Coasting in neutral

Only had my Prius for a week and muat admit I thought of going into Neutral a few times but never tried it. After reading all the comments I think I'll just stick to what I've been doing, I'm happy with getting around 55mpg no need to damage something for just a little extra.

 

I had not visited this thread for nearly a year and a half, and I had forgotten the value it could have -- not only to Newbies, but also to any seasoned Prius owner who has not really grasped the HSD system.

I'd rank this as pert near a sticky, and I will recommend it to all new owners.

I also will add one other comment, particularly in light of a recent post: Shifting into neutral while attempting to coast in a hilly area could be quite dangerous. Aside from the possible damage to the HSD system, the fact is that you'll not have the regen system available to you. This means that in an emergency braking world, you'll have just the friction brakes to help. I'd like to be certain I have all assistance available, and I find no value at all in shift out of drive while the car is in motion (except to get it to the end of the driveway without having to turn on the car).

 

The concept of "neutral" has always mean't a disengagement of the transmission while the engine still ran..... this is a whole new concept that can be quite confusing.

Maybe they should label it something else... like "no worky"

 

Too funny. We could relabel the switch NW. That would really solve the confusion.

 

Hi a-priori,

While your caution is worthwhile to make, the technical detail is wrong. Do a rapid depression of the brake pedal, as is done in an emergency situation, the Prius instantly turns off electric braking, and fires (like a gun) the brake pistons into the brake pads. Its a boosted response, similar to what it available on high end sedans (like S-class Mercedes). This is a side benefit of having the braking system being a powered hydraulic system, with an accumlator, etc. If you have not done that accidentally, or intentionally, be sure to tense your neck muscles before doing. Its quite impressive and loud (BANG from both front brake calipers). And of course this system is fully armed while your in neutral or not. Its also important to keep your disk rotors clean for proper operation. A a few brakes into a stop light in neutral does this nicely.

 

"Freewheel" mode maybe...

 

"No field" mode.

Tom

 

Nice post.

 

Donee,

Thanks for the clarification!

I had thought the accumulator would not be pressurized unless the whole HSD system was engaged. Of course we hear some of this after turning off the car, but I had thought that if the car was placed in neutral with the ICE off that all we had for a power assist was what was left in the accumulator at that point.

Could you provide a bit more of an explanation? Clearly, I'm not fully understanding what's happening in this situation.

 

I"m sure this is discussed elsewhere, but what would solve the whole problem is to remove the need to put it in neutral.

They need to reprogram the computer to use stealth mode more.

It takes tedious attention and skill to consistently be able to not regen or charge but merely coast where there are no arrows showing any charge nor regen.

Why I think the drag of coasting is a good thing due to people not being able to adjust from a normal type transmission to what would be the freeglide of the prius and back and forth, but I do think it would be quite simple to achieve both with the computer.

Even as with the 2010, they have adjusted the sensitivity of the accelerator to include an "eco, normal, and power" mode, it would be just as simple to have a 5 or 10% pedal adjustment whereas when you let off the gas, if you relaxed and held the pedal within 5 - 10% of its play from the point to where it would accelerate, that would cause it to simply freeglide instead.

The car would know when you really wanted to coast because you would let off the pedal "past" that 5 - 10% tolerance and would in those cases do regen as normal.

I think its a bit ridiculous to watch the battery charge/regen/charge/regen all within 2 seconds... .almost like the cpu can't make up its mind what it wants to do.

We all know, every time it regens.... the conversion waste power, and every time it charges, the conversion waste power.

In those indecisive "in between" times.. why not freeglide and let pure kinetic energy propel you down the road?.... its the most efficient means to travel when acceleration is not required.

For drivers who didn't want to engage this "pulse and glide" type driving, they would simply hold the accelerator steady like normal.

Of course you always have some drivers who are constantly "inconsistent" on their pressure on the accelerator. But even in those case, this should work.

They could also simply incorporate this "feature" into the "eco" mode of the 2010 and later. Normal would be "normal" as now, and power would be power.

 

The brake accumulator pump is electric, running off the 12V electrical system. In neutral (with the ICE on or off), the Skid Control ECU is still in charge and will control the pressure in the accumulator and brake lines as appropriate. The HV ECU just won't do any regen.

It only falls back to fail-safe mode if the Skid Control ECU fails or the sensors are coming up with contradictory answers about the brake pedal position/pressure. In that case various valves open which direct one half of the master cylinder pressure to the front left wheel, and the other half to the front right wheel. However, you don't get any assist.

 

There is no drawback for you to apply shift N to coasting you Prius. think about this, if you are driving down hill, you are using N mode, when your MG1 reaches a very high speed say 6,500 rpm then the Prius computer knows that speed will be harmful to your MG1, gears, motors and etc. then the computer will start the ICE ,that means Engine, to compensate/reduce the MG1's high spinning speed. So all things are under computer's control. don't worry about it.

 

The only time you should be in neutral is to clean the brakes. Brakes making sounds clean 'em.

In neutral regen braking is shut off and then you will have all the braking power of a carny go kart.

 

Specifically, the kind of carny go cart that has an accumulator always pumped to 2,000+ psi with brake fluid and valves to send it instantly to heavy brakes at all four wheels.

 

... except that it can't start the ICE, because the MG1/2 armature magnetics are disabled. At least, that is what we have been told is the purpose of N mode.

 

... and it is, but when it is all really controlled by a computer, it can mean some things are ... negotiable.



In particular, that third bullet point, if the ECU sees that either MG is about to overrev, it will say "yes, I know you selected neutral, but neutral isn't a suicide pact" and do the needful anyway.

One caution: these exceptions are first described in the 2004 New Car Features manual, for Prius Gen 2. If you are driving a Gen 1 (rock on! I loved that car), you should not count on it having your back like this.

 

In a dozen years here, that is a fairly important exception that seems to have been missed in the numerous threads I've read.

 

I like the ABS exception myself. You get a wheel skidding, it doesn't just release that brake and wait for the wheel to roll again—it releases that brake and uses a motor to kick the wheel into rolling again. What'll they think of next?

 

Might that apply to an all wheel lockup, or just a single wheel lockup? Or is that an unknown?

Having once experienced a four wheel lockup on fresh smooth ice in an older AWD, effectively disabling ABS because it didn't know we were still moving, this sounds like a good idea. That was in a stick shift, so with the clutch depressed there was no engine torque to help get any wheels going again. Without this feature a Prius might be in the same boat. Or should I say toboggan. At least a traditional automatic would be constantly applying some torque.

Fortunately that experience happened at very low speed, with a very long runout remaining. I slowly circled the block back home, and called the Christmas party hostess to say that we couldn't safely attend due to the sudden ice storm. As it turned out, none of the many guests were able to get there.

 

Well, I don't know anything more than what the book says. Of course the front wheels are the only ones it can kick.

The stability control does sense g forces as well as wheel speeds, so I'd think it could recognize wheels locking up without slowing the car.