driving in EV mode

<div class='quotetop'>QUOTE(efusco @ Jun 9 2007, 09:24 PM) [snapback]458950[/snapback]</div>

Evan,

What I said was:"The only way I can see the EV switch helping in mileage would be a situation where you can increase use of regenerative energy."

This is not a statement of fact, it is a statement of opinion. If I had phrased it as you stated it would have been different.

Now if someone could enlighten me on how the EV switch could increase mileage in other ways other than to increase energy stored from regenerative braking, I would be interested in hearing about it. I guess you have a chance to prove my original assertion wrong.

As far as Ken is concerned, I don't share your opinion. Months ago I asked him a simple question on whether the HCH came with a manual transmission in Japan, and apparentl;y it was beneath his dignity to give a simple yes or no answer.

And no, I do not now drive a Prius. There are still several things about the car that needs improvement, so I will probably wait until the next generation. What I find is that a lot of members here are very sensitive about any criticism of the car, and have a tendency to put down anyone that may appear to criticize the car. I have read the posts that make malicious statements--I am merely trying to increase my knowledge. But also, as a licensed engineer, I don't buy BS, or rude posters. If you expect all posters to worship the car, you may drive away many who want to know more about the car that gets better mileage than any other car in the U.S.

 

Per: The question of whether or how long you've driven a Prius is relevant, because (and you will know this as an engineer) very often real-world experience is contrary to expectations, due to effects one has not taken into account.

Ken explained one way the EV switch can help mileage two days before you posted your comment saying you didn't see how it could: he specifically referred to to coasting during the warm-up period when the computer would not otherwise shut off the engine. During coasting, power is not being drawn from the batteries to push the car.

If you had been a Prius driver, you would have known that during the warm-up period, feathering the pedal alone will not cause the engine to shut down, and P&G driving only works if the engine stops during coasting. The EV switch allows the P&G (hypermiler) driver to employ this technique before the car is fully warmed up.

 

<div class='quotetop'>QUOTE(daniel @ Jun 10 2007, 08:40 AM) [snapback]459120[/snapback]</div>

Daniel,

I can certainly see how the warm-up period costs extra in mileage, however, sooner or later you would have to pay this back. The only advantage I could see would be to drive on electric until you got to a higher speed area, where the engine would warm up quicker to to higher HP demands. However, when you coast, you also lose kinetic energy which has to be made up at a later time. Any time you use battery power, the energy has to be replenished--either by the ICE or regenerative, and regenerative in reality comes from the ICE as well. No free lunch--not even in the Prius!

 

I guess noone can come up with an explanation on how the EV switch can improve mileage?

 

<div class='quotetop'>QUOTE(Per @ Jun 10 2007, 07:07 PM) [snapback]459298[/snapback]</div>

I'll give you one small example of many I have experienced. At the end of my morning commute is a stoplight, usually red, about 200 yards before I turn into my office parking lot. The commute is such that the car is usually not in S4 operation, which means when I give it the gas coming off that light the ICE will remain on until I park the car. Before the EV switch installation I've watched the trip MPG on the ScanGauge drop by about 2 MPG just during that short distance. The first time I tried it there after the installation, trip MPG went up by 1. So I can claim a 3 MPG net improvement, or about 4% of the 65-75 MPG on that commute, just from the effect seen during that one short segment. The minimal battery drain was recovered at the beginning of the evening commute during the car's normal warmup routine, so there was no noticeable adverse effect there.

I can cite other examples, but I've already done so (as have others) in other threads.

 

<div class='quotetop'>QUOTE(JimboK @ Jun 10 2007, 06:55 PM) [snapback]459320[/snapback]</div>

I appreciate your reply! I can see how a short-term use could show an increase in mileage. However, over a tankfull, it seems you would lose mileage using it the way you described. Follow my reasoning if you will:

You use battery power to propel the car. You convert chemical energy to electrical energy to kinetic energy in the motor, each of these steps waste some energy--you cannot convert energy with no loss. Then you make up the lost chemical energy by taking the chemical energy in the fuel, converting it to heat, converting the heat to kinetic energy to electical energy to chemical energy in the battery. Each of these energy conversion steps occur with a loss. Seems like you can see a short-term MPG increase with the EV switch, but with the energy losses involved in the process described, I don't see how it could improve overall mileage. If you can find fault with my analysis, I'm willing to listen!

 

<div class='quotetop'>QUOTE(Per @ Jun 10 2007, 11:26 AM) [snapback]459217[/snapback]</div>

This actually results in worse mileage! It is most efficient to warm up at low speeds, because the Prius is using more battery power during warm-up if you are driving faster. But then, since you do not understand how the car works, your confusion above is understandable.

<div class='quotetop'>QUOTE(Per @ Jun 10 2007, 04:07 PM) [snapback]459298[/snapback]</div>

You keep ignoring that Ken's use does not consume battery energy: It shuts off the engine when no power is wanted from the car.


<div class='quotetop'>QUOTE(Per @ Jun 10 2007, 05:12 PM) [snapback]459327[/snapback]</div>

Here again, your problem is failing to take all factors into account. You said earlier that you are an engineer??? What's relevant here, and many people fail to understand this, is that an internal combustion engine is much less efficient outside a very narrow range of RPMs. I do not know whether you understand the geometry and mechanics of the Prius Power-Split Device. The unique thing about THS and HSD is that it allows the engine to turn at its design rpm regardless of vehicle speed.

Thus the inefficiency of converting chemical energy to electrical energy and then to mechanical energy can be more than compensated for by the improved efficiency of allowing the engine to always turn at its design rpm.

There is no free lunch, as you say. But conventional cars waste such a mountain of energy by their enormously-inefficient engines, that the Prius can come out ahead, by comparison, by eliminating the principal source of inefficiency, even though there are some lesser inefficiencies in the method it uses to do this.

Hypermiling via pulse-and-glide makes use of the peculiar abilities of the Prius. You state that it cannot work. Well, people DO make it work. And they do this by maximizing the effects of those peculiar traits of the Prius I mentioned before. Theoretically, you could get better steady-state mileage just with a much smaller engine. But car buyers want more power than that would provide. And the way Prius addresses this issue, opens up the potential for very high mpg through the erratic driving style of P&G.

Rather than stating, as you do, that the Prius cannot do what it does, a more sensible approach would be to recognize what it does do, and then study the methods it does to do it.

 

<div class='quotetop'>QUOTE(Per @ Jun 10 2007, 05:12 PM) [snapback]459327[/snapback]</div>

The fault is pretty simple actually: gas engines are most efficient when they are run for a longer period of time. the shorter the time the engine is on, the more gas it burns on average. So if the battery energy is coming from a higher-efficiency ICE use, it can be more efficact even with the various conversions.

 

<div class='quotetop'>QUOTE(daniel @ Jun 10 2007, 07:48 PM) [snapback]459346[/snapback]</div>

I think I have a pretty good understanding of how the car works! Ken's example works at the cost of energy that has to be paid back later.
You are saying that the design of the engine/HSD compensates basic thermodynamic and energy conservation laws? Let me guess--you are not an engineer, are you?
Conventional cars were not part of this discussion--certainly the Prius is much more efficient than conventional cars.
I have never said the Prius cannot do what it does (does that even make sense?)
You may want to review Eric Sweden's post--he has a much better understanding of the basics of energy use in the Prius and the effect of the EV switch.

<div class='quotetop'>QUOTE(Phoenix-D @ Jun 10 2007, 07:50 PM) [snapback]459348[/snapback]</div>

No energy conversion used in the Prius comes at 100% efficiency. You will always have a loss any time you convert.

I am still waiting for someone who can give me a fault with the analysis and explain how the EV switch can improve mileage other than for short distances.

Seems to me it would just be neat, as some posters have said, to use it in certain situations, but I find it very difficult to believe it improves overall mileage. Frankly, Once I get my Prius, I will probably get an EV switch!

 

<div class='quotetop'>QUOTE(Per @ Jun 10 2007, 07:46 PM) [snapback]459421[/snapback]</div>

One nice thing is that to activate the EV mode all you need is a temporary short to ground from a certain pin (the software is already in the Prius). This means that you don't have to spend a lot of money (for the OEM switch or Coastal's) to get it operational. You can convert the "Flash To Pass" arm or install a button of your own.

 

<div class='quotetop'>QUOTE(Per @ Jun 11 2007, 11:46 AM) [snapback]459421[/snapback]</div>

You didn't understand my comments correctly.
It doesn't be paid back later.

Ken@Japan

 

Per,

You have rephrased your question halfway through the thread. You switched from "how does the EV switch inprove mileage" to "how does the EV switch improve mileage other than for short periods".

In the end, the switch can only improve mileage for short, specific periods. This leads to an overall increase in a tanks average mpg.

It is not a magic mpg button, and no one is implying that it is. However, the overall operation of an engine, especially a Prius engine is complicated. I believe there are 5-6 warm up stages in a prius. The all affect the operation/cooperation of the Prius engine and elec motors. Sometimes the operation of those devices is to maximize fuel economy, and other times it is to minimize emissions, etc, etc. The switch helps you control those warm up stages a bit, in order to maximize fuel economy.

Yes, I am an engineer. I love my Prius. I am happy to argue about its pluses and minuses. Every car sold in the world had good things and bad things about it.

 

<div class='quotetop'>QUOTE(Per @ Jun 10 2007, 08:12 PM) [snapback]459327[/snapback]</div>

I'm not the one to find fault with your analysis. In fact it seems to make sense to this relatively uneducated mind. The problem is that I don't have the technical knowledge that you and many others here have. I have to trust the education, reasoning, and results of others, validated by my own results.

So all I can bring to the discussion are results. I can tell you that after the EV switch installation I have seen what appears to be a modest improvement in fuel mileage for many of my regular trips, the mileage for which I have been watching quite closely for months. My current tank so far is my best ever. If there's a payback, I have yet to notice it.

