JP7380262B2 - Oxidation catalyst diagnostic equipment - Google Patents

Description

The present invention includes an engine body in which cylinders are formed, an exhaust passage through which exhaust gas discharged from the cylinders flows, and an engine body provided in the exhaust passage that is capable of adsorbing and oxidizing hydrocarbons and occluding and desorbing oxygen. The present invention relates to an oxidation catalyst diagnostic device installed in an engine equipped with an oxidation catalyst.

In engines installed in vehicles, etc., an oxidation catalyst capable of adsorbing and oxidizing hydrocarbons is provided in the exhaust passage in order to purify hydrocarbons in exhaust gas, and furthermore, an oxidation catalyst capable of adsorbing and oxidizing hydrocarbons is installed in the exhaust passage. The use of desorbable catalysts as oxidation catalysts has been carried out. Furthermore, in engines equipped with the oxidation catalyst, diagnosis is also performed to determine whether the oxidation catalyst is normal.

As an example of an engine equipped with an oxidation catalyst and a configuration for determining whether or not the oxidation catalyst is normal, the one disclosed in Patent Document 1 below is known. In the engine disclosed in Patent Document 1, the oxidation catalyst is diagnosed when the vehicle is stopped and idling. Specifically, when the engine is idling, post-injection is performed to add unburned fuel, or hydrocarbons, to the exhaust gas, and the theoretical calorific value that is thought to be generated by the reaction of the hydrocarbons on the oxidation catalyst is calculated as follows: Estimate based on amount of hydrocarbon added and exhaust gas flow rate. Then, by comparing the actual calorific value of the oxidation catalyst obtained from the detected value of the temperature sensor with the estimated theoretical calorific value, it is diagnosed whether or not the oxidation catalyst is normal.

Japanese Patent Application Publication No. 2016-17502

In the engine of Patent Document 1, the oxidation catalyst is diagnosed only when the vehicle is stopped and idling. Therefore, there is a problem that there are few opportunities to diagnose the oxidation catalyst, and abnormalities in the oxidation catalyst cannot be detected early.

In contrast, the present inventors have discovered that there is a high correlation between the amount of hydrocarbons that react with the oxidation catalyst during engine operation and the amount of hydrocarbons that are adsorbed on the oxidation catalyst, and that the engine operating conditions Focusing on the high correlation between the amount of hydrocarbons adsorbed on the oxidation catalyst and the amount of hydrocarbons adsorbed on the oxidation catalyst during engine operation, we constructed the following configuration. In other words, the amount of hydrocarbons adsorbed on the oxidation catalyst during engine operation is estimated based on the engine operating conditions, and based on this estimate, the amount of heat generated by the reaction of the hydrocarbons on the oxidation catalyst is estimated. We then constructed a configuration that compares this estimated calorific value with the actual calorific value detected by the sensor. According to this configuration, it is possible to diagnose the oxidation catalyst regardless of whether or not the engine is in an idling state.

However, it has been found that even with this configuration, an error may occur in estimating the amount of hydrocarbons adsorbed on the oxidation catalyst immediately after the engine is started, resulting in a decrease in diagnostic accuracy.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an oxidation catalyst diagnostic device that can accurately diagnose an oxidation catalyst and can secure more opportunities for diagnosis.

The present invention for solving the above problems includes an engine main body in which cylinders are formed, an exhaust passage through which exhaust gas discharged from the cylinder flows, and an engine that is provided in the exhaust passage and is capable of adsorbing and oxidizing hydrocarbons. The oxidation catalyst diagnostic device is provided in an engine equipped with an oxidation catalyst capable of storing and desorbing oxygen, the device comprising: a catalyst temperature detection device for detecting the temperature of the oxidation catalyst; and a catalyst temperature detection device for detecting the temperature of the oxidation catalyst; and a determination device that determines whether or not the amount of hydrocarbons adsorbed on the oxidation catalyst is determined based on the operating conditions of the engine when the output shaft of the engine body rotates. An HC adsorption amount estimating section that estimates a certain HC adsorption amount, and an amount of temperature rise of the oxidation catalyst that occurs when the oxidation catalyst is assumed to be normal, are estimated by the HC adsorption amount estimating section. a temperature rise amount estimation unit that estimates based on the temperature rise amount estimation unit; a temperature rise amount of the oxidation catalyst based on the detected value of the catalyst temperature detection device during engine operation; and the temperature rise amount estimated by the temperature rise amount estimation unit. and a determination unit that determines whether or not the oxidation catalyst is normal based on the comparison result, the HC adsorption amount immediately before the engine is stopped estimated by the HC adsorption amount estimating unit. If the pre-stop HC adsorption amount is equal to or greater than the predetermined amount, the determination unit stops the determination for a predetermined period after the engine starts, and if the pre-stop HC adsorption amount is less than the predetermined amount, the determination unit (Claim 1) characterized in that the determination is started before the predetermined period of time has elapsed after the engine is started.

In this configuration, when the engine is operating, the amount of HC adsorption is estimated based on the operating conditions of the engine, and the amount of temperature rise of the oxidation catalyst is estimated based on this estimated amount. Therefore, regardless of whether or not the engine is in an idling state, the amount of temperature rise can be estimated and the oxidation catalyst can be diagnosed based on this estimated value, thereby increasing the chances of diagnosing the oxidation catalyst.

However, as mentioned above, in a configuration in which the amount of HC adsorption during engine operation is simply estimated based on the engine operating conditions and the oxidation catalyst is diagnosed based on this, the diagnostic performance of the oxidation catalyst after the engine is started deteriorates. There is a risk of On the other hand, the inventors of the present application have found the following as a result of intensive research. In other words, the amount of hydrocarbons adsorbed on the oxidation catalyst decreases while the engine is stopped, and if the amount of hydrocarbons adsorbed on the oxidation catalyst when the engine is stopped is more than a predetermined amount, If the oxidation catalyst is diagnosed based on the amount of HC adsorbed during engine operation immediately after the engine starts, the diagnostic performance of the oxidation catalyst will deteriorate due to the increase in the amount of decrease in the generated hydrocarbons. They found that the accuracy of estimating the amount of HC adsorption based on engine operating conditions once again increased.

Based on this knowledge, in the present invention, as described above, the pre-stop HC adsorption amount, which is the HC adsorption amount estimated by the HC adsorption amount estimating section immediately before the engine stop, is equal to or greater than a predetermined amount, and when the engine is started, If the diagnosis accuracy of the oxidation catalyst based on the amount of HC adsorption during engine operation tends to be low, the diagnosis is stopped for a predetermined period after the engine is started. Therefore, according to the present invention, misdiagnosis of the oxidation catalyst can be prevented. According to the present invention, if the pre-shutdown HC adsorption amount is less than a predetermined amount and the oxidation catalyst diagnosis accuracy can be increased even after the engine is started, the accuracy can be improved by performing the diagnosis after the engine is started. It is possible to increase the chances of diagnosing high oxidation catalysts.

In the configuration, preferably, when the pre-stop HC adsorption amount is equal to or greater than the predetermined amount, the determination unit starts the determination when the predetermined period has elapsed after the engine is started, and the pre-stop HC adsorption amount is equal to or greater than the predetermined amount. If the amount is less than a fixed amount, the determination unit starts the determination immediately after starting the engine (Claim 2).

According to this configuration, the chances of diagnosing the oxidation catalyst can be increased more reliably.

