Engine Control Unit

Abstract

To prevent interruption of diagnosis of an exhaust system component due to a rise in catalyst temperature caused by lean combustion.SOLUTION: An engine control device 10 finds a first catalyst temperature as an estimated value for a catalyst temperature of a filter device 19 reflecting heat generation due to the combustion of particulate matters in the filter device 19 and a second catalyst temperature as an estimated value for a catalyst temperature not reflecting the heat generation. Besides, the engine control device 10 diagnoses whether a catalyst device 18 is abnormal or not while performing lean combustion. Then, the engine control device 10 determines whether the conditions for executing the diagnosis are established or not by using the second catalyst temperature out of estimated values for the two catalyst temperatures.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an engine control device that performs abnormality diagnosis for exhaust system components. [Background technology]

[0002] Patent Document 1 describes an engine control device that performs abnormality diagnosis for exhaust system components. The engine control device described in the document is applied to an engine in which a catalytic device for exhaust purification carrying a three-way catalyst is installed in an exhaust passage. The engine control device in the document performs abnormality diagnosis for the catalytic device while performing active air-fuel ratio control that alternately switches the air-fuel ratio of the mixture burned in the combustion chamber between a rich air-fuel ratio and a lean air-fuel ratio. The rich air-fuel ratio indicates an air-fuel ratio that is richer than the stoichiometric air-fuel ratio, and the lean air-fuel ratio indicates an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. The engine control device in the document performs abnormality diagnosis for the catalytic device on the condition that the catalyst temperature of the catalytic device is within a predetermined temperature range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-255490 A Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, as a catalytic device for purifying exhaust gas, there is a four-way catalytic device that supports a three-way catalyst and has a function of collecting particulate matter. On the other hand, during combustion at a lean air-fuel ratio, exhaust gas containing excess oxygen that is not used for combustion is discharged from the combustion chamber into the exhaust passage. Therefore, when active air-fuel ratio control is performed in an engine equipped with a four-way catalytic device, the particulate matter in the four-way catalytic device is burned by the inflow of excess oxygen, and the catalyst temperature of the four-way catalytic device increases due to the heat generated by the combustion. As a result, the catalyst temperature may exceed the upper limit of the above-mentioned predetermined temperature range, and the abnormality diagnosis may be interrupted.

[0005] In addition, a diagnosis using active air-fuel ratio control may be performed on exhaust system components other than the catalytic converter, such as an air-fuel ratio sensor. In addition, it may be possible to set an upper limit value for the catalyst temperature that allows the execution of the diagnosis even when diagnosing exhaust system components other than the catalytic converter. In such a case, the catalyst temperature may rise due to combustion at a lean air-fuel ratio during the diagnosis, causing the diagnosis to be interrupted. [Means for solving the problem]

[0006] The engine control device that solves the above problem is applied to an engine in which a four-way catalyst device that supports a three-way catalyst and has a filter function for collecting particulate matter in the exhaust gas is installed in an exhaust passage. When diagnosing whether or not there is an abnormality in an exhaust system component of the engine, the engine control device performs lean combustion with an air-fuel ratio leaner than the theoretical air-fuel ratio. The engine control device further includes, as a process for estimating the catalyst temperature of the four-way catalyst device, a first estimation process that estimates a catalyst temperature that reflects heat generated by the combustion of particulate matter in the four-way catalyst device, and a second estimation process that estimates a catalyst temperature that does not reflect heat generated by the combustion of particulate matter in the four-way catalyst device. The engine control device includes, as a condition for executing the diagnosis, that the estimated value of the catalyst temperature by the second estimation process is equal to or lower than a predetermined diagnosis upper limit temperature.

