JPS62186029A - Abnormality judging method for lean sensor - Google Patents

Abstract

PURPOSE:To judge abnormality in a lean sensor with a simple method while controlling air-fuel ratio by judging whether or not the feed-back correction factor for lean control has a value outside a predetermined range. CONSTITUTION:When in step 110 is judged that an engine is not started, and in step 114 is judged that the feed-back controlling requirement is not established, the feed-back correction factor FAFO for controlling theoretical air fuel ratio and the feed-back correction factor FAFl for lean controlling are set to 1.0 in step 116. On the other hand, when in step 114 is judged that said requirement is established and in step 118 is judged that the lean controlling requirement is established, the feed-back correction factor FAFl for lean controlling is calculated in step 124. And whether or not this correction factor FAFl has values outside a predetermined range at least a predetermined number of times is judged to judge abnormality in a lean sensor.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a lean sensor abnormality determination method, and is particularly used when feedback-controlling the air-fuel ratio of an internal combustion engine to a target air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. The present invention relates to a lean sensor abnormality determination method.

[Conventional technology]

Conventionally, the objective has been to simultaneously purify HC, Co, and NOX in exhaust gas, and to prevent changes in the fuel injection amount due to deposits on the fuel injection valve due to changes over time, changes in the clearance of the fuel injection valve, etc. , the fuel injection 11TAUo is determined according to the following formula, and the air-fuel ratio is controlled to feed to the stoichiometric air-fuel ratio by opening the fuel injection valve for a predetermined time and injecting fuel corresponding to the fuel injection fiTAUo. There is.

TAUO-TP -KGi -F 8FO-K
, -・(+)(jsτ-L, i=1.2.3) -11=====←→Yoki However, TP is the engine load (intake air amount or intake pipe pressure) and engine speed KGi is the learning value for correcting changes in fuel injection amount due to changes over time, FAFO is the feedback correction coefficient, and K is 1IAaX.
These are other correction coefficients including a 1m positive coefficient at the time.

The feedback correction coefficient FAFO has an initial value of 1.
0 is determined, and when the 02 sensor output is richer than the stoichiometric air-fuel ratio, it is gradually decreased, and when the 0□ sensor output is leaner than the stoichiometric air-fuel ratio, it is gradually increased, and 1. Centered around 0, it changes according to the 02 sensor output. Since the above basic fuel injection j51TP is set to a value corresponding to approximately the stoichiometric air-fuel ratio, the air-fuel ratio is normally controlled to be near the stoichiometric air-fuel ratio by correcting the basic fuel injection jj1TP to the feedback correction coefficient F using FO. .

The learned value K G i is determined according to the region of the intake pipe pressure PM, and is 200 mws Hg≦PM<280
When dragon Hg, learning value KG,, 280 days - Hg≦PM〈4
When 00 m Hg, learning value KG,, 400n+ Hg
≦P M < 50 Learning value K G when On+ Hg
:1 is defined. This learning value KGi (i=
The value of 1.2.3) is written in the backup ram tα, and during air-fuel ratio feedback control to the stoichiometric air-fuel ratio at times other than idling, the intake temperature THA is 40'C≦THA≦9.
When 0°C and the engine cooling water A T Hw satisfies the conditions of T HW≧80°C, the following correction is made. That is,
First, the average value FAF of the feedback correction coefficient FAFO
AV is calculated, and it is determined whether the average value FAFAV is within a predetermined range centered around the value corresponding to the stoichiometric air-fuel ratio.

The feedback correction coefficient FAFO is 02 as described above.
The average value FAFAV is normally a value corresponding to the stoichiometric air-fuel ratio (usually 1.0 ) is taken. When the average value FAFAV exceeds the upper limit of the predetermined range due to changes over time, the learned value of the area to which the current intake pipe pressure belongs is increased, and when the average value FAFAV is less than the lower limit of the predetermined range, The learning value of the area to which the current intake pipe pressure belongs is changed to be smaller. The learning value changed in this way is employed in the above equation (1) in the region of intake pipe pressure determined as above, and the fuel injection amount is thereby corrected. In addition, P M < 200 m
When m HH, the learned value KGI is adopted, and PM≧5
When the value is 00 Dragon Hg, the learned value K G s is adopted. Therefore, when the clearance of the fuel injector becomes wider and more fuel than the command value is injected, the average value FAFAV
becomes smaller, and accordingly, the learned value is changed to be smaller, and the product of the basic fuel injection 11TP and the learned KGi becomes a value corresponding to approximately the stoichiometric air-fuel ratio. Additionally, if a deposit is attached to the fuel injection valve and less fuel than the command value is injected, the learned value KGi is changed to be larger, and the product of the basic fuel injection amount TP and the learned value KGi is The value corresponds to approximately the stoichiometric air-fuel ratio.

On the other hand, in recent years, with the aim of reducing fuel consumption and the amount of HC and Co emissions in exhaust gas, a lean sensor that outputs a signal proportional to the residual oxygen concentration in exhaust gas has been used to reduce exhaust gas. The air-fuel ratio is feedback-controlled to a target air-fuel ratio on the leaner side than the stoichiometric air-fuel ratio based on the following equation under steady-state operating conditions in which the amount of harmful component emissions is reduced.

TAUjl-TP-KLEAN-FAFj! -K...
(2) However, KLIEAN is a lean correction coefficient less than 1 to control the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio by reducing the fuel injection amount according to the operating condition, and FAFl is an initial value of 1.
．． This is a feedback correction coefficient for lean control that is set to 0 and is decreased when the lean sensor output is smaller than the target value corresponding to the target air-fuel ratio, and is increased when the lean sensor output is larger than the target value.

According to such feedback control to the target air-fuel ratio, fuel corresponding to approximately the target air-fuel ratio is injected by the basic fuel injection 1iITp and the lean positive coefficient KLEAN, and this fuel is corrected by the feedback correction coefficient FAFl. The air-fuel ratio is controlled to a value near the target air-fuel ratio.

[Problem that the invention seeks to solve]

However, if an abnormality occurs in the lean sensor due to heater disconnection, element cracking, etc., there is no technology to determine this abnormality, and if feedback control is performed in a state where an abnormality has occurred, the air-fuel ratio will reach the target air-fuel ratio. However, there was a problem in that it shifted toward the rich or lean side. Therefore, when the air-fuel ratio shifts to the lean side and enters the misfire region, drivability deteriorates and the HC concentration increases, and when the air-fuel ratio shifts to the rich side, fuel efficiency deteriorates and the NoliIll degree increases.

Therefore, an object of the present invention is to provide a lean sensor abnormality determination method that determines whether the lean sensor is abnormal so that the above-mentioned problems do not occur.

[Means for solving problems]

In order to achieve the above object, the present invention corrects the basic fuel injection amount when determining an abnormality in a lean sensor that outputs a signal proportional to the residual oxygen concentration in exhaust gas in a region leaner than the stoichiometric air-fuel ratio. ■Feedback for stoichiometric air-fuel ratio control to feedback control the air-fuel ratio to the stoichiometric air-fuel ratio? The ili positive coefficient is determined based on the output of the 02 sensor that outputs a signal that is inverted from the stoichiometric air-fuel ratio, and the average value of the feedback correction coefficient for stoichiometric air-fuel ratio control is determined when the air-fuel ratio is feedback-controlled at the stoichiometric air-fuel ratio. The basic fuel injection amount is learned and corrected so that it becomes a value within a predetermined range, and the lean control feedback correction is determined based on the lean sensor output and the value obtained by multiplying the learned and corrected basic fuel injection amount by XI according to the driving condition. When the feedback correction coefficient for lean control becomes a value outside a predetermined range when the air-fuel ratio is feedback-controlled to a target air-fuel ratio on the lean side than the stoichiometric air-fuel ratio based on the coefficient, it is determined that the lean sensor is abnormal. Features.

[Effect]

Next, the operation of the present invention will be explained. According to the invention,
A feedback correction coefficient for stoichiometric air-fuel ratio control is determined based on the 0□ sensor output, and the basic fuel injection amount is learned and corrected based on the average value of this feedback correction coefficient for stoichiometric air-fuel ratio control. The air-fuel ratio becomes approximately the stoichiometric air-fuel ratio by injecting fuel while determining the time for opening the fuel injection valve based on the learning-corrected basic fuel injection amount. When feedback controlling the air-fuel ratio to leaner than the stoichiometric air-fuel ratio,
The fuel injection amount is determined by reducing the learning-corrected basic fuel injection amount according to the operating condition and the feedback correction coefficient for engine control, and the air-fuel ratio is feedback-controlled. This approximately corresponds to the target air-fuel ratio determined depending on the state. Therefore, this −Ml
When fuel having a value of 1 is injected, the lean control feedback correction coefficient changes within a predetermined range around the target air-fuel ratio when the lean sensor is normal. On the other hand, when an abnormality occurs in the lean sensor, the lean control feedback correction coefficient becomes a value outside the predetermined range. Therefore, by determining whether the lean control feedback correction coefficient has reached a value outside the predetermined range, it is possible to determine whether the lean sensor is abnormal.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to determine whether there is an abnormality in the lean sensor in a simple manner while controlling the air-fuel ratio without removing the lean sensor.

〔Example〕

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

FIG. 2 schematically shows an internal combustion engine to which the present invention is applicable.

This engine is controlled by an electronic control circuit such as a microcomputer, and a throttle valve 8 is arranged downstream of an air cleaner (not shown). The idle contact to be turned on and the throttle valve degree are set to a predetermined value (for example, 5
A throttle switch 10 is installed with a power contact that turns on when the temperature exceeds 0'), and the throttle valve 8
A surge tank 12 is provided downstream.

A diaphragm type pressure sensor 2 is attached to this surge tank 12. Further, a bypass passage 14 is provided so as to bypass the throttle valve 8 and communicate the upstream side of the throttle valve with the surge tank 12 on the downstream side of the throttle valve. This bypass path 14 has an idle speed control (ISC) valve 16 whose opening degree is adjusted by a pulse motor 16A equipped with a 4-pole stator.
B/'+<attached. The surge tank 12 is
It communicates with the combustion chamber of the engine 20 via an intake manifold 18 and an intake port 22. A fuel injection valve 24 is attached to each cylinder or cylinder group so as to protrude into the intake manifold 18.

The combustion chamber of the engine 20 is communicated via an exhaust port 26 and an exhaust manifold 28 to a catalyst device (not shown) filled with a three-way catalyst. This exhaust manifold 28 includes an 02 sensor 30 that outputs a signal that is inverted around the stoichiometric air-fuel ratio, and a lean sensor that outputs an air-fuel ratio signal as a current proportional to the residual oxygen concentration in the exhaust gas in a region leaner than the stoichiometric air-fuel ratio. 52 is installed.

A cooling water temperature sensor 34 is attached to the engine block 32 so as to penetrate through the block 32 and protrude into the water jacket. This cooling water) l! ! sensor 34
detects the engine coolant temperature and outputs a water temperature signal.

The cylinder head 36 of the engine 20) iiffl! ,
A spark plug 38 is installed in each cylinder so as to protrude into the combustion chamber.
is installed. The spark plug 38 is connected via a distributor 40 and an igniter 42 to an electronic control circuit 44 composed of a microcomputer or the like. A cylinder discrimination sensor 46 and a rotation angle sensor 48 are installed inside the disc repeater 40, each consisting of a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing. In the case of a 6-cylinder engine, the cylinder discrimination sensor 46 is, for example, ? A cylinder discrimination signal is output every 20'CA, and the rotation angle sensor 48 outputs an engine rotation speed signal, for example, every 30'CA.

As shown in FIG. 3, the electronic control circuit 44 is a central processing bag!
(MPU) 60, read-only memory (ROM
) 62, Lambdom Access Memory (RAM) 64,
It is configured to include a backup RAM (BU-RAM) 66, an input/output capotro 8, an input port door 0°, an output port door 2.74.76, and a bus 78 such as a data bus or a control bus that connects these. A pressure sensor 2 and a water temperature sensor 34 are connected to the input/output capotro 8 via an analog-digital (A/D) converter 78, a mile multiplexer 80, and buffers 82,84. The manual port door 0 has an A/D converter 88 and a hicon valator 86.
The 02 sensor 32 is connected via the waveform shaping circuit 90, and the cylinder discrimination sensor 46 and the rotation angle sensor 4 are connected via the waveform shaping circuit 90.
8 is connected, and the throttle switch IO is directly connected to the current-voltage converter 53 that converts the current value into a voltage value, and the A/D converter 55 that converts the output of the current-voltage converter 53 into a digital signal. A lean sensor 52 is connected. The output port door 4 is connected to the fuel injection valve 24 via a drive circuit 94, and the output port door 6 is connected to an SC pulp pulse motor 16 via a drive circuit 96.
Connected to A. Note that 98 is a clock and 100 is a timer. The ROM 62 stores in advance a control routine program, etc., which will be explained below.

Next, a control routine of an embodiment in which the present invention is applied to the above engine will be explained. This embodiment performs switching between feedback control to the stoichiometric air-fuel ratio and feed-balance control to lean, and also determines whether there is an abnormality in the lean sensor and stops feedback control to lean when it is determined to be abnormal. This is how it was done.

FIG. 1 shows the main routine of this embodiment, which is executed every 12 m5ec. In step 110, it is determined whether the engine is being started, that is, whether cranking is being performed or if the engine speed NE is at a predetermined speed (500 rpm).
) or less. When it is determined that the engine is starting, the flag XLSNG is reset in step 112. When it is determined in step 110 that the engine is not starting, that is, when it is determined that the engine speed has exceeded a predetermined value and a complete explosion has occurred, the power contact of the throttle switch 10 is turned off in step 114. By determining whether the feedback control condition is satisfied or not, it is determined whether the feedback control condition is satisfied or not. When the feedback control condition is not satisfied, that is, when the oven loop control condition is satisfied, the feedback correction coefficient FAFO for stoichiometric air-fuel ratio control and the feedback correction coefficient FAFf for lean control are set to 1 and 0 in step 116. .

On the other hand, when it is determined in step 114 that the feedback control condition is satisfied, in step 118, the lean control condition for controlling the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio is established, or the air-fuel ratio is adjusted to the stoichiometric air-fuel ratio. It is determined whether the stoichiometric air-fuel ratio control conditions to be controlled are satisfied. When the stoichiometric air-fuel ratio control conditions are satisfied, a feedback correction coefficient FAFO for stoichiometric air-fuel ratio control is calculated in step 120, and a learned value KGi is calculated in step 122.

When it is determined in step 118 that the lean control condition is satisfied, a lean control feedback correction coefficient FAFf is calculated in step 124, and
1-FAFM Determine whether l≧0.2 continues five or more times in a row.

If the determination in step 126 is affirmative, step 12
The flag XLSNG is set at step 8, and if the determination at step 126 is negative, the next main routine is executed.

Here, fuel injection f during lean feedback control
f1TAtz is determined from the above equation (2), and the amount of fuel determined by factors other than the feedback correction coefficient FAF1 is TP-KG i -KLEAN・K, and this amount of fuel is determined even if the lean sensor is normal. is also constant. Therefore, by dividing the fuel injection [TAUA' by the amount of fuel determined by a factor other than the above feedback correction coefficient, the feedback correction coefficient FAF is calculated.
1 is required. This feedback correction coefficient FAF
If the lean sensor is normal, ffi will take a value near 1.0, and if the lean sensor is abnormal, it will take a value outside a predetermined range centered around 1.0. By determining whether a value outside the range has been taken, it is determined that the lean sensor is abnormal, and at this time, a flag XLSNG is set. Note that in determining whether the lean sensor is abnormal, the feedback correction coefficient FAF 1 calculated in FIG. 5, which will be described below, may be used as is.

FIG. 4 shows a detailed routine for calculating the feedback correction coefficient FAFO in step 120 in FIG. 1. In step 130, the A/D converter 88 is activated and the A/D converter 55 is deactivated. A of the 02 sensor 32 output which is input via the comparator 86,
/ Executes D i conversion processing. In the next step 132, o2 is determined based on the A/D converted value in step 130.
Determine whether the sensor output indicates a rich air-fuel ratio.

When the determination in step 132 is affirmative, it is determined in step I34 whether or not the 08 sensor output has changed from lean air-fuel ratio to rich air-fuel ratio. When it is determined that the zero sensor output is changing from lean to rich, step 136
The feedback correction coefficient FAFO for stoichiometric air-fuel ratio control is reduced by a predetermined value α, and when it is determined that the 02 sensor output has not changed from lean to rich, that is, the 0□ sensor continues to send the air-fuel ratio rich signal. When outputting,
In step 138, the air-fuel ratio feedback correction coefficient FAF is
O is decreased by a predetermined value β (α).

On the other hand, if it is determined in step 132 that the 0□ sensor output indicates a lean air-fuel ratio, then in step 140 the 0□
Determine whether the sensor output changes from rich to lean. When it is determined that the 02 sensor output has changed from rich to lean, the feedback correction coefficient FAFO is increased by a predetermined value α in step 142, and it is determined that the 02 sensor output continues to indicate a lean air-fuel ratio. If so, the feedback correction coefficient FAFO is increased by a predetermined value β in step 144.

As a result of the above, as shown in FIG. 7, the theoretical empty pressure control feedback correction coefficient F A F O is skipped by a predetermined value α when the O2 sensor output is reversed, and when the O2 sensor output indicates lean It is gradually increased by a predetermined value β, and when the 02 sensor output indicates rich, it is decreased by a predetermined value β.

FIG. 5 shows the feedback correction coefficient FAF/! for lean control in step 124 of FIG. In step 150, the operation of the A/D converter 88 is stopped, the A/D converter 55 is activated, and the lean sensor 52 is manually inputted via the current-voltage converter 53.
Execute A/D conversion processing of the output. Next step 15
2, as shown in Figure 6 (1), (2), and (3),
The lean correction coefficient KLEAN is calculated from the three-dimensional map defined by intake pipe pressure - PM, engine speed NE, and engine cooling water>WTHHW, and the lean correction coefficient KLEAN is
From the target voltage map shown in 4), the lean correction coefficient KLE is calculated.
A target voltage corresponding to ΔN is calculated. Next step 15
4, the A/D conversion value calculated in step 150 and the target voltage calculated in step 152 are compared, and the A/D conversion value is calculated in step 152.
If the converted value is larger than the target voltage, the lean control feedback correction coefficient FAF1 is increased by a predetermined value γ in step 156, and if the A/D conversion value is less than the target voltage, the lean control feedback correction coefficient FAF/ is increased in step 15B.
is decreased by a predetermined value γ.

As a result of the above, as shown in FIG. 8, the lean control feedback correction coefficient FAII! is increased by a predetermined value T if the lean sensor output is greater than the target voltage, and is decreased by a predetermined value T if the lean sensor output is smaller than the target voltage.

FIG. 9 shows a detailed routine for calculating the learning value KG1 at step 122 in FIG.
Each time FAFAV is skipped, the average value FAFAV of the feedback correction coefficients is calculated according to the following two.

2, 2, 2, ... (3) In steps 162 to 168, it is determined to which region of the predetermined intake pipe pressure regions the current intake pipe pressure PM belongs, and the MaroHg≦PM<
Step 170 and Step 1 for 280 ■ Hg
In step 72, it is determined whether the average value FAFAV of the feedback correction coefficient FAFO satisfies 0.98≦FAFAV≦1.02. When it is determined that FAFAV<0.98, the learned value KG is set to a predetermined value (
For example, 0.002) and FAFAV>1.02
At step 184, the learning value KG is set to a predetermined value (0,0
02) Increase it to 0. When 98≦FAFAV≦1.02, it returns as is. In step 174 and step 176, step 178 and step l' 80, the average value FAFAV of the feedback correction coefficient is 0.98≦FAF as in step 170 and step 172.
Determine whether or not AV≦1.02 is satisfied, 0.9
When 8≦FAFAV11.02 is satisfied, return as is, and when FAFAV<0.98, step 18
6. In step 190, the learning value KG! , learning value KG
j is reduced by a predetermined value (for example, 0.002), and FAFA
When V>1.02 (7), step 188, step 19
In step 2, the learned values KG, , and K G s are each increased by a predetermined value (0,002).

As a result of the above, the learned values KG1, KO2, and KO2 are learned in a predetermined intake pipe pressure region and stored in the backup ram.

FIG. 10 shows a fuel injection amount calculation routine executed every 180° CA. In step 200, the air-fuel ratio is feedback-controlled to a target air-fuel ratio on the leaner side than the stoichiometric air-fuel ratio. In the case of feedback control of lean control, it is determined whether the flag XLSNG is set in step 202 or not. When the flag XLSNC is reset, that is, when the lean sensor is operating normally, the basic fuel injection amount TP is calculated in accordance with the intake pipe pressure PM and the engine speed NE in step 204. In the next step 206, FIG. 6 (]), (2), (3)
A lean correction coefficient KLEAN corresponding to the current engine operating condition is calculated from the three-dimensional map shown in FIG. Then, in step 208, a correction coefficient K for correction of intake air temperature and increase/decrease correction during acceleration/deceleration is calculated, and in step 2]0, fuel injection iTΔUIl is calculated based on the above equation (2).

As a result of the above, the product of the basic injection amount TP, the learned value KGr, and the lean correction coefficient KLEAN is set to a value that approximately corresponds to the target air-fuel ratio, the fuel injection amount is corrected by the feedback correction factor IFAPI, and the air-fuel ratio becomes lower than the stoichiometric air-fuel ratio. The air-fuel ratio is controlled to a value close to the target air-fuel ratio on the lean side.

When it is determined in step 200 that the feedback control is not lean control, it is determined in step 212 whether the feedback control is to the stoichiometric air-fuel ratio. When it is determined that the feedback control is to the stoichiometric air-fuel ratio, step 216
In step 218, the basic fuel injection amount TP is calculated based on the intake pipe pressure PM and the engine speed NE, in the same manner as above, the correction coefficient K is calculated, and in step 220, the above (1) is calculated.
The fuel injection amount TAUO is calculated based on the formula.

As a result of the above, the product of the basic fuel injection amount TP and the learned value K is feedback-controlled to the value of .

When it is determined in step 202 that the flag XLSNG is set, that is, when it is determined that an abnormality has occurred in the lean sensor, the process proceeds to step 212, where it is determined whether feedback control to the stoichiometric air-fuel ratio is to be performed. Whether or not the flag XLSNG is set is determined during lean feedback control (2), so the process advances from step 212 to step 214 to execute open loop control.

In the case of open loop control, the feedback correction coefficient FAFO is set at step 116 in FIG.

Since FAFffi is set to 1.0, the above (2)
) Based on the formula, the fuel injection amount is calculated using the basic fuel injection amount and the lean correction coefficient, and an amount of fuel corresponding to this fuel injection amount is injected.

Figure 11 shows changes in the air-fuel ratio feedback correction coefficient FAFJ, lean sensor output, and air-fuel ratio when controlled as described above. When an abnormality occurs in the lean sensor and the lean sensor output decreases, Therefore, the lean correction coefficient FAFffi is reduced. As a result, the exhaust gas air-fuel ratio gradually becomes leaner. Then, the lean feedback correction coefficient FAF# is set to the lower limit value of the predetermined range (0,98
), the air-fuel ratio control switches from feedback control to lean control to open-loop control to lean control, and the air-fuel ratio is controlled to a constant air-fuel ratio near the target air-fuel ratio. Therefore, by discontinuing feedback control when the lean sensor is abnormal, operation can be continued without deteriorating drivability or exhaust emissions.

In addition, although the engine in which the basic fuel injection amount is determined by the intake pipe pressure and the engine speed has been described above, the present invention is not limited to this, and the basic fuel injection amount can be determined by the intake air amount and the engine speed. It is also possible to apply it to the specified engine.

Moreover, although an example has been described above in which the air-fuel ratio is controlled in open loop to a target air-fuel ratio on the lean side than the stoichiometric air-fuel ratio when the lean sensor is abnormal, feedback control may be performed to the stoichiometric air-fuel ratio. Further, an alarm may be issued when the lean sensor is abnormal.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing the main routine of an embodiment of the present invention, FIG. 2 is a schematic diagram showing an engine to which the present invention can be applied, FIG. 3 is a block diagram showing details of the control circuit shown in FIG. 2, and FIG.
FIG. 5 is a flowchart showing details of step 120 of FIG.
The figure is a flowchart showing the details of step 124 in Figure 1, Figure 6 (1), (2), and (3) are diagrams showing a map of lean correction coefficients, and Figure 6 (4) is a line diagram. A line diagram showing the target voltage with respect to the correction coefficient, FIG. 7 is a line diagram showing the change in the feedback correction coefficient with respect to the change in the 02 sensor output, and FIG. 8 is a line diagram showing the change in the feedback correction coefficient with respect to the change in the lean sensor output. FIG. 9 is a flowchart showing the details of step 122 in FIG. 1, FIG. 10 is a flowchart showing the fuel injection amount 13it calculation routine of this embodiment, and FIG. 11 is a feedback correction coefficient, air-fuel ratio, etc. when the lean sensor is abnormal. FIG. 2... Pressure sensor, 10... Throttle sensor, 20... Fuel injection valve, 30... 0□ sensor, 52... Lean sensor.

Claims (1)

[Claims] (1) When determining an abnormality in the lean sensor, which outputs a signal proportional to the residual oxygen concentration in exhaust gas in a region leaner than the stoichiometric air-fuel ratio, the basic fuel injection amount is corrected to feedback the air-fuel ratio to the stoichiometric air-fuel ratio. The feedback correction coefficient for stoichiometric air-fuel ratio control is determined based on the output of the O_2 sensor that outputs a signal that is inverted from the stoichiometric air-fuel ratio. The basic fuel injection amount is learned and corrected so that the average value of the feedback correction coefficient for fuel ratio control falls within a predetermined range, and the learned and corrected basic fuel injection amount is changed to a value reduced according to the operating condition and the lean sensor output. When the air-fuel ratio is being feedback-controlled to a target air-fuel ratio on the leaner side than the stoichiometric air-fuel ratio based on the lean control feedback correction coefficient determined based on the lean control feedback correction coefficient, the lean control feedback correction coefficient becomes a value outside the predetermined range. A method for determining abnormality in a lean sensor, characterized in that it is determined that the lean sensor is abnormal when: