JP2790898B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control method for an internal combustion engine applied to an automobile having an O ₂ sensor on the upstream and downstream sides of a catalytic converter.

[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 having an injector, the air-fuel ratio feedback correction coefficient for adjusting the amount of fuel injection finely may be provided, the output voltage of the O ₂ sensor disposed on the upstream side of the catalytic converter indicates an air-fuel ratio rich state In this case, the fuel supply amount is reduced by reducing the correction coefficient after a predetermined delay time to change the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio. When the output voltage indicates the air-fuel ratio lean state, the fuel supply amount is increased by increasing the correction coefficient after a predetermined delay time, and the air-fuel ratio of the air-fuel mixture is changed to the stoichiometric air-fuel ratio. I try to make it.

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.
As a mode of changing the control center of the air-fuel ratio based on the output voltage of the second O ₂ sensor, when changing the skip amount or rich integration of the air-fuel ratio feedback correction coefficient, lean integration, or air-fuel ratio rich, There are cases where the determination delay time of the air-fuel ratio lean is changed.

[Problems to be solved by the invention] However, the control center of the air-fuel ratio is not always constant,
May vary depending on engine load conditions. For this reason,
When the engine load changes rapidly, there is a time delay before the control center of the air-fuel ratio is adjusted to a value suitable for the engine load based on the output voltage of the second O ₂ sensor. Therefore, immediately after the change in the engine load, the control center temporarily deviates from the window of the three-way catalyst, and the emission deteriorates. In order to solve such problems,
A plurality of learning zones are set according to the engine load, and the learning value is determined based on the maximum value and the minimum value of the feedback control value determined by the output voltage of the second O ₂ sensor in each learning zone. Can be considered. This feedback control value is a coefficient for finely adjusting the fuel supply amount so that the air-fuel ratio converges around the stoichiometric air-fuel ratio. When the engine load changes, the air-fuel ratio control center is immediately changed to the vicinity of the required value by performing feedback control of the air-fuel ratio starting from the learning value of the learning zone corresponding to the engine load. Can be

However, in such a method, as schematically shown in FIG. 8, when the engine load changes frequently,
At engine load where the required value is away from the initial value,
Since the learning of the feedback control value FACF is not performed, the emission cannot be improved at the engine load.

An object of the present invention is to solve such a problem.

[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,
The air-fuel ratio of the air-fuel mixture supplied to the combustion chamber is feedback-controlled near the stoichiometric air-fuel ratio by successively updating the air-fuel ratio feedback correction coefficient based on the output voltage, and a second air-fuel ratio is arranged downstream of the catalytic converter. The feedback control value is determined based on the output voltage of the O ₂ sensor, and the skip amount, the rich integration value or the lean integration value of the air-fuel ratio feedback correction coefficient, or the air-fuel ratio corresponding to the feedback control value is determined. A direct control element such as a rich determination delay time or a lean determination delay time is determined, and the feedback control is continued using the direct control element to change the control center of the air-fuel ratio to near the stoichiometric air-fuel ratio. An air-fuel ratio control method for an internal combustion engine, comprising a plurality of learning zones corresponding to an engine load. In each learning zone, the value when the feedback control value changes from the increasing side to the decreasing side is stored as the maximum value, and the value when the feedback control value changes from the decreasing side to the increasing side is stored as the minimum value. The learning value in each learning zone is determined based on the obtained maximum value and minimum value, and when the engine load changes, the feedback control of the air-fuel ratio is performed from the learning value of the learning zone corresponding to the engine load. When the learning zone is changed, when the final feedback control value in the learning zone before the change is larger than the value stored as the maximum value in the learning zone before the change, the value is set to the maximum value in the learning zone before the change. When the learning zone changes, the final feedback control value in the learning zone before the change changes in the learning zone before the change. If smaller than the small value is characterized in that so as to update the minimum value in the learning zone before the change that value.

Note that the control center of the air-fuel ratio is changed based on the feedback control value as a skip amount of air-fuel ratio feedback correction coefficient determined based on the output voltage of the first O ₂ sensor, rich integration, lean integration, and the like. In some cases, the air-fuel ratio rich determination delay time and the lean determination delay time are changed.

[Operation] According to such a configuration, in the engine load learning zone in which the initial value of the feedback control value is relatively close to the required value, the feedback control value is quickly shifted to the vicinity of the required value. , And the learning value is determined based on the feedback control value that changes in the vicinity.
When the engine load changes, the feedback control of the air-fuel ratio is immediately performed starting from the learning value of the corresponding engine load.

In the learning zone of the engine load where the initial value and the required value of the feedback control value are relatively separated, first, the learning value is determined based on the maximum value and the minimum value,
When the engine load is shifted to a similar one, feedback control is performed starting from the learning value. Then, when the learning zone changes, if the final feedback control value in the learning zone before the change is larger than the value stored as the maximum value in the learning zone before the change, the value is the maximum value in the learning zone before the change. If the final feedback control value in the learning zone before the change is smaller than the minimum value in the learning zone before the change when the learning zone changes, the value is set as the minimum value in the learning zone before the change. Be updated. As a result, in the learning zone before the change described above, even when the feedback control value does not change from increasing to decreasing or from decreasing to increasing, the learning value can be updated, and the learning value gradually increases. The engine load will approach the required value.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

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 schematically shown in FIG. Assuming that the execution condition of the feedback F / B by the sub O ₂ sensor 7 is satisfied, it is determined in step 51 whether or not the learning zone has changed based on the engine speed and the intake pressure. If it is determined, the process proceeds to step 52, and if it is determined that there is no change, the process proceeds to step 58. The learning zone is set for an idling state and a non-idling state. Further, in the case of the non-idling state, the fourth
As shown in the figure, are a sub-O ₂ sensor 7 by the feedback area classified based on the intake pressure PM and engine speed NE. In step 52, the maximum value of the feedback control value FACF feedback control value determined by the output voltage of the sub O ₂ sensor 7 FACF is in the former zone before the change to determine whether exceeds the MAX, it is determined that the above In this case, the process proceeds to step 53, and if it is determined that the value is not exceeded, the process proceeds to step 54. In step 53, the feedback control value FACF in the learning zone after the shift is set to the maximum value MAX.
After that, the process proceeds to step 54. In step 54, it is determined whether or not the feedback control value FACF is lower than the minimum value MIN of the feedback control value FACF in the old zone before the change.If it is determined that the feedback control value FACF is lower, the process proceeds to step 55. If it is determined, the process proceeds to step 56. In step 55, the process proceeds to step 56 after updating the feedback control value FACF in the learning zone after the transition as the minimum value MIN. In step 56, the learning value in the old zone before the change is determined, and the process proceeds to step 57. In step 57, the learning value in the learning zone after the transition is set to a predetermined address. In step 58, the sub O ₂
The feedback F / B control is performed based on the output voltage of the sensor 7, and the feedback control value FACF is appropriately updated, and the process proceeds to step 59. In step 59, a learning value is appropriately calculated based on the feedback control value FACF.

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.
More specifically, as shown in FIG. 3, when the output voltage of the main O ₂ sensor 6 exceeds the determination voltage, the idle state occurs after the rich determination delay time TDR which is a direct control element of the air-fuel ratio feedback correction coefficient FAF. The fuel ratio feedback correction coefficient FAF is skipped toward the decreasing side by a predetermined value RSM as a skip amount which is a direct control element, and then gradually decreased by a constant value based on a lean integral KIM which is a direct control element. 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 lean determination delay time TDL which is a direct control element
Thereafter, the air-fuel ratio feedback correction coefficient FAF is skipped to the increasing side by a predetermined value RSP as a skip amount which is a direct control element, and then gradually increased by a constant value based on the rich integration KIP which is a direct control element. 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.

If the feedback F / B condition by the sub O ₂ sensor 7 is satisfied during the feedback control, for example,
_The predetermined time has elapsed since the start of the feedback execution of the air-fuel ratio by the _two sensors 6, the predetermined time has elapsed since the main O ₂ sensor 6 was activated, and the engine cooling water temperature is 70 ° C.
Above, the transient fuel correction amount is less than the predetermined amount, the engine is idling, the vehicle speed is 0, or the engine is in one of the operating regions of each learning zone. learning number of determined control value signals by the output voltage of _{the secondary} sensor 7 is below the predetermined number of times, if the conditions are satisfied all equal, feedback F / B control by the sub-O ₂ sensor 7 is performed. In addition,
Downstream of the maniverter 14, in a state in which exhaust gas discharged from the cylinders is sufficiently agitated, since the oxygen concentration in the exhaust gas close to equilibrium, the output voltage of the sub O ₂ sensor 7, main O _{2 The} change is slower than that of the sensor 6. More specifically, when the feedback control is performed by the main O ₂ sensor 6 and the air-fuel ratio control center is on the rich side and the air-fuel mixture is generally rich, the output of the sub O ₂ sensor 7 is voltage indicates a rich state, on the contrary, when the control center of the air-fuel ratio is from the lean overall air-fuel mixture in a lean side, the output voltage of the sub O ₂ sensor 7 indicates a lean state. Therefore, in this feedback control, as shown in FIG. 5, a predetermined time (for example, 40 msec)
The gate time CDUTYSO of each) is provided for control. More specifically, when the output voltage of the sub O ₂ sensor 7 exceeds the determination voltage is continuously detected, the rich time DUTYSO is counted up every predetermined time. When there is no change in the learning zone and the rich time DUTYSO is counted up and reaches a certain value, the rich flag SOFL
G is set to signal 1 indicating that the air-fuel ratio is rich, and the feedback control value FACF is set to the lean integral FACFKIM
Is reduced by a constant value. Sub O ₂ lower than the output voltage determining voltage sensor 7, if the signal 0 indicating that shows the air-fuel ratio lean to the flag SOFLG is set, and the feedback control value FACF to skip only the increase side predetermined value FACFRSP Thereafter, the value is gradually increased by a constant value based on the rich integration FACKIP. When the feedback control value FACF is determined based on such a procedure, the learning value of the feedback control value FACF is determined in each learning zone, and the sixth value is determined based on the feedback control value FACF.
The rich determination delay time TDR and the lean determination delay time TDL are determined from the map shown in FIG. Here, if the feedback control value FACF increases, the rich determination delay time TD
While R increases, the lean determination delay time TDL decreases. Therefore, the timing at which the air-fuel ratio feedback correction coefficient FAF is switched from the increasing side to the decreasing side is delayed, and the timing at which the air-fuel ratio feedback correction coefficient FAF is switched from the decreasing side to the increasing side is earlier, and the amount of fuel supplied from the injector 1 is increased. Will be.
When the feedback control value FACF decreases, the fuel supply amount decreases.

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 air-fuel ratio of the air-fuel mixture is gently and finely adjusted. At that time, a learning value of the feedback control value is calculated in each predetermined learning zone corresponding to each engine load. That is, as schematically shown in FIG. 7, when the engine load changes, if the initial value of the feedback control value FACF and the required value at the engine load are relatively close, the feedback control value FACF becomes Shift quickly from the initial value to the vicinity of the required value,
The learning value is determined based on the value that changes in the vicinity.
Then, when the engine load after the change is the same engine load, the feedback control of the air-fuel ratio is immediately performed starting from the learning value.

In the case of an engine load in which the initial value of the feedback control value FACF is relatively different from the required value, first,
The learning value will be determined based on the maximum value MAX and the minimum value MIN, and if the engine load shifts to the same,
Feedback control is performed starting from the learning value. If the feedback control value FACF at the changed engine load exceeds the previous maximum value MAX, the learning value is increased. As a result, the learned value of the engine load gradually approaches the required value of the engine load.
Then, at the time of the next load change, feedback control is performed starting from this learning value.

