JP4263286B2 - In-cylinder injection engine combustion control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion control apparatus for an in-cylinder injection engine that switches between stratified combustion and uniform combustion in accordance with engine operating conditions.
[0002]
[Prior art]
Generally, in an in-cylinder injection engine in which fuel is directly injected into a cylinder and burned by spark ignition, the combustion mode of stratified combustion and the combustion mode of uniform combustion are switched according to the engine operating state. In particular, in stratified combustion, the mixture of fuel and air is stratified to ignite a relatively rich mixture in the vicinity of the spark plug, and as a whole, operation with a significantly leaner air-fuel ratio becomes possible. Low fuel consumption can be realized.
[0003]
In this case, an ordinary three-way catalyst that is premised on operation at the stoichiometric air-fuel ratio cannot purify NOx discharged in the lean air-fuel ratio region. For example, JP-A-6-66135 and JP-A-9-72229 NOx generated during lean air-fuel ratio operation is temporarily stored, and when a certain accumulation amount is reached, the air-fuel ratio is brought into a rich state for a very short time (a rich spike is given) to reduce NOx. In many cases, a so-called NOx storage catalyst for purification is employed.
[0004]
[Problems to be solved by the invention]
By the way, in the cylinder injection engine, when the fuel injection amount is increased in order to give a rich spike during stratified combustion, a higher concentration of air-fuel mixture gathers in the vicinity of the spark plug, and misfire occurs due to lack of oxygen. For this reason, in general, in a cylinder injection engine, when a rich spike is applied, the combustion mode is switched from stratified combustion to uniform combustion.
[0005]
However, if the combustion mode is switched in order to give a rich spike, the air-fuel ratio of the air-fuel mixture changes suddenly, so that not only torque shock occurs and drivability deteriorates, but also combustion becomes unstable and misfire may occur. There is.
[0006]
The present invention has been made in view of the above circumstances, and an in-cylinder injection engine capable of preventing deterioration in drivability and misfire due to torque fluctuation when enriching the air-fuel ratio in order to purify NOx stored in the catalyst. It aims at providing the combustion control apparatus of this.
[0007]
[Means for Solving the Problems]
According to the first aspect of the invention, the fuel directly injected into the cylinder is burned by stratified combustion or uniform combustion, and the air-fuel ratio is temporarily enriched to reduce and purify NOx of the NOx storage catalyst interposed in the exhaust system. When the NOx storage amount of the NOx storage catalyst exceeds the first set value and the current combustion mode is stratified combustion, uniform combustion from stratified combustion to lean air-fuel ratio is performed. And the NOx occlusion amount of the NOx occlusion catalyst exceeds the NOx occlusion amount saturation judgment value as the second set value which is larger than the first set value, and the current combustion mode is uniform combustion And a means for temporarily enriching the air-fuel ratio.
[0010]
That is, according to the first aspect of the present invention, when the NOx occlusion amount of the NOx occlusion catalyst interposed in the exhaust system exceeds the first set value and the current combustion mode is stratified combustion, the stratified combustion is reduced to the lean air. Transition to uniform combustion at the fuel ratio, and in the state of uniform combustion after the transition, the NOx occlusion amount of the NOx occlusion catalyst exceeds the saturation judgment value of the NOx occlusion amount as the second set value that is larger than the first set value. When this happens, the air-fuel ratio is temporarily enriched to reduce and purify NOx stored in the NOx storage catalyst.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 relate to a first embodiment of the present invention, FIG. 1 is a flowchart of a rich spike control routine, FIG. 2 is a flowchart of a combustion mode control routine, FIG. 3 is a flowchart of a combustion mode transition control routine, and FIG. Is a schematic configuration diagram of an engine control system, FIG. 5 is an explanatory diagram of a combustion mode by an operation region, and FIG. 6 is an explanatory diagram showing a transition from stratified combustion to uniform combustion.
[0014]
In FIG. 4, reference numeral 1 denotes an in-cylinder injection engine that directly injects fuel into a cylinder and burns an air-fuel mixture by spark ignition. A throttle valve 3 a and a throttle valve 3 a that drives the throttle valve 3 a are disposed in the middle of the intake pipe 2. A throttle body 3 provided with an actuator 3b is interposed, and an air cleaner 5 is interposed on the upstream side of the throttle body 3 via an intake air amount sensor 4.
