JP2796182B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides separate upstream and downstream catalytic converters.
The present invention relates to an air-fuel ratio control method for an internal combustion engine applied to an automobile or the like having an O ₂ sensor.

[Prior Art] In a three-way catalyst widely used as one of exhaust gas purifying means, an air-fuel ratio of an air-fuel mixture is maintained in a narrow region (a window of a three-way catalyst) around a stoichiometric air-fuel ratio. no When, CO contained in the exhaust gas, HC, can not be efficiently purify all nO _x. Therefore, in the engine provided with an injector, when the output voltage of the O ₂ sensor disposed on the upstream side of the catalytic converter exhibited a rich air-fuel ratio state, it reduces the amount of fuel supplied from the injector, the mixture The air-fuel ratio is changed to the stoichiometric air-fuel ratio, and when the output voltage indicates an air-fuel ratio lean state, the fuel supply amount is increased to change the air-fuel ratio of the mixture to the stoichiometric air-fuel ratio. I have to.

However, when feedback control of the air-fuel ratio is performed using a single O ₂ sensor, the intended air-fuel ratio control is performed due to variations in the output characteristics of the O ₂ sensor, changes over time, and variations in the fuel injection amount of the injector. As a result, the control center of the air-fuel ratio may deviate from the window of the three-way catalyst.
In addition, when a catalytic converter is connected to an exhaust manifold that can easily secure the catalyst activation temperature, and an O ₂ sensor is arranged at the upstream of the exhaust manifold, the exhaust gas discharged from a specific cylinder is used. The output voltage of the O ₂ sensor may be affected or the deterioration may be accelerated due to high heat or the like.

In order to avoid such a problem, as a prior art of the present invention, for example, as disclosed in Japanese Patent Application Laid-Open No. 62-29738, the output voltage of a first O ₂ sensor disposed upstream of a catalytic converter is disclosed. The feedback control of the air-fuel ratio is performed based on
There is one in which the control center of the air-fuel ratio is corrected within the window of the three-way catalyst based on the output voltage of the O ₂ sensor.
That is, on the downstream side of the catalytic converter, since the exhaust gas discharged from each cylinder is in a stirred state, the air-fuel mixture adjusted based on the output voltage of the first O ₂ sensor has a rich tendency as a whole. In this case, the time during which the output voltage of the second O ₂ sensor indicates a rich state is prolonged, and when the mixture is generally lean, the time during which the output voltage of the second O ₂ sensor indicates a lean state. Becomes longer. Therefore, the oxygen concentration in the exhaust gas is detected by the second O ₂ sensor every fixed gate time, and when the output voltage indicates the air-fuel ratio rich, the fuel supply amount is reduced to reduce the air-fuel ratio. The control center is changed to the lean side, and when the output voltage indicates the air-fuel ratio lean, the fuel supply amount is increased to change the control center of the air-fuel ratio to the rich side.

[Problems to be Solved by the Invention] However, as described above, the time from when the control center of the air-fuel ratio is changed to when the reaction appears differs depending on the deterioration state of the catalytic converter. That is, when the catalytic converter is relatively new, the time required for the reaction by the air-fuel ratio control to appear as the output of the second O ₂ sensor becomes longer. Therefore, during this time, as schematically shown in FIG. 6, the control center of the air-fuel ratio changes every time to the rich side or the lean side at every fixed gate time, and the control center of the air-fuel ratio becomes The swing width increases. On the other hand, as the deterioration of the catalytic converter progresses, the time required for the reaction by the air-fuel ratio control to appear becomes shorter due to changes in the oxidation / reduction actions. Therefore, if the control reaction speed and the gate time match, the swing width of the control center can be reduced as schematically shown in FIG. 7, but if the gate time is too long, the control There will be a delay.
Therefore, irrespective of the state of deterioration of the catalytic converter, if the air-fuel ratio is controlled every fixed gate time, there is a limit to efficiently purifying exhaust gas in a high purification efficiency region over a long period of time. , It is difficult to effectively improve emissions.

An object of the present invention is to eliminate all such disadvantages.

[Means for Solving the Problems] The present invention employs the following configuration to achieve the above object.

That is, in the air-fuel ratio control method for an internal combustion engine according to the present invention, a first O ₂ sensor for detecting an oxygen concentration in exhaust gas is arranged on an upstream side of a catalytic converter for purifying exhaust gas,
With the feedback control of the air-fuel ratio of a mixture supplied to the combustion chamber the stoichiometric air-fuel ratio near on the basis of the output voltage, given by the oxygen concentration of the second O ₂ sensor in the exhaust gas downstream of the catalytic converter An air-fuel ratio control method for an internal combustion engine configured to detect at each gate time and change the control center of the air-fuel ratio to near the stoichiometric air-fuel ratio based on the output voltage. Before the timing operation of the gate time of
While interposing a hold time for delaying the start of the timing operation, the deterioration of the catalytic converter is detected, and as the deterioration of the catalytic converter progresses, the hold time is changed in a direction to shorten the hold time. It is characterized by having done.

Here, the deterioration state of the catalytic converter is determined by the first
O ₂ may be determined based on the correlation coefficient between the output and the output of the second O ₂ sensor of the sensor, or so as to determine based on the operating period of the running distance and the engine of the vehicle or the like You may.

[Operation] According to such a configuration, when the catalytic converter is relatively new, each gate time is temporarily held and the hold time is lengthened. With this configuration, the detection interval of the air-fuel ratio by the second O ₂ sensor becomes long, and the control of the air-fuel ratio based on the detection result is temporarily held at each gate time, so that the control center is instantaneously In addition to preventing the change, the swing width of the control center can be suppressed.

On the other hand, when the deterioration of the catalytic converter progresses, the hold time is reduced. In this case,
Since the detection interval of the air-fuel ratio by the second O ₂ sensor is shortened, the control center of the air-fuel ratio is quickly adjusted based on the detection result, and the follow-up performance of the air-fuel ratio control is improved.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS.

The engine, which is an internal combustion engine schematically shown in FIG. 1, is used for an automobile, and includes an injector 1, a crank angle sensor 2, a pressure sensor 3, and an idle switch 4.
When, and includes a water temperature sensor 5, a first O ₂ sensor serving main O ₂ sensor 6, and a second O ₂ sensor serving sub O ₂ sensor 7.

The injector 1 is mounted on an intake pipe 8 and has a built-in electromagnetic coil and the like. When a fuel injection signal a is applied from the electronic control unit 9 to the electromagnetic coil, an amount of fuel corresponding to the application time is injected near the intake port. The crank angle sensor 2 is built in the distributor 10, and is configured to generate an engine rotation signal b corresponding to the engine rotation speed. The pressure sensor 3 is provided in the surge tank 11 and outputs an intake pressure signal c in proportion to the intake pressure. The idle switch 4 is connected to the throttle shaft 12 and is turned on when the throttle valve 13 is closed.
, And an ON / OFF switch which is turned off when the throttle valve 13 is opened outputs a throttle signal d. The water temperature sensor 5 incorporates, for example, a thermistor or the like, and outputs a water temperature signal e according to the engine cooling water temperature. Main O ₂ sensor 6
Is arranged on the upstream side of the maniverter 14, which is a catalytic converter, and outputs a feedback signal f corresponding to the oxygen concentration in the exhaust gas. Specifically, as shown in FIG. 3, when the air-fuel ratio A / F of the air-fuel mixture is leaner than the determination voltage existing near the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is high, It is configured to generate a low voltage and generate a high voltage when the air-fuel ratio A / F of the air-fuel mixture is richer than the determination voltage and the oxygen concentration in the exhaust gas is low. is there. Sub O ₂ sensor 7
Is of the same configuration as the main O ₂ sensor 6, and outputs a feedback signal g corresponding to the oxygen concentration in the exhaust gas. That is, when the air-fuel ratio of the air-fuel mixture is leaner than the determination voltage existing near the stoichiometric air-fuel ratio and the oxygen concentration in the exhaust gas is high, a low voltage is generated. When the oxygen concentration in the exhaust gas is lower than the voltage on the rich side, a high voltage is generated.

The electronic control unit 9 has a role of adjusting the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 15.
, A memory 17, an input interface 18, and an output interface 19. The input interface 18 includes at least an engine rotation signal b from the crank angle sensor 2, an intake pressure signal c from the pressure sensor 3, a throttle signal d from the idle switch 4, and a water temperature sensor 5.
, A feedback signal f from the main O ₂ sensor 6, and a feedback signal g from the sub O ₂ sensor 7. The output interface 19 outputs a fuel injection signal a to the injector 1. Thus, the electronic control unit 9 calculates the intake air amount from the engine rotation signal b, the intake pressure signal c, and the like, and determines the basic injection amount TP according to the intake air amount. Next, this basic injection amount TP
Is corrected by the air-fuel ratio feedback correction coefficient FAF determined by the feedback signal f of the main O ₂ sensor 6, the various correction coefficients K determined according to the operating condition of the engine, and the invalid injection time TAUV. The energization time T is determined based on the following equation, and plays a role of injecting an amount of fuel corresponding to the time T from the injector 1.

T = TP × FAF × K + TAUV Further, the electronic control unit 9 has a built-in program as schematically shown in FIG. Assuming that the sub-O ₂ execution conditions of the feedback by the sensor 7 is established, the hold time is determined whether or not it is completed at step 51, the process proceeds to step 52 only when completed. Step 52
Then, the gate time measurement routine is processed, and the routine proceeds to step 53. In the gate time measurement routine, for example, the following processing is performed. As shown schematically in Figure 4, the air-fuel ratio is determined whether or not rich based on the output voltage of the sub O ₂ sensor 7 for each gate time. When the air-fuel ratio changes from lean to rich, the fuel supply amount is reduced to change the control center of the air-fuel ratio from rich to lean. If the air-fuel ratio is still rich at the time of the previous detection, the control center is further changed to the lean side. When the air-fuel ratio changes from rich to lean, the fuel supply amount is increased in a skipping manner, and the control center is rich skipped from lean to rich. If the air-fuel ratio is lean following the previous time, the control center is further changed to the rich side by increasing the fuel supply amount. In step 53, it is determined whether or not the steady condition of the engine is satisfied. For example, when the change amount of the intake pressure detected every certain time is within a certain range and the fuel acceleration increase is not performed, the process proceeds to step 54, and when the engine is not in a steady state,
Proceed to step 56. In step 54, the main O ₂ sensor 6
The process proceeds to step 55 to seek a correlation coefficient from the output OX2 of the output OX1 and sub O ₂ sensor 7. In step 55, a hold time for the correlation coefficient is determined. The hold time is for delaying the start of the clock operation from the time when each gate time is completed to the time when the clock operation for the next gate time is started. Generally, when the anniversator 14 is relatively new, the correlation coefficient becomes small, and as the anniverser 14 deteriorates, the correlation coefficient becomes large. Therefore,
When the correlation coefficient is small, the hold time is lengthened, and when the correlation coefficient is large, the hold time is shortened. In step 56, the previous gate time is used.

Next, feedback control by the main O ₂ sensor 6 and the sub O ₂ sensor 7 will be described.

First, the feedback control condition of the air-fuel ratio by the main O ₂ sensor 6, for example, the engine cooling water temperature is 40 ° C. or higher, the fuel is not cut, the power is not increased,
Has passed after starting the engine a predetermined time, the main O ₂ sensor 6 is being active, are normal pressure sensor 3, if the conditions of the like have all met, the main O ₂ sensor 6
Feedback control is performed based on the output voltage.
Specifically, as shown in FIG. 3, when the output voltage of the main O ₂ sensor 6 exceeds the determination voltage, the air-fuel ratio feedback correction coefficient FAF is reduced by the predetermined value RSM after the rich determination delay time TDR. Side, then lean integral KIM
, And is gradually decreased by a constant value. Therefore, the fuel supply amount from the injector 1 is reduced, and the air-fuel ratio of the air-fuel mixture changes toward the stoichiometric air-fuel ratio. On the other hand, when the output voltage of the main O ₂ sensor 6 falls below the determination voltage, the air-fuel ratio feedback correction coefficient FAF is skipped to the increasing side by the predetermined value RSP after the lean determination delay time TDL, and then the rich integration KIP The value is gradually increased based on a constant value. As a result, the amount of fuel supplied from the injector 1 increases, and the air-fuel ratio of the air-fuel mixture changes to the stoichiometric air-fuel ratio.

When the feedback condition is satisfied by the sub O ₂ sensor 7 in such a feedback control, for example, predetermined time has elapsed from the feedback execution start of the air-fuel ratio by the main O ₂ sensor 6, the main O ₂ sensor 6 after becoming active When a predetermined time has elapsed, the engine coolant temperature is 70 ° C. or higher, the fuel correction amount during the transition is less than a predetermined amount, the engine is idling, the vehicle speed is 0, or the engine is not idling. It is in a predetermined operating region, if the conditions are satisfied all equal, feedback control by the sub-O ₂ sensor 7 is performed. When the output voltage of the sub O ₂ sensor 7 is higher than the determination voltage, the rich integration KIP is reduced, or the skip amount RSM to the lean side is reduced.
Is increased, the fuel supply amount is reduced, and the control center is changed to the lean side. In this case, the fuel supply amount may be reduced by shortening the rich determination delay time TDR. Conversely, when the output voltage of the sub O ₂ sensor 7 is lower than the judgment voltage, the fuel supply amount is increased by increasing the rich integration KIP or decreasing the lean side skip amount RSM. Then, the control center is changed to the rich side. In this case, the rich determination delay time TDR may be lengthened to increase the fuel supply amount.

Note that the above control is repeatedly executed during the operation of the engine.

According to such a configuration, when the feedback control of the air-fuel ratio is performed based on the output voltage of the main O ₂ sensor 6, if the control center of the air-fuel ratio shifts to the rich side or the lean side, the sub O ₂ sensor 7 The control center of the air-fuel ratio is finely adjusted by the output voltage. That is, sub O ₂
If it is detected at the end of the gate time that the air-fuel ratio is lean based on the output voltage of the sensor 7, the fuel supply amount is increased by a small amount, and the control center is changed to the rich side. . Conversely, when it is detected at the end of the gate time that the air-fuel ratio is rich based on the output voltage of the sub O ₂ sensor 7, the fuel supply amount is slightly reduced and the control center is changed to the lean side. Will be done.

When the maniverter 14 is relatively new, as shown schematically in FIG. 4, each gate time is temporarily held and the hold time becomes long. Therefore, the detection interval of the air-fuel ratio due to the sub-O ₂ sensor 7 becomes long, so that the air-fuel ratio control based on the detection result is temporarily held in each gate time. As a result, the control center of the air-fuel ratio gradually changes at a speed corresponding to the reaction time of the control, and the control center is not excessively controlled to the rich side or the lean side, and the swing width is reduced. Can be suppressed.

On the other hand, if the deterioration of the maniverter 14 progresses, the fifth
As shown schematically in the figure, the hold time is reduced. Therefore, the detection interval of the air-fuel ratio is reduced by the sub O ₂ sensor, will be controlled center of the air-fuel ratio is adjusted quickly based on the detection result, control delay is avoided.

Therefore, according to the configuration described above, the main O variation or aging of the output characteristics of ₂ sensor 6, a variation or the like of the fuel injection amount of the injector 1, or the main O ₂ by the exhaust gas discharged from a certain cylinder Even if the output voltage of the sensor 6 is influenced and the predetermined air-fuel ratio control cannot be obtained, the air-fuel ratio of the air-fuel mixture can be effectively controlled by the feedback control by the sub O ₂ sensor 7 within the window of the three-way catalyst. And the exhaust gas can be efficiently purified.

In addition, the sub O ₂
If the detection interval of the air-fuel ratio by the sensor 7 is changed, the control center can be changed according to the reaction time of the air-fuel ratio control, thereby preventing the control center from being excessively controlled to the rich side or the lean side. And the swing width of the control center can be effectively reduced. As a result, exhaust gas can be efficiently purified over a long period of time in a region with high purification efficiency, and emission can be effectively improved over a long period.

The state of deterioration of the catalytic converter may be determined based on the traveling distance of the vehicle, the operating period of the engine, and the like.

[Effects of the Invention] Since the present invention has the above-described configuration, it is possible to effectively prevent the air-fuel ratio of the air-fuel mixture from deviating from the vicinity of the stoichiometric air-fuel ratio, and is affected by a change in the function of the catalytic converter. Without this, it is possible to effectively reduce the swing width of the control center of the air-fuel ratio and converge it near the stoichiometric air-fuel ratio. As a result, it is possible to provide an air-fuel ratio control method for an internal combustion engine which is capable of purifying exhaust gas in a region having high purification efficiency over a long period of time and improving emission over a long period of time and having excellent control accuracy. can do.

[Brief description of the drawings]

1 to 5 show an embodiment of the present invention, FIG. 1 is a schematic overall configuration diagram, FIG. 2 is a flowchart diagram schematically showing a control procedure, and FIG. 3 shows a control mode. FIGS. 4 and 5 are timing charts for explaining the operation.
FIG. 6 is an operation explanatory view corresponding to FIG. 4 showing a conventional example, and FIG. 7 is an operation explanatory view equivalent to FIG. 5 showing a conventional example. 1 Injector 6 First O ₂ sensor (main O ₂ sensor) 7 Second O ₂ sensor (sub O ₂ sensor) 9 Electronic control unit 14 Catalyst converter (maniverter) 15 … Combustion chamber

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-8857 (JP, A) JP-A 1-211634 (JP, A) JP-A-3-249320 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) F02D 41/00-45/00 395

Claims (1)

(57) [Claims] 1. A first O ₂ sensor for detecting the oxygen concentration in the exhaust gas upstream of the catalytic converter for purifying exhaust gas is disposed, an empty air-fuel mixture supplied to the combustion chamber on the basis of the output voltage The fuel ratio is feedback-controlled near the stoichiometric air-fuel ratio, and the oxygen concentration in the exhaust gas on the downstream side of the catalytic converter is detected by the second O ₂ sensor at predetermined gate times, and the air-fuel ratio is determined based on the output voltage. An air-fuel ratio control method for an internal combustion engine configured to change the control center of the vicinity of the stoichiometric air-fuel ratio, from the time when each gate time has expired to the time when the timing operation of the next gate time is started, In addition to interposing a hold time for delaying the start of the timing operation, the deterioration of the catalytic converter is detected, and as the catalytic converter deteriorates, the e Air-fuel ratio control method for an internal combustion engine, characterized in that so as to change the direction to shorten the hold time.