JP2003201834A - Diagnostic method for secondary air supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diagnostic method for a secondary air supply device which accurately judges any temporary failure resulting from freezing of the secondary air supply device. <P>SOLUTION: If the result from a failure judgment when AI (secondary air supply) is started is such that there is possibility of a closing failure resulting from freezing (Step S1), a rejudgement process 1 is made as rejudgement after machine warming-up (Step S4), and if the result from judgement when AI is stopped is such that there is possibility of an opening failure resulting from freezing (Step S5), a rejudgement process 2 is made as rejudgement after machine warming-up (Step S7). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method of a secondary air supply system for supplying secondary air upstream of an exhaust purification system for an exhaust system of an internal combustion engine.

[0002]

2. Description of the Related Art As an exhaust gas purifying apparatus for an internal combustion engine, there is known an apparatus in which a catalyst is arranged in an exhaust system to purify CO, HC, NOx components and the like in exhaust gas. Further, secondary air is supplied into the exhaust pipe through a secondary air supply passage having an opening / closing valve connected to the exhaust pipe to increase the oxygen concentration, thereby secondary burning HC and CO in the exhaust gas. There is known a technology for promoting purification of exhaust gas.

In such a secondary air supply device, if the above components such as an air pump and an on-off valve occur,
Since the exhaust gas purification efficiency decreases and the emission deteriorates, it is necessary to determine the abnormality early.
Therefore, as a technique for detecting this type of abnormality, Japanese Patent Laid-Open No.
The techniques disclosed in Japanese Patent Laid-Open No. 21312 and Japanese Patent Laid-Open No. 9-125945 are known.

In the former, a pressure sensor is arranged between the air pump and the opening / closing valve in the secondary air supply passage to detect an abnormality in the secondary air supply device based on the detected pressure value. In the latter, a pressure sensor is arranged in the secondary air supply passage, and an abnormality of the secondary air supply device is detected based on the detected pressure pulsation or the difference between the maximum value and the minimum value thereof.

[0005]

However, according to these techniques, although the abnormality of the secondary air supply device itself can be detected, it is possible to accurately determine which component is abnormal and what kind of abnormality. difficult. Further, even when the component parts are not functioning normally, the abnormality cannot be detected in the case of a malfunction in which the pressure value and the pressure pulsation show normal values. In particular,
There is a problem that a temporary abnormality due to freezing cannot be accurately determined.

Therefore, it is an object of the present invention to provide a method for diagnosing a failure in a secondary air supply device, which can accurately determine a temporary abnormality due to freezing of the secondary air supply device.

[0007]

In order to solve the above-mentioned problems, a method for diagnosing a failure in a secondary air supply device according to the present invention comprises:
If the failure diagnosis result during cold is expected to be abnormal due to freezing of the secondary air supply system, it is characterized in that the determination is performed again after warming up.

In the case of a temporary abnormality due to freezing of condensed water or the like, if the condensed water or the like, which has been frozen by warming up, is melted, the device comes to function normally. Therefore, by performing the determination again after warming up, it is possible to determine whether the abnormality is a temporary abnormality due to freezing or a permanent abnormality due to other reasons.

It is preferable that re-determination after warm-up is performed only during fuel cut or during light load. By doing so, it is possible to suppress the deterioration of the NOx purification performance due to the dilution of the air-fuel ratio due to the supply of the secondary air, and to suppress the deterioration of the emission due to the supply of the secondary air.

It is preferable to stop the supply of the secondary air when the result of the failure diagnosis during cold is expected to be a closing abnormality due to freezing of the secondary air supply system. When there is a possibility of blockage due to freezing, the secondary failure of other devices can be prevented by stopping the secondary air supply.

If the result of the failure diagnosis during cold is expected to be a freezing failure of the air pump, it is preferable to stop the air pump sooner than when another abnormality in the secondary air supply system is detected. Attempting to keep the air pump running in the event of an air pump freeze failure can, in the worst case, cause damage to the air pump. Since this damage can occur in a relatively short time, the air pump is prevented from being damaged by stopping the air pump sooner than when other abnormalities are detected.

If the failure diagnosis result during cold is predicted to be an opening abnormality due to freezing of the secondary air supply system, the secondary air supply may be continued. This is because, in the case of an opening abnormality due to freezing, there is no possibility that a secondary failure will occur even when the secondary air supply is continued, and there is a high possibility that the secondary failure will be restored to normal by warming up during operation.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same constituent elements in each drawing as much as possible in the drawings, and redundant description will be omitted.

FIG. 1 is a schematic diagram showing the configuration of a secondary air supply apparatus 1 in which the failure diagnosis method according to the present invention is carried out.
The secondary air supply device 1 is attached to a multi-cylinder gasoline engine (hereinafter simply referred to as an engine) 2 which is an internal combustion engine. Here, an intake pipe 20 and an exhaust pipe 21 are attached to the engine 2, and the intake pipe 20
A throttle 24 is disposed in the engine and is connected to the intake filter 25. An air flow meter 26 for measuring the air amount (primary air amount) and an intake air temperature sensor 27 for measuring the intake air temperature THA are arranged between the intake air filter 25 and the throttle 24. Also, engine 2
A cooling water temperature sensor 28 for measuring the engine cooling water temperature THW is attached to the. The engine ECU 23 that controls the engine includes the air flow meter 2
6, the intake air temperature sensor 27, the cooling water temperature sensor 28, the output of a rotation speed sensor (not shown), the opening of the throttle 24, and the like are input.

On the other hand, a three-way catalyst 22 is provided downstream of the exhaust pipe 21.
Is arranged, and O ₂ sensors 31 and 32 for detecting the oxygen concentration in the exhaust are arranged both upstream and downstream of the catalyst 22. Further, a temperature sensor 33 for detecting the exhaust temperature on the upstream side of the catalyst 22 and a temperature sensor 34 for detecting the catalyst temperature of the catalyst 22 are arranged.
Instead of the O ₂ sensor, A / F sensor may also be used a linear O ₂ sensor. Further, the temperature sensor 33 is connected to the exhaust pipe 21.
It may be arranged at any position as long as it is downstream of the air supply passage 11.

The secondary air supply system 1 includes the exhaust pipe 2 and the position of the intake pipe 20 between the intake filter 25 and the throttle 24.
1 is provided with a secondary air supply passage 11 that connects between the engine 2 and the upstream O ₂ sensor 31. An electric motor driven air pump (AP) is provided on the secondary air supply passage 11 from the intake pipe 20 side. ) 12, Air switching valve (AS
V) 13 and a reed valve (RV) 14 which is a check valve are arranged. The pressure sensor 15 is arranged between the AP 12 and the ASV 13. A pipe 16 extending from a downstream side of the throttle 24 of the intake pipe 20 is connected to the ASV 13, and a solenoid valve 17 is further arranged in the pipe 16.

The control device 10 for controlling the operation of the secondary air supply device 1 is connected to the engine ECU 23 by a signal line so as to exchange information with each other, and outputs of the pressure sensor 15, the O ₂ sensors 31, 32. A signal is input and the motor drive of AP12 and opening / closing of the solenoid valve 17 are controlled. It should be noted that the control device 10 uses the engine ECU 2
It may be a part of 3.

This secondary air supply device 1 has a high fuel concentration mainly during cold start, a low air-fuel ratio (A / F), and the function of the catalyst 22 is not sufficiently raised. When the control device 10 opens the solenoid valve 17 in a state in which the intake valve 20 is not sufficiently exerted, the negative pressure in the intake pipe 20 is reduced to ASV1.
3, the ASV 13 is controlled to be opened, and the air pump 12 is driven to guide a part of the air that has passed through the air filter 25 into the exhaust pipe 21 through the secondary air supply passage 11 to exhaust the exhaust gas. Increase the oxygen concentration, and
F is raised to 2 in the exhaust pipe 21 of HC and CO in the exhaust.
The secondary combustion is promoted to purify the exhaust gas, and the exhaust gas temperature is raised to accelerate the temperature rise of the catalyst 22 to suppress the deterioration of the emission. Hereinafter, this 2 o'clock air supply control is referred to as AI control. Instead of the combination of the ASV 13 and the solenoid valve 17, the solenoid valve can be used directly in the ASV 13 part.

As described above, since the secondary air supply device is often operated at a low temperature, if condensed water remains in the supply passage 11, it freezes and the passage 11 is closed, or A
There is a possibility of causing malfunction of P12, ASV13, and RV14. Attempting to supply air at 2 o'clock during such a freeze failure can cause damage to the components. On the other hand, it is also necessary to prevent erroneous determination that a temporary failure due to freezing is determined as a normal failure. The failure diagnosis method for the secondary air supply system according to the present invention enables such temporary failure due to freezing to be detected separately from failures in other components. The specific control method will be described below.

FIG. 2 is a main flowchart of the present diagnostic method, and FIGS. 3 to 6 are flowcharts showing in detail a part of the processing shown in FIG. This control is performed by the control device 1 in cooperation with the engine ECU 23.
The process is started when the engine 2 is started, and is executed only once in parallel with other processes.

First, in step S1, a failure determination at AI startup is performed. Details of the processing are shown in FIG. First, in step S101, it is checked whether or not the AI condition is satisfied. The AI execution condition is determined by the engine cooling water temperature sent from the engine ECU 23, the intake air temperature, the elapsed start time, the battery voltage, the load condition, and the like. When it is determined that the AI control is not required because the condition is not satisfied, the process proceeds to step S101 and ends the process. If the AI execution condition is not completed, it waits until the execution condition is satisfied, and if the execution condition is satisfied, step S102.
Transition to.

In step S102, the AI system is activated. Specifically, by opening the solenoid valve 17, the negative pressure in the intake pipe 20 is guided to the ASV 13, the ASV 13 is controlled to be opened, and the AP 12 is driven, so that part of the air that has passed through the air filter 25. Are introduced into the exhaust pipe 21 via the secondary air supply passage 11.

In step S103, it is determined whether t1 hours have elapsed after the AI system was activated. If the time has not elapsed, the process returns to step S102 and the loop process is performed to perform the AI control while waiting. t1
When the time has elapsed, the process proceeds to step S104, and the pressure value P and the pressure fluctuation value ΔP are read. In step S105, based on the read pressure value P and pressure fluctuation value ΔP, the secondary air supply passage 11 is closed (AP12 is inoperative, AS
(Including closed fixation of V13 and RV14) has not occurred. Specifically, in the normal case where there is no blockage, it is considered that the pressure P is equal to or higher than the atmospheric pressure as shown in the pattern 1 of FIG. 4 and the pressure fluctuates with the pressure fluctuation on the downstream side. On the other hand, when the passage including the closed fixation of the ASV 13 and the RV 14 is closed but the AP 13 is operating normally, the pressure P is maintained at a constant high pressure as shown in the pattern 3. it is conceivable that. Also, AP
In the case of 13 non-operation, if there is no blockage of the passage, it fluctuates as shown in pattern 2, and if the passage is blocked, it is maintained at atmospheric pressure as shown in pattern 4. Therefore, in the case other than the pattern 1, it may be determined that the blockage is abnormal.

When there is no occlusion abnormality (including the open-sticking abnormality of the ASV 13 and RV 14 and the normal operation abnormality of the AP 13), the process proceeds to step S106 and the value of the abnormality continuation time Δt_an is reset to 0. Then, the process proceeds to step S107, and it is determined whether or not the AI ending condition is satisfied.
If the AI ending condition is not satisfied, step S1 is performed again.
The AI control is continued unless a blockage abnormality is detected by performing a loop process for shifting to 02. When the end condition is satisfied, the process proceeds to step S108, the AI system is stopped, and the process ends. Specifically, the solenoid valve 17 is closed to control the ASV 13 to be closed, and the driving of the AP 12 is stopped.

If it is determined in step S105 that it is blocked, the flow advances to step S110 to determine the value of the abnormal continuation time Δt_an. When Δt_an is 0, the current time t is set in tstart. Abnormality is detected continuously, and Δt_an
If is not 0, the process proceeds to step S112 while holding the value of tstart. In step S112, it is determined whether the freezing condition is satisfied. For example, if either the minimum intake air temperature THAmin from the start or the engine cooling water temperature TWAS at the start is less than 5 ° C., it is set as a freezing condition that may freeze. If the freezing condition is not satisfied, it is considered not a freezing but a device failure. Therefore, the process proceeds to step S113, and the flag XAI indicating the determination result is set to 1
Is set and a flag XFAI indicating a device failure is set.
Is set to 1, the process proceeds to step S108, the AI system is stopped to prevent the secondary failure, and the process ends.

When it is determined in step S112 that the freezing condition is satisfied, the process proceeds to step S114 and it is determined whether or not there is an AP abnormality. Here, when the time variation of the pressure value P is shown in pattern 3 of FIG. 4, it is determined that there is no abnormality, and when it is shown in pattern 2 or 4, it is determined that there is abnormality. If there is an abnormality, step S11
Then, the process proceeds to step 5, and the determination threshold Δt_th for the abnormal duration Δt_an is changed to Δ
If ta is not abnormal, the process proceeds to step S116, and Δtb is set to the determination threshold Δt_th of the abnormal duration Δt_an. Here, Δta <Δtb.

In step S117, the duration Δt_an is calculated by calculating the difference between tstart and the current time t. After the calculation, the process proceeds to step S118 to compare the set determination threshold Δt_th with the abnormal continuation time Δt_an. Δ
If t_an is equal to or less than Δt_th, the process returns to step S102 to continue the process. On the other hand, when Δt_an exceeds Δt_th, the process proceeds to step S119, and the freeze close flag XF is set.
After setting 1 to CL, the process proceeds to step S109 to stop the AI system.

In this way, when there is a possibility of freezing failure, by continuing the operation of AP12 for a relatively long time when AP12 is operating, in the case of a temporary failure due to freezing, dissolution is promoted and reliable failure determination is performed. On the other hand, when there is a possibility that the AP 12 is inoperable due to freezing, the threshold value for determining the abnormal duration is set to a short time to forcibly stop the AP 12 to prevent secondary damage to the AP 12.
FIG. 5 is a graph showing changes in current and temperature of the motor driving the AP 12 with respect to the state of the AI system.
When AP12 is frozen, it is faster than when other lines are frozen.
Since the temperature of the motor for driving 12 may reach the allowable temperature and be damaged, AP1 is set by setting Δta and Δtb shorter than the time required to reach the allowable temperature.
It is possible to make a reliable determination while suppressing the damage of item 2.

After the processing of FIG. 3 is completed, the processing returns to the processing of FIG. 2, and in the next step S2, the value of the determination result XAI is checked. If XAI is 1, it is determined that a component failure has occurred, the subsequent processing is skipped, and the processing ends. If XAI is 0, it is determined that the determination has not been completed, and the process proceeds to step S3. In step S3, the value of the freeze close flag XFCL is checked. If XFCL is 1, it is determined in step S1 that there is a possibility of temporary blockage due to freezing. Therefore, the process proceeds to step S4 and redetermination processing 1 is performed. Details of the processing are shown in FIG.

First, in step S401, a loop process is performed that does not shift to the next step until the warm-up is completed.
The determination of warm-up completion may be made based on the engine cooling water temperature TWA and the exhaust temperature detected by the temperature sensor 33. If it is determined that the warm-up is completed, the process proceeds to step S402,
A loop process is performed that does not shift to the next step until the fuel cut (F / C) or the light load condition is satisfied. If the conditions are satisfied, the process proceeds to step S403 to activate the AI system. In step S404, AI
It is determined whether or not t2 time has elapsed after the system operation. If it has not elapsed, a loop process of returning to step S403 is performed, and if it has elapsed, the process proceeds to step S405.

In step S405, the pressure value P and its fluctuation value ΔP are read. In step S406, the secondary air supply passage 11 is closed (A
It is again determined whether or not P12 does not operate and ASV13 and RV14 are closed and fixed). In the case of a temporary failure due to freezing, the condensed water that had been frozen will be dissolved by warming up and the equipment will operate normally. It is possible to judge whether it is a failure or another failure.

If it is determined to be blocked, step S407.
The flag XAI indicating the determination result is set to 1 and the flag XFAI indicating the device failure is set to 1 and the process proceeds to step S408 to stop the AI system to prevent the secondary failure. Ends the process.
If the blockage is not determined, the process directly proceeds from step S406 to step S408 to stop the AI system and terminate the process. In this case, the value of XAI remains the initial value 0.

After the process of FIG. 6 is completed, the process returns to the process of FIG. 2 and proceeds to the next step S5. On the other hand, if the freeze-close flag XFCL is 0 in step S3, the step S3 is directly executed.
Move to 5. In this step S5, the failure determination of the AI supply system is performed based on the pressure behavior when the AI is stopped. Details of this processing are shown in FIG.

In step S501, step S503
Then, it is determined whether or not the AP 12 is operating. This can be determined by whether or not the pressure value is increasing. A
When the P12 is in operation, the AP12 is in a constant operation abnormality, so the process proceeds to step S506, and the flag XAI indicating the determination result is set to 1, and the flag XFAI indicating the device failure is set to 1 and the process ends. To do.

If the AP 12 is stopped, step S
The process proceeds to 504, and it is determined whether the ASV 13 and the RV 14 are in the open failure state. When it is determined that the ASV 13 and the RV 14 are not in the open failure state, the subsequent processing is skipped and the processing ends. When it is determined that the open failure state is present, the process proceeds to step S505, and it is determined whether the freezing condition is satisfied. Freezing conditions are step S11
It may be the same as the freezing conditions of 2. If the freezing condition is not satisfied, it is considered that the device is not frozen but a device failure. Therefore, the process proceeds to step S506, and the flag XA indicating the determination result is displayed.
A flag X indicating a device failure while setting I to 1
The FAI is set to 1 and the process ends. On the other hand, if the freezing condition is satisfied, there is a possibility of a temporary failure due to freezing, so the process moves to step S507, the freeze opening flag XFOP is set to 1, and the process ends.

After the processing of FIG. 7 is completed, the processing returns to the processing of FIG. 2 and proceeds to the next step S6 to check the value of the freeze opening flag XFOP. If XFOP is 1, step S5
(More specifically, since it is determined in step S507 in FIG. 7) that there is a possibility of a temporary open failure due to freezing, the process proceeds to step S7 and redetermination processing 2 is performed.
The details of this processing are shown in FIG.

First, in step S701, a loop process is performed in which the process does not move to the next step unless t4 hours elapse after AI stop. Here, t4> t3, and a sufficient time is set so that the condensed water frozen in the AI system is melted by the high temperature exhaust gas. When t4 hours have passed after the AI stop, the process proceeds to step S702, and the pressure value P and its fluctuation value ΔP are read.

In step S703, it is checked whether the ASV 13 is in the closed state. At this time, since the AI system is stopped, the control state of the ASV 13 by the solenoid valve 17 should be set to the closed state. When it is determined that the ASV 13 is in the open state in step S703, there is a possibility of open sticking failure due to a reason other than freezing, so the process proceeds to step S708 (the details of the subsequent processing will be described later). On the other hand, if the closed state is set according to the control state, the process proceeds to step S704. In step S704, the opening of the ASV 13 is controlled by operating the solenoid valve 17 while the AP 12 is stopped.
In step S705, a loop process that does not shift to the next step is performed until t5 time has elapsed after the opening control. When t5 time has elapsed after the opening control, the process proceeds to step S706 and the pressure value P and the pressure fluctuation value ΔP are read again. Step S7
At 07, it is determined whether the RV 14 is normal or abnormal. When the pressure fluctuation is shown in the pattern 2 of FIG. 4, it is determined that the RV 14 is in the open and fixed state, the process proceeds to step S708,
After the flag XAI indicating the determination result is set to 1 and the flag XFAI indicating the device failure is set to 1, the process proceeds to step S709. If normal, the process directly goes to step S709 to close the ASV 13.

After the processing of FIG. 8 is completed, the processing returns to the processing of FIG. 2 and proceeds to the next step S8. On the other hand, X in step S6
If FOP is 0, the process directly goes to step S8. In step S8, the value of the determination result XAI is checked again. If XAI is 1, it is determined that a component failure has occurred, the subsequent processing is skipped, and the processing ends. When the XAI is 0, it means that the failure of the component is not determined and the XAI is set to 1. Therefore, it is determined that the component is functioning normally, the process proceeds to step S9, and the XAI is determined. At the same time that 1 is set to indicate the end, the flag XNAI is set to 1 indicating that the component is normal, and the process ends.

The processing flow described above is merely an example.
Various changes and modifications are possible. For example, it is possible to simultaneously perform the AI stop determination (step S5) and the redetermination process 2 (step S7).

[0041]

As described above, according to the present invention, when there is a possibility of blockage due to freezing or AP stoppage, AI
By stopping the system not immediately after the determination of blockage but when it continues for a predetermined time, it is possible to suppress secondary damage and make a reliable fault determination. In addition, it is possible to distinguish between a temporary failure and another failure by making a re-determination after warming up. Furthermore, if there is a possibility of open failure, A
By making a determination after closing while continuing the I control, it is possible to reliably determine a temporary failure and another failure.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine including a secondary air supply device that implements a failure diagnosis method for a secondary air supply device according to the present invention.

FIG. 2 is a flowchart of a main process of a failure diagnosis method for a secondary air supply device according to the present invention.

FIG. 3 is a flowchart showing details of an AI start-up failure determination process in FIG.

FIG. 4 is a graph showing a pressure fluctuation pattern.

FIG. 5 is a graph showing changes in current and temperature of a motor driving the AP 12 with respect to the state of the AI system.

FIG. 6 is a flowchart showing details of redetermination processing 1 in FIG.

FIG. 7 is a flowchart showing details of a failure determination process during AI stop in FIG.

FIG. 8 is a flowchart showing details of re-determination processing 2 in FIG.

[Explanation of symbols]

1 ... Secondary air supply device, 2 ... Engine, 10 ... Control device, 11 ... Secondary air supply passageway, 12 ... Air pump, 13
... ASV (air switching valve), 14 ... Reed valve (check valve), 15 ... Pressure sensor, 16 ... Piping, 17 ... Solenoid valve, 20 ... Intake pipe, 21 ... Exhaust pipe, 22 ... Exhaust purification device, 23 ... Engine ECU, 24 ... Throttle, 25 ...
Intake filter, 31, 32 ... O ₂ sensor, 33, 34 ...
Temperature sensor.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3G084 AA03 BA25 DA27 EB22 EC03                       FA02 FA07 FA10 FA20 FA27                       FA30 FA33                 3G091 AA02 AA17 AA28 AB03 BA31                       BA34 CA22 DA08 EA01 EA05                       EA07 EA14 EA16 EA17 EA18                       EA34 FA02 FA04 FA05 FA13

Claims (5)

[Claims] 1. A method for diagnosing a failure in a secondary air supply device for diagnosing a failure in a secondary air supply device that supplies secondary air upstream of an exhaust purification device for an exhaust system of an internal combustion engine under predetermined conditions. If the failure diagnosis result during cold is expected to be abnormal due to freezing of the secondary air supply system, the failure diagnosis method for the secondary air supply system is performed after warming up. 2. The method for diagnosing a failure in a secondary air supply system according to claim 1, wherein re-determination after warm-up is performed only during fuel cut or light load. 3. The secondary air supply is stopped when the failure diagnosis result during cold is expected to be a closing abnormality due to freezing of the secondary air supply system. A method for diagnosing a failure in the secondary air supply system described. 4. When the failure diagnosis result at the time of cold is predicted to be a freezing failure of the air pump, the air pump is stopped more promptly than when another abnormality of the secondary air supply system is detected. Item 3. A method for diagnosing a failure in the secondary air supply system according to item 3. 5. The secondary air supply is continued when the failure diagnosis result during cold is expected to be an opening abnormality due to freezing of the secondary air supply system. The method for diagnosing a failure in the secondary air supply system according to any one of claims.