JPH10184418A - Exhaust purifying device for lean combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of the difference in level of torque when nitrogen oxide is reduced and discharged, and prevent worsening of fuel consumption, in a lean combustion engine having a nitrogen oxide storage reduction catalyst. SOLUTION: A fuel injection valve 11 is arranged at the peripheral part of the inner wall surface of a cylinder head 4 in the vicinity of the first and second intake valves 6a and 6b of an engine 1, and fuel from the fuel injection valve 11 is injected directly in a cylinder 1a. A throttle valve 23 opened and closed by a step motor 22 is disposed in an intake duct 20, and a nitrogen oxide storage reduction catalyst 56 is arranged in an exhaust duct 55. When an electronic control device(ECU) 30 performs rich spike control, an air-fuel ratio is increased by fundamentally reducing a throttle opening not merely by increasing a fuel injection amount. This constitution controls an air-fuel ratio to the rich side and executes reduction of a nitrogen oxide. Thus, torque is not rapidly increased and there is no need to effect a delay of an ignition timing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device for a lean burn engine, and more particularly to an exhaust emission control device for a lean burn engine having a nitrogen oxide storage reduction catalyst in an exhaust passage of the engine. .

[0002]

2. Description of the Related Art In a conventionally used engine, fuel from a fuel injection valve is injected into an intake port, and a homogeneous mixture of fuel and air is supplied to a combustion chamber in advance. In such an engine, an intake passage is opened and closed by a throttle valve linked to an accelerator operation, and by this opening and closing, the amount of intake air supplied to a combustion chamber of the engine (consequently, a gas mixture in which fuel and air are homogeneously mixed). ) Is adjusted, thereby controlling the engine output.

[0003] However, in the technique based on the so-called homogeneous combustion described above, a large intake negative pressure is generated in accordance with the throttle operation of the throttle valve, and the pumping loss increases to lower the efficiency. On the other hand, by reducing the throttle of the throttle valve and supplying fuel directly to the combustion chamber, a combustible mixture is present near the ignition plug, and the air-fuel ratio of the portion is increased,
There is known a so-called "stratified combustion" technique for improving ignitability.

In this technique, when the engine is under a low load, the injected fuel is supplied unevenly around the spark plug, and the throttle valve is almost fully opened to perform stratified combustion. Thereby, the pumping loss is reduced, and the fuel efficiency is improved.

[0005] Incidentally, in an engine that operates at a lean air-fuel ratio, such as the above-described stratified combustion,
Nitrogen oxides (NOx) easily generated in the lean air-fuel ratio range
In order to purify NOx, a NOx storage reduction catalyst device is used.

[0006] The NOx storage reduction catalyst is mainly composed of, for example, zeolite, and contains hydrocarbons (H
It is estimated that C) temporarily adsorbs C) and reduces NOx with this HC. As a technology having such a NOx storage reduction catalyst device, for example, Japanese Unexamined Patent Publication No.
One disclosed in Japanese Patent No. 824 is known. In this technique, so-called rich spike control is performed as basic control. That is, if the operation at the lean air-fuel ratio is continued, the NOx adsorbed on the catalyst reaches a saturated state, and there is a possibility that excess NOx may be released into the exhaust gas. Therefore, in the present control, the air-fuel ratio is temporarily and forcibly controlled to be rich in anticipation of a predetermined timing. By performing such control, the amount of HC in the exhaust gas increases, and NOx is reduced to nitrogen gas (N ₂ ) and released to the atmosphere.

[0007]

However, the above technique has the following problems. That is, during the rich spike control, the air-fuel ratio is forcibly made rich. In this case, the fuel injection amount is increased. For this reason, the torque may increase sharply, and a so-called torque shock may occur. In particular, when combustion is performed in a super-lean state represented by stratified charge combustion, the amount of intake air is large. Therefore, when the fuel is forcibly made rich, the fuel injection amount also increases, and the torque increases. There was a risk that the degree of increase would be large.

In order to suppress such an increase in torque, it is conceivable to retard the ignition timing together with an increase in the amount of fuel. However, in such a case, the generated torque per unit injection amount becomes small, and as a result, the fuel consumption is reduced.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a lean-burn engine having a nitrogen oxide storage-reduction catalyst and capable of performing lean-burn and stoichiometric combustion. In the exhaust purification device of
To provide an exhaust gas purification device for a lean burn engine that can suppress the occurrence of a torque step when reducing and releasing nitrogen oxides stored in a nitrogen oxide storage reduction catalyst and prevent deterioration of fuel efficiency. It is in.

[0010]

In order to achieve the above object, according to the first aspect of the present invention, as shown in FIG. 1, a cylinder of an engine M1 is used to perform lean combustion and combustion at a stoichiometric air-fuel ratio. Fuel injection means M2 capable of supplying fuel to the inside
An intake air amount adjusting unit M3 for adjusting an intake air amount introduced into the engine M1, an operating state detecting unit M4 for detecting an operating state of the engine M1, and a detection result of the operating state detecting unit M4. An exhaust gas purification device for a lean burn engine, comprising: an intake air amount control means M5 for controlling the intake air amount adjusting means M3; and a nitrogen oxide storage reduction catalyst M7 provided in an exhaust passage M6 of the engine M1. When reducing and releasing the nitrogen oxides stored in the nitrogen oxide storage reduction catalyst M7, the amount of intake air introduced into the engine M1 is reduced by controlling the intake amount adjusting means M3. The gist of the invention is to provide an intake amount decrease control unit M8 for enriching the air-fuel ratio.

