JPH01110852A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To uniformize an air-fuel ratio by disposing a main O2 sensor upstream from the catalyst of a first cylinder group while a first sub O2 sensor downstream therefrom and a second sub O2 sensor downstream from the catalyst of a second cylinder group, and compensating a fuel injection quantity to the first cylinder group on the basis of an output from the second sub O2 sensor. CONSTITUTION:A main O2 sensor 19 is disposed upstream from the catalyst 17 of a first bank 2 in a V-type engine, while a first sub O2 sensor 20 is disposed downstream therefrom, and a second sub O2 sensor 21 is disposed downstream from the catalyst 18 of a second bank 3. An electronic control unit 30 varies a feedback correction factor in response to a signal outputted from the main O2 sensor 19, and further corrects it on the basis of another signal outputted from the first sub O2 sensor 20 so as to determine a fuel injection quantity to the first bank. The feedback correction factor corrected by means of the first sub O2 sensor 20 is compensated on the basis of a signal outputted from the second sub O2 sensor 21, thereby determining a fuel injection quantity to the second bank.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an air-fuel ratio control device for an internal combustion engine.

[Conventional technology]

It has a pair of banks, and each bank has an independent and separate exhaust passage, and an oxygen concentration sensor is disposed in each exhaust passage, and an oxygen concentration sensor is provided for each bank independently based on the output signal of each oxygen concentration sensor. There is a known air-fuel ratio control device that controls the air-fuel ratio by
(see publication). This air-fuel ratio control device can control the air-fuel ratio of the air-fuel mixture supplied to each bank to the stoichiometric air-fuel ratio.

In order to improve the responsiveness of feedback control based on the output signal of the oxygen concentration sensor in such an air-fuel ratio control device, it is necessary to arrange an oxygen concentration sensor in the exhaust passage near the engine exhaust port. However, if the oxygen concentration sensor is placed in the exhaust passage near the engine exhaust port, the oxygen concentration sensor will be exposed to high-temperature exhaust gas, which will deteriorate the oxygen concentration sensor and change its output characteristics. Since the oxygen concentration in the exhaust gas is detected before the gases are sufficiently mixed, the average air-fuel ratio of all cylinders cannot be detected accurately. Therefore, placing an oxygen concentration sensor in the exhaust passage near the engine exhaust port can improve the responsiveness of feedback control, but the problem is that it is difficult to accurately match the air-fuel ratio to the stoichiometric air-fuel ratio over a long period of time. There is.

To solve this problem, a sub-oxygen concentration sensor is placed further downstream than the catalytic converter, which is installed downstream of the oxygen concentration sensor, and the air-fuel ratio is controlled based on the output signals of these pair of oxygen concentration sensors. Air-fuel ratio control devices are known (for example, Japanese Patent Application Laid-Open No. 55-37562, Japanese Patent Application Laid-Open No. 58-48755, or Japanese Patent Application Laid-Open No. 58-1989).
(See Publication No. 72647). If the oxygen concentration sensor is placed downstream of the catalytic converter in this way, the response will be poor, but the oxygen concentration sensor will not deteriorate due to heat, so the oxygen concentration sensor will continue to generate a regular output signal for a long period of time, and the catalytic converter will Since the oxygen concentration in the exhaust gas that has been sufficiently mixed by the converter is detected, the sub-oxygen concentration sensor placed downstream of the catalytic converter detects that the average air-fuel ratio of all cylinders is the stoichiometric air-fuel ratio over a long period of time. This means that it is possible to detect whether or not there is a vehicle. Therefore, as in the air-fuel ratio control device described above, the output of the main oxygen concentration sensor is adjusted such that the average value of the air-fuel ratio controlled based on the output signal of the main oxygen concentration sensor located near the engine exhaust port becomes the stoichiometric air-fuel ratio. If the feedback control based on the signal is corrected using the output signal of the sub-oxygen concentration sensor, it is possible to perform air-fuel ratio control that has good responsiveness and allows the air-fuel ratio to accurately match the stoichiometric air-fuel ratio.

