JP4508045B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine.

  Conventionally, lean burn engines and in-cylinder injection engines that control the air-fuel ratio leaner than the stoichiometric air-fuel ratio have been developed for the purpose of improving fuel efficiency. In these engines, a NOx occlusion reduction catalyst is provided in the exhaust system in order to purify NOx (nitrogen oxides) generated during lean combustion. The NOx storage-reduction catalyst has a characteristic of storing NOx in the exhaust when the air-fuel ratio of the exhaust is lean, and reducing and purifying the stored NOx when the air-fuel ratio becomes rich.

  Here, in the NOx occlusion reduction catalyst, when the NOx occlusion amount is saturated and reaches the occlusion limit, the NOx purification capacity is lowered. Therefore, in order to suppress a decrease in the NOx purification capacity, rich combustion is temporarily performed, and the stored NOx is reduced by reducing components such as HC and CO in the exhaust discharged at that time. This technique is generally called a rich spike, and its control method is disclosed in, for example, Patent Document 1.

  By the way, when performing rich spike control, if the air-fuel ratio in the combustion chamber is excessively enriched, particulate matter (particulate matter) is generated during the combustion. Therefore, it is desired to suppress the generation of particulate matter during rich spike control.

Incidentally, as a technique for removing the particulate matter discharged from the internal combustion engine, a technique is proposed in which a particulate filter (PF) is provided in the exhaust system and the particulate matter in the exhaust gas is collected by this particulate filter. (For example, Patent Documents 2 and 3). However, the configuration in which the particulate filter is provided in the exhaust system has a disadvantage that the cost increases with the installation of the filter.
JP 2004-84617 A JP 2003-206786 A JP 2003-254039 A

  The main object of the present invention is to provide a control device for an internal combustion engine that can suppress the generation of particulate matter during the rich spike control and thus improve exhaust emission.

In the configuration in which the NOx occlusion reduction type catalyst is provided in the exhaust system of the internal combustion engine, rich spike control is performed in order to regenerate the NOx purification ability of the catalyst. In such a case, when an overrich atmosphere is generated in the combustion chamber of the internal combustion engine, particulate matter (particulate matter) is generated along with the overrich combustion. Particularly in a direct injection internal combustion engine, it is considered that an excessively rich atmosphere is locally generated, and the problem of generation of particulate matter is likely to occur. In this regard, in the first invention, when the rich spike control is performed, the generation state of the particulate matter is monitored, and the air-fuel ratio at the rich spike control is variably set based on the monitoring result. Thereby, generation | occurrence | production of the particulate matter accompanying implementation of rich spike control can be suppressed, and improvement of an exhaust mission can be aimed at.

  Here, “monitoring the occurrence of particulate matter” includes monitoring whether or not particulate matter is generated and determining the amount of particulate matter generated when it occurs. It is. “Particulate matter” is a material generally called particulate matter, and is a generic term for soluble organic component SOF, insoluble organic component ISF, and the like. In the following description, the particulate matter (particulate matter) is also referred to as “PM”.

In the second invention, when the rich spike control is performed, the amount of particulate matter in the exhaust gas is obtained by measurement or estimation, and the generation state of the particulate matter is monitored by the amount of particulate matter obtained by the measurement or estimation. . Then, the richness of the air-fuel ratio at the time of rich spike control is determined based on the amount of particulate matter. In this case, since the generation amount of the particulate matter is obtained directly or indirectly, suitable rich spike control corresponding to the generation amount can be implemented even when the generation amount changes sequentially.

  More specifically, when the amount of the particulate matter is larger than a predetermined amount, the richness of the air-fuel ratio at the time of rich spike control is decreased, or the air-fuel ratio at the time of rich spike control is increased as the amount of the particulate matter is larger. A configuration that reduces the richness of the image can be considered.

  Here, as a method for obtaining the amount of particulate matter (PM amount) in the exhaust by measurement, a measurement device such as a PM sensor is provided upstream of the catalyst in the exhaust pipe of the internal combustion engine, and measurement by the measurement device is performed. A method of calculating the amount of particulate matter (PM amount) based on the result can be considered. Further, as a method for obtaining the particulate matter in the exhaust gas by estimation, a method of calculating by a map or an arithmetic expression using the intake air amount or the fuel injection amount as a parameter can be considered.

In the third invention, the relationship between the operating state of the internal combustion engine and the generation amount of the particulate matter is defined in advance and held as data, and the particulate data is used based on the respective operating state using the specified data. Monitor the occurrence of substances. In this case, it is possible to monitor the generation state of the particulate matter without directly or indirectly obtaining the amount of the particulate matter.

The prescribed data representing the relationship between the operating state of the internal combustion engine and the amount of particulate matter generated is preferably as follows. That is,
The prescribed data defines the relationship between the rotational speed of the internal combustion engine and the amount of particulate matter generated ( fourth invention ). At this time, a relationship is assumed in which the amount of particulate matter generated increases as the rotational speed of the internal combustion engine increases.
The prescribed data defines the relationship between the fuel injection timing by the fuel injection valve and the amount of particulate matter generated ( fifth invention ).
The prescribed data defines the relationship between the ignition timing and the amount of particulate matter generated ( sixth invention ). At this time, a relationship is assumed such that the later the ignition timing, the greater the amount of particulate matter generated.

