JP2845088B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

Relates to an exhaust purifying apparatus of the present invention is an internal combustion engine BACKGROUND OF THE relates effectively removable exhaust purification apparatus NO _X in the exhaust gas in particular.

[0002]

2. Description of the Prior Art As this kind of exhaust purification device, the present applicant in Japanese Patent Application No. Hei 3-284095, the air-fuel ratio of the exhaust flowing absorbs NO _X when the lean, lowering the oxygen concentration of the exhaust gas flowing into then place the _the NO _X absorbent to release the sucked NO _X in an exhaust passage of an internal combustion engine causing combustion of lean air-fuel ratio, the exhaust gas purifying apparatus for an internal combustion engine which is adapted to absorb NO _X in the exhaust gas already proposed ing.

In the above exhaust gas purifying apparatus, the air-fuel ratio of the air-fuel mixture supplied to the engine is usually maintained at a lean air-fuel ratio while NO _x
Together to absorb NO _X in the exhaust gas to the absorbent, NO _X
When NO _X is to be released from the absorbent, the air-fuel ratio of the mixture supplied to the engine is set to a rich air-fuel ratio and NO
The oxygen concentration of the exhaust gas flowing into the _X absorbent is reduced.
As described above, regularly NO absorbed from _the NO _X absorbent
By releasing _X, absorption capacity of the NO _X absorbent is prevented from being lowered by the increase of the NO _X absorption.

[0004]

[SUMMARY OF THE INVENTION However, as described above, when switching the air-fuel ratio of the mixture supplied to the engine in order to release the NO _X from _the NO _X absorbent from lean air-fuel ratio to a rich air-fuel ratio, A large torque fluctuation occurs at the time of switching due to a change in the air-fuel ratio, causing a problem that the drivability deteriorates.

[0005] The present invention has been made in view of the above problems, to reduce the torque fluctuations at the time of releasing the NO _X lowers the oxygen concentration of the exhaust gas flowing to the NO _X absorbent from _the NO _X absorbent, the degradation of vehicle drivability It is an object of the present invention to provide an exhaust gas purification device capable of preventing the exhaust gas.

[0006]

According to the present invention, there is provided an exhaust system for an internal combustion engine having a plurality of cylinder groups each including at least one or more cylinders and independent exhaust passages for each of the cylinder groups. a purification apparatus, wherein arranged in each exhaust passage, the air-fuel ratio of the exhaust flowing absorbs NO _X in the exhaust gas when the lean, the oxygen concentration of the exhaust flowing absorbed when reduced NO comprising a _the NO _X absorbent to release the _X, and said plurality of cylinders independently controllable air-fuel ratio control system an air-fuel ratio of a mixture supplied to each of the other cylinder group of the group, the air-fuel ratio control device, usually to absorb NO _X in the exhaust gas to the _the NO _X absorbent holds mixture supplied to each cylinder group to a lean air-fuel ratio, when it should be released NO _X from _the NO _X absorbent is the NO _X absorption The air-fuel ratio of the air-fuel mixture supplied to the cylinder group corresponding to the absorbent is maintained at the rich air-fuel ratio, and the air-fuel ratio of the air-fuel mixture supplied to at least a predetermined number of cylinder groups is simultaneously maintained at the rich air-fuel ratio. The present invention provides an exhaust gas purification device for an internal combustion engine that inhibits the exhaust gas.

[0007]

[Action] The air-fuel ratio of the mixture supplied to the engine is determined by the cylinder glue.
Control for each cylinder, and more than a predetermined number of cylinder groups
NO operation by prohibiting operation with
_XNO from absorbent_XSome cylinder groups always on release
Only operate on a rich mixture, the other cylinder groups
It is operated with a mixture of air and fuel. All cylinders of engine are simultaneous
The air-fuel ratio is not switched to the rich air-fuel ratio
Output torque fluctuation due to switching is greatly reduced.

[0008]

FIG. 1 is a diagram showing an embodiment of an internal combustion engine to which the present invention is applied. Referring to FIG. 1, reference numeral 1 denotes an engine body, 2
Indicates an intake passage. In this embodiment, the engine 1 is a four-cylinder engine having cylinders 101 to 104, and an intake passage 2 is connected to intake ports of the cylinders 101 to 104 via an intake manifold 3. The intake passage 2 is provided with a throttle valve 4 and an air flow meter 5 that outputs a signal corresponding to the amount of intake air of the engine 1. In the present embodiment, fuel injection valves 61 to 64 that inject fuel into the intake ports of the cylinders are provided in the connection branch pipes of the intake manifold 3 to the cylinders 101 to 104, respectively.

