Cars

Under the skin: The future of transmission tech

A good engine can make a car but a bad gearbox can ruin it. Those almost unfathomable concoctions of gears, bearings, shaft seals and complex mechanisms almost always make the difference between a great drive and a mediocre one.

The gearbox has been underestimated, then, playing second fiddle to the engine; always the bridesmaid, never the bride. But electrification has given automatic gearbox designers a golden opportunity to have a greater influence on the way a car performs by integrating a hybrid electric motor-generator inside the gearbox casing instead of attached to the engine.

Transmission giant ZF Friedrichshafen has been steadily building a portfolio of hybridised automatic transmissions for years, giving car makers a kind of modular toolkit of gearboxes to choose from. They work in the same way as their conventional counterparts, except for the addition of an electric motor in place of a torque converter.

The external package is pretty much the same too, so they’re an easy fit. There’s no variable-transmission effect and the drivability feels the same as a conventional car, but the powertrain can harvest energy through regenerative braking or boost torque to the driveline from the electric motor-generator like any other hybrid.

ZF’s hybridised transmission range starts with a 20bhp 48V mild hybrid. This is followed by 54bhp and 121bhp full-hybrid, high-voltage versions and, at the top of the pile, a 134bhp full-hybrid version producing 295lb ft that can be used in both rear-wheel-drive and four-wheel-drive configurations.

The full-hybrid versions can decouple themselves from engines for driving in electric-only mode and incorporate electric pumps to keep the internal hydraulic mechanisms working when the engine is shut down for coasting or stop-start. More down-to-earth aspects of the gearboxes, such as torsional vibration dampers, can be tailored to suit an individual engine.

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