AT525555B1 - METHOD OF OPERATING AN INTERNAL ENGINE - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (1), in which exhaust gas is recirculated from an exhaust system (4) to an intake system (3) at least in one operating range via at least one EGR valve (18) and at least one exhaust gas recirculation line (6). , wherein base values for the EGR quantity (mEGR) of recirculated exhaust gas and/or an opening of the EGR valve (18) are specified in an engine map of the internal combustion engine (1) and a corrective measure for the EGR quantity (mEGR) is carried out, by measuring the speed (n) of the internal combustion engine (1) and determining a speed difference (Δn) and/or a degree of rotational non-uniformity (δ) within a defined observation period (Δt) and reducing the EGR quantity (mEGR) of recirculated exhaust gas if the speed difference (Δn) and/or the degree of rotational non-uniformity (δ) exceeds a defined threshold value (ΔnG, δG). In order to improve the EGR control and to minimize NOx emissions, it is provided that the combustion of the internal combustion engine (1) is monitored with regard to knocking and the EGR quantity (mEGR) is increased if at least one knocking event (K) - preferably via at least one knock sensor (21) - determined and a defined value (KG) for the at least one detected knock event (K) and/or a defined knock control depth (KR) is exceeded.

Description

Description

The invention relates to a method for operating an internal combustion engine, in which exhaust gas is recirculated from an exhaust system to an intake system at least in one operating range via at least one EGR valve and at least one exhaust gas recirculation line, with base values for an EGR quantity of recirculated exhaust gas and /or an opening of an EGR valve can be specified in an engine map of the internal combustion engine and a corrective measure for the EGR quantity is carried out by measuring the speed of the internal combustion engine and determining a speed difference and/or a degree of rotational non-uniformity within a defined observation period and the EGR quantity of recirculated exhaust gas is reduced when the speed difference and/or the degree of rotational non-uniformity exceeds a defined threshold value, with the combustion of the internal combustion engine being monitored with regard to knocking. The invention also relates to an internal combustion engine for carrying out such a method.

At high combustion temperatures, polluting nitrogen oxides are produced in the engine. It is known that the formation of nitrogen oxides from combustion products can be reduced by recirculating part of the exhaust gas from the exhaust system into the intake system. In internal combustion engines with EGR (EGR = "Exhaust Gas Recirculation") or EGR (AGR = ""Exhaust Gas Recirculation"), part of the exhaust gas, for example 20%, is therefore recirculated into the intake system to reduce the amount of nitrogen oxide in the exhaust gas.

With external exhaust gas recirculation, environmental influences such as air pressure, geodetic altitude, humidity or other influences such as changing the exhaust gas back pressure, for example due to particle filter loading, can lead to a change in the EGR quantity actually carried out. However, a change in the EGR quantity can lead to a deterioration in driving behavior such as jerking and misfiring if the EGR quantity is too high or knocking if the EGR quantity is too low - particularly in the case of high-compression internal combustion engines.

[0004] For this reason, EGR control is used in current internal combustion engines. This usually uses the measured values of a differential pressure sensor across the EGR valve, the flow rate characteristic of the EGR valve as a function of the pressure difference and the EGR temperature for control. This EGR control can keep the EGR rate constant in a range of around +/- 3%, but it cannot decrease the EGR amount when the engine is not smooth or increase the EGR amount when there is knocking.

In production engines, the ignition point is regulated. When knocking occurs, the ignition angle is reduced, ie the ignition angle is retarded. When the knocking stops again, the ignition angle is adjusted back to the original map value. A sensor is used for regulation, which measures vibrations in the engine caused by knocking.

[0006] The knock control can prevent knocking and subsequent damage, but it cannot regulate the internal combustion engine—especially with external exhaust gas recirculation—to an operating point that is the best possible for consumption.

In production engines, the smooth running of the internal combustion engine is evaluated for diagnosis. To do this, the degree of rotational non-uniformity of the crankshaft is calculated, for example from the signals from a speed sensor formed by a 60-2 sensor wheel. Above a certain degree of rotational non-uniformity, it is assumed that this is due to misfiring during combustion. These misfires are counted. From a certain number of misfires, damage to the catalytic converter must be expected, and the driver is then asked to visit a workshop.