Incidentally, it has been confirmed that particulate matter is generated in the combustion chamber of the internal combustion engine when the air-fuel ratio (combustion air-fuel ratio) of the combustion gas that is actually used for combustion becomes 9.5 or less. By the way, this number is known as the OAU (Otto A. Uyehara) number. In view of this point, as in the seventh invention , the specified data may be specified so that the local air-fuel ratio in the combustion chamber does not become 9.5 or less. Alternatively, as in the eighth aspect of the invention , the specified data is preferably specified so that the air-fuel ratio of the entire combustion chamber does not become 9.5 or less. Thereby, generation | occurrence | production of the particulate matter at the time of rich spike control can be suppressed.

In the ninth invention, a measuring device for measuring the amount of particulate matter contained in the exhaust is provided in the exhaust system of the internal combustion engine. Then, the amount of the particulate matter obtained from the prescribed data is compared with the amount of the particulate matter measured by the measuring device, and the validity of the prescribed data is determined based on the result.

  In short, when the internal combustion engine is used for a long period of time, the fuel injection amount differs from the appropriate amount due to deposits (deposits) adhering to the fuel injection valve, etc., resulting in the operating state of the internal combustion engine and particulate matter. It is conceivable that there will be a deviation in the prescribed data that defines the relationship with the generation amount of When the deviation of the prescribed data occurs, the amount of the particulate matter may be excessive in a state where the amount of the particulate matter is originally limited to a predetermined level or less. In this case, if a measuring device such as a PM sensor is used, the actual amount of particulate matter can be measured, and the deviation of the prescribed data can be known from the result. Therefore, the correctness of the prescribed data can be properly evaluated. If the legitimacy of the prescribed data is impaired, it is preferable to correct the air-fuel ratio of the rich spike control at that time or correct the prescribed data. If these corrections are impossible, a warning may be issued.

Further, the amount of particulate matter generated during the rich spike control is related not only to the air-fuel ratio but also to the fuel injection timing and ignition timing by the fuel injection valve. Therefore, as in the tenth aspect of the invention, it is preferable to variably set the fuel injection timing by the fuel injection valve based on the monitoring result by the monitoring means (the generation state of particulate matter during the rich spike control). Alternatively, as in the eleventh aspect of the invention , the ignition timing may be variably set based on the monitoring result by the monitoring means (the generation state of particulate matter during rich spike control).

According to the tenth and eleventh aspects, the restriction on the richness of the air-fuel ratio can be relaxed in suppressing the generation of particulate matter. Therefore, it is possible to efficiently regenerate the NOx purification capacity of the desired catalyst. At this time, since the desired NOx purification capacity is regenerated quickly, the duration of the rich spike can be shortened.

In the twelfth aspect of the invention, the richness is gradually reduced with respect to the target air-fuel ratio set at the start of the rich spike control based on the generation state of the particulate matter. As a result, it is possible to secure a rich component necessary for regenerating the catalyst purification capacity while reducing the amount of particulate matter.

In the thirteenth invention, the execution of rich spike control is prohibited when the amount of particulate matter is equal to or greater than a predetermined limit value. The “limit value” is a value considered that it is impossible to suppress the particulate matter within an allowable level even if the above-described variable setting of the air-fuel ratio or other processing is performed. When the limit value is exceeded, generation of particulate matter is suppressed by not performing rich spike.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In the present embodiment, an engine control system is constructed with an in-cylinder injection gasoline engine for a vehicle configured to inject fuel directly into a cylinder (combustion chamber) by an injector as a fuel injection valve. In this control system, fuel injection amount control, ignition timing control, electronic throttle control, and the like are performed with an electronic control unit (hereinafter referred to as ECU) as a center. As is well known, in a cylinder injection engine, the operating state can be switched between a homogeneous combustion operation in which fuel is injected in the intake stroke and homogeneous combustion is performed, and a stratified combustion operation in which fuel is injected in the compression stroke and stratified combustion is performed. It has become. First, the outline of the engine control system will be described with reference to FIG.

  In the in-cylinder injection engine (hereinafter referred to as the engine 10) shown in FIG. 1, the cylinder block 11 is provided with an electromagnetically driven injector 12. The injector 12 is supplied with high-pressure fuel from a fuel supply system (not shown), and the fuel is directly injected into the combustion chamber 13 from the injector 12 when the injector 12 is opened.

  An intake valve 17 and an exhaust valve 18 are respectively provided at the intake port leading to the intake pipe 15 and the exhaust port leading to the exhaust pipe 16, and the intake valve 17 opens to suck into the combustion chamber 13 from the intake pipe 15. Air is introduced, and the exhaust after combustion is discharged to the exhaust pipe 16 by opening the exhaust valve 18. At least the intake valve 17 is provided with a variable valve mechanism 19. The variable valve mechanism 19 has a structure that can vary the valve opening / closing operation conditions such as the lift amount and valve opening timing (working angle) of the intake valve 17, and according to the engine operating state each time. The valve opening / closing operation conditions are adjusted as appropriate. The intake pipe 15 is provided with an air flow meter 20 for detecting the amount of intake air.

  A spark plug 21 is attached to the cylinder head of the engine 10 for each cylinder, and a high voltage is applied to the spark plug 21 at a desired ignition timing through an ignition coil (not shown). By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 21, and the fuel is ignited in the combustion chamber 13 and used for combustion.

  The exhaust pipe 16 is provided with a three-way catalyst 23 for purifying CO, HC, NOx and the like in the exhaust gas, and a NOx storage reduction catalyst 24 is provided downstream thereof. As is well known, the NOx occlusion reduction catalyst 24 selectively adsorbs and absorbs NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and absorbs or holds both, and the air-fuel ratio of the inflowing exhaust gas is rich ( (Or the stoichiometric air-fuel ratio), the stored NOx is reduced and purified using reducing components such as HC and CO in the exhaust gas.

