JP3775158B2 - Engine exhaust purification system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an engine, and more particularly, to an engine that operates lean (lean mixture).
[0002]
[Prior art]
A technique is known in which an NOx catalyst that adsorbs NOx in exhaust when the exhaust air-fuel ratio is lean and disposes NOx already adsorbed when the oxygen concentration in the exhaust decreases is disposed in the exhaust passage of the engine. (Refer to Unexamined-Japanese-Patent No. 11-107813).
[0003]
In this conventional apparatus, when the NOx catalyst adsorbs the sulfur component (SOx) in the exhaust gas and the catalytic capacity is lowered, the temperature of the NOx catalyst is raised to release the sulfur component to recover the catalytic capacity. As for the method, when the engine operating conditions are a low rotational speed and a low load, fuel injection (twice injection) is performed in two steps, an intake stroke and an expansion stroke, and the temperature of the NOx catalyst is increased. There is a disclosure that in the load region, only the intake stroke (injection once) and the ignition timing are retarded to raise the temperature of the NOx catalyst.
[0004]
[Problems to be solved by the invention]
However, this publication does not disclose fuel injection control when releasing NOx adsorbed by the NOx catalyst, and this conventional apparatus may not be able to perform appropriate NOx release control.
[0005]
That is, when the NOx catalyst adsorbs a certain amount of NOx, exhaust gas containing a low oxygen concentration and containing excessive reducing agent components (CO, HC) is caused to flow into the NOx catalyst to release adsorbed NOx and reduce and purify the released NOx. However, when performing this NOx release reduction control (hereinafter referred to as “catalyst regeneration control”), it has been found that the optimum fuel injection mode varies depending on the state of the engine. This will be described below.
[0006]
When the air-fuel ratio enrichment control in the catalyst regeneration control is performed by one injection, the fuel is partially oxidized by oxygen molecules existing in the combustion chamber during combustion, and a large amount of CO is generated. However, this is divided into an intake stroke and an expansion stroke for injection, and the target fuel amount of the first injection is set so that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio (hereinafter referred to as “stoichiometric”). In addition, when the second injection is performed when the combustion by the first injection is almost finished, the partial oxidation hardly occurs and the fuel for the rich air-fuel ratio (the fuel injected the second time) Is almost entirely supplied to the NOx catalyst as HC. However, if it is left as it is, the exhaust HC will increase compared to the case of the first injection, but if the temperature in the combustion chamber at the time of the second injection is sufficiently high, the fuel for the rich air-fuel ratio will be hot. Compared with the case of single injection, the ratio of HC species (paraffinic component) that does not have multiple bonds is reduced and the ratio of HC species (olefinic component) that has multiple bonds is reduced instead. It was found to increase. Due to this action, the reactivity of the reducing agent is higher than in the case of single injection, and the efficiency of NOx reduction purification is increased (see FIG. 1). In other words, according to the twice injection in this case, the NOx reduction and purification efficiency equivalent to that in the case of the one-time injection can be obtained with less fuel than in the case of the one-time injection. The amount of injection can be made smaller than in the case of one-time injection, and an increase in HC discharged without being subjected to NOx reduction purification can be suppressed.
[0007]
On the other hand, when the temperature in the combustion chamber when performing the second injection is insufficient, the second injected fuel is discharged without being reformed. Since the ratio of paraffinic components in the fuel is usually higher than that of exhaust gas, if the injection is performed twice under such low temperature conditions, the reaction of the reducing agent becomes worse than the case of the single injection, and NOx reduction purification is performed. Efficiency and exhaust HC increase.
[0008]
Therefore, the present invention estimates the temperature in the combustion chamber at the time of the second injection, and based on the estimated temperature, the fuel of the second injection is reformed into a fuel having a high ratio of highly reactive HC species. An object is to increase the efficiency of NOx reduction purification by determining whether or not the temperature is within the temperature range and performing air-fuel ratio enrichment control by twice injection in the temperature range where reforming is performed. Further, by performing air-fuel ratio enrichment control by one injection in a temperature range where reforming is not performed, NOx reduction purification is performed by performing air-fuel ratio enrichment control by twice injection even in a temperature region where reforming is not performed. The purpose is to prevent a decrease in efficiency and an increase in exhaust HC.
[0009]
[Means for Solving the Problems]
As shown in FIG. 20, the first invention traps and holds NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is a lean air-fuel ratio, and holds it when the air-fuel ratio of the inflowing exhaust is a rich air-fuel ratio. The catalyst 21 having the function of releasing the NOx that has been discharged and reducing and purifying with HC and CO in the exhaust, and means for temporarily enriching the exhaust air-fuel ratio when the NOx retention amount of the catalyst 21 exceeds a predetermined value 22, means 23 for directly injecting and supplying fuel to the combustion chamber, and a timing associated with generation of engine torque using the fuel injection and supplying means 23 and subsequent generation of engine torque. A means 24 capable of switching between a two-time fuel injection divided into two times that are not connected and a one-time fuel supply only at a time that leads to the generation of engine torque, Based on the means 25 for estimating the combustion chamber temperature at the time of the second injection, the fuel of the second injection is changed to a fuel in which the ratio of the highly reactive HC species is increased based on the temperature of the combustion chamber at the second injection. Quality The temperature of the second injected fuel is higher than the temperature range where it is not reformed. And means 26 for determining whether or not the exhaust gas is in a temperature range in which the fuel for the second injection is reformed when the exhaust air-fuel ratio is temporarily enriched. And means 27 for selecting twice injection.
[0010]
In the second invention, in the first invention, the time associated with the generation of the engine torque is the intake stroke or the compression stroke in the combustion cycle, and the time not associated with the generation of the engine torque is the expansion stroke.
[0011]
In the third invention, the first injection is selected when it is determined in the first or second invention that the fuel of the second injection is in a temperature range where the fuel is not reformed.
[0012]
In the fourth invention, when the exhaust air-fuel ratio is temporarily enriched in the third invention, the total target equivalent ratio TFBYA (TFBYA + TFBYAa) when the two-time injection is selected is set, and the exhaust air-fuel ratio is temporarily set. In the case of enrichment, the target equivalence ratio TFBYAm when the one-time injection is selected is set on the lean side.
[0013]
In a fifth aspect of the invention, in any one of the first to fourth aspects of the invention, the combustion chamber temperature at the second injection is set to any or all of the engine speed, the engine load, the ignition timing, and the engine coolant temperature. Estimate accordingly.
[0014]
In a sixth aspect of the invention, the combustion peak temperature TCpeak is calculated based on the engine speed Ne and the engine load in the fifth aspect of the invention, and the temperature drop in the period from the time when the combustion temperature reaches the peak to the second injection time The correction rate TCadv for taking into account the engine speed Ne and the ignition timing ADV, and the correction rate TCtw for taking into account the temperature drop due to cooling of the combustion gas is set to the engine speed Ne and the A value obtained by correcting the combustion peak temperature TCpeak with the two temperature drop correction factors TCadv and TCtw, respectively, is estimated as the combustion chamber temperature TC2 at the second injection.
[0015]
According to a seventh aspect of the invention, in any one of the first to sixth aspects, the second injection is performed when combustion by the first injection is almost completed or when a predetermined period has elapsed from that point. is there.
[0016]
In the eighth invention, the target fuel amount (target equivalent ratio TFBYAm) of the first injection so that the exhaust air-fuel ratio by the first injection becomes stoichiometric or in the vicinity thereof when the second injection is selected in the seventh invention. ) Is set.
[0017]
In the ninth invention, the target fuel amount (target equivalent ratio TFBYAa) of the second injection in the eighth invention is calculated based on the released NOx concentration RNOx and the reducing agent efficiency REFF.
[0018]
According to a tenth aspect, in the ninth aspect, the reducing agent efficiency REFF is set according to the combustion chamber temperature TC2 at the time of the second injection.
[0019]
In the eleventh aspect of the invention, when either the one-time injection or the two-time injection is selected when the exhaust air-fuel ratio is temporarily enriched in the third aspect, a predetermined period ( Time) continues the selected injection.
