JPH0663468B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

The present invention relates to an air-fuel ratio control system for an internal combustion engine, which is effective for purification of exhaust gas during cold operation.

[Prior Art] Conventionally, using a three-way catalyst, harmful components (HC, C
O, NOx), the residual oxygen concentration in the exhaust gas is detected as an air-fuel ratio signal, and feedback control is performed based on the air-fuel ratio signal so that the air-fuel ratio of the internal combustion engine becomes the target air-fuel ratio. It has been known.

In the air-fuel ratio control device as described above, for example, the basic fuel injection amount calculated according to the load of the internal combustion engine, the correction coefficient obtained by adding or subtracting the air-fuel ratio signal with a predetermined integration constant or skip constant Feedback control was carried out to obtain the actual fuel injection amount.

By the way, Japanese Patent Application Laid-Open Nos. 52-144536 and 58-27848 have been proposed for changing the integration constant or the skip constant for the purpose of improving the response of the control.

Further, in order to set the target air-fuel ratio to a required value in consideration of the characteristics of the internal combustion engine or the oxygen concentration detection sensor, the above-mentioned integral constant or the control center of the air-fuel ratio control is changed to, for example, JP-A-52 -81433 and Japanese Patent Laid-Open No. 52-81434 are also known.

[Problems to be Solved by the Invention] In the related art, the correction coefficient for the air-fuel ratio control in consideration of the combustion characteristics when the internal combustion engine is cold is not set. That is, when the internal combustion engine is in a low temperature state, since the combustion temperature is also low, the emission amount of NOx is small, but the emission amounts of HC and CO are large, and the exhaust characteristic is deteriorated.

It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which appropriately changes a correction coefficient in air-fuel ratio control and prevents deterioration of exhaust characteristics when cold.

Configuration of the Invention [Means for Solving the Problems] In order to solve the above problems, the present invention, as illustrated in FIG. 1, is an operating state detecting means M2 for detecting the operating state of an internal combustion engine M1.
And a control means M3 for supplying a fuel amount determined based on the detected operating state to the internal combustion engine M1 and performing feedback control so that the air-fuel ratio of the internal combustion engine M1 becomes a target air-fuel ratio. In the air-fuel ratio control device for an internal combustion engine, temperature detecting means for detecting the temperature of the internal combustion engine M1 and M4, when the detected temperature is lower than or equal to a predetermined temperature, the target air-fuel ratio is leaner than the stoichiometric air-fuel ratio. The gist is an air-fuel ratio control device for an internal combustion engine, which is provided with a leaning means for setting and M5.

The operating state detecting means M2 is for detecting the operating state of the internal combustion engine M1, such as the load and the air-fuel ratio. For example,
The air flow meter or the intake pipe pressure sensor, the intake air temperature sensor, the rotation speed sensor, the throttle position sensor, the oxygen concentration sensor, or the like can be used.

The control means M3 supplies fuel so that the air-fuel ratio of the internal combustion engine M1 becomes the target air-fuel ratio. For example, internal combustion engine
The actual fuel injection amount calculated by correcting the basic fuel injection amount determined according to the load of M1 by the correction coefficient based on the air-fuel ratio detected by the operating state detection means M2 may be supplied.

The temperature detecting means M4 is for detecting the temperature of the internal combustion engine M1. For example, it can be realized by a water temperature sensor that detects the cooling water temperature of the internal combustion engine M1. Further, an oil temperature sensor that detects the temperature of the lubricating oil of the internal combustion engine M1 may be used.

As the leaning means M5, when the detected temperature is equal to or lower than a predetermined temperature, when the output signal of the oxygen sensor changes between the lean state and the rich state, when starting the control of the air-fuel ratio to the rich side Means to extend the lean delay time can be adopted. Further, as the leaning means M5, when the detected temperature is equal to or lower than a predetermined temperature, the skip constant and the correction coefficient for greatly changing the correction coefficient of the fuel amount used when controlling the air-fuel ratio to the target air-fuel ratio. It is possible to employ a means for increasing the skip constant and / or the integration constant for changing the air-fuel ratio to the lean side among the integration constants for gradually changing the. Furthermore,
As the leaning means M5, when the detected temperature is equal to or lower than a predetermined temperature, it is possible to employ means for setting a low reference value to be compared with the output of the oxygen sensor for air-fuel ratio determination in the rich state or the lean state. .

