Electric hub motor improves EV range: Part 1—Technology basics

May 03, 2011 // By Roland Marbot, EZ Consulting
The type and location of motors used to power electric vehicles is a strategic decision. Wheel hub motors are regarded as the most elegant solution since they provide a high degree of design liberty for the car manufacturer, and they allow torque vectoring. Nevertheless, they represent a number of challenges with regard to cooling and control.

Most of the electric cars currently available are using brushless permanent magnet (PM) motors. These motors have very good characteristics, but their control circuitry consumes a lot of power, that may require liquid cooling. This wasted energy is taken from the energy stored in the battery, reducing the range of the car.

For hybrid vehicles using series power train technology (the combustion engine drives an electrical generator charging the battery), this waste of energy translates into a reduction of the miles covered per gallon of gas.

This series describes the concept of a brushless DC motor with an "electronic gearbox," requiring an almost lossless control circuitry. This translates into improved range, which is also increased by a nearly 100% regenerative braking energy recovery, as well as reduced manufacturing cost and better reliability.

The motor described here is designed to fit into the wheels of a 4WD car. The same concept can be used for implementations of a centralized electrical motor with mechanical transmission. Other implementations of the concept can be considered.

Motor and gearbox basics
The axle of the motor is fixed, with no transmission of any mechanical energy from the vehicle to the wheels (which allows for simplified shock absorbers and improvement of the energy transmission yield). The stator of the motor, "tied" to the axle, is made of printed circuits with copper electric wires. The rotor of the motor is made of magnets and is joined to the rim of the wheel, turning around the axle.

The described motor is made up of a dozen “stacks.” Each stack is 5-mm thick, and is made of a disk of magnets, 3-mm thick, and a printed-circuit disk, 1.8-mm thick, with a 0.2-mm gap between the stator and rotor.

Below is a front view (top) and side view of the motor.

To read the entire article which describes the calculations required to dimension the motor please click here , courtesy of

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