I know electric cars don’t need multiple gears, but wouldn’t they benefit from them in anyway at high speed for example?
In: Technology
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Depends on the type of electric motor but that’s generally covered with a fixed, single-speed, speed multiplying gear set.
Electric motors generally make their full power from ~0RPM to their max speed rating, which doesn’t have nearly the kind of complexity or restrictions as an internal combustion engine.
Electric motors are superior in basically every way and don’t need pleb transmissions for most vehicle types, in practice.
We can draw analogy from trains.
Diesel locomotives of trains are actually diesel-electric. Transmission adds so much weight to the system, that it’s impractical. The Diesel engine is actually just a generator and electric motors are mounted directly on the wheels/axels.
Much like we see in fans, you don’t need transmissions/gears to change torque/speed. Changing the input does the trick.
It adds an unnecessary point of failure. Tesla tried a 2 speed with the roadster and it was too unreliable.
They opted for a 1 speed transmission instead. It was still an unnecessary point of failure. Hence why they no longer use transmissions.
A gas engine is only efficient at a certain rpm range. Outside that specific range of speeds it loses power rapidly. So gearing let’s the motor stay in its sweet spot over a larger range of speeds.
Electric motors do not have this problem. They basically push as hard as tge amount of electricity you run through them regardless of what speed they are spinning at. The trick there is controlling the electricity to make that true … and we have very awesome computers to control the power flow nowadays.
That having been said… the faster an electric motor is spinning the harder it is to push more power into it. One solution to that could be a transmission but in practice it is easier just to raise the voltage of the battery so you can push harder. Modern EVs are running on 408V batteries for the traction motor. 🙂
There’s a big thing to keep in mind: Transmissions require energy to work.
It’s called a “parasitic loss”, the friction of gears/lubricant/bearings etc. results in around 10-20% of the motor’s energy not making it to the tires because it’s turned to heat by friction.
Single-gear drives are as efficient as possible. Since the motor has the low-end torque to accelerate with ease, and the high-end RPM to handle highway speed and beyond with ease, there’s nothing to be gained.
Some dual motor Teslas use different gearing in the front and rear motors, so one is optimized for acceleration and the other for steady speed. https://insideevs.com/news/338618/has-tesla-changed-how-it-controls-front-amp-rear-motors-for-model-3/. Why use a transmission when you have multiple motors to choose from?
Hydro Quebec 1995 7 minutes https://youtu.be/jHmxJPTWD-M I still wonder why companies such as Tesla don’t use this technology.
They actually do! Bosch and some other companies are working on two speed and continuously variable transmissions for this space! The hang is that you don’t benefit that much but you add a good deal of cost, complexity, and packaging. The reason they don’t benefit that much is because an electric motor has a much wider range where it operated at high efficiency vs a combustion engine.
Look up “permanent magnet synchronous motor efficiency map” and “gas engine efficiency map” for some more technical insight!
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