Particulate Matter Sensor Degradation Diagnosis via Water Vapor
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Solution Overview
Problem
Particulate matter sensors in engine exhaust systems can be difficult to diagnose for degradation, as they may exhibit high resistance when there is little particulate matter, making it challenging to distinguish between a properly operating sensor and an open circuit, especially when the sensor output is affected by water vapor in exhaust gases.
Innovation Solution
A method is developed to diagnose a resistive particulate matter sensor by monitoring its output during engine start, where the presence of water vapor in exhaust gases causes a change in sensor state, allowing for the identification of sensor degradation without requiring special hardware, using the existing engine controller and particulate heater systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a particulate matter sensor is used to monitor exhaust gases, then emissions can be controlled, but the sensor output becomes ambiguous when high resistance occurs due to low particulate matter versus sensor degradation
Solution Approach 1:
Water vapor acts as an intermediary substance to test the sensor's functionality. By introducing water vapor into the exhaust stream during engine cold start, the system creates a known condition that should produce a measurable sensor response. The absence or inadequacy of this response indicates sensor degradation, thus using water vapor as a mediator to reveal sensor status without requiring additional hardware.
Solution Approach 2:
The system changes the chemical composition parameter of the exhaust gas by introducing water vapor during cold start conditions. This parameter change creates a temporary condition where the sensor should detect a specific signal level. By monitoring whether the sensor output changes appropriately in response to this parameter change, the system can diagnose sensor health without adding complex measurement equipment.
2Measurement precision
If special hardware is added to monitor sensor degradation, then diagnostic accuracy improves, but system cost and complexity increase
Solution Approach 1:
The existing engine controller and particulate heater system perform dual functions: their original purposes plus sensor diagnostics. The engine controller already monitors exhaust conditions and controls the particulate heater; by utilizing these existing components for sensor testing during cold start, the system achieves self-diagnosis capability without requiring separate monitoring hardware, thus avoiding increased complexity and cost.
Solution Approach 2:
The engine controller is made multi-functional by assigning it the additional role of sensor diagnostics. The particulate heater system is also utilized for diagnostic purposes beyond its original function of heating the filter. This universal use of existing components eliminates the need for dedicated diagnostic hardware, reducing system complexity while maintaining measurement precision.
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 approach enables early detection of degraded sensors, potentially improving engine emissions by allowing for timely replacement, reducing system costs, and avoiding the need for additional monitoring or stimulating hardware.
Implementation Method 1
When particulate matter bridges the gap between electrodes, the resistance and conductance of the particulate matter sensor is changed
Implementation Method 2
the presence of water vapor in exhaust gases causes a change in sensor state
Data Source
AI summary
A system for improving operation of an engine having a particulate matter sensor is presented. The system may be used to improve engine operation during cold starts especially under conditions where water vapor or entrained water droplets are present in vehicle exhaust gases. In one embodiment, particulate sensor degradation is indicated in response to an output of said particulate matter sensor staying below a threshold as engine temperature increases past the dewpoint temperature.