JP4305174B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to a catalyst purification device for an internal combustion engine, and more particularly to a device equipped with a bypass catalyst system.

  As an exhaust gas purification apparatus for an internal combustion engine, as shown in FIG. 7, two catalysts (103, 104) are installed in series in an exhaust passage 102, and further provided with a bypass passage 105 that bypasses the upstream side catalyst 103, and upstream when the load is low. On the side catalyst 103 side, there is a so-called bypass catalyst system configured to allow exhaust gas to flow directly into the downstream catalyst 104 via the bypass passage 105 at high load (see, for example, Patent Document 1). Whether the exhaust gas flows into the upstream catalyst 103 or directly into the downstream catalyst 104 via the bypass passage 105 is adjusted by switching the bypass valve 106.

  Further, an air-fuel ratio sensor (107, 108) is provided immediately before the exhaust flow direction of each of the upstream catalyst 103 and the downstream catalyst 104, and when exhaust is flowing into the upstream catalyst 103, immediately before the upstream catalyst 103. Based on the output value of the arranged air / fuel ratio sensor 107, when exhaust gas is directly flowing into the downstream catalyst 104, based on the output value of the air / fuel ratio sensor 108 arranged just before the downstream catalyst 104, The ECU 109 controls the air-fuel ratio in the cylinder.

On the other hand, conventionally, air-fuel ratio sensors have been provided upstream and downstream of the catalyst, and basically the air-fuel ratio in the cylinder is controlled based on the output value of the upstream air-fuel ratio sensor provided upstream. Based on the output value of the air-fuel ratio sensor provided on the side, the variation in the output value of the upstream air-fuel ratio sensor and the influence per gas are corrected.
Japanese Patent Laid-Open No. 10-205374 JP-A-8-240140 Japanese Patent Laid-Open No. 9-16253

  7 also includes air-fuel ratio sensors (107, 108) on the upstream side and the downstream side of the upstream catalyst 103, so that exhaust gas is allowed to flow into the upstream catalyst 103. The air-fuel ratio in the cylinder is controlled based on the output value of the upstream air-fuel ratio sensor 107, and the output of the upstream air-fuel ratio sensor 107 is controlled based on the output value of the downstream air-fuel ratio sensor 108 provided on the downstream side. It is also possible to correct variations in values and effects per gas.

  However, even though the position of the bypass valve 106 is controlled so that the exhaust gas flows only into the upstream catalyst 103 side, the exhaust gas also enters the bypass passage 105 side due to the failure of the bypass valve 106. There is a risk that the gas flows in and passes directly through the downstream air-fuel ratio sensor 108 and the downstream catalyst 104 without passing through the upstream catalyst 103.

  In such a case, when there is a difference between the air-fuel ratio of the exhaust gas that directly passes through the downstream-side air-fuel ratio sensor 108 via the bypass passage 105 and the air-fuel ratio of the exhaust gas that has passed through the upstream catalyst 103. The ECU 109 recognizes that the output value of the downstream air-fuel ratio sensor 108 is the air-fuel ratio of the exhaust gas after passing through the upstream catalyst 103, so that the air-fuel ratio in the cylinder cannot be controlled appropriately.

Similarly, the upstream catalyst 103 can store an appropriate amount of oxygen therein, and when the exhaust gas contains NOx, the NOx is reduced by storing oxygen and the exhaust gas is exhausted. When HC and CO are contained in the catalyst, the O ₂ storage amount cannot be controlled to an appropriate amount if the catalyst can oxidize them by releasing oxygen.

  Further, the bypass valve 106 in the exhaust purification apparatus shown in FIG. 7 switches whether exhaust gas flows into the upstream catalyst 103 or directly flows into the downstream catalyst 104 via the bypass passage 105. From the viewpoint of purification, it is desirable to pass as much exhaust gas as possible through the upstream catalyst within a range in which the performance of the internal combustion engine does not deteriorate due to an increase in exhaust pressure. For this purpose, it is preferable that the amount of exhaust gas flowing through the bypass passage (hereinafter referred to as “bypass gas amount”) can be adjusted according to the operating state of the internal combustion engine.

However, in such a configuration, the air-fuel ratio of the exhaust gas that flows into the downstream catalyst without passing through the upstream catalyst and the exhaust gas that passes through the upstream catalyst and flows into the downstream catalyst is reduced downstream. Since the side air-fuel ratio sensor detects, the air-fuel ratio in the cylinder and the O ₂ storage amount of the upstream catalyst are accurately controlled based on the output values of the both air-fuel ratio sensors provided upstream and downstream of the upstream catalyst. It becomes difficult.

The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a bypass gas amount that can accurately control the air-fuel ratio in the cylinder and the O ₂ storage amount of the upstream catalyst. It is an object of the present invention to provide an exhaust emission control device for an internal combustion engine having an adjustable bypass catalyst system.

Another object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that detects a failure of the bypass valve when the bypass catalyst system is configured to adjust the amount of bypass gas using the bypass valve.

  In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, an upstream catalyst located upstream and provided in series in an exhaust passage of the internal combustion engine and located downstream A bypass catalyst, a bypass passage that bypasses the upstream catalyst and joins another exhaust gas upstream of the downstream catalyst, and a bypass gas that is an exhaust gas flowing through the bypass passage. Bypass gas amount adjusting means for adjusting the amount of exhaust gas, upstream air-fuel ratio detecting means for detecting the air-fuel ratio of exhaust gas provided upstream of the upstream catalyst, upstream of the downstream catalyst and the exhaust gas A downstream air-fuel ratio detection means for detecting an air-fuel ratio of the exhaust gas, a bypass gas amount estimation means for estimating the amount of the bypass gas, and a bypass gas amount estimation device provided downstream of the junction of the passage and the bypass passage. Correcting the detection value of the upstream air-fuel ratio detection means based on the amount of bypass gas estimated by the means, the detection value of the upstream air-fuel ratio detection means and the detection value of the downstream air-fuel ratio detection means, Air-fuel ratio control means for controlling the air-fuel ratio in the cylinder of the internal combustion engine based on the corrected detection value of the upstream air-fuel ratio detection means.

  A bypass passage that bypasses the upstream catalyst and joins another exhaust gas on the upstream side of the downstream catalyst with a part of the exhaust gas, and an amount of the bypass gas that is an exhaust gas flowing through the bypass passage is adjusted. Also in an exhaust purification device having a so-called bypass catalyst system having a bypass gas amount adjusting means, when the bypass gas is adjusted to zero by the bypass gas amount adjusting means, the air-fuel ratio control means, The detection value of the upstream air-fuel ratio detection means provided on the upstream side of the upstream catalyst is corrected based on the detection value of the downstream air-fuel ratio detection means provided on the downstream side, and the corrected upstream air-fuel ratio is corrected. The air-fuel ratio in the cylinder of the internal combustion engine (hereinafter referred to as “engine air-fuel ratio”) can be accurately controlled based on the detection value of the detection means.

In addition, since the engine air-fuel ratio and the air-fuel ratio of the exhaust gas flowing into the upstream catalyst are equal, the upstream catalyst can store an appropriate amount of oxygen therein, and when the exhaust gas contains NOx In the case where the NOx is reduced by occlusion of oxygen and HC and CO are contained in the exhaust gas, the air-fuel ratio is a catalyst that can oxidize them by releasing oxygen. When the control means accurately controls the engine air-fuel ratio, the air-fuel ratio of the exhaust gas flowing into the upstream catalyst can be accurately controlled, and the O ₂ storage amount can be controlled to an appropriate amount.

Further, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, even when the exhaust gas flows through the bypass passage, the amount of bypass gas estimated by the bypass gas amount estimating means is reduced by the air-fuel ratio control means. Based on the detected value of the upstream air-fuel ratio detecting means for detecting the air-fuel ratio of the gas and the detected value of the downstream air-fuel ratio detecting means, the detected value of the upstream air-fuel ratio detecting means is corrected, and the corrected upstream air-fuel ratio is corrected. Since the engine air / fuel ratio is controlled based on the detection value of the fuel ratio detection means, the engine air / fuel ratio or the O ₂ storage amount can be accurately controlled to an appropriate amount.

  Specifically, the air-fuel ratio control means is configured to: (1) the downstream air-fuel ratio detection means based on the amount of bypass gas estimated by the bypass gas amount estimation means and the detected value of the upstream air-fuel ratio detection means. The detection value correction amount of the upstream air-fuel ratio detection means is corrected based on the detected value of the upstream air-fuel ratio detection means, and the upstream air-fuel ratio detection means is corrected based on the corrected correction value of the detection value of the upstream air-fuel ratio detection means. Correct the detection value, or (2) correct the detection value of the downstream air-fuel ratio detection means, and based on the corrected detection value of the downstream air-fuel ratio detection means, the detection value of the upstream air-fuel ratio detection means It is preferable to control the air-fuel ratio in the cylinder of the internal combustion engine based on the corrected detection value of the upstream air-fuel ratio detection means.

  If the amount of bypass gas passing through the downstream side air-fuel ratio detecting means and the air-fuel ratio of the bypass gas can be grasped, the value of the detected value of the downstream side air-fuel ratio detecting means can be grasped because of the influence of the bypass gas. The correction amount of the detection value of the upstream air-fuel ratio detection means based on the detection value of the downstream air-fuel ratio detection means or the detection value of the downstream air-fuel ratio detection means can be corrected.

  The downstream air-fuel ratio detection means is an oxygen concentration sensor that detects an oxygen concentration in the exhaust gas, and the air-fuel ratio control means includes the amount of bypass gas estimated by the bypass gas amount estimation means and the upstream side Based on the amount of oxygen in the bypass gas estimated based on the detection value of the air-fuel ratio detection means, (1) the correction amount of the detection value of the upstream air-fuel ratio detection means based on the detection value of the downstream air-fuel ratio detection means Or (2) correcting the detection value of the downstream air-fuel ratio detection means.

  The bypass gas amount adjusting means includes a bypass valve capable of changing a flow passage area of the bypass passage and a valve opening degree control means for controlling the opening degree of the bypass valve, and the intake air in the cylinder of the internal combustion engine An intake air amount detecting means for detecting the amount of air, and a valve opening degree detecting means for detecting the opening degree of the bypass valve, wherein the bypass gas amount estimating means is a bypass valve detected by the valve opening degree detecting means. It is preferable that the bypass gas amount be estimated based on the opening degree and the intake air amount detected by the intake air amount detection means.

  The amount of bypass gas can be estimated from the opening of the bypass valve and the amount of exhaust gas discharged from the internal combustion engine, and the amount of exhaust gas discharged from the internal combustion engine may be considered to be approximately equal to the amount of intake air. The gas amount can be accurately estimated based on the opening degree of the bypass valve detected by the valve opening degree detection means and the intake air quantity detected by the intake air amount detection means.

In the present invention , the valve opening control means changes the opening of the bypass valve by a predetermined amount when the engine is in steady operation where the rotation speed of the crankshaft of the internal combustion engine is substantially constant. When the amount of change in the detected value of the downstream air-fuel ratio sensor detected while changing by the predetermined amount is smaller than a threshold value, it is detected that the bypass valve has failed.

  Here, the failure of the bypass valve can be exemplified by a case where the valve has a deposit and becomes a resistance of exhaust gas flowing through the bypass passage.

  If the opening of the bypass valve is changed by a predetermined amount during steady operation, the amount of bypass gas that has not reacted with the upstream catalyst fluctuates when the bypass valve is normal. The detection value of the fuel ratio sensor should also fluctuate by a predetermined value accordingly. Therefore, if the change amount of the detected value of the downstream air-fuel ratio sensor detected while the bypass valve changes by a predetermined amount is smaller than the threshold value, it is detected that the actual bypass gas amount has not changed by the predetermined amount. It is possible to reliably detect that a failure such as a deposit is present in the bypass valve. As a result, it is possible to prevent the output performance of the internal combustion engine from being deteriorated due to the increase in the exhaust pressure or the engine air-fuel ratio being erroneously controlled.

As described above, according to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the air-fuel ratio in the cylinder, the O ₂ storage amount of the upstream catalyst, even when the bypass catalyst system capable of adjusting the bypass gas amount is provided. Can be accurately controlled.

  In addition, according to the bypass valve failure detection method of the present invention, it is possible to reliably detect a bypass valve failure.

  The best mode for carrying out the present invention will be exemplarily described in detail below based on the following embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention only to those unless otherwise specified.

A configuration of an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention will be described.
FIG. 1 is a diagram showing a schematic configuration of an exhaust emission control device for an internal combustion engine 1 according to an embodiment of the present invention.

  The internal combustion engine 1 is a spark ignition type internal combustion engine (gasoline engine) using gasoline as fuel, and is an engine mounted on an automobile or the like. In the exhaust passage 2 of the internal combustion engine 1, two catalysts, that is, an upstream catalyst 3 provided on the upstream side of the exhaust passage 2 and a downstream catalyst 4 provided on the downstream side are installed in series.

  The catalysts 3 and 4 can store an appropriate amount of oxygen inside, and when NOx is contained in the exhaust gas, the NOx is reduced by storing oxygen, and HC and When CO is included, it is a three-way catalyst that can oxidize them by releasing oxygen.

Further, the exhaust gas purification apparatus according to the present embodiment has a so-called bypass catalyst system, and branches into the exhaust passage 2 upstream of the upstream catalyst 3, bypassing the upstream catalyst 3 and downstream catalyst 4. The bypass passage 5 is connected so as to join again at the upstream. The bypass passage 5 is provided with a bypass valve 6 capable of changing the flow passage area of the bypass passage 5, and the degree of opening of the bypass valve 6 is controlled by an ECU 15 described later. Therefore, the ECU 15 can adjust the amount of exhaust gas (hereinafter referred to as “bypass gas”) flowing through the bypass passage 5 by controlling the opening of the bypass valve 6, that is, the amount of bypass gas. The bypass valve 6 functions as a bypass gas amount adjusting means.

  When the opening degree of the bypass valve 6 is zero and the flow path of the bypass passage 5 is closed, the exhaust gas does not flow through the bypass passage 5 but flows only into the exhaust passage 2 and is discharged from the internal combustion engine. All of the exhaust gas thus passed passes through the upstream catalyst 3. On the other hand, when the opening degree of the bypass valve 6 is not zero and the flow path of the bypass passage 5 is opened, the amount of the bypass gas corresponding to the opening degree of the bypass valve 6 in the exhaust gas from the internal combustion engine 1 is increased. And the remaining exhaust gas passes through the upstream catalyst 3. Then, upstream of the downstream catalyst 4, the exhaust gas that has passed through the bypass gas and the upstream catalyst 3 merges, and the merged gas passes through the downstream catalyst 4. The exhaust gas that has passed through the upstream catalyst 3 and before joining with the bypass gas is referred to as “pre-merging gas”.

A main A / F sensor 7 (upstream air-fuel ratio detection) having an output characteristic substantially proportional to the air-fuel ratio of the exhaust gas immediately after being discharged from the internal combustion engine 1 is upstream of the branch point of the exhaust passage 2 to the bypass passage 5. Means). Further, downstream of the upstream side catalyst 3 and downstream of the junction of the exhaust passage 2 and the bypass passage 5, a so-called for detecting whether the air-fuel ratio of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio. A sub O ₂ sensor 8 (downstream air-fuel ratio detecting means) which is an oxygen concentration sensor having Z characteristics is provided. The engine basically controls the air-fuel ratio in the cylinder (hereinafter referred to as “engine air-fuel ratio”) based on the output value of the main A / F sensor 7 provided on the upstream side, and the downstream side. This is an engine that performs feedback control for correcting variations in the output value of the main A / F sensor 7 and the influence per gas on the basis of the output value of the sub O ₂ sensor 8 provided in FIG.

  On the other hand, in the intake system, a throttle valve 10 for adjusting the flow rate of air flowing through the intake passage 9 is provided, and its opening degree is controlled by an ECU 15 described later. Then, the air flowing through the air cleaner 11 and flowing into the intake passage 9 is sucked into the cylinder with the flow rate adjusted by the throttle valve 10. An air flow meter 12 as an intake air amount detection means for detecting an intake air amount (GA) is attached to the intake passage 9 downstream of the throttle valve 10.

  Further, a fuel injection valve 13 for injecting fuel into the intake port of the internal combustion engine 1 is provided. When a drive current is applied to the fuel injection valve 13, the fuel injection valve 13 is opened, and a fuel tank (not shown) is opened. The supplied fuel is injected into the intake port.

  Further, the internal combustion engine 1 is provided with a crank position sensor 14 for detecting the rotational phase of the output shaft (crank shaft). A pulse generated from the crank position sensor 14 is input to an ECU 15 to be described later, and the ECU 15 calculates the rotational speed of the crankshaft (hereinafter referred to as “engine speed”) at regular intervals.

  An electronic control unit (ECU: Electronic Control Unit) 15 is provided together with the internal combustion engine including the exhaust purification device having the bypass catalyst system configured as described above.

The ECU 15 includes a main A / F sensor 7, a sub O ₂ sensor 8, an air flow meter 12, a crank position sensor 14, a valve opening sensor (valve opening detecting means) 16 that detects the opening of a bypass valve, and the like. Are electrically connected and their output signals are
5 is input. Further, the bypass valve 6, the throttle valve 10, the fuel injection valve 13, and the like described above are connected to the ECU 15 through electrical wiring, and the ECU 15 outputs a command signal, thereby opening the opening of the bypass valve 6 and the throttle valve 10. The amount of fuel injected from the fuel injection valve 13 can be controlled.

  The engine air-fuel ratio is determined by the amount of gas sucked into the cylinder (the amount of intake air when only air from outside the internal combustion engine is sucked into the cylinder) and the amount of fuel supplied into the cylinder. The ECU 15 capable of controlling the opening of the throttle valve 10 and the fuel injection valve 13 so as to achieve an air-fuel ratio functions as an air-fuel ratio control device (air-fuel ratio control means). Further, since the ECU 15 also controls the opening degree of the bypass valve 6, it functions as a valve opening degree control means.

  Here, in the bypass catalyst system as described above, all the exhaust gas discharged from the internal combustion engine with the opening degree of the bypass valve 6 set to zero in order to more reliably purify the exhaust gas at the time of low load is the upstream side catalyst 3. To pass through. Then, as the required load increases, the opening of the bypass valve 6 is increased so that the load can be met. In other words, the opening degree is set so that the exhaust pressure increases due to the exhaust gas passing through the upstream catalyst 3 so that the output of the internal combustion engine cannot meet the required load. It is determined for each engine speed and load.

  On the other hand, as described above, the upstream catalyst 3 can store an appropriate amount of oxygen therein, and when NOx is contained in the exhaust gas, the NOx is reduced by storing oxygen, Moreover, when exhaust gas contains HC and CO, it is a three-way catalyst that can oxidize them by releasing oxygen.

The O ₂ storage capacity of this three-way catalyst is to store excess oxygen when the exhaust gas is in a lean state, and release the insufficient oxygen when the exhaust gas is in a rich state. Although purifying, this ability is finite. Therefore, in order to effectively use the O ₂ storage capacity, the amount of oxygen occluded in the catalyst (in order that the air-fuel ratio of the exhaust gas may be either the rich state or the lean state next ( It is important to maintain the O ₂ storage amount at a predetermined amount (for example, half of the maximum oxygen storage amount), and if it is maintained as such, a constant O ₂ storage / release action is always possible. As a result, a constant oxidation / reduction ability by the catalyst is always obtained.

In order to maintain the O ₂ storage amount at a predetermined amount, the air-fuel ratio of the exhaust gas discharged from the upstream side catalyst 3 (and hence the air-fuel ratio of the exhaust gas flowing into the upstream side catalyst 3) becomes the stoichiometric air-fuel ratio. It is necessary to control so as to be very close.

Therefore, the air-fuel ratio control apparatus according to the present embodiment relates to the exhaust gas from the internal combustion engine 1 when the opening degree of the bypass valve 6 is zero and all the exhaust gas from the internal combustion engine passes through the upstream catalyst 3. The detection value of the sub O ₂ sensor 8 (that is, the exhaust gas downstream of the upstream catalyst 3) is set so that the detection value of the sub O ₂ sensor 8 which is one of the state quantities becomes a target value substantially corresponding to the theoretical air-fuel ratio. The engine air-fuel ratio is feedback-controlled based on the air-fuel ratio. Since the engine air-fuel ratio and the air-fuel ratio of the exhaust gas upstream of the upstream catalyst 3, that is, the air-fuel ratio detected by the main A / F sensor 7, are equal, the air-fuel ratio control apparatus operates on the upstream side of the upstream catalyst 3. It can be said that the air-fuel ratio of the exhaust gas is feedback controlled.

More specifically, the air-fuel ratio control apparatus, when the detection value of the sub-O ₂ sensor 8 has a value indicative of the air-fuel ratio leaner than the stoichiometric air-fuel ratio, substantially equivalent to the detected value and the theoretical air-fuel ratio of the sub O ₂ sensor 8 The sub-feedback control amount (hereinafter referred to as “sub F / B control amount”) is obtained by proportional / integral processing (PI processing) of the deviation from the target value to be processed, and the main A / The detection value of the F sensor 7 is corrected. As a result, the actual engine air-fuel ratio is set to be apparently leaner than the air-fuel ratio (detected air-fuel ratio) based on the detection value of the main A / F sensor 7.

  Then, a feedback correction amount for adjusting the amount of fuel (fuel injection amount) supplied to the internal combustion engine is calculated so that the corrected apparent air-fuel ratio becomes equal to the target air-fuel ratio which is the stoichiometric air-fuel ratio. The engine air-fuel ratio feedback control is executed by correcting the basic injection amount determined according to the value obtained by dividing the value corresponding to the cylinder intake air amount in the intake stroke by the theoretical air-fuel ratio by the calculated feedback correction amount. To do.

Similarly, when the detected value of the sub O ₂ sensor 8 is a value representing an air / fuel ratio richer than the stoichiometric air / fuel ratio, the deviation between the detected value of the sub O ₂ sensor 8 and the target value substantially corresponding to the stoichiometric air / fuel ratio is proportionally Integration processing (PI processing) is performed to obtain the sub F / B control amount, and the output of the main A / F sensor 7 is corrected by the sub F / B control amount, so that the actual engine air-fuel ratio becomes the main A / F ratio. / F sensor 7 is set so that it is apparently richer than the detected air-fuel ratio, and the amount of fuel supplied to the internal combustion engine (fuel) so that the corrected apparent air-fuel ratio becomes equal to the target air-fuel ratio which is the theoretical air-fuel ratio The basic injection amount determined according to the value obtained by dividing the value corresponding to the in-cylinder intake air amount in one intake stroke of the internal combustion engine by the stoichiometric air-fuel ratio. According to the calculated feedback correction amount By correcting, it executes a feedback control of the engine air-fuel ratio.

When the opening degree of the bypass valve 6 is zero and all the exhaust gas from the internal combustion engine passes through the upstream catalyst 3, the detected air-fuel ratio of the main A / F sensor 7 is detected by the sub O ₂ sensor 8 as described above. By correcting with the air-fuel ratio, the engine air-fuel ratio (the air-fuel ratio of the exhaust gas upstream of the upstream catalyst 3) can be accurately controlled, but if the opening of the bypass valve 6 is not zero, the upstream side Since there exists exhaust gas that passes through the sub-O ₂ sensor 8 without passing through the catalyst 3 and passes through the sub O ₂ sensor 8, that is, bypass gas exists, oxygen consumed by the catalytic reaction when passing through the upstream catalyst 3 is originally Then, it flows through the bypass passage 5 and is detected by the sub O ₂ sensor 8 as it is. As a result, the detected value of the sub O ₂ sensor 8 becomes a value representing the lean air-fuel ratio by the amount of the bypass gas as compared with the case where all of the exhaust gas passes through the upstream side catalyst 3. The amount of fuel (fuel injection amount) supplied to the internal combustion engine is adjusted so that the apparent air-fuel ratio is set to be on the lean side of the bypass gas and the target air-fuel ratio, which is the theoretical air-fuel ratio, is equal. The amount of feedback correction for calculating is calculated.

  Therefore, in the present embodiment, the sub F / B control amount described above is corrected in accordance with the bypass gas amount as described below, and feedback control is executed based on the corrected sub F / B control amount. To.

  Specifically, FIG. 2 shows a flowchart of a control routine for determining the supply fuel amount (fuel injection amount) of the feedback control of the present embodiment. This control routine is stored in advance in the ROM of the ECU 15 and is executed by the ECU 15 as an interrupt process triggered by the passage of a fixed time or the input of a pulse signal from the crank position sensor 14.

  In this routine, first, the ECU 15 detects the opening degree of the bypass valve 6 in step (hereinafter referred to as “S”) 101. This is detected by the valve opening sensor 16.

Thereafter, the process proceeds to S102, and the amount of bypass gas is estimated. This is because there is a correlation as shown in FIG. 3 between the opening of the bypass valve 6, the amount of intake air sucked into the cylinder and the amount of bypass gas, and this relationship derived in advance and stored in the ROM. And the opening degree of the bypass valve 6 detected in S101 and the intake air amount detected by the air flow meter 12. Thus, this step functions as bypass gas amount estimation means.

  Thereafter, the process proceeds to S103, and the amount of oxygen in the bypass gas flowing through the bypass passage 5 is estimated. This is because the air-fuel ratio of the exhaust gas immediately after being discharged from the internal combustion engine, that is, the air-fuel ratio of the bypass gas, can be ascertained from the detected air-fuel ratio of the main A / F sensor 7, so that the air-fuel ratio of the bypass gas and S102 This is estimated from the amount of bypass gas estimated in (1).

  Thereafter, the process proceeds to S104, and a correction value for correcting the sub F / B control amount is calculated. This is because there is a correlation as shown in FIG. 4 between the amount of oxygen in the bypass gas and the correction value. Therefore, this relationship that is derived in advance and stored in the ROM, and the bypass gas estimated in S103. It is calculated based on the amount of oxygen in it. As shown in FIG. 4, when the amount of oxygen in the bypass gas is zero, that is, when the opening degree of the bypass valve 6 is zero, the correction value is zero. The correction value is increased to the rich side.

Thereafter, the process proceeds to S105, and the sub F / B control amount is calculated. This is because the correction value calculated in S104 is the value obtained by proportional / integral processing (PI processing) of the deviation between the detected value of the sub O ₂ sensor 8 and the target value substantially corresponding to the theoretical air-fuel ratio as described above. This is to be corrected.

For example, if the opening degree of the bypass valve 6 is not zero, that is, when the bypass gas passes through the sub-O ₂ sensor 8, the sub-O ₂ sensor 8 air-fuel ratio leaner than the value corresponding to the air-fuel ratio of the pre-merging gas And a value obtained by proportional / integral processing (PI processing) of a deviation between the detected value and a target value substantially corresponding to the theoretical air-fuel ratio is rich by the correction value calculated in S104. Is corrected to the sub-F / B control amount. On the other hand, if the opening degree of the bypass valve 6 is zero, the correction value becomes zero is calculated in S104 also, since the bypass gas does not pass through the sub-O ₂ sensor 8, the sub-O ₂ sensor 8 upstream A value corresponding to the air-fuel ratio of the exhaust gas that has passed through the catalyst 3 is detected. Therefore, a value obtained by proportional / integral processing (PI processing) of the deviation between the detected value of the sub O ₂ sensor 8 and the target value substantially corresponding to the theoretical air-fuel ratio is calculated as the sub F / B control amount. .

  Thereafter, the process proceeds to S106, and the amount of fuel (fuel injection amount) supplied to the internal combustion engine is determined. First, the detection value of the main A / F sensor 7 is corrected by the sub F / B control amount calculated in S105, and the actual engine air-fuel ratio is set. Thereafter, a feedback correction amount for adjusting the amount of fuel supplied to the internal combustion engine is calculated so that the set engine air-fuel ratio becomes equal to the target air-fuel ratio which is the stoichiometric air-fuel ratio. The basic injection amount determined according to the value obtained by dividing the value corresponding to the intake air amount by the stoichiometric air-fuel ratio is determined by correcting with the calculated feedback correction amount.

  When the fuel injection amount is determined as described above, the ECU 15 controls the fuel injection valve 13 to inject the determined fuel amount.

By doing so, the engine air-fuel ratio can be feedback-controlled with high accuracy even in the exhaust purification system provided with the bypass catalyst system. Similarly, the O ₂ storage amount of the upstream catalyst 3 can be controlled to an optimum amount.

In the flowchart shown in FIG. 2, a correction value for further correcting the sub F / B control amount for correcting the detection value of the main A / F sensor 7 is calculated in S104, and the correction value is considered in S105. Thus, the sub F / B control amount is calculated, but the present invention is not particularly limited to this. In S104, the detection value of the sub O ₂ sensor 8 is based on the oxygen amount in the bypass gas estimated in S103. A correction value for correcting itself is calculated. In S105, the deviation between the detection value of the sub O ₂ sensor 8 corrected by the correction value and the target value substantially corresponding to the theoretical air-fuel ratio is proportionally / integrated (PI process). Then, the sub F / B control amount may be calculated. In such a case, a correlation between the amount of oxygen in the bypass gas and the correction value for correcting the detection value of the sub O ₂ sensor 8 is derived in advance and stored in the ROM.

Further, a sub O ₂ sensor 8 that is an oxygen concentration sensor is provided downstream of the upstream catalyst 3 and downstream of the junction of the exhaust passage 2 and the bypass passage 5, but the exhaust gas is used instead of the oxygen concentration sensor. Needless to say, an air-fuel ratio sensor having an output characteristic substantially proportional to the air-fuel ratio of the gas may be provided.

  The feedback control described above is effective when the bypass valve 6 is normal. However, for example, when a deposit exists in the bypass valve 6, even if the bypass valve 6 is open, the deposit becomes a resistance, and there is a difference between the bypass gas amount estimated in S102 and the actual bypass gas amount. Become. In such a case, it is difficult to accurately perform feedback control. Further, since a desired amount of exhaust gas does not flow through the bypass passage 5, the exhaust pressure rises and the desired output performance cannot be obtained.

Therefore, in an internal combustion engine that includes a bypass catalyst system and performs sub-feedback control based on a detection value of the sub O ₂ sensor 8, it is important to detect a failure of the bypass valve 6.

Accordingly, a method for detecting a failure of the bypass valve will be described next. As an outline, when the ECU 15 forcibly drives the bypass valve 6 until the opening degree of the bypass valve 6 becomes zero to the maximum during steady operation, and the change amount of the detection value of the sub O ₂ sensor 8 changed during that time is smaller than the threshold value. Detecting that the bypass valve 6 is out of order.

When the bypass valve 6 is normal, when forcibly driven to the maximum opening degree of the bypass valve 6 from zero to the steady operation, since the amount of bypass gas increases, the detected value of the sub-O ₂ sensor 8 Accordingly, the predetermined value changes to the lean side. Therefore, the fact that the amount of change in the actual detection value of the sub O ₂ sensor 8 is smaller than the predetermined value means that the bypass gas has not increased by a predetermined amount due to the presence of deposit in the bypass valve 6 or the like. To do. The failure detection method for the bypass valve according to the present embodiment uses this property.

  Below, the failure detection method for the bypass valve according to the present embodiment will be described based on the flowchart shown in FIG. This control routine is stored in advance in the ROM of the ECU 15, and is executed by the ECU 15 as an interrupt process triggered by the passage of a fixed time or the input of a pulse signal from the crank position sensor 14.

  In this routine, the ECU 15 first determines in S201 whether or not the operating state of the internal combustion engine 1 is a steady operation. Here, the steady operation refers to a state in which the engine speed is substantially constant (the engine speed fluctuation is within a predetermined range). As a method for determining whether or not the operating state of the internal combustion engine 1 is a steady operation, it is determined whether or not the engine speed calculated based on the pulse from the crank position sensor 14 is substantially constant for a predetermined time. Can be illustrated. If an affirmative determination is made in this step, the process proceeds to S202.

In step S202, the bypass valve 6 is forcibly driven until the opening degree of the bypass valve 6 reaches a maximum from zero. Thereafter, in S203, the amount of change in the detected value of the sub O ₂ sensor 8 detected while forcibly driving the bypass valve 6 until the opening degree of the bypass valve 6 reaches the maximum from zero is calculated.

Thereafter, the process proceeds to S204, and a threshold value for determining whether or not the bypass valve 6 has failed in this step is determined. Here, the threshold value is the amount of change in the detection value of the sub O ₂ sensor 8 when the bypass valve 6 is forcibly driven from zero to the maximum when the bypass valve 6 is normal. The engine speed, the intake air amount, and the air-fuel ratio of the bypass gas are parameters. Such a threshold value is derived in advance for each engine speed, intake air amount, and bypass gas air-fuel ratio, and a map is created and stored in the ROM. Alternatively, it may be a value set smaller than the amount of change in the detected value of the sub O ₂ sensor 8 when the bypass valve 6 is normal, as long as the feedback control is not affected. In this step, values corresponding to the engine speed, the intake air amount, and the air-fuel ratio of the bypass gas detected in the current operating state are determined as threshold values.

Thereafter, the process proceeds to S205, in which it is determined whether or not the amount of change in the detected value of the sub O ₂ sensor 8 calculated in S203 is smaller than the threshold value determined in S204. If a positive determination is made, the process proceeds to S206, and if a negative determination is made, the process proceeds to S207.

  In S206, it is detected that the bypass valve 6 is abnormal, and the execution of this routine is terminated. That the amount of change calculated in S203 is smaller than the threshold value determined in S204 means that the amount of bypass gas is small relative to the degree of opening of the bypass valve 6, which is deposited on the bypass valve 6. This means that there is an abnormality such as the presence of.

  On the other hand, if a negative determination is made in S206, the process proceeds to S207, where it is detected that the bypass valve 6 is normal, and the execution of this routine is terminated. That the amount of change calculated in S203 is equal to or greater than the threshold value determined in S204 means that an appropriate amount of bypass gas is circulating in the opening degree of the bypass valve 6, which means that the bypass valve 6 It means that is normal.

  If a negative determination is made in S201, execution of this routine is terminated. If the internal combustion engine is not in steady operation, that is, if the engine speed fluctuates beyond a predetermined range, is the difference between the amount of change calculated in S203 and the threshold value determined in S204 due to a failure of the bypass valve 6? This is because it is difficult to determine whether it is due to fluctuations in engine speed.

In the above-described bypass valve failure detection method, the amount of change in the detected value of the sub O ₂ sensor 8 is calculated, and whether or not the amount of change is smaller than the threshold is detected to detect an abnormality in the bypass valve 6. However, it is not particularly limited to such a case, and a value obtained by proportional / integral processing (PI processing) of a deviation between the detected value of the sub O ₂ sensor 8 and a target value substantially corresponding to the theoretical air-fuel ratio. It may be determined whether or not the amount of change is smaller than a threshold value.

However, the threshold value in this case is the detection value of the sub O ₂ sensor 8 when the bypass valve 6 is forcibly driven from zero to the maximum when the bypass valve 6 is normal. Is a change amount of a value obtained by proportional / integral processing (PI processing) of a deviation between the target value and the target value substantially corresponding to the theoretical air-fuel ratio, and the engine speed, intake air amount and air-fuel ratio of the bypass gas are parameters. Value. Such a threshold value is derived in advance for each engine speed, intake air amount, and bypass gas air-fuel ratio, and a map is created and stored in the ROM. Or the deviation proportional-integral processing of the target value substantially corresponding to the detection value and the stoichiometric air-fuel ratio of the detected value sub O ₂ sensor 8 sub O ₂ sensor 8 when the bypass valve 6 is normal (PI processing) and A value set smaller than the amount of change of the value obtained in this way as long as it does not affect the feedback control may be used. In S204, values corresponding to the engine speed, the intake air amount, and the air-fuel ratio of the bypass gas detected in the current operating state are determined as threshold values.

Further, in the above-described bypass valve failure detection method, the case where the opening degree of the bypass valve 6 is forcibly driven from zero to the maximum is described. Forcibly driven only by the opening degree may be detected based on whether or not the amount of change in the detected value of the sub O ₂ sensor 8 is smaller than the threshold value. However, in such a case, it is necessary to determine the threshold value using the predetermined opening degree as a parameter in addition to the engine speed, the intake air amount, and the air-fuel ratio of the bypass gas.

  Further, in the above-described bypass valve failure detection method, when it is detected that the bypass valve 6 is abnormal, a warning lamp is turned on to notify a user of a vehicle or the like on which the internal combustion engine 1 is mounted. It is preferable to do so.

It is a figure which shows schematic structure of the exhaust gas purification apparatus of the internal combustion engine which has the bypass catalyst system which concerns on embodiment. It is a figure which shows the flowchart of the control routine for determining supply fuel amount. It is a figure which shows the relationship between a bypass valve opening degree, bypass gas amount, and intake air amount. It is a figure which shows the relationship between the oxygen amount in bypass gas, and the correction value of sub F / B control amount. It is a figure which shows the flowchart of the control routine which concerns on the failure detection method of a bypass valve. It illustrates a detection value of the amount of change in the relationship between the bypass valve opening and the sub-O ₂ sensor. It is a figure which shows schematic structure of the exhaust gas purification apparatus of the internal combustion engine which has a bypass catalyst system which concerns on a prior art.

Explanation of symbols

1 internal combustion engine 2 exhaust passage 3 upstream catalyst 4 downstream catalyst 5 bypass passage 6 the bypass valve 7 main A / F sensor 8 sub _{O 2} sensor 9 intake passage 10 throttle valve 11 an air cleaner 12 air flow meter 13 fuel injection valve 14 a crank position sensor 15 ECU
16 Valve opening sensor

Claims (7)

An upstream catalyst located upstream and a downstream catalyst located downstream, provided in series in the exhaust passage of the internal combustion engine;
A bypass passage that bypasses the upstream catalyst and joins other exhaust gas on the upstream side of the downstream catalyst with a part of the exhaust gas;
Bypass gas amount adjusting means for adjusting the amount of bypass gas that is exhaust gas flowing through the bypass passage;
Upstream air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas provided on the upstream side of the upstream catalyst;
A downstream air-fuel ratio detecting means that is provided upstream of the downstream catalyst and downstream of the junction of the exhaust passage and the bypass passage and detects the air-fuel ratio of the exhaust gas;
A bypass gas amount estimating means for estimating the amount of the bypass gas;
Based on the amount of bypass gas estimated by the bypass gas amount estimating means, the detected value of the upstream air-fuel ratio detecting means, and the detected value of the downstream air-fuel ratio detecting means, the detected value of the upstream air-fuel ratio detecting means Air-fuel ratio control means for controlling the air-fuel ratio in the cylinder of the internal combustion engine based on the corrected detection value of the upstream air-fuel ratio detection means,
An exhaust emission control device for an internal combustion engine, comprising: The air-fuel ratio control means is based on the detected value of the downstream air-fuel ratio detecting means based on the amount of bypass gas estimated by the bypass gas amount estimating means and the detected value of the upstream air-fuel ratio detecting means. Correcting the detection value of the upstream air-fuel ratio detection means, correcting the detection value of the upstream air-fuel ratio detection means based on the corrected correction value of the detection value of the upstream air-fuel ratio detection means, The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio in the cylinder of the internal combustion engine is controlled based on the corrected detection value of the upstream air-fuel ratio detection means. The downstream air-fuel ratio detection means is an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas,
The air-fuel ratio control means is based on the amount of oxygen in the bypass gas estimated based on the amount of bypass gas estimated by the bypass gas amount estimation means and the detected value of the upstream air-fuel ratio detection means. 3. An exhaust emission control device for an internal combustion engine according to claim 2, wherein the correction amount of the detection value of the upstream air-fuel ratio detection means is corrected based on the detection value of the air-fuel ratio detection means. The air-fuel ratio control means corrects the detection value of the downstream air-fuel ratio detection means based on the amount of bypass gas estimated by the bypass gas amount estimation means and the detection value of the upstream air-fuel ratio detection means, The detection value of the upstream air-fuel ratio detection means is corrected based on the corrected detection value of the downstream air-fuel ratio detection means, and the cylinder of the internal combustion engine is corrected based on the corrected detection value of the upstream air-fuel ratio detection means. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio in the engine is controlled. The downstream air-fuel ratio detection means is an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas,
The air-fuel ratio control means is configured to control the downstream side air based on the amount of bypass gas estimated by the bypass gas amount estimation means and the amount of oxygen in the bypass gas estimated based on the detection value of the upstream air-fuel ratio detection means. 5. The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the detection value of the fuel ratio detection means is corrected. The bypass gas amount adjusting means includes a bypass valve capable of changing a flow passage area of the bypass passage and a valve opening degree controlling means for controlling the opening degree of the bypass valve,
An intake air amount detecting means for detecting an intake air amount in a cylinder of the internal combustion engine; and a valve opening degree detecting means for detecting an opening degree of the bypass valve,
The bypass gas amount estimating means estimates the bypass gas amount based on the opening degree of the bypass valve detected by the valve opening degree detecting means and the intake air amount detected by the intake air amount detecting means. An exhaust purification device for an internal combustion engine according to any one of claims 1 to 5, wherein During steady operation in which the rotation speed of the crankshaft of the internal combustion engine is substantially constant, the valve opening control means changes the opening of the bypass valve by a predetermined amount, and the bypass valve changes by the predetermined amount. The exhaust gas purification of an internal combustion engine according to claim 6, wherein when the amount of change in the detected value of the downstream air-fuel ratio sensor detected in (5) is smaller than a threshold value, it is detected that the bypass valve has failed. apparatus.

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