Misfire Detection Device Fast Idle Engine Noise
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Solution Overview
Problem
Conventional misfire detection devices struggle to accurately detect misfires during fast idle conditions due to unstable combustion, leading to false detections and reduced diagnostic accuracy, especially during rapid catalyst warm-up control and small torque generation.
Innovation Solution
A misfire detection device that includes a crank angle detector, rotational speed calculator, and misfire detector, which calculates and compares the rotational speed differences between a diagnosis target cylinder and adjacent cylinders, using correction terms to account for engine speed changes and sensor errors, and employs a three-point model detection method to improve signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional misfire detection is used during fast idle, then the detection system operates continuously, but the signal-to-noise ratio decreases leading to false detections
Solution Approach 1:
The patent extracts and removes the unstable combustion noise component from the diagnostic value calculation. By identifying and eliminating the noise sources specific to fast idle conditions (unstable combustion, rapid catalyst warm-up effects), the system isolates the true misfire signal, thereby improving the signal-to-noise ratio without sacrificing detection reliability
Solution Approach 2:
The patent changes the parameters used in misfire detection by introducing correction terms that account for fast idle-specific conditions. The diagnostic value is modified to include corrections for unstable combustion characteristics and catalyst warm-up effects, transforming the detection algorithm to operate accurately under these specific operating conditions
2Measurement precision
If correction terms are added to account for engine speed changes and sensor errors, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent introduces intermediary correction terms that mediate between the raw diagnostic value and the final misfire determination. These correction terms act as intermediate calculations that compensate for engine speed changes and sensor errors, improving measurement precision while keeping the overall system structure relatively simple by adding only computational steps rather than physical components
Data Source
AI summary
A misfire detection device for an engine having cylinders includes: a crank angle detector that detects an angular position of a crankshaft; a rotational speed calculator that calculates a rotational speed of the crankshaft on the basis of an output from the crank angle detector; and a misfire detector that obtains a difference between a rotational speed of the crankshaft in a combustion process in a diagnosis target cylinder and a rotational speed of the crankshaft in a combustion process in a last cylinder whose ignition order is immediately before the diagnosis target cylinder, and carries out a misfire detection by using a diagnostic value set on the basis of the difference.