However, when trying to apply air-fuel ratio control using the above-mentioned sub-oxygen concentration sensor to the V-type engine described in the above-mentioned Japanese Utility Model Publication No. 60-32356, a pair of main oxygen concentration sensors and a pair of sub-oxygen concentration sensors, i.e. Since four oxygen concentration sensors are required, a complicated control device is required, and the increased number of parts causes a problem in that the manufacturing cost of the air-fuel ratio control device becomes high.

Therefore, a main oxygen concentration sensor is placed in one exhaust passage upstream of the catalytic converter, a first sub oxygen concentration sensor is placed downstream of the catalytic converter, and a second sub oxygen concentration sensor is placed in the other exhaust passage downstream of the catalytic converter. The present applicant has proposed a V-type engine in which concentration sensors are arranged and the air-fuel ratio is controlled based on the output signals of these three oxygen concentration sensors (see Utility Model Application No. 11514/1982). In this V-type engine, the fuel injection amount for the first cylinder group that is equipped with the main oxygen concentration detector and the first sub-oxygen concentration detector, and the fuel injection amount for the first cylinder group that is equipped with only the second sub-oxygen concentration detector In calculating the fuel injection amount for each cylinder group, different feedback correction coefficients are used, and the skip timing of these feedback correction coefficients is controlled by the output signal of the main oxygen concentration detector. Then, the skip amount of the feedback correction coefficient for the first cylinder group is corrected based on the output signal of the first sub-oxygen concentration detector so that the air-fuel ratio of the first cylinder group becomes the stoichiometric air-fuel ratio, and the feedback correction coefficient of the second cylinder group is The skip amount of the correction coefficient is corrected based on the output signal of the second sub-oxygen concentration detector so that the air-fuel ratio of the second cylinder group becomes the stoichiometric air-fuel ratio.

[Problem that the invention seeks to solve]

However, in this type II engine, as shown in Figure 6, the feedback correction coefficient FAF of the second cylinder group is unstable and tends to cause undulations and divergence, and thus the air-fuel ratio of the second cylinder group tends to fluctuate. There is a problem. That is,
When the average value of the air-fuel ratio of the first cylinder group becomes lean, the first
Lynch skip iR when increasing the feedback correction coefficient FAF when detected by the sub oxygen concentration detector
is increased, and lean skip measurement when reducing FAF is reduced. As a result, the average value of FAF increases as a whole, so that the average air-fuel ratio of the first cylinder group approaches the stoichiometric air-fuel ratio. However, at this time, the second sub-oxygen concentration detector of the second cylinder group does not necessarily judge that the average value of the air-fuel ratio of the second cylinder group is on the lean side, and therefore the second cylinder group lynch skip amount R and lean skip amount is maintained constant. As a result, as shown in FIG. 6, the feedback correction coefficient FAF of the second cylinder group gradually becomes smaller, and the air-fuel ratio of the second cylinder group shifts toward the lean side.

[Means for solving problems]

In order to solve the above problems, according to the present invention, the cylinder is
The first cylinder group is connected to a first exhaust passage, the second cylinder group is connected to a second exhaust passage, and a catalytic converter is installed in each exhaust passage. The amount of fuel injected into each cylinder is corrected by a feedback correction coefficient that changes according to the output signal of an oxygen concentration detector installed in the exhaust passage. In an internal combustion engine, a main oxygen concentration detector is disposed in a first exhaust passage upstream of the catalytic converter, and a main oxygen concentration detector
A first sub-oxygen concentration detector is disposed in the exhaust passage, a second sub-oxygen concentration detector is disposed in the second exhaust passage downstream of the catalytic converter, and feedback is provided according to the output signal of the main oxygen concentration detector. While changing the correction coefficient, the feedback correction coefficient is corrected using the output signal of the first sub-oxygen concentration detector so that the air-fuel ratio of the first cylinder group becomes the stoichiometric air-fuel ratio, and the corrected feedback correction coefficient and basic fuel injection amount are The fuel injection amount to be injected to the first cylinder group is determined from , and the fuel injection amount for the second cylinder group is determined from the corrected feedback correction coefficient and the basic fuel injection amount so that the air-fuel ratio of the second cylinder group is the stoichiometric air-fuel ratio. The correction is made based on the output signal of the second sub-oxygen concentration detector.

