JP2790899B2 - 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, on the downstream side of the catalytic converter, the exhaust gas discharged from each cylinder is in a stirred state,
Since the oxygen concentration in the exhaust gas is close to the equilibrium state, the second O ₂
The output voltage of the sensor shows a slow change than the output voltage of the first O ₂ sensor. That is, when the air-fuel mixture adjusted based on the output voltage of the first O ₂ sensor has a tendency to be rich as a whole, the time during which the output voltage of the second O ₂ sensor indicates a rich state becomes longer, and the air-fuel mixture becomes longer. Is lean as a whole, the time during which the output voltage of the second O ₂ sensor indicates a lean state becomes longer. Then, the feedback control value for finely adjusting the fuel supply amount gradually increases or decreases by a small value based on the output voltage of the second O ₂ sensor, and this control is repeated, thereby controlling the air-fuel ratio. The center will be adjusted near the stoichiometric air-fuel ratio. For this reason, as schematically shown in FIG. 8, even if feedback control of the air-fuel ratio is performed near the stoichiometric air-fuel ratio based on the feedback control value FACF, the engine switch is once turned off.
When (key-off) is set, the feedback control is restarted from the initial value at the next feedback start. As a result, when the feedback control is performed, the control center of the air-fuel ratio deviates from the vicinity of the stoichiometric air-fuel ratio at each start, and the emission deteriorates during that time.

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, wherein the feedback control value decreases from an increase. Is updated as a maximum value, the value when the feedback control value is changed from a decreasing side to an increasing side is updated as a minimum value, and feedback is performed based on the updated maximum value and minimum value. A learning value of the control value is determined, and when the feedback control is started, the feedback control is started with the learning value.

The control center of the air-fuel ratio is changed based on the feedback control value as a skip amount, a rich integration, which is a direct control element of an air-fuel ratio feedback correction coefficient determined based on an output voltage of the first O ₂ sensor. , The lean integral or the like is changed, or the air-fuel ratio rich determination delay time or lean determination delay time, which is a direct control element, is changed.

[Effect] According to such a configuration, during the first air-fuel ratio feedback control, while the control center of the air-fuel ratio is adjusted to near the required value from the start of the control, the emission slightly deteriorates, but the feedback is performed near the required value. When the control value is learned, the value when the feedback control value changes from the increasing side to the decreasing side is updated as the maximum value, and the value when the feedback control value changes from the decreasing side to the increasing side is the minimum value. The learning value of the feedback control value is determined based on the updated maximum value and minimum value. Then, at the time of the next feedback control, the feedback control of the air-fuel ratio is started immediately from the learning value as a starting point.

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 unit 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. First, step 51
Then, it is determined whether or not the condition for executing the feedback F / B by the sub O ₂ sensor 7 is satisfied. If it is determined that the condition is satisfied, the process proceeds to step 53. If it is determined that the condition is not satisfied, Then, go to step 52. In step 52, it keeps holding the learned value of the feedback control value determined by the output voltage of the sub O ₂ sensor 7. In step 53, by executing the feedback F / B control of the air-fuel ratio by the sub O ₂ sensor 7, the process proceeds to step 54. In step 54, the sub O ₂
It is determined whether or not the control direction of the feedback control value determined by the output voltage of the sensor 7 has changed. If it is determined that the control direction has changed, the process proceeds to step 55. In step 55, as schematically shown in FIG. 6, the value when the feedback control value FACF changes from the increasing side to the decreasing side is updated as the maximum value MAX, and the value when the feedback control value FACF switches from the decreasing side to the increasing side is updated. Is the minimum
After appropriately updating each as MIN, the process proceeds to step 56. In step 56, a learning value determined based on a procedure described later is set in a predetermined memory.

