JPH08312337A - Secondary air supply device for internal combustion engine - Google Patents

Abstract

PURPOSE: To enable detection of the state of discharge failure and supply capacity lowering in secondary air by setting a diagnostic area within the specified exhaust-pressure range centered on a point that is somewhat less than the shutoff exhaust pressure, and in the case where a driving state is accorded with this diagnostic area, discharging the secondary air from a secondary air supplying means. CONSTITUTION: On the basis of a voltage value of an air pump 21, a diagnostic area is set up in referring to a flow map being situated at this side as far as the specified pressure from each shutoff exhaust pressure and set up with the specified width. Driving conditions of an engine such as engine speed and load are read, and whether they are accorded with the diagnostic conditions or not is judged. When it is YES, drive of the air pump 21 is checked, an air-fuel ratio in exhaust is read out of an air-fuel ratio sensor 16. After the elapse of the specified time, the air-fuel ratio in the exhaust is read out of the air-fuel ratio sensor 16, comparing it with the initial value, and a portion of alteration in the air-fuel ratio is calculated, and a fact that whether it goes beyond the present specified value or not is judged. If secondary air is supplied normally, it is judged to be YES, but when this secondary air is not suppliable due to defective in the air pump 21 and an air cut valve 22, it is so judged as being NO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is designed for use under certain operating conditions.
Secondary air is introduced into the exhaust passage through the secondary air introduction passage,
The present invention relates to a secondary air supply device for an internal combustion engine that maintains and improves the conversion efficiency of a catalytic converter.

[0002]

2. Description of the Related Art HC in exhaust gas discharged from an engine body,
In order to remove CO, NO _X, etc., a catalytic converter including a three-way catalyst or the like is provided in the middle of the exhaust passage. Since this catalytic converter exhibits conversion performance (oxidation reaction) in an environment near the stoichiometric air-fuel ratio, it is provided with a secondary air supply device that supplies secondary air into the exhaust passage via the secondary air introduction passage. ing.

That is, 2 provided connected to the exhaust passage
It is provided in the middle of the secondary air introduction path and the secondary air introduction path,
An electric air pump as a secondary air supply means for discharging and supplying the secondary air, and an air cut valve which is located on the downstream side of the air pump and which is provided in the secondary air introduction passage and which connects and disconnects the secondary air introduction passage. The secondary air supply device is configured to have the secondary air supply device. For example, when the air-fuel ratio is clamped to the rich side,
The conversion performance of the catalytic converter is maintained by supplying the secondary air under operating conditions where the oxygen in the exhaust gas is insufficient.

Therefore, for example, when the secondary air cannot be supplied sufficiently due to the obstruction of the secondary air introduction passage, sufficient oxidation is not performed, so that HC and the like in the exhaust gas increase and
The temperature of the catalytic converter itself also falls below the activation temperature, further degrading the conversion efficiency. Therefore, for example, Japanese Patent Laid-Open No. 5-30
In Japanese Patent No. 2511, Japanese Unexamined Patent Publication No. 5-296033, Japanese Unexamined Patent Publication No. 4-1443, Japanese Unexamined Patent Publication No. 4-308312, the air-fuel ratio in the exhaust gas after the introduction of secondary air is measured by an air-fuel ratio sensor (oxygen sensor). When the detected air-fuel ratio is on the lean side, it is determined that the secondary air is being supplied normally, while on the other hand, when the detected air-fuel ratio is on the rich side, it is abnormal. A self-diagnosis function is provided to determine whether there is an abnormality in the secondary air supply system based on whether or not the air-fuel ratio feedback correction coefficient during air-fuel ratio feedback control shifts to the rich side.

[0005]

By the way, in the secondary air supply device for the internal combustion engine having the self-diagnosis function described above,
The air-fuel ratio in the exhaust gas after the introduction of secondary air is monitored, and if this air-fuel ratio is on the rich side, it can be determined that there is an abnormality in the supply of secondary air. However, only "whether or not the secondary air is being supplied" can be determined, and it cannot be detected until "whether or not the supply amount of the secondary air is appropriate". Therefore, unless an abnormal condition of supply failure occurs, self-diagnosis There is room for improvement in reliability of self-diagnosis, usability, etc., because the function is not exerted.

That is, the failure or abnormality of the secondary air supply system is caused by, for example, disconnection of the coil of the pump motor.
"Sudden abnormal condition" where secondary air cannot be supplied
Alternatively, “inability to supply” and “slow abnormal state” in which the adhesive component in the exhaust gradually adheres to the secondary air introduction passage or the discharge port of the pump and the secondary air flow rate gradually decreases or “ Although it is considered that the supply capacity is deteriorated, in the conventional technology, the abnormality of the secondary air supply system is determined only by the presence / absence of the detection of the secondary air, so that only the supply impossible state can be detected. .

Therefore, in the prior art, for example, carbon or gum components in the exhaust gas adhere to the secondary air flow passage and
Since it is not possible to cope with the gradual change in the secondary air flow rate, the secondary air is being discharged, but there is a possibility that the secondary air will be supplied in an insufficient quantity. As a result, there is a risk that the catalytic converter will continue to run while its conversion performance is reduced.

The present invention has been made in view of the problems of the prior art, and an object thereof is to make it possible to easily determine whether or not the supply amount of secondary air is appropriate. It is to provide a secondary air supply device for an internal combustion engine.

[0009]

In view of the above, the present invention focuses on the deadline discharge pressure determined by the pressure (exhaust pressure) in the exhaust passage and the supply capacity of the secondary air supply means, and the flow near the deadline discharge pressure. By detecting the small amount of secondary air that can be obtained, it is decided to detect both the state in which secondary air cannot be supplied and the state in which the supply capacity of secondary air has deteriorated. That is, the features of the configuration adopted by the secondary air supply device for an internal combustion engine according to the present invention are: secondary air supply means for discharging and supplying secondary air to the middle of the exhaust passage via the secondary air introduction passage; Detect the secondary air inside 2
A secondary air supply device for an internal combustion engine comprising secondary air detection means, wherein a diagnostic region is set within a predetermined exhaust pressure range centered on a point slightly below the dead pressure exhaust pressure of the secondary air supply means. Diagnostic region setting means, a diagnosing possibility determining means for deciding whether or not the operating condition of the engine conforms to the diagnosing region, and this diagnosing feasibility determining device determines that the operating condition of the engine conforms to the diagnosing region Occasionally, secondary air is discharged and supplied through the secondary air supply means, and if this secondary air is not detected by the secondary air detection means, it is determined that the supply of secondary air is abnormal 2 A secondary air supply system abnormality determination means is provided.

