JP4799495B2 - Internal combustion engine catalyst deterioration judgment system - Google Patents

Description

  The present invention relates to a catalyst deterioration determination system for an internal combustion engine.

  As regulations on harmful components (for example, HC, CO, NOx) in exhaust discharged from an internal combustion engine of an automobile are strengthened, a technology for purifying harmful components in exhaust with an exhaust purification catalyst has been proposed. Here, as a typical exhaust purification catalyst, there is a three-way catalyst that simultaneously processes NOx reduction and HC and CO oxidation.

The three-way catalyst has an oxygen storage capacity (OSC: Oxygen Storage Capacity), and has a property of storing and releasing oxygen in exhaust gas. More specifically, when the exhaust air-fuel ratio flowing into the three-way catalyst is a rich air-fuel ratio, oxygen stored in the three-way catalyst is released, and HC and CO in the exhaust are oxidized. On the other hand, when the exhaust air-fuel ratio is a lean air-fuel ratio, NOx is reduced by storing oxygen in the three-way catalyst. “Occlusion” includes the concept of adsorption and absorption.

  When the exhaust purification catalyst having the oxygen storage capacity as described above deteriorates, the oxygen storage capacity decreases and the exhaust purification capacity deteriorates. Since there is a correlation between the oxygen storage capacity and the degree of deterioration of the catalyst, there has been proposed a technique for performing deterioration determination control for determining whether or not the catalyst is deteriorated based on the oxygen storage capacity of the exhaust purification catalyst ( For example, see Patent Document 1.)

  Patent Document 1 performs air-fuel ratio control in which the exhaust air-fuel ratio flowing into the exhaust purification catalyst is periodically reversed from the rich side to the lean side or from the lean side to the rich side. That is, it is determined whether or not the catalyst has deteriorated based on the length of the period from when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is reversed until the air-fuel ratio of the exhaust gas flowing out from the catalyst is reversed. .

However, since the operation state of the internal combustion engine changes according to the driver's request even during the air-fuel ratio control, the change in the operation state may affect the air-fuel ratio control. That is, there is a possibility that the determination accuracy related to the catalyst deterioration determination control is deteriorated. In addition, drivability may be deteriorated if the air-fuel ratio control is forcibly executed regardless of the operating state of the internal combustion engine.
JP-A-6-74025 JP 2006-275007 A Japanese Patent No. 2557477 JP-A-2005-98205 JP-A-2005-140011 JP 2002-188436 A

  The present invention has been made in view of the above-described prior art, and an object of the present invention is to accurately determine the degree of deterioration of the exhaust purification catalyst and to determine the state of operation of the internal combustion engine when determining the degree of deterioration. It is to provide a technology capable of suppressing deterioration of drivability due to influence.

To achieve the above object, the internal combustion engine catalyst deterioration determination system according to the present invention employs the following means. That is,
An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine and having an oxygen storage capacity;
When the exhaust purification catalyst has a rich atmosphere and the fuel cut of the internal combustion engine is executed, the catalyst bed temperature of the exhaust purification catalyst is measured, and oxygen in the exhaust is stored in the exhaust purification catalyst Occlusion reaction heat detection means for detecting the generated occlusion reaction heat;
A deterioration degree determination means for determining a deterioration degree of the exhaust purification catalyst based on a detection timing of the storage reaction heat by the storage reaction heat detection means;
It is characterized by providing.

  In the present invention, when the fuel cut (fuel cut) is executed in a state where the exhaust purification catalyst is in a rich atmosphere, the degree of deterioration of the exhaust purification catalyst is determined. Here, the inside of the exhaust purification catalyst being in a rich atmosphere means a state in which the inside of the exhaust purification catalyst is in a rich atmosphere. For example, when the load (torque) of the internal combustion engine increases, the rich purification atmosphere A state in which the oxygen stored in the exhaust purification catalyst is released by the flow of the exhaust gas at the fuel ratio into the exhaust purification catalyst, and the oxygen storage amount is substantially zero can be exemplified. The degree of deterioration of the exhaust purification catalyst means the degree of deterioration of the exhaust purification catalyst.

  In this state, for example, when a fuel cut is performed, such as when a deceleration request is made to the internal combustion engine, exhaust having an oxygen concentration substantially equal to air flows into the exhaust purification catalyst. Then, by shifting from the state where the rich air-fuel ratio exhaust gas flows into the exhaust purification catalyst to the state where exhaust gas containing more excess oxygen flows, excess oxygen contained in the exhaust gas is reduced in the exhaust purification catalyst. Oxygen storage reaction occurs.

  Here, since the oxygen storage reaction is an exothermic reaction, the catalyst bed temperature at the position where the oxygen storage reaction occurs in the exhaust purification catalyst increases. In the present invention, before the fuel cut is performed, the exhaust purification catalyst is in a rich atmosphere, so an oxygen storage reaction first occurs only in the vicinity of the front end of the catalyst.

  When the oxygen storage amount in the vicinity of the front end portion increases, it becomes difficult to store more oxygen only in the vicinity of the front end portion. As a result, the exhaust gas containing excess oxygen passes through the region in the vicinity of the front end portion to the downstream side, and an oxygen storage reaction occurs in a more downstream region in the exhaust purification catalyst. That is, the location where the oxygen storage reaction occurs shifts from the upstream side to the downstream side of the exhaust purification catalyst with time.

  Here, the oxygen storage capacity of the exhaust purification catalyst is a concept representing the high oxygen storage capacity of the catalyst. Further, the oxygen storage capacity in the present invention may mean the oxygen storage capacity related to the entire exhaust purification catalyst, or may mean the oxygen storage capacity related to a partial region of the catalyst. And the higher the oxygen storage capacity of the exhaust purification catalyst is, the slower the speed at which the location where the oxygen storage reaction occurs is shifted to the downstream side. Therefore, in the present invention, the above-described occlusion reaction heat is detected by the occlusion reaction heat detection means, and the degree of deterioration of the exhaust purification catalyst is determined based on the detection timing of this occlusion reaction heat.

  Here, the oxygen storage capacity tends to decrease as the degree of deterioration of the exhaust purification catalyst increases. Therefore, in the present invention, it is determined that the oxygen storage capacity of the exhaust purification catalyst is higher as the detection time of the heat of storage reaction is delayed. That is, it is determined that the degree of deterioration of the exhaust purification catalyst is low. On the other hand, it is determined that the earlier the detection timing of the occlusion reaction heat is, the lower the oxygen storage capacity of the exhaust purification catalyst is, and the higher the degree of deterioration of the exhaust purification catalyst is. That is, according to the present invention, the degree of deterioration of the exhaust purification catalyst can be suitably determined.

In the present invention, when the operating state of the internal combustion engine is changed, the timing at which the rich air-fuel ratio exhaust gas flows into the exhaust gas purification catalyst shifts to a state where exhaust gas containing a large amount of excess oxygen flows. Therefore, it is not necessary to execute the control related to the exhaust air-fuel ratio. Therefore, when determining the degree of deterioration of the exhaust purification catalyst, there is no possibility of affecting the operating state of the internal combustion engine, and deterioration of drivability can be suppressed.

  Further, it has been found from the earnest research by the present inventors that the generation timing of the oxygen storage reaction falls within the range of about 1 second after the fuel cut is performed on the internal combustion engine. That is, according to the present invention, the determination relating to the degree of deterioration can be completed in a short period of time until the operating state returns from the fuel cut state. Therefore, since the degree of deterioration of the catalyst can be determined without being affected by the operating state of the internal combustion engine, it is possible to prevent the determination accuracy from deteriorating.

  Here, the deterioration degree determination means in the present invention may estimate the oxygen storage capacity of the exhaust purification catalyst based on the detection time of the storage reaction heat. For example, for each detection position of the occlusion reaction heat in the exhaust flow direction of the exhaust purification catalyst (position of the occlusion reaction heat detection means), the relationship between the detection timing of the occlusion reaction heat and the oxygen storage capacity of the exhaust purification catalyst is experimentally determined in advance. The oxygen storage capacity of the exhaust purification catalyst may be estimated based on the detection timing of the storage reaction heat.

  In the present invention, the degree of deterioration of the exhaust purification catalyst may be determined based on the estimated oxygen storage capacity. That is, for example, when the oxygen storage capacity of the exhaust purification catalyst is not more than a predetermined threshold value, it may be determined that the catalyst has deteriorated. The threshold here is the oxygen storage capacity when the degree of deterioration increases as the catalytic function of the exhaust purification catalyst decreases, and may be obtained experimentally in advance. Further, instead of determining whether or not the catalyst has deteriorated, the degree of deterioration of the exhaust purification catalyst may be determined in more detail by setting a plurality of threshold values.

  Here, it is considered that the oxygen storage capacity of the exhaust purification catalyst is affected by the difference in the catalyst bed temperature of the catalyst. For example, the oxygen storage capacity of the exhaust purification catalyst is higher when the catalyst bed temperature is higher (for example, 600 ° C.) than when the catalyst bed temperature is lower (for example, 400 ° C.). Therefore, the deterioration degree determination means in the present invention may further determine the deterioration degree of the exhaust purification catalyst based on the catalyst bed temperature measured by the occlusion reaction heat detection means.

  For example, when the oxygen storage capacity is estimated based on the detection timing of the heat of storage reaction, the oxygen storage capacity may be corrected according to the catalyst bed temperature. According to the present invention, the degree of deterioration of the exhaust purification catalyst can be estimated more accurately even if the catalyst bed temperature of the exhaust purification catalyst is greatly different.

  In the present invention, a lean determination means for determining whether or not the inflow exhaust air-fuel ratio is a lean air-fuel ratio may be further provided. Thereby, it is possible to accurately grasp the timing at which the oxygen storage reaction starts at the front end portion of the exhaust purification catalyst. The deterioration degree determination means may determine the deterioration degree of the exhaust purification catalyst based on a reaction heat detection period from when it is determined that the inflow exhaust air-fuel ratio is a lean air-fuel ratio until the occlusion reaction heat is detected. good.

  That is, the reaction heat detection period means a difference in the timing at which the oxygen storage reaction occurs between the front end portion of the exhaust purification catalyst and the position where the storage reaction heat detection means is disposed. Therefore, it means that the longer the reaction heat detection period, the greater the oxygen storage amount (hereinafter also referred to as “upstream storage amount”) in the region upstream of the position at which the storage reaction heat detection means is disposed. Therefore, in the present invention, a threshold value may be set for the upstream storage amount, and the degree of deterioration of the exhaust purification catalyst may be determined based on the magnitude relationship with the threshold value.

Further, since the upstream storage amount and the oxygen storage capacity of the exhaust purification catalyst are correlated, the oxygen storage capacity is estimated based on the upstream storage amount, and the deterioration degree is determined based on the estimated oxygen storage capacity. good. Therefore, in the present invention, an upstream storage amount calculating means for calculating the upstream storage amount based on the reaction heat detection period may be further provided. For example, the upstream storage amount may be calculated based on the integrated value of the oxygen amount contained in the exhaust gas flowing into the exhaust purification catalyst during the reaction heat detection period.

  The deterioration degree determining means in the present invention estimates the oxygen storage capacity of the exhaust purification catalyst as a whole based on the volume ratio from the front end of the catalyst to the arrangement position and the upstream storage amount with respect to the entire exhaust purification catalyst. Also good. That is, the oxygen storage capacity of the entire exhaust purification catalyst can be accurately estimated by dividing the upstream storage amount by the volume ratio. Thereby, the deterioration degree of the exhaust purification catalyst can be suitably determined.

  In the present invention, a plurality of occlusion reaction heat detection means may be provided in the exhaust flow direction of the exhaust purification catalyst. The deterioration degree determination means determines the deterioration degree of the exhaust purification catalyst based on a reaction heat detection delay period that is a difference in the detection timing of the occlusion reaction heat detected by the two selected occlusion reaction heat detection means. You may judge. The two occlusion reaction heat detection means can be arbitrarily selected from a plurality.

  Here, as the reaction heat detection delay period is longer, the oxygen storage amount (hereinafter referred to as “intermediate portion storage amount”) in the region sandwiched between the two storage reaction heat detection means (hereinafter also referred to as “detection position intermediate portion”). "Also means"). Therefore, in the present invention, a threshold value may be set for the intermediate storage amount, and the degree of deterioration of the exhaust purification catalyst may be determined based on the magnitude relationship with this threshold value.

  In addition, since the intermediate storage amount and the oxygen storage capacity of the exhaust purification catalyst are correlated, the oxygen storage capacity of the exhaust purification catalyst is estimated based on the intermediate storage amount, and the degree of deterioration is determined based on the estimated oxygen storage capacity. You may judge. Therefore, in the present invention, an intermediate storage amount calculating means for calculating the intermediate storage amount based on the detection delay period may be further provided. For example, the intermediate storage amount can be calculated with high accuracy by multiplying the integral value of the amount of oxygen contained in the exhaust gas flowing into the exhaust purification catalyst during the detection delay period and the detection delay period.

  Then, the deterioration degree determination means may estimate the oxygen storage capacity of the entire exhaust purification catalyst based on the volume ratio of the detection position intermediate portion relative to the entire exhaust purification catalyst and the intermediate storage amount. That is, the oxygen storage capacity of the entire exhaust purification catalyst can be calculated by dividing the intermediate storage amount by the volume ratio. Thereby, the deterioration degree of the exhaust purification catalyst can be suitably determined.

  In the present invention, the intermediate storage amount may be calculated for each intermediate detection position. According to this, it is possible to calculate the oxygen storage capacity related to the entire exhaust purification catalyst by adding up the storage amounts of the respective intermediate portions, and to suitably determine the degree of deterioration of the exhaust purification catalyst. Further, since the degree of deterioration for each detection position intermediate portion can be determined, the distribution of the degree of deterioration of the exhaust purification catalyst in the exhaust flow direction can be acquired.

  In the present invention, the degree of deterioration of the exhaust purification catalyst can be accurately determined. Further, it is possible to suppress the deterioration of drivability due to the influence on the operation state of the internal combustion engine when determining the degree of deterioration.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. It should be noted that the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the technical scope of the invention only to those unless otherwise specified. is not.

  Here, the case where the present invention is applied to a gasoline engine for driving a vehicle will be described as an example. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 according to the present embodiment, and its intake / exhaust system and control system. In FIG. 1, the inside of the internal combustion engine 1 is omitted.

  An intake passage 2 through which intake air flowing into the internal combustion engine 1 flows is connected to the internal combustion engine 1. The internal combustion engine 1 is connected to an exhaust passage 3 through which exhaust from the internal combustion engine 1 flows, and the exhaust passage 3 is connected downstream to a muffler (not shown). In the middle of the exhaust passage 3, a three-way catalyst 4 for purifying exhaust from the internal combustion engine 1 is provided. Upstream of the three-way catalyst 4 in the exhaust passage 3, the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 4 (hereinafter referred to as “inflow exhaust air-fuel ratio”) AFin and the three-way catalyst 4 flowed out. An upstream air-fuel ratio sensor 5 and a downstream air-fuel ratio sensor 6 are provided for detecting an air-fuel ratio of exhaust (hereinafter referred to as “outflow exhaust air-fuel ratio”) AFout. The three-way catalyst 4 is provided with a thermocouple 7 that detects the catalyst bed temperature of the three-way catalyst 4.

The three-way catalyst 4 has an oxygen storage capacity (OSC: Oxygen) containing ceria (CeO ₂ ) or the like as a component.
Storage capacity), and has the property of storing and releasing oxygen in the exhaust.
That is, when the inflowing exhaust air-fuel ratio AFin is a rich air-fuel ratio, oxygen stored in the three-way catalyst 4 is released, so that HC and CO in the exhaust are oxidized. On the other hand, when the inflowing exhaust air-fuel ratio AFin is a lean air-fuel ratio, NOx is reduced by storing oxygen in the three-way catalyst 4. In this embodiment, the three-way catalyst 4 corresponds to the exhaust purification catalyst in the present invention.

  In the exhaust purification system configured as described above, the exhaust discharged from the internal combustion engine 1 is discharged into the atmosphere through the muffler after the three-way catalyst 4 purifies the harmful substances (CO, HC, NOx) in the exhaust. The

The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1 and the intake / exhaust system. The ECU 10 is a unit that controls the operating state of the internal combustion engine 1 and performs deterioration degree determination control for determining the deterioration degree of the three-way catalyst 4 described later.

  In addition to sensors related to control of the operating state of the internal combustion engine 1 such as a crank position sensor and an accelerator position sensor (not shown), the upstream air / fuel ratio sensor 5, the downstream air / fuel ratio sensor 6, and the thermocouple 7 are electrically connected to the ECU 10. These output signals are input to the ECU 10.

  The ECU 10 includes a CPU, a ROM, a RAM, and the like. The ROM stores a program for performing various controls of the internal combustion engine 1 and a map storing data.

  Next, the deterioration degree determination control in this embodiment will be described. It is known that the oxygen storage capacity of the three-way catalyst 4 decreases as the degree of deterioration of the catalyst increases. Since the three-way catalyst 4 purifies harmful substances contained in the exhaust gas by the oxygen storage / release action in the exhaust gas, the exhaust gas purifying performance deteriorates when the oxygen storage capacity decreases. Therefore, in this embodiment, the deterioration degree determination control for the three-way catalyst 4 is executed.

In the present embodiment, the deterioration degree determination control is performed when the internal combustion engine 1 is subjected to the fuel cut F / C when the three-way catalyst 4 is in a rich atmosphere. FIG. 2 is an explanatory diagram of the atmosphere state inside the catalyst and the exhaust air / fuel ratio flowing into and out of the catalyst when the deterioration degree determination control in the present embodiment is performed.

  FIG. 2A shows a state in which the fuel injection amount is increased as the load (torque) of the internal combustion engine 1 increases, and the inflow exhaust air-fuel ratio AFin is maintained at the rich air-fuel ratio AFrich. In this state, oxygen stored in the three-way catalyst 4 is released into the exhaust gas, and when this state is maintained, the stored oxygen amount Co in the entire catalyst becomes substantially zero. As a result, the entire area in the three-way catalyst 4 becomes a rich atmosphere (illustrated by hatching in the figure), and the exhaust of the rich air-fuel ratio AFrich flows out from the three-way catalyst 4.

  FIG. 2B shows a state after the inflow exhaust air-fuel ratio AFin has shifted from the rich air-fuel ratio AFrich to the lean air-fuel ratio AFlean by executing the fuel cut F / C in the internal combustion engine 1. In the present embodiment, the oxygen concentration of the exhaust gas at the lean air-fuel ratio AFlean may be substantially equal to the oxygen concentration of air. When the inflowing exhaust air-fuel ratio AFin becomes the lean air-fuel ratio AFlean, excess oxygen in the exhaust is first stored in the front end portion of the three-way catalyst 4.

  However, if it becomes difficult to store excess oxygen in the exhaust only with the front end portion of the three-way catalyst 4, oxygen is stored in the downstream portion of the three-way catalyst 4 in the exhaust flow direction. Here, when the occurrence location of the oxygen storage reaction is illustrated by X1, the oxygen storage reaction hardly occurs in the upstream region and the downstream region from the position X1. That is, in the region upstream of the position X1 (hereinafter referred to as “upstream region”) Aup, oxygen has already been stored to the limit where it can be stored, and more oxygen is stored in the upstream region Aup. I can't. Further, in the region downstream of the position X1 (hereinafter referred to as “downstream region”) Allow, excess oxygen in the exhaust gas is stored at the position X1, so that no oxygen storage reaction occurs.

  As a result, the three-way catalyst 4 is maintained in a rich atmosphere in the downstream region Alow, and the outflow exhaust air-fuel ratio AFout is still maintained at the rich air-fuel ratio AFrich. And when time passes further and it transfers to the state of FIG.2 (c), the generation | occurrence | production location of oxygen storage reaction will transfer to X2 more downstream. As a result, the region maintained in the rich atmosphere is reduced as compared with the state of FIG. Then, after the oxygen of the maximum oxygen storage amount Comax that can be stored by the whole of the three-way catalyst 4 is finally stored, as shown in FIG. 2 (d), the outflow exhaust air-fuel ratio AFout becomes lean from the rich air-fuel ratio AFrich. Transition to the fuel ratio AFlean.

  Here, paying attention to the catalyst bed temperature THc of the three-way catalyst 4, since the oxygen storage reaction is an exothermic reaction, the catalyst bed temperature THc increases at the location where the oxygen storage reaction occurs. More specifically, since the amount of heat generated by the oxygen storage reaction is taken away by the exhaust, the catalyst bed temperature THc increases only for a short time. Since the location where the oxygen storage reaction occurs gradually shifts from the upstream side to the downstream side of the three-way catalyst 4, the location where the storage reaction heat THca occurs in the three-way catalyst 4 also shifts from the upstream side toward the downstream side. become.

  Therefore, in the deterioration degree determination control according to the present embodiment, after the fuel cut F / C is performed on the internal combustion engine 1 in a state where the three-way catalyst 4 is in a rich atmosphere, the occlusion is performed based on the output value of the thermocouple 7. The heat of reaction THca is detected. The maximum oxygen storage amount Comax is estimated based on the detection timing of the storage reaction heat THca, and the degree of deterioration of the three-way catalyst 4 is determined. In this embodiment, the thermocouple 7 corresponds to the occlusion reaction heat detection means in the present invention.

  Here, FIG. 3 shows ON / OFF (a) of the fuel cut F / C, the inflow exhaust air-fuel ratio AFin (b), and the catalyst bed temperature THc (c) when performing the deterioration degree determination control in the present embodiment. It is a time chart which illustrated time transition.

  As shown in FIG. 3A, at time t0, the fuel cut F / C is ON, that is, the fuel cut F / C is executed. Here, it is assumed that the state shown in FIG. That is, the entire three-way catalyst 4 has a rich atmosphere, and the inflow exhaust air-fuel ratio AFin and the outflow exhaust air-fuel ratio AFout are maintained at the rich air-fuel ratio AFrich.

  When fuel cut F / C is executed at time t0, the ECU 10 detects the inflow exhaust air-fuel ratio AFin based on the output value of the upstream air-fuel ratio sensor 5, and whether the inflow exhaust air-fuel ratio AFin is the lean air-fuel ratio AFlean. Determine whether or not. In this embodiment, the ECU 10 corresponds to the lean determination means in the present invention.

  At time t1, when the ECU 10 determines that the inflow exhaust air-fuel ratio AFin has shifted to the lean air-fuel ratio AFlean, the ECU 10 detects the occlusion reaction heat THca based on the output value of the thermocouple 7. Then, a reaction heat detection period Δt corresponding to a period from time t1 when it is determined that the inflow exhaust air-fuel ratio AFin has shifted to the lean air-fuel ratio AFlean to time t2 when the occlusion reaction heat THca is detected is measured.

  Here, FIG. 4 is a diagram illustrating the relationship between the reaction heat detection period Δt and the maximum oxygen storage amount Comax when the deterioration degree determination control in the present embodiment is executed. In this embodiment, the maximum oxygen storage amount Comax is estimated with reference to a map storing the relationship between the reaction heat detection period Δt and the maximum oxygen storage amount Comax as shown in the figure. In the present embodiment, it is estimated that the maximum oxygen storage amount Comax increases as the reaction heat detection period Δt increases. The maximum oxygen storage amount Comax corresponds to the oxygen storage capacity in the present invention.

  Here, since the relationship between the reaction heat detection period Δt and the maximum oxygen storage amount Comax is different depending on the arrangement position of the thermocouple 7 in the exhaust flow direction of the three-way catalyst 4, the above map is previously set according to the arrangement position of the thermocouple 7. Build experimentally. In this embodiment, the reaction heat detection period Δt corresponds to the reaction heat detection period in the present invention.

  Further, it is considered that the maximum oxygen storage amount Comax varies depending on the difference in the catalyst bed temperature THc of the three-way catalyst 4. When the catalyst bed temperature THc is low (for example, 400 ° C.), the maximum oxygen storage amount Comax of the three-way catalyst 4 increases when the catalyst bed temperature THc is high (for example, 600 ° C.).

  Therefore, in this embodiment, the maximum oxygen storage amount Comax may be corrected based on the catalyst bed temperature THc when the deterioration degree determination control is executed. Specifically, the relationship between the reaction heat detection period Δt, the catalyst bed temperature THc, and the maximum oxygen storage amount Comax is experimentally obtained in advance, and the maximum oxygen storage is based on the reaction heat detection period Δt and the catalyst bed temperature THc. The quantity Comax may be estimated. Thereby, even if the catalyst bed temperature THc of the three-way catalyst 4 is different every time the deterioration degree determination control is executed, the maximum oxygen storage amount Comax can be accurately estimated according to the catalyst bed temperature THc.

  As described above, when the maximum oxygen storage amount Comax of the three-way catalyst 4 is estimated, the ECU 10 determines whether or not the maximum oxygen storage amount Comax is equal to or less than the reference oxygen storage amount Cob. The reference oxygen storage amount Cob is an oxygen storage amount when the degree of deterioration increases as the catalytic function of the three-way catalyst 4 decreases, and is determined experimentally in advance. When the maximum oxygen storage amount Comax is equal to or less than the reference oxygen storage amount Cob, it is determined that the three-way catalyst 4 has deteriorated. In that case, the driver may be notified by a warning display or the like. In the present embodiment, the ECU 10 that executes the deterioration degree determination control corresponds to the deterioration degree determination means in the present invention.

As described above, the example in which the maximum oxygen storage amount Comax is estimated based on the map as shown in FIG. 4 has been described. However, the present invention is not limited to this. For example, reaction heat detection period Δ
The maximum oxygen storage amount Comax may be calculated based on t.

  That is, the reaction heat detection period Δt in this example can be regarded as a period during which oxygen can be occluded in the region upstream of the position where the thermocouple 7 is arranged. Therefore, in this embodiment, the upstream oxygen storage amount Coup, which is the amount of oxygen stored in the region upstream of the arrangement position of the thermocouple 7, is calculated based on the reaction heat detection period Δt. More specifically, the upstream oxygen storage amount Coup is calculated by multiplying the integrated value of the oxygen amount contained in the exhaust gas flowing into the three-way catalyst 4 over the reaction heat detection period Δt by the reaction heat detection period Δt. The integrated value of the oxygen amount is calculated based on the output value of an air flow meter (not shown). The amount of oxygen is obtained by multiplying the amount of intake air by the oxygen partial pressure.

  Then, the maximum oxygen storage amount Comax is calculated by dividing the upstream oxygen storage amount Coup by the volume ratio of the upstream region Aup to the entire three-way catalyst 4. In this embodiment, the upstream oxygen storage amount Coup corresponds to the upstream storage amount in the present invention, and the ECU 10 for calculating the upstream oxygen storage amount Coup corresponds to the upstream storage amount calculation means.

  In this embodiment, the oxygen storage capacity of the three-way catalyst 4 is estimated or calculated based on the reaction heat detection period Δt. The degree of deterioration may be determined. For example, it may be determined that the three-way catalyst 4 has deteriorated when the reaction heat detection period Δt is shorter than a predetermined threshold.

  Hereinafter, the catalyst deterioration determination control executed by the ECU 10 will be described with reference to the flowchart of FIG. FIG. 5 is a flowchart showing a deterioration degree determination control routine in this embodiment. This routine is a program stored in the ROM in the ECU 10, and is executed every predetermined period.

  When this routine is executed, first, in step S101, it is determined based on the output value of the upstream air-fuel ratio sensor 5 whether or not the inflow exhaust air-fuel ratio AFin is the rich air-fuel ratio AFrich. If the determination is affirmative, it is determined that the oxygen stored in the three-way catalyst 4 has been released or that all the oxygen has already been released, and the process proceeds to step S102. If a negative determination is made, it is determined that oxygen is being occluded in the three-way catalyst 4, and it is determined that the condition for determining the degree of deterioration of the catalyst is not satisfied, and this routine is temporarily terminated.

  In step S102, it is determined based on the output value of the downstream air-fuel ratio sensor 6 whether or not the outflow exhaust air-fuel ratio AFout is the rich air-fuel ratio AFrich. If an affirmative determination is made in this step, it is determined that the entire interior of the three-way catalyst 4 has a rich atmosphere, and the process proceeds to step S103. On the other hand, if a negative determination is made, it is determined that the oxygen stored in the three-way catalyst 4 remains, and this routine is temporarily terminated.

  In step S103, it is determined whether or not a fuel cut F / C has been performed on the internal combustion engine 1. If a positive determination is made in this step, the process proceeds to step S014. On the other hand, if a negative determination is made, the process of this step is repeatedly executed until the fuel cut F / C is executed. Alternatively, when a negative determination is made in this step, this routine may be temporarily exited.

  In step S104, it is determined based on the output value of the upstream air-fuel ratio sensor 5 whether or not the inflow exhaust air-fuel ratio AFin has shifted from the rich air-fuel ratio AFrich to the lean air-fuel ratio AFlean. If an affirmative determination is made in this step, it is determined that oxygen has begun to be stored in the three-way catalyst 4, and the process proceeds to step S105. On the other hand, if a negative determination is made, the process of this step is repeatedly executed until an affirmative determination is made.

  In step S105, detection of the catalyst bed temperature THc is started based on an output signal from the thermocouple 7, and measurement of the reaction heat detection period Δt is started. When the process of this step is finished, the process proceeds to step S106.

  In step S106, it is determined whether or not the occlusion reaction heat THca is detected based on the output signal from the thermocouple 7. If a positive determination is made in this step, the process proceeds to step S107. On the other hand, if a negative determination is made, the process returns to step S105, and measurement of the reaction heat detection period Δt is continued.

  In step S107, the measurement of the reaction heat detection period Δt ends, and the maximum oxygen storage amount Comax is calculated based on the reaction heat detection period Δt acquired in step S105 in this step. Since the calculation of the maximum oxygen storage amount Comax is already described, a detailed description is omitted.

  In step S108, the degree of deterioration of the three-way catalyst 4 is determined based on the calculated maximum oxygen storage amount Comax. That is, the above determination is made based on whether or not the maximum oxygen storage amount Comax is equal to or less than the reference oxygen storage amount Cob. When the maximum oxygen storage amount Comax is equal to or less than the reference oxygen storage amount Cob, it is determined that the three-way catalyst 4 has deteriorated, and the driver is notified of the deterioration by a warning light or the like. On the other hand, when the maximum oxygen storage amount Comax is larger than the reference oxygen storage amount Cob, it is determined that the three-way catalyst 4 has not deteriorated. When the processing of this step is finished, this routine is once ended.

  As described above, according to the deterioration degree determination control in the present embodiment, the maximum oxygen storage amount Comax can be accurately calculated based on the reaction heat detection period Δt, so it is preferable whether or not the three-way catalyst 4 is deteriorated. Can be determined. Here, in this embodiment, the reaction heat detection period Δt may be measured a plurality of times, and the averaging process of these values may be executed. And based on the average value of this reaction heat detection period (DELTA) t, you may determine whether the three-way catalyst 4 has deteriorated.

  Further, it has been found by the present inventors' extensive research that the reaction heat detection period Δt is approximately in the range of about 1 second. That is, according to the deterioration degree determination control in the present embodiment, the catalyst deterioration determination can be completed in a short period of time until the operating state of the internal combustion engine 1 returns from the fuel cut state. That is, the accuracy of the determination control can be improved without being affected by the operating state of the internal combustion engine 1.

  In addition, since the inflowing exhaust air-fuel ratio AFin shifts from the rich air-fuel ratio AFrich to the lean air-fuel ratio AFlean as the operating state of the internal combustion engine 1 changes, it is not necessary to perform control related to the air-fuel ratio. That is, there is no possibility that drivability deteriorates when performing the deterioration degree determination control.

  Next, Example 2 will be described with reference to FIGS. The hardware configuration of the catalyst deterioration determination system for the internal combustion engine in the present embodiment is different from that in the first embodiment in that a plurality of thermocouples are provided in the exhaust flow direction of the three-way catalyst 4, and the other configurations are the same. is there.

FIG. 6 is a diagram illustrating a first arrangement example of thermocouples in the three-way catalyst 4 according to the present embodiment. In the first arrangement example, the three-way catalyst 4 is arranged on the upstream side, the central part, and the downstream side in the exhaust flow direction. The upstream thermocouple 7a, the central thermocouple 7b, and the downstream thermocouple 7c are referred to from the upstream side, and their positions in the exhaust flow direction are indicated by Y1, Y2, and Y3 in the figure. These thermocouples (7a to 7c) are connected to the ECU 10 via electric wiring, and these output signals are input to the ECU 10.

  As described in Example 1, since the oxygen storage reaction shifts from the upstream side to the downstream side of the three-way catalyst 4, the detection timing of the storage reaction heat THca is different for each thermocouple. Specifically, the occlusion reaction heat THca is detected in the order of the upstream thermocouple 7a, the central thermocouple 7b, and the downstream thermocouple 7c.

  In the deterioration degree determination control according to the present embodiment, the difference in detection timing of the occlusion reaction heat THca detected by two thermocouples arbitrarily selected from the upstream thermocouple 7a, the central thermocouple 7b, and the downstream thermocouple 7c. Based on a certain reaction heat detection delay period Δtd, the degree of deterioration of the three-way catalyst 4 is determined.

  In the deterioration degree determination control according to the present embodiment, the occlusion reaction is performed when the inside of the three-way catalyst 4 is in a rich atmosphere and the fuel cut F / C is executed on the internal combustion engine 1. The point that the heat THca is detected is the same as that in the first embodiment. Here, considering the downstream thermocouple 7c with respect to the central thermocouple 7b as an example, the ECU 10 detects the occlusion reaction heat THca generated at each position based on at least the output values of the central thermocouple 7b and the downstream thermocouple 7c. To do. The central thermocouple 7b and the downstream thermocouple 7c correspond to two occlusion reaction heat detection means selected from the plurality.

  A period from when the occlusion reaction heat THca is detected at the position of the central thermocouple 7b to when the occlusion reaction heat THca is detected at the position of the downstream thermocouple 7c is obtained as a reaction heat detection delay period Δtd. In this embodiment, the reaction heat detection delay period Δtd corresponds to the reaction heat detection delay period in the present invention.

  Here, the reaction heat detection delay period Δtd was able to continue occlusion of oxygen in the region sandwiched between the central thermocouple 7b and the downstream thermocouple 7c (hereinafter referred to as “region between the downstream thermocouples”) Amidlow. Means period. Then, it is determined that the maximum oxygen storage amount Comax of the three-way catalyst 4 as a whole increases because the oxygen storage amount Co in the downstream thermocouple region Amidlow increases as the reaction heat detection delay period Δtd increases.

  In this embodiment, the relationship between the reaction heat detection delay period Δtd and the maximum oxygen storage amount Comax is experimentally obtained in advance, and the maximum oxygen storage amount Comax is estimated based on the reaction heat detection delay period Δtd. That is, it is estimated that the maximum oxygen storage amount Comax increases as the reaction heat detection delay period Δtd increases. Then, it is determined whether or not the maximum oxygen storage amount Comax is equal to or less than the reference oxygen storage amount Cob. If the determination is affirmative, it is determined that the three-way catalyst 4 has deteriorated.

  In this embodiment, the downstream thermocouple storage amount Comidlow, which is the amount of oxygen stored in the downstream thermocouple region Amidlow, is calculated, and the maximum oxygen storage amount is calculated based on the downstream thermocouple storage amount Comidlow. The amount Comax may be calculated.

More specifically, the downstream inter-thermocouple storage amount Comidlow is calculated by multiplying the integral value of the oxygen amount contained in the exhaust gas flowing into the three-way catalyst 4 over the reaction heat detection delay period Δtd by the reaction heat detection delay period Δtd. Is done. Then, the storage amount Comidlow between the downstream thermocouples is divided by the volume ratio of the downstream thermocouple region Amidlow with respect to the entire three-way catalyst 4 to calculate the maximum oxygen storage amount Comax.

In the present embodiment, the downstream-side thermocouple storage amount Comidlow corresponds to the intermediate storage amount in the present invention, and the ECU 10 that calculates the downstream-side thermocouple storage amount Comidlow corresponds to the intermediate storage amount calculation means.

  In the above example, the reaction heat detection delay period Δtd is calculated as the downstream thermocouple storage amount Comidlow stored in the downstream thermocouple region Amidlow, but the present invention is not limited to this. For example, a period from when the occlusion reaction heat THca is detected by the upstream thermocouple 7a to when it is detected by the central thermocouple 7b is obtained, and this period may be used as the reaction heat detection delay period Δtd.

  In that case, the region between the upstream thermocouples 7a and the central thermocouple 7b (hereinafter referred to as “the region between the upstream thermocouples”) the amount of oxygen stored in the upstream thermocouple, which is the amount of oxygen stored in Aupmid. Coupmid may be calculated, and the maximum oxygen storage amount Comax may be calculated based on the upstream thermocouple storage amount Coupmid and the volume ratio of the upstream thermocouple region Aupmid to the entire three-way catalyst 4. Alternatively, the amount of oxygen stored in the region sandwiched between the upstream thermocouple 7a and the downstream thermocouple 7c may be calculated, and various variations can be employed.

  In addition, the number of thermocouples arranged in the three-way catalyst 4 in the present embodiment may be plural, and the first arrangement example shown in FIG. 6 is merely an example, and within the scope not departing from the gist of the present invention. The number of thermocouples and the arrangement position can be variously changed.

  Next, a modified example of the deterioration degree determination control of this embodiment will be described with reference to FIG. FIG. 7 is a diagram illustrating a second arrangement example of thermocouples in the three-way catalyst 4 according to the present embodiment. In the second arrangement example, a total of four thermocouples are arranged at the front end, the middle, and the rear end of the three-way catalyst 4. These thermocouples are referred to as a first thermocouple 7d to a fourth thermocouple 7g from the upstream side. And the area | region pinched | interposed by each thermocouple of the 1st thermocouple 7d-the 4th thermocouple 7g is called 1st area | region A1, 2nd area | region A2, and 3rd area | region A3 from the upstream.

  In this modification, the oxygen storage amount in each of the first region A1 to the third region A3 is calculated, and the maximum oxygen storage amount Comax is calculated by adding them. That is, based on each detection time of the occlusion reaction heat THca detected by each thermocouple of the first thermocouple 7d to the fourth thermocouple 7g, a reaction heat detection delay period Δtd between the thermocouples is acquired, and the first The oxygen storage amounts in the region A1, the second region A2, and the third region A3 are calculated. Then, the maximum oxygen storage amount Comax is calculated by adding the respective oxygen storage amounts. Thereby, the deterioration degree of the three-way catalyst 4 can be determined suitably.

  Further, as in the present modification, the oxygen in each region (that is, the first region A1, the second region A2, and the third region A3) when the three-way catalyst 4 is divided into a plurality of regions in the exhaust flow direction. Since the amount of occlusion can be calculated, the difference in the degree of deterioration of the three-way catalyst 4 in the exhaust flow direction can be acquired. For example, it can be determined whether the three-way catalyst 4 is partially deteriorated by comparing the oxygen storage amount per unit volume in each region. Thereby, it is possible to carry out the deterioration degree determination control with higher accuracy.

1 is a diagram illustrating a schematic configuration of an internal combustion engine according to a first embodiment and its intake and exhaust systems and a control system. FIG. It is explanatory drawing of the exhaust gas air-fuel ratio which flows in and out of the atmosphere inside a catalyst when the deterioration degree determination control in Example 1 is implemented. 6 is a time chart illustrating time transitions of fuel cut F / C ON-OFF, inflow exhaust air-fuel ratio AFin, and catalyst bed temperature THc when performing deterioration degree determination control in the first embodiment. It is the figure which illustrated the relationship between the reaction heat detection period (DELTA) t at the time of performing the deterioration degree determination control in Example 1, and the largest oxygen storage amount Comax. 6 is a flowchart illustrating a deterioration degree determination control routine in the first embodiment. 6 is a diagram illustrating a first arrangement example of thermocouples in a three-way catalyst according to Example 2. FIG. 6 is a diagram showing a second arrangement example of thermocouples in the three-way catalyst according to Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 3 ... Exhaust passage 4 ... Three-way catalyst 5 ... Upstream air-fuel ratio sensor 6 ... Downstream air-fuel ratio sensor 7 ... Thermocouple 10 ... ECU

Claims (7)

An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine and having an oxygen storage capacity;
When the exhaust purification catalyst has a rich atmosphere and the fuel cut of the internal combustion engine is executed, the catalyst bed temperature of the exhaust purification catalyst is measured, and oxygen in the exhaust is stored in the exhaust purification catalyst Occlusion reaction heat detection means for detecting the generated occlusion reaction heat;
A deterioration degree determination means for determining a deterioration degree of the exhaust purification catalyst based on a detection timing of the storage reaction heat by the storage reaction heat detection means;
A catalyst deterioration determination system for an internal combustion engine, comprising:   The deterioration degree determining means estimates the oxygen storage capacity of the exhaust purification catalyst based on the detection timing of the storage reaction heat, and determines the deterioration degree of the exhaust purification catalyst based on the estimated oxygen storage capacity. The catalyst deterioration determination system for an internal combustion engine according to claim 1, characterized in that:   The catalyst deterioration of the internal combustion engine according to claim 1 or 2, wherein the deterioration degree determination means further determines the deterioration degree based on the catalyst bed temperature measured by the occlusion reaction heat detection means. Judgment system. A lean determination means for determining whether or not the exhaust air-fuel ratio flowing into the exhaust purification catalyst is a lean air-fuel ratio;
The deterioration degree determination means determines the deterioration degree of the exhaust purification catalyst based on a reaction heat detection period from when it is determined that the inflowing exhaust air-fuel ratio is a lean air-fuel ratio until the occlusion reaction heat is detected. The catalyst deterioration determination system for an internal combustion engine according to any one of claims 1 to 3, wherein: Lean determination means for determining whether or not the exhaust air-fuel ratio flowing into the exhaust purification catalyst is a lean air-fuel ratio;
Based on the reaction heat detection period from when it is determined that the inflowing exhaust air-fuel ratio is a lean air-fuel ratio until the occlusion reaction heat is detected, occlusion is performed on the upstream side of the arrangement position of the occlusion reaction heat detection means. Upstream portion storage amount calculating means for calculating the upstream portion stored amount,
Further comprising
The deterioration degree determining means estimates the oxygen storage capacity of the exhaust purification catalyst as a whole based on the volume ratio from the catalyst front end to the arrangement position with respect to the entire exhaust purification catalyst and the upstream storage amount. The catalyst deterioration determination system for an internal combustion engine according to claim 2. A plurality of the occlusion reaction heat detection means are provided in the exhaust flow direction in the exhaust purification catalyst,
The deterioration degree determination means is a deterioration of the exhaust purification catalyst based on a reaction heat detection delay period which is a difference in detection timing of the occlusion reaction heat detected by the second occlusion reaction heat detection means selected from the plurality. The catalyst deterioration determination system for an internal combustion engine according to any one of claims 1 to 3, wherein the degree is determined. A plurality of the occlusion reaction heat detection means are provided in the exhaust flow direction in the exhaust purification catalyst,
A region sandwiched between the second occlusion reaction heat detection means based on a reaction heat detection delay period which is a difference in detection timing of the occlusion reaction heat detected by the two selected occlusion reaction heat detection means among the plurality An intermediate storage amount calculating means for calculating the intermediate storage amount stored in
In addition,
The deterioration degree determination means estimates the oxygen storage capacity of the exhaust purification catalyst as a whole based on the volume ratio of the region sandwiched by the second storage reaction heat detection means relative to the entire exhaust purification catalyst and the intermediate storage amount. The catalyst deterioration determination system for an internal combustion engine according to claim 2.

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