JP3237090B2 - Control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control system for an internal combustion engine, and more particularly, to a control system for an internal combustion engine, which is provided with first and second catalytic devices in the exhaust passage in order from the upstream side, and further bypasses the first catalytic device. The present invention relates to a control device for an internal combustion engine provided with a control device.

[0002]

2. Description of the Related Art First and second catalyzers arranged in the exhaust passage of an internal combustion engine in order from the upstream side, a bypass passage for bypassing the first catalyzer, and a first passage for exhaust gas from the engine. An exhaust bypass valve for switching to one of the catalyst device side and the bypass passage side; a first exhaust gas concentration sensor disposed upstream of the exhaust bypass valve and having an output characteristic substantially proportional to the exhaust gas concentration; A second exhaust gas concentration sensor disposed downstream of the first catalyst device, and feedback-controls the air-fuel ratio to a target air-fuel ratio based on the output of the first exhaust gas concentration sensor. In the internal combustion engine control device for correcting the air-fuel ratio based on the output of the second exhaust gas concentration sensor, when the exhaust gas passage is switched to the bypass passage side, the second exhaust gas That so as to prohibit the correction of the target air-fuel ratio based on the degree sensor output has been known (JP-A-6-74071).

[0003]

However, in the above-mentioned conventional apparatus, since the failure of the exhaust bypass valve or the mechanism for operating the exhaust bypass valve is not detected, when a failure occurs, the exhaust gas passage is located on the bypass passage side. However, there is a problem that the correction of the target air-fuel ratio is prohibited even when it is not switched to the above.

The present invention has been made in view of this point, and a first object of the present invention is to provide a control device for an internal combustion engine which can detect a failure of an exhaust bypass valve or a mechanism for operating the exhaust bypass valve. It is a second object of the present invention to provide a control device for an internal combustion engine that can perform an appropriate fail-safe operation when a failure is detected.

[0005]

In order to achieve the first object, the present invention provides a first catalyst device (16) disposed in an exhaust passage of an internal combustion engine, and a first catalyst device (16). A second catalyst device (1) disposed in the exhaust passage on the downstream side
7), a bypass passage (14a) for bypassing the first catalyst device, and an exhaust bypass valve (19) for switching exhaust gas from the engine to either the first catalyst device side or the bypass passage side. And an exhaust gas concentration sensor (1) disposed downstream of the first catalyst device.
8) a control device for an internal combustion engine having at least an engine operating state detecting means for detecting whether or not the engine is in a starting state, and an exhaust bypass valve when detecting that the engine is in a starting state. To a first operating state in which the exhaust gas passes through the first catalyst device side, and when it is detected that the engine is not in the starting state, the exhaust gas passes through the exhaust bypass valve through the bypass passage side. An exhaust bypass valve actuating means to be in a second operating state, and detecting that the engine is in a starting state, and when an inversion cycle of a lean side and a rich side of the exhaust gas concentration sensor output is shorter than a predetermined cycle, A first failure determination for determining that the exhaust bypass valve operating means has failed, and a detection that the engine is not in the starting state; When the inversion period is longer than the predetermined period, it is obtained by the so provided and failure determining means for performing at least one of the failure determination of the failure and determines the second failure determination of the exhaust bypass valve actuating means.

In order to achieve the second object, the present invention provides a first catalyst device (16) provided in an exhaust passage of an internal combustion engine, and the exhaust gas downstream of the first catalyst device. A second catalyst device (17) disposed in the passage, and a bypass passage (14a) for bypassing the first catalyst device.
An exhaust bypass valve (19) for switching exhaust gas from the engine to either the first catalyst device side or a bypass passage side; and an exhaust bypass valve (19) disposed upstream of the exhaust bypass valve in the exhaust passage; A first exhaust gas concentration sensor (1) having an output characteristic substantially proportional to the exhaust gas concentration
5) and a second catalyst device disposed downstream of the first catalyst device.
An engine operating state detecting means for detecting at least whether or not the engine is in a starting state, based on a detection result of the engine operating state detecting means. Target air-fuel ratio calculating means for calculating a target air-fuel ratio, target air-fuel ratio correcting means for correcting the target air-fuel ratio based on an output value of the second exhaust gas concentration sensor, and detection by the first exhaust gas concentration sensor Feedback control means for performing feedback control on the air-fuel ratio of the air-fuel mixture to be adjusted to the target air-fuel ratio corrected by the correction means; failure determination means for determining a failure of the exhaust bypass valve; When it is determined that the engine has failed and the engine is in the starting state, the correction of the target air-fuel ratio is prohibited. It is obtained so as to provide a correction prohibiting means.

