JP2010133375A - Device for correcting output of sensor and method for correcting output for sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology for more accurately correcting output value of a NOx sensor disposed at a downstream side of a selective reduction type NOx catalyst. <P>SOLUTION: This device includes: an upstream ratio estimation means (S102) estimating a ratio of at least one of NO and NO<SB>2</SB>in NOx flowing into a NOx catalyst; a temperature detection means detecting the temperature of the NOx catalyst; a downstream ratio estimation means (S103) estimating a ratio of at least one of NO and NO<SB>2</SB>in NOx at downstream of the NOx catalyst based on the ratio estimated by the upstream ratio estimation means and the temperature detected by the temperature detection means when a reducing agent is being supplied; and a correction means (S105) correcting an output value of the NOx sensor based on the ratio estimated by the downstream ratio estimation means. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sensor output correction device and a sensor output correction method.

When the supply of the reducing agent to the selective reduction type NOx catalyst (hereinafter referred to as the NOx catalyst) is stopped, the estimated value of the NOx concentration flowing into the NOx catalyst and the downstream of the NOx catalyst are provided. There is known a technique for determining an abnormality of the NOx sensor by comparing the output value of a sensor that measures the NOx concentration (hereinafter referred to as NOx sensor) (for example, refer to Patent Document 1).

However, the output value of the NOx sensor, the NOx concentration different values in accordance with the ratio also of NO or NO ₂ be the same. Furthermore, since the exhaust gas can vary the ratio between NO and NO ₂ as it passes through the NOx catalyst, an output value of the NOx sensor may also vary depending on the state of the NOx catalyst. For these reasons, it may be difficult to determine abnormality of the NOx sensor.
JP 2008-133780 A Japanese Patent Laid-Open No. 2007-100508 JP 2004-100700 A JP 2007-255345 A

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of more accurately correcting the output value of the NOx sensor provided downstream of the selective reduction type NOx catalyst. It is to provide.

In order to achieve the above object, the sensor output correction apparatus according to the present invention employs the following means. That is, the sensor output correction device according to the present invention is:
A selective reduction type NOx catalyst that is provided in an exhaust passage of the internal combustion engine and selectively reduces NOx by a reducing agent;
Reducing agent supply means for supplying a reducing agent into the exhaust gas upstream of the selective reduction type NOx catalyst;
A NOx sensor for measuring a NOx concentration downstream of the selective reduction type NOx catalyst;
In the sensor output correction device comprising:
Upstream ratio estimating means for estimating a ratio of at least one of NO or NO ₂ in NOx flowing into the selective reduction type NOx catalyst;
Temperature detecting means for detecting the temperature of the selective reduction type NOx catalyst;
Based on the ratio estimated by the upstream ratio estimating means and the temperature detected by the temperature detecting means when the reducing agent is supplied by the reducing agent supply means, the selective reduction type NOx Downstream ratio estimating means for estimating a ratio of at least one of NO or NO _{2 in} NOx downstream of the catalyst;
Correction means for correcting the output value of the NOx sensor based on the ratio estimated by the downstream ratio estimation means;
It is characterized by providing.

The selective reduction type NOx catalyst selectively reduces NOx by supplying ammonia, for example. The reducing agent supply means may include an injection device that injects ammonia or urea water, for example. Upstream ratio estimating means may detect the ratio between NO and NO ₂ in NOx. The temperature detection means may estimate the temperature from the operating state of the internal combustion engine, or may measure the temperature with a sensor. The NOx sensor measures the NOx concentration in the exhaust gas. Although NOx reacts in the selective reduction type NOx catalyst, not all NOx reacts, so the concentration of NOx remaining in the exhaust gas is measured. This is the NOx includes NO and NO _2. A reducing agent may be supplied based on this NOx concentration.

Here, NO or the ratio of NO ₂ in NOx is changed when passing through the NOx selective reduction catalyst. That is, since NO or NO ₂ is reduced by the selective reduction type NOx catalyst, the respective ratios can be lowered. At this time, the degree of reduction of NO or NO ₂ varies depending on the temperature of the selective reduction NOx catalyst. The relationship between this ratio and temperature can be obtained in advance by experiments or the like. Further, the ratio of NO or NO _{2 in} NOx downstream of the selective reduction type NOx catalyst also varies depending on the ratio of NO or NO ₂ in NOx flowing into the selective reduction type NOx catalyst. That is, the higher the ratio of NO or NO ₂ flowing into the selective reduction type NOx catalyst, the higher the downstream NO or NO ₂ ratio. According to these relationships, the downstream ratio estimating means estimates the ratio of NO or NO _{2 in} NOx. For example, if a correction value is calculated from this ratio, a correction value corresponding to the ratio of NO or NO ₂ can be calculated, so that the output value of the NOx sensor can be corrected with high accuracy. The relationship between the ratio estimated by the downstream ratio estimating means and the correction value of the output value of the NOx sensor may be obtained by experiments or the like.

In the present invention, a catalyst having an oxidation ability is provided upstream of the selective reduction type NOx catalyst,
The upstream ratio estimating means is based on the selective reduction type based on the ratio of at least one of NO or NO _{2 in} NOx discharged from the internal combustion engine and the ratio of NOx that reacts with the catalyst having the oxidation ability. The ratio of at least one of NO or NO ₂ in NOx flowing into the NOx catalyst can be calculated.

For example, the ratio of NO and NO _{2 in} NOx discharged from the internal combustion engine changes according to the operating state of the internal combustion engine (for example, the engine speed and the engine load). If the relationship between the operating state of the internal combustion engine and the ratio of NO and NO _{2 in} NOx is obtained in advance, at least one ratio of NO or NO _{2 in} NOx discharged from the internal combustion engine is determined from the operating state of the internal combustion engine. Can be sought.

Here, if the catalyst having the oxidizing ability is in the active state, NOx is oxidized by the passage of NOx through the catalyst having the oxidizing ability to become NO ₂ , so that these ratios change.

Then, based on the ratio of NO or NO _{2 in} NOx discharged from the internal combustion engine and the ratio of NOx to react with the catalyst having oxidation ability, N flowing out from the catalyst having oxidation ability
The ratio of NO or NO ₂ in Ox (that is, NOx flowing into the selective reduction type NOx catalyst) can be obtained.

Note that NOx exhausted from the internal combustion engine when no catalyst having oxidation ability is provided.
At least one of the ratio of NO or NO ₂ in, can be treated as equal to the at least one of the ratio of NO or NO ₂ in NOx flowing into the selective reduction type NOx catalyst.

In the present invention, the correction means can correct the output value of the NOx sensor according to the degree of deterioration of the selective reduction type NOx catalyst.

Here, when the degree of deterioration of the selective reduction type NOx catalyst becomes large, NOx hardly reacts with the selective reduction type NOx catalyst, so that the ratio of NO or NO ₂ does not change much. That is, since the reactivity of NOx changes according to the degree of deterioration of the selective reduction type NOx catalyst, if the output value of the NOx sensor is corrected according to this degree of deterioration, the output value of the NOx sensor can be corrected more accurately. Can do. This degree of deterioration may be a degree of decrease in the NOx purification rate in the selective reduction type NOx catalyst. In other words, the output value of the NOx sensor can be corrected based on how much the purification rate has decreased compared to when it is new.

In the present invention, the correction means can correct the output value of the NOx sensor in accordance with the flow rate of the exhaust gas passing through the selective reduction type NOx catalyst.

Here, as the flow rate of the exhaust gas is high, since the NOx is unlikely to react at selective reduction type NOx catalyst, the ratio of NO or NO ₂ is not so changed. That is, since the reactivity of NOx changes according to the flow rate of exhaust gas, the output value of the NOx sensor can be corrected more accurately if the output value of the NOx sensor is corrected according to the flow rate of exhaust gas. The exhaust flow rate may be the exhaust flow rate or the intake air amount.

  In the present invention, the correction means can correct the output value of the NOx sensor in accordance with the NOx concentration of the exhaust gas flowing into the selective reduction type NOx catalyst.

When NOx concentration in the exhaust gas is high, because the reaction of NOx is promoted in the selective reduction NOx catalyst, the ratio of NO or NO ₂ is further changed. That is, since the reactivity of NOx changes according to the NOx concentration of the exhaust, if the output value of the NOx sensor is corrected according to this NOx concentration, the output value of the NOx sensor can be corrected more accurately.

