Engine System

Abstract

To suppress deterioration of emission.SOLUTION: An engine system is equipped with first and second sensors that are respectively disposed on an upstream side and a downstream side of a catalyst with an oxygen storage capacity, and respectively detect first and second detection air / fuel ratios, and a control device that alternately switches rich correction and lean correction. The control device is equipped with a correction switching portion that switches to the lean correction if the second detection air / fuel ratio becomes less than a rich finishing determination value that is larger than a theoretical air / fuel ratio during the rich correction, and switches to the rich correction if the second detection air / fuel ratio becomes a lean finishing determination value or less that is smaller than the theoretical air / fuel ratio during the lean correction, a calculating portion that calculates an integrated value of suction air amount of an engine during the rich correction and if the second detection air / fuel ratio is larger than an excessive lean determination value that is larger than a rich finishing determination value, and a learning portion that changes at least either one of a rich air / fuel ratio and a lean air / fuel ratio so as to deviate toward a rich side a center value of the rich air / fuel ratio and the lean air / fuel ratio if the integrated value is larger than a threshold value and learns it.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Based on the air-fuel ratio detected by a sensor located downstream of a catalyst having oxygen storage capacity, the air-fuel ratio of the engine is corrected to be rich or lean so that the air-fuel ratio detected by a sensor located upstream of the catalyst becomes a predetermined rich or lean air-fuel ratio (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-067070 Summary of the Invention [Problem to be solved by the invention]

[0004] If the rich correction or lean correction continues for a long period of time as described above, the amount of oxygen stored in the catalyst may deviate from the desired range, which may result in a deterioration in emissions.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an engine system that suppresses deterioration of emissions. [Means for solving the problem]

[0006] The object is to provide an engine having an engine catalyst and an oxygen storage capacity, the engine catalyst being arranged in an exhaust passage of the engine, first and second sensors being arranged in the exhaust passage on the upstream and downstream sides of the catalyst, respectively, for detecting first and second detected air-fuel ratios, which are air-fuel ratios of the exhaust, and a control device that alternately switches between a rich correction that corrects the air-fuel ratio of the engine so that the first detected air-fuel ratio becomes a predetermined rich air-fuel ratio which is smaller than the stoichiometric air-fuel ratio, and a lean correction that corrects the air-fuel ratio of the engine so that the first detected air-fuel ratio becomes a predetermined lean air-fuel ratio which is larger than the stoichiometric air-fuel ratio, and the control device that alternately switches between a rich end correction when the second detected air-fuel ratio becomes larger than the stoichiometric air-fuel ratio during the rich correction. and switching to the rich correction when the second detected air-fuel ratio becomes equal to or less than a lean end judgment value that is smaller than the stoichiometric air-fuel ratio during the lean correction; a calculation unit that calculates an integrated value of the intake air amount of the engine when the second detected air-fuel ratio is greater than an excessively lean judgment value that is larger than the rich end judgment value during the rich correction; and a learning unit that, when the integrated value is larger than a threshold value, changes and learns at least one of the rich air-fuel ratio and the lean air-fuel ratio so that a center value between the rich air-fuel ratio and the lean air-fuel ratio shifts to the rich side.

[0007] The above object is also achieved by providing an engine comprising: an engine; a catalyst having an oxygen storage capacity that is arranged in an exhaust passage of the engine; first and second sensors that are arranged in the exhaust passage upstream and downstream of the catalyst, respectively, and that detect first and second detected air-fuel ratios that are air-fuel ratios of the exhaust; and a control device that alternately switches between a rich correction that corrects the air-fuel ratio of the engine so that the first detected air-fuel ratio becomes a predetermined rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, and a lean correction that corrects the air-fuel ratio of the engine so that the first detected air-fuel ratio becomes a predetermined lean air-fuel ratio that is larger than the stoichiometric air-fuel ratio, and a correction switching unit that switches to the lean correction when the second detected air-fuel ratio becomes equal to or less than a lean end judgment value that is smaller than the stoichiometric air-fuel ratio, and switches to the rich correction when the second detected air-fuel ratio becomes less than a lean end judgment value that is smaller than the lean end judgment value during the lean correction; a calculation unit that calculates an integrated value of the intake air amount of the engine when the second detected air-fuel ratio during the lean correction is smaller than an excessively rich judgment value that is smaller than the lean end judgment value; and a learning unit that, when the integrated value is larger than a threshold value, changes and learns at least one of the rich air-fuel ratio and the lean air-fuel ratio so that a center value between the rich air-fuel ratio and the lean air-fuel ratio shifts to the lean side.

