JPH05288046A - Secondary air supply device for internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce the operation noise of an air pump when the self-diagnosis function of a secondary air supply device is actuated. CONSTITUTION:The self-diagnosis process routine of an ECU 70 is at first to shift air-fuel ratio on the lean side, by increasing a fuel injection quantity by 4%. Thereafter, the impressed voltage VP on an air pump 54 based on a suction air quantity 83 is computed by the use of a map. The impressed voltage VP is necessary for discharging a target secondary air quantity (a secondary air quantity to make excess air ratio 1.06) to realize air-fuel ratio of nearly minimum value for outputting stable lean judgement voltage from an oxygen concentration sensor 85 by means of the air pump 54, and air of the target secondary air quantity is supplied, by driving the air pump 54 at the impressed voltage VP. Thereafter, it is judged whether the air-fuel ratio is shifted from the rich side to the lean side by receiving supply of secondary air or not, and if it is not shifted to the lean side, a secondary air supply device 50 is judged to be abnormal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary air supply device for an internal combustion engine having a function of self-diagnosing abnormality of a secondary air supply system.

[0002]

2. Description of the Related Art Generally, an internal combustion engine is known to include a secondary air supply device for sending secondary air to an exhaust system for the purpose of purifying HC and CO among exhaust gas components by an oxidation reaction. (For example, Japanese Utility Model Laid-Open No. 3-87912). Some of such secondary air supply devices have a self-diagnosis function of detecting an abnormality related to the secondary air supply system such as clogging of an air cleaner and sticking of reed valve due to condensed water.

This self-diagnosis function temporarily supplies the secondary air when the secondary air is not supplied, and determines whether or not there is an abnormality based on the output value of the oxygen concentration sensor provided in the exhaust system. To do. That is, when secondary air is supplied to the exhaust system, the excess air ratio of the exhaust system increases, so the oxygen concentration sensor should output an output value indicating that the air-fuel ratio shifts from the stoichiometric air-fuel ratio to the lean side. However, if an abnormality is found in the secondary air supply system, the secondary air is not sufficiently supplied and the oxygen concentration sensor outputs an output value indicating that the air-fuel ratio shifts to the lean side. Therefore, the abnormality of the secondary air supply system is judged from the output value of the oxygen concentration sensor.

[0004]

By the way, in the secondary air supply system, usually, the specific operation in which the air-fuel ratio feedback system for controlling the fuel injection amount to the internal combustion engine based on the output value of the oxygen concentration sensor is not operating. In the state, for example,
Since the secondary air is sent during warm-up after the engine is started, the rotation speed of the drive motor is relatively high so that the air pump as the secondary air discharge source can sufficiently discharge the air even during cold weather. The high rotation type is used. For this reason, the operating noise of the air pump becomes considerably large.

Even if the drive motor of the air pump rotates at a high speed, during the specific operation in which the secondary air supply device operates,
Since the engine is running at high speed, it is hidden by the engine noise and the operating noise of the air pump is not particularly noticeable.On the other hand, the self-diagnosis function is activated to detect an abnormality in the secondary air supply system. In this case, there is a problem that the operation noise of the air pump is worrisome because the engine is not in the specific operation but in the steady state in which the engine operates stably. In particular, when the self-diagnosis function is activated when the engine is running at a low engine speed such as during idling, the operating noise of the air pump becomes even more disturbing.

A secondary air supply system for an internal combustion engine according to the present invention is
The present invention has been made in view of these problems, and aims to reduce the operating noise of the air pump when the self-diagnosis function is activated.

[0007]

In order to achieve such an object, the following constitution was adopted as a means for solving the above problems.

