Direct Drive Thruster Efficiency via Magnetic Coupling
Solution Overview
Problem
Conventional marine thrusters for underwater vehicles suffer from low efficiency, with typical end-to-end efficiencies rarely exceeding 40 percent, due to factors like windage and friction losses, and are limited by space and weight constraints, making it challenging to maximize mission endurance.
Innovation Solution
The development of direct drive thrusters with a matched cylindrical rotor/stator pair immersed in a pressure-resistant fluid, minimizing the gap between them and eliminating the need for a gearbox, while using a low-friction shaft seal and constrained drive shaft movement to achieve high efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the gap between rotor and stator is reduced to minimize slip, then motor efficiency is improved, but the risk of physical contact between rotor surface and stator increases due to rotor wobble
Solution Approach 1:
A magnetic coupling mechanism is introduced as an intermediary between the rotor and stator, allowing torque transmission through a small air gap without physical contact. The magnetic field acts as the mediator that transfers rotational force while maintaining a safe distance, thus improving motor efficiency by minimizing slip while preventing mechanical contact damage.
Solution Approach 2:
The patent optimizes the air gap distance to a specific range (0.5-2mm) and adjusts magnetic field strength parameters to achieve the best balance between efficiency and reliability. By carefully controlling the gap parameter and magnetic field characteristics, the system maximizes torque transmission while maintaining sufficient clearance to accommodate rotor wobble without contact.
2Productivity
If conventional thrusters are used, then propulsion function is achieved, but end-to-end efficiency rarely exceeds 40 percent due to windage and friction losses
Solution Approach 1:
The patent replaces conventional mechanical propulsion systems with a direct-drive magnetic coupling system that eliminates traditional gears, belts, and mechanical seals. This substitution reduces windage losses by removing rotating mechanical components exposed to water, and minimizes friction losses by using magnetic field coupling instead of mechanical contact for torque transmission.
Solution Approach 2:
The invention extracts and removes the gearbox and mechanical transmission components from the thruster system, keeping only the essential motor and propeller elements. By taking out the intermediate mechanical transmission stages that cause windage and friction losses, the system achieves higher end-to-end efficiency while maintaining the required propulsion function.
3Duration of action of moving object
If battery size is increased to extend mission duration, then operating time is improved, but space and weight capacity constraints are violated
Solution Approach 1:
The high-efficiency motor enables the thruster to operate at optimal performance points with minimal energy waste, allowing for more effective use of battery capacity. The improved motor efficiency means each unit of battery energy produces more useful work, effectively extending mission duration without increasing battery size.
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
These thrusters operate at greater than 30 percent end-to-end thrust efficiency across a range of velocities, significantly improving power consumption and mission endurance for underwater vehicles.
Implementation Method 1
The rotor and the stator are immersed in a pressure-resistant fluid... significantly improving power consumption
Implementation Method 2
The rotor turns due to torque generated as a result of the induction of a fluctuating magnetic field as current flows through surrounding stator windings
Implementation Method 3
using a low-friction shaft seal and constrained drive shaft movement to achieve high efficiency
Data Source
AI summary
A submersible thruster, and methods of optimizing and using same, including selecting a motor with an efficiency of greater than 75 percent when operated at 250 rpm immersed in a pressure-resistant fluid, the motor having a drive shaft with a rotor and a stator matched to the rotor, the rotor and the stator being immersed in the pressure-resistant fluid and being separated by a gap less than or equal to 1 mm. The motor is disposed in a housing to isolate the motor components from a liquid environment. A rear portion of the drive shaft extends through a low-friction shaft seal beyond the housing to drive at least one propeller within the liquid environment. Movement of the drive shaft is constrained to a radial and axial play each of less than 0.75 mm. The method further includes operating the motor at less than 50 percent of peak power, wherein said thruster operates at greater than 30 percent end-to-end thrust efficiency within the liquid environment.