Engine controller

Abstract

To provide an engine controller capable of estimating a degree of blockage (a degree of clogging) of an exhaust pipe due to condensate water generated by condensed moisture in exhaust gas during operation of an engine.SOLUTION: When an EGR valve 42 is open, an ECU 50 estimates a degree of blockage of an exhaust pipe 18 due to condensate water according to a degree of increase in a recirculation amount of exhaust gas (actual EGR flow rate) detected by an EGR flow rate sensor 44 relative to a recirculation amount of exhaust gas when the exhaust pipe 18 is not blocked at all (unblocked EGR flow rate).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an engine control device. [Background technology]

[0002] Engine exhaust contains a lot of water (water vapor) produced by the combustion of fuels such as gasoline. Therefore, for example, when the exhaust is cooled in the process of being discharged through the exhaust pipe, the water (water vapor) in the exhaust condenses inside the exhaust pipe, producing condensed water. This condensed water can then accumulate inside the exhaust pipe.

[0003] In particular, when the exhaust gas temperature or the outside air temperature is low, the formation of condensed water is promoted, which may cause the exhaust pipe to become clogged with condensed water. Furthermore, if the engine is operated with the exhaust pipe becoming clogged with condensed water, the pressure (back pressure) behind the exhaust valve increases, making it difficult to expel (scavenge) the combustion gas from the combustion chamber. The combustion gas that is not expelled (scavenged) remains in the combustion chamber as an internal EGR, which may cause abnormal combustion such as knocking or pre-ignition (i.e., there is a risk of abnormal combustion occurring).

[0004] For example, Patent Document 1 discloses a technology in which, when the engine is stopped for a period of time equal to or longer than a reference value, an electric air pump is driven and controlled while the engine is stopped to guide intake air from the intake pipe to the exhaust pipe via a scavenging passage, and condensed water generated by condensation of moisture in the exhaust is blown downstream of an EHC (Electric Heating Catalyst) (discharged outside the vehicle). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-242724 Summary of the Invention [Problem to be solved by the invention]

[0006] However, with the technology of Patent Document 1, it was not possible to know the degree of blockage (level of clogging) of the exhaust pipe due to condensed water while the engine was running. Also, it was not possible to discharge the condensed water (to alleviate or eliminate blockage of the exhaust pipe due to condensed water) while the engine was running. Therefore, there was a demand for knowing the degree of blockage (level of clogging) of the exhaust pipe due to condensed water while the engine was running.

[0007] The present invention has been made to solve the above problems, and aims to provide an engine control device that can estimate the degree of blockage (clogging) of an exhaust pipe caused by condensed water generated by condensation of moisture in the exhaust while the engine is running. [Means for solving the problem]

[0008] An engine control device according to one aspect of the present invention comprises an EGR pipe connecting the exhaust pipe and intake pipe of an engine, an EGR valve interposed in the EGR pipe and adjusting the amount of exhaust gas recirculated through the EGR pipe, an EGR flow sensor that detects the amount of exhaust gas recirculated, and a control unit that controls the opening of the EGR valve depending on the operating state of the engine, and is characterized in that when the EGR valve is open, the control unit estimates the degree of blockage of the exhaust pipe due to condensed water depending on the degree of increase in the amount of exhaust gas recirculated detected by the EGR flow sensor relative to the amount of exhaust gas recirculated when the exhaust pipe is not blocked.

[0009] However, as the degree of exhaust pipe clogging due to condensed water increases, the amount of exhaust gas recirculated (EGR flow rate) tends to increase under the same operating conditions. Therefore, an engine control device according to one aspect of the present invention can estimate the degree of exhaust pipe clogging due to condensed water based on the degree of increase in the actual amount of exhaust gas recirculated relative to the amount of exhaust gas recirculated when the exhaust pipe is not clogged. [Effects of the Invention]

[0010] According to the present invention, it is possible to estimate the degree of blockage (degree of clogging) of an exhaust pipe caused by condensed water generated by condensation of moisture in the exhaust while the engine is running. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing the configuration of an engine control device according to an embodiment and an engine to which the engine control device is applied; [Figure 2] FIG. 4 is a diagram showing an example of an unblocked EGR flow rate map. [Figure 3] 4 is a flowchart showing a procedure for determining the degree of blockage and performing a blockage resolution process by the engine control device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Unless otherwise specified, the same or corresponding parts in the drawings will be designated by the same reference numerals. Furthermore, the same elements in each drawing will be designated by the same reference numerals, and redundant explanations will be omitted.

[0013] First, the configuration of an engine control device 1 according to the embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing the configuration of the engine control device 1 and an engine 10 to which the engine control device 1 is applied.

[0014] The engine 10 may be of any type, but may be, for example, a horizontally opposed, four-cylinder gasoline engine. The engine 10 is a direct-injection engine that directly injects fuel into the cylinders. In the engine 10, air is drawn in through an air cleaner 16, throttled by an electronically controlled throttle valve (hereinafter simply referred to as a "throttle valve") 13 provided in an intake pipe 15, passes through an intake manifold 11, and is drawn into each cylinder formed in the engine 10. The amount of air drawn in through the air cleaner 16 is detected by an air flow meter 14 disposed between the air cleaner 16 and the throttle valve 13. A vacuum sensor 30 is disposed inside a collector (surge tank) that constitutes the intake manifold 11, and detects the pressure within the intake manifold 11 (intake manifold pressure). The throttle valve 13 is also provided with a throttle opening sensor 31 that detects the opening of the throttle valve 13.

[0015] The cylinder head is formed with an intake port 22 and an exhaust port 23 for each cylinder (only one bank is shown in FIG. 1). Each intake port 22 and exhaust port 23 is provided with an intake valve 24 and an exhaust valve 25 that open and close the intake port 22 and exhaust port 23, respectively. A variable valve timing mechanism 26 is disposed between the intake camshaft that drives the intake valve 24 and the intake cam pulley. The variable valve timing mechanism 26 rotates the intake cam pulley and the intake camshaft relatively to continuously change the rotational phase (displacement angle) of the intake camshaft with respect to the crankshaft 10a, thereby advancing or retarding the valve timing (opening / closing timing) of the intake valve 24. The variable valve timing mechanism 26 variably sets the opening and closing timing of the intake valve 24 according to the engine operating conditions.

[0016] Similarly, a variable valve timing mechanism 27 is disposed between the exhaust camshaft and the exhaust cam pulley, which rotates the exhaust cam pulley and the exhaust camshaft relatively to continuously change the rotational phase (displacement angle) of the exhaust camshaft with respect to the crankshaft 10a, thereby advancing or retarding the valve timing (opening / closing timing) of the exhaust valve 25. The variable valve timing mechanism 27 variably sets the opening / closing timing of the exhaust valve 25 according to the engine operating state.

[0017] An injector 12 that injects fuel into the cylinder is attached to each cylinder of the engine 10. The injector 12 directly injects fuel pressurized by a high-pressure fuel pump (not shown) into the combustion chamber of each cylinder.

[0018] The cylinder head of each cylinder is also fitted with a spark plug 17 that ignites the air-fuel mixture, and an igniter-integrated coil 21 that applies high voltage to the spark plug 17. In each cylinder of the engine 10, the air-fuel mixture of intake air and fuel injected by the injector 12 is ignited by the spark plug 17 and combusted. Exhaust gas after combustion is discharged through an exhaust pipe 18.

[0019] An air-fuel ratio sensor 19 is attached downstream of the collecting portion of the exhaust pipe 18 and upstream of the exhaust purification catalyst 20. As the air-fuel ratio sensor 19, a linear air-fuel ratio sensor (LAF sensor) is used which can output a signal corresponding to the oxygen concentration and unburned gas concentration in the exhaust gas (i.e., a signal corresponding to the air-fuel ratio of the mixture) and can linearly detect the air-fuel ratio.

[0020] An exhaust purification catalyst 20 is disposed downstream of the LAF sensor 19. The exhaust purification catalyst 20 is a three-way catalyst that simultaneously oxidizes hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and reduces nitrogen oxides (NOx), converting harmful gas components in the exhaust gas into harmless carbon dioxide (CO2), water vapor (H2O), and nitrogen (N2). A silencer (muffler) 43 is attached downstream of the exhaust purification catalyst 20 to reduce exhaust noise.

[0021] An exhaust gas recirculation device (hereinafter referred to as "EGR (Exhaust Gas Recirculation) device") 40 is provided in the exhaust pipe 18, which recirculates a portion of the exhaust gas emitted from the engine 10 to the intake pipe 15 of the engine 10. The EGR device 40 has an EGR pipe 41 that connects the exhaust pipe 18 of the engine 10 with the intake pipe 15, and an EGR valve 42 that is installed on the EGR pipe 41 and adjusts the amount of exhaust gas recirculated (EGR flow rate).

[0022] An EGR flow rate sensor 44 that detects the amount of recirculated exhaust gas (EGR flow rate) is attached to the EGR valve 42 or the EGR pipe 41. As the EGR flow rate sensor 44, for example, a sensor that outputs an electric signal (voltage or the like) corresponding to the rotation angle (valve opening) of the EGR valve 42 (valve shaft), or a hot-wire mass flow meter that detects the mass flow rate of the exhaust gas (EGR gas) flowing through the EGR pipe 41 can be suitably used.

[0023] In normal control, the opening degree (EGRSTP) of the EGR valve 42 is controlled by the ECU 50 (described later) in accordance with the operating conditions (e.g., engine speed, intake air amount, etc.) of the engine 10. More specifically, for example, a target EGR valve opening degree map that defines the relationship between the engine speed, intake air amount, and target EGR valve opening degree is stored in advance in the EEPROM or the like of the ECU 50, the target EGR valve opening degree is calculated based on the real-time engine speed and intake air amount, and the EGR valve 42 is controlled (F / B control) so that the actual EGR valve opening degree matches the target EGR valve opening degree.

[0024] In addition to the air flow meter 14, LAF sensor 19, vacuum sensor 30, throttle opening sensor 31, and EGR flow sensor 44, a cam angle sensor 32 for identifying the cylinders of the engine 10 is attached near the camshaft of the engine 10. A crank angle sensor 33 for detecting the rotational position of the crankshaft 10a is attached near the crankshaft 10a of the engine 10. A timing rotor 33a having 34 protrusions, with two teeth missing, formed at 10° intervals, is attached to the end of the crankshaft 10a. The crank angle sensor 33 detects the rotational position of the crankshaft 10a by detecting the presence or absence of the protrusions on the timing rotor 33a. The cam angle sensor 32 and the crank angle sensor 33 may be, for example, electromagnetic pickup types.

[0025] These sensors are connected to the ECU 50. In addition, various sensors are also connected to the ECU 50, such as a water temperature sensor 34 that detects the temperature of the coolant for the engine 10, an oil temperature sensor 35 that detects the temperature of the lubricating oil, an accelerator sensor 36 that detects the amount of depression of the accelerator pedal, i.e., the amount of operation of the accelerator pedal, a vehicle speed sensor 37 that detects the speed of the vehicle, and an exhaust temperature sensor 45 that detects the temperature of the exhaust pipe 18 (or exhaust).

[0026] The ECU 50 is configured to include a microprocessor that performs calculations, an EEPROM that stores programs and the like for causing the microprocessor to execute various processes, a RAM that stores various data such as calculation results, a backup RAM in which the stored contents are maintained by a battery or the like, and an input / output I / F, etc. The ECU 50 also includes an injector driver that drives the injector 12, an output circuit that outputs an ignition signal, a motor driver that drives the electric motor 13a that opens and closes the electronically controlled throttle valve 13, a driver circuit that drives the EGR valve 42, etc.

[0027] The ECU 50 identifies the cylinder from the output of the cam angle sensor 32, and determines the rotational angular velocity and engine speed from the output of the crank angle sensor 33. The ECU 50 also acquires various information such as the intake air amount, intake pipe negative pressure, accelerator operation amount, air-fuel ratio of the mixture, and water temperature and oil temperature of the engine 10 based on detection signals input from the various sensors described above. The ECU 50 then comprehensively controls the engine 10 by controlling the fuel injection amount, ignition timing, and various devices such as the throttle valve 13 and EGR valve 42 based on the acquired information. The ECU 50 functions as a control unit as recited in the claims.

[0028] The exhaust gas from the engine 10 contains a large amount of moisture (water vapor) produced by the combustion of fuel such as gasoline. Therefore, for example, when the exhaust gas is cooled in the process of being discharged through the exhaust pipe 18, the moisture (water vapor) in the exhaust gas condenses inside the exhaust pipe 18, producing condensed water. This condensed water may then accumulate inside the exhaust pipe.

[0029] In particular, when the exhaust gas temperature or the outside air temperature is low, the generation of condensed water is promoted, which may cause clogging of the exhaust pipe 18. Furthermore, if the engine 10 is operated with the exhaust pipe 18 becoming increasingly clogged with condensed water, the pressure (back pressure) behind the exhaust valve 25 increases, making it difficult to discharge (scavenge) the combustion gas from the combustion chamber. The combustion gas that is not discharged (scavenged) remains in the combustion chamber as internal EGR, which may cause abnormal combustion such as knocking or pre-ignition (i.e., there is a risk of abnormal combustion occurring).

[0030] Therefore, the ECU 50 has a function to estimate (determine) the degree of blockage (level of clogging) of the exhaust pipe 18 due to condensed water while the engine 10 is running, and a function to alleviate (remove) the blockage if the blockage of the exhaust pipe 18 due to condensed water progresses. In the ECU 50, these functions are realized by a microprocessor executing a program stored in an EEPROM or the like.

[0031] Therefore, when the EGR valve 42 is open, the ECU 50 estimates (determines) the degree of blockage (degree of clogging) of the exhaust pipe 18 due to condensed water based on the degree of increase (rate of increase or amount of increase) of the actual exhaust gas recirculation amount (actual EGR flow rate) detected by the EGR flow rate sensor 44 relative to the EGR flow rate (unblocked EGR flow rate) when the exhaust pipe 18 is not blocked at all (i.e., when no condensed water has accumulated). In other words, the ECU 50 estimates (determines) that the greater the increase in the actual EGR flow rate relative to the unblocked EGR flow rate, the more severe the blockage of the exhaust pipe 18 due to condensed water is (the greater the degree of blockage).

[0032] More specifically, the ECU 50 stores in advance in an EEPROM or the like a map (look-up table) that defines the relationship between the engine speed, intake air amount, and exhaust gas recirculation amount (non-blocked EGR flow rate) when the EGR valve 42 is opened in a state where the exhaust pipe 18 is not blocked at all (i.e., in a state where no condensed water has accumulated).The ECU 50 then estimates (determines) the degree of blockage of the exhaust pipe 18 by comparing the non-blocked EGR flow rate (the EGR flow rate when the exhaust pipe 18 is not blocked at all) obtained from the map (look-up table) using the real-time engine speed and intake air amount with the actual EGR flow rate (the actual EGR flow rate detected by the EGR flow rate sensor 44).

[0033] Here, we will explain how to obtain the EGR flow rate (non-blocked EGR flow rate) when the exhaust pipe 18 is not blocked at all (i.e., when no condensed water has accumulated). An non-blocked EGR flow rate map that defines the relationship between the engine speed (rpm), intake air amount (g), and non-blocked EGR flow rate (g / sec) is stored in the EEPROM or the like of the ECU 50, and the non-blocked EGR flow rate is obtained by searching this non-blocked EGR flow rate map based on the engine speed and intake air amount.

[0034] Here, an example of the non-blocking EGR flow rate map is shown in FIG. 2. In FIG. 2, the horizontal axis (row) is the intake air amount (g), and the vertical axis (column) is the engine speed (rpm). In the non-blocking EGR flow rate map, the non-blocking EGR flow rate (g / sec) is given for each combination (grid point) of the engine speed and the intake air amount. Here, in the non-blocking EGR flow rate map shown in FIG. 2, the relationship of "EGR flow rate A < EGR flow rate B < EGR flow rate C < EGR flow rate D" holds. Also, the data of the non-blocking EGR flow rate map can be obtained, for example, by an engine bench test or the like.

[0035] Note that here, since the region of EGR flow rate A is usually an operating region where EGR gas is not recirculated, the EGR valve 42 is forcibly opened when estimating the degree of blockage. In this case, considering the detectable flow rate (detection lower limit flow rate) of the EGR flow rate sensor 44, the EGR valve 42 is opened in a range of about 1% to 5% (low opening degree), for example. On the other hand, the regions of EGR flow rates B, C, and D are operating regions where EGR gas is recirculated even during normal operation. For example, considering fuel consumption and emissions (such as NOx), as described above, the opening degree of the EGR valve 42 is adjusted based on the engine speed and the intake air amount.

[0036] And when the degree of blockage of the exhaust pipe 18, that is, the ratio (increase rate) of the actual EGR flow rate to the non-blocking EGR flow rate or the deviation (increase amount) between the actual EGR flow rate and the non-blocking EGR flow rate becomes equal to or greater than a predetermined threshold value, the ECU 50 changes (controls) the operating state of the engine 10 so as to evaporate the condensed water. That is, when the blockage of the exhaust pipe 18 due to the condensed water progresses, the ECU 50 evaporates the condensed water to relieve (eliminate) the blockage of the exhaust pipe 18.

[0037] More specifically, the ECU 50 retards (retards) the ignition timing of the engine 10 when the degree of blockage of the exhaust pipe 18 (i.e., the rate or amount of increase in the actual EGR flow rate relative to the non-blocked EGR flow rate) becomes equal to or greater than a predetermined threshold. That is, by retarding (retarding) the ignition timing, the ECU 50 increases the exhaust temperature, promotes evaporation of condensed water, and alleviates (eliminates) blockage of the exhaust pipe 18 caused by condensed water. Note that retarding the ignition timing deteriorates fuel economy, so it is preferable to set the predetermined threshold so that the ignition timing is not retarded (to prevent deterioration of fuel economy) when the degree of blockage is such that abnormal combustion such as knocking or pre-ignition does not occur, but is retarded when the degree of blockage is such that abnormal combustion may occur.

[0038] It is preferable that the ECU 50 increase the frequency of estimating (determining) the degree of blockage of the exhaust pipe 18 as the temperature of the exhaust pipe 18 or the exhaust becomes lower, i.e., as condensed water becomes more likely to accumulate and blockage of the exhaust pipe 18 becomes more likely. In other words, the ECU 50 increases the frequency of estimating the degree of blockage of the exhaust pipe 18 as the temperature of the exhaust pipe 18 or the exhaust becomes lower, thereby reliably preventing blockage of the exhaust pipe 18 before it occurs.

[0039] More specifically, it is preferable that the ECU 50 performs the blockage degree estimation approximately once every five minutes (opens the EGR valve 42 for approximately 30 seconds) when the exhaust port temperature is 900°C and the muffler temperature is 300°C, performs the blockage degree estimation approximately once every three minutes (opens the EGR valve 42 for approximately 30 seconds) when the exhaust port temperature is 500°C and the muffler temperature is 60°C, and performs the blockage degree estimation approximately once every minute (opens the EGR valve 42 for approximately 30 seconds) when the exhaust port temperature is 400°C and the muffler temperature is 30°C. In other words, since it is difficult for a large amount of condensed water to accumulate in an operating state where the muffler temperature exceeds 100°C, it is preferable to maintain the frequency of the blockage degree estimation (the frequency of opening the EGR valve 42) unchanged and increase the frequency when the operating state becomes one where the muffler temperature is below 100°C.

[0040] As described above, when the EGR valve 42 is forcibly opened in an operating region where EGR gas is not recirculated under normal control, it is preferable to open the EGR valve 42 in a range of, for example, 1% to 5% (low opening), taking into consideration the detectable flow rate (lower detection limit flow rate) of the EGR flow sensor 44.

[0041] Next, the operation of the engine control device 1 will be described with reference to Fig. 3. Fig. 3 is a flowchart showing the procedure for determining the degree of blockage and performing blockage resolution processing by the engine control device 1. This processing is repeatedly executed by the ECU 50 at predetermined timings.

[0042] First, in step S100, it is determined whether the conditions for determining the degree of blockage and for executing the blockage resolution process are met. If the execution conditions are not met, the process is temporarily terminated. On the other hand, if the execution conditions are met, the process proceeds to step S102.

[0043] In step S102, the EGR valve 42 is opened either in response to the operating state (engine speed, intake air amount, etc.) of the engine 10 or forcibly. Note that the method for setting the target opening of the EGR valve 42 is as described above, and therefore a detailed description thereof will be omitted here.

[0044] Next, in step S104, the actual EGR flow rate detected by the EGR flow rate sensor 44 (actual EGR flow rate) is read.

[0045] In the next step S106, the EGR flow rate when the exhaust pipe 18 is not blocked at all (non-blocked EGR flow rate) is obtained from the (real-time) engine speed and intake air amount that have been read. Note that the method for obtaining the non-blocked EGR flow rate is as described above, and therefore a detailed description thereof will be omitted here.

[0046] Next, in step S108, it is determined whether the actual EGR flow rate is greater than the non-blocked EGR flow rate (whether it has increased). If the actual EGR flow rate is equal to or less than the non-blocked EGR flow rate (if it has not increased), it is estimated (determined) that no blockage has occurred in step S110, and the process then temporarily exits. On the other hand, if the actual EGR flow rate is greater than the non-blocked EGR flow rate (if it has increased), the process proceeds to step S112.

[0047] In step S112, it is determined whether the rate or amount of increase in the actual EGR flow rate relative to the non-blocked EGR flow rate is equal to or greater than a predetermined threshold. If the rate or amount of increase is less than the predetermined threshold, in step S114, it is estimated (determined) that although blockage has occurred, the degree of blockage is relatively light, and the process then exits. On the other hand, if the rate or amount of increase is equal to or greater than the predetermined threshold, the process proceeds to step S116.

[0048] If it is estimated (determined) that the blockage is progressing, the ignition timing of the engine 10 is retarded in step S116. By retarding the ignition timing, the exhaust temperature rises, which promotes evaporation of the condensed water and alleviates (eliminates) the blockage of the exhaust pipe 18 caused by the condensed water. Then, the process temporarily exits.

[0049] As described above in detail, according to this embodiment, when the EGR valve 42 is open, the degree of blockage of the exhaust pipe 18 due to condensed water can be estimated based on the degree of increase in the actual exhaust gas recirculation amount (actual EGR flow rate) relative to the exhaust gas recirculation amount when the exhaust pipe 18 is not blocked (unblocked EGR flow rate). In other words, it is possible to estimate (determine) the degree of blockage of the exhaust pipe 18 due to condensed water while the engine 10 is running.

[0050] In particular, according to this embodiment, an unobstructed EGR flow rate map is stored in advance, which defines the relationship between the engine speed, intake air amount, and EGR flow rate (unobstructed EGR flow rate) when the exhaust pipe 18 is not obstructed at all, and the degree of obstruction of the exhaust pipe 18 is estimated (determined) by comparing the unobstructed EGR flow rate obtained from the unobstructed EGR flow rate map based on the engine speed and intake air amount with the actual EGR flow rate detected by the EGR flow rate sensor 44. Therefore, the degree of obstruction of the exhaust pipe 18 due to condensed water can be estimated (determined) more accurately (more precisely).

[0051] According to this embodiment, when the degree of blockage of the exhaust pipe 18 (the rate or amount of increase in the actual EGR flow rate) becomes equal to or greater than a predetermined threshold, the operating state of the engine 10 is changed (controlled) to evaporate the condensed water. Therefore, when the blockage of the exhaust pipe 18 due to the condensed water progresses, the blockage of the exhaust pipe 18 can be alleviated (removed) by evaporating the condensed water.

[0052] More specifically, according to this embodiment, when the degree of blockage of the exhaust pipe 18 (the rate or amount of increase in the actual EGR flow rate) becomes equal to or greater than a predetermined threshold, the ignition timing of the engine 10 is retarded. This increases the exhaust temperature, promoting the evaporation of condensed water and alleviating (eliminating) blockage of the exhaust pipe 18 caused by condensed water. Furthermore, by limiting the retardation of the ignition timing to cases when the degree of blockage becomes equal to or greater than a predetermined threshold, it is possible to suppress deterioration of fuel economy due to retardation of the ignition timing.

[0053] According to this embodiment, the lower the temperature of the exhaust pipe 18 or the exhaust, the more frequently the degree of blockage of the exhaust pipe 18 is estimated. Therefore, blockage of the exhaust pipe 18 can be reliably prevented beforehand.

[0054] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, although the above embodiment has been described using a gasoline engine that uses gasoline as fuel, the present invention can also be applied to, for example, a hydrogen engine that uses hydrogen as fuel, a diesel engine that uses light oil as fuel, etc.

[0055] Furthermore, in the above embodiment, a naturally aspirated engine has been described as an example, but the present invention can also be applied to an engine having a supercharger (for example, a turbo engine).

[0056] Furthermore, although the above embodiment has been described with reference to an example where the present invention is applied to a conventional gasoline engine vehicle, the present invention can also be applied to an engine of a hybrid electric vehicle (HEV) that has an engine and an electric motor as a driving force source. When applied to a hybrid electric vehicle, instead of or in addition to ignition retard, for example, the load (engine intake air amount) can be increased by increasing the amount of regeneration by the electric motor, thereby raising the exhaust temperature (and also increasing the exhaust flow rate). [Explanation of symbols]

[0057] 1 Engine control device 10 Engine 11 Intake manifold 15 Intake pipe 18 Exhaust pipe 19 Air-fuel ratio sensor 20 Exhaust purification catalyst 40 Exhaust Gas Recirculation System 41 EGR piping 42 EGR valve 43 silencer (muffler) 44 EGR flow sensor 45 Exhaust gas temperature sensor 50 ECU

Claims

1. an EGR pipe that connects the exhaust pipe and the intake pipe of the engine; an EGR valve interposed in the EGR pipe to adjust the amount of exhaust gas recirculated through the EGR pipe; an EGR flow rate sensor that detects the amount of recirculated exhaust gas; a control unit that controls the opening degree of the EGR valve in accordance with an operating state of the engine, The control unit estimates the degree of blockage of the exhaust pipe due to condensed water based on the degree of increase in the amount of exhaust gas recirculation detected by the EGR flow sensor when the EGR valve is open relative to the amount of exhaust gas recirculation when the exhaust pipe is not blocked.

2. The control unit a look-up table is stored in advance, which defines the relationship between the engine speed, the intake air amount, and the exhaust gas recirculation amount when the exhaust pipe is not blocked; The degree of blockage of the exhaust pipe is estimated by comparing the amount of recirculation of exhaust gas when the exhaust pipe is not blocked, which is obtained from the lookup table based on the engine speed and the amount of intake air, with the actual amount of recirculation of exhaust gas detected by the EGR flow sensor.

2. The engine control device according to claim 1.

3. 3. The engine control device according to claim 2, wherein the control unit changes the operating state of the engine so as to evaporate condensed water when the degree of blockage of the exhaust pipe reaches a predetermined threshold value or more.

4. 4. The engine control device according to claim 3, wherein the control unit retards the ignition timing of the engine when the degree of blockage of the exhaust pipe reaches a predetermined threshold value or more.

5. 5. The engine control device according to claim 4, wherein the control unit increases the frequency of estimating the degree of blockage of the exhaust pipe as the temperature of the exhaust pipe or the exhaust becomes lower.

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