Method for operating an internal combustion engine

Abstract

Method for operating an internal combustion engine with a plurality of cylinders (Z) of a motor vehicle, in which, in at least one first engine operating range (M1), exhaust gas is guided from an exhaust system (3) to an intake system (4) via at least one exhaust gas recirculation valve (21), an exhaust gas recirculation line (19), and an air / EGR flow path (30), and in the first (M1) or at least one further engine operating range, fresh air is guided from a first fresh air flow path (9a) via a second fresh air flow path (9b) into the air / EGR flow path (30), wherein in at least one engine operating range, a purge mode (Ms) is started, in which the air / EGR flow path (30) is purged with fresh air, and wherein at the start of the purge mode (Ms), the exhaust gas recirculation valve (21) is closed or will be closed, characterized in that the purge mode (Ms) is in at least one - preferably prosperous - transient engine operating range (M T) is started, wherein in the purge mode (Ms) a fresh air valve (23) is at least partially opened.

Description

[0001] The invention relates to a method for operating an internal combustion engine with several cylinders of a motor vehicle, in which, in at least one first engine operating range, exhaust gas is guided from an exhaust system to an intake system via at least one exhaust gas recirculation valve, an exhaust gas recirculation line and an air / EGR flow path, and in the first or at least one second engine operating range, fresh air is guided from a first fresh air flow path into the air / EGR flow path via a second fresh air flow path, wherein in at least one engine operating range, a purge mode is started in which the air / EGR flow path is purged with fresh air, wherein at the start of the purge mode the exhaust gas recirculation valve is closed or is closed.

[0002] US Pat. No. 6,062,026 A discloses an internal combustion engine with an exhaust gas recirculation system, wherein an electric compressor is arranged in an air / EGR flow path (EGR = Exhaust Gas Recirculation). The electric compressor can be bypassed via a bypass line with a bypass valve. A mixing valve is arranged in the area where the exhaust gas recirculation line and a fresh air flow path meet.

[0003] WO 2007 / 083131 A1 discloses a turbocharged diesel internal combustion engine in which an electric compressor is arranged in a bypassable air / EGR flow path. A controllable throttle valve is arranged in the air / EGR flow path. Furthermore, controllable valves are arranged to regulate the fresh air in the bypass line and to regulate the amount of recirculated exhaust gas in the exhaust gas recirculation line.

[0004] AT 512 890 B1 describes an internal combustion engine of the type mentioned above with an electric compressor arranged in an air / EGR flow path, wherein an exhaust gas recirculation line having an exhaust gas recirculation valve opens into the air / EGR flow path. Downstream of the electric compressor, the air / EGR flow path is divided into cylinder-selective supply channels, with at least one supply channel per cylinder opening into an intake channel. A first fresh air flow path originating from a compressor of an exhaust gas turbocharger divides into a second and a third fresh air flow path, wherein a fresh air valve is arranged in the second fresh air flow path and a throttle valve is arranged in the third fresh air flow path. Fresh air flows through the second and third fresh air flow paths alternatively or in parallel. The second fresh air flow path and the exhaust gas recirculation line merge into the air / EGR flow path.The recirculated exhaust gas quantity is regulated via the exhaust gas recirculation valve, the fresh air via the fresh air valve.

[0005] In these internal combustion engines, conditions can occur in which only concentrated exhaust gas is present in the air / EGR flow path and in the electrically driven compressor. If the electrically driven compressor is suddenly activated, the concentrated exhaust gas is very quickly fed into the combustion chambers of the internal combustion engine. This leads to poor combustion and a loss of power.

[0006] DE 10 2013 213 364 A1 discloses closing the exhaust gas recirculation valve and flushing the exhaust gas recirculation line with fresh gas when the internal combustion engine decelerates. DE 10 2011 013 496 A1 describes an internal combustion engine with an exhaust gas recirculation line between the exhaust and intake systems, whereby the exhaust gas recirculation line can be flushed with air via a purge line. Purging takes place during normal engine operation. However, this can negatively impact nitrogen oxide emissions.