That is, the secondary air supply system for an internal combustion engine of the present invention is provided in the exhaust passage M2 of the internal combustion engine M1 as shown in FIG. 1, and detects the air-fuel ratio from the oxygen concentration in the exhaust gas. The detection means M3 and the air-fuel ratio detection means M so that the air-fuel ratio of the internal combustion engine M1 becomes a predetermined target air-fuel ratio.
Feedback control means M4 for feedback-controlling the amount of fuel supplied to the internal combustion engine M1 based on the air-fuel ratio detected by the internal combustion engine M1 and the internal combustion engine M1 using the air pump M5 when the internal combustion engine M1 is in a predetermined operating state. Secondary air supply means M6 for supplying secondary air into the exhaust passage of
In the secondary air supply device for an internal combustion engine, the exhaust air is exhausted by forcibly operating the secondary air supply means M6 when the secondary air is not supplied by the secondary air supply means M6. Forced control means M7 for temporarily supplying secondary air into the passage M2, and the forced control means M7.
When the secondary air is supplied by the air-fuel ratio detecting means M3
It is determined whether or not the detection result of the shift to the lean side is detected, and when it is determined that the shift does not shift to the lean side, the diagnosis means M for performing a diagnosis that the secondary air supply means M6 is in an abnormal state
8, and the forced control means M7 predetermines a target secondary air amount for realizing an air-fuel ratio at or near the minimum at which the air-fuel ratio detection means M3 stably outputs the lean side detection result, Based on an air pump control amount calculation unit M71 that calculates a control amount such as a drive voltage that determines the rotation speed of the air pump M5 according to the target secondary air amount, and a control amount calculated by the air pump control amount calculation unit M71. The gist is to include an air pump rotation speed control unit M72 that controls the rotation speed of the air pump M5.

[0009]

In the secondary air supply system for an internal combustion engine of the present invention configured as described above, when the secondary air is not supplied by the secondary air supply means M6, the secondary air supply means by the forced control means M7. By forcibly operating M6, secondary air is temporarily supplied into the exhaust passage M2, and at that time, the diagnosis means M8 determines whether the detection result of the air-fuel ratio detection means M3 shifts to the lean side. By determining whether or not the secondary air supply means M6 is in an abnormal state, a diagnosis is made.

When the secondary air supply means M6 is forcibly operated by the forced control means M7, the secondary air supply means M
The target secondary air that realizes an air-fuel ratio at or near the minimum at which the air-fuel ratio detecting means M3 stably outputs the lean side detection result of the control amount such as the drive voltage that determines the rotation speed of the air pump M5 provided in the air conditioner 6. The air pump control amount calculation unit M71 calculates the amount in accordance with the amount, and the air pump rotation speed control unit M72 controls the rotation speed of the air pump M5 based on the control amount.

Therefore, the secondary air supply means M6 is required to supply a secondary air quantity (target secondary air quantity) which is smaller than the conventional one and which is a minimum or sufficient flow rate necessary for operating the diagnosis means M8. Then, the rotation speed of the air pump M5 that discharges the target secondary air amount is suppressed to the necessary and sufficient minimum rotation speed.

[0012]

Preferred embodiments of the present invention will be described below in order to further clarify the constitution and operation of the present invention described above. FIG. 2 is a schematic configuration diagram showing an automobile engine equipped with a control device according to an embodiment of the present invention and peripheral devices thereof.

As shown in FIG. 1, in the intake passage 2 of the engine 1, from the intake air intake port to the air cleaner 3,
Throttle valve 5, surge tank 6 for suppressing intake air pulsation, and fuel injection valve 7 for supplying fuel to engine 1.
Is provided. The intake air taken in through the intake passage 2 is mixed with the fuel injected from the fuel injection valve 7 and taken into the combustion chamber 11 of the engine 1. The fuel-air mixture is spark-ignited by the spark plug 12 in the combustion chamber 11 to drive the engine 1. The gas (exhaust gas) burned in the combustion chamber 11 is guided to the catalyst device 16 via the exhaust passage 15, is purified, and is then discharged to the atmosphere side.

A high voltage from an igniter 22 is applied to the spark plug 12 via a distributor 21,
The ignition timing is determined by this application timing. The distributor 21 is for distributing the high voltage generated by the igniter 22 to the ignition plugs 12 of the respective cylinders. The distributor 21 outputs a rotation speed sensor 23 that outputs a pulse signal of 24 times per revolution. Is provided.

A bypass passage 31 is formed in the intake passage 2 of the engine 1 so as to bypass the intake passage portion where the throttle valve 5 is provided. The bypass passage 31 has an idle speed control valve ( Hereinafter, this is referred to as ISCV) 32 is provided. IS
The CV 32 has a valve body whose valve opening degree is controlled by a solenoid, and controls the air flow rate by outputting to the solenoid a duty signal having a duty ratio corresponding to the time ratio of closing and opening the valve body. Thus ISCV3
By controlling 2, the idling speed is controlled to the target speed.

The exhaust passage 15 of the engine 1 is provided with an EGR 40 for returning exhaust gas to the intake passage 2. E
The GR 40 communicates the exhaust passage 15 and the intake passage 2 with an exhaust gas recirculation passage 41, and an EGR cooler 43 and an EGR valve (hereinafter referred to as EGRV) 44 in the middle of the exhaust gas recirculation passage 41.
And is provided. The EGR cooler 43 is for reducing the temperature of the exhaust gas flowing through the exhaust gas recirculation passage 41. The EGRV 44 has a structure in which the rotor 44a of the step motor rotates in response to a command signal from the outside (an electronic control unit described later), the lift amount of the valve element 44b changes, and the valve opening degree changes. .. Therefore, EG
By controlling the valve opening degree of the RV 44, the passage flow rate of the exhaust gas recirculated through the EGR cooler 43 is controlled, and thereby the exhaust gas recirculation amount to the intake passage 2 is controlled.

Further, the exhaust passage 15 is provided with a secondary air supply device 50 for supplying intake air to the exhaust passage.
The secondary air supply device 50 includes an air cleaner 3 and an exhaust passage 1.
A secondary air supply path 51 that connects with 5 is provided. The secondary air supply passage 51 is provided with pipes 52, in order from the air cleaner 3 side.
Silencer 53, air pump 54, silencer 55, air switching valve (hereinafter referred to as ASV) 56, check valve 57, and air injection pipe 58.
It has a structure that is connected.

The ASV 56 is of a negative pressure type which operates by introducing a negative pressure of the surge tank 6, and a throttle is provided in a control passage 59 via a vacuum switching valve (hereinafter referred to as VSV) 60. It is connected to the port 61 near the valve. The VSV 60 is opened / closed in response to a command signal from the outside (electronic control unit described later) to open / shut off intake air from the port 61 to the ASV 56 side. Therefore, when the VSV 60 is opened, the negative pressure of the surge tank 6 is applied to the ASV 56, and the ASV 56 is opened. On the other hand, when the VSV 60 is closed, the ASV 56 is closed. In this way, the secondary air supply passage 5 between the air cleaner 3 and the exhaust passage 15 is provided.
1 is opened and closed to control the execution and suspension of the supply of secondary air.

The air is sent to the secondary air supply passage 51 by an air pump 54. Air pump 54
Is driven by receiving a high voltage from an electronic control unit (hereinafter referred to as an ECU) 70, and the ECU 70 and the applied voltage input terminal of the air pump 54 are connected via a relay 71 and a resistor 72. .. Specifically, relay 71
Is composed of a relay coil 71a and a relay switch 71b, and the contact a of the relay switch 71b is the air pump 5
4, the contact b is an empty contact, the relay coil 71a has one end connected to the ECU 70, and the other end connected to the applied voltage input terminal of the air pump 54 via the resistor 72. ..

When a drive request for the air pump 54 is made, the ECU
A relatively large current flows from 70 to the relay coil 71a to connect the relay switch 71b to the contact a. As a result, both ends of the resistor 72 are short-circuited, so that the resistor 7
There is no voltage drop due to 2, and a high voltage is applied from the ECU 70 to the air pump 54 via the relay 71. The high voltage applied to the air pump 54 is, as described above,
The voltage applied from the CU 70 is
It is variably controlled by 70. As a result, the rotation speed of the drive motor of the air pump 54 is controlled, and the air pump 5
The discharge amount of air from 4 is controlled.

Further, the engine 1 detects not only the rotational speed sensor 23 described above but also the opening degree of the throttle valve 5 and the fully closed state of the throttle valve 5 as a sensor for detecting its operating state. A throttle position sensor 81 having a built-in idle switch 80 (FIG. 3), an intake air temperature sensor 82 arranged in the intake passage 2 for detecting the temperature of intake air (intake air), an air flow meter 83 for detecting the amount of intake air, and a cylinder block. A water temperature sensor 84 for detecting the cooling water temperature, and an oxygen concentration sensor 8 for detecting the oxygen concentration in the exhaust gas provided in the exhaust passage 15.
5 and a vehicle speed sensor 86 for detecting the speed V of the vehicle.

The detection signal of each sensor described above is sent to the ECU 70.
Entered in. As shown in FIG. 3, the ECU 70 is configured as a logical operation circuit centered on a microcomputer. More specifically, the ECU 70 includes a CPU 70a and a CPU 70a that execute various kinds of arithmetic processing for controlling the engine 1 according to a preset control program. A ROM 70b in which control programs and control data necessary for executing various arithmetic processes are stored in advance, a RAM 70c in which various data necessary for executing various arithmetic processes by the CPU 70a are temporarily read and written, and the above sensors A / D converter 70d and input processing circuit 70 for inputting the detection signal from
e, the igniter 2 according to the calculation result in the CPU 70a
2, fuel injection valve 7, ISCV32, EGRV44, VS
An output processing circuit 70f for outputting a drive signal to the V60, the relay 71, etc. is provided. Further, the ECU 70 includes a power supply circuit 70g connected to the battery 88, and is capable of applying a high voltage from the output processing circuit 70f.

With the ECU 70 thus constructed,
The igniter 22, the fuel injection valve 7, the ISCV 32, the EGRV 44, the VSV 60, and the relay 71 are drive-controlled according to the operating state of the engine 1, and fuel injection control, ignition timing control, ISC control, EGR control, secondary air supply control are performed. And so on.

Next, the fuel injection control processing routine executed by the CPU 70a of the ECU 70 will be described with reference to FIG. It should be noted that this control processing routine is executed every predetermined crank angle, for example, every 360 ° CA. C
When the process is started, the PU 70a first executes a process of reading the intake air amount Q detected by the air flow meter 83 and A / D converted by the A / D converter 70d from the RAM 70c (step 100). Next, a process of reading the rotation speed Ne detected by the rotation speed sensor 23 is executed (step 110).

Then, the basic fuel injection amount TP is calculated according to the following equation (1) using the intake air amount Q and the rotation speed Ne read in steps 100 and 110 (step 120). TP ← k · Q / Ne (where k is a constant) (1)

Next, the actual fuel injection amount TAU is calculated by multiplying the basic fuel injection amount TP by various correction coefficients so as to comply with the following equation (2) (step 130). TAU ← TP · FAF · FWL · FDG · α · β (2) Here, FAF is an air-fuel ratio correction coefficient, which is calculated by an air-fuel ratio feedback control processing routine described later. FWL is a warm-up increase correction coefficient, and the cooling water temperature TH
It takes a value of 1.0 or more while W is 60 ° C. or less. FDG
Is a self-diagnosis increase correction coefficient relating to the secondary supply device, and is calculated by a secondary air supply device self-diagnosis processing routine described later. α and β are other correction factors,
For example, correction coefficients relating to intake air temperature correction, transient correction, power supply voltage correction, etc. are applicable.

When the actual fuel injection amount TAU is calculated in step 130, the fuel injection time corresponding to the actual fuel injection amount TAU is subsequently set in a counter (not shown) that determines the valve opening time of the fuel injection valve 7 ( Step 140). As a result, the fuel injection valve 7 is driven to open for the valve opening time set in the counter.

Next, an air-fuel ratio feedback (hereinafter referred to as F / B) control processing routine executed by the CPU 70a of the ECU 70 will be described with reference to FIG. Note that this processing routine is executed every predetermined time. When the process is started, the CPU 70a first sets a flag XAI related to the secondary air supply (set by a secondary air supply control process routine described later).
A process for determining whether or not to perform the air-fuel ratio F / B control is executed based on (step 200). The value 0 of the flag XAI indicates that the secondary air is in the non-supply state, the value 1 of the flag XAI indicates that the secondary air is in the supply state, and the flag XAI is set to the value in step 200. If it is determined to be 0, the process proceeds to step 205.

