NOx Sensor Line Diagnosis via Capacitance Modulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing NOx sensors in automotive technology are prone to interference and coupling due to capacitive coupling and leakage currents during pulse width modulation, making continuous and reliable diagnosis of line interruptions challenging, especially at low NOx concentrations.
Innovation Solution
The method involves changing the capacitance of the second pump cell to generate a measurement signal at a measuring resistor, allowing for the detection of open or closed circuits, even at zero current conditions, and using a constant pump current or temperature variations to distinguish between intact and defective IP2 lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If pulse width modulation is used to control heater supply voltage, then temperature control is achieved, but capacitive coupling and leakage currents cause interference with the NOx measurement signal
Solution Approach 1:
The patent segments the control functions by separating the heater control (PWM) from the measurement signal reading. The measurement is performed during the off-phase of the PWM cycle when the heater is not active, thus eliminating capacitive coupling interference while maintaining temperature control capability.
Solution Approach 2:
The patent employs periodic action by utilizing the off-phase intervals of the PWM cycle for measurements. This periodic timing strategy allows the system to alternate between heating (on-phase) and measuring (off-phase), avoiding interference while maintaining both functions.
2Productivity
If the measurement signal is read during PWM on-phase, then continuous monitoring is possible, but interference and coupling affect the small measurement current
Solution Approach 1:
The system performs periodic measurements during the off-phase of the PWM cycle. Although not continuous in the strict sense, the frequent periodic sampling maintains effective continuous monitoring while avoiding the interference present during the on-phase, thus preserving measurement precision.
Solution Approach 2:
The useful action of temperature control continues uninterrupted during the on-phase, while measurements are continuously performed during the off-phase. This ensures both functions remain active and effective throughout the operational cycle.
3Reliability
If diagnosis is performed frequently, then line interruptions are detected reliably, but measurement values may be influenced or disturbed
Solution Approach 1:
The patent implements periodic diagnosis during the off-phase intervals of the PWM cycle. This allows frequent diagnosis to be performed without interfering with the heating function or the measurement signal, as diagnosis occurs during periods when neither heating nor normal measurement is active.
Solution Approach 2:
The system performs preliminary actions by preparing the measurement circuit during the off-phase before the next measurement cycle begins. This includes resetting integrators and preparing diagnostic test signals, ensuring that diagnosis can be performed frequently without affecting subsequent measurements.
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 reliable and continuous diagnosis of NOx sensor lines without influencing measured values, ensuring accurate detection of line integrity even at low NOx concentrations, thereby meeting environmental authority requirements.
Implementation Method 1
a sensor element (110) having a first pump cell (112) having an outer pump electrode (114) and an inner pump electrode (116) and having a first electrically conductive connection (120) and a second electrically conductive connection (124), a reference cell (130) having a Nernst electrode (132) and a reference electrode (134) and having a third electrically conductive connection (136), a second pump cell (140) having a pump electrode (142) and a counter electrode (144) and having a fourth electrically conductive connection (146), wherein the sensor element has a solid electrolyte
Implementation Method 2
The oxygen pump cell consists of an outer pump electrode exposed to the exhaust gas and an inner pump electrode located in a first cavity separated from the exhaust gas by a diffusion barrier... oxygen is removed from the first cavity of the so-called O2 cell, which is connected to the exhaust gas via a diffusion barrier. The resulting pumping current is then proportional to the oxygen content
Implementation Method 3
A nitrogen oxide sensor comprises a Nernst concentration cell, also called a reference cell... The Nernst electrode is also located in this first cavity, and the reference electrode is situated in a reference gas chamber; together, these form the Nernst cell or reference cell
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a method for operating a sensor (100) for detecting at least one portion of a measurement gas component having bound oxygen in a measurement gas, more particularly in an exhaust gas of an internal combustion engine. In the method, an electronic control unit (122), which at least has a first separate connection point (P1) for a first pump cell (112), a second separate connection point (P2) for a second pump cell (140), a connection point for a supply voltage (Vs) and a common connection point (COM), is connected to the sensor element (110) of the sensor (100), a measurement resistor (160) being provided in a fourth electrically conductive connection (146), a predefined voltage (UCOM) being present at the common connection point (COM), a capacity of the second pump cell (140) for generating a measurement signal (180) on the measurement resistor (160) is modified for a predefined amount of time by a control device (122).