JP2618966B2 - Engine air-fuel ratio control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an engine having an air-fuel ratio feedback control system of two or more systems and an exhaust gas purifying means provided downstream of a confluence of two or more exhaust systems. Regarding the air-fuel ratio control device,
In particular, it relates to improving the activation of the exhaust gas purifying means.

(Prior Art) Conventionally, a technique of performing feedback control of an air-fuel ratio of an air-fuel mixture supplied to an engine based on an output of an air-fuel ratio sensor provided in an exhaust system in order to improve emission characteristics is well known. . This feedback control technology
The characteristics of the exhaust gas purification device are based on the fact that the exhaust gas exhibits maximum efficiency when the air-fuel ratio in the exhaust gas has the stoichiometric air-fuel ratio.

There are two factors that affect the purification performance of this exhaust gas purification device. One is the temperature of the purifier and one is the storage effect. This storage effect is, for example, as described in JP-A-60-190630, in which oxygen is stored in the catalyst in a lean atmosphere, and the stored oxygen in a rich atmosphere. This is a phenomenon in which CO and HC are oxidized, and is considered to be useful for increasing the purification ability of a three-way catalyst.

Japanese Patent Application Laid-Open No. 60-190630 discloses that, for example, an exhaust system is divided into two (left and right) banks, such as a V-type engine, and an oxygen sensor is provided in each of the exhaust systems for each of the banks. The present invention relates to a technique for performing feedback control of the air-fuel ratio independently of both banks based on the outputs of the two sensors. The reason for providing two sensors is to achieve both the prevention of back pressure in the exhaust system and the improvement in the accuracy of the air-fuel ratio sensor. The problem to be solved in Japanese Patent Application Laid-Open No. 60-190630 is that if feedback control is performed independently between two banks, a phase shift of the feedback control between the two banks occurs. It is based on the fact that the oxygen concentration in the exhaust gas becomes unstable and the storage effect cannot be sufficiently expected. For this purpose, this Japanese Patent Application Publication No. JP-A-H08-19764 discloses that the phase of the control signal for feedback control between the two banks is synchronized to stabilize the change of the excess oxygen concentration in the exhaust gas regularly, thereby improving the purifying action by the storage effect. I am trying to make it.

(Problems to be Solved by the Invention) In the above-mentioned Japanese Unexamined Patent Publication No.
Control is performed so that the phases of the feedback correction amount (fuel injection amount correction coefficient) calculated based on the output of the air-fuel ratio sensor match. However, in order for the storage effect to be exhibited, the phase of the air-fuel ratio of the exhaust gas needs to match at the position of the exhaust gas purification device. This is not a sufficient condition for the phases of the fuel ratios to match. The reason is that even if the phase between the feedback correction amounts is matched, only the phase of the air-fuel ratio of the mixture at the injector position is guaranteed, and the air-fuel ratio of the exhaust gas from the two systems at the purification device position It is only probable that the phases are the same. In the feedback control system for the air-fuel ratio, the injector and the purifier are the most distant positional combination.
It should be said that the likelihood that the phases of the exhaust gas air-fuel ratio match at the purifier position is low. Furthermore, if there is a deviation between the two air-fuel ratio sensor positions and the distance between the one purifying device in the two exhaust systems, the phase of the feedback correction amount (fuel injection amount correction coefficient) may be matched. That is not.

Therefore, the present invention has been proposed to eliminate the above-mentioned drawbacks of the conventional example. An object of the present invention is to provide an engine having two or more air-fuel ratio control systems in which the storage effect of the exhaust gas purifying device is more likely to be enhanced. Is proposed.

(Means and Actions for Solving the Problems) As shown in FIG. 1, the configuration of the present invention for attaining the above-mentioned problems is based on the exhaust gas emptying in each exhaust system of two or more provided cylinder groups. Two or more air-fuel ratio detecting means for detecting a fuel ratio; and at least a downstream of each of the air-fuel ratio detection positions detected by the two or more air-fuel ratio detecting means, and disposed in the collective portion of the plurality of exhaust systems. Two or more feedbacks that feedback-control the air-fuel ratio of the air-fuel mixture supplied to the cylinder of the engine to a target value based on the output of each of the exhaust gas purifying means and the two or more air-fuel ratio detecting means. Control means and feedback control so as to synchronize the phases of changes in the air-fuel ratio of the exhaust gas that respectively reach from the cylinder groups to the exhaust system assembly located upstream of the exhaust gas purification means. Characterized in that and a correcting means for correcting the control characteristics.

Since the control characteristics of each feedback control are corrected, the air-fuel ratio of the exhaust gas from each exhaust system is synchronized in the collective part of the exhaust system, that is, the air-fuel ratio of each exhaust gas is , The rich state and the lean state are repeated, and the storage effect of the exhaust gas purifying means is promoted.

The correction of the control characteristics by the correction means of the first aspect is realized in various modes.

For example, according to the air-fuel ratio control device of the second aspect, the start of the air-fuel ratio feedback control in one cylinder group is delayed by a predetermined time from the start of the air-fuel ratio feedback control in another cylinder group, whereby the air-fuel ratio feedback control is performed. , The phases of the changes in the air-fuel ratio of the exhaust gas reaching the collecting section from each of the cylinder groups are synchronized with each other.

The predetermined time is, for example, a time determined by a difference in the pipe length between the exhaust systems and the flow rate of the exhaust gas. Although the difference between the pipe lengths is a fixed value, the flow rate of the exhaust gas differs depending on the time. Further, since the flow rate of the exhaust gas is proportional to the amount of intake air, the predetermined time difference is changed by the amount of intake air.

The correction of the control characteristics by the correction means of claim 1 is as follows.
The synchronization of the change in the air-fuel ratio of the exhaust gas in each exhaust system can be further improved by using the output signal of the air-fuel ratio detecting means. That is, according to the air-fuel ratio control device of the third aspect, a phase difference detection for detecting a phase difference of an output signal representing an air-fuel ratio of exhaust gas in each cylinder group detected by the two or more air-fuel ratio detection means. Means for correcting the control characteristic of each feedback control so that the phase difference of the output signal detected by the phase difference detecting means has a predetermined value. According to this control, the phases of the changes in the air-fuel ratio of the exhaust gas reaching the collecting portion from each of the cylinder groups are synchronized with each other, which is smaller than the control at the start of the feedback control by the air-fuel ratio control device according to claim 2. Thus, improved synchronization is obtained.

According to the air-fuel ratio control device of the fifth aspect, the correction of the feedback control characteristic in each cylinder group is achieved by changing the cycle of the feedback control.
Therefore, the integration constant of the feedback control is changed.

(Example) Hereinafter, an example in which the present invention is applied to a six-cylinder V-type engine will be described with reference to the accompanying drawings.

<Overview of Example System> As shown in FIG. 2, the engine 10 includes an air filter 12 for filtering intake air, and the air filtered by the air filter 12 passes through an intake pipe 14 and passes through an intake valve 16a. , 16
It is introduced into cylinders 18a, 18b arranged in a V-shape via b. In FIG. 2, the other four cylinders are arranged on the opposite side of the drawing, but are not shown. Further, if the six cylinders are respectively a first cylinder to a sixth cylinder,
Assuming that the first cylinder is equivalent to 18a and the second cylinder is equivalent to 18b,
The cylinder 18a and the two opposite cylinders form a left bank cylinder, and the cylinder 18 and the two opposite cylinders form a right bank cylinder.

An air flow meter 20 for measuring the flow rate (Q _a ) of the intake air passing therethrough and an intake air temperature sensor 22 for measuring the temperature (T _a ) of the intake air are provided upstream of the intake pipe.

