Muffler Cover Design for Standing Wave and Flow Noise Reduction
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Solution Overview
Problem
Mufflers with perforated outlet pipes experience increased sound pressure due to standing waves and generate flow noise from the interaction of main and tributary exhaust gas flows, which existing designs fail to adequately address.
Innovation Solution
A muffler configuration featuring a cover with a wall portion and opening that increases the flow path length of tributary exhaust gas, reducing its speed relative to the main flow, and includes communication holes with auxiliary holes to control flow rates and minimize noise generation, while being designed to enhance productivity and reduce material costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the outer circumferential surface of the outlet pipe is perforated to reduce standing wave sound pressure, then sound pressure of the standing wave is reduced, but flow noise is generated due to interaction between main flow and tributary flow
Solution Approach 1:
A cover is introduced as an intermediary component between the communication holes and the outlet pipe interior. The cover includes a flow path that connects the communication holes to the outlet pipe while increasing the flow path length, thereby reducing the flow speed of tributary exhaust gas and minimizing flow noise generation when tributary flow merges with main flow.
Solution Approach 2:
The design extends the tributary flow path in the radial dimension by incorporating a cover with increased flow path length. This dimensional extension allows the tributary flow to travel a longer distance before merging with the main flow, reducing its speed and the resulting flow noise.
2Object-affected harmful factors
If the total area of communication holes is increased to reduce standing wave sound pressure, then sound pressure is reduced, but flow noise generation increases due to higher tributary flow rate
Solution Approach 1:
The cover acts as a flow speed reduction intermediary, ensuring that even when communication hole area is increased to reduce standing wave sound pressure, the tributary flow speed remains low due to the extended flow path, thereby preventing excessive flow noise.
3Object-generated harmful factors
If a cover with extended flow path is added to reduce flow noise, then flow noise is inhibited, but device complexity increases
Solution Approach 1:
The cover serves multiple functions simultaneously: it covers the communication holes, extends the tributary flow path to reduce flow speed, and acts as a flow noise reduction structure. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
4Productivity
If the opening of the cover is positioned at the main flow path to facilitate exhaust gas flow, then exhaust gas flow efficiency is improved, but flow noise is generated at the opening
Solution Approach 1:
The opening position is strategically selected within the flow path to optimize local flow conditions. By positioning the opening at a specific location rather than directly in the high-speed main flow, the design achieves adequate exhaust gas flow efficiency while minimizing flow noise generation at the opening.
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 solution effectively reduces sound pressure from standing waves and inhibits flow noise by managing exhaust gas flow speeds and paths, while also improving manufacturing efficiency and reducing material usage.
Implementation Method 1
The cover, which includes the wall portion and the opening, contributes to increase in flow path length of a tributary flow that runs into the outlet pipe from the at least one communication hole. As a result, it is possible to decrease a flow speed of the exhaust gas in the tributary flow relative to a flow speed of the exhaust gas in a main flow that runs into the outlet pipe from the outlet end.
Implementation Method 2
with a help of the at least one communication hole, sound pressure of a standing wave in the outlet pipe is reduced
Implementation Method 3
generation of flow noise, which occurs when the tributary flow and the main flow are merged together in the outlet pipe, is inhibited
Data Source
AI summary
Provided is a muffler that can reduce sound pressure of a standing wave in an outlet pipe and, at the same time, can inhibit generation of flow noise. In one aspect of the present disclosure, the muffler includes a housing, an outlet pipe, a cover that covers the outlet pipe. The outlet pipe includes an outlet end and at least one communication hole. The outlet end opens into the housing. The at least one communication hole is formed in an outer circumferential surface of the outlet pipe. The cover includes a wall portion and an opening. The wall portion is disposed to overlap with the at least one communication hole in a radial direction of the outlet pipe. The opening communicates the at least one communication hole and an internal space of the housing with each other.