JPH10205384A - Device and method for exhaust emission control of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detecting precision of concentration of oxygen in exhaust gas, detected by an oxygen concentration sensor, in a system for supplying unburnt hydrocarbon to an NOx catalyst by after-infection. SOLUTION: An NOx catalyst 19 and an oxygen concentration sensor 20 are provided in an exhaust pipe 18 of a diesel engine 10. An output signal of the oxygen concentration sensor 20 is corrected on the basis of the after- injection command for supplying hydrocarbon to the NOx catalyst 19. The oxygen concentration corresponding to a case where after-injection is not performed can be estimated by estimating the decrease of the detected oxygen concentration after after-injected unburnt hydrocarbon is burnt by an oxygen concentration sensor 20, and the adverse effect of after-injection to the oxygen concentration detection can be eliminated. Any one of the ERG gas flow rate, the fuel injection amount, or the intake air amount is corrected on the basis of the corrected oxygen concentration detected value, and therefore, exhaust emission control in which the adverse effect by after-injection is eliminated is made possible, and the NOx purifying factor can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine exhaust purification apparatus and an exhaust purification method for reducing and purifying nitrogen oxides (NOx) in exhaust gas discharged from an internal combustion engine with a catalyst.

[0002]

2. Description of the Related Art N 2 in exhaust gas discharged from an internal combustion engine, such as a diesel engine, in which fuel is burned under an excess of oxygen.
In order to purify Ox, a technique has been proposed in which a NOx catalyst is provided in an exhaust pipe, and hydrocarbon (fuel) is supplied to the NOx catalyst as a reducing agent to reduce and purify NOx. As an example thereof, in Japanese Patent Application Laid-Open No. 5-156993, a main injection command for generating an engine output is given to a fuel injection valve of each cylinder of an internal combustion engine to perform a main injection, and in an expansion stroke after the main injection, A post-injection command is given to post-inject fuel of 0.3 to 3% of the main injection fuel amount from the fuel injection valve, and the post-injection supplies unburned fuel (hydrocarbon) as a reducing agent to the NOx catalyst. ing.

[0003]

SUMMARY OF THE INVENTION In order to further improve the NOx purification rate, the present inventors detect the oxygen concentration in exhaust gas with an oxygen concentration sensor, and control the internal combustion engine according to the detected value. For example, a technique for appropriately controlling the hydrocarbon concentration and the NOx concentration in the vicinity of the NOx catalyst by correcting the EGR gas flow rate, the fuel injection amount, the intake air amount, or the like is being studied.

However, during operation, since the oxygen concentration sensor is heated by a built-in heater and becomes high temperature, the post-injected unburned hydrocarbon is burned by the oxygen concentration sensor, and the oxygen concentration is accordingly detected low. As a result, the control accuracy of the internal combustion engine is reduced.

[0005] Generally, many diesel engines are equipped with an EGR (exhaust gas recirculation device) for purifying NOx. Therefore, the present inventors aimed to further improve the NOx purification rate by using this EGR and the above-mentioned EGR. Consideration is also given to using a combined NOx catalyst. In this case, for example, as disclosed in JP-A-63-223359 (this publication relates to a gasoline engine), the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the detected oxygen concentration is determined as a target oxygen concentration. It is conceivable to control the EGR flow rate so as to be as follows.

However, as described above, the detected value of the oxygen concentration sensor is lower than the actual oxygen concentration of the EGR gas by an amount corresponding to the decrease in the oxygen concentration due to the post-injected unburned hydrocarbon burning by the oxygen concentration sensor. Therefore, when the post-injection is performed, the EGR gas flow rate is corrected to decrease in order to increase the oxygen amount (intake air amount) supplied to the internal combustion engine.
The control accuracy of GR deteriorates and the amount of NOx emission from the internal combustion engine increases. In addition, part of the exhaust gas containing hydrocarbons supplied by the post-injection is returned to the intake system by EGR, and accordingly, the amount of hydrocarbons supplied to the NOx catalyst decreases and the NOx purification rate by the NOx catalyst also decreases. Will drop.

In addition, the present inventors have also developed an exhaust purification system that purifies NOx with a NOx catalyst alone without combining with EGR, for example, based on the oxygen concentration in exhaust gas detected by an oxygen concentration sensor. A method of properly controlling the hydrocarbon concentration and the NOx concentration in the vicinity of the NOx catalyst by correcting the amount or the intake air amount is considered,
Even in this case, the expected improvement in the NOx purification rate cannot be obtained unless the problem of lowering the detection accuracy of the oxygen concentration sensor due to the post-injection is solved.

[0008] To generalize this problem, an exhaust gas purifying apparatus having a control means for controlling a system including an internal combustion engine so as to increase a purifying rate of a catalyst by an output value of a sensor for detecting a concentration of a specific component in exhaust gas. In this case, if post-injection is performed to increase the purification rate of a catalyst that reduces and purifies nitrogen oxides in exhaust gas, the output value of the sensor changes, and as a result, the purification rate of the catalyst decreases.

The present invention has been made in view of such circumstances, and a first object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine and an exhaust gas purifying apparatus capable of suppressing a reduction in the purification rate of a catalyst even after injection. The way is to get.

A second object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine and an exhaust gas purifying apparatus, which can accurately detect the oxygen concentration in exhaust gas by an oxygen concentration sensor even after injection, thereby improving the NOx purification rate. It is to get a purification method.

A third object is to detect the concentration in a state where there is substantially no post-injection by devising a mounting position of a sensor for detecting the concentration of a specific component in the exhaust gas, thereby lowering the purification rate of the catalyst. It is an object of the present invention to obtain an exhaust gas purification device for an internal combustion engine that can suppress the occurrence of exhaust gas.

A fourth object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine which can suppress a decrease in the purifying rate of a catalyst by devising a mounting position of the EGR.

A fifth object of the present invention is to estimate the hydrocarbon concentration in the exhaust gas due to the post-injection, thereby detecting the oxygen concentration in a state where the post-injection is substantially absent, thereby suppressing a decrease in the purification rate of the catalyst. And a method of purifying exhaust gas.

[0014]

According to the present invention, there is provided an exhaust gas purifying apparatus and method for an internal combustion engine according to claims 1 and 10 of the present invention. In addition to providing a catalyst for reducing and purifying oxides, an oxygen concentration sensor for detecting the oxygen concentration in the exhaust gas is provided, and the oxygen concentration sensor is corrected by the oxygen concentration sensor correction means based on a post-injection command for supplying hydrocarbons to the catalyst. Correct the output value. By this correction, it is possible to estimate the oxygen concentration corresponding to the case where there is no post-injection, in anticipation that the post-injection unburned hydrocarbon is burned by the oxygen concentration sensor and the detected oxygen concentration decreases, and the post-injection can be performed. Can have an adverse effect on oxygen concentration detection. Therefore, based on the corrected output value of the oxygen concentration sensor, the control amount (for example, E
Any of GR gas flow rate, fuel injection amount, intake air amount, etc.)
Is corrected, exhaust gas purification control that eliminates the adverse effects of the post-injection can be performed, and the NOx purification rate can be improved. The target oxygen concentration in the exhaust gas may be corrected based on the post-injection command, and the control amount of the internal combustion engine may be corrected based on the corrected target oxygen concentration and the output value of the oxygen concentration sensor. Items 11 and 20), the same effect can be obtained in this case.

Further, when the output value of the oxygen concentration sensor is corrected by the oxygen concentration sensor correcting means, the exhaust flow rate estimating means is based on the operating state of the internal combustion engine detected by the operating state detecting means. The exhaust gas flow rate is estimated by using the estimated exhaust gas flow rate and the post-injection command, and the hydrocarbon concentration in the exhaust gas around the oxygen concentration sensor is estimated by the hydrocarbon concentration estimating means. The output value of the oxygen concentration sensor may be corrected based on this. In other words, the amount of oxygen consumed when the hydrocarbons in the exhaust gas are burned by the oxygen concentration sensor changes according to the hydrocarbon concentration in the exhaust gas. Therefore, the hydrocarbon concentration is estimated and the output value of the oxygen concentration sensor is calculated. By making the correction, it is possible to accurately detect the oxygen concentration corresponding to the case where there is no post-injection, in anticipation of the amount of oxygen consumed by the oxygen concentration sensor. still,
The target oxygen concentration may be corrected based on the estimated value of the hydrocarbon concentration (claim 12), and the same effect can be obtained in this case.

Further, a delay time until the exhaust reaches the oxygen concentration sensor is calculated based on the operating state of the internal combustion engine detected by the operating state detecting means.
Based on the exhaust flow rate before the delay time and the post-injection command, the current hydrocarbon concentration in the exhaust gas around the oxygen concentration sensor is estimated, and the output value of the oxygen concentration sensor is estimated based on the estimated value of the hydrocarbon concentration. The correction may be made. That is, the delay time from when the exhaust gas flow rate is detected based on the operation state of the internal combustion engine to when the exhaust gas reaches the oxygen concentration sensor and the delay time until the post-injected hydrocarbon reaches the oxygen concentration sensor are: On the other hand, when the operating state of the internal combustion engine is in a transient state, the accuracy of estimating the hydrocarbon concentration is reduced. Therefore, by considering this delay time, even when the operation state of the internal combustion engine is in a transient state, the hydrocarbon concentration in the exhaust gas around the current oxygen concentration sensor can be accurately estimated, and there is no after-injection. The oxygen concentration corresponding to the case can be accurately detected.

The post-injection may be performed for all the cylinders, but may be performed for only some of the cylinders (ie, intermittent post-injection). Hydrogen can be supplied, and the NOx purification rate can be improved. When intermittent post-injection is performed, exhaust gas containing hydrocarbons and exhaust gas not containing hydrocarbons by the post-injection flow alternately. It is conceivable that the output is performed at a cycle longer than the cycle determined from the detection response of the density sensor. With this configuration, the oxygen concentration in the exhaust gas containing no hydrocarbons by the post-injection is accurately detected by the oxygen concentration sensor before the exhaust gas containing hydrocarbons by the next post-injection reaches the oxygen concentration sensor. be able to. In this case,
Even without correcting the output value of the oxygen concentration sensor as described above, the oxygen concentration in the exhaust gas around the oxygen concentration sensor can be accurately detected.

Further, in this case, based on the change amount of the output of the oxygen concentration sensor within a predetermined time longer than the cycle determined from the detection response of the oxygen concentration sensor, as in claims 5 and 15, The post-injection command may be corrected.
In other words, the change in the output of the oxygen concentration sensor is caused by the alternating flow of the exhaust gas containing hydrocarbons and the exhaust gas not containing hydrocarbons caused by the post-injection. From the quantity, the quantity of post-injected hydrocarbons can be estimated. Therefore, by correcting the post-injection command based on the change amount of the output of the oxygen concentration sensor, individual differences (variation) of the fuel injection valve, deterioration over time,
It is possible to correct a deviation in the amount of post-injected hydrocarbons due to a control system error or the like, to constantly supply a sufficient amount of hydrocarbons to the catalyst stably, thereby contributing to an improvement in the NOx purification rate.

In the case where post-injection is performed only for a specific cylinder, the oxygen concentration sensor may be connected to the exhaust gas of the cylinder farthest from the specific cylinder for performing post-injection. It may be arranged in a manifold. As described above, when the post-injection is performed only for a specific cylinder, the exhaust gas containing hydrocarbons by the post-injection flows only to the exhaust manifold of the specific cylinder, and the post-injection to the exhaust manifolds of the other cylinders. The exhaust gas does not contain hydrocarbons. In this case, a phenomenon occurs in which a part of the exhaust gas containing hydrocarbons flowing out of the exhaust manifold of the specific cylinder flows backward and diffuses into the exhaust manifold of other cylinders. The farther away from a specific cylinder, the smaller the number. Therefore, in the exhaust manifold of the cylinder farthest from the specific cylinder that performs the post-injection, the backflow and diffusion phenomenon of the post-injected hydrocarbon is most unlikely to occur, so by arranging the oxygen concentration sensor in the exhaust manifold of that cylinder. This makes it possible to detect oxygen concentration with relatively high accuracy, which is not easily affected by hydrocarbons caused by post-injection. In this case, the oxygen concentration in the exhaust gas can be relatively accurately detected without correcting the output value of the oxygen concentration sensor as described above.

Further, in a system in which an EGR (exhaust gas recirculation device) and a NOx catalyst are combined, the exhaust gas recirculation passage is provided in a cylinder located farthest from a specific cylinder for performing post-injection. May be connected to the exhaust manifold. With this configuration, it becomes difficult for the exhaust gas containing hydrocarbons discharged from the specific cylinder performing the post-injection to return to the intake system through the exhaust gas recirculation passage, thereby suppressing a decrease in the hydrocarbon supply amount due to EGR. Thus, a decrease in the NOx purification rate of the catalyst can be prevented. As a result, high-efficiency NOx purification by effectively exhibiting both functions of the catalyst and the EGR becomes possible.

Further, the exhaust gas recirculation passage may be connected to the exhaust passage on the downstream side of the catalyst. In this way, part of the exhaust gas containing hydrocarbons by the post-injection flows into the catalyst and is used for NOx reduction and purification, and then a part of the exhaust gas passes through the exhaust gas recirculation passage to the intake system. Will be returned. Therefore, even if EGR is performed, the amount of hydrocarbon supply to the catalyst by the post-injection does not decrease at all, and high-efficiency NOx purification by effectively exhibiting both functions of the catalyst and EGR becomes possible.

Further, an exhaust gas recirculation catalyst for reducing and purifying nitrogen oxides in the exhaust gas recirculation gas may be provided in the exhaust gas recirculation passage. If you do this,
In the process in which a part of the exhaust gas including the post-injected hydrocarbon flows through the exhaust gas recirculation passage as the exhaust gas recirculation gas and passes through the exhaust gas recirculation gas catalyst, the hydrocarbon in the exhaust gas recirculation gas is removed by the catalytic action of the exhaust gas recirculation gas catalyst. The NOx reacts and the NOx is reduced and purified. As a result, NOx in the exhaust gas recirculated to the internal combustion engine is reduced, and accordingly, NOx discharged from the internal combustion engine is reduced.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment (1)] An embodiment (1) in which the present invention is applied to, for example, a four-cylinder diesel engine will be described below with reference to FIGS.

First, the configuration of the entire engine control system will be described with reference to FIG. An intake pipe 11 of a diesel engine 10 which is an internal combustion engine is provided with an air flow sensor 12 for detecting an intake air amount, and the intake air passing through the air flow sensor 12 passes through an intake manifold 13 so that each of the diesel engine 10 Inhaled into cylinder.
Each cylinder of the diesel engine 10 is provided with an electromagnetic valve type fuel injection valve 14 as a fuel injection means, and the fuel stored at a high pressure from a high pressure fuel pump 15 is supplied to each fuel injection valve 14 through a fuel pipe 16. Is done.

The exhaust gas discharged from each cylinder of the diesel engine 10 is supplied to an exhaust manifold 17 (exhaust passage).
The exhaust gas is discharged to one exhaust pipe 18 (exhaust passage). A catalyst for reducing and purifying NOx in the exhaust gas, that is, a NOx catalyst 19 is provided in the exhaust pipe 18. An oxygen concentration sensor 20 for detecting the oxygen concentration in the exhaust gas is provided upstream of the NOx catalyst 19.
Downstream of the exhaust gas temperature sensor 21 for detecting the exhaust gas temperature
Is installed.

On the other hand, an EGR pipe 22 is connected between the exhaust pipe 18 and the intake pipe 11 to form an exhaust gas recirculation passage for recirculating a part of the exhaust gas to the intake pipe 11. A valve 23 is provided. This EG
The opening of the R valve 23 is adjusted by the EGR control valve 24, and the EG passing through the EGR pipe 22 is adjusted by the opening adjustment.
The R gas flow is controlled.

During the operation of the diesel engine 10, the engine electronic control circuit (hereinafter referred to as "ECU") 25 controls the fuel injection valve 14 and the EGR control valve 24 of each cylinder. The ECU 25 includes the air flow sensor 1
2. Accelerator sensor 26 and engine speed sensor 27
(These correspond to operating state detecting means.) The operating state of the diesel engine 10 is detected based on a signal read from the operating state detecting means, and the temperature of the NOx catalyst 19 is set to a predetermined activation temperature based on the output signal of the exhaust temperature sensor 21. It is determined whether it is within the range.

An engine control program shown in FIG. 2 is stored in a ROM (storage medium) built in the ECU 25. The ECU 25 executes the engine control program of FIG. 2 to output a main injection command for generating engine output and a post-injection command for supplying hydrocarbons to the NOx catalyst 19 to the fuel injection valves 14 of each cylinder. In addition to functioning as the injection control means, it also functions as an oxygen concentration sensor correction means for correcting the output value of the oxygen concentration sensor 20. Further, based on the corrected output value of the oxygen concentration sensor 20, the control amount of the diesel engine 10 is controlled. It also functions as an engine control amount correction unit that corrects one of the EGR gas flow rates in a direction to increase the NOx purification rate.

Hereinafter, the contents of the engine control executed by the ECU 25 will be described with reference to the flowchart of FIG. This engine control program is repeatedly executed at every predetermined time or every predetermined crank angle. When this engine control program is started, first, at step 10
1, an accelerator sensor 26, an engine speed sensor 2
7. Read each signal output from the air flow sensor 12, the oxygen concentration sensor 20, and the exhaust temperature sensor 21.

Thereafter, the routine proceeds to step 102, where the pilot injection amount and its injection timing are calculated from the output signals of the accelerator sensor 26 and the engine speed sensor 27, and the main injection amount and its injection timing are calculated. Next, step 10
Then, the process proceeds to 3 to estimate the NOx emission amount from the diesel engine 10 based on the output signals of the accelerator sensor 26 and the engine speed sensor 27. Calculate the injection timing. The post-injection is executed when it is determined that the temperature of the NOx catalyst 19 is within a predetermined activation temperature range based on the output signal of the exhaust temperature sensor 21.

Here, the pilot injection, main injection, and post-injection will be described with reference to FIG. FIG. 3 is a time chart showing a fuel injection waveform of the fuel injection valve 14 of each cylinder based on a fuel injection signal from the ECU 25. Main injection is performed in the vicinity of the compression top dead center to generate engine output for each cylinder. Prior to this main injection, pilot injection is performed to inject a small amount of fuel, and when this fuel is ignited, main injection is performed to reduce premixed combustion at the beginning of combustion and reduce NOx emissions. Let it. The post-injection is performed in an expansion stroke or an exhaust stroke after combustion. Therefore, the post-injected fuel is discharged from the diesel engine 10 in the unburned state, mixed with the exhaust gas, supplied to the NOx catalyst 19, and consumed for NOx reduction purification. In this embodiment (1), the same pilot injection, main injection,
After-injection is performed.

In steps 102 and 103 in FIG. 2, after calculating the injection amount and the injection timing of the pilot injection, the main injection, and the post-injection, the routine proceeds to step 104, where the fuel injection valve 14 of each cylinder is calculated.
, An injection command for pilot injection, main injection, and post-injection is sequentially output.

Next, in step 105, an exhaust gas flow rate is detected at a predetermined position, a first predetermined time required for exhaust gas to reach the oxygen concentration sensor 20 after the detection of the exhaust gas flow rate is calculated, and post-injection is performed. Then, a second predetermined time required for the exhaust gas to reach the oxygen concentration sensor 20 is calculated. Hereinafter, a method of calculating the first and second predetermined times will be described in detail. The predetermined position in the present embodiment is the position of the air flow sensor 12. During the first predetermined time, the exhaust gas is supplied from the airflow sensor 12 to the diesel engine 10.
And a second time required to stay in the diesel engine 10,
Third required to move from 0 to oxygen concentration sensor 20
Consists of time.

First, a method of calculating the first time will be described. An intake flow rate per unit time is obtained from the intake flow rate detected by the air flow sensor 12. The intake flow rate per unit time is determined by the mass flow rate, and the volume flow rate per unit time can be determined by conversion using temperature and pressure. The first time is obtained by dividing the volume flow rate per unit time by the intake pipe volume calculated from the intake pipe diameter (known) and the distance (known) from the air flow sensor 12 to the diesel engine 10.

The second time is determined by the number of revolutions of the diesel engine 10. Diesel engine 10 intake
It is one cycle, that is, two rotations, and the rotation period (the time required for one rotation)
And the second time is obtained by doubling this rotation cycle. For example, when the rotation speed is 1000 (r / min), the rotation cycle is 6.0 × 10 ^-2 (sec), and the second
The time is 1.2 × 10 ⁻¹ (sec). When the rotation speed is 2000 (r / min), the rotation cycle is 3.0 × 1.
0 ^-2 (min), and the second time is 6.0 × 10 ^-2 (s).
ec).

The third time is obtained in the same manner as the first time. Here, it is assumed that the exhaust flow rate is substantially equal to the intake flow rate detected by the air flow sensor 12. Similarly to the first time, the exhaust flow rate per unit time is determined from the exhaust flow rate, and the exhaust flow rate as a volume flow rate is determined by converting using the temperature and the pressure. Exhaust pipe diameter (known) and distance from diesel engine 10 to oxygen concentration sensor 20 (known)
The third time is obtained by dividing the volume flow per unit time by the exhaust pipe volume calculated from. The calculated values of the intake flow rate and the exhaust flow rate may be corrected based on the EGR rate.

