JPH089390Y2 - Air-fuel ratio feedback control system for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an air-fuel ratio feedback control device for an internal combustion engine, and more specifically, a control for feedback-correcting a fuel supply amount so that an actual air-fuel ratio approaches a target air-fuel ratio. Regarding the device.

<Prior Art> An electronically controlled fuel injection internal combustion engine having an air-fuel ratio feedback control function is conventionally disclosed in Japanese Patent Application Laid-Open No. 62-107251.

That is, an oxygen sensor for detecting the oxygen concentration in the exhaust gas, which is closely related to the air-fuel ratio of the engine intake air-fuel mixture, is provided in the exhaust system,
Output signal of this oxygen sensor and target air-fuel ratio (theoretical air-fuel ratio)
By comparing with a corresponding slice level, it is detected whether the actual air-fuel ratio is rich or lean with respect to the target air-fuel ratio, and based on the detection result, the actual air-fuel ratio is brought close to the target air-fuel ratio. Fuel injection amount (fuel supply amount)
Air-fuel ratio feedback correction coefficient LA to increase / decrease
MBDA (feedback correction value) is set.

Here, the value of the air-fuel ratio feedback correction coefficient LAMBDA is changed by, for example, proportional-plus-integral (P1) control so that stable control is achieved. This is because the output signal (output voltage) of the oxygen sensor is compared with the slice level, and when the slice level is high or low, the air-fuel ratio does not suddenly become rich or thin, When the fuel ratio is rich (thin), the specified proportion (P) is first
The air-fuel ratio feedback correction coefficient LAMBDA is decreased (increased) only, and then gradually decreased (increased) by a predetermined integral amount (I minute) to control the air-fuel ratio to be thin (dark). To do.

<Problems to be solved by the invention> By having the function of feedback-controlling the air-fuel ratio in this way, changes in fuel properties and matching errors can occur in the feedback control region especially during transient operation in which deviation of the air-fuel ratio is likely to occur. Even if the air-fuel ratio is disturbed due to engine variations or the like, the disturbance can be controlled to be near the target air-fuel ratio although there is a delay.

However, the proportional and integral control constants in the proportional-plus-integral control cannot be set so large in order to ensure the stability of the air-fuel ratio during steady operation, so that, for example, as shown in FIG. The air-fuel ratio feedback correction coefficient is used to correct the over-lean or over-rich air-fuel ratio that occurs during acceleration operation.
When LAMBDA is set to greatly increase or decrease from the reference value (1), the actual air-fuel ratio crosses the target air-fuel ratio and the air-fuel ratio is reversed, so LAMBDA is returned to near the reference value (shaded line in the figure)
There was a problem that LAMBDA could not be quickly converged to the vicinity of the reference value when performing, and hesitation and stumble were generated due to the disturbance of the air-fuel ratio during this period.

The present invention has been made in view of the above problems, and provides an air-fuel ratio feedback control device capable of improving the convergence of the air-fuel ratio feedback correction coefficient LAMBDA (feedback correction value) with respect to a reference value while ensuring air-fuel ratio stability. The purpose is to provide.

<Means for Solving the Problem> Therefore, in the present invention, as shown in FIG. 1, based on the engine operating state detecting means for detecting the engine operating state and the engine operating state detected by the engine operating state detecting means. A basic fuel supply amount setting means for setting a basic fuel supply amount, an air-fuel ratio detecting means for detecting an engine exhaust gas component and thereby detecting a rich lean of an air-fuel ratio of an engine intake air-fuel mixture with respect to a target air-fuel ratio, and this air-fuel ratio A predetermined control of a feedback correction value for correcting the basic fuel supply amount so that the actual air-fuel ratio approaches the target air-fuel ratio based on the rich lean of the actual air-fuel ratio detected by the detection means with respect to the target air-fuel ratio A rich / lean state with respect to the target air-fuel ratio of the actual air-fuel ratio is determined by the feedback correction value setting means for increasing / decreasing based on a constant and the air-fuel ratio detecting means. Feedback correction value deviation detection means for detecting a deviation of the feedback correction value from the reference value when it is detected that the feedback correction value deviation detection means is provided for each reversal of the rich / lean state with respect to the target air-fuel ratio. Correct the basic value of the control constant according to the deviation detected in
Feedback control constant correcting means for increasing / decreasing the feedback correction value in the feedback correction value setting means based on the corrected control constant, basic fuel supply amount and feedback correction set by the basic fuel supply amount setting means Fuel supply amount setting means for setting the fuel supply amount based on the feedback correction value set by the value setting means, and fuel supply means for supplying fuel to the engine based on the fuel supply amount set by the fuel supply amount setting means ,
And an air-fuel ratio feedback control system for an internal combustion engine is configured.

