Tokyo-headquartered Hitachi has developed an in-wheel motor system which combines a motor, inverter and mechanical brake into a single unit with a power density of 2.5kW/kg.
The company states that the in-wheel motor approach should encourage the adoption of electric drivetrains due to a reduction in installation complexity, while also removing the losses inherent in systems that rely on transmissions and their associated driveshafts and other ancillaries. The unit is designed to fit inside a 19in wheel and has an output of 60kW funning at just over 400V.
According to the company, the motor employs a Halbach array of magnets, in which the orientation of the N pole of each magnet is rotated 90° to create high-density magnetic flux at each of the magnetic poles of a motor. This has been done to increase the driving force of each magnetic pole, while overcoming some of the disadvantages of using a large number of poles. Furthermore, Hitachi says that through the use of beam welding it has been able to create a high-density array of flat coils, further increasing power density.
The system also uses direct-cooling where both the power electronics and the motor windings are cooled using a dielectric oil. Hitachi notes that, when combined with the single-unit drive system, the integrated cooling system enables in-wheel installation without having to significantly alter the existing configuration of suspension and other components.
