JP4729990B2 - 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, and more particularly to a technique for suppressing deterioration in fuel consumption associated with oxidation removal processing of particulate matter such as soot.

  In recent years, a technique for reducing particulate matter (PM) such as soot discharged from the automobile or the like driven by a compression ignition internal combustion engine (diesel engine) into the atmosphere has been desired. Therefore, a technique is known in which a particulate filter (hereinafter sometimes referred to as a “filter”) is disposed in the exhaust passage of the internal combustion engine, and PM discharged from the internal combustion engine is collected by the filter.

  However, if PM is excessively collected on the filter and PM is excessively deposited on the filter, the filter is clogged, causing an increase in exhaust resistance and a reduction in the output of the internal combustion engine. For this reason, it is necessary to appropriately execute a so-called PM oxidation removal process in which PM collected by the filter is oxidized and removed from the filter.

Further, it is necessary to remove nitrogen oxides (hereinafter sometimes referred to as “NOx”) contained in the exhaust from the compression ignition internal combustion engine. Patent Document 1 includes a filter carrying an ammonia selective reduction catalyst and a urea addition mechanism for supplying urea water from the upstream side of the filter. PM is collected in the filter and added from the urea addition mechanism. An exhaust purification device that reduces NOx with ammonia generated by hydrolyzing urea water has been proposed.
JP 2004-60494 A JP 2000-8833 A JP 2002-339729 A

  The above-described PM oxidation removal treatment is performed by increasing the temperature of the filter to a temperature range where PM can be oxidized (about 500 ° C. to 700 ° C.) while making the inside of the filter an oxidizing atmosphere (that is, an oxygen-excess atmosphere). Oxidation and removal.

  The means for raising the temperature of the filter can be exemplified by raising the temperature of the filter by raising the temperature of the exhaust from the internal combustion engine and transmitting the heat of the exhaust to the filter. Specifically, the combustion timing of the air-fuel mixture in the internal combustion engine is retarded. During the expansion stroke of the internal combustion engine, fuel is injected from the fuel injection valve into the cylinder (sub-injection) and burned. A method for prolonging the period can be exemplified.

  As described above, in order to oxidize and remove PM, extra fuel is required, for example, by performing sub-injection. Therefore, fuel efficiency deteriorates as the PM oxidation removal process is performed. Therefore, it is necessary to suppress fuel consumption deterioration associated with the PM oxidation removal process.

  On the other hand, even if a urea addition mechanism is provided as described above, there is still a technology for improving the performance of the PM oxidation removal process using urea water or ammonia as an ammonia compound added by the urea addition mechanism. Not proposed.

  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 for improving the performance of oxidizing and removing PM.

  In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a particulate filter that is disposed in an exhaust passage of the internal combustion engine and collects particulate matter contained in the exhaust, and the particulate filter. In an exhaust gas purification apparatus for an internal combustion engine, having an ammonia compound supply means for supplying an ammonia compound from upstream of a curate filter, and performing a PM oxidation removal process for oxidizing and removing particulate matter collected by the particulate filter, By supplying an ammonia compound by an ammonia compound supply means, the PM compound is removed after the ammonia compound or ammonia is adsorbed on the particulate filter.

  According to the research of the present inventor, when urea is removed as an ammonia compound or ammonia and PM are mixed, the oxidation removal treatment of PM is performed. It was found that the performance of oxidation removal treatment of PM is improved by performing the above.

  That is, when the PM oxidation removal process is performed in a state where urea or ammonia is present in the PM or filter, the PM oxidation removal process is performed as compared with the case where the PM oxidation removal process is performed in a state where urea or ammonia is not present in the PM or filter. It has been found that the rate of oxidation removal of is increased.

  In addition, when urea or ammonia is not present in the filter or PM, PM is not easily removed by oxidation unless the temperature of the filter is 500 ° C. or higher. On the other hand, when urea or ammonia is present in the filter or PM, the filter is not filtered. It has been found that PM is easily removed by oxidation even when the temperature is around 440 ° C.

  Therefore, when performing the PM oxidation removal process, if urea or ammonia as an ammonia compound is present, the PM oxidation removal process performance can be improved, and the execution time of the PM oxidation removal process can be shortened. . In addition, since the temperature at which all PM can be oxidized and removed can also be lowered, it is possible to suppress the melt damage of the filter due to the excessively high temperature of the filter.

