Why are torque curves for electric vehicle motors not linear?


I am studying how electric motors work. In doing so, I came across multiple contradictory information on the torque curve of electric motors. For hobby-sized motors DC motors, the torque curve tends to be linear (e.g. [D.C. Motor Torque/Speed Curve Tutorial:::Understanding Motor Characteristics (mit.edu)](http://lancet.mit.edu/motors/motors3.html) ). AC motors on the other hand have different torque characteristics (e.g. [main-qimg-a7895103f0f37d89e82e18b928786d64-lq (602×395) (quoracdn.net)](https://qph.cf2.quoracdn.net/main-qimg-a7895103f0f37d89e82e18b928786d64-lq)).

My problem has to do with electric vehicles; they have both a constant torque region and a constant power region, and it resembles nothing like the above two types of motors, despite both being used in Teslas and other BEVs. I couldn’t find much information about why that is the case, but my research points toward some form of voltage / current control to shape the torque curve. Please ELI5, thanks.

In: 1

You are not being very specific. There are multiple types of motors both DC (stepper, permanent magnet, brushed/non-brushed etc) and AC (induction, synchronous, single/poly phase etc). They all use electricity and magnetism, but do so in different manners which explains why their behavior is different.

If it makes you feel any better, nothing real is really linear over the full range of inputs–everything has non-linear behavior at extremes. Conversely any real system IS linear over a some (possibly very limited) range (non-differentiable functions everywhere are really just a mathematical curiosity–like infinity).

The “torque plateau” is not (directly) a physical characteristic of the motor, it is really an artificial current limit to prevent overheating. The nominal torque limit applies to continuous operation, it can be temporarily exceeded.