JP2008038603A - Failure diagnostic method for internal combustion engine, and failure diagnostic device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To diagnose the presence of an exhaust gas leakage from a passage selector valve 5. <P>SOLUTION: A main passage through which exhaust gas flows in normal operation is composed of an upstream main passage 3, a downstream main passage 8 and a main catalytic converter 9. A by-pass passage branches off from the upstream main passage 3. When the passage selector valve 5 is put in a closed state to close the upstream main passage 3, the temperature of exhaust gas exhausted from a cylinder is temporarily changed to diagnose whether there is a leakage in the passage selector valve 5 from the temperature change in the upstream main passage 3. When exhaust gas leaks downstream from the passage selector valve 5, high-temperature exhaust gas exhausted from the cylinder flows into the upstream main passage 3, and the internal temperature of the upstream main passage 3 rises. The exhaust gas leakage from the passage selector valve 5 can be positively detected from the internal temperature change of the upstream main passage 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine failure diagnosis method and an internal combustion engine failure diagnosis device.

  As is conventionally known, in a configuration in which a catalytic converter is disposed relatively downstream of an exhaust system such as under the floor of a vehicle, after the cold start of the internal combustion engine, the temperature of the catalytic converter rises and is activated. In the meantime, a sufficient exhaust purification action cannot be expected. On the other hand, the closer the catalytic converter is to the upstream side of the exhaust system, that is, the internal combustion engine side, the lower the durability due to thermal degradation of the catalyst.

Therefore, as disclosed in Patent Document 1, a bypass flow path is provided in parallel with the upstream portion of the main flow path including the main catalytic converter, and another bypass catalytic converter is interposed in the bypass flow path. However, an exhaust device has been conventionally proposed in which exhaust gas is guided to the bypass flow path side immediately after the cold start by a switching valve for switching between the two. In this configuration, the bypass catalytic converter is positioned relatively upstream of the main catalytic converter in the exhaust system and is activated relatively early, so that exhaust purification can be started from an earlier stage. it can.
Japanese Patent Laid-Open No. 2005-351088

  However, in Patent Document 1, when the switching valve is in the closed state and the exhaust gas leaks from the switching valve, the exhaust performance deteriorates unless the main catalytic converter is sufficiently activated. Therefore, when the switching valve is closed, it is necessary to diagnose whether or not exhaust gas leaks from the switching valve.

  Therefore, the present invention is provided with a bypass passage in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side, and having a relatively small total cross-sectional area with respect to the total cross-sectional area of the main passage. Failure of the internal combustion engine in which a bypass catalytic converter is provided in the passage, and a flow path switching valve and a temperature detecting means are provided in the upstream portion of the main passage that is bypassed by the bypass passage. In the diagnosis method, when the flow path switching valve is closed and the main passage is closed, the temperature of the exhaust discharged from the cylinder is temporarily changed, and the temperature change in the main passage It is characterized by diagnosing whether there is a leak in the flow path switching valve. If there is a leak in the flow path switching valve, a part of the exhaust gas flows into the upstream portion of the main passage.

  According to the present invention, when diagnosing whether or not there is a leak in the flow path switching valve, the temperature of the exhaust gas discharged from the cylinder is temporarily increased, so that the flow path switching valve is leaked. In some cases, the exhaust temperature of the upstream portion of the main passage will necessarily change, and the leakage of exhaust from the flow path switching valve can be reliably detected from the change in the internal temperature of the upstream portion of the main passage. it can.

  Hereinafter, an embodiment in which the present invention is applied to an in-line four-cylinder internal combustion engine will be described in detail with reference to the drawings.

  FIG. 1 and FIG. 2 are explanatory views schematically showing the piping layout and control system of the internal combustion engine 1 according to the present invention, and the schematic configuration of the internal combustion engine 1 will be described based on these FIG. 1 and FIG. .

  In the cylinder head 1a of the internal combustion engine 1, exhaust ports 2 of cylinders # 1 to # 4 arranged in series are formed so as to open toward the side surfaces, respectively. Further, the upstream main passage 3 is connected. Each upstream main passage 3 is provided with a flow path switching valve 5 that is opened and closed by an appropriate actuator 4.

  The flow path switching valve 5 is closed when cold, and is configured to block communication between the upstream main passages 3 when closed. The flow path switching valve 5 includes four valve elements 6 provided in the respective upstream main passages 3, and the valve bodies 6 a included in the respective valve elements 6 are connected to the four upstream main passages 3. Each end is opened and closed. The flow path switching valve 5 (valve element 6) is capable of completely blocking the flow without allowing leakage, for example, when the valve body 6a contacts the seal surface. The upstream main passages 3 merge with each other at a junction 7 located downstream of the flow path switching valve 5 to form one downstream main passage 8. A main catalytic converter 9 is interposed in the middle of the downstream main passage 8. The catalyst in the main catalytic converter 9 includes a three-way catalyst and an HC trap catalyst. The main catalytic converter 9 has a large capacity disposed under the floor of the vehicle. The upstream main passage 3, the downstream main passage 8, and the main catalytic converter 9 constitute a main passage through which exhaust gas flows during normal operation. That is, the flow path switching valve 5 is provided in the upstream main passage 3 that is the upstream portion of the main passage.

  On the other hand, an upstream bypass passage 11 branches from each of the upstream main passages 3 as bypass passages. The upstream bypass passage 11 has a sufficiently smaller passage cross-sectional area than the upstream main passage 3, and the branch point 12 serving as the upstream end thereof is set at a position as upstream as possible of the upstream main passage 3. Has been.

  The upstream bypass passages 11 join together as a single downstream bypass passage 14 at the junction 13. In FIG. 1 schematically showing each passage, each upstream bypass passage 11 is drawn relatively long, but in practice, it is as short as possible.

  The downstream end of the downstream bypass passage 14 joins the downstream main passage 8 at a junction 15 upstream of the main catalytic converter 9 in the downstream main passage 8. A bypass catalytic converter 16 using a three-way catalyst is interposed in the middle of the downstream bypass passage 14. The bypass catalytic converter 16 is disposed as upstream as possible in the bypass flow path, that is, in the downstream bypass path 14.

  The bypass catalytic converter 16 includes a known monolithic catalyst carrier, is a small-sized one having a capacity smaller than that of the main catalytic converter 9, and preferably uses a catalyst excellent in low-temperature activity. One end of an exhaust gas recirculation passage 18 is connected to the downstream bypass passage 14 at a branch point 17 on the downstream side of the bypass catalytic converter 16. The other end of the exhaust gas recirculation passage 18 extends to the engine intake system via an exhaust gas recirculation control valve (not shown). That is, this branch point 17 serves as a recirculation exhaust outlet.

  An upstream air-fuel ratio sensor 19 is disposed on the inlet side of the bypass catalytic converter 16, and a downstream air-fuel ratio sensor 20 is disposed on the outlet side. Similarly, air-fuel ratio sensors 21 and 22 are arranged on the inlet side and the outlet side of the main catalytic converter 9, respectively.

  As these air-fuel ratio sensors 19, 20, 21, and 22, a so-called oxygen sensor that outputs a binary signal in response to rich or lean exhaust air-fuel ratio, or continuously corresponding to the value of the exhaust air-fuel ratio. Any of so-called linear air-fuel ratio sensors capable of obtaining a changing output may be used. As is well known, the detection signals of these air-fuel ratio sensors 19, 20, 21, and 22 are used for general air-fuel ratio control (especially when the exhaust gas is being guided to the bypass passage side) in addition to catalyst deterioration diagnosis. For example, linear air-fuel ratio sensors are used for the upstream air-fuel ratio sensor 19 and the air-fuel ratio sensor 21, and the downstream air-fuel ratio sensor 20 and the air-fuel ratio sensor are used from the viewpoint of ensuring accuracy and component costs. 22 is an oxygen sensor.

  The detection signals of these air-fuel ratio sensors 19, 20, 21, and 22 are input to an engine control unit (hereinafter abbreviated as ECU) 23 serving as failure diagnosis means and exhaust temperature temporary change means. As is well known, the ECU 23 performs various controls of the internal combustion engine including air-fuel ratio control, ignition timing control, flow path switching valve 5 open / close control and the like in addition to catalyst deterioration diagnosis.

  In the present embodiment, an upstream temperature sensor 24 is disposed in the upstream main passage 3 as temperature detecting means for detecting a temperature change in the upstream main passage 3. The upstream temperature sensor 24 is disposed on the upstream side of the flow path switching valve 5. Further, in the downstream bypass passage 14, a bypass passage temperature sensor 25 as a bypass passage temperature detecting means for detecting the temperature in the downstream bypass passage 14 is arranged at a position upstream of the bypass catalytic converter 16. Has been. Detection signals from these temperature sensors 24 and 25 are also input to the ECU 23 described above.

  The internal combustion engine 1 includes a spark plug 31, and a fuel injection valve 33 is disposed in the intake passage 32. Further, a so-called electronically controlled throttle valve 34 that is opened and closed by an actuator such as a motor is disposed upstream of the intake passage 32, and an air flow meter 35 that detects the intake air amount is provided downstream of the air cleaner 36. Yes.

  Further, a swirl control valve 37 that generates a swirl is provided as a gas flow control valve for generating a gas flow in the cylinder in the vicinity of the intake port of the intake passage 32. The swirl control valve 37 is opened and closed via an appropriate actuator (not shown), and when it is closed, a part of the passage cross section of the intake passage 32 is shielded to generate a swirl. As the swirl control valve 37, there are various known types such as a butterfly valve type having a notch in a part of a plate-like valve body and a type that opens and closes one of a pair of intake ports. Can be used.

  Various control parameters of the internal combustion engine 1, for example, the fuel injection amount by the fuel injection valve 33, the ignition timing by the spark plug 31, the opening of the throttle valve 34, the open / close state of the flow path switching valve 5 and the swirl control valve 37, etc. The ECU 23 is controlled. In addition to the sensors described above, the ECU 23 includes detection signals from various sensors such as a coolant temperature sensor 38 and an accelerator opening sensor 39 that detects the opening (depression amount) of an accelerator pedal operated by the driver. Is entered.

  In such a configuration, when the engine temperature or the exhaust temperature after the cold start is low, the flow path switching valve 5 is closed via the actuator 4 and the upstream main passage 3 is blocked. Therefore, the entire amount of exhaust discharged from each cylinder flows from the branch point 12 to the bypass catalytic converter 16 through the upstream bypass passage 11. The bypass catalytic converter 16 is located upstream of the exhaust system, that is, close to the exhaust port 2 and is small in size, so that it is activated quickly and exhaust purification is started at an early stage.

  On the other hand, if the engine warm-up proceeds and the engine temperature or the exhaust temperature becomes sufficiently high, it is considered that the catalyst of the main catalytic converter 9 is activated as one of the trigger conditions, and the flow path switching valve 5 is opened. The Thus, the exhaust discharged from each cylinder mainly passes through the main catalytic converter 9 from the upstream main passage 3 through the downstream main passage 8. At this time, the upstream bypass passage 11 and the downstream bypass passage 14 are not particularly cut off, but the upstream bypass passage 11 side has a smaller passage cross-sectional area than the upstream main passage 3 side, and the bypass catalytic converter 16 is Therefore, most of the exhaust flow passes through the upstream main passage 3 and hardly flows into the upstream bypass passage 11 due to the difference in passage resistance between the two. Therefore, the thermal deterioration of the bypass catalytic converter 16 is sufficiently suppressed.

  When the flow path switching valve 5 is closed and the exhaust flow flows through the upstream bypass passage 11, the flow path switching valve 5 is closed because the exhaust flow rate cannot be accommodated in a high speed range or a high load range. Is controlled only when the engine operating conditions (load and engine speed) are within a predetermined region on the low speed and low load side, and in other regions, the main catalytic converter 9 is inactive. In addition, the flow path switching valve 5 is opened.

  Further, when an exhaust gas recirculation control valve (not shown) interposed in the exhaust gas recirculation passage 18 is opened under the condition that the flow path switching valve 5 is opened, a part of the exhaust discharged from each cylinder is diverted to the branch point 12. From the branch point 17 to the exhaust gas recirculation passage 18 after passing through the bypass catalytic converter 16. That is, even when the flow path switching valve 5 is guiding the exhaust flow to the main passage side, most of the recirculation amount passes through the bypass catalytic converter 16 during exhaust gas recirculation. A part of the recirculation amount flows back from the junction 15 of the downstream main passage 8 through the downstream bypass passage 14 and is taken into the exhaust recirculation passage 20.

  In the internal combustion engine configured as described above, when the flow path switching valve 5 is closed and the upstream main passage 3 is closed, exhaust leakage from the closed flow path switching valve 5 occurs. Fault diagnosis is performed to see if it has occurred.

When the flow path switching valve 5 is closed in the cold state, the exhaust discharged from the cylinder flows into the upstream bypass passage 11, and the cold exhaust in the upstream main passage 3 is downstream of the branch point 12. It is in a staying state. When the exhaust gas leaks from the flow path switching valve 5 in such a state, the exhaust gas discharged from the cylinder flows into the upstream main passage 3 correspondingly, and a branch point in the upstream main passage 3 Therefore, the exhaust gas temperature rises on the downstream side of 12. Therefore, in the cold state, the flow path switching valve 5 is compared by comparing the temperature T _{EO of the} exhaust discharged from the cylinder with the temperature change of the exhaust downstream of the branch point 12 in the upstream main passage 3. It is possible to diagnose whether or not exhaust leakage has occurred.

On the other hand, in a state where the warm-up has progressed, even if leakage occurs from the flow path switching valve 5 and the exhaust discharged from the cylinder flows into the upstream main passage, the upstream main passage is caused by heat conduction or radiant heat. 3, the temperature rise width (temperature change amount) of the exhaust gas at a position downstream of the branch point 12 is small, and unlike the case of the cold state, the temperature T _EO and the upstream main passage 3 are branched. It is difficult to diagnose the occurrence of exhaust leakage from the flow path switching valve 5 by comparing the temperature change of the exhaust gas downstream of the point 12.

Therefore, in the present embodiment, when the failure diagnosis of the flow path switching valve 5 (diagnosis of occurrence of exhaust leakage) is performed, the temperature T _EO of the exhaust discharged from the cylinder is temporarily changed, and the upstream side By forcibly increasing the temperature difference between the temperature T _M of the exhaust gas downstream of the branch point 12 in the main passage 3 and the temperature T _EO , it is higher than that of the branch point 12 in the upstream main passage 3. The failure diagnosis of the flow path switching valve 5 can be performed from the temperature change of the exhaust gas on the downstream side.

Specifically, as shown in FIG. 3, the temperature T _EO is temporarily increased, so that the downstream side of the upstream main passage 3 is downstream of the branch point 12 regardless of the cold state or the warm state. The temperature difference between the exhaust gas temperature T _M and the temperature T _EO is increased, and the temperature rise width (temperature change amount) of the temperature T _M when the exhaust gas leaks from the flow path switching valve 5 is secured.

L1 in FIG. 3 is a characteristic curve showing an example of a change with time of the temperature T _EO when temporarily raised the temperature T _EO, L2 is when the temperature T _EO is changed as described above L1 FIG. 6 is a characteristic line showing an example of the change over time of the temperature T _M when there is an exhaust leak from the flow path switching valve 5, and L3 is the flow path switching valve 5 when the temperature T _EO changes as in L1. from a characteristic curve showing an example of a change with time of the temperature T _M in the case the leakage of the exhaust gas is not.

Note that the temperature T _EO is substituted by the exhaust temperature detected by the bypass passage temperature sensor 25. Further, the temperature T _M is substituted with the exhaust temperature detected by the upstream temperature sensor 24.

FIG. 4 is a first embodiment of the present invention, and is a timing chart of various parameters when the ignition timing is temporarily and relatively retarded to increase the temperature T _EO .

  The diagnosis of the occurrence of exhaust leakage from the flow path switching valve 5 is performed in a state where the flow path switching valve 5 is closed, and torque is measured during the diagnosis of the occurrence of leakage of the flow path switching valve 5. Various parameters are controlled cooperatively so that there is no fluctuation.

The ignition timing is gradually retarded (retarded) from time t2 toward a predetermined target value. When the ignition timing is released, the ignition timing is gradually increased toward the original ignition timing (normal ignition timing). Is advanced to As the ignition timing is retarded, the temperature T _EO temporarily rises between times t2 and t3.

  As the ignition timing is retarded, the swirl control valve 37 is controlled in the valve closing direction from time t2 to enhance the gas flow in the combustion chamber, and the combustion stability during the ignition timing retard is increased. On the other hand, the throttle valve 34 is controlled in the valve opening direction from time t1 prior to retarding the ignition timing in consideration of the delay of the actual intake amount increase, and increases the intake amount.

FIG. 5 shows the leakage criteria used when diagnosing the presence or absence of exhaust leakage from the flow path switching valve 5 using the temperature T _EO and the temperature T _M, and information regarding this leakage criterion is the ECU 23 described above. Is stored in advance. As apparent from FIG. 5, the leakage Criteria the temperature T _EO and the temperature T _M and are determined in accordance with, the passage from the temperature T _EO and the temperature T _M of the time obtained by retarding the ignition timing The presence or absence of the occurrence of exhaust leakage from the switching valve 5 is diagnosed. In other words, the presence or absence of exhaust leakage from the flow path switching valve 5 is diagnosed from a comparison between the temperature T _EO and the temperature T _M.

FIG. 6 is a timing chart of various parameters when the EGR amount is temporarily and relatively decreased in order to increase the temperature T _EO , and is a second embodiment of the present invention different from FIG. 4 described above. It is.

  Also in the second embodiment, the diagnosis of the occurrence of exhaust leakage from the flow path switching valve 5 is performed with the flow path switching valve 5 closed and the occurrence of leakage in the flow path switching valve 5. Various parameters are controlled in a coordinated manner so that there is no torque fluctuation during the presence / absence diagnosis.

The EGR amount is controlled so as to gradually decrease toward a predetermined target value from time t2, and when the decrease of the EGR amount is canceled, the EGR amount is gradually increased toward the original EGR amount. As the EGR amount decreases, the actual intake air amount increases (as a result of the increase in supplied fuel in accordance with the intake air amount), and the temperature T _EO temporarily rises between times t2 and t3. The throttle valve 34 is controlled in the valve closing direction from time t1 prior to the EGR reduction, and suppresses an extreme increase in the actual intake air amount based on the EGR reduction.

Also in the second embodiment, by using the above-mentioned temperature T _EO and the temperature T _M of the time obtained by relatively decreasing the EGR amount, the leakage criteria shown in FIG. 5 described above, the flow path switching valve The presence or absence of exhaust leakage from 5 is diagnosed.

Further, the valve mechanism on the intake valve side of the internal combustion engine is a variable valve mechanism that can change the opening / closing timing of the intake valve, and the valve mechanism on the exhaust valve side of the internal combustion engine can change the closing timing of the exhaust valve. With the variable valve mechanism, the temperature T _EO can be raised by advancing (rapidly opening) the opening timing of the exhaust valve (third embodiment).

In this third embodiment, as shown in FIG. 7, by advancing the opening timing exhaust valve from the time t1, to temporarily increase between times t1~t2 the temperature T _EO. When the exhaust valve opening timing is advanced, the intake valve opening timing and the exhaust valve closing timing are changed so that the valve overlap amount of the intake valve and the exhaust valve becomes zero at the same timing. Specifically, the valve overlap of the intake and exhaust valves that are usually set to cross the top dead center is realized by setting both the exhaust valve closing timing and the intake valve opening timing to the vicinity of the top dead center. Is possible. In this way, by setting the valve overlap amount of the intake valve and the exhaust valve to zero, the blowback to the intake port side is eliminated, and the internal EGR is relatively reduced, so the fresh air amount can be increased. The fuel can be increased according to the increased fresh air, and the total heat can be increased. Further, the throttle valve 34 is controlled in the valve opening direction from time t1 to increase the intake air amount in order to compensate for the torque drop caused by advancing the exhaust valve opening timing.

Then, as in the fourth and fifth embodiments described later, the temperature T _EO can be temporarily changed by manipulating the air-fuel ratio.

In the fourth embodiment, the temperature T _EO is temporarily increased by operating the air-fuel ratio. More specifically, if the fuel is stable on the relatively high load side and more fuel than that at the stoichiometric air-fuel ratio is injected to cool the fuel by the heat of vaporization of the fuel, the theoretical air The temperature T _EO can be temporarily increased by decreasing the fuel injection amount so as to obtain the fuel amount at the fuel ratio and stopping the fuel cooling. That is, as shown in FIG. 8, the temperature T _EO can be temporarily increased by reducing the fuel amount so that the equivalence ratio becomes 1. Note that the valve opening of the throttle valve 34 at this time is constant.

In the fifth embodiment, the temperature T _EO is temporarily reduced by manipulating the air-fuel ratio. More specifically, the temperature T _EO can be temporarily lowered by injecting more fuel than the fuel amount at the stoichiometric air-fuel ratio to cool the fuel by heat of vaporization of the fuel. That is, as shown in FIG. 9, the temperature T _EO can be temporarily increased by increasing the fuel amount so that the equivalence ratio is greater than 1. Note that the valve opening of the throttle valve 34 at this time is constant.

In such fourth and fifth embodiments, with reference to, and leakage criteria shown in Fig. 5 described above with the temperature T _EO of Oyobi the temperature T _M of the time that was air-fuel ratio operation as described above The presence or absence of exhaust leakage from the flow path switching valve 5 is diagnosed.

In each of the above-described embodiments, the exhaust gas temperature detected by the upstream temperature sensor 24 is used as the temperature T _M , but the flow rate switching valve 5 of the upstream main passage 3 and the junction 7 are If a temperature sensor is provided in between, and the temperature T _M is determined from the temperatures before and after the flow path switching valve 5, the accuracy of the temperature T _M is improved, and consequently the exhaust from the flow path switching valve 5. It is possible to improve the accuracy of diagnosis for occurrence of leakage. In addition, a temperature sensor is provided at a position upstream of the junction 15 in the downstream main passage 8, and the exhaust temperature detected by the temperature sensor and the exhaust temperature detected by the upstream temperature sensor 24 are used as described above. Even if the temperature T _M is determined, the accuracy of the temperature T _M can be improved.

  If the position of the air-fuel ratio sensor 21 arranged upstream of the main catalytic converter 9 is changed to a position upstream of the pour point 15 in the downstream main passage 8, the air-fuel ratio sensor 21 is used. The temperature downstream of the flow path switching valve 5 can be estimated, and the presence or absence of the occurrence of exhaust leakage from the flow path switching valve 5 can be diagnosed.

  More specifically, as shown in FIG. 10, when the exhaust gas temperature rises, the internal resistance of the air-fuel ratio sensor 21 increases. Further, the current applied to the air-fuel ratio sensor 21 is reduced and the electromotive force is reduced. Therefore, the output value of the air-fuel ratio sensor 21 is monitored, and the output value of the air-fuel ratio sensor 21 is compared with the leakage criteria obtained in advance by experimental adaptation or the like. However, the temperature of the exhaust gas on the downstream side of the flow path switching valve 5 rises even though the flow path switching valve 5 is closed, and the exhaust gas leaks downstream from the flow path switching valve 5. Can be diagnosed. That is, it is possible to diagnose the occurrence of exhaust leakage from the flow path switching valve 5 without using the upstream temperature sensor 24 or the bypass passage temperature sensor 25.

If the position of the air-fuel ratio sensor 21 is changed to a position upstream of the pour point 15 in the downstream main passage 8, the exhaust gas temperature is estimated using the output value of the air-fuel ratio sensor 21, and this estimation is performed. it the value may be above the temperature T _M, or from this estimate and the upstream temperature sensor 24 detects exhaust temperature so as to determine the temperature T _M.

Further, in the above-described embodiment, the temperature T _EO is detected by the bypass passage temperature sensor 25. However, the temperature T _EO is not detected directly, but from the ignition timing retard amount and the EGR reduction amount. It is also possible to estimate the temperature T _EO .

  The technical idea of the present invention that can be grasped from the above embodiment will be listed together with the effects thereof.

  (1) A bypass passage having a relatively small total cross-sectional area relative to the total cross-sectional area of the main passage is provided in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side. A failure diagnosis method for an internal combustion engine in which a catalytic converter is provided and a flow path switching valve for closing the main passage and a temperature detection means are provided in the upstream portion of the main passage that is bypassed by the bypass passage. When the flow path switching valve is closed and the main passage is closed, the temperature of the exhaust discharged from the cylinder is temporarily changed, and the flow path switching is performed from the temperature change in the main passage. Diagnose the valve for leaks. As a result, when diagnosing whether or not the flow path switching valve has a leak, the temperature of the exhaust gas discharged from the cylinder is temporarily raised. Therefore, the temperature inside the upstream portion of the main passage always changes, and the leakage of exhaust gas from the flow path switching valve can be reliably detected from the change in the internal temperature of the upstream portion of the main passage.

  (2) In the internal combustion engine failure diagnosis method described in (1) above, specifically, in order to temporarily change the temperature of the exhaust discharged from the cylinder, the ignition timing is retarded to temporarily Increase the temperature of the exhaust discharged from the cylinder.

  (3) In the internal combustion engine failure diagnosis method according to (2) above, a gas flow control valve that shields a part of the intake passage is provided upstream of the intake valve of the intake system to enhance gas flow in the cylinder. When the ignition timing is retarded, the gas flow control valve is operated in the valve closing direction. Thereby, the gas flow in the combustion chamber is strengthened, and the combustion stability at the time of ignition timing retard is enhanced.

  (4) In the internal combustion engine failure diagnosis method described in (1) above, specifically, in order to temporarily change the temperature of the exhaust gas discharged from the cylinder, the EGR amount is temporarily reduced to temporarily Increase the temperature of the exhaust discharged from the cylinder.

  (5) In the internal combustion engine failure diagnosis method described in (1) above, specifically, in order to temporarily change the temperature of the exhaust gas discharged from the cylinder, the exhaust valve opening timing is set closer to the bottom dead center. To temporarily increase the temperature of the exhaust gas discharged from the cylinder.

  (6) In the internal combustion engine failure diagnosis method according to (1) above, more specifically, in a stable high-load operation state, more fuel than that at the stoichiometric air-fuel ratio is injected to inject fuel. When performing fuel cooling by vaporization heat, in order to temporarily change the temperature of the exhaust discharged from the cylinder, the fuel injection amount is decreased so that the fuel amount at the stoichiometric air-fuel ratio is obtained, and fuel cooling is performed. By stopping, the temperature of the exhaust gas exhausted from the cylinder is temporarily raised.

  (7) The failure diagnosis method for an internal combustion engine described in (1) above is more specifically based on the amount of fuel at the stoichiometric air-fuel ratio in order to temporarily change the temperature of the exhaust gas discharged from the cylinder. The fuel is cooled by the vaporization heat of the fuel by injecting a lot of fuel, and the temperature of the exhaust discharged from the cylinder is temporarily lowered.

  (8) In the internal combustion engine failure diagnosis method according to any one of (1) to (7), specifically, the temperature detection means is an upstream side disposed upstream of the flow path switching valve. A temperature sensor, and a downstream temperature sensor disposed downstream of the flow path switching valve.

  (9) In the failure diagnosis method for an internal combustion engine according to any one of (1) to (7), the temperature detection means is an air-fuel ratio sensor, and the main passage is changed from a change in internal resistance of the air-fuel ratio sensor. Estimate the temperature change inside.

  (10) The failure diagnosis method for an internal combustion engine according to any one of (1) to (9), specifically, in a bypass passage that detects a temperature upstream of the bypass catalytic converter in the bypass passage. There is a temperature detection means, and there is a leak in the flow path switching valve using the temperature change in the main passage and the temperature of the exhaust discharged from the cylinder detected by the temperature detection means in the bypass passage. Diagnose whether or not.

  (11) A bypass passage having a relatively small total cross-sectional area relative to the total cross-sectional area of the main passage is provided in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side. In an internal combustion engine provided with a catalytic converter and provided with a flow path switching valve and a temperature detecting means for closing the main passage in the upstream portion of the main passage that is bypassed by the bypass passage. Temporary exhaust temperature changing means for temporarily changing the temperature of exhaust gas discharged, and exhaust gas temporarily discharged from the cylinder when the flow path switching valve is closed and the main passage is closed. Fault diagnosis means for diagnosing whether or not there is a leak in the flow path switching valve from a temperature change in the main passage.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows an example of the structure of the intake / exhaust system of the internal combustion engine which concerns on this invention, and a control system. The explanatory view showing typically the piping layout composition of the internal-combustion engine concerning the present invention. Schematic diagram showing an example of the temperature characteristics of the temperature T _M of the exhaust gas in the downstream side of the branching point of the temperature T _EO and upstream main passage of the exhaust gas discharged from the cylinder. The timing chart in 1st Embodiment of this invention. The schematic diagram which shows an example of the leakage criteria. The timing chart in 2nd Embodiment of this invention. The timing chart in 3rd Embodiment of this invention. The timing chart in 4th Embodiment of this invention. The timing chart in 5th Embodiment of this invention. Explanatory drawing which shows the correlation of exhaust temperature and the internal resistance of an air fuel ratio sensor.

Explanation of symbols

3 ... Upstream side main passage 5 ... Flow path switching valve 8 ... Downstream side main passage 9 ... Main catalytic converter 5 / Flow path switching valve 11 ... Upstream side bypass passage 14 ... Downstream side bypass passage 16 ... Bypass catalytic converter 24 ... Upstream side Temperature sensor 25 ... Bypass passage temperature sensor

Claims (11)

A bypass passage having a relatively small total cross-sectional area with respect to the total cross-sectional area of the main passage is provided in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side. In the internal combustion engine failure diagnosis method, the flow path switching valve for closing the main passage and the temperature detection means are provided in the upstream portion of the main passage that is bypassed by the bypass passage.
When the flow path switching valve is closed and the main passage is closed, the temperature of the exhaust discharged from the cylinder is temporarily changed, and the flow path switching valve is changed from the temperature change in the main passage. A method for diagnosing a failure in an internal combustion engine, characterized by diagnosing whether or not there is a leak in the engine.   The temperature of the exhaust gas discharged from the cylinder is temporarily increased by retarding the ignition timing in order to temporarily change the temperature of the exhaust gas discharged from the cylinder. A failure diagnosis method for an internal combustion engine. A gas flow control valve is provided on the upstream side of the intake valve of the intake system to shield a part of the intake passage in order to strengthen the gas flow in the cylinder.
3. The failure diagnosis method for an internal combustion engine according to claim 2, wherein when the ignition timing is retarded, the gas flow control valve is operated in a valve closing direction.   2. The temperature of exhaust gas exhausted from the cylinder is temporarily increased by decreasing the EGR amount in order to temporarily change the temperature of exhaust gas exhausted from the cylinder. A failure diagnosis method for an internal combustion engine.   In order to temporarily change the temperature of the exhaust discharged from the cylinder, the exhaust valve opening timing is changed to near the bottom dead center, and the temperature of the exhaust discharged from the cylinder is temporarily raised. The failure diagnosis method for an internal combustion engine according to claim 1. In a stable high-load operation state, when fuel is cooled by the vaporization heat of fuel by injecting more fuel than the fuel amount at the stoichiometric air-fuel ratio,
In order to temporarily change the temperature of the exhaust discharged from the cylinder, the fuel injection amount is decreased so that the fuel amount at the stoichiometric air-fuel ratio is reduced, and fuel cooling is stopped, so that the fuel cooling is temporarily stopped. 2. The internal combustion engine failure diagnosis method according to claim 1, wherein the temperature of the exhaust gas discharged is increased.   In order to temporarily change the temperature of the exhaust discharged from the cylinder, the fuel is cooled by the vaporization heat of the fuel by injecting more fuel than the amount of fuel at the stoichiometric air-fuel ratio. The failure diagnosis method for an internal combustion engine according to claim 1, wherein the temperature of the exhaust gas discharged from the engine is lowered.   The said temperature detection means has an upstream temperature sensor arrange | positioned in the upstream of the said flow-path switching valve, and a downstream temperature sensor arrange | positioned in the downstream of the said flow-path switching valve, It is characterized by the above-mentioned. The internal combustion engine failure diagnosis method according to any one of 1 to 7.   The internal combustion engine according to any one of claims 1 to 7, wherein the temperature detection means is an air-fuel ratio sensor and estimates a temperature change in the main passage from a change in internal resistance of the air-fuel ratio sensor. Fault diagnosis method. A bypass passage temperature detecting means for detecting a temperature upstream of the bypass catalytic converter of the bypass passage;
Diagnosing whether there is a leak in the flow path switching valve using the temperature change in the main passage and the temperature of the exhaust gas discharged from the cylinder detected by the temperature detection means in the bypass passage. A failure diagnosis method for an internal combustion engine according to any one of claims 1 to 9, A bypass passage having a relatively small total cross-sectional area with respect to the total cross-sectional area of the main passage is provided in parallel with the upstream portion of the main passage provided with the main catalytic converter on the downstream side. In the internal combustion engine provided with a flow path switching valve and a temperature detecting means for closing the main passage in the upstream portion of the main passage that is bypassed by the bypass passage.
Exhaust temperature temporary change means for temporarily changing the temperature of the exhaust gas exhausted from the cylinder, and when the flow passage switching valve is closed and the main passage is closed, the exhaust is temporarily exhausted from the cylinder. Failure diagnosis means for diagnosing whether or not there is a leak in the flow path switching valve from the temperature change in the main passage by changing the temperature of the exhaust gas.

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