JP5070770B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

When supplying the reducing agent to the NOx catalyst provided in the exhaust passage, the temperature of the catalyst rises as the reducing agent is oxidized by the catalyst. Here, when the supply amount of the reducing agent is too large, the reducing agent passes through the catalyst, and when the supply amount of the reducing agent is too small, the exhaust gas purification ability of the catalyst is lowered. Therefore, it is desirable to supply an appropriate amount of reducing agent to the catalyst.

For example, in an exhaust gas purification apparatus for an internal combustion engine, a ratio between a target temperature increase amount and an actual temperature increase amount is obtained as a correction coefficient, and a reducing agent supply amount multiplied by the correction coefficient is used as a corrected reducing agent supply amount. There is known a technique for eliminating excess and deficiency of a reducing agent by supplying to (for example, see Patent Document 1).
JP 2003-148133 A Japanese Patent Laid-Open No. 7-119514

  However, the target temperature of the catalyst changes every moment according to the load of the internal combustion engine and the like. For example, when the internal combustion engine 1 is idling, since the flow rate of exhaust gas is small, the temperature tends to rise when the reducing agent is supplied. Therefore, the target temperature is lowered during idle operation. Therefore, there may be a difference between the target temperature when the correction value of the reducing agent supply amount is calculated and the target temperature when the reducing agent based on the correction value is actually supplied. In this case, there is a possibility that an appropriate amount of reducing agent cannot be supplied.

  Further, when the exhaust gas temperature is low, the exhaust gas purifying ability of the catalyst is reduced, and the catalyst bed temperature cannot be maintained, and the reducing agent slips through easily. Therefore, it is necessary to reduce the supply amount of the reducing agent.

  Furthermore, it may be possible to prohibit correction or learning of the reducing agent supply amount when the target temperature of the catalyst is changing, but this makes it difficult to adjust the actual temperature of the catalyst to the target temperature during that time. Become.

  The present invention has been made in view of the above-described problems. In an exhaust gas purification apparatus for an internal combustion engine, an appropriate amount of reducing agent can be supplied even when the target temperature of the catalyst changes. The purpose is to provide technology that can be used.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention comprises:
A catalyst that is provided in the exhaust passage of the internal combustion engine and has an oxidizing ability;
Reducing agent supply means for supplying a reducing agent to the catalyst from the upstream side of the catalyst;
Catalyst temperature estimating means for estimating the temperature of the catalyst from the amount of heat generated in the catalyst by the reducing agent supplied by the reducing agent supply means;
Catalyst temperature detection means for detecting the temperature of the catalyst when the reducing agent is supplied by the reducing agent supply means;
Correction means for correcting the amount of reducing agent supplied from the reducing agent supply means so as to reduce the difference between the temperature obtained by the catalyst temperature estimation means and the temperature obtained by the catalyst temperature detection means;
It is characterized by providing.

  The greatest feature of the present invention is that the temperature of the catalyst is estimated based on the supply amount of the reducing agent, and the estimated temperature is set as a target value at that time. In other words, the correction value of the reducing agent supply amount is obtained using the temperature of the catalyst obtained by calculation.

  For this reason, the catalyst temperature estimating means estimates how much the temperature of the catalyst increases due to the supply of the reducing agent. Here, when the reducing agent is supplied to the catalyst by the reducing agent supply means, the temperature of the catalyst rises as the reducing agent is oxidized by the catalyst. At this time, there is a correlation between the amount of the reducing agent that reacts with the catalyst and the temperature increase value of the catalyst, and as the amount of the reducing agent that reacts with the catalyst increases, the temperature increase value of the catalyst increases. Based on this relationship, the catalyst temperature estimation means estimates the theoretical temperature of the catalyst (that is, the desired temperature) by supplying the reducing agent. Hereinafter, the temperature estimated by the catalyst temperature estimating means is referred to as “model open estimated value”.

  This model open estimated value is a value obtained by calculation, and the actual temperature should be the same. Therefore, when there is a difference between the detected temperature and the model open estimated value, it can be determined that the reducing agent supply amount is excessive or insufficient. Here, the catalyst temperature detecting means directly detects at least a parameter relating to the temperature of the catalyst. This may be detected directly by attaching a temperature sensor to the catalyst, or may be detected by attaching a sensor to the exhaust passage and detecting the temperature of the exhaust, from the temperature of the exhaust.

  When the detected temperature is lower than the model open estimated value, the amount of reducing agent supplied is increased because the reducing agent is insufficient. Further, when the detected temperature is larger than the model open estimated value, the amount of reducing agent supplied is decreased because the reducing agent is excessive. In this way, the correction means can correct the supply amount of the reducing agent. Thereby, the actual temperature can be brought close to the model open estimated value. That is, the actual temperature can be brought close to the theoretical temperature.

  Note that the temperature of the catalyst estimated by the catalyst temperature estimating means may change depending on causes other than the reducing agent supply amount. For example, the temperature of the catalyst may vary depending on the heat capacity of the catalyst, the amount of exhaust flowing into the catalyst, the temperature of the exhaust flowing into the catalyst, and the like. Therefore, it is possible to provide means for detecting these or obtaining them in advance and estimating the temperature of the catalyst based on the values obtained by these means. Here, the relationship between these numerical values and the temperature of the catalyst may be obtained in advance.

  According to the present invention, an appropriate amount of reducing agent can be supplied to an exhaust gas purification apparatus for an internal combustion engine even when the target temperature of the catalyst changes.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine 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 1 to which an exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and an intake / exhaust system thereof. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

  The internal combustion engine 1 is provided with a fuel injection valve 11 that supplies fuel into the cylinder of the internal combustion engine. Further, an exhaust passage 2 leading to the combustion chamber is connected to the internal combustion engine 1. This exhaust passage 2 communicates with the atmosphere downstream.

An occlusion reduction type NOx catalyst 3 (hereinafter referred to as NOx catalyst 3) is provided in the middle of the exhaust passage 2. The NOx catalyst 3 stores NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and the NOx that has been stored when the oxygen concentration of the inflowing exhaust gas is low and a reducing agent is present.
Has the function of reducing The NOx catalyst 3 may be supported on a particulate filter that collects particulate matter in the exhaust gas. In this embodiment, the NOx catalyst 3 is
This corresponds to the catalyst having oxidation ability in the present invention.

A downstream exhaust temperature sensor 4 that outputs a signal corresponding to the temperature of the exhaust gas flowing through the exhaust passage 2 is attached to the exhaust passage 2 downstream of the NOx catalyst 3. In addition, NOx
An upstream exhaust temperature sensor 9 that outputs a signal corresponding to the temperature of the exhaust gas flowing through the exhaust passage 2 is attached to the exhaust passage 2 upstream of the catalyst 3. The downstream exhaust temperature sensor 4 detects the temperature of the exhaust gas flowing out from the NOx catalyst 3, and the upstream exhaust temperature sensor 9
The temperature of the exhaust gas flowing into the Ox catalyst 3 is detected.

The exhaust passage 2 upstream of the NOx catalyst 3 is provided with a fuel addition valve 5 for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust passage 2. The fuel addition valve 5 is opened by a signal from the ECU 6 described later and injects fuel into the exhaust. The fuel injected from the fuel addition valve 5 into the exhaust passage 2 makes the air-fuel ratio of the exhaust flowing from the upstream of the exhaust passage 2 rich. At the time of NOx reduction, so-called rich spike control is executed in which the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 3 is rich in a spike (short time) in a relatively short cycle. The reducing agent is NOx
It is added from the fuel addition valve 5 when NOx is reduced by the catalyst 3, when sulfur poisoning of the NOx catalyst 3 is recovered, or when the temperature of the particulate filter is raised. In this embodiment, the fuel addition valve 5 corresponds to the reducing agent supply means in the present invention.

  Furthermore, an intake passage 7 that leads to the combustion chamber is connected to the internal combustion engine 1. An air flow meter 8 that outputs a signal corresponding to the amount of air flowing through the intake passage 7 is provided in the intake passage 7.

  The internal combustion engine 1 configured as described above is provided with an ECU 6 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 6 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 6 outputs an electric signal corresponding to the amount of depression of the accelerator pedal 12 by the driver, and an accelerator opening sensor 13 that can detect the engine load, and a crank position that detects the engine speed. Sensors 14 are connected via electrical wiring, and output signals from these various sensors are input to the ECU 6. On the other hand, the fuel injection valve 11 and the fuel addition valve 5 are connected to the ECU 6 via electric wiring, and the ECU 6 controls the opening and closing timing of the fuel injection valve 11 and the fuel addition valve 5.

In this embodiment, when the fuel addition amount from the fuel addition valve 5 is corrected, the difference between the model open estimated value and the actually measured value is set to zero. Here, the model open estimated value is set as a value that the temperature of the NOx catalyst 3 should increase by the amount of fuel added from the fuel addition valve 5.

