Dear Mahmoud,

The formula you have used is correct. The power and torque requirements for a car traveling at constant speed are indeed very low. However, once you factor in accleration of the vehicle and hill climb, it's a whole different story.

There is also a second approach you can use, the simple formula P=M*Omega:

Aussuming the average energy demand for an electric vehicle is 10 kWh/100 km, at an average speed of 100 km/h the power demand is roughly 10 kW. Considerung an average tire circumference of ~ 2 m, a rotational speed of 14 rev/sec or ~ 88 rad/sec is required. 10000 Watts devided by 88 rad/sec = ~ 114 Nm, which is a value very similar to the 140 Nm you came up with.

So yes, your calculation is correcnt, but only valid for constant speeds on a horizontal road!

Good luck, Armin

To give you a practical perspective thw the torque required to rotate an electrically assisted power steering on a last generation vehicle by hand is approximately 2 Nm. So 8 Nm is significantly low for traction. The equation for toque during transient situation is:

Te - Tl = JW'+BW

Te = electromagnetic torque of the machine

Tl = load torque

J = inertia

W' = rotational acceleration

B = friction coefficient

W = rotational speed

The higher the difference (Te-Tl) the higher the acceleration which is possible. You should consider the worst case Tl so that you size the rated Te of the machine accordingly. Most machines are designed to allow for a higher torque than rated to be generated for brief periods of time so that is something you might want to look into.

Best of luck with your research!

Well, thanks for the tip Mr Kris