External Rotor Synchronous Motor for High Torque Low Speed Boat Drive
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Solution Overview
Problem
Existing electric boat drives face limitations in efficiency and weight due to the need for large, heavy batteries, and conventional motors are not suitable for outboard installations, requiring a high-torque, low-speed solution with reduced weight and increased range.
Innovation Solution
A brushless synchronous motor with a different number of poles for the stator and rotor, designed as an external rotor with a radial magnetic field, achieving high torque at low speeds and reduced centrifugal forces, allowing for a compact, lightweight design suitable for outboard use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If an oversized electric motor is used to generate high torque at low speeds, then the necessary torque is achieved, but the weight of the motor increases significantly
Solution Approach 1:
The patent replaces the conventional mechanical gear reduction system with an electrical speed reduction mechanism. By using a synchronous motor with a different number of poles between stator and rotor, the motor inherently produces reduced speed and increased torque without requiring mechanical gears, thereby reducing overall system weight while maintaining high torque output.
Solution Approach 2:
The patent changes the fundamental parameter of pole count mismatch between stator and rotor to achieve electrical speed reduction. This parameter change allows the motor to operate at lower speeds with higher torque directly, eliminating the need for oversized motors or mechanical gearboxes and thus reducing weight.
2Force
If the magnetic field is directed radially with rotor poles farther from the axis than stator poles, then high torque is achieved at low speeds, but the motor geometry becomes more complex
Solution Approach 1:
The patent transitions from a conventional axial magnetic field configuration to a radial magnetic field configuration. By directing the magnetic field radially and positioning rotor poles farther from the rotation axis than stator poles, the invention exploits the radial dimension to increase the lever arm for torque generation, achieving high torque without proportionally increasing overall motor complexity.
3Force
If a propeller with large diameter is used to increase thrust, then the thrust increases quadratically, but the motor must be oversized to drive it at low speeds
Solution Approach 1:
The patent replaces mechanical gear reduction with electrical speed reduction through pole count mismatch. This substitution enables the motor to directly drive large-diameter propellers at low speeds with high torque without requiring mechanical gearboxes, thereby reducing overall system weight while maintaining the quadratic thrust increase from larger propeller diameter.
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 solution provides high torque and efficiency at low speeds, enabling larger propellers and increased range with reduced weight, suitable for large and heavy boats, and eliminates the need for additional cooling and gear systems, achieving a high power-to-weight ratio.
Implementation Method 1
The three-phase or multi-phase current supplied by the speed controller flows through the individual windings, which generates a rotating magnetic field in the stator
Implementation Method 2
The rotating magnetic field in the stator acts on the magnetic poles of the rotor and causes it to rotate
Implementation Method 3
the magnetic field generated between the poles of the stator and the poles of the rotor is directed essentially radially to the axis of rotation of the rotor and the poles of the rotor are further from the axis of rotation of the rotor than the poles of the stator
Data Source
Figure 1~2
Figure 3~5
AI summary
The drive has a permanent magnet-excited, electronically commutated synchronous motor with a bell-shaped rotor (12) arranged outside of a stator (10). The number of poles of the stator and the number of poles of the rotor are different. A magnetic field created between the poles of the stator and the rotor is a radial field which is perpendicular to a shaft of the rotor. The poles of the rotor have a greater distance from the shaft of the rotor than the poles of the stator. An airgap between stator windings (9a-9f) and rotor magnets has a large distance from rotation axis or rotor shaft.