Vortex Shedding Flow Meter for Marine Outboard Motor Air Intake
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Solution Overview
Problem
Hot wire and hot film mass airflow sensors used in marine environments are sensitive to salt spray and humidity, leading to inaccurate readings and reduced durability, which affects the performance of marine outboard motors, particularly in diesel engines where air flow measurement is crucial for emissions control.
Innovation Solution
A marine outboard motor with a vortex shedding flow meter located in the air intake duct, featuring a bluff body that generates vortices proportional to air flow rate, eliminating the need for sensitive components and improving air mixing and flow sensing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If hot wire or hot film mass airflow sensors are used in the air intake duct, then flow rate measurement capability is provided, but the sensor becomes sensitive to salt spray and humidity leading to inaccurate readings and reduced durability
Solution Approach 1:
The patent replaces the thermal-based hot wire/hot film sensor system with a mechanical vortex shedding flow meter system. The bluff body generates vortices in the airflow, and these vortices are detected by a sensor that measures vortex frequency rather than temperature changes. This mechanical approach eliminates the sensitivity to salt spray and humidity that plagues thermal sensors in marine environments, while maintaining accurate flow rate measurement capability through vortex frequency proportionality.
Solution Approach 2:
The invention changes the measurement parameter from thermal properties (temperature, resistance) to mechanical properties (vortex frequency). By measuring the frequency of vortices shed by the bluff body rather than temperature changes in a heated wire, the system achieves both measurement accuracy and environmental robustness. The vortex frequency is directly proportional to flow rate, providing accurate measurements without thermal sensitivity to marine conditions.
2Measurement precision
If hot wire or hot film sensors are used, then flow rate signal is generated, but salt spray and humidity cause inaccurate sensor readings
Solution Approach 1:
The patent replaces the thermal-based hot wire/hot film sensor system with a mechanical vortex shedding flow meter system. The bluff body generates vortices in the airflow, and these vortices are detected by a sensor that measures vortex frequency rather than temperature changes. This mechanical approach eliminates the sensitivity to salt spray and humidity that plagues thermal sensors in marine environments, while maintaining accurate flow rate measurement capability through vortex frequency proportionality.
Solution Approach 2:
The vortex shedding flow meter creates an measurement mechanism that is inherently insensitive to the marine atmosphere. By using mechanical vortex generation and detection rather than thermal measurement, the system operates in an effectively 'inert' manner regarding salt spray and humidity - these environmental factors no longer interfere with the measurement process, allowing accurate flow rate readings in harsh marine conditions.
3Reliability
If vortex shedding flow meter with bluff body is used, then resistance to salt spray and humidity is achieved, but additional component (bluff body) is introduced in the air intake duct
Solution Approach 1:
The bluff body in the vortex shedding flow meter serves multiple functions: it generates vortices for flow measurement, and simultaneously acts as a flow mixer to homogenize the air intake. This multi-functionality reduces the need for separate mixing components that would otherwise be required, offsetting the addition of the bluff body and reducing overall system complexity despite the improved reliability in marine environments.
Solution Approach 2:
The invention merges the flow measurement function and the air mixing function into a single component - the bluff body. By combining these two functions that would traditionally require separate components, the overall device complexity is minimized while achieving both accurate flow measurement and improved air homogeneity, making the system more efficient despite the harsh marine environment requirements.
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
The vortex shedding flow meter provides accurate flow rate measurements and enhances air mixing, leading to consistent engine performance and reduced maintenance needs, while being resistant to marine environmental factors.
Implementation Method 1
the bluff body causes flow separation in the flow of air passing along the air intake duct to generate vortices
Implementation Method 2
a flow meter located in the air intake duct and configured to generate a signal indicative of a flow rate of the flow of air through the air intake duct, and a bluff body located in the air intake duct upstream of the flow meter, wherein the flow meter is a vortex shedding flow meter
Data Source
AI summary
A marine outboard motor is provided with an internal combustion engine comprising an engine block defining at least one cylinder, an air intake configured to deliver a flow of air to the at least one cylinder; and an air intake duct forming part of an air intake path for delivering the flow of air to the air intake. The engine further includes a flow sensing arrangement located in the air intake duct and comprising a flow meter configured to generate a signal indicative of a flow rate of the flow of air through the air intake duct, and a bluff body located in the air intake duct upstream of the flow meter, wherein the flow meter is a vortex shedding flow meter.