HOW IT ALL WORKS

4 x 4 Australia - - Gear -

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.

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