JP2009097474A - Catalyst deterioration diagnostic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst deterioration diagnostic device capable of suppressing an influence of sulfur included in fuel, and capable of detecting the deterioration of a catalyst with further high precision. <P>SOLUTION: The catalyst deterioration diagnostic device measures an oxygen storage capacity of the catalyst during the active control of a catalyst upstream air/fuel ratio, and carries out a catalyst deterioration diagnosis according to the measured oxygen storage capacity. When the measured oxygen storage capacity reaches an abnormal value, the catalyst deterioration diagnosis is carried out on the basis of the oxygen storage capacity measured again under the condition that a catalyst temperature is not lower than a predetermined temperature and a center air/fuel ratio when active-controlling the catalyst upstream air/fuel ratio is close to a rich side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a catalyst deterioration diagnosis apparatus.

For example, in an internal combustion engine for a vehicle, a catalyst for purifying exhaust gas is installed in the exhaust system. Some of these catalysts have an oxygen storage capacity (O ₂ storage capacity). This is because when the air-fuel ratio of the exhaust gas flowing into the catalyst becomes larger than the stoichiometric air-fuel ratio (stoichiometric), that is, the exhaust gas becomes lean. Excess oxygen present in the gas is adsorbed and held, and when the air-fuel ratio of the catalyst inflow exhaust gas becomes smaller than the stoichiometric, that is, becomes rich, the adsorbed and held oxygen is released. For example, in a gasoline engine, air-fuel ratio control is performed so that the exhaust gas flowing into the catalyst is in the vicinity of the stoichiometric. However, such an air-fuel ratio shift can be absorbed by the oxygen storage / release action of the three-way catalyst.

  When the catalyst deteriorates, the purification efficiency of the catalyst decreases. There is a correlation between the degree of deterioration of the catalyst and the degree of reduction of the oxygen storage capacity because they are reactions through noble metals. Therefore, it is possible to detect that the catalyst has deteriorated by detecting that the oxygen storage capacity has decreased. In general, active air-fuel ratio control that forcibly switches the air-fuel ratio of exhaust gas flowing into the catalyst to rich and lean is performed, and the oxygen storage capacity of the catalyst is measured and measured along with the execution of this active air-fuel ratio control. A so-called Cmax method for diagnosing deterioration of the catalyst based on the oxygen storage capacity is employed.

  In the measurement of the oxygen storage capacity, for example, as disclosed in Patent Document 1 and the like, in the case of a fuel having a high sulfur concentration, it is known that the measured oxygen storage capacity decreases due to sulfur poisoning. .

JP 2006-291773 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a catalyst deterioration diagnosis apparatus capable of detecting the deterioration of a catalyst with higher accuracy by suppressing the influence of sulfur contained in the fuel. Is to provide.

  A catalyst deterioration diagnosis device according to the present invention is a catalyst deterioration diagnosis device for an internal combustion engine that diagnoses deterioration of a catalyst disposed in an exhaust passage of the internal combustion engine, and an air-fuel ratio control unit that actively controls a catalyst upstream air-fuel ratio; A storage capacity measuring means for measuring the oxygen storage capacity of the catalyst during active control of the catalyst upstream air-fuel ratio; and a deterioration diagnosis means for making a catalyst deterioration diagnosis based on the oxygen storage capacity measured by the storage capacity measuring means. When the oxygen storage capacity measured by the storage capacity measuring means is an abnormal value, the deterioration diagnosis means has a catalyst temperature that is equal to or higher than a predetermined temperature, and the central air space when the catalyst upstream air-fuel ratio is actively controlled. The catalyst deterioration diagnosis is performed based on the oxygen storage capacity remeasured under the condition where the fuel ratio is brought closer to the rich side.

  In the above-described configuration, it is possible to employ a configuration having a determination unit that determines whether the measured oxygen storage capacity is a normal value or an abnormal value based on the measured change amount of the oxygen storage capacity.

