Is it possible for an AT to disengage from motor at idle?

[ray7792]

Silly question but I haven't found an answer anywhere on the web.

A M3 with a dual clutch will not roll forward automatically at idle because well... it has a clutch that will be disengaged at a stop.

Is it possible to replicate this with a torque converter? Can you have 100% slippage during idle so that the car won't roll forward? Or possibly tune the car idle lower or make less power so that there isn't enough energy being transferred through the TC to move the car?

Is the latter safe? Should be pretty easy to lower in-gear idle in romraider or retard the timings at idle RPMs in gear.

Don't really have a real reason to actually needing this, might be fun though lol

Thanks!

[Speed2th]

Just push the gear into N?

[juliog]

Originally Posted by ray7792

Can you have 100% slippage during idle so that the car won't roll forward?

100% slippage is already happening when you keep your foot on the brake at a stoplight, and the car is still in Drive.

[Itzed]

You really can't just turn down the idle speed these days with all the computer controlled parameters.

[drewbot]

One thing that comes to mind though is that the idle RPM varies also, probably making it hard to program in. ie. when AC is on or not

One would probably need to crack the TCM and figure out how to tell the tranny to disengage when throttle = 0%, when brakes are not being used, and when RPM is less than 1500.

[aznatama]

Why do you want to do this?

To disengage the Tq Converter, push transmission into N... however, if you are concerned about moving, you'll still need to engage brakes. The newer high end dual clutch/smg/dsg/fancypants-transmission cars have auto-brake, which keeps the brakes engaged until you hit the accelerator.

[NickTC]

Originally Posted by drewbot

One thing that comes to mind though is that the idle RPM varies also, probably making it hard to program in. ie. when AC is on or not

One would probably need to crack the TCM and figure out how to tell the tranny to disengage when throttle = 0%, when brakes are not being used, and when RPM is less than 1500.

At the very least, it would teach you not to lug your engine ever.

[Poodles]

Originally Posted by ray7792

Silly question but I haven't found an answer anywhere on the web.

A M3 with a dual clutch will not roll forward automatically at idle because well... it has a clutch that will be disengaged at a stop.

Is it possible to replicate this with a torque converter? Can you have 100% slippage during idle so that the car won't roll forward? Or possibly tune the car idle lower or make less power so that there isn't enough energy being transferred through the TC to move the car?

Is the latter safe? Should be pretty easy to lower in-gear idle in romraider or retard the timings at idle RPMs in gear.

Don't really have a real reason to actually needing this, might be fun though lol

Thanks!

Short answer: No.


Long answer: Even when in Park or Neutral, the torque converter is still being powered by the engine. It's never completely disconnected as it's a fluid coupling. To disconnect the engine from the drive wheels, it has to be disconnected in the transmission, not at the converter. Also, newer cars can "lock" the torque converter so it's in essence a direct drive much like a clutch. This, as well as the better gearing allowed by the torque multiplication of the torque converter allows automatic transmissions to get great gas mileage today.


The transmission is always connected to the engine, and needs to be as the transmission fluid pump is driven off of it as well.


Lowering the idle wouldn't do anything as the way the torque converter works allows it to multiply torque. Stall speed of the converter comes into play here, but it's quite complicated.


If you want more info, look up how a torque converter works and stall speeds, ect. The rest of the transmission isn't as important to your question.