In step 205, whether the air-fuel ratio F / B control is performed based on the flag XDG (set in the secondary air supply device self-diagnosis processing routine described later) involved in the self-diagnosis of the secondary air supply device. The process of determining whether or not to execute is executed. A value of 0 for the flag XDG indicates that the self-diagnosis function of the secondary air supply device 50 is not operating, and a value of 1 for the flag XDG is that the self-diagnosis function of the secondary air supply device 50 is operating. That is, step 205
When it is determined that the flag XDG is 0, the process proceeds to step 220, and the air-fuel ratio F / B control process is executed.

When it is determined in step 200 that the flag XAI is not 0, or when it is determined in step 205 that the flag XDG is not 0, the air-fuel ratio F / B control process is not executed and A value 1 is set to the fuel ratio correction coefficient FAF (step 210).

In step 220, it is judged whether or not the F / B condition of the air-fuel ratio is satisfied. The F / B condition mentioned here corresponds to, for example, a post-warming state in which the cooling water temperature THW is equal to or higher than a predetermined value. When it is determined in step 220 that the F / B condition is not satisfied, the above-mentioned flag XA
As when I is 1 or the flag XDG is 1,
The process proceeds to step 210 without executing the air-fuel ratio F / B control.
Proceed to. On the other hand, if it is determined in step 220 that the F / B condition is satisfied, then it is determined from the detection signal of the oxygen concentration sensor 85 whether or not the air-fuel ratio is lean (step 230).

Here, if it is determined that the air-fuel ratio is in the lean state, then whether or not the lean state is the first lean state after the transition from the rich state, that is, whether or not it is the change point from rich to lean. Is determined (step 240). When it is determined in step 240 that the engine is in the first lean state, the air-fuel ratio correction coefficient FAF is set to a predetermined amount (skip amount) A.
(A> 0) is added (step 250). On the other hand, when it is determined that the initial lean state is not achieved, the air-fuel ratio correction coefficient FA
A predetermined amount a (a> 0) is added to F (step 26)
0). The skip amount A is set to be sufficiently larger than the predetermined amount a.

If it is determined in step 230 that the air-fuel ratio is not lean but rich, then whether the rich is the first rich that has transitioned from lean, that is, change from lean to rich. It is determined whether it is a dot (step 270). When it is determined in step 270 that it is the first rich state, a predetermined amount (skip amount) B (B> 0) is subtracted from the air-fuel ratio correction coefficient FAF (step 280), while it is determined that it is not the first rich state. Then, the predetermined amount b (b> 0) is subtracted from the air-fuel ratio correction coefficient FAF (step 290). The skip amount B is set to be sufficiently larger than the predetermined amount b.

Here, the control shown in steps 260 and 290 is called integral control, and step 25
The control indicated by 0 and 280 is called skip control. By both controls, the air-fuel ratio will be balanced before and after the stoichiometric air-fuel ratio. Steps 210 and 25
After executing 0, 260, 280, or 290, the process proceeds to step 295, and the calculated air-fuel ratio correction coefficient FA
F is stored in the RAM 70c. After that, the process exits to "return" and the present routine is ended.

Next, the secondary air supply control processing routine executed by the CPU 70a of the ECU 70 will be described with reference to FIG.
It will be explained based on. Note that this processing routine is executed every predetermined time. When the process is started, the CPU 70a first determines whether or not the current operating state satisfies the secondary air supply condition. The secondary air supply conditions mentioned here are the following conditions. The cooling water temperature THW is 50 [° C] or higher and the throttle is other than full load, that is, the engine is warming up. The idle switch is on and the vehicle speed V is 4 [k].
m] or more

When the above condition or is satisfied,
Since the secondary air supply condition is satisfied, step 3
An affirmative decision is made at 00, and the processing advances to step 310. In step 310, the flag XAI is set to a value of 1, then a high voltage (for example, 14V) is applied to the air pump 54 to drive the air pump 54 (step 320), and the VSV 60 is opened (step 330). .. As a result, when the VSV 60 is opened, the negative pressure of the surge tank 6 is applied to the ASV 56, the ASV 56 is opened, and the secondary air is supplied by the air pump 54.

On the other hand, when the above conditions and are not satisfied, the secondary air supply condition is not satisfied,
A negative determination is made in step 300, and the processing is step 340.
Proceed to. In step 340, the value X is set to the flag XAI, and then the air pump is stopped (step 35
0) and then the VSV 60 is closed (step 36).
0). As a result, the ASV 56 is closed and the supply of secondary air is stopped. After execution of step 330 or 360, the process exits to "return", and this routine is once ended.

Next, the secondary air supply device self-diagnosis processing routine executed by the CPU 70a of the ECU 70 will be described with reference to FIG. It should be noted that this processing routine shows a flow of processing for self-diagnosis of abnormality of the secondary air supply device 50, and is executed every predetermined time. CPU7
When the process is started, 0a first executes a process of initializing various variables used in the subsequent steps (step 400). Specifically, the timer counter T and the flag X
The DG and the diagnosis result flag FLGDG are cleared to zero, and the self-diagnosis increase correction coefficient FDG is set to the value 1.

Then, it is determined whether or not the current operating condition satisfies the condition for self-diagnosis (step 41).
0). The self-diagnosis condition mentioned here means a condition that the engine 1 is in a stable operating state after warming up and the vehicle is in a stopped state, and specifically, the following conditions 1 to 4 are all satisfied. Cooling water temperature THW is 70 [° C.] or higher. Engine rotation speed Ne is 600 to 700 [r. p.
m]] The air-fuel ratio feedback control is operating. The idle switch is on. The vehicle speed V is 2 [km] or more.

When all of the above conditions are satisfied, the self-diagnosis condition is satisfied, and therefore step 4
An affirmative decision is made in 10, and the processing advances to Step 420. In step 420, it is determined whether the timer counter T is smaller than a value corresponding to 7 [seconds]. Here, if it is determined that the timer counter T has not passed 7 [seconds], then the timer counter T is incremented by 1 (step 430), and the flag XDG indicating that self-diagnosis has started is set. Set value 1 (step 44)
0). When the value 1 is set in the flag XDG, a negative determination is made in step 205 in the above-mentioned air-fuel ratio F / B control processing routine, and the air-fuel ratio F / B control processing is suspended. .. Then, the value 1.04 is set to the above-mentioned self-diagnosis increase correction coefficient FDG to increase the fuel injection amount TAU by 4 [%] (step 450). When the fuel injection amount TAU is increased in this way, the air-fuel ratio is always shifted to the rich state regardless of the air-fuel ratio before the fuel increase.

After execution of step 450, it is determined whether the timer counter T is smaller than a value corresponding to 2 [seconds]. Here, if it is determined that the timer counter T has not passed 2 [seconds], the process returns to step 410, and the processes of steps 410 to 460 are repeatedly executed.

When the timer counter T has passed 2 [seconds] and a negative determination is made in step 460, it is considered that the air-fuel ratio has sufficiently shifted to a stable state after the fuel injection amount TAU has been increased by 4 [%]. The process proceeds to step 470. In step 470, A /
Intake air amount Q A / D converted by the D converter 70d
Is executed from the RAM 70c, and then,
The map A stored in advance in the ROM 70b of the ECU 70 is used to calculate the applied voltage VP of the air pump 54 based on the intake air amount Q (step 480).

The map A stored in the ROM 70b defines the relationship between the intake air amount Q and the applied voltage VP of the air pump 54, as shown in FIG. By comparing them, the air pump 54
Applied voltage VP (0 to 14 [V]) can be obtained.

How the map A shown in FIG. 8 was created will be described below. Considering the dilution ratio of the secondary air amount AI to the intake air amount Q, as shown in the graph of FIG. 9, when the excess air ratio AR is set to 1.06, the temporary time as shown by the solid line in FIG. It has a relationship represented by a function. Here, the excess air ratio AR is set to 1.06 because the fuel injection amount TAU is increased by 4% in step 450. Is the fuel injection amount TA
By increasing U by 4 [%], the air-fuel ratio becomes 4 on the rich side.
This is because the air excess ratio AR can be set to 1.06 in order to transfer it to the lean side by supplying secondary air. The ratio of 1.06 is
The oxygen concentration sensor 85 is an excess air ratio that realizes an air-fuel ratio that outputs a stable lean determination voltage, and also realizes an air-fuel ratio that is close to the minimum air-fuel ratio that obtains the stable output.