The fuel injection valves 61 to 64 are respectively connected to a pressurized fuel supply source, and are connected to an electronic control circuit (ECU) 3 described later.
A predetermined amount of fuel is injected into an intake port of a corresponding cylinder according to a control signal from 0. The fuel injection valves 61 to 64 can be controlled independently of each other, and therefore each cylinder 101 to 64
The air-fuel ratio of the air-fuel mixture supplied to 104 can be adjusted independently of each other.

On the other hand, the exhaust ports of the cylinders 101 to 104 are connected to an exhaust passage via an exhaust manifold. In this embodiment, the engine 1 has two exhaust passages 81 and 82 which are independent from each other. The cylinders 101 and 104 are connected to an exhaust passage 81 through an exhaust manifold 91, and are connected to the cylinders 10 and 104.
2 and 103 are connected to the exhaust passage 8 through the exhaust manifold 92.
2 are connected to each other. That is, in the present embodiment, the cylinders 101 and 104 and the cylinders 102 and 103 each form one group and are connected to independent exhaust passages (hereinafter, a cylinder group formed by the cylinders 101 and 104). To cylinder group 1, cylinders 102 and 103
Is referred to as a cylinder group 2). The cylinder grouping is determined in consideration of the cylinder ignition order, so that interference of exhaust from each cylinder is reduced as much as possible. Further, NO _X absorbent 71 and 72 to be described later are respectively disposed in the exhaust passage 81, 82.

In FIG. 1, reference numeral 30 denotes an electronic control unit (ECU) 30 of the engine 1. The ECU 30 includes a ROM (Read Only Memory) 32 and a RAM (Random Access Memory) 3 interconnected by a bidirectional bus 31.
3, CPU (microprocessor) 34, input port 3
5 and consists of a known type of digital computer having an output port 36, the fuel injection amount control of the engine 1, in addition to performing the basic control of the ignition timing control, etc., from _the NO _X absorbent 71, 72 described later in this embodiment It performs the control of NO _X emission.

For these controls, an output signal of the air flow meter 5 is input to an input port 35 of the ECU 30 via an AD converter 37 and a rotation speed sensor 23 for generating a pulse representing the engine rotation speed is provided. It is connected. The output port 36 of the ECU 30 is connected to a spark plug of each cylinder (not shown) via a corresponding drive circuit, and controls the engine ignition timing.
Via the fuel injection valves 61 to 64 of the cylinders 101 to 104
It is connected to the.

In the internal combustion engine shown in FIG. 1, the fuel injection time TAU is calculated based on, for example, the following equation. TAU = TP · K Here, TP indicates a basic fuel injection time, and K indicates an air-fuel ratio correction coefficient. The basic fuel injection time TP indicates a fuel injection time required for setting the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder to the stoichiometric air-fuel ratio. This basic fuel injection time TP is obtained in advance by an experiment, and the engine load Q
/ N (intake air amount Q / engine speed N) and RO speed in the form of a map as shown in FIG.
It is stored in M32.

The air-fuel ratio correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder.
= 1.0, the air-fuel mixture supplied into the engine cylinder has the stoichiometric air-fuel ratio. On the other hand, if K <1.0, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes larger than the stoichiometric air-fuel ratio, that is, lean, and K> 1.
When it becomes 0, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes smaller than the stoichiometric air-fuel ratio, that is, becomes rich.

The fuel injection time TAU of each of the fuel injection valves 61 to 64 can be set independently of each other, and the air-fuel ratio of each cylinder can be controlled independently. And 104, and cylinders 102 and 10
3 are controlled to the same air-fuel ratio as one group. That is, the fuel injection times of the fuel injection valves 61 and 64 of the cylinders 101 and 104 (cylinder group 1) are always set to the same value (hereinafter referred to as TAU1).
Fuel injection valve 6 for cylinders 102 and 103 (cylinder group 2)
The fuel injection times (hereinafter, referred to as TAU2) for Nos. 2 and 63 are always set to the same value. In this embodiment, the air-fuel ratio correction coefficient K is, for example, K = 0.7 during normal operation, as described later.
, And both the cylinder group 1 and the cylinder group 2 are operated at a lean air-fuel ratio.