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. Can be converged.

Further, according to such a control method, even if the engine load changes rapidly, the control communication of the air-fuel ratio can be immediately shifted to the vicinity of the required value of the engine load. As a result, when the engine load changes, feedback control of the air-fuel ratio can be performed from near the stoichiometric air-fuel ratio, and emission after the change in the engine load can be effectively improved. Moreover, even when the required value of the engine load is far from the initial value, the control center can be shifted to the vicinity of the required value of each engine load by updating the learning value, so that the engine load is frequently reduced. Even if it changes, feedback control of the air-fuel ratio can be immediately performed from near the stoichiometric air-fuel ratio, and emission at the time of load change can be effectively improved.

Note that the feedback control value determined based on the output signal of the second O ₂ sensor is not limited to the case determined based on the control procedure described above. Further, the control center of the air-fuel ratio can be adjusted by changing the rich integration, the lean integration, and the skip amount, which are direct control elements of the air-fuel ratio feedback correction coefficient, based on the feedback control value. Further, the learning zone may be set more finely in accordance with the engine load.

The present invention [Effect of the invention] is as described above because construction is that, it is possible to prevent the air-fuel ratio of the mixture by the first O ₂ sensor being displaced from the vicinity of the stoichiometric air-fuel ratio by a second O ₂ sensor In addition, when the engine load changes, the control center of the air-fuel ratio can be immediately shifted to the vicinity of the stoichiometric air-fuel ratio in response to the load change. Therefore, it is possible to effectively avoid deterioration of the emission due to a temporal change or the like. While being able to
Emissions when the engine load changes can be effectively improved.

[Brief description of the drawings]

1 to 7 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. FIG. 4 is a timing chart showing a learning zone, FIG. 5 is a timing chart showing a control mode, FIG. 6 is a view showing control setting conditions, and FIG. 7 is an operation explanatory view. FIG. 8 is an operation explanatory view corresponding to FIG. 7 showing a conventional example. 1 Injector 6 First O ₂ sensor (main O ₂ sensor) 7 Second O ₂ sensor (sub O ₂ sensor) 14 Catalytic converter (maniverter) 15 Combustion chamber FACF Feedback control value

Claims (1)

(57) [Claims] 1. A place first O ₂ sensor for detecting the oxygen concentration in the exhaust gas upstream of the catalytic converter for purifying exhaust gas, and sequentially updates the air-fuel ratio feedback correction coefficient on the basis of the output voltage determining as well as feedback controlled to the stoichiometric air-fuel ratio near the air-fuel ratio of a mixture supplied to the combustion chamber, a feedback control value based on the second O ₂ sensor output voltage that is disposed downstream of the catalytic converter by In such a manner, in accordance with the feedback control value, the skip amount of the air-fuel ratio feedback correction coefficient, a rich integration value or a lean integration value, or
A direct control element such as an air-fuel ratio rich determination delay time or a lean determination delay time is obtained, and the feedback control is continued using the direct control element to change the control center of the air-fuel ratio to near the stoichiometric air-fuel ratio. An air-fuel ratio control method for an internal combustion engine, wherein a plurality of learning zones are provided in accordance with an engine load, and a value when the feedback control value is changed from an increasing side to a decreasing side in each learning zone is set as a maximum value. Memorize, memorize the value when changing from the decreasing side to the increasing side as the minimum value, determine the learning value in each learning zone based on the stored maximum value and minimum value, respectively, When the load changes, feedback control of the air-fuel ratio is performed based on the learning value of the learning zone corresponding to the engine load. If the final feedback control value in the learning zone is larger than the value stored as the maximum value in the learning zone before the change, the value is updated as the maximum value in the learning zone before the change. When the final feedback control value in the previous learning zone is smaller than the minimum value in the learning zone before the change, the value is updated as the minimum value in the learning zone before the change; Control method.