JP2006226190A - Controller of lean burn engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently regenerate an NOx storage/reduction type catalyst 16 and a DPF 17. <P>SOLUTION: A metal carrier catalyst 15 is disposed in an exhaust passage 3 on the upstream side of a turbo supercharger 11, and the temperature of the NOx storage/reduction type catalyst 16 on the downstream side of the turbo supercharger is increased by utilizing the catalyst reaction heat of the catalyst 15. When the catalyst 16 is regenerated, the air-fuel ratio of an engine is made rich to act the metal carrier catalyst 15 as a hydrogen generating catalyst to supply hydrogen gas to the catalyst 16 so as to increase the regenerating efficiency of the catalyst. When the filter 17 is regenerated, post-injection is performed to supply unburned fuel to the catalyst 16 with a high temperature to rapid increase the temperature of the filter by utilizing the oxidation reaction heat of the catalyst so as to increase the regenerating efficiency of the filter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a lean burn engine control apparatus.

    In a lean burn engine such as a diesel engine or lean burn gasoline engine that is basically operated with the air-fuel ratio of the engine lean, an ordinary three-way catalyst uses NOx (nitrogen oxide) in the exhaust gas. It cannot be purified sufficiently. As a catalyst to solve this problem, NOx in the exhaust gas is occluded during the air-fuel ratio lean operation of the engine, and when the engine is switched to the air-fuel ratio rich operation, the occluded NOx is released and purified by the reducing components in the exhaust gas. NOx occlusion reduction type catalysts are known. However, even with this catalyst, it is difficult to reduce and purify NOx when the exhaust gas temperature is low.

    On the other hand, a hydrogen generation catalyst that generates hydrogen from exhaust gas components is disposed in the exhaust passage upstream of the NOx storage reduction catalyst, and the NOx storage reduction type using the hydrogen having a strong reducing power obtained by the catalyst There is a proposal to reduce and purify NOx of a catalyst (see Patent Document 1).

    Further, in a diesel engine, it is desired to regenerate the filter by burning and removing the exhaust particulate when the amount of the filter that collects the exhaust particulate contained in the exhaust gas increases.

On the other hand, there is a proposal to supply unburned fuel to the oxidation catalyst by disposing an oxidation catalyst in the exhaust passage upstream of the filter and injecting fuel into the cylinder immediately before closing the exhaust valve of the cylinder ( Patent Document 2). That is, the temperature of the filter is increased by utilizing the reaction heat generated by the oxidation of the unburned fuel by the oxidation catalyst, and the combustion of the exhaust particulates is promoted.
Japanese Patent Laid-Open No. 8-04326 JP 2002-364343 A

    In a lean burn engine, the exhaust gas temperature is generally low, but in the case of an engine with a turbocharger, the temperature of the exhaust gas further decreases by passing through the turbocharger. For this reason, the temperature of the NOx occlusion reduction type catalyst disposed in the exhaust passage downstream of the turbocharger tends to be low. Therefore, even if the NOx occlusion amount increases and the air-fuel ratio of the engine is switched from lean to rich, the released NOx may not be sufficiently reduced and purified. This point is the case where an oxidation catalyst is placed upstream of the NOx storage reduction catalyst and the reaction heat is used to raise the temperature of the NOx storage reduction catalyst, or a hydrogen generation catalyst is placed to store hydrogen in the NOx storage reduction. Even if it is supplied to the mold catalyst, there is not much difference. This is because the exhaust gas that has passed through the turbocharger has a low temperature, so that the oxidation catalyst and the hydrogen generation catalyst do not function sufficiently.

    Moreover, the fact that the exhaust gas temperature is lowered by the turbocharger is also a problem in filter regeneration of a diesel engine. Even if unburned fuel is supplied to the oxidation catalyst upstream of the filter in order to regenerate the filter, the oxidation catalyst is downstream of the turbocharger and its temperature is low. This is because the temperature of the filter is insufficient.

    Therefore, an object of the present invention is to solve the problem that the regeneration efficiency of the NOx occlusion reduction type catalyst or filter of the lean burn engine is lowered by the turbocharger.

    With respect to such a problem, the present invention arranges a catalyst useful for NOx reduction or combustion of exhaust particulates downstream of the turbocharger in the exhaust passage upstream of the turbocharger. I did it.

