Thermally Isolated Reductant Dosing Unit Hermetic Seal
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Solution Overview
Problem
Current reductant dosing units (RDUs) face challenges in achieving thermal isolation and hermetic sealing efficiently, particularly in lean-burn engine exhaust systems, where nitrogen oxide emissions require effective treatment, and existing methods using mica for sealing are costly and complex, or lead to poor packaging and potential clogging.
Innovation Solution
The use of a thermal isolator like mica, supported by a laser weld between the flange and coolant jacket extension, where mica is only used for mechanical support and thermal isolation, and the laser weld provides the hermetic seal, allowing for cost-effective and simplified packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If mica is used to provide both thermal barrier and hermetic seal, then thermal isolation is improved, but device complexity and cost increase due to requiring significant sealing force from bolts or V-clamp
Solution Approach 1:
The invention divides the functions of thermal isolation and hermetic sealing into separate components: mica provides thermal isolation while a dedicated gasket provides hermetic sealing. This segmentation allows each component to be optimized for its specific function without the complexity of combining both functions in a single component.
Solution Approach 2:
The sealing function is extracted from the mica thermal barrier and assigned to a separate gasket component. This extraction eliminates the need for complex sealing mechanisms on the mica itself, simplifying the overall device structure while maintaining both thermal isolation and hermetic sealing.
2Reliability
If large bolts or V-clamp are used to apply sealing force to mica, then hermetic seal is improved, but ease of manufacture and packaging decrease due to space requirements
Solution Approach 1:
The invention uses a disposable gasket that provides hermetic sealing without requiring large, space-consuming bolts or V-clamps. The gasket is a simple, cost-effective component that can be easily manufactured and packaged, while still providing reliable sealing when combined with standard mounting hardware.
3Reliability
If sealing bead is machined into mounting flange to concentrate force, then hermetic seal with mica is improved, but device complexity and cost increase due to machining requirements
Solution Approach 1:
The sealing function is extracted from the mounting flange and assigned to a separate gasket component. This eliminates the need for complex machining of the flange to create sealing beads, simplifying both the flange design and the manufacturing process while maintaining reliable hermetic sealing.
4Device complexity
If air gap is used as isolator with metal-to-metal crimp seal, then packaging is improved, but reliability decreases due to potential clogging with urea crystals
Solution Approach 1:
The invention uses a gasket that provides reliable hermetic sealing without the complexity of metal-to-metal crimp seals. The gasket is resistant to clogging by urea crystals and can be easily replaced if needed, providing long-term reliability while maintaining compact packaging.
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 approach reduces costs and complexity by using mica solely for thermal isolation and mechanical support, while the laser weld ensures reliable exhaust gas hermiticity, improving packaging and reliability over thermal cycles.
Implementation Method 1
A thermal isolator member is disposed between the fluid outlet of the fluid injector and the flange
Implementation Method 2
A laser weld joins the housings and seals exhaust gases
Implementation Method 3
The isolator is used only for mechanical support and thermal isolation
Data Source
AI summary
A reductant dosing unit is disclosed, including a fluid injector having a fluid inlet and a fluid outlet. A flange is disposed proximal to the fluid outlet of the fluid injector and configured to secure to a boss associated with an exhaust path of an internal combustion engine. The flange has a largely flat body portion with a through-bore in fluid communication with the fluid outlet of the fluid injector. The flange further includes an extension which extends from the body portion toward the fluid injector and which is connected to thereto. A thermal isolator is disposed between the fluid outlet of the fluid injector and the flange. The connection between the extension of the flange and the fluid injector includes a hermetic seal, preventing exhaust gases in the exhaust path from passing between the flange extension and the fluid injector. The thermal isolator is only used as a support and thermal isolator.