JP4613787B2 - 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.

  As an exhaust gas purification device applied to internal combustion engines such as diesel engines, a PM filter that collects particulates (PM) mainly containing soot is provided in the exhaust system of the engine, and nitrogen oxide (NOx) A NOx storage reduction catalyst for purifying exhaust gas is supported on a catalytic converter provided in the exhaust system or the PM filter.

  In such an exhaust purification device, the PM filter and the catalytic converter are clogged due to the accumulation of fine particles, or the NOx occlusion capacity of the NOx catalyst is reduced by occlusion of sulfur oxide (SOx) or the like in the NOx catalyst. Therefore, many of this type of exhaust purification devices are designed to recover the NOx occlusion ability of the NOx catalyst, which has been reduced by the SOx occlusion, and the PM regeneration control for eliminating clogging caused by the particulate matter of the PM filter and the catalytic converter. S poison recovery control is performed.

  The PM regeneration control is executed when the accumulation amount of the particulates in the exhaust system estimated from the engine operating state exceeds the allowable value, and is continued until the accumulation amount of the particulates becomes “0”. In this PM regeneration control, an unburned fuel component is supplied to a NOx catalyst supported by an exhaust system catalytic converter or a PM filter, so that NOx is generated due to heat generated by oxidation of the unburned fuel component in the exhaust or on the catalyst. The temperature of the catalyst is raised to, for example, about 600 to 700 ° C., and fine particles around the catalyst are burned. Then, the fine particles are burned and discharged as carbon dioxide (CO2) and water (H2O) to eliminate clogging of the PM filter and the catalytic converter due to the fine particles.

  Further, the S poison recovery control is executed when the SOx occlusion amount of the NOx catalyst calculated based on the history of the engine operation state exceeds the allowable value. In this S poison recovery control, the temperature of the catalyst is raised to, for example, about 600 to 700 ° C. through the supply of the unburned fuel component to the exhaust system catalyst, and the exhaust air-fuel ratio is made rich at that high temperature, The release of SOx from the NOx catalyst and its reduction are promoted to restore the NOx storage capacity. If the exhaust air-fuel ratio continues to be rich, the heat generated by the oxidation of the unburned fuel component in the exhaust or on the catalyst increases, and the catalyst may be excessively heated. For this reason, in the S poison recovery control, the supply of the unburned fuel component to the catalyst for enriching the air-fuel ratio of the exhaust gas is intermittently performed, whereby the air-fuel ratio of the exhaust gas is intermittently enriched. In this way, excessive heating of the catalyst is suppressed.

  By the way, if particulates are accumulated in the exhaust system when performing the S poison recovery control, when exhaust gas air-fuel ratio is enriched at a high temperature by supplying unburned fuel components to the catalyst, There is a possibility that the accumulated fine particles burn at once and the catalyst is overheated. For this reason, as shown in Patent Document 1, prior to the execution of the S poison recovery control, the PM regeneration control is executed regardless of whether or not the amount of particulates accumulated in the exhaust system is greater than or equal to an allowable value. It has been proposed to remove particulates accumulated in the exhaust system before execution of poisoning recovery control.

Thus, before executing the S poisoning recovery control, the PM regeneration control is forcibly executed regardless of the amount of particulates accumulated in the exhaust system, so that the particulates deposited in the exhaust system during the execution of the S poisoning recovery control. It is possible to prevent the catalyst from being overheated due to combustion. In Patent Document 1, the temperature increase rate of the catalyst in the PM regeneration control performed before the execution of the S poison recovery control is set to be smaller as the amount of the fine particles deposited is smaller. It also tries to suppress the overheating.
JP 2002-38930 A

  As described above, the PM regeneration control is always executed before the execution of the S poison recovery control, so that the catalyst overheated due to the combustion of the fine particles accumulated in the exhaust system when the S poison recovery control is executed. Can be suppressed. However, if the PM regeneration control is forcibly executed regardless of the amount of particulates accumulated in the exhaust system before the execution of the S poison recovery control, the PM regeneration control is wastefully performed depending on the situation. Thus, the fuel consumption of the internal combustion engine is deteriorated by the amount of unburned fuel component supplied to the catalyst.