The control means M3 and the dilution means M5 can be realized by, for example, independent discrete logic circuits. Further, for example, a well-known CPU, a ROM, a RAM, and other peripheral circuit elements may be configured as a logical operation circuit, and both means may be realized according to a predetermined processing procedure.

[Operation] As illustrated in FIG. 1, the air-fuel ratio control apparatus for an internal combustion engine of the present invention changes the operating state detected by the operating state detecting means M2 in order to set the air-fuel ratio of the internal combustion engine M1 to the target air-fuel ratio. When the control means M3 supplies the fuel amount determined on the basis of the internal combustion engine M1, when the temperature detected by the temperature detection means M4 is equal to or lower than a predetermined temperature, the leaning means M5 leans the target air-fuel ratio above the theoretical air-fuel ratio. Set to the side. That is, when the internal combustion engine M1 is cold, feedback control is performed in which the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. As a result, although the NOx emission amount is small in the cold state, it is possible to perform the preferable air-fuel ratio control without causing the problem of deterioration of the exhaust characteristic that the emission amounts of HC and CO increase.

[Embodiment] Next, a detailed description will be given based on the first embodiment of the present invention and the drawings. FIG. 2 is a system configuration diagram of an engine equipped with the air-fuel ratio control device for an internal combustion engine of the present invention.

In the figure, the engine 1 includes a cylinder 2, a piston 3,
It has a fuel chamber 6 formed by a cylinder block 4 and a cylinder head 5. An ignition plug 7 is arranged in the combustion chamber 6.

The intake system of the engine 1 has an intake port 9 communicating with an intake pipe 10 via an intake valve 8 of a cylinder 2. A surge tank 11 that absorbs pulsation of intake air is provided upstream of the intake pipe 10, and a throttle valve 12 is provided upstream of the surge tank 11.

On the other hand, in the exhaust system of the engine 1, the exhaust port 14 communicates with the exhaust pipe 15 via the exhaust valve 13 of the cylinder 2.

The fuel system includes a fuel supply source including a fuel tank and a fuel pump (not shown), a fuel supply pipe, and a fuel injection valve 16 disposed near the intake port 9.

The ignition system includes an igniter 17 that outputs a high voltage necessary for ignition, and a distributor 18 that distributes and supplies the high voltage generated by the igniter 17 to the ignition plug 7 in conjunction with a crankshaft (not shown). It is configured.

The sensor system includes an intake pipe internal pressure sensor 21, which is provided in the intake pipe 10 and measures the intake air pressure, and the intake pipe 10.
Intake air temperature sensor 2 installed inside to measure intake air temperature
2, the throttle valve 1 in conjunction with the throttle valve 12
2, a throttle position sensor 23 that detects the opening degree, a water temperature sensor 24 that is provided in the cooling system of the cylinder block 4 to detect the temperature of the cooling water, and an exhaust pipe 15 that is provided with the residual oxygen concentration in the exhaust gas as an analog signal. An oxygen concentration sensor 25 for detecting is provided.

Further, inside the distributor 18, a rotation angle sensor which also functions as a rotation speed sensor which outputs a rotation angle signal every 1/24 rotation of the camshaft of the distributor, that is, every integer multiple of the crank angle of 0 ° to 30 °. 26 and a cylinder discrimination sensor 27 that outputs a reference signal once for each rotation of the camshaft of the distributor 18, that is, for every two rotations of a crankshaft (not shown).

Each signal from each sensor is input to an electronic control unit (hereinafter simply referred to as ECU) 30 and the ECU 30 controls the engine 1.

Next, the configuration of the ECU 30 will be described with reference to FIG.

The ECU 30 is configured as a logical operation circuit centering on the CPU 30a, ROM 30b, RAM 30c, backup RAM 30d, etc.
It is connected to the input / output port 30f, the input port 30g, and the output port 30h via the input / output port for inputting / outputting with the outside.

Further, the ECU 30 is provided with buffers 30i, 30j, 30k, 30m, 30q for the detection signals from the above-mentioned sensors, and a multiplexer 30 that selectively outputs each detection signal to the CPU 30a.
n, and A for converting analog signals to digital signals
A / D converter 30p is also provided. The detection signals are input to the CPU 30a via the input / output port 30f.

Further, the ECU 30 includes a waveform shaping circuit that shapes the waveforms of the detection signals from the rotation angle sensor 26 and the cylinder discrimination sensor 27 described above.
30r is provided, and the above detection signals are input port 30g
It is input to the CPU 30a via.

The ECU 30 also includes the igniter 17 and the fuel injection valve 16 described above.
Drive circuits 30s and 30t for supplying a drive current to the drive circuit. CPU30
The a outputs a control signal to the drive circuits 30s and 30t via the output port 30h.

Further, the ECU 30 is a clock circuit 30u that sends a clock signal that becomes a control timing to the ROM 30b, RAM 30c, etc., including the CPU 30a at predetermined intervals, and a timer circuit 30v that is a hard timer that generates an interrupt signal to the CPU 30a at preset time intervals. Also has.

Next, the processing executed by the ECU 30 will be described with reference to FIGS.
This will be described with reference to each flowchart in the figure.

FIG. 4 shows the main control processing for calculating the fuel injection time, FIG. 5 shows the details of the constant setting processing of the processing shown in FIG.
The figure shows the first interrupt process for air-fuel ratio determination, and Fig. 7 shows the fourth interrupt process.
6 is a flowchart showing details of air-fuel ratio feedback control processing in the processing shown in the drawing.

First, details of the main control process shown in FIG. 4 will be described. This process is repeatedly executed every predetermined time.

After the key switch is turned on by the driver and the ECU 30 starts,
It is determined whether or not this processing is the first one (step 100). If this process is the first one, initial setting is performed (step 102). That is, the initial reset of each of the input / output ports 30f, 30g, 30h described above is performed. Next, the memory of the RAM 30c is cleared, and initial data is set in the registers, timers, flags, etc. set in the RAM 30c (step 10
Four). After completion of each of the processes described above, or when this process is the second or subsequent one, the process proceeds to step 106. Here, the intake air pressure from the intake pipe internal pressure sensor 21 is
A process of reading the intake air temperature from the intake air temperature sensor 22, the rotation angle of the crankshaft from the rotation angle sensor 26, and the water temperature THW from the water temperature sensor 24, respectively, or reading the values stored in the RAM 30c after A / D conversion. Is performed (step 106). Next, the intake air amount Q per unit time is calculated from the intake air pressure and intake temperature read in step 106, and the engine rotation speed Ne per unit time is calculated from the rotation angle. Here, the engine rotation speed Ne is calculated from the reciprocal of the interval of the output signal of the rotation angle sensor 26 stored in the RAM 30c. Then, the engine load Q / Ne is calculated based on the intake air amount Q and the engine rotation speed Ne (step 108). Next, based on the engine load Q / Ne and the engine speed Ne calculated in step 108, the ignition timing is calculated from the ignition timing map stored in the ROM 30b in advance (step 110). The ignition timing may be calculated from the intake air pressure and the rotation speed based on a map.

Next, at step 120, a process of setting various constants which are correction coefficients for air-fuel ratio control is performed. Details of the constant setting process will be described with reference to the flowchart shown in FIG. In step 120a, it is determined whether the water temperature THW is 70 [° C] or higher. When the determination is affirmative, the routine proceeds to step 120b, where the lean delay time TDL and the rich delay time TDR are both set to 16 [msec]. On the other hand, the water temperature THW is 70 in step 120a.
If it is determined that the temperature is less than [° C.], the process proceeds to step 120c, where the lean delay time TDL is set to 20 [msec] and the rich delay time TDR is set to 16 [msec]. After the execution of step 120b or step 120c, the process proceeds to step 130 in FIG. 4 and the air-fuel ratio feedback control process is performed.

Here, details of the air-fuel ratio feedback control processing will be described with reference to both the flowcharts of FIG. 6 and FIG.
FIG. 6 is a flow chart showing a first interrupt process which is executed by interrupting the main control process at predetermined time intervals in relation to the air-fuel ratio feedback control process, and FIG. 7 is the main control process. 6 is a flowchart showing the details of step 130 of FIG.

In Fig. 6, the first interrupt process is the hard timer 30V.
In accordance with the instruction of 4), the above main control processing is interrupted and executed every 4 [msec]. First, the output OX of the oxygen concentration sensor 25 is detected (step 200), and it is determined whether the output is higher than the reference value OS, that is, the air-fuel ratio is in the rich state (step 201). If this condition is met,
Go to step 202. Here, the lean flag FL indicating the lean state is reset (step 202). Next, it is determined whether or not the lean flag FR set when the control for shifting the air-fuel ratio to the lean state is being performed (step 204). If this condition is met, that is, if the control to shift the air-fuel ratio to the lean state is not executed, the routine proceeds to step 206, where the value of the delay time timer Cd is incremented by 4 [msec] and this processing is executed. finish. On the other hand, when the condition of step 204 is not satisfied, that is, when the control for shifting the air-fuel ratio to the lean state is being executed, the process proceeds to step 212, the value of the delay time timer Cd is cleared, and the present process ends. .

On the other hand, when the condition of step 201 is not satisfied, that is, when the lean state is entered, the process proceeds to step 208,
Set the lean flag FL above. Next, it is judged whether or not the lean flag FR is reset (step 210). When this condition is met, that is, when the control for shifting the air-fuel ratio to the lean state is not executed, the routine proceeds to step 212, where the value of the delay time timer Cd is cleared, and this processing ends. On the other hand, when the condition of step 210 is not satisfied, that is, when the control for shifting the air-fuel ratio to the lean state is being executed, step 20
The process proceeds to 6 and the value of the delay time timer Cd is incremented by 4 [msec], and this processing is terminated. This process is executed in order to give a delay time to the air-fuel ratio control process described later when the oxygen concentration sensor output signal changes between the lean state and the rich state. Therefore, in the air-fuel ratio feedback control process described later, the oxygen concentration sensor 25
Even if the air-fuel ratio detected by the engine changes from the lean state to the rich state or vice versa, the fuel supply amount is not immediately reduced or increased, and the delay time timer
When the value of Cd becomes equal to or more than the lean delay time TDL or the rich delay time TDR, the above fuel supply amount control is started for the first time. The first interrupt process is repeatedly executed every 4 [msec] and is executed by interrupting the main control process.

Next, details of the air-fuel ratio feedback control process will be described with reference to FIG. First, the state of the lean flag FL is checked to determine whether the air-fuel ratio is lean (step 130a). If this condition is met,
That is, when the air-fuel ratio detected by the oxygen concentration sensor 25 is in the lean state, the routine proceeds to step 130b. here,
It is determined whether the lean flag FR is reset. If this condition is met, that is, if the process of shifting the air-fuel ratio to the lean state has not been performed, the routine proceeds to step 130c. Here, the air-fuel ratio feedback correction coefficient FAF is increased by the integration constant KI1, and this processing ends. On the other hand, if the condition of step 130b is not met,
That is, when the process of shifting the air-fuel ratio to the lean state is being performed, the routine proceeds to step 130d. Here, it is determined whether or not the value of the delay time timer Cd described above is equal to or longer than the lean delay time TDL. If this condition is met,
That is, the process of shifting the air-fuel ratio to the lean state is performed, and the lean state is continuously detected for the lean delay time TDL or more set in the constant setting process after the oxygen concentration sensor 25 detects the lean state, and the lean state is detected. If yes, step 13
Proceed to 0e to reset the lean flag FR. Next, the routine proceeds to step 130f, where the air-fuel ratio feedback correction coefficient FAF is increased by the skip constant RS1 and this processing is ended. Here, the skip constant is a process for greatly increasing the air-fuel ratio feedback correction coefficient FAF when it is determined that the air-fuel ratio has changed from the rich state to the lean state with respect to the target value, that is, a skip constant for performing the skip process. is there. Further, the integration constant KI1 is an integration constant for integration processing for increasing the air-fuel ratio feedback correction coefficient FAF for removal. On the other hand, if the condition of step 130d is not satisfied, the routine proceeds to step 130h, where the process of gradually making the air-fuel ratio lean is continued.

