DE19928824C2 - Method for operating an internal combustion engine - Google Patents

Description

State of the art

The invention relates in particular to a method for operating an internal combustion engine of a motor vehicle in which fuel in at least two modes Combustion chamber is injected, and in the exhaust gas via an external and an internal Exhaust gas recirculation is returned to the combustion chamber, with the exhaust gas at the external Exhaust gas recirculation via an exhaust gas recirculation pipe and for internal exhaust gas recirculation an outlet valve is guided. The invention also relates to an internal combustion engine especially for a motor vehicle, with a combustion chamber, in the fuel in at least two modes of operation is injectable, and in the exhaust via an external and an internal Exhaust gas recirculation is recyclable, the exhaust gas in the external exhaust gas recirculation via an exhaust gas recirculation pipe and, in the case of internal exhaust gas recirculation, via an exhaust valve is guided, and with a control unit for control and / or regulation.

Such a method and such an internal combustion engine are, for example, from one known as gasoline direct injection. There is fuel in one Homogeneous operation during the intake phase or in a shift operation during the Compression phase injected into the combustion chamber of the internal combustion engine. The Homogeneous operation is preferably provided for full-load operation of the internal combustion engine, while shift operation is suitable for idling and part-load operation. For example depending on the requested torque is such direct injection  Internal combustion engine switched between the above modes.

In a so-called external exhaust gas recirculation, the exhaust gas is discharged from the exhaust pipe a separate exhaust gas recirculation pipe is returned to the intake pipe. In the exhaust gas recirculation pipe An exhaust gas recirculation valve is included, which is used to control and / or regulate the amount of recycled exhaust gas is used. A so-called internal exhaust gas recirculation is created that not only the intake valve is opened during the intake phase of the internal combustion engine is, but at least temporarily also the outlet valve. This turns exhaust gas from the Exhaust pipe sucked back into the combustion chamber.

The different operating modes of the internal combustion engine are with a plurality of Problems connected. For example, it is necessary that the internal and the external Exhaust gas recirculation varies depending on the different operating modes have to be influenced. At the same time, there is a desire that the internal and the External exhaust gas recirculation as much inert gas as possible is recycled to the proportion To reduce nitrogen oxides in the exhaust gas.

From DE 42 22 414 C2 a method is known with which an internal combustion engine an external exhaust gas recirculation is controlled and / or regulated.

The object of the invention is to provide a method for operating an internal combustion engine create with the simplest and yet effective control and / or Regulation of internal and external exhaust gas recirculation is possible.

This object is achieved according to the invention in a method of the type mentioned at the outset solved that a setpoint for the inert gas proportion in the internal and the external exhaust gas recirculation is recirculated to the combustion chamber. At a  Internal combustion engine of the type mentioned is the Task achieved in that by Control unit a setpoint for the proportion of inert gas in the the internal and external exhaust gas recirculation in the Combustion chamber recirculated exhaust gas can be determined.

By determining the target value according to the invention, it is possible the proportion of inert gas in the internal and external Exhaust gas recirculation to be recorded precisely. With that, exactly controlled and / or regulated how much inert gas in the Combustion chamber is returned. Overall this results a control or regulation of the internal combustion engine, the a reduction in the nitrogen oxides generated Has.

In an advantageous development of the invention the setpoint for the proportion of inert gas in the internal and the external exhaust gas recirculation into the combustion chamber recirculated exhaust gas from an exhaust gas recirculation target rate determined. It is particularly advantageous if the Exhaust gas recirculation target rate using a map from a Torque setpoint is determined.

In an advantageous embodiment of the invention a setpoint for the proportion of inert gas in the internal Exhaust gas recirculation recirculated exhaust gas determined. This The setpoint only refers to the internal one Exhaust gas recirculation. This makes it possible to make comparisons with the Setpoint for internal and external exhaust gas recirculation perform.

In an advantageous development of the invention the setpoint for the proportion of inert gas in the internal Exhaust gas recirculation recirculated exhaust gas from a Overlap of the opening times of the outlet and the Inlet valve determined. It is particularly advantageous  if the target value for the inert gas portion in the over the internal exhaust gas recirculation Dependence on lambda is determined.

In a further advantageous embodiment of the Invention is the target value for the proportion of inert gas in the via the internal exhaust gas recirculation into the combustion chamber recirculated exhaust gas from the setpoint for the Inert gas proportion in the internal and external Exhaust gas recirculation exhaust gas recirculated to the combustion chamber deducted. This already represents one of the above mentioned possibilities of a comparison. The result this subtraction then only refers to the external exhaust gas recirculation.

In an advantageous development of the invention with the difference resulting from the two setpoints the exhaust gas recirculation valve of the external exhaust gas recirculation driven. Since this last mentioned only as mentioned still referring to the external exhaust gas recirculation can a control and / or regulation of the exhaust gas recirculation valve be derived.

It when the position of the Exhaust gas recirculation valve depending on the difference is regulated.

In a further advantageous embodiment of the Invention is the target value for the proportion of inert gas in the via the internal and external exhaust gas recirculation in the Combustion chamber recirculated exhaust gas does not become smaller than that Setpoint for the proportion of inert gas in the internal Exhaust gas recirculation exhaust gas recirculated to the combustion chamber. This ensures that a minimal internal Exhaust gas recirculation, which is always present in the design is taken into account in every case.  

Of particular importance is the implementation of the method according to the invention in the Form of a digital storage medium that is used for a control unit of an internal combustion engine, in particular a motor vehicle is provided. Thereby is on the storage medium Program stored on a computing device, especially on a Microprocessor, executable and suitable for executing the method according to the invention is. In particular, a read-only memory can be used as the storage medium come.

Further features, possible applications and advantages of the invention result from the following description of exemplary embodiments of the invention, which in the Figures of the drawing are shown.

Fig. 1 shows a schematic block diagram of an embodiment of an internal combustion engine according to the invention, and

FIG. 2 shows a schematic block diagram of an exemplary embodiment of a method according to the invention for operating the internal combustion engine of FIG. 1.

In FIG. 1, an internal combustion engine 1 is shown a motor vehicle, in which a piston 2 reciprocating in a cylinder 3 and is movable. The cylinder 3 is provided with a combustion chamber 4 which is delimited inter alia by the piston 2 , an inlet valve 5 and an outlet valve 6 . An intake pipe 7 is coupled to the inlet valve 5 and an exhaust pipe 8 is coupled to the exhaust valve 6 .

In the area of the intake valve 5 and the exhaust valve 6, an injection valve 9 and a spark plug 10 protrude into the combustion chamber 4 . Fuel can be injected into the combustion chamber 4 via the injection valve 9 . The fuel in the combustion chamber 4 can be ignited with the spark plug 10 .

In the intake pipe 7 , a rotatable throttle valve 11 is accommodated, via which air can be supplied to the intake pipe 7 . The amount of air supplied is dependent on the angular position of the throttle valve 11 . A catalytic converter 12 is accommodated in the exhaust pipe 8 and serves to clean the exhaust gases resulting from the combustion of the fuel.

An exhaust gas recirculation pipe 13 leads from the exhaust pipe 8 back to the intake pipe 7 . An exhaust gas recirculation valve 14 is accommodated in the exhaust gas recirculation pipe 13 , with which the amount of the exhaust gas recirculated into the intake pipe 7 can be adjusted. The exhaust gas recirculation pipe 13 and the exhaust gas recirculation valve 14 form a so-called external exhaust gas recirculation EGR.

There is also a so-called internal exhaust gas recirculation. This means that due to an overlap of the opening times of the intake and exhaust valves 5 , 6, exhaust gas is sucked into the combustion chamber 4 of the internal combustion engine 1 from the exhaust pipe 8 . This overlap of the opening times corresponds to an overlap angle of the camshaft.

Overall, exhaust gas is thus supplied to the combustion chamber 4 of the internal combustion engine 1 via the external and internal exhaust gas recirculation. Due to the possibility of operating the internal combustion engine 1 with lambda not equal to "1", the exhaust gas contains a non-combustible inert gas component and a residual air component in both cases. The last-mentioned residual air fraction and the fresh air drawn in via the throttle valve 11 then form the total air supplied to the combustion chamber and determining the combustion.

A tank ventilation line 16 leads from a fuel tank 15 to the intake pipe 7 . In the tank ventilation line 16 , a tank ventilation valve 17 is accommodated, with which the amount of fuel vapor supplied to the intake pipe 7 from the fuel tank 15 can be adjusted. The tank ventilation line 16 and the tank ventilation valve 17 form a so-called tank ventilation TE.

The combustion of the fuel in the combustion chamber 4 causes the piston 2 to move back and forth, which is transmitted to a crankshaft (not shown) and exerts a torque thereon.

A control unit 18 is acted upon by input signals 19 , which represent operating variables of the internal combustion engine 1 measured by sensors. For example, the control unit 18 is connected to an air mass sensor, a lambda sensor, a speed sensor and the like. Furthermore, the control unit 18 is connected to an accelerator pedal sensor which generates a signal which indicates the position of an accelerator pedal which can be actuated by a driver and thus the requested torque. The control unit 18 generates output signals 20 with which the behavior of the internal combustion engine 1 can be influenced via actuators or actuators. For example, the control unit 18 is connected to the injection valve 9 , the spark plug 10 and the throttle valve 11 and the like and generates the signals required to control them.

Among other things, the control device 18 is provided to control and / or regulate the operating variables of the internal combustion engine 1 . For example, the fuel mass injected into the combustion chamber 4 by the injection valve 9 is controlled and / or regulated by the control unit 18, in particular with regard to low fuel consumption and / or low pollutant development. For this purpose, the control unit 18 is provided with a microprocessor, which has stored a program in a storage medium, in particular in a read-only memory, which is suitable for carrying out the control and / or regulation mentioned.

In a first operating mode, a so-called homogeneous operation "hom" of the internal combustion engine 1 , the throttle valve 11 is partially opened or closed depending on the desired torque. The fuel is injected into the combustion chamber 4 by the injection valve 9 during an induction phase caused by the piston 2 . The injected fuel is swirled by the air sucked in simultaneously via the throttle valve 11 and is thus distributed substantially uniformly in the combustion chamber 4 . The fuel / air mixture is then compressed during the compression phase in order to then be ignited by the spark plug 10 . The piston 2 is driven by the expansion of the ignited fuel. The resulting torque essentially depends on the position of the throttle valve 11 in homogeneous operation. In view of a low pollutant development, the fuel / air mixture is set to lambda = 1 or lambda <1 if possible.

In a second operating mode, a so-called homogeneous lean operation "hmm" of the internal combustion engine 1 , the fuel is injected into the combustion chamber 4 during the intake phase, as in the homogeneous operation. In contrast to homogeneous operation, the fuel / air mixture can also occur with lambda <1.

In a third operating mode, a so-called stratified operation "sch" of the internal combustion engine 1 , the throttle valve 11 is opened wide. The fuel is injected from the injection valve 9 into the combustion chamber 4 during a compression phase caused by the piston 2 , specifically locally in the immediate vicinity of the spark plug 10 and at a suitable time before the ignition point. Then the fuel is ignited with the aid of the spark plug 10 , so that the piston 2 is driven in the now following working phase by the expansion of the ignited fuel. The resulting torque largely depends on the injected fuel mass in shift operation. The stratified operation is essentially provided for the idle operation and the partial load operation of the internal combustion engine 1 .

In a fourth operating mode, a so-called homogeneous stratified operation "hos" of the internal combustion engine 1 , a double injection takes place in the same work cycle. Fuel is injected into the combustion chamber 4 from the injection valve 9 during the intake phase and during the compression phase. Homogeneous shift operation thus combines the properties of shift operation and homogeneous operation. With the help of homogeneous shift operation, for example, a particularly smooth transition from shift operation to homogeneous operation and vice versa can be achieved.

In a fifth operating mode, a so-called stratified heating "skh" of the internal combustion engine 1 , a double injection also takes place. Fuel is injected into the combustion chamber 4 from the injection valve 9 during the compression phase and during the working phase. In this way, essentially no additional torque is achieved, but rather a rapid heating of the catalytic converter 12 is brought about by the fuel injected in the working phase. This is important, for example, when the internal combustion engine 1 is cold started.

It is possible to switch back and forth or toggle between the described operating modes of the internal combustion engine 1 . Such switching operations are carried out by the control unit 18 . A changeover is triggered by an operating state of the internal combustion engine 1 or by its executing function of the control device 18 . For example, in the case of a cold start, the fifth operating mode, namely the stratified cat heating, can be triggered, with which the catalytic converter 12 is quickly heated to an operating temperature.

FIG. 2 shows a method that can be carried out by control unit 18 and that is suitable for generating a signal for actuating exhaust gas recirculation valve 14 . The blocks shown in FIG. 2 are represented in the control unit 18 by programs.

The signals described below and in particular the setpoints described differ in the respective operating modes of the internal combustion engine 1 . This is expressed below in that the setpoints are provided with a "$" sign, which represents a placeholder for the respective operating mode.

A map 21 is supplied with a torque setpoint msoll for filling the combustion chamber 4 and the rotational speed nmot of the internal combustion engine 1 . Depending on this, the map 21 generates an exhaust gas recirculation target rate rr $ s. This is a target value for the exhaust gas rate resulting from the internal and external exhaust gas recirculation. This exhaust gas recirculation target rate rr $ s represents the exhaust gas rate that is required to obtain a desired proportion of inert gas via the exhaust gas in the combustion chamber 4 of the internal combustion engine 1 . This desired proportion of inert gas is intended to lower the nitrogen oxides NOx in the exhaust gas. For this purpose, the proportion of inert gas can be adjusted to the respectively desired value using the map 21 .

With the help of a block 22 , the exhaust gas recirculation target rate rr $ s for the exhaust gas rate resulting from the internal and external exhaust gas recirculation is converted into a target value rfr $ s for the filling resulting from the internal and external exhaust gas recirculation in the combustion chamber 4 of the internal combustion engine 1 . This setpoint rfr $ s represents that portion of the filling in the combustion chamber 4 which results from the internal and external exhaust gas recirculation and at which the desired proportion of inert gas is present in the combustion chamber 4 .

In a block 23 , the target value rfr $ s for the filling in the combustion chamber 4 of the internal combustion engine 1 resulting from the internal and external exhaust gas recirculation is multiplied by a target value rlr $ s for the air filling in the combustion chamber 4 resulting from the internal and external exhaust gas recirculation connected. An output signal as1 is thus available at the output of block 23 , which represents a setpoint for the inert gas filling in the combustion chamber 4 resulting from the internal and external exhaust gas recirculation. In other words, the output signal as1 represents the target value for that portion of inert gas that is fed to the combustion chamber 4 via the internal and external exhaust gas recirculation.

An overlap angle NW is supplied to a characteristic diagram 24 , which characterizes the overlap of the opening times of the inlet valve 5 and the outlet valve 6 . Such an overlap of the opening times has the result that during the intake phase, in which only the inlet valve 5 should be open, the outlet valve 6 is at least temporarily open. This not only draws fresh air from the intake pipe 7 into the combustion chamber 4 of the internal combustion engine 1 , but also exhaust gas from the exhaust pipe 8 . As already mentioned, the exhaust gas is composed of the inert gas portion and the residual air portion.

Overall, the internal exhaust gas recirculation thus results from the overlap of the opening times of the intake valve 5 and the exhaust valve 6 . The greater the overlap angle NW, the greater the proportion of inert gas returned. Due to the minimal overlap of the opening times, there is always a minimal amount of inert gas via the internal exhaust gas recirculation.

The speed map nmot of the internal combustion engine 1 is also supplied to the map 24 . From these input signals, the characteristic diagram 24 generates a target value rfri $ s for the exhaust gas portion of the filling in the combustion chamber 4 resulting from the internal exhaust gas recirculation. The setpoint rfri $ s is thus controlled as a function of the overlap angle NW via the map 24 .

This setpoint rfri $ s is first subjected to a density correction with the aid of a block 25 , in order to then be linked with the reciprocal lambda value with the aid of a block 26 . Multiplications are carried out in blocks 25 and 26 . At the output of block 26 , a setpoint riri $ s is then available for the proportion of inert gas in the exhaust gas returned to combustion chamber 4 via the internal exhaust gas recirculation.

As mentioned, the output signal as1 represents the setpoint for the proportion of inert gas that is supplied to the combustion chamber 4 via the internal and external exhaust gas recirculation. As described above, the signal riri $ s represents the target value for the proportion of inert gas that is only supplied to the combustion chamber 4 via the internal exhaust gas recirculation. These two signals act on a maximum value selection 27 .

If the output signal as1 and thus the proportion of inert gas resulting from the internal and external exhaust gas recirculation is greater than the signal riri $ s, the output signal as1 is present as the setpoint rir $ s at the output of the maximum value selection 27 . If, on the other hand, the signal riri $ s and thus the proportion of inert gas resulting only from the internal exhaust gas recirculation is greater than the output signal as1, then this signal riri $ s is present as the setpoint rir $ s at the output of the maximum value selection 27 .

The first case is particularly typical of shift operation. A high proportion of inert gas is desirable there. This manifests itself in a large desired proportion of inert gas resulting from the internal and external exhaust gas recirculation. This proportion of inert gas is usually greater than the proportion of inert gas that can only be generated from the internal exhaust gas recirculation. For this reason, the output signal as1 is passed on in the maximum value selection 27 , which is then present at its output as the setpoint rir $ s.

The second case is particularly typical for homogeneous operation. A small proportion of inert gas is desired there, since the inert gas would reduce the power that is usually required by the internal combustion engine 1 in homogeneous operation. The output signal as1 and therefore the setpoint for the inert gas portion is therefore small. It is possible that the setpoint riri $ s for the proportion of inert gas resulting from the internal exhaust gas recirculation is greater than the output signal as1. In this case, the maximum value selection 27 makes the setpoint rir $ s available as setpoint rir $ s at the output. In other words, this means that due to its insignificance, the desired proportion of inert gas is achieved solely by the internal exhaust gas recirculation.

Through the functions described above in connection with the maximum value selection 27 , it is further achieved that the minimum inert gas fraction already mentioned, which is always present via the internal exhaust gas recirculation, in any case, that is to say also when an output signal as1 becomes zero, via the maximum value selection 27 is passed on as setpoint rir $ s.

The setpoint rir $ s is the proportion of inert gas in the exhaust gas which is returned to the combustion chamber 4 via the internal and external exhaust gas recirculation. This setpoint rir $ s can be used in further controls and / or controls of the internal combustion engine 1 .

Furthermore, the target value rir $ s for the inert gas portion in the exhaust gas returned to the combustion chamber 4 via the internal and external exhaust gas recirculation can be used to control the exhaust gas recirculation valve 14 of the external exhaust gas recirculation. For this purpose, with the aid of a subtraction 28 , the setpoint rir $ s, which relates only to the internal exhaust gas recirculation, is subtracted from the setpoint rir $ s, which, as said, relates to the internal and external exhaust gas recirculation. The output signal as2 of the subtraction 28 , alsi the difference between the two setpoints, only affects the external exhaust gas recirculation.

If the output signal as1 is present at the output of the maximum value selection 27 as the target value rir $ s, the multiplication 28 results in an output signal as2 which is greater than zero. This means that external exhaust gas recirculation is required. However, if the setpoint rir $ s is present at the output of the maximum value selection 27 as the setpoint rir $ s, the subtraction 28 results in the value zero. This means that no external exhaust gas recirculation is required.

The output signal as2 is the setpoint for the proportion of inert gas in the exhaust gas fed to the combustion chamber 4 via the external exhaust gas recirculation. The associated required position of the exhaust gas recirculation valve 14 can be determined therefrom with the aid of lambda. This position can then be set and regulated by means of a sensor assigned to the exhaust gas recirculation valve 14 .

Claims (12)

1. Method for operating an internal combustion engine ( 1 ), in particular a motor vehicle, in which fuel is injected into a combustion chamber ( 4 ) in at least two operating modes, and in which exhaust gas is returned to the combustion chamber ( 4 ) via external and internal exhaust gas recirculation, wherein the exhaust gas in the external exhaust gas recirculation is guided via an exhaust gas recirculation pipe ( 13 ) and in the internal exhaust gas recirculation via an outlet valve ( 6 ), characterized in that a setpoint (rir $ s) for the inert gas component in the internal and external exhaust gas recirculation Exhaust gas returned to the combustion chamber ( 4 ) is determined. 2. The method according to claim 1, characterized in that the target value (rir $ s) for the inert gas portion in the exhaust gas recirculated to the combustion chamber ( 4 ) via the internal and external exhaust gas recirculation is determined from an exhaust gas recirculation target rate (rr $ s) , 3. The method according to claim 2, characterized in that the exhaust gas recirculation target rate (rr $ s) is determined by means of a map ( 21 ) from a torque setpoint (msoll). 4. The method according to any one of claims 1 to 3, characterized in that a setpoint (riri $ s) for the inert gas portion in the recirculated via the internal exhaust gas recirculation Exhaust gas is determined. 5. The method according to claim 4, characterized in that the target value (riri $ s) for the inert gas portion in the exhaust gas recirculated via the internal exhaust gas recirculation is determined from an overlap of the opening times of the exhaust and intake valves ( 5 , 6 ). 6. The method according to any one of claims 4 or 5, characterized in that the target value (riri $ s) for the inert gas portion in the recirculated via the internal exhaust gas recirculation Exhaust gas is determined as a function of lambda. 7. The method according to any one of claims 4 to 6, characterized in that the target value (riri $ s) for the inert gas portion in the exhaust gas returned via the internal exhaust gas recirculation to the combustion chamber ( 4 ) from the target value (rir $ s) for the inert gas portion in which the exhaust gas returned to the combustion chamber ( 4 ) is drawn off via the internal and external exhaust gas recirculation. 8. The method according to claim 7, characterized in that the exhaust gas recirculation valve ( 14 ) of the external exhaust gas recirculation is controlled with the difference (as2) resulting from the two target values. 9. The method according to any one of claims 7 or 8, characterized in that the position of the exhaust gas recirculation valve ( 14 ) is regulated as a function of the difference (as2). 10. The method according to any one of claims 5 to 9, characterized in that the target value (rir $ s) for the inert gas portion in the exhaust gas recirculated to the combustion chamber ( 4 ) via the internal and external exhaust gas recirculation does not become smaller than the target value (riri $ s) for the proportion of inert gas in the exhaust gas returned to the combustion chamber ( 4 ) via the internal exhaust gas recirculation. 11. Digital storage medium, in particular read-only memory, for a control unit ( 18 ) of an internal combustion engine ( 1 ), in particular a motor vehicle, on which a program is stored which can be run on a computing device, in particular on a microprocessor, and for executing a method is suitable according to one of claims 1 to 10. 12. Internal combustion engine ( 1 ), in particular for a motor vehicle, with a combustion chamber ( 4 ) into which fuel can be injected in at least two operating modes, and can be returned to the exhaust gas via an external and an internal exhaust gas recirculation system, the exhaust gas in the external exhaust gas recirculation system an exhaust gas recirculation pipe ( 13 ) and in the internal exhaust gas recirculation via an outlet valve ( 6 ), and with a control unit ( 18 ) for control and / or regulation, characterized in that the control unit ( 18 ) generates a setpoint (rir $ s) for the proportion of inert gas in the exhaust gas returned to the combustion chamber ( 4 ) via the internal and external exhaust gas recirculation.