JPH04191440A - Self-diagnostic device of air-fuel ratio feedback control system in internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent an erroneous diagnosis and improve the self-diagnostic precision by detecting a condition in which a fouling degree by carbon of the film of an air-fuel sensor, and prohibiting the failure diagnosis of an air-fuel ratio feedback control system at the time of detecting this. CONSTITUTION:On the basis of the output signal of an air-fuel ratio sensor B installed to the exhaust passage of an internal combustion engine A, the failure of an air-fuel ratio feedback control system C is self-diagnosed. In the above device, on the basis of the feedback control signal of the air-fuel ratio feedback control system C, the presence of the failure is judged by a means D. The operating time every time of the engine is measured by a means E. Further, the engine temperature is detected by a means F. The frequency of a determined operating state in which the measured operating time is less than a determined value and the engine temperature at the time of operation end is less than a determined value is detected by a means G. When the detected frequency of the determined operating state is a determined value or more, the failure judgment is prohibited by a means H. Namely, the operating state in which the carbon generated by imperfect combustion is easily adhering to the film of the air-fuel ratio sensor B is detected, whereby the erroneous judgement of the failure judgment is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a device for self-diagnosing a failure in an air-fuel ratio feedback control system in an internal combustion engine.

<Prior Art> In an internal combustion engine equipped with an electronically controlled fuel injection device that feedback-controls the air-fuel ratio of the air-fuel mixture supplied into the cylinders of the engine to a target air-fuel ratio (stoichiometric air-fuel ratio), the fuel injection valve is clogged or When an abnormality such as a short circuit in the output circuit of the fuel injection valve drive circuit occurs, the fuel injection amount deviates from the appropriate amount, the air-fuel ratio changes significantly, and the air-fuel mixture becomes lean or rich. In this case, the problem was that the engine would stop or the output would drop, resulting in poor drivability.

In order to solve this problem, it is determined whether the air-fuel mixture is lean or rich based on the air-fuel ratio feedback control signal, and thereby it can be determined whether the air-fuel ratio control device is malfunctioning. A self-diagnosis device has already been proposed (Japanese Patent Laid-Open No. 63-10025)
(See Publication No. 5, etc.)

<Problem to be Solved by the Invention> Incidentally, although such conventional self-diagnosis devices examine the current operating state of the engine to determine the operating conditions for performing fault diagnosis, Since the influence on failure diagnosis is not taken into consideration, the following problems may arise.

In other words, if the operation time is extremely short and the operating condition is such that the engine stops operating before the engine temperature rises sufficiently (for example, when the vehicle is shipped from the factory and delivered to the sales company) In the internal combustion engine, incomplete combustion such as diffusion combustion is likely to occur. As a result, the carbon generated in the exhaust gas was removed from the oxygen sensor (
If the film on the air-fuel ratio sensor (air-fuel ratio sensor) becomes contaminated, the detected amount of oxygen concentration decreases compared to the actual amount. Based on the detection signal from the oxygen sensor, the air-fuel ratio feedback control system determines that the air-fuel ratio has deviated to the rich side and controls the fuel injection amount in the direction of decreasing. The signal on the a side will be output continuously.

Therefore, even though the air-fuel ratio feedback control system is operating normally, it may be mistakenly determined to be abnormal.

The present invention has been made in view of such conventional problems, and provides an internal combustion engine that solves the above problems by finding an engine state unsuitable for self-diagnosis as described above and prohibiting diagnosis in that engine state. An object of the present invention is to provide a self-failure diagnosis device for an air-fuel ratio feedback control system.

<Means for Solving the Problems> For this reason, the present invention provides air-fuel ratio feedback control for feedback-controlling the air-fuel ratio based on the output signal of an air-fuel ratio sensor installed in the exhaust passage of an internal combustion engine, as shown in FIG. A device for self-diagnosing a system failure, comprising a failure determination means for determining the presence or absence of a failure based on a feedback control signal of the air-fuel ratio feedback control system, and an operation time measurement means for measuring the operation time of the engine each time. , an engine temperature detection means for detecting the engine temperature; and an operation frequency for detecting the frequency of a predetermined operating state in which the measured operating time is less than or equal to a predetermined value and the engine temperature at the end of the operation is less than or equal to the predetermined value. The present invention is configured to include a detection means, and a failure determination prohibition means for prohibiting failure determination by the failure determination means when the frequency of the detected predetermined operating state is equal to or higher than a predetermined value.

<Function> In an operating state in which the driving time measured by the driving time measuring means is less than a predetermined value and the engine temperature detected by the engine temperature detecting means at the end of the driving is less than the predetermined value, It tends to adhere to the air-fuel ratio sensor film caused by incomplete combustion.

Therefore, if the frequency of such operating conditions is detected by the operating frequency detection means, and if the frequency is greater than a predetermined value, the degree of contamination of the film of the air-fuel ratio sensor due to carbon adhesion is large, and there is a possibility that the failure will be incorrectly determined. Therefore, the failure determination prohibition means prohibits the failure determination means from making a failure determination.

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

FIG. 2 shows the system configuration of this embodiment, in which the engine main body 10
An injector 12 for injecting and supplying fuel is attached to the intake manifold 11 connected to the intake manifold 11 .

A throttle valve 13 is installed in the intake passage upstream of the injector 12, and an air flow meter I4 for detecting the intake air flow rate is installed further upstream. The throttle valve 13
A throttle sensor 15 for detecting the opening degree of the throttle valve 13 is attached to the throttle valve 13 .

On the other hand, the exhaust manifold 16 is equipped with an air-fuel ratio sensor 17 that detects the air-fuel ratio by detecting oxygen concentration in the exhaust gas. Further, a water temperature sensor 18 is attached to the engine body 10 as an engine temperature detection means for detecting water temperature as a representative of the engine temperature.

In addition, a rotation speed sensor 19 for detecting the engine rotation speed and a starter switch 20 are provided.

Electronic control unit 50 that performs air-fuel ratio feedback control
consists of a digital computer and has a bidirectional bus 51.
ROM (read only memory) 52, RAM (random access memory) 53, CPU (microprocessor) 54, which are connected to each other so that data can be transmitted between them.
It has an input port 55 and an output port 56. The input port 55 has the throttle sensor 15. Air fuel ratio sensor 17. Water temperature sensor 18° rotation speed sensor 19. Each detection signal from the starter switch 20 is input. and,
The CPU 54 calculates a fuel injection amount according to the operating state based on each of the detection signals, and outputs a fuel injection signal having a pulse width commensurate with the fuel injection amount from the output port 56 to the injector 12. Thereby, the injector 12 is energized and driven to inject and supply the calculated amount of fuel. Here, the calculation of the fuel injection amount is based on the basic fuel injection amount T calculated based on the intake air flow rate Q and the engine speed N,
(=Q/N) is corrected by the water temperature Tw, while under predetermined operating conditions, as will be described later, proportional-integral control is performed to make the air-fuel ratio detected by the air-fuel ratio sensor 17 the target air-fuel ratio (theoretical air-fuel ratio). Feedback correction amount α set by
Corrected by

Figure 3 shows changes in the output voltage V of the air-fuel ratio sensor 17. When the air-fuel mixture is rich, an output voltage of about 0.9 (V) is generated, and when the air-fuel mixture is lean, it generates an output voltage of about 0.9 (V). ), an output voltage of about 0.1 (V) is generated. The output voltage V of the air-fuel ratio sensor 17 is set to 0.
It is compared with a reference voltage vF of about 5 (V), and if the output voltage (2) is higher than the reference voltage V, it is determined to be rich, and if it is lower than vF, it is determined to be lean.

FIG. 4 shows a calculation routine for the feedback correction amount α, which is performed based on the rich/lean judgment. This routine is executed at predetermined time intervals, for example every 4 ms.

In step 60, the air-fuel ratio is determined to be rich or lean, and when it is determined to be lean, the process proceeds to step 61, where it is determined whether or not it has changed from rich to lean between the previous processing cycle and the current processing cycle. .

If it is inverted, the process proceeds to step 62, where a predetermined proportional amount P is added to α, and if it is not inverted, the process proceeds to step 63, where an integral value (2) is added to α.

On the other hand, when it is determined in step 60 that the oil is rich, the process proceeds to step 64, where it is determined whether or not there has been an inversion from lean to rich between the previous processing cycle and the current processing cycle. If it is inverted, the process proceeds to step 65, where the proportional portion P is subtracted from α; if it is not inverted, the process proceeds to step 66, where the integral value (2) is subtracted from α.

Therefore, as shown in Fig. 3, when α is reversed from rich to lean, α rapidly increases by a proportional amount P, and then gradually increases by an integral integral I, and when reversed from lean to rich, α suddenly increases by a proportional amount After decreasing by P, it gradually decreases by integral ■.

Further, as shown in FIG. 3, the normal feedback correction amount α is between the set upper limit value MAX and lower limit value MIN, and the air-fuel ratio sensor 17 is rich.

It moves up and down to periodically repeat lean detection.

However, if the air-fuel mixture continues to become rich for some reason, it reaches MIN, and if it continues to become lean, it reaches MAX. Therefore, it is possible to diagnose a failure in the air-fuel ratio feedback control system depending on whether α has reached MAX or MIN. However, if this is the case, failure diagnosis will be performed even if it is inappropriate as described above, so the present invention detects the operating conditions that occur in such cases and prohibits diagnosis under those conditions. do.

5 and 6 show a control routine for fault diagnosis according to the present invention performed by the CPU 54. FIG. These routines are executed by interrupts at fixed time intervals.

In FIG. 5, step 70 is the starter switch 2.
0 is on or off, and if it is off, the process proceeds to step 71, where it is determined whether the starter switch 20 was switched from on to off between the previous processing cycle and the current processing cycle.

If it is determined that the switch has been made from on to off, the process proceeds to step 72, where the engine speed N is compared with a predetermined value, for example 500 rpm, and if N≧500, it is determined that the engine has started and is rotating. Then proceed to step 73.

Further, when it is determined in step 70 that the starter switch 20 is on, when it is determined in step 71 that the starter switch 20 is not turned on immediately after being switched from ON to OFF, in step 72 it is determined that the engine speed N<500. In either case, exit this routine.

In step 73, a timer is set to measure the elapsed time after the engine is started, and the process proceeds to step 74, in which it is determined whether the engine rotation speed N has become 0, that is, whether the engine has been stopped after starting, and then stopped. This step 73
Repeat the judgment and wait for the stop.

When the engine is stopped, the process proceeds to step 75, and it is determined based on the measured value of the timer whether a certain period of time has elapsed since the engine was started. The routine decrements (decreases the value by l) a fault diagnosis prohibition counter for setting a fault diagnosis prohibition period. Note that the timer corresponds to a driving time measuring means.

If it is determined in step 75 that a certain period of time has not elapsed since the start of the engine, the process proceeds to step 76, where it is determined whether the water temperature T, which represents the engine temperature, is less than or equal to the set value Tse.

T≦T, 6. If it is determined that
increase) and TNT. If it is determined to be 1, the process advances to step 78 and the failure diagnosis prohibition counter is decremented.

In other words, in this routine, the failure diagnosis prohibition period is increased each time a single operation is performed for a short time and the water temperature is low immediately after stopping, and the failure diagnosis is performed each time an operation other than the above is performed. Reduce the period of ban. Here, in the operation that increases the failure diagnosis prohibition period, because the water temperature is low, carphone generated due to incomplete combustion adheres to the air-fuel ratio sensor 17, and is not removed because the operation is stopped. If such operation is repeated, the attached carphone will accumulate. On the other hand, in other operations, the water temperature rises until the end of the operation, causing the car horn to occur or stop, and at the same time, the exhaust temperature rises and the carbon attached to the air-fuel ratio sensor 17 is burned off by the high-temperature exhaust gas. Therefore, the count value C of the failure diagnosis prohibition counter, which is measured as the difference between the number of times of operation, is an index of the degree of contamination of the film of the air-fuel ratio sensor by the car horn. On the other hand, the count value C
is also an index of a value corresponding to the frequency of driving in which the car phone sticks, so the failure diagnosis prohibition counter corresponds to driving frequency detection means.

FIG. 6 shows a fault diagnosis routine.

In step 80, the count value C of the failure diagnosis prohibition counter measured in the routine shown in FIG. 4 is compared with the set value C8,1.

And C<C,. 1, the air-fuel ratio sensor 17
Since the degree of contamination caused by the car phone is small, it is determined that it is safe to perform a failure diagnosis, and the process proceeds to step 81, or the process proceeds to step C2.
When the degree of contamination is 04°, it is determined that the degree of contamination is large and there is a possibility of erroneous diagnosis if failure diagnosis is performed, and this routine is terminated without performing diagnosis. Is this step 81 a function that prohibits failure diagnosis when C≧C8゜1?
This corresponds to a failure determination prohibition means.

In step 81, it is determined whether the current operating state is in the failure diagnosis range of the air-fuel ratio control system, and if it is not in the range, this routine is ended. Since the fault diagnosis area here is the diagnosis of the air-fuel ratio feedback control system, it is natural that the feedback control is in progress, or transient conditions such as an increase in the amount of fuel injection at engine startup or warm-up. Areas are avoided and stationary areas are selected.

If it is determined that the area is in the failure diagnosis area, step 82
Proceed to the following steps to perform fault diagnosis.

First, in step 82, the feedback correction amount α is
MIN for the upper limit value MAX and lower limit value MIN shown in the diagram.
It is determined whether or not it is in the range <α<MAX.

If it is within the range of MIN<α<MAX, it is determined that the air-fuel ratio feedback restriction system is normal, and the process proceeds to step 85, where the failure flag Fα is reset to 0.

On the other hand, when it is determined that MIN<α<~fAX is outside the range, that is, in a lean abnormal state where α≦MIN or α≧M
If it is determined that one of the rich abnormal states AX is present, the process proceeds to step 83, where it is determined whether these abnormal states are transient (for example, 10 seconds or longer).

If the abnormal condition continues for more than 10 seconds,
It is determined that the air-fuel ratio feedback control system has failed, and the process proceeds to step 84, where the failure flag Fα is set to 1.

In this way, the presence or absence of a failure is indicated by the value of the failure flag Fα. Note that the functions of steps 82 to 85 correspond to failure determination means.

With this configuration, failure diagnosis is prohibited in a state where the film of the air-fuel ratio sensor 17 is contaminated with carbon and there is a possibility of erroneously diagnosing a failure, thereby improving diagnostic accuracy.

<Effects of the Invention> As explained above, the present invention has a configuration that detects conditions in which the degree of carbon contamination of the film of the air-fuel ratio sensor becomes high, and prohibits failure diagnosis of the air-fuel ratio feedback control system when the condition is detected. This prevents misdiagnosis in the above situations and improves self-diagnosis accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a system configuration diagram of an embodiment of the present invention, and FIG. 3 is a diagram showing the relationship between the output voltage of the air-fuel ratio sensor and the feedback correction amount. FIG. 4 is a flowchart showing a routine for setting the feedback correction amount, FIG. 5 is a flowchart showing a routine for setting a fault diagnosis prohibition period, and FIG. 6 is a flowchart showing a fault diagnosis routine. 12... Injector 16... Exhaust manifold 17... Air-fuel ratio sensor I8... Water temperature sensor
19... Rotation speed sensor 20... Starter switch 50... Electronic control unit Fig. 1 Fig. 3 Fig. 5 Fig. 6

Claims (1)

[Claims] In a device for self-diagnosing a failure of an air-fuel ratio feedback control system that performs feedback control of an air-fuel ratio based on an output signal of an air-fuel ratio sensor installed in an exhaust passage of an internal combustion engine, the system comprises: a failure determining means for determining the presence or absence of a failure; an operating time measuring means for measuring the operating time of the engine each time; an engine temperature detecting means for detecting the engine temperature; and an operating frequency detection means for detecting the frequency of a predetermined operating state in which the engine temperature at the end of the operation is below a predetermined value; 1. A self-diagnosis device for an air-fuel ratio feedback control system of an internal combustion engine, comprising: a failure determination prohibition means for prohibiting failure determination by the determination means.