〔Example〕

Referring to FIG. 1, 1 indicates a V-type engine body having a pair of banks 2.3, each bank 2.3 having four cylinders 4.5. Reference numeral 6 indicates an intake manifold, and fuel injection valves 7.8 are arranged in branch pipes of the intake manifold leading to each cylinder 4.5. The intake manifold 6 is connected to an air cleaner 11 via an intake duct 9 and an air flow meter 10, and a throttle valve 12 is disposed within the intake duct 9. Each bank 2, 3 has an independent exhaust manifold 13, 14, respectively, and the l air manifolds 13, 14 have independent exhaust pipes 15, 16, respectively.
connected to the atmosphere via. A catalytic converter 17 with a built-in three-way catalyst is arranged at the connection between the exhaust manifold 13 and the exhaust pipe 15, and a catalytic converter 18 with a built-in three-way catalyst is arranged at the connection between the exhaust manifold 14 and the exhaust pipe 16. . Exhaust manifold 13 upstream of catalytic converter 17
A main oxygen concentration sensor (hereinafter referred to as 0□ sensor) 19 is arranged inside the exhaust pipe 1 downstream of the catalytic converter 17.
A first sub-02 sensor 20 is arranged within the sub-02 sensor 5. Furthermore, a second sub-02 sensor 21 is arranged within the exhaust pipe 16 downstream of the catalytic converter 18.

The output signals of these 02 sensors 19 , 20 , 21 are input to an electronic control unit 30 .

The electronic control unit 30 consists of a digital computer with ROMs interconnected by a bidirectional bus 31.
(read only memory) 32, RAM (random access memory) 33, CPU (microprocessor) 3
4, an input port 35 and an output port 36.

The air flow meter IO generates an output voltage proportional to the amount of intake air, and this output voltage is input to the input port 35 via the AD converter 37. Further, a rotation speed sensor 22 is attached to the engine body 1 and generates an output pulse every time the engine crankshaft rotates by a certain crank angle, and this output pulse is input to the input port 35. Main 02 sensor 19, first sub 0□ sensor 20 and second sub 02
If the sensor 21 is operating normally, the output voltage will change suddenly around the stoichiometric air-fuel ratio, and when the exhaust gas is in an oxidizing atmosphere, that is, the air-fuel ratio is larger than the stoichiometric air-fuel ratio, the output voltage will be about 0.1 volt. When the exhaust gas is in a reducing atmosphere, that is, when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, 0.
Generates an output voltage of about 9 volts. The output voltages of these 02 sensors 19, 20, 21 are input to the input port 35 via the corresponding AD converters 3B, 39, 40. On the other hand, the output boat 36 is connected to each fuel injection valve 7.8 via a drive circuit 41, 42. For convenience, the signal lines from the drive circuits 41 and 42 to each fuel injection valve 7.8 are shown as lines, but it goes without saying that fuel injection control is performed independently for each fuel injection valve every 71 days. do not have.

When exhaust gas is discharged into the exhaust manifold 13, the oxygen concentration in this exhaust gas is 0! Detected by sensor 19, this exhaust gas then flows into catalytic converter 17 and is thoroughly mixed.

Next, the sufficiently mixed exhaust gas is discharged into the exhaust pipe 15, and the oxygen concentration in this sufficiently mixed exhaust gas is detected by the first sub-02 sensor 20. On the other hand, the exhaust gas discharged into the exhaust manifold 14 flows into the catalytic converter 18 and is sufficiently mixed within the catalytic converter 18.

Next, the sufficiently mixed exhaust gas is discharged into the exhaust pipe 16, and the oxygen concentration in this sufficiently mixed exhaust gas is detected by the second sub-0□ sensor 21. The temperature of the exhaust gas that has passed through each catalytic converter 17, 18 is relatively low, so the temperature of the exhaust gas that has passed through each catalytic converter 17, 18 is relatively low.
Since the 2 sensor 21 does not undergo thermal deterioration even after long-term use, it can accurately detect whether or not the theoretical air-fuel ratio is maintained over a long period of time. Furthermore, since the first sub-AT sensor 20 detects the oxygen concentration in the exhaust gas sufficiently mixed within the catalytic converter 17, the first sub-0! The sensor 20 can detect whether the average air-fuel ratio of the air-fuel mixture supplied to the bank 2 is the stoichiometric air-fuel ratio over a long period of time. Since the oxygen concentration in the sufficiently mixed exhaust gas is detected, the second sub-O2 sensor 21 determines whether the average air-fuel ratio of the mixture supplied to the bank 3 is the stoichiometric air-fuel ratio or not over a long period of time. It can be detected over a wide range of areas.

