Abstract:
A measured value (MAP_MES) of the pressure in a suction pipe is the command variable of a control loop. The regulating variable is an estimated value (MAP_EST) of the pressure in the suction pipe, the estimated value being determined according to the manipulated variable of the control loop. The manipulated variable is calculated according to the difference between the estimated value (MAP_EST) and a measured value (MAP_MES) of the pressure in the suction pipe and according to the temporal change of the measured value (MAP_MES) of the pressure in the suction pipe. An estimated value (MAF_EST) of the mass flow in the intake passage ( 1 ) is calculated according to the manipulated variable.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is a continuation of copending International Application No. PCT/DE01/04929 filed Dec. 27, 2001 and claiming a priority date of Jan. 23, 2001, which designates the United States, and claims priority of German Patent Application No. 10102914.4 filed on Jan. 23, 2001. 

   TECHNICAL FIELD OF THE INVENTION 
   The invention relates to a method for determining an estimated value of a mass flow in the intake channel of an internal combustion engine. 
   BACKGROUND OF THE INVENTION 
   EP 0 886 725 B1 discloses a method for determining an estimated value of a mass flow in the cylinders of an internal combustion engine. In this case, the estimated value of the mass flow in the cylinders of the internal combustion engine is determined depending on a measured value of a mass flow upstream of a throttle valve in the intake channel, on the degree of opening of the throttle valve, on the rotational speed, on the crankshaft, on a measured value of the induction manifold pressure, and on further operating variables of the internal combustion engine. A dynamic model of the intake channel of the internal combustion engine is provided for this purpose. The dynamic model is corrected during operation, depending on the measured value of the mass flow in the intake channel and on a difference between a measured value and an estimated value of the induction manifold pressure, which difference is supplied to a controller, whose manipulated variable is used for correcting the dynamic model of the intake channel. 
   Under specific load conditions of the internal combustion engine—in particular in the case of an internal combustion engine with four cylinders—significant pulsations of the gas mass in the intake channel occur, and these pulsations can cause a significant corruption of the measurement signal of the mass flow meter. It is therefore known from EP 0 886 725 B1 that the measured value of the mass flow meter should not be used for correcting the dynamic model of the intake channel under these conditions. However, this can lead to a loss of precision when determining estimated values using the dynamic model of the intake channel. 
   SUMMARY OF THE INVENTION 
   The invention addresses the problem of establishing a method for determining an estimated value of a mass flow in the intake channel of an internal combustion engine, which method is also highly precise when pulsations of the mass flow occur in the intake channel. 
   The problem can be solved by a method for determining an estimated value of a mass flow in the intake channel of an internal combustion engine, comprising the steps of:
         determining a measured value of an induction manifold pressure as the command variable of a control loop,   determining an estimated value of the induction manifold pressure as a regulating variable of the control loop,   determining the estimated value depending on a manipulated variable of the control loop,   calculating the manipulated variable depending on the difference between the estimated value and a measured value of the induction manifold pressure and depending on the time-related change of the measured value of the induction manifold pressure, and   calculating the estimated value of the mass flow in the intake channel depending on the manipulated variable.       