  Therefore, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, ammonia compound or ammonia is adsorbed on the particulate filter (deposited on the filter) by supplying the ammonia compound from upstream of the particulate filter by the ammonia compound supply means. PM adsorption removal processing is executed after adsorbing to PM.).

  Thereby, when performing the PM oxidation removal process, urea or ammonia which is an ammonia compound exists, so the PM oxidation removal process performance is improved, and the execution time of the PM oxidation removal process is shortened. As a result, fuel consumption deterioration associated with the PM oxidation removal process can be suppressed.

  In another exhaust gas purification apparatus for an internal combustion engine according to the present invention, a particulate filter disposed in an exhaust passage of the internal combustion engine for collecting particulate matter contained in the exhaust, and an upstream of the particulate filter. In the exhaust gas purification apparatus for an internal combustion engine that has an ammonia compound supply means for supplying an ammonia compound from the exhaust gas and performs a PM oxidation removal process for oxidizing and removing particulate matter collected by the particulate filter, the PM oxidation removal process The ammonia compound is supplied by the ammonia compound supply means during the period of executing the operation.

As described above, urea or ammonia as an ammonia compound is present when the PM oxidation removal process is performed by supplying the ammonia compound by the ammonia compound supply means during the period during which the PM oxidation removal process is being performed. Therefore, the PM oxidation removal processing performance is improved and the execution time of the PM oxidation removal processing is shortened. As a result, fuel consumption deterioration associated with the PM oxidation removal process can be suppressed.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention described above, the exhaust gas passage may be downstream of the particulate filter or upstream of the particulate filter and downstream of the ammonia compound supply position by the ammonia compound supply means. A denitration catalyst provided, and an ammonia oxidation catalyst provided in an exhaust passage downstream of the denitration catalyst, and when the ammonia compound is supplied by the ammonia compound supply means, the bed temperature of the ammonia oxidation catalyst When the temperature is such that ammonia can be oxidized, it is preferable to supply more ammonia compound than when the bed temperature of the catalyst is a temperature at which ammonia cannot be oxidized. However, ammonia is not released during the PM oxidation removal process in a denitration catalyst having a high ammonia compound adsorptivity.

When urea water that is an ammonia compound is supplied by the ammonia compound supply means, the supplied urea water flows downstream along with the exhaust gas flowing from the upstream. A part of the supplied urea water is heated by the exhaust gas and hydrolyzed as in the following formula to generate ammonia.
CO (NH ₂ ) ₂ + H ₂ O → CO ₂ + 2NH ₃

When ammonia reaches the denitration catalyst, NO and NO ₂ in the exhaust are reduced as in the following equation.
6NO + 4NH ₃ → 5N ₂ + 6H ₂ O
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O

  In this denitration catalyst, the reduction rate of NOx can be improved by supplying urea water in excess. However, if urea water is supplied excessively, surplus ammonia flows downstream of the denitration catalyst, so that it is necessary to treat this ammonia.

Therefore, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, an ammonia oxidation catalyst is provided in the exhaust passage downstream of the denitration catalyst to oxidize and remove ammonia. That is, in an oxygen-excess atmosphere, NO is generated from a part of ammonia by the following formula.
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O
The NO produced in this way reacts with the remaining ammonia as shown in the following formula.
4NH ₃ + 4NO + 5O ₂ → 4N ₂ + 6H ₂ O
By such a reaction, ammonia is removed and release into the atmosphere is suppressed.

  On the other hand, according to the research of the present inventors, it was found that when urea or ammonia, which is an ammonia compound, is present in a larger amount, the oxidation removal treatment performance of PM is further improved.

  Therefore, when the ammonia compound is supplied by the ammonia compound supply means, if the bed temperature of the ammonia oxidation catalyst is a temperature at which ammonia can be oxidized, the ammonia is removed by the ammonia oxidation catalyst provided downstream. Considering that it is oxidized and removed, more ammonia compound is supplied than when the bed temperature of the ammonia oxidation catalyst is a temperature at which ammonia cannot be oxidized. As a result, the PM oxidation removal processing performance can be further improved, and the execution time of the PM oxidation removal processing can be further shortened. As a result, fuel consumption deterioration associated with the PM oxidation removal process can be further suppressed.

The ammonia compound supply means supplies any one of urea water, solid urea, and ammonia water, which are ammonia compounds, and the bed temperature of the ammonia oxidation catalyst is a temperature at which ammonia cannot be oxidized. For this, it is preferable to control the supply amount of the ammonia compound so that the equivalent ratio of NOx discharged from the internal combustion engine and flowing into the denitration catalyst and ammonia in the supplied ammonia compound becomes 1.

  Thus, more urea or ammonia as an ammonia compound can be present when the PM oxidation removal process is performed within a range in which ammonia can be prevented from being discharged to the atmosphere. Therefore, the PM oxidation removal processing performance can be improved to the maximum, and the execution time of the PM oxidation removal processing can be further shortened, so that the fuel consumption deterioration associated with the PM oxidation removal processing can be further suppressed. .

  When the bed temperature of the ammonia oxidation catalyst is a temperature at which ammonia can be oxidized, the equivalent ratio between NOx discharged from the internal combustion engine and flowing into the denitration catalyst and ammonia in the ammonia compound to be supplied is 1 It is preferable to control the supply amount of the ammonia compound so as to increase.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the performance of oxidizing and removing PM can be improved. Therefore, fuel consumption deterioration associated with the PM oxidation removal process can be suppressed.

  The best mode for carrying out the present invention will be exemplarily described in detail below based on the following embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention only to those unless otherwise specified.

The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine. An exhaust pipe 2 is connected to the internal combustion engine 1, and a filter 3 is provided in the middle of the exhaust pipe 2. A denitration catalyst 4 is provided in the exhaust pipe 2 downstream of the filter 3. The denitration catalyst 4 reduces and purifies NOx by selective catalytic reduction using ammonia (NH ₃ ) as a reducing agent.

A urea addition mechanism 5 for adding urea water ((NH ₂ ) ₂ CO), which is an ammonia compound, is provided in the exhaust pipe 2 upstream of the denitration catalyst 4. The urea addition mechanism 5 includes a tank 51 that stores urea water, a supply pipe 52 that is a flow path of urea water, a pump 53 that is interposed in the flow path, and an injection nozzle 54 that sprays urea water into the exhaust pipe 2. It is prepared for.

In the urea addition mechanism 5 configured as described above, urea water adjusted in advance to a predetermined concentration is stored in the tank 51, and when the pump 53 is operated, the urea water is pumped out of the tank 51.
The urea water reaches the injection nozzle 54 via the supply pipe 52. The urea water that has reached the injection nozzle 54 is injected into the exhaust pipe 2 when the injection nozzle 54 is opened. The amount of urea water injected at this time is adjusted by the valve opening time of the injection nozzle 54.

When urea water is added by the urea addition mechanism 5, the added urea water flows downstream along with the exhaust gas flowing from the upstream. A part of the added urea water is heated by exhaust gas and hydrolyzed as shown by the following formula to generate ammonia.
CO (NH ₂ ) ₂ + H ₂ O → CO ₂ + 2NH ₃

When the ammonia reaches the denitration catalyst 4, NO in the exhaust gas as shown in the following equation, NO ₂ is reduced.
6NO + 4NH ₃ → 5N ₂ + 6H ₂ O
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O

  In the denitration catalyst 4, the reduction rate of NOx can be improved by supplying excessive urea water. However, when excessive urea water is supplied, excess ammonia is adsorbed on the denitration catalyst 4. The ammonia adsorbed in this way flows out from the denitration catalyst 4 when the flow rate of the exhaust gas increases at a high load or the like, and this ammonia needs to be treated.

Therefore, in this embodiment, the ammonia oxidation catalyst 6 is provided in the exhaust pipe 2 downstream of the denitration catalyst 4 so that ammonia is oxidized and removed. That is, in an oxygen-excess atmosphere, NO is generated from a part of ammonia by the following formula.
4NH ₃ + 5O ₂ → 4NO + 6H ₂ O
The NO produced in this way reacts with the remaining ammonia as shown in the following formula.
4NH ₃ + 4NO + 5O ₂ → 4N ₂ + 6H ₂ O
By such a reaction, ammonia is removed and release into the atmosphere is suppressed.

  The exhaust pipe 2 upstream from the filter 3, the exhaust pipe 2 downstream from the filter 3 and upstream from the denitration catalyst 4, and the exhaust pipe 2 downstream from the denitration catalyst 4 respectively flow through the exhaust pipe 2. Exhaust temperature sensors 7, 8, 9 for outputting an electrical signal corresponding to the temperature of the exhaust are attached.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. The ECU 10 is an arithmetic logic operation circuit including a CPU, a ROM, a RAM, a backup RAM, and the like, and is a unit that controls an operation state of the internal combustion engine 1 in accordance with an operation condition of the internal combustion engine 1 and a driver's request.

