Counter-Rotating Propeller Shaft Support for Gear Mesh Alignment

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Solution Overview

Problem

Existing systems for counter-rotating propeller shafts in marine propulsion devices face challenges in providing stable and rigid gear mounting, particularly in high-power density configurations, due to inadequate rotational support at central regions, leading to misalignment of gear meshes and deflections under load.

Innovation Solution

The introduction of a stub shaft that extends between the forward and aft ends of the gearcase, allowing for additional bearings to be installed across the propeller shafts, along with a shock absorbing coupler to absorb torsional shocks and facilitate proper gear meshing, enabling easier assembly and alignment of gears while allowing propeller shafts to be inserted through a rear opening.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If additional bearings are installed across the propeller shafts to provide rotational support, then gear mesh alignment and stability are improved, but device complexity increases

Engineering Contradiction:

Improvegear mesh alignmentVSAvoidnumber of bearings

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The propeller shaft system is segmented into multiple supported sections by distributing bearings along the shaft length, including forward, intermediate, and aft positions. This segmentation provides rotational support at critical locations without requiring a single complex bearing assembly, thereby improving gear mesh alignment while managing device complexity through modular bearing placement.

Inventive Principle:

Principle #1Segmentation

2Reliability

If a shock absorbing coupler is introduced to absorb torsional shocks, then reliability of gearcase components is improved, but device complexity increases

Engineering Contradiction:

Improvedurability of gearcase componentsVSAvoidnumber of couplings

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

A shock absorbing coupler is introduced between the propeller shaft and driveshaft to provide beforehand cushioning against torsional shocks. This coupler absorbs shock loads before they can damage gearcase components, improving reliability by pre-positioning a protective element that mitigates harmful torsional forces during operation.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Ease of manufacture

If propeller shafts are inserted through a rear opening with a stub shaft configuration, then ease of assembly is improved, but rotational support at central regions deteriorates

Engineering Contradiction:

Improveease of assemblyVSAvoidrotational support

Core Design Contradiction:

Ease of manufactureVSStability of the object's composition

Solution Approach 1:

The shaft support structure utilizes a stub shaft configuration that extends through the rear opening, creating a multi-dimensional support architecture. The stub shaft provides a central mounting point that enables rotational support at intermediate positions while maintaining the simplified rear-opening assembly approach, effectively adding spatial dimensions to the support system without complicating assembly procedures.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 provides a robust and stable mounting system for gears, reduces misalignment and deflections, and enhances the durability of gearcase components by allowing for independent assembly and adjustment of bearings and gears, while maintaining ease of installation through the rear opening.

Implementation Method 1

The coupler is torsional between the forward and aft ends such that shock is absorbable between the inner propeller shaft and the driveshaft

Methodology Applied

Scientific EffectTorsion: Torsion Spring

Implementation Method 2

a shock absorbing coupler to absorb torsional shocks

Methodology Applied

Scientific EffectShock absorption: Damping

Data Source

PatentUS11364987B1Systems and methods for absorbing shock with counter-rotating propeller shafts in a marine propulsion device

Publication Date: 2022.06.21 BRUNSWICK CORP

AI summary

A system for rotating an inner propeller shaft within a gearcase via a driveshaft. The system includes a stub shaft that extends between forward and aft ends and is rotatable within the gearcase. A forward gear is rotatably coupled to the stub shaft, where the forward gear meshes with the driveshaft and is engageable to become rotatably fixed to the stub shaft such that rotating the driveshaft rotates the stub shaft. A shock absorbing coupler is positioned within the gearcase, where the coupler has forward and aft ends, where the forward end of the coupler is engageable with the aft end of the stub shaft, and where the aft end of the coupler engageable with the inner propeller shaft. The coupler is torsional between the forward and aft ends such that shock is absorbable between the inner propeller shaft and the driveshaft.