External Rotor Motor Converter Thermal Management
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Solution Overview
Problem
Existing outboard drives with underwater gondolas face challenges in accommodating electronically commutated synchronous motors due to space constraints and the risk of water damage to converter electronics, which are sensitive to moisture and magnetic interference from high magnetic field densities.
Innovation Solution
The electric motor and converter are housed in the underwater gondola with a carrier body of good thermal conductivity, where the converter is in thermal contact with the carrier body and the electric motor is designed as an external rotor, minimizing electromagnetic interference and allowing for effective heat dissipation without the need for separate air cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the converter is housed in the underwater nacelle with the electric motor, then the connecting cables are kept very short avoiding electromagnetic interference, but the converter electronics are exposed to water and high magnetic field densities which would destroy them
Solution Approach 1:
The converter is extracted from the conventional location outside the underwater nacelle and placed inside, but positioned in a specific region (the nose section ahead of the motor) where it is exposed to the water flow. This extraction allows the converter to be cooled by water while maintaining short cable connections to the motor, thus resolving the contradiction between avoiding electromagnetic interference and protecting from water damage.
Solution Approach 2:
The water that would normally be harmful to the converter electronics is converted into a beneficial cooling medium. By positioning the converter in the water flow path, the harmful water becomes the cooling agent that dissipates heat from the converter, transforming the potential harm into a useful function.
2Reliability
If the converter is encapsulated in synthetic resin to protect from moisture, then the converter is protected from water damage, but there is insufficient space to install the encapsulated converter in the underwater nacelle
Solution Approach 1:
The converter is taken out of the space-constrained region inside the motor housing and repositioned to the nose section of the underwater nacelle. This extraction frees up critical space while allowing the converter to be exposed to water for cooling without requiring bulky encapsulation.
Solution Approach 2:
The converter positioning moves from a three-dimensional constraint problem (insufficient internal space) to a surface/exposure problem (positioning in water flow). By utilizing the external water flow environment rather than trying to fit the converter inside the motor housing, the solution transforms the spatial challenge into a flow-exposure opportunity.
3Volume of moving object
If an internal rotor motor is used, then the structure is more compact, but the distance between permanent magnets and axis of rotation is smaller resulting in lower torque
Solution Approach 1:
Instead of using the conventional internal rotor configuration, the patent inverts the structure to use an external rotor design. This inversion places the permanent magnets on the outside of the stator, increasing their distance from the rotation axis and thereby generating higher torque for the same motor power, which resolves the contradiction between compactness and torque output.
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 configuration reduces electromagnetic interference, minimizes electrical losses, and ensures efficient heat dissipation, making it suitable for high-current applications without the risk of overheating or water damage, while maintaining aerodynamic design and ease of assembly.
Implementation Method 1
the converter is in thermal contact with the carrier body, wherein the carrier body is made of a material with good thermal conductivity
Implementation Method 2
The connecting cables between the inverter and the electric motor act as antennas. High currents, sometimes exceeding 80 A, flow, especially in high-performance motors. If these currents are switched quickly by the inverter, high, steep-edged currents must be transmitted via the connecting cables between the inverter and the electric motor, which causes electromagnetic interference.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
An outboard propulsion system with an underwater nacelle comprises a heat-conducting support body (1) provided with a central bore (2). A shaft (4) extends through the bore (2), supporting a propeller (3) and connected to an outboard-rotor electric motor (7, 15). The electric motor (7, 15) is electronically controlled by a converter (5, 12, 13) that is in thermal contact with the support body.