The middle of the intake pipe 14 is connected to the left and right banks 2
Each of the divided passages is provided with a throttle valve 24a, 24b. One throttle valve 24a has an opening sensor 27 for detecting its opening (TVO).
Is attached. Also, the throttle valves 24a, 24
A bypass pipe 26 is connected to the intake pipe 14 so as to bypass the intake pipe 14 on the upstream side and the downstream side of b.
An idle speed control valve 28 is mounted in the middle of the bypass pipe 26. A / C operation, power steering operation,
When the heater is activated, the ISC valve 28
ON / OFF operation is controlled according to the signal ISC, and the ISC valve 28
Flow rate of bypass pipe 26 passing through
Is controlled.

The downstream side of the intake pipe 14 is branched and connected to cylinders 18a, 18b and the like belonging to the left and right banks, and each branch connection pipe has a fuel injection valve for supplying fuel into the corresponding cylinder.
34a and 34b are provided. Each fuel injection valve 34a, 34b is connected to an engine control unit (hereinafter simply referred to as ECU) 3 described later.
6, the width of the fuel injection pulse (τ _A , τ _B ) is specified. Note that the subscript “A” indicates a signal related to the left bank system, and “B” indicates a signal related to the right bank system.

Pistons 32a, 32b are slidably disposed in the left and right cylinders 18a, 18b. Each piston is a cylinder 18, 18b
By sliding inside and back and forth, the crankshafts to which each is connected are rotationally driven. Although not shown, an ignition plug for burning the fuel injected here is provided above the cylinders 18a and 18b. Further, the cylinders 18a, 18b are provided with cooling water passages 40a, 40b for cooling the cylinders 18a, 18b, respectively. In the cooling water passages, the temperature of the cooling water passing therethrough is controlled by the engine temperature (T _W ) Is attached.

On the other hand, the combustion gas burned in each of the cylinders 18a and 18b passes through the corresponding exhaust valves 44a and 44b as exhaust gas.
The exhaust gas passes through the exhaust manifolds 46a and 46b and is further collected in the exhaust pipe 48. A catalytic converter 50 for purifying exhaust gas is provided in the middle of the exhaust pipe 48.

As in the case of the intake pipe, the exhaust manifold 46a from the cylinder 18a in the left bank and the exhaust manifold 46c from the other two cylinders in the left bank (the other one cylinder) (The exhaust manifold is not shown) and the cylinder in the right bank
An exhaust manifold 46b of 18b and an exhaust pipe 46d from the remaining cylinders of the right bank (an exhaust manifold of another cylinder is not shown) are combined into one to form an exhaust pipe 48. The collecting portion upstream of the exhaust pipe 48, O ₂ sensor 52a for measuring the concentration of oxygen remaining in the exhaust gas passing (O _2), 52b is attached. These sensors 52a, an oxygen concentration signal output from 52 b, respectively, E _A, and E _B.

Reference numeral 53 denotes a temperature sensor (output is T _C ) of the catalytic converter 50. Based on the output E _A from the oxygen sensor 52a, the air-fuel ratio control of the left bank (cylinder 18a, etc.) is performed, based on the output E _B from the oxygen sensor 52 b, the right bank (cylinder 18b
) Is independently performed between the respective banks.

25 is a fuel tank. The fuel gas component evaporated in this tank is trapped by the canister 19. The trapped gas passes through pipes 15a and 15b when the solenoid valve 17 is opened by a signal PC from the ECU 36.
It is supplied to the left and right banks. As will be described later, the ECU 36
By monitoring the signal PC, it is possible to detect the start and end of the supply of the evaporated fuel.

The ECU 36 can know the engine speed N from a signal from a distributor (not shown in FIG. 2).

<Outline of Operation of Embodiment> The outline of the operation of this embodiment will be described with reference to FIG.
FIG. 3 schematically shows the exhaust system of the engine shown in FIG. Injiekuta 34a, the fuel injection quantity injected from 34b is represented as _{τ A = τ 0 (1 +} C AFB + C 0) τ B = τ 0 (1 + C BFB + C 0). Here, τ ₀ is the basic fuel injection amount,
C _AFB and C _BFB are correction coefficients for air-fuel ratio feedback control, C ₀
Is a correction term based on the engine water temperature and the like. The distance from the left bank air-fuel ratio sensor 52a to the catalytic converter 50 is determined by the right bank air-fuel ratio sensor 52b to the catalytic converter 5b.
Assuming that the distance is slightly shorter than zero, the exhaust gas from the left bank system reaches the converter 50 slightly earlier than that of the right bank system. Therefore, in this embodiment, the fuel injection amount from the injectors 34a and 34b is
Sensor 52a, the air-fuel ratio signal E _A detected by 52 b, both the phase difference between the E _B is, before such is also detected with a time difference so as to compensate for the connexion the distance difference (phase difference), the set is there. By doing so, the catalytic converter based on the distance difference
The phase difference of the air-fuel ratio of the exhaust gas at the position of 50 is wiped out, and the rich (or lean) exhaust gas from the left bank and the rich (or lean) exhaust gas from the right bank system are synchronized, Moreover, the lean state and the rich state alternate,
Further, since they are separated from each other and reach the catalyst 50, the storage effect is enhanced.

At the position of the air-fuel ratio sensor, in order to make the phase difference corresponding to the difference in the distance between the left and right exhaust systems appear in the output of the air-fuel ratio sensor, the following three methods are employed in the control of the embodiment described below. I have.

: The distance difference between the exhaust systems of the left and right banks (referred to as て い る L) has already passed, but the phase difference changes according to the flow rate of the exhaust gas. Since this flow rate corresponds to the intake air amount Q _a, the phase difference (time difference t ₀₎ is Determined by The value of this t ₀ is also stored in the connexion the ECU36 before a table corresponding to Q _a.

: Since the air-fuel ratio feedback control is executed only when a certain operating condition is satisfied, when the feedback control execution condition is satisfied, the left and right banks do not execute the feedback control at the same time, and the left and right banks are not operated. ,
The start of the fed back control of the bank system of the person who is advanced in phase manner, delayed by the above-mentioned t ₀ hours. As a result, the phase is roughly adjusted.

: When the t ₀ hours has elapsed, fed back control is executed in two banks. At this stage, there is no guarantee that the phase difference between the output of both banks sensor is above t _0. Therefore, by detecting the phase difference between the outputs of the both banks sensors, such that the sensor outputs of both banks are obtained with a shift by the phase difference t ₀ hours, the control period of the fed back control of one of the banks to change is to change the integration constant of the fed back control (the C _AFB, constants for computing the C _BFB). In the present embodiment, the control cycle is changed, for example, in the feedback control of the left bank system.

<Control Procedure> The control procedure of the embodiment will be described with reference to the flowcharts of FIGS. 4A to 4C. FIG. 4A shows a data input routine and a non-feedback control routine. Figure 4B is fed back control of the right bank system, and during the initial of the t ₀ hours when going to fed back control region from the non-fed back control region, in flow chart representing a control for stopping the fed back control of the left bank system FIG. 4C is a flowchart showing the feedback control of the left bank system and the control of the phase matching described in the above.

First, at step S2 in FIG. 4A, the intake air amount Q _a, reading the engine speed N, and the like. In step S4, the intake air amount Q _a, calculates the basic fuel injection amount tau _O from the engine speed N, and the like.

Here, K is a predetermined constant. In step S6, the intake air temperature T _a , the engine water temperature T _{W and the} like are read. In step S8, the intake air temperature T _a, and calculates the correction coefficient C ₀ of the fuel injection amount from the engine water temperature T _W and the like. In step S10, the air-fuel ratio sensor output E _A, reads the E _B, in step S12, binarizes this output with a predetermined slice level. In step S14, with the phase difference time t _0, it is read by searching the time below t ₁ from Matsupu. In step S16, the engine water temperature T _W, the catalyst temperature T _C, the engine speed N, and the like, checks whether the current operating condition is in the fed back control execution region, and the result is stored in the flag F _FB.

Currently, if it is not in the feedback control execution area,
Step S20, in step S22, fed back control correction coefficient C _AFB, a C _BFB to "0". Step S24, Step S26
Then, the final fuel injection amounts τ _A and τ _B of the left and right bank systems are determined, and fuel is injected from the injectors 34a and 34b in step S28.

A description will be given of a case where it is presently in the feedback control execution area in step S18. In this case, step S4
Go to 0 or less. In step S40, whether the current value of the binarization result of the sensor output of the right bank E _B is "1", it is checked whether it is "0". It indicates it is currently Ritsuchi when E _B is "1", it is "0" indicating that the lean state. Therefore, in step S42 and step S44, integral control in the plus or minus direction is performed in accordance with the sensor output. The constants of the integration control fed back control of the right bank system, when △ i _B0, integral control, C _BFB = C _BFB - △ in I _B0 (step _{S42) C BFB = C BFB +} △ I B0 ( step S44) is there. In this manner, positive integration control in the gradually increasing direction is performed while the sensor output is "0", and negative integration control in the gradually decreasing direction is performed when the sensor output is "1". When the sensor output is inverted from “0” to “1”, the output changes from gradually increasing to gradually decreasing. When the sensor output is inverted from “1” to “0”, the output changes from gradually decreasing to gradually increasing. This will be more apparent with reference to FIG.

Next, at step S46, fed back control execution condition flag F _FB is in the current cycle from the previous cycle,
Check whether the status has changed from “0” to “1”. As described above, only when shifting from the non-execution region of the feedback control to the execution region, the start of the feedback control of the bank system which is advanced in phase among the left and right banks is performed at the time t _0. This is because the control for delaying by the time is performed in step S50 or less. In the engine of FIG. 2, it is assumed that the distance of the exhaust system in the left bank is longer.

When it is determined that when shifted from the non-execution region fed back control in the execution area, at step S48, the integral constant △ I _A of the left bank system and allowed temporarily to match the constant △ I _B0 in the right bank system. That is, ΔI _A = ΔI _B0 . Step S50~ step step S54, shall apply in control performed only during transition of the control is for initializing the left bank system stop time (t _0, t ₁₎ to the timer T _S. still,
Depending on whether or not the sensor output is E _A = E _B , the value set in the timer T _S may be set not only at t ₀ but also at t ₁ in steps S52 and S54. This will be described later with reference to FIG.

In the step S56, it decrements the timer T _S. At step S58, it is checked whether the timer T _S has timed out (T _S ≦ 0). While the timeout does not occur (T _S > 0), in order to stop the feedback control of the left bank system, in step S60, the feedback correction coefficient C of the left bank system is set.
_{The AFB} is set to C _AFB = 0, and the process proceeds to step S24 and thereafter to perform fuel injection.
In other words, until the timer T _S times out,
Steps S2 to S18, step S40, step S46, step S56, step S56, step S58, step S60, and step S24 to step S28, perform feedback control of only the right bank system.

Referring to FIG. 5, the flowchart of FIG. 4B will be further described. FIG. 5 shows a process in which the flag _FFB changes from “0” to “1” and a subsequent control operation. In step S46, upon detecting a 01 change in the F _FB, step S52, to set the initial value of the timer T _S at step S54. In FIG. 5, when F _FB becomes “0” or “1”, E _A ≠ E
_In the case where _B is assumed (for example, E _A = 0, E _B = 1), the operation of C _AFB and E _A of the left bank system when T _S = t ₁ is shown by a solid line. . Here, t ₁ > t ₀ . In FIG. 5, with T _S times out, the fed back control of the left bank is started up from Atsuta by E _A is "0" it is fed back control of the left bank system starts in the positive direction of the integral control Is done.