Here, when the temperature of the oxidation catalyst rises above a predetermined temperature after the engine starts, the amount of hydrocarbons adsorbed on the oxidation catalyst approaches zero, and after that, the amount of hydrocarbons adsorbed on the oxidation catalyst approaches zero, and from then on, the amount of hydrocarbons adsorbed by the oxidation catalyst approaches zero. It was found that the amount of hydrocarbon adsorption can be estimated accurately based on the operating conditions of the engine. Therefore, in the above configuration, if the predetermined period is a period from when the engine starts until the temperature of the oxidation catalyst reaches a predetermined temperature or higher, misdiagnosis of the oxidation catalyst can be prevented. , the period during which the diagnosis of the oxidation catalyst is stopped can be shortened to increase the number of diagnosis opportunities (Claim 3).

Furthermore, if the pre-stop HC adsorption amount is less than the predetermined amount, the hydrocarbons adsorbed on the oxidation catalyst react with the oxygen desorbed from the oxidation catalyst while the engine is stopped. It was found that the amount of hydrocarbons present in

From this, in the configuration, the determination device estimates the O2 desorption rate, which is the rate of oxygen desorbed from the oxidation catalyst while the engine is stopped, and based on the O2 desorption rate, The oxidation catalyst further includes an HC reduction amount estimation unit that estimates an HC reduction amount at the time of shutdown, which is a total reduction amount of hydrocarbons adsorbed on the oxidation catalyst, and when the pre-shutdown HC adsorption amount is less than the predetermined amount, the HC adsorption amount is lower than the predetermined amount. Preferably, the amount estimating section corrects the estimated value of the HC adsorption amount during engine operation based on the HC reduction amount at the time of stop estimated by the HC reduction amount estimating section (Claim 4).

According to this configuration, when the amount of HC adsorption before stopping is less than the predetermined amount, it is possible to accurately estimate the amount of HC reduction during stopping and the amount of HC adsorbing during engine operation, and the diagnostic accuracy of the oxidation catalyst can be further improved. .

In the above configuration, the HC reduction amount estimating unit estimates the amount of oxygen stored in the oxidation catalyst immediately before stopping the engine, and is configured such that the larger the estimated oxygen storage amount, the larger the HC reduction amount at the time of engine stop. It is preferable that the HC reduction amount at the time of stop is estimated (Claim 5).

According to this configuration, it is possible to estimate the HC reduction amount at the time of stoppage and diagnose the oxidation catalyst with even higher accuracy.

According to the present invention, as described above, when the pre-shutdown HC adsorption amount is less than the predetermined amount, the oxidation catalyst can be accurately diagnosed from an early stage after the engine is started. Therefore, an opportunity for diagnosing the oxidation catalyst can be secured even in a configuration in which an engine is mounted on a vehicle having a motor as a drive source for running, and the engine is stopped and started relatively frequently. Therefore, the present invention is effective when applied to a hybrid vehicle in which the engine has a motor as a drive source for driving (claim 6).

As explained above, according to the oxidation catalyst diagnostic device of the present invention, the oxidation catalyst can be diagnosed with high accuracy and more opportunities for this diagnosis can be secured.

1 is a schematic system diagram showing a preferred embodiment of an engine to which an oxidation catalyst diagnostic device of the present invention is applied. FIG. 2 is a block diagram showing a control system of the vehicle. FIG. 3 is a block diagram showing a procedure for calculating the operating oxygen storage amount performed by the HC reduction amount estimating section. 3 is a graph schematically showing the relationship between catalyst temperature, exhaust O2 concentration, exhaust flow rate, and oxygen storage rate. FIG. 2 is a block diagram showing a procedure for calculating an HC species adsorption ratio performed by an HC reduction amount estimating section. 2 is a graph schematically showing the relationship between the excess air ratio and the discharge rate of HC species. 2 is a graph schematically showing the relationship between the effective compression ratio and the discharge rate of HC species. FIG. 3 is a block diagram showing a procedure for estimating the amount of HC reduction performed by the amount estimating section of HC reduction. 2 is a graph schematically showing the relationship between oxygen storage amount, catalyst temperature, and O2 desorption rate. FIG. 3 is a block diagram showing a procedure for calculating the HC oxidation rate at stop, which is performed by the HC oxidation rate at stop calculation section. FIG. 2 is a block diagram showing a procedure for calculating a theoretical temperature increase amount performed by a theoretical temperature increase amount estimating section. It is a graph schematically showing the relationship between catalyst temperature, exhaust flow rate, and first HC adsorption rate. 2 is a graph schematically showing the relationship between HC adsorption amount, catalyst temperature, exhaust flow rate, and HC release rate. It is a graph schematically showing the relationship between HC release rate, catalyst temperature, and HC oxidation rate during operation. 3 is a flowchart showing a procedure for diagnosing an oxidation catalyst. 3 is a flowchart showing a procedure for diagnosing an oxidation catalyst.

(1) Overall configuration of engine FIG. 1 is a schematic system diagram showing a preferred embodiment of an engine according to the present invention. The engine 70 shown in this figure is a four-stroke diesel engine, and is mounted on a vehicle. In this embodiment, the engine 70 is installed in a hybrid vehicle that is equipped with a motor 80 (FIG. 2) as a drive source for driving. In this embodiment, the engine 70 operates to generate driving force for traveling when the driving force of the motor 80 alone is insufficient. The engine 70 also operates when the amount of electric power of a power supply device (not shown) that supplies the motor 80 is reduced, and drives a generator 81 (FIG. 2) for supplying power to the power supply device. Generate electricity.

The engine 70 includes an engine body 1 that is driven by receiving fuel mainly composed of light oil, an intake passage 30 through which intake air introduced into the engine body 1 flows, and an exhaust gas discharged from the engine body 1. It includes an exhaust passage 40 that circulates, an EGR device 44 that recirculates a part of the exhaust gas that flows through the exhaust passage 40 to the intake passage 30, and a turbo supercharger 36 that is driven by the exhaust gas that passes through the exhaust passage 40. ing.

The engine body 1 is of an in-line multi-cylinder type having a plurality of cylinders 2 (only one of which is shown in FIG. 1) arranged in a direction perpendicular to the paper surface of FIG. The engine body 1 includes a cylinder block 3 including a plurality of cylindrical cylinder liners defining a plurality of cylinders 2, and a cylinder head 4 attached to the upper surface of the cylinder block 3 so as to close the upper opening of each cylinder 2. , and a plurality of pistons 5 accommodated in each cylinder 2 so as to be able to reciprocate and slide. Note that since the structure of each cylinder 2 is the same, the following description will basically focus on only one cylinder 2.

A combustion chamber 6 is formed above the piston 5. The combustion chamber 6 is a space defined by the lower surface of the cylinder head 4, the inner peripheral surface (cylinder liner) of the cylinder 2, and the crown surface 50 of the piston 5. The combustion chamber 6 is supplied with the fuel by injection from an injector 15, which will be described later. The supplied mixture of fuel and air is combusted in the combustion chamber 6, and the piston 5, which is pushed down by the expansion force caused by the combustion, reciprocates in the vertical direction.

A crankshaft 7, which is an output shaft of the engine body 1, is provided below the piston 5. The crankshaft 7 is connected to the piston 5 via a connecting rod 8, and rotates around a central axis in accordance with the reciprocating motion (up and down motion) of the piston 5. A crank angle sensor SN1 is attached to the cylinder block 3. The crank angle sensor SN1 detects the angular velocity of the crankshaft 7, that is, the engine rotation speed.

The cylinder head 4 is formed with an intake port 9 and an exhaust port 10 that communicate with the combustion chamber 6 . An intake side opening, which is the downstream end of the intake port 9, and an exhaust side opening, which is the upstream end of the exhaust port 10, are formed on the lower surface of the cylinder head 4. The cylinder head 4 is assembled with an intake valve 11 that opens and closes an intake side opening and an exhaust valve 12 that opens and closes an exhaust side opening.

The cylinder head 4 is provided with an intake valve mechanism 13 and an exhaust valve mechanism 14 including a camshaft. The intake valve 11 and the exhaust valve 12 are driven to open and close by these valve mechanisms 13 and 14 in conjunction with the rotation of the crankshaft 7. The intake side valve operating mechanism 13 has a mechanism that can change the opening timing of the intake valve 11, and changes the closing timing of the intake valve 11 according to the operating conditions of the engine. When the closing timing of the intake valve 11 changes, the ratio of the volume of the combustion chamber 6 when the intake valve 11 is closed to the volume of the combustion chamber 6 at compression top dead center, which is the effective compression ratio of the engine, also changes.

One injector 15 for injecting fuel into the combustion chamber 6 is attached to the cylinder head 4 for each cylinder 2 . The injector 15 is attached to the cylinder head 4 so that its tip faces the combustion chamber 6 from the ceiling surface of the combustion chamber 6. The injector 15 is provided with an injection pressure sensor SN3 (FIG. 2) that detects the pressure of the fuel inside the injector 15, in other words, the injection pressure that is the pressure of the fuel injected from the injector 15. One injection pressure sensor SN3 is provided for each of the plurality of injectors 15 corresponding to the plurality of cylinders 2. Furthermore, an in-cylinder pressure sensor SN4 (FIG. 2) is attached to the cylinder head 4 to detect in-cylinder pressure, which is the pressure within the combustion chamber 6. One cylinder pressure sensor SN4 is provided in each combustion chamber 6 of each cylinder 2.

The turbocharger 36 includes a compressor 37 disposed in the intake passage 30, a turbine 38 disposed in the exhaust passage 40, and a turbine shaft 39 connecting the compressor 37 and the turbine 38. The turbine 38 rotates by receiving the energy of the exhaust gas flowing through the exhaust passage 40. The compressor 37 compresses (supercharges) the air flowing through the intake passage 30 by rotating in conjunction with the rotation of the turbine 38 .

The intake passage 30 is connected to one side of the cylinder head 4 so as to communicate with the intake port 9. Air (fresh air) taken in from the upstream end of the intake passage 30 is introduced into the combustion chamber 6 through the intake passage 30 and the intake port 9. In the intake passage 30, an air cleaner 31, a compressor 37, a throttle valve 32, an intercooler 33, and a surge tank 34 are arranged in order from the upstream side. An air flow sensor SN2 is attached to the intake passage 30 for detecting the amount of intake air, which is the amount of air taken into the engine body 1. The air flow sensor SN2 is disposed downstream of the air cleaner 31 and detects the flow rate of intake air passing through this portion.

The exhaust passage 40 is connected to the other side of the cylinder head 4 so as to communicate with the exhaust port 10. Burnt gas (exhaust gas) generated in the combustion chamber 6 is exhausted to the outside of the vehicle through the exhaust port 10 and the exhaust passage 40. In the exhaust passage 40, a turbine 38 and an exhaust purification device 41 are arranged in this order from the upstream side. The exhaust purification device 41 includes an oxidation catalyst 42 and a DPF (diesel particulate filter) 43 built in in this order from the upstream side.

The oxidation catalyst 42 is for oxidizing carbon monoxide and hydrocarbons in the exhaust gas to render them harmless. The oxidation catalyst 42 is configured to be able to adsorb and release hydrocarbons and to store and desorb oxygen. For example, the oxidation catalyst 42 used is a honeycomb carrier on which platinum and ceria (cerium oxide) are supported. The DPF 43 collects particulate matter contained in exhaust gas.

An exhaust O2 sensor SN5 is attached to the exhaust passage 40 to detect the exhaust O2 concentration, which is the oxygen concentration of exhaust gas. The exhaust O2 sensor SN5 is provided in a portion of the exhaust passage 40 between the turbine 38 and the exhaust purification device 41, and detects the oxygen concentration of the exhaust gas passing through this portion.

Further, in the exhaust passage 40, a first exhaust temperature sensor SN6 is provided at a portion downstream of the exhaust O2 sensor SN5 and upstream of the exhaust purification device 41 for detecting the temperature of the exhaust gas passing through this portion. installed. Further, a second exhaust temperature sensor SN7 is attached to a portion of the exhaust purification device 41 between the oxidation catalyst 42 and the DPF 43 to detect the temperature of exhaust gas passing through this portion. The temperature of the oxidation catalyst 42 and the amount of temperature rise occurring in the oxidation catalyst 42 (the amount of temperature rise of the exhaust gas due to passing through the oxidation catalyst 42) are detected by the first exhaust temperature sensor SN6 and the second exhaust temperature sensor SN7. These exhaust temperature sensors SN6 and SN7 correspond to the "catalyst temperature detection device" in the claims.

The EGR device 44 includes an EGR passage 45 that connects the exhaust passage 40 and the intake passage 30, and an EGR valve 46 that is provided in the EGR passage 45 and can be opened and closed. The EGR passage 45 connects a portion of the exhaust passage 40 upstream of the turbine 38 and a portion of the intake passage 30 between the intercooler 33 and the surge tank 34. The EGR valve 46 adjusts the flow rate of exhaust gas (EGR gas) that is returned from the exhaust passage 40 to the intake passage 30 through the EGR passage 45.

(2) Control System FIG. 2 is a block diagram showing a control system for the engine 70 and motor 80. A PCM 100 shown in this figure is a microprocessor for controlling all parts of the engine such as the injector 15, the motor 80, and the generator 81, and is composed of a well-known CPU, ROM, RAM, and the like.

Detection information from various sensors is input to the PCM 100. For example, the PCM 100 is electrically connected to the aforementioned crank angle sensor SN1, air flow sensor SN2, injection pressure sensor SN3, cylinder pressure sensor SN4, exhaust O2 sensor SN5, first exhaust temperature sensor SN6, and second exhaust temperature sensor SN7. has been done. The PCM 100 includes information detected by each of these sensors SN1 to SN7, that is, engine speed, intake air amount, injection pressure, in-cylinder pressure, exhaust O2 concentration, exhaust temperature upstream of the oxidation catalyst 42, and the temperature of the oxidation catalyst 42. Information such as downstream exhaust temperature is input sequentially. The vehicle is also provided with an accelerator opening sensor SN8 that detects the opening of an accelerator pedal operated by the driver of the vehicle. Information detected by this accelerator opening sensor SN8 is also sequentially input to the PCM 100.

The PCM 100 executes various determinations and calculations based on information etc. input from each sensor SN1 to SN8. The PCM 100 controls each part of the engine as described above, and also diagnoses the oxidation catalyst 42, that is, determines whether the oxidation catalyst 42 is normal. In this embodiment, this PCM 100 corresponds to the "determination device" in the claims. Further, a system including the PCM 100, the first exhaust temperature sensor SN6, and the second exhaust temperature sensor SN7 corresponds to an "oxidation catalyst diagnostic device."

A configuration for diagnosing the oxidation catalyst 42 included in the PCM 100, which is a characteristic configuration of the present invention, will be described.

The PCM 100 functionally includes a theoretical temperature increase amount calculation section 101, a determination section 120, and an HC reduction amount estimation section 130. The theoretical temperature increase amount calculation section 101 functionally includes an HC adsorption amount estimation section 102 and a temperature increase amount estimation section 103.

