JPS61247837A - Air-fuel ratio controller for internal-combustion engine - Google Patents

Abstract

PURPOSE:To improve the anti engine stall performance by suspending the air- fuel ratio feedback control when the increase of the load is detected in idle operation and carrying out the switching to the excessively dense side in comparison with the theoretical air-fuel ratio, thus suppressing the variation of the number of revolution. CONSTITUTION:The idle operation state of an internal-combustion engine 1 is detected by an idle switch built in a throttle sensor 11. When the increase of the load is judged by detecting the operation of an air-conditioner operating switch 28, variation of power voltage of a battery 22, etc., rich control is performed in an electronic control circuit 20. In other words, feedback correction coefficient is set to 1.00 in order to suspend feedback control, and the rich correction coefficient is calculated by using the learned value of the correction coefficient calculated in the feedback control in order to make rich the air-fuel ratio in comparison with the theoretical air-fuel ratio. The valve opening time calculated in the above is given into a fuel injection valve 6 for a prescribed time, and excessively dense fuel injection is carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device for an internal combustion engine, and particularly to control of the air-fuel ratio when an increase in load on the internal combustion engine is observed during idling.

[Prior Art] Conventionally, when operating an internal combustion engine, air-fuel ratio control is performed to strictly adjust the air-fuel ratio in order to improve fuel efficiency and emissions. This is no exception even when the internal combustion engine is running at idle; this allows the internal combustion engine to always maintain its best operating condition.

On the other hand, with the aim of further improving the fuel efficiency of internal combustion engines, improvements are being made such as reducing the number of revolutions during idling, that is, the number of idle revolutions, to the lowest possible speed, and reducing the weight of the internal combustion engine itself. It is being

As a result of the fusion of the various technologies mentioned above, internal combustion engines can be operated with good emissions and fuel efficiency.

[Problems to be solved by the invention] However, the above-mentioned conventional techniques are not sufficient,
It had the following problems.

That is, when the internal combustion engine is idling, its rotational speed is kept low, and since the engine weight is light, it does not have sufficient inertia, and is extremely susceptible to stalling.

Moreover, as shown in the relationship between the output (PS) of the internal combustion engine and the air-fuel ratio in Figure 2, under air-fuel ratio control, 1 is the stoichiometric air-fuel ratio selected from the conditions of fuel economy etc. Since the fuel engine is being operated, its output is also kept below its maximum value.

Therefore, in conventional air-fuel ratio control devices for internal combustion engines, if some load is applied during idling, the torque of the internal combustion engine is not sufficient for the load, resulting in an undershoot in the rotational speed, and as a result, the engine speed increases. There was a possibility that it would even lead to a stall.

The present invention has been made in view of the above-mentioned problems, and is an air-fuel ratio control device for an internal combustion engine, which is capable of suppressing fluctuations in internal combustion engine speed even when an increase in load occurs during idling, and improving engine stall resistance. Its purpose is to provide.

[Means for solving the problems] The means configured by the present invention to solve the above problems are as follows:
As shown in the basic configuration diagram of FIG. 1, in an air-fuel ratio control device for an internal combustion engine that performs feedback control of the air-fuel ratio of the internal combustion engine EG to near the stoichiometric air-fuel ratio at least during idle operation of the internal combustion engine EG, an idle detection means C1 for detecting an idle operating state of the internal combustion engine EG; a load increase detection means C2 for detecting an increase in the load of the internal combustion engine EG; and a load increase detection means C2 for detecting an increase in the load of the internal combustion engine EG; When the rich changing means C3 and the idle detecting means C1 detect idle operation and the load increase detecting means C2 detects an increase in load, the feedback control is stopped and the rich changing means C3 is activated. The gist of the present invention is an air-fuel ratio control device for an internal combustion engine characterized by comprising means C4.

[Operation] The idle detection means C1 in the present invention refers to the internal combustion engine E.
This detects the idling state of the G. It can have any configuration and detects the operating state of the normal idle switch and the operating state of the transmission, such as the state in which the neutral range (hereinafter referred to as N range) or parking range (hereinafter referred to as P range) is operated. This can be realized in various ways, such as by detecting the rotational speed of the internal combustion engine EG.