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 coolant temperature is 70 °
The output of the sub O ₂ sensor 7 is as described above, the fuel correction amount during the transition is less than a predetermined amount, the vehicle speed is 0 when the engine is idling, or the engine is in a predetermined operation region when the engine is not idling. the learning number of the feedback control value determined by the voltage is below the set number of times, if the conditions are satisfied all equal, the sub-O ₂ feedback F / B control by the sensor 7 is performed (step 51 → step 5
3). In this feedback control, as shown in FIG. 4, the gate time CD for a predetermined time (for example, every 40 msec)
UTYSO is provided for control. In particular,
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 the rich time DUTYSO counts up and reaches a certain value, the rich flag SOFLG
Is set to the signal 1 indicating that the air-fuel ratio is rich, and when the feedback control value FACF is changed from the decrease side to the increase side, the signal 0 indicating the air-fuel ratio lean is set to the flag SOFLG. When the signal 1 indicating that the air-fuel ratio is rich is set, the lean integration FACFKIM
, The feedback control value FACF is decreased by a constant value. On the other hand, when the rich flag SOFLG is switched to the signal 0 indicating that the air-fuel ratio is lean, the feedback control value FACF is skipped to the increasing side by a constant value FACFRSP, and then gradually increased by a constant value based on the rich integration FACFKIP. To increase. The feedback control value FACF is changed based on such a procedure, and the feedback control value FACF is changed.
Based on the FACF, the rich determination delay time TDR and the lean determination delay time TDL are determined from the map shown in FIG.
Here, when the feedback control value FACF increases, the rich determination delay time TDR increases, while 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.
Also, while appropriately updating the maximum value MAX when the feedback control value FACF reverses from the increasing side to the decreasing side and the minimum value MIN when the feedback control value FACF reverses from the decreasing side to the increasing side, based on these values, Determine the learning value FKG (Step 54-
Step 56).

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 by increasing or decreasing the feedback control value determined by the output voltage. that time,
As schematically shown in FIG. 6, the feedback control value FA
Learning of the CF is performed, and the learning value is determined. Thus, the stoichiometric air-fuel ratio is, as shown in FIG. 7, a value MAX when the feedback control value FACF changes from the increasing side to the decreasing side and a value MIN when the feedback control value FACF changes from the decreasing side to the increasing side. The learning value becomes a value corresponding to the stoichiometric air-fuel ratio. Then, from the next operation, when the feedback control is started, the feedback control of the air-fuel ratio is started from the learning value as a starting point.

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.

In addition, according to this control method, during the first air-fuel ratio feedback control, while the control center of the air-fuel ratio is adjusted to near the required value from the start of the control, although the emission slightly deteriorates, the feedback control value near the required value is reduced. Is performed, the feedback control of the air-fuel ratio can be immediately performed from the learning value at the time of the next feedback control. Therefore, when the feedback control of the air-fuel ratio is performed, the emission in the early stage of the start can be effectively improved.

Further, the rich determination delay time TDR and the lean determination delay time TDL are determined by the learning value, and the control center to be determined can be determined thereby, so that the feedback control by the sub O ₂ sensor 7 is stopped during engine cooling,
When the feedback control by the main O ₂ sensor is also carried out immediately because the learning value can be carried out feedback control in the vicinity of the starting point, deterioration of the emission during such feedback control can be suppressed.

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.

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 Not only can the feedback control be started near the stoichiometric air-fuel ratio when the air-fuel ratio feedback control is performed, it is possible to effectively avoid deterioration of the emission due to aging or the like, and to start the feedback control. Early emissions 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 control mode, FIG. 5 is a view showing control setting conditions, and FIGS. 6 and 7 are operation explanatory diagrams. FIG. 8 is an operation explanatory view corresponding to FIG. 6 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, comprising: updating a value when the feedback control value changes from an increasing side to a decreasing side as a maximum value, and changing the feedback control value from a decreasing side to an increasing side. Is updated as the minimum value, a learning value of the feedback control value is determined based on the updated maximum value and minimum value, and the feedback control is started with the learning value at the start of the feedback control. An air-fuel ratio control method for an internal combustion engine, characterized in that: