JP2007024002A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize excellent air-fuel ratio controllability even in an area smaller than minimum injection time in fuel injection time of a cylinder injection injector. <P>SOLUTION: An engine ECU executes a program including a step (S100) of detecting a target engine speed, a step (S110) of detecting an engine intake load rate, a step (S120) of calculating target fuel pressure by referring to a two-dimensional map by using the target engine speed and the engine intake load rate, a step (S130) of calculating a correction factor of integral gain on the basis of the target fuel pressure and a unidimensional map (the correction factor is small as the target fuel pressure becomes high), and a step (S140) of calculating the corrected integral gain used in air-fuel ratio feedback control. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus for an internal combustion engine that directly injects fuel into a cylinder.

An internal combustion engine equipped with an in-cylinder injector for injecting fuel into a combustion chamber of the internal combustion engine is known. In such an internal combustion engine, when the internal combustion engine is under a low load, such as during idling, the fuel is injected into the cylinder during the compression stroke, and weakly stratified combustion is performed. During a high load, the fuel is injected during the intake stroke. A homogeneous combustion is performed by injecting into the cylinder, thereby achieving both low fuel consumption and high output. Generally, an exhaust system of an internal combustion engine has a catalyst for purifying harmful components in the exhaust gas. A converter is provided. As this catalytic converter, a three-way catalytic converter is widely used, which oxidizes carbon monoxide (CO) and unburned hydrocarbon (HC), which are three components in exhaust gas, and nitrogen oxide (NOx). Is converted into carbon dioxide (CO ₂ ), water vapor (H ₂ O), and nitrogen (N ₂ ).

  The purification characteristics of the three-way catalytic converter depend on the air-fuel ratio of the air-fuel mixture formed in the combustion chamber, and the three-way catalytic converter functions most effectively when it is close to the stoichiometric air-fuel ratio. This is because if the air-fuel ratio is lean and the amount of oxygen in the exhaust gas is large, the oxidizing action becomes active but the reducing action becomes inactive, and if the air-fuel ratio is rich and the amount of oxygen in the exhaust gas is small, On the contrary, the reducing action becomes active, but the oxidizing action becomes inactive, and it is not possible to purify all of the above-mentioned harmful three components satisfactorily. Therefore, an internal combustion engine having a three-way catalytic converter is provided with an output linear oxygen sensor in its exhaust passage, and the air-fuel ratio of the air-fuel mixture in the combustion chamber is converted to the stoichiometric air-fuel ratio by using the oxygen concentration measured thereby. The air-fuel ratio feedback control is performed so that the stoichiometric air fuel ratio (hereinafter sometimes referred to as stoichiometric) may be used.

  On the other hand, when determining the fuel injection time, the basic fuel injection time is calculated based on the rotational speed and load factor of the internal combustion engine, and various correction amounts including the correction coefficient by the air-fuel ratio feedback control described above are calculated. The required injection time is calculated by superimposing. At this time, the calculated required injection time may be a very small value when the load is light. However, the fuel injection valve (injector) that actually injects fuel has a minimum value of the fuel that can be injected (the minimum amount of fuel that can be injected is referred to as the minimum injection time), and injection that is less than this minimum injection time can be performed. I am trying not to. Therefore, when the calculated required injection time is smaller than the minimum injection time, the fuel is injected with the required injection time fixed at the minimum injection time.

  Since fuel cannot be injected below such minimum injection time, this state is a state in which excessive injection is performed with respect to the required injection time, and the air-fuel ratio is rich. Therefore, if the air-fuel ratio feedback control is continuously executed in this state, the correction coefficient decreases to the lower limit value. When shifting from such a light load state to a steady operation state, a phenomenon occurs in which exhaust emission and drivability deteriorate due to overlean until the correction coefficient by air-fuel ratio feedback control returns to an appropriate value.

