JP3663921B2 - Oxygen sensor diagnostic device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diagnostic device for an oxygen sensor installed in an exhaust system of an engine, and more particularly to a diagnostic device suitable for deterioration diagnosis of a rear oxygen sensor provided downstream of a catalyst.
[0002]
[Prior art]
Conventional rear oxygen sensor diagnostic devices are disclosed in Japanese Patent Application Laid-Open No. 7-71299 and Japanese Patent Application Laid-Open No. 9-33478. (1) The rear oxygen sensor downstream of the catalyst with respect to the output waveform of the front oxygen sensor upstream of the catalyst. Response deterioration is determined based on the phase difference of the output waveform of the oxygen sensor and (2) the inversion frequency of the output of the downstream rear oxygen sensor.
[0003]
[Problems to be solved by the invention]
However, since the rear oxygen sensor has a slow response in the first place, even if a failure judgment value (Criteria) for the phase difference or inversion frequency is set, the correlation between the phase difference or inversion frequency and the exhaust emission is low. It was difficult to make a high-accuracy diagnosis by setting criteria corresponding to the regulation values. In addition, there is a problem that the diagnosis itself is affected by the deterioration of the catalyst performance.
[0004]
The present invention has been made in view of such circumstances, and an object of the present invention is to make it possible to accurately diagnose deterioration of an oxygen sensor (with good correlation with exhaust emission).
[0005]
[Means for Solving the Problems]
For this reason, in the invention according to claim 1, as shown in FIG. 1, the set value of the slice level voltage for control with respect to the output voltage of the oxygen sensor is VSL, and the set value of the rich side maximum value of the output voltage of the oxygen sensor is set. When the floating margin of V1 and the minimum value on the lean side of the output voltage is ΔV, the calculated slice level voltage represented by V1 × (VSL−ΔV) / (V1−ΔV) is a predetermined regulation value VNG. Floating allowance determination value storage means for storing a floating allowance ΔV = V1 × (VSL−VNG) / (V1−VNG) as a floating allowance determination value is provided.
[0006]
Then, the output voltage minimum value detecting means for detecting the minimum value of the actual output voltage of the oxygen sensor and the detected minimum value of the actual output voltage of the oxygen sensor are compared with the floating allowance determination value. Lean side abnormality diagnosis means for diagnosing an abnormality of the oxygen sensor when the floating allowance determination value is exceeded is provided to constitute a diagnostic device for the oxygen sensor.
In the invention according to claim 2, the output voltage maximum value detecting means for detecting the maximum value of the actual output voltage of the oxygen sensor, and the detected maximum value of the actual output voltage of the oxygen sensor for controlling the slice level An oxygen sensor diagnostic device comprising: a rich-side abnormality diagnosis means for diagnosing an abnormality of the oxygen sensor when the maximum value is lower than the set value of the slice level voltage for control as compared with the voltage setting value (See FIG. 1).
[0007]
In the invention according to claim 3, the calculated control value VNG of the slice level voltage is calculated based on the characteristic value of the exhaust harmful component emission when the control slice level voltage is changed. The slice level voltage at the regulation value is read and determined.
[0008]
【The invention's effect】
According to the first aspect of the present invention, it is possible to accurately diagnose deterioration of the oxygen sensor, in particular, the lean-side output floating due to this, with good correlation with the exhaust emission, and to the diagnosis of the rear oxygen sensor downstream of the catalyst. In this case, the diagnosis can be made without being affected by the deterioration of the catalyst performance.
[0009]
According to the invention which concerns on Claim 2, abnormality of the rich side output of an oxygen sensor can be diagnosed accurately.
According to the invention of claim 3, the correlation with the exhaust emission can be ensured.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
FIG. 2 is a system diagram of an air-fuel ratio control apparatus for an engine.
An exhaust purification catalyst (three-way catalyst) 3 is provided in the exhaust passage 2 of the engine 1, a front oxygen sensor 4 is provided upstream of the catalyst 3, and a rear oxygen sensor 5 is provided downstream of the catalyst 3. The output voltages of these oxygen sensors 4 and 5 are input to the control unit 6.
[0011]
Further, an intake air amount Qa detected by an air flow meter 8 provided in the intake passage 7, an engine speed Ne detected by a crank angle sensor (not shown), a water temperature Tw detected by a water temperature sensor (not shown), and the like are given to the control unit 6. Have been entered.
Based on the input information, the control unit 6 controls the operation of the fuel injection valve 9 by setting the fuel injection amount while feedback controlling the air-fuel ratio.
[0012]
Here, the rear oxygen sensor 5 and the control by this will be described. The output voltage of the rear oxygen sensor 5 changes in the range of, for example, 0 mV to 820 mV, corresponding to the lean to rich exhaust air / fuel ratio.
The control unit 6 compares the output voltage of the rear oxygen sensor 5 with a predetermined control slice level voltage VSL. When the output voltage> VSL, the control unit 6 determines that the output is rich and shifts the air-fuel ratio to the lean side. When the output voltage is less than VSL, it is determined that the engine is lean and the air-fuel ratio is controlled to be shifted to the rich side. The slice level voltage VSL for control is set to 700 mV, for example. The reason why the slice level voltage VSL is set higher is to shift the air-fuel ratio to the rich side as much as possible to reduce NOx.
[0013]
The control unit 6 also performs deterioration diagnosis of the rear oxygen sensor 5 according to the flowchart of FIG.
In step 1 (denoted as S1 in the figure, the same applies hereinafter), it is determined whether or not a predetermined diagnosis permission condition is satisfied. If the diagnosis permission condition is satisfied, the process proceeds to step 2.
In step 2, the output voltage of the rear oxygen sensor is monitored for a predetermined time.
[0014]
In step 3, the minimum value VMIN and the maximum value VMAX of the output voltage of the rear oxygen sensor are detected from the monitor result. This portion corresponds to output voltage minimum value detection means and output voltage maximum value detection means.
In step 4, the detected minimum value VMIN of the output voltage is compared with a floating allowance determination value (criteria) VCR in a memory (floating allowance determination value storage means) that has been determined and stored in advance. If VMIN ≧ VCR, an abnormality is diagnosed. This portion corresponds to lean side abnormality diagnosis means. A method for setting the floating allowance determination value (criteria) VCR will be described later.
[0015]
In step 5, the maximum value VMAX of the detected output voltage is compared with the slice level voltage VSL for control to determine whether VMAX <VSL. If VMAX <VSL, an abnormality is diagnosed. This portion corresponds to rich side abnormality diagnosis means. As a result of these diagnoses, if VMIN <VCR and VMAX ≧ VSL, it is regarded as normal and an OK determination is made in step 6. In the case of OK determination, the diagnosis is not performed until the next trip (after engine restart).
[0016]
If VMIN ≧ VCR or VMAX <VSL and an abnormality is diagnosed, further diagnosis is performed.
In step 7, feedback control by the rear oxygen sensor is performed, and the output voltage of the rear oxygen sensor being controlled is monitored.
In step 8, the intake air amount Qa is detected and integrated (ΣQa = ΣQa + Qa).
[0017]
In step 9, the integrated value ΣQa of the intake air amount is compared with a predetermined value to determine whether ΣQa ≧ predetermined value. If ΣQa <predetermined value, the process returns to step 7. That is, feedback control by the rear oxygen sensor is performed until ΣQa ≧ predetermined value, and the output voltage of the rear oxygen sensor is monitored.
In step 10, the minimum value VMIN and the maximum value VMAX of the output voltage of the rear oxygen sensor are detected from the monitor result. This part also corresponds to the output voltage minimum value detecting means and the output voltage maximum value detecting means.
[0018]
In step 11, as in step 4, the detected minimum value VMIN of the output voltage is compared with the floating allowance determination value (criteria) VCR to determine whether or not VMIN ≧ VCR. If VMIN ≧ VCR, Finally diagnosed as abnormal. This portion also corresponds to lean side abnormality diagnosis means.
In step 12, as in step 5, the detected maximum value VMAX of the output voltage is compared with the slice level voltage VSL for control to determine whether VMAX <VSL. If VMAX <VSL, Finally diagnosed as abnormal. This portion also corresponds to rich side abnormality diagnosis means.
[0019]
As a result of these diagnoses, if VMIN <VCR and VMAX ≧ VSL, it is regarded as normal and an OK determination is made in step 13. In the case of OK determination, the diagnosis is not performed until the next trip (after engine restart).
If VMIN ≧ VCR or VMAX <VSL and finally an abnormality is diagnosed, an NG determination is made in step 14 and the warning lamp (MIL) is turned on.
[0020]
In this embodiment, the diagnosis is performed in two stages (the first stage in steps 2 to 5 and the second stage in steps 7 to 12) to improve the diagnosis accuracy, and the diagnosis of the second stage is performed. Since the rear oxygen sensor performs feedback control for a long period, there is a concern about emission and deterioration of drivability. Therefore, the final diagnosis is made when the first stage diagnosis is NG.
[0021]
Next, a method for setting a floating allowance determination value (criteria) VCR with respect to the minimum value of the output voltage of the oxygen sensor (lean output floating level) VMIN will be described with reference to FIGS.
FIG. 4 shows a case where the slice level voltage for control is changed with the horizontal axis for the slice level voltage (mV) for control and the vertical axis for the NOx emission amount (g / mile) and the HC emission amount (g / mile). It is the characteristic view which showed the change of NOx discharge | emission amount and HC discharge | emission amount.
[0022]
Here, if the control slice level voltage is set near the middle of the change range (0 to 820 mV) of the output voltage of the oxygen sensor, the NOx emission amount increases and exceeds the regulation value. For example, the voltage is set to 700 mV to reduce the NOx emission amount (of course, the HC emission amount is ensured within the regulation value).
Here, when the rear oxygen sensor is deteriorated, generally, the maximum value (820 mV) of the output voltage hardly changes, but the minimum value of the output voltage changes as shown in FIG. A so-called lean output is generated.
[0023]
When the lean side output is floated by 100 mV, the calculated slice level voltage is 820 × (700−100) / (820−100) = 683 mV.
When the lean output is 200 mV, the calculated slice level voltage is 820 × (700−200) / (820−200) = 661 mV.
That is, the set value of the slice level voltage for control with respect to the output voltage of the oxygen sensor is VSL (= 700 mV), the set value of the rich side maximum value of the output voltage of the oxygen sensor is V1 (= 820 mV), and the lean side minimum of the output voltage When the value floating margin is ΔV, the calculated slice level voltage is V1 × (VSL−ΔV) / (V1−ΔV).
[0024]
Based on such a relationship, the relationship between the lean side output floating margin and the calculated slice level voltage is also shown in FIG.
Further, when the slice level voltage at the regulation value (NG point) of the NOx emission amount is read from the characteristic diagram of FIG. 4, it is 420 mV, which is the calculated slice level regulation value VNG.
[0025]
Therefore, the floating allowance ΔV = V1 × (VSL−VNG) / (when the calculated slice level voltage represented by V1 × (VSL−ΔV) / (V1−ΔV) becomes a predetermined regulation value VNG. V1-VNG) is set as a floating allowance determination value (criteria) VCR.
That is, if 820 × (700−ΔV) / (820−ΔV) = 420 and ΔV is calculated from this equation, ΔV = 574 mV, which is the floating allowance determination value VCR = 574 mV.
[0026]
In other words, if the set value of the slice level voltage for control with respect to the output voltage of the oxygen sensor is VSL, the set value of the rich side maximum value of the output voltage of the oxygen sensor is V1, and the regulation value for the calculated slice level voltage is VNG. The floating determination value VCR = V1 × (VSL−VNG) / (V1−VNG).
With this method, the floating allowance determination value VCR is calculated for each vehicle type (engine), stored, and used for the deterioration diagnosis shown in FIG. Diagnosis is possible.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing the configuration of the present invention. FIG. 2 is a system diagram of an air-fuel ratio control device for an engine. FIG. 3 is a flowchart for diagnosis of deterioration of a rear oxygen sensor. )
FIG. 5 is an explanatory diagram of a diagnostic method (part 2).
[Explanation of symbols]
1 Engine 2 Exhaust passage 3 Catalyst 4 Front oxygen sensor 5 Rear oxygen sensor 6 Control unit

Claims (3)

A diagnostic device for an oxygen sensor installed in an engine exhaust system,
When the set value of the slice level voltage for control with respect to the output voltage of the oxygen sensor is VSL, the set value of the rich side maximum value of the output voltage of the oxygen sensor is V1, and the floating margin of the minimum value of the lean side of the output voltage is ΔV, Floating allowance ΔV = V1 × (VSL−VNG) / (V1−V1) when the calculated slice level voltage represented by V1 × (VSL−ΔV) / (V1−ΔV) becomes a predetermined regulation value VNG. (VNG) is stored as a floating allowance determination value;
An output voltage minimum value detecting means for detecting the minimum value of the actual output voltage of the oxygen sensor;
A lean side abnormality diagnosis means for comparing the minimum value of the detected actual output voltage of the oxygen sensor with the floating margin determination value and diagnosing an abnormality of the oxygen sensor when the minimum value exceeds the floating margin determination value;
Oxygen sensor diagnostic apparatus comprising: Output voltage maximum value detecting means for detecting the maximum value of the actual output voltage of the oxygen sensor;
Comparing the detected maximum value of the actual output voltage of the oxygen sensor with the control slice level voltage setting value, the oxygen sensor malfunctions when the maximum value is lower than the control slice level voltage setting value Rich side abnormality diagnosis means for diagnosing,
The oxygen sensor diagnostic apparatus according to claim 1, comprising: The calculated slice level voltage regulation value VNG is a slice level voltage at the regulation value of exhaust harmful component emission from the characteristic value of exhaust harmful component emission when the control slice level voltage is changed. 2. The oxygen sensor diagnostic apparatus according to claim 1, wherein the oxygen sensor diagnostic apparatus is determined by reading.

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