Capacitance-Based PM Sensor for Continuous Exhaust Monitoring
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Solution Overview
Problem
Electrical resistance-type PM sensors face challenges in accurately estimating particulate matter (PM) in exhaust gases due to detachment of PM at increased exhaust flow rates and inability to estimate during regeneration periods, limiting their utility to diagnosing downstream failures in Diesel Particulate Filters (DPF).
Innovation Solution
A PM sensor with a filter member, electrodes forming a capacitor, and an electrical heater, where the electrostatic capacitance between electrodes is used to continuously estimate PM amounts by calculating interval and regeneration period PM amounts based on capacitance changes, ensuring precise and real-time PM estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electrical resistance-type PM sensor is used with simple electrode structure, then manufacturing simplicity is improved, but PM detachment occurs at increased exhaust flow rates reducing measurement precision
Solution Approach 1:
The patent employs a porous filter member as the electrode substrate, which physically traps PM particles within its porous structure. This prevents PM detachment during high exhaust flow rates while maintaining the simple electrode configuration. The porous structure provides mechanical retention of PM without requiring complex electrode geometries or additional retention mechanisms.
2Device complexity
If electrical resistance-type PM sensor is used, then device complexity is reduced, but PM amount cannot be estimated during regeneration periods
Solution Approach 1:
The patent transitions from measuring electrical resistance to measuring electrostatic capacitance between electrodes. During regeneration when resistance values remain constant, capacitance values continue to change in response to PM accumulation and removal. This parameter change enables continuous PM monitoring throughout all operational phases including regeneration periods, without adding structural complexity to the sensor.
3Ease of manufacture
If electrodes are arranged to face each other on insulation substrate, then manufacturing simplicity is improved, but PM amount estimation is delayed until electrodes are interconnected by PM
Solution Approach 1:
By measuring electrostatic capacitance rather than electrical resistance, the system detects PM accumulation from the initial stage when PM first deposits on the filter member surface. Capacitance changes occur continuously as PM accumulates, providing immediate detection without the delay inherent in resistance-based methods that require complete electrode interconnection. This maintains the simple facing electrode arrangement while eliminating detection delays.
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 and precise estimation of PM in exhaust gases, even at increased exhaust flow rates, by utilizing electrostatic capacitance changes to calculate PM amounts during regeneration periods, enhancing the sensor's utility beyond DPF diagnosis.
Implementation Method 1
a filter member (31) having a plurality of cells (C1, C2)
Implementation Method 2
at least a pair of electrode members (32, 33) which are alternately inserted into the respective electrode cells (C2), and an electrostatic capacitance detection circuit (not shown)
Implementation Method 3
a heater member (34) which heats the measurement cells (C1) to burn and remove particulate matters accumulated in the measurement cells (C1)
Data Source
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AI summary
A sensor that continuously estimates a PM amount in exhaust gas. The sensor includes a filter member 31 including a plurality of cells that trap PM in exhaust gas; electrode members 32, 33 arranged to face each other with the cell interposed therebetween and forming a capacitor, an electric heater 34 that executes, when a predetermined amount of PM has accumulated in the cells, filter regeneration of heating the cells to combust and remove the PM, a storage unit 40 that stores therein a reference reduction amount, which is an electrostatic capacitance reduction amount between the electrode members 32, 33 in a case where the filter regeneration is executed in a state where the PM is not flowing into the filter member 31, and estimation units 42, 43, 44 that estimate a PM amount based on an actual electrostatic capacitance change amount between the electrode members 32, 33 during a regeneration interval period, and estimate the PM amount based on a difference between an actual electrostatic capacitance reduction amount between the electrode members 32, 33 and the reference reduction amount during a filter regeneration period.