Adjustable Air Gap Electric Machine Using Piezoelectric Actuators

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Solution Overview

Problem

Variations in the air gap width between the rotor and stator of electric machines due to centrifugal forces, temperature effects, and vibrations lead to irregularities in power and torque, potentially causing damage from contact between the rotor and stator.

Innovation Solution

The implementation of movement devices controlled by a unit to selectively adjust the radial air gap width in an electric machine, allowing for angularly resolved adjustments by using piezoelectric stacks or actuators to influence the position of magnetic devices on the rotor and stator, enabling precise control of the air gap.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If the air gap width is reduced to increase magnetic flux density and power, then the power and torque of the electric machine are improved, but the risk of contact between rotor and stator increases due to vibrations and centrifugal forces

Engineering Contradiction:

ImprovepowerVSAvoidrisk of contact between rotor and stator

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The patent applies dynamics by making the air gap width adjustable rather than fixed. Movement devices with actuators dynamically adjust the radial position of magnetic devices on the rotor or stator, allowing the air gap to be optimized for power while maintaining sufficient clearance to prevent contact during vibrations and centrifugal forces.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the parameter of air gap width from a fixed design value to a variable parameter that can be adjusted during operation. By using actuators to modify the radial position of magnetic devices, the system can adapt the air gap width to balance power output and reliability requirements under different operating conditions.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If movement devices are added to adjust the air gap width, then the controllability and adaptability of the electric machine are improved, but the device complexity increases

Engineering Contradiction:

Improvecontrollability of air gap widthVSAvoidcomplexity of movement devices

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent segments the air gap adjustment function into multiple independent movement devices, each with its own actuator. These devices are distributed along the circumferential direction and can be controlled independently or in coordination, allowing localized adjustment of the air gap width at different angular positions while maintaining overall system manageability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The movement devices serve multiple functions: they adjust the air gap width for power optimization, compensate for vibrations and centrifugal forces, and prevent contact between rotor and stator. This multi-functionality reduces the need for separate systems for each purpose, thereby limiting the increase in overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Measurement precision

If angularly resolved adjustment of air gap width is implemented, then the precision of magnetic flux control is improved, but the manufacturing precision requirements increase

Engineering Contradiction:

Improveangularly resolved air gap controlVSAvoidprecision of movement device positioning

Core Design Contradiction:

Measurement precisionVSManufacturing precision

Solution Approach 1:

The patent implements feedback control where the actual positions of magnetic devices and the resulting air gap width are monitored. This feedback information is used to adjust the movement devices, compensating for manufacturing tolerances and ensuring precise angularly resolved control of the air gap width during operation rather than relying solely on manufacturing precision.

Inventive Principle:

Principle #23Feedback

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 solution allows for adjustable power and torque, improved efficiency, and enhanced durability by preventing contact between rotor and stator, while also simplifying the manufacturing process through precise air gap control.

Implementation Method 1

using piezoelectric stacks or actuators to influence the position of magnetic devices on the rotor and stator

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

the respective magnetic means interact electromagnetically with one another

Methodology Applied

Scientific EffectElectromagnetic interaction: Electromagnetic Induction

Data Source

PatentUS11611271B2Electric machine with an adjustable air gap

Publication Date: 2023.03.21 ROLLS ROYCE DEUT LTD & CO KG

AI summary

An electric machine includes a rotor, a stator, and an air gap formed between a magnetic device of the rotor and the stator. For the selective setting of the air gap, movement devices implemented by piezoelectric stacks are provided on the rotor and/or on the stator. The movement devices may influence radial positions of the respective magnetic device and thus set the radial air gap width. It is thereby possible to exert open-loop and/or closed-loop control over a power or torque of the electric machine without adjusting stator currents. Vibration or unbalance of the rotor may also be counteracted quickly and effectively during operation of the machine.