JP2001271680A - Control device for direct injection engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly return to a temperature area with a high NOx purification rate after recovering from sulfur poisoning of a lean NOx catalyst. SOLUTION: In step S62 to S70, an air-fuel ratio is set to λ≈1, while the swirl is intensified before the air-fuel ratio is transferred from an enrich area, where λ<=1 to a stratified charge combustion area of λ>1 after a sulfur poisoning recovering processing. At divided injection and time for transferring the air-fuel ratio from an operation state of λ<1 to λ≈1 to a lean area of λ>1, at least later injection timing is advanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for an in-cylinder injection engine for recovering catalytic poisoning of the in-cylinder injection engine.

[0002]

2. Description of the Related Art Conventionally, in order to raise the catalyst temperature during recovery of sulfur poisoning of a lean NOx catalyst, the air-fuel ratio is set to approximately the stoichiometric air-fuel ratio λ ≒ 1, and the air-fuel ratio is divided into two, an intake stroke and a compression stroke Injecting fuel by using a fuel cell has been proposed.
-107740).

[0003] When recovering from the sulfur poisoning of the lean NOx catalyst, it is required that the temperature of the exhaust gas be rapidly raised and that the fuel efficiency improvement, which is an advantage of the direct injection engine, be maintained.

[0004]

On the other hand, lean NOx
After the recovery of sulfur poisoning of the catalyst, the catalyst temperature is higher than the NOx purification possible temperature range. Therefore, even if the operating state of the engine is shifted to the lean range, the catalyst temperature is reduced to the temperature range where the NOx purification rate is high. During the period, there is an inconvenience that the NOx purification rate decreases.

The present invention has been made in view of the above-mentioned problems, and has as its object to reduce NOx after recovery from sulfur poisoning of a lean NOx catalyst.
x quickly return to the temperature region where the purification rate is high, then switch to operation in the lean region
An object of the present invention is to provide a control device for an in-cylinder injection engine capable of maintaining a high Ox purification rate.

[0006]

In order to solve the above-mentioned problems and achieve the object, a control apparatus for a direct injection type engine according to the present invention comprises a fuel injection valve for directly injecting fuel into a combustion chamber, and an exhaust gas. A NOx catalyst that adsorbs NOx in a passage in an oxygen-excess atmosphere and releases the adsorbed NOx as the oxygen concentration decreases, and a lean region with an air-fuel ratio of λ> 1 is set in a partial load region of the engine. A control device for the injection engine, comprising: a temperature detecting means for detecting a temperature state of the NOx catalyst; and a variable means for forcibly changing the intake flow strength in the cylinder, wherein the NOx catalyst has a NOx purifying temperature range. When the operating temperature of the engine deviates from the range, the air-fuel ratio is set to λ ≒ 1 while the intake air flow strength is increased before the operating state of the engine is shifted from the region of the air-fuel ratio λ ≦ 1 to the lean region of λ> 1. Operating said varying means.

[0007] Preferably, during the period from the intake stroke to the ignition timing, the late injection after the middle stage of the compression stroke;
The fuel is injected in at least two times, that is, the early injection earlier than the latter injection, and the fuel is injected. When the air-fuel ratio shifts from the operating range of λ <1 to λ ≒ 1 to the lean range of λ> 1, at least the latter injection timing is changed. Hasten.

[0008] Preferably, at the time of executing NOx release reduction, the air-fuel ratio is operated at an air-fuel ratio of λ <1 to λ ≒ 1, and fuel is injected at least twice during a period from an intake stroke to an ignition timing. At a high temperature when the NOx catalyst deviates from the NOx purifying temperature range, the air-fuel ratio λ <1
Before shifting from the operating range of λ ≒ 1 to the lean range of λ> 1, the variable means is operated so as to set the air-fuel ratio to λ ≒ 1 while increasing the intake flow strength.

A control device for a direct injection type engine according to the present invention adsorbs NOx in a fuel injection valve for directly injecting fuel into a combustion chamber and NOx in an exhaust passage in an oxygen excess atmosphere, and adsorbs as the oxygen concentration decreases. A control device for a direct injection type engine including a NOx catalyst for releasing NOx and having a lean region where the air-fuel ratio is λ> 1 in the low engine load region, forcibly changes the intake air flow strength in the cylinder. A variable means for setting the air-fuel ratio in the cylinder to an operation range of λ ≒ 1 to λ ≦ 1 during the execution of the sulfur poisoning recovery process of the NOx catalyst, and performing compression during the period from the intake stroke to the ignition timing. The fuel injection is divided into at least two times, that is, a late injection after the middle stage of the stroke and an early injection earlier than the latter injection, and the variable means is operated so that the intake flow strength is weakened. Before moving to the lean region of al lambda> 1, while setting the air-fuel ratio to lambda ≒ 1, the variable means is operated so as to increase the intake flow strength, hasten least later injection timing.

[0010] Preferably, the intake air flow strength is increased in a low load or low rotation region of the engine.

