JP4061676B2 - Self-diagnosis device for secondary air supply device of internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a self-diagnosis device in a secondary air supply device for an internal combustion engine. More specifically, the failure of a secondary air supply device that supplies secondary air to the upstream side of a catalyst is detected when the exhaust air / fuel ratio is reduced. The present invention relates to a technique for diagnosis based on leaning.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a secondary air supply apparatus that promotes an oxidation reaction in an exhaust passage and a catalyst by supplying secondary air to the upstream side of the catalyst, for example, when starting a cold machine with a low catalyst temperature, etc., and purifies exhaust gas. An internal combustion engine provided is known.
Japanese Patent Laid-Open No. 9-137717 discloses a device for diagnosing a failure of the secondary air supply device.
[0003]
The failure diagnosis device disclosed in the publication discloses whether or not the exhaust air-fuel ratio is in a lean state commensurate with the supply of secondary air when the supply of secondary air is performed during a predetermined period at the time of cold start. Judgment is made based on the output of an oxygen sensor provided downstream of the secondary air supply port and upstream of the catalyst. When the desired lean state is detected, normality is determined. When the rich state is detected The failure determination is performed assuming that the secondary air is not actually supplied.
[0004]
[Problems to be solved by the invention]
By the way, in the above failure diagnosis, it is a requirement that the lean determination is made only when it is normal, but the fuel injection amount increase correction factor according to the coolant temperature decreases as the warm-up progresses and increases When the correction rate approaches 0, there is a possibility that the malfunction is caused and the secondary air is not actually supplied, but the output of the oxygen sensor becomes lean due to sensor variation or the like, and the normal determination is made. There was a problem.
[0005]
In other words, if the increase correction rate is small, the oxygen sensor output is normal when it is lean, and when it is rich, it cannot be completely separated as a failure, which may reduce the accuracy of failure diagnosis. .
The present invention has been made in view of the above problems, and an object thereof is to provide a self-diagnosis device that can stably and accurately diagnose a failure of a secondary air supply device based on rich / lean determination of an exhaust air / fuel ratio. And
[0006]
[Means for Solving the Problems]
Therefore, the invention according to claim 1 is configured as shown in FIG. In FIG. 1, the secondary air supply device is a device that supplies secondary air to the exhaust passage on the upstream side of the catalyst under predetermined operating conditions.
[0008]
The exhaust air / fuel ratio detecting means detects the exhaust air / fuel ratio in an exhaust passage upstream of the catalyst and downstream of the secondary air supply port of the secondary air supply device. The failure diagnosis means is means for diagnosing a failure of the secondary air supply device based on a detection result of the exhaust air / fuel ratio detection means at the time of secondary air supply control by the secondary air supply device . Diagnosis is started after the fuel injection amount increase correction rate becomes less than a predetermined minimum value.
[0009]
Here, the increase correction rate limiting means holds the increase correction rate at the minimum value at the time of failure diagnosis by the failure diagnosis means. According to such a configuration, the secondary air supply port, the exhaust air / fuel ratio detecting means, and the catalyst are provided in this order from the upstream side with respect to the exhaust passage, and in the state where the secondary air is supplied, the exhaust air mixed with the secondary air is exhausted. After the fuel ratio is detected by the exhaust air / fuel ratio detection means, it is introduced into the catalyst. The failure diagnosis is performed based on whether or not the exhaust air-fuel ratio has become lean due to the supply of secondary air. For example, immediately after starting, the diagnosis is not performed in a state where the increase correction rate is larger than the minimum value. The diagnosis is started when the value is reduced to the minimum value, and after the diagnosis is started, the increase correction rate is held at the minimum value, and the diagnosis is performed with the increase correction rate = the minimum value.
[0010]
According to a second aspect of the present invention, the failure diagnosis unit performs failure diagnosis on the condition that the exhaust air-fuel ratio detection unit is in an active state. According to such a configuration, the exhaust air / fuel ratio detecting means is activated and outputs a signal corresponding to the rich state and the lean state of the exhaust air / fuel ratio, and then the failure diagnosis is performed.
[0011]
According to a third aspect of the present invention, the secondary air supply device is configured to supply secondary air during a predetermined period at a low temperature start, and the increase correction rate held at the minimum value by the increase correction rate limiting means. Has an increase correction factor for increasing the fuel injection amount according to at least the engine temperature. According to such a configuration, the increase correction factor gradually decreases as the warm-up progresses, but the increase is made so that the exhaust air-fuel ratio is reliably determined to be rich without the secondary air being supplied. Hold the correction factor at the minimum value.
[0012]
According to a fourth aspect of the present invention, after the failure diagnosis by the failure diagnosis unit is completed, the increase correction rate limiting unit gradually returns the increase correction rate held at the minimum value to the normal increase correction rate. The configuration. According to such a configuration, when the increase correction rate that has been held at the minimum value for diagnosis is returned to the normal value that is smaller than the minimum value, the normal value is gradually changed from the minimum value to the normal value instead of being stepped. Return to the value.
[0014]
【The invention's effect】
According to the first aspect of the present invention, in the configuration in which the failure diagnosis of the secondary air supply device is performed based on the change in the exhaust air / fuel ratio accompanying the supply of the secondary air, the exhaust air / fuel ratio is ensured when the secondary air is not supplied. Therefore, even if there are various variations and disturbances, it is possible to accurately diagnose a failure of the secondary air supply device from the rich lean of the exhaust air / fuel ratio, and a large increase correction factor is required. When this is done, the fuel injection amount is increased and corrected with a large increase correction factor to ensure engine operation stability, while the diagnosis is performed with the increase correction factor set to the minimum value. There is an effect that the diagnosis can be performed as the most suitable value without excess or deficiency .
[0015]
According to the second aspect of the present invention, when the exhaust air / fuel ratio detecting means is in an inactive state and the actual exhaust air / fuel ratio cannot be detected with high accuracy, the failure diagnosis is performed, and the secondary air supply device has failed or is normal. It is possible to prevent misdiagnosis. According to the third aspect of the invention, when the fuel injection amount of increasing correction rate decreases with the progress of the warm-up, exhaust air-fuel ratio in the state where the secondary air is not supplied is reliably detected as Rich bulking Since the correction factor is maintained, there is an effect that the accuracy of failure diagnosis during warm-up can be improved.
[0016]
According to a fourth aspect of the present invention, since return increase correction factor which has been held at the minimum value gradually to the normal value, it says possible to prevent the air-fuel ratio worsens the operability change step at the time of diagnosis end effect There is.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.
FIG. 2 shows a system diagram of the internal combustion engine in the embodiment.
In this figure, air is drawn into the internal combustion engine 1 through an air cleaner 2, an intake duct 3, a throttle chamber 4 and an intake manifold 5.
[0018]
An air flow meter 6 is provided in the intake duct 3 and detects an intake air flow rate Q. The throttle chamber 4 is provided with a throttle valve 7 that is linked to an accelerator pedal (not shown), and controls the intake air flow rate Q.
The intake manifold 5 is provided with an electromagnetic fuel injection valve 8 for each cylinder. The fuel is pumped from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator to be supplied to the engine 1.
[0019]
The fuel injection valve 8 may be configured to inject fuel directly into the combustion chamber.
Control of fuel injection by the fuel injection valve 8 is performed by a control unit 9 with a built-in microcomputer.
The control unit 9 determines the basic fuel injection amount Tp = from the intake air flow rate Q detected by the air flow meter 6 and the engine speed N calculated based on the signal from the crank angle sensor 10 built in the distributor 13. The final fuel injection amount Ti is set by calculating K × Q / N (K is a constant) and applying various corrections to the basic fuel injection amount Tp. Then, a drive pulse signal having a pulse width corresponding to the fuel injection amount Ti is output to the fuel injection valve 8 in synchronization with the engine rotation, so that the fuel injection valve 8 is intermittent for a time corresponding to the fuel injection amount Ti. The predetermined amount of fuel is injected and supplied to the engine 1.
[0020]
Here, as the correction amount for correcting the basic fuel injection amount Tp, the water temperature increase correction coefficient KTW based on the cooling water temperature Tw representing the engine temperature detected by the water temperature sensor 14 is increased in the high load / high rotation range. In addition to an increase correction amount such as an air-fuel ratio correction coefficient KMR for performing an increase correction immediately after the engine is started, an actual air-fuel ratio is feedback-controlled to a target air-fuel ratio (for example, a theoretical air-fuel ratio). There are an air-fuel ratio feedback correction coefficient α and a correction amount Ts for correcting a change in the invalid injection time of the fuel injection valve 8 due to the battery voltage.
[0021]
The air-fuel ratio feedback correction coefficient α is determined based on the oxygen concentration in the exhaust gas detected by an oxygen sensor 19 as exhaust air-fuel ratio detection means interposed in the exhaust passage 20. Is determined and controlled by, for example, proportional-integral control so that the actual air-fuel ratio approaches the target air-fuel ratio.
[0022]
A three-way catalyst 17 for oxidizing and purifying CO, HC and NOx in the exhaust gas is provided in the downstream exhaust passage 20 of the oxygen sensor 19, and the downstream side of the three-way catalyst 17. A muffler 18 is provided.
Each cylinder of the engine 1 is provided with a spark plug 11, to which a high voltage generated in the ignition coil 12 is sequentially applied via a distributor 13, thereby spark ignition and igniting and burning the air-fuel mixture. . Here, the ignition coil 12 is controlled to generate a high voltage via a power transistor 12a attached thereto. Therefore, the ignition timing (ignition advance value) ADV is controlled by controlling the ON / OFF timing of the power transistor 12a with the ignition signal from the control unit 9.
[0023]
Here, a secondary air supply pipe 16 for supplying secondary air to the exhaust passage 20 upstream of the oxygen sensor 19 is connected in communication, and the secondary air supplied from an electric air pump (hereinafter simply referred to as air pump) 21 The exhaust gas is supplied to the exhaust passage 20 via the secondary air supply pipe 16. The air pump 21 is ON / OFF controlled by a command from the control unit 9, and the supply of secondary air is ON / OFF controlled in response to the command, and the secondary air supply pipe 16 and the air pump 21 are controlled accordingly. The control unit 9 constitutes a secondary air supply device.
[0024]
As the secondary air supply device, a method of directly sucking air from the intake duct 13 using the pulsation of the exhaust passage 20 may be used.
Here, the failure diagnosis control of the secondary air supply device performed by the control unit 9 according to the program shown in the flowchart of FIG. 3 will be described.
In the present embodiment, the functions as the failure diagnosis means and the increase correction rate restriction means are provided in software by the control unit 9 as shown in the flowchart of FIG.
[0025]
In the flowchart of FIG. 3, first, in step 1 (denoted as S1 in the figure, the same applies hereinafter), it is determined whether or not it is a low temperature start time for supplying secondary air. In the present embodiment, when the water temperature at the start is a low temperature state of, for example, about 0 to 55 ° C., secondary air is supplied to the exhaust passage by the secondary air supply device for a predetermined time (for example, 60 seconds) after the start. Supply.
[0026]
If it is determined in step 1 that the secondary air is to be supplied at a low temperature start time, the process proceeds to step 2 where the secondary air supply device is operated to supply the secondary air upstream of the three-way catalyst 17. Supply. In the state where the secondary air is supplied, the air-fuel ratio feedback control using the oxygen sensor 19 is not performed, and the open control state is set.
[0027]
When the secondary air is supplied, the process proceeds to step 3 to calculate an increase correction factor TFBYA including the water temperature increase correction coefficient KTW, the air-fuel ratio correction coefficient KMR, the post-startup increase correction coefficient KAS, and the like. Then, it is determined whether or not the increase correction rate TFBYA is larger than a predetermined minimum value MIN.
The minimum value MIN is reliably detected as rich in the exhaust air-fuel ratio in the non-supplied state of the secondary air even when there is a variation in the oxygen sensor 19, and when the secondary air is supplied, The detection result of the air-fuel ratio is preset as a value that reverses lean.
[0028]
When it is determined that the increase correction rate TFBYA is larger than the minimum value MIN, the process returns to step 3 without starting diagnosis, and when the increase correction rate TFBYA is smaller than the minimum value MIN, Proceed to 5.
In step 5, the minimum value MIN is set as the increase correction rate TFBYA so that the normal increase correction rate TFBYA is maintained at the minimum value MIN even when the normal increase correction rate TFBYA gradually decreases as the warm-up progresses. (See FIG. 4).
[0029]
In the next step 6, it is determined whether or not the oxygen sensor 19 is activated. For example, the activity of the oxygen sensor 19 can be determined based on the fact that the output of the oxygen sensor 19 exceeds the slice level.
When it is determined in step 6 that the oxygen sensor 19 is not activated, diagnosis based on the output of the oxygen sensor 19 cannot be performed, so the process returns to step 5 and the increase correction factor TFBYA is held at the minimum value MIN. Wait.
[0030]
On the other hand, if it is determined in step 6 that the oxygen sensor 19 is active, the process proceeds to step 7 in order to diagnose the secondary air supply device.
In step 7, the output of the oxygen sensor 19 is monitored, and in step 8, it is determined whether or not the monitored sensor output is a lean output exceeding an output corresponding to a reference air-fuel ratio (theoretical air-fuel ratio). As shown in the figure, when the lean output is obtained, it is determined that the secondary air is actually supplied, and normal determination is performed in step 9. On the other hand, when the lean output exceeding the output corresponding to the reference air-fuel ratio is not obtained and the rich output is obtained, the control is performed so as to supply the secondary air, but actually the supply of the secondary air is performed. It is determined that the rich exhaust from the engine is detected by the oxygen sensor 19 as it is, and the routine proceeds to step 10 where failure determination is performed. When a failure determination is made, it is preferable to warn the vehicle driver of the occurrence of the failure with a lamp or the like.
[0031]
Here, the increase correction factor TFBYA of the fuel injection amount is held at the minimum value MIN and does not fall below the minimum value MIN, so that the output of the oxygen sensor 19 becomes lean even when the secondary air is not supplied. When the secondary air is not actually supplied, it can be reliably diagnosed as the rich output state of the oxygen sensor 19. Further, if the increase correction rate TFBYA is in the state of the minimum value MIN, the increase correction rate is too large so that diagnosis in a state where the output of the oxygen sensor 19 becomes rich even though the secondary air is supplied can be avoided. Also become.
[0032]
That is, the minimum value MIN is set to a value that reliably separates the output of the oxygen sensor 19 lean and rich depending on whether or not the secondary air is supplied. This makes it possible to accurately diagnose the supply device failure.
However, if the increase correction rate TFBYA is forcibly reduced to the minimum value MIN and the diagnosis is performed in a state where the increase correction rate TFBYA exceeds the minimum value MIN, operation stability in a low temperature state cannot be secured. The diagnosis execution is waited until the increase correction rate TFBYA falls below the minimum value MIN, and then the increase correction rate TFBYA is held at the minimum value MIN to perform diagnosis.
[0033]
The oxygen sensor 19 output in step 7 is monitored at the time when control is performed to stop the supply of secondary air by integrating the output of the oxygen sensor 19 every sample time (for example, every second) (or start of monitoring). When the elapsed time from the time reaches a predetermined monitoring time (for example, 20 seconds), the integrated value is divided by the number of samples so as to obtain the average value of the outputs. It is preferable to compare the output corresponding to the air-fuel ratio.
[0034]
In addition, when the predetermined monitoring time cannot be secured as the time for monitoring the output of the oxygen sensor 19, it is preferable to end the diagnosis without making any judgment of failure or normality. That is, since the supply of the secondary air is performed only for a predetermined time from the start, when the supply of the secondary air is stopped before the predetermined monitoring time has elapsed since the start of the monitoring in step 7, Skip 8-10 and go to step 11.
[0035]
Alternatively, as another method, it is determined whether or not a diagnosis can be performed by determining the remaining time from the elapsed time until the condition up to step 6 is satisfied, and if it is determined that the diagnosis cannot be performed, 7-10 can also be skipped. In this case as well, the increase rate may be held at the minimum value MIN or another predetermined value until the supply of secondary air is completed. Thereby, unburned HC is supplied to the catalyst and the activation of the catalyst is accelerated.
[0036]
In step 11, a process of gradually returning the increase correction rate that has been limited to the minimum value or more in step 5 to the normal value is performed.
When the supply of secondary air and the diagnosis during the supply are completed and the increase correction factor TFBYA returns to the normal value, air-fuel ratio feedback control using the oxygen sensor 19 is started in step 12 (see FIG. 4). ).
[0039]
In the above, the control for supplying the secondary air and the oxygen sensor being activated are the conditions for the failure diagnosis of the secondary air supply device. It is preferable to add.
[0040]
-The outside air temperature is within the specified temperature range-The atmospheric pressure is above the reference pressure-The air-fuel ratio learning value is within the specified range-Each component (oxygen sensor, water temperature sensor, outside air temperature sensor, atmospheric pressure sensor) It is preferable that the battery voltage is equal to or higher than a predetermined voltage and the output of the oxygen sensor 19 is monitored on the condition that the following conditions are satisfied.
[0041]
・ Boost below the specified value (low load condition)
・ The basic fuel injection amount is below a predetermined value ・ Engine speed is within a predetermined speed range (for example, 40-1800rpm) ・ The intake air amount is below a predetermined value ・ The fuel is not cut ・ Engine speed, basic fuel injection amount, throttle The degree of opening does not indicate a change over a predetermined ratio, and the change over a predetermined ratio is not within a predetermined period. The air conditioner is not within a predetermined period after switching ON / OFF.
FIG. 1 is a block diagram showing a configuration of an invention according to claim 1 ;
FIG. 2 is a system configuration diagram of the internal combustion engine in the embodiment.
FIG. 3 is a flowchart showing the contents of diagnostic control in the embodiment. FIG. 4 is a time chart of diagnostic control in the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 9 ... Control unit 16 ... Secondary air supply pipe 17 ... Three-way catalyst 19 ... Oxygen sensor 20 ... Exhaust passage 21 ... Air pump

Claims (4)

In an internal combustion engine comprising a secondary air supply device that supplies secondary air to an exhaust passage on the upstream side of the catalyst under predetermined operating conditions,
An exhaust air / fuel ratio detecting means for detecting an exhaust air / fuel ratio in an exhaust passage upstream of the catalyst and downstream of a secondary air supply port by the secondary air supply device;
A means for diagnosing a failure of the secondary air supply device based on a detection result of the exhaust air / fuel ratio detection means at the time of secondary air supply control by the secondary air supply device, and increasing the amount of fuel injection to the engine A failure diagnosis means for starting diagnosis after the correction rate is equal to or lower than a predetermined minimum value ;
An increase correction rate limiting means for holding the increase correction rate at the minimum value at the time of failure diagnosis by the failure diagnosis means;
A self-diagnosis device for a secondary air supply device for an internal combustion engine, comprising: The failure diagnosis means, the exhaust air-fuel ratio detecting means self-diagnosis system in the secondary air supply device for an internal combustion engine according to claim 1, characterized in that the failure diagnosing a condition that is active. The secondary air supply device is configured to supply secondary air during a predetermined period at a low temperature start, and the increase correction rate held at the minimum value by the increase correction rate limiting means is a fuel corresponding to at least the engine temperature. self-diagnosis device in the secondary air supply device for an internal combustion engine according to claim 1 or 2, wherein the containing increasing correction factor for increasing correction of the injection quantity. After the failure diagnosis by said failure diagnosing means is completed, according to claim 1, wherein the increase correction factor limiting means, and returning to the increase correction factor which has been held by the minimum value gradually normal increase correction factor The self-diagnosis apparatus in the secondary air supply apparatus of the internal combustion engine as described in any one of -3 .

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