JP2009030568A - Exhaust emission control device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately determine deterioration of a catalyst, by accurately grasping a combustion characteristic of PM captured in a DPF carrying the catalyst thereon. <P>SOLUTION: An exhaust emission control device of a diesel engine 1 has the DPF 13 carrying the catalyst thereon and disposed in an exhaust passage 10. The exhaust emission control device includes a deterioration determination means 9 determining the deterioration of the catalyst. The deterioration determination means 9 determines the deterioration of the catalyst based on a parameter for deterioration determination indicating the degree of deterioration of the catalyst and a threshold valve for deterioration determination set on the basis of an oxidation reaction rate of the PM accumulated in the DPF 13. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a deterioration diagnosis of a DPF (diesel particulate filter), and more particularly to a deterioration diagnosis of a DPF having a catalyst supported on a filter surface.

  A DPF is known as a device for collecting fine particles (PM) contained in exhaust gas from a diesel engine. Since the exhaust pressure increases when the amount of PM trapped in the DPF increases, when the amount of PM trapped exceeds a certain level, the temperature of the DPF is increased by, for example, increasing the exhaust temperature, and the PM is burned. It is necessary to perform so-called reproduction processing to be removed.

  By the way, DPF carrying a catalyst containing a noble metal such as platinum is also known for the purpose of lowering the temperature required for the regeneration treatment. As a method for diagnosing the deterioration of the catalyst function of the DPF carrying such a catalyst, Patent Document 1 discloses a method for diagnosing the deterioration of the catalyst based on the difference in exhaust temperature before and after the DPF during DPF regeneration.

Specifically, paying attention to the characteristic that when the catalyst deteriorates, the oxidation reaction of PM decreases and the reaction heat decreases, and when the difference in exhaust temperature before and after the DPF becomes smaller than a preset threshold, the catalyst Diagnosed as degraded.
JP 2004-115578 A

  By the way, the exothermic reaction (oxidation reaction) of PM follows the Arrhenius equation in terms of reaction kinetics, DPF temperature, catalyst deterioration status, PM combustion characteristics (mainly crystallinity), oxygen concentration, carbon dioxide concentration, PM in DPF Since it varies depending on the amount of deposition, the regeneration characteristics of the DPF are not uniformly determined by the temperature of the DPF.

  However, since Patent Document 1 does not consider the crystallinity of PM, there is a risk of erroneous diagnosis in catalyst deterioration diagnosis. For example, when a large amount of highly crystalline PM is deposited, the highly crystalline PM is difficult to burn, and the reaction heat at the catalyst is smaller than when there is much PM having low crystallinity and flammability. For this reason, there is a possibility of diagnosing that the catalyst is deteriorated because the exhaust gas temperature difference before and after the DPF is small even though the catalyst is not deteriorated.

  In view of this, an object of the present invention is to accurately perform deterioration diagnosis in consideration of PM combustion characteristics.

  The present invention relates to an exhaust emission control device for a diesel engine provided with a DPF carrying a catalyst in an exhaust passage. In particular, a deterioration determining means for determining deterioration of the catalyst is provided, and the deterioration determining means is set based on a deterioration determining parameter indicating the degree of deterioration of the catalyst and an oxidation reaction rate of PM accumulated in the DPF. The deterioration of the catalyst is determined based on the determination threshold value.

  According to the present invention, it is possible to set an appropriate deterioration determination threshold according to the oxidation reaction rate of PM that varies depending on the environment in which regeneration is performed, and as a result, deterioration determination can be performed with high accuracy.

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

  1 is a diesel engine body, 2 is a fuel injection valve for each cylinder, 3 is a fuel injection device having a pressure accumulating chamber for storing high-pressure fuel (hereinafter referred to as a common rail fuel injection device), 4 is an intake collector, 5 is an intake passage, 10 is an exhaust passage, 9 is a control unit (degradation determining means) for performing various controls such as setting of a target regeneration temperature and temperature rise control during regeneration processing, and 14 is for transmitting the driving force of the diesel engine body 1 to the drive shaft. It is a transmission. The transmission 14 may be a stepped transmission or a continuously variable transmission.

  High pressure fuel is supplied to the fuel injection valve 2 by a common rail fuel injection device 3. Each fuel injection valve 2 opens and closes in response to an injection signal from a control unit (ECU) 9 to inject high-pressure fuel into the cylinder.

  An intake passage 4 is connected to an intake collector 4 connected to each intake port of the diesel engine body 1, and a compressor 6 a of a variable nozzle turbocharger 6 for supercharging from the upstream side is added to the intake passage 5. An intercooler 7 for cooling air that has been pressurized and heated, and an intake throttle valve 8 for controlling the intake air amount are arranged. Further, from the upstream side of the exhaust passage 10, the turbine 6 b of the variable nozzle turbocharger 6, an oxidation catalyst 11 that oxidizes unburned components in the exhaust, and a particulate filter (DPF) that collects PM in the exhaust ) 13 are sequentially arranged.

  Further, an EGR passage 15 branched from the upstream of the turbine 6b in the exhaust passage 10 and connected to the intake collector 4 is provided, and an EGR valve 16 is installed in the EGR passage 15 so that the exhaust gas recirculates into the intake air according to the operating conditions. Control the amount.

  The ECU 9 includes an engine speed sensor 17 that detects the engine speed, an accelerator position sensor 18 that detects the accelerator pedal position, and an exhaust pressure that detects the exhaust pressure between the oxidation catalyst 11 and the DPF 13 in the exhaust passage 10. An atmospheric pressure sensor 19, an exhaust pressure sensor 12 for detecting an exhaust pressure downstream of the DPF 13, an exhaust air / fuel ratio sensor 20 for detecting an exhaust air / fuel ratio downstream of the DPF 13, a temperature sensor 21 for detecting an intake air temperature downstream of the DPF 13, and an oxidation catalyst Each detection signal from the temperature sensor 22 that detects the exhaust gas temperature between 11 and the DPF 13 is input. Based on these detection signals, a signal for controlling the opening degree of the variable nozzle vane of the variable nozzle type turbocharger 6, a signal for controlling the opening degree of the EGR valve 16, and the opening degree of the intake throttle valve 8 are controlled. A signal for controlling the PM accumulation amount in the DPF 13 as a PM accumulation amount detection means, a signal for controlling the fuel injection amount by the fuel injection valve 2, and a regeneration timing of the DPF 13 as a DPF regeneration control start timing judgment means. Then, a signal for operating the fuel injection valve 2 for supplying the fuel necessary for raising the exhaust gas temperature for regeneration is calculated and output as a temperature raising means.

  Next, regeneration control of the DPF 13 will be described with reference to FIG. FIG. 2 is a flowchart showing a control routine executed by the ECU 9 for regeneration control of the DPF 13. This control routine is repeatedly executed at regular intervals, for example, every 10 ms.

  In step S1, detection signals from the engine speed sensor 17 and the accelerator opening sensor 18 are read as operating states.

  In step S2, the subroutine shown in FIG. 3 is executed. This subroutine divides the operation region according to the oxidation temperature of PM to be discharged, and estimates the combustion characteristics (oxidation temperature Toxi under instantaneous operation conditions) and the PM accumulation amount for each operation region. For example, as shown in FIG. 4, the operation region is divided into A, B, and C from the lower engine torque, that is, from the lower PM oxidation temperature. Since the oxidation temperature is less sensitive to the engine speed, the operation region is divided according to only the engine torque in FIG.

  In step S1001, the base oxidation temperature Tb is calculated from the map of FIG. FIG. 5 shows the engine torque on the vertical axis and the engine speed on the horizontal axis, and the base oxidation temperature of PM is assigned to the engine torque and the engine speed.

  This map is created based on the property that the oxidation temperature of PM increases as the crystallinity of PM increases. The crystallinity increases as the crystallite diameter increases and the layer spacing in the crystallite decreases. As shown in FIG. 9, the crystallite diameter increases as the engine torque increases, and the layer spacing decreases as the engine torque increases as shown in FIG. Therefore, in FIG. 5, the oxidation temperature of PM increases as the engine torque increases.

  By the way, when the catalyst is supported on the DPF 13, the oxidation temperature of PM is lower than when the catalyst is not supported, but as shown in FIG. 20, the characteristic itself that the oxidation temperature increases as the engine torque increases does not change. FIG. 20 is a graph showing the relationship between crystallinity and oxidation temperature and engine torque when the engine speed is constant. The vertical axis represents the oxidation temperature of PM, and the horizontal axis represents crystallinity. In the figure, Po1 to Po3 represent cases where no catalyst is supported, and Pc1 to Pc3 represent cases where a catalyst is supported. The magnitudes of the engine torque are Po1 <Po2 <Po3 and Pc1 <Pc2 <Pc3.

The oxidation temperature tends to increase as the engine speed increases, but the sensitivity to the engine speed is smaller than the sensitivity to the engine torque. Therefore, the base oxidation temperature may be searched using only the engine torque in order to reduce the calculation load.
In step S1002, the excess air ratio correction coefficient K for correcting the oxidation temperature due to the difference in excess air ratio is calculated from the excess air ratio λ to the oxidation temperature correction coefficient using the table shown in FIG. Find K. FIG. 11 shows the correction coefficient K on the vertical axis and the excess air ratio λ on the horizontal axis, and the correction coefficient K increases as the excess air ratio decreases.

  In step S1003, the oxidation temperature Toxi under the instantaneous operation condition is calculated by the following equation (1) using the oxidation temperature correction coefficient K due to the difference in excess air ratio as the base oxidation temperature Tb.

Tb × K = Toxi (1)
As shown in FIG. 12, even if the engine torque and the engine speed are the same, only the engine torque and the engine speed are considered in consideration of the characteristic that the crystallinity of PM increases as the excess air ratio λ decreases. This is to correct the oxidation temperature obtained from the above.

  In addition, when performing exhaust gas recirculation (EGR), you may further correct | amend the oxidation temperature Toxi calculated by Formula (1) using the correction coefficient F according to the EGR rate. For example, as shown in the table of FIG. 13, the correction coefficient F is set so as to decrease as the EGR rate increases. This is because the higher the EGR rate, the lower the in-cylinder temperature, thereby lowering the crystallinity and lowering the oxidation temperature.

  FIG. 12 is a diagram schematically showing the difference between the crystallinity when λ = 1.5 and the crystallinity when λ = 1 when the engine speed and the engine torque are the same. This difference is considered because the in-cylinder temperature during combustion increases as the excess air ratio λ decreases.

  The oxidation temperature Toxi under the instantaneous operation condition thus calculated is stored in memory every time it is calculated from the end of the previous regeneration to the next regeneration.

  In step S1004, when the oxidation temperature Toxi of the instantaneous operation condition is lower than the threshold B, it is determined as the region A, when it is higher than the threshold B and lower than the threshold C, it is determined as the region B, and when higher than the threshold C, it is determined as the region C. To do. The threshold values B and C are set in advance. In addition, a representative regeneration temperature is set for each region, and the product of the representative regeneration temperature and the instantaneous discharge amount M is stored as a deposition amount in each region.

  In the present embodiment, Steps S9 to S11 are executed after Step S2 every fixed time T-time. Note that steps S1 to S8 are performed independently while steps S9 to S11 are performed.

  In step S9, the detection signal of the temperature sensor 22, that is, the exhaust gas temperature flowing into the DPF 13, is read as the bed temperature of the DPF 13.

  In step S10, a change in combustion characteristics of PM accumulated in the DPF 13 is grasped. Specifically, the flammability index value G as an index value for determining combustion characteristics based on the PM accumulation amount for each operation region estimated in step S2 and the temperature of the DPF 13 read in step S9 is as follows. To calculate.

GA = Initial + ∫adt (2)
GB = Binary + ｉbdt (3)
GC = Initial + ∫ cdt (4)
Ainitial, Binitial, and Cinitial are oxidation temperatures Toxi under instantaneous operation conditions estimated in step S3004, and a, b, and c are crystallinity increase coefficients. The crystallinity increase coefficient is a value representing how much the crystallinity increases per unit time when the DPF 13 is maintained at a predetermined temperature, that is, how much the oxidation temperature increases per unit time.

  For example, as shown in FIG. 6, the crystallinity increase coefficient of the region A is a3 when the temperature is T3, but when the temperature is increased to T2, the crystallinity increase coefficient increases and becomes a2. Therefore, the higher the temperature of the DPF 13 or the longer the holding time at the temperature, the higher the crystallinity of PM and the higher the oxidation temperature.

  Further, as shown in FIG. 7, when compared at the same temperature T3, the crystallinity increase coefficient b of the region B, which is a region having higher crystallinity than the region A, is smaller than the crystallinity increase coefficient a. This indicates that the higher the crystallinity is, the smaller the increase in crystallinity due to the temperature history in the DPF 13. Accordingly, the crystallinity increase coefficient c in the region C is further smaller than the crystallinity increase coefficient b.

  Based on these characteristics, the table shown in FIG. 8 is created in advance. In FIG. 8, the horizontal axis represents the temperature of the DPF 13 and the vertical axis represents the crystallinity increase coefficient. The higher the temperature of the DPF 13, the greater the crystallinity increase coefficient of each region. Further, the magnitude of the crystallinity increase coefficient remains a> b> c even when the temperature of the DPF 13 increases.

When executing the equations (2) to (4), the crystallinity increase coefficients a, b, and c of each region are obtained by searching the map of FIG. 8 with the temperature of the DPF 13 read in step S9.
The combustibility index value G of each region calculated in this way is stored in memory.

  In step S11, it is determined whether or not a predetermined time T-time has elapsed. If it has elapsed, the process proceeds to step S3. If not, the process returns to step S9.

  That is, the calculation of the combustibility index value G is repeated for a predetermined time T-time. During this time, the combustibility index value G is updated every time it is calculated. When the flammability index value GA of the PM in the region A exceeds the threshold value B, the PM that has been treated as the region A until now is incorporated into the region B, and the subsequent calculation is performed. The same applies to the regions B and C.

  In step S3, the PM deposition amount in each region is updated based on the PM newly deposited during the predetermined time T-time and the calculation result in step S10.

  Returning to the flowchart of FIG.

  In step S4, it is determined whether or not a regeneration request flag (T_DPF_cal) is set. If T_DPF_cal = 0, the process proceeds to step S5, and if T_DPF_cal = 1, a DPF regeneration temperature setting subroutine described later is entered.

  In step S5, it is determined whether or not a later-described deterioration flag (Aged) is set. If Aged = 0, the process proceeds to step S6. If Aged = 1, the subroutine of FIG. 16 is entered. In step S3001 of the subroutine, the regeneration target temperatures T1 and T2 are changed to values higher than the current values. In step S3002, the MIL lamp (engine check lamp) is turned on to notify the driver that the vehicle has deteriorated.