The timer T _S, in regardless of the value of E _A and E _B, T _S
= T ₀ (<t ₁ ), _CAFB , E of left bank system
The operation of _A is indicated by a broken line in the same FIG. This means that T _S
Is timed out and the feedback control of the left bank is started, the feedback control of the left bank is started by the integral control in the positive direction (because E _A = 0), but as shown by the broken line in FIG. in, and a C _AFB and C _BFB would summer antiphase. That is, in order to avoid the opposite phase, when E _A ≠ E _B , T _S = t ₁ (> t ₀ ).

Feedback control was started in the left bank system (T _S =
0) The following description will be given. At this time, steps S2 to S18, step S40, step S46, and step S56 are performed.
Proceed to step S58 and step S62. In step S62~ step S66, performs integral operation of the left bank system as a function of the value of the sensor output E _A.

_{C AFB = C AFB - △ I} A ( step _{S64) C AFB = C AFB -} △ I A ( step S66) integration constant of the first time it proceeds to step S64,66 △
The value of I _A is the same value as the constant △ I _B0 of right bank system set at step S48. That is, first, the left bank system performs an integration operation with the same constant as that of the right bank system so as to maintain the same cycle as that of the right bank system.

In step S68, it detects a change in time of the sensor output E _A of the left bank system. Step S78 compares the E _A and E _B,
Regarding a counter T for counting the phase difference (time), it is assumed that E _A = E _B T = 0 E _A ≠ E _B T = T + 1. That is, since the difference between the sensor output E _B of the sensor output E _A and the right bank system of the left bank system has occurred, it is to start counting of the counter T. This count is then continued until the E _A = E _B is detected. Generally, in an engine in which two feedback control systems are set, the deviation of the control cycle between the two systems is calculated as long as the air-fuel ratio sensor is not deteriorated.
Approximately within ± 10%. In addition, in step S68, before the step S78, trying to detect the change of the left bank sensor output E _A. That is, as when there is no change in the left bank sensor output E _A (NO at step S68), it is detected E _A ≠ E _B at step S78, the count of the counter T is started,
Always, E _B is, 0 → 1, or, it is time to change the 1 → 0. Accordance connexion, in the next counting cycle, before the count of the counter T is reset at step S80, in step S68, always change in E _A, 0 → 1, or, 1 → 0 is detected. In this case, the process proceeds to step S70, and compares the timer T and the phase difference constant t _0.

Here, when T <t ₀ is detected, the detected phase difference T between the two banks is shorter than the known phase difference t ₀ , that is,
Since it's are too advances the control of the left bank system, in order to delay the control period longer, at step S76, △ I _A = △ set the I _A2, to gentle the slope of C _AFB. Here, there is a relationship of _{ΔI A1} > ΔI _B0 > ΔI _A2 between this constant value ΔI _A2 , ΔI _B0 described above, and ΔI _A1 described later. Step S78~ In step S82, E _A = E since the detected E _A ≠ E _B after _B, the detection operation of the next phase difference time T is started, the counting phase difference time T again step S70 When it is determined that T = t ₀ , the phase difference between the two banks matches the time difference required for the exhaust gas to flow through the distance difference between the two banks. This shows that the cycle of the exhaust gas littling is the same between the two banks, indicating that it is optimal for exhibiting the storage effect.
Therefore, in step S74, ΔI _A = ΔI _B0 , and the control constants between the two banks are made to be the same so that the subsequent control cycles are the same. The control operation at this time is shown in the left half of FIG. In the left half, the phase difference detected by the counter T is initially t ₀ '.
A (<t _0), then the change the [Delta] I _A to △ I _A2, then the detected phase difference is if t _0, changes the △ I _A to △ I _B0.

Next, at step S70, when it is detected that T> t _0, the phase difference T between the detected two banks is longer for the than known phase difference t _0, i.e.,
Since the control of the left bank system is too late, step S72 is performed to shorten the control cycle and recover the delay.
Then, set ΔI _A = ΔI _A1 to make the slope of _CAFB steep. The control operation at this time is shown in the right half of FIG. In the figure on the right half,
The phase difference detected by the counter T is initially t ₀ ″ (>
t ₀ ), at which time ΔI _A is changed to ΔI _A1 , and if the detected phase difference is t ₀ , ΔI _A is changed to _{ΔI B0} .

In the FIG. 5, the sensor output E _A of the connexion left bank system different from the Figure 6 there is shown the case where ahead of the sensor output E _B of the right bank system. It is filed in this case, according to the control shown in FIGS. 4A, second 4C view, E _A is 0 →
When the value changes from 1 or 1 to 0, the coefficient value of the counter T is checked in step S70. In this case, the coefficient value T is "0".
To be _{(T = 0 <t 0)} , the △ I _A of the left bank system chosen is △ I _A2 at step S76, is in the phase of the fed back control of the left bank system is delayed.

According to the embodiment described above, according to the embodiment described above, I: the distance difference between the exhaust systems of the left and right banks (△
L), a phase difference (time difference t ₀ ) is set, and when the feedback control execution condition is satisfied, the left and right banks do not execute the feedback control at the same time, and the phase of the left and right banks is advanced. How to the start of the fed back control of the bank system of Dale, delayed by the above-mentioned t ₀ hours. As a result, the approximate phase adjustment is performed, and the time required for the next accurate phase adjustment is reduced.

II: Furthermore, the period of the feedback control of the left bank is changed so that the phase difference between the outputs of the sensors of both banks coincides with the time difference corresponding to the distance difference between the exhaust systems of both banks.
As a result, the sensor (52a, 52 b) the phase between the two banks are shifted already t ₀ hr at position, lean / Ritsuchi phase of the exhaust gas from both banks arriving to the position of the cleaning device 50 is consistent I have. Therefore, the storage effect is promoted. In order to obtain this effect, the control phase of the right bank may be advanced or delayed.

III: In the control of the above-described embodiment, in addition to the normal air-fuel ratio feedback control, the control cycle of the feedback control is changed so that the air-fuel ratio of the exhaust gas at the position of the air-fuel ratio sensor has a predetermined phase relationship. It is. Here, a case where there is no difference in the exhaust system distance between the two banks will be considered. At this time, t ₀ is “0”. Even in such a case, according to this embodiment, the air-fuel ratio of the exhaust gas at the position of the air-fuel ratio sensor has a predetermined phase relationship (that is, no phase difference).
In other words, when t ₀ is “0”, the change in the air-fuel ratio of the exhaust gas at the air-fuel ratio sensor position is the same between the two banks. That is, in this embodiment, as long as consistent between both banks at the air-fuel ratio sensor position, fed back control correction coefficient C _AFB, the phase of the C _BFB is does not matter whether they match. The above-mentioned Japanese patent
In No. 60-190630, the feedback control correction coefficient C _AFB , C
_{Since it is hard} to match the phase of the _BFB, no matter how much the air-fuel ratio of the air-fuel mixture supplied to the engine is synchronized between the two banks, suction into the combustion chamber → combustion → exhaust manifold →
It is overlooked that in the course of the transfer of the gas from the air-fuel ratio sensor, the phase difference that has been aligned is shifted by the time the gas arrives at the air-fuel ratio sensor. In this respect, the present embodiment is not limited to the case where there is a difference in the exhaust gas travel distance between the two banks, but also the case where the air-fuel ratio can be detected as close as possible to the catalyst device 50, that is, the air-fuel ratio. At the sensor position, the phase difference between the two banks is controlled to be equal to a predetermined value, so that the rich state and the lean state are more reliably separated and the separated exhaust gas reaches the catalyst device. And thus the storage effect is promoted.

IV: Further, since the expected phase difference time t ₀ changes according to the exhaust gas flow velocity, more accurate phase matching can be performed.

Although FIG. 3 illustrates the case where there is a difference in the distance from the injector position to the air-fuel ratio sensor position between the two banks, the present invention is based on the difference in the pipe resistance between the two banks. The same applies to the case where a phase difference of the gas air-fuel ratio appears.