[0007] AT 504 178 A2 describes a method for operating an internal combustion engine with at least one exhaust gas recirculation line in which an exhaust gas recirculation valve is arranged. The exhaust gas recirculation valve is actuated depending on the operating state of the internal combustion engine. In the event of an increased torque demand, a transient function is activated, which reduces or interrupts the exhaust gas flow in the exhaust gas recirculation line and only increases the exhaust gas flow again after a defined torque increase has been reached.

[0008] The object of the invention is to avoid performance losses in transient conditions in the simplest possible way.

[0009] According to the invention, this is achieved by starting the purge mode in at least one—preferably prosperous—transient engine operating range. The exhaust gas recirculation valve remains closed throughout the purge mode, with a fresh air valve being at least partially opened in the purge mode.

[0010] A prosperous transient operating range is understood here as a non-stationary operating range of the internal combustion engine in which the speed and / or torque increases.

[0011] Conveniently, the internal combustion engine is operated in the transient engine operating range in which the purge mode is initiated during or immediately after at least one defined acceleration and / or load request, wherein the defined acceleration and / or load request is preferably associated with a predetermined acceleration or load parameter, for example, an accelerator pedal position, a throttle valve position, an intake manifold pressure, or its simple or double time derivative. The transient operation of the internal combustion engine, which is crucial for triggering the start of the purge process, is thus directly attributable to an acceleration and / or load request—for example, from the driver or an assistance system of the motor vehicle—to the internal combustion engine.A transient engine operating range that is crucial for starting purge mode is detected, for example, when the accelerator pedal gradient exceeds a certain threshold. Furthermore, a transient engine operating range that is crucial for starting purge mode can also be detected from other load parameters such as throttle position or intake manifold pressure, or from their temporal changes.

[0012] The purge mode is expediently carried out following at least a first engine operating range in which exhaust gas recirculation with a high exhaust gas recirculation rate has taken place.

[0013] Purging is particularly necessary when a sudden power demand is made by the driver, requiring operation of the electrically driven compressor. Purging mode is therefore activated particularly when a sudden power demand is detected. In a simple embodiment of the invention, purging mode is initiated depending on the position or gradient of the motor vehicle's accelerator pedal.

[0014] To enable sufficient and rapid purging of the air / EGR flow path, it is advantageous if at least 15%, preferably 25% to 40%, of the flow cross-section is released in the open position of the fresh air valve in purge mode. The fresh air valve is formed, for example, by a simple adjustable flap. The fresh air valve can be arranged either in the first fresh air flow path—i.e., upstream of its branching into the second and third fresh air flow paths—or in the second fresh air flow path, whereby the flow cross-section of the first fresh air path or the second fresh air path is changed by the fresh air valve. If the fresh air valve is arranged in the first fresh air flow path, it can be formed by a conventional throttle valve, which controls the entire fresh air mass flow directed to the internal combustion engine.This eliminates the need for a separate fresh air valve in addition to the throttle valve. In this case, it is particularly advantageous if the flow cross-section of the controlled first fresh air path changes with a defined gradient in purge mode. This enables rapid purging without impairing driving behavior.

[0015] Conveniently, when purge mode starts, an electrically operated compressor located in the air / EGR flow path is deactivated or operated at a defined initial speed - for example, idle speed. In purge mode, the speed of the electrically operated compressor is only increased after a defined lead time. The lead time is selected such that even in the worst case scenario - i.e., with 100% exhaust gas concentration and low fresh air flow velocities - it is guaranteed that the concentrated exhaust gas is predominantly removed from the air / EGR flow path. The lead time can be specified as a fixed value or as a function depending on at least one parameter. Such a parameter can be, for example, a measured exhaust gas component in the air / EGR flow path and / or the engine speed and / or the intake manifold pressure and / or a load signal.

[0016] In a simple embodiment of the invention, the purge mode is terminated after a predefined purge duration. As an alternative to a preset, fixed purge duration, the end of the purge mode can also be variable and calculated depending on at least one purge parameter—for example, an exhaust gas component or the EGR (exhaust gas recirculation) rate. In particular, the EGR rate in the air / EGR flow path or in the intake system can be determined, and the purge mode can be terminated as soon as a target value for the EGR rate is reached or undershot.

[0017] To meet emissions requirements, after purge mode is terminated, the fresh air valve and / or the speed of the electrically driven compressor are set to a setting corresponding to the EGR rate target.

[0018] The invention is explained in more detail below with reference to non-limiting embodiments shown in the figures. These schematically show: Fig. 1 an internal combustion engine for carrying out the method according to the invention in a first embodiment; Fig. 2 shows the course of selected engine operating parameters during the implementation of the method according to the invention in this embodiment; Fig. 3 an internal combustion engine for carrying out the method according to the invention in a second embodiment; and Fig. 4 the course of selected engine operating parameters during the execution of the method according to the invention in this embodiment variant.

[0019] Parts with the same function are provided with the same reference symbols in the different versions.

[0020] The internal combustion engine 1, designed for multiple cylinders Z, has an exhaust gas recirculation system 2 between an exhaust system 3 and an intake system 4. Reference numeral 5 denotes an exhaust gas turbocharger, whose exhaust gas turbine 6 is arranged in the exhaust line 7 of the exhaust system 3 and whose compressor 8 is arranged in the intake line 9 of the intake system 4. Exhaust gas purification devices 10 and silencers 11 are arranged downstream of the turbine 6 of the exhaust gas turbocharger 5.

[0021] In the intake line 4, an air filter 12 is arranged upstream of the compressor 8 of the exhaust turbocharger 5, and a charge air cooler 13 is arranged downstream of the compressor 8. Reference numeral 14 denotes a lambda probe arranged in the exhaust line 7 downstream of the exhaust turbine 6, and reference numeral 15 denotes a boost pressure sensor arranged in the intake line 9 downstream of the compressor 8. A throttle valve 17 is arranged upstream of the inlet of the intake line 9 into the intake manifold 16. Cylinder-specific intake ports 18 lead from the intake manifold 16 to the individual cylinders Z.

[0022] The exhaust gas recirculation system 2 has an exhaust gas recirculation line 19, which originates from the exhaust system 7 and leads to the intake system 4. An exhaust gas recirculation cooler 20 is arranged in the exhaust gas recirculation line 19, and downstream of this, an exhaust gas recirculation valve 21 designed as a simple control valve.

[0023] Reference numeral 22 denotes an electric compressor, which is positioned in an air / EGR flow path 30 between the exhaust gas recirculation system 2 and the intake system 4 such that it can selectively convey recirculated exhaust gas, fresh air, or a mixture of recirculated exhaust gas and fresh air. An exhaust gas recirculation cooler 31 is arranged downstream of the electric compressor 22 in the air / EGR flow path 30. On the fresh air side, in the fresh air flow path 9a, 9b upstream of the electric compressor 22, a fresh air valve 23 is arranged, which can be designed as a flap. The electric charger 22 can be bypassed on the fresh air side via a bypass line leading from the fresh air flow path 9a—the fresh air flow path 9c—in which a check valve 25 is arranged.

[0024] The exhaust gas recirculation system 2 is designed as a high-pressure exhaust gas recirculation system, with the exhaust gas recirculation line 19 branching off from the exhaust system 7 upstream of the exhaust turbine 6 and flowing into the intake system 4 downstream of the compressor 8. A distributor rail 26 with cylinder-selective supply channels (not further designated) is arranged in the area where the air / EGR flow path 30 flows into the intake system 4. The supply channels open into the Fig. 1 shown variant directly into the intake ports 18 leading to each cylinder Z.

[0025] The first fresh air flow path 9a of the intake line 9 branches into a second fresh air flow path 9b and a third fresh air flow path 9c. The second fresh air flow path 9b and the exhaust gas recirculation line 2 merge upstream of the electric compressor 22 driven by an electric motor to form the air / EGR flow path 30. The third fresh air flow path 9c leads via the check valve 25 and the throttle valve 17 to the intake manifold 16. The check valve 25 opens toward the intake manifold 16 and closes in the opposite direction.

[0026] In at least a first engine operating range—for example, at low partial load—the exhaust gas recirculation valve 21 is opened, and exhaust gas is conducted from the exhaust system 3 to the intake system 4 via the exhaust gas recirculation line 19 and the air / EGR flow path 30. Fresh air can be directed from the first fresh air flow path 9a into the air / EGR flow path 30 via the second fresh air flow path 9b.