<Operation> According to the air-fuel ratio feedback control device having such a configuration, the basic fuel supply amount setting means sets the basic fuel supply amount based on the engine operating state detected by the engine operating state detecting means. On the other hand, the feedback correction value setting means sets the basic fuel supply amount so that the actual air-fuel ratio approaches the target air-fuel ratio based on the rich lean of the actual air-fuel ratio detected by the air-fuel ratio detecting means with respect to the target air-fuel ratio. The feedback correction value for correction is increased or decreased based on a predetermined control constant. The fuel supply amount setting means sets the fuel supply amount based on the basic fuel supply amount and the feedback correction value, and the fuel supply means supplies fuel to the engine based on the set fuel supply amount.

Here, when it is detected by the air-fuel ratio detection means that the rich / lean state of the actual air-fuel ratio with respect to the target air-fuel ratio is detected, the feedback correction value deviation detection means detects the deviation of the feedback correction value from the reference value. To detect. Then, the feedback control constant correction means is
Every time the rich / lean state is reversed with respect to the target air-fuel ratio, the basic value of the control constant is corrected according to the deviation detected by the feedback correction value deviation detecting means, and the control constant is set by correcting the basic value. The feedback correction value is increased or decreased based on

That is, when the actual air-fuel ratio reverses from the rich state (lean state) to the lean state (rich state) with respect to the target air-fuel ratio, if the feedback correction value has a large deviation from the reference value, the control constant is that much. Is increased from the basic value so that it can be quickly changed from a state having a large deviation to the vicinity of the reference value.When the deviation is small, the control constant is not increased and corrected, so hunting for air-fuel ratio control is performed. By avoiding the above, the stability of the air-fuel ratio can be secured.

<Embodiment> An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, air is drawn into the engine 1 from an air cleaner 2 through an intake duct 3, a throttle valve 4 and an intake manifold 5. At the branch portion of the intake manifold 5, a fuel injection valve 6 as a fuel supply means is provided for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that is energized by a solenoid to open the valve, and the energization is stopped to close the valve. The fuel injection valve 6 is energized and opened by a drive pulse signal from a control unit 12 described later, and is not shown. Fuel that is pumped from the fuel pump and adjusted to a predetermined pressure by the pressure regulator is injected and supplied.

Although this example is a multi-point injection system, a single-point injection system in which a single fuel injection valve is provided in common to all cylinders upstream of the throttle valve 4 or the like may be used.

A spark plug 7 is provided in the combustion chamber of the engine 1 to ignite sparks to ignite and burn the air-fuel mixture.

Exhaust gas is discharged from the engine 1 through the exhaust manifold 8, the exhaust duct 9, the three-way catalyst 10 and the muffler 11. The three-way catalyst 10 oxidizes CO and HC in the exhaust components, and
It is an exhaust gas purification device that reduces O _X and converts it to other harmless substances, and its conversion efficiency is closely related to the air-fuel ratio of the air-fuel mixture.

The control unit 12 includes a CPU, ROM, RAM, a microcomputer including an A / D converter and an input / output interface, receives input signals from various sensors, and performs arithmetic processing as described later, The operation of the fuel injection valve 6 is controlled.

As the various sensors, a hot-wire type air flow meter 13 is provided in the intake duct 3 and outputs a voltage signal according to the intake air flow rate Q.

In addition, the crank angle sensor 14 is provided, and in the case of four cylinders, the reference signal and the crank angle 1 for each crank angle of 180 ° are set.
Outputs a unit signal for each ° or 2 °. Here, the engine speed N can be calculated by measuring the cycle of the reference signal or the number of times the unit signal is generated within a predetermined time.

Further, the water jacket of the engine 1 is provided with a water temperature sensor 15 for detecting the cooling water temperature Tw.

The air flow meter 13, the crank angle sensor 14 and the like correspond to the engine operating state detecting means.

Further, an oxygen sensor 16 as an air-fuel ratio detecting means is provided in the collecting portion of the exhaust manifold 8 to detect the air-fuel ratio of the intake air-fuel mixture via the oxygen O ₂ concentration in the exhaust gas.

The oxygen sensor 16 is, for example, zirconia (ZrO ₂ ) which is an oxygen ion conductor used as a solid electrolyte for concentration cells.
The closed-end cylindrical closed end of the tube is exposed to the exhaust gas, and an electromotive force is generated according to the ratio of oxygen concentration between the atmosphere inside the tube and the exhaust gas outside the tube. Then, a platinum catalyst layer formed by vapor-depositing platinum that functions as an oxidation catalyst is provided on the outer surface of the zirconia tube, and generally exists slightly when burned with a mixture richer than the theoretical air-fuel ratio.
By combining O ₂ and unburned components such as CO to make the outside oxygen concentration almost zero, the oxygen concentration ratio inside and outside is increased to generate a large electromotive force. Is small, almost no voltage is generated, and as shown in Fig. 3, the well-known rich
It is a lean sensor.

Further, the throttle valve 4 has an opening TV of the throttle valve 4.
A throttle sensor 17 for detecting O with a potentiometer is attached.

Here, the CPU of the microcomputer incorporated in the control unit 12 performs arithmetic processing according to the program on the ROM shown in the flowcharts of FIGS. 4 to 6 to control the fuel injection.

In the present embodiment, the functions of the control unit 12 as the basic fuel supply amount setting means, the fuel supply amount setting means, the feedback correction value setting means, the feedback correction value deviation detecting means, and the feedback control constant correcting means are shown in the above flow chart. It is provided as software.

The routine shown in the flowchart of FIG. 4 is a fuel injection amount calculation routine. First, in step 1, the engine is calculated based on the intake air flow rate Q detected by the air flow meter 13 and the signal from the crank angle sensor 14. Read the rotation speed N and.

In the next step 2, the basic fuel injection amount (basic fuel supply amount) Tp (= K × Q / N; K is a constant) is calculated based on the intake air flow rate Q and the engine speed N detected in step 1. .

In step 3, the change rate of the throttle valve opening TVO detected based on the signal from the throttle sensor 17 or the acceleration correction amount based on the switching of the idle switch (not shown) from ON to OFF, and the signal from the water temperature sensor 15 are used. Various correction coefficients COEF including a water temperature correction amount based on the cooling water temperature Tw detected by the above are set.

In step 4, the condition (air-fuel ratio feedback control condition) for performing feedback correction control of the fuel injection amount so that the actual air-fuel ratio approaches the target air-fuel ratio based on the air-fuel ratio feedback correction coefficient LAMBDA set as described below. It is determined whether or not it holds. The condition for stopping (clamping) the air-fuel ratio feedback control is, for example, a low water temperature or a high load operation.

When it is determined in step 4 that the feedback control condition is satisfied, the process proceeds to step 5, and the fifth control described below is performed.
The air-fuel ratio feedback correction coefficient LAMBDA set according to the routine shown in the flowchart of the figure is read.

On the other hand, when it is determined in step 4 that the air-fuel ratio feedback control condition is not satisfied, the routine proceeds to step 6, where the air-fuel ratio feedback correction coefficient LAMBDA is set to a predetermined clamp value.

If the air-fuel ratio feedback correction coefficient LAMBDA is set in step 5 or step 6, in the next step 7,
A correction amount Ts for correcting the change in the effective valve opening time of the fuel injection valve 6 due to the battery voltage change is set.

Then, in the next step 8, the final fuel injection amount Ti is calculated according to the following equation.

Ti = Tp × COEF × LAMBDA + Ts In step 9, the calculated fuel injection amount Ti is set in the output register. As a result, at a predetermined fuel injection timing in synchronization with engine rotation, a drive pulse signal having a pulse width corresponding to Ti is given to the fuel injection valve 6, and fuel injection is performed.

The routine shown in the flowchart of FIG. 5 is a proportional / integral control routine for setting the air-fuel ratio feedback correction coefficient LAMBDA.

First, in step 21, it is determined whether or not the current operating state is an operating region in which feedback control of the air-fuel ratio is performed, and when the operating state is in which feedback control is not performed, this routine is ended.

On the other hand, when the air-fuel ratio feedback control is in the operating state, the routine proceeds to step 22, where the output voltage Vo ₂ of the oxygen O ₂ sensor 16 is read, and at the next step 23 the slice level voltage equivalent to the theoretical air-fuel ratio which is the target air-fuel ratio. Rich lean against the theoretical air-fuel ratio of the actual air-fuel ratio is judged by comparing with Vref.

When the air-fuel ratio is lean (Vo ₂ <Vref), step 23
To step 24, it is determined whether or not it is during the reversal from rich to lean (immediately after reversal), and when reversing, the process proceeds to step 25 to set the air-fuel ratio feedback correction coefficient LAMBDA to a predetermined proportional constant P with respect to the previous value. Increase by minutes. Except when reversing, the routine proceeds to step 26, where the air-fuel ratio feedback correction coefficient LAMBDA is increased by a predetermined integral constant I from the previous value, and thus the air-fuel ratio feedback correction coefficient LAMBDA is increased.
Increase DA with a constant slope.

When the air-fuel ratio is rich (Vo ₂ > Vref), the routine proceeds from step 23 to step 27, and it is determined whether or not the lean-to-rich reversal is occurring (immediately after the reversal). Air-fuel ratio feedback correction coefficient LAMBDA
Is decreased by a predetermined proportional constant P with respect to the previous value. Except when reversing, the routine proceeds to step 29, where the air-fuel ratio feedback correction coefficient LAMBDA is decreased by the predetermined integration constant I from the previous value, and thus the air-fuel ratio feedback correction coefficient LAMBDA
Decrease DA with a constant slope.

By the way, the proportions shown in the flow chart of FIG.
The proportional constant P and the integral constant I used in the integral control routine are set in the P, I constant setting routine shown in the flowchart of FIG.

That is, first, at step 31, the output voltage Vo ₂ from the oxygen sensor 16 and the air-fuel ratio feedback correction coefficient LAMBDA set according to the flowchart of FIG. 5 are read.

Then, in the next step 32, it is determined whether or not the air-fuel ratio feedback control is being performed (the air-fuel ratio feedback control condition is satisfied).

Here, if it is determined that the air-fuel ratio feedback control is being performed, the process proceeds to the next step 33, and it is determined whether the rich / lean state of the air-fuel ratio is inverted based on the output voltage Vo ₂ from the oxygen sensor 16. To judge. Then, when it is determined that the air-fuel ratio is being inverted in the same manner as in step 24 and step 27 described above, the process proceeds to step 34, where LAMB is calculated from the value of the air-fuel ratio feedback correction coefficient LAMBDA read in step 31.
Deviation ΔLAMB of the absolute value of the value obtained by subtracting 1 which is the standard value of DA
DA. That is, the deviation ΔLAMBDA is a value representing the absolute value of the deviation of the air-fuel ratio feedback correction coefficient LAMBDA from the reference value (1).

In the next step 35, the basic values of the proportional constant P and the integral constant I are multiplied by (1 + ΔLAMBDA) to perform a correction operation, and new P and I minutes are set. In this way,
If the basic values for P and I are corrected and calculated, P and I are increased and corrected as the value of the air-fuel ratio feedback correction coefficient LAMBDA at the time of air-fuel ratio inversion has a large deviation from the reference value. Therefore, by proportionally integrating the air-fuel ratio feedback correction coefficient LAMBDA with the increased P and I components after the air-fuel ratio reversal, the value LAMBDA far from the reference value at the time of air-fuel ratio reversal can be promptly obtained. It can be changed to a value close to the reference value.

