Outboard Engine Idle Relief System for Exhaust Odor Control
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Solution Overview
Problem
Outboard engine assemblies experience exhaust gas being routed onto the rear deck during idle or low speeds due to air vortices, causing unpleasant odors for occupants.
Innovation Solution
The outboard engine assembly incorporates an idle relief system with an idle relief passage and outlet positioned vertically higher than the main exhaust outlet, extending through the engine unit housing, and disposed below the waterline to direct exhaust gases away from the rear deck, utilizing a high-rise exhaust passage and anti-ventilation plate to prevent ventilation onto the deck.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the exhaust outlet is positioned at the center of the propeller for high-speed operation, then exhaust can be expelled into the low-pressure region behind the propeller, but during idle or low speeds water fills the exhaust system and prevents exhaust expulsion
Solution Approach 1:
The exhaust system is segmented into two separate outlets: a primary exhaust outlet for high-speed operation and a secondary idle relief outlet for idle/low-speed operation. This segmentation allows each outlet to be optimized for its specific operating condition, resolving the contradiction between high-speed exhaust expulsion efficiency and idle-speed reliability.
Solution Approach 2:
The system changes the exhaust expulsion parameter by providing different outlet positions based on operating speed. At idle speeds, the idle relief outlet is positioned to expel exhaust above the waterline, while at higher speeds the main exhaust outlet expels exhaust through the propeller center. This parameter change resolves the water filling issue at idle speeds.
2Reliability
If the idle relief outlet is positioned to expel exhaust above the waterline, then exhaust can be released during idle speeds, but air vortices form and carry exhaust onto the rear deck creating unpleasant odors
Solution Approach 1:
The idle relief outlet is positioned with specific local characteristics: it is located on the port side of the engine assembly, positioned vertically between the waterline and the rear deck, and oriented to expel exhaust laterally rather than vertically upward. This local quality modification prevents exhaust from being carried onto the rear deck by air vortices while maintaining idle-speed expulsion capability.
3Productivity
If the exhaust system is routed through the gearcase, then exhaust can be expelled through the propeller center at high speeds, but water fills the exhaust passage during idle speeds preventing exhaust expulsion
Solution Approach 1:
The exhaust system is segmented into a primary exhaust passage through the gearcase for high-speed operation and a secondary idle relief passage that bypasses the gearcase water-filled section. This segmentation allows exhaust to be expelled through the propeller center at high speeds while providing an alternative water-free path at idle speeds.
Solution Approach 2:
The idle relief passage acts as an intermediary bypass route that connects the engine exhaust manifold to the exterior without passing through the gearcase. This intermediary path eliminates the water filling problem while maintaining the primary exhaust system's functionality at higher speeds.
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
Effectively prevents exhaust gases from being conveyed to the rear deck, reducing unpleasant smells and improving occupant comfort by ensuring exhaust gases are expelled below the waterline, thus avoiding air vortex-induced exhaust routing onto the deck.
Implementation Method 1
air vortices are formed at idle or low speeds that can carry the exhaust above and onto the rear deck
Data Source
AI summary
An outboard engine assembly has an engine unit including an engine unit housing, an internal combustion engine disposed in the engine unit housing, the engine defining at least one combustion chamber, a gearcase connected to the engine unit housing, and an exhaust system, the exhaust system including an idle relief passage fluidly communicating with an exhaust passage, the idle relief passage having an idle relief outlet, the idle relief passage extending through the engine unit housing for supplying exhaust gases from the at least one combustion chamber to an exterior of the engine unit housing via the idle relief outlet, the idle relief outlet being disposed vertically higher than the exhaust outlet and vertically lower than a waterline when the outboard engine assembly is mounted to a watercraft and the watercraft is at rest, and a propulsion device operatively connected to the engine.