Engine-off Refueling Detection via Fuel Tank Pressure Rate of Change
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Solution Overview
Problem
Existing EVAP system diagnostic leak detection tests are confounded by refueling events during engine-off conditions, leading to false indications and premature shutdowns due to increased fuel system pressure, especially when the canister vent valve is closed.
Innovation Solution
A method to indicate a refueling event based on the rate of change in fuel tank pressure, with different thresholds when the canister vent valve is open or closed, allowing for reliable detection and aborting the diagnostic leak detection test to prevent false positives and premature refueling pump shutdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the canister vent valve is closed to perform a diagnostic leak detection test, then system integrity can be monitored, but refueling events cause greater pressure increases that may be misinterpreted as leaks
Solution Approach 1:
The patent changes the detection parameter from absolute pressure to rate of change of pressure (dP/dt). This allows the system to distinguish between refueling events (high dP/dt) and actual leaks (low dP/dt) even when the canister vent valve is closed, resolving the contradiction between leak detection accuracy and refueling event detection reliability
Solution Approach 2:
The patent implements dynamic threshold adjustment based on the state of the canister vent valve. When the valve is closed during diagnostic testing, the system uses a higher pressure threshold to accommodate the expected pressure increases from refueling events, while maintaining sensitive leak detection when the valve is open
2Device complexity
If a single pressure threshold is used for refueling detection, then the system is simple to implement, but it produces false positives during diagnostic tests when the canister vent valve is closed
Solution Approach 1:
The system dynamically adjusts the pressure threshold based on the canister vent valve state. When the valve is closed during diagnostic testing, a higher threshold is applied to prevent false positives from refueling events. When the valve is open during normal operation, a lower threshold enables sensitive refueling detection. This dynamic adaptation maintains reliability without excessive complexity
Solution Approach 2:
The system uses feedback from the canister vent valve state to adjust detection parameters. The control module receives feedback about whether the valve is open or closed and automatically adjusts the pressure threshold accordingly, preventing false positives during diagnostic tests while maintaining accurate refueling detection during normal operation
3Ease of operation
If refueling detection is based on absolute pressure increase, then detection is straightforward, but it causes premature refueling pump shutdown due to pressure buildup during closed-valve diagnostic tests
Solution Approach 1:
The patent changes from monitoring absolute pressure increase to monitoring the rate of change of pressure (dP/dt). During closed-valve diagnostic tests, the system can tolerate higher absolute pressure increases without triggering premature pump shutdown, as long as the rate of change remains consistent with normal refueling patterns rather than indicating a blockage
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 enhances the reliability of refueling event detection and prevents diagnostic test interruptions, ensuring accurate system integrity assessment and preventing premature refueling pump shutdowns by differentiating between refueling events and sensor noise.
Implementation Method 1
measuring a fuel tank pressure with a fuel tank pressure sensor
Data Source
AI summary
A method for an engine fuel system comprises, during an engine-off condition, indicating a refueling event based on a rate of change in fuel tank pressure, and aborting a diagnostic leak detection test based on the refueling event indication. Indicating a refueling event further comprises indicating a refueling event based on the rate of change in fuel tank pressure being greater than a first threshold when the canister vent valve is open, and greater than a second threshold when the canister vent valve is closed, the first threshold being less than the second threshold.