JP2010261320A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simultaneously restrain an ammonia slip and NOx deterioration when regenerating a particulate filter. <P>SOLUTION: A selective reduction type NOx catalyst is arranged in an exhaust passage of an internal combustion engine, and a reducing agent is supplied to its upstream side. The particulate filter is also arranged in the exhaust passage. When a filter temperature rise control performing condition is realized, filter temperature rise control is started simultaneously when stopping supply of the reducing agent, and a filter is raised in the temperature stepwise by repeating a temperature rise and temperature rise stopping. The NOx deterioration can be restrained by eliminating a waiting time up to starting the filter temperature rise control. The NOx catalyst can also be raised in the temperature stepwise, and an adsorbed ammonia discharge quantity per one time temperature rise can be restrained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus for an internal combustion engine in which a selective reduction type NOx catalyst and a particulate filter are provided in an exhaust passage.

  For example, a selective reduction type NOx catalyst is provided in an exhaust passage of an internal combustion engine such as a diesel engine, urea as a reducing agent is supplied to the NOx catalyst from the upstream side, and NOx contained in exhaust gas is selectively selected by ammonia generated from urea. An exhaust emission control device that is reduced to the above is known.

  This selective reduction type NOx catalyst has an ammonia adsorption capability of adsorbing ammonia within a predetermined limit, and this ammonia adsorption capability has a characteristic that the higher the catalyst temperature is, the lower it is. On the other hand, when a so-called ammonia slip in which ammonia is discharged from the NOx catalyst occurs, it causes a strange odor and the like, and it is necessary to prevent this as much as possible.

  Incidentally, a particulate filter that removes particulates (PM) such as soot contained in the exhaust gas may be installed in the exhaust passage of the internal combustion engine. In this case, the temperature of the filter may be raised in order to burn and remove PM accumulated on the filter and regenerate the filter.

  When the temperature of the particulate filter is raised, the temperature of the NOx catalyst may also rise. When the temperature of the NOx catalyst rises rapidly, ammonia adsorbed on the NOx catalyst may be desorbed from the NOx catalyst and discharged downstream.

  In order to suppress such ammonia slip, in Patent Document 1, when the execution condition of the filter temperature increase control is satisfied, the urea supply to the selective reduction type NOx catalyst is stopped, and after a predetermined period has elapsed from this stop point. Filter temperature rise control is executed. In this way, during the predetermined period from the urea supply stop time to the filter temperature raising control start time, the adsorbed ammonia of the NOx catalyst can be reacted and consumed by the NOx in the exhaust gas, and then the amount of adsorbed ammonia decreases. Since the filter temperature raising control is started, the amount of adsorbed ammonia desorbed and discharged can be reduced and ammonia slip can be suppressed.

JP 2008-255905 A

  However, if a waiting time until the start of the filter temperature raising control is provided as in the technique described in Patent Document 1, NOx deteriorates during this waiting time. In other words, during the waiting time, the NOx in the exhaust gas reacts and consumes the adsorbed ammonia of the NOx catalyst, but as the adsorbed ammonia amount decreases, the NOx purification rate of the NOx catalyst decreases. Therefore, it cannot be said that the NOx in the exhaust gas is sufficiently purified during the waiting time, and the amount of NOx released to the atmosphere increases during this time.

  On the other hand, when the filter temperature raising control is started immediately without providing a waiting time, the ammonia slip as described above occurs. As described above, ammonia slip and NOx deterioration are contradictory problems.

  Accordingly, the present invention has been made in view of the above circumstances, and one object thereof is to provide an exhaust purification device for an internal combustion engine that can simultaneously suppress ammonia slip and NOx deterioration during regeneration of the particulate filter. is there.

According to one aspect of the invention,
A selective reduction NOx catalyst provided in an exhaust passage of the internal combustion engine;
Reducing agent supply means for supplying urea or ammonia as a reducing agent upstream of the NOx catalyst;
A particulate filter provided in the exhaust passage;
Filter temperature raising means for performing filter temperature raising control for raising the temperature of the particulate filter;
With
When the execution condition of the filter temperature increase control is satisfied, the supply of the reducing agent by the reducing agent supply unit is stopped and the filter temperature increase control by the filter temperature increase unit is started at the same time. An exhaust gas purification apparatus for an internal combustion engine is provided, wherein the particulate filter is heated stepwise by repeatedly executing temperature and temperature rise stop.

  When the conditions for executing the filter temperature increase control are satisfied, the filter temperature increase control is started simultaneously with the urea supply stop. Therefore, the waiting time until the filter temperature increase control starts is eliminated, and NOx deterioration can be suppressed.

  In addition, since the temperature of the particulate filter is raised stepwise by repeatedly executing the temperature rise and the temperature rise stop, the temperature of the NOx catalyst is similarly raised stepwise. In this way, it is possible to limit the discharge amount of the adsorbed ammonia per one temperature increase to an allowable amount or less, and it is possible to suppress the discharge amount of the adsorbed ammonia by slowing the temperature increase rate as a whole by stopping the temperature increase.

  In this way, ammonia slip and NOx deterioration during particulate filter regeneration can be suppressed at the same time.

  Preferably, the filter temperature raising means increases the amount of temperature raised once as the NOx catalyst becomes hot. As a result, the amount of ammonia discharged at each temperature increase can be equalized, efficient filter temperature increase control becomes possible, and the time required for filter regeneration can be shortened.

  Preferably, the filter temperature raising means sets a target temperature raising amount related to the NOx catalyst temperature based on the temperature of the NOx catalyst at the time of starting temperature raising once, and the actual temperature of the NOx catalyst temperature is set to the target temperature raising amount. One temperature increase is executed so that the temperature increases match.

  Preferably, the filter temperature raising means increases the temperature raising rate as the NOx catalyst becomes higher in temperature. As a result, the rate of temperature increase can be more positively controlled, and the time required for filter regeneration can be further shortened compared to the case where the rate of temperature increase is constant.

  Alternatively, the filter temperature raising means may make the amount of temperature rise once, regardless of the temperature of the NOx catalyst. Thus, the filter temperature increase control can be executed by a simple method.

  According to the present invention, an excellent effect that ammonia slip and NOx deterioration at the time of regeneration of a particulate filter can be simultaneously suppressed is exhibited.

1 is a diagram schematically showing an internal combustion engine according to an embodiment of the present invention. It is a graph which shows the ammonia adsorption characteristic of a NOx catalyst, and the filter temperature rising control as a comparative example. It is a graph which shows the ammonia adsorption characteristic of a NOx catalyst, and the filter temperature increase control of this embodiment. It is a flowchart of filter temperature rising control.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

  FIG. 1 schematically shows an internal combustion engine according to an embodiment of the present invention. Reference numeral 1 denotes a compression ignition internal combustion engine or diesel engine for automobiles, 2 an intake manifold communicated with an intake port, 3 an exhaust manifold communicated with an exhaust port, and 4 a combustion chamber. In the present embodiment, fuel supplied from a fuel tank (not shown) to the high pressure pump 5 is pumped to the common rail 6 by the high pressure pump 5 and accumulated in a high pressure state. The high pressure fuel in the common rail 6 is transferred from the injector 7 to the combustion chamber. 4 is directly supplied by injection.

  The exhaust gas from the engine 1 passes through the turbocharger 8 from the exhaust manifold 3 and then flows into the exhaust passage 9 downstream thereof. After being purified as described later, the exhaust gas is discharged to the atmosphere. In addition, as a form of a diesel engine, it is not restricted to the thing provided with such a common rail type fuel injection device. It is also optional to include other exhaust purification devices such as EGR devices.

