Frontiers in Mechanical Engineering· 2026Q2· Review
A review of structural design for hairpin windings and ultra-high slot fill factor in electric motors for new energy vehicles
- 1citations
- Q2SCImago
- 2026year
Short summary
Hairpin windings enable electric motor slot fill factors over 70%, significantly boosting power density and thermal management in new energy vehicles compared to conventional round-wire designs (35%-45%).
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Key points
- Hairpin windings achieve >70% slot fill factor, improving power density and thermal management in EV motors.
- Review covers hairpin, X-pin, continuous wave, and I-pin configurations, focusing on conductor geometry, end-winding, and AC loss.
- Examines electromagnetic/mechanical trade-offs of rectangular conductors, including skin/proximity effects and welding quality.
- Synthesizes advances in laser welding, variable cross-section conductors, and model-based defect monitoring.
AI-generated from the title and abstract; the full text is not read.
Abstract
Hairpin winding technology has emerged as a transformative structural design paradigm for new energy vehicle traction motors, enabling slot fill factors exceeding 70% compared to 35%–45% for conventional round-wire windings, thereby delivering significant improvements in power density, thermal management, and manufacturing automation. This review systematically examines the structural design aspects of hairpin, X-pin, continuous wave, and I-pin winding configurations, encompassing conductor geometry optimization, end-winding shortening strategies, AC loss mitigation, and manufacturing process control. Particular emphasis is placed on the electromagnetic and mechanical trade-offs associated with rectangular conductors, including skin and proximity effects, welding quality control, and insulation integrity under high-voltage pulse-width modulation stress. The paper synthesizes recent advances in laser welding technology, variable cross-section conductors, and model-based defect monitoring systems. By analyzing comparative performance metrics across different flat-wire architectures and identifying persistent technical barriers including manufacturing complexity, AC loss management, and slot opening design, this review aims to provide a comprehensive reference for researchers and engineers engaged in next-generation high-efficiency electric motor development.
The authors' abstract, as published at the source. Frontiers in Mechanical Engineering, 2026 · DOI ↗
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