Further, the diagnostic area setting means is within a predetermined exhaust pressure range in which a predetermined small flow rate of secondary air can flow when the secondary air is discharged from the secondary air supply means in a normal state. The diagnostic area may be set.

Further, the secondary air detecting means is an air-fuel ratio sensor which is located downstream of the exhaust passage connecting portion of the secondary air introducing passage and provided in the middle of the exhaust passage. The air supply system abnormality determination means causes the secondary air to be discharged through the secondary air supply means when the diagnosis possibility determination means determines that the operating condition of the engine matches the diagnosis range, and the air-fuel ratio. If the detection signal from the sensor does not change by a predetermined value or more, it is preferable to determine that the supply of the secondary air is abnormal.

Further, as the secondary air detecting means, based on a detection signal from an air-fuel ratio sensor which is located on the downstream side of the exhaust passage connecting portion of the secondary air introducing passage and provided in the middle of the exhaust passage. The secondary air supply system abnormality determination means uses the air-fuel ratio feedback correction coefficient corrected by the secondary air supply system abnormality determination means when the operation condition of the engine is determined to match the diagnostic range by the diagnostic availability determination means. When the secondary air is discharged through the supply means and the air-fuel ratio feedback correction coefficient does not change by a predetermined value or more, 2
It is desirable to determine that the supply of secondary air is abnormal.

Further, an electric secondary air pump is used as the secondary air supply means, voltage detection means for detecting a voltage value supplied to the secondary air pump is provided, and the diagnostic area setting means is provided with this voltage. More preferably, the diagnostic area is set based on the value.

[0014]

Since the supply amount of the secondary air is determined by the differential pressure between the discharge pressure of the secondary air supply means and the exhaust pressure of the exhaust passage and the flow passage area of the secondary air introducing passage, the exhaust passage increases as the exhaust pressure increases. When the flow rate of the secondary air flowing into the inside decreases and the exhaust pressure rises to a certain value (closed exhaust pressure), the secondary air can no longer be sent into the exhaust passage. In other words, when the discharge pressure of the secondary air supply means decreases or the flow path of the secondary air introduction path narrows, the dead pressure exhaust pressure also decreases accordingly. Further, the exhaust pressure in the exhaust passage is determined by the operating conditions of the engine such as the rotation speed.

According to the first aspect of the invention, the diagnostic region is set within a predetermined exhaust pressure range centered on a point slightly below the dead pressure, and when the operating conditions are met in this diagnostic region. In order to discharge the secondary air from the secondary air supply means and monitor whether or not the secondary air is detected in the exhaust passage, the secondary air cannot be supplied and the secondary air supply capacity is lowered. Even if any of the above occurs, this defect can be reliably detected.

That is, since the flow rate of the secondary air that originally flows into the exhaust passage is small in the vicinity of the cutoff exhaust pressure, carbon or the like adheres to the secondary air introduction passage to narrow the passage, and deterioration due to aged deterioration or the like occurs. When the supply capacity (discharging capacity) of the secondary air supply means decreases, the actual dead pressure is lower than the original normal dead pressure, and secondary air does not flow at all. . Therefore, by setting the diagnostic region in the vicinity of the limit at which the secondary air can flow (in the vicinity of the deadline exhaust pressure), it is possible to detect both the supply failure state and the supply capacity reduction state. Here, "the engine operating conditions match the diagnostic region" means that the exhaust pressure generated by the operating conditions of the engine is within the diagnostic region set within a predetermined exhaust pressure range.

According to the second aspect of the present invention, which further clarifies the diagnosis area, a predetermined small flow rate of the secondary air flows when the secondary air is discharged from the secondary air supply means in the normal state. Since the diagnostic region is set within the predetermined exhaust pressure range to be obtained, the diagnostic region can be set more clearly near the limit at which the secondary air can flow, thereby obtaining the same effect as that of claim 1. You can

Further, according to the structure of claim 3, when the air-fuel ratio sensor is used as the secondary air detecting means and the detection signal from the air-fuel ratio sensor does not change by a predetermined value or more, it is set to 2
Since it is determined that the supply of the secondary air is abnormal, it is possible to more accurately detect the state in which the supply capacity of the secondary air has deteriorated.

In other words, even if the diagnostic region is set near the limit of the secondary air flow near the cutoff discharge pressure, the cutoff discharge pressure at the normal time may fluctuate due to various factors. Even if the air supply capacity is lowered, a small amount of secondary air may be detected in the diagnosis area. However, according to the configuration of claim 3, if the secondary air does not flow to some extent, the detection signal of the air-fuel ratio sensor does not change by a predetermined value or more, and it is determined that the secondary air supply is abnormal. It is possible to more accurately detect the state of ability deterioration. In other words, it is possible to correct the deviation of the diagnostic region due to the variation of the dead pressure, to a certain extent, by the “change of the detection signal by a predetermined value or more”.

Further, the air-fuel ratio feedback correction coefficient is set to 2
According to the configuration of claim 4, when the air-fuel ratio feedback correction coefficient does not change by a predetermined value or more, it is determined that the supply of secondary air is abnormal.
Basically, the same effect as that of claim 3 can be obtained.

Further, according to the structure of claim 5, the electric secondary air pump is used as the secondary air supply means, and the diagnostic region is set based on the voltage value supplied to the secondary air pump. It is possible to accurately predict the change in the discharge capacity due to and set the diagnostic region in the vicinity of the actual dead pressure.

[0022]

Embodiments of the present invention will now be described in detail with reference to FIGS.

First, FIGS. 1 to 6 relate to a first embodiment of the present invention, and FIG. 1 is an explanatory view showing the overall structure of a secondary air supply system for an internal combustion engine according to the present embodiment. A piston 3 is provided in each of the plurality of cylinders 2 arranged in line in the cylinder block 1, and the piston 3 is provided between the cylinder head 4 and the cylinder head 4, which is provided by covering the upper side of the cylinder 2 in a gas-liquid tight manner. It defines the combustion chamber 5. Also, the cylinder head 4
The intake passage 6 and the exhaust passage 7 face each other and are connected to each of the cylinders 2, and the air-fuel mixture in the combustion chamber 5 is ignited and burned at the top thereof by a signal from a control unit 32 described later. A spark plug 8 is provided to allow the spark plug 8 to operate.

The intake passage 6 has a pair of intake ports 6A on its downstream side, which branch into two branches in the cylinder head 4,
The upstream side is connected to the intake collecting passage 9. The exhaust passage 7 has a pair of exhaust ports 7A whose upstream side branches into two in the cylinder head 4 and whose downstream side is connected to a muffler (not shown). Then, these intake passages 6,
The exhaust passage 7 communicates with the inside of the combustion chamber 5 at a predetermined timing via an intake valve 10 and an exhaust valve 11 driven by a valve mechanism (not shown).

A fuel injection valve 12 for injecting fuel into the intake port 6A by opening the valve in response to a fuel injection pulse from the control unit 32 is provided in the middle of the intake passage 6, and the intake collecting passage 9 is provided. An air filter 13 for removing dust in the air, an air flow meter 14 for detecting the intake air amount, and a throttle valve 15 for adjusting the intake air amount are provided in this order from the upstream side.

On the other hand, in the middle of the exhaust passage 7, the first air-fuel ratio sensor 16 as an "air-fuel ratio sensor" for detecting the air-fuel ratio (oxygen concentration) in the exhaust, in order from the upstream side, Catalytic converter 17 that removes HC, CO, NO _x, etc. by redox reaction, exhaust temperature sensor 18 that detects the temperature of exhaust gas, second air-fuel ratio sensor 19 that detects the air-fuel ratio in the exhaust gas after passing through catalytic converter 17. Is provided. Each of the air-fuel ratio sensors 16 and 19 outputs an electromotive force corresponding to the residual oxygen concentration in the exhaust gas as a detection signal to the control unit 32. For example, a zirconia tube type oxygen sensor is used. Each of the air-fuel ratio sensors 16 and 19 suddenly changes its electromotive force stepwise at the stoichiometric air-fuel ratio and generates a reference voltage of about 280 mV at room temperature.

2 are provided between the intake collecting passage 9 and the exhaust passage 7.
A secondary air introducing passage 20 for circulating the secondary air is provided, and the secondary air introducing passage 20 has an inflow port 20A located between the air flow meter 14 and the air filter 13 and is provided in the intake collecting passage 9. Open in the middle, "Exhaust passage connection part"
Is located near the upstream side of the first air-fuel ratio sensor 16 and opens in the middle of the exhaust passage 7. Further, in the middle of the secondary air introduction passage 20, an electric air pump 21 and an air cut valve 22 as “secondary air supply means” are provided.
Are provided.

The air pump 21 pressurizes the air sucked from the intake air collecting passage 9 and discharges it into the secondary air introducing passage 20. As shown in the block diagram of FIG. 2, the air pump 21 is driven by the control unit 32. It is composed of a motor unit 21A that rotates by a signal and a pump unit 21B that is driven by this motor unit 21A, and a silencer (not shown) is provided at its inflow port and discharge port. The air pump 21 resists the exhaust pressure in the exhaust passage 7,
The secondary air is forcibly discharged and supplied into the secondary air introduction passage 20. The pump portion 21B of the air pump 21
For example, various pump parts such as turbine vanes, scrolls, screws, pistons, and rotary pistons can be used. Further, an air tank may be provided on the discharge side of the air pump 21 and the secondary air may be supplied via this air tank. In this case, the number of parts increases and the overall size increases, but the discharge pressure can be raised quickly.

On the other hand, the air cut valve 22 is for forcibly shutting off the flow of the secondary air, and the casing 2
2A, a diaphragm 22D that defines a control pressure chamber 22B located on the upper side in the casing 22A and a secondary air chamber 22C located on the lower side, and a diaphragm 22D located in the secondary air chamber 22C. A valve body 22F that is seated on and off a valve seat 22E that is formed in the middle of the secondary air introduction passage 20, and a valve spring 22G that biases the valve body 22F in a valve closing direction via a diaphragm 22D. It is configured. The air cut valve 22 is operated by the pilot pressure from a solenoid valve 23 for negative pressure control, which will be described later.
By opening and closing F, the secondary air introduction passage 20
It is designed to connect and disconnect the middle of. Therefore, the air cut valve 22 can be understood as, for example, an opening / closing means, and can also be regarded as a secondary air supply means in a broad sense together with the electromagnetic valve 23 and the air pump 21.

The electromagnetic valve 23 is constructed as a spring return type electromagnetic solenoid valve with 3 ports and 2 positions, for example. Further, this solenoid valve 23 has its outflow port 23A.
Is connected to the control pressure chamber 22B of the air cut valve 22 via the pilot conduit 24, and its first inflow port 23B is connected between the air flow meter 14 and the air filter 13 via the first pressure guiding conduit 25. It is connected to the intake collecting passage 9, and the second inflow port 23C is connected to the intake collecting passage 9 on the downstream side of the throttle valve 15 via the second pressure guiding conduit 26. And this solenoid valve 23 is always (when not energized)
When the air cut valve 22 is closed by connecting the outflow port 23A and the first inflow port 23B to introduce atmospheric pressure into the control pressure chamber 22B, the air cut valve 22 is switched by a control signal from the control unit 32. The air cut valve 22 is opened by connecting the outflow port 23A and the second inflow port 23C to introduce a suction negative pressure into the control pressure chamber 22B.

In the secondary air introducing passage 20, a first check valve 27 for preventing backflow from the exhaust passage 7 is provided downstream of the air cut valve 22, and a second guide valve 27 is provided. A second check valve 28 is provided in the pressure line 26.

On the other hand, 29 is a water temperature sensor for detecting the cooling water temperature, 30 is a throttle sensor for detecting the valve opening of the throttle valve 15, and 31 is a crank angle sensor for detecting the engine speed. , These respective sensors 29, 30, 31 are the above-mentioned respective air-fuel ratio sensors 16,
19 and the like are connected to the control unit 32.

The control unit 32 for electrically centrally controlling the engine includes an arithmetic circuit such as a CPU, ROM, RAM.
It is configured as a microcomputer system including a storage circuit such as the above and an input / output circuit.

