JP2885871B2 - Method for measuring purification rate of catalyst using air-fuel ratio sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring a purification rate of a catalyst using an air-fuel ratio sensor.

[Conventional technology]

As a conventional method for detecting the deterioration time of a catalyst, there is known a method in which oxygen sensors are provided on the upstream side and the downstream side, respectively, and the deterioration time is detected based on a difference between the maximum values of the respective output voltages (Japanese Patent Laid-Open No. 2000-157421). JP-A-63-231252).

[Problems to be solved by the invention]

Since the output characteristic of the oxygen sensor that detects the stoichiometric air-fuel ratio shows a sharp rise near λ = 1, it only shows an output waveform that fluctuates alternately on the lean side and the rich side as shown mainly in FIG. , A waveform corresponding to the intermediate value is not shown. Therefore, in the method for detecting the deterioration time of the catalyst using the two oxygen sensors, the system processing performed by comparing the two waveforms is complicated, and the purification rate is reduced as shown in FIG.
If it is less than 70%, it is difficult to detect with sufficient accuracy.

The present invention has been made in view of the above-described viewpoints, and has as its object to provide a purification rate measuring method capable of accurately measuring in a wide purification rate range.

[Means for solving the problem]

According to the first aspect of the present invention, there is provided a method of measuring a purification rate, wherein an oxygen sensor is disposed upstream of a catalyst for purifying harmful components in exhaust gas, and an air-fuel ratio sensor is disposed downstream of the catalyst.
C) measuring the linear relationship between the average purification rate of the three components of carbon monoxide (CO) and nitrogen oxide (NOx) in the range of 100 to 30% and the output width of the air-fuel ratio sensor. The average purification rate of the catalyst is measured from the output width of the air-fuel ratio sensor using the linear relationship.

This output width is usually a voltage width, but may be a current width corresponding to this.

Here, the “air-fuel ratio sensor” in this specification refers to an oxygen sensor that measures an oxygen partial pressure, an oxygen ratio, or an oxygen amount in exhaust gas, among others.

[Action]

An oxygen sensor is provided upstream of the catalyst. Therefore, feedback is performed by this sensor according to the fluctuation of the operating condition, and the operating condition is always set so as to be near the stoichiometric air-fuel ratio (λ = 1). Therefore, the width in which the output voltage waveform swings can be kept constant.

On the other hand, as shown in FIG. 6, the air-fuel ratio sensor disposed downstream has a predetermined curve curve in which the relationship between the air-fuel ratio and the output characteristic shows, and the air-fuel ratio A / F = 14.
There is no sudden rise at 6. Therefore, for example, as shown in FIG.
Width, waveform when completely purified (in this case, in effect,
It takes various values, such as the width (= 0) in B).

From the above, the output width of the air-fuel ratio sensor and the HC / CO / NOx of the catalyst
For example, as shown in FIG. 4, the average purification rate shows a substantially linear relationship, and shows a good relationship for all the purification rates.

〔Example〕

 Hereinafter, the present invention will be described specifically with reference to examples.

(1) Overview of Deterioration Timing Detector FIG. 1 is a schematic configuration diagram of an air-fuel ratio measuring device of an internal combustion engine capable of implementing a catalyst degradation timing detecting method and a purification rate measuring method using an air-fuel ratio sensor of the present embodiment, and FIG. 2 is an explanatory view of an apparatus showing a sensor arrangement place and the like for a test.

As shown in these figures, a three-way catalyst 3 is attached to the exhaust passage 2 of the internal combustion engine 1.
Sensor (λ sensor for control) in the exhaust passage upstream of
4. An air-fuel ratio sensor 5 is attached to the exhaust passage on the downstream side. The sensors 4 and 5 are electrically connected to the electronic control device 6 and the sensor control device 7, respectively, and obtain sensor outputs from them. The electronic control unit 6 is electrically connected to a fuel injection valve 9 disposed in an intake passage 8 of the internal combustion engine 1, and controls the fuel of the fuel injection valve 9 according to an output voltage from the oxygen sensor 4. Control the injection volume. That is, the sensor output content of the electronic control unit 6 is fed back to make the air-fuel ratio substantially constant, and the sensor output is made substantially constant.

As the air-fuel ratio sensor 5, a known sensor can be used. For example, the principle will be briefly described with reference to FIG. First, pump-up is performed so that the oxygen partial pressure in the exhaust gas flowing into the diffusion chamber 53 formed between the Ip cell 51 and the Vs / Icp cell 52 becomes constant.
A voltage (for example, 450 mV) generated due to the ratio of the oxygen partial pressure in the diffusion chamber 53 to the oxygen partial pressure in the oxygen reference chamber 54
Is to read an output current value (or a voltage value) for keeping the constant. Incidentally, 45 indicates a heater.

The oxygen sensor 4 is not particularly limited. For example, a zirconia oxygen sensor, a titania oxygen sensor, or the like can be used.

Further, as a comparative example, the same oxygen sensor was attached instead of the air-fuel ratio sensor.

The three-way catalyst 3 may be one supporting ordinary Pt, Rh, Pd, or the like, and the structure thereof may be appropriately selected from a monolith type such as a honeycomb or a particle type such as a pellet, cylindrical, or spherical shape. .

(2) Measurement of HC / CO / NOx average purification rate and detection of deterioration time Using this device, engine operating conditions (1.5L x 4 cylinders, engine speed; 1900rpm, boost pressure; -40mmHg)
Then, the output width (a1) of the air-fuel ratio sensor 5 is obtained under various purification rates and used for a calibration curve. The output waveform of the air-fuel ratio sensor 5 is, as shown in FIG. 3, substantially straight line B when a new catalyst is used, since the air-fuel ratio sensor 5 is almost completely purified. When the deteriorated catalyst was used, a waveform A having a predetermined output width was shown according to the degree of deterioration.
The purification rate at the time when the predetermined output width is shown is 2% shown in FIG.
Each exhaust gas is sampled at each position, and the amount of each component (HC, CO, NOx) is measured and measured by each analyzer.

The results are shown in FIG. According to this result, a good linear relationship between the output width and the average purification rate was obtained in a purification rate range of about 30% or more. In addition, it is possible to accurately detect the deterioration time.

It should be noted that the output width, which is a guide for the deterioration timing, is set variously depending on the purpose and the like. Further, the relationship between the average purification rate and the output width of the air-fuel ratio sensor changes depending on the engine speed, the load, and the like. Deterioration can be detected.

Further, as shown in FIG. 4, since the output width and the average purification rate have a linear relationship, if the output width is known, the purification rate of the catalyst can be accurately determined. In particular, although only a purification rate of about 30% or more is required in the figure, it is possible to measure a purification rate of less than about 30%. Therefore, according to the present measuring method, the purification rate can be accurately measured in all the purification rate ranges.

On the other hand, when the relationship between the sensor output width and the purification rate is obtained in the conventional oxygen sensor of the comparative example, as shown in FIG. 8, the purification rate cannot be accurately obtained at 70% or less.

It should be noted that the present invention is not limited to the specific embodiments described above, but can be variously modified within the scope of the present invention according to the purpose and application.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION The purification rate measuring method of this invention can measure the purification rate of a catalyst simply, accurately, inexpensively, and without requiring a large-scale apparatus. In particular, the degree of deterioration can be determined, which is very useful as compared with the conventional method using two oxygen sensors. Further, according to the present measurement method, the measurement range is not limited as in the case of the conventional two oxygen sensors, and the measurement can be performed accurately even at a purification rate of 70% or less.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an air-fuel ratio measuring device used in the embodiment,
FIG. 2 is an explanatory view of an air-fuel ratio measuring device used in the embodiment, and FIG.
The graph shows the output waveform of the air-fuel ratio sensor.
FIG. 5 is a graph showing the relationship between the output width and the average purification rate of HC / CO / NOx in the embodiment, FIG. 5 is an explanatory diagram showing the principle of the air-fuel ratio sensor used in the embodiment, and FIG. FIG. 7 is a graph showing the relationship between the air-fuel ratio and the sensor output characteristic in the illustrated air-fuel ratio sensor, FIG. 7 is a graph showing the output waveform of the oxygen sensor in the comparative example, and FIG. 8 is a graph showing the relationship between the sensor output width and the average purification rate in the comparative example. It is a graph which shows a relationship. 1; engine, 2; exhaust passage, 3; three-way catalyst, 4; oxygen sensor,
5; air-fuel ratio sensor, 51; Ip cell, 52; Vs / Icp cell, 53; diffusion chamber, 54; oxygen reference chamber, 55; heater, 6; electronic control device, 7; sensor control device, 8; intake passage, 9; fuel injection valve.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-3-74540 (JP, A) JP-A-62-153546 (JP, A) JP-A-3-281960 (JP, A) JP-A 61-153960 286550 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01N 3/20 F01N 41/14 G01N 27/00 G01N 27/12

Claims (1)

(57) [Claims] An oxygen sensor is disposed upstream of a catalyst for purifying harmful components in exhaust gas, and an air-fuel ratio sensor is disposed downstream of the catalyst. Hydrocarbon (HC) and carbon monoxide (HC) in exhaust gas are provided. The linear relationship between the average purification rate and the output width of the air-fuel ratio sensor in a region where the average purification rate of the three components of CO) and nitrogen oxide (NOx) is 100 to 30% is measured. A method for measuring a purification rate of a catalyst by an air-fuel ratio sensor, wherein the average purification rate of the catalyst is measured from an output width of the air-fuel ratio sensor using the relationship.