Do electric motors have a torque curve?

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Monique Spencer asked a question: Do electric motors have a torque curve?
Asked By: Monique Spencer
Date created: Wed, Mar 3, 2021 12:25 AM
Date updated: Thu, Jun 23, 2022 1:32 PM

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Electric vehicle torque delivery

As a current flows through the electric motor, a related electrical charge causes an armature to rotate… This explains why the torque curve begins to diminish on an EV dyno graph as the car's electric motors are pushed into the upper ranges of their performance limits.

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What you mean is why do they have a flat(ish) torque curve? Electric motors generate rotational motion by design. Internal combustion engines generally dont, they transfer a linear motion to a rotation via the cranksahft. The reason why electric motors have a constant torque, is becuase it used a magnetic field to rotate it.

For every motor, there is a specific Torque/Speed curve and Power curve. The graph above shows a torque/speed curve of a typical D.C. motor. Note that torque is inversely proportioal to the speed of the output shaft. In other words, there is a tradeoff between how much torque a motor delivers, and how fast the output shaft spins. Motor characteristics are frequently given as two points on this graph:

may not be available on the speed–torque curve. It is possible that in such cases the T st may be the highest torque developed by the motor in the entire speed range (Figure 2.2). T r = rated or the full-load torque and should occur as near to the synchronous speed as possible to reduce slip losses.

The torque of an electric motor is proportional to the electric current flowing through the windings. The heat generated in the windings is proportional to the square of the current through the motor. To avoid burning out the motor windings, the maximum current must be limited, and this will determine the maximum torque.

Like pumps, motors produce a torque-speed curve of their own. By overlaying the torque-speed curve of a pump and a motor, one can verify that the motor is producing enough accelerating torque to drive the pump to full speed, as shown below. In this overlay the shaded area reflects the accelerating torque available from the motor to drive the pump.

The Tesla Model S's torque curve doesn't decline nearly as quickly as ebike motors' do: Obviously, comparing 350W/500W ebike motors to a 300+kW Tesla is comparing apples to oranges, but I'm curious to know why they differ so much.

From 0 to 40 mph acceleration is limited by traction, so car cannot use full power. Above 40 mph acceleration is limited by available power. Above 73 mph (M SP above) acceleration is limited by available torque and power goes down. When power is low enough car cannot accelerate more. Motor RPM is almost 30* frequency of 3 phase AC into motor.

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