JPS6276444A - Method for detecting abnormality of oxygen concentration sensor - Google Patents

Abstract

PURPOSE:To decide whether an oxygen concentration sensor is abnormal or not by detecting the output level of the oxygen concentration sensor when the control of an air/fuel ratio feed back is stopped. CONSTITUTION:In terms of an air/fuel ratio control circuit 20, information on absolute pressure and cooling temperature in an air intake manifold 4, that an oxygen concentration in an exhaust gas and vehicle velocity from an A/D converter 63 and information expressing the rotational frequency of an engine from a counter 65 are alternately supplied to a CPU 69 through an I/O bus 72. The CPU 69 is so constituted as to generate an inner interruption signal by one duty period, and executes an action for duty-controlling the supply of a secondary air intake in accordance with the interruption signal. At the time of stopping the control of the air/fuel ratio feed back, the oxygen concentration comes to below O1 (for instance, 2%) by opening an electromagnetic opening/closing valve 9. If a pump current value is I1, the output voltage Vs' of the oxygen concentration sensor exceeds V1 in normal operation. Accordingly, if said voltage is below V1, the oxygen concentration sensor 14 is considered to be abnormal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting an abnormality in an oxygen concentration sensor in an air-fuel ratio control device for an internal combustion engine.

1. In order to purify the exhaust gas of internal combustion engines and improve fuel efficiency, the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the air-fuel ratio of the air-fuel mixture supplied to the engine is adjusted to the target air-fuel ratio according to this detection level. There is an air-fuel ratio control device that performs feedback control.゛As an oxygen concentration sensor used in such an air-fuel ratio control device, the so-called lean oxygen concentration sensor generates an output proportional to the oxygen concentration in the exhaust gas in a region where the air-fuel ratio of the mixture supplied to the engine is greater than the stoichiometric air-fuel ratio. There is a sensor (Japanese Patent Laid-Open No. 153155/1983). Such a lean oxygen concentration sensor is provided with an oxygen concentration detector having a pair of flat oxygen ion conductive solid electrolyte members. The solid electrolyte member is arranged in exhaust gas, and electrodes are formed on each front and back surface of the solid electrolyte member, and the solid electrolyte members are arranged in parallel so as to face each other with a predetermined gap in between. ing. One of the solid electrolyte members acts as an oxygen pump element, and the other acts as a battery element for oxygen concentration ratio measurement. When a current is supplied between the electrodes of the oxygen pump element so that the electrode on the gap side becomes the negative electrode in the exhaust gas, the oxygen gas in the gap is ionized on the negative electrode side of the oxygen pump element, and the oxygen gas inside the oxygen pump element is ionized. moves toward the positive electrode surface and is released from the positive electrode surface as oxygen gas. At this time, the decrease in oxygen gas in the gap creates an oxygen m difference between the gas in the gap and the gas outside the battery element, so that a voltage is generated between the electrodes of the battery element. If the pump current value supplied to the oxygen pump element is changed to maintain this voltage at a constant value, the pump current value will be approximately proportional to the oxygen concentration in the exhaust gas at a constant temperature, and will be output as the oxygen concentration detection value. be done. Based on the pump current value supplied to the oxygen pump cord, it is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine is richer or leaner than the target air-fuel ratio. When controlling the air-fuel ratio using secondary air, if it is determined to be rich, secondary air is supplied to the engine, and if it is determined to be lean, the supply of secondary air is stopped to reach the target air-fuel ratio. Controlled by air fuel ratio. Furthermore, if the pump current value supplied to the oxygen pump element is controlled to a constant value, the voltage generated between the electrodes of the battery element will be approximately proportional to the oxygen concentration in the exhaust gas, and the voltage generated between the electrodes of the battery element will be approximately proportional to the oxygen concentration in the exhaust gas. The air-fuel ratio can also be determined from the voltage.

When air-fuel ratio feedback control is performed according to the output level of the lean oxygen concentration sensor, the target air-fuel ratio can be set to a value within the lean range depending on the engine operating state, and fuel efficiency can be improved. I can do it.

By the way, if an abnormality such as an internal disconnection, short-circuit, or output fluctuation due to element deterioration occurs in such an M element concentration proportional type oxygen concentration sensor, the operating condition will worsen if the operation is continued, so the abnormality should be detected. It is desirable to instruct the operator to stop operation. However, there has been a problem in that it is difficult to easily detect abnormalities in oxygen concentration sensors proportional to acid/N concentration.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an abnormality detection method that can easily detect an abnormality in an oxygen concentration proportional type oxygen concentration sensor.

The abnormality detection method of the present invention is characterized in that an abnormality in the oxygen concentration sensor is determined from the output level of the oxygen concentration sensor when the air-fuel ratio feedback control is stopped.

Published by JL Embodiments of the present invention will be described below with reference to the drawings.

In the air-fuel ratio control device to which the abnormality detection method of the present invention shown in FIG. Supplied. The vaporizer 3 has a throttle valve 6
A venturi 7 is formed upstream of the throttle valve 6.

The intake manifold 4 and the vicinity of the air discharge port of the air cleaner 2 are communicated through an intake secondary air supply passage 8.

An electromagnetic on-off valve 9 is provided in the intake secondary air supply passage 8 . The electromagnetic on-off valve 9 is opened by energizing the solenoid 9a.

On the other hand, 10 is an absolute pressure sensor installed in the intake manifold 4 and generates an output level according to the absolute pressure inside the intake manifold 4. 11 is an absolute pressure sensor of the engine 5 (
12 is a cooling water temperature sensor that generates an output at a level corresponding to the cooling water temperature of the engine 5; 14 is a cooling water temperature sensor installed in the exhaust manifold 15 of the engine 5; This is an oxygen concentration sensor that generates an output proportional to the oxygen concentration in the gas. Exhaust manifold 1 downstream from the location of the oxygen concentration sensor 14
5 is provided with a catalytic converter 18 to promote the reduction of harmful components in exhaust gas. Electromagnetic quantity valve closing 9,
The absolute pressure sensor 10, crank angle sensor 11, water temperature sensor 12, and oxygen concentration sensor 14 are connected to an air-fuel ratio control circuit 20. Further connected to the air-fuel ratio control circuit 20 are a vehicle speed sensor 116 that generates an output at a level corresponding to the speed of the vehicle, and a lamp 17 that indicates an abnormality in the oxygen temperature sensor.

As shown in FIG. 2, the oxygen temperature sensor 14 consists of a pair of flat elements parallel to each other, including an oxygen pump cord 21 and a battery element 2.
It has 2. Oxygen pump element 21 and battery element 22
The main body is made of an oxygen ion conductive solid electrolyte material, and a gap 23 is formed between one end thereof, and the (I!! end is connected to η through a spacer 24. Also, the oxygen pump element 21 and the battery element 22 - rectangular electrode plates 25 to 28 made of porous heat-resistant metal in the surface direction at the ends thereof;
are provided, and lead lines 25a to 28a of the electrode plates 25 to 28 are formed on the other end surface.

The control section of the oxygen concentration sensor 14 is a constant current circuit 30.
, limiter circuit 31, programmable voltage generation circuit 32
and a non-inverting amplifier 33.

A current is supplied between the electrode plates 25 and 26 of the oxygen pump element 21 by a constant current circuit 30. The constant current circuit 30 includes an operational amplifier 34. NPN transistor 35, diode 36
and resistors 37 to 40. The output terminal of the operational amplifier 34 is connected to the base of a transistor 35 via a resistor 37.゛The emitter of the transistor 35 is grounded via a resistor 38, connected to the inverting input terminal of the operational amplifier 34 via a resistor 39, and further connected to the output terminal of the operational amplifier 34 via a diode 36 in the forward direction. There is. The resistor 38 is provided to detect the pump current value Ip flowing between the electrode plates 25 and 26 of the oxygen pump element 21. 1- The collector of the transistor 35 is connected to the lead wire 26 to the inner electrode plate 26 of the oxygen pump element 21.
a, and a voltage VB is supplied to the outer electrode plate 25 via a lead wire 25a.

A non-inverting input terminal of the operational amplifier 34 is connected to the programmable voltage generation circuit 32 via a resistor 40. The programmable voltage generation circuit 32 generates a voltage according to the Ip value command data output from the air-fuel ratio control circuit 20.

On the other hand, the inner electrode plate 27 of the battery element 22 has a lead wire 27
a, and the outer electrode plate 28 is connected to the lead wire 2.
The operational amplifier 41.8a is connected to the operational amplifier 41.8a. It is connected to a non-inverting amplifier 33 consisting of resistors 42-44. The output terminal of the non-inverting amplifier 33 is connected to the air-fuel ratio control circuit 20.

As shown in FIG. 3, the air-fuel ratio control circuit 20 includes a level conversion circuit 61 that converts the output levels of the absolute pressure sensor 10, water temperature sensor 12, oxygen 1 degree sensor 14, and vehicle speed sensor 16.
, a multiplexer 62 that selectively outputs one of the sensor outputs that have passed through the level conversion circuit 61, a Δ/D converter 63 that converts the signal output from the multiplexer 62 into a digital signal, and a crank angle sensor 11. a waveform shaping circuit 64 that shapes the output signal of the waveform shaping circuit 6;
4, a drive circuit 67 that drives the lamp 17 to turn on, a drive rn circuit 68 that drives the LA on/off valve 9, and performs digital calculations according to a program. c.
pu <central processing circuit) 69, ROM 70, etc. in which various processing programs and data are pre-installed, RAM,
71, and a latch circuit 73 that holds Ip value command data. Multiplexer 62, Δ/D converter 6
3, counter 65, drive circuit 67, 68, CPU 69,
The ROM 70XRAM 71 and the latch circuit 73 are connected to each other by the input/output cover 2.

In this configuration, when the IP value command data is output from the air-fuel ratio control circuit 20 to the programmable voltage generation circuit 32, the programmable voltage generation circuit 32 converts the voltage corresponding to the IP value command data to the reference voltage Vr+ and applies the voltage to the resistor 4.
0 to the non-inverting input terminal of the operational amplifier 34.

The pump current value ip flowing through the electrode plates 25 and 26 of the oxygen pump element 21 when the reference voltage Vr+ is supplied is detected by the terminal voltage Vρ of the resistor 38, and the terminal voltage Vp is detected by the terminal voltage Vρ of the resistor 38.
9 to the inverting input terminal of the operational amplifier 34.

When the terminal voltage Vp is lower than the reference voltage Vr+, the output level of the operational amplifier 34 becomes a high level and increases the base current of the transistor 35, so that the pump current increases, and when the terminal voltage Vp is higher than the reference voltage Vr+, the operational amplifier 34 outputs a high level. The output level of 34 becomes a low level, which reduces the base current of transistors 1 to 35, so that the pump current decreases. Since this operation is repeated at high speed, the pump current 1p becomes the reference voltage Vr+, that is, a constant current value according to the Ip value command data.

On the other hand, a voltage Vs is applied between the electrode plates 27 and 28 of the battery element 22.
is generated, and the voltage Vs is amplified by the non-inverting amplifier 33 and supplied to the air-fuel ratio control circuit 20 as the output voltage Vs' of the oxygen concentration sensor 14.

In the air-fuel ratio control circuit 20, information on the absolute pressure in the intake manifold 4, cooling water temperature, oxygen concentration in exhaust gas, and vehicle speed is alternatively received from the A/D converter 63, and information on the absolute pressure in the intake manifold 4, the oxygen concentration in the exhaust gas, and the vehicle speed is alternatively received from the counter 6.
5, information representing the engine speed is supplied to the CPU 69 via the input/output cover 2. The CPU 69 is configured to generate an internal interrupt signal every duty period, and in response to this interrupt signal, performs an operation to duty-limit the intake secondary air supply as described later.

Next, the operation of the air-fuel ratio control device including the abnormality detection method according to the present invention will be explained with reference to the operation flowchart of the CPU 69 shown in FIGS. 4 and 5.

In the CPU 69, first, a valve opening drive stop command is issued to the drive circuit 68 to close the electromagnetic on-off valve 9 every time an interrupt signal is generated (step 81). This is CP
This is to prevent malfunction of the electromagnetic on-off valve 9 during the calculation operation of LJ69. Next, the closing time TAF of the electromagnetic on-off valve 9 is made equal to one duty period TsOL (step 8
2), and the A/F routine shown in FIG. 6 is executed to calculate the output opening time TOUT of the electromagnetic on-off valve 9 (step 83).

In the △/F routine, first, the operating state of the vehicle (including the operating state of the engine) is determined by air-fuel ratio feedback (F/B).
It is determined whether the control conditions are satisfied (step 831). This determination is determined from the absolute pressure in the intake manifold, cooling water temperature, vehicle speed, and engine rotation speed. For example,
It is assumed that the air-fuel ratio feedback control conditions are not satisfied at low vehicle speeds and low cooling water temperatures. Here, if it is determined that the air-fuel ratio feedback control conditions are not satisfied, the valve opening time To is set to stop the air-fuel ratio feedback control.
UT is set to "o" (step 832), and Ip
If the content of the value command data is Ip=1+ (for example, 10m
A) and is supplied to the latch circuit 73 (step 833). As a result, the oxygen pump element 21
A pump current of current value I is supplied between the electrode plates 25 and 26 of. And the output voltage Vs- of the oxygen cJ failure sensor 14
is read and its output voltage Vs- becomes the predetermined voltage V+
(for example, 40 mV) is determined (step 834). If vs'≧■1, it is determined that the oxygen concentration sensor 14 is not abnormal. If Vs-<V+,
The oxygen concentration sensor 14 is determined to be abnormal, and a lamp lighting command is issued to the drive circuit 67 (step 835).
). The drive circuit 67 turns on the lamp 17 in response to a lamp lighting command.
is turned on to alert the driver to the abnormality of the oxygen concentration sensor 14.

On the other hand, if it is determined that the air-fuel ratio feedback control conditions are satisfied, the 1-duty Shumei Ts.

Secondary air supply to L, that is, reference duty ratio (reference amount valve time) of opening of electromagnetic on-off valve 9 DaASE
7')' is set (step 836), and the intake manifold internal absolute pressure PBA and engine rotation speed N are stored in the ROM 70.
The reference duty ratio DBASE determined from e is DBAS
Since it has been read in advance as an E data map, the CP
U69 reads the absolute pressure PBA and engine speed Ne, and sets the standard duty ratio D8A corresponding to the 8 values read.
Search the SE from the DBASE data map. Next, C
It is determined whether the counting time of the internal time counter A (not shown) of the PU 69 has elapsed for a predetermined time Δt1 (
step 837). The predetermined time Δt1 corresponds to a response delay time from when the secondary air is supplied until the result is detected by the oxygen concentration sensor 14 as a change in the oxygen concentration in the exhaust gas. When a predetermined time Δ1+ has elapsed since the time counter A was reset and started counting, the time counter A is reset and counting starts from the initial value. (Step 838). That is, after the time force "Kunta A starts counting 81 from the initial value by executing step 838, it is determined in step 837 whether or not a predetermined time Δt1 has elapsed. In this way, the time Predetermined time △t by counter A
When counting of 1 is started, a target air-fuel ratio leaner than the stoichiometric air-fuel ratio is set (step 839). In order to set this target air-fuel ratio, DBA S is stored in the ROM70.
Similar to the E data map, absolute pressure inside the intake manifold P8
A reference level L ref corresponding to the target air-fuel ratio determined from Δ and the engine speed Ne is written in advance as an A/F data map separately from the D8ASε data map. Therefore, the CPU 69 searches the reference level 1ref'/j-A/F data map according to the absolute pressure PBA and the engine speed Ne. Next, in step 839, the output level LO2 of the oxygen concentration sensor 14 is determined from the information on the M cumulative concentration.
It is determined whether or not the reference level L ref is greater than the reference level L ref determined in (step 8310). That is,
It is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine 5 is leaner than the target air-fuel ratio. L02>1r
If ef, the air-fuel ratio is higher than the target air-fuel ratio, so the calculated value IL is calculated (step 8311). The reduction value IL is 1 as a constant, the engine speed Ne and the absolute value PB
It is obtained by multiplying A by 1Ei (Kt·Ne-PBA), and depends on the intake air content of the engine 5.

After calculating the subtraction value I, the correction value four, which has already been calculated by executing this Δ/F routine, is read out from the memory location and al of the RAM 71, and the read out correction value 1
The subtraction value ■ is subtracted from 01JT, and the calculated value is set as a new correction value 10LJT and written to storage location a1 of the RAM 71 (step 8312>.On the other hand, if LO2≦L ref in step 8310, the air-fuel ratio is Since it is richer than the target air-fuel ratio, the additional value IRff
iEj is issued (step 8313). The additional value IR is 2 for the constant (1 for ≠), engine speed Ne and absolute pressure P
It is obtained by multiplying B and A by each other (K2.Ne-PBA), and is made to depend on the intake air amount of the engine 5. After calculating the additional value IR, the correction value 10UT, which has already been calculated by executing the A/F routine, is
The correction value IOU is read from the memory location a1 of M71 and added to the read correction value IOU! The J value IR is added and the calculated value becomes the new correction value I.

UT and written to storage location a+lc of RAM 71 (step 8314). In this way, the correction value [0LJT
is calculated in step 8312 or 8314, the correction value I O (J ).

Note that if it is determined in step 837 that the predetermined time Δt1 has not elapsed after the time counter A is reset in step 838 and starts counting from the initial value, step 8315 is immediately executed; , the correction value ■0LJT obtained by executing the A/F routine up to the previous time is read out.

When the execution of the A/F routine is completed, the output valve opening time To! from 1 duty cycle TSOL! Valve closing time TAF is determined by subtracting JT (step 84). Next, a value corresponding to the valve closing time TAF is set in an internal time counter B (not shown) of the CPU 69, and down counting of the time counter B is started (step 85). Then, it is determined whether the y1 value of time counter B has reached "0" (step 86), and time counter B
When the count value reaches 0'', a valve opening drive command is generated to the drive circuit 68 (step 87).During this time, the drive circuit 68 drives the electromagnetic on-off valve 9 in accordance with the valve drive command. However, during this time, the valve driving state continues until step 81 is executed next.If the count value of time counter B does not reach ``00'' in step 86, step 86
is executed repeatedly.

Therefore, in such an air-fuel ratio control device, the interrupt signal I
In response to the occurrence of NT, the electromagnetic on-off valve 9 is immediately closed, and the supply of intake secondary air to the engine 5 is stopped. In addition, the closing time TAF of the solenoid on-off valve 9 is calculated during one duty cycle TsOL, and when the valve closing time TAF has elapsed from the time when the interrupt signal was generated, the solenoid on-off valve 9 is opened and the engine starts running. Intake secondary air is supplied to the intake air 5 via an intake secondary air supply passage 8. Because this operation is repeated, the intake secondary air is duty-controlled.

As described above, in the abnormality detection method of the present invention, the oxygen concentration sensor 14 has the oxygen intensity-bomb current characteristic as shown in FIG. If the oxygen concentration is below 0+ (for example, 2)% due to the valve and the pump current value is ■1,
Since the output voltage VS- of the oxygen concentration sensor is higher than V+ during normal operation, if it is lower than 1, the oxygen concentration sensor 14
This can be considered an abnormality.

As described in Section 21 and above, in the oxygen concentration sensor abnormality detection method of the present invention, an abnormality in the oxygen concentration sensor is determined according to the output level of the oxygen concentration sensor when the air-fuel ratio feedback control is stopped. When the air-fuel ratio feedback control is stopped, the air-fuel ratio is controlled in a rich direction by stopping the secondary air supply and becomes relatively stable, so it is easy to determine whether there is an abnormality in the oxygen concentration sensor from the output level of the oxygen concentration sensor at that time. This is possible.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an air-fuel ratio control device according to the present invention, FIG. 2 is a diagram showing the configuration of an oxygen concentration sensor in the device shown in FIG. 1, and FIG. 3 is a circuit diagram showing an air-fuel ratio control device in the device shown in FIG. 1. 4 and 5 are flowcharts showing the operation of the CPU, and FIG. 6 is a diagram showing the oxygen concentration-pump current characteristics of the oxygen concentration sensor. Explanation of symbols of main parts 2... Air cleaner 3... Carburetor 4... Intake manifold 6... Throttle valve 7... Venturi 8 ...Intake secondary air supply passage 9 ...Solenoid on-off valve 10 ...Absolute pressure sensor 11 ...Crank angle sensor 12 ...Cooling Water temperature sensor 14...Oxygen concentration sensor 15...Exhaust manifold 21...Oxygen pump element 22...Battery element 23...Gap portion 24・・・・・・Spacer 25 to 28・・・・・・Electrode plate'$7I section tail, concave tail 4, bottom 5TZJ

Claims (2)

[Claims] (1) An oxygen concentration sensor is installed in the exhaust gas passage of an internal combustion engine and generates an output proportional to the oxygen concentration in the exhaust gas, and the air-fuel ratio of the air-fuel mixture supplied to the engine is determined by the output level of the oxygen concentration sensor. An abnormality detection method of the oxygen concentration sensor in an air-fuel ratio control device that performs feedback control according to the output level of the oxygen concentration sensor and stops air-fuel ratio feedback control according to the output level of the oxygen concentration sensor during a predetermined operation of the engine, the method comprising: An abnormality detection method, characterized in that an abnormality in the oxygen concentration sensor is determined from an output level of the oxygen concentration sensor when control is stopped. (2) The intake secondary air supply passage communicating with the downstream side of the carburetor throttle valve is opened and closed by an on-off valve according to the output level of the oxygen concentration sensor, and when the air-fuel ratio feedback control is stopped, the intake air is closed by closing the on-off valve when the air-fuel ratio feedback control is stopped. The abnormality detection method according to claim 1, characterized in that the secondary air supply passage is closed.