Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
2001-11-19
2004-08-31
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
Reexamination Certificate
active
06782873
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to control arrangements in general for monitoring the emission of fuel vapors in motor vehicles. The invention especially relates to a method and an arrangement for operating a fuel tank system of a motor vehicle, especially for carrying out a time-to-time tightness check of the fuel tank system wherein an active charcoal filter is provided for taking up gaseous or vaporous fuel formed in the fuel tank system.
BACKGROUND OF THE INVENTION
Present-day combustion-driven motor vehicles mostly include a fuel supply tank as well as a control arrangement for monitoring and, if required, for preventing the emission of fuel vapors formed the fuel supply tank. The control arrangement functions especially for collecting occurring fuel vapor by means of an active charcoal filter and to temporarily store the fuel vapor in the active charcoal filter. Volatile fuel vapors, that is, mostly hydrocarbon vapors, form, for example, during a tanking operation of the vehicle or because of an increasing fuel temperature in the tank and because of an increase of the fuel vapor pressure which is associated therewith.
The storage capacity of the active charcoal filter drops continuously with an increase in the quantity of the stored hydrocarbon and it is therefore necessary to regenerate the active charcoal filter at regular intervals; that is, it is necessary to again remove the stored hydrocarbons from the active charcoal filter. For this purpose, the active charcoal filter is connected via a regeneration valve to an intake manifold of the engine which functions to induct combustion air. By opening the regeneration valve, a pressure drop develops between the active charcoal filter and the intake manifold by means of which the hydrocarbon, which is stored in the active charcoal filter, is conducted into the intake manifold in order to finally be combusted in the engine and thereby be disposed of.
With respect to the foregoing, attention is called to the stricter statutory regulations for the operation of internal combustion engines sought by governments in several countries, such as the United States of America. According to these regulations, it is, for example, required that motor vehicles, in which volatile fuels such as gasoline are used, have control arrangements referred to initially herein which can detect an existing leakage in the tank or in the entire tank-venting system.
A corresponding method and arrangement for diagnosing leaks in fuel tank systems of motor vehicles is suggested in U.S. patent application Ser. No. 10/221,856, filed on Sep. 17, 2002. This application is based on a recognition of pressure changes which are detected by a pressure sensor mounted within the fuel tank and those pressure changes which occur in the blocked fuel tank during a parked phase of the vehicle. In this context, one utilizes especially the underpressure of the tank content which develops with a possible cooling down of the fuel tank. In the case of an existing leak, the pressure increases slowly because ambient air can flow into the tank via the leak. With a simple pressure measurement, the presence of a leak in the tank or in the entire tank system can be determined.
Alternatively, the underpressure can also be generated actively by the internal combustion engine. The tank or the entire fuel tank system is connected to the intake manifold for a short time in a pressure-conducting connection whereby an underpressure, which corresponds to the intake manifold underpressure, develops in the tank. Such a procedure is described, for example, in U.S. Pat. No. 5,957,115.
Furthermore, a method and an arrangement are described in U.S. Pat. No. 5,146,902 wherein, in contrast to the two previous examples, an overpressure is generated in the tank and the drop of the overpressure is checked for leak diagnosis.
In the above-mentioned U.S. patent application Ser. No. 10/221,856, filed on Sep. 17, 2002, it is furthermore described that, with the pressure sensor, also an overpressure, which develops in the case of a warming of the tank content, can be applied correspondingly in the opposite direction for leakage diagnosis. The frequency of defective diagnoses can be reduced by using underpressure and overpressure conditions in the leakage test.
The known tests and arrangements have the disadvantage that an overpressure develops when an untightness or a leak of the fuel tank develops after a warming of the fuel tank and therefore of the tank content which leads to hydrocarbon-containing gas or vapor flowing past the active charcoal filter and into the ambient through the leak. In a motor vehicle, this is especially then the case when this overpressure forms during a parked phase of the vehicle because, in this case, the excess gas or vapor cannot be drawn off by suction actively by means of an engine-driven pump or by an underpressure (for example, via the intake manifold) effected by the engine itself.
The above-mentioned situation, which leads to the overpressure in the fuel tank, can furthermore occur without the described warming of the fuel tank, namely, for example, when the ambient pressure drops because of weather conditions.
SUMMARY OF THE INVENTION
It is a task of the present invention to provide a method and an arrangement as described initially herein which avoid the above disadvantages and which minimize especially the above-mentioned loading of the ambient with hydrocarbons. Furthermore, it should be possible to implement such a method and arrangement as simply as possible and therefore as cost effectively as possible. Especially in view to a use in a motor vehicle, the arrangement should furthermore cause the least possible increase in weight of the fuel tank system.
What is special with respect to the method of the invention is that first a gas-referred or vapor-referred physical state quantity is detected such as the gas pressure or vapor pressure or the gas temperature or the vapor temperature in the interior of the fuel tank system and/or in the vicinity of the vehicle. From the data so obtained, a gas or vapor pressure in the fuel tank system, which is to be expected, is determined. Accordingly, a probable prediction is made as to how the gas or vapor pressure will develop because of the present state quantities, that is, whether an overpressure or an underpressure is to be expected after a pregivable time. In the case of an overpressure of the gaseous or vaporous fuel in the tank system, which is to be expected, compared to the corresponding pressure in the ambient of the vehicle, the gaseous or vaporous fuel is guided out of the fuel tank system via the active charcoal filter into the ambient of the vehicle. In the opposite case of an underpressure, which is to be expected, the fuel tank system or the fuel tank alone is closed off so as to be gas tight or vapor tight, that is, hermetically sealed off in order to make possible especially a tightness check of the fuel tank system by means of the underpressure which is present.
Preferably, and before the above-mentioned method steps have been run, a check is made as to whether parking the vehicle is to be expected. The usual mechanisms for drawing off existing excess fuel gases or vapors cannot be activated because of the engine at standstill. For this reason, a higher risk is present in precisely this situation that hydrocarbons can escape to the outside via a possibly present leak.
To improve the quality of the prediction in connection with the determination of the mentioned pressure conditions, it can be further provided that the particular physical condition quantity, that is, the temperature and/or the pressure, are detected in the fuel tank system as well as also in the ambient of the vehicle. Here, it can be provided that the fuel tank system is only closed off gas tight or vapor tight when a pregivable negative gradient is determined between the outside temperature (temperature outside of the vehicle) and the interior temperature of the fuel tank. In this case, one can expect an underpressure
Moulis Thomas N.
Ottesen Walter
LandOfFree
Method and device for the low-emission operation of a fuel... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for the low-emission operation of a fuel..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for the low-emission operation of a fuel... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3330728