Parallel Sided Rotor Bars with Shims for Motor Stress Reduction

Solution Overview

Problem

High-speed motor rotors face mechanical and thermal stress issues due to differential radial expansion of steel and aluminum components, leading to potential failure and reduced efficiency, as conventional rotor bar designs are difficult to insert and shim, causing stress and uneven thermal expansion.

Innovation Solution

A motor rotor design featuring parallel sided rotor bars with angled tips and a rotor bar shim, allowing for easier insertion, reduced mechanical stress, and improved thermal management, enabling higher torque and efficiency while accommodating a rotor bar shim for enhanced performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If conventional rotor bars with non-parallel sides are used, then the rotor bar can be inserted into the slot, but the rotor bar causes mechanical stress and thermal expansion issues at high speeds

Engineering Contradiction:

Improve rotor bar insertion easeVSAvoid rotor bar mechanical stress resistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The rotor bar cross-sectional geometry is changed from conventional tapered sides to parallel sides, fundamentally altering the stress distribution characteristics. This parameter change allows the bar to maintain uniform stress distribution during radial expansion, preventing the mechanical stress concentration that occurs with conventional tapered designs at high speeds.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

A shim layer is introduced between the rotor bar and the steel core, creating a composite structure. This shim acts as a stress-distributing interface that accommodates differential thermal expansion between the aluminum bar and steel core, preventing bar failure while maintaining the benefits of parallel-sided geometry.

Inventive Principle:

Principle #40Composite materials

2Reliability

If rotor bars with parallel sides and angled tips are used, then mechanical stress is reduced and insertion is easier, but the manufacturing precision requirements increase

Engineering Contradiction:

Improve rotor bar stress resistanceVSAvoid parallel side geometry precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The rotor bar manufacturing process is segmented into multiple stages: casting the basic parallel-sided bar shape, followed by precision machining of the angled tips. This segmentation allows the bulk of the bar to be manufactured with relaxed tolerances using cost-effective casting, while only the critical tip regions require high-precision machining, thereby reducing overall manufacturing precision requirements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The parallel-sided geometry is established during the initial casting process with relatively loose tolerances, preparing the bar for subsequent precision tip machining. This preliminary action creates a robust base structure that is easier and less costly to manufacture, while the critical precision features are added later when necessary.

Inventive Principle:

Principle #10Preliminary action

3Ease of manufacture

If rotor bars are designed for easier insertion, then manufacturing cost is reduced, but the rotor bar may cause uneven thermal expansion at high speeds

Engineering Contradiction:

Improve rotor bar insertion easeVSAvoid thermal expansion uniformity

Core Design Contradiction:

Ease of manufactureVSStability of the object's composition

Solution Approach 1:

The rotor bar cross-sectional geometry is changed from conventional tapered sides to parallel sides, fundamentally altering the stress distribution characteristics. This parameter change allows the bar to maintain uniform stress distribution during radial expansion, preventing the mechanical stress concentration that occurs with conventional tapered designs at high speeds.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

A shim layer is introduced between the rotor bar and the steel core, creating a composite structure. This shim acts as a stress-distributing interface that accommodates differential thermal expansion between the aluminum bar and steel core, preventing bar failure while maintaining the benefits of parallel-sided geometry.

Inventive Principle:

Principle #40Composite materials

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 facilitates easier rotor bar insertion, reduces mechanical and thermal stresses, and enhances motor performance by allowing sharper angled tips and parallel sides, leading to improved starting torque and reduced manufacturing costs through reduced rotor bar cracking and failure.

Implementation Method 1

as the rotor temperature and/or speed increases, the steel rotor core expands radially at a rate and to an extent different from the expansion rate and extent of the aluminum rotor bars and end rings

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

If the stresses become substantial, the end rings can break away from the rotor bars and the rotor would fail, or in some cases the rotor bar would slide out of the rotor bar slot

Methodology Applied

Scientific EffectMechanical stress:

Data Source

PatentUS7851961B2System and method with a rotor having parallel sided rotor bars

Publication Date: 2010.12.14 INNOMOTICS LLC

AI summary

The present invention relates generally to motor rotors. More particularly, the invention encompasses a motor rotor having at least one rotor bar. The invention also includes a system and method with a rotor having parallel sided rotor bars. The rotor bar preferably has a core and at least one layer of a rotor bar shim.