If we compare a petrol engine and an electric engine car, it is sufficient for the...

If we compare a petrol engine and an electric engine car, it is sufficient for the electric engine car (e.g Tesla Roadster) just to have 1 gear (forward), whereas petrol engine can have up to 7. Why is it sufficient for the electric engine to have a single gear? Is it because it can deliver the required torque always?

Expert Solution

Yes, electric motors can always deliver the required torque. What really matters is the efficiency of the conversion. Over a long range of speeds, the motors may convert 90 percent of the energy to its mechanical form. You know, it's just some electromagnetic fields that may become arbitrarily stronger - depending on how much energy is sent into them - and that always do the required work.

On the other hand, petrol engines are only highly efficient over a relatively narrow interval of the number of revolutions per minute (RPM) of the engine. It takes a certain time for the fuel to get burned or explode, for the pressure to spread in the cylinders, and whatever else needs to be done in each cycle. Moreover, at too high frequencies, the motor could get overheated and damaged, among other things. That's why petrol engines want to keep the number of RPM relatively constant and a gearbox is needed to translate the fixed frequency of the motor to a variable speed of the car.

genius_generous answered 2 years ago

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