DE102016205951B4 - Method and control device for operating an internal combustion engine - Google Patents

Abstract

Method for operating an internal combustion engine (1) with an exhaust gas tract which has an exhaust gas catalytic converter (2), a first exhaust gas probe (3) at an exhaust gas catalyst inlet (5) and a second exhaust gas probe (4) at an exhaust gas catalytic converter outlet (6), wherein the internal combustion engine (1) is operable in a super-purge mode and a normal mode, - in which an air-fuel ratio in a combustion chamber of the internal combustion engine (1) is controlled by adjusting an injection amount and / or an amount of intake air and / or a supercharging duration, wherein, in the normal mode, a set of normal control parameters is used to maintain the air-fuel ratio in the combustion chamber within predetermined limits, wherein in the over-purge mode, a set of over-purge control parameters is used to adjust the air-fuel ratio to the exhaust catalyst Input (5) based on measured values of the air-fuel ratio of the first exhaust gas probe (3) and / or the second exhaust gas probe (4) ) within predetermined limits and in which, in the over-purge mode, the over-purge duration is controlled based on the measurements of the air-fuel ratio of the first exhaust gas probe (3) and / or the second exhaust gas probe (4).

Description

The present invention relates to a method, a computer program and a control device for operating an internal combustion engine in a normal mode and an overflushing mode with an exhaust tract comprising a first exhaust gas probe, a second exhaust gas probe and an exhaust gas catalyst, in particular consisting of one or more monoliths.

In internal combustion engines with a turbocharger, it is known to operate the internal combustion engine at a low speed range in a super-purge mode in which both intake and exhaust valves of a cylinder are intersectingly opened during an exhaust stroke so that a certain amount of fresh air flows through the cylinder. without participating in a combustion. As a result, the speed increase of the turbocharger is improved, whereby a rapidly increasing boost pressure of the turbocharger can be achieved. However, the flushing leads in an exhaust tract to the mixing of exhaust gases and fresh air. As a result of this mixing, the composition of a fuel / air ratio λ changes, so that an exhaust gas catalyst no longer optimally cleans the exhaust gas.

In previous internal combustion engines, a control for adjusting the air-fuel ratio during the over-purge is performed such that a stoichiometric lambda is set in a combustion chamber. As a result, the exhaust gas of the internal combustion engine consists of an exhaust gas stream mixed with a stream of fresh air that has been flushed through the respective cylinder. As a result, the A of the exhaust gas shifts to an air-rich side and the exhaust gas catalyst no longer operates in the optimum range, whereby deteriorate exhaust gas values of the internal combustion engine.

In previous internal combustion engines, a trim control is also used. In the trim control, a second exhaust gas probe downstream of the catalytic converter is used to maintain a first exhaust gas probe upstream of the catalytic converter, which regulates the fuel-air ratio in a combustion chamber of the internal combustion engine in its optimal control position.

In the overflow mode, there is an admixture of fresh air to the exhaust gas, especially when changing into or out of the overflushing mode. As a result, there are large fluctuations in the air-fuel ratio. A trim control could not react quickly enough to this change, so that there are large fluctuations in the regulation. Therefore, so far in overflow mode, the trim control is disabled.

The document DE 10 2009 045 792 A1 Proposes to use a known trim control even when the internal combustion engine is operating in a Überspülmodus. For this purpose, for some operating points which are characterized by the degree of flushing and the rotational speed, compensation values for a first measuring probe located upstream of the catalytic converter are determined and stored by means of a second measuring probe located downstream of an exhaust gas catalyst, which compensate for the measured value of the first measuring probe in the overflushing mode.

The document DE 10 2012 204 885 B3 discloses a method of operating an internal combustion engine, which also includes two probes, one upstream and one downstream of a catalytic converter. In this case, depending on operating parameters of the internal combustion engine, either the first or the second measuring probe is used for the regulation of the air ratio.

