EXHAUST PURIFICATION SYSTEM FOR INTERNAL COMBUSTION ENGINE

Abstract

Exhaust gas purification system (100) for an internal combustion engine (10), comprising: a particulate filter (24) which is arranged in an exhaust stream (14) of the internal combustion engine (10) and serves to collect particles in the exhaust gas; an automatic transmission (26) which includes a torque converter (28) with a lock-up clutch (29); and a control unit (30) that controls the internal combustion engine (10) to perform a fuel interruption when the internal combustion engine (10) decelerates and a temperature correlation value of the lubricating oil of the automatic transmission (26) is higher than a specified value, and that controls the automatic transmission (26) to engage the lock-up clutch (29) during the execution of the fuel interruption, wherein the controller (30) is configured to include: a deposition estimation unit (312) for estimating the amount of particles deposited on the particle filter (24); and a determination value change unit (314) which, when the deposit quantity exceeds a predetermined first deposit quantity, changes the determination value to a smaller value than before the first deposit quantity was exceeded, wherein the control (30) further comprises an air-fuel ratio control unit (316) to change, when the deposit quantity exceeds a second deposit quantity which is larger than the first deposit quantity, a target air-fuel ratio of the internal combustion engine (10) to a leaner air-fuel ratio than before the second deposit quantity was exceeded.

Description

BACKGROUND OF THE INVENTION AREA

[0001] The present disclosure relates to an exhaust gas purification system for an internal combustion engine and in particular to an exhaust gas purification system for an internal combustion engine with a particulate filter for collecting particles. background

[0002] To improve the fuel economy of an internal combustion engine-powered vehicle, a fuel cut-off is sometimes performed to stop fuel injection when the vehicle decelerates. During the fuel cut-off, the internal combustion engine can stall due to a decrease in the output shaft speed. In the technology described in JP 2008-025376A, in a vehicle equipped with a lock-up torque converter, the lock-up clutch is controlled to an engaged or partially engaged state during a fuel cut-off to prevent stalling.

[0003] DE 10 2014 006 692 A1 discloses a method for regenerating a particulate filter in a gasoline engine, preferably with direct injection. The method is implemented in the engine control unit of a vehicle and employs a multi-stage regeneration strategy. This strategy includes determining the soot content in the particulate filter, testing various regeneration strategies, at least one of which is passive, and subsequently regenerating the filter using the selected strategy. A vehicle implementing this method is also disclosed. SUMMARY

[0004] Some gasoline engines with stoichiometric combustion are equipped with a gasoline particulate filter (also known as a gasoline particulate filter or OPF) in the exhaust system. The OPF collects particles (also known as fine dust) emitted by combustion engines, thus preventing fine dust from escaping the OPF. During a regeneration process to remove fine dust deposited on the OPF, it is necessary to increase the OPF's temperature and supply it with oxygen. In a gasoline engine, OPF regeneration is primarily performed during a fuel interruption, at which point oxygen is supplied to the OPF.

[0005] During a fuel cut-off, it is necessary to engage the automatic transmission's lock-up clutch to prevent the engine from stalling. However, the lock-up clutch cannot always be engaged. This is because engaging the lock-up clutch can cause vibrations, known as shuddering, when the automatic transmission fluid (ATF) temperature is extremely low (for example, -10°C). Therefore, under conditions where lock-up clutch engagement is limited, such as when the ATF temperature is extremely low, the fuel cut-off procedure is also limited.

[0006] Fine particulate matter is emitted particularly easily when the combustion engine is cold. Therefore, under conditions where combustion engines are frequently operated for short periods (for short trips), such as in extremely cold environments, the OPF (Otto Particulate Filter) may not have sufficient opportunity for the regeneration process, and the amount of fine particulate matter deposited can increase. As the amount of fine particulate matter deposited in the OPF increases, the exhaust pressure rises due to the increased pressure drop, leading to a deterioration in combustion or reduced fuel efficiency of the combustion engine.

[0007] The present disclosure was made with regard to the above problems and its aim is to provide an exhaust gas purification system for an internal combustion engine with an OPF with a particulate matter collection function, which can prevent an increase in the amount of particulate matter deposited by increasing the regeneration capability of the OPF.

[0008] The object of the present disclosure is solved by an exhaust gas purification system for an internal combustion engine according to independent claim 1.

[0009] To solve the aforementioned problems, the first aspect of the disclosure is applied to an exhaust aftertreatment system of an internal combustion engine. The exhaust aftertreatment system includes a particulate filter located in the exhaust stream of the internal combustion engine to collect particles in the exhaust gas, an automatic transmission including a torque converter with a lock-up clutch, and a control unit that directs the internal combustion engine to perform a fuel cut-off when the engine decelerates / slows down and the temperature correlation value of the automatic transmission's lubricating oil is higher than a specified value, and that directs the automatic transmission to engage the lock-up clutch during the fuel cut-off.The control unit is configured to include a deposit estimation unit for estimating the amount of particles deposited on the particulate filter, and a setpoint adjustment unit that, if the deposit amount exceeds a predetermined initial deposit amount, adjusts the setpoint to a lower value than before the initial deposit amount was exceeded. The control unit also includes an air-fuel ratio control unit that, if the deposit amount exceeds a second deposit amount that is larger than the initial deposit amount, adjusts the target air-fuel ratio of the combustion engine to a leaner air-fuel ratio than before the deposit amount exceeded the second deposit amount.

[0010] The second aspect of the disclosure further exhibits the following characteristics. The air-fuel ratio control unit is designed to prevent a change in the target air-fuel ratio to a lean air-fuel ratio when the intake air quantity of the internal combustion engine is greater than a predetermined target air quantity.

[0011] The third aspect of the disclosure has the following characteristics. The air-fuel ratio control unit is designed to change the target air-fuel ratio of the internal combustion engine to a lean air-fuel ratio within a range that does not reach the combustion variation limit of the internal combustion engine.

