JP2888023B2 - Failure diagnosis method for secondary air supply device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a secondary air supply device for purifying exhaust gas by supplying secondary air to an exhaust system of an internal combustion engine during a warm-up operation or a deceleration operation of a vehicle or the like. The present invention relates to a failure diagnosis method performed.

[0002]

2. Description of the Related Art Conventionally, for example, in an internal combustion engine for a vehicle, as a method for achieving both emission control and reduction of fuel consumption, a three-way catalyst and an oxygen sensor are used to remove carbon monoxide (CO), hydrocarbons, etc. (HC), nitric oxide (NOx)
At the same time, a method of purifying exhaust gas by this reaction is adopted. At this time, it is necessary to always operate the internal combustion engine near the stoichiometric air-fuel ratio in order to efficiently purify the three components in the exhaust gas simultaneously and efficiently. Therefore,
Generally, closed loop control is performed based on a detection signal from the oxygen sensor so that the exhaust air-fuel ratio A / F approaches the stoichiometric air-fuel ratio.

[0003] In the internal combustion engine, when the engine is in a specific operation state, for example, when the cooling water temperature is low, when the engine is decelerated, or the like, the secondary purification is performed to improve the purification efficiency of the catalyst (improve the warm-up property of the catalyst). The air supply device is operated to supply secondary air to the exhaust system. When the secondary air is supplied in this way, it is general that the air-fuel ratio A / F is open-loop controlled, and the closed-loop control of the air-fuel ratio A / F by the oxygen sensor is restarted at the same time as the secondary air supply is stopped. It is.

In the above-described air-fuel ratio control technique, when a failure occurs in the secondary air supply device, there arises a problem that emission is deteriorated. Therefore, for example, Toyota Technical Publications (issued October 28, 1988), issue number 2801
Discloses a device for performing a failure diagnosis of a secondary air supply device. In this device, the secondary air is supplied temporarily under the condition that the secondary air is not supplied to the exhaust system. At this time, if the secondary air supply device is operating normally, the output signal of the oxygen sensor should change to lean. From this, in the device, if the output signal of the oxygen sensor does not change when the secondary air is supplied, it is determined that the secondary air supply device has failed.

[0005]

However, in the prior art, even when the air-fuel ratio A / F changes transiently and the output signal of the oxygen sensor changes, failure diagnosis is performed in accordance with the change. I will.

For example, the output characteristic of an oxygen sensor is A / F
It rapidly changes around = 14.6. Therefore, the air-fuel ratio A
Even when / F is a very small amount such as “14.5”, it may be determined to be rich based on the output signal of the oxygen sensor.

In general, exhaust gases discharged from a plurality of cylinders are mixed in an exhaust pipe, and the air-fuel ratio A / F of the mixed exhaust gas is detected by one oxygen sensor. Therefore, if the air-fuel ratio A / F varies between cylinders, the output signal of the oxygen sensor may be affected by the exhaust gas of the specific cylinder. Then, even if the air-fuel ratio A / F between the cylinders is lean on average, it may be determined that the air-fuel ratio is rich.

Further, the oxygen sensor tends to easily output a lean signal when its own temperature (element temperature) decreases. For this reason, even if the air-fuel ratio A / F is rich,
Lean may be determined due to a decrease in the element temperature.

Therefore, if the failure diagnosis is performed only by the change of the output signal of the oxygen sensor as in the prior art, the operation of the secondary air supply device may be erroneously diagnosed due to the above various factors.

The present invention has been made in view of the above-mentioned circumstances, and has as its object to accurately diagnose the operation of the secondary air supply device even when the air-fuel ratio changes transiently, and to prevent erroneous diagnosis. Another object of the present invention is to provide a method for diagnosing a failure of the secondary air supply device which can be prevented.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for supplying secondary air to an exhaust system when an operation state of an internal combustion engine is other than a predetermined state. A failure diagnosis method used in a secondary air supply device configured to stop supply of secondary air to a system, wherein secondary air is supplied to an exhaust system for a predetermined time when the operation state of the internal combustion engine is in the predetermined state. Supply, determine the lean time of the exhaust hollow fuel ratio during the secondary air supply, when the ratio of the lean time to the secondary air supply time is less than or equal to a predetermined value,
The secondary air supply has been diagnosed as having failed.

