JP3453899B2 - Method and apparatus for evaluating characteristics of air-fuel ratio sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for evaluating the characteristics of an air-fuel ratio sensor for detecting the air-fuel ratio of engine exhaust gas.

[0002]

2. Description of the Related Art The characteristic evaluation of an air-fuel ratio sensor for exhaust gas of an automobile is most preferably carried out using an actual engine. However, the characteristic evaluation method that uses an actual engine is affected by the type and control method of the target engine, sensor mounting position, operating conditions, ambient conditions, etc. It is not suitable for use in etc.

Therefore, there is a method in which various kinds of gases are supplied from a gas cylinder or the like, mixed and heated to generate a gas composition close to the actual composition of exhaust gas, and this is used as a test gas. (Model gas method). However, this method has the drawback that the equipment is large and the cost is high because many types of gases contained in the exhaust gas are adjusted to a certain ratio.

Therefore, as another method for making equipment cheap, there is a method in which a gas burner is used to burn a mixture of a few kinds of gases and the combustion gas is used as a test gas (gas burner method). However, this method of burning with a gas burner has a drawback in that the composition is considerably different from the composition of the exhaust gas of the engine due to too good combustion. Therefore, it can be used only when accuracy is not required, such as inspecting the air-fuel ratio sensor stepwise at two points, the characteristic at the time of rich gas and the characteristic at the time of lean gas. Therefore, as an improved method, a method is proposed in which an oxidizing or reducing gas is appropriately added to the above combustion gas to strengthen the correlation with the actual exhaust gas and obtain a measurement result similar to the exhaust gas. (See Japanese Patent Publication No. 6-70619).

[0005]

[Problems to be Solved] However, the above-mentioned Japanese Patent Publication No. 6
The improved gas burner method disclosed in Japanese Patent Publication No. 70619 has a problem in that the control is complicated, such as increasing or decreasing the additive gas at a frequency of 10 Hz or more. Even if it is improved, the composition of the actual exhaust gas is improved. Has the drawback of being quite different from. The present invention has been made in view of such conventional problems, and efficiently produces a test gas having a high correlation with an actual exhaust gas by using a simple and inexpensive facility, thereby accurately and accurately An air-fuel ratio sensor characteristic evaluation method and an evaluation device capable of evaluating a sensor are provided.

[0006]

A first invention of the present application is a characteristic evaluation method for an air-fuel ratio sensor of an engine, which supplies a test gas to measure the characteristic, and uses three kinds of gases of nitrogen, oxygen and hydrocarbons. By preparing and heating the mixed gas to spontaneously ignite and burn it, and adjusting the mixing ratio of the above gases, it is possible to obtain a combustion gas for testing that has a high correlation with the engine exhaust gas with the desired air-fuel ratio. It is a characteristic evaluation method of a characteristic air-fuel ratio sensor.

The most remarkable thing in the first invention is that
The test gas is generated by adjusting the mixing ratio of the mixed gas composed of nitrogen gas, oxygen gas and hydrocarbon gas, and spontaneously igniting the mixed gas. That is, in the present invention, a combustion gas is generated by spontaneous combustion by heating without using a gas burner and the combustion gas is used as a test gas. Then, by changing the mixing ratio of the mixed gas, a combustion gas having a composition highly correlated with the exhaust gas having a desired air-fuel ratio is generated.

In addition to adjusting the mixing ratio of the mixed gas as described above, it is preferable to further adjust the heating temperature of the mixed gas. This is because the composition of the combustion gas generated by changing the heating temperature changes,
This is because the combustion gas having the target composition can be obtained with higher accuracy by controlling the heating temperature to a predetermined value with high accuracy.

Regarding the influence of the heating temperature, for example, taking propane as an example, when propane (C ₃ H ₈ ) is burned in a state of insufficient oxygen gas, different reactions such as the following will occur depending on the temperature. Progresses. C ₃ H ₈ + 4O ₂ → CO ₂ + 2CO + 4H ₂ O, or → 2CO ₂ + CO + 3H ₂ O + H ₂ , or → 3CO ₂ + 2H ₂ O + 2H ₂

The range of the heating temperature for changing the composition of the combustion gas as described above depends on the kind of the hydrocarbon gas, but is usually 400 ° C. or higher.
This is because at a temperature lower than 400 ° C., the above-mentioned reaction of hydrocarbons hardly occurs, and it becomes difficult to carry out the evaluation method of the present invention. The heating temperature is preferably 400 to 1100 ° C.

In order to obtain the composition of the combustion gas corresponding to the exhaust gas having the desired air-fuel ratio (rich or lean) by a relatively simple control calculation, the total flow rate of the three types of gas is made constant and It is very easy to carry out by making the flow rate of the hydrocarbon gas constant and adjusting the ratio of the oxygen gas and the nitrogen gas in the total value (constant) of the flow rates of the oxygen gas and the nitrogen gas. This is because the amount of hydrocarbon gas is relatively smaller than that of other gases, so that the mixing ratio of the two can be controlled accurately by adjusting the oxygen gas side.