  As described above, for example, the useless PM regeneration control is executed before the execution of the S poison recovery control. For example, the S poison recovery control is executed immediately after the particulates accumulated in the exhaust system are removed by the PM regeneration control. The situation that is done. In this case, the accumulation amount of the fine particles in the exhaust system is “0”, or is a value that does not cause the excessive temperature rise of the catalyst when the S poison recovery control is executed, but before the execution of the S poison recovery control. Therefore, the PM regeneration control is forcibly executed, and the control is executed wastefully.

  In Patent Document 1, when the PM regeneration control is forcibly executed before the execution of the S poisoning recovery control, if the amount of accumulated particulates is small at that time, the catalyst temperature increase rate in the PM regeneration control is small. Therefore, when the control is performed wastefully, it is estimated that the amount of unburned fuel component supplied to the catalyst decreases. However, even if the same control is executed in this way, the unburned fuel component is still supplied to the catalyst accordingly, so that the fuel consumption of the internal combustion engine is inevitably deteriorated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to prevent the PM regeneration control prior to the execution of the S poison recovery control from being performed wastefully and deteriorating the fuel consumption of the internal combustion engine. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine.

In the following, means for achieving the above object and its effects are described.
In order to achieve the above object, the invention according to claim 1 is applied to an internal combustion engine in which a PM filter that collects particulates in exhaust gas and a NOx storage reduction catalyst are provided in the exhaust system, and is provided in the exhaust system. PM regeneration control that burns and removes particulates accumulated in the exhaust system through the supply of unburned fuel components to the catalyst, and the supply of unburned fuel components to the catalyst provided in the exhaust system. In the exhaust gas purification apparatus for an internal combustion engine that executes the S poison recovery control for releasing the sulfur oxide stored in the NOx catalyst by enriching the exhaust air-fuel ratio at the engine, the S poison recovery control is executed. When requested, the control means determines whether or not to execute the PM regeneration control prior to the execution of the S poison recovery control according to the amount of particulates accumulated in the exhaust system, the S poison recovery Control execution When the particulate matter accumulated in the exhaust system burns through the supply of unfueled components to the catalyst for the execution of S poison recovery control, PM regeneration control is executed prior to the execution of S poison recovery control if the amount of accumulation of the fine particles that does not cause excessive temperature rise of the catalyst in the exhaust system is greater than the predetermined value, If it is less than the predetermined value, the execution of the PM regeneration control prior to the execution of the S poison recovery control is stopped, the initial value of the predetermined value is set to a value smaller than the allowable upper limit value, and a parameter representing the engine operating state Control means for increasing the predetermined value toward the allowable upper limit as the parameter that affects the exhaust temperature of the internal combustion engine changes to a side that lowers the exhaust temperature .

  According to the above configuration, when the S poisoning recovery control execution request is made, the PM regeneration control is executed prior to the execution of the S poisoning recovery control when the amount of particulate deposition in the exhaust system is large, and the amount of deposition is small. Sometimes it becomes possible to stop the execution of the PM regeneration control prior to the execution of the S poison recovery control. Therefore, it is possible to prevent the PM regeneration control prior to the execution of the S poison recovery control from being performed wastefully under a situation where the amount of accumulation in the exhaust system is small and the fuel consumption of the internal combustion engine to deteriorate.

Further , according to the above configuration, when the S poison recovery control execution request is made, if the amount of particulate deposition in the exhaust system is less than a predetermined value, the PM regeneration control is executed prior to the execution of the S poison recovery control. Therefore, the PM regeneration control can be prevented from being performed wastefully and the fuel consumption of the internal combustion engine from being deteriorated.

