Torque of the town | Learning about torque converters

When it comes to handling huge horsepower and drag launches, it’s hard to beat an automatic. Rather than using a solid mechanical connection like a manual or twin-clutch transmission, an automatic transmission transfers power through fluid using what are essentially special fans. This key interaction happens inside the torque converter, a device with three major components: the impeller, turbine and …

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I think that incremented some of my (reluctant) automatic knowledge, but it needed pictures. Centerline on what axis? What's the overall shape internally? Shape of the impeller? Of the turbine? of the stator? Of their fins? Arrows for fluid flow?

How does torque multiplication work? I assume it's something like converting levers or gears to a hydraulic context, but outside of positive displacement hydraulics that's not intuitive.

It's a topic that's not well covered, and I'm thankful for a stab at it that improved my understanding, but the better-than-average explanation makes the bits I still don't get stand out all the more!

Please explain the switch pitch converters of the late 60s GM cars , 

These seemed like a great idea to basically have 2  converter styles at once ( if I understand the principles)
 

Thanks

In reply to Jesse Ransom :

The stator controls the torque manipulation. It is what drives the fluid back against the impeller. It is always turning until it quits and that is the stall speed because the stator "stalls out" and doesn't turn faster than the impeller anymore.

The "attack" angles of the stator and impeller dictate the desired stall speed. If you don't have these components complementing each other, you end up with a junk converter or one that does not operate as intended.

In reply to californiamilleghia :

There was a triggered solenoid that moved the angle of the stator which gave the 2 separate stall speeds. It's a sucky system that works in theory mostly and just overly complicates everything else.

In reply to Jesse Ransom :

If you can visualize a block and tackle arrangement that gives you mechanical advantage, you can get how there can be torque multiplication.

A better analogy, although a little less inside our normal reference, is getting thrust by throwing a ball in a zero G room.  If you throw the ball hard enough to hit the wall, you thrust yourself in one direction and you thrust the room the other way.  If the room geometry is such that when the ball bounces back it hits you, then that is 3x the thrust for the same initial effort.

Now instead of zero G rooms and balls, imagine spraying a water hose at a curve that directs it back at you.  Actually a better analogy would be to imagine the inside of a torque converter...

californiamilleghia said:

Please explain the switch pitch converters of the late 60s GM cars , 

These seemed like a great idea to basically have 2  converter styles at once ( if I understand the principles)
 

Thanks

I always wondered if there was a way to have both switch pitch AND lockup.  It'd be like a 3 stage converter.  First 2 stages for banging around the street and then lockup for highway. Probably overkill though since you can get away with a fairly loose (high stall) converter when you have the lock up ability 

In reply to A 401 CJ :

Yup.  I have a maybe 4000-4500 stall speed converter in my S60R.  (Drive by wire makes it hard to tell exactly)  It drives normally most of the time.

One thing about loose converters and lockup is that it is tricky to tune the lockup point.  I did an MS3Pro in a Grand National with a 3000rpm converter.  What would happen is when you would lock the converter at highway speeds, engine load would go up, which would unlock the converter... Tuning lockup by throttle position would probably make more sense in that case, plus there was probably some more to be had in the timing curve but I ran out of time for messing with it.

This is probably the clearest picture on how a torque converter works (at least to me) that I could find in a quick Google search:

Technically I think the stator is connected to the gearbox as well through a one way clutch.  The stator increases the energy harvested from the fluid, making the torque converter more efficient.  By mostly recirculating the fluid through the vanes you reduce pumping losses.  If you were constantly circulating new fluid through you'd be losing a bunch of energy to just pumping the fluid around, instead of moving the car, like you want to.

In reply to BA5 :

Thanks for the diagram! Having rebuilt several 4L60e and 1 FWD Mopar auto successful, and even attended a few GM auto trans classes I understand the transmission itself pretty well, but the converter always seemed like voodoo to me. This diagram and the explanation in the OP made it much clearer.

A simplified diagram...