  The ECU 10 is connected with various sensors such as exhaust temperature sensors 7, 8, 9, a crank position sensor (not shown), an accelerator position sensor (not shown), an air flow meter (not shown), etc. via electric wiring. Is output to the ECU 10.

  On the other hand, the ECU 10 is connected to a pump 53, an injection nozzle 54, a fuel injection valve for injecting fuel into the cylinder, and the like via electric wiring, and these can be controlled. The ECU 10 can store various application programs and various control maps and control the urea addition mechanism described above.

Here, when PM collected by the filter 3 accumulates on the filter 3, the filter 3 may be clogged. When this clogging occurs, the pressure of the exhaust gas upstream of the filter 3 increases, which may cause a decrease in the output of the internal combustion engine 1 or damage to the filter 3. In such a case, it is necessary to regenerate the filter 3 for removing the PM deposited on the filter 3 by oxidation.

  Therefore, the ECU 10 executes a temperature raising process for raising the temperature of the filter 3 to a high temperature range when the PM oxidation removal process start condition for the filter 3 is satisfied.

  The temperature raising process is to raise the temperature of the filter 3 by raising the exhaust gas temperature and transferring the heat of the exhaust gas to the filter 3. As a specific method thereof, a method of retarding the combustion timing of the air-fuel mixture in the internal combustion engine 1, and during the expansion stroke of the internal combustion engine 1, fuel is injected into the cylinder from the fuel injection valve (sub-injection). For example, a method of extending the combustion period can be exemplified.

  An example of the PM oxidation removal processing start condition is a condition that the amount of PM collected in the filter 3 is a predetermined amount or more. This predetermined amount is slightly lower than the amount by which PM is collected by the filter 3 and the filter 3 is clogged, and this clogging causes an increase in exhaust resistance and a decrease in the output of the internal combustion engine. The amount is set in advance by experiments and the like.

  Further, as a method for determining whether or not the amount of PM collected in the filter 3 is a predetermined amount or more, a differential pressure across the filter 3 (exhaust pressure upstream of the filter 3 and exhaust pressure downstream of the filter 3). Or the fuel injection amount from the end of the previous PM oxidation removal process execution, or a method for determining that the amount of PM trapped in the filter 3 is equal to or greater than a predetermined amount. A method of determining that the amount of PM collected by the filter 3 is greater than or equal to a predetermined amount when the integrated value is greater than or equal to a predetermined amount can be exemplified.

  When the PM oxidation removal process is executed, the PM collected in the filter 3 is oxidized and the PM is removed from the filter 3. Thereafter, when the PM oxidation removal process termination condition is satisfied, the execution of the PM oxidation removal process is terminated.

  As the PM oxidation removal process end condition, for example, the execution time of the PM oxidation removal process is a predetermined time or more, or the differential pressure across the filter 3 is lower than a predetermined pressure, or the filter from the start of the process. The condition that the history of the product of the temperature and time is a predetermined value or more can be exemplified.

  When the PM oxidation removal process is executed as described above, extra fuel is consumed in the process, such as by sub-injection. Therefore, the fuel consumption increases as the PM oxidation removal process is executed. Therefore, it is necessary to suppress the deterioration in fuel consumption associated with the PM oxidation removal process, and for that purpose, it is preferable to shorten the time for executing the PM oxidation removal process.

  Here, according to the inventor's study, urea or ammonia and PM, which are ammonia compounds, are mixed and PM is oxidized and removed, in other words, urea or ammonia that is an ammonia compound is present in the filter or PM. It was found that the PM oxidation removal treatment performance is improved when the PM oxidation removal treatment is performed.

That is, when the PM oxidation removal process is performed in a state where urea or ammonia is present in the filter or PM, the PM oxidation removal process is performed in a state where urea or ammonia is not present in the filter or PM. The rate of oxidation removal of becomes higher. In addition, when urea or ammonia is not present in the filter or PM, PM is not easily removed by oxidation unless the temperature of the filter is 500 ° C. or higher. On the other hand, when urea or ammonia is present in the filter or PM, the filter is not filtered. At a temperature of 440 ° C. or higher, PM is easily removed by oxidation. Therefore, the execution time of the PM oxidation removal process can be shortened if urea or ammonia as an ammonia compound is present when the PM oxidation removal process is executed.

