JPH05321652A - Diagnosis method of secondary air supplying device - Google Patents

Abstract

PURPOSE:To realize accurate diagnosis of the operation of a secondary air supplying device even when the output signal of an air fuel ratio sensor becomes temporarily lean, and preliminarily prevent erroneous diagnosis. CONSTITUTION:The air fuel ratio of the mixture to an engine 1 is detected by an oxygen sensor 18. When the operational condition of the engine 1 is the preset one, the fuel injection from fuel injection valves 8A-8D is adjusted so that the air fuel ratio may be the theoretical value. When the operational condition is not the preset one, a secondary air supplying device 23 is activated and the secondary air is supplied to an exhaust passage 3. The return time by the oxygen sensor 18 during the secondary air supply is measured by the count action of the timer, and when the return time exceeds the specified value, a judgement is made that the secondary air supplying device 23 is normal. In such diagnostic operation, when the air fuel ratio by the oxygen sensor 18 becomes rich, the count action is stopped and the current timer value is maintained, and the count action is continued after elapse of the specified period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diagnostic method applied to a secondary air supply device for supplying secondary air to an exhaust system of an internal combustion engine such as a vehicle to purify exhaust gas. ..

[0002]

2. Description of the Related Art Conventionally, for example, in an internal combustion engine for a vehicle, carbon monoxide (CO) and carbonization in exhaust gas have been used as a method for satisfying both exhaust gas regulation and fuel consumption reduction by using a three-way catalyst and an air-fuel ratio sensor. Hydrogen (HC), Nitric oxide (NO
x) is simultaneously subjected to a redox reaction, and exhaust gas is purified by this reaction. At this time, in order to efficiently purify the three components in the exhaust gas at the same time, it is necessary to always operate the internal combustion engine near the stoichiometric air-fuel ratio (14.5). Therefore, generally, the air-fuel ratio A / F of the air-fuel mixture introduced into the combustion chamber of the internal combustion engine is detected by an air-fuel ratio sensor provided in the exhaust passage, and the air-fuel ratio A / F becomes the theoretical air-fuel ratio. The closed-loop control (feedback control) of the fuel injection amount from the fuel injection valve is performed so as to approach.

On the other hand, in the internal combustion engine, when the engine is in a specific operating state, for example, when the temperature of the cooling water is low and when the engine is decelerating, the purification efficiency of the catalyst is improved (the catalyst warming up is improved). The secondary air supply device is operated to supply the secondary air to the exhaust passage upstream of the air-fuel ratio sensor. When the secondary air is supplied in this way, the fuel injection amount is open-loop controlled, and at the same time when the secondary air supply is stopped, the closed-loop control of the fuel injection amount by the air-fuel ratio sensor is restarted.

Here, when the secondary air supply device is stopped, the air-fuel ratio of the air-fuel mixture introduced into the combustion chamber of the internal combustion engine matches the air-fuel ratio after combustion. However, during the operation of the secondary air supply device, the air-fuel ratios of the both air have different values due to the secondary air. Therefore, in this specification, the air-fuel ratio when the secondary air supply device is stopped is simply represented by the air-fuel ratio A / F. Further, when the secondary air supply device is operating, the air-fuel ratio of the air-fuel mixture introduced into the combustion chamber is represented by the base air-fuel ratio (A / F) a, and the air-fuel ratio of the exhaust gas after the secondary air supply is exhausted. The air-fuel ratio (A / F) b will be used.

By the way, in the above-mentioned control technique, when some trouble occurs in the secondary air supply device, there arises a problem that the emission is deteriorated. Therefore, for example, JP-A-63-1
Japanese Patent No. 11256 discloses a technique for diagnosing a failure of the secondary air supply device. In this technique, in a specific operation state in which secondary air is supplied, if the output of the air-fuel ratio sensor becomes rich and remains rich for a predetermined time, it is determined that the secondary air supply device has an abnormality.

[0006]

However, in the above-mentioned prior art, even when the air-fuel ratio changes transiently during the supply of the secondary air and the output signal of the air-fuel ratio sensor also changes, the failure diagnosis according to the change. Will go. That is, even if the secondary air is supplied during cold time immediately after the internal combustion engine is started, if the base air-fuel ratio (A / F) a is rich, the exhaust air-fuel ratio (A / F)
F) There are areas where b does not become lean. In this region, if a diagnosis is made only by a change in the output signal of the air-fuel ratio sensor, there is a possibility that the secondary air supply device may be erroneously determined to be a failure even if the secondary air supply device is operating normally.

The case where the base air-fuel ratio (A / F) a is rich means that the low temperature increase is large, the exhaust gas amount is large relative to the secondary air supply amount, immediately after the asynchronous injection is performed,
Immediately after starting deceleration. In these cases, the base air-fuel ratio (A / F) a becomes temporarily rich, so even if a normal amount of secondary air is supplied, the air-fuel ratio sensor will not reach the lean state. Absent.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to supply the secondary air even when the output signal of the air-fuel ratio sensor becomes transiently rich during the supply of the secondary air. An object of the present invention is to provide a method for diagnosing a secondary air supply device, which can accurately diagnose the operation of the device and prevent erroneous diagnosis.

[0009]

In order to achieve the above object, the present invention detects the air-fuel ratio of an air-fuel mixture to an internal combustion engine by an air-fuel ratio sensor provided in an exhaust passage to determine the operating state of the internal combustion engine. Is a predetermined predetermined state, the fuel injection amount from the fuel injection valve is adjusted so that the air-fuel ratio becomes the stoichiometric air-fuel ratio, and when the operating state of the internal combustion engine is other than the predetermined state, the secondary air The supply device is operated to supply the secondary air to the exhaust passage upstream of the air-fuel ratio sensor, and the lean time by the air-fuel ratio sensor during the supply of the secondary air is measured by a timer counting operation. A method for diagnosing a secondary air supply device, wherein the secondary air supply device is determined to be normal when the time exceeds a predetermined time, the air-fuel ratio sensor during the secondary air supply. When the air-fuel ratio due has become rich,
The counting operation of the timer is interrupted, the timer value at that time is held, and the counting operation of the timer is continued after a lapse of a predetermined time.

[0010]

The air-fuel ratio of the air-fuel mixture introduced into the internal combustion engine is detected by the air-fuel ratio sensor provided in the exhaust passage. Then, when the operating state of the internal combustion engine is a predetermined state, the fuel injection amount from the fuel injection valve is adjusted so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Further, when the operating state of the internal combustion engine is other than the predetermined state, the secondary air supply device is operated and the secondary air is supplied to the exhaust passage upstream of the air-fuel ratio sensor.

In diagnosing the secondary air supply device,
The lean time by the air-fuel ratio sensor during the supply of the secondary air is measured by the counting operation of the timer. And
When the lean time exceeds the predetermined time, it is determined that the secondary air supply device is normal. On the contrary, when the lean time is less than the predetermined time, it is determined that the secondary air supply device may be out of order.

That is, if the secondary air supply device is operating normally under the condition that the secondary air supply device is to be operated, the residual oxygen concentration in the exhaust gas becomes high, so the air-fuel ratio (exhaust air The fuel ratio becomes lean and the output of the air-fuel ratio sensor becomes lean. On the contrary, if some trouble occurs in the secondary air supply device and an appropriate amount of secondary air is not supplied under the condition that the secondary air should be supplied, the residual oxygen concentration in the exhaust gas becomes thin and the air-fuel ratio (( The exhaust air-fuel ratio) becomes rich, and the output of the air-fuel ratio sensor becomes rich. Therefore, by measuring the lean time during the supply of the secondary air as described above, the operating state of the secondary air supply device can be determined.

By the way, even if the secondary air supply device is operating normally, the air-fuel ratio (base air-fuel ratio) of the air-fuel mixture introduced into the combustion chamber of the internal combustion engine during the secondary air supply is temporarily theoretical. It may become richer than the air-fuel ratio. This is because when the internal combustion engine is cold, a large amount of low temperature increase is performed, the amount of exhaust gas is large relative to the amount of secondary air supply, asynchronous injection is performed, or deceleration is performed. It occurs when the operating condition changes. At this time, even if the secondary air is supplied, the air-fuel ratio of the exhaust gas (exhaust air-fuel ratio) does not become lean, and the output of the air-fuel ratio sensor may become rich. In this case, there is a possibility that an operation for failure determination may be performed even if the secondary air supply device is operating normally.

However, in the present invention, when the air-fuel ratio (exhaust air-fuel ratio) by the air-fuel ratio sensor during secondary air supply becomes rich, the counting operation of the timer is interrupted and the timer value at that time is held. .. Then, after a lapse of a predetermined time, the counting operation of the timer is continued. Therefore, even if the air-fuel ratio becomes transiently rich when the secondary air is supplied, accurate lean time measurement can be performed without being affected by the rich air-fuel ratio.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a secondary air supply device and a gasoline engine to which the diagnosis method of this embodiment is applied. The vehicle is equipped with a multi-cylinder (four cylinders in this embodiment) 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 via these. Be done. The throttle valve 5 is for adjusting the amount of intake air flowing through the intake passage 2, and is opened / closed in conjunction with the 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. Then, the air-fuel mixture including 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. The engine 1 is equipped with spark plugs 9A, 9B, 9C and 9D for igniting the air-fuel mixture introduced into each combustion chamber.
The spark 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 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 thus generated in the combustion chamber is discharged to the outside through the exhaust passage 3.

In the exhaust passage 3, an exhaust manifold 13 and a catalytic converter 14 are arranged in this order from the engine 1 side toward the downstream.
Are arranged. The catalytic converter 14 includes hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (N) in the exhaust gas.
It 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 as an air-fuel ratio sensor,
Water temperature sensor 19, rotation speed sensor 20, cylinder discrimination sensor 2
1, a vehicle speed sensor 22 and the like are provided. The air flow meter 15 is provided downstream of the air cleaner 4 and detects the amount of air taken into the engine 1 (intake air amount Q). 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 in the vicinity of the throttle valve 5, and is turned on when the throttle valve 5 is at the fully closed position to output the fully closed signal LL.

Further, the oxygen sensor 18 is the exhaust manifold 1
3 and the catalytic converter 14, and the residual oxygen concentration in the exhaust gas, that is, the air-fuel ratio A in the exhaust passage 3.
/ F is detected. The oxygen sensor 18 has a theoretical air-fuel ratio (1
4.5) It has a characteristic that the output voltage suddenly changes in the vicinity.
Zirconia or titania is used as the material of the element of the oxygen sensor 18, and a heater is provided to keep the temperature of these elements stable.

The water temperature sensor 19 is attached to a water outlet housing or the like and detects the temperature of the cooling water of the engine 1 (cooling water temperature THW). The rotation speed sensor 20 is
The rotation speed of the engine 1 (engine speed NE) is detected from the rotation of a rotor (not shown) built in the distributor 11. The cylinder discrimination sensor 21 also 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 in a transmission (not shown) drivingly connected to the engine 1 and detects the vehicle speed SPD.

In addition, the engine 1 is provided with a secondary air supply device 23 for introducing air into the exhaust system. The secondary air supply device 23 includes a communication passage 24 and an electric air pump 25. The communication passage 24 branches from between 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 upstream of the oxygen sensor 18.

