JP4895555B2 - Method and apparatus for operating direct injection internal combustion engine with exhaust gas recirculation device - Google Patents

Description

  The present invention relates to a method for operating a direct injection internal combustion engine with an exhaust gas recirculation device, and an apparatus for carrying out the method.

  German Patent Application Publication No. 19936201A1 discloses a method of operating an internal combustion engine in which fuel is directly injected into the combustion chamber of each cylinder of the internal combustion engine (see Patent Document 1). In the first operating mode, the so-called homogeneous operation of the internal combustion engine, the throttle valve is partially opened or closed according to the required torque. Fuel is injected by the injection valve into the combustion chamber during the intake process induced by the piston. At the same time, fuel is swirled by the air sucked in through the throttle valve and thereby distributed essentially homogeneously in the combustion chamber. The air / fuel mixture is then compressed during the compression process and then ignited by a spark plug. The piston is driven by the expansion of the ignited fuel.

  The torque generated during homogeneous operation depends inter alia on the position of the throttle valve. From the point of view of reducing the generation of toxic substances in the internal combustion engine, the air / fuel mixture is at least approximately equal to 1 excess air lambda, or in combination with an exhaust gas recirculation device, an excess air ratio slightly greater than 1. Adjusted to lambda.

  In the second operating mode, so-called stratified operation of the internal combustion engine, the throttle valve is opened widely. Fuel is injected from the injection valve directly into the combustion chamber during the compression process induced by the piston, spatially around the spark plug, and in time, for an appropriate period before the ignition point. The torque produced during stratification operation is highly dependent on the injected fuel mass.

  During the third operation mode, double injection of fuel is performed. This means a combination of homogeneous operation and stratified operation. The fuel is injected with a first injection during the intake process and with a second injection during the compression process. This third operating mode is particularly useful for reducing the ease of knocking of the internal combustion engine.

  The ease of knocking of the internal combustion engine decreases as the air-fuel mixture in the so-called end gas zone of the combustion chamber becomes leaner. The end gas zone refers to a zone in which all the supply air in the combustion chamber is not yet ignited after ignition of the spark plug. In the example described here, fuel that is injected essentially by the spark plug during the compression process and that is directly in the region of the spark plug as a mist is ignited. The fuel injected during the intake process and outside the mist is ignited for the first time thereafter. The fuel that is homogeneously distributed in the combustion chamber before ignition becomes the end gas zone.

  The third mode of operation can be combined with, among other things, an exhaust gas recirculation device to reduce nitrogen oxide (NOx) emissions of internal combustion engines. The exhaust gas recirculation device reduces the generation of NOx during combustion of fuel in the cylinder of the internal combustion engine by mixing the exhaust gas into fresh air fed into the internal combustion engine. Since the exhaust gas recirculation device lowers the injection temperature during the fuel combustion process, the conditions for NOx generation are exacerbated. The amount of mixed exhaust gas and the size of the engine operating region that is problematic with respect to exhaust gas recirculation are limited by the operational stability of the internal combustion engine. This is because the exhaust gas recirculation rate increases and the ignition characteristics and combustion characteristics deteriorate until the misfire occurs. Misfires degrade the operational stability of the internal combustion engine while increasing undesirable hydrocarbon emissions of the internal combustion engine.

From European Patent No. 793803B1, there is known a misfire detection method for an internal combustion engine based on a temporal change in rotational movement of a sensor wheel coupled to a crankshaft of the internal combustion engine (see Patent Document 2). The segment time for a given segment of the sensor wheel to pass the sensor, or the average segment time assigned to the sensor wheel segment, is grasped and scaled into a measure for the instability of the internal combustion engine. Fire determination is performed. This measure of operational instability is formed by digital filtering of segment time using predetermined filter coefficients.
German Patent Application Publication No. 19936201A1 Specification European Patent No. 793803B1

  It is an object of the present invention to provide a method for operating a direct injection internal combustion engine with an exhaust gas recirculation device and an apparatus for carrying out the method, which fully utilize the potential capability of the exhaust gas recirculation device. To do.

