JP3835664B2 - In-cylinder injection engine catalyst temperature control method and engine control apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst temperature control method for an in-cylinder injection engine that recovers catalyst sulfur poisoning in an in-cylinder injection engine and an engine control apparatus.
[0002]
[Prior art]
A lean NOx catalyst that adsorbs NOx (nitrogen oxides) in the exhaust gas when the air-fuel ratio of the air-fuel mixture is lean and releases NOx when the oxygen concentration in the exhaust gas decreases is provided in the exhaust passage of the engine; A device in which this released NOx is reduced and purified is generally known. The lean NOx catalyst has a characteristic that when the fuel or engine oil contains a sulfur component, it absorbs SOx (sulfur oxide) in the exhaust gas more easily than NOx in the exhaust gas. When sulfur poisoning occurs due to SOx adsorption, the NOx adsorption capacity is significantly reduced.
[0003]
In order to recover this sulfur poisoning, Japanese Patent Application Laid-Open No. 6-272541 uses the fact that barium oxide on a lean NOx catalyst becomes barium sulfate by sulfur poisoning, and exhausts the catalyst after heating the catalyst to a high temperature. A method of enriching the gas air-fuel ratio and a method of decomposing barium sulfate and desorbing it as SO ₂ gas are described.
[0004]
In addition, in order to increase the temperature of the sulfur-poisoned lean NOx catalyst, an air-fuel ratio is set to λ≈1, and fuel is injected in two steps, an intake stroke and a compression stroke (special feature). Kaihei 11-107740).
[0005]
[Problems to be solved by the invention]
When the sulfur poisoning of the lean NOx catalyst is recovered, it is required that the exhaust gas temperature be raised rapidly and the fuel efficiency improvement that is an advantage of the direct injection engine is not impaired.
[0006]
The present invention has been made in view of the above-described problems, and its object is to rapidly increase the exhaust gas temperature at the time of recovery of sulfur poisoning of the lean NOx catalyst, thereby impairing the fuel efficiency improvement that is an advantage of the direct injection engine. It is an object of the present invention to provide a catalyst temperature control method and an engine control device for an in-cylinder injection engine without any problems.
[0007]
[Means for Solving the Problems]
To solve the problems described above and achieve the object, the control device of the engine of the present invention is to adsorb the fuel injection valve for injecting fuel directly into the combustion chamber, the NOx in an oxygen-rich atmosphere in the exhaust passage, the oxygen A NOx catalyst that releases adsorbed NOx as the concentration decreases is provided. When performing sulfur poisoning recovery processing of the NOx catalyst, the air-fuel ratio in the cylinder is set to λ≈1, and from the intake stroke to the ignition timing In the engine control device for increasing the temperature of the NOx catalyst by injecting the fuel into at least two times of the late injection after the middle of the compression stroke and the early injection earlier than the late injection within the period of Temperature detecting means for detecting the temperature state of the NOx catalyst, and variable means for forcibly changing the intake flow strength in the cylinder, and at the time of sulfur poisoning recovery processing of the NOx catalyst, the NOx catalyst temperature The higher temperature requirements, the intake flow strength is to operate the changing means so weak.
[0008]
Preferably, the intake flow strength is weakened and the late injection timing is delayed according to the heightening request for the NOx catalyst temperature.
[0009]
Preferably, when the temperature increase request for the NOx catalyst temperature is highest, the intake flow strength is weakened, the late injection timing is delayed, and the ignition timing is delayed.
[0010]
Further, preferably, the height of the temperature increase request for the NOx catalyst temperature is set higher as the temperature state of the NOx catalyst and the engine load are lower.
[0011]
Preferably, the sulfur poisoning recovery process is executed when the temperature increase request for the NOx catalyst temperature is high in an operation region where the engine load is low and the air-fuel ratio is λ> 1.
[0012]
The control device of the engine of the present invention, emits a fuel injection valve for injecting fuel directly into the combustion chamber, NOx adsorbs oxygen-rich atmosphere in the exhaust passage, the NOx adsorbed in accordance with the oxygen concentration decreases The NOx catalyst is provided, and when the sulfur poisoning recovery process of the NOx catalyst is executed, the air-fuel ratio in the cylinder is set to λ≈1, and the late injection after the middle of the compression stroke within the period from the intake stroke to the ignition timing And an ignition timing control means for controlling the ignition timing, in an engine control device for increasing the temperature of the NOx catalyst by injecting fuel at least twice as early injection earlier than the late injection, Variable means for forcibly changing the intake flow strength of the fuel, and injection timing control means for controlling the fuel injection timing. The ignition timing control means is configured such that the temperature state of the NOx catalyst is a target catalyst temperature. When not reached, the ignition timing is delayed for a predetermined first period, and when the target catalyst temperature is not reached, the variable means weakens the intake flow strength for a predetermined second period, and then the target catalyst temperature is not reached The injection timing control means delays the third period late injection timing.
[0013]
Further, it is preferably executed at a low engine load when the NOx catalyst temperature is low.
[0014]
Preferably, a supercharger is disposed upstream of the NOx catalyst in the exhaust passage.
[0015]
Preferably, a bypass passage that bypasses the supercharger is formed in the exhaust passage, and the bypass passage is opened when a temperature increase request of the NOx catalyst is required at a low engine load.
[0016]
The engine control apparatus of the present invention, a fuel injection valve for injecting fuel directly into the combustion chamber, NOx adsorbs oxygen-rich atmosphere in the exhaust passage, the NOx catalyst to release the adsorbed NOx in accordance with the oxygen concentration decreases And during the execution of the sulfur poisoning recovery process of the NOx catalyst, while setting the air-fuel ratio in the cylinder to λ≈1, during the period from the intake stroke to the ignition timing, In an engine control device that raises the temperature of the NOx catalyst by injecting fuel at least twice with early injection earlier than the late injection, an ignition timing control means for controlling the ignition timing , and intake air in the cylinder and changing means for forcibly changing the flow strength, and a fuel injection timing control means for controlling the fuel injection timing, the ignition timing control means, non-temperature state to the target catalyst temperature of the NOx catalyst Retards ignition timing when, while thereafter the when the temperature state of the NOx catalyst is not achieved at the target catalyst temperature back to the ignition timing before delaying the ignition timing by delaying said ignition timing control means, said variable means intake When the flow strength is weakened and then the temperature state of the NOx catalyst does not reach the target catalyst temperature, the injection timing control means delays the late injection timing .
[0019]
The method for controlling the catalyst temperature of a direct injection engine according to the present invention includes a fuel injection valve that directly injects fuel into a combustion chamber, and NOx that is adsorbed as NOx is adsorbed in an oxygen excess atmosphere in an exhaust passage and the oxygen concentration decreases. During the period from the middle of the compression stroke within the period from the intake stroke to the ignition timing, while setting the air-fuel ratio in the cylinder to λ≈1 when performing the sulfur poisoning recovery process of the NOx catalyst. In a cylinder injection engine in which fuel is injected to increase the temperature state of the NOx catalyst by dividing it into at least two times, ie, late injection and early injection earlier than the late injection, the temperature state of the NOx catalyst is a target When the catalyst temperature has not been reached, the ignition timing is delayed for a predetermined first period. After that, when the target catalyst temperature is not reached, the intake flow strength is reduced for a predetermined second period. After that, when the target catalyst temperature is not reached, Place Delaying the third period late injection timing.
[0020]
Further, it is preferably executed at a low engine load when the NOx catalyst temperature is low.
[0021]
Preferably, a supercharger is disposed upstream of the NOx catalyst in the exhaust passage.
[0022]
Preferably, a bypass passage that bypasses the supercharger is formed in the exhaust passage, and the bypass passage is opened when a temperature increase request of the NOx catalyst is required at a low engine load.
[0023]
The method for controlling the catalyst temperature of a direct injection engine according to the present invention includes a fuel injection valve that directly injects fuel into a combustion chamber, and NOx that is adsorbed as NOx is adsorbed in an oxygen excess atmosphere in an exhaust passage and the oxygen concentration decreases. During the period from the middle of the compression stroke within the period from the intake stroke to the ignition timing, while setting the air-fuel ratio in the cylinder to λ≈1 when performing the sulfur poisoning recovery process of the NOx catalyst. In the in-cylinder injection engine in which the fuel is injected and the temperature of the NOx catalyst is increased by dividing the injection into at least two times of the late injection and the early injection earlier than the late injection, the temperature state of the NOx catalyst is the target catalyst retards ignition timing when the unreached temperature, while subsequent temperature state of the NOx catalyst is returned to the ignition timing before delaying the ignition timing which is delayed when the unreached the target catalyst temperature, intake of the cylinder Weakening the flow strength followed the temperature state of the NOx catalyst is when the unreached the target catalyst temperature delaying the later injection timing.
[0026]
【The invention's effect】
As described above, according to the first aspect of the present invention, during the sulfur poisoning recovery process of the NOx catalyst, the higher the NOx catalyst temperature increase request, the weaker the intake flow strength, so that the exhaust gas temperature is rapidly increased. It is possible to suppress the deterioration of the high fuel efficiency improvement rate, which is an advantage of the cylinder injection engine.
[0027]
According to the second aspect of the present invention, the intake flow strength is decreased and the late injection timing is delayed in accordance with the high temperature increase request of the NOx catalyst temperature, thereby increasing the temperature increase effect while suppressing fuel consumption deterioration. be able to.
[0028]
According to the invention of claim 3, when the temperature increase request for the NOx catalyst temperature is the highest, the intake flow strength is weakened, the late injection timing is delayed, and the ignition timing is delayed, thereby reducing the fuel consumption deterioration margin. The temperature raising effect can be further increased.
[0029]
According to the invention of claim 4, the height of the temperature increase request for the NOx catalyst temperature is set higher as the temperature state of the NOx catalyst and the engine load are lower, thereby satisfying the temperature increase request when the exhaust gas temperature is low. I can deal with it.
[0030]
According to the invention of claim 5, in the sulfur poisoning recovery process, the temperature of the catalyst is rapidly raised even in a state where the NOx catalyst temperature is relatively low in an operating region where the engine load is low and the air-fuel ratio is λ> 1. it can.
[0031]
According to the sixth and eleventh aspects, when the temperature state of the NOx catalyst does not reach the target catalyst temperature, the ignition timing is delayed for a predetermined first period, and thereafter, when the target catalyst temperature is not reached, the intake air for the predetermined second period Decreasing the flow strength and then delaying the late injection timing of the third period when the target catalyst temperature has not been reached delays the exhaust gas temperature rapidly, improving fuel efficiency, which is an advantage of the direct injection engine The deterioration of the rate can be suppressed.
[0032]
According to the seventh and twelfth aspects of the present invention, the temperature of the catalyst can be rapidly increased in a region where the operation frequency is relatively high by executing the engine at a low engine load with a low temperature of the NOx catalyst.
[0033]
According to the eighth, ninth, thirteen, and fourteenth aspects, the supercharger is disposed upstream of the NOx catalyst in the exhaust passage, and the bypass passage that bypasses the supercharger is formed in the exhaust passage. By opening the bypass passage when the NOx catalyst temperature rise is requested, the heat release to the turbine is reduced and the temperature rise effect can be further enhanced.
[0034]
According to the tenth and fifteenth aspects of the present invention, when the temperature state of the NOx catalyst does not reach the target catalyst temperature, the ignition timing is delayed, whereby the temperature of the catalyst can be rapidly raised while reducing the fuel consumption deterioration margin. .
[0035]
Further , when the temperature state of the NOx catalyst does not reach the target catalyst temperature, the intake flow strength is weakened, and when the target catalyst temperature is not reached after that, the late injection timing is delayed, thereby reducing the fuel deterioration rate. Can be heated rapidly.
[0036]
Further , when the temperature state of the NOx catalyst has not reached the target catalyst temperature, the ignition flow strength is reduced while returning to the ignition timing before delaying the delayed ignition timing, and later when the target catalyst temperature is not reached, late injection is performed. By delaying the timing, the temperature of the catalyst can be rapidly raised while minimizing deterioration in fuel consumption.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[In-cylinder injection engine structure]
FIG. 1 is a schematic cross-sectional view showing the structure of the combustion chamber portion of the direct injection engine of the present embodiment.
