China’s EV giant files patent for variable-flux motors that promise longer range, stability

Recent patent disclosures indicate that BYD has strengthened its work on variable-flux permanent-magnet synchronous motor technology, with four filings published by the China National Intellectual Property Administration (CNIPA). 

The documents outline technical solutions that allow the magnetic flux of the rotor to be adjusted dynamically, enabling the motor to operate more efficiently across a wide range of speeds and load conditions. By actively managing magnetic intensity, the designs aim to reduce energy losses at high speeds while maintaining strong torque at lower speeds. 

The newly published patents build on BYD’s earlier research into variable-flux motor systems and reflect a further technical refinement of the concept, suggesting continued in-house development focused on improving electric drivetrain performance and overall efficiency.

Why variable-flux motors matter for EV efficiency

A variable flux permanent magnet synchronous motor is designed to adjust the magnetic strength inside the rotor depending on how the motor is operating. Unlike conventional permanent magnet motors, which rely on a fixed magnetic field, this approach allows the motor to adapt to different speed and load conditions. 

In standard designs, fixed rotor flux delivers strong low-speed torque but can hurt efficiency at higher speeds due to increased counter-electromotive forces. By dynamically regulating magnetic flux, a variable-flux motor can maintain higher efficiency across both low- and high-speed operation, while delivering more stable torque and reducing overall energy losses, CarNewsChina writes.

In a variable-flux motor design, magnetic flux is managed using movable or controllable elements within the rotor or the surrounding magnetic circuit. During low-speed operation, the system increases magnetic flux to deliver higher torque. As rotational speed rises, the flux is reduced to limit opposing electromagnetic forces and preserve efficiency without unnecessary energy use. 

Patents outline practical paths for variable-flux motor design

The newly published BYD patent filings outline several practical ways to apply variable-flux permanent magnet motor technology in electric drivetrains. The documents describe different approaches to regulating magnetic flux inside the motor, including integrating flux-adjustment components directly into the motor and drive system, and using movable magnetic elements that shift relative to the rotor to widen the motor’s high-efficiency operating range. 

Other designs focus on adjusting magnetic flux along the rotor’s axis or changing the effective area of magnetic conductive parts to fine-tune internal magnetic fields. Together, these concepts illustrate how BYD is translating variable-flux theory into concrete engineering solutions aimed at improving efficiency, flexibility, and performance in real-world electric vehicle applications.

In electric and other new energy vehicles, variable-flux permanent magnet motor technology helps deliver more efficient performance across different driving scenarios. By actively adjusting the rotor’s magnetic flux, the motor can reduce energy losses at higher speeds while maintaining strong and stable torque at lower speeds. This results in longer driving range, more predictable energy use on long trips, reduced heat buildup in motor components, and more effective battery utilisation in both fully electric vehicles and hybrid powertrains.