High speed in N (and ICE @ 0 RPM)

[The Tramp]

Hi Everybody,

As you may know, I run a forum in Italy.

One of the members, misinterpreting my warnings, has taken the habit of letting his prius go downhill, with ICE off, in N.

He afferms that he has touched a top speed of 135 Kph ( 84 mph) in these conditions.

I pointed out to him that in doing so MG1 has reached an astonishing speed of -12200 RPM when the phisical limit is -10500 and the Prius is programmed not to overtake -6000 RPM.

My question is (I will later tell him) what damages can happen by overrevving the MG1?

Oh, for the books, he does slow down to 50-60 mph before shifting back to D.

[efusco]

That's interesting...he's gone that fast with a true ICE off Neutral? Must be a hell of a hill and he must be starting pretty slow. I guess that rules out "The MG will explode over 10k rpm" theory doesn't it!

[Bob64]

He should try shifting back into D to see if it'll even start the ICE at that speed...

Anyway, if hes applying the brakes to slow back down in neutral, hes wasting more energy then hes saving by going ice-off.

[The Tramp]

Originally Posted by efusco

That's interesting...he's gone that fast with a true ICE off Neutral? Must be a hell of a hill and he must be starting pretty slow. I guess that rules out "The MG will explode over 10k rpm" theory doesn't it!

All you have to do is to glide below 40mph and put it in N before the downhill. I do this here where it's an underground highway with a low downhill gradient that keeps the car at a steady 55 mph in N and I know that I am within the RPM limit and putting it in D at the end causes ho harm. (I hope).

On a motorway with a 2.9% gradient on my old car (Cx 0,30) I used to achieve 65-70 mph in neutral - never tried it on the Prius because I know that with a better aereodinamics the car will go faster and I will overtake the MG1 Max RPM.

Maybe there is no physical limit on the RPM of MG1 when free-wheeling but I dare not imagine what would happen if the Roman would put the car in D while free-wheeling at over 80 mph.

And I don't want to be the guineapig!

[The Tramp]

Originally Posted by Bob64

He should try shifting back into D to see if it'll even start the ICE at that speed...

BOOM!

Anyway, if hes applying the brakes to slow back down in neutral, hes wasting more energy then hes saving by going ice-off.

We do not know the characteristics of the hill. Many hills go back up so he is on the top of the first hill at, say 35 MPH, glides, shifts into N just before the descent, reaches 90 mph on the apex, and climbs again with momentum and when he reaches a decent speed, shifts into D.

[efusco]

Originally Posted by The Tramp

All you have to do is to glide below 40mph and put it in N before the downhill. I do this here where it's an underground highway with a low downhill gradient that keeps the car at a steady 55 mph in N and I know that I am within the RPM limit and putting it in D at the end causes ho harm. (I hope).

On a motorway with a 2.9% gradient on my old car (Cx 0,30) I used to achieve 65-70 mph in neutral - never tried it on the Prius because I know that with a better aereodinamics the car will go faster and I will overtake the MG1 Max RPM.

Maybe there is no physical limit on the RPM of MG1 when free-wheeling but I dare not imagine what would happen if the Roman would put the car in D while free-wheeling at over 80 mph.

And I don't want to be the guineapig!

Oh, I know how to do it, I use an ICE off glide up to about 61mph daily on my commute. Just getting up to 80-85mph from that slow must be a pretty long and fairly steep hill.

As far as putting the car back in D...not a problem at all...in fact it's certainly better for the car than exceeding 10-12k rpm for MG1--remember that MG1 will automatically slow down with the ICE spinning. Quite safe to do.

[David Beale]

He will eventually destroy MG1. There is obviously a "safety margin" built in, otherwise he would have already heard a terrible crunching sound as MG1 destroyed itself and the rest of the HSD. But if he keeps doing it the MG will eventually disintegrate, taking out the rest of the drive system with pieces flying/floating around in there.

Isn't coasting in N downhill illegal in Italy? It is here in North America. I don't understand why anyone would do it. Too lazy to use the accelerator pedal to find "hyper stealth"? He -may- have saved a few euros in fuel. He -may- do about 3000 euros in damage real soon now.

[hobbit]

I agree that that's a heck of a hill, because I think the most
I've ever touched in warp-neutral is 68, maybe 70 MPH by which
time both air-resistance against the car and the windage from
the MG1 rotor screaming around a touch over 10K RPM were exerting
significant retarding force on the vehicle! MG1 is likely good
for shortish bursts of that sort of speed; you wouldn't want to
spin it that fast all the time, and it would be almost impossible
to do so. But in random experiments with engine-out conditions
I've made the butt-dyno determination that over 50 or 55 MPH,
warp-stealth [spinning the engine too] is less drag on the car.
.
_H*

[richard schumacher]

Tell him that his action re-inforces unfortunate stereotypes of Italians and machinery :_>

[The Tramp]

Originally Posted by David Beale

Isn't coasting in N downhill illegal in Italy?

Allow me to tell you a joke:

Q. How do you make an Italian jump a cliff?
A. Tell him it's illegal.



And no, it's not illegal.