On the other hand, the relationship between the secondary air amount AI supplied from the secondary air supply device 50 and the applied voltage V to the air pump 54 is represented by a quadratic function as shown in the graph of FIG. is there. Therefore, the graph of FIG.
8 and the relationship between the intake air amount Q and the applied voltage VP of the air pump 54 is a relationship represented by a quadratic function, as shown in FIG. A has been created.

When the applied voltage VP of the air pump 54 is calculated in step 480, the applied voltage VP is applied to the air pump 54 to drive the air pump 54 (step 320), and the VSV 60 is opened (step 320). 330). As a result, when VSV60 is opened, A
The negative pressure of the surge tank 6 is added to the SV56, and the ASV
56 is opened, and the secondary air amount AI corresponding to the applied voltage VP is supplied to the exhaust passage 15 by the air pump 54. The secondary air amount AI changes according to the applied voltage VP to the air pump 54 because the rotation speed of the motor of the air pump 54 changes according to the applied voltage VP.

After execution of step 500, it is then determined from the detection signal of the oxygen concentration sensor 85 whether or not the air-fuel ratio is lean (step 510). This determination is to determine whether or not the secondary air has changed the air-fuel ratio from the rich side to the lean side after the secondary air supply command is issued in steps 490 and 500. Here, if a negative determination is made, that is, it is determined that there is no change to the lean side, it is assumed that there is some abnormality in the secondary air supply device 50 and secondary air may not be actually supplied, and the processing is performed. Returning to step 410, the processes of steps 410 to 510 are repeatedly executed. If this repetition is executed even after the timer counter T reaches 7 [seconds], a negative determination is made in step 420, the process proceeds to step 520, and a diagnosis indicating that the secondary air supply device 50 has an abnormality is made. The result flag FLGDG is set to the value 1, and then the process exits to "return" to end this routine.

When the diagnostic result flag FLGDG becomes the value 1, the secondary air supply device is operated by another processing routine, for example, by turning on an abnormality indicator lamp of the vehicle instrument panel or sounding an alarm or the like. Notify the driver of 50 abnormalities.

On the other hand, when it is determined in step 510 that the air-fuel ratio is in the lean state, it is determined that the secondary air supply device 50 has no abnormality, and the process proceeds to step 530.
In step 530, the diagnostic result flag FLGDG has a value of 0.
Is set, and then the air pump is stopped (step 540) and the VSV 60 is closed (step 55).
0). After execution of step 550, the fuel injection amount T is set by setting the value 1.00 in the self-diagnosis increase correction coefficient FDG.
At the same time as eliminating the 4% increase in AU (step 56
0), the value 0 is set to the flag XDG because the self-diagnosis is completed (step 570). After that, the process exits to "return" and the present routine is ended.

As described above in detail, in this embodiment, the ECU 7 executes the above-described secondary air supply device self-diagnosis processing routine.
By executing 0, the abnormality diagnosis of the secondary air supply device 50 is performed as follows. First, as a preparatory work, the air-fuel ratio is changed from the current state to the rich side by increasing the fuel injection amount TAU by 4 [%]. Then, the applied voltage VP of the air pump 54 based on the intake air amount Q is calculated using the map A. This calculated applied voltage VP
Is a target secondary air amount (secondary air amount for which the excess air ratio AR is 1.06) that achieves an air-fuel ratio close to the minimum value at which the oxygen concentration sensor 85 outputs a stable lean determination voltage. The applied voltage VP required for discharging is supplied, and the air is supplied by the target secondary air amount by driving the air pump 54 with the calculated applied voltage VP. After that, it is determined whether the air-fuel ratio shifts from the rich side to the lean side in response to the supply of the secondary air, and if it does not shift to the lean side, it is diagnosed that the secondary air supply device 50 has an abnormality. To do.

Therefore, the applied voltage VP applied to the air pump 54 is suppressed to the minimum voltage necessary and sufficient for self-diagnosis of the secondary air supply device 50. For this reason,
The rotation speed of the air pump 54 is suppressed, and the operation noise of the air pump 54 during the operation of the self-diagnosis function can be reduced. Furthermore, there is an effect that the power consumption of the air pump 54 during the operation of the self-diagnosis function can be reduced.

