JPH0658079B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly, to an air-fuel ratio control device for an internal combustion engine, which controls a transient air-fuel ratio to a target air-fuel ratio by learning control. The present invention relates to a fuel ratio control device.

[Prior Art] Conventionally, an air-fuel ratio feedback back correction coefficient FAF for controlling the air-fuel ratio to a stoichiometric air-fuel ratio is calculated based on the output of an O ₂ sensor that detects the air-fuel ratio from the residual oxygen concentration in exhaust gas, and the basic fuel The fuel injection amount is determined by multiplying the fuel injection amount TP and the air-fuel ratio feedback back correction coefficient FAF, and the amount of fuel corresponding to this fuel injection amount is injected to perform control so that the air-fuel ratio converges to the stoichiometric air-fuel ratio. Has been. O above
₂ sensor output inverts the boundary of the stoichiometric air-fuel ratio are determined so as to integral action between the fuel injection valve until the air-fuel ratio fed back correction coefficient FAF is then inverted O ₂ sensor output is inverted. Further, there is a response delay before a change in the air-fuel ratio of the intake system appears in the exhaust system. Therefore, the above-mentioned motion time period is set to be somewhat long in order to prevent hunting and the like. Therefore, the air-fuel ratio controlled by the air-fuel ratio control device described above gradually repeats rich and lean with the theoretical air-fuel ratio as the center.

However, if the valve clearance changes due to aging and the characteristics change due to deposits depositing on the injection port of the fuel injection valve, the air-fuel ratio cannot be controlled to the stoichiometric air-fuel ratio. Further, if an alcohol-mixed fuel or a fuel having different distillation characteristics is used, the air-fuel ratio cannot be controlled to the stoichiometric air-fuel ratio not only in the steady state but also in the transient state.

Therefore, as shown in Japanese Patent Laid-Open No. 60-27746, the average value F of the air-fuel ratio feedback back correction coefficient FAF is set.
A deviation e between AF ₀₁ and the peak value of the air-fuel ratio feedback back correction coefficient FAF is calculated, and the air-fuel ratio during acceleration is learned and controlled by changing the air-fuel ratio feedback back correction coefficient FAF according to the magnitude of this deviation. (Second
Figure).

[Problems to be Solved by the Invention] However, in the conventional air-fuel ratio learning control, learning control is performed by calculating the deviation between the average value of the air-fuel ratio feedback back correction coefficient FAF and the peak value of the air-fuel ratio feedback back correction coefficient FAF. However, as described above, the integration operation time is long, that is, the air-fuel ratio feedback back correction coefficient FAF
Since the inclination between the peaks of the air-fuel ratio is gentle, the deviation does not increase as shown in FIG. 2 even if spy clean occurs during acceleration. Therefore, the air-fuel ratio feedback correction coefficient F
There is a problem that the AF is not learned and it is impossible to prevent the variation of the air-fuel ratio due to the occurrence of spy clean.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine, which performs learning even when spy clean occurs to prevent the air-fuel ratio from varying. And

[Means for Solving Problems] In order to achieve the above object, the present invention calculates an air-fuel ratio feedback correction coefficient for controlling the air-fuel ratio to a target air-fuel ratio based on a signal proportional to the engine air-fuel ratio. At the same time, the fuel injection amount is calculated based on the air-fuel ratio feedback correction coefficient and the increase coefficient for increasing the fuel injection amount during acceleration, and the air-fuel ratio is injected by injecting the fuel in an amount corresponding to the calculated fuel injection amount. In the air-fuel ratio control device for an internal combustion engine for controlling, the deviation calculating means for calculating the deviation between the engine air-fuel ratio and the target air-fuel ratio, and the increase so that the deviation becomes a value within a predetermined range when accelerating. A coefficient changing means for changing the coefficient is provided.

[Operation] According to the present invention, the air-fuel ratio feedback correction coefficient for controlling the air-fuel ratio to the target air-fuel ratio is calculated based on the signal proportional to the engine air-fuel ratio, and the deviation calculation means is a signal proportional to the engine air-fuel ratio. The deviation between the engine air-fuel ratio, which is determined from, and the target air-fuel ratio is calculated. Then, the coefficient changing means changes the increase coefficient so that the deviation becomes a value within a predetermined range during acceleration. For example, when the deviation obtained by subtracting the target air-fuel ratio from the engine air-fuel ratio is not less than the upper limit of the above-mentioned predetermined range, the increase coefficient is increased by a predetermined value. As a result, the fuel injection amount is greatly increased in accordance with the increased increase coefficient at the time of acceleration, the air-fuel ratio feedback correction coefficient is decreased, and the deviation is set within the predetermined range. On the contrary, when the deviation is less than or equal to the lower limit of the predetermined range, the increase coefficient is decreased by a predetermined value. As a result, the fuel injection amount is increased in accordance with the increased amount coefficient that is reduced during acceleration, the air-fuel ratio feedback correction coefficient is increased, and the deviation is set to a value within a predetermined range.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 3 shows an internal combustion engine (engine) to which the present invention can be applied. A throttle valve 8 is disposed downstream of an air cleaner (not shown), and the throttle valve 8 is in a fully closed state. An idle switch 10 that is turned on at an idle position) is attached, and a surge tank 12 is provided on the downstream side of the throttle valve 8. This surge tank 1
A diaphragm type pressure sensor 6 is attached to 2. Further, a bypass passage 14 is provided so as to bypass the throttle valve 8 and connect the upstream side of the throttle valve and the surge tank 12 on the downstream side of the throttle valve. A pulse motor 1 having a 4-pole stator in the bypass passage 14
An idle speed control (ISC) valve 16B whose opening is adjusted by 6A is attached. The surge tank 12 communicates with the combustion chamber of the engine 20 via the intake manifold 18 and the intake port 22. A fuel injection valve 24 is attached to each cylinder or each group of cylinders so as to project into the intake manifold 18.

The combustion chamber of the engine 20 is connected to a catalyst device (not shown) filled with a three-way catalyst via an exhaust port 26 and an exhaust manifold 28. A lean sensor 30 that outputs an air-fuel ratio signal proportional to the residual oxygen concentration in the exhaust gas in the air-fuel ratio region leaner than the stoichiometric air-fuel ratio is attached to the exhaust manifold 28. A cooling water temperature sensor 34 is attached to the engine block 32 so as to penetrate the engine block 32 and project into the water jacket. This cooling water temperature sensor 34
Detects the engine cooling water temperature and outputs a water temperature signal.

A spark plug 38 is attached to each cylinder so as to penetrate the cylinder head 36 of the engine 20 and project into the combustion chamber. The ignition plug 38 is connected via a distributor 40 and an igniter 42 to an electronic control circuit 44 composed of a microcomputer or the like.
Inside the distributor 40, a cylinder discriminating sensor 46 and a rotation angle sensor 48, each of which is composed of a signal rotor fixed to the distributor viewer and a pick-up fixed to the distributor housing, are mounted. . In the case of a 6-cylinder engine, the cylinder discrimination sensor 46 outputs a cylinder discrimination signal, for example, every 720 ° CA, and the rotation angle sensor 48 outputs an engine rotation speed signal, for example, every 30 ° CA.

As shown in FIG. 4, the electronic control circuit 44 includes a central processing unit (MPU) 60, a read only memory (ROM) 6
2, RAMDAM access memory (RAM) 64, backup RAM (BU-RAM) 66, input / output port 6
8, an input port 70, output ports 72, 74, 76, and a bus 78 such as a data bus or a control bus connecting these components. The pressure sensor 6 and the cooling water temperature sensor 34 are connected to the input / output port 68 via an analog-to-digital (A / D) converter 78, a multiplexer 80, and buffers 82 and 84. MP
U60 is a multiplexer 80 and an A / D converter 78.
The output of the pressure sensor 6 and the output of the water temperature sensor 34 are sequentially converted into digital signals and stored in the RAM 64. The lean sensor 30 is connected to the input port 70 via the A / D converter 88 and the current-voltage converter 86, and the cylinder discrimination sensor 46 and the rotation angle sensor 48 are connected via the waveform shaping circuit 90. The idle switch 10 is connected. The output port 72 is a drive circuit 92
Is connected to the igniter 42 via the drive circuit 94, the output port 74 is connected to the fuel injection valve 24 via the drive circuit 94, and the output port 76 is connected to the pulse motor 16A of the ISC valve via the drive circuit 96. Note that 98 is a clock and 100 is a timer. The ROM 62 stores in advance programs and the like for control routines described below.

