JPH10169494A - Diagnosing device for exhaust emission control catalyst and abnormality diagnosing device for oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform abnormality diagnosing for an exhaust emission control catalyst highly accurately and by a relatively simple structure. SOLUTION: Determination is made as to whether an abnormality diagnosing condition is established or not (S1). If established, an objective air-fuel ratio is switched to another (S2). The output of a downstream side oxygen sensor is monitored (S3). Based on a degree of changing in the output of the downstream side oxygen sensor, the abnormality of an exhaust emission control catalyst is determined (S4). If normal, 'OK determined' is made (S5). If abnormal, then 'NG determined' is made (S6), and an MIL is lit (S7). Thus, the abnormality of the exhaust emission control catalyst is diagnosed highly accurately and by a relatively simple structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for diagnosing an abnormality of an exhaust purification catalyst and an apparatus for diagnosing an abnormality of an oxygen sensor.

[0002]

2. Description of the Related Art As a conventional diagnostic device for an exhaust gas purifying catalyst, for example, there is one disclosed in Japanese Patent Application Laid-Open No. 4-116239. As shown in FIG. 8, a three-way catalyst 33 as an exhaust gas purifying catalyst is interposed in an exhaust passage 32 of an internal combustion engine 31, and an exhaust gas is provided upstream and downstream of the three-way catalyst 33. The stoichiometric air-fuel ratio ｛A according to the oxygen concentration of
/ F (weight of air / weight of fuel) {14.7, in other words, an upstream oxygen sensor 34 and a downstream oxygen sensor 35 for outputting a rich / lean signal with respect to the excess air ratio λ = 1} are provided. The fuel injection amount from the fuel injection valve 36 based on the rich / lean inversion output signal of the upstream oxygen sensor 34 so that the fuel ratio (the stoichiometric air-fuel ratio) can be obtained (the air-fuel ratio control target).
While the air-fuel ratio feedback control for increasing / decreasing the air-fuel ratio is performed by proportional integral control, the control unit 37 outputs the outputs of the upstream oxygen sensor 34 and the downstream oxygen sensor 35 during the air-fuel ratio feedback control as shown in FIG. The abnormality of the three-way catalyst 3 is diagnosed using the value. That is, the inversion frequency ratio (HZRATE = f2) based on the rich / lean inversion period (T1) of the output signal of the upstream oxygen sensor 34 and the rich / lean inversion period (T2) of the output signal of the downstream oxygen sensor 35. / F1), and when the HZRATE is equal to or smaller than a predetermined value, the oxygen storage capacity of the exhaust purification catalyst is high, and the amplitude of the air-fuel ratio upstream of the exhaust purification catalyst is offset by the adsorption and desorption of oxygen on the catalyst surface. Since it can be determined that the rich / lean inversion cycle (T2) of the output signal of the downstream oxygen sensor 35 is long, the three-way catalyst 33 is diagnosed to be normal. Diagnosis is made that storage capacity has decreased (FIG. 10,
See FIG. 11).

In recent years, the air-fuel ratio at the inlet of the exhaust purification catalyst has been controlled more precisely to a target air-fuel ratio (for example, a stoichiometric air-fuel ratio) so that the exhaust purification performance of the exhaust purification catalyst can be maximized. In response to the demand for higher accuracy of the fuel ratio feedback control, a so-called wide area that can linearly detect the air-fuel ratio over a wide range from rich to lean instead of an oxygen sensor that can output only a rich / lean signal for the stoichiometric air-fuel ratio Air-fuel ratio feedback control using an air-fuel ratio sensor has also been proposed.

[0004]

However, this wide-range air-fuel ratio sensor can linearly detect the air-fuel ratio over a wide range from rich to lean.
There is a concern that the abnormality diagnosis method disclosed in Japanese Patent No. 119239 cannot diagnose an abnormality of the three-way catalyst. In other words, when the air-fuel ratio feedback control is performed by the proportional integral control using the output value of the oxygen sensor that can output only the rich / lean signal with respect to the stoichiometric air-fuel ratio, the deviation amount between the stoichiometric air-fuel ratio and the actual air-fuel ratio itself is Cannot be accurately grasped, the air-fuel ratio control target (fuel injection amount or intake air flow rate) is increased or decreased until the output value of the oxygen sensor is next rich or lean inverted, and as a result, the output of the oxygen sensor is returned again. When the value is rich or lean inverted,
Since the process of increasing or decreasing the air-fuel ratio control target is performed again until the output value of the oxygen sensor is rich or lean inverted, the actual air-fuel ratio oscillates at a predetermined cycle around the stoichiometric air-fuel ratio. At the same time, the output value of the oxygen sensor is rich / lean inverted with respect to the stoichiometric air-fuel ratio in a predetermined cycle.

Therefore, the abnormality diagnosis method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 4-119239, that is, the rich / lean reversal cycle of the upstream oxygen sensor and the rich / lean reversal cycle of the downstream oxygen sensor are determined. In comparison, an abnormality diagnosis method of diagnosing an abnormality of the exhaust purification catalyst can be adopted. In contrast, when performing air-fuel ratio feedback control using a wide-range air-fuel ratio sensor that can linearly detect the air-fuel ratio over a wide range from rich to lean, even if the actual air-fuel ratio deviates slightly from the stoichiometric air-fuel ratio, Since the deviation itself can be detected, the air-fuel ratio control target (fuel injection amount or intake air flow rate) corresponding to the deviation is required to correct the deviation.
The actual air-fuel ratio does not oscillate around the stoichiometric air-fuel ratio, and the output value of the wide-range air-fuel ratio sensor is larger than the stoichiometric air-fuel ratio. Thus, there is little possibility of rich / lean inversion at a predetermined cycle.

Therefore, it is not accurate to determine the rich / lean inversion cycle of the wide area air-fuel ratio sensor provided on the upstream side of the exhaust purification catalyst, and the exhaust gas maintained at a substantially constant stoichiometric air-fuel ratio is introduced into the exhaust purification catalyst. Therefore, there is an opportunity that the air-fuel ratio of the exhaust gas coming out of the exhaust purification catalyst oscillates in a predetermined cycle and that the output value of the downstream oxygen sensor provided downstream of the exhaust purification catalyst is rich-lean inversion in a predetermined cycle. Few.

For this reason, when performing the air-fuel ratio feedback control using the wide-range air-fuel ratio sensor, the above-mentioned Japanese Patent Laid-Open Publication No. Hei.
An abnormality diagnosis method as disclosed in JP-A-119239,
That is, it is difficult to directly adopt the abnormality diagnosis method of diagnosing the abnormality of the exhaust purification catalyst by comparing the amplitude periods of the air-fuel ratio on the upstream side and the downstream side of the exhaust purification catalyst.

The present invention has been made in view of the above-mentioned conventional circumstances, and is directed to a case where a wide-range air-fuel ratio sensor is disposed upstream of an exhaust purification catalyst and an oxygen sensor is disposed downstream of the exhaust purification catalyst. In particular, it is an object of the present invention to provide an exhaust gas purifying catalyst abnormality diagnosis device capable of quickly and accurately diagnosing an exhaust gas purifying catalyst abnormality. Further, the air-fuel ratio switching means constituting the exhaust gas purification catalyst abnormality diagnosis device according to the present invention can be used for abnormality diagnosis of an oxygen sensor disposed downstream of the exhaust gas purification catalyst. Another object of the present invention is to provide a device for diagnosing abnormality of an oxygen sensor using the device.

