Control device for an internal combustion engine

Abstract

In a control device of an internal combustion engine, a control section determines whether or not the amount of oxygen stored in a prescribed portion on the upstream side of a three-way catalyst is less than a prescribed amount in accordance with the case where a fuel cut condition is established. In the case where it is determined that the amount of oxygen stored in the prescribed portion is less than the prescribed amount, the control section delays the execution of fuel cut for a prescribed period and sets the air-fuel ratio of the internal combustion engine during the prescribed period to a lean air-fuel ratio. Also, in the case where it is determined that the amount of oxygen stored in the prescribed portion is the prescribed amount or more, the control section immediately executes fuel cut.

Description

Technical Field

[0001] This invention relates to a control device for an internal combustion engine. Background Technology

[0002] It is known that when the temperature of the exhaust purification catalyst disposed in the exhaust passage of an internal combustion engine is high, the execution period of fuel cut-off is delayed, the air-fuel ratio of the internal combustion engine is set to a lean air-fuel ratio during the delay period, and the length of the delay period is set according to the oxygen storage capacity of the exhaust purification catalyst (for example, see Japanese Patent Application Laid-Open No. 2009-191665). Summary of the Invention

[0003] The purpose of this invention is to provide a technique for delaying fuel cut-off that can be appropriately performed.

[0004] One aspect of the present invention is a control device for an internal combustion engine, wherein a three-way catalytic converter with oxygen storage capacity is disposed in the exhaust passage, and the control device for the internal combustion engine is configured to perform the following steps:

[0005] Based on the fuel cut-off condition of the internal combustion engine being met, determine whether the oxygen content at a specified location upstream of the three-way catalyst is less than a specified amount.

[0006] If it is determined that the amount of oxygen stored in the specified location is less than the specified amount, the execution of fuel cutoff in the internal combustion engine is delayed for a specified period, and the air-fuel ratio of the internal combustion engine is set to a lean air-fuel ratio during the specified period; and

[0007] If it is determined that the amount of oxygen stored in the specified location is above the specified amount, the fuel cut-off of the internal combustion engine is immediately executed.

[0008] According to the present invention, a technique for delaying fuel cut-off can be provided. Attached Figure Description

[0009] Hereinafter, with reference to the accompanying drawings, the features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described, in which the same reference numerals denote the same elements, and wherein:

[0010] Figure 1 This is a diagram illustrating an example of the structure of the vehicle in the implementation method.

[0011] Figure 2 This is a diagram schematically illustrating an example of the time-dependent changes in the oxygen storage portion of the three-way catalyst in the embodiment.

[0012] Figure 3A This is a diagram used to illustrate the first threshold and the second threshold in the implementation method.

[0013] Figure 3B This is a diagram used to illustrate the first threshold and the second threshold in the implementation method.

[0014] Figure 4 This is a time series diagram illustrating the time-dependent changes in the richness indicator, oxygen storage capacity (OSA) of the three-way catalytic converter, temperature of the three-way catalytic converter (bottom plate temperature), degradation inhibition indicator, air-fuel ratio (A / F), fuel-fuel ratio (F / C) of the internal combustion engine, and fuel cut-off (F / C).

[0015] Figure 5 It is a flowchart representing an example of the first processing routine executed by the ECU in each cycle.

[0016] Figure 6 This is a flowchart illustrating an example of a second processing routine executed by the ECU when the F / C condition is met. Detailed Implementation

[0017] A proposed technology involves placing a three-way catalytic converter with oxygen storage capacity in the exhaust manifold of an internal combustion engine. When fuel cutoff conditions are met, if the temperature of the three-way catalytic converter is high, the engine operates at a lean air-fuel ratio, thus delaying fuel cutoff. This technology allows the three-way catalytic converter to gradually store oxygen before fuel cutoff occurs. This suppresses the rapid oxygen storage reaction that occurs during fuel cutoff and inhibits the thermal degradation of the three-way catalytic converter.

[0018] However, whether a three-way catalytic converter is prone to thermal degradation when fuel cut-off is performed depends on the amount of oxygen stored in the upstream portion of the catalytic converter. Specifically, the inventors of this application, through in-depth experiments and verification, have obtained the following insight: when the amount of oxygen stored in the upstream portion of the three-way catalytic converter is high, the three-way catalytic converter is less prone to thermal degradation when fuel cut-off is performed; conversely, when the amount of oxygen stored in the upstream portion of the three-way catalytic converter is low, the three-way catalytic converter is prone to thermal degradation when fuel cut-off is performed. Based on this insight, delaying fuel cut-off when the amount of oxygen stored in the upstream portion of the three-way catalytic converter is high may lead to an unnecessary deterioration in the fuel consumption rate and / or emissions of the internal combustion engine.

[0019] Therefore, in the control device for the internal combustion engine according to the present invention, the control unit determines whether the amount of oxygen stored in a predetermined location upstream of the three-way catalyst is less than a predetermined amount based on whether the fuel cut-off condition of the internal combustion engine is met. In one example, the predetermined location may be a location on the upstream side of the three-way catalyst in the exhaust flow direction, and approximately 40% of the total three-way catalyst. In another example, the predetermined amount is simply the amount at which, if the amount of oxygen stored in the predetermined location is less than that predetermined amount, the three-way catalyst would easily suffer thermal degradation by performing fuel cut-off.

[0020] If the control unit determines that the amount of oxygen stored in a specified location is less than a specified amount, it delays the execution of fuel cut-off in the internal combustion engine for a specified period. During this time, the control unit sets the air-fuel ratio of the internal combustion engine to a lean air-fuel ratio during the specified period, allowing the three-way catalytic converter to gradually store oxygen. Simultaneously, the control unit immediately executes fuel cut-off. Based on this control, if the control unit determines that the amount of oxygen stored in a specified location upstream of the three-way catalytic converter is greater than a specified amount, even if the temperature of the three-way catalytic converter is high, fuel cut-off will not be delayed but will be executed immediately. As a result, delayed fuel cut-off is suppressed when the three-way catalytic converter is less prone to thermal degradation. Therefore, it is possible to suppress the deterioration of fuel consumption rate and emissions caused by delayed fuel cut-off, and to suppress the thermal degradation of the three-way catalytic converter.

[0021] Implementation

[0022] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. Unless otherwise specified, the dimensions, materials, shapes, relative arrangements, etc., of the constituent parts described in these embodiments are not limited to the technical scope of the invention.

[0023] Vehicle Overview

[0024] Figure 1 This is a diagram illustrating an example of the structure of a vehicle to which the present invention is applied. Figure 1 The vehicle VH1 illustrated herein is an internal combustion engine vehicle powered by an internal combustion engine 1. Alternatively, vehicle VH1 can also be a hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV) equipped with a hybrid system including the internal combustion engine 1. The internal combustion engine 1 is a spark-ignition, four-stroke engine that uses gasoline as fuel.

[0025] The internal combustion engine 1 is provided with multiple gas cylinders 10, multiple fuel injection valves 11 that inject fuel into the interior of each of the multiple gas cylinders 10, multiple ignition plugs 12 that ignite the mixture generated inside each of the multiple gas cylinders 10, and a crank position sensor 13 that detects the rotation angle of the output shaft (crankshaft).

[0026] An intake manifold 110 is connected to the internal combustion engine 1. The intake manifold 110 forms a passage for air to be drawn into the internal combustion engine 1. A throttle valve 111 for adjusting the amount of air drawn into the internal combustion engine 1 and an air flow meter 112 for detecting the amount of air drawn into the internal combustion engine 1 are disposed midway through the intake manifold 110. An exhaust manifold 120 is also connected to the internal combustion engine 1. The exhaust manifold 120 forms a passage for the flow of combusted gas (exhaust) burned in the cylinder of the internal combustion engine 1. A catalyst housing 121 for housing a three-way catalyst 121a is disposed midway through the exhaust manifold 120. In this embodiment, the three-way catalyst 121a carries cerium for achieving oxygen storage capacity (OSC). A catalyst temperature sensor 121b for detecting the temperature (base plate temperature) of the three-way catalyst 121a is installed on the catalyst housing 121. Additionally, the temperature of the three-way catalytic converter 121a can be obtained using an exhaust temperature sensor located downstream of the catalytic converter housing 121 in the exhaust pipe 120. An air-fuel ratio sensor 122 is installed on the exhaust pipe 120 upstream of the catalytic converter housing 121 to detect the air-fuel ratio of the internal combustion engine (the air-fuel ratio of the mixture burned in the internal combustion engine 1) based on the oxygen concentration of the exhaust gas.

[0027] Furthermore, the vehicle VH1 in this embodiment is equipped with an Electronic Control Unit (ECU) 20 for controlling the operation of the internal combustion engine 1. The ECU 20 is an example of a "control device" according to the present invention, and can be configured as a computer having a processor (CPU, GPU, etc.), main storage (RAM, ROM, etc.), and auxiliary storage (EPROM, hard disk drive, removable media, etc.). The ECU 20 in this embodiment has a control unit 200 and a storage unit 210. The control unit 200 is an arithmetic unit that implements various functions of the ECU 20 by executing a predetermined program stored in the auxiliary storage device. The control unit 200 can be implemented, for example, by a hardware processor such as a CPU. Furthermore, the control unit 200 can be configured to include RAM, ROM, cache memory, etc. The functions implemented by the control unit 200 will be described later.

[0028] Storage unit 210 is a unit for storing various types of information, and is configured to include RAM and auxiliary storage devices. Storage unit 210 stores programs executed by control unit 200, data used by those programs, etc. The data stored in storage unit 210 includes rich flags and degradation suppression flags, which will be described later.

[0029] Multiple sensors are connected to the ECU 20 to acquire sensor data used in controlling the operation of the internal combustion engine 1. In addition to the crank position sensor 13, air flow meter 112, catalyst temperature sensor 121b, and air-fuel ratio sensor 122 mentioned above, the sensors connected to the ECU 20 also include a throttle sensor 21, a brake sensor 22, and a vehicle speed sensor 23. The throttle sensor 21 detects the amount of throttle pedal operation (throttle opening) mounted on the vehicle VH1. The brake sensor 22 detects the amount of brake pedal operation mounted on the vehicle VH1. The vehicle speed sensor 23 detects the vehicle speed VH1. The ECU 20 controls the operation of the internal combustion engine 1 based on the output signals from these multiple sensors.

[0030] ECU software structure

[0031] Here, the functions (software modules) implemented by ECU20 in this embodiment will be described. In this embodiment, as... Figure 1 As shown, the control unit 200 of the ECU 20 is composed of multiple software modules, including an OSA calculation unit F201, a flag setting unit F202, a determination unit F203, a delay processing unit F204, and an F / C processing unit F205. Each software module is implemented by the control unit 200 executing a program stored in the storage unit 210. Furthermore, at least some of the aforementioned multiple software modules can be implemented using hardware circuits such as ASICs or FPGAs. In the following description, the information processing performed by the OSA calculation unit F201, the flag setting unit F202, the determination unit F203, the delay processing unit F204, and the F / C processing unit F205 has the same meaning as the information processing performed by the control unit 200.

[0032] The OSA calculation unit F201 calculates the oxygen storage amount (OSA) of the three-way catalytic converter 121a at the current time. The OSA calculation can be performed using known logic. In one example, it is sufficient to accumulate the amount of oxygen released from the three-way catalytic converter 121a when the internal combustion engine 1 is in a rich-fuel operation (internal combustion engine air-fuel ratio = rich air-fuel ratio) and the amount of oxygen stored in the three-way catalytic converter 121a when the internal combustion engine 1 is in a lean-fuel operation (internal combustion engine air-fuel ratio = lean air-fuel ratio). The amount of oxygen released from the three-way catalytic converter 121a and the amount of oxygen stored in the three-way catalytic converter 121a are calculated using the amount of exhaust gas flowing into the three-way catalytic converter 121a (intake air amount + fuel injection amount) and the internal combustion engine air-fuel ratio. This OSA calculation is repeatedly performed at predetermined intervals (e.g., each cycle) during the operation of the internal combustion engine 1. The OSA calculation unit F201 transmits the calculation result (the latest OSA) to the flag setting unit F202, which will be described later, each time an OSA is calculated.

[0033] The flag setting unit F202 switches the deterioration inhibition flag on and off. In this embodiment, the deterioration inhibition flag is turned on when the three-way catalytic converter 121a is in a specified state and turned off when the three-way catalytic converter 121a is not in the specified state. The specified state is the state in which the three-way catalytic converter 121a is prone to thermal deterioration when the fuel cut-off (F / C) of the internal combustion engine 1 is performed when the three-way catalytic converter 121a is in the specified state. The specified state in this embodiment is the state in which the OSA is less than a threshold and the bottom plate temperature of the three-way catalytic converter 121a is above a specified temperature (for example, about 700°C). The threshold at this time is a value that serves as an indicator for judging whether the amount of oxygen stored in a specified part on the upstream side of the three-way catalytic converter 121a is less than a specified amount, and it varies depending on the value of the richness flag.

[0034] In this embodiment of the internal combustion engine 1, when the rich air-fuel ratio indicator is on, the fuel injection quantity is controlled by feedback so that the air-fuel ratio of the internal combustion engine detected by the air-fuel ratio sensor 122 is a predetermined rich air-fuel ratio A / F1. When the rich air-fuel ratio indicator is off, the fuel injection quantity is controlled by feedback so that the air-fuel ratio of the internal combustion engine detected by the air-fuel ratio sensor 122 is a predetermined lean air-fuel ratio A / F2. The rich air-fuel ratio indicator is a storage area set in the storage unit 210, which is opened during the period when the OSA decreases from the maximum amount (oxygen storage rate = 100%) to the minimum amount (oxygen storage rate = 0%), and closed during the period when the OSA increases from the minimum amount to the maximum amount.

[0035] As described above, if feedback control of the fuel injection quantity is performed, the location where oxygen is stored in the three-way catalyst 121a (hereinafter, sometimes referred to as the "oxygen storage location") can be different when the rich indicator is on and when the rich indicator is off, even if the amount of OSA is the same. Figure 2 This is a schematic diagram illustrating an example of the time-dependent changes in the oxygen storage site within the three-way catalyst 121a. Figure 2 In the example shown, time progresses from T1 to T11. Furthermore, Figure 2 The blank areas represent regions where oxygen has not been stored (regions where oxygen has been released). Figure 2 The shaded areas in the image represent the sites where oxygen is stored. Furthermore, in... Figure 2 In each combination of T2 and T10, T3 and T9, T4 and T8, and T5 and T7, the OSA values ​​are the same.

[0036] exist Figure 2 In T1, the OSA is increased to its maximum (oxygen storage rate = 100%), thus the rich air-fuel ratio is activated. Subsequently, the air-fuel ratio of the internal combustion engine is controlled to the specified rich air-fuel ratio A / F1. Under these conditions, by releasing oxygen from the three-way catalytic converter 121a, the three-way catalytic converter 121a becomes a stoichiometric environment, and the exhaust gas is properly purified. As a result, the OSA... Figure 2The oxygen content decreases over time from T1 to T6. During this oxygen release process, oxygen is released sequentially from the upstream portion of the three-way catalyst 121a towards the downstream portion. Furthermore, as... Figure 2 As shown in T6, if the OSA decreases to its minimum (oxygen storage rate = 0%), the rich air indicator switches from on to off, and consequently, the air-fuel ratio of the internal combustion engine switches from the specified rich air-fuel ratio A / F1 to the specified lean air-fuel ratio A / F2. In this case, oxygen in the exhaust is stored by the three-way catalytic converter 121a, thus creating a stoichiometric environment for the three-way catalytic converter 121a, and the exhaust is properly purified. As a result, Figure 2 The OSA increases over time from T6 to T11. During this oxygen storage process, oxygen is stored sequentially from the upstream portion of the three-way catalyst 121a towards the downstream portion. Furthermore, as... Figure 2 As shown in T11, if the OSA is increased to its maximum (oxygen storage rate = 100%), the rich air flag switches from off to on, and the air-fuel ratio of the internal combustion engine is subsequently controlled to a rich air-fuel ratio. Then, the same transition as from T1 to T11 is repeated.

[0037] In the three-way catalyst 121a with oxygen storage capacity, such as Figure 2 As shown, even with the same OSA level, the oxygen storage location may differ depending on whether the richness indicator is on or off. For example, if we consider... Figure 2 In T5, the oxygen storage site is located near the downstream end of the three-way catalyst 121a, while in T7, the oxygen storage site is located near the upstream end of the three-way catalyst 121a.

[0038] Furthermore, according to the inventors of this application, it is known that when the oxygen content in the upstream portion (i.e., the designated portion) of the three-way catalyst 121a is above a designated amount, thermal degradation of the three-way catalyst 121a due to fuel cut-off (F / C) is more likely to occur when the oxygen content in the designated portion is below a designated amount. In one example, the designated portion may be the upstream portion of the three-way catalyst 121a in the exhaust flow direction, approximately 10% to 40% of the total three-way catalyst 121a. However, the range of the designated portion is not limited to 10% to 40%, and can be varied depending on the size, shape, and composition of the three-way catalyst 121a. Furthermore, the designated amount is conceived as the amount at which thermal degradation due to fuel cut-off (F / C) becomes significant if the oxygen content stored in the designated portion is less than this designated amount.

[0039] When using OSA to determine whether the amount of oxygen stored in the aforementioned specified locations is less than a specified amount, the aforementioned factors need to be considered. Figure 2The threshold is set based on the observed tendency. That is, when the richness indicator is off, the amount of oxygen stored in the specified location is relatively high when OSA is relatively low. Conversely, when the richness indicator is on, the amount of oxygen stored in the specified location is also low if OSA is low. Therefore, when the richness indicator is off, thermal degradation of the three-way catalytic converter 121a caused by fuel cut-off (F / C) is less likely to occur even if OSA is low, but when the richness indicator is on, thermal degradation of the three-way catalytic converter 121a caused by fuel cut-off (F / C) is more likely to occur if OSA is low.

[0040] Therefore, in this embodiment, as Figure 3A , Figure 3B As shown, the threshold for determining whether the oxygen content stored in a specified location of the three-way catalyst 121a is less than a specified amount is set to the threshold when the rich flag is turned off. Figure 3B The second threshold) and the threshold when the rich flag is turned on ( Figure 3A Compared to the first threshold, it becomes a larger value. In one example, the first threshold can be set to an OSA with an oxygen storage rate of 80% to 90% (more preferably 100%), and the second threshold can be set to an OSA with an oxygen storage rate of 40%.

