JPH0245750A - Characteristic evaluating method for oxygen sensor - Google Patents

Abstract

PURPOSE:To accurately measure characteristics of the oxygen sensor to be measured which have relation to emission and to improve characteristic evaluation by leading out the output of the oxygen sensor to be measured. CONSTITUTION:A reference oxygen sensor 12 which outputs a specific electromotive force signal is provided on the downstream side of a purifying device 8 which purifies unburnt components of carbon monoxide present in test gas. Then the test gas is switched periodically between a rich atmosphere where fuel is excessive and a lean atmosphere where air is excessive about an ideal air fuel ratio point according to the electromotive force signal of the reference oxygen sensor 12 corresponding to the oxygen concentration in the test gas which is purified by the purifying device 8. Further, the oxygen sensor 6 whose characteristics are to be evaluated is arranged on the upstream side of the purifying device 8 and the time ratio of the rich signal time and lean signal time of the oxygen sensor 16 is measured according to the electromotive force signal which is outputted by the oxygen sensor 16 according to the test gas switched periodically between the rich atmosphere and lean atmosphere, thereby improving the characteristic evaluation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for evaluating the characteristics of an oxygen sensor, and particularly to a method for evaluating the sensor characteristics of an oxygen sensor that outputs a predetermined electromotive force signal based on the principle of an oxygen concentration battery. This relates to a simple method of measurement.

(Background technology) Conventionally, air-fuel ratio detection devices detect the oxygen concentration contained in the exhaust gas (combustion exhaust gas) of an automobile internal combustion engine, and optimally control the combustion state of the internal combustion engine based on the detected signal. So-called oxygen sensors are known that purify exhaust gas and reduce fuel consumption.

By the way, the oxygen concentration detection element used in this type of oxygen sensor typically has a structure that uses zirconia porcelain, which is an isoelectrolyte that conducts oxygen ions, to determine the oxygen concentration using the principle of an oxygen concentration battery. has been put into practical use, where each isoelectrolyte is provided with
Combustion exhaust gas obtained by detecting the electromotive force caused by the difference in oxygen concentration between the measurement electrode exposed to the measured gas and the reference electrode exposed to the reference gas with the reference oxygen concentration, and then burning at the stoichiometric air-fuel ratio. Based on this, it is determined whether the gas to be measured is in a lean atmosphere or a rich atmosphere, using neutral atmosphere gases as the boundary, and based on this, the gas to be measured is The engine that generates the combustion exhaust gas is controlled so that the combustion exhaust gas is in a range near the stoichiometric air-fuel ratio where the three-way catalyst that purifies the exhaust gas is effective.

For this reason, knowing the sensor characteristics of such oxygen sensors and performing more accurate air-fuel ratio control based on them is considered effective in improving the purification characteristics of the three-way catalyst. Various methods for evaluation have been introduced.

For example, by using propane combustion exhaust gas in a rich atmosphere obtained by combustion at a state lower than the stoichiometric air-fuel ratio point (λ-1) and a lean atmosphere obtained by combustion at a state higher than that, a rich atmosphere can be obtained. By measuring the rich voltage or the lean voltage corresponding to a lean atmosphere, or by periodically flowing these gases, you can measure the response time from rich to lean or from lean to rich of the oxygen sensor. There are methods to measure the asymmetry of these response times. However, in these methods, there was almost no correlation between sensor characteristic values and emission values, and none of them were preferable from the viewpoint of emission control, which is the original purpose of oxygen sensors. It is.

Furthermore, a so-called dynamic lambda measurement method is also known, in which the engine is operated in a closed state and the A/F value of exhaust gas is measured using an oxygen sensor attached to the engine exhaust system. According to this method, although it is recognized that there is a relationship between the characteristic values of the oxygen sensor and the emission values, the measurement accuracy is not very high because it takes time to measure and measures A/F. It has inherent problems such as. This is A/
This is because a gas analysis system is used to measure F, which also causes problems such as a large-scale measurement system and high measurement costs.

(Solving Section B) The present invention has been made against this background, and the problem to be solved is to measure emissions related to emissions without using a large-scale measurement system. The objective is to accurately measure sensor characteristics and evaluate the characteristics more accurately.

