Fuel Tank Leak Diagnosis via Pressure Comparison
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Solution Overview
Problem
Reliable leak diagnosis in fuel tank systems is challenging due to pressure fluctuations caused by temperature changes and mechanical shocks, which can mask the presence of leaks, making it difficult to determine the system's tightness using only a pressure sensor.
Innovation Solution
A method involving closing and opening specific valves in the fuel tank system to measure pressure changes with a pressure sensor, building overpressure using a scavenging air pump, and comparing pressure changes within predetermined time intervals to derive leak diagnosis results, allowing for precise and reliable leak detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pressure sensor is used to detect leaks in the fuel tank system, then leak detection capability is provided, but reliable leak diagnosis is compromised due to pressure fluctuations from temperature changes and mechanical shocks
Solution Approach 1:
The system performs a preliminary sealing action by closing the first and second valves before measurement to isolate the fuel tank system from external pressure fluctuations. This preliminary isolation enables accurate leak detection by eliminating interfering temperature and mechanical shock effects during the measurement phase
Solution Approach 2:
The leak diagnosis is performed through periodic cyclic operation where valves are alternately opened and closed to create controlled pressure changes. The system repeatedly cycles through sealing, pressurization, and measurement phases, allowing comparison of pressure behavior across multiple cycles to reliably distinguish leaks from normal pressure fluctuations
2Measurement precision
If the fuel tank system is sealed for leak testing, then leak detection is enabled, but the system cannot operate normally during testing
Solution Approach 1:
The system dynamically switches between operational mode and diagnostic mode through controlled valve actuation. During normal vehicle operation, valves remain open for fuel vapor management. When leak diagnosis is required, valves are temporarily closed to seal the system for testing, then reopened to resume normal operation. This dynamic state transition allows both continuous vehicle operation and periodic tightness assessment
Solution Approach 2:
The leak diagnosis system is self-integrated into the existing fuel tank system components (valves, pressure sensor, scavenging air pump) and can be activated during normal vehicle operation without requiring external workshop equipment. The system performs self-diagnosis by utilizing its own components to create test conditions and evaluate leak status, enabling on-board assessment during normal operation
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
Enables reliable and precise detection of leaks in fuel tank systems by distinguishing between pressure changes caused by leaks and external influences, ensuring the system's tightness is accurately assessed during normal vehicle operation.
Implementation Method 1
a pressure sensor is arranged in the fuel tank system
Implementation Method 2
an overpressure is built up in the fuel tank system with the scavenging air pump
Implementation Method 3
An increase in temperature in the fuel tank and thus in the fuel causes the vapor pressure of the hydrocarbons to increase significantly
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a method for leakage diagnosis in a fuel tank system (1) of an internal combustion engine (2) of a motor vehicle, wherein the fuel tank system (1) has a fuel tank (16) and a storage element (19) for the temporary storage of hydrocarbons (23), wherein the fuel tank (16) and the storage element (19) are connected to one another in such a way that the hydrocarbons (23) which outgas from a fuel (17) which is situated in the fuel tank (16) are stored temporarily in the storage element (19), wherein the storage element (19) can be emptied by way of a purge air pump (7), wherein fresh air (24) can be conveyed by way of the purge air pump (7) through a fresh air line (42) to the storage element (19), as a result of which the hydrocarbons (23) can be released from the storage element (19) and can be fed through a hydrocarbon/air mixture line (43) to the internal combustion engine (2) for combustion, wherein the fresh air line (42) can be closed by way of a first valve (10), and the hydrocarbon/air mixture line (43) can be closed by way of a second valve (15), and wherein a pressure sensor (8) is arranged in the fuel tank system (1). In order to obtain reliable statements about the state of the fuel tank system, a stationary period of the motor vehicle is waited for in a first method step, the first valve (10) and the second valve (15) are closed in a second method step, the pressure change in the fuel tank system (1) is measured by way of the pressure sensor (8) within a predefined first time interval in a third method step, the first valve (10) or the second valve (15) is opened, and a positive pressure is built up in the fuel tank system (1) by way of the purge air pump (7) until a predefined positive pressure is reached in a fourth method step, the valve (10, 15) which was opened in the fourth method step is closed again in a fifth method step, the pressure change in the fuel tank system (1) is measured by way of the pressure sensor (8) within a predefined second time interval in a sixth method step, and the pressure changes which were measured in the third method step and in the sixth method step are compared with one another in a seventh method step, and the results are derived from said comparison for leakage diagnosis.