JP4123041B2 - Engine exhaust gas purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device for an engine, and more particularly, to control for NOx regeneration that releases NOx trapped by a NOx trap catalyst.
[0002]
[Prior art]
A NOx trap catalyst is known as an apparatus for removing nitrogen oxides (hereinafter referred to as “NOx”) in exhaust gas. The NOx trap catalyst traps NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, while releasing the trapped NOx when it turns rich. NOx is purified by the reducing agent component in the exhaust gas upon release. According to the NOx trap catalyst, when the air-fuel ratio of the engine is lean, NOx is removed from the exhaust gas, and when the NOx trap catalyst traps a certain amount of NOx, the air-fuel ratio is temporarily changed to rich, The trapped NOx can be released to recover its function. Note that the recovery of the function of the NOx trap catalyst by releasing the trapped NOx is called NOx regeneration.
[0003]
Here, the following methods are known as methods for determining the timing for performing NOx regeneration. The first is a method of accumulating the engine speed and setting the time when the value reaches a predetermined value as the time for performing NOx regeneration (Patent Document 1). The second is a method of calculating the cumulative mileage of the automobile, and setting the time when it reaches a predetermined distance as the timing for performing NOx regeneration (Patent Document 2).
[0004]
[Patent Document 1]
Japanese Patent No. 2600492 (column 12, lines 8-24)
[Patent Document 2]
JP 2002-201985 (paragraph number 0042)
[0005]
[Problems to be solved by the invention]
However, the method by simply comparing the rotational speed integrated value or the accumulated traveling distance with a predetermined value as described above has the following problems. That is, the amount of NOx discharged from the engine varies depending on the environment in which the engine is placed, such as altitude and temperature, even at the same rotation speed and vehicle speed. Therefore, the amount of NOx that is actually trapped by the NOx trap catalyst at the time when the rotational speed integrated value and the cumulative travel distance reach the respective threshold values differs depending on the environment in which the engine is placed. When NOx regeneration is performed in a state where the NOx trap catalyst traps an amount of NOx smaller than the set value, NOx regeneration is repeated unnecessarily, and fuel consumption is excessively deteriorated. On the other hand, when NOx regeneration is performed in a state where a larger amount of NOx than the set value is trapped, NOx exceeding the specified amount may be released into the atmosphere before NOx regeneration. This is because the NOx removal rate by the NOx trap catalyst decreases after the NOx trap catalyst traps a certain amount of NOx.
[0006]
Therefore, the present invention estimates the amount of NOx trapped by the NOx trap catalyst at the start of NOx regeneration, and reflects this in the control for NOx regeneration, thereby suppressing emissions and fuel consumption deterioration associated with NOx regeneration. The purpose is to do.
[0007]
[Means for Solving the Problems]
The present invention provides an engine exhaust gas purification device that includes a NOx trap catalyst installed in an exhaust passage.
[0008]
  The engine exhaust gas purifying apparatus according to the present invention removes NOx in the exhaust gas by trapping it in the NOx trap catalyst at the normal time when the air-fuel ratio of the exhaust gas becomes lean. On the other hand, during NOx regeneration in which NOx trapped by the NOx trap catalyst is released, the air-fuel ratio of the exhaust gas turns rich. The first time point when the concentration of oxygen or the reducing agent component in the exhaust gas upstream of the NOx trap catalyst changes and reaches a predetermined value is detected, and the oxygen or reduction in the exhaust gas downstream of the NOx trap catalyst is detected. The second time point at which the concentration of the agent component changes and reaches a predetermined value is detected, and the time from the first time point to the second time point (hereinafter referred to as “sensor output change time difference”) or during that time, the NOx trap catalyst Detected the amount of reducing agent component supplied toSensor output changetimeDifferenceIs the amount of reducing agent component suppliedOn the basis of theThe amount of NOx trapped by the NOx trap catalyst at the start of NOx regeneration (hereinafter referred to as “starting trap amount”).EstimateTo do.Here, in the present invention, the amount of NOx trapped by the NOx trap catalyst (hereinafter referred to as “NOx trap amount”) is estimated based on the operating state of the engine, and NOx regeneration is performed when this amount reaches a predetermined value. The predetermined value is changed to a smaller value as the estimated start trap amount is larger.
[0009]
  If you do this,Sensor output change time difference, etc.Estimated starting trap volume based onIs reflected in the control for NOx regeneration, the timing of NOx regeneration and the amount of the reducing agent component supplied during NOx regeneration can be optimized, and the deterioration of emissions and fuel consumption accompanying NOx regeneration can be suppressed.Specifically, the larger the estimated start trap amount is, the smaller the predetermined value related to the determination of the NOx regeneration timing is, and if the start trap amount is large, the predetermined value is set to a smaller value. The next NOx regeneration can be performed at an early stage to avoid a decrease in the NOx removal rate. On the other hand, when the start trap amount is small, the predetermined value is set to a large value, so that deterioration of fuel consumption due to unnecessary repetition of NOx regeneration can be prevented.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a configuration diagram of an automotive diesel engine (hereinafter referred to as “engine”) 1 according to an embodiment of the present invention.
[0011]
An air cleaner (not shown) is attached to the introduction portion of the intake passage 11, and dust in the intake air is removed by the air cleaner. A compressor 12a of a variable nozzle turbocharger 12 is interposed in the intake passage 11, and the intake air is compressed and sent out by the compressor 12a. An intercooler 13 is installed downstream of the compressor 12a, and the intake air compressed by the intercooler 13 is cooled. The intake air that has passed through the intercooler 13 flows into the surge tank 14 and is distributed to each cylinder in the manifold portion. An intake throttle valve 15 is installed upstream of the surge tank 14. The intake throttle valve 15 is connected to an actuator 15a that operates in response to a signal from an electronic control unit (hereinafter referred to as "ECU") 41, which will be described later, and the opening degree is controlled by the actuator 15a.
[0012]
In the engine body, the cylinder head is provided with an injector 21 for each cylinder. The injector 21 operates in response to a signal from the ECU 41. Fuel delivered by a fuel pump (not shown) is supplied to the injector 21 via the common rail 22 and is injected into the combustion chamber by the injector 21. Injection by the injector 21 is performed in a plurality of times. The injector 21 performs main injection for generating power and post-injection after main injection. The exhaust gas temperature rises due to the post injection.
[0013]
In the exhaust passage 31, a turbine 12b of the variable nozzle turbocharger 12 is installed downstream of the manifold portion. When the turbine 12b is driven by the exhaust gas, the compressor 12a rotates. The movable vane 121 of the turbine 12b is connected to the actuator 121a, and the angle is controlled by the actuator 121a. An oxidation catalyst 32, a NOx trap catalyst 33, and a diesel particulate filter 34 are installed in this order from the upstream side downstream of the turbine 12b. The oxidation catalyst 32 purifies hydrocarbons (hereinafter referred to as “HC”) and carbon monoxide (hereinafter referred to as “CO”) in the exhaust gas. The NOx trap catalyst 33 has different properties according to the air-fuel ratio of the exhaust gas, and traps NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is lean, while trapping when the exhaust gas is rich. Releases NOx. NOx is purified by reducing agent components such as HC and CO contained in the exhaust gas when released. The NOx trap catalyst 33 traps sulfur contained in the exhaust gas in addition to NOx. The diesel particulate filter 34 includes a porous filter element made of ceramic or the like. The exhaust gas is filtered by the filter element, and the particulates in the exhaust gas are removed. The exhaust passage 31 and the intake passage 11 are connected by an EGR pipe 35, and an EGR valve 36 is installed in the EGR pipe 35. The EGR valve 36 is connected to an actuator 36a, and the opening degree is controlled by the actuator 36a.
[0014]
In the exhaust passage 31, an upstream air-fuel ratio sensor 51 serving as a first exhaust gas sensor is disposed upstream of the oxidation catalyst 32, and a downstream side serving as a second exhaust gas sensor is disposed between the NOx trap catalyst 33 and the diesel particulate filter 34. An air-fuel ratio sensor 52, a pressure sensor 53 for detecting the exhaust gas pressure Texh, a temperature sensor 54 for detecting the catalyst bed temperature Tnox for the NOx trap catalyst 33, and a filter bed temperature Tdpf for the diesel particulate filter 34 A temperature sensor 55 for detection is installed. A crank angle sensor 56 and an accelerator sensor 57 are provided. The output of each sensor is input to the ECU 41. The ECU 41 calculates the engine speed Ne based on the output of the crank angle sensor 55 and calculates the accelerator opening APO based on the output of the accelerator sensor 56.
[0015]
Hereinafter, the operation of the ECU 41 will be described with reference to a flowchart.
FIG. 2 shows a flowchart of a routine for selecting the reproduction mode.
In S1, the engine speed Ne and the accelerator opening APO are read as the operating state. In S2, the amount of NOx trapped by the NOx trap catalyst 33 (hereinafter referred to as “NOx trap amount”) NOX is calculated. The NOx trap amount NOX is estimated as an integrated value of the engine speed Ne from the time of shipment or when the NOx regeneration performed last time is completed. The NOx trap amount NOX can be calculated by the following equation (1), for example, assuming that the NOx trap amount calculated when this routine was executed last time is NOXn-1 and the execution cycle of this routine is Δt. The NOx trap amount NOX can be estimated based not only on the engine speed Ne but also on the travel distance. In this case, a predetermined amount may be added to the NOx trap amount NOX every time the vehicle travels a certain distance.
[0016]
NOX = NOXn−1 + Ne × Δt (1)
In S3, the amount of sulfur content trapped by the NOx trap catalyst 33 (hereinafter referred to as “sulfur content trap amount”) SOX is calculated. The sulfur trap amount SOX can be estimated as an integrated value of the engine speed Ne, similarly to the NOx trap amount NOX. The sulfur content trapped by the NOx trap catalyst 33 needs to be periodically released, and the ECU 41 performs control for that purpose as will be described later. Release of the sulfur content trapped by the NOx trap catalyst 33 is called poisoning release. In the calculation of the sulfur trap amount SOX, the starting point of the integration of the engine speed Ne is the time when shipping or the previous poisoning release is completed.
[0017]
In S4, the amount PM of particulates deposited on the diesel particulate filter 34 (hereinafter referred to as “particulate deposition amount”) PM is calculated. The particulate accumulation amount PM is estimated based on the exhaust gas pressure Pexh as a larger value as the exhaust gas pressure Pexh is higher. Since the amount of particulate discharged from the engine 1 correlates with the operating state at that time, the particulate accumulation amount PM is calculated by calculating the amount of discharge per unit time based on the engine speed Ne and the travel distance. These can be integrated and estimated.
[0018]
In S5, it is determined whether or not DPF regeneration is being performed based on the flag Freg. Incineration of particulates deposited on the diesel particulate filter 34 is called DPF regeneration. When the flag Freg is 0, the process proceeds to S6, and when it is not 0, the process proceeds to S101 in the flowchart shown in FIG. 4 to perform control for DPF regeneration.
[0019]
In S6, it is determined by the flag Fdesul whether or not the poisoning is being released. When the flag Fdesul is 0, the process proceeds to S7. When the flag Fdesul is not 0, the process proceeds to S201 in the flowchart shown in FIG.
[0020]
In S7, it is determined whether or not NOx regeneration is being performed based on the flag Fsp. When the flag Fsp is 0, the process proceeds to S8. When the flag Fsp is not 0, the process proceeds to S301a in the flowchart shown in FIG. 9, and control for NOx regeneration is performed.
[0021]
In S8, it is determined whether or not failure avoidance is being performed based on the flag Frec. The flag Frec is changed from 0 to 1 in a routine for performing DPF regeneration or poisoning cancellation to be described later. When the flag Frec is 0, the process proceeds to S9, and when it is not 0, the process proceeds to S401 in the flowchart of FIG. 11 to perform control for failure avoidance.
[0022]
In S9, it is determined whether or not the particulate accumulation amount PM has reached the specified amount PM1. When PM1 has not been reached, the process proceeds to S10, and when PM1 has been reached, the process proceeds to S501 in the flowchart shown in FIG. Whether the particulate accumulation amount PM has reached the specified amount PM1 is determined by comparing the exhaust gas pressure Pexh with a predetermined value Pexh1. The map shown in FIG. 3 is searched by the engine speed Ne and the fuel injection amount Qm by main injection, and a predetermined value Pexh1 is set. It is assumed that when the exhaust gas pressure Pexh reaches a predetermined value Pexh1, the particulate deposition amount PM has reached a specified amount PM1. Further, in order to prevent the DPF regeneration from being repeated unnecessarily, it is possible to calculate the cumulative travel distance since the last DPF regeneration was completed and assume that this has reached a predetermined value.
[0023]
In S10, it is determined whether or not the sulfur trap amount SOX has reached the specified amount SOX1. When SOX1 has not been reached, the process proceeds to S11. When SOX1 has been reached, the process proceeds to S601 in the flowchart shown in FIG.
[0024]
In S11, it is determined whether or not the NOx trap amount NOX has reached the specified amount NOX1. When NOX1 has not been reached, this routine is returned, and when NOX1 has been reached, the routine proceeds to S701 in the flowchart shown in FIG.
[0025]
FIG. 4 shows a flowchart of a routine for performing control for DPF regeneration.
In DPF regeneration, post-injection is performed by the injector 21 to raise the exhaust gas temperature. As a result, the filter bed temperature Tdpf rises to a temperature at which the particulates can be incinerated.
[0026]
In S101, the filter bed temperature Tdpf is read. In S102, the excess air ratio λ of the exhaust gas is controlled to the target excess air ratio tλreg corresponding to the particulate accumulation amount PM. The excess air ratio λ is controlled by operating the intake throttle valve 15. The ECU 41 searches the table shown in FIG. 5 based on the particulate accumulation amount PM, and sets the target excess air ratio tλreg during DPF regeneration. The target excess air ratio tλreg is set to a smaller value as the particulate accumulation amount PM is larger. When controlling the excess air ratio λ, the ECU 41 searches the map shown in FIG. 6 based on the engine speed Ne and the fuel injection amount Qm, and calculates a target intake air amount tQa that gives an excess air ratio corresponding to stoichiometry. The target excess air rate tλreg and the target intake air amount tQa are integrated to set the target intake air amount tQareg during DPF regeneration.
[0027]
In S103, it is determined whether or not the filter bed temperature Tdpf is equal to or higher than the lower limit value Tdpf1. When it is equal to or greater than Tdpf1, the process proceeds to S105, and when it is less than Tdpf1, the process proceeds to S104. In S104, the post injection amount is increased and the exhaust gas temperature is increased. The ECU 41 searches the map shown in FIG. 7 based on the engine speed Ne and the fuel injection amount Qm, sets a post injection amount correction value ΔPOST, and adds this to the post injection amount. When the post injection amount changes, the excess air ratio λ of the exhaust gas changes and deviates from the target excess air ratio tλreg. The ECU 41 operates the intake throttle valve 15 to adjust the excess air ratio λ, and suppresses the change in the filter bed temperature Tdpf.
[0028]
In S105, it is determined whether the filter bed temperature Tdpf is equal to or lower than the upper limit value Tdpf2. When it is equal to or lower than Tdpf2, the process proceeds to S107, and when higher than Tdpf2, the process proceeds to S106. In S106, the post injection amount correction value ΔPOST is set as described above, and is subtracted from the post injection amount to lower the exhaust gas temperature.
[0029]
In S107, it is determined whether or not a predetermined time tdpf1 has elapsed after the post injection with the injection amount corrected in S104 or S106. When tdpf1 has elapsed, the process proceeds to S108, and when tdpf1 has not elapsed, this routine is returned. Particulates are incinerated between the time when post injection is performed and the time tdpf1 has elapsed. In S108, it is determined that the DPF regeneration has ended, the post injection amount is set to 0, and the exhaust gas temperature is returned to the normal temperature. In S109, the flag Freg is set to 0. In S110, the flag Frec is set to 1, and control for avoiding a failure of the diesel particulate filter 34 is performed. When there is unburned residue in the particulate, assuming that the excess air ratio λ is immediately restored to the normal value, the unburned residue burns rapidly, and an excessive heat load is applied to the diesel particulate filter 34, and the filter element This is because there is a risk of cracking.
[0030]
FIG. 8 shows a flowchart of a routine for performing control for releasing poisoning.
In S201, the catalyst bed temperature Tnox is read. In S202, the excess air ratio λ of the exhaust gas is stoichiometrically controlled. The excess air ratio λ is controlled by operating the intake throttle valve 15. The ECU 41 searches the map shown in FIG. 6, sets a target intake air amount tQa that gives an excess air ratio corresponding to stoichiometry, and controls the intake throttle valve 15 to achieve this.
[0031]
In S203, it is determined whether or not the catalyst bed temperature Tnox is equal to or higher than a predetermined value Tnox1. In order to detoxify the NOx trap catalyst 33, not only the reducing agent component in the exhaust gas is increased and a stoichiometric or rich atmosphere is formed, but also the NOx trap catalyst 33 is heated to promote decomposition of the sulfur content. There is a need. The NOx trap catalyst 33 using, for example, a Ba-based catalyst component is heated to a temperature of 600 ° C. or higher. When the catalyst bed temperature Tnox is equal to or higher than Tno1, the process proceeds to S205, and when it is lower than Tnox, the process proceeds to S204.
[0032]
In S204, post-injection is performed by the injector 21 to increase the exhaust gas temperature. Although the excess air ratio λ changes due to the post injection, the ECU 41 operates the intake throttle valve 15 and adjusts the intake air amount to compensate for this deviation.
[0033]
In S205, it is determined whether or not a predetermined time tdesul1 has elapsed after the post injection. When tdesul1 has elapsed, the process proceeds to S206, and when tdesul1 has not elapsed, this routine is returned. Sulfur content is decomposed and released from the execution of post injection until a predetermined time tdesul1 elapses. The sulfur content is purified by the reducing agent component in the exhaust gas when released. In S206, it is determined that the poisoning release has been completed, and the excess air ratio λ is returned to the normal value. In S207, the flag Frec is set to 1. Assuming that the excess air ratio λ is immediately restored to a normal value at a high temperature when the poisoning release is completed, the particulates accumulated in the diesel particulate filter 34 are rapidly burned, and the diesel particulate filter 34 This is because an excessive heat load may be applied. In S208, flags Fdesul and Fsp are set to 0. In S209, the sulfur trap amount SOX and the NOx trap amount NOX are set to zero. This is because when the excess air ratio λ is stoichiometrically controlled by releasing the poisoning, NOx is also released together with the sulfur content, and NOx regeneration is simultaneously performed.
[0034]
  FIG. 9 shows a flowchart of a routine for performing control for NOx regeneration.
  In S301a, the excess air ratio λ is controlled to a target excess air ratio tλsp (for example, tλsp = 0.9 indicating rich) set in advance for NOx regeneration. The excess air ratio λ is controlled by feeding back the output from the upstream air-fuel ratio sensor 51 (hereinafter referred to as “upstream sensor output”) LAMB1. In S302a, the upstream sensor output LAMB1 and the downstream air-fuel ratio sensor 52 output (hereinafter referred to as “downstream sensor output”) LAMB2 are read. In S303a, a first time point at which the upstream sensor output LAMB1 reaches the predetermined value LAMBsl is detected, and a second time point at which the downstream sensor output LAMB2 reaches the predetermined value LAMBsl is detected. When the first time point and the second time point are detected, the time between the two time points is calculated and stored as a sensor output change time difference ΔTn. Each of the sensor outputs LAMB1 and LAMB2 reaches a predetermined value LAMBsl when the excess air ratio λ of the exhaust gas at the sensor installation portion becomes 1.In S304a, the table shown in FIG. 16 is searched based on the sensor output change time difference ΔTn, and a predetermined value NOX1 (S11 in the flowchart shown in FIG. 2) regarding NOx regeneration timing determination is calculated. The predetermined value NOX1 is calculated as a smaller value as ΔTn is longer.S305In a, the sensor output change time difference ΔTn−1 calculated when this routine was executed last time is read, and based on this, the period during which the air-fuel ratio is controlled to be rich (hereinafter referred to as “rich spike period”) tspike1 correction value tx is calculated. The correction value tx is calculated as a larger value as ΔTn−1 is longer by searching the map shown in FIG. 10 based on the sensor output change time difference ΔTn−1. S306In a, the correction value tx is added to the basic value of the rich spike period tspike1 to set tspike1 (= tspike1 + tx). S307In a, after the NOx regeneration is started, it is determined whether or not the rich spike period tspike1 has elapsed. When tspike1 has elapsed, S308Proceed to a. If tspike1 has not elapsed, this routine is returned. The NOx trapped until the rich spike period tspike1 elapses is decomposed and released from the NOx trap catalyst 33. NOx is purified by the reducing agent component in the exhaust gas when released. S308In a, it is determined that NOx regeneration has ended, the flag Fsp is set to 0, and the excess air ratio λ is returned to the normal value. S309In a, the NOx trap amount NOX is set to zero.
[0035]
  Thus, the NOx regeneration can be started at the optimum time by calculating the sensor output change time difference ΔTn and changing the predetermined value NOX1 relating to the determination of the NOx regeneration time based on this. The sensor output change time difference ΔTn changes according to the trap amount at the start. When this is long, a large amount of NOx is trapped before the start of the NOx regeneration, and the NOx trap catalyst 33 before the NOx regeneration starts. There is a possibility that the NOx removal rate is lowered. When the sensor output change time difference ΔTn is long, by changing the predetermined value NOX1 to a small value, the next NOx regeneration can be started early, that is, while the NOx removal rate is kept good. it can. On the other hand, when the sensor output change time difference ΔTn is short, the amount of NOx trapped before NOx regeneration is small. Therefore, by changing the predetermined value NOX1 to a large value, fuel consumption deterioration due to unnecessary repetition of NOx regeneration is prevented. be able to.
  Also, Sensor output change time difference ΔTnBased on the change of the rich spike period tspike1, the amount of the reducing agent component supplied to the NOx trap catalyst 33 during the NOx regeneration can be optimized. Sensor output change time difference ΔTn isOpenInitial trapamount,That is, it changes depending on the amount of NOx to be reduced during NOx regeneration. When the sensor output change time difference ΔTn is long, the amount of trap at the start is large and the amount of NOx to be reduced is large. Therefore, by extending the rich spike period tspike1, the regeneration failure due to the insufficient amount of the reducing agent component Occurrence can be prevented. On the other hand, when the sensor output change time difference ΔTn is short, the trap amount at the start is small and the amount of NOx to be reduced is small. Therefore, by reducing the rich spike period tspike1, an excessive amount of reducing agent component is supplied. It is possible to suppress the emission and the deterioration of fuel consumption.
[0036]
FIG. 11 shows a flowchart of a routine for performing control for failure avoidance.
In S401, the filter bed temperature Tdpf is read. In S402, the diesel particulate filter 34 is at a high temperature and the excess air ratio λ of the exhaust gas is controlled to the target excess air ratio tλrec at the time of failure avoidance in order to prevent the unburned particulates from burning rapidly. The target excess air ratio tλrec is rich and is set to a value of 1.4 or less. The ECU 41 searches the map shown in FIG. 12 based on the engine speed Ne and the fuel injection amount Qm, sets the target intake air amount tQa, and feeds back the upstream sensor output LAMB1 to achieve the target excess air ratio tλrec. To do.
[0037]
In S403, it is determined whether or not the filter bed temperature Tdpf is equal to or lower than a predetermined temperature Tdpf3. When it is equal to or lower than Tdpf3, the process proceeds to S404, and when it is higher than Tdpf, this routine is returned. In S404, it is determined that the risk that the unburned particulates will burn rapidly has been canceled, and the excess air ratio λ is returned to the normal value. In S405, the flag Frec is set to 0.
[0038]
FIG. 13 is a flowchart of a routine for setting the flag Freg. In S501, since the particulate accumulation amount PM has reached the specified amount PM1, the flag Freg is set to 1 in order to perform DPF regeneration.
[0039]
FIG. 14 is a flowchart of a routine for setting the flag Fdesul. In S601, since the sulfur trap amount SOX has reached the specified amount SOX1, the flag Fdesul is set to 1 in order to cancel the poisoning.
[0040]
FIG. 15 is a flowchart of a routine for setting the flag Fsp. In S701, since the NOx trap amount NOX has reached the specified amount NOX1, the flag Fsp is set to 1 in order to perform NOx regeneration.
[0041]
  Regarding this embodiment, S2 and S11 in the flowchart shown in FIG.as well asFIG.S304a of the flowchart shown in FIG.Constitutes a reproduction time determination means. Further, S301a to S301 in the flowchart shown in FIG.7a(Excluding S304a)Constitutes a catalyst regeneration means.
[0042]
  Hereinafter, another embodiment of the present invention will be described.
[0046]
  FIG.7The second27 shows a flowchart of a routine for performing control for NOx regeneration according to the embodiment.
