JPH0385347A - Fuel supply controller of internal combustion engine using heterogeneous fuel - Google Patents

Abstract

PURPOSE:To keep good control at unusual time when the abnormal situation comes in a reference fuel concentration detecting means, by forcibly changing the concentration to a direction where a direction of increasing or reducing compensation of the fuel supply is reversed, and by controlling the fuel supply based o the concentration at the point where the direction of increasing or reducing compensation is reversed. CONSTITUTION:The amount of fuel supply is controlled by a fuel supply controlling means B based on a driving condition including a detected concentration valve by a reference fuel concentration detecting means A, while the amount of fuel supply is feedback-compensated by an air-fuel ratio feedback controlling means D based on the air-fuel ratio by an air-fuel ratio detecting means C. When the abnormality of the reference fuel detecting means A is detected by an abnormality detecting means E, the detected concentration value is forcibly changed to a direction where a direction of increasing or reducing compensation of the amount of fuel supply is reversed, by a concentration forcibly changing means F, and the fuel supply control is performed based on the changed value. The detected concentration value at the point where the direction of increasing or reducing compensation is reversed is fixed as a fail safe concentration by a fail safe concentration setting means G.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a fuel supply control device for an internal combustion engine that uses different types of fuel, and more specifically, for an internal combustion engine that can use different types of fuel by switching or mixing them. The present invention relates to a technique for improving fail-safe control when a sensor that detects the concentration of reference fuel in fuel supplied to an engine is abnormal.

<Prior Art> As an internal combustion engine that can be used by switching or mixing different types of fuel, there is, for example, one disclosed in Japanese Patent Laid-Open No. 56-98540.

This product is designed to be able to use gasoline and alcohol by switching or mixing them, and is equipped with an alcohol sensor that detects the alcohol concentration, which is the reference fuel, in the fuel, and the detection value of the alcohol) Lt sensor. In addition to correcting and controlling the fuel supply amount based on the amount, an oxygen sensor is provided to detect the oxygen concentration in the exhaust gas, and the actual air-fuel ratio is compared to the target air-fuel ratio through the oxygen concentration in the exhaust gas detected by the oxygen sensor. Rich/lean conditions are detected, and in a predetermined operating state, feedback correction control of the fuel supply amount is performed based on the detection results so that the actual air-fuel ratio approaches the target air-fuel ratio.

<Problems to be Solved by the Invention> By the way, in the conventional internal combustion engine that supports the use of different types of fuels as described above, when the alcohol sensor becomes abnormal and outputs a false detection value, this false alcohol Because the fuel supply amount is incorrectly set based on the detected concentration value, the air-fuel ratio deviates significantly from the target air-fuel ratio when air-fuel ratio feedback control is not performed, and
Even when air-fuel ratio feedback control is performed,
Feedback correction may not be able to fully correct the problem, resulting in a large air-fuel ratio deviation.

For this reason, there is a problem that when the alcohol sensor is abnormal, the engine operating performance and exhaust characteristics deteriorate.In order to solve this problem, the applicant has proposed a method for detecting the concentration of alcohol sensor when the alcohol sensor is abnormal. When the value is forcibly changed at a fixed rate and the air-fuel ratio detected through the oxygen concentration in the exhaust gas detected by the oxygen sensor installed in the exhaust passage is reversed, that is, the air-fuel ratio detected by the oxygen sensor is We previously proposed a control device configured to fix the concentration detected value when approximately the target air-fuel ratio is reached, and control the fuel supply amount, etc. based on this fixed concentration (Japanese patent application No. 6).
3-242273).

By the way, as shown in Fig. 6, if the alcohol sensor becomes abnormal while performing air-fuel ratio feedback control, a large air-fuel ratio deviation occurs due to the abnormal concentration detection value, and it is difficult to eliminate this air-fuel ratio deviation. As a result, the air-fuel ratio feedback correction coefficient LAMBDA is set to increase or decrease so that it sticks to the limit value. Here, if the detected concentration value is forcibly changed to bring it closer to the true concentration, it becomes possible to perform a correction that can reverse the air-fuel ratio using the correction coefficient LANBDA, which is the limit value, and the detected value is detected by the oxygen sensor. Since the air-fuel ratio is reversed, the alcohol concentration is fixed at this point according to the device previously proposed by the present applicant.

However, if the alcohol concentration is fixed when the oxygen sensor is first reversed, the target air-fuel ratio will be obtained near the limit value of the air-fuel ratio feedback correction coefficient LAMBDA. will be changed around the limit value,
There was a problem in that the correction coefficient LAMBDA stuck to the limit value during the control, making it impossible to perform good feedback control, and as a result, the target air-fuel ratio could not be obtained with high accuracy.

