Driveline Drag

[vehdynamics]

Can someone help me out: I am curious, on a vehicle with an automatic transmission, torque converters are designed for power transfer from the engine to the driveline, but from what I understand, they are ineffective in the opposite direction. So when the wheels decelerate faster than the engine components would decelerate due to their own friction, how are these components slowed down?

[Schister66]

the engine isnt' revving anymore so the engine side slows on its own, seperate from the other side.

Someone needs to elaborate on this a lot....i know how it all works, i just don't know the names of things anymore because i dont know autos that well.....

[vehdynamics]

no, no, that's not necessary. I understand that the engine will decelerate due to its own friction, inertia, etc...

I'm not really sure what you mean when you say that the engine isn't "revving" anymore, as revving refers to revolving and the engine doesn't just stop. Perhaps you're referring to the fact that the throttle is released?

I just wasn't sure whether or not the crankshaft is decelerated by some other mechanism or if it (as you said) slows down on its own.
Thanks for the help

[Schister66]

no the crank, and the entire engine, slows because the throttle is shut....

[curtis73]

+1 to schister. The engine's free-spooling RPM is entirely based on how much air you're letting in and how much fuel the injectors give.

When you close the throttle, the engine is sucking vacuum HARD. Since it can't get any air it slows down.

When you're accerating, the engine pushes the TC which fluidly trasfers the power to the tranny and wheels. When decelerating, the engine wants to return to idle speed, but the wheels are pushing the transmission which pushes the TC. The fluid coupling still works in that direction just not as well.

Its just engine braking. Its similar to operating a manual transmission vehicle with the clutch only about 80% engaged.