and analyzed.