JP2011226350A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device of an internal combustion engine preventing emission from being deteriorated or of preventing driveability from being deteriorated during the cold start of the engine.SOLUTION: When an air-fuel ratio upon the completion of the warm-up of an air fuel ratio sensor is separated from a target air-fuel ratio by an open control performed during the warm-up of the air-fuel ratio sensor, a combustion stability FB control is performed to set a rate at which an actual air-fuel ratio approaches the target air-fuel ratio based on the stability of the combustion state of the internal combustion engine. Since the actual air-fuel ratio gradually approaches the target air-fuel ratio, the combustion state is prevented from being abruptly changed. Consequently, the emission is prevented from being deteriorated and also the driveability is prevented from being deteriorated.

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that controls an air-fuel ratio.

  In order to stabilize the combustion of the internal combustion engine, so-called air-fuel ratio feedback control (hereinafter referred to as air-fuel ratio FB control) that corrects the exhaust air-fuel ratio based on the exhaust air-fuel ratio to be a desired target air-fuel ratio is widely known. . As a means for detecting the air-fuel ratio, for example, Patent Document 1 discloses a method using an air-fuel ratio sensor provided on the upstream side of the catalyst. In this document, air-fuel ratio FB control is performed so that the exhaust air-fuel ratio becomes the target air-fuel ratio based on the difference between the detected value of the air-fuel ratio sensor and the target air-fuel ratio.

  By the way, the air-fuel ratio sensor is greatly influenced by temperature. For example, when the air-fuel ratio sensor is at a low temperature, the detection accuracy is remarkably lowered. That is, when the internal combustion engine is started in the cold state, the detected value of the air-fuel ratio sensor may be different from the actual air-fuel ratio. Therefore, when the air-fuel ratio sensor is at a low temperature, a predetermined warm-up time is required until the detection accuracy of the air-fuel ratio sensor becomes effective, and the above-described air-fuel ratio FB control cannot be performed until the air-fuel ratio sensor has been warmed up. Therefore, at the time of cold start, open control is performed instead of the air-fuel ratio FB control until the warm-up of the air-fuel ratio sensor is completed.

JP 2005-163746 A

  In the open control, since a predetermined amount of fuel is injected regardless of the actual air-fuel ratio, it is not certain whether the actual air-fuel ratio is approaching the target air-fuel ratio. Therefore, there is a case where the air-fuel ratio detected when the air-fuel ratio sensor for which the air-fuel ratio FB control is started is completed is deviated from the target air-fuel ratio. If the air-fuel ratio FB control described above is performed in such a case, the correction amount of the fuel injection amount increases because the difference between the detected value of the air-fuel ratio sensor and the target air-fuel ratio is large. That is, the combustion state suddenly changes to the lean side or the rich side. As a result, the combustion state becomes unstable, and there is a possibility that the emission and drivability are deteriorated. In particular, when stratified combustion is performed in an in-cylinder direct injection internal combustion engine, in addition to the above-described deterioration of emission and drivability, the spark plug may smolder and misfire.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an air-fuel ratio control apparatus for an internal combustion engine that prevents deterioration of emission and drivability at the start of air-fuel ratio feedback.

In order to solve the above problems, the invention described in claim 1 includes a fuel injection unit that injects fuel into an internal combustion engine, an air-fuel ratio detection unit that is installed in an exhaust pipe of the internal combustion engine and detects an air-fuel ratio of exhaust gas,
A warm-up determination unit that determines that the warm-up of the air-fuel ratio detection unit is completed, a combustion stability detection unit that detects the stability of the combustion state of the internal combustion engine, and a warm-up determination unit that warms up the air-fuel ratio detection unit The air-fuel ratio feedback control means (hereinafter, referred to as the fuel injection amount of the fuel injection means) is corrected based on the air-fuel ratio detected by the air-fuel ratio detection means (hereinafter referred to as the actual air-fuel ratio) and the target air-fuel ratio. The combustion stability detected by the combustion stability control detecting means when there is a difference of a predetermined value or more between the actual air fuel ratio and the target air fuel ratio at the time when the warm-up of the air fuel ratio detecting means is completed. And an air-fuel ratio gradual change control means for setting the speed at which the actual air-fuel ratio approaches the target air-fuel ratio. The air-fuel ratio FB control means controls the air-fuel ratio FB based on the speed set by the air-fuel ratio gradual change control means. Run And wherein the door.

  According to the above configuration, the speed at which the actual air-fuel ratio approaches the target air-fuel ratio is set based on the combustion stability by the air-fuel ratio gradual change control means. As a result, the actual air-fuel ratio can be gradually brought closer to the target air-fuel ratio. As a result, even if the actual air-fuel ratio detected when the warm-up of the air-fuel ratio detection unit is completed is deviated from the target air-fuel ratio, the actual air-fuel ratio does not rapidly change to the rich or lean side. Therefore, it is possible to prevent deterioration of emission and drivability.

