JP5151818B2 - Diesel engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust emission control device for a diesel engine.

  In an engine equipped with a NOx trap catalyst, normally, lean combustion operation is performed, NOx generated during that time is deposited on the NOx absorbent, and when a certain amount of NOx is deposited, the excess air ratio of the exhaust (hereinafter referred to as the sign in this specification) Is temporarily enriched to remove NOx from the absorbent for reduction treatment. Such control is referred to as rich spike control because λ is temporarily manipulated in the rich direction. A diesel engine is usually operated in a lean combustion state where λ is 2 to 3, and λ is changed to about 0.8 in the above-described rich spike control.

In the conventional rich spike control method disclosed in Patent Document 1, when predicting the NOx amount accumulated on the NOx trap catalyst located on the downstream side of the oxidation catalyst, the NOx desorption amount at the time of rich spike control is set to the rich amount. This is determined according to the engine speed at the time of the spike, the fuel injection amount, and the exhaust air excess ratio based on the exhaust sensor that detects the upstream exhaust air-fuel ratio or oxygen concentration of the oxidation catalyst.
JP 2005-48673 A

  However, when performing post-injection between the late stage of the combustion stroke and the exhaust stroke at the time of rich spike control, unburned HC that is not detected by the excess air ratio detection means because it is not gasified among the post-injected fuel, Since the exhaust sensor does not substantially detect it, the excess air ratio based on the detection value of the exhaust sensor has an error.

  That is, unburned HC, which is not detected by the exhaust sensor because it is not gasified, reacts and gasifies in the oxidation catalyst upstream of the NOx trap catalyst, so that the excess air ratio at the inlet (upstream side) of the oxidation catalyst is increased. On the other hand, the excess air ratio at the outlet (downstream side) of the oxidation catalyst becomes small, and the exhaust air-fuel ratio becomes rich.

  For this reason, if rich spike control is performed with a value misrecognized on the lean side as compared with the actual excess air ratio, the exhaust air-fuel ratio will be excessively rich, and the fuel efficiency and exhaust performance may be deteriorated.

  Therefore, when the exhaust air-fuel ratio enrichment control is performed based on the NOx accumulation amount accumulated on the NOx trap catalyst, the diesel engine exhaust gas purification apparatus according to the present invention performs the fuel injection amount of the engine during the exhaust air-fuel ratio enrichment control. The first correction based on the excess air ratio detected by the excess air ratio detection means during the exhaust air / fuel ratio enrichment control with respect to the NOx desorption speed estimated based on the rotation speed and the exhaust air / fuel ratio enrichment The second correction is performed in consideration of unburned HC that is not detected by the excess air ratio detection means during control.

Therefore, when the exhaust air-fuel ratio enrichment control is performed based on the NOx accumulation amount accumulated on the NOx trap catalyst, the diesel engine exhaust gas purification apparatus according to the present invention performs the fuel injection amount of the engine during the exhaust air-fuel ratio enrichment control. The first correction based on the excess air ratio detected by the excess air ratio detection means during the exhaust air / fuel ratio enrichment control with respect to the NOx desorption speed estimated based on the rotation speed and the exhaust air / fuel ratio enrichment And a second correction in consideration of unburned HC that is not detected by the excess air ratio detection means at the time of control . The second correction includes post injection fuel injection timing, post injection fuel injection amount, and oxidation catalyst. in at least one based on compensation is configured to perform, and the more the fuel injection timing of the post injection is retarded, characterized in that the correction to NOx desorption rate becomes larger the bed temperature It is.

  According to the present invention, when performing exhaust air-fuel ratio enrichment control, the excess air ratio required by the NOx trap catalyst can be realized with high accuracy, and HC can be introduced into the NOx trap catalyst without excess or deficiency. , Fuel economy and exhaust performance can be improved.

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

  FIG. 1 is a schematic configuration diagram showing an example of a diesel engine with a supercharger to which the present invention can be applied. As shown in the figure, the engine body 1 is provided with a common rail fuel injection system including a common rail 2, a fuel injection valve 3 and a fuel pump (not shown) as components, and supplies high-pressure fuel to the engine body 1. The fuel injection valve 3 directly injects fuel into the combustion chamber and can perform pilot injection before main injection, and can change the fuel injection pressure by changing the set fuel pressure in the common rail 2.

  The compressor 4 a of the supercharger 4 is interposed in the intake passage 5 and is driven by the exhaust turbine 4 b to supply compressed air to the engine body 1. The exhaust turbine 4b is interposed in the exhaust passage 6, and rotates by the exhaust from the engine body 1 to drive the compressor 4a. In the present embodiment, a variable capacity type turbocharger 4 is used, and in a low speed range, a variable nozzle (not shown) provided on the turbine 4b side is narrowed to increase turbine efficiency, and high speed. In the region, a high supercharging effect can be obtained in a wide operation region by opening the variable nozzle and expanding the turbine capacity.

  In the intake passage 5, an air flow meter 7 is interposed upstream of the compressor 4a, and an intake throttle valve 8 is interposed downstream. The intake throttle valve 8 is, for example, an electronic control type whose opening can be changed using a step motor, and controls the intake air amount Qa sucked into the engine body 1 according to the opening.

  The exhaust passage 6 is provided with an EGR passage 9 that branches from between the engine body 1 and the exhaust turbine 4 b and is connected to the intake passage 5, and an EGR valve 10 is interposed in the EGR passage 9. The EGR valve 10 is, for example, an electronically controlled type using a step motor, and controls the amount of exhaust gas recirculated to the intake side according to the opening, that is, the EGR amount sucked into the engine body 1. In the exhaust passage 6, a three-way catalyst 11 having an HC adsorption function as an oxidation catalyst, a NOx trap catalyst 12, and an exhaust particulate filter (hereinafter referred to as DPF) 13 are sequentially provided on the downstream side of the exhaust turbine 4 b.

The three-way catalyst 11, when the air excess ratio is approximately "1", HC in the inflowing exhaust gas, CO, the three components of NOx is to purify. The three-way catalyst 11 carries an HC adsorbent as HC adsorption / release means for adsorbing or releasing adsorbed HC in the inflowing exhaust gas according to the carrier temperature. HC is adsorbed and held at a low temperature when 11 cannot purify HC.

  Instead of the three-way catalyst 11, it is also possible to use an oxidation catalyst with an HC adsorption function that has the property of releasing HC in the exhaust adsorbed at a low temperature at a high temperature and oxidizes HC and CO in an active state. is there.

  The NOx trap catalyst 12 has a characteristic of releasing NOx in the exhaust adsorbed in the lean air-fuel ratio operation state in the rich air-fuel ratio operation state. In the active state, NOx is reduced and purified. The NOx trap catalyst 12 also traps sulfur contained in the exhaust gas in addition to NOx. The sulfur content in the exhaust gas trapped by the NOx trap catalyst 12 is released when the excess air ratio of the exhaust is stoichiometric. In other words, when the excess air ratio of the exhaust is stoichiometric, the NOx trap catalyst 12 performs the release of sulfur poisoning and the release of trapped NOx in parallel.

  The DPF 13 collects PM (particulate matter) in the exhaust gas. The collected PM is combusted by regeneration control that raises the exhaust temperature. Further, the NOx trap catalyst and the DPF 13 also have a function as an oxidation catalyst.

  As sensors for detecting various states, in addition to the air flow meter 7 for detecting the intake air amount Qa, the rotational speed sensor 14 for detecting the engine rotational speed Ne, the accelerator opening sensor 15 for detecting the accelerator opening, and the cooling water temperature Tw. A water temperature sensor 16 for detecting the fuel pressure, a rail pressure sensor 17 for detecting the fuel pressure in the common rail 2 (ie, fuel injection pressure), and the like are provided. Between the exhaust turbine 4 b and the three-way catalyst 11, an exhaust sensor 20 that detects the exhaust air-fuel ratio or oxygen concentration, and a first temperature detection unit that detects the temperature of the exhaust gas on the inlet side of the three-way catalyst 11. 1 temperature sensor 21 is provided. Between the NOx trap catalyst 12 and the DPF 13, a second temperature sensor 22 is provided as second temperature detection means for detecting the temperature of the exhaust downstream of the three-way catalyst 11. The exhaust passage 6 is provided with a differential pressure sensor 23 that detects a pressure difference between the inlet side and the outlet side of the DPF 13. In the present embodiment, the bed temperature TWCBedTemp of the three-way catalyst 11 is calculated in consideration of the heat capacity of the three-way catalyst 11 using the detection value of the first temperature sensor 21 and the detection value of the water temperature sensor 16. Yes. Therefore, the bed temperature TWCBedTemp is a value that takes into account the response delay of the temperature increase of the three-way catalyst 11 with respect to the exhaust temperature. Further, the bed temperature of the NOx trap catalyst 12 is calculated using the detection value of the second temperature sensor 22.

  Reference numeral 19 in FIG. 1 denotes a control unit composed of a microcomputer comprising a CPU and its peripheral devices, and sets the fuel injection amount Qf and the injection timing IT based on detection signals from the various sensors, and the fuel injection valve 3 And the opening control of the intake throttle valve 8 and the EGR valve 10 are performed. In particular, as control according to the present invention, rich spike control as exhaust air-fuel ratio enrichment control is performed for regeneration (NOx desorption) of the NOx trap catalyst 12. In relation to the present invention, the control unit 19 corresponds to the functions of the exhaust air / fuel ratio enrichment control means, NOx accumulation amount calculation means, NOx desorption speed calculation means, and bed temperature calculation means.

  2 and 3 show a control routine of the rich spike control executed by the control unit 19. This control routine is periodically executed at predetermined time intervals on the condition that a predetermined condition is predetermined during engine operation, for example, a low-load low-speed operation state including idle.

  In this control, first, signals from the various sensors shown in FIG. 1 are read in S11, and then the NOx accumulation amount of the NOx trap catalyst 12 is calculated in S12 using these signals. In this embodiment, the SNOx addition amount that is the addition amount of the NOx accumulation amount is calculated according to the engine speed Ne, the fuel injection amount Qf, the intake air amount Qa, and the bed temperature of the NOx trap catalyst 12, and the previously calculated NOx is calculated. This is added to the accumulation amount NOx0 to obtain the current NOx accumulation amount NOx0 (details will be described later). Various methods for calculating the NOx accumulation amount are known. For example, the NOx amount estimated from the operation state signals such as the engine speed Ne, the fuel injection amount Qf, and the cooling water temperature Tw is integrated according to the operation history. Thus, the NOx accumulation amount can be obtained.

  In S13, the NOx accumulation amount NOx0 obtained by the calculation is compared with the reference value NOx1, and if the NOx accumulation amount NOx0 is equal to or less than NOx1, nothing is done and the current routine is terminated. When the NOx accumulation amount exceeds NOx1, the sp flag is set to 1 in S14 to indicate the rich spike control state, and then the routine proceeds to a rich spike control routine in S15.

  FIG. 3 is a subroutine showing the rich spike control described above, and corresponds to S15 of FIG.