[0011]

As described above, according to the first aspect of the present invention, when the temperature of the NOx catalyst deviates from the temperature range in which NOx can be purified, the operating state of the engine is changed from the range of the air-fuel ratio λ ≦ 1 to λ> 1. By setting the air-fuel ratio to λ ≒ 1 while increasing the flow strength of the intake air before shifting to the lean region, after the sulfur poisoning recovery of the lean NOx catalyst, the NOx purification rate becomes higher due to high thermal efficiency. By setting the air-fuel ratio λ ≒ 1 while returning (reducing) the temperature to the temperature range, the three-way function of the NOx catalyst can be exhibited to purify the exhaust gas. Further, in the specification provided with the three-way catalyst, the exhaust gas can be purified by the three-way catalyst. Thereafter, when the temperature decreases to the target temperature (the temperature range), the operation is switched to the operation in the lean range and NOx is reduced.
High purification rate can be maintained.

According to the second aspect of the present invention, during the period from the intake stroke to the ignition timing, the fuel is divided into at least two times: the late injection after the middle stage of the compression stroke and the early injection earlier than the latter injection. When the fuel is injected and the air-fuel ratio shifts from the operating range of λ <1 to λ ≒ 1 to the lean range of λ> 1, at least the late injection timing is advanced to lower the exhaust gas temperature and reduce the catalyst temperature to reduce the NOx purification rate. It can be quickly returned to a high temperature range.

According to the third aspect of the present invention, the air-fuel ratio is set to λ <1 to λ ≒ 1 during the NOx release reduction, and the fuel is divided into at least two times during the period from the intake stroke to the ignition timing. And the NOx catalyst makes NOx
At the time of high temperature deviating from the purifiable temperature range, before the air-fuel ratio λ <1 to λ 流動 1 shifts from the operating region to the lean region of λ> 1, the air-fuel ratio is increased by λ while increasing the intake flow strength. By setting ≒ 1, the exhaust gas temperature is lowered to return the catalyst temperature to a temperature region where the NOx purification rate is high, and the exhaust gas is purified while utilizing the three-way function of the NOx catalyst at λ ≒ 1. You can move to the lean area.

According to the fourth aspect of the present invention, the air-fuel ratio in the cylinder is set to an operating range of λ ≒ 1 to λ <1 when the sulfur poisoning recovery processing of the NOx catalyst is executed, and from the intake stroke to the ignition timing. During the period of the compression stroke, the variable means is operated so as to divide the fuel into at least two times of the late injection after the middle stage of the compression stroke and the early injection earlier than the latter injection to inject the fuel and to reduce the intake flow strength. While λ> 1 from the operating region.
Before the shift to the lean region, the sulfur poisoning recovery processing can be quickly performed by setting the air-fuel ratio to λ ≒ 1, increasing the intake flow strength, and at least advancing the late injection timing, Thereafter, the temperature of the exhaust gas is lowered to quickly return the catalyst temperature to a temperature region where the NOx purification rate is high, and
It is possible to quickly shift to the lean region while purifying the exhaust gas by utilizing the three-way function of the NOx catalyst in # 1.

According to the fifth aspect of the present invention, by increasing the flow strength of the intake air in the low load or low engine speed range of the engine, the exhaust gas temperature is reduced while suppressing the deterioration of fuel efficiency, and the catalyst temperature is reduced to the NOx purification rate. Can be quickly returned to the high temperature range.

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. [Structure of In-Cylinder Injection Engine] FIG. 1 is a schematic sectional view showing a structure of a combustion chamber portion of the in-cylinder injection engine of the present embodiment.

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 fitted 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. And
An intake port 6 and an exhaust port 7 communicating with the combustion chamber 5 and an intake valve 8 and an exhaust valve 9 for opening and closing these ports 6 and 7 are arranged.
And an injector 11 are provided. Injector 1
1 injects fuel directly into the combustion chamber 5.

On the lower surface of the cylinder head 3, a recess having a substantially trapezoidal cross section is formed, and defines an upper portion of the combustion chamber 5. An intake port 6 is open on the upper surface of the combustion chamber 5, and an exhaust port 7 is open on the inclined surface. The intake port 6 and the exhaust port 7 are provided two by two in a direction orthogonal to the paper surface, and an intake valve 8 and an exhaust valve 9 are provided respectively.
The intake valve 8 and the exhaust valve 9 are operated by a valve mechanism including a camshaft (not shown) and open and close at a predetermined timing.

The ignition plug 10 is disposed substantially at the center of the upper portion of the combustion chamber 5, and is attached to the cylinder head 3 such that the ignition gap faces the inside of the combustion chamber 5.

The injector 11 is disposed at the periphery of the combustion chamber 5, and is located on the side of the intake port 6.
The nozzle portion of the injector 11 faces the wall surface 12 between the upper surface of the combustion chamber 5 where the intake port 6 opens and the mating surface with the cylinder block 2, and injects fuel obliquely downward.

A concave stratification cavity 13 is formed near the injector 11 at the top of the biston 4. The fuel is injected from the injector 11 toward the cavity 13 in the latter half of the compression stroke when the piston 4 is close to the top dead center, and is reflected by the cavity 13 so as to reach the vicinity of the spark plug 10. The position and direction, the position of the cavity 1, and the positional relationship of the spark plug 10 are set in advance.