[0012] The fourth aspect of the disclosure has the following characteristics. The air-fuel ratio control unit is configured to change the target air-fuel ratio to a lean air-fuel ratio when the (cooling) water temperature of the internal combustion engine is higher.

[0013] According to one aspect of the revelation, if the amount of particulate matter deposited on the particulate filter is increased, it is possible to increase the likelihood of performing a fuel cut-off during deceleration. This, in turn, increases the possibility of regenerating the particulate filter, thereby preventing a further increase in the amount of particulate matter deposited.

[0014] According to the first aspect of the revelation, it is possible to improve the regeneration performance of the particulate filter by changing the target air-fuel ratio to a lean air-fuel ratio.

[0015] According to the second aspect of the disclosure, if the intake air volume is greater than the specified air volume, changing the target air-fuel ratio to a lean air-fuel ratio is prohibited. This prevents an increase in the amount of NOx emitted.

[0016] Furthermore, according to the aspect of the third disclosure, it can be prevented that the lean air-fuel ratio is controlled beyond the combustion fluctuation limit of the internal combustion engine.

[0017] Furthermore, according to the fourth aspect of the revelation, it is possible to optimize the lean air-fuel ratio depending on the (cooling) water temperature. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram illustrating a configuration of an exhaust gas purification system according to a first embodiment; Fig. 2 is a diagram showing the functional blocks of an ECU; Fig. Figure 3 is a flowchart showing a routine of a delay fuel interruption control system as implemented in the first embodiment; Fig. Figure 4 is a time diagram to illustrate the difference in OPF regeneration performance depending on whether a process for changing the permissible oil temperature is carried out to bridge the delay; Fig. 5 is a flowchart showing a control routine of a particulate matter deposition quantity estimation process that is executed in the ECU; Fig. Figure 6 is a diagram showing an example of a particulate matter emission map that defines an estimated deposit amount for engine speed NE and engine load KL; Fig. Figure 7 is a diagram that shows an example of an air-fuel ratio correction map for calculating a correction coefficient of an estimated deposit quantity in relation to an air-fuel ratio; Fig. Figure 8 is a diagram that shows an example of a water temperature correction map for calculating a correction coefficient of an estimated deposit amount in relation to the engine water temperature (cooling water temperature); Fig. Figure 9 is a diagram showing an example of a regeneration quantity characteristic curve for calculating an estimated regeneration quantity; Fig. Figure 10 is a flowchart showing a routine of a process for changing the permissible oil temperature, which is carried out by the exhaust gas purification system according to the first embodiment; Fig. Figure 11 is a diagram showing a relationship between the amount of regeneration and the amount of particulate matter deposited in the OPF for each air-fuel ratio; Fig. Figure 12 is a diagram showing a relationship between combustion variation and the amount of NOx emitted in relation to the air-fuel ratio; Fig. Figure 13 is a time diagram to illustrate the difference in the changes in the amount of NOx emitted and the OPF bed temperature according to the implementation time of the lean air-fuel ratio control of a second embodiment; Fig. 14 is a flowchart of a control routine that is executed in the exhaust gas purification system according to the second embodiment; and Fig. Figure 15 is a diagram that defines a relationship between the target air-fuel ratio and the engine water temperature. DETAILED DESCRIPTION

[0018] Embodiments of the present disclosure are described below with reference to the accompanying drawings. It should be understood, however, that even if the number, quantity, amount, range, or other numerical attribute of each element is mentioned in the following description of the embodiment, the present disclosure is not limited to the mentioned numerical attribute unless expressly described otherwise or the present disclosure is expressly specified theoretically by the numerical attribute. Furthermore, structures, steps, or the like described in connection with the following embodiment are not necessarily essential to the present disclosure unless explicitly described otherwise or the present disclosure is explicitly specified theoretically by the structures, steps, or the like. 1. First embodiment

[0019] The first embodiment is described with reference to the drawings. 1-1. Configuration of the first embodiment

[0020] Fig. Figure 1 is a diagram illustrating a configuration of an exhaust gas purification system according to the first embodiment. As shown in Fig. Figure 1 shows an exhaust gas purification system 100 of the present embodiment comprising an internal combustion engine 10 (also simply referred to as the engine). The engine 10 is mounted on / in a vehicle as a power source. The engine 10 is a gasoline engine based on stoichiometric combustion. The engine 10 is equipped with four cylinders in a row, with an injector 8 provided for each cylinder. The engine 10 is connected to an intake manifold and an exhaust manifold (not shown). The intake manifold is connected to an intake port 12 to supply intake air to the engine 10. The exhaust manifold is connected to an exhaust system 14 to discharge exhaust gases from the engine 10 into the atmosphere.

[0021] An air flow meter 16 for measuring the intake air volume is located in the center of the intake duct 12. A throttle valve 18 is located on the intake side downstream of the air flow meter 16 in the intake duct 12. A start converter / start catalyst (also referred to as S / C) 22, which is a three-way catalyst, is located in the exhaust system 14. A particulate filter (also referred to as OPF) 24 is located on the exhaust side downstream of the start converter 22 in the exhaust system 14. The OPF 24 collects the particles emitted by the engine 10.

[0022] A crankshaft of the engine 10 is connected to an input shaft of an automatic transmission 26 via a torque converter 28. The torque converter 28 includes a lock-up clutch 29 to directly couple an output shaft of the engine 10 to the input shaft of the automatic transmission 26.

[0023] The exhaust gas purification system 100 according to the present embodiment includes an ECU (also referred to as electronic control unit) 30. The ECU 30 is a control unit for the comprehensive control of the entire exhaust gas purification system and the control is designed as a function of the ECU 30 according to the present disclosure.

[0024] The ECU 30 has at least one input / output interface, a ROM, a RAM, and a CPU. The input / output interface receives signals from sensors provided in the exhaust aftertreatment system 100 and outputs operating signals to actuators provided in the engine 10. The sensors are located at various points in the exhaust aftertreatment system 100. An air-fuel ratio sensor 40 for measuring the air-fuel ratio (A / F) of the exhaust gas is located on the upstream side of the starter converter 22 in the exhaust stream 14. An exhaust gas temperature sensor 38 for measuring the bed temperature of the OPF 24 is located on the upstream side of the OPF 24 in the exhaust stream 14.Furthermore, a speed sensor 32 for detecting the engine speed NE of engine 10, a (cooling) water temperature sensor 34 for detecting the engine water temperature / cooling water temperature thw of engine 10, an oil temperature sensor 36 for detecting the temperature of the lubricating oil (ATF) of the automatic transmission 26 (ATF temperature), and the like are arranged. The ECU 30 processes the detected signals from the respective sensors and controls the respective actuators according to predefined control programs.

[0025] The actuator operated by the ECU 30 includes the injector 8, the throttle valve 18, the lock-up clutch 29 of the torque converter 28, and similar components. The ROM stores various control data, including different control programs and maps for controlling the engine 10. The CPU reads one or more control programs from the ROM and executes them, generating one or more operating signals based on the input sensor signal. Many more actuators and sensors are connected to the ECU 30 than shown in the drawing, but their descriptions are omitted from the specification.

[0026] Fig. Figure 2 is a diagram showing the functional blocks of the ECU. The ECU 30 contains a delay fuel interruption control unit 310, a deposit quantity estimation unit 312, a permissible oil temperature change unit for delay bridging 314, and an air-fuel ratio control unit 316 as functional blocks for controlling the exhaust aftertreatment system 100. The processing carried out in each functional block is described in detail below. 1-2. Basic Functioning of the Exhaust Gas Purification System of the First Embodiment 1-2-1. Delay Fuel Interruption Control

[0027] The control of the engine 10, which is carried out by the ECU 30 of the exhaust aftertreatment system 100, includes a delay fuel cut-off control. The delay fuel cut-off control is implemented in the delay fuel cut-off control unit 310 of the ECU 30. In the delay fuel cut-off control of the present embodiment, if a predetermined operating condition is met during deceleration of the vehicle in which the engine 10 is installed, the fuel injection from the injector 8 is stopped for the purpose of improving fuel consumption.

[0028] However, since the rotational speed of the output shaft of engine 10 decreases during deceleration, there is a possibility that engine 10 will stall. Therefore, the ECU 30 controls the lock-up clutch 29 of the torque converter 28 to the engaged state during the deceleration fuel interruption. Because the output shaft of engine 10 is forcibly rotated by the vehicle's output shaft during the deceleration fuel interruption, engine 10 is prevented from stalling.

[0029] The operating conditions for the deceleration fuel cut-off include the vehicle decelerating and the ability to engage the lock-up clutch 29. Typically, the ECU 30 allows the lock-up clutch 29 to engage if the ATF temperature, i.e., the oil temperature of the automatic transmission 26's lubricating oil, is higher than a predetermined oil temperature permissible for deceleration lock-up during vehicle deceleration, and prevents the lock-up clutch 29 from engaging if the ATF temperature is lower than the predetermined oil temperature permissible for deceleration lock-up. The permissible oil temperature for deceleration lock-up is a determining factor to establish whether or not the lock-up clutch 29 is allowed to engage. Engaging the lock-up clutch 29 in an extremely cold environment can lead to an unacceptable deterioration in drivability due to jerking.Therefore, the permissible oil temperature for bridging the deceleration is set to the lower limit temperature that is acceptable, for example, from the perspective of drivability. This prevents the engine stalling during the deceleration interruption and also prevents the deterioration of driving characteristics due to the jerking phenomenon. 1-2-2. Specific process of controlling the delay fuel interruption control

[0030] Next, a specific process of delay fuel interruption control, which is implemented in the exhaust gas purification system 100 according to the first embodiment, is described with reference to a flowchart. Fig. Figure 3 is a flowchart showing a routine of the delay fuel interruption control, which is implemented in the first embodiment. The in Fig. The routine shown in Figure 3 is executed repeatedly by the ECU 30 in a predetermined control cycle during the operation of the engine 10.

[0031] In step S100 of the in Fig. The routine shown in step 3 determines whether the vehicle is decelerating with engine 10. If the vehicle is decelerating, the process continues with step S102; if the vehicle is not decelerating, the routine terminates.

[0032] In step S102, it is determined whether the ATF temperature is higher than the predetermined oil temperature permissible for the delay bridging. If the condition is not met, the process proceeds to step S104, and the bridging clutch 29 is held in a disengaged / open state (also referred to as "bridging OFF"). Once step S104 is complete, the current routine terminates.

[0033] On the other hand, if the condition in step S102 is met, the process proceeds to step S106, where the bypass clutch 29 is engaged (also referred to as "bypass ON"). Once the process in step S106 is complete, the process continues to step S108. In step S108, the fuel cut-off is performed. When the operation of step S108 is complete, the current routine is terminated. 1-2-3. Fine dust collection and regeneration process of the OPF

[0034] The OPF 24 collects the particulate matter contained in the exhaust gas emitted by the engine 10. The collected particulate matter accumulates in the OPF 24. To continuously collect particulate matter in the OPF 24, a regeneration process is required to remove the accumulated particulate matter and restore its collection capacity. This regeneration process involves passively burning off the collected particles by exposing the OPF 24 to a high temperature and a lean atmosphere. In gasoline engines based on stoichiometric combustion, the heat from the exhaust gas during normal operation can be used to raise the temperature of the OPF 24 to a level at which the regeneration process can be performed. Furthermore, the lean atmospheres in the OPF 24 are typically achieved during the engine 10's deceleration fuel cut-off.This means that the regeneration process of the OPF 24 is carried out passively during the retarding fuel interruption, after the OPF 24 has warmed up. 1-3. Characteristic operation of the exhaust gas purification system of the first embodiment 1-3-1. Description of the process for changing the permissible oil temperature for delay bridging

[0035] Next, a process for changing the permissible oil temperature for delay bridging is described, which is a characteristic process of the exhaust gas purification system according to the first embodiment. During the period from engine start until the cylinder walls and other parts have warmed up, the engine 10 emits a large amount of particulate matter. The amount of particulate matter emissions tends to increase with lower cylinder wall temperatures. In particular, in extremely cold environments where the ambient temperature is below 0 °C, particulate matter emissions tend to increase exponentially.