(Solution Means) In order to solve this problem, the present invention purifies unburned components such as carbon monoxide, hydrocarbons, and nitrogen oxides present in a test gas consisting of combustion exhaust gas or a simulated gas equivalent to it. A reference oxygen sensor that outputs a predetermined electromotive force signal based on the principle of an oxygen concentration battery is disposed downstream of the purification device, and the test gas purified by the purification device is output from the reference oxygen sensor. Based on the electromotive force signal corresponding to the oxygen concentration in the test gas, the test gas is periodically switched to a rich atmosphere with excess fuel and a lean atmosphere with excess air, centering on the stoichiometric air-fuel ratio point, while An oxygen sensor to be measured to be characterized is arranged upstream of the purification device, and from the oxygen sensor to be measured, according to the test gas which is periodically switched between a rich atmosphere and a lean atmosphere according to the principle of an oxygen concentration cell. Based on the output electromotive force signal, the time ratio between the rich signal time and the lean signal time of the oxygen sensor to be measured is measured.

Furthermore, in order to solve the above-mentioned problems, the present invention provides a purification device for purifying unburned components such as carbon monoxide, hydrocarbons, and nitrogen oxides present in a test gas consisting of combustion exhaust gas or a simulated gas equivalent thereto. A reference oxygen sensor that outputs a predetermined electromotive force signal based on the principle of an oxygen concentration battery is disposed downstream of the sensor, and the oxygen in the test gas purified by the purification device is output from the reference oxygen sensor. Based on the electromotive force signal corresponding to the concentration, the test gas is periodically switched between a rich atmosphere with excess fuel and a lean atmosphere with excess air around the stoichiometric air-fuel ratio point. An oxygen sensor to be measured whose characteristics are to be evaluated is arranged upstream of the oxygen sensor, and the oxygen sensor outputs an output according to the test gas which is periodically switched between a rich atmosphere and a lean atmosphere according to the principle of an oxygen concentration battery. Another feature is that the lean voltage or output amplitude of the oxygen sensor to be measured is measured based on the electromotive force signal.

(Specific Configuration/Examples) The present invention will be explained in more detail below with reference to the drawings.

First, FIG. 1 shows a specific example of the measurement system according to the present invention, in which 2 is an engine as a gas supply device. The engine 2 generates a rich atmosphere corresponding to combustion exhaust gas obtained by combustion in an excess fuel condition and a lean atmosphere corresponding to combustion exhaust gas obtained by combustion in an excess air condition. The gas is guided through the exhaust manifold 4 and the first exhaust pipe 6 to a purification device 8 such as a three-way catalyst device, and in this purification device 8, carbon monoxide present in the test gas is removed. (CO), hydrocarbons (HC), nitrogen oxides (NOX)
”) and other unburned components are purified.

Note that the gas supply device includes, in addition to the engine 2 as described above,
It may be a simulating gas supply device that simulates exhaust gas components emitted from such an engine and provides a simulated gas corresponding to such exhaust gas, for example, a mixture of CO2Hz, No, Cot, etc. to combustion exhaust gas of air and propane gas. There is no problem even if it is a gas supply device that combines gases, and as the purification device 8, in addition to the well-known three-way catalyst device and oxidation catalyst device, it is also possible to use a gas supply device that balances combustion exhaust gas (test gas). Any device may be used as long as it promotes the reaction (cleaning reaction); for example, a simple heating device may be used.

The test gas purified in the purification device 8 is discharged into the atmosphere through the second exhaust pipe 10. is equipped with a reference oxygen sensor 12 that outputs a predetermined electromotive force signal based on the principle of an oxygen concentration battery, and outputs an electromotive force signal corresponding to the oxygen concentration in the purified test gas flowing out from the purifier 8. It is designed to be output. This reference oxygen sensor 12 has a known structure including an oxygen ion conductive solid electrolyte, a measuring electrode, and a reference electrode. In particular, in the present invention, the oxygen sensing portion is heated to a desired temperature using a heater. It is recommended to use a heating type sensor (see Japanese Patent Application Laid-Open No. 57-142555, Japanese Patent Application Laid-Open No. 55-140145, etc.) that is heated to a certain temperature. This is because the operating point, which will be described later, is closer to the stoichiometric air-fuel ratio point than in a non-heating type sensor.

Further, the reference oxygen sensor 12 is connected to an air-fuel ratio control computer 14 as a gas component control device, and the air-fuel ratio of the engine 2 is determined based on the signal output from the reference oxygen sensor 12. The gas component in the combustion exhaust gas as the test gas discharged from the engine 2 is controlled by the engine 2 to be varied between rich and lean. In other words, the air-fuel ratio of the engine 2 is controlled by the air-fuel ratio control computer 14, and the test gas is combusted in an over-combustion state around the stoichiometric air-fuel ratio point, resulting in a rich atmosphere and an over-air condition. It is designed to periodically switch to a lean atmosphere obtained by causing combustion to occur downward. Therefore, the engine 2 is operated in a closed state based on the signal from the reference oxygen sensor 12 installed at the rear of the purifying device 8.

On the other hand, the oxygen sensor 16 to be measured whose characteristics should be evaluated is located at a location where it is normally installed in the exhaust system of a vehicle.
In other words, it is attached to the first exhaust pipe 6 which is the front (upstream side) of the purifier 8, and the test gas guided from the engine 2, in other words, the oxygen A predetermined electromotive force signal is output based on the principle of a concentration battery, and the signal is recorded by a recorder 18. From the waveform recorded by the recorder 18, the time ratio between the rich signal and the lean signal of the oxygen sensor 16 to be measured is determined.

By the way, in this measurement system, the test gas guided from the engine 2 to the purifier 8 is passed through the reference oxygen sensor 12.
Air-fuel ratio control computer 14 based on output signals from
Under the control of , the atmosphere is periodically switched around the stoichiometric air-fuel ratio point between a rich atmosphere obtained by combustion in an excess fuel condition and a lean atmosphere obtained by combustion in an excess air condition. In Figures 2(a) and (b),
Such a signal from the reference oxygen sensor 12 and an air-fuel ratio control signal output from the air-fuel ratio control computer 14 based on the signal are shown. In those figures, the signal from the reference oxygen sensor 12 is processed according to thresholds for rich-to-lean or lean-to-rich reversal set in the air-fuel ratio control computer 14; As shown in Figure (b), an air-fuel ratio control signal having a reversal point: Sl, St, Sz, 34'' is output from the air-fuel ratio control computer 14, and the air-fuel ratio of the engine 2 is switched and controlled. That is, between the reversal point S and Sz, and between S and S4, control is performed such that the air-fuel ratio shifts from the rich side to the lean side, while the reversal point: 32 and S, In between, the air-fuel ratio will be controlled to shift from the lean side to the rich side.The threshold value for such rich/lean reversal will be determined as appropriate. However, here, as shown in FIG. 2(a), the rich time: T*++ lean time of the reference oxygen sensor 12:
Air-fuel ratio control is performed so that the TLI ratio is 1:1.

In this manner, the test gas, which is the combustion exhaust gas, is periodically switched between a rich atmosphere and a lean atmosphere according to changes in the air-fuel ratio of the engine 2. Depending on the gas composition of the test gas that changes, the signal from the sensor 16 gives a waveform, for example, as shown in FIG. At a predetermined level, the waveform provides a longer rich signal time: TR□ and a shorter lean signal time: TL□. Note that this oxygen sensor to be measured 1
6 rich signal time: TRz and lean signal time: TLZ
The time ratio of T RZ / (T R2 + T L Z
), which is 65% here, and the ratio of rich signal time is high. Here, such a ratio: TR□/(TR□+TLz) will be referred to as a duty ratio.

The present invention uses such a duty ratio to evaluate the sensor characteristics of the oxygen sensor 16 to be measured. That is, in FIG. 3, which shows the relationship between the air-fuel ratio and the output of the oxygen sensor, the output characteristics of the oxygen sensor differ greatly depending on whether the sensor is installed before or after the purifier 8. For example, if the sensor is installed in front of the purification device 8, the output characteristics of the sensor, in other words, the output characteristics of the oxygen sensor 16 to be measured, will become thicker (shifted to the lean side) as shown by the broken line. The air-fuel ratio (operating point ■), which is the threshold voltage for rich/lean judgment, shifts significantly from the stoichiometric air-fuel ratio point to the lean side, but if the sensor is installed after the purifier 8, the sensor output The characteristics, in other words, the output characteristics of the reference oxygen sensor 12 form a substantially theoretical λ curve, as shown by the solid line, and the operating point (2) of the sensor 12 completely coincides with the stoichiometric air-fuel ratio point. .

The reason for the lean shift in the output characteristics of such a sensor is that even if the exhaust gas (test gas) is lean, unburned components such as HC, Co, and NoX remain in the exhaust gas. This is because electromotive force is generated locally at the three-phase interface, so electromotive force is generated even in a lean atmosphere. However, the purifier 8
Since the exhaust gas (test gas) that has passed through has almost no remaining unburned components, the lean shift described above does not occur and a theoretical λ curve can be obtained.

According to the present invention, the reference oxygen sensor 12 for controlling the engine 2 is installed after the purification device 8 as described above, and therefore the air-fuel ratio of the engine 2 is lower than the stoichiometric air-fuel ratio point. The oxygen sensor 16 attached to the front of the purification bag W8 changes its output characteristics to the oxygen sensor 16 installed in front of the purification bag W8. Because of the shift to the lean side, the response time from rich to lean becomes longer, and the duty ratio becomes larger as described above. This duty ratio changes in accordance with the output characteristics of the oxygen sensor 16 to be measured (the output curve shown by the broken line in FIG. 3). If the reference oxygen sensor 12 is arranged after the purifier 8, the measurement system will always operate at the stoichiometric air-fuel ratio point (λ=1) even if the gas temperature of the test gas changes, which is convenient.

However, if it is installed in front of the purifier 8, the λ point will shift depending on the gas temperature, resulting in loss of data consistency.

As described above, in the present invention, the combustion exhaust gas as the test gas is accurately enriched around the stoichiometric air-fuel ratio point based on the signal of the reference oxygen sensor 12 operating under ideal conditions. The oxygen sensor 1 to be measured measures the signal of the oxygen sensor 16 to be measured under conditions in which the atmosphere is periodically changed to a lean atmosphere.
This makes it possible to clearly grasp the deviation of the sensor characteristics from the ideal state shown in No. 6.

Incidentally, FIGS. 4(a), (b), and (C) show the duty ratios obtained by the measurement method according to the present invention described above by replacing various oxygen sensors 16 to be measured, and the values for such oxygen to be measured. The relationship with emissions (COlHC, No.) emitted from a car equipped with the sensor 16 is shown. In addition, the driving mode of the car at the time of emission measurement was set to LA-4 mode. and,
As is clear from the relationships in FIG. 4, there is a strong correlation between the duty ratio determined by the measurement method according to the present invention and emissions (Co, HC, NOx). By doing so, emissions can be easily estimated, and it has been recognized that this is an effective method for evaluating oxygen sensors.

Note that in the above specific example, the oxygen sensor to be measured 16
The time ratio between rich signal time and lean signal time in the output waveform from duty ratio [T, I2/(T, l
□+Ttz) ), but it is not limited to this duty ratio, and any form that expresses these ratios may be equivalent, for example, T * z / T L z , T Lm/
(T R2 + T L2 ) or the reciprocal of these may be used.Furthermore, instead of such a time ratio such as a duty ratio, the output waveform of the oxygen sensor 16 to be measured may be It is also possible to measure the lean voltage (lean electromotive force) and its output amplitude and evaluate its characteristics.

That is, as shown in FIG.
Based on the output from 2, the air-fuel ratio of the exhaust gas as the test gas fluctuates in the range of the arrow around the stoichiometric air-fuel ratio point, and for such a changing air-fuel ratio of the exhaust gas, the purification In the output waveform of the oxygen sensor 16 to be measured installed in front of the device 8, its lean voltage rises from the ideal state due to the lean shift described above, and its output amplitude also becomes small. There is also a strong correlation between this amplitude width or lean voltage and emissions, as well as the time ratio such as the duty ratio, and therefore it can be advantageously adopted as an evaluation method for oxygen sensors. It is something.

By the way, in the specific method according to the present invention illustrated above, only one oxygen sensor to be measured 16 whose characteristics are to be evaluated is attached to the first exhaust pipe 6 on the upstream side of the purifier 8. However, it is also possible to attach a plurality of such oxygen sensors to be measured 16 and to evaluate the characteristics of each oxygen sensor at the same time.

In addition, the time ratio such as duty ratio, output amplitude, and lean voltage determined from the output waveform of the oxygen sensor 16 to be measured are as follows.
It is also possible to process them simultaneously using an appropriate arithmetic device such as a computer, and furthermore, the time ratio such as duty ratio, output amplitude, or lean voltage can be controlled for a certain period of time, for example, 10 seconds or more. Preferably, it is expressed as an average value over a period of time within minutes. Note that this measurement time is
It will be selected appropriately in relation to measurement accuracy.

Although not illustrated, it goes without saying that the present invention can be implemented in various forms without departing from the spirit of the invention, and such embodiments include: It should be understood that both fall within the scope of the present invention.

(Effects of the Invention) As is clear from the above description, the present invention is applicable to tests in which a rich atmosphere and a lean atmosphere are periodically changed based on the output signal of a reference oxygen sensor operating under ideal conditions. Depending on the gas, the output from the oxygen sensor to be measured (
This method extracts the electromotive force signal) and uses it to determine the time ratio such as duty ratio, output amplitude, or lean voltage, and because it does not require conventional equipment such as a gas analysis system, it can be used on a large scale. This makes it possible to accurately measure sensor characteristics related to emissions without requiring a new measurement system and without significantly increasing measurement costs. It has industrial significance.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of the measurement system according to the present invention, and FIGS. 2(a), (b), and (C) respectively show the reference oxygen sensor signal, air-fuel ratio control signal, and measured FIG. 3 is an explanatory diagram showing an example of a signal of an oxygen sensor; FIG. 3 is a graph showing the relationship between air-fuel ratio and sensor output based on different locations of oxygen sensors; FIGS. c) are the emissions (Co, HC, No.
, ) and the duty ratio. FIG. 5 is a graph showing an example of the air-fuel ratio-output characteristic of the oxygen sensor to be measured and the output waveform of the oxygen sensor to be measured. 2: Engine 4: Exhaust manifold 6: First exhaust pipe 8: Purifier 10: Second exhaust pipe 12: Reference oxygen sensor 14: Air-fuel ratio control computer 16: Oxygen sensor to be measured 18: Recorder

Claims (2)

[Claims] (1) On the downstream side of a purification device that purifies unburned components such as carbon monoxide, hydrocarbons, and nitrogen oxides present in a test gas consisting of combustion exhaust gas or a simulated gas equivalent to it, an oxygen concentration battery is installed. A reference oxygen sensor that outputs a predetermined electromotive force signal is arranged, and based on the electromotive force signal output from the reference oxygen sensor that corresponds to the oxygen concentration in the test gas purified by the purification device, The test gas,
While periodically switching between a rich atmosphere with excess fuel and a lean atmosphere with excess air around the stoichiometric air-fuel ratio point, an oxygen sensor to be measured whose characteristics are to be evaluated is arranged upstream of the purification device. The rich signal time of the oxygen sensor to be measured is determined based on the electromotive force signal output from the oxygen sensor to be measured according to the test gas which is periodically switched between rich atmosphere and lean atmosphere according to the principle of an oxygen concentration battery. A method for evaluating the characteristics of an oxygen sensor, characterized by measuring the time ratio of the lean signal time and the lean signal time. (2) On the downstream side of a purification device that purifies unburned components such as carbon monoxide, hydrocarbons, and nitrogen oxides present in a test gas consisting of combustion exhaust gas or a simulated gas equivalent to it, an oxygen concentration battery is installed. A reference oxygen sensor that outputs a predetermined electromotive force signal is arranged, and based on the electromotive force signal output from the reference oxygen sensor that corresponds to the oxygen concentration in the test gas purified by the purification device, The test gas,
While periodically switching between a rich atmosphere with excess fuel and a lean atmosphere with excess air around the stoichiometric air-fuel ratio point, an oxygen sensor to be measured whose characteristics are to be evaluated is arranged upstream of the purification device. The lean voltage or A method for evaluating characteristics of an oxygen sensor, characterized by measuring output amplitude.