Abstract:
A method is provided for operating an internal combustion engine that includes, but is not limited to ascertaining a possible instant of a stoppage of the internal combustion engine and injecting fuel to fill a cylinder of the internal combustion engine. The injection performed shortly before the instant of the stoppage of the internal combustion engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to German Patent Application No. 10 2011 016 638.6, filed Apr. 9, 2011, which is incorporated herein by reference in its entirety. 
       TECHNICAL FIELD 
       [0002]    The technical field relates to a method for operating an internal combustion engine, a control unit, a computer program product, a computer program, and a signal sequence, with the aid of which an internal combustion engine, in particular a fuel supply and ignition of the internal combustion engine, can be operated. 
       BACKGROUND 
       [0003]    Motor vehicles having an automated start/stop mechanism, a deactivation of the internal combustion engine and an activation of the internal combustion engine, which follows in a short time, can occur. For this purpose, the fuel supply of the internal combustion engine is interrupted, so that the internal combustion engine comes to a stop. To start the internal combustion engine, a crankshaft of the internal combustion engine is set into motion with the aid of an electrical drive unit, in order to suction an ignitable fuel/air mixture into cylinders of the internal combustion engine and start it. However, there is a need to improve the starting comfort of internal combustion engines. 
         [0004]    It is at least one object of an embodiment to disclose measures with the aid of which good starting comfort of an internal combustion engine is made possible. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
       SUMMARY 
       [0005]    One embodiment relates to a method for operating an internal combustion engine, having the steps of ascertaining a possible instant of a stoppage of the internal combustion engine and injecting fuel to fill a cylinder of the internal combustion engine, the injection occurring shortly before the instant of the stoppage of the internal combustion engine. 
         [0006]    Because fuel is introduced one more time shortly before the stoppage of the internal combustion engine, at least one cylinder can still be filled with a fuel/air mixture using the last rotations of the crankshaft before the stoppage, so that a cylinder having an ignitable mixture is already provided for a subsequent start of the internal combustion engine. This cylinder can be ignited essentially immediately after the detection of a starting request, so that the full power of the internal combustion engine is available particularly rapidly. Good starting comfort of an internal combustion engine is thus made possible. In particular, the energy introduction of an electrical drive unit, for example, an electrical starter or a starter generator, can be reduced, because a significantly smaller angular amount of a rotation of the crankshaft is already sufficient so that the internal combustion engine can be operated independently without the aid of the electrical drive unit. Because of the lower demand for electrical energy for the electrical drive unit, more start/stop procedures are possible for the internal combustion engine until a motor vehicle battery, which is connected to the electrical drive unit, must first be recharged. This allows a reduction of the fuel consumption and results in a reduction of CO 2  emissions. In particular, it is possible to start an internal combustion engine having intake manifold injection rapidly and comfortably, because the duration until the fuel/air mixture reaches a cylinder of the internal combustion engine from the intake manifold can be taken into consideration at the instant of the injection of the fuel. The ascertainment of the possible instant of the stoppage of the internal combustion engine can be performed in particular by a detection of the curve of the angle and/or the speed of a crankshaft of the internal combustion engine, in that, for example, the instant at which the stoppage of the internal combustion engine will be reached is preferably estimated by an extrapolation of the detected curve. 
         [0007]    The injection preferably occurs one or two strokes before the instant of the stoppage of the internal combustion engine. This allows exclusively those cylinders of the internal combustion engine to be filled with an ignitable fuel/air mixture that are located during a following start of the internal combustion engine in a stroke phase that can provide a prompt power introduction upon immediate ignition. Fuel can thus be prevented from being moved unburned through a cylinder. 
         [0008]    During a subsequent start of the internal combustion engine, the cylinder filled with fuel is preferably immediately ignited. In particular, if the information about which cylinder of the internal combustion engine is filled with an ignitable fuel/air mixture is available through the ascertainment of the possible instant of the stoppage of the internal combustion engine, it is not necessary to initiate an ignition in all cylinders as a precaution, but rather exclusively in the cylinder which is located in the stroke phase suitable for this purpose. Furthermore, the period of time of an activated electrical drive unit can be reduced. 
