Rotor Core Interpole Bridge Layout for Lower Q-Axis Inductance
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Solution Overview
Problem
The existing rotating electrical machines with arc-shaped outer circumferential surfaces between poles experience increased q-axis inductance at high speeds, leading to reduced rotation speed-torque characteristics and a limited operable range, particularly in applications like electric power steering devices that require high torque output at high speeds.
Innovation Solution
A rotating electrical machine design featuring a rotor core with arc-shaped petal portions and interpole bridges having flat surfaces facing the magnetic gap, which increases magnetic resistance and reduces q-axis inductance, thereby improving high-speed rotation characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the outer circumferential surface between the poles of the rotor core is formed in an arc shape, then torque is improved and torque pulsation is reduced, but q-axis inductance increases leading to reduced high-speed rotation characteristics
Solution Approach 1:
The invention applies different surface geometries to different regions of the rotor core: arc-shaped petal portions at the magnetic poles for torque improvement, and flat interpole bridges at the non-magnetic portions for inductance reduction. This local differentiation resolves the contradiction by optimizing each region for its specific function.
Solution Approach 2:
The outer circumferential surface of the rotor core is segmented into distinct functional zones: petal portions corresponding to magnetic poles and interpole bridges corresponding to non-magnetic portions. This segmentation allows independent optimization of torque characteristics and inductance characteristics in different regions.
2Area of moving object
If the outer circumferential surface between the poles is formed in an arc shape, then the width of each magnet in the circumferential direction is increased, but the path of magnetic flux becomes short and magnetic resistance decreases
Solution Approach 1:
Different surface geometries are applied to different regions: arc-shaped surfaces at magnetic poles increase magnet width for torque improvement, while flat surfaces at interpole bridges extend the magnetic flux path for magnetic resistance improvement. Each region's geometry is optimized for its local requirement.
3Stress or pressure
If the q-axis inductance is increased, then the terminal voltage is increased, but the rotation speed-torque characteristics decrease and the operable range is reduced
Solution Approach 1:
The invention changes the geometric parameters of the rotor core surface (from entirely arc-shaped to a combination of flat and arc-shaped regions). This parameter change modifies the magnetic circuit characteristics, specifically reducing q-axis inductance while maintaining terminal voltage requirements, thereby expanding the operable range.
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 design enhances the rotation speed-torque characteristics by reducing q-axis inductance and torque pulsation, expanding the operable range and improving the performance of electric power steering devices.
Implementation Method 1
the path of a magnetic flux passing through the magnetic gap becomes short, so that the magnetic resistance between the portion between the poles and the stator is decreased
Implementation Method 2
the magnetic resistance of the path of the magnetic flux is increased
Implementation Method 3
three-phase currents are applied from an inverter to coils wound around a plurality of tooth portions formed in a stator core
Implementation Method 4
permanent magnets for forming magnetic poles are embedded in the rotor core
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A rotor core (22) of a rotating electrical machine has petal portions (26) disposed so as to correspond to respective magnetic poles, interpole bridges (27) each disposed on an outer circumferential side with respect to a permanent magnet (23) in a non-magnetic portion between the poles, and interpole diameter bridges (28) each surrounded by two permanent magnets (23) and an interpole bridge (27). The outer circumferential surface of each interpole bridge (27) is formed by a first flat surface (27a). Thus, a path of a magnetic flux passing through a magnetic gap (10) is lengthened, so that a q-axis inductance is reduced. In addition, a width (W3) in a radial direction of each interpole bridge (27) and a width (W4) in a circumferential direction of each interpole diameter bridge (28) are constant, and each interpole bridge (27) and each interpole diameter bridge (28) are disposed so as to be perpendicular to each other to form a T shape. Thus, the concentration of stress during press-fitting of the permanent magnet (23) into a magnet hole 22b can be reduced.