Lundell Rotor Claw Cross-Section Reduction for Flux Leakage
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Solution Overview
Problem
Rotating electrical machine rotors with claw structures experience significant magnetic flux leakage due to the geometry of the interpolar space, leading to inefficiencies and increased costs from using expensive rare-earth magnets to fill the entire space.
Innovation Solution
The side faces of the claws are designed to reduce in section from the free ends of the magnetic assembly towards the head end, guiding magnetic field lines through the interpolar space and reducing leakage paths, allowing for a more efficient use of magnets and lower material costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the interpolar space is completely filled with magnets, then magnetic flux leakage is prevented, but manufacturing cost increases due to expensive rare-earth magnets
Solution Approach 1:
The patent applies local quality by modifying the claw geometry specifically in the interpolar region. The claw cross-section is reduced from the free end toward the head, creating a localized tapered shape that guides magnetic flux. This localized geometric modification prevents flux leakage in the critical interpolar space without requiring magnets to fill the entire space, thereby reducing magnet material usage and manufacturing cost while maintaining magnetic efficiency.
2Loss of energy
If the claw cross-section is reduced from the free end, then magnetic flux leakage is minimized, but the structural strength of the claw may be compromised
Solution Approach 1:
The patent applies preliminary action by designing the reduced cross-section geometry in advance during the manufacturing process. The tapered shape is built into the claw structure from the beginning, with the reduction starting from the free end and progressing toward the head. This pre-planned geometric configuration ensures that the magnetic flux is guided along the desired path while the overall claw structure maintains sufficient strength through its design, avoiding the need for additional reinforcement that would increase complexity.
3Ease of manufacture
If magnets are positioned using clips or fasteners, then assembly is simplified, but magnetic flux leakage increases due to gaps between magnets and claw surfaces
Solution Approach 1:
The patent applies the taking out principle by removing the need for separate fastening elements like clips or fasteners. Instead of adding external components to hold magnets, the invention integrates the magnetic assembly directly into the claw structure through the reduced cross-section design. The tapered geometry creates a self-contained configuration where the magnet is held in place by the claw's own structure, eliminating gaps that would cause flux leakage while maintaining assembly simplicity.
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
This design minimizes magnetic flux leakage, increases the efficiency of the rotating electrical machine, and reduces production costs by optimizing the shape of the claws to direct magnetic field lines effectively, resulting in higher current production in motor vehicle alternators.
Implementation Method 1
a significant portion of the magnetic flux generated by the rotor winding passes through leakage paths instead of traversing the machine's air gap
Implementation Method 2
the pole wheels, advantageously made of ferromagnetic material, become magnetized, thus creating south poles at the claws of one pole wheel and north poles at the claws of the other
Implementation Method 3
When the excitation winding is electrically energized, the pole wheels, advantageously made of ferromagnetic material, become magnetized
Data Source
Figure 1a~1b
Figure 2
Figure 3a~3b
AI summary
The invention relates to a rotor (1) of a rotary electric machine of the alternator or alternator-starter type. The rotor (1) comprises two pole wheels including a series of axial claws having a generally trapezoidal shape that extend from the edge of the outer radial end of one pole wheel towards the other pole wheel, such that each claw of one pole wheel is located in the space (30) between two consecutive claws of the other pole wheel. The rotor also comprises an interpolar magnetic assembly (20) in the interpolar space (30) defined between a first claw (4) of a first pole wheel (3) and a second claw (6a) of a second pole wheel (5), said magnetic assembly (20) comprising two first faces (22) defined by first and second free ends (23, 24), said two first faces (22) extending respectively the length of first and second claws (4, 6a). Each of the first and second claws (4, 6a) has a side face (7) such that the adjacent side face (7) faces same, said side face (7) comprising third and fourth opposing ends (8, 9) between which the magnet (21) is in contact. In addition, the side faces of each of the first and second claws (4, 6a) define a reduction in cross-section (6) from one of the free ends (23, 24) of the magnetic assembly (20) extending towards a claw head end (40) along a side facet (12).