  Therefore, in this embodiment, as shown in FIG. 1, a urea addition mechanism 5 is provided so that urea water can be added to the exhaust pipe 2 upstream of the filter 3. Before the start of the PM oxidation removal process, urea water is added by the urea addition mechanism 5 so that urea or ammonia as an ammonia compound is adsorbed on the filter 3 (adsorbed on the PM deposited on the filter 3). After that, the PM oxidation removal process is executed.

  Normally, how much NOx discharged from the internal combustion engine is purified is determined according to the operating state of the internal combustion engine. If all the NOx discharged from the internal combustion engine is denitrated, the amount of urea water added so that the equivalent ratio of NOx flowing into the denitration catalyst 4 and ammonia in the urea water (ammonia compound) is 1. To control.

  In this embodiment, when urea water is added by the urea addition mechanism 5 before the start of the PM oxidation removal process, NOx flowing into the denitration catalyst 4 and ammonia in the urea water (ammonia compound) The amount of urea water added is controlled so that the equivalent ratio of becomes 1.

  As a method for estimating the NOx amount discharged from the internal combustion engine, the exhaust flow rate is estimated based on the intake air amount detected by the air flow meter and the fuel amount supplied into the cylinder by the fuel injection valve, A method of estimating by multiplying the exhaust flow rate by a NOx concentration detected by a NOx sensor (not shown) provided in the exhaust pipe 2, an engine speed (Ne) detected by a crank position sensor, an engine load A method of estimating based on (accelerator opening degree, fuel injection amount) and a map created in advance and stored in the ROM of the ECU 10 can be exemplified.

  In addition, when EGR gas is introduced into the cylinder, it is preferable that the estimation is performed in consideration of the EGR amount (EGR opening degree). Further, when a turbine housing of a variable nozzle centrifugal supercharger (variable nozzle turbocharger) is provided upstream of the urea addition mechanism 5, the estimation can be performed in consideration of the opening degree of the nozzle vane (VNT opening degree). Is preferred.

  In the present embodiment, the correlation between the amount of NOx discharged from the internal combustion engine 1 and flowing into the denitration catalyst 4 in advance and the amount of urea water added is such that the equivalent ratio of NOx to ammonia in the urea water is 1. A map is created by an experiment or the like so that the relationship is satisfied, and is stored in the ROM of the ECU 10.

  Then, the NOx amount is estimated from parameters such as the intake air amount, the fuel injection amount, the engine speed, the engine load, the EGR opening degree, and the VNT opening degree when urea water is added before the start of the PM oxidation removal process. The amount of urea water added is calculated and determined based on the estimated NOx amount and the map.

  The urea water addition control at the time of PM oxidation removal processing according to the present embodiment will be specifically described below with reference to the flowchart shown in FIG. This control routine is a routine that is stored in advance in the ROM of the ECU 10, and is a routine that is executed by the ECU 10 as an interrupt process triggered by the passage of a fixed time or the input of a pulse signal from the crank position sensor.

  In this control routine, the ECU 10 first determines whether or not the PM oxidation removal processing start condition is satisfied in S101. If it is determined that the PM oxidation removal process start condition is satisfied, the ECU 10 proceeds to S102.

  In S102, the urea addition mechanism 5 determines whether or not the condition for adding urea water is satisfied. The conditions can exemplify that the temperature of the filter 3 is equal to or lower than a predetermined temperature. In addition, as predetermined temperature, 440 degreeC which is the upper limit of the temperature which urea or ammonia adsorb | sucks to the filter 3 can be illustrated, for example.

  Further, as a method of grasping the temperature of the filter 3, there are a method of estimating based on a detection value of the exhaust temperature sensor 7, an engine speed (Ne) detected by a crank position sensor, an engine load (accelerator opening, fuel). A method of estimating based on the injection amount) and a map created in advance and stored in the ROM of the ECU 10 can be exemplified.

  If the determination in step S102 is affirmative, the process proceeds to step S103, and the amount of urea water added by the urea addition mechanism 5 is calculated as described above. Thereafter, the process proceeds to S104, and the urea water amount calculated in S103 is added.

