Power Watts TorqueN na x speedradss

The power-torque relation in hp and ft-lb is

Figure 5.1 depicts that the IC engine does not produce torque below a certain speed. A transmission is essential for an IC engine to match the vehicle speed with the narrow high hp speed range of the engine. On the other hand, the electric motor produces high torque even at zero speed and typically has constant power characteristics over a wide speed range. Therefore, the electric motor can be attached directly to the drive wheels and accelerate the vehicle from zero speed all the way to top speed. The motor and, hence, the vehicle speed can be controlled directly through the power electronic converter feeding the current into the motor. There is essentially no requirement for a transmission with an electric motor, other than a fixed gear for appropriately sizing the motor.

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