[0020]
【The invention's effect】
In the first and second inventions, when the air-fuel ratio enrichment control for reducing and purifying NOx held in the catalyst is performed by the second injection, the fuel of the second injection depends on the atmospheric temperature in the combustion chamber. Focusing on the improved reactivity of the reducing agent that is reformed and contained in the exhaust, the air-fuel ratio is enriched by the second injection when it is determined that the temperature of the fuel injected for the second injection is within the temperature range to be reformed Since the control is performed, it is possible to efficiently reduce and purify NOx held by the catalyst particularly at a high load when the temperature in the combustion chamber becomes high.
[0021]
On the other hand, if the injection is performed twice until the temperature in the combustion chamber at the time of the second injection is insufficient, the reactivity of the reducing agent becomes lower than that in the case of the first injection, and the efficiency of NOx reduction purification is improved. According to the third aspect of the invention, when the temperature in the combustion chamber becomes inadequate, the air-fuel ratio enrichment control is performed by switching to once injection. Even in the region, it is possible to prevent a decrease in the efficiency of NOx reduction purification and an increase in exhaust HC caused by performing the injection twice.
[0022]
According to the fourth aspect of the present invention, when the injection is performed twice in the temperature range where the temperature in the combustion chamber becomes high, the reactivity of the reducing agent is higher than that in the case of the single injection, and the NOx reduction purification efficiency is increased. Focusing on the fact that the NOx reduction and purification efficiency equivalent to that in the case of the one-time injection can be obtained with less fuel than in the case of the one-time injection, according to the fourth invention, the injection at the time of performing the rich control of the air-fuel ratio The amount can be made smaller than in the case of single injection, and an increase in HC discharged without being subjected to NOx reduction purification can be suppressed.
[0023]
According to the fifth and sixth inventions, the temperature in the combustion chamber at the time of the second injection can be accurately estimated even if the engine rotation speed, the engine load, the ignition timing, and the engine coolant temperature change.
[0024]
If the second injection is performed before the completion of the combustion by the first injection, the fuel is partially oxidized by the oxygen molecules existing in the combustion chamber at the time of combustion, so that a lot of CO is generated, and its reactivity is high. Although the amount of fuel that is reformed to HC species decreases, according to the seventh aspect, the amount of fuel that is partially oxidized decreases. Further, according to the eighth aspect of the invention, when the second injection is selected, the exhaust air / fuel ratio by the first injection is set so as to be stoichiometric or in the vicinity thereof, so that partial oxidation is almost generated in the fuel of the second injection. Therefore, almost all of the fuel rich in the air-fuel ratio (fuel injected for the second time) can be supplied to the catalyst as HC.
[0025]
The target fuel amount for the second injection was set without considering the released NOx concentration and the reducing agent efficiency representing the proportion of fuel actually used for NOx reduction purification among the fuel supplied for NOx reduction purification. In this case, the amount of fuel as the reducing agent is insufficient or excessive with respect to the amount of NOx released from the catalyst. However, according to the ninth aspect, the amount of NOx released from the catalyst is not excessive or insufficient. The amount of fuel as a reducing agent can be supplied.
[0026]
According to the tenth invention, the reducing agent efficiency can be provided with high accuracy even if the temperature in the combustion chamber during the second injection changes.
[0027]
If the same torque is to be obtained for one-time injection and two-time injection, the required air amount may change. In this case, the temperature in the combustion chamber changes up and down in response to changes in the engine load, and in response to this, there is no If these two injections are frequently switched during the enrichment control of the fuel ratio, the operability may be deteriorated from the viewpoint of the followability of the throttle and the intake air amount, etc. According to the eleventh invention, In addition, it is possible to prevent hunting in which the one-time injection and the two-time injection are frequently switched during the air-fuel ratio enrichment control.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
In FIG. 2, 1 is an engine body, 2 is an intake passage, 3 is a combustion chamber, 4 is an exhaust passage, 5 is a throttle device driven by a throttle actuator 5a composed of a DC motor or the like, and 6 is an ECM (Electronic Control Module) 11. This is a fuel injection valve that injects and supplies fuel so as to achieve a predetermined air-fuel ratio in accordance with operating conditions by means of an injection signal from.
[0029]
The ECM 11 includes a reference position signal and a unit angle signal from the crank angle sensor 12, an intake air flow rate signal from the air flow meter 13, an accelerator opening signal from the accelerator opening sensor 14, and an engine cooling water temperature signal from the water temperature sensor 15. A gear position signal from a transmission gear position sensor (not shown), a vehicle speed signal from a vehicle speed sensor (not shown), and the like are input, and based on these, the driving state is determined, and a predetermined operation with a not so large load is performed. The operation is performed with a lean air-fuel ratio in the region, and the air-fuel ratio is mainly controlled to stoichiometric in the other operation regions.
[0030]
Although not shown, the exhaust passage 4 is connected to the engine outlet and collects exhaust from all cylinders. The exhaust manifold 4 is connected to the exhaust manifold and is connected to the exhaust manifold to carry the exhaust to the rear of the vehicle body under the floor of the vehicle. It consists of a muffler or the like connected to the end of the pipe, and among these, the three-way catalysts 7 and 8 are arranged at positions near the manifold and under the floor of the pipe-like exhaust pipe, respectively. In order to distinguish these two three-way catalysts, the three-way catalyst 7 in the vicinity of the manifold is called a manifold catalyst, and the three-way catalyst 8 in the under-floor position is called an under-floor catalyst.
[0031]
Since the manifold catalyst 7 is close to the engine exhaust outlet, it is activated early after the engine is started. In the active state, when the excess oxygen is present in the exhaust, the manifold catalyst 7 retains the oxygen in the exhaust, and the excess reducing agent (HC, It has a function (oxygen storage function) of oxidizing the reducing agent in the exhaust gas with the oxygen retained when (CO) is present. On the other hand, the underfloor catalyst 8 has a function of simultaneously performing oxidation purification of HC and CO in the exhaust gas and reduction purification of NOx when the air-fuel ratio of the inflowing exhaust gas is stoichiometric. A function of trapping and holding NOx in the exhaust when lean, releasing the held NOx when the air-fuel ratio of the inflowing exhaust becomes rich, and reducing and purifying the released NOx with HC and CO in the exhaust Have.
[0032]
Now, when the NOx retention amount of the underfloor catalyst reaches a certain level during the lean air-fuel ratio operation, it is necessary to regenerate the underfloor catalyst by performing air-fuel ratio enrichment control.
[0033]
Here, according to an experiment by the inventor of the present application, an air-fuel ratio enrichment control using a fuel injection valve that can inject and supply fuel directly into the combustion chamber is performed by dividing the intake stroke and the expansion stroke in the combustion cycle into two (2 In the case of the second injection, the fuel that has been injected a second time is reformed according to the atmospheric temperature in the combustion chamber, and the new finding has been obtained that the reactivity of the reducing agent contained in the exhaust is improved. Focusing on this point, the ECM 11 estimates the temperature in the combustion chamber at the time of the second injection (in the expansion stroke) (this temperature in the combustion chamber is hereinafter referred to as “the temperature in the combustion chamber at the time of the second injection”). When it is determined that the fuel is reformed for the second time based on the temperature in the combustion chamber, the air-fuel ratio enrichment control is performed by the second fuel injection, and in the temperature region where the effect of reforming cannot be obtained. The air-fuel ratio enrichment control is performed by switching to the one-time injection.
[0034]
This control content executed by the ECM 11 will be described in detail according to the following flowchart.
[0035]
Before starting the description of the flow, the regeneration control of the underfloor catalyst in this embodiment will be outlined with reference to the waveform diagram of FIG. 18 because the engine load is relatively high at the start of the catalyst regeneration control. Although the combustion chamber temperature TC2 (estimated value) at the time of the second injection is in the temperature range where the injected fuel is reformed in the combustion chamber, TC2 cannot obtain the effect of fuel reforming from the timing of t2 due to a decrease in load. This is an example in which the catalyst regeneration control is finished at the timing of t3 after moving to the temperature range.
[0036]
In such a case, the following operation is performed.
