Torque converter scheduling.

[sprasad6]

Hi PHers,

I'm new here, have many questions, but I'll start with this:
Across the different vehicle operating conditions what strategy does one use to decide whether the torque converter should be locked or opened? My apologies if the question is vague.

[anonymous-user]

LOCKED, as much and as soon as possible.

Things that stop it being locked are:

1) speed too low (obviously can't stall the engine)
2) TV too high (high load at low rpm means lots of Torsional vibration, enough to wreck the converter or gearbox. Leaving converter un-locked means the fluid coupling smooths out these oscillations
3) Average Torque too high. Back in the day, the locking clutch in the converter wasn't sized for full torque, so had to be unlocked at high torque demands. However these days, it is generally rated to remain locked pretty much at all load conditions
4) Gearbox oil very cold. TC remains unlocked so the extra losses in the fluid coupling help warm the transmission up faster (cold oil is more draggy, so gearbox losses increasse with decreasing oil temp.

[GreenV8S]

Maybe related to point (3) below, I guess that you would want to avoid lock-up while there was excessive slip in the coupling such as immediately after a shift. This might fall under the scope of excessive torque if torque is being measured at the output.