The document DE 10 2009 007 572 A1 discloses an internal combustion engine including two probes, one upstream and one downstream of a catalytic converter, employing a trim control in which a control parameter of a trim regulator is adjusted to an oxygen load of the exhaust gas.

It is the object of the invention to provide a method, a computer program and a control device which, even in the overflow mode, keep the air / fuel ratio within predefined limits so that the exhaust gas catalytic converter operates in the optimum range.

This object is solved by the features of claims 1, 8 and 9. Advantageous embodiments will be apparent from the dependent claims.

The invention provides a method of operating an internal combustion engine having an exhaust tract having an exhaust catalyst, a first exhaust gas probe at an exhaust catalyst inlet, and a second exhaust gas probe at an exhaust catalyst outlet, wherein the internal combustion engine is operable in a super-purge mode and a normal mode. In the method, an air-fuel ratio in a combustion chamber of the internal combustion engine is controlled by adjusting an injection amount and / or an amount of intake air and / or an over-purge duration. In the method, in the normal mode, a set of normal control parameters is used to maintain the air-fuel ratio in the combustion chamber within predetermined limits, and in the over-purge mode, a set of over-purge control parameters is used to determine the air-fuel ratio on the engine Exhaust catalyst inlet based on measurements of the air-fuel ratio of the first exhaust gas probe and / or the second exhaust gas probe to keep within predetermined limits. Further, in the over-purge mode, the over-purge duration is controlled based on the measured values of the air-fuel ratio of the first exhaust gas probe and / or the second exhaust gas probe.

The control of the air-fuel ratio also in the over-purge mode with its own set of over-purge control parameters based on measured values of the air-fuel ratio of the first exhaust gas probe and / or the second exhaust gas probe, prevents fluctuations of the control when changing from one operating mode to another. Further, therefore, in each mode of operation, accurate and appropriate control is possible that will accommodate the different compositions of the exhaust gas in the different modes of operation.

In an expedient embodiment of the method, the fuel-air ratio is also controlled in the over-purge mode based on the first and the second exhaust gas probe. This makes it possible to precisely control the air-fuel ratio and to improve a control position of the first exhaust gas probe by the second exhaust gas probe.

In an expedient embodiment, it is provided that in the set of over-purge control parameters, the desired value is a stoichiometric air-fuel ratio at the exhaust-gas catalyst inlet. As a result, the catalytic converter is able to optimally clean the exhaust gas.

In an expedient embodiment, provision is made for a measured value of the fuel / air ratio of the first exhaust gas probe to be used in the overflush mode for PI control of the air / fuel ratio, so that a stoichiometric air / fuel ratio is present at the exhaust gas catalyst inlet. By the PI control of the air-fuel ratio, based on the measured value of the air-fuel ratio of the first exhaust gas probe, both a fast control and a stationary accuracy of the control is ensured.

In an expedient refinement, it is provided that in the over-purge mode, a measured value of the air-fuel ratio of the second exhaust gas probe is used for an I control of the first exhaust gas probe. This regulation keeps the measuring and control range of the first exhaust gas probe in the optimum control position. As a result, the control of the air-fuel ratio by the first exhaust gas probe becomes more accurate and less subject to fluctuation.

In an expedient refinement, it is provided that in the overflush mode, a measured value of the fuel / air ratio of the second exhaust gas probe is used for a P control of the air / fuel ratio, so that a stoichiometric air / fuel ratio is present at the exhaust gas catalyst inlet. Such a regulation has the effect that, in the event of high fluctuations or in the case of incorrect measurements of the first exhaust gas probe, regulation of the air-fuel ratio is still provided. Furthermore, this second control serves to control and correct the control based on the measured values of the first exhaust gas probe.

In an expedient refinement, it is provided that in the overflush mode, the fuel injection quantity is regulated based on the measured values of the air-fuel ratio of the first exhaust gas probe and / or the second exhaust gas probe. Since, in the over-purge mode, the exhaust gas consists not only of the combusted fuel-air mixture from the combustion chamber but also of the amount of over-purged air, there is thus the possibility, in the over-purging mode, of both components of the exhaust gas, i. Exhaust gas and overflowed fresh air to regulate. By the control, based on the measured values of the air-fuel ratio of the first and / or the second exhaust gas probe, a higher accuracy is achieved.

