JPH11166438A - Air-fuel ratio sensor deterioration detector for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a oxygen sensor deterioration detector for an internal combustion engine, which is capable of properly determining the deterioration of an oxygen sensor even when the load condition of the internal combustion engine is changed during the detection of the deterioration of the oxygen sensor provided in the exhaust system of the internal combustion engine. SOLUTION: An inversion cycle tmCYCL of the output VO2 of an O2 sensor 14F is calculated (S23), and when the calculated inversion cycle tmCYCL is longer than a specified deterioration determining value TMCYLOK, the deterioration of the O2 sensor 14F is determined (S28). In this case, the specified deterioration detemtining value TMCYCLOK is set to be smaller as the intake air amount integrated value GAIRSUM 2 of an engine 1 integrated over a specified period TMWAVET is larger (S40). Thus, even if the load condition of the engine 1 is changed during the detection of the deterioration of the O2 sensor, the deterioration of the O2 sensor is properly determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting deterioration of an air-fuel ratio sensor of an internal combustion engine which detects deterioration of an air-fuel ratio sensor provided in an exhaust system of the internal combustion engine.

[0002]

2. Description of the Related Art Generally, in order to control the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine to a desired value, the exhaust gas is disposed upstream of a three-way catalyst disposed in an exhaust system of the internal combustion engine. An upstream oxygen sensor for detecting the oxygen concentration of
The air-fuel ratio of the air-fuel mixture is controlled according to the output of the upstream oxygen sensor.

The characteristics (internal resistance, electromotive force, response time) of such an upstream oxygen sensor are liable to change due to thermal deterioration or the like, and if the characteristics deteriorate, the control accuracy of the air-fuel ratio deteriorates. become.

[0004] As a method of detecting the deterioration of the upstream oxygen sensor, the feedback control of the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to the target air-fuel ratio based on the output of the upstream oxygen sensor is performed. The output of the upstream oxygen sensor is monitored over a predetermined period, the reversal cycle of the upstream oxygen sensor is calculated from the number of reversals of the output of the upstream oxygen sensor during the predetermined period, and the reversal cycle is determined according to the intake air amount of the internal combustion engine. The present applicant has already proposed a method of detecting the deterioration of the upstream oxygen sensor by comparing the deterioration judgment value set in advance with the present invention (see, for example, Japanese Patent Application Laid-Open No.
No. 50200).

[0005]

However, in the above-mentioned prior art, the reversal cycle varies depending on the load conditions of the internal combustion engine, for example, conditions such as the engine speed and the absolute pressure in the intake air pipe. Since the deterioration judgment value is set according to the intake air amount which is an unstable parameter that changes instantaneously according to the load fluctuation of the internal combustion engine, the deterioration judgment value is determined with respect to the load condition of the internal combustion engine when deterioration is detected. It cannot be set properly and there is a risk of erroneous detection.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to change the load condition of an internal combustion engine during detection of deterioration of an oxygen sensor provided in an exhaust system of the internal combustion engine. It is still another object of the present invention to provide an oxygen sensor deterioration detection device for an internal combustion engine that can appropriately determine the deterioration of the oxygen sensor.

[0007]

In order to achieve the above object, an air-fuel ratio sensor deterioration detecting device for an internal combustion engine according to claim 1 is provided in an exhaust system of an internal combustion engine to detect an air-fuel ratio of exhaust gas of the engine. An air-fuel ratio sensor, and air-fuel ratio control means for controlling an air-fuel ratio of an air-fuel mixture supplied to the engine based on an output of the air-fuel ratio sensor. Reversal cycle detecting means for detecting a reversal cycle of the output of the air-fuel ratio sensor over a period of time, and a deterioration determination for determining that the air-fuel ratio sensor has deteriorated when the detected reversal cycle is longer than a predetermined deterioration determination value. Means, an intake air amount integrating means for integrating the intake air amount of the engine over the predetermined period, and setting the predetermined deterioration determination value according to the integrated intake air amount. Characterized in that it comprises a deterioration determining value setting means that.

With this configuration, the reversal cycle of the output of the air-fuel ratio sensor is detected, and when the detected reversal cycle is longer than a predetermined deterioration determination value, it is determined that the air-fuel ratio sensor has deteriorated. Since the predetermined deterioration determination value is set according to the intake air amount of the internal combustion engine integrated in the predetermined period, the deterioration determination of the oxygen sensor is performed even if the load condition of the internal combustion engine changes during the detection of the deterioration of the air-fuel ratio sensor. It can be done properly.

The predetermined period is a period during which the deterioration judgment of the air-fuel ratio sensor is executed.

According to a second aspect of the present invention, there is provided an air-fuel ratio sensor deterioration detecting device for an internal combustion engine, wherein the deterioration determining value setting means is configured to accumulate the predetermined deterioration determining value. The smaller the set intake air amount is, the smaller it is set.

According to this configuration, the deterioration determination by the air-fuel ratio sensor deterioration detecting device for the internal combustion engine according to the first aspect can be performed more accurately.

[0012]

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

FIG. 1 is a diagram showing an overall configuration of an internal combustion engine (hereinafter referred to as an "engine") using an air-fuel ratio sensor deterioration detecting device according to an embodiment of the present invention, and a control device therefor. In the figure, reference numeral 1 denotes, for example, a four-cylinder engine, and a throttle valve 3 is arranged in the intake pipe 2 of the engine 1. The throttle valve 3 has a throttle valve opening (θ
TH) sensor 4 is connected to the throttle valve 3
An electric signal corresponding to the degree of opening is output and supplied to an electronic control unit (hereinafter referred to as “ECU”) 5.

A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) of the intake pipe 2, and each injection valve is connected to a fuel pump (not shown). The ECU 5 is electrically connected to the ECU 5 and controls a valve opening time of fuel injection based on a signal from the ECU 5.

On the other hand, an intake pipe absolute pressure (PBA) sensor 7 is provided immediately downstream of the throttle valve 3, and a pressure signal converted into an electric signal by the intake pipe absolute pressure sensor 7 is supplied to the ECU 5. You. Further, an intake air temperature (TA) sensor 8 is attached downstream thereof, detects the intake air temperature TA, outputs a corresponding temperature signal, and supplies it to the ECU 5.

An engine water temperature (TW) sensor 9 composed of a thermistor or the like is mounted on a cylinder block of the engine 1, detects an engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 5. .

Around a camshaft or a crankshaft (not shown) of the engine 1 is located at a crank angle position before a predetermined crank angle with respect to the top dead center (TDC) at the start of the intake stroke of each cylinder (a crank angle of 180 in a four-cylinder engine). T)
An engine speed (NE) sensor 10 that generates a DC signal pulse, and a cylinder discrimination sensor (hereinafter, a “CYL sensor”) that outputs a signal pulse (hereinafter, referred to as a “CYL signal pulse”) at a predetermined crank angle position of a specific cylinder of the engine 1. "
), And the CYL signal pulse and the TDC signal pulse are supplied to the ECU 5.

An exhaust pipe 12 of the engine 1 is provided with a three-way catalyst (catalytic converter) 13 for purifying components such as HC, CO and NOx in the exhaust gas. Exhaust pipe 12
Upstream of the three-way catalyst 13 is provided with an upstream oxygen sensor 14F.
(Hereinafter referred to as “O2 sensor 14F”), and a downstream oxygen sensor 14R (hereinafter referred to as “O2 sensor 14R”) is mounted downstream of the three-way catalyst 13. These O2 sensors 14F and 14R detect the oxygen concentration in the exhaust gas, output an electric signal corresponding to the detected value, and supply it to the ECU 5.

An atmospheric pressure (PA) sensor 15 for detecting an atmospheric pressure is connected to the ECU 5, and a detection signal is supplied to the ECU 5.

The ECU 5 shapes input signal waveforms from various sensors including the above-described sensors, corrects a voltage level to a predetermined level, and converts an analog signal value to a digital signal value. A central processing circuit (hereinafter referred to as "CPU") 5b, a storage means 5c for storing various calculation programs executed by the CPU 5b and calculation results, and an output circuit 5d for supplying a drive signal to the fuel injection valve 6 and the like. Be composed.

Based on engine parameter signals from various sensors, the CPU 5b of the ECU 5 determines various engine operating states such as an air-fuel ratio feedback control operation area and an open loop control operation area corresponding to the oxygen concentration in the exhaust gas. At the same time, the fuel injection time Tout of the fuel injection valve 6 is calculated in synchronization with the TDC signal pulse based on the following equation (1) according to the engine operating state.

Tout = Ti × KO2 × K1 + K2 (1) Here, Ti is the basic fuel amount, specifically, the engine speed NE and the intake pipe absolute pressure PBA such that the air-fuel ratio of the mixture becomes the stoichiometric air-fuel ratio. , And a Ti map for determining the Ti value is stored in the storage unit 5c.