[0038]
As shown in FIG. 1, reference numeral 1 denotes an engine. A plurality of cylinders are formed in a cylinder block 2, and a cylinder head 3 is fixed to the top of the cylinder block 2 via a gasket. A piston 4 is inserted into each cylinder, and a combustion chamber 5 is formed between the top surface of the piston 4 and the lower surface of the cylinder head 3. An intake port 6 and an exhaust port 7 are provided so as to communicate with the combustion chamber 5, and an intake valve 8 and an exhaust valve 9 that open and close the ports 6 and 7 are disposed. An injector 11 is provided. The injector 11 directly injects fuel into the combustion chamber 5.
[0039]
A concave portion having a substantially trapezoidal cross section is formed on the lower surface of the cylinder head 3 to delimit the upper portion of the combustion chamber 5. An intake port 6 is opened in the upper surface portion of the combustion chamber 5, and an exhaust port 7 is opened in the inclined surface portion. Two intake ports 6 and two exhaust ports 7 are provided side by side in the direction orthogonal to the paper surface, and an intake valve 8 and an exhaust valve 9 are provided. The intake valve 8 and the exhaust valve 9 are operated by a valve mechanism including a camshaft (not shown) and the like, and open and close at a predetermined timing.
[0040]
The spark plug 10 is disposed at a substantially central portion above the combustion chamber 5, and is attached to the cylinder head 3 so that the ignition gap faces the combustion chamber 5.
[0041]
The injector 11 is disposed on the peripheral edge of the combustion chamber 5 and is attached to the cylinder head 3 at the side of the intake port 6. The injector 11 is disposed between the upper surface of the combustion chamber 5 where the intake port 6 opens and the mating surface with respect to the cylinder block 2. The nozzle portion of the injector 11 faces the wall surface 12 and injects the fuel obliquely downward.
[0042]
A concave stratification cavity 13 is formed near the injector 11 at the top of the biston 4. Then, fuel is injected from the injector 11 toward the cavity 13 in the latter half of the compression stroke at which the piston 4 is close to top dead center, and is reflected by the cavity 13 to reach the vicinity of the spark plug 10. The positional relationship between the position and direction, the position of the cavity 1 and the spark plug 10 is set in advance.
[0043]
FIG. 2 is a schematic view of the entire in-cylinder injection engine.
[0044]
As shown in FIG. 2, an intake passage 15 and an exhaust passage 16 are connected to the engine 1. Downstream of the intake passage 15, each cylinder is branched in the intake manifold, and two branch passages are formed in parallel in the cylinder-by-cylinder passage 15 a, and two intake ports 6 are formed at the downstream end of the combustion chamber 5 in FIG. 1. Is open. An intake flow control valve 17 is provided in one branch passage, and by controlling the opening degree of the intake flow control valve 17, intake air flow (swirl or tumble) into the combustion chamber 5 by intake air introduced from the other branch passage. Is generated and the strength of the intake flow is controlled. Note that the strength of the intake flow can be controlled by controlling the opening of one of the two intake valves or by variable control of the valve timing.
[0045]
A throttle valve 18 is provided in the middle of the intake passage 15, and the throttle valve 18 is operated by an electric actuator 19 such as a step motor so that the amount of intake air can be controlled.
[0046]
The exhaust passage 16 is provided with an O ₂ sensor 21 for detecting an air-fuel ratio in the exhaust, and a catalyst device 22 having a catalyst for purifying exhaust gas. The catalytic device 22 includes a three-way catalyst 22a that purifies HC, CO, and NOx disposed upstream of the exhaust passage 16, and a NOx catalyst 22b that adsorbs NOx disposed downstream of the three-way catalyst 22a. It consists of. The NOx catalyst 22b adsorbs NOx at the air-fuel ratio λ> 1 when stratified combustion is performed with the air-fuel ratio in the lean region of λ> 1 after warm-up. Further, the NOx catalyst 22b exhibits a three-way function in the vicinity of the theoretical air-fuel ratio λ = 1, releases NOx adsorbed at an air-fuel ratio of λ ≦ 1, and reacts with HC and CO.
[0047]
When the catalyst device 22 in the exhaust passage 16 is arranged immediately downstream of the exhaust manifold 16a (directly connected to the exhaust manifold), the catalyst temperature tends to rise excessively at high speed and high load, and the exhaust manifold is moved away from the engine for catalyst protection. It arrange | positions in the middle of the exhaust pipe 16b connected to 16a.
[0048]
An EGR passage 43 is connected between the exhaust passage 16 and the intake passage 15 to recirculate −portion of exhaust gas to the intake system, and an EGR valve 44 is interposed in the EGR passage 43.
[0049]
A turbocharger turbine 40 and a wastegate 41 that bypasses the turbine 40 are provided upstream of the catalyst device 22 in the exhaust pipe 16 b. The wastegate 41 is opened and closed by a wastegate valve 42 to suppress the boost pressure from rising excessively.
[0050]
The engine control ECU (electric control unit) 30 detects an O ₂ sensor 21 that detects the oxygen concentration in the exhaust gas, a crank angle sensor 23 that detects the crank angle of the engine, and an accelerator opening (depressing amount of the accelerator pedal). Signals from an accelerator opening sensor 24, an air flow meter 25 for detecting the amount of intake air, a water temperature sensor 26 for detecting the temperature of engine cooling water, an engine speed sensor 27, an intake air temperature sensor 28, an atmospheric pressure sensor 29, and the like are input. The
[0051]
FIG. 3 is a diagram showing various parameters input to the engine control ECU for executing engine and catalyst state detection and engine control.
[0052]
The engine control ECU 30 includes a temperature state determination unit 31, an operation state detection unit 32, a fuel supply control unit 33, an injection amount calculation unit 34, an ignition timing control unit 35, and a rotation speed control unit 36.
[0053]
The temperature state determination unit 31 detects an engine speed detection signal from the engine speed sensor 27, an accelerator position detection signal from the accelerator position sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature detection from the water temperature sensor 26. The catalyst temperature is estimated based on past history such as signal, fuel injection amount Ta, injection mode, etc., and the NOx purification rate is detected from the estimated catalyst temperature to raise the catalyst temperature and perform sulfur poisoning recovery processing. It is determined whether or not to execute. Further, the temperature state determination unit 31 also estimates the engine temperature, and determines that the engine is cold when the water temperature is lower than the set temperature, and the engine is warm when the water temperature is equal to or higher than the set temperature. Note that the estimation of the catalyst temperature may be performed using both the water temperature detection and the determination of the elapsed time from the engine start, or the catalyst temperature may be directly detected.
[0054]
The injection mode has an injection mode of intake stroke injection (uniform combustion region) or compression stroke injection (stratified combustion region), and divided injection in these regions, and is set in advance for each operation region. It is set by determining the area.
[0055]
The operating state detection unit 32 detects an engine speed detection signal from the engine speed sensor 27, an accelerator position detection signal from the accelerator position sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature detection from the water temperature sensor 26. Based on the signal, the intake air temperature detection signal from the intake air temperature sensor 28, and the atmospheric pressure detection signal from the atmospheric pressure sensor 29, an engine operating region such as a lean region or a rich region is determined. Further, a transient operation state such as a rapid acceleration of the engine or a high load operation is determined from the intake flow rate detection signal. Further, the engine cold or warm operation state is determined from the water temperature detection signal. Further, O ₂ detection signal from the O ₂ sensor 21 is output when the activity of the O ₂ sensor 21 is used when O ₂ feedback control.
[0056]
The fuel injection control unit 33 detects the engine speed from the engine speed sensor 27, the accelerator position detection signal from the accelerator position sensor 24, the intake flow rate detection signal from the air flow meter 25, and the water temperature detection from the water temperature sensor 26. The fuel injection timing Qa is calculated from the signal and the O ₂ detection signal from the O ₂ sensor 21.
[0057]
The injection amount calculation unit 34 detects an engine speed detection signal from the engine speed sensor 27, an accelerator position detection signal from the accelerator position sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature detection from the water temperature sensor 26. The fuel injection amount Ta is calculated based on the signal, the fuel pressure, and the injection mode.
[0058]
The fuel pressure is the discharge pressure of the high-pressure fuel pump acting on the injector, and the injection amount Ta is corrected by the differential pressure between the fuel pressure sensor output and the in-cylinder pressure (estimated value).
[0059]
The fuel injection control unit 33 and the injection amount calculation unit 34 control the fuel injection timing Qa and the injection amount (pulse width) Ta from the injector 11 via the injector drive circuit 37, and when in the catalyst cold state, While the air-fuel ratio of the entire combustion chamber 5 is substantially the stoichiometric air-fuel ratio λ≈1, during the period from the intake stroke to the ignition timing, the late injection after the middle of the compression stroke and the early injection in the first half of the intake stroke earlier than this late injection By split injection in which the fuel is injected into at least two of the above, the stoichiometric air-fuel ratio (λ = 1) or a richer air-fuel ratio λ <1 is mixed in the region near the spark plug 10 in the combustion chamber 5. At the same time, control is performed so as to form an air-fuel mixture λ> 1 that is leaner than the theoretical air-fuel ratio λ = 1 around the region near the spark plug 10.
[0060]
The ignition timing control unit 35 detects an engine speed detection signal from the engine speed sensor 27, an accelerator position detection signal from the accelerator position sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature detection from the water temperature sensor 26. The ignition timing θig is calculated according to the signal and the injection mode.
[0061]
The ignition timing control unit 35 outputs a control signal to the ignition device 38 and controls the ignition timing θig according to the operating state of the engine. Basically, the ignition timing θig is set to MBT (exhibiting the best torque). The ignition timing is retarded in the stratified operation region of the engine low load during the sulfur poisoning recovery process as will be described later.
[0062]
The engine control ECU 30 also controls the intake air amount by outputting a control signal to the actuator 19 that drives the throttle valve 18, and stratified combustion is performed by fuel injection only during the compression stroke after the engine is warmed up. In such a case, the intake air amount is adjusted so that the air-fuel ratio becomes lean. The throttle valve opening degree θtv is calculated based on the engine speed detection signal from the engine speed sensor 27, the accelerator position detection signal from the accelerator position sensor 24, the intake flow rate detection signal from the air flow meter 25, and the intake temperature sensor 28. Calculation is performed based on the temperature detection signal, the atmospheric pressure detection signal from the atmospheric pressure sensor 29, and the injection mode.
[0063]
Further, the engine control ECU 30 controls the intake flow control valve 17 so as to generate a swirl in the combustion chamber 5 at the time of split injection or the like, and at the same time stratified combustion when the air-fuel ratio is made lean from λ = 1. The EGR valve 44 is controlled to be performed.
[0064]
Opening and closing of the intake flow control valve 17 is controlled by an engine speed detection signal from the engine speed sensor 27, an accelerator position detection signal from the accelerator position sensor 24, an intake flow rate detection signal from the air flow meter 25, and an injection mode. The swirl ratio in the cylinder (the swirl angular velocity / engine rotational angular velocity) is controlled.
[0065]
The EGR valve opening degree θegr is an engine speed detection signal from the engine speed sensor 27, an accelerator opening degree detection signal from the accelerator opening sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature detection from the water temperature sensor 26. Calculated by signal and injection mode.
[0066]
The engine control ECU 30 determines engine start from the engine speed detection signal and the starter signal from the engine speed sensor 27.
[0067]
Further, the engine control ECU 30 increases the amount of exhaust gas flowing through the lean NOx catalyst 22b by opening the wastegate 41 by the wastegate valve 42 if the engine load is low during the sulfur poisoning recovery process, thereby enhancing the temperature rise effect.
[Catalyst temperature control]
<Temperature control of catalyst for sulfur poisoning recovery treatment>
First, the temperature rise control of the catalyst for rapidly increasing the catalyst temperature to 600 ° C. or higher when sulfur poisoning of the lean NOx catalyst is recovered will be described.
[0068]
4 and 5 are flowcharts showing the temperature rise control of the catalyst in the direct injection gasoline engine of the present embodiment.
[0069]
First, an overview of catalyst temperature rise control will be described.
[0070]
In the present embodiment, in order to rapidly increase the catalyst temperature to 600 ° C. or higher during the sulfur NOx recovery process of the lean NOx catalyst while the lean NOx catalyst is warmed up, the following control is performed in the lean operation region of the engine low load. Execute. However, the NOx catalyst is in a warmed-up state.
[0071]
(1) While setting the air-fuel ratio in the cylinder to λ≈1, at least two times of the late injection after the middle of the compression stroke and the early injection earlier than the late injection in the period from the intake stroke to the ignition timing Divide and inject fuel.
[0072]
(2) The intake flow control valve is opened so that the swirl becomes weak according to the high temperature rise requirement of the catalyst temperature, and the required injection timing when the swirl is weak (required when the swirl is strong in the same operating range) The timing set to the retard side from the injection timing).
[0073]
{Circle around (3)} The swirl is weakened in accordance with the request for raising the catalyst temperature, and the late injection timing is retarded with respect to the required injection timing when the swirl is weak.
[0074]
(4) When the demand for raising the catalyst temperature is highest, the swirl is weakened, and the ignition timing is retarded in addition to the retard of the late injection timing.
[0075]
Next, a specific flow by the engine control ECU 30 for executing the controls (1) to (4) will be described with reference to FIGS.
[0076]
As shown in FIG. 4, in step S1, the flag F is reset to zero, and in step S2, the engine control ECU 30 performs an O ₂ sensor 21, a crank angle sensor 23 for detecting the crank angle of the engine, an accelerator opening sensor 24, The detection signals from the air flow meter 25, the water temperature sensor 26, the engine speed sensor 27, the intake air temperature sensor 28, the atmospheric pressure sensor 29, the fuel pressure sensor, and the starter are read.
[0077]
In step S3, an engine speed detection signal from the engine speed sensor 27, an accelerator position detection signal from the accelerator position sensor 24, an intake flow rate detection signal from the air flow meter 25, a water temperature detection signal from the water temperature sensor 26, fuel The NOx catalyst temperature Tcat is estimated from past histories such as the injection amount Ta and the injection mode. The exhaust gas temperature may be measured and substituted for the NOx catalyst temperature Tcat.
[0078]
In step S4, the NOx purification rate C is detected from the NOx catalyst temperature Tcat estimated in step S2.
[0079]
In step S6, timers N1 to N3 are set. The periods N1 to N3 are set to optimum times by experiments or the like.
[0080]
In step S8, it is determined whether or not the NOx purification rate C is less than a predetermined value C1.
[0081]
If the NOx purification rate C is greater than or equal to the predetermined value C1 in step S8 (NO in step S8), normal engine control is executed in step S9.
[0082]
If the NOx purification rate C is less than the predetermined value C1 in step S8 (YES in step S8), the process proceeds to step S10 because the NOx purification rate C has decreased due to sulfur poisoning.
[0083]
In step S10, the difference ΔT between the temperature Tre (for example, 600 ° C.) required for the sulfur poisoning recovery process and the current NOx catalyst temperature Tcat is calculated to calculate the catalyst temperature increase request degree.
[0084]
In step S12, it is determined whether or not the catalyst temperature difference ΔT is equal to or higher than a predetermined temperature T1. If the catalyst temperature difference ΔT is greater than or equal to the predetermined temperature T1 in step S12 (YES in step S12), the catalyst temperature increase request is high, so the process proceeds to step S14, and if the catalyst temperature difference ΔT is less than the predetermined temperature T1 (NO in step S12) ) Since the temperature increase request of the catalyst is low, the process proceeds to step S22.
[0085]
In step S14, since the catalyst temperature increase request is high, the intake flow control valve is opened to weaken the swirl and the exhaust gas temperature is raised.
[0086]
In step S16, the injection pulse width Ta is allocated to α: 1−α, and the early injection pulse Tak (= α × Ta) and the late injection pulse Tad (= (1−α) × Ta) in the divided injection are obtained. calculate. However, α <0.5 is set to increase the late injection pulse width Tad.
[0087]
In step S18, the early basic injection timing θakb and the late basic injection timing θadb required when the swirl is weak are set.
[0088]
In step S20, the late basic injection timing θadb required when the swirl is weak is set. This late basic injection timing θadb is on the retard side with respect to the required value when the required value when the swirl is weak is relatively strong.
[0089]
On the other hand, when the temperature increase request of the catalyst is low, the intake flow control valve 17 is closed in step S22 to make the swirl strong.
[0090]
In step S24, the injection pulse width Ta is allocated to α: 1−α, and the early injection pulse Tak (= α × Ta) in the divided injection and the late injection pulse Tad (= (1−α) × Ta) are obtained. calculate. However, α ≧ 0.5 is set to reduce the late injection pulse width Tad.
[0091]
In step S26, the early basic injection timing θakb and the late basic injection timing θadb required when the swirl is strong are set.
[0092]
In step S28, the late basic injection timing θadb required when the swirl is strong is set. It should be noted that the late basic injection timing θadb required when the swirl is strong is relatively advanced than the value required when the swirl is weak.
[0093]
In Step S30, it is determined whether or not the flag F is 1. If the ignition timing θig retard flag F is 1 (YES in Step S30), the ignition timing θig (ignition retard) set in Step S45 remains unchanged. Proceed to S32.
[0094]
On the other hand, if the flag F is not 1 in step S30 (NO in step S30), the process proceeds to step S31.
[0095]
In step S31, an appropriate ignition timing θig that is more advanced than the ignition timing θig set in step S45 is set.
[0096]
In step S32, if the engine crank angle detected from the crank angle sensor 23 has reached the set injection timing (YES in step S32), the process proceeds to step S34.
[0097]
In step S34, fuel is injected from the injector 11 with the injection pulse widths Tak and Tad calculated in step S16 or S24.
[0098]
As shown in FIG. 5, in step S36, if the ignition timing θig set in steps S31 to S45 is reached (YES in step S36), the process proceeds to step S38.
[0099]
In step S38, the spark plug 10 is ignited at the ignition timing θig set in steps S31 to S45.
[0100]
In step S39, it is determined whether or not the flag F is 1. If the flag F of the ignition timing θig retard is 1 (YES in step S39), the process proceeds to step S44.
[0101]
On the other hand, if the flag F is not 1 (NO in step S39), the process proceeds to step S40.
[0102]
In steps S40 and S42, the engine control from steps S8 to S38 is continued until the timer N2 finishes counting down.
[0103]
In step S44, it is determined whether or not the catalyst temperature difference ΔT has risen to zero or less, that is, the catalyst temperature Tcat has increased to the temperature Tre necessary for the sulfur poisoning recovery process.
[0104]
If the catalyst temperature Tcat rises to the temperature Tre required for the sulfur poisoning recovery process in step S44 (YES in step S44), the process proceeds to step S47.
[0105]
If the catalyst temperature Tcat has not risen to the temperature Tre necessary for the sulfur poisoning recovery process (NO in step S44), the process proceeds to step S45.
[0106]
In step S45, in order to further increase the catalyst temperature Tcat, the ignition timing θig is retarded. In step S46, the retard flag F of the ignition timing θig is set to 1, and the engine control from the above steps S8 to S38 is continued.
[0107]
In step S47, engine control from steps S8 to S38 based on the flow up to step S46 is continued.
[0108]
In steps S48 and S50, the engine control in steps S8 to S38 is continued until the timer N1 finishes counting down.
[0109]
In step S52, it is determined whether or not the NOx purification rate C is less than a predetermined value C2 (a value slightly larger than the predetermined value C1).
[0110]
If the NOx purification rate C is greater than or equal to the predetermined value C2 in step S52 (YES in step S52), the sulfur poisoning has sufficiently recovered, so the process proceeds to step S54, where the sulfur poisoning recovery control end process is executed and the process returns.
[0111]
If the NOx purification rate C is less than the predetermined value C2 in step S52 (NO in step S52), the sulfur poisoning has not sufficiently recovered, and the process proceeds to step S56.
[0112]
In steps S56, 58, and 60, the engine control in steps S8 to S38 is continued until the countdown of the timer N3 ends, and the sulfur poisoning recovery process is extended.
[0113]
FIG. 7 is a map showing the operating region of the engine. FIG. 8 is a diagram showing a change in the exhaust gas temperature by the temperature rise control of the catalyst of the present embodiment. FIG. 9 is a diagram showing the relationship between the exhaust gas temperature corresponding to the ignition timing and the indicated mean effective pressure. FIG. 10 is a timing chart showing the fuel injection amount and the injection timing in the two-part injection.
[0114]
The stratified combustion region shown in FIG. 7 is a region where stratified combustion is performed by injecting fuel only in the latter half of the compression stroke so that the air-fuel mixture is unevenly distributed around the spark plug 10. The region of λ = 1 is a region in which fuel is injected during the first half of the intake stroke and from the middle to the second half of the compression stroke, and the air-fuel ratio of the entire combustion chamber is set to a substantially theoretical air-fuel ratio (λ≈1). The enriched region is a region where fuel is injected only during the first half of the intake stroke or the middle of the compression stroke.
[0115]
The engine 1 shown in FIG. 1 is provided with a stratification cavity 12 at the top of a piston 4 for trapping the fuel ejected from the injector 11 and guiding it in the direction of the spark plug 10. The swirl ratio (swirl flow angular velocity / engine angular velocity) in the cylinder is set so that the local air-fuel ratio in the vicinity of the spark plug 10 becomes rich by late injection when fuel is injected.
[0116]
The sulfur poisoning recovery process of the present embodiment is executed in the stratified combustion region shown in FIG. 7 and in the region where the engine load is low. The air-fuel ratio is set to λ≈1, and the intake flow control valve 17 is opened to operate the swirl. Within a period from the intake stroke to the ignition timing, the fuel is injected in two parts, that is, a late injection after the middle of the compression stroke and an early injection earlier than the late injection. Furthermore, the late injection ratio is made larger than the previous injection ratio.
[0117]
As shown in FIG. 8, when the late injection ratio is changed from 20 to 60%, the exhaust gas temperature increases as the late injection ratio increases, and the combustion speed is suppressed by the weak swirl, resulting in slow combustion. Since the exhaust gas temperature is increased, the catalyst temperature can be rapidly increased. Further, since the engine is a stratified region and the engine load is low, deterioration of fuel consumption can be minimized.
[0118]
Here, as shown in FIG. 10, the middle stage of the compression stroke is the middle stage when the compression stroke is divided into three equal parts in the first, middle, and second half, that is, the crank angle is BTDC (before top dead center) 120 ° to BTDC 60 °. Means period. Therefore, the late injection is after BTDC 120 °. However, if the timing of the late injection is too late as will be described later, the combustion stability is impaired. Therefore, it is desirable to start the late injection until the ¾ period of the compression stroke has elapsed (until BTDC 45 °).
[0119]
That is, as shown in FIG. 10, the late injection is set to start within a period from 120 ° before top dead center to 45 ° before top dead center in the compression stroke, and the early injection is an appropriate time before the late injection. The timing is set to start within, for example, the period of the intake stroke.
[0120]
Further, in addition to the above control, as shown by the dotted line in FIG. 10, the exhaust gas temperature can be rapidly increased by retarding the late injection timing and, if necessary, the ignition timing.
[0121]
As shown in FIG. 9, the ignition timing retard is executed when the fluctuation rate of the engine Pi (the indicated mean effective pressure) is about 5%. The Pi variation rate is defined by the standard deviation σ of Pi / cycle average of Pi × 100 (%).
<Temperature control of other catalysts>
As another temperature increase control procedure, when the air-fuel ratio is set to λ≈1 and divided injection is performed, if the NOx catalyst temperature does not reach the temperature Tre required for the sulfur poisoning recovery process, the ignition timing is set. When the NOx catalyst temperature does not reach the temperature Tre, the swirl is weakened. When the NOx catalyst temperature is not reached yet, the late injection timing is delayed or the ignition timing is retarded. When the temperature Tre required for the poison recovery process has not been reached, the ignition timing is returned and the swirl is made weaker. After that, when the temperature Tre is not reached, the late injection timing is retarded to minimize fuel consumption deterioration. Can do.
[0122]
If the engine is equipped with a supercharger as in this embodiment, supercharging is not required in the engine low load region, so opening the wastegate during the sulfur poisoning recovery process will reduce heat dissipation to the turbine. By reducing the temperature, the temperature of the exhaust gas flowing through the catalyst can be kept high, and the temperature rise effect can be further enhanced.
<Catalyst temperature recovery control after sulfur poisoning recovery control>
Next, after the sulfur poisoning recovery control of the lean NOx catalyst, the temperature return of the catalyst for rapidly returning the catalyst whose temperature is raised to 600 ° C. or higher and has a low NOx purification rate to a temperature range of about 400 ° C. with a high NOx purification rate Control will be described.
[0123]
FIG. 6 is a flowchart showing the temperature return control of the catalyst in the direct injection gasoline engine of the present embodiment.
[0124]
First, an overview of catalyst temperature recovery control will be described.
[0125]
If the operating state of the engine shifts from the region where the air-fuel ratio λ ≦ 1 to the lean region where λ> 1 in the catalyst high temperature state that deviates from the purifiable temperature range after the sulfur poisoning recovery process, the NOx catalyst temperature decreases. There is a disadvantage that the NOx adsorption performance is low.
[0126]
For this reason, in the present embodiment, the NOx catalyst temperature that deviates from the purifiable temperature range after the sulfur poisoning recovery process in a state where the lean NOx catalyst is warmed up is quickly returned to the temperature region where the NOx purification rate is high (temperature The following control is executed.
[0127]
{Circle around (1)} The air / fuel ratio is set to λ≈1 while increasing the swirl before shifting from λ ≦ 1 to the lean region of λ> 1.
[0128]
(2) At least the late injection timing is advanced when the air-fuel ratio shifts from the operating state by split injection to λ <1 to λ≈1 to the lean region where λ> 1.
[0129]
(3) When releasing the adsorbed NOx, at the time of so-called NOx purge, the air-fuel ratio is set to λ <1 to λ≈1, and the fuel is divided into at least twice within the period from the intake stroke to the ignition timing. At the same time as injection, the air-fuel ratio is set to λ≈1 while increasing the swirl before shifting to the lean region of λ> 1 from this operating state.
[0130]
Next, a specific flow by the engine control ECU 30 for executing the controls (1) to (3) will be described with reference to FIG.
[0131]
As shown in FIG. 6, in step S62, the engine control ECU 30 determines whether or not the intake air flow control valve 17 is closed with the air-fuel ratio maintained at λ≈1.
[0132]
If it is in the closed state in step S62 (YES in step S62), the swirl strength is maintained and the process proceeds to step S64.
[0133]
In step S64, the retard of the ignition timing θig set in step S45 is terminated.
[0134]
In step S66, the split injection is terminated and the operation is returned to the operation in the stratified combustion region, and the normal engine control in step S9 is executed.
[0135]
If it is in the open state in step S62 (YES in step S62), the process proceeds to step S68, where the intake flow control valve is closed and the swirl is strong.
[0136]
In step S70, the late basic injection timing θadb set in step S18 or S26 is advanced, and the process proceeds to step S66.
[0137]
FIG. 11 is a diagram showing the characteristics of the NOx purification rate accompanying the temperature change of the lean NOx catalyst and the three-way catalyst. FIG. 12 is a diagram showing a change in the exhaust gas temperature by the temperature return control of the catalyst of the present embodiment.
[0138]
As shown in FIG. 7 and FIG. 12, the temperature return control is performed by setting the air-fuel ratio to a strong swirl before shifting from the rich region of λ ≦ 1 to the stratified combustion region of λ> 1 after the sulfur poisoning recovery process. As shown in FIG. 11, the exhaust gas temperature is rapidly lowered and the catalyst heated to about 600 ° C. after the sulfur poisoning recovery control is rapidly increased in NOx purification rate while suppressing deterioration in fuel consumption and combustion stability. The temperature can be returned to a temperature range of about 400 ° C. During this time, NOx purification can be achieved in the purification window of the three-way catalyst by setting the air-fuel ratio to λ≈1.
[0139]
Even in a specification without a three-way catalyst, the exhaust gas can be purified by utilizing the three-way function of the NOx catalyst by setting the air-fuel ratio λ≈1.
[0140]
In addition, the intake flow control valve closing operation for increasing the swirl is performed in the engine low load and low rotation regions where the amount of intake air into the combustion chamber is small, and is performed in the high load and high rotation regions where the output efficiency decreases. Desirably not. In addition, you may reinforce an intake flow using other means, such as an intake valve, instead of a swirl.
[0141]
Further, when the air-fuel ratio shifts from the operation state by split injection with λ <1 to λ≈1 to the lean region where λ> 1, the exhaust gas temperature is rapidly decreased by at least advancing the late injection timing. be able to.
[0142]
In particular, when catalyst refresh is performed in which the NOx adsorbed by the lean NOx catalyst is released and NOx is reduced by the reduction purification function of the catalyst, the air-fuel ratio is set to λ <1 to λ≈1, and the intake air If fuel is injected at least twice during the period from the stroke to the ignition timing, CO that reacts with NOx can be increased, so that NOx can be efficiently purified.
[0143]
Note that the present invention can be applied to modifications or variations of the above-described embodiment without departing from the spirit of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of a combustion chamber portion of a direct injection engine according to the present embodiment.
FIG. 2 is a schematic view of the entire cylinder injection engine.
FIG. 3 is a diagram showing various parameters input to an engine control ECU for executing engine and catalyst state detection and engine control.
FIG. 4 is a flowchart showing catalyst temperature increase control in the direct injection gasoline engine of the present embodiment.
FIG. 5 is a flowchart showing catalyst temperature increase control in the direct injection gasoline engine of the present embodiment.
FIG. 6 is a flowchart showing temperature return control of the catalyst in the direct injection gasoline engine of the present embodiment.
FIG. 7 is a map showing an engine operating region.
FIG. 8 is a diagram showing a change in exhaust gas temperature by temperature increase control of the catalyst of the present embodiment.
FIG. 9 is a diagram showing the relationship between the exhaust gas temperature corresponding to the ignition timing and the indicated mean effective pressure.
FIG. 10 is a timing chart showing the fuel injection amount and the injection timing in the two-part injection.
FIG. 11 is a graph showing the characteristics of the NOx purification rate associated with the temperature change of the lean NOx catalyst and the three-way catalyst.
FIG. 12 is a diagram showing a change in exhaust gas temperature by temperature return control of the catalyst of the present embodiment.