That is, according to the fail-safe control previously proposed by the present applicant, if a sensor abnormality occurs during air-fuel ratio feedback control, the limit that can be corrected by air-fuel ratio feedback correction control is exceeded before the alcohol concentration changes to the true alcohol concentration. When the concentration changes to an error level, the concentration has been fixed at that point, and for this reason, after the fail-safe concentration is fixed, feedback control is performed near the limit value, resulting in good fail-safe performance. It's something that didn't exist.

The present invention has been made in view of the above problems, and when an abnormality occurs in the alcohol sensor during air-fuel ratio feedback control, the air-fuel ratio feedback control is improved by setting a fail-safe concentration close to the true concentration. It is an object of the present invention to provide a fuel supply control device that can accurately obtain a target air-fuel ratio even when a sensor is abnormal.

<Means for Solving the Problems> Therefore, the present invention provides an internal combustion engine that can be used by switching or mixing different types of fuel, as shown in FIG. a reference fuel concentration detection means for detecting a reference fuel concentration; a fuel supply control means for controlling the amount of fuel supplied to the engine based on operating conditions including at least a concentration value detected by the reference fuel concentration detection means; air-fuel ratio detection means for detecting whether the air-fuel ratio of the intake air-fuel mixture is rich or lean with respect to the target air-fuel ratio; and air-fuel ratio feedback for feedback correction control of the fuel supply amount so as to bring the detected air-fuel ratio closer to the target air-fuel ratio. A fuel supply control device for an internal combustion engine using different types of fuel, comprising: an abnormality detecting means for detecting an abnormality in the reference fuel concentration detecting means; and an abnormality detecting means for detecting an abnormality in the reference fuel concentration detecting means; Concentration forced change that gradually forcibly changes the detected value in a direction that reverses the direction of increase/decrease correction of the fuel supply amount by the air-fuel ratio feedback control means, and controls the fuel supply amount by the fuel supply control means based on this change value. and fixing the detected concentration value as a fail-safe concentration when the direction of increase/decrease correction of the fuel supply amount by the air-fuel ratio feedback control means is reversed while the detected concentration value is forcibly changed by the forced concentration changing means. A fail-safe concentration setting means is provided.

<Operation> According to this configuration, the reference fuel concentration detection means detects the reference fuel concentration in the fuel supplied to the engine, and the fuel supply control means controls the fuel supply based on the operating conditions including at least the basic fuel concentration. Control quantity. On the other hand, the air-fuel ratio feedback control means controls the richness of the air-fuel ratio of the engine intake air-fuel mixture detected by the air-fuel ratio detection means with respect to the target air-fuel ratio.
Based on lean, the fuel supply amount is feedback corrected and controlled so that the actual air-fuel ratio approaches the target air-fuel ratio.

Here, when the abnormality detection means detects an abnormality in the reference fuel concentration detection means, the concentration forced change means gradually forcibly changes the concentration detection value in the direction of reversing the increase/decrease correction direction in the air-fuel ratio feedback control. Fuel supply amount control is performed based on the change value. The fail-safe concentration setting means determines the concentration detected value when the direction of increase/decrease correction of the fuel supply amount by the feedback control means is reversed while the detected value of the reference fuel concentration is forcibly changed as described above. is fixed as a fail-safe concentration.

Therefore, when a large increase/decrease correction is performed by the feedback control means, the detected concentration value is forced to change continuously, and the correction ratio by the feedback correction becomes smaller, resulting in a change in the correction direction when the correction direction is reversed. Since the concentration is fixed, the fail-safe concentration is set to a concentration close to the true concentration that does not require large feedback correction, and subsequent feedback correction control is performed near the reference value for increase/decrease correction to achieve the target empty concentration. The fuel ratio can now be obtained with high accuracy.

<Example> The present invention will be explained in detail below.

In FIG. 2 showing one embodiment, an engine 1 is configured to be able to use alcohol mixed fuel by switching between gasoline and alcohol as fuel, or by mixing these. Duct 3
．． Air is taken in via the throttle valve 4 and the intake manifold 5.

A fuel injection valve 6 is provided in a branch portion of the intake manifold 5 for each cylinder. The fuel injection valve 6 includes:
This is an electromagnetic fuel injection valve that opens when the solenoid is energized and closes when the energization is stopped. The pressure regulator then injects and supplies fuel that has been adjusted to a predetermined pressure.

