JPH0533632A - Deterioration judging method of three way catalyst - Google Patents

Abstract

PURPOSE:To perform a judgment so accurate enough by adopting an amplitude of vibration in and around a threshold level, at the lower limit of output amplitude in the case where any deterioration of a three way catalyst is judged by this output amplitude in an oxygen content sensor. CONSTITUTION:A three way catalyst 11 is installed in an exhaust passage 10 of a gas engine E, and a main oxygen sensor 12 is installed at the upstream side and a sub oxygen sensor 13 at the downstream side, respectively. Each detection signal out of these main and sub oxygen sensors 12, 13, a pressure sensor 6, an engine speed sensor 9 and a temperature measuring sensor 14 is inputted into an engine control unit 15 and thereby a control signal is outputted to an air-fuel ratio control valve 8. The engine control unit 15 is provided with a catalyst deterioration judging means 19, since output amplitude becomes minimized when an output amplitude value of the sub oxygen sensor 13 exists in a threshold level, it judges any deterioration of the catalyst through this minimum amplitude. Therefore the deterioration is accurately judged by the extent of the amplitude.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas engine in which an oxygen concentration sensor is provided on each of an upstream side and a downstream side of a three-way catalyst, and an air-fuel ratio is controlled in response to an output signal of the oxygen concentration sensor. The present invention relates to a method for determining deterioration of a three-way catalyst in an air-fuel ratio control device.

[0002]

2. Description of the Related Art A device for increasing the purification rate of a three-way catalyst by controlling the air-fuel ratio of a gas engine in the vicinity of the theoretical air-fuel ratio in response to an output signal of an oxygen concentration sensor provided upstream of the three-way catalyst. Has been proposed in the past.

Further, as disclosed in, for example, Japanese Patent Application Laid-Open No. 61-286550, an oxygen concentration sensor is provided on each of the upstream side and the downstream side of the three-way catalyst, and the oxygen concentration sensors are provided on the upstream side of the three-way catalyst. By correcting the output of the first oxygen concentration sensor according to the output signal of the second oxygen concentration sensor provided downstream of the three-way catalyst (for example, controlling the delay time of the air-fuel ratio control by the first oxygen concentration sensor). There has been proposed a technique for preventing the controllability from being deteriorated due to a change in characteristics of the first oxygen concentration sensor or a variation in characteristics.

[0004]

Generally, when determining the deterioration of the three-way catalyst by the output amplitude of the second oxygen concentration sensor, the output amplitude is affected by the potential level, that is, the air-fuel ratio and the feedback cycle. Receive. That is, the output amplitude of the second oxygen concentration sensor differs depending on the potential level. The amplitude tends to decrease when the feedback cycle is fast, and conversely, the amplitude tends to increase when the feedback cycle is slow. Therefore, it is difficult to accurately determine the deterioration.

The present invention has been proposed in view of the above-mentioned problems of the prior art, and it is an object of the present invention to provide a deterioration determination method for a three-way catalyst that can accurately determine that the three-way catalyst has deteriorated. Has an aim.

[0006]

A method for determining deterioration of a three-way catalyst according to the present invention comprises a three-way catalyst arranged in an exhaust passage of a gas engine to purify exhaust gas, and an upstream side of the three-way catalyst. In the exhaust gas in response to the output of the first oxygen concentration sensor, the second oxygen concentration sensor disposed downstream of the three-way catalyst, and the first and second oxygen concentration sensors. An air-fuel ratio control device that detects whether the air-fuel ratio of the gas engine is rich or lean with respect to the stoichiometric air-fuel ratio from the oxygen concentration of the gas engine, and controls the air-fuel ratio of the gas engine based on the result. In a method of determining deterioration of a three-way catalyst for determining deterioration of a three-way catalyst used in a gas engine, the determination of the deterioration of the three-way catalyst based on the output amplitude of the second oxygen concentration sensor is performed. Below the output amplitude as a level There is characterized by employing the amplitude near threshold level.

The three-way catalyst deterioration determination method of the present invention is a three-way catalyst arranged in the exhaust passage of a gas engine to purify exhaust gas, and a first three-way catalyst disposed upstream of the three-way catalyst. Of the oxygen concentration in the exhaust gas in response to the outputs of the oxygen concentration sensor, the second oxygen concentration sensor disposed downstream of the three-way catalyst, and the first and second oxygen concentration sensors. An air-fuel ratio control device that detects whether the air-fuel ratio of the gas engine is in a rich state or a lean state with respect to the stoichiometric air-fuel ratio, and controls the air-fuel ratio of the gas engine based on the result, In the deterioration determination method of the three-way catalyst for determining the deterioration of the three-way catalyst used in the engine,
When determining the deterioration of the three-way catalyst based on the output amplitude of the second oxygen concentration sensor, the correction is performed based on the feedback cycle.

In the above determination, the catalyst deterioration determination unit provided in the control device determines that the catalyst is normal when the product of the amplitude whose lower limit of amplitude is near the threshold level and the reciprocal of the feedback period is within the predetermined range. When out of range,
It is preferable to determine that the catalyst has deteriorated.

[0009]

In the above method, the catalyst deterioration determining unit determines, based on the output signal from the sub oxygen concentration sensor, that the product of the amplitude whose lower limit of amplitude is near the threshold level and the reciprocal of the feedback period is within the predetermined range. Determine if there is.
Therefore, if it is within the predetermined range, it is determined that the catalyst is normal, and if it is outside the predetermined range, it is determined that the catalyst is deteriorated.

[0010]

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

In an intake passage 1 of a gas engine shown in FIG. 1, a mixer 4 for mixing fuel (for example, city gas 13A) from a fuel passage 2 and air from an air intake 3 and a throttle valve 5 are provided in an intake passage 1. And a pressure sensor 6 for detecting the intake pressure. Further, a bypass passage 7 that connects the upstream side of the throttle valve 5 of the intake passage 1 and the fuel passage 2 by bypassing the mixer 4 is provided, and a valve for adjusting the bypass flow rate, that is, an empty passage, is provided in the bypass passage. A fuel ratio control valve 8 is provided.

Here, the gas engine E is provided with a rotation speed sensor 9 for detecting the engine rotation speed.

On the other hand, a three-way catalyst 11 is interposed in the exhaust passage 10 of the gas engine 4, and a first catalyst is provided upstream of the catalyst 11.
Oxygen concentration sensor (hereinafter referred to as the main oxygen sensor) 12
And a second oxygen concentration sensor (hereinafter referred to as a sub oxygen sensor) 13 is provided on the downstream side of the catalyst 11. In the illustrated embodiment, the temperature measuring sensor 14 is also provided on the downstream side of the catalyst 11.

Detection signals from the pressure sensor 6, the rotation speed sensor 9, the main and sub oxygen sensors 12, 13 and the temperature measuring sensor 14 are input to an electronic control unit (ECU) 15.
After a predetermined process is performed by the control device 15, it is output to the air-fuel ratio control valve 8 as a control signal.

In the control device 15, the output signals of the pressure sensor 6 and the rotation speed sensor 9 are the total gas consumption amount calculating means 16.
The total gas consumption amount TG that is input to and calculated there is sent to the bypass gas amount calculation means 17. The bypass gas amount calculation means 17 determines from the bypass ratio table 18 the bypass ratio BR required for operating the engine near the stoichiometric air-fuel ratio.

The output V2 of the sub oxygen sensor 13 is input to the catalyst deterioration determining means 19 and the control constant calculating means 20. Then, the control constant calculation means 20 uses the sub oxygen sensor 1
3 in response to the output V2 of the delay time TDL, TD
The main feedback constants such as R (rise and fall delay time) are calculated and sent to the air-fuel ratio correction amount calculation means 21. Here, the air-fuel ratio correction amount calculation means 21 calculates the air-fuel ratio correction amount FAF based on the delay times TDL and TDR calculated by the control constant calculation means 20 and the output V1 from the main oxygen sensor 12, and the correction amount. The FAF is sent to the bypass gas amount calculation means 17.

The bypass gas amount calculation means 17 includes a total gas consumption amount TG calculated by the total gas consumption amount calculation means 16, a bypass ratio BR calculated from the bypass ratio table 18, and an air-fuel ratio correction amount calculation means 21. The bypass gas amount BG is calculated by the following equation (1) on the basis of the air-fuel ratio correction amount FAF calculated in.

BG = TG × (BR + FAF) (1) Here, the air-fuel ratio adjustment amount FAF is + or − with zero as the center.
Is a variable that should vibrate to. Therefore, the air-fuel ratio correction amount F
When the AF has an offset value and vibrates in the + or-region, the bypass ratio calculation unit 22 changes the bypass ratio BR and updates the bypass ratio table 18 so as to vibrate around zero. .

The bypass gas amount BG calculated by the bypass gas amount calculating means 17 is sent to the air-fuel ratio adjusting means 23. Then, the air-fuel ratio adjusting means 23 controls the bypass gas amount BG.
The opening degree of the air-fuel ratio control valve 8 is set on the basis of the calculation result of, and the opening degree of the valve 8 is controlled.

In the catalyst deterioration determining means 19 to which the output V2 of the sub oxygen sensor 13 is input, a potential level at which the purification rate of nitrogen oxide NOx deteriorates when the output V2 becomes lower than that level, that is, a threshold value (threshold level). ) Is preset. The threshold level is set to, for example, 0.6V.

Next, the mode of determination will be described with reference to FIG. In the drawings, the amplitudes are indicated by reference signs A0 and A1, but in the following description, the amplitude in a general sense is expressed by reference sign A (not shown).

The catalyst deterioration determining means 19 detects the amplitude A and the cycle T of the output waveform based on the output signal from the sub oxygen sensor 13 (step S1). Next, of the amplitudes A, the amplitude A1 whose lower limit of the amplitude is near the threshold level S (FIG. 6) is selected (step S2), and the value (A1 × 1 /
It is determined whether T) is within a predetermined range (step S
3). Here, as the determination value (A1 × 1 / T),
For example, A1 = 160 (mV) and T = 1.6 (s) are adopted, and A1 × 1 / T = 100 (mV / s) is used.

If step S3 is YES, that is, if the determination value (A1 × 1 / T) is within the predetermined range, the three-way catalyst 11 is determined to be normal (step S4). On the other hand, if step S3 is NO, that is, the value (A1 × 1 / T)
Is not within the predetermined range, it is determined that the three-way catalyst 11 has deteriorated (step S5). And step S4
Alternatively, after S5 ends, the process returns.

The amplitude A changes when the air-fuel ratio differs, and when the three-way catalyst 11 is new and in a highly active state, the amplitude A0 is small as shown in FIG. 3, and it is almost zero near the stoichiometric air-fuel ratio. Is the smallest. On the other hand, when the three-way catalyst 11 deteriorates, it has a maximum value near the stoichiometric air-fuel ratio as shown in FIG.
In other words, in order to determine the degree of deterioration of the catalyst by the amplitude, it is necessary to limit the air-fuel ratio for measuring the amplitude.

On the other hand, as is clear from FIGS. 3 and 4, in the relationship between the output amplitude lower limit value of the sub oxygen sensor 13 and the output amplitude, when the output amplitude lower limit value is at the threshold level, the catalyst is new. The output amplitude is the smallest regardless of whether the product is a deteriorated product or a deteriorated product. Therefore, the degree of catalyst deterioration is determined using this minimum amplitude.

The output signal of the sub oxygen sensor 13 when the actual air-fuel ratio control is performed will be described as an example with reference to FIGS.

When the three-way catalyst 11 is new, the amplitude A0 becomes substantially zero near the threshold level S as shown in FIG. 5, and the amplitude A0 is about 80 mV in the region apart from the threshold level S. To have. On the other hand, three-way catalyst 11
When the lower limit of the amplitude is in contact with the threshold level S (as in the case of FIG. 5), the amplitude A1 becomes the minimum and the amplitude increases as the distance from the threshold level S increases. . Therefore, if the deterioration determination of the catalyst is performed using the amplitude A0 or A1 at the time of contacting the threshold level S, the influence of the air-fuel ratio on the amplitude can be removed.

Here, when the feedback cycle T is large (long), the amplitude A also becomes large, while on the other hand, when the feedback cycle T is small, the amplitude A becomes small. Therefore, as shown in FIG. 7, a clear correlation cannot be obtained between NOx and the amplitude A, and the catalyst deterioration determination based on the amplitude A cannot be accurately performed.

On the other hand, if correction is performed using the period T and the relationship between NOx and (A × 1 / T) is obtained, good correlation can be obtained as shown in FIG. Therefore, (A × 1 /
It can be understood that the value of T) can accurately determine the deterioration of the catalyst.

[0030]

As described above, according to the present invention, the lower limit of the amplitude is set to an amplitude in the vicinity of the threshold level, and the correction is performed based on the feedback cycle, so that the catalyst deterioration can be accurately determined by the amplitude. can do.

Therefore, the catalyst deterioration determination work is facilitated and the determination accuracy is improved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an example of a control device for implementing the present invention.

FIG. 2 is a control flowchart.

[Fig. 3] Sub-oxygen sensor output amplitude, air-fuel ratio of a new catalyst,
The characteristic view which shows the mutual relationship of a sub oxygen sensor output amplitude lower limit.

FIG. 4 is a sub-oxygen sensor output amplitude of the deteriorated catalyst, an air-fuel ratio,
The characteristic view which shows the mutual relationship of a sub oxygen sensor output amplitude lower limit.

FIG. 5 is a characteristic diagram showing the output of a sub oxygen sensor of a new catalyst.

FIG. 6 is a characteristic diagram showing an output of a sub oxygen sensor of a deteriorated catalyst.

FIG. 7 is a characteristic diagram showing the correlation between NOx and the output amplitude of the sub oxygen sensor.

FIG. 8 shows N when correction is performed in consideration of a cycle T.
The characteristic view which shows the correlation of Ox and the output amplitude of a sub oxygen sensor.

[Explanation of symbols]

1 ... Intake passage 2 ... Fuel passage 3 ... Air intake 4 ... mixer 5 ... Throttle valve 6 ... Pressure sensor 7: Bypass passage 8: Air-fuel ratio control valve 9 ... Revolution sensor 10 ... Exhaust passage 11 ... Three-way catalyst 12 ... Main oxygen concentration sensor 13 ... Sub oxygen concentration sensor 14 ... Temperature sensor 15 ... Control device 16 ... Total gas consumption calculation means 17: Bypass gas amount calculation means 18-Bypass ratio table 19: catalyst deterioration determination means 20 ... Control constant determination means 21 ... Air-fuel ratio correction amount calculation means 22 ... Bypass gas amount calculation means 23 ... Air-fuel ratio adjusting means V1 ... Main oxygen concentration sensor V2: Sub oxygen concentration sensor TG: total gas consumption TDR, TDL ... delay time FAF: Air-fuel ratio correction amount BR: Bypass fuel ratio BG: bypass gas amount

Claims (2)

[Claims] 1. A three-way catalyst arranged in an exhaust passage of a gas engine to purify exhaust gas, a first oxygen concentration sensor arranged on an upstream side of the three-way catalyst, and a downstream of the three-way catalyst. In response to the outputs of the second oxygen concentration sensor disposed on the side and the first and second oxygen concentration sensors, the air-fuel ratio of the gas engine is changed from the stoichiometric air-fuel ratio from the oxygen concentration in the exhaust gas. A rich state or a lean state, and based on the result, an air-fuel ratio control device that controls the air-fuel ratio of the gas engine, and a deterioration of the three-way catalyst used in the gas engine is determined. In the method of determining the deterioration of a three-way catalyst, when determining the deterioration of the three-way catalyst based on the output amplitude of the second oxygen concentration sensor, the lower limit of the output amplitude is an amplitude near the threshold level as a determination level. To hire Characteristic three-way catalyst deterioration determination method 2. A three-way catalyst arranged in an exhaust passage of a gas engine to purify exhaust gas, a first oxygen concentration sensor disposed upstream of the three-way catalyst, and a downstream of the three-way catalyst. In response to the outputs of the second oxygen concentration sensor disposed on the side and the first and second oxygen concentration sensors, the air-fuel ratio of the gas engine is changed from the stoichiometric air-fuel ratio from the oxygen concentration in the exhaust gas. A rich state or a lean state, and based on the result, an air-fuel ratio control device that controls the air-fuel ratio of the gas engine, and a deterioration of the three-way catalyst used in the gas engine is determined. In a method for determining deterioration of a three-way catalyst, when determining deterioration of the three-way catalyst based on an output amplitude of the second oxygen concentration sensor, correction is made based on a feedback cycle. Method.