JP2005351127A - Control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine for restraining generation of an offensive odor from a catalyst after speed reduction, in the control device of the internal combustion engine for restraining the deterioration in the catalyst by prohibition of a fuel cut. <P>SOLUTION: This control device of the internal combustion engine has a fuel cut performing means for cutting fuel supply to the internal combustion engine mounted on a vehicle when the vehicle is put in a speed reduction state, and a fuel cut prohibiting means for prohibiting the fuel cut by the fuel cut performing means when a gear position of a transmission exists in a high speed gear and the temperature of the catalyst arranged in san exhaust system is the predetermined temperature or more. The control device is characterized in that the fuel cut prohibiting means does not prohibit the fuel cut when a speed SPD of the vehicle is a predetermined vehicle speed Sh or less when becoming the speed reduction state in a predetermined period after performing fuel quantity increasing operation for performing operation of the internal combustion engine by setting the combustion air-fuel ratio rich. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a control device for an internal combustion engine.

  Conventionally, when it is determined that the vehicle is in a decelerating state (for example, an engine brake state) and fuel supply to the internal combustion engine mounted on the vehicle is not necessary for the purpose of improving fuel consumption, etc. 2. Description of the Related Art A control device for an internal combustion engine that performs a fuel cut to stop the supply of this fuel is known. Among them, when the temperature of the catalyst provided in the exhaust system of the internal combustion engine is high, the fuel cut is prohibited in the vehicle deceleration state as described above, and the catalyst is placed in a high temperature and excessive oxygen state. There is one (for example, Patent Document 1) that attempts to suppress the deterioration of the catalyst by preventing the deterioration.

  Further, some control devices for internal combustion engines that prohibit the execution of fuel cuts for the above-described purposes are prohibited from performing fuel cuts only when they are more suitable. In other words, for example, if it is prohibited to perform fuel cuts, it is not necessary to obtain a feeling of deceleration of the vehicle, and in general, it is not necessary to obtain a feeling of deceleration, taking into account that the catalyst temperature becomes higher during high-speed driving. When the gear position of the transmission that is highly necessary to be prohibited is a high-speed gear (for example, 4th or 5th speed in a 5-speed transmission, or 5th or 6th speed in a 6-speed transmission) There are only those which prohibit the implementation of the above fuel cut.

JP-A-10-252532 JP-A-6-307271 JP 63-117139 A JP-A-63-134835 Japanese Patent Laid-Open No. 11-117790

However, when the internal combustion engine control device that prohibits the execution of the fuel cut only when the gear position is in the high speed gear as described above, the speed is reduced with the gear position kept at the high speed gear. In addition, there is a problem that a strange odor is generated when the vehicle is stopped after deceleration, more specifically, a hydrogen sulfide (H ₂ S) odor.

  The present invention has been made in view of such problems, and an object of the present invention is to perform a fuel cut that stops the supply of fuel to an internal combustion engine mounted on a vehicle when the vehicle is in a deceleration state. When the gear position of the transmission is in the high speed gear and the temperature of the catalyst provided in the exhaust system of the internal combustion engine is equal to or higher than a predetermined temperature, the fuel cut is performed by the fuel cut execution unit. An internal combustion engine control apparatus comprising a fuel cut prohibiting means for prohibiting the internal combustion engine, wherein the control apparatus for the internal combustion engine is configured to suppress generation of a strange odor after deceleration.

  The present invention provides a control device for an internal combustion engine described in each claim as a means for solving the above-mentioned problems.

  According to a first aspect of the present invention, when the vehicle is in a decelerating state, fuel cut execution means for performing fuel cut for stopping the supply of fuel to the internal combustion engine mounted on the vehicle, and the gear position of the transmission is changed to a high speed gear. And a control device for the internal combustion engine, comprising: a fuel cut prohibiting means for prohibiting the fuel cut by the fuel cut executing means when the temperature of the catalyst provided in the exhaust system of the internal combustion engine is equal to or higher than a predetermined temperature. When the vehicle is decelerated within a predetermined period after the fuel increasing operation for operating the internal combustion engine so that the combustion air-fuel ratio becomes rich, the speed of the vehicle is determined in advance. When the vehicle speed is less than or equal to the vehicle speed, the fuel cut prohibiting means does not prohibit the fuel cut.

  By prohibiting the fuel cut by the fuel cut prohibiting means as described above, it is possible to prevent the catalyst from being placed in a state of high temperature and excessive oxygen and to suppress the deterioration of the catalyst. However, on the other hand, when the control device for an internal combustion engine provided with the fuel cut prohibiting means as described above is used, when the vehicle is decelerated with the gear position kept at the high speed gear, There was a strange odor.

  This strange odor is a hydrogen sulfide odor generated from the catalyst, and it is thought that the cause is that the fuel cut was prohibited from the start of deceleration until the vehicle stopped because the vehicle was decelerated with the gear position kept at the high speed gear. That is, in this case, the fuel cut is prohibited from the start of deceleration to the stop of the vehicle, and the operation is performed with the combustion air-fuel ratio (that is, the air-fuel ratio in the combustion chamber) as the stoichiometric air-fuel ratio. This is considered to be because the air-fuel ratio of the exhaust gas does not become lean, and as a result, the sulfur oxide retained in the catalyst when the vehicle is stopped becomes hydrogen sulfide and is easily released to the outside. In particular, when the engine is decelerated immediately after the fuel increase operation is performed, the catalyst does not hold enough oxygen (that is, the catalyst is in the “reduced state”), and therefore, as described above. Release of hydrogen sulfide to the outside is more likely to occur.

  On the other hand, in the first aspect of the invention, when the vehicle is decelerated within a predetermined period after the fuel increase operation is performed, and the vehicle speed is equal to or lower than the predetermined vehicle speed, the fuel is increased. The cut prohibiting means does not prohibit fuel cut. In this way, even when the vehicle is decelerated while keeping the gear position at the high speed gear, the fuel cut can be performed when the speed of the vehicle becomes equal to or lower than the predetermined vehicle speed. As a result, oxygen can be supplied to the catalyst before the vehicle is stopped, and the catalyst is in a reduced state after deceleration, and hydrogen sulfide is prevented from being easily released to the outside. As a result, the generation of a strange odor after deceleration can be suppressed. That is, according to the first invention, it is possible to achieve both the suppression of catalyst deterioration and the suppression of the generation of off-flavors.

  The predetermined period can be defined by, for example, an elapsed time after the end of the fuel increase operation. Alternatively, the integrated value of the intake air amount from the end of the fuel increase operation may be defined as a reference. That is, an integrated value of the intake air amount serving as a determination criterion is determined in advance, and the predetermined period of time is set when the integrated value of the intake air amount after completion of the fuel increase operation reaches the integrated value of the determination criterion. It is assumed that it has passed.

  When an air-fuel ratio sensor is provided downstream of the catalyst, the predetermined period may be defined based on the output of the air-fuel ratio sensor. That is, in this case, for example, it is assumed that the predetermined period has elapsed when the output of the air-fuel ratio sensor indicates that the air-fuel ratio of the exhaust gas is lean. Alternatively, in the case where an air-fuel ratio sensor is provided upstream of the catalyst, the elapsed time from the time point when the output of the air-fuel ratio sensor indicates that the air-fuel ratio of the exhaust gas is lean during the predetermined period. It may also be defined by the integrated value of the intake air amount from the time when the output of the air-fuel ratio sensor indicates that the air-fuel ratio of the exhaust gas is lean.

  According to a second aspect, in the first aspect, when the vehicle is decelerated within a predetermined period after the fuel increase operation is performed, the speed of the vehicle is equal to or lower than a predetermined vehicle speed and the brake is activated. In this case, the fuel cut prohibiting means does not prohibit the fuel cut.

  If the fuel cut prohibition means originally prohibits fuel cut, if the fuel cut is not prohibited, the catalyst may be put in a high temperature and excessive oxygen state and deteriorate. Therefore, it is desirable that the fuel cut prohibiting means does not prohibit the fuel cut only when there is a high possibility that the problem of strange odor will occur. The problem of off-flavor is difficult to occur because the exhaust gas easily diffuses while the vehicle is running, but the exhaust gas diffuses when the vehicle speed is significantly reduced or the vehicle is stopped. It becomes easy to occur because it becomes difficult.

  For the above reasons, it is desirable that the fuel cut prohibition means should not prohibit fuel cuts only when the vehicle speed is significantly reduced or the vehicle is likely to stop. I can say that.

  In this regard, in the second invention, in the above case where the vehicle is decelerated within a predetermined period after the fuel increase operation is performed, the speed of the vehicle is equal to or lower than the predetermined vehicle speed and the brake is operated. The fuel cut prohibiting means does not prohibit the fuel cut. When the brake is operating, the driver is willing to decelerate or stop, and there is a high possibility that the speed of the vehicle will drop considerably or the vehicle will stop. Therefore, according to the second aspect of the present invention, the fuel cut prohibiting means is prevented from prohibiting the fuel cut only when the problem of strange odor is more likely to occur, so that the progress of the catalyst deterioration can be suppressed.

  In addition, since the time until the vehicle stops is short when the brake is operating, it is necessary to bring the catalyst into an oxidized state more quickly in order to reliably suppress the off-flavor, but in the second invention, In such a case, fuel cut can be performed. When the fuel cut is performed, air flows as it is to the exhaust system, so that more oxygen can be supplied to the catalyst quickly. Therefore, according to the second aspect of the invention, it is possible to more reliably suppress the odor.

  According to a third aspect, in the first aspect, when the vehicle is decelerated within a predetermined period after the fuel increase operation is performed, the speed of the vehicle is equal to or lower than a predetermined vehicle speed and the vehicle The fuel cut prohibiting means is configured not to prohibit the fuel cut when the degree of deceleration in the deceleration state is greater than a predetermined degree of deceleration.

  When the degree of deceleration is large, it can be said that there is a high possibility that the speed of the vehicle is considerably reduced or the vehicle is stopped. Therefore, according to the third invention, as in the second invention, the fuel cut prohibition means does not prohibit the fuel cut only when the problem of strange odor is more likely to occur, thereby suppressing the progress of the deterioration of the catalyst. Can do. In addition, when the degree of deceleration is large, the time until the vehicle stops is short, so that it is necessary to bring the catalyst into an oxidized state more quickly in order to reliably suppress the odor. In this regard, according to the third invention, since the degree of deceleration is large, the time until the vehicle stops is short, and when it is necessary to bring the catalyst into an oxidized state more quickly, the fuel cut is performed to increase the amount of catalyst to the catalyst. Since oxygen can be supplied quickly, the above-mentioned odor can be more reliably suppressed.

  In the fourth aspect of the invention, in the first aspect of the invention, the fuel cut is not performed when the gear position of the transmission is in the neutral state when the vehicle is decelerated within a predetermined period after the fuel increase operation is performed. In the decelerating state or in the decelerating state and the idling state that follows, the operation in which the combustion air-fuel ratio becomes lean is performed.

  When the gear position of the transmission is neutral, the fuel cut is not prohibited by the fuel cut prohibiting means, but as a result, the fuel cut is not related to other conditions for performing the fuel cut. It can happen when not done. That is, for example, in order to prevent the occurrence of engine stall due to the fuel cut, if the engine speed is set to not perform the fuel cut when the engine speed is equal to or lower than the predetermined speed, the engine speed is The fuel cut is not performed when the rotation speed is equal to or lower than the predetermined rotation speed. When the gear position of the transmission is set to neutral, the engine speed decreases rapidly. Therefore, if it is set as described above, there is a high possibility that the fuel cut will not be performed as a result. If the fuel cut is not performed, there is a possibility that, for example, the combustion air-fuel ratio is set to the stoichiometric air-fuel ratio until the vehicle is stopped. In this case, the air-fuel ratio of the exhaust gas flowing through the catalyst is Since it does not become lean, as a result, the sulfur oxide held by the catalyst when the vehicle is stopped becomes hydrogen sulfide and is likely to be released to the outside, which may cause a problem of off-flavor.

  On the other hand, in the fourth aspect of the present invention, the fuel cut is not performed when the gear position of the transmission is neutral in the above-described case where the vehicle is decelerated within a predetermined period after the fuel increase operation is performed. In this case, in the deceleration state or in the deceleration state and the idling state that follows, the operation in which the combustion air-fuel ratio becomes lean (lean operation) is performed. When the lean operation is performed, the air-fuel ratio of the exhaust gas flowing into the catalyst becomes lean, so that oxygen is supplied to the catalyst. Therefore, according to the fourth aspect of the present invention, the lean operation is performed even when the gear position of the transmission is neutral in the above-described case where the vehicle is decelerated within a predetermined period after the fuel increase operation is performed. As a result, it is possible to reliably supply oxygen to the catalyst, and as a result, it is possible to reliably prevent the catalyst from being in a reduced state after deceleration and being in a state in which hydrogen sulfide is easily released to the outside. And thereby, generation | occurrence | production of the strange odor after deceleration can be suppressed more reliably.

  The invention described in each of the claims includes a fuel cut executing means for performing fuel cut for stopping fuel supply to an internal combustion engine mounted on the vehicle when the vehicle is in a deceleration state, and a gear position of the transmission. An internal combustion engine comprising a high-speed gear and a fuel cut prohibiting means for prohibiting fuel cut by the fuel cut executing means when the temperature of a catalyst provided in the exhaust system of the internal combustion engine is equal to or higher than a predetermined temperature This control device has a common effect that the generation of a strange odor after deceleration can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram for explaining a case where the present invention is applied to a gasoline engine mounted on a vehicle. In FIG. 1, 2 is an internal combustion engine (engine) main body, 3 is a transmission attached to the internal combustion engine main body 2, 4 is an intake passage, and 6 is an exhaust gas passage. An exhaust gas purification device 10 is provided in the exhaust gas passage 6. As the exhaust gas purification device 10 installed in this portion, various devices described later with reference to FIGS. 2 and 3 may be used. it can.

  The electronic control unit (ECU) 8 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a well-known digital computer in which input / output ports are connected by a bidirectional bus. Parameters necessary for control of engine speed, intake air amount, etc. are exchanged by exchanging signals with sensors and driving devices, and fuel injection amount control including fuel cut (or combustion air-fuel ratio control based on the calculated parameters) ) And ignition timing control and the like.

  2 and 3 schematically show an example of the configuration of the exhaust gas purification device 10 that is installed in the portion of the exhaust gas purification device 10 shown in FIG. 1 and constitutes a part of the exhaust gas passage 6. FIG. Here, the exhaust gas flows from the left side to the right side of the drawing as indicated by arrows. FIG. 2 shows one having a three-way catalyst 12, and FIGS. 2 (a), 2 (b), and 2 (c) show the air-fuel ratio for detecting the air-fuel ratio of the exhaust gas, respectively. A sensor (or an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas) is not provided, an upstream air-fuel ratio sensor 14 is provided upstream of the three-way catalyst 12, and a downstream of the three-way catalyst 12 A downstream air-fuel ratio sensor 16 is provided.

  On the other hand, FIG. 3 shows one having two three-way catalysts 18 and 20, more specifically, three-way catalysts 18 and 20 being provided in two separate locations in series in the exhaust system. 3 (a), FIG. 3 (b), FIG. 3 (c), and FIG. 3 (d), respectively, are provided with no air-fuel ratio sensor, upstream air-fuel ratio upstream of the three-way catalyst 18 on the upstream side. A sensor 14 is provided, an intermediate air-fuel ratio sensor 15 is provided between the upstream side three-way catalyst 18 and the downstream side three-way catalyst 20, and a downstream side empty air is provided downstream of the downstream side three-way catalyst 20. The one provided with the fuel ratio sensor 16 is shown.

  As will be described later, in the embodiment of the present invention, the three-way catalyst (hereinafter simply referred to as “catalyst”) 12, 18, and 20 sufficiently holds oxygen depending on the configuration of the exhaust gas purification device 10 used. The method of determining whether it is in an oxidized state or a reduced state that does not sufficiently hold oxygen (that is, a method for determining a catalyst state) is different.