Therefore, for example, even when the air-fuel ratio feedback correction coefficient LAMBDA is changed to a value having a large deviation from the reference value in order to correct over lean or over rich of the air fuel ratio during acceleration / deceleration operation, feedback is performed. When the air-fuel ratio is reversed according to the correction result, the LAMBDA return control can be performed with a large control constant according to the increase in the deviation, and hesitation or stumble due to the delay of the return control can be avoided.

The basic values for P and I, which are increased / decreased based on the deviation from the reference value of LAMBDA at the time of reversing the air-fuel ratio, are divided into a plurality of operating regions, for example, the basic fuel injection amount Tp and the engine speed N. It may be a value set for each time, or may be a constant value.

<Effects of the Invention> As described above, according to the present invention, even if the feedback correction value is set to be greatly increased or decreased from the reference value to correct the disturbance of the air-fuel ratio during transient operation of the engine, the air-fuel ratio is When reversing according to the correction result, the control constant is increased and corrected from the basic value according to the increase in the deviation of the feedback correction value from the reference value at that time, so the correction value is set to the reference value at a change rate that does not occur after the air-fuel ratio is reversed. It is possible to control the return to the vicinity, and it is possible to avoid the occurrence of hesitation, stumble, etc. due to the disturbance of the air-fuel ratio due to the delay of the return control, and the control constant increases from the basic value when the feedback correction value is near the reference value. There is an effect that the stability of the air-fuel ratio controllability can be secured without correction.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention, FIG. 2 is a schematic diagram of a system showing an embodiment of the present invention, FIG. 3 is an output characteristic diagram of an oxygen sensor as an air-fuel ratio detecting means in the same embodiment, FIG. 4 to 6 are flowcharts showing various control routines in the above-mentioned embodiment, respectively, and FIG. 7 is a time chart for explaining the problems of the prior art. 1 ... Engine, 6 ... Fuel injection valve, 12 ... Control unit, 13 ... Air flow meter, 14 ... Crank angle sensor, 15
… Water temperature sensor, 16… Oxygen sensor

Claims (1)

[Scope of utility model registration request] 1. An engine operating state detecting means for detecting an engine operating state, a basic fuel supply amount setting means for setting a basic fuel supply amount based on the engine operating state detected by the engine operating state detecting means, and an engine exhaust. Air-fuel ratio detecting means for detecting a component and thereby detecting a rich lean of the air-fuel ratio of the engine intake air-fuel mixture with respect to the target air-fuel ratio, and a rich lean lean of the actual air-fuel ratio detected by the air-fuel ratio detecting means with respect to the target air-fuel ratio Feedback correction value setting means for increasing or decreasing a feedback correction value for correcting the basic fuel supply amount so as to bring the actual air-fuel ratio closer to the target air-fuel ratio on the basis of a predetermined control constant, and the air-fuel ratio Reference of the feedback correction value when the detection means detects that the rich / lean state of the actual air-fuel ratio with respect to the target air-fuel ratio is detected to be reversed. And a feedback correction value deviation detecting means for detecting a deviation relative to the target air-fuel ratio, and every time the rich / lean state is reversed with respect to the target air-fuel ratio, the basic value of the control constant is corrected according to the deviation detected by the feedback correction value deviation detecting means. A feedback control constant correcting means for increasing / decreasing the feedback correction value in the feedback correction value setting means based on the corrected control constant; a basic fuel supply amount and the feedback set by the basic fuel supply amount setting means; Fuel supply amount setting means for setting the fuel supply amount based on the feedback correction value set by the correction value setting means, and fuel supply means for supplying fuel to the engine based on the fuel supply amount set by the fuel supply amount setting means An air-fuel ratio feedback control device for an internal combustion engine, comprising: