JPH0291435A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To continue the engine operation without any trouble by constantly varying the fuel concentration output at a specific rate until the air-fuel ratio detection signal is inverted with respect to the target air-fuel ratio, when an error of a fuel concentration detecting means is detected, and then fixing the output to the value gained at the inverted time. CONSTITUTION:According to both the operation state detected by an operation state detecting means and the basic concentration of fuel detected by a fuel concentration detection means, a basic fuel supply quantity setting means sets the basic quantity of fuel supplied During the specified operation, a feedback correction quantity setting means sets the feedback correction quantity as to approach the air fuel ratio detected by an air fuel ratio detecting means to the target air fuel ratio, and finally, a fuel supply quantity setting means sets the quantity of fuel supplied. When an error of the fuel concentration detecting means is detected by an error detecting means, the fuel concentration setting means varies the fuel concentration output at the constant rate until air and fuel mixture changes from the rich to the lean range or vice versa with respect to the target air fuel ratio and finally, fixes the value of the inverted point.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides an internal combustion engine that can use different types of fuel, such as gasoline and Alsil, by switching or mixing them. The present invention relates to a device for controlling an air-fuel ratio, and in particular to a countermeasure technique when an abnormality occurs in a means for detecting the concentration of a reference fuel.

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

This device allows gasoline and alcohol to be used by switching or mixing them, and is equipped with an alcohol sensor that detects the alcohol concentration in the fuel, and adjusts the amount of fuel supplied based on the detected value of the alcohol sensor. At the same time, an 02 sensor is installed to detect the air-fuel ratio based on the oxygen concentration in the exhaust gas, and during a predetermined operation, feedback correction is performed on the fuel supply amount 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 that is compatible with the use of different types of fuel as described above, if an abnormality occurs in the alcohol sensor, the detected value of alcohol concentration becomes abnormal, and this erroneous Since the fuel supply amount is set based on the detected value, when the air-fuel ratio is not subjected to feedback control, the air-fuel ratio deviates significantly, and even during feedback control, it cannot be corrected with the feedback correction amount, resulting in a large deviation in the air-fuel ratio. Therefore, control of ignition timing and the like is impaired, which in turn impairs engine operating performance and exhaust emission characteristics, which may lead to engine seizure or engine stalling.

The present invention has been made in view of the above-mentioned conventional circumstances, and is designed to prevent malfunctions of the fuel concentration detection means by changing the fuel concentration output when the fuel concentration detection means is detected to be abnormal. The aim is to improve engine operating performance and exhaust emission characteristics by addressing these issues.

Means for Solving the Problems> Therefore, as shown in FIG. 1, the present invention provides an operating state detection means for detecting the operating state of an internal combustion engine that can be used by switching or mixing different types of fuel. a fuel concentration detection means for detecting a reference fuel concentration in the fuel supplied to the engine; and a basic fuel supply based on the detected operating state of the engine and the reference fuel concentration. basic fuel supply amount setting means for setting the amount, air-fuel ratio detection means for detecting the air-fuel ratio of the air-fuel mixture supplied to the engine, and air-fuel ratio detection signal from the air-fuel ratio detection means, feedback correction amount setting means for setting a feedback correction amount for correcting the set basic fuel supply amount so as to bring the air-fuel ratio closer to the target air-fuel ratio; An air-fuel ratio control device for an internal combustion engine, comprising: a fuel supply amount setting means for setting a fuel supply amount based on the fuel concentration detection means; and an abnormality detection means for detecting an abnormality in the fuel concentration detection means; is detected, the fuel concentration output of the fuel concentration detection means is controlled at a constant rate until the air-fuel ratio detection signal from the air-fuel ratio detection means reverses from rich to lean or from lean to rich with respect to the target air-fuel ratio. The fuel concentration setting means is configured to change the fuel concentration and then fix it at the value when it is reversed.

Function> The basic fuel supply amount setting means theoretically determines the desired fuel property based on the operating state detected by the operating state detecting means and the reference fuel concentration detected by the fuel concentration detecting means. Set the basic fuel supply amount to a value that provides the air-fuel ratio.

