JPH10159637A - Fuel injection controller for internal combustion engine and method for controlling fuel injection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct with high accuracy, the fuel injection amount of each air cylinder per air cylinder on the basis of the detected value of an oxygen concentration sensor, in an internal combustion engine such as a diesel engine. SOLUTION: The fuel injection amount of each air cylinder is corrected per air cylinder on the basis of the detected value of an oxygen concentration sensor 17 during a high load/low rotational period. Hereby, in an operational range having no influences of an EGR device 20 and a turbosupercharger 13 at all, and in a range having a low oxygen concentration that the detecting characteristics of the oxygen concentration sensor 17 is excellent, and besides, in a low rotational range where corresponding relation between fuel injection of each air cylinder and the detected value of the oxygen concentration sensor 17 is easily discriminated, the dispersion of the fuel injection amount of each air cylinder due to difference in individuals when manufactured (dispersion) and secular deterioration and the like are corrected with high accuracy per air cylinder by detecting the oxygen concentration of each air cylinder with high accuracy per air cylinder. As to the discrimination of each air cylinder, a specific air cylinder can be discriminated by temporarily increasing or decreasing the fuel injection amount of the specific air cylinder, and the other air cylinder is discriminated from the order of ignition on the basis of this specific air cylinder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection system for an internal combustion engine having a function of detecting an oxygen concentration in exhaust gas discharged from an internal combustion engine such as a diesel engine and correcting variations in fuel injection amount of each cylinder. The present invention relates to a control device and a fuel injection control method.

[0002]

2. Description of the Related Art In a fuel injection device for an internal combustion engine such as a diesel engine, a deviation occurs between a fuel injection amount command value and an actual fuel injection amount due to individual differences (variation) during manufacture and deterioration over time. Makes the idle speed unstable,
It caused the engine vibration to increase. In an internal combustion engine with an exhaust gas recirculation device (EGR device),
The deviation of the fuel injection amount of each cylinder has also caused an increase in smoke.

[0003] As a countermeasure for this, in gasoline engines,
As disclosed in Japanese Patent Application Laid-Open No. 57-126527, the oxygen concentration in the exhaust gas discharged from each cylinder is detected by an oxygen concentration sensor installed in an exhaust pipe, and the rich signal of each cylinder is detected from the output signal of the oxygen concentration sensor. / Lean is determined, and the valve opening time (fuel injection amount) of the fuel injection valve of each cylinder is corrected so that the fuel injection amount of each cylinder becomes uniform.

[0004]

Generally, in a gasoline engine, in order to purify exhaust gas with a three-way catalyst, feedback control is performed based on an output signal of an oxygen concentration sensor so as to maintain an air-fuel ratio at a stoichiometric air-fuel ratio. Therefore, the fuel injection amount of each cylinder is controlled so that the oxygen concentration in the exhaust gas becomes almost 0%. Therefore, currently available oxygen concentration sensors can accurately detect an oxygen concentration close to 0%, and as shown in FIG. 4, a sensor whose detection error increases as the oxygen concentration increases. It is a characteristic.

[0005] On the other hand, a diesel engine is characterized in that the fuel is burned under excess oxygen, so that the oxygen concentration in the exhaust gas is high. In addition, in a diesel engine equipped with an EGR device or a turbocharger, the oxygen concentration in the exhaust fluctuates greatly depending on the operating state of the EGR device or the turbocharger. It cannot be determined whether the difference is due to the variation in the fuel injection amount or the operation of the EGR device or the turbocharger. From these circumstances,
In a diesel engine, even if an oxygen concentration sensor is installed in the exhaust pipe, it is not possible to accurately determine the variation in the fuel injection amount of each cylinder from the output signal of the oxygen concentration sensor. It was not possible to correct the fuel injection amount for each.

The above-mentioned Japanese Patent Application Laid-Open No. 57-126527 is also known.
In order to determine which cylinder the oxygen concentration detected by the oxygen concentration sensor is the oxygen concentration of the exhaust gas discharged from, the exhaust gas discharged from each cylinder reaches the oxygen concentration The delay time Δt required until the output signal of the concentration sensor changes is uniquely determined from the intake air amount and the engine speed, and the cylinder having the oxygen concentration detected by the oxygen concentration sensor is discharged before the delay time Δt. Thus, the cylinders are estimated to have been lost, and the fuel injection amount of each cylinder is corrected.