The invention according to claim 1 is a lean burn engine control device comprising a turbocharger and a NOx occlusion reduction type catalyst provided in an exhaust passage downstream of the turbocharger,
A metal carrier catalyst provided in an exhaust passage upstream of the turbocharger, wherein the metal carrier carries a noble metal acting as an oxidation catalyst in the presence of oxygen;
Means for detecting a parameter value related to the NOx occlusion amount of the NOx occlusion reduction catalyst;
When the NOx occlusion amount exceeds a predetermined value based on the parameter value, the air-fuel ratio of the engine is changed from lean so that the metal carrier catalyst acts as a hydrogen generation catalyst that reforms the HC component in the exhaust gas into hydrogen. And air-fuel ratio control means for shifting to an air-fuel ratio richer than stoichiometric for a predetermined period.

    According to such a configuration, the metal-supported catalyst is exposed to high-temperature exhaust gas that does not have a cooling loss due to the turbocharger. For this reason, it becomes advantageous for the early temperature rise and maintenance of the activation temperature. Moreover, the metal carrier has a smaller specific heat and a smaller heat capacity than the ceramic carrier, which is advantageous for the rapid temperature increase and activity maintenance.

    Therefore, even when the exhaust gas temperature is relatively low, the metal-supported catalyst effectively works to oxidize HC (hydrocarbon) components in the exhaust gas, and the exhaust gas temperature is increased by the reaction heat generated at that time. Therefore, although the NOx occlusion reduction type catalyst is arranged downstream of the turbocharger, the temperature becomes high due to the influence of reaction heat generated in the metal carrier catalyst.

    For this reason, when the NOx occlusion amount of the NOx occlusion reduction catalyst becomes equal to or greater than a predetermined value and the engine air-fuel ratio is switched to rich, it is advantageous for reducing and purifying NOx released from the NOx occlusion reduction catalyst. In addition, when the air-fuel ratio of the engine is switched to rich, the metal carrier catalyst functions as a hydrogen generation catalyst, and hydrogen having a strong reducing power is supplied to the NOx storage reduction catalyst, so that the reduction and purification of NOx proceeds efficiently. Become.

    In addition, the metal carrier catalyst can reduce the volume without impairing the strength and reducing the exhaust gas contact area as compared with the catalyst using the ceramic carrier. For this reason, the ventilation resistance can be reduced, which is advantageous in avoiding an increase in the back pressure of the engine or a decrease in the efficiency of the turbocharger and thus improving the fuel consumption.

The invention according to claim 2 is a turbocharger, a NOx occlusion reduction catalyst provided in an exhaust passage downstream of the turbocharger and acting as an oxidation catalyst in the presence of oxygen, and the NOx occlusion reduction catalyst A lean burn engine control device comprising a filter provided in an exhaust passage on the downstream side of the exhaust gas to collect exhaust particulates and a fuel injection valve for injecting fuel into the engine cylinder,
A metal carrier catalyst provided in an exhaust passage upstream of the turbocharger, wherein the metal carrier carries a noble metal acting as an oxidation catalyst in the presence of oxygen;
Means for detecting a parameter value related to the collected amount of exhaust particulates of the filter;
After the main injection that injects fuel near the top dead center of the compression stroke of the engine when the collected amount becomes equal to or greater than the predetermined value based on the parameter value, post-injection that injects fuel in the expansion stroke or exhaust stroke is performed. And a fuel injection control means for controlling the operation of the fuel injection valve to be executed.

    Therefore, as in the invention according to claim 1, the NOx occlusion reduction type catalyst is disposed downstream of the turbocharger, but the metal carrier catalyst disposed upstream of the turbocharger is Since it works effectively as an oxidation catalyst, the temperature rises due to the influence of reaction heat generated in the metal carrier catalyst.

    For this reason, when the post-injection is executed when the collected amount of exhaust particulates of the filter exceeds a predetermined value, the oxidation reaction of the post-injected fuel efficiently proceeds by the NOx storage reduction type catalyst. As a result, the temperature of the exhaust gas discharged from the NOx storage reduction catalyst becomes high, and the temperature of the filter disposed downstream thereof can be quickly raised, and the combustion removal of exhaust particulates collected in the filter Goes efficiently. Therefore, it is possible to improve the regeneration efficiency of the filter and improve the fuel consumption.

    Further, in the NOx occlusion reduction type catalyst, since the reduction of NOx proceeds simultaneously when the post-injected fuel is oxidized, the release to the atmosphere is prevented.

    In addition, the metal carrier catalyst has an advantage in avoiding an increase in the back pressure of the engine or a reduction in the efficiency of the turbocharger as compared with a catalyst using a ceramic carrier, and thus improving fuel efficiency. This is the same as the invention.

