JP2005120870A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device of an internal combustion engine, more positively controling the air-fuel ratio so that the oxygen occulusion state of catalyst is kept in the optimum state. <P>SOLUTION: A fuel oil consumption is feedback controlled using an output signal 100 from an upstream exhaust gas sensor 6 so that the air fuel ratio of exhaust gas flowing into a catalyst 4 agrees with the target air fuel ratio. A signal 110 showing output change in an output sudden change region near the theoretic air fuel ratio taken from an output signal 102 of a downstream exhaust gas sensor 8 by a signal obtaining means 54 is reflected in the feedback correction value 1 in the feedback control. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio of an internal combustion engine in which exhaust gas sensors are arranged on the upstream side and downstream side of the catalyst, respectively, and the fuel supply amount is controlled based on the output signals of these exhaust gas sensors. The present invention relates to a control device.

Conventionally, as disclosed in Patent Document 1, an A / F sensor (wide-area exhaust gas sensor) is disposed on the upstream side of the catalyst, and an O ₂ sensor (oxygen sensor) is disposed on the downstream side of the catalyst. An air-fuel ratio control apparatus that performs feedback control based on an output signal of an exhaust gas sensor is known. The A / F sensor is an exhaust gas sensor showing a linear output characteristic with respect to the air-fuel ratio, and the O ₂ sensor is a so-called Z characteristic in which the output changes suddenly between the rich side and the lean side with respect to the air-fuel ratio. This is an exhaust gas sensor. In such an air-fuel ratio control apparatus including two exhaust gas sensors, fuel injection is performed so that the air-fuel ratio of the exhaust gas flowing into the catalyst becomes the target air-fuel ratio based on the output signal (air-fuel ratio signal) from the A / F sensor. The amount is feedback controlled (hereinafter, this control is referred to as main feedback control). In addition to this main feedback control, control for feeding back the output signal from the O ₂ sensor to the fuel injection amount is also performed (hereinafter, this control is referred to as sub-feedback control).

  The sub feedback control is executed to complement the main feedback control and improve the emission characteristics of the internal combustion engine. The target air-fuel ratio used in the main feedback control is set to an air-fuel ratio at which the catalyst can purify the exhaust gas most efficiently. In the main feedback control, the air-fuel ratio signal from the A / F sensor, the target air-fuel ratio, The feedback correction value is calculated based on the deviation. However, due to the effects of various variations in the internal combustion engine, the actual air-fuel ratio of the exhaust gas may be biased to the rich side or the lean side with respect to the target air-fuel ratio even though the main feedback control is being executed. If such a trend continues, the oxygen storage state of the catalyst will eventually become depleted and HC and CO cannot be purified (when biased to the rich side), or conversely, the oxygen storage state of the catalyst will become saturated. This makes it impossible to purify NOx (when leaning toward the lean side).

The oxygen storage state of the catalyst affects the output of the O ₂ sensor, and when the oxygen storage state of the catalyst becomes a depletion state, the output signal from the O ₂ sensor becomes a rich output. Conversely, when the oxygen storage state of the catalyst becomes saturated, the output signal from the O ₂ sensor becomes a lean output. Therefore, when the output signal from the O ₂ sensor is inverted from the lean output to the rich output, it can be determined that the actual air-fuel ratio of the exhaust gas flowing into the catalyst is biased to the rich side, and conversely from the O ₂ sensor. When the output signal is inverted from the rich output to the lean output, it can be determined that the actual air-fuel ratio is biased toward the lean side.

In the sub-feedback control, the air-fuel ratio correction amount is calculated based on the output signal from the O ₂ sensor, and this air-fuel ratio correction amount is fed back to the main feedback control, so that the air-fuel ratio signal from the A / F sensor and the target air-fuel ratio. And the deviation is corrected. Specifically, in the control device disclosed in Patent Document 1, the air-fuel ratio correction amount is calculated by performing PI control based on the output signal from the O ₂ sensor, and this is added to the target air-fuel ratio to achieve the target. The air-fuel ratio is corrected. According to this, it is possible to bring the deviation between the air-fuel ratio signal from the A / F sensor and the target air-fuel ratio closer to the deviation between the actual air-fuel ratio and the target air-fuel ratio, and the control accuracy of the air-fuel ratio by the main feedback control Can be increased.
Japanese Patent Laid-Open No. 8-291738

The sub-feedback control can be said to be control for maintaining the oxygen storage state of the catalyst in an appropriate state that is neither depleted nor saturated so that the exhaust emission does not deteriorate. If the output signal from the O ₂ sensor is representative of the oxygen storage state of this catalyst, the output signal from the O ₂ sensor is PI-controlled as in the above prior art to calculate the air-fuel ratio correction amount. Is reflected in the main feedback control, so that the oxygen storage state of the catalyst can be converged to an appropriate state.

However, in reality, the output signal from the O ₂ sensor does not represent the oxygen storage state of the catalyst. Figure 9 is a representation of the dynamic characteristics of the O ₂ sensor-catalyst oxygen storage amount (OSA) and O ₂ in relation to the output of the sensor. As can be seen from this figure, the oxygen storage amount in the catalyst and the output of the O ₂ sensor are in a non-linear relationship. Even when the oxygen storage amount is the same, when the oxygen storage state of the catalyst shifts from the depleted state to the saturated state, The output trajectory of the O ₂ sensor is different from when the state shifts to the exhaustion state. For this reason, even if feedback control based on the output signal from the O ₂ sensor is performed as in the above prior art, the oxygen storage state of the catalyst cannot be converged to an appropriate state. The oxygen storage state of the catalyst shifts in order of a depleted state, an appropriate state, a saturated state, and an appropriate state along the circle in FIG.

  In order to improve exhaust emission under the above characteristics, an area where exhaust emission deteriorates (area surrounded by a broken line in FIG. 9) is passed as quickly as possible, and the oxygen storage state of the catalyst is maintained as long as possible. I want to keep it in proper condition.

  The present invention has been made to solve the above-described problems, and is an air-fuel ratio of an internal combustion engine in which the air-fuel ratio can be more actively controlled so that the oxygen storage state of the catalyst is maintained in an appropriate state. An object is to provide a control device.

In order to achieve the above object, a first invention is an air-fuel ratio control apparatus for an internal combustion engine,
An upstream side exhaust gas sensor disposed upstream of the catalyst in the exhaust passage of the internal combustion engine;
A downstream-side exhaust gas sensor having an output characteristic that is disposed downstream of the catalyst, and whose output signal changes suddenly in the vicinity of the theoretical air-fuel ratio with respect to the air-fuel ratio of the exhaust gas;
A signal acquisition means for extracting a signal indicating an output change in an output sudden change region near the theoretical air-fuel ratio from an output signal from the downstream exhaust gas sensor;
Main feedback control means for feedback-controlling the fuel injection amount using an output signal from the upstream exhaust gas sensor so that the air-fuel ratio of the exhaust gas flowing into the catalyst matches the target air-fuel ratio;
Sub-feedback control means for reflecting the output change signal extracted by the signal acquisition means in a feedback correction value in the feedback control;
It is characterized by having.

  In a second aspect based on the first aspect, the signal acquisition means includes differential value calculation means for calculating a differential value of an output signal from the downstream exhaust gas sensor, and the differential value is output to the output change signal. It is used as a feature.

  According to a third aspect, in the second aspect, the signal acquisition unit includes a low-pass filter, and the signal obtained by passing the differential value through the low-pass filter is used as the output change signal.

  In a fourth aspect based on the first aspect, the signal acquisition means includes a high-pass filter, and the output signal from the downstream exhaust gas sensor passed through the high-pass filter is used as the output change signal. It is characterized by.

  Further, a fifth invention is characterized in that, in any one of the first to fourth inventions, the sub-feedback control means corrects an output signal from the upstream side exhaust gas sensor by the output change signal. .

According to a sixth invention, in any one of the first to fourth inventions, the main feedback control means determines a deviation between an output signal from the upstream side exhaust gas sensor and the target air-fuel ratio as a feedback correction value. Including an integral value calculating means for calculating an integral value;
The sub-feedback control means reflects the output change signal in the integral value.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects, when the deviation between the output signal from the downstream side exhaust gas sensor and a reference value exceeds a predetermined range, the deviation corresponds to the deviation. Signal generating means for generating a correction signal;
Air-fuel ratio correction means for correcting an output signal from the upstream side exhaust gas sensor by the correction signal;
Is further provided.

In order to achieve the above object, an eighth invention is an air-fuel ratio control apparatus for an internal combustion engine,
An upstream side exhaust gas sensor disposed upstream of the catalyst in the exhaust passage of the internal combustion engine;
A downstream-side exhaust gas sensor having an output characteristic that is disposed downstream of the catalyst, and whose output signal changes suddenly in the vicinity of the theoretical air-fuel ratio with respect to the air-fuel ratio of the exhaust gas;
A signal acquisition means for extracting a signal indicating an output change in an output sudden change region near the theoretical air-fuel ratio from an output signal from the downstream exhaust gas sensor;
Main feedback control means for feedback-controlling the fuel injection amount using an output signal from the upstream exhaust gas sensor so that the air-fuel ratio of the exhaust gas flowing into the catalyst matches the target air-fuel ratio;
Sub-feedback control means for reflecting the output change signal extracted by the signal acquisition means to the target air-fuel ratio;
It is characterized by having.

In a ninth aspect based on the eighth aspect, the sub-feedback control means includes a determination value calculation means for calculating a determination value for switching the target air-fuel ratio from the output change signal,
And a target air-fuel ratio switching means for switching the target air-fuel ratio to a predetermined correction air-fuel ratio by comparing the determination value with a threshold value.

  When the oxygen storage state of the catalyst becomes exhausted or saturated due to the bias of the air-fuel ratio to the rich side or lean side of the exhaust gas flowing into the catalyst, the output signal from the downstream side exhaust gas sensor changes suddenly. According to the first invention, the signal indicating the output change in the output sudden change region of the downstream side exhaust gas sensor is reflected in the feedback correction value in the main feedback control, so the air-fuel ratio of the exhaust gas flowing into the catalyst is positively controlled. Thus, the oxygen storage state of the catalyst can be quickly shifted from a depleted state or a saturated state to an appropriate state. Further, when the oxygen storage state of the catalyst is in an appropriate state, the output signal from the downstream side exhaust gas sensor is out of the sudden output change range and indicates rich output or lean output, so the output change signal is reflected in the feedback correction value. Therefore, the oxygen storage state of the catalyst is maintained in an appropriate state. Therefore, according to the first invention, the oxygen storage state of the catalyst can be maintained in an appropriate state, and the exhaust emission can be improved.

  According to the second aspect of the invention, by using the differential value of the output signal from the downstream exhaust gas sensor as the output change signal, the output change in the output sudden change region of the downstream exhaust gas sensor is quickly reflected in the feedback correction value. Can be made.

  According to the third aspect of the invention, the output change in the output sudden change region of the downstream exhaust gas sensor is obtained by using, as the output change signal, the differential value of the output signal from the downstream exhaust gas sensor further passed through the low pass filter. Can be continuously reflected in the feedback correction value.

  Further, according to the fourth invention, by using the high-pass filter, it is possible to easily take out the output change in the output sudden change region from the output signal from the downstream side exhaust gas sensor.

  According to the fifth aspect of the invention, by correcting the output signal from the upstream side exhaust gas sensor based on the output change signal, the output change in the output sudden change region of the downstream side exhaust gas sensor can be reliably reflected in the feedback correction value. Can do.

  According to the sixth aspect of the invention, the output change signal is reflected in the integrated value of the deviation between the output signal from the upstream side exhaust gas sensor as the feedback correction value and the target air-fuel ratio, so that the output change of the downstream side exhaust gas sensor suddenly changes. The output change in the region can be reliably reflected in the feedback correction value.

  Further, according to the seventh aspect, when the deviation between the output signal from the downstream exhaust gas sensor and the reference value exceeds a predetermined range, the output signal from the upstream exhaust gas sensor is generated by the correction signal according to the deviation. By correcting, the air-fuel ratio of the exhaust gas flowing into the catalyst can be more positively controlled, and the oxygen storage state of the catalyst can be quickly shifted from the exhausted state or the saturated state to the appropriate state.

  According to the eighth aspect of the invention, since the signal indicating the output change in the output sudden change region of the downstream side exhaust gas sensor is reflected in the target air-fuel ratio in the main feedback control, the air-fuel ratio of the exhaust gas flowing into the catalyst is positively increased. The oxygen storage state of the catalyst can be quickly shifted from a depleted state or a saturated state to an appropriate state. In addition, when the oxygen storage state of the catalyst is in an appropriate state, the output signal from the downstream side exhaust gas sensor is out of the sudden output change range and indicates rich output or lean output, so the output change signal is reflected in the target air-fuel ratio. Therefore, the oxygen storage state of the catalyst is maintained in an appropriate state. Therefore, according to the eighth aspect of the invention, the oxygen storage state of the catalyst can be maintained in an appropriate state, and exhaust emission can be improved.

  According to the ninth aspect of the invention, a determination value for switching the target air-fuel ratio is calculated from the output change signal, and the target air-fuel ratio is switched to a predetermined correction air-fuel ratio by comparing the determination value with a threshold value. Thus, the air-fuel ratio of the exhaust gas flowing into the catalyst can be reliably controlled, and the oxygen storage state of the catalyst can be quickly shifted from a depleted state or a saturated state to an appropriate state.

Embodiment 1 FIG.
The first embodiment of the present invention will be described below with reference to FIG.
FIG. 1 is a block diagram showing a configuration of an air-fuel ratio control apparatus according to Embodiment 1 of the present invention. As shown in FIG. 1, the air-fuel ratio control apparatus of this embodiment includes an A / F sensor 6 as an upstream side exhaust gas sensor upstream of the catalyst 4 disposed in the exhaust passage of the internal combustion engine 2, and downstream of the catalyst 4. Further, it is configured as a double sensor system provided with an O ₂ sensor 8 as a downstream exhaust gas sensor. The A / F sensor 6 is an exhaust gas sensor that detects the air-fuel ratio of the exhaust gas flowing into the catalyst 4 from the internal combustion engine 2, and the O ₂ sensor 8 is the air-fuel ratio state (lean or rich) of the exhaust gas that flows out of the catalyst 4. ) Is an exhaust gas sensor.

The air-fuel ratio control apparatus of this embodiment includes a main feedback control unit 10 that feeds back the air-fuel ratio signal 100 from the A / F sensor 6 to the fuel injection amount, and an output signal 102 from the O ₂ sensor 8 that is fed into the main feedback control unit 10. And a sub-feedback control unit 50 for reflecting the feedback correction value. The air-fuel ratio control apparatus according to the present embodiment is particularly characterized in the content of sub feedback control by the sub feedback control unit 50.

  First, the configuration of the main feedback control unit 10 and the content of the main feedback control by the main feedback control unit 10 will be described.

  The air-fuel ratio signal 100 from the A / F sensor 6 is corrected by a sub-feedback control unit 50 described later, and the corrected air-fuel ratio signal 116 is input to the main feedback control unit 10. The input air-fuel ratio signal 116 is converted from a voltage value to an air-fuel ratio 118 in the conversion map 12.

  The air-fuel ratio 118 output from the conversion map 12 is input to the dividing unit 14 together with the intake air amount 122. The intake air amount 122 is obtained by processing the intake air amount signal (Mc) 120 from an air flow meter (not shown) by the signal processing unit 16. An arithmetic expression shown in the frame of the signal processing unit 16 in FIG. 1 is a transfer function of a dead time element, and L indicates a time from passing through the air flow meter until being sucked into the cylinder. In the dividing unit 14, the actual fuel injection amount 126 is calculated by dividing the intake air amount 122 by the air-fuel ratio 118. Further, in another division unit 18, the target fuel injection amount 128 is calculated by dividing the intake air amount 122 by the MFB target value (target air-fuel ratio) 124. The target fuel injection amount 128 and the actual fuel injection amount 126 are compared by the comparison unit 20, and a deviation fuel amount 130 that is a deviation between the target fuel injection amount 128 and the actual fuel injection amount 126 is calculated from the comparison unit 20.

The main feedback control unit 10 includes a main FB controller 22. The main FB controller 22 is a means for calculating a fuel correction amount 132 as a feedback correction value from the deviation fuel amount 130. The main FB controller 22 performs PI control on the deviation fuel amount 130 input from the comparison unit 20 and calculates a fuel correction amount 132. An arithmetic expression shown in the frame of the main FB controller 22 in FIG. 1 is a transfer function for PI control, Gp _mfb represents a proportional gain of the P term, and Gi _mfb represents an integral gain of the I term.

  The fuel correction amount 132 calculated by the PI control by the main FB controller 22 is added to the base injection amount 150 by the adding unit 26. The base injection amount 150 is calculated from the MFB target value 124. When the deviation fuel amount 130 is positive, that is, when the actual fuel injection amount 126 is smaller than the MFB target value 124, the fuel correction amount 132 is positive (the final fuel injection amount 154 obtained by adding the fuel correction amount 132 to the base injection amount 150). In the direction of increasing On the contrary, when the deviation fuel amount 130 is negative, that is, when the actual fuel injection amount 126 is larger than the MFB target value 124, it is updated in the negative direction (the direction in which the final fuel injection amount 154 is decreased).

  Next, the configuration of the sub-feedback control unit 50, which is a characteristic part of the air-fuel ratio control apparatus of the present embodiment, and the contents of the sub-feedback control by the sub-feedback control unit 50 will be described.

The sub-feedback control unit 50 has a function of reflecting the output signal 102 from the O ₂ sensor 8 in the fuel correction amount (feedback correction value) 132 in the main feedback control unit 10. In the sub feedback control unit 50, the output signal 102 from the O ₂ sensor 8 is first input to the comparison unit 52. In the comparison unit 52, the output signal 102 from the O ₂ sensor 8 is compared with an SFB target value (reference value) 104 that is an output value corresponding to the theoretical air-fuel ratio, and the SFB target value 104 and the output signal from the O ₂ sensor 8. An output deviation 106 with respect to 102 is output. The SFB target value 104 is an output value corresponding to the stoichiometric air-fuel ratio. When the air-fuel ratio of the exhaust gas flowing out from the catalyst 4 is rich, the output signal 102 from the O ₂ sensor 8 has a value larger than the SFB target value 104. Conversely, a small value is shown when lean. Therefore, the output deviation 106 becomes a negative value when the air-fuel ratio of the exhaust gas flowing out from the catalyst 4 is rich, and becomes a positive value when the air-fuel ratio of the exhaust gas flowing out from the catalyst 4 is lean.

The sub feedback control unit 50 includes a sub FB controller 54. The output deviation 106 output from the comparison unit 52 is input to the sub FB controller 54. The sub FB controller 54 is a means for calculating the sub FB correction amount 110 as the air-fuel ratio correction amount based on the input output deviation 106. In this embodiment, the sub FB controller 54 calculates the sub FB correction amount 110 by ID control. That is, P control is not performed as in the prior art, and D control for calculating the differential value of the output deviation 106 is performed. 1 is a transfer function for ID control, Gi _sfb is an integral gain of the I term (integral term), and Gd _sfb is a derivative of the D term (differential term). Each gain is shown. In the present embodiment, the integral gain Gi _sfb is set lower than the differential gain Gd _sfb .

The calculated sub FB correction amount 110 includes an I term and a D term, and both are added to the air-fuel ratio signal 100 from the A / F sensor 6 in the adder 56. The I term of the sub FB correction amount 110 indicates the steady component of the output deviation 106, that is, the steady deviation of the output signal 102 from the O ₂ sensor 8 with respect to the SFB target value 104. By adding the I term of the sub FB correction amount 110, the air-fuel ratio signal 100 from the A / F sensor 6 is compensated for variations in its control center.

On the other hand, the D term of the sub FB correction amount 110 is a differential value of the output deviation 106 and indicates a change rate of the output deviation 106, in other words, a change rate of the output signal 102 from the O ₂ sensor 8. For this reason, when the change in the output signal 102 from the O ₂ sensor 8 is small, the D term is almost zero, and when the output signal 102 from the O ₂ sensor 8 changes greatly, the D term is in the positive or negative direction. Increase.

The output signal 102 from the O ₂ sensor 8 has dynamic characteristics as shown in FIG. 9 as described above, and suddenly changes from lean output to rich output when the oxygen storage state of the catalyst 4 becomes depleted. When it reaches saturation, it suddenly changes from rich output to lean output. When the oxygen storage state of the catalyst 4 is in an appropriate state, the output signal 102 from the O ₂ sensor 8 shows a substantially constant lean output or rich output. Since the O ₂ sensor 8 has such dynamic characteristics, the D term of the sub FB correction amount 110 temporarily changes in the negative direction when the oxygen storage state of the catalyst 4 becomes depleted, and When the oxygen storage state is saturated, it temporarily changes in the positive direction. Further, when the oxygen storage state of the catalyst 4 is in an appropriate state, the D term is substantially zero.

  By adding the D term to the air-fuel ratio signal 100 from the A / F sensor 6 according to the change characteristic of the D term with respect to the oxygen occlusion state of the catalyst 4 as described above, the following effects can be obtained. First, when the oxygen storage state of the catalyst 4 is depleted, the air-fuel ratio signal 100 from the A / F sensor 6 is temporarily corrected to decrease to the negative side (lean side) by the action of the D term. As the air-fuel ratio signal 110 is temporarily corrected to decrease, the fuel correction amount 132 calculated based on the corrected air-fuel ratio signal 116 is temporarily set to decrease. As a result, the exhaust air-fuel ratio is temporarily corrected to the lean side, and the oxygen storage state of the catalyst 4 quickly shifts from the exhausted state to the appropriate state.

  Conversely, when the oxygen storage state of the catalyst 4 becomes saturated, the air-fuel ratio signal 110 from the A / F sensor 6 is temporarily corrected to increase to the positive side (rich side) by the action of the D term. As the air-fuel ratio signal 110 is temporarily increased and corrected, the fuel correction amount 132 calculated based on the corrected air-fuel ratio signal 116 is temporarily increased. As a result, the exhaust air-fuel ratio is temporarily corrected to the rich side, and the oxygen storage state of the catalyst 4 quickly shifts from the saturated state to the appropriate state.

As described above, according to the air-fuel ratio control apparatus of the present embodiment, the signal indicating the output change in the output sudden change region of the O ₂ sensor 8 is extracted as the D term of the sub FB correction amount 110 by the D control. Since the term is reflected in the fuel correction amount 132, the exhaust air-fuel ratio can be positively controlled in a situation where the oxygen storage state of the catalyst 4 is in a depleted state or a saturated state. As a result, the oxygen storage state of the catalyst 4 can be quickly shifted from the exhausted state or the saturated state to the appropriate state. Further, when P control is performed as in the prior art, the air-fuel ratio signal 100 from the A / F sensor 6 is corrected according to the output deviation 106 even when the oxygen storage state of the catalyst 4 is in an appropriate state. However, according to the air-fuel ratio control apparatus of this embodiment, when the output signal from the O ₂ sensor 8 indicates a rich output or a lean output, the D term indicates substantially zero. Is not corrected, the air-fuel ratio signal 100 from the A / F sensor 6 is not corrected. That is, according to the air-fuel ratio control apparatus of the present embodiment, the oxygen storage state of the catalyst 4 can be maintained in an appropriate state, and exhaust emission can be improved.

  In the embodiment described above, the main feedback control unit 10 corresponds to the “main feedback control unit” of the first invention, and the sub feedback control unit 50 corresponds to the “sub feedback control unit” of the first invention. It corresponds to. The sub FB controller 54 of the sub feedback control unit 50 corresponds to the “signal acquisition unit” of the second invention.

Embodiment 2. FIG.
Hereinafter, Embodiment 2 of the present invention will be described with reference to FIGS.
FIG. 2 is a block diagram showing a configuration of an air-fuel ratio control apparatus according to Embodiment 2 of the present invention. In FIG. 2, parts that are the same as those in the first embodiment are given the same reference numerals, and redundant descriptions thereof are omitted.

The air-fuel ratio control apparatus according to the present embodiment differs from the air-fuel ratio control apparatus according to the first embodiment in the configuration of the sub-feedback control unit 60, particularly the configuration of the sub-FB controller 62. As shown in FIG. 2, the sub FB controller 62 includes an ID control unit 64, a dead zone map 66, and a P control unit 68. The output deviation 106 between the SFB target value 104 calculated by the comparison unit 52 and the output signal 102 from the O ₂ sensor 8 is input to the ID control unit 64 and the dead zone map 66 in parallel.

The ID control unit 64 has the same function as the sub feedback control unit 54 in the first embodiment. That is, the ID control unit 64 performs ID control on the output deviation 106 to calculate an I term that is a steady component of the output deviation 106 and a D term that is a differential value of the output deviation 106. An arithmetic expression shown in the frame of the ID control unit 64 in FIG. 2 is a transfer function for ID control, Gi _sfb indicates an integral gain of the I term, and Gd _sfb indicates a differential gain of the D term. The ID control unit 64 outputs an ID signal 160 that is a sum of the I term and D term.

  The dead zone map 66 and the P control unit 68 are characteristic parts of the air-fuel ratio control apparatus of the present embodiment. In the first embodiment, the oxygen storage state of the catalyst 4 can be maintained in an appropriate state by performing the D control without performing the P control. However, in the present embodiment, under the predetermined condition, By performing the P control, a higher effect can be obtained. The dead zone map 66 defines the execution conditions for the P control.

  Specifically, the dead zone map 66 is set as shown in FIG. In FIG. 3, the horizontal axis indicates the value of the output deviation 106 input to the dead zone map 66, and the vertical axis indicates the value of the output signal 162 from the dead zone map 66. As shown in FIG. 3, the output deviation 106 is a dead band between “SFB target value−OXSL” and “SFB target value−OXSH”, and the output signal 162 becomes zero. When the output deviation 106 becomes larger than “SFB target value−OXSL”, the output signal 162 increases in proportion to the increase amount of the output deviation 106, and the output deviation 106 becomes larger than “SFB target value−OXSH”. When it becomes smaller, the output signal 162 decreases in proportion to the decrease amount of the output deviation 106.

Thus, the dead zone is provided for the output deviation 106 for the following reason. As shown in FIG. 9, when the oxygen storage state of the catalyst 4 is depleted, the output signal 102 from the O ₂ sensor 8 suddenly changes from lean output to rich output, but the oxygen storage state of the catalyst 4 is in an appropriate state. Until this time, the output signal 102 from the O ₂ sensor 8 is a strong rich output. On the contrary, when the oxygen storage state of the catalyst 4 becomes depleted, the output signal 102 from the O ₂ sensor 8 suddenly changes from rich output to lean output, but until the oxygen storage state of the catalyst 4 becomes an appropriate state. The output signal 102 from the O ₂ sensor 8 is a strong lean output. Therefore, when the output signal 102 from the O ₂ sensor 8 is strongly rich (0.8 V or higher in FIG. 9) or strongly lean (0.1 V or lower in FIG. 9), the oxygen storage state of the catalyst 4 is not in an appropriate state. Can be determined. The above OXSH is a strong rich threshold that can be determined that the oxygen storage state of the catalyst 4 is in a depleted state, and OXSL is a strong lean threshold that can be determined that the oxygen storage state of the catalyst 4 is in a saturated state.

The P control unit 68 performs P control on the output signal 162 from the dead zone map 66 to calculate a P term that is a proportional value. An arithmetic expression shown in the frame of the P control unit 68 in FIG. 2 is a transfer function for P control, and Gp _sfb represents a proportional gain of the P term. The P control unit 68 outputs a P signal 164 corresponding to the P term. By setting the dead zone map 66 as described above, the P signal 164 becomes zero when the output signal 102 from the O ₂ sensor 8 is within the range of OXSH to OXSL. When the output signal 102 from the O ₂ sensor 8 exceeds OXSH, it decreases in accordance with the magnitude of the deviation from OXSH, and when the output signal 102 from the O ₂ sensor 8 falls below OXSL, the deviation from OXSL is reduced. Increases with size.

  In the air-fuel ratio control apparatus of the present embodiment, the sum value of the ID signal 160 from the ID control unit 64 and the P signal 164 from the P control unit 68 is the sub FB correction amount. Both the ID signal 160 and the P signal 164 are input to the adder 56 and added to the air-fuel ratio signal 100 from the A / F sensor 6. As a result, the air-fuel ratio signal 100 from the A / F sensor 6 is also corrected by the P term in addition to the correction by the D term as in the first embodiment.

  By adding the P term to the air-fuel ratio signal 100 from the A / F sensor 6 in addition to the D term, the following effects can be obtained. First, when the oxygen storage state of the catalyst 4 is depleted, the air-fuel ratio signal 100 from the A / F sensor 6 is temporarily corrected to decrease to the negative side (lean side) by the action of the D term, and further P By the action of the term, it is temporarily corrected to decrease more negatively. As a result, the exhaust air / fuel ratio is temporarily more strongly corrected to the lean side, and the oxygen storage state of the catalyst 4 shifts more quickly from the exhausted state to the appropriate state as compared with the first embodiment. When the oxygen storage state of the catalyst 4 becomes saturated, the air-fuel ratio signal 110 from the A / F sensor 6 is temporarily increased and corrected to the positive side (rich side) by the action of the D term. Due to the action, the increase is temporarily corrected to the positive side. As a result, the exhaust air-fuel ratio is temporarily temporarily corrected to the rich side, and the oxygen storage state of the catalyst 4 quickly shifts from the saturated state to the appropriate state.

As described above, according to the air-fuel ratio control apparatus of the present embodiment, when the output deviation 106 between the SFB target value 104 and the output signal 102 from the O ₂ sensor 8 exceeds the predetermined range, Since the air-fuel ratio signal 100 from the A / F sensor is corrected by the P term proportional to the magnitude of the deviation, the exhaust air-fuel ratio is more actively increased in a situation where the oxygen storage state of the catalyst 4 is in a depleted state or a saturated state. Can be controlled. As a result, the oxygen storage state of the catalyst 4 can be quickly shifted from the exhausted state or the saturated state to the appropriate state.

  In the above-described embodiment, the main feedback control unit 10 corresponds to the “main feedback control unit” of the first invention, and the sub feedback control unit 60 corresponds to the “sub feedback control unit” of the first invention. It corresponds to. The ID control unit 64 of the sub-feedback control unit 60 corresponds to the “signal acquisition unit” of the second invention. The dead zone map 66 corresponds to the “signal generating means” of the eighth invention, and the P control unit 68 corresponds to the “air-fuel ratio correcting means” of the eighth invention.

Embodiment 3 FIG.
Hereinafter, Embodiment 3 of the present invention will be described with reference to FIG. 4 and FIG.
FIG. 4 is a block diagram showing a configuration of an air-fuel ratio control apparatus according to Embodiment 3 of the present invention. In FIG. 4, parts that are the same as those in the first embodiment are given the same reference numerals, and redundant descriptions thereof are omitted.

In the air-fuel ratio control apparatus of the first embodiment, the sub FB correction amount 110 is calculated as a signal indicating an output change in the output sudden change region of the O ₂ sensor 8, and the sub FB correction amount 110 is calculated from the A / F sensor 6. By adding to the fuel ratio signal 100, the output change signal is reflected in the fuel correction amount 132 as a feedback correction value in the main feedback control. The air-fuel ratio control apparatus of the present embodiment is different from the first embodiment in the method of reflecting the output change signal in the feedback correction value, and the characteristic configuration associated with this difference is the main of the main feedback control unit 30. The FB controller 32 and the sub FB controller 72 of the sub feedback control unit 70 are provided.

As shown in FIG. 4, the sub FB controller 72 includes a D control unit 74 and an I control unit 76. This is equivalent to the sub feedback control unit 54 according to the first embodiment divided into a function for performing D control and a function for performing I control. The D control unit 74 performs D control on the output deviation 106 to calculate a D term that is a differential value of the output deviation 106. The I control unit 76 performs I control on the output deviation 106, thereby calculating an I term that is a steady component of the output deviation 106. The arithmetic expression shown in the frame of the D control unit 74 in FIG. 2 is a transfer function for D control, and the arithmetic expression shown in the frame of the I control unit 76 is a transfer function for I control. Gd _sfb represents the differential gain of the D term, and Gi _sfb represents the integral gain of the I term. The D control unit 74 outputs a D signal 170 corresponding to the D term, and the I control unit 76 outputs an I signal 172 corresponding to the I term.

  A combination of the D signal 170 and the I signal 172 corresponds to the sub FB correction amount 110 in the first embodiment. In the first embodiment, the entire sub FB correction amount 110 is input to the adding unit 56. However, in this embodiment, only the I signal 172 is input to the adding unit 56 and the air-fuel ratio signal from the A / F sensor 6 is input. It is added to 100. Thereby, the variation of the control center of the air-fuel ratio signal 100 from the A / F sensor 6 is compensated. The main feedback control unit 30 calculates the deviation fuel amount 130 to be input to the main FB controller 32 based on the corrected air-fuel ratio signal 116 in which the variation of the control center is compensated.

In the present embodiment, the D signal 170 output from the D control unit 74 is an output change signal indicating an output change in the output sudden change region of the O ₂ sensor 8. In the present embodiment, the D signal 170 is input to the main FB controller 32. The main FB controller 32 includes a P control unit 34, an I control unit 36, and a summing unit 38. The main FB controller 32 as a whole performs PI control. The deviation fuel amount 130 output from the comparison unit 20 is input to the P control unit 34 and the I control unit 36 in parallel. The D signal 170 from the D control unit 74 is input to the I control unit 36.

The P control unit 34 performs P control on the deviation fuel amount 130 input from the comparison unit 20 and calculates a P term that is a proportional value. An arithmetic expression shown in the frame of the P control unit 34 in FIG. 4 is a transfer function for P control, and Gp _mfb represents a proportional gain of the P term. The P control unit 34 outputs a P signal 174 corresponding to the P term.

The I control unit 36 performs I control on the deviation fuel amount 130 input from the comparison unit 20, thereby calculating an I term that is a steady component of the deviation fuel amount 130. In the present embodiment, the D signal 170 from the D control unit 74 is reflected in the calculation of the I term. Hereinafter, a method for calculating the I term in the I control unit 36 will be described. 4 is a transfer function for I control, and Gi _mfb represents an integral gain of the I term.

First, in the D control unit 74, the D signal 170 is calculated by the following equation (1).
sfbd (k) = (doxs (k) −doxs (k−1)) * Gd _sfb (1)
In the above equation (1), sfbd is the D signal (D term) 170, and doxs is the output deviation 106. K in each term means that the term is the current value (calculated value in the current cycle), and k-1 means the previous value (calculated value in the previous cycle). The output deviation 106 is calculated by the comparison unit 52 by the following equation (2).
doxs (k) = SFBref (k) −OXS (k) (2)
In the above equation (2), SFBref is the SFB target value 104, and OXS is the output signal 102 from the O ₂ sensor 8.

The I control unit 36 calculates the I term by the following equation (3).
sdfc (k) = sdfc (k-1) + dfc (k) + sfbd (k) (3)
In the above equation (3), dfc is the deviation fuel amount 130, and sdfc is an integral value of dfc and sfbd. The sdfc multiplied by the gain Gi _mfb is the I term calculated by the I control unit 36. That is, the I control unit 36 calculates the I term by integrating the deviation fuel amount 130 and the D signal 170 from the D control unit 74. From the I control unit 36, an I signal 176 corresponding to the I term is output.

  The P signal 174 from the P control unit 34 and the I signal 176 from the I control unit 36 are added together by the adding unit 38. In this embodiment, the total value becomes the fuel correction amount 178 as a feedback correction value, and is added to the base injection amount 150 by the adding unit 24. That is, in the present embodiment, the output change signal is reflected in the feedback correction value by integrating the D signal 170 that is the output change signal together with the deviation fuel amount 130.

By reflecting the output change signal in the feedback correction value by the method as described above, the air-fuel ratio control apparatus of the present embodiment can obtain the following effects. Hereinafter, the effect of the air-fuel ratio control apparatus of this embodiment will be described with reference to FIG. FIG. 5 is a diagram showing a control behavior by the air-fuel ratio control apparatus of the present embodiment. 5 is the time change of the air-fuel ratio signal 100 from the A / F sensor 6, the second stage OXS is the time change of the output signal 100 from the O ₂ sensor 8, and the third stage sfbd is The time change of the D signal 170 from the D control unit 74 and the lowermost sdfc indicate the time change of the I signal 176 from the I control unit 36, and the time axes of the respective graphs coincide. Here, it is assumed that A / F indicates a lean output on the upper side and a rich output on the lower side, while OXS indicates a rich output on the upper side and a lean output on the lower side. Further, sfbd and sdfc are assumed to have negative values on the upper side and positive values on the lower side.

As shown in this figure, when OXS changes from lean output to rich output, sfbd temporarily increases in the negative direction according to the change rate. In the first embodiment, so to speak, this sfbd is directly reflected in the feedback correction value, but as shown in the figure, the change in sfbd is an instantaneous change. In the first embodiment, the output change of the O ₂ sensor 8 can be reflected in the feedback correction value only at the moment when sfbd changes. In order to correct the fuel injection amount in such a short reflection time and to optimize the oxygen storage state of the catalyst 4, it is necessary to set the gain Gd _sfb for setting sfbd to a very high gain. However, from the viewpoint of combustion, the air-fuel ratio has an appropriate range, and the fuel injection amount must be corrected to the extent that the air-fuel ratio falls within the appropriate range. For this reason, when the fuel injection amount cannot be sufficiently corrected in relation to the appropriate range of the air-fuel ratio, there is a possibility that the optimization cannot be made as quickly as intended.

  On the other hand, in this embodiment, sdfc is used for setting the feedback correction value. By incorporating sfbd into the integration, sdfc gradually increases in the negative direction according to the magnitude of sfbd, and the A / F becomes leaner as the sdfc increases in the negative direction due to the action of the main feedback control. It will be corrected. As A / F is corrected to the lean side, sdfc gradually attenuates due to the action of the main feedback control. As a result, as shown in the figure, the change in sdfc continues for a long time even after sfbd has attenuated. Therefore, by using sdfc for setting the feedback correction value, the influence of sfbd can be continuously reflected in the feedback correction value rather than sfbd itself.

As described above, according to the air-fuel ratio control apparatus of the present embodiment, the O ₂ sensor 8 is obtained by reflecting the D signal 170 that is the output change signal in the calculation of the I term of the fuel correction amount 178 that is the feedback correction value. The output change in the output sudden change region can be continuously reflected in the feedback correction value. As a result, the fuel injection amount can be corrected as much as intended within the appropriate range of the air-fuel ratio, and the oxygen storage state of the catalyst 4 can be reliably and quickly shifted from the exhausted state or the saturated state to the appropriate state. Can be made.

Further, since the fuel injection amount is determined by the air-fuel ratio and the intake air amount, in the first embodiment, even when the sub FB correction amount 110 having the same value is added to the air-fuel ratio signal 100, the final fuel correction is performed depending on the operation state. The amount will be different. However, according to the air-fuel ratio control apparatus of the present embodiment, the fuel correction amount is calculated directly from the D signal 170 that is the output change signal, so that it corresponds to the output change of the O ₂ sensor 8 regardless of the operating state. A fuel correction amount can be obtained.

  In the embodiment described above, the main feedback control unit 30 corresponds to the “main feedback control means” of the sixth invention, and the sub feedback control unit 70 corresponds to the “sub feedback control means” of the sixth invention. It corresponds to. Further, the D control unit 74 of the sub feedback control unit 70 corresponds to the “signal acquisition unit” of the second invention.

Embodiment 4 FIG.
Hereinafter, a fourth embodiment of the present invention will be described with reference to FIGS.
FIG. 6 is a block diagram showing a configuration of an air-fuel ratio control apparatus according to Embodiment 4 of the present invention. In FIG. 4, parts that are the same as those in the first embodiment are given the same reference numerals, and redundant descriptions thereof are omitted.

The air-fuel ratio control apparatus of the present embodiment can obtain the effect that the output change in the output sudden change region of the O ₂ sensor 8 obtained in the third embodiment can be continuously reflected in the feedback correction value with a simpler configuration. It is intended to be. The air-fuel ratio control apparatus of the present embodiment is characterized by the configuration of the sub-feedback control unit 80, particularly the configuration of the sub-FB controller 82, as will be described below.

As shown in FIG. 6, the sub FB controller 82 includes a D control unit 84, a low pass filter 86, and an I control unit 88. D control unit 84 and I control unit 88 are equivalent to those obtained by dividing sub feedback control unit 54 in the first embodiment into a function for performing D control and a function for performing I control. The output deviation 106 between the SFB target value 104 calculated by the comparison unit 52 and the output signal 102 from the O ₂ sensor 8 is input to the D control unit 84 and the I control unit 88 in parallel.

The D control unit 84 performs D control on the output deviation 106, thereby calculating a D term that is a differential value of the output deviation 106. The I control unit 88 performs I control on the output deviation 106 to calculate an I term that is a steady component of the output deviation 106. The arithmetic expression shown in the frame of the D control unit 84 in FIG. 6 is a transfer function for D control, and the arithmetic expression shown in the frame of the I control unit 88 is a transfer function for I control. Gd _sfb represents the differential gain of the D term, and Gi _sfb represents the integral gain of the I term. The D control unit 84 outputs a D signal 180 corresponding to the D term, and the I control unit 88 outputs an I signal 184 corresponding to the I term.

  A combination of the D signal 180 and the I signal 184 corresponds to the sub FB correction amount 110 in the first embodiment. In the first embodiment, the entire sub FB correction amount 110 is input to the adder 56 as it is, but in this embodiment, the D signal 180 is input to the adder 56 after passing through the low-pass filter 86. That is, the I signal 184 and the low-pass processed D signal 182 are added to the air-fuel ratio signal 100 from the A / F sensor 6. The arithmetic expression shown in the frame of the low-pass filter 86 in FIG. 6 is a transfer function indicating the configuration of the low-pass filter, and a first-order lag element is used here as the low-pass filter. T represents the response time constant of the low-pass filter. The transfer function shown here is merely an example of a low-pass filter, and a low-pass filter represented by another transfer function may be used.

By performing low-pass processing without adding the D signal 180 to the air-fuel ratio signal 100 as it is, according to the air-fuel ratio control apparatus of the present embodiment, the following effects can be obtained. Hereinafter, the effect of the air-fuel ratio control apparatus of this embodiment will be described with reference to FIG. FIG. 7 is a diagram showing a control behavior by the air-fuel ratio control apparatus of the present embodiment. 7 indicates the time change of the output signal 100 from the O ₂ sensor 8, and the lower sfbd and sfbd ′ indicate the time change of the D signal 180 before the low pass (sfbd, indicated by a dotted line), and after the low pass. A time change (sfbd ′, indicated by a solid line) of the D signal 182 is also shown. The upper and lower graphs have the same time axis. In addition, it is assumed that OXS indicates rich output on the upper side and lean output on the lower side, and sfbd and sfbd ′ indicate negative values on the upper side and positive values on the lower side.

  As shown in this figure, when OXS changes from lean output to rich output, sfbd before the low pass temporarily increases in the negative direction according to the rate of change. The change in sfbd before the low pass is an instantaneous change, and is attenuated immediately after a large rise. On the other hand, the change of sfbd 'after the low pass is slow, slowly increases in the negative direction with the change of OXS, and then slowly decays. That is, even after sfbd before the low pass is attenuated, the change of sfbd ′ after the low pass continues for a long time. Therefore, as in this embodiment, by adding the low-pass D signal 182 to the air-fuel ratio signal 100, the influence of the D signal 180 is continuously reflected in the air-fuel ratio signal 100 rather than the D signal 180 itself before the low-pass. Can be made.

As described above, according to the air-fuel ratio control apparatus of the present embodiment, the third embodiment has a simple configuration in which the D signal 180 that is the differential value of the output signal 100 from the O ₂ sensor 8 is passed through the low-pass filter 86. Similarly to the above, it is possible to continuously reflect the output change in the output sudden change region of the O ₂ sensor 8 in the feedback correction value.

  In the above-described embodiment, the main feedback control unit 10 corresponds to the “main feedback control unit” of the first invention, and the sub feedback control unit 80 corresponds to the “sub feedback control unit” of the first invention. It corresponds to. Further, the D control unit 84 and the low-pass filter 86 of the sub feedback control unit 80 correspond to the “signal acquisition unit” of the third invention.

Embodiment 5 FIG.
Hereinafter, a fifth embodiment of the present invention will be described with reference to FIG.
In Embodiments 1 to 4 described above, the output change signal is reflected in the feedback correction value, but the same effect can be obtained by reflecting the output change signal in the target air-fuel ratio.

  Although not shown in the drawings, the air-fuel ratio control apparatus of the present embodiment includes a main feedback control unit and a sub-feedback control unit as in the other embodiments. The main feedback control unit has a configuration in which the target air-fuel ratio (MFB target value) can be switched in the configuration of the main feedback control unit 10 in the first embodiment. In this embodiment, a target air-fuel ratio for normal control, a target air-fuel ratio for rich correction (RA / F), and a target air-fuel ratio for lean correction (LA / F) are set as the target air-fuel ratio. . The rich correction target air-fuel ratio is set to be richer than the normal target air-fuel ratio, and the lean correction target air-fuel ratio is set to be leaner than the normal target air-fuel ratio.

Similar to the other embodiments, the sub-feedback control unit has a function of D-controlling at least the reference air-fuel ratio (SFB target value) and the output deviation of the output signal from the O ₂ sensor. The sub feedback control unit calculates a control determination term for switching the target air-fuel ratio from the D term calculated by the D control.

  In the present embodiment, this control determination term is calculated by integrating the D term and the deviation fuel amount, respectively, similarly to sdfc in the third embodiment. However, this control determination term is merely a determination value for switching the target air-fuel ratio, and does not itself become a feedback correction value like sdfc in the third embodiment. The control judgment term includes a lean control threshold and a rich control threshold that determine the upper and lower limits of the appropriate range.When the control judgment term exceeds the lean control threshold, the sub-feedback control unit When the target air-fuel ratio for correction is switched to within the appropriate range, the normal target air-fuel ratio is switched. Further, when the control determination term exceeds the rich control threshold, the target air-fuel ratio is switched to the rich correction target air-fuel ratio, and when it returns to the appropriate range, it is switched to the normal target air-fuel ratio. Although the D term itself can be used as the control determination term, since the change in the D term is an instantaneous change, the target air-fuel ratio may not be switched for a sufficient time. Therefore, in the present embodiment, the control determination term is calculated by the same method as sdfc in the third embodiment so that the influence of the D term can be continued as described above.

FIG. 8 shows the above control behavior in a time chart. The uppermost part of FIG. 8 shows the time change of the air-fuel ratio signal (A / F) from the A / F sensor and the setting of the target air-fuel ratio (target A / F). The second row shows the time change of the output signal (OXS) from the O ₂ sensor. The third row shows the time change of the D term (sub-FB differential term), and the bottom row shows the time change of the control determination term. The time axis of each graph is the same. Here, it is assumed that the upper part of the A / F and the target A / F indicates a lean output and the lower part indicates a rich output, and OXS indicates that the upper part indicates a rich output and the lower part indicates a lean output. Further, it is assumed that the D term and the control determination term indicate a negative value at the top and a positive value at the bottom.

  As shown in this figure, when OXS changes from lean output to rich output, the D term temporarily increases in the negative direction according to the rate of change. The control determination term gradually increases in the negative direction according to the magnitude of the D term, and when the lean control threshold is exceeded, the target air-fuel ratio is switched from the normal target air-fuel ratio to the lean correction target air-fuel ratio. Since the base injection amount is determined by the target air-fuel ratio and the intake air amount, the base injection amount is reduced according to the target air-fuel ratio by correcting the target air-fuel ratio to the lean side. As a result, the actual air-fuel ratio shifts to the lean side, sufficient oxygen is supplied to the catalyst, and the oxygen storage state of the catalyst is quickly optimized.

  After the D term is attenuated, the control determination term is gradually attenuated by the action of the main feedback control. The attenuation speed at this time is a speed corresponding to the amount of intake air. When the control determination term eventually falls below the lean control threshold, the target air-fuel ratio is switched again from the lean correction target air-fuel ratio to the normal target air-fuel ratio. The same behavior is exhibited when OXS changes from rich output to lean output, and the target air-fuel ratio is switched from the normal target air-fuel ratio to the target air-fuel ratio for rich correction according to the movement of the control judgment term, and the normal target air-fuel ratio is again displayed. Switched to fuel ratio.

As described above, according to the air-fuel ratio control apparatus of the present embodiment, the exhaust air-fuel ratio can be reliably controlled by reflecting the output change in the output sudden change region of the O ₂ sensor in the target air-fuel ratio. The oxygen storage state of the catalyst can be reliably and promptly shifted from a depleted state or a saturated state to an appropriate state. In particular, by using the control judgment term that dulls the D term instead of the D term itself as a judgment value for switching the target air-fuel ratio, the output change in the sudden change region of the O ₂ sensor is controlled more continuously. Can be reflected. As a result, as in the third embodiment, the fuel injection amount can be reliably corrected, and the oxygen storage state of the catalyst can be reliably and quickly shifted from the exhausted state or the saturated state to the appropriate state. .

  In the above-described embodiment, the function of performing the D control of the sub-feedback control unit corresponds to the “signal acquisition unit” of the eighth invention. The main feedback control unit corresponds to the “main feedback control unit” of the eighth invention, and the function of the sub feedback control unit described in FIG. 8 corresponds to the “sub feedback control unit” of the eighth invention. doing.

Others.
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, the above-described embodiments can be combined with each other. The configuration that corrects the air-fuel ratio signal by the P term subjected to the dead-zone process, which is a technical feature of the second embodiment, can be applied to both the configuration of the third embodiment and the configuration of the fifth embodiment. The configuration that is a technical feature of the fourth embodiment and that performs low-pass processing of the output change signal can also be applied to the configurations of the second, third, and fifth embodiments.

  In the first embodiment, the sub FB controller performs ID control, but PID control can also be performed. In this case, however, the proportional gain of the P control must be set to an extremely small value compared to the differential gain of the D control, like the integral gain of the I control. In the present invention, D control is important, and when performing I control or P control, it is necessary to set the magnitude of each gain so as not to impair the effects obtained by D control. The same applies to other embodiments.

Further, in the respective embodiments described above, the output signal from the O ₂ sensor are fetched output change signal by controlling D, the output change signal by passing the output signal from the O ₂ sensor to a high pass filter Can be obtained. By passing the high-pass filter, a sudden change in the vicinity of the theoretical air-fuel ratio is extracted as a signal from the output signal from the O ₂ sensor. In this case, the high-pass filter corresponds to the “signal acquisition means” of the fourth invention.

Furthermore, in this embodiment, the A / F sensor is used as the upstream side exhaust gas sensor, but an O ₂ sensor may be used similarly to the downstream side exhaust gas sensor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining a configuration of an air-fuel ratio control apparatus for an internal combustion engine as Embodiment 1 of the present invention. It is a figure for demonstrating the structure of the air fuel ratio control apparatus of the internal combustion engine as Embodiment 2 of this invention. It is a figure which shows an example of a dead zone map used in Embodiment 2 of this invention. It is a figure for demonstrating the structure of the air fuel ratio control apparatus of the internal combustion engine as Embodiment 3 of this invention. It is a time chart which shows the control behavior of the air fuel ratio control apparatus of the internal combustion engine as Embodiment 3 of this invention. It is a figure for demonstrating the structure of the air fuel ratio control apparatus of the internal combustion engine as Embodiment 4 of this invention. It is a time chart which shows the effect of the low pass filter used in Embodiment 4 of this invention. It is a time chart which shows the control behavior of the air fuel ratio control apparatus of the internal combustion engine as Embodiment 5 of this invention. The dynamic characteristics of the O ₂ sensor is a graph showing the relationship between the output of the catalyst in the oxygen storage amount and O ₂ sensor.

Explanation of symbols

2 Internal combustion engine 4 Catalyst 6 A / F sensor 8 O ₂ sensor 10 Main feedback control unit 12 Conversion map 22 Main FB controller 30 Main feedback control unit 32 Main FB controller 34 P control unit 36 I control unit 38 Summation unit 50 Sub feedback control Unit 52 comparison unit 54 sub FB controller 56 addition unit 60 sub feedback control unit 62 sub FB controller 64 ID control unit 66 dead zone map 68 P control unit 70 sub feedback control unit 72 sub FB controller 74 D control unit 76 I control unit 80 sub Feedback control unit 82 Sub FB controller 84 D control unit 86 Low pass filter 88 I control unit

Claims (9)

An upstream side exhaust gas sensor disposed upstream of the catalyst in the exhaust passage of the internal combustion engine;
A downstream-side exhaust gas sensor having an output characteristic that is disposed downstream of the catalyst, and whose output signal changes suddenly in the vicinity of the theoretical air-fuel ratio with respect to the air-fuel ratio of the exhaust gas;
A signal acquisition means for extracting a signal indicating an output change in an output sudden change region near the theoretical air-fuel ratio from an output signal from the downstream exhaust gas sensor;
Main feedback control means for feedback-controlling the fuel injection amount using an output signal from the upstream exhaust gas sensor so that the air-fuel ratio of the exhaust gas flowing into the catalyst matches the target air-fuel ratio;
Sub-feedback control means for reflecting the output change signal extracted by the signal acquisition means in a feedback correction value in the feedback control;
An air-fuel ratio control apparatus for an internal combustion engine, comprising:   The internal combustion engine according to claim 1, wherein the signal acquisition means includes differential value calculation means for calculating a differential value of an output signal from the downstream side exhaust gas sensor, and uses the differential value as the output change signal. Air-fuel ratio control device.   3. The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the signal acquisition means includes a low-pass filter, and uses the differential value further passed through the low-pass filter as the output change signal.   2. The air-fuel ratio of the internal combustion engine according to claim 1, wherein the signal acquisition unit includes a high-pass filter, and uses the output change signal obtained by passing the output signal from the downstream exhaust gas sensor through the high-pass filter as the output change signal. Control device.   The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the sub-feedback control unit corrects an output signal from the upstream side exhaust gas sensor based on the output change signal. The main feedback control means includes an integral value calculating means for calculating an integral value of a deviation between an output signal from the upstream side exhaust gas sensor and the target air-fuel ratio as a feedback correction value,
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the sub-feedback control means reflects the output change signal in the integral value. A signal generating means for generating a correction signal corresponding to the deviation when a deviation between an output signal from the downstream exhaust gas sensor and a reference value exceeds a predetermined range;
Air-fuel ratio correction means for correcting an output signal from the upstream side exhaust gas sensor by the correction signal;
The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 6, further comprising: An upstream side exhaust gas sensor disposed upstream of the catalyst in the exhaust passage of the internal combustion engine;
A downstream-side exhaust gas sensor having an output characteristic that is disposed downstream of the catalyst, and whose output signal changes suddenly in the vicinity of the theoretical air-fuel ratio with respect to the air-fuel ratio of the exhaust gas;
A signal acquisition means for extracting a signal indicating an output change in an output sudden change region near the theoretical air-fuel ratio from an output signal from the downstream exhaust gas sensor;
Main feedback control means for feedback-controlling the fuel injection amount using an output signal from the upstream exhaust gas sensor so that the air-fuel ratio of the exhaust gas flowing into the catalyst matches the target air-fuel ratio;
Sub-feedback control means for reflecting the output change signal extracted by the signal acquisition means to the target air-fuel ratio;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: The sub-feedback control means; a determination value calculation means for calculating a determination value for switching the target air-fuel ratio from the output change signal;
9. The air-fuel ratio control apparatus for an internal combustion engine according to claim 8, further comprising target air-fuel ratio switching means for switching the target air-fuel ratio to a predetermined correction air-fuel ratio by comparing the determination value with a threshold value.

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