Driving on "N" Neutral

My opinion is that this just isn't necessary for the Prius since you'll always get infinate MPG numbers going downhill. Driving in "N" also adds danger and I've heard coasting in neutral is actually illegal. The problem is that you can't accelerate if you need to do so to avoid an obsticle.

 

No chance of damage, since there's no mechanical engagement/
disengagement. Try to make sure you're engine's off first,
though, or you wind up idling through the whole run.
.
_H*

 

When you're in "N" you are not regenerating. Therefore, your mileage could take a hit as the ICE has to work more to charge the traction battery.

 

Then why do it? Is your life really worth a small increase in gas mileage? What about the life of the person you hit because your brakes are compromised?

 

Shifting to neutral simply stops the inverter from accepting energy from the motors, which causes them to freewheel. The drag you get when you release the gas in drive is actually from one of the motors regenerating a small amount of energy. You probably already know this already, but neutral also disables regen, so you'll want to go back into drive when you have to brake. It's a good habit to get into anyway. Whenever I use neutral (which is rarely since I prefer glide), I always keep my hand on the shifter both to remind me it's in N and so I can quickly shift back to D if I need to brake.

The only possibility of damage I've heard of involving neutral is if you put it in N when you're going under 41 mph (or is it 42...), and then the car coasts very far above 41, you can supposedly overspin one of the motors. This can't happen if you put it in neutral while going above 41 because the engine is running, but above 41 you would want to use warp stealth instead anyway.

 

Yup, in most states you can't "coast". It does deal with a lack of control one might have.

Don't have the book with me, but I think Toyota says this is a NO NO.

 

Depending on how fast you were going when you switched to "N", it is quite possible that the engine is still idling. In that case your MPG wouldn't be infinity, but would be higher than 99.9 The MFD displays 99.9 for anything higher than 99.9 up to and including infinity (or more specifically "undefined").

As for the releasing of the gears, yes we are sure. The gears are never "released" The 2 electric motors and the gasoline powered Internal Combustion Engine (ICE) are always connected to the wheels at all times.

When you don't switch to "N" and you remove your foot from the brake, the car immediately starts using one of the electric motors as a generator and pushes the generated electricity into the battery to charge it up some. The turning of this generator is the drag you are feeling. When you switch to "N" the car stops using the electric motor as a generator and the rotor in the motor is allowed to spin freely. This is why you feel so much less drag.

So as mentioned, you don't need to worry about wear or damage to the gears, as they never disengage.

On the other hand, if the ICE is idling when you switch to "N" it will stay idling until you switch out of "N". It will do this even if you come to a complete stop. This will waste fuel and reduce your fuel efficiency over all. If you leave it in "D" the car will shut the ICE off if conditions allow. At that point you will completely stop using fuel (great for fuel efficiency!).

Additionally, if you switch to "N" at the top of a hill after the ICE has stopped spinning, the car will not start the ICE back up again until you switch out of "N". It won't start it up to charge the battery if the battery needs charging, and it won't start it up if you accelerate down the hill because of gravity, even if you egt up to 100 mph. There are some concerns that if the engine doesn't start up, and the car reaches high enough speeds, one of the electric motors can spin faster than it's design specifications allow for. In general, there is probably enough safety margin inherent in the electric motor that this won't be a problem, but you are "at your own risk" that you could damage the electric motor.

Furthermore, while you are in "N" the car will not use regenerative braking at all. So you will wear out your brake pads faster, and you will loose out on the opportunity to improve your fuel efficiency. All the energy from braking will be dissipated by the brake pads as heat, whereas with regenerative braking some of the energy is converted to electricity to be saved in the battery for future use. This means the ICE will need to run more often, harder, and longer to keep enough electricity in the battery for the cars needs.

 

Hobbit, how about over-revving MG1? Will that be an issue at very high speeds?

Tom

 

The question I always ask is, "Would you do this in a 'regular' car?". If not, it's probably not a good idea to do in the Prius. Toyota tried to make this automobile operate similarly to every other car on the road, so it follows that you should drive it like one.

This isn't necessarily true in the case of Pulse and Glide or Warp Stealth, since those techniques wouldn't be good for fuel economy in a non-hybrid car. But they're certainly things that you could do safely.

 

Yes. How fast is an iffy thing, probably much more than 42 MPH.

It's silly to gain a few MPGs at the risk of damaging the drive system.

 

Have you tried gliding without using neutral? To do this, you release the gas all the way when you start going downhill, then immediately push it in a tiny bit, slowly. At some point, all the arrows on the display should disappear and you'll essentially be in neutral with some key advantages:
1: You're still in D, so you don't need to worry about shifting when you brake or compromised braking.
2: You can do it above 41 mph, the engine will turn but will not burn fuel. You don't need to worry about overspinning MG1 either.
3: You can keep the glide going much longer by occasionally giving it little boosts with the electric motor (though if you need to increase your speed your better off using the engine as it'll have to run anyway if you run the battery down)
4: It's legal everywhere

 

Due to the nature of HSD, I don't believe there is any appreciable benefit to shifting to Neutral for a downhill; only increasing risk of damage or accidents.

When normal driving in a Prius, lifting off the accelerator will generate a small charge to the battery, in exchange for a small amount of drag.

If you choose to eliminate the drag by shifting into Neutral, you may gain a slight bit more speed, but you are sacrifice "free" energy regeneration in the process, possibly increasing brake pad wear if you brake while in N, and generally increase the risk of losing control of the car or causing damage considered outside 'normal operation' (i.e. overspinning an electric motor). Also, as previously mentioned, if the engine happened to be spinning when you shifted to N, you'll be idling the whole way to boot.

In summary, since the "free regen" energy is "wasted", you are in fact "paying" for this extra momentum anyway, with the added joy of endangering yourself and your car's health in the process.

Bottom line... there is really no reason to do it. Just my $0.02.