Fuel Tank Pressure Transducer Offset Diagnosis via Canister Venting
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Solution Overview
Problem
Existing vehicle evaporative emissions systems face challenges in accurately diagnosing fuel tank pressure transducer (FTPT) offset, often leading to premature automatic shut-off events and increased emissions due to misidentification of canister vent pathway restrictions as FTPT degradation.
Innovation Solution
A method involving venting the fuel vapor canister to the engine intake during a vehicle-off soak, where the canister purge valve is opened if the FTPT output exceeds a threshold, allowing differentiation between FTPT degradation and canister vent pathway restrictions by observing the pressure equilibration to atmospheric pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the fuel tank pressure transducer output is tested after a vehicle-off soak to detect FTPT offset, then FTPT degradation can be identified, but canister vent pathway restrictions are misdiagnosed as FTPT degradation leading to premature automatic shut-off events and increased emissions
Solution Approach 1:
The diagnostic process is segmented into multiple conditional steps: first checking FTPT offset, then checking for canister vent pathway restrictions by monitoring pressure changes during engine operation. This segmentation allows the system to distinguish between FTPT degradation and vent pathway restrictions, preventing misdiagnosis and premature automatic shut-off events.
Solution Approach 2:
The system uses pressure change monitoring as an intermediary test to differentiate between FTPT offset and canister vent pathway restrictions. By observing whether pressure changes occur during engine operation, the system can determine if the issue is with the transducer or the vent pathway, thereby improving diagnosis reliability.
2Loss of information
If the canister purge valve is opened to vent the fuel vapor canister to the engine intake, then canister vent pathway restrictions can be detected, but the system complexity increases
Solution Approach 1:
The system performs preliminary checks of FTPT offset before proceeding to more complex diagnostic actions like opening the canister purge valve. This preliminary action allows the system to identify simple FTPT issues without triggering additional diagnostic sequences, thereby reducing unnecessary system complexity while maintaining complete diagnostic information.
Solution Approach 2:
The system uses feedback from pressure sensor readings to determine whether to proceed with opening the canister purge valve. If pressure changes are detected during engine operation, the system infers a canister vent pathway restriction and opens the purge valve for further testing. This feedback-based approach ensures that additional diagnostic actions are only taken when necessary, optimizing system complexity.
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 on-board diagnosis of FTPT offset causes without mechanical intervention, reducing unnecessary repairs and emissions by accurately distinguishing between FTPT degradation and canister vent pathway issues.
Implementation Method 1
a pressure or vacuum will develop there within responsive to changes in ambient temperature
Implementation Method 2
vacuum supplemented from a vacuum pump
Implementation Method 3
using engine intake manifold vacuum
Data Source
AI summary
A method for a fuel system is provided, wherein a fuel vapor canister is vented to an engine intake during a first condition, and wherein a restriction in a canister vent pathway is indicated, responsive to a change in a fuel tank pressure transducer output greater than a threshold. If the fuel tank pressure transducer output changes less than the threshold, degradation of the fuel tank pressure transducer is indicated. In this way, a fuel tank pressure transducer offset may be distinguished from a canister vent pathway restriction if a fuel tank pressure transducer indicates a significant pressure or vacuum in a fuel tank following a vehicle-off soak.