I ran in ev mode going 53mph

Hi Ken,

Do you know how much energy in kW is used to spin the ICE when the car is travelling over 42 mph, and no arrows on the MFD ? Is there a power drain from the HV ?

Dave, I drive a 3 - 4 mile decline a couple times a week, and so experience this often. The MFD always shows ICE off; depending on how much I push the gas pedal, I can see arrow to the HV, from the HV, or no arrows at all.

The HV -> PSD state would seem to contradict the notion of kinetic energy to M/G, because some of that energy would be split and sent to the battery, and energy flow to and from the HV at the same time does not make sense.

Make sense ?

 

actually i base my conclusions on

amperage being -1 to -2 amps... this is the normal range of vehicle when on and NOT moving.

ICE RPM's at zero. does happen at times...usually though, its at its "idle" position of around 900 RPM.

zero gasoline consumption

instaneous mpg reading infinite

also, if you put the car in neutral and coast down a hill you will see the same reading on the energy screen... now what is making the car go then?

 

No, I have no specific data now.
Have you ever spun a crank shaft by hand?
We can't keep the crank shaft at 1,000rpm by hand.

Ken@Japan

 

Never have. I do not understand your point. Please explain for slow people.

 

I have not noticed it yet, but I could see going over 42 is possible with 0 rpm.
This is because I can coast over 34 mph in EV mode and still stay in EV if I don't accelerate and I coast back down under 34 before using power.

And you can definitely coast with no gas flow over 42 with engine spinning. Just means the energy is coming from the battery for MG1 and you may not see it because the hills energy is feeding power back into the battery. You are still wasting energy over driving under 42 with engine at 0 rpm.

Hopefully the next Prius will allow engine at 0 rpm for speeds up to about 55 mph.
We have very few roads here we can drive at only 42 mph.

 

We need some energy to spin the ICE.

Let's assume we have a plugin Prius-B.
The Prius-B has no limitation of EV mode speed and we can drive at any speed in EV mode, but the ICE should be spun above 42MPH.
Now, we start the Prius-B and it's speed is increasing.
Below 42MPH, the ICE is at 0 rpm and we enjoy the EV driving.
Now, passing to the 42MPH boundary, we have to spin the ICE.
We need some energy to spin the ICE.

I think it is wasting some energy to spin the ICE and it's not a pure EV mode.
How do you, everybody, think?

Ken@Japan

 

Ken has brought up a very interesting point here: just what is there about this 'magic' 42 mph limit?

Without access to Toyota's design criteria, I have to fall back on the power-split basics:
I guess by now nobody disputes the power split equation

MG1 rpm = (ICE rpm x 3.6) - (MG2 rpm x 2.6)

At the 'magic' 42 mph, MG2 is doing about 2860 rpm +/- few % for tire variations.
So MG1 = ICE rpm x 3.6 - about 7436
So if ICE is stopped then MG1 = -7436 rpm.

Now as MG1 is rated at 10,000 rpm, this obviously isn't the reason to stop EV mode at 42mph.

Conversely, if we drove MG1 to -10,000 rpm, just like it goes to +10,000 rpm under initial acceleration, then if ICE was held stopped, we would get MG2=3846rpm and so road speed of ~67 mph. So again, no obvious reason to limit EV to 42 mph.

I am going to suggest one possible reason for technically limiting zero engine rpm to 42mph max. (No doubt someone will think of others) MG1 certainly reaches +10,000 rpm during acceleration from standstill, but this is only temporary because as road speed rises, MG1 rpms drop down again. So what if MG1s rpm limit is a transient one, ok for 10 seconds of full power but not rated continuously?
Allowing it to run at 10,000 rpm at 67mph even assuming there was enough batetry power to do that and it was tail wind or slightly downhill, that would allow a continuous MG2 high rpm rather than a short burst. So maybe in the interests of reliability, Toyota
chose 42mph and 7400 odd rpm as the maximum rpm it would allow MG1 to run continuously. Maybe it would still allow higher rpms for a short burst, which might explain some people seeing zero ICE rpm above 42mph, for short periods.

Please point out the flaws in this!

 

quick revision: last post had typo of MG2 instead of MG1
Ken has brought up a very interesting point here: just what is there about this 'magic' 42 mph limit?

Without access to Toyota's design criteria, I have to fall back on the power-split basics:
I guess by now nobody disputes the power split equation

MG1 rpm = (ICE rpm x 3.6) - (MG2 rpm x 2.6)

At the 'magic' 42 mph, MG2 is doing about 2860 rpm +/- few % for tire variations.
So MG1 = ICE rpm x 3.6 - about 7436
So if ICE is stopped then MG1 = -7436 rpm.

Now as MG1 is rated at 10,000 rpm, this obviously isn't the reason to stop EV mode at 42mph.

Conversely, if we drove MG1 to -10,000 rpm, just like it goes to +10,000 rpm under initial acceleration, then if ICE was held stopped, we would get MG2=3846rpm and so road speed of ~67 mph. So again, no obvious reason to limit EV to 42 mph.

I am going to suggest one possible reason for technically limiting zero engine rpm to 42mph max. (No doubt someone will think of others) MG1 certainly reaches +10,000 rpm during acceleration from standstill, but this is only temporary because as road speed rises, MG1 rpms drop down again. So what if MG1s rpm limit is a transient one, ok for 10 seconds of full power but not rated continuously?
Allowing it to run at 10,000 rpm at 67mph even assuming there was enough battery power to do that and it was tail wind or slightly downhill, that would allow a continuous MG1 high rpm rather than a short burst. So maybe in the interests of reliability, Toyota
chose 42mph and 7400 odd rpm as the maximum rpm it would allow MG1 to run continuously. Maybe it would still allow higher rpms for a short burst, which might explain some people seeing zero ICE rpm above 42mph, for short periods.

Please point out the flaws in this!

 

I think you're basically right, but your maths is slightly off. By my calculations, 42mph with engine stationary corresponds to roughly 2400rpm on MG2 and -6200rpm on MG1. And 6500rpm has long been believed to be the MG1 rev limit, although HSD lifted it to 10000rpm, but apparently only forwards for bursts of acceleration.

 

And I don't really understand Ken's point. Over 42mph, you're still running on electric only. Yes, it's less efficient than under 42mph because you're spinning the engine, but so what? It's just an extra load, just like air conditioning. Doesn't stop it being purely electric. Do you claim the new Honda Civic can't run on electric only because it spins its engine?

And because that extra load makes it inefficient, it won't tend to bother attempting electric-only operation at that speed in most cases, unless it wants to drain a full battery, or is running downhill.

 

Yup, you're right, MG2 2400 rpm at 42mph so MG1=-6240. Sorry.
I have looked high and low in the past for MG1 specs and have never actually seen a number quoted by a Toyota source for the 2003-2005 MG1 limit. Just for the 2001 and its not clear if the assumption that no changes occurred for the newer model is reasonable.
Anybody have any more info?

 

My point is that it is a pure EV mode or not.
The pure EV mode does not consume any extra energy.
No, I don't recognize the '06 Honda Civic Hybrid runs on electric only mode.

Ken@Japan

PS. It's now 4AM my time. Good night every body.

 

Okay, I'll leave Ken off in cloud-cuckoo land, and try to address Windstring's question...

It's all to do with the 3-way power-split device. Roughly speaking (ignoring multipliers), the power split arranges that

MG1 rpm = Engine rpm - Wheel/MG2 rpm

The faster the car is travelling, the faster MG1 spins backwards. At around 42 mph, MG1 reaches its rev limit. This can be counteracted if the engine starts spinning forwards. 1000rpm on the engine is sufficient to keep MG1 below its rev limit at all speeds up to 106mph (the point at which MG2 reachs its rev limit).

When you're accelerating, the engine spins faster, and MG1 spins faster, FORWARDS. So, depending on load, MG1 may either be going forwards or backwards. Its limit going forwards (when being driven by the engine) is 10000rpm.

So, there are 3 restraining factors:

1) to stop MG1 going too fast backwards, the engine has to start spinning above about 42mph.
2) to stop MG1 going too fast forwards, the engine revs are kept lower at low speeds - it can't reach its maximum of 5000rpm until at 54mph or above.
3) to stop MG2 going too fast, the car's speed has to stay below 106mph.

This is all very hard to explain - it's clearer if you use one of those interactive animations that are around on the net.

 

page 7 of the blurb that Toyota Canada gave the dealers. Not much else on it some stuff on the MG2 output and some black and white drawings of the magnet placement in the rotors. If your really interested I'll scan and email.

 

I expect the 42 mph limit comes from two things:

1 42 is the max speed that Toyota feels is economical to drive on battery power, on level ground. Coasting down hill probably was not considered important to make a special case for.

2 If the engine did not spin above 42, there might be too much lag in getting the engine up to speed in case you needed to accelerate fast. The lag we already have bothers some people here. And at higher speeds the start up acceleration can't come from the electric power the way it does starting up from a stop.

Maybe Toyota will give us a switch to keep engine off longer with a sw update someday?
We could keep engine off longer where we were cruising and knew we would not need to floor it. It would be like a car with overdrive where you have to shift out of it to accelerate.

 

It's all in the geometry of the PSD and the specs of the components. Remember that Toyota selected a design that they felt would be the best balance of price, performance, and efficiency for the normal mass-market consumer. And remember also that the normal Prius driver is not here on Prius Chat, because he/she does not care about any of this technical stuff. She/he just wants a reliable, efficient car that can be driven just as though it was a normal car, but consuming less gas and having less emissions.

They're not likely to give us any special switches to tweak performance because there's not enough demand for it. However, if the price/benefit ratio becomes favorable, they may give us more battery capacity, because that would improve efficiency, as Wayne Brown has demonstrated. And/or, since the battery is severely limited in how fast it can receive or provide charge, they may incorporate capacitors as a buffer between the battery and the motor-generators, which would also improve efficiency.

There's a big market for better gas mileage. There is very little market for gadgets that allow the driver to tweak the performance. (Which is why we had to install our own EV switches!)

 

Well, it's clear to me why 42 is the fastest you can drive in "pure EV" mode...After all, 42 is the answer to life, the universe and all.

-Roger

 

Ken asked if ICE spinning is not EV mode by definition. If no petrol is used, and all energy comes from the battery, then I say EV. Less efficient, yes.

In the case of the Prius, the battery's energy has started in petrol, but does not define the argument, because the battery may in the future be charged from the grid.

So perhaps a place to start is: Can the battery spin the ICE thorugh the PSD ? Not if it happens, but is it mechanically possible.

Parenthetically, although this is a fascinating topic, I'm Aok with a Prius+ that uses 0.2 - 0.3 gallons of petrol/hour at highway speeds if that turns out to be the case in a plug-in augmentation.