Outboard Engine Cam-to-Cam Drive Width Reduction
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Solution Overview
Problem
Outboard marine engines face challenges in minimizing width to accommodate packaging and performance requirements, particularly in dual- or quad-outboard arrangements, where the widest portion is typically the cam-to-cam drive, necessitating a reduction in width to allow for steering and clearance without compromising engine height or increasing weight.
Innovation Solution
The cam-to-cam drive is relocated vertically higher on the intake and exhaust camshafts, above the lowermost valves, allowing for a recess in the engine head and the use of a hydraulically-actuated chain tensioner to maintain chain tension, which reduces the engine's width and weight by eliminating the need for a lowermost cam bearing and optimizing the cowling seal location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the cam-to-cam drive is positioned at the lower portion of the engine, then the engine structure is simplified, but the engine width increases
Solution Approach 1:
The cam-to-cam drive is repositioned from the lower horizontal portion to the upper vertical portion of the engine, changing the spatial dimension of the drive mechanism. This dimensional shift allows the drive chain to operate in the vertical space above the valves rather than expanding the horizontal width at the lower portion, thus resolving the contradiction between structural simplicity and compact width.
Solution Approach 2:
Instead of placing the cam-to-cam drive at the conventional lower position for structural simplicity, the invention inverts the arrangement by positioning it at the upper portion of the engine. This inversion allows the use of a recess in the engine head to accommodate the drive, thereby reducing overall engine width while maintaining structural integrity.
2Length of moving object
If the engine width is reduced for better packaging, then steering and clearance are improved, but the cam-to-cam drive space is compromised
Solution Approach 1:
The cam-to-cam drive mechanism is nested within a recess formed in the engine head. This nesting approach allows the drive components to be accommodated within the existing engine structure without increasing external dimensions, thereby reducing engine width while providing adequate space for drive installation and maintenance.
Solution Approach 2:
The cam-to-cam drive is relocated to the vertical dimension above the valves rather than occupying horizontal space. This dimensional repositioning creates a compact horizontal footprint for better packaging while maintaining sufficient vertical space for the drive mechanism, resolving the contradiction between reduced width and ease of manufacture.
3Length of moving object
If the cam-to-cam drive is positioned higher on the camshafts, then engine width is reduced, but the valve clearance is decreased
Solution Approach 1:
The cam-to-cam drive is nested within a recess in the engine head, positioned vertically above the lowermost valves. This nesting configuration allows the drive to occupy vertical space without encroaching on the horizontal valve clearance, thereby reducing engine width while maintaining adequate valve operation space.
Solution Approach 2:
The cam-to-cam drive is repositioned to the vertical dimension above the valves rather than occupying horizontal space near the valve stems. This dimensional separation allows the drive to be positioned higher on the camshafts for compact width while the valves maintain their full horizontal clearance for proper operation.
Data Source
AI summary
An outboard marine engine comprises a vertically aligned bank of piston-cylinders; an intake camshaft that operates a plurality of intake valves for controlling inflow of air to the bank of piston-cylinders; an exhaust camshaft that operates a plurality of exhaust valves for controlling outflow of exhaust as from the bank of piston-cylinders; and a cam-to-cam connector that connects the intake camshaft to the exhaust camshaft such that rotation of one of the intake and exhaust camshafts causes rotation of the other of the intake and exhaust camshafts. The cam-to-cam connector is located vertically above a lowermost intake valve in the plurality of intake valves, vertically above a lowermost exhaust valve in the plurality of exhaust valves, vertically below an uppermost intake valve in the plurality of intake valves and vertically below an uppermost exhaust valve in the plurality of exhaust valves.