[0007] In the present specification, the "starting state" of the engine is defined as the time when the engine is started and for a predetermined period after the start (specifically, for example, a period until the engine temperature reaches a predetermined temperature, etc.). Shall mean.

[0008]

According to the control device of the first aspect, it is detected that the engine is in the starting state, and when the inversion cycle of the lean side and the rich side of the output of the exhaust gas concentration sensor is shorter than a predetermined cycle, and / or If it is detected that the engine is not in the starting state and the reversal cycle is longer than the predetermined cycle, it is determined that the exhaust bypass valve operating means has failed.

According to the second aspect of the present invention, when the failure determination means determines that the exhaust bypass valve has failed and detects that the engine is in the starting state, the failure determination means is based on the output of the second exhaust gas concentration sensor. Correction of the target air-fuel ratio is prohibited.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an overall configuration diagram of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a DOHC in-line four-cylinder internal combustion engine (hereinafter, simply referred to as an "engine") provided with a pair of intake valves and exhaust valves (not shown) for each cylinder. A throttle body 3 is provided in the middle of an intake pipe 2 of the engine 1, and a throttle valve 3 ′ is disposed inside the throttle body 3. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3 ′, and outputs an electric signal according to the opening of the throttle valve 3 ′ to output an electronic control unit (hereinafter referred to as “ECU”) 5. To supply.

The fuel injection valve 6 is disposed in the intake pipe 2 between the engine 1 and the throttle valve 3 'for each cylinder, connected to a fuel pump (not shown), and
It is electrically connected to U5, and the valve opening time of fuel injection is controlled by a signal from the ECU5.

A branch pipe 7 is provided downstream of the throttle valve 3 ′ of the intake pipe 2, and an intake pipe absolute pressure (PBA) sensor 8 is attached to a tip of the branch pipe 7. The PBA sensor 8 is electrically connected to the ECU 5,
The absolute pressure PBA in the intake pipe 2 is converted into an electric signal by the PBA sensor 8 and supplied to the ECU 5.

An intake air temperature (TA) sensor 9 is mounted on the pipe wall of the intake pipe 2 on the downstream side of the branch pipe 7, and the intake air temperature TA detected by the TA sensor 9 is converted into an electric signal to be supplied to the ECU 5. Supplied to

An engine water temperature (TW) sensor 10 composed of a thermistor or the like is inserted into the cylinder peripheral wall of the cylinder block of the engine 1 filled with cooling water, and the engine cooling water temperature TW detected by the TW sensor 10 is converted into an electric signal. The converted data is supplied to the ECU 5.

An engine speed (NE) sensor 11 and a cylinder identification (CYL) sensor 12 are mounted around a camshaft or a crankshaft (not shown) of the engine 1.

The NE sensor 11 outputs a signal pulse (hereinafter, referred to as a "TDC signal pulse") at a predetermined crank angle position every time the crankshaft of the engine 1 rotates by 180 degrees.
The L sensor 12 outputs a signal pulse at a predetermined crank angle position of a specific cylinder.
Supplied to

The ignition plug 13 of each cylinder of the engine 1
It is electrically connected to the ECU 5, and the ignition timing is controlled by the ECU 5.

An exhaust pipe (exhaust passage) 14 of the engine 1
A LAF sensor 15 is disposed near the engine. In the LAF sensor 15, a pair of upper and lower battery elements and an oxygen pump element are attached to predetermined positions of a sensor element made of zirconia solid electrolyte (ZrO ₂ ), and the sensor element is electrically connected to an amplifier circuit. Have been. The LAF sensor 15 outputs an electric signal substantially proportional to the oxygen concentration in the exhaust gas passing through the inside of the sensor element, and supplies the electric signal to the ECU 5.

The exhaust pipe 14 on the downstream side of the LAF sensor 15
In the middle of the first catalytic device 16 and the second catalytic device 1
7 are arranged in series.

The first catalytic device 16 is provided for quickly activating the first catalytic device 16 when the engine 1 is started at a low temperature to improve emission characteristics of exhaust gas at the time of low temperature start. The second catalyst device 17 is formed to have a smaller capacity than that of the second catalyst device 17. The first and second catalyst devices 16 and 17 control the amount of HC and C in the exhaust gas.
Harmful components such as O and NOx are purified.

An O2 sensor 18 is disposed in the exhaust pipe 14 between the first catalyst device 16 and the second catalyst device 17.

