Arc Magnet Rotor Design for Low Cogging Torque
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Solution Overview
Problem
Permanent magnetic rotors for motors are typically expensive and can produce significant vibration, which is undesirable in applications like dishwasher drain pumps.
Innovation Solution
A synchronous motor design featuring a rotor with two magnets fixed to a rotary shaft, each covering half the circumference, with a radial outer surface having an arc section and specific geometric configurations to reduce cogging torque and cost, including an over-molding piece for magnet fixation and a stator with opposing poles and windings for efficient rotation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an annular magnet with multiple magnetic poles is used, then the motor produces high power, but the cost increases significantly
Solution Approach 1:
The patent divides the annular magnet into multiple separate arc magnets, each with a specific pole arc angle ratio (0.75-0.94). This segmentation allows for simpler, more cost-effective manufacturing of individual magnet pieces while maintaining the overall magnetic field configuration needed for high power output. The separate arc magnets can be manufactured more easily than a single complex annular magnet.
2Ease of manufacture
If a conventional arc magnet with pole arc angle ratio outside the specified range is used, then the manufacturing cost is reduced, but the vibration increases
Solution Approach 1:
The patent specifies a precise parameter range for the pole arc angle ratio (0.75-0.94) that optimizes the balance between manufacturing cost and vibration reduction. By controlling this geometric parameter within the specified range, the design achieves low vibration operation while maintaining cost-effectiveness through simpler magnet configurations compared to traditional annular magnets.
3Ease of operation
If the pole arc angle ratio is increased to reduce cogging torque, then the rotor rotation becomes smoother, but the magnet geometry becomes more complex
Solution Approach 1:
The patent applies local quality by specifying that only the radial outer surface of each arc magnet needs to have a precisely controlled pole arc angle ratio (0.75-0.94), while other surfaces can have simpler geometries. This localized precision requirement reduces overall magnet geometry complexity while still achieving the desired smooth rotor rotation and reduced cogging torque.
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 reduces cogging torque, resulting in smoother rotor rotation and lowers the overall cost compared to conventional arc or annular magnets, while maintaining low vibration levels.
Implementation Method 1
When the stator windings are connected in series to an alternating current power supply, the rotor rotates at a constant speed of 60f/p RPM during a steady state
Implementation Method 2
The rotor comprises a rotary shaft and two magnets fixed to the rotary shaft... each magnet comprising a radial outer surface, a radial inner surface, and two connecting surfaces
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A rotor, motor, pump and a cleaning apparatus are provided. The rotor (26) includes a shaft (28) and two magnets (30) fixed to the rotary shaft. Each magnet comprises a radial outer surface (40), a radial inner surface (42), and two connecting surfaces (44) that connect the radial outer surface and the radial inner surface at opposite ends of the magnet. The radial outer surface has an arc section (46). The radial inner surfaces of the two magnets cooperatively define an inner bore (50) for the shaft to pass therethrough. A ratio of a pole arc angle (θ) of each magnet to a 180-degree angle is in the range of 0.75 to 0.95.