On the other hand, the main 02 sensor 19 is the exhaust manifold 1
Since the oxygen concentration in the exhaust gas is detected immediately after it is discharged into the main 0□ sensor 19, good feedback responsiveness can be ensured by feedback controlling the fuel injection amount based on the output signal of the main 0□ sensor 19. be able to. However, there is a main 0 upstream of the catalytic converter 17! When the sensor 19 is placed, the exhaust gas from the specific cylinder 4 that forms around the main 0□ sensor 19 mainly flows. The sensor 19 does not necessarily detect the average oxygen concentration in the exhaust gas of all cylinders 4, so even if the fuel injection amount is controlled based on the output signal of this main 08 sensor 19, the average air-fuel ratio of all cylinders 4 cannot be detected. It is difficult to precisely match the stoichiometric air-fuel ratio. In addition, the main 0□ sensor 19 easily deteriorates because it is exposed to high-temperature exhaust gas, and if the O2 sensor deteriorates, the output voltage will not change suddenly at the stoichiometric air-fuel ratio, so the air-fuel ratio will be changed based on the output signal of the 02 sensor. It becomes difficult to accurately match the stoichiometric air-fuel ratio.

Therefore, in the present invention, the feedback control by the main 02 sensor 19 is corrected based on the output signal of the first sub-02 sensor 20, so that the average air-fuel ratio of all cylinders 4 can be made to match the stoichiometric air-fuel ratio with good responsiveness. Further, in the present invention, the amount of fuel injected from the fuel injection valve 7 of bank 2 is controlled based on the output signals of the main 0□ sensor 19 and the first sub 0□ sensor 20, and the fuel injection amount of the fuel injection valve 8 of bank 3 is controlled.
The amount of fuel injected from the engine is also controlled. However, in this way, the fuel injection amount from the fuel injection valve 8 of bank 3 is controlled by the main O2 sensor 19 and the first sub O2 sensor 2.
Even if control is performed based on an output signal of 0, it is unclear whether the average air-fuel ratio of the air-fuel mixture supplied to bank 3 will be the stoichiometric air-fuel ratio. Therefore, in the present invention, the fuel injection valve 8 is
The average air-fuel ratio of the air-fuel mixture supplied to each cylinder 5 of the bank 3 can be adjusted to the stoichiometric air-fuel ratio by feedback-controlling the fuel injection amount and correcting this fuel injection amount using the output signal of the second sub-02 sensor 21. It is controlled so that

Next, the air-fuel ratio control method according to the present invention will be explained with reference to FIGS. 2 to 5.

FIG. 2 shows a calculation routine for the feedback correction coefficient FAF, which is performed by interruption at regular intervals based on the output signal of the main Oz sensor 19. This feedback correction coefficient FAF is commonly used for calculating the amount of fuel injected from the fuel injection valve 7 and for calculating the amount of fuel injection from the fuel injection valve 8.

Referring to FIG. 2, first, in step 50, it is determined whether or not the feedback condition is satisfied. If the feedback condition is satisfied, the process proceeds to step 51 and the output voltage V of the main Ot sensor 19 is read. . This output voltage V is shown in FIG. 5(a). Next, in step 52, this output voltage V and the reference voltage V, (Fig. 5 (
(Refer to a)), and if ① and vR, that is, if the air-fuel mixture is lean, the process proceeds to step 53. Step 5
In step 3, it is determined whether or not there has been a reversal from rich to lean between the previous interrupt routine and the current interrupt routine.
If it is reversed from rich to lean, the process proceeds to step 54, where the skip value R is added to the feedback correction coefficient FAF. On the other hand, if it is lean in the previous interrupt routine, the process goes to step 55 and the integral value F (<R
) is added. Therefore, as shown in FIG. 5(b), when the engine becomes lean, FAF immediately increases by the skip value R, and then gradually increases.

On the other hand, when it is determined in step 52 that V≧VIl, that is, the air-fuel mixture is rich, the process proceeds to step 56. If it is determined whether or not the lean state has changed to rich state, the process proceeds to step 57, where the skip value is subtracted from the FAF.

On the other hand, if it is rich in the previous interrupt routine as well, the process proceeds to step 58 and the integral value F (<L) is subtracted from FAF. Therefore, as shown in FIG. 5(b), when the fuel becomes rich, the FAF decreases at once by the skip value, and then gradually decreases.

FIG. 3 shows a variable control routine performed by interrupts at fixed time intervals based on the output signals of the first sub-02 sensor 20 and the second sub-02 sensor 21.

Referring to FIG. 3, it is first determined in step 60 whether or not the feedback condition is satisfied. If the feedback condition is satisfied, the process proceeds to step 61 and the output voltage ■1 of the first sub-Ot sensor 20 is determined. Load. This output voltage V is the output voltage ■ of the main Ot sensor 19, as seen from FIG. 5(C). changes slowly compared to

Next, in step 62, the output voltage v1 and the reference voltage V*+
(see FIG. 5(C)), and if V<V□, that is, if lean, proceed to step 63. Step 6
In step 3, a constant value α is added to the skip value R, and then in step 64, the constant value α is subtracted from the skip value R.

On the other hand, if it is determined in step 62 that v1≧■□, that is, it is rich, the process proceeds to step 65. In step 65, a constant value α is added to the skip value, and then in step 66, the constant value α is subtracted from the skip value R. Therefore, as shown in FIG. 5(d), the skip value R increases while the engine is lean, and decreases when the engine becomes rich. On the other hand, as shown in FIG. 5(e), the skip value decreases when the fuel is lean, and increases when the fuel becomes rich. When the skip value R increases and the skip value decreases, the FAF increases and the mixture as a whole shifts to the rich side. When the skip value R decreases and the skip value increases, the FAF decreases and the mixture shifts to the rich side. Shift to the lean side as a whole.

Next, in step 67, the output voltage V2 of the second sub-O2 sensor 21 is read. This output voltage v8 also changes slowly as in 1 shown in FIG. The reference voltage Vat (reference voltage VII, almost the same voltage as V□) is compared, and V! <
If it is V□, that is, if it is lean, the process proceeds to step 69, where a constant value β is added to the injection amount correction coefficient K. On the other hand, if it is determined in step 68 that v2≧v0, that is, rich, the process proceeds to step 70, where the injection amount correction coefficient K
β is subtracted from . Therefore, the injection amount correction coefficient increases while the fuel is lean and decreases while the fuel is rich.

FIG. 4 shows a fuel injection time calculation routine, which is executed by an interrupt at a predetermined crank angle.

Referring to FIG. 4, first, in step 80, the output signal of the air flow meter 10 representing the intake air amount Q and the output signal of the rotation speed sensor 22 representing the engine speed N are read. Next, in step 81, it is determined whether the fuel injection period of the fuel injection valve 7 of bank 2 is to be calculated. When calculating the fuel injection period of the fuel injection valve 7 of bank 2, the process proceeds to step 82 and the fuel injection period TAU is calculated from the following equation.

TAU=-Q/N·(FAF+FX) where k is a constant value, and FX is a correction coefficient predetermined from the periodic cooling water temperature and the like. Further, k-Q/N indicates the basic fuel injection amount. The feedback correction coefficient FAF is controlled based on the output signals of the main 02 sensor 19 and the first sub 0□ sensor 20, so that the fuel injection amount of the fuel injection valve 7 of bank 2 is controlled based on the output signal of the main 02 sensor 19 and the first sub Ot sensor 20. is controlled based on the output signal of That is,
The fuel injection amount of the fuel injection valve 7 of bank 2 is controlled so that the average value of the air-fuel ratio of bank 2 becomes the stoichiometric air-fuel ratio by controlling the FAF skips liR and L based on the output signal of the first sub-02 sensor 20. controlled by.

By the way, as described above, the first sub-0□ sensor 20 accurately detects whether the air-fuel ratio of the entire air-fuel mixture supplied to the bank 2 is the stoichiometric air-fuel ratio. Since the skip value R9L is controlled based on the output signal of the sensor 20 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio, the average air-fuel ratio of all the air-fuel mixtures supplied to the bank 2 can be made to accurately match the stoichiometric air-fuel ratio.

On the other hand, when calculating the fuel injection period of the fuel injection valve 8 of bank 3, the process proceeds from step 81 to step 83, and the fuel injection period TAU is calculated from the following equation.

TAU=K -Q/N・(FAF+FX) Here, K is the injection amount correction coefficient determined in the routine shown in FIG. 3, and the feedback correction coefficient FAF is
It is the same as FAF in 2.

Therefore, the fuel injection amount of the fuel injection valve 8 of bank 3 is main 0.
2 sensors 19 and the first sub O! By correcting the injection 13 Q/N・(PAP+PX) determined from the output signal of the sensor 20 by the injection amount correction coefficient K based on the output signal of the second sub-Ox sensor 21, the average value of the air-fuel ratio of bank 3 is theoretically calculated. The air-fuel ratio is controlled to be the same.

By the way, the second sub 0. As mentioned above, the sensor 21 accurately detects whether the air-fuel ratio of the entire mixture supplied to the bank 3 is the stoichiometric air-fuel ratio or not, and the air-fuel ratio is determined based on the output signal of the second sub-02 sensor 21. Since the injection amount correction coefficient K is controlled so that the air-fuel ratio becomes the stoichiometric air-fuel ratio, the average air-fuel ratio of all the air-fuel mixtures supplied to the bank 3 can be made to accurately match the stoichiometric air-fuel ratio.

Note that the feedback correction coefficient FAF is common to the fuel injection valves 7 of bank 2 and the fuel injection valves 8 of bank 3, and this FAF is controlled so that the air-fuel ratio of bank 2 becomes the stoichiometric air-fuel ratio. FAF never becomes unstable.

〔Effect of the invention〕

By preventing the feedback correction coefficient from becoming unstable, the average air-fuel ratio of the entire air-fuel mixture supplied to each bank can be made to accurately match the theoretical air-fuel ratio by using only three 02 sensors.

[Brief explanation of the drawing]

Figure 1 is an overall diagram of the internal combustion engine, Figure 2 is a flowchart for calculating feedback correction coefficients, Figure 3 is a flowchart for executing variable control, and Figure 4 is a flowchart for calculating fuel injection time. , Figure 5 is O!
FIG. 6 is a time chart showing changes in sensor output signals, feedback correction coefficients, etc., and FIG. 6 is a diagram showing changes in a conventional feedback correction coefficient. 2.3... Bank, 13.14... Intake manifold, 15, 16... Exhaust pipe, 17, 18...
Catalytic converter, 19... Main Ot sensor, 20... First sub 0□ sensor, 21... Second sub Ot sensor. Figure 1 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] The cylinders are divided into a first cylinder group and a second cylinder group, and the first cylinder group is connected to the first exhaust passage, and the second cylinder group is connected to the second cylinder group.
A catalytic converter is placed in each exhaust passage, and the basic fuel injection amount, which is determined according to the operating condition of the engine, changes according to the output signal of an oxygen concentration detector installed in the exhaust passage. In an internal combustion engine in which the amount of fuel injected into each cylinder is determined by correction using a feedback correction coefficient, a main oxygen concentration detector is arranged in a first exhaust passage upstream of the catalytic converter, and a main oxygen concentration detector is arranged in a first exhaust passage upstream of the catalytic converter. A first sub-oxygen concentration detector is disposed in the exhaust passage, a second sub-oxygen concentration detector is disposed in the second exhaust passage downstream of the catalytic converter, and feedback is provided according to the output signal of the main oxygen concentration detector. While changing the correction coefficient, the feedback correction coefficient is corrected using the output signal of the first sub-oxygen concentration detector so that the air-fuel ratio of the first cylinder group becomes the stoichiometric air-fuel ratio, and the corrected feedback correction coefficient and basic fuel injection amount are The fuel injection amount to be injected to the first cylinder group is determined from , and the fuel injection amount for the second cylinder group is determined from the corrected feedback correction coefficient and the basic fuel injection amount so that the air-fuel ratio of the second cylinder group is the stoichiometric air-fuel ratio. An air-fuel ratio control device for an internal combustion engine that adjusts the air-fuel ratio according to the output signal of a second sub-oxygen concentration detector.