The load increase detection means C2 detects that the load applied to the internal combustion engine EG has changed to the increase side. The detection result of the load increase detection means C2 is used by the control means C4 under the idle operating state of the internal combustion engine EG, as will be described later. Therefore, it is sufficient to have a function for detecting an increase in load at least during an idle period. Therefore,
By detecting in advance the condition in which the load on the internal combustion engine EG increases when it is idling, it is possible, for example, to detect when the air conditioner switch is turned on, or to detect the start of operation of various electrical components connected to the battery by adjusting the power supply voltage. It is configured to detect a decrease in the rotational speed, which is a phenomenon that occurs in the internal combustion engine EG due to a change in the internal combustion engine EG, or an increase in load, either singly or in combination.

The rich changing means C3 changes the air-fuel ratio of the internal combustion engine EG to a richer side than the stoichiometric air-fuel ratio. As shown in FIG. 2, when the air-fuel ratio is changed to a richer side than the stoichiometric air-fuel ratio, the output torque of the internal combustion engine EG also increases. The rich changing means C3 changes the air-fuel ratio to the rich side in order to cause the internal combustion engine EG to increase this output torque. Therefore, it is preferable to increase the fuel injection amount to such an extent that the air-fuel ratio is preferably near the output air-fuel ratio.

During normal feedback control, the amount of fuel injected into the internal combustion engine EG is kept close to the stoichiometric air-fuel ratio. Therefore, the fuel injection amount at this time is learned, and a change to the rich side is achieved by adding a predetermined amount of increase to the fuel injection amount.

The control means C4 means that during the period when the idle operation is detected by the above-mentioned idle detection means C1,
When the load increase detection means C2 detects that some load has been newly applied to the internal combustion engine EG,
The rich changing means C stops the air-fuel ratio control of the internal combustion engine EG.
Activate 3.

That is, when an increase in load occurs on the internal combustion engine EG during idling operation under air-fuel ratio feedback control, the air-fuel ratio feedback control is stopped and the air-fuel ratio of the internal combustion engine EG is made richer than the stoichiometric air-fuel ratio. be.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The air-fuel ratio control device for an internal combustion engine according to the present invention will be described in detail below by way of examples in order to explain it more specifically.

Embodiment" First, FIG. 3 is a block diagram of an internal combustion engine system equipped with an air-fuel ratio control device according to an embodiment.

1 is the internal combustion engine body, 2 is the piston, 3 is the spark plug, 4
is an exhaust manifold, 5 is an oxygen sensor provided in the exhaust manifold 4 and detects the residual oxygen concentration in the exhaust gas, 6 is a fuel injection valve that injects fuel into the intake air of the internal combustion engine body 1, 7 is an intake manifold, and 8 is an oxygen sensor An intake temperature sensor 9 detects the temperature of intake air sent to the internal combustion engine main body 1; a water temperature sensor 9 detects the temperature TI-IW of internal combustion engine cooling water;
0 is a throttle valve, 11 is a throttle sensor that has a built-in idle switch and detects the idle state and the opening of the throttle valve, 14 is a surge tank that absorbs the pulsation of intake air, and 15 is an air flow meter that detects the amount of intake air. each represents.

16 is an igniter that outputs the high voltage necessary for ignition; 17 is a distributor that is linked to a crankshaft (not shown) and distributes the high voltage generated by the igniter 16 to the spark plugs 3 of each cylinder; and 18 is a distributor 17 A rotation angle sensor that also serves as a rotation speed sensor that outputs 24 pulse signals for one revolution of the distributor 17, that is, two revolutions of the crankshaft, and 19 is a pulse signal that outputs one pulse signal for one revolution of the distributor 17. 20 is an electronic control circuit as a control means, 21 is a key switch, 22 is a battery that supplies power to the electronic control circuit 20 via the key switch 21, 24 is an on-vehicle transmission, 26 28 represents a vehicle speed sensor that detects the vehicle speed from the rotational speed of the output shaft of the transmission 24, and an air conditioner operation switch that operates the air conditioner.

Further, the internal configuration of the electronic control circuit 20 will be explained as follows.
In the figure, 30 is a central processing unit (CPU) that inputs and calculates data output from each sensor according to a control program and performs processing to control the operation of various devices, and 31 stores control programs and initial data. read-only memory (ROM), 3
2 is a random access memory (RAM) in which data input to the electronic control circuit 20 and data necessary for arithmetic control are temporarily read and written; 33 is a random access memory (RAM) in which the real time for control can be read at any time by the CPU 30; CPU
30 is a timer having a register (hereinafter referred to as conveyor A) that generates an interrupt routine; 36 is an input port into which signals from each sensor are input; 38 is an igniter 16 and a fuel injection valve 6 provided in each cylinder. An output port 39 is a common bus that connects each of the above elements to each other. Input port 36 is connected to oxygen sensor 5. Intake temperature sensor 8
．． Water temperature sensor9. Throttle sensor 11゜An analog input section (not shown) that A/D converts and inputs an analog signal from the air flow meter 15, an idle switch (not shown) in the throttle sensor 11, and a rotation angle sensor]8. It consists of a pulse input section (not shown) into which a pulse signal from the cylinder discrimination sensor 19 is input. Furthermore, when the output port 38 receives a command to start fuel injection from the CPU 30, it outputs a control signal to open the fuel injection valve 6, and the fuel control signal is a signal from the output port 38 that instructs the CPU 30 to terminate the fuel injection. will continue to be output until it is received. The command to end the fuel injection is sent from the CPU 30 to the conveyor A inside the timer 33.
It is configured to be given by a conveyor A coincidence interrupt routine (described later) that occurs when the fuel injection end time set by and the real time that the timer 33 continues to count match.

Next, the control executed by the electronic control device 20 of this embodiment will be described in detail.

The flowchart shown in FIG. 4 is the main control routine. This routine is started when the key switch 21 is turned on, and first performs initialization such as clearing the internal register of the CPLJ 30 (step 100), then sets initial values of data used for controlling the internal combustion engine 1, For example, processing is performed such as setting a flag indicating that a fuel cut is in progress to O (step 105). Next, the operating state of the internal combustion engine 1, for example, the air flow meter 152, the rotation angle sensor 18,
Processing is performed to read signals from the water temperature sensor 9, etc. (step 110), and from the various data read in this way, the intake air amount Q and rotational speed N of the internal combustion engine 1, or the load Q/
A process is performed to calculate various quantities that are the basis of control of the N-type internal combustion engine 1 (step 120). Thereafter, the well-known ignition timing control 1ll (step 130) is carried out based on the various quantities determined in step 120, and then the process moves on to calculation of the amount of fuel injected to the internal combustion engine 1. In order to calculate the fuel amount, it is first determined whether the conditions for feedback control of the fuel amount are met (step 140). If the conditions are not met, the fuel amount is controlled by the most suitable control for the operating state of the internal combustion engine 1 at that time. The color is calculated in an open loop. For example, conventionally implemented fuel increase control at the time of starting the internal combustion engine 1, power increase control during high load operation, etc. are examples of this. When it is determined in step 140 that the feedback condition is satisfied, that is, when the internal combustion engine 1
When the internal combustion engine 1 is performing stable operation in a normal steady state, another condition for open loop control is determined in step 160, which is the condition when the engine is idling and the load on the internal combustion engine 1 has suddenly increased. If this condition is not met, normal feedback control is executed in step 170.
), when this open loop control condition is met, rich control in step 180, which will be described later, is executed. After the optimal control for the operating state of the internal combustion engine 1 is selected in this way and the amount of fuel to be injected and supplied is calculated, step 190
The fuel injection control is executed to actually supply fuel to the internal combustion engine 1. After this process, the process returns to step 110 and the above process is repeated.

In the processing of the main routine described above, control performed when it is determined that the feedback condition is satisfied in step 140, which is a feature of this embodiment, will be described.

First, the details of the air-fuel ratio feedback control process will be explained in the fifth section.
This will be explained based on both the flowcharts in FIG. 6 and the explanatory diagram in FIG. 7. FIG. 5 is a flowchart showing an interrupt process that is executed by interrupting the main routine process at predetermined time intervals in connection with the air-fuel ratio feedback control process, and FIG. 3 is a flowchart showing details of step 170.

In FIG. 5, the water interrupt process is executed by interrupting the main routine process every 4 [m5eC] according to the command from the timer 33. First, it is determined whether the output of the oxygen sensor 5 is at a high level, that is, the air-fuel ratio is in a rich state (200>).

If this condition is met, the process proceeds to step 202.

Here, the lean flag FL indicating the lean state is reset (202). Next, it is determined whether the lean flag FR, which is set when control for shifting the air-fuel ratio to a lean state is being performed, has been reset (204).

If this condition is met, that is, if the control to shift the air-fuel ratio to the return state is not being executed, the process proceeds to step 206, in which the noise prevention delay timer counter Cd is counted up by 1, and the main processing is started. end. On the other hand, if the conditions in step 204 are not met, that is, if control to shift the air-fuel ratio to the leaf state is being executed, the process proceeds to step 212, where the value of the noise prevention delay timer counter Cd is cleared and the main processing is performed. end.

On the other hand, if the condition at step 200 is not met, that is, if the lean state is present, the process proceeds to step 208, where the lean flag FL is set. Next, the lean flag FR is reset, and it is determined whether or not (210>).If this condition is met, that is, if the control to shift the air-fuel ratio to a lean state is not executed, , the process proceeds to step 212, clears the value of the noise prevention delay timer counter Cd, and ends the process.On the other hand, if the condition of step 210 is not met, that is, if the control to shift the air-fuel ratio to a lean state is executed. If so, proceed to step 206, count up the delay timer counter Cd, and end this process.This process is aimed at preventing noise in the oxygen concentration sensor output signal. When the oxygen concentration sensor output signal changes between a rich state and a rich state, this is performed in order to capture only large changes and remove small changes as noise.
In the air-fuel ratio feedback control process described later, the air-fuel ratio detected by the oxygen sensor 5 changes from a lean state to a rich state.
Or even if it changes in the opposite way, the fuel supply amount is not controlled immediately until the value of the delay timer counter CD reaches a predetermined value or more, without immediately reducing or increasing the fuel supply amount. has started. Note that the water interrupt process is thereafter repeated every 4 [m5ec] and executed by interrupting the main routine process.

Next, details of the air-fuel ratio feedback control process (step 170) will be explained based on FIG. 6. First, the state of the lean flag FL is checked to determine whether the air-fuel ratio is in a lean state (170a>. If this condition is met, that is, the air-fuel ratio detected by the oxygen sensor 5 is lean. If so, step 170
Proceed to b.

Here, it is determined whether the lean flag FR has been reset. If this condition is met, that is, if the process of shifting the air-fuel ratio to a lean state is not being performed, the process advances to step 170C. Here, the air-fuel ratio feedback correction coefficient Kt is increased by α1 and the process is ended. On the other hand, if the condition of step 170b is not met, that is, if the process of shifting the air-fuel ratio to a lean state is being performed, the process proceeds to step 170d. Here, the above-mentioned delay timer counter Cd
It is determined whether the value of is 2 or more. If this condition is met, that is, the process of shifting the air-fuel ratio to a lean state is being performed, and the lean state has been detected continuously for 8 [m5ec] or more after the oxygen sensor 5 detected the lean state. It is determined whether or not there is. If this condition is met, the process proceeds to step 170e and the lean flag FR is reset. Then proceed to step 170f,
The air-fuel ratio feedback correction coefficient Kt is increased by 5KP1, and the process ends. Here 5KP1 and the above α
1 is a constant, and 5KP1 is chosen to be much larger than α1. 5KP1, when it is determined that the air-fuel ratio has shifted from a rich state to a lean state with respect to its target value,
This is a constant for performing a process of greatly increasing the air-fuel ratio feedback correction coefficient Kt, that is, a skip process. Further, α1 is a constant for the process of gradually increasing the air-fuel ratio feedback correction coefficient Kt. On the other hand, if the conditions in step 170d are not met, step 17
0h, and the process of gradually bringing the air-fuel ratio to a lean state continues.

Further, if the condition of step 170a is not met, that is, if the air-fuel ratio detected by the oxygen sensor 5 is in a rich state, the process proceeds to step 1709. Here, it is determined whether the lean flag FR is set. If this condition is met, that is, if the process of shifting the air-fuel ratio to a lean state is being performed, the process advances to step 170h. Here, the air-fuel ratio feedback correction coefficient Kt is decreased by α2 and the present process is ended.

On the other hand, if the condition of step 170C1 is not met, that is, if the process of shifting the air-fuel ratio to a lean state is not performed, the process proceeds to step 1701. Here, it is determined whether the value of the delay timer counter Cd mentioned above is 20 or more. If this condition applies,
That is, it is determined whether the process of shifting the air-fuel ratio to a lean state has not been performed and the rich state has been detected continuously for 80 [m5ec] or more since the oxygen sensor 5 detected the rich state. Ru. If this condition is met, the process advances to step 170j and the lean flag FR is set. Then, the process proceeds to step □'170k, where the air-fuel ratio feedback correction coefficient Kt is decreased by 5KP2. Here, SKP'2 and the above α2 are constants,
The size relationship and purpose of both are determined by the constant 5KPI and α mentioned above.
This is the same as in case 1. On the other hand, if the condition in step 1701 is not met, the process proceeds to step 170C, and the process of gradually bringing the air-fuel ratio into a rich state is continued.

Further, step 17OΩ is executed following step 170k. Here, a process is performed in which the correction coefficient learning value MKt stored in the previous process is calculated and updated by the method shown in equation (1) in the current process.

MKt= (1/100)X (99xMKt+(Kt
+5KP2/2>) ... (1) However, Kt ... Air-fuel ratio feedback correction coefficient 5KP2 calculated in step 170 ... Skip used in step i70,
In the processing constant step 170Q, the correction coefficient learning value MK is
After updating t, this process ends.

This correction coefficient learning value 1vlkt is used to calculate the fuel injection amount during the open loop control described above.

FIG. 7 is an explanatory diagram of changes in the air-fuel ratio feedback correction coefficient kt calculated in the above process.

As shown in the figure, it is determined whether the combustion state of the internal combustion engine 1 is lean or rich based on the magnitude relationship between the output voltage of the oxygen sensor 5 and the comparison voltage, and the air-fuel ratio feedback correction coefficient kt is determined by the process of the above-described flowchart. It is calculated.

The air-fuel ratio feedback control detailed above is performed not during idling due to the processing in step 160 of the main routine.
It is executed when it is determined that there is no sudden increase in load, and in other cases, rich control (step 180) is executed. The relationship between this rich control and air-fuel ratio feedback control is shown in detail in FIG.

As shown in the figure, feedback control (step 170
) and rich control (step 180) is shown in step 160. In step 160, it is first determined whether the internal combustion engine 1 is in an idle state (step 160a) and whether a load increase is being performed (step 160b). In other words, it detects when the engine is idle and there is an increase in load. Judgment as to whether the vehicle is idling or not is made using normal technology, such as by detecting when the transmission is operated in N or P range, or when the throttle valve is fully open, and the determination of increase in load is made by detecting when the air conditioner is operating. This is done by detecting the operation of the switch 28, fluctuations in the power supply voltage of the battery 22, etc. and,
When it is not idling, the process proceeds to the feedback control step 170 described above, and when it is idling and an increase in load is detected, rich control (step 1) is executed.
80). Furthermore, even if no load increase is detected, it is assumed that a load will be applied to the rotational output of the internal combustion engine 1 for some reason. Therefore, even when there is no load increase, the rotation speed NE of the internal combustion engine 1 is set to the predetermined lower limit value N.
It is detected whether the load has decreased below EL (step 160c), and if NE≦NEL, it is determined that there has been some kind of load increase, and the process proceeds to rich control (step 180). On the other hand, if NE>NEL, then it is determined whether or not flag F, which is operated as described later, is in the reset state (step 160d), and when F=O, feedback control is performed, and when F=1, rich control is performed. I'll proceed with the process. This flag F is operated as described below,
A state of F=1 indicates that a predetermined time has not elapsed since the rich control was started.

In this way, the rich control (step 180) is selected during the idle time and for a predetermined time after some load increase is detected in the process of step 160.

Here, first, in step 180a, it is determined whether or not a timer that measures the execution period of rich control is operating. If not, step 180b is once processed and the timer is activated. Then, when the timer activation is completed or when the timer is in operation, the feedback correction coefficient kt is set to N, OOJ in order to stop the feedback control described above in step 180c, and the air-fuel ratio is made lower than the stoichiometric air-fuel ratio. A rich correction coefficient kR for making it rich is calculated. For example, by using Mkt calculated during the feedback control described above, it is possible to calculate the rich correction coefficient kR that achieves the output air-fuel ratio with extremely high accuracy.

FIG. 9 shows the routine of the timer activated in step 180b. This routine performs interrupt processing at regular intervals after step 180b is processed, and each time the contents of timer T are incremented (step t-1
), and it is determined whether the predetermined time has elapsed (
Step t-2). If T≦Tc and the predetermined time has not yet elapsed, flag F is set in step t-3 and the routine ends; if T>Tc and the predetermined time has elapsed, flag F is reset, and In order to wait for the restart of this routine, the reset of timer T, etc. is completed and this routine is ended.

When the air-fuel ratio control, feedback control, rich control, and open control most suitable for the operating condition of engine 1 of the internal combustion engine are completed through the various controls detailed above, the various correction coefficients determined by these controls are , for example kt
, kR, etc., the amount of fuel actually injected and supplied to the internal combustion engine 1, that is, the opening time of the fuel injection valve 6 is calculated in step 190.

In parallel with the execution of various controls in the main routine in this way, fuel injection is executed based on the optimum opening time of the fuel injection valve 6 calculated in step 190 as follows. Executed in interrupt routine. The flowchart in FIG. 10 (A>) is the interrupt routine,
This is a 30'CA interrupt routine that controls the start of fuel injection. This control routine is started as an interrupt routine by a pulse input from the rotation angle sensor 18 every 30'CA of the crank angle, and first, in step 300, the rotation angle sensor The current crank angle is determined by knowing the value of a counter (not shown) that is repeatedly counted up from 1 to 24 every time a pulse is input from 18.

In the following step 310, it is determined from the crank angle determined in step 300 whether or not the intake stroke of the first cylinder or the sixth cylinder is currently starting.

Since fuel injection is performed twice per revolution of the internal combustion engine 1, the current stroke of the internal combustion engine is the stroke in which fuel injection is performed in synchronization with the rotation of the internal combustion engine, that is, the first or sixth stroke.
This corresponds to determining whether the crank angle is at the start of the cylinder's intake stroke. If the determination at step 310 is rNOJ, it is assumed that there is no need to start fuel injection, and the process proceeds to RTN, and this interrupt routine ends.

If the determination at step 310 is rYEsJ, the process proceeds to step 320, where it is determined whether the flag FCUT=O. The flag FCLIT is a flag indicating whether or not to implement a fuel cut, and its initial value is O, and is set by control of another routine depending on the operating state of the internal combustion engine 1. Now, if the value of the flag FCUT is 1, it is assumed that a fuel cut is being performed, and the process can proceed to RTN and end this interrupt routine. On the other hand, if the flag FCUT=O, the process proceeds from step 320 to step 330, where a command signal is output to the output port 38 to start fuel injection, and the fuel injection valve 6 is opened. In the following step 340, the value added to the real time Tr read from the timer 33 for the opening time of the fuel injection valve 6 determined in step 190 in FIG. Processing to set it to A is performed. After step 340 is completed, the process can be handled as RTN, and this interrupt routine ends.

The conveyor A in the timer 33 continues to compare the set fuel injection end time t1 with the control real time Tr, and when the control real time Tr reaches the fuel injection end time t1, the CPU 30 An interrupt request □ is issued to the conveyor A match interrupt routine. This is the routine shown in the flowchart of FIG. 10(B). In step 345, a signal for ending fuel injection is output to the output port 38, the fuel injection valve 6 is closed, and fuel injection is started. Terminate it. After completing the process in step 345,
It is immediately transferred to RTN and the match interrupt routine to the main conveyor is completed.

According to the air-fuel ratio control device of the present embodiment described in detail above, feedback control of the air-fuel ratio is executed under normal operating conditions, and both fuel efficiency and emissions are maintained in a good state. Furthermore, when the internal combustion engine 1 is under some kind of load during idling operation, the rich control is selected, so that it exhibits good characteristics as shown in the explanatory diagram of FIG. 11.

That is, as shown in the explanatory diagram of FIG. 11, the undershoot of the rotational speed of the internal combustion engine 1 is kept low.

The figure shows the temporal changes in the air-fuel ratio of the internal combustion engine, the air-fuel ratio feedback correction coefficient kt, and the rotational speed NE of the internal combustion engine when a load is suddenly applied at time t during idling operation. The solid line represents the control result by the air-fuel ratio control device of this embodiment, and the dotted line represents the control result by the conventional air-fuel ratio control device, that is, the control result without rich control.

As is clear from the figure, even if the load increases at time t,
Conventionally, the air-fuel ratio was constant (stoichiometric air-fuel ratio) and feedback control was continuously performed for this purpose, but according to the air-fuel ratio control device of this embodiment, the air-fuel ratio is changed to the rich side from time t for a predetermined period ( The feedback correction coefficient kt is fixed to rl and OOJ (see Figures (A) and (8)).Therefore, at that point, the output torque of the internal combustion engine 1 increases rapidly. In order to become a thing,
As shown in the diagram (C), even when the load suddenly increases at time t, the undershoot of the internal combustion engine speed NE can be kept extremely low compared to the conventional case.

As a result, the internal combustion engine can be operated while maintaining even better operating conditions.

In this embodiment, the rich control is executed for a predetermined period (T=Tc), but the rich control may be continued during a period when the rotational speed NE of the internal combustion engine recovers to a predetermined rotational speed. Also, when returning from rich control to normal air-fuel ratio feedback control, instead of changing the air-fuel ratio all at once,
It is also possible to adopt a mode in which control is gradually made to the lean side in a certain number of stages. In this way, sudden changes in the driving state are avoided, resulting in better driving control.

[Effects of the Invention] As described above in detail with reference to the embodiments, the air-fuel ratio control device for an internal combustion engine of the present invention feeds back the air-fuel ratio of the internal combustion engine to near the stoichiometric air-fuel ratio at least during idling operation of the internal combustion engine. An air-fuel ratio control device for an internal combustion engine to be controlled, comprising: idle detection means for detecting an idle operating state of the internal combustion engine; load increase detection means for detecting an increase in load on the internal combustion engine; rich changing means for changing the air-fuel ratio to a richer side; and when the idle detecting means detects idle operation and the load increase detecting means detects an increase in load, the feedback control is stopped and the rich change is made. The present invention is characterized by comprising a control means for operating the changing means.

Therefore, during normal idling, the air-fuel ratio of the internal combustion engine is maintained near the stoichiometric air-fuel ratio, which provides good fuel efficiency and engine efficiency, by feedback control, and when a sudden load is applied, the rich side air-fuel ratio, which produces a large output torque, is immediately maintained. The fuel ratio is changed. As a result, even in internal combustion engines that have adopted the recent trend of reducing the weight of the internal combustion engine itself and lowering the idle speed, even if the load suddenly increases during idle, the undershoot of the engine speed can be kept low. Therefore, the engine stall resistance can be further improved.

[Brief explanation of the drawing]

Fig. 1 is a basic configuration diagram of the present invention, Fig. 2 is an explanatory diagram of the relationship between air-fuel ratio and output torque, Fig. 3 is a block diagram illustrating the schematic configuration of the embodiment, and Fig. 4 is its main control. A flowchart of a main routine, FIG. 5 is a flowchart of the oxygen sensor output processing, FIG. 6 is a detailed flowchart of feedback control in the main routine, FIG. 7 is an explanatory diagram of the feedback control, and FIG. 8 is the main routine. A detailed flowchart of the rich control in FIG. 9 is a flowchart of a timer routine activated by the rich control, and FIG. 10(A). (B) is a flowchart of an interrupt routine for executing fuel injection as determined by air-fuel ratio control;
FIG. 1 shows an explanatory diagram for comparing the effects of the embodiment with the conventional example. 1... Internal combustion engine 6... Fuel injection valve 9... Water temperature sensor 11... Throttle valve 15... Air flow meter 18... Rotation angle sensor 20... Electronic control circuit 24... Speed change Machine 26...Vehicle speed sensor 30...CPLJ

Claims (1)

[Scope of Claims] 1. An air-fuel ratio control device for an internal combustion engine that feedback-controls the air-fuel ratio of the internal combustion engine to near the stoichiometric air-fuel ratio at least during idling operation of the internal combustion engine, comprising: an idling device that detects the idling operating state of the internal combustion engine; a detection means; a load increase detection means for detecting an increase in the load of the internal combustion engine; a rich change means for changing the air-fuel ratio of the internal combustion engine to a richer side than a stoichiometric air-fuel ratio; and the idle detection means detects an increase in the load of the internal combustion engine. an air-fuel ratio control device for an internal combustion engine, comprising: control means for detecting the current time and for stopping the feedback control and activating the rich change means when the load increase detection means detects an increase in load; . 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the control means operates the rich changing means for a predetermined period of time.