  2 and 3 that have an air-fuel ratio sensor, the outputs of the air-fuel ratio sensors 14, 15, and 16 are transmitted to the electronic control unit 8. It is configured.

  By the way, in this embodiment, when it is determined that the vehicle on which the internal combustion engine is mounted is in a deceleration state (for example, an engine brake state), a “fuel cut” is performed to stop the supply of fuel to the internal combustion engine. It has come to be. More specifically, in the present embodiment, in principle, fuel cut is performed when the vehicle is in a decelerating state, the accelerator opening is zero, and the engine speed is greater than a predetermined speed.

  Further, in the present embodiment, even if the conditions for executing the fuel cut as described above (deceleration state, accelerator opening zero, engine speed is equal to or higher than the predetermined speed) are satisfied, the gear of the transmission 3 The position is in a high-speed gear (for example, 4th or 5th speed in a 5-speed transmission, or 5th or 6th speed in a 6-speed transmission), and the temperature of the catalyst 12, 18, 20 is predetermined. When the temperature is higher than the temperature, the fuel cut is prohibited. This prevents the catalyst 12, 18, 20 from being placed in a high temperature and excessive oxygen state by performing a fuel cut when the temperature of the catalyst 12, 18, 20 is high, thereby suppressing deterioration of the catalyst. Because. Also, here, the fuel cut is prohibited only when the gear position is in the high speed gear, because if the fuel cut is prohibited, the vehicle will not feel a deceleration, This is because the fuel cut is prohibited only when it is more suitable in consideration of the fact that the catalyst temperature generally increases during high-speed traveling.

However, conventionally, when the fuel cut is prohibited as described above, there is a problem that a strange smell, more specifically a hydrogen sulfide (H ₂ S) odor, is generated when the vehicle stops after deceleration. This problem is thought to occur for the following reasons. That is, a catalyst (for example, a three-way catalyst) provided in an exhaust system of an internal combustion engine is generally sulfur oxidation produced by combustion of sulfur components in fuel when the air-fuel ratio of the exhaust gas flowing is lean. It has the effect | action which hold | maintains a thing (SOx) in the same catalyst. In addition, in such a catalyst, when sufficient oxygen is retained in the catalyst (that is, when the catalyst is in an “oxidized state”), the air-fuel ratio of the exhaust gas flowing is the stoichiometric air-fuel ratio. In this case, the sulfur oxide in the exhaust gas can be retained in the catalyst. By such an action, during normal operation when the internal combustion engine is operated with the combustion air-fuel ratio (that is, the air-fuel ratio in the combustion chamber) as the stoichiometric air-fuel ratio, the sulfur oxide in the exhaust gas becomes a catalyst provided in the exhaust system. Will be retained.

  On the other hand, when the catalyst does not hold enough oxygen (that is, when the catalyst is in the “reduced state”), if the air-fuel ratio of the exhaust gas flowing becomes rich or stoichiometric, It has the property of releasing sulfur oxides retained in the catalyst. The sulfur oxide released into the exhaust gas in this way reacts with the hydrogen produced in the combustion process of the fuel to form hydrogen sulfide. Therefore, when it is released to the outside, a strange odor (hydrogen sulfide odor) is produced. It will be.

  Further, such a bad odor due to hydrogen sulfide is less likely to cause a problem because the exhaust gas easily diffuses while the vehicle is running. However, when the vehicle is stopped, it is difficult for the exhaust gas to diffuse. A strange odor drifts in the vicinity, making it easier for the passengers of the vehicle to feel uncomfortable.

  For example, consider the case where deceleration is performed while maintaining the gear position at a high speed gear, and the fuel cut is prohibited as described above. In the prior art, if the fuel cut is prohibited, the combustion air-fuel ratio is reduced. Since the operation is performed with the stoichiometric air-fuel ratio, the air-fuel ratio of the exhaust gas flowing through the catalyst during deceleration does not become lean, and as a result, hydrogen sulfide is easily released to the outside. In particular, if the amount of fuel is increased for the purpose of increasing the output or lowering the catalyst temperature before deceleration and the combustion air-fuel ratio is still rich, the catalyst does not hold enough oxygen. The possibility of releasing hydrogen sulfide is higher. In addition, when the vehicle speed drops considerably as a result of deceleration, or when the vehicle is stopped, it is difficult for the exhaust gas to diffuse as described above. Get higher.

  Therefore, in the present embodiment, in order to cope with the above-mentioned problem of strange odor, special operation control based on the speed of the vehicle is performed to suppress the occurrence of strange odor. In short, this operation control is performed when the engine is decelerated within a predetermined period after the fuel increasing operation for operating the internal combustion engine so that the combustion air-fuel ratio becomes rich. When the vehicle speed is equal to or lower than a predetermined vehicle speed, even if the gear position of the transmission is in the high speed gear and the temperature of the catalyst provided in the exhaust system of the internal combustion engine is equal to or higher than the predetermined temperature, The fuel cut is not prohibited.

  Before the specific description of the operation control performed in the present embodiment, first, in the operation control, first, in the operation control, a catalyst state (whether it is an oxidation state) required for determining the predetermined period is determined. A method for determining whether or not a reduction state is present will be described. As described above, this determination method differs depending on the configuration of the exhaust gas purification device 10 used. FIGS. 4 to 6 are flowcharts showing control routines for implementing each of different determination methods depending on the configuration of the exhaust gas purification apparatus 10 used. These control routines are repeatedly executed during the operation of the internal combustion engine, and the current catalyst state is determined.

  First, in the determination method shown in the flowchart of FIG. 4, the exhaust gas purification device 10 has a configuration as shown in FIGS. 2A and 2B, and FIGS. 3A and 3B. It is applied when having That is, the present invention is applied when no air-fuel ratio sensor is provided or when an upstream air-fuel ratio sensor 14 is provided.

  When the control routine shown in FIG. 4 is started, first, at step 101, it is determined whether or not a fuel increasing operation for operating the internal combustion engine so that the combustion air-fuel ratio becomes rich is being performed. Such fuel increase operation is performed for the purpose of increasing the output or lowering the catalyst temperature.

  The determination as to whether or not the fuel increase operation is being performed is made based on the current target combustion air-fuel ratio used for operation control of the internal combustion engine when no air-fuel ratio sensor is provided. Further, when the upstream air-fuel ratio sensor 14 is provided, it is performed based on the air-fuel ratio indicated by the output. That is, in any case, when the air-fuel ratio used for the determination is rich, it is determined that the fuel increase operation is being performed, and when the air-fuel ratio used for the determination is not rich, the fuel increase operation is performed. Is determined not to be in progress.

  If it is determined in step 101 that the fuel increase operation is being performed, the process proceeds to step 103, where it is determined that the catalyst state is the reduction state, and the catalyst state flag XLEAN is set to 0 (reduction state determination). . On the other hand, if it is determined in step 101 that the fuel increase operation is not being performed, the process proceeds to step 105, where the integrated value TGaS1 of the intake air amount after the completion of the fuel increase operation is a predetermined integrated value of the intake air amount. It is determined whether or not it is greater than a1.

  If it is determined at step 105 that the integrated value TGaS1 is greater than the integrated value a1, the routine proceeds to step 107, where it is determined that the catalyst state is an oxidized state, and the catalyst state flag XLEAN is set to 1. (Oxidation state determination). On the other hand, when it is determined in step 105 that the integrated value TGaS1 is equal to or less than the integrated value a1, the determination result of the catalyst state when the present control routine was performed last time (that is, the value of the catalyst state flag XLEAN). Is maintained.

  As is clear from the above description, the integrated value a1 that is the determination criterion in step 105 is a value that determines that all of the catalysts are in the oxidized state if the integrated value TGaS1 is larger than that value. In consideration of such a purpose, it is determined in advance by an experiment or the like. Further, as the intake air amount for obtaining the integrated value TGaS1 or the like, an intake air amount estimated from the operating state of the internal combustion engine or the like may be used, or an air flow meter is provided and the detected value is used. May be.

  Here, the determination of the catalyst state is performed based on the integrated value TGaS1 of the intake air amount after the end of the fuel increase operation. Instead, for example, the catalyst state is determined based on the elapsed time after the end of the fuel increase operation. You may make it perform determination. That is, for example, when the elapsed time after the end of the fuel increase operation exceeds an elapsed time that is a predetermined determination criterion, it is determined that the catalyst state is an oxidized state, and the catalyst state flag XLEAN is set to 1.

  Next, the determination method shown in the flowchart of FIG. 5 will be described. This determination method is applied when the exhaust gas purification device 10 has a configuration as shown in FIG. That is, the present invention is applied when the catalysts 18 and 20 are separately provided in two locations in series in the exhaust system, and the intermediate air-fuel ratio sensor 15 is provided between the catalysts 18 and 20.

  When the control routine shown in FIG. 5 starts, first, at step 201, it is determined whether or not a fuel increase operation is being performed. This determination is made based on the current target combustion air-fuel ratio used for operation control of the internal combustion engine when only the intermediate air-fuel ratio sensor 15 is provided. If an upstream air-fuel ratio sensor as shown in FIG. 3B is also provided in addition to the intermediate air-fuel ratio sensor 15, the determination is made based on the air-fuel ratio indicated by the output of the upstream air-fuel ratio sensor. You may make it do. In any case, if the air-fuel ratio used for the determination is rich, it is determined that the fuel increase operation is being performed. If the air-fuel ratio used for the determination is not rich, the fuel increase operation is performed. It is determined that it is not inside.

  If it is determined in step 201 that the fuel increase operation is being performed, the process proceeds to step 203, where it is determined that the catalyst state is the reduction state, and the catalyst state flag XLEAN is set to 0 (reduction state determination). . Further, in this case, the output of the intermediate air-fuel ratio sensor 15 is assumed to be rich, and the intermediate sensor determination flag XML is set to 0 (rich determination). On the other hand, if it is determined in step 201 that the fuel increase operation is not being performed, the routine proceeds to step 205, where it is determined whether or not the intermediate sensor determination flag XML is zero. This step is for confirming the determination result when this control routine was performed last time.

  If it is determined in step 205 that the intermediate sensor determination flag XML is 0, it is determined that the output of the intermediate air-fuel ratio sensor 15 indicates rich when this control routine was performed last time. In this case, the routine proceeds to step 207, where it is determined whether or not the current output of the intermediate air-fuel ratio sensor 15 shows lean. On the other hand, if it is determined in step 205 that the intermediate sensor determination flag XML is not 0 (that is, 1), the output of the intermediate air-fuel ratio sensor 15 indicates lean when this control routine is performed last time. In this case, the process proceeds to step 211.

  If it is determined in step 207 that the current output of the intermediate air-fuel ratio sensor 15 indicates lean, the routine proceeds to step 209, where the intermediate sensor determination flag XML is set to 1 (lean determination), and step 211 is performed. Proceed to On the other hand, if it is determined in step 207 that the current output of the intermediate air-fuel ratio sensor 15 does not indicate lean, the determination of the catalyst state and the intermediate air-fuel ratio sensor output when this control routine was performed last time. The current control routine ends while maintaining the results (that is, the value of the catalyst state flag XLEAN and the value of the intermediate sensor determination flag XML).

  In step 211, the integrated value TGaS2 of the intake air amount after the output of the intermediate air-fuel ratio sensor 15 indicates that the air-fuel ratio of the exhaust gas is lean is greater than the predetermined integrated value a2 of the intake air amount. It is determined whether there are many. If it is determined in step 211 that the integrated value TGaS2 is greater than the integrated value a2, the process proceeds to step 213, where it is determined that the catalyst state is an oxidized state, and the catalyst state flag XLEAN is set to 1. (Oxidation state determination). On the other hand, if it is determined in step 211 that the integrated value TGaS2 is less than or equal to the integrated value a2, the determination result of the catalyst state when the present control routine was performed last time (that is, the value of the catalyst state flag XLEAN). Is maintained.

  Here, when the output of the intermediate air-fuel ratio sensor 15 indicates that the air-fuel ratio of the exhaust gas is lean, it is considered that the upstream catalyst 18 is in an oxidized state. Therefore, it can be said that the integrated value a2 serving as a determination criterion is a value that determines that the downstream side catalyst 20 is also in an oxidized state when the integrated value TGaS2 is larger than that value. In consideration of various purposes, it is determined in advance by experiments or the like. As in the case of the integrated value TGaS1, the intake air amount for obtaining the integrated value TGaS2 may be an intake air amount estimated from the operating state of the internal combustion engine, or an air flow meter. It is also possible to use the detected value.

  Here, the catalyst state is determined based on the integrated value TGaS2 of the intake air amount after the output of the intermediate air-fuel ratio sensor 15 indicates that the air-fuel ratio of the exhaust gas is lean. For example, the catalyst state may be determined based on an elapsed time after the output of the intermediate air-fuel ratio sensor 15 indicates that the air-fuel ratio of the exhaust gas is lean. That is, for example, when the elapsed time after the output of the intermediate air-fuel ratio sensor 15 indicates that the air-fuel ratio of the exhaust gas is lean exceeds the elapsed time that is a predetermined criterion, the catalyst state is oxidized. It is determined that the catalyst is in a state, and the catalyst state flag XLEAN is set to 1.

  Next, the determination method shown in the flowchart of FIG. 6 will be described. This determination method is applied when the exhaust gas purification apparatus 10 has a configuration as shown in FIG. 2C or FIG. 3D. That is, it is applied when the downstream air-fuel ratio sensor 16 is provided.

  When the control routine shown in FIG. 6 starts, as in the case of the control routine shown in FIGS. 4 and 5, first, in step 301, it is determined whether or not a fuel increase operation is being performed. This determination is performed based on the current target combustion air-fuel ratio used for operation control of the internal combustion engine when only the downstream air-fuel ratio sensor 16 is provided. Further, in the case where an upstream air-fuel ratio sensor 14 as shown in FIG. 2B or FIG. 3B is also provided in addition to the downstream air-fuel ratio sensor 16, You may make it determine based on the air fuel ratio which an output shows. In any case, if the air-fuel ratio used for the determination is rich, it is determined that the fuel increase operation is being performed. If the air-fuel ratio used for the determination is not rich, the fuel increase operation is performed. It is determined that it is not inside.

  If it is determined in step 301 that the fuel increase operation is being performed, the process proceeds to step 303, where it is determined that the catalyst state is the reduction state, and the catalyst state flag XLEAN is set to 0 (reduction state determination). . Further, in this case, it is assumed that the output of the downstream air-fuel ratio sensor 16 is rich, and the downstream sensor determination flag XDL is set to 0 (rich determination). On the other hand, if it is determined in step 301 that the fuel increase operation is not being performed, the routine proceeds to step 305, where it is determined whether or not the downstream sensor determination flag XDL is zero. This step is for confirming the determination result when this control routine was performed last time.

  If it is determined in step 305 that the downstream sensor determination flag XDL is 0, it is determined that the output of the downstream air-fuel ratio sensor 16 indicates rich when this control routine is performed last time. In this case, the routine proceeds to step 307, where it is determined whether or not the current output of the downstream air-fuel ratio sensor 16 shows lean. On the other hand, if it is determined in step 305 that the downstream sensor determination flag XDL is not 0 (that is, 1), the output of the downstream air-fuel ratio sensor 16 becomes lean when this control routine is performed last time. In this case, the determination result of the catalyst state and the downstream air-fuel ratio sensor output (that is, the value of the catalyst state flag XLEAN and the downstream sensor determination flag XDL when the present control routine was performed last time) The current control routine is terminated while maintaining (value). More specifically, in this case, the determination result that the catalyst state is the oxidation state (XLEAN = 1) and the downstream air-fuel ratio sensor output indicates lean (XDL = 1) is maintained.

