Does Prius refuse to go into N above 42 mph?

I put mine into N at about 60mph earlier today

 

I had never heard that putting the Prius in neutral above 42 mph could harm the electric motor. So, on the way home this evening I put the car in neutral under various situations, all at highway speeds (65+ mph). I engaged cruise control and put the car in neutral. I accelerated using the cruise control and put the car in neutral. I accelerated manually with the pedal and put the car in neutral. I accelerated using both the cruise control and the pedal and put the car in neutral. No matter what I did, the car simply went into neutral. I would also like to know if the driver in San Diego attempted to put his car in neutral.

I have had the Prius not switch to Drive or Reverse on the first try, though. In fact, this evening after I backed out of my parking spot I switched to drive to drive off. The car was still in reverse so I lurched backward.

If my car is totaled from the neutral test, at least you have the published results. It seems to be running fine, though. I didn't keep it in neutral but for a brief moment each time.

 

I had my '05 Prius in Neutral at 70 or 75 MPH several times when I first got it. I didn't know about the issue of MG1 over speed and that was how I glided. Then I got around to reading some of the posts on here and quit doing it, didn't seem to hurt a thing though.

I think if the engine is running when you put it in N it will keep running and there won't be a problem; but if you were on a very steep long hill and had it in N before you got to 41 MPH with the engine off and coasted up to a higher speed the over speed might occur.

 

Bravo. You have covered almost all possibilities. I've tried to put it in N while driving -forgot what speed it was. I think it was at about 40-50 mph. The car did put itself in N and keep on gliding.

 

I also have shifted to N and R at highway speed (60) many times without problem. R is the fastest way to N (skipping the normal N delay) because the control logic is smart enough to know that you don't really want R when speeding forward. Even if it did try to shift, it has no physical gears or splines to grind, only some electric motor controls that ought to be designed to handle it without self-destruction.

I also understand the MG1 overspeed risk to be a rare corner case, to be triggered only when going N at low speed with the ICE stationary, then rolling down steep hills to high speed where the ICE needs to spin to protect MG1. If an engine is surging, you are already out of this corner.

 

Hi All,

The MG1 will overspeed above 42 mph, when the engine is at 0 RPM in a 1st Generation Prius. This same operational limit is set in the 2nd Generation Prius, although the MG1 speed rating is much greater. That is, rising above 42 mph, when running in EV mode below 42 mph, the engine comes on automatically, and MG1 slows.

The warp-stealth engine speed is 1100 RPM. Go downhill in a Prius at any speed below the rated 105 mph with your foot off the gas pedal, and MG1 will not overspeed.

The engine idle speed is about 900 RPM, nearly the same as the engine warp-stealth speed. The engine idle speed will be the speed the engine will run at, when the car is shifted to neutral, from a condition with the engine originally running.

So, put the 2nd Generation Prius in neutral above 40 mph, with the engine running at idle rpm and MG1 will not overspeed, until well above 40 mph.

In order to put MG1 in danger, one needs to slow down below 40 mph, so that the engine will drop out to 0 RPM, THEN shift into Netral (which locks the engine at 0 RPM), THEN proceed downhill for a long time on a steep hill, until the car is going well above 40 mph. I believe the commonly quoted speed for 10000 RPM rating of MG1 is 62 mph in the 2nd Generation Prius.

So, as long as the engine is running, its highly unlikely you will overspeed MG1. And in an runaway engine situation, impossible.

And as there is no mechanically stiff link between the engine and the drive wheels, even if the engine were to cease, the wheels would keep turning.

This is a quick response. I am sure somebody else will fill in the exact detail.

 

I tried this a few weeks ago to see if a "runaway" Prius could be controlled. Worked fine and I was travelling over 55 mph. Make sure that you push your shift lever over far enough to actually go into neutral.

 

Wouldn't the fastest way to shift into Neutral when you're traveling at speed (the purported unintended acceleration/no brakes scenario) -- or at any speed above 5-10 mph -- is to just press the P (Park) button?

See: http://priuschat.com/forums/gen-iii...td-happen-if-you-press-p-while-you-drive.html

 

In the scenario you describe (accelerating through gravity beyond 42 MPH with the engine initially stopped), as MG2 speeds up proportionally with road speed, MG1 would keep accelerating the other way, as the MG1, MG2 and the engine are all connected to different shafts of the PSD planetary gears.

42 MPH with the ICE at 0 RPM on the G2 corresponds to 6500 RPM on MG1, which is specified to survive 10,000 RPM, although it normally never exceeds 6500 RPM. So if the ICE remained completely stopped, things get critical for MG1 somewhere around 60 MPH.

Once MG1 approaches its RPM limit, the control unit could limit its speed via drag (i.e. run it as a generator). Even with no fuel being injected and ignited that will have the effect of passively spinning the ICE from the counter-torque of the generator, which would let MG1 survive. If MG1 was not rev-limited (i.e. MG1 never acts as a generator in N) then MG1 damage could occur in this situation.

 

Carolyn shifts into N at 75 mph and then at 81 mph in this video:

[ame=http://www.youtube.com/watch?v=II_03lbr-Jw]YouTube - Prius "runaway" unintended acceleration? Shift into neutral[/ame]

 

The MG1 can survive brief periods above 10,000 rpm, prolonged exposure would mean the back emf would damage the field coils and/or the battery charging system or the batteries themselves. However this can't happen in the shift to neutral scenario, since there is no power forward by the ICE or MG2 (probably power backwards from MG2), the back emf on MG1 would quickly bleed speed off of the car. Unless you were on a steep downhill.

So San Diego dude should have shifted into neutral at speed, the car's regen would have kicked in by it's very nature. He would have slowed down. Also once in neutral, regardless of throttle position, the ICE would not have throttled higher, MG2 would not provide forward acceleration.

But instead the dude hit the brakes, at 80mph +, it would take about two seconds on full throttle to heat the brakes up to: poof, no brakes...

 

From what the man said in the interview I saw, he was afraid to try to shift into neutral, because he was afraid in his panic, he'd accidently put it into reverse and he thought it would flip his car. He also said he was afraid to turn the car off because he didn't know if he would then be unable to steer-something he did not want to experience at 94 mph.
If you've never had a situation like this happen, and have never tried these things in a "simulation/test", I can understand his fears. I wouldn't know what my car would do either. Imagine your mind racing and feeling like you were about to die-and try to think rationally.
You can be sure I will be looking through this site, reading and then starting to practice emergency measures. If it happened to his 2008, it may happen to my 2007.

 

That looked difficult! not.
There is nothing wrong with the Prius that Charles Darwin wouldn't approve of.

 

i find it odd that nowhere in any of the stories is the question asked "did you try to put your car in neutral?". You mean to tell me this guy was afraid for his life because his car was accelerating and that thought didn't cross his mind? Or that it did but he was afraid it would flip his car? Give me break. This whole thing stinks of manufactured outrage.

 

While the "afraid to flip it" is plausible in some alternate reality, it really shouldn't be an excuse.

We should all know how to operate our vehicles in an emergency. PERIOD.

 

A quick look at the nomograph shows safe MG1 spin speeds when the
engine is idling around 1000 RPM. A little research before
posting would have helped eliminate a lot of noise here.
.
_H*

 

I'll try the "unintended acceleration" argument next I pass a police patrol car over the limit.. just floor it..

I tried the "P" button at 75mph yesterday.. goes into neutral in the blink of an eye!

The news will be full of these bogus claims of the next few weeks...

 

+1

Very funny.

 

If you know that little about your car, you shouldn't be driving. We really need decent standards in this country for driver education.

Tom