CN101037954A - Internal combustion engine exhaust purification system diagnostic device, exhaust purification system, and diagnostic method - Google Patents

Abstract

The invention relates to an internal combustion engine exhaust gas purification system diagnostic apparatus, an exhaust gas purification system, and a diagnostic method. An apparatus for an exhaust system comprising: the exhaust system includes a main exhaust passage, a main catalytic converter disposed in the main exhaust passage, a bypass catalytic converter disposed in the bypass exhaust passage, and a valve for opening or closing a portion of the main exhaust passage. The bypass exhaust passage bypasses the main exhaust passage between a branch point at which the bypass exhaust passage branches off from the main exhaust passage and a junction, at an upstream side of the main catalytic converter, at which the bypass passage merges into the main exhaust passage. The first sensor indicates a first air-fuel ratio of the exhaust gas in the bypass exhaust passage, and the second sensor indicates a second air-fuel ratio of the exhaust gas flowing into the main catalytic converter. The controller determines whether the valve in the closed setting leaks exhaust gas based on the air-fuel ratios of the first and second exhaust gases.

Description

Internal combustion engine exhaust purification system diagnostic device, exhaust purification system, and diagnostic method

technical field

The present invention relates to the technical field of purifying exhaust gas discharged from an internal combustion engine (hereinafter also referred to as "engine"). As used herein, the term "purification" refers to reducing the toxicity of exhaust gas emitted by an internal combustion engine. In particular, the present invention relates to the diagnosis of whether there is leakage in a flow path switching valve in an exhaust purification system.

Exhaust is introduced into a bypass exhaust passage containing a bypass catalytic converter. Preferably, the bypass exhaust passage is arranged relatively upstream of the main catalytic converter of the conventional exhaust system, and the flow switching valve diverts the exhaust gas through the bypass exhaust passage after the start of the cold start of the engine.

Background technique

As a rule, the exhaust gas cannot be sufficiently purified between a cold start of the internal combustion engine and full activation of the catalytic converter, ie when the temperature of the catalytic converter rises sufficiently high. This is especially the case when the main catalytic converter is arranged some distance downstream of the engine (for example, under the car). However, if the main catalytic converter is located closer to the engine, the durability or life of the catalyst may be significantly compromised due to thermal degradation.

The associated exhaust system includes a bypass exhaust passage and a bypass catalytic converter arranged in parallel with an upstream portion of the main exhaust passage leading to the main catalytic converter. The flow path switching valve is used to introduce exhaust gas into the bypass exhaust passage immediately after cold start of the engine starts. In this way, since the bypass catalytic converter is arranged upstream of the exhaust system relative to the main catalytic converter, it can be activated more quickly, so that the purification of the exhaust gas starts earlier.

In a related exhaust system, when the flow path switching valve does not completely switch the flow path (for example, when the flow path switching valve prevents the exhaust gas from leaking to the main exhaust passage, the exhaust gas leaks to the main exhaust passage), Raw exhaust may be vented into the air until the main catalytic converter is fully activated.

The associated exhaust system includes a method for detecting a reduction in flow caused by use of a flow path switching valve; however, the associated exhaust system does not include any mechanism related to diagnosing leaks of raw exhaust. Therefore, a device capable of accurately diagnosing the leakage of the flow path switching valve is required.

Contents of the invention

The invention relates to a device for diagnosing an exhaust gas purification system of an internal combustion engine. The exhaust purification system includes a main exhaust passage connected to the internal combustion engine and a main catalytic converter disposed downstream along the main exhaust passage. A bypass exhaust passage for bypassing the main exhaust passage is provided at a part of the main exhaust passage upstream of the main catalytic converter. In addition, a bypass catalytic converter is provided along the bypass exhaust passage. Furthermore, the portion of the main exhaust passage that is bypassed by the bypass exhaust passage is provided with a valve for closing the main exhaust passage. The bypass exhaust passage has a first sensor for detecting an air-fuel ratio of exhaust gas flowing through the bypass exhaust passage. In addition, the main exhaust passage has a second sensor for detecting the air-fuel ratio of exhaust gas introduced into the main catalytic converter. The first and second sensors are connected to the controller.

Leakage of the valve is diagnosed when the valve is in the closed state. According to an aspect of an embodiment of the present invention, based on the first sensor for detecting the air-fuel ratio of exhaust gas passing through the bypass exhaust passage and the second sensor for detecting the air-fuel ratio of exhaust gas passing through the main exhaust passage Diagnose the leak. Since leakage of a valve is diagnosed using an air-fuel ratio sensor conventionally available in control of an internal combustion engine, diagnosis may be performed without an additional sensor.

According to an aspect of an embodiment of the invention, there is provided an apparatus for diagnosing an exhaust purification system of an internal combustion engine. The device includes: a main exhaust passage; a main catalytic converter disposed in the main exhaust passage; a bypass exhaust passage in fluid communication with the main exhaust passage such that the main exhaust passage is in bypass exhaust Partial bypass between the branch point where the passage diverges from the main exhaust passage and the junction where the bypass exhaust passage merges into the main exhaust passage on the upstream side of the main catalytic converter; the bypass catalytic converter, which is disposed in the bypass exhaust passage; a valve disposed in said portion of the main exhaust passage for opening or closing said portion of the main exhaust passage; a first sensor disposed in the bypass exhaust passage to output a first signal representing a first air-fuel ratio of exhaust gas flowing in the bypass exhaust passage; a second sensor which is provided in the main exhaust passage to output a second signal representing exhaust gas flowing into the main catalytic converter; a second signal of the air-fuel ratio; and a controller receiving the first and second signals based on which the controller determines whether the valve in the closed setting is leaking exhaust gas into the portion of the main exhaust passage.

According to another aspect of an embodiment of the present invention, there is provided a method for diagnosing an exhaust purification system of an internal combustion engine, the method comprising: detecting a first air-fuel ratio of exhaust gas flowing through a main exhaust passage including a main catalytic converter; Detecting the second air-fuel ratio of the exhaust gas flowing through the bypass exhaust passage, the bypass exhaust passage is in fluid communication with the main exhaust passage, so that the main exhaust passage is separated from the main exhaust passage Partial bypass between the branch point and the junction at the upstream side of the main catalytic converter where the bypass exhaust passage, including the bypass catalytic converter, joins the main exhaust passage; prevents exhaust with a valve flowing along the main exhaust passage; and determining whether exhaust gas is leaking through the valve based on the first and second air-fuel ratios.

Description of drawings

The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate preferred embodiments of the invention and, together with the general description given above and the detailed description given below, serve to explain the features of the invention.

FIG. 1 is a schematic diagram showing an exhaust system of an internal combustion engine constructed in accordance with the present invention.

FIG. 2 is a graph showing leak diagnosis according to the first embodiment of the present invention.

FIG. 3 is a graph showing leak diagnosis according to a second embodiment of the present invention.

Fig. 4 is a flowchart showing the processing of leak diagnosis according to the third embodiment of the present invention.

FIG. 5 is a timing diagram showing leak diagnosis according to the embodiment shown in FIG. 4 .

FIG. 6 is a timing chart showing processing for diagnosing the degree of catalyst degradation.

FIG. 7 is a graph showing the relationship between the time difference ΔT and the degree of catalyst degradation.

FIG. 8 is a graph showing the relationship between the degree of catalyst degradation and the threshold L. FIG.

FIG. 9 is a timing chart showing leak diagnosis according to a fourth embodiment of the present invention.

Detailed ways

Hereinafter, various preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Although the exhaust gas purification system of a four-cylinder internal combustion engine is described, it is of course not limited thereto. This means that internal combustion engines with different configurations, numbers of cylinders and implementations are also foreseen.

FIG. 1 shows a schematic arrangement of an exhaust passage and a controller used in an exhaust system for driving an internal combustion engine of a vehicle.

The cylinder head 1 a of the internal combustion engine 1 has exhaust ports 2 which open laterally from first to fourth cylinders (only one is shown in FIG. 1 ) which can be arranged inside. Each of exhaust ports 2 (only one is shown in FIG. 1 ) is connected to an upstream portion of each main exhaust passage 3 . The upstream parts of the four main exhaust passages 3 corresponding to the first to fourth cylinders (only one is shown in FIG. 1 ) are preferably merged at the part where the flow path switching valve 5 is provided, thereby forming a channel leading to the main catalytic converter. A single main exhaust gas flow passage of the device 4 located in the downstream portion of the main exhaust passage 3 . The main catalytic converter 4, which is preferably located under the vehicle, may have a large capacity and may contain a three-way catalyst as well as a hydrogen carbon (HC) trap catalyst. Exhaust gas discharged from the exhaust port 2 flows through the upstream portion of the main exhaust passage 3, the portion where the flow path switching valve 5 is placed, the downstream portion of the main exhaust flow passage 3, until used for purifying the exhaust gas during normal operation of the engine. The exhaust gas of the main catalytic converter 4. The flow path switching valve 5 may be provided with a closing member that changes the flow path by allowing or preventing exhaust gas from flowing through the exhaust passage 3 . A flow path switching valve 5 (only one is shown in FIG. 1 ), which may be a butterfly valve, a flap valve or any equivalent form, is provided to open or close the main exhaust passage 3 . A single flow path switching valve 5 may be provided behind, for example, a junction of upstream portions of a plurality of main exhaust passages 3 connected to upstream portions of four main exhaust passages 3 of the first to fourth cylinders. The flow path switching valve 5 is preferably driven by an actuator 5 a for reconfiguring the flow path switching valve 5 such as an electric motor, a solenoid, a vacuum switch or any equivalent.

Upstream portions of the four bypass exhaust passages 7 (only one is shown in FIG. 1 ) branch from upstream portions of the corresponding four main exhaust passages 3 . The bypass exhaust passage 7 has a smaller cross-sectional area than that of the main exhaust passage 3 . The branch point 6 (ie, the upstream end of the upstream portion of each bypass exhaust passage 7; only one is shown in FIG. 1 ) is preferably arranged as far upstream as possible upstream of the corresponding main exhaust passage 3 upstream portion. , that is, as close as possible to the cylinder head 1a. The upstream portions of the four bypass exhaust passages 7 preferably merge to form a single bypass exhaust flow passage to the bypass catalytic converter 8 as the downstream portion of the bypass exhaust passage 7 . Preferably, a bypass catalytic converter 8 that can use a three-way catalyst is provided immediately after the confluence of upstream portions of the four bypass exhaust passages 7 . Preferably, the bypass catalytic converter 8 has a capacity smaller than that of the main catalytic converter 4 and contains a catalyst that can be activated optimally at low temperatures. The single exhaust flow passage extending from the outlet of the bypass catalytic converter 8 is preferably connected at the junction 9 of the main exhaust passage 3 (ie upstream of the inlet of the main catalytic converter 4 and downstream of the flow switching valve 5) . That is, bypass exhaust passage 7 is provided to bypass a part of main exhaust passage 3 upstream of main catalytic converter 4 . A flow path switching valve 5 may be installed in this portion of the main exhaust passage 3 .

A main upstream air-fuel ratio sensor 10 and a main downstream air-fuel ratio sensor 11 are provided at the inlet and outlet of the main catalytic converter 4, respectively. Further, a bypass upstream air-fuel ratio sensor 12 and a bypass downstream air-fuel ratio sensor 13 are provided at the inlet and outlet of the bypass catalytic converter 8, respectively. After the main catalytic converter 4 is activated, the main upstream air-fuel ratio sensor 10 and the main downstream air-fuel ratio sensor 11 can perform conventional feedback control of the air-fuel ratio. The air-fuel ratio of the engine may be controlled in response to an output signal from the main upstream air-fuel ratio sensor 10, for example by controlling the amount of fuel injected into the first to fourth cylinders. Any deviation in the control characteristic can be compensated for using the output signal from the main downstream air-fuel ratio sensor 11 . Similarly, when the bypass catalytic converter 8 is used, the bypass upstream air-fuel ratio sensor 12 and the bypass downstream air-fuel ratio sensor 13 can perform conventional feedback control of the air-fuel ratio. That is, when the bypass catalytic converter 8 is used, the air-fuel ratio of the engine can be controlled in response to the output signal from the bypass upstream air-fuel ratio sensor 12 . Any deviation in the control characteristic can be compensated for using the output signal from the bypass downstream air-fuel ratio sensor 13 . The air-fuel ratio sensors 10, 11, 12, and 13 may include broadband air-fuel ratio sensors having a substantially linear output characteristic with respect to the air-fuel ratio of the exhaust gas, or having two output characteristics (for example, indicating a rich air-fuel ratio, or indicating a lean air-fuel ratio sensor). fuel ratio) oxygen sensor. In general, due to the above-mentioned control characteristics of the air-fuel ratio control, it is preferable to use a broadband air-fuel ratio sensor as the upstream air-fuel ratio sensors 10 and 12 and an oxygen sensor as the downstream air-fuel ratio sensors 11 and 13 to provide advantages in cost. The bypass upstream air-fuel ratio sensor 12 may be provided as a first sensing component for detecting the air-fuel ratio in the bypass exhaust flow passage, and the main upstream air-fuel ratio sensor 10 may be provided as a first sensing component for detecting the air-fuel ratio in the main exhaust flow passage, which flows into the main catalyst. The second sensing part of the air-fuel ratio of the exhaust gas of the converter 4.

In addition, each of the first to fourth cylinders of the internal combustion engine 1 includes: a spark plug 21 (only one is shown in FIG. 1 ), an intake passage 22 (only one is shown in FIG. 1 ), and The fuel injection valve 23 in (only one is shown in FIG. 1 ). Preferably, an electronically controlled throttle valve 24 that can be opened or closed using an actuator such as a motor is provided upstream of the intake passage 22 . A plenum may be provided between intake passage 22 and throttle valve 24 . In addition, an air flow meter 25 used in the engine 1 for detecting the amount of intake air may be provided upstream of the throttle valve 24 and downstream of the air cleaner 26 .

The engine control unit 27 controls various parameters of the internal combustion engine 1 (for example, setting the amount of fuel injected by each fuel injection valve 23, setting the spark timing of each spark plug 21, setting the opening degree of the throttle valve 24, driving the brake 5a To set the opening/closing status of the flow path switching valve 5, etc.). In addition to receiving the output signals of the air-fuel ratio sensors 10, 11, 12, and 13, outputs from other sensors such as the coolant temperature sensor 28 and the sensor 29 for detecting the position (ie, the depression amount) of the accelerator pedal operated by the driver The signal can also be input to the engine control unit 27. Preferably, the engine control unit 27 can also diagnose whether there is leakage in the flow path switching valve 5 .

Preferably, the flow path switching valve 5 closes the exhaust passage 3 in response to the low temperature of the engine 1 or the exhaust gas after the start of the cold start. Therefore, the entire exhaust gas discharged from each cylinder flows from the corresponding branch point 6 to the bypass catalytic converter 8 through the corresponding bypass exhaust passage 7 . Since, for example, the bypass catalytic converter 8 is arranged very close to the exhaust port 2 and its size is relatively small, the bypass catalytic converter 8 can be activated quickly. This allows the exhaust to be purged at an early stage after the start of a cold start.

As the temperature of the engine 1 or exhaust gas increases during the warm-up process, since the catalyst of the main catalytic converter 4 is fully activated by the heat, the flow path switching valve 5 opens. Likewise, most of the exhaust gas discharged from the cylinders reaches the main catalytic converter 4 through the main exhaust passage 3 . Although the bypass exhaust passage 7 is not closed, most of the exhaust gas does not flow through the bypass exhaust passage 7 . Instead, the exhaust gas flows through the main exhaust passage 3 . This is because the cross-sectional area of the bypass exhaust passage 7 is smaller than that of the exhaust passage 3, and the bypass catalytic converter 8 provided in the bypass exhaust flow passage causes greater flow resistance. Thermal degradation of the bypass catalytic converter 8 is also avoided due to the difference in flow resistance.

Next, the diagnosis of whether there is any leakage through the flow path switching valve 5 according to the first embodiment of the present invention will be described. In the following embodiments, the two upstream air-fuel ratio sensors 10 and 12 are preferably broadband air-fuel ratio sensors, and the two downstream air-fuel ratio sensors 11 and 13 are preferably oxygen sensors. When diagnosing a leak according to the first embodiment of the present invention, only two upstream air-fuel ratio sensors 10 and 12 are employed.

2 is a diagram showing that when the flow path switching valve 5 is in the closed state after the cold start starts, and the bypass upstream air-fuel ratio sensor 12 provides feedback control of the air-fuel ratio (that is, after the bypass catalytic converter 8 is activated), it is used for diagnosis A series of graphs of the leaked first embodiment. As described above, since the bypass catalytic converter 8 can be quickly activated, the feedback control starts almost immediately after the cold start. Diagnosis can also be performed after activation of the main catalytic converter 4 by temporarily closing the flow path switching valve 5 .

2( a ) is a graph showing the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 (hereinafter also referred to as A graph showing a comparison between the air-fuel ratio AFB) and the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 (hereinafter also referred to as the air-fuel ratio AFM). As shown in Figure 2(a), according to the traditional air-fuel ratio feedback control, the fuel injection amount fluctuates periodically so that the air-fuel ratio of the exhaust gas changes near the theoretical air-fuel ratio (ie, the state of the theoretical air-fuel ratio). The air-fuel ratio is therefore periodically changed from the stoichiometric air-fuel ratio state to each of the rich state and the lean state of combustion of the engine 1 . However, since the bypass upstream air-fuel ratio sensor 12 is directly affected by the exhaust gas from the engine 1, an output signal corresponding to fluctuations in the air-fuel ratio of the engine can be determined. That is, the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 corresponds to the air-fuel ratio of the engine, or can be considered to be the air-fuel ratio of the engine itself. The graph of the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 compared to the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 shows that the rich/lean state exceeding the theoretical air-fuel ratio can be performed in a shorter achieved within the amount of time. It also shows that the change timing, that is, the point at which the change occurs between stoichiometric air-fuel ratio, rich-lean state, is delayed compared to the point at which the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 changes. This is due to the oxygen capacity of the catalyst of the bypass catalytic converter 8 . Oxygen is absorbed when the air-fuel ratio of the exhaust gas becomes a lean state, and oxygen is released when the air-fuel ratio of the exhaust gas becomes a rich state. Therefore, although the air-fuel ratio of the exhaust gas periodically fluctuates between the rich state and the lean state, no change occurs on the downstream side of the bypass catalytic converter 8 until the oxygen capacity of the bypass catalytic converter 8 is saturated.

