EVAP Canister Detection via Refueling Pressure Dynamics
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Solution Overview
Problem
Existing methods for diagnosing degradation in evaporative emission control systems, such as the absence or tampering with fuel vapor canisters, fail to detect alterations that do not result in detectable leaks, leading to increased emissions and costly repairs.
Innovation Solution
Monitoring the change in fuel tank pressure during refueling, by estimating the fuel fill rate and normalizing it with the fuel tank pressure, allows for the detection of missing or tampered fuel vapor canisters, even if other diagnostic methods do not detect leaks, using pre-calibrated thresholds to infer the presence or absence of canisters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional EVAP diagnostic methods (engine-off natural vacuum test) are used, then leaks can be detected, but tampering without leaks (e.g., replacing canister with straight tube) cannot be detected
Solution Approach 1:
The patent changes the diagnostic parameter from static pressure (engine-off test) to dynamic pressure change rate during refueling. By monitoring how pressure changes over time during the refueling process, the system can detect the presence or absence of a canister based on the characteristic pressure curve, enabling detection of tampering that static tests cannot identify.
Solution Approach 2:
The system performs preliminary calibration to establish expected pressure change curves for different EVAP system configurations (with canister, without canister, with straight tube). During actual refueling, the measured pressure curve is compared against these pre-established patterns to identify tampering, allowing the system to recognize abnormal conditions based on deviations from expected behavior.
2Ease of manufacture
If fuel vapor canister is removed or replaced with straight tube to save costs, then parts cost is reduced, but emissions control capability is lost
Solution Approach 1:
The patent implements a feedback mechanism where the diagnostic system continuously monitors refueling pressure characteristics and compares them against expected patterns. When tampering is detected (pressure curve deviation indicating missing canister), the system can trigger alerts or warnings, providing feedback that enables corrective action to restore proper emissions control functionality.
3Reliability
If EVAP system is sealed for diagnostic testing, then leak detection is enabled, but normal refueling operation is interrupted
Solution Approach 1:
The patent employs periodic action by conducting diagnostics during naturally occurring refueling events rather than requiring separate dedicated test procedures. The system utilizes the periodic refueling cycles that occur during normal vehicle operation to perform diagnostic measurements, eliminating the need to interrupt normal operations for separate testing while still achieving diagnostic objectives.
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 robustness of EVAP system diagnostics, enabling the detection of tampering and degradation, reducing emissions and maintaining emissions compliance by identifying missing or degraded canisters and adjusting vehicle operations accordingly.
Implementation Method 1
fuel vapors from the fuel tank are stored in the fuel vapor canister of the EVAP system
Implementation Method 2
Monitoring the change in fuel tank pressure during refueling
Data Source
AI summary
Methods and systems are provided for diagnosing degradation and/or alteration in an evaporative emission control system of a vehicle. In one example, a method may include, during a refueling, monitoring a fuel tank pressure and a fuel fill level, and detecting a presence or an absence of a fuel vapor canister of the EVAP system based on a change in fuel tank pressure with an increase in fuel level.