DE19753969A1 - Operating IC engine so that signal reload is determined to compute cylinder filling - Google Patents

Abstract

The method is carried out with a signal representing the load being determined to compute the cylinder filling (r1) of the IC engine. For the computing of the filling a model is designed, with which the suction air temperature is taken account of, and this is weighted in such a manner, that the computed air filling signal is essentially independent of the suction air temperature. The suction pipe pressure is the value representing the load of the engine.

Description

State of the art

The invention relates to a method and a device for operating an internal combustion engine according to the general concept fen of the independent claims.

The requirements for a modern internal combustion engine in the rear look at a reduction in fuel consumption and the pollutants emitted are getting higher. The elec tronic control of the internal combustion engine, in particular the Control of the fuel mass to be injected setting ignition angle and / or the air fill to be metered development, must be more and more accurate to meet these requirements work. In particular, the load of the burning size representative of the engine can be determined precisely, since this is used to calculate the control variables. The most appropriate size that represents the load is the Air filling, especially the relative air filling of the Zy linder per stroke. This size is a proportion of fresh air Size, when used to determine the control parameters a very high accuracy of the engine control can be achieved. The air filling is in ge as possible accurately calculated from the existing sizes. For a  Air mass-controlled control system, for example as in the unpublished German patent message 197 40 915.6 from September 17, 1997.

It has been found in some applications that the ambient temperature has a significant impact on the comp air filling. In particular, it was found that with increasing intake air or ambient temperature calculated filling is smaller than that on a test vehicle measured filling is. The mixture will therefore increase the intake air temperature (at least in the pilot control) leaned.

It is an object of the invention to provide measures that Improve accuracy in air charge calculation.

This is due to the characteristic features of the indep gene claims reached.

Advantages of the invention

The accuracy of the calculation of the air filling from the ge measured signal (e.g. air mass, intake manifold pressure) is raised Lich improved. It is particularly advantageous that the result the calculation, the air filling, essentially independent from the ambient temperature or the intake air temperature of the engine.

This ensures in an advantageous manner that physi Calically correct values regardless of the intake air temperature be calculated.

It is also particularly advantageous that the compensation the influence of the intake air temperature on the calculated Air intake model used (intake manifold model)  Applicability of the model is significantly improved because the application of the model for every engine type in principle is valid for all intake air temperatures.

It is also particularly advantageous that an improved loading calculation of the factor representing the combustion chamber temperature tors is provided.

It is particularly advantageous that in the intake manifold used model the influence of the intake air temperature on the zu relationship between the fresh gas partial pressure and the air filling descriptive slope factor is compensated. There the accuracy of this intake manifold model becomes significant improved. Since the calculated fresh gas partial pressure in the we is largely independent of the intake air temperature by compensating the influence of intake air temperature the entire intake manifold model based on the gradient factor independent of air temperature.

Further advantages result from the following Be writing of exemplary embodiments or from the dependent ones Claims.

drawing

The invention is explained below with reference to the embodiments shown in the drawing. Fig. 1 shows a control system for an internal combustion engine, while in Fig. 2 a flowchart is shown on which the calculation of the relative air filling from an intake manifold is shown pressure value. In Fig. 3, finally, the compensation of the intake air temperature dependency of the factor representing the combustion chamber temperature is described as a sequence diagram.

Description of exemplary embodiments

Fig. 1 shows a control system for an internal combustion engine, which comprises at least one control unit 10 , the least least an input circuit 12 , at least one Mikrocom computer 14 and at least one output circuit 16 . These elements are connected to one another via a communication system 18 for mutual data exchange. The input circuit 12 leads to various input lines via which measuring signals determined by appropriate measuring devices are transmitted. Via a first input line 20 , a signal representing the suction pipe pressure Ps is supplied by a pressure sensor 22 . A signal representative of the throttle valve position wdkba is supplied via an input line 24 from a position transmitter 26 . Furthermore, a signal representing the engine speed nmot is fed via an input line 28 from a corresponding measuring device 30 . Via an input line 32 , a signal is transmitted from a camshaft position transmitter 34 , from which the position of the camshaft ° NW can be derived. In addition, input lines 36 and 38 are provided, via which signals are supplied from corresponding temperature sensors 40 and 42 , which present the engine temperature tmot and the intake air or ambient temperature tans re. Another pressure sensor 44 leads via an input line 46 to the control unit 10 to a signal representing the ambient pressure Pu. Via the output circuit 16 , the control unit 10 controls the control variables of the internal combustion engine and in this way influences z. B. the fuel metering ( 48 ), the ignition angle ( 50 ) and in egg nem preferred embodiment, the position of the throttle valve 52nd

Through programs implemented in the microcomputer 14 , the control unit 10 controls, depending on the input variables, at least the fuel quantity to be injected, the ignition angle to be set and, if appropriate, the air filling to be supplied. This is done on the basis of the relative air charge (fresh gas), which represents the (fresh gas) cylinder charge per stroke standardized to certain maximum and minimum values.

To determine this size, the measured suction pipe pressure Ps using a suction pipe model the fresh gas par tial pressure calculated from the by a conversion factor (Slope) the relative air filling is formed.

It has been shown that the connection between filling and intake manifold pressure is substantially linear. This is because because when changing the charge approximately pressure equalization between suction pipe and cylinder. This linear together menhang is disturbed by the residual gas in the cylinder, because at the end of the exhaust process still exhaust gas in the cylinder remains, part of this residual gas temporarily in the intake manifold flows back when the inlet valve is open and after is sucked in again.

When calculating the fresh gas partial pressure is therefore the internal residual gas content to be taken into account by the opened valves flows back into the intake manifold. The measured The intake manifold pressure also contains this internal residual gas part. It is therefore used when calculating the fresh gas saving subtracted from the measured intake manifold pressure. This Residual gas fraction pirg forms an additive correction value for the linear relationship, d. H. an offset. The residual gas Part pirg is determined based on the camshaft over cutting angle of the character of the angle of the camshaft rized, during which both intake and exhaust valve are open. This angle is therefore a measure of the mitt lere cross-sectional area, for overflow of the exhaust gas  from the exhaust tract is available in the intake manifold. Since the overflowing exhaust gas mass also depends on the time span, while the inlet and outlet valves are open, Determination of the internal exhaust gas recirculation rate and the speed can be used as an input variable. The camshaft over cutting angle results from the camshaft position signal ° NW.

A dependency on the camshaft overlap angle and the speed also shows the slope of the model for the Zu connection between pressure and filling.

To calculate the filling from the intake manifold pressure, a linear relationship with one from the camshaft overlap dependent angle and the engine speed, from one Map read offset and one of the same size dependent, also read from a map Given slope.

Since the residual gas fraction and the slope also depend on the order circuit of the suction pipe are dependent on each suction specific maps are provided and it will be after the intake manifold is switched to the associated map tet. To none when switching the flap position Getting leaps and bounds are the factors (Residual gas content pirg and slope) gefil when switching tert.

Furthermore, the residual gas content depends on the ambient pressure gig. With decreasing ambient pressure, the exhaust gas pressure drops and hence the residual gas content in the cylinder. For this reason the residual gas percentage is corrected with an altitude factor.

The slope also depends on the combustion chamber temperature gig. The slope is corrected accordingly with the  Combustion chamber temperature instead. The latter is based on Engine temperature and intake air temperature (ambient temp rature) estimated according to a model.

The air charge size (fresh air proportion) is taken into account when calculating the control variables by, for example, directly or after conversion into a fresh air mass flow by means of a constant the determination of the fuel mass to be injected, the The ignition angle to be set and / or the one to be set Throttle valve position is evaluated.

The relative air filling rl from the intake pipe pressure Ps is determined using the following equation:

rl = (Ps - (KFPIRG × fho)) × KFPSURL × ftbr

With
rl relative air filling
Ps measured intake manifold pressure
KFPIRG map value for residual gas proportion depending on engine speed and camshaft position
fho correction factor depending on the ambient pressure
KFPSURL map value for the slope depending on engine speed and camshaft position
ftbr combustion chamber temperature factor

In at least one application it has been shown that the air charge signal calculated in this way depends fluctuates from the intake air temperature. Result of a ge closer examination was that the temperature influence on the partial residual gas pressure pirg is very low, so that the temperature dependence of the air filling signal from the Dependence of the slope factor fpsurl on the environment temperature results. This is there as part of the provision  the combustion chamber temperature or the combustion chamber temperature right presenting factor ftbr taken into account.

The model for determining the temperature in the combustion chamber at the point in time at which the inlet valve closes is based on the following requirements: The temperature increase of the air on the way to the combustion chamber is proportional to the temperature difference between the cooling water and the intake air. The proportionality factor is, in a first approximation, a function of the air filling. If the air charge calculation is physically correct, the calculated air charge value must be independent of the intake air temperature. Since, as mentioned above, the residual gas partial pressure does not change with the intake air temperature, the slope factor fpsurl must be constant regardless of the air temperature. For the factor ftbr of the combustion chamber temperature, the following relationship results as a model equation that fulfills these requirements:

ftbr = [273K / (273K + tans + KFWTBR. (tmot-tans)] ^x

With
tans intake air temperature, ambient air temperature
tmot cooling water temperature
KFWTBR proportional factor dependent on engine speed and filling

In an application example, there is a value as the exponent x of 0.75, which meets the above criterion of the con constant slope independent of the intake air temperature Fulfills.

Another possibility of the intake air temperature compensation results from the consideration of an intake air temperature-dependent correction factor when determining the factor ftbr, roughly in the following way:

ftbr = [273K / (273K + evtmod)]. FWFTBRTA (tans))

With
evtmod combustion chamber temperature = tans + KFWTBR. (tmot-tans)
FWFTBRTA (tans) correction factor, dependent on intake air temperature.

In summary, it should be noted that an intake air temperature temperature compensation causes the calculated air charge is independent of the air temperature. This realization leaves apply both to systems in which the pressure di is measured directly as well as in systems that work in the same way State of the art mentioned the air mass supplied measure and at least taking into account the engine rotation number derive a pressure signal from this, which by means of the introduced intake manifold pressure model in an air filling is calculated.

The procedure described is shown in the flow chart of FIG. 2, which represents a corresponding program of the microcomputer 14 .

The residual gas portion pirg is subtracted from the measured intake manifold pressure Ps in a connection point 100 . The remaining gas fraction pirg is formed in the map 102 as a function of the engine speed nmot and the camshaft position ° NW. The read-out value KFPIRG is fed to a multiplication point 104 , in which the correction factor fho derived from the ambient pressure Pu is multiplied by the map value KFPIRG. The correction factor is preferably the ambient pressure Pu related to a standard pressure (1013 hPa), to which the values of the map 102 are matched. The output of the multiplication point 104 is the residual gas component pirg, which is subtracted from the measured intake manifold pressure in the connection point 100 (offset of the conversion characteristic curve).

The result of this subtraction is fed to a multiplication point 106 , by which the slope fpsurl of the model is taken into account. In a map 108 , a map value for the slope KFPSURL is read out depending on the engine speed nmot and the camshaft position ° NW. This is multiplied in a multiplication point 110 by a correction factor ftbr depending on the combustion chamber temperature. The slope value fpsurl formed in this way is multiplied in the multiplication point 106 by the difference between the intake manifold pressure and the residual gas component. From the output signal of the multiplication point 106 is the relative air charge rl, which is evaluated for further control of the internal combustion engine (symbolized in 114 ). The combustion chamber temperature factor ftbr is determined in a model 112 at least as a function of the engine temperature tmot and the intake temperature tans. The determined combustion chamber temperature is standardized to form the correction factor to a temperature of 273K, to which the values of the map 108 are matched.

In Fig. 3 is a preferred embodiment for suction air temperature compensation of the intake manifold model Darge presents. The flowchart shows the implementation of the relationship shown above between intake air temperature and combustion chamber temperature factor ftbr in a preferred exemplary embodiment.

First, in 200 the difference between the measured cooling water temperature tmot and the measured intake air temperature tans is formed. This difference is multiplied in the multiplication point 202 by the proportionality factor KFWTBR read from the map 204 . This proportionality factor is read in the map 204 depending on the air filling rl and the engine speed nmot. The map 204 is applied for each engine type. The difference multiplied by the proportionality factor is added in 206 to the measured intake air temperature value tans. This expression is added to the standard temperature 273 K in the following summation position 208 . In the division point 210 , the normalization factor 273 K is divided by the total sum formed in the summation point 208 . This expression is exponentiated with the given exponent x in 212 and the combustion chamber temperature factor ftbr is formed in this way.

If an external exhaust gas recirculation is provided, its partial pressure must also be taken into account as an offset correction value when determining the fresh air partial pressure according to FIG. 2.

Claims (10)

1. Method for operating an internal combustion engine, wherein a signal (Ps) representing the load of the internal combustion engine is detected and, depending on this signal, a measure for the filling (rl) of the cylinders of the internal combustion engine is calculated, the cylinder filling for controlling at least one operating variable such as Fuel metering, ignition angle or air supply is evaluated, characterized in that a model is used to calculate the filling, in which the intake air temperature is taken into account, this consideration is weighted such that the calculated air filling signal is essentially independent of the intake air temperature. 2. The method according to claim 1, characterized in that the quantity representing the load of the internal combustion engine the intake manifold pressure is. 3. The method according to any one of the preceding claims, since characterized in that the size representing the load the air mass is. 4. The method according to any one of the preceding claims characterized in that from the optionally from the Air mass calculated intake manifold pressure taking into account of the residual gas partial pressure, a fresh air partial pressure is formed is that by means of a slope factor in an air fill value is converted.   5. The method according to any one of the preceding claims characterized in that when determining the air filling the combustion chamber temperature is taken into account. 6. The method according to claim 4, characterized in that the combustion chamber temperature when determining the gradient factor rature is taken into account. 7. The method according to any one of claims 4 to 6, characterized ge indicates that the combustion chamber temperature within the scope of a Depending on the engine temperature and intake air temperature is determined. 8. The method according to any one of claims 4 to 7, characterized ge indicates that when calculating the combustion chamber temperature the intake air temperature is taken into account such that the Incline factor independent of the intake air temperature con remains constant. 9. The method according to any one of the preceding claims, since characterized in that the weighting of the consideration the intake air temperature when determining the combustion chamber temperature factor is made such that the Mo door temperature and intake air temperature with a certain factor a specified exponent or an intake air temperature weighted factor is weighted. 10. Device for operating an internal combustion engine with a control unit which is at least one of the load of the Receives signal representing the internal combustion engine (Ps), which, depending on this signal, is a measure of the filling (rl) the cylinder of the internal combustion engine is calculated, the Zy Linden filling for controlling at least one company size such as fuel metering, ignition angle or air supply is evaluated, characterized in that the control unit  Contains means that the filling by means of a model calculates at which the intake air temperature is taken into account is that the control unit has weighting means which the consideration of the intake air temperature so important that the calculated air charge signal essentially is independent of the intake air temperature.