JP2011085047A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, appropriately suppressing deterioration of exhaust characteristics caused by lengthening of unburnt fuel supply time. <P>SOLUTION: An electronic control unit 23 performs post injection by a fuel injection valve 16, thereby supplying unburnt fuel to a PM filter 19 disposed in an exhaust passage 18 to regenerate the PM filter 19. The electronic control unit 23 prohibits the post injection in the next trip period when the unburnt fuel supply time during the previous trip period exceeds regulation time RH. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that recovers the function of an exhaust gas purification member by supplying unburned fuel to an exhaust passage.

2. Description of the Related Art There is known an exhaust purification device for an internal combustion engine that performs a function recovery process for recovering the function of an exhaust purification member provided in the exhaust passage by supplying unburned fuel to the exhaust passage.
For example, in an internal combustion engine equipped with a PM filter as an exhaust purification member that collects particulate matter, if the exhaust pressure rises due to an increase in the amount of particulate matter deposited on the PM filter, the fuel consumption of the internal combustion engine will deteriorate. . Therefore, in the exhaust gas purification apparatus for an internal combustion engine described in Patent Document 1, when the amount of particulate matter accumulated exceeds a preset threshold, post-injection is performed to supply unburned fuel to the exhaust passage. A so-called filter regeneration process is performed in which the PM filter is heated by the supplied unburned fuel to burn and remove particulate matter.

  Here, if post injection is performed at a low temperature of the engine, unburned fuel due to the post injection may adhere to the cylinder bore wall surface and induce dilution of the lubricating oil. Therefore, in the exhaust emission control device described in Patent Document 1, when the internal combustion engine is at a low temperature, the above-described threshold value is set to a larger value than when it is not so that the post injection execution interval becomes longer. The frequency of post injection is reduced.

JP 2008-38659 A

  By the way, in an exhaust gas purification apparatus for an internal combustion engine, for example, an exhaust gas purification member can reach a temperature at which particulate matter can be removed even if fuel is supplied under predetermined operating conditions such as a small amount of intake air of the internal combustion engine. The temperature cannot be raised. Therefore, an execution condition is set when executing the filter regeneration. When this execution condition is not satisfied, the execution of the filter regeneration is prohibited even if the amount of particulate matter accumulated exceeds the threshold value. As described above, when the regeneration of the filter is prohibited, excessive particulate matter larger than the threshold is accumulated on the exhaust purification member. When the execution condition is satisfied in the state where excessive particulate matter is accumulated in this way, the filter regeneration is executed. At this time, more particulate matter is accumulated than usual. Therefore, the removal takes time, and the supply time of unburned fuel is prolonged. Thus, if the supply time of the unburned fuel for removing the particulate matter becomes longer, the supply amount of the unburned fuel also increases, and there is a concern that the exhaust characteristics due to the unburned fuel will deteriorate.

In the exhaust emission control device described in Patent Document 1, although the threshold value is changed in accordance with the engine temperature, the increase in the supply amount of unburned fuel as described above occurs similarly.
Incidentally, the deterioration of the exhaust characteristics due to the unburned fuel is not limited to the fuel supply to the PM filter, but can also occur in the same way when the fuel is supplied to the NOx occlusion reduction type catalyst or the like that processes NOx in the exhaust. Further, not only post-injection but also a fuel addition valve that directly supplies fuel to the exhaust passage and the like may occur in the case where fuel is supplied from the fuel addition valve.

  The present invention has been made in view of the above problems, and an object thereof is to provide an exhaust emission control device for an internal combustion engine that can suitably suppress deterioration of exhaust characteristics due to an increase in the supply amount of unburned fuel. There is to do.

In the following, means for achieving the above object and its effects are described.
The invention according to claim 1 includes an exhaust purification member provided in the exhaust passage, and when there is a request for recovery of the function of the exhaust purification member, by supplying unburned fuel to the exhaust passage, An exhaust gas purification apparatus for an internal combustion engine that performs a function recovery process for recovering a function, wherein when the supply amount of fuel in a predetermined period during engine operation exceeds a predetermined specified amount, the elapse of the predetermined period The gist of the invention is to limit the supply of the fuel.

  In the present invention, if fuel supply of a specified amount or more is performed during a predetermined period, the fuel supply after the elapse of the predetermined period is limited. Therefore, it is possible to suitably suppress deterioration of exhaust characteristics due to an increase in the amount of unburned fuel supplied through execution of the function recovery process.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an internal combustion engine to which the exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention is applied and a peripheral configuration thereof. 6 is a flowchart showing a procedure of filter regeneration permission processing in the embodiment. The timing chart which shows the relationship between PM deposition amount and fuel addition in the embodiment. The timing chart which shows the relationship between PM deposition amount and fuel addition in the embodiment.

Hereinafter, an embodiment in which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is embodied in an exhaust gas purification apparatus for an on-vehicle diesel engine will be described with reference to FIGS.
As shown in FIG. 1, a piston 13 is slidably accommodated in each cylinder 12 (only one is shown in FIG. 1) of the diesel engine 11. A combustion chamber 15 is defined by the cylinder 12, the top surface of the piston 13, and the cylinder head 14. The cylinder head 14 is provided with a fuel injection valve 16 that injects fuel into the combustion chamber 15.

  An intake passage 17 and an exhaust passage 18 are connected to the combustion chamber 15. The exhaust passage 18 is provided with a PM filter 19 as an exhaust purification member formed of a porous material. The PM filter 19 collects particulate matter (hereinafter referred to as PM) mainly composed of soot in the exhaust gas.

  Further, the exhaust passage 18 is provided with an upstream exhaust temperature sensor 20 at a portion upstream of the PM filter 19, and a downstream exhaust temperature sensor 21 is provided at a portion downstream of the PM filter 19. . The upstream exhaust temperature sensor 20 detects the upstream exhaust temperature, which is the temperature of the exhaust flowing into the PM filter 19. The downstream exhaust temperature sensor 21 detects the downstream exhaust temperature that is the temperature of the exhaust gas that has passed through the PM filter 19. Further, the exhaust passage 18 is provided with a differential pressure sensor 22 that detects a differential pressure ΔP between the exhaust upstream side and the exhaust downstream side of the PM filter 19. The upstream side exhaust temperature sensor 20, the downstream side exhaust temperature sensor 21, and the differential pressure sensor 22 are connected to an electronic control unit 23 that collectively executes various controls of the diesel engine 11, and the detection signals of these sensors are electronic. It is taken into the control device 23.

  The electronic control unit 23 calculates an air flow meter 24 that detects the amount of intake air sucked into the diesel engine 11, an accelerator sensor 25 that detects an operation amount of an accelerator pedal, and a travel distance of a vehicle on which the diesel engine 11 is mounted. Various sensors such as a wheel rotational speed sensor 26 that outputs a signal necessary for this purpose and a vehicle speed sensor 27 that detects a vehicle speed are connected. Further, an ignition switch 28 that is operated by a driver of the automobile is connected to the electronic control unit 23. Signals corresponding to a stop request operation (IG off operation) and a start request operation (IG on operation) of the diesel engine 11 are input from the ignition switch 28 to the electronic control device 23.

  The electronic control device 23 takes in detection signals output from these various sensors, executes various calculations based on these detection signals, and performs various controls of the diesel engine 11. For example, the electronic control unit 23 controls the operation of the fuel injection valve 16 based on the detection results of various sensors, and injects necessary fuel into the combustion chamber 15.

  Further, when the electronic control unit 23 determines that it is necessary to restore the function of the filter 19 because the amount of PM accumulated on the PM filter 19 is large, the second half of the expansion stroke, etc. Thus, so-called post-injection, in which fuel is injected from the fuel injection valve 16 at a time when combustion of the fuel is difficult to occur, is performed. When the post injection is executed, unburned fuel is supplied to the exhaust passage 18, and the PM filter 19 is heated by the unburned fuel, and the collected PM is burned and removed.

  The electronic control unit 23 estimates the PM accumulation amount PMsm accumulated on the PM filter 19 based on the detection result of the differential pressure sensor 22. That is, the electronic control unit 23 uses the fact that the differential pressure ΔP increases with an increase in the PM accumulation amount, and estimates the PM accumulation amount based on the differential pressure ΔP. Basically, when the PM accumulation amount PMsm becomes equal to or greater than the predetermined value A and a function recovery request for the PM filter 19 is made, the post-injection is executed to regenerate the PM filter 19, and this post-injection causes the PM When the accumulation amount PMsm becomes equal to or less than the predetermined value B, the post injection is terminated. Such filter regeneration processing by post injection corresponds to the function recovery processing.

Next, the filter regeneration permission process executed by the electronic control unit 23 will be described.
FIG. 2 shows a procedure for filter regeneration permission processing executed by the electronic control unit 23. This filter regeneration permission process is a process that is interrupted and executed at a constant cycle.

  When this process is started, first, in step S11, it is determined whether or not a filter regeneration execution condition is satisfied. In this determination, when all of the following conditions (a) to (c) are satisfied, the process proceeds to step S12 assuming that the filter regeneration execution condition is satisfied. On the other hand, if any one of the conditions (a) to (c) is not satisfied, it is determined that the filter regeneration execution condition is not satisfied, and the process is temporarily terminated.

(A) The intake air amount is equal to or greater than a preset threshold value.
(B) The exhaust gas temperature is equal to or higher than a preset threshold temperature.
(C) The vehicle speed is greater than or equal to a preset threshold value.

  In step S12, it is determined whether or not the PM accumulation amount PMsm is equal to or greater than the predetermined amount A. If the PM accumulation amount PMsm is equal to or greater than the predetermined amount A, the processing after step S13 is performed. On the other hand, when the PM accumulation amount PMsm is less than the predetermined amount A, the present process is temporarily terminated. The predetermined amount A is a value for determining whether or not the PM deposition amount PMsm has increased to some extent that the PM filter 19 needs to be regenerated, and is a value obtained in advance through experiments or the like.

  In step S13, it is determined whether or not the regeneration execution time of the PM filter 19 was insufficient in the previous trip. Here, if the supply time of the unburned fuel by post injection is short, it can be considered that the regeneration execution time of the PM filter 19 is insufficient. Therefore, the unburned fuel supply time T in the previous trip is less than the specified time RH. A determination is made whether or not there is. The unburned fuel supply time T is obtained from the post injection execution time and is a value corresponding to the unburned fuel supply amount. The specified time RH is a value that can be used to determine whether or not the regeneration execution time of the PM filter 19 is insufficient. For example, the decrease amount of the PM accumulation amount PMsm due to regeneration of the PM filter 19 is insufficient. A time corresponding to the regeneration execution time is set to such a degree that the occurrence of inconvenience due to pressure loss in the PM filter 19 is a concern. As an example, a time from when the post injection is started until the PM deposition amount PMsm becomes equal to or less than the predetermined value B can be set.

The trip is a period from when the diesel engine 11 is started to when it is stopped for the first time.
Incidentally, the situation in which the regeneration execution time of the PM filter 19 becomes insufficient in the previous trip is when the regeneration process is stopped due to a change in the engine operating state or the like during the regeneration process of the PM filter 19 in the previous trip. Etc. For example, if the engine is stopped during the regeneration process of the PM filter 19, the regeneration execution time of the PM filter 19 becomes insufficient. Also, when the filter regeneration execution condition is not satisfied during the execution of the regeneration process, the regeneration process is stopped, and in this case, the regeneration execution time of the PM filter 19 becomes insufficient.

  In step S13, if the unburned fuel supply time is equal to or shorter than the specified time RH, the process proceeds to step S14 on the assumption that the filter regeneration is not sufficiently performed in the previous trip, while the unburned fuel in the previous trip. If the supply time exceeds the specified time RH, it is determined that the filter regeneration has been sufficiently performed in the previous trip, and the process proceeds to step S15.

  In step S14, post injection is performed to execute the filter regeneration process. In step S14, the post injection execution time by the fuel injection valve 16 is measured, and the integrated value of the measurement time is counted as the unburned fuel supply time T. The unburned fuel supply time T is reset when the next trip ends, that is, when a stop request signal is input from the ignition switch 28 in the next trip.

  On the other hand, in step S15, it is determined whether or not the travel distance of the vehicle on the current trip is greater than or equal to the determination value D, or whether or not the travel time of the vehicle on the current trip is greater than or equal to the determination value H. The For example, a distance of about 12 km is set as the determination value D. Further, as the determination value H, for example, a time of about 1200 seconds is set.

If the travel distance is equal to or greater than the determination value D or the travel time is equal to or greater than the determination value H, the process of step S14 is performed and the process is temporarily terminated.
On the other hand, if the travel distance is less than the determination value D and the travel time is less than the determination value H in step S15, the process is terminated without performing the filter regeneration process in step S14.

  Next, with reference to FIG. 3 and FIG. 4, the transition of the unburned fuel supply mode and the PM accumulation amount PMsm by the exhaust purification device of the diesel engine of this embodiment will be described. FIG. 3 shows an example in which the PM accumulation amount PMsm at the time of engine start is between the predetermined value A and the predetermined value B. FIG. 4 shows the PM accumulation amount PMsm at the time of engine start. An example when the predetermined value A is exceeded is shown.

  As shown in FIG. 3, at time t0, the ignition switch 28 is turned on to start the engine, and when this trip is started, the PM accumulation amount PMsm increases with the engine operation, and the time t1 Reaches a predetermined amount A. If the filter regeneration execution condition is not satisfied at this time, the post injection is not executed, and the PM accumulation amount PMsm increases beyond the predetermined amount A. The ignition switch 28 is turned off to end the current trip (time t2), and the ignition switch 28 is turned on again to start the next trip (time t3). At this time, the PM accumulation amount PMsm exceeds the predetermined amount A, but the post injection is not started unless the filter regeneration execution condition is satisfied. After that, when the filter regeneration execution condition is satisfied (time t4), the post injection is started, and when the ignition switch 28 is turned off, the post injection is ended (time t5).

  Next, when the ignition switch 28 is turned on again (time t6), the unburned fuel supply time T during the previous trip period (time t3 to time t5) is defined even if the filter regeneration execution condition is satisfied. When the time RH is exceeded, the post injection is not executed. Thereby, post injection is not continuously performed in continuous trips, and unburned fuel is prevented from being supplied over a long period of time. Thereafter, when the ignition switch 28 is turned off (time t7), the current trip is terminated.

  Next, when the ignition switch 28 is turned on (time t8), the unburned fuel supply time T in the previous trip period (from time t6 to time t7) is equal to or shorter than the specified time RH, so that post injection is started. . In this case, since the unburned fuel supply time T was short in the previous trip, even if post injection is performed in the current trip, the supply of unburned fuel over a long period can be suppressed. Then, the PM accumulation amount PMsm is decreased by the post injection, and when the ignition switch 28 is turned off (time t9), the post injection is ended.

  When the filter regeneration permission process is not executed, when the PM accumulation amount PMsm is decreased from the state where PM is accumulated in a predetermined amount A or more, the post injection is performed until the PM accumulation amount PMsm decreases to the predetermined amount B. Executed. On the other hand, in this embodiment, if post injection exceeding the specified time RH is executed in the trip period from time t3 to time t5, post injection is prohibited in the next trip period (time t6 to time t7). Therefore, for example, it is possible to suppress the unburned fuel supply time T from becoming longer in the period from time t3 to time t9, and it is possible to suppress the deterioration of exhaust characteristics due to unburned fuel.

  Further, as shown in FIG. 4, when the ignition switch 28 is turned on (time t10), even if the PM accumulation amount PMsm exceeds the predetermined amount A, the filter regeneration execution condition is not satisfied. Post injection is not executed, and the PM accumulation amount PMsm increases with engine operation. Thereafter, when the filter regeneration execution condition is satisfied (time t11), the post injection is started, and the PM accumulation amount PMsm starts to decrease. Then, when the ignition switch 28 is turned off (time t12), the post injection is terminated.

  Next, when the ignition switch 28 is turned on again (time t13), if the unburned fuel supply time T in the previous trip period (time t10 to time t12) is equal to or shorter than the specified time RH, post injection is performed. Executed. When the PM accumulation amount PMsm decreases and decreases to between the predetermined value A and the predetermined value B, the ignition switch 28 is turned off (time t14), and the ignition switch 28 is turned on again. (Time t15), when the unburned fuel supply time T exceeds the specified time RH in the previous trip period (time t13 to time t14), the post injection is performed even if the filter regeneration execution condition is satisfied. Not executed, the PM deposition amount PMsm increases. Thereafter, when the PM accumulation amount PMsm exceeds the predetermined value A and the travel distance of the vehicle from the time t15 reaches the determination value D (time t16), post injection is performed, and the PM accumulation amount PMsm reaches the predetermined amount B. When it decreases (time t17), the post injection is terminated.

  In this way, if the unburned fuel supply time T by post injection executed in the previous trip period (for example, from time t10 to time t12) is equal to or shorter than the specified time RH, also in the next trip period (time t13 to t14). Post injection is performed. Therefore, it is possible to suppress an increase in the PM deposition amount PMsm while suppressing an increase in the supply time of unburned fuel. Even if the post-injection in the next trip (after time t15) is prohibited because the unburned fuel supply time T has exceeded the specified time RH in the previous trip period (time t13 to t14). If the travel distance of the vehicle is equal to or greater than the determination value D, the prohibition of post injection is canceled. Therefore, an increase in the PM accumulation amount PMsm due to prohibition of post injection can be suppressed. Even when the traveling time of the vehicle after time t15 is equal to or greater than the determination value H, the same processing as when the traveling distance of the vehicle is equal to or greater than the determination value D is performed. Therefore, also in this case, an increase in the PM accumulation amount PMsm due to the prohibition of the post injection can be suppressed.

As described above, according to the present embodiment, the following effects can be obtained.
(1) When the unburned fuel supply time T in the previous trip exceeds the specified time RH, post injection is prohibited even if the PM accumulation amount PMsm is greater than or equal to the predetermined amount A in the current trip. . Therefore, for example, the unburned fuel supply time in a plurality of consecutive trip periods becomes shorter, and an increase in the supply amount of unburned fuel is suppressed. Therefore, it is possible to suppress the deterioration of exhaust characteristics during a plurality of consecutive trip periods.

  (2) When the travel distance of the vehicle in one trip reaches the determination value D, or when the travel time of the vehicle in one trip reaches the determination value H, the prohibition of post injection is canceled and the same The execution of post injection is allowed. Therefore, it is possible to suppress a decrease in functional recovery of the PM filter 19 due to the prohibition of post injection, that is, an increase in the PM deposition amount PMsm.

  (3) When PM is excessively deposited on the PM filter 19, the supply time of unburned fuel for removing the accumulated PM tends to be long. However, in the present embodiment, even if such a PM filter 19 is provided as an exhaust purification member, the above-described effect can be obtained, so that deterioration of exhaust characteristics due to a prolonged supply time of unburned fuel can be suppressed. .

Note that the above-described embodiment can also be implemented in a form in which this is appropriately changed as follows.
In addition to the differential pressure detected by the differential pressure sensor 22, the detection result of the exhaust temperature by the upstream exhaust temperature sensor 20 and the downstream exhaust temperature sensor 21 is also used to estimate the PM accumulation amount more accurately. It may be.

  -You may change the method of estimating PM deposition amount PMsm. For example, the PM discharge amount discharged from all combustion chambers of the internal combustion engine per unit time is calculated using the fuel injection amount of the fuel injection valve 16 and the engine rotation speed as parameters, and the amount of decrease in the PM accumulation amount PMsm due to filter regeneration. Is calculated from the engine operating state and the post injection execution time. Then, the current PM accumulation amount PMsm may be calculated by subtracting the decrease amount of the PM accumulation amount PMsm from the PM discharge amount.

  -You may change the process performed by step S15. For example, in step S15, it may be determined only whether the travel distance on the current trip is a predetermined distance D or more. In step S15, it may be determined whether or not the traveling time on the current trip is equal to or longer than the predetermined time H.

  -The process of step S15 may be omitted. That is, if it is determined in step S13 that the filter regeneration has been sufficiently performed in the previous trip, the filter regeneration permission process may be terminated.

  -The unburned fuel supply time T is measured in units of the trip period, but instead of this trip period, the unburned fuel supply time T is measured within a preset period (within time). Also good.

Although the unburned fuel supply time T is measured as a value corresponding to the unburned fuel supply amount, the unburned fuel supply amount itself may be measured or calculated.
-In order to limit the supply of unburned fuel, post injection is prohibited. In addition, in the case of such restriction, the supply amount of unburned fuel by post injection may be reduced compared to the non-restricted case.

  In this embodiment, unburned fuel is supplied by post injection from the fuel injection valve 16, but a fuel addition valve is provided upstream of the PM filter 19 in the exhaust passage 18, and the unburned fuel is supplied from the addition valve. May be supplied.

  The exhaust purification member to which the present invention is applied is not limited to the PM filter 19. For example, the control of the present invention may be applied to the supply of unburned fuel when the NOx occlusion reduction side catalyst is applied and sulfur is released from this catalyst or when NOx is reduced.

In addition, the technical idea that can be grasped from each of the above-described embodiments or modifications thereof will be described below together with the effects thereof.
(A) In the invention according to claim 1, the internal combustion engine is mounted in a vehicle, and the vehicle after the predetermined period has elapsed when the amount of fuel supply exceeds the specified amount. An exhaust purification device for an internal combustion engine, wherein the restriction on the fuel supply is released when the travel distance of the engine is equal to or greater than a predetermined distance.

  While the supply of unburned fuel is restricted, the function recovery of the exhaust purification member is reduced because the recovery of the function of the exhaust purification member is suppressed. In this regard, in this configuration, the restriction on fuel supply is released when the travel distance of the vehicle has reached a predetermined distance. Therefore, it is possible to suppress the deterioration of the exhaust characteristics while ensuring the functional recovery of the exhaust purification member.

  (B) In the invention according to claim 1 or claim (a), the internal combustion engine is mounted on a vehicle, and the fuel supply amount exceeds the specified amount, and the predetermined period has elapsed. An exhaust gas purification apparatus for an internal combustion engine, wherein the restriction on the supply of the fuel is released when the running time of the vehicle after that is longer than a predetermined time.

  While the supply of unburned fuel is restricted, the function recovery of the exhaust purification member is reduced because the recovery of the function of the exhaust purification member is suppressed. In this regard, in this configuration, the restriction on fuel supply is released when the traveling time of the vehicle has reached a predetermined time. Therefore, it is possible to suppress the deterioration of the exhaust characteristics while ensuring the functional recovery of the exhaust purification member.

  (C) In the invention according to any one of claim 1, claim (a) and claim (b), the predetermined period is a trip period from when the internal combustion engine starts until it stops. An exhaust emission control device for an internal combustion engine, wherein when the amount of fuel supplied during the previous trip period exceeds the specified amount, the fuel supply during the current trip period is limited.

  According to this configuration, when the supply amount of unburned fuel during one trip period exceeds a specified amount, post injection in the next trip is limited. Therefore, an increase in the amount of unburned fuel supplied in successive trips can be suppressed.

  (D) In the invention according to any one of claims 1 and (a) to (c), the exhaust purification member is a PM filter that collects particulate matter in the exhaust. An exhaust emission control device for an internal combustion engine.

  If particulate matter is excessively deposited on the PM filter, the supply time of unburned fuel for removing the accumulated particulate matter tends to be long. However, in the same configuration, even when such an exhaust purification member is provided, the effects of the configurations described in the above claims 1 and (A) to (C) can be obtained. Deterioration of exhaust characteristics based on the period can be suppressed.

  DESCRIPTION OF SYMBOLS 11 ... Diesel engine as an internal combustion engine, 16 ... Fuel injection valve, 18 ... Exhaust passage, 19 ... PM filter, 23 ... Electronic control apparatus.

Claims (1)

An exhaust purification member provided in the exhaust passage is provided, and when there is a request for recovery of the function of the exhaust purification member, a function recovery process for recovering the function of the exhaust purification member by supplying unburned fuel to the exhaust passage is performed. An exhaust purification device for an internal combustion engine,
An exhaust emission control device for an internal combustion engine, wherein when the amount of fuel supplied in a predetermined period during engine operation exceeds a predetermined specified amount, the fuel supply is restricted after the predetermined period has elapsed. .

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