Note that the above-described correction of the output value of the NOx sensor may be performed by changing the ratio estimated by the downstream ratio estimation means. Further, even in a catalyst having oxidation ability, the ratio of NO or NO ₂ can be changed according to the degree of deterioration of the catalyst, the flow rate of exhaust gas, the temperature of the catalyst, etc. The ratio may be estimated.

  Moreover, in order to achieve the said subject, the following means can also be employ | adopted. That is, the output correction method of the NOx sensor according to the present invention is:

A first step of estimating a ratio of NO or NO _{2 in} NOx upstream of a selective reduction type NOx catalyst provided in an exhaust passage of an internal combustion engine and selectively reducing NOx by a reducing agent;
A second step of estimating a ratio of NO or NO _{2 in} NOx downstream of the selective reduction type NOx catalyst based on the temperature of the selective reduction type NOx catalyst and the ratio obtained in the first step;
A third step of correcting an output value of a NOx sensor provided downstream of the selective reduction type NOx catalyst based on the ratio obtained in the second step and the temperature of the selective reduction type NOx catalyst;
It may be comprised including.

  According to the present invention, the output value of the NOx sensor provided on the downstream side of the selective reduction type NOx catalyst can be corrected more accurately.

  Hereinafter, specific embodiments of a sensor output correction apparatus and a sensor output correction method according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its exhaust system according to the present embodiment. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders. In this embodiment, a urea SCR system is employed.

  An exhaust passage 2 is connected to the internal combustion engine 1. In the middle of the exhaust passage 2, an oxidation catalyst 3 and a selective reduction type NOx catalyst 4 (hereinafter referred to as NOx catalyst 4) are provided in order from the upstream side. The oxidation catalyst 3 may be another catalyst having oxidation ability (for example, a three-way catalyst). In this embodiment, the oxidation catalyst 3 corresponds to a catalyst having oxidation ability in the present invention.

An injection valve 5 that injects urea water into the exhaust is attached to the exhaust passage 2 downstream of the oxidation catalyst 3 and upstream of the NOx catalyst 4. The injection valve 5 is opened by a signal from the ECU 10 described later and injects urea water into the exhaust gas. In this embodiment, the injection valve 5 corresponds to the reducing agent supply means in the present invention.

The exhaust passage 2 downstream of the injection valve 5 and upstream of the NOx catalyst 4 is provided with a dispersion plate 6 for dispersing the urea water in a wide range by colliding the urea water.

The urea water injected from the injection valve 5 is hydrolyzed by the heat of the exhaust to become ammonia (NH ₃ ) and is adsorbed on the NOx catalyst 4. This NH ₃ reduces NOx.

A first NOx sensor 7 for measuring the NOx concentration in the exhaust is attached to the exhaust passage 2 downstream of the oxidation catalyst 3 and upstream of the injection valve 5. A second NOx sensor 8 that measures the NOx concentration in the exhaust and a temperature sensor 9 that measures the temperature of the exhaust are attached to the exhaust passage 2 downstream of the NOx catalyst 4. Note that the 1NOx sensor 7 and the 2NOx sensor 8 detects at least NO and NO _2. In this embodiment, the temperature sensor 9 corresponds to the temperature detecting means in the present invention. In the present embodiment, the second NOx sensor 8 corresponds to the NOx sensor in the present invention.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  In addition to the above sensors, the ECU 10 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 11 by the driver, and an accelerator opening sensor 12 that can detect the engine load, and a crank position that detects the engine speed. Sensors 13 are connected via electrical wiring, and output signals from these various sensors are input to the ECU 10.

  On the other hand, the injection valve 5 is connected to the ECU 10 via electric wiring, and the ECU 10 controls the opening and closing timing of the injection valve 5.

Here, the output values of the first NOx sensor 7 and the second NOx sensor 8 change according to the ratio of NO ₂ in NOx. That is, when the ratio of NO ₂ in NOx even NOx concentration same in the exhaust gas are different, the output value changes accordingly.

