2007 Prius - engine does not shut down over 38 mph

There is no gas consumption when you're coasting even thought the engine is rotating. Because of the gearing in the Gen 2 transaxle, stopping the internal combustion engine (ICE) at higher speeds would spin motor generator 1 too fast for safety. So, if the ICE isn't needed for propulsion at higher speeds (ie: coasting down a big hill, etc.) it shuts off the fuel and spark and opens the valves and uses MG1 to spin the ICE almost freely at 1,000 rpm up to about 65 mph. At higher coasting speeds, it has to spin the ICE faster. Not as efficient as stopping it all together, but not burning fuel either.

Heres a nice explanation of the various driving modes. The section on coasting is the one that deals with your situation. Whats Going On As I Drive?

 

This is all you really need to know, but you need to actually believe it.

The other thing you need to know is: Coasting in neutral is also a BAD thing, for several reasons.
One is safety, two is there is no charging of the HV battery and 3 is no regen braking either.

The question is a pretty good example of " A LITTLE knowledge can be a bad thing."

 

otoh, you have to be careful not to overheat your brakes when not using engine braking on long steep downhills.

 

So at 72 miles per hour when mine switches from orange and yellow to just yellow from the battery, to the electric motor generator, to the wheels, my car is not running on purely electricity to maintain speed?

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You are entitled to believe anything that you want.......no matter how wrong it is.

And your other statements show that you don't really understand how the hybrid system works.

What you are doing defeats the best design features.
You charge the battery going down hill because that is, in effect, FREE energy to be used later.

I quit. Probably pointless.
Mind already made up.

 

it is running on electricity, but the engine is spinning so it can start properly.

 

So the engine does shut down fuel & spark, it just maintains its RPM's?

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I'm thinking it must be using a small amount of gas any time it's running, but maybe very little. Each generation has a ceiling for keeping the engine off, by design: with our 3rd gen it's around 73~75 km/hr (45 mph). 4th gen it's higher again.

 

agree with mendel, as long as it is not providing any power, little to no gas.

 

Deceleration fuel cut-off has been a feature of electronic fuel injection systems since the late 1960s. Spin the mill all you want, no fuel goes through.

 

You're half right. No fuel or spark. MG1 maintains the ICE's rpms. This keeps MG1 from spinning too fast and flying apart. It's hyper hard to wrap your brain around even watching the videos of how it works.

 

I wonder what the neutral selection is actually telling the computer to do, since the hybrid power split device does not allow for any kind of physical disconnect between its three connections (MG1, MG2 & ICE)

Technically there is no neutral, at least no full-time neutral. So selecting neutral is really more of an "ignore accelerator pedal" mode.

EDIT: Maybe it's useful as a way to take regenerative braking offline and force friction brakes to be the only braking used?

 

You nailed it with your edit. When you take your foot off the gas, the ICE shuts off, but it will still spin if your speed is more than about about 38 mph or so. But the car is regenerating electricity. When you put it in neutral, it stops regenerating and so the MGs are not providing any resistance. They and the engine never physically disconnect from the wheels, as you said, but in neutral there is no power flow in any direction. Sort of a synthesized neutral. More magic!

 

Synthetic neutral... yes that's probably the right way to look at it. Although you could potentially overspeed the MG1- but this could be mitigated by upping the field voltage at MG1 and then sinking the resultant current in MG2. An electrically-moderated neutral. There would be power flow, but only MG to MG, and it wouldn't be full time. Battery not involved at all. No proper way to illustrate that on the "video game" screen. (aside: I'm really glad I got rid of that when I switched to an aftermarket stereo)

So the N position on the shifter is truly an "ignore skinny pedal and disable regen brakes" switch.

 

It's not electrical damage they are concerned about. It's simply the physical force of spinning too fast and parts flying off of it.

That's a good way to put it.

For those who haven't seen it, here's a popular video that shows how the Gen 2 transaxle works.

 

Weber Auto is so very informative. Just had my friend Matt watch this exact video while he was riding in my Prius because I didn't know how to explain that their is no direct connection between my ICE and my axles... Thanks for sharing.

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