[0037]
<1> If the NOx retention amount of the underfloor catalyst is TNOx, this TNOx gradually increases during the lean air-fuel ratio operation. Therefore, the timing of t0 when TNOx reaches the predetermined value TNOx0 is set as the catalyst regeneration control start timing. At this time, the regeneration flag FNOx is switched from 0 to 1 (see the second stage). Further, the regeneration flag FNOx is switched from 1 to 0 in order to end the catalyst regeneration control at the timing t3 when TNOx is gradually decreased by the air-fuel ratio enrichment control and TNOx becomes zero. The regeneration flag is a flag indicating that the catalyst regeneration control is necessary when FNOx = 1, and that the catalyst regeneration control is not necessary when the regeneration flag FLGNO = 0.
[0038]
<2> The estimation of TC2 is started at t0 of the catalyst regeneration control start timing (see the third stage). Since the TC2 exceeds the determination value TC2INJH at the timing t0 and the fuel is in a temperature range where the fuel is reformed, the two-time injection flag F2INJ is switched from 0 to 1 (see the dashed line in the fourth stage). After that, since the fuel is not reformed after the timing t2 when TC2 drops to another determination value TC2INJL (TC2INJL <TC2INJH), the double injection flag F2INJ is switched from 1 to 0. F2INJ = 1 indicates that the injection is performed twice, and F2INJ = 0 indicates that the injection is not performed twice (that is, the injection is performed once).
[0039]
In the fourth row, a solid line indicates that F2INJ = 1 even before the regeneration flag FNOx becomes 1, but this is a request for another purpose.
[0040]
<3> On the other hand, the target equivalent ratio provisional value TFBYA1 of the first injection is switched from the target equivalent ratio map value (= basic value) TFBYA0 to 1.0 at the start timing t0 of the catalyst regeneration control (fifth stage). See the dash-dot line in the eye). The target equivalent ratio map value TFBYA0 gives a target equivalent ratio (a value less than 1.0) at the time of lean air-fuel ratio operation, whereby the air-fuel ratio during operation becomes lean. On the other hand, setting the target equivalent ratio provisional value TFBYA1 for the first injection to 1.0 means that the air-fuel ratio of the exhaust by the first injection is stoichiometric. Therefore, if the target equivalent ratio provisional value for the first injection is followed, the air-fuel ratio increases stepwise at the timing t0. However, if the equivalence ratio (air-fuel ratio) of the first injection is switched stepwise, a torque step is produced and affects the drivability, so the gradually increasing value is set to the target equivalent of the first injection as shown in the figure. Calculated as the ratio TFBYAm (see the solid line in the fifth row).
[0041]
More specifically, in the lean burn engine of the present embodiment, the engine target torque TTC is calculated based on the engine speed Ne and the accelerator opening (detected by the accelerator opening sensor 14), and the target torque TTC and the first time are calculated. The target intake air amount is calculated from the target equivalence ratio TFBYAm of the injection, and the throttle opening is controlled by the throttle actuator 5a so that the same amount of air as the target intake air amount is sucked. Regardless of the change in the target equivalent ratio TFBYAm, the engine always generates the torque required by the driver. At this time, if the target equivalence ratio of the first injection changes abruptly, intake air control cannot catch up, and torque fluctuations unintended by the driver may occur. For this reason, a process (ramp process) for gradually increasing the target equivalent ratio of the first injection is required.
[0042]
<4> In order to perform air-fuel ratio enrichment control by two injections at the timing t1 when the target equivalent ratio TFBYAm of the first injection coincides with the target equivalent ratio preliminary value TFBYA1 (= 1.0) of the first injection. The equivalent ratio increase FBYARNOx (equivalent ratio increment necessary for reduction and purification of NOx released from the underfloor catalyst) is calculated as the target equivalent ratio TFBYAa for the second injection (see the sixth stage). The equivalent ratio increase FBYARNOx takes into consideration the reducing agent efficiency REFF (representing the proportion of fuel actually used for NOx reduction purification out of the fuel supplied for NOx reduction purification) in addition to the released NOx concentration RNOx. To calculate.
[0043]
<5> The target equivalent ratio TFBYAa of the second injection is set to 0 in order to end the second injection at the timing t2, while the air-fuel ratio enrichment control is performed by switching to the first injection. A value obtained by adding the equivalent ratio increase amount FBYARNOx calculated as described above to 1.0 is calculated as a target equivalent ratio provisional value TFBYA1 for the first injection (see the solid line in the fifth stage).
[0044]
<6> The target equivalent ratio provisional value TFBYA1 for the first injection is returned to the map value TFBYA0 from the value of 1.0 + FBYARNOx at t3 which is the end timing of the catalyst regeneration control. Even at this time, if the target equivalent ratio provisional value TFBYA1 for the first injection is switched stepwise (see the fifth dot-and-dash line), a torque step occurs and affects the drivability, as shown in the figure. Is calculated as the target equivalent ratio TFBYAm for the first injection (see the solid line in the fifth stage).
[0045]
<7> A value obtained by adding the target equivalent ratio TFBYAm of the first injection and the target equivalent ratio TFBYAa of the second injection is the total target equivalent ratio TFBYA (see the bottom row).
[0046]
The outline of the catalyst regeneration control is finished as described above, and a specific explanation will be given by the following routine (flow chart).
[0047]
The routine of FIG. 3 is for determining whether or not regeneration control of the underfloor catalyst is necessary, and this routine is executed at regular intervals (for example, every 10 ms). This calculation cycle is the same for other routines (FIGS. 7, 12, 14, and 17) described later.
[0048]
Of the values calculated or set in this routine, values required for the next calculation in this routine and values required in other routines described later are stored in the ECM 11 when this routine is terminated (RETURN). Stored in the memory. This also applies to other routines described later.
[0049]
In S101 and S102, the intake air flow rate Qa is read from the output signal of the air flow meter 13, and the engine rotation speed Ne, the target torque TTC, the total target equivalent ratio TFBYA, and the previous value of NOx holding amount TNOxz are read from the memory in the ECM 11.
[0050]
The NOx retention amount TNOx is a value calculated by this routine. Since the value read in S102 is calculated and stored in the memory when the routine was executed last time, the subscript z is used to distinguish it from the value calculated this time. Attached. The engine speed Ne is calculated in a separate routine each time the crank angle sensor 12 outputs a reference signal, and the latest value is stored in the memory. The target torque TTC and the total target equivalent ratio TFBYA are calculated by a target intake air amount calculation routine (FIG. 14) and a target equivalent ratio calculation routine (FIG. 12) described later, and the latest values are stored in the memory.
[0051]
In S103, the total target equivalent ratio TFBYA is compared with 1.0. The equivalence ratio is the reciprocal of the excess air ratio λ, and when the total target equivalence ratio TFBYA is smaller than 1.0, it indicates that the air-fuel ratio of the exhaust gas is lean. When the air-fuel ratio of the exhaust gas is lean, NOx is newly trapped and held in the underfloor catalyst. Therefore, in order to calculate the newly held NOx amount and the NOx holding amount TNOx that is the integrated value, S104, S104, The process proceeds to S105.
[0052]
First, in S104, the NOx concentration CNOx in the exhaust is calculated from the engine speed Ne and the target torque TTC. For example, a value may be looked up from a control map (FIG. 4) in which CNOx is stored in correspondence with Ne and TTC. TTC is used as a value representative of engine load. Other parameters may be used as long as they represent the engine load.
[0053]
In S105, a value obtained by adding the NOx trap amount per calculation cycle (per 10 ms) obtained based on the value obtained by multiplying the exhaust gas flow rate by the NOx concentration CNOx in the exhaust gas to the previous NOx retention amount TNOxz (NOx retention amount ( This value) is calculated as TNOx. That is, the arithmetic expression is
[0054]
[Expression 1]
TNOx = TNOXx + K1 × Qa × CNOx × t,
Where Qa: intake air flow rate (≈ exhaust flow rate),
K1: constant,
t: calculation cycle (= 10 ms),
It is. K1 × Qa × CNOx in the second term on the right side of Equation 1 is the NOx trap amount per unit time, and a value obtained by multiplying this by the calculation cycle is the NOx trap amount per calculation cycle. K1 is a coefficient for unit conversion.
[0055]
In S106, the NOx retention amount TNOx is compared with the predetermined amount TNOx0. TNOx0 is about ½ of the saturation NOx retention amount of the underfloor catalyst and is experimentally obtained in advance. When it is possible to determine the deterioration of the underfloor catalyst, it is preferable to decrease TNOx0 as the degree of deterioration progresses.
[0056]
When TNOx is equal to or lower than TNOx0, the current process is terminated as it is. When TNOx exceeds TNOx0 due to repeated operations of S104 and S105 in the lean air-fuel ratio operation region, the process proceeds from S106 to S107, and the regeneration flag FNOx (set to 0) is reached. Initial setting) = 1. FNOx = 1 indicates that catalyst regeneration control is necessary, and FNOx = 0 indicates that catalyst regeneration control is not necessary.
[0057]
On the other hand, when TFBYA is 1.0 or more, since it is a stoichiometric or rich air-fuel ratio operation region, NOx is released from the underfloor catalyst. Therefore, the process proceeds from S103 to S108, and the temperature Tcat of the underfloor catalyst that affects the concentration of released NOx is calculated from the engine rotational speed Ne and the target torque TTC. For example, a value may be looked up from a control map (FIG. 5) in which Tcat is stored in correspondence with Ne, TTC. The TTC is used as a representative value of the engine load (same as S104). Other parameters may be used as long as they represent the engine load. Further, Tcat may be detected directly by attaching a temperature sensor to the underfloor catalyst.
[0058]
Based on the catalyst temperature Tcat and the NOx retention amount TNOx calculated in this way, the released NOx concentration RNOx is calculated in S109. For example, a value may be looked up from a control map (FIG. 6) in which RNOx is stored in association with TNOx and Tcat.
[0059]
In S110, a value obtained by subtracting the NOx emission amount per calculation cycle (per 10 ms) obtained based on the value obtained by multiplying the exhaust gas flow rate by the emission NOx concentration RNOx from TNOxz which is the previous value of the NOx retention amount (this time) Value) Calculated as TNOx. In other words, the arithmetic expression is
[0060]
[Expression 2]
TNOx = TNOXz−K1 × Qa × RNOx × t,
Where Qa: intake air flow rate (≈ exhaust flow rate),
K1: constant,
t: calculation cycle (= 10 ms),
It is. K1 × Qa × RNOx in the second term on the right side of Equation 2 is the NOx release amount per unit time, and a value obtained by multiplying this by the calculation cycle is the NOx release amount per calculation cycle. K1 is a coefficient for unit conversion.
[0061]
In S111, the NOx retention amount TNOx is compared with zero. When TNOx is less than or equal to zero, the process proceeds to S112 and TNOx is limited to zero. Since catalyst regeneration control is not necessary when TNOx = 0, the regeneration flag FNOx = 0 is set in S113.
[0062]
The routine of FIG. 7 is for setting the injection mode.
[0063]
The injection mode includes a two-injection mode and a one-injection mode. By setting the two-injection flag F2INJ as described below, when FNOx = 1 and F2INJ = 1, the two-injection mode, FNOx = 1 and F2INJ = 0 is the one-time injection mode. The combustion chamber temperature TC2 at the time of the second injection is estimated, and it is determined based on this estimated temperature whether or not the second injection mode is suitable as the air-fuel ratio enrichment control.
[0064]
In S201, the regeneration flag FNOx is checked. When FNOx = 1 (catalyst regeneration control is required), the process proceeds to S202 and subsequent steps.
[0065]
S202 to S207 are portions for estimating the combustion chamber temperature TC2 during the second injection. First, in S202 and S203, the coolant temperature Tw is read from the output signal of the water temperature sensor 15, and the engine speed Ne, the target torque TTC, and the ignition timing ADV are read from the memory in the ECM 11. The ignition timing ADV is calculated by another routine (not shown), and the latest value is stored in the memory.
[0066]
In S204, the combustion peak temperature TCpeak is calculated based on the engine speed Ne and the target torque TTC. For example, a value may be looked up from a control map (FIG. 8) in which TCpeak is stored in correspondence with Ne, TTC. In the present embodiment, since the combustion by the first injection in the case of performing the second injection is always performed by stoichiometry, the control map of FIG. 8 may store experimental values under the stoichiometric condition. Note that TTC is used as a representative value of the engine load (same as S104 in FIG. 3). Other parameters may be used as long as they represent the engine load.
[0067]
In S205 and S206, the correction rate TCadv (0 <TCadv ≦ 1) for considering the temperature drop in the period from the time when the combustion temperature reaches a peak to the timing of the second injection is set to the engine speed Ne and the ignition timing ADV. Based on the engine speed Ne and the water temperature Tw, a correction factor TCtw (0 <TCtw ≦ 1) for considering the temperature drop due to the combustion gas being cooled by the cylinder wall or the like is calculated based on these 2 A value obtained by multiplying the two temperature drop correction factors TCadv and TCtw by the combustion peak temperature TCpeak in S207 is calculated as the combustion chamber temperature TC2 during the second injection. For the temperature drop correction factor, for example, the control map (FIG. 9) stores TCadv corresponding to Ne and ADV, and similarly stores the TCtw corresponding to Ne and Tw (FIG. 9). The value may be looked up from FIG. TCadv and TCtw both indicate that the larger the value, the smaller the rate of temperature drop.
[0068]
In S208, S209, S211, S212, and S213, whether or not the double injection mode is suitable as the air-fuel ratio enrichment control is determined by comparing the TC2 calculated in this way with the determination values with hysteresis (TC2INJH, TC2INJL). It is a part to judge. Specifically, TC2 is compared with the determination value TC2INJH at S208, and TC2 is compared with another determination value TC2INJL at S211 and S212, and the two-time injection flag F2INJ is checked.
[0069]
Here, TC2INJH is set to a temperature at which the proportion of HC species effective for NOx reduction increases as the fuel injected the second time is thermally decomposed well in the combustion chamber. On the other hand, TC2INJL is a lower temperature than TC2INJH, and good thermal decomposition of the fuel injected at the second time cannot be expected, but the lower limit temperature that does not deteriorate the exhaust emission as compared with the case of the first injection. Set to.
[0070]
In the following cases (1) and (2), the double injection flag F2INJ = 1 (S209), and in the cases (3) and (4), the double injection flag F2INJ = 0 (S213). F2INJ = 1 indicates that it is suitable for twice injection, and F2INJ = 0 indicates that it is not suitable for twice injection.
[0071]
(1) If TC2> TC2INJH,
(2) When TC2INJH ≧ TC2> TC2INJL and F2INJ = 1,
(3) When TC2INJH ≧ TC2> TC2INJL and F2INJ = 0,
(4) If TC2INJL ≧ TC2,
With this configuration, for example, when TC2 changes from a high state to a low state, the two-time injection flag F2INJ = 1 remains even when TC2 becomes TC2INJH or less, and the temperature drops to TC2INJL or less. Only then will it switch from 1 to 0. On the other hand, when TC2 changes from a low state to a high state, even if TC2 exceeds TC2INJL, the two-time injection flag F2INJ = 0 is maintained, and the temperature rises and exceeds TC2INJH for the first time from 0 to 1 Switch to.
[0072]
The reason why the determination value for determining the suitability of the two-time injection is provided with hysteresis is to prevent frequent switching between the two-time injection and the one-time injection. That is, the combustion by the first injection at the time of the second injection is performed by stoichiometry, whereas the combustion at the time of the first injection by the rich air-fuel ratio is accompanied by a slight torque shock. However, frequent switching of the air-fuel ratio can be avoided by adding hysteresis.
[0073]
When the two-time injection flag F2INJ = 1, the reducing agent efficiency REFF representing the ratio of the fuel actually used for NOx reduction purification out of the fuel supplied for NOx reduction purification based on the engine rotational speed Ne and TC2 is calculated. (S209, S210). For example, a value may be looked up from a control map (FIG. 11) in which REFF is stored in correspondence with Ne and TC2. When fuel for NOx reduction purification is supplied to the underfloor catalyst by twice-injection, the higher the TC2, the more the thermal decomposition of the fuel injected the second time proceeds, so the reductant efficiency REFF increases, and the engine speed Ne increases. The lower the value, the longer the time that the fuel injected for the second time is exposed to the combustion gas and the thermal decomposition proceeds, so that the reducing agent efficiency REFF increases. FIG. 11 shows this.
[0074]
On the other hand, when F2INJ = 0, the reducing agent efficiency REFF is set to a predetermined value K3 (S213, S214). When the injection is not performed twice, the excess fuel that is burned at the rich air-fuel ratio by the one-time injection is used as a reducing agent for NOx reduction purification. However, this excess fuel is not thermally decomposed much, and Since the degree of thermal decomposition hardly changes depending on the operating conditions, REFF is set to a fixed value here. The size of K3 is approximately the same as the map value when TC2 = TC2INJL in the control map of FIG.
[0075]
On the other hand, when the regeneration flag FNOx = 0, the process proceeds from S201 to S215, and the two-time injection flag F2INJ = 1. At this time, since the regeneration flag FNOx = 0, there is no influence on the actual fuel injection even if the double injection flag F2INJ = 1 here, but when FNOx = 0, by setting F2INJ = 1, Next, when the regeneration flag FNOx becomes 1, it becomes easy to select the twice injection mode.
[0076]
By setting the two-injection flag F2INJ in this way, when FNOx = 1, the two-injection mode is set when F2INJ = 1 and the one-injection mode is set when F2INJ = 0.
[0077]
The routine of FIG. 12 is for calculating three types of target equivalent ratios. Here, based on the engine operating conditions (Ne, TTC) and the necessity of catalyst regeneration control (FNOx value), the suitability of the second injection (F2INJ value), the target equivalent ratio TFBYAm for the first injection, the second time Three types of target equivalence ratio TFBYAa for injection and total target equivalence ratio TFBYA as the sum of these two values are calculated.
[0078]
In S301, the engine rotational speed Ne, the target torque TTC, the released NOx concentration RNOx, the reducing agent efficiency REFF, and the previous value of the target equivalence ratio of the first injection are read from the memory in the ECM11. The target equivalence ratio TFBYAm is a value calculated in this routine, and the value read in S301 is calculated when the routine was executed last time and stored in the memory. The letter z is attached (same as S102 in FIG. 3).
[0079]
In S302, the basic value TFBYA0 of the target equivalence ratio is calculated from the engine speed Ne and the target torque TTC. For example, a value may be looked up from a control map (FIG. 13) in which TFBYA0 is stored in correspondence with Ne and TTC.
[0080]
In S303, the regeneration flag FNOx is checked. When FNOx = 1 (catalyst regeneration control is required), the routine proceeds to S304, where the released NOx concentration RNOx is divided by the reducing agent efficiency REFF, that is,
[0081]
[Equation 3]
FBYARNOx = RNOx / REFF
The equivalent ratio increase FBYARNOx required for the reduction purification of NOx released from the underfloor catalyst is calculated by the following equation.
[0082]
Here, the equivalent ratio increment FBYARNOx is a value obtained by subtracting 1.0, which is the stoichiometric equivalent ratio, from the total target equivalent ratio TFBYA, which is obtained as follows. First, the amount of NOx released from the underfloor catalyst per unit time is as described in S110 of FIG.
Qa x RNOx
It becomes. On the other hand, the amount of fuel that flows into the underfloor catalyst per unit time is obtained by Qa × FBYARNOx, and the proportion of the fuel that is actually used as a reducing agent in this fuel is represented by REFF. If you try to supply the reducing agent
Qa x RNOx = Qa x FBYARNOx x REFF
The relationship may be established. If this equation is rearranged for FBYARNOx, the above Equation 3 is obtained.
[0083]
Strictly speaking, a constant for unit conversion is required, but when the REFF control map (FIG. 13) is created, the value including the constant may be stored.
[0084]
In S305, the double injection flag F2INJ is checked. When F2INJ = 1 (appropriate for the second injection), all the fuel for NOx reduction purification is supplied by the second injection, and the first injection supplies the stoichiometric fuel. The process proceeds to S307 in order to supply all the fuel including the fuel for NOx reduction purification by one injection when the temporary equivalent value TFBYA1 of the target equivalent ratio is 1.0 and when the two-injection flag F2INJ = 0. Set 1.0 + FBYARNOx to TFBYA1.
[0085]
On the other hand, when the regeneration flag FNOx = 0, the process proceeds from S303 to S308, and the basic value TFBYA0 of the target equivalence ratio is set to TFBYA1 as it is.
[0086]
In S309, TFBYAmz, which is the previous value of the target equivalence ratio of the first injection, is compared with 1.0. When TFBYAmz is smaller than 1.0, the process proceeds to S310 to S316, and processing (ramp processing) for gradually changing the target equivalent ratio of the first injection is performed. That is, in step S310, TFBYAmz is compared with the provisional value TFBYA1 of the target equivalent ratio of the first injection. When TFBYA1 is switched from the basic value TFBYA0 (value smaller than 1.0) to 1.0 due to the start of the catalyst regeneration control in the lean air-fuel ratio operation region, since TFBYAmz is smaller than TFBYA1 at first, the process proceeds to S311 and becomes TFBYAmz. A value obtained by adding a predetermined step value DMP is calculated as a target equivalent ratio (current value) TFBYAm. The operation of S311 is repeated while TFBYAmz is smaller than TFBYA1, and when TFBYAm becomes TFBYA1 or more, the process proceeds from S312 to S313, and the value of TFBYAm is limited to TFBYA1.
[0087]
Similarly, if TFBYA1 is switched from the value of 1.0 + FBYARNOx to the basic value TFBYA0, for example, if TFBYAmz is equal to or greater than TFBYA1, the process proceeds from S310 to S314, and the target equivalent ratio ( This value) is calculated as TFBYAm. The operation of S314 is repeated while TFBYAmz is greater than TFBYA1, and when TFBYAm becomes equal to or less than TFBYA1, the process proceeds from S315 to S316, and the value of TFBYAm is limited to TFBYA1.
[0088]
The target equivalence ratio TFBYAm for the first injection is a value that affects the output torque of the engine (which leads to the generation of engine torque), so the ramp processing of S310 to S316 is performed so that the output torque of the engine does not change suddenly. In the engine of this embodiment, the target intake air amount TQa is obtained from the target torque TTC and the target equivalence ratio TFBYAm of the first injection, and the throttle opening is controlled based on this TQa. The target torque can be obtained regardless of the change in the target equivalent ratio TFBYAm of the injection, but if the TTFYAm changes suddenly, the intake air amount cannot be controlled, so the above-described ramp processing is performed.
[0089]
On the other hand, when TFBYAmz is 1.0 or more, the process proceeds from S309 to S317, and TFBYA1 is set as TFBYAm as it is. That is, the ramp process is not performed when TFBYAmz, which is the previous value of the target equivalence ratio of the first injection, is 1.0 or more. In this case, when the air-fuel ratio enrichment control is performed by one injection, the ramp process is performed until the air-fuel ratio is enriched from the equivalent ratio of 1.0 to the equivalent ratio required for NOx reduction. In this case, it is possible that the air-fuel ratio is gradually enriched and a situation occurs in which the amount of the reducing agent is insufficient due to a delay in supplying the reducing agent with respect to the NOx release amount. Further, it is conceivable that a situation in which the amount of reducing agent is insufficient occurs if the above-described ramp processing is performed even when the one-time injection and the two-time injection are switched during a series of air-fuel ratio enrichment control. On the other hand, when the TFBYAm is set to 1.0 or more in accordance with the driving conditions, the driver is requesting a high output. In such a case, there is no problem even if the generated torque changes slightly.