FIG. 2 is a graph showing the relationship between the NOx concentration and the output values of the first NOx sensor 7 and the second NOx sensor 8. The horizontal axis is the actual NOx concentration, and the vertical axis is the sensor output value before correction. A solid line indicates a case where NO ₂ / NOx is 0, that is, a case where NO ₂ is not included.
₂ / NOx is 0.5, that is, NO ₂ is 50%, and the two-dot chain line is NO ₂ / N
The case where Ox is 1, that is, the case where all are NO ₂ is shown. When NOx in only contains at least one of NO and NO ₂ is the solid line indicates the case where all that is, when NO / NOx is 1 NO, dashed line NO / NOx is sometimes i.e. NO of 0.5 Shows 50% case,
The two-dot chain line may be a case where NO / NOx is 0, that is, NO is not included.

Thus, the sensor output value decreases as the ratio of NO ₂ in NOx increases. For this reason, in this embodiment, the output values of the first NOx sensor 7 and the second NOx sensor 8 are corrected.

Next, FIG. 3 is a diagram showing the relationship between the correction coefficient for correcting the output value of the first NOx sensor 7 and the ratio of NO ₂ in NOx. The correction coefficient is used by multiplying the sensor output value. Since NO ₂ ratio is higher sensor output value decreases, the higher the NO ₂ ratio correction coefficient increases.

Note that the ratio of NO ₂ in NOx discharged from the internal combustion engine 1 can be estimated based on the engine speed, the amount of fuel (which may be an engine load), the combustion temperature, and the like. Since a well-known technique can be used for this estimation, description is abbreviate | omitted. Further, these relationships may be obtained in advance by experiments or the like and mapped and stored in the ECU 10.

By the way, when the exhaust gas passes through the oxidation catalyst 3, the ratio of NO ₂ in NOx changes. N
How much the ratio of NO ₂ in Ox changes depends on how much NO ₂ is produced in the oxidation catalyst 3. When the temperature of the oxidation catalyst 3 increases, the NOx reaction is promoted, so that NO ₂ is more easily generated. Further, as the exhaust gas flow rate increases, the NOx passing through the oxidation catalyst 3 before reacting with the oxidation catalyst 3 increases, so that NO ₂ is less likely to be generated. Further, as the deterioration of the oxidation catalyst 3 progresses, NO ₂ becomes difficult to be generated.

For this reason, the ratio of NO ₂ in NOx flowing out from the oxidation catalyst 3 (ie, N
Ox ratio of NO ₂ in NOx flowing into the catalyst 4), the ratio of NO ₂ in NOx discharged from the internal combustion engine 1, the temperature of the oxidation catalyst 3 may be the amount of the intake air amount (exhaust) oxide This can be estimated based on the degree of deterioration of the catalyst 3. Since this estimation can also use a well-known technique, a description thereof will be omitted. Note that these relationships may be obtained in advance by experiments or the like and stored in the ECU 10. The temperature of the oxidation catalyst 3 may be measured by a sensor, or may be estimated from the operating state of the internal combustion engine 1. The amount of intake air can be measured by attaching an air flow meter. The degree of deterioration of the oxidation catalyst 3 can be estimated based on the temperature history.

If the relationship shown in FIG. 3 is followed, the output value of the first NOx sensor 7 can be corrected. However, since the ratio of NO ₂ in NOx changes when exhaust passes through the NOx catalyst 4, the relationship shown in FIG. 3 cannot be applied to the output value of the second NOx sensor 8.

Here, the purification rate of NOx in the NOx catalyst 4 varies depending on the temperature of the NO ₂ ratio and the NOx catalyst 4 in the NOx. FIG. 4 is a graph showing an example of the relationship between the ratio of NO ₂ in NOx flowing into the NOx catalyst 4 and the NOx purification rate in the NOx catalyst 4. The solid line indicates a low temperature (for example, about 200 ° C. before the NOx catalyst 4 is activated but fully activated), and the alternate long and short dash line indicates a medium temperature (for example, the NOx catalyst 4 is completely activated). From 300 ℃
In the case of about 50 ° C.), the alternate long and two short dashes line indicates the case of high temperature (for example, higher than 350 ° C.).