It is needless to say that the present invention is not limited to the configurations of the above-described embodiments and modified examples, and can be variously modified without departing from the gist of the present invention.

(Effects of the Invention) As described in detail above, according to the engine air-fuel ratio control apparatus of the present invention, in an engine having one exhaust gas purifying means and a plurality of feedback control systems,
The control characteristics of each feedback control are corrected so that the air-fuel ratios of the exhaust gas from all the exhaust systems have a predetermined phase difference in the collective portion of the exhaust system. The gas alternates between a rich state and a lean state alternately, thereby promoting the storage effect of the exhaust gas purifying means.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of the present invention, FIG. 2 is a diagram showing a configuration of an embodiment when the present invention is applied to a V-type engine, FIG. 4A to 4C are flow charts of a program related to air-fuel ratio control according to the present embodiment, and FIGS. 5 and 6 are timing charts for explaining the operation of the embodiment. In the figure, 10 ... engine, 11a, 11b ... intake manifold, 1
2 ... Air filter, 13 ... Dash pot, 14 ...
Intake pipes, 15a, 15b ... evaporative fuel supply pipes, 16a, 16b ... intake valves, 17 ... evaporative fuel supply control solenoid valves, 18a, 18
b …… Cylinder, 19 …… Canister, 20 …… Air flow meter, 22 …… Intake air temperature sensor, 24a, 24b …… Throttle valve, 25 …… Fuel tank, 26 …… ISC supply pipe, 27 …… Throttle open Degree sensor, 28 ... Idle speed control valve (ISC valve), 32a, 32b ... Piston, 34a, 34b ...
Fuel injection valve, 36 ... Engine control unit (ECU), 40
a, 40b …… Cooling water passage, 42 …… Water temperature sensor, 44a, 44b…
Exhaust valve, 46a, 46b, 46c, 46d …… Exhaust manifold, 48 ……
Exhaust pipe, 50: Catalytic converter, 53: Temperature sensor, 52
a, 52b ... Air-fuel ratio sensors.

Claims (5)

(57) [Claims] 1. An air-fuel ratio detecting means for detecting an air-fuel ratio of exhaust gas in each exhaust system of two or more cylinder groups, and an air-fuel ratio detected by the two or more air-fuel ratio detecting means. An exhaust gas purifying means disposed at least downstream of each of the detection positions and disposed in a collective portion of the plurality of exhaust systems; and an engine of the engine based on outputs of the two or more air-fuel ratio detecting means. Two or more feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the cylinder to a target value, and each of the cylinder groups reaches the exhaust system collecting section located upstream of the exhaust gas purification means. An air-fuel ratio control device for an engine, comprising: a correction unit that corrects a control characteristic of each feedback control so as to synchronize a phase of a change in an air-fuel ratio of each exhaust gas. The correction means includes feedback start control means for delaying the start of the air-fuel ratio feedback control in another cylinder group by a predetermined time after the start of the air-fuel ratio feedback control in one cylinder group. The air-fuel ratio control device for an engine according to claim 1, wherein the phases of changes in the air-fuel ratio of the exhaust gas that respectively reach the collecting portion from each of the cylinder groups are synchronized with each other. 3. An air-fuel ratio controller further comprising a phase difference detecting means for detecting a phase difference of an output signal representing an air-fuel ratio of exhaust gas in each cylinder group detected by the two or more air-fuel ratio detecting means. The device, wherein the correction means corrects the control characteristic of each feedback control so that the phase difference of the output signal detected by the phase difference detection means has a predetermined value, thereby obtaining 2. The air-fuel ratio control device for an engine according to claim 1, wherein the phases of changes in the air-fuel ratio of the exhaust gas respectively reaching the collecting portion from each other are synchronized with each other. 3. 4. An air-fuel ratio control device for an engine according to claim 2, further comprising means for changing said predetermined time in accordance with an amount of intake air. 5. An air-fuel ratio control system for an engine according to claim 3, wherein said correction means includes means for changing a cycle of the feedback control by changing an integration constant of the feedback control.