JP2006250043A - Catalyst deterioration-detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect deterioration of a catalyst without deteriorating emission. <P>SOLUTION: The catalyst deterioration-detecting device is equipped with: a first oxygen concentration detecting means for detecting the concentration of oxygen between a first catalyst arranged in an exhaust passage of an internal combustion engine, and a second catalyst arranged on the downstream side thereof; an oxygen occlusion state-determination means for determining, based on the oxygen concentration, whether or not the first catalyst is in a maximum released state where occluded oxygen is completely released, or a maximum occluded state where oxygen is occluded to the maximum; a first air-fuel ratio controlling means for controlling a first air-fuel ratio so that the oxygen amount occluded by the second catalyst is substantially half the amount of the oxygen occlusion ability of the second catalyst; and a second air-fuel ratio controlling means for performing a second air-fuel ratio control for detecting deterioration of the first catalyst after the first catalyst has been estimated to be in a maximum released state or a maximum occluded state and the first air-fuel ratio has been controlled. By the second air-fuel ratio control, the second catalyst can be set to a desired oxygen occluded state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a catalyst deterioration detection device.

Conventionally, by performing air-fuel ratio control that changes the A / F (air-fuel ratio) of air and fuel supplied to the internal combustion engine between rich (rich air-fuel ratio combustion state) and lean (lean combustion state), Deterioration detection of the catalyst (exhaust purification catalyst) provided on the exhaust passage and evaluation of the oxygen storage capacity (maximum oxygen storage amount) are carried out (hereinafter such air-fuel ratio control is also referred to as “deterioration detection control”). Call it.) Generally, deterioration detection control is executed by switching the air-fuel ratio from rich to lean or from lean to rich based on the output of an oxygen sensor (O ₂ sensor) provided on the downstream exhaust passage. Yes.

  By the way, in the deterioration detection control, the timing of switching the air-fuel ratio deviates from the timing at which the output of the oxygen sensor is reversed, so that rich gas (oxygen-deficient gas) flows further to the catalyst in the limit release state, or the limit In some cases, lean gas (oxygen-rich gas) may further flow into the occluded catalyst. In this case, the catalyst cannot purify the supplied gas and flows downstream. For this reason, normally, another catalyst is provided on the downstream side of this catalyst, and the gas that could not be purified by the upstream catalyst is purified by the downstream catalyst. However, when the downstream side catalyst is also in the limit occlusion state or the limit release state, the downstream side catalyst cannot purify the gas that the upstream side catalyst could not purify, such as NOx, HC, CO, etc. There is a possibility of exhausting gas to the outside. As a result, even when another catalyst is provided on the downstream side, there is a case in which emission deteriorates due to execution of the deterioration detection control.

  As a method for solving the above problems, for example, Patent Document 1 discloses that a catalyst on the downstream side is provided in a catalyst deterioration detection device that includes two catalysts in the exhaust passage and detects deterioration of the upstream catalyst. Describes a method for detecting the deterioration of the catalyst only when the amount of oxygen stored by the catalyst (hereinafter also referred to as “oxygen storage amount”) satisfies a predetermined condition. Specifically, the output of the oxygen sensor provided on the downstream side of the downstream side catalyst is a lean output (determination value of the output of the oxygen sensor used to switch the air-fuel ratio from rich to lean) or a rich output (lean the air-fuel ratio). It is determined whether or not the output of the oxygen sensor used for switching from the rich to the rich is not stuck to the lean output or the rich output, and the deterioration of the catalyst is detected. Furthermore, when the output of the oxygen sensor sticks to the lean output, the downstream catalyst is in a state of storing oxygen to the limit (limit storage state), so that the air-fuel ratio is maintained rich, and the oxygen sensor If the output is stuck to the rich output, the downstream catalyst is in a state where the stored oxygen is completely released (limit release state), so air-fuel ratio control is performed to maintain the air-fuel ratio lean. is doing.

JP 2003-97334 A

  However, in the technique described in Patent Document 1 described above, a strict determination is made with respect to the oxygen storage state of the downstream catalyst (the extent that the actual oxygen storage amount occupies the oxygen storage capacity). Further, the air-fuel ratio control for bringing the downstream side catalyst into an appropriate oxygen storage state has not been performed strictly. Therefore, for example, even if the output of the oxygen sensor does not stick to the lean output or the rich output at the time of determination, the oxygen sensor output outputs a value near the lean output or the rich output. At the start, the downstream catalyst may be in a limit occlusion state or a limit release state.

  The present invention has been made to solve such problems, and the object of the present invention is to appropriately determine the oxygen storage state of the downstream catalyst and to prevent the downstream catalyst from appropriately storing oxygen. An object of the present invention is to provide a catalyst deterioration detection device capable of detecting deterioration of a catalyst without causing deterioration of emission by executing air-fuel ratio control so as to be in a state.

  In one aspect of the present invention, a catalyst deterioration detection device includes a first catalyst disposed in an exhaust passage of an internal combustion engine, and a second catalyst disposed in the exhaust passage on the downstream side of the first catalyst. A first oxygen concentration detecting means provided in the exhaust passage between the first catalyst and the second catalyst for detecting the oxygen concentration in the exhaust passage, and based on the oxygen concentration, Oxygen storage state estimation means for estimating whether the first catalyst is in a limit release state in which the stored oxygen is completely released or in a limit storage state in which oxygen is stored up to the limit; The first air-fuel ratio control means for executing the first air-fuel ratio control so that the amount of oxygen stored by the second catalyst is approximately half of the oxygen storage capacity of the second catalyst; It is estimated that the first catalyst is in the limit release state or the limit storage state. And, after execution of the first air-fuel ratio control, and a second air-fuel ratio control means for executing a second air-fuel ratio control for performing the deterioration detection of the first catalyst.

  The above-described catalyst deterioration detection device executes air-fuel ratio control that changes the air-fuel ratio of air and fuel supplied to the internal combustion engine between rich and lean, thereby allowing the first catalyst provided on the exhaust passage to It is a device that performs deterioration detection. A second catalyst is provided on the downstream side of the first catalyst, and a first oxygen concentration detection means for detecting the oxygen concentration on the exhaust passage between the first catalyst and the second catalyst ( For example, an oxygen sensor) is provided. The oxygen storage state estimation means estimates whether the first catalyst is in a limit release state or a limit storage state. The first air-fuel ratio control means executes the first air-fuel ratio control so that the oxygen storage amount of the second catalyst is approximately half of the oxygen storage capacity of the second catalyst. The second air-fuel ratio control means detects the deterioration of the first catalyst after the first catalyst is in the limit release state or the limit storage state and the first air-fuel ratio control is performed. The second air-fuel ratio control is executed.

  As described above, by executing the first air-fuel ratio control before executing the second air-fuel ratio control, there is a difference between the time when the output of the first oxygen concentration detecting means is reversed and the time when the air-fuel ratio is switched. Yes, even if the first catalyst discharges the rich gas or lean gas downstream, the second catalyst is in a state of storing oxygen that is approximately half of the oxygen storage capacity, so the first catalyst cannot be purified. The released gas can be purified at a high purification rate. Therefore, the catalyst deterioration detection device can prevent the deterioration of the emission that may be caused by executing the deterioration detection control.

  Preferably, the second air-fuel ratio control means can execute air-fuel ratio control that changes the air-fuel ratio of the fuel and air supplied to the internal combustion engine between a rich state and a lean state.

  In one aspect of the above-described catalyst deterioration detection device, the first air-fuel ratio control means is executed immediately after the fuel cut of the internal combustion engine is completed, and the amount of oxygen stored in the second catalyst is the oxygen storage capacity. The air-fuel ratio continues to be set to be slightly rich until it is approximately half of the amount.

  In this aspect, the catalyst deterioration detection device performs the first air-fuel ratio control after the fuel cut ends. Specifically, the catalyst deterioration detection device executes control for setting the air-fuel ratio to be slightly rich. This is because the first catalyst can effectively purify the exhaust gas after the fuel cut by setting the air-fuel ratio to be slightly rich. In other words, the catalyst deterioration detection device uses the control that is generally executed immediately after the fuel cut to set the air-fuel ratio to be slightly rich, and then enters the appropriate oxygen storage state for the second air-fuel ratio control. One catalyst and a second catalyst are set. As a result, the first catalyst is brought into an appropriate oxygen storage state for deterioration detection control while obtaining a high purification rate from the first catalyst for a long time without lowering the purification rate of the first catalyst after the fuel cut. It becomes possible to set the catalyst and the second catalyst.

  In another aspect of the catalyst deterioration detection device, the first air-fuel ratio control means may be configured such that the integrated air amount taken in by the internal combustion engine after the first catalyst enters the limit release state is a predetermined amount. The air / fuel ratio is continuously set to be slightly rich until the value reaches.

  In this aspect, the catalyst deterioration detection device continues to set the air-fuel ratio to be slightly rich until the accumulated air amount taken in by the internal combustion engine reaches a predetermined amount, so that the oxygen storage amount of the second catalyst is substantially equal to the oxygen storage capacity. Half the amount. This makes it possible to reliably set the oxygen storage state of the second catalyst to a desired state.

  In another aspect of the catalyst deterioration detection device, the storage capacity calculation means for calculating the oxygen storage capacity of the first catalyst based on the oxygen concentration, and the oxygen storage capacity of the first catalyst. Storage capacity prediction means for predicting the oxygen storage capacity of the second catalyst, the first air-fuel ratio control means based on the predicted oxygen storage capacity of the second catalyst. A predetermined amount is calculated, and the air-fuel ratio is continuously set to be slightly rich until the integrated air amount taken in by the internal combustion engine reaches the predetermined amount.

  In this aspect, the storage capacity calculation means calculates the oxygen storage capacity of the first catalyst based on the detected oxygen concentration, and the storage capacity prediction means uses the second catalyst based on the oxygen storage capacity of the first catalyst. Predict the oxygen storage capacity of the catalyst. Then, the first air-fuel ratio control means calculates a predetermined amount based on the predicted oxygen storage capacity of the second catalyst, and the air-fuel ratio until the integrated air amount taken in by the internal combustion engine reaches the calculated predetermined amount. Is set to a weak rich state. In this case, the predetermined amount of the calculated integrated air amount reflects the degree of deterioration of the first catalyst and the second catalyst. Thus, the catalyst deterioration detection device can accurately set the second catalyst in a desired oxygen storage state without being affected by the degree of deterioration of the second catalyst. Therefore, it is possible to more effectively prevent the deterioration of the emission that may occur due to the execution of the second air-fuel ratio control.

  Preferably, when the oxygen storage capacity of the first catalyst has already been calculated, the first air-fuel ratio control means is configured such that the amount of oxygen stored in the first catalyst is approximately half of the oxygen storage capacity. The air-fuel ratio is set to be slightly rich until the amount reaches. As a result, it is possible to prevent deterioration of fuel consumption after the end of fuel cut and improve the purification rate of the first catalyst with respect to exhaust gas.

  In another aspect of the catalyst deterioration detection device, the apparatus further includes second oxygen concentration detection means provided in the exhaust passage on the downstream side of the second catalyst and detecting the oxygen concentration in the exhaust passage. The second air-fuel ratio control means executes the second air-fuel ratio control only when the output of the oxygen concentration detection means is approximately in the range of 0.3 to 0.5 (V).

  In this aspect, the catalyst deterioration detection device includes the second oxygen concentration detection means in the exhaust passage downstream of the second catalyst, and the second air-fuel ratio control means has an output of the oxygen concentration detection means of approximately 0. The second air-fuel ratio control is executed only when it is in the range of 3 to 0.5 (V). When an output in the range of approximately 0.3 to 0.5 (V) is obtained from the second oxygen concentration detection means, oxygen of approximately half the oxygen storage capacity is stored in the second catalyst. Has been. Accordingly, it is possible to determine whether or not to execute the second air-fuel ratio control based on the output of the oxygen concentration detection means provided on the downstream side of the second catalyst. Also by this, the catalyst deterioration detection apparatus can prevent the deterioration of the emission that may be caused by executing the deterioration detection control.

  In another aspect of the catalyst deterioration detection device, the first air-fuel ratio control means may be configured such that the integrated air amount taken in by the internal combustion engine after the first catalyst enters the limit release state is a predetermined amount. The second air-fuel ratio control means continues to set the air-fuel ratio until the air reaches the predetermined amount until the integrated air amount reaches the predetermined amount until the output of the oxygen concentration detection means is approximately 0.3. The second air-fuel ratio control is executed only when it is in the range of -0.5 (V).

  In this aspect, the catalyst deterioration detection device continues to set the air-fuel ratio to be slightly rich until the integrated air amount taken in by the internal combustion engine reaches a predetermined amount, and thereafter determines the output of the oxygen concentration detection means, and the oxygen concentration detection means The second air-fuel ratio control is executed only when the output is in the range of approximately 0.3 to 0.5 (V). As a result, the oxygen storage state of the second catalyst can be reliably set to a desired state for executing the second air-fuel ratio control.

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

[Configuration of catalyst deterioration detector]
First, a catalyst deterioration detection apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a schematic configuration of a vehicle 10 on which a catalyst deterioration detection device 100 is mounted.

  The vehicle 10 includes an internal combustion engine 1, catalysts 2a and 2b, an ECU (Engine Control Unit) 3, an intake passage 4, an exhaust passage 5, a fuel injection valve 6, an A / F sensor 7, and an oxygen sensor 8a. And comprising. The catalyst deterioration detection apparatus 100 according to the present embodiment is mainly configured by the catalysts 2a and 2b, the ECU 3, the fuel injection valve 6, and the oxygen sensor 8a.

  The internal combustion engine 1 is a device that generates power by exploding an air-fuel mixture in a combustion chamber. The internal combustion engine 1 introduces air 9 a and fuel from the intake passage 4, and discharges the exhaust gas 9 b after burning the fuel to the exhaust passage 5. The internal combustion engine 1 can be, for example, an engine such as a gasoline engine or a diesel engine.

  The catalysts 2a and 2b are provided on the exhaust passage 5, and purify the exhaust gas 9b discharged from the internal combustion engine 1. The catalyst 2a is provided on the exhaust passage 5 upstream of the catalyst 2b. For example, as the catalysts 2a and 2b, a three-way catalyst for purifying NOx (nitrogen oxide), HC (hydrocarbon), CO (carbon monoxide) and the like in the exhaust gas can be used.

  The fuel injection valve 6 is a device capable of adjusting the amount of fuel supplied to the internal combustion engine 1 (that is, the fuel injection amount). The fuel injection valve 6 is controlled by a control signal S3 supplied from an ECU 3 described later.

  The A / F sensor 7 is provided on the exhaust passage 5 on the upstream side of the catalyst 2a. The A / F sensor 7 detects the air-fuel ratio of the exhaust gas 9b and outputs a signal S1 corresponding to the detected air-fuel ratio to the ECU 3.

  On the other hand, the oxygen sensor 8a is provided on the exhaust passage 5 between the catalyst 2a and the catalyst 2b. The oxygen sensor 8a detects the oxygen concentration in the exhaust gas 9c after passing through the catalyst 2a, and outputs a signal S2a corresponding to the detected oxygen concentration to the ECU 3. Thus, the oxygen sensor 8a functions as a first oxygen concentration detection unit.

  The ECU 3 includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown). The ECU 3 supplies the control signal S3 to the fuel injection valve 6 on the basis of the signals S1 and S2a output from the A / F sensor 7 and the oxygen sensor 8a, thereby performing air-fuel ratio control (ie, air-fuel ratio feedback control). ). Specifically, the ECU 3 performs air-fuel ratio control (first air-fuel ratio control) for bringing the catalysts 2a, 2b into an appropriate oxygen storage state, and air-fuel ratio control (second air-fuel ratio control for detecting deterioration of the catalyst 2a). Air-fuel ratio control), that is, deterioration detection control.

