JP2002227689A - Air fuel ratio controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute a sub-feedback control for making response and stability compatible by correctly changing the control to a proper control condition corresponding to the operating state of an internal combustion engine or the change of the catalyst condition in a system executing a main/sub-feedback control using an intermediate target value. SOLUTION: Exhaust gas sensors 24, 25 are provided on an upstream side and a downstream side of the catalyst 23 respectively to set the intermediate target value based on the output of the exhaust gas sensor 25 on the downstream side at the last calculation time and the final target value (final downstream side target air fuel ratio). The correction amount for the upstream side target air fuel ratio is calculated based on the deviation between the output of the current downstream side exhaust gas sensor 25 and the intermediate target value. In this case at least one of the updated amount of the intermediate target value, an updated speed, a control gain of the sub-feedback control, a control cycle and a control range is changed corresponding to a parameter related to the exhaust gas flow amount or catalyst reaction speed, thus executing the highly responsive sub-feedback control faithfully following the change of the operational condition and the change of the catalyst 23 condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio sensor (linear A) provided upstream and downstream of an exhaust gas purifying catalyst.
/ F sensor) or an air-fuel ratio control device for an internal combustion engine that performs feedback control of the air-fuel ratio of the internal combustion engine by installing an oxygen sensor.

[0002]

2. Description of the Related Art In today's automobiles, a three-way catalyst is installed in an exhaust pipe to purify exhaust gas. However, in order to increase the exhaust gas purification rate of the catalyst, the air-fuel ratio of the exhaust gas must be reduced by using a catalyst purification window. It is necessary to control within (around the stoichiometric air-fuel ratio). Therefore, an exhaust gas sensor (air-fuel ratio sensor or oxygen sensor) is installed on each of the upstream and downstream sides of the catalyst, and the fuel injection amount is adjusted so that the air-fuel ratio of the exhaust gas detected by the upstream exhaust gas sensor becomes the upstream target air-fuel ratio. And performs a sub-feedback control to correct the upstream target air-fuel ratio so that the air-fuel ratio of the exhaust gas detected by the downstream exhaust gas sensor becomes the downstream target air-fuel ratio.

In such a main / sub feedback system, as shown in Japanese Patent No. 2518247, as the deviation between the detected air-fuel ratio of the downstream exhaust gas sensor and the downstream target air-fuel ratio increases, the air-fuel ratio feedback control constant ( It has been proposed to increase the update amount (eg, skip amount).

[0004]

The dynamic characteristics of the catalyst vary depending on the degree of deterioration of the catalyst, the state of adsorbing lean / rich components in the catalyst, and the operating state of the engine. The responsiveness of the sub-feedback control to the change in the dynamic characteristics of the catalyst is not sufficient. Therefore, a response delay of the sub-feedback control with respect to the change in the dynamic characteristics of the catalyst occurs, and the air-fuel ratio on the downstream side of the catalyst (output of the downstream side exhaust gas sensor) becomes unstable, and hunting may occur.

[0005] In order to solve this drawback, the inventors of the present invention, as described in Japanese Patent Application No. 2000-404671, describe the past detected air-fuel ratio of the downstream exhaust gas sensor and the final air-fuel ratio. A sub-feedback control that sets an intermediate target value of the sub feedback control based on the downstream target air-fuel ratio and corrects the upstream target air-fuel ratio based on a deviation between the detected air-fuel ratio of the downstream exhaust gas sensor and the intermediate target value. Is under development for practical use.

In putting this system into practical use,
The following new technical issues have been identified. That is, the catalyst has a large delay system (dead time and time constant), which greatly changes depending on the exhaust gas flow rate and the catalytic reaction speed. In that case, update of the intermediate target value used for sub feedback control (responsiveness of sub feedback control)
If the exhaust gas flow rate is low or the catalytic reaction speed is low (when the purification performance of the catalyst is low), the update of the intermediate target value will be appropriate, If the exhaust gas flow rate is large or the catalytic reaction speed is high, the update of the intermediate target value (responsiveness of the sub-feedback control) becomes too slow, and sufficient exhaust gas purification performance cannot be secured.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and accordingly, it is an object of the present invention to provide a system for performing main / sub feedback control using an intermediate target value in an operating state of an internal combustion engine and a state of a catalyst. Sub-feedback control that achieves both responsiveness and stability while changing to appropriate control conditions in accordance with changes in the exhaust gas, and achieves stable exhaust gas purification performance independent of the operating state of the internal combustion engine and the state of the catalyst. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can be ensured.

