BYD Advances EV Efficiency with Variable-Flux Motor Patents

BYD has published four new patents detailing advances in variable-flux permanent-magnet synchronous motor (VF-PMSM) technology, reports CarNewsChina.

The filings were made in May 2024 and recently released by the China National Intellectual Property Administration (CNIPA). 

The patents — CN121055622A, CN121055630A, CN121055623A and CN121055631A — outline methods to actively adjust rotor magnetic flux to improve efficiency across different operating speeds, a concept almost similar to variable valve timing in the internal combustion engine world. 

A VF-PMSM differs from a conventional permanent-magnet motor by allowing its magnetic flux to change with driving conditions. Traditional PMSMs rely on fixed rotor flux, which delivers strong torque at low speeds but becomes less efficient at higher speeds due to rising counter-electromotive forces. Variable-flux designs aim to balance both ends of the operating range.

In practice, magnetic flux is increased at low speeds to maximise torque, then reduced at higher speeds to limit energy losses and maintain efficiency. This approach widens the efficient operating window, improves high-speed performance and optimises torque delivery without requiring a larger battery.

The newly published BYD patents describe several ways to achieve this. CN121055622A focuses on a flux-adjustment component integrated with the motor and drive system. CN121055630A introduces a magnetic regulation part that can move relative to the rotor to expand high-efficiency zones.

CN121055623A details an axial adjustment mechanism that alters magnetic flux along the rotor’s axis. CN121055631A describes a configuration where the radial area of a magnetic conductive component can be adjusted for finer internal flux control. 

Beyond these VF-PMSM filings, BYD has also published other 2025 patents covering motor structures, rotor and stator hardware, and magnetic flux management. These filings point to ongoing powertrain development, although there is no public confirmation yet of commercial deployment or test results for the variable-flux motors.

For electric and other new energy vehicles, VF-PMSM technology could deliver tangible benefits. By reducing losses at high speeds while preserving low-speed torque, such motors can extend driving range, improve thermal stability and make energy use more predictable in real-world driving.

Taken together, the patents highlight BYD’s continued push to overcome the limits of fixed-flux permanent-magnet motors, signalling a move toward more adaptable and efficient electric powertrains.