Capacitance PM Sensor with Porosity-Graded Filters
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Solution Overview
Problem
Existing PM sensors cannot continuously detect the particle size distribution and emission amount of PM in exhaust gas, requiring exhaust gas flow cessation for measurement, leading to increased device size, weight, and cost, making them unsuitable for automotive applications.
Innovation Solution
A sensor design with multiple filter members of different porosities and electrodes, where exhaust gas flows continuously, allowing for real-time PM detection by measuring capacitance changes across electrodes, enabling continuous PM estimation and filter regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If exhaust gas flow is stopped for measurement, then measurement precision is improved, but productivity deteriorates
Solution Approach 1:
The patent implements continuous detection by maintaining exhaust gas flow throughout the measurement process. The sensor design allows PM to be collected on filter members while exhaust gas continues to flow, eliminating the need to stop flow for measurement and enabling continuous monitoring of PM emissions.
Solution Approach 2:
The patent divides the detection system into multiple filter members with different porosity levels arranged in series. Each filter member captures PM of different size ranges, allowing simultaneous measurement of various PM fractions while maintaining continuous gas flow through the segmented filtration stages.
2Measurement precision
If chamber is enclosed for measurement, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent eliminates the need for flow cessation by designing a system where PM collection and measurement occur simultaneously with continuous exhaust gas flow. This removes complex flow control valves and enclosures required in traditional systems, simplifying the overall device structure.
Solution Approach 2:
The patent pre-positions multiple filter members with different porosity levels in the exhaust flow path before measurement begins. This preliminary arrangement of filtration stages allows PM to be continuously separated and collected by size fraction without requiring dynamic flow control or chamber enclosure during measurement.
3Measurement precision
If multiple filter members are added for particle size separation, then measurement precision is improved, but device size increases
Solution Approach 1:
The patent arranges multiple filter members with different porosity levels in a nested or series configuration within a compact housing. Each filter member is positioned to capture progressively smaller PM fractions, allowing comprehensive particle size distribution measurement while minimizing the overall sensor volume through efficient spatial arrangement.
Solution Approach 2:
The patent assigns different porosity characteristics to different filter members based on their specific function in capturing PM of particular size ranges. This local differentiation of filter properties enables precise particle size separation without requiring uniformly large dimensions across the entire sensor assembly.
4Measurement precision
If electromotive force method is used, then measurement precision is improved, but device weight increases
Solution Approach 1:
The patent replaces the electromotive force measurement method with a capacitance-based detection system. This substitution eliminates the need for heavy solid electrolyte layers and associated high-temperature measurement infrastructure, reducing sensor weight while maintaining measurement precision through electrical field-based PM detection.
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
Enables continuous, accurate estimation of PM amounts by each particle size in exhaust gas, reducing device size and weight, and improving cost-effectiveness for automotive integration.
Implementation Method 1
a first filter member (31L) and a second filter member (31M) having different porosities are arranged in the flow path of the exhaust gas in this order from the upstream side
Implementation Method 2
filters having different porosities are arranged in descending order of the porosity from an upstream side of a flow direction of the exhaust gas so as to section a chamber
Implementation Method 3
a capacitance detection circuit, and a control unit... measures a capacitance value between the electrodes
Implementation Method 4
which burns and removes the accumulated PM... a heating device to heat the filter element
Data Source
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AI summary
The sensor includes: a collection part 30L, 30M, 30S in which a plurality of filter members for collecting particulate matter in exhaust gas are arranged in descending order of porosity from an exhaust upstream side to an exhaust downstream side of the exhaust gas; a pair of electrodes 32, 33 which is arranged to each of the plurality of filter members 30L, 30M, 30S and facing each other with the plurality of filter members interposed therebetween; and estimation means 42 to 44 for estimating a particulate matter amount collected on each of the plurality of filter members having different porosities based on a capacitance change amount between the pair of electrodes 32, 33.