  In the invention according to claim 2, the air-fuel ratio gradual change control means makes the speed at which the actual air-fuel ratio approaches the target air-fuel ratio slows down when the combustion stability deteriorates, and the combustion stability is smaller than a predetermined value. In this case, the actual air-fuel ratio is set so as to increase the speed at which the actual air-fuel ratio approaches the target air-fuel ratio.

  According to the above configuration, when the combustion stability is good, the speed at which the actual air-fuel ratio approaches the target air-fuel ratio is set to be faster, and when the combustion stability is deteriorated, the actual air-fuel ratio becomes the target air-fuel ratio. It is set so that the approaching speed becomes slower. Thereby, compared with the case where it always approaches a target air fuel ratio at a fixed speed, the possibility of deteriorating combustion stability can be reduced. Further, when the combustion state is good, the target fuel pressure can be reached earlier than when the target air-fuel ratio is approached at a constant speed.

  According to a third aspect of the present invention, the air-fuel ratio gradual change control means has the air-fuel ratio detection means when there is a difference between the actual air-fuel ratio and the target air-fuel ratio at the time when the warm-up of the air-fuel ratio detection means is completed by a predetermined value or more. The actual air-fuel ratio detected when the warm-up of the engine is completed is set as the starting point of the temporary target air-fuel ratio, and the rate of change in speed at which the temporary target air-fuel ratio is brought close to the target air-fuel ratio based on the combustion stability The air / fuel FB control means corrects the fuel injection amount based on the temporary target air / fuel ratio and the actual air / fuel ratio set by the target value gradual change rate.

  According to the above configuration, the temporary target air-fuel ratio is set by the target value gradual change rate set by the air-fuel ratio gradual change control means based on the combustion stability. Then, the FB control is performed based on the temporary target air-fuel ratio and the actual air-fuel ratio. Therefore, even if the actual air-fuel ratio detected at the completion of warm-up of the air-fuel ratio detection means and the target air-fuel ratio are deviated, the values referred to in the air-fuel ratio FB control are the temporary target air-fuel ratio and the actual air-fuel ratio. Therefore, it is possible to prevent the correction amount of the fuel injection amount from increasing.

  According to a fourth aspect of the present invention, the air-fuel ratio gradual change control means changes the value of the fuel injection amount correction coefficient (hereinafter referred to as FB gain) by the air-fuel ratio FB control based on the combustion stability, thereby A speed at which the fuel ratio is brought close to the target air-fuel ratio is set.

  According to the above configuration, the fuel injection amount is adjusted by changing the FB gain by the air-fuel ratio FB control based on the combustion stability. Therefore, as in the third aspect of the invention, the speed at which the actual air-fuel ratio approaches the target air-fuel ratio can be set without setting the temporary target air-fuel ratio.

  As the combustion stability detecting means, it is preferable to detect the combustion stability of the internal combustion engine based on the detection value of the in-cylinder pressure sensor as in the fifth aspect of the invention. Further, the combustion stability of the internal combustion engine may be detected based on the detected value of the crank angle sensor as in the sixth aspect of the invention.

Schematic diagram of overall air-fuel ratio control system Flow chart showing processing procedure of air-fuel ratio control at start-up Flow chart showing processing procedure of normal air-fuel ratio FB control Flow chart showing processing procedure of combustion stability FB control Time chart showing the transition state of air-fuel ratio control at start-up The flowchart which shows the process sequence of the combustion stability FB control in 2nd Embodiment. Time chart showing transition state of air-fuel ratio control at start-up in the second embodiment

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of the entire air-fuel ratio control system. In FIG. 1, only one cylinder is shown for convenience.

  As shown in FIG. 1, an air cleaner 3 is provided at the most upstream portion of an intake pipe 2 of an engine 1 that is a cylinder injection type internal combustion engine. A throttle valve 5 whose opening degree is adjusted by a DC motor 4 is provided on the downstream side of the air cleaner 3. The DC motor 4 is driven based on a signal from an accelerator opening sensor that detects a user's accelerator depression amount (accelerator opening). Specifically, the opening (throttle opening) of the throttle valve 5 is controlled based on a signal output from the engine control device 6 (hereinafter referred to as “ECU”) according to the accelerator opening. The intake air amount to each cylinder is adjusted according to the throttle opening. A throttle sensor 7 for detecting the throttle opening is provided in the vicinity of the throttle valve 5. An air flow meter 8 is provided between the air cleaner 3 and the throttle valve 5 to detect the amount of air taken in (hereinafter referred to as “intake amount”).

  A surge tank 9 is provided on the downstream side of the throttle valve 5, and an intake pressure sensor 10 for detecting the pressure in the intake pipe is provided in the surge tank 9. The surge tank 9 is connected to an intake manifold that introduces air into each cylinder of the engine 1. An intake port is formed in the intake manifold of each cylinder, and this intake port is connected to an intake valve 11 formed in each cylinder of the engine 1.

  Each cylinder of the engine 1 is provided with an injector 12 (fuel injection means in the claims) that injects fuel directly into the combustion chamber of each cylinder. The fuel is supplied to the injector 12 by two pumps, a fuel pump (not shown) and a high-pressure pump (not shown). In order to inject fuel directly into the combustion chamber, the injection fuel pressure needs to be higher than the pressure in the combustion chamber. Therefore, fuel is first sucked up by a fuel pump (not shown) disposed in a fuel tank (not shown) to increase the pressure of the fuel (hereinafter referred to as “fuel pressure”). Further, the pressure is increased by a high-pressure pump provided in the fuel pipe, and the pressure is fed to a delivery pipe (not shown). The fuel pressurized by the high-pressure pump has a predetermined pressure within a range of 2 to 10 MPa, for example, and is distributed to the injectors 12 of each cylinder by the delivery pipe. This high-pressure fuel is injected from the injector 12 into the combustion chamber and mixed with the intake air supplied from the intake port to form an air-fuel mixture.

  The air-fuel mixture in the combustion chamber is ignited by a spark plug 13 attached to the cylinder head of the engine 1. The spark plug 13 is attached to each cylinder, and the air-fuel mixture in the cylinder is ignited by the spark discharge of each spark plug 13.

  The air-fuel mixture explodes (expands) by ignition, and the piston 14 moves downward in FIG. 1, whereby the crankshaft rotates through the connecting rod. A crank angle sensor 15 is provided outside the diameter of the crankshaft. The crank angle sensor 15 detects the rotation angle (crank angle) of the crankshaft and outputs it to the ECU 6. Further, a water temperature sensor 16 is provided in the cylinder block of the engine 1 to detect the cooling water temperature of the engine 1 and output it to the ECU 6.

  The exhaust gas discharged from the exhaust valve 17 of the engine 1 merges into one exhaust pipe 18 through the exhaust manifold. Connected to the exhaust pipe 18 is a three-way catalyst 19 for purifying exhaust gas near the stoichiometric air-fuel ratio. Further, an air-fuel ratio sensor 20 (air-fuel ratio detecting means in the claims) for detecting the air-fuel ratio of the exhaust gas is provided upstream of the three-way catalyst 19. The air-fuel ratio sensor 20 is greatly affected by temperature, and requires a predetermined warm-up time until the detected value becomes effective. The ECU 6 corrects the fuel injection amount of the injector 12 based on the air-fuel ratio (hereinafter, actual air-fuel ratio) detected after the air-fuel ratio sensor 20 has completed the warm-up and the target air-fuel ratio set according to the operating state of the engine. Air-fuel ratio feedback control (hereinafter referred to as “air-fuel ratio FB control”) is performed.

  Output signals from the various sensors described above are input to the ECU 6. The ECU 6 is mainly composed of a microcomputer, and includes a CPU (Central Processing Unit), a ROM (storage medium), a RAM (temporary storage medium), and the like. The ECU 6 stores a control program and a control map. For example, a target air-fuel ratio map for calculating a target air-fuel ratio according to the engine operating status (engine speed and intake air amount) is stored. The above-described DC motor 4, injector 12, and spark plug 13 are controlled based on various sensor outputs by such a control program and control map.

  Hereinafter, the procedure of air-fuel ratio control performed by the ECU will be described with reference to FIG. This control is repeatedly executed every predetermined period (for example, 4 msec).

  First, at step 100, it is determined whether the air-fuel ratio sensor 20 is valid. In other words, it is determined whether or not the air-fuel ratio sensor 20 has been warmed up (warm-up determination means in the claims). As described above, since the air-fuel ratio sensor 20 is greatly affected by the temperature, the detection accuracy is significantly reduced before the air-fuel ratio sensor 20 is warmed up. For this reason, the detected value of the air-fuel ratio sensor 20 before the completion of warm-up may be different from the actual air-fuel ratio. “Air-fuel ratio sensor is valid” in this step is a state where the air-fuel ratio sensor 20 has been warmed up, and the detected value of the air-fuel ratio sensor 20 in this state is substantially equal to the actual air-fuel ratio.

  If it is determined in step 100 that the air-fuel ratio sensor 20 has not been warmed up, the routine proceeds to step 200. In step 200, air-fuel ratio control is performed in an open loop (hereinafter referred to as “open control”). Specifically, the fuel injection amount set in advance through experiments or the like is injected, and combustion is performed by being ignited at a preset ignition timing. The air-fuel ratio sensor 20 is gradually warmed up by this open control combustion. Then, this routine is temporarily terminated.

  On the other hand, if it is determined in step 100 that the air-fuel ratio sensor 20 has been warmed up, that is, if it is determined that the air-fuel ratio sensor 20 is valid, the routine proceeds to step 300. In step 300, it is determined whether the difference between the actual air-fuel ratio and the target air-fuel ratio is equal to or greater than a predetermined value. When the difference between the target air-fuel ratio and the actual air-fuel ratio is greater than or equal to a predetermined value, if the normal air-fuel ratio FB control described later is performed, the combustion state changes rapidly because the correction amount of the fuel injection amount is large. As a result, emissions and drivability may be deteriorated. Therefore, when the difference between the target air-fuel ratio and the actual air-fuel ratio is equal to or greater than a predetermined value, the routine proceeds to step 400 where air-fuel ratio FB control based on combustion stability (hereinafter referred to as “combustion stability FB control”) is performed. The On the other hand, when the difference between the target air-fuel ratio and the actual air-fuel ratio is smaller than the predetermined value, the routine proceeds to step 500 where normal air-fuel ratio FB control is performed.

  Since this routine is executed every predetermined period, the combustion stability FB control is performed when the difference between the actual air-fuel ratio detected at the time when the air-fuel ratio sensor becomes effective and the target air-fuel ratio is equal to or greater than a predetermined value. To be implemented. That is, not only at the time of start-up, but also when the warm-up of the air-fuel ratio sensor is completed and the difference between the actual air-fuel ratio and the target air-fuel ratio is greater than or equal to a predetermined value at the start of FB control, combustion stability FB control is performed. The

  The air-fuel ratio control is terminated by the above processing procedure.

  Next, the combustion stability FB control performed in step 400 and the normal air-fuel ratio FB control performed in step 500 will be described with reference to FIGS.

  First, normal air-fuel ratio FB control (step 500) will be described with reference to FIG.

  In normal air-fuel ratio FB control, first, in step 501, a basic injection amount Tp is calculated. Specifically, the basic fuel injection amount Tp is calculated from the engine operating state, for example, a map based on the rotational speed output from the crank angle sensor, the intake pipe pressure output from the intake pressure sensor, or the like.

  After calculating the basic injection amount Tp, the routine proceeds to step 502, where the air-fuel ratio FB correction coefficient FAF is calculated from the target air-fuel ratio and the actual air-fuel ratio. The air-fuel ratio FB correction coefficient FAF becomes a value that greatly changes the fuel injection amount TAU as the difference between the target air-fuel ratio and the actual air-fuel ratio increases. However, this routine is executed when it is determined in step 300 that the difference between the target air-fuel ratio and the actual air-fuel ratio is smaller than a predetermined value. Accordingly, since the fuel injection amount TAU does not change greatly, the air-fuel ratio does not change abruptly.

  Next, at step 503, the fuel injection amount TAU that is actually injected is calculated by the following equation using the basic injection amount Tp and the air-fuel ratio FB correction coefficient FAF.

TAU = Tp × FAF × FALL
Here, FALL is a correction coefficient other than the air-fuel ratio FB correction coefficient FAF (for example, a correction coefficient due to cooling water temperature, a correction coefficient during acceleration / deceleration, etc.).

  Normal air-fuel ratio FB control is performed by the above processing procedure.

  Next, the combustion stability FB control (air-fuel ratio gradual change control means in the claims) performed in step 400 will be described with reference to FIG. In the normal air-fuel ratio FB control described above, the fuel injection amount is corrected based on the target air-fuel ratio and the actual air-fuel ratio. On the other hand, in the combustion stability FB control, the fuel injection amount is corrected based on the temporary target air-fuel ratio and the actual air-fuel ratio set based on the combustion stability. This will be described in detail below.

  First, in step 401, a temporary target air-fuel ratio is set. Specifically, the detected value at the time when the air-fuel ratio sensor 20 becomes effective is set as the temporary target air-fuel ratio start point. At the time of the first fuel injection after setting the temporary target air-fuel ratio start point, the temporary target air-fuel ratio and the actual air-fuel ratio have the same value, so that the engine operating state is not corrected without performing correction by the air-fuel ratio FB control. A basic fuel injection amount set in accordance with is injected.

  After setting the temporary target air-fuel ratio, it is determined in step 402 whether the combustion stability has deteriorated. Combustion stability is detected based on a detection value of an in-cylinder pressure sensor (stability detection means in the claims). Specifically, the stability of the combustion state is detected using the variation in the pressure change in the combustion chamber detected by the in-cylinder pressure sensor. Immediately after setting the tentative target air-fuel ratio start point, the combustion stability that changes due to the combustion of the basic fuel injection amount described above is detected. Immediately after setting the tentative target air-fuel ratio start point, it has changed due to the previous combustion. Detect combustion stability. Combustion stability can also be detected based on the detected value of the crank angle sensor 15 (stability detection means in the claims). In this case, the stability of the combustion state is detected based on the variation in the rotation of the crankshaft detected by the crank angle sensor 15.

  Whether the combustion stability has deteriorated is determined by comparing the combustion stability with a predetermined value (hereinafter referred to as “stability limit”). Specifically, if the combustion stability is above the stability limit, it is judged that the combustion stability has deteriorated, that is, the previous combustion has not been performed properly, and the combustion stability is smaller than the stability limit. In this case, it is determined that the previous combustion is performed well. It is determined whether or not the combustion stability has deteriorated by such a method. If the combustion stability has deteriorated, the process proceeds to step 403, and if the combustion stability has not deteriorated, the process proceeds to step 404.

  In step 403 and step 404, a rate of change in speed at which the temporary target air-fuel ratio is brought close to the target air-fuel ratio based on combustion stability (hereinafter referred to as “target value gradual change rate”) is set. For example, if the current temporary target air-fuel ratio is set at the same value as the previous target value gradual change rate, the temporary target air-fuel ratio approaches the target air-fuel ratio at the same speed as the previous time. That is, the target value gradual change rate can also be regarded as a gradient of the temporary target air-fuel ratio, which is how close the temporary target air-fuel ratio set this time is to a value close to the target air-fuel ratio compared to the previous time. Therefore, if the combustion stability deteriorates as a result of the FB control using the temporary target air-fuel ratio set at the previous target value gradual change rate, the current temporary target air-fuel ratio is set at the same target value gradual change rate as the previous time. Then, combustion stability may further deteriorate.

  In step 403, where it is determined in step 402 that the combustion stability has deteriorated, as described above, if the current temporary target air-fuel ratio is set at the same target value gradual change rate as the previous time, the combustion stability further deteriorates. End up. Therefore, the target value gradual change rate is set to a value smaller than the previous value. As a result, the temporary target air-fuel ratio gradually approaches the target air-fuel ratio. In other words, it is set so that the speed at which the temporary target air-fuel ratio approaches the target air-fuel ratio becomes slow. Then, after setting the target value gradual change rate, the routine proceeds to step 405.

  In Step 404, in which it is determined that the previous combustion has been performed well with respect to Step 403, there is still a margin with respect to the stability limit, so the target value gradual change rate is set to be higher than the previous target value gradual change rate. Even if it is set to a large value, there is little possibility of deterioration in combustion stability. Therefore, it is set to a value larger than the previous target value gradual change rate. Thus, the speed at which the temporary target air-fuel ratio approaches the target air-fuel ratio is set to be high. Then, after setting the target value gradual change rate, the routine proceeds to step 405.

  In step 405, the temporary target air-fuel ratio is updated based on the target value gradual change rate set in step 403 or step 404, and the routine proceeds to step 406.

  In step 406, the air-fuel ratio is corrected from the temporary target air-fuel ratio updated in step 405 and the actual air-fuel ratio. Specifically, the fuel is obtained by the following equation using the combustion stability FB coefficient FAF2 calculated based on the temporary target air-fuel ratio set in accordance with the combustion stability and the actual air-fuel ratio and the basic fuel injection amount Tp. An injection amount TAU is calculated.

TAU = Tp × FAF2 × FALL
The combustion stability FB coefficient FAF2 greatly changes the fuel injection amount TAU as the difference between the temporary target air-fuel ratio and the actual air-fuel ratio increases. However, since the temporary target air-fuel ratio is set according to the combustion stability as described above, the actual air-fuel ratio and the temporary target air-fuel ratio do not greatly deviate.

  In step 407, it is determined whether or not the actual air-fuel ratio after combustion is performed with the fuel injection amount corrected based on the temporary air-fuel ratio has reached the target air-fuel ratio. If the actual air-fuel ratio has reached the target air-fuel ratio, this routine is terminated. If the actual air-fuel ratio has not reached the target air-fuel ratio, the routine proceeds to step 402, and the processing from step 402 to step 407 is performed. Combustion stability FB control is performed by the above processing procedure.

  Next, transition states of various controls corresponding to the processing procedure of the air-fuel ratio control at the time of starting described above will be described with reference to FIG.

  First, the engine is started at time t0. Immediately after startup, the air-fuel ratio sensor 20 has not been warmed up, so the air-fuel ratio sensor availability flag and the air-fuel ratio FB flag are “OFF”. Therefore, during time t0 to t1, fuel predetermined by open control is injected (step 200). As described above, the actual air-fuel ratio cannot be detected because the warm-up of the air-fuel ratio sensor 20 is not completed, but the air-fuel ratio sensor 20 provisionally outputs a value indicating the stoichiometric air-fuel ratio between t0 and t1. . Moreover, since it is necessary to start the engine reliably at the time of starting, it is set so that more fuel is injected than during normal time. Therefore, the actual air-fuel ratio immediately after starting becomes rich as shown in FIG.

  The air-fuel ratio sensor is warmed up by the open control, and at time t1, the air-fuel ratio sensor is warmed up. That is, the air-fuel ratio sensor is effective. As a result, the air-fuel ratio sensor availability flag and the air-fuel ratio FB flag are turned “ON”, and the combustion stability FB control or the air-fuel ratio FB control can be executed (step 100). Since the difference between the detected value of the air-fuel ratio sensor (actual air-fuel ratio) and the target air-fuel ratio is greater than or equal to a predetermined value at time t1 (step 300), combustion stability FB control is performed after time t1 (step 300). 400). Therefore, the actual air-fuel ratio at time t1 is set as the temporary target air-fuel ratio start point (step 401). Note that a one-dot chain line in FIG. 5 indicates a temporary target air-fuel ratio.

  Between time t1 and time t2, since the combustion stability is a value smaller than the stability limit (step 402), the target value gradual change rate is set to a large value. That is, the provisional target air-fuel ratio is set so as to approach the target air-fuel ratio quickly (step 404). Then, the fuel injection amount is corrected from the temporary target air-fuel ratio and the actual air-fuel ratio, and the air-fuel ratio is corrected. At times t2, t3, and t4, the combustion stability exceeds the stability limit and the combustion state deteriorates, so the target value gradual change rate is set to a small value. That is, the speed at which the temporary target air-fuel ratio approaches the target air-fuel ratio is set to be slow (step 405).

  Then, at time t5, when the actual air-fuel ratio reaches the target air-fuel ratio, the air-fuel ratio control at the time of start is ended.

  Next, the effect of this embodiment is demonstrated.

  According to the above configuration, if there is a difference between the actual air-fuel ratio detected when the air-fuel ratio sensor 20 is enabled and the target air-fuel ratio more than a predetermined value, the temporary target air-fuel ratio is set by the air-fuel ratio gradual change control means. In addition to being set, a target value gradual change rate is set according to the combustion stability. That is, the speed at which the temporary target air-fuel ratio approaches the target air-fuel ratio is adjusted based on the combustion stability. Then, by setting the target air-fuel ratio referred to by the normal air-fuel ratio FB control as the temporary target air-fuel ratio, the fuel injection amount is corrected by the temporary target air-fuel ratio and the actual air-fuel ratio. Accordingly, since the fuel injection amount is corrected based on the temporary target air-fuel ratio and the actual air-fuel ratio set so as to gradually approach the target air-fuel ratio, the actual air-fuel ratio gradually approaches the target air-fuel ratio. Go. Specifically, the actual air-fuel ratio approaches the target air-fuel ratio at substantially the same speed as the temporary target air-fuel ratio approaches the target air-fuel ratio. That is, the speed at which the actual air-fuel ratio is brought close to the target air-fuel ratio is set based on the combustion stability. Thus, even when the actual air-fuel ratio deviates from the target air-fuel ratio due to the open control, the correction amount of the fuel injection amount does not change abruptly. Therefore, since the actual air-fuel ratio does not change suddenly to the lean or rich side, it is possible to prevent the combustion state from becoming unstable, and as a result, to prevent the deterioration of emission and drivability. Can do.

  Further, since the fuel injection amount does not change abruptly, it is possible to prevent the ignition plug from smoldering and misfiring.

[Second Embodiment]
In the following embodiments including the second embodiment, the same or corresponding configurations as the configurations of the already described embodiments are denoted by the same reference numerals, and redundant description thereof is omitted.

  In the first embodiment, the provisional target air-fuel ratio is set based on the combustion stability, so that the actual air-fuel ratio is controlled to gradually approach the target air-fuel ratio. On the other hand, in the second embodiment, the fuel injection amount is corrected by setting the FB gain according to the combustion stability without setting the temporary target air-fuel ratio, and the actual air-fuel ratio gradually becomes the target air-fuel ratio. Control to approach.

  Here, the FB gain will be described. The FB gain is a coefficient for calculating the air-fuel ratio FB coefficient FAF. For example, when the air-fuel ratio FB coefficient FAF is calculated by PID control, it is calculated from the following equation based on a proportional term, an integral term, and a differential term with respect to the deviation between the target air-fuel ratio and the actual air-fuel ratio.

FAF = Kp × deviation + Ki × integrated value of deviation + Kd × difference from previous deviation Kp, Ki, and Kd are a proportional coefficient, an integral coefficient, and a differential coefficient, respectively, and these coefficients are called FB gains.

  Considering the first embodiment in terms of PID control, in the first embodiment, the combustion stability FB coefficient FAF2 is calculated using the deviation between the temporary target air-fuel ratio and the actual air-fuel ratio set based on the combustion stability. The calculated FB gain value is the same as that in the normal air-fuel ratio FB control. On the other hand, in the second embodiment, these coefficients (FB gain) are changed according to the combustion stability.

  Hereinafter, the processing procedure of the combustion stability FB control in the second embodiment will be described with reference to FIG.

  Combustion stability FB control (step 400) is performed when it is determined in step 300 of FIG. 2 that the difference between the target air-fuel ratio and the actual air-fuel ratio is greater than or equal to a predetermined value. In step 601, the combustion stability is detected, and it is determined whether the combustion stability has deteriorated. Similar to the first embodiment, the combustion stability is detected based on variations in pressure change in the combustion chamber detected by the in-cylinder pressure sensor and variations in rotation of the crankshaft detected by the crank angle sensor 15.