  On the other hand, the intake air introduced from the air cleaner 10 into the intake passage 11 passes through the air flow meter 12, the turbocharger 8, the intercooler 13, and the throttle valve 14 in order to reach the intake manifold 2. The air flow meter 22 is a sensor for detecting the intake air amount, and specifically outputs a signal corresponding to the flow rate of the intake air. The throttle valve 14 is an electronically controlled type.

  In the exhaust passage 9, in order from the upstream side, an oxidation catalyst 20 that oxidizes and purifies unburned components (especially HC) in the exhaust gas and a particulate matter (PM) such as soot in the exhaust gas is collected. A curate filter (hereinafter referred to as DPF) 22 and a selective reduction type NOx catalyst (SCR: Selective Catalytic Reduction) 24 for reducing and removing NOx in the exhaust gas are provided in series.

  The NOx catalyst 24 continuously reduces and removes NOx in the exhaust gas when a reducing agent made of urea or ammonia is supplied. In this embodiment, urea water is used as a reducing agent for ease of handling. Further, the NOx catalyst 24 can reduce NOx when the catalyst temperature is in a predetermined activation temperature range (for example, 200 to 400 ° C.).

  A urea addition valve 40 for supplying urea water is provided on the upstream side of the NOx catalyst 24. The urea addition valve 40 is supplied with urea water via a pump from a urea tank (not shown). The urea addition valve 40 is connected to and controlled by an electronic control unit (hereinafter referred to as ECU) 100.

When urea water into the NOx catalyst 24 is supplied, ammonia NH ₃ is produced urea water is evaporated and hydrolyzed, ammonia NH ₃ reacts with NOx in the NOx catalyst, NOx is reduced. This reaction is represented by the following chemical formula.
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O
In particular, the NOx catalyst 24 has ammonia adsorption ability and contains an ammonia adsorption component such as zeolite. The NOx catalyst 24 is configured, for example, by supporting a noble metal such as Pt on the surface of a zeolite base material.

  On the other hand, the DPF 22 has a noble metal on the surface. When rich exhaust gas containing a lot of HC is supplied to the DPF 22, the rich gas is oxidized and burned through the noble metal, and at the same time, PM deposited on the DPF burns. Thereby, the DPF 22 is regenerated.

  An exhaust temperature sensor 34 for detecting the temperature of the exhaust gas and a NOx sensor 36 for detecting the NOx concentration of the exhaust gas are provided upstream of the NOx catalyst 24 and the urea addition valve 40.

  Further, an exhaust temperature sensor 30 for detecting the temperature of the exhaust gas is provided on the upstream side of the DPF 22. Hereinafter, the exhaust temperature sensors 30 and 34 are referred to as an upstream exhaust temperature sensor 30 and a downstream exhaust temperature sensor 34, respectively. Furthermore, a differential pressure sensor 32 for detecting the differential pressure before and after the DPF 22 is provided. This differential pressure sensor 32 is used to detect the amount of PM collected by the DPF 22.

  A fuel supply valve 60 that supplies fuel into the exhaust passage 9 is provided on the upstream side of the oxidation catalyst 20.

  ECU 100 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like. The ECU 100 controls the injector 7, the high-pressure pump 5, the throttle valve 14 and the like so that desired engine control is executed based on detection values and the like of various sensors. Further, the ECU 100 controls the urea addition valve 40 to control the urea addition amount, and controls the fuel supply valve 60 to control the fuel supply amount. The ECU 100 is connected to the air flow meter 22, the NOx sensor 36, the upstream exhaust temperature sensor 30, the downstream exhaust temperature sensor 34, and the differential pressure sensor 32 as sensors.

  The ECU 100 is connected to a crank angle sensor 15 and an accelerator opening sensor 16. The crank angle sensor 15 outputs a crank pulse signal to the ECU 100 when the crank angle rotates, and the ECU 100 detects the crank angle of the engine 1 based on the crank pulse signal and calculates the rotational speed of the engine 1. The accelerator opening sensor 16 outputs a signal corresponding to the accelerator pedal opening (accelerator opening) operated by the user to the ECU 100.