  In step S6, it is determined whether or not a flag (reg) indicating whether or not the DPF regeneration mode is set. If reg = 0, the process proceeds to step S7. If reg = 1, a subroutine for a DPF regeneration mode described later is entered.

  In step S7, it is determined whether or not the deterioration prevention mode flag (rec) is set. When the deterioration prevention mode flag rec = 0, the process proceeds to step S8, and when the deterioration prevention mode flag rec = 1, a subroutine for deterioration prevention mode described later is entered.

  In step S8, it is determined whether or not the PM accumulation amount estimated in step S2 is larger than PM1 set in advance as the accumulation amount when regeneration is necessary. This is a determination as to whether or not it is time to regenerate the DPF 13. In addition to this, for example, as shown in FIG. 14, the engine speed and the engine torque, and the exhaust pressure (exhaust pressure threshold when the accumulation amount reaches a predetermined amount PM1) as shown in FIG. There is a method in which a map representing a relationship with (value) is created in advance and a determination is made based on whether or not the exhaust pressure exceeds the exhaust pressure threshold. Further, a method may be used in which it is determined that the regeneration time is reached when the travel distance from the previous regeneration exceeds a predetermined distance and the exhaust pressure of the DPF 13 exceeds the exhaust pressure threshold.

  If it is determined that the playback time is reached, the process proceeds to a subroutine shown in FIG. 19, and a playback request flag T_DPF_cal is set to 1 in step S6001 to issue a playback request. If it is determined in step S8 that it is not the reproduction time, the process returns.

  Next, each subroutine will be described.

  FIG. 15 is a regeneration temperature setting control routine that is executed when the regeneration request flag T_DPF_cal is set in step S4.

  In step S2001, the sum N of the product of the accumulation amount in all regions and the representative regeneration temperature is calculated by the following equation (5), and the target regeneration temperature T_DPF is searched using the table shown in FIG.

N = A area amount + B area amount + C area amount (5)
However, A region amount = Ta × M, B region amount = Tb × M, C region amount = Tc × M, and M: instantaneous discharge amount.

  In the table of FIG. 21, the horizontal axis represents the sum N, and the vertical axis represents the target regeneration temperature T_DPF. The larger the sum N, the higher the target regeneration temperature T_DPF.

  In step S2002, the upper limit value T1 and the lower limit value T2 of the target regeneration temperature range are determined by the following equations (6) and (7). Note that the target temperature range is set to be a temperature range in which PM can be reliably burned and removed if the target temperature range is maintained within the temperature range. For example, D is set to a value of about 10 degrees.

T1 = T_DPF + D (6)
T2 = T_DPF-D (7)
In step S2003, the regeneration request flag T_DPF_cal is set to zero, and in step S2004, the DPF regeneration mode flag reg is set to 1. Thereby, at the time of the next calculation, the subroutine for the reproduction mode is entered from step S7.

  In step S2005, the temperature increase of the DPF 13 by post injection is started so as to reach the target regeneration temperature T_DPF. The post injection amount is set according to the target regeneration temperature T_DPF and the operation state.

  As shown in FIG. 22, when the temperature of the DPF 13 is high to some extent (T1: in FIG. 22, for example, about 500 degrees), the above control increases the crystallinity of PM deposited in the DPF 13, so that This is based on the knowledge found by the inventors that the temperature rises. That is, regarding the PM in the DPF 13, not only the oxidation temperature at the time of being collected by the DPF 13, but also the change in the oxidation temperature due to the thermal history received from the time of being collected by the DPF 13 to the regeneration is considered. The regeneration temperature T_DPF is set.

  By the way, in the above control, a target regeneration temperature T_DPF that can surely burn and remove PM is set, and the fuel injection amount is increased and the fuel injection timing is retarded in accordance with this, so that the oxidation of the accumulated PM When the temperature is high, the target regeneration temperature T_DPF is also set high. However, the target regeneration temperature T_DPF is set to a constant predetermined temperature (for example, about 600 degrees) regardless of the oxidation temperature of the accumulated PM, and the PM is burned and removed when the oxidation temperature of the accumulated PM is the predetermined temperature. When the temperature is too high, the oxygen concentration in the exhaust gas may be increased. Since combustion is promoted when the oxygen concentration is increased, PM accumulated in the DPF 13 can be removed by combustion. Furthermore, when the target regeneration temperature T_DPF is set to a relatively high temperature, the target regeneration temperature T_DPF may be set high and the oxygen concentration may be increased.

  In addition, since PM deposited on the DPF 13 does not improve crystallinity unless the DPF 13 is at a certain high temperature, the temperature of the DPF 13 is not less than the predetermined temperature, instead of executing S9 to S11 every T-time. It may be executed only when it becomes.

  Moreover, in this embodiment, it divides | segments into 3 area | region of AC, and the fluctuation | variation of the combustion characteristic by the thermal history received in DPF13 is calculated for every area | region, However, By dividing | segmenting into more areas | areas, it calculates. Thus, it becomes possible to control the regeneration temperature more precisely.

  FIG. 17 is a control routine for regeneration control that is executed when the DPF regeneration mode flag reg = 1 in step S6.

  In step S4001, the exhaust λ is controlled to a target value according to the amount of PM accumulated in the DPF 13. Here, the target exhaust λ is controlled by adjusting the opening of the intake throttle valve 8. That is, the intake air amount target value for realizing the exhaust λ according to the PM accumulation amount is set, and the opening degree of the intake throttle valve 8 is adjusted so as to be the intake air amount target value.

  The intake air amount target value is set using a map as shown in FIG. In FIG. 23, the vertical axis represents engine torque and the horizontal axis represents engine speed. Then, the map is changed according to the target value of the exhaust λ. For example, when the target value is λ = 1, the map is as shown by a solid line in FIG. 23. When the target value is λ = 1.5, the map is as shown by a broken line in FIG. Switch to.

  When a high temperature is not required as the DPF regeneration temperature, the target temperature can be reached by adjusting the opening degree of the intake throttle valve 8, the injection timing retard, or a combination thereof without using post injection.

  In step S4002, it is determined whether the temperature of the DPF 13 exceeds the upper limit value T1 of the target temperature range. If not, the process proceeds to step S4003. When exceeding, it progresses to step S4011 and reduces post injection amount only by the unit injection amount according to a driving | running state. The unit injection amount corresponding to the operating state is set using a map as shown in FIG. 24, for example. FIG. 24 is a map in which the unit injection amount is assigned to the engine torque and the engine speed, and the injection amount is smaller as the rotation speed is lower and the torque is lower, and the injection amount is higher as the rotation speed is higher and the torque is higher. Further, in order to prevent the exhaust λ from deviating from the target value due to fluctuations in the post-injection amount, the exhaust λ is achieved while adjusting the intake amount by the intake throttle valve 8 and suppressing the change in the bed temperature.

  In step S4003, it is determined whether the temperature of the DPF 13 is below the lower limit value T2 of the target temperature range. If not, the process proceeds to step S4004. When it is below, it progresses to step S4010 and increases post injection amount only by the unit injection amount according to a driving | running state. The unit injection amount here is set by the same method as in step S4011.

  In step S4004, the virtual cross-sectional area S2 of the DPF 13 is calculated using Expression (8) obtained by modifying the flow rate expression of the orifice, and this is compared with the cross-sectional area Sint of the DPF 13 in a state where PM is not deposited.

S2 = Q / (2 × ΔP / ρ) ^1/2 (8)
S2: Virtual cross-sectional area, Q: Gas flow rate, ΔP: DPF differential pressure before and after, ρ: Density As a result of comparison, if the virtual cross-sectional area S2 is equal to the cross-sectional area Sint, the process proceeds to step S4007.

  This is based on the assumption that the exhaust pressure, which has increased due to PM accumulation and the flow path being blocked, decreases as PM is burned and removed during regeneration, using the virtual cross-sectional area to regenerate. It is determined whether or not the process can be terminated.

  In step S4005, a speed dS2 / dt (degradation determination parameter) at which the virtual cross-sectional area S2 expands due to DPF regeneration is calculated, and this is set to a threshold value Vaged (degradation determination (Threshold). Since the exhaust pressure decreases (recovers) as the virtual sectional area S2 increases, the speed dS2 / dt at which the virtual sectional area S2 increases corresponds to the recovery speed of the exhaust pressure.

  Here, the speed obtained from the reaction kinetic calculation will be described.

FIG. 25 is a diagram showing the relationship between the PM deposition amount and the regeneration speed, and the regeneration speed increases as the PM deposition amount increases. FIG. 26 is a diagram showing the relationship between the O ₂ concentration and the reproduction speed. The higher the O ₂ concentration, the faster the reproduction speed. FIG. 27 is a diagram showing the relationship between the NO ₂ concentration and the regeneration speed. The higher the NO ₂ concentration, the faster the regeneration speed. FIG. 28 is a diagram showing the relationship between the temperature of the DPF and the regeneration speed. The regeneration speed increases as the DPF temperature increases. FIG. 29 is a diagram showing the relationship between the crystallinity of PM and the regeneration speed. The higher the crystallinity, the slower the regeneration speed. The crystallinity of PM affects the activation energy E.

  The frequency factor B depends on the form of PM deposition, but there is no significant change if the shape of the DPF 13 is the same.

As shown in FIGS. 25 to 29, the regeneration characteristics of the DPF 13 are not uniformly determined by the temperature of the DPF 13, but the environment in which regeneration such as PM deposition amount, O ₂ concentration, NO ₂ concentration, and PM crystallinity is performed. It will change depending on. That is, the oxidation reaction rate V can be expressed as in Equation (9).

V = Bexp (−E / RT) × [PM] [O ₂ ] [NO ₂ ] (9)
B: Frequency factor, E: Activation energy, [PM]: PM deposition amount, [O ₂ ]: O ₂ concentration, [NO ₂ ]: NO ₂ concentration The reaction rate V obtained by the equation (9) is the regeneration rate. In this case, the relationship between the regeneration speed and the exhaust pressure recovery speed is mapped as shown in FIG. Based on this, the exhaust pressure recovery speed in the case of an acceptable degree of deterioration is set as a threshold value Vaged for determining whether or not the catalyst has deteriorated. When the catalyst is deteriorated, the recovery of the exhaust pressure is delayed due to the PM combustion being delayed, so that the threshold value Vaged is lower than the exhaust pressure recovery rate with respect to the regeneration speed obtained from the reaction kinetics as shown by the broken line in FIG.

  Note that the exhaust pressure recovery speed with respect to the regeneration speed obtained from the reaction kinetics increases as the regeneration speed increases. This is because when the regeneration speed is faster, the accumulated PM is burned and removed earlier, and the flow path cross-sectional area of the DPF 13 increases faster.

  In this way, the threshold value Vaged set based on the regeneration rate obtained from the reaction kinetics is compared with the exhaust pressure recovery rate calculated based on the detection value. If the threshold value Vaged is larger, the catalyst is deteriorated. In step S4006, the deterioration flag Aged is set. If the threshold value Vaged is smaller, the process returns.

  As described above, it is possible to perform highly accurate deterioration determination by performing deterioration determination using a threshold value in consideration of the environment in which reproduction is performed.

  If the virtual sectional area S2 is equal to the sectional area Sint in step S4004, post-injection is stopped and heating of the DPF 13 is stopped in step 4007 to end the regeneration process.

  In step S4008, the reproduction mode flag reg is set to zero. In step S4009, the deterioration prevention mode flag rec is set and the process returns.

  FIG. 18 is a flowchart showing a control routine executed in the deterioration prevention mode.

  If the exhaust mode λ is suddenly increased after the regeneration mode is finished, if PM remains unburned in the DPF 13, the PM burns rapidly in the DPF 13, and the DPF 13 may be deteriorated by this combustion heat. The mode for preventing the deterioration due to the combustion heat is the deterioration preventing mode.

  In step S5001, the detection signal of the temperature sensor 21 is read and the bed temperature of the DPF 13 is detected.

  In step S5002, the exhaust λ is controlled to a predetermined value, for example, λ ≦ 1.4. As in step S4001 of FIG. 17, the control method may obtain the target intake air amount for realizing the target exhaust λ to control the opening degree of the intake throttle valve 8 or the output of the exhaust air / fuel ratio sensor 20. Based on the above, a predetermined exhaust λ may be realized by feedback control.

  In step S5003, it is determined whether the bed temperature of the DPF 13 is lower than a predetermined temperature T4. The temperature T4 is set to a temperature at which there is no possibility that sudden combustion of PM starts. If it is determined that the temperature is lower than T4, the process proceeds to step S5004, and if it is higher, the process returns.

  In step S5004, the λ control started in step S5002 is stopped. This is because if the temperature is lower than the temperature T4, it is possible to avoid the deterioration of the DPF 13 due to PM burning at a stroke even if the oxygen concentration becomes the level of the atmosphere.

  In step S5005, since the deterioration prevention mode has ended, the deterioration prevention mode flag rec is set to zero.

  As described above, in the present embodiment, the following effects can be obtained.

  (1) Deterioration determination of the catalyst carried on the DPF 13 is based on a deterioration determination parameter representing the degree of deterioration of the catalyst and a deterioration determination threshold value set based on the oxidation reaction rate of PM accumulated in the DPF 13. Therefore, it is possible to set an appropriate deterioration determination threshold according to the oxidation reaction rate of PM that varies depending on the environment in which regeneration is performed, and as a result, deterioration determination can be performed with high accuracy.

  (2) The parameter for deterioration determination is a value based on an oxidation reaction rate at the time of DPF regeneration of PM accumulated in the DPF 13, and the oxidation reaction rate is at least the temperature of the DPF 13, the amount of PM deposited in the DPF 13, Since the calculation is based on the oxygen concentration or the nitrogen dioxide concentration and the combustion characteristics of the PM accumulated in the DPF 13, it depends on the oxidation reaction rate of the PM that changes depending on the environment in which the temperature of the DPF 13 is regenerated. Appropriate deterioration determination parameters can be set.

  (4) When the combustion characteristics of the PM accumulated in the DPF 13 are high when the in-cylinder combustion temperature at the time of PM generation is high, the oxidation rate is slow and the oxidation temperature is estimated high. Therefore, it is possible to perform highly accurate deterioration determination in consideration of the combustion characteristics of

  (5) The combustion characteristics of PM accumulated in the DPF 13 is estimated based on the thermal history of the DPF 13 after PM collection, and the higher the temperature of the DPF 13, the slower the oxidation rate and the higher the oxidation temperature. The longer the maintenance time is, the slower the oxidation rate and the higher the oxidation temperature. Therefore, it is possible to make a highly accurate deterioration determination in consideration of the PM combustion characteristics that change depending on the thermal history received after being collected by the DPF 13.

  A second embodiment will be described.

  The configuration and control of this embodiment are basically the same as those of the first embodiment, but the method for determining the deterioration of the DPF 13 is different.

  A control routine for determining deterioration according to this embodiment will be described with reference to FIG. Steps S7001 to S7003 and S7007 to S7011 are the same as steps S4001 to S4003 and S4007 to S4011 in FIG.

  In step S7004, a temperature difference ΔDPF before and after the DPF 13 is detected as a deterioration determination parameter, and it is determined whether or not this is higher than a deterioration determination threshold Temp_aged. If it is low, it is determined that the battery has deteriorated, and the process advances to step S7005 to set the deterioration flag Aged. If so, the process proceeds to step S7006.

  The threshold value Temp_aged for deterioration determination is set as shown in FIG. 31 based on the reproduction speed obtained from the reaction kinetics, similarly to the threshold value Vaged of the virtual cross section enlargement speed shown in FIG. That is, the temperature difference before and after the DPF 13 due to PM combustion with respect to the regeneration rate obtained from the reaction kinetics is obtained, and based on this, the temperature difference in the case of an acceptable degree of deterioration is set as the determination threshold Temp_aged. When the catalyst is deteriorated, the amount of heat generated by the oxidation reaction is reduced, so that the threshold Temp_aged is smaller than the temperature difference with respect to the regeneration rate obtained from the reaction kinetics as shown in FIG.

  In step S7006, it is determined whether or not the time t1 from the start of reproduction exceeds the specified time t_dpf_reg. The specified time t_dpf_reg is a time during which the accumulated PM can be surely burned, and is set in advance based on the capacity of the DPF 13 or the like.

  If the specified time t_dpf_reg has been exceeded, the process proceeds to step S7007. If not, the process returns and the above steps are repeated.

  Incidentally, in step S7004, another determination method can be used. For example, the deterioration determination can also be performed by calculating the temperature of the DPF 13 (exothermic reaction expression temperature) when the temperature increase of the DPF 13 occurs during the regeneration process and comparing this with a threshold value for deterioration determination.

  That is, the temperature difference between the temperature sensor 22 and the temperature sensor 21 is monitored, and the detected temperature of the temperature sensor 22 when the detected temperature of the temperature sensor 21 exceeds the detected temperature of the temperature sensor 22 after the start of regeneration is the exothermic reaction expression temperature. To do. Then, as shown in FIG. 33, an exothermic reaction onset temperature (solid line in FIG. 33) with respect to the regeneration rate obtained from the reaction kinetics is obtained, and based on this, a threshold for deterioration determination is shown as a broken line in FIG. Set.

  When the catalyst is deteriorated, since the oxidation of PM does not start unless the temperature of the DPF 13 is raised to a higher temperature, the exothermic reaction expression temperature becomes higher than that when the catalyst is not deteriorated. Therefore, a threshold value for determining deterioration is set to a value higher than the exothermic reaction onset temperature for the regeneration rate obtained from the reaction kinetics.

  Further, when the deterioration determination is performed based on the exothermic reaction onset temperature, a difference in the exothermic reaction onset temperature can be detected with higher accuracy by providing a temperature sensor that directly detects the bed temperature of the DPF 13.

  As described above, in the present embodiment, the same effects as in the first embodiment can be obtained.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

It is a block diagram of the system of 1st Embodiment. It is a flowchart showing the control routine of 1st Embodiment. This is a subroutine for PM combustion characteristic discrimination and accumulation amount calculation. It is a driving | operation area | region map classified by the combustion characteristic of PM. It is a map for base oxidation temperature calculation. It is a figure for demonstrating the crystallinity raise of PM within DPF (the 1). It is a figure for demonstrating the crystallinity raise of PM within DPF (the 2). It is a crystallinity increase coefficient map. It is a map showing the relationship between a crystallite diameter and an operation area | region. It is a map showing the relationship between a space | interval and an operation area | region. It is a table for calculating the oxidation temperature correction coefficient according to the excess air ratio. It is a figure for demonstrating the relationship between an air excess rate and crystallinity. It is a table for calculating an oxidation temperature correction coefficient according to the EGR rate. It is an exhaust pressure threshold map. It is a flowchart showing the control routine for reproduction | regeneration temperature setting. It is a flowchart showing the control routine for reproduction | regeneration target temperature change. It is a flowchart showing the control routine for reproduction | regeneration control. It is a flowchart showing the control routine for deterioration prevention mode. It is a flowchart showing the control routine for setting a reproduction | regeneration request | requirement flag. It is a figure showing the relationship between the crystallinity of PM and the oxidation temperature, and the engine torque when not supporting a catalyst. It is a table for target regeneration temperature determination. It is a figure showing the relationship between DPF temperature and crystallinity. This is for calculating the target intake air amount map. It is a map for unit injection amount calculation of post injection. It is a figure showing the relationship between PM deposition amount and a reproduction speed. O ₂ concentration is a diagram representing the relationship between the playback speed. NO ₂ concentration is a diagram representing the relationship between the playback speed. It is a figure showing the relationship between the temperature of DPF, and the reproduction | regeneration speed. It is a figure showing the relationship between the crystallinity of PM and the reproduction | regeneration speed. It is a figure showing the relationship between the regeneration speed calculated | required from reaction kinetics, exhaust pressure recovery speed, and the threshold value for deterioration determination. It is a flowchart showing the control routine of 2nd Embodiment. It is a figure showing the relationship between the regeneration rate calculated | required from reaction kinetics, the temperature increase range by PM oxidation, and the threshold value for deterioration determination. It is a figure showing the relationship between the regeneration rate calculated | required from reaction kinetics, exothermic reaction expression temperature, and the threshold value for deterioration determination.

Explanation of symbols

1 Engine 2 Fuel Injection Valve 3 Fuel Injection Device (Common Rail Type Fuel Injection Device)
4 Intake Collector 5 Intake Passage 6 Variable Nozzle Turbocharger 7 Intercooler 8 Intake Throttle Valve 9 Control Unit 10 Exhaust Passage 11 Oxidation Catalyst 12 Exhaust Pressure Sensor (Downstream)
13 DPF
14 Transmission 15 EGR passage 16 EGR valve 17 Engine speed sensor 18 Accelerator opening sensor 19 Exhaust pressure sensor (upstream side)
20 Exhaust air / fuel ratio sensor 21 Temperature sensor (downstream)
22 Temperature sensor (upstream side)

Claims (10)

In an exhaust emission control device for a diesel engine provided with a DPF carrying a catalyst in an exhaust passage,
A deterioration determining means for determining deterioration of the catalyst;
The deterioration determination means is based on a deterioration determination parameter indicating a deterioration degree of the catalyst and a deterioration determination threshold set based on an oxidation reaction rate of PM accumulated in the DPF. An exhaust emission control device for a diesel engine, characterized in that   2. The exhaust emission control device for a diesel engine according to claim 1, wherein the parameter for deterioration determination is a value based on an oxidation reaction rate during regeneration of DPF of PM accumulated in the DPF.   The deterioration judging means deposits the oxidation reaction rate of the PM accumulated in the DPF at the time of DPF regeneration, at least the temperature of the DPF, the amount of PM accumulated in the DPF, the oxygen concentration or the nitrogen dioxide concentration, and the DPF. 3. An exhaust emission control device for a diesel engine according to claim 1, wherein the exhaust gas purification device is calculated on the basis of the combustion characteristics of PM.   The deterioration determining means calculates an exhaust pressure recovery rate during DPF regeneration as the deterioration determining parameter based on a detected value of exhaust pressure, and the deterioration determining threshold is a reaction rate of PM accumulated in the DPF. The exhaust pressure recovery rate calculated based on the oxidation reaction rate obtained from the theory is set to be lower, and it is determined that the catalyst is deteriorated when the deterioration determination parameter is lower than the deterioration determination threshold value. The exhaust emission control device for a diesel engine according to claim 2 or 3, characterized in that.   The deterioration determination means calculates a temperature increase range of the exhaust temperature at the time of DPF regeneration as the deterioration determination parameter based on the detected values of the upstream and downstream exhaust temperatures of the DPF, and sets the deterioration determination threshold as the deterioration determination parameter. The exhaust temperature increase range calculated based on the oxidation reaction rate obtained from the reaction kinetics of PM accumulated in the DPF is set smaller, and the deterioration determination parameter becomes smaller than the deterioration determination threshold value. The exhaust purification device for a diesel engine according to claim 2 or 3, characterized in that it is sometimes determined that the catalyst has deteriorated.   The degradation determination means uses an exothermic reaction expression temperature in the DPF at the time of DPF regeneration as the degradation determination parameter, and the oxidation reaction obtained from the reaction kinetics of the PM deposited in the DPF using the degradation determination threshold value. The temperature is set to be higher than the exothermic reaction expression temperature calculated based on the speed, and it is determined that the catalyst is deteriorated when the deterioration determination parameter is higher than the deterioration determination threshold. Item 4. The exhaust purification device for a diesel engine according to Item 2 or 3.   The exhaust gas purification apparatus for a diesel engine according to claim 6, wherein the deterioration determining means calculates the exothermic reaction expression temperature based on an exhaust temperature at the DPF inlet and an exhaust temperature at the DPF outlet.   The deterioration determining means indicates that the combustion characteristics of PM accumulated in the DPF is such that the smaller the value of the PM accumulation amount, oxygen concentration, or nitrogen dioxide concentration in the DPF, the slower the oxidation rate and the oxidation temperature. The diesel engine exhaust gas purification apparatus according to any one of claims 3 to 7, wherein the engine is estimated to be high.   The deterioration determining means estimates the combustion characteristics of PM accumulated in the DPF when the combustion temperature in the engine cylinder at the time of PM generation is high and the oxidation rate is slow and the oxidation temperature is high. Item 9. The exhaust emission control device for a diesel engine according to any one of Items 3 to 8.   The deterioration determining means estimates the combustion characteristics of PM accumulated in the DPF based on the thermal history of the DPF after collecting PM, and the higher the DPF temperature, the slower the oxidation rate and the oxidation temperature becomes. The exhaust purification device for a diesel engine according to any one of claims 3 to 9, wherein the oxidation rate is slower and the oxidation temperature is higher as the temperature is higher and the DPF temperature is maintained longer.

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