Air-Fuel Ratio Sensor Failure Detection Using Multi-Functional A/D Conversion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional gas concentration measuring apparatuses for automotive engines face complexity and inefficiency in detecting failures in air-fuel ratio sensors due to the need for multiple A/D converters, which increases structural complexity and reduces accuracy in identifying causes of failure such as wire disconnection, power supply shorts, and ground shorts.
Innovation Solution
A simplified gas concentration measuring apparatus using a sensor control circuit and a failure monitor that applies voltage and current sweeps to detect internal resistance changes, allowing for the detection of sensor failures with only two A/D converters by sampling sensor current and internal resistance signals before and after sensor activation, and identifying failure causes through pre-defined tables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional voltage sampling method is used to detect sensor failures, then failure detection capability is provided, but the number of A/D converters increases structural complexity
Solution Approach 1:
The patent makes the A/D converter multi-functional by using it for both normal sensor signal conversion and failure detection purposes. The same A/D converter that converts sensor voltages during normal operation is also used to convert test voltages applied during failure detection, eliminating the need for separate A/D converters for failure monitoring.
Solution Approach 2:
The system performs self-diagnosis by applying test voltages to the sensor terminals and measuring the resulting currents through the existing A/D converter. The control unit analyzes the measured values to determine terminal states (disconnection, short circuit, ground connection) without requiring external testing equipment or additional conversion components.
2Reliability
If voltage sampling is used for failure detection, then some failures are detected, but accuracy in identifying specific failure causes is insufficient
Solution Approach 1:
The patent segments the failure detection process into distinct phases: applying different test voltages to different terminals, measuring currents through each terminal sequentially, and analyzing results for each terminal independently. This segmented approach allows precise identification of which specific terminal has which specific failure condition.
Solution Approach 2:
The system changes the voltage parameter dynamically during testing by applying different test voltages (V1, V2, V3) to different terminals in sequence. By varying the voltage parameter and measuring the corresponding current responses, the system can distinguish between different failure modes based on their unique electrical characteristics.
3Measurement precision
If multiple A/D converters are added for comprehensive failure monitoring, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent makes the A/D converter multi-functional by using it for both normal sensor signal conversion and failure detection purposes. The same A/D converter that converts sensor voltages during normal operation is also used to convert test voltages applied during failure detection, eliminating the need for separate A/D converters for failure monitoring.
Solution Approach 2:
The system performs periodic self-diagnosis by alternating between normal sensor operation and failure detection modes. During failure detection, test voltages are applied sequentially to different terminals and currents are measured, then the system returns to normal operation. This periodic testing provides comprehensive monitoring without requiring continuous additional hardware.
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 solution enables accurate detection and identification of sensor failures with reduced structural complexity, improving the accuracy of air-fuel ratio measurements and compliance with stringent emission regulations.
Implementation Method 1
the sensor control circuit applying a voltage across the electrodes of the sensor element to produce a flow of electrical current through the sensor element
Implementation Method 2
in the voltage sweep mode, the sensor control circuit applying a voltage to the sensor element and sweeping the applied voltage in an ac form to sample a resulting change in voltage provided by the sensor element
Data Source
AI summary
A gas concentration measuring apparatus for use in air-fuel ratio control of motor vehicle engines is provided which is designed to detect and identify a cause of failure in operation of an A/F sensor. The apparatus works to apply the voltage to a sensor element and sweep it to produce a change in electrical current flowing through the sensor element for measuring the impedance of the sensor element. The apparatus samples values of the change in the current, a sensor output indicating an air-fuel ratio of mixture supplied to the engine, etc., before and/or after the sensor element is activated and uses a combination thereof to identify the cause of the failure of the A/F sensor.