JP2003013792A - Diagnostic device of oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately diagnose responsiveness deterioration of an oxygen sensor having a region where an output value shows linearity to an air-fuel ratio. SOLUTION: A target air-fuel ratio is forcibly changed over to an air-fuel ratio on the lean side (rich) from an air-fuel ratio on the rich side (lean) rather than a linear region (S22-S24), and time t1 (t2) which an output value Es of the oxygen sensor requires to pass the linear region at the time is measured (S126, S30). When the time t1 (t2) exceeds specified time (S27, S31), it is determined that the responsiveness deterioration is caused (S28, S32), and when the time t1 (t2) is not more than the specified time, it is determined that it is normal (S29, S33).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diagnostic device for an oxygen sensor having an approximately linearity with respect to an air-fuel ratio when an output value is within a predetermined range including a stoichiometric air-fuel ratio equivalent value.

[0002]

2. Description of the Related Art Conventionally, in an oxygen sensor whose output value changes in response to the oxygen concentration in engine exhaust, it has been performed to diagnose the deterioration of the response of the sensor based on the rising or falling output waveform of the output. (JP-A-8
(See Japanese Patent No. 254519). Specifically, the integral value determined by the rising waveform or falling waveform of the output value of the oxygen sensor is obtained, and the integral value determined by the rising waveform or falling waveform of the reference output waveform is obtained, and based on the difference between the two integral values. This is a configuration for diagnosing the occurrence of response deterioration of the oxygen sensor.

Further, the actual air-fuel ratio is obtained by converting the output value of the oxygen sensor into the air-fuel ratio data, and the air-fuel ratio control signal is feedback-controlled based on the deviation between the actual air-fuel ratio and the target air-fuel ratio. Is being carried out (Japanese Patent Laid-Open No. Hei 07)
-127505).

[0004]

By the way, in the case where the air-fuel ratio is detected from the output of the oxygen sensor as described above, in order to secure a region where the correlation between the sensor output and the air-fuel ratio is substantially linear, The output characteristic of the sensor is set so that the change in the output value with respect to the change in the fuel ratio becomes gentler than that of the oxygen sensor used when only performing the rich / lean determination with respect to the theoretical air-fuel ratio.

For this reason, the output characteristics of the oxygen sensor capable of performing only rich / lean determination when the response of the oxygen sensor is deteriorated and the output characteristics of the oxygen sensor having the linear output region are close to each other. If the oxygen sensor diagnostics that can only make judgments are directly applied to oxygen sensors that have a linear region, misdiagnosis may occur.Furthermore, in an oxygen sensor that has a linear region, the output change due to a change in the air-fuel ratio is gentle. However, there is a problem that the change in the output characteristic due to the deterioration of the response is small, and the diagnosis accuracy cannot be ensured only by adapting the determination level.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a diagnostic device capable of stably and highly accurately diagnosing a response deterioration of an oxygen sensor having a linear region capable of detecting an air-fuel ratio. And

[0007]

Therefore, the invention according to claim 1 is an oxygen sensor in which the output value changes in response to the oxygen concentration in the engine exhaust, and the sensor output value has a theoretical air-fuel ratio equivalent value. A diagnostic device for an oxygen sensor that has substantially linearity with respect to the air-fuel ratio when it is within a predetermined range including:
The change rate of the output value within the predetermined range corresponding to the switching of the target air-fuel ratio is detected, and the oxygen sensor failure determination is performed when the change rate is smaller than the determination value.

According to this structure, the range in which the response speed is detected is limited to the region where the sensor output is linear with respect to the air-fuel ratio, and the change speed of the output value due to the switching of the target air-fuel ratio is within the range. By measuring, if the rate of change is slow, a sensor failure (response deterioration) is determined. According to the second aspect of the invention, the determination value is set to a different value depending on the switching direction of the target air-fuel ratio.

According to such a configuration, the determination value of the response speed is set to a different value depending on whether the target air-fuel ratio is switched from rich to lean or, conversely, from lean to rich, and the change in the air-fuel ratio is changed. It corresponds to the difference in response speed due to the difference. In the invention according to claim 3, the switching of the target air-fuel ratio is switching between an air-fuel ratio on the rich side of the predetermined range and an air-fuel ratio on the lean side of the predetermined range, and the output value is The time required to substantially cross the predetermined range is measured as a parameter indicating the changing speed.

According to this structure, the target air-fuel ratio is switched from the rich side (lean side) to the lean side (rich side) of the linear region so that the output value changes across the linear region, The time required for substantially crossing is measured as a parameter indicating the changing speed of the output value.

[0011]

According to the first aspect of the present invention, the change speed of the output value due to the switching of the target air-fuel ratio is judged in the linear region, so that there is an effect that the decrease in the response speed can be judged with high accuracy. . According to the invention of claim 2,
There is an effect that it is possible to cope with the difference in response speed depending on the changing direction of the air-fuel ratio, and it is possible to diagnose the response deterioration with high accuracy in both the rich-lean switching and the lean-rich switching of the target air-fuel ratio.

According to the third aspect of the present invention, it is possible to detect the changing speed of the output value with respect to the change of the air-fuel ratio over substantially the entire linear region, and it is possible to detect the changing speed of the output value with high resolution. There is an effect.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a system configuration diagram of an engine in the embodiment. In FIG. 1, air is sucked into a combustion chamber of each cylinder of an engine 1 mounted on a vehicle through an air cleaner 2, an intake passage 3, and an electronically controlled throttle valve 4 which is driven to open and close by a motor.

An electromagnetic fuel injection valve 5 for directly injecting fuel (gasoline) is provided in the combustion chamber of each cylinder, and the fuel injected by the fuel injection valve 5 and the sucked air are introduced into the combustion chamber. A mixture is formed. Fuel injection valve 5
Is energized by the injection pulse signal output from the control unit 20 to open the valve, and injects the fuel whose pressure is adjusted to a predetermined pressure.

The mixture formed in the combustion chamber is ignited by the spark plug 6.
Is ignited and burned. However, the engine 1 is not limited to the above direct injection gasoline engine, and may be an engine configured to inject fuel into the intake port.
Exhaust gas from the engine 1 is discharged from an exhaust passage 7, and an exhaust purification catalyst 8 is provided in the exhaust passage 7.

The catalyst 8 is a three-way catalyst which oxidizes carbon monoxide CO and hydrocarbon HC which are harmful three components in the exhaust gas, and reduces nitrogen oxide NOx to produce harmless carbon dioxide and water vapor. And nitrogen. Further, an evaporative fuel processing device for combusting the evaporative fuel generated in the fuel tank 9 is provided.

The canister 10 is an airtight container filled with an adsorbent 11 such as activated carbon, and an evaporative fuel introduction pipe 12 extending from the fuel tank 9 is connected to the canister 10. Therefore, the evaporated fuel generated in the fuel tank 9 is guided to the canister 10 through the evaporated fuel introducing pipe 12 and adsorbed and collected. Further, the canister 10 has a fresh air introduction port 13
And the purge pipe 14 is led out, and a purge control valve 15 whose opening and closing is controlled by a control signal from the control unit 20 is interposed in the purge pipe 14.

In the above structure, when the purge control valve 15 is controlled to open, the suction negative pressure of the engine 1 is changed to the canister 10.
As a result, the evaporated fuel adsorbed by the adsorbent 11 of the canister 10 is purged by the air introduced from the fresh air introduction port 13, and the purge air passes through the purge pipe 14 to the downstream side of the throttle valve 4 of the intake passage 3. It is taken in, and then burned in the combustion chamber of the engine 1.

The control unit 20 includes a CPU and R
A microcomputer including an OM, a RAM, an A / D converter, an input / output interface, etc.,
Input signals from various sensors are received, arithmetic processing is performed based on these signals, and the throttle valve 4, fuel injection valve 5, spark plug 6
And controlling the operation of the purge control valve 15 and the like. As the various sensors, a crank angle sensor 21 for detecting a crank angle of the engine 1 and a cam sensor 22 for extracting a cylinder discrimination signal from a cam shaft are provided, and the rotation speed of the engine 1 is determined based on the signal from the crank angle sensor 21. It is calculated.

In addition, an air flow meter 23 for detecting the intake air flow rate Qa upstream of the throttle valve 4 in the intake passage 3,
Accelerator sensor 24 for detecting the accelerator pedal depression amount (accelerator opening) APS, throttle valve 4 opening TV
A throttle sensor 25 that detects O, a water temperature sensor 26 that detects the cooling water temperature Tw of the engine 1, an oxygen sensor 27 that changes its output value in response to the oxygen concentration in exhaust gas, a vehicle speed VS
A vehicle speed sensor 28 for detecting P is provided.

The oxygen sensor 27 is the same as that disclosed in JP-A-11-32.
As disclosed in Japanese Patent No. 6266, a zirconia tube is provided so as to project into an exhaust pipe, and the zirconia tube has a ratio of the oxygen concentration in the exhaust outside the zirconia tube to the oxygen concentration in the atmosphere inside. It is an oxygen concentration cell type oxygen sensor that generates electromotive force. As shown in FIG. 2, the output value Es (electromotive force) of the oxygen sensor 27 changes around the theoretical air-fuel ratio, and the electromotive force is high on the rich side of the theoretical air-fuel ratio and lean on the lean side of the theoretical air-fuel ratio. Has a characteristic that the electromotive force becomes low, but in a predetermined range (0.3 (V) ≤ output value Es ≤ 0.8 (V)) including the theoretical air-fuel ratio equivalent value, the output value Es is relative to the air-fuel ratio. The output characteristics are set so as to have substantially linearity.

The control unit 20 controls the fuel injection amount so that the actual air-fuel ratio detected from the output value Es of the oxygen sensor 27 matches the target air-fuel ratio when a predetermined air-fuel ratio feedback control condition is satisfied. The air-fuel ratio feedback correction coefficient for correcting the above is calculated, and the details of the air-fuel ratio feedback control will be described with reference to the flowchart of FIG.

In step S1, the output value Es of the oxygen sensor 27 is within a predetermined range (0.3 (V) ≤output value Es≤0.8 (V)) having a substantially linear relationship with the air-fuel ratio. It is determined whether or not there is. When it is determined in step S1 that the output value Es of the oxygen sensor 27 is within the predetermined range having substantially linearity with respect to the air-fuel ratio, the process proceeds to step S2, and the output value Es of the oxygen sensor 27 is changed. A process of converting to air-fuel ratio data is performed.

The conversion may be performed based on a table showing the correlation between the output value Es and the air-fuel ratio, but in order to further improve the resolution, the conversion of the output value Es based on a preset calculation formula is performed. After substituting the variables, the data of the air-fuel ratio may be obtained from the variables. In step S3, a deviation err (deviation err = actual air-fuel ratio-target air-fuel ratio) between the actual air-fuel ratio obtained from the output value Es and the target air-fuel ratio (theoretical air-fuel ratio) is obtained.

In step S4, the deviation err is multiplied by a proportional constant Kp to calculate a proportional manipulated variable P (P = err × Kp). In step S5, the lean / lean of the actual air-fuel ratio with respect to the target air-fuel ratio (theoretical air-fuel ratio) is determined by determining whether the deviation err is positive or negative. When it is determined in step S5 that the deviation err is negative and the actual air-fuel ratio is richer than the target air-fuel ratio (theoretical air-fuel ratio), the process proceeds to step S6.

In step S6, the result obtained by subtracting the predetermined value ΔI from the previous value of the integrated operation amount I is calculated as the integrated operation amount I of this time.
And When it is determined in step S5 that the deviation err is positive and the actual air-fuel ratio is leaner than the target air-fuel ratio (theoretical air-fuel ratio), the process proceeds to step S7, and the previous value of the integrated operation amount I is set to a predetermined value. The result of adding ΔI is set as the current integrated operation amount I.

Further, when it is determined in step S5 that the deviation err is substantially 0 and the actual air-fuel ratio substantially matches the target air-fuel ratio (theoretical air-fuel ratio), steps S6 and S7 are bypassed to step S12. By advancing to, the integral operation amount I is held at the previous value. In step S12, the air-fuel ratio feedback correction coefficient α is calculated as α = P + I + 1.0.

On the other hand, in step S1, the oxygen sensor 2
The output value Es of 7 is outside the linear range (0.3 (V)> Es
Or, if it is determined that Es> 0.8 (V)), step S8
Go to. In step S8, it is determined whether the output value Es of the oxygen sensor 27 is out of the range higher than the predetermined range, specifically, whether Es> 0.8 (V). It is determined whether the actual air-fuel ratio is richer than the theoretical air-fuel ratio.

In step S8, when it is determined that Es> 0.8 (V) and the actual air-fuel ratio is richer than the stoichiometric air-fuel ratio, the process proceeds to step S9, and a predetermined value ΔI from the previous value of the integrated operation amount I. The result of the subtraction is the integral manipulated variable I
And On the other hand, when it is determined in step S8 that Es> 0.8 (V) is not satisfied, it means that 0.3 (V)> Es is satisfied, so that the process proceeds from step S1 to step S8, and the actual air-fuel ratio is higher than the theoretical air-fuel ratio. Is also judged to be lean.

In this case, the process proceeds to step 10 and the result obtained by adding the predetermined value ΔI to the previous value of the integrated operation amount I is set as the current integrated operation amount I. When the integral operation amount I is set in steps S9 and S10, the proportional operation amount P is set to 0 in the next step S11. The output value Es of the oxygen sensor 27 is within the predetermined range (0.3 (V) ≦ Es ≦ 0.8
(V)), the output value Es has substantially linearity with respect to the air-fuel ratio, and therefore the output value Es can be accurately converted into the air-fuel ratio data. However, if the output value Es is out of the predetermined range, the air-fuel ratio becomes correct. Since it cannot be obtained, the proportional control based on the air-fuel ratio deviation is prohibited, and the air-fuel ratio is prevented from being controlled based on incorrect air-fuel ratio deviation information.

However, since the rich / lean determination with respect to the stoichiometric air-fuel ratio can be performed even in a region outside the predetermined range, the integration based on the rich / lean determination is performed as when the output value Es is within the predetermined range. Control. Therefore, when the output value Es is out of the predetermined range, step S
When the process proceeds to 12, the air-fuel ratio feedback correction coefficient α is substantially calculated with α = I + 1.0.

The air-fuel ratio feedback correction coefficient α is
The final fuel injection amount Ti is obtained by multiplying the basic fuel injection amount Tp corresponding to the target air-fuel ratio, and an injection pulse signal having a pulse width corresponding to this fuel injection amount Ti is supplied to the fuel injection valve 5 of each cylinder. Is output. Next, the oxygen sensor 27
The failure diagnosis (response deterioration diagnosis) will be described with reference to the flowchart of FIG.

In the flowchart of FIG. 4, in step S21, it is determined whether or not the conditions for permitting execution of the failure diagnosis of the oxygen sensor 27 are satisfied. The execution permission condition is a predetermined operating condition that is less affected by the forcible switching of the target air-fuel ratio, which will be described later, and the oxygen sensor 2
Makes it possible to determine that disconnection / short-circuit of 7 has not been detected.

If the execution permission condition is satisfied, the routine proceeds to step S22, where the target air-fuel ratio is switched to the rich air-fuel ratio (or lean air-fuel ratio) stored in advance. In step S23, it is determined whether or not a predetermined time or more has elapsed from the switching of the target air-fuel ratio in step S22 and the oxygen sensor 27 is in a state of detecting the air-fuel ratio after the switching.

When the predetermined time has elapsed, the routine proceeds to step S24, and conversely, the target air-fuel ratio is switched to the lean air-fuel ratio (or rich air-fuel ratio) stored in advance. The rich air-fuel ratio / lean air-fuel ratio is an air-fuel ratio in a region outside the linear range of the oxygen sensor 27, and the target air-fuel ratio is switched so as to cross the linear range of the oxygen sensor 27 by the above processing. .

The switching direction of the target air-fuel ratio may be limited to either rich → lean or lean → rich, but it is preferable to diagnose the responsiveness for each changing direction of the air-fuel ratio. It is advisable to perform response diagnosis bidirectionally, for example, after first switching the target air-fuel ratio from rich to lean to perform response diagnosis, and then switching the target air-fuel ratio from lean to rich to perform response diagnosis.

In step S25, the switching direction of the target air-fuel ratio is determined. When it is determined that the target air-fuel ratio has been switched from rich to lean, the process proceeds to step S26, and the output value Es of the oxygen sensor 27 changes from a predetermined value (1) to a predetermined value (2) with the switching of the target air-fuel ratio. The time t1 required to change is measured. The predetermined value (1) is a value (for example, 0.7 (V)) slightly smaller than the boundary value (0.8 (V)) on the rich side of the linear range, and the predetermined value (2) is Boundary value on the lean side of the linear range (0.3
(V)).

Therefore, the time t1 corresponds to the time until the output value Es exits the linear range from the predetermined value (1) immediately after entering the linear range due to the switching of the target air-fuel ratio (Fig. 2). In step S27, it is determined whether or not the time t1 measured in step S26 is longer than the predetermined time (1).

A predetermined time (1) as the judgment value
Is, for example, about 850 ms. When the time t1 is longer than the predetermined time (1), it is determined that the changing speed of the output value Es corresponding to the change of the target air-fuel ratio is slower than the normal time, the process proceeds to step S28, and the response of the oxygen sensor 27 is returned. Determine deterioration (fault).

On the other hand, if the time t1 is less than the predetermined time (1), it is judged that the changing speed of the output value Es corresponding to the change of the target air-fuel ratio is normal, and the routine proceeds to step S29,
The normality of the oxygen sensor 27 is determined. Also, step S
When it is determined in 25 that the target air-fuel ratio has been switched from lean to rich, the routine proceeds to step S30, where the output value Es of the oxygen sensor 27 changes from the predetermined value (3) to the predetermined value (4) with the switching of the target air-fuel ratio. ) The time t required to change to
Measure 2.

The predetermined value (3) is a value (for example, 0.4 (V)) slightly larger than the lean side boundary value (0.3 (V)) of the linear range, and the predetermined value (4). Is
It is a boundary value (0.8 (V)) on the rich side of the linear range. Therefore, the time t2 corresponds to the time until the output value Es exits the linear range from the predetermined value (3) immediately after entering the linear range due to the switching of the target air-fuel ratio (see FIG. 2). .

At step S31, the step S30 is performed.
It is determined whether or not the time t2 measured in step 3 is longer than the predetermined time (2). A predetermined time (2) as the judgment value
Is, for example, about 700 ms. When the time t2 is longer than the predetermined time (2), it is determined that the changing speed of the output value Es corresponding to the change of the target air-fuel ratio is slower than the normal time, the process proceeds to step S32 and the response of the oxygen sensor 27 is returned. Determine deterioration (fault).

On the other hand, if the time t2 is less than or equal to the predetermined time (2), it is judged that the changing speed of the output value Es corresponding to the change of the target air-fuel ratio is normal, and the routine proceeds to step S33,
The normality of the oxygen sensor 27 is determined. When the response deterioration (fault) of the oxygen sensor 27 is diagnosed, the oxygen sensor 2
The air-fuel ratio feedback control based on the output value Es of 7 is stopped, and a warning lamp is used to warn that the response deterioration (failure) is determined.

In the above linear region, the output change speed corresponding to the change in the target air-fuel ratio can be accurately determined,
The response deterioration can be diagnosed with high accuracy. Further, since a different value is used as the determination value of the output change speed depending on the target air-fuel ratio switching direction, it is possible to accurately determine the response speed in response to the difference in response speed due to the difference in the change direction of the air-fuel ratio.

Further, by measuring the time that crosses almost the entire linear region, the time difference due to response deterioration can be detected with good resolution, and the output changes when the linear region is excluded immediately after being measured. Since the time measurement is not performed in the unstable state immediately after the start of the diagnosis, the diagnostic accuracy can be further improved. By comparing the times t1 and t2 with a plurality of predetermined times, the degree of progress of response deterioration is determined, and when the response deterioration is slight, the feedback gain may be adjusted and the feedback control may be continued. good.

In the above embodiment, the target air-fuel ratio is forcibly switched. However, when similar target air-fuel ratio switching is performed according to the operating condition, the target air-fuel ratio is changed by this operating condition. It is also possible to perform response diagnosis when is switched.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of an engine according to an embodiment.

FIG. 2 is an output characteristic diagram of the oxygen sensor according to the embodiment.

FIG. 3 is a flowchart showing air-fuel ratio feedback control in the embodiment.

FIG. 4 is a flowchart showing failure diagnosis of the oxygen sensor in the embodiment.

[Explanation of symbols]

1 ... engine 4 ... Throttle valve 5 ... Fuel injection valve 6 ... Spark plug 8 ... Catalyst 20 ... Control unit 21 ... Crank angle sensor 23 ... Air flow meter 27 ... Oxygen sensor

Claims (3)

[Claims] Claim: What is claimed is: 1. An oxygen sensor, the output value of which changes in response to the oxygen concentration in engine exhaust, wherein the sensor output value is within the predetermined range including the stoichiometric air-fuel ratio equivalent value. And a substantially linear oxygen sensor diagnosing device, which detects a changing speed of the output value within the predetermined range corresponding to the switching of the target air-fuel ratio, and when the changing speed is smaller than a judgment value, An oxygen sensor failure diagnosis device characterized by making a failure determination of an oxygen sensor. 2. The oxygen sensor failure diagnosis device according to claim 1, wherein the determination value is set to a different value depending on the switching direction of the target air-fuel ratio. 3. The target air-fuel ratio is switched between an air-fuel ratio richer than the predetermined range and an air-fuel ratio leaner than the predetermined range, and the output value is in the predetermined range. The oxygen sensor failure diagnosis device according to claim 1 or 2, wherein a time required for substantially crossing is measured as a parameter indicating the changing speed.