JP2009127596A - Failure diagnosis device for exhaust gas purification system - Google Patents

Abstract

Disclosed is a fault diagnosis device for an exhaust gas purification system capable of accurately diagnosing even if an exhaust gas switching valve is stuck due to freezing.
A first exhaust gas passage 360 for passing exhaust gas from an engine to a catalyst, a second exhaust gas passage 350 formed by bypassing the first exhaust gas passage and provided with an HC adsorbent 340, and A temperature sensor capable of detecting a temperature change upstream of the HC adsorbent 340 in the second exhaust gas passage 350 in an exhaust gas purification system including an exhaust gas passage switching valve 370 that switches the passage to one of the passages; A cold start determination means for determining whether or not the engine start is a cold start lower than a predetermined temperature, and a flow path by the exhaust gas flow path switching valve 370 at the time of fuel cut when the exhaust system warm-up is completed after the cold start. Switching control is performed, and a failure of the exhaust gas flow path switching valve 370 is diagnosed based on a change in temperature upstream of the HC adsorbent detected by the temperature sensor.
[Selection] Figure 4

Description

  The present invention relates to an exhaust gas purification system in an internal combustion engine, and in particular, an exhaust gas comprising an exhaust gas flow path switching valve that switches a flow path at a predetermined time to a bypass path formed by bypassing the exhaust gas path and provided with an HC adsorbent. The present invention relates to a failure diagnosis device for an exhaust gas purification system for diagnosing a failure in a purification system.

  As this type of exhaust gas purification system failure diagnosis device, a device using first and second temperature detection means installed upstream and downstream of the HC adsorbent has been proposed (see, for example, Patent Document 1). ). According to the failure diagnosis device disclosed in Patent Document 1, the detection value by the first temperature detection means is set to a predetermined value or the second temperature detection means in a predetermined detection period set in accordance with opening / closing of the exhaust gas switching valve. It is said that a failure of the exhaust gas switching valve can be detected by comparing with the detection value obtained by.

  In addition, the exhaust temperature of each of the downstream side of the adsorption device and the return flow path is measured by a temperature sensor, the degree of correlation between the two exhaust temperatures is calculated, and the degree of this correlation does not reach a certain level. In some cases, an exhaust gas purification system having a failure diagnosis device that determines that the device has failed has also been proposed (refer to Patent Document 2 if it is collapsed).

JP 2000-230416 A Japanese Patent No. 3648792

  By the way, in the exhaust gas purification system using the HC adsorbent, the starting HC is adsorbed to the HC adsorbent at a low temperature of the catalyst, and the adsorbed HC is released from the HC adsorbent by switching the exhaust switching valve after the catalyst warms up. In this system, the purification process is performed with the catalyst that has been warmed up in the downstream. In the above-described conventional techniques, failure diagnosis of the exhaust gas switching valve is performed based on the temperature correlation of the exhaust gas detected over a certain period. Failure diagnosis based on such temperature correlation can be performed without any factor that hinders the operation of the exhaust gas switching valve if the entire exhaust system has been warmed up.

  However, in reality, the automobile may be exposed to a sub-freezing atmosphere including the engine and its exhaust system. In such a case, the exhaust gas switching valve may be fixed due to freezing. If the failure diagnosis is performed in such a fixed state due to freezing, there is a risk of performing an erroneous diagnosis in which the changeover valve is erroneously diagnosed even though there is no actual failure.

  Therefore, in view of the above-described circumstances, the present invention provides an exhaust gas that can accurately diagnose a failure of the exhaust gas flow path switching means without making a false diagnosis even when the exhaust gas switching valve is stuck due to freezing. It is an object of the present invention to provide a failure diagnosis device for a gas purification system.

In order to solve the above-described problems, an embodiment of a failure diagnosis device for an exhaust gas purification system according to the present invention includes a first exhaust gas passage for flowing exhaust gas from an engine to a catalyst, and the first exhaust gas passage. An exhaust gas purification system comprising a second exhaust gas passage formed by bypass and provided with an HC adsorbent, and an exhaust gas passage switching means for switching the passage to one of the first and second exhaust gas passages In the second exhaust gas passage, a temperature detecting means capable of detecting a temperature change at least upstream of the HC adsorbent, and a cold for determining whether the engine start is a cold start lower than a predetermined temperature Flow path switching control by the exhaust gas flow path switching means at the time of fuel cut when the exhaust system warm-up is completed after the cold start determined by the cold start determination means and the start determination means Failure diagnosis means for diagnosing a failure of the exhaust gas flow path switching means based on a change in temperature upstream of the HC adsorbent detected by the temperature detection means at that time. To do.

  According to this aspect, it is determined whether or not the engine start is a cold start lower than a predetermined temperature by the cold start determination means, and at the time of fuel cut when the exhaust system warm-up is completed after the start is determined as the cold start Failure diagnosis by the failure diagnosis means is performed. As a result, even if the exhaust gas flow path switching means is cold start lower than a predetermined temperature at which the exhaust gas flow path switching means may be stuck due to freezing, failure diagnosis by the failure diagnosis means is performed at the time of fuel cut when exhaust system warm-up is completed. Therefore, the exhaust gas flow path switching means is thawed, and since it is at the time of fuel cut, the exhaust gas temperature is stable without increasing, and the failure diagnosis means is exhaust gas flow path without erroneous diagnosis. A failure of the switching means can be diagnosed with high accuracy.

  Here, it is preferable to provide exhaust gas temperature lowering means for lowering engine exhaust gas temperature during the fuel cut.

  According to this embodiment, since the change margin of the temperature upstream of the HC adsorbent detected by the temperature detection means becomes large, the diagnostic accuracy is improved.

  The exhaust gas temperature lowering means may increase the intake air amount.

  Further, the exhaust gas purification system includes an upstream catalyst provided upstream of the exhaust gas flow switching means, a bypass passage that bypasses the upstream catalyst, and either the upstream catalyst or the bypass passage. A second exhaust gas flow path switching means for switching the flow path, wherein the exhaust gas temperature lowering means switches the second exhaust gas flow path switching means to the bypass passage side flow path. Good.

  In the present invention, “diagnosis” means that the degree of failure is specified in multiple stages according to a predetermined standard or some algorithm in addition to binary detection of the presence or absence of failure in the exhaust gas flow path switching means. It is a concept that includes what is done.

(First embodiment)
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  First, a configuration of an engine exhaust gas purification system to which the present invention is applied will be described with reference to FIG. FIG. 1 is a partial cross-sectional view showing a system configuration of an engine exhaust gas purification system.

  In FIG. 1, the engine exhaust gas purification system includes an electronic control unit (ECU) 100, an engine 200, and a main exhaust gas purification device 300. The ECU 100 includes a digital computer and includes a ROM (Read Only Memory), a RAM (Random Access Memory), a CPU (Central Processor Unit), an input port, an output port, and the like that are connected to each other via a bidirectional bus. It is possible to control the operation. Further, the ECU 100 is configured to be able to execute a failure diagnosis process, which will be described later, by executing a program stored in the ROM, and together with the main exhaust gas purification device 300, the ECU 100 of the exhaust gas purification system according to the present invention. It is also configured to function as an example of a failure diagnosis apparatus.

  The engine 200 can cause the air-fuel mixture to explode in the cylinder 201 by the spark plug 202, and can convert the reciprocating motion of the piston 203 generated according to the explosive force into the rotational motion of the crankshaft 205 via the connecting rod 204. It is an example of the internal combustion engine which concerns on this invention comprised. Below, the principal part structure of the engine 200 is demonstrated.

  When the fuel is burned in the cylinder 201, the air sucked from the outside passes through the intake pipe 206 and is mixed with the fuel injected from the injector 207 to become the above-mentioned air-fuel mixture. The injector 207 is supplied with fuel (gasoline) from a fuel tank (not shown), and the injector 207 is laid out so that the supplied fuel can be injected into the intake pipe 206 in accordance with the control of the ECU 100. ing.

  The communication state between the inside of the cylinder 201 and the intake pipe 206 is controlled by opening and closing the intake port by the intake valve 208. The air-fuel mixture combusted inside the cylinder 201 becomes exhaust gas, passes through the exhaust valve 209 that opens and closes the exhaust port in conjunction with opening and closing of the intake valve 208, and is exhausted to the exhaust pipe 210.

  An air cleaner 211 is disposed upstream of the intake pipe 206 to purify air sucked from the outside. An air flow meter 212 is disposed on the cylinder side of the air cleaner 211. The air flow meter 212 is, for example, a hot wire type, and is configured to be able to directly measure the mass flow rate of inhaled air. The intake pipe 206 is further provided with an intake air temperature sensor 213 for detecting the temperature of the intake air.

  A throttle valve 214 that adjusts the amount of intake air into the cylinder 201 is disposed on the cylinder side of the air flow meter 212 in the intake pipe 206. The throttle valve 214 is provided with a throttle valve motor 217 and a throttle position sensor 215, and constitutes an electronically controlled throttle valve. In this embodiment, the electronically controlled throttle valve also serves as an idle control valve that adjusts the intake air amount during idling. On the other hand, the depression amount of the accelerator pedal 223 is input to the ECU 100 via the accelerator position sensor 216, and a signal indicating the throttle valve opening corresponding to the output of the accelerator position sensor 216 is output from the ECU 100 to the throttle valve motor 217. The intake air amount is controlled.

  A crank position sensor 218 that detects the rotational position of the crankshaft 205 is installed in the vicinity of the crankshaft 205. The crank position sensor 218 is a sensor configured to be able to detect the rotational position of the crankshaft 205, and the ECU 100 determines the position of the piston 203 and the rotational speed of the engine 200 based on the output signal of the crank position sensor 218. Configured to be able to get. The position of the piston 203 is used for controlling the ignition timing in the spark plug 202 described above. The ignition timing in the spark plug 202 is, for example, retarded or advanced with respect to a preset basic value associated with the position of the piston 203.

  Further, a knock sensor 219 capable of measuring the knock strength of the engine 200 is disposed in the cylinder block that accommodates the cylinder 201, and the cooling water of the engine 200 is placed in the water jacket in the cylinder block. A water temperature sensor 220 for detecting the temperature is provided.

  A relatively small-capacity start-up catalyst 222 is installed at the collecting portion of the exhaust pipe 210. The start-up catalyst 222 is a three-way catalyst that can purify CO (carbon monoxide), HC (hydrocarbon), and NOx (nitrogen oxide) discharged from the engine 200, for example. An air-fuel ratio sensor 221 is disposed upstream of the startup catalyst 222 in the exhaust pipe 210. The air-fuel ratio sensor 221 is configured to detect the air-fuel ratio of the air-fuel mixture supplied to the engine 200 from the exhaust gas discharged from the exhaust pipe 210.

  The main exhaust gas purification device 300 is a catalyst device installed in the exhaust pipe 210 on the downstream side of the start-up catalyst 222, and functions together with the ECU 100 as an example of a failure diagnosis device for the exhaust gas purification system according to the present invention. It is configured to be possible. The main exhaust gas purifying device 300 and the ECU 100 are electrically connected via a control bus line.

  The ECU 100 is configured to receive a signal representing the vehicle speed VS from a vehicle speed sensor (not shown) that can detect the traveling speed of the vehicle and a range signal RS selected from the shift position sensor.

  Next, a detailed configuration of the main exhaust gas purification apparatus 300 will be described with reference to FIG. FIG. 2 is a schematic cross-sectional view of the main exhaust gas purification device 300. In the figure, the same reference numerals are assigned to the same parts as in FIG. 1, and the description thereof is omitted.

  Inside the outer cylinder 310 of the main exhaust gas purification apparatus 300, the inner cylinder 320 is concentric with the outer cylinder 310 and has a gap in the radial direction through a flange 322 formed integrally with the end thereof. Is provided. The inner cylinder 320 is installed in an open state in the main exhaust gas purification apparatus 300 with its upstream side extending to the vicinity of the corresponding end of the outer cylinder 310. Further, the downstream end of the inner cylinder 320 is installed in an open state while facing the end surface of the underfloor catalyst 330 disposed in the outer cylinder 310 via a predetermined space. A plurality of vent holes 324 are formed in the flange portion 322 of the inner cylinder 320. An annular HC adsorbent 340 is provided in an annular space formed between the outer cylinder 310 and the inner cylinder 320 of the main exhaust gas purification device 300, that is, a bypass passage 350 described later. An exhaust pipe 210 is connected to the upstream and downstream ends of the outer cylinder 310 of the main exhaust gas purification device 300.

  Further, in FIG. 2, the main exhaust gas purification apparatus 300 of the present embodiment can detect temperature changes upstream of the switching control valve 370 and the HC adsorbent 340 in addition to the above-described underfloor catalyst 330 and HC adsorbent 340. A temperature sensor 380 and a heat insulating layer 395 are provided as appropriate temperature detecting means.

  The underfloor catalyst 330 is, for example, a three-way catalyst installed under the floor of the vehicle, and purifies the exhaust gas that passes through the upstream startup catalyst 222 (not shown in FIG. 2) and flows in the direction of arrow A.

  The bypass flow path 350 is an example of a “second exhaust gas passage” according to the present invention, and is a “first exhaust gas passage” (hereinafter referred to as bypassed flow path or This is a flow path for bypassing the normal flow path 360) and guiding the exhaust gas to the underfloor catalyst 330.

  The HC adsorbent 340 is, for example, a filter formed of zeolite, and is a mesh-like filter that adsorbs (or traps) HC molecules at a low temperature (approximately less than 100 ° C.). At about 100 ° C. or higher), desorption starts spontaneously as the kinetic energy increases due to heat.

  The switching control valve 370 is configured to be able to selectively switch the flow path of the exhaust gas that has passed through the startup catalyst 222 between the bypass flow path 360 and the bypass flow path 350. The switching control valve 370 can switch the flow path of the exhaust gas by rotating the shaft portion 372 rotatably supported in the arrow B direction along with the linear motion of the rod 374 in the horizontal direction of the paper surface. It is configured. The operation of the rod 374 is controlled by an actuator 376, and the actuator 376 is electrically connected to the ECU 100 via the control bus line described above. That is, the main exhaust gas purification device 300 is configured such that the open / close bear of the switching control valve 370 changes in accordance with a control signal from the ECU 100.

  The temperature sensor 380 of the present embodiment is composed of a thermistor element, and is configured to be able to detect the temperature T upstream of the HC adsorbent 340 in the bypass channel 350. The temperature sensor 380 detects the temperature as a voltage value corresponding to the temperature and outputs it to the ECU 100, and the temperature T is specified by the ECU 100.

  The heat insulating layer 395 is a heat insulator formed between the bypass flow channel 350 and the bypass flow channel 360, and heat exchange between the bypass flow channel 350 and the bypass flow channel 360 is suppressed.

  Next, with reference to FIGS. 3 and 4, an exhaust gas flow path formed in accordance with the operation of the switching control valve 370 will be described. FIG. 3 is a schematic diagram of the exhaust gas flow when the switching control valve 370 is closed in the main exhaust gas purification apparatus 300. FIG. 4 is a schematic diagram of the switching control valve 370 opened in the main exhaust gas purification apparatus 300. It is a schematic diagram of the exhaust gas flow in the case of. In these drawings, the same reference numerals are given to the same portions as those in FIG. 2 and the description thereof is omitted.

  In FIG. 3, the exhaust gas flowing in the direction of arrow A does not flow into the bypassed flow channel 360 but is guided to the bypass flow channel 350 because the switching control valve 370 is closed. Then, after HC is adsorbed by the HC adsorbent 340, the HC adsorbent 340 flows out from the vent 324 formed on the downstream side of the HC adsorbent 340 in the direction of arrow C and flows into the underfloor catalyst 330.

  In FIG. 4, the exhaust gas flowing in from the direction of arrow A is guided to the bypassed flow path 360 due to the difference in exhaust resistance because the switching control valve 370 is open. On the other hand, a part of the exhaust gas passing through the bypassed flow channel 360 changes its direction in the direction of the arrow D shown in the vicinity of the end of the bypassed flow channel 360 and is formed in the flange 322 at the end of the bypass flow channel 350. It flows into the bypass channel 350 from the downstream side through the vent hole 324 formed. Then, the direction of the exhaust gas is changed again in the exhaust gas flow direction (arrow A direction) at the upstream end of the bypass flow channel 350 and guided to the bypass flow channel 360. That is, part of the exhaust gas recirculates inside the main exhaust gas purification device 300. In the main exhaust gas purification apparatus 300, the cross-sectional area ratio between the bypassed flow path 360 and the bypass flow path 350, the curvature of the flange 322 that defines the terminal end of the bypass flow path 350, the shape and size of the vent hole 324, and the like However, it is determined in advance to cause such a reflux phenomenon. Note that it is not essential to cause such a reflux phenomenon in the context of the present invention.

  The ECU 100 is configured to be able to diagnose a failure of the switching control valve 370 by executing a failure diagnosis process according to a program stored in the ROM during the operation of the exhaust gas purification system 10.

  Here, an example of the procedure of the failure diagnosis process in the first embodiment of the present invention will be described with reference to the flowchart of FIG. Here, the failure diagnosis processing routine performed in the flowchart of FIG. 5 is executed at a predetermined cycle at the time of start-up performed when the outside air is below freezing point or when the cooling water temperature of the engine 200 is colder than a predetermined temperature at which freezing is possible. Is done. It should be noted that a normal failure diagnosis process is performed at the time of starting without the possibility of freezing.

  Here, in the exhaust gas purification system 10 according to the present embodiment, since the engine 200 is not warmed as a whole at the time of starting, the start-up three-way catalyst 222 and the underfloor catalyst 330 normally reach the catalyst activation temperature. Absent. For this reason, it is difficult to purify the hydrocarbon HC contained in the exhaust gas, and the ECU 100 controls the switching control valve 370 to be closed when the engine 200 is cold-started, and guides the exhaust gas to the bypass passage 350. Thus, the hydrocarbon HC in the exhaust gas is adsorbed on the HC adsorbent 340. Then, after a predetermined catalyst warm-up period that can be considered that the start-up three-way catalyst 222 and the underfloor catalyst 330 have reached the catalyst activation temperature, the switching control valve 370 is opened, and the exhaust gas is guided to the bypass flow path 360. Thus, the exhaust purification capacity is prevented from being lowered and the HC trapped in the HC adsorbent 340 is desorbed and purified.

  When the control starts, the ECU 100 determines whether or not the coolant temperature when the engine 200 is started is lower than the predetermined temperature Tref (for example, 5 ° C.) (step S501). If the coolant temperature of the engine 200 is higher than the predetermined temperature Tref (step S501: NO), the failure diagnosis process is terminated because there is no possibility of freezing. When the coolant temperature is lower than the predetermined temperature Tref (step S501: YES), the process proceeds to step S502, and it is determined whether or not a “switching control valve opening / closing temporary abnormality flag” to be described later is set to ON. When the “switching control valve opening / closing temporary abnormality flag” is not set to ON, that is, when it is OFF (step S502: NO), it is determined that the failure diagnosis processing has already been completed, and this failure diagnosis processing is terminated. When the “switching control valve opening / closing temporary abnormality flag” is set to ON, the process proceeds to step S503, and the intake air amount GA is acquired from the output voltage of the air flow meter 212 and integrated. Furthermore, it progresses to step S504 and it is determined whether it is fuel cut F / C at the time of exhaust system warming-up completion.

  This exhaust system warm-up completion is determined based on the integrated value of the intake air amount GA acquired and integrated in step S503, and when the predetermined integrated value is reached, it is determined that the exhaust system warm-up is complete. The That is, since the intake air amount GA is closely related to the exhaust gas amount to be discharged, the thermal energy discharged by the operation from the start of the engine 200 is estimated by obtaining the integrated value of the intake air amount GA. It is then determined whether exhaust system warm-up is complete. Then, when the fuel cut F / C at the time of completion of the exhaust system warm-up is not reached (step S504: NO), the failure diagnosis process is temporarily ended. Whether or not the exhaust system warm-up is complete is determined by determining the elapsed time from when the engine 200 is started, that is, the time required for this thawing when the switching control valve 370 or its operating system is frozen ( In general, it is longer than the catalyst warm-up period) and is performed based on a fixed value that is obtained in advance through experiments or the like and stored in a ROM or the like. Or you may perform based on the fluctuation value which multiplied this correction value by the correction coefficient according to the cooling water temperature at the time of a start start.

  If it is determined in step S504 that the fuel cut F / C at the time of exhaust system warm-up completion is reached, the process proceeds to step S505, and the maximum value Ts of the upstream temperature of the HC adsorbent 340 after the start of the fuel cut F / C. Is acquired based on the detection value of the temperature sensor 380. This is obtained by comparing the temperature detected by the temperature sensor 380 in each routine cycle with the temperature detected in the previous routine cycle, and updating the temperature data only when the current temperature is high. Can do.

  Then, the process proceeds to the next step S506, and it is determined whether or not the “switching control valve closing normal flag” is set to ON. When the “switching control valve closing normal flag” is not set to ON (step S506: NO), in other words, when the switching control valve 370 is not considered to be closed, the process proceeds to step S507, and the switching control valve 370. Is closed, and an instruction to close the exhaust gas flow path from the bypass flow path 360 to the bypass flow path 350 is given. Then, in the next step S508, the temperature Ta on the upstream side of the HC adsorbent 340 after the first predetermined period (for example, A seconds) has elapsed since the start of the fuel cut F / C described above is set to the detected value of the temperature sensor 380. Get based on. Further, in the next step S509, the maximum temperature Ts on the upstream side of the HC adsorbent 340 acquired in step S505 described above and the upstream side of the HC adsorbent 340 after the elapse of the first predetermined period acquired in step S508. It is determined whether or not the difference from the temperature Ta is greater than a first predetermined value α1.

  If it is determined in step S509 that the difference (Ts−Ta) is larger than the first predetermined value α1, the process proceeds to step S510, the “switching control valve closing normal flag” is set to ON, and this fault diagnosis is performed. The processing routine is temporarily terminated. On the other hand, if it is determined in step S509 that the difference (Ts−Ta) is not greater than the first predetermined value α1, the process proceeds to step S511, and the difference (Ts−Ta) is determined to be a second predetermined value α2 (here Thus, it is determined again whether or not α1> α2). If the difference (Ts−Ta) is smaller than the first predetermined value α1 but larger than the second predetermined value α2 in the determination in step S511, the final diagnosis is suspended and this failure diagnosis processing routine is executed. Exit once. If the difference (Ts−Ta) is not greater than the second predetermined value α2 in the determination in step S511, the process proceeds to step S512, where it is determined that the switching control valve 370 is abnormal.

  On the other hand, when the above-described “switching control valve closing normal flag” is set to ON (step S506: YES), in other words, when the switching control valve 370 is considered to be in the closed state, the process proceeds to step S513, where the switching is performed. The control valve 370 is opened, and an opening instruction for switching the flow path of the exhaust gas from the bypass flow path 350 to the bypass flow path 360 is performed. Then, in the next step S514, the HC adsorbent 340 after the elapse of a second predetermined period (for example, B seconds, which may be equal to the above-mentioned A seconds) after the start of the fuel cut F / C described above. The upstream temperature Tb is acquired based on the detection value of the temperature sensor 380. Further, in the next step S515, the maximum temperature Ts on the upstream side of the HC adsorbent 340 acquired in step S505 described above and the upstream side of the HC adsorbent 340 after the second predetermined period acquired in step S514 are obtained. It is determined whether or not the difference from the temperature Tb is greater than a third predetermined value β1.

  If the difference (Ts−Tb) is smaller than the third predetermined value β1 in the determination in step S515, the process proceeds to step S516, the “switching control valve closing normal flag” is reset to OFF, and “switching control” Set “valve open normal flag” to ON. The process further proceeds to step S517, where the “switching control valve opening / closing temporary abnormality flag” is reset from ON to OFF, and this failure diagnosis processing routine ends. On the other hand, if it is determined in step S515 that the difference (Ts−Tb) is not smaller than the third predetermined value β1, the process proceeds to step S518, and the difference (Ts−Tb) is equal to the fourth predetermined value β2 (here Thus, it is determined again whether it is smaller than β1 <β2). If the difference (Ts−Tb) is smaller than the fourth predetermined value β2 in the determination in step S518, the final diagnosis is suspended and the present failure diagnosis processing routine is temporarily ended. If the difference (Ts−Tb) is not smaller than the fourth predetermined value β2 in the determination in step S518, the process proceeds to step S512, and it is determined that the switching control valve 370 is abnormal.

  Here, referring to the time chart of FIG. 6, the switching control valve 370 is normal based on the detected value of the temperature T on the upstream side of the HC adsorbent 340 during the fuel cut F / C according to the present embodiment described above. A mechanism that makes it possible to diagnose whether or not the device is in an operating state will be described. FIG. 6 (A) shows the ON / OFF switching timing of the fuel cut F / C, and FIG. 6 (B) shows the closing operation or opening operation from the reverse state of the switching control valve 370 after the switching timing. The temperature change with the passage of time on the upstream side of the HC adsorbent 340 is shown. That is, the solid line a in FIG. 6B indicates the temperature change when the switching control valve 370 is closed from the open state, and the alternate long and short dash line b indicates the temperature change when the switching control valve 370 is opened from the closed state.

  Therefore, when the fuel cut F / C is switched from the OFF state to the ON state at the time t corresponding to the operating conditions of the engine 200, combustion in the engine 200 is stopped, and only the intake air having a low temperature is exhausted. Will be discharged into the exhaust system. As described above, the temperature sensor 380 detects the maximum temperature Ts on the upstream side of the HC adsorbent 340 at the start or immediately after the fuel cut F / C. Here, the maximum temperature Ts on the upstream side of the HC adsorbent 340 immediately after the start of the fuel cut F / C is detected because the exhaust gas from the engine 200 to the temperature sensor 380 is detected. This is because the time lag of the flow is taken into consideration. And if the state of ON of fuel cut F / C continues, inflow of exhaust gas with low temperature will continue increasingly.

  Therefore, as indicated by the solid line a in FIG. 6B, when the switching control valve 370 is normally closed from the open state, the exhaust gas flows to the bypass flow path 350 side and is detected by the temperature sensor 380. T will drop with a significant slope. That is, the temperature on the upstream side of the HC adsorbent 340 detected by the temperature sensor 380 is Ta after the first predetermined period A seconds have elapsed after the start of the fuel cut F / C at the time t described above.

  On the other hand, as indicated by the alternate long and short dash line b in FIG. 6B, when the switching control valve 370 is normally opened from the closed state, the exhaust gas flows to the bypassed flow path 360 side and is detected by the temperature sensor 380. The temperature is not significantly affected by the low temperature exhaust gas, and does not decrease much. That is, the temperature on the upstream side of the HC adsorbent 340 detected by the temperature sensor 380 is higher than Ta even after the second predetermined period B seconds have elapsed after the start of the fuel cut F / C at time t described above. It becomes.

  As is clear from the above-described mechanism, the maximum temperature Ts on the upstream side of the HC adsorbent 340 after the start of the fuel cut F / C and the start of the fuel cut F / C after the start of the fuel cut F / C are determined in step S509 in the flowchart of FIG. The difference (Ts−Ta) from the temperature Ta on the upstream side of the HC adsorbent 340 after the elapse of the first predetermined period A seconds is larger than the first predetermined value α1 illustrated in FIG. 6B. 5 means that the switching control valve 370 is normally switched from the open state to the closed state in accordance with the closing instruction to the switching control valve 370 in step S506 in the flowchart of FIG. 5, and thus the switching control valve 370 is normal. It is determined. In the determination in step S511 in the flowchart of FIG. 5, the difference (Ts−Ta) is smaller than the first predetermined value α1 illustrated in FIG. 6B but larger than the second predetermined value α2. This means that even if there is a close instruction, the switching control valve 370 may not be normally switched from the open state to the closed state, so the final diagnosis is suspended.

  On the other hand, in the determination of step S515 in the flowchart of FIG. 5, the maximum temperature Ts on the upstream side of the HC adsorbent 340 after the start of the fuel cut F / C and the second predetermined period B seconds after the start of the fuel cut F / C. The difference (Ts−Tb) from the upstream temperature Tb of the HC adsorbent 340 after the elapse of time is smaller than the third predetermined value β1 illustrated in FIG. This means that the switching control valve 370 is normally switched from the closed state to the opened state in accordance with the opening instruction of the switching control valve 370 in S513, and therefore it is determined that the switching control valve 370 is normal. In the determination in step S515 in the flowchart of FIG. 5, the above difference (Ts−Ta) is larger than the third predetermined value β1 illustrated in FIG. 6B but smaller than the fourth predetermined value β2. This means that even if there is an opening instruction, the switching control valve 370 may not be normally switched from the closed state to the opened state, and therefore the final diagnosis is suspended.

  Contrary to the above, when the difference (Ts−Ta) is smaller than the second predetermined value α2 and larger than the fourth predetermined value β2, the switching is performed regardless of the closing instruction or the opening instruction. Assuming that the control valve 370 is not normally switched, the switching control valve 370 is determined to be abnormal. Such an abnormal state of the switching control valve 370 is such that the switching control valve 370 is kept closed for some reason and cannot be opened, and the switching control valve 370 is kept open for some reason and cannot be closed. In addition, it includes an open adhering state and an adhering state at an intermediate position between the closed position and the open position.

  In the first embodiment, failure diagnosis is performed in a state where the thawing is completed even when the switching control valve 370 is frozen when the fuel cut F / C at the time of exhaust system warm-up is completed. Therefore, it is possible to accurately diagnose the failure of the switching control valve 370 without erroneously diagnosing the fixation due to freezing as a failure of the switching control valve 370. In addition, since it is during fuel cut, the exhaust gas temperature is stable without increasing, and it is possible to diagnose with high accuracy from this point.

  When it is determined that the switching control valve 370 is abnormal and has failed (step S512), although not shown in the flowchart of FIG. 5, the ECU 100 notifies the driver of the vehicle or the like as a result of diagnosis. It is preferable to notify the failure via an indicator or the like.

(Second Embodiment)
Next, a second embodiment of the failure diagnosis processing procedure according to the present invention will be described with reference to the flowchart of FIG. Normally, the higher the temperature T on the upstream side of the HC adsorbent 340 at the start of the fuel cut F / C, the greater the decrease in the temperature T in the fuel cut F / C. Therefore, in the second embodiment, According to the upstream temperature T, correction coefficients ka1, ka2, kb1, which are multiplied by the above-described first to fourth predetermined values α1, α2, β1, β2 used as the criterion for failure diagnosis in the first embodiment. Each kb2 is set to improve diagnostic accuracy. That is, these correction factors (only ka1 and kb1 are illustrated in FIG. 8 but ka2 and kb2 are substantially the same) are determined by the temperature T on the upstream side of the HC adsorbent 340 at the start of fuel cut F / C. While it is “1.0” when the temperature is low, the temperature T is set to gradually increase as the temperature T increases.

  Note that the failure diagnosis processing routine in the second embodiment performed in accordance with the flowchart of FIG. 7 differs from the first embodiment in accordance with the flowchart of FIG. 5 only in the processing in some steps. Therefore, only the different steps will be explained to avoid redundant explanation. More specifically, the flowchart of FIG. 5 includes steps S501 to S518, whereas the flowchart of FIG. 7 includes corresponding steps S701 to S718, and the tenth place is different only in the hundreds. Since the steps having the same numbers are the same as the processing contents except for the steps described below, the description regarding the flowchart of FIG.

  Therefore, in step S705 corresponding to step S505, the maximum temperature Ts on the upstream side of the HC adsorbent 340 after the start of the fuel cut F / C is acquired based on the detection value of the temperature sensor 380, and this acquisition is performed. Correction coefficients ka1, ka2, kb1, and kb2 of the first to fourth predetermined values α1, α2, β1, and β2 corresponding to the maximum temperature value Ts are obtained, respectively.

  Then, in steps S709 and S711 corresponding to steps S509 and S511, the first and second predetermined values α1 and α2 are multiplied by the correction coefficients ka1 and ka2, respectively, and the upstream of the HC adsorbent 340 acquired in step S705. The difference between the maximum temperature Ts on the side and the temperature Ta on the upstream side of the HC adsorbent 340 after the first predetermined period acquired in step S708 is compared, and a failure diagnosis is performed. Similarly, in steps S715 and S718 corresponding to steps S515 and S518, the third and fourth predetermined values β1 and β2 are respectively multiplied by the correction coefficients kb1 and kb2, and the HC adsorbent 340 obtained in step S705 is obtained. The difference between the maximum upstream temperature value Ts and the upstream temperature Tb of the HC adsorbent 340 obtained in step S714 after the elapse of the second predetermined period is compared to perform fault diagnosis.

(Third embodiment)
Furthermore, a third embodiment of the above-described failure diagnosis process will be described with reference to the flowchart of FIG. In the third embodiment, there is provided an exhaust gas temperature lowering means for increasing the intake air amount GA in accordance with the start of the fuel cut F / C to lower the temperature of the exhaust gas from the engine 200. Thus, the diagnostic accuracy is improved and the temperature detection time is shortened. That is, as shown in the time chart of FIG. 10 corresponding to the time chart of FIG. 6 described above, the fuel cut F / C is switched from the OFF state to the ON state at the time t, and the switching control valve 370 is changed from the open state to the normal state. When the intake air amount GA is small (indicated by a solid line in FIG. 10B), as shown by a solid line a in FIG. The detected temperature T decreases with a considerable gradient, and after the first predetermined period A seconds from the start of the fuel cut F / C, the temperature on the upstream side of the HC adsorbent 340 detected by the temperature sensor 380 is Ta. By the way, when the intake air amount GA is increased in accordance with the start of the fuel cut F / C (shown by a broken line in FIG. 10B), the exhaust gas flows to the bypass channel 350 side, and the broken line in FIG. 10C. As indicated by c, the temperature T detected by the temperature sensor 380 further decreases with a steep slope, and after the first predetermined period A seconds have elapsed from the start of the fuel cut F / C at the time t described above, the temperature T The temperature on the upstream side of the HC adsorbent 340 detected by the sensor 380 becomes Taga lower than Ta in the previous embodiment. Therefore, in the third embodiment, the above-described diagnosis accuracy is improved and the temperature detection time is shortened by utilizing the characteristic that the temperature reduction margin is further increased by increasing the intake air amount GA. Since the basic failure diagnosis processing procedure is the same as that in the flowchart of FIG. 5, the different steps will be mainly described to avoid redundant description.

  When the control starts here, the ECU 100 determines whether or not the coolant temperature when the engine 200 is started is lower than a predetermined temperature Tref (for example, 5 ° C.) (step S901). If the cooling water temperature of the engine 200 is higher than the predetermined temperature Tref (step S901: NO), it is determined that there is no possibility of freezing, the process proceeds to step S914, and the “intake air amount GA increase control” described later is stopped. The diagnosis process is terminated. When the cooling water temperature is lower than the predetermined temperature Tref (step S901: YES), the process proceeds to step S902, and it is determined whether or not the “switching control valve opening / closing temporary abnormality flag” is set to ON. When the “switching control valve opening / closing temporary abnormality flag” is not set to ON, that is, when it is OFF (step S902: NO), it is determined that the failure diagnosis processing has already been completed, and the process proceeds to step S914 and “intake air amount” After the “GA increase control” is stopped, the fault diagnosis process is terminated. When the “switching control valve opening / closing temporary abnormality flag” is set to ON, the process proceeds to step S903, and the intake air amount GA is acquired from the output voltage of the air flow meter 212 and integrated. Furthermore, it progresses to step S904 and it is determined whether it is fuel cut F / C at the time of exhaust system warming-up completion.

  If it is not the fuel cut F / C at the time when the exhaust system warm-up is completed (step S904: NO), the process proceeds to step S914, and the "intake air amount GA increase control" is stopped, and then this failure diagnosis process is temporarily terminated. To do. When it is determined in step S904 that the fuel cut F / C at the time when exhaust system warm-up is completed, the process proceeds to step S905, and the above-described increase control of the intake air amount GA is executed. The increase control of the intake air amount GA is performed by sending a signal from the ECU 100 to open the throttle valve 214 by a predetermined angle from its idle opening position. Then, the process proceeds to the next step S906, and the maximum temperature Ts on the upstream side of the HC adsorbent 340 after the start of the fuel cut F / C is acquired based on the detected value of the temperature sensor 380.

  Then, the process proceeds to the next step S907 to determine whether or not the “switching control valve closing normal flag” is set to ON. When the “switching control valve closing normal flag” is not set to ON (step S907: NO), in other words, when the switching control valve 370 is not considered to be closed, the process proceeds to step S908, and the switching control valve 370 is reached. Is closed, and an instruction to close the exhaust gas flow path from the bypass flow path 360 to the bypass flow path 350 is given. Then, in the next step S909, the temperature Taga on the upstream side of the HC adsorbent 340 after the first predetermined period (for example, A seconds) has elapsed after the start of the fuel cut F / C described above is set as the detection value of the temperature sensor 380. Get based on. Further, in the next step S910, the first predetermined value in which the increase control of the maximum temperature Ts on the upstream side of the HC adsorbent 340 acquired in step S906 and the intake air amount GA acquired in step S910 is performed. It is determined whether or not the difference from the temperature Taga on the upstream side of the HC adsorbent 340 after the lapse of time is larger than a first predetermined value α1ga at the time of increase control.

  If it is determined in step S910 that the difference (Ts−Taga) is larger than the first predetermined value α1ga during the increase control, the process proceeds to step S911, and the “switching control valve closing normal flag” is set to ON. At the same time, this failure diagnosis processing routine is temporarily terminated. On the other hand, if it is determined in step S910 that the difference (Ts−Taga) is not greater than the first predetermined value α1ga at the time of increase control, the process proceeds to step S912, and the difference (Ts−Taga) is at the time of increase control. It is determined again whether or not it is larger than the second predetermined value α2ga (where α1ga> α2ga). If the difference (Ts−Taga) is smaller than the first predetermined value α1ga at the time of increase control but larger than the second predetermined value α2ga in the determination in step S912, the final diagnosis is suspended and this failure occurs. The diagnostic processing routine is temporarily terminated. Further, when the difference (Ts−Taga) is not larger than the second predetermined value α2ga during the increase control in the determination in step S912, the process proceeds to step S913, and it is determined that the switching control valve 370 is abnormal.

  On the other hand, when the above-described “switching control valve closing normal flag” is set to ON (step S907: YES), in other words, when the switching control valve 370 is considered to be in the closed state, the process proceeds to step S915. The control valve 370 is opened, and an opening instruction for switching the flow path of the exhaust gas from the bypass flow path 350 to the bypass flow path 360 is performed. In the next step S916, the HC adsorbent 340 after the second predetermined period (for example, B seconds, which may be equal to the above-mentioned A seconds) after the start of the fuel cut F / C described above. The upstream temperature Tbga is acquired based on the detection value of the temperature sensor 380. Furthermore, in the next step S917, the maximum temperature Ts on the upstream side of the HC adsorbent 340 acquired in step S906 described above and the upstream side of the HC adsorbent 340 after the second predetermined period acquired in step S916 are obtained. It is determined whether or not the difference from the temperature Tbga is smaller than a third predetermined value β1ga during the increase control.

  If it is determined in step S917 that the difference (Ts−Tbga) is smaller than the third predetermined value β1ga during the increase control, the process proceeds to step S918 to reset the “switching control valve closing normal flag” to OFF. , “Switching control valve opening normal flag” is set to ON. The process further proceeds to step S919, where the “switching control valve opening / closing temporary abnormality flag” is reset from ON to OFF, and this failure diagnosis processing routine is ended. On the other hand, if it is determined in step S917 that the difference (Ts−Tbga) is not smaller than the third predetermined value β1ga during the increase control, the process proceeds to step S920, where the difference (Ts−Tbga) is the fourth predetermined value. It is determined again whether or not the value is less than the value β2ga (where β1ga <β2ga). If the difference (Ts−Tbga) is smaller than the fourth predetermined value β2ga in the determination in step S920, the final diagnosis is suspended and the present failure diagnosis processing routine is temporarily ended. If the difference (Ts−Tbga) is not smaller than the fourth predetermined value β2ga in the determination in step S920, the process proceeds to step S913, and it is determined that the switching control valve 370 is abnormal.

  As described above, in the third embodiment, the intake air amount GA is increased in accordance with the start of the fuel cut F / C to reduce the temperature of the exhaust gas from the engine 200, thereby obtaining a larger temperature reduction allowance. In this way, the diagnostic accuracy is improved and the temperature detection time is shortened. However, instead of lowering the exhaust gas temperature by the increase control of the intake air amount GA, as shown in FIG. In the case of an exhaust system with a catalyst bypass mechanism in which a bypass passage opening / closing valve 226 is provided in the bypass passage 224 and the bypass passage opening / closing valve 226 is controlled to open / close The passage opening / closing valve 226 may be opened to switch the exhaust gas flow path to the bypass passage 224 side. In FIG. 11, the same reference numerals are used for the same functional parts as those described with reference to FIGS.

(Fourth embodiment)
Therefore, an example of a failure diagnosis processing procedure when the present invention is applied to the exhaust gas purification system including the exhaust system with the catalyst bypass mechanism shown in FIG. 11 is described as a fourth embodiment with reference to the flowchart of FIG. explain.

  When the control starts here, the ECU 100 determines whether or not the coolant temperature when the engine 200 is started is lower than a predetermined temperature Tref (for example, 5 ° C.) (step S1201). If the cooling water temperature of the engine 200 is higher than the predetermined temperature Tref (step S1201: NO), it is determined that there is no possibility of freezing, the process proceeds to step S1214 and the bypass passage opening / closing valve 226 is closed. finish. When the cooling water temperature is lower than the predetermined temperature Tref (step S1201: YES), the process proceeds to step S1202 to determine whether or not the “switching control valve opening / closing temporary abnormality flag” is set to ON. When the “switching control valve opening / closing temporary abnormality flag” is not set to ON, that is, when it is OFF (step S1202: NO), it is determined that the failure diagnosis processing has already been completed, and the process proceeds to step S1214 and the bypass passage opening / closing valve After executing the closing of the valve 226, the failure diagnosis process is terminated. When the “switching control valve opening / closing temporary abnormality flag” is set to ON, the process proceeds to step S1203, and the intake air amount GA is acquired from the output voltage of the air flow meter 212 and integrated. Furthermore, it progresses to step S1204 and it is determined whether it is fuel cut F / C at the time of exhaust system warming-up completion.

  If it is not the fuel cut F / C at the time when the exhaust system warm-up is completed (step S1204: NO), the process proceeds to step S1214 and the bypass passage opening / closing valve 226 is closed, and then the failure diagnosis process is temporarily terminated. . When it is determined in step S1204 that the fuel cut F / C at the time when exhaust system warm-up is completed, the process proceeds to step S1205, and a signal is sent from the ECU 100 to open the bypass passage on-off valve 226. When the bypass passage opening / closing valve 226 is opened, the exhaust gas discharged from the engine 200 flows to the side of the passage 224 that bypasses the startup catalyst 222 based on the difference in flow path resistance, and is heated by the startup catalyst 222. Is suppressed. Then, the process proceeds to the next step S1206, and the maximum temperature Ts on the upstream side of the HC adsorbent 340 after the start of the fuel cut F / C is acquired based on the detected value of the temperature sensor 380.

  Then, the process proceeds to the next step S1207 to determine whether or not the “switching control valve closing normal flag” is set to ON. When the “switching control valve closing normal flag” is not set to ON (step S1207: NO), in other words, when the switching control valve 370 is not considered to be closed, the process proceeds to step S1208, and the switching control valve 370 is reached. Is closed, and an instruction to close the exhaust gas flow path from the bypass flow path 360 to the bypass flow path 350 is given. In the next step S1209, the temperature Tab on the upstream side of the HC adsorbent 340 after the first predetermined period (for example, A seconds) has elapsed after the start of the fuel cut F / C described above is set as the detection value of the temperature sensor 380. Get based on. Further, in the next step S1210, the maximum temperature Ts on the upstream side of the HC adsorbent 340 acquired in step S1206 described above, and the upstream side of the HC adsorbent 340 after the first predetermined period acquired in step S1210. It is determined whether or not the difference from the temperature Tab is greater than a first predetermined value α1b when the bypass passage opening / closing valve 226 is opened.

  If it is determined in step S1210 that the difference (Ts−Tab) is larger than the first predetermined value α1b when the bypass passage opening / closing valve 226 is opened, the process proceeds to step S1211, and “the switching control valve is normally closed”. “Flag” is set to ON, and this failure diagnosis processing routine is once ended. On the other hand, if it is determined in step S1210 that the difference (Ts−Tab) is not larger than the first predetermined value α1b when the bypass passage opening / closing valve 226 is opened, the process proceeds to step S1212 and the difference (Ts− It is determined again whether Tab) is larger than a second predetermined value α2b (where α1b> α2b) when the bypass passage opening / closing valve 226 is opened. When the difference (Ts−Tab) in the determination in step S1212 is smaller than the first predetermined value α1b when the bypass passage opening / closing valve 226 is opened but larger than the second predetermined value α2b, The final diagnosis is suspended and this failure diagnosis processing routine is temporarily terminated. If it is determined in step S1212 that the difference (Ts−Tab) is not greater than the second predetermined value α2b when the bypass passage opening / closing valve 226 is opened, the process proceeds to step S1213, and the switching control valve 370 is activated. Judged to be abnormal.

  On the other hand, when the above-mentioned “switching control valve closing normal flag” is set to ON (step S1207: YES), in other words, when the switching control valve 370 is considered to be in the closed state, the process proceeds to step S1215, and switching is performed. The control valve 370 is opened, and an opening instruction for switching the flow path of the exhaust gas from the bypass flow path 350 to the bypass flow path 360 is performed. Then, in the next step S1216, the HC adsorbent 340 after the second predetermined period (for example, B seconds, which may be equal to the above-mentioned A seconds) after the start of the fuel cut F / C described above. The upstream temperature Tbb is acquired based on the detection value of the temperature sensor 380. Further, in the next step S1217, the maximum temperature Ts on the upstream side of the HC adsorbent 340 acquired in step S1206 described above and the upstream side of the HC adsorbent 340 after the second predetermined period acquired in step S1216. It is determined whether or not the difference from the temperature Tb is smaller than a third predetermined value β1b when the bypass passage opening / closing valve 226 is opened.

  If it is determined in step S1217 that the difference (Ts−Tbb) is smaller than the third predetermined value β1b when the bypass passage opening / closing valve 226 is opened, the process proceeds to step S1218, and “the switching control valve is normally closed”. "Flag" is reset to OFF and "Switching control valve opening normal flag" is set to ON. In step S1219, the “switching control valve opening / closing temporary abnormality flag” is reset from ON to OFF, and the present failure diagnosis processing routine is terminated. On the other hand, if it is determined in step S1217 that the difference (Ts−Tbb) is not smaller than the third predetermined value β1b when the bypass passage opening / closing valve 226 is opened, the process proceeds to step S1220, and the difference (Ts− It is determined again whether Tbb) is smaller than a fourth predetermined value β2b (here, β1b <β2b). If the difference (Ts−Tbb) is smaller than the fourth predetermined value β2b in the determination in step S1220, the final diagnosis is suspended and this failure diagnosis processing routine is temporarily ended. If the difference (Ts−Tbb) is not smaller than the fourth predetermined value β2b in the determination in step S1220, the process proceeds to step S1213, and it is determined that the switching control valve 370 is abnormal.

  In the fourth embodiment, the bypass passage opening / closing valve 226 serves as a second exhaust gas passage switching means for switching the passage to either the startup catalyst 222 as the upstream catalyst or the bypass passage 224 that bypasses the upstream catalyst 222. Correspondingly, the one that opens the bypass passage opening / closing valve 226 and switches to the bypass passage 224 side passage corresponds to the exhaust gas temperature lowering means.

  Next, the failure diagnosis processing procedure of the bypass passage opening / closing valve 226 used in the exhaust gas purification system including the exhaust system with the catalyst bypass mechanism described above is used as a modification of the fourth embodiment, and the flowchart of FIG. The description will be given with reference. In this modified embodiment, the temperature sensor 380 used for failure diagnosis of the switching control valve 370 can be used, so that the cost can be reduced accordingly. The failure diagnosis processing routine of the bypass passage opening / closing valve 226 is preferably executed after it is confirmed that the switching control valve 370 operates normally as a result of the failure diagnosis of the switching control valve 370.

  Therefore, in the failure diagnosis processing routine of the bypass passage opening / closing valve 226, first, in step S1301, it is determined whether or not the fuel cut F / C at the time of exhaust system warm-up completion. If it is not the fuel cut F / C at the time of exhaust system warm-up completion (step S1301: NO), this failure diagnosis process is temporarily ended. If it is determined in step S1301 that the fuel cut F / C at the time when exhaust system warm-up is completed, the process proceeds to step S1302, and the ECU 100 closes the switching control valve 370 by sending a close instruction signal. Then, the process proceeds to step S1303, where it is determined whether or not the “bypass passage opening / closing valve opening normality determination flag” is OFF.

  Therefore, when the “bypass passage opening / closing valve opening normality determination flag” is OFF (step S1303: YES), the process proceeds to step S1304, and the maximum value of the upstream temperature of the HC adsorbent 340 after the start of the fuel cut F / C. Ts is acquired based on the detection value of the temperature sensor 380. Then, in the next step S1305, an instruction to open the bypass passage opening / closing valve 226 is given. Then, the process proceeds to the next step S1306, where the temperature Ta on the upstream side of the HC adsorbent 340 after the first predetermined period (for example, A second) has elapsed after the start of the fuel cut F / C described above is detected by the temperature sensor 380. Get based on. Further, in the next step S1307, the maximum temperature Ts on the upstream side of the HC adsorbent 340 acquired in step S1304 described above, and the upstream side of the HC adsorbent 340 after the first predetermined period acquired in step S1306. It is determined whether or not the difference from the temperature Ta is greater than a first predetermined value α1.

  If it is determined in step S1307 that the difference (Ts−Ta) is larger than the first predetermined value α1, it is determined that the bypass passage opening / closing valve 226 is opened as instructed to open the valve in step S1305. Therefore, the process proceeds to step S1308, where the “bypass passage opening / closing valve opening normality determination flag” is set to ON, and this failure diagnosis processing routine is once ended. On the other hand, if it is determined in step S1307 that the difference (Ts−Ta) is not greater than the first predetermined value α1, the process proceeds to step S1309, and the difference (Ts−Ta) is determined to be a second predetermined value α2 (here Thus, it is determined again whether or not α1> α2). If the difference (Ts−Ta) is smaller than the first predetermined value α1 but larger than the second predetermined value α2 in the determination in step S1309, the final diagnosis is suspended and this failure diagnosis processing routine is performed. Is temporarily terminated. If the difference (Ts−Ta) is not larger than the second predetermined value α2 in the determination in step S1309, the process proceeds to step S1310, where it is determined that the bypass passage opening / closing valve 226 is abnormally open, The failure diagnosis processing routine is once terminated.

  On the other hand, if the “normal bypass opening / closing determination flag of the bypass passage on / off valve” is already ON (step S1303: NO), the process proceeds to step S1311, where the upstream of the HC adsorbent 340 after the start of the fuel cut F / C. The maximum temperature value Ts on the side is acquired based on the detected value of the temperature sensor 380. In the next step S1312, the execution of closing the bypass passage opening / closing valve 226 is instructed. Then, the process proceeds to the next step S1313, and the upstream side of the HC adsorbent 340 after the second predetermined period (for example, B seconds, A may be equal to B) after the start of the fuel cut F / C described above. The side temperature Tb is acquired based on the detection value of the temperature sensor 380. Further, in the next step S1314, the maximum temperature Ts on the upstream side of the HC adsorbent 340 acquired in step S1311 described above and the upstream side of the HC adsorbent 340 after the second predetermined period acquired in step S1313. It is determined whether or not the difference from the temperature Tb is smaller than a third predetermined value β1.

  When the difference (Ts−Tb) is smaller than the third predetermined value β1 in the determination in step S1314, it is determined that the bypass passage opening / closing valve 226 is closed according to the valve closing execution instruction in step S1312. Therefore, the process proceeds to step S1315, where the “bypass passage opening / closing valve closing normality determination flag” is set to ON, and this failure diagnosis processing routine is once ended. On the other hand, if it is determined in step S1314 that the difference (Ts−Tb) is not smaller than the third predetermined value β1, the process proceeds to step S1315, and the difference (Ts−Tb) is the fourth predetermined value β2 (here Thus, it is determined again whether it is smaller than β1 <β2). If the difference (Ts−Tb) is smaller than the fourth predetermined value β2 in the determination in step S1316, the final diagnosis is suspended and the present failure diagnosis processing routine is temporarily ended. If it is determined in step S1316 that the difference (Ts−Tb) is larger than the fourth predetermined value β2, the process proceeds to step S1317, where it is determined that the bypass passage opening / closing valve 226 is abnormally closed, and this failure occurs. End the diagnostic processing routine.

  Thus, according to the modification of the fourth embodiment, the failure diagnosis of the bypass passage opening / closing valve 226 can be performed using the temperature sensor 380 used for the failure diagnosis of the switching control valve 370. It is possible to reduce costs.

  It should be noted that the present invention is not limited to the above-described exemplary embodiments, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification. Such a failure diagnosis apparatus is also included in the technical scope of the present invention.

1 is a system configuration diagram of an exhaust gas purification system according to an embodiment of the present invention. It is a schematic cross section of the main exhaust gas purification apparatus in the exhaust gas purification system of FIG. FIG. 3 is a schematic diagram of an exhaust gas flow when a switching control valve is closed in the main exhaust gas purification device of FIG. 2. FIG. 3 is a schematic diagram of an exhaust gas flow when a switching control valve is open in the main exhaust gas purification device of FIG. 2. 3 is a flowchart showing a first embodiment of a failure diagnosis processing routine executed by an ECU in the exhaust gas purification system of the present invention. (A) is the ON / OFF switching timing of the fuel cut F / C, and (B) is the time elapsed upstream of the HC adsorbent due to the closing operation or opening operation from the reverse state of the switching control valve after the switching timing. It is a time chart which shows the temperature change accompanying with. It is a flowchart which shows 2nd Embodiment of the failure diagnosis processing routine which ECU performs in the exhaust-gas purification system of this invention. It is a graph which shows the relationship between the correction coefficient multiplied to the predetermined value used for the criterion in the 2nd Embodiment of this invention, and the temperature of the upstream of HC adsorbent. 7 is a flowchart showing a third embodiment of a failure diagnosis processing routine executed by an ECU in the exhaust gas purification system of the present invention. (A) is the ON / OFF switching timing of the fuel cut F / C, (B) is the magnitude of the intake air amount GA after the switching timing, and (C) is the reverse state of the switching control valve after the switching timing. 6 is a time chart showing a temperature change with the passage of time on the upstream side of the HC adsorbent corresponding to the magnitude of the intake air amount GA due to the closing operation or the opening operation. It is a mimetic diagram showing simply an exhaust gas purification system provided with an exhaust system with a catalyst bypass mechanism. It is a flowchart which shows 4th Embodiment of the failure diagnosis processing routine which ECU performs in the exhaust-gas purification system of this invention. It is a flowchart of the deformation | transformation aspect of 4th Embodiment in this invention.

Explanation of symbols

100 Electronic control unit (ECU)
200 Engine 212 Airflow meter 222 Start-up three-way catalyst 300 Main exhaust gas purifier 330 Underfloor catalyst 340 HC adsorbent 340
350 Bypass passage (second exhaust gas passage)
360 Bypassed channel (first exhaust gas channel, normal channel)
370 Switching control valve 376 Actuator 380 First temperature sensor

Claims (4)

A first exhaust gas passage through which exhaust gas from the engine flows to the catalyst, a second exhaust gas passage formed by bypassing the first exhaust gas passage and provided with an HC adsorbent, and the first and second In an exhaust gas purification system comprising exhaust gas flow path switching means for switching the flow path to any of the exhaust gas passages,
A temperature detecting means capable of detecting a temperature change in the second exhaust gas passage and at least upstream of the HC adsorbent;
Cold start determination means for determining whether the engine start is a cold start lower than a predetermined temperature;
At the time of fuel cut when the exhaust system warm-up is completed after the cold start determined by the cold start determination means, the exhaust gas flow path switching means performs flow path switching control, and at that time, the temperature Failure diagnosis means for diagnosing a failure of the exhaust gas flow path switching means based on a change in temperature upstream of the HC adsorbent detected by the detection means;
An exhaust gas purification system failure diagnosis device comprising:   The failure diagnosis device for an exhaust gas purification system according to claim 1, further comprising exhaust gas temperature lowering means for lowering the temperature of the exhaust gas of the engine during the fuel cut.   The failure diagnosis device for an exhaust gas purification system according to claim 2, wherein the exhaust gas temperature lowering means increases the amount of intake air.   The exhaust gas purification system includes an upstream catalyst provided upstream of the exhaust gas flow path switching means, a bypass passage that bypasses the upstream catalyst, and a flow path that is either one of the upstream catalyst and the bypass passage. And a second exhaust gas flow path switching means for switching the exhaust gas temperature lowering means for switching the second exhaust gas flow path switching means to the bypass passage side flow path. The failure diagnosis device for an exhaust gas purification system according to claim 2.

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