EVAP Canister Airflow Reversal for HC Breakthrough
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Solution Overview
Problem
Hybrid vehicles face challenges in reducing hydrocarbon breakthrough during diagnostic routines of evaporative emissions control (EVAP) systems, leading to potential emissions and false leak detection issues, especially when canisters are saturated with fuel vapor, and frequent engine restarts to meet diagnostic conditions can reduce fuel efficiency.
Innovation Solution
A method involving a three-way valve and bypass passage in the EVAP system, which switches air-flow direction based on temperature changes within the fuel vapor canister during diagnostics, allowing for continuous evacuation and reduced hydrocarbon breakthrough by routing air through the purge port when HCs migrate towards the vent port.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a vacuum pump is used to evacuate the canister during diagnostic testing, then leak detection capability is improved, but hydrocarbon breakthrough occurs causing emissions and false leak detection
Solution Approach 1:
The system performs a canister purge operation before the diagnostic test to remove saturated fuel vapors from the canister. This preliminary action ensures the canister is not saturated with HCs, preventing breakthrough during the subsequent vacuum evacuation phase of the diagnostic test.
Solution Approach 2:
The system accumulates purge flow measurements during engine operation and uses this accumulated data to determine when purge flow summation exceeds a threshold. This continuous monitoring and accumulation allows the system to identify optimal moments to perform diagnostics without aborting tests, maintaining continuous useful action.
2Object-generated harmful factors
If the diagnostic test is aborted when HC breakthrough is detected, then emissions are reduced, but the required number of diagnostic tests cannot be completed to meet regulations
Solution Approach 1:
The system performs canister purge operations before diagnostic tests to prepare the canister in a state that prevents HC breakthrough. This preliminary purging ensures that when diagnostics are performed, the canister will not release HCs, allowing tests to complete successfully and meet regulatory requirements.
Solution Approach 2:
The system continuously monitors purge flow measurements and accumulates them over time. This feedback mechanism allows the system to determine when purge flow summation has exceeded the threshold, enabling intelligent decision-making about when to perform diagnostics to ensure both emissions compliance and test completion requirements are met.
3Measurement precision
If the engine is restarted frequently to meet diagnostic conditions, then diagnostic testing capability is improved, but fuel efficiency is reduced
Solution Approach 1:
The system continuously accumulates purge flow measurements during normal engine operation without requiring engine shutdowns or restarts. This continuous data collection enables the system to determine when diagnostic conditions are met based on accumulated purge flow summation, allowing diagnostics to be performed during normal operation and eliminating unnecessary engine restarts that would waste fuel.
Solution Approach 2:
The system performs canister purge operations during normal engine operation as a preliminary step before diagnostics, using the accumulated purge flow data to determine optimal timing. This approach prepares the canister for testing without requiring engine restarts, maintaining continuous operation and preserving fuel efficiency while still enabling diagnostic capability.
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 enables uninterrupted EVAP system diagnostics, improving the frequency of completing mandated tests and maintaining emissions quality by reducing hydrocarbon breakthrough and avoiding the need for frequent engine restarts.
Implementation Method 1
the canister may include a temperature sensor coupled proximal to the vent port of the canister. During an EVAP system diagnostic routine, the three-way valve may be actuated to the first position and the canister may be evacuated by drawing out air via the vent port of the canister while the temperature of the canister is monitored. An increase in temperature proximal to the vent port of the canister may indicate migration of hydrocarbons (HCs) towards the vent port
Implementation Method 2
a vacuum pump may be placed between the fuel vapor canister and atmosphere... the canister may be evacuated by drawing out air via the vent port of the canister
Implementation Method 3
switching a direction of air-flow through the canister based on a change in temperature within the canister... in response to the migration of HCs towards the vent line, the three-way valve may be actuated to the second position and evacuation of the canister may be continued by drawing out air via the purge port
Data Source
AI summary
Methods and systems are provided for reducing a possibility of hydrocarbon (HC) breakthrough during a diagnostic routine of an evaporative emissions control (EVAP) system. In one example, a method may include, during the diagnostic routine, switching a direction of air-flow through a fuel vapor canister via adjustments to a three-way valve in response to a higher than threshold a change in temperature within the canister.