The HC adsorption amount estimation unit 102 estimates the amount of hydrocarbons adsorbed on the oxidation catalyst 42 at each time when the engine is operating, that is, when the crankshaft 7 is rotating. Hereinafter, the amount of hydrocarbons adsorbed on the oxidation catalyst 42 will be referred to as the HC adsorption amount.

The temperature rise estimation section 103 calculates the amount of temperature rise of the oxidation catalyst 42 caused by oxidation of hydrocarbons, based on the HC adsorption amount estimated by the HC adsorption amount estimation section 102, assuming that the oxidation catalyst 42 is normal. Estimate. Hereinafter, the amount of temperature increase estimated by the temperature increase amount estimating unit 103 will be referred to as the theoretical temperature increase amount.

The determination unit 120 determines the temperatures on the upstream and downstream sides of the oxidation catalyst 42 detected by the first exhaust temperature sensor SN6 and the second exhaust temperature sensor SN7, and the theoretical temperature increase amount estimated by the temperature increase amount estimation unit 103. It is determined whether the oxidation catalyst 42 is normal or not based on the comparison result.

Here, when the engine body 1 stops, the flow of exhaust gas from the engine body 1 to the oxidation catalyst 42 stops, and the flow of oxygen to the oxidation catalyst 42 also stops. From this, it was considered that while the engine was stopped, the oxidation reaction in the oxidation catalyst 42 was stopped, and the amount of HC adsorbed by the oxidation catalyst 42 was maintained at the amount immediately before the engine was stopped. However, the inventors of the present application have found that the amount of HC adsorbed by the oxidation catalyst 42 may decrease while the engine is stopped. When the HC adsorption amount of the oxidation catalyst 42 decreases while the engine is stopped, if the oxidation catalyst 42 is diagnosed as described above (i.e., the HC adsorption amount is estimated based on the engine operating conditions when the engine is running). , the theoretical temperature increase amount is calculated based on this, and the oxidation catalyst 42 is diagnosed based on the theoretical temperature increase amount). Diagnostic accuracy may be reduced.

As a result of intensive research on this matter, the inventors of the present application found that when the temperature of the oxidation catalyst 42 exceeds a predetermined temperature, the amount of HC adsorbed by the oxidation catalyst 42 becomes almost zero. It was also found that the HC adsorption amount of the oxidation catalyst 42 decreases significantly when the engine is stopped when the oxidation catalyst 42 has a large HC adsorption amount.

Furthermore, the inventors of the present application have found that when the amount of HC adsorbed by the oxidation catalyst 42 immediately before the engine is stopped is small, the decrease in the amount of HC adsorbed during the engine is We found that it can be estimated by quantity. This is because while the engine is stopped, the oxygen desorbed from the oxidation catalyst 42 reacts with the hydrocarbons adsorbed on the oxidation catalyst 42, and when the amount of HC adsorption is small, the amount of HC adsorption mainly decreases due to this reaction. This is thought to be due to the fact that

Based on the above knowledge, if the HC adsorption amount immediately before the engine is stopped is equal to or greater than the preset determination adsorption amount (predetermined amount), the determination unit 120 determines that the temperature of the oxidation catalyst 42 after the engine is started is set to the preset reference temperature. Diagnosis of the oxidation catalyst 42 based on the theoretical temperature increase amount is stopped until the temperature reaches (predetermined temperature) or higher. That is, the determination by the determination unit 120 as to whether or not the oxidation catalyst 42 is normal is stopped. Then, when the temperature of the oxidation catalyst 42 reaches or exceeds the reference temperature, the HC adsorption amount estimation section 102 sets the estimated value of the HC adsorption amount to zero. Note that the determined adsorption amount is based on experiments and the like, even if the amount of decrease in the HC adsorption amount of the oxidation catalyst 42 while the engine is stopped is not taken into account in the estimation of the HC adsorption amount of the oxidation catalyst 42 after the engine is started. The maximum value of the HC adsorption amount that does not cause erroneous diagnosis of 42 is set and stored in the PCM 100. Further, the reference temperature is set based on experiments and the like to be the minimum value of the temperature of the oxidation catalyst 42 when the amount of HC adsorbed by the oxidation catalyst 42 becomes almost zero, and is stored in the PCM 100. The reference temperature is set, for example, to 300°C.

In addition, if the HC adsorption amount immediately before the engine is stopped is less than the determined adsorption amount, the total decrease in the HC adsorption amount while the engine is stopped is estimated based on the amount of oxygen desorbed from the oxidation catalyst 42 to estimate the HC adsorption amount. The HC adsorption amount estimated by the section 102 is corrected by this total decrease amount, and the diagnosis of the oxidation catalyst 42 based on the theoretical temperature increase amount by the determination section 120 is started immediately after the engine is started.

The HC reduction amount estimating section 130 is a section that estimates the total reduction amount of the HC adsorption amount while the engine is stopped. The HC reduction amount estimating unit 130 estimates the amount of oxygen desorbed from the oxidation catalyst 42 while the engine is stopped, and based on this amount, calculates the HC reduction amount during stoppage, which is the total reduction in the amount of HC adsorption while the engine is stopped. Estimate. Then, the HC adsorption amount estimating unit 102 corrects the HC adsorption amount using the HC reduction amount at the time of stop.

(3) Details of each calculation unit (HC reduction amount estimation unit)
The HC reduction amount estimation section 130 functionally includes an oxygen storage rate calculation section 131 shown in FIG. The oxygen storage rate calculation unit 131 calculates the oxygen storage rate X4, which is the rate of oxygen stored in the oxidation catalyst 42 at each time during engine operation, that is, the amount of oxygen stored in the oxidation catalyst 42 per unit time. Calculate.

The oxygen storage rate calculation unit 131 calculates oxygen storage based on the catalyst temperature X1 that is the temperature of the oxidation catalyst 42, the exhaust O2 concentration X2 detected by the exhaust O2 sensor SN5, and the exhaust flow rate X3 that is the flow rate of exhaust gas. Calculate speed X4. The PCM 100 separately estimates the catalyst temperature X1 based on each detection value of the first exhaust temperature sensor SN6 and the second exhaust temperature sensor SN7, the intake air amount detected by the air flow sensor SN2, and the like. The intake air amount detected by the air flow sensor SN2 is used for the exhaust flow rate X3.

As shown in the graphs in FIG. 4, the oxygen storage rate calculation unit 131 calculates that the higher the catalyst temperature X1, the higher the oxygen storage rate X4, the higher the exhaust O2 concentration X2, the higher the oxygen storage rate X4, and the higher the exhaust flow rate X3. The oxygen storage rate X4 is calculated based on the catalyst temperature X1, the exhaust O2 concentration X2, and the exhaust flow rate X3 such that the larger the oxygen storage rate X4 is, the smaller the oxygen storage rate X4 is.

The HC reduction amount estimation section 130 integrates the oxygen storage speed X4 at each time calculated by the oxygen storage speed calculation section 131 while the engine is operating. Thereby, the operating oxygen storage amount X5, which is the oxygen storage amount of the oxidation catalyst 42 at each time during engine operation, is calculated. Calculation of the operating oxygen storage amount X5 is performed only while the engine is operating, and after the engine has stopped, the operating oxygen storage amount X5 is maintained at the value immediately before the engine was stopped.

The HC reduction amount estimating section 130 functionally includes an adsorbed HC species proportion estimating section 132 shown in FIG. A plurality of types of hydrocarbons having different carbon bond structures are discharged from the engine body 1 . The susceptibility of hydrocarbons to oxidation varies depending on the carbon bond structure. The adsorbed HC species ratio estimating unit 132 calculates the ratio of various types of hydrocarbons with different oxidizability (hereinafter referred to as appropriate) to the total amount of hydrocarbons adsorbed on the oxidation catalyst 42 at each time during engine operation. (referred to as adsorption ratio). In this embodiment, the hydrocarbons include hydrocarbons that are not aromatic and are C5 or higher (5 or more carbons are bonded), hydrocarbons that are lower than C5 (less than 5 carbons are bonded), and aromatic hydrocarbons. The adsorbed HC species ratio estimation unit 132 estimates the adsorption ratio of these three types of hydrocarbons. Hereinafter, hydrocarbons of C5 or higher will be referred to as the first HC type, hydrocarbons of less than C5 will be referred to as the second HC type, and aromatic hydrocarbons will be referred to as the third HC type. The susceptibility to oxidation of these three types of hydrocarbons is in the following order: first HC type, second HC type, and third HC type.

The adsorbed HC species proportion estimating unit 132 first estimates the proportion of each HC species in the total amount of hydrocarbons discharged from the engine body 1 (hereinafter referred to as the discharge proportion as appropriate) at each time during engine operation. The discharge rate of each HC type changes depending on the combustion temperature of the mixture in the combustion chamber 6, and the combustion temperature changes depending on the excess air ratio λ of the mixture in the combustion chamber 6 and the effective compression ratio. Specifically, as shown in FIGS. 6 and 7, the higher the excess air ratio λ and the higher the effective compression ratio, the higher the proportion of the first HC type discharged from the engine body 1. The emission rate of 2HC species and the emission rate of tertiary HC species decrease. From this, the adsorbed HC species proportion estimating unit 132 sets the relationship between the excess air ratio λ (X20), the effective compression ratio (X21), and the discharge rate of each HC species to be the relationship shown in FIGS. 6 and 7. The discharge rate of each HC type is estimated based on the excess air ratio λ (X20) of the air-fuel mixture and the effective compression ratio (X21) at each time. Note that the excess air ratio λ is a value obtained by dividing the air-fuel ratio of the air-fuel mixture by the stoichiometric air-fuel ratio. The PCM 100 separately calculates the excess air ratio λ at each time based on the amount of intake air detected by the air flow sensor SN2 and the amount of fuel injected from the injector 15. Furthermore, the PCM 100 separately calculates the effective compression ratio at each time based on the closing timing of the intake valve 11.

Next, the adsorbed HC species ratio estimation unit 132 averages the estimated emission ratio of each HC species at each time during engine operation for a predetermined period, and calculates each average value for each HC species adsorbed on the oxidation catalyst 42. Let the adsorption ratio be . In this way, the HC reduction amount estimating unit 130 calculates the first HC species adsorption ratio X22_a, which is the ratio of the first HC species adsorbed on the oxidation catalyst 42, the second HC species adsorption ratio X22_b, which is the ratio of the first HC species, and the second HC species adsorption ratio The third HC species adsorption ratio X22_c, which is the ratio of the 3HC species, is estimated. After the engine main body 1 stops, the calculation of each of these HC species adsorption ratios X22_a to X22_c is stopped, and the last calculated value is maintained. That is, after the engine is stopped, until the engine main body 1 is restarted, each HC species adsorption ratio X22_a to X22_c is maintained at the average value for the period from immediately before the engine stops to a predetermined period before.

The HC reduction amount estimation section 130 further functionally includes an O2 desorption rate calculation section 133 shown in FIG. 8 and a stop HC oxidation rate calculation section 134. The calculations of the O2 desorption rate calculation unit 133 and the stop HC oxidation rate calculation unit 134, which will be explained below, are performed only when the HC adsorption amount immediately before the engine stops is less than the determined adsorption amount, as will be described later. Only then, the HC reduction amount estimating unit 130 estimates the HC reduction amount at the time of stop.

The O2 desorption rate calculation unit 133 calculates the O2 desorption rate, which is the desorption rate of oxygen from the oxidation catalyst 42, that is, the amount of oxygen desorbed from the oxidation catalyst 42 per unit time, at each time while the engine is stopped. Estimate the speed X6.

The O2 desorption rate calculation unit 133 calculates the O2 desorption rate X6 based on the operating oxygen storage amount X5 and the catalyst temperature X1. As described above, the operating oxygen storage amount X5 while the engine is stopped is maintained at the value immediately before the engine was stopped. From this, the operating oxygen storage amount X5 used for calculation by the O2 desorption rate calculation unit 133 is the operating oxygen storage amount X5 immediately before the engine is stopped.

As shown in the graph of FIG. 9, the O2 desorption rate calculation unit 133 calculates the O2 desorption rate so that the larger the oxygen storage amount of the oxidation catalyst 42, the greater the O2 desorption rate X6, and the higher the catalyst temperature X1. The O2 desorption rate X6 is estimated based on the oxygen storage amount X5b and the catalyst temperature X1 so that the rate X6 becomes large. In addition, the O2 desorption rate calculation unit 133 calculates the oxygen desorption amount X6a during engine stop, which is the amount of oxygen desorbed from the oxidation catalyst 42 while the engine is stopped, by integrating the estimated O2 desorption rate X6, The oxygen storage amount X5b of the oxidation catalyst 42 is updated by subtracting this oxygen desorption amount X6a when the engine is stopped from the operating oxygen storage amount X5 immediately before the engine is stopped.

The HC oxidation rate calculation unit 134 calculates the oxidation rate of hydrocarbons at the oxidation catalyst 42 at each time while the engine is stopped, that is, the amount of hydrocarbons oxidized by the oxidation catalyst 42 per unit time. Calculate the HC oxidation rate X7.

As mentioned above, the oxidation rate of hydrocarbons varies depending on the type of hydrocarbon. Further, the oxidation rate of hydrocarbons increases as the catalyst temperature X1 increases and as the O2 desorption rate X6 increases. From this, the HC oxidation rate calculation unit 134 at the time of stop calculates the O2 desorption rate X6 calculated by the O2 desorption rate calculation unit 133, the catalyst temperature X1, and each HC type calculated by the adsorbed HC species ratio estimation unit 132. Based on the adsorption ratio X22 (X22_a to X22_c), the HC oxidation rate X7 at the time of stop is estimated.

Specifically, as shown in FIG. 10, the stop HC oxidation rate calculation unit 134 calculates the oxidation rate (first HC species oxidation rate X71) for each HC species based on the O2 desorption rate X6 and the catalyst temperature X1. , the second HC species oxidation rate X72, and the third HC species oxidation rate X73). Next, the HC oxidation rate at stop calculation unit 134 multiplies the calculated oxidation rate of each HC species X71 to X73 by the adsorption ratio of the HC species X22_a to X22_c, and calculates the sum of the obtained values as the HC oxidation rate at stop Calculate as X7.

Then, as shown in FIG. 8, the HC reduction amount estimation unit 130 integrates the HC oxidation rate X7 at the time of engine stop, and calculates the amount of hydrocarbons oxidized by the oxidation catalyst 42 and released from the oxidation catalyst 42 after the engine is stopped. In other words, the HC reduction amount X8, which is the amount of reduction in the HC adsorption amount of the oxidation catalyst 42 that occurred after the engine was stopped, is calculated. HC reduction amount The estimation unit 130 estimates the operating oxygen storage amount X5 immediately before the engine is stopped based on the catalyst temperature X1, the exhaust O2 concentration X2, and the exhaust flow rate X3, and calculates the operating oxygen storage amount X5 and the catalyst temperature X1. Based on the adsorption ratio X22 of each HC species, the HC reduction amount at the time of stop is estimated.

(Theoretical temperature rise estimation section)
As shown in FIG. 11, the HC adsorption amount estimation section 102 of the theoretical temperature increase amount calculation section 101 functionally includes an HC adsorption/release rate calculation section 111. The HC adsorption/release rate calculation unit 111 calculates the adsorption rate of hydrocarbons present in the oxidation catalyst 42 to the oxidation catalyst 42 at each time during engine operation, that is, the rate of adsorption of hydrocarbons present in the oxidation catalyst 42 in unit time. The first HC adsorption rate X9a, which is the amount adsorbed on the oxidation catalyst 42 per hour, is estimated. In addition, the HC adsorption/release rate calculation unit 111 calculates the release rate of hydrocarbons from the oxidation catalyst 42 at each time during engine operation, that is, the amount of hydrocarbons released from the oxidation catalyst 42 per unit time. Estimate a certain HC release rate X10.

As shown in the two graphs in FIG. 12, the HC adsorption/release rate calculation unit 111 calculates that the higher the catalyst temperature X1 is, the lower the first HC adsorption rate X9a is, and the higher the exhaust flow rate X3 is, the lower the first HC adsorption rate X9a is. The first HC adsorption rate X9a is calculated based on the catalyst temperature X1 and the exhaust flow rate X3.

As shown in the three graphs in FIG. 13, the HC adsorption/release rate calculation unit 111 calculates that the larger the HC adsorption amount X11 is, the larger the HC release rate X10 is, and the higher the catalyst temperature X1 is, the larger the HC release rate X10 is. The HC release rate X10 is calculated based on the HC adsorption amount X11, the catalyst temperature X1, and the exhaust flow rate X3 so that the larger the exhaust flow rate X3, the higher the HC release rate X10.

The HC adsorption amount X11 is the total amount of hydrocarbons adsorbed on the oxidation catalyst 42, and is calculated by the following procedure. The HC adsorption amount estimating unit 102 adds the first HC adsorption rate X9a to the exhaust HC flow rate X30, which is the amount of hydrocarbons discharged from the engine body 1 at each time during engine operation, and calculates the HC release from the obtained value. By subtracting the speed X10, the HC adsorption speed X9b is calculated. Then, the HC adsorption amount estimation unit 102 integrates the calculated HC adsorption speed X9b, and calculates the HC adsorption amount X11 of the oxidation catalyst 42 at each time during engine operation.

It is known that the above-mentioned exhaust HC flow rate X30 changes depending on the engine speed, engine load, excess air ratio, in-cylinder pressure, and injection pressure, and the HC adsorption amount estimation unit 102 calculates the exhaust HC flow rate X30 from each of these values. Calculate.

The calculation of the exhaust HC flow rate X30, the first HC adsorption rate X9a, the HC release rate X10, the HC adsorption rate X9b, and the integration of the HC adsorption rate X9b, which are performed by the HC adsorption amount estimation unit 102, are performed only during engine operation. . Accordingly, when the engine is stopped, the HC adsorption amount X11 output from the HC adsorption amount estimating section 102 is maintained at the value immediately before the engine was stopped.

When the engine stops, the HC adsorption amount estimating unit 102 determines whether the HC adsorption amount X11 estimated as described above, that is, the pre-stop HC adsorption amount X11, which is the HC adsorption amount X11 immediately before the engine stop, is greater than or equal to the judgment adsorption amount. Determine whether When the HC adsorption amount X11 is less than the determined adsorption amount, the HC adsorption amount X11 is corrected by the HC reduction amount at stop X8 when the engine is started (for example, when the engine speed exceeds a predetermined value). . Specifically, the HC adsorption amount estimating unit 102 updates the HC adsorption amount X11 by subtracting the HC reduction amount X8 at the time of stop from the pre-stop HC adsorption amount X11. After starting the engine, the HC adsorption amount X11 is updated by integrating the HC adsorption speed X9b with respect to the updated HC adsorption amount X11.

On the other hand, when the pre-stop HC adsorption amount X11 is equal to or greater than the determined adsorption amount, the HC adsorption amount estimation unit 102 stops correcting the HC adsorption amount using the HC reduction amount during stop X8. Further, at this time, the HC adsorption amount estimation unit 102 sets the HC adsorption amount X11 to zero when the temperature of the oxidation catalyst 42 becomes equal to or higher than the reference temperature after the engine is started.

The temperature increase estimation section 103 of the theoretical temperature increase amount calculation section 101 functionally includes an HC oxidation rate calculation section 112 during operation. The operating HC oxidation rate calculation unit 112 calculates the oxidation rate of hydrocarbons at the oxidation catalyst 42 at each time during engine operation, that is, the amount of hydrocarbons oxidized by the oxidation catalyst 42 per unit time. HC oxidation rate X12 is calculated.

As shown in FIG. 14, the operating HC oxidation rate calculating unit 112 calculates the operating HC oxidation rate X12 such that the larger the HC release rate X10 is, the greater the operating HC oxidation rate X12 is, and the higher the catalyst temperature X1 is, the larger the operating HC oxidation rate X12 is. Next, an operating HC oxidation rate X12 is calculated based on the HC release rate X10 and the catalyst temperature X1.

Next, the temperature increase estimation unit 103 multiplies the operating HC oxidation rate X12 by the heat generation coefficient X13, and calculates the product as the theoretical temperature increase X14. The heat generation coefficient X13 is the amount of temperature rise of the oxidation catalyst 42 that occurs when a unit amount of hydrocarbon is oxidized, and is set in advance and stored in the PCM 100.

(Judgment Department)
The determination unit 120 subtracts the temperature on the upstream side of the oxidation catalyst 42 detected by the first exhaust gas temperature sensor SN6 from the temperature on the downstream side of the oxidation catalyst 42 detected by the second exhaust temperature sensor SN7, and determines the temperature of the oxidation catalyst 42 The detected value of the temperature rise amount (hereinafter referred to as the actual temperature rise amount) is calculated. Then, if the absolute value of the difference between the actual temperature increase amount and the theoretical temperature increase amount If the absolute value is less than the determined increase amount, it is determined that the oxidation catalyst 42 is normal. The above-mentioned determination increase amount is set in advance through experiments and the like and is stored in the PCM 100.

As described above, when the pre-stop HC adsorption amount The determination of the oxidation catalyst 42 is stopped, and when the temperature of the oxidation catalyst 42 becomes equal to or higher than the reference temperature, the determination described above is started. On the other hand, if the pre-stop HC adsorption amount X11 is less than the determined adsorption amount, the determination unit 120 starts the above-mentioned determination immediately after the engine is started.

(Flow of oxidation catalyst diagnostic procedure)
The above procedure for diagnosing the oxidation catalyst 42 can be summarized as shown in the flowcharts of FIGS. 15 and 16.

First, the PCM 100 determines whether the engine is operating in step S1. For example, if the engine speed is equal to or higher than a predetermined value, it is determined that the engine is in operation.

If the determination in step S1 is YES and the engine is in operation, the process proceeds to step S2, and the PCM 100 determines whether or not the engine is being started.

If the determination in step S2 is YES and the engine is started, the PCM 100 determines whether or not the pre-stop HC adsorption amount X11, which is the HC adsorption amount X11 estimated immediately before the engine stop, is less than the determined adsorption amount in step S3. Determine whether If this determination is YES and the pre-stop HC adsorption amount After subtracting and correcting the HC adsorption amount X11 by the HC reduction amount X8, step S7 is executed.

If the determination in step S3 is NO and the pre-stop HC adsorption amount It is determined whether the catalyst temperature X1 has risen to a reference temperature or higher. If this determination is YES and the catalyst temperature X1 is equal to or higher than the reference temperature, the process proceeds to step S5 and the HC adsorption amount X11 is set to zero. On the other hand, if the determination in step S4 is NO and the catalyst temperature X1 is less than the reference temperature, step S4 is performed again. That is, after starting the engine, the PCM 100 waits until the catalyst temperature X1 becomes equal to or higher than the reference temperature, and proceeds to the next step only when the temperature becomes equal to or higher than the reference temperature.

After step S6 or step S5, in step S7, the PCM 100 calculates the HC adsorption rate X9b and the HC release rate X10. As described above, the PCM 100 calculates the HC release rate X10 based on the HC adsorption amount X11 calculated one calculation cycle ago, the catalyst temperature X1, and the exhaust flow rate X3. Further, the PCM 100 calculates the HC adsorption rate X9b based on the first HC adsorption rate X9a calculated based on the catalyst temperature X1 and the exhaust flow rate X3, the exhaust HC flow rate X30, and the HC release rate X10, and The adsorption amount X11 is updated.

After step S7, the PCM 100 calculates the operating HC oxidation rate X12 in step S8. As described above, the PCM 100 calculates the operating HC oxidation rate X12 based on the HC release rate X10 and the catalyst temperature X1.

After step S8, the PCM 100 calculates the theoretical temperature increase amount X14 in step S9. As described above, the PCM 100 calculates the theoretical temperature increase amount X14 based on the operating HC oxidation rate X12 and the heat generation coefficient X13.

After step S9, in step S10, the PCM 100 determines the absolute value of the difference between the actual temperature increase amount obtained from the detection values of the first exhaust temperature sensor SN6 and the second exhaust temperature sensor SN7 and the theoretical temperature increase amount X14. is less than the determined increase amount.

If the determination in step S10 is NO and the absolute value of the difference is greater than or equal to the determined increase amount, the PCM 100 determines that the oxidation catalyst 42 is abnormal (step S11). On the other hand, if the determination in step S7 is YES and the absolute value of the difference is less than the determined increase amount, the PCM 100 determines that the oxidation catalyst 42 is normal (step S12).

Further, while the engine is operating, the PCM 100 calculates the operating oxygen storage amount X5 (oxygen storage amount of the oxidation catalyst 42) at each time (step S13). When the processing from step S1 to step S13 is completed, the PCM 100 returns to step S1 again and repeats the processing from step S1 onward.

Returning to step S1, if the determination in step S1 is NO and the engine is not operating, that is, if the engine is stopped, the PCM 100 proceeds to step S20 shown in FIG. 16 and makes the same determination as step S3, that is, before stopping. It is determined whether the HC adsorption amount X11 is less than the determination adsorption amount. If this determination is NO and the pre-stop HC adsorption amount X11 is equal to or greater than the determined adsorption amount, the process is ended without performing the following steps S21 to S26 (return to step S1). On the other hand, if the determination in step S20 is YES and the pre-stop HC adsorption amount X11 is less than the determined adsorption amount, the PCM 100 proceeds to step S21 and determines whether the engine has just been stopped. If this determination is YES and the engine has just stopped, the PCM 100 proceeds to step S22, reads the oxygen storage amount calculated in step S10, that is, the operating oxygen storage amount X5 immediately before the engine stops, and proceeds to step S23. On the other hand, if the determination in step S21 is NO and the engine is not immediately stopped, the PCM 100 proceeds to step S23 without executing step S22.

In step S23, the PCM 100 calculates the O2 desorption rate X6. As described above, the PCM 100 calculates the O2 desorption rate X6 based on the oxygen storage amount of the oxidation catalyst 42, which is calculated based on the operating oxygen storage amount X5 read in step S22, and the catalyst temperature X1.

After step S23, in step S24, the PCM 100 calculates the HC oxidation rate X7 at the time of stop. As described above, the PCM 100 adjusts the HC during shutdown based on the O2 desorption rate X6 calculated in step S22, the adsorption ratio of each HC species (HC species adsorption ratio) X22 calculated in step S10, and the catalyst temperature X1. Calculate the oxidation rate X7.

After step S24, the PCM 100 calculates the HC reduction amount X8 in step S25. As described above, the PCM 100 calculates the HC reduction amount X8 based on the stop HC oxidation rate X7 determined in step S23.

After step S25, in step S26, the PCM 100 updates the oxygen storage amount X5b of the oxidation catalyst 42 and returns to end the process (step S1). As described above, the PCM 100 updates the oxygen storage amount X5b using the O2 desorption rate X6 calculated in step S23.

(4) Effects, etc. As explained above, in this embodiment, when the engine is operating, the exhaust HC flow rate X30, which is the flow rate of hydrocarbons discharged from the engine body 1, and Based on the exhaust flow rate X3, an HC adsorption amount X11, which is the amount of hydrocarbons adsorbed on the oxidation catalyst 42, is estimated. If the pre-stop HC adsorption amount X11, which is the HC adsorption amount before engine stop, is greater than or equal to the determined adsorption amount and the HC adsorption amount decreases significantly while the engine is stopped, HC adsorption is performed for a predetermined period after the engine is started. Diagnosis of the oxidation catalyst 42 based on the theoretical temperature increase amount calculated based on the amount X11 is stopped. On the other hand, if the pre-stop HC adsorption amount X11 is less than the determined adsorption amount and the decrease in the HC adsorption amount while the engine is stopped is small, the oxidation catalyst 42 is Perform diagnosis. As a result, according to the present embodiment, it is possible to prevent the oxidation catalyst 42 from being misdiagnosed due to a significant reduction in the amount of HC adsorption while the engine is stopped, and to ensure many opportunities for diagnosing the oxidation catalyst 42.

Furthermore, in this embodiment, the predetermined period is the period from when the engine starts until the catalyst temperature X1 becomes equal to or higher than the reference temperature. That is, when the pre-stop HC adsorption amount X11 is equal to or greater than the determined adsorption amount, after the engine is started, the catalyst temperature Diagnosis of the oxidation catalyst 42 is stopped until the amount of HC reduction at the time of stop has no effect on the amount of HC, and thereafter the diagnosis is restarted. Therefore, while ensuring the estimation accuracy of the HC adsorption amount X11 and the diagnosis accuracy, it is possible to prevent the suspension period of the diagnosis from becoming excessively long and to ensure a diagnosis opportunity.

In addition, if the pre-stop HC adsorption amount Correct the HC adsorption amount X11 during operation. Therefore, it is possible to improve the estimation accuracy of the HC adsorption amount X11 after the engine is started, and furthermore, the calculation accuracy of the theoretical temperature increase amount calculated based on this HC adsorption amount X11. Therefore, the accuracy of diagnosing the oxidation catalyst in the above case can be further improved.

Further, as the O2 desorption rate X6 increases, the oxidation rate of hydrocarbons increases, and the amount of decrease in hydrocarbons adsorbed on the oxidation catalyst 42 increases. Correspondingly, in this embodiment, as shown in FIG. 10, the larger the O2 desorption rate X6 is, the greater the HC oxidation rate X7 at the time of stop is estimated, and by integrating this, HC reduction amount X8 is being calculated. Therefore, it is possible to reliably improve the estimation accuracy of the HC reduction amount X8 at the time of stop.

Furthermore, in this embodiment, as shown in FIG. 8, the operating oxygen storage amount X5 immediately after the engine is stopped, that is, the oxygen amount stored in the oxidation catalyst 42 immediately after the engine is stopped, is used to store oxygen during the engine stop. Estimating the amount. Therefore, the accuracy of estimating the amount of oxygen stored while the engine is stopped and the O2 desorption rate X6 estimated from this can be increased, and the accuracy of estimating the amount of HC reduction during engine stop X8 can be more reliably increased.

(5) Modification In the above embodiment, when the pre-stop HC adsorption amount X11 is less than the determined adsorption amount, the diagnosis of the oxidation catalyst 42 based on the HC adsorption amount X11 and the theoretical temperature increase amount is started immediately after the engine starts. As described above, even when the pre-stop HC adsorption amount X11 is less than the determined adsorption amount, the diagnosis may be started after a certain amount of time has elapsed since the engine was started. However, in this configuration as well, in order to ensure a large number of diagnostic opportunities, the elapsed time is set to be shorter than the predetermined period in which the diagnosis is stopped when the pre-stop HC adsorption amount X11 is equal to or greater than the determined adsorption amount.

In the embodiment, when the engine 70 is installed in a vehicle equipped with the motor 80 as a drive source for running, and the driving force of the motor 80 alone is insufficient, or when the amount of electric power of the output supply device is reduced, Although the case where only the engine 70 is operated has been described, the vehicle in which the engine 70 according to the embodiment is mounted is not limited to this, and may be mounted in a vehicle that uses only the engine 70 as a drive source for traveling.

However, as mentioned above, in a vehicle where the timing at which the engine 70 operates is limited, the time from when the engine starts until it stops is relatively short, so in order to ensure an opportunity to diagnose the oxidation catalyst 42, It is desirable to diagnose the oxidation catalyst 42 from an early timing after starting the engine. Therefore, if the oxidation catalyst 42 diagnosis device according to this embodiment is applied to a vehicle such as the one described above in which the timing at which the engine 70 operates is limited, it is possible to effectively secure an opportunity to diagnose the oxidation catalyst 42. . For the same reason, it is effective if the oxidation catalyst 42 diagnostic device according to the present embodiment is applied to a vehicle having a so-called idle stop function in which the engine 70 is automatically stopped when the vehicle is stopped.

As described above, when the catalyst temperature X1 becomes equal to or higher than the reference temperature, the HC adsorption amount X11 becomes almost zero, so that the influence of the HC reduction amount X8 during stoppage on the HC adsorption amount X11 is almost eliminated. From this, when the catalyst temperature X1 becomes equal to or higher than the reference temperature, it becomes possible to accurately estimate the HC adsorption amount X11 based on the operating conditions of the engine. Therefore, in the embodiment described above, the HC adsorption amount X11 is set to zero when the catalyst temperature X1 becomes equal to or higher than the reference temperature after the engine is started and the pre-stop HC adsorption amount X11 is equal to or higher than the determined adsorption amount. The HC adsorption amount X11 may be calculated from the operating conditions of the engine.

Furthermore, in the embodiment, after the engine is started in which the pre-stop HC adsorption amount X11 is equal to or higher than the determined adsorption amount, the estimation of the HC adsorption amount and the diagnosis of the oxidation catalyst 42 are restarted when the catalyst temperature becomes equal to or higher than the reference temperature. However, the estimation and diagnosis may be restarted when the elapsed time from the start of the engine reaches a predetermined time or more. In this case, the time from when the engine is started until the catalyst temperature becomes equal to or higher than the reference temperature may be determined through experiments or the like, and the determined time may be set as the predetermined time.

1 Engine body 40 Exhaust passage 42 Oxidation catalyst 70 Engine 80 Motor 100 PCM (judgment device)
102 HC adsorption amount estimation section 103 Temperature rise amount estimation section 120 Judgment section 130 HC reduction amount estimation section SN6 First exhaust temperature sensor (catalyst temperature detection device)
SN7 2nd exhaust temperature sensor (catalyst temperature detection device)

Claims (6)

An engine body in which cylinders are formed, an exhaust passage through which exhaust gas discharged from the cylinder flows, and an oxidation catalyst installed in the exhaust passage and capable of adsorbing and oxidizing hydrocarbons and occluding and desorbing oxygen. An oxidation catalyst diagnostic device installed in an engine equipped with
a catalyst temperature detection device that detects the temperature of the oxidation catalyst;
a determination device that determines whether the oxidation catalyst is normal;
The determination device includes:
an HC adsorption amount estimating unit that estimates an HC adsorption amount, which is the amount of hydrocarbons adsorbed on the oxidation catalyst, based on engine operating conditions when the output shaft of the engine body rotates;
a temperature rise amount estimating unit that estimates a temperature rise amount of the oxidation catalyst that occurs when the oxidation catalyst is assumed to be normal, based on the HC adsorption amount estimated by the HC adsorption amount estimation unit;
During engine operation, the amount of temperature rise of the oxidation catalyst based on the detected value of the catalyst temperature detection device is compared with the amount of temperature rise estimated by the temperature rise amount estimation section, and the a determination unit that determines whether the oxidation catalyst is normal;
If the pre-stop HC adsorption amount, which is the HC adsorption amount immediately before the engine is stopped, estimated by the HC adsorption amount estimating unit is equal to or greater than a predetermined amount, the determination unit stops the determination for a predetermined period after the engine starts. ,
An oxidation catalyst diagnostic apparatus, wherein when the pre-stop HC adsorption amount is less than the predetermined amount, the determination section starts the determination before the predetermined period elapses after starting the engine. The oxidation catalyst diagnostic device according to claim 1,
If the pre-stop HC adsorption amount is equal to or greater than the predetermined amount, the determination unit starts the determination when the predetermined period of time has elapsed after starting the engine;
An oxidation catalyst diagnostic device, wherein when the pre-stop HC adsorption amount is less than the predetermined amount, the determination section starts the determination immediately after starting the engine. The oxidation catalyst diagnostic device according to claim 1 or 2,
The oxidation catalyst diagnostic device, wherein the predetermined period is a period from when the engine starts until the temperature of the oxidation catalyst reaches a predetermined temperature or higher. The oxidation catalyst diagnostic device according to any one of claims 1 to 3,
The determination device estimates an O2 desorption rate that is a rate of oxygen desorbed from the oxidation catalyst while the engine is stopped, and based on the O2 desorption rate, determines the amount of oxygen adsorbed to the oxidation catalyst that occurs while the engine is stopped. further comprising an HC reduction amount estimating unit that estimates an HC reduction amount at the time of shutdown, which is a total reduction amount of hydrocarbons in the vehicle;
When the pre-stop HC adsorption amount is less than the predetermined amount, the HC adsorption amount estimator calculates the HC adsorption amount during engine operation based on the stop HC reduction amount estimated by the HC reduction amount estimator. A diagnostic device for an oxidation catalyst, characterized in that it corrects an estimated value of. The oxidation catalyst diagnostic device according to claim 4,
The HC reduction amount estimating unit estimates the amount of oxygen stored in the oxidation catalyst immediately before stopping the engine, and estimates the HC reduction amount at the time of stop based on the estimated oxygen storage amount. A diagnostic device for oxidation catalysts. The oxidation catalyst diagnostic device according to any one of claims 1 to 5,
An oxidation catalyst diagnostic device, wherein the engine is mounted on a hybrid vehicle having a motor as a drive source for running.

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