JP5195714B2 - Inter-cylinder air-fuel ratio variation detection device - Google Patents

Description

  The present invention relates to an inter-cylinder air-fuel ratio variation detecting device that detects an abnormality in variation in air-fuel ratio between cylinders in an internal combustion engine having a plurality of cylinders.

  In an internal combustion engine having a plurality of cylinders, the exhaust air-fuel ratio of each cylinder is measured by a single air-fuel ratio sensor arranged at the junction of the exhaust passage of each cylinder, and the variation in the exhaust air-fuel ratio between the cylinders is measured from the measured value. There is known air-fuel ratio control for calculating and reducing variation in the operating air-fuel ratio of each cylinder based on the calculation result (see, for example, Patent Document 1).

JP 2004-11435 A

By the way, when the air-fuel ratio changes relative to only one cylinder among a plurality of cylinders, the exhaust air-fuel ratio measured by the single air-fuel ratio sensor fluctuates. For example, in the case of a four-cylinder internal combustion engine, the fluctuation of the exhaust air-fuel ratio occurs at a cycle of a crank angle of 720 °, and the waveform is close to a sine wave.
Here, in a pair of cylinders such as the outer two cylinders and the inner two cylinders in an in-line four-cylinder internal combustion engine, when one air-fuel ratio is lean and the other air-fuel ratio is rich, the waveform of the air-fuel ratio fluctuation is approximate. There is a case. For this reason, it is difficult to identify which of the paired cylinders is the cylinder that causes the exhaust air-fuel ratio to fluctuate.

  In view of the above circumstances, the present invention not only determines the variation of the exhaust air-fuel ratio between cylinders using a single air-fuel ratio sensor, but also identifies the cylinder that causes the exhaust air-fuel ratio to fluctuate. It is another object of the present invention to provide an inter-cylinder air-fuel ratio variation detecting device that can also be used.

  In order to achieve the above object, an inter-cylinder air-fuel ratio variation detecting apparatus according to the present invention is detected by an air-fuel ratio detecting means provided at an exhaust gas merging portion of an internal combustion engine having a plurality of cylinders, and the air-fuel ratio detecting means. Based on the deviation of the detected value from the reference value, air-fuel ratio change degree calculating means for calculating the change degree of the air-fuel ratio, and based on the change degree calculated by the air-fuel ratio change degree calculating means, A variation abnormality detecting means for detecting an abnormality in fuel ratio variation, wherein the variation abnormality detecting means is between 720 ° CA in which the maximum absolute value of the degree of change calculated by the air-fuel ratio change degree calculating means is detected. Based on the phase, the cylinder that causes the air-fuel ratio variation abnormality among the plurality of cylinders is identified.

In the above-described inter-cylinder air-fuel ratio variation detecting device, the variation abnormality detecting means causes the air-fuel ratio variation abnormality based on the positive or negative of the maximum value of the absolute value of the degree of change calculated by the air-fuel ratio change degree calculating means. It may be determined whether the air-fuel ratio is deviated to the rich side or the lean side for the cylinder in question.
In the above-described inter-cylinder air-fuel ratio variation detecting device, the variation abnormality detecting unit includes a determining unit that determines whether or not the degree of change calculated by the air-fuel ratio change degree calculating unit exceeds a predetermined threshold. When it is determined by the means that the degree of change has exceeded the predetermined threshold, it may be determined that the air-fuel ratio varies among the plurality of cylinders.

In the inter-cylinder air-fuel ratio variation detecting device according to another invention of the present application, an air-fuel ratio detecting means provided in an exhaust gas merging portion of an internal combustion engine having a plurality of cylinders, and a detection value detected by the air-fuel ratio detecting means Based on the deviation from the reference value, the air-fuel ratio change degree calculating means for calculating the air-fuel ratio change degree, and the air-fuel ratio variation abnormality among the plurality of cylinders based on the change degree calculated by the air-fuel ratio change degree calculating means Variation abnormality detecting means for detecting the variation abnormality detecting means, wherein the variation abnormality detecting means detects the phase at which the maximum absolute value of the degree of change calculated by the air-fuel ratio change degree calculating means is detected, and the degree of change. based on the positive or negative maximum value of the absolute value, the air-fuel ratio after the variation was primary determining determine an abnormality factors and going on the cylinder, from the reference value of the detected value detected by the air-fuel ratio detecting means The absolute value of the maximum value is detected phase difference and, on the basis of the sign of the maximum absolute value of the deviation, performs secondary determination to determine the cylinder that is a cause of the abnormal air-fuel ratio variation, these Based on the combination of the determination results of the primary and secondary determinations , the cylinder that causes the air-fuel ratio variation abnormality among the plurality of cylinders is determined.

  In the inter-cylinder air-fuel ratio variation detecting device, the air-fuel ratio change degree calculating means calculates an average value of the detected values detected by the air-fuel ratio detecting means between intake and exhaust of the internal combustion engine. The value may be the reference value.

  According to the above-described inter-cylinder air-fuel ratio variation detection device, not only the variation in the exhaust air-fuel ratio among cylinders can be detected using a single air-fuel ratio sensor, but also the cylinder that causes the exhaust air-fuel ratio to fluctuate is specified. You can also

1 is a schematic diagram showing a four-cycle in-line four-cylinder engine to which an inter-cylinder air-fuel ratio variation detecting device according to an embodiment is applied. 5 is a flowchart for explaining the presence / absence of variation in exhaust air-fuel ratio between cylinders and the process of determining a target cylinder in the inter-cylinder air-fuel ratio variation detection device. It is a graph which shows the waveform of the exhaust air-fuel ratio detected by the air-fuel ratio sensor. It is a graph which shows the waveform of the exhaust air-fuel ratio detected by the air-fuel ratio sensor. It is a graph which shows the waveform of the exhaust air-fuel ratio detected by the air-fuel ratio sensor. (A)-(E) is a graph which shows the waveform of the exhaust air-fuel ratio detected by the air-fuel ratio sensor. (A), (B) is a graph which shows the change degree of the deviation of an exhaust air fuel ratio.

Embodiments of the present invention will be described below.
FIG. 1 is a schematic diagram showing a four-cycle in-line four-cylinder engine (internal combustion engine) 100 to which an inter-cylinder air-fuel ratio variation detecting device 10 according to an embodiment is applied. As shown in this figure, in engine 100, four cylinders 102A (# 1), 102B (# 2), 102C (# 3), 102D (# 4) arranged in a row, intake passage 104, An exhaust passage 106, a catalyst 108, and an ECU (Electronic Control Unit) 110 are provided.

  The intake passage 104 includes an intake manifold 112 and four intake ports 114A, 114B, 114C, 114D branched from the intake manifold 112. An air flow meter 115 is disposed upstream of the intake manifold 112 in the intake passage 104. The intake ports 114A to 114D are connected to the cylinders 102A to 102D (# 1 to 4), respectively, and the fuel injection valves 116A, 116B, 116C, and 116D are arranged in the intake ports 114A to 114D, respectively. It is installed. Fuel injection valves 116 </ b> A to 116 </ b> D inject an amount of fuel calculated by ECU 110 to each cylinder 102 </ b> A to D (# 1 to 4) based on the amount of air measured by air flow meter 115.

  The exhaust passage 106 includes four exhaust ports 118A, 118B, 118C, and 118D connected to the cylinders 102A to 102D (# 1 to 4), respectively, and an exhaust manifold 120 where the four exhaust ports 118A to 118D join. And. An air-fuel ratio sensor 122 is disposed at the junction of the four exhaust ports 118A to 118D. The air-fuel ratio sensor 122 detects the exhaust air-fuel ratio as a continuously changing physical quantity based on the oxygen concentration in the exhaust, and transmits it to the ECU 110.

Here, in engine 100 that is a four-cycle four-cylinder engine, one process has a crank angle of 720 ° (720 ° CA), and the exhaust process of each cylinder is shifted by a crank angle of 180 ° (180 ° CA).
The inter-cylinder air-fuel ratio variation detection device 10 includes the ECU 110 and the air-fuel ratio sensor 122 described above. The ECU 110 includes a control circuit 130 that controls the ECU 110, a RAM (storage unit) 124 that stores the value of the exhaust air / fuel ratio A / F measured by the air / fuel ratio sensor 122, and the exhaust air / fuel ratio A / F stored in the RAM 124. Based on the value of F, the arithmetic circuit 126 that performs various arithmetic operations, and based on the arithmetic results of the arithmetic circuit 126, it is determined whether or not the exhaust air-fuel ratio varies among the cylinders 102A to D (# 1 to 4), and the exhaust gas And a determination circuit 128 that determines a cylinder (hereinafter referred to as a target cylinder) that causes a variation in the air-fuel ratio.

Hereinafter, in the inter-cylinder air-fuel ratio variation detection device 10, the presence or absence of variation in the exhaust air-fuel ratio between the cylinders 102A to D (# 1 to 4) and the determination processing of the target cylinder are determined by the flowchart of FIG. This will be described with reference to the graph of FIG. 3 showing the waveform of the measured exhaust air-fuel ratio.
As shown in the flowchart of FIG. 2, first, at step 100, the control circuit 130 is measured by the air-fuel ratio sensor 122 at every predetermined crank angle CAn (for example, 30 ° CA as shown in the graph of FIG. 3). The exhaust air-fuel ratio A / F (indicated by white dots in the graph of FIG. 3) is stored in the RAM 124.

  Next, at step 102, the arithmetic circuit 126 determines a specific crank angle CAtdc (for example, compression of each cylinder) of each cylinder 102A (# 1), 102B (# 2), 102C (# 3), 102D (# 4). Every time the top dead center is 5 ° CA), the average value A / Fave of the exhaust air-fuel ratio A / F of all the cylinders between 720 ° CA 360 ° CA before that time (the white graph in FIG. 3) (Shown with triangles). Then, the control circuit 130 stores the calculated average value A / Fave of the exhaust air / fuel ratio A / F in the RAM 124 as the average value A / Fave of the exhaust air / fuel ratio A / F of all the cylinders at that time.

Here, a straight line (shown by a broken line in the graph of FIG. 3) connecting the average value A / Fave between 720 CAs (determination target period) before the determination time point (CAtdc) is the average value A / F in the determination target period. It is the trajectory of Fave. In step 104, the control circuit 130 calculates a linear function representing the locus of the average value A / Fave and stores it in the RAM 124.
Next, as shown in the graph of FIG. 4, in step 106, the arithmetic circuit 126, for each crank angle CAtdc, is 360 ° CA before each time point (shown by a white star in the graph of FIG. 4). A deviation ΔA / F between the exhaust air-fuel ratio A / F and the average value A / Fave between the previous 180 ° CA is calculated, and the calculation result is stored in the RAM 124. Here, the deviation ΔA / F is a deviation between the average value A / Fave obtained from a linear function representing the locus of the average value A / Fave for each crank angle CAn and the exhaust air / fuel ratio A / F having the same phase. .

  Next, as shown in the graph of FIG. 5, in step 108, the arithmetic circuit 126, for each crank angle CAtdc, before the time 360 ° CA before the time (indicated by a white star in the graph of FIG. 5). The degree of change dA / F of the deviation ΔA / F between 180 CA is calculated and stored in the RAM 124. Here, the degree of change of the deviation ΔA / F is a time differential value of the deviation ΔA / F.

  Here, FIGS. 6A to 6D show 720 ° CA when the air-fuel ratio of any one of the cylinders 102A to 102D (# 1 to # 4) becomes relatively lean or rich. It is a graph which shows the characteristic of deviation (DELTA) A / F in between. FIG. 6E is a graph showing the characteristic of the deviation ΔA / F between 720CA when the air-fuel ratio of the cylinders 102A to 102D (# 1 to 4) is in the stoichiometric (theoretical air-fuel ratio) state.

  The graph on the left side of FIG. 6A shows that the air-fuel ratio of the cylinder 102A (# 1) becomes lean, and the graph on the right side of FIG. 6A shows that the air-fuel ratio of the cylinder 102A (# 1) becomes rich. The characteristic of deviation ΔA / F between 720 ° CA is shown. Similarly, the graphs on the left side of FIGS. 6B to 6D show the case where the air-fuel ratio of the cylinders 102C (# 3), 102D (# 4), and 102B (# 2) becomes lean, respectively. The graphs on the right side of (B) to (D) show deviations between 720 ° CA when the air-fuel ratios of the cylinders 102C (# 3), 102D (# 4), and 102B (# 2) become rich. The characteristic of ΔA / F is shown.

  As shown in the graphs of FIGS. 6A to 6D, the variation of ΔA / F occurs at a period of 720 ° CA, and the waveform approximates a sine wave. Further, as can be seen by comparing the left and right graphs, the ΔA / F fluctuation waveform is reversed between positive and negative when the air-fuel ratio of each cylinder 102A to 102D (# 1 to 4) is lean and rich. become. Further, ΔA / F varies when the air-fuel ratio of the cylinder 102A (# 1) is lean, when the air-fuel ratio of the cylinder 102C (# 3) is lean, and when the air-fuel ratio of the cylinder 102C (# 3) is lean. And when the air-fuel ratio of the cylinder 102D (# 4) is lean, and when the air-fuel ratio of the cylinder 102D (# 4) is lean and when the air-fuel ratio of the cylinder 102B (# 2) is lean, respectively. The phase difference is as follows. Similarly, the change in ΔA / F is caused when the air-fuel ratio of the cylinder 102C (# 3) is rich and when the air-fuel ratio of the cylinder 102C (# 3) is rich, the air-fuel ratio of the cylinder 102C (# 3) is rich. When the air-fuel ratio of the cylinder 102D (# 4) is rich, and when the air-fuel ratio of the cylinder 102D (# 4) is rich and when the air-fuel ratio of the cylinder 102B (# 2) is rich, 180 ° CA With a phase difference of minutes.

