Electric PowerTrain for Two Wheelers

The average vehicle body gives any vehicle its structural integrity, while the electric motor is concerned with the generation of torque or force. The electric motor can be a permanent magnet synchronous motor, brushless dc motor etc. The batteries will power these motors through a power controller (throttle) and a converter (DC to AC type).

What is the Electric PowerTrain?

Simply put, a powertrain includes all the components that thrust a car into locomotion. Electric powertrain systems constitute the major components that create and transfer power to the road surface through wheel movement in vehicles that are electric, and hybrid electric.

Components of the Electric Powertrain

Below are the major components of the electric powertrain in scooters:

Engine: The engine is the driving force behind your car and serves as its heart. The components of an engine called pistons, oscillate inside of cylinders and a crankshaft that converts the oscillating action into a rotating motion.

Transmission: A fundamental part of your scooter called the transmission ensures that the right amount of power is sent to the wheels. Similar to a car's gearbox, the transmission transfers engine power to the wheels by adjusting it in response to road conditions.

Battery: The Battery types can be Lithium ion, Nickel metal hydride, Lead acid etc. The battery capacity is usually mentioned in ampere-hour. Inside the battery, various cells are connected in series as well as in parallel typically.

The DC to AC converter: (an Inverter actually) will provide three-phase input as required by the motors for propulsion, whereas the power controller will control the amount of current flowing in each phase winding.

The electric motor used for vehicle propulsion can be an inner rotor type or an outer rotor type depending upon the applications. The stator in the electric motor is always fixed and produces the required amount of flux in the air gap using the winding provided in the slots. These winding carry currents that can be DC or AC depending upon the motor type. Battery output can be directly applied, and flux produced in the air gap can be increased or decreased by means of a magnet mounted on the rotor part. One typical motor widely used for EV application is BLDC, which has an inherent inverter. 

Rotors in Electric Two Wheelers In Detail

The rotor is usually the rotating part of the machine and carries a shaft wherein the external load can be connected or disconnected. If the rotor is located inside the stator (which is usually the case), the motor is known as the inner rotor type, as shown below.

In the case of Radial flux machines, where flux travels in the radial direction, such as SM PM BLDC as shown above 

                                                         Torque = k * (D)2 * L                                                            equation (1) 

Here, D is the rotor diameter and L is the stack length of the machine.

From equation (1) it is clear that the torque can be increased further by increasing the rotor diameter as well as the stack length of the machine. Generally, inner rotor-type radial flux machines have a lower rotor diameter and a large stack length, which is not the case for outer rotor machines. By employing outer rotor topology, an increase of two times the rotor diameter will increase the amount of torque produced by the machine by four times, which is desirable in the case of in-wheel EV applications characterised by high torque and power density.

Outer rotor BLDC motor can be mounted on the front or rear wheel of the Bicycle / Bike etc.