The second predetermined time is obtained from the time difference between the timing of post-injection and the timing (see FIG. 4) at which the output of the oxygen concentration sensor 20 decreases and is detected.

After the first predetermined time and the second predetermined time have been calculated as described above, the routine proceeds to step 106, where the exhaust flow rate at the first predetermined time before the current time and the post-injection amount at the second predetermined time before the current time are used. The hydrocarbon concentration in the vicinity of the oxygen concentration sensor 20 is estimated. Since the exhaust gas before the first predetermined time from the present time and the post-injection before the second predetermined time have reached the vicinity of the oxygen concentration sensor 20 at the present time, the second exhaust gas flow rate at the first predetermined time before the present time By dividing the post-injection amount before the predetermined time, the hydrocarbon concentration near the oxygen concentration sensor 20 at the present time can be estimated. Then, the oxygen concentration necessary for burning the estimated hydrocarbon concentration is calculated. For example, if the average composition of the hydrocarbon supplied by the post-injection is CH _1.85 , the reaction formula for burning this hydrocarbon is: CH _1.85 + (1 + 1.85 / 4) O ₂ → CO ₂ + (1.
85/2) H ₂ O, and the amount of oxygen necessary to burn the hydrocarbon amount is 1.4625 times the hydrocarbon amount. Since the hydrocarbon concentration can be regarded as the number of hydrocarbon molecules in the exhaust,
The number of required oxygen molecules is 1.4625 times the number of hydrocarbons. That is, the oxygen concentration required to burn the estimated hydrocarbon concentration is 1.462 of the estimated hydrocarbon concentration.
It is calculated as 5 times.

Next, the routine proceeds to step 107, where the output signal of the oxygen concentration sensor 20 is averaged at every 180 ° C. The reason for this is that, as shown in FIG. 4, the output signal of the oxygen concentration sensor 20 fluctuates in the output cycle of the post-injection command (180 ° C.). It is to improve.

In the next step 108, the averaged output signal of the oxygen concentration sensor 20 is corrected (increase correction) with the oxygen concentration calculated in step 106. This is because the post-injected unburned hydrocarbon burns near the oxygen concentration sensor 20 and the detected oxygen concentration is reduced. The output signal of the oxygen concentration sensor 20 is increased and corrected by an amount corresponding to the amount of decrease in the oxygen concentration caused by the combustion. That is, the “oxygen concentration necessary for burning the estimated hydrocarbon concentration” calculated in step 106 is the oxygen concentration sensor 20
Corresponds to the reduced oxygen concentration in the output signal of Accordingly, by correcting the averaged output signal of the oxygen concentration sensor 20 with the oxygen concentration calculated in step 106 (increase correction), it is possible to calculate the oxygen concentration corresponding to the case where there is no after-injection. Thus, the oxygen concentration (oxygen concentration in the EGR gas) required for the EGR control is accurately estimated.

Thereafter, the routine proceeds to step 109, where the output signal (corrected oxygen concentration) of the oxygen concentration sensor 20 which has been increased and corrected in step 108 is compared with the target oxygen concentration, and the EGR control valve 24 is operated in accordance with the comparison result. By controlling the energization of
The GR gas flow rate is controlled to increase or decrease. That is, since the corrected oxygen concentration corresponds to the oxygen concentration (oxygen concentration in the EGR gas) necessary for the EGR control, the corrected oxygen concentration is compared with the target oxygen concentration, and the corrected oxygen concentration is changed to the target oxygen concentration. If it is lower, the EGR gas flow rate is decreased, and if the corrected oxygen concentration is higher than the target oxygen concentration, the EGR gas flow rate is increased.

By performing the above-described control, as shown in FIG. 4, even if there is a situation in which the unburned hydrocarbons after the injection are burned by the oxygen concentration sensor 20 to lower the detected oxygen concentration, the post-injection can be performed. Oxygen concentration corresponding to the absence of
The oxygen concentration in the EGR gas required for the GR control can be accurately detected, and the EGR control accuracy can be improved. Thereby, high-efficiency NOx purification by effectively exhibiting both functions of the NOx catalyst 19 and the EGR becomes possible.

In step 105, the time required for the exhaust gas to flow through the intake pipe 11 and the exhaust pipe 17 and the time required for the intake, compression, expansion, and exhaust strokes in the cylinder are taken into consideration. Even when the engine 10 is in the transient operation state, it is possible to accurately detect the oxygen concentration in the exhaust gas near the oxygen concentration sensor 20 at the present time, perform accurate EGR control, and reduce the NOx purification rate by EGR. Can be increased.

In the embodiment (1) described above, the post-injection is performed on all the cylinders. However, the post-injection may be performed on only some of the cylinders (ie, the intermittent post-injection). . Even in this case, if the total amount of hydrocarbons to be post-injected during one cycle (720 ° C. A) is set to be equal to the target supply amount per one cycle, the hydrocarbons can be supplied to the NOx catalyst 19 without excess or shortage. Can be.

In this embodiment (1), the post-injection is performed for all the cylinders in the four-cylinder diesel engine 10, so that the output signal of the oxygen concentration sensor 20 is set to 180.
Although the average is taken every ° C, for example, in the case of intermittent post-injection every other cylinder, it is averaged every 360 ° C, and in the case of post-injecting only one cylinder in one cycle, 72
What is necessary is just to average out every 0 degreeC A. Generally, when performing post-injection of the M cylinder in one cycle in the N-cylinder engine, the output signal of the oxygen concentration sensor 20 may be averaged for each (720 / M) ° C.

In this embodiment (1), the output signal of the oxygen concentration sensor is increased in step 108 using the oxygen concentration calculated in step 106.
The target oxygen concentration may be corrected for reduction using the oxygen concentration calculated in step 06.

[Embodiment (2)] FIGS. 5 to 8 show an embodiment (2) of the present invention. Hereinafter, parts different from the embodiment (1) will be mainly described. In this embodiment (2), after-injection is performed intermittently as described later, and exhaust gas containing hydrocarbons and exhaust gas not containing hydrocarbons alternately flow by the post-injection. Furthermore, the cycle of performing the post-injection is set to a cycle longer than the cycle determined from the detection response of the oxygen concentration sensor 20. As a result, the oxygen concentration in the exhaust gas discharged from the cylinder in which the post-injection is not performed (the oxygen concentration in the exhaust gas that does not include hydrocarbons due to the post-injection) is
Before the exhaust gas containing hydrocarbons by the next post-injection reaches the oxygen concentration sensor 20, the oxygen concentration sensor 20 can accurately detect the exhaust gas.

Hereinafter, the control performed in the embodiment (2) will be described with reference to the flowcharts of FIGS. 5 and 6 are repeatedly executed at predetermined time intervals or at predetermined crank angles. When this engine control program is started, first, at step 201
Thus, an accelerator sensor 26, an engine speed sensor 27,
Each signal output from the air flow sensor 12, the oxygen concentration sensor 20, and the exhaust temperature sensor 21 is read. Thereafter, the routine proceeds to step 202, where the pilot injection amount and its injection timing are calculated from the output signals of the accelerator sensor 26 and the engine speed sensor 27, and the main injection amount and its injection timing are calculated. Next, the process proceeds to step 203, in which the NOx emission from the diesel engine 10 is estimated based on the output signals of the accelerator sensor 26 and the engine speed sensor 27, and the NOx emission from the estimated NOx emission and the output signal of the exhaust temperature sensor 21 are determined. The injection amount and its injection timing are calculated.

Thereafter, the routine proceeds to step 204, where the program is started from the end of the previous post-injection in order to calculate the post-injection amount according to the elapsed time (crank angle) from the end of the previous post-injection to the present time. Each time the predetermined post-injection amount is integrated, an integrated post-injection amount is obtained. Thereafter, the process proceeds to step 205, where pilot injection and main injection commands are sequentially output to the fuel injection valves 14 of the respective cylinders.

Next, the routine proceeds to step 206, where it is determined whether or not a predetermined time has elapsed since the end of the previous post-injection. Here, the predetermined time is a time longer than a cycle determined from the detection response of the oxygen concentration sensor 20, for example, 20 times.
msec to 500 msec, more preferably 5
Set within the range of 0 msec to 200 msec. If the predetermined time has not elapsed since the end of the previous post-injection, the present program is terminated without performing the subsequent processing. Then, the post-injection command is output to the fuel injection valve 14 of the corresponding cylinder, and the post-injection is performed in the expansion stroke or the exhaust stroke of the cylinder.

Thereafter, the routine proceeds to step 208, where the integrated post-injection amount is cleared to zero, and then proceeds to step 209, where the output signal of the oxygen concentration sensor 20 reaches the maximum value within the above-mentioned predetermined time and is temporally stabilized. It is determined whether or not. That is, it is determined whether or not the oxygen concentration sensor 20 has been able to detect the oxygen concentration in the exhaust gas that does not include unburned hydrocarbons due to the post-injection (oxygen concentration without post-injection). If the determination in step 209 is “No”, the output signal of the oxygen concentration sensor 20 is affected by the post-injection, and the EGR
Since the oxygen concentration (oxygen concentration in the EGR gas) required for control cannot be detected with high accuracy, the subsequent processing is not performed,
Exit this program.

On the other hand, in step 209, "Yes"
Is determined, that is, if the oxygen concentration required for the EGR control can be detected, the process proceeds to step 210, where the output signal of the oxygen concentration sensor 20 is compared with the target oxygen concentration, and EGR is performed according to the comparison result. By energizing the control valve 24,
The EGR gas flow rate is increased or decreased. This allows
Accurate EGR control can be performed, and the NOx purification rate by EGR can be increased.

Thereafter, the routine proceeds to step 211, where the maximum value (that is, the oxygen concentration of the exhaust gas not containing hydrocarbons by the post-injection) and the minimum value (the oxygen concentration of the post-injection-exhaust gas) within the above-mentioned predetermined time are output. In other words, the change amount of the output of the oxygen concentration sensor 20 within a predetermined time is calculated by comparing the oxygen concentration of the exhaust gas containing hydrocarbons after the post-injection, and based on the change amount, the hydrocarbon amount of the post-injected hydrocarbon is calculated. The amount is calculated, and if the calculated value deviates from the target hydrocarbon amount, the post-injection command value is increased or decreased.

In this step 211, the calculation of the amount of change in the output of the oxygen concentration sensor 20 within the predetermined time is performed by calculating the difference between the output of the oxygen concentration sensor 20 within the predetermined time and the oxygen concentration when there is no post-injection. Integration (integration) may be performed,
In this case, the output change amount of the oxygen concentration sensor 20 can be obtained in consideration of the degree of change in the output of the oxygen concentration sensor 20.

In this case, the change in the output of the oxygen concentration sensor 20 is caused by the alternating flow of the exhaust gas containing hydrocarbons and the exhaust gas not containing hydrocarbons by the post-injection. The amount of post-injected hydrocarbon can be estimated from the amount of change in the output of the sensor 20. Therefore, by correcting the post-injection hydrocarbon amount based on the change amount of the output of the oxygen concentration sensor 20, the post-injection amount due to individual differences (variation) of the fuel injection valve 14, deterioration over time, errors in the control system, etc. The deviation can be corrected, and a sufficient amount of hydrocarbon can always be stably supplied to the NOx catalyst 19, which can contribute to an improvement in the NOx purification rate.

FIG. 7 is a time chart showing the fuel injection waveforms from the cylinders to when the engine control program shown in FIGS. 5 and 6 is executed during steady operation. The same pilot injection and main injection are performed in all cylinders to, but after injection is performed in the cylinders, a predetermined time longer than a cycle determined from the detection response of the oxygen concentration sensor 20 elapses. Therefore, the processing is not executed with the cylinder but executed with the cylinder after a predetermined time has elapsed. After the post-injection is executed in this cylinder, the post-injection is not executed again until the predetermined time elapses, so that the post-injection is not executed with the cylinder, but is executed in the cylinder after the predetermined time elapses,
Thereafter, the same processing is repeated.

FIG. 8 is a time chart showing the waveform of the output signal of the oxygen concentration sensor 20 when the post-injection shown in the time chart of FIG. 7 is performed. Each time the post-injection is performed in the cylinder, the cylinder, and the cylinder illustrated in FIG. 7, the output signal of the oxygen concentration sensor 20 decreases, and the fluctuation cycle of the output corresponds to 540 ° C. After the post-injection is performed and before the next post-injection is performed, the exhaust gas containing no unburned hydrocarbon is discharged from the two cylinders by the post-injection, and the exhaust gas flows into the oxygen concentration sensor 20. Since the gas is exchanged in the oxygen concentration sensor 20, the output of the oxygen concentration sensor 20 increases. As a result, after a predetermined time determined by the detection response of the oxygen concentration sensor 20, the output of the oxygen concentration sensor 20 becomes the maximum value (that is, the oxygen concentration in the exhaust gas when there is no post-injection), and this maximum value is detected. Further, the oxygen concentration (oxygen concentration in the EGR gas) required for the EGR control can be accurately detected without being affected by the post-injection.

In the embodiment (2) described above, the post-injection cycle is set longer than the cycle determined from the detection response of the oxygen concentration sensor 20, so that the post-injection is not affected. Since the oxygen concentration required for the EGR control can be accurately detected, the output signal of the oxygen concentration sensor 20 does not need to be corrected unlike the embodiment (1), and the output signal of the oxygen concentration sensor 20 does not need to be corrected. E
Even when used for GR control, accurate EGR control can be performed, and the NOx purification rate by EGR can be increased. Thereby, high-efficiency NOx purification by effectively exhibiting both functions of the NOx catalyst 19 and the EGR becomes possible.

[Embodiment (3)] In the embodiment (3) shown in FIGS. 9 and 10, the post-injection is performed only in a specific cylinder (in this example, a cylinder), and the post-injection is performed only in the specific cylinder. The post-injection amount for the cylinder is injected. In this embodiment (3), the points different from the configuration in FIG. 1 are the installation location of the oxygen concentration sensor 20 and the position of the connection port 31 on the exhaust pipe side of the EGR pipe 22 (exhaust gas recirculation passage). That is, the embodiment (3)
In the example, the oxygen concentration sensor 20 is disposed in the exhaust manifold 17d of the cylinder farthest from a specific cylinder for performing the post-injection. Similarly, the connection port 31 on the exhaust pipe side of the EGR pipe 22 is connected to the exhaust manifold 17d of the cylinder farthest from the specific cylinder for performing the post-injection.
It is connected to the.

FIG. 9 is a time chart showing a fuel injection waveform from cylinder to cylinder in the embodiment (3).
Although the same pilot injection and main injection are performed for all cylinders, post-injection is performed only for a specific cylinder. As described above, when the post-injection is performed only for the specific cylinder, the exhaust gas containing hydrocarbons by the post-injection flows only to the exhaust manifold 17a of the specific cylinder,
Exhaust manifolds 17b, 17 of other cylinders
Exhaust gas not containing hydrocarbons by the post-injection flows through c and 17d.

In this case, a part of the exhaust gas containing hydrocarbons flowing out of the exhaust manifold 17a of the cylinder in which the post-injection is performed is partially replaced with the exhaust manifolds 17b and 17b of the other cylinders.
A backflow / diffusion phenomenon occurs in 17c and 17d, but the backflow / diffusion phenomenon decreases as the distance from the cylinder in which the post-injection is performed increases. Therefore, in the exhaust manifold 17d of the cylinder farthest from the cylinder in which the post-injection is performed, since the backflow and diffusion phenomenon of the post-injected hydrocarbon is most unlikely to occur, the oxygen concentration sensor 20 should be disposed in the exhaust manifold 17d of the cylinder. Thus, relatively accurate oxygen concentration detection that is not easily affected by hydrocarbons due to post-injection becomes possible. In this case, even if the output value of the oxygen concentration sensor 20 is not corrected as in the above-described embodiment (1),
The oxygen concentration in the exhaust gas can be detected relatively accurately.

For the same reason, since the EGR pipe 22 is connected to the exhaust manifold 17d of the cylinder farthest from the specific cylinder for performing the post-injection, even if the post-injection is performed for the cylinder, Exhaust containing hydrocarbons due to the injection becomes difficult to return to the intake system through the EGR pipe 22, and it is possible to suppress a decrease in the amount of hydrocarbons supplied by the EGR and prevent a decrease in the NOx purification rate of the NOx catalyst 19. it can. Thereby, high-efficiency NOx purification by effectively exhibiting both functions of the NOx catalyst 19 and the EGR becomes possible.

FIG. 13 shows the proportion of hydrocarbons recirculated to the intake side by EGR in the amount of post-injected hydrocarbons when the post-injection cylinders are changed in order when the EGR rate is 30%. When the post-injection is performed in the cylinder closest to the EGR pipe 22, the recirculation rate to the intake side is the highest. Conversely, when the post-injection is performed in the cylinder farthest from the EGR pipe 22, the recirculation rate to the intake side is low. Lowest.

In the example of FIG. 9, the oxygen concentration sensor 20 is located upstream of the connection port 31 of the EGR pipe 22 on the exhaust pipe side, but the order may be reversed.

In this embodiment (3), only one cylinder is used for performing the post-injection. However, two or more cylinders may be used. The position of the connection port 31 on the exhaust pipe side of the EGR pipe 22 may be set to the exhaust manifold of the cylinder farthest from the specific cylinder for performing the post-injection.

[Embodiment (4)] FIG. 11 shows an embodiment (4) of the present invention. The difference from the configuration of FIG. 1 is that the connection port 32 of the EGR pipe 22 on the exhaust pipe side is NOx. The connection to the downstream side of the catalyst 19 and the EGR pipe 22
The exhaust throttle valve 33 is located downstream of the connection port 32 on the exhaust pipe side.
It is that was installed. By doing so, the exhaust gas containing unburned hydrocarbons by the post-injection has a total amount of NOx catalyst 1
9 is used for NOx reduction purification and passes through the NOx catalyst 19, and a part of the exhaust gas containing no unburned hydrocarbons or containing only a small amount of unburned hydrocarbons is EGR.
The gas is returned to the intake pipe 11 as gas. Therefore, even if the EGR is performed, the amount of hydrocarbon supply to the NOx catalyst 19 due to the post-injection does not decrease at all, and high-efficiency NOx purification by effectively exhibiting both functions of the NOx catalyst 19 and the EGR becomes possible. .

In this case, since the exhaust pressure on the downstream side of the NOx catalyst 19 is lower than that on the upstream side, a sufficient EGR gas flow rate may not be obtained in this state. Therefore, in this embodiment (4), the exhaust throttle valve 33 is installed downstream of the connection port 32 of the EGR pipe 22 on the exhaust pipe side, and the EG
By reducing the opening of the exhaust throttle valve 33 only during the R control, the EG
The exhaust pressure at the connection port 32 of the R pipe 22 is increased to secure a sufficient EGR gas flow rate.

[Embodiment (5)] FIG. 12 shows an embodiment (5) of the present invention. The difference from the configuration of FIG. 1 is that NOx in the EGR gas is discharged in the EGR pipe 22. That is, the NOx catalyst for EGR gas 34 to be reduced and purified is provided. In this configuration, a part of the exhaust gas containing hydrocarbons after injection flows through the EGR pipe 22 as EGR gas and
In the process of passing through the NOx catalyst 34 for GR gas, the catalytic action of the NOx catalyst 34 for EGR gas causes the hydrocarbons in the EGR gas to react with NOx to reduce and purify NOx.
Thereby, the EGR returned to the diesel engine 10
NOx in the gas is reduced, NOx is reduced efficiently by EGR, and NOx discharged from the diesel engine 10 is reduced.

The location of the NOx catalyst 34 for EGR gas may be either upstream or downstream of the EGR valve 23 as long as it is in the middle of the EGR pipe 22.

[Other Embodiments] Each of the above embodiments is
In each case, the present invention is applied to a four-cylinder diesel engine. However, it is needless to say that the number of cylinders is not limited to four, and may be another number. The internal combustion engine to which the present invention can be applied is not limited to a diesel engine, but can also be applied to a direct injection (direct injection) gasoline engine.

In each of the above embodiments, the EGR gas flow rate is corrected based on the output signal of the oxygen concentration sensor 20 (or the correction value thereof). However, the fuel injection amount or the intake air amount is corrected. You may do it. The correction of the intake air amount may be performed by adjusting the opening of a throttle valve provided in the intake pipe 11.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an entire engine control system showing an embodiment (1) of the present invention.

FIG. 2 is a flowchart showing a process flow of an engine control program according to the embodiment (1).

FIG. 3 is a time chart showing a fuel injection waveform of a fuel injection valve of each cylinder according to the embodiment (1).

FIG. 4 is a time chart showing a waveform of an output signal of the oxygen concentration sensor according to the embodiment (1).

FIG. 5 is a flowchart showing a process flow of an engine control program used in the embodiment (2) of the present invention.

FIG. 6 is a flowchart continued from FIG. 5;

FIG. 7 is a time chart showing a fuel injection waveform of a fuel injection valve of each cylinder according to the embodiment (2).

FIG. 8 is a time chart showing a waveform of an output signal of the oxygen concentration sensor according to the embodiment (2).

FIG. 9 is a configuration diagram of an entire engine control system showing an embodiment (3) of the present invention.

FIG. 10 is a time chart showing a fuel injection waveform of a fuel injection valve of each cylinder in the embodiment (3).

FIG. 11 is an overall configuration diagram of an engine control system showing an embodiment (4) of the present invention.