For example, in the case of completely burning propane, C ₃ H ₈ + 5O ₂ → 3CO ₂ + 4H ₂ O is obtained, and as is known from the above formula, a large amount of oxygen gas is required as compared with propane. Is. Therefore, the fine adjustment of the mixing ratio of the two can be improved by adjusting the oxygen gas. Also, from the viewpoint of safety management, it is preferable that the flow rate of explosive hydrocarbon gas be below the lower explosive limit concentration (2.3% or less for C ₃ H ₈ ),
In order to keep the hydrocarbon gas below the lower explosive limit concentration, it is appropriate to keep the total flow rate and the flow rate of the hydrocarbon gas constant at all times (for example, the flow rate of propane is below the lower explosive limit concentration). 1 to 2%).

On the other hand, the second invention of the present application, gas supply means for supplying nitrogen gas, oxygen gas and hydrocarbon gas, flow rate adjusting means for adjusting the delivery flow rate of each gas, the above three types of delivered gas Combustion means for mixing and heating gases to spontaneously ignite, and measurement means for taking in combustion gas generated in the combustion means and measuring characteristics of the air-fuel ratio sensor,
An air-fuel ratio sensor evaluation device for an engine, comprising: a determination unit that determines whether the air-fuel ratio sensor is good or bad based on output data of the measurement unit.

In the above-mentioned second invention, it is preferable that the combustion means further has a temperature adjusting means for automatically adjusting the heating temperature of the mixed gas based on a given command.
This is because, as described above, it is necessary to accurately control the heating temperature in order to keep the generated combustion gas constant.

Further, in the second aspect of the present invention, the determining means further issues a predetermined control command to the flow rate adjusting means and the combustion means, automatically reads the output data of the measuring means, and converts it into a series of read data. It is preferable to provide an automatic determination function for determining the quality of the air-fuel ratio sensor based on the above. By providing the automatic determination function, the evaluation result can be automatically obtained by setting the air-fuel ratio sensor to be evaluated in the device.

[0016]

In the characteristic evaluation method according to the first aspect of the present invention, the combustion reaction by the mixed gas of three kinds is represented by the following equation by the reaction of oxygen gas and hydrocarbon gas because nitrogen gas hardly reacts. K ₁ O ₂ + K ₂ C _n H _m → K ₃ CO ₂ + K ₄ H ₂ O + K
_{5 CO + K 6 H 2 +} K 7 O 2 + K 8 C x H y And if the excessive lean composition i.e. O _2,
The composition of the combustion gas after the reaction is mostly CO ₂ and H ₂
O and excess O ₂ . Then, by adjusting the flow rate of O _2, because it is possible to control the amount of excess O ₂ in the combustion gas, and the desired lean exhaust gas by adjusting the amount of O ₂ at a desired flow rate Combustibility with high correlation can be easily obtained.

When the stoichiometric gas composition has no excess or deficiency of O ₂ , most of the combustion gas is CO ₂ and H ₂ O. In this case, it is possible to obtain the test combustion gas corresponding to the exhaust gas having the stoichiometric air-fuel ratio. On the other hand, if the combustion is carried out in a state where the rich gas composition, that is, O ₂ is insufficient, the combustion gases become CO ₂ , H ₂ O, CO, H ₂ and hydrocarbon gas. Then, the composition of the hydrocarbon gas or the like changes depending on the degree of lack of O ₂ and the heating temperature. Therefore, by setting the heating temperature to a predetermined value and adjusting the amount of O ₂ , it is possible to obtain the combustion gas for test corresponding to the rich exhaust gas.

As described above, O ₂ for hydrocarbon gas
The combustion gas having a composition corresponding to the exhaust gas with a wide range of air-fuel ratios can be obtained by changing the amount of the gas and changing the heating temperature to a constant temperature at which spontaneous combustion is possible. Further, since the mixed gas is combusted by spontaneous combustion without using a gas burner or the like, the reaction is stable and it is possible to always obtain a combustion gas having a constant composition highly correlated with the exhaust gas.

Since the combustion gas for the test is obtained by mixing only three kinds of gases, the equipment used can be very simple. As described above, according to the first aspect of the present invention, the test gas having a high correlation with the actual exhaust gas is efficiently generated by the simple and inexpensive equipment using the few kinds of gas that are easily available, and the An air-fuel ratio sensor characteristic evaluation method capable of accurately evaluating an air-fuel ratio sensor can be provided.

According to the second aspect of the invention, the test gas having a high correlation with the actual exhaust gas is efficiently generated by the simple and inexpensive equipment using the few kinds of gas that are easily available, and the An evaluation device of an air-fuel ratio sensor that can evaluate an air-fuel ratio sensor with high accuracy can be provided. In addition, in the first and second inventions of the present application, highly toxic C
Do not use the O gas and NO _X gases, are excellent in terms of safety management. Further, since nitrogen gas and oxygen gas are used without using air, the ratio of the hydrocarbon gas to the whole is lower than that when air is used, and there is an advantage that it can be suppressed below the lower explosion limit concentration. .

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method and apparatus for evaluating characteristics of an air-fuel ratio sensor according to an embodiment of the present invention will be described with reference to FIGS. In this example, as shown in FIG. 1, gas cylinders 11 to 13 as gas supply means for supplying a nitrogen gas 81, an oxygen gas 82 and a hydrocarbon gas 83, and a flow rate adjusting means 20 for adjusting a delivery flow rate of each gas. And a combustion means 3 for mixing and heating the above-mentioned three kinds of delivered gases to heat them spontaneously.
0 and measuring means 4 for measuring the characteristics of the air-fuel ratio sensor 7 by taking in the combustion gas 85 generated in the combustion means 30.
The evaluation device 1 for the air-fuel ratio sensor 7 of the engine has 0 and a determination means 45 for determining the quality of the air-fuel ratio sensor 7 based on the output data of the measurement means 40.

Further, the combustion means 30 has a temperature adjusting means for automatically adjusting the heating temperature for the mixed gas based on a given command. Then, the determining means 45 issues a predetermined control command to the flow rate adjusting means 20 and the combustion means 30, automatically reads the output data of the measuring means 40, and determines whether the air-fuel ratio sensor 7 is good or bad based on the read series of data. It has an automatic judgment function for judging.

Then, the evaluation device 1 uses the respective gases 81 to 83.
The mixing temperature is adjusted and the heating temperature is controlled to a predetermined value to obtain a desired combustion gas 85 as a test gas.
At this time, the flow rate Q _c of the total flow rate Q _t with the hydrocarbon gas 83 of the gas 81 to 83 is constant, the flow rate Q _n of the nitrogen gas and oxygen gas, by adjusting the ratio of Q _o obtain the desired combustion gas . Further, the flow rate Q _c of the hydrocarbon gas 83 is set to be equal to or lower than the lower explosion limit concentration (2.3% for C ₃ H ₈ ).
Less than).

A supplementary explanation will be given below for each of them.
The flow rate adjusting means 20 includes mass flow controllers 21 to 2
3 and the flow rate control device 24, and the mass flow controllers 21 to 23 adjust the flow rates Q _n , Q _o , and Q _c of the respective gases 81 to 83 based on a command from the flow rate control device 24. The respective gases 81 to 83 whose flow rates are controlled reach the combustion means 30 through the pipe 61.

The combustion means 30 has an electric furnace 31 and a temperature controller 32. The electric furnace 31 heats the pipe 62 from the outside based on a command from the temperature controller 32, and spontaneously ignites the mixed gas 84. The command temperature of the temperature controller 32 in this example is 700 ° C. Further, the pipe 62 is made of quartz so as to prevent oxidation due to heating unlike a metal pipe. Then, the generated combustion gas 85 is measured by the measuring means 40.
Sent to.

The measuring means 40 has an installation section 41 for setting the air-fuel ratio sensor 7 to be evaluated and a measuring section 42 for measuring the output of the air-fuel ratio sensor 7. The installation unit 41 has a temperature controller 411 and an electric furnace 412, and does not lower the temperature of the combustion gas 85 so much that it is heated to 650 ° C. in order to maintain the temperature necessary for the characteristics of the sensor itself. Supply combustion gas to 7.

The air-fuel ratio sensor 7 includes an oxygen sensor for returning an oxygen concentration difference from the atmosphere to a voltage value and an air-fuel ratio sensor for converting the oxygen concentration difference to a limiting current value. The evaluation results are illustrated for the case of a sensor. FIG. 3 is a graph showing the value of the limiting current (the value of the flat portion) of the air-fuel ratio sensor 7 when the exhaust gas of the actual engine is used. Reference numeral 61 is lean gas corresponding to A / F (air-fuel ratio) = 18. Reference numeral 62 represents a stoichiometric gas corresponding to A / F = 14.5, and reference numeral 63 represents a characteristic value in a rich gas corresponding to A / F = 13. On the other hand, FIG. 2 shows changes in the limiting current when the compositions of the gases 81 to 83 are set as shown in the table below in the evaluation apparatus 1 of this example.

[0028]

[Table 1]

As can be easily understood by comparing FIG. 2 and FIG. 3, the combustion gas A of this example has A / F = 18.
It is possible to obtain extremely similar limiting current characteristics to the actual exhaust gas, the combustion gas B to the stoichiometric exhaust gas, and the combustion gas C to the A / F = 13 actual exhaust gas. The total gas flow rate is 1000 cc / min.
It is preferable to set the degree. The basis for this is from the viewpoint of controllability for controlling the flow rate of hydrocarbon gas to about 1% (1/2 of the lower limit concentration of explosion), gas combustion stability, and economic efficiency.

Further, the flow rates Q _o of oxygen gas and nitrogen gas,
Q _n can be easily set to 0.1 cc / m by the flow rate adjusting means 20.
Since it can be increased / decreased in units, A over a wide range
It is possible to obtain a combustion gas for a test with extremely high accuracy with respect to the / F ratio. As described above, according to the method and apparatus of the present example, the actual exhaust gas is used by using the gas of as few as three kinds, the gas that is very easily available, and the simple and inexpensive equipment. It is possible to obtain a test gas that has a very high correlation with the gas, and thus it is possible to perform highly accurate evaluation of the air-fuel ratio sensor.

Although combustion gas having a correlation with exhaust gas can be generated by a combustion means such as a gas burner in place of the combustion means 30 of this embodiment, the stability of combustion and the composition of the generated gas can be changed. The method (apparatus) of this example is significantly superior in terms of control accuracy.

[Brief description of drawings]

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

FIG. 2 is a limiting current characteristic diagram of the air-fuel ratio sensor when the evaluation device of the embodiment is used.

FIG. 3 is a limit current characteristic diagram of an air-fuel ratio sensor using actual exhaust gas.

[Explanation of symbols]

1. ． ． Evaluation device, 11-13. ． ． Gas supply means (gas cylinder), 20. ． ． Flow rate adjustment means, 30. ． ． Combustion means, 40. ． ． Measuring means, 45. ． ． Determination means, 7. ． ． Air-fuel ratio sensor, 81. ． ． Nitrogen gas, 82. ． ． Oxygen gas, 83. ． ． Hydrocarbon gas, 84. ． ． Mixed gas, 85. ． ． Combustion gas,

Continuation of front page (72) Inventor Naoto Miwa 1-1-1, Showa-cho, Kariya city, Aichi Japan Denso Co., Ltd. (56) Reference JP-A-3-35155 (JP, A) JP-A-63-314450 (JP , A) JP-A-2-132363 (JP, A) JP-A-3-63559 (JP, A) JP-A-8-136494 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB) Name) G01N 27/26-27/49 G01N 1/00 G01N 1/00 102

Claims (8)

(57) [Claims] 1. A method for evaluating the characteristics of an air-fuel ratio sensor for an engine, which supplies a test gas to measure the characteristics, comprising preparing three kinds of gases of nitrogen, oxygen and hydrocarbon and heating the mixed gas. Characteristics of an air-fuel ratio sensor characterized by obtaining combustion gas for testing that is highly correlated with engine exhaust gas having a desired air-fuel ratio by spontaneously igniting and burning, and adjusting the mixing ratio of the above gases Evaluation methods. 2. The characteristic evaluation method for an air-fuel ratio sensor according to claim 1, wherein the mixing ratio of each gas is adjusted and the heating temperature of the mixed gas is adjusted. 3. The characteristic evaluation method for an air-fuel ratio sensor according to claim 2, wherein the adjustment range of the heating temperature is 400 ° C. or higher. 4. The mixing ratio according to claim 1, claim 2 or claim 3, wherein the total flow rate of the three types of gases and the flow rate of hydrocarbons are constant, and the flow rate ratio of nitrogen gas and oxygen gas is changed. A method for evaluating the characteristics of an air-fuel ratio sensor, characterized in that: 5. The characteristic evaluation method for an air-fuel ratio sensor according to claim 1, wherein the flow rate of the hydrocarbon is set to be equal to or lower than the lower explosion limit concentration. 6. A gas supply means for supplying a nitrogen gas, an oxygen gas and a hydrocarbon gas, a flow rate adjusting means for adjusting a delivery flow rate of each gas, and a mixture of the three delivered gases for heating. Combustion means for igniting, measuring means for measuring the characteristics of the air-fuel ratio sensor by taking in the combustion gas generated in the combustion means, and judging means for judging the quality of the air-fuel ratio sensor based on the output data of the measuring means. An air-fuel ratio sensor evaluation apparatus for an engine, comprising: 7. The air-fuel ratio sensor evaluation device according to claim 6, wherein the combustion means has a temperature adjustment means for automatically adjusting the heating temperature for the mixed gas based on a given command. . 8. The determination means according to claim 7, wherein the determination means issues a predetermined control command to the flow rate adjusting means and the combustion means, automatically reads the output data of the measuring means, and converts the output data into a series of read data. An air-fuel ratio sensor evaluation device for an engine, which has an automatic determination function for determining whether the air-fuel ratio sensor is good or bad based on the above.