  The method according to the invention for the operation of a direct injection internal combustion engine with an exhaust gas recirculation device is based on a first operating mode in which a homogeneous operation takes place, in which fuel is injected during the intake process. . In the second operation mode, fuel multiple injection is performed, in which fuel is injected at least by the first injection during the intake process, and fuel is injected by at least the second injection during the compression process. According to the present invention, in the first operating mode, the exhaust gas recirculation rate is increased until the internal combustion engine operating characteristic value or the exhaust gas characteristic value reaches a predetermined first threshold value. It has been proposed to switch to 2 driving modes. In the following description, the first operation mode is referred to as homogeneous operation.

  The method according to the invention raises the exhaust gas recirculation rate, which contributes to the reduction of NOx emissions of the internal combustion engine to the limit, within the range of homogeneous operation in which the internal combustion engine can generate maximum torque. Enable. The arrival of the limit is confirmed by comparing the internal combustion engine operating characteristic value or the exhaust gas characteristic value with the first threshold value.

  The ignition timing in homogeneous operation can be changed so that ignition can be performed at the appropriate timing necessary to achieve high torque and high efficiency despite the relatively high exhaust gas recirculation rate. I can do it.

  Advantageous extensions and embodiments of the method according to the invention will become apparent from the appended claims.

  In one extension, it is proposed that in the second operating mode, the exhaust gas recirculation rate is raised until the internal combustion engine operating characteristic value or the exhaust gas characteristic value reaches a predetermined second threshold value. . The second threshold value may be different from the first threshold value. This extended example achieves the exhaust gas recirculation rate even within the range of the second mode of operation, referred to as homogeneous split operation in the following description, and as little NOx emissions of the internal combustion engine as possible during the homogeneous split operation. It is possible to pull up until the limit is reached again.

  One advantageous extension proposes that the first efficiency of the internal combustion engine in homogeneous operation is required as soon as the first threshold is reached at the latest. Combined with another measure that the second efficiency of the internal combustion engine is required at the latest when the second threshold is reached, the internal combustion engine is under the given conditions based on a comparison of the two required efficiency. It is possible to select driving modes with high efficiency. These measures achieve the minimum fuel consumption of the internal combustion engine to generate a defined torque, together with the smallest possible NOx emissions.

  One embodiment proposes that at least one measure for operational instability is used as the internal combustion engine characteristic value. The determination of the operational instability of the internal combustion engine can be performed based on, for example, evaluation of the existing rotation speed signal and position signal. Another alternative proposes that at least one measure for knocking is used as the operating characteristic value of the internal combustion engine. The non-uniform pressure change in the cylinder caused by the combustion causing the knocking can be measured using a knock sensor, for example.

  When the operating limit of the internal combustion engine is reached, a misfire occurs and as a result, hydrocarbons are discharged. One embodiment therefore uses at least one measure for the hydrocarbon concentration in the exhaust gas as the exhaust gas characteristic value.

  A further embodiment relates to an exhaust gas recirculation device. According to the first embodiment, an external exhaust gas circulation device is proposed that includes an exhaust gas recirculation path between an exhaust gas region and an intake region of an internal combustion engine. If variable valve control within the adjustable range of the camshaft or individual valve controllability is provided, the internal exhaust gas recirculation device can be used with variable valve overlap time.

The device according to the invention for carrying out this method relates first to a control device made for carrying out this method.
This control device includes, inter alia, an efficiency measuring device and an operating mode switching device.

  The control device preferably includes at least one electrical storage device, in which process steps are stored as a computer program.

Other advantageous extensions and embodiments of the method according to the invention emerge from the other dependent claims and the following description.
FIG. 1 shows an internal combustion engine 10. An air sensor 12 and a throttle valve 13 are disposed in the intake region 11 of the internal combustion engine, and a hydrocarbon sensor 15 and an exhaust gas processing device 16 are disposed in the exhaust gas region 14.

  The internal combustion engine 10 has a combustion chamber 21 above a piston 20, and an inlet valve 22, a fuel injection valve 23, a spark plug 24, a knock sensor 25, and an outlet valve 26 protrude from the combustion chamber. The piston 20 is coupled to a flywheel 27, and the rotational speed and position of the flywheel are measured by a position sensor 28.

