DE102004043595B4 - Method for operating a direct injection internal combustion engine with an exhaust gas recirculation and apparatus for carrying out the method - Google Patents

Abstract

Method for operating a direct-injection internal combustion engine (10) with exhaust gas recirculation, in which homogeneous operation is provided in a first operating mode (HOM), in which fuel is injected during an intake phase (70) and in which in a second operating mode (HSP) Homogeneous split operation with a multiple injection is provided, in which fuel is injected in at least one first injection during the intake phase (70) and in at least one second injection during the compression phase (71), characterized in that in the first operating mode (HOM ) an increase in an exhaust gas recirculation rate is provided until an internal combustion engine operating parameter (KI, n) or an exhaust gas parameter (HC) reaches a predetermined first threshold value (60, 62, 64) and that when the threshold value (60, 62, 64) is reached the second operating mode (HSP) is switched.

Description

State of the art

The invention is based on methods for operating a direct injection internal combustion engine with an exhaust gas recirculation and an apparatus for carrying out the method according to the preamble of the independent claims.

From the DE 199 46 730 A1 a method for operating a direct-injection internal combustion engine with an exhaust gas recirculation is known in which a homogeneous operation is provided in a first mode and in a second mode, a shift operation is provided. In the second mode, an increase in exhaust gas recirculation rate is provided until an operating parameter reaches a threshold.

The DE 691 20 632 T2 and the DE 197 27 793 A1 each disclose a method for operating an internal combustion engine with an exhaust gas recirculation, in which a homogeneous operation is provided and in which an increase in the exhaust gas recirculation rate is provided until an operating parameter or an exhaust gas parameter reach a predetermined first threshold value.

From the DE 198 24 915 C1 shows a method for operating an internal combustion engine, in which an increase in the exhaust gas recirculation rate is provided when changing from a homogeneous to a stratified operation.

The DE 198 53 980 B4 shows a method for operating an internal combustion engine, in which in a stratified charge an exhaust gas recirculation and in a homogeneous operation, no exhaust gas recirculation is performed. For such a method is from the publication Osman Sari et al .: "Direct injection in gasoline engine: innovative components for direct injection gasoline engines" (Rennningen, expert verlag, 2000, pages 171 to 194, ISBN 3-8169-1822-0) a solution for a quick change between the modes known.

From the DE 199 36 201 A1 For example, a method for operating an internal combustion engine has become known in which fuel is injected directly into the combustion chamber of the individual cylinders of the internal combustion engine. In a first operating mode, a so-called homogeneous operation of the internal combustion engine, the throttle valve is partially opened or closed depending on the desired torque. The fuel is injected from the injector into the combustion chamber during an intake phase caused by the piston. By simultaneously sucked through the throttle air, the fuel is swirled and thus distributed in the combustion chamber substantially evenly. Thereafter, the air-fuel mixture is compressed during the compression phase to be ignited by the spark plug. The expansion of the ignited fuel drives the piston.

The torque provided in homogeneous operation depends inter alia on the position of the throttle valve. With regard to a low pollutant development of the internal combustion engine, the air-fuel mixture is adjusted to an air ratio lambda of at least approximately one or in connection with an exhaust gas recirculation to an air ratio lambda slightly greater than one.

In a second operating mode, a so-called shift operation of the internal combustion engine, the throttle valve is opened wide. The fuel is injected directly from the injection valve during a compression phase caused by the piston in the combustion chamber, locally in the immediate vicinity of the spark plug and in time at a suitable distance before the ignition. The torque provided in shift operation largely depends on the injected fuel mass.

In a third mode, a double fuel injection is performed. This is a combination of the homogeneous operation and the stratified operation. Fuel is injected in a first injection during the intake phase and in a second injection during the compression phase. The third mode is used inter alia to reduce the knock sensitivity of the internal combustion engine.

The knock sensitivity of the internal combustion engine is the lower, the leaner the air-fuel mixture is in a so-called tail gas region of the combustion chamber. The tail gas area is that area of the entire charge in the combustion chamber which has not yet been ignited after ignition of the spark plug. In the present case, the spark plug essentially ignites the fuel injected during the compression phase, which is present as a cloud directly in the area of the spark plug. Only then does the fuel located outside the cloud and injected during the intake phase ignite. Before ignition, the fuel homogeneously distributed in the combustion chamber represents the abovementioned tail gas region.

The third operating mode can be combined in particular with the exhaust gas recirculation in order to reduce the nitrogen oxide (NOx) emissions of the internal combustion engine. Reduced exhaust gas recirculation the formation of NOx in the combustion of the fuel in the cylinders of an internal combustion engine by the admixture of exhaust gas to the fresh air supplied to the internal combustion engine. The exhaust gas recirculation lowers the peak temperature during the combustion process of the fuel, so that the conditions for the formation of NOx are deteriorated. The amount of admixed exhaust gas and the extent of the exhaust gas recirculation candidate engine operating range are limited by the smoothness of the engine, as deteriorated with increasing exhaust gas recirculation rate, the flame and burn through behavior up to the occurrence of combustion misfires. On the one hand, misfires worsen the smooth running of the internal combustion engine and on the other hand increase unwanted hydrocarbon emissions of the internal combustion engine.

From the EP 793 803 B1 a method for detecting misfiring of internal combustion engines has become known on the basis of the time course of the rotational movement of a sensor wheel coupled to a crankshaft of an internal combustion engine. The segment times in which predetermined segments of the encoder wheel pass through a sensor or the average, the segments of the encoder wheel associated segment times are detected and processed to a measure of the running noise of the internal combustion engine, is closed by the behavior of combustion misfire. The measure of the uneven running is formed by digital filtering of segment times with predetermined filter coefficients.

The invention has for its object to provide a method for operating a direct injection internal combustion engine with an exhaust gas recirculation and an apparatus for performing the method, which exploit the potential of exhaust gas recirculation far.

The object is solved by the features specified in the independent claims.

Advantages of the invention

The method according to the invention for operating a direct injection internal combustion engine with an exhaust gas recirculation starts from a first operating mode in which a homogeneous operation is provided, in which fuel is injected during an intake phase. In a second mode of operation, multiple fuel injection is provided in which fuel is injected in at least one first injection during the intake phase and at least one second injection during the compression phase. According to the invention, an increase in the exhaust gas recirculation rate is provided in the first operating mode until an engine operating parameter or an exhaust gas parameter reaches a predefined first threshold value and the system switches over to the second operating mode when the threshold value is reached. In the following, the first operating mode is referred to as homogeneous operation.

The inventive method allows in the context of the homogeneous operation, in which the internal combustion engine can provide the highest torque, an increase in the exhaust gas recirculation rate, which in particular contributes to reducing the NOx emissions of the internal combustion engine can be increased to a limit. The reaching of the limit is determined by a comparison of an engine operating characteristic or an exhaust gas characteristic with the first threshold value.

Within the homogeneous operation, the ignition timing can be varied such that, despite a comparatively high exhaust gas recirculation rate, a timely ignition, which is required to achieve high torque and high efficiency, can nevertheless take place.

Advantageous developments and refinements of the method according to the invention will become apparent from the dependent claims.

A refinement provides that in the second mode of operation the exhaust gas recirculation rate is increased until an engine operating parameter or an exhaust gas parameter reaches a predetermined second threshold value. The second thresholds may differ from the first thresholds. The development makes it possible, even in the context of the second operating mode, which is referred to below as homogeneous-split operation, to increase the exhaust gas recirculation rate again until reaching the limit in order to minimize the NOx emissions of the internal combustion engine even in homogeneous-split operation to achieve.

An advantageous development provides that at the latest when reaching the first threshold, a first efficiency of the internal combustion engine is determined in the homogeneous operation. In connection with the further measure that a second efficiency of the internal combustion engine is determined at the latest when reaching the second threshold value, that operating mode can be selected based on a comparison of the two determined efficiencies, in which the internal combustion engine has the higher efficiency under the given conditions. With these measures, in addition to the lowest possible NOx emissions, a minimum fuel consumption of the internal combustion engine is achieved in order to provide a specific torque.

An embodiment provides that at least one measure of the uneven running is provided as the engine characteristic. The uneven running of the internal combustion engine can for example be based on the evaluation of an already existing speed and position signal. Another embodiment provides that at least one measure of the knocking is provided as the engine operating parameter. The uneven pressure curve in the cylinder caused by a knocking combustion can be detected, for example, with a knock sensor.

Upon reaching the running limit of the internal combustion engine, combustion misfires occur, which result in an emission of hydrocarbons. An embodiment therefore provides at least one measure of the hydrocarbon concentration in the exhaust gas as the exhaust gas parameter.

Further embodiments relate to the exhaust gas recirculation. According to a first embodiment, an external exhaust gas recirculation can be provided, in which an exhaust gas recirculation line is provided between the exhaust gas region and the intake region of the internal combustion engine. If a variable valve control is provided as part of an adjustment of a camshaft or a control option individual valves, an internal exhaust gas recirculation can be provided with a variable valve overlap time.

The device according to the invention for carrying out the method initially relates to a control device which is prepared for carrying out the method.

The control unit contains in particular an efficiency determination and a mode changeover.

The control unit preferably contains at least one electrical memory in which the method steps are stored as a computer program.

Further advantageous developments and refinements of the procedure according to the invention emerge from further dependent claims and from the following description.

drawing

1 shows a technical environment in which a method according to the invention runs, 2a . 2 B show fuel signals as a function of time or crankshaft angle and 3 shows a flowchart of the method according to the invention.

1 shows an internal combustion engine 10 , in their intake area 11 an air sensor 12 and a throttle 13 and in their exhaust area 14 a hydrocarbon sensor 15 and an exhaust treatment device 16 are arranged.

The internal combustion engine 10 points above a piston 20 a combustion chamber 21 in which an inlet valve 22 , a fuel injection valve 23 , a spark plug 24 , a knock sensor 25 and an exhaust valve 26 protrude. The piston 20 is with a flywheel 27 connected, its speed and position from a position sensor 28 is detected.

The air sensor 12 gives to a control unit 30 an air signal mL, the knock sensor 25 to a knock rating 31 a knock signal KI, the position sensor 28 to a position evaluation 32 a position signal n and the hydrocarbon sensor 15 to an exhaust gas assessment 33 a hydrocarbon signal HC from. The knock signal KI and the position signal n are engine operating characteristics. The hydrocarbon signal HC is an exhaust gas parameter. The controller 30 Furthermore, a torque setpoint MFa is made available.

The control 30 that is an efficiency determination 40 as well as a mode changeover 41 contains, indicates to the throttle 13 a throttle signal dr, to the intake valve 22 an intake valve control signal SEV, to the fuel injection valve 23 a fuel signal mK, to the spark plug 24 an ignition signal to the exhaust valve 26 an exhaust valve control signal SAV and an exhaust gas recirculation actuator 50 an exhaust gas recirculation signal agr.

The knock rating 31 are a first and second knock signal threshold 60 . 61 , the position rating 32 a first and second position signal threshold 62 . 63 and the exhaust gas assessment 33 a first and second hydrocarbon signal threshold 64 . 65 assigned.

In the exhaust gas area, a NOx mass flow dmNOx and a hydrocarbon flow dmHC occur. Between the exhaust area 14 and the intake area 11 is an exhaust gas recirculation line 66 ,

2a shows the fuel signal mK during a first mode, which is referred to hereinafter as the homogeneous operation HOM, as a function of the time t or the crankshaft angle ° KW. The fuel signal mK occurs at a first time t1, which is within an intake phase 70 the internal combustion engine 10 is, and has a first time period ti1. After a bottom dead center UT of the piston 20 the ignition signal zü occurs, which continues before a top dead center OT of the piston 20 lies.

