JP2010096039A - Urea water injection amount control device and urea water injection control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a urea water injection amount control device capable of facilitating reduction in excess or deficiency in supply amount of NH3 by improving estimation accuracy of an NO/NO2 ratio. <P>SOLUTION: The ratio of NO to NO2 (NO/NO2 ratio) flowing into an NOx reduction catalyst of SCR (selective catalytic reduction) is estimated based on a conversion rate of NO2 where NO is oxidized by oxygen and is converted to NO2 in an oxidation catalyst of DOC (diesel oxidation catalyst) and a conversion rate of NO where NO2 is converted to NO as carbon is oxidized by NO2 in DPF (diesel particulate filter). Based on the NO/NO2 ratio estimated in this manner, the amount of urea water injected from an injection valve is controlled. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is applied to an exhaust gas purification system for an internal combustion engine equipped with a NOx reduction catalyst that uses ammonia generated from urea water to reduce NOx in exhaust gas, and controls the injection amount of urea water. The present invention relates to a control device and a control system thereof.

  Conventionally, a NOx reduction catalyst for reducing nitrogen oxide NOx (mainly NO and NO2) in exhaust gas using ammonia NH3 generated from urea water is known, and the reduction reaction is mainly performed by the following reaction formula. This is considered to be due to (1) to (3).

NH ₃ + 1 / 2NO + 1 / 2NO ₂ → N ₂ + 3 / 2H ₂ O (1)
NH ₃ + NO + 1 / 4O ₂ → N ₂ + 3 / 2H ₂ O (2)
NH ₃ + 3 / 4NO ₂ → 7 / 8N ₂ + 3 / 2H ₂ O (3)
This means that the amount of NH3 used for the reduction varies depending on which of the reaction formulas (1) to (3) the NO and NO2 flowing into the NOx reduction catalyst are reduced. . Therefore, when the amount of NOx is simply estimated and the injection amount of urea water is controlled based on the estimated value, depending on the ratio of NO and NO2 (hereinafter referred to as “NO / NO2 ratio”), the excess of NH3 supply amount may be increased. A shortage occurs. When NH3 is insufficient, the NOx purification rate is lowered, and when NH3 is excessive, an ammonia slip is caused such that excess NH3 is discharged from the NOx reduction catalyst. Therefore, conventionally, the NO / NO2 ratio is estimated, and the injection amount of urea water is controlled in accordance with the estimation result, thereby suppressing excess / deficiency of the NH3 supply amount (see Patent Document 1).

  Patent Document 1 focuses on the fact that NO in exhaust gas is oxidized to NO2 according to the following reaction formula (4) in the oxidation catalyst arranged on the exhaust upstream side of the NOx reduction catalyst. The NO / NO2 ratio is estimated based on the conversion rate (NO2 conversion rate).

2NO + O ₂ → 2NO ₂ (4)
Incidentally, among the reaction formulas (1) to (3), the reaction rate of the reaction formula (1) is the fastest. Most of the NOx flowing into the oxidation catalyst is NO, but by converting part of the NO into NO2 as in the above reaction formula (4), the amount of NO2 flowing into the NOx reduction catalyst is brought close to the NO amount. The oxidation catalyst functions so that the reaction according to the reaction formula (1) is promoted in the NOx reduction catalyst, and as a result, the NOx purification rate is improved.
JP 2002-250220 A

  However, the present inventors have found that there is room for improving the estimation accuracy in the conventional control in which the NO / NO2 ratio is estimated based on the NO2 conversion rate on the oxidation catalyst.

  That is, in an exhaust purification system in which a filter (DPF: diesel particulate filter) that collects carbon-based particulate matter (PM) in exhaust gas is disposed upstream of the NOx reduction catalyst, PM collected by DPF主 成分 (C), which is the main component, is oxidized by NO 2 according to the following reaction formula (5). Then, NO2 is converted to NO with such oxidation of soot.

