Abstract:
The invention relates to a method for stopping an internal combustion engine, wherein an amount of air which is supplied via an air metering device of the internal combustion engine, in particular a throttle flap ( 100 ), is reduced after a stopping order has been detected. According to the invention, the amount of air which is supplied via the air metering device of the internal combustion engine is again increased when the detected speed (n) of the internal combustion engine falls below a predefinable speed threshold value (ns), wherein an intake cylinder (ZYL 2 ) to which the amount of air is supplied does not enter any working cycle after the amount of supplied air has been increased.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Particularly in the case of vehicles with start/stop technology, i.e. when the engine is frequently switched off and on again during normal driving operation, comfortable running down of the internal combustion engine and rapid restarting of the internal combustion engine is of great importance. 
         [0002]    JP-2008298031 A describes a method in which the throttle valve of the internal combustion engine is closed during rundown in order to suppress vibration. By means of this measure, the air charge in the cylinders in the internal combustion engine is reduced, thus reducing the roughness of rundown since compression and decompression are minimized. 
         [0003]    To restart the internal combustion engine, however, as much air as possible is required in the cylinders in which ignition takes place for the restart. There is therefore a conflict of aims between rapid engine starting (which requires a large quantity of air in the cylinder) and comfortable, i.e. low-vibration, engine rundown (which requires a small amount of air in the cylinder). This conflict of aims is resolved by means of the present invention. 
         [0004]    Devices which modify the stroke profile particularly of the inlet valves of the internal combustion engine and thus adjust the air charge in the cylinders are common knowledge in the prior art. In particular, the fact that the stroke profile of the inlet valves can be configured as desired within wide limits by means of electrohydraulic actuators is known. Internal combustion engines with such electrohydraulic valve adjustment do not require a throttle valve. It is likewise known that the stroke profile, particularly of the inlet valves, can be varied by adjusting the camshaft. Devices of this kind and the throttle valve, with which the air charge in the cylinders can be modified, are also referred to below as air metering devices. 
       SUMMARY OF THE INVENTION 
       [0005]    If a quantity of air supplied to the internal combustion engine is reduced by means of an air metering device and only increased again shortly before the internal combustion engine comes to a halt, “engine shake”, i.e. the generation of discernible vibration, can be avoided. This is achieved by initially reducing the quantity of air supplied to the internal combustion engine as the internal combustion engine runs down and increasing it again if a detected speed of the internal combustion engine has fallen below a speed threshold value. 
         [0006]    An increased quantity of air is then supplied to an inlet cylinder which is in an intake stroke immediately after or during the increase in the quantity of air supplied, and it then has an increased air charge. If this inlet cylinder then goes into a compression stroke, the increased air charge acts as a gas spring, which exerts a high restoring torque on a crankshaft via the inlet cylinder ZYL 2 . Conversely, the respective air charge in the cylinders which go into a downward movement exerts a torque on the crankshaft acting in the direction of the forward rotation of the crankshaft. However, since these cylinders going into a downward movement have a small air charge, the overall torque acting on the crankshaft is a restoring torque. 
         [0007]    If the speed threshold value is suitably chosen, it is possible to ensure that the inlet cylinder no longer goes into a power stroke after the increase in the quantity of air metered in. This has the advantage that compression of the increased air charge is avoided, preventing unwanted vibration. 
         [0008]    It is particularly advantageous if the speed threshold value is selected in such a way that the inlet cylinder just fails to go into the power stroke after the increase in the quantity of air metered in. If the speed threshold value is selected in such a way and if the speed of the internal combustion engine is higher than the speed threshold value when a request for restarting is detected, it is possible to implement a method for particularly rapid restarting of the internal combustion engine. 
         [0009]    In order to reliably select precisely the speed threshold value which ensures that the inlet cylinder just fails to go into the power stroke after the increase in the quantity of air metered in, the invention proposes an adaptation method. For this purpose, it is necessary to define suitable criteria, according to which the speed threshold value is reduced or increased. 
         [0010]    Reducing the speed threshold value if the inlet cylinder still passes through a top dead center position after the increase in the quantity of air metered in and before the internal combustion engine comes to a halt is a particularly simple way of ensuring that vibration due to impermissible passage through a top dead center position at a high air charge is suppressed during the subsequent operation of the internal combustion engine. 
