JP2012067636A - Catalyst deterioration diagnostic device and catalyst deterioration diagnostic method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst deterioration diagnostic device and catalyst deterioration diagnostic method, which can estimate sulfur concentration of fuel or exhaust gas regardless of deviation of the output of an oxygen sensor.SOLUTION: The catalyst deterioration diagnostic device (80) diagnoses the deterioration of a catalyst (60) arranged in an exhaust gas passage (30) of an internal combustion engine (10). The device includes: an active control performing means which performs active control for switching air-fuel ratio of the exhaust gas flowing into the catalyst between rich and lean alternately in a center air fuel ratio as a boundary; and a sulfur concentration estimating means which uses an initial value of oxygen storage amount serving as the oxygen storage amount of the catalyst during performance start of the active control and a convergence value of the oxygen storage amount serving as the oxygen storage amount of the catalyst when the active control is continued until the oxygen storage amount of the catalyst converges for estimating the sulfur concentration of the fuel or the exhaust gas.

Description

  The present invention relates to a catalyst deterioration diagnosis apparatus and a catalyst deterioration diagnosis method.

  2. Description of the Related Art Conventionally, an internal combustion engine system that includes an exhaust gas purification catalyst in an exhaust passage of an internal combustion engine is known. Some of these catalysts have oxygen storage capacity. When the air-fuel ratio of the exhaust gas becomes larger than the stoichiometric air-fuel ratio (that is, becomes lean), the catalyst having oxygen storage capacity adsorbs and holds excess oxygen in the exhaust gas, and the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio. When rich, the adsorbed oxygen is released. Therefore, by using a catalyst having an oxygen storage capacity, even if the actual air-fuel ratio slightly deviates from the stoichiometric air-fuel ratio depending on the operating conditions, the air-fuel ratio shifts due to the oxygen storage / release action by the three-way catalyst. Can be absorbed.

  However, when the catalyst having oxygen storage ability deteriorates, the purification ability of the catalyst is lowered. Moreover, sulfur (S) may be contained in the fuel at a relatively high concentration depending on the region of use. When such a fuel is supplied, the sulfur component of the exhaust gas accumulates in the catalyst and the oxygen adsorption reaction of the catalyst is hindered, so that the oxygen storage capacity of the catalyst may be reduced.

  However, since the performance degradation of the catalyst due to this sulfur accumulation is temporary, it is preferable to eliminate the influence of the sulfur concentration in the deterioration diagnosis of the catalyst. Therefore, Patent Document 1 discloses an exhaust gas purification device for an internal combustion engine that estimates the sulfur concentration of exhaust gas based on the output of an oxygen sensor arranged on the downstream side of the catalyst. This exhaust purification system determines that the sulfur concentration of the exhaust gas is high when the output voltage of the oxygen sensor arranged downstream of the catalyst does not reach the specified output when the air-fuel ratio upstream of the catalyst is switched from lean to rich. To do.

  As another prior art document related to the present invention, Patent Document 2 is cited. Patent Document 2 discloses a technique related to active control, catalyst deterioration determination, and the like.

JP 2002-349250 A JP 2009-121414 A

  By the way, when there is an individual difference in the oxygen sensor, the output of the oxygen sensor may deviate from the original design value. In addition, the output of the oxygen sensor may deviate from the original design value due to the influence of exhaust gas. Thus, when the output of the oxygen sensor deviates from the original design value, the technology according to Patent Document 1 may deteriorate the accuracy of sulfur concentration estimation.

  An object of the present invention is to provide a catalyst deterioration diagnosis device and a catalyst deterioration diagnosis method capable of estimating the sulfur concentration of fuel or exhaust gas regardless of the deviation of the output of the oxygen sensor.

  A catalyst deterioration diagnosis device according to the present invention is a device for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine, wherein an air-fuel ratio of exhaust gas flowing into the catalyst is rich and lean with a central air-fuel ratio as a boundary. Active control execution means for performing active control that alternately switches to, an oxygen storage amount initial value that is an oxygen storage amount of the catalyst at the start of execution of the active control, and the active storage until the oxygen storage amount of the catalyst converges And a sulfur concentration estimation means for estimating the sulfur concentration of the fuel or exhaust gas using the oxygen storage amount convergence value that is the oxygen storage amount of the catalyst when the control is continued.

  According to the catalyst deterioration diagnosis device of the present invention, the sulfur concentration estimating means estimates the sulfur concentration of the fuel or the exhaust gas using the oxygen storage amount initial value and the oxygen storage amount convergence value. Even if the output of the oxygen sensor is deviated, the sulfur concentration of the fuel or exhaust gas can be estimated. That is, according to the catalyst deterioration diagnosis device, the sulfur concentration of the fuel or the exhaust gas can be estimated regardless of the deviation of the output of the oxygen sensor.

  According to the above configuration, the deterioration determination means for determining the deterioration state of the catalyst based on the oxygen storage amount of the catalyst, and the oxygen storage amount of the catalyst used for the determination of the deterioration determination means are calculated by the sulfur concentration estimation means. Correction means for correcting based on the estimation result. According to this configuration, the influence of the sulfur concentration of the fuel or exhaust gas on the deterioration determination of the catalyst can be reduced or eliminated. Thereby, the deterioration of the catalyst can be diagnosed with high accuracy.

  A catalyst deterioration diagnosis method according to the present invention is a method for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine, wherein the air-fuel ratio of exhaust gas flowing into the catalyst is rich and lean with a central air-fuel ratio as a boundary. The oxygen storage amount of the catalyst when the active control is continued until the oxygen storage amount initial value which is the oxygen storage amount of the catalyst at the start of execution of the active control and the oxygen storage amount of the catalyst converge. And a sulfur concentration estimation step of estimating the sulfur concentration of the fuel or exhaust gas using the oxygen storage amount convergence value which is a quantity.

  According to the catalyst deterioration diagnosis method of the present invention, since the sulfur concentration of fuel or exhaust gas is estimated using the oxygen storage amount initial value and the oxygen storage amount convergence value in the sulfur concentration estimation step, it is provided downstream of the catalyst. Even when the output of the obtained oxygen sensor is deviated, the sulfur concentration of the fuel or exhaust gas can be estimated. That is, according to the catalyst deterioration diagnosis method, the sulfur concentration of the fuel or the exhaust gas can be estimated regardless of the deviation of the output of the oxygen sensor.

  The method includes a deterioration determination step of determining a deterioration state of the catalyst based on an oxygen storage amount of the catalyst, and an oxygen storage amount of the catalyst used for the determination of the deterioration determination step of the sulfur concentration estimation step. And a correction step of correcting based on the estimation result. According to this method, the influence of the sulfur concentration of the fuel or the exhaust gas on the deterioration determination of the catalyst can be reduced or eliminated. Thereby, the deterioration of the catalyst can be diagnosed with high accuracy.

  According to the present invention, it is possible to provide a catalyst deterioration diagnosis device and a catalyst deterioration diagnosis method capable of estimating the sulfur concentration of fuel or exhaust gas regardless of the deviation of the output of the oxygen sensor.

1 is a schematic diagram illustrating a configuration of an internal combustion engine system including an ECU (catalyst deterioration diagnosis device) according to Embodiment 1. FIG. It is a figure which shows the relationship between the OSC of a catalyst, and the sulfur accumulation amount of a catalyst. It is a figure which shows the change of the OSC of a catalyst when active control is performed. It is a figure which shows an example of the flowchart at the time of ECU performing a deterioration diagnosis. It is a figure which shows an example of the flowchart at the time of ECU performing a deterioration diagnosis.

  Hereinafter, modes for carrying out the present invention will be described.

  The ECU 80 (catalyst deterioration diagnosis device) according to the first embodiment of the present invention will be described. FIG. 1 is a schematic diagram illustrating a configuration of an internal combustion engine system 5 including an ECU 80. The internal combustion engine system 5 includes an internal combustion engine 10, an intake passage 20, an exhaust passage 30, an injector 40, a throttle valve 50, a first catalyst 60, a second catalyst 65, various detection means (crank position sensor 70, throttle position sensor 71, air flow Meter 72, accelerator position sensor 73, air-fuel ratio sensor 74 and oxygen sensor 75) and ECU 80 are provided.

  The internal combustion engine 10 includes a piston 11 in a cylinder. The piston 11 is connected to the crankshaft via a connecting rod. A crank position sensor 70 is disposed in the vicinity of the crankshaft. The output of the crank position sensor 70 is transmitted to the ECU 80. The ECU 80 acquires the crank angle and the rotational speed of the internal combustion engine 10 based on the output of the crank position sensor 70.

  An intake passage 20 is connected to the intake port of the internal combustion engine 10. An exhaust passage 30 is connected to the exhaust port of the internal combustion engine 10. An injector 40 is disposed upstream of the intake passage 20. The injector 40 is controlled by the ECU 80 to inject fuel. The injected fuel is supplied into the cylinder of the internal combustion engine 10 together with the intake air.

  A throttle valve 50 for adjusting the amount of air supplied to the internal combustion engine 10 is disposed upstream of the injector 40 in the intake passage 20. The throttle valve 50 is controlled by the ECU 80. A throttle position sensor 71 is disposed in the vicinity of the throttle valve 50. The output of the throttle position sensor 71 is transmitted to the ECU 80.

  An air flow meter 72 is disposed upstream of the throttle valve 50 in the intake passage 20. The output of the air flow meter 72 is transmitted to the ECU 80. Further, the ECU 80 is informed of the output of the accelerator position sensor 73 for detecting the operation amount of the accelerator 100. The ECU 80 controls the throttle valve 50 based on the outputs of the crank position sensor 70, the throttle position sensor 71, the air flow meter 72, and the accelerator position sensor 73 so that an appropriate throttle opening is obtained.

A first catalyst 60 and a second catalyst 65 for purifying exhaust gas are arranged in series downstream of the exhaust passage 30. The first catalyst 60 is disposed upstream of the second catalyst 65. As the first catalyst 60 and the second catalyst 65, a three-way catalyst having an oxygen storage capacity is used. As such a three-way catalyst, for example, a coating material containing an oxygen storage component such as cerium dioxide, zirconia, or the like, in which particulate catalyst components (Pt, Pd, etc.) are arranged can be used. The oxygen storage capacity is represented by the size of the oxygen storage amount (OSC; O ₂ Storage Capacity, the unit is g), which is the maximum amount of oxygen that can be stored by the first catalyst 60 and the second catalyst 65 at present.

  An air-fuel ratio sensor 74 is disposed upstream of the first catalyst 60 in the exhaust passage 30. An oxygen sensor 75 is disposed between the first catalyst 60 and the second catalyst 65 in the exhaust passage 30. Outputs of the air-fuel ratio sensor 74 and the oxygen sensor 75 are transmitted to the ECU 80.

  Here, the first catalyst 60 and the second catalyst 65 exhibit the exhaust purification function most when the air-fuel ratio (A / F) of the inflowing exhaust gas is the stoichiometric air-fuel ratio (stoichiometric). Therefore, the ECU 80 controls the air-fuel ratio of the exhaust gas so that the output of the air-fuel ratio sensor 74 matches the stoichiometric air-fuel ratio. Specifically, the ECU 80 stores a target air / fuel ratio close to the theoretical air / fuel ratio. The ECU 80 performs feedback control on the fuel injection amount injected from the injector 40 so that the output of the air-fuel ratio sensor 74 matches the target air-fuel ratio. Thereby, the air-fuel ratio of the exhaust gas flowing into the first catalyst 60 is kept near the stoichiometric air-fuel ratio. As a result, the exhaust gas purification performance of the first catalyst 60 is maximized.

  The ECU 80 is a microcomputer including a CPU 81 as a calculation unit, and a ROM 82 and a RAM 83 as storage units. The ECU 80 has a function as control means for controlling the throttle valve 50 and the injector 40 when the CPU 81 operates while using the RAM 83 as a temporary storage memory based on a program or the like stored in the ROM 82.

  The ECU 80 also has a function as a catalyst deterioration diagnosis device that diagnoses the deterioration of the first catalyst 60 by operating the CPU 81 while using the RAM 83 as a temporary storage memory based on a program or the like stored in the ROM 82. is doing.

  Subsequently, the deterioration diagnosis of the first catalyst 60 by the ECU 80 will be described. In the following description, the first catalyst 60 is abbreviated as “catalyst”. The ECU 80 according to the present embodiment performs a deterioration determination process for determining the deterioration state of the catalyst. In the deterioration determination process, the ECU 80 determines the deterioration state of the catalyst by comparing the OSC of the catalyst with a reference value. For example, when the OSC of the catalyst is larger than the reference value, the ECU 80 determines that the catalyst is normal. When the OSC of the catalyst is equal to or less than the reference value, the ECU 80 determines that the catalyst is abnormal (that is, deteriorated).

  However, the catalyst deterioration determination may be affected by the sulfur concentration of the fuel and exhaust gas. FIG. 2 is a graph showing the relationship between the OSC of the catalyst and the sulfur accumulation amount of the catalyst. The vertical axis represents OSC, and the horizontal axis represents the sulfur accumulation amount of the catalyst. Line 200a shows the OSC when normal fuel having a sulfur concentration lower than a predetermined value is used. Line 200b shows the OSC when a fuel having a higher sulfur concentration than the normal fuel is used. Line 200c shows the OSC when a fuel having a higher sulfur concentration than line 200b is used.

  As can be seen from FIG. 2, the OSC and the sulfur accumulation amount of the catalyst have an inversely proportional relationship. Further, when compared with the same sulfur accumulation amount, the higher the sulfur concentration of the fuel, the smaller the OSC. As the sulfur concentration of the fuel is higher, the sulfur concentration of the exhaust gas is also higher, so that the amount of sulfur accumulation in the catalyst is also increased. As a result, the higher the fuel sulfur concentration (or the higher the exhaust gas sulfur concentration), the lower the catalyst OSC. When the internal combustion engine 10 is idling for a long time, or when it is used at a low load, sulfur tends to accumulate in the catalyst. In particular, the sulfur accumulation amount of the catalyst tends to increase at low temperatures.

  Thus, since the OSC of the catalyst is affected by the sulfur concentration of the fuel and the sulfur concentration of the exhaust gas, the deterioration determination of the catalyst may also be affected by the sulfur concentration of the fuel and the exhaust gas. However, the sulfur accumulation of the catalyst can be eliminated, for example, when a fuel having a low sulfur concentration is refueled. As described above, since the catalyst performance deterioration (deterioration) due to sulfur accumulation is temporary, it is preferable to eliminate the influence of the sulfur concentration in the catalyst deterioration determination.

  Therefore, the ECU 80 according to the present embodiment performs a sulfur concentration estimation process for estimating the sulfur concentration of the fuel. The ECU 80 performs a correction process for correcting the OSC of the catalyst used in the deterioration determination process based on the estimation result. The ECU 80 performs the deterioration determination process using the OSC corrected by the correction process. That is, the ECU 80 has a function as a sulfur concentration estimating means for estimating the sulfur concentration of the fuel, a function as a correcting means for correcting the OSC of the catalyst, and a function as a deterioration determining means for determining the deterioration state of the catalyst. .

  The outline of the sulfur concentration estimation process by the ECU 80 is as follows. First, the ECU 80 performs active control in which the air-fuel ratio of the exhaust gas flowing into the catalyst is alternately switched between rich and lean with the central air-fuel ratio as a boundary. That is, the ECU 80 has a function as active control execution means. In this embodiment, the stoichiometric air-fuel ratio is used as the central air-fuel ratio. The specific execution method of the active control can be described in Patent Document 2 and other known techniques related to active control, and thus description thereof is omitted.

  FIG. 3 is a diagram showing changes in the OSC of the catalyst when active control is performed. The vertical axis represents the OSC of the catalyst, and the horizontal axis represents the elapsed time from the start of execution of active control. Line 200d shows the OSC when the normal fuel is used, and line 200e and line 200f show the OSC when the fuel having a higher sulfur concentration than the normal fuel is used. Line 200e indicates the OSC when the ECU 80 switches the air-fuel ratio from the center air-fuel ratio to the lean side, and line 200f indicates the OSC when the ECU 80 switches the air-fuel ratio from the center air-fuel ratio to the rich side. Yes.

  As can be seen from FIG. 3, the OSC of the catalyst converges to a predetermined value (A) as the elapsed time from the start of the active control progresses. This means that the sulfur accumulation amount and sulfur release amount of the catalyst are balanced. This convergence value (A) is uniquely determined by the sulfur concentration and the temperature of the catalyst.

  Therefore, the ECU 80 detects the OSC of the catalyst at the start of the active control execution (hereinafter referred to as the OSC initial value) and the convergence value (hereinafter referred to as the OSC convergence value) where the execution of the active control has continued and the catalyst OSC has converged. Based on the above, the sulfur concentration of the fuel is estimated.

  For example, the ECU 80 calculates an OSC initial value and an OSC convergence value, and obtains a ratio between them (hereinafter referred to as an OSC ratio). The ECU 80 estimates the sulfur concentration of the fuel using the magnitude of the OSC ratio. For example, the lower the fuel sulfur concentration, the smaller the OSC initial value. Therefore, the OSC ratio obtained by dividing the OSC initial value by the OSC convergence value decreases as the fuel sulfur concentration decreases, and increases as the fuel sulfur concentration increases. Thus, the sulfur concentration of the fuel can be estimated based on the OSC ratio. For example, the ECU 80 stores a map to be referred to when calculating the sulfur concentration of the fuel from the OSC ratio in the storage unit in advance. The ECU 80 can estimate the sulfur concentration of the fuel by referring to the map based on the calculated OSC ratio.

  In order to estimate the sulfur concentration of the fuel, the ECU 80 needs to calculate the OSC initial value and the OSC convergence value. Subsequently, a method of calculating the OSC initial value and the OSC convergence value by the ECU 80 will be described.

  The ECU 80 calculates the OSC initial value based on the OSC of the catalyst immediately before the execution of the active control and the OSC immediately after the start of the active control. For example, the ECU 80 calculates the OSC initial value based on the difference between the OSC of the catalyst immediately before execution of active control and the OSC immediately after start of execution of active control.

  The OSC of the catalyst immediately before execution of active control can be calculated based on, for example, the temperature of the catalyst immediately before execution of active control. The lower the catalyst temperature, the greater the amount of sulfur accumulation in the catalyst, and the lower the OSC of the catalyst. Thus, since the catalyst temperature and the catalyst OSC have a correlation, the OSC of the catalyst immediately before execution of active control can be calculated based on the catalyst temperature. That is, the ECU 80 according to the present embodiment calculates the OSC initial value based on the temperature of the catalyst immediately before execution of active control and the OSC immediately after start of active control.

  For example, the ECU 80 stores a map indicating the relationship between the catalyst temperature and the catalyst OSC in the storage unit. Then, the ECU 80 obtains the temperature of the catalyst immediately before the execution of the active control, and calculates the OSC of the catalyst immediately before the execution of the active control by referring to the map based on the obtained temperature.

  The method for acquiring the catalyst temperature by the ECU 80 is not particularly limited. The ECU 80 may acquire the temperature of the catalyst based on, for example, the output of a temperature sensor arranged on the catalyst, or may be acquired by estimating from the operating state of the internal combustion engine 10. For example, Patent Document 2 and other known catalyst temperature estimation methods can be used for this catalyst temperature estimation method, and thus description thereof is omitted.

  On the other hand, the OSC of the catalyst immediately after execution of active control is calculated based on the air-fuel ratio change amount when active control is executed once. Note that when the active control is executed once, any one of when the air-fuel ratio is switched once to the lean side and when the air-fuel ratio is switched once to the rich side can be used.

Specifically, the OSC of the catalyst immediately after execution of active control is calculated using the following formula (1). In the following formula (1), a fuel injection amount may be used instead of the air amount.
OSC = ∫ ((detected value of air / fuel ratio sensor 74−theoretical air / fuel ratio) × air amount) dt (1)

  On the other hand, the OSC convergence value used for the sulfur concentration estimation is calculated based on the air-fuel ratio change amount when the active control is last executed. Specifically, the ECU 80 obtains the OSC when the active control is last executed using the above formula (1), and obtains this OSC as the OSC convergence value.

  Next, the correction process will be described. The ECU 80 corrects the OSC of the catalyst so that the influence of the fuel sulfur concentration on the deterioration determination of the catalyst is reduced or eliminated. For example, in the correction process, the ECU 80 increases the OSC so as to compensate for the OSC decrease due to sulfur accumulation. For example, the ECU 80 calculates α so that the value of α × OSC increases as the sulfur concentration estimated in the sulfur concentration estimation process increases, and multiplies the calculated α by OSC. In the deterioration determination process, the ECU 80 compares the corrected OSC with the reference value for the deterioration determination process. In this case, since the OSC used in the deterioration determination process is increased and corrected so as to compensate for the OSC decrease due to the influence of the fuel sulfur concentration by the correction process, the influence of the fuel sulfur concentration on the catalyst deterioration determination is reduced. Can be done or eliminated.

  4 and 5 are diagrams illustrating an example of a flowchart when the ECU 80 performs the deterioration diagnosis. 4 and 5 show one flowchart divided into two. The ECU 80 repeatedly executes the flowcharts of FIGS. 4 and 5 at a predetermined cycle. As shown in FIG. 4, the ECU 80 determines whether or not a start condition for starting the deterioration diagnosis of the catalyst is satisfied (step S10). The start condition is not particularly limited. For example, the ECU 80 can determine that the start condition is satisfied when the internal combustion engine 10 is in a steady operation state and the temperature of the catalyst is in a predetermined activation temperature range. The ECU 80 repeatedly executes step S10 until it is determined that the start condition is satisfied.

  When it is determined in step S10 that the start condition is satisfied, the ECU 80 determines whether or not the sulfur concentration estimation completion flag is cleared (step S20). In this embodiment, the ECU 80 sets a sulfur concentration estimation completion flag when a sulfur concentration estimation process (step S110) described later is performed. On the other hand, every time the internal combustion engine 10 is refueled, the ECU 80 clears the sulfur concentration estimation completion flag. That is, in the present embodiment, the fact that the sulfur concentration estimation completion flag is clear means that the sulfur concentration estimation processing has not yet been performed after refueling.

  When it is determined in step S20 that the sulfur concentration estimation completion flag is cleared, the ECU 80 sets an active control extension request flag (step S30).

  Next, the ECU 80 performs active control (step S40). Note that the ECU 80 also performs step S40 when it is not determined in step S20 that the sulfur concentration estimation completion flag is cleared (that is, when the sulfur concentration has already been estimated). The active control in step S40 is performed for calculating the OSC initial value (step S50). In step S40, the ECU 80 according to the present embodiment performs active control so that the air-fuel ratio is switched once to the rich side or the lean side.

  Next, the ECU 80 calculates the OSC initial value and stores the calculation result in a storage unit such as the RAM 83 (step S50).

  Next, as shown in FIG. 5, the ECU 80 determines whether or not the OSC initial value is smaller than a predetermined reference value (hereinafter referred to as a first reference value) (step S60). The first reference value is not particularly limited. In this embodiment, when it is determined that the value is equal to or greater than the first reference value, the deterioration determination process (steps S130 to S150) is performed without performing the correction process (step S120). Therefore, for example, it is considered that the OSC corresponding to the sulfur concentration of the fuel that can accurately determine the deterioration of the catalyst without performing the correction process, that is, the influence of the sulfur concentration of the fuel on the deterioration determination process of the catalyst is hardly present. An OSC corresponding to the sulfur concentration of the fuel can be used as the first reference value.

  When it is determined in step S60 that the OSC initial value is smaller than the first reference value, the ECU 80 determines whether or not an active control extension request flag is set (step S70).

  When it is determined in step S70 that the active extension request flag is set, the ECU 80 performs active control (step S80).

  Next, the ECU 80 determines whether or not a predetermined time has elapsed since the start of execution of active control in step S80 (step S90). The predetermined time is not particularly limited as long as it is equal to or longer than the time at which the catalyst OSC converges. The predetermined time may be stored in a storage unit such as the ROM 82, for example. If it is not determined in step S90 that the predetermined time has elapsed, the ECU 80 executes step S80. That is, the active control in step S80 is continuously executed until it is determined that the predetermined time in step S90 has elapsed.

  If it is determined in step S90 that the predetermined time has elapsed, the ECU 80 calculates an OSC convergence value and stores the calculation result in a storage unit such as the RAM 83 (step S100).

  Next, the ECU 80 performs a sulfur concentration estimation process (step S110). Specifically, the ECU 80 estimates the sulfur concentration of the fuel based on the OSC ratio. The ECU 80 stores the estimation result in a storage unit such as the RAM 83. In addition, ECU80 sets a sulfur concentration estimation completion flag, when performing step S110.

  Next, the ECU 80 performs a correction process (step S120). Specifically, the ECU 80 corrects the OSC convergence value calculated in step S100 so as to reduce or eliminate the influence of the sulfur concentration of the fuel on the deterioration determination of the catalyst.

  In addition, also when it determines with the active control extension request | requirement flag not being set in step S70, ECU80 performs step S120. Here, when it is determined in step S70 that the active control extension request flag is not set, this corresponds to the case where it is determined in step S20 that the sulfur concentration estimation completion flag is set. Therefore, even in this case, step S110 has already been performed, and the storage unit stores the sulfur concentration of fuel and the OSC convergence value. Therefore, the ECU 80 can correct the OSC convergence value in step S120.

  Next, the ECU 80 performs a deterioration determination process (steps S130 to S150). Specifically, after step S120 is performed, ECU 80 determines whether or not the corrected OSC convergence value is greater than a predetermined reference value (hereinafter referred to as a second reference value) (step S130). . When it is determined that the corrected OSC convergence value is greater than the second reference value, the ECU 80 determines that the catalyst is normal (step S140). If it is not determined that the corrected OSC convergence value is greater than the second reference value, the ECU 80 determines that the catalyst is abnormal (that is, deteriorated) (step S150). The ECU 80 may display the determination result in step S140 and the determination result in step S150 on, for example, a display.

  Also, when it is not determined in step S60 that the OSC initial value is smaller than the first reference value, the ECU 80 executes step S130. In this case, in step S130, the ECU 80 determines whether or not the OSC initial value is larger than the second reference value. When it is determined that the OSC initial value is greater than the second reference value, the ECU 80 determines that the catalyst is normal (step S140). When it is not determined that the OSC initial value is greater than the second reference value, the ECU 80 determines that the catalyst is abnormal (step S150). Next, the ECU 80 ends the execution of the flowchart.

  As described above, according to the ECU 80 according to the present embodiment, since the sulfur concentration of the fuel is estimated using the OSC initial value and the OSC convergence value in the sulfur concentration estimation processing, the output of the oxygen sensor 75 is initially set. Even if it deviates from the design value, the sulfur concentration can be estimated. That is, according to the ECU 80, the sulfur concentration can be estimated regardless of the deviation of the output of the oxygen sensor 75.

  Further, according to the ECU 80, in the deterioration determination process, the deterioration state of the catalyst is determined using the OSC corrected in the correction process based on the estimation result of the sulfur concentration estimation process. Thereby, the influence of the sulfur concentration of the fuel on the deterioration determination of the catalyst in the deterioration determination process can be reduced or eliminated. As a result, it is possible to accurately diagnose the deterioration of the catalyst.

  In the present embodiment, the ECU 80 estimates the sulfur concentration of the fuel in the sulfur concentration estimation process, but is not limited thereto. The ECU 80 may estimate the sulfur concentration of the exhaust gas in the sulfur concentration estimation process. The exhaust gas sulfur concentration estimation process can use the same technique as the fuel sulfur concentration estimation process. Therefore, a detailed description of the exhaust gas sulfur concentration estimation process is omitted. When the ECU 80 estimates the sulfur concentration of the exhaust gas in the sulfur concentration estimation process, the ECU 80 has a function as a sulfur concentration estimating means for estimating the sulfur concentration of the exhaust gas.

  In the present embodiment, the ECU 80 performs the deterioration diagnosis for the first catalyst 60, but is not limited thereto. The ECU 80 may diagnose the deterioration of the second catalyst 65. The deterioration diagnosis method of the first catalyst 60 can be applied to the deterioration diagnosis method of the second catalyst 65. For example, the air-fuel ratio sensor 74 and the oxygen sensor 75 are arranged upstream and downstream of the second catalyst 65, respectively, so that the ECU 80 performs the deterioration diagnosis of the second catalyst 65 by the same method as the deterioration diagnosis method of the first catalyst 60. It can be performed.

  Since the catalyst deterioration diagnosis method according to the present invention can be realized by the ECU 80, detailed description thereof is omitted. Specifically, the sulfur concentration estimation process performed by the ECU 80 corresponds to a sulfur concentration estimation step according to the catalyst deterioration diagnosis method, the correction process performed by the ECU 80 corresponds to a correction step according to the catalyst deterioration diagnosis method, and the deterioration performed by the ECU 80 The determination process corresponds to a deterioration determination step according to the catalyst deterioration diagnosis method.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

5 Internal combustion engine system 10 Internal combustion engine 20 Intake passage 30 Exhaust passage 40 Injector 50 Throttle valve 60 First catalyst 65 Second catalyst 74 Air-fuel ratio sensor 75 Oxygen sensor 80 ECU
100 accelerator

Claims (4)

An apparatus for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine,
Active control execution means for executing active control for alternately switching the air-fuel ratio of the exhaust gas flowing into the catalyst to rich and lean with a central air-fuel ratio as a boundary;
An oxygen storage amount initial value that is an oxygen storage amount of the catalyst at the start of execution of the active control, and an oxygen storage amount of the catalyst when the active control is continued until the oxygen storage amount of the catalyst converges And a sulfur concentration estimating means for estimating a sulfur concentration of fuel or exhaust gas using an oxygen storage amount convergence value. Deterioration determining means for determining the deterioration state of the catalyst based on the oxygen storage amount of the catalyst;
The catalyst deterioration diagnosis apparatus according to claim 1, further comprising: a correction unit that corrects an oxygen storage amount of the catalyst used for determination by the deterioration determination unit based on an estimation result of the sulfur concentration estimation unit. A method for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine,
An oxygen storage amount initial value that is an oxygen storage amount of the catalyst at the start of execution of active control for alternately switching the air-fuel ratio of the exhaust gas flowing into the catalyst to rich and lean with the central air-fuel ratio as a boundary; A sulfur concentration estimation step of estimating a sulfur concentration of fuel or exhaust gas using an oxygen storage amount convergence value that is an oxygen storage amount of the catalyst when the active control is continued until the storage amount converges Catalyst deterioration diagnosis method. A deterioration determination step for determining a deterioration state of the catalyst based on the oxygen storage amount of the catalyst;
The catalyst deterioration diagnosis method according to claim 3, further comprising: a correction step of correcting the oxygen storage amount of the catalyst used for the determination of the deterioration determination step based on the estimation result of the sulfur concentration estimation step.

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