JPS6328214B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control method for an internal combustion engine that performs air-fuel ratio feedback control.

Generally, according to air-fuel ratio feedback control,
Operating state parameters of the internal combustion engine, such as the intake air amount and rotational speed of the engine, are detected, and the basic fuel amount of the fuel injection valve is calculated according to these detected values.On the other hand, specific components in the engine exhaust gas, such as oxygen components, are calculated. The air-fuel ratio correction amount is calculated according to the detection signal of the concentration sensor (hereinafter referred to as O ₂ sensor) that detects the concentration of The amount of fuel actually supplied to the engine is adjusted according to the amount of fuel that is supplied to the engine. By repeating the above steps, the air-fuel ratio correction amount is converged to a predetermined range, or in other words, the air-fuel ratio is converged to near the stoichiometric air-fuel ratio. Therefore, a three-way catalytic device installed in the engine's exhaust system is used to reduce CO, HC, and CO contained in the exhaust gas.
The catalyst device's purification ability, which can simultaneously purify three harmful components called NO _x , can be maintained at a high level.

However, in an internal combustion engine that performs the air-fuel ratio feedback control described above, if the slot valve is suddenly closed in a rotation range where fuel is not cut or during racing under conditions where fuel is not cut,
The negative pressure in the intake pipe increases rapidly, and as a result, fuel adhering to the intake manifold rapidly evaporates and is sucked into the combustion chamber of the engine. Therefore, the air-fuel ratio becomes rich, and the air-fuel ratio is largely controlled to the lean side. Therefore, there is a problem in that the rotational speed of the engine falls below the idle rotational speed and it takes a long time to return to the idle rotational speed, resulting in the possibility of rough idling and engine stalling.

In view of the problems with the conventional methods described above, an object of the present invention is to reduce the air-fuel ratio when detecting a sudden change in the engine speed change rate (decrease rate) due to the sudden closing of the throttle valve during racing. By setting a lower limit on the lean side feedback, the engine rotational speed can be quickly returned to the idle rotational speed, and rough idle and engine stall can be prevented from occurring.

According to the present invention, in order to achieve the above object,
A basic fuel amount and an air-fuel ratio correction amount are calculated according to the operating state parameters of the internal combustion engine, the basic fuel amount is corrected according to the air-fuel ratio correction amount, and the engine is actually supplied to the engine according to the corrected fuel amount. In an air-fuel ratio control method for an internal combustion engine that controls the amount of fuel supplied, the air-fuel ratio is determined to be rich based on the concentration of a specific component in the exhaust gas of the engine, and the rotational speed reduction rate of the engine is set to a constant value. In this case, there is provided an air-fuel ratio control method for an internal combustion engine, characterized in that a predetermined limit is imposed on the variation of the air-fuel ratio correction amount.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a characteristic diagram showing air-fuel ratio control characteristics of an internal combustion engine. In FIG. 1, area indicates a feedback area, and area indicates a non-feedback area. That is, the feedback area,
In the , the air-fuel ratio is controlled based on the detection signal of the O _{2 sensor that detects the oxygen concentration in the exhaust gas of the engine, and in the non-feedback region, the air-fuel ratio is controlled based on the detection signal of the O 2} sensor that detects the oxygen concentration in the engine exhaust gas. Thus, the air-fuel ratio is controlled according to predetermined operating state parameters.

When racing, i.e. rotational speed N ₁
When the throttle valve is suddenly closed after rapidly increasing the intake manifold, the adhering fuel in the intake manifold rapidly evaporates, and the air-fuel ratio A/F ₁ (arrow a) becomes richer. At this time, the air-fuel ratio correction amount VF ₁ (arrows b, c) increases once and then decreases.
The air-fuel ratio A/F ₁ (arrow d) is controlled to the lean side. As a result, in the feedback region, even if the rotational speed N ₁ approaches the idle rotational speed N _i , the amount of drop is large (arrow e), and the air-fuel ratio correction amount VF ₁ (arrow f) is small, so the air-fuel ratio Since AF ₁ is on the lean side and the amount of exhaust gas is small, the speed of feedback control is low, and until the original air-fuel ratio is restored, that is, until the rotation speed N ₁ returns to the idle rotation speed N _i ,
It may take several seconds to several tens of seconds. Therefore, during the period indicated by arrow e, rough idling and engine stall may occur.

According to the present invention, racing is detected by determining the change ΔT in the engine rotation period, and when racing is detected (arrow g), a lower limit X is set for the air-fuel ratio correction amount. As a result, the air-fuel ratio correction amount A/
F ₂ is limited, and the air-fuel ratio A/F ₂ is controlled to be richer than the above-mentioned A/F ₁ , so that the rotational speed
N ₂ quickly returns to the idle rotational speed N _i , and the amount of drop in rotational speed N ₂ becomes smaller. As a result, rough idle and engine stall can be prevented from occurring.

FIG. 2 is a schematic diagram of an apparatus for executing an air-fuel ratio control method for an internal combustion engine as an embodiment of the present invention. In FIG. 2, an air flow meter 2 is provided in the intake passage of the engine body 1. The air flow meter 2 directly measures the amount of intake air, has a built-in potentiometer, and generates an analog voltage electrical signal proportional to the amount of intake air. Further, a throttle sensor 4 is provided on the shaft of a throttle valve 3 provided in an intake passage of the engine body 1 for detecting that the throttle valve 3 is in a fully closed state.

The distributor 5 of the engine is provided with two rotation angle sensors 6 and 7 that generate angular position signals each time the shaft rotates, for example, by 360 degrees or 30 degrees in terms of a crankshaft. The angular position signals of the rotation angle sensors 6 and 7 act as reference timings for fuel injection timing and ignition timing, and as interrupt request signals for fuel injection calculation and ignition timing calculation.

Further, in the intake passage of the engine, a fuel injection valve 8 is provided for each cylinder for supplying pressurized fuel from a fuel supply system to an intake port portion.

An O ₂ sensor 9 is provided in the exhaust passage of the engine and generates an output depending on the oxygen concentration in the exhaust gas. This O ₂ sensor 9 generates a binary output depending on whether the air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio. Further, in the exhaust passage downstream of the O ₂ sensor 9, a three-way catalytic converter 11 is provided that can simultaneously purify CO, HC, and NO _x components, which are three harmful components in the exhaust gas.

The control circuit 10 digitally processes signals from the air flow meter 2, rotation angle sensors 6, 7, throttle sensor 4, and _O2 sensor 9 to control fuel injection time and the like. Control circuit 1
As the 0, for example, a microcomputer type one can be used.

FIG. 3 is a detailed block circuit diagram of control circuit 10 of FIG. 2. In FIG. 4, the output analog signal of air flow meter 2 is sent to multiplexer 10.
1 to the A/D converter 102. That is, the A/D converter 102
Multiplexer 101 selectively controlled by 7
The output signal of the air flow meter 2 sent through the clock generator circuit 108 is
A/D conversion is performed using CLK, and an interrupt signal is sent to the CPU 107 after the A/D conversion is completed. As a result, in the interrupt routine, airflow meter 2
The latest data Q will be stored in a predetermined area of the RAM 109.

Each output digital signal of the rotation angle sensors 6, 7 is supplied to a timing generation circuit 103 for generating an interrupt signal and a reference timing signal. Further, the output digital signal of the rotation angle sensor 7 is supplied to the input port 105 via the rotation speed forming circuit 104. Rotational speed forming circuit 104
is a gate that is controlled to open and close at every 30° crank angle.
and a clock generation circuit 10 passing through the gate.
It consists of a counter that counts the number of pulses of the clock signal CLK of 8, thus forming a binary signal that is inversely proportional to the rotational speed of the engine. This rotational speed data N is stored by the CPU 107 into a predetermined area of the RAM 108 via the input port 105.

The output signal of the O ₂ sensor 9 is supplied to an air-fuel ratio signal forming circuit 106 . This air-fuel ratio signal forming circuit 1
06 is equipped with a comparator that compares the output voltage of the O ₂ sensor 9 with a reference voltage, and a latch circuit that temporarily stores the output of this comparator, so that the air-fuel ratio of the engine is compared to the stoichiometric air-fuel ratio. A binary air-fuel ratio signal of "1" or "0" is generated depending on whether the side is rich or lean.

The ROM 110 stores programs such as a main routine, a fuel injection time calculation routine, and an ignition timing calculation routine, as well as various data necessary for these processes.
Constants etc. are stored in advance.

The CPU 107 uses RAM in the fuel injection routine.
The fuel injection time stored in 109 is read out and sent to drive circuit 112 via output port 111. As a result, the drive circuit 112 energizes the fuel injection valve 8 for the fuel injection time.

The operation of the control circuit 10 shown in FIG. 3 will be explained with reference to the flowchart shown in FIG.

In FIG. 4, the operation of the control circuit 10 starts at step 401, but the CPU 107 uses the RAM 10 in a fuel injection time calculation routine (not shown).
9, the intake air amount data Q of the air flow meter 2 and the rotation speed data N of the rotation angle sensor 7 are read out, and interpolation calculations are performed using the map stored in the ROM 110 to determine the basic fuel injection time (pulse width). τ _B is calculated and stored in a predetermined area of the RAM 109.

In step 402, the CPU 107 determines whether the current state of the engine satisfies the air-fuel ratio feedback condition based on the predetermined operating state parameters of the engine that have been taken in, and when the feedback condition is satisfied, the process proceeds to step 403. , on the other hand,
If the feedback conditions are not met, proceed to step 409.

In step 403, the CPU 107 takes in the air-fuel ratio signal from the air-fuel ratio signal forming circuit 106 via the input port 105, and determines whether the current air-fuel ratio of the engine is rich or lean. As a result, if it is rich, the process advances to step 404. On the other hand, if it is lean, the process proceeds to step 406, where a constant value Δ is added to the air-fuel ratio correction amount VF, that is, after calculating VF←VF+Δ, the process proceeds to step 414.

In step 404, the CPU 107
109, the rate of decrease in the rotation speed N, that is, the rotation period difference ΔT is read out and compared with a constant value t ₀ . As a result,
If ΔT<t ₀ , it is assumed that racing is not being performed, and the process proceeds to step 405, where the air-fuel ratio correction amount VF is
After subtracting a constant value Δ, that is, VF←VF−
After calculating Δ, the process advances to step 414. On the other hand,
If ΔT≧ _t0 , it is assumed that racing is being performed, and the process proceeds to steps 407 and 408 to set the lower limit X of the air-fuel ratio correction amount VF.

Note that in steps 405 and 406, the air-fuel ratio correction amount VF by feedback control is obtained by integrating the air-fuel ratio signal with respect to time. Further, the constant value t ₀ in step 404 is the magnitude of the periodic change empirically determined from the engine rotational speed and rate of decline during racing. Further, the rotation period difference ΔT in step 404 is calculated using a timing signal generated by the timing generation circuit 103 based on the angular position signal of the rotation angle sensor 6 in an interrupt routine (not shown), and the calculation result is stored in a predetermined value in the RAM 109. Assume that it is stored in the area.

In step 407, it is determined whether the air-fuel ratio correction amount VF is larger than the lower limit set value X or not. VF≧
If it is X, the process proceeds to step 414; on the other hand, if VF<X, in step 408 VF is set to the lower limit X, and then the process proceeds to step 414.

On the other hand, in step 409, the air-fuel ratio correction amount is set to a predetermined value according to the operating state parameters of the engine, and thereafter, steps 403, 404, 407, and
Proceed to steps 410, 411, 412, and 413 similar to 408.
That is, when the air-fuel ratio is rich and the rotation period difference ΔT is greater than or equal to the constant value t ₀ , the lower limit value X is set to the air-fuel ratio correction amount VF.

In step 414, the CPU 107 calculates the actual fuel injection time τ as follows: τ=τ _B・VF・(1+K)+τ _V Where, τ _B : Basic fuel injection time VF : Air-fuel ratio correction amount K : Transient correction factor τ _V : Calculate using the invalid injection time, store it in a predetermined area of the RAM 109, and proceed to step 415.

The above-mentioned actual fuel injection time τ is read by the CPU 107 in a fuel injection interrupt routine (not shown) and is supplied to the drive circuit 112 via the output port 111, and the fuel injection valve 8 is activated according to the injection time τ. will be energized.

In the above embodiment, the basic fuel injection time τ _B and the actual fuel injection time τ are calculated digitally within the control circuit 10, but the times τ _B and τ are calculated based on the basic fuel injection time τ, respectively. pulse forming circuit,
It can also be performed using an analog circuit such as a multiplication correction circuit. In this case, the above-mentioned air-fuel ratio correction amount VF acts as an air-fuel ratio control voltage of the multiplication correction circuit.

As explained above, according to the present invention, when racing is performed, since a limit is set on the lean side feedback of the air-fuel ratio, the amount by which the engine rotational speed drops from the idle rotational speed at the time of recovery is correspondingly reduced. and its time can be reduced, and therefore rough idling and engine stall can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing air-fuel ratio control characteristics of an internal combustion engine, FIG. 2 is a schematic diagram of an apparatus for carrying out an air-fuel ratio control method for an internal combustion engine as an embodiment of the present invention, and FIG. FIG. 2 is a detailed block circuit diagram of the control circuit 10, and FIG. 4 is a flowchart for explaining the operation of the control circuit 10 of FIG. 1: Engine body, 2: Air flow meter, 3: Throttle valve, 4: Throttle sensor, 5: Distributor, 6, 7: Rotation angle sensor, 8:
Fuel injection valve, 9: O ₂ sensor, 10: control circuit.

Claims (1)

[Claims] 1 Calculate the basic fuel amount and air-fuel ratio correction amount according to the operating state parameters of the internal combustion engine, correct the basic fuel amount according to the air-fuel ratio correction amount, and actually adjust the engine according to the corrected fuel amount. In the air-fuel ratio control method for an internal combustion engine, the air-fuel ratio is determined to be rich based on the concentration of a specific component in the exhaust gas of the engine, and the rate of decrease in rotational speed of the engine is constant. When the value is greater than or equal to
An air-fuel ratio control method for an internal combustion engine, characterized in that a predetermined limit is imposed on a variation in the air-fuel ratio correction amount.