[0015]
A catalyst 9 for purifying exhaust gas is interposed in the exhaust pipe 8 of the engine 1, and a muffler 10 is attached to the downstream side of the catalyst 9. The catalyst 9 is, for example, a NOx occlusion type catalyst in which a NOx occlusion material such as alkali metal, alkaline earth or rare earth and a noble metal such as platinum are supported on a carrier such as alumina, and has a storage function of NOx and O2. Therefore, when the oxygen concentration of the exhaust gas is high, HC and CO are oxidized and reduced and NOx is occluded. When the oxygen concentration in the exhaust gas decreases, the stored NOx is released, and NOx is reduced and purified by HC and CO that are left without being oxidized and reduced.
[0016]
Reference numeral 20 denotes an electronic control unit (ECU) 20 that electronically controls the engine 1 to perform fuel injection control and ignition timing control. The electronic control unit (ECU) 20 is mainly composed of a microcomputer and includes various sensors / switches and various actuators. Is connected.
[0017]
Sensors and switches connected to the ECU 20 include the intake air amount sensor 4 described above, a crank angle sensor 11 that outputs a pulse signal at every predetermined crank angle, a water temperature sensor 12 for detecting a cooling water temperature, and an accelerator (not shown). An accelerator opening sensor 13 that is connected to the pedal and outputs a voltage signal corresponding to the depression amount of the accelerator pedal, an idle switch 14 that is turned on when the accelerator is fully closed (the depression amount of the accelerator pedal is substantially 0), and the vehicle speed is detected. There is a vehicle speed sensor 15 for the purpose.
[0018]
The actuators connected to the ECU 20 include the throttle actuator 3b described above, the injector 16 of each cylinder for injecting fuel, and an igniter 17 for intermittently connecting a primary current of an ignition coil connected to an ignition plug for each cylinder. Etc.
[0019]
The ECU 20 calculates various control amounts such as the fuel injection amount and ignition timing based on the operation state detected by various sensors and switches, and outputs a drive signal corresponding to the control amount to various actuators according to the operation state. The air-fuel ratio in the combustion mode is always controlled to be an appropriate air-fuel ratio. Specifically, the output target value of the engine 1 is set from the accelerator opening and the engine speed, the fuel injection amount is controlled according to the set output target value, and the throttle opening is adjusted to adjust the intake air amount. To control.
[0020]
In the engine 1, stratified combustion in which a mixture of fuel and air is stratified to ignite a relatively rich mixture in the vicinity of the spark plug, and to the lean mixture in the combustion chamber by the ignited fire type, The air-fuel mixture is mixed with the air in the cylinder and then the combustion is switched to the uniform combustion. In the stratified combustion, the lean burn operation is performed with the lean air-fuel ratio. Operation with stoichiometric (theoretical air / fuel ratio) or lean air / fuel ratio is performed outside the power range.
[0021]
The ECU 20 is provided with a map of fuel injection timing, ignition timing, target air-fuel ratio, and target air amount for each combustion mode, referring to the map based on target torque Te and engine speed Ne described later, and fuel injection. Determine the timing, ignition timing, target air-fuel ratio, and target air amount.
[0022]
Further, in order to release and reduce NOx occluded in the catalyst 9 when the operation at the lean air-fuel ratio is continued, a rich spike that temporarily enriches the air-fuel ratio is inserted. Hereinafter, processing related to execution of the rich spike by the ECU 20 will be described using the flowcharts of FIGS. 1 to 3.
[0023]
FIG. 2 is a combustion mode control routine executed at predetermined time intervals. First, in step S101, the sensor values are read from the accelerator opening sensor 13, the crank angle sensor 11, and the water temperature sensor 12, and the accelerator opening α, the engine are read. When the rotational speed Ne and the water temperature Tw are calculated, the target torque Te, which is the target value of the engine output shaft torque, is calculated in step S102 by referring to a map using the accelerator opening α as the accelerator operation amount and the engine rotational speed Ne as a grid. calculate.
[0024]
Next, the process proceeds to step S103, and the target combustion mode is determined from the current water temperature Tw, the current operation region, and the like. That is, when the water temperature Tw is equal to or lower than the set temperature, the uniform stoichiometric combustion mode is selected, and when the water temperature Tw exceeds the set temperature, the combustion mode corresponding to the operation region is selected as shown in FIG. To do.
[0025]
For example, the current operation region is specified by the target torque Te and the engine speed Ne, and in the high load operation region, the uniform stoichiometric combustion mode, in the medium load operation region, the uniform lean combustion mode, or in the low load operation region In this case, the combustion mode of stratified combustion is selected. Furthermore, a uniform rich combustion mode is selected during transient operation such as acceleration.
[0026]
When the target combustion mode is determined as described above, the process proceeds to step S104. In step S104, whether or not to execute rich spike is checked by a rich spike control routine described later. When rich spike is executed, flag 1 is set. When the rich spike is not executed, the flag 1 is turned off.
[0027]
In step S105, when the flag 1 is on and the rich spike is executed, the process branches to step S107. When the flag 1 is off and the rich spike need not be executed, the process proceeds to step S106.
[0028]
In step S106, the combustion mode transition control is performed so as to shift the current combustion mode to the target combustion mode, and in step S107, rich spike control is performed.
[0029]
In the combustion mode transition control routine for shifting the current combustion mode to the target combustion mode, it is checked in step S301 whether or not the current combustion mode matches the target combustion mode. As a result, when the current combustion mode is the target combustion mode, the process proceeds to step S304, and then in step S305, the current combustion mode is set to the target combustion mode.
[0030]
When the current combustion mode does not match the target combustion mode, the process proceeds to step S302. In step S302, it is checked whether or not the count value N is 1 or more. When the count value N is 1 or more, the process proceeds to step S304, and the count value is cleared. If the count value is smaller than 1, the process proceeds to step S303, and the count value N is incremented by a predetermined amount α.
[0031]
This count value N is a value representing the degree of transition from the current combustion mode to the target combustion mode. When the count value N is 0, the current combustion mode is implemented, and when the count value N is 1 or more, Assuming that the transition of the combustion mode from the current combustion mode to the target combustion mode is completed, the count value is cleared in step S304, and the current combustion mode is set as the target combustion mode in step S305.
[0032]
Further, when the count value N is a value between 0 and 1, it indicates that the combustion mode is implementing a combustion mode in the middle of transition from the current combustion mode to the target combustion mode.
[0033]
Next, in step S306, various control amounts for engine control are calculated, and drive control is performed based on this.
[0034]
For the target air-fuel ratio ABFI, the target air-fuel ratio ABFI1 in the current combustion mode and the target air-fuel ratio ABFI2 in the target combustion mode are obtained by referring to the map of the target torque Te and the engine speed Ne, and the target air-fuel ratio ABFI is calculated by the following equation. calculate.
ABFI = (N−1) × ABFI1 + N × ABFI2
[0035]
For the combustion injection timing TJ_M, the fuel injection timing TJ_M1 in the current combustion mode and the combustion injection timing TJ_M2 in the target combustion mode are obtained by referring to the map of the target torque Te and the engine speed Ne, and the combustion injection timing is calculated by the following formula To do.
TJ_M = (N−1) × TJ_M1 + N × TJ_M2
[0036]
For the ignition timing IG_M, the ignition timing IG_M1 in the current combustion mode and the ignition timing IG_M2 in the target combustion mode are obtained with reference to the map of the target torque Te and the engine speed Ne, and the ignition timing IG_M is calculated by the following equation.
IG_M = (N−1) × IG_M1 + N × IG_M2
[0037]
As the drive amount of the throttle actuator, the target air amount Qa is calculated from the target air-fuel ratio ABFI and the fuel injection amount GF, and the throttle valve opening Th for obtaining the target air amount Qa is obtained. The ETC is driven and controlled to achieve the throttle valve opening Th. The throttle valve opening degree Th is obtained with reference to a map of the target air amount Qa and the engine speed.
[0038]
Based on these control amounts, fuel injection amount, ignition timing control, and ETC control are performed.
[0039]
In step S301 and step S302, when the current combustion mode and the target combustion mode match, the count value N = 0, so in step S306, the current combustion mode is set as the target combustion mode and the target air-fuel ratio ABFI, The fuel injection timing TJ_M, the ignition timing IG_M, the target air amount Qa, and the fuel injection amount GF are obtained.
[0040]
As shown in FIG. 6, when the combustion mode shift control from stratified combustion to uniform lean is performed, after the target air-fuel ratio ABFI reaches the rich side from the stratified limit A / F, the combustion mode is changed to uniform lean step by step. Control is performed with the switching, the current combustion mode and the target combustion mode as uniform lean. Also, during the combustion mode transition control from uniform lean to stratified combustion, after the target air-fuel ratio ABFI reaches the lean side from the stratification limit A / F, the combustion mode is switched to stratified combustion step by step, and the subsequent control is performed. You may carry out based on stratified combustion.
[0041]
In the above combustion mode control routine, the rich spike control routine (FIG. 1) in step S104 is periodically executed to release and reduce NOx occluded in the catalyst 9 in the lean air-fuel ratio operation.
[0042]
In the rich spike control routine, first, the NOx occlusion amount of the catalyst 9 is estimated in step S201. The NOx occlusion amount of the catalyst 9 is determined, for example, for each operating region specified by the engine speed Ne and the intake air amount Q, with the elapsed time t from the transition to stratified combustion or uniform lean combustion as a parameter. A value obtained by integrating the NOx emission amount obtained by analyzing the exhaust gas is stored in advance in a map and is estimated by referring to this map.
[0043]
Then, after estimating the NOx occlusion amount of the catalyst 9, the process proceeds to step S202, and it is checked whether or not the NOx occlusion amount of the catalyst 9 is equal to or greater than the set value A. For the set value A, when the NOx occlusion amount by the catalyst 9 is small, processing for not performing rich spike control is performed, and when the NOx occlusion amount becomes smaller than the set value A due to execution of rich spike control, execution of rich spike is performed. This is the judgment value to end.
[0044]
If it is determined in step S202 that the NOx occlusion amount is smaller than the set value A, the process proceeds to step S208, and if it is determined that the NOx occlusion amount is greater than or equal to the set value A, the process proceeds to step S203.
[0045]
In step S203, it is checked whether or not the NOx occlusion amount of the catalyst 9 exceeds the set value B (first set value; set value B> set value A). When the NOx occlusion amount of the catalyst 9 is less than or equal to the set value B, the routine is exited. When the NOx occlusion amount of the catalyst 9 exceeds the set value B, the routine proceeds to step S204, where it is determined whether or not the current combustion mode is uniform combustion. Check out.
[0046]
As a result, when the current combustion mode is the stratified combustion mode, the process proceeds from step S204 to step S205, the target combustion mode is set to uniform lean, the routine is exited, and when the current combustion mode is already uniform combustion, step Proceed to S206. When the current combustion mode is the stratified combustion mode, the combustion mode shift control to uniform lean is performed in step S106 in the combustion mode control routine (FIG. 2).
[0047]
When the process proceeds from step S204 to step S206, it is checked in step S206 whether the NOx occlusion amount of the catalyst 9 has reached the set value C (second set value; set value C> set value B). The set value C is a determination value corresponding to the saturation value of the NOx occlusion amount of the catalyst 9, and when the NOx occlusion amount of the catalyst 9 is equal to or less than the set value C, the routine is exited, and the NOx occlusion amount of the catalyst 9 becomes equal to the set value C. If exceeded, the process proceeds to step S207 to turn on flag 1 and exit the routine.
[0048]
When flag 1 is turned on, the routine proceeds from step S105 to step S107 in the combustion mode control routine (FIG. 2), and stepwise shifts to the combustion mode of uniform rich (or uniform stoichiometric) to temporarily enrich the air-fuel ratio. Rich spike control is performed, and NOx occluded in the catalyst 9 is released and reduced.
[0049]
When rich spike control is performed and the NOx occlusion amount of the catalyst 9 becomes smaller than the set value A, as described above, the process proceeds from step S202 to step S208, and the flag 1 is turned off. When flag 1 is turned off, the routine proceeds from step S105 to step S106 in the combustion mode control routine, and the rich spike control is terminated.
[0050]
That is, instead of inserting a rich spike when it is determined that the NOx storage amount of the catalyst 9 has reached saturation as in the prior art, a determination is made that the NOx storage amount of the catalyst 9 has a margin with respect to the saturation determination value. When the value reaches the value, transition from stratified combustion to uniform lean is performed, and then it is determined that the NOx storage amount of the catalyst 9 has reached saturation. In addition, it is possible to prevent misfire caused by switching of the combustion mode.
[0051]
FIG. 7 is a flowchart of a rich spike control routine according to the second embodiment of the present invention.
[0052]
The second form changes the timing of putting a rich spike by changing a part of the rich spike control routine with respect to the first form.
[0053]
That is, in the rich spike control routine of the second embodiment, as shown in FIG. 7, when the NOx occlusion amount of the catalyst 9 is estimated in step S201, the NOx occlusion amount of the catalyst 9 is set in step S203 'via step S202. Check if the value has been reached. The set value in step S203 ′ corresponds to the set value C in step S206 in the rich spike control routine of the first embodiment.
[0054]
When the NOx occlusion amount of the catalyst 9 is equal to or less than the set value in step S203 ′, the routine is exited. When the NOx occlusion amount of the catalyst 9 exceeds the set value, the routine proceeds to step S204, where the current combustion mode is uniform combustion. In the case of stratified combustion, as in the first mode, the target combustion mode is set to uniform lean by the process of step S205, and the routine is exited. In step S106 of the combustion form control routine (FIG. 2), the combustion form is shifted from stratified combustion to uniform lean. When the current combustion mode is uniform combustion, the process proceeds from step S204 to step S209.
[0055]
In step S209, it is checked whether or not the current vehicle speed exceeds the set value. When the vehicle speed is less than the set value, the routine is exited. When the vehicle speed exceeds the set value, the idle switch 14 is turned on in step S210. Whether the throttle valve 3a is in a closed deceleration state or not is determined. The determination of the deceleration state may be made by determining whether or not the accelerator opening changes in the closing direction and the throttle valve 3a is in the closing direction instead of the idle switch 14.
[0056]
As a result, when the idle switch 14 is not ON, the routine exits without performing the rich spike control, and when the idle switch 14 is ON, the flag 1 is turned on and the routine exits in step S211 as in the first embodiment. .
[0057]
When flag 1 is turned on, the routine proceeds from step S105 to step S107 in the combustion mode control routine (FIG. 2), and stepwise shifts to the combustion mode of uniform rich (or uniform stoichiometric) to temporarily enrich the air-fuel ratio. Rich spike control is performed, and NOx occluded in the catalyst 9 is released and reduced.
[0058]
When rich spike control is performed and the NOx occlusion amount of the catalyst 9 becomes smaller than the set value A, the process proceeds from step S202 to step S212 as described above, and the flag 1 is turned off. When flag 1 is turned off, the routine proceeds from step S105 to step S106 in the combustion mode control routine, and the rich spike control is terminated.
[0059]
In the second mode, after the combustion mode becomes uniform combustion, when the vehicle speed is equal to or higher than the set value, the influence of torque shock is small, and when the throttle valve 3a is closed or closed and the intake air amount is small Since the rich spike is inserted for the first time, it is possible to more effectively prevent the occurrence of a misfire caused by the torque shock prevention and the combustion mode switching due to the sudden execution of the rich spike.
[0060]
FIG. 8 is a flowchart of a rich spike control routine according to the third embodiment of the present invention.
[0061]
In the third mode, when a predetermined condition is satisfied during stratified combustion, a rich spike is performed regardless of the NOx occlusion amount of the catalyst 9.
[0062]
For this reason, in the rich spike control routine of the third embodiment, as shown in FIG. 8, first, the NOx occlusion amount of the catalyst 9 is estimated in step S401, and the process proceeds to step S402. In step S402, it is determined whether or not the NOx occlusion amount is greater than or equal to the set value A. If it is less than the set value A, the process proceeds to steps S412 and S413.
[0063]
When the NOx occlusion amount is greater than or equal to the set value A, the process proceeds to step S403, where it is determined whether or not the current combustion form is a stratified combustion form. If it is stratified combustion, the process proceeds to steps S404 and S405. Otherwise, the process proceeds to step S411. In steps S404 and S405, it is checked whether or not the vehicle speed exceeds the set value and whether or not the idle switch 14 is ON (or whether or not the accelerator opening has changed in the closing direction).
[0064]
As a result, when the current combustion mode is stratified combustion and the vehicle speed exceeds the set value and the condition that the idle switch 14 is ON (or the accelerator opening is changed in the closing direction) is satisfied, in step S406 The flag 2 is turned ON, the target combustion mode is set to uniform lean in step S407, the routine is exited, and the combustion mode is shifted to uniform lean in step S106 of the combustion mode control routine (FIG. 2).
[0065]
When the combustion mode is shifted to uniform lean, the process proceeds from step S403 to step S411, and it is determined whether or not the flag 2 is ON. When the flag 2 is ON, the vehicle speed exceeds the set value by stratified combustion. In addition, it is determined that the condition that the idle switch 14 is ON (or the accelerator opening changes in the closing direction) is satisfied, and the process proceeds to step S410. In step S410, flag 1 is turned ON and the routine is exited. When flag 1 is turned on, the routine proceeds from step S105 to step S107 in the combustion mode control routine (FIG. 2), and rich spike control is performed.
