JPH0861165A - Air-fuel ratio control device of multicylinder internal combustion engine - Google Patents

Abstract

PURPOSE: To realize a purge of evaporated fuel and learning of an air-fuel ratio and the vapor concentration in their early stages. CONSTITUTION: A cylinder is divided into first cylinder groups #1, #2 and #3 and second cylinder groups #4, #5 and #6. When a learning condition is realized, a first purge control valve 10a is opened, and evaporated fuel is supplied to the first cylinder groups, and a second purge control valve 10b is maintained in a closed condition, and the evaporated fuel is not supplied to the second cylinder groups. At this time, an air-fuel ratio of the respective cylinder groups is learnt from output of a second air-fuel ratio sensor 14b, and the vapor concentration of the purged evaporated fuel is calculated from output of a first air-fuel ratio sensor 14a and the second air-fuel ratio sensor 14b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for a multi-cylinder internal combustion engine.

[0002]

2. Description of the Related Art In an internal combustion engine in which an air-fuel ratio sensor is arranged in an engine exhaust passage and the air-fuel ratio of an air-fuel mixture is controlled to a target air-fuel ratio on the basis of an output signal of the air-fuel ratio sensor, usually, for example, secular change The learning value representing the deviation amount of the air-fuel ratio is calculated by learning the deviation amount of the air-fuel ratio due to, and the air-fuel ratio is made to exactly match the target air-fuel ratio based on this learning value. However, if the evaporated fuel is supplied into the engine intake passage while learning the deviation amount of the air-fuel ratio, the learned value will reflect the deviation of the air-fuel ratio due to the supply of evaporated fuel, so the learned value is a normal value. It will fall off. In this case, in order to prevent the learned value from deviating from the normal value, it is necessary not to learn the air-fuel ratio when the evaporated fuel is being supplied.

Therefore, there is known an internal combustion engine in which the learning of the air-fuel ratio is not performed when the evaporated fuel is supplied, and the evaporated fuel is not supplied when the learning of the air-fuel ratio is performed (Japanese Patent Laid-Open No. HEI 3). No. 121232).

[0004]

The evaporated fuel is usually adsorbed and held by the charcoal canister, and in order to increase the adsorbed capacity of the evaporated fuel by the charcoal canister, the evaporated fuel already adsorbed and held by the charcoal canister should be adsorbed as soon as possible. It must be supplied into the engine intake passage. Further, in order to accurately match the air-fuel ratio with the target air-fuel ratio, learning of the air-fuel ratio must be completed as soon as possible. However, the above-described internal combustion engine cannot simultaneously perform the supply of the evaporated fuel and the learning of the air-fuel ratio, and the other can be performed only after the completion of one, so that both the supply of the evaporated fuel and the learning of the air-fuel ratio are performed. There is a problem that we cannot do both together quickly.

[0005]

According to the first aspect of the present invention, the multi-cylinder internal combustion engine is divided into a first cylinder group and a second cylinder group, and each of the cylinder groups Of the first cylinder group by means of evaporative fuel supply means for supplying the evaporated fuel to at least one of them, and an air-fuel ratio sensor capable of detecting the air-fuel ratio of the air-fuel mixture of each cylinder group. The evaporated fuel is supplied only to the second cylinder group, and the air-fuel ratio of the air-fuel mixture in the second cylinder group is learned based on the output signal of the air-fuel ratio sensor provided for the second cylinder group.

In order to solve the above problems, the second aspect of the present invention is based on the output signals of the air-fuel ratio sensors respectively provided for the first cylinder group and the second cylinder group in the first aspect. Then, a calculating means for calculating the average value of the air-fuel ratio of the air-fuel mixture of the first cylinder group and the second cylinder group, respectively, and calculating the concentration of the evaporated fuel supplied to the first cylinder group from the difference between these average values is provided. It has.

In order to solve the above problems, in the third aspect of the invention, in the first aspect of the invention, after the learning of the air-fuel ratio of the air-fuel mixture of the second cylinder group is completed, the fuel vapor to the first cylinder group is evaporated. Of the air-fuel ratio of the air-fuel mixture of the first cylinder group based on the output signal of the air-fuel ratio sensor provided for the first cylinder group Trying to learn.

[0008]

In the first aspect of the invention, the supply of the evaporated fuel and the learning of the air-fuel ratio are carried out simultaneously. In the second aspect, the concentration of the evaporated fuel is easily and accurately calculated. In the third aspect of the invention, the cylinder groups that supply the evaporated fuel are replaced, and the air-fuel ratio is learned again.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is an engine body
It has 6 cylinders from No. cylinder # 1 to No. 6 cylinder # 6,
These cylinders are the first cylinder group consisting of the first cylinder # 1, the second cylinder # 2 and the third cylinder # 3, and the fourth cylinder # 4, the fifth cylinder # 5 and the sixth cylinder # 6. It is divided into two cylinder groups. Each cylinder group # 1, # 2, # 3 of the first cylinder group is connected to a first surge tank 3a via a corresponding intake branch pipe 2a, and each intake branch pipe 2a is provided with a fuel injection valve 4a. To be done. On the other hand, each cylinder # 4, # 5, # 6 of the second cylinder group is connected to the second surge tank 3b via the corresponding intake branch pipe 2b, and each intake branch pipe 2b has a fuel injection valve 4b. Will be placed.

The first surge tank 3a and the second surge tank 3b are connected to a common intake duct 6 via corresponding first intake duct 5a and second intake duct 5b, respectively, and the intake duct 6 is connected via an air flow meter 7. Connected to an air cleaner (not shown). A throttle valve 8 is arranged in the intake duct 6. On the other hand, in the first intake duct 5a and the second intake duct 5b, the purge port 9a for the evaporated fuel,
9b are formed, and these purge ports 9a and 9b are respectively associated with the corresponding first purge control valve 10a and second purge control valve 1
Connected to the charcoal canister 11 via 0b,
The charcoal canister 11 is supplied with the evaporated fuel generated in the fuel tank 12.

On the other hand, each cylinder of the first cylinder group # 1, # 2,
# 3 is connected to the first exhaust manifold 13a, and the first air-fuel ratio sensor 14a is provided at the collecting portion of the first exhaust manifold 13a.
Is arranged. Also, each cylinder # 4, # of the second cylinder group
5 and # 6 are connected to the second exhaust manifold 13b, and
The second air-fuel ratio sensor 1 is provided at the collecting portion of the exhaust manifold 13b.
4b is arranged. The first exhaust manifold 13a and the second exhaust manifold 13b correspond to the corresponding exhaust pipes 15a,
It is connected to the common three-way catalytic converter 16 via 15b.

The electronic control unit 20 is composed of a digital computer, and is connected to a ROM (read only memory) 22, a RAM (random access memory) 23, a CPU (microprocessor) 24, and a constant power source which are interconnected by a bidirectional bus 21. Backup RAM2
5, the input port 26 and the output port 27 are provided.
The air flow meter 7 generates an output voltage proportional to the intake air amount, and this output power is input to the input port 26 via the corresponding AD converter 28. Further, the output voltage of each air-fuel ratio sensor 14a, 14b is input to the input port 26 via the corresponding AD converter 28. Further input port 2
A rotation speed sensor 17 for generating an output pulse representing the engine rotation speed is connected to 6. On the other hand, the output port 27 is connected via the corresponding drive circuit 29 to the purge control valves 10a and 1a, respectively.
0b.

The opening amounts of the purge control valves 10a and 10b are controlled based on the output signal of the electronic control unit 20.
When the purge control valves 10a and 10b are opened, the evaporated fuel adsorbed on the activated carbon in the charcoal canister 11 is desorbed from the activated carbon, and the desorbed evaporated fuel is purged into the corresponding intake ducts 5a and 5b, respectively. It In the embodiment according to the present invention, the fuel injection time TAU is basically calculated based on the following equation.

TAU = TP · FAF · GA · (1-FAFP) Here, TP represents the basic fuel injection time, FAF represents the feedback correction coefficient, GA represents the learning coefficient, and FA
FP indicates the concentration of purged evaporated fuel. The basic fuel injection time TP indicates the injection time required to make the air-fuel ratio of the air-fuel mixture the stoichiometric air-fuel ratio, and this injection time is a function of the engine speed and the engine load (intake air amount / engine speed). It is stored in the ROM 22 in advance in the form of a map.

On the other hand, the air-fuel ratio sensors 14a and 14b are shown in FIG.
As shown in (1), when the air-fuel ratio of the air-fuel mixture is lean, an output voltage of about 0.1 (V) is generated, and when the air-fuel ratio is rich, an output voltage of about 0.9 (V) is generated, and feedback is performed. The correction coefficient FAF is controlled based on the output voltages of the air-fuel ratio sensors 14a and 14b as shown in FIG. The control of the feedback correction coefficient FAF shown in FIG. 2 is performed using the calculation routine of the feedback correction coefficient FAF shown in FIG.

That is, referring to FIG. 4, first, at step 50, the output voltage V of the air-fuel ratio sensors 14a, 14b is compared with a reference voltage Vr (FIG. 2) of about 0.45 (V). When V <Vr, that is, when the air-fuel ratio of the air-fuel mixture is lean, the routine proceeds to step 51, where it is determined whether or not V ≧ Vr in the previous processing cycle, that is, whether the air-fuel ratio of the air-fuel mixture is rich. To be done. When V ≧ Vr, the routine proceeds to step 52, where the constant skip value S is added to FAF. On the other hand, when it is determined in step 51 that V <Vr, the routine proceeds to step 53, where the constant integral value K (K << S) is added to FAF. Therefore, as shown in FIG. 2, when the air-fuel ratio of the air-fuel mixture changes from rich to lean, the feedback correction coefficient FAF is immediately increased by the skip value S, and then gradually increased by the integral value K.

On the other hand, when it is judged in step 50 that V ≧ Vr, that is, when the air-fuel ratio of the air-fuel mixture is rich, the routine proceeds to step 54, where it is determined whether V <Vr in the previous processing cycle, that is, It is determined whether or not the air-fuel ratio of the air-fuel mixture is lean. When V <Vr, the routine proceeds to step 55, where the constant skip value S is subtracted from FAF. On the other hand, when it is determined in step 54 that V ≧ Vr, the routine proceeds to step 56, where the constant integral value K is subtracted from FAF. Therefore, as shown in FIG. 2, when the air-fuel ratio of the air-fuel mixture changes from lean to rich, the feedback correction coefficient FAF is immediately decreased by the skip value S, and then gradually decreased by the integral value K.

Thus, if the air-fuel mixture becomes lean, the feedback correction coefficient FAF is increased, so the fuel injection amount is increased, and if the air-fuel mixture is lean, the feedback correction coefficient FAF is decreased, so the fuel injection amount is reduced. However, the air-fuel ratio of the air-fuel mixture is thus maintained at the stoichiometric air-fuel ratio. As shown in FIG. 2, the feedback correction coefficient FAF moves up and down around a reference value, for example, 1.0.

The learning coefficient GA indicates the amount of deviation of the air-fuel ratio due to secular change, for example, and the learning coefficient GA is set to a value such that the average value of the feedback correction coefficient FAF becomes 1.0. The vapor concentration FAFP represents the vapor concentration when the evaporated fuel is purged. In the embodiment of the present invention, this vapor concentration is the air-fuel ratio sensor 1 as described later.
It is calculated based on the output signals of 4a and 14b. As can be seen from the above formula for calculating the fuel injection time TAU, when the evaporated fuel is purged, the fuel injection amount is (1-FAFP) times. That is, the fuel injection amount is reduced by the amount corresponding to the purge of the evaporated fuel. Therefore, the average value of the feedback correction coefficient FAF is maintained at about 1.0 even when the evaporated fuel is purged.

