Dave,

When the pack gets low enough it stops depleting? No, that is when it is too low!! Below 2 bars of battery pack charge, auto stop no longer works, and you no longer get assist, but the battery pack still depletes, especially in forced auto stop mode. I have often depleted it until there are no, zero, battery charge bars showing, nada. And in glide mode with the engine off, the 12 volt is on its own running the radio, fan, instruments, and at night, the lights, and it is not being supported by the pack. When the 12 volt gets too low it does not have even enough power to engage the IMA and battery pack, let alone start the ICE. At that point all you can do is get out the jumper cables. I know, I have been there many times, testing the limits of the HCH.

As far as lean burn is concerned, despite all of my experiences in the HCH, I don't really know when the HCH goes into lean burn mode. I do think, however, that I am in lean burn above 30mph, accelerating in 4th gear until 42mph, then 5th gear (manual transmission) when I have green battery charge bars showing. But maybe I don't know what I am talking about.

In any event, whether it is in lean burn or not, P&G in the HCH gets better mpg than in cruise control at any speed. In cruise control mode, I prefer 44mph (55mph on an interstate) for a good balance of mpg, flow of traffic and going fast enough and with enough rpms to deal with the hills. I don't even know if 44mph gets me into lean burn mode, but the FE is better there than any faster.

Bob

 

This is pretty interesting.I still think that the reason that P&G works is because you pay the internal friction penality of the ICE motor with as few RPMs as possible,which would probably mean that it will cost less ICE friction loss accelerating to a speed and shutting the ICE off-or dropping the RPMS a lot like the Hinda does.This would explain why rjbarlows hard acceleration "works".Normally hard acceleration would be a killer,but not in this case.For example-a gasoline motor only car
Accelerate to 60 mph with a 4 cyl-take 12 seconds at constant accel.You will probably average 4000 rpms over the 12 seconds.It will cost 800 rpms,you will travel maybe .1 mile.A crude guess is that you could glide at least another .9 mile,and the total one mile trip would average ~30 mph-2 minutes-.
Now start the trip at 30 mph-your Toyota Corolla will be turning about 1500 rpms to do 30 mph.It will take 2 minutes to go 1 mile.It will take 3000 revs of the motor to go 2 miles.
PG takes 800 revolutions-to go 2 miles in 2 minutes
Steady speed-3000 mph- takes 3000 revolutions to go 2 miles.
Granted those 800 REVs will be higher friction revs-higher piston speed,and more pressure on rings from increased cc pressure.
I can't see any reason for the P&G to work otherwise.Pay the internal friction and general inefficiency penality of the ICE motor with as few Revolutions as possible ,and in the range where the ICE motor is efficient-close to full throttle near the torque peak where you are getting good volumetric efficiency.Of course you don't want to go way above the torque peak to near the hp peak-too inefficient.
The numbers used here are rank guesses to to help my thinking out loud.I didn't really do the arithmetic to show that 800(hard revs) revs cost less friction than 3000-soft- revs-I'm not up to chasing down the formulas for that.
In short get up to speed using revs near the torque peak with fairly heavy throttle pressure(doesn't the Prius CVT motor do essentially that?),and then do whatever it takes to get the ICE to go off,or to drop the revs waay down.
The aerodynamic forces seem to be against P&G-takes 1.33 squared times the power to overcome aero forces at 40 mph vs 30 mph-this is 1.7 times the power.The other forces are generally just proportional to speed-not the square of the speed.The payoff has to be the decreased revs.If 1 hp is the power it takes to overcome areo forces at 30 mph-it takes 1.77 hp at 40 mph and .44 hp at 20 mph.
I think the decreased revolutions have to be where the payoff is on P&G.Now,I could be wrong-not 1st time.Thanks.Charlie

 

[QUOTE=solecondad]I've found true lean burn over extended periods of time, i.e. maybe 3+ miles of 40-50 MPH roads w/o heavy traffic and w/o any stops has come very close to equalling P&G over the same period. Then again, my tests are slighted as I only enter P&G or execute FASs on those same roads when traffic conditions do not allow for a steady optimal lean burn pace, i.e. they're worse conditions but yield equal results. If I've got all the space in the world and want to get from X to Y in decent time, I'm totally content with lean burn. Either method makes the same argument for hard acceleration, as it takes you into lean burn quicker and allows for longer tenure there.