         [0009]    Another embodiment relates to a method for operating an internal combustion engine, having the steps of monitoring the curve of the angle and/or the speed of a crankshaft of the internal combustion engine, storing the curve of the angle and/or the speed of the crankshaft over a defined minimum measuring period of time, in the case of a decelerating crankshaft, extrapolating the curve of the angle and/or the speed of the crankshaft, and determining the angle of the crankshaft upon an extrapolated stoppage of the crankshaft. This method and the refinements of the method described hereafter can particularly be combined with the above-described method. 
         [0010]    This makes it possible to establish which cylinder of the internal combustion engine, upon the stoppage of the internal combustion engine, is located in a stroke phase, in particular intake or compression, which allows immediate ignition of a fuel/air mixture after the detection of a starting request of the internal combustion engine. The fuel/air mixture can have been suctioned in shortly before the stoppage of the internal combustion engine or can be introduced into the cylinder suitable for this purpose immediately after the detection of the starting request of the internal combustion engine. This cylinder can be ignited essentially immediately after the detection of the starting request, so that the full power of the internal combustion engine is available particularly rapidly. Good starting comfort of an internal combustion engine is thus made possible. Upon a deactivation of the internal combustion engine, the curve of the angle and/or the speed of the crankshaft is essentially linear, so that the angle of the crankshaft and therefore the stroke phase of the cylinders of the internal combustion engine can be estimated very precisely by an essentially linear extrapolation. This information can be stored, so that the correct cylinder can be identified immediately upon a start of the internal combustion engine. In particular, the energy introduction of an electrical drive unit can be reduced, since a significantly smaller angular amount of a rotation of the crankshaft is already sufficient so that the internal combustion engine can be operated independently without the aid of the electrical drive unit. Because of the lesser demand for electrical energy for the electrical drive unit, more start/stop procedures for the internal combustion engine are possible until a motor vehicle battery, which is connected to the electrical drive unit, must first be recharged. This allows a reduction of the fuel consumption and results in a reduction of CO 2  emissions. 
         [0011]    In particular, a cylinder of the internal combustion engine which is located at the angle of the crankshaft upon an extrapolated stoppage of the crankshaft in its intake stroke or in its compression stroke is filled with fuel before the extrapolated stoppage of the crankshaft and is ignited immediately upon a subsequent start of the internal combustion engine. An ignitable fuel/air mixture is therefore already provided in the corresponding cylinder, which can be ignited immediately upon a start of the internal combustion engine. 
         [0012]    A particularly bidirectional crankshaft sensor is preferably used to determine the possible instant of the stoppage of the internal combustion engine and/or to monitor the curve of the angle and/or the speed of a crankshaft. The curve of the angle and the speed of the crankshaft can be determined simply and precisely by the crankshaft sensor. With the aid of the bidirectional crankshaft sensor, the cylinder which is filled with an immediately ignitable fuel mixture can be unambiguously determined, so that it is not necessary to first wait through two compression strokes in order to find out which cylinder located essentially in the state of top dead center (TDC) is located in the ignition TDC or in the charge cycle TDC. This allows the cylinder located in the ignition TDC, having the ignitable fuel mixture, to be ignited immediately after actuating a starter and the internal combustion engine to be started at once. 
         [0013]    Particularly preferably, measured values which were measured at a defined minimum period of time before the stoppage of the internal combustion engine are used to determine the possible instant of a stoppage of the internal combustion engine and/or to monitor the curve of the angle and/or the speed of a crankshaft. Irregularities of the crankshaft movement shortly before the stoppage thus cannot corrupt the measurement. 
         [0014]    In particular, an ignition is exclusively initiated in the cylinder filled with fuel to start the internal combustion engine. Because it is known through the extrapolated determination of the angle of the crankshaft which cylinder of the internal combustion engine is filled with an ignitable fuel/air mixture, it is not necessary to initiate an ignition in all cylinders as a precaution, but rather exclusively in the cylinder which is located in the stroke phase suitable for this purpose. Furthermore, the period of time of an activated electrical drive unit can be reduced. 
         [0015]    The internal combustion engine is preferably connected to an automatic start/stop mechanism. Due to the starting of the internal combustion engine shortly after a previous deactivation, it is particularly favorable for the starting comfort to be able to ignite a precisely identifiable cylinder which is filled with an ignitable fuel/air mixture. 
         [0016]    One embodiment relates to a control unit for operating an internal combustion engine, in particular for performing the above-described method, comprising an input port for inputting measured values about the angle and/or the speed of a crankshaft of the internal combustion engine, a storage unit for storing a time curve of the angle and/or the speed of the crankshaft of the internal combustion engine, a computer unit for calculating a possible instant of a stoppage of the internal combustion engine and/or the angle of the crankshaft upon an extrapolated stoppage of the crankshaft, and an output port for controlling a fuel supply and/or for controlling an ignition of a cylinder of the internal combustion engine. 
         [0017]    This allows, after the detection of a starting request of the internal combustion engine, an immediate ignition of a fuel/air mixture in a cylinder of the internal combustion engine to be performed. Good starting comfort of an internal combustion engine is thus made possible. The control unit can particularly be implemented and refined as described above on the basis of the method. 
         [0018]    In particular, the input port and/or the output port are connected to a data bus, in particular a CAN bus. This allows the ascertained information about the angle of the crankshaft to also be provided to other vehicle components and/or to be compared to other data, for example, for a plausibility check. Additionally or alternatively, the input port and/or the output port can preferably be exclusively connected to an engine control unit, to be able to exchange data particularly rapidly. 
         [0019]    The input port is preferably connected to an automatic start/stop mechanism of the internal combustion engine. A signal from an automatic start/stop mechanism can thus be considered promptly by the control unit, in order, in the event of a stop signal from the automatic start/stop mechanism, for example, to initiate measurements on the curve of the angle and/or the speed of the crankshaft and/or to determine an instant of the stoppage and/or to process the corresponding measurement results. 
         [0020]    One embodiment relates to a computer program product having program code means, which are stored on a computer-readable data carrier, in order to perform the above-described method when the program product is executed on a computer, in particular a control unit. The control unit can be implemented and refined as described above. Good starting comfort of an internal combustion engine is made possible with the aid of the computer program product. 
         [0021]    One embodiment relates to a computer program having coded instructions for performing the above-described method when the computer program is executed on a computer, in particular a control unit. The control unit can be implemented and refined as described above. Good starting comfort of an internal combustion engine is made possible with the aid of the computer program. The computer program can particularly be stored on the above-described computer program product, for example, a diskette, CD-ROM, DVD, memory, or a computer unit connected to the Internet. The computer program can particularly be designed as a compiled or uncompiled data sequence, which is preferably based on a higher-level, in particular object-based computer language, such as C, C++, Java, Smalltalk, Pascal, or Turbo Pascal. 
         [0022]    One embodiment relates to a signal sequence having computer-readable instructions for performing the above-described method when the signal sequence is processed by a computer, in particular a control unit. The control unit can be implemented and refined as described above. Good starting comfort of an internal combustion engine is made possible with the aid of the signal sequence. The signal sequence can be generated in particular with the aid of the above-described computer program and/or with the aid of the above-described computer program product. The signal sequence can be provided as electrical pulses and/or electromagnetic waves and/or optical pulses in a wireless or wired manner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
           [0024]      FIG. 1  shows a schematic diagram of a drivetrain; 
           [0025]      FIG. 2  shows a schematic graph of the time curve of parameters of the drivetrain shown in  FIG. 1 ; and 
           [0026]      FIG. 3  shows a schematic graph of the time curve of further parameters of the drivetrain shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The following detailed description is merely exemplary in nature and is not intended to limit application and uses. Furthermore, there is no intention to be bound by any theory presented in the preceding background or summary or the following detailed description. 
         [0028]    The drivetrain  10  shown in  FIG. 1  has an internal combustion engine  12  and a crankshaft  14 , which is driven by the internal combustion engine  12 . The internal combustion engine  12  has multiple cylinders  16 , which can be filled with fuel by a fuel supply  18 , in order to introduce a torque into the crankshaft  14  through combustion of a fuel/air mixture in the respective cylinder  16 . For this purpose, fuel is injected by the fuel supply  18  in the illustrated embodiment into an intake manifold  20  leading to the internal combustion engine  12 . Furthermore, an automatic start/stop mechanism  22 , which is connected to the internal combustion engine  12 , and which can automatically open and close the fuel supply  18 , is provided. 
         [0029]    The angle and the speed of the crankshaft  14  can be measured with the aid of a bidirectional crankshaft sensor  24  and supplied via an input port  26  to a control unit  28 . The control unit  28  has a storage unit  30  for storing the measured data obtained from the crankshaft sensor  24  according to the FIFO principle. The data stored in the storage unit  30  can be processed by a computer unit  32 , in order, in the event of a deactivation of the internal combustion engine triggered by the automatic start/stop mechanism  22 , to be able to estimate the angle of the crankshaft  14  at the instant of the stoppage of the crankshaft  14 , in particular by interpolation. In particular, the signals triggered by the automatic start/stop mechanism  22  can be input via the input port  26 , in order to start the corresponding calculation and be able to react early. With the aid of the information calculated by the control unit  28 , via an output port  34  of the control unit  28 , the fuel supply  18  can be opened shortly before the stoppage of the internal combustion engine  12 , so that a cylinder  16 , which is located in an intake or compression stroke in the stoppage of the crankshaft  14 , can be filled with an ignitable fuel/air mixture. Upon a subsequent start of the internal combustion engine  12 , which is triggered by the automatic start/stop mechanism  22 , this cylinder  16  can be ignited immediately, so that the full performance of the internal combustion engine  12  is available particularly rapidly and the start accordingly occurs comfortably. 
         [0030]    The method according to which the control unit  28  operates can be stored as a computer program  36  on a computer program product  38  in the form of a data memory and can operate the control unit  28  as a signal sequence  40 . The computer program product  38  can also be part of the control unit  28 , for example, as a computer unit  32  of the control unit  28 . 
         [0031]      FIG. 2  shows the time curve of a fuel quantity  42  and the time curve of a fuel quantity  44  of a comparative example. An illustrated time curve of a speed  46  and a time curve of a speed  48  of the comparative example result therefrom. Before reaching a stoppage instant  50 , in the invention, the fuel quantity  42  is increased, while in the comparative example the fuel quantity  44  is zero. At a common starting instant  52 , the respective internal combustion engine  12  is started, the speed  46  increasing more rapidly than in the case of the speed  48  of the comparative example. Experiments have shown that in the case of the embodiments, the internal combustion engine  12  can be operated without the aid of an electrical starter approximately 150 ms more rapidly. 
         [0032]    As shown in  FIG. 3 , an angle  54  of the crankshaft  14  at the stoppage instant  50  can be determined very well by an extrapolation straight line  56 . For this purpose, the curve of the speed  46  can be measured during the spinning down of the internal combustion engine  12  without fuel supply and extrapolated essentially linearly into the future, the corresponding angle  54  of the crankshaft being able to be estimated very precisely based on the stoppage instant  50  which can thus be calculated. A minimum period of time  58  before the stoppage instant  50  remains unconsidered in particular in this case, so that in particular irregularities shortly before the stoppage of the crankshaft  14  cannot impair the precision of the extrapolation. Furthermore, within the minimum period of time  58  after determining the extrapolation straight line  56 , the injection of fuel can be stopped shortly before the stoppage instant  50 , so that this injected fuel can still be suctioned into one of the cylinders  16 . 
         [0033]    While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.