FIG. 2( b ) shows the relevant characteristics when the flow path switching valve 5 in the closed state has an exhaust gas leak. Since this leak does not affect the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12, there is no change from the normal state shown in FIG. 2(a). However, the main upstream air-fuel ratio sensor 10 detects the exhaust gas leaking through the flow path switching valve 5 , that is, the exhaust gas not passing through the bypass catalytic converter 8 . Therefore, while the bypass upstream air-fuel ratio sensor 12 detects the air-fuel ratio AFB, the detected air-fuel ratio AFM fluctuates between rich and lean states. In addition, the value of the rich/lean state (ie, the magnitude of the periodic change) is lower than the value of the rich/lean state in which the air-fuel ratio AFB is detected by the bypass upstream air-fuel ratio sensor 12 . This is due to dilution caused by mixing with the exhaust gas passing through the bypass catalytic converter 8 .

For example, it is possible to change the rich state to the lean state (and vice versa) in the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 and the corresponding time in the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 ( That is, a time delay Δt is determined between when the rich state changes to the lean state and vice versa). If the time delay Δt is smaller than the threshold value, it is judged that a leak has occurred.

Referring again to FIG. 2( a ), the interval t1 of the rich state or the lean state in the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 can be compared with the corresponding interval t1 in the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 . The interval t2 of the rich state or the lean state is compared. If the intervals t1 and t2 are substantially equal, it is determined that a leak has occurred.

Alternative methods of determining whether a leak has occurred can provide additional reliability. For example, judging a leak may include calculating an average value from multiple air-fuel ratio changes, or evaluating a time delay Δt substantially equal to the difference (t1-t2) between intervals t1 and t2. Methods of using these features are now described.

FIG. 2( c ) shows changes in the air-fuel ratio AFM when the catalyst of the catalytic converter 8 is somewhat deteriorated. When the oxygen capacity decreases due to the deterioration of the catalyst, the basic change of the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 does not change. However, rich/poor status fluctuates faster. That is, the time delay Δt with respect to the change in the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 becomes shorter. However, the time interval t2 of the rich/poor state becomes longer. If the catalyst has degraded to the point of zero oxygen capacity, the time delay Δt or the time intervals t1 and t2 may not be distinguishable from the situation shown in Figure 2(b). However, since the deterioration of the catalyst actually progresses slowly, the time delay Δt or the time intervals t1 and t2 take intermediate values between the characteristics shown in FIGS. 2(a) and 2(b) when the catalyst is partially deteriorated. Therefore, at this stage, it can be judged that the catalyst has deteriorated. Therefore, the deterioration of the catalyst can be distinguished from the judgment that there is leakage of the flow path switching valve 5 .

For example, if the time delay Δt is smaller than the first threshold, it may be determined that a leak has occurred. However, if the time delay Δt is greater than the second threshold, it can be determined that no leakage has occurred. Furthermore, if the time delay Δt falls within a predetermined range, such as itself between the first and second thresholds, the third and fourth thresholds, it can be judged that the catalyst in the bypass catalytic converter 8 has deteriorated . The third and fourth thresholds may be equal to the first and second thresholds, respectively.

The interval t1 at which the rich state or the lean state in the air-fuel ratio AFB is detected by the bypass upstream air-fuel ratio sensor 12 and the interval t2 at which the corresponding rich state or lean state in the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 are performed. judge. If the intervals t1 and t2 are substantially equal to each other, it is judged that a leak has occurred. Also, if the interval t2 is sufficiently smaller than the interval t1, it can be determined that no leakage has occurred. If the interval t2 is slightly smaller than the interval t1, it can be judged that the catalyst in the bypass catalytic converter 8 has deteriorated.

According to the above embodiments, even when the conventional feedback control of the air-fuel ratio continues, the leak of the flow path switching valve 5 can be diagnosed. Furthermore, when this diagnosis is performed, the toxicity of the exhaust gas does not worsen. In addition, accurate leak diagnosis including judging whether or not the catalyst has deteriorated can be performed.

3 is a series of graphs showing a second embodiment according to the present invention for diagnosing a leak after activation of the bypass catalytic converter 8 when the flow path switching valve 5 is in the closed state after the start of a cold start. During this diagnosis, the air-fuel ratio of the engine is forced to change (ie from rich to lean and vice versa) by feed-forward control with a constant period and magnitude.

Similar to Fig. 2(a) ~ 2(c), Fig. 3(a) shows the normal state (no leakage, no catalyst degradation), while Fig. 3(b) shows the occurrence of leakage, Fig. 3(c) shows the catalyst deteriorating. It should be noted that the diagnosis method is the same as that in the first embodiment.

According to the first embodiment shown in FIG. 2 , the change in period and magnitude of the rich/lean state of the air-fuel ratio of the engine need not be constant with respect to the driving conditions of the engine 1 . However, according to the second embodiment, the air-fuel ratio of the engine is regularly changed with a constant period and magnitude. This can improve the accuracy of diagnosing leaks and catalyst degradation. In addition, even when the air-fuel ratio of the engine is forcibly changed in the feedforward control, the rich/lean state is periodically changed with respect to the theoretical air-fuel ratio, so that the average air-fuel ratio can be kept near the theoretical air-fuel ratio. Therefore, the toxicity of the exhaust gas does not deteriorate. Preferably, the period in which the air-fuel ratio of the engine is changed may not be set so long as to significantly reduce the oxygen capacity of the catalyst.

According to an embodiment of the present invention, an apparatus for diagnosing an exhaust purification system of an internal combustion engine is provided. The device includes a bypass exhaust passage arranged upstream of the main catalytic converter. A bypass catalytic converter is provided along the bypass exhaust passage, and a flow path switching valve for diverting exhaust gas through the bypass exhaust passage is provided. The apparatus also includes: a first air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas upstream of the bypass catalytic converter; and a second air-fuel ratio sensor for detecting the air-fuel ratio of the exhaust gas upstream of the main catalytic converter. Leakage of the flow path switching valve can be diagnosed by using detected signals from the first and second sensors when the flow path switching valve is in the closed state.

When the air-fuel ratio of the engine changes periodically between a rich state and a lean state, the leakage of the flow path switching valve can be diagnosed according to the following two steps: (i) determining the rich state and the a time delay of a change between lean states relative to a similar change between states detected by the first air-fuel ratio sensor; and (ii) based on the time delay, it is determined whether there is a leak.

Alternatively, when the air-fuel ratio of the engine is periodically changed between a rich state and a lean state, the leakage of the flow path switching valve may be diagnosed according to the following two steps: (i) determining the value detected by the second air-fuel ratio sensor A time interval in change between the rich state and the lean state and a similar time interval between states detected by the first air-fuel ratio sensor; and (ii) by comparing the time intervals, it is determined whether there is a leak.

To periodically change between the rich state and the lean state, a periodic change of the air-fuel ratio of the engine by feedback control using the first air-fuel ratio sensor may be employed.

Alternatively, during the diagnosis, the air-fuel ratio of the engine may be changed periodically at a predetermined period. In addition, since the average air-fuel ratio is kept substantially at the theoretical air-fuel ratio, the toxicity of exhaust gas does not deteriorate even when the air-fuel ratio of the engine is forcibly changed periodically.

When the flow path switching valve 5 for opening/closing the main exhaust passage 3 is in the closed position, the entire exhaust gas from the internal combustion engine 1 is introduced into the bypass exhaust passage and passes through the bypass catalytic converter. However, when the flow path switching valve 5 is in the open position, most of the exhaust gas from the internal combustion engine 1 bypasses the bypass catalytic converter 8 and then passes through the main catalytic converter 4 . This is due to the different flow resistances in the main exhaust passage 3 and the bypass exhaust passage 7 .

Preferably, the diagnosis for judging whether there is any leakage through the flow path switching valve 5 is performed when the flow path switching valve 5 is in the closed position. For example, diagnosis may be performed by using periodic changes in the air-fuel ratio of the engine in response to feedback control of the air-fuel ratio. When the air-fuel ratio of the engine changes periodically, the signal detected by the first air-fuel ratio sensor 12 also changes periodically together with the air-fuel ratio of the engine. This is because the first air-fuel ratio sensor 12 is provided upstream of the bypass catalytic converter 8 . However, due to the oxygen capacity of the catalyst, the air-fuel ratio of the exhaust gas downstream of the bypass catalytic converter 8 changes within a relatively small range with a time delay with respect to the air-fuel ratio of the engine.

If flow path switching valve 5 does not leak, second air-fuel ratio sensor 10 provided upstream of main catalytic converter 4 receives only exhaust gas that has passed through bypass catalytic converter 8 . As a result, as described above, the air-fuel ratio detected by the second air-fuel ratio sensor 10 changes within a relatively small range with a time lag relative to the periodic variation of the exhaust air-fuel ratio. However, if the flow path switching valve 5 leaks, the air-fuel ratio detected by the second air-fuel ratio sensor 10 changes at approximately the same timing as the exhaust air-fuel ratio. Therefore the air-fuel ratio detected by the second air-fuel ratio sensor 10 also changes with respect to the air-fuel ratio detected by the first air-fuel ratio sensor 12 . This is because at least some of the exhaust gas from the engine 1 passes directly through the second air-fuel ratio sensor 10 , ie without bypassing the catalytic converter 8 . For example, if the difference between the effect of the distance from the exhaust port 2 to the first air-fuel ratio sensor 12 and the distance from the exhaust port 2 to the second air-fuel ratio sensor 10 is ignored, the first air-fuel ratio sensor 12 The rich/lean state of the air-fuel ratio detected by the second air-fuel ratio sensor 10 will change at the same time as the flow path switching valve 5 leaks.

It is thus possible to diagnose whether or to what extent a leak has occurred by means of a time delay or a time interval between changes in the rich/lean state.

As noted above, oxygen capacity can be affected by degradation of the catalyst. However, if deterioration has occurred, the timing of change between the rich/lean states detected by the first air-fuel ratio sensor 12 and the second air-fuel ratio sensor 10 does not completely coincide with each other. Also, the time delay becomes shorter according to the degree of deterioration. Therefore, even if there is catalyst degradation, it can be judged whether or not leakage has occurred.

According to the above embodiments, any leakage of the flow path switching valve 5 can be correctly and easily diagnosed, thereby preventing unpurified exhaust gas from being discharged into the air during the early stages of engine startup.

During the diagnosis, if the rich/lean state changes periodically with respect to stoichiometric air-fuel ratio, the average air-fuel ratio may be equal to or at least close to stoichiometric ratio. Therefore, the toxicity of exhaust gas release does not worsen.

Next, for the diagnosis of the leakage of the flow path switching valve 5, a third embodiment according to the present invention will be described. In the third embodiment, the exhaust system is the same as that in the first embodiment, and the configuration of the exhaust and control systems is the same as that shown in FIG. 1 . In the third embodiment, the bypass upstream air-fuel ratio sensor 12 may be provided as the first air-fuel ratio detection means, and the main upstream air-fuel ratio sensor 10 may be provided as the second air-fuel ratio detection means. A main upstream air-fuel ratio sensor 10 is mounted on a part of the main exhaust flow passage between the junction 9 and the main catalytic converter 4 . This sensor 10 is used to detect the air-fuel ratio of the exhaust gas downstream of the junction 9 where the bypass exhaust flow passage is connected to the main exhaust flow passage. Preferably, the two upstream air-fuel ratio sensors 10 and 12 include broadband air-fuel ratio sensors, and the two downstream air-fuel ratio sensors 11 and 13 include oxygen sensors. Furthermore, in the third embodiment, although the air-fuel ratio of the engine can be changed instantaneously from rich to lean and vice versa, only the change from poor to rich is described.

Fig. 4 shows a flowchart of diagnostic processing according to the third embodiment. First, the angular velocity NE of the engine (for example in terms of revolutions per minute), the load TP of the engine (for example in terms of the amount of injected fuel) and the degree of opening TVO of the throttle valve 24 are read (step S1 ). A judgment is then performed as to whether or not diagnosis can be performed based on the operating conditions NE, TP, and TVO (step S2). The diagnosis is performed when the bypass catalytic converter 8 is activated, the main catalytic converter 4 is not in high-temperature air, and the flow path switching valve 5 is in the closed position. If it is judged that the diagnosis can be performed, the target air-fuel ratio of the internal combustion engine is set to a lean state (step S3). Then, a waiting mode is generated until the signal output from the bypass downstream air-fuel ratio sensor 13 shows a lean state (step S4). That is, the air-fuel ratio of the engine is kept in a lean state until the oxygen capacity of bypass catalytic converter 8 is saturated. Thereafter, the target air-fuel ratio is instantaneously changed to a rich state (step S5). In this case, while monitoring changes in the output signals of the bypass upstream air-fuel ratio sensor 12 and the main upstream air-fuel ratio sensor 10 , diagnostic parameters (described below) are calculated (step S6 ). If the diagnosis for a predetermined period of time is completed after setting the target air-fuel ratio to the rich state (step S7), the target air-fuel ratio is returned to the theoretical air-fuel ratio (step S8). Then, the diagnostic parameter is compared with the threshold L for judging leakage (step S9). Based on, for example, the time elapsed from the change to the rich state (step S5), it can be judged whether the diagnosis is complete. Alternatively, the diagnosis may be completed when the output signal of the bypass downstream air-fuel ratio sensor 13 indicates a rich state. In step S9, if it is determined that the diagnostic parameter is greater than the threshold L, it is determined that the flow path switching valve 5 has leaked, and an alarm can be generated, such as starting an alarm light (not shown) to notify the operator of the vehicle or the vehicle service personnel A fault condition exists (step S10).

FIG. 5, which is a time chart for judging leaks, shows changes in the target engine air-fuel ratio of the internal combustion engine 1, the output signal of the bypass downstream air-fuel ratio sensor 13, the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10, and the output signal from the bypass downstream air-fuel ratio sensor 10. The air-fuel ratio AFB detected by the free air-fuel ratio sensor 12 . As described above, for diagnosis, the target engine air-fuel ratio is forcibly changed from the stoichiometric air-fuel ratio to a lean state, and then instantaneously changed to a rich state. Then, since the flow path switching valve 5 is closed, the exhaust gas flows through the bypass exhaust passage 7, and oxygen is stored in the catalyst of the bypass catalytic converter 8 during the lean state. Heretofore, the output signal of the bypass downstream air-fuel ratio sensor 13 provided downstream of the bypass catalytic converter 8 becomes to show a lean state after a time delay. Furthermore, both the bypass upstream air-fuel ratio sensor 12 and the main upstream air-fuel ratio sensor 10 show that the air-fuel ratio of the exhaust gas is in a lean state. Furthermore, in the third embodiment, after the signal from the bypass downstream air-fuel ratio sensor 13 shows the lean state, the target air-fuel ratio is changed to the rich state with a time delay.

When the air-fuel ratio of the engine changes to a rich state, the air-fuel ratio AFB detected by bypass upstream air-fuel ratio sensor 12 provided upstream of bypass catalytic converter 8 instantaneously changes to a rich state. However, since the oxygen stored in the bypass catalytic converter 8 is released to the downstream of the bypass catalytic converter 8, the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 does not change immediately, that is, as shown by the solid line. Change to rich state after a time delay. That is, as shown by the solid line, when there is no leak, the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 is significantly different from the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 .

However, if the flow path switching valve 5 leaks due to, for example, a sealing defect of the valve body or the like, a part of the amount of exhaust gas reaches the main upstream air-fuel ratio sensor 10 without passing through the bypass catalytic converter 8 . Therefore, the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 shows a relatively richer state, as indicated by the dotted line. In other words, when a leak occurs, the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 is relatively closer to the air-fuel ratio AFB detected by the bypass upstream air-fuel ratio sensor 12 according to the degree of the leak. Likewise, there is at least a small difference between the two air-fuel ratios. Furthermore, when all the oxygen stored in the catalyst is released, the output signal of the bypass downstream air-fuel ratio sensor 13 shows a lean state with a predetermined level, and the target engine air-fuel ratio is changed back to the stoichiometric air-fuel ratio at this stage.

As described above, based on the output signals from the main upstream air-fuel ratio sensor 10 and the bypass upstream air-fuel ratio sensor 12, it can be judged whether there is any leakage. This determination may be performed after the air-fuel ratio of the engine changes between a lean state or a rich state with respect to a stoichiometric air-fuel ratio between the lean state or the rich state. More specifically, the diagnosis may be made using the detected change timing of the air-fuel ratio or the detected difference in the air-fuel ratio (described later).

In other words, in order to express the degree of leakage using a numerical value, it is preferable to determine the average value (AVAFM) of the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 within a predetermined time period T after the change in the target engine air-fuel ratio The average value (AVAFB) of the air-fuel ratio AFB detected by the road upstream air-fuel ratio sensor 12 . Therefore, the above diagnostic parameters can be determined as the difference between the mean values, ie AVAFM-AVAFB. The diagnostic parameter is then compared with a predetermined threshold L. The threshold L can be predetermined according to the degree of leakage to be detected. If diagnostics for detecting lower levels of leaks are desired, the threshold should be set to a larger value (however, more false detections may occur with larger thresholds). Furthermore, the time period T may be set to include, for example, the entire time period during which the target engine air-fuel ratio is in the lean state, or only a part of the entire time period.

The diagnosis using the diagnosis parameter based on the detected air-fuel ratio provides the following effects. In the range where the wideband air-fuel ratio sensor is very sensitive to even small changes in air-fuel ratio, its output signal can change instantaneously even in response to small changes in exhaust air-fuel ratio without any leakage (even at the catalyst's downstream, see Figure 5). Therefore, it may be difficult to perform diagnostics based only on the timing of changes in the output signal. However, when a difference between the air-fuel ratios is detected depending on whether the flow path switching valve 5 leaks, the average value of the air-fuel ratios detected at predetermined intervals is particularly useful as a diagnostic parameter. Therefore, the accuracy of diagnosis can be improved compared to using a time difference using only a set of points according to the varying timing method.

As described above, with respect to the third embodiment, by using the conventional air-fuel ratio sensors 10, 11, 12 and 13 additionally provided for the conventional air-fuel ratio feedback control, any leakage of the flow path switching valve 5 can be easily diagnosed. Therefore, unnecessary discharge of toxic exhaust gas due to a sealing defect of the flow path switching valve 5 or the like can be avoided without an additional sensor.

In addition, oxygen may be sufficiently stored in the catalyst until a saturated state is reached, or the catalyst may be maintained in an oxygen-free state until the air-fuel ratio changes from lean to rich relative to theoretical air-fuel ratio, or vice versa. Since this maximizes the difference between detected air-fuel ratios, the accuracy of diagnosis can be improved. In the third embodiment, after the output signal from the bypass downstream air-fuel ratio sensor 13 indicates a lean condition, an appropriate time delay is given to initially set the engine's air-fuel ratio to a lean condition, thereby increasing the stored value in the bypass catalytic converter. The amount of oxygen in the catalyst of the converter 8. Likewise, the catalyst can be fully saturated. Furthermore, raw HC is not discharged until oxygen saturation.

However, when the air-fuel ratio of the engine is initially set to a rich state, the amount of oxygen stored in the catalyst decreases. Furthermore, after the engine air-fuel ratio is set to a lean state, the oxygen introduced into the catalyst remains stored in the catalyst. Therefore, if there is no leak, the primary upstream air-fuel ratio sensor 10 indicates a change to a lean state after a time delay. If the primary upstream air-fuel ratio sensor 10 changes rapidly to a lean state, there is a leak.

Since the above diagnosis depends on the oxygen capacity of the catalyst in the bypass catalytic converter 8, the diagnosis may be affected if the oxygen capacity decreases due to deterioration of the catalyst. Therefore, although the threshold L may be a constant value, it is helpful to adjust the threshold according to the degree of deterioration of the catalyst, thereby improving the accuracy of diagnosis.

FIG. 6 is a timing chart showing a preferred method for diagnosing the degree of catalyst degradation of bypass catalytic converter 8 . This diagnostic method is performed in the open condition of the flow path switching valve 5 . The flow path switching valve 5 may be forcibly opened for the purpose of diagnosing the deterioration of the catalyst. Furthermore, in the open state of the flow path switching valve 5, the target air-fuel ratio of the internal combustion engine 1 is instantaneously changed from a lean state to a rich state. The time difference ΔT is then measured. The time difference ΔT refers to the difference between the time of the change in the air-fuel ratio AFM state detected by the main upstream air-fuel ratio sensor 10 and the change in the air-fuel ratio AFB state detected by the bypass downstream air-fuel ratio sensor 13 . If the air-fuel ratio of the engine is set to a rich state, the air-fuel ratio AFM detected by the main upstream air-fuel ratio sensor 10 immediately shows a rich state. This is because the flow path switching valve 5 is in the open state, and the air-fuel ratio AFB detected by the bypass downstream air-fuel ratio sensor 13 (also referred to as the exhaust gas for detecting the downstream side of the bypass catalytic converter 8 ) is caused by the oxygen capacity of the catalyst. The third component of air-fuel ratio) changes to show a rich state after a time delay. Therefore, if the bypass catalytic converter 8 is relatively new without deterioration, the time difference ΔT is large. As the degree of deterioration increases, the time difference ΔT becomes smaller. Therefore, as shown in FIG. 7, the deterioration degree of the catalyst can be determined according to the time difference ΔT. Also, for example, the degree of catalyst degradation can be measured by using changes in the air-fuel ratio during so-called "fuel cut and recovery" processing in which fuel is cut during deceleration and recovery is performed after fuel cut.

Referring additionally to FIG. 8 , the threshold L may be determined, for example, by using the degree of degradation of the catalyst. As a result, the threshold L can be adjusted to reflect the degree of catalyst degradation. Therefore, leak diagnosis can be accurately performed. As long as the diagnosis of the degree of catalyst deterioration is performed while the flow path switching valve 5 is open, it is possible to accurately determine whether or not the flow path switching valve 5 has leaked. This is because the open state of the valve allows the degree of catalyst degradation to be measured without being affected by any leakage. In addition, it is possible to judge whether a leak occurs based on the measured degree of deterioration of the catalyst. Although linear behavior is shown schematically in Figures 7 and 8, non-linear behavior is also foreseeable. In addition, other methods can also be used to diagnose the degree of deterioration of the catalyst.

In a third embodiment of the invention, the exhaust purification system includes a bypass exhaust passage 7 arranged upstream of the main exhaust flow passage leading to the main catalytic converter 4 . The bypass exhaust passage 7 leads to a bypass catalytic converter 8 . A flow path switching valve 5 for blocking exhaust flow is provided upstream of the main exhaust flow path. In addition, the purification system includes: a first air-fuel ratio detection part for detecting the air-fuel ratio of the exhaust gas upstream of the bypass catalytic converter 8; a second air-fuel ratio detection part for detecting the exhaust gas upstream of the main catalytic converter 4 the air-fuel ratio of the engine; the air-fuel ratio control part for instantaneously changing the air-fuel ratio of the engine between a lean state and a rich state relative to the stoichiometric air-fuel ratio when the flow path switching valve 5 is in a closed state; and a diagnostic part for After a momentary change in the air-fuel ratio of the engine, based on the air-fuel ratios detected by the first and second air-fuel ratio detecting means, it is diagnosed whether there is any leakage in the flow path switching valve 5 .

The instantaneous change of the air-fuel ratio of the engine is preferably from a lean state to a rich state when a sufficient time required to saturate the oxygen in the bypass catalytic converter 8 is maintained.

In the exhaust purification system according to the third embodiment, when the flow path switching valve 5 is in the closed state, preferably all the exhaust gas from the engine 1 is introduced into the bypass exhaust passage 7 and passes through the bypass catalytic converter 8 . However, when the flow path switching valve 5 is in an open state, most of the exhaust gas from the engine 1 preferably avoids the bypass exhaust passage 7 due to the large flow resistance difference relative to the exhaust passage 3 .

When the flow path switching valve 5 is set in a closed state, diagnosis as to whether the flow path switching valve 5 leaks can be performed by changing the air-fuel ratio of the engine, for example, from a lean state to a rich state. In this case, the excess oxygen during the lean state of the engine air-fuel ratio is stored in the catalyst according to the oxygen capacity of the bypass catalytic converter 8 . However, when the air-fuel ratio of the engine is set to a rich state, oxygen is exhausted. Therefore, although the air-fuel ratio of the engine is set to a rich state, as long as the flow path switching valve 5 does not leak, the air-fuel ratio detected by the second air-fuel ratio detection means does not immediately show a rich state due to the influence of exhaust oxygen. In other words, the air-fuel ratio of the exhaust gas detected by the second air-fuel ratio detecting means is relatively leaner than the air-fuel ratio of the engine immediately after the change in the air-fuel ratio of the engine. However, when the flow path switching valve 5 leaks, the air-fuel ratio of the exhaust gas detected by the second air-fuel ratio detection means may be even leaner due to the relatively rich state of the leaked exhaust gas. Therefore, by using these factors, the leakage of the flow path switching valve and the degree of the leakage can be judged. The oxygen capacity of the bypass catalytic converter 8 may also affect the diagnosis of leaks when the air-fuel ratio of the engine is changed from rich to lean.

In the third embodiment of the present invention, after a momentary change in the air-fuel ratio of the engine, the presence or absence of a leak is judged based on the difference between the average air-fuel ratios detected by the first and second air-fuel ratio detecting means.

The degree of catalyst degradation may affect oxygen capacity. Therefore, it is preferable to provide catalyst deterioration detection means for measuring the degree of deterioration of the catalyst. This makes it possible to correct or adjust the leak diagnosis according to the degree of degradation of the catalyst.

For example, when the diagnosis is performed by comparing the difference between the average air-fuel ratio and the threshold value, the threshold value may be modified according to the degree of deterioration of the catalyst. In doing so, the accuracy of diagnosis can be improved.

According to the third embodiment, judging whether or not the flow path switching valve 5 is leaking at an early stage helps to avoid discharging unpurified exhaust gas into the air.

In addition, adjusting the diagnosis to reflect the degree of catalyst degradation can improve the accuracy of the diagnosis.

Next, a method of diagnosing whether or not the flow path switching valve 5 is leaking will be described with respect to the fourth embodiment of the present invention. The exhaust system of the fourth embodiment is the same as that of the first embodiment, and the configuration of the exhaust passage and the control system of the exhaust system are the same as those shown in FIG. 1 . In the fourth embodiment, the bypass downstream air-fuel ratio sensor 13 is provided as the first air-fuel ratio detection means, and the main upstream air-fuel ratio sensor 10 is provided as the second air-fuel ratio detection means. A main upstream air-fuel ratio sensor 10 is mounted on a part of the main exhaust flow passage between the junction 9 and the main catalytic converter 4 . The sensor 10 is used to detect the air-fuel ratio of the exhaust gas downstream of the junction 9 where the bypass exhaust flow passage is connected to the main exhaust flow passage. Preferably, the bypass upstream air-fuel ratio sensor 12 includes a broadband air-fuel ratio sensor, and the three air-fuel ratio sensors 10, 11, and 13 include oxygen sensors. Furthermore, in the fourth embodiment, although the air-fuel ratio of the engine can be changed instantaneously between the rich state and the lean state, only the change from the lean state to the rich state is described.

In the fourth embodiment, the diagnostic processing is the same as that in the second embodiment. In addition, the flowchart showing the diagnostic processing of this embodiment is the same as the flowchart shown in FIG. 4 .

FIG. 9, which is a time chart showing the diagnosis of the fourth embodiment, shows: changes in the target air-fuel ratio of the internal combustion engine, the output signal O2B of the bypass downstream air-fuel ratio sensor 13 and the output signal O2M of the main upstream air-fuel ratio sensor 10; The air-fuel ratio detected by the upstream air-fuel ratio sensor 12 is bypassed. In addition, FIG. 9 shows the situation when the flow path switching valve 5 leaks (to be described later). As described above, in order to diagnose a leak, the target engine air-fuel ratio is forcibly changed from the stoichiometric air-fuel ratio to a lean state, and then instantaneously changed to a rich state. Then, since the flow path switching valve 5 is closed, the exhaust gas flows through the bypass exhaust passage 7, and oxygen is stored in the catalyst of the bypass catalytic converter 8 during the lean state. Heretofore, the output signal O2B of the bypass downstream air-fuel ratio sensor 13 provided downstream of the bypass catalytic converter 8 becomes to show a lean state after a time delay. Furthermore, the bypass upstream air-fuel ratio sensor 12 immediately starts to show a lean state of the exhaust air-fuel ratio with respect to the air-fuel ratio of the engine. Furthermore, in the fourth embodiment, after the signal O2B of the bypass downstream air-fuel ratio sensor 13 shows a lean state, the target engine air-fuel ratio is changed to a rich state with a time delay.

When the target engine air-fuel ratio changes from a lean state to a rich state, the air-fuel ratio detected by the bypass upstream air-fuel ratio sensor 12 provided upstream of the bypass catalytic converter 8 immediately starts changing to show a rich state. Since the oxygen stored in the bypass catalytic converter 8 is discharged to the downstream of the bypass catalytic converter 8, the output signal O2B of the bypass downstream air-fuel ratio sensor 10 is delayed after a time delay after the air-fuel ratio of the engine becomes a rich state. Rollover is displayed as a rich state. In addition, unless the flow path switching valve 5 leaks exhaust gas, the output signal O2M of the main upstream air-fuel ratio sensor 10 reverses almost simultaneously to show a rich state. For example, if the difference between the distance from the exhaust port 2 of the engine 1 to the bypass downstream air-fuel ratio sensor 13 and the distance from the exhaust port 2 of the engine 1 to the main upstream air-fuel ratio sensor 10 is ignored, then if no Leakage, both output signals O2B and O2M simultaneously flip from showing a rich state to showing a lean state.

However, if exhaust gas leaks through the flow path switching valve 5 due to, for example, a sealing defect of the valve body or the like, a part of the exhaust gas reaches the main upstream air-fuel ratio sensor 10 without passing through the bypass catalytic converter 8 . As a result, as shown in FIG. 9 , the output signal O2M of the main upstream air-fuel ratio sensor 10 reverses to show a rich state. That is, when the leak does occur, the difference between the timing at which the output signal O2M of the main upstream air-fuel ratio sensor 10 and the output signal O2B of the bypass downstream air-fuel ratio sensor 13 changes to a rich state increases. Furthermore, when the output signal O2B of the bypass downstream air-fuel ratio sensor 13 reaches a predetermined level (corresponding to a lean state) and all the oxygen stored in the catalyst is discharged, the target air-fuel ratio returns to the stoichiometric air-fuel ratio.

As described above, based on the output signals of the main upstream air-fuel ratio sensor 10 and the bypass upstream air-fuel ratio sensor 12, it is possible to determine whether or not a leak occurs. This determination may be made after a momentary change in the engine air-fuel ratio between the lean state and the rich state with respect to the theoretical air-fuel ratio between the lean state and the rich state. More specifically, a diagnosis (described below) may be performed using the difference in output and the time difference between changes in output.

In the fourth embodiment, it can be based on the output signal O2M of the main upstream air-fuel ratio sensor 10 and the output signal O2B of the bypass downstream air-fuel ratio sensor 13 respectively across the time point when the intermediate reference voltage V0 is turned over from the lean state to the rich state ( Shown in Fig. 9) judgment, use numerical value to represent leakage degree. The time difference ΔT between two points in time, ie the time delay of the change of the output signal O2B relative to the change of the output signal O2M, is set as a diagnostic parameter. Then, the diagnostic parameter is compared with a predetermined threshold value L for judging a leak. The threshold L is predetermined according to the degree of leakage to be detected. If one wants to detect a diagnosis of a slight degree of leak, the threshold can be set lower (however, when the threshold is low, more detection errors may occur). Therefore, when the time difference ΔT is large, it is determined that a leak has occurred.

Diagnosis based on the time difference ΔT has the following effects. Because the output of the oxygen sensor changes rapidly depending on the specific conditions (ie, lean state or rich state), large output differences may be easily detected even when no actual leak occurs. This is because the timing of changes in output due to the relative positions of the sensors in the exhaust system (ie, relative upstream or downstream) do not coincide with each other. However, as mentioned above, the time difference ΔT provides a more clearly indicated diagnostic parameter as to whether a leak has occurred. Therefore, the diagnostic accuracy can be further improved compared to using output differences.

In the fourth embodiment, whether or not the flow path switching valve 5 is leaking can be easily diagnosed by using the conventional air-fuel ratio sensors 10 , 11 , 12 and 13 for feedback control of the air-fuel ratio. Therefore, without an additional sensor, unnecessary discharge of toxic exhaust gas due to a sealing defect of the flow path switching valve 5 or the like can be avoided.

In addition, oxygen can be sufficiently stored in the catalyst until a saturated state is reached, or the catalyst can be kept in an oxygen-free state until the air-fuel ratio changes from lean to rich relative to the theoretical air-fuel ratio between a lean state and a rich state, and vice versa The same is true. Since this maximizes the difference between detected air-fuel ratios, the accuracy of diagnosis can be improved. In the fourth embodiment, after the output signal of the bypass downstream air-fuel ratio sensor 13 shows a lean state, an appropriate time delay is given to initially set the air-fuel ratio of the engine to a lean state, thereby increasing the stored value in the bypass catalytic converter. The amount of oxygen in the catalyst of vessel 8. Likewise, the catalyst can be fully saturated. Furthermore, raw HC is not discharged until oxygen saturation.

However, when the engine air-fuel ratio is initially set to a rich state, the amount of oxygen stored in the catalyst decreases. Furthermore, after the air-fuel ratio of the engine is set to a lean state, the oxygen introduced into the catalyst remains stored in the catalyst. Therefore, if there is no leak, the primary upstream air-fuel ratio sensor 10 indicates a change to a lean state after a time delay. If the primary upstream air-fuel ratio sensor 10 changes rapidly to a lean state, there is a leak.

Since the above diagnosis depends on the oxygen capacity of the catalyst in the bypass catalytic converter 8 (similar to the second embodiment), if the oxygen capacity decreases due to the deterioration of the catalyst, the diagnosis may be affected. Therefore, although the threshold L may be a constant value, it is useful to adjust the threshold according to the level of the degree of degradation of the catalyst, thereby improving the accuracy of diagnosis.

The method of the second embodiment with reference to FIG. 6 can be used as a method of diagnosing the degree of catalyst degradation of bypass catalytic converter 8 .

For example, the threshold L may be determined based on the degree of degradation of the catalyst. As a result, the threshold L can reflect the degree of catalyst degradation. Therefore, diagnosis of leaks can be accurately performed. As long as the diagnosis of the degree of catalyst deterioration is performed with the flow path switching valve 5 open, it is possible to accurately determine whether or not the flow path switching valve 5 is leaking. This is because the open state of the valve allows the measurement of catalyst degradation to be unaffected by leakage. In addition, it is possible to judge whether a leak occurs based on the measured degree of catalyst deterioration. In addition, other methods may be used to diagnose the degree of catalyst degradation.

In the fourth embodiment of the present invention, the exhaust purification system includes a bypass exhaust passage 7 arranged upstream of the main exhaust flow passage leading to the main catalytic converter 4 . The bypass exhaust passage 7 leads to a bypass catalytic converter 8 . A flow path switching valve 5 for blocking exhaust flow is provided upstream of the main exhaust flow path. In addition, the purification system includes: a first air-fuel ratio detection part for detecting the exhaust air-fuel ratio downstream of the bypass catalytic converter 8; a second air-fuel ratio detection part for detecting the exhaust air-fuel ratio upstream of the main catalytic converter 4 an air-fuel ratio control part for instantaneously changing the engine air-fuel ratio between a lean state and a rich state with respect to the stoichiometric air-fuel ratio when the flow path switching valve 5 is in a closed state; and a diagnostic part for changing the air-fuel ratio of the engine After the instantaneous change of , based on the air-fuel ratio detected by the first and second air-fuel ratio detecting means, it is diagnosed whether there is any leakage in the flow path switching valve 5 .

The instantaneous change of the air-fuel ratio of the engine is preferably from a lean state to a rich state when a sufficient time required to saturate the oxygen in the bypass catalytic converter 8 is maintained.

In the exhaust purification system according to the fourth embodiment, when the flow path switching valve 5 is in the closed state, it is preferable to introduce all of the exhaust gas from the engine 1 into the bypass exhaust passage 7 and pass through the bypass catalytic converter 8 . However, when the flow path switching valve 5 is in an open state, most of the exhaust gas from the engine 1 preferably avoids the bypass exhaust passage 7 due to the larger flow resistance difference relative to the exhaust passage 3 .

When the flow path switching valve 5 is set in the closed state, diagnosis as to whether the flow path switching valve 5 leaks can be performed by changing the air-fuel ratio of the engine from, for example, a lean state to a rich state. In this case, depending on the oxygen capacity of bypass catalytic converter 8, excess oxygen during the engine air-fuel ratio is in a lean state is stored in the catalyst. However, when the air-fuel ratio of the engine is set to a rich state, oxygen is exhausted. Therefore, although the air-fuel ratio of the engine is set to a rich state, as long as the flow path switching valve 5 does not leak, the air-fuel ratio detected by the first and second air-fuel ratio detection means does not immediately show a rich state due to the influence of exhaust oxygen. In other words, the air-fuel ratio of the exhaust gas detected by the second air-fuel ratio detecting means is relatively leaner than the engine air-fuel ratio immediately after the change in the engine air-fuel ratio. However, when the flow path switching valve 5 leaks, since the leaked exhaust gas is in a relatively rich state, the exhaust gas air-fuel ratio detected by the second air-fuel ratio detecting means may be even leaner. Therefore, by using these factors, the leakage of the flow path switching valve and the degree of the leakage can be judged. The oxygen capacity of the bypass catalytic converter 8 may also affect the diagnosis of a leak when the engine air-fuel ratio is changed from rich to lean.

Preferably, when the flow path switching valve 5 is set in the closed state, the diagnosis of the flow path switching valve 5 can be performed by changing the air-fuel ratio of the engine, for example, from a lean state to a rich state. In this case, due to the oxygen capacity of the bypass catalytic converter 8, excess oxygen during the lean state of the engine air-fuel ratio is stored in the catalyst. However, when the air-fuel ratio of the engine becomes a rich state, oxygen is exhausted. Therefore, although the air-fuel ratio of the engine becomes rich, the air-fuel ratios detected by the first and second air-fuel ratio detection means do not immediately become rich. This is due to oxygen discharge as long as the flow path switching valve 5 does not leak. If all the oxygen stored in the catalyst has been consumed, the air-fuel ratios detected by the first and second air-fuel ratio detecting means show a rich state at about the same time. However, when the flow path switching valve 5 leaks, since the leaked exhaust gas is in a rich state, the exhaust gas air-fuel ratio detected by the second air-fuel ratio detecting means immediately shows a lean state. Therefore, based on these factors, it is possible to judge whether or not the flow path switching valve 5 leaks and the degree of the leak. The effect of leaks can be due to oxygen capacity when the air-fuel ratio of the engine changes from rich to lean.

In the fourth embodiment, after instantaneously changing the engine air-fuel ratio, the determination of whether a leak occurs is performed based on the difference between the change timings of the air-fuel ratio detected by the first and second air-fuel ratio detecting means.

The degree of catalyst degradation may affect oxygen capacity. Therefore, it is preferable to provide catalyst deterioration detection means for measuring the degree of deterioration of the catalyst. This makes it possible to correct or adjust the leak diagnosis according to the degree of degradation of the catalyst.

For example, after a momentary change in the air-fuel ratio of the engine, when the timing of the change in the air-fuel ratio detected by the first air-fuel ratio detecting means is compared with the timing of the change in the air-fuel ratio detected by the second air-fuel ratio detecting means by comparing the threshold value When leak diagnosis is performed with a delay, the threshold can be modified according to the degree of catalyst degradation. Likewise, the accuracy of diagnosis can be improved.

According to the fourth embodiment, judging at an early stage whether or not the flow path switching valve 5 is leaking can avoid discharging unpurified exhaust gas into the air.

In addition, adjusting the diagnosis to reflect the degree of degradation of the catalyst can improve the accuracy of the diagnosis.

Although the invention has been disclosed by reference to certain preferred embodiments, various modifications, changes and variations to the described embodiments are possible without departing from the field of the invention as defined by the appended claims and their equivalents and range. It is, therefore, intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the appended claims.

Pursuant to Section 119 of the U.S. Patent Act, this application claims Japanese Patent Application No. 2006-070232, filed March 15, 2006, and two Japanese Patent Applications, No. 2006-072001 and No. Priority No. 2006-072004. Here, the entire contents of these three Japanese patent applications are incorporated herein by reference.

Claims (38)

1. equipment that is used for the emission control system of disgnosizing internal combustion engine, described equipment comprises:

Main exhaust passageway;

Main catalytic converter, it is set in the described main exhaust passageway;

Bypass exhaust passage, itself and described main exhaust passageway intercommunication fluid, thus make described main exhaust passageway at point of branching that described bypass exhaust passage is told from described main exhaust passageway with converge part bypass between the junction point of described main exhaust passageway in bypass exhaust passage described main catalytic converter upstream side, described;

The bypass catalytic converter, it is set in the described bypass exhaust passage;

Be arranged in the described part of described main exhaust passageway, be used for opening or closing the valve of the described part of described main exhaust passageway;

First sensor, it is arranged on first signal that is illustrated in first air fuel ratio of the exhaust of flowing in the described bypass exhaust passage in the described bypass exhaust passage with output;

Second sensor, it is arranged in the described main exhaust passageway secondary signal of second air fuel ratio that flows into the exhaust of described main catalytic converter with the output expression; And

Controller, it receives described first and second signals, and described controller judges based on described first and second signals whether be in the described valve of closing setting makes exhaust gas leakage arrive the described part of described main exhaust passageway.

2. equipment according to claim 1 is characterized in that, described first sensor detects described first air fuel ratio of exhaust of the upstream of described bypass catalytic converter.

3. equipment according to claim 2 is characterized in that, described second air fuel ratio of the exhaust in the downstream of the described valve of described second sensor.

4. equipment according to claim 2, it is characterized in that, described first signal indication is by the rich state of described first air fuel ratio of the exhaust of described bypass exhaust passage and the variation between the poor state, and described secondary signal is represented by the rich state of described second air fuel ratio of the exhaust of described main exhaust passageway and the variation between the poor state.

5. equipment according to claim 4, it is characterized in that, judge be in described described valve of closing setting whether leak described first signal that comprises the rich state of determining described first air fuel ratio of expression and the variation between the poor state and represent the rich state of described second air fuel ratio and the described secondary signal of the variation between the poor state between time lag, described time lag is corresponding with the cyclically-varying of the engine air-fuel ratio that offers internal-combustion engine.

6. equipment according to claim 5 is characterized in that, judges whether be in described described valve of closing setting leaks and comprise:

When described time lag is not more than threshold value, is judged as to exist and leaks; And

When described time lag during, be judged as and do not have leakage greater than described threshold value.

7. equipment according to claim 5 is characterized in that, judges whether be in described described valve of closing setting leaks and comprise:

When described time lag during, be judged as to exist and leak less than first threshold;

When described time lag during, be judged as and do not have leakage greater than second threshold value; And

When described time lag is in prespecified range between described first threshold and described second threshold value, be judged as described bypass catalytic converter deteriorate.

8. equipment according to claim 4, it is characterized in that, judge whether be in described described valve of closing setting leaks and comprise: more described first signal be in one of the described rich state of described first air fuel ratio and poor state first at interval and described secondary signal be in second interval of one of the described rich state of described second air fuel ratio and poor state, the described rich state and the variation between the poor state of described first and second air fuel ratios are corresponding with the cyclically-varying of the engine air-fuel ratio that offers internal-combustion engine.

9. equipment according to claim 8 is characterized in that, judges whether be in described described valve of closing setting leaks and comprise:

Be substantially equal at interval described second at interval the time when described first, be judged as to exist and leak; And

When described first at interval less than described second at interval the time, be judged as and do not have leakage.

10. equipment according to claim 8 is characterized in that, judges whether be in described described valve of closing setting leaks and comprise:

Be substantially equal at interval described second at interval the time when described first, be judged as to exist and leak;

When described first and second the differences between at interval during, be judged as and do not have leakage greater than threshold value; And

When the difference between described first and second intervals is not more than described threshold value, be judged as described bypass catalytic converter deteriorate.

11. equipment according to claim 4, it is characterized in that, judge whether be in described described valve of closing setting leaks and comprise and periodically change the engine air-fuel ratio that offers internal-combustion engine that described engine air-fuel ratio changes between poor state and rich state with respect to the chemically correct fuel engine air-fuel ratio.

12. equipment according to claim 11 is characterized in that, reponse system comprises described first sensor and described controller, and described reponse system makes the engine air fuel ratio periodic variation between richness, poor state that offers described internal-combustion engine.

13. equipment according to claim 12 is characterized in that, described reponse system is set the chemically correct fuel level of the described engine air fuel ratio that offers described internal-combustion engine.

14. equipment according to claim 11 is characterized in that, feedforward system makes the engine air fuel ratio periodic variation between richness, poor state that offers described internal-combustion engine.

15. equipment according to claim 2, it is characterized in that, described controller is carried out transient change between the rich or poor state, the engine air fuel ratio, and described first signal and described secondary signal are represented described first air fuel ratio and described second air fuel ratio after the described transient change respectively.

16. equipment according to claim 15, it is characterized in that, described first signal indication is by the mean state of detected described first air fuel ratio of described first sensor, described secondary signal represent by described second sensor to the mean state of described second air fuel ratio, and the scheduled period after changing described engine air-fuel ratio determine the mean state of described first and second air fuel ratios.

17. equipment according to claim 15 is characterized in that, described second air fuel ratio of the exhaust in the downstream of the described bypass exhaust passage of described second sensor.

18. equipment according to claim 15 is characterized in that, the described engine air fuel ratio of described transient change is to described rich state from described poor state.

19. equipment according to claim 18 is characterized in that, the transient change of described engine air-fuel ratio occurs in and is used for making the approaching oxygen-saturated long enough of described bypass catalytic converter after the time.

20. equipment according to claim 15, it is characterized in that, described controller is determined the catalyst degradation degree of described bypass catalytic converter, and described controller based on the described catalyst degradation degree adjustment of described bypass catalytic converter to being in the judgement whether described described valve of cutting out setting leaks.

21. equipment according to claim 20 is characterized in that, also comprises:

Be arranged on the 3rd sensor in the described bypass exhaust passage, the 3rd air fuel ratio of the exhaust in the downstream of the described bypass catalytic converter of described the 3rd sensor, the 3rd signal of described the 3rd air fuel ratio of described the 3rd sensor output expression, described controller receives described the 3rd signal, and, determine described catalyst degradation degree with the variation of described engine air-fuel ratio that is changing corresponding described first and the 3rd air fuel ratio based on be in described opening when being provided with when described valve.

22. equipment according to claim 20, it is characterized in that, described first signal indication is by the mean state of detected described first air fuel ratio of described first sensor, described secondary signal represent by described second sensor to the mean state of described second air fuel ratio, determine the mean state of described first and second air fuel ratios in the scheduled period that described engine air-fuel ratio changes, judge that whether be in described described valve of closing setting leaks and comprise threshold value and difference between described first and second signals of representing average air-fuel ratio are compared, and revises described threshold value based on the catalyst degradation degree of described bypass catalytic converter.

23. equipment according to claim 1, it is characterized in that, described first sensor detects described first air fuel ratio of exhaust in the downstream of described bypass catalytic converter, described second air fuel ratio of the exhaust in the downstream of the described bypass exhaust passage of described second sensor.

24. equipment according to claim 23, it is characterized in that, described controller is carried out the transient change of engine air fuel ratio between rich or poor state, described first signal and described secondary signal are represented first air fuel ratio and second air fuel ratio after the described transient change respectively.

25. equipment according to claim 24, it is characterized in that, judge whether leak comprise judgement at described first signal list illustrate the rich state of described first air fuel ratio and variation poor state between and described secondary signal express the rich state of described second air fuel ratio and variation poor state between between whether time of origin poor, the described time difference is corresponding with the described engine air-fuel ratio that is changing if being in described described valve of closing setting.

26. equipment according to claim 24 is characterized in that, the described engine air fuel ratio of described transient change is to described rich state from described poor state.

27. equipment according to claim 26 is characterized in that, the transient change of described engine air-fuel ratio occurs in and is used for making the approaching oxygen-saturated long enough of described bypass catalytic converter after the time.

28. equipment according to claim 24, it is characterized in that, described controller is determined the catalyst degradation degree of described bypass catalytic converter, and described controller based on the described catalyst degradation degree adjustment of described bypass catalytic converter to being in the judgement whether described described valve of cutting out setting leaks.

29. equipment according to claim 28 is characterized in that, also comprises:

Be arranged on the 3rd sensor in the described bypass exhaust passage, the 3rd air fuel ratio of the exhaust of the upstream of the described bypass catalytic converter of described the 3rd sensor, the 3rd signal of described the 3rd air fuel ratio of described the 3rd sensor output expression, described controller receives described the 3rd signal, and, determine described catalyst degradation degree with the variation of described engine air-fuel ratio that is changing corresponding described first and the 3rd air fuel ratio based on be in described opening when being provided with when described valve.

30. equipment according to claim 28 is characterized in that, judges whether be in described described valve of closing setting leaks and comprise:

Judgement illustrates the rich state of described first air fuel ratio and the variation between the poor state and described secondary signal at described first signal list and expresses whether time of origin is poor between the rich state of described second air fuel ratio and the variation between the poor state, and the described time difference is corresponding with the described engine air-fuel ratio that is changing;

Compare threshold and described time difference; And

Described catalyst degradation degree based on described bypass catalytic converter is revised described threshold value.

31. an equipment that is used for the emission control system of disgnosizing internal combustion engine, described equipment comprises:

Main exhaust passageway;

Main catalytic converter, it is set in the described main exhaust passageway;

Bypass exhaust passage, itself and described main exhaust passageway intercommunication fluid, thus make described main exhaust passageway at point of branching that described bypass exhaust passage is told from described main exhaust passageway with converge part bypass between the junction point of described main exhaust passageway in bypass exhaust passage described main catalytic converter upstream side, described;

The bypass catalytic converter, it is set in the described bypass exhaust passage;

Be arranged in the described part of described main exhaust passageway, be used for opening or closing the valve of the described part of described main exhaust passageway; And

Deagnostic package, it is used for based on the comparison between second air fuel ratio of the exhaust of first air fuel ratio of the exhaust of the described bypass exhaust passage of flowing through and the described main exhaust passageway of flowing through, and whether diagnosis is in described described valve of closing setting makes exhaust gas leakage arrive described main exhaust passageway.

32. equipment according to claim 31 is characterized in that, described valve is arranged in the described main exhaust passageway.

33. equipment according to claim 31 is characterized in that, also comprises:

Be used to change the parts of the engine air-fuel ratio that offers internal-combustion engine, described engine air-fuel ratio changes between with respect to the poor state of the engine air-fuel ratio of chemically correct fuel and rich state;

And with the corresponding diagnostic parts of parts that change described engine air-fuel ratio.

34. a method that is used for the emission control system of disgnosizing internal combustion engine, described method comprises:

Flow through first air fuel ratio of exhaust of the main exhaust passageway that comprises main catalytic converter of detection;

Flow through second air fuel ratio of exhaust of bypass exhaust passage of detection, described bypass exhaust passage and described main exhaust passageway intercommunication fluid, thereby make described main exhaust passageway at point of branching that described bypass exhaust passage is told from described main exhaust passageway with converge part bypass between the junction point of described main exhaust passageway in bypass exhaust passage described main catalytic converter upstream side, described, described bypass exhaust passage comprises the bypass catalytic converter;

Prevent that with valve exhaust is mobile along described main exhaust passageway; And

Based on described first and second air fuel ratios, judge whether exhaust leaks by described valve.

35. method according to claim 34, it is characterized in that, described first air fuel ratio that detects exhaust comprises the air fuel ratio that detects the exhaust that enters described bypass catalytic converter, and described second air fuel ratio that detects exhaust comprises the air fuel ratio that detects the exhaust that enters described main catalytic converter.

36. method according to claim 34 is characterized in that, also comprises:

Determine the deterioration of described bypass catalytic converter.

37. method according to claim 36 is characterized in that, also comprises:

Use valve to allow exhaust to flow along described main exhaust passageway.

38. method according to claim 36 is characterized in that, also comprises:

The 3rd air fuel ratio of the exhaust of described bypass catalytic converter is left in detection.

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