  In the rich spike control, as shown in FIG. 3, first, in S21, control for reducing the opening of the intake throttle valve 8 and the EGR valve 10 is performed as engine control for enriching the exhaust λ to a theoretical air-fuel ratio or less. At the same time, since it is necessary to achieve the target λ, control is performed to add fuel by performing post-injection between the latter half of the combustion stroke and the exhaust stroke. NOx deposited on the NOx trap catalyst 12 in the lean combustion operation state where λ is large is desorbed from the NOx absorbent by the concentration of λ by the rich spike control, and is purified by the reduction process at the catalyst. If post injection is performed so that the excess air ratio of the exhaust gas becomes stoichiometric, sulfur poisoning of the NOx trap catalyst 12 can be released in parallel with the release of NOx trapped in the NOx trap catalyst 12. .

  In S22, the NOx desorption rate Reg_spd is calculated. The NOx desorption speed Reg_spd is the amount of NOx desorbed from the NOx trap catalyst 12 per unit time (in this case, one control cycle), and is basically the engine operating state, in this case, the fuel injection amount Qf and the rotational speed. Since it is determined according to Ne, a table (not shown) created experimentally in advance so as to give Reg_spd according to Qf and Ne is searched for and obtained.

  Next, in order to obtain a more accurate NOx desorption rate, a correction coefficient Reg_spd_hos_base corresponding to the exhaust λ is obtained in S23. That is, in S23, a correction coefficient Reg_spd_hos_base for performing the first correction based on the excess air ratio is obtained. The correction coefficient Reg_spd_hos_base is obtained by searching a table formed in advance from the exhaust λ as shown in FIG. Reg_spd_hos_base is a correction coefficient for weighting the NOx desorption rate Reg_spd, and its characteristic is set such that the NOx desorption rate increases as the exhaust λ decreases, that is, the excess air ratio decreases. Note that λ can be directly detected by the air-fuel ratio sensor 24 or can be obtained by calculation from the engine operating state.

  In S24, a correction coefficient Reg_spd_hos_post1 corresponding to the post injection is obtained in order to obtain a more accurate NOx desorption rate. That is, the correction coefficient Reg_spd_hos_post1 for performing the second correction in consideration of unburned HC not detected by the exhaust sensor 20 is obtained. This correction coefficient Reg_spd_hos_post1 is a correction coefficient obtained by multiplying three correction coefficients (details will be described later) of Reg_spd_hos_post1_it, Reg_spd_hos_post1_Q, and Reg_spd_hos_TWCBBedTemp.

  In S25, the NOx desorption rate Reg_spd obtained as described above is multiplied by the correction coefficient Reg_spd_hos_base and the correction coefficient Reg_spd_hos_post1, that is, the NOx desorption amount at that time is obtained by the processing of FIG. It is subtracted from NOx0 and updated as a new NOx accumulation amount (remaining amount) NOx0.

  Based on the determination in S26, the NOx desorption amount subtraction process result NOx0 is compared with a predetermined end reference value NOx2, and while NOx0> NOx2, the process returns to S22 and the subtraction process is executed again. As a result of repeating this subtraction process, when NOx0 ≦ NOx2, the routine proceeds to S27, where the rich spike control is terminated. At the end of rich spike control, the sp flag is set to 0 in S28 and the routine returns to the routine of FIG.

  FIG. 5 is a subroutine for calculating the correction coefficient Reg_spd_hos_post1 described above, and corresponds to S24 in FIG.

  In S31, a correction coefficient Reg_spd_hos_post1_it corresponding to the fuel injection timing of post injection is calculated. The correction coefficient Reg_spd_hos_post1_it is obtained by searching a table formed in advance as shown in FIG. 6 from the fuel injection timing of post injection. Reg_spd_hos_post1_it is a correction coefficient that weights the NOx desorption rate Reg_spd, and is characterized in that the NOx desorption rate increases as the post-injection fuel injection timing is retarded (retarded). As the post-injection timing is retarded, the injected fuel becomes more unburned HC and flows into the exhaust passage 6. Therefore, the NOx desorption speed can be corrected in consideration of this.

  In S32, a correction coefficient Reg_spd_hos_post1_Q corresponding to the post-injection fuel injection amount is calculated. This correction coefficient Reg_spd_hos_post1_Q is obtained by searching a table formed in advance as shown in FIG. 7 from the fuel injection amount of post injection. Reg_spd_hos_post1_Q is a correction coefficient that weights the NOx desorption speed Reg_spd, and is characterized in that the NOx desorption speed increases as the post-injection fuel injection amount increases. As the amount of post-injection fuel increases, the amount of injected fuel becomes more unburned HC and flows into the exhaust passage 6, so that the NOx desorption speed can be corrected in consideration thereof. In FIG. 7, Reg_spd_hos_post1_Q is constant regardless of the post-injection fuel injection amount when the post-injection fuel injection amount increases by a predetermined value A or more. However, this predetermined amount A is equal to the capacity of the three-way catalyst 11. It is determined accordingly.

  In S33, a correction coefficient Reg_spd_hos_TWCBedTemp corresponding to the bed temperature TWCBedTemp of the three-way catalyst 11 is calculated. The correction coefficient Reg_spd_hos_TWCBedTemp is obtained by searching a table previously formed as shown in FIG. 8 from the bed temperature TWCBedTemp of the three-way catalyst 11. Reg_spd_hos_TWCBedTemp is a correction coefficient for weighting the NOx desorption rate Reg_spd, and is characterized in that the NOx desorption rate increases as the bed temperature TWCBedTemp of the three-way catalyst 11 increases. More specifically, with the activation temperature of the three-way catalyst 11 as a boundary, the NOx desorption rate is set to be greatly increased on the higher temperature side than the activation temperature than on the lower temperature side than the activation temperature. . As the bed temperature of the three-way catalyst 11 increases, the unburned HC that has not been gasified upstream of the three-way catalyst 11 will be gasified in the three-way catalyst 11, so that the NOx desorption rate is taken into consideration. Can be corrected.

  In S34, the correction coefficient Reg_spd_hos_post1_it is multiplied by the correction coefficient Reg_spd_hos_post1_Q and Reg_spd_hos_TWCBBedTemp, thereby calculating the correction coefficient Reg_spd_host_post1 corresponding to the post injection.

  FIG. 9 is a block diagram showing a method for calculating the NOx accumulation amount NOx0 deposited on the NOx trap catalyst 12 in the present embodiment.

  In S101, the engine outlet NOx is calculated using a table (not shown) created experimentally in advance using the engine speed Ne, the air amount, the load, and the like. In S102, temperature correction is performed based on the catalyst bed temperature of the NOx trap catalyst 12, and the NOx accumulation amount on the NOx trap catalyst 12 is multiplied by S103 based on the correction table (not shown) based on the engine speed Ne and load in S104. (Per unit time) is calculated. This accumulation amount corresponds to the addition of the SNOx calculation.

  In S105, a table (not shown) created experimentally in advance using the engine speed Ne and load is searched to calculate the NOx desorption rate Reg_spd in the NOx trap catalyst 12.

  In S106, the correction coefficient Reg_spd_hos_base is calculated by searching the table formed as shown in FIG. 4 using the output value of the exhaust sensor.

  Using S107 to S9, the correction coefficient Reg_spd_hos_post1 corresponding to the post injection is obtained. That is, the correction coefficient Reg_spd_hos_post1_it (S108) according to the fuel injection timing of the post injection, the correction coefficient Reg_spd_hos_post1_Q (S107) according to the fuel injection amount of the post injection, and the correction coefficient Reg_spd_hosTmp_TW_Tmp_Tmp_TW_Tmp_TW_Tmp_TW_Tmp_TW_Tmp_TW_Tmp (S109) is obtained by searching the tables (FIGS. 6 to 8 described above), and the correction coefficient Reg_spd_hos_post1 (S111) is calculated by multiplying these three correction coefficients by S110 and S111. In S113, the NOx desorption rate Reg_spd calculated in S105 is multiplied by the correction coefficient Reg_spd_hos_base calculated in S106 and the correction coefficient Reg_spd_hos_post1 calculated in S111, and S112 is subtracted from the NOx accumulation amount. calculate. In S114, the SNOx subtraction calculated in S113 is multiplied by “−1”.

  In S115, sp flag information indicating whether or not the rich spike control state is set is input. When the rich spike control state is not set, an SNOx addition amount that is an addition amount of the NOx accumulation amount calculated in S103 is output. In the rich spike control state, a value obtained by multiplying SNOx subtraction, which is the subtraction of the NOx accumulation amount calculated in S114, by "-1" is output.

  In S116, the output value from S115 is added to the previously calculated NOx accumulation amount NOx0 to obtain the current NOx accumulation amount NOx0.

  Note that S101 to S104, S115, and S116 in FIG. 9 correspond to S12 in FIG. 2, and S105 to S113, S115, and S116 in FIG. 9 correspond to S22 to S25 in FIG.

  Unburned HC that is not detected by the exhaust sensor 20 because it is not gasified reacts and gasifies in the three-way catalyst 11 on the upstream side of the NOx trap catalyst 12, and therefore air at the inlet (upstream side) of the three-way catalyst 11. The excess air ratio at the outlet (downstream side) of the three-way catalyst 11 becomes smaller than the excess ratio, and the exhaust air-fuel ratio becomes rich.

  That is, in addition to the first correction based on the excess air ratio detected by the exhaust sensor 20, the second correction considering unburned HC that is not detected by the exhaust sensor 20 during rich spike control as in the above-described embodiment. By performing this, the NOx desorption rate can be calculated with higher accuracy, and HC can be introduced into the NOx trap catalyst 12 without excess or deficiency, so that fuel consumption and exhaust performance can be improved.

  Since the NOx desorption speed during the rich spike control can be calculated with high accuracy, the amount of NOx accumulated in the NOx trap catalyst 12 can be calculated with high accuracy.

  In addition, since the frequency of regeneration of the DPF 13 can be reduced by reducing the exhaust particulates (PM) by improving the exhaust performance, it is possible to improve fuel consumption and suppress oil dilution.

  Further, if post injection is performed so that the excess air ratio of the exhaust gas is close to the stoichiometric range by rich spike control, the NOx trap catalyst 12 is poisoned by sulfur in parallel with the release of NOx trapped in the NOx trap catalyst 12. Can be released.

  Note that the correction coefficient Reg_spd_hos_base, the correction coefficient Reg_spd_hos_post1_it, the correction coefficient Reg_spd_hos_post1_Q, and the correction coefficient Reg_spd_hos_TWCBedTemp described above are set to take values of at least one or more.

  Next, a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected about the component same as 1st Embodiment mentioned above, and the overlapping description is abbreviate | omitted.

  FIG. 10 is a flowchart showing rich spike control as exhaust air-fuel ratio enrichment control in the second embodiment. Note that the flowchart shown in FIG. 2 is common to the second embodiment and the first embodiment described above, and FIG. 10 corresponds to S15 of FIG.

  In the rich spike control of the second embodiment, as engine control for enriching the exhaust λ to a theoretical air fuel ratio or less in S51, control for reducing the opening of the intake throttle valve 8 and the EGR valve 10 is performed. Since it is necessary to achieve the target λ, control is performed to add fuel by performing post-injection between the late stage of the combustion stroke and the exhaust stroke. NOx deposited on the NOx trap catalyst 12 in the lean combustion operation state where λ is large is desorbed from the NOx absorbent by the concentration of λ by the rich spike control, and is purified by the reduction process at the catalyst. If post injection is performed so that the excess air ratio of the exhaust gas becomes stoichiometric, sulfur poisoning of the NOx trap catalyst 12 can be released in parallel with the release of NOx trapped in the NOx trap catalyst 12. .

  In S51, a NOx desorption rate Reg_spd is calculated. The NOx desorption speed Reg_spd is the amount of NOx desorbed from the NOx trap catalyst 12 per unit time (in this case, one control cycle), and is basically the engine operating state, in this case, the fuel injection amount Qf and the rotational speed. Since it is determined according to Ne, a table (not shown) created experimentally in advance so as to give Reg_spd according to Qf and Ne is searched for and obtained.

  Next, in order to obtain a more accurate NOx desorption rate, a correction coefficient Reg_spd_hos_base corresponding to the exhaust λ is obtained in S53. That is, in S53, the correction coefficient Reg_spd_hos_base for performing the first correction based on the excess air ratio is obtained. The correction coefficient Reg_spd_hos_base is obtained by searching a table formed in advance from the exhaust λ as shown in FIG. Reg_spd_hos_base is a correction coefficient for weighting the NOx desorption rate Reg_spd, and its characteristic is set such that the NOx desorption rate increases as the exhaust λ decreases, that is, the excess air ratio decreases. Note that λ can be directly detected by the air-fuel ratio sensor 24 or can be obtained by calculation from the engine operating state.

  In S54, a correction coefficient Reg_spd_hos_post2 corresponding to the post injection is obtained in order to obtain a more accurate NOx desorption rate. That is, the correction coefficient Reg_spd_hos_post2 for performing the second correction in consideration of unburned HC not detected by the exhaust sensor 20 is obtained. The correction coefficient Reg_spd_hos_post2 is a correction coefficient determined in accordance with a temperature difference between the exhaust temperature upstream of the three-way catalyst 11 and the exhaust temperature downstream of the three-way catalyst 11 (details will be described later).

  In S55, the NOx desorption rate Reg_spd obtained as described above is multiplied by the correction coefficient Reg_spd_hos_base and the correction coefficient Reg_spd_hos_post2, that is, the NOx desorption amount at that time is obtained by the above-described processing of FIG. It is subtracted from the accumulation amount NOx0 and updated as a new NOx accumulation amount (remaining amount) NOx0.

  As a result of the determination in S56, the NOx desorption amount subtraction result NOx0 is compared with a predetermined end reference value NOx2, and while NOx0> NOx2, the process returns to S22 and the subtraction process is executed again. As a result of repeating this subtraction process, when NOx0 ≦ NOx2, the routine proceeds to S57, where the rich spike control is terminated. At the end of the rich spike control, the sp flag is set to 0 in S58.

  FIG. 11 is a subroutine for calculating the above-described correction coefficient Reg_spd_hos_post2, and corresponds to S54 in FIG.

  In S61, the temperature rise on the three-way catalyst 11 due to the oxidation reaction of unburned HC is accurately detected. In this step, the first temperature sensor 21 and the second temperature sensor 22 disposed upstream and downstream of the three-way catalyst 11 are used to detect this temperature increase ΔTWCBedTemp.

  Here, in order to see the temperature rise of the exhaust gas passing through the three-way catalyst 11 using these two sensors, “the exhaust gas detected by the first temperature sensor 21 passes through the three-way catalyst 11, and A time delay of “detected by the second temperature sensor” must be taken into consideration.

  Since the exhaust gas detected by the second temperature sensor 22 has already passed through the first temperature sensor 21 and the three-way catalyst 11, it is detected by the first temperature sensor 21 several times before in the processing of the ECU. It is necessary to identify whether the exhaust gas is currently detected by the second temperature sensor 22. This time delay (how many times the exhaust gas is detected before) is determined according to the flow rate of the exhaust gas discharged from the engine and the capacity of the three-way catalyst 11.

  Therefore, in this step, TWCBedTemp_Rr that is the downstream exhaust temperature of the three-way catalyst 11 detected by the second temperature sensor 22 and the upstream exhaust temperature TWCBedTemp_Fr of the three-way catalyst 11 that is detected by the first temperature sensor 21. Then, a correction coefficient Reg_spd_hos_ΔTWCBedTemp corresponding to the temperature difference between the exhaust flow rate flowing into the three-way catalyst 11 and TWCBedTemp_Fr * which is a temperature detected in the past in consideration of the volume of the three-way catalyst 11 is calculated. The exhaust flow rate flowing into the three-way catalyst 11 is calculated by the control unit 19 based on the intake air amount Qa, the fuel injection amount, the engine rotational speed Ne, the EGR valve opening degree, and the like. That is, the control unit 19 corresponds to the function of means for detecting the exhaust flow rate.

  More specifically, first, ΔTWCBedTemp is calculated by subtracting TWCBedTemp_Fr *, which is a past detection value of the first temperature sensor 21, from the detection value TWCBedTemp_Rr of the second temperature sensor 22.

  Here, TWCBedTemp_Fr * is a first time constant determined according to the exhaust flow rate as shown in FIGS. 12 and 13 with respect to TWCBedTemp_Fr which is a detection value of the first temperature sensor 21, and the first temperature sensor 21 and the first temperature sensor 21. This is a past detection value obtained by multiplying the second time constant determined according to the volume of the exhaust system between the two temperature sensors 22.

  The first time constant determined according to the exhaust flow rate flowing into the three-way catalyst is a value determined to specify when the exhaust gas detected by the second temperature sensor 22 is detected by the first temperature sensor 21. Therefore, a table previously formed as shown in FIG. 12 is searched and obtained. The first time constant is set such that TWCBedTemp_Rr * becomes larger than TWCBedTemp_Rr as the exhaust gas flow rate decreases. This is because as the exhaust gas flow rate increases, the exhaust gas flow rate in the three-way catalyst 11 increases, and the time required to reach the second temperature sensor 22 from the first temperature sensor 21 is shortened.