Further , according to the above configuration, when the execution of the S poison recovery control is requested, the amount of particulates accumulated in the exhaust system is less than a value that does not cause an excessive temperature rise of the catalyst accompanying the execution of the S poison recovery control. The execution of the PM regeneration control prior to the execution of the S poison recovery control is stopped. Therefore, it is possible to accurately prevent the PM regeneration control from being performed wastefully. Further, when the S poison recovery control is executed after the execution of the PM regeneration control prior to the execution of the S poison recovery control, the catalyst is not overheated.

Note that when the S poison recovery control is executed, the higher the exhaust temperature of the internal combustion engine, the more likely the catalyst to overheat due to the combustion of particulates deposited in the exhaust system. According to the above configuration, when the engine temperature is high, the predetermined value is close to the initial value, so that the S poison recovery can be performed under the condition that the amount of particulates accumulated in the exhaust system is smaller. Prior to the control, PM regeneration control is executed. Since particulates accumulated in the exhaust system are removed by this PM regeneration control, even if the exhaust temperature during the subsequent S poison recovery control execution is high, the particulates burn in the exhaust system accompanying the execution of the control. As a result, it is possible to accurately suppress the occurrence of excessive heating of the catalyst. Also, in an engine operating state where the exhaust temperature becomes low, the predetermined value increases toward the allowable upper limit as the parameter that affects the exhaust temperature changes to the side that lowers the exhaust temperature. The amount of accumulated fine particles is kept from exceeding a predetermined value as much as possible. As a result, it is possible to prevent the PM regeneration control prior to the S poison recovery control from being performed as much as possible. As described above, the PM regeneration control prior to the S poison recovery control can be accurately performed when necessary, and the PM regeneration control can be prevented from being performed as wastefully as possible.

The invention according to claim 2 is characterized in that, in the invention according to claim 1 , at least one of the fuel injection amount of the internal combustion engine and the engine rotational speed is used as the parameter affecting the exhaust gas temperature.

  When the fuel injection amount of the internal combustion engine increases, the combustion energy at the time of fuel combustion accompanying one fuel injection increases, so the amount of heat applied to the exhaust also increases, and the exhaust temperature of the internal combustion engine tends to rise. is there. Further, when the engine rotational speed increases, the combustion energy at the time of fuel combustion increases per unit time, so the amount of heat applied to the exhaust also increases, and the exhaust temperature of the internal combustion engine tends to increase. According to the above configuration, the predetermined value is increased toward the allowable upper limit value as the fuel injection amount and the engine rotational speed, which are parameters affecting the exhaust gas temperature, are decreased. Therefore, when the engine is in an engine operating state where the exhaust temperature is lowered, the predetermined value can be accurately increased toward the allowable upper limit as the exhaust temperature decreases.

Hereinafter, an embodiment in which the present invention is applied to an internal combustion engine for an automobile will be described with reference to FIGS.
FIG. 1 shows a configuration of an internal combustion engine 10 to which the control device of the present embodiment is applied. The internal combustion engine 10 is a diesel engine including a common rail fuel injection device and a turbocharger 11, and mainly includes an intake passage 12, a combustion chamber 13, and an exhaust passage 14.

  In an intake passage 12 constituting the intake system of the internal combustion engine 10, an air flow meter 16, a compressor 17 of the turbocharger 11, an intercooler 18, And an intake throttle valve 19 is provided. The intake passage 12 is branched at an intake manifold 20 provided on the downstream side of the intake throttle valve 19 and connected to the combustion chamber 13 of each cylinder of the internal combustion engine 10 via an intake port 21.

  On the other hand, in the exhaust passage 14 constituting the exhaust system of the internal combustion engine 10, the exhaust port 22 connected to the combustion chamber 13 of each cylinder is connected to the exhaust turbine 24 of the turbocharger 11 via the exhaust manifold 23. . In addition, a NOx catalytic converter 25, a PM filter 26, and an oxidation catalytic converter 27 are disposed downstream from the exhaust turbine 24 in the exhaust passage 14 in order from the upstream side.