Granted, I haven't done carefully controlled scientific studies. I will acknowledge that my results can be attributed to some other variable(s).

 

<div class='quotetop'>QUOTE(desertbriez @ Jun 7 2007, 12:19 PM) [snapback]457398[/snapback]</div>

I believe I get a small MPG boost from EV mode at startup. The ICE will run for warmup at startup. I want that to run under load, so that I'm using the gas for something other than warming the engine. I don't want that to run as I'm idling out of the neighborhood and standing at a stoplight. I use EV mode to get from my parking place to the point where I am in the flow of traffic. Obviously, that has to be a pretty short distance for the energy losses from discharge/recharge to be less than the efficiency gains from running the ICE under load. But a minute or so of slow-speed EV seems OK. I seem to be able to replace that initial 25 mpg bar with a 35+ mpg bar when I start in EV mode.

With regard to battery temperature, yes, I believe (based on this past week) that if the car sits and bakes in the sun on a hot day, you can't get it into EV mode. Same reason the ICE runs more often when it's really hot, even with the AC off -- I think the Prius is reluctant to make a heavy current draw when the battery temperature is up.

 

The EV switch, used properly, can improve mileage NOT by contravening basic thermodynamics, but by fine-tuning, or over-riding the computer's decisions of when to run the engine and when not to.

As I've noted above, the engine is most efficient in a very narrow range of rpms. Thus it is sometimes more efficient to run on battery power and re-charge later from the engine, BECAUSE THE INEFFICIENCY OF RUNNING THE ENGINE SUB-OPTIMALLY CAN SOMETIMES BE GREATER THAN THE INEFFICIENCY OF AN ADDITIONAL CONVERSION OF MECHANICAL-TO-ELECTRICAL-TO-MECHANICAL ENERGY.

The Prius achieves very great mpg because of the way it manages engine rpm and balances the various efficiencies and inefficiencies of engine and motors.

But there are a very few occasional circumstances when the computer program is less than ideal, and then an experienced driver can achieve very slight improvements by occasionally overriding the computer's decision, and using the EV switch to shut off the engine. Ken gave one example, and there are others.

If I understood you (Per) correctly, you are insisting that the hypermiling technique invented by Japanese Prius drivers and described by Ken, cannot work. But the experimental results are that it does work. And it works, not by violating thermodynamics, but by using the engine only within its most efficient range, and substituting battery power when that would be LESS INEFFICIENT than the engine.

 

<div class='quotetop'>QUOTE(Winston @ Jun 11 2007, 11:01 AM) [snapback]459517[/snapback]</div>

Winston,

It is not as much as rephrasing the question as trying to pin down the benefit of an EV switch other than the neatness of driving in all-electric mode.
Basically what we are talking about is conservation of energy, and the only energy in the Prius comes from the gas tank.
Any time you use battery power, you end up with energy conversions as described above, which are never at 100% efficiency, so there is a net loss. When you coast, at one time you have to accelerate back to speed, and use energy.
The original poster asked about the benefit of the EV switch, and the only way I can see any overall mileage benefit would be to deplete battery energy prior to a downhill stretch so you can benefit more from regenerative energy. Once the battery is full, you can't store more energy, and potential regenerative energy would be lost. In other words, you have to drive smarter than the car can by itself, and so far I have not seen any examples from owners that does this that hold up to basic physics and thermodynamic principles.
Daniel, I can see how shutting off the engine when it is not running efficiently could help mileage. As I said before, it seems holding off on starting the engine until it is under heavier load will shorten the warm-up period, as Chogan stated. However, it would seem this would have a minimal impact on mileage.

 

<div class='quotetop'>QUOTE(daniel @ Jun 11 2007, 12:19 PM) [snapback]459579[/snapback]</div>

I guess all we can hope is for Toyota to fix this glitch in the next version--I'm definitely going to have to wait till next year. Perhaps they will even put a switch in for the regenerative braking as well, so you don't have to worry about feathering the accelerator.

 

<div class='quotetop'>QUOTE(Per @ Jun 12 2007, 02:53 AM) [snapback]459611[/snapback]</div>

The gas/electric hybrid vehicles are not for hypermilers, but for more than one million normal drivers.
People only need a steering wheel, accelerator pedal and brake pedal.
My bet is Toyota won't put a defeating regenerative braking switch. We'll see the result next year.

Anyway, I hope Toyota will install following function...
http://privatenrg.com/#terrainfollowing

Ken@Japan

 

<div class='quotetop'>QUOTE(ken1784 @ Jun 11 2007, 01:12 PM) [snapback]459621[/snapback]</div>

The trouble is, a lot of normal drivers want more than a steering wheel, brake and accelerator out of a car.

 

<div class='quotetop'>QUOTE(Per @ Jun 12 2007, 03:20 AM) [snapback]459624[/snapback]</div>

Please tell us how do you think that how many drivers want the defeating regenerative braking switch?
There are more than one million Toyota hybrid drivers world-wide or more than 500 thousands drivers in the US.

Ken@Japan