Since the temperature of the NOx catalyst 3 changes according to the amount of fuel that reacts in the NOx catalyst 3, the temperature of the NOx catalyst 3 can be calculated based on the amount of fuel that reacts in the NOx catalyst 3. The amount of fuel reacted in the NOx catalyst 3 is the amount of fuel added from the fuel addition valve 5;
It can be obtained based on the rate of fuel that reacts in the NOx catalyst 3 (which may be a purification rate). Furthermore, since the rate of the fuel that reacts in the NOx catalyst 3 is correlated with the temperature of the NOx catalyst 3, it can be obtained based on the actual temperature of the NOx catalyst 3.

Note that the temperature of the NOx catalyst 3 may vary depending on the heat capacity of the NOx catalyst 3, the amount of exhaust gas flowing into the NOx catalyst 3, the temperature of exhaust gas flowing into the NOx catalyst 3, and the like. Therefore, the model open estimated value may be calculated in consideration of these values. Further, the relationship between these numerical values and the model open estimated value may be obtained in advance, mapped and stored in the ECU 6, and a calculation formula for obtaining the model open estimated value from these numerical values is stored in the ECU 6. May be.

Here, the amount of heat of the NOx catalyst 3 can be obtained in advance by experiments or the like. Further, the amount of exhaust gas flowing into the NOx catalyst 3 can be obtained as the sum of the intake air amount detected by the air flow meter 8 and the fuel injection amount injected from the fuel injection valve 11. Further, the temperature of the exhaust gas flowing into the NOx catalyst 3 can be obtained by the upstream side exhaust temperature sensor 9.

  In the present embodiment, the ECU 6 that calculates the model open estimated value corresponds to the catalyst temperature estimating means in the present invention.

  Here, FIG. 2 is a time chart showing the time transition of the target temperature of the NOx catalyst 3, the estimated model open value, and the measured temperature of the NOx catalyst 3.

  The target temperature of the NOx catalyst 3 is set based on the load of the internal combustion engine 1 and the request of the NOx catalyst 3. The requirement of the NOx catalyst 3 indicates a case where, for example, NOx reduction or sulfur poisoning recovery is necessary.

The actually measured temperature of the NOx catalyst 3 is the temperature of the NOx catalyst 3 obtained based on the downstream side exhaust temperature sensor 4. The temperature of the exhaust gas immediately downstream of the NOx catalyst 3 may be the actual measured temperature of the NOx catalyst 3, and the NOx in consideration of the temperature decrease during the period from the NOx catalyst 3 to the downstream side exhaust temperature sensor 4. The temperature of the catalyst 3 may be estimated. Alternatively, the temperature may be detected by attaching a temperature sensor directly to the NOx catalyst 3. Furthermore, a value obtained by correcting the estimated model open value based on the exhaust temperature obtained by the downstream side exhaust temperature sensor 4 may be used as the actual measured temperature of the NOx catalyst.

That is, the measured temperature of the NOx catalyst 3 is a temperature obtained based on a value measured by a sensor. In this embodiment, the ECU 6 that detects the temperature of the NOx catalyst 3 based on the downstream side exhaust temperature sensor 4 and the downstream side exhaust temperature sensor 4 correspond to the catalyst temperature detecting means in the present invention.

  On the other hand, the model open estimated value is an estimated temperature of the NOx catalyst 3 calculated without including a measured value by a sensor relating to temperature.

Here, since the target temperature of the NOx catalyst 3 is changed by the load of the internal combustion engine 1 or the like, it may change greatly in a short time. However, since the NOx catalyst 3 has a heat capacity, the temperature of the NOx catalyst 3 does not change immediately even if the fuel addition amount is changed. That is, it takes time until the actual temperature converges to the target temperature. When the fuel addition amount is corrected before the actual temperature converges to the target temperature, the correction value increases because the difference between the actual temperature and the target temperature is large. However, even if the difference between the actually measured temperature and the target temperature is large at this time, this is due to a response delay and not due to excess or deficiency of the fuel addition amount. For this reason, even if there is a difference between the actually measured temperature and the target temperature, it is not always necessary to correct the fuel addition amount. Therefore, if correction is performed in such a case, it is difficult to obtain an appropriate fuel addition amount, and it becomes difficult to converge the actual temperature to the target temperature.

For example, conventionally, the correction value of the fuel addition amount has been obtained by the following equation.
Correction value = (target temperature−inlet gas temperature T6) / (actually measured temperature−inlet gas temperature T6)
However, the inlet gas temperature T6 is the temperature of the exhaust gas flowing into the NOx catalyst 3, that is, the temperature of the exhaust gas obtained by the upstream side exhaust temperature sensor 9.

When the steady operation of the internal combustion engine 1 is performed for a sufficiently long time without adding fuel, the input gas temperature T6 and the measured temperature of the NOx catalyst 3 are equal. (Target temperature-input gas temperature T6) is a target temperature increase value, and (actual temperature-input gas temperature T6) is an actual temperature increase value due to fuel addition. That is, the correction value is obtained by obtaining the ratio between the target temperature rise value and the measured temperature rise value, and the next fuel addition amount is obtained by multiplying the fuel addition amount at this time by the correction value.

On the other hand, the model open estimated value is the temperature at which the NOx catalyst 3 should be. That is, the value varies depending on the amount of fuel added. If there is a difference between the actually measured temperature and the model open estimated value, it means that the actually measured temperature is not the desired temperature, which means that the fuel addition amount needs to be corrected.

In other words, even if the target temperature of the NOx catalyst 3 changes, the actual temperature of the NOx catalyst 3 does not change immediately, so the difference between the target temperature and the measured temperature does not always indicate an excess or deficiency in the amount of fuel added. Absent. On the other hand, since the model open estimated value is the temperature of the NOx catalyst 3 obtained by calculation, the model open estimated value gradually changes in the same manner as the actual temperature of the NOx catalyst 3. The difference between the model open estimated value and the actually measured temperature represents the excess or deficiency of the fuel addition amount.

  Therefore, the fuel addition amount can be optimized by correcting or learning the fuel addition amount using the model open estimated value.

In this embodiment, the correction value of the fuel addition amount is obtained by the following equation.
Correction value = (model open estimated value−inlet gas temperature T6) / (actually measured temperature−inlet gas temperature T6)

  Here, (model open estimated value−inlet gas temperature T6) is a calculated temperature rise value (that is, a desired temperature rise value) obtained in consideration of the temperature rise due to the actually added fuel. Since this calculated temperature rise value should be equal to the actual temperature rise value, if there is a difference between the two, the fuel addition amount is corrected. That is, the correction value is obtained by calculating the ratio between the calculated temperature rise value and the measured temperature rise value, and the next fuel addition amount is obtained by multiplying the fuel addition amount at this time by the correction value. . This correction value is stored in the ECU 6. In this way, learning control of the fuel addition amount is performed. In this embodiment, the ECU 6 that corrects the fuel addition amount in this way corresponds to the correcting means in the present invention.

In this way, by correcting or learning the fuel addition amount using the model open estimated value instead of the target temperature of the NOx catalyst 3, the fuel addition amount is corrected toward the calculated temperature (that is, the temperature that should be). can do. Thereby, fuel addition amount can be correct | amended appropriately. Therefore, it is possible to suppress the occurrence of erroneous correction or mislearning of the fuel addition amount, or to increase the opportunities for correction or learning of the fuel addition amount. Therefore, the temperature control of the NOx catalyst 3 becomes easy.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification apparatus of the internal combustion engine which concerns on an Example, and its intake / exhaust system. 6 is a time chart showing a time transition of a target temperature of the NOx catalyst, a model open estimated value, and an actually measured temperature of the NOx catalyst.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 3 NOx storage reduction catalyst 4 Downstream exhaust temperature sensor 5 Fuel addition valve 6 ECU
7 Intake passage 8 Air flow meter 9 Upstream exhaust temperature sensor 11 Fuel injection valve 12 Accelerator pedal 13 Accelerator opening sensor 14 Crank position sensor

Claims (1)

A catalyst that is provided in the exhaust passage of the internal combustion engine and has an oxidizing ability;
Setting means for setting a target temperature of the catalyst;
Reducing agent supply means for supplying a reducing agent to the catalyst from the upstream side of the catalyst according to the target temperature ;
From the amount of heat generated in the catalyst by the reducing agent supplied by the reducing agent supply means, and the catalyst temperature estimating means for estimating the temperature of the catalyst at this time,
Catalyst temperature detection means for detecting the temperature of the catalyst at the present time ;
Correction means for correcting the amount of reducing agent supplied from the reducing agent supply means so as to reduce the difference between the temperature obtained by the catalyst temperature estimation means and the temperature obtained by the catalyst temperature detection means;
An exhaust emission control device for an internal combustion engine, comprising:

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