Method for determining the air entering the cylinders of an internal combustion engine having a supercharger

The present invention relates to a method for determining the air entering the cylinders of an internal combustion engine having a supercharger.

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.

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.

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.

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.