Abstract:
A device for determining air entering cylinders of an internal combustion engine having a supercharger. The air is determined as a function of such quantities as rpm, air throughput in the intake manifold, throttle valve position values and temperature, characterized in that at least the following physical relationships are included in the determination: 
     suction equation of the engine 
     balancing equation for a filling in an intake manifold 
     flow rate equation at a throttle valve 
     balancing equation in a volume between the throttle valve and the supercharger.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for determining the air entering the cylinders of an internal combustion engine having a supercharger. 
     BACKGROUND INFORMATION 
     German Patent No. 32 38 190 describes an “Electronic System for Controlling or Regulating Performance Characteristics of an Internal Combustion Engine.” Specifically, it describes a method of determining the pressure in the intake manifold on the basis of the rpm and the air flow rate in the intake manifold and conversely the air flow rate on the basis of the rpm and pressure. The method described therein makes use specifically of physical relationships prevailing in the air intake manifold with the goal of optimal control of the internal combustion engine. 
     International Patent Publication No. WO96/32579 describes a method of model-supported determination of the air entering the cylinders of an internal combustion engine. To do so, a physical model is crated, describing the relationships in the intake system of an internal combustion engine without a supercharger, using parameters representing the degree of opening of the throttle valve, the ambient pressure and the valve position as input quantities of the model. In addition, the instantaneous value determined for the air entering the cylinders of the internal combustion engine is used to predict future values. 
     The conventional system cannot be used with supercharged internal combustion engines, because additional physical factors must also be taken into account due to the supercharging. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a device for determining the air entering the cylinders of an internal combustion engine having a supercharger as a function of quantities such as rpm, air throughput in the intake manifold, throttle valve position values and temperature which comprehensively take into account the physical processes taking place in supercharged internal combustion engines. 
     With this device according to the present invention, it is possible to determine the physically correct or at least approximate relationships prevailing in the intake manifold of an internal combustion engine having a supercharger, and then to base the determination of the quantity of fuel accordingly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a survey diagram of an internal combustion engine having a supercharger. 
     FIG. 2 shows a block diagram of a determination of a relative filling per stroke on a basis of standardized quantities for a throttle valve angle, temperature of an intake air upstream from the throttle valve, a mass flow over a hot film air flow meter and an rpm. 
     FIG. 3 shows a block diagram for calculation of a mass flow over a throttle valve. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows in a rough survey diagram the input side of an internal combustion engine having a supercharger. As seen in the direction of flow, the air intake manifold includes a hot film air flow meter  10  (HFM), a supercharger or compressor  11 , a throttle valve  12  and an intake valve  13  of internal combustion engine  14 . One volume  16  between supercharger  11  and the throttle valve and an additional volume  17  between the throttle valve and intake valve  13  are also important for an understanding of the present invention. The internal combustion engine itself has a piston  18  for each cylinder, with the low position of the piston characterizing piston displacement  19 . 
     FIG. 1 shows that the relationships in the intake manifold can be characterized by 
     a suction equation for the internal combustion engine (air flow through intake valve  13 ), 
     a balancing equation for the filling in the intake manifold between the throttle valve and the intake valve (volume  17 ), 
     a flow equation at throttle valve  12  and 
     a balancing equation in volume  16  between supercharger  11  and throttle valve  12 . 
     The equations are based on a two-mass storage model, with the two mass storages indicating the volumes upstream and downstream from the throttle valve ( 16 ,  17 ). 
     It has proven expedient to use standardized values for the equations. 
     In particular, the goal is to assume mass contents ml in volume  16  upstream from throttle valve  12  and ms in volume vs  17  downstream from the throttle valve, to convert the mass contents into pressures upstream and downstream from the throttle valve and to determine on the basis of these two pressures mass flows which in turn permit updating of the mass contents. The individual calculations are to be performed in iterative processes with assumptions for the output data. 
     FIGS. 2 and 3 show details of the computation steps. 
     FIG. 2 shows a block diagram for determination of the relative filling per stroke (rl), based on standardized quantities for the throttle valve angle, the temperature of the intake air upstream from the throttle valve, the mass flow through the hot film air flow meter (HFM) and the rpm. A block  20  is shown for calculating the throttle valve flow rate, representing the flow equation through the throttle valve. Its input variables are the modeled quantity of intake manifold pressure ps, the measured angle of the throttle valve based on its stop (wdkba), a standardized factor ftvdk, which is based on the measured temperature of the intake air upstream from the throttle valve, a modeled pressure (pvdk) upstream from the throttle valve and the rpm (n). At the output, the relative air mass per stroke through the throttle valve (rlroh) is obtained. This is followed by a difference forming position  21  and then an integrator  22 , both of which represent the balancing equation for the pressure in the intake manifold. At the output of integrator  22 , signal ps is available as an input quantity for block  20  as well as a characteristic curve  23 . Characteristic curve  23  with its relationship between ps and the relative filling per stroke rl represents the suction equation of the combustion chamber. Output signal rl is also sent to difference forming position  21 . 
     The balancing equation in the volume upstream from the throttle valve is implemented by a difference forming position  25  together with a downstream integrator  26 . The additive input quantity of difference forming position  25  is a signal rlhfm of the relative filling through HFM; this signal originates from a division block  27  whose input quantities are the HFM signal (mass flow HFM, mshfm) and an rpm signal n multiplied by a factor KUMSRL (constant for converting from mass flow to relative air filling in the combustion chamber). The output quantity of integrator  26  is signal pvdk (pressure upstream from the throttle valve) which forms the corresponding input quantity of block  20 . 
     An implementation of block  20  from FIG. 2 is shown in FIG.  3 . 
     An input  30  for quantity wdkba is followed by a valve characteristic curve  31  which forms a signal based on standardized angle signal wdkba concerning a standardized mass flow msndk through the throttle valve. This standardization also applies to an air temperature of 273° K. and a pressure of 1013 hPa upstream from the throttle valve. This is followed by multiplication position  32  with additional input signal ftvdk, multiplication position  33  with signal fpvdk, and multiplication position  34  with the output signal of a characteristic curve  35  whose input quantity is the division result between modeled pressure ps and modeled pressure pvdk (block  36 ). The second input signal of multiplication position  33  is fpvdk as the result of a division of input quantity pvdk divided by a standard pressure of 1013 hPa (block  37 ). Output signal msdk (mass flow through the throttle valve) of multiplication position  34  subsequently undergoes division by the product of rpm n and factor KUMSRL in a block  38 . The result of this division is signal rlroh as the relative filling value through the throttle valve. 
     On the basis of the physical conditions, rlhfm=rlroh=rl in steady-state operation, i.e., the air flow rate measured by HFM corresponds to the mass flow through the throttle valve and the mass flow in the combustion chamber. In the case of non-steady-state operation, the integrators simulating the individual air mass storages play a role. 
     The following equations are used in particular: 
     Suction equation of the internal combustion engine in general: 
     