[0027] If the driver now requests a sudden increase in drive power by pressing the accelerator pedal, this increased power must be made available as quickly and immediately as possible. A high exhaust gas concentration remaining in the air / EGR flow path 30, which would first have to be processed as a kind of plug before an increased amount of fresh air in the internal combustion engine 1, would severely impair the increase in power of the internal combustion engine and thus the drivability of the vehicle. To avoid this, the method according to the invention provides that immediately following the first engine operating range in a transient engine operating range, a purge mode Ms is started, in which the air / EGR flow path 30 is purged with fresh air, wherein the exhaust gas recirculation valve 21 is closed or will be closed at the start of the purge mode Ms.The purge mode Ms is started depending on the position or gradient of the accelerator pedal of the vehicle operated by the driver.

[0028] In purge mode Ms, the fresh air valve 23 is at least partially opened, with at least 15% of the flow cross-section of the second fresh air flow path 9b being released in this open position, for example. The electric compressor 22 arranged in the air / EGR flow path 30 is deactivated or operated at idle speed when purge mode Ms starts. The speed of the electric compressor 22 is only increased again, if necessary, after a defined lead time in purge mode Ms.

[0029] After purging the air / EGR flow path 30, purge mode Ms is terminated, and the fresh air valve 23 and, if applicable, the speed of the electric compressor 22 are adjusted to a setting corresponding to the target EGR rate. The purge process can end either after a predefined purge duration has elapsed or when a target exhaust gas quantity in the intake system 4 is reached.

[0030] The Fig. 3 shown variant differs from Fig. 1 essentially in that the throttle valve 17 is arranged in the first fresh air flow path 9a upstream of the branch into the second and third fresh air flow paths 9c, thus assuming the function of the fresh air valve 23 (and is also referred to as such here). The second fresh air flow path 9b is designed entirely without any additional device for changing the flow cross-section, i.e., without any valves or flaps. The third fresh air flow path 9c also contains no controllable valve or flap—apart from the check valve 25.

[0031] By controlling the exhaust gas recirculation valve 21 and the throttle valve 17, the electric compressor 22 delivers either fresh air from the fresh air line 9a of the intake system 4 or a mixture of recirculated exhaust gas and fresh air. Both load control and mixture control are thus carried out via the throttle valve 17. The exhaust gas recirculation valve 21 only needs to be designed for the maximum permissible recirculated exhaust gas quantity, but for high exhaust gas temperatures. The throttle valve 17 is subjected to little thermal stress but must be able to control large intake air quantities. Thus, each of the two control elements 17, 21 can be optimally designed for its respective intended use.

[0032] Furthermore, the third fresh air flow path 9c opens into a first plenum 16a and the air / EGR flow path 30 into a second plenum 16b of the intake manifold 16, the two plenums 16a, 16b being separated from one another by a partition wall 29 which, as a longitudinal partition wall (not shown in further detail), continues into the intake ports 18 of each cylinder Z. The longitudinal partition wall divides each intake port 18, or at least one intake port 18 of each cylinder Z or at least one cylinder Z, into a first sub-port 18a and a second sub-port 18b, the first sub-port 18a extending from the first plenum 16a and the second sub-port 16b extending from the second plenum 16b. The longitudinal partition wall extends into the valve chamber of the respective inlet channel 18, so that the flow of each sub-channel 18a, 18b is guided to immediately before the inlet opening in the cylinder Z.This allows a targeted swirl flow, in particular a tumble movement, or a stratification of the recirculated exhaust gas to be generated in the combustion chamber.

[0033] In at least a first engine operating range—for example, at low partial load—the exhaust gas recirculation valve 21 is opened, and exhaust gas is conducted from the exhaust system 3 to the intake system 4 via the exhaust gas recirculation line 19 and the air / EGR flow path 30. Fresh air can be directed from the first fresh air flow path 9a into the air / EGR flow path 30 via the second fresh air flow path 9b.

[0034] If the driver now requests a sudden increase in drive power by pressing the accelerator pedal, this increased power must be made available as quickly and immediately as possible. A high exhaust gas concentration remaining in the air / EGR flow path 30, which would first have to be processed as a kind of plug before an increased amount of fresh air in the internal combustion engine 1, would severely impair the increase in power of the internal combustion engine and thus the drivability of the vehicle. To avoid this, the method according to the invention provides that immediately following the first engine operating range in a transient engine operating range, a purge mode Ms is started, in which the air / EGR flow path 30 is purged with fresh air, wherein the exhaust gas recirculation valve 21 is closed or will be closed at the start of the purge mode Ms.The purge mode Ms is started depending on the position or gradient of the accelerator pedal of the vehicle operated by the driver.

[0035] In the flushing mode Ms, the fresh air valve 23 ( Fig. 1) or the throttle valve 17 ( Fig. 3) at least partially opened, whereby in this opening position, for example, a maximum of 40% of the flow cross-section of the second fresh air flow path 9b ( Fig. 1) or the first fresh air flow path 9a ( Fig. 3) is released. The electric compressor 22 arranged in the air / EGR flow path 30 is deactivated or operated at idle speed when purge mode Ms starts. The speed n of the electric compressor 22 is only increased again, if necessary, in purge mode Ms after a defined lead time Δt.

[0036] After purging the air / EGR flow path 30, purge mode Ms is terminated, and the fresh air valve 23 and, if applicable, the speed of the electric compressor 22 are adjusted to a setting corresponding to the target EGR rate. The purge process can end either after a predefined purge duration has elapsed or when a target exhaust gas quantity in the intake system 4 is reached.

[0037] Fig. 2 and Fig. 4 shows the parameters AV (position of the fresh air valve 23), GG (gradient of the accelerator pedal), GS (position of the accelerator pedal), L (relative engine load), p (intake manifold pressure), n (speed of the electric compressor 22), EGRV (position of the exhaust gas recirculation valve 21), SF (purge flag), TV (position of the throttle valve 17) plotted over time t during a purge cycle, during a transition from a first operating mode M1 to a transient operating mode M Tof the internal combustion engine 1, plotted over time t. The beginning of the purge mode Ms is designated by t1, and the end of the purge mode Ms is designated by t2.

[0038] Fig. Figure 2 shows the course of the parameters mentioned when applying the method according to the invention in the Fig. 1 shown internal combustion engine 1. Fig. 4 shows the course of the parameters mentioned when applying the method according to the invention in the Fig. 3 shown internal combustion engine 1.

[0039] In both cases, at time t1, the driver presses the accelerator pedal relatively quickly from a low load (exhaust gas recirculation valve 21 open, electric compressor 22 idling, for example, at a speed n of approximately 5000 revolutions per minute). This results in a high gradient of the accelerator pedal GG. The exhaust gas recirculation valve 21 is immediately closed, as can be seen from the EGRV curve. The throttle valve 17 opens.

[0040] At this point in time, the Fig. 1 illustrated embodiment, the fresh air valve 23 is closed (see curve AV, Fig. 2). Concentrated exhaust gas is present in the air / EGR flow path 30. If the electric compressor 22 were to immediately increase its speed without opening the fresh air valve 23, an exhaust gas plug would be pushed into the engine, leading to poor combustion (excessively high EGR rate in some cycles).

[0041] Pre-controlling the fresh air valve to higher opening values ​​is not effective, as this would result in air / EGR ratios in stationary operation that are outside the optimal range.

[0042] The inventive solution to the problem provides for starting a purge mode Ms, wherein a purge function with a special control function for the fresh air valve 23 is used. After detecting the pedal gradient—as already described—the exhaust gas recirculation valve 21 is immediately closed. The position of the fresh air valve 23 is determined. If the position of the fresh air valve 21, formed by an air flap, is above a defined threshold value of, for example, 80% of the closed position (93% would be closed in this case), the purge function is activated by setting the purge flag SF.

[0043] The fresh air valve 21 is immediately opened to a predetermined value, releasing at least 15%, preferably approximately 25% - 40%, of the flow cross-section of the fresh air flow path 9b. The increase in the speed n of the electric compressor 22 is delayed. It is now possible to quickly reduce the high EGR rate with additional air. During or after the purging process - for example, after a defined lead time Δt has elapsed - the speed n of the electric compressor 22 is increased. The boost pressure p rises. Since the EGR rate was reduced before the speed n of the electric compressor 22 was increased (an air / EGR mixture now exists in the air / EGR flow path 30), no combustion defects occur.