  Further, on the upstream side of the three-way catalyst 23, an A / F sensor 31 for detecting an air-fuel ratio (A / F) based on the oxygen concentration or the like in the exhaust gas is provided, and upstream and downstream of the NOx storage reduction catalyst 24. On the side, O2 sensors 32 and 33 for outputting different electromotive force signals depending on whether the exhaust is rich or lean are provided. In addition, the cylinder block 11 includes a coolant temperature sensor 34 that detects the temperature of the engine coolant, and a crank angle sensor that outputs a rectangular crank angle signal for each predetermined crank angle of the engine 10 (for example, at a cycle of 30 ° CA). 35 is attached.

The outputs of the various sensors described above are input to the ECU 40 that controls the engine. The ECU 40 is configured mainly by a microcomputer including a CPU, a ROM, a RAM, and the like, and by executing various control programs stored in the ROM, the air-fuel ratio is adjusted by adjusting the fuel injection amount in accordance with the engine operating state. Control, ignition control by adjusting the ignition timing, etc. are appropriately implemented. At this time, either stratified combustion or homogeneous combustion is appropriately performed based on the engine operating state at each time. Briefly describing the air-fuel ratio control, the ECU 40 performs the air-fuel ratio feedback control based on the deviation between the actual air-fuel ratio detected by the A / F sensor 31 and the target air-fuel ratio set each time. As the predetermined rich spike execution condition is satisfied, rich spike control for temporarily controlling the air-fuel ratio to the rich side is performed. As a result, NOx adsorbed on the NOx storage reduction catalyst 24 is reduced and purified by the reducing components such as HC and CO, and the NOx purification capacity of the catalyst 24 is regenerated.

  The O2 sensors 32 and 33 provided before and after the NOx storage reduction catalyst 24 are used to detect a decrease in the NOx storage capability of the NOx storage reduction catalyst 24, that is, the deterioration of the catalyst 24. At this time, the ECU 40 detects the timing at which the rich component is actually supplied to the NOx storage reduction catalyst 24 based on the detection value of the upstream O2 sensor 32, and also detects the timing of the downstream O2 sensor 33 based on the detection value of the downstream O2 sensor 33. The timing at which the reduction and purification of the stored NOx is completed in the NOx storage reduction catalyst 24 is detected, and the deterioration of the NOx storage reduction catalyst 24 is detected based on the required time between these timings.

  By the way, in the in-cylinder injection type engine 10 as described above, when the rich spike is performed, if an over-rich atmosphere is locally generated in the combustion chamber 13, PM (particulate) is generated along with the combustion of the over-rich portion. Material). At this time, theoretically, PM is generated when rich combustion is performed in a state of combustion air-fuel ratio ≦ 9.5. Therefore, as a countermeasure, the PM occurrence state is monitored during the rich spike, and the air-fuel ratio during the rich spike is variably set based on the monitoring result.

  In the present embodiment, the relationship between the engine operation state and the PM generation amount is defined in advance and stored in the memory (ROM) as map data, and the PM generation is performed based on the respective operation state using the map data. Monitor the situation.

  Specifically, paying attention to the fact that the PM generation amount changes according to the air-fuel ratio (A / F), the engine speed NE, the fuel injection start timing SOI, and the ignition timing IGT, the PM generation is based on these parameters. Guess the situation. FIG. 2 is a diagram showing the difference in PM generation amount with respect to A / F and injection start timing SOI for each engine speed NE. Here, fuel injection is performed in the intake stroke, and the injection start timing SOI in FIG. 2 is 300 BTDC ° CA, 250 BTDC ° CA, and 200 BTDC ° CA in order from the advance side to the retard side.

  As can be seen from FIG. 2, the PM generation amount increases as the A / F becomes richer and the injection start timing SOI becomes the advance side. It can also be seen that the PM generation amount increases as the engine speed NE increases. In FIG. 2, the injection start timing SOI is also related to the intake stroke (300 BTDC ° CA, 250 BTDC ° CA, 200 BTDC ° CA) in which the piston moves downward, and the PM is increased as the injection start timing SOI is advanced. Although the generation amount is increasing, this tendency is considered to be changed depending on the direction of piston operation.

  FIG. 3 is a diagram showing a difference in PM generation amount with respect to A / F and ignition timing IGT. The ignition timing IGT in FIG. 3 is 30BTDC ° CA, 25BTDC ° CA, and 20BTDC ° CA in order from the advance side to the retard side. According to FIG. 3, it can be seen that the PM generation amount increases as the ignition timing IGT is advanced.

  2 and FIG. 3, the PM generation amount can be estimated based on the A / F, the engine rotation speed NE, the injection start timing SOI, and the ignition timing IGT. In the present embodiment, the target air-fuel ratio at the time of rich spike control is variably set based on the PM generation amount estimation result.

  FIG. 4 is a flowchart showing a target air-fuel ratio setting process at the time of rich spike control, and this process is executed by the ECU 40 at a predetermined time period.