2 B shows the fuel signal mK a second mode, hereinafter referred to as the homogeneous-split operation HSP, depending on the time t or the crankshaft angle ° KW. The fuel signal mK occurs at a second time t2, which is within the intake phase 70 and has a second time ti2. After bottom dead center UT of the piston 20 occurs the fuel signal mK in a compression phase 71 of the piston 20 at a third time t3, which has a third time duration ti3. Subsequently, the ignition signal zü occurs, which is again before top dead center TDC.

3 shows a flow chart of the inventive method, which according to a first functional block 80 with the requirement for a consumption-optimal operation of the internal combustion engine 10 starts. In the following second function block 81 the homogeneous operation HOM is specified. In the following third function block 82 an increase in the exhaust gas recirculation rate is provided.

In a first query 83 It is checked whether an engine operating characteristic KI, n the predetermined first threshold 60 . 62 or whether an exhaust gas parameter HC the predetermined first threshold 64 has exceeded. If not, it becomes a third functional block 82 jumps back. If so, it becomes a fourth function block 84 the efficiency ηHOM determined in the homogeneous operation HOM and according to a fifth functional block 85 for the homogeneous split operation HSP.

In the following sixth function block 86 the exhaust gas recirculation rate is increased. In the subsequent second query 87 It is checked whether the engine operating characteristic KI, n the second threshold 61 . 63 or whether the exhaust gas characteristic HC the second threshold 65 has exceeded. If not, it becomes the sixth function block 86 jumps back. If this is the case, in a seventh function block 88 the efficiency ηHSP determined in the homogeneous split mode HSP.

In a third query 89 becomes the fourth function block 84 determined efficiency ηHOM in homogeneous operation HOM with that in the seventh function block 88 determined efficiency ηHSP compared in the homogeneous-split mode HSP. If the efficiency ηHSP in the homogeneous operation HOM is greater than the efficiency ηHOM in the homogeneous operation HOM, the homogeneous split operation HSP according to the fifth functional block 85 maintained. If not, the second function block becomes 81 jumped and transferred to the homogeneous operation HOM.

The method according to the invention works as follows:
The control 30 sets the fuel signal mK as a function of the torque setpoint MFa, which is derived, for example, from a position of an accelerator pedal not shown in more detail of a motor vehicle also not shown in detail. Optionally, the fuel signal mK continues to depend on the air signal mL and / or the position signal n, wherein the position signal not only the position of the flywheel 27 but in particular reflects its speed.

Initially, the starting point is the requirement for optimum operation of the internal combustion engine 10 according to the first functional block 80 , According to the second function block 81 the specification of the homogeneous operation HOM is provided, in which the internal combustion engine can provide the highest torque. In homogeneous operation HOM, the fuel injection takes place in the intake phase 70 during the downward movement of the piston 20 , The throttle 13 is more or less open. The fuel signal mK begins at the first time t1, which corresponds to a determined crankshaft angle ° KW. The fuel signal mK has a first time duration ti1 which, in conjunction with a fuel pressure, is a measure of the metered amount of fuel.

The suction phase 70 lies before bottom dead center UT of the piston 20 , After reaching bottom dead center UT, the compression phase begins 71 in which the ignition signal zü occurs. The ignition signal zü is generally before top dead center TDC. The ignition signal zü is expediently moved so far in the direction early, until the highest efficiency is achieved. At the same time, the knock tendency of the internal combustion engine decreases 10 to.

During the homogeneous operation HOM, an increase in the exhaust gas recirculation rate according to the second functional block 82 performed. An increase in the exhaust gas recirculation rate reduces the NOx emissions of the internal combustion engine 10 by lowering the peak temperature occurring during the combustion process.

The exhaust gas recirculation further reduces the combustion speed. In order to ensure a combustion point location that is optimal for consumption, therefore, the ignition timing must be shifted in the direction of early.

The increase in the exhaust gas recirculation rate can be carried out in homogeneous operation until, for example, 30%. With a further increase in the exhaust gas recirculation rate increases the rough running of the internal combustion engine, which is initially stochastic Fluctuations in the generated mechanical power up to the occurrence of misfires expresses.

In the first query 83 it is checked whether the knock signal KI the first knock signal threshold 60 or whether the position signal n is the first position signal threshold 62 exceeds. The increasing uneven running appears first in the position signal n. When the knock limit is reached, the knock signal KI occurs. The knock signal KI and the position signal n are referred to below as the engine operating characteristic at KI, n.

Combustion misfires affect the hydrocarbon stream dmHC due to the presence of unburned fuel in the exhaust region 14 , In the first query 83 Therefore, it may alternatively be checked whether the hydrocarbon signal HC is the first hydrocarbon signal threshold 64 exceeds. The hydrocarbon signal HC is referred to below as the exhaust gas characteristic HC.

If one of the first thresholds 60 . 62 . 64 is not reached, according to the third function block 82 a further increase in the exhaust gas recirculation rate can be made. If in the first query 83 Threshold overrun is determined according to the fifth function block 85 to the second mode, the homogeneous-split operation HSP passed, which in the intake phase 70 at least a first fuel injection and in the compression phase 71 at least one further fuel injection provides.

With the transition to at least twice the fuel injection results in the stratified charge area an improved ignition safety by better flammability. The optimal combustion center position can be at a higher exhaust gas recirculation rate than in homogeneous operation HOM with still acceptable smoothness of the internal combustion engine 10 be respected. The exhaust gas recirculation rate in homogeneous split operation can be, for example, up to 35%. If necessary, this leads to a further reduction in the NOx emissions of the internal combustion engine 10 and possibly to a reduction in fuel consumption.

In the homogeneous split mode HSP is according to the sixth function block 86 again provided an increase in the exhaust gas recirculation rate until in the second query 87 again exceeding a second threshold 61 . 63 . 65 is detected. The second thresholds 61 . 63 . 65 can with the first thresholds 60 . 62 . 64 match if necessary. Switching between the operating modes is carried out by the mode selector switch 41 in the controller 30 is included.

To the demand for a consumption-optimal operation of the internal combustion engine 10 can be suitably, in the fourth function block 84 the determination of the highest possible efficiency ηHOM in homogeneous operation HOM and / or in the seventh function block 88 the determination of the highest possible efficiency ηHSP in the homogeneous-split mode HSP can be provided in each case. In the third query 89 the two efficiencies ηHOM, ηHSP are compared. Depending on the result of the comparison then optionally that mode HOM, HSP by jumping either to the second Funktiotisblock 81 or to the fifth function block 85 can be specified, which allows the higher efficiency η. The efficiency is determined by the efficiency determination 40 in the control unit 30 is included.

The fourth function block 84 with the determination of the efficiency in homogeneous operation HOM can before the first query 83 and the seventh function block 88 with the efficiency determination in the homogeneous-split-operation (HSP) can before the second query 87 to be ordered. The efficiency ηHOM in homogeneous operation HOM and the efficiency ηHSP in homogeneous split operation HSP is then available at any time.

The highest possible efficiency ηHOM, ηHSP in the two operating modes HOM, HSP is then returned with the last return from the first query 83 to the third function block 82 or with the last return from the second query 87 to the sixth function block 86 reached. The embodiment of the embodiment provided arrangement of the functional blocks 84 . 88 after the queries 83 . 87 allows an optimization of the computing time in the control unit 30 contained signal processing arrangement.

It is particularly advantageous if the determination of the efficiency is always provided in at least one operating mode, preferably in all operating modes, ie also for the operating mode which is currently not set. With this measure, an unnecessary change between operating modes can be avoided.