  The NOx catalytic converter 25 carries an NOx storage reduction catalyst. The NOx catalyst stores NOx in the exhaust when the oxygen concentration of the exhaust is high, and releases the stored NOx when the oxygen concentration of the exhaust is low. Further, the NOx catalyst reduces and purifies the released NOx if there is sufficient unburned fuel component as a reducing agent at the time of releasing the NOx.

  The PM filter 26 is made of a porous material and collects fine particles (PM) mainly composed of soot in the exhaust gas. Similarly to the NOx catalytic converter 25, the PM filter 26 also carries an NOx storage reduction catalyst so that NOx in the exhaust gas can be purified. Further, the collected PM is burned (oxidized) and removed by a reaction triggered by the NOx catalyst.

The oxidation catalyst converter 27 carries an oxidation catalyst. This oxidation catalyst oxidizes and purifies hydrocarbons (HC) and carbon monoxide (CO) in the exhaust.
In addition, on the upstream side and the downstream side of the PM filter 26 in the exhaust passage 14, an inlet gas temperature sensor 28 that detects the inlet gas temperature that is the temperature of the exhaust gas flowing into the PM filter 26, and the exhaust gas after passing through the PM filter 26. An outgas temperature sensor 29 for detecting an outgas temperature, which is a temperature, is provided. The exhaust passage 14 is provided with a differential pressure sensor 30 for detecting a differential pressure between the exhaust upstream side of the PM filter 26 and the exhaust downstream side thereof. Further, two oxygen sensors 31 and 32 for detecting the oxygen concentration in the exhaust gas are arranged on the exhaust gas upstream side of the NOx catalytic converter 25 in the exhaust passage 14 and between the PM filter 26 and the oxidation catalytic converter 27, respectively. It is installed.

  Further, the internal combustion engine 10 is provided with an exhaust gas recirculation (hereinafter referred to as EGR) device that recirculates a part of the exhaust gas to the air in the intake passage 12. The EGR device includes an EGR passage 33 that allows the exhaust passage 14 and the intake passage 12 to communicate with each other. The most upstream portion of the EGR passage 33 is connected to the exhaust upstream side of the exhaust turbine 24 in the exhaust passage 14. The EGR passage 33 is provided with an EGR catalyst 34 for reforming the recirculated exhaust, an EGR cooler 35 for cooling the exhaust, and an EGR valve 36 for adjusting the flow rate of the exhaust from the upstream side. The most downstream portion of the EGR passage 33 is connected to the downstream side of the intake throttle valve 19 in the intake passage 12.

  On the other hand, an injector 40 for injecting fuel to be used for combustion in the combustion chamber 13 is disposed in the combustion chamber 13 of each cylinder of the internal combustion engine 10. The injector 40 of each cylinder is connected to a common rail 42 via a high pressure fuel supply pipe 41. High pressure fuel is supplied to the common rail 42 through a fuel pump 43. The pressure of the high-pressure fuel in the common rail 42 is detected by a rail pressure sensor 44 attached to the common rail 42. Further, low pressure fuel is supplied from the fuel pump 43 to the addition valve 46 through the low pressure fuel supply pipe 45.

  Various controls of the internal combustion engine 10 are performed by the electronic control unit 50. The electronic control unit 50 includes a CPU that executes various arithmetic processes related to engine control, a ROM that stores programs and data necessary for the control, a RAM that temporarily stores CPU arithmetic results, and signals between the outside The input / output port for inputting / outputting is provided.

  In addition to the above-described sensors, the input port of the electronic control unit 50 includes an NE sensor 51 that detects the engine speed, an accelerator sensor 52 that detects the accelerator operation amount, and a throttle valve sensor that detects the opening of the intake throttle valve 19. 53, an intake air temperature sensor 54 for detecting the intake air temperature of the internal combustion engine 10, a water temperature sensor 55 for detecting the cooling water temperature of the engine 10, and the like are connected. The output port of the electronic control unit 50 is connected to drive circuits such as the intake throttle valve 19, the EGR valve 36, the injector 40, the fuel pump 43, and the addition valve 46.