In the NOx catalyst 4, the following reaction is considered to occur depending on the temperature.
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O Formula (1)
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O Formula (2)
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O Formula (3)
2NH ₃ + 2NO ₂ → N ₂ + NH ₄ NO ₃ + H ₂ O Formula (4)
Here, the formula (1) is a NO purification reaction mainly occurring at a high temperature. Equation (2) is a NO ₂ purification reaction that occurs mainly at high temperatures. Equation (3) is a purification reaction between NO and NO ₂ that occurs in the entire temperature range. Incidentally, it is purified by an amount according to the reaction NO and the NO ₂ is equal to formula (3). Equation (4) is a NO ₂ purification reaction that occurs mainly at low temperatures.

From this relationship, when the NOx catalyst 4 is at a low temperature, the N ₂ ratio increases as the NO ₂ ratio increases.
It is thought that the purification rate of Ox increases. Further, when the NOx catalyst 4 has an intermediate temperature, it is considered that the purification rate becomes the highest when the NO ₂ ratio is 50%. Furthermore, when the NOx catalyst 4 is high temperature, NOx purification rate regardless of the ratio of NO ₂ is considered to be high. Since these relationships vary depending on the state of the NOx catalyst 4 and the like, they are obtained through experiments and the like. For example, as the NOx catalyst 4 deteriorates, the purification rate decreases as a whole. Further, the NO ₂ ratio at which the purification rate becomes the highest at an intermediate temperature may deviate from 50% due to the deterioration of the NOx catalyst 4.

Here, FIG. 5 shows the case where the temperature of the NOx catalyst 4 is medium and the ratio of NO ₂ is 30%.
3 is a time chart showing the transition of the ratio of NO and NO ₂ downstream from the Ox catalyst 4; The vertical axis represents the NOx amount before the urea water is injected from the injection valve 5 as 100%. The dashed line is N
Represents O ratio of, the solid line indicates a transition of the total amount of NOx by combining the NO and NO _2. That is, the ratio of NO ₂ is shown between the alternate long and short dash line and the solid line.

In FIG. 5, the injection of urea water is started from the injection valve 5 at the time indicated by A. At moderate temperatures, the reaction shown in equation (3) is dominant. That is, NO and NO ₂ decrease at the same rate. When the ratio of NO ₂ is 30%, the ratio of NO is 70%, but 30% of this reacts with NO ₂ . Therefore, what is finally left is 40% of NO. The purification rate at this time is 60%.

For this reason, the ratio of NO ₂ is considered to change as shown in FIG. 6 below. FIG. 6 is a diagram showing an example of the relationship of the NO ₂ ratio between the upstream side and the downstream side of the NOx catalyst 4. A solid line indicates a low temperature, a one-dot chain line indicates a medium temperature, and a two-dot chain line indicates a high temperature. This relationship may change depending on the type of the NOx catalyst 4, the type of the internal combustion engine 1, the state of the NOx catalyst 4, and the like. Further, these relationships can be obtained by experiments or the like. Note that the NOx purification rate is assumed to be constant at high temperatures.

Since the ratio of NO ₂ in NOx flowing in the vicinity of the _second NOx sensor 8 is known from the relationship shown in FIG. 6, the correction coefficient of the _second NOx sensor 8 can be obtained. The correction coefficient may be obtained based on the ratio of NO ₂ downstream of the NOx catalyst 4, and N N upstream of the NOx catalyst 4.
It may be determined based on the ratio of O _2.

FIG. 7 is a view showing the relationship between the ratio of NO ₂ in NOx upstream of the NOx catalyst 4 and the correction coefficient. When the NO ₂ ratio is 0%, the correction coefficient is the smallest and the value is 1. The correction coefficient is increased as the NO ₂ ratio increases.

Note that the ratio of NO _{2 in} the NOx downstream of the NOx catalyst 4 may vary depending on the operating state of the internal combustion engine 1 and the state of the NOx catalyst 4, so the correction coefficient may be calculated in consideration of these.

That is, as the exhaust gas flow rate increases, the NOx passing through the NOx catalyst 4 before reacting with the NOx catalyst 4 increases, so the NOx purification rate decreases. Further, as the deterioration of the NOx catalyst 4 progresses, the NOx purification rate decreases. Further, the lower the NOx concentration, the lower the NOx purification rate in the NOx catalyst 4.