I myself enjoy making use of both strategies depending on traffic. I know FASs shouldn't be recommended for the noob in heavy traffic conditions, but that's where I believe there are able to make the highest relative gains over other techniques. If traffic is light and speeds are right, I rarely reboot.

 

Hi All:

___Some generic discussion of the P&G model can be found at the following: Lakedude takes the Gloves off …

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

 

This discussion seems to be about full-hybrids (e.g. HCH).

Any idea if the same technique would help the mild hybrids (e.g. HAH) where the ICE never switches off (except when coming to a stop) so the savings in ICE friction won't apply.

My commute was 40 mile round trip, mostly freeway but I will be doing a 2000 mile road-trip over Thanksgiving. I willdo the first oil/filter change before I go ( a little early @6500 miles) but wonder if a P&G technique will also be worth trying (up till now I've been a gentle as I can bear on up-hill climbs, and have needed the AC on most of the time here in the humid NC summer)

 

We cannot P&G easily in the HAH because we cannot shut off the ICE and restart it without getting locked out of overdrive (4th and 5th) unless you restart at or below the 1st gear range. So you get stuck in 1-3, with the check engine light on.

(The HCH guys have to manually shut off and restart the engine too, but the CVT and MT don't have the interlocks our AT does)

The best we can do is go into neutral and coast that way, then reengage and pulse back up, coast again, etc.

It is very hard to pulse on 3 cylinders at the lower speeds P&G is often used at. The HAH will almost refuse to go into eco mode, depending on gear selected, at these lower speeds (or at least its tricky to keep it in eco mode). The cost of pulsing, usually on all 6 cylinders, outweighs the benefit of the short coast. You're talking 6-10 cycles per mile- that is a lot of work for the driver, too.

However we have the eco mode trick up our sleeves that nobody else has. I keep it in eco mode at almost all costs and then glide in neutral on any downslope I find. That gets me 41-43mpg, 45 if I'm lucky.

 

Hi All:

___I have been racking my brain for quite some time on this and I have no idea what I am doing anymore … I was comparing the non-hybrid Accord in a high speed P&G to the Prius II in a low speed P&G and the numbers just do not add up when taking the Prius II up to the higher speed P&G of the Accord?

___The Accord is a 3,300 # mid-sized sedan can achieve > 70 mpg in a high speed P&G with an average speed of ~ 55 mph (45 on the low and 65 to 70 mph on the high)? Besides terrain balancing, D-FAS and FAS to achieve the P&G, I am also amongst traffic side drafts to aid that much more … The road, tires(s), bearing(s), ICE rotational parts, and aero-drag effects with the pulses up to 65 - 70 mph have to be horrendous however … The Accord’s instantaneous hangs in the 30 mpg range during the high speed pulse and I estimate ICE-Off vs. ICE-On at ~ 2:1. It just shouldn’t receive that high of FE at those speeds compared to the much cleaner Prius II.

___In the Prius II “Marathon Attempt”, the instantaneous during a “hard pulse” would hang in the 17 - 50 mpg range with a max ICE-Off Time vs. ICE-On of a bit > 3 to 5:1 for 110 + mpg. The speed range was much lower with an 30 mph average w/ the stops and slows for lights.

___A quick study in order to calculate Wh used to sustain 110 mpg from a Prius II in a P&G.

Prius II’s thermal efficiency at 2,500 RPM for example is ~ 35%.

1 gallon of gasoline contains ~ 114,500 Btu’s.

Conversion: 3,413 BTU’s/kWh

1 gallon of gasoline = ~ 33.5 kWh

@ 35% efficiency we have 11.7 kWh via 1 gallon of gasoline.

11,700 Wh/110 mpg = 106 Wh/mile traveled.

___When I plug in the speeds for 55 mph in the Prius II using MPH vs. Wh/mile, the Prius II’s appears to fall far short of what the Accord can do at these much higher P&G speeds?

55 mph = 213 Wh/mile

@ 35% efficiency we have 11.7 kWh per 1 gallon of gasoline.

(11,700Wh/gallon)/(213 Wh/mile) = 54.92 miles/gallon

___How can an Accord achieve higher FE in a high speed P&G vs. the Prius II at a steady state …

___Ahhh, never mind, I see A/C was on in the Prius II calc’s …

___Anyway, maybe someone can use the following to model what the hell is going on inside of a P&G? It has something to do with climbing hills with the inefficient ICE and gliding for longer periods down them with ICE-Off but I do not know what the answer is? My Series or parallel hybrid scenario’s I have been pushing as of late may be all messed up with the above as well???

___RJ, at ~ 6 bars SoC, the HCH-I will stop assisting and will only force charge on the pulse which is exactly what it should do for sustainability.

___I am beginning to ramble like an idiot given the time I was trying to figure out the key to P&G over the past 2 or 3 hours. I think I need a break

___Good Luck

___Wayne R. Gerdes

 

Hi Wayne,

Using Wayne Brown's (WB) simulator, the Prius II is expected to acheive a maximum MPG of about 80 MPG in the 30 - 35 mph range. As you know, the Prius does better than that. I have always thought that the discrepancy lay in the fact the WB obtained his data at steady speeds, in which two additional energy expenditures occur as compared to P&G: 1, More of the ICE->wheels mechanics are creating friction a larger fraction of the time; and 2, the Prius II ICE in the power output range required for steady 35 mph driving of around 4 kW is inefficient.

This last point is a bone of major contention, actually; and as AFAIK, has not been resoved to everybody's content amony the Prius intelligentsia: how good are the Prius brains at lower power output demands. Clearly, the algorithm allows the ICE to produce more power than is demanded by the driver, and shunt the excess to the battery for later consumption, but the efficiency is I think uncertain. And of course the shunting on energy to and from the battery has it's cost.

Bottom line: to the extent that steady rate driving is below the sweet spot of the Prius ICE, P&G will show benefit.

--
Two nitpicks with your analysis to consider:
I have seen estimates of max Prius ICE efficiency of 38%, although there is interplay between rpm and torque, so pinning down exactly where it is has eluded me.

I have to believe you are constitutionaly incapable of NOT drafting , so your accord MPG data may require a fudge factor.

Cheers -- Eric

 

Hi EricGo:

___The only thing I have accomplished with the above post is give myself a headache A Glide should be just that, a powerless coast down but it is not in the Prius II. I included full 213 Wh/mile even in the glide although you won’t use 213 Wh/mile unless you maintain a steady speed and the ICE will be on at that speed of course. There is a lot more current flowing in the Glide below 41 mph that I cannot account for and I have the feeling it is MGSet synch current? In the Accord, a FAS is close to a powerless free coast as possible although again, it is in the coast down only … Add in a D-FAS after every third of fourth pulse and she does allow some incredibly long Glides at way over the limit speeds.

___In the Insight it was a powerless glide in a FAS as well but I never received anything but a traffic side draft which gave her a few more mpg’s. I held onto lean-burn so hard I would not let it go. Lean-burn was that good but was only maximized at much slower speeds. Boy do I wish I had my Insight for a few weeks to see what she would be worth knowing what I do today

___I have to think about this some more because my serial or parallel hybrid calc’s are falling apart with a P&G’ed ICE behind a steady speed EV. I just do not know what the answer is right now although I do know the Prius II’s 1.5 L ICE is way oversized for the envelope I would drive her in if I owned one

___Good Luck

___Wayne R. Gerdes

 

Wayne, if the glide in the Prius is wasting power, how do you explain your fantastic marathon results ? If I remember correctly, your instrumentation told you what fraction of the drive was in glide. If you accelerated at a steady MPG, some quick calcs should lay this question to rest.