[Explanation of symbols]
1 ... engine 10 ... spark plug 11 ... injector 15 ... intake passage 16 ... exhaust passage 21 ... O ₂ sensor 22 ... catalytic device 30 ... ECU

Claims (15)

A fuel injection valve that directly injects fuel into the combustion chamber and a NOx catalyst that adsorbs NOx in an exhaust passage in an oxygen-excess atmosphere and releases the adsorbed NOx as the oxygen concentration decreases, sulfur poisoning of the NOx catalyst At the time of executing the recovery process, at least the late injection after the middle of the compression stroke and the early injection earlier than the late injection are set during the period from the intake stroke to the ignition timing while setting the air-fuel ratio in the cylinder to λ≈1. In an engine control apparatus that increases the temperature of the NOx catalyst by injecting fuel in two steps,
Temperature detecting means for detecting the temperature state of the NOx catalyst;
Variable means for forcibly changing the intake flow strength in the cylinder,
An engine control apparatus, wherein, during the NOx catalyst sulfur poisoning recovery process, the variable means is operated so that the intake flow strength becomes weaker as the NOx catalyst temperature rise request is higher.   2. The engine control device according to claim 1, wherein the intake flow strength is weakened and the late injection timing is delayed in accordance with a high temperature increase request of the NOx catalyst temperature.   2. The engine control device according to claim 1, wherein when the temperature increase request for the NOx catalyst temperature is highest, the intake flow strength is weakened, the late injection timing is delayed, and the ignition timing is delayed.   4. The engine control according to claim 1, wherein the temperature increase request for the NOx catalyst temperature is set higher as the temperature state of the NOx catalyst and the engine load are lower. apparatus.   5. The sulfur poisoning recovery process is executed when the temperature increase request for the NOx catalyst temperature is high in an operation region where the engine load is low and the air-fuel ratio is λ> 1. The engine control device according to any one of the preceding claims. A fuel injection valve that directly injects fuel into the combustion chamber and a NOx catalyst that adsorbs NOx in an exhaust passage in an oxygen-excess atmosphere and releases the adsorbed NOx as the oxygen concentration decreases, sulfur poisoning of the NOx catalyst At the time of executing the recovery process, at least the late injection after the middle of the compression stroke and the early injection earlier than the late injection are set in the period from the intake stroke to the ignition timing while setting the air-fuel ratio in the cylinder to λ≈1. In an engine control apparatus that increases the temperature of the NOx catalyst by injecting fuel in two steps,
Ignition timing control means for controlling the ignition timing;
Variable means for forcibly changing the intake flow strength in the cylinder;
An injection timing control means for controlling the fuel injection timing;
The ignition timing control means delays the ignition timing for a predetermined first period when the temperature state of the NOx catalyst has not reached the target catalyst temperature,
Thereafter, when the target catalyst temperature is not reached, the variable means weakens the intake flow strength for a predetermined second period,
Thereafter, when the target catalyst temperature is not reached, the injection timing control means delays the late injection timing in a predetermined third period.   The engine control apparatus according to claim 6, wherein the engine control apparatus is executed at a low engine load when the NOx catalyst temperature is low.   The engine control device according to claim 6 or 7, wherein a supercharger is disposed upstream of the NOx catalyst in the exhaust passage.   9. The engine according to claim 8, wherein a bypass passage that bypasses the supercharger is formed in the exhaust passage, and the bypass passage is opened when a temperature increase request of the NOx catalyst is required at a low engine load. Control device. A fuel injection valve for injecting fuel directly into the combustion chamber, the NOx adsorbed by an oxygen-rich atmosphere in the exhaust passage, and a NOx catalyst to release the adsorbed NOx in accordance with the oxygen concentration decreases, the sulfur of the NOx catalyst When the poison recovery process is performed, while the air-fuel ratio in the cylinder is set to λ≈1, the late injection after the middle of the compression stroke and the early injection earlier than the late injection are performed during the period from the intake stroke to the ignition timing. In an engine control apparatus for increasing the temperature of the NOx catalyst by injecting fuel at least twice,
Ignition timing control means for controlling the ignition timing ;
Variable means for forcibly changing the intake flow strength in the cylinder;
An injection timing control means for controlling the fuel injection timing ;
The ignition timing control means delays the ignition timing when the temperature state of the NOx catalyst has not reached the target catalyst temperature ,
Thereafter, when the temperature state of the NOx catalyst does not reach the target catalyst temperature, the variable means weakens the intake flow strength while returning to the ignition timing before delaying the ignition timing delayed by the ignition timing control means,
Thereafter, when the temperature state of the NOx catalyst does not reach the target catalyst temperature, the injection timing control means delays the late injection timing . A fuel injection valve that directly injects fuel into the combustion chamber and a NOx catalyst that adsorbs NOx in an exhaust passage in an oxygen-excess atmosphere and releases the adsorbed NOx as the oxygen concentration decreases, sulfur poisoning of the NOx catalyst At the time of executing the recovery process, at least the late injection after the middle of the compression stroke and the early injection earlier than the late injection are set in the period from the intake stroke to the ignition timing while setting the air-fuel ratio in the cylinder to λ≈1. In the in-cylinder injection engine in which fuel is injected in two steps to increase the temperature state of the NOx catalyst,
When the temperature state of the NOx catalyst does not reach the target catalyst temperature, the ignition timing is delayed for a predetermined first period, and when the target catalyst temperature is not reached, the intake flow strength is decreased for a predetermined second period, and then the target A catalyst temperature control method for an in-cylinder injection engine, characterized in that when the catalyst temperature has not been reached, the late injection timing of a predetermined third period is delayed. The catalyst temperature control method for a direct injection engine according to claim 11 , wherein the control is performed at a low engine load when the NOx catalyst temperature is low. The method for controlling the catalyst temperature of a direct injection engine according to claim 11 or 12 , wherein a supercharger is disposed upstream of the NOx catalyst in the exhaust passage. The in-cylinder of claim 13 , wherein a bypass passage that bypasses the supercharger is formed in the exhaust passage, and the bypass passage is opened when a temperature increase request of the NOx catalyst is required at a low engine load. A catalyst temperature control method for an injection engine. A fuel injection valve that directly injects fuel into the combustion chamber and a NOx catalyst that adsorbs NOx in an exhaust passage in an oxygen-excess atmosphere and releases the adsorbed NOx as the oxygen concentration decreases, sulfur poisoning of the NOx catalyst At the time of executing the recovery process, at least the late injection after the middle of the compression stroke and the early injection earlier than the late injection are set in the period from the intake stroke to the ignition timing while setting the air-fuel ratio in the cylinder to λ≈1. In the in-cylinder injection engine that injects fuel in two steps to increase the temperature of the NOx catalyst,
When the temperature state of the NOx catalyst does not reach the target catalyst temperature, the ignition timing is delayed ,
After that, when the temperature state of the NOx catalyst does not reach the target catalyst temperature, the ignition flow strength in the cylinder is weakened while returning to the ignition timing before delaying the delayed ignition timing,
Thereafter, when the temperature state of the NOx catalyst does not reach the target catalyst temperature, the late injection timing is delayed , and the catalyst temperature control method for a direct injection engine is characterized.

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