For this reason, the correction coefficient may be obtained in consideration of the intake air amount (which may be the amount of exhaust), the degree of deterioration of the NOx catalyst 4, and the NOx concentration. Note that these relationships may be obtained in advance by experiments or the like and stored in the ECU 10. The amount of intake air can be measured by attaching an air flow meter. The degree of deterioration of the NOx catalyst 4 can be estimated based on the temperature history. The NOx concentration can be obtained by the first NOx sensor 7.

Next, FIG. 8 is a flowchart showing a correction flow of the second NOx sensor 8 according to the present embodiment. This routine is executed every predetermined time.

In step S101, the ratio of NO ₂ in NOx exhausted from the internal combustion engine 1 is estimated based on the operating state of the internal combustion engine 1. Here, the ratio between NO and NO ₂ may be estimated. The estimation is performed based on the engine speed, the fuel injection amount, the combustion temperature, and the like. Since the combustion temperature is affected by the outside air temperature, the cooling water temperature, the engine speed, and the fuel injection amount, it may be estimated based on these and may be measured by a sensor.

In step S102, the ratio of NO ₂ in NOx flowing into the NOx catalyst 4 is estimated. That is, the ratio of NO ₂ in NOx after passing through the oxidation catalyst 3 is estimated. Since the ratio of NO ₂ varies depending on the operating state of the internal combustion engine 1 and the state of the oxidation catalyst 3, it is estimated accordingly.

For example, as the amount of intake air increases, the flow rate of the exhaust gas increases, so that it becomes difficult for NO to react in the oxidation catalyst 3, so the ratio of NO ₂ decreases. Further, since the NO higher the degree of deterioration of the oxidation catalyst 3 is less likely to react, the ratio of NO ₂ is lowered. Furthermore, since the reaction of NO becomes more difficult as the temperature of the oxidation catalyst 3 becomes lower, the ratio of NO ₂ becomes lower. If these relationships are obtained in advance by experiments or the like, the ratio of NO ₂ in NOx flowing into the NOx catalyst 4 can be estimated. In this embodiment, the ECU 10 that processes step S102 corresponds to the upstream ratio estimation means in the present invention. Further, when the oxidation catalyst 3 is not provided, step S102 is not necessary, and therefore the ECU 10 that processes step S101 corresponds to the upstream ratio estimation means in the present invention.

In step S103, the ratio of NO ₂ in NOx flowing out from the NOx catalyst 4 is estimated. That is, the ratio of NO ₂ after being changed by passing through the NOx catalyst 4 is estimated. The NO ₂ ratio is estimated from the relationship shown in FIG. In this embodiment, the ECU 10 that processes step S103 corresponds to the downstream ratio estimating means in the present invention.

In step S104, a correction coefficient for correcting the output value of the second NOx sensor 8 is calculated. This is obtained from the relationship shown in FIG. At this time, the correction coefficient may be obtained in consideration of the intake air amount (which may be the exhaust gas flow rate), the degree of deterioration of the NOx catalyst 4, and the NOx concentration.

In step S105, the output value of the second NOx sensor 8 is corrected. That is, the output value of the second NOx sensor 8 is multiplied by the correction coefficient obtained in step S104, so that the second NOx sensor 8 is obtained.
Correct the output value of. In this embodiment, the ECU 10 that processes step S105 corresponds to the correcting means in the present invention.
In this way, the output value of the second NOx sensor 8 can be corrected. In this embodiment, the output value of the second NOx sensor 8 is corrected by multiplying the correction coefficient. However, the correction value is calculated, and the output value of the second NOx sensor 8 is corrected by adding or subtracting the correction value. May be. Further, without calculating the correction coefficient, directly from the estimated value of the ratio of NO ₂ in NOx flowing out from the NOx catalyst 4, it may be corrected output value of the 2NOx sensor 8. Furthermore, without estimating the ratio of NO ₂ in NOx flowing out from the NOx catalyst 4, the ratio of NO ₂ in NOx flowing into the NOx catalyst 4 and N
The output value of the second NOx sensor 8 may be corrected directly from the temperature of the Ox catalyst 4. These relationships may be obtained in advance through experiments or the like and mapped.

As described above, according to this embodiment, the output value of the _second NOx sensor 8 can be corrected using the ratio of NO ₂ in NOx. For this reason, the NOx concentration and the NOx amount in the exhaust gas can be obtained with high accuracy. Thereby, the supply amount of a reducing agent can be set appropriately. Further, the deterioration determination of the NOx catalyst 4 can be performed with high accuracy.