[0041] Here, we return to the description of the flag setting unit F202. In this embodiment, when the rich flag is on, if the OSA is less than a first threshold (the amount of oxygen stored in a specified location is less than a specified amount) and the bottom plate temperature of the three-way catalytic converter 121a is above a specified temperature, the flag setting unit F202 determines that the three-way catalytic converter 121a is in a specified state. Furthermore, when the rich flag is off, if the OSA is less than a second threshold (the amount of oxygen stored in a specified location is less than a specified amount) and the bottom plate temperature of the three-way catalytic converter 121a is above a specified temperature, the flag setting unit F202 determines that the three-way catalytic converter 121a is in a specified state.

[0042] Each time the OSA calculation unit F201 calculates the OSA, it determines whether the three-way catalytic converter 121a is in a specified state. Specifically, the flag setting unit F202 acquires the output signal (base plate temperature of the three-way catalytic converter 121a) and the value of a rich flag based on the OSA calculated by the OSA calculation unit F201. Then, when the rich flag is enabled, the flag setting unit F202 determines whether the OSA calculated by the OSA calculation unit F201 is less than a first threshold and whether the base plate temperature detected by the catalyst temperature sensor 121b is above a specified temperature. If the OSA is less than the first threshold and the base plate temperature is above the specified temperature, the flag setting unit F202 determines that the three-way catalytic converter 121a is in a specified state. In this case, the flag setting unit F202 activates the degradation suppression flag. On the other hand, if the OSA is above the first threshold and / or the base plate temperature is less than the specified temperature, the flag setting unit F202 determines that the three-way catalytic converter 121a is not in a specified state. In this case, the flag setting unit F202 turns off the degradation suppression flag.

[0043] Furthermore, when the richness flag is off, the flag setting unit F202 determines whether the OSA calculated by the OSA calculation unit F201 is less than the second threshold and whether the substrate temperature detected by the catalyst temperature sensor 121b is above a specified temperature. If the OSA is less than the second threshold and the substrate temperature is above the specified temperature, the flag setting unit F202 determines that the three-way catalyst 121a is in a specified state. In this case, the flag setting unit F202 activates the degradation suppression flag. On the other hand, if the OSA is above the second threshold and / or the substrate temperature is less than the specified temperature, the flag setting unit F202 determines that the three-way catalyst 121a is not in a specified state. In this case, the flag setting unit F202 deactivates the degradation suppression flag.

[0044] The determination unit F203 determines whether the fuel cut-off delay condition is met based on whether the fuel cut-off condition (F / C condition) is met. In one example, the F / C condition may include: the engine speed calculated based on the output signal of the crank position sensor 13 is above a predetermined speed; the throttle opening detected by the throttle sensor 21 is fully closed; and the driving speed detected by the vehicle speed sensor 23 is above a predetermined speed. Furthermore, in this embodiment, the fuel cut-off delay condition includes the condition that the three-way catalytic converter 121a is in a predetermined state. In this embodiment, when the three-way catalytic converter 121a is in the predetermined state, the flag setting unit F202 activates the degradation suppression flag; when the three-way catalytic converter 121a is not in the predetermined state, the flag setting unit F202 deactivates the degradation suppression flag. Therefore, in this embodiment, when the F / C condition is met, the determination unit F203 determines whether the degradation suppression flag is activated or deactivated. When the degradation suppression flag is activated, the determination unit F203 determines that the fuel cut-off delay condition is met. Furthermore, when the degradation suppression flag is off, the determination unit F203 determines that the fuel cut-off delay condition has not been met.

[0045] The delay processing unit F204 performs F / C delay processing based on the determination unit F203's determination that the fuel cut-off delay condition has been met. In this embodiment, the F / C delay processing is a process that delays the execution of fuel cut-off (F / C) until a predetermined period (the period during which the OSA of the three-way catalyst 121a reaches or exceeds the first threshold or second threshold) has elapsed since the F / C condition was met. During the predetermined period (fuel cut-off delay period), the delay processing unit F204 sets the internal combustion engine air-fuel ratio to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio and falls within the range of the three-way catalyst 121a's purification window. In one example, the internal combustion engine air-fuel ratio during the predetermined period may be the same as or slightly higher than the predetermined lean air-fuel ratio A / F2 (high leanness) used in the feedback control of fuel injection quantity when the rich-fuel flag is closed.

[0046] By performing F / C delay processing by delay processing unit F204, if the OSA calculated by OSA calculation unit F201 becomes the first threshold or the second threshold or higher, and if the degradation suppression flag is switched from on to off by flag setting unit F202 accordingly, the F / C delay processing ends.

[0047] The F / C processing unit F205 performs fuel cut-off (F / C) on the internal combustion engine 1 based on the determination unit F203 determining that the fuel cut-off delay condition has not been met and the completion of the F / C delay processing based on the delay processing unit F204. In one example, the F / C processing unit F205 may stop fuel injection based on the fuel injection valve 11 and stop ignition based on the ignition plug 12.

