JPH0618639U - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Purpose] In an air-fuel ratio control device that provides an oxygen sensor for each cylinder group and performs air-fuel ratio feedback control for each cylinder group,
Highly accurate correction is performed based on the output of an oxygen sensor provided downstream of the catalyst into which the exhaust gas of each cylinder group merges and flows. [Structure] Air-fuel ratio feedback correction coefficient α for the first cylinder group
The average value of ₁ is calculated (S3) and clamped to this average value (S4). Then, only the air-fuel ratio feedback control of the second cylinder group is executed, and the correction amount of the air-fuel ratio feedback control in the second cylinder group is set based on the output of the oxygen sensor on the catalyst downstream side (S5, S6). Next, the air-fuel ratio feedback control of the second cylinder group is clamped (S7-S
9), the air-fuel ratio feedback control of the first cylinder group is executed (S10). Then, the correction amount of the air-fuel ratio feedback control in the first cylinder group is set (S11, S12).

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more specifically, it is configured to detect an air-fuel ratio on each of an upstream side and a downstream side of a catalytic exhaust purification device and execute an air-fuel ratio feedback control based on these detected values. And a controlled air-fuel ratio control device.

[0002]

[Prior art]

 Conventionally, in order to maintain good conversion efficiency in a three-way catalyst provided in an exhaust system for exhaust gas purification, feedback control has been performed on the air-fuel ratio of the engine intake air-fuel mixture to the stoichiometric air-fuel ratio. In such air-fuel ratio feedback control, an oxygen sensor (air-fuel ratio sensor) that detects the air-fuel ratio of the engine intake air-fuel mixture based on the oxygen concentration in the exhaust gas is used in the exhaust manifold relatively close to the combustion chamber to ensure responsiveness. It is installed in the collecting part, etc., and based on the oxygen concentration in the exhaust gas detected by this oxygen sensor, rich lean of the actual air-fuel ratio with respect to the theoretical air-fuel ratio is detected, and the fuel supply amount to the engine is feedback-controlled. I am trying to do it.

However, as described above, the oxygen sensor provided in the exhaust system relatively close to the combustion chamber is exposed to high-temperature exhaust gas, and therefore has characteristics (internal resistance, electromotive force, response time, etc.) due to thermal deterioration. ) Is likely to change, and it is difficult to detect the average air-fuel ratio of all cylinders because the exhaust gas mixture for each cylinder is insufficient.Therefore, the detection accuracy of the air-fuel ratio may vary, resulting in a highly accurate air-fuel ratio. It was difficult to maintain the fuel ratio controllability.

In view of this point, various proposals have been made in which an oxygen sensor is provided on the downstream side of the catalyst and the air-fuel ratio is feedback-controlled using the detection values of the two oxygen sensors (Japanese Patent Laid-Open No. 58-48756). (See gazette, etc.). That is, the oxygen sensor on the downstream side of the catalyst delays the output by the O ₂ storage effect of the three-way catalyst (the state in which the oxygen amount is large when leaner than the stoichiometric air-fuel ratio and is small when rich, continues for a certain period of time. ), The responsiveness is poor, but the air-fuel ratio with the highest CO, HC, and NOx conversion efficiency for the three-way catalyst can be detected. Therefore, the deterioration of the upstream oxygen sensor is compensated for with high accuracy and stability. The detection characteristic is obtained.

Therefore, independent feedback control of the air-fuel ratio is performed based on the detection values of the two oxygen sensors, and the characteristics of the air-fuel ratio feedback control by the oxygen sensor on the upstream side of the catalyst are set to the oxygen sensor on the downstream side. In order to ensure high responsiveness with the sensor on the upstream side, the accuracy of the control point is compensated on the downstream side to perform highly accurate air-fuel ratio feedback control.

As a device for compensating the characteristics of the air-fuel ratio feedback control by the upstream oxygen sensor with the downstream oxygen sensor, for example, while performing the air-fuel ratio feedback control based on the detection of the upstream sensor with good response, When the downstream sensor detects a deviation of the control point and the downstream sensor detects rich / lean against the target, the control constant (control operation amount) of the air-fuel ratio feedback control based on the upstream sensor output is set to the target. By gradually changing the rich / lean direction toward elimination, the air-fuel ratio detected by the downstream sensor repeats rich / lean with respect to the target, and as a result, feedback control based on the upstream sensor is performed. Control is performed so that the average of the points is near the target air-fuel ratio.

[0007]

[Problems to be solved by the device]

 By the way, in a V-type engine or a horizontally opposed engine, an oxygen sensor (hereinafter referred to as an upstream oxygen sensor) is provided for each exhaust manifold for each bank (for each cylinder group), and each oxygen sensor is provided for each bank. In some cases, the detected value was used to set the air-fuel ratio feedback correction value independently, and the air-fuel ratio feedback control was executed in parallel for each bank.

Here, an oxygen sensor (hereinafter, referred to as a downstream oxygen sensor) is provided on the downstream side of the main catalyst interposed downstream from the confluence portion where the exhausts of the cylinder groups are merged. As described above, when the air-fuel ratio feedback control for each cylinder group that is executed in parallel is configured to be corrected based on the output of the downstream oxygen sensor, the output characteristic variation of each upstream oxygen sensor Due to this, there was a fear that the following problems would occur.

That is, due to variations in the output characteristics of the oxygen sensor, the actual air-fuel ratio obtained by the air-fuel ratio feedback control in each cylinder group is unbalanced, and the frequency of the feedback control in each cylinder group is different for each oxygen sensor. The oxygen sensor on the downstream side of the catalyst detects the oxygen concentration in the mixed exhaust gas of each cylinder group, and the deviation of the air-fuel ratio control point in the air-fuel ratio feedback control for each cylinder group Since it is not possible to detect each of them individually, there is a possibility that the deviation of the control point may be erroneously detected and optimal correction may not be performed for any upstream oxygen sensor (air-fuel ratio feedback control system).

Further, there are cases where a pre-catalyst is provided on the downstream side of the upstream oxygen sensor, and in this case as well, if there is a difference in the degree of deterioration between the pre-catalysts, the downstream oxygen sensor causes a shift in the air-fuel ratio control point. However, there is a problem in that it is not possible to detect with high accuracy, and thus it becomes impossible to perform optimum correction. The present invention has been made in view of the above problems, and in a system that detects an air-fuel ratio for each of a plurality of cylinder groups and individually executes an air-fuel ratio feedback control for each cylinder group, Due to the air-fuel ratio sensor installed on the downstream side of the main catalyst that joins and flows in, even if the output characteristics of the air-fuel ratio sensor provided for each cylinder group vary, the air-fuel ratio feedback control for each cylinder group can be performed individually. The purpose is to enable highly accurate correction.

[0011]

[Means for Solving the Problems]

 Therefore, the air-fuel ratio control device for an internal combustion engine according to the present invention is provided with an independent exhaust system for each of a plurality of cylinder groups, and the catalytic exhaust purification is provided downstream of the confluence portion where the exhaust systems for each cylinder group are joined. It is applied to an internal combustion engine equipped with a device and is configured as shown in FIG.

In FIG. 1, an air-fuel ratio sensor is provided in each of the exhaust systems for each of the cylinder groups and on the downstream side of the catalytic exhaust purification device, and the exhaust gas changes according to the air-fuel ratio of the engine intake air-fuel mixture. It is a sensor whose output value changes in response to the concentration of a specific component inside. Then, the air-fuel ratio feedback control means executes the air-fuel ratio feedback control for each cylinder group based on the output value of each air-fuel ratio sensor provided in each exhaust system of each cylinder group.

Further, the correction amount setting means sets the correction amount of the air-fuel ratio feedback control by the air-fuel ratio feedback control means on the basis of the output value of the air-fuel ratio sensor provided on the downstream side of the catalytic exhaust purification device. Set. Here, the cylinder group-based correction control means causes the air-fuel ratio feedback control means to individually execute the air-fuel ratio feedback control for each cylinder group, and the correction amount setting means to set the correction amount individually for each cylinder group. Let it be done.

[0014]

[Action]

 With this configuration, the exhaust system of each cylinder group is provided with an air-fuel ratio sensor, and the air-fuel ratio feedback control is executed for each cylinder group based on the air-fuel ratio of each cylinder group detected by these air-fuel ratio sensors. It On the other hand, an air-fuel ratio sensor is also provided on the downstream side of the catalytic exhaust purification system provided on the downstream side of the merging portion where the exhaust systems of each cylinder group are joined, and based on the output value of this air-fuel ratio sensor, A correction amount for the air-fuel ratio feedback control is set.

Here, in setting the correction amount of the air-fuel ratio feedback control based on the output value of the air-fuel ratio sensor on the downstream side of the catalyst as described above, the air-fuel ratio feedback control is executed individually for each cylinder group. The correction amount is set for each cylinder group. That is, when setting the correction amount of the feedback control based on the output value of the air-fuel ratio sensor on the downstream side of the catalyst, the air-fuel ratio feedback control is not simultaneously executed in a plurality of cylinder groups, and the air-fuel ratio in only one cylinder group is set. The feedback control is executed, and the correction amount corresponding to the air-fuel ratio feedback control being executed is set based on the detection result of the catalyst downstream side air-fuel ratio sensor at that time.

[0016]

【Example】

 An embodiment of the present invention will be described below. In FIG. 2 showing an embodiment, an intake air flow rate Q is controlled in conjunction with an air flow meter 3 for detecting an intake air flow rate Q of the engine, and an accelerator pedal (not shown) in an intake passage 2 of a V-type internal combustion engine 1. A throttle valve 4 is provided, and an electromagnetic fuel injection valve 5 is provided for each cylinder in a branch portion of a downstream intake manifold.

The fuel injection valve 5 is opened and driven by an injection pulse signal from a control unit 6 having a built-in microcomputer, and is fed from a fuel pump (not shown) under pressure to be controlled to a predetermined pressure by a pressure regulator. To the jet supply. Further, a water temperature sensor 7 for detecting the cooling water temperature Tw in the cooling jacket of the engine 1 is provided.

On the other hand, in the exhaust passage, the cylinder group of one of the V-shaped banks is set as the first cylinder group, and the cylinder group of the other bank is set as the second cylinder group. Niholds 8 and 9 are connected. The downstream side of each exhaust manifold 8 and 9 joins to form one exhaust passage 10. Pre-catalysts 11 and 12 for exhaust gas purification are installed at the confluent portions of the exhaust manifolds 8 and 9, respectively, and a main catalyst 13 (catalytic exhaust gas purification device) is installed in the exhaust passage 10. .

An air-fuel ratio for detecting the air-fuel ratio of the engine intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas at the merging portion of the exhaust manifolds 8, 9 upstream of the pre-catalysts 11, 12. Oxygen sensors 14 and 15 as sensors are attached, and an oxygen sensor 16 is also attached downstream of the main catalyst 13. Also, the distributor (not shown) has a built-in crank angle sensor 17, which counts the crank unit angle signal output from the crank angle sensor 17 in synchronization with the engine rotation for a certain period of time, or the crank reference angle signal. The engine rotation speed Ne is detected by measuring the cycle of.

The control unit 6 calculates the basic fuel injection amount Tp on the basis of the intake air flow rate Q and the engine rotation speed Ne, and calculates the air-fuel ratio of each cylinder group detected by the oxygen sensors 14 and 15. Based on this, the air-fuel ratio feedback correction coefficients α ₁ and α ₂ for each cylinder group for obtaining the target air-fuel ratio (for example, the theoretical air-fuel ratio) are calculated by proportional integral control or the like.

Then, by correcting the basic fuel injection amount Tp with the air-fuel ratio feedback correction coefficients α ₁ and α ₂ , final fuel injection amounts Ti ₁ and Ti ₂ are calculated for each cylinder group, and each of them is calculated. An injection pulse signal is sent to the corresponding fuel injection valve 5 according to the fuel injection amounts Ti ₁ and Ti _{2 for} each cylinder group to control the fuel injection amount while performing air-fuel ratio feedback control for each cylinder group.

Further, the oxygen sensor 16 on the downstream side of the main catalyst 13 detects the deviation of the control point in the air-fuel ratio feedback control using the upstream oxygen sensors 14 and 15, and based on the detection result, the air-fuel ratio feedback control is performed. Set the correction amount in. Specifically, during the air-fuel ratio feedback control using the detected values of the upstream oxygen sensors 14 and 15, the air-fuel ratio toward the target lean air-fuel ratio detected by the downstream oxygen sensor 16 is eliminated. By correcting the control operation amount of the feedback correction coefficient α (for example, a proportional operation amount) and learning the correction amount, the correction amount required for accurate feedback correction of the target air-fuel ratio is obtained. .

Here, the state of correction using the downstream oxygen sensor 16 for the air-fuel ratio feedback control for each cylinder group using the detection values of the upstream oxygen sensors 14 and 15 will be described with reference to the flowchart of FIG. To do. In this embodiment, the control unit 6 is provided with software functions as air-fuel ratio feedback control means, cylinder group correction control means, and correction amount setting means, as shown in the flow chart of FIG. .

First, in step 1 (denoted as S1 in the figure. The same applies hereinafter), from the engine speed Ne, the intake air flow rate Q, the cooling water temperature Tw, and the oxygen sensors (O ₂ / S) 14, 15, 16 Input the detection signal of. In the next step 2, it is determined whether or not a condition for setting the correction amount of the air-fuel ratio feedback control using the upstream oxygen sensors 14 and 15 based on the output of the downstream oxygen sensor 16 is satisfied.

The condition is an operating state in which air-fuel ratio feedback control using at least the upstream oxygen sensors 14 and 15 is performed, and the cooling water temperature Tw is equal to or higher than a predetermined temperature, or a predetermined time or more has elapsed from the start, etc. Is a condition. Here, when the condition for setting the correction amount is not satisfied, the correction amount is not set, so the flow chart ends as it is, but in reality, the condition for performing the air-fuel ratio feedback control is If so, the air-fuel ratio feedback correction coefficients α ₁ and α ₂ using the output values from the upstream oxygen sensors 14 and 15 are calculated in parallel. The control operation amount (proportional operation amount) is corrected using the correction amount set for each cylinder group.

As a condition for setting the correction amount for the air-fuel ratio feedback control based on the output of the downstream oxygen sensor 16, the correction amount may be set only once after the engine is started. On the other hand, if the condition for setting the correction amount is satisfied, when it is determined in step 2, the process proceeds to step 3.

At step 3, the oxygen sensor 14 is used to calculate the average value of the air-fuel ratio feedback correction coefficient α ₁ corresponding to the first cylinder group which is proportionally and integral controlled. In the next step 4, the air-fuel ratio feedback correction coefficient α ₁ used in the first cylinder group is clamped to the average value calculated in the above step 3, the air-fuel ratio feedback control for the first cylinder group is stopped, and the second cylinder Only the air-fuel ratio feedback control using the oxygen sensor 15 for the group is executed.

Subsequently, in step 5, in the state in which only the second cylinder group is subjected to the air-fuel ratio feedback control as described above, a correction for the air-fuel ratio feedback control in the second cylinder group is made from the output value of the downstream oxygen sensor 16. An amount, specifically, a correction amount PHOS2 of the proportional operation amount P used when proportionally controlling the correction coefficient α ₂ is calculated. That is, when the downstream side oxygen sensor 16 detects a rich (lean) state with respect to the target air-fuel ratio, the air-fuel ratio feedback correction coefficient α ₂ is controlled to decrease (increase), and proportional control of the correction coefficient α ₂ is performed. Set the correction amount to decrease (increase) the proportional operation amount used in the increasing direction and conversely increase (decrease) the proportional operation amount in the decreasing direction. Then, the correction amount PHOS2 that allows the average of the air-fuel ratios detected by the downstream oxygen sensor 16 to substantially match the target air-fuel ratio is learned from the correction result. Such learning is performed, for example, by averaging the correction level at the time of detecting rich / lean inversion by the downstream oxygen sensor 16.

In the next step 6, the correction amount PHOS2 for the air-fuel ratio feedback control of the second cylinder group is set to the required level based on the number of times the downstream oxygen sensor 16 reverses the rich / lean determination with respect to the target air-fuel ratio. Correspondingly, it is judged whether or not the necessary and sufficient learning is done. Then, when the necessary correction amount for the air-fuel ratio feedback control of the second cylinder group is obtained, the process proceeds to step 7, and the correction amount PHOS2 is used to execute the air-fuel ratio feedback control for the second cylinder group. In step 8, the average value of the correction coefficient α ₂ in the air-fuel ratio feedback control is calculated.

When the average value is obtained, in step 9, the correction coefficient α ₂ corresponding to the second cylinder group is clamped to the average value, the air-fuel ratio feedback control for the second cylinder group is stopped, and the next step At 10, instead, the air-fuel ratio feedback control for the first cylinder group is restarted. When only the air-fuel ratio feedback control for the first cylinder group is executed, the routine proceeds to step 11, and similarly to the above, the correction coefficient α ₁ is proportionally controlled based on the output of the downstream oxygen sensor 16 at this time. The correction amount PHOS 1 of the proportional operation amount P used at this time is learned. When it is determined in step 12 that the learning is completed, the learned correction amount PHOS1 is actually used to execute the air-fuel ratio feedback control for the first cylinder group.

As described above, in this embodiment, the air-fuel ratio feedback control for each cylinder group is individually executed for each cylinder group, and the correction amount for the air-fuel ratio feedback control being executed is output by the output of the downstream oxygen sensor 16. It is set for each cylinder group based on. With this configuration, since the air-fuel ratio feedback control for the other cylinder group is stopped, the downstream oxygen sensor 16 is controlled to the control point due to the difference in the control frequency based on the variation in the output characteristics of the two oxygen sensors 14 and 15. Highly accurate correction is possible without significantly misdetecting the deviation. Further, even if there is a difference in the control point deviation between the cylinder groups, the correction amount is individually calculated by performing feedback control individually, so that the deviation of each control point can be converged to the vicinity of the target. Further, in the case where the pre-catalysts 11 and 12 are provided in the downstream portions of the upstream oxygen sensors 14 and 15 as in the present embodiment, even if there is a deterioration difference between the pre-catalysts 14 and 15, the deterioration difference causes It is possible to avoid making an erroneous correction.

In this embodiment, the pre-catalysts 14 and 15 are provided as described above, but the main catalyst 13 alone may be provided as a catalyst. Further, it is obvious that the method of setting the correction amount for the air-fuel ratio feedback control based on the oxygen sensor 16 provided on the downstream side of the catalyst is not limited to the above method.

[0033]

[Effect of device]

 As described above, according to the present invention, in a system in which an independent exhaust system is provided for each of a plurality of cylinder groups, and an air-fuel ratio sensor provided for each of these exhaust systems performs air-fuel ratio feedback control for each cylinder group, With the air-fuel ratio sensor installed downstream of the catalyst installed downstream of the confluence of each exhaust system, the air-fuel ratio feedback control for each cylinder group can be corrected with high accuracy. The optimum air-fuel ratio feedback control has the effect of improving the exhaust quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is a system schematic diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart showing air-fuel ratio feedback control according to the embodiment.

[Explanation of symbols]

 1 engine 3 air flow meter 4 throttle valve 5 fuel injection valve 6 control unit 7 water temperature sensor 8, 9 exhaust manifold 10 exhaust passage 11, 12 pre-catalyst 13 main catalyst 14, 15, 16 oxygen sensor (air-fuel ratio sensor) 17 crank angle sensor

Claims (1)

[Scope of utility model registration request] 1. An air-fuel ratio of an internal combustion engine having an independent exhaust system for each of a plurality of cylinder groups, and further comprising a catalytic exhaust purification device on a downstream side of a merging portion where the exhaust systems of the respective cylinder groups are merged. A control device, which is provided on each of the exhaust systems for each of the cylinder groups and on the downstream side of the catalytic exhaust purification device, and is sensitive to the concentration of a specific component in the exhaust gas that changes depending on the air-fuel ratio of the engine intake air-fuel mixture. An air-fuel ratio feedback control means for executing air-fuel ratio feedback control for each cylinder group based on the output values of the air-fuel ratio sensor whose output value changes and each air-fuel ratio sensor provided in each exhaust system of each cylinder group. And a correction amount for the air-fuel ratio feedback control by the air-fuel ratio feedback control means is set based on the output value of the air-fuel ratio sensor provided on the downstream side of the catalytic exhaust purification device. Individual cylinder group in which the positive amount setting means and the air-fuel ratio feedback control by the air-fuel ratio feedback control means are individually executed for each cylinder group, and the correction amount is set by the correction amount setting means individually for each cylinder group. An air-fuel ratio control device for an internal combustion engine, comprising: a correction control means.