Confused by the talk about not using the electric motor

<div class='quotetop'>QUOTE(Olathe Prius\";p=\"99870)</div>

If you can get 60 mpg like Ray can, then go for it! This strategy would not work for me, either because I am too klutzy or my road conditions just don't let me drive much with no arrows. I think it is maybe easier in less densly populated areas, and flatter areas? I also have trouble holding the overdrive mode that gives such great mileage!

I do believe there are speeds where the battery mode is better efficiency with all it's losses than running the engine, or else Toyota would not have programmed it to do this.

I would not worry about the staying green. My car won't except in cold weather! The set point changes with conditions. So maybe try to stay at the current set point. This time of year mine seems to be at 5 or 6 blue bars.

Bottom line is what works for you best is what you should do. The cars programming may or may not vary much but terrain and traffic definitely affect what works. And I find the bar graphs quite useful in testing things. When I want more accuracy I just reset my mileage meter as often as needed, or I just calculate trips leaving that on tank mileage.

Hope everyone knows how to do that, but a friend of mine didn't so I will mention it here:

With tank mileage and miles recorded at intervals, you can easily get gallons and miles for each leg of a trip you are interested in and then go back again to mileage for each leg. Thus making up for the bar graph only really working at constant speeds.

 

I can definitely agree that minimizing braking and slow regen braking is critical. My best ever trip to work was 78 mpg. I was on battery mode only about 2/3 of the trip. And when the engine ran I got like 30 mpg. I have not been able to duplicate this since! I try, but it doesn't work. The reason was I happened on a day with minimal traffic, and I was able to hit most every light so even though I had to slow a bit in places, I never had to stop. On this route the chances of this happening again are remote.

For another example: I sometimes stop, like once a week in a McDonalds drive through to pick up breakfast and bring it to work. When I get to work this one extra stop always shows up as significant lower mileage. And it hurts most because that McDonalds is hit during my early warm up cycle, delaying warmup. I'm not talking about a 1 mpg drop here but more like 4 mpg.

 

<div class='quotetop'>QUOTE(mehrenst\";p=\"99512)</div>

just curious... when you say that your trips are very short, just how far are they? (in miles) Is your engine cold when you start these trips, or are you making multiple short trips during the day before your engine would have a chance to cool down again?

 

LeGrange-
If I am on a street with a 35 MPH speed limit, and it is slightly downhill I will feather the peddle to achieve no arrows or just slip it into neutral if the car is warmed up and there is no traffic congestion to cause me to have to worry about braking unexpectedly. If it is slightly uphill, I will use the Ice to accelerate or maintain speed with no arrows to or from the battery. This results in about half the driving at unlimited mileage and about half at around 40-50 MPG. I try to keep my uphills at 50 MPG and the downhills at infinite MPG. Light speed maintainance with electric only is fine as it does not drain the battery significantly but when I sense that I am asking the battery to supply significant energy, I find it more efficient to let the Ice kick in and maintain a no arrows condition until I can let it kick back out and coast again.

This is something that would be pretty difficult to do on strange roads, but on my normal commute, I know the roads, lights, and traffic patterns to the point that I can use these techniques without much effort at all. It really helps to keep my commute interesting.

Current tank is 386 miles at 63 MPG. Last week, my 61 mile round trip commute used just under 5 gallons.

 

<div class='quotetop'>QUOTE(Legrange\";p=\"100296)</div>

I just went on a short trip down to Norwood, down 128 and Rt 1. Then up Rt 1 to Boston Storrow drive and Mass pike to 128 and home. Speeds were 55-65 on most of route. There were maybe 7 miles at 30-40 mph which was mostly on battery. And two traffic jams going 10-20 mph with frequent stops for maybe 3 miles. I got my best mileage yet for a trip with highway travel:
59.8 mpg for the 63 mile trip. (calculated from the mfd) I stopped in Norwood for a bit, so I had two warm up cycles. Other than those the graphs showed 50 mpg or above the whole way. Maybe if I try this at 3 AM I can avoid the traffic and break 60 mpg! Temperature was 80 degrees F which helped a lot.

I'm finding it takes the same effort to run on battery at low speeds as it does to get overdrive at highway speeds. For both it is mostly trying to get best sync to elevation changes along the route.

I kept up with traffic the whole way at least in the right lane, and had to even pass a few cars. But clearly the mileage would get better the slower I went. At least down to something like 30 mph.

 

Let me see if I understand this correctly: one source of inefficiency is to let the ICE cycle on and off more than necessary. At the very end of my commute, to get to my parking lot, I have to go down a steep driveway, then a short piece of level ground, then up a steep driveway and then on level ground for a few dozen yards. On this tiny stretch I go almost exclusively in "stealth mode," by letting gravity take me down the driveway, momentum to carry me along the first level part. Then I try to hit the accelerator just lightly enough to crawl up that steep uphill driveway (at 4-6 mph) in electric only mode and then use battery to get to my parking spot. Sometimes the ICE will kick in for a few seconds during the uphill stretch. In this case, would an EV switch be efficient to prevent the ICE from kicking on for a few seconds to get me up the uphill part of the driveway, or should I just mash the accelerator and drive up that portion of the driveway in ICE mode at 10-15 mph like a normal person?

Or is this splitting hairs to the point where it really doesn't make a difference?

 

Maybe this is a kinda dumb quesion, but is there any difference in what is being called "no arrows" (which I understand to be like coasting) and what some call "no arrows to and from the battery"? I can do the first, but I'm not sure that I've ever done or seen the second.

Ray, when you say, "... I find it more efficient to let the Ice kick in and maintain a no arrows condition until I can let it kick back out and coast again," are you saying that there are no arrows while the ice is running? You usually explain things so well that I assume I'm not reading well, but I'd like for you to try to re-phrase it so I can get a handle on what you said.

Often the only cure for ignorance is asking those who know the answers.

Thanks,

Beth

 

<div class='quotetop'>QUOTE(ltu1542hvy\";p=\"100345)</div>

I often use my EV button to go down my street and up a hill then down into my driveway. I think it helps a lot mainly in winter to load the engine charging the battery on next start up. Getting going down to the highway is like 25 mph so not much warm up from that. Summer I do this less, since warm up is not as great an issue for me. But you have to be careful about hill size as the discharge will be rapid. My rule is not to bring the battery down by more than 1-2 bars for this end of run.
If it is already down I let engine run on the hill part. I can't prove it helps but it makes sense to me I should get quicker warm ups. But I save plenty of battery power for the first minute when it goes easy on the engine and uses more battery power.

Keep in mind a very steep hill will start the engne even in EV mode, and cold weather makes this occur even more.

If you live where you can get to the highway and go 55 or above pretty quick, this extra battery usage might be a bad idea even in winter. There are lots of efficiency tradeoffs: the rich warm ups, the engine load starting out with cold engine, the amount of battery use needed and its inefficiencies, the engine efficiency at the loads needed. The true break even points may not be clear, but faster warm up gives me cabin heat earlier at least!

The other main EV use I find indispensable is in traffic jams where I stay in EV typically the whole way till I can get off the highway. It gives me just enough more acceleration to keep up with traffic going 0-15-0 mph.

 

Regarding arrows I've started trying a minor variation. I just can't seem to get the no arrows to/from battery acceleration easily. So I am trying to get no arrows or arrows to the battery. My thinking is the battery will go to it's set point anyway at some place whether I want it to or not. And if I accelerate without draining it my net efficiency should stay high. I try to stay close enough to the no arrow point so the engine doesn't step up to higher RPM.

 

Somewhere on this site I got the idea to try to keep the battery high. Therfore, on my last two sojourns, I kept the green arrows going to the battery as much as possible. Had a net gain on my mpg and experienced a much more normal ride. It requires a little slower start (but not much) and more gradual acceleration. I did not lose one bar on the battery and my drive was a lot smoother since I had pulsed a lot.

Question:

Does maintaining a full battery level hurt in any way in the long term?

 

I don't think the regen braking is given enough credit. Empirical data from my driving and theory suggests that the regen braking is the primary source of energy to charge my battery.

A long stretch of my commute is flat and 35 mph. I use the electric motor almost exclusively to maintain speed during this for about 10 minutes. At the end of it is a steep uphill, followed by a 50 mph slightly uphill stretch where I am primarily using the ICE to maintain speed for about two minutes or so. This is followed by a 1/4 mile downhill run with a stop sign at the end and I brake continously for the last 30 seconds or so.

During the flat section, while I'm running on electricity, my SOC goes down from 6 to 4 bars. During the steep uphill, the ICE and electric motor are both providing power, but the SOC remains at 4 bars. On the 50 mph section on top of the hill, the ICE is running and charging the battery, but the SOC remains at 4 bars. However, on the short downhill to the stop sign, my SOC pops back up to 6 and sometimes 7 bars.

In theory, it makes a lot of sense. Lets say from a stop, you accelerate briskly to 40 mph and then moderately apply the brakes and come to a stop. During the acceleration, you are using both the ICE and the battery (but mainly the ICE) to increase the kinetic energy of the car. However when you brake, you use the majority of the car's kinetic energy to spin the generator and provide electricity to recharge the battery. Even with charging inefficiency, you should be able to charge the battery with at least as much energy as you drew from it because you are using the kinetic energy that was produced from both the electric motor and the ICE to charge the battery.

Not all green arrows going into the battery imply the same amount of current flowing to the battery. I would assume that the ECU varies the amount of current drawn from the generator to charge the battery based on the SOC of the battery and the state of the car (accelerating, maintaining speed, braking). The greater the current drawn from the generator to charge the battery, the greater the drag the generator causes on the drive train and engine.

I would assume that during regen coasting, the ECU draws the least amount of current from the generator to charge the battery. When the ICE is providing power without assist from the electric motor, I would assume that the ECU is drawing at least as much current as regen coasting and perhaps a little bit more, but certainly not as much as it draws during braking. Braking would draw the most current from the generator, because it is trying to produce the most drag on the drive train. Therefore, braking is where the greatest charging current occurs.

However, when the SOC is very low, like 2 pink bars, it is very apparent that the ECU draws more current to charge the battery when the ICE is running.

I was at an airshow a couple of months ago, and while creeping out of the grid locked parking lot with the air conditioner running. By the time I got the exit, my SOC was 2 pink bars. When I accelerated away, the car refused to use the electric motor and was very sluggish. The SOC went up to 4 bars very quickly, at a rate I never see from the ICE when I already have 4 or more bars. My assumption from that is that when the SOC is very low, the ECU will draw more current to charge the battery when the ICE is providing power to the car.

For my commute, braking (and particularly downhill braking) appears to be the source of most of my battery charging, because it is almost exclusively during braking that I see the SOC increase the number of bars. Of course, different terrain will provide different results. I have a lot of flat stretches inbetween significant hills. The SOC I lose during long electric-only stretchs, I seem to get back from the downhill stretches. If I was driving in Houston, where any hill higher than 10 feet is probably a freeway onramp, I would not have the benefit of significant downhills to regain the SOC I used up during electric-only driving.

 

Another thought that occurred to me...

Many here state that modest acceleration that does not use the battery achieves the best mpg. The reason stated for this increase is the charging inefficiency of the battery.

But consider this alternate explaination for your results... When you are at cruising speed and then accelerate, the battery kicks in when you accelerate too briskly and put a significant load on the engine. Could it be that in such cases you are simply over accelerating, kind of like a jack-rabit start syndrome kind of thing. That instead of the use of the battery being a cause of decreased mpg, it is merely a symptom of innefficient usage of the ICE?

In other words, even if there was a mechanism to disable battery usage in this instance, you would still get less mpg than you would using a more moderate acceleration.

 

<div class='quotetop'>QUOTE(Legrange\";p=\"100296)</div>

Well, it is not exactly "no real motive power" and using "momentum" only.

If you shift to [N], then yes the above statement will be applicable. In [N] mode, both the control electonics to MG1 & MG2 are turned off and you can feel that there is less resistance to the car's motion as compared to [D] or .

In this "no arrows" state, the motive power actually comes from MG1 which is now acting as a motor and it is consuming the electric power regenerated by MG2. If the SOC is within the upper & lower limits and the requested torque commanded by your accelerator can be provided by MG1, then you will be able to observe this "no arrows" state. Yes, you will slowly slow down but those who practice this technique will tell you that they can "glide" farther then foot-off coasting.

I think you just have to try those techniques yourself to see which works for you. Except for using the MFD during driving, I do use all other techniques extensively, like anticipate stops, keep a following distance, use accelerator rather than brake to control speed, coasting as long as possible without stopping, etc.

I 'm contented with high 50's mpg.

Vincent

 

Beth- I got a little lazy. Yes, I meant to say no arrows to or from the battery. I think that with the engine on and no energy going to or from the battery, you are operating the engine at what the computer believes to be it's most efficient range. You are also avoiding the conversion losses inherent in the use of the electric motor.

I also should voice my opinion that if you keep it close to no arrows, such that arrows in and out of the battery teeter back and forth, then the energy that you are exchanging in and out of the battery is minimal, as are the conversion losses. A slight boost from the electric motor, does not drain the battery in any significant way.

Marlin- Yes, the mileage gains are definitely related to the engine RPMs as well as the avoidance of the conversion losses. The ECU determines at what RPM the engine is operating at peak efficiency and that is the point at which it niether gives to nor takes from the battery. So the no arrows state is just an indication that the system is operating at peak efficiency. This point changes based on engine temperature and state of charge. If you have a low state of charge, the engine RPMs will rise along with fuel consumption.

I think that I'm just restating what is being said by others and I think I got the idea originally from the Japanese mileage freaks. Go figure.

Mileage update- yesterday I drove to work at 75.4 MPG after getting 58.6 going home. I used slightly different routes and the round trip mileage came in at 66 MPG. Not bad for using 55-65 mph for half the drive. This has brought my current display to 455 miles at 63.3 MPG. The fuel guage is still showing five bars but should drop to four soon. 800 miles, here I come. The only big concession to achive this is going to lunch in other people's cars. I have only had two short trips so far on this tank.

 

Temdeimos--What do you mean by the term oveerdrive? Prius has no variable gearing.

Marlin--"During the acceleration, you are using both the ICE and battery (but mainly the ICE) to increase the kinetic energy fo the car." From stop, all the power to the wheels is coming from the MG2. If the ICE is running, it is doing other things (heating the cat. converter, powering MG1). The ICE has little low end ( low speed) torque because it operates in high gear all the time when it drives the wheels.

 

<div class='quotetop'>QUOTE(jtmhog\";p=\"100664)</div>

At the very, very beginning of your acceleration from a stop, you are using battery only. However at any reasonable acceleration rate, the ICE comes on almost immediately. Once the ICE comes on, it is providing power to both the wheels and MG1. The electricity generated by MG1, along with battery energy (if your acceleration is high enough) is used to power MG2.

So, I believe what I said still holds true. The acceleration power comes primarily from the ICE, and that ICE power is split between directly turning the wheels, and generating electricity via MG1 which then powers MG2 to provide extra torque.

The point I was making is that except for that first 1/2 second of acceleration using only battery power, both the ICE and the battery are supplying energy to accelerate the car and increase it's kinetic energy. However, during regenerative braking, most of that kinetic energy that was produce by both the ICE and the battery, is used to recharge the battery.

I have no idea what the ratio would be between energy supplied by the ICE and energy supplied by the battery during acceleration, but lets say it's 70:30 with 70% coming from the ICE and 30% coming from the battery. With such a ratio, the battery is responsible for producing 30% of the kinetic energy of the car, but during regen braking, utilizes 100% of the kinetic energy (minus efficiency losses) to recharge the battery.