Compact Marine Stern Drive With Dual Motors and Planetary Gearing
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Solution Overview
Problem
Existing marine propulsion units face challenges with space requirements, corrosion from saline water cooling, vibration isolation, and sealing issues, particularly in stern drives, which also result in increased marine growth and reduced efficiency.
Innovation Solution
A marine propulsion unit with a stern drive configuration that includes a compact design using vertical electric motors, a planetary gear set, and a closed coolant/lubrication system, eliminating the need for an inboard drive unit and allowing independent motor operation for redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an internal combustion engine and transmission are mounted within the hull of the vessel, then torque can be transmitted to the stern drive, but a significant amount of space is required and corrosion problems occur from saline water cooling
Solution Approach 1:
The patent extracts the drive unit (internal combustion engine) from the hull and relocates it to the stern drive assembly itself. The stern drive housing now contains the drive unit, eliminating the need for internal hull mounting space and removing the drive unit from the corrosive saline cooling environment while maintaining torque transmission capability.
2Temperature
If water is drawn from the ambient marine environment for cooling, then heat from the drive unit can be removed, but corrosion occurs from saline water
Solution Approach 1:
The patent introduces a closed-loop cooling system with a heat exchanger as an intermediary between the drive unit and the marine environment. Fresh water or non-corrosive coolant circulates through the drive unit, and the heat exchanger transfers thermal energy to seawater without direct contact between the coolant and saline water, preventing corrosion while maintaining effective heat removal.
3Object-affected harmful factors
If vibration isolation and dampers are installed to avoid undesirable vibrations, then vibrations from the drive unit can be isolated, but device complexity increases
Solution Approach 1:
The patent combines the vibration isolation function with the existing mounting structure of the stern drive. The drive unit is mounted directly to the stern drive housing using elastomeric dampers that are integrated into the mounting brackets, eliminating the need for separate vibration isolation systems while still effectively reducing vibration transmission to the vessel.
4Power
If a transmission shaft passes through the transom to reach the stern drive, then power can be transmitted to the propellers, but sealing arrangements are required to prevent water leakage
Solution Approach 1:
The patent extracts the drive unit from the hull and relocates it to the stern drive assembly, eliminating the need for a transmission shaft to pass through the transom. The drive unit is now directly mounted in the stern drive housing, and power is transmitted directly to the propellers without requiring complex sealing arrangements at the transom opening.
5Ease of manufacture
If the propulsion unit is mounted extending downwards beneath the hull, then the drive unit can be mounted in a pod, but draft increases and the unit cannot be tilted out of the water
Solution Approach 1:
The patent inverts the conventional mounting approach by placing the drive unit in the stern drive housing above the waterline rather than extending it downwards beneath the hull. The stern drive assembly is mounted to the transom with the drive unit positioned in the upper portion, eliminating the need for deep submersion and reducing draft while maintaining mounting flexibility.
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 a compact, efficient, and reliable propulsion system that maintains torque and efficiency while reducing corrosion and marine growth, and allows operation even if one motor fails, with cost and space savings.
Implementation Method 1
A planetary gear set is arranged between the at least two electric motors in the stern drive housing and the gearbox in the gearbox housing
Implementation Method 2
a closed coolant/lubrication system for the at least two electric motors and the gearbox
Data Source
AI summary
A marine propulsion unit includes a stern drive mounted to a transom. The stern drive comprises an upper unit enclosed in a stern drive housing and a lower unit enclosed in a gearbox housing; wherein the gearbox housing contains a gearbox arranged to drive at least one propeller. The propulsion unit further comprises at least two electric motors arranged in the stern drive housing, which electric motors are mounted with vertical output shafts; a planetary gear set arranged between the at least two electric motors and the gearbox, and a vertical shaft that is attached to a ring gear of the planetary gear set at its upper end and is connected to the gearbox at its lower end; wherein the output shaft of each electric motor is connected to a planetary gear arranged in the planetary gear set to drive the ring gear and the vertical shaft connected to the gearbox.