Variable Lag Time Fuel Vapor Leak Diagnostic Control
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Solution Overview
Problem
Existing leak diagnostic devices for fuel vapor treatment systems face challenges in accurately detecting fuel vapor leaks due to deformation of the fuel tank under negative pressure, which affects the precision of pressure change measurements and makes it difficult to accurately determine the fuel vapor amount.
Innovation Solution
A leak diagnostic apparatus and method that involves measuring a first pressure change rate after applying a negative pressure to the purge line, exposing it to atmospheric conditions after a variable lag time, and measuring a second pressure change rate, with the lag time adjusted based on the estimated fuel vapor amount to improve leak detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a fixed lag time is used after negative pressure application, then the system operation is simplified, but the leak detection accuracy deteriorates due to tank deformation and fuel vapor production variations
Solution Approach 1:
The lag time is changed from a fixed value to a variable parameter that is dynamically adjusted based on fuel temperature and pressure conditions. The control unit selects different lag time values from a predetermined table according to the measured fuel temperature range and pressure change rate, allowing the system to adapt to varying operating conditions and maintain high measurement accuracy.
Solution Approach 2:
The system changes the lag time parameter based on measured physical conditions (fuel temperature and pressure). By establishing a relationship between these parameters and the optimal lag time, the system selects appropriate lag time values from predetermined tables, thereby compensating for the effects of tank deformation and fuel vapor production variations under different operating conditions.
2Measurement precision
If a longer lag time is used to allow tank recovery, then measurement stability improves, but fuel vapor production variations cause errors in leak detection
Solution Approach 1:
The lag time parameter is adjusted based on fuel temperature and pressure conditions to find the optimal balance between tank recovery and vapor production effects. By selecting appropriate lag time values from predetermined tables according to measured conditions, the system minimizes measurement errors while maintaining measurement stability.
Solution Approach 2:
The system measures the actual pressure change rate during the lag time period and uses this feedback to determine the leak detection result. The control unit compares the measured pressure change rate with expected values based on the selected lag time and operating conditions, allowing it to compensate for vapor production effects and accurately detect leaks.
3Reliability
If negative pressure is applied to detect leaks, then leak detection capability is enabled, but fuel tank deformation occurs which affects pressure measurement accuracy
Solution Approach 1:
The system applies negative pressure in a controlled manner and immediately begins measuring the pressure change rate. By establishing the measurement protocol in advance and selecting the appropriate lag time based on predetermined tables before the actual measurement, the system prepares to compensate for tank deformation effects while maintaining leak detection capability.
Solution Approach 2:
The system adjusts the lag time parameter based on the measured fuel temperature and pressure conditions to compensate for tank deformation effects. By selecting optimal lag time values from predetermined tables, the system minimizes the impact of deformation on pressure measurements while maintaining the ability to detect leaks through negative pressure application.
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 accuracy of leak detection by minimizing the lag time as the fuel vapor amount increases, reducing errors caused by tank deformation and fuel vapor production variations, thereby providing precise measurement of fuel vapor leaks.
Implementation Method 1
a pressure detecting means for detecting a pressure in the purge line
Implementation Method 2
the fuel vapor in a fuel tank is led into a canister to be temporarily adsorbed by the same
Data Source
AI summary
A lag time is set in a period from the time when a leak down is finished to the time when measurement of the amount of fuel vapor is started for the purpose of returning a deformed fuel tank to its original shape. A fuel vapor amount estimating means is provided that estimates the amount of fuel vapor produced in the fuel tank during the time of the leak down. This means is so set as to make the lag time shorter as the amount of fuel vapor increases. With this, undesired precision in measuring the amount of fuel vapor produced under a condition wherein the amount of fuel vapor is large can be avoided.