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
Can anyone explain what torque and rpm are in a car , and their relation with the car’s speed , I’ve studied about them in school but still find it difficult to correlate it in car aspect
Also there is centrifugal force. Wouldn’t there be a limit? Anything spinning would be under stress and want to fly apart. If anything, with the immense amount of torque an electric motor generates you could at the very least put an over drive gear on it for highway use. Like would that save on the charge?
They have something called a variable frequency drive that uses the motor to do above and beyond what a transmission would do in the drivetrain. No reason for more moving parts and a heavier, more complex, vehicle.
Edit; One thing I thought about, if we ever start making heavy duty electric trucks, there might be a need for a style of transmission to get a low gear with lots of torque.
Internal combustion engines (almost all) have to convert up-and-down motion to pure rotational motion. If you are cruising along the highway, your engine is probably doing 3,000 rotations per minute. For each and every rotation, the piston has to come to a complete dead stop at the top (top dead center) and the bottom (bottom dead center). After it comes to a complete dead stop, it has to accelerate like mad, only to have to stop again at the bottom.
All this stopping and starting is hard on the internal bits. Most engines *really* don’t want to go past 5 or 6,000 RPM. The engine would literally fly apart because all those forces just got too crazy big. So it’s not just an efficiency thing that cars with gas or diesel engines need a transmission. It’s to keep the rpms down in the non-explody range.
Electric motors don’t have any reciprocating parts. It’s all rotational. No converting. No stopping and starting 6,000 times a minute. It is trivially easy to design an electric motor that zooms all the way to 20,000 rpm. Plus, they make waaaay more torque at very low rpms. They have a huge band of efficiency across a huge rpm range. Thus, no transmission.
This is because an electric motor produces the same force – the same torque – at pretty much any speed, as long as you can keep the voltage up. The torque, or force, that you get out of an electric motor is governed by the electric current you force through it, and when it comes to a motor, that is dictated only by the thickness of the wires and the design of the cooling system. But as an electric motor’s speed increases, it generates an increasing voltbe called a ‘back EMF’ impeding the current flow, meaning you need more and more voltage to push the current through.
And because a high capacity battery contains a lot of individual cells, you can reconfigure them with switches to provide really high voltages.
So really, what you have to do with gears on a petrol engine, you do by switching banks of batteries (or using an inverter to step the voltage up or down) in an electric one, increasing voltage at the expense of current and torque.
No, electric motors have full torque from zero. There is no need to put it through a gear box. Not when trying to achieve automobile speeds anyway.
Not an explanation but I’m a mechanic and I have a few customers with electric converted cars. Some of them do have manual transmissions. They only built them to push so much voltage so you can feel when it is topping out and you need to switch gears.
Yes! Tesla’s original concept for the Roadster utilized a multi speed transmission. Electric motors have lots of torque(what gets a car moving quick), and it’s 100% available right away unlike gas engines, which is great but also a problem: making transmissions that don’t break under the torque is a big challenge. Tesla abandoned them because it was taking them too long to build and they needed to release the car.
Where transmissions would benefit electric cars the most and what a lot of other answers are missing is range and efficiency. Even though electric motors have all the torque available right away, it doesn’t mean they’re efficient at low speeds. Unlike gas motors, electric motors are happiest being spun very fast, spinning them slow and asking for power makes them very hot and uses tons more energy than running very fast. So that means you lose range. Not unlike gas engines that are most efficient running at a certain speed/RPM. Because electric motors hit peak efficiency at high RPM, it also means they REALLY run out of power at high RPM too. Many electric vehicles have pretty poor top speeds for this exact reason: you can’t make a motor/engine that is efficient at low AND high speeds, regardless of electric or gas. High end expensive electric cars compensate with bigger/more powerful motors and larger batteries, but this increases cost dramatically and isn’t really a “solution”.
So the similar gains can be applied to electric motors with a transmission. Or more specifically, you could achieve the same performance with a smaller motor by having multiple gears for different speeds, increasing range dramatically because a smaller motor uses less energy.
Porsche actually used a multi speed transmission in the Taycan, and there’s LOTS of companies investing R&D into developing transmissions that can hold up to electric motors. Electric cars of the future WILL have transmissions.
1) There are electric axle with two (or more) gears, it’s basically a tradeoff between cost, efficiency and performance. For normal passenger vehicles the added cost and complexity of a gearbox is just not worth the benefit (efficiency and performance wise).
2) e-motor/inverter development improved significantly over the last years (higher rotational speeds, higher voltages, higher efficiency, better cooling, …), which makes the need for additional gearboxes even less relevant.
For more commercial and special vehicles, cost of a gearbox becomes more justifiable pending the amount of usage in certain regions and need of torque … .
Some eletric cars and motorcycles have gears.
So I guess it does help some. For instance the Porche Taycan has 2 gears, one for fast acceleration and one for cruising at higher speed, with the latter being better for the battery.
[https://newsroom.porsche.com/en/products/taycan/powertrain-18555.html](https://newsroom.porsche.com/en/products/taycan/powertrain-18555.html)
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