Shifting back into D from N, highway coasting

[brucepick]

I think I finally nailed the optimum technique for shifting back into D from N.
At least in my car, but this likely will work for others.
I think you'll need a tach to do this, but most cars seem to have a tach these days.

This gives me a smooth shift back into D without losing road speed. Best of both worlds, imho.

Coast with foot off gas. Just before shifting into D, rest foot on accelerator. Shift to D. Immediately press down accelerator (moderately) to bring rpms up to their "level". That is, up to where they don't just keep climbing quickly, and the drive system fully engages.

Since my transmission is by AW, Aisin Warner, this method might work for many cars. According to Wikipedia, Aisin AW surpassed General Motors Powertrain Division as the largest producer of automatic transmissions in the world, and supplies automatic transmissions to 35 automotive manufacturers around the world, virtually every major OEM.

In a highway coast (N), my rpms drop to about 800-900. Back in top gear under moderate load at 50-60 mph, the rpms will be about 2000-2500. So how best to accomplish the change in rpms?

How far to press accelerator after returning to D? I think I'm pressing to about the same level as it would be for a steady cruise at the current speed. That is, just enough to put some power to the wheels. You'll have to find the right degree for your car.

You'll see the rpm's climb to the speed needed to match the road speed. After that the rpms will climb slowly as the engine accelerates the car - assuming you give it enough gas to accelerate the car.

Methods that didn't work:

1) Foot off gas, slide shifter back into D.
This gives me a 1-2 mph drop in road speed. Not ideal, but a smooth shift.

2) Rev-match before going into D.
This gives a hard shift into D as the system re-engages, with engine spinning somewhere 1500-2500 rpm. I've tried rev-matching to different rpms, hoping that the correct engine speed would give a smooth shift. Nope, at least not for my car. I finally decided those hard shifts might not be good for the tranny.

But the combination method seems to work well. Back into D with foot barely touching pedal. Then press down to bring up rpms. Try it a few times and let me know what happens.

[Mentalic]

I do a good bit of N coasting and for the most part my speed is less than 40mph when I drop it back into D. Doing this I only get maybe a 100-200 rpm jump in rpm, seems like the transmission just goes to the high gear instantly.


During the fast coast my idle speed still remains a bit high, say 800-900rpm compared to full stop idle of 700rpm. Not sure whats going on here but I suspect its something to do with the radiator fan spinning up the engine. If I ever get my electric fan finished thats one thing I will be watching to see if this behavior changes.

The only reason I like the N coasting is the idle speed drops a bit reducing the fuel burn from .4gph to .3gph which cranks up the FE during the coast. I really don't see much difference in how far it coasts in D or N.

[popimp]

Set the Gallons to Liters I think you'll have a better idea.

[Hockey4mnhs]

i know if im going 59 my rpm is gonna be 2500 so i rev match to the speed. i know all the major rpm ranges and speeds for my car so i just rev it to were it needs to be then its good from there nice and smooth.

[brucepick]

Originally Posted by Mentalic

I...
During the fast coast my idle speed still remains a bit high, say 800-900rpm compared to full stop idle of 700rpm. Not sure whats going on here but I suspect its something to do with the radiator fan spinning up the engine. If I ever get my electric fan finished thats one thing I will be watching to see if this behavior changes...

Mine also. Fast coast, rpms around 800-900. Dead stop neutral, idle around 700.

I do have an e-fan installed, no clutch fan on the engine.

My theory is that the tranny + torque converter is being spun by the drive wheels, feeding back into the engine and spinning it just a bit faster than it would be at a standard idle when stopped.

Yah I know it's in neutral and supposedly the drive wheels are disengaged from the engine - but I think that in reality, somehow they're not fully disengaged. Just my two cents.

[Mentalic]

Originally Posted by brucepick

My theory is that the tranny + torque converter is being spun by the drive wheels, feeding back into the engine and spinning it just a bit faster than it would be at a standard idle when stopped.

Yah I know it's in neutral and supposedly the drive wheels are disengaged from the engine - but I think that in reality, somehow they're not fully disengaged. Just my two cents.

I have considered this as well. Just had a hard time seeing how it could be so. I mean, I can rev the engine in N but it don't move the car. Wonder if engine could spin the rear wheels if the rear wheels were lifted? Still somehow it must be the slushy causing the extra rpms though.
Humm, I wonder if the ECU is raising the idle speed during the coast based on the vehicle speed being so high?

[brucepick]

Originally Posted by Mentalic

...Humm, I wonder if the ECU is raising the idle speed during the coast based on the vehicle speed being so high?

Yah, maybe. I just have to go by how mine acts/reacts. They seem to not all be the same. And they're so complex inside, there's precious little information out there on exactly what's happening inside. So I've tried my best to see whether it coasts better in D or N (looks like better coasting in N for me), and the rest of all those wild variables.

Exception to the "lack of info" thing: the big GM auto trannies that the performance guys use. I think those things are pretty well mapped out by now, especially if you want to use them for more go-power. If using it for increased FE, there might be an information shortage on those too.