  The second time constant determined according to the volume of the exhaust system between the first temperature sensor 21 and the second temperature sensor 22 (mainly, the capacity of the three-way catalyst 11) is formed in advance as shown in FIG. Search the table and ask for it. The second time constant is set such that TWCBedTemp_Rr * increases with respect to TWCBedTemp_Rr as the volume of the exhaust system between the first temperature sensor 21 and the second temperature sensor 22 increases. This is because, as the volume of the exhaust system between the detection position of the first temperature sensor 21 and the detection position of the second temperature sensor 22 is larger, the time to reach the second temperature sensor 22 from the first temperature sensor 21 is shortened. . Then, using the calculated ΔTWCBedTemp, a table previously formed as shown in FIG. 14 is searched to calculate the correction coefficient Reg_spd_hos_ΔTWCBedTemp.

  The correction coefficient Reg_spd_hos_ΔTWCBedTemp is a correction coefficient that weights the NOx desorption rate Reg_spd, and is characterized in that the NOx desorption rate increases as the temperature difference before and after the three-way catalyst 11 increases. A large temperature difference between the three-way catalyst 11 means that the heat of reaction in the three-way catalyst 11 is large, and that the heat of reaction in the three-way catalyst 11 is large in the three-way catalyst 11. Since the amount of reacting HC is large, the correction coefficient Reg_spd_hos_ΔTWCBedTemp is set to increase as the temperature difference between the three-way catalyst 11 increases.

  In S62, the correction coefficient Reg_spd_hos_ΔTWCBBedTemp calculated in S61 is set as the correction coefficient Reg_spd_hos_post2.

  In such a second embodiment, the same operational effects as those of the first embodiment described above can be obtained. That is, by performing the second correction in consideration of the unburned HC that is not detected by the exhaust sensor 20 during the rich spike control, the NOx desorption speed can be calculated more accurately, and the NOx trap catalyst 12 is excessively or deficient in HC. Therefore, fuel consumption and exhaust performance can be improved. Since the NOx desorption speed during the rich spike control can be calculated with high accuracy, the amount of NOx accumulated in the NOx trap catalyst 12 can be calculated with high accuracy. In addition, since the frequency of regeneration of the DPF 13 can be reduced by reducing the exhaust particulates (PM) by improving the exhaust performance, it is possible to improve fuel consumption and suppress oil dilution. If post injection is performed so that the excess air ratio of exhaust becomes stoichiometric by rich spike control, in parallel with the release of NOx trapped in the NOx trap catalyst 12, the sulfur poisoning of the NOx trap catalyst 12 is reduced. Release can be implemented.

  In the second embodiment, the second temperature sensor 22 is arranged on the downstream side of the NOx trap catalyst 12, but the second temperature sensor 22 is arranged between the three-way catalyst 11 and the NOx trap catalyst 12. By doing so, the accuracy of the detection value of TWCBedTemp_Rr can be further improved.

  The technical ideas of the present invention that can be grasped from the above-described embodiments will be listed together with their effects.

  (1) NOx trap catalyst provided in an exhaust passage of a diesel engine, an oxidation catalyst provided in the exhaust passage and located upstream of the NOx trap catalyst, and an excess air ratio of exhaust upstream of the oxidation catalyst Excess air ratio detecting means for detecting NOx, NOx accumulation amount calculating means for calculating the amount of NOx deposited on the NOx trap catalyst in the lean combustion state, and NOx desorbing from the NOx trap catalyst in the rich combustion state NOx desorption rate calculating means for calculating the desorption speed, and exhaust air / fuel ratio enrichment control means for making the air / fuel ratio of the exhaust more than the stoichiometric air / fuel ratio by performing post injection and reducing the excess air ratio of the exhaust, In a diesel engine exhaust purification system that performs the exhaust air-fuel ratio enrichment control based on the amount of NOx deposited on the NOx trap catalyst The NOx desorption speed calculation means is configured to control the NOx desorption speed based on the fuel injection amount and the rotational speed of the engine during the exhaust air / fuel ratio enrichment control, during the exhaust air / fuel ratio enrichment control. A first correction based on the excess air ratio detected by the excess air ratio detection means, and a second correction considering unburned HC that is not detected by the excess air ratio detection means during the exhaust air / fuel ratio enrichment control. Is configured to do.

  Unburned HC, which is not detected by the excess air ratio detection means because it is not gasified, reacts and gasifies in the oxidation catalyst upstream of the NOx trap catalyst, so the excess air ratio at the inlet (upstream side) of the oxidation catalyst is increased. On the other hand, the excess air ratio at the outlet (downstream side) of the oxidation catalyst becomes small, and the exhaust air-fuel ratio becomes rich.

  That is, in addition to the first correction based on the excess air ratio detected by the excess air ratio detection means, the second correction is performed in consideration of the unburned HC that is not detected by the excess air ratio detection means during the exhaust air / fuel ratio enrichment control. Thus, the NOx desorption rate can be calculated with high accuracy, and HC can be introduced into the NOx trap catalyst without excess or deficiency, so that fuel consumption and exhaust performance can be improved.

  Further, since the NOx desorption speed during exhaust air-fuel ratio enrichment control can be calculated with high accuracy, the amount of NOx accumulated in the NOx trap catalyst can be calculated with high accuracy.

  (2) The exhaust emission control device for a diesel engine according to (1), specifically, has a bed temperature calculation means for calculating the bed temperature of the oxidation catalyst, and the second correction is a post-injection The correction is made based on at least one of the fuel injection timing, the post-injection fuel injection amount, and the bed temperature of the oxidation catalyst.

  (3) In the exhaust gas purification apparatus for a diesel engine according to (2), the second correction is performed so that the NOx desorption speed increases as the post-injection fuel injection timing is retarded. As the post injection timing is retarded, the injected fuel becomes more unburned HC and flows into the exhaust passage, so that the NOx desorption speed can be corrected in consideration of this.

  (4) In the exhaust gas purification apparatus for a diesel engine according to (2), the second correction is performed such that the NOx desorption speed increases as the fuel injection amount of post injection increases. As the post-injection fuel injection amount increases, the injected fuel becomes more unburned HC and flows into the exhaust passage, so that the NOx desorption speed can be corrected in consideration of this.

  (5) In the exhaust purification system for a diesel engine according to (2), the second correction is performed such that the NOx desorption rate increases as the bed temperature of the oxidation catalyst increases. The higher the bed temperature of the oxidation catalyst, the more unburned HC that has not been gasified upstream of the oxidation catalyst will be gasified in the oxidation catalyst, so that the NOx desorption rate can be corrected in consideration thereof. .

  (6) The diesel engine exhaust gas purification apparatus according to (1) described above includes a first temperature detection unit that detects an exhaust temperature upstream of the oxidation catalyst, and a first temperature detection unit that detects an exhaust temperature downstream of the oxidation catalyst. 2 temperature detection means, and the second correction is that the NOx desorption rate increases as the exhaust temperature downstream of the oxidation catalyst becomes higher than the exhaust temperature upstream of the oxidation catalyst. Correct as follows. If the temperature difference between the exhaust temperature before and after the oxidation catalyst is large, the reaction heat in the oxidation catalyst will be large, and the amount of unburned HC reacting will increase. Can be corrected.

  (7) The exhaust purification device for a diesel engine according to (6) includes a means for detecting an exhaust flow rate flowing into the oxidation catalyst, and the exhaust gas detected by the first temperature detection means is the second temperature detection. A time delay until detection by the means is obtained in consideration of the exhaust flow rate detected by the exhaust flow rate detection means, and an increase in the exhaust temperature is obtained. As a result, the time delay that the exhaust gas detected by the first temperature detection means passes through the oxidation catalyst and reaches the second temperature detection means varies depending on the exhaust flow rate, but the exhaust flow rate is taken into consideration. Therefore, it is possible to detect an increase in exhaust temperature with high accuracy.

  (8) In the exhaust gas purification apparatus for a diesel engine according to (6) or (7), the exhaust gas detected by the first temperature detection unit is temporally detected until the second temperature detection unit detects the exhaust gas. The delay is obtained in consideration of the volume of the exhaust system between the detection position of the first temperature detection means and the detection position of the second temperature detection means, and the rise in the exhaust temperature is obtained. As a result, the time delay that the exhaust gas detected by the first temperature detecting means passes through the oxidation catalyst and reaches the second temperature detecting means depends on the volume of the exhaust system. Therefore, it is possible to accurately detect the rise in exhaust temperature.

  (9) An exhaust gas purification device for a diesel engine includes an oxidation catalyst interposed in an exhaust passage of the diesel engine, an air excess ratio detection unit that is located upstream of the oxidation catalyst and detects an excess air ratio of exhaust gas, Exhaust air / fuel ratio rich that removes components accumulated on the catalyst located on the downstream side of the oxidation catalyst by making post-injection and reducing the excess air ratio of the exhaust to make the air / fuel ratio of the exhaust more than the stoichiometric air / fuel ratio An excess air ratio detected by the excess air ratio detection means, a fuel injection amount at the time of post injection, a fuel injection timing at the time of post injection, and a downstream side of the oxidation catalyst at the time of post injection The specific component of the exhaust gas downstream of the excess air ratio detecting means is estimated using the temperature of the catalyst located at the position. This makes it possible to estimate a specific component of the exhaust downstream of the excess air ratio detection means when performing exhaust air-fuel ratio enrichment control, and the excess air required by the catalyst located downstream of the catalyst is required. Rate can be realized, and fuel consumption and exhaust performance can be improved.

The schematic block diagram which shows an example of the diesel engine which can apply this invention. The flowchart which shows the flow of control implemented in the exhaust gas purification apparatus of the diesel engine which concerns on this invention. It is a flowchart which shows the flow of control implemented in the exhaust gas purification apparatus of the diesel engine which concerns on this invention, Comprising: The flowchart which shows the flow of control at the time of rich spike control in 1st Embodiment of this invention. The schematic explanatory drawing of the table which provides the correction coefficient Reg_spd_hos_base which is the correction amount of NOx desorption speed. A subroutine for calculating the correction coefficient Reg_spd_hos_post1. The schematic explanatory drawing of the table which provides the correction coefficient Reg_spd_hos_post1_it which is the correction amount of NOx desorption speed. The schematic explanatory drawing of the table which provides the correction coefficient Reg_spd_hos_post1_Q which is the correction amount of NOx desorption speed. The schematic explanatory drawing of the table which provides the correction coefficient Reg_spd_hos_TWCBedTemp which is the correction amount of NOx desorption speed. The block diagram which shows the calculation method of the NOx accumulation amount implemented in 1st Embodiment of the exhaust gas purification apparatus of the diesel engine which concerns on this invention. It is a flowchart which shows the flow of control implemented in the exhaust gas purification apparatus of the diesel engine which concerns on this invention, Comprising: The flowchart which shows the flow of control at the time of rich spike control in 2nd Embodiment of this invention. A subroutine for calculating the correction coefficient Reg_spd_hos_post2. The schematic explanatory drawing of the table which provides a 1st time constant. The schematic explanatory drawing of the table which provides a 2nd time constant. The schematic explanatory drawing of the table which provides the correction coefficient Reg_spd_hos_ (DELTA) TWCBedTemp which is the correction amount of NOx desorption speed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 4 ... Supercharger 4a ... Compressor 4b ... Exhaust turbine 5 ... Intake passage 6 ... Exhaust passage 7 ... Air flow meter 8 ... Intake throttle valve 9 ... EGR passage 10 ... EGR valve 11 ... Three-way catalyst 12 ... NOx trap catalyst 13 ... DPF (Exhaust particulate filter)
DESCRIPTION OF SYMBOLS 14 ... Rotational speed sensor 15 ... Accelerator opening degree sensor 16 ... Water temperature sensor 19 ... Control unit 20 ... Exhaust sensor 21 ... 1st temperature sensor 22 ... 2nd temperature sensor 23 ... Differential pressure sensor