Further, during a predetermined operation, the feedback correction amount setting means sets a feedback correction amount for correcting the set basic fuel supply amount so that the actual air-fuel ratio detected by the air-fuel ratio detection 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 an abnormality in the fuel concentration detection means is detected by the abnormality detection means, the fuel concentration setting means changes the air-fuel ratio detection signal from the air-fuel ratio detection means from rich to lean or from lean to the target air-fuel ratio. The fuel concentration output of the fuel concentration detecting means is changed at a constant rate until the fuel concentration is reversed to rich, and then fixed at the value when the fuel concentration is reversed.

Since the air-fuel ratio when the air-fuel ratio detection signal is inverted substantially corresponds to the target air-fuel ratio, the fuel concentration setting value at this time indicates a value that substantially matches the actual fuel concentration.

Therefore, good air-fuel ratio control can be achieved by clamping to this value.

<Example> Embodiments of the present invention will be described below based on the drawings.

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

Further, a fuel supply pipe that supplies fuel to the engine 1 is provided with an alcohol sensor 5 that detects 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 fuel concentration detection means.

Detection signals from these sensors are input to the CPU UIOA via the microcomputer 11010B built in the control unit 10, and are calculated by the CPU 10A. Furthermore, the microcomputer is CPU10A.
, l10IOB, RAMl0C, non-volatile RAMl0
D.

In this configuration, the fuel supply amount Ti to the fuel injection valve (not shown) installed in the intake passage of the engine is calculated by the following equation.

Ti=2X(TpXC0EFxαxKMET) 10Ts Here, Tp is the basic fuel supply amount,
The basic fuel supply amount Tp = -Q/N (K is a constant) is calculated from the intake air mIQ detected based on the signal from the crank angle sensor 3 and the engine rotation speed N calculated based on the signal from the crank angle sensor 3. be done.

That is, the air flow meter 2 and the crank angle sensor 3 constitute operating state detection means.

Further, C0EF is various correction coefficients, α is a feedback correction coefficient of the air-fuel ratio, and KMET is 1.0 as the concentration of the reference fuel (alcohol) increases as shown in FIG.
This is a concentration correction coefficient for the alcohol sensor that increases from 0.

In this case, the value obtained by correcting the basic fuel supply amount Tp, excluding the feedback correction coefficient α, corresponds to the operating state of the engine.
This corresponds to the basic fuel supply amount depending on the concentration of the reference fuel (alcohol), and the feedback correction coefficient α corresponds to the feedback correction amount for feedback-correcting it depending on the air-fuel ratio. Therefore, the microcomputer built into the control unit 10 that performs such calculations has the functions of basic fuel supply amount setting means, feedback correction means, and fuel supply means.

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

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

In step 2, it is determined whether the amount of change in the detected alcohol concentration value from the previous detected value is within a set range.

If the amount of change is outside the set range, the process proceeds to step 3, where an NG flag indicating that the alcohol sensor 5 is abnormal is set.

That is, since it is actually impossible for the alcohol concentration to change to be extremely large, when such a situation occurs, it is determined that the alcohol sensor 5 is abnormal.

Further, if it is determined in step 2 that the amount of change is within the set range, the process proceeds to step 4.

In step 4, it is determined whether the air-fuel ratio feedback correction control based on the signal from the 0□ sensor 4 described above is currently being executed.

If it is determined that the process is being executed, the process proceeds to step 5, where it is determined whether or not the uncontrollable clamp is set.

This is when the feedback correction control of the air-fuel ratio is executed, but the feedback correction coefficient αΦ value sticks to the upper limit value or the lower limit value for a long time, and good feedback correction is not actually performed. This is detected in a separate routine and a flag indicating an uncontrollable clamp is set, so the determination is made based on this.

In other words, the alcohol sensor is corrected by the feedback correction coefficient α, and if it continues for 4 times, it means that the setting of the basic fuel supply amount has a large deviation from the value equivalent to the target air-fuel ratio. 5 may not be correctly detecting the alcohol concentration (see Figure 5).