[0009]

For this reason, according to the first aspect of the present invention, as shown in FIG. 1, in an abnormality diagnosing apparatus for an exhaust gas purifying catalyst for purifying exhaust gas of an internal combustion engine, an air-fuel mixture of an engine intake air-fuel mixture is used. Air-fuel ratio switching means for switching the fuel ratio; and a downstream device provided downstream of the exhaust purification catalyst for detecting the concentration of a specific component in the exhaust downstream of the exhaust purification catalyst and outputting a rich / lean signal for a predetermined air-fuel ratio. Side oxygen sensor, based on the output change of the downstream oxygen sensor from when the air-fuel ratio is switched by the air-fuel ratio switching means,
Abnormality diagnosis means for diagnosing an abnormality of the exhaust gas purification catalyst.

According to this configuration, the air-fuel ratio is forcibly switched (that is, the control state of the air-fuel ratio control target (fuel injection amount or intake air flow rate)), and the output change (response) of the downstream oxygen sensor in response to the switching. By observing the time, the amplitude frequency, the slope of the change, etc.), the abnormality of the exhaust purification catalyst is diagnosed, so that the conventional abnormality such as when a wide-range air-fuel ratio sensor is provided upstream of the exhaust purification catalyst is used. Even if the diagnosis cannot be performed by the diagnosis method, it is possible to quickly and accurately diagnose the abnormality of the exhaust purification catalyst with a simple configuration.

According to the second aspect of the present invention, the abnormality diagnosing means sets the output of the downstream oxygen sensor to a predetermined amount from the time when the air-fuel ratio is switched by the air-fuel ratio switching means toward the air-fuel ratio after the switching. An abnormality of the exhaust purification catalyst is diagnosed based on a time required until the change occurs. With this configuration, it is possible to quickly and accurately diagnose the presence or absence of an abnormality in the exhaust gas purification catalyst with a simple configuration.

According to the third aspect of the present invention, when an upstream air-fuel ratio sensor for detecting the concentration of a specific component in exhaust gas and linearly detecting an air-fuel ratio is provided upstream of the exhaust gas purification catalyst, The switching of the air-fuel ratio by the fuel-ratio switching means is detected based on a change in the output of the upstream-side air-fuel ratio sensor toward the air-fuel ratio after the switching.

With this configuration, even if the air-fuel ratio switching instruction is issued, the air-fuel ratio on the upstream side of the exhaust purification catalyst is not actually switched well, or the air-fuel ratio switching instruction is issued. Since it is possible to prevent the possibility of erroneous diagnosis occurring when there is a response delay for a relatively long time until the air-fuel ratio on the upstream side of the exhaust purification catalyst is actually switched after being performed, the abnormality diagnosis accuracy of the present invention can be further improved. Can be enhanced.

[0014] In the invention described in claim 4, the air-fuel ratio switching means is configured to oscillate the air-fuel ratio. In this way, for example, during the catalyst perturbation control, the abnormality diagnosis of the exhaust gas purification catalyst can be performed, so that the purification performance of the exhaust gas purification catalyst is maximized by the catalyst perturbation control, and at the same time, the simple configuration and the rapid In addition, it is possible to diagnose with high accuracy whether or not the exhaust gas purification catalyst is abnormal.

According to a fifth aspect of the present invention, the abnormality diagnosing means determines whether or not the exhaust gas purifying catalyst is based on a switching cycle of the air-fuel ratio by the air-fuel ratio switching means and an output change cycle of the downstream oxygen sensor. It is configured as a means for diagnosing abnormalities. In this way, it is possible to diagnose the abnormality of the exhaust purification catalyst with higher accuracy.

According to the present invention, when an upstream air-fuel ratio sensor for detecting the concentration of a specific component in the exhaust gas and linearly detecting the air-fuel ratio on the upstream side of the exhaust purification catalyst is provided, The air-fuel ratio control target is feedback-controlled based on the output of the upstream-side air-fuel ratio sensor so that the actual change in the air-fuel ratio on the upstream side of the exhaust purification catalyst accompanying the switching of the air-fuel ratio by the fuel-ratio switching means becomes predetermined. Configured.

By doing so, for example, the engine individual difference,
Due to manufacturing variations of fuel / intake systems, aging, etc., the actual air-fuel ratio changed more than the change in the given air-fuel ratio, or the actual air-fuel ratio did not change until the change in the expected air-fuel ratio. In such a case, the air-fuel ratio may become richer or leaner than a predetermined value, thereby deteriorating the exhaust purification performance or deteriorating the engine stability and hunting. The change width, the amplitude period, etc.) can be controlled to a predetermined (target), so that such a concern can be reliably eliminated.

According to the present invention, the concentration of a specific component in the exhaust gas on the downstream side of the exhaust gas purification catalyst is provided downstream of the exhaust gas purification catalyst for purifying the exhaust gas of the internal combustion engine. In the abnormality diagnosis device for a downstream oxygen sensor that outputs a rich / lean signal, an air-fuel ratio switching unit that switches an air-fuel ratio of an engine intake air-fuel mixture, and a downstream oxygen sensor after the air-fuel ratio is switched by the air-fuel ratio switching unit. Downstream oxygen sensor abnormality diagnosing means for diagnosing an abnormality of the downstream oxygen sensor based on a change in the output of the downstream oxygen sensor from the time when the output starts to change toward the air-fuel ratio after the switching. To be configured.

According to this configuration, the air-fuel ratio is forcibly switched, that is, the control state of the air-fuel ratio control target (fuel injection amount or intake air flow rate) is switched, and the output of the downstream oxygen sensor becomes rich according to the switching. An abnormal response of the downstream oxygen sensor is diagnosed based on the output change degree of the downstream oxygen sensor from the time when the transition (change) from the side to the lean side or from the lean side to the rich side is started. Therefore, with a simple configuration, it is possible to quickly and accurately diagnose the presence or absence of an abnormality in the downstream oxygen sensor. Further, even in the case where the air-fuel ratio feedback control is performed using a wide-range air-fuel ratio sensor that has few opportunities for the exhaust air-fuel ratio to undergo rich / lean reversal and few diagnostic opportunities, it is possible to secure an abnormality diagnosis opportunity for the downstream oxygen sensor. .

[0020] In the invention described in claim 8, the downstream oxygen sensor abnormality diagnosing means switches the output of the downstream oxygen sensor to the air-fuel ratio after the switching after the air-fuel ratio is switched by the air-fuel ratio switching means. Then, the abnormality of the downstream oxygen sensor is diagnosed based on the required time from the start of the change to the change of the predetermined amount.

According to this structure, the operation and effect of the invention described in claim 7 can be achieved quickly and accurately with a simple structure. According to the ninth aspect of the present invention, the air-fuel ratio switching unit is configured as a unit that oscillates the air-fuel ratio. In this way, for example, during the catalyst perturbation control, the abnormality diagnosis of the exhaust gas purification catalyst can be performed, so that the purification performance of the exhaust gas purification catalyst is maximized by the catalyst perturbation control, and at the same time, the simple configuration and the rapid In addition, it is possible to diagnose with high accuracy whether or not the downstream oxygen sensor is abnormal.

According to a tenth aspect of the present invention, when an upstream air-fuel ratio sensor for detecting the concentration of a specific component in exhaust gas and detecting the air-fuel ratio linearly is provided upstream of the exhaust gas purification catalyst, The air-fuel ratio control target is feedback-controlled based on the output of the upstream-side air-fuel ratio sensor so that the actual change in the air-fuel ratio on the upstream side of the exhaust purification catalyst accompanying the switching of the air-fuel ratio by the fuel-ratio switching means becomes predetermined. Configured.

In this way, for example, the engine individual difference,
Due to manufacturing variations of fuel / intake systems, aging, etc., the actual air-fuel ratio changed more than the change in the given air-fuel ratio, or the actual air-fuel ratio did not change until the change in the expected air-fuel ratio. In such a case, the air-fuel ratio may become richer or leaner than a predetermined value, thereby deteriorating the exhaust purification performance or deteriorating the engine stability and hunting. Since the change width, the amplitude cycle, etc.) can be controlled to a predetermined (target), even if the air-fuel ratio is switched for the purpose of diagnosing an abnormality of the downstream oxygen sensor, such a concern can be surely eliminated.

According to an eleventh aspect of the present invention, there is provided the exhaust gas purifying catalyst abnormality diagnostic apparatus, wherein the downstream side oxygen sensor operates normally by the oxygen sensor abnormality diagnostic apparatus according to any one of the seventh to tenth aspects. When the diagnosis is made, the abnormality diagnosing device for the exhaust purification catalyst is activated. With this configuration, the abnormality of the exhaust purification catalyst is diagnosed after confirming that the downstream oxygen sensor is normal, so that the abnormality diagnosis accuracy of the exhaust purification catalyst can be significantly improved.

[0025]

An embodiment of the present invention will be described below with reference to the accompanying drawings. In FIG. 2 showing the configuration of an embodiment of the present invention, an air flow meter 13 for detecting an intake air flow rate Qa and a throttle valve 14 for controlling the intake air flow rate Qa in conjunction with an accelerator pedal are provided in an intake passage 12 of an engine 11.
Is provided, and an electromagnetic fuel injection valve 15 is provided for each cylinder in a downstream manifold portion.

The fuel injection valve 15 is driven to open by a drive pulse signal set in the control unit 50 as will be described later, and is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator (not shown). Injected fuel is supplied. Further, a water temperature sensor for detecting a cooling water temperature Tw in a cooling jacket of the engine 11.
16 are provided.

On the other hand, an upstream wide-range air-fuel ratio sensor 18 is provided in the exhaust passage 17 in the vicinity of the manifold assembly so as to detect the air-fuel ratio over a wide range from rich to lean by detecting the oxygen concentration in the exhaust gas. On the downstream side, the stoichiometric air-fuel ratio {A / F (air weight / fuel weight)} 14.7,
In other words the air excess ratio λ = 1} CO in the exhaust to a maximum in the vicinity of the three-way catalyst 20 as an exhaust gas purifying catalyst for purifying exhaust by performing the reduction of oxidation and NO _X of HC is interposed. The exhaust purification catalyst is not limited to a three-way catalyst, but may be an oxidation catalyst, a lean NOx catalyst, or the like.

The upstream wide-range air-fuel ratio sensor 18 has, for example, a configuration as shown in FIG. That is, FIG.
As shown in (1), a body (formed of, for example, a heat-resistant porous insulating material such as zirconia Zr ₂ O ₃ having oxygen ion conductivity) having a heater portion 2 communicates with the atmosphere (standard gas). And a gas diffusion layer (or gas diffusion gap) 6 communicating with a gas to be detected (for example, exhaust gas from an internal combustion engine) via the gas introduction hole 4, the protective layer 5, and the like. ing. The sensing unit electrodes 7A and 7B are provided facing the air introduction hole 3 and the gas diffusion layer 6, and the oxygen pump electrodes 8A and 8B are provided on the gas diffusion layer 6 and the corresponding periphery of the main body 1. It has become.

The sensing portion electrodes 7A and 7B (sensor portions) apply a voltage generated according to the oxygen partial pressure ratio between the sensing portion electrodes which is affected by the oxygen ion concentration (oxygen partial pressure) in the gas diffusion layer 6. It is designed to detect.
On the other hand, oxygen pump electrodes 8A and 8B (specific component pump section)
, A predetermined voltage is applied. That is, the sensing unit electrodes 7A and 7B detect the voltage generated by the oxygen partial pressure ratio between the sensing unit electrodes, and determine whether the air-fuel ratio is rich with respect to the stoichiometric air-fuel ratio (in other words, the excess air ratio λ = 1). It can detect whether it is lean.

On the other hand, in the oxygen pump electrode portions 8A and 8B, which can be shown by a model diagram as shown in FIG. 4, when a predetermined voltage is applied, oxygen ions in the gas diffusion layer 6 move according to the predetermined voltage. Thus, a current flows between the oxygen pump electrode portions 8A and 8B. The current value (limit current) Ip flowing between the oxygen pump electrode portions 8A and 8B when a predetermined voltage is applied between the electrodes is affected by the oxygen ion concentration in the gas diffusion layer 6, so that the current value (Limit current)
If Ip is detected, the air-fuel ratio of the detection target gas (in other words, the excess air ratio λ) can be detected.

Accordingly, for example, a correlation between the current / voltage between the oxygen pump electrodes and the air-fuel ratio of the gas to be detected (in other words, excess air ratio λ) as shown in Table A of FIG. 4 is obtained. Will be. In addition, the sensing unit electrode 7A,
By inverting the application direction of the voltage to the oxygen pump electrode units 8A and 8B based on the rich / lean output of 7B, the oxygen pump electrode units 8A and 8B can be connected in both the lean and rich air-fuel ratio regions. This enables detection of a wide range of air-fuel ratios based on the current value (limit current) Ip flowing through.

Based on the above-described air-fuel ratio detection principle, the control unit 50 detects the current value Ip between the oxygen pump electrode portions 8A and 8B of the upstream wide area air-fuel ratio sensor 18,
For example, the actual air-fuel ratio of the exhaust gas (excess air ratio λ) is linearly detected over a wide range by referring to Table B in FIG. On the outlet side of the three-way catalyst 20, a downstream oxygen sensor 19 (a sensor that outputs a rich / lean signal with respect to the stoichiometric air-fuel ratio) having the same function as the conventional one is provided.

A distributor (not shown in FIG. 2) has a built-in crank angle sensor 21. The control unit 50 controls a crank unit angle signal output from the crank angle sensor 21 in synchronization with the engine rotation. The engine rotation speed Ne is detected by counting time or measuring the generation cycle of the crank reference angle signal. Incidentally, the control unit 50 includes a CPU, a ROM, a RAM,
And a microcomputer including an I / D converter and an input / output interface. The microcomputer receives input signals from various sensors, and receives, for example, the injection amount of the fuel injector 15 (that is, the air-fuel ratio) as follows. Control object). Examples of the various sensors include the above-described upstream wide-area air-fuel ratio sensor 18, the air flow meter 13, the water temperature sensor 16, the crank angle sensor 21, and the like.

That is, the intake air flow rate Qa obtained from the voltage signal from the air flow meter 13 and the crank angle sensor
The basic fuel injection pulse width (corresponding to the fuel injection amount) Tp = c × Q from the engine rotation speed Ne obtained from the signal from 22
a / Ne (where c is a constant) is calculated, and a final temperature is calculated by a water temperature correction coefficient Kw forcibly correcting to a rich side at a low water temperature, a start and post-start increase correction coefficient Kas, an air-fuel ratio feedback correction coefficient α, and the like. Effective fuel injection pulse width Te
= Tp x (1 + Kw + Kas + ...) x α + Ts. Ts is a voltage correction amount.

Then, the effective fuel injection pulse width Te is sent to the fuel injection valve 15 as a drive pulse signal, and the fuel adjusted to a predetermined amount is injected and supplied. The air-fuel ratio feedback correction coefficient α is a control unit for correcting a deviation of a detection value (actual air-fuel ratio) detected by the upstream wide-range air-fuel ratio sensor 18 from a target air-fuel ratio.
The control unit 50 corrects the basic fuel pulse width Tp based on the coefficient, and the air-fuel ratio is feedback-controlled to a target air-fuel ratio (for example, a stoichiometric air-fuel ratio).

Here, the basic concept of the abnormality diagnosis control of the exhaust purification catalyst executed by the control unit 50 in the present embodiment will be described. That is, the abnormality diagnosis of the exhaust gas purification catalyst in the present embodiment is performed during the steady running state (the steady state of the engine 11) during the upstream wide area air-fuel ratio sensor.
When the air-fuel ratio control target (fuel injection amount or intake air flow rate) is feedback-controlled so that the actual air-fuel ratio (detected value) detected by 18 becomes the target air-fuel ratio, the target air-fuel ratio is forcibly set. The amplitude is set to a predetermined period and a predetermined width.

In this way, the air-fuel ratio control target (fuel injection amount or intake air flow rate) is changed according to the compulsory amplitude of the target air-fuel ratio. The exhaust gas which repeats the rich / lean inversion is introduced. At this time, if the three-way catalyst 20 is normal, its oxygen storage capacity is sufficiently exhibited, so that when the introduced air-fuel ratio is on the lean side during the rich / lean reversal, the oxygen adsorbing component on the catalyst surface is reduced. The air-fuel ratio in the vicinity of the catalyst surface is brought closer to the stoichiometric air-fuel ratio from the lean side (thus, the three components of NOx, CO, and HC are satisfactorily purified). The air-fuel ratio of the exhaust gas derived from the catalyst 20 approaches the stoichiometric air-fuel ratio.

On the other hand, if the three-way catalyst 20 is normal, if the introduced air-fuel ratio is on the rich side during the rich / lean reversal, the separation of oxygen molecules from the oxygen adsorbed component is performed on the catalyst surface. Therefore, the air-fuel ratio in the vicinity of the catalyst surface approaches the stoichiometric air-fuel ratio from the rich side (this allows NOx, C
The three components of O and HC are satisfactorily purified), so that the air-fuel ratio of the exhaust gas derived from the three-way catalyst 20 approaches the stoichiometric air-fuel ratio.

That is, if the three-way catalyst 20 is normal, even if the air-fuel ratio is rich / lean reversed at the inlet side of the three-way catalyst 20 (on the side where the upstream wide-range air-fuel ratio sensor 18 is mounted), the oxygen contained in the catalyst is not affected. Due to the molecule adsorbing / desorbing action, exhaust gas in which the rich / lean reversal of the air-fuel ratio has been attenuated is led to the outlet side (downstream oxygen sensor 19 side) of the three-way catalyst 20.

On the other hand, if there is an abnormality in the three-way catalyst 20,
Since the oxygen storage capacity is reduced, the adsorption and desorption of oxygen molecules cannot be exhibited as well as in a normal state, so the inlet side of the three-way catalyst 20 (the upstream side wide air-fuel ratio sensor 18 mounting side).
If the air-fuel ratio is reversed rich / lean with
Lean reversal is exhausted to the outlet side (downstream oxygen sensor 19 side) without being greatly attenuated.

Therefore, during the air-fuel ratio feedback control, the target air-fuel ratio is forcibly made to have a predetermined period and a predetermined width, and the rich / lean inversion period of the output signal of the upstream wide area air-fuel ratio sensor 18 at that time. (T1 or the fluctuation period of the target air-fuel ratio given by the control unit 50 may be used)
When observing the rich-lean inversion cycle (T2) of the output signal of the downstream oxygen sensor 19, the abnormality of the three-way catalyst 20 (deterioration of oxygen storage capacity due to thermal deterioration, poisoning, melting, etc.) The diagnosis can be made.

Even if the air-fuel ratio feedback control is not being performed, the air-fuel ratio control target is forcibly directly changed by the air-fuel ratio feedforward control so that the exhaust air-fuel ratio is rich / lean inverted. Observing the rich / lean inversion cycle (T1) of the output signal of the upstream wide area air-fuel ratio sensor 18 and the rich / lean inversion cycle (T2) of the output signal of the downstream oxygen sensor 19, the three-way catalyst
It can diagnose 20 abnormalities (decrease in oxygen storage capacity due to thermal deterioration, poisoning, melting, etc.).

By the way, if the exhaust air-fuel ratio is changed without limitation for abnormality diagnosis of the exhaust purification catalyst,
Since the exhaust gas purification performance of the three-way catalyst 20 may be deteriorated, the range in which the exhaust air-fuel ratio is changed (fluctuation cycle, amplitude)
It is preferable to restrict the change in the exhaust gas purification performance of the three-way catalyst 20 to an allowable range. Incidentally, in the catalyst perturbation control proposed by the present applicant, etc. ｛the air-fuel ratio feedback control using a wide-range air-fuel ratio sensor capable of detecting the air-fuel ratio over a wide range, it is only necessary to determine whether the stoichiometric air-fuel ratio is rich or lean. Compared to air-fuel ratio feedback control using an undetectable oxygen sensor, there is less opportunity for rich / lean reversal of the exhaust air-fuel ratio at the exhaust purification catalyst inlet, so adsorption and desorption of oxygen molecules on the catalyst surface is performed effectively. There is a concern that the efficiency of purifying the three components (NOx, CO, HC) at the same time may decrease, but in order to suppress this, the air-fuel ratio at the catalyst inlet (in other words, the purification of the three components) is forcibly reduced. In order to maximize efficiency, the upstream wide-range air-fuel ratio sensor is monitored during execution of control さ せ る, in which the target air-fuel ratio is made to have a predetermined period and a predetermined amplitude while monitoring with the wide-range air-fuel ratio sensor.
Observing the rich / lean inversion cycle (T1) of the output signal of the output signal 18 and the rich / lean inversion cycle (T2) of the output signal of the downstream oxygen sensor 19, the abnormality of the three-way catalyst 20 (thermal deterioration,
By diagnosing the decrease in oxygen storage capacity due to poisoning or melting, etc.), it is possible to maximize the exhaust gas purification performance of the three-way catalyst 20 by controlling the catalyst perturbation, and at the same time, to diagnose the abnormality of the three-way catalyst 20 This is also effective because it can be performed with high accuracy.

In the above description, the target air-fuel ratio or the air-fuel ratio control target is controlled so that the exhaust air-fuel ratio at the inlet of the three-way catalyst 20 repeats the rich-lean inversion, and based on the rich-lean inversion cycle and the like. Although the description has been made on the assumption that the abnormality of the three-way catalyst 20 is diagnosed, the present invention is not limited to this. For example, the control state of the air-fuel ratio / air-fuel ratio control object is changed so that the exhaust air-fuel ratio at the inlet of the three-way catalyst 20 is switched to the rich side or the lean side, and the switching timing (or the air-fuel ratio or the air-fuel ratio control object) is changed. Of the downstream oxygen sensor 19, such as the time (response time) from the time when the upstream air-fuel ratio sensor 18 changes by a predetermined amount to the time when the downstream oxygen sensor 19 changes by a predetermined amount (the response time). This makes it possible to diagnose an abnormality of the three-way catalyst 20 (a decrease in oxygen storage capacity due to thermal deterioration, poisoning, melting, etc.).

That is, if the three-way catalyst 20 is normal, even if the exhaust air-fuel ratio is switched to the rich side or the lean side at the inlet side of the three-way catalyst 20, the three-way catalyst 20 has a three-way At the outlet side of the catalyst 20, the switching will appear after a relatively long period of time, but if there is an abnormality in the three-way catalyst 20, the oxygen storage capacity of the three-way catalyst 20 is reduced, When the exhaust air-fuel ratio is switched to the rich side or the lean side on the inlet side of the catalyst 20, the switching appears on the outlet side of the three-way catalyst 20 in a relatively short time.

Accordingly, the degree of change in the output signal of the downstream oxygen sensor 19, such as the time from when the air-fuel ratio or the control state of the air-fuel ratio control object is switched to when the switching is detected by the downstream oxygen sensor 19, is determined. By observing, it is possible to diagnose an abnormality of the three-way catalyst 20.
The abnormality diagnosis control of the exhaust purification catalyst performed by the control unit 50 of the present embodiment based on the above-described concept is described with reference to FIG.
This will be described according to the flowchart shown in FIG. The functions of the air-fuel ratio switching unit and the abnormality diagnosis unit according to the present invention are provided by the control unit 50 as software as described below.

In step (denoted by S in the figure, the same applies hereinafter), it is determined whether or not a diagnosis permission condition is satisfied. That is, for example, until the following conditions are satisfied:
Abnormality diagnosis is not allowed. For example, engine start key on → off (Key on → o
ff) It is determined whether or not a predetermined time has elapsed since the start (in other words, whether or not a predetermined time has elapsed after the start), and if it has not elapsed, the start of diagnosis is not permitted. For example, erroneous diagnosis due to the effect of increased amount at start-up and wall flow formation, and upstream wide area air-fuel ratio
This is to prevent erroneous diagnosis due to the diagnosis being performed under the inactive state of the downstream oxygen sensor 19 and the three-way catalyst 20.

It is determined whether or not the activity determination of the upstream wide-area air-fuel ratio sensor 18 and the downstream oxygen sensor 19 has been completed. If not, the abnormality diagnosis is not permitted. This is for preventing erroneous diagnosis due to the diagnosis being performed in the inactive state of each sensor. It is determined whether the air-fuel ratio feedback control (A / F control) condition (for example, the engine operation is in a steady state) is satisfied and the above-described catalyst perturbation control is executed, and if not, the abnormality diagnosis is not permitted. It has become. For example, during execution of the catalyst perturbation control, the air-fuel ratio at the inlet of the three-way catalyst 20 is determined by a wide-range air-fuel ratio sensor.
Since the conversion efficiency (purification efficiency) of three components (NOx, CO, HC) is increased by a predetermined amount in a predetermined period while monitoring at 18, the abnormality diagnosis is performed with high accuracy while maintaining the exhaust performance well. It is because it can perform.

It is determined whether or not the three-way catalyst 20 is activated, and if it is not activated, the start of diagnosis is not permitted. This is because when the three-way catalyst 20 is not activated, the oxygen storage capacity is also reduced, so that it is not possible to perform the abnormality diagnosis of the three-way catalyst 20 with high accuracy. When the above conditions are satisfied, the process proceeds to step 2,
In step 2, the target air-fuel ratio {} or the control state {} of the air-fuel ratio control target (fuel injection amount or intake air flow rate) is switched. If the catalyst perturbation control is being executed, this step can be omitted.

In step 3, monitoring of the output of the downstream oxygen sensor 19 is started. In the following step 4, the response of the downstream oxygen sensor 19 is determined. For example, as shown in FIG. 7, from the time when the target air-fuel ratio is switched (or the time when the output of the upstream wide-range air-fuel ratio sensor 18 changes by a predetermined amount in accordance with the switching of the target air-fuel ratio), the downstream oxygen sensor 19 Is a predetermined time (CATN)
GT) or more. If the time is equal to or longer than the predetermined time (CATNGT) (YES), the process proceeds to step 5, and if the time is shorter than the predetermined time (CATNGT) (NO), the process proceeds to step 6.

The time required for changing the target air-fuel ratio and for the output value of the downstream oxygen sensor 19 to converge to a value corresponding to the changed target air-fuel ratio is measured. It can also be determined based on whether or not. When the target air-fuel ratio is switched at a predetermined cycle and a predetermined amplitude in step 2 or when the catalyst perturbation control is performed, the upstream wide-range air-fuel ratio sensor 18 and the downstream oxygen sensor 19 are controlled. The output signal is read, the rich / lean inversion cycle (T1, T2) is detected, the inversion frequency ratio (HZRATE) is calculated, and the abnormality of the three-way catalyst 20 can be diagnosed by referring to, for example, FIG. . Note that the rich / lean inversion cycle (T1) of the upstream wide area air-fuel ratio sensor 18 may be set to the amplitude cycle of the target air-fuel ratio.

In step 5, the time required for the output of the downstream oxygen sensor 19 to change by a predetermined amount is equal to a predetermined time (CATN).
GT) or more, the forcible change in the target air-fuel ratio
Since it can be determined that the three-way catalyst 20 has been stolen by the oxygen storage capacity of the three-way catalyst 20, it is determined that the three-way catalyst 20 is normal (OK determination), the process returns, and the abnormality diagnosis is continued. On the other hand, in step 6, since the time required for the output of the downstream oxygen sensor 19 to change by a predetermined amount is shorter than the predetermined time (CATNGT), the forcible change of the target air-fuel ratio is determined by the oxygen storage of the three-way catalyst 20. The three-way catalyst 20 is abnormal (for example, thermal deterioration, poisoning, erosion due to misfiring at high temperature conditions, or physical or thermal It is determined that the oxygen storage capacity is reduced due to damage due to a shock or the like (NG determination), and the process proceeds to step 7.

In step 7, a warning light (MIL) is turned on to make the driver or the like aware that there is some abnormality in the three-way catalyst 20 and urge the driver to take measures such as repair. In addition, when NG determination is made twice (or two trips) continuously,
If the process proceeds to step 7, if the first NG determination is made and the next OK determination is made, the first NG determination is made.
Although there is a concern that the determination may be erroneous, such erroneous determination can be omitted from consideration in the abnormality diagnosis, so that the abnormality diagnosis accuracy of the three-way catalyst 20 can be further improved.

In the above description, the abnormality diagnosis is performed during the air-fuel ratio feedback control. However, the present invention is not limited to this. For example, the target air-fuel ratio or the air-fuel ratio control target (intake air flow rate or fuel injection amount) may be controlled by feedforward control. Even when the control state is switched, the abnormality diagnosis of the three-way catalyst 20 can be performed by observing the state of the change in the detection value of the downstream oxygen air-fuel ratio sensor 18 after the switch, as described above. It is.

Accordingly, it is merely an example that the diagnosis permission condition is satisfied when all of the above-mentioned diagnosis permission conditions are satisfied, and the diagnosis is performed when any of these or any combination thereof is satisfied. The permission condition can be satisfied. Further, for example, even if the diagnosis permission condition is simply set to the steady state of the engine operating state, the downstream side oxygen caused by the switching of the target air-fuel ratio is not affected by the air-fuel ratio change caused by the change in the engine operating state. Since the change in the detection value of the sensor 19 can be detected with high accuracy (regardless of whether the air-fuel ratio is feedback-controlled or feed-forward controlled), it is possible to diagnose the abnormality of the three-way catalyst 20 with high accuracy. You can do it.

As described above, according to this embodiment, the control state of the air-fuel ratio or the control target of the air-fuel ratio (fuel injection amount or intake air flow rate) is forcibly changed, and the output of the downstream oxygen sensor 19 in response to the change. Since the abnormality of the three-way catalyst 20 is diagnosed by observing the change (response time, amplitude frequency, change gradient, etc.), when the wide-range air-fuel ratio sensor 18 is provided upstream of the three-way catalyst 20 Also, with the simple configuration, it is possible to quickly and accurately diagnose whether or not there is an abnormality in the three-way catalyst 20.

Even when the air-fuel ratio feedback control is performed based on the output value of the wide-range air-fuel ratio sensor, the air-fuel ratio on the inlet side of the three-way catalyst 20 is increased so that the exhaust gas purification performance of the three-way catalyst 20 can be maximized. The target air-fuel ratio is changed at a predetermined cycle and a predetermined amplitude while monitoring the (target air-fuel ratio) with a wide area air-fuel ratio sensor. Based on the degree of change (response time, amplitude frequency, change gradient, etc.) of the output value of the downstream oxygen sensor 19 (after the output of the output 18 changes by a predetermined amount), it is diagnosed whether the three-way catalyst 20 is abnormal. By doing so, it is possible to simultaneously determine whether the three-way catalyst 20 has an abnormality while maximizing the exhaust gas purification performance of the three-way catalyst 20.

Next, abnormality diagnosis of the downstream oxygen sensor 19 will be described. In the present embodiment, in step 2 of the flowchart of FIG. 5, the target air-fuel ratio {or the control state of the air-fuel ratio control target (fuel injection amount or intake air flow rate)} is switched, but this target air-fuel ratio or air-fuel ratio control target is switched. Using the switching of the control state, it is also possible to diagnose the abnormality of the downstream oxygen sensor 19.

That is, when the control state of the target air-fuel ratio or the control target of the air-fuel ratio is switched, the output of the downstream oxygen sensor 19 is changed from rich to lean inversion or from lean to rich inversion. At this time, the output of the downstream oxygen sensor 19 at the rich → lean inversion change rate or the lean → rich inversion change rate is determined by the deterioration of the downstream oxygen sensor 19 (heat, poisoning, misfire under high temperature conditions, water It changes according to the degree of element breakage due to weighing, poor contact or disconnection of the harness / connector, circuit failure, heater disconnection, etc.).

Accordingly, after switching the control state of the target air-fuel ratio or the control target of the air-fuel ratio, the output of the downstream oxygen sensor 19 is changed from rich to lean inversion or from lean to rich inversion (for example, from the start of rich / lean inversion). By observing the time required for the output of the predetermined amount to change, or the slope of the change, the abnormality of the downstream oxygen sensor 19 can be diagnosed. In this way, the control state of the target air-fuel ratio or the air-fuel ratio control target is forcibly switched, and the output change degree of the downstream oxygen sensor 19 from the start of the rich / lean inversion of the output of the downstream oxygen sensor 19 is observed. By doing so, even when the air-fuel ratio feedback control is performed using the wide area air-fuel ratio sensor, it is possible to diagnose the abnormality of the downstream oxygen sensor 19 with high accuracy while securing a diagnosis opportunity.

That is, when the air-fuel ratio feedback control is performed using the wide-range air-fuel ratio sensor, the air-fuel ratio has less chance of rich / lean reversal than when the air-fuel ratio feedback control is performed using the oxygen sensor. There is less opportunity to observe the degree of output change of the downstream oxygen sensor 19 from the start of rich / lean reversal of the output of the oxygen sensor 19, and there is less diagnostic opportunity for the downstream oxygen sensor 19, but this can be improved. . Also, since the target air-fuel ratio or the amount of change in the control state of the air-fuel ratio control target is set in advance,
It is also possible to improve the diagnostic accuracy of the abnormality diagnosis based on the output change degree of the downstream oxygen sensor 19 from the start of the rich / lean inversion of the output of the downstream oxygen sensor 19.

The abnormality diagnosis of the downstream oxygen sensor 19 is performed prior to the abnormality diagnosis of the three-way catalyst 20 described above, and after confirming that the downstream oxygen sensor 19 is normal, the three-way catalyst 20 is checked. It is preferable to perform the abnormality diagnosis of the three-way catalyst 20 in order to enhance the diagnosis accuracy of the abnormality diagnosis of the three-way catalyst 20. Here, the abnormality diagnosis control of the downstream oxygen sensor 19 performed by the control unit 50 will be described with reference to the flowchart of FIG. Incidentally, the air-fuel ratio switching means of the present invention,
The function as the downstream oxygen sensor abnormality diagnosis means is provided by the control unit 50 as software as described below.

In step 11, it is determined whether a condition for permitting diagnosis of the downstream oxygen sensor 19 is satisfied. That is, for example, whether a predetermined time has elapsed after the start, whether the engine 11 is in a steady operation state,
It can be determined based on whether the downstream oxygen sensor 19 is in the active state or the like. In step 12, target air-fuel ratio ｛or air-fuel ratio control target (fuel injection amount or intake air flow rate)
Switch control state｝. Note that this step can be omitted if the catalyst perturbation control for forcibly increasing the target air-fuel ratio is performed during the air-fuel ratio feedback control using the wide area air-fuel ratio sensor.

In step 13, monitoring of the output of the downstream oxygen sensor 19 is started. In the following step 14, the response of the downstream oxygen sensor 19 is determined. For example, as shown in FIG. 7, the target air-fuel ratio {or the control state of the air-fuel ratio control target (fuel injection amount or intake air flow rate)} is switched, and the output of the downstream oxygen sensor 19 changes from the rich side to the lean side. The time required for the output of the downstream oxygen sensor 19 to change by a predetermined amount (downstream oxygen sensor output change time) from the time when the shift (change) from the lean side to the rich side is started is detected. If the time required for the change by the predetermined amount is shorter than the predetermined time (RO2NGT) (YES), the process proceeds to step 15, and if it is equal to or longer than the predetermined time (RO2NGT) (NO), the process proceeds to step 16. .

In step 15, the time required for the output of the downstream oxygen sensor 19 to change by a predetermined amount is equal to a predetermined time (RO2N
GT), the output of the downstream oxygen sensor 19 also changes with good responsiveness in response to the forcible change in the target air-fuel ratio. Therefore, it is determined that the downstream oxygen sensor 19 is normal (OK).
Judgment) and return to continue the abnormality diagnosis. On the other hand, in step 16, since the time required for the output of the downstream oxygen sensor 19 to change by the predetermined amount is as long as the predetermined time (RO2NGT) or more, the detection of the downstream oxygen sensor 19 is performed according to the forcible change in the target air-fuel ratio. It is determined that the output cannot be changed with good responsiveness and the responsiveness is reduced, and the downstream oxygen sensor 19 is abnormal (for example, heat, deterioration due to poisoning, misfire under high temperature conditions, element cracking due to water splash, It is determined that there is a possibility that the harness / connector may have a contact failure, disconnection, circuit failure, heater disconnection, etc.) (NG determination), and the process proceeds to step S17.

When the output of the downstream oxygen sensor 19 starts to change (change) from the rich side to the lean side or from the lean side to the rich side, the output value of the downstream oxygen sensor 19 changes to the target value after the change. The time required to converge to a value corresponding to the air-fuel ratio may be measured, and the determination may be made based on whether the measurement result is equal to or longer than a predetermined time. In addition, by detecting the slope of the change in the output value of the downstream oxygen sensor 19 from the time when the output of the downstream oxygen sensor 19 starts shifting (change) from the rich side to the lean side or from the lean side to the rich side. It is also possible to diagnose an abnormality of the downstream oxygen sensor 19.

In step 37, a warning lamp (MIL) is turned on to make the driver or the like aware that the downstream oxygen sensor 19 has something abnormal, and to urge the driver to take measures such as repair. Then, for example, processing such as prohibiting the abnormality diagnosis control of the three-way catalyst 20 according to the flowchart of FIG. 5 is performed so that the abnormality diagnosis of the three-way catalyst 20 does not occur. If the NG determination is made twice (or two trips) consecutively, the process proceeds to step 37. If the first NG determination is made and the next OK determination is made, the first NG determination is made. May be erroneously determined, but such erroneous determination can be omitted from the abnormality diagnosis, so that the accuracy of the abnormality diagnosis of the downstream oxygen sensor 19 can be further improved.

As described above, according to this embodiment, the control state of the air-fuel ratio or the control target of the air-fuel ratio (fuel injection amount or intake air flow rate) is forcibly changed, and the downstream oxygen sensor 19 is changed in accordance with the change. Diagnosis of abnormal response of the downstream oxygen sensor 19 based on the degree of output change of the downstream oxygen sensor 19 from the time when the output of the sensor starts to shift (change) from the rich side to the lean side or from the lean side to the rich side Therefore, even when the air-fuel ratio feedback control is performed using the wide-range air-fuel ratio sensor 18 provided on the upstream side of the three-way catalyst 20, the downstream oxygen sensor 19 can be quickly and accurately formed with a simple configuration. It is possible to diagnose the presence or absence of abnormalities.

If the above flow is executed during the catalyst perturbation control, the exhaust gas purifying performance of the three-way catalyst 20 can be maximized, and at the same time, it can be diagnosed whether the downstream oxygen sensor 19 is abnormal. .

[0070]

As described above, according to the first aspect of the present invention, the air-fuel ratio (that is, the control state of the air-fuel ratio control object) is forcibly switched, and the downstream oxygen sensor responds to the switching. Since the abnormality of the exhaust purification catalyst is diagnosed by observing the output change, the abnormality diagnosis cannot be performed by the conventional abnormality diagnosis method as in the case where the wide area air-fuel ratio sensor is provided on the upstream side of the exhaust purification catalyst. Even in such a case, it is possible to quickly and accurately diagnose the abnormality of the exhaust gas purification catalyst with a simple configuration.

According to the second aspect of the present invention, it is possible to quickly and accurately diagnose the presence or absence of an abnormality in the exhaust purification catalyst with a simple configuration. According to the invention described in claim 3,
Even when the air-fuel ratio switching instruction is issued, the air-fuel ratio on the upstream side of the exhaust purification catalyst is not actually switched well, or after the air-fuel ratio switching instruction is issued, Since it is possible to prevent the possibility of erroneous diagnosis occurring when there is a response delay for a relatively long time until the air-fuel ratio on the side is switched, the abnormality diagnosis accuracy of the present invention can be further enhanced.

According to the invention described in claim 4, for example,
Diagnosis of exhaust gas purifying catalyst can be diagnosed during catalyst perturbation control, so maximizing the purifying performance of exhaust gas purifying catalyst by catalyst perturbation control, and at the same time, with a simple configuration, quickly and with high accuracy. It is possible to diagnose the presence or absence of abnormalities. According to the fifth aspect of the present invention, the abnormality of the exhaust gas purification catalyst can be diagnosed with higher accuracy.

According to the invention described in claim 6, for example,
The actual air-fuel ratio changes more than the given air-fuel ratio, or the actual air-fuel ratio changes until the given air-fuel ratio changes due to engine individual differences, fuel / intake system manufacturing variations, aging, etc. If not, the air-fuel ratio may become richer or leaner than a predetermined value, resulting in deterioration of the exhaust purification performance and deterioration of engine stability and hunting. Since the change in the fuel ratio (change width, amplitude cycle, etc.) can be controlled to a predetermined (target), such fear can be reliably eliminated.

According to the seventh aspect of the invention, the air-fuel ratio (ie, the control state of the air-fuel ratio control target) is forcibly switched, and the output of the downstream oxygen sensor is switched from the rich side to the lean side in response to the switching. Since the responsiveness abnormality of the downstream oxygen sensor is diagnosed based on the output change degree of the downstream oxygen sensor from the time when the transition (change) from the lean side or the lean side to the rich side is started, a simple configuration and a quick In addition, it is possible to diagnose with high accuracy whether or not the downstream oxygen sensor is abnormal.
Further, even in the case where the air-fuel ratio feedback control is performed using a wide-range air-fuel ratio sensor that has few opportunities for the exhaust air-fuel ratio to undergo rich / lean reversal and few diagnostic opportunities, it is possible to secure an abnormality diagnosis opportunity for the downstream oxygen sensor. .

According to the eighth aspect of the invention, the operation and effect of the seventh aspect of the invention can be achieved quickly and accurately with a simple configuration. According to the ninth aspect of the present invention, for example, an abnormality diagnosis of the exhaust gas purification catalyst can be performed during the catalyst perturbation control. Therefore, while maximizing the purification performance of the exhaust gas purification catalyst by the catalyst perturbation control, at the same time, With a simple configuration, it is possible to quickly and accurately diagnose the presence or absence of an abnormality in the downstream oxygen sensor.

According to the tenth aspect of the present invention, the actual air-fuel ratio may change more than the given air-fuel ratio due to, for example, engine individual differences, manufacturing variations of the fuel system / intake system, and aging. If the actual air-fuel ratio does not change until the change in the air-fuel ratio that should have been given, the air-fuel ratio becomes richer or leaner than a predetermined value and the exhaust purification performance deteriorates, and the engine stability and hunting deteriorate. However, since the actual change in the air-fuel ratio (change width, amplitude cycle, etc.) on the upstream side of the exhaust purification catalyst can be controlled to a predetermined value (target), it is necessary to diagnose the abnormality of the downstream oxygen sensor. Even if the air-fuel ratio is switched, such fear can be reliably eliminated.

According to the eleventh aspect of the present invention, the abnormality of the exhaust gas purifying catalyst is diagnosed after confirming that the downstream oxygen sensor is normal. Therefore, the exhaust gas based on the output of the downstream oxygen sensor is determined. The abnormality diagnosis accuracy of the purification catalyst can be remarkably improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is an overall configuration diagram of an embodiment of the present invention.

FIG. 3 is a diagram showing an example of the structure of a wide area air-fuel ratio sensor;

FIG. 4 is a diagram illustrating the detection principle of a wide area air-fuel ratio sensor.

FIG. 5 is a flowchart illustrating abnormality diagnosis control of the exhaust gas purification catalyst according to the embodiment.

FIG. 6 is a flowchart for explaining abnormality diagnosis control of a downstream oxygen sensor in the embodiment.

FIG. 7 is a time chart for explaining abnormality diagnosis control of the exhaust gas purification catalyst and the downstream oxygen sensor according to the embodiment;

FIG. 8 is an overall configuration diagram of a conventional device.

FIG. 9 shows a conventional inversion frequency ratio (HZRATE = f2 / f).
Flowchart for explaining three-way catalyst abnormality diagnosis control based on 1)

FIG. 10 is a diagram illustrating a rich / lean inversion cycle (T1) of an output signal of an upstream oxygen sensor and a rich / lean inversion cycle (T2) of an output signal of a downstream oxygen sensor.

FIG. 11 is a diagram showing the relationship between the degree of catalyst deterioration and HZRATE.

[Explanation of symbols]

 11 Internal combustion engine 12 Intake passage 13 Air flow meter 14 Throttle valve 15 Fuel injection valve 17 Exhaust passage 18 Upstream wide area air-fuel ratio sensor 19 Downstream oxygen sensor 20 Three-way catalyst (exhaust purification catalyst) 21 Crank angle sensor 50 Control unit

Claims (11)

[Claims] 1. An abnormality diagnosis device for an exhaust purification catalyst for purifying exhaust gas of an internal combustion engine, comprising: air-fuel ratio switching means for switching an air-fuel ratio of an engine intake air-fuel mixture; A downstream oxygen sensor that detects the concentration of a specific component in the exhaust gas downstream of the exhaust purification catalyst and outputs a rich / lean signal for a predetermined air-fuel ratio; and a downstream oxygen sensor when the air-fuel ratio is switched by the air-fuel ratio switching unit. An abnormality diagnosing device for an exhaust purification catalyst, comprising: an abnormality diagnosing means for diagnosing an abnormality of the exhaust purification catalyst based on a change in the output of the side oxygen sensor. 2. The time required for the abnormality diagnosis means to change the output of the downstream oxygen sensor by a predetermined amount toward the air-fuel ratio after switching from when the air-fuel ratio is switched by the target air-fuel ratio switching means. The abnormality diagnosis device for an exhaust purification catalyst according to claim 1, wherein the abnormality of the exhaust purification catalyst is diagnosed on the basis of: 3. An air-fuel ratio switching device comprising: an upstream-side air-fuel ratio sensor for detecting a concentration of a specific component in exhaust gas and detecting an air-fuel ratio linearly on an upstream side of the exhaust purification catalyst; 3. An abnormality diagnosis of the exhaust purification catalyst according to claim 1, wherein the switching is detected based on a change in the output of the upstream air-fuel ratio sensor toward the air-fuel ratio after the switching. apparatus. 4. The apparatus for diagnosing abnormality of a wide-range air-fuel ratio sensor according to claim 1, wherein said air-fuel ratio switching means is means for oscillating an air-fuel ratio. 5. An abnormality diagnosis means for diagnosing an abnormality of an exhaust purification catalyst based on a switching cycle of an air-fuel ratio by the air-fuel ratio switching means and an output change cycle of the downstream oxygen sensor. The method according to claim 1,
An abnormality diagnosis device for an exhaust purification catalyst according to any one of claims 3 and 4. 6. An air-fuel ratio switching means for detecting an air-fuel ratio by an air-fuel ratio switching means, comprising an upstream air-fuel ratio sensor for detecting a concentration of a specific component in exhaust gas and detecting an air-fuel ratio linearly on an upstream side of the exhaust purification catalyst. An air-fuel ratio control target is feedback-controlled based on an output of an upstream-side air-fuel ratio sensor so that a change in an actual air-fuel ratio on the upstream side of the exhaust purification catalyst accompanying the switching becomes a predetermined value. An air-fuel ratio control device for an internal combustion engine according to claim 5. 7. An exhaust purification catalyst for purifying exhaust gas from an internal combustion engine, which detects a concentration of a specific component in exhaust gas downstream of the exhaust purification catalyst and outputs a rich / lean signal for a predetermined air-fuel ratio. An abnormality diagnosis device for a downstream oxygen sensor, comprising: air-fuel ratio switching means for switching an air-fuel ratio of an engine intake air-fuel mixture; and after the output of the downstream oxygen sensor is switched after the air-fuel ratio is switched by the air-fuel ratio switching means. Downstream oxygen sensor abnormality diagnosing means for diagnosing an abnormality of the downstream oxygen sensor based on a change in the output of the downstream oxygen sensor from when the change is started toward the air-fuel ratio of Diagnostic device for oxygen sensor. 8. The method according to claim 1, wherein the downstream oxygen sensor abnormality diagnostic means starts changing the output of the downstream oxygen sensor toward the switched air-fuel ratio after the air-fuel ratio is switched by the air-fuel ratio switching means. The oxygen sensor abnormality diagnostic device according to claim 7, wherein the abnormality of the downstream oxygen sensor is diagnosed based on a time required until the predetermined amount changes. 9. The air-fuel ratio switching device according to claim 7, wherein the air-fuel ratio switching device is a device for making the air-fuel ratio oscillate.
An abnormality diagnostic device for an oxygen sensor according to claim 1. 10. When an upstream air-fuel ratio sensor for detecting the concentration of a specific component in exhaust gas and linearly detecting an air-fuel ratio is provided upstream of the exhaust gas purification catalyst, The air-fuel ratio control target is feedback-controlled based on an output of an upstream air-fuel ratio sensor so that a change in an actual air-fuel ratio on the upstream side of the exhaust purification catalyst accompanying the switching becomes a predetermined value. An air-fuel ratio control device for an internal combustion engine according to claim 9. 11. An abnormality diagnosing device for an exhaust purification catalyst when the oxygen diagnosing device for an oxygen sensor according to any one of claims 7 to 10 diagnoses that the downstream oxygen sensor is normal. The abnormality diagnosis device for an exhaust purification catalyst according to any one of claims 1 to 6, wherein the device operates.