Passive Magnetic Unloading Circuit Reduces Bearing Thrust
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Solution Overview
Problem
In electrical machines, such as motors and generators, the axial thrust force on bearings can be excessive due to rotor weight, leading to increased mechanical friction losses and reduced bearing life, which existing magnetic unloading circuits often fail to adequately address, especially in flywheel motor/generator devices where thrust loads are substantial.
Innovation Solution
A passive magnetic unloading circuit is implemented using a series magnetic circuit with permeable pole pieces and air gaps, where the magnetic flux induces a magnetic force that varies with coil current, allowing for a controlled net thrust load profile that reduces the net thrust load below the rotor weight by optimizing the ratio of air gap areas and lengths, and exploiting magnetic saturation characteristics to manage force levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnetic unloading circuits are implemented, then bearing life is extended and mechanical friction losses are reduced, but device complexity increases
Solution Approach 1:
The patent combines the magnetic unloading function with the existing primary magnetic circuit of the electrical machine. The pole pieces serve dual purposes: generating the main magnetic flux for machine operation and providing the magnetic path for the unloading circuit. This integration eliminates the need for separate magnetic unloading components, reducing device complexity while maintaining bearing life extension benefits
Solution Approach 2:
The pole pieces in the magnetic circuit are designed to perform multiple functions simultaneously: they generate the primary magnetic flux required for the electrical machine's operation and also serve as the magnetic path for the unloading circuit that reduces bearing thrust. This multi-functionality reduces the overall component count and simplifies the device structure while achieving the reliability improvement of extended bearing life
2Force
If explicit magnetic unloading circuits are used, then thrust force reduction is achieved, but magnetic coupling between unloading and primary circuits causes performance degradation
Solution Approach 1:
The patent extracts the magnetic unloading function from a separate explicit circuit and integrates it into the existing primary magnetic circuit. By using the same pole pieces and magnetic path for both the primary machine operation and the unloading function, the design eliminates the harmful magnetic coupling between separate circuits while maintaining effective thrust force reduction
3Force
If implicit magnetic unloading circuits with feedback control are implemented, then thrust unloading is maintained within appropriate range, but device complexity and control requirements increase
Solution Approach 1:
The patent employs a passive magnetic unloading circuit that automatically maintains appropriate thrust unloading without requiring external feedback control. The magnetic circuit itself provides the necessary self-regulation through its inherent magnetic properties and flux distribution, eliminating the need for sensors, controllers, and complex feedback mechanisms while maintaining effective thrust force management
4Device complexity
If passive magnetic unloading circuits are used, then device complexity is reduced and reliability is improved, but control over unloading forces is limited
Solution Approach 1:
The patent achieves adaptability in unloading force control by modifying physical parameters of the magnetic circuit, specifically the geometry and positioning of the pole pieces. By adjusting parameters such as pole piece area, gap dimensions, and magnetic material properties, the circuit can provide appropriate unloading forces for different operating conditions without requiring complex active control mechanisms
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 effectively reduces the net thrust load on bearings, extending bearing life and minimizing mechanical friction losses while maintaining a controlled force profile, even under varying operational conditions.
Implementation Method 1
A coil induces a magnetic flux in this series magnetic circuit, wherein the flux magnitude varies as a function of both the current magnitude flowing in the coil and a series magnetic circuit with known magnetic saturation characteristics
Implementation Method 2
As magnetic circuit flux flows a magnetic force results on the rotor and may provide a rotor net thrust load profile as a function of coil current
Implementation Method 3
exploiting magnetic saturation characteristics to manage force levels
Data Source
AI summary
Apparatus and methods for providing a pre-determined axial thrust force profile for use in a rotating machine that includes a magnetically permeable rotor with first and second surfaces and a generally perpendicular shaft is disclosed. One or more bearings support the shaft and a coil induces flux in the rotor. First and second pole pieces disposed adjacent to the first and second surfaces define first and second gaps. A series magnetic circuit including the pole pieces, the gaps and the rotor carries flux generated by current flowing in the coil. Pole pieces and gaps provide substantially similar reluctance in both gaps. Magnetic saturation characteristics of a series magnetic circuit may provide a pre-determined axial force profile as a function of coil current. A first magnetic saturation characteristic may provide a maximum axial force at a first current magnitude. A second magnetic saturation characteristic may provide a lower axial force at a current greater than the first current. The saturation characteristic may be formed by configuring the geometry and dimensions of the poles. The axial force profile may be formed to reduce the net axial thrust load on the bearings.