  In FIG. 4, in step S101, it is determined whether or not the rich spike execution condition is satisfied. In the present embodiment, the rich spike execution condition is established when the NOx adsorption amount of the NOx occlusion reduction catalyst 24 exceeds a predetermined determination level. At this time, the NOx adsorption amount of the NOx occlusion reduction catalyst 24 can be estimated based on each engine operating state (operation mode), for example, based on the engine rotational speed and load (intake air amount, etc.). The combustion temperature is calculated, and the NOx generation concentration is calculated based on the combustion temperature. Then, the NOx amount is obtained from the NOx generation concentration and the exhaust flow rate, and the NOx adsorption amount of the NOx storage reduction catalyst 24 is estimated by integrating the NOx amount. Further, using the in-cylinder pressure as a parameter, the NOx adsorption amount is estimated in the order of calculation of combustion temperature → calculation of NOx generation concentration → calculation of NOx amount → calculation of NOx adsorption amount, or a NOx sensor is provided in the exhaust pipe. It is also possible to calculate the NOx adsorption amount based on the detection value of the sensor. In addition, the rich spike execution condition may be satisfied every time a predetermined time elapses, or the rich spike execution condition may be satisfied every time the travel distance of the vehicle becomes a predetermined distance.

  If the rich spike execution condition is not satisfied, this process is terminated. At this time, the lean operation of the engine is continued. If the rich spike execution condition is satisfied, the process proceeds to step S102.

  In step S102, the PM generation amount is estimated based on the engine operating state at each time. Specifically, the PM generation amount is estimated from map data defined on the basis of the relationship shown in FIGS. 2 and 3 using A / F, engine rotation speed NE, injection start timing SOI, and ignition timing IGT as parameters. At this time, A / F is set to a reference A / F at the time of rich spike (for example, A / F = 12), and other values are used for other parameters. For simplicity, it is also possible to exclude at least one of the injection start timing SOI and the ignition timing IGT from the estimation parameters and estimate the PM generation amount using other parameters.

  In a succeeding step S103, it is determined whether or not the estimated PM generation amount is equal to or greater than a predetermined limit value. The limit value is a value that is assumed that the PM generation amount does not fall within the allowable value even if the target air-fuel ratio correction process described later is performed. If PM generation amount ≧ limit value, this processing is terminated as it is. In other words, the rich spike is not performed this time. If the PM generation amount <the limit value, the process proceeds to step S104, and the subsequent rich spike process is executed.

  In step S104, the base target air-fuel ratio at the time of rich spike is set based on the engine speed and the temperature of the NOx storage reduction catalyst 24 (catalyst temperature). At this time, for example, the base target air-fuel ratio is set with reference to a predetermined target air-fuel ratio map. The catalyst temperature can be estimated from the elapsed time after the engine is started, or can be measured by installing a temperature sensor on the catalyst. However, it is possible to set the base target air-fuel ratio as a fixed value.

  Thereafter, in step S105, it is determined whether the PM generation amount (PM generation amount calculated in step S102) is equal to or greater than a predetermined allowable value. If PM generation amount <allowable value, the process proceeds to step S106, and the base target air-fuel ratio is set as the final target air-fuel ratio as it is. If PM generation amount ≧ allowable value, the process proceeds to step S107, and the A / F on the lean side of the base target air-fuel ratio is set as the final target air-fuel ratio. Specifically, the target air-fuel ratio is set such that the PM generation amount is less than the allowable value using map data defined based on the relationship of FIG. 2 or FIG.

  The correction of the target air-fuel ratio will be described with reference to FIG. In FIG. 5, the base target air-fuel ratio is calculated as “AFR1”. At this time, when A / F = AFR1, it is estimated that the PM generation amount exceeds the allowable value, and therefore, correction is performed so as to reduce the rich degree of the base target air-fuel ratio. As a result, the final target air-fuel ratio is set to “AFR2”.

  When the target air-fuel ratio for rich spike control is set as described above, rich spike is performed based on the target air-fuel ratio. The rich spike is ended when a predetermined time has elapsed from the start.

  According to the embodiment described above in detail, the following excellent effects can be obtained.

  When the rich spike control is performed, the PM occurrence state is monitored based on the map data defining the PM generation amount (map data defined based on the relationship shown in FIGS. 2 and 3), and the rich spike control is performed based on the monitoring result. Since the hourly air-fuel ratio is variably set, the generation of PM accompanying the execution of rich spike control can be suppressed, and the exhaust mission can be improved. In this case, by using the map data, it is possible to monitor the PM generation status without directly or indirectly obtaining the PM generation amount.

  In addition, PM emission during rich spike control can be suppressed without adding an external device such as a particulate filter. Even if an external device such as a particulate filter is added, there is an advantage that a relatively small size is sufficient.

  Paying attention to the fact that the PM generation amount changes according to the air-fuel ratio (A / F), the engine rotation speed NE, the fuel injection start timing SOI and the ignition timing IGT, map data relating to the PM generation amount is defined using these as parameters. Therefore, it is possible to appropriately grasp the occurrence state of PM.

  Since the execution of rich spike control is prohibited when the PM generation amount is equal to or greater than a predetermined limit value, PM generation can be reliably prevented.

(Second Embodiment)
In the first embodiment, map data defined in advance is used, and the amount of PM generated during rich spike control is estimated based on the engine operating state every time. However, in the present embodiment, this is changed to the exhaust pipe. 16, a PM sensor is provided on the upstream side of the three-way catalyst 23, and the PM generation amount is directly detected based on the detection signal of the PM sensor. The system configuration is different from the configuration of FIG. 1 only in that a PM sensor is provided in the exhaust pipe 16, and the difference is very small.

