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How do electric car transmission systems work? Does it have an auto or manual gear concept like gasoline vehicles? As an electric motor can run in any speed (slow), is it necessary to have a clutch?

  • That sounds great on a 0 degree grade, 25 degrees and above, the torque to weight ratio is reduced and another gear would be beneficial. – ken Aug 27 '17 at 6:37
  • The torque to weight ratio stays the same, but the force necessary changes - unless you have added some bags of cement .... – Solar Mike Aug 27 '17 at 7:29
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I'm sure it can be done different ways, but I'll describe the Nissan Leaf, since it is one of the true electric cars on the market today (not a hybrid gas/electric).

The Nissan Leaf does not use a typical automatic or manual transmissions. It uses a single speed reduction gear with a final drive ratio of 7.9377. The motor itself can spin at ~10k rpm. This gives the Leaf a top speed of around 94MPH.

If you were wondering why a purely electric vehicle doesn't need a "regular" transmission, but instead uses the single speed reduction gear, the reason is two fold:

  • It doesn't need one: Typical gasoline (petrol) engines have a very narrow torque band. This requires varying the gearing (with multiple gear ratios) to allow the engine to perform efficiently and propel the vehicle down the road with some amount of respect. Electric motors create torque throughout the RPM range. They can create a large amount of torque from 0 RPM almost all the way through to their maximum RPM (whatever that is for an individual motor). Since almost the entire RPM range for the motor produces usable torque, there's no need for a transmission. Because the motor can produce torque from 0RPM, there is no need for a clutch, either.
  • Simplicity: A multispeed electric vehicle transmission would add weight, complexity, friction, and inefficiency to an otherwise simple system, actually robbing the powertrain of torque, power, and efficiency.

Another example is the Tesla Model S. It uses a single speed stepdown transmission (if you want to call it that) with a ratio of 9.73:1. Even with this, the motor is fully capable of propelling the car at 130MPH and going from 0-60MPH in ~4 seconds. No need for a multispeed transmission there, either.

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    do I understand right, that because the motor can produce torque from 0 RPM, that it is not possible to stall an electric car such as the Nissan Leaf or Tesla Model S? – Keith Hall Jun 13 '16 at 11:48
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    actually, nevermind - I think I found the answer: since an electric engine does not idle and will not shutdown and require restarting if the RPMs drop below a certain point it cannot stall in the same sense as a gas engine. :) – Keith Hall Jun 13 '16 at 11:50
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    @KeithHall - That is exactly right. Since it produces torque from 0 RPM, there's no stall. If the electric motor stops, you press the go pedal more for more current to go through the engine to produce more torque. It may stop turning, but it doesn't stall like an internal combustion engine might. – Pᴀᴜʟsᴛᴇʀ2 Jun 13 '16 at 21:01
  • That sounds great on a 0 degree grade, 25 degrees and above, the torque to weight ratio is reduced and another gear would be beneficial. – ken Aug 27 '17 at 6:37

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