JPH04237851A - Air-fuel ratio sensor deterioration diagnostic device - Google Patents

Abstract

PURPOSE:To provide such an air-fuel ratio sensor deterioration diagnostic device capable of detecting any deterioration in an air-fuel ratio sensor accurately through inexpensive cost. CONSTITUTION:This diagnoser is provided with a sensor 7 installed in an exhaust system 4 of an internal combustion engine 1, a means changing an air-fuel ratio on the basis of a detected value of this sensor 7, a means determining a feedback control factor by changing the air-fuel ratio, and a means detecting a parameter showing an engine driving state such as an intake air quantity or the like, and it is also provided with another means for finding a feedback control factor imparting a theoretical air-fuel ratio from the air-fuel ratio feedback control factor, thus it comes to fruition. With this constitution, a diagnosis of deterioration in the air-fuel ratio sensor is accurately performable, thereby calling upon makers, users and so on to replace the deteriorated sensor, so that an exhaust gas emission control effect is well improved, thus an environmental problem is surmountable.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to deterioration diagnosis of an air-fuel ratio sensor of an internal combustion engine, and in particular, it
The present invention relates to a device that obtains a stoichiometric air-fuel ratio, moves the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio, and diagnoses deterioration of an air-fuel ratio sensor.

0002

[Prior Art] The conventional device is
As described in No. 5, air-fuel ratio sensors are installed on the upstream and downstream sides of the catalytic converter, and by comparing the output characteristics of both, a deterioration diagnosis of the air-fuel ratio sensor on the upstream side is performed, and the user is prompted to replace the parts. This was to prevent deterioration of emissions due to component deterioration.

0003

[Problems to be Solved by the Invention] The above conventional technology compares the air-fuel ratio sensor outputs on the upstream side and the downstream side, so it is necessary to take into account factors such as the difference in exhaust gas components before and after the catalyst and the time difference. Therefore, it cannot be said that an accurate judgment is necessarily made. Also, the comparison logic is complicated.

[0004] The present invention uses the air-fuel ratio feedback coefficient to
To provide a device capable of accurately and inexpensively diagnosing deterioration of an air-fuel ratio sensor by calculating a stoichiometric air-fuel ratio and varying the air-fuel ratio before and after the stoichiometric air-fuel ratio.

[0005]

[Means for Solving the Problems] In order to achieve the above object, we have provided a buffer that holds the air-fuel ratio sensor output, a comparison device that compares the air-fuel ratio sensor output, a memory that holds the air-fuel ratio feedback coefficient, and a stoichiometric air-fuel ratio. an arithmetic device that calculates;
This system includes a calculation device that calculates the fuel injection amount from the air-fuel ratio feedback coefficient, a control device and sensor that controls the input and output of engine parameters, and an air-fuel ratio sensor.

[0006]

[Operation] The above means changes the air-fuel ratio feedback coefficient to change the fuel injection amount to before or after the stoichiometric air-fuel ratio, so the unit of the air-fuel ratio feedback coefficient is abnormal when calculating the amount of fuel. I don't set it as large as possible, so
No abnormal operation occurs.

[0007]

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of the present invention. The engine body 1 is provided with an engine cooling water temperature sensor 5, an air flow sensor 3 in the intake passage 2, a throttle sensor 4, and an air-fuel ratio sensor 7 in the exhaust passage 6. Also, 1
2 is a control unit that calculates the fuel injection amount, ignition timing, idle speed control valve pulse width, etc. based on the above-mentioned sensor output signal information, and controls the injector 8, boost and distribution device 9, and idle speed control valve 11, respectively. Output a signal.

FIG. 2 is a diagram illustrating the calculation of the average value αave of the air-fuel ratio feedback coefficient α. Hereinafter, the air-fuel ratio feedback coefficient α will be abbreviated as α. N peak values of α during air-fuel ratio closed loop control are sampled, and the average value αave =Σ(α peak)/n is determined. This calculated value αave can be approximated to the correction coefficient value of the stoichiometric air-fuel ratio in that operating region.

FIG. 3 shows the average value αa of α explained in FIG.
It is a figure explaining correction calculation of ve. Figure 2 shows
It shows the operating range in which α moves overall during air-fuel ratio closed loop control. When the peak value of α is sampled in this region, as shown in FIG. 2, α4 and α5 are far apart from α1 and α2. In this case, it cannot be said that the simple average αave of the α peak values necessarily approximates the correction coefficient value of the stoichiometric air-fuel ratio. Therefore, the average value αave = Σ(α
At the same time as calculating the second half of the number of sampled values of α, αave(n/2) = Σ(α peak)/(n/2), that is, the n/2nd peak of α. Find the average value αave(n/2) from the value to the nth value (
n=n/2, n/2+1...n). Next, their deviation σ=|αave(n/2)| is calculated. The deviation σ is
If it is larger than the reference value l (σ>l), it is determined that the engine operating state in the current region is not stable, and this diagnostic control is terminated. When the deviation σ is smaller than the reference value l (σ≦l)
Assume that the operating conditions in the current region are stable, and furthermore,
Individual deviation calculations σn=|αave−αn| of the sampled values for which the average value αave has been calculated are performed. Next, among those deviations σn, those σn larger than the reference value m
>m, the sampling peak values αx (x pieces) are deleted, and the corrected average value αa of the sampling peak values of α is
Calculate ve0.

αave0=(Σα−Σσx)/(n−x
) With the above correction αave0, the deviation of the simple average value αave from the stoichiometric air-fuel ratio equivalent coefficient value at the time of diagnosis is corrected as shown in FIG. Here, the number of samples n
, reference values l and m are constants or variables determined by the engine control system.

FIGS. 5 and 6 are diagrams showing an example of how the air-fuel ratio feedback coefficient is operated to obtain an air-fuel ratio sensor output response waveform when diagnosing deterioration of the air-fuel ratio sensor. Figure 5 shows α
After calculating ave0, α is the stoichiometric air-fuel ratio equivalent coefficient value αave0
By clamping the value of α to a constant value and changing the value of α stepwise so as to straddle αave0 shown in the figure, the air-fuel ratio can be reliably changed in the vicinity of the stoichiometric air-fuel ratio, thereby increasing the output starting force of the air-fuel ratio sensor. is suddenly changed, and the response waveform shown in FIG. 7 is obtained. A method for determining the deterioration of the air-fuel ratio sensor output response waveform is shown in FIG. The figure shows a normal output response waveform (solid line) and a degraded output response waveform (dotted line) of the air-fuel ratio sensor when the fuel amount is changed stepwise from lean to rich by the air-fuel ratio coefficient. This deterioration determination is performed by first applying the rich side output voltage deterioration determination level v to the air-fuel ratio sensor output.
1 and the lean side output voltage deterioration determination level v2 are set as lower and upper limit values, respectively, and a comparative determination is performed in terms of output values. Next, deterioration is determined by looking at the slope (differential value dv/dt) of the air-fuel ratio sensor output response waveform when the output rises. In addition, for example, the air-fuel ratio feedback coefficient may be
When moving from an to rich, the sensor output response is l
There is also a method of determining deterioration by measuring the time from ean to rich. It is also shown in FIG. A deterioration determination method using a response waveform when a or b is varied may also be considered. A and b shown in FIG. 5 are set to values that can reliably cross the stoichiometric air-fuel ratio, except in the case of deterioration determination in which a and b are varied. This is a constant or variable determined by the engine control system and operating range. Also, when a and b are clamped to αave0, (
(i) Clamping from lean side operation and (ii)
Clamping from the rich side operation may cause a deviation in the clamp position, so this needs to be taken into account depending on the engine control system and operating range.

In FIG. 6, unlike FIG. 5, a step waveform with a random frequency is input to αave0 or α into the air-fuel ratio feedback coefficient, and as a result, an air-fuel ratio sensor output response waveform is obtained, and their correlation is FIG. 3 is a diagram illustrating an example in which deterioration of an air-fuel ratio sensor is determined by taking the following values.

FIG. 9 is a diagram showing a flow chart of one embodiment of the present invention. First, it is determined whether or not the air-fuel ratio sensor is activated. If not activated, terminate. If activated, it is determined whether air-fuel ratio closed loop control is being performed. If closed loop control is not in progress, it ends. If closed-loop control is in progress, the process moves on to determining whether or not it is in a steady-state operating region. The determination as to whether or not the engine is in the steady operation region is made based on the amount or magnitude of change in engine control parameters such as the basic fuel injection pulse width Tp, engine speed, and throttle opening. If the operation is not steady, it will end. In the case of steady operation, a deterioration diagnosis of the air-fuel ratio sensor is performed in accordance with the explanation of FIGS. 1 to 8 described above.

[0014]

According to the present invention, it is possible to accurately diagnose the deterioration of an air-fuel ratio sensor, thereby producing the following effects.

By diagnosing the deterioration of the air-fuel ratio sensor, manufacturers and users are encouraged to replace the deteriorated sensor, the exhaust gas cleaning effect is enhanced, and environmental problems can be overcome.

[Brief explanation of the drawing]

FIG. 1 is an overall conceptual diagram of an embodiment of the apparatus of the present invention.

FIG. 2 is a diagram illustrating calculation of the average value of feedback coefficient α.

FIG. 3 is a diagram illustrating a correction calculation of the average value αave.

FIG. 4 is a diagram illustrating a correction calculation of the average value αave.

FIG. 5 is a diagram illustrating an example of how the air-fuel ratio feedback coefficient is operated.

FIG. 6 is a diagram illustrating an example of how the air-fuel ratio feedback coefficient is operated.

FIG. 7 is a diagram illustrating an air-fuel ratio sensor output response.

FIG. 8 is a diagram illustrating an example of a method for determining deterioration of an air-fuel ratio sensor output response.

FIG. 9 is a diagram showing a flowchart explaining one embodiment of the present invention.

Claims (6)

[Claims] 1. At least one air-fuel ratio detection means disposed in an exhaust system path of an internal combustion engine; means for changing the air-fuel ratio based on the air-fuel ratio detection value; by changing the air-fuel ratio,
In an internal combustion engine having means for performing air-fuel ratio feedback control and means for detecting a parameter indicating an engine operating state, the present invention further includes means for determining a feedback coefficient value giving a stoichiometric air-fuel ratio from an air-fuel ratio feedback control coefficient. Features: Air-fuel ratio sensor deterioration diagnosis device. [Claim 2] A claim characterized in that the steady-state operating state is determined, the air-fuel ratio feedback coefficient is changed in the vicinity of the stoichiometric air-fuel ratio, and the deterioration diagnosis of the air-fuel ratio sensor is performed based on the air-fuel ratio sensor output response characteristic at that time. Item 1. The air-fuel ratio sensor deterioration diagnostic device according to item 1. 3. Diagnosing deterioration of the air-fuel ratio sensor by changing the air-fuel ratio feedback coefficient near the stoichiometric air-fuel ratio based on a random signal and checking the correlation with the air-fuel ratio sensor response waveform at that time. The air-fuel ratio sensor deterioration diagnostic device according to claim 1. 4. The air-fuel ratio sensor deterioration diagnosing device according to claim 2 or 3, characterized in that when the air-fuel ratio sensor is diagnosed as deteriorating, the air-fuel ratio sensor deterioration diagnosis device is provided with a notification means to notify a driver or a maintenance person of the abnormality. 5. A deterioration of an air-fuel ratio sensor characterized in that the feedback coefficient value giving the stoichiometric air-fuel ratio according to claim 1 is determined by sampling a plurality of peak values of the feedback coefficient and finding the average value thereof. Diagnostic equipment. [Claim 6] When calculating the average value of the peak values of the feedback coefficients according to claim 5, peak values whose values are far apart from the average value are not included in the calculation to obtain more accurate results. A deterioration diagnostic device for an air-fuel ratio sensor, characterized by determining a feedback coefficient value that provides a stoichiometric air-fuel ratio.