         [0011]    Increasing the speed threshold value if the inlet cylinder no longer goes into a compression stroke after the increase in the amount of air metered in is a particularly simple way of ensuring that the inlet cylinder exhibits an oscillatory behavior when stopping during the subsequent operation of the internal combustion engine. 
         [0012]    Modifying the speed threshold value in accordance with a reverse oscillation angle is a particularly simple way of ensuring that the inlet cylinder exhibits a defined oscillatory behavior in the future operation of the internal combustion engine. 
         [0013]    Increasing the speed threshold value if the reverse oscillation angle is less than a specifiable minimum reverse oscillation angle ensures that the inlet cylinder just fails to reach the top dead center position with a particularly high degree of reliability. 
         [0014]    If the speed threshold value is increased to a specifiable initial threshold value, the adaptation method according to the invention has defined entry points and is therefore particularly robust. 
         [0015]    If the selected magnitude of the initial threshold value is such that the inlet cylinder reliably passes through the top dead center position, this ensures that the speed threshold value ns is always adapted starting from values that are too high, making the adaptation method particularly simple. 
         [0016]    The dead center positions are the simplest points at which to monitor the speed of the internal combustion engine. If the system determines, at one dead center position, that the speed has fallen below the speed threshold, the inlet cylinder is just going into the inlet stroke. If the quantity of air metered in by the air metering device is increased while the outlet valve of the inlet cylinder is still open, an increased quantity of air is pumped into an exhaust pipe from an intake pipe. This leads to disadvantageous noise generation. If, on the other hand, the quantity of air metered in by the air metering device is increased too late during the inlet stroke of the inlet cylinder, there is a high pressure drop between the intake pipe and the cylinder. In this case, the inflow of air leads to considerable unwanted noise generation. To minimize this noise generation, it is advantageous if the quantity of air metered in by the air metering device is increased immediately after the end of valve overlap in the inlet cylinder, i.e. immediately after the closure of the outlet valve. 
         [0017]    Since the internal combustion engine is halted, fuel injection is switched off. For rapid restarting of the internal combustion engine, this is disadvantageous since the cylinders do not contain an ignitable mixture. Since, in the method according to the invention, air is passed into the inlet cylinder from the intake pipe, it is possible to ensure, given appropriate injection before the end of the inlet stroke, that there is an ignitable fuel/air mixture in the inlet cylinder. Since the inlet cylinder comes to rest in the vicinity of a bottom dead center position or in the compression stroke, this is very advantageous for a rapid restart since a starter has to carry out a rotation of the crankshaft of just 180° before ignition can take place in the inlet cylinder. 
         [0018]    If the fuel is injected before or immediately after the inlet cylinder goes into the inlet stroke, this is particularly advantageous for mixture formation. In the case of intake pipe injection, the amount of fuel metered in can be particularly finely metered and, in the case of direct injection, early injection of fuel is advantageous for the turbulent mixing of air and fuel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Embodiments of the invention are explained in greater detail below with reference to the attached drawings, in which: 
           [0020]      FIG. 1  shows an illustration of a cylinder of an internal combustion engine, 
           [0021]      FIG. 2  shows schematically the profile of a number of characteristic quantities of the internal combustion engine as the internal combustion engine is stopped, 
           [0022]      FIG. 3  shows the sequence of the method according to the invention for stopping the internal combustion engine, 
           [0023]      FIG. 4  shows a speed profile during the stopping and restarting of the internal combustion engine, 
           [0024]      FIG. 5  shows a detailed view of the speed profile during the stopping and restarting of the internal combustion engine, 
           [0025]      FIG. 6  shows the sequence of the method according to the invention during the restarting of the internal combustion engine, 
           [0026]      FIG. 7  shows schematically a final oscillatory motion of the internal combustion engine at different speed threshold values, and 
           [0027]      FIG. 8  shows the sequence of the method according to the invention for determining the speed threshold value. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]      FIG. 1  shows a cylinder  10  of an internal combustion engine having a combustion chamber  20 , a piston  30 , which is connected by a connecting rod  40  to a crankshaft  50 . The piston  30  performs an up and down motion in a known manner. The reversal points of the motion are referred to as dead center positions. The transition from an upward motion to a downward motion is referred to as the top dead center position, while the transition from a downward motion to an upward motion is referred to as the bottom dead center position. An angular position of the crankshaft  50 , referred to as a crank angle, is conventionally defined relative to the top dead center position. A crankshaft sensor  220  detects the angular position of the crankshaft  50 . 