Next, the process proceeds to step 6, where it is determined whether or not feedback control of the idle rotation speed is being performed, based on whether or not the lSC clamp flag is set. Although not shown, feedback control of the engine speed is performed to bring the engine speed closer to the target speed by controlling the flow rate of air that bypasses the throttle valve in the intake passage during idling. Since the engine speed fluctuates around the target rotational speed, the air-fuel ratio may also fluctuate.

In this case, the air-fuel ratio also fluctuates and is inappropriate as a condition for detecting an abnormality in the alcohol sensor 5. Therefore, the lSC clamp flag that is set when the feedback control of the idle speed is stopped by another routine is used. , determines whether or not there is feedback control of the idle rotation speed. However, this determination may be made by directly determining the fluctuation in engine speed.

Then, in step 6, when the engine speed is stable, such as when the lSC clamp flag is set, and the alcohol sensor 5 abnormal conditions in steps 4 and 5 are satisfied, the alcohol sensor 5 It is determined that this is abnormal, and the process proceeds to step 3, where an NG flag is set.

Therefore, the routine described above corresponds to the abnormality detection means.

Next, a fail-safe control routine when the alcohol sensor 5 is determined to be abnormal according to the above routine will be described.

First, an overview of air-fuel ratio feedback control will be explained.

0□Sensor 4 is sensitive to the oxygen concentration in the exhaust gas, and when the air-fuel ratio is lower than the target value of the stoichiometric air-fuel ratio, the output becomes H level, and when it is lean. , the output becomes L level.

Therefore, when rich is detected, the air-fuel ratio feedback correction coefficient α is gradually decreased in order to reduce the fuel supply amount in order to make the air-fuel ratio leaner, and when lean is detected, the fuel supply amount is increased in order to make the air-fuel ratio richer. Increase the feedback correction coefficient α.

Therefore, during air-fuel ratio feedback control, the air-fuel ratio is alternately in a rich state and a lean state at a substantially constant cycle. Then, when the alcohol sensor 5 normally detects the fuel mixture ratio, the basic fuel supply 1iTp is set corresponding to the stoichiometric air-fuel ratio based on the detected value, so in the air-fuel ratio feedback control. In the air-fuel ratio, the time ratio in which the air-fuel ratio is rich is approximately equal to the time ratio in which the air-fuel ratio is lean.

However, as shown in Fig. 6, if an abnormality occurs in the alcohol sensor 5, such as when the output becomes 0 due to a disconnection, the control unit 0 determines that the alcohol percentage is 0% and reduces the fuel supply amount. Since the amount is set to be less than the required amount, the output of the 02 sensor 4 continues to be at the L level. In this case, the air-fuel ratio feedback correction coefficient α reaches its maximum value and becomes constant, resulting in a prolonged lean time of the air-fuel ratio.

Here, the fail-safe control routine will be explained according to the flowchart shown in FIG.

First, in step 11, it is determined whether the output of the 0□ sensor 4 is higher or lower than the slice level.

l) level, as mentioned above, the output of the alcohol sensor 5 becomes O due to a wire breakage, etc., that is, the alcohol sensor 5 is abnormal and the fuel supply amount is set to be less than the required amount. Determining, in step 12,
The A/D conversion value ALC of the alcohol concentration detection signal is set to be increased by a certain percentage C, (CI > O) (see FIG. 6).

Since the air-fuel ratio becomes richer by increasing the ALC, in step 13, it is determined whether the air-fuel ratio has reached the stoichiometric air-fuel ratio which is the target air-fuel ratio, that is, the output of the 0□ sensor 4 has changed from the to I level. It is determined whether or not it has been inverted to L level.

In step 13, if the output of the 0□ sensor 4 is inverted, it is determined that air-fuel ratio feedback control can be performed by increasing or decreasing the air-fuel ratio feedback correction coefficient α during feedback control, and step Proceeding to step 14, the A/D conversion value ALC of the alcohol concentration detection signal set in step 12 is clamped (see FIG. 6). Here, the clamped ALC is canceled at the time of fuel replacement or restart, and fail-safe control is performed according to the new reference fuel concentration.

Note that in step 13, 0. If the output of the sensor 4 is not inverted, the process returns to step 12 and the ALC is increased again.