  Whether the combustion stability has deteriorated is determined by comparing the combustion stability with the stability limit. Specifically, if the combustion stability is above the stability limit, it is judged that the combustion stability has deteriorated, that is, the previous combustion has not been performed properly, and the combustion stability is smaller than the stability limit. In this case, it is determined that the previous combustion is performed well. It is determined whether or not the combustion stability is deteriorated by such a method. If the combustion stability is deteriorated, the process proceeds to step 602. If the combustion stability is not deteriorated, the process proceeds to step 603.

  In step 602 and step 603, the speed at which the actual air-fuel ratio approaches the target air-fuel ratio is set based on the combustion stability. Specifically, the FB gain described above is set. This control is performed when the difference between the actual air-fuel ratio and the target air-fuel ratio is equal to or greater than a predetermined value when the warm-up of the air-fuel ratio sensor 20 is completed. Therefore, when the FB gain used for normal air-fuel ratio FB control is used. Since the air-fuel ratio FB correction coefficient becomes a large value and the correction amount of the fuel injection amount increases, there is a possibility that the air-fuel ratio changes rapidly and the combustion state is further deteriorated.

  In step 602, in which it is determined in step 601 that the combustion stability has deteriorated, it is necessary to make the correction amount of the fuel injection amount smaller than the correction amount of the fuel injection amount by the normal air-fuel ratio FB control. Therefore, the FB gain is set to a small value based on the combustion stability as compared with the normal air-fuel ratio FB control. Then, the process proceeds to step 604 after setting the FB gain.

  In Step 603, where it is determined that the previous combustion is being performed satisfactorily with respect to Step 602, there is still a margin with respect to the stability limit, so the FB gain is set to a value larger than the previous FB gain. However, the combustion stability is less likely to deteriorate. Therefore, it is set to a value larger than the previous FB gain. This increases the speed at which the actual air-fuel ratio approaches the target air-fuel ratio. Then, after setting the FB gain, the process proceeds to step 604.

  In step 604, the fuel injection amount is corrected based on the FB gain set in accordance with the combustion stability in step 602 or step 603. Specifically, the combustion stability FB coefficient FAF3 calculated based on the FB gain (Kp · Ki · Kd at the time of PID control), the target air / fuel ratio, and the actual air / fuel ratio set according to the combustion stability, The fuel injection amount TAU is calculated by the following equation using the basic fuel injection amount Tp.

TAU = Tp × FAF3 × FALL
Thus, the fuel injection amount TAU is calculated from the combustion stability FB coefficient set according to the combustion stability. That is, the speed at which the actual air-fuel ratio approaches the target air-fuel ratio is set according to the combustion stability.

  Next, at step 605, it is determined whether or not the actual air-fuel ratio after combustion has been performed with the corrected fuel injection amount has reached the target air-fuel ratio. If the actual air-fuel ratio has reached the target air-fuel ratio, this routine is terminated. If the actual air-fuel ratio has not reached the target air-fuel ratio, the routine proceeds to step 601 and the processing from step 601 to step 605 is performed. Combustion stability FB control is performed by the above processing procedure.

  Next, transition states of various controls corresponding to the processing procedure of the air-fuel ratio control at the time of starting described above will be described with reference to FIG.

  First, the engine is started at time t0. Immediately after start-up, the air-fuel ratio sensor 20 has not been warmed up, so the air-fuel ratio sensor availability flag and the air-fuel ratio FB flag are “OFF” (step 100). Therefore, during time t0 to t1, fuel predetermined by open control is injected (step 200).

  The air-fuel ratio sensor is warmed up by the open control, and at time t1, the air-fuel ratio sensor is warmed up. That is, the air-fuel ratio sensor is effective. As a result, the air-fuel ratio sensor availability flag and the air-fuel ratio FB flag are set to “ON”, and the FB control can be executed (step 100). Further, since the difference between the detected value of the air-fuel ratio sensor (actual air-fuel ratio) and the target air-fuel ratio is greater than or equal to a predetermined value at time t1 (step 300), combustion stability FB control is performed after time t1 (step step). 400). That is, the combustion stability is detected, the FB gain setting and the air-fuel ratio correction are started (steps 601 to 605).

  Between time t1 and time t2, the combustion stability is a value smaller than the stability limit (step 601), so the FB gain is set to a large value. That is, the actual air-fuel ratio is set so as to approach the target air-fuel ratio quickly (step 603). At times t2, t3, and t4, the combustion stability exceeds the stability limit and the combustion state is deteriorated (step 601), so the FB gain is set to a small value. That is, the speed at which the actual air-fuel ratio approaches the target air-fuel ratio is set to be slow (step 602).

  Then, at time t5, when the actual air-fuel ratio reaches the target air-fuel ratio, the air-fuel ratio control at the time of start is ended.

  Next, the function and effect of the second embodiment will be described.

  According to the above configuration, when there is a difference between the actual air-fuel ratio detected when the air-fuel ratio sensor 20 is enabled and the target air-fuel ratio, the FB gain is set based on the combustion stability. Specifically, when the combustion stability is deteriorated, the FB gain is set so that the speed at which the actual air-fuel ratio approaches the target air-fuel ratio becomes slow. Conversely, when the combustion stability is good, the FB gain is set so that the speed at which the actual air-fuel ratio approaches the target air-fuel ratio becomes faster. That is, the speed at which the actual air-fuel ratio approaches the target air-fuel ratio is set according to the combustion stability. Thus, even when the actual air-fuel ratio deviates from the target air-fuel ratio due to the open control, the correction amount of the fuel injection amount does not change abruptly even when the FB control is started. Therefore, since the actual air-fuel ratio does not change suddenly to the lean or rich side, it is possible to prevent the combustion state from becoming unstable, and as a result, to prevent the deterioration of emission and drivability. Can do.

  As described above, according to the first embodiment and the second embodiment, the internal combustion engine that prevents the deterioration of emission and drivability by setting the correction amount of the fuel injection amount by the FB control according to the combustion stability. The air-fuel ratio control apparatus can be provided.

[Other Embodiments]
In the first and second embodiments, in the combustion stability FB control, when the combustion stability is good, the speed at which the actual air-fuel ratio is brought close to the target air-fuel ratio is set to be faster than the previous time. However, it may be set at the same speed as the previous time.

  In the first embodiment and the second embodiment, when the air-fuel ratio sensor is warmed up, combustion stability FB control is performed when there is a difference of a predetermined value or more between the actual air-fuel ratio and the target air-fuel ratio. The combustion stability FB control was repeatedly performed until the air-fuel ratio reached the target air-fuel ratio. However, even before the actual air-fuel ratio reaches the target air-fuel ratio, if the difference between the actual air-fuel ratio and the target air-fuel ratio is not more than a predetermined value by the combustion stability FB control, the combustion stability FB is reduced. It is also possible to switch to normal air-fuel ratio FB control without repeating.

1 engine (internal combustion engine)
6 ECU
12 Injector (fuel injection means)
15 Crank angle sensor (combustion stability detection means)
20 Exhaust pipe 20 Air-fuel ratio sensor (air-fuel ratio detection means)

Claims (6)

Fuel injection means for injecting fuel into the internal combustion engine;
Air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas installed in the exhaust pipe of the internal combustion engine;
A warm-up determination unit for determining that the warm-up of the air-fuel ratio detection unit is completed;
Combustion stability detecting means for detecting the stability of the combustion state of the internal combustion engine;
When the warm-up determination means determines that the air-fuel ratio detection means has been warmed up, the fuel injection is performed based on the air-fuel ratio detected by the air-fuel ratio detection means (hereinafter referred to as the actual air-fuel ratio) and the target air-fuel ratio. Air-fuel ratio feedback control means (hereinafter referred to as air-fuel ratio FB control means) for correcting the fuel injection amount of the means;
If there is a difference between the actual air-fuel ratio and the target air-fuel ratio at the time when the air-fuel ratio detection means has been warmed up by a predetermined value or more, the actual air-fuel ratio detection means is based on the combustion stability detected by the combustion stability control detection means. Air-fuel ratio gradual change control means for setting a speed at which the air-fuel ratio approaches the target air-fuel ratio,
An air-fuel ratio control apparatus for an internal combustion engine, wherein the air-fuel ratio FB control means executes air-fuel ratio FB control based on a speed set by the air-fuel ratio gradual change control means.   The air-fuel ratio gradual change control means sets so that the speed at which the actual air-fuel ratio approaches the target air-fuel ratio becomes slow when the combustion stability deteriorates, and when the combustion stability is good, the actual air-fuel ratio gradually changes. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein a speed at which the fuel ratio approaches the target air-fuel ratio is increased. The air-fuel ratio gradual change control means completes warming-up of the air-fuel ratio detection means when there is a difference between the actual air-fuel ratio and the target air-fuel ratio at the time when warm-up of the air-fuel ratio detection means is completed. The actual air-fuel ratio detected from time to time is set as the starting point of the temporary target air-fuel ratio, and the rate of change in speed at which the temporary target air-fuel ratio is brought close to the target air-fuel ratio based on the combustion stability (target value gradual change rate) Set
3. The air-fuel ratio FB control unit corrects the fuel injection amount based on a temporary target air-fuel ratio set by the target value gradual change rate and the actual air-fuel ratio. An air-fuel ratio control device for an internal combustion engine according to claim 1.   The air-fuel ratio gradual change control means changes the fuel injection amount correction coefficient (feedback gain) by the air-fuel ratio FB control based on the combustion stability, thereby speeding the actual air-fuel ratio closer to the target air-fuel ratio. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein   The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the combustion stability detection means detects the combustion stability of the internal combustion engine based on a detection value of an in-cylinder pressure sensor. .   6. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the combustion stability detection means detects the combustion stability of the internal combustion engine based on a detection value of a crank angle sensor. .

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