Exhaust Gas Sensor Pin Diagnostics Using DC and AC Current
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Solution Overview
Problem
Existing methods for diagnosing exhaust gas sensors, such as lambda probes, face challenges in distinguishing between short circuits and line breaks due to temperature-dependent impedance, which limits accurate diagnosis to specific operating states.
Innovation Solution
A diagnostic method and apparatus that utilize direct or alternating currents applied to the connections of an exhaust gas sensor to measure voltage potentials, allowing for the evaluation of these potentials to diagnose short circuits or line breaks in the Nernst cell and further cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a simple voltage measurement is used for short-circuit diagnosis, then the diagnosis can be carried out easily, but the very low impedance of the warm exhaust gas sensor prevents a distinction between individual sensor pins
Solution Approach 1:
The patent segments the diagnosis process by applying different current types (direct current and alternating current) to different measurement scenarios. Direct current is used for pin-specific voltage measurements to identify short circuits, while alternating current is used for impedance measurements to detect line breaks. This segmentation allows each measurement type to be optimized for its specific diagnostic purpose, resolving the contradiction between ease of operation and measurement precision.
2Measurement precision
If measurement currents exceeding a few μA are used, then sufficient voltage drops can be achieved for measurement, but the current sensitivity of Lambda sensors is exceeded and sensors are damaged
Solution Approach 1:
The patent employs periodic alternating current measurements superimposed on the direct current measurement. The alternating current component allows for impedance measurements without requiring high current levels, as the periodic nature enables detection through voltage variations. This periodic action resolves the contradiction by enabling sufficient measurement precision while keeping the average current low enough to prevent sensor damage.
3Measurement precision
If high impedances in cold exhaust gas sensors are measured, then line break diagnosis should be possible, but the high impedances cannot be distinguished from a line break
Solution Approach 1:
The patent changes the measurement parameter from direct voltage measurement to alternating current impedance measurement for detecting line breaks in cold sensors. By using alternating current and measuring impedance rather than simple voltage, the system can distinguish between high impedance states (cold sensor operation) and actual line breaks. This parameter change resolves the contradiction by enabling accurate line break detection despite the inherently high impedance of cold sensors.
4Measurement precision
If pin-specific short-circuit diagnosis is performed in cold exhaust gas sensor, then the diagnosis can be accurate, but the diagnosis is limited to cold state only
Solution Approach 1:
The patent creates a universal diagnosis system that can operate in both cold and warm sensor states by implementing multiple measurement modes. The system uses direct current measurements for pin-specific short-circuit diagnosis in cold states and alternating current impedance measurements for line break detection in both cold and warm states. This multi-functionality resolves the contradiction by enabling accurate diagnosis across all operating states rather than limiting it to cold state only.
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 reliable and cost-effective diagnosis of short circuits and line breaks in exhaust gas sensors across various operating states, without damaging the sensors, by leveraging existing hardware resources and algorithms.
Implementation Method 1
a series circuit comprising a Nernst cell and a first further cell
Data Source
AI summary
A method and a device for performing diagnostics on an exhaust gas sensor includes a series circuit of a Nernst cell and a first other cell. The exhaust gas sensor has a first, a second, and a third connection where a voltage drop can be measured between the first connection and the second connection by the Nernst cell and a voltage drop between the second connection and the third connection can be measured by the first other cell. The diagnostic method has steps for feeding a direct or alternating current into the first, second, and third connections; for directly or indirectly sensing an electrical voltage potential at at least one of the first, second, and third connections; and for evaluating the voltage potential sensed to diagnose a short circuit or an open circuit in the Nernst cell and/or in the first other cell.