However, the delay time Δt not only fluctuates due to a difference in the length of the exhaust manifold of each cylinder and exhaust interference, but also fluctuates greatly depending on the operating state of the EGR device and the turbocharger. Therefore, if the delay time Δt is uniquely determined from the intake air amount and the engine speed as described in the above publication, there is a possibility that the cylinder discrimination may be erroneous, and the reliability of the correction of the fuel injection amount is secured. Can not do it.

The present invention has been made in view of such circumstances, and a first object is to provide a diesel engine and the like.
Even in an internal combustion engine having a high oxygen concentration in exhaust gas, the fuel injection amount of each cylinder can be accurately corrected for each cylinder based on the detection value of the oxygen concentration detection means. It is an object of the present invention to accurately perform cylinder discrimination based on a detection value of an oxygen concentration detection unit and improve the reliability of fuel injection amount correction.

[0009]

In order to achieve the first object, according to the first and seventh aspects of the present invention, the oxygen concentration in exhaust gas discharged from each cylinder of an internal combustion engine is detected. The fuel injection amount of each cylinder is corrected for each cylinder based on the detection value of the oxygen concentration detecting means when the internal combustion engine is at a high load and a low speed.

Here, the reason why the fuel injection amount of each cylinder is corrected at the time of high load and low rotation will be described. At a high load, the fuel injection amount is large, so that the oxygen concentration in the exhaust gas becomes low, and the oxygen concentration in the exhaust gas can be detected in a region where the detection error of the oxygen concentration detecting means is relatively small. In addition, at a high load, the EGR device (exhaust gas recirculation means) does not operate,
The oxygen concentration in the exhaust is not affected by the EGR at all.

In addition, when the engine speed is low, the time interval between the fuel injection of each cylinder becomes sufficiently long in view of the detection response of the oxygen concentration detecting means, so that the difference between the fuel injection of each cylinder and the detection value of the oxygen concentration detecting means is obtained. It is easy to determine the correspondence. In addition, at the time of low rotation, the turbocharger (intake supercharger) does not operate, and the oxygen concentration in the exhaust is not affected by the turbocharger at all.

Therefore, when the fuel injection amount of each cylinder is corrected for each cylinder based on the detection value of the oxygen concentration detecting means at the time of high load and low rotation as in the present invention, the following effects can be obtained. it can.

There is no influence from the EGR or the turbocharger. Since the oxygen concentration in the exhaust gas is relatively low, the oxygen concentration can be detected in a region where the detection characteristics of the oxygen concentration detecting means are relatively good,
Oxygen concentration detection accuracy can be improved. Since the time interval of the fuel injection of each cylinder is long, it is easy to determine the correspondence between the fuel injection of each cylinder and the detection value of the oxygen concentration detecting means.

With these effects, the oxygen concentration corresponding to the fuel injection amount of each cylinder can be accurately detected for each cylinder, and the fuel concentration of each cylinder due to individual differences (variation) during manufacturing and deterioration over time can be detected. Variations in the injection amount can be accurately corrected for each cylinder.

However, the scope of application of the present invention is not limited to a system equipped with both an EGR device and a turbocharger, and is also applicable to a system having only one of them or a system having neither of them. .

When the present invention is applied to a system having both an EGR device and a turbocharger, the EGR device (exhaust recirculation means) and the turbocharger (intake supercharger) When both of them are not operating, the fuel injection amount of each cylinder may be corrected for each cylinder based on the detection value of the oxygen concentration detecting means. Thus, the oxygen concentration corresponding to the fuel injection amount of each cylinder can be accurately detected for each cylinder without being affected by the EGR or the turbocharger, and the variation of the fuel injection amount of each cylinder can be detected. Correction can be made accurately every time.

On the other hand, a third aspect is a technique for correcting the fuel injection amount of each cylinder when the operating state of the internal combustion engine fluctuates (that is, in a transient state). One cycle is based on the detection value of the oxygen concentration detecting means. In addition to calculating an oxygen concentration average value (hereinafter referred to as “oxygen concentration cycle average value”) for each (720 ° C. A), a target oxygen concentration for each cylinder is calculated from a variation amount of the oxygen concentration cycle average value during a plurality of cycles. . Thereby, the target oxygen concentration for each cylinder can be calculated with high accuracy. Then, the fuel injection amount of each cylinder is corrected for each cylinder in a direction in which the deviation between the oxygen concentration for each cylinder detected by the oxygen concentration detection means and the target oxygen concentration for each cylinder decreases. Thus, even during a transition, the oxygen concentration of each cylinder can be controlled to the target oxygen concentration for each cylinder, and the variation in the fuel injection amount of each cylinder can be accurately corrected for each cylinder.

In the case where the correction amount of the fuel injection amount of each cylinder is large, if the correction is performed at a stretch, torque fluctuation and engine vibration may occur and drivability may be reduced.

As a countermeasure, the fuel injection amount of each cylinder may be gradually corrected over a plurality of cycles. With this configuration, the correction amount of the fuel injection amount per correction can be reduced, torque fluctuation and engine vibration due to correction of the fuel injection amount can be suppressed, and drivability can be improved. .

Further, it is preferable that the fuel injection amount of each cylinder is corrected for each cylinder so that the total value of the fuel injection amounts of all cylinders does not change before and after the correction. This can prevent the torque from fluctuating before and after the correction,
Drivability can be improved.

In order to achieve the above-mentioned second object, according to the present invention, it is determined in which cylinder the oxygen concentration detected by the oxygen concentration detecting means is the oxygen concentration of the exhaust gas discharged from which cylinder. For this purpose, the fuel injection amount of the specific cylinder is temporarily increased or decreased, and the specific cylinder is determined by the cylinder determining means from the relationship between the increase and decrease and the detection value of the oxygen concentration detecting means. That is, when the fuel injection amount of a specific cylinder is temporarily increased or decreased, the oxygen concentration in the exhaust gas discharged from the specific cylinder changes in comparison with the oxygen concentration in the exhaust gas discharged from the other cylinders. Therefore, by detecting the change in the oxygen concentration, a specific cylinder can be determined with high accuracy, and the other cylinders can be accurately determined from the ignition order with reference to the specific cylinder.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment (1)] An embodiment (1) of the present invention will be described below with reference to FIGS. First, a schematic configuration of the entire engine control system will be described with reference to FIG. An intake pipe 12 of a diesel engine 11 that is an internal combustion engine includes:
Intake turbine 1 of turbocharger 13 as intake supercharging means
4 are installed. An exhaust turbine 15 connected to an intake turbine 14 of the turbocharger 13 is installed in an exhaust pipe 16 of the diesel engine 11, and the exhaust turbine 15 is rotationally driven by the kinetic energy of the exhaust gas so that the intake turbine 14 Is rotated to generate supercharging pressure. In the exhaust pipe 16 on the downstream side of the exhaust turbine 15,
A limiting current type oxygen concentration sensor 17 is provided as oxygen concentration detection means for detecting the oxygen concentration in the exhaust gas.

An EG is provided between an exhaust pipe 16 on the upstream side of the exhaust turbine 15 and the intake pipe 12 on the downstream side of the intake turbine 14.
The R pipe 18 is connected, and an EGR valve 19 of an electronic control type is installed at the outlet side of the EGR pipe 18.
By adjusting the valve opening of No. 9, the EGR flow rate passing through the EGR pipe 18 is controlled. These EGR pipes 18 and E
An exhaust gas recirculation device (E
GR device 20 is configured. A fuel injection valve 21 is attached to a cylinder head of each cylinder of the diesel engine 11.

The air supercharged by the turbocharger 13 is drawn into each cylinder of the diesel engine 11 through the intake manifold 22. Fuel is injected from the fuel injection valve 21 into the high-temperature air compressed in each cylinder and self-ignites, and the exhaust gas of each cylinder merges into one exhaust pipe 16 through the exhaust manifold 23 and is discharged into the atmosphere. You.

The operating state of the diesel engine 11 is detected by an engine speed sensor 24, an accelerator sensor 25, an oxygen concentration sensor 17, and the like, and these output signals are read into a control circuit 26 for engine control. The control circuit 26 is mainly composed of a microcomputer, and based on the engine speed detected by the engine speed sensor 24 and the accelerator opening detected by the accelerator sensor 25, a program shown in FIGS. The fuel injection amount of each cylinder is calculated according to the following formula (this function corresponds to an injection amount calculating means in the claims), and an injection signal corresponding to the fuel injection amount is output to the fuel injection valve 21 of each cylinder to produce fuel. In addition to executing the injection control, the EGR flow rate of the EGR device 20 (valve opening of the EGR valve 19) so that the oxygen concentration in the exhaust gas detected by the oxygen concentration sensor 17 matches the target oxygen concentration.
To reduce NOx emissions.

Various programs for engine control, such as the cylinder-by-cylinder injection amount correction program shown in FIG. 2 and the fuel injection correction amount correction program shown in FIG. 3, are stored in a ROM (storage medium) incorporated in the control circuit 26. I have.

The cylinder-by-cylinder injection amount correction program of FIG. 2 is repeatedly executed by the control circuit 26 at every predetermined crank angle.
It serves as a cylinder-by-cylinder injection amount correction means described in the claims. When the cylinder-by-cylinder injection amount correction program is started, first, in step 101, based on the output signals of the engine speed sensor 24 and the accelerator sensor 25, it is determined whether or not the current engine operating state is in the high-load low-speed region. Is determined. Here, the high-load low-rotation region corresponds to an operation region in which both the turbocharger 13 and the EGR device 20 do not operate.

If the engine is not in the high-load low-speed range, the program is terminated without performing the subsequent cylinder determination and injection amount correction processing. An injection amount correction process is performed. The reason for this is as follows.

From the detection characteristics of the oxygen concentration sensor 17 shown in FIG. 4, the oxygen concentration in the exhaust gas can be detected with higher accuracy when the load is high. That is, the detection characteristics of the oxygen concentration sensor 17 are as follows:
There is a characteristic that the detection error increases as the oxygen concentration increases. At a high load, the fuel injection amount is large, so that the oxygen concentration in the exhaust gas becomes low, and the oxygen concentration in the exhaust gas can be detected in a region where the detection error is relatively small.

At a high load, the EGR valve 19 is closed, the EGR flow becomes zero, and the oxygen concentration in the exhaust gas becomes
Not affected by flow rate. On the other hand, when the load is low, the EGR valve 19 operates, so that the oxygen concentration in the exhaust fluctuates under the influence of the EGR flow rate, and the variation in the oxygen concentration in the exhaust is caused by the variation in the fuel injection amount. It cannot be determined whether it is due to the EGR flow rate.

When the engine speed is low, the time interval between the fuel injection of each cylinder becomes sufficiently long in view of the detection response of the oxygen concentration sensor 17, so that the fuel injection of each cylinder and the oxygen concentration sensor 17
It is easy to determine the correspondence relationship with the detected value, and the cylinder determination described later becomes easy.

At the time of low rotation, the turbocharger 13 does not operate (that is, the supercharging pressure becomes lower than the atmospheric pressure), and the oxygen concentration in the exhaust is not affected by the turbocharger 13 at all.
On the other hand, at the time of high rotation, since the turbocharger 13 operates, the oxygen concentration in the exhaust fluctuates due to the influence of the turbocharger 13, and the cause of the fluctuation in the oxygen concentration in the exhaust is as follows. It cannot be determined whether it is due to a variation in the fuel injection amount or to the turbocharger 13.

For these reasons, the fuel injection amount of each cylinder is corrected as follows at high load and low rotation. First, at step 102, a cylinder discrimination threshold value (see FIG. 5) of the oxygen concentration according to the engine operating state is determined by the control circuit 26.
From the data table stored in the ROM and starts fuel injection for cylinder discrimination. As shown in FIG. 5, the fuel injection for the cylinder discrimination is based on the basic injection amount determined according to the engine operating state, and the fuel injection amount of a specific cylinder (cylinder in the example of FIG. 5) is determined. Temporarily increase until the end. The cylinder determination threshold value of the oxygen concentration is set slightly higher than the oxygen concentration corresponding to the cylinder whose fuel injection amount has been increased. As a result, as shown in FIG. 5, the oxygen concentration in the exhaust gas discharged from the cylinder in which a large amount of fuel is injected falls below the oxygen concentration threshold value for cylinder identification, and the oxygen concentration of the other cylinders decreases. Becomes higher than the threshold. Using this relationship, cylinder determination is performed as follows.

That is, in step 103, it is determined whether or not the oxygen concentration detected by the oxygen concentration sensor 17 has dropped below the cylinder determination threshold value (ie, whether or not the oxygen concentration of a specific cylinder has been detected). It waits until the concentration falls below the cylinder discrimination threshold. Thereafter, when the oxygen concentration falls below the cylinder determination threshold value, the oxygen concentration is determined to be the oxygen concentration in the exhaust gas discharged from the specific cylinder (specific cylinder is determined). Thereafter, in step 104, the delay time from when fuel is injected into the cylinder to when it is detected as the oxygen concentration is converted into the crank angle of the diesel engine 11 and calculated as the crank angle delay Δθ. The fuel injection for cylinder discrimination ends.

The processing of steps 101 to 105 described above plays a role as cylinder discriminating means in the claims. As shown in FIG. 5, since the order in which the oxygen concentration in the exhaust gas discharged from each cylinder reaches the oxygen concentration sensor 17 and is detected is the same as the ignition order, the ignition order is based on a specific cylinder. The other cylinders are discriminated from the order.

After the cylinder discrimination is completed, the fuel injection amount of each cylinder is corrected for each cylinder based on the value detected by the oxygen concentration sensor 17 as follows. First, in step 106, an oxygen concentration average value (oxygen concentration cycle average value) for each cycle (720 ° C. A) is calculated as a target value, and the oxygen concentration of each cylinder detected by the oxygen concentration sensor 17 is calculated as the target value. Compare. Thereafter, in step 107, in a cylinder having an oxygen concentration higher than the target value, the valve opening time of the fuel injection valve 21 is lengthened to inject more fuel, and conversely, in a cylinder having an oxygen concentration lower than the target value, the fuel injection valve The correction amount ΔQ of the fuel injection amount of each cylinder is determined for each cylinder so that the valve opening time of 21 is shortened to reduce the fuel injection amount. In the method of calculating the correction amount ΔQ, first, an oxygen concentration error of each cylinder is calculated from a difference between the oxygen concentration of each cylinder and a target value, and the correction amount ΔQ of the fuel injection amount of each cylinder is calculated in accordance with the oxygen concentration error. Is calculated for each cylinder.

Thereafter, in step 108, after the corrected fuel is injected, the oxygen concentration detected by the oxygen concentration sensor 17 coincides with the target value after a lapse of time corresponding to the crank angle delay Δθ obtained in step 104. Judge whether or not
If the oxygen concentration coincides with the target value, the program ends.If the oxygen concentration deviates from the target value, the process returns to step 106, and the above-described correction of the fuel injection amount of each cylinder is repeated. This program ends when the oxygen concentration in the cylinder matches the target value.

According to the cylinder-by-cylinder injection amount correction program described above, when the fuel injection amount of a specific cylinder is increased as shown in FIG. Since the oxygen concentration in the exhaust gas is lower than the oxygen concentration in the exhaust gas discharged from other cylinders, a specific cylinder can be accurately determined by detecting the decrease in the oxygen concentration. The other cylinders can be accurately determined based on the ignition order based on the cylinder number. Thus, unlike Japanese Patent Application Laid-Open No. 57-126527, based on the detection value of the oxygen concentration sensor 17 without being affected by the difference in the length of the exhaust manifold 23 of each cylinder and the mounting position of the oxygen concentration sensor 17. Thus, cylinder discrimination can be performed with high accuracy.

Further, since the fuel injection amount of each cylinder is corrected for each cylinder based on the value detected by the oxygen concentration sensor 17 at high load and low rotation, the influence of the EGR device 20 and the turbocharger 13 is not affected. A low-rotation region in which the operation is not received at all and the oxygen concentration sensor 17 has good detection characteristics and the oxygen concentration is low, and it is easy to determine the correspondence between the fuel injection of each cylinder and the detection value of the oxygen concentration sensor 17. Thus, it is possible to accurately detect the oxygen concentration of each cylinder for each cylinder, and to accurately correct the variation of the fuel injection amount of each cylinder due to individual differences (variation) during manufacturing and deterioration over time for each cylinder. it can.

When the fuel injection amount is corrected in step 107, if the total value of the fuel injection amounts of all the cylinders changes before and after the correction during steady operation, torque fluctuations occur and drivability decreases.

As a countermeasure, the control circuit 26 executes a fuel injection correction amount correction program shown in FIG. 3, and performs a fuel injection correction so as not to change the total value of the fuel injection amounts of all the cylinders before and after the correction during steady operation. The correction amount is corrected in the following procedure.
First, in step 201, it is determined whether or not the engine operation state is a steady state. If not, the program is terminated without performing the subsequent processing. That is,
At the time of transition, the total value (torque) of the fuel injection amount of all cylinders changes every moment in accordance with the engine operating state. Therefore, the fuel injection correction amount of each cylinder is reduced only during the steady operation in which the fuel injection amount is controlled to be constant. This is to correct the total value of the fuel injection amounts of the cylinders so as to be constant.

If it is in the steady state, the process proceeds to step 202, where the total value of the fuel injection amounts of all the cylinders corrected in step 107 of FIG.
Then, it is determined whether or not the total value of the fuel injection amounts of all cylinders before and after the correction is the same, and if they are the same, the process proceeds to step 208 and the fuel injection amount of each cylinder obtained in step 107 of FIG. The correction amount is used without correction.

On the other hand, if the total value of the fuel injection amounts of all the cylinders before and after the correction is not the same, the process proceeds from step 203 to step 204, where the total value of the fuel injection amounts of all the cylinders after the correction is It is determined whether or not the number is larger than the above. If the number is larger, the correction amount of the cylinder whose amount has been corrected is reduced (step 205). ). Thereafter, in step 207, it is determined whether or not the total value of the fuel injection amounts of all the cylinders after the correction is the same as that before correction, and if not, the process returns to step 204 to correct the correction amount described above. repeat. In this way, if the total value of the fuel injection amounts of all cylinders after correction becomes the same as that before correction, step 20 is executed.
In step 20, the fuel injection correction amount for each cylinder is
At 5,206, the corrected value is determined.

By performing the above processing, the total value of the fuel injection amounts of all the cylinders can be kept constant before and after the correction during the steady operation, and the torque can be prevented from fluctuating before and after the correction. Can be improved.

For the same purpose, it is preferable to control the cylinders so that the total value of the fuel injection amounts of all the cylinders is the same during the cylinder discrimination. That is, at the time of cylinder discrimination, in order to increase the fuel injection amount of a specific cylinder, the total value of the fuel injection amounts of all cylinders increases if the fuel injection amounts of the other cylinders are the same as during normal operation. The torque increases instantaneously.

As a countermeasure, when the fuel injection amount of a specific cylinder is increased by a predetermined amount F at the time of cylinder discrimination, the fuel injection amount of the other cylinders is increased to F / 3 (in the case of a four-cylinder engine). In this case, the total value of the fuel injection amounts of all the cylinders is kept constant (generally, in an N-cylinder engine, the other cylinders may be reduced by F / (the number of all cylinders N-1)).
As a result, even when the fuel injection amount of a specific cylinder is increased at the time of cylinder determination, the torque can be kept constant, and drivability can be improved.

In the cylinder discrimination, the fuel injection amount of a specific cylinder may be reduced by a predetermined amount F. In this case, the fuel injection amount of another cylinder is reduced by F / (total number of cylinders). N-
The fuel injection amount of all cylinders may be kept constant by increasing the amount by 1). At the time of cylinder discrimination, if the fuel injection amount of a specific cylinder is reduced, the oxygen concentration in the exhaust gas discharged from the specific cylinder increases as compared with the oxygen concentration in the exhaust gas discharged from other cylinders. By detecting the increase in the oxygen concentration, a specific cylinder can be accurately determined.

[Embodiment (2)] When the fuel injection amount is corrected in a high load region as in the embodiment (1),
The operating state of the engine is not limited to a steady state, but may be in a transient state in which a change in the engine speed, a change in the fuel injection amount command value, or the like occurs. In the transient state, the target oxygen concentration for each cylinder changes.

As a countermeasure, in the embodiment (2) of the present invention shown in FIGS. 6 and 7, the target oxygen concentration of each cylinder is calculated to determine the fuel injection correction amount ΔQ of each cylinder. Hereinafter, the details of the cylinder-by-cylinder injection amount correction program of FIG. 6 that performs this correction processing will be described. Also in this embodiment (2), the same method as in steps 101 to 105 in FIG.
At the time of high-load low-speed rotation, the cylinder is determined (steps 301 to 301).
305).

After the cylinder discrimination is completed, in step 306, an average value of the oxygen concentration for each cylinder is calculated based on the detection value of the oxygen concentration sensor 17 (hereinafter, referred to as "oxygen concentration cylinder-specific average value"), and one cycle ( The average value of oxygen concentration (hereinafter referred to as “oxygen concentration cycle average value”) for each 720 ° A) is calculated. Thereafter, in step 307, the average value of the current oxygen concentration cycle is compared with the average value of the oxygen concentration cycle in the previous cycle, and the amount of change (gradient) of the average value of the oxygen concentration cycle is calculated. The target oxygen concentration of each cylinder is calculated from the amount of change in the average value. here,
As shown in FIG. 7, the target oxygen concentration of each cylinder is determined by a straight line connecting the average value of the oxygen concentration cycle at the center of each cycle. Therefore, at the time of transition when the oxygen concentration cycle average changes, the target oxygen concentration of each cylinder differs for each cylinder.

Thereafter, the routine proceeds to step 309, where the average value of the oxygen concentration of each cylinder determined in step 306 is compared with the target oxygen concentration of each cylinder, and the average value of the oxygen concentration of each cylinder is higher than the target oxygen concentration. Then, the valve opening time of the fuel injection valve 21 is lengthened to inject a large amount of fuel.
The correction amount ΔQ of the fuel injection amount of each cylinder is determined for each cylinder so that the valve opening time of 1 is shortened to reduce the fuel injection amount. In the method of calculating the correction amount ΔQ, first, oxygen concentration errors Δa to Δd (see FIG. 7) of each cylinder are calculated from the difference between the oxygen concentration of each cylinder and the target oxygen concentration. The correction amount ΔQ of the fuel injection amount of each cylinder is calculated for each cylinder according to Δa to Δd.

Thereafter, in step 310, after the corrected fuel injection, the crank angle delay Δ
It is determined whether or not the oxygen concentration detected by the oxygen concentration sensor 17 (the average value of the oxygen concentration cylinders) detected by the oxygen concentration sensor 17 after the lapse of time corresponding to θ matches the target oxygen concentration. When the program is completed and the oxygen concentration deviates from the target oxygen concentration, the process returns to step 306 to repeat the above-described correction of the fuel injection amount of each cylinder, and when the oxygen concentration of all cylinders matches the target oxygen concentration. Then, the program ends.

According to the above-described cylinder-by-cylinder injection amount correction program, the target oxygen concentration for each cylinder is calculated from the variation in the oxygen concentration cycle average value, and the target oxygen concentration is adjusted so that the oxygen concentration of each cylinder matches the target oxygen concentration. Since the fuel injection amount of each cylinder is corrected for each cylinder, individual changes (variations) during manufacturing and changes over time due to individual differences (variations) during manufacture, even when the engine speed changes or the fuel injection amount command value increases / decreases. Variations in the fuel injection amount of the cylinder can be accurately corrected for each cylinder.

[Embodiment (3)] Step 208 of FIG.
Alternatively, the fuel injection correction amount ΔQ of each cylinder calculated in step 309 of FIG. 6 may be corrected at once, but if the fuel injection correction amount ΔQ is large, if the correction is performed at once, torque fluctuations and engine vibrations may occur. This may result in reduced drivability.

As a countermeasure, in the embodiment (3) of the present invention shown in FIG. 8, the fuel injection correction amount (target correction amount) of each cylinder calculated in step 208 of FIG. 3 or step 309 of FIG. Then, in the first cycle, for example, 1/2 of the target correction amount is corrected as the actual correction amount, and the same correction is performed in the subsequent cycles, whereby the correction of the fuel injection amount of each cylinder is gradually performed over a plurality of cycles. Do. By doing so, the correction amount of the fuel injection amount per cycle can be reduced, torque fluctuation and engine vibration due to correction of the fuel injection amount can be suppressed, and drivability can be improved.

In this case, 1 cycle of the target correction amount is 1 / cycle.
2 is corrected as the actual correction amount, but the correction ratio may be another ratio such as 1/3, 2/3, or the like. Alternatively, the maximum correction amount per cycle may be set, and the correction of the fuel injection amount may be gradually performed over a plurality of cycles only for the cylinders exceeding the maximum correction amount. In this case, for example, for a cylinder whose target correction amount exceeds the maximum correction amount,
The maximum correction amount may be corrected in the first cycle, and the remaining correction may be performed in the next and subsequent cycles. [Other Embodiments] In the system configuration example of FIG. 1, both the turbocharger 13 and the EGR device 20 are provided.
The present invention is also applicable to a system having only one of them or a system having neither of them.

Other internal combustion engines to which the present invention can be applied include:
The present invention is not limited to the diesel engine, and is applicable to an in-cylinder injection (direct injection) gasoline engine, a gasoline lean burn engine, and the like.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an entire engine control system showing an embodiment (1) of the present invention.

FIG. 2 is a flowchart showing a processing flow of a cylinder-by-cylinder injection amount correction program according to the embodiment (1).

FIG. 3 is a flowchart showing a processing flow of a fuel injection correction amount correction program according to the embodiment (1).

FIG. 4 is a characteristic diagram showing a relationship between an oxygen concentration and a detection error of an oxygen concentration sensor.

FIG. 5 is a time chart showing a relationship between a fuel injection amount of each cylinder and an oxygen concentration in exhaust gas detected by an oxygen concentration sensor.

FIG. 6 is a flowchart showing a processing flow of a cylinder-by-cylinder injection amount correction program according to the embodiment (2) of the present invention;

FIG. 7 is a time chart showing a change in oxygen concentration in exhaust gas during a transition.

FIG. 8 is a time chart for explaining a fuel injection amount correction method according to the embodiment (3) of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Diesel engine (internal combustion engine), 12 ... Intake pipe, 13 ... Turbocharger (intake supercharging means), 16 ... Exhaust pipe, 17 ... Oxygen concentration sensor (oxygen concentration detection means), 18
... EGR pipe, 19 ... EGR valve, 20 ... EGR device (exhaust gas recirculation means), 21 ... fuel injection valve, 22 ... intake manifold, 23 ... exhaust manifold, 24 ... engine speed sensor, 25 ... accelerator sensor, 26 ... control Circuit (fuel injection amount calculation means, cylinder-specific injection amount correction means).

Claims (7)

[Claims] 1. An injection amount calculating means for calculating a fuel injection amount of each cylinder according to an operation state of an internal combustion engine, and an oxygen concentration detecting means for detecting an oxygen concentration in exhaust gas discharged from each cylinder of the internal combustion engine. And a cylinder-by-cylinder injection amount correction unit that corrects the fuel injection amount of each cylinder for each cylinder based on the detection value of the oxygen concentration detection unit when the internal combustion engine is at high load and low rotation. For controlling internal combustion engine fuel injection. 2. An injection recirculation means for recirculating a part of exhaust gas to an intake system of the internal combustion engine, and an intake supercharging means for applying a supercharging pressure to an intake system of the internal combustion engine; The correction unit corrects the fuel injection amount of each cylinder for each cylinder based on the detection value of the oxygen concentration detection unit when both the exhaust gas recirculation unit and the intake supercharging unit are not operating. The fuel injection control device for an internal combustion engine according to claim 1, wherein A means for calculating an oxygen concentration average value for each cycle (hereinafter referred to as an "oxygen concentration cycle average value") based on a detection value of the oxygen concentration detection means; and an oxygen concentration cycle average value for a plurality of cycles. Means for calculating a target oxygen concentration for each cylinder from the amount of change in the value, the cylinder-by-cylinder injection amount correction means, the oxygen concentration for each cylinder detected by the oxygen concentration detection means and the target oxygen concentration for each cylinder, 3. The fuel injection amount of each of the cylinders is corrected for each cylinder in a direction in which the deviation of the cylinder becomes smaller.
3. The fuel injection control device for an internal combustion engine according to claim 1. 4. The internal combustion engine according to claim 1, wherein the cylinder-by-cylinder injection amount correction means gradually corrects the fuel injection amount of each cylinder over a plurality of cycles. Fuel injection control device. 5. The cylinder-by-cylinder injection amount correction means corrects the fuel injection amount of each cylinder for each cylinder so as not to change the total value of the fuel injection amount of all cylinders before and after the correction. A fuel injection control device for an internal combustion engine according to any one of claims 1 to 4. 6. An injection amount calculating means for calculating a fuel injection amount of each cylinder according to an operation state of the internal combustion engine, and an oxygen concentration detecting means for detecting an oxygen concentration in exhaust gas discharged from each cylinder of the internal combustion engine. Cylinder-based injection amount correction means for correcting the fuel injection amount of each cylinder based on the detection value of the oxygen concentration detection means, and exhaust gas whose oxygen concentration detected by the oxygen concentration detection means is exhausted from any cylinder In order to determine whether or not the oxygen concentration is, the fuel injection amount of the specific cylinder is temporarily increased or decreased, and the specific cylinder is determined from the relationship between the increase and decrease amount and the detection value of the oxygen concentration detection means. A fuel injection control device for an internal combustion engine, comprising: 7. A fuel injection control method for controlling a fuel injection amount of each cylinder of an internal combustion engine for each cylinder, wherein an oxygen concentration in exhaust gas discharged from each cylinder of the internal combustion engine is detected by oxygen concentration detection means, A fuel injection control method for an internal combustion engine, wherein the fuel injection amount of each cylinder is corrected for each cylinder based on a value detected by the oxygen concentration detection means when the internal combustion engine is at a high load and a low speed.