  Japanese Patent Application Laid-Open No. 4-362246 (Patent Document 1) discloses an air-fuel ratio control apparatus for an internal combustion engine that solves such a problem. The air-fuel ratio control apparatus for an internal combustion engine is configured to perform a feedback control stop condition when the required injection time determined by the engine state of the internal combustion engine is smaller than the minimum injection time determined by the minimum valve opening time of the injector. An air-fuel ratio control apparatus for an internal combustion engine configured to cancel execution, wherein a period measurement unit that measures a period during which a feedback control stop condition is satisfied, and a period measured by the period measurement unit is within a predetermined period In this case, a prohibiting means for prohibiting the suspension of the execution of the air-fuel ratio feedback control means is provided.

According to this air-fuel ratio control apparatus for an internal combustion engine, even if the condition for stopping feedback control is satisfied, if the established time is within a predetermined time, the execution state is not stopped without stopping the air-fuel ratio feedback control. Maintained. Therefore, it is possible to improve the air-fuel ratio controllability after the speed change process for acceleration and prevent the drivability from deteriorating.
JP-A-4-362246

  However, in the air-fuel ratio control apparatus for an internal combustion engine disclosed in Patent Document 1, when a certain condition is satisfied (a stop condition that the requested injection time is smaller than the minimum injection time is in a light load operation state or the like) If the period is exceeded, the air-fuel ratio feedback control is stopped. Therefore, at that time, since air-fuel ratio feedback control is not performed, the air-fuel ratio is not controlled, and exhaust emission and drivability deteriorate.

  On the other hand, even if the required injection time is shorter than the minimum injection time in a light load operation state or the like, even if fuel is injected from the in-cylinder injector with the short required injection time, the injection time and the injection amount In an extreme example, even if the control is corrected to the rich side, it is possible to inject less fuel than the required injection amount during the required injection time. Therefore, it is corrected to the lean side. Under such a condition, the integral term of the feedback control is accumulated so as to correct further to the rich side, and the deviation from the target value in the air-fuel ratio control does not become small, or the integral term is not properly calculated. Target value and air-fuel ratio hunting.

  The present invention has been made to solve the above-described problems, and its object is to realize good air-fuel ratio controllability and exhaust emission even in a region where the required injection time is smaller than the minimum injection time. It is another object of the present invention to provide an air-fuel ratio control apparatus for an internal combustion engine that can prevent deterioration of drivability.

  An air-fuel ratio control apparatus for an internal combustion engine according to a first aspect of the invention controls the air-fuel ratio of an internal combustion engine provided with fuel injection means for injecting fuel into a cylinder. The air-fuel ratio control device is provided in a control means for controlling the fuel injection means so as to inject fuel on the basis of conditions required for the internal combustion engine, and an exhaust system of the internal combustion engine. And air-fuel ratio control means for performing feedback control based on the detected air-fuel ratio so that the air-fuel ratio becomes the target air-fuel ratio. The air-fuel ratio control means includes adjustment means for adjusting the feedback gain based on the relationship between the fuel injection time and the fuel injection amount in the fuel injection means.

  According to the first invention, for example, since the fuel injection amount is small at a light load, the fuel injection time becomes shorter as the pressure of the fuel supplied to the fuel injection means is higher. When the fuel injection time is shortened, a linear characteristic (linearity characteristic) is not established in the relationship between the fuel injection time and the fuel injection amount in the fuel injection means. In such a case, the fuel injection unit may inject an amount of fuel different from the amount of fuel commanded by the control unit. For this reason, in such a case, the air-fuel ratio feedback control is hardly executed normally. For this reason, in such a case, the feedback gain (particularly the integral gain) in the air-fuel ratio feedback control is corrected to be small. As a result, even in a region where the required injection time is shorter than the minimum injection time (region where the linearity characteristic is not established), it is possible to realize a favorable air-fuel ratio feedback control characteristic and prevent deterioration of exhaust emission and drivability. An air-fuel ratio control apparatus for an internal combustion engine can be provided.

  In the air-fuel ratio control apparatus according to the second aspect of the invention, in addition to the configuration of the first aspect of the invention, the control means injects the fuel amount calculated based on the conditions required for the internal combustion engine. Means for controlling the fuel injection time during which the fuel is injected from. The adjusting means includes means for adjusting the feedback gain when the linear relationship between the fuel injection time and the fuel injection amount is one of a region where the linear relationship is not satisfied and a region where the fuel injection time may not be satisfied.

  According to the second aspect of the invention, the adjustment means causes a region where the linear relationship between the fuel injection time and the fuel injection amount is not established (a region where the linearity characteristic is not established) and a region where the linear relationship may not be established (a linearity characteristic may not be established). The feedback gain is adjusted to be small. For this reason, good air-fuel ratio feedback control characteristics can be realized, and deterioration of exhaust emission and drivability can be prevented.

  In the air-fuel ratio control apparatus according to the third aspect of the invention, in addition to the configuration of the second aspect of the invention, the adjusting means includes means for adjusting the feedback gain to be small.

  According to the third aspect of the invention, it is possible to avoid hunting of the air-fuel ratio by adjusting the feedback gain to be small and disturbing the air-fuel ratio feedback control.

  In the air-fuel ratio control apparatus according to the fourth aspect of the invention, in addition to the configuration of the second aspect of the invention, the adjustment means includes means for adjusting the integral gain of feedback control to be small.

  According to the fourth invention, it is possible to avoid the hunting of the air-fuel ratio by adjusting the integral gain of the feedback control so that the air-fuel ratio feedback control is disturbed.

  In the air-fuel ratio control apparatus according to the fifth aspect of the invention, in addition to the configuration of any one of the first to fourth aspects, the control means is a pressure of fuel supplied to the fuel injection means when the internal combustion engine is cold. Means for controlling the fuel injection means so as to inject the fuel in a high state.

  According to the fifth invention, since the fuel injected from the fuel injection means is difficult to atomize when cold, the fuel pressure of the fuel supplied to the fuel injection means is increased and injected into the cylinder in a high pressure state. . If it does in this way, the injected fuel will become easy to atomize and the homogeneity of air-fuel | gaseous mixture can be improved. However, when the fuel pressure is increased in this way, it is difficult to establish a linear relationship between the fuel injection time and the fuel injection amount in the fuel injection means, the air-fuel ratio feedback control is disturbed, and the air-fuel ratio may be hunted. Therefore, it is possible to avoid hunting of the air-fuel ratio by adjusting the feedback gain (adjusting the integral gain small) so that the air-fuel ratio feedback control is not disturbed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

<First Embodiment>
FIG. 1 shows an overall configuration diagram of a direct injection engine controlled by the air-fuel ratio control apparatus according to the present embodiment.

  The engine body 10 has a cylinder head 110 covered over the cylinder block 100, and a piston 120 is slidably held in a cylinder 100A formed in the cylinder block 100. The reciprocating motion of the piston 120 in the cylinder 100A is converted into the rotational motion of the crankshaft 130 and transmitted to a transmission or the like. The crankshaft 130 is connected to the starter 30 via the flywheel 140 when the engine is started.

  A combustion chamber 1000 is formed above the piston 120 with the cylinder block 100 and the cylinder head 110 as chamber walls. In the combustion chamber 1000, a mixture of fuel and air is burned, and the piston 120 moves up and down by the explosive force. Move it. The air-fuel mixture is ignited by a spark plug 150 provided through the cylinder head 110 and protruding into the combustion chamber 1000.

  Supply of air constituting the air-fuel mixture is performed by an intake passage 1010 formed in the intake pipe connected to the cylinder head 110 and the cylinder head 110. Further, exhaust from the combustion chamber 1000 is performed by an exhaust passage 1020. The cylinder head 110 is provided with an intake valve 160 for switching communication between the intake passage 1010 and the combustion chamber 1000 and an exhaust valve 170 for switching communication between the exhaust passage 1020 and the combustion chamber 1000. ing.

  A flap-like throttle valve 190 is provided in the intake pipe, and the air flow in the intake passage 1010 is adjusted according to the opening.

  The fuel constituting the mixture is supplied by an electromagnetic in-cylinder injector 210. The in-cylinder injector 210 is provided to penetrate the cylinder head 110 and injects fuel into the combustion chamber 1000 from the tip nozzle portion.

  The fuel supplied to the in-cylinder injector 210 is supplied by boosting the fuel sucked from the fuel tank 250 in two stages by the low pressure pump 240 and the high pressure pump 230. The high-pressure pump 230 is driven by power transmitted from the crankshaft 130 of the engine body 10 via a belt or the like. On the other hand, the low pressure pump 240 is driven electrically.

  Further, an engine control computer (hereinafter referred to as an engine ECU (Electronic Control Unit)) 60 that controls each part of the engine such as the spark plug 150, the throttle valve 190, the in-cylinder injector 210, and the like is provided. The engine ECU 60 has a general configuration including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like, and the ignition plug 150 is installed on the basis of detection signals from various sensors. Actuate, output a control signal to the throttle valve 190 to adjust the opening degree of the throttle valve 190 (throttle opening degree), energize the in-cylinder injector 210 by the control signal, and in the cylinder for a predetermined time at a predetermined timing The nozzle of the injector 210 for injection is opened.

  The sensor that inputs a signal to the engine ECU 60 includes a mass flow meter 510 that measures the flow rate of air flowing through the intake passage 1010, a crank angle sensor 520, an A / F sensor 530, and a cooling that detects an engine cooling water temperature that represents the engine temperature. There are water temperature sensors. Further, when the driver operates the key at the time of start-up, an ignition (IG) on signal and a starter on signal are input to the engine ECU 60, and when the driver depresses the accelerator pedal 420, the amount of depression is input. It has become.

  The engine ECU 60 controls the combustion injection amount based on the intake air amount detected by the mass flow meter 510 or the like. At this time, the engine ECU 60 controls the injection amount and the injection timing according to the engine speed and the engine load so as to achieve an optimal combustion state based on signals from the sensors. In the engine main body 10, in order to inject fuel directly into the cylinder, injection timing control and injection amount control are performed simultaneously. Further, the engine ECU 60 performs ignition timing control so as to achieve an optimal ignition timing based on signals (including a knocking sensor and the like) detected by the crank angle sensor 520, the cam position sensor, and the like. Such control realizes both high output and low emission of the engine body 10. The engine ECU 60 operates the engine in a stoichiometric state throughout the normal operation region.

  Further, the engine ECU 60 performs air-fuel ratio feedback control so as to eliminate the deviation between the air-fuel ratio detected by the A / F sensor 530 and the target air-fuel ratio so that the air-fuel ratio of the exhaust becomes the target air-fuel ratio. . PI (or PID) control is used as the air-fuel ratio feedback control. The P component (proportional term, proportional gain) affects responsiveness, and the D component (integral term, integral gain) affects steady-state deviation.

  Further, the engine ECU 60 controls the pressure of fuel supplied to the in-cylinder injector 210 by controlling the high-pressure pump 230. At this time, for example, the high pressure pump 230 is controlled as follows to control the fuel pressure.

  The high-pressure pump 230 includes a pump plunger that reciprocates in the cylinder by the rotation of the cam, and a pressurizing chamber that includes the cylinder and the pump plunger. The pressurizing chamber includes a pump supply pipe that communicates with a feed pump that feeds fuel from the fuel tank, a return pipe that causes the fuel to flow out from the pressurizing chamber and return it to the fuel tank, and in-cylinder injector 210 High-pressure delivery pipes that are pumped toward are connected to each other. The high-pressure pump 230 is provided with an electromagnetic spill valve that opens and closes a pump supply pipe and a high-pressure delivery pipe and a pressurizing chamber.

  When the electromagnetic plunger spill valve is open and the pump plunger moves in the direction of increasing the volume of the pressurizing chamber, that is, when the high-pressure pump 230 is in the suction stroke, fuel is supplied from the pump supply pipe into the pressurizing chamber. Inhaled. Further, when the pump plunger moves in the direction in which the volume of the pressurizing chamber decreases, that is, when the high-pressure pump 230 is in the pumping stroke, if the electromagnetic spill valve is closed, the pump supply pipe, the return pipe, and the pressurizing chamber The gap is cut off, and the fuel in the pressurized chamber is pumped to the in-cylinder injector 210 via the high-pressure delivery pipe.

  In such a high-pressure pump 230, the fuel is pumped toward the in-cylinder injector 210 only during the closing period of the electromagnetic spill valve during the pumping stroke, and therefore, the closing timing of the electromagnetic spill valve is controlled. (By adjusting the closing period of the electromagnetic spill valve), the fuel pumping amount is adjusted. In other words, the fuel pumping amount increases by increasing the closing period by increasing the closing timing of the electromagnetic spill valve, and the fuel pumping amount by shortening the closing period by delaying the closing period of the electromagnetic spill valve. Less. When the fuel pumping amount increases, the fuel pressure in the high-pressure delivery pipe increases. When the fuel pumping amount decreases, the fuel pressure in the high-pressure delivery pipe decreases.

  In this way, the fuel delivered from the feed pump is pressurized by the high-pressure pump 230, and the pressurized fuel is pumped toward the in-cylinder injector 210 at an appropriate fuel pressure, so that the fuel directly into the combustion chamber. Even in an internal combustion engine that injects fuel, the fuel injection can be performed accurately.

  When the pressure of the fuel is increased by the high-pressure pump 230, atomization of the fuel directly injected into the combustion chamber is promoted, and a uniform air-fuel mixture can be formed. In particular, such an effect is remarkable when the engine is cold. However, the higher the fuel pressure, the shorter the fuel injection time for the same required fuel amount, which may be less than the minimum injection time when there is no linearity between the injection time and the injection amount. In such a case, in the air-fuel ratio feedback control, the integral term is integrated including an error in the fuel injection amount, so that it cannot be calculated with high accuracy. The air-fuel ratio control apparatus according to the present embodiment improves the control characteristics of the air-fuel ratio feedback control by reducing the influence of the integral term in such a case.

  Referring to FIG. 2, the correction coefficient of the integral term of air-fuel ratio feedback PI control with respect to the target fuel pressure stored in engine ECU 60 according to the present embodiment is shown. The higher the target fuel pressure, the shorter the fuel injection time. Therefore, the correction coefficient is determined to be small so that the influence of the integral term of the air-fuel ratio feedback control is reduced. For example, the correction coefficient is 1.0 at 4 PMa, whereas the correction coefficient is 0.3 at 13 PMa.

  Further, the actual fuel pressure may be used instead of the target fuel pressure. However, when this actual fuel pressure is used, the fuel pressure subjected to annealing treatment is used.

  With reference to FIG. 3, a control structure of a program executed by engine ECU 60 according to the present embodiment will be described. This program is a program for air-fuel ratio control.

  In step (hereinafter step is abbreviated as S) 100, engine ECU 60 detects the target engine speed. In S110, engine ECU 60 detects the intake load factor of the engine. In S120, engine ECU 60 calculates a target fuel pressure using these two-dimensional maps based on the target engine speed and the intake load factor.

  In S130, engine ECU 60 calculates an integral gain correction coefficient from the calculated target fuel pressure using the one-dimensional map shown in FIG.

  In S140, engine ECU 60 multiplies the integral gain of air-fuel ratio feedback control by the correction coefficient calculated in S130 to calculate a corrected integral gain of air-fuel ratio feedback control.

  Using this integral gain or proportional gain, an operation amount (fuel injection amount) of air-fuel ratio feedback control that eliminates the deviation between the target air-fuel ratio and the actual air-fuel ratio is calculated.

  An operation in the case of executing the air-fuel ratio control of the engine controlled by engine ECU 60 according to the present embodiment based on the above-described structure and flowchart will be described.

  The engine is started and the required injection amount is small during light load operation. When the fuel pressure is high in this state, an injection time that is less than the minimum injection time is calculated, and linearity is not established between the injection time and the injection amount.

  The target engine speed is detected (S100), the engine intake load factor is detected (S110), and the target fuel pressure is calculated based on the target engine speed and the intake load factor (S120).

  A correction coefficient is calculated based on the target fuel pressure (S130), and this correction coefficient is multiplied by the integral gain to correct the integral gain of the air-fuel ratio feedback control. At this time, as shown in FIG. 2, the higher the fuel pressure is, the smaller the correction coefficient that is multiplied by the integral gain is set, so the integral gain is calculated to be smaller (S140).

  As described above, at a light load, the higher the pressure of the fuel supplied to the in-cylinder injector, the shorter the fuel injection time, and the linearity characteristic is established in the relationship between the injection time and the injection amount. Disappear. In such a case, an amount of fuel different from the amount commanded from the engine ECU is injected from the in-cylinder injector. For this reason, in such a case, the air-fuel ratio control is difficult to be executed normally. For this reason, it correct | amends so that the integral gain in air-fuel ratio feedback control may become small, so that fuel pressure becomes high. As a result, even if the fuel injection amount is small and the linearity characteristic is not established between the injection time and the injection amount, it can be avoided that the control characteristic of the air-fuel ratio feedback control is greatly deteriorated, and the exhaust emission and drivability are deteriorated. Can be prevented.

<Second Embodiment>
Hereinafter, a second embodiment of the present invention will be described. Since the hardware configuration is the same as that of the first embodiment described above, detailed description thereof will not be repeated here. In the present embodiment, engine ECU 60 executes a program different from the program in the above-described embodiment.

  In order to execute the program, the engine ECU 60 stores the maps shown in FIGS. 4 and 5.

  FIG. 4 shows the correction factor of the integral gain of the air-fuel ratio feedback control when the low temperature high fuel pressure control is being executed, and FIG. 5 shows the integral gain of the air-fuel ratio feedback control when the low temperature normal fuel pressure control is being executed. Correction coefficients are shown respectively. The integral gain itself of the air-fuel ratio feedback control may be used instead of the correction coefficient of the integral gain of the air-fuel ratio feedback control.

  Referring to FIGS. 4 and 5, the air-fuel ratio when the low-temperature high-fuel pressure control with high fuel pressure is executed to improve the atomization of the fuel injected from the in-cylinder injector 210 when the engine is cold. The correction coefficient for the integral gain of the feedback control is set to be smaller than the correction coefficient for the integral gain of the air-fuel ratio feedback control when the low temperature normal fuel pressure control is being executed, and the integral gain becomes small. Similarly to the first embodiment described above, the fuel injection time is shortened as the fuel pressure is increased. Therefore, the low temperature and high fuel pressure control is performed in which the fuel is injected at a high fuel pressure in the cold state. When the normal fuel pressure control is executed, the correction coefficient is determined to be small so that the influence of the integral term of the air-fuel ratio feedback control is small, and as a result, the integral gain is small.

  A control structure of a program executed by engine ECU 60 according to the present embodiment will be described with reference to FIG. In this flowchart, the same steps as those in the flowchart of FIG. 3 are given the same step numbers. The contents of those processes are also the same. Therefore, detailed description thereof will not be repeated here.

In S200, engine ECU 60 detects engine coolant temperature THW.
In S210, engine ECU 60 determines whether engine coolant temperature THW is equal to or lower than a cold threshold value. When the temperature is lower than the cold threshold value, low temperature high fuel pressure control in which fuel is injected at a high fuel pressure during cold may be executed. If engine coolant temperature THW is equal to or lower than the cold threshold value (YES in S210), the process proceeds to S220. Otherwise (NO in S210), this process ends.

  In S220, engine ECU 60 determines whether or not high fuel pressure control is being executed. At this time, by maintaining a high fuel pressure, fuel atomization can be promoted even at low temperatures by injecting fuel from the in-cylinder injector 210. If high fuel pressure control is being executed (YES in S220), the process proceeds to S230. If not (NO in S220), the process proceeds to S240.

  In S230, engine ECU 60 calculates a correction coefficient for the integral gain of the air-fuel ratio feedback control using map (A) shown in FIG. 4 from the target engine speed and the intake load factor.

  In S240, engine ECU 60 calculates a correction coefficient for the integral gain of the air-fuel ratio feedback control using map (B) shown in FIG. 5 from the target engine speed and the intake load factor.

  An operation in the case of executing the air-fuel ratio control of the engine controlled by engine ECU 60 according to the present embodiment based on the above-described structure and flowchart will be described.

  When the engine is started in the cold state, fuel is supplied to the in-cylinder injector 210 at a high fuel pressure. When the required injection amount is small in such a state, an injection time that is less than the minimum injection time is calculated, and linearity is not established between the injection time and the injection amount.

  The target engine speed is detected (S100), and the engine intake load factor is detected (S110). When engine coolant temperature THW is equal to or lower than the cold threshold value (YES in S210), and when high fuel pressure control is being executed to promote fuel atomization (YES in S220), the engine From the target rotational speed and the intake load factor, the correction coefficient of the integral gain of the air-fuel ratio feedback control is calculated to be small using the map (A) shown in FIG. This correction coefficient is multiplied by the integral gain so that the integral gain of the air-fuel ratio feedback control is corrected. At this time, when the high fuel pressure control is executed using the map (A) shown in FIG. 4, the integral gain is multiplied more than when the normal fuel pressure control is executed using the map (B) shown in FIG. Therefore, the integral gain is calculated to be smaller. As described above, in the process in S230, the integral gain itself may be calculated to be small instead of the integral gain correction coefficient.

  As described above, when the engine is cold, the pressure of the fuel supplied to the in-cylinder injector is maintained high (for example, 13 MPa), and fuel atomization is promoted. At this time, the fuel injection time is shortened, and the linearity characteristic is not established in the relationship between the injection time and the injection amount. In such a case, an amount of fuel different from the amount commanded from the engine ECU is injected from the in-cylinder injector. For this reason, in such a case, the air-fuel ratio control is difficult to be executed normally. For this reason, when the high fuel pressure control in the cold state is being executed, the integral gain in the air-fuel ratio feedback control is corrected to be small. As a result, even if the high fuel pressure control in the cold state is executed and the linearity characteristic is not established between the injection time and the injection amount, it can be avoided that the control characteristic of the air-fuel ratio feedback control is greatly deteriorated. Deterioration of emissions and drivability can be prevented.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is an overall configuration diagram of an engine controlled by an engine control device according to a first embodiment of the present invention. It is a figure which shows the map memorize | stored in engine ECU which is an engine control apparatus which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the control structure of the program performed by engine ECU which is an engine control apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the map (A) memorize | stored in engine ECU which is an engine control apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows the map (B) memorize | stored in engine ECU which is an engine control apparatus which concerns on the 2nd Embodiment of this invention. It is a flowchart which shows the control structure of the program performed by engine ECU which is an engine control apparatus which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

  10 engine body, 30 starter, 60 engine ECU, 150 spark plug, 160 intake valve, 170 exhaust valve, 190 throttle valve, 210 injector, 520 crank angle sensor, 1000 combustion chamber, 1010 intake passage, 1020 exhaust passage.

Claims (5)

An air-fuel ratio control apparatus for an internal combustion engine comprising fuel injection means for injecting fuel into a cylinder,
Control means for controlling the fuel injection means to inject fuel based on conditions required for the internal combustion engine;
Means provided in the exhaust system of the internal combustion engine for detecting the air-fuel ratio of the exhaust;
Air-fuel ratio control means for performing feedback control so that the air-fuel ratio becomes the target air-fuel ratio based on the detected air-fuel ratio,
The air-fuel ratio control device for an internal combustion engine, wherein the air-fuel ratio control means includes adjustment means for adjusting a feedback gain based on a relationship between a fuel injection time and a fuel injection amount in the fuel injection means. The control means includes means for controlling a fuel injection time during which fuel is injected from the fuel injection means so as to inject a fuel amount calculated based on conditions required for the internal combustion engine,
The adjusting means includes means for adjusting the feedback gain when the linear relationship between the fuel injection time and the fuel injection amount is one of a region where the linear relationship is not established and a region where the fuel injection time may not be established. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1.   The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the adjusting means includes means for adjusting the feedback gain to be small.   The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the adjusting means includes means for adjusting so that an integral gain of the feedback control becomes small.   The control means includes means for controlling the fuel injection means so that fuel is injected in a state where the pressure of the fuel supplied to the fuel injection means is high when the internal combustion engine is cold. Item 5. The air-fuel ratio control apparatus for an internal combustion engine according to any one of Items 1 to 4.

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