Curved-Slot PMSRM Rotor for High-Torque Compact Power Tools
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Solution Overview
Problem
Existing power tools with brushless DC motors face challenges in achieving high startup torque and high no-load speed while maintaining a compact size, leading to oversized and inefficient motor designs.
Innovation Solution
Implementing a permanent magnet synchronous reluctance machine (PMSRM) with a stator and rotor design featuring curved slots and magnets, which enhances torque and speed performance without increasing motor size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If brushless DC motors are used to achieve high startup torque, then torque is improved, but motor size increases and efficiency decreases
Solution Approach 1:
The patent changes the motor type from brushless DC to permanent magnet synchronous reluctance machine (PMSRM), fundamentally altering the electromagnetic parameters and operating characteristics to achieve higher torque density and efficiency without increasing motor size
Solution Approach 2:
The patent employs curved slots in the rotor instead of straight slots, which optimizes the magnetic flux distribution and enhances torque production while maintaining compact motor dimensions
2Speed
If brushless DC motors are used to achieve high no-load speed, then speed is improved, but motor size increases
Solution Approach 1:
The PMSRM design with specific winding configurations and magnetic circuit parameters enables higher no-load speed operation while maintaining a compact motor size through optimized electromagnetic design
Solution Approach 2:
The motor uses multiple slots and magnets arranged in a segmented pattern around the rotor, which allows for optimized magnetic flux paths and higher speed operation without increasing overall motor volume
3Force
If more rare earth magnet material is used to improve torque performance, then torque is improved, but cost increases
Solution Approach 1:
The patent optimizes the magnetic circuit design and slot configurations to achieve high torque output with reduced rare earth magnet material usage, lowering material costs while maintaining performance
Solution Approach 2:
Curved slots improve the utilization of magnet material by optimizing flux distribution, allowing for reduced magnet quantity while maintaining or enhancing torque production
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 PMSRM provides improved startup torque and no-load speed compared to brushless DC motors, while reducing the need for larger motor sizes and costly rare earth magnet material.
Implementation Method 1
The rotor includes a rotor body with a first slot positioned a first distance from a center of the rotor body and a second slot positioned a second distance from the center of the rotor body. The first slot and the second slot are curved about a common center. The rotor further includes a first magnet positioned within the first slot and a second magnet positioned within the second slot.
Data Source
AI summary
A power tool including a housing and a motor assembly positioned within the housing. The motor assembly includes a stator with winding slots that receive stator windings and a rotor. The rotor includes a rotor body with a first slot positioned a first distance from a center of the rotor body, a second slot positioned a second distance from the center of the rotor body, and a third slot positioned a third distance from the center of the rotor body. The first slot, the second slot, and the third slot are curved about a common center. The rotor further includes a first magnet positioned within the first slot, a second magnet positioned within the second slot, and a third magnet positioned within the third slot.