JPH09236034A - Exhaust gas purifier for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of a driving feeling during a normal period or an accelerating period caused by such a condition that rotational fluctuation is transmitted to a driver by a little rotational fluctuation accompanied by cycle fluctuation of combustion. SOLUTION: Air-fuel ratio control means 22 controls an air-fuel ratio control rate so that when a catalyst is partially activated, at least one air cylinder is made to serve as a rich air cylinder so that an air-fuel ratio of exhaust is leant to a rich side by the exhaust of this rich air cylinder, and at least one air cylinder is made to serve as a lean air cylinder so that the air-fuel ratio of exhaust is leant to a lean side by the exhaust of this lean air cylinder. Ignition timing setting means 24 sets the ignition timing of the rich air cylinder so that a torque generated by the rich air cylinder is set to the same as the lean air cylinder, and ignition executing means 25 ignites each air cylinder by using the ignition timing of the rich air cylinder and the ignition timing of the lean air cylinder. In this case, terminating means 27 terminates air-fuel ratio control during a normal period or an accelerating period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust purification system.

[0002]

2. Description of the Related Art In order to warm up a three-way catalyst provided in an exhaust pipe at an early stage, the fuel injection amount is increased / decreased every predetermined period (for example, every combustion) (that is, the exhaust air-fuel ratio is set to a rich side with respect to the theoretical air-fuel ratio). The rich combustion and lean combustion are repeated by alternating the lean side) operation, and carbon monoxide C is produced by the rich combustion.
A large amount of oxygen O ₂ is produced by lean combustion of O and unburned hydrocarbon HC, and exhaust gas temperature is raised by the heat generated by the oxidation reaction of both, and at the same ignition timing, a rich cylinder (the air-fuel ratio is enriched). Since there is a difference in the torque generated between the lean cylinder and the lean cylinder (the cylinder whose air-fuel ratio is lean), the ignition timing of the rich cylinder is adjusted so that the torque generated by the rich cylinder is the same as that of the lean cylinder. A device for further retarding the angle has been proposed (see Japanese Patent Laid-Open No. 4-308311).

[0003]

By the way, when performing an operation of swinging the exhaust air-fuel ratio alternately to the rich side and the lean side,
Even if the ignition timing of the rich cylinder is retarded from that of the lean cylinder so that the torque generated by the rich cylinder is the same as that of the lean cylinder, in reality, the combustion cycle fluctuations occur between the rich cylinder and the lean cylinder. As a result, a slight torque difference remains, which causes a slight rotation fluctuation.Therefore, if the exhaust air-fuel ratio is alternately changed to the rich side and the lean side during steady state or acceleration, The driving feeling is poor at all times and during acceleration.

If there is a slight fluctuation in rotation during steady state and during acceleration (state of stepping on the accelerator), the driving feeling will deteriorate, so it is necessary to improve engine stability during steady state and during acceleration. On the other hand, it is not necessary to consider the drivability during deceleration, and even if the stability of the engine is somewhat poor, it does not matter. In addition, since the engine rotation is pulled by the vehicle inertia during deceleration, the vehicle inertia, not the engine output, becomes dominant.Therefore, even if the engine stability is somewhat poor, the vehicle inertia will assist the rotation fluctuation. Is hard to reach the driver. Therefore, when a slight rotation fluctuation occurs due to the combustion cycle fluctuation between the rich cylinder and the lean cylinder during steady state and acceleration, the rotation variation is transmitted to the driver and the driving feeling during steady state and acceleration is improved. It gets worse.

Therefore, according to the present invention, by suspending the operation of swinging the exhaust air-fuel ratio alternately to the rich side and the lean side at the steady state or during the acceleration, the rotational fluctuation is caused by a slight rotational fluctuation due to the combustion cycle fluctuation. The purpose is to prevent the driving feeling from deteriorating during normal operation or acceleration due to being transmitted to a person.

[0006]

According to the first invention, FIG.
As shown in FIG. 5, a means 21 for determining whether or not the catalyst is partially activated while the catalyst is provided in the exhaust passage, and at least 1 when the catalyst is partially activated based on the determination result.
With one cylinder as a rich cylinder, the exhaust air-fuel ratio swings to the rich side by the exhaust of this rich cylinder, and at least one cylinder as a lean cylinder so that the exhaust air-fuel ratio swings to the lean side by the exhaust of this lean cylinder. Control amount (for example, target fuel-air ratio equivalent amount TFBYAR of rich cylinder)
And a means 22 for controlling the target fuel-air ratio equivalent amount TFBYAL of the lean cylinder, a means 23 for setting the ignition timing ADVL of the lean cylinder, and a torque generated by the rich cylinder to be the same as the lean cylinder. A means 24 for setting the ignition timing ADVR of the rich cylinder, a means 25 for igniting each cylinder by using the ignition timing of the rich cylinder and the ignition timing ADVL of the lean cylinder, and whether it is in a steady state or during acceleration. There is provided a means 26 for judging the above, and a means 27 for stopping the air-fuel ratio control at the time of steady state or acceleration based on the result of this judgment.

In a second aspect of the present invention, the air-fuel ratio control is performed by increasing the swing range of the exhaust air-fuel ratio swinging between the rich side and the lean side in deceleration in the first aspect.

According to a third aspect of the present invention, the number of the lean cylinders is greater than that of the rich cylinders in the first or second aspect.

In a fourth invention, the number of the rich cylinders in the first or second invention is made larger than that of the lean cylinders.

In the fifth aspect of the present invention, as shown in FIG. 12, while a catalyst is provided in the exhaust passage, a means 21 for determining whether or not the catalyst is partially activated, and a part of the catalyst based on this determination result are provided. A means for controlling the air-fuel ratio control amount (for example, the target fuel-air ratio equivalent amount TFBYAR of the rich cylinder) so that when activated, at least one cylinder is regarded as a rich cylinder and the exhaust air of the rich cylinder causes the air-fuel ratio of the exhaust gas to swing to the rich side. 31 and means 32 for fuel-cutting at least one cylinder when the catalyst is partially activated based on the determination result,
Means 26 for deciding whether it is a constant time or during acceleration
And means 33 for stopping the air-fuel ratio control during steady state or acceleration based on the determination result.

In a sixth aspect of the present invention, the air-fuel ratio control is performed by increasing the swing range of the exhaust air-fuel ratio swinging to the rich side during deceleration in the fifth aspect.

In a seventh invention, the ignition timing ADVR2 of the rich cylinder is set so that the torque generated by the rich cylinder in the fifth or sixth invention is reduced.

In the eighth invention, in the seventh invention, the ignition timing ADVR2 of the rich cylinder is a value corresponding to the air-fuel ratio control amount TFBYAR of the rich cylinder and the cooling water temperature Tw.

In a ninth aspect of the present invention, the number of the fuel cut cylinders is greater than that of the rich cylinder in any one of the fifth to eighth aspects.

In a tenth aspect of the present invention, the number of the rich cylinders is greater than that of the fuel cut cylinders in any one of the fifth to eighth aspects of the invention.

In an eleventh invention, in any one of the first to tenth inventions, the air-fuel ratio control amount TFBYA of the rich cylinder is controlled so that the CO concentration becomes a predetermined value A1 or more.
Set R.

In a twelfth aspect of the invention, in the eleventh aspect of the invention, when the predetermined value A1 is a region where the low temperature activity of the catalyst does not change so much even if the CO concentration is changed, and when the CO concentration is changed, the low temperature activity of the catalyst becomes low. This is the boundary value with the area that changes significantly.

In a thirteenth aspect of the invention, in any one of the first to twelfth aspects of the invention, it is determined whether or not the catalyst is partially activated, based on the engine coolant temperature or the temperature of the catalyst.

In a fourteenth invention, in any one of the first to fourth inventions, the air-fuel ratio control amount TFBYAL of the lean cylinder corresponds to a lean limit.

In a fifteenth invention, in the fourteenth invention, the air-fuel ratio control amount corresponding to the lean limit is a value corresponding to the cooling water temperature of the engine.

In a sixteenth invention, in the fourteenth or fifteenth invention, the ignition timing ADVL of the lean cylinder is MBT with respect to the air-fuel ratio control amount corresponding to the lean limit.

In a seventeenth invention, the ignition timing A of the rich cylinder in any one of the first to fourth inventions is used.
The DVR is a value according to the air-fuel ratio control amount of the lean cylinder (a value that advances as the air-fuel ratio control amount of the lean cylinder becomes richer).

In an eighteenth invention, the air-fuel ratio control means 22 in any one of the first to fourth inventions is,
As shown in FIG. 13, a means 41 for calculating a basic injection amount for obtaining a substantially theoretical air-fuel ratio in accordance with operating conditions, and a means 42 for increasing the basic injection amount for the rich cylinder and decreasing the lean injection amount for the lean cylinder. Means 4 for supplying the increased injection amount of fuel to the intake pipe of the rich cylinder and the decreased injection amount of fuel to the intake pipe of the lean cylinder
3

In a nineteenth invention, the air-fuel ratio control means 31 in any one of the fifth to tenth inventions is used.
However, as shown in FIG. 14, means 41 for calculating a basic injection amount that substantially obtains a theoretical air-fuel ratio according to operating conditions, and means 51 for increasing the basic injection amount for the rich cylinder.
And means 52 for supplying the increased injection amount of fuel to the intake pipe of the rich cylinder.

[0025]

When the exhaust air-fuel ratio is alternately changed between the rich side and the lean side, the ignition timing of the rich cylinder is retarded from that of the lean cylinder so that the torque generated by the rich cylinder becomes the same as that of the lean cylinder. Even if it is, since a slight rotation fluctuation occurs due to the combustion cycle fluctuation between the rich cylinder and the lean cylinder, the exhaust air-fuel ratio is set to the rich side and the lean side until the steady state or acceleration. If the shaking operation is performed alternately, the driving feeling during normal operation or acceleration deteriorates. However, in the first aspect of the invention, the exhaust air-fuel ratio alternates between the rich side and the lean side during normal operation or acceleration. Since the shaking operation is stopped, it is possible to prevent the driving feeling from deteriorating during steady state or during acceleration due to combustion cycle fluctuations.

However, as a result of giving priority to drivability at the time of steady state or acceleration, the warm-up of the catalyst is delayed, but the second aspect of the present invention makes it easier than before when decelerating without deteriorating the driving feeling. When the swing of the exhaust air-fuel ratio is increased and the exhaust air-fuel ratio is alternately swung to the rich side and the lean side, the warm-up delay of the catalyst is recovered.

When the number of lean cylinders is made larger than that of the rich cylinders in the third aspect of the invention, the O ₂ concentration of the lean cylinders becomes larger than that when the number of the lean cylinders and the rich cylinders are the same, so a sufficient CO concentration is secured. Under these conditions, the time until the activation of the catalyst is completed is shortened by the increase of the O ₂ concentration.

When the number of rich cylinders is larger than that of the lean cylinders in the fourth aspect of the invention, the CO concentration of the rich cylinders becomes sufficiently large, and the larger the number of rich cylinders, the smaller the number of rich cylinders in the air-fuel ratio control amount per cylinder. Since it can be set to the lean side as compared with the case, the torque difference with the lean cylinder is reduced, and the stability of the engine is improved.

Even when a fuel cut cylinder is used instead of the lean cylinder, the operation of alternately changing the exhaust air-fuel ratio between the rich side and the lean side can be performed. In this case, however, in the fifth aspect of the invention, the exhaust gas is exhausted during steady state or acceleration. Since the operation of alternating the air-fuel ratio to the rich side and the lean side is stopped, deterioration of the driving feeling during steady state or acceleration due to fluctuation of combustion cycle is prevented, and it is used for combustion in the fuel cut cylinder. Since there is no O ₂ left and the amount of heat of oxidation reaction in the catalyst increases by the amount of the remaining O ₂ , the time until the completion of activation of the catalyst becomes shorter than in the case of using a lean cylinder.

However, as a result of giving priority to drivability at the time of steady state or acceleration, catalyst warm-up is delayed, but in contrast to this, according to the sixth aspect of the present invention, during deceleration where the driving feeling does not deteriorate, compared to the conventional case. When the swing of the exhaust air-fuel ratio is increased and the exhaust air-fuel ratio is alternately swung to the rich side and the lean side, the warm-up delay of the catalyst is recovered.

In the seventh aspect of the invention, the ignition timing of the rich cylinder is set so that the torque generated by the rich cylinder is reduced, so that the torque difference from the fuel cut cylinder in which torque due to combustion heat is not generated is reduced. This improves the engine stability during deceleration.

In the ninth invention, when the number of fuel cut cylinders is made larger than that of the rich cylinders, the O ₂ concentration of the fuel cut cylinders becomes larger than that when the number of the fuel cut cylinders is the same as that of the rich cylinders, so a sufficient CO concentration is secured. As long as the above conditions are satisfied, the time until the activation of the catalyst is completed is shortened by the increase of the O ₂ concentration.

In the tenth aspect of the invention, when the number of rich cylinders is made larger than that of the fuel cut cylinders, the CO concentration of the rich cylinders becomes sufficiently high, and as the number of rich cylinders increases, the air-fuel ratio control amount per cylinder becomes richer. Since it can be set to the lean side compared to when it is low, the torque difference with the fuel cut cylinder is reduced, and the stability of the engine is improved.

In the fourteenth aspect of the invention, the air-fuel ratio control amount of the lean cylinder corresponds to the lean limit, so the fuel efficiency is improved.

In the fifteenth aspect of the invention, since the air-fuel ratio control amount corresponding to the lean limit is a value corresponding to the cooling water temperature, the air-fuel ratio of the lean cylinder does not deviate from the lean limit even if the cooling water temperature differs. Therefore, even if the cooling water temperature is different, the lean cylinder can be operated with the minimum fuel consumption.

In the sixteenth aspect of the invention, the air-fuel ratio control amount of the lean cylinder corresponds to the lean limit, and the ignition timing of the lean cylinder corresponds to the air-fuel ratio control amount of the lean limit corresponding to M.
Since it is a BT, fuel efficiency is further improved.

Although the torque generated by the lean cylinder changes according to the air-fuel ratio control amount of the lean cylinder, in the seventeenth aspect of the invention, the ignition timing of the rich cylinder is a value corresponding to the air-fuel ratio control amount of the lean cylinder ( Since the air-fuel ratio control amount of the lean cylinder is a value that advances toward the rich side), the torque difference between the rich cylinder and the lean cylinder can be eliminated even when the air-fuel ratio control amount of the lean cylinder changes.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 is an engine body, a fuel injection valve 7 is provided in an intake passage 8 thereof, which is located downstream of a throttle valve 5, and a control unit (abbreviated as C / U in the figure). 2) Fuel is injected and supplied into the intake air by the injection signal from 2. The flow rate of fuel supplied to the engine is controlled by volume flow rate, and the flow rate is adjusted by the valve opening time of the injection valve.

On the other hand, the cylinder head is provided with an electrode of the spark plug 13 facing the combustion chamber, and when the ignition coil primary current is cut off at a predetermined timing by the ignition signal from the control unit 2, the spark plug 13 is turned off. Sparks fly to the electrodes and ignite the mixture in the cylinder. The gas burned by this ignition is purified by the catalyst (three-way catalyst) 10 provided in the exhaust passage 9.

In the control unit 2, the Ref signal from the crank angle sensor 4 (in every four cylinders, every 180 °, 6
It is generated every 120 ° in the cylinder), 1 ° signal, intake air amount signal from the air flow meter 6, air-fuel ratio (oxygen concentration) signal from the O ₂ sensor 3 installed upstream of the three-way catalyst 10 in the exhaust passage 9. The engine cooling water temperature signal and the like from the water temperature sensor 11 are input, and the control unit 2 controls the fuel injection amount (air-fuel ratio) based on these signals.

In a multi-cylinder engine, in order to warm up the catalyst 10 early with the catalyst 10 partially activated, every other cylinder in the ignition order is a rich cylinder and the remaining cylinders are lean cylinders. The ignition timing of the rich cylinder is retarded more than that of the lean cylinder so that the torque generated by the rich cylinder is the same as that of the lean cylinder while performing the operation of alternately swinging the rich side and the lean side. Even when it is set, since some rotation fluctuation actually occurs due to combustion cycle fluctuation between the rich cylinder and the lean cylinder, the exhaust air-fuel ratio alternates between the rich side and the lean side until steady state or acceleration. If you shake it, the driving feeling will be poor.

To deal with this, in the present invention, the operation of alternately swinging the exhaust air-fuel ratio to the rich side and the lean side is stopped during steady state or acceleration.

The contents of this control executed by the control unit 2 will be described with reference to the following flow chart.

The flowchart of FIG. 2 is for calculating the fuel injection pulse width and the ignition timing to be given to the fuel injection valve 7 for each cylinder, and is executed in synchronization with the Ref signal.

First, in step 1, it is judged from the signal detected by the crank angle sensor 4 whether the engine is rotating or not. If the engine is rotating, the process proceeds to step 2 and the engine speed Ne and the air flow detected by the crank angle sensor 4 are determined. Using the intake air amount Qa from the meter 6, Tp = (Qa / Ne) × K (1) However, the basic injection pulse width Tp at which a mixture of almost stoichiometric air-fuel ratio is obtained by the formula of K: constant To do.

Steps 3 and 4 are the parts for judging the conditions for performing the operation of alternately swinging the exhaust air-fuel ratio to the rich side and the lean side. For the judgment of the conditions, check the contents of steps 3 and 4 one by one. It is determined that the condition is satisfied when both of them are satisfied, and that the condition is not satisfied when any of them is not satisfied. That is, when step 3: the catalyst 10 is partially activated, step 4: when decelerating, it is determined that the condition is satisfied, and the process proceeds to step 9. If not, the process proceeds to step 5.

Here, whether or not the catalyst 10 is partially activated is judged from the cooling water temperature (or the temperature of the catalyst 10) and the like. A predetermined value (for example, 10
It is also possible to determine that the catalyst is partially activated when the temperature rises above a certain temperature (° C.) or above or when the elapsed time from start-up reaches a predetermined value (eg 20 seconds) or above. In the experiment, room temperature (20 ~
Since the starting at 30 ° C. was assumed, the catalyst 1 is used when the cooling water temperature Tw is within a predetermined range (40 ° C. <Tw <60 ° C.).
It was judged that 0 was partially activated.

When the catalyst 10 is inactive, even if the exhaust air-fuel ratio is alternately swung to the rich side and the lean side, CO and HC from the rich cylinder and O2 from the lean cylinder are left in the catalyst 10. Since it is exhausted as it is without undergoing an oxidation reaction in the interior (no heat generation), when the catalyst is in an inactive state immediately after the cold start, the operation of alternating the exhaust air-fuel ratio to the rich side and the lean side is not performed.

Whether or not the vehicle is decelerating is determined by an idle switch (or throttle valve opening) and a vehicle speed sensor. For example, it is determined that the vehicle is decelerating when the idle switch is in the ON state and the vehicle speed is equal to or higher than a predetermined value (for example, 10 km / h).

Even when the catalyst is partially activated, the exhaust air-fuel ratio after step 9 is alternately changed to the rich side and the lean side when the deceleration is not performed (that is, the steady state and the acceleration). The reason why the process is advanced to step 9 and subsequent steps only during deceleration without advancing is as follows.

When the exhaust air-fuel ratio is alternately changed between the rich side and the lean side, the ignition timing of the rich cylinder is retarded from that of the lean cylinder so that the torque generated by the rich cylinder becomes the same as that of the lean cylinder. However, in reality, a slight torque difference due to the combustion cycle fluctuation remains between the rich cylinder and the lean cylinder, which causes a slight rotation fluctuation.

On the other hand, considering the drivability, it is necessary to improve the stability of the engine during steady state and during acceleration. On the other hand, it is not necessary to consider the drivability during deceleration, and even if the stability of the engine is somewhat poor, it does not matter. Also, during deceleration, the engine rotation is pulled by the inertia of the vehicle,
Since the inertial force of the vehicle is dominant rather than the engine output, even if the stability of the engine is somewhat poor, the inertial force of the vehicle helps to prevent the rotation fluctuation from being transmitted to the driver. Therefore, when running the vehicle in a state where the catalyst activation is not completed, by stopping the operation of swinging the exhaust air-fuel ratio alternately to the rich side and the lean side at the time of steady state and acceleration, the operation accompanying the fluctuation of combustion cycle is stopped. The deterioration of the feeling is prevented, and the activation of the catalyst 10 is promoted only during deceleration when the driving feeling is not deteriorated.

From the determination result of the conditions, when the catalyst 10 is in the inactive state (Tw ≦ 40 ° C.) or when the activation of the catalyst 10 is completed (Tw ≧ 60 ° C.), the catalyst 10 is partially activated. However, during steady state and during acceleration, the routine proceeds to step 5 and thereafter, and each control of the air-fuel ratio and the ignition timing is performed as in the conventional case.
Regarding the air-fuel ratio control, in step 5, the target fuel-air ratio equivalent amount TFBYA is calculated by the following formula: TFBYA = KAS + KTW + KMR (2) where KAS: post-start increase amount correction coefficient KTW: water temperature increase correction coefficient KMR: mixture ratio correction coefficient .

Each correction coefficient in the equation (2) is well known,
KAS has a value corresponding to the cooling water temperature Tw as an initial value, which decreases at a constant rate with the time after starting and finally becomes 0,
KTW is a value according to the cooling water temperature Tw. KMR is a value exceeding 1.0 (1.0 in other cases) because the air-fuel ratio is set to the rich side when the load is high.

Using the target fuel-air ratio equivalent amount TFBYA calculated in this way, in step 6 Ti (n) = Tp × TFBYA × 2 + Ts (3) where Ts: invalid injection pulse width corresponding to the battery voltage The cylinder-by-cylinder fuel injection pulse width Ti (n) (where n is the cylinder number) is calculated and is transferred to the output register for fuel injection control in step 8.

Here, the fuel injection is a sequential injection system (once every two revolutions of the engine, a system in which the exhaust stroke of each cylinder is the injection timing), so that it is a 4-cylinder engine (ignition sequence # 1- # 3-. # 4 to # 2) as an example, if Ti (1) fuel is supplied in the exhaust stroke of the No. 1 cylinder at the input of the Ref signal this time, the Ref (next time) Ref When the signal is input, the exhaust stroke of the 3rd cylinder is performed. When the Ref signal is input twice, the exhaust stroke of the 4th cylinder is performed. When the Ref signal is input 3 times, the exhaust stroke of the 2nd cylinder is Ti (3). , Ti
(4), Ti (2) fuel is supplied. Such a sequential injection method is performed in all operating ranges, including when the engine is started.

Further, in step 7, a predetermined map is searched from the rotational speed Ne and the basic injection pulse width Tp to obtain the ignition advance value MADV, which is obtained for each cylinder.
(N) (where n is the cylinder number), this ignition advance value ADV (n) is transferred to the output register for ignition timing control in step 8. MADV is set to MBT to improve fuel efficiency.

Here, the ignition advance value ADV (n) for each cylinder
Is the crank angle before compression top dead center, and after ADV (n) is transferred to the output register, a 1 ° signal is output from the Ref signal (for example, rising at 70 ° before compression top dead center) in the input / output interface. When the counted number is equal to 70-ADV (n), the primary current of the ignition coil of the nth cylinder is cut off.

On the other hand, if the catalyst 10 is in a partially activated state and is in deceleration, the process proceeds to step 9 and thereafter, and the air-fuel ratio of every other cylinder (for example, the first cylinder and the fourth cylinder) in the ignition order is set. In addition to making the cylinder rich (cylinders 3 and 2) in the meantime, the exhaust air-fuel ratio is alternately changed to the rich side and the lean side. The ignition timing is set for each cylinder according to each set air-fuel ratio.

When the lean cylinder is used, the routine proceeds from step 9 to step 10, where the table having the contents of FIG. 3 is searched to obtain the target fuel-air ratio equivalent amount TFBYAL of the lean cylinder, and Ti (n) is used in step 11 using this TFBYAL. = Tp × TFBYAL × 2 + Ts (4) The fuel injection pulse width of the lean cylinder is calculated.
TFBYAL in the equation (4) is a value smaller than 1.0,
In the lean cylinder, Tp is reduced by TFBYAL to swing the exhaust air-fuel ratio to the lean side (the value of 1.0-TFBYAL determines the swing range of the exhaust air-fuel ratio to the lean side).

Further, TFBYAL sets a value corresponding to the lean limit in the combustible air-fuel ratio range. Air-fuel ratio at lean limit (M at lean limit, as will be described later)
(BT also) changes according to the cooling water temperature Tw (shifts to the lean side as the cooling water temperature becomes higher), and accordingly the value of TFBYAL is made smaller as the cooling water temperature Tw becomes higher as shown in FIG. . The main reason why the lean limit changes depending on the cooling water temperature is that the vaporization state of the fuel greatly changes depending on the temperature, and at low temperatures the fuel is difficult to vaporize and combustion becomes difficult.

Although the combustion itself is affected by the load, this is smaller than the effect of the cooling water temperature. Further, at the time of high load at which combustion is improved, the generated torque is originally large, and the combustion fluctuation range is also large, so the lean limit does not substantially change. From these results, the target fuel-air ratio equivalent amount TF of the lean cylinder is changed according to the engine load.
It is not necessary to change BYAL. The reason why the lean limit does not change even when the combustion is improved at high load is explained in detail. The lean limit is determined by the stability (the fluctuation range of Pi). This depends on the variation rate of combustion and the indicated mean effective pressure at that time. It is determined by the size of Pi. The image is as follows: σPi = (coefficient) × (combustion variation rate) × Pi However, σPi is the fluctuation range of Pi. In this equation, the combustion variation rate becomes smaller due to improved combustion, but at high load, Pi Because it will grow
As a result, σPi does not change much. In step 12, a table having the contents of FIG. 4 is searched from the cooling water temperature Tw to obtain an ignition advance value ADVL of the lean cylinder, and this is entered in the ignition advance value ADV (n) of the lean cylinder.

Here, since the set air-fuel ratio of the lean cylinder (that is, TFBYAL) is at the lean limit, the ignition timing (that is, ADVL) of the lean cylinder is set at MBT corresponding to the lean-limit air-fuel ratio accordingly. Since TFBYAL changes according to the cooling water temperature Tw as described above,
As shown in FIG. 4, the value of ADVL becomes a value on the advance side as the cooling water temperature Tw is lower.

Next, in the case of the rich cylinder, the routine proceeds from step 9 to step 13, where the predetermined value D is put into the target fuel-air ratio equivalent amount TFBYAR of the rich cylinder, and this TFBYAR is used in step 14 in which Ti (n) = Tp × TFBYAR. The fuel injection pulse width of the rich cylinder is calculated by the formula of × 2 + Ts (5).
The value of D is greater than 1.0, and T in a rich cylinder.
By increasing Tp by FBYAR, the exhaust air-fuel ratio is swung to the rich side (the value of D-1.0 determines the swing range of the exhaust air-fuel ratio to the rich side).

Here, the value of D was matched as follows.

As shown in FIG. 5, the low temperature activity of the catalyst 10 basically becomes better as the CO concentration and the O ₂ concentration increase, and particularly in the region where the CO concentration is above the predetermined value A1, even if the CO concentration is increased (that is, It was found by experiments that the low temperature activity itself did not change much (even if TFBYAR was set to the rich side), so the CO concentration in the exhaust gas was A
It was found that the TFBYAR should be set to be 1 or more. On the other hand, since there is a relationship shown in FIG. 6 between the CO concentration and TFBYAR, a value equal to or higher than the value TFBYAR1 when the CO concentration becomes A1 is adopted as the value of D.

At step 15, the ignition advance value ADVR of the rich cylinder is obtained by searching a table having the contents shown in FIG. 7 from the target fuel-air ratio equivalent amount TFBYAL of the lean cylinder, and the ignition advance value ADV (of the rich cylinder is obtained. n).

Here, if the ignition timings are the same, the rich cylinder produces a larger torque than the lean cylinder, and the torque difference causes a rotational fluctuation. Therefore, in order to eliminate the torque difference between the rich cylinder and the lean cylinder. The ignition timing of the rich cylinder must be set so that the same torque as that generated by the lean cylinder is also generated in the rich cylinder. In this case, since the torque generated by the lean cylinder changes according to the set air-fuel ratio of the lean cylinder (that is, TFBYAL), TFBYAL is changed by setting the ignition advance value ADVR of the rich cylinder according to TFBYAL. Even if it does, the torque difference between the rich cylinder and the lean cylinder can be eliminated. Actually, as shown in FIG. 5, the leaner the set air-fuel ratio of the lean cylinder becomes, the more the (T
The smaller FBYAL), the more the value of ADVR is on the retard side. As described above, even if the ignition timing of the rich cylinder is set in this way, a slight rotation fluctuation actually occurs between the rich cylinder and the lean cylinder due to the combustion cycle fluctuation.

Next, even when the condition for performing the operation of swinging the exhaust air-fuel ratio alternately to the rich side and the lean side is satisfied, the lean cylinder is operated by the operation in step 8 by the Ti (n) of the formula (4). The fuel injection valve 7 is opened in the exhaust stroke of
Ignition is performed using the ignition advance value ADVL. In the rich cylinder, the fuel injection valve 7 is opened in the exhaust stroke of the lean cylinder by Ti (n) of the equation (5), and ignition is performed using the ignition advance value ADVR. The operation of the embodiment of the present invention will now be described. In the embodiment of the present invention, the operation of alternately swinging the exhaust air-fuel ratio to the rich side and the lean side is stopped at the time of steady state and acceleration. Deterioration of driving feeling is prevented.

