Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
2000-01-27
2001-11-27
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
Reexamination Certificate
active
06321727
ABSTRACT:
TECHNICAL FIELD
This invention pertains to evaporative emission control systems. More specifically, it pertains to a method for detecting leaks in such fuel vapor handling systems.
BACKGROUND OF THE INVENTION
Fuel evaporative emission control systems have been in use on automotive vehicles for over 30 years. The gasoline fuel used in many internal combustion engines is quite volatile. The fuel typically consists of a hydrocarbon mixture ranging from high volatility butane (C-4) to lower volatility C-8 to C-10 hydrocarbons. When a vehicle is parked in a warm environment during the daytime heating (i.e., diurnal heating), the temperature in the fuel tank increases. The vapor pressure of the heated gasoline increases and fuel vapor will flow from any opening in the fuel tank. Normally, to prevent vapor loss into the atmosphere, the tank is vented through a conduit to a canister containing suitable fuel adsorbent material. High surface area activated carbon granules are widely used to temporarily adsorb the fuel vapor.
The fuel vapor enters the canister through a top inlet of the canister and into the carbon granule mass. The vapor diffuses downwardly under its own pressure and gravity into the volume of carbon granules where it is adsorbed in temporary storage. The total volume of adsorbent is specified so as to be suitable to retain a quantity of fuel vapor expected to evaporate from the fuel tank during normal or representative usage of the vehicle.
The canister is molded of a thermoplastic material and shaped so that ambient air can be drawn through the carbon granule bed during engine operation to purge adsorbed fuel from the surfaces of the carbon particles and carry the removed fuel into the air induction system of the vehicle. Typically, a partition is formed in the canister to lengthen the flow of vapor and air through the volume of carbon particles. Thus, the fuel vapor enters at one end, the vapor inlet, of the flow path and escapes at the opposite end, the vent outlet, if the quantity of fuel exceeds the adsorption capacity of the carbon volume. Air, induced to flow through the carbon under engine intake vacuum, enters the canister at the vapor vent end of the flow path. The air traverses the full length of the flow path and exits the canister with desorbed, i.e., purged, fuel through a purge outlet at the vapor inlet end of the carbon volume.
The described emission control system obviously works in a repeating cyclical mode. When the engine is not running, fuel vapor generated by diurnal heating, the previous return of hot fuel or the like, flows to the canister and is adsorbed up to the capacity of the adsorbent volume. The vehicle may remain idle for several days and fuel vapor will accumulate in the canister. The initial loading will be at the inlet end of the adsorbent volume, but the fuel gradually becomes distributed along the entire adsorbent bed pathway. When the vehicle engine is started and can accommodate a fuel-air mixture, a purge valve is opened and purge air is drawn through the adsorbent volume. Purging can continue as long as the engine is running and the air can cause the removal of a substantial portion of the stored fuel vapor.
Environmental regulators are proposing lower limits on the amount of fuel vapor that can escape the evaporative emission system during a prescribed test of the system in a closed space. For example, the California Air Resources Board (CARB) has proposed “zero” and “near zero” evaporative emission standards for automotive vehicles for year 2004. The proposed standards require that there cannot be any leaks in the vapor emission control system. Also, CARB onboard diagnostics regulations require that the evaporative emission control system diagnostics should be able to detect a 0.02 inch diameter leak in the system.
Recently, vehicles have incorporated diagnostic systems to detect problems or malfunctions in the operation of vehicle operating and emission control systems including the evaporative emission control system. However, in the case of the fuel vapor handling systems, there has been no practical on-board diagnostic procedure capable of detecting small leaks, of the order of 0.02 inch, in the evaporative emission control system of some vehicles, especially those equipped with vacuum compliant plastic fuel tanks. It is desirable to have such a diagnostic procedure that can be automatically performed by the vehicle computer control system and suitable complementary sensors to detect such small leaks and provide a notice of the leak to the vehicle operator.
SUMMARY OF THE INVENTION
This invention provides a method of detecting small leaks, e.g., about 0.02 inches, that release fuel vapor from the fuel system of an automotive vehicle. The method utilizes an on-board computer, such as the engine or powertrain control module, to evaluate fuel tank pressure and temperature signals to consider whether a diagnostic test can be conducted and, when appropriate, whether there is a leak in the fuel tank, fuel vapor vent line, adsorption canister or other parts of the system.
The method is practiced in connection with a fuel vapor control system that includes a fuel tank with fuel level, temperature and pressure sensors; a vapor vent line from the tank to a carbon granule filled vapor adsorption canister; and a vapor purge valve and a vapor vent/air inlet valve for the canister. Further, the invention is practiced by continuing to operate the engine or powertrain control computer for a brief time after the engine has been shut off.
A basic aspect of the method is to temporarily seal the vapor control system at an appropriate time after an engine shut-off and then to quickly determine whether the pressure in the fuel tank drops below atmospheric pressure when the fuel in the tank cools and its vapor pressure decreases markedly. The sensing of a vacuum indicates that no significant leak exists while a failure to sense a suitable vacuum indicates the presence of a leak. However, critical features of the invention also include determining when ambient conditions are such that a suitable leak test can be performed. In principle, a leak test could be conducted each time the engine is turned off. But, as a practical matter, there is not always an appropriate amount of fuel in the tank or ambient conditions do not always permit timely cooling of the fuel within a suitable time, and the procedure is aborted to conserve battery energy.
The fuel tank temperature and pressure data and time data are accumulated for just a suitable brief time and stored in the engine control module database. The computer is than preferably shut down and analysis of the data and the provision of a leak signal if required undertaken after the engine is later started. It is intended that the subject leak test method be conducted or aborted within a period of minutes up to about an hour of engine shut-off so as to accomplish the object of the invention without prolonged operation of the engine control module when the engine is not running.
The size of a perceived leak can be estimated in the control module utilizing data such as the observed and recorded temperature decrease, pressure decrease and vapor volume during a leak test. The reference basis of the analysis may be predetermined leak data stored in a look-up table in the module or a predetermined mathematical model for leak estimation stored in the module.
Other objects and advantages of the invention will become more apparent from a detailed description of the invention which follows. Reference will be had to the drawings which are described in the following section.
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patent: 5263462 (1993-11-01), Reddy
patent: 5275144 (1994-01-01), Gross
patent: 5437257 (1995-08-01), Giacomazzi et al.
patent: 5494021 (1996-02-01), Yoneyama
patent: 5635630 (1997-06-01), Dawson et al.
patent: 6073487 (2000-06-01), Dawson
patent: 6089081 (2000-07-01), Cook et al.
Labus Gregory Edward
Mc Carthy Timothy E.
Reddy Sam Raghuma
Rich Gregory Earl
General Motors Corporation
Gimie Mahmoud
Grove George A.
Sedlar Jeffrey A.
Yuen Henry C.
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