New way to use EV mode to increase MPG?

<div class='quotetop'>QUOTE(grasshopper @ Jul 3 2006, 12:30 PM) [snapback]280605[/snapback]</div>

Snicker.... you trying to make it sound like a *bad* thing?

 

<div class='quotetop'>QUOTE(Three60guy @ Jul 3 2006, 09:47 PM) [snapback]280842[/snapback]</div>

Wrong. Because the alternative (no stop signs or traffic lights) will result in grid block and nobody goes anywhere. And all those cars idling and burnig gas. And even the Priuses burning gas occasionally to keep the SOC up.
<div class='quotetop'>QUOTE(Three60guy @ Jul 4 2006, 10:37 PM) [snapback]281286[/snapback]</div>

You are partly right, but your reasoning is not applicable to the situation. Here's why:

The electric motor is more efficient at low speeds, and that is why when you use the gas engine at low speeds, it mostly drives MG1 as a generator, and the power goes directly to MG2, which acts as a motor, and all the time the gas engine is operating at or near its most efficient rpm.

But your system uses not merely the electric motor, it uses the battery!!! And the battery is a relatively inefficient storage device (sorry, Darell!) compared to the direct use of MG1's output in MG2. It is precisely the battery charging and discharging losses all of us are talking about, which you are ignoring.

You are also being fooled by those very low MPG numbers when you accelerate using the gas engine, but those numbers apply over very short distances, while the mpg numbers at cruising speed apply over much longer distances. It's like the discussions we had a couple of years ago over those 5-minute segments: If you creep along at 5 mph for 5 minutes on electric and show 99.9 mpg, and then you drive for 5 minutes on a thoroughfare at 50 mpg, you can not average those and claim 75 mpg. You make the same mistake by averaging the low mpg during a brief period of acceleration at slow speed with the cruising mpg later, only in this case you are trying to claim that the acceleration phase is pulling your average mpg down much more than it really is.

It is not the speed of the car that determines whether gas or battery power is more efficient. It is the power demand: at very low power demand the charge/discharge losses are less than the engine inefficiency losses. But at higher power demand, the charge/discharge losses are greater. That's why Toyota designed the car to use the battery when power demand is low, and the gas engine when power demand is high.

You are trying to claim that Toyota got it backwards. Those Toyota engineers are very clever folks. They knew what they were doing:

At low speeds, when electric motors are more efficient, MG2 provides most of the power to the wheels. But when power demand is high, that power comes from the gas engine by way of MG1. It is drawn from the battery only when power demand is low. (Or when power demand is so high that the low-torque gas engine needs a boost from the battery.)

Finally, please note that the ultra-high-mileage P&G drivers use the gas engine for accelerating but minimize use of the battery!!!!! They do not use the battery for accelerating. This point alone should convince you that your method is counter-productive.

Sorry for shouting. But that point offers experimental proof, much more reliable for its extended duration than your very brief observations of the very misleading MFD.

 

I only read the last couple of posts -- so apologies if this point has been belabored:

A low mpg reading at low speed does not an inefficient engine make. It just reflects the low speed !

If you were to look at the electricity use in EV on the MFD, the same picture would emerge. Consider power use at 20 kW: initially at a speed of 1 meter/second, and then later at a speed of 2 meter/second. The MFD would show that the car used 20 kWs/meter initially, but only 10 kWs/meter at the higher speed. Twice as efficient battery/motor use at the higher speed ?? Nah. Just a faster moving car

360, I have to join the crowd that thinks your technique will yield poor results.

There is *so* much arcane trivia floating around how to maximize FE in a Prius, that I think people get lost in the forest. It all really just boils down to:

1. Don't speed on the highway
2. Anticipate driving conditions (the less brake, the better; and just about NO friction braking)
3. ICE on ? Run it at ~ 1750 - 3000 rpm.
4. Avoid cold engine starts as much as possible by bunching short trips together in the winter
5. Modesty is a virtue -- for AC anyway. Tint for hot climates, and a nice shade tree to park under are great in the summer; in the winter add a sweater and gloves (and heater off when ICE off, for the ambitous)

That is pretty much all I do, anyway. Our Prius FE is not marathoner spectacular, but would probably satisfy most owners. Details in my sig.

 

Speed is a non issue here as far as efficiency is concerned. The motor and even including the battery can and is more efficient in some cases than the engine use, but this is determined by the load not the speed one is going.

Speed is a secondary effect in that faster steady speeds cause more loading.

So whether to use EV to accelerate in a given case has much to do with how fast you want to accelerate. It also has to do with if you are going a bit uphill or down hill. Finally it has to do with if accelerating in EV can be done for a short period and eliminate an extra engine start up due to an upcoming down grade where you can coast.

You need to consider all of this to calculate which is more efficient. But Toyota has presumably done most of this. That is why accelerating on electric can be done without the ev button but only very slowly.

The one part Toyota can't pre-calculate for you is the issue of engine start ups. Besides my example above, there is the traffic jam where the engine might be starting and stopping many times a minute without an EV button, or extra careful accelerator use.

For those with can view or other current meters I think a key value is to look at what Toyota does for current limits in non-EV mode and then use the same limits for using EV but still allowing some higher currents for very small time intervals. You only need to watch the big red blob on the graph once when the engine is starting to get an idea where the tradeoff might be.

Keep in mind if the battery and motor together were less efficient than the engine at light loading, Toyota would not make the car able to cruise at 40 mph in electric mode. And if you can do that you can equally get better efficiency with EV mode accelerating up to only 30 mph ie using the extra air drag saved at the lower speed to accelerate with.

And also note the new Prius will accelerate in EV effectively more full time with the new better battery system.

There is one other thing I can think of and that is whenever you use battery power you have to consider what is coming next.
For example if you have a choice of using battery to accelerate for 30 seconds, or hold your speed on a slight down grade not good enough for coasting, for 4 minutes, clearly the latter is the better use of the electric mode. In other words with x amount of battery power your best use of it will always be over the max miles. Then it has to be put back in at a point where that is not too costly, like not stopped at a traffic light.

Since I virtually never can pulse and glide, due to terrain and traffic I maximize my EV and electiic mode use based on this, and to keep it all manageable I generally try to stay electric or use EV when starting up going down hills, and use engine power to go up hills. Where I can drive under 40 mph for extended periods I regularly can get over 70 mpg doing this.

Now if I get up at 4 am and go for a drive when there is no traffic I can do better using the pulse and glide some.

 

Ok, as I understand, the Prius is almost always generating electricity, even when running on the highway at a cruising speed. The only way for MG1 to not spin freely and for power from the ICE to go to the wheels is if a current is drawn from MG1 or if a current from the battery is applied to MG1.

So, what happens at highway cruising speeds if the battery is full? Does the Prius stop drawing current from MG1 and instead source current to it from the battery? If so, then you are throwing away electricity that was previously generated.

So, is it that far fetched that this cruising speed generated electricity that might otherwise be discarded, might actually be used to replenish the charge that was consumed during acceleration?

Of course, this would require that you don't use EV for so long that you run the battery down below 4 bars or so, at which point the Prius goes into panic charge mode, refuses to consume from the battery and really revs up the ICE. But, I would think that if you only consumed a bar or so, say from 6 to 5 bars, or 6 to 4 bars, during your acceleration, then it might be conceivable that you could regain it at cruising speed without taking a milage hit.

 

When your butt recovers, be sure to come back and follow up with
*LONG-TERM* observations. If you're right, then the whole concept
of a parallel hybrid will be knocked into a cocked hat.
.
_H*

 

<div class='quotetop'>QUOTE(Marlin @ Jul 6 2006, 04:15 AM) [snapback]281568[/snapback]</div>

Where is your MG2?
The combination of MG1 and MG2 works as an electric type of a torque converter.

The target SOC is about 60% and the battery never been full at highway cruising speeds.

Ken@Japan

 

well gee even if i did use EV to accelerate unfortunately, WAAAY too much traffic around here to get away with that. max acceleration in EV mode simply too low. i never speed, especially at street speeds. but i always try to accelerate fairly briskly and then stealth it. works for me

 

<div class='quotetop'>QUOTE(Marlin @ Jul 5 2006, 12:15 PM) [snapback]281568[/snapback]</div>

At highway speed the battery is alternately charging and discharging. The MFD shows it switching back and forth every few seconds, but that's because of its slow refresh rate. CAN-View shows it switching several times a second.