The present invention further includes a computer program with computer program code stored on a machine-readable medium which can be loaded directly into the internal memory of a digital computer and comprises software sections for carrying out the inventive method when the program is executed on a computer.

The invention further comprises a control device having a control unit for operating an internal combustion engine with an exhaust gas tract, which has an exhaust gas catalyst, a first exhaust gas probe at an exhaust gas catalyst inlet and a second exhaust gas probe at an exhaust gas catalyst outlet, wherein the internal combustion engine can be operated in an overflushing mode and a normal mode is. The control device is configured to regulate an air-fuel ratio in a combustion chamber of the internal combustion engine by adjusting an injection quantity and / or an amount of intake air and / or an overflush duration; in the normal mode, using a set of normal control parameters to maintain the air-fuel ratio in the combustion chamber within predetermined limits; and in the over-purge mode, using a set of over-purge control parameters to maintain the air-fuel ratio at the exhaust catalyst inlet within predetermined limits.

The control device further comprises further means for carrying out the method according to the invention.

As a result, the invention provides the means required for carrying out the method according to the invention.

The present method makes it possible to use measured values of the first and / or the second exhaust probe for regulating the air / fuel ratio even in the overflush mode, in order to precisely regulate this ratio and adapted to the respective operating mode. Furthermore, by using separate rule sets for each of the modes of operation, excessive vibration of the control when changing between the modes of operation is prevented.

The figure shows a schematic structure of an engine with an exhaust gas catalyst, which illustrates the various control circuits of the method according to the invention.

The figure shows a motor 1 which is installed in a motor vehicle. The motor 1 is an internal combustion engine with direct fuel injection. However, an embodiment of the engine with intake manifold injection is just as possible. For cleaning exhaust gases of the engine 1 is the engine 1 an exhaust gas catalyst 2 downstream. The catalytic converter 2 is designed as a three-way catalyst. At a catalytic converter inlet 5 ie, in the exhaust stream upstream of or upstream of the exhaust catalyst 2 , is a first exhaust gas probe 3 arranged. Furthermore, at an exhaust gas catalytic converter output 6 that is, in the exhaust stream downstream of or after the exhaust catalyst 2 , a second exhaust gas probe 4 arranged.

In a normal mode of the engine 1 goes through the engine 1 a sequence of four bars: a suction, a compression, a working and an exhaust stroke. It is in combustion chambers of the engine 1 burned a fuel-air mixture. The resulting exhaust gas is in the exhaust gas catalyst 2 cleaned. This converts nitrogen oxides, carbon monoxide and burnt fuel into carbon dioxide, nitrogen and water.

For optimal conversion of the exhaust gas through the catalytic converter 2 is a stoichiometric air-fuel ratio λ advantageous. This is the case when λ is the value 1 or assumes a value close to 1 in the so-called lambda window (λ C [0.97, 1.03]). If the lambda value lies below the lambda window, ie λ <0.97, the air-fuel ratio is low in air or rich in fuel, and this is referred to as a rich mixture. If λ is above the window, ie λ> 1.03, then the air-fuel ratio is rich in air or fuel and one speaks of a lean mixture.

The first exhaust gas probe 3 and the second exhaust gas probe 4 are each lambda probes, with the aid of the fuel-air ratio λ is detected. A reading of the air-fuel ratio of the first exhaust gas probe 3 is for a PI control 7 the air-fuel ratio A used. The PI control 7 causes it in the combustion chambers of the engine 1 a stoichiometric lambda is set. The manipulated variables used here are an injection quantity of the fuel into the combustion chamber or a quantity of the intake air. These manipulated variables are influenced by a throttle valve and the injectors.