       
           ma   —   Punkt =( ps−pirg )* n *( VH/ 2)/( R*Ts ) 
       
     
     where 
     ma_Punkt=air flow rate sucked from the combustion chamber 
     ps=intake manifold pressure 
     pirg=partial pressure caused by residual gas in the combustion chamber 
     n=rpm 
     VH=piston displacement of the engine 
     Ts=gas temperature in the intake manifold. 
     Conversion from mass flow ma_Punkt to air mass ma in the combustion chamber and division by rpm n:              ma   =                air                 mass                 in                 the                 combustion                 chamber                 =                  ma   -        Punkt        /        n                 =                  (       p                 s     -   pirg     )     *       (     VH        /        2     )     /       (     R   *   Ts     )     .                                      
     Standardized quantities are used for the control unit: standard air mass in the combustion chamber 
     
       
           m   —   norm =( Pn*VH/ 2)/( R*Tn ). 
       
     
     Definition of rl as the relative air filling in the combustion chamber:              rl   =                  ma   /     m   -          norm                 =                  (       p                 s     -   pirg     )     *     Tn   /     (     Pn   *   Ts     )                                      
     under the standard conditions: Tn=273 K, Pn=1013 hPa where              fupsrl   =                factor                 for                 converting                 pressure                 in                 the                 intake                 manifold                              into                 relative                 air                 filling                 in                 the                 combustion                 chamber                 =                Tn   /     (     pn   *   Ts     )                                    
     the suction equation is obtained in control unit quantities as 
     
       
           rl =( ps−pirg )* fupsrl.   
       
     
     Balancing equation for the filling in the intake manifold (volume  17 ) in general (implemented by addition position  21  with a downstream integrator  22 ): 
     
       
           d ( ms )/ dt=mdk   —   Punkt−ma   —   Punkt.   
       
     
     With standardized control quantities 
     
       
           d ( ms/m   —   norm )/ dt =( mdk   —   Punkt−ma   —   Punkt )/ m   —   norm   
       
     
     and 
     
       
         
           rl 
           — 
           Punkt=ma 
           — 
           Punkt/m 
           — 
           norm 
         
       
     
     and 
     
       
         
           rlroh 
           — 
           Punkt=mdk 
           — 
           Punkt/m 
           — 
           norm 
         
       
     
     it holds that: 
     
       
           d ( ms/m   —   norm )/ dt=rlroh   —   Punkt−rl   —   Punkt.   
       
     
     The gas equation yields the relationship between air mass ms in the intake manifold and intake manifold pressure ps: 
       ps*Vs=ms*R*Ts.   
     Solving for ms yields: 
     
       
           ms =( ps*Vs )/( R*Ts ). 
       
     
     Based on a standard mass, this yields:                m                 s        /          m   -        norm     =                  (       (     p                 s   *   Vs     )     /     (     R   *   Ts     )       )     *     (       (     R   *   Tn     )          /          (     Pn   *   VH        /        2     )       )                   =                  (     p                 s   *   VS   *   Tn     )          /            (     Pn   *   VH        /        2   *   Ts     )     .                                    
     Inserting this into the standardized balancing equation yields: 
     
       
           d *(( ps*Vs*Tn )/( Pn*VH/ 2* Ts ))/ dt =( rlroh   —   Punkt−rl   —   Punkt ). 
       
     
     This yields: 
     
       
           d*ps/dt =( rlroh   —   Punkt−rl   —   Punkt )*(( VH/ 2* Ts*Pn )/( Vs*Tn )). 
       
     
     With 
     
       
         
           rl 
           — 
           Punkt=rl*n 
         
       
     
     and 
     
       
         
           rlroh 
           — 
           Punkt=rlroh*n 
         
       
     
     this yields: 
     
       
           d*ps/dt =(( VH/ 2* Ts*Pn*n )/( Vs*Tn ))*( rlroh−rl ). 
       
     
     Finally, with substitution, this yields:              KIS   =                integration                 constant                 for                 the                 intake                 manifold                 model                 =                  (     VH        /        2   *   Ts   *   Pn   *   n     )          /          (     Vs   *   Tn     )                                    
     the control unit equation in differential form 
     
       
           d*ps/dt=KIS* ( rlroh−rl ) 
       
     
     and in integral form 
     
       
           ps=KIS *integral(( rlroh−rl )* dt.   
       
     
     Flow rate equation for the throttle valve (block  20 , individual elements in FIG. 3) in general: 
     
       
           msdk ( wdkba )= pvdk *(1/( R*Tvdk ))**(1/2)* Adk ( wdkba )* my*Xi ( Ps/pvdk )* k   
       
     
     where 
     msdk: mass flow through the throttle valve 
     wdkba: throttle valve angle based on stop 
     pvdk: pressure upstream from the throttle valve 
     Tvdk: temperature upstream from the throttle valve 
     Adk: cross-section of the opening of the throttle valve 
     my: coefficient of friction 
     Xi: outflow characteristic curve. 
     The throttle valve is measured as a function of the throttle valve angle under standard conditions: 
     
       
           msndk ( wdkba )= pn *(1/( R*Tn ))**(1/2)* Adk ( wdk ) *my*Xi ( Psn/pvdk )* k.   
       
     
     With the following substitutions: 
     fpvdk=pvdk/Pn 
     ftvdk=(Tn/Tvdk)**(1/2) 
     KLAF=Xi(ps/pl)/Xi(psn/pl) 
     psn=standard pressure downstream from the throttle valve 
     the quotient msdk(wdkba)/msndk(wdkba) from the two equations yields the relationship: 
     
       
           msdk ( wdkba )= msndk ( wdkba )* ftvdk*fpvdk*KLAF.   
       
     
     This yields the value for rlroh at the output of division position  38  from FIG. 3 as follows: 
     
       
           rlroh=msdk /( n* KUMSRL ) 
       
     
     where 
     KUMSRL=conversion constant. 
     Balancing equation in volume  16  between the throttle valve and the supercharger (addition position  25  and integrator  26  from FIG. 3) in general: 
     
       
           d ( ml )/ dt=mhfm   —   Punkt−mdk   —   Punkt.   
       
     
     With standardized control quantities, this yields: 
     
       
           d ( ml/m   —   norm )/ dt =( mhfm   —   Punkt−mdk   —   Punkt )/ m   —   norm   
       
     
     If 
       rlhfm   —   Punkt=mhfm   —   Punkt/mnorm   
     and 
     
       
         
           rlroh 
           — 
           Punkt=mdk 
           — 
           Punkt/m 
           — 
           norm 
         
       
     
     then it follows that: 
     
       
           d ( ml/m   —   norm )/ dt=rlhfm   —   Punkt−rlroh   —   Punkt.   
       
     
     The relationship between air mass ml in the boost volume and boost pressure pl yields the gas equation: 
     
       
         
           pl*Vl=ml*R*Tl. 
         
       
     
     Solving for ml yields: 
     
       
           ml =( pl*Vl )/( R*Tl ). 
       
     
     Based on a standard mass, this yields:                m                 l        /          m   -        norm     =                  (       (     pl   *   Vl     )     /     (     R   *   Tl     )       )     *     (       (     R   *   Tn     )     /     (     Pn   *   VH        /        2     )       )                   =                  (     pl   *   Vl   *   Tn     )     /       (     Pn   *   VH        /        2   *   Tl     )     .                                    
     Inserting into the standardized balancing equation 
     
       
           d ( ml/m   —   norm )/ dt=rlroh   —   Punkt−rl   —   Punkt   
       
     
     and solving for d(pl)/dt yields: 
     
       
           d ( pl )/ dt =( rlroh   —   Punkt−rl   —   Punkt )/( VH/ 2* Tl*Pn )/( Vl*Tn ). 
       
     
     With rlhfm_punkt=rlhfm*n 
     and rlroh_punkt=rlroh*n 
     and the substitution              KIL   =                integration                 constant                 for                 the                 boost                 volume                 =                  (     VH        /        2   *   Tl   *   Pn   *   n     )          /          (     Vl   *   Tn     )                                    
     this yields the control unit equation in differential form: 
     
       
           d ( pl )/ dt=KIL* ( rlhfm−rlroh ) 
       
     
     and in integral form 
     
       
           pl=KIL *integral( rlhfm−rlroh )* dt.