Cam Profile Switching Diagnostic via Cylinder Air Flow Ratios
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Solution Overview
Problem
Existing diagnostic methods for camshaft condition in internal combustion engines are insufficient in detecting the correct functioning of cam profile switching systems, as they rely on monitoring oxygen content and cannot differentiate between electrical or hydraulic malfunctions and system degradation.
Innovation Solution
A method that calculates the mass air flow ratio between cylinder subsets under standard and alternative camshaft conditions, momentarily forcing the cam profile switching system to detect significant changes and adjust fuelling to maintain stoichiometric air-fuel ratios, thereby confirming correct camshaft operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If oxygen content monitoring is used to diagnose camshaft condition, then emissions control is maintained, but the diagnostic cannot differentiate between electrical/hydraulic malfunctions and system degradation
Solution Approach 1:
The diagnostic method segments the analysis by comparing air flow ratios between different cylinder subsets (first subset vs. second subset) rather than relying on a single oxygen measurement. This segmentation allows differentiation between system-wide issues and bank-specific malfunctions, improving diagnostic accuracy while maintaining emissions control.
Solution Approach 2:
The invention changes the diagnostic parameter from oxygen content alone to mass air flow ratio between cylinder subsets. By monitoring how the air flow ratio changes when cam profile switching is activated, the system can detect both electrical/hydraulic malfunctions (no ratio change) and system degradation (abnormal ratio change), resolving the information loss problem.
2Reliability
If cam profile switching is monitored by checking oil supply presence, then switching activation is confirmed, but tappet malfunctions cannot be detected
Solution Approach 1:
The invention uses mass air flow ratio as an intermediary measurement to indirectly assess tappet functionality. Instead of directly monitoring tappet position or oil pressure, the system measures the effect of cam profile switching on air flow through the cylinders. This intermediary measurement provides precise detection of tappet malfunctions while confirming switching activation.
3Reliability
If forced cam condition change is applied periodically to each bank, then degradation detection is enabled, but diagnostic time and engine disruption increase
Solution Approach 1:
The diagnostic method employs periodic action by momentarily forcing cam profile switching during suitable engine operating conditions and comparing air flow ratios at different times. This periodic comparison enables degradation detection while minimizing diagnostic time by only performing measurements during brief, targeted intervals rather than continuous monitoring.
Data Source
AI summary
A momentary diagnostic for determining correct operation of a cam profile switching system of an internal combustion engine by calculation of changes in cylinder bank to bank air mass flow ratios: operating said engine in one condition of the cam profile switching system; providing for a first cylinder subset the inlet fuel flow and the corresponding oxygen content of the exhaust flow, and calculating the mass of air passing through the first cylinder subset in a defined time period; providing for a second cylinder subset the inlet fuel flow and the corresponding oxygen content of the exhaust flow; calculating the mass of air passing through the second cylinder subset in said defined time period; comparing the mass air flow the oxygen content for the first and second cylinder subsets to give a standard ratio; momentarily forcing the cam profile switching system of one of said cylinder subsets to an alternative condition; re-calculating providing the corresponding mass of air oxygen content passing through the first and second cylinder subsets; and comparing said recalculated air flows oxygen contents to give a revised ratio; and comparing said standard ratio and revised ratio.