JP7380263B2 - 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 total 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. a determination unit that compares the oxidation catalyst and determines whether or not the oxidation catalyst is normal based on the comparison results; and a determination unit that determines in advance whether or not the oxidation catalyst is normal based on the comparison results , and a purification rate of the oxidation catalyst among various hydrocarbons contained in the exhaust gas is set in advance. a determination HC adsorption amount estimating unit that estimates a determination HC adsorption amount, which is the amount of hydrocarbons having a reference purification rate or higher adsorbed on the oxidation catalyst immediately before the engine is stopped; When the HC adsorption amount is equal to or greater than a preset determination amount, the determination section stops the determination for a predetermined period after the engine starts, and when the determination HC adsorption amount is less than the determination amount, the determination section (Claim 1) is characterized in that the determination is started before the predetermined period of time has elapsed after starting the engine.

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 value. Therefore, whenever the engine is operating, the amount of temperature rise can be estimated and the oxidation catalyst can be diagnosed based on this estimated value, increasing the number of opportunities for diagnosing the oxidation catalyst.

However, as described 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 has started is poor. There is a risk that it will decrease. 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 even while the engine is stopped, and the amount of easily oxidized hydrocarbons adsorbed on the oxidation catalyst exceeds a predetermined amount immediately before the engine stops. In this case, the amount of decrease in the hydrocarbons that occurs while the engine is stopped increases, and the performance of estimating the amount of HC adsorption and diagnosing the oxidation catalyst based on the engine operating conditions immediately after the engine is started will deteriorate. Furthermore, it was found that the accuracy of estimating the amount of HC adsorption based on the operating conditions of the engine increases again after a predetermined period of time has elapsed since the engine was started.

Based on this knowledge, in the present invention, as described above, the determination HC adsorption amount, which is the amount of easily oxidized hydrocarbons adsorbed on the oxidation catalyst immediately before the engine is stopped, is determined to be equal to or greater than the preset determination amount. However, if the diagnosis accuracy of the oxidation catalyst based on the HC adsorption amount during engine operation tends to be low immediately after the engine is started, 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 HC adsorption amount for determination is less than the determination amount and the diagnosis accuracy of the oxidation catalyst can be increased even after the engine is started, the diagnosis is performed from an early stage after the engine is started. This provides more opportunities for highly accurate oxidation catalyst diagnosis.

In the configuration, preferably, when the determination HC adsorption amount is equal to or greater than the determination amount, the determination unit starts the determination when the predetermined period of time has elapsed after starting the engine, and the determination HC adsorption amount is preferably If it is less than the determination amount, the determination unit starts the determination immediately after starting the engine (Claim 2).

According to this configuration, while avoiding erroneous diagnosis of the oxidation catalyst, it is possible to more reliably increase the opportunities for the diagnosis.

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. From this, 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, while preventing erroneous diagnosis of the oxidation catalyst, Diagnosis opportunities can be increased by shortening the diagnostic stop period of the oxidation catalyst (Claim 3).

Here, hydrocarbons are broadly classified into aromatic, non-aromatic and having 5 or more carbons, and non-aromatic and having less than 5 carbons. It is known that it can be classified as

Therefore, in the above configuration, preferably, the determination HC adsorption amount estimating unit includes a first HC type that is aromatic, a second HC type that is not aromatic and has 5 or more carbons, and a second HC type that is not aromatic and has 5 or more carbons. For the third HC type having less than 5 carbons, calculate the pre-shutdown adsorption amount, which is the amount adsorbed on the oxidation catalyst immediately before the engine is stopped, and calculate the pre-shutdown adsorption amount of each HC type and the oxidation catalyst. The determination HC adsorption amount is estimated based on the temperature of the catalyst (Claim 4).

According to this configuration, it is possible to accurately estimate the determination HC adsorption amount with a relatively simple configuration.

It has also been found that the proportions of the first to third HC types in the total amount of hydrocarbons adsorbed on the oxidation catalyst vary depending on the excess air ratio and the effective compression ratio during engine operation.

Therefore, the configuration preferably includes an effective compression ratio changing means capable of changing the effective compression ratio of the cylinder, and the determination HC adsorption amount estimating section adjusts the excess air ratio and the effective compression ratio during engine operation. Based on this, the proportions each of the first HC type, second HC type, and third HC type account for in the total amount of hydrocarbons adsorbed on the oxidation catalyst are calculated, and the calculated proportions are calculated based on the calculated proportions and the proportions estimated by the HC adsorption amount estimator. The pre-stop adsorption amount of each of the first HC type, second HC type, and third HC type is calculated based on the HC adsorption amount.

According to this configuration, the amount of the first to third HC species adsorbed on the oxidation catalyst and the adsorption amount before each stop can be estimated with high accuracy.

According to the present invention, as described above, when the determination HC adsorption amount is less than the determination amount, the oxidation catalyst can be accurately diagnosed from an earlier period 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. 2 is a block diagram showing a procedure for calculating a theoretical temperature increase amount performed by a theoretical temperature increase amount calculation 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. 1 is a graph schematically showing the relationship between HC release rate, catalyst temperature, and HC oxidation rate. FIG. 2 is a block diagram illustrating a procedure for calculating a determination HC adsorption amount performed by a determination HC adsorption amount estimator. It is a graph schematically showing the relationship between the excess air ratio and the discharge rate of each HC species. 2 is a graph schematically showing the relationship between the effective compression ratio and the discharge rate of each HC species. 2 is a graph schematically showing the relationship between catalyst temperature and purification rate for each HC type. 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. The intake side valve operating mechanism 13 corresponds to the "effective compression ratio changing means" in the claims.

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 calculation section 101, a determination section 120, and a determination HC adsorption 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 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 results.

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 when the engine is running is estimated based on the engine operating conditions). However, if the theoretical temperature increase amount is calculated based on this, and the oxidation catalyst 42 is diagnosed by the determination unit 120 based on the theoretical temperature increase amount), the decrease in the amount of HC adsorption during engine stop is not taken into account. , the diagnostic accuracy of the oxidation catalyst 42 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. Furthermore, the reason why the amount of HC adsorbed by the oxidation catalyst 42 decreases significantly when the engine is stopped is due to the type of hydrocarbons that are easily oxidized. It was found that this is the case when the engine is stopped in a state where a large amount of hydrocarbons with a large percentage) are adsorbed on the oxidation catalyst 42.

Based on the above knowledge, in this embodiment, the determination HC adsorption amount estimating unit 130 estimates the amount of hydrocarbons whose purification rate is equal to or higher than a preset reference purification rate adsorbed on the oxidation catalyst 42 immediately before the engine is stopped. The determination HC adsorption amount is estimated. Then, when the determination HC adsorption amount is equal to or higher than a preset determination amount, the determination unit 120 performs a theoretical Diagnosis of the oxidation catalyst 42 based on the amount of temperature rise is stopped. If the determination HC adsorption amount is equal to or higher than the determination amount, the HC adsorption amount estimating unit 102 determines the HC adsorption amount after the engine starts and the temperature of the oxidation catalyst 42 reaches a preset reference temperature or higher. Set the estimate of to zero. Note that the standard purification rate and the above-mentioned determination amount are based on experiments and the like when 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. Even if the oxidation catalyst 42 is not erroneously diagnosed, the purification rate and determination amount are set to maximum values 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.

On the other hand, if the determination HC adsorption amount is less than the determination amount, the determination unit 120 starts diagnosing the oxidation catalyst 42 based on the theoretical temperature increase amount immediately after the engine is started.

(3) Details of each calculation section (theoretical temperature rise calculation section)
As shown in FIG. 3, 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 X4a, which is the amount adsorbed to 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 X5.

As shown in the two graphs in FIG. 4, the HC adsorption/release rate calculation unit 111 calculates that the higher the catalyst temperature X1 is, the lower the first HC adsorption rate X4a is, and the higher the exhaust flow rate X2 is, the lower the first HC adsorption rate X4a is. The first HC adsorption rate X4a is calculated based on the catalyst temperature X1 and the exhaust flow rate X2.

As shown in the three graphs in FIG. 5, the HC adsorption/release rate calculation unit 111 calculates that the larger the HC adsorption amount X6, the larger the HC release rate X5, and the higher the catalyst temperature X1, the larger the HC release rate X5. The HC release rate X5 is calculated based on the HC adsorption amount X6, the catalyst temperature X1, and the exhaust flow rate X2 so that the larger the exhaust flow rate X2, the higher the HC release rate X5.

The HC adsorption amount X6 is the total amount of hydrocarbons adsorbed on the oxidation catalyst 42, and is calculated by the following procedure. The HC adsorption amount estimation unit 102 adds the first HC adsorption rate X4a to the exhaust HC flow rate X3, 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 X5, the HC adsorption speed X4b is calculated. Then, the HC adsorption amount estimation unit 102 integrates the calculated HC adsorption speed X4b, and calculates (estimates) this integrated value as the HC adsorption amount X6 of the oxidation catalyst 42 at each time during engine operation.

It is known that the exhaust HC flow rate X3 described above 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 X3 from each of these values. Calculate.

The calculation of the exhaust HC flow rate X3, the first HC adsorption rate X4a, the HC release rate X5, the HC adsorption rate X4b, and the integration of the HC adsorption rate X4b, which are performed by the HC adsorption amount estimation unit 102, are performed only during engine operation. . Therefore, when the engine is stopped, the HC adsorption amount X6 output from the HC adsorption amount estimating section 102 is maintained at the value immediately before the engine was stopped.

When the engine starts, the HC adsorption amount estimating unit 102 determines whether the determination HC adsorption amount X40 calculated by the determining HC adsorption amount estimating unit 130 in a procedure described later is equal to or greater than the aforementioned determination amount. When the determination HC adsorption amount X40 is equal to or greater than the determination amount, the HC adsorption amount X6 is set to zero at the time when the temperature of the oxidation catalyst 42 becomes equal to or higher than the reference temperature after starting (restarting) the engine.

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

As shown in FIG. 6, the HC oxidation rate calculation unit 112 calculates the HC release rate X5 so that the higher the HC release rate X5, the higher the HC oxidation rate X12, and the higher the catalyst temperature HC oxidation rate X12 is calculated based on and catalyst temperature X1.

Next, the temperature increase estimation unit 103 multiplies the HC oxidation rate X12 by the exothermic coefficient X11, and calculates the product as the theoretical temperature increase X13. The exothermic coefficient X11 is the amount of temperature increase in 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.

(HC adsorption amount estimator for judgment)
As shown in FIG. 7, the determination HC adsorption amount estimating section 130 functionally includes an adsorption ratio estimating section 132.

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 adsorption ratio estimating unit 132 calculates the ratio of various hydrocarbons having different oxidizability (hereinafter referred to as adsorption ratio as appropriate) to the total amount of hydrocarbons adsorbed on the oxidation catalyst 42 at each time during engine operation. ) are estimated respectively. 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 adsorption 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 adsorption ratio estimating unit 132 first estimates the ratio of each HC type to the total amount of hydrocarbons discharged from the engine main body 1 (hereinafter referred to as the discharge ratio 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. 8 and 9, 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, and the higher the effective compression ratio. The emission rate of 2HC species and the emission rate of tertiary HC species decrease. From this, the adsorption ratio estimating unit 132 calculates at each time so that the relationship between the excess air ratio λ (X20), the effective compression ratio (X21), and the discharge ratio of each HC type becomes the relationship shown in FIGS. 8 and 9. The discharge ratio 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 . 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 adsorption ratio estimating unit 132 averages the estimated emission ratio of each HC type at each time during engine operation for a predetermined period, and calculates each average value as the adsorption ratio of each HC type adsorbed on the oxidation catalyst 42. Take it as a percentage. In the following, the proportion of the first HC species adsorbed on the oxidation catalyst 42 calculated by the adsorption proportion estimating unit 132 will be expressed as the first adsorption proportion X22_a, the proportion of the second HC species as the second adsorption proportion X22_b, and the proportion of the third HC species. is called the third adsorption ratio X22_c.

Next, the determination HC adsorption amount estimation unit 130 multiplies each of the first to third adsorption ratios X22_a to X22_c by the HC adsorption amount X6 estimated by the HC adsorption amount estimation unit 102, and The amount of each type of hydrocarbon adsorbed on the oxidation catalyst 42 is calculated. That is, the determination HC adsorption amount estimating unit 130 multiplies the first adsorption ratio X22_a by the HC adsorption amount X6, and calculates the resulting product as the amount ( The second adsorption ratio X22_b is calculated as the first HC adsorption amount X31), and the second adsorption ratio The third adsorption ratio X22_c is multiplied by the HC adsorption amount X33). This calculation is also performed at each time during engine operation, and at each time during engine operation, based on the latest first to third adsorption ratios X22_a to X22_c and the latest HC adsorption amount X6. , the latest first to third HC adsorption amounts X31 to X33 are calculated.

The determination HC adsorption amount estimating section 130 further functionally includes a specific HC adsorption amount determining section 133. The specific HC adsorption amount determination unit 133 identifies hydrocarbons whose purification rate is equal to or higher than the reference purification rate at each time of the engine, and determines the specific HC whose type is the amount adsorbed on the oxidation catalyst 42. Calculate the adsorption amount X40.

As shown in FIG. 10, the purification rate of hydrocarbons in the oxidation catalyst 42 changes depending on the temperature of the oxidation catalyst 42, and the types of hydrocarbons whose purification rate is equal to or higher than the reference purification rate also vary depending on the temperature of the oxidation catalyst 42. From this, the specific HC adsorption amount determining unit 133 first identifies the type of hydrocarbon whose purification rate is equal to or higher than the reference purification rate based on the catalyst temperature X1.

Specifically, as shown in FIG. 10, when the temperature of the oxidation catalyst 42 is less than the predetermined first catalyst temperature Tc1, the purification rate of any of the first to third HC type hydrocarbons is less than the purification rate. . From this, the specific HC adsorption amount determining unit 133 calculates the specific HC adsorption amount X40 as zero when the catalyst temperature X1 is less than the first catalyst temperature Tc1. Note that the first catalyst temperature Tc1 is set in advance and stored in the PCM 100.

On the other hand, when the temperature of the oxidation catalyst 42 is equal to or higher than the first catalyst temperature Tc1 and lower than the predetermined second catalyst temperature Tc2, only the purification rate of the first HC type hydrocarbon is equal to or higher than the reference purification rate. From this, the specific HC adsorption amount determination unit 133 determines that when the catalyst temperature 42) is calculated as the specific HC adsorption amount X40. Note that the second catalyst temperature Tc2 is set in advance and stored in the PCM 100.

Further, when the temperature of the oxidation catalyst 42 is higher than the second catalyst temperature Tc2 and lower than the predetermined third catalyst temperature Tc3, the purification rate of the first HC type and the second HC type hydrocarbon is equal to or higher than the reference purification rate. From this, when the catalyst temperature (the amount of hydrocarbons adsorbed on the oxidation catalyst 42) is calculated as the specific HC adsorption amount X40. Note that the third catalyst temperature Tc3 is set in advance and stored in the PCM 100.

Further, when the temperature of the oxidation catalyst 42 is equal to or higher than the third catalyst temperature Tc3, the purification rate of the first to third HC types of hydrocarbons is equal to or higher than the reference purification rate. From this, the specific HC adsorption amount determining unit 133 determines that when the catalyst temperature The total amount of the amount X33 (the amount of third HC type hydrocarbons adsorbed on the oxidation catalyst 42), that is, the HC adsorption amount X6, is calculated as the specific HC adsorption amount X40.

The determination HC adsorption amount is the value immediately before the engine stops out of the specified HC adsorption amount X40 at each time during engine operation calculated as described above. The amount of adsorption is calculated (estimated). Here, after the engine main body 1 stops, the above-mentioned calculations by the determination HC adsorption amount estimating section 130 are stopped, and the last calculated values, that is, the respective values immediately before the engine stops, are maintained. From this, the value output from the determination HC adsorption amount estimating unit 130 after the engine body 1 stops until the next engine start is the specific HC adsorption amount immediately before the engine stops, that is, the determination HC adsorption amount. Maintained in quantity.

Note that the first to third HC adsorption amounts X31 to X33 calculated immediately before engine stop correspond to the "pre-stop adsorption amount" in the claims. In addition, in this embodiment, as described above, the specific HC adsorption amount determination unit 133 calculates the specific HC adsorption amount As described above, the calculation of the specific HC adsorption amount determination unit 133, that is, the identification of hydrocarbons whose purification rate is equal to or higher than the reference purification rate, and the calculation of the adsorption amount of the specified type of hydrocarbons are carried out only immediately before the engine is stopped. The calculated amount of hydrocarbons may be determined as the determination HC adsorption amount.

(Judgment Department)
The determination unit 120 subtracts the temperature on the upstream side of the oxidation catalyst 42 detected by the first exhaust 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 amount of temperature rise at step 42 (hereinafter referred to as the actual amount of temperature rise) 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.

Further, as described above, when starting the engine, the determination unit 120 determines whether the determination HC adsorption amount X40 is equal to or greater than the determination amount, and if the determination HC adsorption amount 120 stops the determination of the oxidation catalyst 42 based on the theoretical temperature increase amount until the temperature of the oxidation catalyst 42 becomes equal to or higher than the reference temperature. Then, in the above case, the determination unit 120 starts the above determination when the temperature of the oxidation catalyst 42 becomes equal to or higher than the reference temperature. On the other hand, if the determination HC adsorption amount X40 is less than the determination amount, the determination unit 120 starts the 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 flowchart of FIG. Note that steps S1 to S10 in FIG. 11 are performed only when the engine main body 1 is in operation.

First, in step S1, the PCM 100 determines that the engine is starting (for example, the PCM 100 determines that the engine is starting when the engine rotation speed exceeds a predetermined rotation speed), and determines the amount of HC adsorption for determination. It is determined whether or not X40 is greater than or equal to the determination amount.

If the determination in step S1 is NO and it is not the time to start the engine, or if the determination HC adsorption amount Calculate. As described above, the PCM 100 calculates the HC release rate X5 based on the HC adsorption amount X6 calculated one calculation cycle ago, the catalyst temperature X1, and the exhaust flow rate X2. Further, the PCM 100 calculates the HC adsorption rate X4b based on the first HC adsorption rate X4a calculated based on the catalyst temperature X1 and the exhaust flow rate X2, the exhaust HC flow rate X3, and the HC release rate X5, and Update the adsorption amount X6.

On the other hand, if the determination in step S1 is YES, the engine is starting, and the determination HC adsorption amount In other words, it is determined whether the catalyst temperature X1 has risen to a reference temperature or higher after the engine is started. If this determination is YES and the catalyst temperature X1 is equal to or higher than the reference temperature, the process proceeds to step S3 and the HC adsorption amount X6 is set to zero. On the other hand, if the determination in step S2 is NO and the catalyst temperature X1 is less than the reference temperature, step S2 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 when the catalyst temperature X1 becomes equal to or higher than the reference temperature, the process proceeds to step S3. After step S3, the PCM 100 executes step S4 described above.

After step S4, in step S5, the PCM 100 calculates the HC oxidation rate X12. As described above, the PCM 100 calculates the HC oxidation rate X12 based on the HC release rate X5 and the catalyst temperature X1.

After step S5, the PCM 100 calculates the theoretical temperature increase amount X13 in step S6. As described above, the PCM 100 calculates the theoretical temperature increase amount X13 based on the HC oxidation rate X12 and the exothermic coefficient X11.

After step S6, in step S7, 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 X13. is less than the determined increase amount.

If the determination in step S7 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 S9). 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 S8).

Further, while the engine is operating, the PCM 100 calculates the adsorption ratios X22_a to X22_c of the first to third HC types at each time, the specific HC adsorption amount X40, and the determination HC adsorption amount X40 (step S10). When the processing from step S1 to step S10 is completed, the PCM 100 returns to step S1 again and repeats the processing from step S1 onward.

(4) Effects, etc. As explained above, in this embodiment, when the engine is operating, the exhaust HC flow rate X3, which is the flow rate of hydrocarbons discharged from the engine body 1, and Based on the exhaust flow rate X2, an HC adsorption amount X6, which is the amount of hydrocarbons adsorbed on the oxidation catalyst 42, is estimated. When the determination HC adsorption amount X40, which is the amount of easily oxidized hydrocarbons whose purification rate is equal to or higher than the reference purification rate, is adsorbed on the oxidation catalyst 42 immediately before the engine is stopped, the engine is stopped. If the amount of HC adsorption decreases significantly during the engine operation, the diagnosis of the oxidation catalyst 42 based on the theoretical temperature rise amount calculated based on the amount of HC adsorption X6 is stopped for a predetermined period after engine startup. On the other hand, if the determination HC adsorption amount X40 is less than the determination amount and the decrease in the HC adsorption amount while the engine is stopped is small, the oxidation catalyst 42 is diagnosed based on the HC adsorption amount X6 and the theoretical temperature rise amount immediately after the engine is started. Implement. 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. In other words, when the determination HC adsorption amount X40 is equal to or greater than the determination amount, after the engine is started, the catalyst temperature X1 becomes equal to or higher than the reference temperature and the amount of hydrocarbons adsorbed on the oxidation catalyst 42 becomes almost zero, and when the engine is running The diagnosis of the oxidation catalyst 42 is stopped until the decrease in the HC adsorption amount while the engine is stopped has no effect on the estimation of the HC adsorption amount based on the operating state of the engine, and the diagnosis is restarted when the catalyst temperature X1 becomes equal to or higher than the reference temperature. let Therefore, while ensuring the accuracy of estimating the amount of HC adsorption and the accuracy of the diagnosis, it is possible to prevent the suspension period of the diagnosis from becoming excessively long and to ensure an opportunity for diagnosis.

Furthermore, in the present embodiment, when the determination HC adsorption amount X40 is equal to or greater than the determination amount, the HC adsorption amount is set to zero when the catalyst temperature X1 becomes equal to or higher than the reference temperature after the engine is started. Therefore, the subsequent amount of HC adsorption can be estimated more reliably and accurately.

Furthermore, in the present embodiment, the hydrocarbons adsorbed on the oxidation catalyst 42 are classified into three types (first HC type, second HC type, and third HC type), and the hydrocarbons adsorbed on the oxidation catalyst 42 are classified into three types (first HC type, second HC type, and third HC type). The adsorbed amount is calculated, and based on this amount, the determination HC adsorption amount X40 is calculated. Therefore, the determination HC adsorption amount X40 can be calculated and estimated with a simpler configuration than when calculating the adsorption amounts of all types of hydrocarbons.

Furthermore, in this embodiment, the ratio of various hydrocarbons discharged from the engine body 1 and adsorbed to the oxidation catalyst 42 changes depending on the excess air ratio λ and the effective compression ratio during engine operation. , based on these excess air ratio λ and effective compression ratio, calculate the proportions (first to third adsorption proportions X22_a to X22_ c ) of the first to third HC types of hydrocarbons in the total amount of hydrocarbons. Therefore, these ratios can be calculated with high accuracy. Then, based on the above-mentioned ratio and the HC adsorption amount The first to third HC adsorption amounts X31 to X32) are calculated, and the determination HC adsorption amount X40 is calculated based on these amounts, and the determination HC adsorption amount X40 can be calculated and estimated with high accuracy.

(5) Modification In the embodiment described above, HC species whose purification rate is equal to or higher than the standard purification rate are identified according to the catalyst temperature X1, and the amount of the identified HC species adsorbed on the oxidation catalyst 42 immediately before the engine stops Based on this, a case has been described in which it is determined whether or not to stop the diagnosis of the oxidation catalyst 42 after the engine is started, but the configuration for identifying the HC type according to the catalyst temperature X1 may be omitted. That is, the HC species to be used for the determination is determined in advance through experiments, etc., and the oxidation catalyst 42 is diagnosed after the engine is started based on the predetermined adsorption amount of the HC species on the oxidation catalyst 42, regardless of the catalyst temperature X1. It may be determined whether or not to stop. For example, regardless of the catalyst temperature It may be determined whether or not the diagnosis is to be stopped depending on whether or not the adsorption amount X31 is equal to or greater than a determination amount. Note that in this case, estimation of the adsorption amount of hydrocarbons of types that are not used for determination may be omitted.

In the embodiment described above, when the HC adsorption amount for determination X40 is less than the determination amount, the diagnosis of the oxidation catalyst 42 based on the HC adsorption amount X6 and the theoretical temperature increase amount is started immediately after the engine starts. Even when the HC adsorption amount X40 is less than the determination amount, the diagnosis may be started after a certain amount of time has passed after the engine is 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 above-described predetermined period during which the diagnosis is stopped when the determination HC adsorption amount X40 is equal to or greater than the determination 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 mentioned above, when the catalyst temperature The effect of this effect 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 amount of HC adsorption based on the operating conditions of the engine. From this, in the embodiment described above, the HC adsorption amount X6 is set to zero when the catalyst temperature X1 becomes equal to or higher than the reference temperature after the engine is started when the determination HC adsorption amount X40 is equal to or higher than the determination amount. The HC adsorption amount X6 may be calculated from the operating conditions of the engine.

Furthermore, in the embodiment, after the engine is started when the determination HC adsorption amount X40 is equal to or higher than the determination amount, the estimation of the HC adsorption amount and the diagnosis of the oxidation catalyst 42 are restarted when the catalyst temperature X1 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 X1 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 13 Intake side valve mechanism (effective compression ratio changing means)
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 adsorption amount estimation section for judgment 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 estimation unit that estimates an HC adsorption amount, which is the total 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;
When the engine is operating, 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 based on the results of these comparisons, a determination unit that determines whether the oxidation catalyst is normal;
Determining that among the various hydrocarbons contained in the exhaust gas, the amount of hydrocarbons for which the purification rate at the oxidation catalyst is equal to or higher than a preset reference purification rate is adsorbed on the oxidation catalyst immediately before the engine is stopped. and a determination HC adsorption amount estimator for estimating the HC adsorption amount for use,
When the HC adsorption amount for determination is equal to or greater than a preset determination amount, the determination unit stops the determination for a predetermined period after starting the engine;
An oxidation catalyst diagnostic device, wherein when the determination HC adsorption amount is less than the determination amount, the determination unit starts the determination before the predetermined period elapses after the engine is started. The oxidation catalyst diagnostic device according to claim 1,
When the determination HC adsorption amount is equal to or greater than the determination amount, the determination unit starts the determination when the predetermined period of time has elapsed after starting the engine;
An oxidation catalyst diagnostic apparatus, wherein when the determination HC adsorption amount is less than the determination 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 HC adsorption amount estimating unit includes a first HC type that is aromatic, a second HC type that is not aromatic and has 5 or more carbons, and a third HC type that is not aromatic and has less than 5 carbons. For each HC species, calculate the pre-stop adsorption amount, which is the amount adsorbed on the oxidation catalyst immediately before the engine stops, and calculate the adsorption amount before stop for each HC species and the temperature of the oxidation catalyst for the determination. An oxidation catalyst diagnostic device characterized by estimating the amount of HC adsorption. The oxidation catalyst diagnostic device according to claim 4,
comprising effective compression ratio changing means capable of changing the effective compression ratio of the cylinder,
The determination HC adsorption amount estimating unit estimates the first HC type, second HC type, and second HC type out of the total amount of hydrocarbons adsorbed on the oxidation catalyst based on the excess air ratio and effective compression ratio during engine operation. The proportion occupied by each of the 3 HC species is calculated, and based on the proportion and the HC adsorption amount estimated by the HC adsorption amount estimator, each pre-stop adsorption of the 1st HC species, 2nd HC species, and 3rd HC species is calculated. A diagnostic device for an oxidation catalyst, characterized in that it calculates each quantity. 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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