  The electronic control unit 50 outputs a command signal to the drive circuit of each device connected to the output port according to the engine operating state grasped from the detection signal input from each sensor. Thus, the opening control of the intake throttle valve 19, EGR control based on the opening control of the EGR valve 36, control of the fuel injection amount, fuel injection timing, and fuel injection pressure from the injector 40, Various controls such as fuel addition control are performed by the electronic control unit 50.

  In the present embodiment configured as described above, by PM regeneration control for eliminating clogging by PM in the NOx catalytic converter 25 and the PM filter 26, and occlusion in the NOx catalyst such as sulfur oxide (SOx). S poisoning recovery control is performed to recover the reduced NOx storage capacity of the NOx catalyst.

  The PM regeneration control is executed when the PM accumulation amount in the exhaust system estimated from the engine operating state exceeds an allowable value, and is continued until the PM accumulation amount becomes “0”. In this PM regeneration control, an unburned fuel component is supplied to the NOx catalyst carried on the NOx catalytic converter 25 and the PM filter 26, thereby generating heat due to oxidation of the unburned fuel component in the exhaust or on the catalyst. The temperature of the catalyst is raised to, for example, about 600 to 700 ° C., and PM around the catalyst is burned (oxidized). Then, the PM is burned and discharged as carbon dioxide (CO2) and water (H2O), so that clogging due to PM in the NOx catalytic converter 25 and the PM filter 26 is eliminated. The unburned fuel component is supplied to the NOx catalyst in the PM regeneration control by adding fuel to the exhaust from the addition valve 46 or the like.

  Further, the S poison recovery control is executed when the SOx occlusion amount of the NOx catalyst calculated based on the history of the engine operation state exceeds the allowable value. In this S poison recovery control, the temperature of the catalyst is raised to, for example, about 600 to 700 ° C. through the supply of the unburned fuel component to the NOx catalyst, and the exhaust air-fuel ratio is made rich at that high temperature, thereby reducing the NOx. The release of SOx from the catalyst and its reduction are promoted to restore the NOx storage capacity. In addition, the supply of the unburned fuel component to the NOx catalyst in the S poison recovery control is also performed by adding fuel to the exhaust from the addition valve 46 or the like. However, if the exhaust air / fuel ratio rich as described above continues due to the fuel addition from the addition valve 46, the heat generated by the oxidation of the unburned fuel component in the exhaust or on the catalyst becomes large, and the catalyst is excessively heated. There is a fear. For this reason, in the S poison recovery control, fuel addition from the addition valve 46 for enriching the exhaust air-fuel ratio is intermittently performed to reverse the exhaust air-fuel ratio between rich and lean, thereby The exhaust air-fuel ratio is enriched intermittently to suppress the above-described excessive temperature rise of the catalyst.

  By the way, when PM is accumulated in the exhaust system when the S poison recovery control is executed, the PM accumulated in the exhaust system is increased along with fuel addition from the addition valve 46 for enriching the exhaust air-fuel ratio. There is a risk that the NOx catalyst will overheat when burned at once. In order to suppress such excessive temperature rise of the NOx catalyst, when executing the S poison recovery control, the PM regeneration control is forcibly executed prior to the removal of the PM accumulated in the exhaust system. Done.

  Next, the execution procedure of the PM regeneration control prior to the execution of the S poison recovery control will be described with reference to the flowchart of FIG. This scavenging payment control routine is periodically executed through the electronic control unit 50, for example, with a time interruption every predetermined time (for example, every 16 ms).

