JP4122676B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for an internal combustion engine, and more particularly to improvement of exhaust emission performance by feedback control during warm-up operation.
[0002]
[Prior art and problems to be solved]
In general, even in an internal combustion engine that performs feedback control, during cold start, the fuel injection amount is increased in order to stabilize combustion, and the fuel injection amount is feedback controlled so that the target air-fuel ratio is reached after warm-up is completed. Yes. In order to improve exhaust emission performance, it is desirable to start feedback control from a lower temperature before the completion of warm-up, but if so, the air-fuel ratio that has been enriched by increasing the fuel injection amount until then will be feedback control A problem arises that the engine rotation is greatly reduced because the correction to stoichiometry is made with the shift to.
[0003]
In order to solve such a problem, there has been proposed one in which the amount of intake air is increased to prevent a decrease in rotation when feedback control is started (see Japanese Patent Application Laid-Open No. 7-119519). However, since the time delay due to the intake system volume is inevitable for the increase in the intake air amount, this cannot cope with the rapid decrease in rotation accompanying the change in the air-fuel ratio described above.
[0004]
The present invention has been made paying attention to such a conventional problem, and aims to prevent a reduction in rotation due to the start of feedback control during warm-up operation and to improve exhaust emission performance.
[0005]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a detecting means for detecting an operating state including a load, a rotational speed, a temperature and an exhaust oxygen concentration of an internal combustion engine, and an open loop control so as to coincide with a target air-fuel ratio determined according to the operating state. Or an air-fuel ratio control means for controlling the actual air-fuel ratio by feedback control based on the exhaust oxygen concentration, wherein the detected temperature after engine startup is lower than the warm-up completion temperature. Open loop control is performed when the temperature is below the set reference temperature, feedback control is performed when the reference temperature is exceeded, and the difference between the previous value and the current value of the rotational speed detected by the detection means during feedback control is performed. When the amount of decrease in the rotational speed determined from is greater than the reference value, the control speed in the lean direction of the feedback control is reduced. Than during normal operation Decrease At the same time, the control speed is gradually decreased while the rotation speed decrease amount is larger than the reference value, and then the control speed is gradually increased when the rotation speed decrease amount becomes smaller than the reference value. It was configured as follows.
[0007]
Claim 2 According to the invention, the air-fuel ratio control means is returned to the open loop control when the rotational speed reduction amount during the feedback control is larger than the second reference value set larger than the reference value. Configured.
[0008]
Claim 3 According to the present invention, the air-fuel ratio control means is configured to change the control speed in the lean direction by correcting at least one of the lean proportional control constant or the lean integral control constant in the PI control.
[0009]
Claim 4 According to the invention, the air-fuel ratio control means is configured to determine the decrease in the rotational speed only during the idling operation.
[0010]
Claim 5 According to the present invention, the air-fuel ratio control means is configured to permit the transition from the open loop control to the feedback control on condition that the activation of the sensor for detecting the exhaust oxygen concentration is completed after the engine is started.
[0011]
Claim 6 In the present invention, the air-fuel ratio control means is configured to perform open-loop control by clamping an air-fuel ratio feedback correction coefficient that reflects the oxygen concentration in feedback control.
[0012]
Claim 7 According to the present invention, the air-fuel ratio control means is executed such that the feedback control is executed with the stoichiometric air-fuel ratio as the target air-fuel ratio, and the open-loop control is executed with the air-fuel ratio set richer than the stoichiometric air-fuel ratio as the target air-fuel ratio. Configured.
[0013]
Claim 8 According to the invention, the rich air-fuel ratio at the time of the open loop control is corrected in the stoichiometric air-fuel ratio direction according to at least one of a temperature increase after engine start and a time lapse.
[0014]
[Action / Effect]
In each of the first and subsequent aspects of the invention, the open loop control is executed when the detected temperature after engine startup is equal to or lower than a reference temperature set lower than the warm-up completion temperature. The reference temperature is, for example, a temperature at which the sensor for detecting the exhaust oxygen concentration is activated to some extent and feedback control based on the oxygen concentration is possible. If the air-fuel ratio feedback control using the oxygen concentration is premised, the open loop control at this time can be realized by clamping an air-fuel ratio feedback correction coefficient that reflects the oxygen concentration. As a result, stable warm-up operation can be continued by open-loop control using the rich air-fuel ratio as a target air-fuel ratio, for example, immediately after cold start where air-fuel ratio feedback control is difficult or at extremely low temperatures.
[0015]
If the rich air-fuel ratio at the time of the open loop control is corrected in the theoretical air-fuel ratio direction according to at least one of the temperature increase after engine start and the time elapse, it will respond to the temperature increase after start or time elapse. In addition, the air-fuel ratio can be optimized to improve the rotational stability, and the fuel consumption can be further improved.
[0016]
On the other hand, when the engine warms up and the engine temperature exceeds the reference temperature, air-fuel ratio feedback control is started. However, during this feedback control, if the amount of decrease in the rotational speed determined from the difference between the previous value and the current value of the rotational speed detected by the detection means is greater than the reference value, the control speed in the lean direction of the feedback control The Than during normal operation Decrease. This is realized, for example, by correcting the control speed in the lean direction by correcting at least one of the leaning proportional control constant and the leaning integral control constant in the PI control. As a result, since the control operation in the air-fuel ratio lean direction is suppressed with respect to the decrease in the rotational speed, the combustion becomes a stable direction, and the warm-up operation can be stably continued. Thus, exhaust emission and fuel consumption can be improved by performing air-fuel ratio feedback control under the temperature condition before completion of warm-up. In addition, since the air-fuel ratio control responds to a decrease in the rotational speed, there is little time delay until the combustion state is stabilized, and a good rotational stability can be obtained.
[0017]
In the feedback control described above, the control speed in the lean direction of the air-fuel ratio is set when the rotational speed reduction amount becomes larger than a certain reference value. gradually After that, when the rotational speed reduction amount becomes smaller than the reference value, the control speed is reduced. gradually By increasing the configuration, it is possible to improve the control responsiveness when the decrease in the rotational speed is subsequently recovered while securing the rotational stability during the shift to the feedback control. In addition, when the amount of decrease in the rotational speed during feedback control becomes larger than the second reference value set to be larger than the reference value, it is configured to return to the open loop control so that the feedback control can cope. Stalls due to a sudden decrease in rotational speed that cannot be achieved can be prevented.
[0018]
Even when the engine is warming up, when the required load and rotation speed increase due to the accelerator pedal being depressed by the driver, there is no risk of rotation reduction or stalling. Therefore, the reduction in rotation speed need only be determined during idle operation. .
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a mechanical configuration of an embodiment according to the present invention. In the figure, reference numeral 1 denotes a control unit composed of a microcomputer and its peripheral devices, which controls the fuel injection amount and ignition timing of the spark ignition internal combustion engine 2 based on various operation state signals. The basic detection amount for engine control is an intake air amount signal from the air flow meter 3 and an engine rotation speed signal from the crank angle sensor 4, which will be described in detail later. For example, the fuel injection amount is determined based on these signals. The signal value is determined by correcting the value in accordance with a cooling water temperature signal from the water temperature sensor 5, an oxygen concentration signal from an exhaust oxygen sensor (hereinafter referred to as "O2 sensor") 6, and the like. The fuel injection amount signal is given to the injector 7, whereby a required amount of fuel is supplied to the internal combustion engine 2. Further, the ignition timing is determined by correcting a basic value determined from an accelerator operation amount from an unillustrated accelerator sensor and an engine rotation speed by a water temperature or the like, and a crank position signal from the crank angle sensor 4 is determined. With reference to the ignition plug 8, an ignition current is supplied at a timing according to the signal value. In addition, 9 is a throttle valve and 10 is a catalytic converter.
[0020]
Next, a control operation example of the air-fuel ratio control by the control unit 1 will be described with reference to the flowchart of FIG. FIG. 2 shows a fuel injection amount calculation routine that is the basis of air-fuel ratio control, and this routine is periodically executed, for example, every 10 ms. Hereinafter, the steps of the control routine will be described in order.
S101: The intake air amount QA is read from the output signal of the air flow meter 3, and the engine speed NE is read from the output signal of the crank angle sensor 4.
