What is the future of gearboxes?

Purely electric power units and electrified powertrains are taking control of the future of vehicles, but the gearbox is here to stay

A good engine can make a car, but a bad gearbox can ruin everything. These highly complex mixtures of gears, bearings, shaft seals and mechanisms almost always make the difference between a great drive and a mediocre one.

The gearbox has been underestimated, but we must remember that a good engine without a good gearbox is nothing. Electrification has given automatic gearbox designers a golden opportunity to have a greater influence on a vehicle’s performance. How? By being able to integrate a hybrid electric motor/generator inside the gearbox housing instead of being connected to the engines.

Transmission giant ZF Friedrichshafen has been building a portfolio of hybridised automatic transmissions for years, offering carmakers a kind of modular gearbox toolkit to choose from. They work in the same way as conventional ones, except for the addition of an electric motor instead of a torque converter.

Transmissions: what will change in the future of electric cars?

The external package is also virtually the same, so they fit easily. There is no variable transmission effect, and the driving capability is the same as that of a conventional car, but the powertrain can ‘take’ energy through the regenerative braking system or increase torque to the transmission line from the electric motor-generator like any other hybrid.

The ZF hybridised transmission range starts with a 20 CV, 48 V mild hybrid version. These are followed by the 55 CV and 125 CV high-voltage full hybrid versions and, at the top of the manufacturer’s transmission models, a 140 CV full hybrid version producing around 400 Nm that can be used in both rear-wheel and four-wheel drive configurations.

The fully hybrid versions can decouple from the engines to drive in electric-only mode and incorporate electric pumps to keep the internal hydraulic mechanisms running when the engine is switched off by coasting or by the start-stop system.

Pure electric vehicle gearboxes are much simpler, with, in most cases, a single-speed reduction gear to reduce the speed of the electric motor from around 12,000 rpm to a more modest speed. Smaller high-speed electric motors (over 20,000 rpm), which produce less torque but save weight and space, are combined with a two-speed automatic gearbox. But even simple single-speed gearboxes have more to them than meets the eye. We can use as an example the Volkswagen ID.3, which uses a two-stage single-speed gearbox.

The engine revolutions must be reduced 10 times at the wheels, and doing that with only two gears would mean that the diameter of one of them would be too large to fit in the available space. Instead, the gearbox has two pairs of gears: the first reduces the engine revolutions in one stage and the second pair finishes the job. This is almost as complicated as a single-speed reduction gearbox, and although they can be electronically complex, it is a good illustration of how mechanically simple pure electric drive systems are, and how some of the most familiar and basic components have a fundamental role to play.