[0036] In such an extremely cold environment, a situation is assumed in which the engine 10 repeatedly performs short trips. Since the OPF 24 is located in the exhaust system 14, it is warmed to the operating temperature at which the regeneration process is possible even during a cold start in an extremely cold environment. However, the ATF lubricating the automatic transmission 26 tends to have a slower temperature rise than the OPF 24. Therefore, in a situation where the engine 10 repeatedly performs short trips in the extremely cold environment, the ATF temperature may not reach the permissible oil temperature for the delay bypass, and there is a possibility that the delay fuel interruption will not be sufficiently effective. If the accumulated amount of particulate matter continues to be greater than the amount of particulate matter regenerated in the OPF 24, the amount of particulate matter deposited in the OPF 24 will continue to increase.Excessive fine dust deposition in the OPF 24 leads to a deterioration of combustion and a deterioration of fuel consumption / fuel efficiency due to the increase in exhaust pressure.

[0037] Therefore, the exhaust gas purification system 100 of the present embodiment is characterized in that the process for changing the permissible oil temperature is carried out in accordance with the amount of particulate matter deposited in the OPF 24. Typically, the deposit amount estimation unit 312 of the ECU 30 estimates the amount of particulate matter deposited in the OPF 24 based on the operating state of the engine 10. Then, the unit for changing the permissible oil temperature for deceleration bridging 314 of the ECU 30 changes the permissible oil temperature for deceleration bridging as a determined value during vehicle deceleration to a lower value than the normal value if the estimated deposit amount, which is the estimated amount of particulate matter deposited, is greater than a predetermined threshold value A.The unit for changing the permissible oil temperature for the delay bridge 314 is also referred to as the "determination value change unit" because it changes the permissible oil temperature for the delay bridge as a determination value. The threshold value A is an experimentally or simulation-determined value for the amount of particulate matter deposited that can lead to a deterioration of the combustion of the engine 10. The threshold value A is also referred to as the first deposit amount. According to such control, it is possible to increase the possibility of carrying out moderate fuel interruption in extreme cold, and it is expected that the amount of particulate matter deposited will be reduced by the regeneration process of the OPF 24.

[0038] Fig. Figure 4 is a time diagram illustrating the difference in OPF regeneration performance depending on whether the process for changing the permissible oil temperature is used to bridge the delay. Fig. Figure 4 shows (a) the time course of the bed temperature of OPF 24. (b) in Fig. Figure 4 shows the time course of the vehicle speed of the vehicle with engine 10. (c) in Fig. 4 shows whether the fuel cut-off is executed if the permissible oil temperature for delay bridging is not reduced. (d) in Fig. Figure 4 shows the time course of the amount of particulate matter deposited in the OPF 24 when the permissible oil temperature for bridging the delay was not reduced. (e) in Fig. Figure 4 shows the time course of the ATF temperature, and (f) in Fig. Figure 4 shows whether the fuel cut-off is executed when the permissible oil temperature for delay bridging is reduced. Fig. Figure 4 (g) shows the time course of the amount of fine dust deposited in the OPF 24 when the permissible oil temperature for bridging the delay is reduced.

[0039] As in (e) of Fig. As shown in Figure 4, the ATF temperature reaches the permissible oil temperature for the delay bridging at time t2 if, for example, the process to change the permissible oil temperature is not carried out. In this case, as shown in (e) of Fig. As shown in Figure 4, the regeneration process of the OPF 24 is also carried out after time t2, since a possibility of executing the delay fuel interruption after time t2 is maintained. Consequently, as shown in (d) of Fig. Figure 4 shows that the amount of fine dust deposits continues to increase until time t2, and consequently the possibility of carrying out the regeneration process is lost.

[0040] In contrast, as in (e) in Fig. As shown in Figure 4, the ATF temperature is the permissible oil temperature for delay bridging at an earlier time t1 than time t2 if the permissible oil temperature for delay bridging is reduced, for example, by the process of changing the permissible oil temperature. In this case, as shown in (f) of Fig. As shown in Figure 4, the regeneration process of the OPF 24 also takes place after time t1, since there is a possibility of performing the delay fuel interruption after time t1. As a result, as shown in (g) of Fig. 4 shows that the amount of particulate matter deposited decreases from time t3 onwards, and the final amount of particulate matter deposited is lower than that shown in (d). Fig. The amount of fine dust deposits shown in section 4 has been significantly reduced.

[0041] If the engine is started in an extremely cold environment, the OPF 24 regeneration process can be initiated at an early stage after the process of changing the permissible oil temperature. This makes it possible to reduce the amount of particulate matter deposited in the OPF 24 and prevent a deterioration in combustion and increased fuel consumption of the engine 10. 1-3-2. Specific process of the change process of the permissible oil temperature for delay bridging

[0042] In the OPF 24, particulate matter collection and removal are performed simultaneously through the regeneration process. The deposit quantity estimation unit 312 of the ECU 30 continuously calculates an estimated total deposit quantity during engine 10 operation, which is an estimate of the total amount of particulate matter deposited in the OPF 24. First, a deposit quantity estimation process in the OPF 24 is described, before the specific process of changing the permissible oil temperature for delay bridging is explained. 1-3-3. Deposit volume estimation process

[0043] Fig. Figure 5 is a flowchart showing a control routine of the particulate matter deposition quantity estimation process, which is executed in the ECU 30. The in Fig. The control routine shown in Figure 5 is executed repeatedly in a predetermined control cycle during the operation of the motor 10.

[0044] In step S120 of the in Fig. In the control routine shown in section 5, the estimated amount of particulate matter newly deposited in the OPF 24 is calculated in the present control routine. Fig. Figure 6 is a diagram showing an example of a particulate matter emission map that defines an estimated deposit amount for engine speed NE and engine load KL. Here, using the [reference to be inserted], Fig. The estimated amount of deposits is calculated according to the current engine speed NE and the current engine load KL of engine 10 in the fine dust emission map shown in Figure 6.

[0045] In the next step S122, the estimated deposit amount calculated in the procedure of step S120 is corrected using the air-fuel ratio. Fig. Figure 7 is a diagram showing an example of an air-fuel ratio correction map for calculating a correction coefficient for an estimated amount of particulate matter in relation to an air-fuel ratio. The leaner the air-fuel ratio of the engine 10, the lower the amount of particulate matter released into the exhaust stream 14. Therefore, the air-fuel ratio correction coefficient Kaf is calculated as a value that decreases as the air-fuel ratio becomes leaner. Here, using the one in Fig. The air-fuel ratio correction coefficient Kaf, shown in Figure 7, is calculated using the air-fuel ratio correction map. This coefficient corresponds to the current air-fuel ratio detected by the air-fuel ratio sensor 40. The estimated amount of deposits after correction is then calculated by multiplying the estimated amount of deposits calculated in the procedure of step S120 by the air-fuel ratio correction coefficient Kaf.

[0046] In the next step S124, the estimated amount of deposits calculated in the process of step S122 is further corrected by the engine water temperature (cooling water temperature). Fig. Figure 8 is a diagram showing an example of a water temperature correction map for calculating a correction coefficient for an estimated amount of particulate matter in relation to the engine water temperature. The higher the engine water temperature thw of the engine 10, the lower the amount of particulate matter released into the exhaust system 14. Therefore, the water temperature correction coefficient Kthw is calculated as a value that decreases as the engine water temperature increases. Here, using the one in Fig. The water temperature correction coefficient Kthw is calculated from the water temperature correction map shown in Figure 8. This coefficient corresponds to the current engine water temperature thw as measured by water temperature sensor 34. The estimated amount of deposits after correction is then calculated by multiplying the estimated amount of deposits calculated in step S122 by the water temperature correction coefficient Kthw.

[0047] In the next step, S126, it is determined whether the OPF bed temperature of OPF 24 is higher than a predetermined bed temperature threshold. The predetermined bed temperature threshold is a predefined value representing the lower limit of the bed temperature at which the regeneration process in OPF 24 is performed. If the condition is not met, the estimated regeneration quantity, which is the estimated value of the regeneration quantity in OPF 24, is 0 (zero), and the process proceeds to step S130. Conversely, if the condition in step S126 is met, the process continues with step S128.

[0048] In step S128, the estimated regeneration quantity in the OPF 24 is calculated. Fig. Figure 9 is a diagram showing an example of a regeneration quantity map for calculating an estimated regeneration quantity. The greater the amount of particulate matter deposited in the OPF 24, the greater the regeneration quantity in the OPF 24. The higher the bed temperature of the OPF 24, the greater the regeneration quantity in the OPF 24. Furthermore, the leaner the air-fuel ratio of the exhaust air flowing into the OPF 24, the greater the regeneration quantity in the OPF 24. This is shown in Fig. The regeneration quantity map shown in Figure 9 relates the regeneration quantity in the OPF 24 to the amount of particulate matter deposited in the OPF 24, the bed temperature of the OPF 24, and the air-fuel ratio of the exhaust gas. Here, the estimated total deposit quantity, calculated in the previous routine, is used to calculate the regeneration quantity corresponding to the bed temperature of the OPF 24 as measured by the exhaust gas temperature sensor 38, from the regeneration quantity map. Once the process of step S128 is complete, the process continues with step S130.

[0049] In step S130, the final estimated deposit amount is calculated in the routine by subtracting the estimated regeneration amount calculated in step S128 from the estimated deposit amount calculated in step S124. In the next step, S132, a current value of the estimated total deposit amount in OPF 24 is calculated. This is done by adding the estimated deposit amount calculated in step S130 of the current routine to a previous value of the estimated total deposit amount calculated in the previous routine. 1-3-4. Change process of the permissible oil temperature for delay bridging

[0050] Next, the process for changing the permissible oil temperature for the delay bridging function is described. This process is performed by the ECU 30's permissible oil temperature change unit 314. Fig. Figure 10 is a flowchart showing a routine of the permissible oil temperature change process performed by the exhaust gas purification system according to the first embodiment. The in Fig. The control routine shown in section 10 is executed repeatedly during the operation of motor 10 in a predefined control cycle. In step S140 of the [section / routine] Fig. In step 10, it is determined that MODE = 0. The permissible oil temperature for the delay bridging is then set either to "Töl_normal", which is a normal permissible oil temperature for the delay bridging, or to "Töl_niedrig", which is lower than "Töl_normal". "MODE" is an indicator used to determine the currently set permissible oil temperature for the delay bridging. If MODE = 0, the permissible oil temperature for the delay bridging is set to Töl_normal, and if MODE = 1, the permissible oil temperature for the delay bridging is set to Töl_niedrig. As a result of the determination in step S140, if MODE = 0, the process continues with step S142.

[0051] In the next step, S142, it is determined whether the estimated total deposit amount, as determined in the particulate matter deposit amount estimation process, is greater than a threshold value A. If the result shows that the threshold is not met, the process proceeds to step S154, and the permissible oil temperature for the delay bridging is maintained at Töl_normal.

[0052] If, on the other hand, step S142 determines that the condition is met, the process continues with step S144. In step S144, MODE is set to 1 and the process continues with step S146. In step S146, the permissible oil temperature for bridging the delay is set to Töl_low.

[0053] If MODUS in the determination of step S140 is not 0, the current allowable oil temperature for delay bridging has been set to Töl_low. In this case, the process proceeds to step S150 and determines whether the estimated total deposit amount, as estimated in the particulate matter deposit amount estimation process, is greater than a threshold value C. Threshold C is a threshold for the estimated total deposit amount to prevent self-regulation of the allowable oil temperature for delay bridging and is set to a value adjacent to threshold A. If the determination is met, the process proceeds to step S146 and the allowable oil temperature for delay bridging is maintained at Töl_low. Conversely, if the determination in step S150 is not met, the process proceeds to step S152.

[0054] In step S152, MODE is set to 0 and the process continues with step S154. In step S154, the permissible oil temperature for bridging the delay is set to Töl_normal.

[0055] As described above, according to the method for changing the permissible oil temperature, which is implemented in the exhaust aftertreatment system 100 of the first embodiment, the permissible oil temperature for delay bridging is changed in accordance with the estimated total deposit amount in the OPF 24. This makes it possible to start the regeneration process of the OPF 24 at an early stage, since the possibility of delay fuel interruption can be maintained at an early stage when the engine is started in an extremely cold environment. 1-4. Modification of the system of the first embodiment

[0056] The exhaust gas purification system 100 according to the first embodiment can assume a modified configuration, which is described below.

[0057] The specific method of the deposit quantity estimation process is not limited. That is, the estimated total amount of particulate matter deposited in the OPF 24 can be calculated using another known method, such as one that uses a differential pressure between the front and back of the OPF 24. This modification can be similarly applied to the exhaust gas purification system of the second embodiment described later.

[0058] In the process of changing the permissible oil temperature for the delay bypass, the permissible oil temperature for the delay bypass can be changed in three or more stages according to the estimated total amount of accumulated particulate matter in the OPF 24. According to such a configuration, since the setting of the permissible oil temperature for the delay bypass is more finely subdivided according to the amount of particulate matter deposited in the OPF 24, it is possible to optimize both the suppression of excessive particulate matter deposition and driving performance.

[0059] The process for changing the permissible oil temperature for the lock-up clutch is designed to modify the permissible oil temperature during vehicle deceleration and does not include any modification of the permissible oil temperature during deceleration outside of deceleration. Therefore, the setting of the permissible oil temperature outside of deceleration is not limited; it can, for example, be set to a fixed value (e.g., Töl_normal) regardless of the amount of particulate matter deposited. When the lock-up clutch 29 is disengaged, more work is required from the engine 10 due to the lower transmission efficiency compared to the engaged state. Therefore, according to such a configuration, it is possible to limit the engagement of the lock-up clutch 29 outside of deceleration until the ATF oil temperature exceeds Töl_normal.This makes it possible to promote an increase in exhaust gas temperature, which contributes to early warming of the OPF 24. This modification can be applied similarly to the exhaust gas purification system of the second embodiment described later.

[0060] The authorization setting for the bypassing of the bypass clutch 29 is not limited to control via the ATF temperature, and other values ​​that correlate with the ATF temperature can also be used. Such temperature correlation values ​​include, for example, the engine coolant temperature of the engine 10, the oil temperature of the engine oil used to lubricate the interior of the engine 10, and the like. This modification can be applied similarly to the exhaust gas purification system of the second embodiment described later. 2. Second embodiment

[0061] Next, an exhaust gas purification system according to a second embodiment will be described. 2-1. Configuration of the exhaust gas purification system according to the second embodiment

[0062] The configuration of the exhaust gas purification system according to the second embodiment is the same as that of the exhaust gas purification system 100 of the first embodiment, which is described in Fig. Figure 1 is shown. Therefore, a detailed description of the exhaust gas purification system according to the second embodiment is omitted. 2-2. Features of the exhaust gas purification system according to the second embodiment

[0063] In the exhaust gas purification system 100 of the first embodiment, the regeneration process is accelerated from an early stage by providing an opportunity for a delayed fuel cut-off at an early stage in a cold environment. In contrast, the exhaust gas purification system 100 of the second embodiment is characterized by lean air-fuel ratio control, which changes the target air-fuel ratio to lean when an opportunity arises that cannot be handled solely by the delayed fuel cut-off. The lean air-fuel ratio control is performed by the air-fuel ratio control unit 316 of the ECU 30.

[0064] Fig. Figure 11 is a diagram showing the relationship between the amount of regeneration and the amount of particulate matter deposited in the OPF for each air-fuel ratio. As in Fig. As shown in Figure 11, the regeneration rate in the OPF 24 tends to increase when the air-fuel ratio becomes leaner. Therefore, if the target air-fuel ratio is adjusted to a leaner ratio, the regeneration performance of the OPF 24 can be increased.

[0065] However, the target air-fuel ratio is not controlled to be completely lean when controlling the lean air-fuel ratio. Fig. Figure 12 is a diagram showing the relationship between combustion variation and the amount of NOx emitted in relation to the air-fuel ratio. As in Fig. As shown in Figure 12, the amount of NOx emitted tends to reach a maximum at slightly lean conditions, for example, A / F=16, and then decreases as the mixture becomes leaner. Furthermore, the combustion variation tends to be small during the period from stoichiometric to slightly lean, but then increases sharply as the air-fuel ratio becomes leaner. Therefore, with lean air-fuel ratio control, it is possible to increase the regeneration performance of the OPF 24 and simultaneously reduce NOx emissions by controlling the lean air-fuel ratio within a range that does not exceed the combustion variation limit determined for each engine coolant temperature.

[0066] Lean air-fuel ratio control is preferably only carried out during a period in which the intake air volume is low, such as during deceleration of the vehicle. Fig. Figure 13 is a time graph illustrating the difference in the changes in the amount of NOx emitted and the OPF bed temperature according to the implementation time of the lean air-fuel ratio control of the second embodiment. (a) in Fig. 13 shows a change over time in the vehicle speed of the vehicle to which the motor 10 is attached, and (b) in Fig. Figure 13 shows a change in the intake air volume over time. As in (a) and (b) in Fig. Figure 13 shows that the periods from time t2 to time t3, from time t4 to time t5, and from time t6 to time t7 are deceleration periods in which the vehicle is mainly decelerating, and also periods in which the intake air volume is smaller than in other periods. (c) in Fig. Figure 13 shows the time course of the OPF bed temperature when the lean air-fuel ratio control is limited to this delay period, and (d) in Fig. Figure 13 shows the time course of the OPF bed temperature when lean air-fuel ratio control is implemented throughout the entire period. Furthermore, (e) shows in Fig. 13 the temporal evolution of the amount of NOx emitted when the lean air-fuel ratio is limited to this delay period, and (f) in Fig. Figure 13 shows the time course of the amount of NOx emitted when the lean air-fuel ratio control is implemented over the entire period.

