torque requirement at the wheel depend on operating conditions", justify the statement with example
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Explanation:
The required tractive torque of the motor shall be equal to the tractive torque at wheel, Tw = Ft.rw , (i.e. Tractive Torque = Tractive Force x mean wheel radius).
Where,
rw = mean wheel effective radius
Ft = Fr + Fg + Fd + Fie
Fr = Tyre rolling resistance ( can be in the form of CrN - simplified and treated as independent of velocity)
Fg = forces due to gradient (depending on slope angle, can be positive of negative)
Fd = aerodynamics drag (as a function of air density, drag coefficient, vehicle cross sectional area, and squared of vehicle velocity)
Fie = equivalent inertial force (during acceleration) - (including linear and rotational inertias, due to vehicle mass and rotating component of gear train and wheels)
So you must determine the acceleration required to reach you designed speed.
And must also include overall transmission efficiency in order to get the right size of the motor.
Just to visualize;
for 1000 kg car and everything else constant;
on flat road, @ 25 km/h requires 1.0 kW power
on 5o gradient climbing, @ 25 km/h requires 6.9 kW Power
on flat road, accelerating @ 1.4 m/s2 (i.e. 0 - 25 km/h in 5 sec), requires 10.6 kW power.
So you really need to determine you design specifications in order to size the right motor..
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