The feedback correction coefficient FAF, the learning coefficient GA, and the vapor concentration FAFP are provided for each cylinder group. Hereinafter, those for the first cylinder group are represented by FAF1, GA1, FAFP1 and the second cylinder group, respectively. Those for the cylinder group are represented by FAF2, GA2, FAFP2. Next, the calculation routine of the fuel injection time TAU shown in FIG. 5 will be described.

Referring to FIG. 5, first step 6
At 0, the basic fuel injection time TAU is calculated from the map stored in the ROM 22. Next, at step 61, the feedback correction coefficient FAF1 for the first cylinder group is calculated from the FAF calculation routine shown in FIG. 4 based on the output signal of the first air-fuel ratio sensor 14a. Next, at step 62, the fuel injection time TAU for the first cylinder group is calculated based on the following equation.

TAU = TPFAF1GA1 (1-FAFP1) Next, in step 63, based on the output signal of the second air-fuel ratio sensor 14b, the FAF calculation routine shown in FIG.
The feedback correction coefficient FAF2 for the cylinder group is calculated. Next, at step 64, the fuel injection time TAU for the second cylinder group is calculated based on the following equation.

TAU = TP.FAF2.GA2. (1-FAFP2) By the way, as described above, the air-fuel ratio is accurately set to the target air-fuel ratio. Learned, that is, learning coefficients GA1 and G
Determine A2 and vapor concentration FAFP1, F as soon as possible
It is preferable to learn AFP2. Therefore, in the present invention, as soon as the learning condition is satisfied, the air-fuel ratio is learned and the vapor concentration is learned. Next, a method of learning the air-fuel ratio and the vapor concentration will be described with reference to FIG.

When the learning condition is satisfied, one of the two purge control valves 10a and 10b, that is, the first purge control valve 10a in the embodiment shown in FIG. 3, is opened by a predetermined small opening. Be blamed. When the first purge control valve 10a is opened, the evaporated fuel is purged into the first cylinder group through the first intake duct 5a, and as a result, the first cylinder
The feedback correction coefficient FAF1 for the first cylinder group is lowered in order to maintain the air-fuel ratio of the cylinder group at the stoichiometric air-fuel ratio. Then, after a while, the feedback correction coefficient FAF
1 moves up and down around M1. On the other hand, at this time the second
The purge control valve 10b is kept closed, and therefore the feedback correction coefficient FAF for the second cylinder group is set.
2 moves up and down around M2, which is larger than M1.

M1 and M2 are, for example, a, in FIG.
It is the average of the latest four values immediately before the FAF indicated by b, c, and d skips. Therefore, M1 indicates the average value of FAF1 after the learning condition is satisfied, and M2 indicates the average value of FAF2 after the learning condition is satisfied. By the way, M2 represents a basic shift amount of the air-fuel ratio when the evaporated fuel is not purged, and thus this shift amount M
2 is set as the learning coefficient GA2. When M2 is set to GA2, FAF2 moves up and down around 1.0.
On the other hand, at this time, since the basic deviation amount of the air-fuel ratio in the first cylinder group is also estimated to be M2, FAF1
The learning coefficient GA1 with respect to is also set to M2.

Further, as described above, since the basic deviation amount of the air-fuel ratio in the first cylinder group is estimated to be M2, the first amount due to purging the evaporated fuel into the first cylinder group
ΔFAF, which is the amount of deviation of the air-fuel ratio of the cylinder group, is represented by the difference between M1 and M2. That is, this air-fuel ratio deviation amount ΔFAF (= M2-M1) represents the basic vapor concentration when the first purge control valve 10a is opened by a predetermined small opening θ _0. . Vapor concentration F when the opening of the first purge control valve 10a becomes θ
Since AFP1 can be expressed by ΔFAF · θ / θ ₀ , if ΔFAF is obtained, the vapor concentrations FAFP1 and FAFP2 corresponding to the opening of the purge control valves 10a and 10b can be calculated.

As described above, in the embodiment according to the present invention, the learning coefficients GA1 and GA2 with respect to the basic deviation amount of the air-fuel ratio can be calculated at the same time when the evaporative fuel purge is started, without being affected by the evaporative fuel purging action. Become.
As soon as the evaporative fuel purge is started, the learning coefficient GA
This means that the basic vapor concentration can be calculated from ΔFAF (= M2-M1) as well as 1, GA2.

Next, the learning routine for the air-fuel ratio and the vapor concentration will be described with reference to FIG. Referring to FIG. 6, first, at step 70, it is judged if the learning condition is satisfied. When the learning condition is satisfied, the routine proceeds to step 71, where the first purge control valve 10a is opened by a predetermined small opening degree θ ₀ . At this time, the second purge control valve 10b is kept closed. After the first purge control valve 10a is opened for a while, the routine proceeds to step 72, where the average air-fuel ratio of the first cylinder group, that is, F
The average value M1 of AF1 is calculated, and then, in step 73, the average air-fuel ratio of the second cylinder group, that is, the average value M2 of FAF2 is calculated. Next, at step 74, the deviation amount ΔFAF (= M2-M of the air-fuel ratio due to the purge of the evaporated fuel).
1) is calculated, and then in step 75, the average value M2 of FAF2 is set as the learning coefficients GA1 and GA2. Next, at step 76, the basic vapor concentration is calculated from ΔFAF.

FIG. 7 shows another embodiment of the learning routine for the air-fuel ratio and the vapor concentration. In this embodiment, in order to improve the learning accuracy, after the learning by purging the evaporated fuel into the first cylinder group is completed, the learning is performed again by purging the evaporated fuel into the second cylinder group. . That is, referring to FIG. 7, first, step 8
At 0, it is determined whether the learning condition is satisfied. When the learning condition is satisfied, the routine proceeds to step 81, where it is judged if the learning completion flag 1 is set.
When the learning completion flag 1 is not set, the routine proceeds to step 82, where it is judged if the learning completion flag 2 is set. When the learning completion flag 2 is not set, the routine proceeds to step 83.

In step 83, the first purge control valve 10a
Is opened by a predetermined small opening θ ₀ . At this time, the second purge control valve 10b is kept closed. After the first purge control valve 10a is opened for a while, the routine proceeds to step 84, where the average air-fuel ratio of the first cylinder group, that is, the average value M1 of FAF1 is calculated, and then at step 85, the average of the second cylinder group is averaged. Air-fuel ratio, ie F
The average value M2 of AF2 is calculated. Then step 86
Then, the deviation amount ΔFAF of the air-fuel ratio due to the purge of the evaporated fuel
(= M2-M1) is calculated, and then in step 87, the average value M2 of FAF2 is set as the learning coefficients GA1 and GA2. Next, at step 88, the basic vapor concentration is calculated from ΔFAF. Next, at step 89, completion flag 2
Is set, and then, at step 90, the first purge control valve 10a is closed.

When the completion flag 2 is set, in the next processing cycle, the routine proceeds from step 82 to step 91, where it is judged whether or not the learning condition is satisfied again after the learning condition is once not satisfied. When the learning condition is once satisfied and then the learning condition is again satisfied, the routine proceeds to step 92. In step 92, the second purge control valve 10b is opened this time by a predetermined small opening degree θ ₀ . At this time, the first purge control valve 10a is kept closed. After the second purge control valve 10b is opened for a while, the routine proceeds to step 93, where it is calculated from the average air-fuel ratio of the first cylinder group, that is, the average value M1 of FAF1, and then at step 94, the average value M1 of FAF1 is learned. Coefficient GA1
It is said. Next, at step 95, the average air-fuel ratio of the second cylinder group, that is, the average value M2 of FAF2 is calculated.
Next, at step 95, the deviation amount ΔFAF (= 1.0−M2) of the air-fuel ratio due to the purge of evaporated fuel is calculated.

Next, at step 97, the basic vapor concentration is calculated from ΔFAF obtained at step 96. When this basic vapor concentration is calculated, the vapor concentrations FAFP1 and FAFP2 are calculated based on this basic vapor concentration.
Next, at step 98, the completion flag 1 is set, then at step 99, the second purge control valve 10b is closed.

In this embodiment, the learning coefficient GA1 is also calculated by actually learning, so that the learning accuracy of the air-fuel ratio of the first cylinder group can be improved. Further, since the vapor concentration is calculated after the learning of the air-fuel ratio of both cylinder groups is completed, that is, after the learning coefficients GA1 and GA2 of the air-fuel ratio are updated, the vapor concentration is calculated in the first cylinder group. And the basic difference in the air-fuel ratio between the second cylinder group and the second cylinder group is not included, and therefore, this vapor concentration accurately represents the actual vapor concentration. In addition, by waiting until the learning condition is reestablished in step 91 of FIG. 7 until the learning in step 92 and thereafter is performed, the first purge control valve 10a
It is possible to prevent the fluctuation of the air-fuel ratio due to the overlapping of the valve closing operation and the valve opening operation of the second purge control valve 10b.

[0034]

According to the first aspect of the invention, the purge of the evaporated fuel and the learning of the air-fuel ratio can be performed at an early stage. In the second aspect, the vapor concentration when the evaporated fuel is purged can be easily and accurately detected.

In the third aspect, the accuracy of learning the air-fuel ratio can be improved.

[Brief description of drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing changes in an output voltage of an air-fuel ratio sensor and a feedback correction coefficient FAF.

FIG. 3 is a diagram showing changes in feedback correction coefficients FAF1 and FAF2.

FIG. 4 is a flowchart for calculating a feedback correction coefficient FAF.

FIG. 5 is a flowchart for calculating a fuel injection time TAU.

FIG. 6 is a flowchart for learning an air-fuel ratio and a vapor concentration.

FIG. 7 is a flowchart showing another example for learning the air-fuel ratio and the vapor concentration.

[Explanation of symbols]

 3a, 3b ... Surge tank 10a, 10b ... Purge control valve 13a, 13b ... Exhaust manifold 14a, 14b ... Air-fuel ratio sensor

Claims (3)

[Claims] 1. A multi-cylinder internal combustion engine is divided into a first cylinder group and a second cylinder group, and evaporated fuel supply means for supplying evaporated fuel to at least one of the cylinder groups, and each cylinder. An air-fuel ratio sensor capable of detecting the air-fuel ratios of the air-fuel ratios of the air-fuel mixtures of the groups, and supplying the evaporated fuel to only the first cylinder group by the evaporated fuel supply means and providing the air-fuel ratio to the second cylinder group. An air-fuel ratio control device for a multi-cylinder internal combustion engine, which learns the air-fuel ratio of an air-fuel mixture in a second cylinder group based on an output signal of a fuel ratio sensor. 2. A first cylinder group based on output signals of air-fuel ratio sensors provided for the first cylinder group and the second cylinder group, respectively.
And a calculating means for calculating an average value of the air-fuel ratios of the air-fuel mixture of the second cylinder group and the concentration of the evaporated fuel supplied to the first cylinder group from the difference between the average values. Item 2. An air-fuel ratio control device for a multi-cylinder internal combustion engine according to item 1. 3. After the learning of the air-fuel ratio of the air-fuel mixture of the second cylinder group is completed, the supply of the evaporated fuel to the first cylinder group is stopped and the evaporated fuel is supplied only to the second cylinder group. The air-fuel ratio of the multi-cylinder internal combustion engine according to claim 1, wherein the air-fuel ratio of the air-fuel mixture of the first cylinder group is learned based on an output signal of an air-fuel ratio sensor provided for the first cylinder group. Control device.