Claims (7)

A NOx trap catalyst provided in the exhaust passage of the diesel engine;
An oxidation catalyst provided in the exhaust passage and located upstream of the NOx trap catalyst;
An excess air ratio detecting means for detecting an excess air ratio of the exhaust gas upstream of the oxidation catalyst;
NOx accumulation amount calculating means for calculating the amount of NOx accumulated on the NOx trap catalyst in the lean combustion state;
NOx desorption rate calculating means for calculating the desorption rate of NOx desorbing from the NOx trap catalyst in a rich combustion state;
Exhaust air-fuel ratio enrichment control means for making post-injection and making the air-fuel ratio of the exhaust richer than the exhaust air-fuel ratio during normal operation ;
An exhaust purification device for a diesel engine, comprising: a bed temperature calculating means for calculating a bed temperature of the oxidation catalyst, and performing the exhaust air-fuel ratio enrichment control based on the amount of NOx deposited on the NOx trap catalyst;
The NOx desorption speed calculation means is configured to control the NOx desorption speed based on the fuel injection amount and the rotational speed of the engine during the exhaust air / fuel ratio enrichment control, during the exhaust air / fuel ratio enrichment control. A first correction based on the excess air ratio detected by the excess air ratio detection means, and a second correction considering unburned HC that is not detected by the excess air ratio detection means during the exhaust air / fuel ratio enrichment control. Configured to do and
The second correction is configured to perform correction based on at least one of a post-injection fuel injection timing, a post-injection fuel injection amount, and a bed temperature of the oxidation catalyst, and the post-injection fuel injection timing is delayed. An exhaust emission control device for a diesel engine, wherein correction is made so that the NOx desorption speed increases as the angle increases.   2. The diesel engine exhaust gas purification apparatus according to claim 1, wherein the second correction is performed such that the NOx desorption rate increases as the post-injection fuel injection amount increases.   The exhaust gas purification apparatus for a diesel engine according to claim 1 or 2, wherein the second correction is performed such that the NOx desorption rate increases as the bed temperature of the oxidation catalyst increases. A NOx trap catalyst provided in the exhaust passage of the diesel engine;
An oxidation catalyst provided in the exhaust passage and located upstream of the NOx trap catalyst;
An excess air ratio detecting means for detecting an excess air ratio of the exhaust gas upstream of the oxidation catalyst;
NOx accumulation amount calculating means for calculating the amount of NOx accumulated on the NOx trap catalyst in the lean combustion state;
NOx desorption rate calculating means for calculating the desorption rate of NOx desorbing from the NOx trap catalyst in a rich combustion state;
Exhaust air-fuel ratio enrichment control means for making post-injection and making the air-fuel ratio of the exhaust richer than the exhaust air-fuel ratio during normal operation ;
First temperature detection means for detecting the exhaust temperature upstream of the oxidation catalyst;
And a second temperature detection means for detecting an exhaust temperature downstream of the oxidation catalyst, and performing exhaust gas air-fuel ratio enrichment control based on a NOx accumulation amount accumulated on the NOx trap catalyst. In the device
The NOx desorption speed calculation means is configured to control the NOx desorption speed based on the fuel injection amount and the rotational speed of the engine during the exhaust air / fuel ratio enrichment control, during the exhaust air / fuel ratio enrichment control. A first correction based on the excess air ratio detected by the excess air ratio detection means, and a second correction considering unburned HC that is not detected by the excess air ratio detection means during the exhaust air / fuel ratio enrichment control. Configured to do and
The second correction is performed so that the NOx desorption rate increases as the exhaust temperature downstream of the oxidation catalyst becomes higher than the exhaust temperature upstream of the oxidation catalyst. Exhaust purification equipment. Means for detecting an exhaust flow rate flowing into the oxidation catalyst;
A time delay until the exhaust gas detected by the first temperature detecting means is detected by the second temperature detecting means is determined in consideration of the exhaust flow rate detected by the exhaust flow rate detecting means, and the exhaust temperature The exhaust purification device for a diesel engine according to claim 4, wherein an increase in the exhaust gas is obtained. The time delay until the exhaust gas detected by the first temperature detection means is detected by the second temperature detection means is determined between the detection position of the first temperature detection means and the detection position of the second temperature detection means. The exhaust gas purification device for a diesel engine according to claim 4 or 5 , wherein the exhaust gas temperature is calculated in consideration of the volume of the exhaust system between the exhaust gas and the exhaust gas temperature rise . An oxidation catalyst interposed in the exhaust passage of the diesel engine;
An excess air ratio detecting means which is located upstream of the oxidation catalyst and detects the excess air ratio of the exhaust;
Exhaust air / fuel ratio rich that removes components accumulated on the catalyst located on the downstream side of the oxidation catalyst by making post-injection and reducing the excess air ratio of the exhaust to make the air / fuel ratio of the exhaust more than the stoichiometric air / fuel ratio Control means,
The excess air ratio detected by the excess air ratio detection means, the fuel injection amount at the time of post injection, the fuel injection timing at the time of post injection, and the temperature of the catalyst located downstream of the oxidation catalyst at the time of post injection, An exhaust gas purification apparatus for a diesel engine, wherein a specific component of exhaust gas on the downstream side of the air excess rate detecting means is estimated using

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