JP2001234805A - Degradation diagnostic device of air-fuel ratio sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately judge the degradation of an air-fuel ratio sensor even when the fuel property is different. SOLUTION: The fuel injection from a fuel injection valve 4 is controlled based on the output of the air-fuel ratio sensor 11 so as to obtain the target air-fuel ratio to be set based on the operational condition. This degradation diagnostic device comprises a means to judge the fuel property, a means to judge the diagnostic range of the air-fuel ratio sensor 11, a means to judge the degradation of the air-fuel ratio sensor 11 by comparing the output change of the air-fuel ratio sensor 11 with a predetermined reference value in this diagnostic range, and a means to stop the diagnosis of the air-fuel ratio sensor 11 by the fuel property.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for diagnosing deterioration of an air-fuel ratio sensor of an internal combustion engine.

[0002]

2. Description of the Related Art In order to accurately control the air-fuel ratio of an internal combustion engine to a different target air-fuel ratio according to operating conditions, a wide-range air-fuel ratio sensor is provided in an exhaust system, and fuel injection is performed based on the output of the wide-range air-fuel ratio sensor. Devices for feedback controlling the quantity are known.

In this case, if the output characteristics fluctuate due to deterioration of the wide-range air-fuel ratio sensor or the like, the control accuracy of the air-fuel ratio decreases. Therefore, a function of self-diagnosing deterioration or failure of the wide-range air-fuel ratio sensor is provided, and when the fluctuation range of the sensor output exceeds a limit value, replacement or repair is urged.

[0004] Diagnosis of this deterioration or the like is performed, for example, as follows. The output of the wide-range air-fuel ratio sensor changes according to the (exhaust) air-fuel ratio. Generally, the response time to the change in the air-fuel ratio differs between a normal product and a deteriorated product, and the longer the deterioration, the longer the response time. In other words, the more the deterioration proceeds, the smaller the change in output for the same reaction time.

Therefore, the degree of deterioration can be determined by judging the amount of change in the sensor output per unit time when the air-fuel ratio is changed by a fixed value, and when the amount of change becomes smaller than a specified value. The sensor abnormality due to deterioration is determined.

[0006] By the way, commercially available fuels for internal combustion engines include fuels with standard fuel components and fuels with a large amount of heavy components. Heavy fuel has a lower fuel volatility than the standard fuel, and there is a time lag before the fuel injected into the intake pipe by the fuel injection valve actually reaches the combustion chamber and burns.

For this reason, when diagnosing the wide-range air-fuel ratio sensor, it may not be possible to accurately determine the deterioration depending on the fuel component.

When the air-fuel ratio is changed, the delay time until the change in the air-fuel ratio is detected by the wide area air-fuel ratio sensor installed in the exhaust pipe differs between the standard fuel and the heavy fuel.
For heavy fuel, the output change of the air-fuel ratio sensor per unit time is
It is smaller than the standard fuel. Therefore,
When comparing the change in the output of the air-fuel ratio sensor with the reference value for the deterioration determination, the result differs between the standard fuel and the heavy fuel, and the deterioration may be erroneously determined even if the air-fuel ratio sensor is normal.

The delay in the response of the air-fuel ratio detected by the air-fuel ratio sensor due to the difference in the fuel component is described in
In this publication, it is pointed out that the standard fuel and the heavy fuel are determined from the output change of the air-fuel ratio sensor when the air-fuel ratio is switched, and the fuel injection is performed based on the determined fuel property. It has been proposed to correct the amount.

[0010]

Conventionally, when diagnosing deterioration of an air-fuel ratio sensor, taking into account such differences in fuel properties, a diagnosis criterion serving as a comparison criterion at the time of diagnosing deterioration is determined based on the standard fuel (light fuel). The average value criteria taking into account the characteristics up to the heavy fuel are taken into consideration, or the operating range at the time of diagnosis is limited to prevent erroneous diagnosis.

However, in this case, there has been a problem that the accuracy is lowered in order to give a margin to the diagnostic criteria, or the diagnostic region is limited, and the frequency of the deterioration diagnosis of the air-fuel ratio sensor is reduced.

An object of the present invention is to solve such a problem, and it is possible to accurately judge deterioration of an air-fuel ratio sensor even if fuel properties are different.

