JP2689829B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art In an internal combustion engine in which a lean air-fuel mixture is burned in most engine operating regions, NOx is absorbed when the air-fuel ratio of the inflowing exhaust gas is lean,
NOx absorbed when the oxygen concentration in the inflowing exhaust gas decreases
The NOx absorbent that releases the NOx is placed in the engine exhaust passage, and the NOx generated when the lean air-fuel mixture is burned is NOx.
Before the NOx absorbent absorbs NOx and releases the NOx from the NOx absorbent, the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is temporarily made rich before the NOx absorbent capacity of the NOx absorbent is saturated. An internal combustion engine designed to be reduced has already been proposed by the present applicant (Japanese Patent Application No. 3-
284095).

[0003]

However, when the temperature of the NOx absorbent is relatively high, this NOx absorbent promptly releases NOx when the oxygen concentration in the inflowing exhaust gas is lowered, but the temperature of the NOx absorbent is low. Then, even if the oxygen concentration in the inflowing exhaust gas is reduced, NOx is hardly released. Therefore, in the above-mentioned internal combustion engine, even if the air-fuel ratio of the inflowing exhaust gas is made rich in order to release NOx from the NOx absorbent, at this time, if the temperature of the NOx absorbent is low, NOx will not be easily released from the NOx absorbent, and thus the NOx absorption In order to release most of the NOx absorbed in the agent, it is necessary to lengthen the time period during which the air-fuel ratio of the inflowing exhaust gas is made rich, which causes a problem that the fuel consumption rate deteriorates.

[0004]

In order to solve the above problems, according to the present invention, NOx is absorbed when the air-fuel ratio of the inflowing exhaust gas is lean, and it is absorbed when the oxygen concentration in the inflowing exhaust gas decreases. A NOx absorbent that releases NOx is placed in the engine exhaust passage, an oxidation catalyst is placed in the engine exhaust passage upstream of the NOx absorbent, and an engine exhaust gas upstream of the oxidation catalyst is placed.
A secondary air supply device is arranged in the air passage, and when the temperature of the NOx absorbent should be raised when releasing NOx from the NOx absorbent, the secondary air supply device is used to exhaust the engine exhaust upstream of the three-way catalyst. The secondary air is supplied into the passage and the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is made rich.

[0005]

[Function] When NOx should be released from the NOx absorbent, N
When the temperature of the Ox absorbent is low and the air-fuel ratio of the exhaust gas supplies secondary air to the rich, the oxidation catalyst at this time
Since the temperature of the NOx absorbent is raised by the heat of oxidation reaction generated in the NOx, NOx is promptly released from the NOx absorbent.

[0006]

Referring to FIG. 1, 1 is an engine body, 2 is a piston, 3 is a combustion chamber, 4 is a spark plug, 5 is an intake valve, 6 is an intake port, 7 is an exhaust valve, and 8 is an exhaust port. Show. The intake port 6 is connected to a surge tank 10 via a corresponding branch pipe 9, and a fuel injection valve 11 for injecting fuel into the intake port 6 is attached to each branch pipe 9. The surge tank 10 includes an intake duct 12 and an air flow meter 13.
Is connected to the air cleaner 14 through the
Inside, a throttle valve 15 is arranged. On the other hand, the exhaust port 8 is connected via an exhaust manifold 16 to a catalytic converter 18 containing an oxidation catalyst 17, and this catalytic converter 18 is connected via an exhaust pipe 19 to a casing 21 containing an NOx absorbent 20.

As shown in FIG. 1, the exhaust manifold 16
A secondary air supply device 22 is provided in the. The secondary air supply device 22 includes a secondary air supply conduit 23 connected to the inside of the exhaust manifold 16, a check valve 24 including a reed valve that can flow only toward the inside of the exhaust manifold 16, and a secondary air amount. A secondary air control valve 25 for controlling and an air filter 26
It is composed of When the secondary air control valve 25 is opened, the secondary air flows through the check valve 24 when the negative pressure is generated in the exhaust manifold 16 due to the exhaust pulsation.
6 is supplied. The secondary air control valve 25 is, for example, a linear solenoid valve, and the amount of secondary air supplied into the exhaust manifold 16 is controlled by the secondary air control valve 25.

The electronic control unit 30 is composed of a digital computer, and a ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and an input port 35 interconnected by a bidirectional bus 31. And an output port 36. The air flow meter 13 generates an output voltage proportional to the amount of intake air, and the output voltage is input to the input port 35 via the AD converter 37. Also, input port 3
A rotation speed sensor 27, which generates an output pulse representing the engine rotation speed, is connected to 5. On the other hand, the output port 36 is connected via the corresponding drive circuit 38 to the spark plug 4 and the fuel injection valve 1 respectively.
Connected to the primary and secondary air control valves 25.

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 a 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
As a function of (intake air amount Q / engine speed N) and engine speed N, the ROM 3 is previously stored in the form of a map as shown in FIG.
2 is stored. The correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder. If K = 1.0, the air-fuel mixture supplied to the engine cylinder becomes 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> 1.0
, 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.

In the internal combustion engine shown in FIG.
= 0.6, that is, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is maintained lean, and therefore, in the internal combustion engine shown in FIG. 1, the lean air-fuel mixture is normally burned. Become. FIG. 3 schematically shows the concentrations of representative components in the exhaust gas discharged from the combustion chamber 3. As can be seen from FIG. 3, the amounts of unburned HC and CO in the exhaust gas discharged from the combustion chamber 3 increase as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 increases, and the amount of the exhaust gas discharged from the combustion chamber 3 increases. The amount of oxygen O ₂ in the exhaust gas increases as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes leaner.

The NOx contained in the casing 21
The absorbent 20 is made of, for example, alumina as a carrier. On this carrier, for example, potassium K, sodium Na, lithium Li, alkali metals such as cesium Cs, barium Ba, alkaline earths such as calcium Ca, lanthanum La, and yttrium Y At least one selected from such rare earths and a noble metal such as platinum Pt are supported. When the ratio of air and fuel supplied into the engine intake passage and the exhaust passage upstream of the NOx absorbent 20 is referred to as the air-fuel ratio of the exhaust gas flowing into the NOx absorbent 20, this NOx absorbent 20 is the air-fuel ratio of the inflow exhaust gas. Is lean, it absorbs NOx, and when the oxygen concentration in the inflowing exhaust gas is low, it absorbs Nx.
It acts to absorb and release NOx, which releases Ox. Note that NO
x If no fuel or air is supplied into the exhaust passage upstream of the absorbent 20, the air-fuel ratio of the inflowing exhaust gas matches the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3, and therefore NOx absorption in this case. The agent 20 absorbs NOx when the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 3 is lean, and releases the absorbed NOx when the oxygen concentration in the air-fuel mixture supplied to the combustion chamber 3 decreases. Become.

If the above-described NOx absorbent 20 is disposed in the engine exhaust passage, the NOx absorbent 20 actually performs the absorption / release operation of NOx, but there is a portion where the detailed mechanism of the absorption / release operation is not clear. 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 the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases.
As shown in (A), these oxygens O ₂ adhere to the surface of platinum Pt in the form of O ₂ ⁻ . On the other hand, N
O is O ₂ on the surface of the platinum Pt ^- reacted with, and _{NO 2 (2NO + O 2 →} 2NO 2). NO ₂ generated
Part of Pd is absorbed in the absorbent while being oxidized on platinum Pt, and is combined with barium oxide BaO to diffuse into the absorbent in the form of nitrate ion NO ₃ ⁻ as shown in FIG. 4 (A). In this way, NOx is absorbed in the NOx absorbent 20.

[0014] NO ₂ is produced on the surface of the platinum Pt so long as the oxygen concentration in the inflowing exhaust gas is high, as long as NO ₂ to NOx absorption ability of the absorbent is not saturated it is absorbed in the absorbent and nitrate ions NO ₃ ^- is Generated. 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 opposite direction (NO ₃ ⁻ → NO ₂ ), thus the nitrate ion NO ₃ ⁻ in the absorbent. There are released from the absorbent in the form of NO _2. That is, when the oxygen concentration in the inflowing exhaust gas decreases, NOx is released from the NOx absorbent 20. As shown in FIG. 3, if the lean degree of the inflowing exhaust gas is low, the oxygen concentration in the inflowing exhaust gas is low. Therefore, if the leaning degree of the inflow exhaust gas is low, even if the inflowing exhaust gas is lean. NOx will be released from the NOx absorbent 20.

[0015] In this case, the above-mentioned reverse reaction when the temperature is relatively high and the inflow of oxygen concentration in the exhaust gas is lowered in the NOx absorbent ^{_{20 (NO 3 - → NO 2}} ) NO to proceeds rapidly ₂ is released from the absorbent immediately.
However reverse reaction even if the temperature of oxygen concentration of the inflowing exhaust gas is low and lowering of the NOx absorbent 20 (NO ₃ ^- → NO
₂ ) does not progress easily, and thus NOx is not easily released from the NOx absorbent 20. Therefore N
In order to promptly release NOx from the Ox absorbent 20, it is necessary to raise the temperature of the NOx absorbent 20 to some extent.

On the other hand, if the air-fuel ratio of the inflowing exhaust gas is made rich in order to reduce the oxygen concentration in the inflowing exhaust gas, FIG.
As shown in Fig. 5, a large amount of unburned HC and CO are discharged from the engine, and these unburned HC and CO are oxygen O ₂ on platinum Pt.
^- reaction to be oxidized with. Further, when the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas is extremely lowered, so that NO ₂ is released from the absorbent, and this NO ₂ is unrecovered as shown in FIG. 4 (B). It is reduced by reacting with fuel HC and CO. In this way, when NO ₂ is no longer present on the surface of platinum Pt, NO ₂ is released from the absorbent one after another. Therefore, when the air-fuel ratio of the inflowing exhaust gas is made rich, NOx is released from the NOx absorbent 20 within a short time if the temperature of the NOx absorbent 20 is high.

That is, the air-fuel ratio of the inflowing exhaust gas is made rich.
First, unburned HC and CO are converted to O on platinum Pt._Two ^-When
Immediately reacted and oxidized, then on platinum Pt
O_Two ^-If unburned HC and CO still remain even if
N released from the absorbent by unburned HC and CO
Ox and NOx emitted from the engine are reduced
You. Therefore, when the air-fuel ratio of the inflow exhaust gas is made rich,
Total NOx released from the absorbent and exhaust from the engine
In order to reduce all NOx, O on platinum Pt_Two ^-
The amount of unburned HC and CO required to consume all NOx
The amount of unburned HC and CO required to reduce the NOx absorption
The rich air-fuel ratio of the inflowing gas so that it flows into the sorbent 20.
You will have to control the degree.

FIG. 5 shows rich control of the air-fuel ratio of the inflowing gas used in the embodiment according to the present invention.
In the embodiment shown in FIG. 5, the NOx absorbent 20 changes the NOx
Is to be released, the correction coefficient K used for the calculation of the fuel injection time TAU described above is indicated by the solid line KK1.
The air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is made rich by increasing it to (> 1.0), and then the air-fuel ratio is kept rich (K = KK1) during the time C ₁ . Next, the correction coefficient K is gradually decreased, and then the correction coefficient K is maintained at 1.0, that is, the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is maintained at the stoichiometric air-fuel ratio. Next, when C ₂ hours have elapsed after the rich control was started, the correction coefficient K is again made smaller than 1.0, and the combustion of the lean mixture is started again.

When the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes rich (K = KK1), if the temperature of the NOx absorbent 20 is high, most of the NOx absorbed in the NOx absorbent 20 will suddenly increase. Is released. The value of the correction coefficient KK1 is set so that the amount of unburned HC and CO necessary for consuming O ₂ ⁻ on platinum Pt and reducing all NOx is generated at this time. In this case, the exhaust gas temperature rises and NO
As the temperature of the x absorbent 20 increases, the amount of NOx released from the NOx absorbent 20 increases. Therefore, FIG.
As indicated by the solid line in, the value of the correction coefficient KK1 is increased as the exhaust gas temperature T increases. FIG.
The relationship between the correction coefficient KK1 and the exhaust gas temperature T shown in (A) is stored in the ROM 32 in advance.

In this case, the exhaust gas temperature T can be directly detected, but can also be estimated from the intake air amount Q and the engine speed N. Therefore, in the embodiment according to the present invention, the relationship between the exhaust gas temperature T, the intake air amount Q, and the engine speed N is previously obtained by an experiment, and this relationship is stored in advance in the ROM 32 in the form of a map as shown in FIG. The exhaust gas temperature T is calculated from this map.

On the other hand, as described above, when the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes rich (K = KK1), N
When the temperature of the Ox absorbent 20 is high, the NOx absorbent 20
Most of the NOx absorbed in the NOx absorbent 20 is rapidly released, and thereafter, even if the air-fuel ratio is made rich, the NOx absorbent 20 is absorbed.
Emits NOx little by little. Therefore, if the air-fuel ratio is kept rich, unburned HC and CO are released to the atmosphere. Therefore, as shown in FIG. 5, after the air-fuel ratio is made rich (K = KK1), the degree of rich is gradually decreased, and then the air-fuel ratio is set to the theoretical air-fuel ratio (K = 1.0).
Maintained at N, which is gradually released from the NOx absorbent 20
Ox is reduced in sequence.

When the air-fuel ratio is made rich, NOx
The larger the amount of NOx released from the absorbent 20, the smaller the amount of NOx released from the NOx absorbent 20 thereafter, and therefore the shorter the time until the NOx absorbent 20 finishes releasing NOx. As described above, when the air-fuel ratio is made richer as the exhaust gas temperature T becomes higher, the NOx absorbent 2
The amount of NOx released from 0 increases, so that FIG.
As shown in (B), the time C ₂ from when the air-fuel ratio is made rich to when it is returned to lean again is made shorter as the exhaust gas temperature T becomes higher. The relationship between the time C ₂ and the exhaust gas temperature T shown in FIG. 6B is stored in the ROM 32 in advance.

By the way, as described above, even if the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is made rich, the NOx absorbent 2
When the temperature of 0 is low, NOx is hardly released from the NOx absorbent 20. Therefore, in the embodiment according to the present invention, NOx
When the temperature of the absorbent 20 is low, the secondary air control valve 25 is opened and the secondary air is supplied into the exhaust manifold 16 when the air-fuel ratio is made rich as shown by the chain line in FIG. I have to. When secondary air is supplied into the exhaust manifold 16 when the air-fuel ratio is made rich and a large amount of unburned HC and CO are discharged from the engine, the secondary air will contribute to unburned HC and CO. Part is oxidation catalyst 17
Is immediately oxidized at. As a result, the temperature of the exhaust gas discharged from the oxidation catalyst 17 is immediately raised by the heat of oxidation generated at this time, and thus NOx
The temperature of the absorbent 20 is immediately raised. Thus, NOx is released from the NOx absorbent 20 immediately.

The lower the exhaust gas temperature T, the lower the temperature of the NOx absorbent 20. Therefore, the NOx absorbent 2
As the temperature of 0 is lower, the amount of secondary air is increased to increase the oxidation catalyst 17
It is preferable to increase the heat of oxidation reaction generated in (1). Therefore, in the embodiment according to the present invention, as shown in FIG. 8, the opening degree S of the secondary air control valve 25 is increased as the exhaust gas temperature T becomes lower.

On the other hand, when the secondary air is supplied, a part of the unburned HC and CO discharged from the engine is oxidized by the secondary air, and therefore the unburned HC and C for reducing NOx.
The amount of O is insufficient. Therefore, in the embodiment according to the present invention, when the secondary air is supplied so that sufficient unburned HC and CO are generated to reduce NOx even when the secondary air is supplied, the correction as shown by the chain line in FIG. The coefficient KK is increased to KK2 (> KK1). That is, the rich degree of the air-fuel ratio is increased. This KK2 is larger than KK1 regardless of the exhaust gas temperature T, but as can be seen from FIG. 8, the supply amount of secondary air decreases as the exhaust gas temperature T increases, so that as shown in FIG. 6 (A). KK
The difference between 2 and KK1 decreases as the exhaust gas temperature T increases. The relationship between the correction coefficient KK2 and the exhaust gas temperature T shown in FIG. 6A is stored in the ROM 32 in advance.

Further, the temperature of the NOx absorbent 20 becomes low when the exhaust gas temperature is low, that is, when the engine load Q / N is low, especially during idling operation. Therefore, in the embodiment according to the present invention, the secondary air is supplied only when the engine load Q / N is lower than a predetermined set load (Q / N) ₀ . Next, with reference to FIG. 9 to FIG. 11, one embodiment of the control for absorbing and releasing the NOx absorbent 20 according to the present invention will be explained.

FIGS. 9 and 10 show an interrupt routine executed at regular time intervals. Referring to FIGS. 9 and 10, first, at step 60, it is judged if the correction coefficient K is smaller than 1.0, that is, if the lean air-fuel mixture is burned. When K ≧ 1.0, that is, when the air-fuel mixture supplied into the combustion chamber 3 is at the stoichiometric air-fuel ratio or rich, the routine proceeds to step 88, where the secondary air control valve 25 is closed, and then the processing cycle is completed. . On the other hand, when K <1.0, that is, when the lean air-fuel mixture is being combusted, the routine proceeds to step 61, where the NOx amount W absorbed in the NOx absorbent 20 is calculated. That is, the NOx amount discharged from the combustion chamber 3 increases as the intake air amount Q increases and increases as the engine load Q / N increases, so the NOx amount W absorbed by the NOx absorbent 20 is W and k _1. · Q · Q / N (k 1 is a constant) will be represented by the sum of the.

Next, at step 62, it is judged if the execution flag is set or not. When the execution flag is not set, the routine proceeds to step 63, where it is judged if the NOx amount W absorbed in the NOx absorbent 20 is larger than a preset set amount W ₀ . This set amount W ₀ is, for example, the maximum NOx that the NOx absorbent 20 can absorb.
About 30 percent of the volume. If W ≦ W ₀ , the processing cycle is completed through step 88, and if W> W ₀ , the process proceeds to step 64 and the execution flag is set. Therefore, the execution flag is set when W> W ₀ .

When the execution flag is set, step 65
Then, it is judged whether the engine load Q / N is lower than the set load (Q / N) ₀ . When Q / N ≧ (Q / N) ₀ , the routine proceeds to step 66, where the correction coefficient KK1 is calculated from the relationship shown in FIG. 6 (A) and the map shown in FIG. Then, it proceeds to step 70. On the other hand, Q / N <(Q /
When N) _0, the routine proceeds to step 67, where the correction coefficient KK2 is calculated from the relationship shown in FIG. 6 (A) and the map shown in FIG. Next, at step 68, the opening degree S of the secondary air control valve 25 is calculated from the map shown in FIG. 7 and the relationship shown in FIG. Next, at step 69, the secondary air flag indicating that secondary air should be supplied is set, and then the routine proceeds to step 70.

In step 70, the final correction coefficient KK is calculated by multiplying KK by k ₂ · W (k ₂ is a constant). That is, the smaller the NOx amount W absorbed by the NOx absorbent 20, the richer the degree (KK1 or KK).
2) is reduced. Next, in step 71, FIG.
(B) from the map shown in relationship and Figure 7 shows a time C ₂
Is calculated. Next, at step 72, C ₂ has k ₃ · W
(K ₃ is a constant) to obtain the final time C
₂ is calculated. That is, the time C ₂ is shortened as the NOx amount W absorbed by the NOx absorbent 20 decreases. Then the processing cycle is completed.

When the execution flag is set, in the next processing cycle, step 62 of FIG. 9 to step 73 of FIG.
Then, the NOx releasing flag is set. Next, at step 74, the count value C is incremented by 1. Next, at step 75, it is determined whether or not the count value C has become larger than the time C ₁ , that is, whether or not the period for maintaining a constant rich air-fuel ratio (k = KK1 or KK2) has elapsed after starting the rich control. Is determined. When C <C _1, the routine proceeds to step 76, where it is judged if the secondary air flag is set or not. When the secondary air flag is not set, the processing cycle is completed. Therefore, at this time, the correction coefficient K is maintained at KK1 without supplying the secondary air as shown by the solid line in FIG. On the other hand, when the secondary air flag is set, the routine proceeds to step 77, where the secondary air control valve 25 is opened to the opening degree S. Therefore, at this time, the secondary air is supplied and the correction coefficient K is maintained at KK2.