Then, this control unit 32
As shown in the block diagram of FIG. 2, the battery 3 connected to the motor portion 21A of the air pump 21 via the conductor 33.
Voltage detector 32A as "voltage detecting means" for detecting the voltage V of No. 4 and diagnostic area setting as "diagnostic area setting means" for setting a diagnostic area by a flow rate characteristic map 36 described later based on this detected voltage V. 32B and engine speed N
And engine load T _P (determined by intake air amount Q and rotation speed N)
And a diagnostic possibility determination unit 32C as "diagnostic propriety determination means" that determines whether or not the operating conditions of the engine match the diagnostic range, and when the diagnostic propriety determination unit 32C determines that diagnostic is possible. Is driven by the air pump 21 via the drive unit 32D.
"Secondary air supply system abnormality determination means" for determining whether or not there is an abnormality in the supply of secondary air based on the air-fuel ratio detection signal A / F of the first air-fuel ratio sensor 16
The secondary air supply system abnormality determination unit (hereinafter, referred to as “abnormality determination unit”) 32E is provided as an internal function thereof.

Further, the drive unit 32D excites the coil of the pump relay 35 interposed in the middle of the conductor 33 to close the normally open contact, and supplies the electric current from the battery 34 to the motor unit 21A. The air pump 21 is driven.

Next, the flow rate characteristic map 36 for setting a predetermined diagnostic region will be described with reference to FIG.

In FIG. 3, the horizontal axis indicates the secondary air introduction path 2
The exhaust pressure in the exhaust passage 7 in the vicinity of the outlet port 20B of 0 is taken in the unit of [kilopascal], while the vertical axis indicates the flow rate of the secondary air flowing into the exhaust passage 7 through the secondary air introduction passage 20. The (supply amount) is taken as a unit [liter / minute], and the flow characteristics of the secondary air are shown for each of the voltage values V _{1 to} V ₅ .

Here, for example, the voltage value V ₁ is 8 V, the voltage value V ₂ is 10 V, the voltage value V ₃ is 12 V, and the voltage value V ₄ is 14.
The V and the voltage value V ₅ are 16 V, respectively.
That is, various high current loads such as an air conditioner and a headlamp are connected to the battery 34, and the voltage value of the battery 34 itself gradually decreases due to deterioration over time. Therefore, due to these various factors, the air pump 21 is discharged from the battery 34. There is a possibility that the voltage value V supplied to the power source fluctuates, but if the voltage value V changes, the driving force of the motor unit 21A also changes, so the higher the voltage value V,
The discharge pressure increases, and the dead pressure exhaust pressure P _E shifts to the high pressure side.
Therefore, in the present embodiment, the voltage value V ₁ to
The flow rate characteristic is set and stored for each V ₅ . However, the specific content of the map is not limited to this, for example, 10 to 1
The flow rate characteristic may be set for each 1V in the range of 4V.

As described above, the flow rate of the secondary air depends on the differential pressure between the discharge pressure of the air pump 21 and the exhaust pressure, and the secondary air introducing passage 2.
Since it is determined by the flow passage area of 0, as shown in FIG. 3, if the discharge pressure and the flow passage area are constant, 2
When the flow rate of the secondary air decreases and the exhaust pressure rises to a certain value, the secondary air cannot flow into the exhaust passage 7. That is, when the exhaust pressure reaches the dead pressure exhaust pressures P _{E1 to} P _E5 in FIG. 3, the secondary air is shut off, and when the exhaust pressure rises further, the exhaust gas is introduced into the secondary air. Road 2
There will be a backflow into 0 (but this backflow is blocked by the first check valve 27).

Then, in the vicinity of each dead pressure exhaust pressure P _{E1 to} P _E5 in the flow rate characteristic of each voltage value V _{1 to} V ₅ , a diagnostic region C is provided.
_{1 to} C ₅ are set respectively. More specifically, each of these diagnostic region C ₁ -C _5, rather than the deadline exhaust pressure P _E1 to P _E5 located in front only pressure ΔP _E1 ~ΔP _E5, are set respectively with a predetermined width. That is, they each diagnostic areas C ₁ -C _5, like the secondary air flows in the low flow rate Q _AH to Q _AL serving "secondary air predetermined small flow rate" in the vicinity of the shut-off exhaust pressure P _E1 to P _E5 Is set to. Here, the “point slightly lower than the deadline exhaust pressure” in the present specification means each of the diagnostic regions C _{1 to} C ₅
Will mean the midpoint.

Next, based on FIGS. 4 and 5, the diagnostic area C ₁
The relationship between C ₅ and abnormality diagnosis will be described. FIG.
For easy understanding of the invention, only the flow rate characteristic of the voltage value V ₃ is extracted from each flow rate characteristic line in FIG. 3 and displayed. When the air pump 21 normally exerts its discharge capacity and the flow path of the secondary air introduction passage 20 is not narrowed by carbon or the like, the exhaust pressure P _E is increased as shown by the solid line in FIG. As a result, the flow rate of secondary air decreases,
Diagnostic region C ₃ is set around a point below the deadline exhaust pressure P _E3 slightly, the secondary air of the small flow rate Q _AH to Q _AL flows slightly.

On the other hand, when the discharge capacity of the air pump 21 is decreased or the flow path of the secondary air introduction path 20 is narrowed to decrease the supply capacity of the secondary air, two points are shown in FIG. As indicated by the chain line, the flow rate characteristic is lowered by ΔQ _A as a whole as compared with the flow rate characteristic at the normal time, and only the secondary air having the maximum lower limit small flow rate Q _AL or less flows in the diagnosis region C ₃ (specifically, The secondary air does not flow at the upper limit C _3H of the diagnostic region C _{3 and} the lower limit small flow rate Q _AL of the secondary air flows at the lower limit C _3L ). That is, near the limit of whether or not the secondary air flows,
Not only the state in which the secondary air cannot be supplied, but even the state in which the supply capacity of the secondary air is reduced appears as a significant change in the secondary air flow rate. Therefore, by monitoring the secondary air in the vicinity of the dead pressure exhaust pressure P _E3. The secondary air supply system can be diagnosed more accurately than before.

That is, for example, when the diagnosis is performed at the judgment point R separated from the dead pressure exhaust pressure P _{E3 as} in the conventional secondary air supply device, even if the secondary air supply capacity is lowered, Since the influence of the width of decrease ΔQ _A is relatively small, it is difficult to detect this decrease in the supply capacity unless a highly accurate flow meter is provided in the middle of the secondary air introduction passage 20. . On the other hand, in this embodiment, since the diagnostic region C ₃ having a predetermined width is set near the limit of the flow of the secondary air, even a decrease in the supply capacity can be detected as described above.