  If it is determined in step 307 that the current output of the downstream air-fuel ratio sensor 16 indicates lean, the routine proceeds to step 309, where the downstream sensor determination flag XDL is set to 1 (lean determination). At the same time, in step 311, it is determined that the catalyst state is the oxidation state, and the catalyst state flag XLEAN is set to 1 (oxidation state determination). On the other hand, if it is determined in step 307 that the current output of the downstream air-fuel ratio sensor 16 does not indicate lean, the downstream sensor determination flag XDL is not 0 in step 305 (that is, 1). As in the case where it is determined that there is, the determination result of the catalyst state and the downstream air-fuel ratio sensor output (that is, the value of the catalyst state flag XLEAN and the downstream sensor determination flag XDL when the control routine was performed last time) The current control routine is terminated while maintaining (value). However, in this case, the determination result that the catalyst state is the reduction state (XLEAN = 0) and the downstream air-fuel ratio sensor output indicates rich (XDL = 0) is maintained.

  As described above, in the determination method shown in the flowchart of FIG. 6, the catalyst state is determined using the output of the downstream air-fuel ratio sensor 16. By doing so, it is ensured that the entire catalyst, especially when the catalyst is provided in two separate locations in series in the exhaust system, is in an oxidized state up to the catalyst provided on the downstream side. Can be determined. Conversely, when the catalyst is provided in two separate locations in series in the exhaust system, if it is determined by this determination method that the catalyst state is an oxidized state, the catalyst provided downstream is provided. Can be said to have been determined to be in an oxidized state.

  Next, operation control performed in the present embodiment will be described with reference to FIG. 7 in order to cope with the above-mentioned problem of strange odor. FIG. 7 is a flowchart showing a control routine for carrying out this operation control. This control routine is executed by the ECU 8 by interruption every predetermined time.

  When this control routine is started, first, at step 401, it is determined whether or not a basic condition for fuel cut is satisfied. The fuel cut execution basic conditions in the present embodiment are that the vehicle is in a decelerating state and that the accelerator opening is zero. If it is determined in step 401 that the fuel cut execution basic conditions are not satisfied, the routine proceeds to step 411, where the normal operation is performed in which the combustion air-fuel ratio is determined according to the engine speed, the accelerator opening, and the like. At the same time, the fuel cut execution flag XFC is set to 0, and this control routine ends.

  On the other hand, if it is determined in step 401 that the fuel cut execution basic conditions are satisfied, the process proceeds to step 403, where the catalyst temperature CT when the vehicle starts decelerating is less than a predetermined temperature Tc. It is determined whether or not. As will be apparent from the following description, this determination is made in order to prevent the fuel cut from being performed when the temperature of the catalyst is high so that the catalyst is not placed in a high temperature and excessive oxygen state. The temperature Tc is determined in advance by experiments or the like based on such a purpose, and is 800 ° C., for example. Further, the catalyst temperature CT may be determined based on the output of the catalysts 12, 18 and 20 provided with temperature sensors, or may be determined based on the temperature detected by detecting the exhaust gas temperature. Also good. Or you may make it estimate from the driving | running state or driving | running history of the internal combustion engine before deceleration.

  If it is determined in step 403 that the catalyst temperature CT is lower than the predetermined temperature Tc, the process proceeds to step 405, and whether or not the engine speed NE is greater than a predetermined first engine speed Ec1. Is determined. This determination is performed in order to prevent the fuel cut from being started and causing engine stall when the engine speed NE is low. The predetermined first engine speed Ec1 is used for this purpose. Is determined in advance by experiments or the like.

  If it is determined in step 405 that the engine speed NE is larger than the predetermined first engine speed Ec1, the routine proceeds to step 407, where the fuel cut is performed and the fuel cut execution flag XFC is set to 1. This control routine ends. On the other hand, if it is determined in step 405 that the engine speed NE is equal to or lower than the first engine speed Ec1 determined in advance, the routine proceeds to step 409, where it is determined whether or not the fuel cut execution flag XFC is 1. Is done. This determination is a determination of whether or not a fuel cut is being performed.

  If it is determined in step 409 that the fuel cut execution flag XFC is not 1, that is, the fuel cut is not being executed, the routine proceeds to step 411 and the normal operation is executed. That is, in this case, since engine speed NE is low, there is a possibility that engine stall occurs when fuel cut is started, and normal operation is performed without performing fuel cut. On the other hand, if it is determined in step 409 that the fuel cut execution flag XFC is 1, that is, it is determined that the fuel cut is being performed, the routine proceeds to step 410, where the engine speed NE is set to a predetermined second engine speed. It is determined whether or not it is greater than Ec2. Here, the second engine speed Ec2 is a value smaller than the first engine speed Ec1.

  If it is determined in step 410 that the engine speed NE is greater than the predetermined second engine speed Ec2, the present control routine ends as it is, that is, in a state where fuel cut is being performed. . On the other hand, if it is determined in step 410 that the engine speed NE is equal to or lower than the second engine speed Ec2, the process proceeds to step 411, where the fuel cut is stopped and the normal operation is resumed. In this case, the fuel cut is stopped and the normal operation is started, the fuel cut execution flag XFC is set to 0, and this control routine ends.

  Thus, in the present embodiment, the engine speed Ec2 (<Ec1) for determining whether or not to stop the fuel cut is set separately from the engine speed Ec1 for determining whether or not to start the fuel cut. Yes. In addition, by providing the hysteresis with respect to the condition of the engine speed related to the execution of the fuel cut as described above, it is possible to suppress the start and stop of the fuel cut from being repeated.

  On the other hand, when it is determined in step 403 that the catalyst temperature CT is equal to or higher than the predetermined temperature Tc, the routine proceeds to step 412 where it is determined whether or not the gear position of the transmission 3 is in the high speed gear. As will become clear from the following explanation, the existence of this step makes it unnecessary to obtain a feeling of deceleration of the vehicle and, in general, it is highly necessary to prohibit the execution of the fuel cut due to the high catalyst temperature, etc. The fuel cut is prohibited only when the gear position of the transmission, which is more preferable to prohibit the transmission, is in the high speed gear.

  The current gear position used for the determination here may be obtained based on a sensor for detecting the gear position, or may be estimated from the relationship between the engine speed and the vehicle speed. Also good.

  When it is determined in step 412 that the gear position of the transmission 3 is not in the high speed gear, the process proceeds to step 405 and the control from there is performed as described above. That is, in this case, if the engine speed NE is larger than the first engine speed Ec1 determined in advance, the fuel cut is performed. On the other hand, if it is determined in step 412 that the gear position of the transmission 3 is in the high speed gear, the process proceeds to step 413, where it is determined whether the catalyst state flag XLEAN is 1. This determination is a determination of whether or not the catalyst state is an oxidation state.

  If it is determined in step 413 that the catalyst state flag XLEAN is 1, that is, the catalyst state is in the oxidized state, the process proceeds to step 425, and the operation (theoretical air fuel ratio) is performed so that the combustion air fuel ratio becomes the stoichiometric air fuel ratio. (Fuel ratio operation) is performed, and this control routine ends. In other words, in this case, the present control routine ends in an operation in which the air-fuel ratio becomes the stoichiometric air-fuel ratio in the deceleration state or in the deceleration state and the idling state that follows the deceleration state (more specifically, This control routine is executed again from the beginning). In this case, even when the stoichiometric air-fuel ratio operation is performed as described above, the generation of a strange odor is suppressed because the catalyst is in an oxidized state.

  On the other hand, if it is determined in step 413 that the catalyst state flag XLEAN is not 1, that is, if the catalyst state flag XLEAN is 0 and the catalyst state is the reduced state, the process proceeds to step 415, where the current vehicle speed SPD is It is determined whether or not the vehicle speed Sh is greater than a predetermined value. Here, the predetermined vehicle speed Sh is used to determine whether or not the current vehicle speed is a speed that should be taken into consideration when the vehicle stops, and is, for example, 50 km / h.

  If it is determined in step 415 that the current vehicle speed SPD is equal to or lower than the predetermined vehicle speed Sh, the process proceeds to step 405, and the control from there is performed as described above. That is, in this case, if the engine speed NE is larger than the first engine speed Ec1 determined in advance, the fuel cut is performed. That is, in this case, even if the gear position of the transmission is in the high speed gear and the temperature CT of the catalyst is equal to or higher than the predetermined temperature Tc, the fuel cut is not prohibited.