  The temperature of the NOx catalyst 24 can be directly detected by a temperature sensor embedded in the catalyst, but in the present embodiment, this is estimated. Specifically, the ECU 100 estimates the catalyst temperature based on the exhaust temperature detected by the downstream exhaust temperature sensor 34, the operation history of the engine 1, and the like. Note that the estimation method is not limited to such an example.

  Similarly, the temperature of the DPF 22 is also estimated by the ECU 100 based on the exhaust temperatures detected by the upstream exhaust temperature sensor 30 and the downstream exhaust temperature sensor 34, respectively. Of course, the temperature can be directly detected by a temperature sensor embedded in the DPF 22.

  In the configuration of the present embodiment, the NOx catalyst 24 can adsorb ammonia. Then, the ammonia adsorption capacity of the NOx catalyst 24, that is, the ammonia adsorbable amount, changes according to the catalyst temperature of the NOx catalyst 24 as shown by a line L in FIG. 2, and tends to decrease as the catalyst temperature increases. The NOx catalyst 24 also uses this adsorbed ammonia to reduce NOx in the exhaust gas.

  On the other hand, the urea addition amount is controlled by the ECU 100 as follows so that the actual ammonia adsorption amount in the NOx catalyst 24 matches the target adsorption amount T which is smaller than the adsorbable amount L by a predetermined margin.

  First, based on the estimated catalyst temperature, the NOx purification rate and the target adsorption amount of the NOx catalyst 24 are calculated. Next, based on the NOx concentration detected by the NOx sensor 36 and the intake air amount (substitute value of the exhaust gas flow rate) detected by the air flow meter 12, the supplied NOx amount (or from the combustion chamber 4) supplied to the NOx catalyst 24. The amount of discharged NOx) is calculated. Thereafter, the consumption amount of ammonia used for NOx purification is calculated based on the NOx purification rate and the supplied NOx amount.

Thereafter, the ammonia addition amount is calculated based on the target adsorption amount and the ammonia consumption amount. The above calculation is sequentially performed every predetermined calculation cycle. When the target adsorption amount is T, the ammonia consumption amount is A, the ammonia addition amount is B, and the current value and the previous value are represented by n and n-1, respectively, the ammonia addition amount B is expressed by the formula: B _n = T _n −T _n− It is calculated by the ₁ + _{A n.} An amount of urea water corresponding to the ammonia addition amount B is added from the urea addition valve 40.

Here, T _n -T _n-1 represents the amount of ammonia adsorbed this time. Accordingly, T _n −T _n−1 is sequentially integrated, and the integrated value is obtained as the amount of ammonia adsorbed up to this time, that is, the ammonia adsorption amount.

  On the other hand, regarding the DPF 22, it is necessary to periodically burn and remove the PM collected and deposited in the DPF 22 to regenerate the DPF 22. For this reason, the ECU 100 executes filter temperature increase control for increasing the temperature of the DPF 22. Here, the filter temperature increase control as a comparative example will be described, and the filter temperature increase control of the present embodiment will be described later.

  First, the detection value of the differential pressure sensor 32 is compared with a predetermined value. When the detected value is less than the predetermined value, it is determined that the PM accumulation amount is small and the filter temperature increase control is unnecessary (that is, there is no DPF regeneration request), and the filter temperature increase control is not executed. On the other hand, when the detected value is equal to or greater than a predetermined value, it is determined that the PM deposition amount is large and that the filter temperature increase control is necessary (that is, there is a DPF regeneration request), and the filter temperature increase control is executed.

  When executing the filter temperature raising control, fuel is supplied from the fuel supply valve 60 to the exhaust passage 9. Then, first, rich exhaust gas containing a lot of HC is supplied to the oxidation catalyst 20, and HC is oxidized and burned in the oxidation catalyst 20 to generate high-temperature and rich exhaust gas. This high temperature and rich exhaust gas is then supplied to the DPF 22. Then, HC in the exhaust gas is burned by the action of the noble metal supported on the DPF 22, and PM is simultaneously burned and removed. Thus, when the filter temperature increase control is executed, the DPF 22 is heated.

  Note that the oxidation catalyst 20 may be omitted, and the fuel may be directly burned by the DPF 22 to simultaneously burn PM. In addition to a method of separately supplying fuel from the fuel supply valve 60, a so-called post-injection method of injecting fuel from the injector 7 during an engine expansion stroke or exhaust stroke is also possible.

  By the way, referring to FIG. 2, the temperature of the exhaust gas supplied to the NOx catalyst 24 is usually low, and therefore the temperature of the NOx catalyst 24 is also normally in a low temperature range as indicated by T1 to T2 in the figure. This low temperature range is 200-300 degreeC, for example.

  On the other hand, when the filter temperature raising control as the above-described comparative example is executed, the temperature of the DPF 22 rapidly rises. As a result, the temperature of the exhaust gas discharged from the DPF 22 and supplied to the NOx catalyst 24 rapidly rises. The temperature of the catalyst 24 itself also increases rapidly. For this reason, the temperature of the NOx catalyst 24 may reach a high temperature range of T3 or more in the drawing. This high temperature region is, for example, 600 ° C. or higher.

  On the other hand, as described above, the ammonia adsorption amount of the NOx catalyst 24 is controlled to become the target adsorption amount T. Then, when the filter temperature raising control as a comparative example is executed in a state where the temperature of the NOx catalyst 24 is in the normal low temperature range T1 to T2, the temperature of the NOx catalyst 24 rapidly increases as shown by a in the figure. Therefore, the ammonia exceeding the allowable amount, which is equal to the difference b between the actual ammonia adsorption amount and the adsorbable amount L, is desorbed and discharged from the NOx catalyst 24.

  On the other hand, as described above, when a waiting time until the start of the filter temperature raising control is provided as in Patent Document 1, the NOx purification rate of the NOx catalyst 24 decreases during this waiting time, and NOx deteriorates. Thus, ammonia slip and NOx deterioration are contradictory problems.

  Therefore, in order to simultaneously suppress ammonia slip and NOx deterioration during DPF regeneration, in this embodiment, the DPF temperature is raised stepwise instead of raising the DPF temperature all at once when the filter temperature raising control is executed. . More specifically, when the conditions for executing the filter temperature increase control are satisfied, the supply of urea by the urea addition valve 40 is stopped and the filter temperature increase control is started at the same time. In the filter temperature increase control, the temperature increase and the temperature increase stop are repeatedly executed to increase the temperature of the DPF 22 stepwise.

  When the conditions for executing the filter temperature increase control are satisfied, the filter temperature increase control is started at the same time as the urea supply is stopped. Therefore, there is no waiting time until the filter temperature increase control is started, and NOx deterioration is suppressed.

  Further, since the temperature rise and the temperature rise stop are repeatedly executed to raise the temperature of the DPF 22 stepwise, the NOx catalyst 24 on the downstream side of the DPF 22 is similarly raised in steps.

  For example, as shown in FIG. 3, when the filter temperature increase control according to the present embodiment is executed in a state where the temperature of the NOx catalyst 24 is in the normal low temperature range T1 to T2, as shown in FIG. The temperature of the NOx catalyst 24 is slightly increased by the first temperature increase. As a result, an allowable amount of ammonia equal to the difference d between the actual ammonia adsorption amount and the adsorbable amount L is desorbed and discharged from the NOx catalyst 24.