Next, the relationship between the detection of secondary air and the abnormality diagnosis will be described with reference to FIG. 5. If an operating condition suitable for the diagnosis region C is satisfied at a certain time T _1, it will be described later with reference to FIG. As described above, the air pump 21 is driven for a predetermined time t ₁ , and the secondary air is sent into the exhaust passage 7. Therefore, before this time T ₁ , if the air-fuel ratio in the exhaust (shown as “A / F” in the figure) is on the rich side, the air-fuel ratio in the exhaust due to the secondary air sent from the normal air pump 21. Moves to the lean side.

On the other hand, when the air pump 21 does not operate or the air cut valve 22 does not open (inability to supply), as indicated by the dotted line in FIG.
Since the secondary air does not flow into the exhaust passage 7, there is no change in the air-fuel ratio in the exhaust.

Although the secondary air is supplied,
If the amount is not sufficient (supply capacity is reduced),
As indicated by the alternate long and short dash line in FIG. 5, the air-fuel ratio slightly changes toward the lean side depending on the insufficient secondary air flow rate. Therefore, if the air-fuel ratio in the exhaust gas detected by the first air-fuel ratio sensor 16 does not change by the predetermined value N _{A / F} or more within the predetermined time t ₁ , it is determined that the secondary air supply system is abnormal. By doing so, it is possible to make a diagnosis including a state in which the supply capacity is lowered.

Next, regarding the diagnostic processing according to this embodiment,
This will be described with reference to the flowchart of FIG.

First, step (abbreviated as "S" in the figure)
In 1, the voltage value V supplied to the motor unit 21A of the air pump 21 is read via the voltage detection unit 32A, and then the diagnostic region setting unit 32B is based on this voltage value V and the flow rate characteristic map 36 shown in FIG. The predetermined diagnostic region C is set by referring to.

Next, in step 2, the engine speed N and the engine load T _P as the engine operating conditions are read through the crank angle sensor 31 and the air flow meter 14 (to be exact, the intake air amount Q and the engine load). The basic injection amount T _P as the engine load is calculated based on the engine speed N). In step 3, the diagnosis propriety determination unit 32C determines whether the current operating condition matches the diagnosis region C set in step 1 above. Whether or not, that is, whether or not the exhaust pressure generated in the exhaust passage 7 according to the current operating conditions is in the diagnostic region C is determined. That is, although not shown in the drawing, the relationship between the operating conditions of the engine and the exhaust pressure generated thereby is obtained in advance by an actual machine test, a simulation, etc. Based on this relationship, the diagnosis propriety determination unit 32C determines that the engine It is determined whether the operating condition is within the diagnostic area C.

When it is judged "NO" in this step 3, the operating condition of the engine is out of the diagnostic range C,
Moving to step 4, the driving of the air pump 21 is stopped, the air cut valve 22 is closed, and the process returns to step 1.
At the time of starting the program, the air pump 21 is not yet driven, so the process of step 4 becomes redundant. However, if the operating condition of the engine deviates from the diagnostic region C by this step 4, Immediately the air pump 21
To stop the supply of useless secondary air.

On the other hand, if "YES" is determined in step 3, it means that the current operating condition of the engine is within the diagnostic range C corresponding to the voltage value V. Therefore, the process proceeds to step 5, The drive state of the air pump 21 is read via the drive unit 32D, and in the next step 6, it is determined whether or not the air pump 21 is being driven. Since the air pump 21 is stopped at the start of the program, it is judged "NO" in this step 6 and moves to step 7. In this step 7, the air pump 21 is driven and the air cut valve 22 is opened. Further, after the air-fuel ratio in the exhaust gas at the time of driving the air pump 21 etc. is stored as an initial value, the process returns to step 1.

As a result, as long as the operating condition of the engine is within the diagnostic range C, the determination at step 6 is "YES". However, during execution of the program, the motor unit 21A
When the voltage value V applied to the engine fluctuates, another diagnostic region C is set in the step 1, so if the engine operating condition is not within the newly set diagnostic region C, In step 3, it is determined to be "NO".

When it is determined to be "YES" in step 6, the process proceeds to step 8, in which the timer is started to wait until the predetermined time t ₁ shown in FIG. 5 elapses. Here, the predetermined time t ₁ is the rising time required for the discharge pressure of the air pump 21 to stabilize, and the secondary air discharged from the air pump 21 actually flows out from the outlet 20B of the secondary air introducing passage 20. Then, it is determined in consideration of a delay time until reaching the vicinity of the first air-fuel ratio sensor 16, and is set to, for example, about 5 seconds. Therefore, this predetermined time t ₁ is, for example, “a short time sufficient to determine the influence (change) that occurs on the air-fuel ratio in the exhaust due to the secondary air sent into the exhaust passage 7”.
Can be defined as, and is not necessarily limited to the time of about 5 seconds described above.

As described with reference to FIG. 5, the diagnostic region C set according to the voltage value V and the operating condition of the engine are matched, and the diagnostic condition is satisfied at time T ₁ , and then a predetermined time t ₁ Is passed, the process proceeds to step 9 by making a “YES” determination in step 8, and in step 9, the current air-fuel ratio in the exhaust gas is read from the first air-fuel ratio sensor 16, and the current value and the step are read. By comparing with the initial value stored in 7, the change amount ΔA / F of the air-fuel ratio caused by the secondary air introduction is calculated.

Then, in step 10, it is judged whether or not the change amount ΔA / F of the air-fuel ratio exceeds a preset predetermined value N _{A / F} shown in FIG. As mentioned above,
When the supply of the secondary air is normally performed, the air-fuel ratio in the exhaust changes by a predetermined value N _{A / F} or more before and after the supply of the secondary air. Therefore, it is determined as “YES” in this step 10. However, when the air pump 21 is out of order or the air cut valve 22 is not open properly (including the malfunction of the solenoid valve 23), the secondary air cannot be supplied and the air in the exhaust air is not supplied. Since the fuel ratio does not change, step 10 determines “NO”.

Further, due to deterioration over time, the air pump 2
The discharge capacity of 1 is reduced, the flow path of the secondary air introduction path 20 is narrowed, foreign matter is caught, and the air cut valve 22
If the valve cannot be opened sufficiently, the secondary air can be supplied, but the amount of supply is low. As a result, as shown in FIG. 4, the secondary air is set near the limit. In the diagnosed region C, the secondary air does not flow into the exhaust passage 7, or the amount of secondary air flowing into the exhaust passage 7 decreases sharply,
Since the air-fuel ratio does not change more than the specified value N _{A / F} , step 1
0 is determined as “NO”.

Therefore, if "YES" is determined in the above step 10, it is determined in step 11 that the supply of the secondary air is normally performed. On the other hand, if "NO" is determined in the above step 10, the process proceeds to step 12 and it is determined that the supply of the secondary air is abnormal, and necessary processing such as outputting an alarm signal or setting a failure flag is performed. I do. Then, in step 13, the air pump 21 is stopped via the drive unit 32D, and the diagnostic program ends.

In this embodiment having such a configuration, the secondary air is supplied under normal operating conditions, such as at the time of starting, by the normal secondary air supply control, and the secondary air is exhausted. The conversion performance of the catalytic converter 17 is maintained by maintaining the air-fuel ratio of the above in the vicinity of the theoretical air-fuel ratio. Further, when the operating condition of the engine enters the diagnostic region C set based on the voltage value V supplied to the air pump 21 (for example, the operating condition is such that the diagnostic region C is reached during one minute after the start). Inside), the above-mentioned self-diagnosis processing is performed.

Thus, the present embodiment constructed as described above has the following effects.

First, a diagnostic region setting section 32B for setting the diagnostic region C within a predetermined exhaust pressure range centered on a point slightly below the dead pressure exhaust pressure P _E of the air pump 21, and this diagnostic region C
When the engine operating condition is determined to match the diagnostic range C by the diagnostic feasibility determining unit 32C and the diagnostic feasibility determining unit 32C,
Secondary air is discharged through the air pump 21, and
When the secondary air is not detected, the abnormality determination unit 32E that determines that the supply of the secondary air is abnormal is provided. Therefore, the discharge capacity of the air pump 21 is reduced, the flow passage area of the secondary air introduction passage 20 is reduced, and the like. Even if the supply capacity of the secondary air is lowered by this, it can be detected simply and surely as an abnormality.

Second, from the normal state air pumps 21 to 2
Since the diagnostic region C is set within a predetermined exhaust pressure range in which the secondary air having a predetermined small flow rate Q _{AL to} Q _AH can flow when the secondary air is discharged, the secondary air can flow near the limit. It is possible to set a diagnostic region in the, and it is possible to reliably detect a state of decrease in supply capacity.

Thirdly, if the detection signal from the first air-fuel ratio sensor 16 does not change by the predetermined value N _{A / F} or more, it is determined that the supply of secondary air is abnormal. Even if the cutoff exhaust pressure in the normal state fluctuates due to a factor and the diagnostic region C is slightly displaced, it is possible to reliably detect the state in which the supply capacity of the secondary air is deteriorated.

Fourthly, since the diagnosis area C is set based on the voltage value V supplied to the air pump 21, it is affected by the voltage fluctuation caused by the evaporation of the electrolytic solution, the operation of the head lamp and the like. Without a diagnosis area C near the deadline exhaust pressure P _E
Can be set, and stable diagnosis can be performed.

Fifth, in the present embodiment, the upper limit Q _AH and the lower limit Q _AH
C _{L to} C _H so that a small flow rate of secondary air flows between it and _AL
Since the diagnosis region C having a width of is set, it is possible to obtain a sufficient opportunity for self-diagnosis and detect an abnormal state. That is, for example, as shown in FIG. 4, the lower limit judgment point C _3L (Q _AH
It is also possible to perform self-diagnosis at any one of the upper limit judgment point C _3H (corresponding to Q _AL ) but the operating condition (exhaust pressure) of the engine changes from moment to moment, so the diagnostic condition is Opportunities are reduced during the period when it is established. On the other hand, in the present embodiment, since the diagnostic region C having the widths C _{L to} C _H corresponding to the small flow rates Q _{AH to} Q _AL is set, the opportunity and period of self-diagnosis are sufficiently obtained, and the abnormal state is detected. It can be reliably detected.

Next, a second embodiment of the present invention will be described with reference to FIGS. In this embodiment, the same components as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted. The feature of this embodiment is that secondary air is detected by using the air-fuel ratio feedback correction coefficient in the air-fuel ratio control.

FIG. 7 is a block diagram of a control unit 41 used in the secondary air supply system for an internal combustion engine according to this embodiment. The control unit 41 of this embodiment is shown in FIG.
Also, the control unit 32 of the first embodiment described above
Similarly to the above, the diagnosis area C is configured based on the flow rate characteristic map 36 and the voltage detection unit 32A configured to detect the applied voltage value V of the air pump 21 as a microcomputer system.
A diagnostic region setting unit 32B, a diagnostic feasibility determining unit 32C that determines whether the operating conditions of the engine match the diagnostic region C, and a drive unit 32D that operates the air pump 21 via the pump relay 35. I have it.

However, the abnormality judging section 41A of this embodiment is
As will be described later, the second embodiment is different from the first embodiment in that secondary air is detected based on the air-fuel ratio feedback correction coefficient α used in the air-fuel ratio control unit 42 and abnormality of the secondary air supply system is determined.

That is, the air-fuel ratio control unit 42 uses the following equation 1
As shown in, the fuel injection amount T _i is corrected by performing pseudo proportional-integral control of the air-fuel ratio feedback correction coefficient α based on the detection signal from the first air-fuel ratio sensor 16,
The air-fuel ratio in the exhaust is made to converge to the target air-fuel ratio.
Here, in the following equation 1, C _OEF represents various correction coefficients, such as the water temperature increase correction coefficient and startup increase correction coefficient, T _S is a reactive voltage component respectively.

[0069]

[Number 1] _{T i = T P × C oef} × α + T S Next, based on FIG. 8, illustrating the relationship between the abnormal state and the air-fuel ratio feedback correction coefficient of the secondary air supply system alpha. Under operating conditions in which the air-fuel ratio feedback correction coefficient α is not clamped, such as during idling when performing air-fuel ratio feedback (idle λ control), the air-fuel ratio feedback correction coefficient α is for rapidly correcting the lean state. The lean side proportional control component P _L , the lean side integral control component I _L for gently correcting the lean state, and the rich side proportional control component P _R for rapidly correcting the rich state.
Based on the detection signal of the air-fuel ratio sensor 16, the average air-fuel ratio is set to the target air-fuel ratio (in FIG. 8) by the pseudo proportional-plus-integral control by the rich side integral control I _R for gently correcting the rich state. It is adjusted so that it converges to the time axis of.

Then, when the operating condition of the engine reaches the diagnostic region C at a certain time T ₂ , as in the above embodiment,
The air pump 21 discharges the secondary air into the exhaust passage 7 for a predetermined time t ₂ . Here, when the secondary air is discharged in a sufficient quantity, the air-fuel ratio in the exhaust gas shifts to the lean side, so the air-fuel ratio feedback correction coefficient α sets the air-fuel ratio in the exhaust gas to the target air-fuel ratio. In order to correct it, the lean side integral control component I
_L becomes longer (increase in integration time) and shifts to the increasing direction (rich side). That is, when the secondary air is normally discharged, the average value of the air-fuel ratio feedback correction coefficient α changes to the rich side during the time t ₂ , as shown by the dotted line in FIG.

On the other hand, in the case where the secondary air cannot be discharged and the supply is impossible, the air-fuel ratio in the exhaust gas does not change before and after the time T ₂ , so that the air-fuel ratio feedback correction coefficient α also changes. Absent. In addition, although the secondary air is discharged, if the supply capacity is reduced in an insufficient amount, as indicated by the alternate long and short dash line in FIG. However, the average value of the air-fuel ratio feedback correction coefficient α changes to the rich side.

Therefore, if a predetermined value N _α is set between the average value of α in the normal state shown by the dotted line and the average value of α in the case where the supply capacity decreases shown by the alternate long and short dash line, the empty space before and after the introduction of the secondary air is set. Change in fuel ratio feedback correction coefficient α Δ
When α does not exceed the predetermined value N _α , it can be determined that the secondary air supply system is abnormal. A moving average, for example, is used as the average value of the air-fuel ratio feedback correction coefficient α.

Next, the diagnosis processing according to this embodiment will be described with reference to the flow chart shown in FIG.

First, in steps 21 to 26, the same processing as steps 1 to 6 described in FIG. 6 is performed. In step 21, the flow rate characteristic map 36 is based on the voltage value V.
The diagnostic region C is set from the above, the rotational speed N and the basic injection amount T _P are read as the operating condition of the engine in step 22, and it is determined in step 23 whether the operating condition of the engine conforms to the diagnostic region C. . Then, in this step 23, "N
If “O” is determined, the air pump 21
To prevent unnecessary discharge of secondary air,
When it is determined to be “YES” in step 23, the process proceeds to step 25 to read the driving state of the air pump 21,
In the following step 26, it is monitored whether or not the air pump 21 is being driven.

If "NO" is determined in this step 26, the process proceeds to step 27, the air pump 21 is driven, and the air-fuel ratio feedback correction coefficient α at this time is driven.
The average value of is stored as an initial value. On the other hand, when it is determined to be “YES” in step 26, the predetermined time t ₂ is waited for in step 28, and when the predetermined time t ₂ is elapsed, in step 29, the air-fuel ratio before and after the introduction of the secondary air is increased. A change amount Δα in the average value of the feedback correction coefficient α is calculated, and in step 30, the change amount Δα is calculated to be a predetermined value N.
It is determined whether _α is exceeded.

As described above with reference to FIG. 8, if the discharge of the secondary air is normal, the air-fuel ratio feedback correction coefficient α changes by a predetermined value N _α or more, so step 30 is “YES”.
To determine. On the other hand, if the supply failure state in which the secondary air is not supplied occurs, the air-fuel ratio feedback correction coefficient α does not change before and after the introduction of the secondary air.
0 is determined as “NO”. Further, when the supply capacity lowering state in which the amount of the secondary air is insufficient occurs, the air-fuel ratio feedback correction coefficient α slightly changes, but the predetermined value N
_Since it does not reach _α , step 30 determines “NO”.

Therefore, when the determination in step 30 is "YES", the process proceeds to step 31 and it is determined that the supply of the secondary air is normal, while step 30 is "NO".
If it is determined that it is determined that the supply of the secondary air is abnormal, necessary processing such as turning on the warning lamp is performed. Then, finally, in step 33, the air pump 21 is stopped and the diagnosis process is ended.

Also in this embodiment having such a configuration, the same effect as that of the above-mentioned first embodiment can be obtained.

In each of the above embodiments, the case where the air cut valve 22 which operates by the suction negative pressure from the solenoid valve 23 is used has been described as an example, but the present invention is not limited to this and, for example, a modification shown in FIG. As in the example, the air cut valve 51 may be an electromagnetic solenoid valve and may be directly operated by a control signal from the control unit 32.

In each of the above embodiments, the air pump 21
The case where the diagnostic regions C having substantially the same width are set for each of the voltage values V is exemplified, but the present invention is not limited to this, and the diagnostic regions C having different widths may be set for each voltage value V. P _E
The distance ΔP _E from the distance may be set independently.

Further, the range of the small flow rates Q _{AH to} Q _AL for determining the diagnostic region C is determined, for example, by changing the set positions of the small flow rates Q _{AH to} Q _AL based on the detection signal of the raindrop sensor.
It may be variably adjusted based on one or a plurality of parameters that affect the secondary air flow rate such as relative humidity.

Further, in each of the above-described embodiments, an example is given in which an abnormality determination is made without making a distinction between the state where the secondary air cannot be supplied and the state where the supply capacity of the secondary air has deteriorated. It is also possible to distinguish the state from the state in which the supply capacity is lowered and output a warning lamp or a message corresponding to each state. For example, as described in each example, was determined to be abnormal by the deadline exhaust pressure P _E near the diagnostic region C is further deadline exhaust pressure P again secondary air at decision point R shown in distant 4 in _E It is possible to distinguish between the two by determining that the supply capability is in a non-supply state when the determination point R is abnormal, and the supply capacity is in a reduced state when the determination point R is normal. is there.