[0012]

The secondary air supply device supplies secondary air to the exhaust system when the operation state of the internal combustion engine is other than a predetermined state, and stops the supply of the secondary air to the exhaust system when the operation state is in the predetermined state. I do.

[0013] The failure diagnosis of the secondary air supply device is performed as follows. First, when the operating state of the internal combustion engine is in the predetermined state, secondary air is supplied to the exhaust system for a predetermined time. Further, the lean time of the exhaust hollow fuel ratio during the supply of the secondary air is determined. When the ratio of the lean time to the secondary air supply time is equal to or less than a predetermined value, it is diagnosed that the secondary air supply device has failed. That is, when the secondary air is supplied for a predetermined time under the condition that the secondary air is not supplied, if the secondary air supply device is operating normally, the idle time is longer than a predetermined ratio to the secondary air supply time. The fuel ratio should be lean. Therefore, the operating state of the secondary air supply device can be determined by looking at the ratio of the lean time to the secondary air supply time.

Therefore, even if the air-fuel ratio changes transiently during the secondary air supply time, the operating state of the secondary air supply device is diagnosed without being affected by the instantaneous change.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will now be described with reference to FIGS.
This will be described with reference to FIG. FIG. 1 is a diagram showing a schematic configuration of a secondary air supply device and a gasoline engine to which the failure diagnosis method of the present embodiment is applied. The vehicle is equipped with a multi-cylinder (in this embodiment, four-cylinder) gasoline engine 1 as an internal combustion engine. The engine 1 has a combustion chamber (not shown) for each cylinder, and an intake passage 2 and an exhaust passage 3 communicate with these combustion chambers.

In the intake passage 2, an air cleaner 4, a throttle valve 5, a surge tank 6, and an intake manifold 7 are arranged in this order from the upstream side to the engine 1, and outside air is taken into the engine 1 through these. It is. The throttle valve 5 is for adjusting the amount of intake air flowing through the intake passage 2, and is opened and closed in conjunction with operation of an accelerator pedal (not shown). The surge tank 6 is for smoothing the pulsation of the intake air.

The intake manifold 7 is provided with fuel injection valves 8A, 8B, 8C and 8D for injecting and supplying fuel to each cylinder. A mixture of the fuel injected from each of the fuel injection valves 8A to 8D and the outside air introduced into the intake passage 2 is introduced into each combustion chamber. In order to ignite the air-fuel mixture introduced into each combustion chamber, the engine 1 is provided with spark plugs 9A, 9B, 9C, 9D.
The ignition plugs 9A to 9D are driven based on the ignition signal distributed by the distributor 11. The distributor 11 synchronizes the high voltage output from the igniter 12 with the crank angle of the engine 1 and ignites the spark plugs 9A to 9D.
Distribute to Then, the air-fuel mixture introduced into the combustion chamber is exploded and burned by the ignition of the spark plugs 9A to 9D, and the driving force of the engine 1 is obtained. The combustion gas generated in the combustion chamber as described above is discharged to the outside through the exhaust passage 3.

The exhaust passage 3 includes an exhaust manifold 13 and a catalytic converter 14 in order from the engine 1 side to the downstream.
Are arranged. The catalytic converter 14 is used to convert hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (N
This is a device for purifying Ox) by the action of a catalyst.

In order to detect the operating state of the engine 1, an air flow meter 15, a fully closed switch 16, a throttle sensor 17, an oxygen sensor 18, a water temperature sensor 19, a rotational speed sensor 20, a cylinder discriminating sensor 21, a vehicle speed sensor 22, etc. Is provided. The air flow meter 15 is provided downstream of the air cleaner 4 and detects the amount of air (intake air amount Q) taken into the engine 1. The throttle sensor 17 is provided near the throttle valve 5 and detects the opening of the throttle valve 5 (throttle opening TA). The fully-closed switch 16 is also provided near the throttle valve 5, and is turned on when the throttle valve 5 is at the fully-closed position to output a fully-closed signal LL.