According to a second aspect of the present invention, in the exhaust gas purifying apparatus for a lean burn engine according to the first aspect,
Further, when the intake air amount is reduced by the intake amount decrease control unit M8, the fuel injection unit M2 is controlled to increase the fuel supply amount in accordance with the degree of the decrease, and the injection amount control for suppressing the torque decrease is performed. The point is that the means M9 is provided.

Further, according to a third aspect of the present invention, in the exhaust gas purifying apparatus for a lean burn engine according to the first or second aspect, the intake air amount adjusting means M3 includes the engine M1.
The gist of the present invention is that the electronically controlled throttle mechanism is constituted by a throttle valve provided in the intake passage and an actuator for opening and closing the throttle valve.

According to a fourth aspect of the present invention, in the exhaust gas purifying apparatus for a lean burn engine according to the first or second aspect, the intake air amount adjusting means M3 includes the engine M1.
Exhaust gas recirculation passage connecting the exhaust passage M6 to the intake passage and an EG for opening and closing the exhaust gas recirculation passage
An EGR mechanism for recirculating a part of exhaust gas discharged from the engine M1 to intake air taken into the engine M1 has an R valve, and the amount of intake air introduced into the engine M1 is controlled by an EGR mechanism. The gist of the present invention is to increase the degree of opening of the EGR valve when decreasing it.

In addition, according to the fifth aspect of the present invention, in the exhaust purification system for a lean burn engine according to any one of the second to fourth aspects, the degree of increase in the fuel supply amount by the injection amount control means M9 is as follows. The gist is that the determination is made based on the difference between the calculated pressure in the intake passage and the actual pressure.

Furthermore, in the invention according to claim 6,
The exhaust purifying apparatus for a lean burn engine according to any one of claims 1 to 5, wherein the gist is that the engine M1 is capable of performing stratified combustion.

(Operation) According to the first aspect of the present invention,
As shown in FIG. 1, fuel is supplied into the cylinder of the engine M1 by the fuel injection means M2, and the fuel in the cylinder burns, so that the engine M1 obtains a driving force. Also,
Lean combustion and combustion at the stoichiometric air-fuel ratio can be performed by the fuel in the cylinder of the engine M1.

Further, the intake air amount introduced into the engine M1 is adjusted by the intake air amount adjusting means M3. Then, the operating state of the engine M1 is detected by the operating state detecting means M4, and based on the detection result, the intake air amount adjusting means M3 is controlled by the intake air amount controlling means M5.

In the present invention, the exhaust passage M6 of the engine M1
The nitrogen oxides can be stored by the nitrogen oxide storage-reduction catalyst M7 provided in the above. The stored nitrogen oxides can be reduced by making the air-fuel ratio rich. Now, in the present invention, when the nitrogen oxides stored in the nitrogen oxide storage reduction catalyst M7 are reduced and released, the intake air amount adjustment means M3 is controlled by the intake air amount reduction control means M8, The amount of intake air introduced into engine M1 is reduced. Thereby, the air-fuel ratio is controlled to the rich side, and the reduction of nitrogen oxides is executed. Accordingly, a sudden increase in torque is suppressed by increasing the fuel injection amount in response to a decrease in torque due to pumping loss due to a decrease in the intake air amount. Further, since there is no need to retard the ignition timing, a reduction in output per unit time can be suppressed.

According to the second aspect of the present invention, in addition to the operation of the first aspect, when the intake air amount is reduced by the intake amount decrease control means M8, The fuel injection means M2 is controlled by the injection amount control means M9 according to the degree of the decrease to increase the fuel supply amount. For this reason, a decrease in torque due to a decrease in the intake air amount can be suppressed.

Further, according to the third aspect of the present invention,
In addition to the functions of the invention described in claims 1 and 2, the intake air amount adjusting means M3 includes an electronically controlled throttle comprising a throttle valve provided in an intake passage of the engine M1 and an actuator for opening and closing the throttle valve. It is constituted by a mechanism. For this reason, the above-mentioned operation is achieved with existing equipment.

In addition, according to the invention described in claim 4,
In addition to the functions of the invention described in claims 1 and 2, the intake air amount adjusting means M3 opens and closes an exhaust gas recirculation passage connecting the exhaust passage M6 and the intake passage of the engine M1 and the exhaust gas recirculation passage. And a part of the exhaust gas discharged from the engine M1.
It is constituted by an EGR mechanism for recirculating to the intake air taken into the engine. When the amount of intake air introduced into the engine M1 is reduced, the opening of the EGR valve is increased. For this reason, the above-mentioned action is also exerted by the existing equipment. Further, the fuel efficiency can be improved as compared with the case of the third aspect of the invention.