Further, in each of the above-mentioned embodiments, the exhaust pressure in the exhaust passage 7 is predicted based on the operating conditions of the engine, so that the secondary air supply system can be diagnosed with a simple structure without increasing the manufacturing cost. However, in place of this, a semiconductor type pressure sensor may be provided in the middle of the exhaust passage 7 to detect the exhaust pressure. In this case, although the structure is complicated by the pressure sensor and the manufacturing cost is increased, more accurate diagnosis can be performed.

Since a person skilled in the art can add or delete processing steps, etc., the present invention
The present invention is not limited to each of the above-described embodiments, but is determined only by the scope of the claims.

[0085]

As described in detail above, according to the secondary air supply system for an internal combustion engine according to the present invention, a diagnostic region is set around a point slightly below the deadline exhaust pressure, and operating conditions are set in this diagnostic region. If it is suitable, the secondary air is discharged from the secondary air supply means and it is monitored whether or not the secondary air is detected in the exhaust passage. It is possible to easily detect a state in which the supply capacity of the secondary air is deteriorated.

In addition, the secondary air supply means in the normal state is replaced by 2
The limit of the secondary air flow more clearly in the configuration of claim 2, wherein the diagnostic region is set within a predetermined exhaust pressure range in which the secondary air of a predetermined small flow rate can flow when the secondary air is discharged. A diagnostic region can be set in the vicinity, and the same effect as that of claim 1 can be obtained.

Further, the air-fuel ratio sensor is used as the secondary air detecting means, and when the detection signal from the air-fuel ratio sensor does not change by a predetermined value or more, it is determined that the supply of the secondary air is abnormal. With the above configuration, it is possible to more accurately detect the state in which the supply capacity of the secondary air is reduced by avoiding the influence of the variation in the dead pressure.

Further, the air-fuel ratio feedback correction coefficient is set to 2
When the air-fuel ratio feedback correction coefficient does not change by a predetermined value or more and is used as the secondary air detecting means, it is determined that the supply of secondary air is abnormal. The effect of can be obtained.

Further, in the configuration of claim 5, the electric secondary air pump is used as the secondary air supply means, and the diagnostic region is set based on the voltage value supplied to the secondary air pump. Accurately predict changes in ability,
It is possible to set a diagnostic area near the actual dead pressure.
The abnormality of the secondary air supply system can be diagnosed more accurately.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view showing an overall configuration of a secondary air supply system for an internal combustion engine according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a control unit shown in FIG.

FIG. 3 is a characteristic diagram showing a configuration of a flow rate characteristic map.

FIG. 4 is a characteristic diagram showing a part extracted from the flow rate characteristic map in FIG.

FIG. 5 is a characteristic diagram showing the relationship between the supply of secondary air and the change in the air-fuel ratio in the exhaust gas.

FIG. 6 is a flowchart showing a self-diagnosis process of a secondary air supply system.

FIG. 7 is a structural explanatory view showing an overall structure of a secondary air supply system for an internal combustion engine according to a second embodiment of the present invention.

FIG. 8 is a characteristic diagram showing the relationship between the supply of secondary air and the average value change of the air-fuel ratio feedback correction coefficient.

FIG. 9 is a flowchart showing a self-diagnosis process of the secondary air supply system.

FIG. 10 is a structural explanatory view of a secondary air supply device for an internal combustion engine according to a modified example of the present invention.

[Explanation of symbols]

7 ... Exhaust passage 16 ... 1st air-fuel ratio sensor (air-fuel ratio detection means) 20 ... Secondary air introduction path 21 ... Air pump (secondary air supply means) 32, 41 ... Control unit 32A ... Voltage detection part (voltage detection means) ) 32B ... Diagnosis area setting section (diagnosis area setting means) 32C ... Diagnosis possibility setting section (diagnosis possibility setting means) 32E, 41A ... Abnormality determination section (secondary air supply system abnormality determination means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location F02D 41/22 301 F02D 41/22 301Z 45/00 368 45/00 368G 376 376H

Claims (5)

[Claims] 1. A secondary air supply means for discharging and supplying secondary air in the middle of an exhaust passage via a secondary air introduction path, and a secondary air detection means for detecting secondary air in exhaust gas. A secondary air supply device for an internal combustion engine, comprising: diagnostic region setting means for setting a diagnostic region within a predetermined exhaust pressure range centered at a point slightly below the dead pressure of the secondary air supply means; Diagnosis possibility determining means for determining whether or not the operating condition conforms to the diagnosis area, and the secondary air supply means when the operation condition of the engine is determined to conform to the diagnosis area by the diagnosis possibility determining means. Secondary air supply system abnormality determining means for determining that the supply of secondary air is abnormal when the secondary air is discharged and supplied via the air conditioner and the secondary air detecting means does not detect the secondary air. Secondary of internal combustion engine characterized by the provision of Air supply apparatus. 2. The diagnostic region setting means is within a predetermined exhaust pressure range in which a predetermined small flow rate of secondary air can flow when the secondary air is discharged from the secondary air supply means in a normal state. The secondary air supply device for an internal combustion engine according to claim 1, wherein a diagnostic region is set. 3. An air-fuel ratio sensor provided in the middle of the exhaust passage, which is located downstream of the exhaust passage connecting portion of the secondary air introducing passage, is used as the secondary air detecting means. The air supply system abnormality determination means, when the diagnosis availability determination means determines that the operating condition of the engine matches the diagnosis range, the air supply system abnormality determination means 2 is operated via the secondary air supply means.
The secondary air is discharged, and when the detection signal from the air-fuel ratio sensor does not change by a predetermined value or more, it is determined that the supply of the secondary air is abnormal. Secondary air supply device for internal combustion engine. 4. The secondary air detecting means is based on a detection signal from an air-fuel ratio sensor provided on the downstream side of an exhaust passage connecting portion of the secondary air introducing passage and provided in the middle of the exhaust passage. The secondary air supply system abnormality determining means uses the air-fuel ratio feedback correction coefficient corrected by 2 via supply means
The internal combustion engine according to claim 1 or 2, wherein secondary air is determined to be abnormal when secondary air is discharged and the air-fuel ratio feedback correction coefficient does not change by a predetermined value or more. Secondary air supply for the engine. 5. An electric secondary air pump is used as the secondary air supply means, voltage detection means for detecting a voltage value supplied to the secondary air pump is provided, and the diagnostic area setting means uses this voltage. The secondary air supply system for an internal combustion engine according to any one of claims 1 to 4, wherein the diagnostic region is set based on the value.