How does a torque converter work when it is being back driven?


Assuming there is no lockup clutch that locks the turbine and impeller together, how does a torque converter work when it is being back driven (turbine spins faster than impeller) such as during engine braking or going down hill (wheels pushing engine)?

Wouldn’t it be less effective because the curly blade angles design of the turbine?

If the turbine is bolted directly to a differential and the torque converter is filled and sealed, by pushing the car, will there be enough torque turning over the engine?


In: Engineering

The engine turns the torque converter the same way if you’re backing up or going forward. The transmission just has extra gears that let it rotate its output shaft in the reverse direction – this happens when you’ve selected reverse instead of drive.

This is like two fans pushed up against each other – a faster the difference in spinning speeds mean, more torque is applied, but also more drag. This coupling transmits torque works both ways – but I suspect they’re designed to be most efficient when the engine side is spinning faster than the transmission side.

I think you might be getting mixed up about ‘needing’ to apply torque to the engine to keep it spinning. Even if the engine is producing zero torque (e.g. while engine braking), the control system will restart the flow of fuel before the engine can stall. Typically using a moving speed envelope so it can be softly ‘caught’ and restarted without jerking the powertrain.