JP2001140687A - Air-fuel ratio controlling device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce emission by properly disposing the output of an air-fuel ratio detecting means according to the operation state of an internal combustion engine (diesel engine) and suppressing the air-fuel ratio to a desired value by controlling the fuel injection quantity and EGR quantity of each cylinder. SOLUTION: An ECU compensates EGR quantity based on the average air- fuel ratio of each cylinder in a relatively lower range out of the EGR range. In a relatively higher range out of the EGR range, the ECU compensates EGR quantity based on the average air-fuel ratio of each cylinder after compensating the fuel injection quantity of each cylinder based on the air-fuel ratio of each cylinder. In a non-EGR range, the average fuel injection quantity between cylinders is compensated based on the average air-fuel ratio of each cylinder after the compensation of the fuel injecting quantity of each cylinder. This can lessen the dispersion of air-fuel ratio of each cylinder and correct the deviation of the average air-fuel ratio of each cylinder. This makes it possible to suppress the quantity of the smoke generated to a specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio to a predetermined value by adjusting a fuel injection amount or an EGR amount of the internal combustion engine.

[0002]

2. Description of the Related Art Since the fuel injection amount of an internal combustion engine directly affects the engine output and emission amount, and the EGR amount of the internal combustion engine directly affects the emission amount, the fuel injection amount and the EGR amount can be precisely determined. It is very important to control the value. However, these change due to variations in characteristics of the fuel injection valve, the EGR valve, and the like, changes in environmental conditions, deterioration over time, and the like. On the other hand, emissions
There is a strong correlation with the oxygen concentration (air-fuel ratio) in the exhaust. In diesel engines, in particular, reducing smoke (black smoke) in the exhaust gas is an important issue. However, the amount of smoke is generated by the local lack of oxygen in the cylinder during fuel combustion. It has a very strong correlation with the oxygen concentration in the exhaust. Therefore, it is extremely useful to use the air-fuel ratio as an index for setting emission (particularly, smoke of a diesel engine) in an internal combustion engine to a predetermined value.

Therefore, there is a conventional technique in which the fuel injection amount and the EGR amount are feedback-controlled based on the air-fuel ratio. For example, in a fuel injection control device for a diesel engine disclosed in Japanese Patent Application Laid-Open No. 2-61347, an EGR amount is adjusted in an EGR region so that an air-fuel ratio becomes a predetermined value, and a non-EGR amount is adjusted.
In the region, the emission is controlled to a predetermined value by adjusting the average fuel injection amount of all cylinders. However, under the non-EGR range (high load range) or high load operation of the EGR range of the diesel engine, even if the air-fuel ratio detected by the sensor (average air-fuel ratio of all cylinders) is the target value, the When there is a variation in the air-fuel ratio at, as shown in FIG.
There is a problem that the smoke amount increases rapidly as the variation increases. In order to solve this problem, it is difficult to sufficiently reduce the smoke because the above-described related art cannot correct the variation in the air-fuel ratio between the cylinders.

On the other hand, Japanese Patent Application Laid-Open No. 9-2033 discloses a prior art.
No. 37 discloses an air-fuel ratio control device for an internal combustion engine. This prior art solves the variation of the air-fuel ratio between cylinders, calculates the air-fuel ratio for each cylinder from the output of the air-fuel ratio sensor and the exhaust timing of each cylinder, and based on the calculated air-fuel ratio for each cylinder. In addition, the fuel injection amount is feedback-controlled for each cylinder. However, when this conventional technology is applied to a diesel engine, since the oxygen concentration in the exhaust gas is high when the engine is under a low load, a very high air-fuel ratio detection accuracy can be used to detect a deviation in the air-fuel ratio between cylinders. This is practically difficult.

When the air-fuel ratio of the internal combustion engine is detected by a sensor, the following problem occurs. The air-fuel ratio of an internal combustion engine is generally detected by, for example, a limiting current type oxygen concentration sensor, and the output of this sensor changes in principle depending on the atmospheric pressure, that is, the magnitude of the exhaust pressure, and the exhaust pressure is high. It becomes bigger. Therefore,
When this type of sensor is applied to a diesel engine, the diesel engine has a characteristic that the pulsation of the exhaust pressure is large because the compression ratio is high, so even if the air-fuel ratio is constant, the sensor output is caused by the exhaust pressure pulsation. 1 cycle / periodic variation corresponding to the number of cylinders (for example, 4
In the cylinder internal combustion engine, a variation at every 180 crank angles occurs. Since the magnitude of this variation varies depending on the operating conditions of the engine, it is difficult to obtain accurate information on the air-fuel ratio. In particular, when trying to obtain the air-fuel ratio of each cylinder separately from the output of one sensor, the above problem becomes remarkable, and the accurate detection of the air-fuel ratio of each cylinder and control based on the detected air-fuel ratio are performed. Becomes very difficult.

It takes a long time for the exhaust gas discharged from the exhaust valve of the internal combustion engine to reach the sensor provided in the exhaust pipe, so that a time delay occurs, and this delay varies depending on the operation state of the internal combustion engine. I do. Therefore, if this delay is not taken into account, the air-fuel ratio for each cylinder cannot be accurately detected when trying to obtain the air-fuel ratio for each cylinder separately from the output of one sensor. In particular, in a diesel engine, since the combustion is caused by self-ignition of fuel, temporal or spatial stability of combustion in each cycle is low, and information on the obtained air-fuel ratio varies in each cycle.

In particular, in a diesel engine, the degree of effective use of air in the cylinder (ie, the air utilization rate) due to a change in the atmospheric pressure at high altitude or a change in the fuel injection pressure due to the specifications and characteristics of the injection system, for example. ) Changes, the relationship between the air-fuel ratio and the amount of smoke generated changes as shown in FIGS. Therefore, if the target air-fuel ratio is kept constant irrespective of these changes, the smoke amount cannot be controlled to a predetermined value. As described above, there are many problems when attempting to control the emission of a diesel engine based on the detected air-fuel ratio using the above-described conventional technology.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to appropriately process the output of an air-fuel ratio detecting means in accordance with each operating state of an internal combustion engine, An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can reduce the emission of the internal combustion engine (particularly, smoke in a diesel engine) by controlling the air-fuel ratio to a desired value by controlling the fuel injection amount and the EGR amount of the internal combustion engine.

[0009]

The air-fuel ratio control means corrects the EGR amount on the basis of the second characteristic value in the EGR region where the load is relatively low, and adjusts the EGR amount.
In the region where the load is relatively high in the R region, the fuel injection amount for each cylinder is corrected based on the first characteristic value, and the EGR amount is corrected based on the second characteristic value. In the non-EGR region, The fuel injection amount for each cylinder is corrected based on the first characteristic value, and the average injection amount is corrected based on the second characteristic value.

In the non-EGR region (high load region) and the relatively high load region of the EGR region, as shown in FIG.
If the variation in the air-fuel ratio between the cylinders increases, the amount of smoke generated increases rapidly. Therefore, it is necessary to correct the fuel injection amount for each cylinder to suppress the variation in the air-fuel ratio between the cylinders. Here, especially for diesel engines, when the load is high,
Since the oxygen concentration in the exhaust gas is lower than at low load, extremely high detection accuracy is not required to detect the air-fuel ratio deviation for each cylinder. A first characteristic value corresponding to an air-fuel ratio for each cylinder is calculated based on the output, and the fuel injection amount for each cylinder can be corrected based on the first characteristic value.

On the other hand, in the relatively low load region of the EGR region, as described above, the oxygen concentration in the exhaust gas is high, and in order to detect the deviation of the air-fuel ratio, the detection accuracy of the air-fuel ratio is extremely high. Therefore, it is practically difficult to detect the air-fuel ratio for each cylinder. However, in the low load region,
As shown in FIG. 6, even if the air-fuel ratio varies among the cylinders, the amount of smoke generated is lower than when the load is high, and the amount of smoke generated is larger even if the air-fuel ratio between the cylinders increases. Hardly changes. Therefore, the injection amount correction for each cylinder is not performed, and the EGR amount is corrected to control the average air-fuel ratio between the cylinders. As a result, the air-fuel ratio detecting means having a practically accurate accuracy makes it possible to control the cylinder-by-cylinder or average air-fuel ratio appropriately in accordance with the operating state of the internal combustion engine, thereby making it possible to improve the emission.

According to a second aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to the first aspect, a target value corresponding to the target air-fuel ratio in a relatively low load region in the EGR region;
The EGR amount is corrected so that the difference from the second characteristic value corresponding to the average air-fuel ratio of all cylinders becomes small. This allows
Average air-fuel ratio deviation between cylinders (deviation from target air-fuel ratio)
The deterioration of emission caused by the above can be improved.

(3) The air-fuel ratio control apparatus for an internal combustion engine according to the above (1) or (2), wherein the first characteristic corresponding to the air-fuel ratio of each cylinder in a relatively high load region in the EGR region. The fuel injection amount for each cylinder is corrected so that the variation in the value becomes smaller among the cylinders, and then the EGR amount is corrected so that the difference between the target value corresponding to the target air-fuel ratio and the second characteristic value becomes smaller. are doing. As a result, it is possible to improve the deterioration of the emission caused by the variation of the air-fuel ratio between the cylinders and the deviation of the average air-fuel ratio between the cylinders (the deviation from the target air-fuel ratio).

After correcting the fuel injection amount for each cylinder,
E is set so that the difference between the average air-fuel ratio and the target air-fuel ratio becomes small.
By correcting the GR amount, it is possible to prevent the smoke generation amount from increasing during the correction of the air-fuel ratio. That is, because the load on the internal combustion engine is large, smoke is likely to occur,
In addition, if the EGR amount for all cylinders is corrected first while the inter-cylinder air-fuel ratio remains varied, if the average air-fuel ratio of all cylinders is corrected to be low, cylinders lacking oxygen due to variations in air-fuel ratios will have a further problem. An oxygen deficiency state occurs, and a large amount of smoke is generated. On the other hand, the above problem can be solved by first adjusting the fuel injection amount for each cylinder to correct the air-fuel ratio for each cylinder, and then correcting the EGR amount for all cylinders.

According to a fourth aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to any one of the first to third aspects, the non-EG
In the R region, the fuel injection amount for each cylinder is corrected so that the variation in the first characteristic value corresponding to the air-fuel ratio for each cylinder becomes smaller between the cylinders. The average injection amount between the cylinders is corrected so that the difference from the characteristic value 2 becomes smaller. As a result, it is possible to improve the deterioration of the emission caused by the variation of the air-fuel ratio between the cylinders and the deviation of the average air-fuel ratio between the cylinders (the deviation from the target air-fuel ratio). Further, after correcting the fuel injection amount for each cylinder, the average injection amount between the cylinders is corrected so that the difference between the average air-fuel ratio and the target air-fuel ratio is reduced, so that the air-fuel ratio is reduced as in the case of claim 3. It is possible to prevent an increase in the amount of smoke generated during correction of the fuel ratio.

(Claim 5) The cylinder-by-cylinder air-fuel ratio calculating means outputs the output of the air-fuel ratio detecting means sampled a plurality of times during one cycle of the internal combustion engine for each section corresponding to one cycle of the internal combustion engine / the number of cylinders. The characteristic value is calculated by averaging, and the start timing of the section to be averaged is changed for each operating condition of the internal combustion engine. With this, when a general limiting current type oxygen concentration sensor is used as the air-fuel ratio detecting means, the influence of the exhaust pressure pulsation is removed even in a diesel engine having a large exhaust pressure pulsation, and an accurate The air-fuel ratio can be determined. In addition, since the delay until the exhaust reaches the air-fuel ratio detecting means changes in accordance with the operating state of the internal combustion engine, it is possible to obtain an accurate air-fuel ratio for each cylinder regardless of the operating state. .

(Claim 6) In the air-fuel ratio control apparatus for an internal combustion engine according to claim 5, the cylinder-by-cylinder air-fuel ratio control means controls each cylinder so as to reduce variation in characteristic values among the cylinders. Adjust the fuel injection amount. Thus, it is possible to improve the deterioration of the emission caused by the variation in the air-fuel ratio between the cylinders.

According to a seventh aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to the sixth aspect, the cylinder-by-cylinder air-fuel ratio calculating means converts the characteristic value obtained for each section into a plurality of cycles for each cylinder. And averaged over the range to obtain the characteristic value of each cylinder.
As a result, since the combustion is caused by the self-ignition of the fuel, the temporal or spatial stability of each combustion is low, and the information on the obtained air-fuel ratio varies from cycle to cycle. It becomes possible.

(Eighth Means) In the air-fuel ratio control apparatus for an internal combustion engine according to any one of the fifth to seventh aspects, the cylinder-by-cylinder air-fuel ratio calculation means includes a section for averaging the output of the air-fuel ratio detection means. The start timing is set earlier as the rotation speed or the load of the internal combustion engine increases. In this case, in consideration of the fact that the delay until exhaust reaches the air-fuel ratio detecting means decreases as the rotation speed and the load of the internal combustion engine increase, an accurate air-fuel ratio for each cylinder regardless of the operation state of the internal combustion engine is taken into consideration. Can be obtained.

According to a ninth aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to any one of the first to eighth aspects, the target air-fuel ratio calculating means sets the target air-fuel ratio as the output of the intake pressure detecting means decreases. (Target exhaust oxygen concentration) is increased. When the atmospheric pressure decreases at high altitudes and the intake pressure of an internal combustion engine, especially a diesel engine, decreases, the absolute amount of oxygen drawn into the cylinder decreases even if the air-fuel ratio (oxygen concentration in exhaust gas) is the same. I do. For this reason, the oxygen utilization in the cylinder during fuel combustion decreases, and as a result, the region in the cylinder where oxygen becomes insufficient locally increases, and the amount of smoke generated increases. On the other hand, according to the present invention, as the intake pressure is smaller, the target air-fuel ratio is increased, so that the above-described problem can be prevented and the amount of generated smoke can be reduced to a predetermined value or less.

According to a tenth aspect of the present invention, in the air-fuel ratio control apparatus for an internal combustion engine according to any one of the first to ninth aspects, the target air-fuel ratio calculating means sets the target air-fuel ratio as the output of the injection pressure detecting means decreases. Enlarge. If the fuel injection pressure decreases due to a change in the characteristics of the internal combustion engine or the like, the atomization of the fuel spray and the state of mixing with air deteriorate even if the air-fuel ratio (oxygen concentration in the exhaust gas) is the same. For this reason, the oxygen utilization in the cylinder during fuel combustion decreases, and as a result, the region in the cylinder where oxygen becomes insufficient locally increases, and the amount of smoke generated increases. On the other hand, according to the present invention, in order to increase the target air-fuel ratio as the injection pressure decreases, it is possible to prevent the above-described problem and reduce the smoke generation amount to a predetermined value or less.

[0022]

Next, an embodiment in which the present invention is applied to a four-cylinder diesel engine will be described with reference to the drawings. FIG. 2 is a system diagram of an air-fuel ratio control device for a diesel engine. A diesel engine 1, which is an internal combustion engine of the present invention, has a solenoid-operated fuel injection valve 2 for each cylinder.
Is attached. The fuel injection valve 2 is supplied with high-pressure fuel via a common rail 4 (accumulation chamber) that accumulates fuel fed from the high-pressure fuel pump 3 and performs fuel injection into the cylinder as the solenoid valve opens and closes. An injection pressure sensor 5 that detects the internal pressure (injection pressure) of the common rail 4 is provided on the common rail 4.

The diesel engine 1 is connected to an intake passage for introducing air into each cylinder and an exhaust passage for discharging exhaust gas generated by combustion in each cylinder. The intake passage has an intake pipe 6 that introduces air through an air cleaner (not shown), and an intake manifold 7 that branches and connects the intake pipe 6 to each cylinder. An intake pressure sensor 8 is installed in the intake pipe 6. ing. The exhaust passage has an exhaust pipe 9 that opens to the atmosphere and an exhaust manifold 10 that sends exhaust gas discharged from each cylinder to the exhaust pipe 9. The exhaust pipe 9 detects an oxygen concentration (air-fuel ratio) in the exhaust gas. Acidity concentration sensor 11
(Air-fuel ratio detecting means of the present invention) is provided.

The oxygen concentration sensor 11 is a limiting current type oxygen concentration sensor 11 widely used particularly for gasoline engines. The sensor 11 can obtain an output corresponding to the oxygen concentration. However, in principle, the output has a pressure dependency. Therefore, even if the oxygen concentration is constant, the output increases as the pressure increases. An EG for recirculating a part of the exhaust gas to the intake pipe 6 is provided between the exhaust pipe 9 and the intake pipe 6.
The R pipe 12 is connected, and E
A GR valve 13 is provided. The EGR valve 13 is an EGR valve.
The valve opening is adjusted by the control valve 14, and the amount of exhaust gas flowing through the EGR pipe 12 (hereinafter, referred to as EGR amount) is controlled according to the valve opening.

This system is controlled by an engine electronic control circuit (hereinafter referred to as ECU 15) having a function as air-fuel ratio control means. The ECU 15 includes an oxygen concentration sensor 11, an injection pressure sensor 5, an intake pressure sensor 8, an engine speed sensor 16, an accelerator opening sensor 17, and various other sensors used in a normal electronically controlled diesel engine 1. And the fuel injection valve 2 and the EGR
The control valve 14, the high-pressure fuel pump 3 and the like are connected to the output circuit. The ECU 15 determines the fuel injection timing, fuel injection amount, and E based on the sensor signals input from each of the above sensors.
The GR amount and the like are calculated, and the operations of the high-pressure fuel pump 3, the fuel injection valve 2, and the EGR control valve 14 are electronically controlled based on the calculation result.

However, if the fuel injection amount or the EGR amount of each cylinder deviates from a predetermined amount due to variations in characteristics of the fuel injection valve 2, the EGR valve 13, etc., changes in environmental conditions, or deterioration over time, etc. Diesel engine 1
There is a possibility of increasing smoke, which is an important issue for the user. Therefore, in the present system, the air-fuel ratio having a strong correlation with the emission (especially, smoke) of the diesel engine 1 is detected by the oxygen concentration sensor 11, and the fuel injection amount and the EGR amount of each cylinder are feedback-controlled based on the air-fuel ratio. , Emission (especially, smoke) is set to a predetermined value.

Next, the operation of the present system for correcting the fuel injection amount and the EGR amount of each cylinder based on the air-fuel ratio will be described with reference to the ECU 1.
A description will be given according to the processing procedure of No. 5. FIG. 1 is a flowchart showing a processing procedure of the ECU 15. Step 100: The current operating condition of the engine 1 is read based on information from the engine speed, the accelerator opening, the intake pressure, and other various sensors. Step 101: A target air-fuel ratio (target exhaust oxygen concentration) is calculated by combining a map or the like previously stored in the ECU 15 with the information obtained in Step 100. Step 102: The actual air-fuel ratio is read from the signal of the oxygen concentration sensor 11. Step 103: An average air-fuel ratio of all cylinders and an air-fuel ratio of each cylinder are calculated by a method described later.

Step 104: It is determined whether or not the engine load (output torque) is larger than a predetermined value. Specifically, the magnitude is determined by comparing the accelerator opening and the fuel injection command amount calculated in the ECU 15 with a predetermined value. Step10
4 when it is determined that the engine load is low (determination result N
O) goes to Step 105. If the engine load is low,
EGR control is performed to reduce NO _X in the exhaust gas (region shown in FIG. 7). Further, when the engine load is low, as shown in FIG. 6, even if the inter-cylinder air-fuel ratio varies, it does not significantly affect the amount of smoke generated. On the other hand, when the average air-fuel ratio between the cylinders deviates from the target value due to the deviation of the EGR amount, the emission (especially, smoke) deteriorates significantly as shown in FIG.

Therefore, in Step 105, the following determination is made to determine whether the EGR amount needs to be corrected. Step 105: It is determined whether or not the difference between the target air-fuel ratio calculated in Step 101 and the average air-fuel ratio calculated in Step 103 is smaller than a predetermined value. If it is determined in this Step 105 that the deviation of the average air-fuel ratio is equal to or larger than the predetermined value (determination result NO), the process proceeds to Step 106. Step 106 (low load correction means of the present invention): Here, since the deviation of the average air-fuel ratio from the target air-fuel ratio is large, the EGR control valve 14 is operated based on the deviation, and the EGR valve 1
The EGR amount is corrected by changing the valve opening degree of No. 3. Thereby, the average air-fuel ratio can be controlled to a predetermined value, so that the emission can be improved.

On the other hand, if it is determined in Step 104 that the engine load is high (determination result YES), Step
Proceed to 107. Step 107: It is determined whether or not the variation of the air-fuel ratio for each cylinder calculated in Step 103 is larger than a predetermined value. If it is determined that the variation in the air-fuel ratio between the cylinders is equal to or greater than the predetermined value (determination result NO), the process proceeds to Step 108. Step 108 (high load correction means and non-EGR correction means of the present invention): The injection amount for each cylinder is corrected. That is, when the engine load is large, as shown in FIG. 6, if the variation in the air-fuel ratio between the cylinders is large, the emission is greatly deteriorated. Therefore, first, the air-fuel ratio of each cylinder is made uniform (to eliminate the variation).
By improving emissions. Specifically, a cylinder with a low air-fuel ratio and a low oxygen concentration reduces the injection amount, and conversely, a cylinder with a high air-fuel ratio and a high oxygen concentration increases the injection amount.

If it is determined in step 107 that the air-fuel ratio variation among the cylinders is smaller than a predetermined value (determination result YES), the flow proceeds to step 109. Step 109: As in Step 105, it is determined whether or not the difference between the target air-fuel ratio calculated in Step 101 and the average air-fuel ratio calculated in Step 103 is smaller than a predetermined value. Step 107 and Step
It is better to set Step 109 in this order, that is, Step 109 after Step 107. The reason is that if the variation in the air-fuel ratio between cylinders is equal to or greater than a predetermined value, the deviation of the average air-fuel ratio is adjusted first, and if the average air-fuel ratio of all cylinders is corrected to be low, oxygen is insufficient due to the variation in the air-fuel ratio. In such a cylinder, a further oxygen deficiency occurs, and a large amount of smoke is generated. On the other hand, the above problem can be solved by first adjusting the fuel injection amount of each cylinder to correct the air-fuel ratio of each cylinder, and then correcting the average air-fuel ratio of all cylinders.

When it is determined in Step 109 that the deviation of the average air-fuel ratio from the target air-fuel ratio is equal to or larger than a predetermined value (determination result NO)
Goes to Step110. Step 110: It is determined whether the operating condition is in the EGR region. If it is determined that the operating condition is in the EGR region (the determination result is YES), the process proceeds to Step 111. Step 111 (high load correction means of the present invention): The EGR amount is corrected. On the other hand, when it is determined in Step 110 that the operating condition is not in the EGR region (the determination result is NO), the process proceeds to Step 112.

Step 112 (Non-EGR correction means): The average injection amount of all cylinders is corrected. That is, the injection amounts of all the cylinders are uniformly increased or decreased. Note that, in order to correct the deviation of the average air-fuel ratio, in Steps 106 and 111, not EG but EG
The reason for correcting the R amount is as follows. That is,
As shown in FIG. 7, since the engine load is relatively low under the full load condition in the region where the EGR is performed, if the injection amount is increased or decreased in such a region, the engine output changes sensitively to the increase or decrease. In some cases, the driving performance may be adversely affected. To prevent this, the EGR amount is corrected instead of the injection amount.

Next, the method of calculating the average air-fuel ratio and the air-fuel ratio for each cylinder in Step 103 will be described in detail with reference to the flowchart shown in FIG. Step 102: The output of the oxygen concentration sensor 11 is sampled every 10 crank angles (CA), for example. Step200: Signal sampled in Step102 (sensor output)
Is averaged over one cycle (720 CA for a four-cylinder engine) to calculate an average air-fuel ratio. Step 201: Subsequently, the air-fuel ratio for each cylinder is calculated.

The exhaust gas discharged from each cylinder is sent to the oxygen concentration sensor 11 in the order of # 1 cylinder → # 3 cylinder → # 4 cylinder → # 2 cylinder in the order of combustion in each cylinder, for example, as shown in FIG. To reach. At this time, there is a time delay (ΔCA in FIG. 9) until the exhaust gas reaches the oxygen concentration sensor, and this delay decreases as the engine speed increases and the engine load increases. Therefore, ΔCA (the crank angle at which the engine 1 rotates from the time when the # 1 TDC is detected to the time when the exhaust gas of the # 1 cylinder reaches the oxygen concentration sensor 11) is calculated based on the engine conditions read in Step 100.

Step 202: A sample signal is averaged every 180 CA based on ΔCA calculated in Step 201 to calculate a value corresponding to the air-fuel ratio for each cylinder. For example, 0 to 180 CA
Average value of # 1 cylinder, average value of 180 to 360 CA → #
3-cylinder, average value of 360 to 540 CA → # 4 cylinder, 54
Average value of 0 to 720 CA → # 2 cylinder. Thereby, the influence of the exhaust pressure pulsation can be eliminated. Subsequently, in the case of the diesel engine 1 in particular, as shown in FIG. 10, since the combustion variation between cycles is large, it is difficult to obtain an accurate air-fuel ratio (particularly, air-fuel ratio information for each cylinder). Therefore, in Steps 203 to 207, as shown below, Step 200
The average air-fuel ratio calculated in step 202 and the air-fuel ratio for each cylinder calculated in step 202 are averaged over a plurality of cycles (for example, five cycles).

Step 203: It is detected whether or not the operating conditions of the engine 1 have changed due to changes in the number of revolutions, accelerator opening, and the like. Here, if the operating conditions have changed significantly (determination result YES), the process proceeds to Step 204. Step 204: Reset the counter N (N = 0) and end this control. This is because accurate information cannot be obtained because the air-fuel ratio changes every moment while the driving conditions are largely changed, for example, when the vehicle is accelerating. On the other hand, Step20
If it is determined in 3 that the operating conditions have not changed (determination result NO), the process proceeds to Step 205.

Step 205: The counter N has a predetermined value (for example, N
= 5) is determined. Here, if it is not the predetermined value (the determination result is NO), the average air-fuel ratio and the air-fuel ratio for each cylinder calculated this time are stored and stored in Step 206.
Proceed to. Step 206: Increment the counter N (N = N + 1)
Then, the process returns to Step 102 again, and repeats the processes of Steps 102 to 203 described above. On the other hand, if the counter N has reached the predetermined value in Step 205 (determination result YES), the flow proceeds to Step 207. Step 207: The average air-fuel ratio and cylinder-by-cylinder air-fuel ratio for the plurality of cycles are calculated by averaging the average air-fuel ratio and cylinder-by-cylinder air-fuel ratio values stored in Step 205. As a result, as shown in FIG. 11, the value corresponding to the air-fuel ratio for each cylinder can be stably obtained after removing the influence of the exhaust pressure pulsation and the variation for each cycle.

(Effects of the present embodiment) As described above, in the relationship between the air-fuel ratio and the amount of smoke generation, when the deviation of the average air-fuel ratio between the cylinders with respect to the target air-fuel ratio increases, both at high load and low load The amount of smoke generated increases (see FIG. 5). On the other hand, if the variation in the air-fuel ratio between cylinders becomes large,
At high load, the amount of smoke increases, but at low load, the amount of smoke hardly changes (see FIG. 6). From the correlation between the air-fuel ratio and the smoke, when the engine 1 is under a low load, that is, in the low load region of the EGR region, the smoke is reduced even if the injection amount for each cylinder is corrected to reduce the variation in the inter-cylinder air-fuel ratio. It can be seen that the effect that can be reduced is extremely small.

Therefore, in the present system, in the low load range of the EGR range, the injection amount correction for each cylinder is not performed, and the EGR is not performed.
The engine 1 controls the average air-fuel ratio between cylinders by correcting the amount.
When the load is high (in the non-EGR region and the high load region in the EGR region), the variation in the air-fuel ratio between the cylinders is reduced by correcting the injection amount for each cylinder, and the deviation of the average air-fuel ratio between the cylinders is corrected. , Respectively, to control the amount of smoke generation to a predetermined value. This makes it possible to perform appropriate cylinder-by-cylinder or average air-fuel ratio control in accordance with the operating state of the engine 1 using the oxygen concentration sensor 11 with practical accuracy, and to improve emission. In addition, when the engine 1 is under a high load (high load region in the non-EGR region and the EGR region), the deviation of the average air-fuel ratio between the cylinders is corrected before the deviation of the average air-fuel ratio between the cylinders. It is possible to prevent the smoke generation amount from increasing during the fuel ratio correction.

The present system is applied to the diesel engine 1 having a large exhaust pressure pulsation.
Since the output of 1 is averaged for each cycle / number of cylinders = 180 CA to calculate the value corresponding to the air-fuel ratio for each cylinder,
Even when a general limiting current type oxygen concentration sensor 11 is used as the air-fuel ratio detecting means, it is possible to remove the influence of the exhaust pressure pulsation and detect an accurate air-fuel ratio. Further, by averaging the average air-fuel ratio calculated in the above-described Step 200 and the air-fuel ratio of each cylinder calculated in the Step 202 over a plurality of cycles (for example, five cycles), the influence of the combustion variation in each cycle can be reduced. Thus, it is possible to stably obtain the air-fuel ratio for each cylinder.

(Modification) The influence of the shape of the exhaust pipe 9 and the influence of the exhaust turbine in an engine with a supercharger cause
There is a case where the exhaust of each cylinder is not clearly separated for each cylinder, and the exhaust of the cylinders whose combustion order is before and after (for example, the # 3 cylinder and the # 2 cylinder with respect to the # 1 cylinder) is mixed and reaches the oxygen concentration sensor 11. is there. Further, due to a response delay of the oxygen concentration sensor 11, particularly when the engine speed is high, the change in the sensor output may not catch up with the change in the air-fuel ratio for each cylinder. In any of these cases, the air-fuel ratio for each cylinder obtained by the method shown in FIG. 8 is not exactly equal to the air-fuel ratio of each cylinder in a precise sense, and the characteristic value corresponding to the relative magnitude of the air-fuel ratio of each cylinder (( (A first characteristic value of the present invention).

In this system, the air-fuel ratio of each cylinder is directly
Rather than correcting to the target air-fuel ratio, the correction is performed so that the deviation of the characteristic value (the value obtained by averaging the sensor output over 180 CA) corresponding to the air-fuel ratio of each cylinder is minimized. Therefore, it is possible to provide an air-fuel ratio control device having extremely large versatility capable of coping with the above-described cases and the like. Also, in FIG.
When calculating the target air-fuel ratio in Step 101, if the target air-fuel ratio is determined only from the engine conditions such as the engine speed and the accelerator opening, the smoke may not be suppressed to a predetermined value or less. Specifically, this is a case where the intake pressure or the fuel injection pressure changes. For example, if the atmospheric pressure decreases at high altitudes and the intake pressure decreases, the absolute amount of oxygen drawn into the cylinder decreases even if the air-fuel ratio remains the same. As a result, the area where oxygen is locally insufficient in the cylinder increases, and the amount of smoke generated increases.

On the other hand, when the fuel injection pressure decreases due to a change in the characteristics of the fuel injection valve 2 or a change in the injection pressure target value, for example, even if the air-fuel ratio is the same, the atomization of the fuel spray and the mixing state with air deteriorate. Therefore, the utilization rate of oxygen in the cylinder at the time of fuel combustion decreases, and as a result, the region where oxygen is insufficient in the cylinder locally increases, and the amount of smoke generated increases. Therefore, in the present system, in order to cope with these, as shown in FIG. 12, the correction is changed so that the target air-fuel ratio increases as the intake pressure decreases, and as shown in FIG. 13, the fuel injection pressure decreases. The correction is changed so that the target air-fuel ratio increases as the value increases. This makes it possible to set the smoke amount to a predetermined value regardless of changes in the intake pressure or the injection pressure.

In the above embodiment, the four-cylinder common rail diesel engine 1 has been described as an example. However, the present invention can be applied to a multi-cylinder internal combustion engine in which the injection amount can be adjusted for each of the other cylinders. For example, when applied to a six-cylinder engine, when determining a value corresponding to the cylinder-by-cylinder air-fuel ratio, an averaging section for eliminating the influence of exhaust pressure pulsation is set to 720 CA /
6 = 120 CA.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a processing procedure of air-fuel ratio control.

FIG. 2 is a system diagram of an air-fuel ratio control device.

FIG. 3 is a correlation diagram between intake pressure and smoke.

FIG. 4 is a correlation diagram between fuel injection pressure and smoke.

FIG. 5 is a correlation diagram between the deviation of the average air-fuel ratio and smoke.

FIG. 6 is a correlation diagram of a variation in air-fuel ratio between cylinders and smoke.

FIG. 7 is a torque characteristic diagram showing an EGR region.

FIG. 8 is a flowchart showing a processing procedure for calculating an air-fuel ratio.

FIG. 9 is a time chart for explaining a time delay of the oxygen concentration sensor.

FIG. 10 is a drawing in which the output of the oxygen concentration sensor is sampled every 10 CA and overwritten for a plurality of cycles.

FIG. 11 is a drawing in which the output of the oxygen concentration sensor is averaged for each cylinder.

FIG. 12 is a correlation diagram between an intake pressure and a target air-fuel ratio.

FIG. 13 is a correlation diagram between a fuel injection pressure and a target air-fuel ratio.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine (internal combustion engine) 5 Injection pressure sensor (injection pressure detection means) 6 Intake pipe (intake passage) 7 Intake manifold (intake passage) 8 Intake pressure sensor (intake pressure detection means) 11 Oxygen concentration sensor (air-fuel ratio detection means) 13) EGR valve (EGR means) 14 EGR control valve (EGR means) 15 ECU (air-fuel ratio control means)

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F02D 43/00 301 F02D 43/00 301E 301H 301N 45/00 312 45/00 312J 312K 324 324 F02M 25/07 570 F02M 25 / 07 570F 570G 570J G05B 11/36 G05B 11/36 MF term (reference) 3G062 AA01 BA04 CA06 GA05 GA06 GA13 GA15 GA17 3G084 AA01 AA03 BA09 BA13 BA20 CA03 CA04 CA09 DA05 DA10 DA12 DA23 EA05 FA10 EB09 FA09 FA33 3G092 AA02 AA17 AA18 BA04 BB01 DC09 DC10 DE06S EA03 EA08 EA17 EB01 EB05 EC01 FA08 FA18 FA36 GA05 GA06 HA05Z HB01X HB03Z HD05Z HD07X HE01Z HF08Z 3G301 HA02 HA06 JA03 JA05 NA13 NA08 NA13 NA03 NA01 NA03 NA01 NA03 NA01 NA08 PD02Z PE01Z PF03Z 5H004 GA16 GB12 HA13 HB03 HB04 JA13 JA14 JB20 KC56 LA19 LB06

Claims (10)

[Claims] 1. An air-fuel ratio detecting means for detecting an air-fuel ratio in exhaust gas discharged from each cylinder of an internal combustion engine; an EGR means for recirculating a part of exhaust gas to an intake passage of the internal combustion engine; Target air-fuel ratio calculating means for calculating a target air-fuel ratio based on the operating state of the engine; and cylinder-by-cylinder air for calculating a first characteristic value corresponding to the air-fuel ratio for each cylinder based on an output of the air-fuel ratio detecting means. Fuel ratio calculation means, average air-fuel ratio calculation means for calculating a second characteristic value corresponding to the average air-fuel ratio of all cylinders based on the output of the air-fuel ratio detection means, and a fuel injection amount to each cylinder or The air-fuel ratio for each cylinder and the average air-fuel ratio for all cylinders are adjusted so that the air-fuel ratio detected by the air-fuel ratio detection means becomes the target air-fuel ratio by correcting the amount of EGR recirculated to the intake passage by EGR means. Control the air-fuel ratio And a stage, the air-fuel ratio control means is a relatively low load region in the EGR region, the second
Low load correction means for correcting the EGR amount based on the characteristic value of the above. In the EGR region where the load is relatively high, the first load
High load correction means for correcting the fuel injection amount for each cylinder based on the characteristic value of the above, and correcting the EGR amount based on the second characteristic value. In the non-EGR region, the first characteristic value A fuel injection amount for each cylinder based on the second characteristic value, and non-EGR correction means for correcting an average injection amount based on the second characteristic value. . 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the low load correction means reduces a difference between a target value corresponding to the target air-fuel ratio and the second characteristic value. E
An air-fuel ratio control device for an internal combustion engine, which corrects a GR amount. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein said high load correction means is provided for each of said cylinders such that a variation in said first characteristic value among said cylinders is reduced. Air-fuel ratio control for an internal combustion engine, wherein the EGR amount is corrected so that a difference between a target value corresponding to the target air-fuel ratio and the second characteristic value is reduced. apparatus. 4. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the non-EGR correction means is configured to reduce the variation in the first characteristic value among the cylinders. Correcting the fuel injection amount for each cylinder, and then correcting the average injection amount between the cylinders so that the difference between the target value corresponding to the target air-fuel ratio and the second characteristic value is reduced. An air-fuel ratio control device for an internal combustion engine. 5. An air-fuel ratio detecting means for detecting an air-fuel ratio in exhaust gas discharged from each cylinder of the internal combustion engine, and a target air-fuel ratio calculating means for calculating a target air-fuel ratio based on an operation state of the internal combustion engine. Based on the output of the air-fuel ratio detection means, a cylinder-by-cylinder air-fuel ratio calculation means for calculating a characteristic value corresponding to the air-fuel ratio for each cylinder, adjusting the fuel injection amount to each cylinder based on the characteristic value,
A cylinder-to-cylinder air-fuel ratio control unit that controls an air-fuel ratio of each of the cylinders such that an air-fuel ratio detected by the air-fuel ratio detection unit is the target air-fuel ratio. The output of the air-fuel ratio detecting means sampled a plurality of times during one cycle of the engine is averaged for each section corresponding to one cycle / number of cylinders of the internal combustion engine to calculate the characteristic value, and the characteristic value is calculated. An air-fuel ratio control device for an internal combustion engine, wherein a start timing is changed for each operating condition of the internal combustion engine. 6. An air-fuel ratio control apparatus for an internal combustion engine according to claim 5, wherein said cylinder-by-cylinder air-fuel ratio control means controls a fuel injection amount to each cylinder such that a variation in the characteristic value among the cylinders becomes small. An air-fuel ratio control device for an internal combustion engine, characterized by adjusting the following. 7. An air-fuel ratio control apparatus for an internal combustion engine according to claim 6, wherein said cylinder-by-cylinder air-fuel ratio calculating means converts said characteristic value obtained for each section over a plurality of cycles for each corresponding cylinder. An air-fuel ratio control device for an internal combustion engine, wherein the air-fuel ratio control device is characterized by averaging the characteristic values of each cylinder. 8. An air-fuel ratio control apparatus for an internal combustion engine according to claim 5, wherein said cylinder-by-cylinder air-fuel ratio calculating means sets a start timing of a section for averaging the output of said air-fuel ratio detecting means. An air-fuel ratio control device for an internal combustion engine, wherein the earlier the higher the rotation speed or the load of the internal combustion engine, the earlier. 9. The air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising: an intake pressure detection unit configured to detect an intake pressure of the internal combustion engine; An air-fuel ratio control device for an internal combustion engine, wherein the target air-fuel ratio is increased as the output of the intake pressure detecting means decreases. 10. The air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising: an injection pressure detection unit configured to detect a fuel injection pressure of the internal combustion engine, wherein the target air-fuel ratio calculation unit includes: An air-fuel ratio control device for an internal combustion engine, wherein the target air-fuel ratio is increased as the output of the injection pressure detecting means decreases.