[0008] The control device may include an estimation unit that estimates the oxygen storage amount of the catalyst, and the correction switching unit may switch to the lean correction when the second detected air-fuel ratio becomes less than the rich end judgment value during the rich correction and the oxygen storage amount is less than a target lower limit value, and may switch to the rich correction when the second detected air-fuel ratio becomes equal to or less than the lean end judgment value during the lean correction and the oxygen storage amount is greater than a target upper limit value.

[0009] The estimation unit may estimate the oxygen storage amount based on the first detected air-fuel ratio and an intake air amount of the engine. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an engine system in which deterioration of emissions is suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of an engine system 1. As shown in FIG. [Figure 2] FIG. 2 is a flowchart illustrating the correction switching control. [Figure 3] FIG. 3 is a flowchart illustrating the learning control. [Figure 4] FIG. 4 is a timing chart illustrating the correction switching control and the learning control. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Engine system overview] 1 is a schematic diagram of an engine system 1. This engine system 1 is equipped with an engine 10 and is mounted on a vehicle. The vehicle may be, for example, an engine vehicle equipped with only the engine 10 as a power source for running, or may be a hybrid vehicle equipped with both the engine 10 and a motor as a power source for running.

[0013] An exhaust passage 20 is connected to the engine 10. A catalyst 30 is provided in the exhaust passage 20. The catalyst 30 is a three-way catalyst containing catalytic metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) and having oxygen storage capacity. The three-way catalyst has catalytic activity and oxygen storage capacity, and therefore purifies NOx and HC according to the amount of oxygen stored. That is, when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is lean, if the oxygen storage capacity of the three-way catalyst is low, the three-way catalyst stores oxygen in the exhaust gas, thereby reducing and purifying NOx in the exhaust gas. If the oxygen storage capacity of the three-way catalyst increases, the concentrations of oxygen and NOx in the exhaust gas flowing out of the three-way catalyst increase. If the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is rich, if the oxygen storage capacity of the three-way catalyst is high, the oxygen stored in the three-way catalyst is released, and HC in the exhaust gas is oxidized and purified. When the amount of oxygen stored in the three-way catalyst decreases, the concentration of HC in the exhaust gas flowing out from the three-way catalyst increases.

[0014] An air-fuel ratio sensor 4a is provided in the exhaust passage 20 upstream of the catalyst 30. The air-fuel ratio sensor 4a outputs a signal corresponding to the air-fuel ratio of the exhaust gas discharged from the engine 10 and flowing into the catalyst 30. An air-fuel ratio sensor 4b is provided in the exhaust passage 20 downstream of the catalyst 30. The air-fuel ratio sensor 4b outputs a signal corresponding to the air-fuel ratio of the exhaust gas that has passed through the catalyst 30. In this specification, the air-fuel ratio detected by the air-fuel ratio sensor 4a is referred to as the detected air-fuel ratio AFa, and the air-fuel ratio detected by the air-fuel ratio sensor 4b is referred to as the detected air-fuel ratio AFb. The detected air-fuel ratio AFa is an example of a first detected air-fuel ratio. The detected air-fuel ratio AFb is an example of a second detected air-fuel ratio. The air-fuel ratio sensor 4a is an example of a first sensor. The air-fuel ratio sensor 4b is an example of a second sensor. An oxygen concentration sensor may be used instead of the air-fuel ratio sensor.

