Pulse and glide in neutral??

[shastaprius]

The thread Title says it all...what is the disadvantage of using Neutral vice Drive for the pulse and glide...

also do hypermilers draft a truck in neutral? where is the drafting sweet spot?


I have had my prius for almost 2 years and seem to be stuck on mid 40's mileage...

[AndreJ]

<div class='quotetop'>QUOTE(not another screenname @ May 15 2007, 02:10 PM) [snapback]442571[/snapback]</div>

The thread Title says it all...what is the disadvantage of using Neutral vice Drive for the pulse and glide...

also do hypermilers draft a truck in neutral? where is the drafting sweet spot?
I have had my prius for almost 2 years and seem to be stuck on mid 40's mileage...
[/b]

If you do mostly city driving that may be why? Ive noticed that my MPG in the city isnt that great due to alot of accelleration and stopping. Repeat and you get bad MPG, at least in my opinion. I drive 15 miles to and from work and thats where my AVG MPG comes from, if i do only city the mpg is horrible.

Other than that i have no idea what your talking about with "hypermilers draft a truck in neutral" ????

[kdk84]

I have had my prius a couple of weeks I do draft trucks but I never use neutral while driving. I find that the optimal draft range is 1-2 car lengths. I have filled up twice so far. First tank as 55mpg second as 58mpg. I use pure p&g method of driving. I also drive slower than I used to which i find slower avg. speeds can really boost mpg.

[bwilson4web]

<div class='quotetop'>QUOTE(not another screenname @ May 15 2007, 01:10 PM) [snapback]442571[/snapback]</div>

The thread Title says it all...what is the disadvantage of using Neutral vice Drive for the pulse and glide...
[/b]

There are two: (1) technically illegal to be in "N" going "down grade" but this is difficult to enforce and there is a risk on a down grade of exceeding MG1 rpm by rolling through 42 mph to a higher speed, and (2) you might forget it is in "N" and try to accelerate, nothing will happen.
<div class='quotetop'>QUOTE(not another screenname @ May 15 2007, 01:10 PM) [snapback]442571[/snapback]</div>

also do hypermilers draft a truck in neutral? where is the drafting sweet spot?
[/b]

I follow heavily loaded trucks but I do not draft them. I use heavily loaded trucks as a 'screen' so vehicles following me will pass us both. In some states, the trucks are limited to 65 mph and a few truck lines also use 65 mph as their upper limit. So I can follow them comfortably and traffic will flow around us smoothly. Better still, in hilly areas, a heavily loaded truck climbs the hills at the best Prius climb speed. We go up the hill together and I don't burn as much fuel nor worry about following traffic.

In the 1970s with a VW MicroBus, I did some drafting. The 'sweet spot' is in front of the turbulence burble. However, it is fatiguing and you can't see tire parts, junk and dead (or soon to be dead) critters before you have to run over them. Worse, in bad weather, you are blind and you have to be aggressive on the brakes (and pray there is no truck accident!)

Bob Wilson

[Bob64]

I'm scared to drive too closely to trucks because of the increased risk of gravel being shot into my windshield and cracking it or chipping/denting the hood. Am I the only one? Any other opinions about following behind trucks?

[gazz]

<div class='quotetop'>QUOTE(bwilson4web @ May 16 2007, 09:19 AM) [snapback]443273[/snapback]</div>

There are two: (1) technically illegal to be in "N" going "down grade" but this is difficult to enforce and there is a risk on a down grade of exceeding MG1 rpm by rolling through 42 mph to a higher speed, and (2) you might forget it is in "N" and try to accelerate, nothing will happen.

[/b]

Is that true that if you put it into "N" while at say 40mph therefore no energy being used and then going down hill you go up to say 47mph you could damage MG1. I have being trying this on very long slight down hills (more than a mile) and find it much easyer than gliding plus the ICE does not spin up and therefore use some energy if you exceed 42mph.

Is there a risk to the MG1?

[bwilson4web]

Hi,

<div class='quotetop'>QUOTE(gazz @ May 21 2007, 07:04 AM) [snapback]446554[/snapback]</div>

Is that true that if you put it into "N" while at say 40mph therefore no energy being used and then going down hill you go up to say 47mph you could damage MG1. I have being trying this on very long slight down hills (more than a mile) and find it much easyer than gliding plus the ICE does not spin up and therefore use some energy if you exceed 42mph.

Is there a risk to the MG1?
[/b]

We had discussed this in Prius_Technical_Stuff and there are two hypothesis: (1) mechanically stressing MG1, and (2) electrically stressing the inverter. The mechanical stress has been supported by various Toyota statements that the 2001-2003, NHW11 Prius has a maximum rpm limit of 6,500 rpm. In the 2004 Prius, the maximum MG1 rpm was moved to 10,000 rpm. However, I have been up to just under 50 mph and my MG1 didn't 'explode' or fall apart. Some of the Dept. of Energy studies suggest the NHW11 rotors have some thinner sections. To my knowledge, the 'forbidden experiment,' spinning MG1 to destruction has yet to be performed.

The electrical challenge is potentially a greater risk. As MG1 spins faster and faster, it will be generating a greater and greater voltage. If the voltage exceeds the breakdown voltage of the inverter electronics, it will convert those semiconductors into 'power resistors.' This would be a bad thing because these power semiconductors are also connected to the battery bus. But to my knowledge, no one has conducted this forbidden experiment.

Most engineering systems have margins of error. My thinking is you are likely to be OK but it would be wiser to try and stay closer to 42 mph than going much over 47 mph. I would probably slide it back into "D" around 42 mph enough to moderate the speed but otherwise continue coasting. Since there is a velocity squared aerodynamic factor in drag, slower, even when going down hill, is better since you'll have that energy in the battery for later use.

When I find myself coasting above 42 mph with the ICE off and in "N", I keep it in "N" and use the mechanical brake to slow down. My thinking is putting the car in "D" or any other gear will enable the inverter electronics and potentially reduce the breakdown voltage, a bad thing. It has to do with the "H" configuration of the power switches.

I hope this helps.

Bob Wilson

[gazz]

<div class='quotetop'>QUOTE(bwilson4web @ May 21 2007, 08:47 AM) [snapback]446605[/snapback]</div>

Hi,
We had discussed this in Prius_Technical_Stuff and there are two hypothesis: (1) mechanically stressing MG1, and (2) electrically stressing the inverter. The mechanical stress has been supported by various Toyota statements that the 2001-2003, NHW11 Prius has a maximum rpm limit of 6,500 rpm. In the 2004 Prius, the maximum MG1 rpm was moved to 10,000 rpm. However, I have been up to just under 50 mph and my MG1 didn't 'explode' or fall apart. Some of the Dept. of Energy studies suggest the NHW11 rotors have some thinner sections. To my knowledge, the 'forbidden experiment,' spinning MG1 to destruction has yet to be performed.

The electrical challenge is potentially a greater risk. As MG1 spins faster and faster, it will be generating a greater and greater voltage. If the voltage exceeds the breakdown voltage of the inverter electronics, it will convert those semiconductors into 'power resistors.' This would be a bad thing because these power semiconductors are also connected to the battery bus. But to my knowledge, no one has conducted this forbidden experiment.

Most engineering systems have margins of error. My thinking is you are likely to be OK but it would be wiser to try and stay closer to 42 mph than going much over 47 mph. I would probably slide it back into "D" around 42 mph enough to moderate the speed but otherwise continue coasting. Since there is a velocity squared aerodynamic factor in drag, slower, even when going down hill, is better since you'll have that energy in the battery for later use.

When I find myself coasting above 42 mph with the ICE off and in "N", I keep it in "N" and use the mechanical brake to slow down. My thinking is putting the car in "D" or any other gear will enable the inverter electronics and potentially reduce the breakdown voltage, a bad thing. It has to do with the "H" configuration of the power switches.

I hope this helps.

Bob Wilson
[/b]

Thanks for that explanation, you have put a lot thought into it. Thanks again