Do electric cars have gearboxes?
When you drive a fully electric car for the very first time, you may wonder why there isn’t a gearstick next to you. And once you set off, you may be quite surprised to note that, as the car speeds up and slows down, it doesn’t automatically shift through gears like an automatic car would. That’s because there are no gears at all in an electric car.
Electric cars don't have multi-speed gearboxes like all petrol or diesel ones do. Instead, they get away with just a single gear. This is especially impressive considering how fast some electric cars can accelerate. The Tesla Model S Performance, for example, can do the 0-60mph sprint in under 2.5 seconds, making it quicker than most supercars.
Why do electric cars have only one gear?
There are many reasons why electric cars have only one gear. The first is that electric motors rev to a significantly higher rate than internal-combustion engines. A typical electric motor can rev up to 20,000rpm, far higher than the usual 4,000-6,000rpm limit for conventional cars.
Also, electric motors are power-efficient throughout this rev range, meaning they don't have to operate within a small, narrow rev band to deliver optimum performance. This also means electric cars make almost instant torque from zero revs, so they don't have a specific rev range suited to low-speed driving or acceleration.
The reason conventional diesel and petrol cars need a gearbox with multiple gears is because the engine is on;y capable of generating useable torque and power in a very narrow band of engine speeds.
The varying gear ratios help the conventional engine keep within that 'power band' at different speeds. That’s why a petrol car will easily accelerate to 20mph in first gear, but won’t go much faster without reaching the engine’s rev limit, or 'redline'. By the same logic, you'll struggle to pull away from lights in sixth, as this ratio is designed for faster driving.
Electric cars can reach top speed in a single gear, with little compromise in low-speed driving or usability. What engineers do is pick a gear ratio that strikes a good balance between acceleration and top speed. Pick a ratio too low, and the engine will accelerate very fast but may be limited to only a low top speed. Conversely, if engineers pick an extremely high ratio, the gearing may be optimal for top-speed runs but acceleration will suffer.
Can electric vehicles have more than one gear?
There are some electric cars that have a multi-stage gearbox. Some teams contesting the Formula E electric single-seater race series have chosen to run their vehicles with a three-speed gearbox.
Although the cars are limited to a maximum power output of 170kW, the speed at which they reach this is crucial. Some teams, like Audi, ran their 2017 car with a three-speed gearbox. The addition of a gearbox helped the car reach maximum power slightly quicker. However, for the 2018 season, the team opted to run a high-efficiency transmission system with a single gear.
For road cars, engineering firm GKN Driveline recently introduced a two-speed eTwisterX electric driveline. In simple terms, the addition of a second gear allows for better acceleration and top speed than single-speed electric drive units.
For low-speed acceleration, the electric vehicle sits in first gear, helping it launch quicker. When on the motorway, the car will automatically shift to the second gear for better high-speed driving and a higher top speed. A setup similar to this is used in the Porsche Taycan high-performance electric car.
Does that mean plug-ins and hybrids have an electric motor with more than one gear?
Most hybrids (plug-in or otherwise) have a standard electric motor with a single gear, as this is cheaper and less complicated to manufacture. And as explained above, single-geared units give away very little in terms of performance or efficiency, mitigating the need for a two or three-speed gearbox.
What are the benefits of having just a single gear?
From a manufacturing point of view, the biggest benefits of having just a single gear to operate the electric motor concern cost and simplicity. Installing a driveline system with multiple gears immediately adds cost and complexity, which increases the car's price.
Given that electric cars already tend to cost more than their diesel and petrol counterparts, it's unlikely manufacturers will want to add unnecessarily to the price. This is especially true when the single gear setup is already optimal for most electric cars, and delivers equal or even better performance than conventional powertrains can offer.
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