If the condition of step 130a is not satisfied, that is, if the air-fuel ratio detected by the oxygen concentration sensor 25 is in the rich state, the process proceeds to step 130g. Here, it is determined whether or not the lean flag FR is set. If this condition is met, that is, if the process of shifting the air-fuel ratio to the lean state is being performed, the routine proceeds to step 130h. Here, the air-fuel ratio feedback correction coefficient FAF is reduced by the integration constant KI2, and this processing ends.
On the other hand, when the condition of step 130g is not satisfied, that is, when the process of shifting the air-fuel ratio to the lean state is not performed, the process proceeds to step 130i. Here, it is determined whether or not the value of the delay time timer Cd described above is equal to or greater than the rich delay time TDR. If this condition is satisfied, that is, the process of shifting the air-fuel ratio to the lean state is not performed, and the oxygen concentration sensor 25 detects the rich state and continues for the rich delay time TDR or more determined by the constant setting process. If a rich condition is detected, step 130j
Proceed to and set the lean flag FR. Then, the routine proceeds to step 130k, where the air-fuel ratio feedback correction coefficient FAF is decreased by the skip constant RS2. Where the skip constant R
The purpose of S2 and the integration constant KI2 is the same as that of the skip constant RS1 and the integration constant KI1 described above. On the other hand, if the condition of step 130i is not satisfied, the routine proceeds to step 130c, where the process of gradually increasing the air-fuel ratio is continuously performed, and the air-fuel ratio feedback control process is ended.

Returning to FIG. 4 again, the control proceeds to step 140. In step 140, a process of calculating the actual fuel injection time τ as in the following equation (1) is performed.

τ = TP × FAF × K (1) However, TP ... Basic fuel injection time determined based on load Q / Ne (may be determined based on intake air pressure rotation speed) FAF ... Air-fuel ratio feedback correction Coefficient K ... Correction constant determined by intake air temperature, water temperature, etc. After that, the process returns to "RETURN" and this main control process ends.
After that, the main control process is repeatedly executed at predetermined time intervals.

Next, the state of the above control will be described based on the timing chart shown in FIG. When the water temperature THW is 70 [° C.] or higher, both the lean delay time TDL and the rich delay time TDR are set to 16 [msec] by the constant establishment process (step 120). Therefore, from the time t1 when the air-fuel ratio A / F changes from the rich state to the lean state, the lean delay time 16
At time t2 after [msec] has elapsed, the air-fuel ratio feedback correction coefficient FAF increases as shown by the broken line in the figure. Further, time t5 after the rich delay time 16 [msec] has elapsed from time t4 when the air-fuel ratio A / F changes from the lean state to the rich state.
At, the air-fuel ratio feedback correction coefficient FAF decreases as shown by the broken line in FIG. Therefore, the control center is near the stoichiometric air-fuel ratio at which the excess air ratio λ has a value of 1.

On the other hand, when the water temperature is lower than 70 [° C], the lean delay time TDL is extended to 20 [msec] and the rich delay time TDR is left unchanged at 16 [msec] by the constant setting process (step 120). Therefore, even if the air-fuel ratio A / F changes from the rich state to the lean state at time t1, the leaning process is continued until time t3 after the lean delay time 20 [msec] elapses, and the air-fuel ratio feedback correction coefficient FAF becomes Decrease. Therefore, as shown by the alternate long and short dash line in FIG.
The value becomes the above value, and slightly shifts to the lean side from the stoichiometric air-fuel ratio.

In the present embodiment, the engine 1 corresponds to the internal combustion engine M1, and the intake pipe pressure sensor 21, the rotation angle sensor 26, the ECU 30, and the processing executed by the ECU 30 (step 106) are used as the operating state detecting means M2 by the ECM 30. The processing (steps 108, 130, 140) executed by the ECU 30 functions as the control means M3. Further, the water temperature sensor 24, the ECU 30, and the ECU
The processing executed by 30 (step 106) functions as the temperature detecting means M4, and the processing executed by the ECM 30 and the ECU 30 (steps 120a, 120c) functions as the balance registering means M5.

As described above, in the first embodiment, the water temperature THW is 70 [° C].
When it is less than, the lean delay time TDL is extended to 20 [msec], and the air-fuel ratio control center is shifted to the lean side from the stoichiometric air-fuel ratio.

Therefore, when the engine 1 is cold, HC and CO emissions are reduced and fuel efficiency is improved.

Next, a second embodiment of the present invention will be described. The difference between the first embodiment and the second embodiment is that, in the constant setting process described in the first embodiment, the skip constant RS2 and the integration constant KI2 in the lean conversion are used instead of the lean delay time TDL. It is to change according to THW. Since the system configuration and other processing are the same as those in the first embodiment, the same parts are denoted by the same reference numerals and the description thereof will be omitted.

Regarding the constant setting process executed in the second embodiment,
A description will be given based on the flowchart shown in FIG. In step 120d, it is determined whether the water temperature THW is 70 [° C] or higher. If an affirmative decision is made, the operation proceeds to step 120e, in which the integration constant K12 in the leaning process is set to the value 3.67 and the skip constant RS2 is set to the value 2.93. On the other hand, if it is determined in step 120d that the water temperature THW is less than 70 [° C], the process proceeds to step 120f, where the integration constant KI2 in the lean process is set to 4.0 and the skip constant is set.
The process of setting RS2 to the value 3.17 is performed. After the execution of step 120e or step 120f, the process proceeds to step 130 of FIG. 4 described above, and the air-fuel ratio feedback control process is performed.

Next, the manner of the above control will be described based on the timing chart shown in FIG. When the water temperature THW is 70 [° C.] or higher, the constant setting process (step 120) sets the integration constant KI2 and the skip constant RS2 at the leaning process to the above-described predetermined values. Therefore, the air-fuel ratio feedback coefficient FAF changes as shown by the broken line in the figure, and the control center is near the stoichiometric air-fuel ratio at which the excess air ratio λ has a value of 1.

On the other hand, when the water temperature is lower than 70 [° C.], the integration constant KI2 and the skip constant RS2 during the leaning process are changed to large values by the constant setting process (step 120). For this reason,
The air-fuel ratio feedback coefficient FAF decreases as shown by the solid line in the figure, and the control center becomes slightly leaner than the theoretical air-fuel ratio, where the excess air ratio λ becomes a value of 1 or more as shown by the chain line in the figure. Transition.

In the second embodiment, the ECU 30 and the processing (steps 120d and 120f) executed by the ECU 30 function as the bookkeeping means M5.

As described above, in the second embodiment, the water temperature THW is 70 [° C].
When it is less than the above, it is configured to increase the integration constant KI2 and the skip constant RS2 during the leaning process to shift the air-fuel ratio control center to the lean side from the stoichiometric air-fuel ratio. Therefore, the exhaust characteristic can be improved by executing the air-fuel ratio feedback control process when the engine 1 is cold.

Next, a third embodiment of the present invention will be described. The difference between the first embodiment and the third embodiment is that in the constant setting process described in the first embodiment, the lean state or the rich state is determined based on the oxygen concentration sensor output instead of the lean delay time TDL. It is to change the reference value OS according to the water temperature THW. Since the system configuration and other processing are the same as those in the first embodiment, the same parts are denoted by the same reference numerals and the description thereof will be omitted.

Regarding the constant setting process executed in the third embodiment,
Description will be made based on the flowchart shown in FIG. In step 120g, it is determined whether the water temperature THW is 70 [° C] or higher. If the affirmative judgment is made, the routine proceeds to step 120h, where the reference value OS for judging the oxygen concentration sensor output is set to 0.45.
The process of setting to [V] is performed. On the other hand, when it is determined in step 120g that the water temperature THW is less than 70 [° C], the process proceeds to step 120i, and the reference value OS is 0.3 [V].
The process of setting to is performed. After the above step 120h or step 120i is executed, the processing is the step shown in FIG.
At 130, air-fuel ratio feedback control processing is performed.

With the above configuration, when the water temperature THW is less than 70 [° C], the reference value OS is set to a low value of 0.3 [V], so it is determined that the lean side is already on the lean side of the stoichiometric air-fuel ratio, and lean The conversion process is started. Therefore, the control center of the air-fuel ratio shifts slightly to the lean side of the stoichiometric air-fuel ratio.

In the third embodiment, the ECU 30 and the processing (steps 120g, 120i) executed by the ECU 30 function as the bookkeeping means M5.

As described above, in the third embodiment, the water temperature THW is 70 [° C].
When it is less than the above, the reference value OS used for the determination of the oxygen concentration sensor output is lowered to shift the air-fuel ratio control center to the lean side from the stoichiometric air-fuel ratio. Therefore, the same effects as those of the first and second embodiments described above can be obtained.

Lean delay time TDL, integration constant KI2, skip constant R
S2 and the reference value OS are, for example, the intake air amount Q and the rotation speed Ne.
The effect of the present invention can be obtained even if the value is changed according to the operating state such as the above or the engine temperature.

Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and it goes without saying that the present invention can be implemented in various modes without departing from the scope of the present invention. .

As described above in detail, the air-fuel ratio control device for an internal combustion engine of the present invention is such that, when the temperature of the internal combustion engine detected by the temperature detecting means is equal to or lower than the predetermined temperature, the target air-fuel ratio is leaner than the stoichiometric air-fuel ratio. Is configured to. For this reason, the HC and CO emissions in the cold state where the combustion temperature is low are reduced, and the excellent effect that the exhaust characteristics can be improved is exhibited.

In addition, since the air-fuel ratio is feedback controlled to the lean side of the stoichiometric air-fuel ratio in the cold state, the fuel efficiency is improved, and since the air-fuel ratio feedback control is performed, the set air-fuel ratio slightly leaner than the stoichiometric air-fuel ratio is set. Since there is no departure from the above, there is an advantage that the idle operating state such as the idle rotation speed is also stabilized.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram conceptually illustrating the present invention, and FIG.
FIG. 4 is a system configuration diagram of the first embodiment of the present invention, FIG. 3 is a block diagram for explaining the configuration of the electronic control device thereof, and FIGS. 4 to 7 are flowcharts thereof.
FIG. 9 is a timing chart showing changes in various amounts, FIG. 9 is a flow chart of the second embodiment of the present invention, FIG. 10 is the same timing chart, and FIG. 11 is a flow chart of the third embodiment of the present invention. M1 ...... Internal combustion engine M2 ...... Operating state detection means M3 ...... Control means M4 ...... Temperature detection means M5 ...... Randomization means 1 ...... Engine 21 ...... Intake pipe pressure sensor 24 ...... Water temperature sensor 25 ...... Oxygen Concentration sensor 26 …… Rotation angle sensor 30 …… Electronic control unit (ECU) 30a …… CPU

Claims (4)

[Claims] 1. An operating state detecting means for detecting an operating state of an internal combustion engine, and a fuel amount determined based on the detected operating state is supplied to the internal combustion engine, and the air-fuel ratio of the internal combustion engine is a target air-fuel ratio. In an air-fuel ratio control device for an internal combustion engine, the control means for feedback control so that the temperature of the internal combustion engine is detected, and when the detected temperature is equal to or lower than a predetermined temperature, An air-fuel ratio control device for an internal combustion engine, comprising: a leaning unit that sets the target air-fuel ratio to a leaner side than a theoretical air-fuel ratio. 2. When the detected temperature is equal to or lower than a predetermined temperature, the leaning means changes the air-fuel ratio to the rich side when the output signal of the oxygen sensor changes between the lean state and the rich state. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the lean delay time when starting the control to the above is extended. 3. The skip constant for greatly reducing the correction coefficient of the fuel amount used when controlling the air-fuel ratio to the target air-fuel ratio when the detected temperature is equal to or lower than a predetermined temperature. And an integration constant for gradually changing the correction coefficient, wherein a skip constant and / or an integration constant for changing the air-fuel ratio to the lean side are increased, and the empty space of the internal combustion engine according to claim 1. Fuel ratio control device. 4. When the detected temperature is equal to or lower than a predetermined temperature, the leaning means sets a low reference value to be compared with an output of an oxygen sensor for determining an air-fuel ratio in a rich state or a lean state. Claim 1 which is characterized by the above-mentioned.
An air-fuel ratio control device for an internal combustion engine according to the above item.