The invention according to claim 3 is the method according to claim 2,
Air-fuel ratio control means for controlling the air-fuel ratio of the engine,
The metal carrier catalyst functions as a hydrogen generation catalyst that reforms the HC component in the exhaust gas into hydrogen when the air-fuel ratio of the engine becomes richer than stoichiometric.

    Therefore, when the air-fuel ratio of the engine is switched from lean to rich, NOx is released from the NOx occlusion reduction catalyst. At that time, hydrogen, which is a strong reducing agent, is generated by the metal carrier catalyst. It is advantageous for reducing and purifying.

The invention according to claim 4 is the method according to claim 3, further comprising:
Means for detecting a parameter value related to the NOx occlusion amount of the NOx occlusion reduction type catalyst;
The air-fuel ratio control means shifts the air-fuel ratio of the engine from lean to the rich air-fuel ratio for a predetermined period when the NOx storage amount becomes a predetermined value or more based on the parameter value related to the NOx storage amount. It is characterized by.

    Accordingly, when the NOx occlusion amount of the NOx occlusion reduction catalyst becomes equal to or greater than a predetermined value, the air-fuel ratio of the engine switches to rich, so that the NOx occlusion reduction catalyst is appropriately regenerated to maintain its good NOx occlusion capacity. This is advantageous in preventing NOx emission into the atmosphere.

The invention according to claim 5 is the invention according to claim 1 or claim 4,
Means for detecting a parameter value related to the air-fuel ratio of the exhaust gas in the exhaust passage downstream of the NOx storage reduction catalyst;
During the period when the air-fuel ratio of the engine is set to the rich air-fuel ratio, the air-fuel ratio of the exhaust gas obtained based on the parameter value related to the air-fuel ratio is richer than a predetermined value than when the engine air-fuel ratio is lean. It is a period until it becomes.

    That is, when the air-fuel ratio of the engine is made rich, when NOx is released and reduced by the NOx storage reduction catalyst, the HC component in the exhaust gas is consumed for NOx reduction. The air-fuel ratio of the exhaust gas that passes through is less rich than the air-fuel ratio of the engine. For example, the stoichiometric level is rich. When the regeneration of the NOx occlusion reduction catalyst is completed, HC in the exhaust gas is not consumed for the reduction, so the air-fuel ratio of the exhaust gas that has passed through the NOx occlusion reduction catalyst corresponds to the engine air-fuel ratio. Become rich.

    Therefore, according to the present invention, the period during which the air-fuel ratio of the engine is rich is set until the air-fuel ratio of the exhaust gas becomes richer than a predetermined value, so that the NOx occlusion reduction type can be performed without causing deterioration in fuel consumption. The catalyst can be reliably regenerated.

    As described above, according to the first aspect of the present invention, the metal carrier catalyst that functions as an oxidation catalyst in the presence of oxygen is disposed upstream of the turbocharger, and the NOx occlusion downstream of the turbocharger is disposed. When the NOx occlusion amount of the reduction catalyst exceeds a predetermined value, the engine air-fuel ratio is shifted from lean to an air-fuel ratio richer than stoichiometric for a predetermined period so that the metal-supported catalyst acts as a hydrogen-generating catalyst. Thus, exhaust gas having a high temperature can be supplied to the NOx occlusion reduction type catalyst to increase the temperature, and hydrogen with a strong reducing power can be supplied during regeneration of the catalyst, increasing exhaust resistance and increasing engine output. The catalyst can be efficiently regenerated while avoiding a decrease, which is advantageous in improving fuel consumption.

    According to the second aspect of the present invention, the metal carrier catalyst that functions as an oxidation catalyst in the presence of oxygen is disposed upstream of the turbocharger, and the NOx storage reduction catalyst is disposed downstream of the turbocharger. The exhaust particulate filter is disposed so that the former is on the upstream side and the latter is on the downstream side. Therefore, exhaust gas having a high temperature can be supplied to the NOx storage reduction catalyst to increase its temperature. Since the post-injection of the fuel is executed when the collected amount of exhaust particulates exceeds a predetermined value, the filter temperature can be ensured by performing an oxidation reaction with the NOx occlusion reduction type catalyst having a high temperature when the filter is regenerated. This is advantageous in improving the regeneration efficiency of the filter and improving the fuel efficiency while avoiding an increase in exhaust resistance and a decrease in engine output.

    According to a third aspect of the present invention, in the second aspect, since the metal carrier catalyst functions as a hydrogen generation catalyst when the air-fuel ratio of the engine becomes rich, the NOx occlusion reduction type catalyst can be used for reducing and purifying NOx. Become advantageous.

