KR100879326B1 - Exhaust purifying apparatus and exhaust purifying method for internal combustion engine - Google Patents

Abstract

In the exhaust purification apparatus for an internal combustion engine of a vehicle according to the present invention, heating control for supplying fuel to the exhaust purification catalyst is executed to increase the catalyst bed temperature. The heating control is suspended when it is determined that the vehicle is driving downhill. The adverse effects due to deactivation of the exhaust purification catalysts during the heating control can be reliably avoided.

Description

EXHAUST PURIFYING APPARATUS AND EXHAUST PURIFYING METHOD FOR INTERNAL COMBUSTION ENGINE}

The present invention relates to an exhaust purification apparatus and an exhaust purification method for an internal combustion engine of a vehicle, wherein the apparatus performs heating control to increase the temperature of the exhaust purification catalyst by adding fuel to the catalyst.

As disclosed in Japanese Patent Laid-Open No. 5-44434, a typical exhaust purification apparatus applied to an internal combustion engine of a vehicle includes an exhaust purification catalyst located in an exhaust system. The exhaust purification catalyst functions to capture particulate matter (PM) and nitrogen oxides (NOx) contained in exhaust gas.

Such an exhaust purification apparatus estimates the amount of particulate matter accumulated in the exhaust purification catalyst based on the operating state of the engine. If the amount of accumulated particulate matter is not less than an acceptable value, the apparatus performs heating control to regenerate the catalyst whose performance is degraded due to clogging of particulate matter. In the heating control, the apparatus supplies fuel to the exhaust purification catalyst to heat the catalyst, and uses this heat to burn and remove particulate matter accumulated in the exhaust purification catalyst.

Performing heating control is known to cause the following problems. In other words, depending on the operating state of the engine, the exhaust temperature is reduced, which deactivates the catalyst. This hinders the oxidation of the fuel supplied to the catalyst. If fuel supply to the exhaust purification catalyst is continued in an inactive state, a large amount of fuel will collect on the surface of the catalyst. This increases the amount of particulate matter that accumulates. In addition, since part of the fuel supplied to the exhaust purification catalyst is discharged through the catalyst, the properties of the exhaust gas are lowered.

Heating control is performed not only for burning and removing particulate matter, but also for regenerating a catalyst contaminated with sulfur contained in exhaust gas, for example. If the heating control is performed to release sulfur, if the catalyst is deactivated, the sulfur release cannot be completed, thus causing the problem described above.

It is therefore an object of the present invention to provide an exhaust purification apparatus and an exhaust purification method for an internal combustion engine of a vehicle, which eliminate the problems caused by deactivation of the exhaust purification catalyst during heating control.

In order to achieve the above and other objects and in accordance with the object of the present invention, there is provided an exhaust purification apparatus for an internal combustion engine of a vehicle. The apparatus has a regeneration control unit. The regeneration control unit increases the bed temperature of the catalyst by controlling the regeneration of the exhaust purification catalyst through heating control in which fuel is supplied to the exhaust purification catalyst. The apparatus further includes a determining section for determining whether the vehicle is driving downhill. The regeneration control unit suspends the heating control when the determination unit determines that the vehicle is driving downhill.

The present invention also provides an exhaust purification method for an internal combustion engine of a vehicle. The method comprises: regenerating the exhaust purification catalyst by supplying fuel to the exhaust purification catalyst to raise the bed temperature of the catalyst; Determining whether the vehicle is driving downhill; And if it is determined that the vehicle is driving downhill, suspending fuel supply to the exhaust purification catalyst.

1 is a block diagram illustrating an internal combustion engine of a vehicle to which the first embodiment of the present invention is applied;

2 is a timing chart showing an example of processes related to the PM elimination control mode of the first embodiment;

3 is a flowchart showing a holding process of the first embodiment;

4 is a flowchart showing a process for turning on a downhill flag of the first embodiment;

5 is a timing chart including sections (a) to (d) showing an example of the control of the downhill flag of the first embodiment;

6 is a flowchart showing a process for turning off the downhill flag of the first embodiment;

7 is a flowchart showing a holding process according to the second embodiment of the present invention;

8 is a flowchart showing a process for determining deactivation according to the second embodiment; And

9 is a timing chart including sections (a) to (c) showing an example of the holding step according to the second embodiment.

The exhaust purification apparatus for an internal combustion engine 2 of a vehicle according to the first embodiment of the present invention will be described below.

1 illustrates a configuration example of an internal combustion engine 2 to which an exhaust purification apparatus according to the embodiment is applied. The internal combustion engine 2 is mounted on a vehicle such as an automobile and functions as a power source.

The engine 2 has cylinders. In this embodiment, the number of cylinders is four, and these cylinders are indicated by # 1, # 2, # 3, and # 4. The combustion chamber 4 of each cylinder # 1 to # 4 includes an intake port 8 opened and closed by an intake valve 6. The combustion chamber 4 is connected to a surge tank 12 through an intake port 8 and an intake manifold 10. The surge tank 12 is connected to an outlet of a supercharger having an intercooler 14 and an intake passage 13. In the above embodiment, the supercharger is the compressor 16a of the exhaust turbocharger 16. The inlet of the compressor 16a is connected to the air cleaner 18. An exhaust gas circulation (hereinafter EGR) passage 20 is connected to the surge tank 12. Specifically, the EGR gas supply port 20a of the EGR passage 20 opens to the surge tank 12. The throttle valve 22 is located in the cross section of the intake passage 13 between the surge tank 12 and the intercooler 14. The intake airflow sensor 24 and the intake air temperature sensor 26 are located in the portion between the compressor 16a and the air cleaner 18.

The combustion chamber 4 of each cylinder # 1 to # 4 includes an exhaust gas opening 30 which is opened and closed by an exhaust gas valve 28. The combustion chamber 4 is connected to the inlet of the exhaust turbine 16b via the exhaust gas port 30 and the exhaust manifold 32. The outlet of the exhaust turbine 16b is connected to the exhaust passage 34. The exhaust turbine 16b draws exhaust gas from the cross section of the exhaust manifold 32 corresponding to the side of the fourth cylinder # 4.

Three catalytic converters 36, 38, and 40 containing an exhaust purification catalyst are located in the exhaust passage 34. The first catalytic converter 36 located most upstream contains the NOx storage reduction catalyst 36a. When the exhaust gas is an oxidizing atmosphere (lean) in the normal operation of the engine 2, the NOx storage reduction catalyst 36a stores NOx. When the exhaust gas is in a reducing atmosphere (stoichiometric or lower air-fuel ratio), NOx stored in the NOx storage reduction catalyst 36a is released to NO and reduced to hydrocarbons and carbon oxides contained in the exhaust gas. In this way NOx is removed.

The second catalytic converter 38 including the filter 38a is located at the second position from the most upstream side. The filter 38a has a monolithic wall. The wall has pores through which the exhaust gases pass. The areas around the pores of the exhaust filter 38a are coated with a layer of NOx storage reduction catalyst. Therefore, the NOx storage reduction catalyst functions as an exhaust purification catalyst for removing NOx as described above. The filter wall also traps particulate matter in the exhaust gas. Therefore, active oxygen generated in the high temperature oxidizing atmosphere when NOx is stored starts to oxidize the particulate matter. In addition, the surrounding excess oxygen oxidizes the entire particulate matter. As a result, NOx is removed and particulate matter is removed.

The third catalytic converter 40 is located most downstream. The third catalytic converter 40 contains an oxidation catalyst 40a for oxidizing and purifying hydrocarbons and carbon monoxide in the exhaust gas to purify the exhaust gas.

The first exhaust temperature sensor 44 is located between the NOx storage reduction catalyst 36a and the filter 38a. The second exhaust temperature sensor 46 and the air-fuel ratio sensor 48 are located between the filter 38a and the oxidation catalyst 40a. The second exhaust temperature sensor 46 is closer to the filter 38a than the oxidation catalyst 40a. The air-fuel ratio sensor 48 is located closer to the oxidation catalyst 40a than the filter 38a. The air-fuel ratio sensor 48, including the solid electrolyte, detects the air-fuel ratio of the exhaust gas based on the components of the exhaust gas. The air-fuel ratio sensor 48 outputs a voltage signal in proportion to the detected air-fuel ratio. The first exhaust temperature sensor 44 detects the exhaust temperature Ti at the corresponding position. Similarly, the second exhaust temperature sensor 46 detects the exhaust temperature To at the corresponding position.

The tubes of the pressure differential sensor 50 are connected upstream of the filter 38a and downstream of the filter 38a. The pressure difference sensor 50 detects the pressure difference ΔP between the upstream and downstream portions of the filter 38a, thereby detecting the degree of clogging of the filter 38a. The degree of clogging indicates the degree of accumulation of particulate matter in the filter 38a.

An EGR gas inlet 20b of the EGR passage 20 is provided to the exhaust manifold 32. The EGR gas inlet 20b is opened in a section corresponding to the first cylinder # 1 side opposite to the fourth cylinder # 4 side, and the exhaust turbine 16b introduces the exhaust gas.

The EGR catalyst 52 is located in the EGR passage 20. The EGR catalyst 52 improves the EGR gas from the EGR gas inlet 20b of the EGR passage 20. In addition, an EGR cooler 54 for cooling the EGR gas is located in the EGR passage 20. The EGR catalyst 52 also functions to prevent clogging of the EGR cooler 54. The EGR valve 56 is located upstream of the EGR gas supply port 20a. The opening degree of the EGR valve 56 is changed to adjust the amount of EGR gas supplied from the EGR gas supply port 20a to the intake system.

Each cylinder # 1 to # 4 is provided with a fuel injection valve 58 for directly injecting fuel into the corresponding combustion chamber 4. The fuel injection valve 58 is connected to a common rail 60 by a fuel supply pipe 58a. The variable displacement fuel pump 62 supplies fuel to the common rail 60. The high pressure fuel supplied from the fuel pump 62 to the common rail 60 is distributed to the fuel injection valve 58 through the fuel supply pipe 58a. A fuel pressure sensor 64 for detecting the pressure of the fuel is attached to the common rail 60.

In addition, the fuel pump 62 may supply fuel of low pressure to the fuel adding valve 68 through the fuel supply pipe 66. The fuel addition valve 68 is provided in the exhaust gas port 30 of the fourth cylinder # 4 to inject fuel toward the exhaust turbine 16b. In this way, the fuel adding valve 68 adds fuel to the exhaust gas. The catalyst control mode described later is executed by this fuel addition.

The electronic control unit (ECU) 70 is mainly composed of a digital computer having a driving circuit for driving a CPU, a ROM, a RAM and other devices. In this embodiment, the ECU 70 functions as a regeneration control unit and a determination unit. As the regeneration controller, the ECU 70 controls the regeneration of the exhaust purification catalyst. As the determination unit, the ECU 70 determines whether the vehicle is driving downhill.

The ECU 70 includes an intake air flow sensor 24, an intake air temperature sensor 26, a first exhaust air temperature sensor 44, a second exhaust air temperature sensor 46, an air-fuel ratio sensor 48, and a pressure difference sensor 50. The signals from the EGR openness sensor, fuel pressure sensor 64, and throttle openness sensor 22a of the EGR valve 56 are read. Further, the ECU 70 includes an accelerator opening degree sensor 74 for detecting the decompression degree of the accelerator pedal 72 (accelerator opening degree ACCP), and a coolant temperature for detecting the temperature THW of the coolant of the engine 2. Read signals from sensor 76. In addition, the ECU 70 identifies the cylinder by detecting an engine speed sensor 80 that detects the rotational speed NE of the crankshaft 78, a rotational phase of the crankshaft 78, or a rotational phase of the intake cam. The signals from the cylinder identification sensor 82 and the vehicle speed sensor 84 for detecting the speed SPD of the vehicle are read.

Based on the operating state of the engine 2 obtained from the signals, the ECU 70 controls the amount and timing of fuel injection by the fuel injection valve 58. The fuel injection amount control includes, for example, "fuel cutoff" control for suspending fuel injection when the vehicle is decelerating. In addition, the ECU 70 controls the opening degree of the EGR valve 56, the throttle opening degree by the motor 22b, and the displacement of the fuel pump 62. In addition, the ECU 70 executes catalyst control such as PM elimination control, sulfur release control and NOx reduction control, and other controls by controlling the opening degree of the fuel adding valve 68.

The ECU 70 selects one of the normal combustion mode and the low temperature combustion mode according to the operation state. The low temperature combustion mode is a combustion mode in which the EGR openness map for the low temperature combustion mode is used to circulate a large amount of exhaust gas (increasing the amount of EGR) and delay the increase in the combustion temperature, thereby simultaneously reducing NOx and smoke. Say. In the low temperature combustion mode executed at a low load, the low-medium speed rotational speed range and the air-fuel ratio feedback control are performed by adjusting the throttle opening degree TA based on the air-fuel ratio AF detected by the air-fuel ratio sensor 48. The other combustion mode is a normal combustion mode in which normal EGR control (including the case where EGR is not executed) is performed using the EGR openness degree map for the normal combustion mode.

The ECU 70 performs four catalyst control modes, which are modes for controlling catalysts. The catalyst control modes include a PM elimination control mode, a sulfur release control mode, a NOx reduction control mode, and a normal control mode.

In the PM elimination control mode, the particulate matter deposited on the filter 38a in the second catalytic converter 38 is heated and combusted. Thereafter, the particulate matter is converted into CO ₂ and H ₂ O and discharged. In this mode, fuel is added to the exhaust gas to oxidize the fuel or catalyst in the exhaust gas to generate heat, thereby raising the catalyst bed temperature to, for example, 600 to 700 ° C. In addition, particulate matter around the catalyst is burned. The manner in which the mode is executed will be described later.

In the sulfur release control mode, if the NOx storage reduction catalyst 36a and the filter 38a are contaminated with sulfur and the NOx storage capacity is lowered, sulfur components are released from the catalyst 36a and the filter 38a, and the catalyst ( 36a) and filter 38a are allowed to recover from sulfur contamination. In this mode, sulfur temperature increase control is performed in which the fuel addition from the fuel addition valve 68 is repeated so that the catalyst bed temperature is increased (for example, to 650 ° C). In addition, the air-fuel ratio reduction control is performed in which the catalyst bed temperature is kept high by intermittently adding fuel to the exhaust gas by the fuel addition valve, and the air-fuel ratio is changed to a value which is slightly lower than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio. In this embodiment, the air / fuel ratio is enriched to be slightly lower than the stoichiometric air / fuel ratio. The air-fuel ratio reduction control is considered to be a manner of heating control because fuel addition is performed to keep the catalyst bed temperature high. As in other modes, in some cases after injection is performed by the fuel injection valve 58 in this mode. The post injection refers to the combustion injection into the combustion chamber 4 during the expansion stroke and the exhaust stroke.

In the NOx reduction control mode, NOx stored in the NOx storage reduction catalyst 36a and the filter 38a is reduced to N ₂ , CO ₂ , H ₂ O and discharged. In this mode, the fuel addition from the fuel addition valve 68 is intermittently performed at relatively long intervals, such that the catalyst bed temperature is relatively low (e.g., at a temperature in the range of 250 ° C to 500 ° C). Accordingly, the air-fuel ratio is lowered below the stoichiometric air-fuel ratio.

In the state where none of the PM elimination control mode, the sulfur release control mode, and the NOx reduction control mode are executed, fuel addition from the fuel addition valve 68 and post injection by the fuel injection valve 58 are not performed. Does not correspond to the normal control mode.

Next, processes related to the PM elimination control mode among the processes executed by the ECU 70 will be described.

If a large amount of fuel is added to the exhaust gas at the time for burning particulate matter accumulated in the exhaust purification catalyst, the temperature of the catalyst suddenly increases, resulting in thermal degradation of the catalysts. On the other hand, the reduced amount of added fuel prevents thermal degradation of the catalyst, but particulate matter accumulating on the catalyst will remain unburned.

Therefore, as shown in the timing chart of Fig. 2, the first heating control is performed in the PM elimination control mode. In the first heating control, a relatively small amount of fuel is added to the exhaust gas at a time from t11 to t12 to increase the temperature while reducing the total amount of particulate matter accumulated in the NOx storage reduction catalyst 36a and the filter 38a. Minimize Then, at the time t12 to t13, the second heating control is performed in which the amount of fuel added to the exhaust gas is larger than in the first heating control. This completely burns the particulate matter accumulated in the NOx storage reduction catalyst 36a. Also in this mode, fuel is added to the exhaust gas by the fuel addition from the valve 68 or after injection by the fuel injection valve 58.

The PM elimination control starts when the amount of particulate matter (estimated accumulation amount PMsm) accumulated in the NOx storage reduction catalyst 36a calculated on the basis of the engine operating state reaches the reference value PMstart (time t11). Is completed when the second heating control ends (time t13). In the first heating control, fuel is repeatedly added to the exhaust gas at an air-fuel ratio higher than the stoichiometric air-fuel ratio, thereby increasing the catalyst bed temperature. In the second heating control, a process in which the air-fuel ratio is set to a stoichiometric air-fuel ratio or an air-fuel ratio slightly less than the stoichiometric air-fuel ratio is repeatedly executed, and intermittent fuel addition is allowed such that there is no fuel addition between runs. do. In this embodiment, the air-fuel ratio is concentrated to be slightly less than the stoichiometric air-fuel ratio.

If the vehicle is driving downhill, the engine load is reduced and thus the exhaust temperature is lowered. In addition, relative wind reduces the catalyst bed temperature to a significant extent. Therefore, there is a high possibility that the exhaust purification catalyst is inactivated.

According to this case, when the ECU 70 determines that the vehicle is driving downhill as shown in the flowchart of Fig. 3 (positive result in step S100), the following process is executed in the above embodiment. That is, if processes related to PM elimination control (first and second heating control) or processes related to sulfur release control (sulfur temperature increase control and air-fuel ratio control) are being executed, the processes are suspended in step S102. If the processes are requested to be started, the request is canceled in step S102.

Also, when the processes are suspended, if the ECU 70 determines that the vehicle is not driving downhill (negative result in step S100), the processes resume when the resume requirements are met (positive result in step S104). (Step S106). The resumption requirements include that the exhaust purification catalysts are determined not to be deactivated. For example, when the catalyst bed temperature is sufficient to burn fuel collected on the exhaust purification catalyst, and when the engine operating state is likely to increase to a sufficient temperature, for example, after the engine is operated at a high load for a predetermined time. It is determined that the exhaust purification catalysts are not deactivated.

The series of processes shown in the flowchart of FIG. 3 is executed by the ECU 70 at predetermined intervals. The ECU 70 determines whether the vehicle is driving downhill in step S100 based on whether the downhill flag described later is ON or OFF.

Hereinafter, processes related to the downhill flag will be described. The flowchart of FIG. 4 shows a procedure for turning on the downhill flag. The series of processes shown in the flowchart of FIG. 4 is executed by the ECU 70 at predetermined intervals.

First, it is determined in step S200 whether both of the following requirements are satisfied.

(1) The vehicle speed SPD is faster than or equal to the predetermined speed.

(2) The fuel injection amount is 0 or fuel cutoff control is being executed.

If both of the above requirements are satisfied (positive result in step S200), it is determined that the vehicle is driving downhill, and the count value Cs of the downhill counter is incremented in step S202. If the procedure is repeatedly executed and the count value Cs reaches a predetermined value (positive result in step S204), the downhill flag is turned on in step S206.

The count value Cs is cleared in step S212 when the requirements of the list are not met (negative result in step S200). However, even if the above requirements are not satisfied, the count value Cs is determined when the fuel injection amount is greater than or equal to the predetermined amount (positive result in step S208), and for a time when the unmet state of the requirements is less than the predetermined time. When it is continued (negative result in step S210) is not cleared. Even when the vehicle is driving downhill, fuel injection is temporarily executed due to the gear shift. In this case, the count value Cs is maintained without being cleared.

As shown in the timing chart of Fig. 5, when the vehicle starts driving downhill at time t21, the downhill driving start duration is measured by the downhill counter. When the measured time reaches a predetermined time at time t22, the downhill flag is turned on. Then, when the ECU 70 determines that the vehicle is driving downhill based on the fact that the downhill flag is ON in step S100 of FIG. 3, the processes related to the PM elimination control and the process related to the yellow release control. Are reserved as described above.

6 shows a procedure for turning off the downhill flag. The series of processes shown in the flowchart of FIG. 6 is executed by the ECU 70 at predetermined intervals.

First, it is determined in step S300 whether the fuel injection amount is not less than the predetermined amount. If the fuel injection amount is not less than the predetermined amount (positive result in step S300), it is determined that the vehicle is not driving downhill, and the non-downhill count value Cn is incremented in step S302. If the above procedure is repeatedly executed and the count value Cn reaches a predetermined value (positive result in step S304), the downhill flag is turned off in step S306.

The count value Cn is cleared in step S310 when the fuel injection amount is kept below a predetermined amount (negative result in step S300), and when this state continues for more than a predetermined time (positive result in step S308). That is, even if the fuel injection amount is less than the predetermined amount, the count value Cn is not cleared if the duration is not less than the predetermined time (negative result in step S308). Even when the vehicle is not driving downhill, the fuel cut control may be executed due to the operation of the brake, or the fuel injection amount may be reduced to a considerable extent. In this case, the count value Cn is maintained without being cleared.

As shown in Fig. 5, if the vehicle stops driving downhill at time t23, the duration of non-downhill driving start is measured by the non-downhill counter. If the measured time reaches a predetermined time at time t24, the downhill flag is turned off. Then, if the ECU 70 determines that it is not driving downhill based on the fact that the downhill flag is OFF in step S100 of Fig. 3, the suspended processes are positive (step S104 positive). The result is resumed in step S106.

The above-described embodiment has the following advantages.

(1) The ECU 70 determines whether the vehicle is driving downhill. If it is determined that the vehicle is driving downhill, processes related to PM elimination control and processes related to sulfur release control are suspended. Accordingly, the processes are suspended if the vehicle is driving downhill. In other words, the processes are suspended when the engine load is reduced and thus the exhaust temperature is reduced, and the relative wind reduces the catalyst bed temperature to a significant extent, making it more likely that the exhaust purification catalyst is deactivated. Therefore, under the situation where the oxidation of the fuel is insufficient, the fuel is not supplied to the NOx storage reduction catalyst 36a and the filter 38a, so that adverse effects caused by the fuel supply are reliably avoided.

It is also possible to directly detect the catalyst bed temperature and determine the deactivation of the exhaust purification catalyst based on the catalyst bed temperature. However, in this configuration, even if the fuel supply from the fuel addition valve 68 is suspended after the drop of the catalyst bed temperature is detected, the fuel injected until then continues to store the NOx storage reduction catalyst 36a for a predetermined period of time. And filter 38a. In contrast, even a drop in exhaust temperature and even deactivation of the exhaust purification catalyst due to the temperature drop are predicted based on the running state of the vehicle in this embodiment. Therefore, when the NOx storage reduction catalyst 36a and the filter 38a are deactivated, disadvantages caused by adding fuel to the NOx storage reduction catalyst 36a and the filter 38a can be avoided.

(2) The ECU 70 determines that the vehicle is driving downhill when the fuel cutoff control is being executed. Therefore, the disadvantages are reliably avoided if the fuel shutoff control is being executed. In other words, disadvantages when there is no engine combustion heat and thus the catalyst bed temperature drops abruptly are avoided, and there is a possibility that the catalysts are deactivated in a short time compared to the state in which the engine is idle (idle state).

(3) Processes related to PM elimination control and processes related to sulfur release control are suspended only when a predetermined time has elapsed since it is determined that the vehicle is driving downhill. In other words, the processes are suspended only when the exhaust purification catalysts are likely to be deactivated. Therefore, sufficient time for the processes is obtained in most cases while avoiding the disadvantages. Further, even if the fuel injection amount during the non-downhill driving is temporarily equal to the downhill driving due to the gear shift or the operation of the brake, the ECU 70 can prevent the vehicle from erroneously determining that the vehicle is driving downhill. In other words, the determination accuracy of the ECU 70 is improved.

(4) When the processes related to the PM elimination control and the processes related to the sulfur release control are suspended based on the determination of the ECU 70 that the vehicle is driving downhill, the processes are executed by the ECU 70 when the vehicle is driving downhill. When it determines that it determined that it was not busy, it resumes. This ensures that the processes are executed when the vehicle stops driving downhill.

(5) Also, the processes related to the PM elimination control and the processes related to the sulfur release control are resumed only when a predetermined time has elapsed since it is determined that the vehicle is not driving downhill. Thus, the processes are resumed when the catalyst bed temperature is increased after the vehicle stops driving downhill. Therefore, the processes are resumed under the desired conditions.

Hereinafter, an exhaust purification apparatus for an internal combustion engine of a vehicle according to a second embodiment of the present invention will be described.

The second embodiment is different from the first embodiment in a manner in which processes related to PM elimination control and processes related to sulfur release control are suspended.

The flowchart of FIG. 7 shows a procedure for withholding the processes. The series of processes shown in the flowchart of FIG. 7 is executed by the ECU 70 at predetermined intervals. Since steps S100 to S106 of FIG. 7 are the same as steps S100 to S106 of the flowchart according to the first embodiment shown in FIG. 3, the same reference numerals are used for the steps of FIG. 7, and a description thereof will be omitted.

In the flowchart of FIG. 7, the ECU 70 first determines in step S100 whether the vehicle is driving downhill. If the ECU 70 determines that the vehicle is driving downhill (positive result at step S100), it is determined at step S400 whether the determination has been continued for a predetermined time. Specifically, it is determined whether the downhill flag has been turned on for a predetermined period.

If the determination that the vehicle is driving downhill has not continued for a predetermined period (negative result at step S400), it is determined at step S402 whether the exhaust purification catalysts are deactivated (deactivation determination).

If the exhaust purification catalysts are not determined to be deactivated (negative result in step S404), the processes related to the PM elimination control and the processes related to the sulfur release control are continued without being suspended. On the other hand, if it is determined that the exhaust purification catalysts are deactivated (positive result in step S404), the processes are suspended in step S102 in the manner described above.

Then, the procedure continues to be executed, and if the duration of the on state of the downhill flag reaches a predetermined time (positive result in step S400), the processes are suspended in step S102 without determining deactivation.

Hereinafter, a specific procedure of the deactivation determination will be described with reference to the flowchart of FIG. 8. The series of processes shown in the flowchart of FIG. 8 is executed by the ECU 70 at predetermined intervals.

First, it is determined in step S500 whether the exhaust temperature Ti detected by the first exhaust temperature sensor 44 is greater than or equal to a predetermined value. Specifically, when the exhaust temperature Ti is greater than or equal to a predetermined value, it is determined that processes related to the PM elimination control and processes related to the sulfur release control are currently being executed.

If the processes are not currently executed (negative result at step S500), the exhaust purification catalysts are not determined to be inactivated.

On the other hand, if the processes are currently executed (positive result in step S500), the difference (Ti-Tb) between the exhaust temperature Ti and the reference temperature Tb calculated based on the engine operating state is predetermined for a predetermined time. It is determined in step S502 whether or not the value is smaller than?.

The temperature Ti is used as an indicator of the temperature of the NOx storage reduction catalyst 36a layer. The catalyst bed temperature in which no fuel is added to the exhaust gas, or in which no procedure for raising the catalyst bed temperature is performed is used as the reference temperature Tb. Specifically, the reference temperature Tb is continuously calculated based on the engine operating state having a high correlation with the exhaust temperature, or the engine rotation speed NE and the fuel injection amount.

If the temperature difference is less than the predetermined value γ for a predetermined period (positive result in step S502), even when fuel is added to the exhaust gas to raise the temperature of the catalyst layer, as in the case where the fuel is hardly burned It is determined that the exhaust temperature Ti is low. That is, it is determined that the layer temperature of the NOx storage reduction catalyst 36a is low. In this case, the exhaust purification catalysts are determined to be deactivated in step S504.

On the other hand, when the temperature difference is greater than or equal to the predetermined value γ, or when the temperature difference is less than the predetermined value γ for a period shorter than the predetermined period (negative result in step S502), the exhaust purification The catalysts are not determined to be inactive.

In the above embodiment, when the duration of the ON state of the downhill flag is short (from time t31 to time t32 shown in the timing chart of FIG. 9), that is, the vehicle runs downhill for a short time, so that the exhaust purification catalysts are not easily deactivated. In this case, the deactivation determination described above is executed. If the exhaust purification catalysts are not determined to be deactivated, the processes related to the PM elimination control and the processes related to the sulfur release control are continued. The time for performing the processes is maximized.

On the other hand, if the ECU 70 determines that the exhaust purification catalysts are deactivated during the execution of the processes (time t32), or if the duration of the downhill run exceeds the predetermined time, the exhaust purification catalysts are deactivated. If very easy (time t33), the running processes are suspended. Therefore, the above disadvantages are avoided.

The illustrated embodiments may be modified as follows.

In the second embodiment, the processes associated with the determination of deactivation may be changed. For example, while the processes related to the PM elimination control and the processes related to the sulfur release control are executed, the exhaust purification catalysts are exhaust temperature Ti and second exhaust temperature detected by the first exhaust temperature sensor 44. It may be determined that it is deactivated when the difference To-Ti between the exhaust temperatures To detected by the sensor 46 is larger than a predetermined value. In this case, it is detected that the bed temperature of the NOx storage reduction catalyst 36a is low and the bed temperature of the catalyst on the filter 38a is high, that is, the fuel added by the fuel addition valve 68 is reduced to the NOx storage reduction catalyst. It is not burned in the catalyst 36a, but is burned in the filter 38a. Accordingly, the NOx storage reduction catalyst 36a is determined to be inactivated.

In the illustrated embodiment, the requirements for determining that the vehicle is driving downhill include that fuel cut control is being executed. Instead, the vehicle may be determined to be driving downhill when the fuel injection amount of the engine is less than or equal to the predetermined amount. Alternatively, a tilt sensor may be mounted on the vehicle, and the vehicle may be determined to be driving downhill when the tilt sensor detects that the front portion of the vehicle is lower than the rear portion.

In the illustrated embodiments, the processes related to the PM elimination control and the processes related to the yellow release control are suspended only when a predetermined time has elapsed since it is determined that the vehicle is driving downhill. The predetermined period may be changed based on the engine load and the vehicle speed SPD. Specifically, the lower the engine load or the higher the vehicle speed SPD, the shorter the predetermined time may be set. Even when the vehicle is driving downhill, the amount of decrease in the catalyst bed temperature varies depending on the engine load (exhaust temperature) and the vehicle speed SPD (relative wind). However, according to the configuration of the modification, the predetermined period is set according to the rate of decrease of the catalyst bed temperature. Therefore, the aforementioned disadvantages are reliably avoided.

The processes related to the PM elimination control and the processes related to the sulfur release control may be suspended when it is determined that the vehicle is driving downhill.

In the illustrated embodiments, if the ECU 70 determines that the vehicle is not driving downhill, the processes related to the PM elimination control and the processes related to the sulfur release control are based on the determination that the vehicle is driving downhill. It may be resumed even if the resumption requirements are not met. This configuration can also allow the aforementioned disadvantages to be avoided when the vehicle is driving downhill.

If it is determined that the vehicle is driving downhill, one of three processes of the first heating control and the second heating control related to the PM elimination control and the yellow heating control and the air-fuel ratio control associated with the sulfur release control may be selectively suspended. . Since a relatively large amount of fuel is added to the exhaust gas in the second heating control by the fuel adding valve 68, the above disadvantages are remarkable when adding fuel to the exhaust purification catalyst in an inactivated state. Therefore, in order to eliminate the disadvantages associated with the execution of the second heating control, at least the second heating control is preferably suspended when it is determined that the vehicle is driving downhill.

In addition, if it is determined that the vehicle is not driving downhill, one of three processes of the first heating control, the second heating control related to the PM elimination control, the yellow heating control, and the air-fuel ratio reduction control related to the sulfur release control is selectively resumed. May be If the second heating control is suspended, particulate matter remains on the upstream end face of the NOx storage reduction catalyst 36a. In excessive cases, the accumulated amount of particulate matter causes clogging of the NOx storage reduction catalyst 36a. In addition, when the excess accumulation of particulate matter is burned at once, the catalyst bed temperature is excessively increased. In order to reliably remove the particulate matter, it is preferable that at least the second heating control be resumed when it is determined that the vehicle is not driving downhill.

Step S106 of Figs. 3 and 7 may be omitted. That is, the processes related to the PM elimination control and the processes related to the sulfur release control may be configured not to resume even if it is determined that the vehicle is not driving downhill.

The exhaust purification apparatus of the present invention can be applied to any internal combustion engine having a configuration example other than that shown in FIG. That is, the present invention includes any of the above-described embodiments or forms belonging to the above embodiments, including a regeneration control unit which performs heating control to supply fuel to the exhaust purification catalyst to increase the catalyst bed temperature. As long as it is regenerated, it can be applied to any type of exhaust purification apparatus for an internal combustion engine of a vehicle.

Claims (8)

In the exhaust purification apparatus for an internal combustion engine of a vehicle having a regeneration control unit, wherein the regeneration control unit controls the regeneration of the exhaust purification catalyst through heating control in which fuel is supplied to the exhaust purification catalyst, thereby increasing the bed temperature of the catalyst. And a determination unit for determining whether the vehicle is driving downhill, The regeneration control unit suspends the heating control when the determination unit determines that the vehicle is driving downhill, And the regeneration control unit suspends the heating control only when the determination unit continuously determines that the vehicle is driving downhill for a predetermined time. The method of claim 1, And the determination unit determines that the vehicle is driving downhill when the amount of fuel injected by the fuel injection valve of the engine is less than or equal to a predetermined amount and the vehicle speed is faster than or equal to the predetermined speed. . The method of claim 2, And the determination unit determines that the amount of fuel injected by the fuel injection valve is less than or equal to the predetermined amount when the fuel cutoff control for which fuel injection by the fuel injection valve is suspended is executed. . delete The method according to claim 1 or 2, The regeneration control unit resumes the heating control when the determination unit determines that the vehicle is not driving downhill while the heating control is suspended due to the determination of the determination unit that the vehicle is driving downhill. Exhaust purifier. The method of claim 5, And the regeneration control unit resumes the heating control only when the determination unit continuously determines that the vehicle is not driving downhill for a predetermined time. The method according to claim 1 or 2, The heating control includes a first heating control having a relatively small amount of fuel supplied to the exhaust purification catalyst, and a second heating control having a relatively large amount of fuel supplied to the exhaust purification catalyst, wherein the regeneration control unit is configured to determine the vehicle by the determination unit. And at least the second heating control is suspended when it is determined that the vehicle is running downhill. In the exhaust purification method for an internal combustion engine of a vehicle, Regenerating the exhaust purification catalyst by supplying fuel to the exhaust purification catalyst to increase the bed temperature of the catalyst; Determining whether the vehicle is driving downhill; And If it is determined that the vehicle is driving downhill, suspending fuel supply to the exhaust purification catalyst, And the fuel supply to the exhaust purification catalyst is suspended only when the vehicle is continuously determined to be driving downhill for a predetermined time.

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