[0007] In the second estimation process, the catalyst temperature is estimated as a value that does not reflect heat generated by the combustion of particulate matter in the four-way catalyst device. Therefore, even if the actual catalyst temperature rises due to lean combustion during diagnosis, the rise is not reflected in the estimated value of the catalyst temperature by the second estimation process. The engine control device uses the estimated value of the catalyst temperature by the second estimation process to determine whether the conditions for performing the diagnosis are met. Therefore, with the engine control device, it is less likely that the catalyst temperature will rise due to lean combustion during diagnosis, causing the diagnosis to be interrupted. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a schematic configuration of an embodiment of an engine control device; [Diagram 2] FIG. 11 is a time chart showing, during an abnormality diagnosis of a catalytic converter by the engine control device, (a) the progress of an actual air-fuel ratio, (b) the progress of an output of a front air-fuel ratio sensor, (c) the progress of an output of a rear air-fuel ratio sensor, and (d) the progress of an oxygen storage amount OSA of the catalytic converter. [Diagram 3] 4 is a flowchart of a catalyst temperature estimation routine executed by the engine control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of an engine control device will be described in detail with reference to FIGS. <Engine 11 Configuration> First, referring to FIG. 1, the configuration of an engine 11 to which an engine control device 10 of the present embodiment is applied will be described. The engine 11 is mounted on a vehicle. The engine 11 includes a combustion chamber 12 in which a mixture is burned. The engine 11 also includes an intake passage 13 which is an intake passage to the combustion chamber 12, and an exhaust passage 14 which is an exhaust passage from the combustion chamber 12. The intake passage 13 includes a throttle valve 15 which is a flow rate control valve for the intake air. An injector 16 which injects fuel into the intake air is installed in a portion downstream of the throttle valve 15 in the intake passage 13. An ignition device 17 which ignites the mixture by spark discharge is installed in the combustion chamber 12 to which the intake air mixed with fuel, i.e., the mixture, is introduced through the intake passage 13. On the other hand, a catalyst device 18 for purifying exhaust gas is installed in the exhaust passage 14. A filter device 19 for collecting particulate matter in the exhaust gas is installed in a portion downstream of the catalyst device 18 in the exhaust passage 14. The catalytic device 18 and the filter device 19 support a three-way catalyst that simultaneously oxidizes HC and CO in the exhaust gas and reduces NOx. The catalytic device 18 and the filter device 19 also support an oxygen storage agent as a promoter for enhancing the catalytic action of the three-way catalyst. In this embodiment, the filter device 19 corresponds to a four-way catalytic device that supports a three-way catalyst and has a filter function for collecting particulate matter in the exhaust gas.

[0010] <Configuration of engine control device 10> Next, a configuration of the engine control device 10 that controls the engine 11 will be described. The engine control device 10 is configured as an electronic control unit that includes an arithmetic processing device 20 and a storage device 21. The arithmetic processing device 20 is a device that executes arithmetic processing for engine control. The storage device 21 is a device that stores programs and data for engine control.

[0011] The engine control device 10 is connected to various sensors that detect state quantities that indicate the operating state of the engine 11. These sensors include an air flow meter 22, a throttle opening sensor 23, an intake pressure sensor 24, a crank angle sensor 25, a front air-fuel ratio sensor 26, and a rear air-fuel ratio sensor 27. In addition, the above sensors also include an accelerator pedal sensor 28, a vehicle speed sensor 29, an outside air temperature sensor 30, and a water temperature sensor 31. The air flow meter 22 is a sensor that detects the intake flow rate GA of the intake passage 13. The throttle opening sensor 23 is a sensor that detects the throttle opening TA, which is the opening of the throttle valve 15. The intake pressure sensor 24 is a sensor that detects the intake pressure PM, which is the pressure of the intake air in the portion of the intake passage 13 downstream of the throttle valve 15. The crank angle sensor 25 is a sensor that detects a crank angle θ, which is the rotation angle of the crankshaft, which is the output shaft of the engine 11. The front air-fuel ratio sensor 26 is a sensor that detects the air-fuel ratio of the exhaust gas flowing into the catalytic device 18. The rear air-fuel ratio sensor 27 is a sensor that detects the air-fuel ratio of the exhaust gas flowing out from the catalytic converter 18. The accelerator pedal sensor 28 is a sensor that detects the accelerator pedal opening degree ACC, which is the amount of accelerator pedal operation by the driver. The vehicle speed sensor 29 is a sensor that detects the vehicle's traveling speed V. The outside air temperature sensor 30 is a sensor that detects the outside air temperature THA, which is the temperature of the air outside the vehicle. The water temperature sensor 31 is a sensor that detects the engine water temperature THW, which is the temperature of the engine cooling water. The engine control device 10 obtains the engine speed NE from the detection result of the crank angle θ by the crank angle sensor 25. The engine control device 10 also obtains the engine load factor KL from the intake flow rate GA, the throttle opening degree TA, the engine speed NE, etc. The engine load factor KL represents the intake filling rate of the combustion chamber 12.

[0012] The engine control device 10 determines each operation amount of the engine 11 according to the operating state of the engine 11 grasped from the detection results of these sensors. The operation amounts of the engine 11 determined by the engine control device 10 include the throttle opening TA, the fuel injection amount Q of the injector 16, and the ignition timing SA of the mixture by the ignition device 17. The engine control device 10 controls the engine by driving the throttle valve 15, the injector 16, the ignition device 17, etc. according to the determined operation amounts. Note that the engine control device 10 performs air-fuel ratio feedback control as part of the engine control. In the air-fuel ratio feedback control, the engine control device 10 feedback-adjusts the fuel injection amount Q of the injector 16 so that the output λf of the front air-fuel ratio sensor 26 approaches a value indicating the theoretical air-fuel ratio.

[0013] In addition, the engine control device 10 calculates the oxygen storage amount OSA, which is the amount of oxygen stored in the catalytic device 18, during the operation of the engine 11. The calculation of the oxygen storage amount OSA is performed in the following manner. In the following description, the amount of oxygen stored in the catalytic device 18 during a predetermined calculation period is referred to as the oxygen storage speed VO of the catalytic device 18. Note that the oxygen storage speed VO when the catalytic device 18 is releasing oxygen is a negative value. The oxygen storage speed VO of the catalytic device 18 is determined by the flow rate of the exhaust gas flowing into the catalytic device 18, the concentration of unburned fuel components / excess oxygen in the exhaust gas, the catalyst temperature, the oxygen storage amount OSA, and the like. The flow rate of the exhaust gas flowing into the catalytic device 18 can be calculated from the engine speed NE and the engine load factor KL. The concentration of unburned fuel components and excess oxygen in the exhaust gas flowing into the catalytic device 18 can be calculated from the air-fuel ratio of the mixture being burned in the combustion chamber 12. The engine control device 10 also estimates the catalyst temperature, which is the temperature of the catalyst supported by the catalytic device 18, through a catalyst temperature estimation process described later. Furthermore, the engine control device 10 obtains the oxygen storage speed VO of the catalytic device 18 from the engine speed NE, engine load factor KL, actual air-fuel ratio AF, catalyst temperature, oxygen storage amount OSA, and the like for each predetermined calculation period. The engine control device 10 then obtains an integrated value of the calculated oxygen storage speed VO for each calculation period as the value of the oxygen storage amount OSA of the catalytic device 18. The actual air-fuel ratio AF represents the air-fuel ratio of the mixture being burned in the combustion chamber 12. The actual air-fuel ratio AF is obtained, for example, from the detection result of the front air-fuel ratio sensor 26. The actual air-fuel ratio AF can also be obtained from the result of calculation based on the engine load factor KL and the fuel injection amount Q.

[0014] <Abnormality diagnosis of catalytic converter 18> The catalytic converter 18 installed in the exhaust passage 14 of the engine 11 configured as described above may lose its oxygen storage capacity due to deterioration, and may become unable to perform sufficient exhaust purification performance. As part of engine control, the engine control device 10 performs an abnormality diagnosis of the catalytic converter 18 to determine whether the catalytic converter 18 has deteriorated to the point where it is unable to perform sufficient exhaust purification performance.

[0015] When diagnosing the catalytic device 18, the engine control device 10 performs active air-fuel ratio control to set the air-fuel ratio of the mixture burned in the combustion chamber 12 to a value other than the stoichiometric air-fuel ratio. In the active air-fuel ratio control when diagnosing the catalytic device 18, the air-fuel ratio of the mixture burned in the combustion chamber 12 is alternately switched between a rich air-fuel ratio and a lean air-fuel ratio. The rich air-fuel ratio is an air-fuel ratio richer than the stoichiometric air-fuel ratio, and the lean air-fuel ratio is an air-fuel ratio leaner than the stoichiometric air-fuel ratio. In the following description, the combustion of the mixture whose air-fuel ratio is the stoichiometric air-fuel ratio is referred to as stoichiometric combustion. Also, the combustion of the mixture whose air-fuel ratio is the rich air-fuel ratio is referred to as rich combustion, and the combustion of the mixture whose air-fuel ratio is the lean air-fuel ratio is referred to as lean combustion. Exhaust gas containing a large amount of unburned fuel components such as HC and CO is discharged from the combustion chamber 12 into the exhaust passage 14 during rich combustion. In the following description, exhaust gas containing a large amount of unburned fuel components discharged from the combustion chamber 12 during rich combustion will be referred to as rich exhaust gas. On the other hand, exhaust gas containing a large amount of surplus oxygen not used in combustion is discharged from the combustion chamber 12 into the exhaust passage 14 during lean combustion. In the following description, exhaust gas containing a large amount of surplus oxygen discharged from the combustion chamber 12 during lean combustion will be referred to as lean exhaust gas.

[0016] Fig. 2 shows an example of an embodiment of abnormality diagnosis of the catalytic device 18. Fig. 2(a) to (d) respectively show the transitions of the following parameters during abnormality diagnosis of the catalytic device 18. That is, Fig. 2(a) shows the transitions of the actual air-fuel ratio AF, Fig. 2(b) shows the transitions of the output λf of the front air-fuel ratio sensor 26, Fig. 2(c) shows the transitions of the output λr of the rear air-fuel ratio sensor 27, and Fig. 2(d) shows the transitions of the oxygen storage amount OSA of the catalytic device 18.

[0017] 2, at time t0, abnormality diagnosis of the catalytic converter 18 is started. Before time t0, stoichiometric combustion is performed in the combustion chamber 12 by air-fuel ratio feedback control. At this time, the output λf of the front air-fuel ratio sensor 26 and the output λr of the rear air-fuel ratio sensor 27 are both stoichiometric output values ​​ST, which are values ​​corresponding to the stoichiometric air-fuel ratio.

[0018] When the abnormality diagnosis is started at time t0, the engine control device 10 starts the active air-fuel ratio control at that time t0. In this embodiment, during the active air-fuel ratio control, the air-fuel ratio feedback control is performed with the feedback gain set smaller than normal. In FIG. 2, the engine control device 10 changes the actual air-fuel ratio AF to a rich air-fuel ratio at time t0. When the combustion of a rich air-fuel ratio mixture, i.e., rich combustion, is started in the combustion chamber 12, rich exhaust gas containing a large amount of unburned fuel components is discharged from the combustion chamber 12. Then, when the rich exhaust gas reaches the front air-fuel ratio sensor 26, the output λf of the front air-fuel ratio sensor 26 changes from the stoichiometric output value ST to a rich output value RI, which is a value corresponding to the rich air-fuel ratio. After that, the rich exhaust gas also flows into the catalytic device 18. If oxygen is stored in the catalytic device 18 at this time, the catalytic device 18 releases oxygen even when the rich exhaust gas flows in, and oxidizes the unburned fuel components in the exhaust gas. Therefore, immediately after the start of rich combustion, the exhaust gas flowing out of the catalytic device 18 is maintained at stoichiometric exhaust gas. And the output λr of the rear air-fuel ratio sensor 27 is also maintained at a value close to the stoichiometric output value ST.

[0019] After rich combustion begins, the oxygen storage amount OSA of the catalytic converter 18 gradually decreases over time. Eventually, the catalytic converter 18 releases all of its oxygen and its oxygen storage amount OSA becomes "0." As a result, the catalytic converter 18 is no longer able to sufficiently oxidize the unburned fuel components in the exhaust gas, and emits rich exhaust gas. In the following explanation, the start of the outflow of rich exhaust gas from the catalytic converter 18 at this time is referred to as rich failure.

[0020] When rich bankruptcy occurs, the output λr of the rear air-fuel ratio sensor 27 changes from a value close to the stoichiometric output value ST to the rich side. The engine control device 10 confirms the occurrence of rich bankruptcy when the output λr of the rear air-fuel ratio sensor 27 becomes a value richer than a predefined rich bankruptcy determination value XR. The rich bankruptcy determination value XR is preset with a value of the output λr corresponding to an air-fuel ratio richer than the stoichiometric air-fuel ratio. When the engine control device 10 confirms rich bankruptcy, it switches the combustion in the combustion chamber 12 from rich combustion to lean combustion. In FIG. 2, switching from rich combustion to lean combustion in response to rich bankruptcy is performed at time t1 and time t3.

[0021] When lean combustion starts, lean exhaust gas containing a large amount of excess oxygen is discharged from the combustion chamber 12. Then, when the lean exhaust gas reaches the front air-fuel ratio sensor 26, the output λf of the front air-fuel ratio sensor 26 changes from the rich output value RI to the lean output value LE, which is a value corresponding to the lean air-fuel ratio. After that, the lean exhaust gas also flows into the catalytic device 18. At this time, the catalytic device 18 stores the excess oxygen in the inflowing lean exhaust gas. Therefore, for a while after the start of lean combustion, the output λr of the rear air-fuel ratio sensor 27 is maintained at a value close to the stoichiometric output value ST.

[0022] After lean combustion starts, the oxygen storage amount OSA of the catalytic converter 18 gradually increases over time. There is a limit to the amount of oxygen that the catalytic converter 18 can store. Therefore, if lean combustion continues, the catalytic converter 18 will eventually reach a state where it cannot store any more oxygen. As a result, the catalytic converter 18 will discharge lean exhaust gas containing the oxygen that was not stored. In the following description, the start of the outflow of lean exhaust gas from the catalytic converter 18 at this time will be referred to as lean failure.

[0023] When lean breakdown occurs, the output λr of the rear air-fuel ratio sensor 27 changes from a value close to the value "λst" corresponding to the stoichiometric air-fuel ratio to a value corresponding to the lean air-fuel ratio. The engine control device 10 confirms the occurrence of lean breakdown when the output λr of the rear air-fuel ratio sensor 27 becomes a value leaner than a preset lean breakdown determination value XL. The lean breakdown determination value XL is preset with a value of the output λr corresponding to an air-fuel ratio leaner than the stoichiometric air-fuel ratio. When the engine control device 10 confirms lean breakdown, it switches the combustion in the combustion chamber 12 from lean combustion to rich combustion. In FIG. 2, switching from lean combustion to rich combustion in response to lean breakdown is performed at time t2 and time t4.

[0024] In this way, the engine control device 10 performs active air-fuel ratio control so as to alternately switch between rich combustion and lean combustion in response to rich bankruptcy and lean bankruptcy. The engine control device 10 measures the maximum oxygen storage amount Cmax of the catalytic device 18 in the following manner while performing active air-fuel ratio control. In the following description, the period during which rich combustion continues from the start of rich combustion in response to lean bankruptcy until the occurrence of rich bankruptcy is referred to as a rich combustion period. Also, the period during which lean combustion continues from the start of lean combustion in response to rich bankruptcy until the occurrence of lean bankruptcy is referred to as a lean combustion period. The engine control device 10 measures the maximum oxygen storage amount Cmax of the catalytic device 18 using each of the rich combustion period and the lean combustion period as a measurement period. Specifically, the engine control device 10 obtains the integrated value of the oxygen storage speed VO for each calculation cycle in each measurement period as a measurement value of the maximum oxygen storage amount Cmax.

[0025] When diagnosing an abnormality, the engine control device 10 averages the measured values ​​of the maximum oxygen storage amount Cmax during a plurality of measurement periods to determine the current maximum oxygen storage amount Cmax of the catalytic device 18. The engine control device 10 then diagnoses whether or not there is an abnormality in the catalytic device 18 based on whether or not the maximum oxygen storage amount Cmax is below a lower limit value that is allowable for ensuring the exhaust purification performance of the engine 11.

[0026] The engine control device 10 executes such abnormality diagnosis of the catalytic device 18 in response to the establishment of a preset execution condition. The execution condition is established when all of a plurality of pre-set requirements are satisfied. The requirements for the establishment of such execution conditions include the following requirements (a) to (d). Requirement (a) is that the abnormality diagnosis of the catalytic device 18 is incomplete in the current trip. Requirement (b) is that the warm-up of the engine 11 is completed. Requirement (c) is that the operating conditions of the engine 11 are stable, that is, the changes in the engine speed NE and the engine load factor KL are small. Requirement (d) is that the catalyst temperature of the filter device 19 is equal to or lower than a preset diagnosis upper limit temperature. Note that the diagnosis upper limit temperature is set to a temperature lower than the upper limit of the catalyst temperature that is allowable for maintaining the durability of the filter device 19.

[0027] <Catalyst temperature estimation> Next, the details of the process for estimating the catalyst temperature will be described. The engine control device 10 estimates two temperatures, a first catalyst temperature THC1 and a second catalyst temperature THC2, as the catalyst temperatures of the filter device 19. The first catalyst temperature THC1 is obtained as an estimated value of the catalyst temperature reflecting heat generated by the combustion of particulate matter in the filter device 19. The second catalyst temperature THC2 is obtained as an estimated value of the catalyst temperature not reflecting heat generated by the combustion of particulate matter in the filter device 19. In other words, the second catalyst temperature THC2 is an estimated value of the catalyst temperature obtained by assuming that the amount of heat generated by the combustion of particulate matter is always "0".

[0028] 3 shows the procedure of a catalyst temperature estimation routine executed by the engine control device 10 to estimate the first catalyst temperature THC1 and the second catalyst temperature THC2. The engine control device 10 repeatedly executes this routine at every predetermined control period while the engine 11 is in operation.

[0029] When this routine is started, the engine control device 10 first calculates, in step S100, a filter inflow exhaust amount G1, which is the flow rate of the exhaust flowing into the filter device 19, and a filter inflow exhaust temperature T1, which is the temperature of the exhaust, based on the operating state of the engine 11. In this embodiment, the exhaust flow rate GE is used as the filter inflow exhaust amount G1. Meanwhile, the filter inflow exhaust temperature T1 is obtained using a thermal model of the engine exhaust system. This thermal model is constructed as a model of heat balance regarding each of the following heat quantities: the amount of heat generated by the combustion of the mixture in the combustion chamber 12, the amount of heat transferred from the burned mixture to the wall surface of the combustion chamber 12, the amount of heat transferred between the exhaust system components constituting the exhaust passage 14 and the exhaust, the amount of heat released from the exhaust system components to the outside air, the amount of heat generated by the combustion of unburned fuel components in the catalytic converter 18, and the like.

[0030] Next, in step S110, the engine control device 10 calculates the inflow amount GO of excess oxygen to the filter device 19. The inflow amount GO of excess oxygen is obtained from the output λr of the rear air-fuel ratio sensor 27 and the filter inflow exhaust gas amount G1.

[0031] In the next step S120, the engine control device 10 calculates the amount of heat dissipated Q1 from the filter device 19 to the outside air based on the value of the first catalyst temperature THC1 before the update, the outside air temperature THA, and the traveling speed V. In the same step S120, the engine control device 10 also calculates the amount of heat Q2 received by the filter device 19 from the exhaust gas based on the value of the first catalyst temperature THC1 before the update, the filter inflow exhaust amount G1, and the filter inflow exhaust temperature T1. In addition, in the same step S120, the engine control device 10 calculates the amount of heat Q3 generated by the combustion of particulate matter in the filter device 19. The amount of heat Q3 is calculated based on the value of the first catalyst temperature THC1 before the update, the inflow amount GO of excess oxygen, and the amount M of particulate matter captured by the filter device 19. Furthermore, in the next step S130, the engine control device 10 obtains the difference obtained by subtracting the amount of heat released Q1 from the sum of the amount of heat received Q2 and the amount of heat generated Q3, and calculates the quotient obtained by dividing the difference by the heat capacity C of the filter device 19 as the value of the temperature change amount ΔT1. Then, in step S140, the engine control device 10 updates the value of the first catalyst temperature THC1 so that the sum of the value before the update plus the amount of temperature change ΔT1 becomes the updated value.

[0032] On the other hand, in step S150, the engine control device 10 calculates the amount of heat dissipated Q4 from the filter device 19 to the outside air based on the value of the second catalyst temperature THC2 before the update, the outside air temperature THA, and the traveling speed V. In addition, in step S150, the engine control device 10 calculates the amount of heat received by the filter device 19 from the exhaust gas based on the value of the second catalyst temperature THC2 before the update, the filter inflow exhaust gas amount G1, and the filter inflow exhaust gas temperature T1. Furthermore, in the next step S160, the engine control device 10 obtains the difference obtained by subtracting the amount of heat dissipated Q4 from the amount of heat received Q5, and calculates the quotient obtained by dividing the difference by the heat capacity C of the filter device 19 as the value of the temperature change amount ΔT2. Then, in the following step S170, the engine control device 10 updates the value of the second catalyst temperature THC2 so that the sum of the value before the update and the temperature change amount ΔT2 becomes the updated value.

[0033] The engine control device 10 calculates the first catalyst temperature THC1 and the second catalyst temperature THC2 through this catalyst temperature estimation process. Then, the engine control device 10 uses the second catalyst temperature THC2 to determine whether or not an execution condition for abnormality diagnosis of the catalytic device 18 is satisfied. That is, the above-mentioned requirement (iv) for the execution condition to be satisfied is actually determined by whether or not the second catalyst temperature THC2 is equal to or lower than the diagnosis upper limit temperature.

[0034] In response to this, the engine control device 10 uses the first catalyst temperature THC1 as the catalyst temperature to be referenced in engine control other than the above-mentioned judgment. For example, the first catalyst temperature THC1 is used to judge whether or not to execute filter OT prevention control. The filter OT prevention control is a control that limits the output of the engine 11 when the temperature of the filter device 19 becomes too high, thereby preventing the catalyst device 18 from overheating.

[0035] In the present embodiment configured as described above, the processes of steps S120 to S140 in the catalyst temperature estimation routine of Fig. 3 correspond to the first estimation process. Also, in the present embodiment, the processes of steps S150 to S170 in the catalyst temperature estimation routine correspond to the second estimation process.

[0036] <Actions and Effects of the Embodiment> As described above, in this embodiment, two temperatures, the first catalyst temperature THC1 and the second catalyst temperature THC2, are obtained as estimated values ​​of the catalyst temperature. The first catalyst temperature THC1 is obtained as an estimated value of the catalyst temperature that reflects heat generated by the combustion of particulate matter in the filter device 19. In contrast, the second catalyst temperature THC2 is obtained as an estimated value of the catalyst temperature that does not reflect heat generated by the combustion of particulate matter in the filter device 19.

[0037] On the other hand, in this embodiment, the catalytic converter 18 is diagnosed for an abnormality while alternately switching between rich combustion and lean combustion by active air-fuel ratio control. The conditions for executing such an abnormality diagnosis include that the second catalyst temperature THC2 is equal to or lower than the diagnosis upper limit temperature.

[0038] In addition, when the catalytic converter 18 fails lean during active air-fuel ratio control, exhaust gas containing excess oxygen flows into the filter device 19. When the excess oxygen flows in, the particulate matter in the filter device 19 is burned. Then, the catalyst temperature of the filter device 19 temporarily rises due to heat generated by the combustion. The first catalyst temperature THC1 rises in accordance with the heat generated by the particulate matter at this time. Therefore, if the first catalyst temperature THC1 is used to determine whether the execution condition for the abnormality diagnosis is satisfied, the first catalyst temperature THC1 may exceed the diagnosis upper limit temperature due to heat generated by the combustion of the particulate matter, and the diagnosis may be interrupted. In contrast, in this embodiment, the second catalyst temperature THC2 is used to determine whether the execution condition for the abnormality diagnosis is satisfied. The second catalyst temperature THC2 does not reflect the influence of heat generated by the combustion of the particulate matter. Therefore, even if the particulate matter in the filter device 19 is burned during the diagnosis and the actual catalyst temperature rises, the diagnosis is not interrupted by that alone.

[0039] According to the engine control device 10 of the present embodiment described above, the following effects can be achieved. (1) In this embodiment, the first catalyst temperature THC1 is calculated as an estimate of the catalyst temperature that reflects heat generated by the combustion of particulate matter in the filter device 19. In addition, the second catalyst temperature THC2 is calculated as an estimate of the catalyst temperature that does not reflect heat generated by the combustion of particulate matter in the filter device 19. Of these two catalyst temperature estimates, the second catalyst temperature THC2 is used to determine whether or not the conditions for performing the diagnosis are met. Therefore, even if particulate matter in the filter device 19 burns due to lean combustion during the diagnosis, the diagnosis is not interrupted by a rise in catalyst temperature caused by the combustion. Therefore, the abnormality diagnosis of the catalytic device 18 is less likely to be interrupted.

[0040] (2) Since the abnormality diagnosis is unlikely to be interrupted, the time required from the start of the engine 11 to the completion of the abnormality diagnosis is likely to be short. (3) When active air-fuel ratio control is being performed, the properties of the exhaust gas released into the atmosphere are worse than those during stoichiometric combustion. Meanwhile, the execution time of active air-fuel ratio control until the abnormality diagnosis is completed becomes longer each time the abnormality diagnosis is interrupted. Therefore, according to this embodiment, since the abnormality diagnosis is less likely to be interrupted, deterioration of the exhaust performance of the engine 11 due to the execution of active air-fuel ratio control during abnormality diagnosis is suppressed.

[0041] This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction. In the above embodiment, the air-fuel ratio feedback control is continued with the feedback gain set to a value smaller than normal even during active air-fuel ratio control. The air-fuel ratio feedback control may be stopped during active air-fuel ratio control.

[0042] As long as the first catalyst temperature THC1 is obtained as an estimate of the catalyst temperature that reflects the heat generated by the combustion of particulate matter, and the second catalyst temperature THC2 is obtained as an estimate of the catalyst temperature that does not reflect the same heat, the details of the estimation logic for these may be changed as appropriate.

[0043] Some abnormality diagnoses of exhaust system components other than the catalytic converter 18 are performed by changing the air-fuel ratio from the stoichiometric air-fuel ratio to another air-fuel ratio. For example, the front air-fuel ratio sensor 26 may be diagnosed for abnormality based on a change in the output λf of the front air-fuel ratio sensor 26 in response to the change in the air-fuel ratio. It is also possible to perform such abnormality diagnoses of exhaust system components other than the catalytic converter 18 on the condition that the catalyst temperature is equal to or higher than the diagnostic lower limit temperature. In this case, it is also preferable to use the second catalyst temperature THC2 to determine whether the conditions for executing the abnormality diagnosis are met. In such a case, the abnormality diagnosis is less likely to be interrupted. [Explanation of symbols]

[0044] 10...Engine control device 11…Engine 12…Combustion chamber 13…Intake passage 14...Exhaust passage 15...Throttle valve 16...Injector 17...Ignition device 18...Catalyst device 19...Filter device 20...Processing device 21…Storage device 22...Air flow meter 23...Throttle opening sensor 24...Intake pressure sensor 25...Crank angle sensor 26...Front air-fuel ratio sensor 27...Rear air-fuel ratio sensor 28...Accelerator pedal sensor 29...Vehicle speed sensor 30...Water temperature sensor

Claims

[Claim 1] An engine control device is applied to an engine in which a four-way catalyst device carrying a three-way catalyst and having a filter function for collecting particulate matter in the exhaust gas is installed in an exhaust passage, and performs lean combustion by making the air-fuel ratio leaner than the theoretical air-fuel ratio when diagnosing whether or not there is an abnormality in an exhaust system component of the engine, The engine control device includes, as a process for estimating a catalyst temperature of the four-way catalyst device, a first estimation process for estimating the catalyst temperature reflecting heat generated by combustion of particulate matter in the four-way catalyst device, and a second estimation process for estimating the catalyst temperature not reflecting heat generated by combustion of particulate matter in the four-way catalyst device, The execution condition of the diagnosis includes that the estimated value of the catalyst temperature by the second estimation process is equal to or lower than a predetermined diagnosis upper limit temperature. Engine control device.

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