S102: Based on the intake air amount QA and the engine speed NE, the basic fuel injection amount Tp is calculated by calculating Tp = K · QA / NA. K is a coefficient, and Tp is a fuel injection amount in which the air-fuel ratio is the theoretical air-fuel ratio. The injector 7 is configured to control the fuel injection amount in accordance with the valve opening time under pressure-adjusted fuel supply. In this case, the fuel injection amount Tp is the ratio of the valve opening time or the opening / closing time ratio of the injector 7. give.
S103: A final fuel injection amount Ti is calculated based on the basic fuel injection amount Tp, the target equivalent ratio TFBYA, and the feedback correction coefficient α. TFBYA is the ratio of the fuel / air ratio of the air / fuel mixture to be controlled to the stoichiometric air / fuel ratio, and corresponds to the target air / fuel ratio of the present invention. When TFBYA = 1, the stoichiometric air-fuel ratio is represented. When TFBYA> 1, the rich air-fuel ratio is represented. When TFBYA <1, the lean air-fuel ratio is represented. The feedback correction coefficient α is a correction coefficient for converging the actual air-fuel ratio to the target air-fuel ratio according to the output of the O 2 sensor 6. When α> 1, it is on the rich side, and when α <1, it is on the lean side. Correct the air / fuel ratio. When α = 1 is fixed (clamped), feedback control is not performed, and open-loop control is performed using the target air-fuel ratio given by TFBYA.
[0021]
Next, a routine for calculating the target equivalent ratio TFBYA will be described with reference to FIG. This routine is also repeatedly executed at the same cycle as in FIG. Here, TFBYA is corrected in the rich direction by adding the post-startup increase correction coefficient KAS or the water temperature increase correction coefficient KTW to the basic value = 1 representing the theoretical air-fuel ratio = 1.
[0022]
The post-startup increase correction coefficient KAS is a correction coefficient for stabilizing combustion at the start and immediately after the start, and is set to a value of 0 or more. The water temperature increase correction coefficient KTW is a correction coefficient for stabilizing combustion at low water temperature and is set to a value of 0 or more.
S201: The engine cooling water temperature TWK is read from the output signal of the water temperature sensor 5.
S202: It is determined whether or not the starter SW is ON, that is, whether or not cranking for starting the engine is currently being performed.
S203: When the starter SW is ON, the initial value TKAS of the post-startup increase correction coefficient is obtained by table search or the like based on the water temperature TWK. TKAS is set to a larger value as the water temperature TWK is lower.
S204: The time correction coefficient TMKAS of the post-startup increase correction coefficient KAS is set to 1. TMKAS is a correction coefficient for decreasing KAS over time after starting. KAS is not limited to the elapsed time, and may be decreased, for example, as the water temperature rises after starting.
S205: The initial value TKAS is set to the post-startup increase correction coefficient KAS as it is.
S206: When the starter SW is OFF, the decrease ΔTMK is subtracted from the previously calculated value TMKASz of the time correction coefficient. As a result of the processing in this step, the value of the time correction coefficient TMKAS gradually decreases with the passage of time after the starter SW is turned off. That is, the increased fuel gradually decreases after starting.
S207: It is determined whether or not the time correction coefficient TMKAS is greater than zero.
S208: When the time correction coefficient TMKAS is greater than 0, the post-startup increase correction coefficient KAS is calculated by multiplying the initial value TKAS by the time correction coefficient TMKAS.
S209: When the time correction coefficient TMKAS is 0 or less, the post-startup increase correction coefficient KAS is set to 0.
S210: A water temperature increase correction coefficient KTW is calculated based on the water temperature TWK. KTW is set to a larger value as the water temperature TWK is lower, and becomes 0 when the engine warm-up completion temperature is exceeded.
S211: The post-startup increase correction coefficient KAS and the water temperature increase correction coefficient KTW are added to calculate a temporary equivalent value TFBYA1 for the target equivalence ratio.
S212: It is determined whether the air-fuel ratio feedback correction coefficient α is clamped to 1, that is, whether the air-fuel ratio feedback control is in a non-execution state. The conditions for clamping α will be described later.
S213: When the air-fuel ratio feedback correction coefficient α is clamped to 1, the temporary placement value TFBYA1 calculated in S211 is set as the final target equivalent ratio TFBYA. Accordingly, the control routine shown in FIG. 2 performs the open loop control by TFBYA, in this case, the warm-up operation by the target air-fuel ratio corrected to the rich side.
S214: When the feedback correction coefficient α is not clamped to 1, that is, when feedback control is being executed, the target equivalent ratio TFBYA is clamped to 1. In this case, air-fuel ratio feedback control in which the theoretical air-fuel ratio is the target air-fuel ratio is performed using the feedback correction coefficient α set by the control routine shown in FIG.
[0023]
FIG. 4 shows a routine for calculating the air-fuel ratio feedback correction coefficient α, which is repeatedly executed at the same cycle as in FIG. In this control routine, normal feedback control is performed under conditions that may not cause a sudden decrease in engine speed, for example, when sufficient time has elapsed since the start and the engine has been warmed up, or when the engine is not idling. In addition to the above, even under conditions that may cause a sudden decrease in the engine speed, after the activation of the O2 sensor 6 is completed, feedback control is performed as much as possible (hereinafter, the activation of the O2 sensor 6 is completed). The air-fuel ratio feedback control that starts on condition of this is called early feedback control).
S301: The output signal OSF of the O2 sensor 6 is read, and the engine cooling water temperature TWK is read from the output signal of the water temperature sensor 5.
S302: Based on the OSF, it is determined whether or not the activation of the O2 sensor 6 is completed, that is, whether or not the O2 sensor 6 is in a state of generating an output corresponding to the oxygen concentration in the exhaust gas.
S303 to S310: Based on the state of the idle SW, the water temperature, and whether or not the increase correction after starting is performed, it is determined whether or not the engine is in a state in which it is possible to perform the air-fuel ratio feedback control, and the control permission state is indicated as follows. The flags FFBH and FFBL are set.
-When the idle switch is OFF, that is, when the accelerator is depressed, there is no problem with a sudden decrease in the engine speed. Feedback control is permitted (FFBH = 1) (S310).
-If the idle SW is ON, the water temperature TWK is equal to or higher than the warming-up water temperature TWFBH, and the post-start-up increase correction has been completed (KAS = 0), the engine speed will drop sharply even if feedback control is performed. Therefore, the normal air-ratio feedback control is permitted (FFBH = 1) (S310).
・ If the idle SW is ON and the water temperature TWK is lower than the warm-up water temperature TWFBH or the post-startup increase correction has not been completed (KAS> 0), the engine speed may drop sharply if feedback control is performed Therefore, normal air-ratio feedback control is not permitted (FFBH = 0), and early feedback control is performed while monitoring the engine speed (FFBL = 1) (S307, S309).
-If the idle SW is ON and the water temperature TWK is lower than the predetermined low temperature threshold value TWFBL, it is clear that combustion becomes unstable and it is difficult to maintain idle operation. Disallowed (FFBL = 0) (S305).
S311 to S318: The air-fuel ratio feedback control is set or calculated as follows according to the air-fuel ratio feedback control permission flags FFBH and FFBL and the engine speed monitoring flag FNE.
When the normal air-ratio ratio feedback control is permitted, the output signal OSF of the O2 sensor 6 and control constants for the normal feedback control (the rich proportional constant PL, the lean proportional constant PR, the rich integral constant IL, the lean The air-fuel ratio feedback correction coefficient α is calculated using the integration constant IR) (S317). Details of this processing will be described later with reference to FIG.
When only the early feedback control is permitted and the engine speed monitoring flag FNE is 1, the output signal OSF of the O2 sensor 6 and the control constants for the early feedback control (the rich proportional constant PLs, the lean proportional constant PRs, the rich The feedback correction coefficient α is calculated using the integration integral constant ILs and the lean integration constant IRs) (S316). Details of this processing will be described later with reference to FIG. The control constant for early feedback control may be set to exactly the same value as the control constant for normal control, but here, the control speed in the lean direction becomes small so that the engine speed is difficult to reduce rapidly. Setting (IRs <IR, PRs <PR).
If the early feedback control is not permitted, or if the early feedback control is permitted but the engine speed monitoring flag FNE is 0, the feedback control is stopped and the air-fuel ratio feedback correction coefficient α is set to 1. Clamp to (S313, S315)
S318: Since the feedback control cannot be executed when the activation of the O2 sensor 6 is not completed, the feedback correction coefficient α is clamped to 1.
[0024]
FIG. 5 and FIG. 6 show subroutines for calculating the air-fuel ratio feedback correction coefficient α executed in S317 and S316, respectively.
S401 and S421: It is determined whether or not this step is executed only after the state in which the air-fuel ratio feedback correction coefficient α is clamped to 1 is released.
S402 and S422: In the case of normal feedback control (FIG. 5), 1 is set as the initial value of α when immediately after α clamp release. On the other hand, in the case of early feedback control (FIG. 6), if it is immediately after α clamp release, the temporary equivalent value TFBYA1 of the target equivalent ratio calculated at the time of execution of the immediately preceding target equivalent ratio calculation routine is set to the initial value of α. Set as.
S403 to S405 / S423 to S425: The output signal OSF of the O2 sensor 6 is compared with the slice level SLF, and the flag F11 indicating whether the air-fuel ratio is rich or lean is set. When the air-fuel ratio is lean, F11 = 0 is set, and when the air-fuel ratio is rich, F11 = 1 is set.
S406 to S412, S426 to S432: Depending on the presence or absence of inversion of the flag F11 and the value of the flag F11, in the case of normal control (FIG. 5), α is determined by the normal control proportional constants (PL, PR) when F11 is inverted. When it is not inverted, α is increased or decreased by the normal constant for control (IL, IR). However, as described above, at the time of the early air-fuel ratio feedback (FIG. 6), the control constants set for early control (PLs, PRs, ILs, IRs) are used.
[0025]
FIG. 7 is an engine speed monitoring routine for setting a flag FNE indicating a decrease state of the engine speed. This process is executed at the minimum cycle in which the effect of the air-ratio feedback control is executed or stopped, or the influence of the change in the control constant is reflected in the engine speed, but longer than the execution cycle of the routine of FIG. In this routine, it is determined whether the engine speed is rapidly decreasing or slowly, and the engine speed monitoring flag FNE is set.
S501: The engine speed NE is read from the output signal of the crank angle sensor 4.
S502: It is determined whether or not the early air ratio feedback control permission flag FFBL is 1, that is, whether or not it is necessary to monitor a decrease in engine speed.
S503: When the flag FFBL is 1, the rotational speed decrease amount ΔNE is calculated. ΔNE is calculated by subtracting the engine speed NE read this time from the engine speed NEz read this time when this routine was executed last time, so that the engine speed decreases when the value is positive. When it is negative, it indicates that the engine speed is increasing.
S504: It is determined whether or not the rotational speed decrease amount ΔNE is larger than a reference value DNELMT for determining a rapid decrease.
S505: When the rotational speed decrease amount ΔNE is larger than the reference value DNELMT, the engine rotational speed monitoring flag FNE = 0 (early air ratio feedback control prohibition) is set.
S506: It is determined whether or not the rotational speed reduction amount ΔNE is a positive value.
S507: When the engine speed reduction amount ΔNE is a positive value, the engine speed monitor flag FNE = 1 is set. That is, when the engine speed is in a state of decreasing but the speed of decrease is slow, FNE = 1 is set, and the early air-to-air ratio feedback control is performed.
S508: When the rotational speed decrease amount ΔNE is a negative value in S506, this means that the rotational speed is increasing as described above, so the FNE value that has already been set is used as it is. maintain.
S509: When the flag FFBL is 0 in S502, the flag FNE is initialized to 1.
[0026]
FIG. 8 shows the state of the cooling water temperature TWK, the target equivalence ratio TFBYA, the air / fuel ratio feedback correction coefficient α, the engine speed change ΔNE, the O2 sensor active state, and the state of each flag when the air-fuel ratio control is executed. It is a timing chart showing changes. This shows the state of control when the engine is started under a temperature condition where the cooling water temperature TWK is between the upper and lower determination threshold values TWFBH-TWFBL as shown in the figure, and then the idling operation is continued.
[0027]
Since the O2 sensor 6 is not in an active state at the start of engine starting, the air-fuel ratio feedback control is prohibited (FFBL = 0, FFBH = 0). Therefore, the air-fuel ratio feedback correction coefficient α is clamped and the target equivalent ratio TFBYA. Is set so as to give a rich air-fuel ratio corresponding to the water temperature at that time and the elapsed time after start-up, and open-loop control is executed with this set equivalent ratio TFBYA1 as the target air-fuel ratio. When the operation is continued in this state and the O2 sensor 6 is activated in a short time, the early feedback control permission flag FFBL is inverted to 1, so that the clamp of the air-fuel ratio feedback correction coefficient α is released and the target equivalent ratio TFBYA is Thus, feedback control with the stoichiometric air-fuel ratio as the target air-fuel ratio is started.
[0028]
However, at this time, since the decrease amount ΔNE of the engine speed exceeds the reference value DNELMT, the feedback control is temporarily stopped and the process returns to the open loop control. Thereafter, after the rotational speed is recovered, feedback control is started again. As a result, the rotation is reduced again, but since the amount of decrease ΔNE at this time is less than or equal to the reference value DNELMT, feedback control with a moderate control speed in the lean direction is continued without returning to open loop control. ing. As a result, the amount of decrease in the rotational speed is gradually recovered.
[0029]
In the above control process, when the cooling water temperature TWK exceeds the upper limit threshold value TWFBH, it is determined that the warm-up is completed, and FFBL = 0 and FFBH = 1 are set, so that the control speed in the leaning direction is suppressed and early feedback is performed. The control is terminated and the routine shifts to normal feedback control.
[0030]
Next, a second embodiment regarding air-fuel ratio control according to the present invention will be described. While the first embodiment controls execution and prohibition of early feedback control by the flag FNE, in this embodiment, FNE is calculated as an integer in the range of 0 to N, and prohibition and execution of early feedback control are performed. Variably set the control constant for early feedback control.
[0031]
FIG. 9 shows a subroutine for calculating the air-fuel ratio feedback correction coefficient α for this purpose. The processing method of FIG. 6 differs from the calculation method of the coefficient α when the rich / lean flag F11 indicates the rich state in the determination of S430. In the process of FIG. 6, the leaning integral control constant IRs for early feedback control is set in S432, but in this embodiment, the lean for normal control is calculated from the previous calculated value αz of the air-fuel ratio feedback control coefficient in S452. A new α is calculated by subtracting FNE / N of the integration control constant IR. For example, when N = 3 and FNE = 1, the lean integration control constant is 1/3 of the normal value, and the control speed in the lean direction is 1/3.
[0032]
Next, the engine speed monitoring routine in this embodiment is shown in FIG.
S521 to S524: Same as S501 to S504 in FIG.
S525: 1 is subtracted from the previous setting value FNEz of FNE to calculate a new FNE. That is, while the sudden decrease in the engine rotation speed is detected, the lean integration control constant is gradually reduced, and the control speed in the lean direction is gradually reduced.
S526: It is determined whether FNE is 0 or less.
S527: When FNE is 0 or less, the value of FNE is limited to 0.
S528: It is determined whether or not the rotation speed decrease amount ΔNE is larger than a reference value DNETH set on the side smaller than the reference value DNELMT.
S529: When ΔNE is larger than the reference value DNETH, the previous setting value FNEz of FNE is maintained this time.
S530: It is determined whether or not the rotational speed reduction amount ΔNE is a positive value.
S531: 1 is added to the previous setting value FNEz of FNE to calculate a new FNE. That is, when it is detected that the engine speed is slowly decreasing, the lean integration control constant is gradually increased, and the control speed in the lean direction is gradually increased.
S532: It is determined whether or not FNE is greater than N.
S533: When FNE is larger than N, the value of FNE is limited to N.
S534: When the rotational speed decrease amount ΔNE is a negative value in S530, the previous setting value FNEz of FNE is maintained this time as well.
S535: When the flag FFBL is 0 in S522, the flag FNE is initialized to N.
[0033]
FIG. 11 shows a timing chart of the air-fuel ratio control operation by the control of the second embodiment. The premise at the time of control execution is the same as FIG. In this control, as shown in the figure, with respect to the rotation decrease after the start of the early feedback control, the value of the rotation speed decrease monitoring flag FNE gradually increases / decreases in accordance with the rotation decrease amount ΔNE, whereby the air / fuel ratio feedback correction coefficient α is increased. Since it is finely variably set, a more appropriate air-fuel ratio is set according to the rotation reduction amount, and smooth rotation control characteristics are exhibited.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a mechanical configuration example of an internal combustion engine to which the present invention can be applied.
FIG. 2 is a first flowchart showing control according to the first embodiment of the present invention;
FIG. 3 is a second flowchart showing control according to the first embodiment of the present invention;
FIG. 4 is a third flowchart showing the control according to the first embodiment of the present invention.
FIG. 5 is a fourth flowchart showing the control according to the first embodiment of the present invention.
FIG. 6 is a fifth flowchart showing the control according to the first embodiment of the present invention.
FIG. 7 is a seventh flowchart showing the control according to the first embodiment of the present invention;
FIG. 8 is a timing chart showing an air-fuel ratio control operation by the control of the first embodiment of the present invention.
FIG. 9 is a first flowchart showing control according to the second embodiment of the present invention;
FIG. 10 is a second flowchart showing the control according to the first embodiment of the present invention.
FIG. 11 is a timing chart showing an air-fuel ratio control operation by the control of the second embodiment of the present invention.
[Explanation of symbols]
1 Control unit
2 Internal combustion engine
3 Air flow meter
4 Crank angle sensor
5 Water temperature sensor
6 O2 sensor
7 Injector
8 Spark plug
9 Throttle valve
10 Catalytic converter

Claims (8)

Detection means for detecting an operating state including the load, rotation speed, temperature, and exhaust oxygen concentration of the internal combustion engine, and by open loop control so as to coincide with a target air-fuel ratio determined according to the operating state, or based on the exhaust oxygen concentration In an internal combustion engine provided with an air-fuel ratio control means for controlling the actual air-fuel ratio by feedback control,
The air-fuel ratio control means performs an open loop control when the detected temperature after engine start is equal to or lower than a reference temperature set lower than the warm-up completion temperature, and executes feedback control when the reference temperature exceeds the reference temperature.
Also, during feedback control, when the amount of decrease in the rotational speed determined from the difference between the previous value and the current value of the rotational speed detected by the detecting means becomes larger than the reference value, the control speed in the lean direction of the feedback control is normally set. The control speed is gradually decreased while the rotational speed decrease amount is larger than the reference value, and then the control speed is gradually decreased when the rotational speed decrease amount becomes smaller than the reference value. An air-fuel ratio control apparatus for an internal combustion engine configured to increase . The air-fuel ratio control means is configured to return to open loop control when the amount of decrease in rotational speed during feedback control is greater than a second reference value set larger than the reference value. An air-fuel ratio control device for an internal combustion engine according to claim 1. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio control means changes the control speed in the lean direction by correcting at least one of the leaning proportional control constant or the leaning integral control constant in the PI control. . 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio control means determines a decrease in rotational speed only during idle operation . 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio control means permits the transition from the open loop control to the feedback control on condition that the sensor for detecting the exhaust oxygen concentration is completed after the engine is started. . The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio control means performs open loop control by clamping an air-fuel ratio feedback correction coefficient that reflects the oxygen concentration in the feedback control . 2. The internal combustion engine according to claim 1, wherein the air-fuel ratio control means executes the feedback control with the stoichiometric air-fuel ratio as a target air-fuel ratio, and performs the open-loop control with the air-fuel ratio set to a richer side than the stoichiometric air-fuel ratio as the target air-fuel ratio. Engine air-fuel ratio control device. 8. The air-fuel ratio control device according to claim 7, wherein the air-fuel ratio control means corrects the air-fuel ratio at the time of open-loop control in the stoichiometric air-fuel ratio direction according to at least one of a temperature increase after engine start and a time lapse. .

Images