SR Machine Position Sensor Flux Concentration
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Solution Overview
Problem
Existing switched reluctance (SR) machines face issues with position sensing due to non-linear magnetic flux decay, thermal expansion affecting sensor-magnet alignment, and electromagnetic interference, leading to sensor saturation, errors, and potential loss of control.
Innovation Solution
A position sensing system comprising a magnet carrier and sensor shield that concentrates magnetic flux and shields the sensor from external interference, using a 'horseshoe' magnet arrangement and external shield to enhance the working range and reduce stray field effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single magnet is used in the sensing system, then the structure is simple, but the magnetic flux is not concentrated and the working range is limited
Solution Approach 1:
The single magnet is divided into two separate magnets arranged in a specific configuration. This segmentation allows each magnet to contribute to concentrating magnetic flux in a particular direction, thereby expanding the effective working range of the sensor while maintaining a relatively simple overall structure.
Solution Approach 2:
The magnetic flux concentration is achieved by arranging magnets in a specific spatial configuration (side-by-side arrangement with poles facing the sensor). This dimensional arrangement creates a well-defined magnetic flux path that concentrates flux in the normal direction to the shaft centerline, effectively extending the sensor's working range.
2Device complexity
If no shield is used, then the device complexity is low, but electromagnetic interference affects sensor accuracy
Solution Approach 1:
A magnet shield is introduced as an intermediary component between the magnets and the external environment. This shield selectively blocks electromagnetic interference from reaching the sensor while allowing the magnetic flux from the magnets to reach the sensor, thereby protecting sensor accuracy without completely isolating the magnetic field.
Solution Approach 2:
The shielding is applied locally around the sensor and magnets rather than as a complete enclosure. This localized shielding approach provides protection against electromagnetic interference in the critical areas while minimizing the overall device complexity and avoiding unnecessary obstruction of magnetic flux paths.
3Device complexity
If thermal expansion is not considered, then the design is simpler, but position errors increase at extreme temperatures
Solution Approach 1:
The design anticipates thermal expansion effects by pre-configuring the magnet and sensor positions to account for expected dimensional changes across the operating temperature range. This beforehand compensation ensures that the magnetic flux density remains within the sensor's working range even when thermal expansion occurs, maintaining position accuracy without adding complex active compensation mechanisms.
4Measurement precision
If magnets are placed close to the sensor, then the magnetic flux density is high, but the working range is limited
Solution Approach 1:
Instead of increasing flux density by reducing the distance along the axis normal to the shaft, the invention uses a side-by-side magnet arrangement that creates a concentrated flux path in a different spatial dimension. This configuration maintains high flux density at the sensor while allowing a larger axial working range because the flux concentration is achieved through geometric arrangement rather than minimal spacing.
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 system significantly increases the functional range of the sensing system, reducing position errors by 70 times and minimizing the impact of stray magnetic fields, ensuring stable operation across a wide temperature range.
Implementation Method 1
the magnet carrier and magnet shield allows a pair of magnets to be held in a magnet carrier in such a manner so as to concentrate the magnetic flux within a well formed by the magnet and magnet carrier
Implementation Method 2
The stationary sensor senses changes in a magnetic field produced by the magnet
Implementation Method 3
a sensor shield, which surrounds the sensor element, and which screens the sensor element from external electric interference
Data Source
AI summary
A position sensing system for a switched reluctance machine, such as that of an Integrated Starter Generator, Turbogenerator or electric Supercharger wherein the system comprises a pair magnets, a magnet carrier, and a sensor element, wherein the sensor element is mounted upon an end of a rotatable shaft of the SR machine, and wherein the sensor element is mounted on a circuit board, and sits in a well formed by the magnets which are arranged such that the magnetic flux follows a path similar to that of a horseshoe magnet, and whereby magnetic flux produced by the magnets is concentrated within the well of the magnet carrier in a direction normal to the axial direction of the shaft of the SR machine.