[0015] The engine system 1 includes an ECU (Electronic Control Unit) 50. The ECU 50 is mainly composed of a computer including a CPU (Central Processing Unit) and volatile and non-volatile memories such as RAM (Random Access Memory) and ROM (Read Only Memory). The ECU 50 executes programs installed in the memory on the CPU to realize various control processes related to the engine 10. The ECU 50 is an example of a control device, and functionally realizes a correction switching unit, a calculation unit, a learning unit, and an estimation unit, which will be described in detail later.

[0016] The ECU 50 executes correction switching control that alternates between rich correction and lean correction. The rich correction is control that corrects the air-fuel ratio of the engine 10 so that the detected air-fuel ratio AFa becomes a predetermined rich air-fuel ratio TR that is smaller than the stoichiometric air-fuel ratio ST. The lean correction is control that corrects the air-fuel ratio of the engine 10 so that the detected air-fuel ratio AFa becomes a predetermined lean air-fuel ratio TL that is larger than the stoichiometric air-fuel ratio ST. Specifically, the fuel injection amount and intake air amount of the engine 10 are feedback-controlled so that the detected air-fuel ratio AFa becomes the rich air-fuel ratio TR or the lean air-fuel ratio TL.

[0017] The ECU 50 constantly estimates the oxygen storage amount OSA of the catalyst 30 based on the following equation. Amount of change ΔOSA = Oxygen mass ratio in the atmosphere × Predetermined time × Intake air amount × (Detected air-fuel ratio AFa - Stoichiometric air-fuel ratio ST) / Detected air-fuel ratio AFa The oxygen storage amount OSA is calculated by accumulating the change amount ΔOSA calculated at predetermined time intervals. The oxygen weight percentage in the atmosphere is stored in advance in the ROM of the ECU 50. When the detected air-fuel ratio AFa is greater than the stoichiometric air-fuel ratio ST, the change amount ΔOSA is a positive value. When the detected air-fuel ratio AFa is smaller than the stoichiometric air-fuel ratio ST, the change amount ΔOSA is a negative value. The intake air amount is calculated by the ECU 50 based on the detection value of the air flow meter. Estimation of the oxygen storage amount OSA is an example of processing executed by the estimation unit.

[0018] [Correction switching control] FIG. 2 is a flowchart illustrating the correction switching control. First, the target upper limit value OU, the target lower limit value OL, the rich end determination value SL, the lean end determination value SR, the excessive lean determination value EL, and the excessive rich determination value ER shown in FIG. 2 will be described. The target upper limit value OU is the upper limit value of the target range of the oxygen storage amount OSA and is a positive value. The target lower limit value OL is the lower limit value of the target range of the oxygen storage amount OSA and is a negative value. The target upper limit values ​​OU and Target lower limit OL The target range determined by is set to a range of oxygen storage amount in which the catalyst 30 can maintain its purification performance. The rich end determination value SL is a value larger than the stoichiometric air-fuel ratio ST. The rich end determination value SL is a determination value for ending rich correction and switching to lean correction. The lean end determination value SR is a value smaller than the stoichiometric air-fuel ratio ST. The lean end determination value SR is a determination value for ending lean correction and switching to rich correction. The excessive lean determination value EL is a value larger than the rich end determination value SL. The excessive lean determination value EL is a determination value indicating that the detected air-fuel ratio AFb is excessively lean during rich correction. The excessive rich determination value ER is a value smaller than the lean end determination value SR. The excessive rich determination value ER is a determination value indicating that the detected air-fuel ratio AFb is excessively rich during lean correction.

[0019] This control is repeatedly executed while the ignition is on. The ECU 50 determines whether or not rich correction is being performed (step S1). If the answer is Yes in step S1, the ECU 50 determines whether or not the oxygen storage amount OSA is less than the target lower limit value OL (step S2a). If the answer is Yes in step S2a, the ECU 50 determines whether or not the detected air-fuel ratio AFb is less than a rich end determination value SL (step S3a). If the answer is No in step S2a, the ECU 50 determines whether or not the detected air-fuel ratio AFb is less than an excessively rich determination value ER (step S4a). If the answer is Yes in step S3a or Yes in step S4a, the ECU 50 executes lean correction (step S5). If the answer is No in step S3a or No in step S4a, the ECU 50 executes rich correction (step S6).

[0020] That is, even if step S2a returns "Yes" during rich correction, rich correction is continued until step S3a returns "Yes." This allows switching from rich correction to lean correction at an appropriate timing based on the detected air-fuel ratio AFb even if the estimated oxygen storage amount OSA is smaller than the actual oxygen storage amount. Steps S5 and S6 are an example of processing executed by the correction switching unit.

[0021] If the answer is No in step S1, the ECU 50 determines whether the oxygen storage amount OSA is greater than the target upper limit value OU (step S2b). If the answer is Yes in step S2b, the ECU 50 determines whether the detected air-fuel ratio AFb is greater than the lean end determination value SR (step S3b). If the answer is No in step S2b, the ECU 50 determines whether the detected air-fuel ratio AFb is greater than the excessive lean determination value EL (step S4b). If the answer is Yes in step S3b or Yes in step S4b, the ECU 50 performs rich correction (step S6). If the answer is No in step S3b or No in step S4b, the ECU 50 performs lean correction (step S5).

[0022] That is, even if the answer to step S2b is Yes during the lean correction, the lean correction is continued until the answer to step S3b is Yes. As a result, even if the estimated oxygen storage amount OSA is greater than the actual oxygen storage amount, the lean correction can be switched to the rich correction at an appropriate timing based on the detected air-fuel ratio AFb.

[0023] [Learning control] FIG. 3 is a flowchart illustrating the learning control. FIG. 3 is repeatedly executed while the ignition is on. This control is executed in parallel with the correction switching control described above. The ECU 50 determines whether or not a rich correction is being performed (step S11). If the answer is Yes in step S11, the ECU 50 determines whether or not the detected air-fuel ratio AFb is greater than the excessively lean determination value EL (step S12a). If the answer is Yes in step S12a, the ECU 50 calculates the lean accumulated intake air amount LAI (step S13a). The lean accumulated intake air amount LAI is the accumulated value of the intake air amount of the engine 10 when the detected air-fuel ratio AFb is excessively lean. The lean accumulated intake air amount LAI is calculated based on the detected value of the air flow meter. Step S13a is an example of processing executed by the calculation unit.

[0024] Next, the ECU 50 determines whether the lean cumulative intake air amount LAI is equal to or greater than a threshold value (step S14a). If the result in step S14a is Yes, it can be assumed that the detected air-fuel ratio AFb has been excessively lean for a long period of time despite the rich correction being performed. Therefore, the threshold value is set to the time when the detected air-fuel ratio AFb has been excessively lean for a long period of time and the purification ability of the catalyst 30 has decreased.

[0025] In this case, the ECU 50 changes and learns the lean air-fuel ratio TL and the rich air-fuel ratio TR so that the center value C between the lean air-fuel ratio TL and the rich air-fuel ratio TR is shifted to the rich side by a predetermined value (step S15a). This makes it possible to prevent the detected air-fuel ratio AFb from becoming excessively lean during the re-correction to the rich side, thereby preventing emissions from deteriorating. In this embodiment, the lean air-fuel ratio TL and the rich air-fuel ratio TR are each changed to the rich side by the same value. If the answer is No in step S14a, this control ends. If the answer is No in step S12a, the lean integrated intake air amount LAI is reset to zero (step S16a).

[0026] If the answer is No in step S11, the ECU 50 determines whether the detected air-fuel ratio AFb is less than an excessively rich determination value ER (step S12b). If the answer is Yes in step S12b, the ECU 50 calculates a rich integrated intake air amount RAI (step S13b). The rich integrated intake air amount RAI is an integrated value of the intake air amount of the engine 10 when the detected air-fuel ratio AFb is excessively rich. The rich integrated intake air amount RAI is calculated based on the detected value of the air flow meter. Step S13b is an example of processing executed by the calculation unit.

[0027] Next, the ECU 50 determines whether the rich cumulative intake air amount RAI is equal to or greater than a threshold value (step S14b). If the result in step S14b is Yes, it can be assumed that the detected air-fuel ratio AFb has been excessively rich for a long period of time despite the lean correction being performed. Therefore, the threshold value is set to the time when the detected air-fuel ratio AFb has been excessively rich for a long period of time and the purification ability of the catalyst 30 has decreased.

[0028] In this case, the ECU 50 changes and learns the lean air-fuel ratio TL and the rich air-fuel ratio TR so that the center value C between the lean air-fuel ratio TL and the rich air-fuel ratio TR is shifted to the lean side by a predetermined value (step S15b). This makes it possible to prevent the detected air-fuel ratio AFb from becoming excessively rich during the lean correction again, which would cause emissions to deteriorate. In this embodiment, the lean air-fuel ratio TL and the rich air-fuel ratio TR are each changed to the lean side by the same value. If the answer is No in step S14b, this control ends. If the answer is No in step S12b, the rich integrated intake air amount RAI is reset to zero (step S16b).

[0029] 4 is a timing chart illustrating the correction switching control and the learning control, which shows the transitions of the detected air-fuel ratio AFa, the oxygen storage amount OSA, the detected air-fuel ratio AFb, and the lean cumulative intake air amount LAI.

[0030] If the oxygen storage amount OSA becomes less than the target lower limit OL during the rich correction and the detected air-fuel ratio AFb becomes less than the rich end judgment value SL, the system switches to lean correction and the detected air-fuel ratio AFa becomes the lean air-fuel ratio TL (time t1). If the oxygen storage amount OSA becomes greater than the target upper limit OU during the lean correction and the detected air-fuel ratio AFb becomes greater than the lean end judgment value SR, the system switches to rich correction and the detected air-fuel ratio AFa becomes the rich air-fuel ratio TR (time t2).

[0031] When the detected air-fuel ratio AFb becomes larger than the excessive lean determination value EL, calculation of the lean accumulated intake air amount LAI is started (time t3). During the rich correction, even if the oxygen storage amount OSA becomes smaller than the target lower limit value OL, if the detected air-fuel ratio AFb is larger than the rich end determination value SL, the rich correction is continued (time t4).

[0032] Thereafter, if the detected air-fuel ratio AFb does not decrease and the lean accumulated intake air amount LAI becomes larger than the threshold value, the lean air-fuel ratio TL and the rich air-fuel ratio TR are changed to the rich side and learning is performed (time t5). Also, the lean accumulated intake air amount LAI is reset and calculation is started again (time t5). If the detected air-fuel ratio AFb becomes less than the excessively lean determination value EL, the lean accumulated intake air amount LAI is reset (time t6).

[0033] When the detected air-fuel ratio AFb becomes less than the rich end determination value SL, the control is switched from rich correction to lean correction, and the detected air-fuel ratio AFa is controlled to the learned lean air-fuel ratio TL (time t7). If the oxygen storage amount OSA becomes greater than the target upper limit value OU during the lean correction and the detected air-fuel ratio AFb becomes greater than the lean end determination value SR, the control is switched to rich correction, and the detected air-fuel ratio AFa is controlled to the learned rich air-fuel ratio TR (time t8). If the oxygen storage amount OSA becomes less than the target lower limit value OL during the rich correction and the detected air-fuel ratio AFb is less than the rich end determination value SL, the control is switched to lean correction, and the detected air-fuel ratio AFa is controlled to the learned lean air-fuel ratio TL (time t9).

[0034] In this way, the lean air-fuel ratio TL and the rich air-fuel ratio TR are changed to the rich side, and the changed lean air-fuel ratio TL and rich air-fuel ratio TR are learned. Therefore, it is possible to prevent the detected air-fuel ratio AFb from becoming excessively lean again during the rich correction, thereby preventing emissions from deteriorating.

[0035] In the above embodiment, the case where both the lean air-fuel ratio TL and the rich air-fuel ratio TR are changed to the rich side or the lean side has been described. However, only one of the lean air-fuel ratio TL and the rich air-fuel ratio TR may be changed to the rich side or the lean side. Furthermore, the amount by which the lean air-fuel ratio TL is changed and the amount by which the rich air-fuel ratio TR is changed may be the same or different.

[0036] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0037] 10 Engine 50 ECU (controller, correction switching unit, calculation unit, learning unit, estimation unit)

Claims

1. The engine and a catalyst having an oxygen storage capacity disposed in an exhaust passage of the engine; first and second sensors disposed in the exhaust passage upstream and downstream of the catalyst, respectively, for detecting first and second detected air-fuel ratios, which are the air-fuel ratios of the exhaust gas; a control device that alternately switches between a rich correction that corrects the air-fuel ratio of the engine so that the first detected air-fuel ratio becomes a predetermined rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, and a lean correction that corrects the air-fuel ratio of the engine so that the first detected air-fuel ratio becomes a predetermined lean air-fuel ratio that is larger than the stoichiometric air-fuel ratio, The control device a correction switching unit that switches to the lean correction when the second detected air-fuel ratio becomes less than a rich end determination value that is greater than the stoichiometric air-fuel ratio during the rich correction, and that switches to the rich correction when the second detected air-fuel ratio becomes greater than a lean end determination value that is less than the stoichiometric air-fuel ratio during the lean correction; a calculation unit that calculates an integrated value of an intake air amount of the engine when the second detected air-fuel ratio is greater than an excessively lean determination value that is greater than the rich end determination value during the rich correction; a learning unit that, when the integrated value is greater than a threshold value, changes and learns at least one of the rich air-fuel ratio and the lean air-fuel ratio so that a central value between the rich air-fuel ratio and the lean air-fuel ratio shifts to the rich side; the control device includes an estimation unit that estimates an oxygen storage amount of the catalyst, the correction switching unit switches to the lean correction when the second detected air-fuel ratio becomes less than the rich end determination value during the rich correction and the oxygen storage amount is less than a target lower limit value, and switches to the rich correction when the second detected air-fuel ratio becomes greater than the lean end determination value during the lean correction and the oxygen storage amount is greater than a target upper limit value, the estimation unit estimates the oxygen storage amount based on the first detected air-fuel ratio and an intake air amount of the engine, The control device calculates the intake air amount based on a detection value of an air flow meter.

2. The engine and a catalyst having an oxygen storage capacity disposed in an exhaust passage of the engine; first and second sensors disposed in the exhaust passage upstream and downstream of the catalyst, respectively, for detecting first and second detected air-fuel ratios, which are the air-fuel ratios of the exhaust gas; a control device that alternately switches between a rich correction that corrects the air-fuel ratio of the engine so that the first detected air-fuel ratio becomes a predetermined rich air-fuel ratio that is smaller than the stoichiometric air-fuel ratio, and a lean correction that corrects the air-fuel ratio of the engine so that the first detected air-fuel ratio becomes a predetermined lean air-fuel ratio that is larger than the stoichiometric air-fuel ratio, The control device a correction switching unit that switches to the lean correction when the second detected air-fuel ratio becomes less than a rich end determination value that is greater than the stoichiometric air-fuel ratio during the rich correction, and that switches to the rich correction when the second detected air-fuel ratio becomes greater than a lean end determination value that is less than the stoichiometric air-fuel ratio during the lean correction; a calculation unit that calculates an integrated value of an intake air amount of the engine when the second detected air-fuel ratio is smaller than an excessively rich determination value that is smaller than the lean end determination value during the lean correction; a learning unit that, when the integrated value is greater than a threshold value, changes and learns at least one of the rich air-fuel ratio and the lean air-fuel ratio so that a central value between the rich air-fuel ratio and the lean air-fuel ratio shifts to the lean side; the control device includes an estimation unit that estimates an oxygen storage amount of the catalyst, the correction switching unit switches to the lean correction when the second detected air-fuel ratio becomes less than the rich end determination value during the rich correction and the oxygen storage amount is less than a target lower limit value, and switches to the rich correction when the second detected air-fuel ratio becomes greater than the lean end determination value during the lean correction and the oxygen storage amount is greater than a target upper limit value, the estimation unit estimates the oxygen storage amount based on the first detected air-fuel ratio and an intake air amount of the engine, The control device calculates the intake air amount based on a detection value of an air flow meter.

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