JP4440824B2 - Catalytic converter deterioration detector - Google Patents

Description

  The present invention relates to a deterioration detection device that detects deterioration of a catalytic converter that is provided in an exhaust system of an internal combustion engine and purifies exhaust gas.

  It is widely practiced to provide a catalytic converter in the exhaust system of an internal combustion engine to purify the exhaust. Since the purification performance of a catalytic converter deteriorates when used for a long period of time, various methods for detecting the deterioration have been proposed.

For example, a method for forcibly changing the air-fuel ratio during engine operation and determining deterioration based on the output of an oxygen concentration sensor arranged downstream of the catalytic converter is widely known. May cause torque fluctuations and deterioration of exhaust characteristics.
Patent Document 1 includes a temperature sensor that detects the temperature near the inlet of the catalytic converter and a temperature sensor that detects the temperature inside or at the outlet of the catalytic converter, and deterioration of the catalyst based on the output values of the two temperature sensors. A method for determining the above is shown.

According to this method, when a predetermined time elapses from the stop point of the internal combustion engine and the difference between the temperatures detected by the two temperature sensors is smaller than a predetermined value, it is determined that the catalyst has deteriorated.
JP-A-7-180536

  Since the above-mentioned conventional method is to make a determination when the engine is stopped, it is possible to solve the problem of forcibly changing the air-fuel ratio during engine operation. However, since the temperature detected by the temperature sensor is influenced not only by the deterioration state of the catalytic converter but also by the catalyst temperature and the outside air temperature when the engine is stopped, there is room for improvement in terms of determination accuracy.

  The present invention has been made paying attention to this point, and provides a deterioration detection device for a catalytic converter that can solve the problem in performing deterioration determination during engine operation and can improve the determination accuracy. Objective.

  In order to achieve the above object, a first aspect of the present invention provides a catalytic converter (11) for detecting deterioration of a catalytic converter (11) for purifying exhaust gas provided in an exhaust system (4) of an internal combustion engine (1). ) In accordance with an oxygen concentration sensor (23) provided in the vicinity of the catalytic converter (11) and an oxygen concentration (OXYC) detected by the oxygen concentration sensor (23) after the engine is stopped. Deterioration determining means for determining deterioration of the catalytic converter (11).

According to a second aspect of the present invention, in the deterioration detection device for a catalytic converter according to the first aspect, the deterioration determination unit is configured to change the oxygen concentration over time (ALT) after the engine is stopped. Judgment is performed.
According to a third aspect of the present invention, in the deterioration detection device for a catalytic converter according to the first aspect, the deterioration determination means determines the determination according to a minimum value (Lm) of the oxygen concentration after the engine is stopped. It is characterized by performing.

  According to a fourth aspect of the present invention, in the deterioration detection device for a catalytic converter according to the first aspect, the deterioration determining means increases the oxygen concentration and reaches a predetermined value (LTH) from the time when the engine is stopped. The determination is performed according to a time (TR) to a time point.

According to a fifth aspect of the present invention, in the deterioration detection device for a catalytic converter according to the first aspect, the deterioration determination means determines the determination according to an integrated value (INT) of the oxygen concentration after the engine is stopped. It is characterized by performing.
According to a sixth aspect of the present invention, in the catalytic converter deterioration detecting device according to the first aspect, the deterioration determining means supplies combustion products to the catalytic converter immediately before the engine is stopped.

  According to the first aspect of the present invention, after the engine is stopped, the deterioration of the catalytic converter is determined according to the oxygen concentration detected by the oxygen concentration sensor provided in the vicinity of the catalytic converter. Immediately after the engine is stopped, the oxidation reaction of unburned fuel components remaining in the catalytic converter occurs, so the oxygen concentration in the vicinity of the catalytic converter tends to decrease, and the amount of decrease in oxygen concentration decreases as the catalytic converter deteriorates. It has been confirmed that Therefore, the deterioration determination can be accurately performed by monitoring the change tendency of the oxygen concentration in the vicinity of the catalytic converter. In addition, since the determination is performed after the engine is stopped, it is possible to solve the problem of performing deterioration determination during engine operation.

  According to the second aspect of the present invention, the determination is performed according to the time change rate of the oxygen concentration after the engine is stopped. The time change rate (absolute value) of the oxygen concentration tends to decrease as the catalytic converter deteriorates. Therefore, the deterioration of the catalytic converter can be accurately determined by monitoring the rate of change of the oxygen concentration with time.

  According to the invention described in claim 3, the determination is performed according to the minimum value of the oxygen concentration after the engine is stopped. The minimum value of the oxygen concentration after the engine stops tends to increase as the catalytic converter deteriorates. Therefore, the deterioration of the catalytic converter can be accurately determined by monitoring the minimum value of the oxygen concentration.

  According to the fourth aspect of the present invention, the determination is performed according to a period from when the engine is stopped to when the oxygen concentration increases and reaches a predetermined value. The time until the oxygen concentration increases and reaches a predetermined value tends to become shorter as the catalytic converter deteriorates. Therefore, the deterioration of the catalytic converter can be accurately determined by monitoring the period until the oxygen concentration increases to reach a predetermined value.

  According to the fifth aspect of the present invention, the determination is performed according to the integrated value of the oxygen concentration after the engine is stopped. The integrated value of the oxygen concentration tends to increase as the catalytic converter deteriorates. Therefore, the deterioration of the catalytic converter can be accurately determined by monitoring the integrated value of the oxygen concentration.

  According to the sixth aspect of the present invention, the combustion product is supplied to the catalytic converter immediately before the engine is stopped. When the catalyst temperature is high when the engine is stopped, the adsorbing action of the adsorbent in the catalytic converter is reduced, so that the fuel component (HC) adsorbed during engine operation cannot be retained. As a result, although the catalytic converter has not deteriorated, the detected oxygen concentration becomes high, and it may be erroneously determined that the catalyst converter has deteriorated. By supplying the combustion product immediately after the engine is stopped, such erroneous determination at a high temperature can be prevented.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an internal combustion engine including a catalytic converter according to an embodiment of the present invention and a control device thereof. An internal combustion engine (hereinafter simply referred to as “engine”) 1 is a diesel engine that directly injects fuel into a cylinder, and a fuel injection valve 16 is provided in each cylinder. The fuel injection valve 16 is electrically connected to an electronic control unit (hereinafter referred to as “ECU”) 20, and the valve opening time and valve opening timing of the fuel injection valve 16 are controlled by the ECU 20.

The engine 1 includes an intake pipe 2, an exhaust pipe 4, and a supercharger 8. The supercharger 8 includes a turbine 10 that is driven by exhaust kinetic energy, and a compressor 9 that is rotationally driven by the turbine 10 and compresses intake air.
The turbine 10 includes a plurality of variable vanes (not shown), and is configured to change the turbine rotational speed (rotational speed) by changing the opening degree of the variable vanes. The vane opening degree of the turbine 10 is electromagnetically controlled by the ECU 20.

  An intercooler 5 for cooling the pressurized air and an intake shutter (throttle valve) 3 for controlling the intake air amount are provided in the intake pipe 2 downstream of the compressor 9. The intake shutter 3 is controlled to be opened and closed by the ECU 20 via an actuator (not shown).

  Between the upstream side of the turbine 10 in the exhaust pipe 4 and the downstream side of the intake shutter 5 in the intake pipe 2, an exhaust gas recirculation passage 6 for returning the exhaust gas to the intake pipe 2 is provided. The exhaust gas recirculation passage 6 is provided with an exhaust gas recirculation control valve (hereinafter referred to as “EGR valve”) 7 for controlling the exhaust gas recirculation amount. The EGR valve 7 is an electromagnetic valve having a solenoid, and the valve opening degree is controlled by the ECU 20.

  On the downstream side of the turbine 10 in the exhaust pipe 4, an oxygen concentration sensor 23 that detects the oxygen concentration OXYC in the exhaust, a catalytic converter 11 that purifies the exhaust, and a diesel particulate filter (hereinafter referred to as “DPF”) 12 Are provided in this order from the upstream side.

  The oxygen concentration sensor 23 is provided in the vicinity of the catalytic converter 11. The catalytic converter 11 incorporates an oxidation catalyst for promoting the oxidation of hydrocarbons and carbon monoxide contained in the exhaust gas. However, it is desirable that the catalytic converter 11 does not have oxygen storage capability. Note that the catalytic converter 11 may be added with a NOx adsorbent that adsorbs NOx and a NOx reduction action.

  When the exhaust gas passes through the fine holes in the filter wall, the DPF 12 deposits soot, which is a particulate material mainly composed of carbon (C) in the exhaust gas, on the surface of the filter wall and the holes in the filter wall. Collect by letting. As a constituent material of the filter wall, for example, ceramics such as silicon carbide (SiC) or a porous metal body is used. A regeneration process for burning the particulates deposited on the DPF 12 is executed in a timely manner. The regeneration process is performed, for example, by executing post injection (fuel injection in the exhaust stroke). That is, the oxidation of the fuel post-injected by the oxidation catalyst of the catalytic converter 11 is promoted, the temperature of the exhaust gas flowing into the DPF 12 rises, and the accumulated particulates burn.

  Further, a crank angle position sensor 22 that detects the rotation angle of the crankshaft of the engine 1, an intake air flow rate sensor 21 that detects the intake air flow rate GA of the engine 1, and a cooling water temperature sensor (not shown) that detects the cooling water temperature of the engine 1. The detection signals of these sensors are supplied to the ECU 20. The engine speed NE of the engine 1 is calculated from the output of the crank angle position sensor.

  The ECU 20 shapes input signal waveforms from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, a central processing unit (hereinafter referred to as “CPU”). A storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, and an output circuit that supplies control signals to the fuel injection valve 16, the EGR valve 7, and the like.

  Next, with reference to FIG. 2, a method for determining the deterioration of the catalytic converter 11 in the present embodiment will be described. Immediately after the engine 1 is stopped, an oxidation reaction of hydrocarbons adsorbed on the adsorbent of the catalytic converter 11 occurs, and therefore, as shown by a solid line (purification rate CE = 99%) in FIG. The detected oxygen concentration OXYC in the vicinity of the catalytic converter 11 gradually decreases with time. In FIG. 2, the time t0 is the stop point of the engine 1.

  When the adsorption of the adsorbed hydrocarbon is finished, the oxygen concentration OXYC gradually increases and returns to the original level. The broken lines in FIG. 2 indicate the characteristics in a state where the catalytic converter 11 has deteriorated (purification rate CE = 60%). Thus, it has been confirmed that when the catalytic converter 11 deteriorates, the amount of decrease in the oxygen concentration OXYC after the engine stops decreases.

Therefore, in the present embodiment, the purification value CE is calculated by applying the minimum value Lm of the measured oxygen concentration OXYC (indicated by a thin solid line in FIG. 2) to the following equation (1), and the purification rate CE is determined by the determination threshold CETH. When it becomes (for example, 65%) or less, it is determined that the catalytic converter 11 has deteriorated.
CE = {(Lm−L99) / (L60−L99)} (60−99) +99
(1)
Here, L60 is the minimum value of the oxygen concentration OXYC corresponding to the catalytic converter degraded to a purification rate of 60%, and L99 is the minimum value of the oxygen concentration OXYC corresponding to the catalytic converter having a purification rate of 99%.

FIG. 3 is a flowchart showing a procedure for determining deterioration of the catalytic converter 11 using the above-described determination method.
In step S11, it is determined whether or not a deterioration determination execution condition is satisfied. Specifically, during operation of the engine 1, operating parameters such as engine cooling water temperature, exhaust temperature, intake air temperature, intake air amount, engine speed, vehicle speed (travel speed of the vehicle driven by the engine 1) are within a predetermined range. The deterioration determination execution condition is satisfied when the abnormality of the oxygen concentration sensor 23 is not detected and the stop time of the engine 1 is within the predetermined range. When the deterioration determination execution condition is not satisfied, this process is immediately terminated.

  If the answer to step S11 is affirmative (YES) and the deterioration determination execution condition is satisfied, it is determined whether or not the engine 1 is stopped. When the engine 1 is in operation, this process is immediately terminated. If the engine 1 is stopped, step S13 and subsequent steps are executed.

  In step S13, the intake shutter 3 is closed to prevent air from flowing in from the outside. In step S14, the oxygen concentration sensor 23 measures the oxygen concentration OXYC. In step S15, the minimum value Lm of the oxygen concentration OXYC is applied to the equation (1) to calculate the purification rate CE.

  In step S16, it is determined whether or not the purification rate CE is equal to or less than a determination threshold value CETH. If the purification rate CE is equal to or less than the determination threshold value CETH, it is determined that the catalytic converter 11 has deteriorated (step S17). On the other hand, when the purification rate CE is larger than the determination threshold value CETH, it is determined that the catalytic converter 11 is normal (step S18).

  As described above, in the present embodiment, the purification of the catalytic converter 11 is performed based on the minimum value Lm of the oxygen concentration OXYC detected after the engine 1 is stopped by the oxygen concentration sensor 23 disposed in the vicinity of the upstream side of the catalytic converter 11. When the rate CE is calculated and the purification rate CE is equal to or less than the determination threshold value CETH, it is determined that the catalytic converter 11 has deteriorated. By making the determination after the engine 1 is stopped in this way, it is possible to eliminate a problem in the case of performing the deterioration determination during engine operation. Further, by performing the determination according to the oxygen concentration in the vicinity of the catalytic converter 11, the determination accuracy can be improved as compared with the conventional method.

(Modification)
FIG. 4 is a time chart showing the change over time in the oxygen concentration OXYC after the engine is stopped when the temperature of the catalytic converter 11 (hereinafter referred to as “catalyst temperature”) TCAT is changed. However, the time axis is expanded as compared with FIG. 2, and the time range shown in FIG. 4 is narrower than that of FIG. Line L1 shows the characteristics when there is no catalytic converter, and lines L3 and L4 show the characteristics when the catalyst temperature TCAT is 150 ° C. and 200 ° C., respectively. Line L2 shows the characteristics when the catalyst temperature TCAT is 300 ° C. As is clear from this characteristic, when the catalyst temperature TCAT increases, the amount of decrease in the oxygen concentration decreases, and the characteristic similar to that of the deterioration of the catalytic converter 11 is exhibited. This is presumably because when the catalyst temperature TCAT increases, the adsorption capacity of the adsorbent of the catalytic converter 11 decreases, and the unburned component (unburned HC) of the fuel cannot be retained.

  Therefore, in this modification, a catalyst temperature sensor for detecting the catalyst temperature TCAT is attached to the catalytic converter 11, and when the catalyst temperature TCAT detected by the catalyst temperature sensor is high, the hydrocarbon (combusted matter) immediately before the engine 1 is stopped. Is supplied to the catalytic converter 11 so that the oxidation reaction is likely to occur and the deterioration is determined.

  FIG. 5 is obtained by adding steps S21, S22, and S23 to the flowchart shown in FIG. In step S21, it is determined whether or not the engine switch has been turned off. If the answer to step S21 is negative (NO), the process immediately ends. When the engine switch is turned off, it is determined whether or not the catalyst temperature TCAT is equal to or higher than a predetermined temperature TCATH (for example, 250 ° C.). If this answer is negative (NO), the process immediately proceeds to step S11. If the answer to step S22 is affirmative (YES) and the catalyst temperature TCAT is high, the EGR valve 7 is opened to supply the unburned fuel component remaining in the exhaust gas recirculation passage 6 to the catalytic converter 11. (Step S23). Note that when the amount of combustion products is insufficient by this alone, it is desirable to supply a fuel to the catalytic converter 11 by executing a small amount of fuel injection by the fuel injection valve 16.

  According to this modification, even when the catalyst temperature TCAT is 300 ° C., the oxygen concentration OXYC is sufficiently lowered as shown by the line L5 in FIG. This can be prevented.

(Other variations)
In the above-described embodiment, the purification rate CE is calculated according to the minimum value Lm of the oxygen concentration OXYC detected after the engine is stopped. However, the purification rate CE is calculated by the method described below. May be.

  As shown in FIG. 6A, the return time TR from the time t0 until the detected oxygen concentration OXYC returns to the predetermined concentration LTH (TR60: when the purification rate is 60%, TR99: when the purification rate is 99%) Since the purification rate CE is substantially proportional as shown in FIG. 7, the recovery time TR from the time t0 until the oxygen concentration OXYC returns to the predetermined concentration LTH is obtained, and the purification rate is obtained using the relationship shown in FIG. CE may be obtained.

  Further, the absolute value (hereinafter referred to as “slope parameter”) ALT of the time differential value of the oxygen concentration change characteristic becomes the maximum immediately after time t0, and the purification rate of the catalytic converter 11 is high as shown in FIG. 6B. As the slope parameter ALT increases, the slope parameter ALT increases. Since the slope parameter ALT also has a relationship that is substantially proportional to the purification rate CE, the purification rate CE is obtained using the relationship shown in FIG. 7 according to the slope parameter ALT.

  Further, as shown in FIG. 6C, a parameter INT (hereinafter referred to as “integrated value parameter”) INT corresponding to the time integrated value of the oxygen concentration OXYC detected within the predetermined integration period TINT is obtained, and according to the integrated value parameter INT. Thus, the purification rate CE may be obtained. For example, the area of the hatched area shown in FIG. 6C corresponds to the integral parameter INT when the purification rate is 99%.

  Since the integral value parameter INT tends to decrease as the purification rate CE increases, the relationship between the integral value parameter INT and the purification rate CE is experimentally obtained in advance and stored in the storage circuit of the ECU 20 as a table. The purification rate CE is obtained by table search according to the measured integral value parameter INT.

  Further, the determination thresholds corresponding to these determination parameters are set without converting the above-described determination parameters, that is, the minimum value Lm of the oxygen concentration, the return time TR, the inclination parameter ALT, or the integral value parameter INT into the purification rate CE. Then, the deterioration of the catalytic converter 11 may be determined from the relationship between the determination parameter and the corresponding determination threshold value. That is, when the minimum value Lm is used as a determination parameter, when the minimum value Lm is equal to or greater than the corresponding determination threshold LmTH, it is determined that the catalytic converter 11 has deteriorated, and when the return time TR is used as a determination parameter, When the return time TR is equal to or less than the corresponding determination threshold value TRTH, it is determined that the catalytic converter 11 has deteriorated, and when the inclination parameter ALT is used as the determination parameter, when the inclination parameter ALT is equal to or less than the corresponding determination threshold value ALTTH, When it is determined that the catalytic converter 11 has deteriorated and the integral value parameter INT is used as a determination parameter, it is determined that the catalytic converter 11 has deteriorated when the integral value parameter INT is equal to or greater than the corresponding determination threshold ALTTH.

  In the embodiment described above, the ECU 20 constitutes a deterioration determination unit. Specifically, the arithmetic processing for executing the procedure shown in FIG. 3 or FIG. 5 corresponds to the deterioration determination means.

The oxygen concentration sensor 23 may be provided in the vicinity of the downstream side of the catalytic converter 11.
The present invention is also applicable to detection of deterioration of a catalytic converter provided in an exhaust system of a marine vessel propulsion engine such as an outboard motor having a vertical crankshaft.

It is a figure which shows the structure of the internal combustion engine and its control apparatus concerning one Embodiment of this invention. It is a time chart for demonstrating the deterioration determination method of a catalytic converter. It is a flowchart which shows the procedure of deterioration determination. It is a time chart for demonstrating the influence of the temperature of a catalytic converter. It is a flowchart of the modification of the procedure shown in FIG. It is a time chart for demonstrating another modification. It is a figure which shows the relationship between the determination parameter (TR, ALT) and the purification rate (CE) of a catalytic converter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 4 Exhaust pipe 11 Catalytic converter 20 Electronic control unit (deterioration determination means)
23 Oxygen concentration sensor

Claims (6)

In a deterioration detection device for a catalytic converter, which is provided in an exhaust system of an internal combustion engine and detects deterioration of a catalytic converter for purifying exhaust gas,
An oxygen concentration sensor provided in the vicinity of the catalytic converter;
A deterioration detection device for a catalytic converter, comprising: deterioration determination means for determining deterioration of the catalytic converter according to an oxygen concentration detected by the oxygen concentration sensor after the engine is stopped.   The catalytic converter deterioration detection device according to claim 1, wherein the deterioration determination unit performs the determination according to a time change rate of the oxygen concentration after the engine is stopped.   The catalytic converter deterioration detection device according to claim 1, wherein the deterioration determination unit performs the determination according to a minimum value of the oxygen concentration after the engine is stopped.   2. The catalytic converter according to claim 1, wherein the deterioration determination unit performs the determination according to a time from when the engine is stopped to when the oxygen concentration increases and reaches a predetermined value. Deterioration detection device.   2. The deterioration detection device for a catalytic converter according to claim 1, wherein the deterioration determination means performs the determination according to an integrated value of the oxygen concentration after the engine is stopped.   2. The deterioration detection device for a catalytic converter according to claim 1, wherein the deterioration determination unit supplies a combustion product to the catalytic converter immediately before the engine is stopped.

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