Does the geometric design of tile-type magnets optimize the air gap magnetic field distribution in the motor and improve torque smoothness?
Publish Time: 2025-08-21
In the design of modern high-performance motors, especially in small appliances such as hair dryers, beauty devices, and electric toothbrushes, which require high operating smoothness and energy efficiency, the geometric design of tile-type magnets plays a crucial role. This type of magnet, whose curved profile matches the outer diameter of the rotor core, is widely used in brushless DC motors and permanent magnet synchronous motors. Its shape is not only designed to fit the structural space, but also has a deeper significance in precisely controlling the internal magnetic field of the motor, particularly optimizing the magnetic field distribution in the air gap region, which directly affects the motor's torque output characteristics and operating smoothness.The air gap is the tiny space between the stator and rotor of a motor and serves as a key channel for magnetic flux transmission. The distribution of the magnetic field in the air gap determines the way the electromagnetic force acts, which in turn affects the magnitude and degree of torque fluctuation. The ideal air gap magnetic field should be as close to a sinusoidal waveform as possible, with a uniform and symmetrical distribution to reduce torque ripple and vibration noise. The curved surface design of tile-type magnets is precisely designed to achieve this goal. Its curvature is highly consistent with the rotor's outer diameter, ensuring a large contact area and close fit between the magnet and the core. This reduces discontinuities in the magnetic circuit and prevents local saturation and magnetic field distortion caused by flux concentration or leakage.Through appropriate arc length and pole arc coefficient design, tile-type magnets achieve a smoother and more symmetrical magnetic flux distribution in the air gap. This distribution reduces the impact of cogging, the periodic drag torque generated by the interaction between the stator slots and the permanent magnets during rotor rotation. Cogging torque is a major cause of motor starting problems, low-speed jitter, and increased noise. Optimized magnet geometry can mitigate this discontinuous magnetic resistance variation, ensuring smooth operation at low speeds and improving the user experience, especially in handheld devices.In addition, the magnet's thickness, radial height, and edge transition curve also contribute to fine-tuning the magnetic field. Appropriate magnet thickness ensures sufficient flux output, while smooth edge rounding helps mitigate magnetic field concentration at the pole edges, preventing localized high flux density from increasing iron losses or the risk of demagnetization. This "peak-shaving" effect brings the air-gap magnetic field waveform closer to the ideal state, thereby reducing the pulsating component of the electromagnetic torque and improving output continuity and stability.In a multi-pole motor, multiple tile-type magnets are evenly arranged along the rotor circumference, forming a closed magnetic ring structure. This layout requires that each magnet be highly consistent in size, magnetization direction, and mounting position to ensure overall magnetic field symmetry. Any deviation in any individual magnet can lead to magnetic field imbalance, causing torque fluctuation and mechanical vibration. Therefore, high-precision molding processes and assembly control are essential for achieving excellent magnetic field distribution. Modern manufacturing techniques ensure high consistency in the curvature, thickness, and magnetization direction of the magnet tiles, maintaining stable performance in mass production.More importantly, the tile-type magnet design must be compatible with the stator winding, core slot configuration, and control strategy. For example, in sinusoidal drive or field-oriented control (FOC) systems, the air-gap magnetic field requires even higher sinusoidality, and the magnet geometry must be optimized through simulation to achieve near-constant torque output in conjunction with electronic commutation. This electromechanical synergy ensures not only excellent motor performance under rated operating conditions but also stable operation across a wide speed range.In summary, the tile-type magnet is not simply a curved permanent magnet but a carefully considered electromagnetic structural element. Its geometric design, by precisely shaping the air-gap magnetic field, effectively improves the motor's torque stability, reduces vibration and noise, and enhances dynamic response. This inherent performance optimization is the key to achieving quiet, efficient, and smooth operation in high-performance small appliance motors.
