PM Sensor Electrostatic Capacity Estimation
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Solution Overview
Problem
Electric resistance-type PM sensors face challenges in ensuring accurate estimation of particulate matter (PM) in exhaust gas due to PM adherence issues at increased exhaust gas flow rates, leading to inaccurate real-time PM estimation and limited application in on-board diagnosis, especially downstream of diesel particulate filters (DPF).
Innovation Solution
A PM sensor design that includes a filter member with porous ceramic partition walls, conductive electrodes, and an electric heater, utilizing electrostatic capacity detection to estimate PM amounts in real time by integrating PM accumulation over regeneration intervals, allowing for accurate and timely PM estimation and filter regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If PM is caused to adhere to each electrode in an electric resistance-type PM sensor, then the construction is simple, but under increased exhaust gas flow rates, PM may come off the electrodes leading to reduced estimation accuracy
Solution Approach 1:
The patent introduces a filter member as an intermediary component between the exhaust gas and the electrodes. PM particles are trapped on the filter member's surface rather than directly on the electrodes, preventing PM detachment while maintaining measurement accuracy. The filter member acts as a stable substrate that holds PM particles firmly even under high flow rate conditions.
Solution Approach 2:
The patent segments the sensor into distinct functional components: a filter member for PM trapping and separate electrodes for measurement. This segmentation allows the filter member to specialize in stable PM retention while the electrodes focus on electrical measurement, resolving the contradiction between simple construction and measurement precision.
2Device complexity
If PM adheres to electrodes in an electric resistance-type PM sensor, then the structure is simple, but the electric resistance value does not change until electrodes are connected by accumulated PM, preventing real-time PM amount estimation
Solution Approach 1:
The filter member serves as an intermediary that provides a large surface area for PM accumulation, enabling the electrodes to detect resistance changes earlier in the accumulation process. This allows real-time PM amount estimation without requiring complete electrode bridging, thus maintaining simple structure while enabling timely detection.
Solution Approach 2:
The patent transitions from a direct electrode-to-electrode measurement approach to a distributed measurement approach where the filter member's three-dimensional structure provides numerous measurement points. This dimensional expansion enables real-time detection of PM accumulation at various stages, not just when electrodes are fully connected.
3Device complexity
If PM adheres to electrodes, then the sensor has simple construction, but the electric resistance of PM may change under exhaust gas flow rate influence, causing inaccurate PM amount estimation
Solution Approach 1:
The filter member acts as a stable intermediary that isolates PM particles from the direct influence of exhaust gas flow. PM particles trapped on the filter member experience reduced flow rate effects compared to particles on exposed electrodes, stabilizing their electrical resistance properties and improving measurement accuracy.
Solution Approach 2:
The patent creates a localized measurement environment on the filter member surface where PM particles are held in a controlled position. This local stabilization of PM particles reduces the influence of varying exhaust gas flow rates on particle resistance, enabling more accurate PM amount estimation while maintaining simple construction.
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 accurate real-time estimation of PM amounts in exhaust gas, reducing filter regeneration time and enhancing engine control and DPF failure detection, with improved estimation accuracy and reduced regeneration time.
Implementation Method 1
an electric heating means for heating particulates trapped on the filter is mounted in the detector device
Implementation Method 2
a PM amount is estimated by making use of the fact that an electric resistance value changes due to conductive PM (mainly, a soot component) adhering to these electrodes
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A PM sensor estimates an amount of PM contained in exhaust gas in real time while reducing a regeneration time effectively. The PM sensor includes: a filter member 31 having a plurality of measuring cells which are defined by a porous partition wall and configured to trap particulate matters in exhaust gas; at least a pair of electrode members 32, 33 which are disposed to face each other with the measuring cell sandwiched therebetween to form a condenser; a heater member 34 which heats the measuring cell to burn and remove particulate matters accumulated in the measuring cell; and an estimation unit 42 which estimates an amount of the particulate matters contained in the exhaust gas based on an electrostatic capacity between the pair of electrode members 32, 33.