Particulate Matter Sensor Nested Shield Design
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Solution Overview
Problem
Existing particulate matter sensors in diesel engines are susceptible to liquid water contamination, which can lead to electrode coating, shorting, and increased response time due to inadequate shielding designs that allow water to reach the sensing elements and restrict exhaust gas flow.
Innovation Solution
A particulate matter sensor design featuring an inner and outer shield arrangement that prevents liquid water from reaching the electrodes while maintaining optimal exhaust gas exposure, with the inner shield having a smaller outlet than the outer shield and strategically placed inlet and outlet apertures to promote gas flow and prevent water ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inner shield is spaced away a significant distance from the electrodes to protect them, then liquid water protection is improved, but the flow of exhaust gases becomes ineffective for collecting particulate matter on the sensing element
Solution Approach 1:
The patent employs a nested shield structure where an inner shield is positioned within an outer shield, both surrounding the sensing element. The inner shield has an outlet smaller than the outer shield outlet, creating a nested arrangement that protects the sensing element from liquid water while maintaining effective exhaust gas flow for particulate matter collection. This nested configuration resolves the contradiction by providing layered protection without excessive spacing.
2Device complexity
If the inner shield and outer shield are placed in close proximity to each other, then device complexity is reduced, but the flow of exhaust gases into the outer shield is limited
Solution Approach 1:
The patent applies asymmetry by designing the inner shield outlet to be smaller than the outer shield outlet. This asymmetric configuration allows the shields to be in close proximity (reducing device complexity) while the differential outlet sizes create sufficient space for effective exhaust gas flow into the outer shield, resolving the contradiction between compact structure and gas flow productivity.
3Productivity
If the inner shield outlet is made much larger than the outer shield outlet, then exhaust gas flow is improved, but liquid water can more easily reach the sensing element through the larger opening
Solution Approach 1:
The patent inverts the conventional approach by making the inner shield outlet smaller than the outer shield outlet, rather than larger. This inverted configuration allows the larger outer shield outlet to maintain effective exhaust gas flow while the smaller inner shield outlet provides enhanced liquid water protection, directly resolving the contradiction by reversing the traditional size relationship.
4Loss of time
If the shield arrangement allows significant exhaust gas flow, then sensor response time is improved, but liquid water contamination risk increases
Solution Approach 1:
The nested shield structure with the inner shield positioned within the outer shield, and the inner shield outlet smaller than the outer shield outlet, creates a protective configuration that allows significant exhaust gas flow (maintaining fast sensor response time) while providing layered protection against liquid water contamination.
5Measurement precision
If the electrodes are exposed directly to the exhaust stream for accurate sensing, then measurement precision is improved, but electrode coating and shorting from liquid water increases
Solution Approach 1:
The sensing element with electrodes is nested within the inner shield chamber, which is itself nested within the outer shield. This nested arrangement allows the electrodes to be exposed to exhaust gases for accurate particulate matter sensing while the concentric shields provide protective barriers against liquid water contamination.
Solution Approach 2:
The inner and outer shields act as intermediary structures between the sensing element and the exhaust stream. These intermediary shields allow exhaust gases to reach the electrodes for accurate sensing while blocking liquid water from causing electrode coating and shorting, thus resolving the contradiction between measurement precision and reliability.
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
The design effectively prevents liquid water from reaching the electrodes while ensuring adequate exposure to particulate matter, enhancing sensor reliability and response time by maintaining desired exhaust gas flow and minimizing water entry.
Implementation Method 1
The two electrodes may be formed in a pattern with inter-digitized fingers that maximizes the perimeter between the two electrodes. When the sensing element is disposed in the exhaust stream of a diesel engine, 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.
Data Source
AI summary
A particulate matter sensor includes a sensing element with a first electrode and a second electrode, an inner shield with the sensing element disposed therein, and an outer shield with the inner shield disposed therein. The inner shield includes a first portion with an inner shield inlet and a second portion which is smaller in diameter that the first portion such that the first and second electrodes are within the second portion. The outer shield includes an outer shield inlet which communicates exhaust gases to the inner shield inlet.