A possible replacement for a torque converter

[Serj]

I was reading up on torque converters. They looked very bulky and heavy. I was thinking perhaps a torque converter could be made better if it was simply two turbines and a tube of varing x-sectional area. The idea is a small centrifugel turbine pumps fluid through a pipe with a very small cross sectional area. The fluid flows at a high velocity. The tube expands and the fluid moves slower but at higher pressures. This slow high pressure fluid spins another turbine of equal or greater size of the first turbine. The second, or output, turbine has more pressure behind it so it has more torque.
Will this be better than a conventional torques converter? It would be lighter but the high speed fluid may cause resistance reducing efficiency. This could be reduced by giving the majority of the pipe a large x-sectional area, but that would would mean more weight from the extra metal needed to conatin those high pressures.

 

[faust9]

You basically described the current Torque Converter design except you've added a requirement for a higher pressure pump (remember, the entire transmission uses the same pump and fluid so changing the pump requires a redesign of the valve body, actuators and accumulators as well) and a variable cross-section pipe.

Torque converters are actually very efficient now-a-days because newer cars include a lock-up feature when the vehicle is in third and/or forth gear. The lock-up prevents torque converter slip thus removing the source of ineffeciency from the system. At lower speeds the slip is needed for the torque converter to work properly (the engine spins from 5%(highly efficient) to 15%(race) faster than the transmission input shaft). The slip acts like the clutch in a manual trans. You can't dump a clutch and expect the engine to run well--most cars will stall if the clutch is dumped. You have the slowly let off the clutch. That's what the TC is doing.

[edit] Here: http://auto.howstuffworks.com/torque-converter.htm
Notice the outer shell is one turbine--the drive turbine-- and located in the center of the unit is a second turbine--the driven turbine. The flexplate connects to the outer shell, and the trans input shaft connects to the inner turbine. The outer turbine spins the fluid, and the spinning fluid drives the inner turbine.