In addition, according to the fifth aspect of the present invention,
In addition to the effect of the invention according to claims 2 to 4, the degree of increase in the fuel supply amount by the injection amount control means M9 is determined based on the difference between the calculated pressure in the intake passage and the actual pressure. Is done. Here, the difference between the calculated pressure in the intake passage and the actual pressure corresponds to the degree of pumping loss.
Therefore, the fuel supply amount is increased according to the loss,
It is possible to minimize fluctuations in torque.

According to the sixth aspect of the present invention, in addition to the functions of the first to fifth aspects, the engine M1 can perform stratified combustion. Here, when stratified combustion is performed, the amount of intake air is also large. For this reason, the above-mentioned operation becomes more effective.

[0024]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an exhaust gas purifying apparatus for a stratified combustion engine according to the present invention.

FIG. 2 is a schematic configuration diagram showing a fuel injection control device for a direct injection type engine mounted on a vehicle in the present embodiment. The engine 1 as an internal combustion engine includes, for example, four cylinders 1a, and the combustion chamber structure of each of the cylinders 1a is shown in FIG. As shown in these figures,
The engine 1 includes a piston in a cylinder block 2, and the piston reciprocates in the cylinder block 2. The cylinder head 4 is located above the cylinder block 2.
Is provided, and a combustion chamber 5 is formed between the piston and the cylinder head 4. Further, in the present embodiment, four valves are arranged per cylinder 1a, and in the figure, the first intake valve 6a, the second intake valve 6b, the first intake port 7a, and the first intake port 7b in the figure. Two intake ports, a pair of exhaust valves as 8, and a pair of exhaust ports as 9 are shown.

As shown in FIG. 3, the first intake port 7a
Is composed of a helical intake port, and the second intake port 7
b consists of a straight port extending almost straight.
In addition, an ignition plug 10 is disposed at the center of the inner wall surface of the cylinder head 4. This spark plug 10 includes:
The igniter 12 via a distributor (not shown)
Is applied. And
The ignition timing of the ignition plug 10 is determined by the igniter 1
2 is determined by the output timing of the high voltage. Further, a fuel injection valve 11 as a fuel injection means is disposed around the inner wall surface of the cylinder head 4 near the first intake valve 6a and the second intake valve 6b. That is, in the present embodiment, the fuel from the fuel injection valve 11 is directly injected into the cylinder 1a.

As shown in FIG. 2, the first intake port 7a and the second intake port 7b of each cylinder 1a are respectively connected via a first intake path 15a and a second intake path 15b formed in each intake manifold 15. Connected to the surge tank 16. A swirl control valve 17 is arranged in each second intake passage 15b. These swirl control valves 17 are connected to, for example, a step motor 19 via a common shaft 18. The step motor 19 is controlled based on an output signal from an electronic control unit (hereinafter simply referred to as “ECU”) 30 described later. Instead of the step motor 19, a motor controlled according to the negative pressure of the intake ports 7a and 7b of the engine 1 may be used.

The surge tank 16 includes an intake duct 20
Is connected to the air cleaner 21 through the intake duct 20.
Inside, a throttle valve 23 as an intake air amount adjusting means which is opened and closed by a step motor 22 is provided.
That is, the throttle valve 23 of the present embodiment is of a so-called electronic control type. Basically, the throttle valve 23 is opened and closed by the step motor 22 being driven based on the output signal from the ECU 30. Controlled.
By opening and closing the throttle valve 23, the amount of intake air introduced into the combustion chamber 5 through the intake duct 20 is adjusted. In the present embodiment, the intake duct 20, the surge tank 16, and the first intake path 15a
The second intake passage 15b and the like constitute an intake passage.

In the vicinity of the throttle valve 23, a throttle sensor 25 for detecting the opening (throttle opening TA) is provided. An exhaust manifold 14 is connected to the exhaust port 9 of each cylinder.
Then, the exhaust gas after combustion is discharged to an exhaust duct 55 forming an exhaust passage via the exhaust manifold 14.

Further, in the present embodiment, a known exhaust gas recirculation (EGR) mechanism 51 is provided. This E
The GR mechanism 51 includes an EGR passage 52 as an exhaust gas recirculation passage, and an EGR valve 53 provided in the middle of the EGR passage 52. The EGR passage 52 is provided so as to communicate between the intake duct 20 downstream of the throttle valve 23 and the exhaust duct 55. The EGR valve 53 has a built-in valve seat, valve body, and step motor (all not shown). The opening degree of the EGR valve 53 fluctuates when the stepping motor intermittently displaces the valve body with respect to the valve seat. When the EGR valve 53 is opened, a part of the exhaust gas discharged to the exhaust duct 55 flows to the EGR passage 52. The exhaust gas is E
It flows to the intake duct 20 via the GR valve 53. That is, a part of the exhaust gas is recirculated into the intake air-fuel mixture by the EGR mechanism 51. At this time, the recirculation amount of the exhaust gas is adjusted by adjusting the opening degree of the EGR valve 53.

