Round Wire Motor

The round wire motor is a traditional yet widely adopted technology in the field of new energy vehicle (NEV) drive motors. In contrast to flat wire motors that utilise hairpin windings, the stator winding of a round wire motor is wound from multiple strands of circular cross-section enamelled copper wire using conventional processes. Although flat wire motors have gained widespread popularity across many mid-to-high-end models in recent years due to their higher slot fill factor, round wire motors continue to hold a vital position in the automotive industry thanks to their outstanding cost advantages, manufacturing maturity, and well-balanced performance.

Core Working Principle and Technical Structure

The defining characteristic of a round wire motor lies in its use of circular cross-section conductors for wiring within the stator slots.

During manufacturing, multiple strands of fine round copper wire are arranged mechanically or manually and inserted into the slots of the stator core. Because round wires naturally have a circular cross-section, microscopic gaps are inherently left between the conductors as well as between the conductors and the stator slot walls. While these gaps reduce the copper slot fill factor to a certain extent, they provide ample space for insulating varnish penetration. Through the Vacuum Pressure Impregnation (VPI) process, the insulating resin thoroughly coats each individual wire, delivering exceptional electrical insulation as well as robust resistance to vibration and moisture.

Application Scenarios and Market Value

Round wire motors are extensively used in entry-level battery electric vehicles (BEVs), auxiliary motors for hybrid electric vehicles (HEVs), and various industrial and automotive components where manufacturing costs and reliability are paramount.

For entry-level to mainstream NEVs focused on delivering strong value for money, the well-established supply chain and lower tooling development costs of round wire motors significantly reduce manufacturing barriers. Furthermore, round wire motors feature highly mature calibration for low-end torque delivery, providing smooth and dependable power for daily urban commuting.

Safety Specifications and Physical Limitations

It is strictly prohibited to run the motor under prolonged high-load, high-current conditions with insufficient coolant flow, as extreme temperatures can cause thermal ageing and insulation breakdown of the internal enamelled wires:

Due to the relatively lower slot fill factor and smaller contact area between conductors, the heat dissipation efficiency and peak power density of a round wire motor are generally inferior to those of a flat wire motor of equivalent dimensions. Under sustained extreme track driving or heavy towing, localised heat build-up can easily degrade the insulating varnish and trigger turn-to-turn short circuits. 

It is strictly prohibited to damage the insulating varnish film of the stator windings during motor servicing or dismantling: 

The multi-strand fine wires of a round wire motor are highly susceptible to damage if scratched by external forces during rewinding or overhauls, posing serious electrical leakage hazards. Unauthorised personnel and non-specialist workshops are strictly prohibited from dismantling the internal motor assembly; all inspections and maintenance must be carried out in strict accordance with standard procedures by certified high-voltage technicians.