  The air sensor 12 sends the air signal mL to the control device 30, the knock sensor 25 sends the knock signal Kl to the knock evaluation device 31, the position sensor 28 sends the position signal n to the position evaluation device 32, and the hydrocarbon sensor 15 sends the exhaust gas evaluation device 33. Sends a hydrocarbon signal HC. Knock signal Kl and position signal n are internal combustion engine operating characteristic values. The hydrocarbon signal HC is an exhaust gas characteristic value. The control device 30 is further fed with a torque reference value MFa.

  The control device 30 including the efficiency evaluation device 40 and the operation mode switching device 41 includes a throttle valve signal dr for the throttle valve 13, an inlet valve control signal SEV for the inlet valve 22, a fuel signal mK for the fuel injection valve 23, and an ignition plug. The ignition signal zue is sent to 24, the outlet valve control signal SAV is sent to the outlet valve 26, and the exhaust gas recirculation signal agr is sent to the exhaust gas recirculation adjustment element 50.

  The knock evaluation device 31 has first and second knock signal threshold values 60 and 61, the position evaluation device 32 has first and second position signal threshold values 62 and 63, and the exhaust gas evaluation device 33 has first and second values. A second hydrocarbon signal threshold 64, 65 is assigned.

In the exhaust gas region, a NOx mass flow dmNOx and a hydrocarbon flow dmHC are generated. There is an exhaust gas recirculation path 66 between the exhaust gas region 14 and the intake region 11.
FIG. 2a shows the relationship between the fuel signal mK and the time t or the crankshaft angle ° KW during a first operating mode, referred to as homogeneous operation HOM in the following description. The fuel signal mK appears at a first time t1 during the intake process 70 of the internal combustion engine 10 and has a first time period ti1. An ignition signal zue appears after the bottom dead center UT of the piston 20, which is further in front of the top dead center OT of the piston 20.

  FIG. 2b shows the relationship between the fuel signal mK and the time t or the crankshaft angle ° KW during a second mode of operation, referred to as homogeneous split operation HSP in the following description. The fuel signal mK appears at a second time t2 during the intake process 70 and has a second time period ti2. After the bottom dead center UT of the piston 20, the fuel signal mK reappears at a third time point t3 during the compression process 71 of the piston 20, which signal has a third time period ti3. An ignition signal zue then appears, which is again before the top dead center OT of the piston 20.

  FIG. 3 shows a flowchart of the method according to the invention, which is started according to the first function block 80 with a request for the best fuel economy operation of the internal combustion engine 10. In the subsequent second function block 81, the homogeneous operation HOM is set in advance. In the subsequent third function block 82, the exhaust gas recirculation rate is increased.

  In the first check 83, whether or not the internal combustion engine operating characteristic value Kl, n exceeds the first threshold value 60, 62 given in advance, or the exhaust gas characteristic value HC is given in advance. It is checked whether or not the threshold value 64 is exceeded. If not, the process returns to the third function block 82. If so, the fourth functional block 84 determines the efficiency ηHOM under the homogeneous operation HOM, and the fifth functional block 85 proceeds to the homogeneous split operation HSP.

  In the subsequent sixth function block 86, the exhaust gas recirculation rate is increased. In the subsequent second check 87, it is determined whether the internal combustion engine operating characteristic value Kl, n exceeds the second threshold value 61, 63, or whether the exhaust gas characteristic value HC exceeds the second threshold value 65. Is checked. If not, the process returns to the sixth function block 86. If so, the seventh function block 88 determines the efficiency ηHSP under the homogeneous split operation HSP.

  In the third check 89, the efficiency ηHOM under the homogeneous operation HOM determined in the fourth function block 84 is compared with the efficiency ηHSP under the homogeneous split operation HSP determined in the seventh function block 88. Is done. If the efficiency ηHSP under the homogeneous split operation HSP is greater than the efficiency ηHOM under the homogeneous operation HOM, the homogeneous split operation HSP is maintained based on the fifth functional block 85. If not, the process returns to the second function block 81 and shifts to the homogeneous operation HOM.

