The engine is the distinctive element of a motorcycle and determines its character and image: two-cylinder, single-cylinder, in-line 4 cylinders, V, L. In the case of electric motorcycles, the engine is replaced by the electric motor. Its function is to convert the electrical energy supplied by the battery into mechanical energy to move the bike.
The components used to rotate the shaft of the electric motor are the stator and the rotor; the first is fixed while the second is integral with the shaft and rotates with it. The rotor is rotated by the magnetic field generated by the alternating current flow passing through the stator windings. The motion of the rotor is transmitted to the pinion by different types of final transmission: through a gear, a belt, a gearbox. There are also cases in which the pinion is fixed directly on one end of the motor shaft.
The permanent magnet motor is the currently most used type in the automotive and motorcycle applications due to its high efficiency and reliability. Its most advanced version is called Permanent Magnet AC Motor (PMAC).
The element that supplies power to the motor is the battery, but this delivers direct current while the motor needs alternating current to generate the magnetic field in the stator. The conversion function from direct current to alternating current is carried out by the inverter while the modulation of the current to vary the motor rpm is performed by the converter.
At present we do not want to go into the details of the operating principle of an electric motor for automotive applications, but we prefer to describe how this component characterizes the bike and the riding style.
An internal combustion engine is characterized by power and torque which increase with the rpm to a maximum and decrease after that. An electric motor has a power curve that increases with the rotational speed for most of the range until it stabilizes at high revs. The torque curve, on the other hand, has its maximum from zero speed and remains constant for a large part from the range, until it halves at the maximum number of revolutions.
The torque curves of the electric motor and the endothermic engine have opposite trends with major effects on the behaviour of the bike. Referring to the judgments of the riders of the MotoE, coming out of a slow curve, therefore at low engine rpm, the torque of the bike is surprising even at small rotation of the throttle. In fast corners, on the other hand, the electric motor works in the area where the torque value has dropped and you can fully twist the throttle; something unbelievable, for example, with a Moto2 that in the same scenario has the maximum engine torque.
One more important effect of the motor on the riding style of an electric motorcycle is the handling. An endothermic engine is characterized by considerable moving masses, whose gyroscopic effect acts to reduce the handling of the bike. This can be reduced by varying the engine configuration but cannot be fully eliminated. In an electric motor, the only rotating mass is that of the rotor and is extremely little. As a consequence, its gyroscopic effect of very little too. For this reason, an electric motorcycle is much easier to handle than a motorcycle with an endothermic engine of similar weight.
Other elements whose characterize the electric motors installed on the bikes are the simplicity of construction, the reduced maintenance, the high reliability and the low heat generated.
In addtion, we mention the regenerative capacity: during braking, the wheel that is connected to the engine through the transmission slows it down, reversing its operating principle. The result is a flow of current from the motor to the battery which is thus recharged by the motor brake.