JPH076429B2 - Air-fuel ratio controller for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to an internal combustion engine in which different kinds of fuels, for example, gasoline and alcohol can be switched or mixed and used according to the concentration of a reference fuel. The present invention relates to a device for controlling an air-fuel ratio, and more particularly, to a countermeasure technique when an abnormality occurs in a unit for detecting the concentration of reference fuel.

<Prior Art> An air-fuel ratio control device for an internal combustion engine of this type is disclosed in, for example, Japanese Patent Laid-Open No. 56-98540.

This is one that can be used by switching between gasoline and alcohol, or by mixing them. An alcohol sensor for detecting the alcohol concentration in the fuel is provided, and the fuel supply amount is determined based on the detection value of the alcohol sensor. In addition to the control, an O ₂ sensor is provided to detect the air-fuel ratio from the oxygen concentration in the exhaust gas, and during a predetermined operation, feedback control of the fuel supply amount is performed so that the air-fuel ratio approaches the target air-fuel ratio. .

<Problems to be Solved by the Invention> However, in the conventional internal combustion engine corresponding to the use of different types of fuel as described above, when the feedback correction of the fuel supply amount is performed, the feedback correction amount has upper and lower limit values. However, the upper and lower limits are fixed values (for example ±
Since it was set to 25%), there were problems as described below.

That is, when an abnormality occurs in the alcohol sensor, the detected value of the alcohol concentration becomes abnormal, but the feedback correction amount is controlled in the direction of correcting the abnormality of the air-fuel ratio due to the abnormality, and thus the alcohol correction is performed by this feedback correction value. It is conceivable to calibrate the detection value of or substitute for the output of the alcohol sensor.

However, in this case, if the upper and lower limit values are set in conformity with the normal time of the alcohol sensor as described above, the feedback correction value will stick to the upper limit value or the lower limit value,
It is difficult to calculate an accurate value, and in order to eliminate sticking, correction is performed in several steps, so the calculation time also increases, and there is a delay in returning the air-fuel ratio to normal, which impairs drivability. Had a problem.

The present invention has been made in view of such a conventional problem, and by using the alcohol using the above problem, the upper and lower limit values of the feedback correction amount are variably set according to the presence or absence of abnormality of the alcohol sensor. An object is to provide an air-fuel ratio control device for an internal combustion engine.

<Means for Solving the Problems> Therefore, the present invention, as shown in FIG. 1, is an operating state detecting means for detecting an operating state of an internal combustion engine that can be used by switching or mixing different types of fuels, From the fuel supplied to the engine, a fuel concentration detecting means for detecting the concentration of the reference fuel in the fuel, and a basic fuel supply amount based on the detected operating state of the engine and the concentration of the reference fuel. Basic fuel supply amount setting means for setting, air-fuel ratio detecting means for detecting the air-fuel ratio of the air-fuel mixture supplied to the engine,
Feedback correction for setting a feedback correction amount for correcting the basic fuel supply amount set so as to bring the air-fuel ratio closer to the target air-fuel ratio during a predetermined operation based on the air-fuel ratio detection signal from the air-fuel ratio detection means. In the air-fuel ratio control device for an internal combustion engine, the fuel concentration control means comprises: an amount setting means; and a fuel supply amount setting means for setting a fuel supply amount based on the set basic fuel supply amount and feedback correction amount. An abnormality detection unit that detects an abnormality of the detection unit, and an upper limit value and a lower limit value of the feedback correction amount set by the feedback correction amount setting unit when the fuel concentration detection unit is detected to be an abnormality And upper and lower limit value setting means for changing and setting the detecting means in the normal state.

<Operation> The basic fuel supply amount setting means theoretically desires the property of the fuel according to the operating state detected by the operating state detecting means and the reference fuel concentration detected by the fuel concentration detecting means. The basic fuel supply amount is set so as to obtain the air-fuel ratio.

Further, during a predetermined operation, the feedback correction amount setting means corrects the basic fuel supply amount set so that the actual air-fuel ratio detected by the air-fuel ratio detecting means approaches the target air-fuel ratio. The fuel supply amount setting means finally sets the fuel supply amount based on the basic fuel supply amount and the feedback correction amount.

When the abnormality of the fuel concentration detecting means is detected by the abnormality detecting means, the upper and lower limit value setting means accordingly sets the upper limit value and the lower limit value of the feedback correction amount to the normal value of the fuel concentration detecting means. Change the setting so that the correction width is expanded.

As a result, the sticking to the upper limit value or the lower limit value is eliminated, the calibration time of the fuel concentration detecting means and the calculation time of the output substitute value are shortened, and the fail safe function is improved.