It is known that the rough running, ie the degree of rotational non-uniformity, increases with an increasing amount of EGR. Therefore, the rough running or the degree of rotational non-uniformity is a limiting factor for the EGR amount.

The US 3,872,846 A describes a control system for an internal combustion engine with exhaust gas

recirculation, wherein the rotational non-uniformity of the internal combustion engine is controlled within a defined range. The control system receives a rotational non-uniformity signal and uses it to generate a control signal for changing the position of the exhaust gas recirculation valve. This is intended to set the maximum possible amount of recirculated exhaust gas at a defined permissible maximum degree of non-uniformity. The EGR amount is reduced if the running is very uneven, and the EGR amount is increased if the running is smooth.

This regulation, which is only based on the rotational non-uniformity as a controller input variable, cannot prevent that in certain operating ranges--particularly at high loads where combustion knock occurs--too little EGR is supplied to the internal combustion engine. This type of control without taking knocking into account therefore only works in areas in which no knocking occurs - i.e. at part load of an engine.

DE 10 2016 123 636 A1 discloses a method and system for regulating engine operating parameters such as exhaust gas recirculation based on road roughness conditions. The EGR flow rate is increased based on an increased road roughness estimate. This is to mask NVH associated with increased EGR the NVH associated with rough road conditions. As an additional measure, a knock threshold value of an engine knock sensor is switched from a first knock threshold value associated with less spark timing advance to a second knock threshold value associated with more spark timing advance when the engine is operated with the increased EGR flow rate.

[0012] The object of the invention is to improve the EGR control and to include the operating parameters that occur in the control in the best possible way. This means that regulation is not only possible at partial load, but also at high loads including full load.

The object is achieved according to the invention by a method mentioned at the outset in that the exhaust gas quantity is increased when at least one knocking event is detected—preferably via at least one knock sensor—and a defined value for the at least one knocking event detected and/or a defined knock control depth is exceeded.

The combustion is therefore monitored with regard to knocking and with regard to smooth running and the amount of exhaust gas is increased if at least one knocking event is detected with satisfactory running smoothness and a defined value for the at least one knocking event detected and/or a defined knock control depth is exceeded. If the engine runs too rough and the combustion does not knock at the same time, the amount of exhaust gas that is recirculated is reduced.

With the method according to the invention, not only the rotational non-uniformity, but also the knocking of the internal combustion engine is included in the control and the EGR control is thus improved. This means that regulation is not only possible at partial load, but also at high loads including full load.

The change in engine speed is observed over a defined period of time. If the engine speed change exceeds a defined value, the amount of EGR is reduced. The control can take place via an EGR controller, for example a PI controller or an I controller.

[0017] On the other hand, too low an EGR amount may lead to knocking. If the knock sensor signals knocking, the EGR amount may be increased. This can happen, for example, by opening the EGR valve further. When the EGR valve is wide open or fully open, the EGR amount can be further increased by closing the pre-throttle valve, which is arranged in the intake system upstream of an orifice of the exhaust gas recirculation line. Closing the pre-throttle valve increases the pressure difference to the EGR line and thus the EGR throughput.

Advantageously, an EGR valve arranged in the exhaust gas recirculation is opened to increase the EGR quantity.

Alternatively or additionally, a pre-throttle valve is closed to increase the EGR amount, which is arranged in the intake system upstream of a mouth of the exhaust gas recirculation line in the intake system.

In one embodiment of the invention, it is provided that the position of the EGR valve and/or the position of the pre-throttle valve is corrected as a function of at least one operating parameter, the operating parameter preferably being selected from the following group: operating mode of an electric exhaust gas turbocharger; pressure ratio across the EGR valve; Loading of a particle filter arranged in the exhaust system.

The opening position of the EGR valve is further increased when the electric exhaust gas turbocharger is operated as a motor. The opening position of the EGR valve is reduced when the electric exhaust gas turbocharger is operated as a generator.

The opening position of the EGR valve is decreased as the pressure ratio of the pressure in the exhaust pipe upstream of the EGR valve to the pressure in the exhaust pipe downstream of the EGR valve is increased. The opening position of the EGR valve is increased as the pressure ratio of the pressure in the exhaust pipe upstream of the EGR valve to the pressure in the exhaust pipe downstream of the EGR valve is reduced. If the pressure difference is too low, this can be increased by closing the pre-throttle valve upstream of where the exhaust gas recirculation line opens into the intake system.

[0023] A higher loading of a particle filter arranged in the exhaust system for gasoline engines (GPF=Gasoline Particle Filter) leads to a higher back pressure in the exhaust system. As a result, the opening position of the EGR valve can be reduced.

After retarding the ignition timing due to knocking being detected, the ignition timing is advanced again if no further knock event occurs. However, during this advance adjustment, a later ignition angle than stored in the basic map is still output. This still later ignition angle can be ignored when reducing the EGR rate. When the knock control is reversed, no further opening of the EGR valve is therefore necessary.

In a further embodiment of the invention it is provided that at least one - preferably several times - carried out corrective measure of the EGR amount is entered in the engine map. The control of the exhaust gas recirculation is therefore self-learning. This means that repeatedly required corrective measures, which have to be carried out again and again in the case of a repeatable configuration of engine parameters, are automatically entered into the engine characteristics map by the electronic control unit.

[0026] In order to avoid interventions in the EGR control being carried out by incorrect signals

it is advantageous if the EGR control is selectively activated and deactivated. Is to

provided in an embodiment of the invention that corrective action of the EGR

Quantity to be carried out only if

* the determined degree of rotational non-uniformity corresponds to at least a defined minimum degree of rotational non-uniformity, and/or

* a certain knock control depth is exceeded, and/or

* a current accelerator pedal gradient corresponds at most to a defined maximum accelerator pedal gradient and/or

* a current engine load corresponds to at least a defined minimum engine load and/or

* the engine load gradient does not exceed a predefined value and/or

* a current engine speed corresponds to at least a defined minimum engine speed and/or

* a shift clutch arranged in the drive train of the internal combustion engine is completely separated or completely closed.

[0027] With the method according to the invention, exhaust gas recirculation quantities can be regulated very close to the optimum without the engine running unevenly or combustion knocking.

An initially mentioned internal combustion engine is suitable for carrying out the method, in which exhaust gas can be recirculated from an exhaust system to an intake system at least in one operating range via at least one exhaust gas recirculation line, with a speed sensor for determining a degree of rotational non-uniformity of the internal combustion engine, the EGR quantity of recirculated Exhaust gas can be reduced when the degree of rotational non-uniformity exceeds a defined threshold value for the degree of rotational non-uniformity.

To achieve the object, the invention provides that the internal combustion engine has at least one knock sensor for detecting knock events during combustion, and that the EGR quantity can be increased depending on the occurrence of at least one knock event and/or a defined knock control depth.

The invention will be explained in more detail using a non-limiting exemplary embodiment, which is illustrated in the figures.

[0031] Therein schematically show:

1 shows an internal combustion engine for carrying out the method according to the invention, [0033] FIG. 2 shows a control map for the EGR control,

3 and 4 show an operating diagram of the internal combustion engine during the method according to the invention and

5 shows the method according to the invention in a block diagram.

Fig. 1 shows a schematic view of a spark-ignited internal combustion engine 1 with a plurality of cylinders 2, with an intake system 3 and an exhaust system 4, and a low-pressure exhaust gas recirculation system 5 with an exhaust gas recirculation line 6 between the intake system 3 and the exhaust system 4. The internal combustion engine 1 has an exhaust gas turbocharger 7 with a compressor 9 arranged in the inlet line 8 of the inlet system 3 and an exhaust gas turbine 11 arranged in the outlet line 10 of the outlet system 4 . An air mass flow meter 12 and a pre-throttle valve 13 are arranged in the intake line 8 upstream of the compressor 9 , and an intercooler 14 and a throttle valve 130 are arranged downstream of the compressor 9 . A catalytic converter 15 and a particle filter 16 are arranged in the exhaust line 10 downstream of the exhaust gas turbine 11 . The exhaust gas recirculation line 6 of the exhaust gas recirculation system 5 branches off from the exhaust line 10 downstream of the exhaust gas turbine 11 and upstream of the particle filter 16, either upstream of the catalytic converter 15 (see dotted lines), or downstream of the catalytic converter 15 (see solid lines). In the exhaust gas recirculation line 6, an EGR cooler 17, an EGR valve 18 and a condensate trap 19 are arranged.

A speed sensor 20 for measuring the engine speed n and at least one knock sensor 21 are provided as standard in the internal combustion engine 1, which vibrations on the engine that are caused by knock events K are measured. The values measured by speed sensor 20 and knock sensor 21 are supplied to an electronic control unit 22 for evaluation and regulation of the exhaust gas recirculation. At least one characteristic map for basic values for the EGR quantity meer or an EGR valve position is stored in the electronic control unit 22 . In a control map, which, for example, controls an I controller as an output value, one axis is described by smooth running and the second axis by the knock control depth, for example averaged over all cylinders.

2 shows a control map for the control correction C:eRr of the recirculated exhaust gas using the example of an II controller, with the rotational non-uniformity degree 5 defined by the engine speed fluctuations An within an observation period At of, for example, 50 ms being used as the first control axis for the control. which represents a measure of smooth running - and the average knock control depth KR is plotted as the second control axis. The lines show l-knob parameters. Negative values of the control correction Ceer close the EGR valve 18, positive values of the control correction Ce:er open the EGR valve 18: the larger the value, the faster the I controller runs.

The degree of rotational non-uniformity 6 within an observation period Δt can be calculated as follows:

Nınax 7 min ö = ar

. Nmean with max seen maximum speed within the observation period At Amin ereen maximum speed within the observation period At, MNmean +... average speed within the observation period At.

The knock control depth KR denotes the value by which the ignition point must be retarded in order to enable the internal combustion engine 1 to be operated without knocking combustion. The knock control depth can be evaluated separately for each cylinder or averaged for all cylinders.

3 and 4 show an operating diagram of the internal combustion engine 1 while the method according to the invention is being carried out. The parameters speed n, opening position Vear of EGR valve 18, engine load L, intake pressure pin (see also FIG. 1), knock control depth KR and control correction CeeRr are plotted against time t.

[0042] FIG. 3 serves to illustrate the measures between the times t; and t, after a knock event has occurred. From time t1 onwards, the occurrence of a knock event leads to a mean knock reduction at the knock control depth KR of, for example, 2.5° CA, as indicated by reference symbol a. The downregulation phase is denoted by arrow b. The knocking event results in the EGR controller of the control unit 22 issuing a positive control correction Ceer (see arrow c), which causes the EGR valve 18 to open further (see arrow d).

4 serves to illustrate the measures taken during the observation period t to ts. The occurrence of a speed change An of around 20 rpm within the observation period At=t3-t2 of around 50 ms (see arrow e) causes the EGR controller of the control unit 22 to output a negative control correction C:eRr (see arrow f) , which causes a smaller opening of the EGR valve 18 (see arrow g).

The method according to the invention provides that the smooth running and the knock sensor signal are used directly as control input for the EGR control. In addition to the first axis defined by the smooth running or the degree of rotational non-uniformity 5, a second axis is therefore defined for the EGR control, which prevents the internal combustion engine 1 from being supplied with too little recirculated exhaust gas. This second axis is the knock control intervention. The EGR quantity meer is not rigidly regulated via the engine map, but rather the EGR quantity mecRr is currently adapted to the smooth running or the knocking of the internal combustion engine 1 .

For this purpose, the speed change An of the engine speed n is observed over a small observation period At between 10 ms to 100 ms, for example 50 ms, and a degree of rotational non-uniformity 6 is determined therefrom. If the speed change An of the engine speed n within the observation period At exceeds a defined limit value Ance, i.e. if the degree of rotational irregularity ö exceeds a defined limit value öe, it is assumed that an excessive EGR quantity meer causes this rough running. The EGR amount MecRr is then decreased by further closing the EGR valve 18 . This takes place in a controlled or regulated manner via an EGR controller integrated, for example, in the electronic control unit 22, for example a PI controller or an I controller. As an alternative to evaluating the speed signal, smooth running determined by the vehicle diagnostic system can also be used.

On the other hand, too low an EGR amount can lead to knocking at high engine loads or at very high compression ratios, even at moderate loads. If the knock sensor 21 signals a knock event, the EGR amount may be increased further by opening the EGR valve 18 further. When the EGR valve 18 is wide open or fully open, the EGR quantity can be increased by closing the pre-throttle flap 13 and thus

representing higher pressure difference across the EGR valve 18 can be further increased.

[0047] Further corrections to the positions of the EGR valve 18 can be made...

* ... depending on the operating status of the electric exhaust gas turbocharger 7: If the electric exhaust gas turbocharger 7 is operated as a motor, the opening position of the EGR valve 18 is increased; "If the electric exhaust gas turbocharger 7 is operated as a generator, the opening position of the EGR valve 18 is reduced;

* ... depending on the pressure difference across the EGR valve 18: A higher pressure ratio leads to a reduction in the opening position of the EGR valve 18;

* ... depending on the loading of the particle filter 16: Higher loading leads to higher back pressure and thus to a reduction in the Oopening position of the EGR valve 18;

* ... depending on the EGR temperature: higher temperature leads to opening of the EGR valve 18;

* ... depending on the intake air and/or intake manifold temperature: Higher temperatures cause the EGR valve 18 to open.

5 schematically shows the method according to the invention in a block diagram. In step S1, it is examined whether the degree of rotational non-uniformity δ exceeds a defined threshold value δ@ and/or whether the speed difference An exceeds a defined threshold value Ane within an observation period At of, for example, 50 ms. If this is the case, then in step S2 the control correction C:eRr is changed in such a way that the EGR quantity is lowered more, ie for example the EGR valve 18 is closed.

In step S3, it is examined whether knocking events K are taking place or whether the number of knocking events K counted within an observation period exceeds a defined threshold value Ka. If this is the case, then in step S4 the control correction C:cR is changed in such a way that the EGR quantity is increased more, ie for example the EGR valve 18 is opened further.

Steps S1 and S3 can be carried out continuously or discontinuously, simultaneously or sequentially and are carried out repeatedly during engine operation as required in those operating ranges of internal combustion engine 1 in which exhaust gas recirculation is provided.

In a further embodiment of the invention it can be provided that the control of the exhaust gas recirculation takes place in a self-learning manner. This means that repeatedly required corrective measures, which have to be carried out again and again given a repeatable configuration of engine parameters, are automatically entered into the engine map by the electronic control unit 22 and the EGR rates stored in the engine map are thus adapted.

In the method according to the invention, the EGR control takes place without any additional sensors, only with the sensors 20, 21 present in production vehicles for determining the speed n and for determining knock events K. Control variables are speed fluctuations or rotational non-uniformity δ and knock control depth or number of knock events K.

The EGR control is selectively activated and deactivated so that poor road conditions, for example, which affect the smooth running of the internal combustion engine 1, do not cause an adaptation of the EGR rate. The same applies, for example, to gear shifts or similar disruptive influences that affect the speed n. For example, it can be provided that a controller intervention is only permitted when the clutch 23 is fully engaged or disengaged (see FIG. 1), but not during the closing process. Furthermore, it is favorable if a minimum degree of rotational non-uniformity δmin,e, a maximum accelerator pedal gradient, a minimum engine load Lmin,a and/or a minimum engine speed nmin,a are/is specified for an EGR controller intervention. Furthermore, the control can be deactivated if the gradient of the engine load exceeds a predefined value.

Claims (13)

patent claims 1. A method for operating an internal combustion engine (1), in which exhaust gas is recirculated from an exhaust system (4) into an intake system (3) at least in one operating range via at least one EGR valve (18) and at least one exhaust gas recirculation line (6), wherein Base values for an EGR quantity (sea) of recirculated exhaust gas and/or an opening of the EGR valve (18) are specified in an engine map of the internal combustion engine (1) and a corrective measure for the EGR quantity (sea) is carried out by the Speed (n) of the internal combustion engine (1) is measured and a speed difference (An) and/or a degree of rotational non-uniformity (3) is determined within a defined observation period (At) and the EGR quantity (meer) of recirculated exhaust gas is reduced if the speed difference ( An) and/or the degree of rotational non-uniformity (6) exceeds a defined threshold value (Anc, öc), the combustion of the internal combustion engine (1) being monitored with regard to knocking, characterized in that the EGR quantity (meer) is increased if at least one knock event (K) - preferably via at least one knock sensor (21) - detected and a defined value (Ke) for the at least one detected knock event (K) and/or a defined knock control depth (KR) is exceeded. 2. The method according to claim 1, characterized in that to increase the EGR quantity (sea) in the exhaust gas recirculation line (6) arranged EGR valve (18) is opened. 3. The method according to claim 1 or 2, characterized in that to increase the EGR quantity (sea) a pre-throttle flap (13) is closed, which is arranged in the intake system (3) upstream of an outlet of the exhaust gas recirculation line (6) into the intake system (3). . 4. The method according to claim 2 or 3, characterized in that a position of the EGR valve (18) and/or a position of the pre-throttle valve (13) is corrected as a function of at least one operating parameter, the operating parameter preferably being selected from the following group: operating mode of a electric exhaust gas turbocharger (7); pressure ratio across the EGR valve (18); Loading of a particle filter (16) arranged in the exhaust system (4). 5. The method according to any one of claims 1 to 4, characterized in that at least one - preferably several times - carried out corrective measure of the EGR quantity (mecR) is entered in the engine map. 6. The method according to any one of claims 1 to 5, characterized in that a corrective measure of the EGR quantity (meer) is only carried out if the determined degree of rotational non-uniformity (5) corresponds to at least a defined minimum degree of rotational non-uniformity (Ömin,p,). 7. The method according to any one of claims 1 to 6, characterized in that a corrective measure of the EGR quantity (meer) is only carried out if a specific knock control depth (KR) is exceeded. 8. The method according to any one of claims 1 to 7, characterized in that a corrective measure of the EGR quantity (sea) is only carried out if a current accelerator pedal gradient corresponds to a maximum of a defined maximum accelerator pedal gradient. 9. The method according to any one of claims 1 to 8, characterized in that a corrective measure of the EGR quantity (mer) is only carried out if a current engine load (L) corresponds to at least a defined minimum engine load (Lmin,e). 10. The method according to any one of claims 1 to 9, characterized in that a corrective measure of the EGR quantity (mer) is only carried out if a gradient of the engine load (L) does not exceed a certain value. 11. The method according to any one of claims 1 to 10, characterized in that a corrective measure of the EGR quantity (mer) is only carried out if a current engine speed (n) corresponds to at least a defined minimum engine speed (nmin,e). 12. The method according to any one of claims 1 to 11, characterized in that a corrective measure of the EGR quantity (sea) is only carried out when a drive train of the internal combustion engine (1) arranged clutch is completely separated or completely closed. 13. Internal combustion engine (1), in which exhaust gas can be recirculated from an exhaust system (4) to an intake system (3) at least in one operating range via at least one exhaust gas recirculation line (6), with a speed sensor (20) for determining a degree of rotational non-uniformity (&) of the Internal combustion engine (1), wherein an EGR quantity (meer) of recirculated exhaust gas can be reduced if the degree of rotational non-uniformity (&) exceeds a defined threshold value (Sc) for the degree of rotational non-uniformity (6), for carrying out the method according to one of Claims 1 to 12 , characterized in that the internal combustion engine (1) has at least one knock sensor (21) for detecting knock events (K) during combustion, and that the EGR quantity (meer) as a function of the occurrence of at least one knock event (K) and/or a defined knock control depth (KR) can be increased. 3 sheets of drawings