Patent Publication Number: US-6698402-B2

Title: Method for operating an internal-combustion engine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for operating an internal-combustion engine and to an installation for performing the method. 
     BACKGROUND INFORMATION 
     German Published Patent Application No. 195 22 075 describes a method for forming a fuel/air mixture and a fuel feed installation for an internal-combustion engine, in which the fuel which is to be fed to the internal-combustion engine is vaporized and the fuel vapor which is generated is fed to the air which is sucked in by the internal-combustion engine. To reduce the emissions of hydrocarbons, the vaporization of the fuel is to be performed at relatively low temperatures. 
     However, a drawback of this method and the associated installation is the considerable additional outlay which is required for the vaporization of the fuel. 
     Since, in particular during and immediately after the cold-starting of an internal-combustion engine, there is as yet no or only an unsatisfactory conversion of the pollutants which are generated by the internal-combustion engine in a downstream catalytic converter, the exhaust emissions from the internal-combustion engine are very high in particular at this time. This fact is made even worse because, due to the poor preparation of the mixture in the cold state of the internal-combustion engine, the raw emissions themselves are particularly high, and because, in order to achieve more rapid heating of the catalytic converter, the mixture is additionally enriched, with the result that some unburnt fuel may leave the internal-combustion engine. However, it is precisely the emissions during a cold start which are the decisive factor in determining whether or not an internal-combustion engine is able to comply with a set exhaust restriction. 
     It is conventional to provide heated or air-surrounded injection valves or alternatively heating of the induction ports. However, practical implementation of these components either requires considerable outlay or means that their action is unsatisfactory with regard to reducing the exhaust emissions, in particular in the cold state of the internal-combustion engine. 
     Therefore, it is an object of the present invention to provide a method for operating an internal-combustion engine which, with the minimum possible outlay, enables emissions to be minimized during the starting operation and the warm-up phase of the internal-combustion engine. 
     SUMMARY 
     The above and other beneficial objects of the present invention are achieved by providing a method and an arrangement as described herein. 
     According to the present invention, fuel in vapor form may be taken either from the fuel tank or from the charcoal canister, an operation which is very easy to control in terms of the process involved and only entails an extremely low outlay on the installation. Fuel in vapor form, which is naturally contained in the fuel tank or in the charcoal canister, does not have to be laboriously generated, but rather may very easily be removed from these containers in order to start and/or warm up the internal-combustion engine. 
     With regard to the preparation of the mixture and the resulting crude emissions from the internal-combustion engine, fuel which is in vapor form is much more suitable than liquid fuel, and consequently replacing at least some of the liquid fuel with fuel which is in vapor form, in accordance with the present invention, enables the emissions from the internal-combustion engine to be reduced considerably while the engine is starting and/or warming up. 
     Fuel may also be removed from the fuel tank or from the charcoal canister simultaneously or sequentially. 
     An arrangement configured to perform the method according to the present invention may require very few additional components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE schematically illustrates an arrangement configured to perform the method for operating an internal-combustion engine according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     An internal-combustion engine  1 , which is illustrated schematically in the FIGURE, includes an induction system  2 , a plurality of combustion chambers  3  and an exhaust system  4 . In a conventional manner, fuel mixed with air is fed to the combustion chambers  3  through the induction system  2  and, after combustion in the combustion chambers  3 , the exhaust gases which are formed during the combustion are discharged through the exhaust system  4 . In this case, the internal-combustion engine  1  operates according to the spark-ignition principle, and petrol is supplied as fuel. 
     A fuel tank  6 , which is connected to the internal-combustion engine  1  via a fuel line  5 , is configured to supply the induction system  2  or the combustion chambers  3  with fuel. The fuel tank  6  contains liquid fuel which is fed to the fuel tank  6  via a filling connection piece  7 , and in the present case fills the fuel tank  6  up to the height of a liquid-fuel level  8 . 
     Two lines  9  and  10  extend from the fuel tank  6  to a charcoal canister  11 , via which the fuel tank  6  is vented, in a manner which is conventional and is therefore not described in more detail herein. In this case, the lines  9  and  10  extend from an area of the fuel tank  6  which is above the liquid-fuel level  8 . 
     Furthermore, a line  12  extends from an area above the liquid-fuel level  8  of the fuel tank  6  to the induction system  2 , in which line there is a suction pump  13 . A further line  14 , which extends from the charcoal canister  11  and in which there is a further suction pump  15 , opens into the induction system  2 . Finally, a further line  16 , in which a pressure pump  17  is arranged, extends to the charcoal canister  11 . The charcoal canister  11  is for this purpose provided with three openings, specifically an opening  18  into which the line  9  opens, an opening  19  from which the lines  10  and  14  extend and an opening  20  into which the line  16  opens. The arrangement of all three pumps  13 ,  15  and  17  is merely an example, since it would also be possible to provide only one or two of the pumps  13 ,  15  or  17 , as will become clear below. If one or more of the pumps  13 ,  15  or  17  is eliminated, it is also possible to eliminate the associated line  12 ,  14  or  16 . By way of example, if the pressure pump  17  were being used, the lines  9  and  14  may be eliminated. Furthermore, in this case the opening  20 , which otherwise serves to vent the charcoal canister  11 , may be closed off. 
     To allow the minimum possible quantity of emissions to pass from the combustion chambers  3  into the exhaust system  4  while the internal-combustion engine  1  is starting and/or warming up, at least some of the liquid fuel is replaced with fuel which is in vapor form at least for a certain period while the internal-combustion engine is starting and/or warming up. This fuel in vapor form may come from the fuel tank  6 , specifically above the liquid-fuel level  8 , since fuel in vapor form is naturally formed in this area and may be fed to the induction system  2  of the internal-combustion engine  1  via the line  12 . For this purpose, the suction pump  13  may suck the fuel in vapor form out of the fuel tank  6 . Alternatively, the suction pump  15  may also be used to suck fuel which is in vapor form in the charcoal canister  11  out of the latter via the line  14  and to feed it to the induction system  2  of the internal-combustion engine  1 . 
     If a valve  21  which is located in the line  9  is open, the suction pump  13  may suck fuel which is in vapor form both out of the fuel tank  6  and, via the line  9 , out of the charcoal canister  11  and feed it to the induction system  2  of the internal-combustion engine  1 . Alternatively, with the valve  21  open, the suction pump  15  may also suck fuel which is in vapor form out of the charcoal canister  11  and/or out of the fuel tank  6 . 
     With the aid of the pressure pump  17 , the fuel which is in vapor form may also be forced out of the charcoal canister  11  via the line  14  or via the line  9  out of the fuel tank  6  into the induction system  2  of the internal-combustion engine  1 . In addition or as an alternative to the measures described above, it is also possible to provide a pump  22  in the line  10 , which sucks fuel which is in vapor form out of the charcoal canister  11  and, at the same time, forces it into the induction system  2  via the fuel tank  6 . In this case too, the fuel which is in vapor form is carried out of the fuel tank  6  to the induction system  2 . 
     The pumps  13 ,  15 ,  17  and  22  may be referred to as devices for producing a pressure difference between the fuel tank  6  and/or the charcoal canister  11  and the induction system  2  of the internal-combustion engine  1 . 
     Alternatively, it is also possible for the fuel which is in vapor form simply to be sucked in with the aid of the induction-pipe vacuum of the internal-combustion engine  1 , in which case the induction system  2  itself forms the device for producing a pressure difference between the fuel tank  6  and/or the charcoal canister  11  and the internal-combustion engine  1 . It is therefore possible to feed the fuel which is in vapor form to the combustion chambers  3  by vacuum or by pressure. 
     Therefore, there are in principle three different options for removing fuel which is in vapor form and feeding it to the internal-combustion engine  1 , specifically either only from the fuel tank  6  or only from the charcoal canister  11  or from the fuel tank  6  and the charcoal canister  11 , one of these three options being selected according to the level of the fuel tank  6  and of the charcoal canister  11  and according to the operating state of the internal-combustion engine  1 . 
     The lines  12  and  14  may be switched over by a reversing valve  23  arranged in these lines  12  and  14 , so that, depending on the position of the reversing valve  23 , the induction system  2  is connected either to the line  12  or to the line  14  and fuel may only be supplied from the corresponding line  12  or  14 . In addition, a further metering valve  24 , by which the amount of fuel in vapor form which is fed to the induction system  2  may be changed, is arranged between the reversing valve  23  and the induction system  2 . If, while fuel which is in vapor form is being sucked out of the fuel tank  6  via the line  12 , the reversing valve  23  closes the line  14  from the charcoal canister  11  to the induction system  2  of the internal-combustion engine  1 , during this time the charcoal canister  11  may be regenerated via the space above the liquid-fuel level  8  in the fuel tank  6 . 
     The quantity of fuel which is in vapor form in the fuel tank  6  above the liquid-fuel level  8 , like the quantity of fuel which is in vapor form in the charcoal canister  11 , is sufficient to start the internal-combustion engine  1  and to warm it up for a certain period without supplying liquid fuel. In this case, it is possible for the fuel which is in vapor form to be introduced into the induction system  2 , in a manner which is not illustrated, via air ducts of so-called air-surrounded injection valves, via special gas injectors or at a central location. 
     The fuel which is in vapor form may in this case be fed to the combustion chambers  3  either as soon as the starting of the internal-combustion engine  1  commences, in which case an increasing proportion of the fuel which is in vapor form is replaced with liquid fuel as the internal-combustion engine  1  warms up, or liquid fuel may be fed to the combustion chambers  3  directly when the internal-combustion engine  1  is starting, but then shortly after the internal-combustion engine  1  has started, this liquid fuel is at least partially replaced with fuel which is in vapor form. In this case too, an increasing proportion of the fuel which is in vapor form would in turn be replaced with liquid fuel as the internal-combustion engine  1  warms up. The liquid fuel is in this case, as described above, fed to the induction system  2  via the fuel line  5 . 
     Supplying liquid fuel in this manner may occur, for example, when a catalytic converter has reached its operating temperature or when the fuel which is in vapor form alone is no longer sufficient to operate the internal-combustion engine  1 . 
     Moreover, to heat the catalytic converter, it is possible for fuel which is in vapor form to be fed, in a manner which is not illustrated, into the exhaust system  4  of the internal-combustion engine  1  and to be burnt in that system. 
     In this case, the combustion air ratio may be determined by a suitable sensor arrangement or a computational model in the engine management system of the internal-combustion engine  1  and may be matched to the desired state by changing the quantity of liquid fuel or fuel in vapor form which is fed to the internal-combustion engine  1 . 
     If appropriate, sensors may be provided in the fuel tank  6 , in one or more of the lines  9 ,  10 ,  12  or  14  or in the exhaust system  4 , in order to determine the quantity of fuel which is fed in vapor form to the induction system  2 .