JPH02256848A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the deterioration of operation characteristics at the time of engine start by applying the constitution wherein judgement is made about the failure of an alcohol sensor, an alcohol correction factor is pertinently modified upon the judgment of the occurrence of a failure and a fuel supply amount is determined for later engine startup on the basis of the modified alcohol correction factor. CONSTITUTION:A control means (i) determines a fuel supply amount by correcting a basic fuel supply amount on the basis of an alcohol correction factor and an air-fuel ratio correction factor. Also, when the failure of an alcohol detecting means (d) is judged to have occurred, the alcohol correction factor is fixed at a constant value and then, the alcohol correction factor is modified, depending upon the then air-fuel ratio correction factor. A startup control means (j) determines a fuel supply amount for engine start on the basis of an alcohol correction factor set up at the previous engine operation, when the occurrence of a failure in the detecting means (d) is not discriminated. Upon discriminating the failure of the detecting means (d), a fuel supply amount for later engine startup is determined on the basis of the modified alcohol correction.

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.
For example, the present invention relates to a device for controlling the air-fuel ratio of an internal combustion engine operated with a mixed fuel mixed with gasoline.

(Prior Art) The fuel currently used in internal combustion engines for automobiles is mainly gasoline, but this gasoline is also gradually becoming depleted. Therefore, as an alternative fuel, alcohol mixed fuel, which is a mixture of gasoline and alcohol such as methanol or ethanol, has been proposed.

As is well known, the output of an internal combustion engine depends on the composition of its fuel.
It is well known that the amount of exhaust gas components generated is affected, and it is also known that the ignition timing must be controlled by the fuel composition. Therefore, it is impossible to optimally control the internal combustion engine simply by supplying alcohol-mixed fuel to the internal combustion engine. Furthermore, there is currently no established supply route for alcohol-mixed fuel.
Alcohol mixing ratios vary, and supplying such fuel to an internal combustion engine is not preferable in terms of output and generation of harmful exhaust components. Therefore, it is important to appropriately control the combustion state of the internal combustion engine according to the alcohol mixing ratio of the alcohol mixed fuel.

As a conventional air-fuel ratio control device for an internal combustion engine using this type of alcohol mixed fuel, for example, Japanese Patent Application Laid-Open No. 56-9854
There is one described in Publication No. 0. In this device, an alcohol sensor is installed in the middle of the alcohol mixed fuel flow path, and the alcohol mixing ratio (alcohol concentration) is detected from the change in capacitance when the alcohol mixed fuel passes through the alcohol sensor. Based on this, the fuel supply amount is corrected to control the air-fuel ratio. Similarly, the ignition timing is also controlled based on the above detection results.

(Problem to be Solved by the Invention) However, in such a conventional air-fuel ratio control device for an internal combustion engine, the air-fuel ratio is controlled by correcting the fuel supply amount based on the output of the alcohol sensor. Therefore, it was based on the premise that the alcohol sensor was normal, and no measures were taken into consideration in the event of alcohol sensor failure.

As a result, there have been problems in that not only the engine cannot be started smoothly, but also warm-up is not stable, which adversely affects drivability.

(Objective of the Invention) Therefore, the present invention determines the malfunction of the alcohol sensor, and
When a failure is determined, the alcohol correction coefficient is appropriately corrected, and at subsequent starts, the amount of fuel supplied at startup is determined based on the corrected alcohol correction coefficient, thereby stabilizing the air-fuel ratio even in the event of an alcohol sensor failure. The purpose is to maintain the engine within limits, obtain stable restartability, and prevent deterioration of drivability during startup.

(Means for Solving the Problems) In order to achieve the above object, the air-fuel ratio control device for an internal combustion engine according to the present invention has an operating state detection means for detecting the operating state of the engine, as a basic conceptual diagram thereof is shown in FIG. a, an air-fuel ratio detecting means for detecting the air-fuel ratio of the intake air-fuel mixture, a starting state detecting means C for detecting the starting state of the engine, an alcohol detecting means d for detecting the alcohol concentration in the fuel, and an alcohol detecting means. failure determination means C for determining whether or not the engine is malfunctioning; basic value calculation means f for calculating the basic supply amount of fuel based on the operating state of the engine; a first correction coefficient calculation means g that calculates an alcohol correction coefficient for correcting the amount; and a second correction coefficient calculation means g that calculates an air-fuel ratio correction coefficient that feedback-controls the air-fuel ratio to a predetermined air-fuel ratio based on the output of the air-fuel ratio detection means g.
a correction coefficient calculation means d, corrects the basic supply amount of fuel based on the alcohol correction coefficient and the air-fuel ratio correction coefficient to determine the fuel supply amount, and an alcohol detection means d.
When it is determined that the alcohol correction coefficient is malfunctioning, the control means i corrects the alcohol correction coefficient according to the value of the air-fuel ratio correction coefficient at that time after fixing the alcohol correction coefficient to a constant value, and the alcohol detection means d is determined to be malfunctioning. If the determination is not made, the fuel supply amount at startup is determined based on the alcohol correction coefficient set during the previous engine operation, and if a failure of the alcohol detection means d is determined, the fuel supply amount at the time of subsequent engine startup is determined based on the alcohol correction coefficient after the correction. The engine includes a starting control means j that determines the amount of fuel to be supplied at the time of starting based on the outputs of the control means i and the starting control means j, and a fuel supply means that supplies fuel to the engine based on the outputs of the control means i and the starting control means j.

(Function) In the present invention, during normal starting, the fuel supply amount at starting is determined based on the starting alcohol correction coefficient set during the previous engine operation. On the other hand, when a failure of the alcohol detection means is determined, the alcohol correction coefficient is fixed at a constant value, and then the alcohol correction coefficient is corrected according to the value of the air-fuel ratio correction coefficient at that time, and is corrected at the time of subsequent startup. The fuel supply amount at startup is determined based on the subsequent alcohol correction coefficient.

- Therefore, even if the alcohol detection means fails, the air-fuel ratio is maintained within the stability limit, the engine starts smoothly, and deterioration of engine drivability is prevented.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 6 are diagrams showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

First, the configuration will be explained. FIG. 2 is an overall configuration diagram of the air-fuel ratio control device, and in this figure, 1 is an engine.

Engine 1 explodes using alcohol mixed fuel, which is gasoline mixed with alcohol such as methanol or ethanol.
It is burned and the exhaust gas is discharged from the exhaust pipe 2.

The air flow rate Qa taken into the engine 1 is detected by an air flow meter 3, and the throttle valve opening degree TVO is detected by a throttle valve opening degree sensor 4. The crank angle of the engine 1 is detected by a crank angle sensor 5, and by counting the output pulses of the crank angle sensor 5, the engine rotation speed N is calculated. The oxygen concentration in the exhaust gas is detected by an oxygen sensor (air-fuel ratio detection means) 6 provided in the exhaust pipe 2, and
The starting state of the engine is detected by a starter signal from the ignition key switch (starting state detection means) 7. The alcohol mixing ratio (corresponding to the alcohol concentration) of the alcohol mixed fuel flowing through the fuel pipe 8 is detected by an alcohol sensor (alcohol detection means) 9. As the alcohol sensor 9, for example, the above-mentioned Japanese Patent Application Laid-open No. 56-98540 is used.
A device based on the same principle as that described in the publication is used.

The air flow meter 3, throttle valve opening sensor 4, and crank angle sensor 5 constitute an operating state detection means 1o.

Outputs from the driving state detection means 10, the oxygen sensor 6, the ignition key switch 7, and the alcohol sensor 9 are input to the control unit 1-20, and the control unit 20 is connected to the CPU 21. , a ROM 22, a nonvolatile RAM 23, a clock oscillator 24, and an I10 port 25, and includes a failure determination means, a basic value calculation means, an I-th correction coefficient calculation means, a second correction coefficient calculation means,
It functions as a control means and a start control means. C
The PU 21 takes in necessary external data from the I10 boat 25 according to the program written in the ROM 22 while synchronizing with the clock timing ticked by the clock oscillator 24, and while exchanging data with the RAM 23, the PU 21 reads alcohol. Processing values necessary for failure determination of the sensor 9 and air-fuel ratio control are processed, and the processed data is output to the I10 boat 25 as necessary. R
The OM 22 stores programs for controlling the CPU 21, and the RAM built into the CPU 21 temporarily stores data used in calculations in the form of a map or the like. Signals from the operating state detection means 10, oxygen sensor 6, ignition key 7, and alcohol sensor 9 are input to the I10 boat 25, and an injection signal Si is output from the I10 port 25 to the injector (fuel supply means) 26. Ru.

The injector 26 injects alcohol mixed fuel into the intake pipe near the intake boat based on the injection signal St.

Next, the effect will be explained.

FIG. 3 is an air-fuel ratio control chart, and this program is executed once every predetermined time. In the figure, Pn (n=1.2...) indicates each step of the flow.

First, it is determined whether the alcohol sensor 8 is malfunctioning (NG) at P+, and after that determination, the final injection amount Ti is calculated. The final injection iTt is determined as follows. The basic injection amount Tp is calculated based on the operating state of the engine I (in particular, the air flow rate Qa and the rotational speed N), and various correction coefficients are calculated. For details, see cooling water temperature, post-start quantity, various correction coefficients COEF for high load increase, dead time correction numerator of injector 16, etc.
Based on the output of the S% oxygen sensor 6, the basic injection amount Tp is corrected according to the air-fuel ratio correction coefficient ALPHA, the learning correction coefficient KBLRC, and the fuel-alcohol mixing ratio for performing feedback control to make the air-fuel ratio match the target air-fuel ratio. The alcohol correction coefficient ALC is calculated. The alcohol correction coefficient ALC is calculated in this way because, unlike regular gasoline, mixed gasolines such as alcohol have problems such as two-phase separation when water is mixed in, changes in the stoichiometric air-fuel ratio, increased volatility, and latent heat of vaporization. This is to correct the basic injection ITp in order to deal with such problems. The optimum ALC value is determined in advance through experiments or the like in accordance with the alcohol mixing ratio, and is stored in the nonvolatile RAM 23 in the form of a map or the like. Then, the final injection amount Ti is calculated according to the following equation (2), and an injection signal St is output at a predetermined injection timing to inject fuel in an amount Ti from the injector 26.

Ti=TpXCOEFXALCXALPHAXKBLR
C+Ts . . . ■Thus, an appropriate amount of fuel is injected in consideration of the alcohol mixing ratio, and an optimal fuel condition according to the fuel composition is obtained.

Returning to the flow of FIG. 3, when the alcohol sensor 9 is determined to be NG, it is determined in P2 whether or not the calibration after the alcohol sensor 9 is determined to be NG is completed, and if the ALC calibration is not completed, Determine whether or not the ALC is fixed with P and N of ALC (alcohol sensor 9).
After G determination, if calibration has not been performed, the ALC value is fixed.

If the ALC is not fixed, the ALC is fixed at P4 and the process proceeds to P. If the ALC is fixed, the process proceeds to P. At P, it is determined whether the learning after the NG determination of the alcohol sensor 9 has been completed. The learning here is learning for calibrating the alcohol sensor 9. When the learning is successful (that is, when the output of the oxygen sensor 6 is reversed), the ALC is calibrated by the subroutine shown in FIG. 5, which will be described later, in P6. Return the air-fuel ratio correction coefficient ALPHA to 100% (ALPHA=1) with
Feedback control is started at P8 and the current process is ended. If learning has not been established, feedback control for the alcohol sensor 9NG is started by a subroutine shown in FIG. 4, which will be described later, at P, and the process is finished.
If the alcohol sensor 9 is not determined to be NG at P, or if the ALC calibration has been completed at P2, the process ends.

FIG. 4 is a subroutine showing a feedback control program for alcohol sensor 9NG, in which steps P,
Alternatively, it is the process of step ps4 in FIG. 6, which will be described later. First, determine rich and lean flags based on pH,
If the Rich or Lean Flag is not ON, the pH
It is determined whether or not the air-fuel ratio correction coefficient ALPHA clamp time is being determined for the first time. The rich/lean judgment is made after the judgment of the clamping direction of the air-fuel ratio feedback control is completed.
This is to determine whether the routine for calibrating the alcohol sensor 9 has started, and the determination of the clamp time is to set the initial value of the ALPHA clamp time of 5 seconds. If the clamp time is the first time, use ALPHA at P+3.
is fixed at 100%, and in P14, set the timer to 5 seconds (Timer = 5) to finish the process, and if it is not the first time, check whether the timer has reached 0 in PIS (Timer
= 0) or not, and if Timer = 0, the process is immediately terminated. When T tmer≠0, use P to determine the direction of air-fuel ratio clamping based on the signal from the oxygen sensor 6. In order to store the value in the Flag, select PI? when the clamp direction is rich or lean. The enrichment flag is turned on with , and when the direction is lean, the lean flag is turned on with pH + to complete the process.

On the other hand, if the rich or lean flag is ON due to pH, the rich or lean clamp direction set in step P4 is determined in PI3, and if the pH is rich, A L P HA is lowered with P2°. If lean, PZI
This process is executed until the A L P HA is increased and the clamping direction of the air-fuel ratio is reversed (learning is established).

FIG. 5 is a subroutine showing ALC calibration, and is the process of step P or step PSI in FIG. 6, which will be described later. First, in P31, the change ΔALPHA from ALPHA 100% (the change in ALPHA at the above step pit or P) is calculated, in p3z, ALCNtw is calculated according to the following formula (■), and in P33, ALCstw is changed to A
The data is stored in memory as LC and processing is completed.

ALCsiw =ALCoto ±ALCOLD 6th
The figure is a flowchart showing a program for air-fuel ratio control after restarting the engine after it has been stopped. First, in Pd2, it is determined whether or not it is starting based on the starter signal from the ignition key switch 7, and when it is starting, it is determined in P4g whether or not the NG judgment of the alcohol sensor 9 was established during the previous engine operation. , when the determination is established, it is determined in Pd3 whether or not the calibration was completed last time. Then, the ALC value is selected and adopted according to the result. In other words, NG
If the judgment is not established, select the previous ALC value in P44, and if ALC calibration has not been completed previously, select Pd.
The fixed ALC value is selected in step 2, and if the calibration has been completed previously, the calibration AL and C values are selected in step Pd2, and the process ends. In other words, when the starter motor is ON (ignition key switch 7 ON), even if the alcohol sensor 9 output changes, the control is not changed accordingly. This is because in the region where the starter motor is ON, almost all the fuel from the previous time has accumulated in the pipe, and it is thought that there will be no problem if the previous ALC output value is used.

On the other hand, when it is not the time of starting, P4? to determine whether there was an NG judgment first, and if there was an NG judgment first, P
Set ALC to a fixed value with dI2. In other words, when the scooter motor is OFF, there is a possibility that newly replenished fuel is being supplied to the engine, so even if the sensor was determined to be NG during the previous engine operation,
Control is performed on the safe side (the ALC value is fixed). On the other hand, when the alcohol sensor 9 has not been determined to be NG, the above control will not be performed (
(The changed value shall be used as is.)

Next, in P49, it is determined whether or not feedback control after restart has been started, and if it is ON, PSO to P2. Then, calibrate the ALC in the same manner as in Figure 3 P, ~P, and O
If it is FF, the process ends immediately.

As shown in the above flow, during air-fuel ratio feedback control during engine operation, when rich clamping or lean clamping is performed, when the sensor output value shows, for example, 35 V or more and 0.5 V or less, or when the sensor output value is changing, for example, When the voltage is 0.5 V/time or more, the alcohol sensor 9 is determined to be NG, and the alcohol sensor correction value is immediately set to, for example, M2O (the proportion of alcohol in the fuel is 50%). Incidentally, if gasoline is 1, then M
2O-M50TE AL C= 1.3~1.45, M8
5te ALC = 1.8.

For example, in the 0th equation, set the ALC term to a constant value (M2O)
Set to . At this time, the value of ALPHA is clamped at 100% (ALPHA = 1), and M2O is
The engine can be operated in a stable range regardless of whether it is powered by S or gasoline.

After that, ALPHA is made rich or lean according to lean clamp or rich clamp, respectively.

In this way, the point where the air-fuel ratio sensor output is reversed is found, and the ALC output is corrected by the value added or subtracted up to that point. In this state, the learning control after the NG determination is established. When this learning is established, the value of ALPHA is returned to 100% and control is started. Then, the correction value adopted at this time is stored in the nonvolatile RAM 23. After this, when engine 1 is stopped and restarted, the value set during the previous engine operation is used (this is because the fuel remaining in the pipe does not change even if new fuel is put into the tank). . There are cases where the engine stops without the above-mentioned learning being established, and in this case, the ALC value remains set to, for example, M2O, so this value is also used when restarting.

In addition, in the case where the learning mentioned above is established, calibration A
Perform a restart using the LC value. Then, after restarting, if the alcohol sensor 9 was determined to be NG last time, the ALC value is fixed to M2O and the ALC value is calibrated again. After this, this value is used until learning is established (this is the same even when the value of M2O is used from the time of startup).

As mentioned above, the ALC value after restart is selected based on the presence or absence of learning after the previous NG judgment, and the ALC value is calibrated even after the current restart, resulting in stable restart performance. At the same time, it becomes possible to operate the engine without causing troubles such as engine stalling and without adversely affecting drivability.

(Effects) According to the present invention, failure of alcohol senna is determined,
When a malfunction is determined, the alcohol correction coefficient is appropriately corrected, and at subsequent starts, the amount of fuel supplied at startup is determined based on the corrected alcohol correction coefficient, so even if the alcohol sensor fails The fuel ratio can be maintained within the stability limit, stable restartability can be obtained, and deterioration of drivability at the time of startup can be prevented.

[Brief explanation of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 6 are diagrams showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention, FIG. 2 is an overall configuration diagram thereof, and FIG. is a flowchart showing the air-fuel ratio control program, FIG. 4 is a subroutine showing the alcohol sensor failure feedback control program, FIG. 5 is a subroutine showing the ALC calibration program, and FIG. 6 is the restart after engine stop. It is a flowchart which shows the program of air-fuel ratio control after starting. ■...Engine, 6...Oxygen sensor (air-fuel ratio detection means), 7...
...Ignition key switch (starting state detection means), 9...Alcohol sensor (alcohol detection means) 10...Driving state detection means, 20...Control unit ( failure determination means, basic value calculation means, first correction coefficient calculation means, second correction coefficient calculation means, control means, starting control means), 26... Injector (fuel supply means). Figure 3

Claims (1)

[Scope of Claims] a) Operating state detection means for detecting the operating state of the engine; b) Air-fuel ratio detection means for detecting the air-fuel ratio of the intake air-fuel mixture; c) Starting state detection for detecting the starting state of the engine. d) alcohol detection means for detecting the alcohol concentration in the fuel; e) failure determination means for determining whether or not the alcohol detection means is malfunctioning; a basic value calculation means for calculating the supply amount; g) a first correction coefficient calculation means for calculating an alcohol correction coefficient for correcting the basic supply amount based on the alcohol concentration in the fuel; and h) an output of the air-fuel ratio detection means. i) a second correction coefficient calculation means for calculating an air-fuel ratio correction coefficient for feedback controlling the air-fuel ratio to a predetermined air-fuel ratio based on the alcohol correction coefficient and the air-fuel ratio correction coefficient; The alcohol correction coefficient is fixed at a constant value, and then the alcohol correction coefficient is corrected according to the value of the air-fuel ratio correction coefficient at that time. and j) determining the amount of fuel to be supplied at the time of startup based on the alcohol correction coefficient set during the previous engine operation when a malfunction of the alcohol detection means is not determined, and when a malfunction of the alcohol detection means is determined; a) a starting control means that determines the fuel supply amount at the time of starting based on the corrected alcohol correction coefficient at the time of subsequent starting; and k) a fuel supplying means that supplies fuel to the engine based on the outputs of the control means and the starting control means. An air-fuel ratio control device for an internal combustion engine, comprising: