JP2009047002A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance exhaust emission control efficiency by suppressing the exhaust of unburned gas in a control device of an internal combustion engine. <P>SOLUTION: An NOx storage reduction catalyst 40 for storing NOx in exhaust gas during operation in a lean air fuel ratio and releasing and reducing the NOx stored during operation in a rich air fuel ratio, is provided to an exhaust pipe 38. An ECU 61 allows the execution of lean operation through the change to the lean air fuel ratio on the basis of the engine operating condition, and prohibits the lean operation when an alcohol concentration in fuel exceeds a prescribed value set in advance. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine that corrects a fuel injection amount based on an air-fuel ratio, and more particularly to a control device for an internal combustion engine that can be operated with an alcohol-mixed fuel in which alcohol is mixed with fuel.

  In recent years, there is a lean burn engine in which an air-fuel ratio is increased and combustion is performed with an air-fuel mixture thinner than normal, and both exhaust gas purification performance and low fuel consumption can be achieved by stable lean combustion. In such a lean burn engine, a three-way catalyst and a NOx occlusion reduction type catalyst are provided in the exhaust pipe. The three-way catalyst can simultaneously purify HC, CO, and NOx contained in the exhaust gas by an oxidation-reduction reaction when the exhaust air-fuel ratio is stoichiometric. The NOx occlusion reduction type catalyst temporarily occludes NOx contained in the exhaust gas when the exhaust air-fuel ratio is lean, and stores the NOx occluded when the oxygen concentration in the exhaust gas is in the rich combustion region or stoichiometric combustion region. And NOx is reduced (rich spike control) by the added fuel as the reducing agent.

  By the way, in recent years, so-called multi-fuel internal combustion engines, which use a plurality of types of fuels having different fuel properties and complement each other by complementing each other, have been adopted in internal combustion engines. A vehicle equipped with this multi-fuel internal combustion engine is generally called a flexible fuel vehicle (FFV). One example is the use of gasoline fuels and alcohol fuels such as ethanol alone or in combination to meet the required performance to improve the internal combustion engine emission performance and control consumption of fossil fuels such as gasoline fuel. Those that improve performance are known.

  In this case, since the NOx emission amount also varies depending on the fuel properties, the NOx storage amount to the NOx storage reduction catalyst is estimated based on not only the operating state of the internal combustion engine but also the fuel properties, and the rich spike time is set. Need to control. For example, the fuel supply device for an internal combustion engine disclosed in Patent Document 1 below detects at least one fuel property among cetane number, octane number, evaporability, calorific value, and aromatic hydrocarbon content based on the specific gravity of the fuel. The amount of NOx discharged and the total amount of NOx traps are calculated according to the amount of air sucked into the internal combustion engine and the fuel properties, and NOx trap control is executed.

Japanese Patent Laid-Open No. 03-037343

  However, in alcohol-mixed fuel, gasoline has a high boiling point and alcohol has a low boiling point. Therefore, when a predetermined amount of alcohol is mixed with gasoline to produce an alcohol-mixed fuel, it is close to the properties of fuel only with gasoline. In addition, a high boiling point component (heavy component) is mixed. Therefore, when the alcohol mixed fuel is stored in the fuel tank, the alcohol mixed fuel in the fuel tank easily evaporates when the high temperature state, the high atmospheric pressure state, or the remaining amount decreases. And since alcohol with a low boiling point evaporates first, the component which remains as fuel increases gasoline and a high boiling point component.

  Therefore, during the lean operation of the above-described lean burn engine, the NOx occluded by the NOx occlusion reduction type catalyst increases, and when the NOx occluded by rich combustion is released and reduced, the fuel contains a lot of high-boiling components. Because it is heavy fuel, it becomes over-rich. Further, since the purge gas of the fuel generated in the fuel tank is discharged to the intake system, it becomes further rich. Then, it is difficult for the fuel to evaporate in the combustion chamber, mixing with air is deteriorated, unburned HC is increased, exhaust purification efficiency is lowered, and there is a risk of misfire.

  An object of the present invention is to provide a control device for an internal combustion engine that improves exhaust purification efficiency by suppressing discharge of unburned gas.

  In order to solve the above-described problems and achieve the object, the control apparatus for an internal combustion engine of the present invention occludes NOx in exhaust gas during operation at a lean air-fuel ratio and occludes during operation at a rich air-fuel ratio. In the internal combustion engine in which the NOx occlusion reduction catalyst for releasing and reducing the NOx is provided in the exhaust passage, air-fuel ratio changing means capable of changing the air-fuel ratio based on the operating state of the internal combustion engine, and the alcohol concentration in the fuel An alcohol concentration detection / estimation means for detecting or estimating the lean air-fuel ratio based on the operating state of the internal combustion engine, the lean air-fuel ratio can be changed and the lean operation can be executed, and the alcohol concentration detection / estimation means detects Or a lean operation control means for prohibiting the lean operation when the estimated alcohol concentration exceeds a predetermined value set in advance. It is intended.

  In the control device for an internal combustion engine of the present invention, purge means for discharging the purge gas of the fuel tank to the intake passage of the internal combustion engine is provided, and when the lean operation is prohibited by the lean operation control means, the purge passage causes the intake passage to It is characterized by increasing the amount of purge gas discharged to the tank.

  In the control apparatus for an internal combustion engine of the present invention, the atmospheric pressure is a predetermined value that is less than a predetermined value, the fuel remaining amount is a predetermined value that is less than a predetermined value, and the fuel purge gas concentration learning value is a predetermined value that is set in advance. Among the above conditions, the lean operation is prohibited by the lean operation control means when at least one of the conditions is satisfied.

  In the control device for an internal combustion engine according to the present invention, when the NOx occlusion amount of the NOx occlusion reduction catalyst exceeds a predetermined value set in advance, the air-fuel ratio changing means changes the first rich air-fuel ratio to occlude. NOx reduction control means for executing NOx reduction control is provided, wherein the lean operation control means has an alcohol concentration detected or estimated by the alcohol concentration detection estimating means exceeding a predetermined value set in advance, and atmospheric pressure When the air-fuel ratio is less than or equal to a predetermined value set in advance, the lean operation is performed by the air-fuel ratio changing means, and the NOx reduction control means is a second richer leaner than the first rich air-fuel ratio by the air-fuel ratio changing means. It is characterized in that NOx reduction control is executed by changing to an air-fuel ratio.

  In the control apparatus for an internal combustion engine according to the present invention, at least one of the conditions where the fuel remaining amount is equal to or less than a predetermined value and the conditions where the fuel purge gas concentration learning value is equal to or greater than a predetermined value is satisfied. In some cases, the lean operation is prohibited by the lean operation control means.

  In the control apparatus for an internal combustion engine according to the present invention, purge means for discharging the purge gas of the fuel tank to the intake passage of the internal combustion engine is provided, and when the NOx reduction control is executed by the NOx reduction control means, the purge is performed by the purge means. It is characterized by stopping the processing.

  In the control apparatus for an internal combustion engine of the present invention, the alcohol concentration detection estimating means estimates the alcohol concentration in the fuel based on the exhaust air-fuel ratio and the ignition timing.

  According to the control apparatus for an internal combustion engine of the present invention, the lean air-fuel ratio can be changed to the lean air-fuel ratio based on the operation state of the internal combustion engine, and the alcohol concentration in the fuel exceeds a predetermined value set in advance. Since the lean operation is prohibited at this time, the exhaust gas purification efficiency can be improved by suppressing the discharge of unburned gas without being over-rich during the NOx reduction process of the NOx storage reduction catalyst.

  Embodiments of an internal combustion engine control apparatus according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this Example.

  FIG. 1 is a schematic configuration diagram illustrating an internal combustion engine control apparatus according to a first embodiment of the present invention, and FIG. 2 is a flowchart illustrating lean burn control performed by the internal combustion engine control apparatus according to the first embodiment.

  In the control apparatus for an internal combustion engine according to the first embodiment, as shown in FIG. 1, a cylinder head 12 is fastened on a cylinder block 11, and pistons 14 are vertically moved to a plurality of cylinder bores 13 formed in the cylinder block 11. Fits freely. A crankcase 15 is fastened to the lower part of the cylinder block 11, and a crankshaft 16 is rotatably supported in the crankcase 15. Each piston 14 is connected to the crankshaft 16 via a connecting rod 17. Has been.

  The combustion chamber 18 is constituted by the wall surface of the cylinder bore 13 in the cylinder block 11, the lower surface of the cylinder head 12, and the top surface of the piston 14, and the combustion chamber 18 has a high central portion at the upper portion (lower surface of the cylinder head 12). It has a pent roof shape that is slanted. An intake port 19 and an exhaust port 20 are formed on the upper portion of the combustion chamber 18, that is, the lower surface of the cylinder head 12, and the intake valve 19 and the exhaust valve 20 are opposed to the intake port 19 and the exhaust port 20. The lower end portions of 22 are respectively positioned. The intake valve 21 and the exhaust valve 22 are supported by the cylinder head 12 so as to be movable in the axial direction, and are urged and supported in a direction (upward in FIG. 1) for closing the intake port 19 and the exhaust port 20. ing. An intake cam shaft 23 and an exhaust cam shaft 24 are rotatably supported on the cylinder head 12, and the intake cam and the exhaust cam are in contact with upper ends of the intake valve 21 and the exhaust valve 22.

  Although not shown, the crankshaft sprocket fixed to the crankshaft 16 and the camshaft sprockets respectively fixed to the intake camshaft 23 and the exhaust camshaft 24 are wound with endless timing chains. The crankshaft 16, the intake camshaft 23, and the exhaust camshaft 24 can be interlocked.

  Accordingly, when the intake camshaft 23 and the exhaust camshaft 24 rotate in synchronization with the crankshaft 16, the intake cam and the exhaust cam move up and down the intake valve 21 and the exhaust valve 22 at a predetermined timing. The exhaust port 20 can be opened and closed to allow the intake port 19 and the combustion chamber 18 to communicate with the combustion chamber 18 and the exhaust port 20. In this case, the intake camshaft 23 and the exhaust camshaft 24 are set to rotate once (360 degrees) while the crankshaft 16 rotates twice (720 degrees). Therefore, the engine performs four strokes of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke while the crankshaft 16 rotates twice. At this time, the intake camshaft 23 and the exhaust camshaft 24 rotate once. Will be.

  The valve mechanism of the engine is a variable intake valve timing mechanism (VVT: Variable Valve Timing-intelligent) 25 that controls the intake valve 21 and the exhaust valve 22 at an optimal opening / closing timing according to the operating state. The intake variable valve mechanism 25 is configured by providing a VVT controller 26 at the shaft end of the intake camshaft 23, and the hydraulic pressure from the oil control valve 27 is supplied to an advance chamber and a retard chamber (not shown) of the VVT controller 26. By acting on this, the phase of the intake camshaft 23 with respect to the cam sprocket can be changed, and the opening / closing timing of the intake valve 21 can be advanced or retarded. In this case, the intake variable valve mechanism 25 advances or retards the opening / closing timing while keeping the operating angle (opening period) of the intake valve 21 constant. The intake camshaft 23 is provided with a cam position sensor 28 for detecting the rotational phase.

  A surge tank 30 is connected to the intake port 19 via an intake manifold 29, and an intake pipe 31 is connected to the surge tank 30. An air cleaner 32 is attached to an air intake port of the intake pipe 31. . An electronic throttle device 34 having a throttle valve 33 is provided on the downstream side of the air cleaner 32. The intake port 19 is provided with a bypass passage 35 that bypasses the throttle valve 33, and an idle speed control valve 36 is provided in the bypass passage 35.

  An exhaust pipe 38 is connected to the exhaust port 20 via an exhaust manifold 37, and the exhaust pipe 38 has a three-way catalyst 39 for purifying harmful substances contained in the exhaust gas and a NOx occlusion reduction type catalyst 40. Is installed. The three-way catalyst 39 simultaneously purifies HC, CO, and NOx contained in the exhaust gas by an oxidation-reduction reaction when the air-fuel ratio (exhaust air-fuel ratio) is stoichiometric. The NOx occlusion reduction type catalyst 40 is in a rich combustion region or stoichiometric combustion region where the NOx contained in the exhaust gas is temporarily stored when the air-fuel ratio (exhaust air-fuel ratio) is lean, and the oxygen concentration in the exhaust gas is reduced. Sometimes, the stored NOx is released and NOx is reduced by the added fuel as a reducing agent.

  An exhaust gas recirculation passage (EGR passage) 41 is provided between the downstream side of the surge tank 30 in the intake pipe 31 and the upstream side of the three-way catalyst 39 in the exhaust pipe 38. Are provided with an EGR valve 42 and an EGR cooler 43. Further, an EGR gas temperature sensor 44 that detects the temperature of the EGR gas is provided on the intake pipe 31 side of the EGR passage 41 from the EGR valve 42.

  The cylinder head 12 is provided with an injector 45 that directly injects fuel into the combustion chamber 18. The injector 45 is positioned on the intake port 19 side and is inclined at a predetermined angle downward from the horizontal upper end. . An injector 45 attached to each cylinder is connected to a delivery pipe 46, and a high pressure fuel pump 48 is connected to the delivery pipe 46 via a high pressure fuel supply pipe 47. The high pressure fuel pump 48 is supplied with a low pressure fuel supply. A low-pressure fuel pump (feed pump) 51 in the fuel tank 50 is connected via a pipe 49. Accordingly, the low-pressure fuel pump 51 pressurizes the fuel in the fuel tank 50 to a predetermined low pressure and supplies it to the low-pressure fuel supply pipe 49, and the high-pressure fuel pump 48 supplies the low-pressure fuel in the low-pressure fuel supply pipe 49 to a predetermined high pressure. The fuel can be pressurized and supplied to the delivery pipe 46 via the high-pressure fuel supply pipe 47, and the injector 45 can inject the high-pressure fuel in the delivery pipe 46 into the combustion chamber 18. The cylinder head 12 is provided with a spark plug 52 that is positioned above the combustion chamber 18 and ignites the air-fuel mixture.

  A canister 53 is provided in the fuel tank 50, and the canister 53 is connected to the upstream side of the surge tank 30 in the intake pipe 31 via a purge passage (purge means) 54. A purge valve 55 is provided in the purge passage 54. The canister 53 adsorbs purge gas including vapor (evaporated fuel) generated in the fuel tank 50, and opens the purge valve 55 to discharge the adsorbed purge gas to the intake pipe 31 through the purge passage 54. be able to.

  The vehicle is equipped with an electronic control unit (ECU) 61, which can control the fuel injection timing of the injector 45, the ignition timing of the spark plug 52, and the like. The fuel injection amount, injection timing, ignition timing, and the like are determined based on engine operating conditions such as temperature, throttle opening, accelerator opening, engine speed, and coolant temperature.

  That is, an airflow sensor 62 and an intake air temperature sensor 63 are mounted on the upstream side of the intake pipe 31, and the measured intake air amount and intake air temperature are output to the ECU 61. The electronic throttle device 34 is provided with a throttle position sensor 64, and the accelerator pedal is provided with an accelerator position sensor 65, which outputs the current throttle opening and accelerator opening to the ECU 61. The crankshaft 16 is provided with a crank angle sensor 66 and outputs the detected crank angle to the ECU 61. The ECU 61 discriminates an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke in each cylinder based on the crank angle, and an engine. Calculate the number of revolutions. The cylinder block 11 is provided with a water temperature sensor 67 and outputs the detected engine cooling water temperature to the ECU 61. The cylinder block 11 is provided with a knock sensor 68 and outputs a detected knocking signal to the ECU 61.

  The vehicle is provided with an atmospheric pressure sensor 69 and outputs the detected atmospheric pressure to the ECU 61. A vehicle speed sensor 70 is provided in the vehicle, and the detected vehicle speed is output to the ECU 61.

An air-fuel ratio (A / F) sensor 71 is provided upstream of the three-way catalyst 39 in the exhaust pipe 38, and an oxygen (O ₂ ) sensor 72 is provided downstream of the three-way catalyst 39. The A / F sensor 71 and the O ₂ sensor 72 detect the exhaust air / fuel ratio (oxygen amount) of the exhaust gas exhausted from the combustion chamber 18 through the exhaust port 20 and the exhaust manifold 37 to the exhaust pipe 38, and the detected exhaust air is detected. The fuel ratio is output to the ECU 61. The ECU 61 corrects the fuel injection amount by feeding back the exhaust air-fuel ratio detected by the A / F sensor 71 and the O ₂ sensor 72 and comparing it with the target air-fuel ratio set according to the engine operating state.

  The fuel tank 50 is provided with a remaining amount sensor 73 for detecting the remaining amount of stored fuel, and outputs the detected remaining fuel amount to the ECU 61. The fuel tank 50 is provided with a tank temperature sensor 74 that detects the temperature of the fuel tank 50, and outputs the detected temperature of the fuel tank 50 to the ECU 61.

  An ignition key switch 75 is provided at the driver's seat of the vehicle, and the ON / OFF state is output to the ECU 61.

  The ECU 61 can control the intake variable valve mechanism 25 based on the engine operating state. That is, when the temperature is low, the engine is started, the engine is idle, or the load is light, the exhaust gas blows back into the intake port 19 or the combustion chamber 18 by eliminating the overlap between the exhaust valve 22 closing timing and the intake valve 21 opening timing. Reduce the amount to enable stable combustion and improved fuel efficiency. Further, at the time of medium load, by increasing the overlap, the internal EGR rate is increased to improve the exhaust gas purification efficiency, and the pumping loss is reduced to improve the fuel consumption. Further, at the time of high-load low-medium rotation, the closing timing of the intake valve 21 is advanced, thereby reducing the amount of intake air that blows back to the intake port 19 and improving the volume efficiency. At the time of high load and high rotation, the closing timing of the intake valve 21 is retarded in accordance with the rotation speed, so that the timing is adjusted to the inertial force of the intake air and the volume efficiency is improved.

  By the way, the engine of the present embodiment can use an alcohol mixed fuel obtained by mixing a predetermined ratio of alcohol fuel such as ethanol with gasoline fuel, thereby improving the emission performance of the engine and consuming fossil fuel such as gasoline fuel. It is intended to improve environmental performance such as suppression. However, alcohol-mixed fuel is produced by mixing low-boiling alcohol fuel with high-boiling gasoline fuel and mixing high-boiling components (heavy components). Therefore, if the alcohol-mixed fuel evaporates while being stored in the fuel tank 50, the fuel component remaining in the fuel tank 50 has a high boiling point component.

  The engine of the present embodiment has a lean burn engine that can be burned with a gas mixture that is thinner than usual. Since the exhaust system has the NOx storage reduction catalyst 40, the NOx storage reduction catalyst 40 includes When the stored amount of NOx exceeds a predetermined amount, it is necessary to release and reduce the stored NOx as a rich air-fuel ratio. At this time, since the fuel is a heavy fuel containing a large amount of high-boiling components, it becomes an over-rich state, the fuel is difficult to vaporize in the combustion chamber 18, the mixing with air deteriorates, the unburned HC increases, and the exhaust There exists a possibility that purification efficiency may fall.

  Therefore, in the control device for the internal combustion engine of the present embodiment, the ECU 61 can change the air-fuel ratio (air-fuel ratio changing means) based on the operating state of the engine, Based on the ignition timing, the alcohol concentration in the alcohol mixed fuel can be estimated (alcohol concentration detection estimating means). The ECU 61 can execute the lean operation by changing to the lean air-fuel ratio based on the operation state of the engine, and performs the lean operation when the alcohol concentration in the alcohol mixed fuel exceeds a predetermined value set in advance. It is prohibited (lean operation control means).

  In this embodiment, when the alcohol concentration in the alcohol-mixed fuel exceeds a predetermined value, the ECU 61 has a condition that the atmospheric pressure is equal to or lower than a predetermined value, and a predetermined value that the fuel remaining amount is set in advance. Lean operation is prohibited when at least one of the following conditions is met and the purge gas concentration learning value of the alcohol-mixed fuel is greater than or equal to a predetermined value, and lean operation is permitted otherwise. ing.

  In this embodiment, when the lean operation is prohibited, the ECU 61 adjusts the opening of the purge valve 55 to increase the amount of purge gas discharged from the canister 53 of the fuel tank 50 to the intake pipe 31. Yes.

  Here, in the control apparatus for an internal combustion engine of the present embodiment described above, the lean burn control will be specifically described based on the flowchart of FIG.

  In the control apparatus for the internal combustion engine of the present embodiment, as shown in FIGS. 1 and 2, in step S11, the ECU 61 corrects the ignition timing based on the feedback value of the knock signal detected by the knock sensor 68. The knock learning value KGKCS is calculated. In step S12, a current air-fuel ratio learning value EFGAF for correcting the fuel injection amount is calculated based on the feedback value of the A / F signal detected by the A / F sensor 71. In step S13, it is determined whether the knock learning value KGKCS is on the advance side with respect to the predetermined value set in advance and the air-fuel ratio learning value EFGAF is greater than the predetermined value set in advance.

  That is, alcohol fuel has a higher octane number than gasoline fuel and is difficult to knock. Therefore, the engine output and fuel consumption can be improved by correcting the ignition timing to the advance side. Also, alcohol fuel contains more oxygen than gasoline fuel, and the stoichiometric air-fuel ratio is richer than gasoline fuel. Therefore, when it is determined that knock learning value KGKCS is more advanced than the predetermined value and air-fuel ratio learning value EFGAF is larger than the predetermined value, that is, the deviation amount between the target air-fuel ratio and the exhaust air-fuel ratio is large. It can be determined that the fuel contains a predetermined ratio or more of alcohol.

  If it is determined in step S13 that the knock learning value KGKCS is more advanced than the predetermined value and the air-fuel ratio learning value EFGAF is larger than the predetermined value, an alcohol mixed fuel determination flag is set in step S14. Set to “ON”.

  If it is determined that the fuel is alcohol mixed fuel, the ECU 61 reads the current atmospheric pressure PA detected by the atmospheric pressure sensor 69 in step S15, and the fuel tank 50 detected by the remaining amount sensor 73 in step S16. The current fuel remaining amount Rfuel is read, and in step S17, the current fuel tank temperature Ttank detected by the tank temperature sensor 74 is read. In step S18, the ECU 61 reads the current purge concentration learning value FGPG. In this case, the current purge concentration learning value FGPG is calculated based on the air-fuel ratio feedback value by the A / F sensor 71 and the purge gas flow rate purged from the canister 53 to the intake pipe 31 through the purge passage 54. The purge gas flow rate is calculated based on the pressure in the fuel tank 50 (canister 53) detected by a pressure sensor (not shown) and the opening of the purge valve 55.

  In step S19, the ECU 61 first determines whether or not the atmospheric pressure PA is equal to or less than a predetermined value set in advance. That is, at high altitude, the atmospheric pressure is low and the alcohol component of the fuel is likely to evaporate, so the amount of purge gas generated in the fuel tank 50 increases. Therefore, if it is determined in step S19 that the atmospheric pressure PA is equal to or lower than the predetermined value, in step S20, the ECU 61 causes the engine to perform stoichiometric (theoretical air-fuel ratio) operation and prohibits lean burn operation. At this time, since the engine is in a stoichiometric operation, the intake negative pressure in the surge tank 30 increases, the flow rate of the purge gas introduced from the canister 53 through the purge passage 54 into the intake pipe 31 increases, and the fuel tank The purge gas in 50 is properly processed. In this case, the purge gas flow rate introduced into the intake pipe 31 from the canister 53 through the purge passage 54 may be positively increased by increasing the opening of the purge valve 55.

  If it is determined in step S19 that the atmospheric pressure PA is not equal to or less than the predetermined value, then in step S21, the ECU 61 determines whether or not the remaining fuel amount Rfuel is equal to or less than a predetermined value. That is, if the amount of fuel remaining in the fuel tank 50 is small, the alcohol component of the fuel is likely to evaporate, and the amount of purge gas generated in the fuel tank 50 increases. Therefore, if it is determined in step S21 that the remaining fuel amount Rfuel is equal to or less than the predetermined value, in step S20, the ECU 61 causes the engine to perform stoichiometric (stoichiometric air-fuel ratio) operation and prohibits lean burn operation.

  Further, if it is determined in step S21 that the remaining fuel amount Rfuel is not less than or equal to a predetermined value, in step S22, the ECU 61 next determines whether or not the purge concentration learning value FGPG is greater than or equal to a predetermined value. To do. That is, the large purge concentration learning value FGPG means that the purge gas in the canister 53 has not been sufficiently processed and the purge gas in the fuel tank 50 is large. Therefore, if it is determined in step S22 that the purge concentration learned value FGPG is greater than or equal to a predetermined value, in step S20, the ECU 61 causes the engine to perform stoichiometric (theoretical air-fuel ratio) operation and prohibits lean burn operation.

  If it is determined in step S22 that the purge concentration learning value FGPG is not equal to or higher than the predetermined value, in step S23, the ECU 61 finally determines whether or not the temperature Ttank of the fuel tank is equal to or higher than a predetermined value. To do. That is, if the temperature Ttank of the fuel tank is high, the alcohol component of the fuel is likely to evaporate, and the amount of purge gas generated in the fuel tank 50 increases. Therefore, if it is determined in step S23 that the temperature Ttank of the fuel tank is equal to or higher than a predetermined value, in step S20, the ECU 61 sets the engine to stoichiometric (theoretical air-fuel ratio) operation and prohibits the lean burn operation.

  On the other hand, if it is determined in step S23 that the temperature Ttank of the fuel tank is not equal to or higher than a predetermined value, the ECU 61 permits the lean burn operation of the engine in step S24. If it is determined in step S13 described above that the knock learning value KGKCS is not advanced from the predetermined value, or if it is determined that the air-fuel ratio learning value EFGAF is not larger than the predetermined value, in step S25. Then, the alcohol mixed fuel determination flag is set to “OFF”, and in step S24, the ECU 61 permits the lean burn operation of the engine.

  As described above, in the control apparatus for the internal combustion engine according to the first embodiment, the NOx in the exhaust gas is occluded during the operation at the lean air-fuel ratio, and the NOx occluded during the operation at the rich air-fuel ratio is released and reduced. The NOx occlusion reduction type catalyst 40 is provided in the exhaust pipe 38, and the ECU 61 can change to the lean air-fuel ratio based on the operating state of the engine and execute the lean operation, and the alcohol concentration in the fuel is preset. Lean operation is prohibited when a predetermined value is exceeded.

  Therefore, when the alcohol concentration in the fuel is high, the lean operation is prohibited, and when the alcohol concentration in the fuel is high, the NOx reduction process for reducing the NOx stored in the NOx storage reduction catalyst 40 is executed. However, it is possible to suppress the discharge of unburned gas due to the over-rich state of the air-fuel ratio, and it is possible to improve the exhaust purification efficiency.

  When the alcohol concentration in the fuel is high and the lean operation is prohibited, the engine is stoichiometrically operated, so that the intake negative pressure in the surge tank 30 increases, and the intake air from the canister 53 passes through the purge passage 54. The flow rate of the purge gas introduced into the pipe 31 increases, and the purge gas in the fuel tank 50 can be properly processed. In this case, the flow rate of the purge gas introduced into the intake pipe 31 from the canister 53 through the purge passage 54 can be further increased by increasing the opening of the purge valve 55.

  In this embodiment, the atmospheric pressure is set to a predetermined value or less, the fuel remaining amount is set to a predetermined value or less, and the fuel purge gas concentration learning value is set to a preset value or more. Among these, when at least one condition is satisfied, lean operation is prohibited. Therefore, by prohibiting the lean operation in an environment where the alcohol concentration in the fuel is high and the vapor gas in the fuel tank 50 is likely to increase, the emission of unburned gas can be suppressed while the lean operation is suppressed. By increasing the driving range, fuel consumption can be improved.

  In this embodiment, the ECU 61 estimates the alcohol concentration in the fuel on the basis of the exhaust air-fuel ratio and the ignition timing, and it is not necessary to provide a separate alcohol concentration sensor or the like, so that an increase in cost can be suppressed. However, when considering simplification of control, an alcohol concentration sensor may be used.

  FIG. 3 is a flowchart showing lean burn control by the control device for an internal combustion engine according to the second embodiment of the present invention. The overall configuration of the control apparatus for an internal combustion engine of the present embodiment is substantially the same as that of the first embodiment described above, and will be described with reference to FIG. 1 and members having the same functions as those described in this embodiment. Are denoted by the same reference numerals, and redundant description is omitted.

  In the control apparatus for an internal combustion engine of the second embodiment, the ECU 61 changes the NOx occluded by changing to the first rich air-fuel ratio when the NOx occlusion amount of the NOx occlusion reduction catalyst 40 exceeds a predetermined value set in advance. When the alcohol concentration in the fuel exceeds a predetermined value that is set in advance and the atmospheric pressure is equal to or lower than the predetermined value that is set in advance, the lean operation is executed. At the same time, the NOx reduction control is executed by changing to the second rich air-fuel ratio that is leaner than the first rich air-fuel ratio.

  In this embodiment, the ECU 61 satisfies at least one of a condition where the remaining amount of fuel is equal to or less than a predetermined value set in advance and a condition where the learning value of the purge gas concentration of fuel is equal to or greater than a predetermined value set in advance. When you do, lean operation is prohibited.

  In this embodiment, the ECU 61 is stopped from discharging the purge gas from the canister 53 of the fuel tank 50 to the intake pipe 31 when executing the NOx reduction control of the NOx storage reduction catalyst 40.

  Here, in the control apparatus for an internal combustion engine of the present embodiment described above, the lean burn control will be specifically described based on the flowchart of FIG.

  In the control apparatus for the internal combustion engine of the present embodiment, as shown in FIGS. 1 and 3, in step S31, the ECU 61 corrects the ignition timing based on the feedback value of the knock signal detected by the knock sensor 68. The knock learning value KGKCS is calculated. In step S32, a current air-fuel ratio learning value EFGAF for correcting the fuel injection amount is calculated based on the feedback value of the A / F signal detected by the A / F sensor 71. In step S33, it is determined whether the knock learning value KGKCS is on the advance side with respect to the predetermined value set in advance and the air-fuel ratio learning value EFGAF is greater than the predetermined value set in advance.

  If it is determined in step S33 that the knock learning value KGKCS is more advanced than the predetermined value and the air-fuel ratio learning value EFGAF is larger than the predetermined value, an alcohol mixed fuel determination flag is set in step S34. Set to “ON”. On the other hand, if it is determined in step S33 that the knock learning value KGKCS is not on the advance side from the predetermined value, or if it is determined that the air-fuel ratio learning value EFGAF is not larger than the predetermined value, in step S46, alcohol The mixed fuel determination flag is set to “OFF”, and in step S45, the ECU 61 permits the lean burn operation of the engine. In this case, when the engine is performing the lean burn operation, the ECU 61 uses the first rich air-fuel ratio map when the NOx occlusion amount of the NOx occlusion reduction type catalyst 40 exceeds a predetermined value set in advance. It is assumed that the reduction control of the stored NOx is executed by changing to 1 rich air-fuel ratio.

  If it is determined that the fuel is alcohol mixed fuel, the ECU 61 reads the current atmospheric pressure PA detected by the atmospheric pressure sensor 69 in step S35, and the fuel tank 50 detected by the remaining amount sensor 73 in step S36. In step S37, the current fuel tank temperature Ttank detected by the tank temperature sensor 74 is read. In step S38, the current purge concentration learning value FGPG is read.

  In step S39, the ECU 61 determines whether or not the atmospheric pressure PA is equal to or less than a predetermined value set in advance. Here, if it is determined that the atmospheric pressure PA is equal to or less than the predetermined value, in step S40, the ECU 61 permits the lean burn operation of the engine. In this case, when the engine is performing lean burn operation, the ECU 61 uses the second rich air-fuel ratio map when the NOx occlusion amount of the NOx occlusion reduction catalyst 40 exceeds a predetermined value set in advance. It is assumed that the reduction control of the stored NOx is executed by changing to the 2-rich air-fuel ratio. Here, the second rich air-fuel ratio is an air-fuel ratio leaner than the first rich air-fuel ratio.

  On the other hand, if it is determined in step S39 that the atmospheric pressure PA is not less than the predetermined value, the ECU 61 permits the lean burn operation of the engine in step S45.

  In step S41, the ECU 61 determines whether the remaining fuel amount Rfuel is equal to or less than a predetermined value set in advance. Here, if it is determined that the remaining fuel amount Rfuel is equal to or less than the predetermined value, in step S42, the ECU 61 sets the engine to stoichiometric (theoretical air-fuel ratio) operation and prohibits the lean burn operation. At this time, since the engine is in a stoichiometric operation, the intake negative pressure in the surge tank 30 increases, the flow rate of the purge gas introduced from the canister 53 through the purge passage 54 into the intake pipe 31 increases, and the fuel tank The purge gas in 50 is properly processed. In this case, the purge gas flow rate introduced into the intake pipe 31 from the canister 53 through the purge passage 54 may be positively increased by increasing the opening of the purge valve 55.

  If it is determined in step S41 that the remaining fuel amount Rfuel is not less than or equal to the predetermined value, in step S43, the ECU 61 determines whether or not the purge concentration learning value FGPG is greater than or equal to a predetermined value. Here, if it is determined that the purge concentration learning value FGPG is equal to or greater than the predetermined value, in step S42, the ECU 61 causes the engine to perform stoichiometric (theoretical air-fuel ratio) operation and prohibits lean burn operation.

  If it is determined in step S43 that the purge concentration learning value FGPG is not equal to or higher than the predetermined value, in step S44, the ECU 61 determines whether or not the fuel tank temperature Ttank is equal to or higher than a predetermined value. Here, if it is determined that the temperature Ttank of the fuel tank is equal to or higher than the predetermined value, in step S42, the ECU 61 sets the engine to stoichiometric (theoretical air-fuel ratio) operation and prohibits the lean burn operation.

  On the other hand, when it is determined in step S44 that the temperature Ttank of the fuel tank is not equal to or higher than the predetermined value, the ECU 61 permits the lean burn operation of the engine and executes the NOx reduction control using the second rich air-fuel ratio map. Continue.

  In step S40 or step S45, when the lean burn operation of the engine is permitted and the NOx occlusion reduction catalyst 40 is controlled to be reduced to the first or second rich air-fuel ratio and the NOx reduction control is executed, the purge valve By closing 55, the purge process for introducing the purge gas from the canister 53 to the intake pipe 31 through the purge passage 54 is stopped.

  As described above, in the control device for the internal combustion engine according to the second embodiment, the ECU 61 can change to the lean air-fuel ratio based on the operating state of the engine and execute the lean operation, and also the NOx storage reduction catalyst 40. When the NOx occlusion amount exceeds a preset predetermined value, the first rich air-fuel ratio is changed to enable execution of NOx reduction control, the alcohol concentration in the fuel exceeds a preset predetermined value, and When the atmospheric pressure is less than or equal to a predetermined value set in advance, the lean operation is permitted, and the NOx reduction control is executed by changing to a second rich air-fuel ratio that is leaner than the first rich air-fuel ratio.

  Accordingly, when the alcohol concentration in the fuel is high but the atmospheric pressure is not low, the lean operation is permitted and the lean operation range is expanded by executing the NOx reduction control at the second rich air-fuel ratio leaner than usual. The fuel consumption can be improved and the NOx occluded in the NOx occlusion reduction type catalyst 40 is reduced at a leaner second air-fuel ratio than usual. Can be suppressed.

  Further, in this embodiment, when at least one of the conditions where the remaining amount of fuel is equal to or less than a preset predetermined value and the conditions where the purge gas concentration learning value of the fuel is equal to or greater than a preset predetermined value is satisfied, Lean driving is prohibited. Therefore, by prohibiting the lean operation in an environment where the alcohol concentration in the fuel is high and the vapor gas in the fuel tank 50 is likely to increase, the emission of unburned gas can be suppressed while the lean operation is suppressed. By increasing the driving range, fuel consumption can be improved.

  When the alcohol concentration in the fuel is high and the lean operation is prohibited, the engine is stoichiometrically operated, so that the intake negative pressure in the surge tank 30 increases, and the intake air from the canister 53 passes through the purge passage 54. The flow rate of the purge gas introduced into the pipe 31 increases, and the purge gas in the fuel tank 50 can be properly processed. In this case, the flow rate of the purge gas introduced into the intake pipe 31 from the canister 53 through the purge passage 54 can be further increased by increasing the opening of the purge valve 55.

  In the present embodiment, when the lean burn operation of the engine is permitted and the NOx reduction control of the NOx occlusion reduction catalyst 40 is executed at the rich air-fuel ratio, the purge valve 55 is closed, so that the purge passage from the canister 53 is closed. The purging process for introducing the purge gas into the intake pipe 31 through 54 is stopped. Therefore, it is possible to suppress the over-richness of the air-fuel ratio and suppress the discharge of unburned gas.

  In the above-described embodiments, the internal combustion engine of the present invention has been described as a cylinder injection engine. However, the internal combustion engine may be a port injection engine and is limited to that type as long as it is an internal combustion engine capable of lean combustion. It is not something.

  As described above, the control device for an internal combustion engine according to the present invention suppresses the discharge of unburned gas by prohibiting lean operation when the alcohol concentration in the fuel exceeds a predetermined value set in advance. It is intended to improve exhaust purification efficiency, and is useful for any internal combustion engine.

1 is a schematic configuration diagram illustrating a control device for an internal combustion engine according to Embodiment 1 of the present invention. 3 is a flowchart illustrating lean burn control by the control device for an internal combustion engine according to the first embodiment. It is a flowchart showing the lean burn control by the control apparatus of the internal combustion engine which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 18 Combustion chamber 19 Intake port 20 Exhaust port 31 Intake pipe 34 Electronic throttle device 38 Exhaust pipe 39 Three way catalyst 40 NOx occlusion reduction type catalyst 45 Injector 50 Fuel tank 52 Spark plug 53 Canister 54 Purge passage (purge means)
55 purge valve 61 electronic control unit, ECU (air-fuel ratio changing means, alcohol concentration detection estimating means, lean operation control means, NOx reduction control means)
68 Knock sensor 69 Atmospheric pressure sensor 71 A / F sensor

Claims (7)

In an internal combustion engine in which an NOx occlusion reduction type catalyst that stores NOx in exhaust gas during operation at a lean air-fuel ratio and releases and reduces NOx occluded during operation at a rich air-fuel ratio is provided in an exhaust passage.
Air-fuel ratio changing means capable of changing the air-fuel ratio based on the operating state of the internal combustion engine;
Alcohol concentration detection and estimation means for detecting or estimating the alcohol concentration in the fuel;
Based on the operating state of the internal combustion engine, the lean air-fuel ratio can be changed by the air-fuel ratio changing means and the lean operation can be executed, and the alcohol concentration detected or estimated by the alcohol concentration detection estimating means is preset. Lean operation control means for prohibiting the lean operation when a value is exceeded;
A control apparatus for an internal combustion engine, comprising:   Purging means for discharging the purge gas of the fuel tank into the intake passage of the internal combustion engine is provided, and when the lean operation is prohibited by the lean operation control means, the purge gas discharge amount to the intake passage is increased by the purge means. The control device for an internal combustion engine according to claim 1.   At least one of a condition where the atmospheric pressure is equal to or lower than a predetermined value, a condition where the remaining amount of fuel is equal to or lower than a predetermined value, and a condition where the learning value of the purge gas concentration of the fuel is equal to or higher than a predetermined value 3. The control apparatus for an internal combustion engine according to claim 1, wherein the lean operation is prohibited by the lean operation control means when the condition is established.   When the NOx occlusion amount of the NOx occlusion reduction catalyst exceeds a predetermined value set in advance, the NOx reduction is performed by reducing the occluded NOx by changing to the first rich air-fuel ratio by the air-fuel ratio changing means. The lean operation control means is provided when the alcohol concentration detected or estimated by the alcohol concentration detection estimating means exceeds a preset predetermined value and the atmospheric pressure is equal to or lower than a preset predetermined value. In addition, the lean operation is executed by the air-fuel ratio changing means, and the NOx reduction control means is changed to a second rich air-fuel ratio that is leaner than the first rich air-fuel ratio by the air-fuel ratio changing means to control NOx reduction. The control apparatus for an internal combustion engine according to claim 1, wherein:   When at least one of a condition in which the remaining amount of fuel is equal to or less than a preset predetermined value and a condition in which the purge gas concentration learning value of the fuel is equal to or greater than a preset predetermined value is satisfied, the lean operation control means performs the lean operation. The control apparatus for an internal combustion engine according to claim 4, wherein operation is prohibited.   A purge means for discharging the purge gas of the fuel tank to the intake passage of the internal combustion engine is provided, and when the NOx reduction control is executed by the NOx reduction control means, the purge process is stopped by the purge means. Item 6. The control device for an internal combustion engine according to Item 4 or 5.   The control apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the alcohol concentration detection estimation means estimates the alcohol concentration in the fuel based on the exhaust air-fuel ratio and the ignition timing.

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