[0008]

In order to achieve the above object, an air-fuel ratio control apparatus for an internal combustion engine according to a first aspect of the present invention is provided.
An intermediate target value of the sub feedback control is set based on the past detected air-fuel ratio of the downstream exhaust gas sensor and the final downstream target air-fuel ratio, and the deviation between the detected air-fuel ratio of the downstream exhaust gas sensor and the intermediate target value is set. Performing sub-feedback control to correct the upstream target air-fuel ratio based on
Depending on the operating state of the internal combustion engine or parameters related to the state of the catalyst, the update amount of the intermediate target value, update speed,
Control gain of the sub-feedback control, control cycle,
At least one of the control ranges is changed by control correction means. If you do this,
Sub feedback control that achieves both responsiveness and stability can be performed while changing to appropriate control conditions in accordance with changes in the operating state of the internal combustion engine and the state of the catalyst. Stable exhaust gas purification performance that is not affected by such conditions.

Here, parameters relating to the operating state of the internal combustion engine include, for example, an exhaust gas flow rate, an intake air amount,
Any one or more of engine rotation speed, intake pipe pressure, throttle opening, vehicle speed, cooling water temperature, exhaust temperature, idle switch signal, elapsed time after starting, etc. may be used. The parameters related to are: catalyst reaction speed, catalyst temperature (can be replaced by exhaust temperature, elapsed time after start, etc.), catalyst deterioration degree, catalyst O
Any one or a plurality of parameters from _two storage amounts (lean / rich component adsorption amounts) and the like may be used.

In this case, in consideration of the fact that the delay system (dead time and time constant) by the catalyst greatly changes depending on the flow rate of the exhaust gas and the reaction speed of the catalyst, the present invention relates to the flow rate of the exhaust gas or the reaction speed of the catalyst. It is preferable that at least one of the update amount of the intermediate target value, the update speed, the control gain of the sub-feedback control, the control cycle, and the control range is changed according to the parameter. This makes it possible to stably perform the high-response sub-feedback control that follows the change in the delay system (dead time and time constant) caused by the catalyst with good response.

According to a third aspect of the present invention, a value obtained by multiplying a difference between a past detected air-fuel ratio of the downstream exhaust gas sensor and a final downstream target air-fuel ratio by an attenuation rate, and a final downstream target air-fuel ratio are used. An intermediate target value may be obtained by adding the fuel ratio, and the damping rate may be changed according to a parameter related to the operating state of the internal combustion engine or the state of the catalyst. With this configuration, the intermediate target value can be set by a simple calculation process, and the control condition can be changed according to a change in the operating state of the internal combustion engine or the state of the catalyst by a simple calculation process.

Further, the value calculated by the proportional integral operation with respect to the deviation between the detected air-fuel ratio of the downstream side exhaust gas sensor and the intermediate target value is limited within a predetermined control range, so that the upstream side target is controlled. The correction amount of the air-fuel ratio may be obtained, and the gain (control gain) and / or the control range of the proportional-integral operation may be changed according to the parameters related to the operating state of the internal combustion engine or the state of the catalyst. In this manner, the change in the dynamic characteristics of the catalyst can be reflected in the correction amount of the upstream target air-fuel ratio in a good response, and the change in the control condition following the change in the operating state of the internal combustion engine or the state of the catalyst can be achieved. , Can be performed by simple arithmetic processing.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment (1)] An embodiment (1) of the present invention will be described below with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of an intake pipe 12 of an engine 11 which is an internal combustion engine, and an air flow meter 14 for detecting an intake air amount is provided downstream of the air cleaner 13. A throttle valve 15 is provided downstream of the air flow meter 14.

