Marine Propulsion Lower Unit Compact Transmission Design
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Solution Overview
Problem
Conventional marine propulsion systems are bulky, occupying excessive space and resulting in additional costs due to the need for different drives to accommodate various engine orientations, and they lack a compact and efficient transmission system that enhances trim adjustments and handling.
Innovation Solution
A marine propulsion system with a compact transmission design featuring an intermediate shaft extending parallel to the input shaft, a pivot gear set of bevel gears, and a clutch assembly with forward and reverse gears, allowing for a longer moment arm and improved trim control while maintaining a streamlined profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional in-board marine propulsion systems are used, then engines can be installed in various orientations, but the systems occupy excessive space inside vessels encroaching on decks, cockpit, load bay or other useful spaces
Solution Approach 1:
The lower unit housing is designed with a universal mounting structure that can accommodate different engine orientations (vertical, horizontal, angled) through adjustable mounting brackets and flexible coupling mechanisms. This allows a single compact propulsion system design to serve multiple installation configurations without requiring separate dedicated drives for each engine orientation
Solution Approach 2:
The propulsion system incorporates adjustable and movable components including telescopic drive shafts, adjustable pitch propellers, and flexible couplings that allow the system to adapt its configuration dynamically. This enables the same compact lower unit to work with various engine orientations and vessel types without sacrificing space efficiency
2Ease of manufacture
If the lower unit housing is made wide enough to house drive shaft and components, then all necessary components can be accommodated, but the lower units tend to be bulky causing drag
Solution Approach 1:
The lower unit housing employs a nested arrangement where the drive shaft, clutch assembly, and propeller shaft are concentrically positioned within the housing. The clutch assembly is nested within the drive shaft assembly, and the propeller is mounted on the propeller shaft that passes through the lower unit. This nested configuration maximizes component density while maintaining a streamlined external profile that minimizes hydrodynamic drag
Solution Approach 2:
Instead of arranging components in a radial or lateral configuration that would increase the housing width, the invention positions components along the longitudinal axis of the drive shaft. The clutch assembly is positioned axially within the drive shaft, and power transmission occurs through axial gear engagements. This axial arrangement keeps the housing width minimal while accommodating all necessary components, resulting in a slender, hydrodynamic profile
3Object-affected harmful factors
If a compact transmission design is used, then the lower unit becomes more hydrodynamic, but the moment arm for trim adjustments is reduced
Solution Approach 1:
The invention introduces a trim tab as an intermediary element on the propeller shaft assembly that can be independently adjusted. This trim tab acts as a lever that amplifies the trimming moment by utilizing water pressure differential. The trim tab is positioned at the aft end of the propeller shaft, extending backward to maximize its lever arm effect in the water, thereby providing sufficient trimming control moment despite the compact overall dimensions of the lower unit
Data Source
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AI summary
A marine propulsion system (10) includes a gearbox housing (18) that is attached to the stern of a vessel hull (14), a pivot casing (22) that can pivot relative to the gearbox housing (18) for trim/tilt and a lower unit (28) that can pivot relative to the pivot casing (22) to steer. The gearbox housing (18) houses an input shaft (20), which is connected via a gear set (38) to an intermediate shaft (36), which is connected via a bevel gear set (42) to a transverse shaft (40), which extends into the pivot casing (22). Inside the pivot casing (22), a drive shaft (26,30) is connected to the transverse shaft (40) via a clutch assembly (44) and the drive shaft (26,30) extends from the pivot casing (22) to the lower unit (28), where it drives a propeller shaft (32). The pivot casing (22) pivots about the axis of the transverse shaft (40) to trim/tilt and the lower unit (28) pivots about the axis of the drive shaft (26,30) to steer.