In addition, in the present embodiment, a nitrogen oxide storage reduction catalyst 56 is provided in the exhaust duct 55. Basically, when the catalyst 56 is operated at a lean air-fuel ratio, nitrogen oxide (NO
x) is absorbed. When the air-fuel ratio is controlled to be rich, the amount of stored NO is increased due to an increase in the amount of HC in the exhaust gas.
x is reduced to nitrogen gas (N ₂ ) and released into the atmosphere.

The above-described ECU 30 is a digital computer, and is connected to a RAM (random access memory) 3 via a bidirectional bus 31.
2, a ROM (Read Only Memory) 33, a CPU (Central Processing Unit) 34 composed of a microprocessor, an input port 35 and an output port 36. In the present embodiment, the ECU 30 constitutes an intake amount control unit, an intake amount decrease control unit, and an injection amount control unit.

Accelerator pedal 2 operated by driver
4 is connected to an accelerator sensor 26A that generates an output voltage proportional to the amount of depression of the accelerator pedal 24,
Accelerator opening ACCP is detected by accelerator sensor 26A. The output voltage of the accelerator sensor 26A is
The signal is input to the input port 35 via the AD converter 37.
Similarly, the accelerator pedal 24 is provided with a fully-closed switch 26B for detecting that the depression amount of the accelerator pedal 24 is "0". That is, the fully closed switch 26B generates a signal of "1" as the fully closed signal when the depression amount of the accelerator pedal 24 is "0", and generates a signal of "0" otherwise. The output voltage of the fully closed switch 26B is also input to the input port 35.

The top dead center sensor 27 generates an output pulse when the first cylinder 1a reaches the intake top dead center, for example.
This output pulse is input to the input port 35. The crank angle sensor 28 has a crankshaft of 30 ° CA, for example.
An output pulse is generated each time the motor rotates, and the output pulse is input to the input port. In the CPU 34, the top dead center sensor 2
7 and the output pulse of the crank angle sensor 28, the engine speed NE is calculated (read).

Further, the rotation angle of the shaft 18 is detected by a swirl control valve sensor 29,
Thereby, the opening of the swirl control valve 17 is measured. The output of the swirl control valve sensor 29 is supplied to an input port 35 via an A / D converter 37.
Is input to

At the same time, the throttle sensor 25 detects the throttle opening degree TA. The output of the throttle sensor 25 is input to an input port 35 via an A / D converter 37.

In addition, in the present embodiment, an intake pressure sensor 61 for detecting the pressure (intake pressure PiM) in the surge tank 16 is provided. Further, a water temperature sensor 62 that detects the temperature of the cooling water of the engine 1 (cooling water temperature THW) is provided. Further, an oxygen sensor 63 for detecting the oxygen concentration OX in the exhaust gas is provided in the middle of the exhaust passage upstream of a three-way catalyst (not shown). The oxygen sensor 63 has a characteristic that the output voltage changes abruptly near the stoichiometric air-fuel ratio. In the present embodiment, the air-fuel ratio A / F is detected based on such characteristics. The outputs of these sensors 61, 62, 63 are also
The data is input to the input port 35 via the A / D converter 37.

In this embodiment, the throttle sensor 25, the accelerator sensor 26A, the full-close switch 26
B, top dead center sensor 27, crank angle sensor 28, swirl control valve sensor 29, intake pressure sensor 61,
The water temperature sensor 62 and the oxygen sensor 63 constitute an operating state detecting means.

On the other hand, the output port 36 is connected to each of the fuel injection valves 11 and each of the step motors 1 via a corresponding drive circuit 38.
9, 22, the igniter 12 and the EGR valve 53 (step motor). Then, the ECU 30 operates according to a control program stored in the ROM 33 based on signals from the sensors 25 to 29 and 61 to 63 and the like.
The fuel injection valve 11, the step motors 19 and 22, the igniter 12 (spark plug 10), the EGR valve 53 and the like are suitably controlled.

Next, a program relating to various controls according to the present embodiment in the exhaust gas purifying apparatus for an engine having the above configuration will be described with reference to a flowchart. 4 and 5 show the throttle valve 2 according to the present embodiment.
3 is a flowchart showing a “rich spike control routine” for controlling combustion of the engine 3 and the like, and is executed by the ECU 30 in an interrupt every predetermined crank angle.

When the processing shifts to this routine, the ECU
30 is a step 101 in which the engine speed N
E and the basic injection amount Qinj calculated by a separate routine
Read.

Next, in step 102, it is determined whether or not the currently set basic rich spike flag Xrich is set to "ON". here,
The basic rich spike flag Xrich is determined by a separate routine.
"ON" based on the amount of NOx adsorbed on the fuel (e.g., set by a counter), the accumulated time of fuel cut, etc.
Alternatively, the setting is switched to “OFF”. And
When the basic rich spike flag Xrich is set to “OFF”, the amount of NOx adsorbed on the nitrogen oxide storage reduction catalyst 56 has not yet reached a saturated state, and there is no need to perform rich spike control. Step 1 as
Shift to 03.

In step 103, a target throttle opening degree trtat is calculated based on the current engine speed NE and the basic injection amount Qinj by referring to a map (map TRTO) (not shown). Similarly, the current engine speed NE and the basic injection amount Qinj
, The target injection amount qinj is calculated by taking into account a map (not shown) (map QINJ0). Further, the current engine speed NE and the basic injection amount Qin
Based on j, the target ignition timing sa is calculated by referring to a map (map SA0) not shown. Then, the ECU 30 once ends the subsequent processing.

If it is determined in step 102 that the basic rich spike flag Xrich is set to "ON", the process proceeds to step 104 on the assumption that the rich spike control needs to be performed.

In step 104, it is determined whether or not the first-stage rich spike flag Xrich (1) is set to "OFF". If the first-stage rich spike flag Xrich (1) is “OFF”, the process proceeds to step 105 on the assumption that the first-stage rich spike control has not been executed. In step 105, the current engine speed NE and the basic injection amount Qinj
, The target throttle opening degree trtat is calculated by taking into account a first-stage rich spike map (map TRT1) (not shown). As a result, the throttle opening becomes somewhat smaller than in the case of step 103, and the air-fuel ratio A / F becomes somewhat richer than before.

Similarly, the current engine speed NE
Based on the basic injection amount Qinj and the first-stage rich spike map (map QINJ1) (not shown), the target injection amount qinj is calculated. As a result, the fuel injection amount is slightly increased by the degree that the throttle opening is somewhat reduced. Therefore, a decrease in the throttle opening may cause a decrease in the torque. However, since the injection amount is increased, the decrease in the torque is suppressed. Further, the current engine speed NE and the basic injection amount Qinj
, The target ignition timing sa is calculated by taking into account a first-stage rich spike map (map SA1) (not shown).

Further, in the following step 106,
The count value crich of the rich spike counter is incremented by "1". Next, step 107
In, it is determined whether or not the count value crich is equal to or greater than a predetermined value (corresponding to a predetermined time) Cr1. If the count value crich has not reached the predetermined value Cr1 or more, the subsequent processing is temporarily terminated. Therefore, in this case, step 1 is performed until the count value crich becomes equal to or more than the predetermined value Cr1.
05 is repeated. On the other hand, the count value c
If rich is equal to or greater than the predetermined value Cr1, the process proceeds to step 108.

In step 108, it is determined whether or not the return rich spike flag Xrich is "OFF". The return rich spike flag Xrich is set to “ON” at a return point (step 405) of the rich spike control described later, and when the rich spike control ends (step 70).
In 1), “OFF” is set. Therefore, when the process proceeds to step 108 for the first time during the trip, the return rich spike flag Xrich is set to “OFF”.
Move to 09.

In step 109, the first-stage rich spike flag Xrich (1) is set to "ON" in order to end the first-stage rich spike control. At the same time, the count value crich of the rich spike counter is set to “0”. Then, the subsequent processing ends once.

In step 104, the first
When the step rich spike flag Xrich (1) is set to “ON” (when step 109 has already been performed)
Then, the process proceeds to step 201 to perform the second-stage rich spike control. In step 201, it is determined whether or not the second-stage rich spike flag Xrich (2) is set to “OFF”. If the second-stage rich spike flag Xrich (2) is “OFF”, it is determined that the second-stage rich spike control has not been executed, and the process proceeds to step 202. Step 2
In 02, the target throttle opening degree trtat is calculated based on the current engine speed NE and the basic injection amount Qinj by referring to a second-stage rich spike map (map TRT2) (not shown). Also,
Similarly, the current engine speed NE and the basic injection amount Qi
Based on nj, a target injection amount qinj is calculated by referring to a second-stage rich spike map (map QINJ2) (not shown). Further, based on the current engine speed NE and the basic injection amount Qinj, a second-stage rich spike map (not shown) (map SA
The target ignition timing sa is calculated by taking into account 2).

Further, in the following step 203,
The count value crich of the rich spike counter is incremented by "1". Next, step 204
In, it is determined whether or not the count value crich is equal to or greater than a predetermined value (corresponding to a predetermined time) Cr2. If the count value crich has not reached the predetermined value Cr2 or more, the subsequent processing is temporarily terminated. Therefore, in this case, step 2 is repeated until the count value crich becomes equal to or more than the predetermined value Cr2.
02 is repeated. On the other hand, the count value c
If rich is equal to or greater than the predetermined value Cr2, the process proceeds to step 205.

In step 205, it is determined whether or not the return rich spike flag Xrich is "OFF". As described above, during the trip, when the process proceeds to step 205 for the first time,
The return rich spike flag Xrich is "OF
Since F is set to “F”, the process proceeds to step 206 in this case.

In step 206, the second-stage rich spike flag Xrich (2) is set to "ON" to end the second-stage rich spike control. At the same time, the count value crich of the rich spike counter is set to “0”. Then, the subsequent processing ends once.

In the step 201, the second
When the step rich spike flag Xrich (2) is set to “ON” (when step 206 has already been performed)
Then, the process proceeds to step 301 to perform the rich spike control of the ith stage (i = 3, 4, 5,...) (See FIG. 5). In step 301, it is determined whether or not the i-th stage rich spike flag Xrich (i) is set to “OFF”. When the i-th stage rich spike flag Xrich (i) is “OFF”, the process proceeds to step 302 on the assumption that the i-th stage rich spike control has not been executed. In step 302, the current engine speed NE and the basic injection amount Qinj
, The target throttle opening degree trtat is calculated by referring to a map (map TRTi) for the i-th stage rich spike (not shown). Similarly, based on the current engine speed NE and the basic injection amount Qinj, a target injection amount qi is obtained by referring to a map (map QINJi) for the i-th stage rich spike (not shown).
Calculate nj. Further, based on the current engine speed NE and the basic injection amount Qinj, the target ignition timing sa is calculated by referring to a map (map SAi) for the i-th stage rich spike (not shown).

Further, in the following step 303,
The count value crich of the rich spike counter is incremented by "1". Next, step 304
In, it is determined whether or not the count value crich is equal to or greater than a predetermined value Cri (corresponding to a predetermined time). Then, if the count value crich has not yet reached the predetermined value Cri, the subsequent processing is temporarily terminated. Therefore, in this case, until the count value crich becomes equal to or more than the predetermined value Cri, the process proceeds to step 3
02 is repeated. On the other hand, the count value c
If rich is equal to or greater than the predetermined value Cri, the process proceeds to step 305.

In step 305, it is determined whether or not the return rich spike flag Xrich is "OFF". As described above, during the trip, when the process proceeds to step 305 for the first time,
The return rich spike flag Xrich is "OF
Since it is set to “F”, the process proceeds to step 306 in this case.

In step 306, the i-th stage rich spike flag Xrich (i) is set to "ON" to terminate the i-th stage rich spike control. At the same time, the count value crich of the rich spike counter is set to “0”. Then, the subsequent processing ends once.

In step 301, the i-th
When the step rich spike flag Xrich (2) is set to “ON” (when step 306 has already been performed)
Then, the process proceeds to step 401 to perform the rich spike control of the e-th stage (e = i + 1). In step 401, it is determined whether or not the e-th stage rich spike flag Xrich is set to “OFF”. Then, the e-stage rich spike flag Xrich is set to “OF”.
In the case of "F", it is determined that the rich spike control of the e-th stage has not been executed yet, and the routine proceeds to step 402.
In step 402, the current engine speed NE
Based on the basic injection amount Qinj and the e-stage rich spike map (map TRTe) (not shown), the target throttle opening degree trtat is calculated. Similarly, based on the current engine speed NE and the basic injection amount Qinj, the target injection amount qinj is calculated by referring to a map (map QINJe) for the rich spike at the e-th stage (not shown). Further, based on the current engine speed NE and the basic injection amount Qinj, the target ignition timing sa is calculated by referring to a map (map SAe) for the rich spike (not shown) in the e-th stage.

Further, in the following step 403,
The count value crich of the rich spike counter is incremented by "1". Next, step 404
In, it is determined whether or not the count value crich is equal to or greater than a predetermined value Cre (corresponding to a predetermined time). If the count value crich has not reached the predetermined value Cre or more, the subsequent processing is temporarily terminated. Therefore, in this case, until the count value crich becomes equal to or more than the predetermined value Cre, step 4 is performed.
02 is repeated. On the other hand, the count value c
If rich is equal to or greater than the predetermined value Cre, the process proceeds to step 405.

In step 405, the return rich spike flag Xrich is set to "ON" in order to end the rich spike control of the e-th stage. Also,
At the same time, the i-th rich spike flag Xrich (i) is executed again to execute the i-th rich spike control.
Is set to “OFF”. Further, the count value crich of the rich spike counter is set to “0”. Then, the subsequent processing ends once.

Now, after step 405, an affirmative determination is made in step 301. Therefore, in this case, the process of step 302 (i-th stage rich spike control) is executed. Then, when an affirmative determination is made in step 304,
In step 305, it is determined whether or not the return rich spike flag Xrich is set to "OFF". In this case, since the return rich spike flag Xrich has already been set to “ON” in step 405, the process proceeds to step 501.

In step 501, the i-th stage rich spike control is terminated, and then the (i-1) th stage rich spike flag Xrich (i-1) is executed to execute the (i-1) th stage rich spike control. ) Is set to “OFF”.
Furthermore, the count value cri of the rich spike counter
ch is set to “0”. Then, the subsequent processing ends once.

When the reverse process is repeated as described above, an affirmative determination is made again in step 202 (see FIG. 4). Therefore, in this case,
The process of step 202 (second-stage rich spike control) is executed again. If an affirmative determination is made in step 204, it is determined in step 205 whether the return rich spike flag Xrich is set to "OFF". In this case, the return rich spike flag X has already been set in step 405.
Since “rich” is set to “ON”, the process proceeds to step 601.

In step 601, the second stage rich spike control is terminated, and then the first stage rich spike flag Xrich is executed to execute the first stage rich spike control.
(1) is set to “OFF”. Further, the count value crich of the rich spike counter is set to “0”. Then, the subsequent processing ends once.

Subsequently, in step 104, a positive determination is made again. Therefore, in this case, the process of step 105 (first-stage rich spike control) is executed again. Then, when an affirmative determination is made in step 107, in step 108,
The return rich spike flag Xrich is "OF
F "is set. in this case,
Since the return rich spike flag Xrich has already been set to “ON” in step 405, the processing shifts to step 701.

In step 701, a rich spike flag Xric is set to end all rich spike control.
Set h to “OFF”. Further, the return rich spike flag Xrich is also set to “OFF”. Also, the count value cri of the rich spike counter
ch is set to “0”. Then, the subsequent processing ends once.

Next, the operation and effect of this embodiment will be described. (A) In the present embodiment, the rich spike flag Xri
When the channel becomes “ON”, rich spike control is performed. In this case, instead of simply increasing the fuel injection amount, the air-fuel ratio A / F is increased by basically reducing the throttle opening. As a result, the air-fuel ratio A / F is controlled to the rich side, and the reduction of the nitrogen oxide adsorbed on the nitrogen oxide storage reduction catalyst 56 is performed. Therefore, as compared with the case where the fuel injection amount is simply increased, the torque does not suddenly increase. Further, since there is no need to retard the ignition timing, a reduction in output per unit time can be suppressed. as a result,
It is possible to suppress the occurrence of a torque step when performing the rich spike control, and it is possible to prevent fuel economy from deteriorating. (B) Further, in the present embodiment, when performing the rich spike control, the engine speed NE and the basic injection amount Qinj
The target throttle opening trtat is calculated by referring to a map for rich spikes based on the above, and the throttle opening is gradually reduced. By the way, as it is, as shown in FIG. 6, there is a concern that the torque may decrease due to the decrease in the throttle opening. However, in the present embodiment, in accordance with the decrease in the torque, that is,
The fuel injection amount is increased somewhat to the extent that the throttle opening is somewhat reduced. Accordingly, the line segment L3 in FIG.
It is possible to shift the air-fuel ratio A / F to the rich side without lowering the torque (from point A to point B in the figure) (c) Further, in the present embodiment, At the time of the rich spike control, the map is switched as needed in the order of step 105, step 202, step 302, step 402, step 302, step 202, and step 105, and the control amounts such as the throttle opening and the injection amount are adjusted. . Therefore, it is possible to perform delicate control according to the current operation state.

(D) In addition, in this embodiment, in order to control the air-fuel ratio A / F to the rich side, an electronically controlled throttle mechanism is adopted as the intake air amount adjusting means.
Therefore, the above-described operation and effect can be achieved with the existing device. As a result, it is possible to simplify the configuration and suppress a rise in cost.

(E) In addition, in the present embodiment, the present invention is applied to the engine 1 capable of performing stratified combustion. Here, when stratified combustion is performed, the amount of intake air is also large. For this reason, the above-described functions and effects are more effective.

The present invention is not limited to the above embodiment, and may be configured as follows, for example. (1) In the above embodiment, when performing rich spike control, steps 105, 202, and 30 are executed.
2, step 402, step 302, step 20
2. The map is switched at any time in the order of step 105, and the control amounts such as the throttle opening and the injection amount are adjusted.
On the other hand, it is also possible to grasp the closing amount of the throttle valve 23 and increase the injection amount in accordance with the closing amount (or pumping loss) at that time.

For example, when the throttle valve 23 is closed, it is clear that the amount of change in the intake pressure PiM increases in accordance with the degree of the increase in the pumping loss. Therefore, as shown in FIG. The calculated intake pressure PiM (Q is calculated from the quantity Qinj and the engine speed NE.
inj, NE) and the actual intake pressure PiM, ΔPiM
May be calculated, and the increase value of the fuel injection amount may be determined based on the difference ΔPiM. By setting the increase value of the fuel injection amount in this way, the fuel supply amount is increased in accordance with the pumping loss, and the fluctuation of the torque can be minimized.

(2) In the above-described embodiment, the opening degree of the electronically controlled throttle valve 23 is controlled by controlling the actuator 22, thereby controlling the intake air amount. Alternatively, by controlling the opening degree of the EGR valve 53, the exhaust gas recirculation amount (EGR
Amount) may be controlled. By performing the combined use with the EGR control, it is possible to easily enrich the air-fuel ratio A / F.

When performing only the EGR control, it is desirable to perform the control when the intake pressure PiM is close to the atmospheric pressure and the degree of lean is small. In this case, at the time of the rich spike control, it is desirable to perform the enrichment by increasing the EGR amount without controlling the throttle valve 23. According to this control, an increase in pumping loss is unlikely to occur, so that a change in torque can be naturally suppressed.

(3) In the above-described embodiment, the opening degree of the electronically controlled throttle valve 23 is controlled by controlling the actuator 22, thereby controlling the intake air amount. Alternatively, an idle speed control valve may be provided in a passage that bypasses the throttle valve 23, and the opening of the idle speed control valve may be controlled.

(4) In the above embodiment, the present invention is embodied in the in-cylinder injection type engine 1. However, the present invention is embodied in a so-called general stratified combustion or weak stratified combustion type. You may. For example, the intake ports 7a, 7b
Of the type which injects toward the back side of the umbrella portion of the intake valves 6a and 6b. Although a fuel injection valve is provided on the intake valves 6a and 6b side, a type in which fuel is injected directly into the cylinder bore (combustion chamber 5) is also included. Further, the present invention can also be embodied in an engine capable of performing lean combustion and stoichiometric combustion, which are higher concepts.

(5) In each of the above embodiments, the helical type intake port is provided, and so-called swirl can be generated. However, it is not always necessary to generate swirl. Therefore, for example, the swirl control valve 17, the step motor 19, and the like in the above embodiment can be omitted.

(6) Further, in each of the above embodiments, the present invention has been embodied in the case of the gasoline engine 1 as the internal combustion engine. However, the present invention can also be embodied in the case of a diesel engine or the like.

[0078]

As described in detail above, according to the present invention,
When an exhaust gas purification device of a lean burn engine that includes a nitrogen oxide storage reduction catalyst and can perform lean combustion and combustion at a stoichiometric air-fuel ratio is used to reduce and release nitrogen oxides stored in the nitrogen oxide storage reduction catalyst. In this case, it is possible to suppress the occurrence of the torque step, and to prevent the fuel efficiency from deteriorating.

[Brief description of the drawings]

FIG. 1 is a conceptual configuration diagram showing a basic concept of the present invention.

FIG. 2 is a schematic configuration diagram illustrating an exhaust purification device of a lean burn engine according to one embodiment.

FIG. 3 is an enlarged sectional view showing a cylinder portion of the engine.

FIG. 4 is a flowchart showing a “rich spike control routine” executed by the ECU.

FIG. 5 is a flowchart showing a “rich spike control routine” and is a continuation of FIG. 4;

FIG. 6 is a view for explaining the operation of the embodiment;
4 is a graph showing a relationship between an air-fuel ratio and a generated torque.

FIG. 7 is a map showing an example of a relationship between an increase value of a fuel injection amount and a difference between a calculated intake pressure and an actual intake pressure in another embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine, 11 ... Fuel injection valve as fuel injection means, 25 ... Throttle sensor which constitutes operating state detecting means, 26A ... Accelerator sensor which constitutes operating state detecting means, 26B ... Fully closed which constitutes operating state detecting means Switch, 27 ... Top dead center sensor constituting operating state detecting means,
28 ... Crank angle sensor constituting operating state detecting means,
29: a swirl control valve sensor that constitutes operating state detection means; 30: an ECU that constitutes intake air amount control means, intake air amount decrease control means, and injection amount control means; 55: an exhaust duct that constitutes an exhaust passage; A substance occlusion reduction catalyst, 61 ... an intake pressure sensor constituting operating state detecting means, 62 ... a water temperature sensor constituting operating state detecting means, 6
3. Oxygen sensor constituting operating state detecting means.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/08 ZAB F01N 3/24 R 3/10 ZAB ZABE 3/24 F02D 9/02 ZAB ZAB 341G F02D 9/02 ZAB 21 / 08 ZAB 341 301A 21/08 ZAB 41/02 ZAB 301 301A 41/02 ZAB 301E 301 41/20 ZAB 310D 41/20 ZAB B01D 53/36 ZAB 310 101B

Claims (6)

[Claims] 1. A fuel injection means capable of supplying fuel into a cylinder of an engine for performing a lean combustion and a combustion at a stoichiometric air-fuel ratio, and an intake air amount adjustment for adjusting an intake air amount introduced to the engine. Means, an operating state detecting means for detecting an operating state of the engine, an intake air amount controlling means for controlling the intake air amount adjusting means based on a detection result of the operating state detecting means, provided in an exhaust passage of the engine. An exhaust gas purification device for a lean burn engine comprising a nitrogen oxide storage reduction catalyst, wherein the nitrogen oxide stored in the nitrogen oxide storage reduction catalyst is reduced and released. Exhaust purification device for a lean-burn engine, characterized in that an intake air amount reduction control means for enriching the air-fuel ratio by reducing the amount of intake air introduced into the engine by controlling the intake air amount is provided. . 2. The exhaust gas purifying apparatus for a lean burn engine according to claim 1, further comprising: when the intake air amount is decreased by the intake amount decrease control means, the fuel supply amount is increased in accordance with the degree of the decrease. An exhaust purification device for a lean burn engine, comprising an injection amount control means for controlling the fuel injection means to suppress the torque reduction. 3. The intake air amount adjusting means is constituted by an electronically controlled throttle mechanism comprising a throttle valve provided in an intake passage of the engine and an actuator for opening and closing the throttle valve. An exhaust purification device for a lean burn engine according to claim 1 or 2. 4. The intake air amount adjusting means includes an exhaust gas recirculation passage communicating the exhaust passage and the intake passage of the engine, and an EGR valve for opening and closing the exhaust gas recirculation passage. The engine is constituted by an EGR mechanism for recirculating a part of the exhaust gas discharged to the intake air taken into the engine.
3. The exhaust gas purifying apparatus for a lean burn engine according to claim 1, wherein the opening of the EGR valve is increased. 5. The degree of increase in fuel supply amount by said injection amount control means is determined based on a difference between a calculated pressure in said intake passage and an actual pressure. An exhaust purification device for a lean burn engine according to any one of claims 2 to 4. 6. The exhaust purification device for a lean burn engine according to claim 1, wherein the engine is capable of performing stratified combustion.