The O2 sensor 18 has the sensor element L
As with the AF sensor 15, the zirconia solid electrolyte (Zr
O ₂ ), whose electromotive force changes abruptly before and after the stoichiometric air-fuel ratio. At the stoichiometric air-fuel ratio, the output signal is inverted from a lean signal to a rich signal or from a rich signal to a lean signal. That is, the O2 sensor 18
Is high on the rich side of the exhaust gas and low on the lean side, and supplies the output signal to the ECU 5.

An exhaust communication passage (hereinafter, referred to as "bypass passage") 14a bypassing the first catalyst device 16 side.
Is provided branching from the exhaust pipe 14 on the downstream side of the LAF sensor 15. That is, the bypass passage 14a
Has one end connected to the exhaust pipe 14 on the upstream side of the first catalyst device 16, and the other end connected to the exhaust pipe 14 on the downstream side of the first catalyst device 16.

In the exhaust pipe 14 at the branch point between the upstream side of the first catalytic device 16 and the bypass passage 14a, exhaust gas from the engine is supplied with the first catalytic device 16 and the bypass passage 14a.
A switching valve (exhaust bypass valve, hereinafter referred to as “BPV”) 19 is provided as switching means for switching to the “a” side.
(For example, a solenoid valve, a motor, and the like).

The electric actuator 20 is connected to the ECU 5 and is driven by a signal from the ECU 5. That is, the BPV 19 is switched by the driving of the electric actuator 20, so that the exhaust gas from the engine can be switched between the first catalyst device 16 side and the bypass passage 14a side.

When the electric actuator 20 is not operated (hereinafter referred to as "BPV OFF"), the BPV 19 is deenergized so that exhaust gas from the engine is directed to the bypass passage 14a side. ,
"BPV ON") is urged so that the exhaust gas is directed to the first catalyst device 16 side. That is,
The BPV 19 is set at the position shown by the solid line in FIG. 1 when the BPV is off, and at the position shown by the broken line in FIG. 1 when the BPV is on.

At the branch point between the first catalyst device 16 side and the bypass passage 14a side, the BPV 19 determines whether the exhaust gas passage is switched to the first catalyst device 16 side or the bypass passage 14a side. Is provided, and the BP sensor 21 detects the position of the BPV 19 and outputs an electric signal to the ECU 5. Since the BPV 19 is driven by the electric actuator 20 based on a signal from the ECU 5, the position of the BPV 19 may be detected by a drive signal of the electric actuator 20. The BP sensor 21 is provided by the BPV 19 or the electric actuator 2.
Even if 0 is delayed due to deterioration or the like, B
This is to improve the controllability by reliably detecting the position of the PV 19.

Further, an atmospheric pressure (PA) sensor 22 is provided at an appropriate position in the engine 1 to detect the atmospheric pressure PA, and supplies an electric signal to the ECU 5.

The ECU 5 has a function of shaping the input signal waveforms from the various sensors described above, correcting the voltage level to a predetermined level, and converting an analog signal value to a digital signal value. A central processing unit (hereinafter referred to as a "CPU") 5b, a storage means 5c comprising a ROM and a RAM for storing various operation programs executed by the CPU 5b, various maps and operation results to be described later, and the fuel injection valve. And an output circuit 5d for supplying a drive signal to the ignition plug 13.

Based on the various engine parameter signals, the CPU 5b determines various engine operation states such as a feedback control operation area and an open loop control operation area corresponding to the oxygen concentration in the exhaust gas, and sets the engine operation state. Accordingly, the fuel injection time TOUT of the fuel injection valve 6 is calculated in synchronization with the TDC signal pulse based on Expression (1) in the case of the basic mode and based on Expression (2) in the case of the start mode. Storage means 5c (RA
M).

TOUT = TiM × KCMDM × KLAF × K1 + K2 (1) TOUT = TiCR × K3 + K4 (2) Here, TiM is the basic fuel injection time in the basic mode, specifically, the engine speed NE and the inside of the intake pipe. This is a basic fuel injection time set according to the absolute pressure PBA.
The storage means 5c stores the TiM map for determining the iM value.
(ROM).

TiCR is a basic fuel injection time in the start mode, and is set in accordance with the engine speed NE and the absolute pressure PBA in the intake pipe similarly to the TiM value, and a TiCR map for determining the TiCR value is stored. Means 5c (RO
M).

KCMDM is a corrected target air-fuel ratio coefficient, which is an air-fuel ratio correction value set based on a target air-fuel ratio coefficient KCMD calculated based on the operating state of the engine and an output value of the O2 sensor 18 as described later. It is set according to ΔKCMD.

KLAF is an air-fuel ratio correction coefficient, which is set so that the air-fuel ratio detected by the LAF sensor 15 matches the target air-fuel ratio during the air-fuel ratio feedback control, and depends on the engine operating state during the open-loop control. Is set to a predetermined value.

K1, K2, K3, and K4 are correction coefficients and correction variables calculated in accordance with various engine parameter signals, and include various parameters such as fuel consumption characteristics and acceleration characteristics according to the operating state of the engine for each cylinder. The predetermined value is set so as to optimize the characteristics.

Next, the air-fuel ratio feedback control method executed by the CPU 5b will be described in detail.

FIG. 2 is a flowchart showing a main routine of the air-fuel ratio feedback control.

First, in step S1, the LAF sensor 15
Read the output value from. Next, it is determined whether or not the engine is in the start mode (step S2). Here, whether or not the engine is in the start mode is determined, for example, based on whether or not a starter switch (not shown) of the engine is turned on and whether or not the engine speed is equal to or lower than a predetermined start speed (cranking speed).

Then, the answer to step S2 is affirmative (YE
In the case of S), that is, in the start mode, the engine is at a low water temperature. The KTWLAF map which is a function of the engine cooling water temperature TW and the absolute pressure PBA in the intake pipe is searched to obtain a target air-fuel ratio coefficient at the low water temperature. KTWLAF is calculated (step S3), and the KTWLAF value is set to the target air-fuel ratio coefficient KCMD (step S4). Next, the flag FLAFFB is set to "0" to stop the feedback control of the air-fuel ratio (step S5), and the air-fuel ratio correction coefficient K
LAF and its integral term (I term) KLAFI are set to 1.0 (step S6, step S7), and this program is terminated.

On the other hand, when the answer to step S2 is negative (NO), that is, in the basic mode, the corrected target air-fuel ratio coefficient KCMDM is calculated based on the flowchart of FIG. 3 described later (step S8), and then the flag FACT is set. It is determined whether or not the value is "1" to determine whether or not the LAF sensor 15 is activated (step S9). Where LA
The activation determination of the F sensor 15 is performed by a LAF sensor activation determination routine (not shown) that is processed in the background. For example, the output voltage VOU of the LAF sensor 15 is determined.
When the difference between T and its center voltage VCENT is smaller than a predetermined value (for example, 0.4 V), it is determined that "LAF sensor 15 has been activated".

Then, the answer to step S9 is negative (NO).
If the answer is affirmative (YES) in step S9, that is, if the activation of the LAF sensor 15 has been completed, the process proceeds to step S10, where LA
Equivalent ratio KACT of air-fuel ratio detected by F sensor 15
(14.7 / (A / F)) (hereinafter, “detected air-fuel ratio coefficient”)
Is calculated. Here, the detected air-fuel ratio coefficient KAC
In consideration of the fact that the exhaust pressure fluctuates due to fluctuations in the absolute pressure PBA in the intake pipe, the engine speed NE, and the atmospheric pressure PA, T
The calculated value is calculated in accordance with these operating parameters, and is calculated by executing a KACT calculation routine (not shown).

Next, at step S11, a feedback processing routine is executed, and this program is terminated. That is, when the predetermined feedback condition is not satisfied, the flag FLAFFB is set to “0” to prohibit the feedback control, while when the predetermined feedback condition is satisfied, the flag FLAFFB is set to “1” to correct the air-fuel ratio. The coefficient KLAF is calculated, the execution of the feedback control is commanded, and the present program ends.

FIG. 3 is a flowchart of the KCMDM calculation routine executed in step S8 (FIG. 2). This program is executed in synchronization with the generation of the TDC signal pulse.

First, it is determined whether or not the engine 1 is in fuel cut (fuel supply stopped) (step S21).
Whether or not the fuel is cut is determined by the engine speed N
The determination is made based on E and the valve opening degree θTH of the throttle valve 3 ', and specifically, is determined by executing a fuel cut determination routine (not shown).

If the answer in step S21 is negative (N
In the case of O), that is, in the basic mode, step S
Proceeding to 22, the target air-fuel ratio coefficient KCMD is calculated. The target air-fuel ratio coefficient KCMD is usually a KCMD map (not shown) in which map values KCMD are given in a matrix in accordance with the engine speed NE and the intake pipe absolute pressure PBA.
, But is appropriately corrected when the vehicle starts, when the water temperature is low, or when a predetermined high load operation is performed.
By executing a calculation routine (not shown), the value is set to a value suitable for these operating conditions.