An electric air pump 25 is interposed in the communication passage 24. The electric air pump 25 is an air pump of a type driven by an electric motor, and a fixed amount of air discharged from the electric air pump 25 serves as secondary air to the communication passage 2
It is led to the exhaust manifold 13 via 4. The electric air pump 25 improves the purification efficiency of the catalyst (improves the warm-up property of the catalyst) when the engine 1 is in a specific operation state, for example, when the cooling water temperature THW is low or when the engine 1 is decelerating. belongs to.

The fuel injection valves 8A to 8D, the igniter 12 and the electric air pump 25 are electrically connected to an electronic control unit (hereinafter simply referred to as "ECU") 26.
Further, an air flow meter 15, a fully closed switch 16, a throttle sensor 17, an oxygen sensor 18, a water temperature sensor 19, a rotation speed sensor 20, a cylinder discrimination sensor 21, and a vehicle speed sensor 22 are connected to the ECU 26, respectively. And
The ECU 26 controls the fuel injection valves 8A to 8D, the igniter 12 and the electric air pump 25 based on the 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 26 will be described with reference to the block diagram of FIG. The ECU 26 includes a central processing unit (CPU) 27 and a read-only memory (ROM)
28, a random access memory (RAM) 29, a backup RAM 31, an external input circuit 32, and an external output circuit 33, which are connected to each other by a bus 34. The CPU 27 executes various kinds of arithmetic processing according to a preset control program, and the ROM 28 stores in advance a control program and initial data necessary for the CPU 27 to execute arithmetic processing. Also RAM
29 temporarily stores the calculation result of the CPU 27. The backup RAM 31 is backed up by a battery so as to retain various data even after the power is turned off.

The external input circuit 32 includes an air flow meter 15, a fully closed switch 16 and a throttle sensor 1 described above.
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 to each other. Further, the above-described fuel injection valves 8A to 8D, the igniter 12, and the electric air pump 25 are connected to the external output circuit 33, respectively. And CPU
27 is an air flow meter 15 via an external input circuit 32,
The output signals from the fully closed switch 16 and the sensors 17 to 22 are read as input values. Further, the CPU 27 drives and controls the fuel injection valves 8A to 8D, the igniter 12 and the electric air pump 25 via the external output circuit 33 based on these input values.

More specifically, the CPU 27 determines whether or not the engine 1 at that time is in an operating state in which feedback control of the air-fuel ratio A / F should be performed based on detection signals from the throttle sensor 17, the water temperature sensor 19, the vehicle speed sensor 22, and the like. To judge. Then, when the feedback control is being performed, the CPU 27 detects the air-fuel ratio A / F of the air-fuel mixture from the output signal of the oxygen sensor 18, and the air-fuel ratio A / F is detected.
The fuel injection amount from the fuel injection valves 8A to 8D is adjusted so that becomes the stoichiometric air-fuel ratio. In order to adjust the fuel injection amount, the CPU 27 causes the fuel injection valves 8A to 8D based on the following equation.
The target fuel injection time TAU of is calculated.

TAU = K × (Q / NE) × FAF where K is a constant, Q is the intake air amount, NE is the engine speed, and K · (Q / NE) is the theoretical air-fuel ratio. It is the set basic fuel injection time. Further, FAF is a feedback correction coefficient that changes with a change in the output signal of the oxygen sensor 18, and the basic fuel injection time K · (Q / NE) so that the air-fuel ratio A / F becomes the stoichiometric air-fuel ratio.
To correct.

The CPU 27 calculates the feedback correction coefficient FAF as follows. The CPU 27 is shown in FIG.
As shown by, the output voltage V from the oxygen sensor 18 is compared with the reference voltage Vr corresponding to the stoichiometric air-fuel ratio, and the output voltage V
Is higher than the reference voltage Vr, it is determined to be rich, and if lower than the reference voltage Vr, it is determined to be lean. In the case of rich, the CPU 27 compares it with the previous detection result and determines whether or not the lean is reversed to the rich. When reversing from lean to rich, the CPU 27 sets FAF-RS (RS is a skip amount) as a new feedback correction coefficient FAF, and when there is no reversal from lean to rich, FAF-KI.
(KI is an integration amount, RS >> KI) is set as a new feedback correction coefficient FAF.

Further, when the air-fuel ratio A / F based on the signal from the oxygen sensor 18 is lean, the CPU 27 compares it with the previous detection result and judges whether the air-fuel ratio is changed from rich to lean. When the CPU 27 reverses from rich to lean,
FAF + RS is used as a new feedback correction coefficient FAF, and if there is no inversion from rich to lean, FAF
Let + KI be a new feedback correction coefficient FAF.

Therefore, when there is a reversal between rich and lean, the CPU 27 changes (skips) the feedback correction coefficient FAF stepwise to increase or decrease the fuel injection amount, and when rich or lean, the feedback correction coefficient FAF. Gradually increase or decrease.

When the air-fuel ratio A / F is controlled to the stoichiometric air-fuel ratio, the feedback correction coefficient FAF is "1.
It fluctuates around 0 ". In addition, the CPU 27 calculates the average value FAFAV of the feedback correction coefficient. Therefore, for example, the air-fuel ratio A / F is reversed between rich and lean, and the feedback correction coefficient F is increased by the skip amount RS.
Each time the AF changes, the feedback correction coefficient FAF immediately before the skip and the feedback correction coefficient FAF immediately before the previous skip are averaged, and this is calculated as FAFAV.
I am trying. In addition, the feedback correction coefficient FAF immediately before the last several skips may be averaged and used as FAFAV.

When the CPU 27 calculates the target fuel injection time TAU based on the above equation, the target fuel injection time TA is supplied to the fuel injection valves 8A to 8D via the external output circuit 33.
A drive signal corresponding to U is output. The output of this signal controls the valve opening time of the fuel injection valves 8A to 8D to inject a predetermined amount of fuel. In this way, feedback control is performed so that the air-fuel ratio A / F becomes the stoichiometric air-fuel ratio.

Next, the operation and effect of this embodiment configured as described above will be described. The flow chart in Figure 4 is CP
It shows a routine for diagnosing the secondary air supply device 23 among the processes executed by U27, which is activated by a regular interruption every predetermined time (0.065 seconds in this embodiment).

In this routine, the diagnosis end flag XJAI is set.
E is prepared. The diagnosis end flag XJAIE is for determining whether or not the diagnosis of the secondary air supply device 24 has been performed previously. Then, the diagnosis end flag XJ
The AIE is set to "0" in an initial routine that is executed when the ignition key is turned on, and is set to "1" when the diagnosis is completed.

When the engine is started by turning on the ignition key, the cooling water temperature THW is, for example, 10 ° C to 3 ° C.
If it is within the range of 5 ° C, the CPU2
7 outputs a drive signal for starting the electric air pump 25 in another routine. The electric air pump 25 is activated by this signal. At this time, the diagnosis end flag XJAIE is set to "0" in the initial routine as described above. In the present embodiment, the state of the engine 1 when the cooling water temperature THW is within the above range (10 ° C. to 35 ° C.) is “cold”, and the engine 1 when the cooling water temperature THW exceeds the above range. The state is "warm".

When the routine shifts to this routine in such a state, the CPU 27 determines in step 100 of FIG. 4 whether the diagnosis end flag XJAIE is "0". Here, since the diagnosis end flag XJAIE is "0", CP
U27 makes a negative decision in step 100, and the next step 2
At 00, it is determined whether or not the electric air pump 25 is operating in the cold state. During the period when the cooling water temperature THW is within the range (10 ° C. to 35 ° C.) described above, the electric air pump 25
Is operating, the CPU 27 makes an affirmative decision in step 200, and proceeds to the cold diagnosis routine of step 300. For details of this cold diagnosis routine, see FIGS.
The flowchart will be described. In this cold diagnosis routine, the CPU 27 determines whether or not the secondary air supply device 23 is operating normally, and when it is operating normally, sets the diagnosis end flag XJAIE to "1".
After executing the processing of step 300, the CPU 27 ends this routine.

In step 300, the diagnosis end flag XJAI
When E is set to "1", the CPU 27 makes a negative determination in step 100 in the next processing routine. Then, this routine is ended without performing the processing of steps 200 and 300.

If the cooling water temperature THW rises without being judged to be normal in the cold diagnosis routine of step 300 and exceeds the range (10 ° C. to 35 ° C.), the electric air pump in the cold state is executed in another routine. The operation of 25 is stopped. Therefore, the CPU 27 makes a negative determination in step 200 and proceeds to the warm diagnosis routine of step 400. For details of this warm diagnosis routine, see FIG.
This will be described with reference to the flowchart of No. 0. In this warm diagnosis routine, the CPU 27 determines whether the secondary air supply device 23 is operating normally or is out of order.
Then, the CPU 27 sets the diagnosis end flag XJAIE to "1" and ends this routine.

As described above, in this embodiment, first, the normal operation of the secondary air supply device 23 is determined in the cold diagnosis routine. If the cold diagnostic routine does not determine normal,
In the warm diagnostic routine, it is determined whether the secondary air supply device 23 is normal or faulty.

Next, the cold failure routine will be described with reference to FIGS.
It will be described according to the flowchart of Step 2 of FIG.
When the routine shifts from 00 to this routine, the CPU 27 determines in step 301 of FIG. 5 whether or not the precondition for performing the cold diagnosis is satisfied. This precondition is, for example, that the abnormality is not diagnosed in a failure diagnosis routine other than the cold failure routine. The failure diagnosis routine here is a routine for diagnosing failures such as misfire, fuel supply system, oxygen sensor 18, water temperature sensor 19, and the like.

Further, in step 302, the CPU 27 determines whether or not a predetermined time (for example, 2.5 seconds) has elapsed since the electric air pump 25 was started. further,
The CPU 27 determines in step 303 whether or not a predetermined time (for example, 30 seconds) has passed since the heater of the oxygen sensor 18 was energized.

If any one of the judgment conditions of the steps 301 to 303 is not satisfied, the CPU 27 causes the step 304 to proceed.
, And lean time counter CJAI as a timer
The value of L is set to "0", and this routine ends. Here, the lean time counter CJAIL is for measuring the time (accumulation time) when the exhaust air-fuel ratio (A / F) b becomes lean during the diagnosis of the secondary air supply device 23. The lower limit value of the lean time counter CJAIL is set to -8.3 seconds, and the upper limit value is set to 8.3 seconds.

Steps 301 to 303 in FIG.
If all of the determination conditions are satisfied, the CPU 27 determines that the engine 1 is in a state in which it is possible to perform a cold diagnosis, and performs the determination processing of steps 305 to 308. These determination processes are processes for determining whether or not the operating state of the engine 1 is changed during the supply of the secondary air and the exhaust air-fuel ratio (A / F) b is temporarily rich.

First, in step 305, the CPU 2
Reference numeral 7 determines whether or not 2 seconds have elapsed after the fully closed signal LL was switched by the fully closed switch 16. Switching of the fully closed signal LL may be performed by switching the fully closed signal LL from on to off or from off to on. The reason for making such a determination is as follows.

For example, when the fully closed signal LL is switched from ON to OFF, asynchronous injection is performed and the base air-fuel ratio (A / F)
a becomes transiently rich. Further, when the fully closed signal LL is changed from OFF to ON immediately after deceleration or the like, the throttle valve 5 is closed and the intake passage 2 becomes negative pressure. Then, the fuel that has been attached to the inner wall surface of the intake passage 2 up to now evaporates at once due to the negative pressure and enters the combustion chamber. Therefore, the base air-fuel ratio (A / F) a becomes considerably rich. Therefore, even if the fully closed signal LL is turned from ON to OFF or from OFF to ON, the exhaust air-fuel ratio (A /
F) b becomes rich. Therefore, the exhaust air-fuel ratio (A / F) b is determined to be rich by switching the fully closed signal LL.

Next, in step 306, the CPU 27 determines whether or not a predetermined time (for example, 3 seconds) has elapsed since the sudden acceleration / deceleration was performed. The rapid acceleration / deceleration is determined by the engine speed in the current routine by the rotation speed sensor 20,
This is performed by obtaining the absolute value of the deviation from the engine speed in the previous routine and comparing that value with a predetermined speed (for example, 34.4 rpm). Thus engine speed N
Acceleration / deceleration is determined based on the amount of change in E, and if the absolute value of the deviation is equal to or greater than a predetermined rotation speed, it is determined that acceleration / deceleration has been performed.

Subsequently, in step 307, the CPU 27 determines whether or not a predetermined time (for example, 3 seconds) has elapsed since the exhaust air-fuel ratio (A / F) b became 14.6 or more. The exhaust air-fuel ratio (A / F) b is calculated by the following equations (1) to (7)
It was obtained according to a).

The air-fuel ratio A / F during warm time is expressed by the following equation (1). A / F = (QA) / (Fuel) ≈14.5 (1) Fuel = (QA) /14.5 (2) where QA is the amount of air introduced into the combustion chamber and Fuel is the fuel Is the amount.

Further, the fuel amount Fuela in the cold state is obtained according to the following equation (3). Fuela = Fuel (1 + FWL) (3) FWL in the formula (3) is a correction coefficient for correcting the fuel amount increase at low water temperature, and FWL = 0 when warm and FWL> when cold. It becomes 0.

The exhaust air-fuel ratio (A / F) b when the electric air pump 25 operates in the cold state is expressed by the following equation (4). (A / F) b = (QA + QEAP) / Fuela = (QA + QEAP) / {Fuel (1 + FWL)} (4) QEAP in the equation (4) is the discharge amount of the electric air pump 25.

The exhaust air-fuel ratio (A / F) b is set to 14.5.
In order to keep the value (lean) larger than (theoretical air-fuel ratio), the following expression (5) must be satisfied. 14.5 <(QA + QEAP) / {Fuel (1 + FWL)} (5) Substituting equation (2) into equation (5) above and transforming it yields equation (6) below.

QA (1 + FWL) <QA + QEAP QA · FWL <QEAP (6) This equation (6) is applied to the exhaust air-fuel ratio (A
/ F) b is an approximate expression for always making it equal to or higher than the stoichiometric air-fuel ratio.

From this equation (6), it is understood that the exhaust air-fuel ratio (A / F) b becomes rich when the following equation (7) is used. QA · FWL ≧ QEAP …… (7) QA · FWL / QEAP ≧ 1 …… (7a) Therefore, whether the exhaust air-fuel ratio (A / F) b is lean is judged from the above (7) and (7a). it can.

Next, in step 308, the CPU 27 determines whether or not fuel cut has been performed. This determination is made according to the state of the flag set by another routine.

When all the judgment conditions of steps 305 to 308 are satisfied, the CPU 27 causes the step 27 of FIG.
Move to 10. That is, 2 seconds or more have passed from the switching of the fully-closed signal LL in step 305, 3 seconds or more have passed since the sudden acceleration / deceleration in step 306, and 3 after the expressions (7) and (7a) are satisfied in step 307.
If seconds have elapsed and fuel cut is not performed in step 308, the CPU 27 determines that the exhaust air-fuel ratio (A / F) b is not transiently rich due to a change in the operating state of the engine 1, Move to 310.

In step 310, the CPU 27 determines the exhaust air-fuel ratio (A / F) based on the output voltage of the oxygen sensor 18.
Determine if b is lean. Here, if the secondary air supply device 23 is operating normally, the exhaust air-fuel ratio (A /
F) b should be lean. Therefore, if the exhaust air-fuel ratio (A / F) b is lean in step 310, C
In step 311, the PU 27 executes the lean time counter C.
The value of JAIL is incremented by "1", and step 31
Move to 3. On the contrary, exhaust air-fuel ratio (A / F) b
Is rich, the CPU 27 determines that the discharge amount of the electric air pump 25 may be reduced due to a failure, that is, the decrement of the value of the lean time counter CJAIL by “1” in step 312, and step 31
Move to 3.

In step 313, the CPU 27 determines whether or not the value of the lean time counter CJAIL is "77" or more. CJAIL = 77 here is "5
Equivalent to "seconds". CPU27 is a lean time counter CJ
When the value of AIL is "77" or more, it is determined in step 314 that the secondary air supply device 23 is operating normally. Then, the CPU 27 sets the diagnosis end flag XJAIE to "1" in step 315, and then ends this routine. If the value of the lean time counter CJAIL is less than “77” in step 313,
The CPU 27 ends this routine without performing the processing of steps 314 and 315.

By the way, if any one of the judgment conditions in the above steps 305 to 308 is not satisfied, the CPU 27 causes the base air-fuel ratio (A / F) a to temporarily become richer than the theoretical air-fuel ratio, and the oxygen sensor at this time is detected. It is judged that there is a risk of erroneous determination if the diagnosis is performed using the output signal (rich signal) of 18, and the process proceeds to step 309. In step 309, the CPU 27 causes the lean time counter CJAIL
The counting operation of is interrupted and the value at that time is held for a certain period of time. That is, in step 305, the fully closed signal LL
2 seconds have passed immediately after the switching of the above, or 3 seconds have passed immediately after the rapid acceleration / deceleration in step 306, or 3 seconds have passed since the above equation (7) was established in step 307. Until, or step 3
If fuel cut is being performed in 08, the CPU 27
Holds the value of the lean time counter CJAIL in the previous routine.

When all the determination conditions of steps 305 to 308 are satisfied after the predetermined time has elapsed, the CPU
27 continues the counting operation of the lean time counter CJAIL.

FIG. 7 shows changes in the output signal of the oxygen sensor 18 and the lean time counter CJAIL when the state of the fully closed signal LL is switched. When the secondary air supply device 23 is operating normally, the exhaust air-fuel ratio (A / F) b becomes lean due to the supply of secondary air during the period when the fully closed signal LL is off (before the timing t1). Therefore, the lean time counter CJAIL counts (increments).
Then the lean time is measured.

When the fully closed signal LL is switched off from this state (timing t1), asynchronous fuel injection is performed,
The base air-fuel ratio (A / F) a becomes extremely rich. On the other hand, the exhaust air-fuel ratio (A / F) b does not become lean even if the normal amount of secondary air is supplied. At this time, the output of the oxygen sensor 18 changes from lean to rich. here,
As shown by the two-dot chain line in FIG. 7, the oxygen sensor 1
When the lean time counter CJAIL is decremented based on the signal of 8, the normal determination is not performed even though the secondary air supply device 23 is operating normally. However, in this embodiment, the counting operation of the lean time counter CJAIL is interrupted and the value at that time is held.

After that, when a predetermined time elapses (timing t2), the counting operation of the lean time counter CJAIL is restarted, and when CJAIL ≧ 77 (timing t3), the normal determination is performed.

Further, FIG. 8 shows the output signal of the oxygen sensor 18 and the lean time counter CJAI when the exhaust air-fuel ratio (A / F) b obtained by the calculation becomes 14.6 or more.
The change in L is shown. When the secondary air supply device 23 is operating normally, the period in which the formula (7a) is not satisfied, that is, the period of QA · FWL / QEAP <1 (timing t
Before 4), the calculated exhaust air-fuel ratio (A / F) b becomes lean. Therefore, the lean time counter CJ
The AIL counts (increments) and the lean time is measured.

When the above equation (7a) is satisfied from this state, that is, when QA · FWL / QEAP ≧ 1 (timing t4), the base air-fuel ratio (A / F) a becomes extremely rich. On the other hand, the exhaust air-fuel ratio (A / F) b does not become lean even if the normal amount of secondary air is supplied. At this time, the output of the oxygen sensor 18 changes from lean to rich. Here, if the lean time counter CJAIL is decremented based on the signal from the oxygen sensor 18, as indicated by the chain double-dashed line in FIG. 8, the secondary air supply device 23 is operating normally, although it is operating normally. No judgment is made. However, in this embodiment, the counting operation of the lean time counter CJAIL is interrupted and the value at that time is held.

After that, when a predetermined time has passed (timing t5), the counting operation of the lean time counter CJAIL is restarted, and when CJAIL ≧ 77 (timing t6), the normal determination is made.

The operating condition in which the air-fuel ratio becomes rich even if the secondary air is supplied in this way can be detected by the determinations in steps 305 to 308. By the way, in the cold diagnosis routine, it may be possible to omit the counting operation (decrement) of the lean time counter CJAIL when the output of the oxygen sensor 18 is rich. However, in this case, when the output of the oxygen sensor 18 repeats lean and rich, finally the step 31
At 3, CJAIL = 77, and the CPU 27 makes a normal determination. Therefore, in the present embodiment, the above problem is solved by decrementing the value of the lean time counter CJAIL when the output of the oxygen sensor 18 is rich.

Next, the warm diagnosis routine will be described with reference to FIGS.
This will be described with reference to the flowchart of FIG. When the routine proceeds to this routine at timing t11 in FIG. 11, in step 401 in FIG. 9, the CPU 27 determines whether or not the cooling water temperature THW by the water temperature sensor 19 belongs to a predetermined range (80 ° C. ≦ THW <100 ° C.), that is, the engine 1 Determines whether is in the state after warm-up,
In step 402, it is determined whether the fully closed signal LL from the fully closed switch 16 is ON. CPU2
In step 403, the engine speed NE measured by the speed sensor 20 is a predetermined value (for example, 1000 rp).
It is determined whether the vehicle speed SPD by the vehicle speed sensor 22 is less than a predetermined value (for example, 2 km / H) in step 404.

If any one of the judgment conditions in steps 401 to 404 is not satisfied, the CPU 27 proceeds to step 420 in FIG. 10 and sets the diagnosis execution counter CJAI to "0".
To clear. The diagnosis execution counter CJAI is for measuring the operation timing of the secondary air supply device 23 and the operation timing of the feedback correction coefficient FAF during the diagnosis period, and measures the time from the start of diagnosis to the end of diagnosis. ing.

The CPU 27 outputs a signal for stopping the operation of the electric air pump 25 in step 421, and ends this routine. When the operation of the electric air pump 25 is stopped, 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 401 to 404 in FIG.
When all of the determination conditions of are satisfied (timing t in FIG.
12), the CPU 27 determines that the engine 1 is in a state in which it is possible to make a diagnosis at the time of warming, and proceeds to step 405.

In step 405, the CPU 27 increments the value of the diagnosis execution counter CJAI by "1". In this case, "0" is changed to "1". At this time, the time required for the diagnostic execution counter CJAI to change from "0" to "1" is 0.065 seconds. Then, the CPU 27 determines in step 406 whether or not the value of the diagnosis execution counter CJAI is "2" or more. That is, it is determined whether or not 0.13 seconds have elapsed since the count operation by the diagnostic execution counter CJAI was started. At timing t12, CJAI = 1 and the determination condition of step 406 is not satisfied, so the CPU 27 does not perform the subsequent processing and ends this routine.

When the determination condition of step 406 is satisfied (timing t13 in FIG. 11), the CPU 27 outputs a signal for operating the electric air pump 25 in step 407. Then, the electric air pump 25 operates and the secondary air is guided to the exhaust manifold 13.

Subsequently, the CPU 27 executes step 4 in FIG.
At 08, it is determined whether the value of the diagnosis execution counter CJAI is "15" or more. That is, it is determined whether or not about 1 second has elapsed since the supply of the secondary air was started. At timing t13, the diagnostic execution counter C
Since the JAI value is “2” and the determination condition of step 408 is not satisfied, the CPU 27 causes the CPU 27 to execute step 409.
Move to.

In step 409, the CPU 27 stops the feedback control of the air-fuel ratio A / F using the feedback correction coefficient FAF and sets the average value FAFAV of the feedback correction coefficient to the new feedback correction coefficient FA.
Set as F. The CPU 27 then proceeds to step 41.
At 0, the lean time counter CJAIL is reset to "0", and this routine ends. When the above processing is repeatedly executed, the value of the diagnostic execution counter CJAI is incremented by "1" by the processing of step 405. When the condition (CJAI ≧ 15) of step 408 is satisfied (timing t14 in FIG. 11), the CPU 27
Shifts to step 411, a predetermined value (for example, 3%) is added to the average value FAFAV of the feedback correction coefficient, and the added value is used as a new feedback correction coefficient FAF.
Set as. The process of step 411 is a process for forcibly making the base air-fuel ratio (A / F) a rich.

Next, in step 412, the CPU 27 determines whether or not the value of the diagnosis execution counter CJAI is "30" or more. That is, it is determined whether or not about 2 seconds have elapsed since the supply of the secondary air was started. At the timing t14, the value of the diagnosis execution counter CJAI is "1".
5 ”, and the determination condition of step 412 is not satisfied. Therefore, the CPU 27 performs the processing of step 410 and subsequent steps. That is, the lean time counter CJAIL
Holds the value of "0" and terminates this routine.

The above process is repeatedly executed, and step 4
When 12 conditions (CJAI ≧ 30) are satisfied (FIG. 11).
Of the exhaust air-fuel ratio (A / F) b by the oxygen sensor 18
Is lean. If the exhaust air-fuel ratio (A / F) b is lean as shown at timing t15,
The CPU 27 increments the value of the lean time counter CJAIL by "1" at step 414. In this case, "0" is changed to "1". At this time, the time taken for the lean time counter CJAIL to change from "0" to "1" is 0.065 seconds.

Then, in step 415, the CPU 27 determines whether or not the value of the diagnosis execution counter CJAI is "77" or more. That is, the diagnostic execution counter C
It is determined whether or not about 5 seconds have elapsed since the counting operation by JAI was started. 5 seconds here is the time when the diagnosis is completed. Since CJAI = 30 at the timing t15 and the determination condition of step 415 is not satisfied,
The CPU 27 ends this routine without performing the subsequent processing.

While the exhaust air-fuel ratio (A / F) b is lean, the process of step 414 is repeated and the value of the lean time counter CJAIL is incremented by "1". Then, when the exhaust air-fuel ratio (A / F) b becomes rich (timing t16 in FIG. 11), the CPU 27 determines that the determination condition of step 413 is not satisfied, and the process of step 414 is not performed, and Step 415 while keeping the value
Perform the following processing.

When the exhaust air-fuel ratio (A / F) b becomes lean again (timing t17 in FIG. 11), the CPU 27 executes the processing of step 414, and the lean time counter CJAI.
Restart the L count operation. That is, the value of the lean time counter CJAIL at the timing t16 is incremented by "1". Then, the exhaust air-fuel ratio (A /
When F) b changes from lean to rich (timing t18 in FIG. 11), the CPU 27 does not perform the process of step 414, but performs the processes of step 415 and thereafter while keeping the value of the previous process. Further, when the exhaust air-fuel ratio (A / F) b becomes lean again (timing t19 in FIG. 11), CP
U27 performs the processing in step 414 and restarts the counting operation of the lean time counter CJAIL.

As described above, the processing in steps 413 and 414 is performed under the determination condition of step 415 (CJAI ≧ 77).
Continues until is satisfied. And step 414
By the process of, the integrated value of the lean time is measured.

When the determination condition of step 415 is satisfied (timing t20 in FIG. 11), the CPU 27 diagnoses the operating state of the secondary air supply device 23 based on the value of the lean time counter CJAIL. Therefore, CPU
First, in step 416, 27 determines whether or not the value of the lean time counter CJAIL is larger than "37". CJAIL = 37 here corresponds to “2.4 seconds”.

The CPU 27 uses the lean time counter CJAI.
If the value of L is larger than "37", it is determined in step 417 that the secondary air supply device 23 is operating normally. On the contrary, if the value of the lean time counter CJAIL is "37" or less, the CPU 27 proceeds to step 41.
In 8, it is determined that the operation of the secondary air supply device 23 is abnormal.

The reason for making the judgment in step 416 "37" (2.4 seconds) is as follows.
That is, when the secondary air is supplied for a predetermined time, if the secondary air supply device 23 is operating normally, the exhaust air-fuel ratio (A / F) b becomes transiently rich even during the secondary air supply. Even so, the rich time is small. Then, a predetermined ratio (for example, 0.
The exhaust air-fuel ratio (A / F) b should be lean for a longer time than 8). Therefore, in the present embodiment, after the operation of the secondary air supply device 23 is started, about 2 seconds elapses until about 5 seconds elapse (about 3 seconds), the exhaust air-fuel ratio (A /
F) It is determined whether the lean time (lean time) of b is longer than 2.4 seconds, and the operating state of the secondary air supply device 23 is grasped based on the determination result.

