Abstract:
An internal combustion engine includes a charge motion flap which influences the combustion in at least one combustion chamber of the internal combustion engine. The function of the charge motion flap is monitored. At least one actual value of a variable characterizing the combustion in the combustion chamber is evaluated and the evaluation result is used for function monitoring of the charge motion flap.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method for operating an internal combustion engine. The present invention further relates to a computer program, an electric memory medium, and a control and/or regulating device.  
       BACKGROUND INFORMATION  
       [0002]     In modern internal combustion engines, in particular those having direct fuel injection, it has been attempted to positively influence the mixture preparation in the combustion chambers in order to achieve optimum conversion of the injected fuel into mechanical energy. In this connection, a comparatively high turbulence of the air charge (“charge motion”) within the combustion chamber is favorable. An increased charge motion or turbulence has a positive impact on the mixture preparation and reduces the exhaust gas emissions.  
         [0003]     In order to adjust the motion of the air charge within the combustion chambers, a specific actuator is present in the air intake system in many internal combustion engines, which influences the flow rate of the drawn-in air or of the drawn-in air-fuel mixture by unblocking a variable cross section. Such an actuator is known as a charge motion flap, tumble valve, or swirl valve.  
         [0004]     In some countries, it is required by law to monitor the function of the charge motion flap (tumble flap) using OBD (“onboard diagnosis”). In this connection, it is tested if an actual position of the charge motion flap corresponds to a setpoint position required by an engine controller. To this end, the charge motion flap has formerly been coupled to at least one position sensor, which reports the actual position of the charge motion flap to the engine controller. Switch contacts at the end positions of the charge motion flap or potentiometers for continuous recording are known.  
         [0005]     An object of the present invention is to refine a method of the type described above so that the internal combustion engine may be manufactured as economically as possible.  
       SUMMARY OF THE INVENTION  
       [0006]     The use of the method according to the present invention makes it possible to monitor the function of an actuator, which influences the combustion in a combustion chamber of the internal combustion engine, for example, a charge motion flap or even a spark plug, without the necessity of additional sensors. Instead, a variable characterizing the combustion in the combustion chamber is evaluated and the function of the actuator is indirectly monitored from the result of this evaluation.  
         [0007]     Such variables characterizing the combustion in the combustion chamber are already recorded in modern internal combustion engines. To this end, pressure sensors are used, for example, which directly detect the pressure in at least one combustion chamber of the internal combustion engine. Structure-borne sound sensors or ion-current sensors may also be used to detect a variable characterizing the combustion in a combustion chamber.  
         [0008]     The basis of the known method is a known dependence of the combustion process on the function of the actuator to be monitored. In the case of a charge motion flap, for example, the turbulence (“charge motion”) in the combustion chamber is directly a function of the position of the charge motion flap, and the combustion process is in turn a function of this turbulence. The greater this turbulence the faster is the conversion of the fuel during the combustion. Variables that are meaningful in particular for characterizing the combustion are therefore combustion characteristic, heating characteristic, and combustion duration. The heating characteristic is preferred in particular since it is comparatively simple to calculate because wall heat losses are not taken into consideration.  
         [0009]     It is advantageous in particular if the combustion duration is determined from an energy conversion, which is calculated using a polytropic equation of state. The combustion duration may be understood, for example, as a crank angle between two percentage values (for example, 10% and 90%) of the energy conversion. The energy conversion is determined in a recording occurring in a time slot pattern of, for example, the cylinder pressure during a combustion cycle by an iterative equation of state and a continuous integration. This is possible with low computational complexity.  
         [0010]     In a specific type of monitoring, a setpoint value for the variable characterizing the combustion is determined as a function of a setpoint operating position of the actuator and an actual operating point of the internal combustion engine and is compared to the actual value, and an action is performed as a function of the result of the comparison. The operating point of the internal combustion engine is defined, for example, by its speed, an air charge, a set rate of exhaust gas recirculation, etc.  
         [0011]     If, for example, the combustion duration is used as a characterizing variable, an actual combustion duration is compared to a setpoint combustion duration. To this end, for example, the difference between a setpoint combustion duration and an actual combustion duration may be compared to a positive and a negative limiting value. These two values take into consideration the tolerances of the calculation of the actual value and the setpoint value. As an action, for example, information may be stored concerning a prohibited deviation of the present charge motion in the combustion chamber so that this may be remedied during servicing, and/or this information may be displayed via suitable devices.  
         [0012]     It is an advantage if the action is only performed if the deviation of the actual value from the setpoint value exceeds the limiting value during a specific number of working cycles in succession. This increases the reliability of the function monitoring. For determining the setpoint value, advantageously at least one characteristic map or characteristic function is used which, for example, was defined in advance on a test bench and stored for the function monitoring.  
         [0013]     However, a determined deviation of the actual value from the setpoint value may also be used for a regulation of the actuator. In this manner, the deviation is minimized and the combustion characteristics are optimized accordingly.  
         [0014]     An extension of the present invention provides that a changed control signal is supplied to the actuator during the operation of the internal combustion engine, and a corresponding change of a setpoint value of the variable characterizing the combustion is determined and a change of the actual value of the variable characterizing the combustion is then compared to the change of the setpoint value.  
         [0015]     The change of the control signal is advantageously selected in such a way that no change of torque or another change of the internal combustion engine behavior noticeable to the user of the internal combustion engine occurs. If the change of the actual value is at least roughly equal to the change of the setpoint value, this means that the actuator is functional. This procedure has the advantage that function monitoring is decoupled from additional influencing variables, which may if necessary be able to influence the variable characterizing the combustion. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  shows a schematic representation of an internal combustion engine.  
         [0017]      FIG. 2  shows a flow chart of a method for operating the internal combustion engine of  FIG. 1 .  
         [0018]      FIG. 3  shows a diagram in which energy transformed during combustion in a combustion chamber of the internal combustion engine of  FIG. 1  is plotted against a crank angle. 
     
    
     DETAILED DESCRIPTION  
       [0019]     In  FIG. 1 , an internal combustion engine is denoted in its entirety by reference numeral  10 . It is used to drive a motor vehicle, which is not shown, and includes an engine block  12  having a plurality of combustion chambers, of which only one in the present case is denoted by reference numeral  14 . Combustion air enters combustion chamber  14  through, among other things, a charge motion channel  16  in which a charge motion flap  18  is situated as an actuator.  
         [0020]     Charge motion channel  16  and charge motion flap  18  are used to produce the greatest possible turbulence (“charge motion”) and thus convert the injected fuel into mechanical energy in as optimal a manner as possible. This favorably influences the fuel consumption and emissions characteristics of internal combustion engine  10 .  
         [0021]     To this end, it is possible to change the position of charge motion flap  18  based on a corresponding control signal U_LBK. This is provided by a control and regulating device  20 . For the control and regulation of internal combustion engine  10 , control and regulating device  20  receives numerous input signals, as well as from an HFM Sensor  22 , which detects the air mass flowing to combustion chamber  14 , from which a corresponding air charge rl is determined in control and regulating device  20 .  
         [0022]     Control and regulating device  20  also receives signals from pressure sensors, of which only one is provided with a reference numeral  24  in  FIG. 1 , specifically the one which detects the pressure in combustion chamber  14 . The curve of the pressure in combustion chamber  14  and variables derived from it are used as input signals for various control and regulating functions. Additional output signals of control and regulating device  20  are, for example, activation signals for fuel metering and control of the ignition of the air-fuel mixture located in combustion chamber  14 .  
         [0023]     For the correct operation of internal combustion engine  10 , it is important to know if charge motion flap  18  functions properly, i.e., its actual position corresponds with a setpoint position. If this is not the case, allowable limiting values for exhaust gas emissions are exceeded and control and regulating device  20  determines non-optimal control signals (for example, ignition points).  
         [0024]     For monitoring of the correct function of charge motion flap  18 , a procedure is followed, which is stored as a computer program in a memory of control and regulating device  20 . This method will now be explained with reference to  FIGS. 2 and 3 .  
         [0025]     In  26 , it is queried whether a combustion cycle starts within a working cycle. If the answer is YES, a pressure p i  is detected in  28 . The corresponding signal is provided by pressure sensor  24 . Pressure p i  is detected repetitively in discrete time steps i=1 to m by incrementing a time step index i in  29 . The corresponding values p i  are stored for the individual time steps i (or crank angle KW of a crankshaft of internal combustion engine  10  which is not shown in  FIG. 1 ) in  30 . In  32  it is queried whether the combustion cycle has ended. If the answer is YES, an actual value BD_actual of a variable characterizing the combustion in combustion chamber  14  is determined in  34  from stored pressure values p i .  
         [0026]     Physically, this variable represents a combustion duration, which is determined in turn from the heating characteristic. This is a thermodynamic parameter which describes the chronological sequence of the combustion. The use of the heating characteristic in the present method has the advantage that it is comparatively simple to calculate because wall heat losses are not taken into consideration. The following relation applies: 
 
 dQh=dU+p*dV    (1) 
 
 where dQh is the quantity of heat supplied, dU is the increase of the internal energy of the gas, and p*dV is the delivered mechanical work. Through integration across the crank angle, the percentage share of energy conversion Qh across the crank angle is determined from variable dQh in  34 .  FIG. 3  shows a typical curve of such an integral across crank angle KW. A value in ° KW between two percentage values of energy conversion Qh is understood to be combustion duration BD_actual. In the present case, as actual combustion duration BD_actual, the crank angle is understood to be between an energy conversion Qh of 10% and an energy conversion Qh of 90%. 
 
         [0027]     A simple possibility for calculating the heating characteristic necessary for determining combustion duration BD_actual from pressure values p i  stored in  30  is to use the following polytropic state equation:  
               Δ   ⁢           ⁢     Q   i       =         n     n   -   1       *     p   i     *     (       V     i   +   1       -     V     i   -   1         )       +       1     n   -   1       *     V   i     *     (       p     i   +   1       -     p     i   -   1         )                 (   2   )             
 
 where i is the running index of cylinder pressure p i  used in  28  and also stored in  30  from the start to the end of the calculation interval; n is the polytrope exponent. It should be pointed out here that the calculation interval does not necessarily have to include the entire combustion cycle. In order to save computing capacity, it is also possible to limit the calculation to the relevant portion of the combustion cycle in which the energy is liberated from the fuel. ΔQi is the energy conversion at time step i. 
 
         [0028]     Energy conversion Qh over crank angle KW is now determined by summation or integration corresponding to the following formula:  
               Qh   m     =       ∑     i   =   1     m     ⁢     Δ   ⁢           ⁢     Q   i                 (   3   )             
 
         [0029]     After integration across the complete combustion cycle, i.e., the determination of the 100% value, crank angle KW is determined for 10% or 90% of the 100% value of energy conversion Qh. The difference between these two crank angles KW produces combustion duration BD_actual.  
         [0030]     In  36 , the setpoint value for the variable characterizing the combustion is determined, i.e., a setpoint combustion duration BD_setpoint. This setpoint value BD_setpoint is based on control variable U_LBK used to actuate charge motion flap  18 . This control variable U_LBK is thus a setpoint operating position of the variable characterizing charge motion flap  18 . Furthermore, a rotational speed nmot of the crankshaft of internal combustion engine  10 , an air charge rl (based on the signal of HFM sensor  22 ) and a set rate AGR of an exhaust gas recirculation are also taken into consideration for the determination of setpoint value BD_setpoint.  
         [0031]     Corresponding characteristic maps and characteristic functions are used for this purpose in 38. Additional operating parameters of internal combustion engine  10  may also be used for the most exact determination possible of setpoint value BD_setpoint. For example, the data of these characteristic maps and characteristic functions have been determined in advance on a test bench for the particular internal combustion engine type for various positions of charge motion flap  18  and at the operating points of internal combustion engine  10  to be expected for monitoring.  
         [0032]     In  40 , the difference between setpoint value BD_setpoint and actual value BD_actual is formed and it is checked if this difference is greater than a limiting value G 1 . If this is not the case, it is checked in  42  if the same difference is smaller than a second limiting value G 2 . If the answer in  40  or  42  is YES, an action is performed in  44 . This action may be that information concerning a deviation of the present charge motion in combustion chamber  14  from a desired charge motion is stored in control and regulating device  20  so that it can be retrieved in a later servicing of internal combustion engine  10 . However, the exceeding of one of the two limiting values G 1  and G 2  may also be displayed immediately. In order to avoid incorrect indications, it is provided that the display in  44  or the storage of a deviation only occurs if one of limiting values G 1  and G 2  was exceeded during a plurality of successive working cycles or combustion cycles of internal combustion engine  10 . The procedure ends in  46 .  
         [0033]     Physically, the method shown in  FIG. 2  is based on the fact that if charge motion flap  18  does not assume a desired position, the charge motion or turbulence in combustion chamber  14  is not as desired. Accordingly, the heating characteristic also deviates from a desired heating characteristic, which is determined by comparing desired combustion duration BD_setpoint with actual combustion duration BD_actual. Such a deviation is therefore an indication and if necessary also a measure of a deviation of the actual position of charge motion flap  18  from a desired position.  
         [0034]     However, actual value BD_actual and setpoint value BD_setpoint may also be used in  48  for regulating charge motion flap  18 . This means that the deviation between setpoint value BD_setpoint and actual value BD_actual is regulated.  
         [0035]     In an exemplary embodiment which is not shown, charge motion flap  18  is actuated in such a way that no change of the torque of internal combustion engine  10  or similar changes in the behavior of internal combustion engine  10  are noticeable to its user. If, however, the expected change of actual value BD_actual occurs, charge motion flap  18  is functional. This version of the method has the advantage that specific influencing variables that also influence the combustion duration and accordingly actual value BD_actual are decoupled from the function test of charge motion flap  18 .