FIG. 3 schematically shows the concentration of typical components in the exhaust gas discharged from the engine combustion chamber. As can be seen from FIG. 3, unburned HC and C in the exhaust gas discharged from the combustion chamber.
The concentration of O increases as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber becomes richer, and decreases as the air-fuel ratio becomes leaner. On the other hand, the concentration of residual oxygen O _{2 in} the exhaust gas discharged from the combustion chamber rapidly decreases when the air-fuel ratio of the supplied air-fuel mixture becomes richer than the stoichiometric air-fuel ratio, and rapidly increases when the air-fuel ratio becomes lean.

[0017] _the NO _X absorbent 71, for example alumina as a carrier, an alkali metal, barium Ba, alkaline earth such as calcium Ca, such as the carrier on, for example, potassium K, sodium Na, lithium Li, cesium Cs , Lanthanum La, and rare earth elements such as yttrium Y, and a noble metal such as platinum Pt. This _the NO _X absorbent is, NO air-fuel ratio of the inflowing exhaust absorbs NO _X when the lean, the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed to decrease
_X absorbs and releases. Here, the air-fuel ratio of the inflowing exhaust shall refer to the ratio of the supplied air and fuel to the engine intake passage and _the NO _X absorbent 71 in the exhaust passage upstream of. The air-fuel ratio of the inflowing exhaust when the fuel or air is not supplied to _the NO _X absorbent upstream of the exhaust passage coincides with the air-fuel ratio of the mixture supplied to the combustion chamber, thus NO _X absorbent in this case The agent absorbs NO _X when the air-fuel ratio of the mixture supplied to the combustion chamber is lean, and releases the absorbed NO _X when the oxygen concentration in the mixture supplied to the combustion chamber decreases.

If the above-mentioned NO _X absorbent is disposed in the engine exhaust passage, the NO _X absorbent actually performs the absorption and release of NO _X , but the detailed mechanism of the absorption and release is not clear. is there. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but other noble metals, alkali metals, alkaline earths,
The same mechanism is obtained even when rare earth elements are used.

That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases, and as shown in FIG. 4 (A), the oxygen O ₂ is converted into O ₂ ⁻ or O ²⁻ . It adheres to the surface of platinum Pt. On the other hand, NO
O ₂ on the surface of the platinum Pt is ^- or O ^2- and react, NO
₂ (2NO + O ₂ → 2NO ₂ ). Next, a part of the produced NO ₂ is oxidized on the platinum Pt, absorbed in the absorbent and combined with the barium oxide BaO.
Nitrate ions NO as shown in (A) ₃ ^- is diffused in the absorbent in the form of. In this way, NO _X is absorbed into the NO _X absorbent.

As long as the oxygen concentration in the inflow exhaust gas is high, platinum Pt
Is NO ₂ on the surface of product, as long as NO ₂ to NO _X absorbing capacity of the absorbent is not saturated is absorbed nitrate ions NO ₃ in the absorbent ^- is produced. On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ⁻ in the absorbent is converted. It is released from the absorbent in the form of NO _2. That is, when the oxygen concentration in the inflow exhaust gas decreases, NO
NO _X will be released from the _X absorbent.

On the other hand, if the air-fuel ratio of the inflowing exhaust gas is made rich at this time, a large amount of unburned H
C and CO are discharged, and these unburned HC and CO are converted to platinum Pt.
It reacts with the above oxygen O ₂ ^- or O ^2- to be oxidized. Further, when the air-fuel ratio of the inflow exhaust gas is made rich, the oxygen concentration in the inflow exhaust gas extremely decreases, so that NO ₂
Is released, and this NO ₂ is reduced by reacting with unburned HC and CO as shown in FIG. 4 (B). When NO ₂ is no longer present on the surface of the platinum Pt, NO ₂ is released from the absorbent one after another. Therefore NO _X from _the NO _X absorbent in a short time when the air-fuel ratio of the inflowing exhaust gas is made rich, the released.

[0022] That is, first, unburned HC and the air-fuel ratio of the inflowing exhaust gas rich, O on CO platinum Pt ₂ ^- or O ^2- immediately be reacted with oxidized and then O ₂ on the platinum Pt ^- or O yet to be ² is consumed retardant H
C, CO is any remaining This unburned HC, discharged from the NO _X and engine released from the absorbent by CO N
O _X is made to reduction.

As described above, in the internal combustion engine shown in FIG. 1, the air-fuel mixture supplied to the cylinder groups 1 and 2 is normally kept lean (for example, K = 0.7). _X is absorbed by the NO _x absorbents 71 and 72. However, if the lean mixture continues to burn, NO _X
The NO _x absorption capacity of the absorbents 71 and 72 is saturated, and the NO _x cannot be absorbed by the NO _x absorbents 71 and 72. Therefore, in the embodiment according to the present invention, when the lean air-fuel mixture is continuously burned, the air-fuel mixture supplied into the cylinder of the engine is temporarily rich (K = KK,
Here is a KK> 1.0), are to be released thereby is absorbed in _the NO _X absorbent 71 and 72 were NO _X from _the NO _X absorbent, respectively.

However, in this case, simply switching the air-fuel mixture supplied to the entire engine from the lean air-fuel ratio to the rich air-fuel ratio causes the engine output torque to fluctuate, causing a large torque shock. Therefore, in this embodiment, the cylinders 101 to 104 of the engine are used.
The divided into two groups (the cylinder group 1, 2), NO _X absorbent 7 in each of the independent exhaust passages 81 and 82
The 1,72 provided, NO _X from _the NO _X absorbent 71
The simultaneous release, that is, the simultaneous inhibition of the rich air-fuel ratio of the cylinder group 1 and the cylinder group 2 is prohibited to reduce the torque shock at the time of switching the air-fuel ratio.

[0025] Next Fig. 5, illustrating the NO _X release control operation from the _the NO _X absorbent 71 and 72 with reference to FIG. FIG.
Shows a flowchart for determining the condition for starting the NO _X release operation from the NO _X absorbents 71 and 72. This routine is executed by the ECU 3
It is executed every predetermined time by 0. In the routine of FIG. 5, NO _X absorbent 71 of cylinder group 1 and 2 of the engine 1,
72 of the NO _X absorption of the estimates respectively, NO _X in each of the NO _X absorbent when the absorption amount becomes a predetermined value or more
Releasing flag (XF1, XF2) is set to start the NO _X release the.

[0026] However, this time, NO _X release flag XF1
And XF2 are not set at the same time. When either one is set, the other NO _X absorbent does not set the flag even if the NO _X absorption amount exceeds a predetermined value. As a result, both cylinder groups are simultaneously operated at the rich air-fuel ratio, and the air-fuel ratio of the entire engine is simultaneously switched from lean to rich, thereby preventing a large output torque fluctuation.

When the routine starts in FIG.
In steps 501 to 505, cylinder group 1
NO _X absorption of the NO _X absorbent 71 disposed in an exhaust passage of is estimated. That is, in step 501, it is determined from the air-fuel ratio correction coefficient K1 of the fuel injection amount whether or not the cylinder group 1 is currently operating at the lean air-fuel ratio. Here, K1 is the fuel injection valve 6 of the cylinder group 1 as described later.
1, 64 are the air-fuel ratio correction coefficients.

[0028] Step 501 K1 <1.0, that is, when the cylinder groups 1 is operated at a lean air-fuel ratio is _the NO _X absorbent 71 is while absorbing NO _X in the exhaust gas, the flow advances to step 503 , NO of _the NO _X absorbent 71
_The counter CN1 representing the _X absorption amount is incremented by a predetermined value α. When K1 ≧ 1.0, that is, when the cylinder group 1 is operated at the rich air-fuel ratio, NO _X
Since the absorbent 71 is in releasing NO _X by the currently absorbed proceeds to step 505, the counter CN1 decrements beta. Accordingly, the counter CN1 is for each routine execution, be increased or decreased depending to the NO _X absorption of the NO _X absorbent 71 becomes a value corresponding to the current of the NO _X absorption of the NO _X absorbent 71.

In this embodiment, NO_XAbsorbent NO_X
The amount of increase α is fixed, but the engine
Load, rotation speed (that is, NO per unit time of the engine)_X
Generated amount) and changes the increase amount α accordingly.
You may make it. Next, steps 507 to 51
In the first case, the same operation as above is performed for the exhaust passage of the cylinder group 2.
Placed NO_XPerformed on absorbent 72, NO_Xabsorption
NO of agent 72 _XThe absorption amount CN2 is calculated. Where K2
(Step 507) is the fuel injection valve 6 of the cylinder group 2
2 and 63 are air-fuel ratio correction coefficients.

[0030] Step 513 indicates the necessity of determination of the NO _X release operation from _the NO _X absorbent 71. In this embodiment,
NO _X absorption of the NO _X absorbent 71 CN1 predetermined value CN0
Performing NO _X release operation when it is above. Here the predetermined value CN0, for example _the NO _X absorbent 71 is capable of absorbing NO
The value is about 50% of the _X amount. Ie, N of the NO _X absorbent 71 of the cylinder group 1 in step 513
When O _X absorption CN1 had exceeded the CN0, the process proceeds to step 515, the cylinder group 2 NO _X absorbent 72
It is determined whether the NO _X release flag XF2 is set (= “1”). When the flag XF2 is set, since the cylinder group 2 is currently operated at the rich air-fuel ratio, if the cylinder group 1 is further switched to the rich air-fuel ratio, the fluctuation of the engine output torque may increase. NO _X in _the NO _X absorbent 71 of the cylinder group 1
Release operation is not performed, the cylinder group 2 NO _X absorbent 72
It is necessary to wait for the end of the NO _X release operation.

[0031] That is, NO _X absorption CN1 of the NO _X absorbent 71 is not exceed the predetermined value, NO in another cylinder group
Only when NO _X is not released from the _X absorbent, in step 517, the NO _X release flag XF1 of the NO _X absorbent 71 is set (= “1”). Next, in steps 519 to 523, the same operation as described above is performed, and NO
_It is determined whether the _X absorbent 72 needs to release NO _X. In this case, similarly to the above, when the NO _X absorption CN2 of the NO _X absorbent 72 is at a predetermined value CN0 or more, and NO _X emission from _the NO _X absorbent in the other cylinder group is not performed Only when the NO _X release flag XF2 is set (=
"1").

[0032] Figure 6, NO _X absorbent by the NO _X release flag XF1, XF2 set by the routine of FIG 7
7 shows a NO _X release control routine from Nos. 1 and 72. This routine is also executed by the ECU 30 at regular time intervals, similarly to the routine of FIG. When the routine starts in Fig. 6, the air-fuel ratio of the cylinder group 1 In steps 601 613 are set according to the value of the NO _X release flag XF1. That is, in step 601, it is determined whether or not the flag XF1 is set (= "1"). If XF1 is not set, the process proceeds to step 603, where the air-fuel ratio correction coefficient K1 of the cylinder group 1 is set to a predetermined value. Set to KL. Here, KL is a value for correcting the fuel injection amount from the fuel injection valves 61 and 64 to an amount that can obtain a lean air-fuel ratio, and is, for example, a constant of about KL = 0.7.

On the other hand, if the flag XF1 is set in step 601, the air-fuel ratio of the cylinder group 1 is made rich for a predetermined time in steps 605 to 613. That is, in step 605, the air-fuel ratio correction coefficient K1 is set to the predetermined value KK, and in step 607, the counter C1 is incremented by one. Here, KK is the fuel injection valve 6
The fuel injection amount from 1, 64 is a value for correcting the amount such a rich air-fuel ratio is obtained, for thereby reducing the NO _X that is consumed and releasing oxygen on the platinum Pt in the foregoing of the NO _X absorbent Is set so that the necessary amounts of HC and CO components are supplied.

At step 609, the counter C1
Is determined to be greater than or equal to a predetermined value C0. If C1> C0, the flag XF1 is reset (= “0”) and the counter C1 is cleared in steps 611 and 613.
If C1 ≦ C0 in step 609, the steps from step 615 are executed without changing the value of the flag XF1 and the value of the counter C1. That is, the air-fuel ratio correction coefficient K1 is kept rich (K = KK) for a predetermined time (C1 = C0), and is returned to lean (K1 = KL) again after the lapse of the predetermined time. The predetermined value C0 is the time required for the NO _X absorbed from _the NO _X absorbent is released, for example, a number of executions of the routine corresponding to several seconds.

After the above steps are completed, the same operation is performed for cylinder group 2 in steps 615 to 627. However, as described in the routine of FIG.
Since F1 and XF2 are not set at the same time,
The coefficients K1 and K2 are not simultaneously set to rich (= KK). FIG. 7 is a fuel injection amount control routine using the air-fuel ratio correction coefficients K1 and K2 set as described above. This routine is executed by the ECU 30 every predetermined rotation angle of the engine crankshaft (for example, every 360 degrees).

When the routine is started in FIG. 7, in step 701, the values of the engine intake air amount Q and the engine speed N are set to R.
Read from AM33. Q and N are read from the air flow meter 5 and the rotation speed sensor 23 by routines which are separately executed periodically, and the latest data is always stored in the RAM 33. Next, in step 703,
An intake air amount Q / N per one rotation of the engine is calculated from the above Q and N, and a basic fuel injection amount TP for providing a stoichiometric air-fuel ratio is calculated from a map (FIG. 2) stored in the ROM 32 based on the Q / N. Is done. Next, steps 705 and 709
Now, the air-fuel ratio correction coefficient K set by the routine of FIG.
The final fuel injection amount TAU1 of the fuel injection valves 61 and 64 and the final fuel injection amount TAU2 of the fuel injection valves 62 and 63 are calculated by using 1, K2, and these values are set in the RAM 33 in step 709. End the routine.
As a result, a rich or lean air-fuel ratio corresponding to the air-fuel ratio correction coefficient set in the routine 6 is obtained for the cylinder groups 1 and 2.

In the above embodiment, the case where the present invention is applied to an internal combustion engine having two cylinder groups each including two cylinders has been described. However, the present invention is applicable to an internal combustion engine having three or more cylinder groups. It is equally applicable to institutions. In addition, an independent exhaust passage is provided for each cylinder,
Needless to say, the present invention can be applied to an engine capable of individually controlling the air-fuel ratio.

[0038]

According to the exhaust gas purifying apparatus of the present invention, each of the NO exhaust gas passages of the plurality of cylinder groups is independent.
The _X absorbent disposed, causes the absorption of the NO _X, when performing the emission and reduction purification of the NO _X from _the NO _X absorbent by switching the combustion air-fuel ratio of each cylinder group rich, at least a predetermined number of cylinders By prohibiting the group from having the rich air-fuel ratio at the same time, it is possible to reduce the engine output torque fluctuation caused by the air-fuel ratio switching and prevent the drivability from deteriorating.

[Brief description of the drawings]

FIG. 1 is a schematic view of an internal combustion engine showing one embodiment of the present invention.

FIG. 2 is a diagram showing a map of a basic fuel injection time.

FIG. 3 is a diagram schematically showing the concentrations of unburned HC, CO and oxygen in exhaust gas discharged from an engine.

FIG. 4 is a diagram for explaining the effect of absorbing and releasing NO _X.

FIG. 5 is a flowchart showing an example of control of NO _X release from a NO _X absorbent.

FIG. 6 is a flowchart illustrating an example of control of NO _X release from a NO _X absorbent.

FIG. 7 is a flowchart illustrating an example of fuel injection amount control.

[Explanation of symbols]

1 ... internal combustion engine 2 ... intake passage 3 ... intake manifold 4 ... throttle valve 5 ... air flow meter 30 ... ECU 61 to 64 ... Fuel injection valve 71 and 72 ... NO _X absorbent 81, 82 ... exhaust passage 91, 92 ... exhaust manifold 101 to 104 ... cylinders

Claims (1)

(57) [Claims] 1. An exhaust purification system for an internal combustion engine, comprising: a plurality of cylinder groups each including at least one or more cylinders; and exhaust passages independent of each other for each of the cylinder groups. disposed in the passage, the air-fuel ratio of the exhaust flowing absorbs NO _X in the exhaust gas when the lean and _the NO _X absorbent to the oxygen concentration of the exhaust gas flowing to release NO _X absorbed when lowered, An air-fuel ratio control device capable of controlling the air-fuel ratio of the air-fuel mixture supplied to each of the plurality of cylinder groups independently of the other cylinder groups, and the air-fuel ratio control device is generally provided for each of the cylinder groups. cylinder group corresponding to the _the NO _X absorbent when the air-fuel mixture to be supplied and held to the lean air-fuel ratio to absorb NO _X in the exhaust gas to the _the NO _X absorbent, should be released NO _X from _the NO _X absorbent To serve An exhaust gas purification device for an internal combustion engine that holds the air-fuel ratio of a mixture to be supplied at a rich air-fuel ratio and simultaneously prevents the air-fuel ratio of the mixture supplied to a predetermined number or more of cylinder groups from being maintained at a rich air-fuel ratio .