How The Automatic Gearbox Has Evolved
Over the last forty years, the automatic gearbox has undergone a dramatic transformation. The changes, driven by the quest for higher fuel economy, have led to an almost unrecognisable gearbox.
Number of Gears
To keep the transmission running in the most efficient part of its cycle required more than the three gears available at the start of the 1980s. By the end of the decade, the leap had been made to four gears. In another ten years, the fifth gear was added. Leaping to six forward gears was a huge technological challenge. The issue was finding the space to squeeze all the gears in.
To fit all the gears into the space required some creative engineering. Planetary gear sets have been around since the 1950s. These involve mounting multiple gears around one main sun gear.
The revolution came when ZF (a German transmission manufacturer) successfully combined numerous varieties of planetary gearsets to increase the range while also reducing the space required. This groundbreaking discovery was made in 2002.
Moving from 5HP to 6HP
To understand the magnitude of this change, it’s helpful to compare ZF’s 5HP to the 6HP, which featured the new gearset. The 6HP had 190 fewer components in it, so weighed around 13% less, took up less space, accelerated faster, and was 7% more efficient.
The 6HP also could disconnect the engine from the torque converter to reduce fuel consumption. It was also the first time that adaptive shift strategies were used.
The refinement has continued. The 6HP then gave way to the 8HP, which has two more gear ratios and has even better efficiency.
The 6HP also marked the begging of integrated drive trains. It is now standard for the engine and the gearbox to ‘talk’ to each other. But this didn’t start until the 6HP.
The next significant innovation came in the 9HP. This transmission was designed for transverse engines and was able to work in a very different manner to its predecessors. It supports start/stop systems. The clutch mechanism was changed to save on space. The gear set was swapped to a nested variety, which further cut down on the space requirements and weight.
Now: Hybrid Compatibility
Many modern automatic transmissions are now compatible with hybrid drive trains with no need for modifications. The modern automatic gearbox is smaller, lighter, more efficient, and has many more gears than its forerunners. It’s exciting to consider where innovation might take it next.
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