  The configuration of the PM sensor is conventionally known (for example, Japanese Patent Application Laid-Open No. 2003-98136), and will be briefly described. The PM sensor has a base made of an insulating material, and the base is formed with a large number of holes for circulating exhaust gas. The hole is provided with a pair of electrodes on the upstream side and the downstream side. In such a configuration, when PM is contained in the exhaust gas, PM adheres to the vicinity of the electrodes, and accordingly, the electrodes are electrically connected. At this time, the PM generation amount is detected by measuring the current flowing between the electrodes.

  FIG. 6 is a flowchart showing a target air-fuel ratio setting process in the present embodiment. This process is executed by the ECU 40 instead of FIG. Note that FIG. 6 includes processing that is the same as that in FIG. 4, and steps S201, S203, S205, and the like are the same processing, and thus the description is simplified.

  In FIG. 6, in step S201, it is determined whether or not a rich spike execution condition is satisfied. If the rich spike execution condition is not satisfied, this process is terminated. At this time, the lean operation of the engine is continued. If the rich spike execution condition is satisfied, the process proceeds to step S202.

  In step S202, the PM generation amount is detected based on the detection signal of the PM sensor. In subsequent step S203, it is determined whether or not the detected PM generation amount is equal to or greater than a predetermined limit value. If PM generation amount ≧ limit value, this processing is terminated as it is. In other words, the rich spike is not performed this time. If the PM generation amount <the limit value, the process proceeds to step S204, and the subsequent rich spike process is executed.

  In step S204, it is determined whether or not the current time is the initial processing of rich spike control. On the condition that the current time is the initial processing, in step S205, the engine speed and the temperature of the NOx storage reduction catalyst 24 (catalyst temperature) are determined. ) To set the base target air-fuel ratio at the time of rich spike. Thereafter, in step S206, it is determined whether or not the detected value of the PM generation amount at that time is equal to or larger than a predetermined allowable value. If PM generation amount <allowable value, the process proceeds to step S207, and the previous target air-fuel ratio is used as it is as the final target air-fuel ratio. In the case of the initial processing, the base target air-fuel ratio is used as it is as the final target air-fuel ratio.

  If PM generation amount ≧ allowable value, the process proceeds to step S208, where the previous target air-fuel ratio (base target air-fuel ratio in the initial processing) is corrected to the lean side by a predetermined increment α, and the corrected air-fuel ratio is corrected. Is the final target air-fuel ratio. Specifically, the previous target air-fuel ratio is increased by 5%. This correction of the target air-fuel ratio is repeated until the PM generation amount becomes less than the allowable level. As a result, when the PM generation amount exceeds the allowable level, the rich degree of the target air-fuel ratio is gradually reduced.

  As described above, according to the second embodiment, similarly to the first embodiment, it is possible to suppress the generation of PM accompanying the execution of the rich spike control, and to improve the exhaust mission. At this time, since the PM generation amount is directly obtained from the detection value of the PM sensor, suitable rich spike control corresponding to the PM generation amount can be implemented even when the PM generation amount changes sequentially.

  Further, at the time of rich spike control, since the rich degree is gradually reduced according to the PM generation state with respect to the target air-fuel ratio set at the time of starting the control, an optimum air-fuel ratio for obtaining PM suppression is obtained, Rich spike control at the air-fuel ratio can be performed. In this case, it is possible to secure a rich component necessary for regenerating the NOx purification ability of the NOx storage reduction catalyst 24 while reducing the PM amount.

(Third embodiment)
In the present embodiment, at the time of rich spike control, the target air-fuel ratio is variably set based on the PM generation amount, and the injection start timing SOI by the injector 12 is variably set. This is intended to reduce the amount of PM generated by the PM suppression effect by variable setting of target air-fuel ratio (reduction of richness) and the PM suppression effect by variable setting of injection start timing SOI. The system configuration is the same as in FIG.

  FIG. 7 is a flowchart showing a target air-fuel ratio setting process in the present embodiment, and this process is executed by the ECU 40 instead of FIG. Note that FIG. 7 includes a process that overlaps with FIG. 4, and steps S301 to S305 are the same process, so the description is simplified.

  In FIG. 7, the PM generation amount is calculated when the rich spike execution condition is satisfied (steps S301 and S302). At this time, the PM generation amount may be calculated using map data as described in the first embodiment, or based on the detection signal of the PM sensor as described in the second embodiment. It may be calculated. Thereafter, the base target air-fuel ratio at the time of rich spike is set on condition that the PM generation amount is less than a predetermined limit value (steps S303 and S304).

  Thereafter, it is determined whether or not the PM generation amount is equal to or greater than a predetermined allowable value (step S305). If the PM generation amount is less than the allowable value, the process proceeds to step S306, and the base target air-fuel ratio is used as it is as the final target air amount. Let the fuel ratio.

  If PM generation amount ≧ allowable value, the process proceeds to step S307, the injection start timing SOI is corrected to the retard side, and the A / F leaner than the base target air-fuel ratio is set as the final target air-fuel ratio. . Specifically, using the map data defined based on the relationship of FIG. 2 and FIG. 3, the injection start timing SOI and the target air-fuel ratio are set such that the PM generation amount is less than the allowable value.

  The correction of the injection start timing SOI and the target air-fuel ratio will be described with reference to FIG. In FIG. 8, the control point before the correction is A1 (A / F = AFR1, SOI = SOI1) in the figure, and it is estimated that the PM generation amount exceeds the allowable value. Therefore, the target air-fuel ratio is corrected to the rich degree decreasing side, the injection start timing SOI is corrected to the retard side, and the control point is changed to A2 (A / F = AFR2, SOI = SOI2) in the figure. At this time, when only the rich degree of the target air-fuel ratio is corrected, that is, when the control point is changed to A3 (A / F = AFR3, SOI = SOI1) in the figure, the rich degree of the target air-fuel ratio is reduced. The degree becomes smaller.

