This invention relates to leak detection methods and systems, and more particularly, to automotive fuel leak detection using a pressure switch, a temperature differential and statistics.
In a vapor handling system for a vehicle, fuel vapor that escapes from a fuel tank is stored in a canister. If there is a leak in the fuel tank, the canister, or any other component of the vapor handling system, fuel vapor could exit through the leak to escape into the atmosphere.
Vapor leakage may be detected through evaporative monitoring. This evaporative monitoring may be performed while an engine is running, where pressure decrease may be analyzed. This type of evaporative monitoring may detect 1 mm and larger leaks, however, it is believed that many parameters influence the accuracy of the diagnosis. Therefore, it is believed that evaporative monitoring when the engine is off is more reliable.
The present invention provides a method of leak detection in a closed vapor handling system of an automotive vehicle, wherein an engine is shut off. The method includes obtaining a start temperature, providing an evaluation temperature, calculating a temperature differential between the start temperature and the evaluation temperature, evaluating whether a pressure switch is closed if the temperature differential is greater than a temperature control value, incrementing a time counter if the pressure switch is not closed, and comparing the time counter to a time control value if the pressure switch is not closed.
The present invention also provides another method of leak detection in a closed vapor handling system of an automotive vehicle, wherein an engine is shut off. This method includes determining whether the engine is off, closing a shut off valve, providing a pressure switch, a temperature sensing element, and an engine management system to receive pressure and temperature signals from the pressure switch and temperature sensing element, obtaining a start temperature and providing an evaluation temperature, calculating a temperature differential between the start temperature and the evaluation temperature, comparing the temperature differential to a temperature control value, evaluating whether the pressure switch is closed when the temperature differential is greater than a temperature control value, determining a no leak condition if the pressure switch is closed, incrementing a time counter if the pressure switch is not closed, comparing the time counter to a time control value if the pressure switch is not closed, determining a leak condition if the time counter is greater than the time control value, and determining a diagnosis not performed condition if the time counter is not greater than the time control value.
The present invention also provides an automotive evaporative leak detection system. The system includes a pressure switch, a temperature sensing element, and a processor operatively coupled to the pressure switch and the temperature sensing element and receiving, respectively, pressure and temperature signals therefrom. The processor calculates a temperature differential between a start temperature and an evaluation temperature, evaluates whether a pressure switch is closed, increments a time counter, and compares the time counter to a time control value.
The present invention further provides another automotive evaporative leak detection system. This system includes a pressure switch located on a conduit between a fuel tank and a canister, a temperature sensor mounted on the fuel tank, a shut off valve located between the canister and an atmosphere, a control valve located between the canister and an engine, and a processor operatively coupled to the pressure switch and the temperature sensor and receiving, respectively, pressure and temperature signals therefrom. The canister communicates with the engine and the atmosphere, the fuel tank communicates with the engine and the processor opens and closes the shut off valve and the control valve. The processor also calculates a temperature differential between a start temperature and an evaluation temperature, evaluates whether a pressure switch is closed, increments a time counter, and compares the time counter to a time control value.