Brushless Wiper Motor Timing Control for Torque Ripple and Noise
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Solution Overview
Problem
SPM brushless motors with segment magnets experience increased torque ripple and noise due to changes in inductance with rotor rotation, which is exacerbated by the need for miniaturization and weight reduction.
Innovation Solution
A brushless motor design with a stator having annular teeth and a rotor with segment magnets, where salient poles protrude beyond the magnets' circumferential ends, and controlled voltage application using a rectangular wave with specific advance and conduction angles to minimize noise and torque ripple.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If SPM brushless motor uses segment magnet for miniaturization and weight reduction, then motor size and weight are reduced, but torque ripple increases and vibration and noises are generated
Solution Approach 1:
The patent applies preliminary action by controlling the voltage application timing to start when the tip of the salient pole and the opening portion of the teeth do not face each other. This advance timing control prevents the harmful interaction between magnetic flux and inductance change that causes torque ripple and noise, while maintaining the benefits of segment magnet design for miniaturization
2Volume of moving object
If SPM brushless motor uses segment magnet for miniaturization, then motor size is reduced, but inductance change with rotor rotation increases torque ripple
Solution Approach 1:
The voltage application is controlled to start in advance when the salient pole tip and tooth opening portion are not yet facing each other. This preliminary timing control stabilizes the torque output by preventing the harmful interaction between magnetic flux and inductance variation that occurs in conventional designs, thereby maintaining torque stability while using compact segment magnet structure
Solution Approach 2:
The patent changes the operational parameters by applying rectangular wave voltage with specific advance angle and conduction angle. This parameter optimization reduces the impact of inductance changes on torque ripple, maintaining stable torque characteristics in the miniaturized motor structure
3Object-generated harmful factors
If rectangular wave voltage with advance angle is applied to coil, then torque ripple and noise are reduced, but control complexity increases
Solution Approach 1:
The control system applies voltage in advance based on predetermined timing when the salient pole tip and tooth opening portion do not face each other. This approach reduces noise and torque ripple while maintaining relatively simple control logic by using fixed timing relationships rather than complex real-time adjustments
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design effectively reduces vibration and noise while maintaining torque, achieving a balance between miniaturization and performance by optimizing magnetic flux distribution and controlling voltage application.
Implementation Method 1
When electric power is supplied to the coil of such a brushless motor, an interlinking magnetic flux is formed in the stator, so that magnetic attractive or repulsive forces are generated between the formed interlinking magnetic flux and the permanent magnets provided on the rotor core
Implementation Method 2
magnetic attractive or repulsive forces are generated between the formed interlinking magnetic flux and the permanent magnets provided on the rotor core, and the rotor continuously rotates
Implementation Method 3
A salient pole located between the magnets circumferentially adjacent to each other on the outer circumferential surface of the rotor core and protruding further outward than a circumferential end of the magnet in the radial direction
Data Source
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AI summary
The purpose of the present invention is to provide a technique for suppressing the occurrence of vibration and noise caused by an SPM brushless motor which has segment magnets as the magnetic circuit. This motor is provided with: a stator which has an annular stator core and multiple teeth protruding radially inwards from the inner peripheral surface of the stator core; a coil which is wound around the teeth; a shaft which rotates around the rotation axis radially inside of the stator core; a rotor core which is fixed to the shaft and which has the rotation axis as the radial center; magnets which are positioned on the outer peripheral surface of the rotor core; a salient pole which is positioned between magnets adjacent to each other in the circumferential direction on the outer peripheral surface of the rotor core and which protrudes radially outwards beyond the circumferential-direction end of the magnets; an applying unit which applies a voltage to the coil; and an applying control unit which controls the applying unit. The ratio of the number of magnetic poles of the magnets and the number of teeth is 2:3, the aforementioned voltage is a square wave, and application of the voltage is started at a time when the tip of the salient pole does not face an opening in the teeth.