[0013]

According to a first aspect of the present invention, there is provided an air-fuel ratio sensor installed in an exhaust system of an internal combustion engine for detecting an exhaust air-fuel ratio, and a fuel injection valve provided in an intake system. In an internal combustion engine that controls the amount of fuel injection from a fuel injection valve based on the output of an air-fuel ratio sensor, a means for determining fuel properties, a means for determining a diagnosis area of the air-fuel ratio sensor, A means for comparing the output change of the fuel ratio sensor with a predetermined reference value to determine the deterioration of the air-fuel ratio sensor, and a means for stopping the diagnosis of the air-fuel ratio sensor according to the fuel property.

A second invention comprises an air-fuel ratio sensor installed in an exhaust system of an internal combustion engine for detecting an exhaust air-fuel ratio, and a fuel injection valve provided in an intake system. Means for determining fuel properties in an internal combustion engine that controls the amount of fuel injection based on the output of an air-fuel ratio sensor;
Means for judging the diagnostic area of the air-fuel ratio sensor according to the fuel property, and comparing the change in output of the air-fuel ratio sensor with a common reference value in each diagnostic area according to the fuel property to determine the deterioration of the air-fuel ratio sensor. Means for determining.

A third invention comprises an air-fuel ratio sensor installed in an exhaust system of an internal combustion engine for detecting an exhaust air-fuel ratio, and a fuel injection valve provided in an intake system. Means for determining fuel properties in an internal combustion engine that controls the amount of fuel injection based on the output of an air-fuel ratio sensor;
Means for determining the diagnostic area of the air-fuel ratio sensor, means for setting a different diagnostic reference value according to the fuel property, and comparing the change in the output of the air-fuel ratio sensor with the diagnostic reference value corresponding to the fuel property in the diagnostic area Means for judging deterioration of the air-fuel ratio sensor.

In a fourth aspect based on the first to third aspects, the diagnosis determination means determines that the vehicle is in the diagnosis area when a diagnosis start delay time has elapsed after fuel cut.

In a fifth aspect based on the fourth aspect, the diagnosis start delay time is set to a different time according to the fuel property.

[0018]

According to the first aspect of the present invention, when the determined fuel property matches the set fuel for performing the diagnosis of the air-fuel ratio sensor, the change in the output of the air-fuel ratio sensor is determined when the diagnosis region is determined. Is compared with the diagnostic reference value to determine the deterioration of the air-fuel ratio sensor. If the fuel property is different from the set fuel, the deterioration determination of the air-fuel ratio sensor is stopped. For this reason,
The diagnosis area for performing the deterioration diagnosis, the diagnosis reference value, and the like can be determined only in accordance with the characteristics of the set fuel, and accordingly, the accuracy of the deterioration diagnosis of the air-fuel ratio sensor is improved.

According to the second aspect of the present invention, the diagnostic region is changed in accordance with the fuel property. Therefore, even if the diagnostic reference value is the same, appropriate diagnosis can be performed in accordance with each fuel characteristic, and the difference in fuel property can be obtained. The air-fuel ratio sensor can be accurately diagnosed without being affected by the change in the response caused by the air-fuel ratio.

In the third aspect, the diagnostic reference value is changed in accordance with the fuel property. Therefore, in this case as well, an appropriate deterioration diagnosis of the air-fuel ratio sensor can be performed in accordance with each fuel property.

In the fourth aspect, the diagnosis area is determined when the delay time has elapsed after the fuel cut, that is, when the air-fuel ratio has been switched in the intake system and a predetermined time has elapsed after the air-fuel ratio in the exhaust system has elapsed. Since the deterioration diagnosis is performed by judging the change allowance, the deterioration judgment can be made in a region where the change in the output of the air-fuel ratio sensor is sufficiently large, and the diagnosis accuracy is improved.

In the fifth aspect, the delay time at which the change in the output of the air-fuel ratio sensor with respect to the change in the air-fuel ratio varies depending on the fuel property is different. Deterioration diagnosis can be performed.

[0023]

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

In FIG. 1, 1 is an engine body, 2 is an intake pipe, 3 is an exhaust pipe, and the intake pipe 2 is provided with a fuel injection valve 4 for injecting necessary fuel. Reference numeral 5 denotes an intake throttle valve for controlling the engine output by controlling the amount of intake air, and reference numeral 6 denotes a catalyst (three-way catalyst) provided in an exhaust pipe for purifying harmful components in exhaust gas.

A controller 10 is provided for controlling the amount of fuel injected from the fuel injection valve 4 to a target air-fuel ratio set according to the operating conditions.

The controller 10 includes an input circuit, a central processing circuit (microprocessor), a storage circuit, an output circuit, and the like. The controller 10 has a crank angle sensor 12 for detecting an engine speed, and an intake air amount. Signals from an air flow meter 13, a throttle valve opening sensor 14 for detecting an intake throttle valve opening, a water temperature sensor 15 for detecting an engine coolant temperature, and a vehicle speed sensor 16 for detecting a vehicle speed are input, and further, an exhaust air-fuel ratio upstream of the catalyst. From the wide-range air-fuel ratio sensor 11 for detecting the air-fuel ratio and the oxygen sensor 20 for detecting the exhaust air-fuel ratio on the downstream side, and calculate the fuel injection amount based on these signals so as to reach the target air-fuel ratio in accordance with the operating conditions.
A fuel injection signal is output to the fuel injection valve 4 in synchronization with the engine rotation.

The controller 10 also has a diagnostic function for determining whether the output characteristics of the wide-range air-fuel ratio sensor 11 are normal. Although this diagnosis is also shown in a flowchart described later, the properties of the fuel supplied to the engine, that is, whether the fuel is standard fuel or heavy fuel, is determined, and the diagnosis area is changed in accordance with the determination result, or a different diagnosis criterion is determined. By using this, accurate judgment can always be made regardless of the fuel property.

FIG. 2 is a flow chart showing the contents of diagnosis according to the first embodiment, which is repeatedly executed by the controller 10 at predetermined time intervals.

First, in step S1, it is determined whether the fuel property is the standard fuel. This determination is made by, for example, changing the air-fuel ratio in a stepwise manner during an idling operation after warm-up, etc., and the output waveform of the air-fuel ratio sensor 11 at this time becomes:
For example, as shown in FIG. 3, for the step waveform A, B is shown for the standard fuel, and for the heavy fuel with low fuel volatility, C is shown. Can be determined.

In step S2, it is determined whether or not the vehicle is in an operation state in which the diagnosis can be shifted. This is, for example, the vehicle speed VS
P is a predetermined lower limit value AFVSPL1 and an upper limit value AFVSPH
1, the fuel injection pulse width TP is between the predetermined lower limit value AFTPL1 and the upper limit value AFTPH1, or the engine speed NE is lower than the predetermined lower limit value AFNEL1.
And the upper limit value AFNEH1 is determined. When the value is within the upper and lower limit values, in other words, when the air-fuel ratio is at the stoichiometric or constant air-fuel ratio,
It is determined that diagnosis transfer is possible, and the process proceeds to step S3.

Here, whether or not the engine is in the diagnosis area is determined by determining whether the operating condition is a predetermined diagnosis start delay time A after the fuel cut.
The determination is made based on whether or not FFCD1 has elapsed. Due to the fuel cut, the output of the air-fuel ratio sensor 11 changes from the stoichiometric state up to the lean state (only air) containing no fuel.

If the operating conditions before the fuel cut are different,
Since the change characteristics of the air-fuel ratio are different and accurate comparisons cannot be made, the determination in step S2 is made to match the conditions.

The reason why the predetermined diagnosis start delay time AFFCD1 is provided after the fuel cut is as shown in FIG.
There is a time delay from the fuel cut until the air-fuel ratio of the exhaust system changes, and the absolute value of the change allowance is small at the beginning,
Since a detection error is likely to occur, a certain time is set before the start of diagnosis.

When the delay time has elapsed, step S4
To calculate the variation ΔA / F of the output of the wide area air-fuel ratio sensor 11. The change amount ΔA / F of the sensor output is calculated as the output change width in a fixed calculation section DAFTM1.

Then, in step S5, the change amount ΔA / F of the sensor output thus calculated is compared with the air-fuel ratio diagnosis criterion DAFNG1.
It is determined whether the response characteristic of No. 1 is in a normal range or abnormal. The diagnostic criterion DAFNG1 is set according to the fuel property, and in the present embodiment, is set as a comparison reference value for determining deterioration with respect to the standard fuel instead of the heavy fuel.

As shown in FIG. 4, in the same fuel property, the output change margin per unit response time of the air-fuel ratio sensor in the normal range is larger than that of the deteriorated air-fuel ratio sensor.
The characteristics of the air-fuel ratio sensor 11 can be accurately diagnosed by comparing with a diagnosis criterion set in advance according to the fuel property.

If the change amount ΔA / F of the air-fuel ratio is larger than the diagnostic criterion DAFNGI, the air-fuel ratio sensor 1
1 is normal, and the diagnostic operation is terminated. When the diagnostic operation is small, it is determined that the deterioration of the air-fuel ratio sensor 11 has advanced, and in step S6, the responsiveness of the air-fuel ratio sensor 11 is determined to be equal to or less than the reference and an abnormality is determined. .

As described above, the diagnosis as to whether or not the output characteristics of the wide-range air-fuel ratio sensor 11 is normal is made by first determining the current fuel property, and performing the deterioration diagnosis only when this is the standard fuel. Therefore, the diagnosis criteria at this time are set based on the sensor response in the case of the standard fuel, so that the difference in the response when switching the air-fuel ratio due to the volatility of the fuel is excluded, and the air-fuel ratio is accurately determined. Only the deterioration of the output characteristics of the sensor 11 can be determined.

Incidentally, since the heavy fuel has low volatility, the delay in the change of the air-fuel ratio in the intake system to the exhaust system is large, and the amount of change per unit time is small. Even if the output characteristic of the sensor is normal, the variation ΔA / F of the sensor output becomes small.

Therefore, if the amount of change ΔA / F in the sensor output is compared based on the diagnostic criteria of the standard fuel, it is impossible to judge an abnormality even though it is normal. When the fuel is heavy fuel, such a diagnosis can be prevented by stopping the diagnosis.

FIG. 5 is a flowchart showing a second embodiment of the present invention, which will be described.

In the present embodiment, the diagnosis start delay time and the change Δ
By differently setting the A / F calculation sections, diagnosis for different fuel properties can be performed accurately.

Steps S11 to S16 are:
This is a determination of deterioration of the air-fuel ratio sensor 11 with respect to the standard fuel, which is exactly the same as the operation from step S1 to step S6 in FIG.

On the other hand, when it is determined in step S11 that the fuel is not the standard fuel, that is, when the fuel is the heavy fuel,
Proceeding to step S17, it is determined whether the current operating state is in a state in which the diagnosis can be shifted to by the vehicle speed, the fuel injection pulse width,
AFV which is the upper limit and lower limit of the engine speed, respectively
SPH2 and AFVSPL2, AFTPH2 and AFTPL
2, and a comparison is made between AFNEH2 and AFNEL2.

Note that these upper and lower limits are different from those of the standard fuel, and are set to optimal values corresponding to the heavy fuel.

If any one of these values falls within the upper and lower limits, it is determined that the diagnosis can be shifted, and the process proceeds to step S18. Here, it waits until the predetermined diagnosis start delay time AFFCD2 elapses after the fuel cut, and when it elapses, the process proceeds to step S19 to calculate the operation section DAFTM.
2, the change ΔA / in the output of the wide area air-fuel ratio sensor 11
Calculate F. Then, in step S20, the calculated change amount ΔA / F is used as a common diagnostic criterion D.
Compared with AFNG1, if smaller than this, it is determined that the air-fuel ratio sensor 11 is normal, and the diagnostic operation ends.

However, if the air-fuel ratio change amount ΔA / F is smaller than the diagnostic criterion DAFNG1 in step S20, the wide-range air-fuel ratio sensor 1 is determined in step S21.
No. 1 determines that the output responsiveness is deteriorated due to deterioration.

The diagnosis start delay time after fuel cut in the case of heavy fuel is longer than the delay time of standard fuel, and the calculation interval of the variation ΔA / F is also longer. This is because the heavy fuel has a lower fuel volatility, and the time delay until the wide-area air-fuel ratio sensor 11 of the exhaust system detects this change with respect to the change in the fuel supply amount in the intake system. . Therefore, when the same delay time is compared with the calculation section, even if the wide-range air-fuel ratio sensor 11 is normal, the amount of change ΔA / F in the air-fuel ratio becomes small in the case of heavy fuel, and this is determined by the same diagnosis. When judging based on criteria, it may be erroneously judged to have deteriorated.

However, in this embodiment, the diagnosis start delay time is made different depending on the fuel property, and a sufficient delay time is taken for heavy fuel with a large time delay. You can judge it.

As shown in FIG. 6, for the heavy fuel, by increasing the diagnosis start delay time and by increasing the calculation interval of the change amount ΔA / F, the change amount ΔA / F of the air-fuel ratio is increased.
Is the same as that of the standard fuel, and the air-fuel ratio sensor 11 has the same diagnostic criteria for any fuel.
Accurate judgment of deterioration was made possible.

Next, a third embodiment of the present invention shown in the flowchart of FIG. 7 will be described.

In this embodiment, the diagnosis start delay time and the change ΔA /
By making the calculation section of F the same, but making the diagnosis criteria different, the diagnosis of the air-fuel ratio sensor 11 can be accurately performed for both fuels.