Further, a surge tank 17 is provided downstream of the throttle valve 15.
Further, an intake manifold 19 for introducing air into each cylinder of the engine 11 is provided. A fuel injection valve 20 for injecting fuel is attached near each intake port of the intake manifold 19 of each cylinder. An ignition plug 21 is attached to a cylinder head of the engine 11 for each cylinder.

On the other hand, a catalyst 23 such as a three-way catalyst for purifying CO, HC, NOx and the like in exhaust gas is provided in the exhaust pipe 22 of the engine 11. Exhaust gas sensors 24 and 25 for detecting an exhaust gas air-fuel ratio or rich / lean are installed upstream and downstream of the catalyst 23, respectively. In the present embodiment, an air-fuel ratio sensor (linear A / F sensor) that outputs a linear air-fuel ratio signal according to the exhaust gas air-fuel ratio is used as the upstream exhaust gas sensor 24, and the downstream exhaust gas sensor 25 is an exhaust gas air-fuel sensor. An oxygen sensor whose output voltage is inverted depending on whether the fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio is used. Therefore, the downstream side exhaust gas sensor 25
Generates an output voltage of about 0.1 V when the air-fuel ratio is lean, and generates an output voltage of about 0.9 V when the air-fuel ratio is rich. The cylinder block of the engine 11 is provided with a water temperature sensor 26 for detecting a cooling water temperature and a rotation speed sensor 27 for detecting an engine rotation speed.

An engine control circuit (hereinafter referred to as "ECU") 28 includes a ROM 29, a RAM 30, a CPU 31,
Backup RAM backed up by battery 32
The microcomputer is mainly composed of a microcomputer including an input port 33, an input port 34, an output port 35, and the like. The output signal of the rotation speed sensor 27 is input to the input port 34, and the output signals of the air flow meter 14, the upstream and downstream exhaust gas sensors 24 and 25, and the water temperature sensor 26 are respectively supplied to the A / D converter 36. Is entered via The output port 35 is connected to the fuel injection valve 20, the ignition plug 21 and the like via a drive circuit 39.

The ECU 28 stores the fuel injection control program and the ignition control program stored in the ROM 29 into the CPU 3.
1, the fuel injection valve 20 and the spark plug 21
By executing the air-fuel ratio control program, the air-fuel ratio (fuel injection amount) is feedback-controlled so that the air-fuel ratio of the exhaust gas becomes the target air-fuel ratio.

Hereinafter, the air-fuel ratio feedback control system of the embodiment (1) will be described with reference to FIGS. Here, FIG. 2 is a block diagram showing the function of the air-fuel ratio control means 40 realized by the arithmetic processing function of the CPU 31, and FIG. 3 is a block diagram showing the function of the entire air-fuel ratio feedback control system.

The air-fuel ratio control means 40 comprises a fuel injection amount feedback control unit 41 and a target air-fuel ratio calculation unit 42. The target air-fuel ratio calculation unit 42 includes a load target air-fuel ratio calculation unit 43 and a target air-fuel ratio correction unit. 44.

The fuel injection amount feedback control unit 41 includes:
The fuel injection time Tinj of the fuel injection valve 20 is calculated so that the detected air-fuel ratio AF of the upstream side exhaust gas sensor 24 converges on the upstream side target air-fuel ratio AFref. This fuel injection time Tinj
Is calculated by the optimal regulator constructed for the linear equation of the model to be controlled. The fuel injection amount feedback control unit 41 plays a role corresponding to an air-fuel ratio feedback control unit described in claims.

On the other hand, the load target air-fuel ratio calculation unit 43
The load target air-fuel ratio AFbase according to the intake air amount (or the intake pipe pressure) and the engine speed is calculated from the function formula or map stored in M29. This load target air-fuel ratio AF
The function formula or map for calculating the base is such that when the output O2out (detected air-fuel ratio) of the downstream exhaust gas sensor 25 is constantly substantially equal to the final target value O2targ (final downstream target air-fuel ratio), If the side target air-fuel ratio AFref is maintained at the load target air-fuel ratio AFbase, the output O2out of the downstream side exhaust gas sensor 25 is set in advance by a test or the like so as to be maintained near the final target value O2targ.

The target air-fuel ratio corrector 44 calculates a correction amount AFcomp of the upstream target air-fuel ratio AFref based on the output O2out of the downstream exhaust gas sensor 25 using an intermediate target value O2midtarg described later. Then, this correction amount AFco
By adding mp to the load target air-fuel ratio AFbase, an upstream target air-fuel ratio AFref is obtained, and this upstream target air-fuel ratio AFref is input to the fuel injection amount feedback control unit 41. AFref = AFbase + AFcomp Note that instead of the above equation, the upstream target air-fuel ratio AFre is calculated by the following equation.
f may be calculated. AFref = (1 + AFcomp) × AFbase

In this case, the target air-fuel ratio calculation unit 42 (the load target air-fuel ratio calculation unit 43 and the target air-fuel ratio correction unit 44) plays a role corresponding to the sub-feedback control means in the claims.

Next, a method of calculating the correction amount AFcomp of the upstream target air-fuel ratio AFref by setting the intermediate target value O2midtarg in the target air-fuel ratio correction unit 44 will be described with reference to FIG.
The control object is a system including the fuel injection amount feedback control unit 41, the fuel injection valve 20, the engine 11, the catalyst 23, the downstream exhaust gas sensor 25, and the like. Target air-fuel ratio correction unit 44
Is the time delay element (1 / z) 45, the intermediate target value calculation unit 4
6. An attenuation rate setting unit 47 and a correction amount calculation unit 48. The time delay element 45 inputs the output O2out (i-1) of the downstream exhaust gas sensor 25 at the time of the previous calculation to the intermediate target value calculation unit 46. .

On the other hand, the intermediate target value calculating section 46 plays a role corresponding to an intermediate target value setting means described in the claims, and the output O2out of the downstream side exhaust gas sensor 25 at the time of the previous calculation.
Based on (i-1) and the final target value O2targ (i) (final downstream target air-fuel ratio), an intermediate target value O2midtarg (i) is calculated using the following equation (1). Thus, the intermediate target value O2midtarg (i) is set between the output O2out (i-1) of the downstream exhaust gas sensor 25 at the time of the previous calculation and the final target value O2targ (i). O2midtarg (i) = O2targ (i) + Kdec × {O2out (i-1) -O2targ (i)} (1)

In the above equation, O2targ (i) is the current final target value, and O2out (i-1) is the output of the downstream exhaust gas sensor 25 at the time of the previous calculation. Kdec is a damping rate, and is set in the range of 0 <Kdec <1 by the damping rate setting unit 47 in accordance with parameters related to the engine operating state or the state of the catalyst 23. Here, the parameters related to the engine operating state include, for example, an exhaust gas flow rate, an intake air amount,
Any one or a plurality of parameters may be used from among the engine rotation speed, intake pipe pressure, throttle opening, vehicle speed, cooling water temperature, exhaust temperature, idle switch signal, elapsed time after starting, and the like. The parameters related to the state include the catalyst reaction speed, the catalyst temperature (the temperature can be replaced by the exhaust gas temperature, the elapsed time after the start, etc.), the catalyst 23
Any one or a plurality of parameters may be used from among the degree of deterioration of the catalyst, the O ₂ storage amount of the catalyst 23 (lean / rich component adsorption amount), and the like.

In the present embodiment (1), the attenuation rate setting unit 4 takes into account that the delay system (dead time and time constant) by the catalyst 23 greatly changes depending on the exhaust gas flow rate and the catalytic reaction speed.
Numeral 7 sets the damping rate Kdec by the map of FIG. 4 or an equation according to parameters related to the exhaust gas flow rate or the catalytic reaction speed. Here, the parameters related to the exhaust gas flow rate include an intake air amount, an engine rotation speed, an intake pipe pressure,
Any one or a plurality of parameters may be used from among the throttle opening and the like, and, of course, the exhaust gas flow rate may be calculated from these parameters. As the parameters associated with the catalytic rate, catalyst temperature (can substitute the like exhaust temperature and the after-start elapsed time), the deterioration degree of the catalyst 23, O ₂ storage amount of the catalyst 23 (lean / rich component adsorption), etc. Any one or a plurality of parameters may be used from among the parameters. Of course, the catalytic reaction rate may be calculated from these parameters.