On the other hand, in step 11, when the output of the 0□ sensor 4 is at L level than the slice level, it is determined that the fuel supply amount is set to be larger than the required amount, and step 15
, the A/D conversion value AL of the alcohol concentration detection signal
C is set by decreasing C by a certain percentage C, (C2>0).

Since the air-fuel ratio becomes lean by decreasing the ALC, in step 16, it is determined whether the air-fuel ratio has reached the stoichiometric air-fuel ratio which is the target air-fuel ratio, that is, whether the output of the sensor 4 has changed from the L level to the H level. Determine whether the level has been reversed.

In step 16, if the output of the 0□ sensor 4 is inverted, the A/D conversion value ALC of the alcohol concentration detection signal set in step 15 is clamped.

Step 12 explained above. The functions of step 14 and step 15 correspond to fuel concentration setting means.

Therefore, the A/D conversion value ALC of the alcohol concentration detection signal
is increased or decreased and then clamped depending on whether or not the air-fuel ratio reaches the stoichiometric air-fuel ratio which is the target air-fuel ratio, so the concentration correction coefficient of the alcohol sensor is similarly increased or decreased and clamped. Therefore, when the alcohol sensor 5 becomes abnormal, there are cases where the basic fuel supply amount is supplied according to the concentration of the reference fuel (alcohol), and cases where the basic fuel supply amount is fed back according to the air-fuel ratio. Even when the air-fuel ratio is corrected and supplied, air-fuel ratio control is performed without the air-fuel ratio deviating significantly from the stoichiometric air-fuel ratio, which is the target air-fuel ratio. Therefore, it becomes possible to perform optimal fail-safe control, and it becomes possible to improve engine operating performance and exhaust emission characteristics.

<Effects of the Invention> As explained above, according to the present invention, when an abnormality is detected in the fuel concentration detection means, the fuel concentration output is changed at a constant rate until a predetermined state is reached, and then fixed at a predetermined value. Even in the event of an abnormality, the air-fuel ratio will not deviate significantly from the stoichiometric air-fuel ratio, which is the target air-fuel ratio, and the air-fuel ratio can be quickly stabilized, allowing the engine to continue operating without any problems. It is possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 3 is a diagram showing changes in the concentration correction coefficient of the alcohol sensor in the same embodiment.
FIG. 4 is a flowchart showing a routine for detecting an abnormality in the alcohol sensor in the above embodiment, FIG. 5 is a diagram showing a deviation in fuel supply amount when the alcohol sensor is abnormal in the above embodiment, and FIG. FIG. 7, which is a diagram illustrating the operation, is a flowchart showing fail-safe control when an abnormality is detected. 1... Engine 2... Air flow meter 3...
・Crank angle sensor 4...0□7 sensor 5...
・Alcohol sensor 10... Control unit patent applicant Japan Electronics Co., Ltd. Agent Patent attorney Fujio Sasashima Figure 3 Figure 5

Claims (1)

[Claims] An operating state detection means for detecting the operating state of an internal combustion engine that can be used by switching or mixing different types of fuel; and a fuel for detecting the concentration of a reference fuel in the fuel supplied to the engine. a concentration detection means, a basic fuel supply amount setting means for setting a basic fuel supply amount based on the detected operating state of the engine and a reference fuel concentration, and detecting an air-fuel ratio of the air-fuel mixture supplied to the engine. an air-fuel ratio detection means,
Feedback correction that sets a feedback correction amount for correcting the set basic fuel supply amount so that the air-fuel ratio approaches the target air-fuel ratio during a predetermined operation based on the air-fuel ratio detection signal from the air-fuel ratio detection means. and a fuel supply amount setting means for setting the fuel supply amount based on the set basic fuel supply amount and the feedback correction amount, the air-fuel ratio control device for an internal combustion engine comprising: an abnormality detection means for detecting an abnormality in the detection means, and an air-fuel ratio detection signal from the air-fuel ratio detection means when the fuel concentration detection means is detected to be abnormal; An air conditioner for an internal combustion engine characterized by comprising: fuel concentration setting means for changing the fuel concentration output of the fuel concentration detection means at a constant rate until the fuel concentration is reversed to rich, and then fixing it at the value when the fuel concentration is reversed. Fuel ratio control device.