Variable-Airgap Electric Machine for Back-EMF and Torque Control
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Solution Overview
Problem
Electric machines in hybrid and electric vehicles face challenges in managing magnetic flux and back-EMF voltage at high speeds, leading to inefficiencies and potential overvoltage issues, which affect torque capability and energy losses.
Innovation Solution
The design incorporates hollow channels in the stator back iron to adjust the airgap length by advancing and retracting magnetic particles, allowing for dynamic control of magnetic flux and back-EMF voltage, optimizing performance across various speed and torque conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If magnetic flux is increased to maintain torque capability, then torque is improved, but back-EMF voltage increases causing overvoltage issues at high speeds
Solution Approach 1:
The patent implements dynamic adjustment of magnetic flux by controlling the position of magnetic material within the stator core. The magnetic material can be moved between different positions to change the effective airgap length, thereby dynamically adjusting magnetic flux to match varying speed and torque requirements. This resolves the contradiction by allowing the system to have high magnetic flux (high torque) at low speeds and low magnetic flux (low back-EMF voltage) at high speeds.
Solution Approach 2:
The patent changes the physical parameter of airgap length by moving magnetic material within the stator core. By adjusting the position of magnetic material, the effective airgap length changes, which directly controls magnetic flux density. This parameter change allows the system to optimize between torque production and back-EMF voltage generation across different operating conditions.
2Loss of energy
If airgap length is increased to reduce magnetic flux and back-EMF voltage, then efficiency at high speeds is improved, but torque capability decreases
Solution Approach 1:
The system dynamically adjusts airgap length by moving magnetic material within the stator core based on operating conditions. At high speeds, the magnetic material is positioned to increase effective airgap length, reducing magnetic flux and improving efficiency. At low speeds, the magnetic material is repositioned to decrease effective airgap length, increasing magnetic flux and maintaining torque capability. This dynamic adjustment resolves the contradiction between efficiency and torque.
Solution Approach 2:
The magnetic material within the stator core serves dual purposes: it provides structural support and simultaneously functions as a flux control mechanism. By moving this existing component, the system self-regulates magnetic flux without requiring external systems, thereby improving efficiency while maintaining torque capability across different operating conditions.
3Force
If magnetic material is advanced into orifices to decrease airgap length, then magnetic flux increases for torque production, but back-EMF voltage increases causing overvoltage
Solution Approach 1:
The system dynamically controls the position of magnetic material in the orifices based on real-time operating conditions. During acceleration or high-torque demand, magnetic material is advanced into orifices to decrease airgap length and increase magnetic flux for torque production. During high-speed operation, magnetic material is retracted from orifices to increase airgap length and reduce back-EMF voltage, preventing overvoltage. This dynamic positioning resolves the contradiction between torque production and overvoltage prevention.
Solution Approach 2:
The control system uses feedback from speed and torque sensors to determine the optimal position of magnetic material. Based on this feedback, the controller adjusts magnetic material position to maintain magnetic flux within acceptable ranges, preventing both insufficient torque and excessive back-EMF voltage. This closed-loop control resolves the contradiction by continuously optimizing the balance between torque production and overvoltage prevention.
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 approach reduces back-EMF voltage and iron losses, improves efficiency at higher speeds, and maintains torque capability, while minimizing manufacturing costs and requiring minimal design modifications.
Implementation Method 1
adjusting a magnetic flux within an airgap defined between the rotor and the stator
Implementation Method 2
The windings are disposed within a first array of orifices that are defined about an inner diameter of the core
Data Source
AI summary
An electric machine includes a rotor and a stator. The rotor is configured to generate rotational motion. The stator is disposed radially about the rotor. The stator has a core and windings. The core defines a first array of orifices about an inner diameter of the core and a second array of orifices radially outward from the first array of orifices. The windings are disposed within the first array of orifices. A magnetic material is configured to advance into and retract from the second array of orifices to adjust a magnetic flux within an airgap defined between the rotor and the stator.