Traction Motor Rotor Tooth-Seat Coupling Against Angular Misalignment

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Solution Overview

Problem

Existing electric motor rotors face issues with angular misalignment between the crankshaft and steel plates at high rotation speeds and torques, leading to performance degradation and mechanical stress, especially during torque reversals and thermal stress due to overheating.

Innovation Solution

A rotor design featuring a crankshaft with an isosceles trapezium radial seat and 'V' shaped teeth on the steel plates, providing an interference coupling that maintains precise contact and self-centering, reducing mechanical stress and preventing angular misalignment through a combination of friction and geometric engagement at varying speeds.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a press-fit coupling is used between the crankshaft and steel plate stacks, then angular misalignment is prevented at low rotation speeds, but significant angular misalignment occurs at high rotation speeds and torques

Engineering Contradiction:

Improveangular alignment stabilityVSAvoidrotation speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The coupling interface is segmented into multiple functional zones: an interference fit zone for radial positioning, a shape coupling zone with interlocking teeth for torque transmission, and a skewing zone allowing controlled angular offset. This segmentation allows each zone to address specific requirements independently, maintaining alignment stability across the full speed range.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The steel plate stacks are deliberately skewed at a specific angle (e.g., 15-30 degrees) relative to the crankshaft axis, creating an asymmetric configuration. This asymmetric skewing compensates for centrifugal forces at high speeds, preventing angular misalignment and maintaining reliable coupling under dynamic operating conditions.

Inventive Principle:

Principle #4Asymmetry

2Ease of manufacture

If a press-fit coupling is used between the crankshaft and steel plate stacks, then assembly is simple, but the coupling fails to prevent angular misalignment under high torque and thermal stress conditions

Engineering Contradiction:

Improveassembly simplicityVSAvoidcoupling integrity under stress

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The interference fit interface incorporates curved or tapered surfaces that conform to centrifugal and thermal expansion forces. The curved geometry allows the coupling to maintain contact and alignment under high torque and temperature conditions while remaining manufacturable through standard machining processes.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Productivity

If the crankshaft and steel plates maintain continuous contact during torque reversals, then motor operation remains optimal, but angular misalignment degrades performance rapidly in skewed rotor designs

Engineering Contradiction:

Improvemotor operation efficiencyVSAvoidangular alignment precision

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The coupling design incorporates dynamic elements that adapt to changing load conditions. The interlocking teeth and skewed configuration allow the coupling to flex and adjust during torque reversals, maintaining continuous contact between the crankshaft and steel plates while preserving angular alignment precision throughout the reversal cycle.

Inventive Principle:

Principle #15Dynamics

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 design effectively prevents angular misalignment and maintains optimal performance under high-speed and torque conditions, ensuring continuous contact and reducing mechanical stress, thus enhancing the longevity and efficiency of the electric motor.

Implementation Method 1

a forced, i.e., interference (press-fit) coupling between the steel plate stacks and the central seat of the crankshaft is known

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS11831219B2Rotor for electric motor, particularly for traction, and related electric motor

Publication Date: 2023.11.28 MARELLI EURO SPA

AI summary

A rotor for an electric motor comprising a crankshaft extending along an axis (X-X) coinciding with an axis of rotation of the crankshaft, and at least one steel plate having slots for housing magnets. The steel plate includes a central seat, keyed to an outer side wall of the crankshaft according to an interference coupling, wherein the steel plate is coupled to the crankshaft at the central seat by a first tooth obtained on the steel plate, which projects towards the associated crankshaft and a first radial seat, obtained on the outer side wall of the crankshaft. The first radial seat has an isosceles trapezium cross-section delimited laterally by a pair of oblique sides converging towards the axis of rotation. The first tooth has a ‘V’ cross-section with a pair of curvilinear side walls, suitable for interfacing against the oblique sides of the first radial seat.