FIG. 2 is a schematic view of the whole cylinder injection type engine.

As shown in FIG. 2, an intake passage 15 and an exhaust passage 16 are connected to the engine 1. Intake passage 1
Downstream of the intake manifold 5, there is a branch for each cylinder in the intake manifold, and two branch passages are formed in parallel in the cylinder-specific passage 15 a, and two intake ports 6 open to the combustion chamber 5 in FIG. are doing. 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, the intake air (swirl or tumble) flows into the combustion chamber 5 by intake air introduced from the other branch passage. Is generated, and the strength of the intake air flow is controlled. The strength of the intake air flow can also be controlled by controlling the opening of one of the two intake valves or by variably controlling the valve timing.

In the middle of the intake passage 15, a throttle valve 18 is provided.
The throttle valve 1 is controlled by an electric actuator 19 such as a step motor so that the amount of intake air can be controlled.
8 is activated.

The exhaust passage 16 is provided with an O ₂ sensor 21 for detecting an air-fuel ratio in the exhaust gas and a catalyst device 22 having a catalyst for purifying exhaust gas. The catalyst device 22 includes a three-way catalyst 22a disposed on the upstream side of the exhaust passage 16 for purifying HC, CO, and NOx, and a NO for adsorbing NOx disposed on the downstream side of the three-way catalyst 22a.
x catalyst 22b. The NOx catalyst 22b
When the stratified charge combustion is performed after the warm-up with the air-fuel ratio in the lean region of λ> 1, NOx is adsorbed at the air-fuel ratio λ> 1.
The NOx catalyst 22b exhibits a three-way function near the stoichiometric air-fuel ratio λ = 1, and releases adsorbed NOx at an air-fuel ratio of λ ≦ 1 to react with HC and CO.

If the catalyst device 22 in the exhaust passage 16 is disposed immediately downstream (directly connected to the exhaust manifold) of the exhaust manifold 16a, the catalyst temperature tends to rise excessively at high speed and high load, and the catalyst device is moved away from the engine for protection of the catalyst. Exhaust pipe 16 connected to the exhaust manifold 16a
It is arranged in the middle of b.

Between the exhaust passage 16 and the intake passage 15,
An EGR passage 43 for recirculating the negative portion of the exhaust gas to the intake system is connected, and an EGR valve 44 is provided in the EGR passage 43.

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 16b. The wastegate 41 is opened and closed by a wastegate valve 42 to suppress the boost pressure from excessively increasing.

An engine control ECU (electric control unit) 30 detects an oxygen concentration in the exhaust gas.
₂ sensor 21, a crank angle sensor 23 for detecting an engine crank angle, an accelerator opening sensor 24 for detecting an accelerator opening (accelerator pedal depression amount), an air flow meter 25 for detecting an intake air amount, and a water temperature of the engine cooling water. Water temperature sensor 26 to detect, engine speed sensor 2
7. Signals from the intake air temperature sensor 28 and the atmospheric pressure sensor 29 are input.

FIG. 3 is a diagram showing various parameters input to the engine control ECU for detecting the state of the engine and the catalyst and performing engine control.

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.

The temperature state discriminator 31 includes an engine speed detection signal from the engine speed sensor 27, an accelerator opening detection signal from the accelerator opening sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature sensor 26. The catalyst temperature is estimated from the past history of the water temperature detection signal, the fuel injection amount Ta, the injection mode, and the like, and the NOx purification rate is detected from the estimated catalyst temperature to raise the catalyst temperature to increase the sulfur poisoning. It is determined whether to execute the recovery process. Further, the temperature state determination unit 31 also estimates the engine temperature, and if the water temperature is lower than the set temperature, the engine cold state,
If the temperature is equal to or higher than the set temperature, it is determined that the engine is warmed up.
Note that the estimation of the catalyst temperature may be performed by using both the detection of the water temperature and the determination of the elapsed time from the start of the engine.
Further, the catalyst temperature may be directly detected.

The injection mode has an injection mode of an intake stroke injection (uniform combustion region), a compression stroke injection (stratified combustion region), and a split injection in these regions, and is set in advance for each operation region. Therefore, it is set by the determination of the operation area.

The operating state detecting section 32 receives an engine speed detection signal from the engine speed sensor 27, an accelerator opening detection signal from the accelerator opening sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature sensor 26. The engine operating region such as a lean region or a rich region is determined based on the water temperature detection 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. Further, a transient operation state such as rapid acceleration of the engine or high load operation is determined from the intake flow rate detection signal. Further, a determination is made as to whether the engine is in a cold or warm operation state from the water temperature detection signal. Further, the O ₂ detection signal from the O ₂ sensor 21 is O ₂
This signal is output when the sensor 21 is activated, and is used during O ₂ feedback control.

The fuel injection control unit 33 includes an engine speed detection signal from the engine speed sensor 27, an accelerator opening detection signal from the accelerator opening sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature sensor 26. water temperature detection signal, calculates the injection timing Qa of fuel by O ₂ detection signal from the O ₂ sensor 21.