In this embodiment, the target secondary air amount AI
Although the excess air ratio AR that achieves the above is set to 1.06, the excess air ratio AR is not limited to this value as long as it is an air excess ratio that realizes an air-fuel ratio at or near the minimum at which the oxygen concentration sensor 85 outputs a stable lean determination voltage. For example, it may be another value such as 1.05.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to such an embodiment and can be implemented in various modes without departing from the scope of the present invention. Of course, you can.

[0054]

As described above, in the secondary air supply system for an internal combustion engine of the present invention, during the operation of the diagnostic function for diagnosing the abnormality of the secondary air supply system, the rotation speed of the air pump determines the diagnostic function. It can be kept at the minimum speed necessary and sufficient for it to work. Therefore, the operation noise of the air pump during the operation of the diagnostic function can be reduced. Further, there is an effect that the power consumption of the air pump during the operation of the diagnostic function can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a secondary air supply device for an internal combustion engine of the present invention.

FIG. 2 is a schematic configuration diagram showing an automobile engine equipped with a control device according to an embodiment of the present invention and peripheral devices thereof.

FIG. 3 is a block diagram showing an electrical configuration of a control system centered on an ECU 70.

FIG. 4 is a flowchart showing a fuel injection control processing routine executed by a CPU 70a of an ECU 70.

FIG. 5 is a flowchart showing an air-fuel ratio feedback control processing routine which is also executed by the CPU 70a.

FIG. 6 is a flowchart showing a secondary air supply control processing routine which is also executed by the CPU 70a.

FIG. 7 is a flowchart showing a secondary air supply device self-diagnosis processing routine, which is also executed by the CPU 70a.

FIG. 8 is a graph showing a map A stored in a ROM 70b of the ECU 70.

FIG. 9 is a graph showing a dilution ratio of the secondary air amount AI to the intake air amount Q.

FIG. 10 is a graph showing the relationship between the secondary air amount AI and the voltage V applied to the air pump 54.

[Explanation of symbols]

 M1 Internal combustion engine M2 Exhaust passage M3 Air-fuel ratio detection means M4 Feedback control means M5 Air pump M6 Secondary air supply means M7 Forced control means M71 Air pump control amount calculation part M72 Air pump rotation speed control part M8 Diagnostic means 1 Engine 3 Air cleaner 7 Fuel injection valve 15 Exhaust Passage 16 Catalyst Device 23 Rotational Speed Sensor 50 Secondary Air Supply Device 51 Secondary Air Supply Channel 52 Pipeline 54 Air Pump 56 ASV 60 VSV 70 ECU 70a CPU 70b ROM 70c RAM 80 Idle Switch 82 Intake Temperature Sensor 83 Air Flow Meter 84 Water temperature sensor 85 Oxygen concentration sensor 86 Vehicle speed sensor

Claims (1)

[Claims] 1. An air-fuel ratio detecting means which is provided in an exhaust passage of an internal combustion engine and detects an air-fuel ratio from an oxygen concentration in exhaust gas; and the air-fuel ratio of the internal combustion engine so that a predetermined target air-fuel ratio is achieved. Feedback control means for feedback-controlling the amount of fuel supplied to the internal combustion engine based on the air-fuel ratio detected by the fuel ratio detection means; and an exhaust passage of the internal combustion engine using an air pump when the internal combustion engine is in a predetermined operating state. In a secondary air supply device for an internal combustion engine, comprising: a secondary air supply means for supplying secondary air therein, when the secondary air is not supplied by the secondary air supply means, the secondary air supply A forced control means for temporarily supplying the secondary air into the exhaust passage by forcibly operating the means, and when the secondary air is supplied by the forced control means, the air-fuel ratio detection It is determined whether or not the detection result of the stage has shifted to the lean side, and when it is determined not to shift to the lean side, a diagnostic means for diagnosing that the secondary air supply means is in an abnormal state is provided. The forced control means predetermines a target secondary air amount that achieves an air-fuel ratio at or near the minimum at which the air-fuel ratio detection means stably outputs the lean side detection result, and determines the rotation speed of the air pump. An air pump control amount calculation unit that calculates a control amount such as a drive voltage according to the target secondary air amount, and an air pump rotation that controls the rotation speed of the air pump based on the control amount calculated by the air pump control amount calculation unit. A secondary air supply device for an internal combustion engine, comprising: a speed control unit.