The characteristic of the attenuation rate setting map shown in FIG. 4 is that the lower the exhaust gas flow rate (the lower the catalytic reaction speed), the greater the attenuation rate Kdec, the larger the update amount of the intermediate target value O2midtarg (i), The higher the flow rate (the faster the catalytic reaction speed), the more the decay rate Kde
It is set so that c becomes smaller and the update amount of the intermediate target value O2midtarg (i) becomes smaller. Note that the attenuation rate setting unit 47 plays a role corresponding to a control correction unit described in the claims.

As described above, after the intermediate target value O2midtarg (i) is calculated by the intermediate target value calculation unit 46 using the attenuation rate Kdec set by the attenuation rate setting unit 47, the intermediate target value O2midtarg (i) is calculated. And the upstream target air-fuel ratio A
The correction amount AFcomp (i) of Fref is calculated. AFcomp (i) = Fsat ｛K1 × (O2midtarg (i) −O2o
ut (i)) + K2 × {(O2midtarg (i) −O2out (i))} = Fsat (K1 × ΔO2 (i) + K2 × ΔΔO2 (i)) where ΔO2 (i) = O2midtarg (i) −O2out ( i)

In the above equation, Fsat is a saturation function having a characteristic as shown in FIG. 5, and the correction amount AFcomp (i) is represented by K1 ×
The calculated value of ΔO2 (i) + K2 × Σ (ΔO2 (i)) is obtained by performing a guard process with an upper guard value and a lower guard value. In the above equation, K1 is a proportional gain, and K2 is an integral gain.
K1 × ΔO2 (i) is a proportional term, and an intermediate target value O2midtarg
The larger the deviation ΔO2 (i) between (i) and the output O2out (i) of the downstream exhaust gas sensor 25 becomes, the larger it becomes. Also, K2
× ΣΔO2 (i) is the integral term and the intermediate target value O2midtarg
The larger the integrated value of the difference ΔO2 (i) between (i) and the output O2out (i) of the downstream side exhaust gas sensor 25, the larger the value. The correction amount AFcomp (i) is obtained by performing a guard process on a value obtained by adding the proportional term and the integral term with an upper guard value and a lower guard value.

The calculation of the correction amount AFcomp (i) by the target air-fuel ratio correction unit 44 described above is performed according to the correction amount calculation program of FIG. This program is executed every predetermined time or every predetermined crank angle. When the program is started, first, in step 101, the current output O2out (i) of the downstream exhaust gas sensor 25 is read, and in the next step 102, parameters related to the exhaust gas flow rate or the catalytic reaction speed are read.

Here, as the parameters related to the exhaust gas flow rate, any one or a plurality of parameters from among the intake air amount, the engine rotation speed, the intake pipe pressure, the throttle opening, etc. may be used. The exhaust gas flow rate may be calculated from the above parameters. As the parameters associated with the catalytic rate, catalyst temperature (can substitute the like exhaust temperature and the after-start elapsed time), the deterioration degree of the catalyst 23, O ₂ storage amount of the catalyst 23 (lean / rich component adsorption), etc. Any one or a plurality of parameters may be used from among the parameters. Of course, the catalytic reaction rate may be calculated from these parameters.

Thereafter, at step 103, the damping rate Kdec is set by the map or the mathematical formula of FIG. 4 according to the parameters related to the exhaust gas flow rate or the catalytic reaction speed. Then, in the next step 104, the output O2out of the downstream side exhaust gas sensor 25 at the time of the previous calculation is used by using this attenuation rate Kdec.
Based on (i-1) and the final target value O2targ (i) (final downstream target air-fuel ratio), the intermediate target value O2midtarg (i) is calculated using the above equation (1). Thus, the intermediate target value O2midtarg (i) is set between the output O2out (i-1) of the downstream exhaust gas sensor 25 at the time of the previous calculation and the final target value O2targ (i).

Thereafter, the routine proceeds to step 105, where the intermediate target value O2midtarg (i) and the output O2o of the downstream side exhaust gas sensor 25 are output.
The deviation ΔO2 (i) from ut (i) is calculated. ΔO2 (i) = O2midtarg (i) −O2out (i) Then, in the next step 106, the deviation ΔO2
The current deviation ΔO2 (i) is integrated with the integrated value ΣΔO2 (i-1) to obtain the integrated value ΣΔO2 (i) of the deviation ΔO2 up to this time. ΣΔO2 (i) = ΣΔO2 (i-1) + ΔO2 (i)

Thereafter, the routine proceeds to step 107, where a correction amount AFcomp (i) of the upstream target air-fuel ratio AFref is calculated by the following equation. AFcomp (i) = Fsat (K1 × ΔO2 (i) + K2 × ΣΔO
2 (i)) Thus, the correction amount AFco of the upstream target air-fuel ratio AFref
mp (i) has a proportional term (K1 × ΔO2 (i)) and an integral term (K2 × Σ
ΔO2 (i)) is obtained by performing guard processing on the value obtained by adding the upper guard value and the lower guard value. Then, in the next step 108, the current ΔO2 (i) and ΣΔO2 (i) are stored as the previous ΔO2 (i-1) and ΣΔO2 (i-1), respectively, and the program ends.

During the operation of the engine, the load target air-fuel ratio A according to the intake air amount (or intake pipe pressure) and the engine speed is determined.
Fbase is calculated, and the correction amount AFcomp calculated by the correction amount calculation program in FIG. 6 is added to the load target air-fuel ratio AFbase, thereby obtaining the upstream target air-fuel ratio AFref. The fuel injection time Tinj (fuel injection amount) is calculated so that the target value converges to the upstream target air-fuel ratio AFref.

According to the embodiment (1) described above,
In consideration of the fact that the delay system (dead time and time constant) by the catalyst 23 largely changes depending on the exhaust gas flow rate and the catalytic reaction speed, the damping rate Kdec is changed according to the parameter related to the exhaust gas flow rate or the catalytic reaction speed to change the intermediate value. Target value O2midtarg
Since the update amount of (i) is changed, high-response sub-feedback control that follows the change of the delay system (dead time and time constant) by the catalyst 23 with good response can be performed stably, and the engine operation can be performed. Stable exhaust gas purification performance that is not affected by the state or the state of the catalyst 23 can be ensured.

In this embodiment (1), the attenuation rate Kdec
Is changed to change the update amount of the intermediate target value O2midtarg (i), but the update amount of the intermediate target value O2midtarg (i) may be changed by other methods.
Alternatively, the update cycle (update rate) of the intermediate target value O2midtarg (i) may be changed according to a parameter related to the exhaust gas flow rate or the catalytic reaction speed.

[Embodiment (2)] In the above-described embodiment (1), the delay system (dead time and time) by the catalyst 23 is changed by changing the attenuation rate Kdec in accordance with the parameters related to the exhaust gas flow rate or the catalytic reaction speed. Although the sub-feedback control is made to follow the change of the (constant) with good response, in the embodiment (2) of the present invention shown in FIGS. 7 to 9, according to the parameters related to the exhaust gas flow rate or the catalytic reaction speed, By changing the proportional / integral gains K1 and K2 and the control range (upper guard value and lower guard value) as shown in FIG. 7 and FIG. 8, sub feedback is provided for the change of the delay system (dead time and time constant) by the catalyst 23. The control is followed with good response.

The proportional gain K1 (integral gain K2) in FIG.
The characteristic of the map for changing the characteristic is that as the exhaust gas flow rate decreases (catalytic reaction speed decreases), the proportional gain K1 (integral gain K2) increases, the control speed increases, and the exhaust gas flow rate increases (catalytic reaction speed increases). In order to prevent hunting, the proportional gain K1 (integral gain K2) is set to be small, and the control speed is set to be slow.

The characteristics of the map for changing the control range (upper guard value and lower guard value) shown in FIG. 8 are such that as the exhaust gas flow rate decreases (catalytic reaction speed decreases), the control range becomes narrower and the exhaust gas flow rate increases. The control range is set to be wider as the (catalytic reaction speed becomes faster).

