At our recent post of videos showing how manual transmissions work, there were a few commenters saying that it was the workings automatic transmissions that were still something of a mystery to them. Well, here’s a couple of well-animated videos that should help.
These focus on the most common type; the torque converter planetary-gear automatic, in this case the six-speed Allison 1000 as used in GM diesel HD pickups and such. There of course other types, but let’s focus on this, even if conventional automatics are starting to be increasingly replaced by CVT’s, which are actually very easy to understand.
This first video is pretty good, covering the basics with lots of 3D graphics.
Trying to perfectly understand the dance of planetary gear sets, especially when there’s multiples of them can be a bit daunting. The key elements are to understand how a torque converter works (below) and a basic conceptual understanding of the magic of planetary gear sets.
Here’s two videos on torque converters. I have some mixed feelings on this one, as it starts a bit backwards, with the torque converter’s ability to disengage the engine from the wheels under braking. Seems to me that explaining how it gets the car underway should come first.
This one is a bit more narrowly focused, but in a good way, with perhaps better graphics in some key aspects. Between the two, you should be able to get a pretty good idea of how they work.
If those are a bit to…um, modern for you, with all those fancy graphics, here’s an Army film from 1954 on fluid couplings. Note that the fluid coupling lacks the stator that allows the torque converter to amplify torque. That requires fluid coupling automatics, like the original Hydramatic, to have more gears, to be able to start from rest without the benefit of torque amplification.
Hope this helps. The dance of the various planetary gear sets can be a bit complicated to fully divine, and there are of course variations of them, but as long as one understands the basic principle, the rest can be left to the transmission. it’s an automatic, after all.
The second video may not be sufficient to totally explain the function of the stator (called the reactor in the first one). I would not skip over the first one. The fluid coupling function in the first is quickly past and easy to comprehend.
My learning about automatics and torque converters was from factory service manuals which explained the operations in text with limited illustrations; specifically a Cadillac manual for a late four-speed HydraMatic which had no torque converter but two fluid couplings, one replacing a clutch pack for smoother shifting; and a Chrysler manual for the three-speed/torque converter TorqueFlite. My first transmission rebuild was a simpler two-speed aluminum PowerGlide, done at home in the garage. The Chevrolet service manual included complete transmission rebuild instructions.
I would not want to even THINK about rebuilding something like the nine-speed ZF transmission! Generally that is not done in the field; Remove and Replace with a new or factory rebuilt one instead.
Thanks Paul for posting this!
When I had the Mustang’s transmission rebuilt a few years ago, Brian, my transmission guy, tried to explain all this to me. Although a mechanical designer/engineer (ME w/o the sheepskin), the operation of these, especially the torque converter, was always a little confusing to me.
Then I come here and here you all use the term “slush-box”. After watching the videos, it would seem that the only “slushy part” is the torque converter itself!
Great 3D modelling in the two 3D graphic videos. When I get a chance, I need to go back and watch the 2D representations.
Good Stuff! (as was the Manual Transmission video the other day).
Would like to see a layout of the ten speed transmissions that Ford and GM are using in there pickups. The 10 speed had only a slight weight gain over the six speed it replaced. I would guess that the solution was using a gear set as a range possibly being a 5 x 2 to get the ten gear ratios. What I noticed on mine is depending on load it either uses all the gears or it skips every other gear. Even at heavy loads, 14-15,000 lbs, in tow/haul mode the trans will go into 10 gear if you are running fast enough and winds are minimal or with a tail wind.
Howard Simpson was an engineer working for Henry Ford on the Model T planetary transmission. He was told he had a fatal condition and retired to Arizona to presumably live a brief life. While there he continued to invent and file patents. I think he ended up living a fairly long life on top of it. His “Simpson gearset” became the standard for 3 speed automatics for Chrysler and Ford and Borg Warner. GM would not pay for royalties on his patent so that’s one reason they were late to the 3 speed automatic party.
But where is the explanation of the maze with the little tiny Minotaur down in the valve body? Planetary gear sets are relatively obvious compared to the hydraulic black magic that actually shifts the gears.
Indeed…when it was all done by hydraulics, the pressurized fluid working the clutches (and bands, which are not even mentioned in either video but which were present in virtually all “heritage” automatics)! With electronics having taken over long ago, things are perhaps simpler now. Electronic servos turn valves on, off, whatever to apply and release clutches.
It definitely made more sense when I saw a fordtechmakuloco video diagnosing an overdrive brake band actuator and solenoid. Fortunately my 4R70W only had a broken wire in the overdrive switch.
To me at least, autos are much like differentials and manual transmissions, much easier to understand if you have one apart in front of you. Take it apart and it starts to make sense. Look at a diagram of how power flows and it will make your head spin.
Electronic autos are even simpler in a sense, which makes lousy ones that do things like endlessly cycle between gears on an incline even worse, they could have made it better, thru programming, they just didn’t care to do so. It might have required another dozen lines of programming in the hundreds already in there. An afternoon for the programmer.
I’m not an auto fan, I think most are crappy to drive, but I have driven a couple that worked so well they made my jaw drop. Proving even more they can do it if they want to.