  S301bThen, the sensor output change time difference ΔTn−1 calculated when this routine was executed last time is used to obtain FIG.8And the target excess air ratio tλsp during NOx regeneration is set. The target excess air ratio tλsp is set to a smaller value as ΔTn−1 is longer as a value indicating richness. S302bThen, the upstream sensor output LAMB1 is fed back to control the excess air ratio λ to the target excess air ratio tλsp. S303bThen, the upstream sensor output LAMB1 and the downstream sensor output LAMB2 are read. S304bThen, based on the read LAMB1 and LAMB2, the sensor output change time difference ΔTn is calculated and stored.In S305b, the table shown in FIG. 16 is searched based on the sensor output change time difference ΔTn, and a predetermined value NOX1 (S11 in the flowchart shown in FIG. 2) regarding NOx regeneration timing determination is calculated.S306bThen, after the NOx regeneration is started, it is determined whether or not the rich spike period tspike1 has elapsed. When tspike1 has elapsed, S307bIf tspike1 has not elapsed, this routine is returned. S307bThen, the flag Fsp is set to 0. S308bThen, the NOx trap amount NOX is set to zero.
[0047]
Thus, by calculating the sensor output change time difference ΔTn and changing the target excess air ratio tλsp during NOx regeneration based on this, the amount of reducing agent component supplied to the NOx trap catalyst 33 during NOx regeneration is optimized. Can be The sensor output change time difference ΔTn changes according to the start trap amount. When this is long, the start trap amount is large, and the amount of NOx to be reduced during NOx regeneration is large. When the sensor output change time difference ΔTn is long, it is possible to prevent the amount of the reducing agent component from being insufficient by setting the target excess air ratio tλsp to a small value. On the other hand, when the sensor output change time difference ΔTn is short, the trap amount at the start is small and the amount of NOx to be reduced is small. Therefore, by setting the target excess air ratio tλsp to a large value, an excessive amount of reducing agent component Can be prevented from being supplied.
[0048]
  Regarding this embodiment, S2 and S11 in the flowchart shown in FIG.as well asFIG.S305b of the flowchart shown inConstitutes a reproduction time determination means. In addition, FIG.7S301 in the flowchart shown in FIG.b~ 306b (excluding S305b)Constitutes a catalyst regeneration means.
[0049]
In the above description, the sensor output change time difference ΔTn is reflected in the control for NOx regeneration on the assumption that the sensor output change time difference ΔTn is proportional to the NOx trap amount at the start of NOx regeneration. explained. The present invention is not limited to this, and can also be applied when the sensor output change time difference ΔTn is not proportional to the start trap amount. When the amount of the reducing agent component supplied to the NOx trap catalyst 33 varies with time, the upstream sensor output LAMB1 reaches the predetermined value LAMBsl until the downstream sensor output LAMB2 reaches the predetermined value LAMBsl. In the meantime, the amount of the reducing agent component supplied to the NOx trap catalyst 33 is reflected. The amount of the reducing agent component supplied can be calculated as the integrated value of the difference with respect to the target equivalent ratio 1 / tλsp or its reference value at the time of NOx regeneration.
[0050]
In addition to the air-fuel ratio sensor, a general oxygen sensor or an excess air ratio sensor can be adopted as the first and second exhaust gas sensors.
[Brief description of the drawings]
FIG. 1 is a configuration of a diesel engine according to an embodiment of the present invention.
FIG. 2 is a flowchart of a playback mode determination routine.
FIG. 3 DPF regeneration timing judgment value setting map
FIG. 4 is a flowchart of a DPF regeneration routine.
FIG. 5 DPF regeneration target air excess ratio setting table
FIG. 6 is a stoichiometric equivalent target intake air amount setting map.
[Fig. 7] Post injection amount correction value setting map
FIG. 8 is a flowchart of a poisoning release routine.
FIG. 9 is a flowchart of a NOx regeneration routine.
FIG. 10 is a rich spike period correction value setting table.
FIG. 11 is a flowchart of a failure avoidance routine.
FIG. 12: Target intake air amount setting map for failure avoidance
FIG. 13 is a flowchart of a DPF regeneration flag setting routine.
FIG. 14 is a flowchart of a poisoning release flag setting routine.
FIG. 15 is a flowchart of a NOx regeneration flag setting routine.
FIG. 16NOx regeneration time judgment value setting table
FIG. 17Flowchart of NOx regeneration routine according to another embodiment of the present invention
FIG. 18NOx regeneration target air excess ratio setting table
[Explanation of symbols]
  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 11 ... Intake passage, 12 ... Variable nozzle turbocharger, 13 ... Intercooler, 14 ... Surge tank, 15 ... Intake throttle valve, 21 ... Injector, 31 ... Exhaust passage, 32 ... Oxidation catalyst, 33 ... NOx Trap catalyst, 34 ... diesel particulate filter, 35 ... EGR pipe, 36 ... EGR valve, 41 ... electronic control unit, 51 ... upstream air-fuel ratio sensor, 52 ... downstream air-fuel ratio sensor, 53 ... exhaust gas pressure sensor, 54 ... Catalyst bed temperature sensor, 55 ... Filter bed temperature sensor.

Claims (7)

NOx in the exhaust gas is trapped when the air-fuel ratio of the exhaust gas flowing into the engine is lean and the air-fuel ratio of the exhaust gas flowing in is lean, while the NOx trapped when the air-fuel ratio of the exhaust gas flowing in is rich A NOx trap catalyst for reduction and release;
A first exhaust gas sensor installed upstream of the NOx trap catalyst and outputting a signal corresponding to the concentration of oxygen or a reducing agent component in the exhaust gas;
A second exhaust gas sensor installed downstream of the NOx trap catalyst and outputting a signal corresponding to the concentration of oxygen or a reducing agent component in the exhaust gas;
And determining regeneration timing determining means for determining whether or not leading to time to thereby release the NOx that the trap performs NOx regeneration for regenerating the NOx trap catalyst,
Increasing amounts of the reducing agent components in the exhaust gas is configured to include a, a catalyst regeneration means for performing the NOx regeneration,
The catalyst regeneration means includes
After increasing the amount of reducing agent components in the exhaust gas for the NOx regeneration, and detects the first time when the output of said first exhaust gas sensor reaches a predetermined value is changed, the second Detecting a second time point when the output of the exhaust gas sensor changes and reaches a predetermined value;
The sensor output change time difference that is the time from the first time point to the second time point or the amount of the reducing agent component increased during that time is detected, and based on the detected sensor output change time difference or the increased amount of the reducing agent component. the NOx trap catalyst at the start of the NOx regeneration estimates the amount of NOx that the trap as start trap amount Te,
The regeneration time determining means is
The NOx trap amount, which is the amount of NOx trapped by the NOx trap catalyst, is estimated based on the operating state of the engine, and when it reaches a predetermined value, it is determined that the timing for performing the NOx regeneration has come. The engine exhaust gas purification apparatus changes the predetermined value related to the determination of the timing for performing the NOx regeneration to a smaller value as the start trap amount estimated by the catalyst regeneration means is larger . The catalyst regeneration means, the exhaust gas of an engine according to claim 1 for estimating whether the detected sensor output change time difference is long, or the start time of the trap quantity smaller the amount of reducing agent component which is increased many as a larger value Purification equipment. The engine exhaust gas purification device according to claim 1 or 2 , wherein the catalyst regeneration means changes the amount of the reducing agent component to be increased in accordance with the estimated starting trap amount. The catalyst regeneration means is a rich spike period in which the air-fuel ratio is controlled to be rich according to the estimated start trap amount when the air-fuel ratio of the engine is controlled to be rich and the amount of the reducing agent component in the exhaust gas is increased. 4. The engine exhaust gas purifying apparatus according to claim 3 , wherein a reduction amount of the air-fuel ratio in the meantime is changed. The catalyst regeneration means, the more time is often at the start trap amount estimated by extending the rich spike time period or an exhaust gas purification device for an engine according to claim 4 for enlarging the reduced cost of the air-fuel ratio. The engine exhaust gas purification device according to any one of claims 1 to 5 , wherein the first and second exhaust gas sensors are oxygen sensors, excess air ratio sensors, or air-fuel ratio sensors. The outputs of the first and second exhaust gas sensors, claim the air-fuel ratio of the exhaust gas reaches a predetermined value for a given value or detection of the second point relates to the detection of the first point in time when a stoichiometric 1 The exhaust gas purifying device for an engine according to any one of to 6 .

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