  On the other hand, if it is determined in step 415 that the current vehicle speed SPD is greater than the predetermined vehicle speed Sh, the process proceeds to step 417, where it is determined whether the fuel cut execution flag XFC is zero. This determination is for determining whether or not a fuel cut is being performed.

  If it is determined in step 417 that the fuel cut execution flag XFC is not 0, that is, the fuel cut is being performed, the process proceeds to step 405, and the control from there is performed as described above. On the other hand, if it is determined in step 417 that the fuel cut execution flag XFC is 0, that is, it is determined that the fuel cut is not being executed, the routine proceeds to step 419, where the operation is performed so that the combustion air-fuel ratio becomes lean (lean). Operation) is performed, and the routine proceeds to step 421. That is, in this case, the process proceeds to step 421 in a state where an operation is performed in which the air-fuel ratio becomes lean in the deceleration state or in the deceleration state and the idling state that follows.

  In step 421, it is determined whether or not the integrated value TGaL of the intake air amount after the start of the lean operation is greater than a predetermined integrated value Gc of the intake air amount. If it is determined in step 421 that the integrated value TGaL is greater than the integrated value Gc, the process proceeds to step 423, where it is determined that the catalyst state is in an oxidized state, and the catalyst state flag XLEAN is set to 1. (Oxidation state determination). In this case, the routine further proceeds to step 425, where the operation in which the combustion air-fuel ratio becomes the stoichiometric air-fuel ratio (theoretical air-fuel ratio operation) is started, and this control routine ends (more specifically, this control routine It is carried out again from the beginning). On the other hand, when it is determined in step 421 that the integrated value TGaL is equal to or less than the integrated value Gc, the present control routine ends as it is, that is, in the state where the lean operation is being performed (more specifically, This control routine is executed again from the beginning).

  As is clear from the above description, the integrated value Gc, which is the determination criterion in step 421, is determined that the catalyst is in an oxidized state when the integrated value TGaL is larger than that value. The value is switched to the theoretical air-fuel ratio operation, and is determined in advance by experiments or the like in consideration of such a purpose. In addition, as the intake air amount for obtaining the integrated value TGaL, an intake air amount estimated from the operating state of the internal combustion engine or the like may be used, or an air flow meter is provided and the detected value is used. Also good.

  As described above, in the present embodiment, when the vehicle is decelerated, the gear position of the transmission 3 is in the high speed gear and the catalyst temperature CT is higher than the predetermined temperature Tc. Even when the catalyst state flag XLEAN is not 1, that is, when it is determined that the catalyst state flag XLEAN is 0 and the catalyst state is the reduction state, the vehicle speed SPD is set in advance. When the vehicle speed is less than or equal to the predetermined vehicle speed Sh, the fuel cut is not prohibited. Here, when the vehicle is decelerating, it is determined that the catalyst state is the reduced state (XLEAN = 0), as is apparent from the description made with reference to FIGS. 4 to 6. This is a period until the predetermined condition is satisfied after the fuel increasing operation for operating the internal combustion engine so as to be rich, that is, a predetermined period. Therefore, in other words, in the present embodiment, when the vehicle is in a decelerating state within a predetermined period after the fuel increase operation is performed, when the speed of the vehicle is equal to or lower than a predetermined vehicle speed, It can be said that the fuel cut is not prohibited even when the gear position of the transmission is in the high speed gear and the catalyst temperature CT is equal to or higher than the predetermined temperature Tc.

  And if it does as mentioned above, even if it is a case where it decelerates with a gear position being a high-speed gear, when the speed of the said vehicle becomes below the predetermined vehicle speed, a fuel cut can be implemented. As a result, oxygen can be supplied to the catalyst before the vehicle is stopped, and the catalyst is in a reduced state after deceleration, and hydrogen sulfide is prevented from being easily released to the outside. As a result, the generation of a strange odor after deceleration can be suppressed.

  In the above description, the catalyst state is determined based on the integrated value TGaL of the intake air amount after the start of the lean operation, and it is determined whether or not to switch from the lean operation to the stoichiometric air-fuel ratio operation. However, instead, for example, the catalyst state is determined based on the elapsed time after the start of the lean operation (that is, the duration of the lean operation), and the switching from the lean operation to the stoichiometric air-fuel ratio operation is performed. It may be determined whether or not to perform. That is, for example, when the elapsed time after the start of the lean operation exceeds an elapsed time Pc that is a predetermined determination criterion, it is determined that the catalyst state is an oxidation state, and the catalyst state flag XLEAN is set to 1, Switching from the lean operation to the stoichiometric air-fuel ratio operation is performed.

  Further, the integrated value Gc serving as the determination criterion in Step 421 and the elapsed time Pc serving as the determination criterion described above may be changed according to the degree of leanness of the combustion air-fuel ratio during the lean operation and the deterioration degree of the catalyst. Good. That is, for example, the higher the degree of leanness of the combustion air-fuel ratio during the lean operation and the higher the degree of deterioration of the catalyst, the smaller the integrated value Gc and the elapsed time Pc are.

  The higher the leanness of the combustion air-fuel ratio during the lean operation, the greater the amount of oxygen supplied to the catalyst. In addition, the higher the degree of deterioration of the catalyst, the smaller the amount of oxygen retained by the catalyst (maximum oxygen retention amount) tends to decrease. Therefore, it can be said that the higher the degree of leanness of the combustion air-fuel ratio during the lean operation and the higher the degree of deterioration of the catalyst, the more easily the catalyst is in an oxidized state. Therefore, as described above, the higher the degree of leanness of the combustion air-fuel ratio during the lean operation and the higher the degree of deterioration of the catalyst, the more appropriately the smaller the integrated value Gc and the elapsed time Pc. It is possible to determine the catalyst state. As a result, it is possible to prevent the catalyst from being deteriorated due to excessive oxygen.

  Hereinafter, other embodiments of the present invention will be described. In addition, each embodiment described below has many parts in common with the above-described embodiments with respect to the configuration and operational effects, and the description of these common parts is omitted in principle.

  In the embodiment described next with reference to FIG. 8, the gear position of the transmission is in the high-speed gear and the gear is in the high-speed gear when the vehicle is decelerated within a predetermined period after the fuel increase operation is performed. Even if the catalyst temperature CT is equal to or higher than a predetermined temperature Tc, the fuel cut is not prohibited when the vehicle speed is equal to or lower than the predetermined vehicle speed and the brake is operating.

  FIG. 8 is a flowchart showing an example of a control routine for carrying out such operation control. Referring to FIG. 8, this control routine is substantially the same as the control routine shown in FIG. 7, and the current vehicle speed SPD is equal to or lower than the predetermined vehicle speed Sh in step 515 corresponding to step 415 in FIG. Steps 516a, 516b, and 516c are provided as controls that are performed (or can be performed) when it is determined that there is, and when normal operation is performed in step 511 corresponding to step 411 in FIG. The difference is that, in addition to the fuel cut execution flag XFC being set to 0, a later-described brake operation flag XBRK is set to 0.

  That is, in the present embodiment, if it is determined in step 515 that the current vehicle speed SPD is equal to or lower than the predetermined vehicle speed Sh, the process proceeds to step 516a. In step 516a, it is determined whether or not the brake is operating. If it is determined in step 516a that the brake is operating, the process proceeds to step 516b, the brake operation flag XBRK is set to 1, and the process further proceeds to step 505 corresponding to step 405 in FIG. That is, in this case, if the engine speed NE is larger than the first engine speed Ec1 determined in advance, the fuel cut is performed. That is, in this case, the fuel cut is not prohibited even when the gear position of the transmission is in the high speed gear and the catalyst temperature CT is equal to or higher than the predetermined temperature Tc.

  On the other hand, when it is determined in step 516a that the brake is not operated, the process proceeds to step 516c, and it is determined whether or not the brake operation flag XBRK is zero. This determination is a determination of whether or not the brake was operating when this control routine was executed last time. In Step 516c, when it is determined that the brake operation flag XBRK is not 0, that is, 1 is reached, the process proceeds to Step 505 corresponding to Step 405 in FIG. If it is determined that the brake operation flag XBRK is 0, the routine proceeds to step 519 corresponding to step 419 in FIG. 7 to perform the lean operation, and the control proceeds to the subsequent steps.

  As can be understood from the above description and FIG. 8, in the present embodiment, the gear position of the transmission is changed to the high speed gear when the deceleration state is achieved within a predetermined period after the fuel increase operation is performed. Even if the catalyst temperature CT is equal to or higher than the predetermined temperature Tc, the fuel cut is not prohibited if the vehicle speed is lower than the predetermined vehicle speed and the brake is operating. Yes. And by doing in this way, while advancing of deterioration of a catalyst can be suppressed, it becomes possible to suppress the said odor more reliably.

  That is, when the fuel cut is originally prohibited, if the fuel cut is not prohibited, the catalyst may be deteriorated due to being placed in a high temperature and excessive oxygen state. Therefore, it is desirable that the fuel cut is not prohibited as described above only when there is a high possibility that the problem of strange odor will occur. The problem of off-flavor is difficult to occur because the exhaust gas easily diffuses while the vehicle is running, but the exhaust gas diffuses when the vehicle speed is significantly reduced or the vehicle is stopped. It becomes easy to occur because it becomes difficult.

  From the above, it can be said that it is desirable that the fuel cut is not prohibited as described above only when the vehicle speed is considerably reduced or the vehicle is likely to be stopped.

  In this regard, in this embodiment, when the vehicle is decelerated within a predetermined period after the fuel increase operation is performed, the speed of the vehicle is equal to or lower than the predetermined vehicle speed and the brake is operating. In such a case, the fuel cut prohibiting means does not prohibit fuel cut. When the brake is operating, the driver is willing to decelerate or stop, and there is a high possibility that the speed of the vehicle will drop considerably or the vehicle will stop. Therefore, according to the present embodiment, since the fuel cut is not prohibited only when the problem of a strange odor is likely to occur, the progress of the deterioration of the catalyst can be suppressed.

  In addition, since the time until the vehicle stops is short when the brake is operating, it is necessary to bring the catalyst into an oxidized state more quickly in order to reliably suppress the strange odor. In some cases, a fuel cut can be performed. When the fuel cut is performed, air flows as it is to the exhaust system, so that more oxygen can be supplied to the catalyst quickly. Therefore, according to the present embodiment, it is possible to more reliably suppress the odor.

  Next, still another embodiment will be described with reference to FIG. In this embodiment, when the vehicle is decelerated within a predetermined period after the fuel increase operation is performed, the gear position of the transmission is in the high speed gear and the catalyst temperature CT is a predetermined temperature Tc. Even in the above case, the fuel cut is not prohibited when the speed of the vehicle is equal to or lower than a predetermined vehicle speed and the degree of deceleration in the deceleration state of the vehicle is greater than the predetermined degree of deceleration. Yes.

  FIG. 9 is a flowchart showing an example of a control routine for carrying out such operation control. Referring to FIG. 9, this control routine is substantially the same as the control routine shown in FIG. 7 as in the control routine of FIG. 8, and the current vehicle speed SPD is obtained at step 615 corresponding to step 415 of FIG. Is provided as a control that is performed (or can be performed) when it is determined that the vehicle speed is equal to or lower than a predetermined vehicle speed Sh, and in step 611 corresponding to step 411 in FIG. The difference is that a fuel cut execution flag XFC is set to 0 when normal operation is performed, and a rapid deceleration flag XDS, which will be described later, is set to 0.

  That is, in the present embodiment, if it is determined in step 615 that the current vehicle speed SPD is equal to or lower than the predetermined vehicle speed Sh, the process proceeds to step 616a. In this step 616a, whether or not the current vehicle speed change degree (acceleration) ΔSPD is smaller than the predetermined vehicle speed change degree ΔSc, that is, the current deceleration degree is larger than the predetermined deceleration degree. It is determined whether or not. When it is determined in step 516a that the current deceleration degree is larger than the predetermined deceleration degree (that is, rapid deceleration), the routine proceeds to step 616b and the rapid deceleration flag XDS is set to 1. Further, the process proceeds to step 605 corresponding to step 405 in FIG. That is, in this case, if the engine speed NE is larger than the first engine speed Ec1 determined in advance, the fuel cut is performed. That is, in this case, the fuel cut is not prohibited even when the gear position of the transmission is in the high speed gear and the catalyst temperature CT is equal to or higher than the predetermined temperature Tc.

  On the other hand, if it is determined in step 616a that the current degree of deceleration is the same as or smaller than the predetermined degree of deceleration (that is, not very rapid deceleration), the process proceeds to step 616c and sudden deceleration is performed. It is determined whether or not the flag XDS is 0. This determination is a determination as to whether or not the degree of deceleration was greater than the predetermined degree of deceleration when the control routine was executed last time (that is, whether or not the deceleration was abrupt). In step 616c, when it is determined that the rapid deceleration flag XDS is not 0, that is, 1, the routine proceeds to step 605 corresponding to step 405 in FIG. 7, and the control from there is performed as described above. . On the other hand, when it is determined that the rapid deceleration flag XDS is 0, the routine proceeds to step 619 corresponding to step 419 in FIG. 7 to perform the lean operation, and the control proceeds to the subsequent steps.

  As can be understood from the above description and FIG. 9, in this embodiment, the gear position of the transmission is changed to the high-speed gear when the deceleration state is achieved within a predetermined period after the fuel increase operation is performed. Even if the catalyst temperature CT is equal to or higher than the predetermined temperature Tc, the speed of the vehicle is equal to or lower than the predetermined vehicle speed, and the degree of deceleration in the deceleration state of the vehicle is larger than the predetermined degree of deceleration. In some cases, fuel cuts are not prohibited. By doing so, as in the embodiment described with reference to FIG. 8, it is possible to suppress the progress of deterioration of the catalyst and to more reliably suppress the odor.

  That is, when the degree of deceleration is large, it can be said that there is a high possibility that the speed of the vehicle is considerably reduced or the vehicle is stopped as in the case where the brake is operated. Therefore, according to the present embodiment, the progress of the deterioration of the catalyst can be suppressed by preventing the fuel cut prohibition means from prohibiting the fuel cut only when the problem of strange odor is likely to occur.

  In addition, when the degree of deceleration is large, the time until the vehicle stops is short as in the case where the brake is operated. Therefore, in order to reliably suppress the off-flavor, it is necessary to quickly bring the catalyst to the oxidized state. is there. In this regard, according to this embodiment, since the degree of deceleration is large, the time until the vehicle stops is short, and when it is necessary to bring the catalyst into an oxidized state more quickly, the fuel cut is performed and more oxygen is supplied to the catalyst. Can be quickly supplied, so that the above-mentioned odor can be more reliably suppressed.

  Next, still another embodiment will be described with reference to FIG. In this embodiment, after the fuel increase operation is performed, when the vehicle is decelerated within a predetermined period, the fuel cut is not performed when the gear position of the transmission is neutral. In the decelerating state or in the decelerating state and the idling state that follows, the operation is performed so that the combustion air-fuel ratio becomes lean.

  FIG. 10 is a flowchart showing an example of a control routine for carrying out such operation control. Referring to FIG. 10, this control routine is substantially the same as the control routine shown in FIG. 7, except that the control content in step 712 at a position corresponding to step 412 in FIG. 7 is different. The difference is that step 714 is provided as a control performed when it is determined in step 713 corresponding to step 413 in FIG. 7 that the catalyst state flag XLEAN is not 1.

  That is, in this embodiment, when it is determined in step 703 (corresponding to step 403 in FIG. 7) that the catalyst temperature CT when the vehicle starts decelerating is equal to or higher than a predetermined temperature Tc, the above step is performed. Proceeding to 712, it is determined whether or not the gear position of the transmission 3 is in the high speed gear or neutral. This determination is substantially a determination of whether or not the gear position of the transmission 3 is in the medium / low speed gear.

  If it is determined in step 712 that the gear position of the transmission 3 is not in the high speed gear or in the neutral position, that is, in the middle or low speed gear, the routine proceeds to step 705 corresponding to step 405 in FIG. Control from there is implemented. On the other hand, if it is determined in step 712 that the gear position of the transmission 3 is in the high speed gear or neutral, the process proceeds to step 713 corresponding to step 413 in FIG. 7 and whether the catalyst state flag XLEAN is 1 or not. Is determined.

  If it is determined in step 713 that the catalyst state flag XLEAN is 1 (that is, the catalyst state is an oxidized state), the routine proceeds to step 725 corresponding to step 425 in FIG. The operation (theoretical air-fuel ratio operation) is performed, and this control routine ends. In other words, in this case, the present control routine ends in an operation in which the air-fuel ratio becomes the stoichiometric air-fuel ratio in the deceleration state or in the deceleration state and the idling state that follows the deceleration state (more specifically, This control routine is executed again from the beginning).

  On the other hand, if it is determined in step 713 that the catalyst state flag XLEAN is not 1 (that is, the catalyst state flag XLEAN is 0 and the catalyst state is the reduced state), the process proceeds to step 714 and the gear of the transmission 3 is It is determined whether the position is in the high speed gear. This determination can be said to be substantially a determination of whether or not the gear position of the transmission 3 is in neutral.

  If it is determined in step 714 that the gear position of the transmission 3 is in the high speed gear, that is, not in neutral, the routine proceeds to step 715 corresponding to step 415 in FIG. 7, and the current vehicle speed SPD is determined in advance. It is determined whether or not the vehicle speed is greater than Sh, and the control from there is performed as described above.

  On the other hand, when it is determined in step 714 that the gear position of the transmission 3 is not in the high-speed gear, that is, in the neutral position, the routine proceeds to step 717 corresponding to step 417 in FIG. 7 and the fuel cut execution flag XFC is set. It is determined whether or not it is zero. If it is determined that the fuel cut execution flag XFC is not 0, that is, the fuel cut is being executed, the process proceeds to step 705.

  On the other hand, when it is determined in step 717 that the fuel cut execution flag XFC is 0, that is, the fuel cut is not being executed, the routine proceeds to step 719 corresponding to step 419 in FIG. The operation (lean operation) is performed, and the process proceeds to step 721 corresponding to step 421 in FIG. That is, in this case, the process proceeds to step 721 in a state in which the air-fuel ratio is made lean in the deceleration state or in the deceleration state and the idling state that follows.

  As can be understood from the above description and FIG. 10, in this embodiment, the gear position of the transmission is neutral when the deceleration state is achieved within a predetermined period after the fuel increase operation is performed. In this case, when the fuel cut is not performed, an operation in which the combustion air-fuel ratio becomes lean is performed in the deceleration state or in the deceleration state and the idling state following the deceleration state. And it becomes possible to suppress generation | occurrence | production of the strange odor after deceleration more reliably by doing in this way.

  That is, when the gear position of the transmission is in the high speed gear and the temperature of the catalyst is equal to or higher than the predetermined temperature, the fuel gear position is neutral when the fuel cut is prohibited. In some cases, the fuel cut is not prohibited, but there may be a case where the fuel cut is not performed as a result in relation to other conditions for performing the fuel cut. That is, for example, in order to prevent the occurrence of engine stall due to the fuel cut as in the present embodiment and the other embodiments described above, the fuel cut is performed when the engine speed NE is equal to or lower than a predetermined speed. If the engine speed NE is set to be equal to or less than the predetermined speed, the fuel cut is not performed. When the gear position of the transmission is set to neutral, the engine speed NE decreases rapidly. Therefore, if the above setting is made, there is a high possibility that the fuel cut will not be performed as a result. If the fuel cut is not performed, there is a possibility that, for example, the combustion air-fuel ratio is set to the stoichiometric air-fuel ratio until the vehicle is stopped. In this case, the air-fuel ratio of the exhaust gas flowing through the catalyst is Since it does not become lean, as a result, the sulfur oxide held by the catalyst when the vehicle is stopped becomes hydrogen sulfide and is likely to be released to the outside, which may cause a problem of off-flavor.

  On the other hand, in the present embodiment, when the fuel reduction operation is performed within a predetermined period after the fuel increase operation is performed, the fuel cut is not performed when the gear position of the transmission is neutral. In the decelerating state or in the decelerating state and the idling state following the decelerating state, an operation in which the combustion air-fuel ratio becomes lean (lean operation) is performed. When the lean operation is performed, the air-fuel ratio of the exhaust gas flowing into the catalyst becomes lean, so that oxygen is supplied to the catalyst. Therefore, according to the present embodiment, even if the gear position of the transmission is in the neutral state when the deceleration state is achieved within a predetermined period after the fuel increase operation is performed, the lean operation makes the catalyst Thus, it is possible to reliably supply oxygen, and as a result, it is possible to reliably prevent hydrogen sulfide from being easily released to the outside because the catalyst is in a reduced state after deceleration. And thereby, generation | occurrence | production of the strange odor after deceleration can be suppressed more reliably.

FIG. 1 is a diagram for explaining a case where the present invention is applied to a gasoline engine mounted on a vehicle. FIG. 2 is an explanatory view schematically showing a configuration example of the exhaust gas purification device that is installed in the exhaust gas purification device of FIG. 1 and constitutes a part of the exhaust gas passage. FIG. 3 is a diagram similar to FIG. 2, and is an explanatory view schematically showing another configuration example of the exhaust gas purification device. FIG. 4 is a flowchart showing a control routine for carrying out one method for determining the catalyst state. FIG. 5 is a flowchart showing a control routine for carrying out another method for determining the catalyst state. FIG. 6 is a flowchart showing a control routine for carrying out still another method for determining the catalyst state. FIG. 7 is a flowchart showing a control routine of operation control implemented in one embodiment of the present invention. FIG. 8 is a flowchart showing a control routine of operation control performed in another embodiment of the present invention. FIG. 9 is a flowchart showing a control routine of operation control executed in still another embodiment of the present invention. FIG. 10 is a flowchart showing a control routine of operation control executed in still another embodiment of the present invention.

Explanation of symbols

2 ... Internal combustion engine (engine) body 3 ... Transmission 4 ... Intake passage 6 ... Exhaust gas passage 8 ... Electronic control unit (ECU)
DESCRIPTION OF SYMBOLS 10 ... Exhaust-gas purification apparatus 12, 18, 20 ... Three-way catalyst 14, 15, 16 ... Air-fuel ratio sensor or oxygen concentration sensor

Claims (4)

Fuel cut execution means for performing fuel cut to stop fuel supply to an internal combustion engine mounted on the vehicle when the vehicle is in a decelerating state, a gear position of the transmission is in a high speed gear, and the internal combustion engine A control device for an internal combustion engine comprising fuel cut prohibiting means for prohibiting fuel cut by the fuel cut execution means when the temperature of the catalyst provided in the exhaust system is equal to or higher than a predetermined temperature;
In the case where the vehicle is decelerated within a predetermined period after the fuel increasing operation for operating the internal combustion engine so that the combustion air-fuel ratio becomes rich, the speed of the vehicle is below a predetermined vehicle speed. In some cases, the fuel cut prohibiting means does not prohibit the fuel cut.   In the case where the vehicle is decelerated within a predetermined period after the fuel increase operation is performed, the fuel cut prohibiting means is operated when the vehicle speed is equal to or lower than the predetermined vehicle speed and the brake is operating. The control device for an internal combustion engine according to claim 1, wherein fuel cut is not prohibited.   When the vehicle is decelerated within a predetermined period after the fuel increase operation is performed, the vehicle speed is equal to or lower than a predetermined vehicle speed, and the degree of deceleration in the vehicle deceleration state is a predetermined deceleration 2. The control apparatus for an internal combustion engine according to claim 1, wherein the fuel cut prohibiting means does not prohibit the fuel cut when the degree is larger than the degree. In the case where the vehicle is in a deceleration state within a predetermined period after the fuel increase operation is performed, and the fuel cut is not performed when the gear position of the transmission is neutral, in the deceleration state or the above 2. The control device for an internal combustion engine according to claim 1, wherein an operation is performed so that the combustion air-fuel ratio becomes lean in the deceleration state and the idling state that follows.

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