Knock Sensor Malfunction Diagnosis via Dual Threshold Logic
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Solution Overview
Problem
Existing knock sensor malfunction diagnosis systems cannot detect malfunctions where the output from the knock sensor becomes excessively large, as they rely solely on the absence of vibration frequency components, failing to account for scenarios where the sensor detects vibrations beyond predetermined thresholds.
Innovation Solution
The system determines knocking by comparing the magnitude of the knocking vibration frequency component to a first threshold value for normal operation and uses a second threshold value under specific diagnostic conditions to diagnose sensor malfunctions, allowing for the detection of excessive output and applying similar control processing to both scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the diagnosis system only checks for absence of vibration frequency components, then the control logic remains simple, but the system cannot detect malfunctions where sensor output becomes excessively large
Solution Approach 1:
The system dynamically adjusts the diagnostic approach based on operating conditions. A diagnostic flag is set when specific conditions are met (fuel cutoff active, engine speed within range, throttle fully closed), enabling the system to switch between normal knocking detection mode and malfunction diagnosis mode. This dynamic adaptation allows comprehensive malfunction detection without permanently increasing control logic complexity.
Solution Approach 2:
The system changes the diagnostic parameter threshold based on the diagnostic flag state. When the flag is set, the system uses a second threshold value for malfunction diagnosis; when not set, it uses the first threshold value for normal operation. This parameter change enables detection of both low-output and high-output malfunctions while maintaining simple control logic through conditional parameter selection.
2Measurement precision
If the system uses a single threshold value for knocking detection, then the control processing is simplified, but the system cannot distinguish between normal knocking and sensor malfunction with excessive output
Solution Approach 1:
The system performs preliminary assessment by setting a diagnostic flag based on predetermined conditions (fuel cutoff status, engine speed, throttle position) before conducting the actual knocking detection. This preliminary action prepares the system to apply the appropriate threshold value, ensuring accurate distinction between normal knocking and sensor malfunction without requiring complex real-time analysis.
Solution Approach 2:
The diagnostic flag acts as an intermediary between the operating conditions and the threshold selection. This flag mediates the decision-making process by encapsulating the complex condition assessment, allowing the system to smoothly transition between using the first threshold value for normal operation and the second threshold value for malfunction diagnosis, thereby simplifying overall control logic.
Data Source
AI summary
To enable, with a simple control, a malfunction of a type wherein the output from a knock sensor becomes excessively large to be detected, a knock-sensor malfunction diagnosis device includes a control section configured to determine that knocking has occurred when the magnitude of a knocking vibration frequency component derived from an output signal from a knock sensor exceeds a first threshold value, and diagnose the knock sensor as malfunctioning when a prescribed diagnostic condition wherein knocking cannot occur is satisfied and the magnitude of the knocking vibration frequency component derived from the output signal from the knock sensor exceeds a second threshold value. The control section is further configured to determine that the diagnostic condition is satisfied for a time interval from a time when a predetermined time period has expired after fuel-cutoff has started to a time when the fuel-cutoff ends, during execution of the fuel-cutoff.