The oxygen sensor 18 is connected to the exhaust manifold 1.
3 and the catalytic converter 14, the oxygen concentration in the exhaust gas, that is, the air-fuel ratio A / F in the exhaust passage 3.
Is detected. The water temperature sensor 19 is attached to a water outlet housing or the like, and detects the temperature of cooling water of the engine 1 (cooling water temperature THW). The rotation speed sensor 20
The rotation speed (engine speed NE) of the engine 1 is detected from the rotation of a rotor (not shown) built in the distributor 11. The cylinder discrimination sensor 21 similarly detects a change in the crank angle of the engine 1 at a predetermined rate according to the rotation of the rotor of the distributor 11. The vehicle speed sensor 22 is provided on a transmission (not shown) that is drivingly connected to the engine 1 and detects a vehicle speed SPD.

In addition, a secondary air supply device 24 for introducing air into an exhaust system is provided for the purpose of purifying HC and CO among exhaust gas components of the engine 1 by an oxidation reaction. In the present embodiment, as the secondary air supply device 24, an air suction type device (AS) that directly draws air from the intake passage 2 using the pulsation of the exhaust passage 3 is used.

The secondary air supply device 24 includes a communication passage 25, a check valve 26, an ASV (air switching valve) 27, a VS
V (vacuum switching valve) 28 and the like. The communication passage 25 branches from the air cleaner 4 and the air flow meter 15 in the intake passage 2, bypasses the engine 1, and is connected to the exhaust manifold 13 which is upstream of the oxygen sensor 18. This communication passage 2
5, the intake passage 2 and the exhaust passage 3 communicate with each other,
Part of the air in the intake passage 2 passes through the communication passage 25 and is guided to the exhaust manifold 13 as secondary air. Further, the check valve 26 includes a reed valve for preventing a backflow of air from the exhaust passage 3 to the intake passage 2.

The ASV 27 is connected to the case 29 disposed in the middle of the communication passage 25, a diaphragm 31 stretched in the case 29, and the diaphragm 31.
The valve body 32 includes a valve body 32 that opens and closes the communication passage 25 and a spring 33 that urges the valve body 32 in a direction to close the communication passage 25 (downward in FIG. 1). In the case 29, the spring 33
The spring chamber 34, which is a space on the side where is accommodated,
5 is connected to the intake passage 2 downstream of the throttle valve 5. The ASV 27 is configured such that the valve element 32 opens when a negative pressure is introduced into the spring chamber 34. A VSV 28 is interposed in the introduction passage 35 for introducing the negative pressure.

The VSV 28 includes a solenoid 28a, and the opening and closing of the introduction passage 35 is controlled by an electric signal to the solenoid 28a. Specifically, the solenoid 28
a is excited, the introduction passage 35 is opened and the spring chamber 34 is opened.
Is communicated with the intake passage 2. Then, the negative pressure downstream of the throttle valve 5 is guided to the spring chamber 34. As a result, the diaphragm 31 is bent upward against the urging force of the spring 33, the valve body 32 is opened, the intake passage 2 communicates with the exhaust passage 3, and the air in the intake passage 2 is exhausted by the exhaust manifold 13. Led to. Conversely, when the solenoid 28a is demagnetized, the spring chamber 34 is opened to the atmosphere. As a result, the spring 3
The valve body 32 is kept closed by the urging force of No. 3, the communication passage 25 is shut off, and the secondary air is not guided to the exhaust manifold 13.

Each of the fuel injection valves 8A to 8D, the igniter 12 and the VSV 28 is an electronic control unit (hereinafter simply referred to as "EC
U ”) 36. Also EC
U36 has an air flow meter 15, a fully closed switch 16,
Throttle sensor 17, oxygen sensor 18, water temperature sensor 1
9, a rotation speed sensor 20, a cylinder discrimination sensor 21, and a vehicle speed sensor 22 are connected respectively. And ECU3
6 controls the fuel injection valves 8A to 8D, the igniter 12, and the VSV 28 based on output signals from the air flow meter 15, the fully closed switch 16 and the sensors 17 to 22.

Next, the electrical configuration of the ECU 36 will be described with reference to the block diagram of FIG. The ECU 36 has a central processing unit (CPU) 37 and a read-only memory (ROM)
38, a random access memory (RAM) 39, a backup RAM 41, an external input circuit 42, and an external output circuit 43, which are connected to each other by a bus 44. The CPU 37 executes various arithmetic processes according to a preset control program, and the ROM 38 previously stores a control program and initial data necessary for the CPU 37 to execute the arithmetic processes. Also, RAM
39 temporarily stores the calculation result of the CPU 37. The backup RAM 41 is backed up by a battery so as to retain various data even after the power is turned off.

The external input circuit 42 includes the air flow meter 15, the fully-closed switch 16, the throttle sensor 1
7, oxygen sensor 18, water temperature sensor 19, rotation speed sensor 2
0, a cylinder discrimination sensor 21 and a vehicle speed sensor 22 are connected respectively. The external output circuit 43 includes the above-described fuel injection valves 8A to 8D, the igniter 12, and the VSV2.
8 are connected respectively. Then, the CPU 37 reads, as input values, output signals from the air flow meter 15, the fully closed switch 16, and the sensors 17 to 22 via the external input circuit 42. The CPU 37 also controls the fuel injection valves 8A to 8A through the external output circuit 43 based on these input values.
D, drives and controls the igniter 12 and the VSV 28.

That is, the CPU 37 determines, based on detection signals from the throttle sensor 17, the water temperature sensor 19, the vehicle speed sensor 22, and the like, whether or not the engine 1 at that time is in an operation state in which feedback control of the air-fuel ratio A / F is to be performed. to decide. When the operation state is such that the feedback control is to be performed, the CPU 37 determines whether the exhaust air-fuel ratio A / F is
The fuel injection amount from the fuel injection valves 8A to 8D is closed-loop controlled (feedback control) using the feedback correction coefficient FAF so that the air-fuel ratio A / F becomes the stoichiometric air-fuel ratio. The air-fuel ratio A /
The operation state in which the feedback control of F is performed includes, for example, that the cooling water temperature THW of the engine 1 is 40 ° C. or more and the throttle opening TA is 70 ° or less.

The CPU 37 is provided with the throttle sensor 1
7, fully closed switch 16, water temperature sensor 19, vehicle speed sensor 2
Based on the detection signals such as 2 and the like, it is determined whether or not the engine 1 is in a specific operation state in which the secondary air supply device 24 should be operated. Then, when the engine 1 is in the specific operation state, the CPU 37 outputs a drive signal to the VSV 28 via the external output circuit 43 to excite the solenoid 28a. This excitation activates the secondary air supply device 24 to supply secondary air to the exhaust manifold 13. The specific operation state includes, for example, a state where the cooling water temperature THW is “50 ° C. or less” and the throttle opening TA is not fully opened (warm-up state), the fully closed signal LL is “on”, and the vehicle speed SPD is “4 km”. / H or more ”(deceleration state).

Next, the operation and effect of the embodiment constructed as described above will be described with reference to the flowcharts of FIGS. 3 and 4 and the timing chart of FIG. The flowcharts of FIGS. 3 and 4 show a routine for performing a failure diagnosis of the secondary air supply device 24 among the processes executed by the CPU 37. The routine is started by a periodic interruption every predetermined time (0.065 seconds). Is done.

In this routine, a diagnosis end flag XJAS
E is prepared. The diagnosis end flag XJASE is for determining whether or not the diagnosis of the secondary air supply device 24 has been performed before. Then, the diagnosis end flag XJ
ASE is set to “0” in an initial routine executed when the ignition key is turned on, and is set to “1” when the diagnosis is completed.

When the routine proceeds to this routine in a state where the diagnosis of the secondary air supply device has not been performed before (timing t1 in FIG. 5), the CPU 37 sets the diagnosis end flag XJASE to "0" in step 101 in FIG. It is determined whether or not.
Here, the diagnosis end flag XJASE is “0”. For this reason, the CPU 37 determines that the diagnosis of the secondary air supply device 24 has not been performed before and determines the next steps 102 to 1.
Move to 05. The processing of steps 102 to 105 is a processing for determining whether or not the engine 1 is in a state capable of performing a failure diagnosis.

The CPU 37 determines in step 102
The cooling water temperature THW detected by the water temperature sensor 19 is within a predetermined range (80
(THC <THW <100 ° C.), that is, whether the engine 1 is in a state after warm-up or not.
It is determined whether or not is output. CPU 37
In step 104, the engine speed NE detected by the speed sensor 20 is set to a predetermined value (for example, 1000 rpm).
It is determined whether it is less than
The vehicle speed SPD by the vehicle speed sensor 22 is a predetermined value (for example, 2 k
m / H).

If at least one of the determination conditions in steps 102 to 105 is not satisfied, the CPU 37 proceeds to step 121 in FIG. 4 and clears the diagnosis execution counter CJAS to "0". The diagnostic execution counter CJAS is used to determine the operation timing of the secondary air supply device 24 during the diagnostic period,
This is for taking the operation timing of the feedback correction coefficient FAF, and measures the time from the start of diagnosis to the end of diagnosis.

The CPU 37 determines in step 122 that VSV2
8 to output a signal for demagnetizing the solenoid 28a,
This routine ends. Then, the spring chamber 34 is opened to the atmosphere, and the valve body 32 of the ASV 27 is kept closed.
The communication passage 25 is shut off. Therefore, at this time, the secondary air is not guided to the exhaust manifold 13. Then, feedback control of the air-fuel ratio A / F using the feedback correction coefficient FAF is performed.

Steps 102 to 105 in FIG.
Are satisfied (at timing t in FIG. 5).
2), the CPU 37 determines that the engine 1 is in a state capable of performing a failure diagnosis, and proceeds to step 106.

In step 106, the CPU 37 increments the value of the diagnosis execution counter CJAS by "1". In this case, the value is changed from “0” to “1”. At this time, the time required for the diagnosis execution counter CJAS to change from “0” to “1” is 0.065 seconds. Then, in step 107, the CPU 37 determines whether or not the value of the diagnosis execution counter CJAS is “2” or more. That is, it is determined whether or not 0.13 seconds have elapsed since the start of the count operation by the diagnosis execution counter CJAS. At timing t2, CJAS = 1, and the determination condition of step 107 is not satisfied. Therefore, the CPU 37 does not perform the subsequent processing and ends this routine.

As described above, the diagnosis execution counter CJ
The routine is terminated when the value of AS is less than "2" for the following reason. That is, the engine 1
0.0
If the time is less than 65 seconds, it is unknown whether the value of the diagnosis execution counter CJAS is “0” or “1”, and the reliability is low. Therefore, when the value of the diagnosis execution counter CJAS is surely equal to or more than "1", that is, in this case, when the diagnosis execution counter CJAS performs a count operation twice or more,
The processing shifts to the next processing (step 108).

When the determination condition of step 107 is satisfied (timing t3 in FIG. 5), the CPU 37 outputs a signal for exciting the solenoid 28a of the VSV 28 in step 108. Then, the introduction passage 35 is opened, and the spring chamber 34 communicates with the intake passage 2. Then, the negative pressure downstream of the throttle valve 5 is guided to the spring chamber 34. As a result, the valve body 32 of the ASV 28 is opened and the intake passage 2
And the exhaust passage 3 communicate with each other, and the air in the intake passage 2 is guided to the exhaust manifold 13 as secondary air.

Subsequently, the CPU 37 proceeds to step 10 in FIG.
9, the value of the diagnosis execution counter CJAS is set to "1".
5 ”or more. That is, it is determined whether about one second has elapsed since the supply of the secondary air was started. At timing t3, the diagnosis execution counter CJAS
Is “2”, and the determination condition of step 109 is not satisfied, so the CPU 37 proceeds to step 110.

In step 110, the CPU 37 stops the feedback control of the air-fuel ratio A / F using the feedback correction coefficient FAF, and sets the average feedback correction coefficient FAFAV to a new feedback correction coefficient FAF.
Set as F. Then, the CPU 37 proceeds to step 11
At 1, the lean time counter CJASL is reset to "0", and this routine ends. Here, the lean time counter CJASL is for measuring the time (integrated time) when the air-fuel ratio A / F becomes lean during the failure diagnosis of the secondary air supply device 24.

When the above processing is repeatedly executed, the diagnosis execution counter CJ is executed by the processing of step 106.
The value of AS increases by “1”. Then, when the condition of step 109 (CJAS ≧ 15) is satisfied (timing t4 in FIG. 5), the CPU 37 proceeds to step 112, where the average value FAFA of the feedback correction coefficient is set.
A predetermined value (for example, 3%) is added to V, and the added value is set as a new feedback correction coefficient FAF. The process of step 112 is a process for forcibly making the air-fuel ratio A / F rich.

Next, in step 113, the CPU 37 determines whether or not the value of the diagnosis execution counter CJAS is "30" or more. That is, it is determined whether about two seconds have elapsed since the supply of the secondary air was started. At the timing t4, the value of the diagnosis execution counter CJAS becomes “1”.
5 ", which does not satisfy the determination condition of step 113. Therefore, the CPU 37 performs the processing of step 111 and subsequent steps. That is, the lean time counter CJASL
Is held at "0", and this routine ends.

The above processing is repeatedly executed, and step 1
When the condition 13 (CJAS ≧ 30) is satisfied (timing t5 in FIG. 5), the CPU 37 proceeds to step 114, and determines whether the air-fuel ratio A / F of the exhaust gas is lean. More specifically, the CPU 37 compares the output voltage of the oxygen sensor 18 with the reference voltage, and determines that the output voltage of the oxygen sensor 18 is rich if the output voltage is higher than the reference voltage, and determines that the output is lean if the output voltage is lower than the reference voltage. I do. Here, if the air-fuel ratio A / F is lean as indicated by the timing t5, the CPU 37 increments the value of the lean time counter CJASL by "1" in step 115. In this case, "0" is changed to "1". At this time, the time required for the lean time counter CJASL to change from "0" to "1" is 0.065 seconds.

Then, in step 116, the CPU 37 determines whether or not the value of the diagnosis execution counter CJAS is equal to or greater than "77". That is, the diagnostic execution counter C
It is determined whether about 5 seconds have elapsed since the start of the count operation by JAS. Here, 5 seconds is the time when the diagnosis is completed. At timing t5, CJAS = 30, and the determination condition of step 116 is not satisfied.
The PU 37 ends this routine without performing the subsequent processing.

While the air-fuel ratio A / F of the exhaust gas is lean, the process of step 115 is repeated, and the value of the lean time counter CJASL increases by "1". And the air-fuel ratio A
When / F becomes rich (timing t6 in FIG. 5), CP
U37 determines that the determination condition of the step 114 is not satisfied, and performs the processing of the step 116 and the subsequent steps without performing the processing of the step 115 and holding the value of the previous processing.

When the air-fuel ratio A / F becomes lean again (FIG. 5).
(Timing t7), the CPU 37 performs the process of step 115, and restarts the counting operation of the lean time counter CJASL. That is, the value of the lean time counter CJASL at the timing t6 is incremented by "1". Then, when the air-fuel ratio A / F changes from lean to rich (timing t8 in FIG. 5), the CPU 37 does not perform the processing of step 115, and performs the processing of step 116 and thereafter while holding the value of the previous processing. Further, when the air-fuel ratio A / F becomes lean again (at the timing t in FIG. 5).
9), the CPU 37 performs the process of step 115, and restarts the counting operation of the lean time counter CJASL.

As described above, the processing in steps 114 and 115 is performed according to the determination condition in step 116 (CJAS ≧ 77).
Is continued until is satisfied. Then, step 115
By this processing, the integrated value of the lean time is measured.

When the determination condition of step 116 is satisfied (timing t10 in FIG. 5), the CPU 37 diagnoses the operation state of the secondary air supply device 24 based on the value of the lean time counter CJASL. Therefore, CPU3
7 first determines in step 117 whether the value of the lean time counter CJASL is greater than "37". Here, CJASL = 37 corresponds to “2.4 seconds”.

The CPU 37 has a lean time counter CJAS.
If the value of L is larger than "37", it is determined in step 118 that the secondary air supply device 24 is operating normally. Conversely, if the value of the lean time counter CJASL is equal to or less than “37”, the CPU 37 proceeds to step 11.
In 9, it is determined that the operation of the secondary air supply device 24 is abnormal.

The criterion for determination in step 117 is "37" (2.4 seconds) for the following reason.
That is, when the secondary air is supplied for a predetermined time, if the secondary air supply device 24 is operating normally, even if the air-fuel ratio A / F becomes rich transiently during the supply of the secondary air, Its rich time is short. Then, the air-fuel ratio A / F should be lean for a time longer than a predetermined ratio (for example, 0.8) to the secondary air supply time. Therefore, in this embodiment, after the operation of the secondary air supply device 24 starts,
During a period from about 2 seconds to about 5 seconds (about 3 seconds), it is determined whether or not the lean time of the air-fuel ratio A / F (lean time) is longer than 2.4 seconds. The operation state of the secondary air supply device 24 is determined based on the determination result.

Then, the CPU 37 proceeds to step 11
In step 120 after the transition from steps 8 and 119, the diagnosis end flag XJASE is set to "1", and the processing from step 121 onward is performed. That is, step 12
In step 1, the diagnostic execution counter CJAS is cleared to "0".
Further, the CPU 37 outputs a signal for demagnetizing the solenoid 28a of the VSV 28 in step 122, and ends this routine. Then, the communication passage 25 is blocked by the valve body 32 of the ASV 27, and the secondary air is exhausted from the exhaust manifold 1
Not lead to 3.

Note that after timing t10,
The diagnosis end flag XJASE becomes “1”, and the step 1
The judgment condition of 01 is not satisfied. Therefore, the CPU 37
Ends this routine without performing the processing of step 102 and thereafter. That is, after the engine is started, the above-described diagnosis of the secondary air supply device 24 is performed only once.

As described above, in this embodiment, when the secondary air is not supplied, the secondary air is supplied to the exhaust manifold 13 of the engine 1 for a predetermined time (step 10).
8), the lean time of the exhaust hollow fuel ratio during the supply of the secondary air is obtained by a lean time counter CJASL (steps 114 and 115), and the ratio of the lean time to the secondary air supply time is a predetermined value (in this case, 0.8) or less, the secondary air supply device is diagnosed as having failed (steps 117 and 119).

For this reason, the air-fuel ratio A / F is in a very rich state such as "14.5", or the air-fuel ratio A
/ F varies or the element temperature of the oxygen sensor 18 decreases, the air-fuel ratio A / F changes transiently and the output signal of the oxygen sensor 18 also changes. The operating state of the secondary air supply device 24 can be accurately diagnosed without being affected by the above.

Therefore, unlike the prior art in which the failure diagnosis is performed only based on the change in the output signal of the oxygen sensor, the erroneous diagnosis of the secondary air supply device 24 due to the transient change in the air-fuel ratio A / F is performed in this embodiment. It can be prevented beforehand.

It should be noted that the present invention is not limited to the configuration of the above embodiment, and may be arbitrarily changed without departing from the spirit of the present invention, for example, as follows. (1) In the above embodiment, a warning light may be provided on an instrument panel or the like in the driver's seat, and the warning light may be turned on when it is determined that the secondary air supply device 24 is abnormal.

(2) In the above embodiment, the present invention is embodied in the four-cylinder engine 1. However, the present invention may be embodied in an engine having a different number of cylinders.

[0059]

As described above in detail, according to the present invention, secondary air is supplied to the exhaust system of the internal combustion engine for a predetermined time in a predetermined state in which the secondary air is not supplied. The lean time of the exhaust hollow fuel ratio is obtained, and when the ratio of the lean time to the secondary air supply time is equal to or less than a predetermined value, the secondary air supply device is diagnosed as having failed. Even when the fuel ratio changes, an excellent effect that the operation of the secondary air supply device is accurately diagnosed and erroneous diagnosis can be prevented beforehand is achieved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a secondary air supply device and an engine to which a failure diagnosis method according to an embodiment of the present invention is applied.

FIG. 2 is a block diagram illustrating an electrical configuration of an ECU according to one embodiment.

FIG. 3 is a flowchart illustrating a failure diagnosis routine executed by a CPU in one embodiment.

FIG. 4 is a flowchart illustrating a failure diagnosis routine executed by a CPU in one embodiment.

FIG. 5 is a timing chart illustrating a correspondence relationship among an operation state of a secondary air supply device, a feedback correction coefficient, an oxygen sensor signal, a diagnosis end flag, a diagnosis execution counter, and a lean time counter in one embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine as an internal combustion engine, 3 ... Exhaust passage which comprises an exhaust system, 24 ... Secondary air supply device, A / F ... Air-fuel ratio,
CJAS: diagnostic execution counter, CJASL: lean time counter

Claims (1)

(57) [Claims] A secondary air supply system supplies secondary air to an exhaust system when an operation state of the internal combustion engine is other than a predetermined state, and stops the supply of secondary air to the exhaust system when the internal combustion engine is in the predetermined state. A failure diagnosis method used in a secondary air supply device, comprising: supplying secondary air to an exhaust system for a predetermined time when the operating state of the internal combustion engine is in the predetermined state, and leaning the exhaust hollow fuel ratio during the secondary air supply. Determining a time, and when the ratio of the lean time to the secondary air supply time is equal to or less than a predetermined value, diagnoses that the secondary air supply device has failed. .