Particulate Matter Sensor Shield Design
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Solution Overview
Problem
Existing particulate matter sensors for diesel engines face issues such as undesirable signal spikes from large particles, temporary adherence of particles due to high exhaust flow velocity, and inadequate sensing of particulate matter at the center of the exhaust conduit, leading to incomplete detection and inefficient particulate matter monitoring.
Innovation Solution
A particulate matter sensor design featuring a sensing element with an inner and outer shield arrangement, where the inner shield allows exhaust gases to impinge on the sensing face and the outer shield directs gases from the center of the conduit to the sensing element, creating a tortuous path that inhibits large particles and ensures effective particulate matter detection near the conduit wall.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensing element is oriented with electrodes facing upstream to allow particulate matter impingement, then particulate matter detection is enabled, but large particles create undesirable signal spikes and particles adhere only temporarily due to high exhaust flow velocity
Solution Approach 1:
A shield structure is introduced as an intermediary component between the exhaust flow and the sensing element. The shield includes a shield inlet facing upstream that directs exhaust gases toward the sensing face while blocking large particles from directly impinging the electrodes. This mediator structure enables indirect sensing of particulate matter in the exhaust stream while preventing harmful direct impingement effects
Solution Approach 2:
The sensing element is segmented into distinct functional zones: a shielded region protected from direct particle impingement and an exposed sensing face that indirectly detects particulate matter. The shield itself is segmented with inlet passages that control flow direction. This segmentation allows different portions to perform different functions - protection versus detection - resolving the contradiction between detection accuracy and signal stability
2Ease of manufacture
If the sensing element is placed near the exhaust conduit wall for easier installation, then installation simplicity is improved, but particulate matter from the center of the conduit cannot be effectively sensed
Solution Approach 1:
The shield inlet is oriented at an angle (e.g., 45 degrees) relative to the exhaust flow direction, creating a diagonal sampling path that extends from the conduit center toward the wall-mounted sensor. This angular orientation in a new dimension allows the sensor to access particulate matter from the high-concentration center region while maintaining its wall-mounted position, effectively adding a spatial dimension to the sampling strategy
3Measurement precision
If the sensing element is inserted far into the exhaust conduit to reach the center where particulate matter is most concentrated, then particulate matter sensing capability is improved, but the sensing element becomes completely surrounded by hot exhaust gases reducing particle adherence
Solution Approach 1:
The sensing element exhibits local quality differences: the sensing face region is positioned to receive directed exhaust flow containing particulate matter from the conduit center, while the body of the sensing element remains relatively cooler due to its thermal mass and partial exposure to cooler ambient air through the shield structure. This local temperature variation ensures optimal particle adherence at the sensing interface without requiring the entire element to be inserted deep into the hot exhaust stream
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 design provides a smoother output signal and enhances the detection of particulate matter from the center of the exhaust conduit, improving the accuracy and reliability of particulate matter monitoring by reducing the impact of large particles and ensuring consistent sensing.
Implementation Method 1
particulate matter will deposit thereupon and cause a high resistance short between the electrodes, thereby lowering the resistance between the two electrodes
Implementation Method 2
The sensing element may be provided with a heater on the side opposite the electrodes in order to clean soot off of the electrodes when desired
Implementation Method 3
the outer shield directs gases from the center of the conduit to the sensing element, creating a tortuous path
Data Source
AI summary
A particulate matter sensor is provided for sensing particulate matter present in exhaust gases in a conduit. The particulate matter sensor includes a sensing element with a sensing face which extends into the exhaust conduit and provides a signal indicative of the amount of particulate matter detected in the exhaust conduit. An inner shield is provided to surround the sensing face and includes an inner shield inlet for admitting exhaust gases therein to be sensed. An outer shield surrounds a portion of the inner shield and defines an outer shield chamber extending axially beyond the inner shield. The outer shield has an outer shield inlet passage to receive exhaust gasses from the conduit. Exhaust gases enter the inner shield from the outer shield chamber through the inner shield inlet.