Outboard Motor Spline Geometry for Easier Tilted Assembly
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Solution Overview
Problem
In outboard motors, aligning splines during assembly is challenging, especially when the motor is horizontally set or tilted, leading to misalignment and difficulty in attaching the lower housing to the upper housing due to shaft rotation.
Innovation Solution
The second spline on the shaft has a larger groove width at the distal end compared to the body, allowing easier meshing even when misaligned, with a smaller root diameter at the distal end to facilitate alignment and reduce wobbling during coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the shaft is inserted into the upper housing while the motor is horizontally set or tilted, then the assembly can be performed in various positions, but the shaft inevitably rotates causing spline misalignment and making attachment difficult
Solution Approach 1:
The groove width parameter of the second spline is changed to be larger at the distal end than at the body portion. This parameter change allows the spline to tolerate rotational misalignment during assembly while maintaining proper engagement, thus resolving the contradiction between assembly position flexibility and spline alignment precision
Solution Approach 2:
The second spline is designed with asymmetric groove widths along its length - wider at the distal end and narrower at the body. This asymmetric design creates a tapered effect that guides alignment during insertion while accommodating rotational deviations, enabling assembly in various positions without compromising alignment precision
2Ease of manufacture
If the groove width of the second spline is uniform along its length, then the manufacturing process is simple, but the spline cannot accommodate misalignment and causes assembly difficulty
Solution Approach 1:
The groove width parameter is deliberately changed along the length of the second spline, being larger at the distal end and smaller at the body. This parameter variation improves ease of operation by accommodating misalignment during meshing, while the change can be achieved through standard manufacturing processes like variable pitch hobbing or progressive die forming
Solution Approach 2:
Different sections of the second spline are given different groove widths - the distal end has wider grooves for alignment tolerance and the body has narrower grooves for secure engagement. This local quality differentiation improves meshing ease without significantly complicating the overall manufacturing process
3Strength
If the root diameter of the second spline is large, then the spline has high strength, but the spline cannot be easily aligned and causes wobbling during coupling
Solution Approach 1:
The root diameter parameter of the second spline is changed to be smaller at the distal end and larger at the body. This gradient design reduces wobbling and improves alignment ease during coupling by creating a tapered guidance effect, while maintaining sufficient strength at the body portion where the load is transmitted
Solution Approach 2:
The second spline features asymmetric root diameter along its length, with the distal end having a smaller diameter for alignment guidance and the body having a larger diameter for strength. This asymmetric configuration resolves the contradiction between strength and alignment ease by optimizing each section for its specific function
Data Source
AI summary
An outboard motor includes a shaft including a second spline that upwardly extends from a housing. The second spline is meshed with a first spline disposed inside either an engine cowl or an upper housing. The second spline includes a distal end and a body. The distal end is provided on an upper end of the shaft. The body is provided below the distal end. In the second spline, a groove width in the circumferential direction at the distal end is larger than a groove width in the circumferential direction at the body.