  Thereafter, the first temperature rise stop is executed. As a result, the temperature of the NOx catalyst 24 is generally maintained, and the rate of temperature increase is moderated as a whole, and the amount of ammonia discharged from the NOx catalyst 24 is suppressed. During this time, the adsorbed ammonia of the NOx catalyst 24 can be reacted and consumed by the NOx in the exhaust gas. Therefore, it is considered that the amount of adsorbed ammonia of the NOx catalyst 24 at the time when the second temperature increase starts is smaller than the amount of adsorbed ammonia at the time when the first temperature increase ends. However, in FIG. 3, for convenience, these are displayed as the same amount.

  Next, when the second temperature increase is executed, the temperature of the NOx catalyst 24 slightly increases again as indicated by e in the figure. As a result, an allowable amount of ammonia equal to the difference f between the actual ammonia adsorption amount and the adsorbable amount L is desorbed and discharged from the NOx catalyst 24. Thereafter, the second temperature increase stop is executed, and the temperature increase rate is made slow.

  Similarly, by the third temperature increase, the NOx catalyst 24 is heated as shown in g in the figure, and as a result, an allowable amount of ammonia that is equal to the difference h between the actual ammonia adsorption amount and the adsorbable amount L is desorbed from the NOx catalyst 24. Separated and discharged. In the illustrated example, the NOx catalyst 24 has reached a high temperature range equal to or higher than T3 due to the third temperature increase, that is, the DPF 22 has reached the final target regeneration temperature. Therefore, immediately after this, or after a predetermined time has elapsed if necessary, the filter temperature raising control is terminated.

  As can be seen from the above description, the amount of adsorbed ammonia discharged at each temperature increase is very small as compared with the case where the filter temperature increase control is executed as a comparative example. All are within the allowable amount. Therefore, ammonia slip can be suppressed as compared with the case where the filter temperature increase control is executed as a comparative example. As a result, it is not necessary to provide an ammonia oxidation catalyst downstream of the NOx catalyst.

  Thus, ammonia slip and NOx deterioration during DPF regeneration can be suppressed at the same time.

  The temperature increase of the NOx catalyst 24 by small amounts as described above is naturally realized by the temperature increase of the DPF 22 by small amounts. This is because the temperature of the NOx catalyst 24 is correlated or linked with the temperature of the DPF 22. The filter temperature increase control of the comparative example continues to supply fuel until the DPF 22 reaches the final target regeneration temperature. On the other hand, the filter temperature increase control according to the present embodiment intermittently supplies a small amount of fuel each time. Even when the temperature of the DPF 22 is raised stepwise, the PM deposited on the DPF 22 is burned little by little each time. Therefore, when the DPF 22 reaches the final target regeneration temperature, it is assumed that the necessary and sufficient amount of accumulated PM has already been burned and removed. Therefore, it is considered that the present embodiment can reduce the total time required for filter regeneration, compared with that described in Patent Document 1.

  Further, the NOx catalyst 24 has a characteristic that the NOx purification rate is improved in a temperature range (for example, 250 to 400 ° C.) slightly shifted to a higher temperature side than the normal low temperature range T1 to T2. In the thing of patent document 1, since it waits for reaction consumption with NOx of adsorption ammonia in normal low temperature range T1-T2, long waiting time is required. On the other hand, in the case of this embodiment, since it passes through the temperature region where the NOx purification rate is improved over time, the consumption of adsorbed ammonia can be promoted especially during the temperature rise stop, and the temperature rise and the temperature rise stop. Each step can be quickly advanced. Therefore, also in this respect, it is considered that the present embodiment can reduce the total time required for filter regeneration as compared with that described in Patent Document 1.

  By the way, in the filter temperature increase control of the present embodiment, it is preferable to increase the temperature increase amount once as the NOx catalyst 24 becomes high temperature. FIG. 3 shows this preferred embodiment. As the temperature of the NOx catalyst 24 becomes higher, the temperature increase amount of each time of the DPF 22 is gradually increased, and as a result, the temperature increase amounts c, e, and g of the NOx catalyst 24 are also increased gradually. Yes. As shown in the figure, the rate of decrease of the adsorbable amount L with respect to the temperature rise of the NOx catalyst 24 (the slope of the line L) has a characteristic that it decreases as the NOx catalyst 24 becomes hot. Therefore, in view of this characteristic, if the temperature rise amount is increased once as the NOx catalyst 24 becomes higher in temperature, the ammonia discharge amounts d, f, and h at each time can be equalized and efficient filter temperature rise control can be performed. In addition, the time required to reach the target regeneration temperature and thus the time required for filter regeneration can be reduced.