FIG. 12 is a configuration diagram of an entire engine control system showing an embodiment (5) of the present invention.

FIG. 13 is a diagram showing a relationship between a post-injection cylinder number and a recirculation ratio of hydrocarbons to an intake side.

[Explanation of symbols]

Reference Signs List 10: diesel engine (internal combustion engine), 11: intake pipe, 12: air flow sensor, 13: intake manifold, 14: fuel injection valve (fuel injection means), 17, 17a
17d: exhaust manifold (exhaust passage), 18: exhaust pipe (exhaust passage), 19: NOx catalyst (catalyst), 20: oxygen concentration sensor, 21: exhaust temperature sensor, 22: EGR pipe (exhaust recirculation passage), 23 ... EGR valve, 24 ... EGR control valve, 25 ... ECU (injection control means, oxygen concentration sensor correction means, engine control amount correction means, target oxygen concentration calculation means,
Oxygen concentration correcting means), 26 ... accelerator sensor, 27 ... engine speed sensor, 33 ... exhaust throttle valve, 34 ... EGR
NOx catalyst for gas (catalyst for exhaust gas recirculation).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/04 385 F02D 41/04 385Z 41/14 310 41/14 310E 310L 41/38 41/38 B F02M 25/07 550 F02M 25/07 550R 550N 580 580D

Claims (21)