Steps S31 to S36, which are diagnostic operations for the standard fuel, are performed in steps S1 to S36 in FIG.
It is substantially the same as step S6, and steps S37 to S41 are the same as steps S2 to S6 except for step S40.

That is, steps S35 and S40
When the diagnostic criterion as a reference value for comparing the change amount ΔA / F of the air-fuel ratio used in
NG1, whereas DAFNG2 for heavy fuel
And their sizes are different. In the same diagnosis delay time and calculation section, the standard criterion DAFNG1 is set to be larger than DAFNG2 because the standard fuel has a larger air-fuel ratio change amount ΔA / F than the heavy fuel.

This makes it possible to appropriately judge the deterioration of the air-fuel ratio sensor 11 when using the standard fuel and when using the heavy fuel.

It is apparent that the present invention is not limited to the above-described embodiment, and that various changes can be made within the scope of the technical idea.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of the present invention.

FIG. 2 is a flowchart illustrating a control operation according to the first embodiment.

FIG. 3 is a graph for explaining a response waveform of an air-fuel ratio sensor with respect to a change in an air-fuel ratio between a standard fuel and a heavy fuel.

FIG. 4 is an explanatory diagram of a response waveform to a change in the air-fuel ratio when the air-fuel ratio sensor is normal and when it is deteriorated.

FIG. 5 is a flowchart illustrating a control operation according to the second embodiment.

FIG. 6 is an explanatory diagram of a response waveform to a change in the air-fuel ratio when the air-fuel ratio sensor is normal and when it is deteriorated.

FIG. 7 is a flowchart illustrating a control operation according to a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 2 Intake pipe 3 Exhaust pipe 4 Fuel injection valve 6 Catalyst 10 Controller 11 Air-fuel ratio sensor 12 Crank angle sensor 13 Air flow meter 16 Vehicle speed sensor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G084 BA09 BA14 DA27 DA30 EA05 EA07 EA11 EB11 FA05 FA07 FA10 FA14 FA20 FA30 FA38 3G301 JB01 JB09 KA26 MA01 MA11 MA24 NA08 NB03 NB11 ND01 NE22 NE23 PA01Z PA11Z PB02Z03 PDB PDZPD PDB PF01Z

Claims (5)

[Claims] 1. An air-fuel ratio sensor installed in an exhaust system of an internal combustion engine for detecting an exhaust air-fuel ratio, and a fuel injection valve provided in an intake system, wherein a fuel injection amount from the fuel injection valve is adjusted to a target air-fuel ratio. Means for judging fuel properties, means for judging a diagnosis area of the air-fuel ratio sensor, and an output change allowance of the air-fuel ratio sensor in the diagnosis area. An apparatus for diagnosing deterioration of an air-fuel ratio sensor, comprising: means for determining deterioration of the air-fuel ratio sensor by comparing the value with a value; and means for stopping diagnosis of the air-fuel ratio sensor according to fuel properties. 2. An air-fuel ratio sensor provided in an exhaust system of an internal combustion engine for detecting an exhaust air-fuel ratio, and a fuel injection valve provided in an intake system, wherein a fuel injection amount from the fuel injection valve is adjusted to a target air-fuel ratio. Means for judging fuel property, means for judging the diagnostic area of the air-fuel ratio sensor according to the fuel property, and each diagnostic area according to the fuel property. Means for comparing the output change of the air-fuel ratio sensor with a common reference value to determine the deterioration of the air-fuel ratio sensor. 3. An air-fuel ratio sensor provided in an exhaust system of an internal combustion engine for detecting an exhaust air-fuel ratio, and a fuel injection valve provided in an intake system, wherein a fuel injection amount from the fuel injection valve is adjusted to a target air-fuel ratio. Means for determining a fuel property, means for determining a diagnostic region of the air-fuel ratio sensor, and means for setting a different diagnostic reference value depending on the fuel property in an internal combustion engine that controls the fuel property based on the output of the air-fuel ratio sensor. Means for comparing the change in the output of the air-fuel ratio sensor in the diagnosis area with a diagnostic reference value corresponding to the fuel property to determine the deterioration of the air-fuel ratio sensor. 4. The deterioration diagnosis of the air-fuel ratio sensor according to claim 1, wherein said diagnosis judgment means judges that the diagnosis is within a diagnosis area when a diagnosis start delay time has elapsed after the fuel cut. apparatus. 5. An apparatus for diagnosing deterioration of an air-fuel ratio sensor according to claim 4, wherein said diagnosis start delay time is set to a different time according to fuel properties.