Rotor Cooling Passage Design for Uniform Heat Removal
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Solution Overview
Problem
Existing rotary electric machine rotor cooling technologies fail to efficiently cool the entire rotor, leading to uneven cooling, reduced torque, and increased drag loss due to inefficient oil flow and discharge patterns.
Innovation Solution
A rotor design featuring a center cooling medium passage extending axially with a radially outside end portion sloped towards the center, paired with inner and outer peripheral side passages, ensures even cooling along the axial direction and prevents interference, enhancing cooling efficiency and reducing drag loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If cooling oil passages extend only in radial direction (JP 2006-067777 A), then cooling uniformity in axial direction is improved compared to no axial passages, but cooling medium accumulates in gap and increases drag loss
Solution Approach 1:
The cooling medium passage is segmented into multiple sections: a first cooling medium passage extending radially, a second cooling medium passage extending axially to guide flow, and a third cooling medium passage extending radially outward to discharge. This segmentation directs cooling medium flow to exit at the axial end portion rather than accumulating in the gap, resolving the contradiction between cooling uniformity and drag loss reduction.
2Temperature
If multiple discharge ports are lined up in axial direction (JP 2006-067777 A), then cooling coverage is improved, but cooling medium from different ports interferes with each other and stays in gap longer
Solution Approach 1:
Instead of discharging cooling medium from multiple ports along the axial direction (which causes interference), the design inverts the discharge strategy by using a single axial end discharge approach. The cooling medium flows through sequential radial and axial passages to exit at the axial end portion, eliminating port interference while maintaining cooling coverage.
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 allows for efficient cooling of the entire rotor core, including the outer peripheral surface, while preventing cooling medium accumulation and interference, thereby maintaining performance and reducing demagnetization risks.
Implementation Method 1
a center cooling medium passage that extends in an axial direction in a position farther toward an inner peripheral side than the permanent magnet, an outer peripheral side cooling medium passage that extends radially outward from a center in the axial direction of the center cooling medium passage and is communicated with the gap
Data Source
AI summary
A rotor of a rotary electric machine, which is supported by a rotating shaft, includes a rotor core, and a permanent magnet embedded in the rotor core. At least one in-core cooling medium passage that leads a cooling medium supplied from an in-shaft cooling medium passage formed inside the rotating shaft to an outer peripheral end of the rotor core, and discharges the supplied cooling medium into a gap between the rotor core and a stator, is formed in the rotor core. The at least one in-core cooling medium passage includes a center cooling medium passage, a pair of inner peripheral side cooling medium passages, and an outer peripheral side cooling medium passage that is communicated with the gap. A radially outside end portion of the center cooling medium passage has a slope that extends toward a radially outer side closer to a center in the axial direction.