[Claims] A fuel injection means provided for each cylinder of the internal combustion engine; a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas; and a catalyst installed in the exhaust passage. An oxygen concentration sensor for detecting an oxygen concentration in exhaust gas; an operating state detecting means for detecting an operating state of the internal combustion engine; and an engine output to fuel injection means for each cylinder based on a detection value of the operating state detecting means. Control means for outputting a main injection command for the fuel injection and a post-injection command for supplying hydrocarbons to the catalyst to the fuel injection means of at least one cylinder; and the oxygen concentration based on the post-injection command. Oxygen concentration sensor correction means for correcting the output value of the sensor; and nitrogen oxide purification based on the control value of the internal combustion engine based on the output value of the oxygen concentration sensor corrected by the oxygen concentration sensor correction means. An exhaust gas purifying apparatus for an internal combustion engine, comprising: engine control amount correction means for correcting the rate in a direction to increase the rate. 2. An exhaust gas flow rate estimating means for estimating an exhaust gas flow rate based on a value detected by the operating state detecting means, and an oxygen concentration sensor correcting means based on the estimated value of the exhaust gas flow rate and the post-injection command. A hydrocarbon concentration estimating means for estimating a hydrocarbon concentration in the exhaust gas around the oxygen concentration sensor, wherein the output value of the oxygen concentration sensor is corrected based on the estimated value of the hydrocarbon concentration. Item 2. An exhaust gas purification device for an internal combustion engine according to item 1. 3. The oxygen concentration sensor correction means includes means for calculating a delay time until exhaust reaches the oxygen concentration sensor based on a detection value of the operating state detection means, and the hydrocarbon concentration estimation means. 3. The exhaust gas of an internal combustion engine according to claim 2, wherein the controller estimates the hydrocarbon concentration in the exhaust gas around the oxygen concentration sensor at the present time based on the exhaust gas flow amount before the delay time and the post-injection command. Purification device. 4. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, and an operation state of the internal combustion engine. Operating state detecting means for detecting, and outputting a main injection command for generating an engine output to the fuel injection means of each of the cylinders based on a detection value of the operating state detecting means, and outputting the main injection command to at least one cylinder of the fuel injection means. Injection control means for outputting a post-injection command for supplying hydrocarbons to the catalyst, an oxygen concentration sensor installed in the exhaust passage, and detecting an oxygen concentration in the exhaust gas, based on an output value of the oxygen concentration sensor. Engine control amount correction means for correcting the control amount of the internal combustion engine in a direction to increase the nitrogen oxide purification rate, wherein the injection control means determines the post-injection command from the detection response of the oxygen concentration sensor. An exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas is output at a cycle longer than a predetermined cycle. 5. The post-injection command corrects a post-injection command based on a change amount of an output of the oxygen concentration sensor within a predetermined time longer than a cycle determined from a detection response of the oxygen concentration sensor. The exhaust gas purifying apparatus for an internal combustion engine according to claim 4, wherein the exhaust gas is output to the fuel injection means. 6. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, and an operation state of the internal combustion engine. Operating state detecting means for detecting, and outputting a main injection command for generating an engine output to the fuel injection means of each cylinder based on the detection value of the operating state detecting means, and outputting the catalyst to the fuel injection means of a specific cylinder. An injection control unit for outputting a post-injection command for supplying hydrocarbons to the fuel cell, an oxygen concentration sensor installed in the exhaust passage, and detecting an oxygen concentration in the exhaust gas, based on an output value of the oxygen concentration sensor. Engine control amount correction means for correcting the control amount of the internal combustion engine in a direction to increase the nitrogen oxide purification rate, wherein the oxygen concentration sensor exhausts a cylinder at a position farthest from the specific cylinder performing post-injection. An exhaust gas purification device for an internal combustion engine, which is disposed in a manifold. 7. An exhaust gas recirculation passage for recirculating a part of exhaust gas to an intake system of the internal combustion engine is connected to an exhaust manifold of a cylinder farthest from a specific cylinder for performing post-injection. An exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 6. 8. The exhaust gas recirculation passage for recirculating a part of the exhaust gas to an intake system of the internal combustion engine is connected to an exhaust passage on the downstream side of the catalyst. An exhaust gas purification device for an internal combustion engine. 9. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, and an operation state of the internal combustion engine. Operating state detecting means for detecting, and outputting a main injection command for generating an engine output to the fuel injection means of each of the cylinders based on a detection value of the operating state detecting means, and outputting the main injection command to at least one cylinder of the fuel injection means. Injection control means for outputting a post-injection command for supplying hydrocarbons to the catalyst, an oxygen concentration sensor installed in the exhaust passage, and detecting an oxygen concentration in the exhaust gas, based on an output value of the oxygen concentration sensor. Engine control amount correction means for correcting the control amount of the internal combustion engine in a direction to increase the nitrogen oxide purification rate; an exhaust gas recirculation passage for recirculating a part of exhaust gas to an intake system of the internal combustion engine; Installed, an exhaust purifying apparatus for an internal combustion engine, characterized in that the nitrogen oxides in the exhaust recirculation gas and an exhaust gas recirculation catalyst for reducing and purifying. 10. A method for reducing and purifying nitrogen oxides in exhaust gas discharged from an internal combustion engine with a catalyst, comprising: detecting an operating state of the internal combustion engine; and detecting an operating state of each cylinder of the internal combustion engine based on the detected value. The main injection is performed by giving a main injection command for generating an engine output to the fuel injection means, and the post injection is performed by giving a post injection command for supplying hydrocarbons to the catalyst to the fuel injection means of at least one cylinder. The oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, the output value of the oxygen concentration sensor is corrected based on the post-injection command, and the control amount of the internal combustion engine is controlled based on the corrected value. An exhaust purification method for an internal combustion engine, wherein the correction is performed in a direction to increase the oxide purification rate. 11. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, and a catalyst installed in the exhaust passage. An oxygen concentration sensor for detecting an oxygen concentration in the exhaust; an operating state detecting means for detecting an operating state of the internal combustion engine; a target oxygen for calculating a target oxygen concentration in the exhaust based on a detection value of the operating state detecting means Concentration calculating means for outputting a main injection command for generating an engine output to the fuel injection means of each cylinder based on the detection value of the operating state detection means, and at least one fuel injection means for at least one cylinder to the catalyst Injection control means for outputting a post-injection command for supplying hydrocarbons, and oxygen concentration correction means for correcting the output value of the oxygen concentration sensor or the target oxygen concentration based on the post-injection command, Engine control amount correction means for correcting the control amount of the internal combustion engine in a direction to increase the nitrogen oxide purification rate based on the output value of the oxygen concentration sensor and the target oxygen concentration after being corrected by the oxygen concentration correction means; An exhaust gas purifying apparatus for an internal combustion engine, comprising: 12. An exhaust gas flow rate estimating means for estimating an exhaust gas flow rate based on a detection value of the operating state detecting means, and the oxygen concentration correcting means, based on the estimated value of the exhaust gas flow rate and the post injection command. A hydrocarbon concentration estimating unit for estimating a hydrocarbon concentration in exhaust gas around the oxygen concentration sensor, and correcting an output value of the oxygen concentration sensor or the target oxygen concentration based on the estimated value of the hydrocarbon concentration. The exhaust gas purifying apparatus for an internal combustion engine according to claim 11, wherein: 13. The oxygen concentration correcting means includes means for calculating a delay time until exhaust reaches the oxygen concentration sensor based on a detection value of the operating state detecting means, wherein the hydrocarbon concentration estimating means is 13. The exhaust gas purification of an internal combustion engine according to claim 12, wherein a hydrocarbon concentration in the exhaust gas around the oxygen concentration sensor at the present time is estimated based on the exhaust flow rate before the delay time and the post-injection command. apparatus. 14. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, and an operation state of the internal combustion engine. Operating state detecting means for detecting, target oxygen concentration calculating means for calculating a target oxygen concentration in the exhaust gas based on the detected value of the operating state detecting means, and each of the cylinders based on the detected value of the operating state detecting means. An injection control unit that outputs a main injection command for generating an engine output to a fuel injection unit and outputs a post-injection command for supplying hydrocarbons to the catalyst to the fuel injection unit of at least one cylinder; An oxygen concentration sensor for detecting an oxygen concentration in exhaust gas, and increasing a control amount of the internal combustion engine based on an output value of the oxygen concentration sensor and the target oxygen concentration to increase a nitrogen oxide purification rate. Internal combustion engine control amount correction means for correcting in the direction, wherein the injection control means outputs the post-injection command at a cycle longer than a cycle determined from the detection response of the oxygen concentration sensor. Engine exhaust purification device. 15. The post-injection command corrects a post-injection command based on a change amount of an output of the oxygen concentration sensor within a predetermined time longer than a cycle determined from a detection response of the oxygen concentration sensor. The exhaust gas purifying apparatus for an internal combustion engine according to claim 14, wherein the output is output to the fuel injection means. 16. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, and an operation state of the internal combustion engine. Operating state detecting means for detecting, target oxygen concentration calculating means for calculating a target oxygen concentration in the exhaust gas based on the detected value of the operating state detecting means, and each of the cylinders based on the detected value of the operating state detecting means. An injection control unit that outputs a main injection command for generating engine output to a fuel injection unit and outputs a post-injection command for supplying hydrocarbons to the catalyst to a fuel injection unit of a specific cylinder; An oxygen concentration sensor that is installed and detects an oxygen concentration in the exhaust gas; and corrects a control amount of the internal combustion engine in a direction to increase a nitrogen oxide purification rate based on an output value of the oxygen concentration sensor and the target oxygen concentration. The oxygen concentration sensor is disposed in an exhaust manifold of a cylinder farthest from the specific cylinder that performs the post-injection. apparatus. 17. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, and an operation state of the internal combustion engine. Operating state detecting means for detecting, and outputting a main injection command for generating an engine output to the fuel injection means of each cylinder based on the detection value of the operating state detecting means, and outputting the catalyst to the fuel injection means of a specific cylinder. Injection control means for outputting a post-injection command for supplying hydrocarbons to the exhaust gas, and an exhaust gas recirculation passage for recirculating a part of exhaust gas to the intake system of the internal combustion engine, and performing post-injection on the exhaust gas recirculation passage. An exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas purifying apparatus is connected to an exhaust manifold located farthest from a specific cylinder. 18. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, and an operation state of the internal combustion engine. Operating state detecting means for detecting, and outputting a main injection command for generating an engine output to the fuel injection means of each cylinder based on the detection value of the operating state detecting means, and outputting the catalyst to the fuel injection means of a specific cylinder. Injection control means for outputting a post-injection command for supplying hydrocarbons to the exhaust gas, and an exhaust gas recirculation passage for recirculating a part of the exhaust gas to the intake system of the internal combustion engine. An exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas purifying apparatus is connected to the exhaust passage. 19. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, and an operation state of the internal combustion engine. Operating state detecting means for detecting, and outputting a main injection command for generating an engine output to the fuel injection means of each of the cylinders based on a detection value of the operating state detecting means, and outputting the main injection command to at least one cylinder of the fuel injection means. Injection control means for outputting a post-injection command for supplying hydrocarbons to the catalyst; an exhaust gas recirculation passage for recirculating a part of the exhaust gas to the intake system of the internal combustion engine; An exhaust gas purification device for an internal combustion engine, comprising: an exhaust gas recirculation gas catalyst that reduces and purifies nitrogen oxides therein. 20. A method for reducing and purifying nitrogen oxides in exhaust gas discharged from an internal combustion engine with a catalyst, comprising: detecting an operating state of the internal combustion engine; and detecting an operating state of each cylinder of the internal combustion engine based on the detected value. The main injection is performed by giving a main injection command for generating an engine output to the fuel injection means, and the post injection is performed by giving a post injection command for supplying hydrocarbons to the catalyst to the fuel injection means of at least one cylinder. The oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the target oxygen concentration in the exhaust gas is calculated from the operating state of the internal combustion engine. And correcting the control amount of the internal combustion engine in the direction of increasing the nitrogen oxide purification rate based on the corrected output value of the oxygen concentration sensor and the target oxygen concentration. Exhaust gas purification method for an internal combustion engine of internal combustion engine that. 21. A fuel injection means provided for each cylinder of the internal combustion engine, a catalyst installed in an exhaust passage of the internal combustion engine for reducing and purifying nitrogen oxides in exhaust gas, A concentration detecting means (20) disposed for detecting the concentration of a specific component in the exhaust gas; and reducing and purifying the catalyst by changing the component in the exhaust gas based on a detection value from the concentration detecting means. Catalyst control means for improving (22, 23, 24); operating state detecting means for detecting the operating state of the internal combustion engine; and engine output to the fuel injection means of each cylinder based on the detection value of the operating state detecting means. Injection control means for outputting a main injection command for generation and outputting a post-injection command for supplying hydrocarbons to the catalyst to fuel injection means of a specific cylinder; and the concentration detection means (20). Is before An exhaust gas purifying apparatus for an internal combustion engine, wherein the concentration is detected in a state where there is substantially no post-injection according to the post-injection command.