BYD Pushes Forward with Variable Flux Permanent Magnet Synchronous Motor Tech, New Patents Revealed
3 min read
Dec 14, 2025 2:05 AM CET
Flux adjustments boost energy efficiency for electric vehicles and NEVs. Credit: CarNewsChina
BYD has unveiled four patents detailing a variable-flux permanent-magnet synchronous motor (VF-PMSM) technology, with filings published by the China National Intellectual Property Administration (CNIPA) after initial submission in May 2024. The patents cited are CN121055622A, CN121055630A, CN121055623A, and CN121055631A. They describe methods for actively modulating rotor magnetic flux to improve efficiency across a wide range of operating speeds. These filings build on BYD’s prior work in variable-flux motor concepts and represent a tangible evolution of the technology.
What VF-PMSM is and why it matters
A Variable Flux Permanent Magnet Synchronous Motor is a type of electric motor in which the rotor’s magnetic flux can be tuned in response to changing operating conditions. Traditional permanent-magnet synchronous motors use a fixed rotor flux, which delivers strong torque at low speeds but tends to be less efficient at higher speeds due to counter-electromotive forces. A VF-PMSM, by contrast, dynamically adjusts the rotor flux to sustain high efficiency during both slow and fast operation. The result is more consistent torque output and lower energy losses, which can translate into longer range and better overall performance.
How flux adjustment works in practice
Flux adjustment relies on components within the rotor or magnetic circuit that can be moved or controlled. At low speeds, the motor increases flux to maximize torque for immediate responsiveness. At higher speeds, it reduces flux to minimize opposing forces, keeping efficiency high without wasting energy. The net effect is improved energy efficiency, a broader high-efficiency operating window, and torque stability without demanding larger batteries.
Insights from BYD’s 2025 filings
CN121055622A describes a magnetic-flux adjustment component integrated with the motor and drive system. CN121055630A covers a magnetic regulation element that can move relative to the rotor to expand the region of high efficiency. CN121055623A introduces an axial-adjustment assembly that tunes rotor flux along the axis. CN121055631A presents a design where the radial area of a magnetic-conductive portion can be altered to fine-tune internal flux. All descriptions align with CNIPA abstracts, ensuring the accuracy of magnetic-flux regulation and rotor design details.
Beyond VF-PMSM: broader motor and drive-system patents
In addition to the VF-PMSM patents, BYD filed other 2025 patents related to electric motor structures and drive systems. These include rotor and stator hardware innovations, magnetic-flux management components, and related motor technology improvements. Public patent records indicate ongoing R&D activity in BYD’s motor and powertrain fields. However, there has been no publicly disclosed evidence of commercial deployment or experimental results specifically tied to the VF-PMSM technology.
Why this matters for EVs and NEVs
VF-PMSM technology has the potential to improve efficiency across diverse driving scenarios. By adjusting rotor magnetic flux, these motors can reduce energy losses at high speeds, extend driving range, and maintain consistent torque at lower speeds. This can lead to more predictable energy consumption on long trips, lower thermal stress on motor components, and more efficient battery usage for both fully electric and hybrid powertrains.
Together, the BYD patents illustrate a continued push toward high-efficiency motors with variable-flux control, addressing a fundamental limitation of fixed-flux permanent-magnet motors.
About the author: Adrian, an Electrical and Computer Engineering graduate with a passion for cars, brings hands-on testing experience to CarNewsChina. He also enjoys audio, photography, and staying active.
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