   The manipulated variable can be calculated by multiplying the difference between the estimated value and the measured value of the induction manifold pressure by a correction factor, which factor is determined depending on the time-related change in the measured value of the induction manifold pressure. The correction factor can be determined from a characteristic curve. The manipulated variable can be corrected depending on a measured value of the air mass flow. The manipulated variable can be determined depending on the integral of the difference between the estimated value and the measured value of the induction manifold pressure. 
   The object can also be achieved by a device for determining an estimated value of a mass flow in the intake channel of an internal combustion engine, comprising a sensor for measuring the value of an induction manifold pressure which is used as the command variable of a control loop. The control loop may comprise an estimation unit for estimating the value of the induction manifold pressure which is used as a regulating variable of the control loop, wherein the estimation unit receives a manipulated variable of the control loop, a calculating unit for calculating the manipulated variable depending on the difference between the estimated value and a measured value of the induction manifold pressure and depending on the time-related change of the measured value of the induction manifold pressure, and a calculating unit for calculating the estimated value of the mass flow in the intake channel depending on the manipulated variable. 
   The calculating unit for calculating the manipulated variable may comprise a multiplier for multiplying the difference between the estimated value and the measured value of the induction manifold pressure by a correction factor, which factor is determined depending on the time-related change in the measured value of the induction manifold pressure. The correction factor can be determined from a characteristic curve. The device may further comprise a air mass flow sensor for providing a variable for correcting the manipulated variable. The calculating unit for calculating the manipulated variable may comprise an integrator for determining the integral of the difference between the estimated value and the measured value of the induction manifold pressure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention are explained in greater detail with reference to the schematic drawings in which: 
       FIG. 1  shows an internal combustion engine with a control unit, 
       FIG. 2  shows a block schematic diagram of a part of the control unit, said part being relevant for the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An internal combustion engine ( FIG. 1 ) includes an intake channel  1 , preferably with a throttle valve  10 , and with an engine block  2 , which has a cylinder  20  and a crankshaft  23 . A piston  21  and a connecting rod  22  are assigned to the cylinder  20 . The connecting rod  22  is connected to the piston and the crankshaft  23 . 
   Provision is made for a cylinder head  3  in which a valve gear having at least one inlet valve  30  and one outlet valve  31  is arranged. A fuel injector  33  is additionally incorporated in the cylinder head  3 . Alternatively, the fuel injector  33  can also be arranged in the intake channel  1 . The internal combustion engine is shown in  FIG. 1  with one cylinder. It can however include a plurality of cylinders. 
   Provision is also made for an exhaust channel  4 , which is connected to the intake channel  1  via an exhaust return  5 . An AGR valve  51  for setting the returned exhaust mass is arranged in the exhaust return  5 . A mass flow meter, which captures an exhaust return mass flow M_EGR, can also be arranged in the exhaust return  5  if necessary. 
   Provision is also made for a control unit  6 , to which sensors are assigned, which sensors capture various measured variables and determine the measured value of the measured variable in each case. Depending on at least one measured variable, the control unit  6  determines one or more actuating signals which control an actuating system in each case. 
   The sensors comprise a pedal position sensor  71  which captures a pedal value of the accelerator pedal  7 ; a throttle valve position sensor  11  which captures a degree of opening of the throttle valve  10 ; an air mass meter  12  which captures an air mass flow; an induction manifold pressure sensor  13  which captures an induction manifold pressure in the intake channel  1 ; a temperature sensor  14  which captures the intake-air temperature; a rotational speed sensor  24  which captures the rotational speed of the crankshaft  23 ; and a temperature sensor  25  which captures a cooling-medium temperature. Depending on the embodiment of the invention, any subsets of the aforementioned sensors or even additional sensors may be present. 
   The actuating systems comprise a servomechanism and an actuator in each case. The servomechanism is an electromotive drive, an electromagnetic drive, a piezoelectric drive, or a further drive which is known to the person skilled in the art. The actuators are designed as a throttle valve  10 , a fuel injector  33  or an EGR valve  51 . In the following, references to the actuating systems also refer to the actuator which is assigned in each case. 
   The control unit  6  is preferably designed as an electronic engine control. However, it can also include a plurality of control devices which are electrically connected to each other, e.g. via a bus system. 
   In a block B 1  (FIG.  2 ), a MAF_MAN within the intake channel  1  is determined in accordance with the following relationship:
 
 MAF   —   MAN=MAF   —   MES+M   —   EGR−MAF   —   CYL 
 
where MAF_MES designates the measured value of the mass flow in the intake channel, which measured value is captured by the mass flow meter  12 ; M_EGR designates the exhaust return mass flow, which is either captured by the mass flow sensor in the exhaust return  5  or is calculated as an estimated value using a model; and MAF_CYL designates a mass flow in the cylinder  2  of the internal combustion engine, which mass flow is preferably determined using a dynamic model of the intake channel, as described in EP 0 886 725 B1, for example, the content of which is hereby included in relation to this.
 
   In a summing point S 1 , the mass flow MAF_MAN within the intake channel  1  is corrected by adding the correction value COR which is described in detail below. 
   In a block B 2 , a gas mass MASS_MAN within the intake channel  1  is determined, depending on the corrected mass flow MAF_MAN_COR, by integrating the corrected mass flow MAF_MAN_COR over time. 
   In a block B 3 , an estimated value MAP_EST of the induction manifold pressure is determined in accordance with the following relationship: 
       MAP_EST   =       R   VOL     ·   TIA   ·   MASS_MAN         
 
where R designates the general gas constants, VOL designates the volume of the intake channel downstream of the throttle valve as far as the inlet to the cylinders of the internal combustion engine, and TIA designates the intake air temperature or the temperature of the mass flow downstream of the throttle valve  10 .
 
   In a summing point S 2 , the difference between the measured value MAP_MES and the estimated value MAP_EST of the induction manifold pressure is calculated. The difference is then integrated in a block B 4 , and the integrated value is then supplied to the summing point S 3 . 
   In a block B 5 , a value is determined which is characteristic of the change in the measured value MAP_MES of the induction manifold pressure. The time-related derivative of the measured value MAP_MES of the induction manifold pressure is preferably determined in the block B 5  for this purpose. This derivative then represents the input variable for a characteristic map, by means of which a correction factor FAC is determined in the block B 6 . In a multiplication point M 1 , the difference between the measured value MAP_MES and the estimated value MAP_EST of the induction manifold pressure is multiplied by the correction factor FAC. This value is then supplied to the summing point S 3  and added to the integral which was determined in the block B 4 . This then produces the correction value COR. 
   In a block B 7 , an estimated value MAF_EST of the air mass flow in the intake channel of the internal combustion engine is determined depending on the corrected mass flow MAF_MAN_COR within the intake channel  1 , the exhaust return mass flow M_EGR, and the mass flow MAF_CYL in the cylinder of the internal combustion engine. This is carried out using the following equation:
 
 MAF   —   EST=MAF   —   MAN   —   COR−M   —   EGR+MAF   —   CYL. 
 
   The blocks B 2 , B 3 , B 4 , B 5 , B 6  therefore form a control loop, in which the command variable is the measured value MAP_MES of the induction manifold pressure, in which the regulating variable is the estimated value MAP_EST of the induction manifold pressure, and in which the manipulated variable is the correction value COR, which is in turn corrected using the mass flow MAF_MAN within the intake channel  1 , thus producing the corrected mass flow MAF_MAN_COR within the intake channel  1 . 
   As a result of multiplying the difference between the measured value MAP_MES and the estimated value MAP_EST of the induction manifold pressure by the correction factor FAC, which is determined depending on the time-related change in the measured value MAP_MES of the induction manifold pressure, an extremely precise determination of the estimated value MAP_EST of the mass flow in the intake channel is ensured in an extremely simple manner, even under load conditions which include significant pulsations of the mass flow in the intake channel. In this case, the correction factor FAC is determined in advance by means of tests at an engine test bench, or by means of simulation, and stored in the characteristic curve. 
   In an alternative embodiment, the estimated value MAF_EST can even be determined without the mass flow MAF_MAN within the intake channel. The mass flow MAF_MAN within the intake channel is simply set to zero in this case, which corresponds to omitting the block B 1 . It is also possible, therefore, to determine a sufficiently precise estimated value MAF_EST of the mass flow in the intake channel in a simplified manner and without the calculations in the block B 1 . However, an inclusion of the block B 1  has the advantage that, by calculating the mass flow MAF_MAN within the intake channel in the block B 1 , an approximate operating point is specified for the control loop as a form of advance control, and a precise estimated value MAF_EST of the mass flow in the intake channel is consequently provided more quickly, which is a significant advantage, particularly in the case of a dynamic running of the internal combustion engine. 
   The calculation of the integral of the measured value MAP_MES and of the estimated value MAP_EST of the induction manifold pressure has the advantage that it ensures a greater stationary accuracy of the estimated value MAF_EST. However, this can likewise be omitted in a simpler embodiment. 
   The estimated value MAF_EST of the mass flow can then be used for the further calculation of actuating signals for actuators of the internal combustion engine, or also for diagnosis.