    According to the fourth aspect of the present invention, when the NOx occlusion amount of the NOx occlusion reduction catalyst becomes a predetermined value or more, the air-fuel ratio of the engine is shifted from lean to rich, so the NOx occlusion reduction catalyst Can be appropriately regenerated to maintain its good NOx storage capacity, which is advantageous in preventing the emission of NOx into the atmosphere.

    According to the invention according to claim 5, in claim 1 or claim 4, the air-fuel ratio of the engine is made rich until the air-fuel ratio of the exhaust gas downstream of the NOx storage reduction catalyst becomes richer than a predetermined value. Therefore, the NOx occlusion reduction type catalyst can be reliably regenerated without deteriorating fuel consumption.

    Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Engine configuration>
In FIG. 1, 1 is a multi-cylinder diesel engine (only one cylinder is shown in FIG. 1), 2 is an intake passage, and 3 is an exhaust passage. A deep dish combustion chamber 5 is formed on the top surface of the piston 4 of the engine 1. The cylinder head of the engine 1 is provided with a fuel injection valve 7 so that fuel can be directly injected into the in-cylinder combustion chamber 5.

    In the intake passage 2, an air cleaner 9, an air flow sensor 10, a blower 11 a of the turbocharger 11, an intercooler 12, and an intake throttle valve 13 are arranged in order from the upstream side to the downstream side. In the exhaust passage 3, in order from the upstream side to the downstream side, the metal carrier catalyst 15, the turbine 11 b of the turbocharger 11, the NOx occlusion reduction type catalyst 16, and a diesel particulate filter that collects particulates in the exhaust gas. (DPF) 17 is provided.

    On the upstream side and downstream side of the filter 17, exhaust pressure sensors 18 and 19 are disposed as means for detecting a parameter value related to the amount of collected exhaust particulates of the filter 17, and the NOx storage reduction catalyst 16 and the filter An air-fuel ratio sensor 20 as a means for detecting a parameter value related to the air-fuel ratio of the exhaust gas is disposed between the air-fuel ratio and the air-fuel ratio. An air-fuel ratio sensor 21 is also arranged upstream of the metal carrier catalyst 15 in the exhaust passage 3.

    Further, the exhaust passage 3 is connected to the upstream side of the metal carrier catalyst 15 and the downstream side of the intake throttle valve 13 of the intake passage 2 by an exhaust gas recirculation passage 22 for returning a part of the exhaust gas to the intake system. . In the middle of the exhaust gas recirculation passage 22, a negative pressure actuator type EGR valve (exhaust gas recirculation amount adjusting valve) 23 and a cooler 24 for cooling the exhaust gas with engine coolant are disposed. 25 is an intake air temperature sensor, 26 is an intake air pressure sensor, and 27 is an engine speed sensor. The engine control device includes an accelerator opening sensor (not shown).

    The metal carrier catalyst 15 is a honeycomb metal carrier in which metal corrugated plate materials and metal flat plate materials are joined so as to be arranged in multiple layers in a roll shape, and a catalyst noble metal such as Pt and Rh, activated alumina, etc. This support material is supported by a binder. The metal carrier catalyst 15 functions as an oxidation catalyst when the air-fuel ratio of the engine is lean (the air-fuel ratio of the exhaust gas is lean), and as a hydrogen generation catalyst when the air-fuel ratio is richer than the stoichiometric (the air-fuel ratio of the exhaust gas is rich). work. The hydrogen is generated because the metal carrier catalyst 15 mainly functions as a catalyst for promoting a steam reforming reaction (a reaction for generating hydrogen by the fuel component HC and steam in the exhaust gas).

    The NOx occlusion reduction type catalyst 16 is a honeycomb-shaped porous ceramic carrier, and a support noble metal such as Pt and Rh, an alkaline earth metal (and / or alkali metal) as an NOx occlusion material, and activated alumina or the like as a binder. It is carried by. That is, the NOx occlusion reduction type catalyst 16 is a three-way catalyst containing a NOx occlusion material. When the engine air-fuel ratio is lean (the exhaust gas air-fuel ratio is lean), the NOx occlusion reduction catalyst 16 stores NOx in the exhaust gas. Acts as an oxidation catalyst that oxidizes and purifies HC and CO in the exhaust gas. When the air-fuel ratio becomes stoichiometric or rich (the air-fuel ratio of the exhaust gas becomes stoichiometric or rich), the HC and CO in the exhaust gas are oxidized and purified, and NOx in the exhaust gas and It functions as a three-way catalyst that reduces and purifies the stored NOx.