However, as a result of giving priority to drivability at the time of steady state and acceleration, the warm-up of the catalyst 10 is delayed. Since it is possible to perform the operation of swinging the exhaust air-fuel ratio to the rich side and the lean side alternately by increasing the swing range of the catalyst 10, the warm-up delay of the catalyst 10 is recovered.

As described above, in the embodiment, by suspending the operation of swinging the exhaust air-fuel ratio alternately to the rich side and the lean side at the time of steady state and acceleration, the operation feeling at steady state and at the time of acceleration accompanying the combustion cycle fluctuation is stopped. In order to prevent the catalyst 10 from being delayed in warm-up, the exhaust air-fuel ratio swing range during deceleration is increased and the exhaust air-fuel ratio is alternately swung between the rich side and the lean side while preventing the deterioration of That is why.

When the exhaust air-fuel ratio is alternately changed between the rich side and the lean side, the target fuel-air ratio equivalent amount TFBYAL of the lean cylinder is set to a value equivalent to the lean limit, so that the fuel efficiency is improved. Further, since the value corresponding to the lean limit is set according to the cooling water temperature, the lean cylinder is not deviated from the lean limit even if the cooling water temperature is different, and thus the lean cylinder is operated with the minimum fuel consumption even if the cooling water temperature is different. be able to. Furthermore, the target fuel-air ratio equivalent amount TF of the lean cylinder
Since BYAL is set to a value equivalent to the lean limit, the ignition advance value ADVL of the lean cylinder is set by MBT with respect to the lean limit air-fuel ratio, so that the fuel efficiency is further improved.

Further, since the torque generated by the lean cylinder changes in accordance with the target fuel-air ratio equivalent amount TFBYAL of the lean cylinder, the target fuel-air ratio equivalent amount TFBYA of this lean cylinder is generated.
By setting the ignition advance value ADVR of the rich cylinder according to L, it is possible to eliminate the torque difference between the rich cylinder and the lean cylinder even when the target fuel-air ratio equivalent amount TFBYAL of the lean cylinder changes.

The flowchart of FIG. 8 is the second embodiment,
Steps 21 and 22 are different from those in FIG. Note that FIG.
The same step numbers are given to the same parts as.

Explaining mainly the parts different from FIG. 2, the fuel injection pulse width Ti (n) is set to Ts in step 21 when the cylinder is not a rich cylinder. At this time, fuel is not injected from the fuel injection valve. That is, in place of the lean cylinder of the first embodiment, the fuel cut cylinder is replaced in the second embodiment, so that O ₂ that is not used for combustion remains in the fuel cut cylinder, and the remaining O ₂ is equivalent to the remaining O ₂ .
Since the heat of oxidation reaction in the catalyst 10 is larger than that in the embodiment, the time required to complete the activation of the catalyst 10 is shorter than that in the first embodiment.

In the case of the rich cylinder, in step 22, a map having the contents of FIG. 9 is searched from the target fuel-air ratio equivalent amount TFBYAR of the rich cylinder and the cooling water temperature Tw to obtain the ignition advance value ADVR2 of the rich cylinder. , And put this in the ignition advance value ADV (n) of the rich cylinder.

Here, unlike the first embodiment, ADVR2 is set so that the torque generated by the rich cylinder is reduced. Therefore, the torque difference between the fuel cut cylinder and the fuel cut cylinder in which torque due to combustion heat is not generated. Is smoothed (decreased), which improves engine stability during deceleration.

In the first embodiment, the same number of rich cylinders and lean cylinders are used, and in the second embodiment, the same number of rich cylinders and fuel cut cylinders are used. Set as many as possible (4 cylinder engine has 1 rich cylinder, 3 lean cylinder or fuel cut cylinder, 6 cylinder engine has 2 rich cylinder, 4 lean cylinder or fuel cut cylinder or rich cylinder) It is also possible to use one, five lean cylinders or five fuel cut cylinders.
At this time, O of the lean cylinder or the fuel cut cylinder
_{Since the 2} concentration becomes larger than that of the first or second embodiment, the number of lean cylinders is set to be larger than that of the rich cylinders, and the control shown in FIG. 2 is performed. If the CO concentration of A1 or more is secured, the time until the activation of the catalyst 10 is completed can be shortened by the increase of the O ₂ concentration.

Similarly, the number of rich cylinders is set to be larger than that of lean cylinders or fuel cut cylinders (for example, in a 4-cylinder engine, one lean cylinder or fuel cut cylinder, three rich cylinders, six cylinder engine). Two lean or fuel cut cylinders, four rich cylinders or one lean or fuel cut cylinder
, 5 rich cylinders). At this time, since the CO concentration of the rich cylinder becomes equal to or higher than A1 shown in FIG. 5, the set air-fuel ratio per cylinder can be set to the lean side as the number of rich cylinders increases as the number of rich cylinders increases. When the set air-fuel ratio per cylinder is on the lean side, the generated torque is small (see FIG. 10), so the torque difference with the lean cylinder is reduced and the stability of the engine is improved.

In the embodiment, all of the four cylinders are assigned to the rich cylinder and the lean cylinder (or the fuel cut cylinder). However, the rich cylinder and the stoichiometric cylinder (even the lean cylinder is rich even if the lean is rich) depending on the ignition order. However, it can be assigned to lean cylinders and normal cylinders.

In the embodiment, the case has been described in which whether or not the catalyst 10 is partially activated is determined based on the cooling water temperature or the catalyst temperature, but the present invention is not limited to this, and various known activation determination methods are available. Can be used.

[0082]

When the exhaust air-fuel ratio is alternately changed between the rich side and the lean side, the ignition timing of the rich cylinder is delayed from that of the lean cylinder so that the torque generated by the rich cylinder becomes the same as that of the lean cylinder. Even in the case of angulation, a slight rotational fluctuation actually occurs due to the combustion cycle fluctuation between the rich cylinder and the lean cylinder, so the exhaust air-fuel ratio is set to the rich side and the lean side until steady state or acceleration. If the operation is performed alternately with and, the operating feeling during normal operation or acceleration will deteriorate, but in the first aspect of the invention, the exhaust air-fuel ratio is set to the rich side and the lean side during normal operation or acceleration. Since the alternating shaking operation is stopped, it is possible to prevent the driving feeling from deteriorating during steady state or acceleration due to combustion cycle fluctuations.

However, as a result of giving priority to drivability at the time of steady state or acceleration, the warm-up of the catalyst is delayed, but the second aspect of the present invention makes it easier than the conventional case during deceleration without deteriorating the driving feeling. If the swing range of the exhaust air-fuel ratio is increased and the exhaust air-fuel ratio is alternately swung to the rich side and the lean side, the warm-up delay of the catalyst can be recovered.

In the third aspect, when the number of lean cylinders is made larger than that of the rich cylinders, the O ₂ concentration of the lean cylinder becomes higher than that when the number of the lean cylinders is the same as that of the rich cylinders, so that a sufficient CO concentration is secured. Under these conditions, the time until the completion of activation of the catalyst can be shortened by the amount of increase in the O ₂ concentration. .

When the number of rich cylinders is larger than that of the lean cylinders in the fourth aspect of the invention, the CO concentration of the rich cylinders becomes sufficiently high, and as the number of rich cylinders increases, the air-fuel ratio control amount per cylinder decreases with the number of rich cylinders. Since it can be set to the lean side as compared with the case, the torque difference with the lean cylinder is reduced, and the stability of the engine is improved.

Even if a fuel cut cylinder is used instead of the lean cylinder, the operation of swinging the exhaust air-fuel ratio alternately to the rich side and the lean side can be performed. In this case, however, in the fifth aspect of the invention, the exhaust gas is exhausted during steady state or acceleration. Since the operation of alternating the air-fuel ratio to the rich side and the lean side is stopped, deterioration of the driving feeling during steady state or acceleration due to fluctuation of combustion cycle is prevented, and it is used for combustion in the fuel cut cylinder. no O ₂ may remain, because the residual O ₂ minutes by oxidation reaction heat in the catalyst is increased, it is possible to shorten the time until the activation completion of the catalyst than if a lean cylinder.

However, as a result of giving priority to the drivability at the time of steady state or acceleration, the warm-up of the catalyst is delayed, but the sixth aspect of the present invention makes it easier than the conventional one at the time of deceleration without deteriorating the driving feeling. If the swing range of the exhaust air-fuel ratio is increased and the exhaust air-fuel ratio is alternately swung to the rich side and the lean side, the warm-up delay of the catalyst can be recovered.

In the seventh aspect of the invention, the ignition timing of the rich cylinder is set so that the torque generated by the rich cylinder is reduced, so that the torque difference from the fuel cut cylinder in which torque due to combustion heat is not generated is reduced. This improves the engine stability during deceleration.

In the ninth invention, when the number of fuel cut cylinders is made larger than that of the rich cylinders, the O ₂ concentration of the fuel cut cylinders becomes larger than that when the number of the fuel cut cylinders is the same as that of the rich cylinders, so a sufficient CO concentration is secured. As long as the above conditions are satisfied, the time until the activation of the catalyst is completed can be shortened by the increase in the O ₂ concentration.

When the number of rich cylinders is made larger than that of the fuel cut cylinders in the tenth aspect of the invention, the CO concentration of the rich cylinders becomes sufficiently large, and the air-fuel ratio control amount per cylinder becomes richer as the number of rich cylinders becomes larger. Since it can be set to the lean side compared to when it is low, the torque difference with the fuel cut cylinder is reduced, and the stability of the engine is improved.

In the fourteenth aspect of the invention, the air-fuel ratio control amount of the lean cylinder corresponds to the lean limit, so the fuel efficiency is improved.

In the fifteenth invention, since the air-fuel ratio control amount corresponding to the lean limit is a value according to the cooling water temperature, the air-fuel ratio of the lean cylinder does not deviate from the lean limit even if the cooling water temperature is different. Therefore, even if the cooling water temperature is different, the lean cylinder can be operated with the minimum fuel consumption.

In the sixteenth aspect of the present invention, the air-fuel ratio control amount of the lean cylinder corresponds to the lean limit, and the ignition timing of the lean cylinder corresponds to the air-fuel ratio control amount of the lean limit corresponding to M.
Since it is a BT, fuel efficiency is further improved.

The torque generated by the lean cylinder changes according to the air-fuel ratio control amount of the lean cylinder. In the seventeenth aspect of the invention, the ignition timing of the rich cylinder has a value according to the air-fuel ratio control amount of the lean cylinder. Therefore, the torque difference between the rich cylinder and the lean cylinder can be eliminated even when the air-fuel ratio control amount of the lean cylinder changes.

[Brief description of drawings]

FIG. 1 is a control system diagram of an embodiment.

FIG. 2 is a flowchart for explaining calculation of a fuel injection pulse width given to a fuel injection valve and an ignition advance value for each cylinder.

FIG. 3 is a characteristic diagram of a target fuel-air ratio equivalent amount TFBYAL of a lean cylinder with respect to a cooling water temperature Tw.

FIG. 4 is a characteristic diagram of an ignition advance value ADVL of a lean cylinder with respect to a cooling water temperature Tw.

FIG. 5 is a characteristic diagram of low temperature activity of the catalyst 10.

FIG. 6 is a characteristic diagram of CO concentration with respect to a target fuel-air ratio equivalent amount TFBYAR of a rich cylinder.

FIG. 7 is a characteristic diagram of the ignition advance value ADVR of the rich cylinder with respect to the target fuel-air ratio equivalent amount TFBYAL of the lean cylinder.

FIG. 8 is a flow chart for explaining calculation of a fuel injection pulse width and an ignition advance value given to the fuel injection valve of the second embodiment for each cylinder.

FIG. 9 is a characteristic diagram of the ignition advance value ADVR2 of the rich cylinder with respect to the target fuel-air ratio equivalent amount TFBYAR of the rich cylinder and the cooling water temperature Tw of the second embodiment.

FIG. 10 is a characteristic diagram of torque with respect to intake air-fuel ratio.

FIG. 11 is a diagram corresponding to a claim of the first invention.

FIG. 12 is a diagram corresponding to a claim of the fifth invention.

FIG. 13 is a diagram corresponding to a claim of the eighteenth invention.

FIG. 14 is a diagram corresponding to a claim of the nineteenth invention.

[Explanation of symbols]

 1 Engine Main Body 2 Control Unit 4 Crank Angle Sensor 6 Air Flow Meter 7 Fuel Injection Valve 10 Three-Way Catalyst 13 Spark Plug

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location F02D 41/10 330 F02D 41/10 330B 41/14 310 41/14 310B 43/00 301 43/00 301B 301E 45/00 301 45/00 301D 301K F02P 5/15 F02P 5/15 K BF

Claims (19)

[Claims] 1. A means for determining whether or not the catalyst is partially activated while a catalyst is provided in an exhaust passage, and at least one cylinder is determined to be a rich cylinder when the catalyst is partially activated based on the determination result. Due to the exhaust of this rich cylinder, the air-fuel ratio of the exhaust swings to the rich side, and at least 1
With one cylinder as a lean cylinder, a means for controlling the air-fuel ratio control amount so that the air-fuel ratio of the exhaust gas swings to the lean side by the exhaust of this lean cylinder, a means for setting the ignition timing of the lean cylinder, and the generation of the rich cylinder Means for setting the ignition timing of the rich cylinder so that the torque to be performed is the same as that of the lean cylinder; and means for performing ignition of each cylinder by using the ignition timing of the rich cylinder and the ignition timing of the lean cylinder. An exhaust gas purifying apparatus for an engine, comprising: means for determining whether it is always or during acceleration, and means for stopping the air-fuel ratio control during steady state or acceleration based on the determination result. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the air-fuel ratio control is performed by increasing a swing range of the exhaust air-fuel ratio swinging between the rich side and the lean side during deceleration. 3. The exhaust emission control device for an engine according to claim 1, wherein the number of lean cylinders is greater than that of the rich cylinders. 4. The exhaust gas purification device for an engine according to claim 1, wherein the number of the rich cylinders is larger than that of the lean cylinders. 5. A means for determining whether or not the catalyst is partially activated while providing a catalyst in the exhaust passage, and at least one cylinder is determined to be a rich cylinder when the catalyst is partially activated based on the result of the determination. Means for controlling the air-fuel ratio control amount so that the air-fuel ratio of the exhaust gas swings to the rich side by the exhaust of the rich cylinder; and means for fuel-cutting at least one cylinder when the catalyst is partially activated from the determination result, An exhaust gas purifying apparatus for an engine, comprising: a unit that determines whether the engine is stationary or accelerating, and a unit that stops the air-fuel ratio control when the engine is stationary or accelerating based on the determination result. 6. The exhaust gas purifying apparatus for an engine according to claim 5, wherein the air-fuel ratio control is performed by increasing a swing range of the exhaust air-fuel ratio swinging to the rich side during deceleration. 7. The exhaust emission control system for an engine according to claim 5, wherein the ignition timing of the rich cylinder is set so that the torque generated by the rich cylinder becomes small. 8. The engine exhaust gas purification apparatus according to claim 7, wherein the ignition timing of the rich cylinder is a value corresponding to an air-fuel ratio control amount of the rich cylinder and a cooling water temperature. 9. The exhaust purification system for an engine according to claim 5, wherein the number of the fuel cut cylinders is larger than that of the rich cylinders. 10. The number of rich cylinders is larger than that of the fuel cut cylinders.
The engine exhaust gas purification device according to any one of items 1 to 3. 11. The exhaust gas purification apparatus for an engine according to claim 1, wherein the air-fuel ratio control amount of the rich cylinder is set so that the CO concentration becomes a predetermined value or more. . 12. The predetermined value is a boundary value between a region where the low temperature activity of the catalyst does not change so much even when the CO concentration is changed and a region where the low temperature activity of the catalyst greatly changes when the CO concentration is changed. The exhaust emission control device for an engine according to claim 11, characterized in that. 13. The engine according to claim 1, wherein whether or not the catalyst is partially activated is determined based on a cooling water temperature of the engine or a temperature of the catalyst. Exhaust purification device. 14. The exhaust gas purification device for an engine according to claim 1, wherein the air-fuel ratio control amount of the lean cylinder corresponds to a lean limit. 15. The exhaust emission control system for an engine according to claim 14, wherein the air-fuel ratio control amount corresponding to the lean limit is a value according to a cooling water temperature of the engine. 16. The exhaust purification system for an engine according to claim 14, wherein the ignition timing of the lean cylinder is MBT with respect to the air-fuel ratio control amount corresponding to the lean limit. 17. The exhaust emission control system for an engine according to claim 1, wherein the ignition timing of the rich cylinder is a value according to an air-fuel ratio control amount of the lean cylinder. . 18. The air-fuel ratio control means calculates means for calculating a basic injection amount that substantially obtains a theoretical air-fuel ratio according to operating conditions, and increases the basic injection amount for the rich cylinder,
And means for reducing the lean cylinder, and means for supplying the increased injection amount of fuel to the intake pipe of the rich cylinder and supplying the reduced injection amount of fuel to the intake pipe of the lean cylinder. The exhaust emission control device for an engine according to any one of claims 1 to 4, which is characterized in that. 19. The air-fuel ratio control means is a means for calculating a basic injection amount for obtaining a theoretical air-fuel ratio in accordance with an operating condition, and an increasing means for increasing the basic injection amount for the rich cylinder. The exhaust gas purification device for an engine according to any one of claims 5 to 10, characterized in that it comprises means for supplying an injection amount of fuel to the intake pipe of the rich cylinder.