  Here, when the air-fuel ratio of the outer two cylinders 102A (# 1) and 102D (# 4) out of the four cylinders 102A to D (# 1 to 4) arranged in series becomes rich or lean The deviation ΔA / F between 720CA is examined. As shown in the left graph of FIG. 6A, when the air-fuel ratio of the cylinder 102A (# 1) becomes lean, and as shown in the right graph of FIG. 6C, cylinder 102D (# 4). ) In which the air-fuel ratio becomes rich, the difference ΔA / F is small in the same phase, and the waveform of the deviation ΔA / F is approximate. Further, as shown in the graph on the right side of FIG. 6A, when the air-fuel ratio of the cylinder 102A (# 1) becomes rich, and as shown in the graph on the left side of FIG. 6C, the cylinder 102D ( When the air-fuel ratio of # 4) becomes lean, the difference ΔA / F is small in the same phase, and the waveform of the deviation ΔA / F is approximate.

  Such a tendency is caused when the air-fuel ratio of the cylinder 102C (# 3) becomes lean and when the air-fuel ratio of the cylinder 102B (# 2) becomes rich (the graph on the left side of FIG. 6B and FIG. 6). (See the graph on the right side of (D)), and when the air-fuel ratio of the cylinder 102C (# 3) becomes rich and when the air-fuel ratio of the cylinder 102B (# 2) becomes lean (FIG. 6B). The same applies to the graph on the right side and the graph on the left side of FIG.

For this reason, which of the outer two cylinders 102A (# 1) and 102D (# 4) causes the exhaust air-fuel ratio to fluctuate, or the inner two cylinders 102B (# 2) and 102C ( It is difficult to identify which cylinder of # 3) is a factor that fluctuates the exhaust air-fuel ratio based only on the deviation ΔA / F.
Here, the air-fuel ratio of the outer two cylinders 102A (# 1) and 102D (# 4) out of the four cylinders 102A to D (# 1 to # 4) arranged in series becomes rich or lean. In this case, the degree of change dA / F of the deviation ΔA / F between 720CA is examined. As shown in the graph on the left side of FIG. 6A, when the air-fuel ratio of the cylinder 102A (# 1) becomes lean, the deviation ΔA / F changes from the negative maximum value to the positive maximum value. The change degree dA / F of the deviation ΔA / F is larger than the change degree dA / F of the deviation ΔA / F when the deviation ΔA / F changes from the positive maximum value to the negative maximum value. On the other hand, as shown in the graph on the right side of FIG. 6C, when the air-fuel ratio of the cylinder 102D (# 4) becomes rich, ΔA / F changes from the negative maximum value to the positive maximum value. The degree of change of the deviation ΔA / F is smaller than the degree of change dA / F of the deviation ΔA / F when the deviation ΔA / F changes from the positive maximum value to the negative maximum value.

  Then, as shown in the graph on the left side of FIG. 6A and the graph on the right side of FIG. 6C, the deviation ΔA / F when the deviation ΔA / F changes from the negative maximum value to the positive maximum value. The degree of change dA / F is greater when the air-fuel ratio of the cylinder 102A (# 1) becomes lean than when the air-fuel ratio of the cylinder 102D (# 4) becomes rich. On the other hand, the change degree dA / F of the deviation ΔA / F when the deviation ΔA / F changes from the positive maximum value to the negative maximum value is obtained when the air-fuel ratio of the cylinder 102D (# 4) becomes rich. The air-fuel ratio of the cylinder 102A (# 1) becomes larger than when lean.

  As shown in the graph on the right side of FIG. 6A and the graph on the left side of FIG. 6C, when the air-fuel ratio of the cylinder 102A (# 1) becomes rich and when the cylinder 102D (# 4) Similarly, even when the air-fuel ratio becomes lean, the change rate dA / F of the deviation ΔA / F when the deviation ΔA / F changes from the negative maximum value to the positive maximum value is larger in the former case. The change degree dA / F of the deviation ΔA / F when the deviation ΔA / F changes from the positive maximum value to the negative maximum value is larger in the latter case.

Further, as shown in the left side graph of shown in FIG. 6 (B) right side of the graph and FIG 6 (D) of the deviation when the deviation .DELTA.A / F varies from a maximum negative value to a positive maximum value .DELTA.A / The change degree dA / F of F becomes larger when the air-fuel ratio of the cylinder 102B (# 2) becomes lean than when the air-fuel ratio of the cylinder 102C (# 3) becomes rich. On the other hand, the change degree dA / F of the deviation ΔA / F when the deviation ΔA / F changes from the positive maximum value to the negative maximum value is obtained when the air-fuel ratio of the cylinder 102C (# 3) becomes rich. The air-fuel ratio of the cylinder 102B (# 2) becomes larger than when lean.

Incidentally, as shown in the right side graph on the left side of the graph and FIG 6 (D) of FIG. 6 (B), and when the air-fuel ratio of the cylinder 102B (# 2) becomes rich, the cylinder 102C (# 3 ), When the deviation ΔA / F changes from the negative maximum value to the positive maximum value, the change degree dA / F of the deviation ΔA / F is the same for the former. The latter becomes larger in the degree of change dA / F of the deviation ΔA / F when the deviation ΔA / F changes from the positive maximum value to the negative maximum value.

  That is, when the cylinder 102A (# 1) becomes rich, when the cylinder 102D (# 4) becomes lean, and when the cylinder 102A (# 1) becomes lean, the cylinder 102D (# 4) In the case of being rich, the phase at which the absolute value | dA / F | of the change degree dA / F of the deviation ΔA / F is maximized is different from the sign of the maximum value | dA / Fmax |. Accordingly, the situation where the cylinder 102A (# 1) becomes rich and the situation where the cylinder 102D (# 4) becomes lean, and the situation where the cylinder 102A (# 1) becomes lean and the cylinder 102D (#) are identified. 4) is distinguished from the situation in which the richness has occurred. The phase where the absolute value | dA / F | of the change degree dA / F of the deviation ΔA / F is maximized and the sign of the maximum value | dA / Fmax | And can be based on.

It should be noted that the situation where the cylinder 102B (# 2) becomes rich and the situation where the cylinder 102C (# 3) becomes lean, and the situation where the cylinder 102B (# 2) becomes lean and the cylinder 102C (# The identification of the situation in which 3) is rich can also be performed in the same manner.
Therefore, in the inter-cylinder air-fuel ratio variation detecting apparatus 10 according to the present embodiment, the phase at which the absolute value | dA / F | of the change degree dA / F of the deviation ΔA / F is maximized and the maximum value | dA of the absolute value | Based on the sign of / Fmax |, the target cylinder is specified and the air / fuel ratio is lean / rich.

First, in step 110, the determination circuit 128 determines whether or not the absolute value | dA / F | of the variation degree dA / F of the deviation ΔA / F exceeds a predetermined threshold value dA / Fdb (dead band). To do. If the determination is affirmative, the routine proceeds to step 112, while if the determination is negative, the routine proceeds to step 126.
In step 112, the determination circuit 128 determines the phase between 720 ° CA where the maximum value | dA / Fmax | of the absolute value | dA / F | of the change degree dA / F of the deviation ΔA / F is detected. Here, for example, when the cylinder 102A (# 1) is detected between 0 ° CA and 180 ° CA, the cylinder 102C (# 1) is detected when it is detected between 180 ° CA and 360 ° CA. When # 3) is detected between 360 ° CA and 540 ° CA, cylinder 102D (# 4) is detected between 540 ° CA and 720 ° CA, and cylinder 102B ( # 2) corresponds to the target cylinder. Such correlation has been confirmed in advance by experiments, and information indicating the correlation is stored in the RAM 124 as a map or a parameter table.

  For example, when the maximum value of the absolute value | dA / F | of the change degree dA / F of the deviation ΔA / F is detected between 0 ° CA and 180 ° CA, the determination circuit 128 It is determined (primary determination) that cylinder 102A (# 1) is the target cylinder (see the graphs of FIGS. 7A and 7B). When the maximum value | dA / Fmax | is detected between 180 ° CA and 360 ° CA, the determination circuit 128 changes the maximum value | dA / Fmax | from 360 ° CA to 540 ° CA. If the maximum value | dA / Fmax | is detected between 540 ° CA and 720 ° CA, the cylinders 102C (# 3), 102D (# 4), 102B (# 2) is determined to be the target cylinder (primary determination).

  Next, in step 114, the determination circuit 128 determines whether the detected maximum value | dA / Fmax | is a positive value or a negative value. Here, for example, when a positive maximum value + dA / Fmax is detected between 0 ° CA and 180 ° CA, the air-fuel ratio of the cylinder 102A (# 1) is lean, and the negative maximum value during this period When the value -dA / Fmax is detected, it is confirmed beforehand by experiments that the air-fuel ratio of the cylinder 102A (# 1) is rich, and information indicating such correlation is obtained as a map or a parameter table. Stored in the RAM 124. Further, when the positive maximum value + dA / Fmax is detected between 180 ° CA and 360 ° CA, the air-fuel ratio of the cylinder 102C (# 3) is lean, and the negative maximum value −dA during this period. When / Fmax is detected, the air-fuel ratio of the cylinder 102C (# 3) is rich. When the positive maximum value + dA / Fmax is detected during the period from 360 ° CA to 540 ° CA, the cylinder If the air-fuel ratio of 102D (# 4) is lean and the negative maximum value −dA / Fmax is detected during this period, it is experimentally determined that the air-fuel ratio of the cylinder 102D (# 4) is rich. Information indicating such correlation is stored in the RAM 124 as a map or a parameter table. Further, when a positive maximum value + dA / Fmax is detected in a period from 540 ° CA to 720 ° CA, the air-fuel ratio of the cylinder 102B (# 2) is lean, and a negative maximum value − When dA / Fmax is detected, it is confirmed beforehand by experiments that the air-fuel ratio of the cylinder 102B (# 2) is rich, and information indicating such correlation is stored in the RAM 124 as a map or parameter table. It is remembered.

  For example, when the determination circuit 128 determines that the target cylinder is the cylinder 102A (# 1) in step 114 and the maximum value | dA / Fmax | is determined to be positive, the cylinder 102A (# 1) is empty. The fuel ratio is determined to be lean (primary determination). On the other hand, when the determination circuit 128 determines that the target cylinder is the cylinder 102A (# 1) in step 112 and determines that the maximum value | dA / Fmax | is negative, the determination circuit 128 determines the air-fuel ratio of the cylinder 102A (# 1). It is determined to be rich (primary determination). The same applies when the determination circuit 128 determines that the target cylinder is the cylinder 102B (# 2), 102C (# 3), or 102D (# 4) in step 112. The determination circuit 128 determines that the maximum value | dA / Fmax If | is determined to be positive, the air-fuel ratio of the cylinders 102B (# 2), 102C (# 3), and 102D (# 4) is determined to be lean (primary determination), while the maximum value | dA / Fmax When | is determined to be negative, the air-fuel ratio of the cylinders 102B (# 2), 102C (# 3), and 102D (# 4) is determined to be rich (primary determination).

Next, at step 116, the determination circuit 128 determines whether or not the absolute value | ΔA / F | of the deviation ΔA / F exceeds a predetermined threshold (dead zone) ΔA / Fdb. If the determination is affirmative, the process proceeds to step 118, whereas if the determination is negative, the process proceeds to step 126.
In step 118, ECU 110 determines the phase between 720 ° CA where the maximum value | ΔA / Fmax | of the absolute value | ΔA / F | of deviation ΔA / F is detected. Here, for example, when detected between 0 ° CA and 180 ° CA and between 360 ° CA and 540 ° CA, the cylinder 102A (# 1) or the cylinder 102D (# 4) is 180 °. When detected between CA and 360 ° CA and between 540 ° CA and 720 ° CA, the cylinder 102B (# 2) or the cylinder 102C (# 3) may correspond to the target cylinder. The information indicating such a correlation is stored in the RAM 124 as a map or a parameter table.

  For example, when the maximum value | ΔA / Fmax | is detected between 0 ° CA and 180 ° CA and between 360 ° CA and 540 ° CA, the determination circuit 128 detects the cylinder 102A. (# 1) or cylinder 102D (# 4) is determined to be the target cylinder (secondary determination). Further, when the maximum value | ΔA / Fmax | is detected between 180 ° CA and 360 ° CA and between 540 ° CA and 720 ° CA, the determination circuit 128 determines the cylinder 102B (# 2). Alternatively, it is determined (secondary determination) that the cylinder 102C (# 3) is the target cylinder.

  Next, in step 120, the determination circuit 128 determines whether the maximum value | ΔA / Fmax | is a positive value or a negative value. Here, for example, when a positive maximum value + ΔA / Fmax is detected between 0 ° CA and 180 ° CA, and a negative maximum value −ΔA / Fmax between 360 ° CA and 540 ° CA is detected. Is detected, the air-fuel ratio of the cylinder 102A (# 1) is lean, or the air-fuel ratio of the cylinder 102D (# 4) is rich. On the other hand, when a negative maximum value −ΔA / Fmax is detected between 0 ° CA and 180 ° CA, and a positive maximum value + ΔA / Fmax is detected between 360 ° CA and 540 ° CA. In this case, the air-fuel ratio of the cylinder 102A (# 1) is rich, or the air-fuel ratio of the cylinder 102D (# 4) is lean. Such correlation is confirmed in advance by experiments, and information indicating the correlation is stored in the RAM 124 as a map or a parameter table.

  Further, when a positive maximum value + ΔA / Fmax is detected between 180 ° CA and 360 ° CA, and a negative maximum value −ΔA / Fmax is detected between 540 ° CA and 720 ° CA. In this case, the air-fuel ratio of the cylinder 102C (# 3) is lean, or the air-fuel ratio of the cylinder 102B (# 2) is rich. On the other hand, when a negative maximum value −ΔA / Fmax is detected between 180 ° CA and 360 ° CA, and a positive maximum value + ΔA / Fmax is detected between 540 ° CA and 720 ° CA. In this case, the air-fuel ratio of the cylinder 102C (# 3) is rich, or the air-fuel ratio of the cylinder 102B (# 2) is lean. Such correlation is confirmed in advance by experiments, and information indicating the correlation is stored in the RAM 124 as a map or a parameter table.

  For example, when the determination circuit 128 determines that the target cylinder is the cylinder 102A (# 1) or the cylinder 102D (# 4) in step 118 and determines that the maximum value | ΔA / Fmax | is positive, the cylinder It is determined that the air-fuel ratio of 102A (# 1) is lean and the air-fuel ratio of cylinder 102D (# 4) is rich. On the other hand, if the determination circuit 128 determines that the target cylinder is the cylinder 102A (# 1) or the cylinder 102D (# 4) in step 118 and the maximum value | ΔA / Fmax | It is determined that the air-fuel ratio of # 1) is rich and the air-fuel ratio of cylinder 102D (# 4) is lean.

  The determination circuit 128 determines that the target cylinder is the cylinder 102B (# 2) or the cylinder 102C (# 3) in step 118 and determines that the maximum value | ΔA / Fmax | is positive, the cylinder 102C ( It is determined that the air-fuel ratio of # 3) is lean and the air-fuel ratio of cylinder 102B (# 2) is rich. On the other hand, if the determination circuit 128 determines in step 118 that the target cylinder is the cylinder 102B (# 2) or the cylinder 102C (# 3) and determines that the maximum value | ΔA / Fmax | It is determined that the air-fuel ratio of # 3) is rich and the air-fuel ratio of cylinder 102B (# 2) is lean.

Next, in step 122, the determination circuit 128 determines whether or not the combination of the primary determination result in steps 112 and 114 and the secondary determination result in steps 118 and 120 is a predetermined combination. To do. If the determination is affirmative, the routine proceeds to step 124, while if the determination is negative, the routine proceeds to step 126.
Here, in one set of the predetermined combinations, the target cylinders determined in steps 112 and 118 match, and the air-fuel ratio lean and rich determination results of the target cylinders in steps 114 and 120 match. It is a combination. Another set of predetermined combinations includes cylinders 102A (# 1) and cylinders 102D (# 4) or cylinders 102B (# 2) and cylinders 102C (# 3) determined in steps 112 and 118. ) And the like, and the air / fuel ratio lean and rich determination results of the target cylinder in steps 114 and 120 are reversed.

  Next, at step 124, the control circuit 130 stores the number (# 1 to 4) of the target cylinder determined at step 112 and the air / fuel ratio lean / rich determination result of the cylinder at step 114 in the RAM 124. Accumulate memorize. That is, when the result of the primary determination and the result of the secondary determination correspond to a predetermined combination, the result of the primary determination is maintained, and the result of the primary determination and the result of the secondary determination become a predetermined combination. If not applicable, the primary determination result is canceled.

Next, in step 126, ECU 110 determines whether or not the number of determinations has reached a predetermined number. When determination is denied, it transfers to step 100 and the process of steps 100-126 is repeated. On the other hand, if the determination is positive, the control circuit 130 holds the integrated value of the determination result. Thus, the processing routine is finished.
As described above, according to the inter-cylinder air-fuel ratio variation detecting apparatus 10 according to the present embodiment, the target cylinder in which the air-fuel ratio fluctuates relatively rich or lean, and the target cylinder and the air-fuel ratio waveform are approximated. Since a single air-fuel ratio sensor can be used to determine the variation of the exhaust air-fuel ratio between cylinders, the target cylinder can be specified, and further, the target cylinder can be identified. The lean / rich air / fuel ratio can be determined. Therefore, based on the determination result of the inter-cylinder air-fuel ratio variation detection device 10, the operating air-fuel ratio for each cylinder in the multi-cylinder internal combustion engine can be controlled with high accuracy, and the operating air between the cylinders in the multi-cylinder internal combustion engine can be controlled. Variation in the fuel ratio can be effectively suppressed.

  Further, the inter-cylinder air-fuel ratio variation detection device 10 performs primary determination of the target cylinder and the rich / lean of the air-fuel ratio of the target cylinder based on the degree of change in the deviation of the exhaust air-fuel ratio, and then the deviation of the exhaust air-fuel ratio. Based on the above, the target cylinder and the rich / lean of the air-fuel ratio of the target cylinder are subjected to secondary determination, and whether the primary determination result and the secondary determination result correspond to a predetermined combination or not It is determined whether or not to adopt the determination result. That is, the inter-cylinder air-fuel ratio variation detection device 10 determines the air / fuel ratio rich / lean of the target cylinder and the target cylinder by double determination of the air / fuel ratio rich / lean of the target cylinder and the target cylinder. Incorrect determination is suppressed.

  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, although an embodiment of the present invention has been described by taking a four-cycle in-line four-cylinder engine as an example, another multi-cylinder internal combustion engine such as a horizontally opposed six-cylinder engine can also be employed.

10 Inter-cylinder air-fuel ratio variation detection device 100 Engines 102A to D (# 1 to 4) Cylinder 104 Intake passage 106 Exhaust passage 108 Catalyst 110 ECU (Rich / lean cylinder determination unit)
112 Intake manifolds 114A-D Intake port 115 Air flow meters 116A-D Fuel injection valves 118A-D Exhaust port 120 Exhaust manifold 122 Air-fuel ratio sensor 124 RAM (storage unit, second storage unit)
126 arithmetic circuit (arithmetic unit, second arithmetic unit)
128 determination circuit (determination unit, second determination unit)
130 Control circuit

Claims (5)

An air-fuel ratio detecting means provided in an exhaust gas merging portion of an internal combustion engine having a plurality of cylinders;
An air-fuel ratio change degree calculating means for calculating a change degree of the air-fuel ratio based on a deviation from a reference value of the detected value detected by the air-fuel ratio detecting means;
A variation abnormality detecting means for detecting an air-fuel ratio variation abnormality among the plurality of cylinders based on the degree of change calculated by the air-fuel ratio change degree calculating means;
With
The variation abnormality detecting means includes
Based on the phase in which the maximum absolute value of the degree of change calculated by the air-fuel ratio change degree calculating means is detected, among the cylinders, the cylinders that identify the cylinder that causes the air-fuel ratio variation abnormality are identified. Air-fuel ratio variation detector. The variation abnormality detecting means includes
Based on the sign of the degree of change calculated by the air-fuel ratio change degree calculating means, it is determined whether the air-fuel ratio has shifted to the rich side or to the lean side for the cylinder that is causing the air-fuel ratio variation abnormality. The inter-cylinder air-fuel ratio variation detection device according to claim 1, which is determined. The variation abnormality detecting means includes
Determining means for determining whether or not the degree of change calculated by the air-fuel ratio change degree calculating means exceeds a predetermined threshold;
The inter-cylinder air-fuel ratio variation detection device according to claim 2, wherein when the determination means determines that the degree of change has exceeded the predetermined threshold, it is determined that the air-fuel ratio varies between the plurality of cylinders. An air-fuel ratio detecting means provided in an exhaust gas merging portion of an internal combustion engine having a plurality of cylinders;
An air-fuel ratio change degree calculating means for calculating a change degree of the air-fuel ratio based on a deviation from a reference value of the detected value detected by the air-fuel ratio detecting means;
A variation abnormality detecting means for detecting an air-fuel ratio variation abnormality among the plurality of cylinders based on the degree of change calculated by the air-fuel ratio change degree calculating means;
With
The variation abnormality detecting means includes
Based on the phase at which the maximum value of the absolute value of the degree of change calculated by the air-fuel ratio change degree calculating means is detected, and the positive / negative of the maximum value of the absolute value of the degree of change , it becomes a factor of the air-fuel ratio variation abnormality. the in and cylinder after the primary determination for determining the air-fuel ratio maximum value of the absolute values of deviations from a reference value of the detected detection value detected by the detection means the phase, and, the absolute value of the deviation based on the positive or negative maximum value, the air-fuel ratio variation performs secondary judgment to decide which interrupt the going on cylinders of abnormality, based on a combination of these primary and secondary determination of the determination result, the air among the plurality of cylinders ratio variation - cylinder air-fuel ratio variation among the detection device for determining the causes and going on cylinder abnormalities. The air-fuel ratio change degree calculating means is:
The average value of the detected values detected by the air-fuel ratio detecting means between the intake and exhaust of the internal combustion engine is calculated, and this average value is used as the reference value. The inter-cylinder air-fuel ratio variation detecting device according to the item.

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