JP2005048751A - Engine control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise exhaust gas temperature and reduce exhaust gas air fuel ratio under a condition of suppressing generation of smoke at a time of regeneration of a NOx trap catalyst or the like. <P>SOLUTION: Precombustion for forming predetermined heat release is made to occur before main combustion for generating engine torque during regeneration. Precombustion is made to occur in proximity of a top dead center by a first fuel injection and main combustion is made to occur later than normal time and after completion of precombustion by a second fuel injection. When excess air ratio is changed together with exhaust gas temperature under such combustion form, timing of the second fuel injection ITm is changed according to change of excess air ratio. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an engine control device, and more particularly, in an engine equipped with an exhaust purification device such as a NOx trap catalyst or a particulate filter, in accordance with the state of the exhaust purification device, excessive air in a state in which the generation of smoke is suppressed. The present invention relates to a technique for decreasing the rate and increasing the exhaust temperature.

  In a diesel engine having a catalyst in the exhaust passage, the following techniques are known as techniques for increasing the exhaust temperature in order to promote the activity of the catalyst. That is, the basic fuel injection amount for generating the required engine torque is calculated according to the operating state of the engine, and the amount of fuel corresponding to the calculated basic fuel injection amount is divided into multiple times near the top dead center. (Patent Document 1).

In addition, a NOx trap catalyst is known as an apparatus for treating nitrogen oxide (hereinafter referred to as “NOx”) in exhaust gas. The NOx trap catalyst has a property of trapping NOx under an oxidizing atmosphere and releasing NOx trapped under a reducing atmosphere. The NOx trap catalyst traps sulfur contained in the exhaust gas in addition to NOx under an oxidizing atmosphere. In order to release the trapped NOx or sulfur content and regenerate the NOx trap catalyst, it is known to reduce the excess air ratio and lower the exhaust air-fuel ratio. When releasing the sulfur content from the NOx trap catalyst, it is common to raise the exhaust temperature in order to not only lower the exhaust air-fuel ratio but also promote the decomposition of the sulfur content.
JP 2000-320386 A (paragraph numbers 0106 to 0111)

  However, the above-described divided injection technique has the following problems. In this technique, the subsequent fuel is injected into the flame of the previously injected fuel so that the combustion of each of the divided injected fuels is not interrupted. The combustion of the produced fuel is mainly diffusion combustion. For this reason, although the exhaust temperature can be raised, the excess air ratio cannot be lowered from the viewpoint of smoke emission suppression, and it cannot be applied to regeneration of a NOx trap catalyst that requires a reduction in the exhaust air-fuel ratio. .

  An object of the present invention is to provide an engine control device that can increase the exhaust temperature while suppressing the generation of smoke, lower the exhaust air-fuel ratio, and regenerate the exhaust purification device such as a NOx trap catalyst. And

  The present invention provides an engine control apparatus. The apparatus according to the present invention switches the combustion mode between the normal time and the exhaust gas temperature raising time when the exhaust gas temperature is raised to a higher temperature than the normal time. When the exhaust gas temperature rises due to combustion, the operation is performed by split retard combustion as the second combustion mode. In normal combustion, combustion for generating engine torque is performed at a time relatively close to top dead center, and in divided retard combustion, main combustion as combustion for generating engine torque and predetermined before main combustion are performed. Pre-combustion to form the heat generation of the main combustion is performed at or near top dead center, while the main combustion is slower than the corresponding combustion of the normal combustion and the pre-combustion is finished I will do it later. Further, when the exhaust temperature is changed during the operation by split retard combustion and the excess air ratio is changed accordingly, the timing for performing the main combustion is changed according to the change of the excess air ratio.

  According to the present invention, it is possible to raise the exhaust gas temperature by setting the combustion mode to split retard combustion and performing the main combustion at a time later than the corresponding combustion at the normal time. Here, the main combustion is delayed, but is stably performed because the in-cylinder temperature rises due to the heat generated by the preliminary combustion. By allowing the main combustion to be performed after the pre-combustion is completed, it is possible to allow time between each combustion and promote premixing of fuel that contributes to the main combustion. Occurrence can be suppressed. In addition, when changing the excess air ratio together with the exhaust temperature during operation by split retard combustion, the exhaust temperature and the excess air ratio can be changed by changing the timing for performing the main combustion according to the change in the excess air ratio. The target value can be changed efficiently.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the configuration of an automotive diesel engine (hereinafter referred to as “engine”) 1 according to an embodiment of the present invention.
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 further flows into the surge tank 14 and is distributed to each cylinder at 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 151, and the opening degree is controlled by the actuator 151.

  In the engine body, the cylinder head is provided with an injector 21 for each cylinder. Fuel delivered by a fuel pump (not shown) is supplied to the injector 21 through the common rail 22 and is directly injected into the combustion chamber by the injector 21. The injector 21 injects the fuel into a plurality of times. Normal fuel injection by the injector 21 includes main injection for generating engine torque and pilot injection that is advanced from the main injection.

  A turbocharger turbine 12b is interposed in the exhaust passage 31 downstream of the manifold portion. When the turbine 12b is driven by the exhaust, the compressor 12a rotates. The turbine movable vane 121 is connected to an actuator 122, and the angle is controlled by the actuator 122. A NOx trap catalyst 32 is installed downstream of the turbine 12b, and a diesel particulate filter 33 is installed downstream thereof. The NOx trap catalyst 32 functions differently depending on the exhaust air-fuel ratio, and traps NOx in the exhaust when the exhaust is lean, while releasing the trapped NOx when the exhaust is rich. NOx is purified by a reducing agent such as hydrocarbon (hereinafter referred to as “HC”) in the exhaust gas when released. The NOx trap catalyst 32 traps sulfur contained in the exhaust gas in addition to NOx. The NOx trap catalyst 32 has a function of oxidizing HC and carbon monoxide (hereinafter referred to as “CO”) in the exhaust gas in addition to such a NOx treatment function. The diesel particulate filter 33 includes a porous filter element made of ceramic or the like. The exhaust gas is filtered by the filter element, and the particulates are removed from the exhaust gas.