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

An ignition plug 7 is provided in the combustion chamber of the engine 1, which ignites a spark to ignite and burn the air-fuel mixture.

From engine 1, exhaust manifold 8° exhaust duct 9. Exhaust gas is discharged via a three-way catalyst 10 and a muffler 11. The three-way catalyst 10 is an exhaust purification device that oxidizes Co and HC in the exhaust components, and also reduces NOx and converts it into other harmless substances, and when the air-fuel mixture is burned at the stoichiometric air-fuel ratio The reconversion efficiency is the best.

The control unit 12 includes a CPU and a ROM.

Equipped with a microcomputer that includes a RAM, an A/D converter, an input/output interface, etc., it receives input signals from various sensors, performs arithmetic processing as described later, and operates the fuel injection valve 6. Control.

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

Further, a crank angle sensor 14 is provided, and in the case of a four-cylinder engine, outputs a reference signal REF for each crank angle of 180 degrees and a unit angle signal PO5 for every crank angle l@ or 2 degrees. Here, the engine rotational speed N can be calculated by measuring the cycle of the reference signal REF or the number of occurrences of the unit angle signal PO3 within a predetermined period of time.

Further, a water temperature sensor 15 and the like for detecting the cooling water temperature Tw of the water jacket of the engine 1 are provided.

Further, an oxygen sensor 16 as an air-fuel ratio detecting means is provided at the gathering part of the exhaust manifold 8, and detects the air-fuel ratio of the air-fuel mixture taken into the engine 1 via the oxygen concentration in the exhaust gas.

The oxygen sensor 16 is a known sensor whose output changes suddenly around the stoichiometric air-fuel ratio, and which detects whether the actual air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio based on the output.

Further, an alcohol sensor 17 as a reference fuel concentration detection means for detecting the alcohol concentration MET, which is the reference fuel in the fuel supplied to the fuel injection valve 6, is installed in a fuel supply pipe or a fuel tank (not shown) on the upstream side of the fuel injection valve 6. It is set in.

Here, the microcomputer built in the control unit 12 performs arithmetic processing according to the program on the ROM shown in the flowcharts of FIGS. 3 and 4, controls fuel injection, and controls the alcohol sensor 1.
7 Perform fail-safe control in the event of an abnormality.

In this embodiment, the functions of the abnormality detection means, concentration forced change means, fuel supply control means, air-fuel ratio feedback control means, and fail-safe concentration setting means are as shown in the flowcharts of FIGS. 3 and 4. is equipped with software.

The program shown in the flowchart of FIG. 3 is executed at every predetermined minute time (for example, IoIls),
First, in step l (indicated as Sl in the figure; the same applies hereinafter), the intake air flow rate Q detected by the air flow meter 13 and the engine rotational speed N calculated based on the detection signal from the crank angle sensor 14 are used. Then, the basic fuel injection amount (basic fuel supply amount) Tp (4-KXQ/N; K is a constant) is calculated.

In step 2, various correction coefficients C0EF are set, mainly based on the cooling water temperature Tw detected by the water temperature sensor 15, including corrections for increasing the amount at startup and increasing when the engine is cold.

In step 3, the air-fuel ratio feedback correction coefficient L is used to bring the actual air-fuel ratio closer to the target air-fuel ratio (theoretical air-fuel ratio).
A? Set 1BDA (reference value = 1) using proportional-integral control. This air-fuel ratio feedback correction coefficient LAMBD
The proportional-integral control of A is shown in steps 11 to 17 of the flowchart in FIG.

That is, first, in step 11, by comparing the output voltage Vow of the oxygen sensor 16 and the slice level voltage SL corresponding to the stoichiometric air-fuel ratio, it is determined that the actual air-fuel ratio is richer than the stoichiometric air-fuel ratio. Determine whether When it is determined that the air-fuel ratio is rich, the process proceeds to step 12, where it is determined whether or not the current rich determination is the first time. When rich determination is performed for the first time, proceed to step 14;
Previous air-fuel ratio feedback correction coefficient LANBDA
The amount of fuel supplied is reduced by subtracting a predetermined proportional amount P from . On the other hand, if it is determined in step 12 that the rich determination is not the first time, the process proceeds to step 13, where a predetermined integral ■ is subtracted from the air-fuel ratio feedback correction coefficient LAMBDA up to the previous time, and this predetermined integral is subtracted until the rich state is eliminated. Repeat the integral decrease setting by ■.

Further, when it is determined that the air-fuel ratio is lean in step 11, as in the case of rich determination, if it is the first time, an additional correction is made by a predetermined ratio, and if it is not the first time, an additional correction is made by a predetermined integral. However, by increasing the air-fuel ratio feedback correction coefficient LAMBDA, the amount of fuel supplied is increased, and the lean state of the air-fuel ratio is eliminated.

Furthermore, the predetermined proportional component P and integral component! may be configured to be set variably based on, for example, the basic fuel injection amount Tp and the engine rotational speed N, or may be a fixed value. In addition, the air-fuel ratio feedback correction coefficient LAMBDA
is not limited to proportional-integral control, but may also include differential control or a combination of proportional control and differential control.

In the next step 4, an alcohol concentration correction coefficient KMET is set based on the alcohol concentration MET in the supplied fuel detected by the alcohol sensor 17. this is,
This is to compensate for differences in stoichiometric air-fuel ratio due to alcohol concentration.

In step 5, a voltage correction numerator s is set for correcting a change in the invalid opening time of the electromagnetic fuel injection valve 6 due to the battery voltage.

Then, in the next step 6, the basic fuel injection amount Tp is corrected according to the following formula to set the final fuel injection amount (fuel supply amount) Ti.

T i + T p X Co E F XLAMBDAX
KMET+T s In the next step 7, the fuel injection amount Ti is set in the output register. As a result, at a predetermined fuel injection timing, the latest fuel injection amount Ti set in this output register is read out, and a drive pulse signal with a pulse width corresponding to this fuel injection amount Ti is applied to the fuel injection valve 6. As a result, fuel is injected and supplied to the engine l.

By the way, since the alcohol concentration correction coefficient KMET used to calculate the fuel injection amount Ti is set based on the detected value of the alcohol sensor 17 as described above, the alcohol concentration correction coefficient KMET used in calculating the fuel injection amount Ti is set based on the detected value of the alcohol sensor 17. If a detected value that is significantly different from the concentration is output, the air-fuel ratio controllability will deteriorate and drivability will be affected.For this reason, a fail-safe control function in the event of an abnormality of the alcohol sensor 17 is implemented. are provided as shown from step 18 onward in the flowchart of FIG.

In step 18, abnormality determination of the alcohol sensor 17 is performed. An abnormality can be determined, for example, when the air-fuel ratio feedback correction coefficient LAMBDA has reached a predetermined limit value (for example, ±25%) and the correction coefficient LAMBDA has remained at the limit value for a predetermined period of time or more, or when the alcohol sensor When the detected value by No. 17 suddenly changes by a predetermined rate or more, it is regarded as abnormal.

If it is determined in this step 18 that the alcohol sensor 17 is abnormal, the process proceeds to step 19 and it is determined whether or not the predetermined fail-safe control has been completed. In this embodiment, when the alcohol sensor 17 becomes abnormal, A fail-safe concentration close to the true alcohol concentration is set instead of the detected value of the alcohol sensor 17, and the alcohol concentration correction coefficient KMET is set based on this fail-safe concentration. Indicates whether the density is set.

If it is determined in step 19 that fail-safe control has not been completed, the process advances to step 20.

In step 20, it is determined whether the previous air-fuel ratio feedback correction coefficient LAMBDA was larger or smaller than the reference value 1, that is, the previous correction coefficient LAMBDA.
It is determined whether the fuel supply amount has been corrected to increase or decrease.

If it is determined in step 20 that the previous correction coefficient LAMBDA was less than 1 and that a reduction has been made, then in step 21 the correction coefficient LAMBDA set in steps 11 to 17 this time is compared with the reference value (1). compare.

If the current correction coefficient LAMBDA is also less than 1 and a reduction correction is still required, the alcohol concentration MET is excessive due to a sensor abnormality, so the fuel supply amount Tt is greater than the amount equivalent to the stoichiometric air-fuel ratio. The process proceeds to step 22 and corrects the alcohol concentration MET by decreasing it by a predetermined value.

On the other hand, when the previous correction coefficient LAMBDA was used for decreasing correction, but this time it is reversed to increasing correction, that is,
When it is determined in step 21 that the current correction coefficient LAMBDA is 1 or more, there is no need for a large proportion of correction by the correction coefficient LAMBDA, and the correction coefficient LAMBDA
Since the fuel injection amount Ti, which is approximately the stoichiometric air-fuel ratio without A, is set, the current alcohol concentration MET can be considered to be close to the true concentration, so this should be fixed as the fail-safe concentration. , the process advances to step 25 to instruct fail-safe completion.

Also, in step 20, the previous correction coefficient LAMBDA is 1.
If the above is the case and it is determined that the increase correction has been made, it is determined in step 23 whether the current correction coefficient LAMBDA is larger or smaller than the reference value l, and whether the increase correction has been continued or not. , it is determined whether the correction has been reversed from increasing correction to decreasing correction.

When the fuel amount is continuously corrected by the correction coefficient LAMBDA, it is assumed that the alcohol concentration is too low due to a sensor abnormality, so the fuel supply amount Ti is less than the amount equivalent to the stoichiometric air-fuel ratio, and the process proceeds to step 24. Proceed to correct the alcohol concentration MET by increasing it by a predetermined value α.
(see figure), when the increase correction is reversed to the decrease correction, the fuel injection amount Ti is set to approximately the stoichiometric air-fuel ratio without the correction coefficient LAMBDA, so the current alcohol concentration MET is used as the fail-safe concentration. In order to fix it, proceed to step 25 and instruct the completion of failsafe.

In this way, according to this embodiment, the alcohol sensor 17
becomes abnormal, the air-fuel ratio feedback correction coefficient LAM
The concentration is gradually changed in the direction of reversing the increase/decrease correction by BDA, and the point where the increase/decrease correction is reversed is considered to be the value corresponding to the true concentration, and the concentration is fixed at that value and used for subsequent fuel control. Therefore, as shown in Fig. 5, the alcohol concentration MET is fixed after the air-fuel ratio feedback correction coefficient LAN0DA reaches around the reference value 1, and the correction coefficient LAMBD^ is changed in the subsequent air-fuel ratio feedback control. Good feedback controllability can be obtained by changing the ratio near the reference, and the target air-fuel ratio can be obtained with high accuracy through feedback correction control.

In this embodiment, the predetermined value α for forcibly changing the detected concentration value when the alcohol sensor 17 is abnormal is set constant, but it is set variably depending on the engine operating state, the air-fuel ratio feedback correction coefficient LAMBDA, etc. You can do it like this.

<Effects of the Invention> As explained above, according to the present invention, when the means for detecting the reference fuel concentration becomes abnormal, the concentration is forced in the direction in which the direction of increase/decrease correction of the fuel supply amount by air-fuel ratio feedback control is reversed. The concentration at which the increase/decrease correction direction is reversed is set as a fail-safe concentration, and the fuel supply amount is thereafter controlled based on this fail-safe concentration. As a result, the fail-safe concentration will not be set when the air-fuel ratio feedback control is near the limit value of increase or decrease correction, and the fail-safe concentration can be brought closer to the true concentration. When controlling the fuel supply, the air-fuel ratio feedback control is performed near the reference to ensure good controllability, and even if an abnormality occurs in the concentration detection means, the fuel supply can be controlled at the target air-fuel ratio.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a system schematic diagram showing an embodiment of the present invention, FIGS. 3 and 4 are flowcharts showing control details in the above embodiment, respectively, and FIG. The figure is a time chart showing the characteristics of the fail-safe control in the above embodiment, and FIG. 6 is a time chart for explaining the problems of the conventional fail-safe control. 1... Engine 6... Fuel injection valve 12... Control unit 13... Air flow meter 14... Crank angle sensor 16... Oxygen sensor 17... Alcohol sensor

Claims (1)

[Scope of Claims] An internal combustion engine that can be used by switching or mixing different types of fuel, comprising a reference fuel concentration detection means for detecting a reference fuel concentration in fuel supplied to the engine; A fuel supply control means for controlling the amount of fuel supplied to the engine based on operating conditions including at least a concentration value detected by the reference fuel concentration detection means, and detecting whether the air-fuel ratio of the engine intake air-fuel mixture is rich or lean with respect to the target air-fuel ratio. an air-fuel ratio detection means,
A fuel supply control device for an internal combustion engine using different types of fuel, comprising: air-fuel ratio feedback control means for feedback correction control of the fuel supply amount so as to bring the detected air-fuel ratio closer to a target air-fuel ratio; an abnormality detection means for detecting an abnormality in the detection means; and when the abnormality detection means detects an abnormality, the concentration detection value by the reference fuel concentration detection means is set in a direction that reverses the direction in which the fuel supply amount is increased or decreased by the air-fuel ratio feedback control means. a concentration forced change means for gradually forcibly changing the concentration and causing the fuel supply control means to control the fuel supply amount based on the change value; and the concentration forced change means forcibly changing the detected concentration value. and fail-safe concentration setting means for fixing a detected concentration value as a fail-safe concentration when the direction of increase/decrease correction of the fuel supply amount by the air-fuel ratio feedback control means is reversed. Fuel supply control device for internal combustion engines.