The correction amount calculation program of FIG. 9 used in the present embodiment (2) is obtained by changing the processing of step 103 of the correction amount calculation program of FIG. 6 described in the above embodiment (1) to the processing of step 103a. And the other steps are the same. In the correction amount calculation program of FIG. 9, after reading parameters related to the exhaust gas flow rate or the catalytic reaction speed in step 102, the program proceeds to step 1
Proceeding to 03a, the proportional / integral gains K1, K2 and the control range (upper guard value and lower guard value) are changed according to the parameters related to the exhaust gas flow rate or the catalytic reaction speed by using the maps of FIGS. Then, the output O2out (i-1) of the downstream side exhaust gas sensor 25 at the time of the previous calculation and the final target value O2
After calculating an intermediate target value O2midtarg (i) based on targ (i), using the proportional / integral gains K1 and K2 set in step 103a and the control range (upper guard value and lower guard value), the upstream target value O2midtarg (i) is calculated. Of target side air-fuel ratio AFref
Comp (i) is calculated (steps 105 to 107).

In this embodiment (2), the attenuation rate Kdec
May be a fixed value for simplification of arithmetic processing.
Further, the intermediate target value O2midtarg (i) is calculated by comparing the output O2out (i-1) of the downstream exhaust gas sensor 25 in the previous calculation with the final target value O2.
It may be calculated by a two-dimensional map using 2targ (i) as a parameter.

As in the embodiment (2) described above,
Even when the proportional / integral gains K1 and K2 and the control range (upper guard value and lower guard value) are changed according to the parameters related to the exhaust gas flow rate or the catalytic reaction speed, the same as in the first embodiment. High-response sub-feedback control, which responds well to changes in the delay system (dead time and time constant) caused by the catalyst 23, can be performed stably, and is stable regardless of the engine operating state and the state of the catalyst 23. Performance can be ensured.

Incidentally, the control cycle of the sub-feedback control (the calculation cycle of the correction amount AFcomp (i)) may be changed in accordance with parameters relating to the exhaust gas flow rate or the catalytic reaction speed.

Further, using parameters not related to the exhaust gas flow rate or the catalytic reaction speed (however, parameters related to the engine operating state), the update amount of the intermediate target value, the update speed, the control gain of the sub-feedback control, the control cycle, the control At least one of the ranges may be changed.

The downstream exhaust gas sensor 25 may use an air-fuel ratio sensor (linear A / F sensor) instead of the oxygen sensor, and the upstream exhaust gas sensor 24 may use an air-fuel ratio sensor (linear A / F sensor). An oxygen sensor may be used instead of the (F sensor).

In each of the above embodiments, the intermediate target value O
When calculating 2midtarg (i), the output O2out (i-1) of the downstream exhaust gas sensor 25 at the time of the previous calculation was used, but the output O2out (in) of the downstream exhaust gas sensor 25 before the predetermined number of calculations was used. Is also good.

In addition, according to the present invention, the intermediate target value O2midtarg
It goes without saying that the present invention can be carried out with various changes, for example, the calculation formula of (i) and the calculation formula of the correction amount AFcomp (i) may be appropriately changed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an entire engine control system showing an embodiment (1) of the present invention.

FIG. 2 is a block diagram showing a function of an air-fuel ratio control unit realized by an arithmetic processing function of a CPU of an ECU;

FIG. 3 is a functional block diagram showing functions of the entire air-fuel ratio feedback control system.

FIG. 4 is a diagram conceptually showing a map for setting an attenuation rate Kdec according to an exhaust gas flow rate (or a catalytic reaction speed).

FIG. 5 is a diagram illustrating a saturation function for calculating a correction amount AFcomp (i).

FIG. 6 is a flowchart showing the flow of processing of a correction amount calculation program according to the embodiment (1).

FIG. 7 is a diagram conceptually showing a map for setting a proportional gain K1 (integral gain K2) according to an exhaust gas flow rate (or a catalytic reaction speed).

FIG. 8 is a diagram conceptually showing a map for setting a control range according to an exhaust gas flow rate (or a catalytic reaction speed).

FIG. 9 is a flowchart showing the flow of processing of a correction amount calculation program according to the embodiment (2).

[Explanation of symbols]

11 ... engine (internal combustion engine), 20 ... fuel injection valve, 22
... exhaust pipe, 23 ... catalyst, 24 ... upstream exhaust gas sensor, 2
5 downstream exhaust gas sensor, 28 ECU (air-fuel ratio feedback control means, sub-feedback control means, intermediate target value setting means), 31 CPU, 40 air-fuel ratio control means, 41 fuel injection amount feedback control unit (air (Fuel ratio feedback control means), 42: target air-fuel ratio calculation section (sub feedback control means), 43: load target air-fuel ratio calculation section, 44: target air-fuel ratio correction section, 45: time delay element (1 / z), 46 ... Intermediate target value calculation unit (intermediate target value setting means), 47 ... Attenuation rate setting unit (control correction means), 47 ...
Correction amount calculation unit.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) F02D 45/00368 F02D 45/00 368G (72) Inventor Koichi Shimizu 1-1-1 Showa-cho, Kariya City, Aichi Prefecture In Denso Co., Ltd. (72) Inventor Hisashi Hisa 1-1-1 Showa-cho, Kariya-shi, Aichi F-term in Denso Co., Ltd. 3G084 BA09 BA13 DA10 DA12 EB14 EB15 EB18 EB20 FA00 FA07 FA11 FA20 FA30 FA33 3G091 AA17 AA28 AB03 BA01 BA14 BA15 BA19 CB02 DA01 DA02 DA03 DA05 DA10 DB04 DB05 DB06 DB07 DB08 DB10 DC01 DC03 EA01 EA05 EA07 EA16 EA21 EA26 EA34 EA39 EA39 FA05 FA07 FA11 FA16 FB10 FB11 FB12 HA36 HA37 HA42 3G301 HA03 JA03 MA01 ND11 PA01Z PA07Z PD09A PD09Z PD12Z PD16Z PE01Z PE08Z

Claims (4)

[Claims] 1. An upstream exhaust gas sensor and a downstream exhaust gas sensor for detecting an air-fuel ratio or rich / lean of exhaust gas on an upstream side and a downstream side of an exhaust gas purifying catalyst, respectively. Air-fuel ratio feedback control means for feedback-controlling the fuel injection amount so as to attain the upstream target air-fuel ratio; and an intermediate target value based on the past detected air-fuel ratio of the downstream exhaust gas sensor and the final downstream target air-fuel ratio. And a sub-feedback control means for performing sub-feedback control for correcting the upstream target air-fuel ratio based on the detected air-fuel ratio of the downstream exhaust gas sensor and the intermediate target value. An air-fuel ratio control device for an internal combustion engine, wherein the intermediate target value is set according to a parameter related to an operation state of the internal combustion engine or a state of the catalyst. Update amount, update speed,
Control gain of the sub feedback control, control cycle,
An air-fuel ratio control device for an internal combustion engine, comprising: control correction means for changing at least one of the control ranges. 2. The control correction means according to a parameter related to an exhaust gas flow rate or a catalytic reaction speed, an update amount of the intermediate target value, an update speed, a control gain of the sub feedback control, a control cycle, and a control range. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein at least one of them is changed. 3. An intermediate target value setting means, comprising: a value obtained by multiplying a deviation between a past detected air-fuel ratio of the downstream exhaust gas sensor and a final downstream target air-fuel ratio by an attenuation rate; Adding the target air-fuel ratio to obtain the intermediate target value, wherein the control correction means changes the attenuation rate according to a parameter related to an operation state of the internal combustion engine or a state of the catalyst. An air-fuel ratio control device for an internal combustion engine according to claim 1 or 2. 4. The sub-feedback control means restricts a value calculated by a proportional integral operation with respect to a deviation between an air-fuel ratio detected by the downstream exhaust gas sensor and the intermediate target value to a predetermined control range, thereby limiting the upstream control. Calculating a correction amount of the side target air-fuel ratio, wherein the control correction means changes a gain of the proportional integration operation and / or the control range according to a parameter related to an operation state of the internal combustion engine or a state of the catalyst. The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 3, wherein: