I've updated the FAQ with a link to a PDS model:

"An operational model that shows operation is available at:
This provides an excellent visual representation of how the Power Split Device works with MG1, MG2 and the ICE.

Bob Wilson

 

That was a very informative link. Thank you. It brings up one question in my mind though. Why then, at 42-55 mph can I get into EV mode in my car? I don't have a picture, but could get a friend to ride along and take one if need be. This definitely happens. Is it just a mistake in the computer display, or is it really on battery only? I know physics rules, and if max rpm limits this from happening, I'm wondering why I always show this on my display.

On my commute, I am forced for much of the time (due to traffic flow), to drive in the bad zone between 42 and 55. Even so, I can adjust my pedal pressure such that I show only yellow on the display. This is not a 1-2 second thing. I can do this for 15-30 seconds, limited mostly by traffic and/or hills. In fact it is easier to get into this mode than the all grey gliding mode at these speeds.

Any ideas?

 

It's not a mistake. What you've achieved there is what is sometimes called "warp stealth". Basically, the ICE is spinning/idling but the battery is sustaining your speed. If you get on a steep enough downhill, you can even pick up speed. The ICE will kick in once it's needed.

Some awesome resources:

• http://john1701a.com/<
• http://john1701a.com/prius/prius-how.htm<
• http://priuschat.com/forums/kb.php?k=14&mode=article<
• http://www.cleanmpg.com/forums/showthread.php?t=1224<

 

Hi,

One of the reasons a few are using OBD scanners or adding custom instrumentation is to really understand what is going on. The MFD, sad to say, has more in common with an 'idiot' light than something showing what is really going on.

So to answer your question, there are times when the ICE has to run to prevent MG1 from over-speeding. In the NHW11 like my 03 Prius, MG1 can not exceed 6,500 rpm or the centrifical forces could cause it to fall apart. On the NHW20, like the 04-current models, the rpm limit was raised to 10,000 rpm. But there are reports that the control laws still kick in at the old speed.

Coasting down a steep hill, the ICE can often turn without fuel or spark. In this mode, it looks like your on some sort of battery power but without real instrumentation, the MFD is misleading.

There are several OBD scanners around for your model but I don't have any experience with them. My approach has been to install custom instrumentation in part because I need to know the realtime state of my vehicle for other purposes.

If you are interested in getting into the 'guts', the Yahoo Group, "Prius_Technical_Stuff" has a rich collection of technical papers and data gathered over the years. Also, PriusChat.com is a good source for Prius technical data. WARNING: very addicitive stuff to engineers.

Bob Wilson

 

The tricky thing about that demo is that it lets you play with the engine and shows it in "Miles Per Hour," but that's not really what the engine is producing - it's producing torque, horsepower. How much horsepower it takes to go 30, or 50, or even 70 varies widely based on what you're doing. So that the electric engine can kick in without gas assistance at even 70 isn't a surprise when you consider the torque required of it may be within its limits. The demo there is a little bit misleading by using MPH, but it's the best way to make the demo simple - measuring it in horsepower would have been more abstract and for most people, less informative.

Try sitting passenger in a Prius while someone drives it on the highway. If they're going 70, and they accellerate a little, you'll see the battery and gas both kick in hard and the mpg crash. Later they might accellerate just a tad less and the gas engine shuts right off, the battery keeps firing, and the MPG maxes out - even though they're doing 70. The difference in speed is almost unnoticeable but the difference in required horsepower is huge.

The one thing I don't get in that demo write-up is the claim that the gas engine has no bearing whatsoever on speed. That seems really dubious given its positioning in the planetary gear arrangement (inner orbit) - the electric engine does drive the outer ring, but the gas engine drives the inner ring which directly interfaces with the outer ring. If the generator (center, "sun") were locked you'd have direct control of the tires by the gas engine like a conventional car.

The claim is also dubious because I frequently see the claimed horsepower of the Prius as being the sum of the horsepower of the gas engine and the electric engine... but if the gas engine has no role but to generate electricity for MG2, then the horsepower of the electric engine is the horsepower for the entire engine.

Maybe the demo is simplified too much to show the gas engine's direct impact on horsepower?