  In this routine, when the SOx occlusion amount of the NOx catalyst exceeds the allowable value and an execution request for S poison recovery control is made (S101: YES), PM regeneration control is performed prior to the execution of the S poison recovery control. Processing for forcibly executing (steps S102 to S104) is performed. The forced execution of such PM regeneration control is performed by rewriting the PM accumulation amount in the exhaust system estimated based on the engine operating state to a value greater than an allowable value, for example, the maximum value (1.1 g, etc.) of the PM accumulation amount. Realized (S103). When the PM accumulation amount is rewritten to a value greater than or equal to the allowable value in this way, an execution request for PM regeneration control is made and the control is started (S104). The PM regeneration control thus started is continued until the PM accumulation amount becomes “0” through execution of the control.

  As described above, the PM regeneration control is forcibly executed prior to the execution of the S poison recovery control, and the PM accumulated in the exhaust system is removed in advance, so that the exhaust is performed when the S poison recovery control is executed thereafter. When fuel addition from the addition valve 46 for enriching the air-fuel ratio is performed, it is possible to suppress the PM accumulated in the exhaust system from burning at a stretch and causing the NOx catalyst to overheat. However, if the PM regeneration control is forcibly executed regardless of the PM accumulation amount prior to the execution of the S poison recovery control, the PM regeneration control is performed wastefully depending on the situation, and the addition valve in the control The fuel consumption of the internal combustion engine 10 is inevitably deteriorated as much as the unburned fuel component is supplied to the NOx catalyst by the fuel addition from 46.

  Therefore, in this embodiment, when the execution request of the S poison recovery control is made (S101: YES), the S poison recovery control is performed according to the PM accumulation amount in the exhaust system estimated based on the engine operating state. Whether or not to execute prior PM regeneration control is determined. More specifically, when the PM accumulation amount is less than the predetermined value a (S102: NO), the processing (S103, S104) for forcibly executing PM regeneration control is skipped, and the PM accumulation amount is predetermined. Only when the value is greater than or equal to the value a (S102: YES), processing for forcibly executing PM regeneration control (S103, S104) is performed. For this reason, when the PM poisoning recovery control execution request is made and the amount of accumulated PM in the exhaust system is less than the predetermined value a, the forcible execution of the PM regeneration control prior to the S poison recovery control is stopped. . Therefore, it is possible to prevent the PM regeneration control from being performed wastefully and deteriorating the fuel consumption of the internal combustion engine 10.

  Here, the predetermined value a used in step S102 is an excessive increase in the NOx catalyst even when PM accumulated in the exhaust system burns through the supply of the unburned fuel component to the NOx catalyst during the execution of the S poison recovery control. The PM deposition amount is set so as not to cause temperature. The predetermined value a is variable based on parameters that affect the exhaust temperature of the internal combustion engine 10 among parameters representing the engine operating state, for example, the fuel injection amount and the engine speed. Details of such variable setting of the predetermined value a will be described with reference to the graph of FIG. 3 showing how the predetermined value a changes with respect to changes in the fuel injection amount and the engine speed.

  As for the predetermined value a, S poisoning is performed under an engine operating state in which the initial value P is smaller than the allowable upper limit value X of the predetermined value a, for example, the exhaust gas temperature of the internal combustion engine 10 is assumed to be the highest value. When the recovery control is performed, the PM accumulation amount is such that no excessive temperature rise occurs in the NO catalyst. Here, the allowable upper limit value X does not cause an excessive increase in temperature of the NOx catalyst when the S poison recovery control is performed in a situation where the exhaust temperature of the internal combustion engine 10 is the lowest value that can be assumed. It is the amount of PM deposition. As the fuel injection amount and the engine rotational speed change to a value that lowers the exhaust temperature with respect to a value that can make the exhaust temperature of the internal combustion engine 10 the minimum value (a value corresponding to the initial value P), the predetermined value a is allowed The value is increased toward the upper limit value X.

  Note that the exhaust temperature of the internal combustion engine 10 tends to increase as the fuel injection amount increases. This is because as the fuel injection amount increases, the combustion energy at the time of fuel combustion accompanying one fuel injection in the internal combustion engine 10 increases, and the amount of heat applied to the exhaust also increases. Further, the exhaust temperature of the internal combustion engine 10 tends to increase as the engine speed increases. This is because as the engine speed increases, the combustion energy during fuel combustion per unit time increases and the amount of heat applied to the exhaust also increases. Therefore, the predetermined value a is increased as the fuel injection amount and the engine rotational speed are smaller than the values corresponding to the initial value P.

  By variably setting the predetermined value a as described above, the PM regeneration control prior to the S poison recovery control is accurately performed when necessary and the following is performed so as not to be performed as wastefully as possible. Is implemented as follows.

  That is, for example, in an engine operating state in which the exhaust gas temperature can take the maximum value, the predetermined value a becomes the above-described initial value P. PM regeneration control is executed prior to poisoning recovery control. Since PM accumulated in the exhaust system is removed by this PM regeneration control, even if the exhaust temperature during the subsequent S poison recovery control execution is high, the PM in the exhaust system accompanying the execution of the control is burned. As a result, it is possible to accurately suppress the excessive temperature rise of the NOx catalyst.

  Further, in an engine operating state in which the exhaust temperature is lower than the maximum value, the fuel injection amount and the engine rotation speed, which are parameters that affect the exhaust temperature, change to the decreasing side (the exhaust temperature decreasing side). The predetermined value a increases toward the allowable upper limit value X, and the amount of PM accumulated in the exhaust system is prevented from exceeding the predetermined value a as much as possible. As a result, useless execution of PM regeneration control prior to execution of S poison recovery control is avoided as much as possible.

According to the embodiment described in detail above, the following effects can be obtained.
(1) At the time of execution request for S poison recovery control, the amount of PM accumulated in the exhaust system is less than a predetermined value a that is a value that does not cause excessive temperature rise of the NOx catalyst with the execution of S poison recovery control. In some cases, the execution of the PM regeneration control prior to the execution of the S poison recovery control is stopped, and the PM regeneration control prior to the execution of the S poison recovery control is executed only when the PM accumulation amount is equal to or greater than the predetermined value a. . Therefore, even if the PM regeneration control is not performed prior to the execution of the S poison recovery control, the PM regeneration control is performed in a situation where there is no possibility that the NOx catalyst will overheat when the S poison recovery control is performed. Can be prevented from being executed wastefully and the fuel consumption of the internal combustion engine 10 is deteriorated.

  (2) The predetermined value a is an engine operating state in which the initial value P is smaller than the allowable upper limit value X of the predetermined value a and the exhaust temperature of the internal combustion engine 10 becomes a maximum value that can be assumed. Originally, when NO poisoning recovery control is executed, the NO catalyst is set to a value that does not cause excessive temperature rise. Further, as the fuel injection amount and the engine speed, which are parameters that affect the exhaust temperature of the internal combustion engine 10, become smaller than the values corresponding to the initial value P, the predetermined value a increases toward the allowable upper limit value X. Is done. As described above, by variably setting the predetermined value a, the PM regeneration control prior to the S poison recovery control is accurately performed when necessary and is not performed as wastefully as possible. Can do.

In addition, the said embodiment can also be changed as follows, for example.
Although both the fuel injection amount and the engine rotational speed are used as parameters that affect the exhaust temperature of the internal combustion engine 10 used when variably setting the predetermined value a, only one of them may be used.

As the above parameters, parameters other than the fuel injection amount and the engine rotational speed, for example, parameters such as the cooling water temperature, the lubricating oil temperature, and the intake air temperature of the internal combustion engine 10 may be used.
The predetermined value a can be a fixed value. In this case, it is conceivable that the predetermined value a is fixed at the initial value P, for example.

  When the NOx catalyst converter 25 in which the NOx catalyst is supported on the exhaust upstream side of the PM filter 26 is provided as in the above embodiment, it is not always necessary to support the NOx catalyst on the PM filter 26.

When the NOx catalyst is supported on the PM filter 26 as in the above embodiment, the NOx catalytic converter 25 is not necessarily provided upstream of the PM filter 26 on the exhaust side.
Sub-injection (after-injection) in which an unburned fuel component is supplied to the catalyst in normal PM regeneration control after the injection of fuel to be used for combustion in the combustion chamber 13 from the injector 40 in the exhaust stroke or expansion stroke ).

1 is a schematic diagram showing an entire internal combustion engine to which an exhaust emission control device of an embodiment is applied. The flowchart which shows the execution procedure of PM reproduction | regeneration control prior to execution of S poison recovery control. The graph which shows the change aspect of the predetermined value a with respect to the change of a fuel injection amount and an engine speed.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Turbocharger, 12 ... Intake passage, 13 ... Combustion chamber, 14 ... Exhaust passage, 15 ... Air cleaner, 16 ... Air flow meter, 17 ... Compressor, 18 ... Intercooler, 19 ... Intake throttle valve, 20 DESCRIPTION OF SYMBOLS ... Intake manifold, 21 ... Intake port, 22 ... Exhaust port, 23 ... Exhaust manifold, 24 ... Exhaust turbine, 25 ... NOx catalytic converter, 26 ... PM filter, 27 ... Oxidation catalytic converter, 28 ... Incoming gas temperature sensor, 29 ... Outgas temperature sensor, 30 ... Differential pressure sensor, 31 ... Oxygen sensor, 32 ... Oxygen sensor, 33 ... EGR passage, 34 ... EGR catalyst, 35 ... EGR cooler, 36 ... EGR valve, 40 ... Injector, 41 ... High pressure fuel supply Pipe 42. Common rail 43 Fuel pump 44 Rail pressure sensor 45 Low pressure fuel supply pipe 6 ... addition valve, 50 ... electronic control device (control means), 51 ... NE sensor 52: accelerator sensor, 53 ... throttle valve sensor, 54 ... intake air temperature sensor, 55 ... water temperature sensor.

Claims (2)

A PM filter that collects particulates in the exhaust and an NOx storage reduction catalyst are applied to an internal combustion engine provided in the exhaust system, and the exhaust system is supplied through the supply of unburned fuel components to the catalyst provided in the exhaust system. PM regeneration control that burns and removes particulates deposited on the exhaust gas, and supply of unburned fuel components to the catalyst provided in the exhaust system to enrich the exhaust air / fuel ratio at high temperatures to the NOx catalyst In an exhaust gas purification apparatus for an internal combustion engine that performs S poison recovery control for releasing stored sulfur oxides,
Control means for determining whether or not to execute the PM regeneration control prior to the execution of the S poison recovery control when the execution of the S poison recovery control is requested according to the amount of particulates deposited in the exhaust system Because
When execution of the S poison recovery control is requested, the amount of particulates deposited in the exhaust system accumulates in the exhaust system through the supply of unfueled components to the catalyst for execution of S poison recovery control. PM regeneration control prior to the execution of the S poison recovery control is performed as long as it is greater than a predetermined value set as the accumulation amount of the fine particles without causing excessive temperature rise of the catalyst in the exhaust system even if the fine particles burned. And if the accumulation amount is less than the predetermined value, the execution of the PM regeneration control prior to the execution of the S poison recovery control is stopped,
The initial value of the predetermined value is set to a value smaller than the allowable upper limit value, and the predetermined value increases as the parameter that affects the exhaust temperature of the internal combustion engine among the parameters representing the engine operating state changes to the side that lowers the exhaust temperature. An exhaust emission control device for an internal combustion engine , comprising control means for increasing the value toward the allowable upper limit value . As the influence on the exhaust temperature parameter, at least one of exhaust purifying apparatus for an internal combustion engine according to claim 1 for use with a fuel injection amount and the engine rotational speed of the internal combustion engine.

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