HOW IT ALL WORKS
A MANUAL gearbox is a simple and straightforward affair; each gear has its own cog in the box, a big lever shifts them, power ensues. Automatic transmissions are a little more complicated. Rather than specific cogs for each ratio, they use planetary gears much like you find in a winch, with one feeding into the next. By using a series of brakes and clutches, the ’box is able to control what gears are engaged and what the final ratio will be.
The clutch has a complicated alternative, too. Up front, a torque convertor acts like two fans pointing at each other; although, they pump fluid not air. It lets the engine-side fan spin harder and harder until the transmission-side fan starts turning, which is what provides torque multiplication and what stops the 4x4 from stalling when you come to a stop. At certain speeds the transmission can completely lock the torque convertor, giving you direct drive to the ’box.
What’s all this got to do with programming? Back when stubbies were in fashion and VL Commodores were considered high-tech, the transmission controlled all these different operations by pumping transmission fluid through complicated valve bodies that’d engage the different clutch packs, giving different gear ratios. This complicated system has now been replaced with simpler solenoids, all controlled by the CU. The CU relies on a whole bunch of inputs, with everything from the throttle position and road speed to how many corners you’ve just taken all being considered before it’ll kick up or down a gear. The result is a more intelligent transmission that does what you want, when you want it, and one that can be easily modified without even dropping the fluid.