  Further, in the filter temperature increase control of the present embodiment, a target temperature increase amount related to the catalyst temperature is set based on the temperature of the NOx catalyst 24 at the time of one temperature increase start, and the actual NOx catalyst is set to this target temperature increase amount. It is preferable to perform one temperature increase so that the temperature increase amounts coincide. According to the ammonia adsorption characteristics shown in FIG. 3, when trying to equalize the ammonia discharge amounts d, f, and h at each time, the required temperature increase amount depends on the temperature of the NOx catalyst 24 at the time of starting the temperature increase once. Change. Therefore, a target temperature increase amount is set based on the temperature of the NOx catalyst 24 at the time of the start of one temperature increase, and one temperature increase is executed so that the actual temperature increase amount matches this target temperature increase amount. Thus, it is possible to suitably equalize the ammonia discharge amounts d, f, and h at each time.

  Furthermore, in view of the ammonia adsorption characteristics shown in FIG. 3, it is also preferable to increase the temperature increase rate at one temperature increase as the NOx catalyst 24 becomes higher in temperature. As a result, the filter can be made to reach the target regeneration temperature earlier than in the case where the temperature increase rate is constant, and the filter regeneration time can be further shortened. Further, according to the ammonia adsorption characteristic, the higher the temperature of the NOx catalyst 24, the smaller the ammonia discharge amount per fixed temperature increase amount, so that the ammonia discharge rate can be limited to an allowable value or less. In this way, it is possible to more positively control the rate of temperature increase.

  Alternatively, the one temperature increase amount in the filter temperature increase control may be constant regardless of the temperature of the NOx catalyst 24. Thus, the filter temperature increase control can be executed by a simple method. At this time, the rate of temperature increase may be increased as the NOx catalyst temperature becomes higher.

  Next, an example of the filter temperature increase control executed by the ECU 100 will be described with reference to FIG.

  First, in step S101, the ECU 100 determines whether there is a DPF regeneration request. That is, as described above, the ECU 100 compares the detected value of the differential pressure sensor 32 with a predetermined value, determines that there is no DPF regeneration request when the detected value is less than the predetermined value, and has a DPF regeneration request when the detected value is greater than or equal to the predetermined value. Is determined.

  When it is determined that there is no DPF regeneration request, the ECU 100 enters a standby state because the execution condition of the filter temperature increase control is not satisfied. On the other hand, when it is determined that there is a DPF regeneration request, the ECU 100 proceeds to step S102, assuming that the execution condition of the filter temperature increase control is satisfied.

  In step S102, the ECU 100 stops the urea addition valve 40 (off), and stops urea addition from the urea addition valve 40.

  Next, in step S103, the ECU 100 sets a target temperature increase amount related to the NOx catalyst temperature based on the estimated catalyst temperature of the NOx catalyst 24. The target temperature increase amount is set according to a map or function (hereinafter referred to as a map or the like) that predefines the relationship between the NOx catalyst temperature and the target temperature increase amount. The target temperature increase amount increases as the NOx catalyst temperature increases.

  When the temperature increase rate is also controlled, the ECU 100 also sets a target temperature increase rate related to the NOx catalyst temperature based on the estimated catalyst temperature of the NOx catalyst 24. The target temperature increase rate is also set according to a map or the like that predefines the relationship between the NOx catalyst temperature and the target temperature increase rate. The target temperature increase rate increases as the NOx catalyst temperature increases.

  Thereafter, in step S104, ECU 100 executes one temperature increase control. This temperature increase control is performed by supplying fuel from the fuel supply valve 60 so that the actual temperature increase amount of the NOx catalyst 24 matches the target temperature increase amount set in step S103. The ECU 100 determines whether the actual temperature increase amount of the NOx catalyst 24 matches the target temperature increase amount by monitoring the estimated catalyst temperature of the NOx catalyst 24. The fuel supply control is performed by using both feedforward control and feedback control for the NOx catalyst temperature.

  When the temperature increase rate is also controlled, the ECU 100 supplies the fuel to the fuel supply valve 60 so that the actual temperature increase rate of the NOx catalyst 24 matches the target temperature increase rate set in step S103. It is done by supplying from. The ECU 100 determines whether or not the actual temperature increase rate of the DPF 22 matches the target temperature increase rate by monitoring the estimated catalyst temperature of the NOx catalyst 24.

  When one temperature increase control is thus completed, the ECU 100 determines in step S105 whether or not a predetermined time has elapsed since the end of the one temperature increase control. During the temperature increase stop time, the fuel supply valve 60 is stopped and the fuel supply is stopped. The predetermined time is determined experimentally mainly considering the amount of ammonia discharged from the NOx catalyst 24 and the like. If the predetermined time has not elapsed, the process enters a standby state. If the predetermined time has elapsed, the process proceeds to step S106.

  In step S106, ECU 100 determines whether estimated DPF temperature Tf has reached a predetermined target regeneration temperature Tft or more. When Tf <Tft, the process returns to step S103, and the temperature increase control and the temperature increase stop control are repeated once again. On the other hand, when Tf ≧ Tft, the filter temperature increase control is terminated.

  As mentioned above, although embodiment of this invention was described, this invention can also take other embodiment. For example, the present invention can be applied to an internal combustion engine other than a diesel engine, that is, a compression ignition type internal combustion engine, for example, a spark ignition type internal combustion engine, particularly a direct injection lean burn gasoline engine. In the above embodiment, the NOx concentration of the exhaust gas supplied to the NOx catalyst 24 is detected by the NOx sensor 36. Instead of this, parameters representing the engine operating state (for example, engine speed and accelerator opening) are used. You may estimate based. As a method for raising the temperature of the DPF and the NOx catalyst, in addition to the method of supplying fuel from the fuel supply valve 60 and the method of performing post injection, a method of reducing the throttle valve opening, for example, an intake throttle or increasing the EGR is possible. is there.

  The embodiment of the present invention is not limited to the above-described embodiment, and includes all modifications, applications, and equivalents included in the concept of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

Claims (5)

A selective reduction NOx catalyst provided in an exhaust passage of the internal combustion engine;
Reducing agent supply means for supplying urea or ammonia as a reducing agent upstream of the NOx catalyst;
A particulate filter provided in the exhaust passage;
Filter temperature raising means for performing filter temperature raising control for raising the temperature of the particulate filter;
With
When the execution condition of the filter temperature increase control is satisfied, the supply of the reducing agent by the reducing agent supply unit is stopped and the filter temperature increase control by the filter temperature increase unit is started at the same time. An exhaust gas purification apparatus for an internal combustion engine, wherein the particulate filter is heated stepwise by repeatedly executing temperature and temperature rise stop.   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the filter temperature raising means increases the amount of temperature raised once as the NOx catalyst becomes high temperature.   The filter temperature raising means sets a target temperature rise related to the NOx catalyst temperature based on the temperature of the NOx catalyst at the time of starting temperature rise once, and the temperature rise of the actual NOx catalyst temperature is set to this target temperature rise. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the temperature is raised once so that the two values coincide with each other.   The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the filter temperature raising means increases the temperature raising rate as the NOx catalyst becomes higher in temperature.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 4, wherein the filter temperature raising means keeps the amount of temperature raised once regardless of the temperature of the NOx catalyst.

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