    The filter 17 is a wall flow type in which the inlets and outlets of the honeycomb holes of the honeycomb made of porous ceramics are alternately sealed, and a catalyst metal and an alkali that promote combustion of exhaust particulates on the passage wall surface through which the exhaust gas passes. A catalyst coat layer containing a metal is formed.

    Next, a control system using a microcomputer for regenerating the NOx storage reduction catalyst 16 and the filter 17 will be described.

    As shown in FIG. 2, the engine control apparatus according to the present invention includes air-fuel ratio control means 31, fuel injection control means 32, and NOx occlusion amount detection means 33 of the NOx occlusion reduction type catalyst 16. The air-fuel ratio control means 31 basically sets an engine target air-fuel ratio (a predetermined lean air-fuel ratio with a small amount of smoke generated) according to the current engine operating state, and is arranged upstream of the metal carrier catalyst 15. The EGR amount by the EGR valve 23 or the fuel injection amount by the fuel injection valve 7 (if necessary, by the intake throttle valve 13 so that the difference between the actual air-fuel ratio obtained from the air-fuel ratio sensor 21 and the target air-fuel ratio becomes small. (Intake air amount) is controlled. The engine operating state is determined based on information from the engine speed, accelerator opening, intake air temperature, intake air pressure, and other sensors.

    On the other hand, when the NOx occlusion amount N detected by the NOx occlusion amount detection means 33 is equal to or greater than the predetermined value γ, the air / fuel ratio control means 31 sets the target air / fuel ratio of the engine to be richer than the stoichiometry, Control is performed so that the fuel ratio approaches the target air-fuel ratio. This is the regeneration control of the NOx storage reduction catalyst 16. That is, the predetermined value γ is a threshold value that determines whether or not the regeneration control of the catalyst 16 should be executed in order to maintain the good NOx storage capacity of the NOx storage reduction catalyst 16. However, in order to suppress fluctuations in engine torque and increase in the amount of smoke generated, the rich control is performed by the intake throttle by the intake throttle valve 13 and the main fuel injection amount by the fuel injection valve 7 (in the vicinity of the top dead center of the compression stroke). The fuel injection amount is increased and the injection timing is retarded. The main fuel injection timing may be advanced.

    Since the NOx emission amount of the engine is basically determined by the engine speed and the accelerator opening, the NOx occlusion amount N is based on the history of the engine speed and the accelerator opening from the previous rich control. Required on the basis. Further, in the rich control, the air-fuel ratio detected by the air-fuel ratio sensor 20 disposed on the downstream side of the NOx storage reduction catalyst 16 becomes richer than a predetermined value than when the air-fuel ratio of the engine is lean. It is done until.

    The fuel injection control means 32 basically determines the main fuel injection amount and the injection timing so that the required engine torque can be obtained based on the accelerator opening and the engine speed, and stores a common rail (not shown). ) Control the operation of the fuel injection valve based on the pressure. However, the main fuel injection amount and the injection timing are corrected by the air-fuel ratio control described above.

    On the other hand, when the exhaust particulate collection amount M of the filter 17 is equal to or greater than a predetermined value α, the fuel injection control means 32 further performs fuel injection by the fuel injection valve 7 in the expansion stroke (or exhaust stroke) after the main fuel injection. The post-injection is executed. This is the regeneration control of the filter 17, and the combustion of the main injection fuel is performed with the lean air-fuel ratio. Therefore, a relatively large amount of oxygen and unburned fuel by the post injection are discharged from the cylinder. The predetermined value α is a threshold value that determines whether or not the regeneration control of the filter 17 should be executed in order to maintain a good exhaust particulate collection capability of the filter 17. The exhaust particulate collection amount M is obtained based on the difference in exhaust pressure detected by the pressure sensors 18 and 19 disposed on the upstream side and the downstream side of the filter 17. The greater the differential pressure, the greater the amount of exhaust particulate collection M of the filter 17. Then, the post-injection control ends when the exhaust particulate collection amount M becomes equal to or less than the predetermined value β. The predetermined value β is a threshold value for determining the end of the filter regeneration control. Note that α> β.

<Flow of NOx storage reduction catalyst regeneration control>
FIG. 3 shows a flow of regeneration control of the NOx storage reduction catalyst 16. In Step A1 after the start, the engine speed, the accelerator opening, and the air-fuel ratio downstream of the NOx storage reduction catalyst are read. In the next step A2, the NOx occlusion amount N of the NOx occlusion reduction type catalyst 16 is calculated from the NOx emission amount of the engine corresponding to the engine speed and the accelerator opening. This NOx occlusion amount N is an integrated value of the NOx emission amount from the previous regeneration control to the present time. In subsequent step A3, it is determined whether or not the NOx occlusion amount N is equal to or greater than a predetermined value γ.