What's actually happening is that 40% of the torque (that's not 40% of the power!!!) is going to MG1 and 60% of the torque is going to MG2 and the wheels. The car then has a myriad of ways to shunt the resulting electricity about, and by controling MG1, to change the ratio betwen engine rpm and vehicle speed. MG1 can generate electricity to send to MG2, but MG2 can also generate electricity to send to MG1, and either can send electricity to the battery, or draw electricity from the battery. The engine can put out more power so there is excess to charge the battery, or it can put out less, so the battery provides some power to the car. The computer sees to it that the battery remains within acceptable SOC levels.

But the bottom line is that on a level highway there will be little net charge or discharge, with the engine providing all or nearly all the power. It's still using the full hybrid system, but does not need to make much use of the battery. It's at slow speeds and stop-and-go conditions that the battery sees more up and down, as it provides a buffer between the high demand for acceleration and the low power needs between whiles.

To answer your question: the battery is never "full" but when the SOC is high (for example after a long downhill) the engine will burn less gas and the car will draw some charge off the battery to help power the car. It's an amazing work of technology

 

If you are going to have a long, steep downhill, where the battery will be recharged by regeneration, then it is indeed beneficial to use all the electricity you can before you get there. We've all always said this.

If the downhill is gradual, such that recharging will come from the engine, I stand by my previous assertion: accelerate using the engine before switching to EV for the steady-speed portion.

 

well we can speculate on how to better use EV or read about someone who also speculated about the best use of the Prius period, then went out and put 1400 miles on to one tank of gas.

in the marathon run he made in which he got 119 mpg, he stated that the only time you should charge the traction battery is during times you need to accelerate. that means gentle NON EV MODE acceleration to cruising speed. with CANVIEW you would know that you charge at about 5-15 amps doing this. now he was in a position where he could do this and maintain 40-50 mpg instaneous... very patient man. this maximizes efficiency and uses the power of the traction battery at a discharge rate of under 30 amps. (best in my experience is around 15 amps)

now this is how i drive to get the better mileage and it works for me. now i dont have the opportunity to drive in this manner all the time. but i do know that i can get 60 mpg tanks by doing this. since this thread started, i started doing this method outlined above as much as possible. i had started this halfway thru the tank with mpg around 55 mpg. see my signature to find out what happened to the last half of the tank.

 

oh im not agreeing or disagreeing with anyone. just letting ya know what im doing. i have tried several different methods as far as manipulating my EV switch, mostly as a means to justify the expense of buying one and have also posted controversial ideas here as well so i know how you are sitting. my problem stems from the lack of opportunity to perform a controlled test for any length of time. i have kinda abandoned hope of trying a few other things simply because i will never really know if they help in my situation. i still do other things that involve short durations, etc.

as far as what works, imm the biggest factor is going to be terrain and traffic. the guy who got 119 mpg did it on a handpicked course. i doubt he could duplicate the feat in even a small percentage of other situations. to me that means that there is most likely no one right answer. there has been a million posts here of people who are not getting 55 mpg and a million answers to those posts by people who are and how they did it.

so why does that not help?? in a lot of cases it does, but there are still some it doesnt. is it driver error?? sure no doubt, when any human intervention is involved, mistakes will be made. but i think that in some areas, 50 mpg on a good day is all you can hope for which leads me to believe there is no one right way to drive the Prius. sure one way on paper, may not be as efficient, but terrain obstacles could be a greater factor

so i say, keep doing what you are doing if you can. i would try it again (have already done what you are doing and results were inconclusive) if i could do it enough to get data to compare. too much traffic in my area to do that though.

i did a test, also inconclusive, using EV at the end of every trip where i knew my car would be sitting long enough to completely cool down. (was done mostly in winter) my thinking was that, why not run the traction battery down?? when i started up again, the ICE would have to run to warm up the car. why not have it do double duty and charge the battery back to 60%. hopefully, it would cause the car to warm up quicker and get my off that 30-35 mpg stage that i see for the first 5-8 minutes of every commute. i do have SOME evidence that the ICE was warming up quicker about a ¼ of the time. but gains were very small (about a minute less time to get to 150º) inconsistent and probably hugely dependent on other weather conditions (l only tracked temps) like wind, solar effects, etc.