When it is judged at step 75 that C> C ₁ , the routine proceeds to step 78, where the count value C
There whether it is larger than the time C _2, i.e. whether the time C ₂ from the start of the rich control has passed or not. When C ≦ C _2, the routine proceeds to step 79, where the constant value α is subtracted from the correction coefficient KK. Next, at step 80, it is judged if the correction coefficient KK has become smaller than 1.0. When KK ≦ 1.0, step 81
And KK is set to 1.0. Next, at step 82, if the secondary air control valve 25 is open, the secondary air control valve 25 is closed.

[0033] Then C> becomes C ₂ execution flag proceeds from step 78 to step 83 are reset, then NOx releasing flag is reset in step 84. Next, at step 85 , the secondary air flag is reset. Next, at step 86, NOx absorbent 2
The NOx amount W absorbed to 0 is set to zero, and then the count value C is set to zero in step 87.

FIG. 11 shows a routine for calculating the fuel injection time TAU, and this routine is repeatedly executed. Referring to FIG. 11, first, in step 90, as shown in FIG.
The basic fuel injection time TP is calculated from the map shown in FIG.
Next, at step 91, it is determined whether or not the NOx release flag is set. When the NOx releasing flag is not set, the routine proceeds to step 92, where K (for example, K = 0.6) is made Kt. Next, at step 94, the fuel injection time TAU is calculated by multiplying the basic fuel injection time TP by the correction coefficient Kt. Therefore, at this time, the lean air-fuel mixture is burned.

On the other hand, when it is judged at step 91 that the NOx releasing flag is set, the routine proceeds to step 93, where the correction coefficient KK calculated by the routines of FIGS. 9 and 10 is made Kt, and then step 9
Proceed to 4. Therefore, at this time, the air-fuel mixture supplied into the combustion chamber 3 is temporarily made rich, and then maintained at the stoichiometric air-fuel ratio for a while.

[0036]

As described above, when NOx should be released from the NOx absorbent, the temperature of the NOx absorbent is raised, so NO
x can be promptly released from the NOx absorbent.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

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

FIG. 3 shows unburned HC and C in exhaust gas discharged from the engine.
FIG. 3 is a diagram schematically showing the concentrations of O and oxygen.

FIG. 4 is a diagram for explaining the effect of absorbing and releasing NOx.

FIG. 5 is a diagram illustrating a change in a correction coefficient K during rich control.

FIG. 6 is a diagram showing a relationship between correction coefficients KK1, KK2, time C ₂ and exhaust gas temperature T.

FIG. 7 is a view showing a map of an exhaust gas temperature T;

FIG. 8 is a diagram showing a relationship between an opening degree S of a secondary air control valve and an exhaust gas temperature T.

FIG. 9 is a flowchart illustrating an interrupt routine.

FIG. 10 is a flowchart showing an interrupt routine.

FIG. 11 is a flowchart for calculating a fuel injection time TAU.

[Explanation of symbols]

 16 ... Exhaust manifold 17 ... Oxidation catalyst 20 ... NOx absorbent 22 ... Secondary air supply device

Claims (1)

(57) [Claims] 1. An NOx absorbent that absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean and releases the absorbed NOx when the oxygen concentration in the inflowing exhaust gas decreases is arranged in the engine exhaust passage to absorb the NOx. In the engine exhaust passage upstream of the agent
An engine exhaust passage upstream of the oxidation catalyst with the oxidation catalyst
A secondary air supply device is installed inside the NOx absorbent to remove NO
When the temperature of the NOx absorbent should be raised when releasing x, the secondary air is supplied by the secondary air supply device into the engine exhaust passage upstream of the oxidation catalyst , and the air-fuel ratio of the exhaust gas flowing into the NOx absorbent is adjusted. An exhaust purification device for an internal combustion engine that is made rich.