Interior Permanent Magnet Motor Eccentric Bulge Cogging Torque
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Interior permanent magnet motors experience undesirable cogging torque due to manufacturing errors, leading to jerky rotor movement, especially at low speeds, as the torque ripple is sensitive to geometric deviations such as bending, twisting, and misalignment of stator and rotor components.
Innovation Solution
The motor design incorporates a rotor with part-elliptical bulges on its outer peripheral surface, where each bulge follows an elliptical path, optimizing the shape to minimize cogging torque variations caused by manufacturing tolerances, with dimensions selected to reduce sensitivity to geometric errors like stator tooth deformation and rotor skewing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the rotor has a constant radius outer periphery, then the motor structure is simple and easy to manufacture, but the cogging torque is high causing jerky rotor movement
Solution Approach 1:
The patent applies curvature by introducing eccentric bulges with part-elliptical shapes on the rotor outer periphery. These bulges create a non-uniform air gap between rotor and stator, which modifies the magnetic flux distribution and reduces cogging torque variations, thereby smoothing rotor movement while maintaining manufacturing feasibility through defined geometric parameters.
Solution Approach 2:
The patent changes the geometric parameters of the rotor by introducing controlled variations in the outer radius through eccentric bulges. The bulge dimensions (major axis, minor axis, position) are optimized to minimize cogging torque sensitivity to manufacturing errors, transforming the rotor from a constant radius to a variable radius profile that compensates for manufacturing tolerances.
2Ease of manufacture
If the motor is manufactured with standard tolerances, then manufacturing cost is low, but cogging torque varies significantly due to geometric manufacturing errors
Solution Approach 1:
The patent introduces asymmetric eccentric bulges on the rotor periphery that are strategically positioned and dimensioned to counteract the effects of manufacturing errors. The asymmetric shape (part-elliptical with specific major and minor axes) creates a magnetic circuit that is less sensitive to variations in tooth alignment and rotor-stator positioning, thereby improving cogging torque consistency without requiring tighter manufacturing tolerances.
Solution Approach 2:
The eccentric bulges act as a pre-designed compensation mechanism that anticipates and cushions against the effects of manufacturing errors. By incorporating these geometric features into the rotor design, the patent creates a built-in tolerance to manufacturing variations, reducing cogging torque sensitivity before the motor is assembled and operated, rather than requiring post-manufacturing adjustment or extremely tight tolerances.
3Manufacturing precision
If the rotor magnets and stator teeth are perfectly aligned, then cogging torque is minimized in theory, but manufacturing errors cause misalignment and increase cogging torque
Solution Approach 1:
The eccentric bulges create a non-uniform air gap profile that modifies the magnetic interaction between rotor magnets and stator teeth. This curved, variable radius profile reduces the sensitivity of cogging torque to misalignment by distributing the magnetic flux more evenly, thereby mitigating the harmful effects of manufacturing errors in magnet-tooth alignment.
Solution Approach 2:
The patent changes the rotor radius parameter from constant to variable through the introduction of eccentric bulges. This parameter modification alters the magnetic circuit characteristics, making the system less sensitive to alignment errors between magnets and teeth, thereby reducing cogging torque even when perfect alignment cannot be achieved in manufacturing.
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 part-elliptical shape significantly reduces the motor's sensitivity to manufacturing errors, providing a higher tolerance for geometric variations and minimizing cogging torque, resulting in smoother rotor movement across a range of manufacturing conditions.
Implementation Method 1
These currents generate a magnetic flux which interacts with the magnets of the rotor, and by varying the currents in each winding as a function of the relative angular position of the rotor and the stator the magnetic flux will cause the rotor to turn
Implementation Method 2
an outer peripheral surface of the rotor that faces the stator across the airgap there between is provided with a respective eccentric bulge in the region of each rotor magnet, the bulge having a part-elliptical shape, the centre of the circumference of the bulge lying on or close to an axis that passes through the axis of rotation of the rotor and through a point on or close to the circumferential centre of the associated magnet
Data Source
AI summary
An interior permanent magnet motor comprising a rotor having a set of permanent magnets placed within the interior of the rotor and a stator which surrounds the rotor and has a set of stator teeth defining slots between adjacent teeth. The stator also includes a plurality of stator windings that extend around the teeth and within the slots, the rotor and stator defining an airgap there between, in which an outer peripheral surface of the rotor that faces the stator across the airgap is provided with a respective eccentric bulge in the region of each rotor magnet. The bulge has a part-elliptical shape, the centre of the circumference of the bulge lying on or close to an axis that passes through the axis of rotation of the rotor and through a point on or close to the circumferential centre of the associated magnet, and in which the two ends of the part-elliptical bulge respectively connect to a region of the periphery that interconnects to an adjacent bulge, in which the dimensions of the bulge are selected so as to optimise the motor in terms of minimising variations in cogging torque that arise due to geometric manufacturing errors.