The injection amount calculating section 34 receives an engine speed detection signal from the engine speed sensor 27, an accelerator opening detection signal from the accelerator opening sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature sensor 26. The fuel injection amount Ta is calculated based on the water temperature detection signal, the fuel pressure, and the injection mode.

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 output of the fuel pressure sensor and the in-cylinder pressure (estimated value).

The fuel injection controller 33 and the injection amount calculator 34
Is connected to the injector 1 via the injector drive circuit 37.
Fuel injection timing Qa and injection amount (pulse width) Ta from 1
When the catalyst is in a cold state, the air-fuel ratio of the entire combustion chamber 5 is set to approximately the stoichiometric air-fuel ratio λ ≒ 1 and the late injection after the middle stage of the compression stroke during the period from the intake stroke to the ignition timing. And a stoichiometric air-fuel ratio (λ = 1) in a region near the ignition plug 10 in the combustion chamber 5 by split injection in which fuel is injected by splitting the fuel into at least two of early injection in the first half of the intake stroke earlier than the latter injection. Alternatively, a rich air-fuel mixture having an air-fuel ratio λ <1 is formed, and the ignition plug 10
Control is performed such that an air-fuel mixture having an air-fuel ratio λ> 1 leaner than the stoichiometric air-fuel ratio λ = 1 is formed around the nearby region.

The ignition timing control unit 35 includes an engine speed detection signal from the engine speed sensor 27, an accelerator opening detection signal from the accelerator opening sensor 24, an intake flow rate detection signal from the air flow meter 25, and a water temperature sensor 26. Timing θig according to the water temperature detection signal and the injection mode
Is calculated.

The ignition timing control unit 35 outputs a control signal to the ignition device 38 to control the ignition timing θig in accordance with the operating state of the engine.
The ignition timing is controlled to MBT (near the ignition timing at which the best torque is exhibited), but the ignition timing is retarded in the stratified operation region with a low engine load during the sulfur poisoning recovery processing as described later.

The engine control ECU 30 also controls the amount of intake air by outputting a control signal to an actuator 19 that drives the throttle valve 18. After the engine is warmed up, the fuel is injected only during the compression stroke. When stratified charge combustion is performed, the intake air amount is adjusted so that the air-fuel ratio becomes lean. The throttle valve opening θtv includes an engine speed detection signal from an engine speed sensor 27, an accelerator opening detection signal from an accelerator opening sensor 24, an intake flow rate detection signal from an air flow meter 25, and an intake air temperature sensor 28. The calculation is performed based on the temperature detection signal, the atmospheric pressure detection signal from the atmospheric pressure sensor 29, and the injection mode.

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 time of stratified combustion in which the air-fuel ratio is leaner than λ = 1. EGR to perform EGR
Control the valve 44.

The opening and closing of the intake flow control valve 17 is controlled by an engine speed detection signal from an engine speed sensor 27, an accelerator opening detection signal from an accelerator opening sensor 24, an intake air flow detection signal from an air flow meter 25, and an injection mode. And the swirl ratio in the cylinder (swirl angular speed / engine rotational angular speed).

The EGR valve opening θegr is determined by an engine speed detection signal from an engine speed sensor 27, an accelerator opening detection signal from an accelerator opening sensor 24, an intake flow rate detection signal from an air flow meter 25, and a water temperature sensor 26. Is calculated based on the water temperature detection signal and the injection mode.

The engine control ECU 30 determines the start of the engine based on the engine speed detection signal from the engine speed sensor 27 and the starter signal.

Further, if the engine load is low during the sulfur poisoning recovery process, the engine control ECU 30 opens the waste gate 41 by the waste gate valve 42 to set the lean NO.
The amount of exhaust gas flowing through the x catalyst 22b is increased to enhance the temperature raising effect. [Catalyst Temperature Control] <Catalyst Temperature Control for Sulfur Poisoning Recovery Processing> First, at the time of sulfur poisoning recovery of the lean NOx catalyst, the temperature of the catalyst for rapidly raising the catalyst temperature to 600 ° C. or higher is raised. The temperature control will be described.

FIGS. 4 and 5 are flow charts showing the control for raising the temperature of the catalyst in the direct injection gasoline engine of the present embodiment.

First, the outline of the control for raising the temperature of the catalyst will be described.

In the present embodiment, the catalyst temperature is rapidly increased to 600 ° C. or more during the sulfur poisoning recovery process of the lean NOx catalyst in a state where the lean NOx catalyst is warmed up. The following control is performed. However, the NOx catalyst has been warmed up.

While setting the air-fuel ratio in the cylinder to λ ≒ 1,
During the period from the intake stroke to the ignition timing, the fuel is divided into at least two times: the late injection after the middle stage of the compression stroke and the early injection earlier than the latter injection.

The intake flow control valve is opened so that the swirl is weakened in accordance with the request for raising the catalyst temperature.
The required injection timing when the swirl is low is set (a timing set on the retard side from the required injection timing when the swirl is high in the same operation region).

The swirl is weakened and the late injection timing is retarded with respect to the required injection timing when the swirl is low, according to the request for raising the catalyst temperature.

When the demand for raising the catalyst temperature is the highest, the swirl is weakened, and the ignition timing is further retarded in addition to the retard of the late injection timing.

Next, referring to FIG. 4 and FIG.
A specific flow by the engine control ECU 30 for executing the above control will be described.

[0055] As shown in FIG. 4, in step S1, the zero reset flag F, in step S2, the engine control ECU30 is, O ₂ sensor 21, a crank angle sensor 23 for detecting the crank angle of the engine, the accelerator opening degree Each detection signal from the sensor 24, the air flow meter 25, the water temperature sensor 26, the engine speed sensor 27, the intake temperature sensor 28, the atmospheric pressure sensor 29, the fuel pressure sensor, the starter and the like is read.

In step S3, an engine speed detection signal from the engine speed sensor 27, an accelerator opening 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 The NOx catalyst temperature Tcat is estimated from the past history of the signal, the fuel injection amount Ta, the injection mode, and the like. Note that the exhaust gas temperature may be measured and used as the NOx catalyst temperature Tcat.

In step S4, the NOx purification rate C is detected from the NOx catalyst temperature Tcat estimated in step S2.

In step S6, timers N1 to N3 are set. The periods N1 to N3 are set to optimal times by experiments and the like.

In step S8, it is determined whether the NOx purification rate C is less than a predetermined value C1.

In step S8, the NOx purification rate C is set to the predetermined value C.
If it is 1 or more (NO in step S8), normal engine control is executed in step S9.

In step S8, the NOx purification rate C is set to the predetermined value C.
If it is less than 1 (YES in step S8), the process proceeds to step S10 because the NOx purification rate C has decreased due to sulfur poisoning.

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 degree of catalyst temperature increase required.

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 equal to or higher than the predetermined temperature T1 in step S12 (step S1
2 is YES), the request for raising the temperature of the catalyst is high, so
If the catalyst temperature difference ΔT is less than the predetermined temperature T1 (NO in step S12), the process proceeds to step S22 because the request for raising the temperature of the catalyst is low.

In step S14, since the request for raising the temperature of the catalyst is high, the intake flow control valve is opened to make the swirl weak,
Increase exhaust gas temperature.

In step S16, the injection pulse width Ta is distributed to α: 1−α, and the early injection pulse Tak (= α × Ta) and the late injection pulse Tad (=
(1−α) × Ta) is calculated. However, α <0.5 is set to increase the late injection pulse width Tad.

In step S18, an early basic injection timing θakb and a late basic injection timing θadb required when the swirl is low are set.

In step S20, the late basic injection timing θadb required when the swirl is low is set. It should be noted that the late basic injection timing θadb is on the retard side with respect to the required value when the swirl is relatively weak.

On the other hand, when the request for raising the temperature of the catalyst is low, the intake flow control valve 17 is closed to increase the swirl in step S22.

In step S24, the injection pulse width Ta is distributed to α: 1−α, and the early injection pulse Tak (= α × Ta) and the late injection pulse Tad (=
(1−α) × Ta) is calculated. However, α ≧ 0.5 is set to reduce the late injection pulse width Tad.

In step S26, an early basic injection timing θakb and a late basic injection timing θadb required when the swirl is strong are set.

In step S28, the late basic injection timing θadb required when the swirl is strong is set. The late basic injection timing θad required when the swirl is strong
b is on the advance side relatively than the value required when the swirl is low.

In step S30, it is determined whether the flag F is 1 or not. If the flag F of the ignition timing θig retard is 1 (YES in step S30), the ignition timing θig (ignition retard) set in step S45 is determined. Then, the process proceeds to step S32.

On the other hand, if the flag F is not 1 in step S30 (NO in step S30), the process proceeds to step S31.

In step S31, an appropriate ignition timing θig that is on the advance side of the ignition timing θig set in step S45 is set.

In step S32, the crank angle sensor 2
When the crank angle of the engine detected from Step 3 reaches the set injection timing (YES in Step S32), the process proceeds to Step S34.

In step S34, fuel is injected from the injector 11 with the injection pulse widths Tak and Tad calculated in step S16 or S24.

As shown in FIG. 5, in step S36,
The ignition timing θig set in steps S31 to S45
Is reached (YES in step S36), the flow proceeds to step S38.

In step S38, the ignition plug 10 is turned on at the ignition timing θig set in steps S31 to S45.
Ignite.

In step S39, it is determined whether the flag F is 1 or not. If the flag F of the ignition timing θig retard is 1 (YES in step S39), the flow proceeds to step S44.

On the other hand, if the flag F is not 1 (NO in step S39), the process proceeds to step S40.

In steps S40 and S42, the engine control in steps S8 to S38 is continued until the countdown of the timer N2 is completed.

In step S44, it is determined whether or not the catalyst temperature difference ΔT is equal to or less than zero, that is, whether or not the catalyst temperature Tcat has increased to the temperature Tre required for the sulfur poisoning recovery process.

If the catalyst temperature Tcat has risen to the temperature Tre required for the sulfur poisoning recovery process in step S44 (YES in step S44), the process proceeds to step S47.

If the catalyst temperature Tcat has not risen to the temperature Tre required for the sulfur poisoning recovery process (NO in step S44), the process proceeds to step S45.

At step S45, the catalyst temperature Tca
In order to increase t, 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 in steps S8 to S38 is continued.

In step S47, the engine control in steps S8 to S38 based on the flow in step S46 is continued.

In steps S48 and S50, steps S8 to S3 are performed until the countdown of the timer N1 is completed.
The engine control up to 8 is continued.

In step S52, it is determined whether the NOx purification rate C is less than a predetermined value C2 (a value slightly larger than the predetermined value C1).

If the NOx purification rate C is equal to or more than the predetermined value C2 in step S52 (YES in step S52), the sulfur poisoning has been sufficiently recovered, so the flow proceeds to step S54 to execute a sulfur poisoning recovery control end process. To return.

If the NOx purification rate C is less than the predetermined value C2 in step S52 (NO in step S52), the process proceeds to step S56 because sulfur poisoning has not been sufficiently recovered.

In steps S56, S58 and S60, steps S8 and S8 are repeated until the countdown of the timer N3 is completed.
The engine control from S38 to S38 is continued to extend the sulfur poisoning recovery process.

FIG. 7 is a map showing the operating range of the engine. FIG. 8 is a diagram showing a change in exhaust gas temperature due to the catalyst temperature increase control of the present embodiment. FIG. 9 is a diagram showing the relationship between the exhaust gas temperature and the indicated mean effective pressure according to the ignition timing. FIG. 10 is a timing chart showing the fuel injection amount and the injection timing in the two-split injection.

The stratified combustion region shown in FIG. 7 is a region in which fuel is injected only in the latter half of the compression stroke, thereby causing the air-fuel mixture to be unevenly distributed around the ignition plug 10 to perform stratified combustion. The region where λ = 1 is a region where fuel is injected during the first half of the intake stroke and the middle to second half of the compression stroke, and the air-fuel ratio of the entire combustion chamber is set to be substantially the stoichiometric air-fuel ratio (λ ≒ 1). The enrichment region is a region in which fuel is injected only in the first half of the intake stroke to the middle of the compression stroke.

The engine 1 shown in FIG. 1 has a stratification cavity 1 at the top of the piston 4 for trapping fuel injected from the injector 11 and guiding the fuel toward the spark plug 10.
2, the swirl ratio (swirl flow angular velocity / engine angular velocity) in the cylinder is such that when fuel is injected from the injector 11 after the middle stage of the compression stroke, the local air-fuel ratio in the vicinity of the spark plug 10 becomes rich due to late injection. ) Is set.

The sulfur poisoning recovery process of this embodiment is executed in the stratified combustion region shown in FIG. 7 and in the region where the engine load is low, and the air-fuel ratio is set to λ ≒ 1 to open the intake flow control valve 17. In this way, the swirl is weakened, and the fuel is injected in two divisions during the period from the intake stroke to the ignition timing, that is, the late injection after the middle stage of the compression stroke and the early injection earlier than the late injection.
Further, the late injection ratio is set larger than the first injection ratio.

As shown in FIG. 8, the ratio of the late injection is set to 20.
When the exhaust gas temperature is changed in the range of ~ 60%, the exhaust gas temperature increases as the late injection ratio increases, and the combustion speed is suppressed due to the weak swirl, the combustion becomes slow, and the exhaust gas temperature increases. Can be raised.
Further, since the engine load is low in the stratified region, deterioration in fuel efficiency can be minimized.

Here, the middle stage of the compression stroke is a middle period when the compression stroke is divided into three equal parts in the first half, the middle half and the second half as shown in FIG. 10, that is, BTDC (before top dead center) 12 in crank angle.
It means a period from 0 ° to BTDC 60 °. Therefore, the late injection is after BTDC 120 °. However, if the timing of the latter injection is too late, the combustion stability is impaired, as described later. Therefore, it is desirable to start the latter injection before the ３ period of the compression stroke elapses (up to 45 ° BTDC).

That is, as shown in FIG. 10, the late injection is set to start within a period from 120 ° before the top dead center to 45 ° before the top dead center in the compression stroke, and the early injection is performed before the late injection. At an appropriate time, for example, during the intake stroke.

Further, in addition to the above control, as shown by a 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.

As shown in FIG. 9, the retardation of the ignition timing is such that the variation rate of Pi (indicated average effective pressure) of the engine is about 5%.
Performed within the range of%. It should be noted that the Pi fluctuation rate is the standard deviation σ of Pi / the cycle average of Pi × 100.
(%). <Temperature increase control of other catalyst> Further, as another temperature increase control procedure, when the air-fuel ratio is set to λ ≒ 1 and divided injection is performed,
If the temperature of the NOx catalyst has not reached the temperature Tre required for the sulfur poisoning recovery process, the ignition timing is retarded. If the temperature of the NOx catalyst has not reached the temperature Tre, the ignition timing is set to a low swirl. Sometimes late injection timing is delayed,
Alternatively, even if the ignition timing is retarded, if the NOx catalyst temperature does not reach the temperature Tre required for the sulfur poisoning recovery processing, the ignition timing is returned, the swirl is lowered, and if it does not reach the temperature Tre, the late injection timing , The deterioration of fuel efficiency can be minimized.

In the case of an engine equipped with a supercharger as in the present embodiment, supercharging is not required in a low engine load region. And the temperature of the exhaust gas flowing through the catalyst is kept high, so that the temperature raising effect can be further enhanced. <Temperature recovery control of catalyst after sulfur poisoning recovery control> Next, after sulfur poisoning recovery control of the lean NOx catalyst, the catalyst which has been heated to 600 ° C. or higher and has a low NOx purification rate has a high NOx purification rate rapidly. A description will be given of the catalyst temperature return control for returning the temperature to the temperature range of about 400 ° C.

FIG. 6 is a flowchart showing the catalyst temperature return control in the direct injection gasoline engine of the present embodiment.

First, an outline of the catalyst temperature return control will be described.

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 a high temperature state of the catalyst that deviates from the purifiable temperature range after the sulfur poisoning recovery process, the NOx catalyst temperature However, there is an inconvenience that the NOx adsorption performance is low until the water content decreases.

Therefore, in this embodiment, the lean NOx
When the catalyst is warmed up, the NOx catalyst temperature that deviates from the purifiable temperature range after the sulfur poisoning recovery processing is immediately replaced with NOx.
The following control is executed to return the temperature to a temperature range where the purification rate is high (lowering the temperature).

Before shifting the air-fuel ratio from λ ≦ 1 to the lean region of λ> 1, the air-fuel ratio is set to λ ≒ 1 while maintaining the swirl strength.

When the air-fuel ratio shifts from the operating state by split injection to the lean region where λ> 1 when the air-fuel ratio is λ <1 to λ ≒ 1, at least the late injection timing is advanced.

When releasing the adsorbed NOx, at the time of so-called NOx purging, the air-fuel ratio is set to λ <1 to λ ≒ 1, and the fuel is divided at least twice during the period from the intake stroke to the ignition timing. In addition to the injection, before the operation state shifts to the lean region of λ> 1, the air-fuel ratio is set to λ ≒ 1 while maintaining the swirl strength.

Next, a specific flow of the engine control ECU 30 for executing the above-mentioned controls will be described with reference to FIG.

As shown in FIG. 6, in step S62,
The engine control ECU 30 determines whether or not the intake flow control valve 17 is in a closed state while the air-fuel ratio is maintained at λ ≒ 1.

If it is in the closed state in step S62 (YES in step S62), the swirl strength is maintained, and
Proceed to 64.

In step S64, step S45 is performed.
The retard of the ignition timing θig set in the step is ended.

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.

If it is in the open state in step S62 (YES in step S62), the flow advances to step S68 to close the intake flow control valve to increase the swirl.

In step S70, step S18 is performed.
Alternatively, the late basic injection timing θadb set in S26 is advanced, and the process proceeds to Step S66.

FIG. 11 is a diagram showing the characteristics of the NOx purification rate with 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 catalyst temperature return control of the present embodiment.

As shown in FIG. 7 and FIG. 12, the temperature return control is performed after the sulfur poisoning recovery process, before the air-fuel ratio is shifted from the rich region where λ ≦ 1 to the stratified combustion region where λ> 1. As a result, the exhaust gas temperature is rapidly decreased as shown in FIG. 11 to suppress NOx purification of the catalyst heated to about 600 ° C. after the sulfur poisoning recovery control, while suppressing the deterioration of fuel efficiency and the decrease in combustion stability. Rate can be returned to a high temperature range of about 400 ° C., during which the air-fuel ratio is set to λ ≒ 1
, NOx can be purified in the purification window of the three-way catalyst.

Further, even in the specification without the three-way catalyst, by setting the air-fuel ratio λ ≒ 1, the exhaust gas can be purified by using the three-way function of the NOx catalyst.

Further, the closing operation of the intake flow control valve for increasing the swirl is performed in the low engine load and low engine speed regions where the amount of intake air to the combustion chamber is small, and the high load and high engine speed in which the output efficiency decreases. It is desirable not to do it in the area. Note that, instead of swirl, other means such as an intake valve may be used to enhance the intake flow.

Further, when the air-fuel ratio shifts from the operating state by the divided injection at λ <1 to λ ≒ 1 to the lean region of λ> 1, at least the advanced injection timing is advanced, so that the exhaust gas temperature can be more rapidly increased. Can be reduced.

In particular, NOx adsorbed by the lean NOx catalyst
And NOx is reduced by the reduction purification function of this catalyst.
When the catalyst refresh for reducing x is executed, the air-fuel ratio is set to λ <1 to λ ≒ 1, and when fuel is injected at least twice during the period from the intake stroke to the ignition timing, NOx and Since the reacting CO can be increased, N
Ox can be efficiently purified.

The present invention can be applied to a modification or modification of the above embodiment without departing from the gist of the invention.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a structure of a combustion chamber portion of a direct injection engine according to an embodiment.

FIG. 2 is a schematic view of the entire in-cylinder injection engine.

FIG. 3 is a diagram showing various parameters input to an engine control ECU for executing state detection and engine control of an engine and a catalyst.

FIG. 4 is a flowchart illustrating control for increasing the temperature of a catalyst in the direct injection gasoline engine of the present embodiment.

FIG. 5 is a flowchart illustrating control for increasing the temperature of the catalyst in the direct injection gasoline engine of the present embodiment.

FIG. 6 is a flowchart showing catalyst temperature return control in the direct injection gasoline engine of the embodiment.

FIG. 7 is a map showing an operation region of the engine.

FIG. 8 is a diagram illustrating a change in exhaust gas temperature due to a catalyst temperature increase control of the present embodiment.

FIG. 9 is a diagram showing the relationship between the exhaust gas temperature and the indicated mean effective pressure according to the ignition timing.

FIG. 10 is a timing chart showing a fuel injection amount and an injection timing in two-split injection.

FIG. 11 is a graph showing characteristics of a NOx purification rate according to a temperature change of a lean NOx catalyst and a three-way catalyst.

FIG. 12 is a diagram showing a change in exhaust gas temperature due to the catalyst temperature return control 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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/28 301 F02B 31/00 321E F02B 31/00 321 F02D 41/02 325G F02D 41/02 325 325A 41 / 34 H 41/34 E 43/00 301U 43/00 301 301H 301J 301T B01D 53/36 101Z (72) Inventor Keiji Araki No.3-1 Fuchi-cho, Fuchu-cho, Aki-gun, Hiroshima F-term (reference) 3G084 AA00 AA04 BA09 BA13 BA15 BA21 CA03 CA09 DA10 FA01 FA02 FA07 FA10 FA20 FA27 FA29 FA33 FA38 3G091 AA02 AA11 AA12 AA17 AA24 AA28 AB03 AB06 BA04 BA11 BA14 BA15 BA19 BA32 BA33 CA13 CB02 DB15 EA01 DA01 CB05 EA05 EA16 EA18 EA26 EA30 EA31 EA34 FB03 FB10 FB11 FB12 FC08 HA08 HA36 HB03 HB05 HB06 3G301 HA01 HA04 HA16 HA17 JA25 KA08 KA24 LA03 LA05 LB04 MA18 MA26 NE11 NE13 NE14 NE15 PA01Z PA09Z PA10Z PD03A PD03Z PD12Z PE01Z PE03Z PE08Z PF03Z 4D048 AA06 AB02 AC02 BC05 DA02 DA13

Claims (5)

[Claims] An engine includes: a fuel injection valve that injects fuel directly into a 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. In a control device for a direct injection engine in which a lean region where an air-fuel ratio is λ> 1 is set in a partial load region, a temperature detecting means for detecting a temperature state of the NOx catalyst, and a forcible flow strength of intake air in the cylinder. Means for changing the operating state of the engine from the region where the air-fuel ratio λ ≦ 1 to the lean region where λ> 1 when the NOx catalyst deviates from the NOx purifying temperature range at a high temperature. A control device for a direct injection engine, wherein the variable means is operated so as to set the air-fuel ratio to λ ≒ 1 while increasing the intake flow strength. 2. During the period from the intake stroke to the ignition timing, fuel is divided into at least two times, namely, late injection after the middle stage of the compression stroke and early injection earlier than the latter injection, and the air-fuel ratio λ < 2. The control device for a direct injection engine according to claim 1, wherein at the time of shifting from the operating region of 1 to λ ≒ 1 to the lean region of λ> 1, at least the late injection timing is advanced. 3. The air-fuel ratio λ <1 during execution of NOx release reduction
To λ ≒ 1, the fuel is injected at least twice during the period from the intake stroke to the ignition timing, and when the NOx catalyst deviates from the NOx purifying temperature range, the air-fuel ratio operating the variable means so as to set the air-fuel ratio to λ ≒ 1 while increasing the intake flow strength before shifting from the operation range of λ <1 to λ ≒ 1 to the lean region of λ> 1. The control apparatus for a direct injection type engine according to claim 1, wherein: And a fuel injection valve for directly injecting fuel into the combustion chamber, and a NOx catalyst for adsorbing NOx in an exhaust passage in an oxygen-excess atmosphere and releasing the adsorbed NOx as the oxygen concentration decreases. Air-fuel ratio is λ in the load range
A control device for an in-cylinder injection engine in which a lean region of> 1 is set, comprising: a variable means for forcibly changing the intake flow strength in the cylinder; The air-fuel ratio in the cylinder is set in the operating range of λ ≒ 1 to λ <1, and during the period from the intake stroke to the ignition timing, at least the late injection after the middle stage of the compression stroke and the early injection earlier than the latter injection. The variable means is operated so as to inject fuel in two parts and to reduce the intake flow strength, while the air-fuel ratio is changed to λ ≒ before shifting from the operation range to the lean range of λ> 1. A control apparatus for a direct injection engine, wherein the variable means is operated so as to increase the intake flow strength while setting it to 1, thereby at least advancing the late injection timing. 5. The control device for a direct injection engine according to claim 1, wherein the intake flow strength is increased in a low load or low rotation region of the engine.