  The method according to the present invention operates as follows. That is, the control device 30 determines the fuel signal mK according to the torque reference value MFa derived from the position of an accelerator pedal that is not explained in detail, for example, in a car that is not explained in detail. In some cases, the fuel signal mK also depends on the air signal mL and / or the position signal n, where the position signal reflects not only the position of the flywheel 27 but, in particular, the speed of the flywheel. ing.

  First, the first function block 80 starts with a request for the best fuel efficiency operation of the internal combustion engine 10. The second functional block 81 sets the homogeneous operation HOM that allows the internal combustion engine to generate the maximum torque. In the homogeneous operation HOM, fuel injection is performed during the downward movement of the piston 20 under the intake process 70. The throttle valve 13 is somewhat open. The fuel signal mK starts at a first time t1 corresponding to the determined crankshaft angle ° KW. The fuel signal mK has a first time period ti1, which in combination with the fuel pressure is a measure for the amount of fuel to be distributed.

  The intake process 70 is before the bottom dead center UT of the piston 20. After reaching the bottom dead center UT, the compression process 71 begins, in which the ignition signal zue appears. The ignition signal zu is generally before top dead center OT. The ignition signal zue is preferably shifted in an early direction until the highest efficiency is achieved. At the same time, the knocking tendency of the internal combustion engine 10 increases.

  During the homogeneous operation HOM, the exhaust gas recirculation rate is increased based on the second functional block 82. Increasing the exhaust gas recirculation rate reduces NOx emissions of the internal combustion engine 10 by lowering the peak temperature that occurs during the combustion process.

Exhaust gas recirculation further reduces the combustion rate. Therefore, the ignition timing must be shifted early in order to ensure the best fuel economy combustion center of gravity position.
The increase of the exhaust gas recirculation rate can be carried out, for example, up to 30% under homogeneous operation. Increasing the exhaust gas recirculation rate further increases the operational instability of the internal combustion engine, and the operational instability is first shown by the probability variation of the generated mechanical output to the occurrence of misfire.

  In the first check 83, it is checked whether or not the knock signal Kl exceeds the first knock signal threshold 60, or whether or not the position signal n exceeds the first position signal threshold 62. The increased operational instability first appears in the position signal n. A knock signal Kl appears upon reaching the knock limit. Knock signal Kl and position signal n are referred to as internal combustion engine operating characteristic values Kl, n in the following description.

  The misfire affects the hydrocarbon flow dmHC due to the generation of unburned fuel in the exhaust gas region 14. Therefore, in the first check 83, as an alternative, it is possible to check whether the hydrocarbon signal HC exceeds the first hydrocarbon signal threshold value 64 or not. The hydrocarbon signal HC is referred to as an exhaust gas characteristic value HC in the following description.

  If any of the first threshold values 60, 62, 64 has not been reached, the exhaust gas recirculation rate can be further increased based on the third functional block 82. When the first check 83 confirms that the threshold value is exceeded, the process proceeds to the second operation mode, the homogeneous split operation HSP based on the fifth functional block 85. In the second operating mode, at least one first fuel injection is performed under the intake process 70 and at least one further fuel injection is performed under the compression process 71.

  With the transition to at least double fuel injection, improved ignition stability with better ignition characteristics is born in the stratified charge area. The best combustion center of gravity position can be maintained under still acceptable operational stability of the internal combustion engine 10 even in the case of higher exhaust gas recirculation rates than under homogeneous operation HOM. The exhaust gas recirculation rate under homogeneous split operation can be up to 35%, for example. This may lead to further reduction of the NOx emissions of the internal combustion engine 10 in some cases, or in some cases fuel consumption.

  Under the homogeneous split operation HSP, the exhaust gas is again exhausted until the second check 87 again confirms that any of the second threshold values 61, 63, 65 is over, based on the sixth functional block 86. Increase in recirculation rate. In some cases, the second threshold values 61, 63, 65 may coincide with the first threshold values 60, 62, 64. Switching between the operation modes is performed by an operation mode switching switch 41 included in the control device 30.

  Measurement of the highest possible efficiency ηHOM under homogeneous operation HOM in the fourth functional block 84 and / or homogeneous split operation HSP in the seventh functional block 88 in order to meet the requirements for the best fuel efficiency operation of the internal combustion engine 10. Measurement of the highest possible efficiency ηHSP can be made appropriately each time. In a third check 89, both efficiencies ηHOM and ηHSP are compared with each other. Then, depending on the result of this comparison, an operating mode HOM or HSP that allows a higher efficiency η is set by returning to the second function block 81 or to the fifth function block 85 in some cases. The efficiency is measured by an efficiency measuring device 40 included in the control device 30.

  The fourth functional block 84, which includes efficiency measurement under homogeneous operation HOM, is the seventh functional block 88, which includes efficiency measurement under homogeneous split operation (HSP), before the first check 83. You may arrange | position in front of the 2nd check 87, respectively. In that case, the efficiency ηHOM under the homogeneous operation HOM and the efficiency ηHSP under the homogeneous split operation HSP can be used at any time.

  The highest possible efficiency ηHOM and ηHSP under the two operating modes HOM and HSP is the last reversal from the first check 83 to the third function block 82 or from the second check 87 to the sixth function block 86. Achieved by last reversion to. The placement of the functional blocks 84, 88 after the checks 83, 87, used in the embodiment shown here, optimizes the computation time of the signal processor included in the controller 30. Enable.

  It is particularly advantageous if the measurement of efficiency under at least one operating mode, preferably under all operating modes, is carried out continuously, so that the measuring of efficiency is also performed for operating modes that are not in use at that time. It becomes. This measure can avoid unnecessary switching between driving modes.

  The efficiency ηHOM and ηHSP of the internal combustion engine 10 can be measured using signals that already exist. For example, based on the air signal mL and the position signal n reflecting the rotation speed, the air filling rate in the combustion chamber 21 can be calculated from these signals. The torque produced by the piston 20 can be calculated taking into account the known fuel signal mK, the excess air lambda for a given combustion process, and the given ignition angle. In some cases, the operating mode HOM, HSP and / or the exhaust gas recirculation rate agr can also be taken into account. When the operation point (rotation speed and torque) of the internal combustion engine 10 is given, the control device 30 specifies the operation modes HOM and HSP that can be the operation point when the fuel consumption is minimal.

  The exhaust gas recirculation can be performed through the exhaust gas recirculation path 66 from the outside. An exhaust gas recirculation adjusting element 50 controlled by an exhaust gas recirculation signal agr is disposed in the exhaust gas recirculation path.

  In another embodiment where an especially small exhaust gas recirculation rate, for example less than 10%, can be achieved, exhaust gas recirculation within the engine can be achieved by controlling the inlet valve 22 and outlet valve 26 in a targeted manner. . The valves 22, 26 can be driven by a single camshaft, not described in detail, or by two camshafts that can be adjusted together or separately. In some cases, the individual valves 22 and 26 may be provided with respective control devices based on the embodiment shown in FIG. The control device 30 can separately control the inlet valve 22 with the inlet valve control signal SEV and the outlet valve 26 with the outlet valve control signal SAV. This internal exhaust gas recirculation is determined by the valve overlap time during which both valves 22, 26 are open simultaneously.

FIG. 1 shows the technical environment in which the method according to the invention is applied. FIG. 2a shows the relationship between fuel signal and time or crankshaft angle. FIG. 2b shows the relationship between fuel signal and time or crankshaft angle. FIG. 3 shows a flowchart of the method according to the invention.

Explanation of symbols

10 internal combustion engine,
11 Intake area,
12 Air sensor,
13 Throttle valve,
14 exhaust gas area,
15 hydrocarbon sensor,
16 exhaust gas treatment device,
20 pistons,
21 Combustion chamber,
22 Inlet valve (intake valve),
23 Fuel injection valve,
24 spark plug,
25 knock sensor,
26 Outlet valve (exhaust valve),
27 Handwheel,
28 position sensor,
31 knock evaluation device,
32 position evaluation device,
33 Exhaust gas evaluation device,
40 Efficiency evaluation device (or measurement device),
41 Operation mode switching device (or changeover switch),
50 exhaust gas recirculation control elements,
60, 61 first and second knock signal thresholds,
62, 63 first and second position signal thresholds,
64,65 first and second hydrocarbon signal thresholds,
66 exhaust gas recirculation path,
agr exhaust gas recirculation signal,
dmHC hydrocarbon stream,
dmNOx NOx mass flow,
dr throttle valve signal,
HC hydrocarbon signal,
HOM homogeneous operation,
HSP homogeneous split operation,
Kl knock signal,
° KW crankshaft angle,
MFa torque reference value,
mK fuel signal,
mL air signal,
n position signal,
SAV outlet valve control signal,
SEV inlet valve control signal,
t hours,
70 Intake process of internal combustion engine,
71 compression process,
OT piston top dead center,
t1, t2, t3 first, second, third time points,
ti1, ti2, ti3 first, second, third time period,
UT piston bottom dead center,
zue Ignition signal.

Claims (10)

In the first operating mode (HOM), a homogeneous operation is performed in which fuel is injected during the intake process (70),
In the second operating mode (HSP), fuel is injected by at least one first injection during the intake process (70) and at least one second injection during the compression process (71). Homogeneous split operation by multiple injection is performed,
Method of operating a direct-injection internal combustion engine with an exhaust gas recirculation system (10),
In the first operational aspect (HOM) to the inner combustion engine operating characteristic values (Kl, n) or exhaust gas characteristic values (HC) reaches a predetermined first threshold value (60, 62, 64), the exhaust The gas recirculation rate was raised ,
When the internal combustion engine operating characteristic value (Kl, n) or the exhaust gas characteristic value (HC) reaches the threshold value (60, 62, 64), the method is switched to the second operating mode (HSP). . In the second operation manner (HSP), until SL engine operating characteristic values (Kl, n) or the exhaust gas characteristic value (HC) reaches a second predetermined threshold (61, 63) The method of claim 1 , wherein the exhaust gas recirculation rate is increased. 2. Method according to claim 1, characterized in that the efficiency (ηHOM) of the homogeneous operation (HOM) of the internal combustion engine (10) is determined. Method according to claim 2, characterized in that the efficiency (ηHSP) of the homogeneous split operation (HSP) of the internal combustion engine (10) is determined. A higher one of the efficiency of the homogeneous operation (ηHOM) and the efficiency of the homogeneous split operation (ηHSP) is required, and the internal combustion engine (10) is an operation showing the higher efficiency (ηHOM, ηHSP). 5. The method according to claim 3 or 4, characterized in that it is operated in a mode (HOM, HSP). The value (Kl) indicating a knock signal and the value (n) indicating a position signal of the flywheel (27) are used as the operating characteristic value (Kl, n) of the internal combustion engine. The method described in 1. The method according to claim 1, wherein a signal indicating a hydrocarbon concentration is used as the exhaust gas characteristic value (HS).   An external exhaust gas recirculation device having an exhaust gas recirculation path (66) between the exhaust gas region (14) and the intake region (11) of the internal combustion engine (10) is provided. The method of claim 1.   2. A method according to claim 1, characterized in that an internal exhaust gas recirculation device is provided such that at least the inlet valve (22) and the outlet valve (26) are controlled by a predetermined valve overlap time. In the first operating mode (HOM), a homogeneous operation is performed in which fuel is injected during the intake process (70),
In the second operating mode (HSP), fuel is injected by at least one first injection during the intake process (70) and at least one second injection during the compression process (71). Homogeneous split operation by multiple injection is performed,
In the operating device of the direct injection internal combustion engine (10) with the exhaust gas recirculation device,
In the first operating mode (HOM), the exhaust gas until the internal combustion engine operating characteristic value (Kl, n) or the exhaust gas characteristic value (HC) reaches a predetermined first threshold (60, 62, 64). A control device (30) is provided that increases the recirculation rate and switches to the second operating mode (HSP) when the exhaust gas recirculation rate reaches the threshold value (60, 62, 64). apparatus.

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