Next, a control routine of one embodiment in which the present invention is applied to the above engine will be described.

FIG. 1 shows a part of the main routine of the above-described embodiment. In step 110, it is determined whether the engine cooling water temperature is equal to or higher than a predetermined value, thereby determining whether the engine has been warmed up. When it is determined that the engine has been warmed up, in step 112, the deviation e is subtracted by subtracting the target air-fuel ratio A / F ₀ previously stored in the ROM from the current air-fuel ratio A / F detected by the lean sensor 30. Calculate In the next step 114, it is determined whether or not the current acceleration operation state is determined by determining whether the rate of change of the intake pipe pressure is equal to or higher than a predetermined value or whether the idle switch is changed from on to off. When it is determined that the acceleration operation state at step 114, the deviation e is determined whether the upper limit value K ₁ or more predetermined range during acceleration to converge the air-fuel ratio in step 116, when the upper limit value K ₁ or more In step 118, the acceleration increase coefficient Ka is increased by a predetermined value α ₁ and the increased acceleration increase coefficient Ka is stored in the BU-RAM. That is, as shown in FIG. 5, the deviation e is the target air-fuel ratio A / F ₀
When the value is equal to or higher than the upper limit value K _{1 in} a predetermined range centered on, the acceleration increase coefficient Ka is increased. As described above, as a result of increasing the acceleration increase coefficient Ka, when the fuel injection is executed using the acceleration increase coefficient Ka, the air-fuel ratio changes to the latch side, so the level of the lean sensor output becomes low and the lean sensor output is reduced. It can be converged to a value within a predetermined range.

On the other hand, when the deviation e is less than the upper limit value K ₁ , step 12
At 0, it is judged whether the deviation e is less than or equal to the lower limit value of the predetermined range −K _{2, and} if this judgment is affirmative, the acceleration increase coefficient Ka is decreased by a predetermined value α _{2 in} step 122 to reduce the acceleration increase coefficient. Are stored in the BU-RAM.

When it is determined in step 114 that it is not in the acceleration operation state, step 124 determines whether it is in the deceleration operation state, and when it is determined that it is in the deceleration operation state, in step 126, the deviation e is the deceleration at which the air-fuel ratio should converge. it is determined whether the upper limit value K ₃ or more predetermined range of time, when the upper limit value or more K ₃ by increasing the deceleration reduction coefficient Kd at step 128 by a predetermined value beta _1, deceleration loss, as greatly to BU-RAM The coefficient Kd is stored.

On the other hand, when the deviation e is less than the upper limit value K ₃ , step 13
At 0, it is determined whether the deviation e is less than or equal to the lower limit value −K _{4 of the} predetermined range, and if this determination is affirmative, the deceleration reduction coefficient Kd is decreased by a predetermined value β _{1 in} step 132 to reduce the deceleration reduction coefficient. Store Kd in BU-RAM.

When it is determined that the vehicle is not in the decelerating operation state in step 124, that is, when it is determined that the vehicle is in the steady operation state, it is determined in step 134 whether the deviation e is the upper limit value K ₅ or more of the predetermined range for converging the air-fuel ratio. If the upper limit value K ₅ or more, the air-fuel ratio feed back correction coefficient FA is determined in step 136.
F is increased by a predetermined value γ ₁ and stored in BU-RAM. On the other hand, when the deviation e is less than the upper limit value K ₅ , it is determined in step 138 whether the deviation e is less than or equal to the lower limit value −K _{6 of the} predetermined range, and if this determination is affirmative, the air-fuel ratio feedback correction coefficient is determined in step 140. FAF is reduced by γ ₂ and B
Store in U-RAM.

FIG. 6 shows an air-fuel ratio feedback back correction coefficient FAF calculation routine. The air-fuel ratio A / F and the target air-fuel ratio A obtained based on the lean sensor output at step 142.
/ F ₀ , if A / F> A / F ₀ , the air-fuel ratio feedback correction coefficient FAF is increased by a predetermined value α in step 144, and if A / F ≦ A / F ₀ , the air-fuel ratio in step 146. The feed back correction coefficient FAF is reduced by a predetermined value α. FIG. 7 shows changes in the air-fuel ratio feedback back correction coefficient FAF when the above control is performed. The initial value of the air-fuel ratio feedback correction coefficient FAF is the value changed in steps 136 and 140 of the routine of FIG.
That is, the learned value is adopted. Therefore, when the air-fuel ratio is controlled to be leaner than the target air-fuel ratio due to aging, etc., the air-fuel ratio feed back correction coefficient F
The average value of AF becomes large.

FIG. 8 shows a fuel injection amount calculation routine executed by interruption at every predetermined crank angle (for example, 720 ° CA). At step 150, the current intake pipe pressure PM _ι and engine speed stored in the RAM are stored. Intake pipe pressure PM taken in this time at step 152
_The intake pipe pressure PM _ι-1 that was previously captured is subtracted from _ι to calculate the change amount ΔPM of the intake pipe pressure. Next step 15
In 4, the basic fuel injection amount τ _{B is} calculated based on the intake pipe pressure PM _ι and the engine speed NE as in the conventional case. Next, in step 156, it is determined whether the current deceleration operation state or the acceleration operation state is present.
The acceleration increase coefficient Ka is read from the U-RAM, and in the deceleration operation state, the deceleration increase coefficient Kd is read from the BU-RAM in step 160, and the fuel injection amount τ is calculated according to the following equation.

τ = τ _B · FAF · (1 + KaΔPM + KdΔPM ...) (1) In the above formula (1), the amount of change ΔPM is positive (K
Since d becomes 0), the fuel injection amount is increased, and the change amount ΔPM becomes negative (Ka is 0) at the time of deceleration, so the fuel injection amount is decreased. Further, when the air-fuel ratio becomes a value outside the predetermined range during acceleration / deceleration, the acceleration / deceleration increase coefficient is learned and the air-fuel ratio is corrected at the next acceleration / deceleration. it can.

In addition, although the engine which determines the basic fuel injection amount by the intake pipe pressure and the engine speed has been described above, the present invention is not limited to this, and the basic fuel injection amount is determined by the intake air amount and the engine speed. It can also be applied to a prescribed engine.

As described above, according to the present invention, the increase coefficient is learned according to the deviation between the engine air-fuel ratio and the target air-fuel ratio.
Even if spy clean occurs, it is possible to prevent the fluctuation of the air-fuel ratio.

[Brief description of drawings]

FIG. 1 is a flow chart showing a main routine of one embodiment of the present invention, and FIG. 2 is a conventional air-fuel ratio feedback back correction coefficient FA.
FIG. 3 is a diagram for explaining changes in F, FIG. 3 is a schematic diagram of an engine equipped with an air-fuel ratio control device according to an embodiment of the present invention, and FIG.
FIG. 5 is a block diagram showing the details of the control circuit of FIG. 3, FIG. 5 is a diagram showing the relationship between deviation and upper and lower limit values, and FIG. 6 shows the air-fuel ratio feedback correction coefficient FAF calculation routine of the above embodiment. 7 is a flow chart, FIG. 7 is a diagram showing changes in the air-fuel ratio feedback back correction coefficient FAF in the above embodiment, and FIG. 8 is a flow chart showing a fuel injection amount calculation routine in the above embodiment. 6 ... Pressure sensor, 10 ... Idle switch, 24 ... Fuel injection valve, 30 ... Lean sensor.

Claims (1)

[Claims] 1. An air-fuel ratio feedback correction coefficient for controlling the air-fuel ratio to a target air-fuel ratio is calculated based on a signal proportional to the engine air-fuel ratio, and the fuel injection amount is increased during acceleration with the air-fuel ratio feedback correction coefficient. In the air-fuel ratio control device of the internal combustion engine for controlling the air-fuel ratio by injecting fuel in an amount corresponding to the calculated fuel injection amount, the fuel injection amount is calculated based on the engine air-fuel ratio and the engine air-fuel ratio. Deviation calculating means for calculating a deviation from the target air-fuel ratio, and coefficient changing means for changing the increase coefficient so that the deviation becomes a value within a predetermined predetermined range at the time of acceleration. Air-fuel ratio control device for internal combustion engine.