Brushless Motor Rotor Position Sensing with Sinusoidal Magnet
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Solution Overview
Problem
Existing electric motor rotor position sensing technologies face challenges in accurately determining the absolute value of rotor position, particularly within the angle range of one sensor pole, limiting their ability to provide reliable position information at any point in time.
Innovation Solution
An electric motor design featuring a ring magnet with a sinusoidal flux profile and at least one rotor position sensor that generates an analog signal to determine the absolute rotor position, with the ring magnet positioned nonrotatably on the rotor shaft and partially within a magnetically transparent bearing tube, allowing for precise rotor position sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a multi-pole sensor magnet with digital value conversion is used, then rotor position information can be obtained within one sensor pole angle range, but the ability to determine absolute rotor position at any point in time is limited
Solution Approach 1:
The patent changes the magnetic flux profile parameter from non-sinusoidal to sinusoidal, and changes the signal type from digital to analog. This allows continuous analog signals to represent absolute rotor position throughout the entire rotation range, resolving the limitation of determining absolute position at any point in time while maintaining high measurement precision within each pole region
2Measurement precision
If an initialization phase is required for rotor position sensing, then the system can establish a reference position, but the response time and productivity are reduced
Solution Approach 1:
The sinusoidal flux profile is designed to provide continuous absolute position information from the start of operation. The analog signals from multiple sensors combined with the sinusoidal profile enable the system to determine absolute rotor position immediately without requiring an initialization phase, thus improving productivity while maintaining accuracy
3Reliability
If the ring magnet is positioned within the bearing tube, then the rotor position can be sensed without interfering with the rotor magnet, but the magnetic flux density at the sensor may be reduced
Solution Approach 1:
The bearing tube serves as an intermediary structure that is magnetically transparent, allowing the magnetic flux from the ring magnet to pass through to the sensors without significant attenuation. This positioning enables reliable position sensing while maintaining sufficient magnetic flux density, as the bearing tube material does not interfere with the magnetic field
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
Enables the determination of the absolute rotor position at any time, eliminating the need for an initialization phase and improving the accuracy and reliability of rotor position signals, thereby enhancing motor performance and efficiency.
Implementation Method 1
it is magnetized in such a way that it has a maximum of n pole pairs and that a substantially sinusoidal magnetic flux profile occurs at its circumference
Implementation Method 2
The at least one rotor position sensor serves to generate an analog signal that maps a property of the magnetic flux and is suitable for determining an absolute value of the rotor position
Implementation Method 3
a ring magnet located at least partially inside a magnetically transparent subregion of the bearing tube which supports the rotor
Data Source
AI summary
An electric motor has a stator (224) having a bearing tube (238) made of a magnetically transparent material; it also has a rotor (222) having a rotor shaft (234) that is at least partially journaled in the bearing tube (238), and has a ring magnet (250) that is fixedly arranged on the rotor shaft (234) inside the bearing tube (238). Two magnetic-field-dependent analog sensors (248′, 248″) are arranged on a circuit board (246) outside the bearing tube (238), at an angular distance (PHI) from one another, in order to generate rotor position signals as a function of the rotational position of the ring magnet (250). A corresponding device (150) that serves to control the motor is provided, in order to process these rotor position signals into a signal that indicates the absolute rotational position of the rotor (222).