SCR Doser Filter Assembly Ice Pressure Bypass
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Solution Overview
Problem
SCR systems face damage due to remaining reagent freezing and expanding in the injector when the engine stops, as existing solutions do not effectively manage the freezing of aqueous reagents like urea, which can cause severe damage.
Innovation Solution
The SCR doser incorporates a filter assembly with a filtering mesh that moves away from its primary position under ice pressure, allowing a bypass for frozen reagent to flow around it, and returns to the original position when the reagent thaws, utilizing either a spring or magnet to maintain the filter's position, ensuring all reagent flows through the mesh when operational.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the filter assembly is fixed in position to ensure all reagent flows through the mesh for proper filtering, then filtering effectiveness is improved, but the injector suffers severe damage when remaining reagent freezes and expands
Solution Approach 1:
The filter assembly is made movable rather than fixed, allowing it to dynamically adjust its position based on operating conditions. During normal operation, the filter assembly is in the first position where all reagent flows through the mesh for effective filtering. When reagent freezes and expands, the filter assembly moves to a second position where bypass channels allow the frozen reagent to flow around the mesh, preventing damage to the injector.
Solution Approach 2:
The patent converts the harmful effect of frozen reagent expansion into a useful function. The expansion force that would normally damage a fixed filter assembly is harnessed to move the filter assembly to the bypass position, where it protects the injector by allowing the frozen reagent to flow around the mesh rather than through it.
2Object-affected harmful factors
If the filter assembly moves away from the first position when reagent freezes, then damage to the injector is prevented, but reagent loss increases due to bypass flow
Solution Approach 1:
The filter assembly dynamically switches between two positions: the first position during normal operation where all reagent flows through the mesh for efficient use, and the second position during freezing conditions where bypass flow prevents damage. This dynamic switching minimizes reagent loss by maintaining efficient filtration during operational conditions while only activating the bypass when necessary for protection.
Solution Approach 2:
The harmful expansion force from frozen reagent is converted into a protective mechanism that automatically activates the bypass flow. The system accepts some reagent loss during bypass operation but prioritizes protecting the expensive injector, converting the potential harm into a protective function that saves the overall system.
3Reliability
If a spring or magnet is used to urge the filter assembly to the first position, then the filter returns to filtering mode when reagent thaws, but the device complexity increases
Solution Approach 1:
The filter assembly is designed to be self-actuating based on the physical state of the reagent. During normal operation, the spring or magnet maintains the filter assembly in the first position. When reagent freezes and expands, the expansion force automatically overcomes the spring or magnetic force, moving the filter assembly to the second position without requiring external control systems, sensors, or complex actuation mechanisms.
Solution Approach 2:
The system uses changes in the physical parameters of the reagent (phase change from liquid to solid) to automatically control the filter assembly position. The phase change causes volume expansion, which directly acts on the filter assembly to move it between positions, eliminating the need for complex control systems while ensuring reliable operation.
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 solution prevents damage to the injector by allowing frozen reagent to bypass the filter, minimizing reagent loss and ensuring the system's functionality during temperature changes, while ensuring all reagent is filtered when operational.
Implementation Method 1
the reagent being an aqueous liquid that freezes and expands below a freezing temperature (i.e. urea freezes below - 11°C)
Implementation Method 2
the reagent has thawed
Implementation Method 3
a magnet urges said filter assembly to said first position, a displacement of the filter assembly away from said first position acting against the magnetic force
Implementation Method 4
a spring urges said filter assembly to said first position, a displacement of the filter assembly away from said first position acting against the spring force
Data Source
Figure 1~2
Figure 3~6
AI summary
A SCR doser (10) comprises a filter assembly (56) arranged in a first position wherein all the reagent is directed to flow through the filter and, being free to move away from said first position when under internal ice pressure.