[0067] As in Fig. As shown in Figure 13, a period from time t1 to time t2 is a period during the vehicle's acceleration, in which the vehicle speed and intake air volume increase, and a period from time t2 to time t3 is a deceleration period. In the equation in (f) in Fig. In the example shown, the amount of NOx emitted increases with an increase in the intake air volume because lean air-fuel ratio control is implemented during the acceleration period. Conversely, since the intake air volume is low during the deceleration period, the amount of NOx emitted is kept at a low value, even when lean air-fuel ratio control is implemented.

[0068] In contrast, in the in (e) in Fig. In example 13, NOx emissions are kept low by stoichiometric combustion because lean air-fuel ratio control is not implemented during the acceleration period. Conversely, while lean air-fuel ratio control is implemented during the deceleration period, exhaust NOx emissions are kept at a low level because the intake air volume is small.

[0069] Therefore, if the lean air-fuel ratio control is limited to the deceleration period, it is possible to effectively suppress the increase in the amount of NOx emitted during both the acceleration and deceleration periods. As shown in (e) and (f) in Fig. As shown in Figure 13, the intake air quantity in the delay period from time t2 to time t3 is small in relation to the heat capacity of the OPF 24 and therefore, even when the lean air-fuel ratio control is implemented, the decrease in the bed temperature of the OPF 24 can be suppressed to a minimum. 2-3. Specific processing of the control system implemented in the exhaust gas purification system of the second embodiment.

[0070] Fig. 14 is a flowchart of a control routine that is executed in the exhaust gas purification system 100 according to the second embodiment. The in Fig. The control routine shown in section 14 is executed repeatedly by the ECU 30 in a predetermined control cycle during the operation of the motor 10. In step S200 of the Fig. In step 14, it is determined that MODE=0 is set. "MODE" is an indicator used to determine the currently set permissible oil temperature for delay bridging and whether lean air-fuel ratio control is executed. If MODE=0 is set, the permissible oil temperature for delay bridging is set to Töl_normal, and lean air-fuel ratio control is not executed. If MODE=1 is set, the permissible oil temperature for delay bridging is set to Töl_low, and lean air-fuel ratio control is not executed. If MODE=2 is set, the permissible oil temperature for delay bridging is set to Töl_low, and lean air-fuel ratio control is executed. As a result of the determination in step S200, if MODE=0, the process proceeds to step S202.

[0071] In the following step S202, it is determined whether the estimated total deposit amount, which is estimated in the particulate matter deposit amount estimation process, is greater than the threshold value A. If it is determined that the threshold is not met, the process proceeds to step S212 and the permissible oil temperature for bridging the delay is maintained at Töl_normal.

[0072] On the other hand, if step S202 determines that the condition is met, the process proceeds to step S204. In step S204, MODE is set to 1, and the process continues with step S206.

[0073] If MODE is not 0 in the determination of step S200, the current allowable oil temperature for delay bridging has been set to Töl_low. In this case, the process continues with step S210 and determines whether the estimated total deposit amount, as estimated in the particulate matter deposit amount estimation process, is greater than the threshold C. The process is the same as step S150 of the Fig. The control routine shown in section 10 is executed as follows. If the condition is not met, it can be determined that the possibility of excessive particulate matter deposition in the OPF 24 is low. In this case, the process continues with step S212, where the permissible oil temperature for the delay bridging is set to Töl_normal. In the next step, S214, the target air-fuel ratio is set to stoichiometric, and in the following step, S216, the target air-fuel ratio is set to MODUS=0. This routine terminates when the process from step S216 is complete.

[0074] If, on the other hand, step S210 determines that the condition is met, the process proceeds to step S220. In step S220, it is determined that MODE=1 is set. Therefore, if the result indicates that the condition is met, the process moves to step S206. In step S206, it is determined whether the estimated total deposit amount, as estimated in the particulate matter deposit amount estimation process, is greater than a threshold B. Threshold B is greater than threshold A and is also referred to as the second deposit amount. If the estimated total deposit amount is less than or equal to threshold B, the process consequently proceeds to the next step, S208, and the permissible oil temperature for delay bridging is set to low. When the process of step S208 is complete, this control routine terminates.

[0075] On the other hand, when determining step S206, if the estimated total deposit amount is greater than threshold B, it may be determined that the possibility of delay fuel interruption is not sufficiently preserved, even if the process to change the permissible oil temperature for delay bridging is carried out. In this case, the process proceeds to the next step S230, and MODE is set to 2. When the process of step S230 is complete, the process proceeds to the next step S232.

[0076] If step S220 determines that MODE=1 is not set, the current MODE is determined to be 2, and the process proceeds to step S232. Step S232 determines whether a lean indicator is set to ON. The lean indicator is used to determine whether the current target air-fuel ratio is set to the lean air-fuel ratio by the lean-air-fuel ratio control. If the lean indicator is OFF, the process continues to step S234.

[0077] In step S234, it is determined whether the intake air quantity Ga detected by the air flow meter 16 is greater than a GALo value, which is a predetermined low Ga value. The GALo value is a target air quantity, determined in advance through experiments or simulations as the intake air quantity Ga that can suppress the emitted NOx to an acceptable level when the air-fuel ratio is controlled to a lean air-fuel ratio. Consequently, if the intake air quantity Ga is equal to or less than GALo, it is determined that lean air-fuel ratio control can be implemented, and the process proceeds to the next step S236.

[0078] In step S236, the lean mixture indicator is set to ON. In the next step, S238, the target air-fuel ratio is adjusted to the lean air-fuel ratio by the lean air-fuel ratio control system. Fig. Figure 15 is a map that defines the relationship between the target air-fuel ratio and the engine coolant temperature. In this map, lean limit values ​​within the combustion variation limit are defined for each engine coolant temperature as the target air-fuel ratio. Typically, this map is set such that the target air-fuel ratio becomes leaner as the engine coolant temperature increases. Here, the target air-fuel ratio is determined according to the... Fig. The characteristic map shown in section 15 is set to the target air-fuel ratio value, which corresponds to the engine coolant temperature thw detected by water temperature sensor 34. When the process of step S238 is complete, the process proceeds to step S208, and the permissible oil temperature for the delay bridging is set to Töl_low.

[0079] On the other hand, in step S234, if the intake air quantity Ga is greater than GALo, which is the specified air quantity, it is determined that the emitted NOx cannot be suppressed to an acceptable range during operation by the lean air-fuel ratio. The process then proceeds to the next step, S240. In step S240, the lean indicator is set to OFF. In the next step, S242, the target air-fuel ratio is adjusted to the stoichiometric air-fuel ratio. Once the process of step S242 is complete, the process switches to step S208, and the permissible oil temperature for the delay bridging is set to Töl_low.

[0080] If the lean indicator is ON in step S232, the process proceeds to step S244. In step S244, it is determined whether the intake air volume Ga detected by the air flow meter 16 is greater than a GAHi value, which is a predetermined high Ga value. The GAHi value is an intake air volume threshold to prevent the air-fuel ratio setting from fluctuating between the lean air-fuel ratio and the stoichiometric air-fuel ratio, and is set to a neighboring value greater than GALo. If the intake air volume Ga is equal to or less than the GAHi value, the process proceeds to step S236 and the lean indicator is set ON; if the intake air volume Ga is greater than the GAHi value, the process proceeds to step S240 and the lean indicator is set OFF.

[0081] As described above, according to the modification process of the permissible oil temperature, including the air-fuel ratio control implemented in the exhaust gas purification system 100 of the second embodiment, the target air-fuel ratio can be controlled to a lean air-fuel ratio if, even in the modification process of the permissible oil temperature, the possibility of delayed fuel interruption cannot be sufficiently maintained. This allows the regeneration process of the OPF 24 to be started early. 2-4. Modification of the system of the second embodiment

[0082] The exhaust gas purification system 100 according to the second embodiment can assume a modified configuration as described below.

[0083] Setting the target air-fuel ratio when controlling the lean air-fuel ratio is not dependent on the procedure using the map of Fig. 15 limited. That is, the target air-fuel ratio in lean air-fuel ratio control can be a fixed value of the lean air-fuel ratio. Reference symbol list: 10 Internal combustion engine 12 Intake channel 14 Exhaust pipe 16 air flow meters 18 Throttle valve 22 Start-up converter / Start-up catalyst 24 Particulate filters / OPF 26 automatic transmissions 28 torque converters 29 Jumper coupling 30 ECU 32 Speed ​​sensor 34 (Cooling) water temperature sensor 36 Oil temperature sensor 38 Exhaust gas temperature sensor 40 Air-fuel ratio sensor 100 Exhaust gas purification system 310 Control unit for overrun fuel cut-off 312 Deposit quantity estimation unit 314 Unit for changing the permissible oil temperature for delay bridging 316 Air-fuel ratio control unit A threshold Kaf air-fuel ratio correction coefficient Kthw water temperature correction coefficient NE engine speed KL Motor load Ga Intake air quantity GALo predetermined low Ga value GAHi predetermined high Ga value Set predetermined bed temperature Töl_normal normal permissible oil temperature for bridging the delay Töl_low is lower than “Töl_normal”

Claims

[1] Exhaust gas purification system (100) for an internal combustion engine (10), comprising: a particulate filter (24) which is arranged in an exhaust stream (14) of the internal combustion engine (10) and serves to collect particles in the exhaust gas; an automatic transmission (26) which includes a torque converter (28) with a lock-up clutch (29); and a control unit (30) that controls the internal combustion engine (10) to perform a fuel interruption when the internal combustion engine (10) decelerates and a temperature correlation value of the lubricating oil of the automatic transmission (26) is higher than a specified value, and that controls the automatic transmission (26) to engage the lock-up clutch (29) during the execution of the fuel interruption, wherein the controller (30) is configured to include: a deposition estimation unit (312) for estimating the amount of particles deposited on the particle filter (24); and a determination value change unit (314) which, when the deposit quantity exceeds a predetermined first deposit quantity, changes the determination value to a smaller value than before the first deposit quantity was exceeded, wherein the control (30) further comprises an air-fuel ratio control unit (316) to change, when the deposit quantity exceeds a second deposit quantity which is larger than the first deposit quantity, a target air-fuel ratio of the internal combustion engine (10) to a leaner air-fuel ratio than before the second deposit quantity was exceeded. [2] Exhaust gas purification system (100) for the internal combustion engine (10) according to claim 1, wherein the air-fuel ratio control unit (316) is configured to prevent a change in the target air-fuel ratio to a lean air-fuel ratio when the intake air quantity of the internal combustion engine (10) is greater than a predetermined target air quantity. [3] Exhaust gas purification system (100) for the internal combustion engine (10) according to claim 1 or 2, wherein the air-fuel ratio control unit (316) is configured to change the target air-fuel ratio of the internal combustion engine (10) to a lean air-fuel ratio within a range which does not reach the combustion variation limit of the internal combustion engine (10). [4] Exhaust gas purification system (100) for the internal combustion engine (10) according to one of claims 1 to 3, wherein the air-fuel ratio control unit (316) is configured to change the target air-fuel ratio to a lean air-fuel ratio when the water temperature of the internal combustion engine (10) is higher.

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