[0090]
In S318, S319, and S320, two flags (regeneration flag FNOx, twice injection flag F2INJ) and the target equivalent ratio TFBYAm of the first injection are observed. When all of FNOx = 1 (catalyst regeneration control is required), F2INJ = 1 (suitable for two-time injection), and TFBYAm = 1.0 are satisfied, the equivalent ratio increase FBYARNOx is set to 2. The target equivalent ratio TFBYAa for the second injection is set, and otherwise, the process proceeds to S322 so that TFBYAa = 0 is set so as not to perform the second injection.
[0091]
The target equivalent ratio TFBYAa for the second injection is set on the condition that TFBYAm = 1.0. If the second injection is performed when the combustion is performed at the lean air-fuel ratio, 2 is set. This is because the fuel of the second injection is burned by the oxygen molecules remaining in the combustion chamber, and the exhaust temperature may be significantly increased to deteriorate the durability of the manifold catalyst.
[0092]
A value obtained by adding the target equivalent ratio TFBYAa of the second injection calculated in this way and the target equivalent ratio TFBYAm of the first injection is calculated as a total target equivalent ratio TFBYA in S323.
[0093]
The routine of FIG. 14 is for calculating the target intake air amount.
[0094]
In S401 and S402, the accelerator opening Aps is read from the output signal of the accelerator opening sensor 14, and the engine rotational speed Ne and the target equivalent ratio TFBYAm of the first injection are read from the memory in the ECM 11.
[0095]
In S403 and S404, the target torque (engine output torque requested by the driver) TTC is calculated based on the accelerator opening Aps, and the engine efficiency ITA is calculated based on the engine rotational speed Ne and the target equivalence ratio TFBYAm of the first injection. Then, a value obtained by dividing the target torque TTC by ITA and TFBYAm in S405 is calculated as a target intake air amount (intake air amount per combustion necessary for obtaining the target torque TTC) TQa.
[0096]
The target torque is a value from a control table (FIG. 15) in which TTC is stored corresponding to Aps, for example, and an engine efficiency is a value from a control map (FIG. 16) in which ITA is stored in correspondence with Ne and TFBYAm, for example. Look up. ITA represents the efficiency with which the energy of the supplied fuel is converted into torque.
[0097]
The target intake air amount TQa calculated in this way is used in a throttle control routine (not shown). Specifically, a target throttle opening for making the actual intake air amount Qa coincide with the target intake air amount TQa is calculated, and the actual throttle opening (detected by the throttle opening sensor 16) is made coincident with the target throttle opening. A throttle opening degree control signal is output to the throttle actuator 5a.
[0098]
The routine of FIG. 17 is for calculating a fuel injection control value (fuel injection pulse width and fuel injection timing).
[0099]
In S501 and S502, the intake air flow rate Qa is read from the output signal of the air flow meter 13, the engine speed Ne is read from the memory in the ECM 11, the target equivalent ratio TFBYAm of the first injection, and the target equivalent ratio TFBYAa of the second injection is read. Among these, the basic injection pulse width Tp for making the air-fuel ratio in the combustion chamber stoichiometric is calculated in S503 from Qa and Ne.
[0100]
In S504 and S505, using this basic injection pulse width Tp and the target equivalent ratio TFBYAm of the first injection,
[0101]
[Expression 4]
Ti1 = Tp × TFBYAm × α × 2 + Ts,
Where α: air-fuel ratio feedback correction coefficient,
Ts: Invalid pulse width,
By using the following formula, the fuel injection pulse width Ti1 of the first injection at the time of sequential injection, and the target equivalent ratio TFBYAa of the basic injection pulse width Tp and the second injection,
[0102]
[Equation 5]
Ti2 = Tp × TFBYAa × 2 + Ts,
Where α: air-fuel ratio feedback correction coefficient,
Ts: Invalid pulse width,
The fuel injection pulse width Ti2 of the second injection at the time of sequential injection is calculated by the following formula.
[0103]
Here, the air-fuel ratio feedback correction coefficient α in the equations (4) and (5) is determined by an air-fuel ratio feedback control routine (not shown). ₂ This is calculated during the stoichiometric operation based on the output of the sensor 17 (see FIG. 1), and the value is clamped to 1 during the catalyst regeneration control. Ts is a value that takes into account the operation delay of the fuel injection valve.
[0104]
In S506, the fuel injection timing IT1 of the first injection is calculated based on TFBYAm, Ne, and Ti1. In the lean burn engine of the present embodiment, stratified combustion is performed during lean air-fuel ratio operation, and homogeneous combustion is performed during stoichiometric or rich air-fuel ratio operation. Therefore, during lean air-fuel ratio operation (TFBYAm is less than 1.0) IT1 is set in the latter half of the compression stroke, and IT1 during stoichiometric or rich air-fuel ratio operation (when TFBYAm is 1.0 or more) is set during the intake stroke. It should be noted that IT1 is the intake stroke when homogeneous combustion is performed even during the lean air-fuel ratio operation.
[0105]
In S506, the fuel injection timing IT2 of the second injection is calculated based on Ne and Ti2. When TFBYAa = 0, Ti2 = Ts from the equation (5), and the fuel injection valve is not opened in this state.
[0106]
The fuel injection pulse width Ti1 for the first injection calculated in this way, the fuel injection timing IT1 for the first injection, the fuel injection pulse width Ti2 for the second injection, and the fuel injection timing IT2 for the second injection. Used in a fuel injection control routine (not shown). For example, in the case of the double injection mode, when the signal of the crank angle sensor 12 coincides with IT1 of the # 1 cylinder, a fuel injection control pulse signal having Ti1 as the valve opening width is output to the fuel injection valve of the # 1 cylinder. When the signal of the crank angle sensor 12 coincides with IT2 of the # 1 cylinder, a fuel injection control pulse signal having Ti2 as the valve opening width is output to the fuel injection valve of the # 1 cylinder.
[0107]
Here, the operation of the present embodiment will be described with reference to the time chart of FIG. 18. As described above, the figure shows that the engine load is relatively high at the start of the catalyst regeneration control, and the combustion chamber temperature TC2 at the second injection is relatively high. Is higher than the determination value TC2INJH, which is an example when TC2 becomes lower than a predetermined value TC2INJL due to a decrease in engine load during the air-fuel ratio enrichment control, and then the catalyst regeneration control ends. T0 to t4 are assigned to timings that are points in control. An explanation will be given along the timings t0 to t4 as follows.
[0108]
t0: Since the NOx retention amount TNOx of the underfloor catalyst exceeds the predetermined amount TNOx0, catalyst regeneration control is required (FNOx = 1).
[0109]
t0 to t1: Ramp processing of the target equivalent ratio TFBYAm for the first injection.
[0110]
t1: Since TFBYAm reaches TFBYA1 (= 1.0), the second injection can be executed, and the supply of fuel to the underfloor catalyst by the second injection is started.
[0111]
t1 to t2: Fuel from the second injection in the expansion stroke is supplied to the underfloor catalyst while achieving stoichiometric combustion by the first injection. At this time, the fuel is thermally decomposed by the high-temperature heat in the combustion chamber and the ratio of highly reactive HC species is increased, so that reduction and purification of released NOx is efficiently performed. As a result, the NOx retention amount TNOx of the underfloor catalyst gradually decreases, and accordingly, the released NOx concentration RNOx also decreases. Therefore, the equivalent ratio increase FBYARNOx for reducing and purifying the NOx whose concentration has decreased is reduced, and the second time. The target equivalent ratio TFBYAa for the injection of becomes gradually smaller.
[0112]
t2: The two-injection mode is switched to the one-injection mode due to a decrease in TC2. At this time, the equivalent ratio increase FBYARNOx slightly increases from before the switching. This is because the reducing agent efficiency REFF at the time of one-time injection is smaller than the reducing agent efficiency REFF at the time of two-time injection, so that the equivalent ratio increase amount at the time of one-time injection is ensured in order to secure the same amount of reducing agent. This is because the minute becomes larger than the equivalent ratio increase at the time of the two-time injection.
[0113]
t2 to t3: The same as t1 to t2. That is, since the NOx retention amount TNOx of the underfloor catalyst is reduced and the released NOx concentration RNOx is further reduced, the equivalent ratio increase FBYARNOx for reducing and purifying this reduced NOx is reduced, and TFBYAm is gradually reduced.
[0114]
t3: The NOx retention amount TNOx of the underfloor catalyst decreases to zero, and the request for catalyst regeneration control is released (FNOx = 0).
[0115]
t3 to t4: Ramp processing of the target equivalent ratio TFBYAm for the first injection.
[0116]
As described above, in the present embodiment, when the air-fuel ratio enrichment control for purifying the NOx held in the underfloor catalyst is performed by two injections divided into a period that is associated with generation of engine torque and a period that is not associated with generation of engine torque, Paying attention to the fact that when the combustion chamber temperature TC2 at the second injection is high, the fuel injected at the second time is reformed into a fuel having a high ratio of those having multiple bonds by thermal decomposition, and the reactivity as a reducing agent is improved. Conditions for estimating the combustion chamber temperature TC2 during the second injection to determine whether the ratio of highly reactive HC species is increased by reforming, and for increasing the ratio of highly reactive HC species by reforming Then, the amount of the reducing agent, that is, the fuel injection amount (FBYANOx) for the enrichment of the air-fuel ratio in the second injection is calculated appropriately, and this is supplied to the underfloor catalyst by the second injection. Because, when the air-fuel ratio enrichment control is performed particularly at the time of high-load combustion chamber temperature becomes higher, it is possible to purify NOx held by the underfloor catalyst efficiently.
[0117]
On the other hand, if the injection is performed twice up to the condition where the combustion chamber temperature TC2 during the second injection is insufficient, such as at low load, the reactivity of the reducing agent becomes worse than in the case of the single injection, and NOx reduction is performed. Although the purification efficiency is reduced and the exhaust HC is increased, when the temperature in the combustion chamber becomes inadequate, the control is performed to enrich the air-fuel ratio by switching to once injection. It is possible to prevent a decrease in the efficiency of NOx reduction purification and an increase in exhaust HC caused by performing the injection twice.
[0118]
In addition, when the injection is performed twice in the temperature range where the temperature in the combustion chamber becomes high, the reactivity of the reducing agent is higher than that in the case of the single injection, and the NOx reduction purification efficiency is increased. Since the NOx reduction purification efficiency equivalent to that in the case of one-time injection is obtained with less fuel than in the case, in this embodiment, the total target equivalent ratio TFBYA (= TFBYAm + TFBYAa) when air-fuel ratio enrichment control is performed with two-time injection. Can be set to be leaner than the target equivalent ratio TFBYAm when air-fuel ratio enrichment control is performed with one-time injection, whereby the injection amount when air-fuel ratio enrichment control is performed is set to the air-fuel ratio with one-time injection. This can be reduced as compared with the case where the enrichment control is performed, and an increase in HC discharged without being subjected to NOx reduction purification can be suppressed.
[0119]
Further, since TC2 is estimated according to all of the engine speed, engine load, ignition timing, and engine coolant temperature, even if the engine speed, engine load, ignition timing, and engine coolant temperature change, the temperature in the combustion chamber is accurate. Can be estimated. That is, the combustion peak temperature TCpeak is calculated based on the engine rotational speed Ne and the target torque TTC (corresponding to the engine load), and the temperature drop in the period from the time when the combustion temperature reaches the peak to the second injection time is taken into consideration. The correction factor TCadv is calculated based on the engine rotational speed Ne and the ignition timing ADV, and the correction factor TCtw for considering the temperature drop due to the cooling of the combustion gas is calculated based on the engine rotational speed Ne and the engine coolant temperature Tw. Since the value obtained by multiplying the two temperature drop correction factors TCadv and TCtw by the combustion peak temperature TCpeak (the value obtained by correcting TCpeak with TCadv and TCtw) is calculated (estimated) as TC2, the ignition timing ADV and its Even when there is a difference in engine speed, the combustion temperature peaks. TC2 accurately reflects the temperature drop in the period from the time point until the second injection, and the temperature drop due to cooling of the combustion gas even if there is a difference in the engine coolant temperature Tw and the engine speed Ne at that time Can be made.
[0120]
In addition, if the second injection is performed before the combustion by the first injection is completed, the fuel is partially oxidized by the oxygen molecules existing in the combustion chamber at the time of combustion, and a lot of CO is generated. However, according to the present embodiment, the second injection is performed when the combustion by the first injection is almost completed, so that partial oxidation occurs. The ratio can be reduced, and the exhaust air-fuel ratio by the first injection becomes stoichiometric, so that the fuel of the second injection hardly generates partial oxidation, and the fuel for the air-fuel ratio enriched fuel Almost all of (the fuel injected the second time) can be supplied to the underfloor catalyst as HC.
[0121]
Further, the target equivalent ratio TFBYAa of the second injection is taken into consideration without considering the released NOx concentration and the reducing agent efficiency representing the ratio of the fuel actually used for NOx reduction purification among the fuel supplied for NOx reduction purification. Is set, the amount of fuel as a reducing agent is insufficient or excessive with respect to the amount of NOx released from the underfloor catalyst. However, according to the present embodiment, the target equivalent ratio TFBYAa for the second injection is set. Since the calculation is based on the released NOx concentration RNOx and the reducing agent efficiency REFF, the amount of fuel as a reducing agent can be supplied without excess or deficiency with respect to the amount of NOx released from the underfloor catalyst.
[0122]
Moreover, according to this embodiment, since the reducing agent efficiency REFF is set according to TC2, even if TC2 changes, the reducing agent efficiency REFF can be given accurately.
[0123]
In addition, if the same torque is to be obtained for the single injection and the double injection, the required air amount may change. In this case, the temperature in the combustion chamber changes up and down in response to changes in the engine load. If these two injections are frequently switched during the air-fuel ratio enrichment control, there is a possibility that drivability will deteriorate from the viewpoint of the followability of the throttle and the intake air amount, etc. , It is determined whether the two-injection mode is suitable by comparing TC2 with determination values with hysteresis (TC2INJH, TC2INJL), so that the one-time injection and the two-time injection frequently occur during the air-fuel ratio enrichment control. Switching hunting can be prevented.
[0124]
The routine in FIG. 19 is a second embodiment, which replaces FIG. 7 in the above-described embodiment (first embodiment).
[0125]
S601 to S604 are almost the same operations as S201 to S207 in FIG. However, the point that the two-injection counter C2INJ and the one-time injection counter C1INJ are read from the memory in the ECM 11 in S603 is different from the first embodiment. Further, the operation of S604 collectively shows the operations of S204 to S207 in FIG.
[0126]
The two-injection counter C2INJ and the one-time injection counter C1INJ are values counted up as follows in a fuel injection control routine (not shown).
[0127]
[1] When two-time injection is executed in any of the cylinders, the two-time injection counter C2INJ is incremented by 1 and the one-time injection counter C1INJ is cleared to zero.
[0128]
[2] When only one injection is executed in any cylinder, the one-time injection counter C1INJ is incremented by one and the two-time injection counter C2INJ is cleared to zero.
[0129]
In S605, the combustion chamber temperature TC2 for the second injection is compared with the determination value TC2INJL. When TC2 is higher than TC2INJL, the process proceeds to S606 and S607, and the two-time injection counter C2INJ and the one-time injection counter C1INJ are viewed. The process proceeds to S608 only when C2INJ = 0 (that is, the immediately preceding combustion cylinder was once-injected) and C1INJ is smaller than the predetermined value S1INJ (that is, the number of continuous executions of one-time injection is small), and the two-injection flag F2INJ = 0 ( Otherwise, the process proceeds to S610, and F2INJ = 1 (appropriate twice injection) is set.
[0130]
On the other hand, when TC2 is equal to or less than TC2INJL, the process proceeds from S605 to S612 and S613, and again, the one-time injection counter C1INJ and the two-time injection counter C2INJ are viewed. The process proceeds to S614 only when C1INJ = 0 (that is, the immediately preceding combustion cylinder was twice-injected) and C2INJ is smaller than the predetermined value S2INJ (that is, the number of times of continuous execution of two-injection is small), and the twice-injection flag F2INJ = 1 ( Otherwise, the process proceeds to S616, and F2INJ = 0 (inappropriate twice injection) is set.
[0131]
Note that the reducing agent efficiency REFF is set to a predetermined value K3 when the two-time injection flag F2INJ = 0 (S608, S609 or S616, S617), and the engine speed Ne is 2 when the two-time injection flag F2INJ = 1. The point (S610, S611 or S614, S615) for calculating the reducing agent efficiency REFF based on the combustion chamber temperature TC2 at the time of the second injection is the same as that in FIG. 7 of the first embodiment.
[0132]
To describe the operation when configured in this way, one-time injection is executed during normal operation (when catalyst regeneration control is not performed), and the one-time injection counter C1INJ has a large value. For this reason, if the combustion chamber temperature TC2 during the second injection is higher than the determination value TC2INJL at the start of the catalyst regeneration control, the flow proceeds as S605 → S606 → S607 → S610 and the two-injection mode is selected (two-injection flag F2INJ = 1). On the other hand, if TC2 is equal to or less than TC2INJL, the flow proceeds from S605 to S612 to S616, and the one-time injection mode is selected (two-time injection flag F2INJ = 0). That is, according to the second embodiment, permission to switch from one injection mode to the other injection mode is that the injection in one injection mode is continuously executed a predetermined number of times (for example, from the one-time injection mode). Since the switching to the two-time injection mode is based on the condition that the one-time injection is continuously executed S1INJ times or more), the switching of the injection mode is less likely to occur than in the first embodiment.
[0133]
As described above, according to the second embodiment, when either the one-time injection mode or the two-time injection mode is selected when the air-fuel ratio enrichment control is performed, a predetermined period (time) is determined from the selected timing. Since the selected injection mode is continued, hunting in which the one-time injection and the two-time injection are frequently switched during the air-fuel ratio enrichment control can be prevented also in the second embodiment.
[0134]
In addition to the second embodiment, the injection mode is selected only once at the start of the catalyst regeneration control (when the regeneration flag FNOx changes from 0 to 1), and the injection mode is continued until the end of the catalyst regeneration control. If it is made, it can be set as simple control.
[0135]
In the embodiment, the case where the second injection is performed when the combustion by the first injection is almost finished has been described. However, the second time when the predetermined period has elapsed from the time when the combustion by the first injection is almost finished. You may make it carry out.
[0136]
In the embodiment, the TC2 is estimated according to all of the engine speed, the engine load, the ignition timing, and the engine coolant temperature. However, the TC2 may be estimated according to any of these.
[0137]
In the embodiment, the case has been described where the target equivalent ratio (target fuel amount) of the first injection is set so that the exhaust air-fuel ratio by the first injection becomes stoichiometric when the second injection is selected. The target equivalence ratio of the first injection may be set so that the exhaust air-fuel ratio by the first injection when the injection is selected is close to the stoichiometry.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram showing the effect of fuel reforming.
FIG. 2 is a control system diagram of one embodiment.
FIG. 3 is a routine for explaining determination of necessity of catalyst regeneration control.
FIG. 4 is a characteristic diagram of NOx concentration in exhaust gas.
FIG. 5 is a characteristic diagram of an underfloor catalyst temperature.
FIG. 6 is a characteristic diagram of the released NOx concentration.
FIG. 7 is a routine for explaining setting of an injection mode.
FIG. 8 is a characteristic diagram of combustion peak temperature.
FIG. 9 is a characteristic diagram of a correction rate.
FIG. 10 is a characteristic diagram of a correction rate.
FIG. 11 is a characteristic diagram of reducing agent efficiency.
FIG. 12 is a routine for explaining calculation of a target equivalent ratio.
FIG. 13 is a characteristic diagram of a basic value of a target equivalent ratio.
FIG. 14 is a routine for explaining calculation of a target intake air amount.
FIG. 15 is a characteristic diagram of target torque.
FIG. 16 is a characteristic diagram of engine efficiency.
FIG. 17 is a routine for explaining calculation of a fuel injection control value.
FIG. 18 is a waveform diagram for explaining the operation of the embodiment;
FIG. 19 is a routine for explaining setting of an injection mode according to the second embodiment.
FIG. 20 is a diagram corresponding to a claim of the first invention.
[Explanation of symbols]
1 Engine body
3 Combustion chamber
6 Fuel injection valve (fuel injection supply means)
7 Manifold catalyst
8 Underfloor catalyst
11 ECM

Claims (11)

When the air-fuel ratio of the inflowing exhaust is a lean air-fuel ratio, NOx in the exhaust is trapped and held, and when the air-fuel ratio of the inflowing exhaust is a rich air-fuel ratio, the held NOx is released and HC in the exhaust A catalyst having a function of reducing and purifying with CO;
In the exhaust emission control device for an engine, comprising means for temporarily enriching the exhaust air-fuel ratio when the NOx retention amount of the catalyst exceeds a predetermined value,
Means for injecting and supplying fuel directly to the combustion chamber;
Using this fuel injection supply means, fuel is supplied only in two times of fuel supply divided into two times, the time that leads to the generation of engine torque and the time that does not lead to the generation of engine torque, and the time that leads to the generation of engine torque Means capable of switching between once injection and
Means for estimating the temperature in the combustion chamber at the second injection of the second injection;
Based on the temperature in the combustion chamber at the time of the second injection, the temperature range in which the fuel of the second injection is reformed into a fuel having a high ratio of highly reactive HC species and the fuel of the second injection is not reformed. means for determining whether the high-temperature der Ru temperature range than,
Means for selecting the second-time injection when it is determined that the temperature of the second-time injection fuel is a reforming temperature range when the exhaust air-fuel ratio is temporarily enriched. Exhaust gas purification device for the engine. 2. The engine exhaust gas purification apparatus according to claim 1, wherein the timing associated with the generation of the engine torque is an intake stroke or a compression stroke in a combustion cycle, and the timing not associated with the generation of the engine torque is an expansion stroke. . 3. The engine exhaust gas purification apparatus according to claim 1, wherein the one-time injection is selected when it is determined that the fuel of the second-time injection is in a temperature range in which the fuel is not reformed. The total target equivalent ratio when the two-time injection is selected when the exhaust air-fuel ratio is temporarily enriched, and the one-time injection when the exhaust air-fuel ratio is temporarily enriched. 4. The engine exhaust gas purification apparatus according to claim 3, wherein the engine exhaust gas purification apparatus is set to be leaner than a target equivalent ratio. The combustion chamber temperature at the time of the second injection is estimated according to any or all of engine speed, engine load, ignition timing, and engine coolant temperature. Exhaust gas purification device for an engine as described in 1. Calculate a combustion peak temperature based on the engine speed and the engine load,
Based on the engine speed and the ignition timing, a correction factor for considering a temperature drop in the period from the time when the combustion temperature reaches a peak to the second injection time, and a temperature drop caused by the combustion gas being cooled A correction factor for taking into account is calculated based on the engine speed and the engine coolant temperature,
6. The engine exhaust gas purification apparatus according to claim 5, wherein a value obtained by correcting the combustion peak temperature with the two temperature drop correction factors is estimated as a combustion chamber temperature at the second injection. The time of the second injection is the time when the combustion by the first injection is almost completed or the time when a predetermined period has elapsed from that time. Engine exhaust purification system. 8. The engine target fuel amount according to claim 7, wherein the target fuel amount of the first injection is set so that the exhaust air-fuel ratio by the first injection when the second injection is selected becomes stoichiometric or in the vicinity thereof. Exhaust purification device. 9. The engine exhaust gas purification apparatus according to claim 8, wherein the target fuel amount of the second injection is calculated based on the released NOx concentration and the reducing agent efficiency. The engine exhaust gas purification apparatus according to claim 9, wherein the reducing agent efficiency is set according to a temperature in the combustion chamber at the time of the second injection. When either the one-time injection or the two-time injection is selected when the exhaust air-fuel ratio is temporarily enriched, the selected injection is continued for a predetermined period from the selected timing. The exhaust emission control device for an engine according to claim 3.

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