  As described above, according to the third embodiment, in the rich spike control, not only the target air-fuel ratio but also the injection start timing SOI is variably set based on the PM generation amount. The restriction on the degree of richness can be relaxed. Therefore, it is possible to efficiently regenerate the NOx purification capacity of the desired NOx storage reduction catalyst 24. In addition, since the desired NOx purification capacity is quickly regenerated, the duration of the rich spike can be shortened.

  In the rich spike control, the target air-fuel ratio and the ignition timing IGT may be variably set based on the PM generation amount. In such a case, if the amount of PM generated during the rich spike control is equal to or greater than the allowable value, the ignition timing IGT is corrected to the retard side, and the A / F on the lean side of the base target air-fuel ratio is set as the final target air-fuel ratio. To do. More specifically, the ignition timing IGT and the target air-fuel ratio are set so that the PM generation amount is less than the allowable value using map data defined based on the relationship shown in FIGS.

  The correction of the ignition timing IGT and the target air-fuel ratio will be described with reference to FIG. In FIG. 9, the control point before correction is B1 (A / F = AFR1, IGT = IGT1) in the figure, and it is estimated that the PM generation amount exceeds the allowable value. Therefore, the target air-fuel ratio is corrected to the rich degree decreasing side, the ignition timing IGT is corrected to the retarding side, and the control point is changed to B2 (A / F = AFR2, IGT = IGT2) in the figure. At this time, when only the richness of the target air-fuel ratio is corrected, that is, when the control point is changed to B3 (A / F = AFR3, IGT = IGT1) in the figure, the richness reduction of the target air-fuel ratio is reduced. The degree becomes smaller.

  Also in this configuration, as described above, the restriction on the richness of the air-fuel ratio can be relaxed in suppressing the generation of PM. Therefore, it is possible to efficiently regenerate the NOx purification capacity of the desired NOx storage reduction catalyst 24. In addition, since the desired NOx purification capacity is quickly regenerated, the duration of the rich spike can be shortened.

  When the PM generation amount exceeds the allowable value during the rich spike control, it is possible to simultaneously perform the correction of the air-fuel ratio, the correction of the injection start timing SOI, and the correction of the ignition timing IGT.

(Fourth embodiment)
When the engine has been used for a long period of time, map data that defines the amount of PM generated due to the difference in fuel injection amount from an appropriate amount due to deposits (deposits) attached to the injector 12 and the like. It is conceivable that a deviation occurs in the map data defined based on the relationship of FIG. 2 or FIG. When the map data shifts, the PM generation amount may be excessive in a state where the PM generation amount is originally limited to a predetermined level or less. Therefore, in the present embodiment, a system configuration in which a PM sensor is provided in the exhaust pipe 16 is adopted (similar to the second embodiment), the PM generation amount obtained from the map data, and the PM generation detected by the PM sensor. The amount is compared, and the validity of the map data is determined based on the result.

  FIG. 10 is a flowchart showing the map data evaluation process, and this process is executed by the ECU 40 in parallel with the target air-fuel ratio setting process of FIG.

  In FIG. 10, in step S401, it is determined whether or not rich spike control is currently being executed. If rich spike control is being executed, the process proceeds to the subsequent step S402. In step S402, the PM generation amount is detected based on the detection signal of the PM sensor. In step S403, it is determined whether the detected PM generation amount is equal to or greater than a predetermined determination value TH. The determination value TH is a determination value for evaluating the validity of the map data, and corresponds to an allowable value of the PM generation amount defined by the map data.

  If the PM generation amount (sensor detection value) ≧ TH, the process proceeds to step S404, and it is determined that the validity of the map data has decreased. In the subsequent step S405, a fail safe process corresponding to a decrease in the validity of the map data is executed. Specifically, the air-fuel ratio of the rich spike control at that time is corrected in the rich degree decreasing direction, or the map data is corrected. For example, when the fuel injection amount is reduced due to deposits deposited on the injector 12, such correction processing is executed because it is possible to cope with the correction. Further, when these corrections are impossible, rich spike control is prohibited, or an abnormal warning is generated by lighting a warning lamp or the like. For example, when the fuel spray shape changes due to deposits deposited on the injector 12, abnormal combustion occurs due to disturbance in the distribution of the in-cylinder air-fuel mixture. In such a case, since it is difficult to deal with correction, an abnormality warning or the like is executed.

  As described above, according to the fourth embodiment, the actual PM generation amount is measured by the PM sensor in parallel with the rich spike control using the map data. Thereby, the shift of map data can be known and the validity of the map data can be evaluated appropriately.

  Further, the fail-safe process is appropriately executed based on the evaluation result of the map data, so that a problem that leads to PM leakage can be solved.

  In addition, this invention is not limited to the content of description of the said embodiment, For example, you may implement as follows.

  In the above embodiment, in the flowchart of FIG. 4, map data (a map defined based on the relationship of FIG. 2 or FIG. 3) using A / F, engine speed NE, injection start timing SOI, and ignition timing IGT as parameters. The PM generation amount is estimated from the data), but it is also possible to change this and estimate the PM generation amount by an arithmetic expression. At this time, the PM generation amount is calculated using an arithmetic expression having parameters such as the intake air amount, the fuel injection amount, the injection start timing SOI, and the ignition timing IGT.

  In each of the above-described embodiments, the air-fuel ratio is variably set in order to suppress the PM generation amount during the rich spike control to less than a predetermined allowable value. However, control is performed so that no PM is generated during the rich spike control. It may be carried out (however, if the allowable value = 0 is included in the above description). In such a case, for example, the map data that defines the PM generation amount may be defined so that the local air-fuel ratio in the combustion chamber 13 does not become 9.5 or less. Or it is good to prescribe | regulate the map data so that the air fuel ratio of the whole combustion chamber 13 may not become 9.5 or less.

  In the above embodiment, the present invention is applied to an in-cylinder injection type gasoline engine. However, the present invention can also be applied to a port injection type gasoline engine. In an engine in which lean combustion is performed even in a port injection engine, a NOx storage reduction catalyst is provided in the exhaust system. In this case, rich spike control is performed as described above, and variable setting of the air-fuel ratio or the like is executed based on the PM generation status.

It is a block diagram which shows the outline of the engine control system in embodiment of invention. It is a figure which shows the difference of PM generation amount with respect to A / F and injection start time for every engine speed. It is a figure which shows the difference of PM generation amount with respect to A / F and ignition timing. It is a flowchart which shows the target air fuel ratio setting process at the time of rich spike control. It is a figure for demonstrating that PM generation amount is reduced with correction of a target air fuel ratio. It is a flowchart which shows the target air fuel ratio setting process at the time of rich spike control in 2nd Embodiment. It is a flowchart which shows the target air fuel ratio setting process at the time of rich spike control in 3rd Embodiment. It is a figure for demonstrating that PM generation amount is reduced with correction of a target air fuel ratio and injection start timing. It is a figure for demonstrating that PM generation amount is reduced with the correction of a target air fuel ratio and ignition timing. It is a flowchart which shows a map data evaluation process.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine, 12 ... Injector, 13 ... Combustion chamber, 16 ... Exhaust pipe, 24 ... NOx storage reduction catalyst, 40 ... ECU.

Claims (22)

A control device for an internal combustion engine that performs rich spike control that temporarily controls the air-fuel ratio to the rich side during lean operation of the internal combustion engine in order to reduce and purify nitrogen oxides stored in a catalyst provided in an exhaust system of the internal combustion engine In
In performing the rich spike control, monitoring means for monitoring the occurrence of particulate matter,
Air-fuel ratio setting means for variably setting the air-fuel ratio at the time of the rich spike control based on the monitoring result by the monitoring means;
Equipped with a,
The relationship between the operating state of the internal combustion engine and the amount of the particulate matter generated is defined in advance and stored as data, and the monitoring unit uses the specified data and uses the specified data to determine the particulate state. Monitor the occurrence of substances,
The control apparatus for an internal combustion engine, wherein the specified data specifies a relationship between an ignition timing and a generation amount of the particulate matter. 2. The control apparatus for an internal combustion engine according to claim 1, wherein the specified data is specified so that a local air-fuel ratio in the combustion chamber does not become 9.5 or less . 2. The control apparatus for an internal combustion engine according to claim 1, wherein the specified data is specified so that the air-fuel ratio of the entire combustion chamber does not become 9.5 or less . A control device for an internal combustion engine that performs rich spike control that temporarily controls the air-fuel ratio to the rich side during lean operation of the internal combustion engine in order to reduce and purify nitrogen oxides stored in a catalyst provided in an exhaust system of the internal combustion engine In
In performing the rich spike control, monitoring means for monitoring the occurrence of particulate matter,
Air-fuel ratio setting means for variably setting the air-fuel ratio at the time of the rich spike control based on the monitoring result by the monitoring means;
With
The relationship between the operating state of the internal combustion engine and the amount of the particulate matter generated is defined in advance and stored as data, and the monitoring unit uses the specified data and uses the specified data to determine the particulate state. Monitor the occurrence of substances,
The control apparatus for an internal combustion engine, wherein the specified data is specified so that a local air-fuel ratio in the combustion chamber does not become 9.5 or less . A control device for an internal combustion engine that performs rich spike control that temporarily controls the air-fuel ratio to the rich side during lean operation of the internal combustion engine in order to reduce and purify nitrogen oxides stored in a catalyst provided in an exhaust system of the internal combustion engine In
  In performing the rich spike control, monitoring means for monitoring the occurrence of particulate matter,
  Air-fuel ratio setting means for variably setting the air-fuel ratio at the time of the rich spike control based on the monitoring result by the monitoring means;
With
  The relationship between the operating state of the internal combustion engine and the amount of the particulate matter generated is defined in advance and stored as data, and the monitoring unit uses the specified data and uses the specified data to determine the particulate state. Monitor the occurrence of substances,
  The control apparatus for an internal combustion engine, wherein the specified data is specified so that the air-fuel ratio of the entire combustion chamber does not become 9.5 or less. A measurement device for measuring the amount of particulate matter contained in the exhaust is provided in the exhaust system of the internal combustion engine,
  The amount of the particulate matter obtained from the prescribed data is compared with the amount of the particulate matter measured by the measuring device, and the validity of the prescribed data is determined based on the result. 6. The control device for an internal combustion engine according to any one of 5 above. A control device for an internal combustion engine that performs rich spike control that temporarily controls the air-fuel ratio to the rich side during lean operation of the internal combustion engine in order to reduce and purify nitrogen oxides stored in a catalyst provided in an exhaust system of the internal combustion engine In
  In performing the rich spike control, monitoring means for monitoring the occurrence of particulate matter,
  Air-fuel ratio setting means for variably setting the air-fuel ratio at the time of the rich spike control based on the monitoring result by the monitoring means;
With
  The relationship between the operating state of the internal combustion engine and the amount of the particulate matter generated is defined in advance and stored as data, and the monitoring unit uses the specified data and uses the specified data to determine the particulate state. Monitor the occurrence of substances,
  A measurement device for measuring the amount of particulate matter contained in the exhaust is provided in the exhaust system of the internal combustion engine,
  Control of an internal combustion engine characterized by comparing the amount of particulate matter obtained from the prescribed data with the amount of particulate matter measured by the measuring device and determining the validity of the prescribed data based on the result apparatus. 8. The control device for an internal combustion engine according to claim 1, wherein a fuel injection timing by the fuel injection valve is variably set based on a monitoring result by the monitoring means. 9. The control apparatus for an internal combustion engine according to claim 1, wherein the ignition timing is variably set based on a monitoring result by the monitoring means. 10. The air-fuel ratio setting unit gradually reduces the rich degree based on the generation state of the particulate matter with respect to the target air-fuel ratio set at the start of the rich spike control. The control apparatus for an internal combustion engine according to any one of the above. 11. The control device for an internal combustion engine according to claim 1, wherein execution of the rich spike control is prohibited when the amount of the particulate matter is equal to or greater than a predetermined limit value. A control device for an internal combustion engine that performs rich spike control that temporarily controls the air-fuel ratio to the rich side during lean operation of the internal combustion engine in order to reduce and purify nitrogen oxides stored in a catalyst provided in an exhaust system of the internal combustion engine In
  In performing the rich spike control, monitoring means for monitoring the occurrence of particulate matter,
  Air-fuel ratio setting means for variably setting the air-fuel ratio at the time of the rich spike control based on the monitoring result by the monitoring means;
With
  A control apparatus for an internal combustion engine, wherein a fuel injection timing by a fuel injection valve is variably set based on a monitoring result by the monitoring means. The control device for an internal combustion engine according to claim 12, wherein the ignition timing is variably set based on a monitoring result by the monitoring means. A control device for an internal combustion engine that performs rich spike control that temporarily controls the air-fuel ratio to the rich side during lean operation of the internal combustion engine in order to reduce and purify nitrogen oxides stored in a catalyst provided in an exhaust system of the internal combustion engine In
  In performing the rich spike control, monitoring means for monitoring the occurrence of particulate matter,
  Air-fuel ratio setting means for variably setting the air-fuel ratio at the time of the rich spike control based on the monitoring result by the monitoring means;
With
  A control apparatus for an internal combustion engine, wherein the ignition timing is variably set based on a monitoring result by the monitoring means. 15. The air-fuel ratio setting means gradually reduces the rich degree of the target air-fuel ratio set at the start of the rich spike control based on the generation state of the particulate matter. The control apparatus for an internal combustion engine according to any one of the above. A control device for an internal combustion engine that performs rich spike control that temporarily controls the air-fuel ratio to the rich side during lean operation of the internal combustion engine in order to reduce and purify nitrogen oxides stored in a catalyst provided in an exhaust system of the internal combustion engine In
  In performing the rich spike control, monitoring means for monitoring the occurrence of particulate matter,
  Air-fuel ratio setting means for variably setting the air-fuel ratio at the time of the rich spike control based on the monitoring result by the monitoring means;
With
  The control device for an internal combustion engine, wherein the air-fuel ratio setting means gradually reduces the rich degree based on the generation state of the particulate matter with respect to the target air-fuel ratio set at the start of the rich spike control. . 17. The control device for an internal combustion engine according to claim 12, wherein execution of the rich spike control is prohibited when the amount of the particulate matter is equal to or greater than a predetermined limit value. A control device for an internal combustion engine that performs rich spike control that temporarily controls the air-fuel ratio to the rich side during lean operation of the internal combustion engine in order to reduce and purify nitrogen oxides stored in a catalyst provided in an exhaust system of the internal combustion engine In
  In performing the rich spike control, monitoring means for monitoring the occurrence of particulate matter,
  Air-fuel ratio setting means for variably setting the air-fuel ratio at the time of the rich spike control based on the monitoring result by the monitoring means;
With
  The control apparatus for an internal combustion engine, wherein execution of the rich spike control is prohibited when the amount of the particulate matter is equal to or greater than a predetermined limit value. When performing the rich spike control, comprising means for measuring or estimating the amount of particulate matter in the exhaust,
  The monitoring means monitors the occurrence state of the particulate matter by the amount of the particulate matter obtained by the measurement or estimation,
  The control of an internal combustion engine according to any one of claims 12 to 18, wherein the air-fuel ratio setting means determines the richness of the air-fuel ratio at the time of the rich spike control based on the amount of the particulate matter. apparatus. The relationship between the operating state of the internal combustion engine and the amount of the particulate matter generated is defined in advance and stored as data, and the monitoring unit uses the specified data and uses the specified data to determine the particulate state. The control apparatus for an internal combustion engine according to any one of claims 12 to 18, wherein the state of generation of the substance is monitored. The control of an internal combustion engine according to any one of claims 1 to 11, wherein the specified data defines a relationship between a rotation speed of the internal combustion engine and an amount of the particulate matter generated. apparatus. The internal combustion engine according to any one of claims 1 to 11, 20, and 21, wherein the specified data defines a relationship between a fuel injection timing by a fuel injection valve and a generation amount of the particulate matter. Engine control device.

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