BYD discloses four patents for variable flux permanent magnet synchronous motors, addressing the efficiency conflict of motors at high and low speeds in automobiles

【PCauto】While an electric vehicle crawls through congested urban traffic, one might not realize that the motor propelling the wheels faces technical challenges entirely distinct from those encountered during high-speed cruising.

Traditional permanent magnet synchronous motors (PMSMs) deliver robust torque at low speeds. However, during high-speed highway operation, their fixed rotor magnetic flux leads to a rise in back electromotive force (EMF), resulting in a significant drop in efficiency. This long-standing industry challenge may now have a potential solution, as evidenced by the recent publication of BYD's latest technology patents.

Four patents for variable flux permanent magnet synchronous motors (VF-PMSMs), filed in May 2024 and recently published by the China National Intellectual Property Administration (CNIPA), highlight BYD's in-depth research in electric drive system technology.

The four patents—CN121055622A, CN121055630A, CN121055623A, and CN121055631A—share a common core principle: enabling the motor rotor's magnetic flux to 'vary on demand.'

Analogous to how internal combustion engines optimize air intake via variable valve timing, VF-PMSM technology actively boosts magnetic flux at low speeds to enhance torque, while reducing flux at high speeds to mitigate back EMF losses. This dynamic adjustment capability promises to substantially broaden the motor's high-efficiency operating range.

A closer examination of the patent documents reveals four distinct technical approaches, each with a specific focus.

CN121055622A details the design of flux adjustment components integrated within the motor and drive system, targeting precise system-level flux control.

CN121055630A introduces a movable magnetic adjustment component that shifts relative to the rotor, altering field strength through mechanical displacement.

CN121055623A employs an axial adjustment mechanism to alter magnetic circuit parameters along the motor's axis.

CN121055631A demonstrates a finer degree of control by adjusting the radial cross-sectional area of magnetic components to regulate flux.

Consumers today expect electric vehicles that excel not only in frequent urban stop-and-go traffic but also in high-speed intercity driving.

The efficiency drop in traditional motors at high speeds typically necessitates longer charging times or larger, more expensive battery packs—directly increasing vehicle cost.

If successfully commercialized, VF-PMSM technology could enable vehicles to balance low-speed torque and high-speed range without requiring a larger battery. This would be particularly attractive for the mid-range EV market, where cost-performance is paramount.

Notably, this is not an isolated effort by BYD in electric motor development.

Other patents published in 2025 indicate its research extends across multiple dimensions, including motor structure optimization, rotor and stator enhancements, and flux management system upgrades. This sustained R&D investment aligns with the broader industry trend toward more efficient and intelligent electric drive systems.

Although there is no public confirmation of these variable flux technologies reaching commercial deployment, nor specific test data verifying their real-world efficiency, the potential benefits outlined in the patents—such as 'extended driving range, enhanced thermal stability, and optimized energy usage predictability'—are sufficient to fuel market anticipation for their future application.

Of course, the path from patent to stable integration in mass-produced vehicles still involves overcoming challenges related to durability, cost control, and system integration. Nevertheless, the prospect is compelling: if motors can one day 'intelligently adjust' flux as seamlessly as breathing, both the driving experience and ownership economics of electric vehicles could be transformed.