 

Both MG2 and ICE controls are active and together, sets the MG1 rpm. Use MG2 to set the vehicle speed and adjust the ICE control to see what different ICE speeds do to MG1 rotation.

Correct since the MG2 setting determines the vehicle speed. When curious about performance at any given speed, I set MG2 and then look at the range of ICE inputs and rpm limited MG1.

Actually the demo is pretty accurate and helps improve one's understanding of what is going on. ICE, MG1 and PSD operations are difficult to understand but it takes is losing outdated concepts like "the gas engine has no role but to generate electricity." Also, you might notice that the ICE drives the planetary gear carrier which means power can be split between driving the ring gear and/or the sun gear . . . power split device.

BTW, the model shows NHW11 red-line of 6,500 rpm by changing the color to red. In the NHW20 model, the MG1 red-line is 10,000 rpm. Also, the MG2 to speed gear ratio changed with the NHW20. However, this has no practical effect on the educational value of the model.

Bob Wilson

 

Well, I'm all for losing outdated concepts but what I said comes from that demo: "changing the speed of the ICE does not directly affect speed."

If it indirectly affects it then that means to me it drives the generator which drives the electric motor faster. If it directly affects it (through the planetary gear) then it revolves the inner orbit while the electric motor rotates the outer orbit and the 2 combined create more horsepower than either alone. The latter is my impression of how things actually work - but the statement about the ICE being indirect, and the demo showing the ICE's accelleration having no effect, seem to counter that. I guess the trick is that in the demo you can't manipulate the sun gear, when from watching Toyota's new Lexus demo you pointed me to, the sun gear is essential in causing the transmission to be a CVT: Once the gas engine is at full speed, the sun gear can be slowly accellerated from full reverse to full forward causing the outer ring to move faster and faster, which drives the wheels.

 

Sometimes it does.

Sometimes it does.

The demo is accurate provided you are setting MG2 and ICE as separate sliders:

MG2 - sets road speed
ICE - in the model, it sets MG1 speed. In real life, the ICE and MG1 work together under computer control.

This is what the Power Split Device and MG1 allows, decoupling the ICE from the wheels except as needed and then at the optimum ICE speed and power. Perhaps this plot of recorded ICE rpm and speed gathered in August 2001 might help:


You'll notice the ICE speed is all over the place including negative rotations. The trick is MG1 rapidly and powerfully rotates in either direction either as a motor OR a generator. MG1 and ICE operation is under computer control.

No doubt you've approached hill under cruse control and then noticed how the engine revs up as the load increases. Then when you reach the crest of the hill and backside, the rpms drop off. That is how the Continiously Variable Transmission works and the combined ICE and MG1 are the keys to how that works.

I don't remember seeing that one. Do you have the URL handy?

Bob Wilson

 

Sure thing:
http://lexus.com/models/hybrid/how_they_work.html

Click "Launch Demo," then when asked, choose the more info options, there's stuff about the planetary gear and the eCVT workings.

You'll see that to get the ICE running optimally the inner orbit spins, then to "change gears" upwards, the sun gear begins to rotate more and more in the direction of that orbit. It's an interesting alternative as CVTs go, since this is done with a physical gearset, leveraging the fact that an electric motor has no minimum RPM requirements. The Civic meanwhile uses a pulley mounted on a pincer that widens or narrows to change the pulley's effective gear ratio. The gearset has its advantages for being inflexible metal, but the pulley has its advantages because one engine never works against the other as it does in a planetary gearset.

I guess the problem with the demo posted in this thread is that it is simplified so that you can only mess with 2 of the 3, as if 2 dictate the other, whereas really all 3 are governed independently by the Prius computers. A more telling demo that keeps with that simplicity might be one that lets you move a 4th bar, "Effective Speed," and the 3 bars adjust themselves similar to the way a Prius would on its own:

0mph: All 3 parts dark
10mph: MG2 spins up, ICE and MG1 dark (MG1 spinning backwards but not absorbing energy)
25mph: MG2 exertion drops as ICE kicks in, MG1 lights up to show regen
etc.

 

Do you know the vehicle speed is determined by the MG2 rpm?
(One exception is on GS 450h.)

Ken@Japan

PS. Would like to see "PSD" instead of "PDS" on the thread title.