C + 2NO ₂ → CO ₂ + 2NO (5)
Therefore, the NO / NO2 ratio not only changes according to the NO2 conversion rate on the oxidation catalyst, but also the rate at which NO2 is converted to NO as NOx is oxidized on the DPF (NO conversion rate). The present inventors have obtained the knowledge that it changes depending on the condition.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the estimation accuracy of the NO / NO2 ratio so as to promote the excess / deficiency reduction of the NH3 supply amount. And providing a urea water injection control system.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  The invention according to claim 1 is arranged in an exhaust pipe of an internal combustion engine, and uses an ammonia generated from urea water to reduce NOx in the exhaust, and on the exhaust upstream side of the NOx reduction catalyst. An injection valve for injecting and supplying urea water, an oxidation catalyst arranged on the exhaust upstream side of the NOx reduction catalyst, an oxidation catalyst capable of oxidizing NO in the exhaust to NO2, and an exhaust upstream side of the NOx reduction catalyst, The present invention is applied to an exhaust gas purification system for an internal combustion engine including a filter that collects the carbon-based fine particles.

  And based on the NO2 conversion rate in which NO is oxidized by oxygen in the oxidation catalyst and converted to NO2, and the NO conversion rate in which NO2 is converted to NO as the carbon is oxidized by NO2 in the filter, Ratio estimating means for estimating the ratio of NO and NO2 flowing into the NOx reduction catalyst (NO / NO2 ratio), and urea injected from the injection valve based on the NO / NO2 ratio estimated by the ratio estimating means And an injection amount control means for controlling the injection amount of water.

  The present invention is based on the above findings by the present inventors, that is, “the NO / NO 2 ratio varies not only according to the NO 2 conversion rate on the oxidation catalyst but also according to the NO conversion rate on the filter”. The NO / NO 2 ratio is estimated based on the NO conversion rate on the filter in addition to the NO 2 conversion rate on the oxidation catalyst, so that the estimation accuracy can be improved. Therefore, it is possible to promote the reduction in excess and deficiency of the injection amount of urea water, and consequently promote the reduction in excess and deficiency of the NH 3 supply amount.

  According to a second aspect of the present invention, there is provided a PM deposition amount acquisition unit that acquires a deposition amount of carbon-based fine particles (PM) on the filter, and the ratio estimation unit is configured to acquire the PM deposition amount acquired by the PM deposition amount acquisition unit. The ratio is estimated by estimating the NO conversion rate based on the above.

  As is clear from the above-described reaction formula (5), the NO conversion rate changes according to the amount of soot (C) which is the main component of PM. Focusing on this point, in the invention according to the second aspect, the NO / NO2 ratio is estimated by estimating the NO conversion rate based on the PM accumulation amount, so that it is easy to ensure sufficient accuracy for the estimation. realizable.

  Further, as the PM deposition amount increases, the amount of C in the reaction formula (5) increases, and as a result, the rate at which NO2 is converted to NO (NO conversion rate) increases. Therefore, it is desirable to estimate that the NO conversion rate increases as the accumulation amount increases.

  In invention of Claim 4, it comprises the filter temperature acquisition means which acquires the temperature of the filter, The ratio estimation means estimates the NO conversion rate based on the filter temperature acquired by the filter temperature acquisition means, The ratio is estimated.

  The reaction rate of the above-described reaction formula (5) depends on the filter temperature. That is, even if the PM accumulation amount is the same, the amount of NO2 converted to NO (NO conversion rate) varies depending on the filter temperature. Focusing on this point, the invention according to claim 4 estimates the NO / NO2 ratio by estimating the NO conversion rate based on the filter temperature, so that it is easy to ensure sufficient accuracy for the estimation. it can.

  Further, the relationship between the NO conversion rate and the filter temperature will be described. The NO conversion rate becomes maximum when the filter temperature is a predetermined temperature. Therefore, as described in claim 5, when estimating the NO conversion rate based on the filter temperature, it is desirable to estimate the NO conversion rate to be maximum when the filter temperature is a predetermined temperature.