    When the NOx occlusion amount N of the NOx occlusion reduction type catalyst 16 is still small, it is determined in step A3 that the NOx occlusion amount N is less than the predetermined value γ. In this case, the process proceeds to step A4, and it is determined whether or not the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor 20 on the downstream side of the NOx storage reduction catalyst 16 is rich. In the situation where the NOx occlusion amount N is small, the air-fuel ratio of the exhaust gas is lean, so the routine proceeds to step A5, where it is determined whether or not the regeneration execution flag is ON. This flag is turned ON when the NOx storage reduction catalyst 16 is regenerated. In the situation where the NOx occlusion amount N is small, the process proceeds to step A6 because it is not ON, and the regeneration execution flag remains OFF and further step is performed. Proceeding to A7, air-fuel ratio lean control is performed in accordance with the operating state of the engine.

    When the air-fuel ratio of the engine is controlled to be lean, the metal carrier catalyst 15 is exposed to high-temperature exhaust gas without cooling loss by the turbocharger 11, and the heat capacity of the carrier is small, so the catalyst temperature is low. Get higher. For this reason, the metal carrier catalyst 16 effectively works to oxidize HC in the exhaust gas, and the temperature of the exhaust gas passing through the catalyst 15 is increased by the reaction heat generated at that time. Therefore, although the NOx occlusion reduction type catalyst 16 is arranged on the downstream side of the turbocharger 11, it is exposed to the exhaust gas having a relatively high temperature passing through the metal carrier catalyst 15, so that the catalyst temperature becomes high. This is advantageous for oxidative purification of HC and CO in the exhaust gas.

    On the other hand, if the NOx occlusion amount N of the NOx occlusion reduction type catalyst 16 increases and becomes equal to or greater than the predetermined value γ, the determination in step A3 is affirmed, the process proceeds to step A8, the regeneration execution flag is turned ON, and the following steps In A9, control is performed to enrich the air-fuel ratio of the engine in order to perform regeneration of the NOx storage reduction catalyst 16.

    By the rich control, the NOx occlusion reduction type catalyst 16 starts releasing NOx occluded, and the NOx is reduced and purified by the reducing agent in the exhaust gas. As the reducing agent, there is hydrogen having strong reducing power in addition to HC (unburned fuel component including partially oxidized HC) and CO contained in the exhaust gas. That is, when the air-fuel ratio of the engine is switched to rich, the metal carrier catalyst 15 functions as a catalyst that promotes a steam reforming reaction that generates hydrogen from HC and steam in the exhaust gas, and reduces the NOx occlusion reduction type catalyst 16 to reducing power. Strong hydrogen is supplied. Moreover, as described above, the temperature of the NOx occlusion reduction catalyst 16 is high due to the influence of the catalytic reaction heat when the metal carrier catalyst 15 functions as an oxidation catalyst when the air-fuel ratio is lean.

    As described above, the NOx occlusion reduction type catalyst 16 is supplied with hydrogen having a strong reducing power by the action of the metal carrier catalyst 15 during regeneration in a state where the temperature is increased by the action of the metal carrier catalyst 15 when the air-fuel ratio is lean. receive. For this reason, the reduction and purification of NOx in the NOx occlusion reduction type catalyst 16 proceeds efficiently, which is advantageous for a short-time regeneration of the catalyst and improvement of fuel consumption.

    When regeneration of the NOx occlusion reduction type catalyst 16 is started, the NOx occlusion amount N is reset, so that in step A3, the NOx occlusion amount N is determined to be less than the predetermined value γ, and the process proceeds to step A4. Thus, the regeneration control is continued until it is determined in step A4 that the air-fuel ratio of the exhaust gas detected by the air-fuel ratio sensor 20 on the downstream side of the NOx storage reduction catalyst 16 has become a predetermined rich value.

    That is, if the air-fuel ratio of the exhaust gas is lean, the routine proceeds to step A5, where it is determined whether or not the regeneration execution flag is turned on. However, since the flag is turned on first, the process proceeds to step A9. The rich control is continued. Thus, when NOx is released and reduced by the NOx occlusion reduction catalyst 16, the HC component in the exhaust gas is consumed for the reduction of NOx, so the air-fuel ratio of the exhaust gas passing through the catalyst is Become a stoichi level. On the other hand, when regeneration of the NOx storage reduction catalyst 16 is completed, HC in the exhaust gas is not consumed for NOx reduction, so the air-fuel ratio of the exhaust gas that has passed through the NOx storage reduction catalyst 16 corresponds to the air-fuel ratio of the engine. And it becomes richer than stoichi. As a result, it is determined in step A4 that the air-fuel ratio of the exhaust gas has become rich, the process proceeds to step A6, the regeneration execution flag is turned off, the regeneration control ends, and the control returns to the lean control corresponding to the engine operating state ( Step A7).

<Flow of filter regeneration control>
FIG. 4 shows a flow of regeneration control of the filter 17. In step B1 after the start, the detected values of the exhaust pressure sensors 18 and 19 are read, and in the subsequent step B2, the exhaust pressure of the filter 17 is detected based on the difference between the exhaust pressures detected by both the sensors 18 and 19, that is, the pressure loss by the filter 17. The amount M of collected fine particles is determined. In subsequent step B3, it is determined whether or not the exhaust particulate collection amount M is equal to or less than a predetermined value β. If the exhaust particulate collection amount M is less than or equal to the predetermined value β, the process proceeds to step B4, where the filter regeneration execution flag is turned OFF, and in step B5, fuel injection control without filter regeneration is executed. The filter regeneration execution flag is a flag that is turned ON when regeneration control of the filter 17 is to be performed. The fuel injection control without filter regeneration is performed by setting the fuel injection amount and the injection timing according to the operating state of the engine. Main fuel injection is executed, and the air-fuel ratio of the engine becomes lean. Be controlled.

    Therefore, as explained in the previous section on regeneration control of the NOx storage reduction catalyst 16, the metal carrier catalyst 15 is exposed to exhaust gas having a relatively high temperature without cooling loss by the turbocharger 11, Works effectively as an oxidation catalyst. Therefore, due to the influence of the catalytic reaction heat generated by the metal carrier catalyst 15, the temperatures of the NOx storage reduction catalyst 16 and the filter 17 also become higher than when the metal carrier catalyst 15 is not provided.

    When the exhaust particulate collection amount M increases and it is determined in step B3 that the collection amount M is greater than the predetermined value β, the process proceeds to step B6, and whether or not the collection amount M is greater than or equal to the predetermined value α. Is determined. When the exhaust particulate collection amount M is equal to or greater than the predetermined value α, the routine proceeds to step B7 where the filter regeneration execution flag is turned ON, and the subsequent injection control, that is, the regeneration control of the filter 17 is performed at the subsequent step B8. .

    In this filter regeneration control, after the main fuel is injected near the top dead center of the compression stroke, further injection is performed in which fuel is injected by the fuel injection valve 7 in the expansion stroke (or exhaust stroke). Since oxygen is required for regeneration of this filter, fuel post-injection is executed with the air-fuel ratio of the engine lean. The fuel injected after this does not substantially work to increase the engine torque, and is heated in the cylinder to become highly unburned fuel (partially partially oxidized) and discharged. And supplied to the NOx storage reduction catalyst 16.

    Thus, since the temperature of the NOx occlusion reduction type catalyst 16 has previously increased due to the influence of the reaction heat of the metal carrier catalyst 15, it functions efficiently as an oxidation catalyst that oxidizes the highly reactive unburned fuel. As a result, the temperature of the exhaust gas discharged from the NOx occlusion reduction catalyst 16 is quickly increased, and the temperature of the filter 17 disposed on the downstream side can be quickly increased. Therefore, the combustion removal of the exhaust particulates collected by the filter 17 proceeds efficiently. Therefore, it is possible to improve the regeneration efficiency of the filter 17 and improve the fuel consumption.

    As the regeneration control of the filter 17 proceeds, the amount M of exhaust particulate collection M decreases accordingly. As a result, if it is determined in step B6 that the exhaust particulate collection amount M is smaller than the predetermined value α, the process proceeds to step B9, and it is determined whether or not the filter regeneration execution flag is ON. When the exhaust particulate collection amount M is less than the predetermined value α due to the progress of the regeneration control, since the flag is ON, the process proceeds to step B8 and the filter regeneration control is continued.

    When the exhaust particulate collection amount M becomes equal to or less than the predetermined value β, the process proceeds from step B3 to step B4, the filter regeneration execution flag is turned OFF, and the process proceeds to step B5 for fuel injection control without filter regeneration. Return.

    In step B9, when the filter regeneration execution flag is not ON, that is, the exhaust particulate collection amount M gradually increases with the operation of the engine and exceeds the predetermined value β, but the predetermined value α Therefore, the regeneration control is not performed. In this case, the routine proceeds to step B4, where fuel injection control without filter regeneration is continued.

    In the above embodiment, the NOx occlusion amount of the NOx occlusion reduction type catalyst is obtained based on the history of the engine operating state. However, an exhaust gas detected by the NOx sensor is provided by providing a NOx sensor downstream of the catalyst. The regeneration control of the catalyst may be executed when the NOx concentration of the catalyst becomes equal to or higher than a predetermined value.

    Further, rich control for NOx occlusion reduction type catalyst regeneration may be performed for a predetermined period.

    Further, since the NOx occlusion reduction catalyst is poisoned by the sulfur component in the exhaust gas, when the sulfur poisoning proceeds to some extent, it is necessary to raise the temperature of the catalyst to recover from the poisoning. Also in this case, the arrangement of the metal carrier catalyst upstream of the turbocharger described above is advantageous in eliminating sulfur poisoning of the NOx storage reduction catalyst. This is because the temperature of the NOx occlusion reduction catalyst can be raised by the oxidation reaction heat generated in the metal carrier catalyst.

    The present invention can also be applied to a lean burn gasoline engine.

It is a figure which shows the structure of the control apparatus of a lean burn engine. It is a block diagram which shows the structure of a control system. It is a flowchart of NOx regeneration control. It is a flowchart of filter regeneration control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Intake passage 3 Exhaust passage 7 Fuel injection valve 11 Turbo supercharger 15 Metal carrier catalyst 16 NOx occlusion reduction type catalyst 17 Filter 18, 19 Means for detecting a parameter value related to the collection amount of exhaust particulates 20 Exhaust gas Means for detecting parameter values related to air-fuel ratio

Claims (5)

A lean burn engine control device comprising a turbocharger and a NOx occlusion reduction type catalyst provided in an exhaust passage downstream of the turbocharger,
A metal carrier catalyst provided in an exhaust passage upstream of the turbocharger, wherein the metal carrier carries a noble metal acting as an oxidation catalyst in the presence of oxygen;
Means for detecting a parameter value related to the NOx occlusion amount of the NOx occlusion reduction catalyst;
When the NOx occlusion amount exceeds a predetermined value based on the parameter value, the air-fuel ratio of the engine is changed from lean so that the metal carrier catalyst acts as a hydrogen generation catalyst that reforms the HC component in the exhaust gas into hydrogen. A lean burn engine control device comprising air-fuel ratio control means for shifting to a richer air-fuel ratio than stoichiometric for a predetermined period. A turbocharger, a NOx occlusion reduction type catalyst provided in an exhaust passage downstream of the turbocharger and acting as an oxidation catalyst in the presence of oxygen, and an exhaust passage downstream of the NOx occlusion reduction type catalyst A lean burn engine control device comprising a filter provided for collecting exhaust particulates and a fuel injection valve for injecting fuel into an engine cylinder,
A metal carrier catalyst provided in an exhaust passage upstream of the turbocharger, wherein the metal carrier carries a noble metal acting as an oxidation catalyst in the presence of oxygen;
Means for detecting a parameter value related to the collected amount of exhaust particulates of the filter;
After the main injection that injects fuel near the top dead center of the compression stroke of the engine when the collected amount becomes equal to or greater than the predetermined value based on the parameter value, post-injection that injects fuel in the expansion stroke or exhaust stroke is performed. A lean burn engine control device comprising fuel injection control means for controlling the operation of the fuel injection valve to be executed. In claim 2, further:
Air-fuel ratio control means for controlling the air-fuel ratio of the engine,
The lean-burn engine control device, wherein the metal carrier catalyst serves as a hydrogen generation catalyst for reforming HC components in the exhaust gas into hydrogen when the air-fuel ratio of the engine becomes richer than stoichiometric. In claim 3, further:
Means for detecting a parameter value related to the NOx occlusion amount of the NOx occlusion reduction type catalyst;
The air-fuel ratio control means shifts the air-fuel ratio of the engine from lean to the rich air-fuel ratio for a predetermined period when the NOx storage amount becomes a predetermined value or more based on the parameter value related to the NOx storage amount. A lean burn engine control device. In claim 1 or claim 4,
Means for detecting a parameter value related to the air-fuel ratio of the exhaust gas in the exhaust passage downstream of the NOx storage reduction catalyst;
During the period when the air-fuel ratio of the engine is set to the rich air-fuel ratio, the air-fuel ratio of the exhaust gas obtained based on the parameter value related to the air-fuel ratio is richer than a predetermined value than when the engine air-fuel ratio is lean. A lean burn engine control device characterized by a period until

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