The efficiency ηHOM, ηHSP of the internal combustion engine 10 can be determined with the available signals. The starting point is, for example, the air signal mL and the position signal n reflecting the rotational speed, from which the air charge in the combustion chamber 21 can be calculated. Taking into account the known fuel signal mK, the predetermined air ratio lambda of the combustion process and the predetermined ignition angle, the torque which the piston 20 provides to be calculated. If appropriate, the operating mode HOM, HSP and / or the exhaust gas recirculation rate agr can furthermore be taken into account. For a given operating point of the internal combustion engine 10 (Speed and torque) are the controller 30 the operating mode HOM, HSP, which can represent the operating point with minimum fuel consumption.

The exhaust gas recirculation can be externally via the exhaust gas recirculation line 66 respectively. In the exhaust gas recirculation line is the exhaust gas recirculation actuator 50 arranged, which is driven by the exhaust gas recirculation signal agr.

Another embodiment, which can be provided in particular at low exhaust gas recirculation rates of, for example, less than 10 percent, sees an internal exhaust gas recirculation through a targeted control of the intake and exhaust valves 22 . 26 in front. The valves 22 . 26 can be driven by one or two camshafts not shown in detail, which are adjustable together or separately. Optionally, a control of each individual valve 22 . 26 according to the in 1 be shown embodiment shown. The control 30 can the inlet valve 22 with the intake valve control signal SEV and the exhaust valve 26 control separately with the exhaust valve control signal SAV. The internal exhaust gas recirculation is determined by a valve overlap time, during which both valves 22 . 26 are open at the same time.

Claims (11)

Method for operating a direct injection internal combustion engine ( 10 ) with an exhaust gas recirculation, in which in a first operating mode (HOM) a homogeneous operation is provided, in which fuel during a suction phase ( 70 ) and in which in a second operating mode (HSP) a homogeneous split operation with a multiple injection is provided, in which fuel in at least one first injection during the intake phase ( 70 ) and in at least a second injection during the compression phase ( 71 ) is injected, characterized in that in the first operating mode (HOM) an increase in an exhaust gas recirculation rate is provided until an engine operating characteristic (KI, n) or an exhaust gas characteristic (HC) has a predetermined first threshold value ( 60 . 62 . 64 ) and that upon reaching the threshold ( 60 . 62 . 64 ) is switched to the second mode (HSP). Method according to Claim 1, characterized in that in the second operating mode (HSP) the exhaust gas recirculation rate is increased until an engine operating parameter (KI, n) or an exhaust gas characteristic variable (HC) reaches a predetermined second threshold value (HSP). 61 . 63 . 65 ) reached. A method according to claim 1, characterized in that a maximum possible efficiency (ηHOM) in the first operating mode (HOM) of the internal combustion engine ( 10 ) is determined. A method according to claim 2, characterized in that a maximum possible efficiency (ηHSP) in the second operating mode (HSP) of the internal combustion engine ( 10 ) is determined. A method according to claim 3 and 4, characterized in that the higher of the two efficiencies (ηHOM, ηHSP) is determined and that the internal combustion engine ( 10 ) is operated in the operating mode (HOM, HSP) which has the higher efficiency (ηHOM, ηHSP). A method according to claim 1 or 2, characterized in that as the engine operating characteristic (KI, n) at least one measure of the uneven running or at least one measure of the knocking is provided. A method according to claim 1 or 2, characterized in that at least one measure of the hydrocarbon concentration is provided as the exhaust gas characteristic (HC). A method according to claim 1, characterized in that an external exhaust gas recirculation is provided, in which between the exhaust gas region ( 14 ) and the intake area ( 11 ) of the internal combustion engine ( 10 ) an exhaust gas recirculation line ( 66 ) is provided. A method according to claim 1, characterized in that an internal exhaust gas recirculation is provided, wherein at least one inlet valve ( 22 ) and an outlet valve ( 26 ) are controlled with a predetermined valve overlap time. Device for operating an internal combustion engine ( 10 ), characterized in that at least one prepared for carrying out the method control device ( 30 ) is provided. Apparatus according to claim 10, characterized in that the control unit ( 30 ) an efficiency determination ( 40 ) and a mode selector switch ( 41 ) contains.

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