         [0029]    Air to be combusted is sucked into the combustion chamber  20  via an intake pipe  80  in a known manner during a downward motion of the piston  30 . This is referred to as the intake stroke or inlet stroke. The combusted air is forced out of the combustion chamber  20  via an exhaust pipe  90  during an upward motion of the piston  30 . This is usually referred to as the exhaust stroke. The quantity of air sucked in via the intake pipe  80  is set by means of an air metering device, in the illustrative embodiment a throttle valve  100 , the position of which is determined by a control device  70 . 
         [0030]    Via an intake pipe injection valve  150 , which is arranged in the intake pipe  80 , fuel is injected into the air sucked out of the intake pipe  80 , and a fuel/air mixture is produced in the combustion chamber  20 . The quantity of fuel injected through the intake pipe injection valve  150  is determined by the control device  70 , generally by means of the duration and/or level of an activation signal. A spark plug  120  ignites the fuel/air mixture. 
         [0031]    An inlet valve  160  at the inlet from the intake pipe  80  to the combustion chamber  20  is driven via cams  180  by a camshaft  190 . An outlet valve  170  at the inlet from the exhaust pipe  90  to the combustion chamber  20  is likewise driven via cams  182  by the camshaft  190 . The camshaft  190  is coupled to the crankshaft  50 . The camshaft  190  generally performs one revolution for every two revolutions of the crankshaft  50 . The camshaft  190  is designed in such a way that the outlet valve  170  opens in the exhaust stroke and closes in the vicinity of the top dead center position. The inlet valve  160  opens in the vicinity of the top dead center position and closes in the inlet stroke. A phase in which the outlet valve  170  and the inlet valve in one system are opened simultaneously is referred to as valve overlap. Such valve overlap is used for internal exhaust gas recirculation, for example. The camshaft  190  can be designed, in particular, for activation by the control device  70 , making it possible to set different stroke profiles for the inlet valve  160  and the outlet valve  170  in accordance with the operating parameters of the internal combustion engine. However, it is also possible for the inlet valve  160  and the outlet valve  170  not to be moved up and down by means of the camshaft  190  but by means of electrohydraulic valve actuators. In this case, the camshaft  190  and the cams  180  and  182  can be omitted. There is likewise no need for the throttle valve  100  with such electrohydraulic valve actuators. 
         [0032]    A starter  200  can be connected mechanically to the crankshaft  50  by a mechanical coupling  210 . The production of the mechanical connection between the starter  200  and the crankshaft  50  is also referred to as meshing. Release of the mechanical connection between the starter  200  and the crankshaft  50  is also referred to as disengagement. Meshing is possible only if the speed of the internal combustion engine is below a speed threshold value dependent on the internal combustion engine and the starter. 
         [0033]      FIG. 2  shows the behavior of the internal combustion engine as the internal combustion engine is stopped.  FIG. 2   a  shows the sequence of the various strokes of a first cylinder ZYL 1  and of a second cylinder ZYL 2 , plotted against the angle of the crankshaft KW. A first dead center position T 1 , a second dead center position T 2 , a third dead center position T 3 , a fourth dead center position T 4  and a fifth dead center position T 5  of the internal combustion engine are plotted. Between these dead center positions, the first cylinder ZYL 1  runs through the exhaust stroke, the inlet stroke, a compression stroke and a power stroke in a known manner. In the illustrative embodiment of an internal combustion engine having four cylinders, the strokes of the second cylinder ZYL 2  are offset by 720°/4=180°. Based on the first cylinder ZYL 1 , the first dead center position T 1 , the third dead center position T 3  and the fifth dead center position T 5  are bottom dead center positions, while the second dead center position T 2  and the fourth dead center position T 4  are top dead center positions. Based on the second cylinder ZYL 2 , the first dead center position T 1 , the third dead center position T 3  and the fifth dead center position T 5  are top dead center positions, while the second dead center position T 2  and the fourth dead center position T 4  are bottom dead center positions. 
         [0034]      FIG. 2   b  shows the profile of a speed n of the internal combustion engine against time t in parallel with the strokes illustrated in  FIG. 2   a . The speed n is defined as the time derivative of the crank angle KW, for example. The first dead center position T 1  corresponds to a first time t 1 , the second dead center position T 2  corresponds to a second time t 2 , the third dead center position T 3  corresponds to a third time t 3 , and the fourth dead center position T 4  corresponds to a fourth time t 4 . Between each two successive times, e.g. between the first time t 1  and the second time t 2 , the speed initially rises briefly, and then falls monotonically. The brief rise in speed is due to the compression of the air charge in the cylinders. A cylinder running through a top dead center position compresses the air charge therein to the maximum extent, and therefore compression energy is stored therein. Part of this compression energy is converted into rotational energy as the internal combustion engine continues to rotate. 
         [0035]      FIG. 2   c  shows the time profile of an activation signal DK of the throttle valve  100  in parallel with  FIG. 2   a  and  FIG. 2   b . As is known from the prior art, the throttle valve  100  is initially closed as the internal combustion engine is stopped, this corresponding to a first activation signal DK 1 . If, as illustrated in  FIG. 2   b , the speed n of the internal combustion engine falls below a speed threshold value ns, e.g. 300 rpm, then, according to the invention, the throttle valve  100  is opened at an opening time tauf, corresponding to a second activation signal DK 2 . Here, the opening time tauf is selected in such a way that it occurs shortly after the third dead center position T 3 , which is the next dead center position after the speed n of the internal combustion engine falls below the speed threshold value ns. At the third dead center position T 3 , the second cylinder ZYL 2  goes into the inlet stroke. In what follows, therefore, it is also referred to as inlet cylinder ZYL 2 . In the illustrative embodiment, the opening time tauf coincides with the end of valve overlap in the inlet cylinder, i.e. with the time at which the outlet valve  170  of the inlet cylinder ZYL 2  closes. Based on the top dead center position of the inlet cylinder ZYL 2 , the opening time tauf corresponds to an opening crank angle KWauf. To determine the time at which the speed n of the internal combustion engine has fallen below the speed threshold value ns, the speed n of the internal combustion engine can either be monitored continuously. Since the rise in the speed n of the internal combustion engine is small after the dead center positions, and the opening time tauf is supposed to be shortly after a dead center position, however, it is also possible to check at each dead center position of the internal combustion engine whether the speed n of the internal combustion engine has fallen below the speed threshold ns. In the illustrative embodiment illustrated in  FIG. 2   b , the fact that the speed n of the internal combustion engine has not yet fallen below the speed threshold ns is detected at the first time t 1  and the second time t 2 . At the third time t 3 , the system detects for the first time that the speed n of the internal combustion engine has fallen below the speed threshold ns, and the throttle valve  100  opens. 
         [0036]    The opening of the throttle valve  100  then allows a large quantity of air to flow into the inlet cylinder in the inlet stroke. If the inlet cylinder ZYL 2  goes into the compression stroke after the fourth time t 4 , the compression work to be performed on the air charge, which is greatly increased relative to the other cylinders, exceeds the compression energy released in the expanding cylinders, and the speed n of the internal combustion engine falls rapidly until it falls to zero at a reverse oscillation time tosc. The rotary motion of the crankshaft  50  is now reversed, and the speed n of the internal combustion engine becomes negative. The reverse oscillation time tosc corresponds to a reverse oscillation angle RPW of the crankshaft  50  which is indicated in  FIG. 2   a . At a stop time tstopp, the internal combustion engine comes to a halt. It should be noted that the time axis is depicted in a nonlinear manner. In accordance with the drop in the speed n of the internal combustion engine, the time interval between the third time t 3  and the fourth time t 4  is longer than the time interval between the second time t 2  and the third time t 3 , which in turn is longer than the time interval between the first time t 1  and the second time t 2 . The fifth dead center position T 5  of the internal combustion engine is not reached. In the time interval between the reverse oscillation time tosc and the stop time tstopp, the crankshaft  50  performs an oscillatory motion, during which the second cylinder ZYL 2  oscillates in the compression stroke and the inlet stroke thereof, while the first cylinder ZYL 1  oscillates in a corresponding manner in the power stroke and the compression stroke thereof. 
         [0037]      FIG. 3  shows the sequence of the method, which corresponds to the method illustrated in  FIG. 2 . With the internal combustion engine running, it is determined in a stop detection step  1000  that the intention is to switch off the internal combustion engine. This is followed by step  1010 , in which injection and ignition are switched off. The internal combustion engine is thus in the rundown mode. There then follows step  1020 , in which the throttle valve is closed. In the case of internal combustion engines with camshaft adjustment, a switchover to a smaller cam can take place in step  1020  as an alternative, thus reducing the air charge in the cylinders. In the case of internal combustion engines with electrohydraulic valve adjustment, the valves of the internal combustion engine can be closed in step  1020 . There follows step  1030 , in which the system checks whether the speed n of the internal combustion engine has fallen below the speed threshold value ns. If this is the case, step  1040  follows. If this is not the case, step  1030  is repeated until the speed n of the internal combustion engine has fallen below the speed threshold value ns. In step  1040 , the throttle valve  100  is opened at opening time tauf. In the case of internal combustion engines with camshaft adjustment, it is possible instead for a switch to be made to a larger cam in step  1040 , for example, resulting in an increase in the air charge in the inlet cylinder ZYL 2 . In the case of internal combustion engines with electrohydraulic valve adjustment, the inlet valve  160  of the inlet cylinder ZYL 2  can be activated in such a way in step  1040  that it is open during the inlet stroke of the inlet cylinder ZYL 2 , thus increasing the air charge in the inlet cylinder ZYL 2 . There follows step  1060 . In the optional step  1060 , fuel is injected via the intake pipe injection valve  150  into the intake pipe  80  of the internal combustion engine. This injection of fuel is performed in such a way that a fuel/air mixture is sucked into the inlet cylinder ZYL 2  in the inlet stroke. In step  1100 , the method according to the invention ends. As illustrated in  FIG. 2   b , the internal combustion engine oscillates into a stationary position, in which the inlet cylinder ZYL 2  comes to rest in the inlet stroke or in the compression stroke. Injection of fuel in step  1060  is advantageous for rapid restarting of the internal combustion engine when it is an internal combustion engine with intake pipe injection. 
         [0038]      FIG. 4  shows the time profile of the speed n of the internal combustion engine when stopping and restarting. The speed n of the internal combustion engine falls during a rundown phase T_Auslauf in the manner illustrated in  FIG. 2   b , and finally the sign changes when the rotary motion of the internal combustion engine is reversed at the reverse oscillation time tosc illustrated in  FIG. 2   b . This is illustrated in  FIG. 4  as the end of the rundown phase T_Auslauf and the beginning of an oscillation phase T_Pendel. While the rundown phase T_Auslauf is still ongoing, the system determines at a starting request time tstart that the internal combustion engine is to be restarted because, for example, the system has detected that a driver has pressed a gas pedal. A determined start request of this kind before the stop time tstopp, is also referred to as a “change of mind”. In the oscillation phase T_Pendel, the profile of the speed n of the internal combustion engine undergoes a resulting variation until it falls to a constant zero at the stop time tstopp illustrated in  FIG. 2   b  and remains there. In  FIG. 4 , the stop time tstopp marks the end of the oscillation phase T_Pendel. 
         [0039]    In the prior art method for starting the internal combustion engine, the oscillation phase T_Pendel is followed by detection of the fact that the internal combustion engine is stationary, the starter  200  is meshed, and the starter is activated. After an activation dead time T_tot of the starter  200  of, for example, 50 ms, which is not illustrated in  FIG. 4 , the starter  200  begins a rotary motion at a time tSdT and thus imparts motion to the crankshaft  50  once again. In the method according to the invention, in contrast, a first meshing time tein 1  and, if appropriate, a second meshing time tein 2  is determined. The first meshing time tein 1  and the second meshing time tein 2  are characterized in that the speed n of the internal combustion engine is sufficiently low for the starter  200  to be meshed. The first meshing time tein 1  and the second meshing time tein 2  are determined by the control device  70 . If the time interval between the starting request time tstart and the first meshing time tein 1  is longer than the activation dead time T_tot, the starter  200  is meshed and activated in such a way that it begins a rotary motion at the first meshing time tein 1 . If the first meshing time tein 1  is too close in time to the starting request time tstart, the starter  200  is meshed and activated in such a way that it begins a rotary motion at the second meshing time tein 2 . 
         [0040]      FIG. 5  illustrates in detail the selection of the first meshing time tein 1  and the second meshing time tein 2 . As described, the speed n of the internal combustion engine falls rapidly to zero after the opening time tauf, and the internal combustion engine begins a reverse motion at reverse oscillation time t_osc. The first meshing time tein 1  is determined by means of characteristic maps or by means of models stored in the control device  70 , for example, after the opening of the throttle valve  100  and corresponds to the estimated reverse oscillation time tosc. It is, of course, also possible for different times at which the speed n of the internal combustion engine passes through zero to be predicted and selected as the first meshing time tein 1  instead of the reverse oscillation time tosc. 
         [0041]    In addition to the passage of the speed n of the internal combustion engine through zero, a second meshing time tein 2  can be selected, from which time onwards it is ensured that the speed n of the internal combustion engine will no longer leave a speed range in which meshing of the starter  200  is possible. This speed range is given, for example, by a positive threshold nplus, e.g. 70 rpm, up to which the starter  200  can be meshed during a forward rotation of the internal combustion engine, and by a negative threshold nminus, e.g. 30 rpm, up to which the starter  200  can be meshed during a reverse rotation of the internal combustion engine. Using characteristic maps, for example, the control device  70  calculates that the kinetic energy of the internal combustion engine has fallen from the second meshing time tein 2  to such an extent that the speed range [nminus, nplus] will no longer be exceeded. At the second meshing time tein 2  or at any time after the second meshing time tein 2 , the starter  200  can be meshed and made to perform a rotary motion. 
         [0042]      FIG. 6  shows the sequence of the method according to the invention for restarting the internal combustion engine. Step  2000  coincides with step  1000  illustrated in  FIG. 3 . In this step, a request to stop the internal combustion engine is determined. There follows step  2005 . In step  2005 , the throttle valve is closed, or other measures, e.g. adjustment of the cams  180 ,  182  or appropriate electrohydraulic activation of the valves  160  and  170 , are taken in order to reduce the air charge in the cylinders. There follows step  2010 . 
         [0043]    In step  2010 , the system determines whether a start request for starting the internal combustion engine is determined while the internal combustion engine is still running down, i.e. during the rundown phase T_Auslauf illustrated in  FIG. 4 . If this is the case, step  2020  follows. If this is not the case, step  2090  follows. In step  2020 , the system checks whether the speed n of the internal combustion engine is above the speed threshold value ns (if appropriate by a minimum amount, e.g. 10 revolutions per minute). These checks can take place continuously or in synchronism with the crankshaft, in particular at each dead center position of the internal combustion engine. If the speed n of the internal combustion engine is above the speed threshold value ns, step  2030  follows and otherwise step  2070  follows. 
         [0044]    In step  2030 , the throttle valve is opened, or other measures, e.g. adjustment of the cams  180 ,  182  or appropriate electrohydraulic activation of the valves  160  and  170 , are taken in order to increase the air charge in the cylinder which is the next to be in the inlet stroke. Via the intake pipe injection valve  50 , fuel is injected into the intake pipe  80 . There follows step  2040 , in which the inlet cylinder ZYL 2  is determined, i.e. the cylinder in which the air charge will be the next to show a significant increase in the inlet stroke. The inlet cylinder ZYL 2  goes into the inlet stroke and sucks in the fuel/air mixture in the intake pipe  80 . The inlet cylinder ZYL 2  then makes a transition to the compression stroke. The speed n is higher than the speed threshold value ns. The speed threshold value ns is selected in such a way that the inlet cylinder ZYL 2  just fails to pass through a top dead center position. At the speed n of the internal combustion engine, it is therefore ensured that the inlet cylinder ZYL 2  passes through a top dead center position once again and makes a transition to the power stroke. There follows step  2050 . In step  2050 , the fuel/air mixture in the inlet cylinder ZYL 2  is ignited, accelerating the rotation of the crankshaft  50 , and step  2060  follows. In step  2060 , further measures are carried out in order to bring about starting of the internal combustion engine, in particular a fuel/air mixture being ignited in a corresponding manner in the other cylinders of the internal combustion engine. With the starting of the internal combustion engine, the method according to the invention ends. 
         [0045]    In step  2070 , fuel is injected into the intake pipe  80  via the intake pipe injection valve  150 . There follows step  2100 . 
         [0046]    In step  2090 , the system checks, in a manner corresponding to step  1030  illustrated in  FIG. 3 , whether the speed n of the internal combustion engine has fallen below the speed threshold value ns. If this is not the case, the program branches back to step  2010 . If this is the case, step  2100  follows. 
         [0047]    Step  2100  corresponds to step  1040  in  FIG. 3 . The throttle valve is opened or some other air metering device, e.g. a camshaft adjustment system or an electrohydraulic valve timing system, is activated in such a way that the quantity of air supplied is increased. There follows step  2110 . 
         [0048]    In step  2110 , the system determines whether there is a request for starting the internal combustion engine. If this is the case, step  2120  follows. If this is not the case, step  2110  is repeated until there is a request for starting the internal combustion engine. In step  2120 , the system checks whether the internal combustion engine is stationary. This corresponds to the time period illustrated in  FIG. 4  following the end of the oscillation phase T_Phase. If this is the case, step  2060  follows, in which conventional measures for starting the internal combustion engine are carried out. As illustrated in  FIG. 4 , the internal combustion engine is started at a time tSdT. 
         [0049]    If the internal combustion engine is not stationary in step  2120 , step  2150  follows. In step  2150 , the first meshing time tein 1  is predicted. This prediction is performed by means of a characteristic map, for example. Using the speed n which was determined during a previous passage through the top dead center position of the inlet cylinder ZYL 2  (at the fourth time t 4  in the illustrative embodiment), the kinetic energy of the internal combustion engine can be determined and, from the second position DK 2  of the air metering device, the air charge in the inlet cylinder ZYL 2  and hence the strength of the gas spring compressed by the inlet cylinder ZYL 2  in the compression stroke can be estimated. From this, it is possible to estimate the reverse oscillation time tosc, which is predicted as the first meshing time tein 1 . There follows step  2160 , in which the system checks whether the time difference between the first meshing time tein 1  and the present time is greater than the activation dead time T_tot of the starter  200 . If this is the case, step  2170  follows. If this is not the case, step  2180  follows. 
         [0050]    In step  2180 , the second meshing time tein 2  is determined. As explained in  FIG. 5 , the second meshing time tein 2  is selected in such way that the speed n of the internal combustion engine from the second meshing time tein 2  onwards remains in the speed interval between the negative threshold nminus and the positive threshold nplus. In the following step  2190 , the starter  200  is meshed and starting is carried out from the second meshing time tein 2 . There follows step  2060 , in which the further measures for starting the internal combustion engine are carried out. As an alternative, it is also possible, in step  2180 , to determine a meshing interval, during which the speed n remains between the negative threshold nminus and the positive threshold nplus. In this case, the starter  200  is meshed and starting carried out in the meshing interval in step  2190 . 
         [0051]    Instead of an intake pipe injection valve  150 , it is also conceivable for injection valves of the internal combustion engine to be arranged in the combustion chamber, i.e. to be configured as a direct injection valve. In this case, injection of fuel into the intake pipe immediately after the opening of the throttle valve can be omitted. The only factor of importance is that fuel should be injected in a suitable manner into the inlet cylinder ZYL 2  before it is ignited upon restarting. 
         [0052]      FIG. 7  illustrates the selection of the speed threshold value ns.  FIG. 7   a  illustrates the oscillatory behavior of the inlet cylinder ZYL 2  when the speed threshold value ns is correctly selected. At the opening crank angle KWauf, the inlet cylinder ZYL 2  is in forward motion, passes through the bottom dead center position UT corresponding to the fourth dead center position T 4  and reverses its direction of rotation at the reverse oscillation angle RPW. The further oscillatory motion of the inlet cylinder ZYL 2  up to the stationary condition is shown only indicatively in  FIG. 7   a.    
         [0053]      FIG. 7   b  illustrates the oscillatory behavior of the inlet cylinder ZYL 2  if the speed threshold value ns selected is too high. A speed threshold value ns which is too high means that the kinetic energy of the internal combustion engine is too high when the throttle valve  100  is opened, i.e. at the opening crank angle KWauf. This leads to the inlet cylinder ZYL 2  passing through the bottom dead center position UT corresponding to the fourth dead center position T 4  and then also the top dead center position OT corresponding to the fifth dead center position T 5 . This leads to unwanted vibration in the drive train, and is felt to be uncomfortable by the driver. 
         [0054]      FIG. 7   c  illustrates the oscillatory behavior of the inlet cylinder ZYL 2  if the speed threshold value ns selected is too low. A speed threshold value ns which is too low means that the kinetic energy of the internal combustion engine is too low when the throttle valve  100  is opened, i.e. at the opening crank angle KWauf. The inlet cylinder ZYL 2  passes through the bottom dead center position UT corresponding to the fourth dead center position, but has a relatively large reverse oscillation angle RPW. If, in step  3020 , it is determined that the speed n of the internal combustion engine is higher than the speed threshold value ns, it is no longer safe to assume that the inlet cylinder ZYL 2  will rotate beyond the top dead center position OT and hence that it will be possible to start the internal combustion engine quickly. 
         [0055]    The selection of the speed threshold value ns is therefore of central importance for the functioning of the method according to the invention but, on the other hand, it is very difficult since it depends on variables which change during the life of the internal combustion engine, e.g. the friction coefficient of the engine oil used. 
         [0056]      FIG. 8  describes an adaptation method, by means of which an initially specified speed threshold value ns can be adapted in order to compensate for errors in the initialization or changes in the properties of the internal combustion engine. In step  3000 , it is determined that there is a stop request to the internal combustion engine, and measures for starting the internal combustion engine are initiated. In step  3010 , the system checks, in a manner corresponding to step  1030 , whether the speed n of the internal combustion engine has fallen below the speed threshold ns. If this is the case, step  3020  follows, in which the throttle valve is opened in a manner corresponding to step  1040 . There follows step  3030 , in which the system checks whether the inlet cylinder ZYL 2  has already passed through the bottom dead center position UT. If this is not the case, step  3040  follows. If it is the case, step  3060  follows. 
         [0057]    Step  3040  takes account of the case where the speed threshold value ns selected is so low that the internal combustion engine comes to a halt even before the inlet cylinder ZYL 2  passes through the bottom dead center position UT. For this purpose, the system checks in step  3040  whether the internal combustion engine is stationary. If this is not the case, the program branches back to step  3030 . If the internal combustion engine is stationary, step  3050  follows. In step  3050 , the speed threshold value ns is increased. There follows step  3100 , with which the method ends. 
         [0058]    In step  3060 , the rotary motion of the internal combustion engine is monitored. If the internal combustion engine turns the inlet cylinder ZYL 2  further beyond the top dead center position OT, step  3070  follows. If the top dead center position OT is not reached, step  3080  follows. In step  3070 , the behavior is as illustrated in  FIG. 7   b , and the speed threshold value ns is reduced. There follows step  3100 , with which the method ends. 
         [0059]    In step  3080 , the reverse oscillation angle RPW is determined by means of the crankshaft sensor  220 , for example. There follows step  3090 . In step  3090 , the system checks whether the reverse oscillation angle RPW is smaller than a minimum reverse oscillation angle RPWS, which is 10° for example. If the reverse oscillation angle RPW is smaller than the minimum reverse oscillation angle RPWS, the correct behavior shown in  FIG. 7   a  is present, and step  3100  follows, with which the method ends. If the reverse oscillation angle RPW is larger than the minimum reverse oscillation angle RPWS, the behavior illustrated in  FIG. 7   c  is present, and step  3050  follows, in which the speed threshold value ns is increased. 
         [0060]    The increase in the speed threshold value ns in step  3050  can either take place incrementally or the speed threshold value ns is increased to an initial threshold value nsi, at which it is ensured that the internal combustion engine exhibits the behavior illustrated in  FIG. 7   b , i.e. that the speed threshold value ns selected is then initially too high. The initial threshold value nsi can be designed as an applicable threshold value, for example. It is selected in such a way that, within the scope of the operating parameters that are possible during the operation of the internal combustion engine, e.g. variations in the leakage of the air charge, differences in the engine oil or individual differences in the scatter of the frictional effect of the internal combustion engine, the internal combustion engine exhibits the behavior illustrated in  FIG. 7   b , i.e. that the inlet cylinder ZYL 2  goes into the power stroke. 
         [0061]    As an option, it is also possible for the adaptation of the speed threshold value ns to be carried out when restarting of the internal combustion engine has not taken place correctly: the speed threshold value ns is increased if the system has decided in step  2020  that the determined speed n of the internal combustion engine is higher than the speed threshold value ns and if, after steps  2030 ,  2040  and  2050  are carried out, it is ascertained in step  2060  that the inlet cylinder ZYL 2  (ZYL 2 ) has not gone into the power stroke.