On the other hand, if the answer in step S21 is affirmative (YE
S), the target air-fuel ratio coefficient KCMD is set to a predetermined value KCM.
DFC (for example, 1.0) (step S2
3), proceed to step S24.

In step S24, it is determined whether or not the engine 1 is in a starting state. Here, the “starting state” refers to a state in which the engine 1 is in the start mode and a state in which the engine 1 is within a predetermined period after the end of the start mode, as described above.
Since the process of FIG. 3 is executed after the end of the start mode, in step S24, it is determined whether or not it is within a predetermined period after the end of the start mode. When the engine 1 is in the starting state, “BPV ON”, that is, the position where the BPV 19 guides the exhaust gas to the first catalyst device 16 side, is set to “BPV OFF” when the engine 1 is not in the starting state. .

If the engine 1 is not in the starting state in step S24, it is further determined whether or not the flag FFAIL is "1". The flag FFAIL is a flag that is set to “1” when it is determined that the BPV 19 (or the drive system such as the actuator 20) has failed in the failure determination process of FIG.

As a result of the determination in steps S24 and S25,
When the engine 1 is not in the starting state or when FFAIL = 1, the process proceeds to step S28 and proceeds to step S22 or S22.
The target air-fuel ratio coefficient KCMD obtained in 23 is used as it is as the corrected target air-fuel ratio coefficient KCMDM, the program is terminated, and the process returns to the main routine (FIG. 2).

As described above, when FFAIL = 1 and BP
When the failure of V19 or its drive system is detected, the correction of the target air-fuel ratio coefficient KCMD in step S26 to be described later is prohibited to prevent inappropriate correction.

On the other hand, if the answers to steps S24 and S25 are negative (NO), that is, if the engine 1 is in the starting state and a failure such as the BPV 19 has not been detected, the process proceeds to step S26 to perform O2 processing. That is, as described later, under a predetermined requirement, the target air-fuel ratio coefficient KCMD is corrected based on the output value from the O2 sensor 18 to calculate the corrected target air-fuel ratio coefficient KCMDM.

Then, in step S27, a limit check of the corrected target air-fuel ratio coefficient KCMDM is performed, the program is terminated, and the routine returns to the main routine (FIG. 2). That is, the magnitude relationship between the KCMDM value calculated in step S26 and the predetermined upper and lower limit values KCMDMH and KCMDML is compared. If the KCMDM value is larger than the upper limit value KCMDMH, the KCMDM value is set to the upper limit value KCMDMH, and the KCMDM value Is smaller than the lower limit KCMDML, the KCMDM value is set to the lower limit KCMDML.

The predetermined period after the end of the start mode of the engine 1 is defined as, for example, a period until the elapsed time from the end of the start mode reaches the predetermined time, but is not limited to this. The period until the water temperature TW reaches the predetermined water temperature may be set, or the temperature of the second catalyst device 17 may be detected and the integrated value of the fuel supply amount to the engine 1 may be set until the detected temperature reaches the predetermined catalyst temperature. May be a period until the predetermined amount is reached.

FIG. 4 is a flowchart of the O2 processing routine executed in step S26 (FIG. 3).
This program is executed in synchronization with the generation of the TDC signal pulse.

First, in a step S31, it is determined whether or not the flag FO2 is "1", and it is determined whether or not the O2 sensor 18 is activated. Whether or not the O2 sensor 18 has been activated is determined by executing an O2 sensor activation determination routine (not shown).

If the answer in step S31 is negative (N
O), that is, when it is determined that the O2 sensor 18 has not been activated yet, the process proceeds to step S32, and after setting the timer tmRX to a predetermined value T2 (for example, 0.25 sec), the flag FVREF is set to “0”. "Or not,
It is determined whether or not an integral term VRREF (n-1) described later has already been set (step S33).

Then, in the first loop, step S3
Since the answer to 3 is affirmative (YES), the process proceeds to step S34, in which the VREF value is set according to the atmospheric pressure PA.
Search the RREF table (not shown), and
The reference value VRREF of the output voltage VO2 of No. 8 is calculated.

Next, the integral term (I term) VREFI (n-
1) is set to the reference value VRREF calculated in step S34 (step S35), and the flag FVREF is set.
Is set to "1" (step S45), the program is terminated, and the process returns to the main routine (FIG. 2). That is,
Initial settings are made for the integral term VREFI (n-1), and the process returns to the main routine (FIG. 2). When step S33 is executed after the next loop, since the flag FVREF is set to "1" as described above, the answer is negative (NO), and the process proceeds to step S33 without executing steps S34 and S35. Quit the program.

If the answer in step S31 is affirmative (Y
ES), it is determined that the O2 sensor 18 has been activated, and the flow advances to step S36 to execute the timer tmRX.
Is determined to be “0”. If the answer is negative (NO), the process proceeds to step S33, while if the answer in step S36 is affirmative (YES), the O2 sensor 1
8, the process proceeds to step S37, and determines whether the target air-fuel ratio coefficient KCMD set in step S22 or S23 (FIG. 3) is larger than a predetermined lower limit KCMDZL (for example, 0.98). Is determined.

If the answer is negative (NO), it means that the air-fuel ratio of the air-fuel mixture has been set to the lean burn state, and this program is terminated while the answer is affirmative (YES). Proceeding to step S38, the target air-fuel ratio coefficient KCMD is set to a predetermined upper limit value KCMDZH (for example,
1.13) Determine if smaller than If the answer is negative (NO), it means that the air-fuel ratio of the air-fuel mixture has been set to fuel rich, and this program is terminated. On the other hand, if the answer is affirmative (YES), This is the case where the air-fuel ratio should be set to the stoichiometric air-fuel ratio (A / F = 14.7), and the process proceeds to step S39 to determine whether or not the engine is in the fuel cut mode. And the answer is affirmative (Y
In the case of (ES), the present program is terminated and the process returns to the main routine (FIG. 2). On the other hand, if the answer is negative (NO), it is determined whether or not the fuel cut state was performed in the previous loop (step S40). . If the answer is affirmative (YES), the counter NAFC is set to a predetermined value N1 (for example, 4) (step S41),
The count value of the counter NAFC is decremented by "1" (step S42), and this program ends.

On the other hand, if the answer to step S40 is negative (NO)
If it becomes, the process proceeds to step S43, where the counter NAF
It is determined whether or not C is "0". When the answer is negative (NO), the count value of the counter NAFC is decremented by "1" (step S42), and the program ends. On the other hand, when the answer is affirmative (YES), fuel cut is performed. It is determined that stable fuel supply is being performed after exiting the state, and the routine proceeds to step S44, where O2
After executing the feedback processing routine, this program ends, and the process returns to the main routine (FIG. 2).

FIG. 5 is a flowchart of the O2 feedback processing routine executed in step S44 (FIG. 4). This program is executed in synchronization with the generation of the TDC signal pulse.

First, in step S61, the thinning variable N
It is determined whether or not the IVR is “0”. This thinning variable NI
VR is a variable that is decremented each time a TDC signal pulse is generated by the number of thinned TDCs NI set in accordance with the engine operating state, as described later. Since VR is initially "0", the answer of step S61 is The result is affirmative (YES), and the process proceeds to step S62.

If the answer to step S61 is negative (NO) in the subsequent loop, the process proceeds to step S63, and the value obtained by subtracting the number of thinned TDCs NI (for example, 1) from the thinned variable NIVR is used as a new thinned variable. After setting to NIVR, the process proceeds to step S73 described later.

However, in step S62, 02
It is determined whether the output voltage VO2 of the sensor 18 is smaller than a predetermined lower limit value VL (for example, 0.3 V). And
When the answer is affirmative (YES), it is determined that the air-fuel ratio of the air-fuel mixture has deviated from the stoichiometric air-fuel ratio (target air-fuel ratio coefficient KCMD = 1.0) to the lean side, and the process proceeds to step S65. If the answer is negative (NO), the process proceeds to step S64, where the output voltage VO2 of the 02 sensor 18 is set to the predetermined upper limit value VH.
(For example, 0.8) is determined. If the answer is affirmative (YES), it is determined that the air-fuel ratio of the air-fuel mixture has shifted from the stoichiometric air-fuel ratio to the rich side, and the routine proceeds to step S65.

Next, in step S65, a KVP map, a KVI map, a KVD map, and a NIVR map (not shown) are searched to change the O2 feedback control, that is, the proportional term (P term) coefficient KVP and the integral term ( I
Term) coefficient KVI, differential term (D term) coefficient KVD, and the thinning number NIVR are calculated.

Next, the thinning variable NIVR is set to the NIVR value calculated in step S65 (step S66), and the reference value VRREF is set in step S65 of FIG.
34 (step S67), the process proceeds to step S68, and the deviation ΔV between the reference value VRREF and the output voltage VO2 of the 02 sensor 18 in the current loop is calculated.
(N) is calculated.

Next, in step S69, equations (3) to (3)
Based on (5), the target correction values VREFP (n), VREFI (n), V
After calculating REFD (n), these correction terms are added to calculate a target correction value VREF (n) in O2 feedback based on Expression (6).

VREFP (n) = ΔV (n) × KVP (3) VREFI (n) = VREFI (n−1) + ΔV (n) × KVI (4) VREFD (n) = (ΔV (n) − ΔV (n−1)) × KVD (5) VREF (n) = VREFP (n) + VREFI (n) + VREFD (n) (6) Next, in step S70, a limit check subroutine of VREF (n) ( (Not shown). After the VREF (n) limit check is completed in step S70, the process proceeds to step S71, where the air-fuel ratio correction value ΔKCMD
Is calculated by searching a ΔKCMD table (not shown).

Next, in step S72, the corrected target air-fuel ratio coefficient KCMDM (= theoretical air-fuel ratio) is calculated by adding the air-fuel ratio correction value ΔKCMD to the target air-fuel ratio coefficient KCMD calculated in step S22 (FIG. 3). , End this program.

If the answer in step S64 is negative (N
O), that is, the output voltage VO2 of the 02 sensor 18 is V
When L ≦ VO2 ≦ VH, O2 feedback control is prohibited, and in steps S72 to S74, a ΔV value (deviation between the correction initial value VRREF and the output value of the 02 sensor 18),
The current value is set equal to the previous value for each of the target correction value VREF and the air-fuel ratio correction value ΔKCMD, and the program ends. Thus, when the air-fuel ratio of the air-fuel mixture can maintain the stoichiometric air-fuel ratio, unnecessary O2 feedback control is prohibited, and good controllability can be maintained. That is, the air-fuel ratio of the air-fuel mixture can be kept stable.

Next, referring to FIG. 6 and FIG.
Alternatively, a method of determining a failure of the drive system will be described.

FIG. 6 is a diagram showing an output voltage waveform of the O2 sensor 18. FIG. 6A shows a waveform when "BPV ON", that is, when the exhaust gas passes through the first catalyst device 16 side. FIG. 3B shows a waveform when “BPV is OFF”, that is, when the exhaust gas passes through the bypass passage 14a. As is apparent from this figure, the reversal period TINV (the period at which the output level changes from the high level to the low level or vice versa) at the time of “BPV ON” is due to the oxygen storage effect of the catalyst device 16 and the time of “BPV OFF” Inversion cycle TIN
V. Accordingly, the ECU 5 sends “BPVO”
N], the inversion cycle T
If the INV is shorter than the predetermined period T0 (set between the period of FIG. 6A and the period of FIG. 6B), it is determined that the BPV 19 is not operating normally (the BPV 19 or its drive system has a failure). Can be determined. Conversely, if the reversal period TINV is longer than the predetermined period T0 despite the output of a control signal to turn off "BPV" from the ECU 5, it can be similarly determined that the BPV 19 is not operating normally.

FIG. 7 is a flowchart showing the procedure of a process for making a failure determination by the above-described method. This processing is C
It is executed by the PU 5b at regular intervals, for example.

In step S81, the inversion cycle TINV of the output of the O2 sensor 18 is measured. This is executed by another subroutine (not shown). For example, measurement is performed ten times, and the average value is set as the TINV value.

In step S82, it is determined whether or not the reversal period TINV is longer than a predetermined period T0. In steps S83 and S84, it is determined whether or not the engine 1 is in the starting state, that is, a command of "BPV ON" is issued. Is determined. When TINV <T0 and the starting state, or when TINV> T0 and other than the starting state, the BPV
It is determined that a failure has occurred in the drive system 19 or its drive system, and the flag FFAIL is set to "1" (step S8).
5), end this processing.

In cases other than the above, the present processing is immediately terminated. The flag FFAIL is reset to "0" at the beginning of the operation.

As described above, according to this embodiment, a failure of the BPV 19 or its drive system can be detected based on the output of the O2 sensor 18. Therefore, the BP sensor 21 can be deleted. Alternatively, BP sensor 2
By comparing the output of the BP sensor 2 with the result of the above-described determination method, the accuracy of the failure determination is further improved.
1 fault can be detected. Also, according to step S25 in FIG. 3, when a failure is detected (when FFAIL = 1)
Does not perform the correction of the target air-fuel ratio coefficient KCMD by the O2 process (step S26).
In the start-up state, the BPV 19 is
When switching to the side is not performed, it is possible to prevent the KCMD value from being corrected to an inappropriate value, thereby preventing the stability of the air-fuel ratio control from being impaired.

In the above-described embodiment, it is needless to say that the inversion frequency may be measured instead of the inversion period TINV to determine whether or not the inversion frequency is lower than the predetermined frequency.

[0082]

As described above in detail, according to the control device of the first aspect, it is detected that the engine is in the starting state.
And when an inversion cycle between the lean side and the rich side of the output of the exhaust gas concentration sensor is shorter than a predetermined cycle and / or when it is detected that the engine is not in the starting state and the inversion cycle is longer than the predetermined cycle, the exhaust bypass is performed. Since it is determined that the valve operating means has failed, the failure of the exhaust bypass valve operating means can be detected.

According to the second aspect of the present invention, when the failure determination means determines that the exhaust bypass valve has failed and detects that the engine is in the starting state, it is based on the output of the second exhaust gas concentration sensor. Since the correction of the target air-fuel ratio is prohibited, it can be prevented that the target air-fuel ratio is corrected to an inappropriate value and the stability of the air-fuel ratio control is impaired.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a flowchart of a main routine of air-fuel ratio feedback control executed by the control device of FIG. 1;

FIG. 3 is a flowchart of a routine for calculating a corrected target air-fuel ratio coefficient (KCMDM).

FIG. 4 is a flowchart of an O2 processing routine.

FIG. 5 is a flowchart of an O2 feedback control routine.

FIG. 6 is a diagram showing an output waveform of an O2 sensor.

FIG. 7 is a flowchart of a process for determining a failure of a switching valve (BPV) or its drive system.

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 5 electronic control unit (ECU) 8 intake pipe absolute pressure sensor 10 engine water temperature sensor 11 engine speed sensor 14 exhaust pipe (exhaust passage) 14a bypass passage 15 LAF sensor 16 first catalyst device 17 second catalyst device 18 O2 sensor 19 Exhaust bypass valve

Continuation of the front page (56) References JP-A-6-74071 (JP, A) JP-A-5-231142 (JP, A) JP-A-5-340238 (JP, A) , U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3/28 F02D 41/22 305

Claims (2)

(57) [Claims] A first catalyst device disposed in an exhaust passage of the internal combustion engine; a second catalyst device disposed in the exhaust passage downstream of the first catalyst device; A bypass passage for bypassing the first catalyst device; an exhaust bypass valve for switching exhaust gas from the engine to one of the first catalyst device side and the bypass passage side;
An internal combustion engine control device having an exhaust gas concentration sensor disposed downstream of the first catalyst device, wherein at least an engine operating state detecting means for detecting whether or not the engine is in a starting state; When detecting that the engine is in the starting state, setting the exhaust bypass valve to the first operating state in which exhaust gas passes through the first catalyst device side, and detecting detecting that the engine is not in the starting state. Exhaust bypass valve operating means for setting the exhaust bypass valve to a second operating state in which exhaust gas passes through the bypass passage; detecting that the engine is in a starting state, and detecting an output of the exhaust gas concentration sensor. When the reversal cycle between the lean side and the rich side is shorter than a predetermined cycle, a first failure judgment is made to determine that the exhaust bypass valve operating means has failed. A failure determination that detects that the engine is not in a starting state and performs at least one failure determination of a second failure determination that determines that the exhaust bypass valve actuating means has failed when the reversal cycle is longer than the predetermined cycle. And a control device for an internal combustion engine. A first catalytic device disposed in an exhaust passage of the internal combustion engine; a second catalytic device disposed in the exhaust passage downstream of the first catalytic device; A bypass passage for bypassing the first catalyst device, an exhaust bypass valve for switching exhaust gas from the engine to one of the first catalyst device side and the bypass passage side,
A first exhaust gas concentration sensor disposed in the exhaust passage upstream of the exhaust bypass valve and having an output characteristic substantially proportional to the exhaust gas concentration; and a first exhaust gas concentration sensor disposed downstream of the first catalyst device. A control device for an internal combustion engine having a second exhaust gas concentration sensor, wherein at least an engine operating state detecting means for detecting whether the engine is in a starting state, and a target based on a detection result of the engine operating state detecting means. Target air-fuel ratio calculating means for calculating an air-fuel ratio; target air-fuel ratio correcting means for correcting the target air-fuel ratio based on an output value of the second exhaust gas concentration sensor; and detection by the first exhaust gas concentration sensor. Feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture to the target air-fuel ratio corrected by the correction means; Failure prohibition means for prohibiting correction of the target air-fuel ratio when the failure determination means determines that the exhaust bypass valve is faulty and detects that the engine is in a starting state. A control device for an internal combustion engine, comprising: