Counter-Rotating Propeller Shaft Support for Gear Mesh Stability

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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, leading to misalignment and deflection issues due to inadequate rotational support at central regions, especially in high-power density configurations where propeller shafts are installed from the rear, resulting in gear mesh misalignment and reduced durability.

Innovation Solution

The introduction of a stub shaft that extends between the forward and aft ends of the gearcase, allowing additional bearings to be positioned across the propeller shafts, and a shock absorbing coupler to provide torsional support and absorb shock, enabling proper gear meshing and reducing deflection, while allowing for easier assembly and position adjustments.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If propeller shafts are installed from the rear in high-power density configurations, then power transmission capability is improved, but gear mesh misalignment and deflection issues occur due to inadequate rotational support at central regions

Engineering Contradiction:

Improvepower transmission capabilityVSAvoidgear mesh alignment

Core Design Contradiction:

PowerVSManufacturing precision

Solution Approach 1:

The propeller shaft system is segmented into multiple sections with intermediate support structures. The shaft is divided into forward and aft portions with a central region that receives additional bearing support, allowing each segment to be properly supported while maintaining overall power transmission capability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The support structure is extended into the central region of the shaft, adding a dimensional element along the shaft's length. This intermediate bearing support at the central region provides rotational stability without interfering with the rear installation approach or power transmission function.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Stability of the object's composition

If additional bearings are positioned across the propeller shafts, then rotational support and stability are improved, but device complexity increases

Engineering Contradiction:

Improverotational support stabilityVSAvoidbearing arrangement complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The intermediate bearing structure serves multiple functions: it provides rotational support at the central region, maintains gear mesh alignment, and supports the shaft during rear installation. This multi-functional design adds stability without proportionally increasing complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If a shock absorbing coupler is introduced, then shock and clunk reduction is achieved, but device complexity increases

Engineering Contradiction:

Improveshock absorption capabilityVSAvoidcoupler mechanism complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

A shock-absorbing coupler is introduced as an intermediary element between the propeller shaft and the drive system. This coupler absorbs torsional shocks and reduces clunk during engagement, protecting the gear train while maintaining a relatively simple overall structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Manufacturing precision

If the propeller shafts are rigidly mounted, then gear mesh stability is improved, but shock transmission increases

Engineering Contradiction:

Improvegear mesh stabilityVSAvoidshock transmission

Core Design Contradiction:

Manufacturing precisionVSObject-generated harmful factors

Solution Approach 1:

The shock-absorbing coupler is installed beforehand in the power transmission path to cushion against torsional shocks before they reach the rigid gear mesh. This allows the gear mounting to remain stable while the coupler preemptively absorbs harmful shock loads.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 solution provides a robust and stable mounting system for high-power density drives, preventing gear misalignment and reducing shock and clunk, thereby enhancing the durability and reliability of the marine propulsion device.

Implementation Method 1

The shock absorbing coupler is positioned within the gearcase to provide torsional support and absorb shock between the propeller shaft and the driveshaft

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS11584500B1Systems and methods for absorbing shock with counter-rotating propeller shafts in a marine propulsion device

Publication Date: 2023.02.21 BRUNSWICK CORP

AI summary

A system for rotating a propeller shaft within a gearcase via a driveshaft. A stub shaft is rotatable within the gearcase. A forward gear is rotatably coupled to the stub shaft. The forward gear is rotatable by 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. The shock absorbing coupler couples the stub shaft to the propeller shaft and is torsional such that shock is absorbable between the propeller shaft and the driveshaft.