The exhaust passage 31 is connected to the intake passage 11 by an EGR pipe 34, and an EGR valve 35 is interposed in the EGR pipe 34. The EGR valve 35 is connected to an actuator 351, and the opening degree is controlled by the actuator 351.
In the exhaust passage 31, a pressure sensor 51 is installed between the NOx trap catalyst 32 and the diesel particulate filter 33, and the exhaust pressure Pexh is detected by the pressure sensor 51. An oxygen sensor 52 and a temperature sensor 53 are installed downstream of the diesel particulate filter 33. The oxygen sensor 52 detects the excess air ratio λ and the temperature sensor 53 detects the exhaust temperature. The temperature sensor 53 estimates the temperature of the NOx trap catalyst 32 (hereinafter referred to as “catalyst temperature”) Tnox and the temperature of the diesel particulate filter 33 (hereinafter referred to as “filter temperature”) Tdpf from the detected exhaust gas temperature. Is. A temperature sensor may be installed in each of the NOx trap catalyst 32 and the diesel particulate filter 33, and their temperatures may be directly detected. An air flow meter 54, a crank angle sensor 55, and an accelerator sensor 56 are installed. The output of each sensor is input to an electronic control unit (hereinafter referred to as “ECU”) 41. The ECU 41 calculates the intake air amount Qac based on the output of the air flow meter 54, the engine speed Ne based on the output of the crank angle sensor 55, and the accelerator opening APO based on the output of the accelerator sensor 56. The ECU 41 controls the injector 21 and the other actuators 122, 151, and 351 based on the calculation result.

Hereinafter, the operation of the ECU 41 will be described with reference to a flowchart.
FIG. 2 shows a flowchart of the operation mode selection routine. The combustion mode is switched according to the operation mode set by this routine.
In S1, the engine speed Ne, the accelerator opening APO, the catalyst temperature Tnox, and the exhaust pressure Pexh are read.

In S2, it is determined whether or not the catalyst temperature Tnox is equal to or higher than a predetermined temperature T11. When it is T11 or more, the process proceeds to S3, and when it is lower than T11, the process proceeds to the routine shown in FIG. T11 corresponds to the activation temperature of the NOx trap catalyst 32.
In S3, the NOx trap amount NOX is detected. The NOx trap amount NOX is the amount of NOx trapped in the NOx trap catalyst 32, and is calculated by the following equation (1) as an integrated value of the engine speed Ne. The symbol n-1 indicates a value calculated when this routine is executed last time, and Δt indicates the execution cycle of this routine. The NOx trap amount NOX can also be calculated by a method of adding a predetermined amount each time the vehicle travels a certain distance.

NOX = NOX _n−1 + Ne × Δt (1)
In S4, the sulfur trap amount SOX is detected. The sulfur trap amount SOX is the amount of sulfur trapped in the NOx trap catalyst 32, and is calculated by the following equation (2) as an integrated value of the engine speed Ne, similarly to the NOx trap amount NOX.
SOX = SOX _n-1 + Ne × Δt (2)
In S5, the particulate deposition amount PM is detected. The particulate accumulation amount PM is the amount of particulates deposited on the diesel particulate filter 33 and is approximated by the exhaust pressure Pexh upstream of the diesel particulate filter 33. The particulate accumulation amount PM can also be calculated by calculating the amount of particulates discharged per unit time from the engine 1 based on the engine speed Ne and the travel distance, and integrating these.

In S6, it is determined whether the PM regeneration execution flag Freg is 0 or not. Freg is normally set to 0. When Freg is 0, the process proceeds to S7, and when it is not 0, the process proceeds to the routine shown in FIG.
In S7, it is determined whether or not the desulfurization regeneration execution flag Fdesul is zero. Fdesul is normally set to 0. When Fdesul is 0, the process proceeds to S8, and when it is not 0, the process proceeds to the routine shown in FIG.

In S8, it is determined whether or not the NOx regeneration execution flag Fsp is zero. Fsp is normally set to 0. When Fsp is 0, the process proceeds to S9, and when it is not 0, the process proceeds to the routine shown in FIG.
In S9, it is determined whether or not the failure avoidance execution flag Frec is zero. Frec is normally set to 0, and is temporarily switched to 1 when PM regeneration or desulfurization regeneration is completed. When Frec is 0, the process proceeds to S10, and when it is not 0, the process proceeds to the routine shown in FIG.

  In S10, it is determined whether or not the PM regeneration request flag rqREG is 0. The rqREG is normally set to 0, and is switched to 1 when it is determined that it is time to perform PM regeneration for processing the particulate accumulated in the diesel particulate filter 33. When rqREG is 0, the process proceeds to S11. When rqREG is not 0, the process proceeds to the routine shown in FIG.

  In S11, it is determined whether or not the desulfurization regeneration request flag rqDESUL is zero. The rqDESUL is normally set to 0, and is switched to 1 when it is determined that it is time to perform desulfurization regeneration in which the sulfur trapped from the NOx trap catalyst 32 is released. When rqDESUL is 0, the process proceeds to S12. When rqDESUL is not 0, the process proceeds to the routine shown in FIG.

  In S12, it is determined whether or not the NOx regeneration request flag rqSP is 0. The rqSP is normally set to 0, and is switched to 1 when it is determined that it is time to perform NOx regeneration for releasing NOx trapped from the NOx trap catalyst 32. When rqSP is 0, the process proceeds to S13, and when it is not 0, the process proceeds to the routine shown in FIG. 28. In S701 of this routine, the NOx regeneration execution flag Fsp is set to 1.

  In S13, it is determined whether or not the particulate accumulation amount PM has reached the specified amount PM1. This determination is made by comparing the back pressure P1 of the engine 1 obtained according to the operating state when the particulate matter of the specified amount PM1 is accumulated and the exhaust pressure Pexh detected by the pressure sensor 51. P1 is searched for the map shown in FIG. 3 based on the engine speed Ne and the required injection amount Qfdrv, and is calculated as a larger value as Ne is higher and Qfdrv is larger. The required injection amount Qfdrv indicates an injection amount by main injection (hereinafter referred to as “main injection amount”) Qmain in normal times, and a second injection amount Qm described later in cases other than normal times. When it is determined that the exhaust pressure Pexh is equal to or higher than P1 and the particulate accumulation amount PM has reached PM1, the routine proceeds to the routine shown in FIG. 29, and the PM regeneration request flag rqREG is set to 1 in S801 of this routine. To do. When it is lower than P1, the process proceeds to S14. In order to prevent the PM regeneration from being repeated unnecessarily, as a premise of switching rqREG to 1, the cumulative travel distance since the last PM regeneration was calculated is calculated, and this has reached the predetermined distance. It may be adopted.

In S14, it is determined whether or not the sulfur trap amount SOX has reached a predetermined amount SOX1. When SOX1 is reached, the routine proceeds to the routine shown in FIG. 30, and the desulfurization regeneration request flag rqDESUL is set to 1 in S901 of this routine. If SOX1 has not been reached, the process proceeds to S15.
In S15, it is determined whether or not the NOx trap amount NOX has reached a predetermined amount NOX1. When NOX1 is reached, the routine proceeds to the routine shown in FIG. 31, and the NOx regeneration request flag rqSP is set to 1 in S1001 of this routine. When NOX1 is not reached, the process proceeds to S16.

Each regeneration request flag rqREG, rqDESUL, and rqSP is set to 0 when the engine 1 is started.
In S16, the operation is performed by normal lean combustion (hereinafter referred to as “normal combustion”).
Here, the process proceeds from S2 to the routine shown in FIG. 32. When the activity of the NOx trap catalyst 32 is promoted, the process proceeds from S6 to the routine shown in FIG. 11, and when PM regeneration is executed, the process proceeds from S7 to the routine shown in FIG. When the desulfurization regeneration is executed and when the routine proceeds from S8 to the routine shown in FIG. 22 and NOx regeneration is executed, the combustion mode is switched and the operation is performed by the split retard combustion according to the present invention.

Here, the concept of each combustion mode will be described.
4 and 5 show the fuel injection pattern and heat generation rate according to the combustion mode, FIG. 4 shows the case of normal combustion, and FIG. 5 shows the case of split retard combustion.
In normal combustion, pilot injection and main injection are performed during operation in the normal operation region. The pilot injection is performed at a timing of 40 to 10 ° CA before top dead center earlier than the main injection, and the injection amount per stroke is set in a range of 1 to ³ mm ³ . The main injection is performed at a time of 10 to −5 ° CA before top dead center, and the interval with the pilot injection is set to a range of 10 to 30 ° CA.

  On the other hand, in the split retard combustion, first, the first fuel injection is performed in the compression stroke, and the second fuel injection is performed in the subsequent expansion stroke. The first fuel injection is for raising the in-cylinder temperature at the top dead center position (hereinafter referred to as “compression end temperature”), and pre-combustion at or near the top dead center by the first fuel injection. And the heat generation P is formed. The injection amount Qp of the first fuel injection (hereinafter referred to as “first injection amount”) Qp varies depending on the operating state, but is set to an amount at which at least heat generation P due to preliminary combustion is confirmed. The second fuel injection is for generating engine torque and is performed after the preliminary combustion is completed. After the preliminary combustion is completed by the second fuel injection, the main combustion is generated and the heat generation M is formed. An interval Δtij between the start timing of the first fuel injection (hereinafter referred to as “first injection timing”) ITp and the start timing of the second fuel injection (hereinafter referred to as “second injection timing”) ITm is: Although it depends on the engine speed Ne, it is set so that a time of at least 20 ° CA elapses from the start of the preliminary combustion to the start of the main combustion. Since the main combustion is combustion in the expansion stroke, the combustion speed is slow, and the end timing is after 50 ° CA after top dead center.

FIG. 6 shows the effect of split retard combustion in relation to the second injection timing ITm. Note that the excess air ratio is constant.
According to the split retard combustion, the exhaust temperature can be raised by delaying the second injection timing ITm and performing the main combustion at a later timing. In addition, by setting the interval Δtij between the first and second fuel injections and performing the main combustion after the completion of the preliminary combustion, the ignition delay period Δtigm of the fuel injected by the second fuel injection is ensured. The premixing ratio of the fuel can be increased during the main combustion. For this reason, when desulfurizing and regenerating the NOx trap catalyst 32, etc., it is possible to achieve a required high exhaust temperature and to suppress the occurrence of smoke against a decrease in the excess air ratio. Here, as the second injection timing ITm is delayed, the exhaust temperature can be raised and the smoke can be suppressed to a small extent. In the present embodiment, the intake air amount is decreased when the exhaust air-fuel ratio is lowered. However, since the compression end temperature is increased by the preliminary combustion, the main combustion can be stably performed. In addition, according to the divided retard combustion, the HC emission is suppressed to a low level regardless of the second injection timing ITm.

  Further, since the original exhaust temperature is low at low loads, it is necessary to raise the exhaust temperature significantly in order to achieve the target temperature during desulfurization regeneration and the like. For this reason, it is necessary to greatly delay the timing of the main combustion, and the in-cylinder temperature may not be maintained high until the timing of the main combustion with only one preliminary combustion. In such a case, as shown in FIG. 7, the preliminary combustion is performed a plurality of times, and the in-cylinder temperature raised by the first preliminary combustion is maintained by the second and subsequent preliminary combustions. It is possible to achieve the target temperature while suppressing the generation of smoke by preventing the heat generation P1 and P2 of each preliminary combustion from overlapping and causing the main combustion to be performed after all the preliminary combustion is completed. Become.

FIG. 8 shows a flowchart of a fuel injection amount setting routine. This routine is executed when split retard combustion is performed, and in this routine, a first injection amount Qp and a second fuel injection amount (hereinafter referred to as “second injection amount”) Qm are set. The
In S51, it is determined whether or not switching of the combustion mode is instructed. The switching of the combustion mode is instructed when the activity of the NOx trap catalyst 32 is promoted, when PM regeneration is performed, when desulfurization regeneration is performed, and when NOx regeneration is performed. When switching is instructed, the process proceeds to S52, and when not instructed, this routine is returned.

In S52, the engine speed Ne and the accelerator opening APO are read as the operating state.
In S53, the second injection amount Qm is calculated. The second injection amount Qm is calculated as a larger value as the APO is larger, when the map shown in FIG. 9 is searched by the engine speed Ne and the accelerator opening APO and Ne is constant.
In S54, the first injection amount Qp is calculated. The first injection amount Qp is calculated by searching the map shown in FIG. 10 based on the engine speed Ne and the second injection amount Qm, and a larger value as Ne is lower and Qm is smaller.

  11 and 12 show a flowchart of the PM regeneration routine. The PM regeneration is performed by raising the exhaust gas temperature and burning the particulates deposited on the diesel particulate filter 33. The operation during PM regeneration is performed by split retard combustion. The exhaust gas temperature is raised by controlling the second injection timing ITm, and the diesel particulate filter 34 is heated to a temperature at which the particulates can be combusted (here, 600 ° C. or higher). In this routine, the first and second injection timings ITp and ITm are set.

  In S71, the excess air ratio is controlled to a target value tλreg corresponding to the amount of particulates accumulated in the diesel particulate filter 34. The excess air ratio is controlled by operating the intake throttle valve 15 and the EGR valve 35. The table shown in FIG. 13 is searched based on the particulate accumulation amount PM, and the target excess air ratio tλreg (= 1 to 1.4) at the time of PM regeneration is calculated. The target excess air ratio tλreg is calculated as a smaller value as the PM increases. Further, the map shown in FIG. 14 is retrieved from the engine speed Ne and the second injection amount Qm, and a reference intake air amount tQac0 that gives an excess air ratio corresponding to stoichiometric is read. The read tQac0 is multiplied by tλreg to calculate a target intake air amount tQac (= tQac0 × tλreg) during PM regeneration, and the intake throttle valve 15 is controlled to an opening corresponding to the calculated tQac. The deviation of the actual excess air ratio from the target value tλreg is adjusted by feeding back the output of the oxygen sensor 52 and controlling the opening degree of the EGR valve 35. The particulate deposition amount PM can be estimated from the exhaust pressure Pexh.

  In operation by split retard combustion, the first injection timing ITp is set to an earlier timing when Ne is higher and Qm is larger by searching the map shown in FIG. 15 based on the engine speed Ne and the second injection amount Qm. Is done. Further, the second injection timing ITm is set to a later timing as Ne is lower and Qm is smaller by searching the map shown in FIG. 16 using Ne and Qm. Here, the retrieved ITm is corrected according to the exhaust temperature and the excess air ratio. A map shown in FIG. 17 is searched based on the exhaust target temperature tTexh (= tTexha) and the target excess air ratio tλ (= tλreg), and a second injection timing correction value ΔITm (= ΔITm1) is calculated. By adding the calculated ΔItm to ITm, the second injection timing ITm is delayed as the exhaust temperature is increased and the excess air ratio is controlled to be higher.

  Further, the second injection timing ITm is much later than the main injection start timing set under the same operating condition in the case of normal combustion. In order to suppress fluctuations in engine torque due to retarded fuel injection, the second injection amount Qm and the target intake air amount tQac are corrected according to the second injection timing ITm. The table shown in FIG. 18 is searched to calculate the correction coefficient Ktr1, and the calculated Ktr1 is multiplied by the second injection amount Qm, thereby increasing Qm as the second injection timing ITm is later. Further, in order to cope with an increase in pumping loss due to a decrease in the excess air ratio, the second injection amount Qm and the target intake air amount tQac are corrected according to the target excess air ratio tλ. The table shown in FIG. 19 is searched to calculate the correction coefficient Ktr2, and the calculated Ktr2 is multiplied by the second injection amount Qm, so that Qm is increased as the target excess air ratio tλ is lower.

In S72, it is determined whether or not the desulfurization regeneration request flag rqDESUL is 1. When it is 1, it progresses to S73, and when it is not 1, it progresses to S101 of the flowchart shown in FIG. The processing of S73 to 78 is performed when PM regeneration is performed continuously from the desulfurization regeneration of the NOx trap catalyst 32.
In S73, the excess air ratio λ is read.

In S74, the map shown in FIG. 16 is searched, and the second injection timing ITm serving as a reference is calculated.
In S75, a correction value ΔITm for the second injection timing is calculated. On the map shown in FIG. 17, the coordinates A (tTexha, λa; λa = tλreg) and B (tTexhb, λb; λb = tλdesul) corresponding to each of PM regeneration and desulfurization regeneration are specified, A straight line L passing through each point is calculated. Based on the excess air ratio λ, the coordinates P (tTexhp, λp) of the point P on the straight line L indicating the current state are calculated, and ΔITm corresponding to the point P is read and set as a correction value. In this embodiment, tTexha is an exhaust temperature required for heating the diesel particulate filter 33 to 600 ° C., and tTexhb is an exhaust temperature required for heating the NOx trap catalyst 32 to 650 ° C. It corresponds to.

  In S76, the correction value ΔITm is added to the reference value ITm, and the obtained value is set to the second injection timing ITm (= ITm + ΔITm). As a result, during the transition from desulfurization regeneration to PM regeneration, the second injection timing ITm is excessive from the target timing ITm2 (= ITm + ΔITm2) during desulfurization regeneration toward the target timing ITm1 (= ITm + ΔITm1) during PM regeneration. It varies with the rate λ.

In S77, it is determined whether or not the correction value ΔITm has reached the target value ΔITm1 during PM regeneration. When it has been reached, it is determined that the transition has been completed, and the process proceeds to S78, where the desulfurization regeneration request flag rqDESUL is set to zero. On the other hand, if not reached, this routine is returned.
In the present embodiment, the actual excess air ratio λ is detected because the target excess air ratio tλ is immediately switched to tλreg together with the switching of the operation mode to PM regeneration. Applying the change of the target excess air ratio tλ according to the response of the working gas, etc., and gradually changing it toward tλreg, the tλ being changed is regarded as the actual excess air ratio. You can also

In the flowchart shown in FIG. 12, in S101, the filter temperature Tdpf is read.
In S102, it is determined whether or not the filter temperature Tdpf is equal to or higher than a predetermined temperature T21. T21 is set to, for example, 600 ° C. as the minimum temperature necessary for burning the particulates. When it is T21 or more, the process proceeds to S103, and when it is lower than T21, the process proceeds to S107. In S107, the second injection timing ITm is delayed and the exhaust temperature is raised. In S108, the correction coefficient Ktr1 is calculated including the retard angle at this time, and is multiplied by the second injection amount Qm.

  In S103, it is determined whether or not the filter temperature Tdpf is equal to or lower than a predetermined temperature T22. T22 is set to, for example, 700 ° C. as a limit temperature for keeping the thermal load on the diesel particulate filter 33 within an allowable range. When it is T22 or less, the process proceeds to S104, and when it is higher than T22, the process proceeds to S109. In S109, the second injection timing ITm is advanced by a predetermined amount. In S110, the correction coefficient Ktr1 is calculated including the advance angle at this time, and this is multiplied by the second injection amount Qm.

  In S104, it is determined whether or not a predetermined time treg has elapsed after the fuel injection at the second injection timing ITm corrected in S107 or S109. If treg has elapsed, it is determined that PM regeneration has ended, and the process proceeds to S105. If treg has not elapsed, this routine is returned. While the filter temperature Tdpf is maintained within the target range, the accumulated particulates are incinerated.

In S105, the PM regeneration execution flag Freg is set to 0, the combustion mode is returned to normal combustion, the excess air ratio is returned to the normal value, and the exhaust gas temperature is returned to the normal temperature. Further, the particulate deposition amount PM is set to zero.
In S106, the failure avoidance execution flag Frec is set to 1, and control for avoiding a failure of the diesel particulate filter 33 is performed. If there is unburned residue in the particulates, assuming that the excess air ratio is immediately restored to the normal value, the unburned residue burns rapidly, and an excessive heat load may be applied to the diesel particulate filter 33. It is.

  FIG. 20 shows a flowchart of the desulfurization regeneration routine. The desulfurization regeneration is performed by controlling the exhaust to a richer side than usual to supply the reducing agent to the NOx trap catalyst 32, and increasing the exhaust temperature to promote the decomposition of the sulfur content. The operation during the desulfurization regeneration is performed by split retard combustion. The NOx trap catalyst 32 using a Ba-based catalyst component needs to be heated to a temperature of 650 ° C. or higher during desulfurization regeneration. In this routine, the first and second injection timings ITp and ITm are set.

  In S91, the excess air ratio is controlled to the target value tλdesul (here, 1). The excess air ratio is controlled by operating the intake throttle valve 15 and the EGR valve 35. A target intake air amount tQac (= tQac0) that gives an excess air ratio corresponding to stoichiometry is calculated by searching the map shown in FIG. 14, and the opening of the intake throttle valve 15 is controlled so that this is achieved. Further, the map shown in FIG. 15 is searched to calculate the first injection timing ITp, and the maps shown in FIGS. 16 and 17 are searched to calculate the second injection timing ITm. In order to suppress the torque fluctuation and reduce the pumping loss, the tables shown in FIGS. 22 and 23 are searched to calculate the correction coefficients Ktr1 and Ktr2, and the calculated Ktr1 and Ktr2 are multiplied by the second injection amount Qm.

  In S92, it is determined whether or not the PM regeneration request flag rqREG is 1. When it is 1, it progresses to S93, and when it is not 1, it progresses to S201 of the flowchart shown in FIG. The process of S93-98 is performed when desulfurization regeneration is performed continuously from PM regeneration of the diesel particulate filter 33. That is, in S93, the excess air ratio λ is read, and in S94, the basic second injection timing ITm is calculated. In S95, a straight line L passing through points A and B is specified on the map shown in FIG. 17, and a correction value ΔITm corresponding to the current excess air ratio is calculated based on the read λ. In S96, the calculated ΔITm is added to the basic value ITm, and the obtained value is set as the second injection timing ITm. In S97, it is determined whether or not the correction value ΔITm has reached the target value ΔITm2 at the time of desulfurization regeneration. If reached, the process proceeds to S78, and the desulfurization regeneration request flag rqDESUL is set to zero. On the other hand, if not reached, this routine is returned.

In the flowchart shown in FIG. 21, in S201, the catalyst temperature Tnox is read.
In S202, it is determined whether or not the catalyst temperature Tnox is equal to or higher than a predetermined temperature T13. T13 is set to, for example, 650 ° C. as the minimum temperature necessary for the decomposition of the sulfur content. When it is T13 or more, the process proceeds to S203, and when it is lower than T13, the process proceeds to S207. In S207, the second injection timing ITm is delayed and the exhaust temperature is raised. In S208, a correction coefficient Ktr1 including the retard angle at this time is calculated, and this is multiplied by the second injection amount Qm.

  In S203, it is determined whether or not a predetermined time tdesul has elapsed after the fuel injection at the second injection timing ITm corrected in S207. If tdesul has elapsed, it is determined that the desulfurization regeneration has been completed, and the process proceeds to S204. If tdesul has not elapsed, this routine is returned. While the catalyst temperature Tnox is maintained within the target range, the trapped sulfur content is decomposed and released from the NOx trap catalyst 32. The sulfur content is purified by the reducing agent in the exhaust when released.

In S204, the desulfurization regeneration execution flag Fdesul is set to 0, the combustion mode is returned to normal combustion, the excess air ratio is returned to the normal value, and the exhaust gas temperature is returned to the normal temperature. Also, the sulfur trap amount SOX is set to zero.
In S205, the NOx trap amount NOX is set to 0, and when the NOx regeneration request flag rqSP is 1, this is set to 0. This is because when the reducing agent is supplied to the NOx trap catalyst 32 by performing desulfurization regeneration, NOx is also released together with the sulfur content, and NOx regeneration is performed simultaneously.

In S206, the failure avoidance execution flag Frec is set to 1. Assuming that the excess air ratio is immediately returned to the normal value at a high temperature at the time when the desulfurization regeneration is completed, the particulates accumulated in the diesel particulate filter 33 are rapidly burned, and the diesel particulate filter 33 is excessively large. This is because a heat load may be applied.
FIG. 22 shows a flowchart of the NOx regeneration routine. NOx regeneration is performed by temporarily controlling the exhaust to be richer than stoichiometric, and the operation during NOx regeneration is performed by split retard combustion. In NOx regeneration, unlike the desulfurization regeneration, it is not necessary to increase the exhaust temperature, but when reducing the exhaust air-fuel ratio, the intake air amount is decreased, and it is necessary to cope with the decrease in the compression end temperature. Adopting operation by split retard combustion. In this routine, the first and second injection timings ITp and ITm are set.

  In S301, the excess air ratio is controlled to the target excess air ratio tλsp set for NOx regeneration. The target excess air ratio tλsp during NOx regeneration is set to 0.9, for example, as a value indicating richness. The target intake air amount tQac is calculated by multiplying the reference intake air amount tQac0 (FIG. 14) that gives the excess air ratio corresponding to the stoichiometric ratio by tλsp. The intake throttle valve 15 is controlled to an opening corresponding to the calculated tQac, and the deviation from the target excess air ratio tλsp is adjusted by operating the EGR valve 35. 15 to 17 are searched to set the first and second injection timings ITp and ITm, and the tables shown in FIGS. 18 and 19 are searched to calculate correction coefficients Ktr1 and Ktr2. Is multiplied by the second injection amount Qm.

  In S302, it is determined whether or not a predetermined time tspike has elapsed after starting NOx regeneration. If tspike has elapsed, it is determined that NOx regeneration has ended, and the process proceeds to S303. If tspike has not elapsed, this routine is returned. The NOx trapped until the predetermined time tspike elapses is decomposed and released from the NOx trap catalyst 32. NOx is purified by the reducing agent in the exhaust when released.

In S303, the NOx regeneration execution flag Fsp is set to 0, the combustion mode is returned to normal combustion, and the excess air ratio is returned to the normal value. Further, the NOx trap amount NOX is set to zero.
FIG. 23 shows a flowchart of a failure avoidance routine. Failure avoidance is performed by controlling the excess air ratio to 1.4 or less on the lean side than during PM regeneration and desulfurization regeneration, and operation during failure avoidance requires lowering the exhaust temperature. The normal combustion is performed.

In S401, the filter temperature Tdpf is read.
In S402, the map shown in FIG. 24 is searched based on the engine speed Ne and the main injection amount Qmain to calculate the target intake air amount tQacrec. The intake throttle valve 15 and the EGR valve 35 are operated according to the calculated tQacrec to achieve the target excess air ratio tλrec.

In S403, it is determined whether or not the filter temperature Tdpf is equal to or lower than a predetermined temperature T23. When it is equal to or less than T23, it is determined that the possibility that the unburned particulates will burn rapidly has been canceled, and the process proceeds to S404. When it is higher than T23, this routine is returned.
In S404, the failure avoidance execution flag Frec is set to 0, and the excess air ratio is returned to the normal value.

  25, 27 and 28 show flowcharts of the regeneration execution flag setting routine, which are executed when the PM regeneration request flag rqREG, the desulfurization regeneration request flag rqDESUL or the NOx regeneration request flag rqSP is switched to 1. The In these routines, the priority order when different reproduction requests are simultaneously generated is determined, and the respective reproduction execution flags Freg, Fdul, or Fsp are set.

  In the flowchart shown in FIG. 25, in S501, it is determined whether or not the sulfur content has progressed since the PM regeneration request flag rqREG is switched to 1, and the desulfurization regeneration request flag rqDESUL is switched to 1. . When switched, the process proceeds to S502, and the desulfurization regeneration execution flag Fdesul is set to 1. Thereby, desulfurization regeneration is performed with priority over PM regeneration. On the other hand, when it is not switched, the process proceeds to S503.

In S503, it is determined whether or not the NOx regeneration request flag rqSP is 0. When it is 0, it progresses to S504, and when it is not 0, it progresses to S506.
In S504, the map shown in FIG. 26 is referred to based on the engine speed Ne and the accelerator opening APO, and it is determined whether or not there is an operating state in the region where the divided retard combustion is possible. Switching to split retard combustion is prohibited in the low rotation and low load region with hatching.

In S505, the PM regeneration execution flag Freg is set to 1.
On the other hand, in S506, it is determined whether or not the engine 1 is in an operation state in which the NOx emission amount is small. This determination is performed, for example, by determining whether or not the engine 1 is in a steady operation state. When the engine 1 is in a steady operation state, it is determined that the NOx emission amount is small, and the process proceeds to S507. On the other hand, when it is not in the steady operation state, it is determined that the amount of NOx emission is large, and the process proceeds to S508 so that NOx regeneration is prioritized over PM regeneration.

  In S507, it is determined whether or not the filter temperature Tdpf is equal to or higher than a predetermined temperature T24. T24 is set to a temperature lower than the target temperature T21 at the time of PM regeneration as the activation temperature of the catalyst supported on the diesel particulate filter 33. If it is equal to or higher than T24, the process proceeds to S504. If it is lower than T24, it is determined that it takes a considerable time to reach the target temperature T21, and the process proceeds to S508 so that NOx regeneration is prioritized.

In S508, the NOx regeneration execution flag Fsp is set to 1.
In the flowchart shown in FIG. 27, in S601, it is determined whether or not the catalyst temperature Tnox is equal to or higher than a predetermined temperature T13. T13 is set to a temperature lower than the target temperature T12 at the time of desulfurization regeneration as a temperature necessary for smooth execution of the desulfurization regeneration. If it is equal to or higher than T13, the process proceeds to S602. If it is lower than T13, it is determined that it takes a considerable time to reach the target temperature T12, and the process proceeds to S604.

In S602, with reference to the map shown in FIG. 26, it is determined whether or not there is an operating state in an area where split retard combustion is possible. If it is in such a region, the process proceeds to S603, and the desulfurization regeneration execution flag Fdesul is set to 1. On the other hand, when it is not in such an area, this routine is returned.
In S604, it is determined whether or not the NOx regeneration request flag rqSP is 0. When it is 0, it progresses to S602. On the other hand, if it is not 0, the process proceeds to S605, and the NOx regeneration execution flag Fsp is set to 1. Thereby, NOx regeneration is performed with priority over desulfurization regeneration.

In the flowchart shown in FIG. 28, the NOx regeneration execution flag Fsp is set to 1 in S701.
FIG. 32 shows a flowchart of the rapid activation routine.
In S1101, the catalyst temperature Tnox is read.
In S1102, the map shown in FIG. 26 is referred to and it is determined whether or not there is an operating state in an area where the divided retard combustion is possible. If it is in such a region, the process proceeds to S1103, and the combustion mode is switched to split retard combustion. On the other hand, when it is not in such an area, this routine is returned. During operation by split retard combustion, the maps shown in FIGS. 15 to 17 are searched to calculate the first and second injection timings ITp and ITm. By setting the second injection timing ITm to a late timing, the exhaust temperature rises and the activity of the NOx trap catalyst 32 is promoted. Further, the map shown in FIG. 18 is searched to calculate the correction coefficient Ktr1, and this is multiplied by the second injection amount Qm. Note that the target excess air ratio tλ is set to a normal value during rapid activation.

In S1104, it is determined whether or not the catalyst temperature Tnox has reached a predetermined temperature T11. When it reaches, this routine is returned, and when it has not reached, the operation by split retard combustion is continued. By returning this routine, the combustion mode is switched to normal combustion (S16).
According to this embodiment, the following effects can be obtained.

  First, when the PM regeneration of the diesel particulate filter 33, the desulfurization regeneration of the NOx trap catalyst 32, and the rapid activation of the catalyst 32, the combustion mode is switched to the split retard combustion, and the second fuel injection is changed from the normal main injection. Also, it was decided to make the crank angle late. For this reason, exhaust gas temperature can be raised and the diesel particulate filter 32 grade | etc., Can be heated to target temperature. Here, in PM regeneration and desulfurization regeneration, the intake air amount is decreased when the exhaust air-fuel ratio is lowered. However, the preliminary combustion is performed by the first fuel injection, and the heat generated thereby generates the cylinder. Since the internal temperature rises, main combustion can be performed stably.

  Second, the interval Δtij between the first and second fuel injections is adjusted so that the main combustion is performed after the preliminary combustion is completed. For this reason, it is possible to allow time between the preliminary combustion and the main combustion to promote the premixing of fuel that contributes to the main combustion, and to reduce the excess air ratio during PM regeneration, NOx regeneration, and desulfurization regeneration. On the other hand, it is possible to suppress the generation of smoke as a combustion mode mainly composed of premixed combustion.

  Thirdly, at the time of transition from desulfurization regeneration of the NOx trap catalyst 32 to PM regeneration of the diesel particulate filter 33 and vice versa, the target excess air ratio tλ is first switched ( S71, 91), the second injection timing ITm is changed according to the actual change in the excess air ratio (S75, 95). For this reason, it is possible to change the excess air ratio while keeping the exhaust temperature in a good range, and it is possible to efficiently achieve the transition of the operation mode. In the present embodiment, for example, at the time of transition to PM regeneration, the second injection timing ITm is retarded as the excess air ratio increases, that is, the in-cylinder temperature increases as the working gas amount increases. .

  Further, with respect to the present embodiment, the transition from desulfurization regeneration to PM regeneration is not in a state where split retard combustion is possible even though the particulate accumulation amount PM has reached a specified amount, and into a region where split retard combustion is possible. Sulfur deposition progresses before the transition, and when desulfurization regeneration is prioritized (S504, 501), when sulfur deposition progresses while NOx regeneration is performed prior to PM regeneration ( S503, 501), and when the sulfur trap amount SOX reaches a specified amount during PM regeneration. On the other hand, the transition from PM regeneration to desulfurization regeneration is performed when the particulate deposition amount PM reaches a specified amount during the desulfurization regeneration.

  In the above description, the case where the NOx trap catalyst 32 and the diesel particulate filter 33 are configured as separate devices has been described as an example. However, the present invention carries the catalyst component of the NOx trap catalyst on the filter element of the diesel particulate filter 33. It is also possible to apply to what has been made.

Configuration of diesel engine according to one embodiment of the present invention Operation mode selection routine flowchart Map of PM regeneration time determination threshold P1 Normal combustion concept Split retard combustion concept Effect of split retard combustion The concept of split retard combustion at low loads. Flow chart of fuel injection amount calculation routine Map of second injection quantity Qm Map of first injection amount Qp PM regeneration routine flowchart Flow chart of exhaust gas temperature adjustment process in the same routine Table of target air excess ratio tλreg during PM regeneration Map of stoichi equivalent target intake air volume tQac0 Map of first injection timing ITp Map of second injection timing ITm Map of correction value ΔITm Table of correction coefficient Ktr1 Table of correction coefficient Ktr2 Flow chart of desulfurization regeneration routine Flow chart of exhaust gas temperature adjustment process in the same routine NOx regeneration routine flowchart Flow chart of failure avoidance routine Map of target intake air amount tQacrec at the time of failure avoidance First regeneration execution flag setting routine flowchart Split retard combustion map Flowchart of second regeneration execution flag setting routine Flowchart of third regeneration execution flag setting routine Flow chart of PM regeneration request flag setting routine Flow chart of desulfurization regeneration request flag setting routine Flow chart of NOx regeneration request flag setting routine Rapid activation routine flowchart

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Diesel engine, 11 ... Intake passage, 12 ... Variable nozzle turbocharger, 15 ... Intake throttle valve, 21 ... Injector, 22 ... Common rail, 31 ... Exhaust passage, 32 ... NOx trap catalyst, 33 ... Diesel particulate filter, 34 ... EGR pipe, 35 ... EGR valve, 41 ... Electronic control unit as controller, 51 ... Exhaust pressure sensor, 52 ... Exhaust air / fuel ratio sensor, 53 ... Exhaust temperature sensor, 54 ... Air flow meter, 55 ... Crank angle sensor, 56 ... Accelerator sensor.

Claims (8)

Switch the combustion mode between normal time and when the exhaust gas temperature is raised to a higher temperature than normal,
The engine is operated by normal combustion as the first combustion mode at normal time, and by split retarded combustion as the second combustion mode at the time of exhaust gas temperature rise,
In normal combustion, combustion to generate engine torque is performed at a time relatively close to top dead center,
In split retard combustion, main combustion as combustion for generating engine torque and pre-combustion for forming predetermined heat generation before main combustion are performed, and pre-combustion is performed at or near top dead center. On the other hand, the main combustion is performed later than the corresponding combustion of the normal combustion and after the preliminary combustion is completed,
Also, when changing the exhaust temperature and changing the excess air ratio during operation with split retard combustion, the engine control changes the timing for performing the main combustion according to the change in the excess air ratio. apparatus. An injector that directly injects fuel into the cylinder;
And a controller that controls the operation of the injector,
The controller switches the injection mode of the injector between normal time and when the exhaust gas temperature rises to raise the exhaust temperature to a target temperature set higher than normal, and generates engine torque for the injector during normal time The first fuel injection for the pre-combustion that forms a predetermined heat generation prior to the combustion for generating the engine torque when the temperature of the exhaust gas is raised, while the fuel injection for the combustion to be performed is performed relatively early And the second fuel injection for the main combustion as the combustion for generating the engine torque is performed later than the corresponding fuel injection at the normal time and at the time when the main combustion is performed after the end of the preliminary combustion. Let
In addition, a first target temperature and a second target temperature different from the first target temperature are set as the target temperature for the controller, and the controller determines that a predetermined condition is satisfied when the exhaust gas temperature rises. Is controlled from the first target temperature to the second target temperature, and when the excess air ratio is changed accordingly, the control for changing the excess air ratio is performed, and the actual excess air ratio is changed. The engine control apparatus which changes the time which performs 2nd fuel injection according to.   When the second target temperature is set as a temperature lower than the first target temperature and the excess air ratio is increased in conjunction with the control from the first target temperature to the second target temperature, the controller The engine control device according to claim 2, wherein the timing for performing the second fuel injection is retarded with respect to the increase in the rate.   The engine control device according to claim 3, wherein the controller gradually delays a timing at which the second fuel injection is performed as the excess air ratio increases. Provided in an engine having an exhaust purification device in an exhaust passage;
The engine control device according to any one of claims 2 to 4, wherein the controller determines a normal time and an exhaust temperature increase time according to a state of the exhaust gas purification device.   The engine control apparatus according to claim 5, wherein the engine control apparatus is provided in an engine including at least one of a particulate filter and a NOx trap catalyst as an exhaust purification device.   The engine control device according to claim 6, wherein the controller sets the time when exhaust gas temperature rises when at least one of PM regeneration of the particulate filter and desulfurization regeneration of the NOx trap catalyst is performed.   When the engine includes both the particulate filter and the NOx trap catalyst, the predetermined condition is that the PM regeneration of the particulate filter is followed by the desulfurization regeneration of the NOx trap catalyst or the desulfurization regeneration of the NOx trap catalyst. The engine control apparatus according to claim 7, which is established when PM regeneration of the particulate filter is performed.

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