[0044] After the purge function has expired, the fresh air valve 21 is returned to the pre-control value (matching the speed n of the electric compressor 22 and the EGR rate - in this case 0).

[0045] At the Fig. In the second embodiment of the internal combustion engine 1 shown in Fig. 3, in which the throttle valve 17 is arranged in the first fresh air flow path 9a, the scavenging function of the fresh air valve is applied to the throttle valve 17 ( Fig. 4). A separate fresh air valve in the second fresh air flow path 9b can thus be omitted.

[0046] As in Fig. 4 by line TV0, the throttle valve 17 is opened relatively slowly without the purge function being activated in order to improve drivability and / or to maintain the specified EGR rate. With the purge function activated, however, the throttle valve 17 is opened rapidly during purge mode Ms in order to achieve efficient purging without adversely affecting combustion. In this way, the purge mode Ms can be ended very quickly, and the specifications for the EGR rate and intake manifold pressure p corresponding to the operating point can be achieved.

Claims

[1] Method for operating an internal combustion engine with a plurality of cylinders (Z) of a motor vehicle, in which, in at least one first engine operating range (M1), exhaust gas is guided from an exhaust system (3) to an intake system (4) via at least one exhaust gas recirculation valve (21), an exhaust gas recirculation line (19) and an air / EGR flow path (30), and in the first (M1) or at least one further engine operating range, fresh air is guided from a first fresh air flow path (9a) via a second fresh air flow path (9b) into the air / EGR flow path (30), wherein in at least one engine operating range, a purge mode (Ms) is started in which the air / EGR flow path (30) is purged with fresh air, and wherein, at the start of the purge mode (Ms), the exhaust gas recirculation valve (21) is closed or is to be closed, characterized by that the purge mode (Ms) is in at least one - preferably prosperous - transient engine operating range (M T) is started, wherein in the purge mode (Ms) a fresh air valve (23) is at least partially opened. [2] Method according to claim 1, characterized by that the internal combustion engine is in the transient engine operating range (M T ) is operated at at least one defined acceleration and / or load requirement, wherein preferably the defined acceleration and / or load requirement is assigned to a predetermined acceleration and / or load parameter. [3] Method according to claim 1 or 2, characterized by that the purge mode is carried out at least after the first engine operating range (M1). [4] Method according to one of claims 1 to 3, characterized by that the purge mode (Ms) is started depending on the position (GS) or a gradient (GG) of an accelerator pedal of the motor vehicle. [5] Method according to one of claims 1 to 4, characterized bythat in the flushing mode (Ms) in the open position of the fresh air valve (23) at least 15%, preferably 25% to 40%, of the flow cross-section is released. [6] Method according to claim 5, characterized by that the flow cross-section of the second fresh air flow path (9b) is changed by the fresh air valve (23). [7] Method according to claim 5, characterized by that the flow cross-section of the first fresh air flow path (9a) is changed by the fresh air valve (23). [8] Method according to claim 6 or 7, characterized by that the change in the flow cross-section in the flushing mode (Ms) occurs with a defined gradient. [9] Method according to one of claims 1 to 8, characterized bythat an electrically operated compressor (22) arranged in the air / EGR flow path (30) is deactivated or operated at a first speed, preferably the idle speed, when the purge mode (Ms) starts, and the speed (n) of the electrically operated compressor (22) in the purge mode (Ms) is only increased after a defined lead time (Δt). [10] Method according to one of claims 1 to 9, characterized by that the rinsing mode (Ms) is terminated after a predefined rinsing time (t2-t1). [11] Method according to one of claims 1 to 10, characterized by that the EGR rate in the air / EGR flow path (30) or in the intake system (4) is determined and the purge mode (Ms) is terminated as soon as a target value for the EGR rate is reached or undercut. [12] Method according to claim 10 or 11, characterized bythat after the purge mode (Ms) has ended, the fresh air valve (23) and / or the speed (n) of the electrically operated compressor (22) is set to a setting corresponding to the setpoint of the EGR rate.

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