Muffler Outlet Stub With Internal Flow Expansion

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Solution Overview

Problem

Conventional mufflers with venturi sections often have a significant heating effect on the environment due to escaping exhaust gases, as they widen outside the muffler housing, leading to inefficient heat dissipation.

Innovation Solution

A muffler design with an outlet stub featuring a continuously increasing flow cross-section from a smallest to a discharge flow cross-section, where the inner wall is closed continuously over its circumference, allowing for gradual widening within the muffler housing, eliminating the need for a venturi section and reducing ambient air intake.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of moving object

If the outlet stub widens outside the muffler housing (conventional design), then the flow cross-section increases, but the heating effect on the environment increases

Engineering Contradiction:

Improveflow cross-sectionVSAvoidheating effect on environment

Core Design Contradiction:

Area of moving objectVSObject-affected harmful factors

Solution Approach 1:

Instead of widening the outlet stub outside the housing as conventionally done, the invention inverts the approach by widening it inside the housing. The outlet channel's flow cross-section increases continuously from the throttle location through the housing discharge opening, achieving flow expansion before the exhaust gases are discharged to the environment, thereby reducing the heating effect while maintaining proper flow characteristics.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention changes the spatial dimension of flow cross-section increase from external (outside housing) to internal (inside housing). The outlet channel is designed with a continuously increasing flow cross-section that extends into the housing discharge opening, utilizing the internal space dimension to achieve flow expansion without external widening, thus solving the heating effect problem.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Area of moving object

If the outlet stub widens outside the muffler housing, then the flow cross-section increases, but the construction becomes less compact

Engineering Contradiction:

Improveflow cross-sectionVSAvoidmuffler construction volume

Core Design Contradiction:

Area of moving objectVSVolume of moving object

Solution Approach 1:

The outlet channel's flow cross-section increase is nested within the muffler housing boundaries. The continuous widening of the outlet channel occurs inside the housing and extends through the housing discharge opening, effectively nesting the flow expansion process within the existing housing volume, thereby achieving compact construction without sacrificing flow cross-section increase.

Inventive Principle:

Principle #7Nested doll (Nesting)

3Ease of manufacture

If the outlet stub has a closed continuous inner wall, then manufacturing is simplified, but flow guidance must be maintained

Engineering Contradiction:

Improveoutlet stub productionVSAvoidflow guidance effectiveness

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The invention changes the geometric parameters of the outlet channel to achieve continuous flow guidance. The flow cross-section increases continuously along the outlet channel from the throttle location through the housing discharge opening, with specific angle ranges (alpha between 10-30 degrees, beta between 30-60 degrees) that ensure proper flow guidance while maintaining a simple closed continuous inner wall structure for ease of manufacture.

Inventive Principle:

Principle #35Parameter changes

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

This design reduces the heating effect on the environment by ensuring efficient heat dissipation and simplifies production, while maintaining effective flow guidance and temperature distribution.

Implementation Method 1

the temperature of the escaping exhaust gas drops more quickly if the outlet channel of the outlet stub widens over a largest possible length section of the outlet stub

Methodology Applied

Scientific EffectHeat dissipation: Convection

Data Source

PatentUS20250012208A1Muffler and outlet stub for a muffler

Publication Date: 2025.01.09 ANDREAS STIHL AG & CO KG

AI summary

A muffler having a muffler housing with a muffler chamber formed therein includes an outlet stub. In the stub, a channel is formed through which exhaust gases escape. The channel has a throttle location with a smallest flow cross-section and a discharge opening with a discharge flow cross-section. The channel is bounded by a wall. The flow cross-section increases substantially continuously from the smallest flow cross-section to the discharge flow cross-section at least in a section in the direction from the throttle location to the discharge opening. The stub has a fastening location at which it is held in an outlet opening of the muffler housing. The wall is closed continuously over its circumference from the throttle location to the discharge opening. The section of the channel extends in a sectional plane containing a center axis of the channel into a longitudinal section of the stub having the fastening location.