Dynamic Heat Rejection Thresholds for Engine-Off Vacuum Leak Testing
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Solution Overview
Problem
Current engine-off natural vacuum (EONV) leak testing methods face challenges due to static entry conditions that do not account for varying fuel levels and ambient temperatures, leading to false test failures and missed opportunities for robust leak testing.
Innovation Solution
Adjusting heat rejection inference thresholds based on current fuel level and ambient temperature to dynamically optimize entry conditions for EONV tests, and adjusting pressure and vacuum thresholds accordingly to enhance the robustness of the leak testing procedure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If static heat rejection thresholds are used for EONV test entry, then the test procedure is simple to implement, but the test accuracy decreases due to false failures caused by varying fuel levels and ambient temperatures
Solution Approach 1:
The patent implements dynamic adjustment of heat rejection thresholds based on real-time fuel level and ambient temperature measurements. The control module continuously monitors these parameters and adjusts the threshold accordingly, transforming the static threshold system into a dynamic one that adapts to varying operating conditions, thereby reducing false failures while maintaining implementation feasibility
Solution Approach 2:
The patent changes the threshold parameter from a fixed value to a variable that depends on fuel level and ambient temperature. By establishing a relationship between these parameters and the required heat rejection threshold, the system optimizes test entry conditions for different operating scenarios, improving leak detection accuracy without excessive complexity
2Productivity
If EONV tests are performed frequently, then In Use Monitoring Performance increases, but false failures increase due to sub-optimal testing conditions
Solution Approach 1:
The patent incorporates feedback mechanisms where the control module continuously monitors fuel level and ambient temperature, uses this information to adjust the heat rejection threshold, and thereby determines optimal test entry timing. This feedback loop ensures tests are performed frequently when conditions are favorable while avoiding tests when conditions would lead to false failures, maintaining both high IUMP and reliability
Solution Approach 2:
The system performs preliminary assessment of fuel level and ambient temperature conditions before initiating an EONV test. By evaluating these parameters in advance and adjusting the threshold accordingly, the system ensures that tests are only entered when optimal conditions are met, preventing false failures while maximizing monitoring performance
3Reliability
If pressure rise portion executes for long duration to ensure adequate pressure increase, then the test robustness improves, but the time limit is exceeded causing test failure
Solution Approach 1:
The patent dynamically adjusts the pressure threshold based on the actual pressure development rate observed during the pressure rise portion. If pressure increases rapidly, the threshold is adjusted accordingly, allowing the test to complete successfully within the time limit while maintaining robustness. This dynamic adaptation prevents time limit exceedance while ensuring adequate pressure increase for reliable leak detection
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 increases the frequency of successful EONV tests, reduces false failures, and improves the accuracy of leak detection, thereby enhancing In Use Monitoring Performance (IUMP) rates and reducing warranty costs.
Implementation Method 1
As a fuel tank cools down, a vacuum is generated therein as fuel vapors condense to liquid fuel
Implementation Method 2
The pressure in such a fuel system will increase if the tank is heated further (e.g., from hot exhaust or a hot parking surface) as liquid fuel vaporizes
Implementation Method 3
as liquid fuel vaporizes... as fuel vapors condense to liquid fuel
Data Source
AI summary
Methods and systems are provided for increasing the robustness of engine off natural vacuum testing. In one example, following an engine-off event, a heat rejection inference is determined, and further adjusted based on a fuel level and ambient temperature. In this way, an evaporative emissions system leak test may be enabled under conditions where the leak test may otherwise not be executed, thus increasing opportunities for evaporative emissions system leak detection and correspondingly reducing bleed emissions.