KO2 is an air-fuel ratio correction coefficient calculated based on the outputs of the O2 sensors 14F and 14R. During the air-fuel ratio feedback control, the mixture supplied to the engine 1 according to the outputs of the O2 sensors 14F and 14R. Is set so as to match the target air-fuel ratio, and is set to a predetermined value according to each open-loop control operation region during open-loop control.

K1 and K2 are other correction coefficients and correction variables calculated according to various engine parameter signals, respectively, to optimize various characteristics such as a fuel consumption characteristic and an engine acceleration characteristic according to an engine operating state. Is set to such a value.

The ECU 5 calculates the calculated fuel injection time T
An output circuit 5d outputs a drive signal of the fuel injection valve 6 in accordance with out.
Output via.

FIG. 2 is a flowchart showing the overall configuration of the process for detecting the deterioration of the O2 sensor 14F. This processing is executed every predetermined time (for example, every 10 msec). Book O2
Sensor 14F deterioration detection processing (O2 sensor deterioration monitor)
Is the O2 sensor 1 during the air-fuel ratio feedback control.
This is performed by measuring the inversion cycle of the output of 4F.

First, at step S10, it is determined whether or not a predetermined condition before deterioration monitoring is satisfied and deterioration detection of the O2 sensor 14F can be executed. As the predetermined condition before deterioration monitoring, for example, an operating parameter of the engine, for example,
Intake temperature TA, engine speed NE, absolute intake pipe pressure PB
A is within a predetermined range, the purge flow rate of the evaporated fuel is less than a predetermined amount, the vehicle speed is in a steady state, and it is determined whether the air-fuel ratio feedback control has been performed for a predetermined time before monitoring is permitted. Then, when all the above conditions are satisfied, it is determined that the condition before deterioration monitoring is satisfied. If the predetermined pre-deterioration-monitoring condition is not satisfied, the process proceeds to step S11, and the O2 sensor deterioration monitor execution flag FO2M indicating "1" indicating that the O2 sensor deterioration monitor is being executed.
Is set to “0”, and the process is terminated. If the predetermined condition before deterioration monitoring is satisfied, the process proceeds to step S12, where the output value VO2 of the O2 sensor 14F is set to the output value VO.
The rich determination flag FPVREF indicating “1” indicating that it is on the rich side with respect to the inversion determination reference value PVREF of 2
Is changed from “1” to “0” or from “0” to “1”.

In step S12, the flag FPVRE
If F is not inverted, this process is immediately terminated. If F is inverted, the process proceeds to step S13 to determine whether or not the rich determination flag FPVREF is "1". As a result of the determination in step S13, the flag FPV
If REF is "0", it is determined that the inversion of the flag FPVREF is from "1" to "0", that is, the output value VO2 of the O2 sensor 14F is inverted from the rich side to the lean side with respect to the RVREF value. While ending immediately
If "1", the inversion of the flag FPVREF is inverted from "0" to "1", that is, the output value VO2 of the O2 sensor 14F is inverted from the lean side to the rich side with respect to the RVREF value. Is set to "1" (step S14), and the process proceeds to step S15.

In step S15, the flag FPVRE is set.
It is determined whether the inversion of F from “0” to “1” is the first inversion after the O2 sensor deterioration monitor is executed, and if it is the first inversion, the number of inversion times counter value NWAVE described later and integration of the measurement time timer Value TMWAVE, intake air amount integrated value GA
IRSUM2 is set to “0” and initialized (step S16), and further, an up-count timer tmWAV
And an intake air amount integrated value gairPO2 to be described later are each set to “0” and initialized (step S17), and this processing ends. Here, the timer integrated value TMWAVE is an integrated value of the value of the timer tmWAV, and is not reset even if the present program is exited during the O2 sensor deterioration monitoring.

If the result of the determination in step S15 is that the flag FPVREF has been inverted from "0" to "1" for the second time since the execution of the O2 sensor deterioration monitor, the next step S18 is to execute the previous step. The flag FO2M
Is "1" or not, and if not "1",
That is, when the flag FO2M is "0", it is determined that the flag FO2M is first inverted from "0" to "1" after the O2 sensor deterioration monitor is executed, and the step S17 is performed.
And terminate the process.

In step S18, the previous flag FO
If 2M is "1", the flow advances to step S19 to increment the inversion counter value NWAVE by "1", add the value of the timer tmWAV to the measured time timer integrated value TMWAVE, and add the current timer integrated value. TMW
AVE, and the previous integrated value of intake air amount GAIRSUM2
The intake air amount integrated value gai calculated by the process of FIG.
rPO2 is added and the current intake air amount integrated value GAIRS
UM2 is calculated (intake air amount integrating means).

FIG. 4 is a flowchart of a program for calculating the girPO2 value used in step S19 of FIG. The process of FIG. 4 is executed every time a TDC signal pulse is generated.

In the process of FIG. 4, in step S40, the current value of the integrated intake air amount gairPO2 is calculated by the following equation (2).

GairPO2 = gairPO2 + TIM × KPA × KPA (2) Here, the intake air amount integrated value gairPO2 on the right side is the previous value, and TIM is the basic fuel amount Ti in the equation (1).
It is a value corresponding to the basic fuel amount converted from.

KPA is an atmospheric pressure correction coefficient obtained by searching the KPA table shown in FIG. 5 according to the atmospheric pressure PA detected by the atmospheric pressure sensor 15.

Returning to FIG. 2, in step S20, the timer t
The value of mWAV and the integrated intake air amount gairPO2 are set to “0” and reset. This timer tmWA
By resetting the value of V, the value of the timer tmWAV in step S19 becomes equal to the processing cycle (10 ms) of the program in FIGS. In addition, since the intake air amount integrated value gairPO2 is reset to the gairPO2 value “0” on the right side of the above equation (2) in step S40 in FIG. 4, the gairPO2 value in step S19 is calculated as shown in FIGS. Is the intake air amount integrated value gairPO2 integrated in step S40 of FIG. 4 over the processing cycle (10 ms) of the program of FIG.

Next, in step S21, it is determined whether or not the inversion number counter value NWAVE is smaller than a predetermined count value NWAVET (for example, three times). Step S2
As a result of the determination of 1, if NWAVE ≧ NWAVET,
The inversion cycle tmCYCL is calculated by the following equation (3) (step S23, inversion cycle detection means).

TmCYCL = TMWAVE / NWAVE (3) As a result of the determination in step S21, NWAVE <NWAVE
If T, the process proceeds to step S22, and it is determined whether or not the measured time timer integrated value TMWAVE exceeds a predetermined period TMWAVE. If TMWAVE ≦ TMWAVE, this process is immediately terminated, while TMWAVE> TM
If it is WAVET, the inversion cycle tmCYCL is calculated in step S23.

According to the discrimination in steps S21 and S22,
The number of inversions (NWAVE) of the output value VO2 of the O2 sensor 14F from the lean side to the rich side is a predetermined count value NWA.
Even if it is less than VET, if the measurement time (TMWAVE) of the O2 sensor deterioration monitor exceeds the predetermined period TMWAVET, the inversion cycle tmCYCL is calculated in step S23.

In the following step S24, GAIRSUM
The TMCYCLOK table shown in FIG. 6 is searched according to the two values, and the deterioration determination value TMCYCLOK of the O2 sensor 14F is calculated (deterioration determination value setting means). The reversal cycle tmCYCL of the O2 sensor 14F tends to become shorter as the engine load increases. This deterioration determination value TMCYCLOK is
It is set so that the larger the value of GAIRSUM2, the smaller the value and the smaller the change rate. The GAIRSUM2 value, which is an integrated value of the intake air amount, can be regarded as a parameter representing the load of the engine 1 during the O2 sensor deterioration monitoring, and is stable regardless of the load fluctuation of the engine 1 during the O2 sensor deterioration monitoring. Parameter.

Further, at step S25, the inversion cycle tm
It is determined whether or not CYCL is equal to or less than a deterioration determination value TMCYCLOK (deterioration determination means), and tmCYCL ≦ TMCYCLO.
In the case of K, it is determined that the responsiveness of the O2 sensor 14F has not deteriorated, and the responsiveness deterioration OK flag FOK indicating that the O2 sensor 14F has not deteriorated is set to "1". (Step S26), Step S30
Proceed to. On the other hand, in step S25, tmCYCL> TM
When the flag is CYCLOK, it is determined that the response of the O2 sensor 14F has deteriorated, and the flag FOK is set to “0”.
(Step S28), and the responsiveness deterioration determination flag FF indicating by "1" that the O2 sensor 14F is deteriorated.
SD is set to "1" (step S29), and the process proceeds to step S30.

Next, the responsiveness deterioration determination end flag FDONE indicating "1" indicating that the responsiveness deterioration determination has been completed is set to "1" (step S30), and the flag FOM is set.
2 is set to "0" (step S31), and the process ends.

According to the present embodiment, the inversion period tmCYCL of the output VO2 of the O2 sensor 14F for a predetermined period (until the O2 sensor 14F is inverted a predetermined number of times (three times) or until a predetermined time TMWAVET has elapsed) is calculated. (Step S23), and the calculated inversion cycle tmCYC
When it is determined that the O2 sensor 14F is deteriorated when L is longer than the predetermined deterioration determination value TMCYCLOK (step S25 → S28), the predetermined deterioration determination value TMCY is determined.
CLOK is set to be smaller as the intake air amount integrated value GAIRSUM2 obtained by integrating the engine intake air amount over the predetermined period becomes larger (step S40).
Even if the load condition of the engine 1 changes during the detection of the deterioration of the O2 sensor 14, the deterioration of the FO2 sensor 14F can be properly determined.

In this embodiment, the integrated intake air amount value GAIRSU of the engine 1 obtained by integrating the predetermined deterioration determination value TMCYCLOK over the predetermined period TMWAVET.
Although it is set to be smaller as M2 is larger, a parameter other than the intake air amount integrated value GAIRSUM2, for example, an integrated value of the exhaust flow rate of the engine 1 may be used.
The deterioration determination value TMCYCLOK may be set to be smaller as the integrated value of the exhaust flow rate is larger.

[0045]

As described above in detail, according to the air-fuel ratio sensor deterioration detecting device for an internal combustion engine of the first aspect, the reversal cycle of the output of the air-fuel ratio sensor is detected, and the detected reversal cycle is set to a predetermined value. When it is determined that the air-fuel ratio sensor has deteriorated when the air-fuel ratio sensor is longer than the deterioration determination value, the predetermined deterioration determination value is set according to the intake air amount of the internal combustion engine integrated in a predetermined period. Even if the load condition of the internal combustion engine changes while the deterioration of the sensor is detected, the deterioration of the air-fuel ratio sensor can be properly determined.

According to the apparatus for detecting deterioration of an air-fuel ratio sensor of an internal combustion engine according to the second aspect, the deterioration can be detected more accurately by the apparatus for detecting deterioration of an air-fuel ratio sensor of an internal combustion engine according to the first aspect.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an internal combustion engine (hereinafter, referred to as “engine”) using an air-fuel ratio sensor deterioration detection device according to an embodiment of the present invention, and a control device therefor.

FIG. 2 is a flowchart illustrating an overall configuration of a deterioration detection process of an O2 sensor 14F.

FIG. 3 is a flowchart illustrating an overall configuration of a deterioration detection process of an O2 sensor 14F.

FIG. 4 shows gairPO used in step S19 of FIG.
It is a flowchart of a program of a binary calculation process.

FIG. 5 is a diagram showing a KPA table used in step S40 of FIG.

6 is TMCYCL used in step S24 of FIG.
It is a figure showing an OK table.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Intake pipe 4 ECU (Air-fuel ratio control means, inversion cycle detection means, deterioration determination means, intake air amount integration means, deterioration determination value setting means) 6 Fuel injection valve 12 Exhaust pipe 13 Three-way catalyst 14F Upstream oxygen Sensor (air-fuel ratio sensor) 14R Downstream oxygen sensor 15 Atmospheric pressure sensor

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Seiichi Hosokai 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Research Institute, Ltd. (72) Inventor Shigeo Hishiro 1-4-1 Chuo, Wako-shi, Saitama No. Within Honda R & D Co., Ltd. (72) Inventor Atsushi Kato 1-4-1 Chuo, Wako-shi, Saitama Pref.

Claims (2)

[Claims] An air-fuel ratio sensor provided in an exhaust system of an internal combustion engine for detecting an air-fuel ratio of exhaust gas of the engine;
An air-fuel ratio control means for controlling an air-fuel ratio of an air-fuel mixture supplied to the engine based on an output of the air-fuel ratio sensor. A reversal cycle detecting means for detecting a reversal cycle of the output of the above; a deterioration determining means for determining that the air-fuel ratio sensor has deteriorated when the detected reversal cycle is longer than a predetermined deterioration determination value; Intake air amount integrating means for integrating the intake air amount of the engine over a period of time; and a deterioration determination value setting means for setting the predetermined deterioration determination value according to the integrated intake air amount. Air-fuel ratio sensor deterioration detection device for an internal combustion engine. 2. The internal combustion engine oxygen sensor deterioration detection according to claim 1, wherein said deterioration determination value setting means sets the predetermined deterioration determination value to be smaller as the integrated intake air amount is larger. apparatus.