JP3603724B2 - Engine exhaust purification device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus for an engine, and more particularly to an apparatus for operating an engine lean (lean mixture).
[0002]
[Prior art]
A three-way catalyst that purifies harmful three components by simultaneously oxidizing HC and CO components and reducing NOx when the exhaust air has a stoichiometric air-fuel ratio (hereinafter referred to as “stoichiometric”). Since the three-way catalyst has a low NOx reduction efficiency at a lean air-fuel ratio, it is difficult to purify NOx in the exhaust of a lean burn engine to a low level, so that the three-way catalyst absorbs NOx when the exhaust air-fuel ratio is lean. When the exhaust air-fuel ratio is rich, a NOx absorbent for desorbing and reducing the NOx absorbed is disposed in the exhaust passage, and the exhausted NOx during the lean operation is absorbed by the NOx absorbent. When the agent becomes a predetermined value or more, the exhaust air-fuel ratio is temporarily made rich, and HC and CO are supplied to the NOx absorbent as a reducing agent, and the NOx absorbed by using this reducing agent component is subjected to desorption reduction treatment. There is known a technique for purifying NOx in exhaust gas of a lean burn engine to a low level while regenerating a NOx absorbent.
[0003]
In addition, when the catalyst is not in an active state, such as immediately after the start of the engine, the catalyst cannot work sufficiently and harmful components in the exhaust gas cannot be efficiently purified. It is known to dispose a catalyst in the vicinity of the exhaust outlet. For this reason, it is conceivable that the NOx absorbent used for the lean burn engine is also disposed near the engine exhaust outlet, but the temperature range in which the NOx absorbent can absorb, desorb, and reduce NOx with high efficiency is considered. Since the temperature may be lower than the temperature near the engine exhaust outlet, it is not always preferable to arrange the NOx absorbent near the engine exhaust outlet.
[0004]
Therefore, there is an engine in which a starting catalyst is arranged near the engine exhaust outlet and a NOx absorbent is arranged downstream of the starting catalyst (see JP-A-11-62563). In this device, a plurality of cylinders are divided into two cylinder groups, and exhaust gas from each cylinder group is first guided to a starting catalyst provided for each cylinder group. It is configured to be led to the NOx absorbent, whereby HC and CO, which are often generated immediately after the engine is started, are oxidized by the starting catalyst, and NOx during the lean operation after the warm-up is completed is reduced to the downstream NOx absorbent. As described above, the harmful three components can be efficiently purified even in a lean burn engine.
[0005]
[Problems to be solved by the invention]
By the way, even in the above-described conventional device in which a starting catalyst is arranged near the engine exhaust outlet and a NOx absorbent is arranged downstream of the starting catalyst, the NOx absorbed by the NOx absorbent is desorbed and reduced in the lean operation range. In this case, the exhaust air-fuel ratio is temporarily made rich to generate a large amount of reducing agent components (HC, CO), which are supplied to the NOx absorbent.
[0006]
At this time, the excess exhaust gas of the reducing agent component discharged from the engine flows into the NOx absorbent on the downstream side after passing through the starting catalyst. Generally, when the starting catalyst of the conventional apparatus has an oxygen storage function, a problem arises in that the reducing agent component to be passed is oxidized by the retained oxygen.
[0007]
Therefore, it is conceivable to control only one of the two divided cylinder groups to the rich air-fuel ratio. That is, since the capacity of the starting catalyst for each cylinder group is half of the total capacity, the amount of oxygen held by one starting catalyst is also half of the entire capacity, and the reducing agent oxidized by the catalyst-holding oxygen. This is because the amount of the component can be reduced by half.
[0008]
At this time, the air-fuel ratio of the cylinder group that is not controlled to the rich air-fuel ratio is desirably about stoichiometric so as not to generate a torque difference from the rich air-fuel ratio cylinder group. Is released, which may reduce the NOx reduction efficiency on the NOx absorbent. In other words, since the amount of oxygen retained by the catalyst is higher as the oxygen concentration in the atmosphere is higher, the starting catalyst of the cylinder group in which the air-fuel ratio is changed from lean to stoichiometric is supplied from the starting catalyst of the cylinder group during lean operation. Most will be released. When this oxygen flows into the NOx absorbent at the same time as the reducing agent component that has passed through the starting catalysts of the rich air-fuel ratio cylinder group, on the NOx absorbent, in addition to the reaction between the NOx and the reducing agent component, oxygen and the reducing agent The reaction with the components is also performed, so that the NOx reduction efficiency decreases.
[0009]
The NOx absorbent of the conventional device releases NOx regardless of the amount of the reducing agent component contained in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas becomes richer than the stoichiometric ratio. When the amount of NOx decreases, the amount of NOx released from the NOx absorbent without being reduced and purified increases.
[0010]
Therefore, the present invention improves the NOx reduction efficiency on the downstream catalyst when the starting catalyst is disposed on the upstream side and the catalyst having the function of trapping and holding NOx is disposed on the downstream side. An object of the present invention is to provide an exhaust gas purification device that can be maintained.
[0011]
[Means for Solving the Problems]
A first invention provides a first cylinder group including one or more cylinders, a second cylinder group including one or more cylinders, a first upstream catalyst to which exhaust gas from the first cylinder group is guided, A second upstream catalyst to which exhaust gas from the second cylinder group is led, the second upstream catalyst having an oxygen storage function; and a downstream catalyst to which exhaust gas from these two upstream catalysts are led, A downstream catalyst having a function of trapping and holding NOx in an excess atmosphere, and a function of releasing and reducing NOx held in an atmosphere of an excess of a reducing agent; When releasing NOx from the catalyst, the air-fuel ratio of each cylinder group is set so that the exhaust air-fuel ratio at the first upstream catalyst inlet becomes rich and the exhaust air-fuel ratio at the second upstream catalyst inlet becomes stoichiometric. Means for controlling In the exhaust gas purifying apparatus for an engine, when the air-fuel ratio control is performed, when oxygen released from the second upstream catalyst and reaching the downstream catalyst is exhausted or after that, the oxygen is passed through the first upstream catalyst. Means are provided for allowing excess exhaust of the coming reducing agent component to reach the downstream catalyst.
[0012]
A second invention provides a first cylinder group including one or a plurality of cylinders, a second cylinder group including one or a plurality of cylinders, a first upstream catalyst to which exhaust gas from the first cylinder group is guided, A second upstream catalyst to which exhaust gas from the second cylinder group is guided and a second upstream catalyst having an oxygen storage function; and a downstream catalyst to which exhaust gas from these two upstream catalysts are guided. A downstream catalyst having a function of trapping and holding NOx when the air-fuel ratio is lean, and a function of releasing and reducing NOx held when the exhaust air-fuel ratio is stoichiometric or rich; When NOx is released from the downstream side catalyst during the lean operation, the exhaust air-fuel ratio of the first cylinder group becomes rich and the exhaust air-fuel ratio of the second cylinder group becomes stoichiometric. Control the air-fuel ratio of The exhaust passage volume from the vicinity of the exhaust outlet of the first cylinder group (for example, an exhaust port) to the downstream side catalyst from the vicinity of the exhaust outlet of the second cylinder group to the downstream side. Make it larger than the volume of the exhaust passage to the catalyst.
[0013]
According to a third aspect, in the second aspect, the exhaust passage volume from the vicinity of the exhaust outlet of the first cylinder group to the first upstream side catalyst is changed from the vicinity of the exhaust outlet of the second cylinder group to the second upstream side catalyst. Larger than the exhaust passage volume.
[0014]
In a fourth aspect based on the third aspect, the length of the exhaust passage from the vicinity of the exhaust outlet of the first cylinder group to the first upstream catalyst is changed from the vicinity of the exhaust outlet of the second cylinder group to the second upstream catalyst. Longer than the length of the exhaust passage.
[0015]
According to a fifth aspect of the present invention, in the third aspect, the exhaust passage diameter from the vicinity of the exhaust outlet of the first cylinder group to the first upstream side catalyst is changed from the vicinity of the exhaust outlet of the second cylinder group to the second upstream side catalyst. Larger than the exhaust path diameter up to.
[0016]
In a sixth aspect based on the second aspect, the exhaust passage volume from the first upstream catalyst to the downstream catalyst is made larger than the exhaust passage volume from the second upstream catalyst to the downstream catalyst.
[0017]
In a seventh aspect based on the sixth aspect, the length of the exhaust passage from the first upstream catalyst to the downstream catalyst is longer than the length of the exhaust passage from the second upstream catalyst to the downstream catalyst.
[0018]
In an eighth aspect based on the sixth aspect, an exhaust passage diameter from the first upstream catalyst to the downstream catalyst is larger than an exhaust passage diameter from the second upstream catalyst to the downstream catalyst.
[0019]
A ninth invention provides a first cylinder group including one or more cylinders, a second cylinder group including one or more cylinders, a first upstream catalyst to which exhaust gas from the first cylinder group is guided, A second upstream catalyst to which exhaust gas from the second cylinder group is guided and a second upstream catalyst having an oxygen storage function; and a downstream catalyst to which exhaust gas from these two upstream catalysts are guided. A downstream catalyst having a function of trapping and holding NOx when the air-fuel ratio is lean, and a function of releasing and reducing NOx held when the exhaust air-fuel ratio is stoichiometric or rich; When NOx is released from the downstream side catalyst during the lean operation, the exhaust air-fuel ratio of the first cylinder group becomes rich and the exhaust air-fuel ratio of the second cylinder group becomes stoichiometric. Control the air-fuel ratio of The exhaust passage volume from the vicinity of an exhaust outlet of the first cylinder group (for example, an exhaust port) to the downstream side catalyst and the vicinity of the exhaust outlet of the second cylinder group to the downstream side. The exhaust passage volume up to the catalyst is configured to be substantially the same, and during the execution of the air-fuel ratio control, the exhaust air-fuel ratio of the second cylinder group is set to stoichiometric and then delayed for a fixed period (constant time). A delay means for making the exhaust air-fuel ratio of the first cylinder group rich is provided.
[0020]
【The invention's effect】
According to the first aspect, when NOx is released from the downstream side catalyst during the lean operation, the air-fuel ratio of the first cylinder group is controlled to be rich and the air-fuel ratio of the second cylinder group is controlled to be stoichiometric. The amount of the reducing agent component that is unnecessarily oxidized by the upstream catalyst can be halved without causing a large torque difference between the groups.
[0021]
In particular, while the oxygen released from the second upstream catalyst is flowing into the downstream catalyst, the reducing agent component is not allowed to flow into the downstream catalyst, so that NOx is not released from the downstream catalyst during this time. The reducing agent component is allowed to flow into the downstream catalyst after the conditions under which the released oxygen has finished flowing into the downstream catalyst and good NOx reduction efficiency is obtained, so that the NOx retained in the downstream catalyst can be efficiently removed. For purification. That is, it is possible to efficiently recover the NOx trap function of the downstream catalyst while maintaining good exhaust performance.
[0022]
According to the second, third, fourth, and fifth aspects of the present invention, the volume of the exhaust passage from the vicinity of the exhaust outlet of the first cylinder group to the downstream catalyst is increased from the vicinity of the exhaust outlet of the second cylinder group to the downstream catalyst. By making the exhaust gas passage volume larger than the exhaust passage volume, when the downstream side catalyst is regenerated in the lean operation range, the exhaust gas of the excessive atmosphere of the reducing agent component from the cylinder group (first cylinder group) in which the exhaust air-fuel ratio becomes rich becomes the first. The timing at which oxygen flows into the downstream catalyst via the upstream catalyst is compared with the timing at which oxygen desorbed from the second upstream catalyst of the cylinder group (second cylinder group) having a stoichiometric exhaust air-fuel ratio flows into the downstream catalyst. Therefore, the downstream catalyst can be efficiently regenerated while maintaining good exhaust performance.
[0023]
Although it is effective to make the length of the exhaust passage of each cylinder substantially equal to the output improvement, the volume of the exhaust passage from the vicinity of the exhaust outlet to the upstream side catalyst may be different between the two cylinder groups. Although the output decreases, according to the sixth aspect, the volume of the exhaust passage from the vicinity of the exhaust outlet to the upstream catalyst is not changed, so that the output can be prevented from decreasing.
[0024]
According to the seventh and eighth aspects, the layout in the engine room becomes easy by changing the volume of the exhaust passage on the downstream side according to the length and diameter.
[0025]
According to the ninth aspect, it is possible to efficiently regenerate the downstream-side catalyst by using the reducing agent component while maintaining the exhaust passage at the same length for improving the output.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
In FIG. 1, 1 is an engine body, 2 is an intake passage, 3 is a throttle device driven by a throttle actuator 3a composed of a DC motor or the like, and 4 is an injection control signal from an ECU (Electronic Control Unit) 10 according to operating conditions. It is a fuel injection valve that injects and supplies fuel so as to have a predetermined air-fuel ratio. Note that the fuel injection valve 4 is provided facing the combustion chamber, but is not limited to this type.
[0027]
The ECU 10 has a reference position signal and a unit angle signal from the crank angle sensor 8, an intake air amount signal from the air flow meter 7, an accelerator opening signal from the accelerator opening sensor 9, and an engine from a water temperature sensor (not shown). A cooling water temperature signal, a gear position signal from a gear position sensor (not shown) of the transmission, a vehicle speed signal from a vehicle speed sensor (not shown), and the like are input, and while the operating state is determined based on these, the load is not so large. In a predetermined operation range, the operation is performed based on the lean air-fuel ratio, and in other operation ranges, the air-fuel ratio is mainly controlled to stoichiometric.
[0028]
The configuration of the engine is an in-line four-cylinder, and when the cylinder numbers are assigned as shown in the figure, the ignition order is # 1- # 3- # 4- # 2. These four cylinders are divided into two cylinder groups. Of these cylinders, the # 1 cylinder and # 4 cylinder are defined as a first cylinder group, the remaining # 2 cylinders and # 3 cylinders are defined as a second cylinder group, and an exhaust passage is provided for each cylinder group. Bundling. That is, the exhaust passage 14a of the # 1 cylinder and the exhaust passage 14d of the # 4 cylinder are bundled into one exhaust passage 15a, and similarly, the exhaust passage 14b of the # 2 cylinder and the exhaust passage 14c of the # 3 cylinder are bundled to form one exhaust passage. An exhaust passage 15b is formed, and the two exhaust passages 15a and 15b are further assembled to form one exhaust passage 16. Since it is necessary to distinguish the exhaust passage of each part, hereinafter, 14a, 14b, 14c, and 14d are referred to as upstream exhaust passages, and 15a and 15b are referred to as downstream exhaust passages.
[0029]
Then, upstream catalysts 11 and 12 are disposed in the downstream exhaust passage 15a of the first cylinder group, downstream exhaust passages 15b of the second cylinder group, and downstream catalysts 13 are disposed in the exhaust passage 16.
[0030]
Of these, the upstream catalysts 11 and 12 are activated early after the engine is started because they are close to the engine body. In the activated state, when there is excess oxygen in the exhaust, oxygen in the exhaust is trapped and held. Has a function (oxygen storage function) of oxidizing the reducing agent component in the exhaust by releasing the oxygen retained when excessive reducing agent components (HC, CO) are present.
[0031]
On the other hand, the downstream side catalyst 13 traps and holds NOx in the exhaust when excess oxygen is present in the exhaust in the active state, and holds NOx when the excess reducing agent component is present in the exhaust. And has the function of reducing the released NOx with a reducing agent component in the exhaust gas.
[0032]
Here, the four upstream exhaust passages 14a to 14d have substantially the same passage length and passage diameter, and the two downstream exhaust passages 15a and 15b have substantially the same passage length and passage diameter. The two upstream catalysts 11 and 12 are selected so as to have substantially the same catalyst capacity and catalyst function.
[0033]
As described above, the downstream catalyst 13 has a function of trapping NOx in the exhaust gas. However, when the retained NOx amount approaches the saturation amount, the NOx trapping efficiency decreases. It is necessary to intentionally supply exhaust gas to release the retained NOx to recover the NOx trap function.
[0034]
The content of the catalyst regeneration control executed by the ECU 10 will be described in detail according to the following flowchart.
[0035]
Here, before starting the description of the flow, the regeneration control of the downstream side catalyst 13 in the present embodiment will be outlined with reference to the waveform diagram of FIG. 6. The diagram shows the case where the lean operation is continued under certain operating conditions. The change of each variable is modeled. In the regeneration control of the present embodiment, as shown at the bottom, when the regeneration timing of the downstream side catalyst 13 is reached at t2 during the lean operation, any of the first and second cylinder groups (first The cylinder group is shown by a solid line, and the second cylinder group is shown by a broken line. In order to clarify the difference between them, they are not slightly overlapped but slightly shifted.) Then, the stoichiometric state is established (at the timing of t3, the stoichiometric state is reached), and the second cylinder group continues the stoichiometric operation until the regeneration end timing of t5. On the other hand, the first cylinder group enriches the air-fuel ratio at a timing t4 after a predetermined delay time (delay period) from the timing t3 when the air-fuel ratio reaches the stoichiometric state, and then changes this air-fuel ratio rich state to a timing t5. Is continued until the playback end timing.
[0036]
Then, from the timing of t5 when the regeneration is completed, the fuel is gradually reduced so as not to cause a large torque step in any of the first and second cylinder groups and returned to the air-fuel ratio before the regeneration control (at the timing of t6). Return to the air-fuel ratio before regeneration control).
[0037]
In order to perform such reproduction control, the following operation is performed.
[0038]
<1> If the integrated value of the amount of NOx trapped in the downstream side catalyst 13 during the lean operation is SNO, this SNO gradually increases (see the third stage), and therefore t2 when the SNO reaches the predetermined value SLNO Is set as the start timing of the regeneration control, and at this time, the NOx flag FLGNO is switched from 0 to 1. This NOx flag is a flag indicating that the regeneration control is executed when FLGNO = 1, and that the regeneration control is not executed when FLGNO = 0 (see the second row).
[0039]
<2> The target equivalence ratio provisional value TFBYA1 is switched from the target equivalence ratio map value TFBYAamp to 1.0 at t2 at the start timing of the reproduction control (see the dashed-dotted line in the fifth row). The target equivalence ratio map value TFBYAmp gives a target equivalence ratio (a value less than 1.0) at the time of lean operation, whereby the air-fuel ratio during operation becomes lean. On the other hand, setting the target equivalence ratio provisional value TFBYA1 to 1.0 means that the air-fuel ratio is stoichiometric. Therefore, according to the target equivalence ratio provisional value, the air-fuel ratio increases stepwise at the timing of t2. However, if the equivalence ratio (air-fuel ratio) is switched in a stepwise manner, a torque step occurs and affects drivability. Therefore, a gradually increasing value (for example, a value increasing stepwise) as shown in the figure is the target equivalent. The ratio is calculated as TFBYA (see the solid line in the fifth row).
[0040]
More specifically, in the lean burn engine of the present embodiment, a target torque TTC of the engine is calculated based on the engine rotation speed Ne and the accelerator opening (detected by the accelerator opening sensor 9), and the target torque TTC and the target equivalent are calculated. By calculating the target intake air amount from the ratio TFBYA and controlling the opening of the throttle valve by the throttle actuator 3a so that the same amount of air as the target intake air amount is sucked, the target equivalent ratio TFBYA changes. Regardless, the engine always generates the torque required by the driver. At this time, if the target equivalent ratio changes suddenly, the control of the intake air cannot keep up, and there is a possibility that a torque fluctuation unintended by the driver may occur. Therefore, a process (ramp process) for gradually increasing the target equivalent ratio is required.
[0041]
<3> At time t3 when the target equivalence ratio TFBYA matches the provisional target equivalence ratio value TFBYA1, the delay time timer DLTM is reset to zero and time measurement is performed (see the second stage from the bottom), and the predetermined delay time is determined. The rich control flag FLGRS is switched from 0 to 1 at the end of t4 (see the third row from the bottom). The rich control flag FLGRS indicates that the air-fuel ratio rich control should be executed when FLGRS = 1, and that the air-fuel ratio rich control should not be executed when FLGRS = 0, or that the standby should be performed before the execution of the air-fuel ratio rich control. It is a flag to indicate.
[0042]
<4> The rich time timer RSTM is increased from the timing of t4 when the rich control flag FLGRS is switched from 0 to 1 (see the fourth stage), and the timing of t5 at which the predetermined rich control time ends is set as the end timing of the regeneration control. At this time, the NOx flag FLGNO and the rich control flag FLGRS are switched from 1 to 0. Further, the trap NOx amount integrated value SNO is returned to 0 in preparation for the next regeneration control.
[0043]
<5> The target equivalence ratio provisional value TFBYA1 is returned from 1.0 to the map value TFBYAmp at t5, which is the end timing of the reproduction control. At this time, if the equivalence ratio (air-fuel ratio) is switched stepwise in accordance with the target equivalence ratio provisional value TFBYA1, a torque step occurs and affects the operability. Is calculated as the target equivalent ratio TFBYA.
[0044]
<6> As long as the lean operation continues, the above <1> to <5> are repeated as a series of processes.
[0045]
The outline of the reproduction control has been described above, and a specific description will be given with reference to the following flowchart.
[0046]
The flowchart in FIG. 2 is for determining whether to execute or not to execute the reproduction control. That is, when the air-fuel ratio rich control is not executed, it is determined whether the regeneration control is to be executed or not by performing the estimation calculation of the retained NOx amount of the downstream side catalyst 13, and the air-fuel ratio rich control is Is executed, the time from the start of the execution of the air-fuel ratio rich control is measured to determine whether or not the end timing of the regeneration control has been reached.
[0047]
Note that the processing performed here is executed at regular intervals (for example, every 10 ms). This calculation cycle is the same in the flowcharts of FIGS. 3 to 5 described later.
[0048]
In S101, the engine speed Ne, the target torque TTC, and the rich control time SLRSTM are read. The engine rotation speed Ne is calculated based on a crank angle signal from the crank angle sensor 8, and the target torque TTC is calculated by a target torque calculation routine (not shown). The rich control time SLRSTM is calculated according to a flowchart (FIG. 5) for calculating a reproduction control time described later, and is stored in a memory (RAM) in the ECM 10. Therefore, the rich control time SLRSTM may be read from the memory.
[0049]
In S102, the rich control flag FLGRS is checked. This flag is necessary only for the first cylinder group. The flag indicates that the air-fuel ratio rich control is to be performed on the first cylinder group when FLGRS = 1, and that the first cylinder group is not performed when FLGRS = 0. Indicates that the air-fuel ratio rich control is not performed or that the vehicle is in a standby state before the air-fuel ratio rich control.
[0050]
During operation at a lean air-fuel ratio, a large amount of NOx is emitted, and this NOx is trapped in the downstream catalyst 13. When the integrated value of the trap NOx amount reaches a predetermined value, regeneration control has to be performed. Here, first, considering that the integrated value of the trap NOx amount has not reached the predetermined value, FIG. As shown, since the rich control flag FLGRS is 0 (the air-fuel ratio rich control is not being executed), the process proceeds to S103, and based on the engine rotation speed Ne and the target torque TTC, per calculation cycle (per predetermined time). The amount of NOx discharged from the engine is calculated, and the product of the NOx amount and the trapping efficiency of the downstream catalyst 13 is calculated as the amount of NOx trapped in the downstream catalyst 13 per calculation cycle 下流 NO.
[0051]
In S104, a value obtained by adding SNOz, which is the previous value of the trap NOx amount integrated value, to the trap NOx amount per calculation cycle 演算 NO is calculated as a trap NOx amount integrated value (current value) SNO, and this value is determined in S105. Compare with value SLSNO.
[0052]
If the SNO is equal to or less than the SLSNO (not the start time of the regeneration control), the current process is terminated. If the operation at the lean air-fuel ratio continues from the next time, the operations of S103 and S104 are repeated. When the SNO becomes larger than the SLSNO, it is determined that the regeneration control needs to be executed, and the process proceeds to S106 to set the NOx flag FLGNO. Set to 1. The NOx flag indicates that regeneration control is executed when FLGNO = 1, and that regeneration control is not executed when FLGNO = 0.
[0053]
In S106, the rich time timer RSTM is reset to zero. The rich time timer RSTM is for measuring the time from the start of the air-fuel ratio rich control.
[0054]
If the operation at the lean air-fuel ratio continues from the next time, the operation of S106 is repeated.
[0055]
On the other hand, when the rich control flag FLGRS becomes FLGRS = 1 (during execution of the air-fuel ratio rich control) according to the flow of FIG. 3 described later, the process proceeds from S102 to S107, where the rich time timer RSTM and the rich control time SLRSTM are compared. The rich control time SLRSTM determines the time during which the air-fuel ratio rich control is continued.
[0056]
When the rich time timer RSTM is less than the rich control time SLRSTM, the process proceeds to S108, and a value obtained by adding the operation cycle t of the present routine to the previous value of the rich time timer, RSTMz, is used as the rich time timer (current value) RSTM. . If FLGRS = 1 and the operation at the rich air-fuel ratio continues from the next time, the operation of S108 is repeated, and when the rich time timer RSTM becomes equal to or longer than the rich control time SLRSTM, the air-fuel ratio rich enough for regeneration is required. When it is determined that the control has been performed, the process proceeds from S107 to S109 to end the regeneration control, the NOx flag FLGNO is returned to 0 (the execution of the regeneration control is unnecessary), and the trap NOx amount integrated value SNO is reset to zero.
[0057]
Although not shown, a value (for example, SNOz, RSTMz) required for the next calculation in this routine or a value (for example, FLGNO value) required for another routine is stored in a memory in the ECM 10.
[0058]
The flowchart of FIG. 3 is for calculating the target equivalent ratio TFBYA.
[0059]
In S201, the engine speed Ne, the target torque TTC, and the rich control delay time SLDLTM are read. Like the rich control time SLRSTM, the rich control delay time SLDLTM is calculated in a flowchart (FIG. 5) for calculating a reproduction control time, which will be described later, and is stored in the memory in the ECM 10. Therefore, the rich control delay time SLDLTM is read from the memory. Just fine.
[0060]
In S202, a target equivalent ratio map value TFBYAmp is calculated by looking up a control map in which the target equivalent ratio is stored in correspondence with Ne and TTC based on the engine rotation speed Ne and the target torque TTC. TFBYAmp is basically set to a value smaller than 1.0, and the engine is operated at a lean air-fuel ratio.
[0061]
In S203, the NOx flag FLGNO is checked. When FLGNO = 0 (regeneration control is not executed), TFBYAmp is set to the target equivalence ratio provisional value TFBYA1, and when FLGNO = 1 (regeneration control is executed), Proceeding from S203 to S205, the target equivalence ratio provisional value TFBYA1 is set to 1.0 ignoring TFBYAmp.
[0062]
Steps S206 to S212 are portions for performing processing (ramp processing) for preventing the target equivalent ratio from suddenly changing. In step S206, TFBYAAz, which is the previous value of the target equivalence ratio, is compared with a provisional value TFBYA1 of the target equivalence ratio. If TFBYAz is smaller than TFBYA1, the process proceeds to S207, and a value obtained by adding a predetermined step value DMP to TFBYAz is calculated as a target equivalent ratio (the current value) TFBYA. In S208 and S209, this TFBYA is compared with the provisional value TFBYA1 (= 1.0) of the target equivalent ratio, and when TFBYA becomes equal to or more than TFBYA1, the value of TFBYA is limited to TFBYA1.
[0063]
Similarly, when TFBYAz is equal to or more than TFBYA1, the process proceeds from S206 to S210, and a value obtained by subtracting a predetermined step value DMP from TFBYAz is calculated as a target equivalent ratio (this value) TFBYA. When it does, the process proceeds from S211 to S212 to limit the value of TFBYA to TFBYA1.
[0064]
In S213, the NOx flag FLGNO is checked. When FLGNO = 1, the target equivalence ratio TFBYA and the previous value TFBYAz of this value are checked in S214 and S215. When TFBYA = 1.0 and TFBYAz <1.0, since the target equivalent ratio TFBYA has just reached 1.0, the delay time timer DLTM is reset to zero in S216. This time timer is for measuring the time from the start of the air-fuel ratio rich control.
[0065]
When TFBYA = 1.0 and TFBYAz = 1.0, the process proceeds from S215 to S217, and a value obtained by adding the calculation cycle t to DLTMz, which is the previous value of the delay time timer, is set as the delay time timer (current value) DLTM.
[0066]
In S218, the delay time timer DLTM and the rich control delay time SLDLTM are compared. When the DLTM is less than the SLDLTM, the process proceeds to S220, where the rich control flag FLGRS = 0 (no execution of the air-fuel ratio rich control) and the equivalence ratio correction coefficient RS = 0.
[0067]
From the next time, the operation of S217 is repeated, and when DLTM becomes equal to or more than SLDLTM, the process proceeds from S218 to S219, where the rich control flag FLGRS is set to 1 (execution of the air-fuel ratio rich control) and the equivalence ratio for the air-fuel ratio rich control is set. The correction coefficient RS is set to 0.2.
[0068]
When FLGNO = 0 and TFBYA ≠ 1.0, the process proceeds from S213 and S214 to S220, and the operation of S220 is executed.
[0069]
The flowchart of FIG. 4 is for calculating the fuel injection pulse width given to the fuel injection valve 4.
[0070]
In S301, the engine rotation speed Ne, the intake air amount Qa (detected by the air flow meter 7), and the target equivalent ratio TFBYA and the equivalent ratio correction coefficient RS from the memory in the ECM 10 are read. Of these, Ne and Qa are used to calculate a basic injection pulse width Tp for making the air-fuel ratio in the combustion chamber stoichiometric in S302. Here, K is a constant.
[0071]
In S303 and S304
[0072]
(Equation 1)
Ti14 = Tp × (TFBYA + RS) × 2 + Ts,
Here, Ts: invalid injection pulse width,
The fuel injection pulse width Ti14 at the time of sequential injection of the first cylinder group (# 1 cylinder, # 4 cylinder) is
[0073]
(Equation 2)
Ti23 = Tp × TFBYA × 2 + Ts,
Here, Ts: invalid injection pulse width,
The fuel injection pulse width Ti23 during the sequential injection of the second cylinder group (# 2 cylinder, # 3 cylinder) is calculated by the following equation.
[0074]
According to the calculation formula of Ti23, while the air-fuel ratio rich control is executed, the air-fuel ratio of the second cylinder group is maintained at the stoichiometric ratio, whereas the calculation formula of Ti14 includes the equivalence ratio correction coefficient RS. Therefore, by the RS which becomes 0.2 at the time of the air-fuel ratio rich control, the fuel injection in which the stoichiometric fuel amount is increased by 20% is performed to the first cylinder group. Contains excess reducing agent components.
[0075]
The Ti14 and Ti23 calculated in this way are stored in a memory in the ECM 10, and are read and used by a fuel injection execution routine (not shown). For example, when the signal of the crank angle sensor 8 coincides with the fuel injection start timing of the # 1 cylinder, a fuel injection control pulse signal with Ti14 as the valve opening time is transmitted to the fuel injection valve 4 of the # 1 cylinder and the crank angle sensor 8 Is coincident with the fuel injection start timing of the # 3 cylinder, a fuel injection control pulse signal with the valve opening time of Ti23 is sent to the fuel injection valve 4 of the # 3 cylinder.
[0076]
When the air-fuel ratio rich control is executed, the fuel corresponding to Ti14 may be injected twice. For example, when the signal of the crank angle sensor 8 coincides with the fuel injection start timing of the # 1 cylinder (in the intake stroke), a fuel injection control pulse signal having a length of Tp × TFBYA × 2 + Ts is supplied to the fuel injector of the # 1 cylinder. 4, a fuel injection control pulse signal having a length of Tp × RS × 2 + Ts may be sent to the fuel injection valve 4 of the # 1 cylinder during the subsequent expansion or exhaust stroke of the # 1 cylinder.
[0077]
The flowchart in FIG. 5 is for calculating the reproduction control time.
[0078]
In S401, the engine speed Ne and the intake air amount Qa are read, and in S402, the NOx flag FLGNO is checked. Only when FLGNO = 1, the process proceeds to S403 and thereafter.
[0079]
In S403 and S404, the ineffective time T1 of the air-fuel ratio rich control is calculated based on the engine speed Ne and the intake air amount Qa, and the ineffective time T1 and the time necessary for reducing the NOx held in the downstream catalyst 13 are required. Is calculated as the rich control time SLRSTM.
[0080]
The above T1 is the time from when the exhaust gas with excess reducing agent component reaches the upstream catalyst 11 inlet of the first cylinder group to when the catalyst outlet becomes excessive with reducing agent component. That is, immediately after the exhaust gas with excess reducing agent component reaches the upstream side catalyst 11 of the first cylinder group, a part of the reducing agent component is oxidized by the oxygen held in the catalyst. The reducing agent component does not flow out to the catalyst outlet until all the oxygen is consumed, and the air-fuel ratio rich control during this period does not contribute to the regeneration of the downstream catalyst 13. Therefore, by calculating the rich control time SLRSTM including the time T1, even if a part of the reducing agent component is consumed by the upstream catalyst 11 of the first cylinder group, the downstream catalyst 13 will be completely regenerated. It is assumed that. Since the invalid time T1 becomes shorter as the exhaust gas flow rate increases, T1 is calculated based on Ne and Qa.
[0081]
When the air-fuel ratio rich control is started, NOx of about the predetermined value SLSNO is always held in the downstream side catalyst 13. Therefore, this held NOx is kept at a constant rich air-fuel ratio (20% increase from stoichiometric). The time required for the reduction treatment can be known in advance by experiments or the like. Therefore, the required time RSTIME may be a fixed value. However, since the time required for the regeneration becomes shorter as the exhaust gas flow rate becomes larger, it is more preferable to calculate the RSTIME based on the engine rotation speed Ne and the intake air amount Qa.
[0082]
In S405 and S406, the release time T2 of the oxygen held by the upstream catalyst 12 of the second cylinder group is calculated based on the engine speed Ne and the intake air amount Qa, and the ineffective time T1 is calculated from the release time T2. Is calculated as the rich control delay time SLDLTM.
[0083]
The above T2 is the time from when the exhaust gas having the stoichiometric air-fuel ratio reaches the upstream catalyst 12 inlet of the second cylinder group to when the exhaust gas at the catalyst outlet reaches the stoichiometric air-fuel ratio. It is known that the amount of oxygen that can be held by the upstream catalyst 12 of the second cylinder group varies depending on the oxygen concentration in the inflowing exhaust gas, and that the higher the oxygen concentration, the more oxygen can be held. For this reason, when the air-fuel ratio of the second cylinder group changes from lean to stoichiometric, oxygen that cannot be maintained in the stoichiometric state is released, and the exhaust air-fuel ratio at the catalyst outlet becomes stoichiometric until this release is completed. No. Since the discharge time T2 becomes shorter as the flow rate of the exhaust gas increases, T2 is calculated based on Ne and Qa.
[0084]
The rich control time SLRSTM and the rich control delay time SLDLTM calculated in this way are stored in a memory in the ECM 10.
[0085]
Here, the operation of the present embodiment will be described with reference to the time chart of FIG. In the figure, the upper half is of a second cylinder group (this cylinder group is referred to as a "stoichiometric control cylinder group", which is the same in FIGS. 8 and 10) for controlling the air-fuel ratio to stoichiometric when the downstream catalyst 13 is regenerated. The lower half is of a first cylinder group that controls the air-fuel ratio to be rich during regeneration of the downstream catalyst 13 (this cylinder group is referred to as a “rich control cylinder group”; the same applies to FIGS. 8 and 10). Here, the following items are assumed for the sake of simplicity.
[0086]
(1) The operating condition of the lean air-fuel ratio is constant.
[0087]
{Circle around (2)} Although combustion in the combustion chambers is not strictly simultaneous in the two cylinder groups, it is considered that combustion occurs simultaneously in the combustion chambers of the two cylinder groups because the deviation is small.
[0088]
{Circle around (3)} The oxygen concentration in the exhaust gas is considered stoichiometric, and the oxygen concentration when the air-fuel ratio in the exhaust gas is stoichiometric is set to zero.
[0089]
(4) The concentration of the reducing agent component in the exhaust gas is set to zero in the case of the lean operation.
[0090]
Hereinafter, the operation of the stoichiometric control cylinder group will be described first, and then the operation of the rich control cylinder group will be described.
(1) Stoichiometric control cylinder group
<B> Air-fuel ratio in the combustion chamber: By the following processing, the air-fuel ratio in the combustion chamber becomes smaller than the timing of t0, which is the start timing of the regeneration control, and becomes stoichiometric at the timing of t2, and after the stoichiometric state continues until the timing of t10. It becomes larger again, and returns to the air-fuel ratio before the start of the regeneration control at the timing of t12. The timing of t0 to t6 shown in FIG. 6 and the timing of t0 to t6 shown in FIG. 7 are different.
[0091]
t0: The trap NOx amount integrated value SNO exceeds the predetermined value SLSNO, and the NOx flag FLGNO is set to 1 (S106 in FIG. 2).
[0092]
t0 to t2: ramp processing of the target equivalent ratio TFBYA.
[0093]
t2 to t10: The air-fuel ratio is controlled stoichiometrically.
[0094]
t10 to t12: ramp processing of the target equivalent ratio TFBYA.
[0095]
<B> Inlet oxygen concentration of upstream catalyst 12: The inlet oxygen concentration of upstream catalyst 12 changes slightly (d1 in time) from the air-fuel ratio control of the stoichiometric control cylinder group (the air-fuel ratio of the stoichiometric control cylinder group When changing from lean to stoichiometric, the inlet oxygen concentration of the upstream side catalyst 12 changes from a large value to zero from the timing of t1, and when the air-fuel ratio of the stoichiometric control cylinder group changes from stoichiometric to lean, the timing of t11. The oxygen concentration at the inlet of the upstream catalyst 12 changes from zero to a large value). In this case, the delay amount d1 is determined by the volume of the upstream side exhaust passages 14b and 14c (passage length × passage diameter) and the exhaust flow velocity.
[0096]
<C> Outlet oxygen concentration of the upstream side catalyst 12: After the inlet oxygen concentration becomes zero at the timing of t3 by releasing the retained oxygen into the exhaust gas by the catalyst, it is released until the outlet oxygen concentration becomes zero. A delay of time T2 occurs. Similarly, after the catalyst traps the oxygen in the exhaust gas, a predetermined time delay occurs after the inlet oxygen concentration returns to a large value at the timing of t13 until the outlet oxygen concentration returns to a large value.
[0097]
<D> Inlet oxygen concentration of the downstream catalyst 13: The oxygen concentration of the inlet of the downstream catalyst 13 is reduced from a large value to zero slightly (d2 in time) from the timing of t1 at which the outlet oxygen concentration of the upstream catalyst 12 changes. It changes to zero at the timing of t8, this state continues until the timing of t13, and thereafter returns to a large value.
[0098]
In this case, the delay amount d2 is determined by the volume (passage length × passage diameter) of the downstream side exhaust passage 15b and the exhaust flow velocity.
(2) Rich control cylinder group
<A> Air-fuel ratio in the combustion chamber: The air-fuel ratio in the combustion chamber moves in the same manner as the air-fuel ratio in the combustion chamber of the stoichiometric control cylinder group by the following processing. The only difference is that the air-fuel ratio becomes rich between the timing of t4 and the timing of t10.
[0099]
tO: The NOx flag FLGNO is set to 1.
[0100]
tO to t2: ramp processing of the target equivalent ratio TFBYA.
[0101]
t2 to t4: delay processing in air-fuel ratio rich control (t4−t2 = SLDLT)
M).
[0102]
t4: The delay process in the air-fuel ratio rich control ends, and the rich control flag FLGRS is set to 1 (S219 in FIG. 3).
[0103]
t4 to t10: Air-fuel ratio rich control (t10-t4 = SLRSTM).
[0104]
t10: The regeneration is completed, and the NOx flag FLGNO and the rich control flag FLGRS are set to 0 (S109 in FIG. 2, S220 in FIG. 3).
[0105]
t10 to t12: ramp processing of the target equivalent ratio TFBYA.
[0106]
<B> Concentration of the reducing agent component at the inlet of the upstream side catalyst 11: The concentration of the reducing agent component at the inlet side of the upstream side catalyst 11 changes slightly (d3 in time) from the air-fuel ratio control of the rich control cylinder group (from stoichiometric to richer). Is changed from the timing of t5 to a side where the concentration of the inlet reducing agent component of the upstream side catalyst 11 becomes larger than zero, and when changing from rich to stoichiometric, the inlet reducing agent component of the upstream side catalyst 11 is changed from the timing of t11. The concentration changes from a large value to zero). In this case, the delay amount d3 is determined by the volume (passage length × passage diameter) of the upstream exhaust passages 14a and 14d and the exhaust flow velocity. Since the lengths and diameters of the four upstream exhaust passages 14a to 14d are almost the same, d1ｄd3.
[0107]
<C> Outlet reducing agent component concentration of the upstream side catalyst 11: From the timing t5 when the inlet reducing agent component concentration increases because the catalyst oxidizes the reducing agent component by releasing the retained oxygen, from the time t5 when the outlet reducing agent component concentration increases. , A delay of the invalid time T1 occurs, and the outlet reducing agent component concentration becomes larger than the timing of t6. On the other hand, when the air-fuel ratio is returned from rich to lean, the outlet reducing agent component concentration also returns to zero at substantially the same timing as t11 when the inlet reducing agent component concentration returns to zero.
[0108]
<D> Concentration of the reducing agent component at the inlet of the downstream-side catalyst 13: From the timing of t8, which is slightly (d4 in time) from the timing of t6 when the concentration of the reducing agent component at the outlet of the upstream-side catalyst 11 changes from zero to a large value. The concentration of the reducing agent component at the inlet of the downstream catalyst 13 changes and increases, and this state continues until the timing of t13, and thereafter returns to zero. In this case, the delay amount d4 is determined by the volume of the downstream exhaust passage 15a (passage length × passage diameter) and the exhaust flow velocity. Since the lengths and diameters of the two downstream exhaust passages 15a and 15b are substantially the same, d2 ≒ d4.
[0109]
As a result, in the section from the timing of t8 to the timing of t13, the oxygen concentration at the inlet of the downstream catalyst 13 becomes zero and the concentration of the reducing agent component at the inlet increases, so that the retained NOx is efficiently reduced in the downstream catalyst 13. Can be processed.
[0110]
As described above, the section where the oxygen concentration at the inlet of the downstream side catalyst 13 becomes zero and the section where the concentration of the reducing agent component at the inlet side of the downstream side catalyst 13 becomes large can be made to coincide with each other because of the following configuration. It is.
[0111]
(I) The delay amount d1 is the volume (passage length × passage diameter) of the upstream exhaust passages 14b and 14c and the exhaust flow velocity, and the delay amount d3 is the volume (passage length × passage length) of the upstream exhaust passages 14a and 14d. Path diameter) and the exhaust flow velocity, the lengths and diameters of the four upstream exhaust paths 14a to 14d are made substantially the same so that d1 ≒ d3.
[0112]
(Ii) The delay amount d2 is the volume (passage length × passage diameter) of the downstream exhaust passage 15b and the exhaust flow velocity, and the delay amount d4 is the volume (passage length × passage diameter) of the downstream exhaust passage 15a. The length and diameter of the two downstream-side exhaust passages 15a and 15b are substantially the same because they are determined by the exhaust flow velocity, so that d2 ≒ d4.
[0113]
(Iii) A predetermined delay time (a section from timing t2 to timing t4 in the figure) is provided until the air-fuel ratio rich control of the first cylinder group is started.
[0114]
Here, in order to further clarify the effect of (iii), FIG. 8 shows a time chart when the delay processing of the air-fuel ratio rich control is removed from the rich control cylinder group under the same other conditions. However, for the stoichiometric control cylinder group, the timing of returning the air-fuel ratio to lean from stoichiometric is slightly advanced from t10 to t8.
[0115]
The timing at which the concentration of the reducing agent component at the inlet of the downstream catalyst 13 changes from zero to a large value (the timing at which the reducing agent component reaches the downstream catalyst 13) due to the elimination of the delay processing of the air-fuel ratio rich control becomes t6. Since it is earlier, the oxygen concentration at the inlet of the downstream side catalyst 13 has a non-zero value for a while after t6. That is, for a while (t6 to t8) after the reducing agent component reaches the downstream side catalyst 13, the oxygen released from the upstream side catalyst 12 of the second cylinder group and the upstream side catalyst 11 of the first cylinder group And the reducing agent component having passed through at the same time flows into the downstream side catalyst 13. In the section where the oxygen and the reducing agent component flow simultaneously, the NOx reduction efficiency of the downstream catalyst 13 decreases, and the amount of NOx that flows out without being reduced increases. In particular, immediately after the atmosphere becomes excessive in the reducing agent component, the amount of NOx released from the downstream side catalyst 13 is large, so that it is not preferable that oxygen coexists in the initial stage after the reducing agent component arrives.
[0116]
In the embodiment, the volume of the exhaust passage from the vicinity of the exhaust outlet of the first cylinder group (for example, the exhaust port) to the downstream catalyst 13 is substantially the same as the volume of the exhaust passage from the vicinity of the exhaust outlet of the second cylinder group to the downstream catalyst 13. After the exhaust air-fuel ratio of the second cylinder group becomes stoichiometric, the delay process of the air-fuel ratio rich control is performed such that the exhaust air-fuel ratio of the first cylinder group becomes rich with a certain delay. In the above description, the simultaneous inflow of oxygen and the reducing agent component to the downstream catalyst 13 has been described. However, even when the air-fuel ratio control delay process is not separately performed, the simultaneous Inflow can be avoided. That is, when making the exhaust air-fuel ratio of the first cylinder group rich and making the exhaust air-fuel ratio of the second cylinder group stoichiometric at the same timing during regeneration of the downstream catalyst 13 in the lean operation range, The exhaust passage volume from the vicinity of the exhaust outlet of the first cylinder group (for example, the exhaust port) to the downstream catalyst 13 is made larger than the exhaust passage volume from the vicinity of the exhaust outlet of the second cylinder group to the downstream catalyst 13 (second). Embodiment).
[0117]
Explaining this, the delay processing of the air-fuel ratio rich control is excluded from the regeneration control of the first embodiment (that is, S215 to S218 in FIG. 3 are deleted).
[0118]
On the other hand, as shown in FIG. 9, the passage diameter and the passage length of the upstream side exhaust passage and the downstream side exhaust passage are configured as follows.
[0119]
<a> Upstream exhaust passage
(1) The four upstream exhaust passages 14a to 14d have the same passage diameter.
[0120]
(2) The upstream exhaust passages 14a and 14d of the first cylinder group have substantially the same passage length.
[0121]
{Circle around (3)} The upstream exhaust passages 14b and 14c of the second cylinder group have substantially the same passage length.
[0122]
(4) The length of the upstream exhaust passages 14a and 14d of the first cylinder group is made longer than the length of the upstream exhaust passages 14b and 14c of the second cylinder group.
[0123]
<B> Downstream exhaust passage
(1) The two downstream exhaust passages 15a and 15b have the same passage.
[0124]
(2) The length of the downstream exhaust passage 15a of the first cylinder group is made longer than the length of the downstream exhaust passage 15b of the second cylinder group.
[0125]
FIG. 10 shows a time chart when the regeneration control is performed as shown in FIG. 9 and the air-fuel ratio rich control excluding the delay processing is performed. In the second embodiment, the configuration of the upstream exhaust passage of <a> described above, in particular, the length of the upstream exhaust passages 14a and 14d of the first cylinder group is changed to the passage of the upstream exhaust passages 14b and 14c of the second cylinder group. Since it is longer than the length (<a> (4)), d3> d1 and the configuration of the downstream exhaust passage of <b>, in particular, the length of the downstream exhaust passage 15a of the first cylinder group is set to the second length. Since it is longer than the length of the exhaust passage 15b on the downstream side of the cylinder group (<b> (2)), d4> d2. As a result, even when the delay processing of the air-fuel ratio rich control is not performed, the timing at which the concentration of the reducing agent component at the inlet of the downstream catalyst 13 becomes larger than zero is delayed, and the timing at t8 when the oxygen concentration at the inlet of the downstream catalyst 13 becomes zero. Is supposed to match. Therefore, also in the second embodiment, the NOx released from the downstream catalyst 13 can be efficiently reduced without being disturbed by the oxygen desorbed from the upstream catalyst 12 of the second cylinder group.
[0126]
In the latter half of the time when the reducing agent component flows into the downstream catalyst 13 (t11 to t13), oxygen and the reducing agent component are simultaneously flowing. However, at such a time, NOx released from the downstream catalyst 13 is discharged. Since the amount is small, the influence on the decrease in the NOx reduction efficiency is small.
[0127]
In the second embodiment, when the downstream side catalyst 13 is regenerated in the lean operation range, the exhaust air-fuel ratio of the first cylinder group is made rich and the exhaust air-fuel ratio of the second cylinder group is made stoichiometric at the same timing. In this case, the diameters of the upstream exhaust passages of the two cylinder groups are made the same, and the diameters of the downstream exhaust passages of the two cylinder groups are also made the same. By making only the length of the passage different between the two cylinder groups, and increasing the passage length of the first cylinder group for performing the air-fuel ratio rich control, the first cylinder group is discharged from the upstream catalyst 12 of the second cylinder group and downstream. The case where excess exhaust of the reducing agent component passing through the upstream catalyst 11 of the first cylinder group reaches the downstream catalyst 13 when the oxygen reaching the side catalyst 13 is exhausted has been described. If the side exhaust passage has the same passage diameter, Also, the diameters of the downstream exhaust passages of the two cylinder groups are made the same, and the exhaust passage lengths of the two cylinder groups are different only for the upstream exhaust passage or only for the downstream exhaust passage. The same purpose can be achieved by increasing the passage length of the first cylinder group for controlling. The same purpose can be further achieved by the following method.
[0128]
<A> The lengths of the upstream exhaust passages of the two cylinder groups are made the same, and the lengths of the downstream exhaust passages of the two cylinder groups are also made the same. The passage diameter of the passage is made different between the two cylinder groups, and the passage diameter of the first cylinder group for performing the air-fuel ratio rich control is increased.
[0129]
<B> The lengths of the upstream exhaust passages of the two cylinder groups are made the same, and the lengths of the downstream exhaust passages of the two cylinder groups are also made the same. Only in the side exhaust passage, the passage diameter of the exhaust passage is made different between the two cylinder groups, and the passage diameter of the first cylinder group for performing the air-fuel ratio rich control is increased.
[0130]
In the first embodiment, the reducing agent component passing through the upstream catalyst 11 of the first cylinder group at the same timing as when oxygen released from the upstream catalyst 12 of the second cylinder group and reaching the downstream catalyst 13 is exhausted. Is described in the case where excessive exhaust gas reaches the downstream side catalyst 13, but after the oxygen exhausted from the upstream side catalyst 12 of the second cylinder group and reaching the downstream side catalyst 13 disappears, the upstream side of the first cylinder group Excessive exhaust of the reducing agent component passing through the catalyst 11 may reach the downstream catalyst 13.
[Brief description of the drawings]
FIG. 1 is a control system diagram of one embodiment.
FIG. 2 is a flowchart for explaining determination of execution / non-execution of catalyst regeneration control.
FIG. 3 is a flowchart for explaining calculation of a target equivalent ratio.
FIG. 4 is a flowchart for explaining calculation of a fuel injection pulse width.
FIG. 5 is a flowchart for explaining calculation of a reproduction control time.
FIG. 6 is a waveform chart for explaining the operation of the embodiment.
FIG. 7 is a waveform chart for explaining the operation of the embodiment.
FIG. 8 is a waveform chart for explaining the operation of the embodiment.
FIG. 9 is a control system diagram of a second embodiment.
FIG. 10 is a waveform chart for explaining the operation of the second embodiment.
[Explanation of symbols]
1 Engine body
4 Fuel injection valve
10 ECU
11 First upstream catalyst
12 Second upstream catalyst
13 Downstream catalyst
14a to 14d Upstream exhaust passage
15a, 15b Downstream exhaust passage

Claims (9)

A first cylinder group including one or more cylinders;
A second cylinder group including one or more cylinders;
A first upstream catalyst to which exhaust gas from the first cylinder group is guided;
A second upstream catalyst to which exhaust gas from the second cylinder group is guided, the second upstream catalyst having an oxygen storage function;
A downstream catalyst to which exhaust gas from these two upstream catalysts is led has a function of trapping and holding NOx in an oxygen-excess atmosphere, while releasing NOx held in an atmosphere of an excess of a reducing agent component. A downstream catalyst having a function of reducing
When NOx is released from the downstream catalyst during the lean operation, the exhaust air-fuel ratio at the first upstream catalyst inlet becomes rich and the exhaust air-fuel ratio at the second upstream catalyst inlet becomes stoichiometric. Means for controlling the air-fuel ratio for each cylinder group in the exhaust gas purifying apparatus for an engine,
During the execution of the air-fuel ratio control, when there is no oxygen released from the second upstream catalyst and reaching the downstream catalyst, or thereafter, excessive exhaust of the reducing agent component passing through the first upstream catalyst is performed. An exhaust purification device for an engine, comprising: means for causing the exhaust gas to reach the downstream catalyst. A first cylinder group including one or more cylinders;
A second cylinder group including one or more cylinders;
A first upstream catalyst to which exhaust gas from the first cylinder group is guided;
A second upstream catalyst to which exhaust gas from the second cylinder group is guided, the second upstream catalyst having an oxygen storage function;
A downstream catalyst to which exhaust gas is guided from these two upstream catalysts, which has a function of trapping and holding NOx when the exhaust air-fuel ratio is lean, and has a function of trapping and holding NOx when the exhaust air-fuel ratio is stoichiometric or rich. A downstream catalyst having a function of releasing and reducing the retained NOx,
When NOx is released from the downstream side catalyst during the lean operation, the exhaust air-fuel ratio of the first cylinder group becomes rich and the exhaust air-fuel ratio of the second cylinder group becomes stoichiometric. Means for controlling the air-fuel ratio of the engine,
An exhaust gas of an engine, wherein an exhaust passage volume from near an exhaust outlet of the first cylinder group to the downstream catalyst is larger than an exhaust passage volume from near an exhaust outlet of the second cylinder group to the downstream catalyst. Purification device. An exhaust passage volume from near the exhaust outlet of the first cylinder group to the first upstream catalyst is larger than an exhaust passage volume from near the exhaust outlet of the second cylinder group to the second upstream catalyst. The exhaust gas purifying apparatus for an engine according to claim 2. The length of the exhaust passage from the vicinity of the exhaust outlet of the first cylinder group to the first upstream side catalyst is longer than the length of the exhaust passage from the vicinity of the exhaust outlet of the second cylinder group to the second upstream side catalyst. The exhaust gas purifying apparatus for an engine according to claim 3, wherein An exhaust passage diameter from near the exhaust outlet of the first cylinder group to the first upstream catalyst is larger than an exhaust passage diameter from near the exhaust outlet of the second cylinder group to the second upstream catalyst. The exhaust gas purifying apparatus for an engine according to claim 3. The engine exhaust according to claim 2, wherein an exhaust passage volume from the first upstream catalyst to the downstream catalyst is larger than an exhaust passage volume from the second upstream catalyst to the downstream catalyst. Purification device. The engine according to claim 6, wherein an exhaust passage length from the first upstream catalyst to the downstream catalyst is longer than an exhaust passage length from the second upstream catalyst to the downstream catalyst. Exhaust gas purification device. 7. The engine exhaust according to claim 6, wherein an exhaust passage diameter from the first upstream catalyst to the downstream catalyst is larger than an exhaust passage diameter from the second upstream catalyst to the downstream catalyst. Purification device. A first cylinder group including one or more cylinders;
A second cylinder group including one or more cylinders;
A first upstream catalyst to which exhaust gas from the first cylinder group is guided;
A second upstream catalyst to which exhaust gas from the second cylinder group is guided, the second upstream catalyst having an oxygen storage function;
A downstream catalyst to which exhaust gas is guided from these two upstream catalysts, which has a function of trapping and holding NOx when the exhaust air-fuel ratio is lean, and has a function of trapping and holding NOx when the exhaust air-fuel ratio is stoichiometric or rich. A downstream catalyst having a function of releasing and reducing the retained NOx,
When NOx is released from the downstream side catalyst during the lean operation, the exhaust air-fuel ratio of the first cylinder group becomes rich and the exhaust air-fuel ratio of the second cylinder group becomes stoichiometric. Means for controlling the air-fuel ratio of the engine,
The exhaust passage volume from the vicinity of the exhaust outlet of the first cylinder group to the downstream side catalyst is substantially equal to the exhaust passage volume from the vicinity of the exhaust outlet of the second cylinder group to the downstream side catalyst. When executing the air-fuel ratio control, a delay means is provided for setting the exhaust air-fuel ratio of the second cylinder group to stoichiometric and then delaying the exhaust air-fuel ratio of the first cylinder group for a certain period to enrich the exhaust air-fuel ratio of the first cylinder group. Engine exhaust purification device.

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