  According to a sixth aspect of the present invention, the apparatus includes an exhaust gas flow rate acquisition unit that acquires a flow rate of exhaust gas, and the ratio estimation unit calculates the estimated value of the NO conversion rate as the exhaust flow rate acquired by the oxidation catalyst temperature acquisition unit increases. It is characterized by correcting less.

  The higher the exhaust gas flow rate, the higher the rate at which NO2 passes through the filter without the reaction of reaction formula (5). In the invention according to claim 6 in view of this point, the estimated value of the NO conversion rate is corrected to be smaller as the exhaust gas flow rate is faster, so that the estimation accuracy of the NO conversion rate can be improved, and consequently the estimated accuracy of the NO / NO2 ratio is improved. Can be improved.

  The invention according to claim 7 further comprises an oxidation catalyst temperature acquisition means for acquiring the temperature of the oxidation catalyst, and the ratio estimation means estimates the NO2 conversion rate based on the oxidation catalyst temperature acquired by the oxidation catalyst temperature acquisition means. Thus, the ratio is estimated.

  The reaction rate of the above-mentioned reaction formula (4) depends on the oxidation catalyst temperature. That is, even if the amount of NO flowing into the oxidation catalyst is the same, the rate at which NO is converted to NO2 (NO2 conversion rate) varies depending on the oxidation catalyst temperature. Focusing on this point, in the invention according to the seventh aspect, the NO2 conversion rate is estimated based on the oxidation catalyst temperature, so that it is possible to easily achieve sufficient accuracy for the estimation.

  The relationship between the NO2 conversion rate and the oxidation catalyst temperature will be described. The NO2 conversion rate becomes maximum when the oxidation catalyst temperature is a predetermined temperature. Therefore, as described in claim 8, when estimating the NO2 conversion rate based on the oxidation catalyst temperature, it is desirable to estimate the NO2 conversion rate to be maximum when the oxidation catalyst temperature is a predetermined temperature.

  According to a ninth aspect of the present invention, the exhaust gas flow rate acquisition means for acquiring the flow velocity of the exhaust gas is provided, and the ratio estimation means calculates the estimated value of the NO2 conversion rate as the exhaust flow velocity acquired by the oxidation catalyst temperature acquisition means increases. It is characterized by correcting less.

  The faster the exhaust gas flow rate, the higher the rate at which NO passes through the oxidation catalyst without the reaction of the reaction formula (4). In the invention according to claim 9 in view of this point, the estimated value of the NO2 conversion rate is corrected to be smaller as the exhaust gas flow rate is faster. Therefore, the estimation accuracy of the NO2 conversion rate can be improved, and thus the estimated accuracy of the NO / NO2 ratio is improved. Can be improved.

  The invention according to claim 10 is provided in the exhaust pipe of the internal combustion engine, and reduces NOx in the exhaust using ammonia generated from urea water, and / on the exhaust upstream side of the NOx reduction catalyst. An injection valve for injecting urea water and / or an exhaust catalyst upstream of the NOx reduction catalyst and capable of oxidizing NO in the exhaust to NO2, and / or an exhaust upstream side of the NOx reduction catalyst. A PM deposit amount acquisition means, which is applied to an exhaust gas purification system for an internal combustion engine comprising a filter that collects carbon-based fine particles in exhaust gas, and acquires a deposit amount of carbon-based fine particles (PM) in the filter; / Ratio estimation means for estimating the ratio of NO and NO2 flowing into the NOx reduction catalyst based on the accumulation amount of carbon-based fine particles acquired by the PM accumulation amount acquisition means; / Estimated by the ratio estimation means Based on the ratio between NO and NO2 which is characterized by comprising a an injection quantity control means for controlling the injection amount of urea water injected from the injection valve.

  According to this, since the NO / NO2 ratio is estimated based on the PM accumulation amount correlated with the rate of conversion of NO2 to NO (NO conversion rate) as the carbon is oxidized by NO2 in the filter, the estimation is performed. Accuracy can be improved. Therefore, it is possible to promote the reduction in excess and deficiency of the injection amount of urea water, and consequently promote the reduction in excess and deficiency of the NH 3 supply amount.

  The invention according to claim 11 is a urea water injection control system comprising the urea water injection amount control device and at least one of the NOx reduction catalyst, the injection valve, the oxidation catalyst, and the filter. is there. According to this urea water injection control system, the above-mentioned various effects can be exhibited similarly.

  Hereinafter, an embodiment embodying the present invention will be described with reference to the drawings. The present embodiment embodies the present invention as an exhaust purification system for a vehicle-mounted diesel engine, and its detailed configuration will be described below.

  First, the configuration of the exhaust purification system according to the present embodiment will be described with reference to FIG. The exhaust purification system shown in FIG. 1 is attached to the exhaust system of an engine (internal combustion engine) and mainly purifies HC, CO, NOx, and PM contained in the exhaust of the engine.

  Specifically, an oxidation device (DOC11: diesel oxidation catalyst) having an oxidation catalyst 11a, a filter (DPF12) for collecting carbon-based fine particles (PM) in exhaust gas, and a reduction device (SCR13: selective) having a NOx reduction catalyst 13a. catalytic reduction) are arranged in order from the exhaust upstream side and attached to the exhaust pipe 10. An injection valve 14 for injecting and supplying urea water into the exhaust is attached to a portion of the exhaust pipe 10 located upstream of the SCR 13 and downstream of the DPF 12.

  The DOC 11 is configured by supporting a platinum-based oxidation catalyst 11a on a base 11b, oxidizing and purifying unburned fuel HC and CO in the exhaust, and oxidizing NO in the exhaust to convert it to NO2. To do. The DPF 12 is a continuously regenerating filter that is formed in a porous partition structure made of a heat-resistant ceramic such as cordierite and collects PM in exhaust gas. For example, the collected PM can be continuously used by repeatedly burning and removing (corresponding to the regeneration process) by post-injection after the main fuel injection.

  The vehicle is equipped with a urea water tank 15 for storing urea water obtained by dissolving urea in pure water. The urea water stored in the urea water tank 15 is pumped up by the electric pump 16 and supplied to the injection valve 14 via the filter 17. The electric pump 16 is controlled by an electronic control unit (ECU 20) so that it is always driven during engine operation, and is controlled so that the supply pressure of urea water to the injection valve 14 is constant by a regulator (not shown).

  The injection valve 14 injects urea water supplied from the electric pump 16 to the exhaust upstream side of the SCR 13 in the exhaust pipe 10. More specifically, the injection valve 14 includes a needle (not shown) that opens and closes the nozzle hole, and the ECU 20 controls the opening and closing state of the nozzle hole by controlling the operation of the needle. And ECU20 controls the injection quantity of urea water by controlling the time which opens a nozzle hole per predetermined time.

  The urea water injected from the injection valve 14 is converted into ammonia (NH 3) by the heat of the exhaust (see the following equation (6)), and is supplied to the SCR 13 downstream of both the exhaust.

(NH ₂ ) 2CO + H ₂ O → 2NH ₃ + CO ₂ (6)
The SCR 13 is configured by supporting a NOx reduction catalyst 13a such as vanadium oxide on a base material 13b, and selectively reacts NOx in exhaust gas with ammonia even in the presence of oxygen (the above formulas (1) to (3)). )), NOx is reduced and purified. Incidentally, most of the NOx flowing into the DOC 11 is NO, but by converting a part of NO into NO2 as in the above reaction formula (4), the amount of NO2 flowing into the SCR 13 approaches the amount of NO. In the SCR 13, the reaction according to the above reaction formula (1) is promoted, and as a result, the NOx purification rate is improved.

  The ECU 20 includes a well-known microcomputer (not shown), and is sucked into the combustion chamber per combustion cycle based on detection values of various sensors such as an air flow meter 21, an accelerator opening sensor 22, and a crank angle sensor 23. The intake air amount, the required torque of the engine, the rotational speed of the crankshaft (engine rotational speed), etc. are calculated. Based on these calculated values, the engine operating state (for example, fuel injection amount, injection timing, EGR amount, supercharging pressure, etc.) is controlled.

  Further, the ECU 20 calculates the amount of NO and NO2 flowing into the SCR 13, calculates the amount of urea water corresponding to ammonia necessary to reduce these amounts of NOx, and injects the calculated amount of urea water. The operation of the injection valve 14 is controlled.

  Next, a procedure for calculating the urea water injection amount for supplying ammonia to the SCR 13 without excess or deficiency will be described with reference to the functional block diagram of FIG. The microcomputer of the ECU 20 calculates the urea water injection amount by executing a predetermined program, and the various processing contents executed in the process of the calculation processing are shown in the estimation units 20a, 20b, 20c and the calculation unit in FIG. This is indicated by 20d.

<NOx amount estimation unit 20a>
First, the NOx amount estimating unit 20a calculates the NOx amount contained in the exhaust from the combustion chamber (that is, the exhaust flowing into the DOC 11) based on the engine operating state (for example, the engine rotation speed, the fuel injection amount, and the intake amount). Instead of calculating the NOx amount based on the engine operating state in this way, a NOx sensor may be provided on the exhaust upstream side of the DOC 11 and the NOx amount may be calculated based on the detected value of the NOx sensor.

<NO / NO2 Ratio Estimator 20b at DOC>
The amount of NO converted to NO2 in the DOC 11 according to the above reaction formula (4) depends on the atmospheric temperature of the reaction, that is, the temperature of the DOC 11 (hereinafter referred to as “DOC temperature”). Therefore, the NO / NO2 ratio estimation unit 20b (ratio estimation means) converts NO2 using the map of FIG. 3A based on the DOC temperature (strictly, the temperature of the base material 11b or the temperature of the oxidation catalyst 11a). Calculate the rate. This map is set so that the NO2 conversion rate becomes maximum when the DOC temperature is a predetermined temperature. What is necessary is just to acquire the DOC temperature used for calculation of NO2 conversion rate based on the detected value of the exhaust temperature sensor 24 installed in the DOC11 upstream. Note that the DOC temperature may be estimated in consideration of the response delay time based on the detection value of the exhaust temperature sensor arranged at a place other than the upstream side of the DOC 11.

  Further, the reaction rate of the reaction formula (4) becomes slower as the intake air amount (strictly speaking, the intake air flow rate per unit time or the intake air amount taken into the combustion chamber per one combustion cycle) increases. That is, the NO2 conversion rate in the DOC 11 according to the reaction formula (4) becomes smaller as the intake amount (that is, the exhaust amount (strictly, exhaust flow rate)) increases. Therefore, the NO / NO2 ratio estimation unit 20b corrects the NO2 conversion rate calculated based on the map of FIG. 3A according to the intake air amount. For example, the relationship between the intake air amount and the NO2 conversion rate correction value (NOx reaction amount correction value) is acquired in advance by a test, and the NO2 conversion rate is calculated using the map of FIG. It may be corrected.

  In other words, the NO2 conversion rate in the DOC 11 decreases as the amount of NOx (absolute amount) flowing into the DOC 11 increases. Therefore, the NO2 conversion rate calculated based on the map of FIG. 3A may be corrected according to the NOx amount using the map shown in FIG.

  Then, the NO / NO2 ratio estimating unit 20b calculates the NO amount and NO2 amount flowing out from the DOC 11 and flowing into the DPF 12 based on the NO2 conversion rate calculated in this way and the NOx amount calculated by the NOx amount estimating unit 20a. calculate.

<NO / NO2 ratio estimation unit 20c in DPF>
The amount of NO2 converted to NO in the DPF 12 according to the above reaction formula (5) is the atmospheric temperature of the reaction, that is, the filter temperature of the DPF 12 (hereinafter referred to as “DPF temperature”) and the PM collected by the DPF 12. It depends on the amount of deposition (strictly speaking, the amount of carbon component contained in PM). Therefore, the NO / NO2 ratio estimation unit 20c (ratio estimation means) calculates the NO conversion rate based on the PM accumulation amount and the DPF temperature in the DPF 12.

  Specifically, first, based on the detection values of the differential pressure sensors 25 and 26, the difference between the upstream and downstream exhaust pressures (DPF differential pressure) of the DPF 12 is acquired. Then, based on the acquired DPF differential pressure, the PM deposition amount is calculated using the map of FIG. Even if the DPF differential pressure is the same, the PM accumulation amount differs depending on the exhaust flow rate at that time. Therefore, the map in FIG. 3B is set so that the PM accumulation amount can be calculated according to the exhaust flow rate. Yes.

  Next, based on the PM deposition amount and the DPF temperature calculated in this way, the NO conversion rate is calculated using the map of FIG. This map is set so that the NO conversion rate increases as the PM deposition amount increases, and the NO conversion rate becomes maximum when the DPF temperature is a predetermined temperature. The DPF temperature used for calculating the NO conversion rate is estimated in consideration of the response delay time based on the detected value of the exhaust gas temperature sensor 24 arranged on the upstream side of the DOC 11. An exhaust temperature sensor is installed in a place other than the upstream side of the DOC 11 (for example, between the DPF 12 and the DOC 11, between the DPF 12 and the SCR 13, or downstream of the SCR 13), and the DPF temperature is calculated based on the detection value of the sensor. It may be.

  Further, the reaction rate of the reaction formula (5) becomes slower as the intake air amount (that is, the exhaust gas amount (strictly, the exhaust gas flow rate)) increases. That is, the NO conversion rate in the DPF 12 according to the reaction formula (5) decreases as the intake air amount increases. Therefore, the NO / NO2 ratio estimating unit 20c corrects the NO conversion rate calculated based on the maps of FIGS. 3B and 3C in accordance with the intake air amount. For example, the relationship between the intake air amount and the NO conversion rate correction value (NOx reaction amount correction value) is acquired in advance by a test, and the NO conversion rate is calculated using the map of FIG. It may be corrected.

  In other words, the NO conversion rate in the DPF 12 decreases as the amount of NOx (absolute amount) flowing into the DPF 12 increases. Therefore, the NO conversion rate calculated based on the maps shown in FIGS. 3B and 3C may be corrected according to the NOx amount using the map shown in FIG.

  The NO / NO2 ratio estimation unit 20c then flows out from the DPF 12 and flows into the SCR 13 based on the NO conversion rate calculated in this way and the NO amount and NO2 amount calculated by the NO / NO2 ratio estimation unit 20b. Amount and NO2 amount are calculated.

<Urea water injection amount calculation unit 20d>
In the SCR 13, when NOx is selectively reduced from exhaust components including oxides such as O2 and NOx, NO and NO2 are reduced according to the above-described reaction formulas (1) to (3). Therefore, in the urea water injection amount calculation unit 20d (injection amount control means), NH3 is excessive in the reaction equations (1) to (3) based on the NO amount and NO2 amount calculated by the NO / NO2 ratio estimation unit 20c. The urea water injection amount from the injection valve 14 is calculated so that it will be supplied without shortage.

  As described above, according to the present embodiment, the following effects can be obtained.

  (1) In addition to the fact that NO is converted to NO2 at DOC11 and the fact that NO2 is converted to NO at DPF12, the amount of NO flowing into SCR13 and the amount of NO2 are calculated, so NO2 at DOC11 The calculation accuracy of the NO amount and the NO2 amount can be improved as compared with the case where the calculation is performed by taking into account only the conversion. Therefore, it is possible to promote the reduction in excess and deficiency of the injection amount of urea water, and consequently promote the reduction in excess and deficiency of the NH 3 supply amount.

  (2) Specifically, the NO2 conversion rate in the DOC 11 is estimated based on the DOC temperature, and the NO amount and NO2 amount flowing into the DPF 12 are calculated based on the estimated NO2 conversion rate. Then, the NO conversion rate in the DPF 11 is estimated based on the DPF temperature and the PM deposition amount, and the NO amount and NO 2 amount flowing into the SCR 13 are calculated based on the estimated NO conversion rate. In short, based on the DOC temperature, the DPF temperature, and the PM accumulation amount, the NO amount and NO2 amount flowing into the SCR 13 are calculated.

  Thus, since the NO2 conversion rate is estimated based on the DOC temperature, it is possible to easily realize sufficient accuracy for the estimation. Further, since the NO conversion rate is estimated based on the DPF temperature and the PM deposition amount, it is possible to easily realize sufficient accuracy for the estimation.

  (3) In estimating the NO conversion rate and the NO2 conversion rate, as the intake air amount increases (that is, the exhaust flow rate increases), the conversion rate is estimated to be reduced so that the estimation accuracy can be improved. .

  (4) Since the NO conversion rate and the NO2 conversion rate are based on the knowledge that the DOC temperature or the DPF temperature is maximized when the temperature is a predetermined temperature, the maps of FIGS. 3A and 3C are set. Therefore, it is possible to improve the estimation accuracy of these conversion rates.

(Other embodiments)
The present invention is not limited to the description of the above-described embodiments, and the characteristic configurations of the respective embodiments may be arbitrarily combined. In addition, each of the above embodiments may be modified as follows.

  In the above embodiment, the PM accumulation amount used for calculating the NO conversion rate is calculated based on the detection values of the differential pressure sensors 25 and 26. However, the differential pressure sensors 25 and 26 are abolished and the engine operating state is calculated. The PM accumulation amount may be calculated based on the above. A specific example of the calculation method will be described below.

  First, the amount of PM discharged from the combustion chamber (PM discharge amount) is estimated based on the engine speed and the fuel injection amount. For example, the relationship between the engine rotational speed, the fuel injection amount, and the PM emission amount may be acquired in advance by testing, and the PM emission amount may be estimated using the map of FIG. . Next, the amount of PM burned and removed by the DPF 12 (PM combustion amount) is estimated based on the DPF temperature. For example, the relationship between the DPF temperature and the PM combustion amount may be acquired in advance by a test, and the PM combustion amount may be estimated using the map of FIG. 4B in which the relationship is stored. Then, a value obtained by subtracting the PM combustion amount from the estimated PM emission amount is calculated as the PM accumulation amount.

  In the above embodiment, the present invention is applied to the exhaust purification system in which the DOC 11 and the DPF 12 are separately configured as shown in FIG. 1, but the configuration in which the DOC 11 and the DPF 12 are integrated, specifically, The present invention may be applied to an exhaust purification system including a DPF with an oxidation catalyst in which an oxidation catalyst 11a is supported on a filter of the DPF 12.

  In the above embodiment, the present invention is applied to a diesel engine. However, even an ignition engine (gasoline engine) is equipped with an SCR 13 such as an engine that burns with an air-fuel mixture that is leaner than the stoichiometric air-fuel ratio. The present invention can be applied to any engine.

The figure which shows the outline | summary of the exhaust gas purification system to which the urea water injection amount control apparatus concerning one Embodiment of this invention was applied. FIG. 2 is a functional block diagram showing a calculation procedure when the ECU shown in FIG. 1 calculates a urea water injection amount. The map used in the various estimation parts of FIG. The modification of the map used in the estimation part 20c of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11a ... Oxidation catalyst which DOC11 has, 12 ... DPF (filter), 13a ... NOx reduction catalyst which SCR13 has, 14 ... Injection valve, 20 ... ECU (PM accumulation amount acquisition means, filter temperature acquisition means, exhaust gas flow rate acquisition means, oxidation Catalyst temperature acquisition means), 20b... NO / NO2 ratio estimation section (ratio estimation means), 20c... NO / NO2 ratio estimation section (ratio estimation means), 20d... Urea water injection amount calculation section (injection amount control means).

Claims (11)

A NOx reduction catalyst that is disposed in the exhaust pipe of the internal combustion engine and reduces NOx in the exhaust using ammonia generated from urea water;
An injection valve that injects urea water on the exhaust upstream side of the NOx reduction catalyst;
An oxidation catalyst disposed upstream of the NOx reduction catalyst and capable of oxidizing NO in the exhaust to NO2;
A filter that is disposed upstream of the NOx reduction catalyst and collects carbon-based fine particles in the exhaust;
Applied to an exhaust gas purification system of an internal combustion engine comprising:
Based on the NO2 conversion rate at which NO is oxidized by oxygen in the oxidation catalyst and converted to NO2, and the NO conversion rate at which NO2 is converted to NO as the carbon is oxidized by NO2 in the filter, the NOx. A ratio estimating means for estimating a ratio of NO and NO2 flowing into the reduction catalyst;
An injection amount control means for controlling the injection amount of urea water injected from the injection valve based on the ratio of NO and NO2 estimated by the ratio estimation means;
A urea water injection amount control device comprising: PM accumulation amount acquisition means for acquiring the accumulation amount of carbon-based fine particles in the filter,
2. The urea according to claim 1, wherein the ratio estimation unit estimates the ratio by estimating the NO conversion rate based on a deposition amount of carbon-based fine particles acquired by the PM deposition amount acquisition unit. Water injection amount control device.   The urea water injection amount control apparatus according to claim 2, wherein the ratio estimation unit estimates that the NO conversion rate increases as the accumulation amount increases. Comprising a filter temperature acquisition means for acquiring the temperature of the filter;
The said ratio estimation means estimates the said ratio by estimating the said NO conversion rate based on the filter temperature acquired by the said filter temperature acquisition means, The ratio is any one of Claims 1-3 characterized by the above-mentioned. Urea water injection amount control device.   The ratio estimation means estimates the NO conversion rate based on the filter temperature so that the NO conversion rate is maximized when the filter temperature is a predetermined temperature. Urea water injection amount control device. An exhaust flow rate acquisition means for acquiring the exhaust flow rate is provided.
The said ratio estimation means correct | amends the estimated value of the said NO conversion rate fewly, so that the exhaust gas flow velocity acquired by the said oxidation catalyst temperature acquisition means is quick. Urea water injection amount control device. An oxidation catalyst temperature acquisition means for acquiring the temperature of the oxidation catalyst;
The said ratio estimation means estimates the said ratio by estimating the said NO2 conversion rate based on the oxidation catalyst temperature acquired by the said oxidation catalyst temperature acquisition means, The said ratio is any one of Claims 1-6 characterized by the above-mentioned. The urea water injection amount control device described in 1.   8. The ratio estimating means estimates the NO2 conversion rate based on the oxidation catalyst temperature so that the NO2 conversion rate is maximized when the oxidation catalyst temperature is a predetermined temperature. The urea water injection amount control device described in 1. An exhaust flow rate acquisition means for acquiring the exhaust flow rate is provided,
9. The urea water injection amount control according to claim 7, wherein the ratio estimating unit corrects the estimated value of the NO 2 conversion rate to be smaller as the exhaust flow rate acquired by the oxidation catalyst temperature acquiring unit is faster. apparatus. A NOx reduction catalyst that is disposed in the exhaust pipe of the internal combustion engine and reduces NOx in the exhaust using ammonia generated from urea water;
An injection valve that injects urea water on the exhaust upstream side of the NOx reduction catalyst;
An oxidation catalyst disposed upstream of the NOx reduction catalyst and capable of oxidizing NO in the exhaust to NO2;
A filter that is disposed upstream of the NOx reduction catalyst and collects carbon-based fine particles in the exhaust;
Applied to an exhaust gas purification system of an internal combustion engine comprising:
PM accumulation amount acquisition means for acquiring the accumulation amount of carbon-based fine particles in the filter;
A ratio estimating means for estimating a ratio of NO and NO2 flowing into the NOx reduction catalyst based on a deposition amount of carbon-based fine particles obtained by the PM deposition amount obtaining means;
An injection amount control means for controlling the injection amount of urea water injected from the injection valve based on the ratio of NO and NO2 estimated by the ratio estimation means;
A urea water injection amount control device comprising: A urea water injection amount control device according to any one of claims 1 to 10,
At least one of the NOx reduction catalyst, the injection valve, the oxidation catalyst, and the filter;
A urea water injection control system comprising:

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