It is a figure which shows schematic structure of the internal combustion engine which concerns on an Example, and its exhaust system. It is the figure which showed the relationship between NOx density | concentration and the output value of a 1st NOx sensor and a 2nd NOx sensor. It is a diagram showing the relationship between the ratio of NO ₂ in the correction coefficient and in NOx for correcting the output value of the 1NOx sensor. The ratio of NO ₂ in NOx flowing into the NOx catalyst is a diagram showing an example of a relationship between the purification rate of NOx in the NOx catalyst. 6 is a time chart showing the transition of the ratio of NO and NO ₂ downstream from the NOx catalyst when the temperature of the NOx catalyst is medium and the ratio of NO ₂ is 30%. Is a diagram showing an example of the relationship between the ratio of NO ₂ in the upstream side and the downstream side of the NOx catalyst. The NOx catalyst is a diagram showing the relationship between the ratio of NO ₂ in the upstream in the NOx and the correction coefficient. It is the flowchart which showed the correction | amendment flow of the 2nd NOx sensor which concerns on an Example.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 3 Oxidation catalyst 4 Selective reduction type NOx catalyst 5 Injection valve 6 Dispersion plate 7 First NOx sensor 8 Second NOx sensor 9 Temperature sensor 10 ECU
11 Accelerator pedal 12 Accelerator opening sensor 13 Crank position sensor

Claims (6)

A selective reduction type NOx catalyst that is provided in an exhaust passage of the internal combustion engine and selectively reduces NOx by a reducing agent;
Reducing agent supply means for supplying a reducing agent into the exhaust gas upstream of the selective reduction type NOx catalyst;
A NOx sensor for measuring a NOx concentration downstream of the selective reduction type NOx catalyst;
In the sensor output correction device comprising:
Upstream ratio estimating means for estimating a ratio of at least one of NO or NO ₂ in NOx flowing into the selective reduction type NOx catalyst;
Temperature detecting means for detecting the temperature of the selective reduction type NOx catalyst;
Based on the ratio estimated by the upstream ratio estimating means and the temperature detected by the temperature detecting means when the reducing agent is supplied by the reducing agent supply means, the selective reduction type NOx Downstream ratio estimating means for estimating a ratio of at least one of NO or NO _{2 in} NOx downstream of the catalyst;
Correction means for correcting the output value of the NOx sensor based on the ratio estimated by the downstream ratio estimation means;
An output correction device for a sensor, comprising: A catalyst having oxidation ability upstream of the selective reduction type NOx catalyst;
The upstream ratio estimating means is based on the selective reduction type based on the ratio of at least one of NO or NO _{2 in} NOx discharged from the internal combustion engine and the ratio of NOx that reacts with the catalyst having the oxidation ability. _2. The sensor output correction device according to claim 1, wherein a ratio of at least one of NO or NO2 in NOx flowing into the NOx catalyst is calculated.   3. The sensor output correction apparatus according to claim 1, wherein the correction unit corrects an output value of the NOx sensor according to a degree of deterioration of the selective reduction type NOx catalyst.   The sensor according to any one of claims 1 to 3, wherein the correction means corrects an output value of the NOx sensor in accordance with a flow rate of exhaust gas passing through the selective reduction type NOx catalyst. Output correction device. 5. The sensor according to claim 1, wherein the correction unit corrects the output value of the NOx sensor in accordance with the NOx concentration of the exhaust gas flowing into the selective reduction type NOx catalyst. Output correction device. A first step of estimating a ratio of NO or NO _{2 in} NOx upstream of a selective reduction type NOx catalyst provided in an exhaust passage of an internal combustion engine and selectively reducing NOx by a reducing agent;
A second step of estimating a ratio of NO or NO _{2 in} NOx downstream of the selective reduction type NOx catalyst based on the temperature of the selective reduction type NOx catalyst and the ratio obtained in the first step;
A third step of correcting an output value of a NOx sensor provided downstream of the selective reduction type NOx catalyst based on the ratio obtained in the second step and the temperature of the selective reduction type NOx catalyst;
A sensor output correction method comprising:

Images