  The process proceeds to S105 after the urea water is added in S104 or after it is determined in S102 that the urea addition mechanism 5 does not satisfy the conditions for adding the urea water. Perform removal processing. Thereafter, the execution of the PM oxidation removal process is continued until it is determined in S106 that the PM oxidation removal process termination condition is satisfied.

  Conditions for adding urea water in the urea addition mechanism 5 such as when the temperature of the filter 3 is relatively low before the start of PM oxidation removal processing by executing such urea water addition control during PM oxidation removal processing Is satisfied, since urea or ammonia is adsorbed to the filter 3 at the start of the PM oxidation removal process, the PM begins to be oxidized and removed when the temperature rises to about 440 ° C. As a result, when the PM oxidation removal process is started in a state where urea or ammonia is not adsorbed on the filter 3, the PM does not start the oxidation removal unless the temperature rises to about 500 ° C. It is possible to shorten the time until the start of oxidation removal.

  Further, when the PM oxidation removal process is performed with urea or ammonia adsorbed on the filter 3, the PM oxidation removal rate is higher than when the PM oxidation removal process is performed without urea or ammonia adsorbed on the filter 3. Become.

  As described above, by performing the urea water addition control during the PM oxidation removal process, the performance of oxidizing and removing the PM can be improved, so the PM oxidation removal process time can be shortened, and the PM oxidation removal process It is possible to suppress deterioration in fuel consumption associated with.

  Further, since the temperature at which all PM can be oxidized and removed can also be lowered, it is possible to suppress the filter melting damage and thermal deterioration caused by the excessive increase in the filter temperature.

  The present embodiment is the same as the first embodiment except for the aspect of addition of urea water by the urea addition mechanism 5 with respect to the first embodiment. Only different points will be described below.

  In the first embodiment, before the start of the PM oxidation removal process, urea water is added by the urea addition mechanism 5 so that urea or ammonia as an ammonia compound is adsorbed to the filter 3, and then the PM oxidation removal process is executed. I am doing so. On the other hand, in the present embodiment, urea water is added by the urea addition mechanism 5 during the execution of the PM oxidation removal process.

  In particular, urea water is added in accordance with the temperature of the filter 3 being raised in the temperature raising process. However, since the temperature raising process is a process as described above, the amount of NOx emission is smaller than that during steady operation. As described above, when urea solution is added by the urea addition mechanism 5, the addition is performed so that the equivalent ratio of NOx flowing into the denitration catalyst 4 and ammonia in the urea solution (ammonia compound) becomes 1. Therefore, the amount of urea water added decreases as the NOx emission decreases. On the other hand, the PM oxidation removal performance improves as the amount of urea or ammonia present in the filter 3 increases.

  Therefore, when adding urea water in accordance with the temperature raising process, the operation state of the internal combustion engine is set to an operation state in which the amount of NOx discharged from the internal combustion engine 1 is increased. Specifically, fuel that stops low-temperature combustion by introducing EGR gas into the cylinder, or the air-fuel ratio of the air-fuel mixture that contributes to combustion in the cylinder becomes an air-fuel ratio that increases the amount of NOx The amount can be exemplified. Hereinafter, an operation state in which the amount of NOx discharged from the internal combustion engine increases is referred to as a “high NOx exhaust operation state”.

  The urea water addition control during the PM oxidation removal process according to the present embodiment will be specifically described below with reference to the flowchart shown in FIG. This control routine is a routine that is stored in advance in the ROM of the ECU 10, and is a routine that is executed by the ECU 10 as an interrupt process triggered by the passage of a fixed time or the input of a pulse signal from the crank position sensor.

  In this control routine, the ECU 10 first determines whether or not the PM oxidation removal process start condition is satisfied in S201. And when it determines with PM oxidation removal process start conditions being satisfied, it progresses to S202.

  In S202, the urea addition mechanism 5 determines whether or not the condition for adding urea water is satisfied. The conditions can exemplify that the temperature of the filter 3 is equal to or lower than a predetermined temperature. In addition, as predetermined temperature, 440 degreeC which is the minimum of the temperature which PM begins to oxidize in the state in which urea or ammonia exists in filter 3 or PM can be illustrated, for example. If urea water is added when the temperature is higher than this temperature, the oxidation reaction of PM is further accelerated, and the temperature of the filter 3 may be excessively increased.

  If the determination in S202 is affirmative, the process proceeds to S203, and the PM oxidation removal process is executed in the high NOx exhaust operation state. Thereafter, the urea water addition amount is calculated in S204, and urea water corresponding to the addition amount calculated in S205 is added.

  The process proceeds to S206 after the urea water is added in S205 or after it is determined in S202 that the urea addition mechanism 5 does not satisfy the conditions for adding the urea water. Perform removal processing.

  Then, the process proceeds to S207, and it is determined whether or not the PM oxidation removal process end condition is satisfied. If an affirmative determination is made, the process proceeds to S208, and the PM oxidation removal process is terminated. On the other hand, if a negative determination is made, the processing from S202 onward is executed again.

By executing the urea water addition control during the PM oxidation removal process, the urea addition mechanism 5 can be used when the temperature of the filter 3 is relatively low during the PM oxidation removal process, particularly during the temperature raising process. When the conditions for adding urea water are satisfied, urea or ammonia is present in the filter 3 or PM during the PM oxidation removal process, so that the PM is oxidized when the temperature rises to about 440 ° C. Start removing. As a result, when the PM oxidation removal process is started in a state where urea or ammonia is not present in the filter 3 or PM, the PM oxidation removal process starts compared with the case where the PM does not start the oxidation removal unless the temperature rises to about 500 ° C. The time from the start of PM to the start of oxidation removal can be shortened.

  Further, when the PM oxidation removal process is performed in a state where urea or ammonia is present in the filter 3 or PM, the oxidation of PM is performed as compared with the PM oxidation removal process performed in a state where urea or ammonia is not present in the filter 3 or PM. The removal rate is increased.

  As described above, by performing the urea water addition control during the PM oxidation removal process, it is possible to improve the performance of oxidizing and removing the PM, so that the PM oxidation removal process time can be shortened, and the PM oxidation removal process It is possible to suppress deterioration in fuel consumption associated with.

  The present embodiment is the same as the second embodiment except for the addition of urea water by the urea addition mechanism 5 with respect to the second embodiment. Only different points will be described below.

  As described above, even if urea water is supplied excessively and excess ammonia flows out from the denitration catalyst 4, the ammonia is oxidized and removed by the ammonia oxidation catalyst 6, and release into the atmosphere is suppressed.

  On the other hand, the PM oxidation removal performance improves as the amount of urea or ammonia present in the filter 3 increases.

  Therefore, in this embodiment, when the bed temperature of the ammonia oxidation catalyst 6 is a temperature (operation temperature) at which ammonia can be oxidized by the catalyst, urea water by the urea addition mechanism 5 is added excessively. To do.

  Hereinafter, the urea water addition control during the PM oxidation removal process according to the present embodiment will be specifically described with reference to the flowchart shown in FIG. This control routine is a routine that is stored in advance in the ROM of the ECU 10, and is a routine that is executed by the ECU 10 as an interrupt process triggered by the passage of a fixed time or the input of a pulse signal from the crank position sensor.

  In this control routine, the ECU 10 first determines whether or not the PM oxidation removal processing start condition is satisfied in S301. If it is determined that the PM oxidation removal processing start condition is satisfied, the process proceeds to S302, where it is determined whether the urea addition mechanism 5 satisfies the condition for adding urea water. Since these processes are the same as S201 and S202 in FIG. 3, detailed description thereof will be omitted.

  If the determination in S302 is affirmative, the process proceeds to S303, and the PM oxidation removal process is executed in the high NOx exhaust operation state. Since this process is the same as S203 in FIG. 3, a detailed description thereof will be omitted.

  In S304, it is determined whether or not the bed temperature of the ammonia oxidation catalyst 6 is the operating temperature. In addition, as a method of grasping the bed temperature of the ammonia oxidation catalyst 6, there is a method of estimating based on the detection value of the exhaust temperature sensor 9 provided upstream of the catalyst, or a temperature sensor that directly detects the bed temperature of the catalyst. And a method of detecting by the sensor can be exemplified.

If the determination in step S304 is affirmative, the process proceeds to step S305, and the urea water addition amount is calculated. When the process proceeds to this step, it is determined that the bed temperature of the ammonia oxidation catalyst 6 is the operating temperature. Therefore, in this step, the added amount is calculated so that the urea water amount becomes excessive (greater than the equivalent ratio 1). Is done.

  On the other hand, when the negative determination is made in S304, the process proceeds to S306, and the urea water addition amount is calculated. In such a case, it is determined that the bed temperature of the ammonia oxidation catalyst is outside the operating temperature. The addition amount is calculated so that the urea water amount becomes an equivalent ratio of 1.

  Then, it progresses to S307 and the urea water for the addition amount calculated in S305 or S306 is added. Subsequent processes of S308 to S310 are the same processes as S206 to S208 of FIG.

  By executing the urea water addition control at the time of the PM oxidation removal process, when the bed temperature of the ammonia oxidation catalyst is the operating temperature, the urea water is excessively added by the urea addition mechanism 5. Further, the PM oxidation removal processing capability is further improved. As a result, since the PM oxidation removal processing time can be further shortened, fuel consumption deterioration associated with the PM oxidation removal processing can be further suppressed.

  In the first to third embodiments described above, it is assumed that the filter 3 is arranged upstream of the denitration catalyst 4 and urea water is added upstream of the filter 3 by the urea addition mechanism 5. However, the present invention is not limited to this configuration, and the denitration catalyst 4 may be arranged upstream of the filter 3 and urea water may be added upstream of the denitration catalyst 4 by the urea addition mechanism 5.

  However, in the case of such a configuration, urea or a part of ammonia by the urea water added by the urea addition mechanism 5 passes through the denitration catalyst 4 so that the urea water is present in the filter 3 during the PM oxidation removal process. Try to determine the amount added.

  Moreover, in Examples 1-3 mentioned above, it is set as the structure which adds urea water as an ammonia compound, However, The structure which supplies solid urea and ammonia water as an ammonia compound may be sufficient.

It is a figure which shows schematic structure of the exhaust gas purification apparatus of the internal combustion engine which concerns on an Example. 3 is a flowchart of urea water addition control during PM oxidation removal processing according to Embodiment 1. 6 is a flowchart of urea water addition control during PM oxidation removal processing according to Embodiment 2. 12 is a flowchart of urea water addition control during PM oxidation removal processing according to Embodiment 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust pipe 3 Filter 4 Denitration catalyst 5 Urea addition mechanism 6 Ammonia oxidation catalyst 7, 8, 9 Exhaust temperature sensor 10 ECU

Claims (4)

A particulate filter which is disposed in the exhaust passage of the internal combustion engine and collects particulate matter contained in the exhaust and does not carry a catalyst, and an ammonia compound supply means for supplying an ammonia compound from upstream of the particulate filter are provided. And
In an exhaust gas purification apparatus for an internal combustion engine that performs PM oxidation removal processing for oxidizing and removing particulate matter collected by the particulate filter,
An exhaust gas purifying apparatus for an internal combustion engine, wherein the PM oxidation removal process is executed after the ammonia compound or ammonia is adsorbed on the particulate filter by supplying the ammonia compound with the ammonia compound supply means. A particulate filter which is disposed in the exhaust passage of the internal combustion engine and collects particulate matter contained in the exhaust and does not carry a catalyst, and an ammonia compound supply means for supplying an ammonia compound from upstream of the particulate filter are provided. And
In an exhaust gas purification apparatus for an internal combustion engine that performs PM oxidation removal processing for oxidizing and removing particulate matter collected by the particulate filter,
An exhaust gas purification apparatus for an internal combustion engine, wherein the ammonia compound is supplied by the ammonia compound supply means during the period during which the PM oxidation removal process is executed. A denitration catalyst provided in an exhaust passage downstream of the particulate filter or upstream of the particulate filter and downstream of the ammonia compound supply position by the ammonia compound supply means;
An ammonia oxidation catalyst provided in an exhaust passage downstream of the denitration catalyst;
Further comprising
When the ammonia compound is supplied by the ammonia compound supply means, if the bed temperature of the ammonia oxidation catalyst is a temperature at which ammonia can be oxidized, the bed temperature of the catalyst cannot oxidize ammonia. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein a larger amount of the ammonia compound is supplied than in the case of the temperature. The ammonia compound supply means supplies any one of urea water, solid urea, and ammonia water, which is an ammonia compound, and when the bed temperature of the ammonia oxidation catalyst is a temperature at which ammonia cannot be oxidized. The supply amount of the ammonia compound is controlled so that the equivalent ratio of the NOx amount discharged from the internal combustion engine and flowing into the denitration catalyst and ammonia in the supplied ammonia compound becomes 1. An exhaust gas purification apparatus for an internal combustion engine as described.

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