  The ECU 3 detects the deterioration of the catalyst 2a based on the air-fuel ratio output from the A / F sensor 7 and the oxygen concentration output from the oxygen sensor 8a during the execution of the deterioration detection control. Thus, the ECU 3 functions as oxygen storage state estimation means, first air-fuel ratio control means, second air-fuel ratio control means, storage capacity calculation means, and storage capacity prediction means in the present invention. The specific process performed by the ECU 3 will be described later in detail.

[Deterioration detection control]
Next, the deterioration detection control performed to detect the deterioration of the catalyst 2a and the deterioration detection method of the catalyst 2a will be described with reference to FIG.

  FIG. 2 is a diagram showing a sensor output and the like obtained when the ECU 3 executes the deterioration detection control, and the horizontal axis shows time.

  FIG. 2A shows the air-fuel ratio output from the A / F sensor 7. In this case, the air-fuel ratio output from the A / F sensor 7 indicates the ratio of fuel to air in the exhaust gas 9 b discharged from the internal combustion engine 1. The A / F sensor 7 outputs a predetermined value when the air-fuel ratio is stoichiometric (theoretical air-fuel ratio), and when the air-fuel ratio is rich, the output becomes smaller than the predetermined value, and when the air-fuel ratio is lean The output becomes larger than the predetermined value.

  FIG. 2B shows the oxygen concentration output from the oxygen sensor 8a. In this case, the output of the oxygen sensor 8a indicates the oxygen concentration in the exhaust gas 9c downstream of the catalyst 2a. As shown in FIG. 2B, the oxygen sensor 8a has a small output when the oxygen concentration in the exhaust gas 9c is large (that is, the air-fuel ratio is lean), and the oxygen concentration in the exhaust gas 9c is small (that is, When the air-fuel ratio is rich), the output becomes large.

  Next, deterioration detection control will be described. As shown in FIGS. 2A and 2B, when the target air-fuel ratio is changed from the lean state to the rich state by the deterioration detection control (time t1), the oxygen that the catalyst 2a has previously stored is Therefore, the oxygen concentration in the exhaust gas 9c increases and the output of the oxygen sensor 8a decreases. However, since the oxygen storage capacity of the catalyst 2a is limited, if all the oxygen stored in the catalyst 2a is released, the oxygen concentration in the exhaust gas 9c rapidly decreases and the output of the oxygen sensor 8a increases rapidly. To increase. That is, the output of the oxygen sensor 8a is inverted. When the output value of the oxygen sensor 8a increases to the predetermined determination value 13a due to the decrease in oxygen concentration, the ECU 3 shifts the target air-fuel ratio from the rich state to the lean state (time t2).

  In the lean state, the exhaust gas 9c is in an excessive oxygen state, but the oxygen concentration in the exhaust gas 9c does not increase initially because the catalyst 2a stores the oxygen. However, when the catalyst 2a stores oxygen to the limit of the storage capacity, the oxygen concentration in the exhaust gas 9c increases rapidly thereafter. That is, the output of the oxygen sensor 8a is inverted. When the output value of the oxygen sensor 8a decreases to the predetermined determination value 13b, the ECU 3 changes the target air-fuel ratio from the lean state to the rich state (time t3). Thereafter, similar control is repeated.

  Thus, by switching the target air-fuel ratio to lean when the catalyst 2a has completely released oxygen, the catalyst 2a can immediately store oxygen, and when the catalyst 2a has fully stored oxygen, the target air-fuel ratio is stored. By switching to rich, oxygen can be released immediately from the catalyst 2a. That is, by performing such deterioration detection control, oxygen can be effectively released from the catalyst 2a, and oxygen can be effectively stored in the catalyst 2a.

  FIG. 2C shows the amount of oxygen released from the catalyst 2a (oxygen release amount) and the amount of oxygen stored by the catalyst 2a (oxygen storage amount). The oxygen release amount and the oxygen storage amount are amounts calculated by the ECU 3 based on the output from the A / F sensor 7, the opening amount of the fuel injection valve 6, and the like. That is, the oxygen release amount and the oxygen storage amount are calculated from the air-fuel ratio (A / F) in the exhaust gas 9b and the fuel injection amount.

  As shown in FIG. 2C, when the air-fuel ratio is rich, the catalyst 2a releases oxygen at a constant rate, and when the air-fuel ratio is lean, the catalyst 2a stores oxygen at a constant rate. To do. Further, when the output of the oxygen sensor 8a reaches the determination value 13a, in other words, when the target air-fuel ratio is reversed from rich to lean, the catalyst 2a switches from the oxygen release state to the oxygen storage state. Normally, when the output of the oxygen sensor 8a reaches the determination value 13a, the catalyst 2a has completely released the stored oxygen. That is, the catalyst 2a is in a limit release state. Further, when the output of the oxygen sensor 8a reaches the determination value 13b, in other words, when the target air-fuel ratio is reversed from lean to rich, the catalyst 2a switches from the oxygen release state to the oxygen storage state. Normally, when the output of the oxygen sensor 8a reaches the determination value 13b, the catalyst 2a stores oxygen to the limit. That is, the catalyst 2a is in the limit storage state.

  When the output of the oxygen sensor 8a reaches the determination value 13a, that is, when the output of the oxygen sensor 8a is inverted, the oxygen release amount is the amount indicated by reference numeral 11. Further, when the output of the oxygen sensor 8a reaches the determination value 13b, that is, when the output of the oxygen sensor 8a is inverted, the oxygen storage amount is an amount indicated by reference numeral 12. In this case, the oxygen release amount 11 is the amount of oxygen when the oxygen stored in the catalyst 2a is almost completely released, and the oxygen storage amount 12 is the amount of oxygen when the catalyst 2a stores oxygen to the limit. It is.

  The ECU 3 calculates the oxygen release amount 11 and the oxygen storage amount 12 based on the outputs of the A / F sensor 7 and the oxygen sensor 8a. Specifically, the ECU 3 calculates the oxygen release amount 11 and the oxygen storage amount 12 based on the time required until the output of the oxygen sensor 8a is reversed. Specifically, the ECU 3 calculates the oxygen release amount 11 based on the time T1 in FIG. 2B, and calculates the oxygen storage amount 12 based on the time T2. Then, the ECU 3 calculates the oxygen storage capacity of the catalyst 2a based on the calculated oxygen release amount 11 and oxygen storage amount 12. For example, the ECU 3 sets the average value of the oxygen release amount 11 and the oxygen storage amount 12 as the oxygen storage capacity.

  The ECU 3 may calculate the oxygen release amount 11 and the oxygen storage amount 12 based on the output of the A / F sensor 7 or the integrated air amount taken in by the internal combustion engine 1.

  Further, the ECU 3 detects the deterioration of the catalyst 2a based on the oxygen storage capacity thus obtained. For example, the ECU 3 determines that the catalyst 2a is normal when the obtained oxygen storage capacity is equal to or greater than a predetermined value, and the catalyst 2a is deteriorated when the oxygen storage capacity is less than the predetermined value. Is determined.

  Here, in the deterioration detection control, a problem that occurs when the timing for switching the air-fuel ratio deviates from the timing at which the output of the oxygen sensor 8a is reversed will be described with reference to FIG.

  FIG. 3 shows a specific example of the output of each sensor when the timing at which the air-fuel ratio is switched is deviated from the timing at which the output of the oxygen sensor 8a is inverted. 3A shows the output of the A / F sensor 7, FIG. 3B shows the output of the oxygen sensor 8a, and the horizontal axis shows time.

  As shown in FIG. 3, it can be seen that the timing at which the air-fuel ratio is switched from rich to lean is shifted by the time ta with respect to the timing at which the output of the oxygen sensor 8a is inverted from rich to lean. Similarly, the timing at which the air-fuel ratio is switched from lean to rich is shifted by time tb with respect to the time when the output of the oxygen sensor 8a is reversed from lean to rich.

  Thus, if the timing at which the air-fuel ratio is switched with respect to the timing at which the output of the oxygen sensor 8a is reversed, the catalyst 2a may discharge the gas that could not be purified downstream. Specifically, the timing at which the air-fuel ratio is switched from rich to lean deviates from the timing at which the output of the oxygen sensor 8a is inverted from rich to lean, so that the rich gas (oxygen) is further added to the catalyst 2a in the limit release state. Insufficient gas) flows in, and the catalyst 2a cannot purify the rich gas and discharges it downstream. On the other hand, the timing at which the air-fuel ratio is switched from lean to rich deviates from the timing at which the output of the oxygen sensor 8a is reversed from lean to rich, so that lean gas (oxygen-rich gas) is further added to the catalyst 2a in the limit storage state. ) Flows in and the catalyst 2a cannot purify the lean gas and discharges it downstream.

  Basically, the gas discharged without being purified by the catalyst 2a is purified by the catalyst 2b located on the downstream side of the catalyst 2a. However, when the catalyst 2b is also in the limit release state or the limit storage state, the catalyst 2b may not be able to purify the gas that could not be purified by the catalyst 2a and may be discharged outside. Specifically, when the catalyst 2a has discharged the rich gas downstream, if the catalyst 2b is also in the limit release state, the catalyst 2b cannot purify the rich gas. On the other hand, when the catalyst 2a has discharged the lean gas downstream, if the catalyst 2b is also in the limit occlusion state, the catalyst 2b cannot purify the lean gas. As described above, when the gas that could not be purified by the catalyst 2a could not be purified by the catalyst 2b, NOx, HC, CO, and the like would be released to the outside of the vehicle 10.

  As described above, in the deterioration detection control, the exhaust gas discharged from the internal combustion engine 1 cannot be purified by the catalyst 2a and the catalyst 2b, and the emission may be deteriorated. Therefore, the catalyst deterioration detection apparatus 100 according to the present embodiment performs air-fuel ratio control, which will be described later, before executing the deterioration detection control for the catalyst 2a in order not to cause the above-described problems.

[Air-fuel ratio control performed before deterioration detection control]
Next, an embodiment of air-fuel ratio control according to the present invention that is performed before the execution of the deterioration detection control will be described. This air-fuel ratio control is mainly executed to set the catalysts 2a and 2b in an appropriate state (oxygen storage state) for executing the deterioration detection control.

  Note that the air-fuel ratio control described below is mainly executed after fuel cut (fuel cut). In general, after the fuel cut is completed, in order to obtain a high purification rate from the catalyst 2a, control for setting the air-fuel ratio to be slightly rich is performed. The air-fuel ratio control according to the present invention (hereinafter, this air-fuel ratio control is referred to as “control after returning to fuel cut”) is desired for the catalysts 2a and 2b by utilizing such generally performed air-fuel ratio control. Set to the oxygen storage state.

(First embodiment)
First, a first embodiment of the control after returning from fuel cut according to the present invention will be described with reference to FIGS.

  The basic concept of the control after fuel cut recovery according to the first embodiment will be described with reference to FIG. FIG. 4 mainly shows the catalysts 2a and 2b, the exhaust passage 5, the A / F sensor 7, and the oxygen sensor 8a. Note that the control after fuel cut recovery according to the first embodiment is executed by the ECU 3 in the catalyst deterioration detection device 100.

  FIG. 4 schematically shows the oxygen storage state of the catalysts 2a and 2b (the ratio of the actual oxygen storage amount to the oxygen storage capacity), and the oxygen storage amount is indicated by hatching. . Therefore, when the whole is hatched, the catalysts 2a and 2b are assumed to be in the limit occlusion state.

  FIG. 4A shows the state of the catalysts 2a and 2b immediately after the end of the fuel cut. Since the lean gas is continuously supplied to the internal combustion engine 1 at the time of fuel cut, the catalysts 2a and 2b are in the limit occlusion state immediately after the end of the fuel cut.

  The ECU 3 executes the fuel cut return control according to the first embodiment after the fuel cut is completed. Specifically, the ECU 3 executes control for setting the air-fuel ratio to be slightly rich (for example, setting the air-fuel ratio to a value such as “14.2”). This is because the catalyst 2a can effectively purify the exhaust gas immediately after the fuel cut by setting the air-fuel ratio to be slightly rich. Further, the ECU 3 continues the control for setting the air-fuel ratio to be slightly rich until the catalyst 2a enters the limit release state and the catalyst 2b enters the desired oxygen storage state. Specifically, the ECU 3 decreases the air-fuel ratio slightly until the oxygen storage capacity of approximately half of the oxygen storage capacity is released from the catalyst 2b, that is, until the oxygen storage capacity of the catalyst 2b becomes approximately half of the oxygen storage capacity. (See FIG. 4B). The ECU 3 executes the deterioration detection control for the catalyst 2a when the oxygen storage state of the catalyst 2b becomes such a state.

  Here, the change in the oxygen storage state of the catalysts 2a and 2b due to the execution of the control after the fuel cut recovery by the ECU 3 will be described. Immediately after the end of the fuel cut, the catalysts 2a and 2b are in the limit storage state. After the fuel cut ends, the catalyst 2a in the limit storage state gradually releases oxygen by setting the air-fuel ratio to be slightly rich. It becomes a limit release state. Further, since the rich gas is further supplied to the catalyst 2a in the limit release state, the catalyst 2a discharges the rich gas downstream.

  Further, the rich gas discharged downstream in this way causes the catalyst 2b that has been in the limit storage state to gradually release oxygen. Further, when the rich gas is further supplied to the catalyst 2b, the catalyst 2b releases approximately half of the oxygen storage capacity, that is, the oxygen storage capacity is approximately half of the oxygen storage capacity. When the oxygen occlusion state of the catalyst 2b becomes the above state, the ECU 3 ends the control after the fuel cut recovery for setting the air-fuel ratio to be slightly rich.

  By executing the above control after the fuel cut is restored, there is a difference between when the output of the oxygen sensor 8a is reversed and when the air-fuel ratio is switched, and even if the catalyst 2a discharges rich gas or lean gas downstream, Since the catalyst 2b is neither in the limit release state nor in the limit storage state, it is possible to purify both the rich gas and the lean gas supplied. Specifically, since the catalyst 2b is storing oxygen that is approximately half of the oxygen storage capacity, both the rich gas and the lean gas released without being purified by the catalyst 2a can be purified at a high purification rate. Is possible. Therefore, according to the control after returning from the fuel cut according to the first embodiment, it is possible to prevent the deterioration of the emission that may be caused by executing the deterioration detection control.

  Furthermore, the control after the fuel cut recovery according to the present embodiment uses a control that is generally executed immediately after the fuel cut and sets the air-fuel ratio to be slightly rich. That is, the catalysts 2a and 2b are set in an appropriate oxygen storage state for executing the deterioration detection control by utilizing the air-fuel ratio control generally executed immediately after the fuel cut. As a result, immediately after the fuel cut, it is possible to set the catalysts 2a and 2b in an appropriate oxygen storage state for executing the deterioration detection control while obtaining a high purification rate from the catalyst 2a for a long time.

  Next, processing that is specifically performed in the control after fuel cut return according to the first embodiment (hereinafter, this processing is referred to as “processing after fuel cut return”) will be described with reference to the flowchart of FIG. 5. The post-fuel-cut return processing is executed to set the catalysts 2a and 2b in an oxygen storage state suitable for performing deterioration detection control of the catalyst 2a, and is executed during the control after fuel-cut return. The fuel cut recovery post-processing is repeatedly executed by the ECU 3 at a predetermined cycle.

  First, in step S101, the ECU 3 determines whether or not the output of the oxygen sensor 8a is reversed. Specifically, the ECU 3 determines whether or not the output of the oxygen sensor 8a is reversed from lean to rich. That is, the ECU 3 determines whether or not the catalyst 2a has reached the limit release state by the control after the fuel cut recovery that sets the air-fuel ratio to be slightly rich. If the output of the oxygen sensor 8a is inverted (step S101; Yes), the process proceeds to step S103. On the other hand, if the output of the oxygen sensor 8a is not inverted (step S101; No), the process proceeds to step S102. In this case, the ECU 3 continues to execute the control after returning from the fuel cut (step S102), and exits the flow.

  In step S103, the ECU 3 executes the control after returning from the fuel cut until the integrated air amount taken in by the internal combustion engine 1 reaches a predetermined amount. In this case, since the catalyst 2a is in the limit release state, the exhaust gas passing through the catalyst 2a flows into the catalyst 2b without being purified. Therefore, a desired amount of oxygen can be released from the catalyst 2b by executing the control after returning from the fuel cut until the integrated air amount reaches a predetermined amount. That is, approximately half of the oxygen storage capacity of oxygen can be released from the catalyst 2b, in other words, approximately half of the oxygen storage capacity can remain in the catalyst 2b. The predetermined amount of the integrated air amount is a value estimated in advance based on the oxygen storage capacity of the catalyst 2b, and is stored in a memory (not shown) in the ECU 3. When the above process ends, the process proceeds to step S104.

  In step S104, the ECU 3 determines whether or not the integrated air amount has reached a predetermined amount. If the integrated air amount has reached the predetermined amount (step S104; Yes), the process proceeds to step S105. On the other hand, when the integrated air amount has not reached the predetermined amount (step S104; No), the process exits the flow. In this case, the control after returning from the fuel cut is continuously executed.

  In step S105, the ECU 3 permits execution of the deterioration detection control. In this case, the catalyst 2a is in the limit release state, and the catalyst 2b stores approximately half of the oxygen storage capacity. Therefore, the ECU 3 permits the execution of the deterioration detection control and ends the control after returning from the fuel cut. Then, the ECU 3 executes deterioration detection control.

  As described above, after the output of the oxygen sensor 8a is reversed, the control after the fuel cut is resumed until the integrated air amount taken in by the internal combustion engine 1 reaches a predetermined amount, so that the oxygen storage state of the catalyst 2b is reliably set to the desired oxygen amount. It is possible to set the storage state.

(Second embodiment)
Next, the control after fuel cut recovery according to the second embodiment will be described with reference to FIGS.

  First, the basic concept of control after fuel cut recovery according to the second embodiment will be described. The control after the fuel cut return according to the second embodiment is also executed before the deterioration detection control similarly to the control after the fuel cut return according to the first embodiment described above, and the oxygen storage amount of the catalyst 2b is approximately the oxygen storage capacity. Control to set half the amount. However, in the control after the fuel cut return according to the second embodiment, the specific control method for setting the oxygen storage amount of the catalyst 2b to approximately half of the oxygen storage capacity is the same as that after the fuel cut return according to the first embodiment. It is different from control. Specifically, in the control after the fuel cut recovery according to the second embodiment, the oxygen storage capacity of the catalyst 2b is predicted, and based on the predicted oxygen storage capacity, a predetermined amount of the integrated air amount to be sucked into the internal combustion engine 1 is set. decide. The predetermined amount of the integrated air amount determined in this way is an amount that takes into consideration the current state of the catalyst 2b (for example, the degree of deterioration of the catalyst 2b). Thereby, since the integrated air amount according to the current state of the catalyst 2b is sucked into the internal combustion engine 1, the catalyst 2b can be accurately set to a desired oxygen storage state.

  A method for predicting the oxygen storage capacity of the catalyst 2b will be specifically described with reference to FIG. In the diagram shown in FIG. 6, the horizontal axis indicates the oxygen storage capacity of the catalyst 2a, and the vertical axis indicates the oxygen storage capacity of the catalyst 2b. As shown in the figure, the oxygen storage capacity of the catalyst 2a and the oxygen storage capacity of the catalyst 2b have a relationship generally indicated by a straight line A. Such a relationship between the oxygen storage capacities of the catalyst 2a and the catalyst 2b reflects the degree of deterioration. That is, the relationship between the oxygen storage capacity of the catalyst 2a and the catalyst 2b shown by the straight line A indicates that when the catalyst 2a is deteriorated, the catalyst 2b is also deteriorated to a degree corresponding to the deterioration degree of the catalyst 2a. ing. For example, when the oxygen storage capacity of the catalyst 2a is reduced, the oxygen storage capacity of the catalyst 2b is also reduced. Note that data indicating the relationship between the oxygen storage capacity of the catalyst 2a and the oxygen storage capacity of the catalyst 2b is obtained in advance by experiments or the like and stored in a memory (not shown) in the ECU 3.

  Here, the post-fuel cut return processing that is specifically performed in the post-fuel cut return control according to the second embodiment will be described with reference to the flowchart of FIG. This process is executed by the ECU 3 in the catalyst deterioration detection apparatus 100 and is repeatedly executed at a predetermined cycle.

  First, in step S201, the ECU 3 determines whether or not the output of the oxygen sensor 8a is reversed. That is, the ECU 3 determines whether or not the catalyst 2a has reached the limit release state by the control after the fuel cut recovery that sets the air-fuel ratio to be slightly rich. If the output of the oxygen sensor 8a is inverted (step S201; Yes), the process proceeds to step S203. On the other hand, if the output of the oxygen sensor 8a is not inverted (step S201; No), the process proceeds to step S202. In this case, the ECU 3 continues to execute the control after returning from the fuel cut (step S202), and exits the flow.

  In step S203, the ECU 3 calculates the oxygen storage capacity of the catalyst 2a. Specifically, the ECU 3 calculates the oxygen storage capacity of the catalyst 2a based on the time from the end of the fuel cut until the output of the oxygen sensor 8a reverses from lean to rich. Then, the process proceeds to step S204.

  In step S204, the ECU 3 predicts the oxygen storage capacity of the catalyst 2b based on the oxygen storage capacity of the catalyst 2a. Specifically, the ECU 3 predicts the oxygen storage capacity of the catalyst 2b based on the stored relationship between the oxygen storage capacity of the catalyst 2a and the oxygen storage capacity of the catalyst 2b (for example, the straight line A in FIG. 6). Then, the ECU 3 calculates a predetermined amount of accumulated air to be taken into the internal combustion engine 1 based on the predicted oxygen storage capacity of the catalyst 2b. The predetermined amount of the integrated air amount calculated in this way is an amount that takes into account the degree of deterioration of the catalyst 2b. That is, the predetermined amount of the integrated air amount is determined based on the oxygen storage capacity corresponding to the current degree of deterioration of the catalyst 2b. Thereby, the catalyst 2b can be set to an appropriate oxygen storage state of the catalyst 2b according to the degree of deterioration of the current catalyst 2b. Therefore, for example, the catalyst 2 never releases more than half of the current oxygen storage capacity. When the above process ends, the process proceeds to step S205.

  In step S205, the ECU 3 executes the control after returning from the fuel cut until the integrated air amount taken in by the internal combustion engine 1 reaches a predetermined amount (the amount predicted in step S204). As described above, by executing the control after returning from the fuel cut until the integrated air amount reaches a predetermined amount, approximately half of the oxygen storage capacity is released from the catalyst 2b, in other words, approximately half of the oxygen storage capacity. An amount of oxygen can remain in the catalyst 2b. When the above process ends, the process proceeds to step S206.

  In step S206, the ECU 3 determines whether or not the integrated air amount has reached a predetermined amount. If the integrated air amount has reached the predetermined amount (step S206; Yes), the process proceeds to step S206. If the integrated air amount has not reached the predetermined amount (step S206; No), the process Exit the flow.

  In step S207, the ECU 3 permits execution of the deterioration detection control. Then, the ECU 3 ends the control after returning from the fuel cut, and executes the deterioration detection control.

  According to the control after the fuel cut recovery according to the second embodiment described above, the predetermined amount of the integrated air amount to be taken into the internal combustion engine 1 is determined in consideration of the deterioration degree of the catalysts 2a and 2b. The catalyst 2b can be accurately set to a desired oxygen storage state without being affected by the degree of deterioration of the catalyst. That is, since the predetermined amount is determined based on the oxygen storage capacity according to the current deterioration degree of the catalyst 2b, the catalyst 2b does not release more than half of the current oxygen storage capacity. Thus, the control for setting the air-fuel ratio to be slightly rich for obtaining a high purification rate of the catalyst 2a with respect to the exhaust gas can be executed for a long time. Further, it is possible to more effectively prevent the deterioration of the emission that can be caused by the deterioration detection control.

(Third embodiment)
Next, control after fuel cut recovery according to the third embodiment will be described with reference to FIGS.

  The control after returning from the fuel cut according to the third embodiment is executed when there is a calculation history of the oxygen storage capacity of the catalyst 2a. That is, the control after fuel cut return according to the third embodiment is executed after the oxygen storage capacity of the catalyst 2a is calculated in the post-fuel cut return processing according to the second embodiment.

  The control after the fuel cut recovery according to the third embodiment is also executed after the fuel cut ends, similarly to the control after the fuel cut recovery according to the first embodiment and the second embodiment. However, the control after the fuel cut return according to the third embodiment is not executed for the purpose of preventing the emission deterioration due to the deterioration detection control, but prevents the deterioration of the fuel consumption after the fuel cut ends, and The main purpose is to improve the purification rate of the catalyst 2a with respect to the exhaust gas.

  With reference to FIG. 8, the basic concept of the control after fuel cut recovery according to the third embodiment will be described. FIG. 8 also schematically shows the oxygen storage state of the catalysts 2a and 2b, and the amount of oxygen stored is indicated by hatching.

  FIG. 8A shows the state of the catalysts 2a and 2b immediately after the end of the fuel cut. Since the lean gas continues to be supplied to the internal combustion engine 1 when the fuel is cut, the catalysts 2a and 2b are in the limit occlusion state immediately after the end of the fuel cut.

  The ECU 3 executes post-fuel-cut return control according to the third embodiment after the end of such fuel cut. Specifically, the ECU 3 executes control for setting the air-fuel ratio to be slightly rich. In this case, the ECU 3 until the oxygen of approximately half the oxygen storage capacity is released from the catalyst 2a, that is, until the oxygen storage capacity of the catalyst 2a is approximately half of the oxygen storage capacity (see FIG. 8B). The air-fuel ratio is set to be slightly rich. Specifically, the ECU 3 calculates a predetermined amount of the integrated air amount to be sucked into the internal combustion engine 1 based on the oxygen storage capacity of the catalyst 2a calculated in the past, and the integrated air amount sucked by the internal combustion engine 1 is the predetermined amount. The control is terminated after the fuel cut is restored.

  Here, the post-fuel cut return processing specifically performed in the post-fuel cut return control according to the third embodiment will be described with reference to the flowchart of FIG. This process is also performed by the ECU 3 in the catalyst deterioration detection apparatus 100.

  In step S301, the ECU 3 determines whether there is a calculation history of the oxygen storage capacity of the catalyst 2a. Specifically, the ECU 3 determines whether or not there is a calculation history of the oxygen storage capacity of the catalyst 2a during the current trip, that is, from the start of the internal combustion engine 1 to the present. If there is a calculation history of the oxygen storage capacity (step S301; Yes), the process proceeds to step S302. On the other hand, when there is no calculation history of the oxygen storage capacity (step S301; No), the process exits the flow. In this case, the ECU 3 can execute the fuel cut return post-processing according to the second embodiment described above.

  In step S302, the ECU 3 executes control after returning from the fuel cut until approximately half of the oxygen storage capacity is released from the catalyst 2a. That is, the ECU 3 sets the air-fuel ratio to be slightly rich until the oxygen storage amount of the catalyst 2a is approximately half of the oxygen storage capacity. Specifically, the ECU 3 calculates a predetermined amount of the integrated air amount to be taken into the internal combustion engine 1 based on the oxygen storage capacity of the catalyst 2a calculated in the past, and cuts the fuel until the integrated air amount reaches this predetermined amount. Execute control after returning. When the above process ends, the process exits the flow.

  According to the control after the fuel cut recovery according to the third embodiment described above, it is possible to prevent the deterioration of the fuel consumption after the end of the fuel cut and to improve the purification rate of the catalyst 2a with respect to the exhaust gas.

(Fourth embodiment)
Next, control after fuel cut recovery according to the fourth embodiment will be described.

  The control after the fuel cut recovery according to the fourth embodiment is executed by the catalyst deterioration detection device 101 shown in FIG. FIG. 10 is a block diagram showing a schematic configuration of the vehicle 11 on which the catalyst deterioration detection device 101 is mounted.

  The catalyst deterioration detection device 101 according to this embodiment is different from the above-described catalyst deterioration detection device 100 in that an oxygen sensor 8b is provided on the exhaust passage 5 on the downstream side of the catalyst 2b. The oxygen sensor 8b detects the oxygen concentration in the exhaust gas 9d after passing through the catalyst 2b, and outputs a signal S2b corresponding to the detected oxygen concentration to the ECU 3. Thus, the oxygen sensor 8b functions as a second oxygen concentration detection unit. Note that, in the catalyst deterioration detection device 101, the same components as those of the catalyst deterioration detection device 100 are denoted by the same reference numerals, and description thereof is omitted.

  The control after return from fuel cut according to this embodiment is different from the control after return from fuel cut described above in that it is executed based on the output of the oxygen sensor 8b. Hereinafter, the post-fuel cut return control according to the present embodiment will be described in detail.

  First, the relationship between the output of the oxygen sensor 8b and the purification rate of the catalyst 2b will be described.

  FIG. 11 is a diagram showing a specific example of the relationship between the output of the oxygen sensor 8b and the purification rate of the catalyst 2b obtained experimentally. In FIG. 11A, the horizontal axis indicates the output (V) of the oxygen sensor 8b, and the vertical axis indicates the NOx purification rate (%). In FIG. 11B, the horizontal axis indicates the output (V) of the oxygen sensor 8b, and the vertical axis indicates the HC purification rate (%). Here, the purification rate shown in FIG. 11 indicates the purification rate of the catalyst 2b with respect to the exhaust gas (NOx, HC). NOx is mainly contained in the lean gas, and HC is mainly contained in the rich gas. In addition, FIG. 11 displays the results when the vehicle 11 is driven at speeds of 60 km / h, 80 km / h, and 100 km / h.

  As shown in FIG. 11A, it can be seen that when the output of the oxygen sensor 8b is approximately in the range of 0.2 to 0.6 (V), the purification rate of the catalyst 2b with respect to NOx is high. That is, in the oxygen occlusion state of the catalyst 2b so that an output in the range of approximately 0.2 to 0.6 (V) can be obtained from the oxygen sensor 8b, the catalyst 2b purifies NOx with a high purification rate. Furthermore, as shown in FIG. 11B, when the output of the oxygen sensor 8b is small (for example, when the output of the oxygen sensor 8b is about 0.2 (V)), the purification rate of the catalyst 2b with respect to HC is high. You can see that it is the highest. That is, in the oxygen occlusion state of the catalyst 2b in which a small output can be obtained from the oxygen sensor 8b, the catalyst 2b purifies HC with a high purification rate.

  From the above, it can be seen that the catalyst 2b can purify both NOx and HC at a high purification rate in a situation where an output in the range of approximately 0.3 to 0.5 (V) can be obtained from the oxygen sensor 8b. Therefore, when the output within the range of approximately 0.3 to 0.5 (V) is obtained from the output of the oxygen sensor 8b, the catalyst 2b is highly purified of the rich gas and the lean gas released without being purified by the catalyst 2a. Can be purified at a rate. The situation in which an output in the range of approximately 0.3 to 0.5 (V) is obtained from the oxygen sensor 8b means that the catalyst 2b is storing approximately half of the oxygen storage capacity. It can be said.

  Therefore, in the control after the fuel cut recovery according to the fourth embodiment, the ECU 3 performs control to set the air-fuel ratio to be slightly rich after the fuel cut ends, and this control is performed when the output of the oxygen sensor 8b is approximately 0.3 to 0.3. Continue until it falls within the range of 0, 5 (V). In other words, the ECU 3 ends the control for setting the air-fuel ratio to be slightly rich when the output of the oxygen sensor 8b falls within the range of approximately 0.3 to 0, 5 (V). Therefore, it is possible to set the catalyst 2a to the limit release state and set the oxygen storage amount of the catalyst 2b to approximately half of the oxygen storage capacity even by the control after the fuel cut recovery according to the present embodiment. . Thereafter, the ECU 3 executes deterioration detection control. That is, the ECU 3 performs the deterioration detection control only when the output of the oxygen sensor 8b is approximately in the range of 0.3 to 0.5 (V).

  A specific example of the output of the oxygen sensor 8b is shown in FIG. FIG. 12 shows time on the horizontal axis and the output of the oxygen sensor 8b on the vertical axis. In this case, the oxygen sensor 8b generates an output as indicated by symbol B. Specifically, since the ECU 3 is executing post-fuel-cut recovery control that sets the air-fuel ratio to be slightly rich, the catalyst 2a gradually releases oxygen, and the output of the oxygen sensor 8b gradually decreases. Yes. At time C, the output of the oxygen sensor 8b falls within the range of 0.3 to 0.5 (V). Therefore, at time C, the ECU 3 ends the control after returning from the fuel cut, and executes the deterioration detection control.

  Even after the fuel cut return control according to the fourth embodiment as described above, there is a difference between the time when the output of the oxygen sensor 8a is inverted and the time when the air-fuel ratio is switched, and the catalyst 2a is rich gas or lean gas downstream. Even if the catalyst 2b is discharged, the rich gas and lean gas supplied can be purified because the catalyst 2b is neither in the limit release state nor in the limit storage state. Specifically, when the output of the oxygen sensor 8b is in the range of approximately 0.3 to 0, 5 (V), the catalyst 2b is in a state of storing approximately half of the oxygen storage capacity. Both the rich gas and the lean gas released without being purified can be purified with a high purification rate. Therefore, according to the control after fuel cut recovery according to the fourth embodiment, it is possible to prevent the deterioration of the emission that may be caused by executing the deterioration detection control.

  Here, the post-fuel cut return processing specifically performed in the post-fuel cut return control according to the fourth embodiment will be described with reference to the flowchart of FIG. This process is executed by the ECU 3 in the catalyst deterioration detection apparatus 101.

  In step S401, the ECU 3 determines whether or not an execution condition for deterioration detection control is satisfied. Specifically, the ECU 3 determines whether a predetermined time has elapsed from the end of the fuel cut and whether the rotational speed and load of the internal combustion engine 1 are within an allowable range. When a predetermined time has elapsed since the end of the fuel cut, the catalysts 2a and 2b are generally set to a desired oxygen storage state for deterioration detection control. That is, the catalyst 2a is in a limit release state, and the catalyst 2b is in a state of storing approximately half of the oxygen storage capacity. If the deterioration detection execution condition is satisfied (step S401; Yes), the process proceeds to step S402. If the deterioration detection execution condition is not satisfied (step S401; No), the process proceeds with the flow. Exit.

  In step S402, the ECU 3 determines whether or not the output of the oxygen sensor 8b is approximately in the range of 0.3 to 0.5 (V). In other words, the ECU 3 determines whether or not the oxygen storage state of the catalyst 2b is a state in which the execution of the deterioration detection control may be permitted based on the output of the oxygen sensor 8b. Specifically, when the output of the oxygen sensor 8b is approximately in the range of 0.3 to 0.5 (V), the catalyst 2b is storing approximately half of the oxygen storage capacity. Therefore, it can be said that the oxygen storage state of the catalyst 2b is a state in which the deterioration detection control may be permitted. When the output of the oxygen sensor 8b is within the above range (step S402; Yes), the process proceeds to step S403, and when the output of the oxygen sensor 8b is not within the above range (step S402; No). The process exits the flow.

  In step S403, the ECU 3 permits execution of the deterioration detection control. In this case, the catalyst 2a is in the limit release state, and the catalyst 2b stores approximately half of the oxygen storage capacity. Therefore, the ECU 3 permits the execution of the deterioration detection control and ends the control after returning from the fuel cut. Then, the ECU 3 executes deterioration detection control.

  In the above description, the example in which the determination with respect to the output of the oxygen sensor 8b is performed immediately after the fuel cut has been described, but instead the determination with respect to the output of the oxygen sensor 8b may be performed at a timing other than immediately after the fuel cut. Good. For example, when the output of the oxygen sensor 8b is determined at a timing other than immediately after the fuel cut, and the output of the oxygen sensor 8b is approximately in the range of 0.3 to 0.5 (V), the deterioration detection control is performed. May be executed. In this case, other conditions (such as the load of the internal combustion engine 1) for executing the deterioration detection control need to be satisfied.

(5th Example)
Next, control after fuel cut recovery according to the fifth embodiment will be described. The control after the fuel cut recovery according to the fifth embodiment is executed by the catalyst deterioration detection device 101 having the oxygen sensor 8b.

  Also in the fifth embodiment, as in the control after the fuel cut recovery according to the fourth embodiment described above, the output of the oxygen sensor 8b is approximately 0.3-0. Execute until it falls within the range of 5 (V). However, in the control after the fuel cut recovery according to the fifth embodiment, the control to make the air-fuel ratio slightly rich after the fuel cut is executed until the integrated air amount sucked by the internal combustion engine 1 reaches a predetermined amount, and the integrated air amount is The deterioration detection control is executed only when the output of the oxygen sensor 8b at the time when the predetermined amount is reached is approximately in the range of 0.3 to 0.5 (V).

  The post-fuel-cut return processing that is specifically performed in the post-fuel-cut return control according to the fifth embodiment will be described with reference to the flowchart of FIG. This process is executed by the ECU 3 in the catalyst deterioration detection apparatus 101.

  In step S501, the ECU 3 determines whether or not the output of the oxygen sensor 8a is reversed. That is, the ECU 3 determines whether or not the catalyst 2a has reached the limit release state by the control after the fuel cut recovery that sets the air-fuel ratio to be slightly rich. If the output of the oxygen sensor 8a is inverted (step S501; Yes), the process proceeds to step S503. On the other hand, if the output of the oxygen sensor 8a is not reversed (step S501; No), the process proceeds to step S502. In this case, the ECU 3 continues to execute the control after returning from the fuel cut (step S502), and exits the flow.

  In step S503, the ECU 3 executes the control after returning from the fuel cut until the integrated air amount taken in by the internal combustion engine 1 reaches a predetermined amount. In this case, since the catalyst 2a is in the limit release state, the exhaust gas passing through the catalyst 2a flows into the catalyst 2b without being purified. Therefore, by executing the control after returning from the fuel cut until the integrated air amount reaches a predetermined amount, approximately half of the oxygen storage capacity can be released from the catalyst 2b, that is, approximately half of the oxygen storage capacity. An amount of oxygen can remain in the catalyst 2b. The predetermined amount of the integrated air amount is calculated in advance based on the oxygen storage capacity of the catalyst 2b and stored in a memory (not shown) in the ECU 3. When the above process ends, the process proceeds to step S504.

  In step S504, the ECU 3 determines whether or not the output of the oxygen sensor 8b is approximately in the range of 0.3 to 0.5 (V). That is, the ECU 3 determines whether or not the oxygen storage state of the catalyst 2b is a state in which the execution of the deterioration detection control may be permitted based on the output of the oxygen sensor 8b. In this case, in step S503, since the integrated air amount taken in by the internal combustion engine 1 has reached a predetermined amount, the output of the oxygen sensor 8b can be approximately in the range of 0.3 to 0.5 (V). High nature. However, for example, when the catalyst 2b is deteriorated, when the integrated air amount taken in by the internal combustion engine 1 reaches a predetermined amount, the oxygen storage amount of the catalyst 2b may be less than half of the oxygen storage capacity. There is sex. In such a case, the output of the oxygen sensor 8b is 0.3 (V) or less. From the above, even if the integrated air amount taken in by the internal combustion engine 1 reaches a predetermined amount, the oxygen storage state of the catalyst 2b is carefully determined by making further determination on the output of the oxygen sensor 8b in step S504. ing.

  When the output of the oxygen sensor 8b is approximately in the range of 0.3 to 0.5 (V) (step S504; Yes), the process proceeds to step S505, and the output of the oxygen sensor 8b is within the above range. If there is not (step S504; No), the process exits the flow.

  In step S505, the ECU 3 permits execution of deterioration detection control. In this case, the catalyst 2a is in the limit release state, and the catalyst 2b stores approximately half of the oxygen storage capacity. Therefore, the ECU 3 permits the execution of the deterioration detection control and ends the control after returning from the fuel cut. Then, the ECU 3 executes deterioration detection control.

  As described above, in the control after returning from fuel cut according to the fifth embodiment, after the output of the oxygen sensor 8a is reversed, the control after returning from fuel cut is performed until the integrated air amount taken in by the internal combustion engine 1 reaches a predetermined amount. After this control, a determination is made on the output of the oxygen sensor 8b. Thereby, according to the control after fuel cut recovery according to the fifth embodiment, it is possible to reliably set the oxygen storage state of the catalyst 2b to a desired state.

  In the present invention, the predetermined range used for determining the output of the oxygen sensor 8b is not limited to being set to 0.3 to 0.5 (V). Since this predetermined range is a value that varies depending on the types of the internal combustion engine 1, the oxygen sensor 8b, and the catalysts 2a and 2b, it is preferable that the predetermined range be determined by experiments or the like. That is, the relationship between the output of the catalyst 2b and the oxygen sensor 8b is obtained by experiment or the like, and based on the obtained relationship, the output of the oxygen sensor 8b when the optimum purification rate is obtained from the catalyst 2b is determined as a predetermined range. It is preferable.

  Note that the present invention is not limited to executing the deterioration detection control for detecting the deterioration of the catalyst 2a after the end of the fuel cut. In other words, the present invention is not limited to executing control (control after returning from fuel cut) for setting the catalysts 2a and 2b to an appropriate oxygen storage state for performing deterioration detection control immediately after the end of fuel cut. . If the state of the internal combustion engine 1 or the like is a state in which deterioration detection control can be executed, control for setting the catalysts 2a and 2b to an appropriate oxygen storage state for performing deterioration detection control at a timing other than after the end of fuel cut. And the deterioration detection control may be executed after this control.

It is a block diagram which shows schematic structure of the vehicle by which the catalyst degradation detection apparatus which concerns on this invention is mounted. It is a figure for demonstrating the deterioration detection control performed for the deterioration detection of a catalyst. It is the figure shown about the case where the timing which reverses an air fuel ratio has shifted with respect to the output of an oxygen sensor. It is a figure for demonstrating the basic concept of the fuel cut return control which concerns on 1st Example. It is a flowchart which shows the fuel cut return post-process which concerns on 1st Example. It is a figure which shows the relationship of the oxygen storage capability of an upstream catalyst and a downstream catalyst. It is a flowchart which shows the fuel cut return post-process which concerns on 2nd Example. It is a figure for demonstrating the basic concept of the control after fuel cut recovery which concerns on 3rd Example. It is a flowchart which shows the fuel cut return post-process which concerns on 3rd Example. It is a block diagram which shows schematic structure of the vehicle by which the catalyst deterioration detection apparatus based on 4th Example is mounted. It is a figure which shows the relationship between the output of a downstream oxygen sensor, and a purification rate. It is a figure which shows the specific example of the output of a downstream oxygen sensor. It is a flowchart which shows the fuel cut return post-process which concerns on 4th Example. It is a flowchart which shows the fuel cut return post-process which concerns on 5th Example.

Explanation of symbols

1 Internal combustion engine 2a, 2b Catalyst 3 ECU
DESCRIPTION OF SYMBOLS 5 Exhaust passage 6 Fuel injection valve 7 A / F sensor 8a, 8b Oxygen sensor 10, 11 Vehicle 100, 101 Catalyst deterioration detection apparatus

Claims (8)

A first catalyst disposed in an exhaust passage of the internal combustion engine;
A second catalyst disposed in the exhaust passage downstream of the first catalyst;
First oxygen concentration detection means provided in the exhaust passage between the first catalyst and the second catalyst and detecting an oxygen concentration in the exhaust passage;
Based on the oxygen concentration, it is estimated whether or not the first catalyst is in a limit release state in which the stored oxygen is completely released or in a limit storage state in which oxygen is stored up to the limit. Means for estimating the oxygen storage state,
First air-fuel ratio control means for executing the first air-fuel ratio control so that the amount of oxygen stored by the second catalyst is approximately half of the oxygen storage capacity of the second catalyst;
It is estimated that the first catalyst is in the limit release state or the limit storage state, and a second empty space for detecting deterioration of the first catalyst after execution of the first air-fuel ratio control. And a second air-fuel ratio control means for executing the fuel-fuel ratio control.   2. The air / fuel ratio control means for executing air / fuel ratio control for changing an air / fuel ratio of fuel and air supplied to the internal combustion engine between a rich state and a lean state. Catalyst deterioration detection device.   The first air-fuel ratio control means is executed immediately after the fuel cut of the internal combustion engine is completed, and until the amount of oxygen stored in the second catalyst becomes approximately half of the oxygen storage capacity, 3. The catalyst deterioration detection device according to claim 1, wherein the fuel ratio is continuously set to be slightly rich.   The first air-fuel ratio control means sets the air-fuel ratio to be slightly rich until the integrated air amount taken in by the internal combustion engine reaches a predetermined amount after the first catalyst enters the limit release state. 4. The catalyst deterioration detection device according to claim 3, wherein the catalyst deterioration detection device is continued. A storage capacity calculating means for calculating the oxygen storage capacity of the first catalyst based on the oxygen concentration;
A storage capacity predicting means for predicting the oxygen storage capacity of the second catalyst based on the oxygen storage capacity of the first catalyst;
The first air-fuel ratio control means calculates the predetermined amount based on the predicted oxygen storage capacity of the second catalyst, and until the accumulated air amount taken in by the internal combustion engine reaches the predetermined amount, 5. The catalyst deterioration detection device according to claim 4, wherein the air-fuel ratio is continuously set to be slightly rich.   When the oxygen storage capacity of the first catalyst has already been calculated, the first air-fuel ratio control means is configured such that the amount of oxygen stored by the first catalyst is approximately half of the oxygen storage capacity. The catalyst deterioration detection device according to claim 5, wherein the air-fuel ratio is set to be slightly rich until A second oxygen concentration detection means provided in the exhaust passage on the downstream side of the second catalyst and detecting an oxygen concentration in the exhaust passage;
The second air-fuel ratio control means executes the second air-fuel ratio control only when the output of the oxygen concentration detection means is approximately in the range of 0.3 to 0.5 (V). The catalyst deterioration detection device according to claim 3. The first air-fuel ratio control means sets the air-fuel ratio to be slightly rich until the integrated air amount taken in by the internal combustion engine reaches a predetermined amount after the first catalyst enters the limit release state. continue,
The second air-fuel ratio control means is only when the output of the oxygen concentration detection means is in a range of approximately 0.3 to 0.5 (V) after the integrated air amount reaches the predetermined amount. The catalyst deterioration detection device according to claim 7, wherein the second air-fuel ratio control is executed.

Images