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

In FIG. 2 showing the configuration of one embodiment, an engine 1 is provided with an air flow meter 2 for detecting an intake air flow rate in its intake passage, and is attached to a crankshaft or a distributor for each unit crank angle of the engine. A crank angle sensor 3 for outputting a pulse signal is provided, and an O ₂ sensor 4 as air-fuel ratio detecting means for detecting an oxygen concentration in exhaust gas to detect an air-fuel ratio is further provided in the exhaust passage.

Further, the fuel supply pipe for supplying fuel to the engine 1 is provided with an alcohol sensor 5 for detecting the concentration of alcohol as a reference fuel in the mixed fuel of alcohol and gasoline flowing through the fuel supply pipe. The alcohol sensor 5 corresponds to a fuel concentration detecting means.

Detection signals from these sensors are control units
CPU10A via I / O10B of 10 built-in microcomputer
Is input to and calculated by the CPU 10A. In addition, CPU10A, I / O10B, RAM10C, non-volatile
It is configured with RAM10D.

In such a configuration, the fuel injection amount T _I to the fuel injection valve (not shown) mounted in the intake passage of the engine is calculated by the following equation.

T _I = T _P × COEF × α × ALC × K _BLRC + T _S where T _P is the basic fuel injection amount, COEF is various correction factors, α
Is the feedback correction coefficient of the air-fuel ratio, ALC is the concentration correction coefficient set based on the alcohol concentration detected by the alcohol sensor, and _KBLRC is the deviation from the reference center value of the variation center value of α as described later. This is a learning correction coefficient for correcting (caused by changes over time and variations in the fuel injection system). And, for example, α is 75% to 125%, AL
C is 10 to 1.92 (100% gasoline to 95% methanol), K _BLRC
Varies in the range of 0.5 to 2.0.

In this case, the value obtained by correcting the basic fuel injection amount T _P , excluding the feedback correction coefficient α, corresponds to the basic fuel supply amount according to the engine operating condition and the reference fuel (alcohol) concentration. The feedback correction coefficient α corresponds to the feedback correction amount for performing feedback correction of the feedback correction coefficient α according to the air-fuel ratio. Therefore, the microcomputer containing the control unit 10 for performing such calculation has the functions of the basic fuel supply amount setting means, the feedback correction means, and the fuel supply amount setting means.

Next, a routine for detecting an abnormality of the alcohol sensor 5 will be described with reference to FIG.

In step (denoted as S in the figure) 1, the A / D conversion value of the alcohol concentration detection signal from the alcohol sensor 5 is read.

In step 2, it is determined whether or not the amount of change in the alcohol concentration detection value from the previous detection value is within the set range.

When the amount of change is outside the set range, the routine proceeds to step 3, where the NG counter for abnormality detection is incremented, and then proceeds to step 4, where it is determined whether the value of the NG counter is greater than or equal to the set value.

When the value of the NG counter reaches or exceeds the set value, the process proceeds to step 5, and an NG flag indicating that the alcohol sensor 5 is abnormal is set.

That is, it is practically impossible for the alcohol concentration to greatly change. Therefore, when such a state occurs frequently, it is determined that the alcohol sensor 5 is abnormal.

When it is determined in step 2 that the amount of change is within the set range, the process proceeds to step 6, and after clearing the NG counter for detecting abnormality of the alcohol sensor 5, the process proceeds to step 7. When it is determined in step 4 that the value is less than the set value, the process proceeds to step 7.

In step 7, it is determined whether or not the feedback correction control of the air-fuel ratio based on the signal from the O ₂ sensor 4 is currently being executed.

When it is determined that the control is being executed, the process proceeds to step 8 and it is determined whether the uncontrollable clamp is set. This is because the feedback correction control of the air-fuel ratio is executed,
When the value of the feedback correction coefficient α clings to the upper limit value or the lower limit value for a long time and substantially no good feedback correction is performed, this is detected in another routine and the flag of uncontrollable clamp is set. Judge by this.

That is, the fact that the feedback correction coefficient α cannot be completely corrected means that the setting of the basic fuel supply amount is largely deviated from the target air-fuel ratio equivalent value. Alcohol concentration may not be detected.

Next, the routine proceeds to step 9, where it is determined whether or not the feedback control of the idle speed is being performed, depending on whether or not the ISC clamp flag is set. Although this is not shown in the figure, feedback control of the idle speed is performed in which the engine speed approaches the target speed by controlling the air flow rate that bypasses the throttle valve in the intake passage during idle, but in this case, the engine speed is Since it fluctuates around the target rotation speed, the air-fuel ratio may also fluctuate. In this case, since the air-fuel ratio also fluctuates and it is unsuitable as a condition for detecting an abnormality of the alcohol sensor 5, a flag of the ISC clamp set when the feedback control of the idle speed is stopped by another routine is used. It is determined whether or not the feedback control of the idle speed is performed.
However, this determination may directly determine the fluctuation of the engine speed.