Then, the CPU 27 executes the above step 41.
In step 419 after shifting from 7, 418, the diagnosis end flag XJAIE is set to "1", and the processing of step 420 and the subsequent steps described above is performed. That is, step 42
At 0, the diagnostic execution counter CJAI is cleared to "0".
Further, the CPU 27 determines in step 421 that the electric air pump 2
A signal for stopping the operation of 5 is output, and this routine is ended. The stop of the electric air pump 25 prevents the secondary air from being guided to the exhaust manifold 13.

As described above, in this embodiment, the air-fuel ratio A / F of the air-fuel mixture to the engine 1 is detected by the oxygen sensor 18, and when the operating condition of the engine 1 is the predetermined condition, the air-fuel ratio A / F is determined. The fuel injection amount from the fuel injection valves 8A to 8D is adjusted so that F becomes the stoichiometric air-fuel ratio (14.5). When the operating state of the engine 1 is other than the predetermined state, the electric air pump 25 is operated to operate the oxygen sensor 1
8 Secondary air is supplied to the exhaust manifold 13 upstream. Then, the lean time by the oxygen sensor 18 during the supply of the secondary air is measured by the counting operation of the lean time counter CJAIL (steps 311 and 312), and when the lean time becomes equal to or longer than the predetermined time (5 seconds), the secondary It is determined that the air supply device 23 is normal (step 31).
3, 314). Further, when the exhaust air-fuel ratio (A / F) b by the oxygen sensor 18 during the supply of the secondary air becomes rich, the counting operation of the lean time counter CJAIL is interrupted and the value at that time is held (step Three
03-309), the counting operation of the lean time counter CJAIL is continued after a predetermined time has elapsed.

Therefore, even if the exhaust air-fuel ratio (A / F) b by the oxygen sensor 18 becomes transiently rich in accordance with the change in the operating state of the engine 1 while the secondary air is being supplied, The operating state of the secondary air supply device 23 is accurately diagnosed without being affected by the instantaneous change.

Therefore, unlike the prior art in which the diagnosis is always made according to the change in the output signal of the oxygen sensor, in this embodiment the secondary air supply device 2 is caused by the transient change in the air-fuel ratio A / F.
It is possible to prevent the erroneous diagnosis 3).

The present invention is not limited to the configuration of the above-mentioned embodiment, and may be arbitrarily modified within the scope not departing from the spirit of the invention as follows. (1) In the above-described embodiment, the electric air pump 25 is used as the secondary air supply device 23, but instead of this, so-called air suction, in which air is directly sucked from the intake passage 2 by utilizing the pulsation of the exhaust passage 3 A method (AS) secondary air supply device may be used.

(2) In the above embodiment, a warning light is provided on the instrument panel of the driver's seat and the warning light is turned on when it is determined that the secondary air supply device 23 is abnormal. Good.

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

[0092]

As described above in detail, according to the present invention, when the air-fuel ratio by the air-fuel ratio sensor during the supply of the secondary air becomes rich, the counting operation of the timer for measuring the lean time is interrupted. Since the timer value at that time is held and the counting operation of the timer is continued after a predetermined time has elapsed, even if the output signal of the air-fuel ratio sensor becomes transiently lean, the lean time is accurately measured and This has an excellent effect of accurately diagnosing the operation of the next air supply device and preventing erroneous diagnosis in advance.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an electrical configuration of an ECU in one embodiment.

FIG. 3 is a diagram showing a correspondence relationship between an output voltage of an oxygen sensor and a feedback correction coefficient in one embodiment.

FIG. 4 is a flowchart illustrating a diagnostic process executed by a CPU in an embodiment.

FIG. 5 is a flowchart illustrating a cold diagnosis routine in FIG.

6 is a flowchart illustrating a cold diagnosis routine in FIG.

FIG. 7 is a timing chart showing a correspondence relationship between a fully closed signal, an air-fuel ratio, a signal from an oxygen sensor, and a lean time counter in one embodiment.

FIG. 8 is a timing chart showing a correspondence relationship between an air-fuel ratio, an exhaust air-fuel ratio, a signal from an oxygen sensor, and a lean time counter in one embodiment.

FIG. 9 is a flowchart illustrating a warm diagnosis routine in FIG.

FIG. 10 is a flowchart illustrating a warm diagnosis routine in FIG.

FIG. 11 is a timing chart illustrating a correspondence relationship between an operating state of an electric air pump, a feedstock 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]

1 ... Engine as internal combustion engine, 3 ... Exhaust passage, 8A ...
8D ... Fuel injection valve, 13 ... Exhaust manifold, 18 ... Oxygen sensor as air-fuel ratio sensor, 23 ... Secondary air supply device, 25 ... Electric air pump, A / F ... Air-fuel ratio, (A /
F) a ... Base air-fuel ratio, (A / F) b ... Exhaust air-fuel ratio, C
JAIL ... Lean time counter as a timer

Claims (1)

[Claims] 1. An air-fuel ratio of an air-fuel mixture to an internal combustion engine is detected by an air-fuel ratio sensor provided in an exhaust passage, and when the operating state of the internal combustion engine is in a predetermined predetermined state, the air-fuel ratio is the theoretical air-fuel ratio. The fuel injection amount from the fuel injection valve is adjusted so that the fuel ratio is obtained, and when the operating state of the internal combustion engine is other than the predetermined state, the secondary air supply device is operated to operate the exhaust passage upstream of the air-fuel ratio sensor. Secondary air is supplied to the secondary air supply device, and the lean time by the air-fuel ratio sensor during the supply of the secondary air is measured by the counting operation of the timer, and when the lean time becomes a predetermined time or more, the secondary air supply device A method of diagnosing a secondary air supply device, which is determined to be normal, wherein when the air-fuel ratio by the air-fuel ratio sensor during the supply of the secondary air becomes rich, the timer To interrupt the count operation retains the timer value at that time, the diagnostic method of the secondary air supply apparatus being characterized in that so as to continue the counting operation of the timer after a predetermined time has elapsed.