[0048] Time series diagram

[0049] Figure 4 This is a time-series diagram illustrating the progression of the following parameters: richness indicator, OSA, temperature (bottom plate temperature) of the three-way catalytic converter 121a, degradation inhibition indicator, air-fuel ratio (A / F), fuel-charge ratio (F / C), and fuel cut-off (F / C). Figure 4 The text shows the movement of the rich symbol when it is turned on. Furthermore, Figure 4 The single-dotted line in the table represents the shift of the temperature (bottom plate temperature) of OSA, three-way catalyst 121a, air-fuel ratio (A / F) of internal combustion engine and fuel cut-off (F / C) when the fuel cut-off (F / C) is executed immediately when the F / C condition is met.

[0050] like Figure 4 As shown, when the rich air-fuel ratio indicator is activated, the fuel injection quantity is controlled by feedback to make the air-fuel ratio (A / F) of the internal combustion engine a predetermined rich air-fuel ratio A / F1. Therefore, the OSA of the three-way catalytic converter 121a decreases over time. Moreover, if the OSA of the three-way catalytic converter 121a decreases to below a first threshold ( Figure 4 If the OSA is less than the first threshold (T10), then the OSA calculated by the OSA calculation unit F201 will be less than the first threshold. If the OSA calculation unit F201 calculates this OSA, the flag setting unit F202 will obtain the bottom plate temperature of the three-way catalyst 121a through the catalyst temperature sensor 121b and determine whether the obtained bottom plate temperature is above a specified temperature. Figure 4 In the example shown, at time T10, the substrate temperature is higher than the specified temperature. Therefore, the flag setting unit F202 determines that the three-way catalytic converter 121a is in the specified state and switches the degradation inhibition flag from off to on. Then, in the state where the degradation inhibition flag is off (the OSA of the three-way catalytic converter 121a is less than the first threshold and the substrate temperature is above the specified temperature), if the F / C condition is met ( Figure 4 If the engine reaches T20, the delay processing unit F204 will perform F / C delay processing. As a result, the air-fuel ratio (A / F) of the internal combustion engine after T10 will be a lower air-fuel ratio (less lean air-fuel ratio) than the air-fuel ratio of the internal combustion engine when fuel cut-off (F / C) is performed.

[0051] If the F / C delay treatment is performed, the OSA of the three-way catalyst 121a increases more smoothly than the OSA when fuel cut-off (F / C) is performed. This suppresses the rapid oxygen storage reaction in the three-way catalyst 121a. As a result, the bottom plate temperature of the three-way catalyst 121a increases at a lower temperature than when fuel cut-off (F / C) is performed immediately. Therefore, thermal degradation of the three-way catalyst 121a is suppressed. Then, if the OSA of the three-way catalyst 121a increases above a first threshold by performing the F / C delay treatment ( Figure 4 If the OSA calculated by the OSA calculation unit F201 exceeds the first threshold (T30), then the degradation suppression flag is switched from on to off by the flag setting unit F202. If the degradation suppression flag is switched from on to off, the F / C delay processing performed by the delay processing unit F204 ends, and the fuel cut-off (F / C) is performed by the F / C processing unit F205.

[0052] Furthermore, when the rich-fuel flag is off, feedback control of the fuel injection quantity is performed to make the internal combustion engine air-fuel ratio (A / F) a predetermined lean air-fuel ratio A / F2, thus the OSA of the three-way catalytic converter 121a decreases over time. Then, as the OSA of the three-way catalytic converter 121a gradually increases, during the period when the OSA is less than the second threshold, the degradation suppression flag can simply be set to on. Moreover, the internal combustion engine air-fuel ratio (A / F) during the F / C delay treatment can simply be set to the same air-fuel ratio (A / F) as the internal combustion engine before the F / C delay treatment (= the predetermined lean air-fuel ratio A / F2).

[0053] ECU operation

[0054] Next, according to Figure 5 and Figure 6 The operation of ECU20 in this embodiment will be explained. Figure 5 This is a flowchart representing an example of the first processing routine executed by ECU20 in each cycle. Figure 6 This is a flowchart illustrating an example of the second processing routine executed by ECU20 when the F / C condition is met. The execution entity for both the first and second processing routines is the control unit 200 (processor) of ECU20, but here we will describe it using the software module of ECU20 as the execution entity.

[0055] First of all, Figure 5In the first processing routine, the OSA calculation unit F201 of ECU20 calculates the OSA of the three-way catalytic converter 121a at the current time (step S101). In one example, the OSA calculation unit F201 calculates the amount of oxygen stored in or released from the three-way catalytic converter 121a in the cycle based on the intake air volume, fuel injection volume, and air-fuel ratio of the internal combustion engine in the cycle being targeted, and adds or subtracts the calculation result to the previously calculated OSA (the OSA calculated in the previous cycle). More specifically, when the rich oxygen indicator is off, the OSA calculation unit F201 calculates the remaining oxygen contained in the exhaust gas based on the intake air volume and fuel injection volume, and adds the calculated oxygen to the previously calculated OSA (the OSA calculated in the previous cycle). Furthermore, when the oxygen deficiency indicator is activated, the OSA calculation unit F201 calculates the oxygen deficiency in the exhaust gas based on the intake air volume and fuel injection volume, and subtracts the calculated deficiency from the previously calculated OSA. If the OSA calculation unit F201 finishes processing step S101, the indicator setting unit F202 executes the processing step S102.

[0056] In step S102, the flag setting unit F202 obtains the bottom plate temperature of the three-way catalyst 121a through the catalyst temperature sensor 121b. After completing the processing in step S102, the flag setting unit F202 executes the processing in step S103.

[0057] In step S103, the flag setting unit F202 determines whether the bottom plate temperature obtained in step S102 is above a predetermined temperature. If the bottom plate temperature of the three-way catalyst 121a is above the predetermined temperature (a positive determination is made in step S103), the flag setting unit F202 performs the processing in step S104.

[0058] In step S104, the flag setting unit F202 accesses the storage unit 210 and determines whether the rich flag is enabled. If the rich flag in the storage unit 210 is enabled (a positive determination is made in step S104), the flag setting unit F202 executes the processing in step S105.

[0059] In step S105, the flag setting unit F202 determines whether the OSA calculated by the OSA calculation unit F201 in step S101 is less than a first threshold (for example, an OSA with an oxygen storage capacity of 80% to 90%). If the OSA calculated by the OSA calculation unit F201 in step S101 is less than the first threshold (a positive determination in step S105), the flag setting unit F202 proceeds to step S106 and sets the degradation suppression flag to "on". On the other hand, if the OSA calculated by the OSA calculation unit F201 in step S101 is greater than or equal to the first threshold (a negative determination in step S105), the flag setting unit F202 proceeds to step S108 and sets the degradation suppression flag to "off".

[0060] Furthermore, if the richness flag is determined to be off in step S104 (a negative determination in step S104), the flag setting unit F202 executes the processing in step S107. In step S107, the flag setting unit F202 determines whether the OSA calculated by the OSA calculation unit F201 in step S101 is less than a second threshold (for example, an OSA with an oxygen storage rate of 40%). If the OSA calculated by the OSA calculation unit F201 in step S101 is less than the second threshold (a positive determination in step S107), the flag setting unit F202 proceeds to step S106 and sets the degradation suppression flag to on. On the other hand, if the OSA calculated by the OSA calculation unit F201 in step S101 is above the second threshold (a negative determination in step S107), the flag setting unit F202 proceeds to step S108 and sets the degradation suppression flag to off.

[0061] Furthermore, if it is determined in step S103 that the base plate temperature is lower than the specified temperature (a negative determination in step S103), the flag setting unit F202 proceeds to step S108 and sets the degradation suppression flag to off.

[0062] If the flag setting unit F202 finishes processing step S106 or step S108, the execution of the first processing routine ends.

[0063] Next, in Figure 6 In the second processing routine, the determination unit F203 of ECU20 determines whether the fuel cut-off delay condition is met (step S201). Specifically, the determination unit F203 determines whether the fuel cut-off delay condition is met. Figure 5 The determination unit F203 determines whether the degradation suppression flag, which is set separately in the first processing routine, is enabled. If the degradation suppression flag is enabled, the determination unit F203 determines that the fuel cut-off delay condition is met (a positive determination in step S201). In this case, the control unit 200 of the ECU 20 operates as the delay processing unit F204 and performs F / C delay processing (steps S202-S203).

[0064] In step S202, the delay processing unit F204 sets a target value (target air-fuel ratio) for the internal combustion engine air-fuel ratio during the execution of the F / C delay processing. In one example, as described above, the target air-fuel ratio can be the same as a predetermined lean air-fuel ratio A / F2. Alternatively, the target air-fuel ratio can be set to a leaner air-fuel ratio resulting from a higher current level of OSA and / or a lower current floor temperature. However, the target air-fuel ratio can be limited to the range of the purification window of the three-way catalytic converter 121a. After the F / C delay processing completes step S202, the control unit 200 of the ECU 20 operates as the F / C processing unit F205 and executes step S203.

[0065] In step S203, the delay processing unit F204 performs F / C delay processing. Specifically, the delay processing unit F204 determines the fuel injection quantity in a manner that ensures the air-fuel ratio of the internal combustion engine in the next cycle is the target air-fuel ratio set in step S202, and controls the fuel injection valve 11 according to the determined fuel injection quantity. Furthermore, the delay processing unit F204 controls the ignition plug 12 to ignite the air-fuel mixture in the next cycle. The ignition timing is not particularly limited at this time, but it can be set to minimize engine output. After the delay processing unit F204 completes the processing in step S203, the control unit 200 of the ECU 20 again executes the processing in step S201.

[0066] Furthermore, if the fuel cut-off delay condition is determined not to be met in step S201 (a negative determination in step S201), the control unit 200 of the ECU 20 operates as the F / C processing unit F205 and executes the processing in step S204. In step S204, the F / C processing unit F205 executes fuel cut-off (F / C) of the internal combustion engine 1. Specifically, the F / C processing unit F205 controls the fuel injection valve 11 and the ignition plug 12 to stop fuel injection and ignition in the next cycle. Fuel cut-off (F / C) continues until the F / C condition is not met. If the F / C processing unit F205 executes the process to end step S204, the control unit 200 of the ECU 20 terminates. Figure 6 The execution of the second processing routine.

[0067] Function and effects of this implementation method

[0068] In the vehicle VH1 of this embodiment, when the F / C condition is met, if it is determined that the amount of oxygen stored in a predetermined location of the three-way catalyst 121a is less than a predetermined amount, an F / C delay treatment is performed. If it is determined that the amount of oxygen stored in a predetermined location of the three-way catalyst 121a is greater than or equal to a predetermined amount, the F / C delay treatment is not performed, and fuel cut-off (F / C) is performed immediately. Therefore, it is possible to suppress the execution of F / C delay treatment when the three-way catalyst 121a is not prone to thermal degradation, or the execution of fuel cut-off (F / C) when the three-way catalyst 121a is prone to thermal degradation.

[0069] Therefore, according to this embodiment, the deterioration of fuel consumption rate and emissions caused by F / C delay treatment can be minimized, and the thermal degradation of the three-way catalyst 121a caused by fuel cut-off (F / C) can be suppressed.

[0070] other

[0071] In the above embodiments, the fuel cut-off delay conditions are exemplified by both the OSA of the three-way catalyst 121a being less than a first threshold or a second threshold and the temperature (bottom plate temperature) of the three-way catalyst 121a being above a predetermined temperature. However, it is also possible to use only the OSA of the three-way catalyst 121a being less than the first threshold or the second threshold as the fuel cut-off delay condition.

Claims

1. A control device for an internal combustion engine, wherein a three-way catalytic converter with oxygen storage capacity is disposed in the exhaust passage, the control device for the internal combustion engine being characterized in that it comprises: The control unit is configured to perform the following steps: Based on the fuel cut-off condition of the internal combustion engine being met, determine whether the oxygen content at a specified location upstream of the three-way catalyst is less than a specified amount. If it is determined that the amount of oxygen stored in the specified location is less than the specified amount, the execution of fuel cutoff in the internal combustion engine is delayed for a specified period, and the air-fuel ratio of the internal combustion engine is set to a lean air-fuel ratio during the specified period; and If it is determined that the amount of oxygen stored in the specified location is above the specified amount, the fuel cut-off of the internal combustion engine is immediately executed.

2. The control device for an internal combustion engine according to claim 1, characterized in that, The step of determining whether the amount of oxygen stored in the specified location is less than the specified amount includes: Based on the fact that the air-fuel ratio of the internal combustion engine is set to a rich air-fuel ratio before the fuel cut-off condition is about to be met, it is determined whether the oxygen storage capacity of the three-way catalyst is less than the first threshold. If it is determined that the oxygen storage capacity of the three-way catalyst is less than the first threshold, then it is determined that the oxygen stored in the designated location is less than the designated amount; and If it is determined that the oxygen storage capacity of the three-way catalyst is above the first threshold, it is determined that the oxygen stored in the specified location is above the specified amount.

3. The control device for an internal combustion engine according to claim 2, characterized in that, The specified period is the period from when the fuel cut-off condition is met until the oxygen storage capacity of the three-way catalyst reaches or exceeds the first threshold.

4. The control device for an internal combustion engine according to claim 1, characterized in that, The step of determining whether the amount of oxygen stored in the specified location is less than the specified amount includes: Based on the fact that the air-fuel ratio of the internal combustion engine is set to a lean air-fuel ratio before the fuel cut-off condition is about to be met, it is determined whether the oxygen storage capacity of the three-way catalyst is less than the second threshold. If it is determined that the oxygen storage capacity of the three-way catalyst is less than the second threshold, then it is determined that the oxygen stored in the specified location is less than the specified amount; and If it is determined that the oxygen storage capacity of the three-way catalyst is above the second threshold, it is determined that the oxygen stored in the specified location is above the specified amount.

5. The control device for an internal combustion engine according to claim 4, characterized in that, The specified period is the period from when the fuel cut-off condition is met until the oxygen storage capacity of the three-way catalyst reaches or exceeds the second threshold.

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