Then, in step 9, when the engine speed is stable, such as when the flag of the ISC clamp is set,
When the abnormal conditions of the alcohol sensor 5 in steps 7 and 8 are satisfied, it is judged that the alcohol sensor 5 is abnormal, and the process proceeds to step 5 to set the NG flag.

Next, the fail-safe control routine when the alcohol sensor 5 is determined to be abnormal by the above routine will be described with reference to the flowchart shown in FIG.

In step 11, the concentration correction coefficient AL of the alcohol sensor 5
C is fixed to the median value, for example, the value when the alcohol concentration is 40 to 50%.

Next, the routine proceeds to step 12, where it is judged whether or not the air-fuel ratio feedback correction control is being performed as in step 7 of the routine.

If it is determined that it is performed, go to step 13,
Upper limit value α _MAX and lower limit value α of the feedback correction coefficient α
_MIN is set by changing the alcohol sensor 5 by a predetermined ratio with respect to the normal value of the alcohol sensor 5, for example, increasing the correction width by 50%. In the above example, α changes in the range of 75 to 125% at the normal time, but it can change in the range of 50 to 150%. The function of step 13 corresponds to the upper and lower limit value setting means.

As a result, the setting error of the basic fuel supply amount due to the abnormality of the alcohol sensor 5 can be absorbed by expanding the setting range of the feedback correction coefficient α, and the air-fuel ratio becomes the target air-fuel ratio in a short time after the abnormality detection. Since it can be stabilized, the operation of the engine can be continued without any trouble.

If the upper and lower limit values are not changed, as soon as the alcohol sensor 5 becomes abnormal, the feedback correction coefficient α clings to the upper limit value or the lower limit value and cannot absorb the deviation of the air-fuel ratio. However, when the learning correction coefficient K _BLRC is provided as in the present embodiment, the feedback correction coefficient α
Is corrected to the reference value, the correction is gradually performed so as to eliminate the sticking, but it takes time, and the deterioration of the driving condition is unavoidable.

Further, since the above learning is not performed during the transient operation, the adverse effect on the drivability is great.

In the steady operation, the control for changing the upper and lower limit values is not performed (the abnormality determination of the alcohol sensor 5 is not performed),
Alternatively, in addition to the above control during steady operation, the upper and lower limit values may be changed depending on the length of time during which the feedback correction coefficient α clings to the upper and lower limit values during transient operation. Accordingly, the clinging time may be variably set. This is because the sticking time increases as the degree of transition increases and the deviation of the detected value of the alcohol concentration increases.

<Effects of the Invention> As described above, according to the present invention, since the abnormality of the fuel concentration detecting means is detected and the upper and lower limit values of the feedback correction amount of the air-fuel ratio are changed, the air-fuel ratio can be maintained even when there is an abnormality. It is possible to quickly stabilize the engine and thus continue the operation of the engine without any trouble.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, and FIG. 2 is
FIG. 3 is a diagram showing a configuration of an embodiment of the present invention, FIG. 3 is a flow chart showing a routine for detecting an abnormality of an alcohol sensor in the same embodiment, and FIG. 4 is a flow chart showing fail safe control at the time of abnormality detection. is there. 1 ... Engine, 2 ... Air flow meter, 3 ... Crank angle sensor, 4 ... O ₂ sensor, 5 ... Alcohol sensor,
10 ... Control unit

Claims (1)

[Claims] 1. An operating state detecting means for detecting an operating state of an internal combustion engine, which can be used by switching or mixing different types of fuel, and a reference fuel in the fuel from the fuel supplied to the engine. Fuel concentration detection means for detecting the concentration, basic fuel supply amount setting means for setting the basic fuel supply amount based on the detected operating state of the engine and the reference fuel concentration, and the air-fuel mixture supplied to the engine. The air-fuel ratio detection means for detecting the air-fuel ratio of, and based on the air-fuel ratio detection signal from the air-fuel ratio detection means, the basic fuel supply amount set to bring the air-fuel ratio close to the target air-fuel ratio during a predetermined operation. Feedback correction amount setting means for setting a feedback correction amount for correction, and fuel supply amount setting means for setting a fuel supply amount based on the set basic fuel supply amount and feedback correction amount. In an air-fuel ratio control device for an internal combustion engine comprising: an abnormality detecting means for detecting an abnormality of the fuel concentration detecting means, and the feedback correction amount setting means when the fuel concentration detecting means is detected to be abnormal. An air-fuel ratio control of an internal combustion engine, characterized in that it comprises upper and lower limit value setting means for changing the upper limit value and the lower limit value of the established feedback correction amount with respect to the normal time of the fuel concentration detecting means. apparatus.