Hub Motor Saliency for Extended Speed Range
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Solution Overview
Problem
Electric two-wheelers with gearless wheel hub motors are limited in maximum speed due to the self-regulation of torque when the voltage induced by the rotor reaches the maximum phase voltage, leading to a restricted speed range and high costs associated with the use of rare earth magnets.
Innovation Solution
The electric two-wheeler design features a rotor with embedded permanent magnets in pockets within the yoke ring, creating saliency, which allows for additional reluctance torque and higher motor speeds by weakening the excitation field, and uses ferrite magnets to reduce costs, along with control methods like pre- or post-commutation to optimize speed and torque ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If permanent magnets are arranged on the inside of the yoke ring lying laterally against one another, then the motor can operate in the armature setting range, but the maximum speed is limited due to self-regulation of torque when induced voltage reaches maximum phase voltage
Solution Approach 1:
The rotor is segmented into multiple independent pockets, each containing a permanent magnet. This segmentation creates distinct magnetic poles and enables the formation of a salient rotor structure, which allows for field weakening operation and extends the speed range beyond the base armature setting range.
Solution Approach 2:
The permanent magnets are positioned to create local magnetic field concentrations at specific rotor positions, forming a salient rotor structure. This local field concentration enables differential reluctance torque generation and facilitates field weakening control for extended speed operation.
2Power
If rare earth magnets are used in high number, then the motor performance is improved, but the overall cost of the drive increases significantly
Solution Approach 1:
Ferrite magnets, which are significantly cheaper than rare earth magnets, are used in the rotor pockets. While ferrite magnets have lower magnetic strength, the salient rotor design compensates for this by generating additional reluctance torque, thereby maintaining acceptable motor performance while dramatically reducing material costs.
Solution Approach 2:
The magnetic material parameter is changed from rare earth magnets to ferrite magnets. This material substitution, combined with the salient rotor geometric configuration, alters the torque generation mechanism to rely more on reluctance torque, achieving a cost-performance balance.
3Speed
If the rotor has a pronounced salience with embedded permanent magnets, then reluctance torque is added and higher motor speeds are achieved, but the device complexity increases
Solution Approach 1:
The rotor is divided into multiple discrete pockets, each housing a permanent magnet. This segmented approach simplifies the embedding process compared to continuous magnetization and allows for modular manufacturing, reducing overall complexity despite the salient structure.
Solution Approach 2:
The permanent magnets are nested within the yoke ring pockets, with the magnet embedded inside the rotor structure. This nested configuration integrates the magnets into the rotor body, reducing the need for separate attachment mechanisms and simplifying the overall rotor assembly.
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 design enhances the speed and torque range of the electric machine, reduces manufacturing costs by using ferrite magnets, and enables sensorless rotor position detection, allowing for efficient operation and noise reduction.
Implementation Method 1
the voltage induced in the stator phases by the rotation of the rotor reaches the maximum phase voltage
Implementation Method 2
the magnetic fluxes generated by the stator current and the permanent magnets are limbed
Implementation Method 3
this allows a reluctance torque to be added to the machine
Data Source
Figure 1
Figure 2A~2B
Figure 3~5
AI summary
The invention relates to an electrically driven two-wheeled vehicle (1) comprising at least one electric machine (4) which has a stator (6) that is fixed to the axle and a rotor (7) that is fixed to the rim. The rotor (7) has a back iron ring (9) with a plurality of permanent magnets (8) which are distributed over the circumference of the back iron ring. The back iron ring (9) has pockets (10) on the back iron ring inner face (11) facing the stator (6), one permanent magnet (8), in particular a ferrite magnet, being at least substantially arranged in each said pocket. The invention further relates to a method for actuating such a two-wheeled vehicle.