[0066]
When the rich spike control is performed and the NOx occlusion amount becomes smaller than the set value A, the process proceeds from step S402 to steps S412, S413, the flag 2 and the flag 1 are turned OFF, and the routine is exited. When flag 1 is turned off, the routine proceeds from step S105 to step S106 in the combustion mode control routine (FIG. 2), and the rich spike control ends.
[0067]
On the other hand, when the current combustion mode is not stratified combustion, the process proceeds from this step to step S411, and it is checked whether or not the flag 2 is ON. In step S411, the vehicle speed exceeds the set value in the stratified combustion, and the condition that the idle switch 14 is ON (or the accelerator opening changes in the closing direction) is satisfied, and the combustion mode is shifted to other than the stratified combustion. This is a step to check whether or not Therefore, when the condition is not satisfied, the process proceeds from step S411 to step S408, and when the NOx occlusion amount exceeds the set value D in steps S408, S409, and S410, and the uniform combustion is performed, flag 1 Set to ON and exit the routine. If the NOx occlusion amount is equal to or less than the set value D in step S408, the routine is exited as it is. The set value D in step S408 is a value smaller than the set value C in step S206 in the rich spike control routine of the first embodiment, and the rich spike is executed before the NOx occlusion amount of the catalyst 9 reaches saturation. Is.
[0068]
Further, even if the current combustion mode is stratified combustion, if the vehicle speed does not exceed the set value or if the idle switch 14 is not ON, the process proceeds from this step to steps S408 and S409, where the NOx occlusion amount is examined and the NOx occlusion is performed. If the amount exceeds the set value D, but the combustion is not uniform, the process proceeds to step S406, the flag 2 is turned on, the target combustion mode is set to uniform lean, and the routine is exited. When the combustion mode is shifted from stratified combustion to uniform lean, the process proceeds from step S403 to step S411, and it is checked whether or not the flag 2 is ON. In this case, since the flag 2 is ON, the process proceeds to step S410, and the flag 1 is turned ON. When the flag 1 is turned ON, the rich spike control is performed as described above until the NOx occlusion amount becomes smaller than the set value A.
[0069]
In the third mode, the condition of stratified combustion with a small amount of air originally and a small torque, the influence of torque shock is small when the vehicle speed is higher than the set value, and the amount of intake air is small when the throttle valve 3a is closed or closed Is satisfied before the NOx occlusion amount of the catalyst 9 reaches saturation, the degree of richness of the air-fuel ratio can be reduced, and the torque shock due to the rich spike and the change of the air-fuel ratio can be reduced. The occurrence of misfire can be kept extremely small.
[0070]
【The invention's effect】
As described above, according to the present invention, when the air-fuel ratio is enriched in order to purify the NOx stored in the catalyst, a sudden shock of rich spikes is avoided, and torque shock and misfire caused by switching of the combustion mode are avoided. Thus, it is possible to prevent the deterioration of drivability due to torque fluctuation and the deterioration of fuel consumption due to the occurrence of misfire.
[Brief description of the drawings]
FIG. 1 is a flowchart of a rich spike control routine according to the first embodiment of the present invention. FIG. 2 is a flowchart of a combustion mode control routine. FIG. 3 is a flowchart of a fuel mode transition control routine. Same as above, schematic configuration diagram of engine control system [FIG. 5] Same as above, explanatory diagram of combustion mode by operation region [FIG. 6] Same as above, [FIG. 5] explanatory diagram showing a transition from stratified combustion to uniform combustion [FIG. 7] FIG. 8 is a flowchart of a rich spike control routine according to the second embodiment. FIG. 8 is a flowchart of a rich spike control routine according to the third embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 ... Engine 3 ... Throttle valve 20 ... ECU
B ... First set value C ... Second set value

Claims (1)

Combustion control of an in-cylinder injection engine in which the fuel directly injected into the cylinder is burned by stratified combustion or uniform combustion, and the air-fuel ratio is temporarily enriched to reduce and purify NOx of the NOx storage catalyst interposed in the exhaust system In the device
Means for shifting from stratified combustion to uniform combustion at a lean air-fuel ratio when the NOx storage amount of the NOx storage catalyst exceeds a first set value and the current combustion mode is stratified combustion;
When the NOx occlusion amount of the NOx occlusion catalyst exceeds the saturation judgment value of the NOx occlusion amount as the second set value that is larger than the first set value, and the current combustion mode is uniform combustion, the air-fuel ratio And a means for temporarily enriching the combustion control device for a cylinder injection engine.

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