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Comment by reycharles | Hacker News Reader

In an electric car? Really? I don't know too much about electric cars, but it's my impression that gears and transmissions are completely unnecessary in an electric car. Please correct me if I am wrong.

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There is usually a speed reduction from the motor towards the wheels.

Direct drive or wheel hub motors are uncommon.

The difference is that one fixed gear ratio is usually good enough.

Heavier vehicles more or less need multiple gear ratios for EV drivetrains too.

Precisely. Electric cars almost universally have one fixed gear, with the engine smoothly providing variable torque.

This is a nitpick for sure, but as I understand it, electric motors provide pretty much constant torque throughout their operating range, which is one of their benefits. It's the speed of the motor that varies, and consequently the power, which is a function of torque times speed.

No, electric motors exert the most torque at zero RPM. That's where you can put the most current through the coil, because there's no back-EMF. It's why EVs are so zippy from a stop. The torque-speed curve is a straight line, with 0 torque at max RPM and a constant power.

Sorry - not constant power, obviously, since at the extremes the power is 0.

For synchronous motors. Induction motors (like the auxiliary/dual motors used on something like the Chevy Equinox EV) have a different torque/speed characteristic.

https://www.engineeringtoolbox.com/electrical-motors-torques...

I believe multi-motor EVs sometimes tune the motors to different uses, switching between one or the other (or both) to provide a similar effect as a gear shift.

this is a cost savings feature that was enabled by electric motor torque at low speed and the consumer's willingness to sacrifice high speed operation to focus on city driving.

electric motors hugely benefit from gearboxes, they're not used as a means to simplify and encheapen.

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