JP3010855B2 - Self-diagnosis device in secondary air supply device of internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary engine for an internal combustion engine which has an oxygen concentration detecting means upstream and downstream of an exhaust gas purification catalyst and performs self-diagnosis based on the output of the oxygen concentration detecting means on the downstream side. The present invention relates to a self-diagnosis device in an air supply device.

[0002]

2. Description of the Related Art In a conventional internal combustion engine, air-fuel ratio control is performed as follows (see Japanese Patent Application Laid-Open No. 60-240840). By detecting the intake air flow rate Q and the number of revolutions N of the engine, a basic fuel supply amount Tp (= K · Q / N; K is a constant) corresponding to the amount of air taken into the cylinder is calculated. Tp corrected by the engine temperature or the like is used by using an air-fuel ratio feedback correction coefficient (air-fuel ratio correction amount) set by a signal from an air-fuel ratio sensor that detects the air-fuel ratio of the air-fuel mixture by detecting the oxygen concentration in the exhaust gas. The feedback correction is performed, and the correction based on the battery voltage is also performed to finally set the fuel supply amount Ti.

[0003] The air-fuel ratio feedback correction based on the signal from the air-fuel ratio sensor is performed so as to control the air-fuel ratio near the target air-fuel ratio (the stoichiometric air-fuel ratio). This is interposed in the exhaust system to oxidize CO and HC in the exhaust gas,
_This is because the conversion efficiency (purification efficiency) of the exhaust purification catalyst (three-way catalyst) that reduces and purifies _X is set so as to function effectively in the exhaust state during stoichiometric air-fuel ratio combustion.

By the way, in the ordinary air-fuel ratio feedback control device as described above, one air-fuel ratio sensor is provided in a collective portion of the exhaust manifold as close as possible to the combustion chamber in order to enhance the response of the sensor. Since the exhaust gas temperature is high in this part, the air-fuel ratio sensor tends to change its characteristics due to thermal effects and deterioration.In addition, since the exhaust gas for each cylinder is insufficiently mixed, the average air-fuel ratio of all cylinders is detected. Difficult,
The accuracy of detecting the air-fuel ratio was difficult, and the accuracy of the air-fuel ratio control was poor.

In view of this point, there has been proposed an air-fuel ratio sensor provided downstream of the exhaust gas purification catalyst and performing feedback control of the air-fuel ratio using the detection values of the two air-fuel ratio sensors (Japanese Patent Laid-Open No. 58-1983). -48756, etc.). That is,
Since the downstream air-fuel ratio sensor is far from the combustion chamber, its response is difficult. However, since it is downstream of the exhaust gas purification catalyst, the characteristic due to the variation of exhaust components (CO, HC, NO _X , CO ₂ ) is low. It is difficult to cause variation, and the poisoning amount of the toxic components in the exhaust gas is small, so it is hard to be affected by the characteristic change due to the poisoning. Moreover, since the exhaust gas is mixed well, the average air-fuel ratio of all cylinders can be detected. As compared with the fuel ratio sensor, a highly accurate and stable detection performance can be obtained.

Here, in an exhaust gas purifying apparatus using an exhaust gas purifying catalyst provided for purifying exhaust gas, an oxygen reaction in an exhaust system is promoted to secure a predetermined conversion rate.
Some are configured to supply secondary air (oxygen) to an exhaust passage on the upstream side of the catalyst. That is, at the time of idling or the like, the air-fuel ratio is clamped to the rich side in order to enhance the combustion stability of the internal combustion engine.
In some cases, secondary air is supplied between the air-fuel ratio sensor on the upstream side and the exhaust gas purification catalyst to cope with the increase in the component, thereby promoting the CO and HC purification function of the exhaust gas purification catalyst.

In the supply of the secondary air as described above,
It is desirable to supply the optimum amount in accordance with the air-fuel ratio state (CO, HC concentration). For example, if excessive secondary air is supplied when the exhaust gas temperature is low, it is not used for combustion of CO and HC. The secondary air may cool the catalyst,
Also, excessive supply of the secondary air will be thus lowering the conversion of the NO _X in the three-way catalyst. Conversely, if the amount of secondary air is too small, the oxidation reaction cannot be sufficiently promoted, and the catalyst temperature cannot be maintained at a high temperature.

[0008]

By the way, in the system for supplying the secondary air as described above, some trouble occurs in the secondary air supply system, for example, a trouble such as clogging of the supply pipe of the secondary air occurs. However, since such a failure does not directly affect the operability of the engine, it is difficult for the driver to notice such a failure. There is a risk that the operation will be continued in a state where good exhaust gas purification cannot be performed by the supply of air. There is a fear that it will be higher.

Therefore, conventionally, a secondary air supply means, an air-fuel ratio sensor, and an exhaust gas purifying catalyst are sequentially provided in the exhaust passage of the internal combustion engine toward the downstream side to perform a specific operation such as when the internal combustion engine is idling or decelerating. Diagnosis of an abnormality in the secondary air supply device has been performed based on the output of the air-fuel ratio sensor in the state (see Japanese Patent Application Laid-Open No. 63-111256).

However, in this case, if an air-fuel ratio sensor is provided upstream of the exhaust purification catalyst only for abnormality diagnosis of the secondary air supply device, there is a possibility that the cost will increase. Further, when the air-fuel ratio sensor for obtaining the signal for setting the feedback correction coefficient is also used for the purpose of abnormality diagnosis of the secondary air supply device, any failure occurs in the secondary air supply system and the When the appropriate air is supplied, even though the actual combustion is performed at the stoichiometric air-fuel ratio, the air-fuel ratio detected by the air-fuel ratio sensor is erroneously detected as lean, resulting in rich combustion. As a result, the vehicle becomes over-rich, and there is a risk that the emission will deteriorate or, in the worst case, engine stall will occur.

[0011] Further, first and second oxygen concentration detecting means provided in an exhaust passage on an upstream side and a downstream side of an exhaust purifying catalyst, respectively, for detecting oxygen concentration in exhaust gas, and the first oxygen concentration detecting means. A secondary air supply unit for an internal combustion engine including: a secondary air supply unit configured to supply secondary air to the exhaust passage between the exhaust purification catalyst and the exhaust passage under predetermined operating conditions. It is conceivable to perform a self-diagnosis of the secondary air supply device based on the oxygen concentration detected by the means.
Here, since the second oxygen concentration detecting means has a long inversion cycle of rich detection and lean detection, it is possible to measure the period with higher accuracy, but on the other hand, it corresponds to an exhaust purification catalyst. Since the amount of O ₂ is stored, it sometimes takes time for the second oxygen concentration detecting means to actually detect a change in oxygen concentration after the supply of the secondary air.

Accordingly, the present invention has been made in view of such a conventional situation, and the secondary air is forcibly supplied and exhausted.
The second oxygen concentration provided in the exhaust passage downstream of the purification catalyst
While it diagnosed with degree detecting means, O ₂ in the exhaust gas purifying catalyst
Of secondary air supply system is diagnosed reliably even if is stored
It is an object of the present invention to provide a self-diagnosis device that can do the above.

[0013]

Therefore, a self-diagnosis device for a secondary air supply device for an internal combustion engine according to the present invention is provided with an exhaust purification catalyst disposed in an exhaust passage of the engine to purify exhaust gas, First and second oxygen concentration detecting means provided in the exhaust passages on the upstream and downstream sides of the purification catalyst to detect the oxygen concentration in the exhaust gas, respectively;
A secondary air supply means for supplying secondary air to the exhaust passage upstream of the exhaust purification catalyst at predetermined operating conditions downstream of the exhaust purification catalyst. And the secondary air supply means 2
Diagnostic supply control means for forcibly supplying the secondary air, and detection by the second oxygen concentration detecting means after a lapse of a predetermined period from the supply of the secondary air by the diagnostic supply control means. Failure diagnosis means for diagnosing that the secondary air supply means has failed when the oxygen concentration does not show a change corresponding to the supply of the secondary air.

[0014]

According to the above construction, the secondary air is forcibly supplied to the exhaust passage by the diagnostic supply control means, and the change in the oxygen concentration corresponding to the supply of the secondary air by the failure diagnostic means is determined by the second supply. The failure of the secondary air supply means is diagnosed based on whether the oxygen concentration is detected by the oxygen concentration detection means.

Here, the second oxygen concentration detecting means has a long reversal cycle, and the change in the oxygen concentration detected by the second oxygen concentration detecting means can be confirmed with higher accuracy. Further, when performing the diagnostic in a predetermined operating condition requiring secondary air, the oxygen storage effect of the catalyst, but actually it takes time for the oxygen to the oxygen sensor reaches the secondary air Correspondingly A predetermined period has elapsed since the start of supply
Later, the change in the oxygen concentration is detected by the second oxygen concentration detecting means.
When delivered, diagnose that the secondary air supply has failed.
Therefore, the failure can be diagnosed reliably.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2 showing the configuration of one embodiment, air is sucked into an engine 1 from an air cleaner 2 via an intake duct 3, a throttle valve 4 and an intake manifold 5. In each branch of the intake manifold 5, a fuel injection valve 6 is provided for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that is energized by a solenoid and opens, and is deenergized and closed by being energized by a drive pulse signal from a control unit 12, which will be described later. Fuel that is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator is injected and supplied to the engine 1.

Each combustion chamber of the engine 1 is provided with an ignition plug 7, which ignites a spark to ignite and burn an air-fuel mixture. Then, exhaust gas is discharged from the engine 1 to the atmosphere via an exhaust manifold 8, an exhaust duct 9, and a three-way catalyst 10 as an exhaust purification catalyst. Here, the three-way catalyst 10 purifies the exhaust gas by oxidizing CO and HC in the exhaust gas and reducing NOx.

The control unit 12 includes a CPU, RO
A microcomputer including an M, a RAM, an A / D converter, an input / output interface, and the like is provided. The microcomputer receives input signals from various sensors, performs arithmetic processing as described later, and operates the fuel injection valve 6. Control. As the various sensors, an air flow meter 13 is provided in the intake duct 3, and outputs a signal corresponding to the intake air flow rate Q of the engine 1.

A distributor (not shown in FIG. 2) has a built-in crank angle sensor 14, and counts a crank unit angle signal output from the crank angle sensor 14 in synchronization with the engine rotation for a certain period of time. Alternatively, the period of the crank reference angle signal is measured to detect the engine speed N. Also, the cooling water temperature Tw in the cooling jacket of the engine 1
Is provided.

The vehicle speed VS of the vehicle on which the engine 1 is mounted
A vehicle speed sensor 19 for detecting P is provided. In addition, a first oxygen sensor 31 is provided at a collecting portion of the exhaust manifold 8. The first oxygen sensor 31 is a known sensor whose output value changes in response to the oxygen concentration in the exhaust gas. For example, the first oxygen sensor 31 is configured to generate an electromotive force corresponding to the oxygen concentration ratio in the exhaust gas with respect to the atmosphere. I have. Since the oxygen concentration in the exhaust changes suddenly at the stoichiometric air-fuel ratio as shown in FIG.
Based on the output value of the first oxygen sensor 31, it can be determined whether the air-fuel ratio of the engine intake air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio. That is, the first oxygen sensor 31 functions as a first oxygen concentration detecting means.

A second air-fuel ratio sensor 32 as second oxygen concentration detecting means having the same function as the first air-fuel ratio sensor is provided downstream of the three-way catalyst 10. Further, the first air-fuel ratio sensor 31 and the three-way catalyst
There is provided a secondary air inlet 23 which constitutes a part of secondary air supply means for supplying secondary air into the exhaust gas from the space between the secondary air supply port and the secondary air supply means.

Incidentally, the internal combustion engine 1 in this embodiment is provided with a secondary air supply device 50 having the following configuration. The secondary air supply device 50 is provided with an opening 3 a provided in the intake duct 3 on the upstream side of the throttle valve 4 and the inlet 23.
, A backflow prevention valve 50b interposed in the passage 50a to prevent only the flow from the introduction port 23 toward the opening 3a, and a side closer to the opening 3a than the backflow prevention valve 50b. Solenoid valve interposed in the passage 50a
50c, and the opening of the solenoid valve 50c is controlled by a signal sent from the control unit 12.

That is, when the solenoid valve 50c is turned on, secondary air is introduced into the secondary air inlet 23, and secondary air supply means is formed. Next, the control unit
The self-diagnosis routine executed by the routine 12 will be described with reference to a flowchart shown in FIG. 4 and a time chart shown in FIG. In this embodiment, the functions of the diagnostic supply control unit and the failure diagnosis unit are provided by software in the control unit 12 as shown in the flowchart of FIG.

First, step 1 (referred to as S1 in the figure)
You. In the following, the vehicle detected by the vehicle speed sensor 19
Speed VSP to a certain vehicle speed that is almost steady above a certain medium speed
It is determined whether or not the vehicle speed VSP is between Lo and Hi.
Judgment is made based on whether it is in between. And, when the vehicle speed is
At the above specified vehicle speed, the exhaust flow rate is large and
O to medium 10_TwoIs stored in the exhaust gas,_TwoThree yuan
O accumulated in the catalyst 10 _TwoThe effect of the accumulation
It is a time when the amount of air is relatively small.
Operating conditions that are suitable for self-diagnosis
Then, proceed to step 2 and subsequent steps.

In step 2, it is determined whether or not a timer 2, which will be described later, is measuring, and if not, the process proceeds to step 3. In step 3, it is determined whether the air-fuel ratio detected by the second air-fuel ratio sensor 32 is rich. That is, if the air-fuel ratio is rich, the process proceeds to step 4 to determine whether the air-fuel ratio is rich for a predetermined time.

In step 4, it is determined whether or not a timer 1 to be described later is counting. If not, the process proceeds to step 5, where the air-fuel ratio feedback correction coefficient α is set to 1 (100 %) in fixed, then the routine proceeds to step 6, to the air-fuel ratio is to measure the time T ₁ which is a rich, starts measurement of the timer 1. On the other hand, if it is determined in step 4 that the timer 1 is counting, the process proceeds to step 7 in which the rich time T
_It is determined whether _{1 has} passed a predetermined time T _S1 . here,
Since the second air-fuel ratio sensor 32 is remote from the combustion chamber and downstream of the three-way catalyst 10, the exhaust components (CO, HC, N
O _X, hardly occurs a variation in the variation due to the characteristics of CO _2), characteristic change less likely due to poisoning due poisoning amount is small due to toxic components in the exhaust, stable detection performance can be obtained with high accuracy.

Therefore, the time during which the air-fuel ratio detected by the second air-fuel ratio sensor 32 is rich is a predetermined time T _S1.
If it is determined that the time has elapsed, it is time when the influence of the accumulation of O ₂ in the three-way catalyst 10 is relatively small when the air-fuel ratio changes thereafter. It is determined that the operating condition is easy to detect by the air-fuel ratio sensor 32, that is, the operating condition is suitable for performing self-diagnosis in the secondary air supply device 50.
Turn on 50 to start self-diagnosis.

In step 9, the time T ₂ required for the air-fuel ratio detected by the second air-fuel ratio sensor 32 to change from the rich state to the predetermined lean state after the secondary air supply device 50 is turned on is determined. Start measurement. On the other hand, in step 2, when the timer 2 is determined to be being measured time T _2, the process proceeds to step 10 and subsequent.

In step 10, it is determined whether the air-fuel ratio detected by the second air-fuel ratio sensor 32 is in a lean state. And if it is determined that it is lean,
The air-fuel ratio, which was initially rich, was introduced into the secondary air inlet 23 by the secondary air supply device 50,
It is determined that the state has been reversed from the rich state to the lean state, and it is determined in step 11 that the secondary air supply device 50 is normal.

In step 10, the second air-fuel ratio sensor
If it is determined that the air-fuel ratio detected by 32 has not been reversed to the lean state, the process proceeds to step 12, and the elapsed time T ₂ from when the secondary air supply device 50 started to be measured in step 9 is turned on. Is determined whether a predetermined time T _{S2 has} elapsed. Here, if the elapsed time T ₂ has not the predetermined time T _S2 elapsed (No), it returns to repeat the previous steps again. On the other hand, when the elapsed time T ₂ is a predetermined time T _S2 elapsed (Yes), despite a time sufficient secondary air supply system 50 from the ON (T _S2) has passed, the second This is the case where the air-fuel ratio detected by the air-fuel ratio sensor 32 is not inverted to the lean state,
At this time, even if the secondary air supply device 50 is turned on, there is an abnormality in the secondary air supply device 50, so it can be determined that the secondary air is not being supplied. Is determined to be abnormal.

Here, after it is determined in step 11 or step 13 that the secondary air supply device 50 is normal or abnormal, the process proceeds to step 15 where it is assumed that the self-diagnosis of the secondary air supply device 50 has been completed. Turn off the secondary air supply device 50,
Stop the forced supply of secondary air. In step 5, the air-fuel ratio feedback correction coefficient α for clamping the operating condition to the operating condition for performing the self-diagnosis
Is released, and the flow returns to the normal air-fuel ratio feedback control.

On the other hand, if it is determined in step 3 that the air-fuel ratio detected by the second air-fuel ratio sensor 32 is not rich, it is determined that the state is not suitable for diagnosis, and the timer 1 and the timer 2 are determined in step 14. Reset,
Proceed to step 15 and subsequent steps. Note that the secondary air supply device 50 may be configured as follows. Engine, or air pumped by an air pump driven by an electric motor,
After the pressure is adjusted to a predetermined value by the pressure regulator, the flow rate may be adjusted by an electromagnetic control valve whose opening is controlled by a duty signal sent from the control unit 12.

[0033]

As described above, according to the present invention, the first oxygen concentration detecting means is controlled by the supply control means for diagnosis.
After a lapse of a predetermined period after the secondary air is forcibly supplied to the exhaust passage between the stage and the exhaust purification catalyst, a change in the oxygen concentration corresponding to the supply of the secondary air is detected by the failure diagnosis means. Since the failure of the secondary air supply means is diagnosed depending on whether or not it is possible , highly accurate diagnosis can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is a system schematic diagram showing the configuration of an embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an exhaust gas component concentration and an air-fuel ratio.

FIG. 4 is a flowchart showing self-diagnosis of the secondary air supply device.

FIG. 5 is a time chart illustrating the operation of the present invention.

[Explanation of symbols]

 Reference Signs List 1 engine 9 exhaust duct 10 three-way catalyst 12 control unit 19 vehicle speed sensor 23 secondary air inlet 31 first air-fuel ratio sensor 32 second air-fuel ratio sensor 50 secondary air supply device 50a secondary air inlet passage 50c solenoid valve

Continuation of front page (56) References JP-A-4-1444 (JP, A) JP-A-4-365919 (JP, A) JP-A 1-216011 (JP, A) JP-A-63-248908 (JP) , A) JP-A-63-111256 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/22 301-321 F02D 41/14 310 G01M 15/00 F02D 45/00 314

Claims (1)

(57) [Claims] An exhaust purification catalyst disposed in an exhaust passage of an engine for purifying exhaust gas, and a first exhaust purification catalyst provided in an exhaust passage upstream and downstream of the exhaust purification catalyst for detecting an oxygen concentration in exhaust gas. A second oxygen concentration detecting means, and an exhaust gas purification catalyst downstream of the upstream oxygen sensor.
A secondary air supply means for supplying secondary air to a downstream exhaust passage under predetermined operating conditions, and a secondary air supply device for an internal combustion engine, the secondary air supply device comprising: Diagnostic supply control means for forcibly supplying the secondary air by the supply means; and the second oxygen concentration detecting means after a lapse of a predetermined period from the supply of the secondary air by the diagnostic supply control means. Failure diagnosis means for diagnosing that the secondary air supply means has failed when the oxygen concentration detected in the step does not show a change corresponding to the supply of the secondary air. A self-diagnosis device in a secondary air supply device of an internal combustion engine.