  In the above configuration, it is possible to employ a configuration having a determination unit that determines whether the measured oxygen storage capacity is a normal value or an abnormal value based on a comparison between the measured oxygen storage capacity and an initial reference value.

  In the above configuration, when re-measuring the oxygen storage capacity, if the catalyst temperature is lower than a predetermined temperature, the system has a temperature raising means for raising the temperature of the catalyst so that the catalyst temperature becomes equal to or higher than the predetermined temperature. Can be adopted.

  According to the present invention, it is possible to detect the deterioration of the catalyst with higher accuracy by suppressing the influence of sulfur contained in the fuel.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing the configuration of the present embodiment. As shown in the figure, the internal combustion engine 1 generates power by burning a mixture of fuel and air inside a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. To do. The internal combustion engine 1 is a multi-cylinder engine (only one cylinder is shown) mounted on a vehicle, and is a spark ignition type internal combustion engine, more specifically, a gasoline engine.

  In the cylinder head of the internal combustion engine 1, an intake valve Vi for opening and closing the intake port and an exhaust valve Ve for opening and closing the exhaust port are provided for each cylinder. Each intake valve Vi and each exhaust valve Ve are opened and closed by a camshaft (not shown). A spark plug 7 for igniting the air-fuel mixture in the combustion chamber 3 is attached to the top of the cylinder head for each cylinder.

  The intake port of each cylinder is connected to a surge tank 8 serving as an intake air collecting chamber via a branch pipe for each cylinder. An intake pipe 13 that forms an intake manifold passage is connected to the upstream side of the surge tank 8, and an air cleaner 9 is provided at the upstream end of the intake pipe 13. An air flow meter 5 for detecting the intake air amount and an electronically controlled throttle valve 10 are incorporated in the intake pipe 13 in order from the upstream side. An intake passage is formed by the intake port, the surge tank 8 and the intake pipe 13.

  An injector (fuel injection valve) 12 that injects fuel into the intake passage, particularly into the intake port, is provided for each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture. The air-fuel mixture is sucked into the combustion chamber 3 when the intake valve Vi is opened, compressed by the piston 4, and ignited and burned by the spark plug 7. It is done.

On the other hand, the exhaust port of each cylinder is connected to an exhaust pipe 6 forming an exhaust collecting passage through a branch pipe for each cylinder, and the exhaust pipe 6 has a three-way catalyst having an O ₂ storage function (oxygen storage capacity). A catalyst 11 comprising: An exhaust passage is formed by the exhaust port, the branch pipe, and the exhaust pipe 6. Air-fuel ratio sensors that detect the exhaust air-fuel ratio based on the oxygen concentration in the exhaust, that is, the pre-catalyst sensor 17 and the post-catalyst sensor 18 are installed on the upstream side and the downstream side of the catalyst 11, respectively. The pre-catalyst sensor 17 is a so-called wide-area air-fuel ratio sensor, can continuously detect an air-fuel ratio over a relatively wide area, and outputs a signal having a value proportional to the exhaust air-fuel ratio. On the other hand, the post-catalyst sensor 18 is a so-called O ₂ sensor, and has a characteristic that the output value changes suddenly at the theoretical air-fuel ratio.

The spark plug 7, the throttle valve 10, the injector 12, and the like described above are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20 as a control means. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. In addition to the air flow meter 5, the pre-catalyst sensor 17, and the post-catalyst sensor 18, the ECU 20 includes a crank angle sensor 14 that detects the crank angle of the internal combustion engine 1 and an accelerator that detects the accelerator opening, as shown in the figure. The opening sensor 15 and other various sensors are electrically connected via an A / D converter or the like (not shown). The ECU 20 controls the ignition plug 7, the throttle valve 10, the injector 12, etc. so as to obtain a desired output based on the detection values of various sensors, etc., and performs ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc.

  The catalyst 11 simultaneously purifies NOx, HC, and CO when the air-fuel ratio A / F of the exhaust gas flowing into the catalyst 11 is near the stoichiometric air-fuel ratio (stoichiometric, for example, A / Fs = 14.6). Correspondingly, during normal operation of the internal combustion engine, the ECU 20 controls the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing into the catalyst 11, that is, the pre-catalyst air-fuel ratio A / Ffr, matches the stoichiometric air-fuel ratio. Specifically, the ECU 20 sets a target air-fuel ratio A / Ft equal to the theoretical air-fuel ratio, and makes the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst sensor 17 coincide with the target air-fuel ratio A / Ft. The fuel injection amount injected from the injector 12 is feedback-controlled. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst 11 is kept in the vicinity of the theoretical air-fuel ratio, and the maximum purification performance is exhibited in the catalyst 11.

Here, the catalyst 11 will be described in more detail. As shown in FIG. 2, in the catalyst 11, a coating material 31 is coated on the surface of a carrier base material (not shown), and the coating material 31 is held in a state in which a large number of particulate catalyst components 32 are dispersedly arranged. The catalyst 11 is exposed inside. The catalyst component 32 is mainly composed of a noble metal such as Pt or Pd, and serves as an active point for reacting exhaust gas components such as NOx, HC and CO. On the other hand, the coating material 31 plays the role of a promoter that promotes the reaction at the interface between the exhaust gas and the catalyst component 32 and includes an oxygen storage component capable of absorbing and releasing oxygen according to the air-fuel ratio of the atmospheric gas. The oxygen storage component is made of, for example, cerium oxide CeO ₂ or zirconia. For example, if the atmosphere gas of the catalyst component 32 and the coating material 31 is richer than the stoichiometric air-fuel ratio, the oxygen stored in the oxygen storage component present around the catalyst component 32 is released, and as a result, the released oxygen As a result, unburned components such as HC and CO are oxidized and purified. On the contrary, when the atmosphere gas of the catalyst component 32 and the coating material 31 is leaner than the stoichiometric air-fuel ratio, the oxygen storage component present around the catalyst component 32 absorbs oxygen from the atmosphere gas, and as a result, NOx is reduced and purified. The

  By such an oxygen absorption / release action, even if the pre-catalyst air-fuel ratio A / Ffr slightly varies from the stoichiometric air-fuel ratio during normal air-fuel ratio control, three exhaust gas components such as NOx, HC and CO are simultaneously purified. can do. Therefore, in normal air-fuel ratio control, it is also possible to purify the exhaust gas by making the pre-catalyst air-fuel ratio A / Ffr oscillate minutely around the theoretical air-fuel ratio and repeating the absorption and release of oxygen.

  By the way, in the catalyst 11 in the new state, as described above, a large number of fine particulate catalyst components 32 are uniformly distributed, and the contact probability between the exhaust gas and the catalyst component 32 is kept high. However, when the catalyst 11 deteriorates, some of the catalyst components 32 are lost, and some of the catalyst components 32 are baked and solidified by exhaust heat (see broken lines in the figure). In this case, the contact probability between the exhaust gas and the catalyst component 32 is lowered, and the purification rate is lowered. In addition to this, the amount of the coating material 31 existing around the catalyst component 32, that is, the amount of the oxygen storage component decreases, and the oxygen storage capacity itself decreases.

Thus, the degree of deterioration of the catalyst 11 and the degree of decrease in the oxygen storage capacity of the catalyst 11 are in a correlation. Therefore, in this embodiment, the degree of deterioration of the catalyst 11 is detected by detecting the oxygen storage capacity of the catalyst 11. Here, the oxygen storage capacity of the catalyst 11 is represented by the size of the oxygen storage capacity (OSC; O ₂ Strage Capacity, the unit is g), which is the maximum amount of oxygen that the current catalyst 11 can store.

Hereinafter, the catalyst deterioration diagnosis in the present embodiment will be described.
The catalyst deterioration diagnosis of the present embodiment is basically based on the Cmax method described above. When the deterioration diagnosis of the catalyst 11 is performed, the active air-fuel ratio control is executed by the ECU 20. In the active air-fuel ratio control, the pre-catalyst air-fuel ratio A / Ffr is forcibly (actively) alternately switched to the rich side and the lean side with a predetermined center air-fuel ratio A / Fc as a boundary. The air-fuel ratio when changed to the rich side is referred to as rich air-fuel ratio A / Fr, and the air-fuel ratio when changed to the lean side is referred to as lean air-fuel ratio A / Fl. When the pre-catalyst air-fuel ratio A / Ffr is changed to the rich side or the lean side by this active air-fuel ratio control, the oxygen storage capacity OSC of the catalyst is measured.

  The deterioration diagnosis of the catalyst 11 is executed during steady operation of the internal combustion engine 1 and when the catalyst 11 is in the active temperature range. Measurement of the temperature of the catalyst 11 (catalyst bed temperature) may be detected directly using a temperature sensor, but in the present embodiment, it is estimated from the operating state of the internal combustion engine. For example, the ECU 20 uses a map or a map set in advance through experiments or the like based on the intake air amount Ga detected by the air flow meter 5 and the engine rotational speed Ne (rpm) detected based on the output of the crank angle sensor 14. The temperature of the catalyst 11 is estimated using the function.

  In FIGS. 3A and 3B, the outputs of the pre-catalyst sensor 17 and the post-catalyst sensor 18 when the active air-fuel ratio control is executed are indicated by solid lines. In FIG. 3A, the target air-fuel ratio A / Ft generated inside the ECU 20 is indicated by a broken line. The output values of the pre-catalyst sensor 17 and the post-catalyst sensor 18 correspond to the values of the pre-catalyst air / fuel ratio A / Ffr and the post-catalyst air / fuel ratio A / Frr, respectively.

  As shown in FIG. 3 (A), the target air-fuel ratio A / Ft is an air that is separated from the center air-fuel ratio A / Fc by a predetermined amplitude (rich amplitude Ar, Ar> 0) on the rich side. Forcibly and alternately between the fuel ratio (rich air-fuel ratio A / Fr) and the air-fuel ratio (lean air-fuel ratio A / Fl) that is away from it by a predetermined amplitude (lean amplitude Al, Al> 0). Can be switched. Following the switching of the target air-fuel ratio A / Ft, the pre-catalyst air-fuel ratio A / Ffr as an actual value is also switched with a slight time delay with respect to the target air-fuel ratio A / Ft. From this, it will be understood that the target air-fuel ratio A / Ft and the pre-catalyst air-fuel ratio A / Ffr are equivalent except that there is a time delay.

  In the illustrated example, the rich amplitude Ar and the lean amplitude Al are equal. For example, the center air-fuel ratio A / Fc = 14.6, the rich air-fuel ratio A / Fr = 14.1, the lean air-fuel ratio A / Fl = 15.1, the rich amplitude Ar = the lean amplitude Al = 0.5. Compared with the normal air-fuel ratio control, the active air-fuel ratio control has a larger amplitude of the air-fuel ratio, that is, the values of the rich amplitude Ar and the lean amplitude Al are larger.

  The timing at which the target air-fuel ratio A / Ft is switched between rich and lean is determined based on the output of the post-catalyst sensor 18. Specifically, as shown in FIG. 3B, the post-catalyst air-fuel ratio A / Frr changes from the rich side to the lean side, and the output of the post-catalyst sensor 18 becomes equal to the lean determination value VL (t1). , T3, etc.), the target air-fuel ratio A / Ft is switched from the lean air-fuel ratio A / Fl to the rich air-fuel ratio A / Fr. When the post-catalyst air-fuel ratio A / Frr changes from the lean side to the rich side and the output of the post-catalyst sensor 18 reaches the rich determination value VR (such as t2), the target air-fuel ratio A / Ft is changed from the rich air-fuel ratio A / Fr. The lean air-fuel ratio A / Fl is switched. Note that VR> VL, for example, VR = 0.59 (V) and VL = 0.21 (V).

  While performing the active air-fuel ratio control that performs such an air-fuel ratio change, the oxygen storage capacity OSC of the catalyst 11 is measured as follows, and the deterioration of the catalyst 11 is determined.

  Before the time t1 shown in FIG. 3, the target air-fuel ratio A / Ft is set to the lean air-fuel ratio A / Fl, and the lean gas flows into the catalyst 11. At this time, the catalyst 11 continues to absorb oxygen, but when it fully absorbs oxygen, it can no longer absorb oxygen, and the lean gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Frr changes to the lean side, and when the output voltage of the post-catalyst sensor 18 reaches the lean determination value VL (t1), the target air-fuel ratio A / Ft becomes the rich air-fuel ratio A / Fr. Can be switched to. In this way, the target air-fuel ratio A / Ft is reversed using the output of the post-catalyst sensor 18 as a trigger.

  This time, rich gas flows into the catalyst 11. At this time, the oxygen stored in the catalyst 11 continues to be released from the catalyst 11. If oxygen is continuously released from the catalyst 11, all of the stored oxygen is eventually released from the catalyst 11, and at that time, no more oxygen can be released, and rich gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Frr changes to the rich side, and when the output voltage of the post-catalyst sensor 18 reaches the rich determination value VR (t2), the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A / Fl. Can be switched to.

  The larger the oxygen storage capacity OSC, the longer the time during which oxygen can be absorbed or released. That is, when the catalyst is not deteriorated, the inversion cycle of the target air-fuel ratio A / Ft (for example, the time from t1 to t2) becomes longer, and the inversion cycle of the target air-fuel ratio A / Ft becomes shorter as the deterioration of the catalyst proceeds. .

  Therefore, using this fact, the oxygen storage capacity OSC is measured as follows. As shown in FIG. 4, immediately after the target air-fuel ratio A / Ft is switched to the rich air-fuel ratio A / Fr at time t1, the pre-catalyst air-fuel ratio A / Ffr as the actual value is slightly delayed with the rich air-fuel ratio A / Fr. Switch to Fr. From the time t11 when the pre-catalyst air-fuel ratio A / Ffr reaches the theoretical air-fuel ratio A / Fs to the time t2 when the target air-fuel ratio A / Ft next reverses, the following equation (1) An oxygen storage capacity dOSC (instantaneous value of the oxygen storage capacity) is calculated, and the oxygen storage capacity dOSC for each minute time is integrated from time t11 to time t2. Thus, the oxygen storage capacity, that is, the amount of released oxygen in this oxygen release cycle is measured.

  Here, Q is a fuel injection amount. When the air-fuel ratio difference ΔA / F is multiplied by the fuel injection amount Q, an air amount that is insufficient or excessive with respect to the stoichiometry can be calculated. K is a constant representing the proportion of oxygen contained in air (about 0.23).

Basically, the oxygen storage capacity OSC measured at one time is used and compared with a predetermined deterioration judgment value OSCs. If the oxygen storage capacity OSC exceeds the deterioration judgment value OSCs, the oxygen storage capacity is normal. If the OSC is equal to or lower than the deterioration determination value OSCs, the deterioration of the catalyst can be determined such as deterioration. However, in this embodiment, in order to improve accuracy, the oxygen storage capacity (in this case, the oxygen storage amount) is also measured in the oxygen storage cycle in which the target air-fuel ratio A / Ft is on the lean side, and these oxygen storage capacities are measured. The average value is measured as an oxygen storage capacity of one unit related to one absorption / release cycle. Further, the absorption / release cycle is repeated a plurality of times to obtain a value of the oxygen storage capacity of a plurality of units, and the average value is used as the final oxygen storage capacity measurement value, and compared with the deterioration determination value to determine the final deterioration determination. Is going. When it is determined that the catalyst is deteriorated, a warning device (check lamp or the like) (not shown) is preferably operated to notify the user (driver) of the fact.

  Regarding the measurement of the oxygen storage capacity (oxygen storage amount) in the oxygen storage cycle, as shown in FIG. 4, after the target air-fuel ratio A / Ft is switched to the lean air-fuel ratio A / Fl at time t2, the pre-catalyst air-fuel ratio is measured. From the time point t21 when A / Ffr reaches the central air-fuel ratio A / Fc to the time point t3 when the target air-fuel ratio A / Ft is reversed to the rich side next, the oxygen storage capacity dOSC for each minute time is calculated from the previous equation (1). The calculated oxygen storage capacity dOSC for each minute time is integrated. Thus, the oxygen storage capacity OSC, that is, the amount of stored oxygen (OSC2 in FIG. 4) in this oxygen absorption cycle is measured. The oxygen storage capacity OSC1 of the previous cycle and the oxygen storage capacity OSC2 of the current cycle should be approximately equal.

  Next, an example of the deterioration detection process of the catalyst 11 by the ECU 20 will be described with reference to a flowchart shown in FIG. Note that the process shown in FIG. 5 is repeatedly executed at predetermined time intervals, for example.

First, the oxygen storage capacity Cmax is measured (step S1). The measurement of the oxygen storage capacity Cmax is as described above.
Next, the fluctuation amount ΔCmax is calculated from the difference between the oxygen storage capacity Cmax measured last time and the oxygen storage capacity Cmax measured this time (step S2).

  Next, the fluctuation amount ΔCmax is compared with a predetermined threshold value C (step S3). Step S3 is a step for determining whether the catalyst 11 is sulfur poisoned.

  Here, it is known that when the catalyst 11 is poisoned with sulfur, for example, as shown in FIG. 6, the measured oxygen storage capacity Cmax is reduced. For this reason, when the fluctuation amount ΔCmax is larger than the threshold value C (in the case of an abnormal value) in step S3, it is determined that the catalyst 11 is sulfur poisoned.

  If it is determined that the catalyst 11 is not sulfur-poisoned, the above-described catalyst deterioration diagnosis is executed based on the oxygen storage capacity Cmax acquired in step S1 (step S7).

  If it is determined in step S3 that the catalyst 11 is poisoned with sulfur, it is determined whether the temperature of the catalyst 11 is higher than a predetermined temperature Tcnd (step S4).

  Here, the amount of decrease in the oxygen storage capacity Cmax due to sulfur differs depending on the temperature (bed temperature) condition of the catalyst 11. For example, as shown in FIG. 7, the higher the temperature (bed temperature) of the catalyst 11, the higher the sulfur (S ) Is small. Therefore, it is determined whether the catalyst 11 is higher than a predetermined temperature Tcnd, which is a temperature that is not easily affected by sulfur poisoning.

  When the temperature of the catalyst 11 is lower than the predetermined temperature Tcnd, for example, the ignition timing is retarded and the temperature of the catalyst 11 is increased (step S5).

  When the temperature of the catalyst 11 is higher than the predetermined temperature Tcnd, the target air-fuel ratio A / Ft when the air-fuel ratio A / F upstream of the catalyst 11 is actively controlled is set to the central air-fuel ratio A / Fc, for example, As shown in FIG. 8, the oxygen storage capacity Cmax is measured again by setting the target air-fuel ratio A / Ft ′ having a new center air-fuel ratio A / Fc ′ toward the rich side (step S6).

  Here, the central air-fuel ratio A / Fc is made closer to the rich side to become the central air-fuel ratio A / Fc ′, for example, when the central air-fuel ratio is on the rich side, as shown in FIG. This is because the influence of sulfur on the water is small. This is because if the central air-fuel ratio is brought closer to the rich side, the rich component increases when the catalyst 11 releases oxygen, and the reaction can be promoted.

  When the oxygen storage capacity Cmax is remeasured in step S6, the above-described catalyst deterioration diagnosis is executed based on the remeasured oxygen storage capacity Cmax (step S7). Thereby, the deterioration diagnosis of the catalyst 11 in which the influence of sulfur is eliminated as much as possible becomes possible.

  Next, another example of the deterioration detection process of the catalyst 11 by the ECU 20 will be described with reference to the flowchart shown in FIG. Note that the process shown in FIG. 10 is repeatedly executed at predetermined time intervals, for example.

  The process shown in FIG. 10 is different from the process shown in FIG. 5 only in step S12.

  Step S12 calculates a difference ΔCmax between the initial reference value Cmax_INIT and the latest oxygen storage capacity Cmax. The initial reference value Cmax_INIT is a learned value of the oxygen storage capacity Cmax of a new catalyst using normal fuel, and a previously calculated learned value is held in the ECU 20.

  Thus, by calculating the difference ΔCmax between the initial reference value Cmax_INIT and the latest oxygen storage capacity Cmax, and determining the presence or absence of sulfur poisoning based on this difference ΔCmax, the engine is not used from the beginning, but from the beginning of use. Detection of poor fuel containing sulfur can be reliably performed.

  In the above embodiment, the case where each means of the present invention is realized by the ECU 20 has been described. However, the present invention is not limited to this, and each means of the present invention can be realized by a plurality of ECUs.

It is the schematic which shows the structure of one Embodiment of this invention. It is a schematic sectional drawing which shows the structure of a catalyst. It is a time chart for demonstrating active air fuel ratio control. FIG. 4 is a time chart similar to FIG. 3 for illustrating a method for measuring the oxygen storage capacity. It is a flowchart which shows the procedure of the catalyst deterioration detection process which concerns on one Embodiment of this invention. It is a figure which shows the influence of sulfur poisoning with respect to oxygen storage capacity. It is a graph which shows the relationship between catalyst temperature and sulfur poisoning. It is a figure for demonstrating the process which brings a center air fuel ratio to the rich side when carrying out active control of the catalyst upstream air fuel ratio. It is a graph which shows the relationship between a center air fuel ratio and sulfur poisoning. It is a flowchart which shows the procedure of the catalyst deterioration detection process which concerns on other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 6 ... Exhaust pipe 11 ... Catalyst 12 ... Injector 14 ... Crank angle sensor 15 ... Accelerator opening sensor 17 ... Pre-catalyst sensor 18 ... Post-catalyst sensor 20 ... Electronic control unit (ECU)

Claims (4)

A catalyst deterioration diagnosis device for an internal combustion engine for diagnosing deterioration of a catalyst disposed in an exhaust passage of the internal combustion engine,
Air-fuel ratio control means for actively controlling the catalyst upstream air-fuel ratio;
Storage capacity measuring means for measuring the oxygen storage capacity of the catalyst during active control of the catalyst upstream air-fuel ratio;
Deterioration diagnosis means for performing catalyst deterioration diagnosis based on the oxygen storage capacity measured by the storage capacity measurement means,
When the oxygen storage capacity measured by the storage capacity measuring means is an abnormal value, the deterioration diagnosis means determines the central air-fuel ratio when the catalyst temperature is equal to or higher than a predetermined temperature and the catalyst upstream air-fuel ratio is actively controlled. Diagnose catalyst deterioration based on the oxygen storage capacity re-measured under the condition approaching the rich side.
A catalyst deterioration diagnosis device characterized by that. Based on the amount of change in the measured oxygen storage capacity, it has a determination means for determining whether the measured oxygen storage capacity is a normal value or an abnormal value.
The catalyst deterioration diagnosis apparatus according to claim 1. Based on a comparison between the measured oxygen storage capacity and the initial reference value, and having a determination means for determining whether the measured oxygen storage capacity is a normal value or an abnormal value,
The catalyst deterioration diagnosis apparatus according to claim 1. When re-measuring the oxygen storage capacity, if the catalyst temperature is lower than a predetermined temperature, it has a temperature raising means for raising the temperature of the catalyst so that the catalyst temperature is equal to or higher than the predetermined temperature.
The catalyst deterioration diagnosis apparatus according to claim 1.

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