In normal mode also the second exhaust gas probe 4 used to regulate the first exhaust gas probe 3 optimally adjusted. A reading of the air-fuel ratio of the second exhaust gas probe 4 is doing for an I-control 8th the first exhaust gas probe 3 used. This method, known as trim control, is used for fine adjustment of the first exhaust gas probe 3 ,

In normal mode of the engine 1 is for the PI control 7 and the I-regulation 8th uses a set of normal control parameters. In this sentence, the setpoint is a stoichiometric lambda in the combustion chamber. Furthermore, in this sentence, the respective I-shares and the P-share of the PI-regulation 7 and the I-regulation 8th stored and these stored values are only used in normal mode for regulation.

Thereby, the air-fuel ratio λ is regulated so that the exhaust gas catalyst 2 can convert the exhaust gases optimally.

In an over-purge mode of the engine 1 There is in each combustion chamber a so-called. Überspülen between the ejection and the intake stroke. In this case, both exhaust valves and intake valves are opened intersectingly in each combustion chamber during the Aushubtaktes. As a result, fresh air flows from the intake valves through the combustion chamber to the exhaust valves. This process is called overflow. With respect to the exhaust gas flow, the purge results in that of each of the exhaust ports the cylinder in the engine 1 alternately a combusted fuel-air mixture and a "fresh air mixture" to the catalytic converter 2 flows. This results in the exhaust gas catalyst inlet 5 a mixture of exhaust gas and "fresh air". In order to achieve a lambda close to 1 in this mixture, the overflow mode method of the present invention uses a set of overflush control parameters that is different from the set of normal control parameters.

In the set of over-purge control parameters, a set point is λ = 1 at the exhaust catalyst inlet 5 given. To the sum of the exhaust flow and the fresh air flow at the exhaust catalyst inlet 5 To achieve the value λ = 1, a rich fuel-air mixture is burned in the combustion chamber. The combustion exhaust gas thus has a λ <1. This exhaust gas is in front of the exhaust catalyst inlet 5 mixed with fresh air streams, so that in the sum of a λ sets close to one.

Similar to the normal mode, the measured value of the first exhaust gas probe is in the overflow mode 3 for a PI control 7 the air-fuel ratio in the engine 1 used. However, for the overflow mode in the set of overflow control parameters, separate values for the P and I portions of this PI control will become 7 created and used. Furthermore, in the over-purge mode, the measured value of the second exhaust gas probe also becomes 4 for an I-regulation 8th the control position of the first exhaust gas probe 3 using a separate I-portion for the over-flush mode in the set of over-purge control parameters. Thus a trim control is also active in the overflow mode. Furthermore, the measured value of the second exhaust gas probe 4 for a P-control 9 the fuel-air mixture in the engine 1 used, with the P component of this P control 9 in the set of overflow control parameters for the overflow mode.

The use of separate control parameter sets for the different operating modes prevents a fluctuation of the learned I component of the respective control when changing between the different operating modes, because in each mode own parameters are used. Thereby, one does justice to the fact that in the overflow mode, unlike in the normal mode, the exhaust additionally contains a part of fresh air. By setting a rich mixture in the combustion chambers of the engine 1 In the over-purge mode, the mixture of combusted exhaust gas and fresh air at the inlet of the catalytic converter can 2 within the lambda window. It is also possible to control a superfluous dwell time, ie, the period of time in which both the intake valves and the exhaust valves of the respective combustion chamber are open. In particular, it is therefore possible that both the PI control 7 as well as the P-control 9 access camshaft setpoints. Thereby, it is possible to control, in particular to reduce, the amount of the overflowed air contained in the exhaust gas flow. The regulations can thus regulate both components, over-purged air and exhaust gas, which consists of the exhaust gas flow in the overflow mode.

Thus, even in the over-purge mode, the method enables setting of an optimal air-fuel ratio for three-way catalyst conversion based on measurements. As a result, it is now possible for an internal combustion engine to use an overflushing mode without the exhaust gas values deteriorating. The use of separate control parameter sets for each of the operating modes additionally has the effect that there is no excessive fluctuation in the control when changing from one operating mode to another, in particular in those controls which have an I component.

LIST OF REFERENCE NUMBERS

1

engine

2

catalytic converter

3

gas probe

4

gas probe

5

Catalytic converter input

6

Catalytic converter output

7

PI control

8th

I control

9

P control

Claims (10)

Method for operating an internal combustion engine (1) with an exhaust gas tract, which has an exhaust gas catalytic converter (2), a first exhaust gas probe (3) at an exhaust gas catalyst inlet (5) and a second exhaust gas probe (4) at an exhaust gas catalytic converter outlet (6), the internal combustion engine (1) being operable in a super-purge mode and a normal mode, in which an air-fuel ratio in a combustion chamber of the internal combustion engine (1) is regulated by adjusting an injection quantity and / or an amount of intake air and / or an overflush duration, in which a set of normal control parameters is used in the normal mode in order to keep the fuel-air ratio in the combustion chamber within predetermined limits, wherein, in the over-purge mode, a set of over-purge control parameters is used to determine the air-fuel ratio at the exhaust catalyst inlet (5) based on measurements of the air-fuel ratio of the first exhaust gas probe (3) and / or the second exhaust gas probe (4) to hold predetermined barriers and wherein, in the over-purge mode, the over-purge duration is controlled based on the measurements of the air-fuel ratio of the first exhaust gas probe (3) and / or the second exhaust gas probe (4). Method according to Claim 1 characterized in that the control of the air-fuel ratio in the over-purge mode is performed based on the first exhaust gas probe (3) and the second exhaust gas probe (4). Method according to one of the preceding claims, characterized in that, in the set of over-purge control parameters, the desired value is a stoichiometric air-fuel ratio at the exhaust gas catalyst inlet (5). Method according to one of the preceding claims, characterized in that in the Überspülmodus a measured value of the air-fuel ratio of the first exhaust gas probe (3) for a PI control (7) of the air-fuel ratio is used, so that at the exhaust catalyst inlet (5) Stoichiometric air-fuel ratio is present. Method according to one of the preceding claims, characterized in that in the Überspülmodus a measured value of the air-fuel ratio of the second exhaust gas probe (4) for an I-control (8) of the first exhaust gas probe (3) is used. Method according to one of the preceding claims, characterized in that in the Überspülmodus a measured value of the air-fuel ratio of the second exhaust gas probe (4) for a P control (9) of the air-fuel ratio is used, so that at the exhaust catalyst inlet (5) Stoichiometric air-fuel ratio is present. Method according to one of the preceding claims, characterized in that in the Überspülmodus the fuel injection quantity is controlled based on the measured values of the air-fuel ratio of the first exhaust gas probe (3) and / or the second exhaust gas probe (4). Computer program with program code stored on a machine-readable medium, which can be loaded directly into the internal memory of a digital computer and comprises software code sections, for carrying out the method according to one of Claims 1 to 7 if the program is running on a computer. Control device with a control unit for operating an internal combustion engine (1) with an exhaust gas tract, which has an exhaust gas catalyst (2), a first exhaust gas probe (3) at an exhaust gas catalyst inlet (5) and a second exhaust gas probe (4) at an exhaust gas catalyst outlet (6 ), wherein the internal combustion engine (1) is operable in a Überspülmodus and a normal mode, that is trained to regulate an air-fuel ratio in a combustion chamber of the internal combustion engine (1) by adjusting an injection quantity and / or an amount of intake air and / or a superfluity duration, to use a set of normal control parameters in the normal mode to maintain the fuel-air ratio in the combustion chamber within predetermined limits, to use a set of over-purge control parameters in the over-purge mode to maintain the air-fuel ratio at the exhaust catalyst inlet (5) within predetermined limits, in the over-purge mode, controlling the over-purge duration based on the measurements of the air-fuel ratio of the first exhaust gas probe (3) and / or the second exhaust gas probe (4). Control device according to Claim 9 , characterized in that this further means for performing the method according to one of Claims 1 to 7 includes.

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