Neutral Downhill Safe?

<div class='quotetop'>QUOTE(gpb5200 @ Mar 7 2007, 01:37 PM) [snapback]401794[/snapback]</div>

You don't need to put it into neutral, you can do the same thing by slightly depressing the accel pedal until you see no arrows in either direction.

Dave

 

<div class='quotetop'>QUOTE(efusco @ Mar 7 2007, 02:44 PM) [snapback]401803[/snapback]</div>

Why? When you start going downhill the ICE turns off. If you then shift into neutral, why would it come back on?

 

<div class='quotetop'>QUOTE(efusco @ Mar 7 2007, 10:44 AM) [snapback]401803[/snapback]</div>

Not only that but when a vehicle is not in gear this is illegal in every state as the driver does not have full control of the vehicle.

 

<div class='quotetop'>QUOTE(Keithnteri @ Mar 7 2007, 03:01 PM) [snapback]401920[/snapback]</div>

Prius doesn't have a traditional transmission. It's always in gear. Neutral, as I understand it, simply prevents the ICE recharging the traction battery.

 

<div class='quotetop'>QUOTE(Keithnteri @ Mar 7 2007, 04:01 PM) [snapback]401920[/snapback]</div>

And you got this info from where? I have never heard of this.

 

Legal or illegal, there is no need to drop a Prius into neutral when you want to coast. Just back off the accelerator all the way, put your foot back on it until you feel the regenerative drag go away, and hold that position until you want to either speed up or slow down. It becomes second nature after some practice.

 

Search the archives for all the prior rants about the legality/sense
of using neutral under an outdated legislative structure.
.
What's the general speed range of your downhill? If you can start
it at less than 42 MPH and make sure the engine's off, and then
pop into neutral, the engine will stay off even if you get *above*
42 on the way down. That's a serious gas-saving state if you can
do it; just be prepared to pop back into D if you have to slow down
so you can at least get the regen.
.
_H*

 

<div class='quotetop'>QUOTE(hobbit @ Mar 7 2007, 09:39 PM) [snapback]402006[/snapback]</div>

I realize the ICE always turns over > 42MPH, but I thought if you were coasting at such a higher speed the engine turned over without burning fuel...? I remember reading that somewhere around here. If so, then engine turning or not (i.e. Drive vs Neutral) should have no impact whatsoever on his FE when coasting, except he will get 'free' regen when in D that would otherwise be sacrificed for nothing in Neutral... :huh:

 

<div class='quotetop'>QUOTE(TomorrowMatters @ Mar 7 2007, 04:05 PM) [snapback]401946[/snapback]</div>

It's at least illegal in CA. I don't know about RI and CO. See http://www.dmv.ca.gov/pubs/vctop/lov/lovd11.htm "21710 Coasting, in neutral on downgrade."

It says it's an infraction. It's also discussed at http://www.dmv.ca.gov/pubs/vctop/d11/vc21710.htm.

 

<div class='quotetop'>QUOTE(hobbit @ Mar 7 2007, 09:39 PM) [snapback]402006[/snapback]</div>

Wouldn't "warp neutral" put you outside the design parameters of HSD? Isn't there some good reason that the engine always spins above 42mph except this special case? I just don't see how this can be a good idea.

 

<div class='quotetop'>QUOTE(cwerdna @ Mar 8 2007, 12:13 AM) [snapback]402126[/snapback]</div>

That 'infraction' sounds like it is for mountain driving. which would make sense, why would you want your car in neutral while going down a mountain?You need the engine to help brake other wise your brakes will overheat. I dont think this applies to GPB5200's situation.

 

<div class='quotetop'>QUOTE(TomorrowMatters @ Mar 8 2007, 05:15 AM) [snapback]402172[/snapback]</div>

"21710. The driver of a motor vehicle when traveling on down grade upon any highway shall not coast with the gears of such vehicle in neutral."

The OP was asking about coasting in neutral while going down a hill. That sounds like a down grade to me.

 

<div class='quotetop'>QUOTE(efusco @ Mar 8 2007, 12:44 AM) [snapback]402045[/snapback]</div>

I thought that, as efusco said, the ICE continues to spin (non-neutral) with MG1 supplying the power to spin the ICE, with no fuel being burned but electricity coming from the battery. However, I thought, as hobbit stated, if you started below 42 mph in N and got above 42 mph by coasting, that the ICE would not spin, and therefore MG1 would be in some danger when D was reengaged or even in N. I know that there is some margin of safety for MG1, but it still seems that it could be possible to exceed that if you are coasting in N.

I never understood why you would want to be in N anyway on a downhill, since you lose the regenerating capability. I have thought about doing the N shifting when coming to a stoplight after braking to 8 mph to eliminate the "creeping" mode built into the transmission programming, but it still doesn't ever seem worth the effort.

The only time I use N is when I'm just starting out and I can delay the ICE from the initial cold-start for a few more seconds while I wait for traffic if necessary. And even that probably isn't worth it, since according to the experts it is better to stand still while the ICE does the warm-up. But in the situation I have there is another stop sign within a few feet to stand and wait at.

 

<div class='quotetop'>QUOTE(TomorrowMatters @ Mar 8 2007, 05:15 AM) [snapback]402172[/snapback]</div>

For rear wheel drive cars and slick roads, there's less chance of spin-out if the car's in neutral. Otherwise the engine could slow down your rear wheels just enough to spin you around or off the road. But we're talking about front wheel drive VSC cars...

 

No, if you *start* below 42 in neutral and wind up going faster
than that, the ICE does *NOT* spin. I know this from watching my
vacuum gauge, and secondarily from listening to the [lack of] crank-
sensor output when I had a little speaker widget hooked up to do so.
Remember, the definition of Neutral is "you may not touch the motors"
and a side effect is that if the engine is in running mode it stays
that way, and if it's off it stays off, NO MATTER WHAT.
.
I've had my '04 up to 68 MPH downhill in warp neutral. Yes, that
would have put MG1 close to the 10,000 rpm limit. Air resistance,
and for all I know windage resistance *around* MG1 inside the case,
prevented my speed from getting any higher than that. But MG1
didn't fly apart, so I guess life is good.
.
On country roads I often get opportunities to cruise down gentle
slopes up to maybe 50 mph like this. The point when doing this is
to *not* regen, but rather to coast as far as you reasonably can
before having to apply power again. Soapbox derby.
.
_H*

 

Hello everyone. I don't post that often, but I did post on this subject a while ago. Everyone is sort of supplying half accurate information. Here is the repost:

<div class='quotetop'>QUOTE(RolfS @ Sep 14 2006, 01:44 AM) [snapback]319358[/snapback]</div>