JP2005330936A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology capable of suppressing excessive temperature rise during regeneration treatment of a filter and suppressing deterioration of emission simultaneously. <P>SOLUTION: If excessive temperature rise of a first filter during regeneration treatment of the first filter collecting particulate matter in an exhaust gas passage of an internal combustion engine is estimated, exhaust gas of the internal combustion engine is made to bypass the first filter (S104) and particulate matter in bypassed exhaust gas is collected by a second filter provided separately from the first filter. If the amount of particulate matter accumulated on the second filter exceeds permissible amount (S106), temperature of the first filter is dropped (S111) and bypassing of exhaust gas is cancelled (S108). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

  The exhaust gas of the internal combustion engine contains particulate matter mainly composed of carbon. A technique for providing a particulate filter (hereinafter referred to as “filter”) for collecting particulate matter in an exhaust system of an internal combustion engine is known in order to prevent such particulate matter from being released into the atmosphere.

  In such a filter, when the amount of collected particulate matter increases, the back pressure in the exhaust increases due to clogging of the filter, and the engine performance decreases. On the other hand, by raising the exhaust gas temperature upstream of the filter, the collected particulate matter is oxidized and removed, and the exhaust gas purification performance of the filter is regenerated (hereinafter referred to as “filter regeneration process”). .)

On the other hand, when the operating state of the internal combustion engine becomes a high engine load and a high engine speed during the regeneration process of the filter, the temperature of the exhaust gas introduced into the filter becomes high, and the particulate matter in the filter is oxidized. Since the reaction becomes excessively active, the temperature of the filter may become abnormally high (hereinafter referred to as “filter OT”). On the other hand, a technique is known that includes a bypass passage that bypasses the filter and lowers the filter temperature by bypassing the filter to high-temperature exhaust when the filter temperature exceeds a predetermined temperature (for example, , See Patent Document 1).

In such a case, during the period when the filter is bypassed by the exhaust gas, the exhaust gas that has passed through the bypass path is not purified by the filter but is released to the atmosphere, resulting in a problem of worsening the emission. In view of this, there has been proposed a technique for purifying exhaust gas that has passed through the bypass passage by providing another filter downstream of the bypass passage that bypasses the filter (see, for example, Patent Document 2).

However, when such a configuration is adopted, if a large amount of particulate matter accumulates on the downstream filter, the back pressure in the exhaust gas may increase due to clogging of the downstream filter, resulting in a decrease in engine performance. Further, when the downstream filter regeneration process is performed independently of the upstream filter regeneration process, a lot of energy is consumed, and the fuel consumption of the internal combustion engine may deteriorate.
Japanese Patent Laid-Open No. 06-173640 JP 2001-342820 A JP 2000-320321 A JP 2003-201821 A Japanese Laid-Open Patent Publication No. 06-26325

  An object of the present invention is to provide a technique capable of suppressing an excessive temperature rise during a filter regeneration process and simultaneously suppressing deterioration of emission.

In the present invention for achieving the above object, when an excessive temperature rise of the first filter is predicted during the regeneration process of the first filter for collecting particulate matter in the exhaust passage of the internal combustion engine, the internal combustion engine The exhaust gas of the engine is bypassed by the first filter, and the particulate matter in the bypassed exhaust gas is collected by a second filter provided separately from the first filter, and the particulate matter in the second filter is further collected. When the amount of accumulated gas increases, the temperature of the first filter is lowered and the exhaust bypass is released.

More specifically, the particulate matter in the exhaust passage of the internal combustion engine is collected and the particulate matter in the exhaust gas passing through the exhaust passage is collected, and the collection ability of the particulate matter is obtained by a regeneration process for oxidizing and removing the collected particulate matter. A first filter to be regenerated;
One end is connected to the upstream side of the first filter in the exhaust passage, the other end is connected to the downstream side of the first filter in the exhaust passage, and the exhaust is discharged from the internal combustion engine to the filter. Bypass passage for bypassing,
Switching means for selecting whether to pass the first filter or the bypass passage through the exhaust gas flowing upstream of the first filter in the exhaust passage;
In the regeneration process, an excessive temperature rise prediction unit that predicts that the temperature of the first filter is higher than a predetermined allowable temperature, and
When the temperature of the first filter is predicted to be higher than the allowable temperature by the excessive temperature rise prediction means, the exhaust gas flowing through the upstream side of the first filter in the exhaust passage by the switching means. An exhaust purification system of an internal combustion engine selected to pass through the bypass passage,
A second filter that is provided on the downstream side of the connection portion of the exhaust passage with the other end of the bypass passage and collects particulate matter in the exhaust gas that passes through the bypass passage;
Further comprising first filter temperature lowering means for lowering the temperature of the first filter by increasing the amount of exhaust passing through the first filter in the exhaust passage;
During the period when the switching means is selected to pass the bypass passage through the exhaust gas flowing upstream of the first filter in the exhaust passage, the particulate matter in the exhaust gas passing through the bypass passage is When the amount of particulate matter collected by the second filter and collected by the second filter reaches a predetermined allowable deposition amount, the first filter temperature lowering means causes the first filter temperature lowering means to The temperature of one filter is lowered, and the switching means is selected to pass the first filter through the exhaust gas flowing in the exhaust passage on the upstream side of the first filter.

  Here, in the regeneration process of the filter in the internal combustion engine, the particulate matter deposited in the filter is oxidized and removed by increasing the temperature of the exhaust gas introduced from the internal combustion engine into the filter. Even after the rise of the exhaust temperature introduced into the filter is stopped, the oxidation reaction of the particulate matter continues. Further, when oxygen in the exhaust gas is continuously supplied to the filter in a state where the filter is heated to a high temperature due to the oxidation reaction of the particulate matter, the oxidation of the particulate matter in the filter is promoted, and the filter is further heated to a higher temperature. Become. As a result, depending on the operation state of the internal combustion engine, the temperature of the filter may be higher than the allowable temperature, and OT may occur. Here, the allowable temperature is a temperature as a threshold at which the filter, the catalyst supported on the filter, or the like may become abnormally hot.

  Therefore, in the present invention, an over-temperature prediction means for predicting that the first filter overheats, and a bypass passage for bypassing the first filter in the exhaust discharged from the internal combustion engine, When the excessive temperature rise prediction means predicts that the first filter is excessively heated, the exhaust gas discharged from the internal combustion engine is bypassed by the first filter. Thereby, it can suppress that the said 1st filter OTs.

However, in this case, during the period in which the exhaust gas discharged from the internal combustion engine is bypassed by the first filter, the exhaust gas that has passed through the bypass passage cannot be purified, and the emission may be deteriorated. . Therefore, in the present invention, the bypass passage includes a second filter independent of the first filter in the exhaust passage after joining the exhaust passage on the downstream side of the first filter.

  By so doing, particulate matter in the exhaust gas passing through the bypass passage can be collected by the second filter during a period in which the exhaust gas discharged from the internal combustion engine is bypassed by the first filter. , Emission deterioration can be suppressed.

  Here, if the period during which the first filter is bypassed is prolonged in the exhaust gas exhausted from the internal combustion engine, the amount of particulate matter accumulated in the second filter increases, and the upstream of the second filter The back pressure increases, which may affect the operation performance of the internal combustion engine. Therefore, in the present invention, when the amount of the particulate matter accumulated in the second filter exceeds an allowable value, the bypass of the first filter is canceled. However, in this case, oxygen supply is started again with respect to the first filter in which the oxidation reaction of the particulate matter is continuing, so that the first filter may be OT. Therefore, in the present invention, when releasing the bypass of the first filter, the first filter temperature lowering control is performed to lower the temperature of the first filter by the first filter temperature lowering means.

  If it carries out like this, while being able to suppress that the amount of deposits of the particulate matter to the 2nd filter exceeds an allowable value, it can control operating performance of an internal-combustion engine, and it can control that the 1st filter carries out OT. That is, according to the present invention, it is possible to achieve both the suppression of the OT of the first filter and the suppression of the deterioration of the emission, and the increase in the back pressure upstream of the second filter causes the operation of the internal combustion engine. The influence on performance can be suppressed.

  Here, the first filter temperature lowering control specifically refers to the first filter by increasing the exhaust amount introduced into the first filter and increasing the amount of heat removed from the first filter. This is control for lowering the temperature of the filter. Examples of this control include control for increasing the engine speed, control for stopping the intake throttle by the intake throttle valve, control for reducing the EGR amount when the internal combustion engine is equipped with an EGR device, and a variable nozzle turbo mechanism. For example, the control for increasing the supercharging pressure can be given.

  Here, when the exhaust from the internal combustion engine passes through the first filter during the regeneration process of the first filter, the temperature of the exhaust discharged from the first filter is, for example, 600 ° C. or more. It is hot. Accordingly, the particulate matter deposited on the second filter during the period when the exhaust gas from the internal combustion engine is allowed to pass through the bypass passage is exhausted by the exhaust gas discharged from the first filter during the regeneration process of the first filter. Oxidized and removed. On the other hand, during normal operation other than the regeneration process period of the first filter, exhaust gas from the internal combustion engine passes through the first filter, so that particulate matter in the exhaust gas from the internal combustion engine is removed from the first filter. To be collected. Accordingly, during the normal operation, the particulate matter hardly accumulates on the second filter. Thus, in the present invention, the regeneration process for the second filter is unnecessary.

  Note that the second filter in the present invention is preferably arranged immediately after the first filter. Here, as described above, the particulate matter deposited on the second filter during the period when the exhaust from the internal combustion engine is allowed to pass through the bypass during the regeneration process of the first filter, During the regeneration process, the exhaust gas discharged from the first filter is oxidized and removed during a period in which the exhaust gas from the internal combustion engine passes through the first filter. In contrast, if the second filter is disposed immediately after the first filter, the exhaust temperature discharged from the first filter can be maintained at a higher temperature when being introduced into the second filter. In addition, the particulate matter deposited on the second filter can be oxidized and removed more efficiently.

  In the present invention, the filter capacity of the second filter may be smaller than the filter capacity of the first filter. That is, as described above, the second filter is in the process of regeneration for the first filter and further bypasses the first filter to the exhaust from the internal combustion engine in order to avoid OT of the first filter. Particulate matter is collected only during the period. From this, it can be said that the amount of particulate matter collected by the second filter is smaller than the particulate matter collected by the first filter. Therefore, the filter capacity of the second filter can be made smaller than that of the first filter.

  By so doing, it is possible to suppress an increase in cost caused by providing the second filter independently of the first filter, and it is possible to easily wind the exhaust passage in the vehicle and improve space efficiency. Here, the filter capacity refers to the volume of the filter, in other words, the amount of particulate matter that can be collected by the filter. Here, for example, the second filter may have a filter capacity that can be stored in the exhaust passage.

In the present invention, the difference in detecting the differential pressure between the exhaust pressure upstream of the branch point to the bypass passage in the exhaust passage and the exhaust pressure downstream of the second filter in the exhaust passage. A pressure detecting means;
From the differential pressure at the time of bypass passage selection detected by the differential pressure detection means when the switching means is selected to pass the bypass passage through the exhaust gas flowing upstream of the first filter in the exhaust passage, It is preferable that a deposition amount of the particulate matter collected by the second filter on the second filter is derived.

  In general, it is known that the amount of particulate matter deposited on a filter of an internal combustion engine can be detected from the differential pressure of the exhaust pressure before and after the filter. On the other hand, the present invention includes two filters, the first filter and the second filter, as described above. In order to independently detect the amount of particulate matter deposited on these two filters, a differential pressure sensor for detecting the differential pressure of the exhaust pressure before and after each filter is provided for the first filter and the second filter. You may make it prepare independently. However, this increases the cost of the exhaust purification system.

  Therefore, in the present invention, there is provided differential pressure detecting means for detecting a differential pressure between the exhaust pressure upstream of the branch point to the bypass passage in the exhaust passage and the exhaust pressure downstream of the second filter. The exhaust pressure upstream of the branch point to the bypass passage in the exhaust passage and the exhaust pressure downstream of the second filter during the period in which the exhaust from the internal combustion engine is passed through the bypass passage. The differential pressure is detected by the differential pressure detection means, and the amount of particulate matter deposited on the second filter is derived from the detected differential pressure when the bypass passage is selected.

  That is, while the exhaust gas from the internal combustion engine passes through the bypass passage, the exhaust gas from the internal combustion engine does not pass through the first filter. It can be considered that it is substantially equivalent to the differential pressure of the exhaust pressure at. Accordingly, the particulate matter is deposited on the second filter by the differential pressure detecting means for detecting the differential pressure between the exhaust pressure upstream of the branch point to the bypass passage in the exhaust passage and the exhaust pressure downstream of the second filter. A quantity can be derived.

In general, it is known that the value of the differential pressure of the exhaust pressure before and after the filter is strictly influenced by the exhaust flow rate passing through the filter and the exhaust temperature. Therefore, in the present invention, the amount of particulate matter deposited on the second filter may be derived after correcting the differential pressure when the bypass passage is selected based on the exhaust flow rate and exhaust temperature when the differential pressure is detected. Specifically, the relationship between the differential pressure when the bypass passage is selected, the exhaust flow rate when the differential pressure is detected, the exhaust temperature when the differential pressure is detected and the amount of particulate matter deposited on the second filter is mapped, and the bypass The amount of particulate matter deposited on the second filter is derived by reading out from the map the value of the amount of particulate matter deposited on the second filter corresponding to the differential pressure at the time of passage selection, the exhaust flow rate at that time, and the exhaust temperature. May be.

  In this way, the differential pressure detecting means for detecting the differential pressure between the exhaust pressure upstream of the branch point to the bypass passage in the exhaust passage and the exhaust pressure downstream of the second filter is provided to the second filter. It is possible to more accurately detect the amount of accumulated particulate matter.

  On the other hand, in the present invention, when the exhaust from the internal combustion engine is selected to pass through the first filter, the first filter selection differential pressure detected by the differential pressure detection means and the bypass passage selection Based on the difference from the time differential pressure, the amount of particulate matter collected by the first filter deposited on the first filter may be derived.

  That is, while the exhaust gas from the internal combustion engine passes through the first filter, the exhaust gas from the internal combustion engine passes through both the first filter and the second filter. The time differential pressure can be considered to be substantially equivalent to the sum of the differential pressure of the exhaust pressure before and after the first filter and the differential pressure of the exhaust pressure before and after the second filter. Therefore, the amount of particulate matter deposited on the first filter can be derived based on a value obtained by subtracting the differential pressure at the time of selecting the bypass passage from the differential pressure at the time of selecting the first filter.

  In this case as well, the value of the differential pressure at the time of selecting the first filter is strictly affected by the exhaust flow rate and the exhaust temperature. In addition, since the time when the differential pressure at the time of selecting the first filter is different from the time when the differential pressure at the time of selecting the bypass passage is detected, when the differential pressure at the time of selecting the first filter is detected, and when the differential pressure at the time of selecting the bypass passage is detected, The exhaust flow rate and exhaust temperature in the exhaust from the internal combustion engine are different. Further, the passage resistance between the exhaust passage and the bypass passage is different between when the first filter is passed through the exhaust from the internal combustion engine and when the bypass passage is passed. Therefore, in the present invention, when performing the calculation of subtracting the differential pressure at the time of bypass passage selection from the differential pressure at the time of selection of the first filter, the value of the differential pressure at the time of bypass passage selection is detected. Correction is made based on the exhaust flow rate difference, the exhaust temperature difference, and the gas passage resistance between the bypass passage and the exhaust passage, and the calculation is performed in accordance with the conditions when the differential pressure is detected when the first filter is selected. May be.

  Further, a value obtained by subtracting the corrected differential pressure at the time of selection of the bypass passage from the differential pressure at the time of selection of the first filter is based on the exhaust flow rate and the exhaust temperature when the differential pressure at the time of selection of the first filter is detected. In this case, the amount of the particulate matter deposited on the first filter may be derived. Specifically, the value obtained by subtracting the corrected differential pressure at the time of selection of the bypass passage from the differential pressure at the time of selection of the first filter, the value of the exhaust flow rate and the exhaust temperature, and the accumulation of particulate matter in the first filter A map storing the relationship with the quantity may be created in advance based on experiments, and correction may be performed using the map.

  By doing so, the differential pressure detecting means for detecting the differential pressure between the exhaust pressure upstream of the branch point to the bypass passage in the exhaust passage and the exhaust pressure downstream of the second filter is used to supply the first filter to the first filter. The amount of particulate matter deposited and the amount of particulate matter deposited on the second filter can be derived more accurately.

In the present invention, it is desirable that the timing for detecting the differential pressure at the time of selecting the first filter and the timing for detecting the differential pressure at the time of selecting the bypass passage are close. By doing so, it is possible to reduce the difference in the exhaust flow rate and the exhaust temperature in the exhaust from the internal combustion engine when the differential pressure at the time of selecting the first filter is detected and when the differential pressure at the time of selecting the bypass passage is detected. . As a result, the correction described above can be omitted, and the amount of particulate matter deposited on the first filter and the amount of particulate matter deposited on the second filter can be more accurately derived by simple processing. Can do.

  In the present invention, in order to bring the timing for detecting the differential pressure at the time of selection of the first filter close to the timing of detection of the differential pressure at the time of selection of the bypass passage, for example, the switching means causes the passage route of the exhaust gas from the internal combustion engine to be the first. The differential pressure when selecting the first filter and the differential pressure when selecting the bypass passage may be detected before and after changing to the bypass passage from the filter. Further, for example, immediately after detecting the differential pressure at the time of selection of the first filter, the switching means allows the exhaust from the internal combustion engine 1 to pass through the bypass passage for a short period of time, and the differential pressure at the time of selection of the bypass passage is detected within that period. It may be.

  Further, as described above, in the present invention, only the differential pressure detection means for detecting the differential pressure between the exhaust pressure upstream of the branch point to the bypass passage in the exhaust passage and the exhaust pressure downstream of the second filter. Since both the amount of particulate matter deposited on the first filter and the amount of particulate matter deposited on the second filter are derived, exhaust gas detection points can be reduced. Cost can be reduced.

  The means for solving the problems in the present invention can be used in combination as much as possible.

  In the present invention, it is possible to suppress an excessive temperature rise during the filter regeneration process, and at the same time, it is possible to suppress the deterioration of the emission.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to the present embodiment and its exhaust system and control system. An internal combustion engine 1 shown in FIG. 1 is a diesel engine. In FIG. 1, the inside of the internal combustion engine 1 and its intake system are omitted.

  In FIG. 1, an exhaust pipe 5 through which exhaust gas discharged from the internal combustion engine 1 flows is connected to the internal combustion engine 1, and this exhaust pipe 5 is connected downstream to a muffler (not shown). Further, an exhaust purification device 10 for purifying particulate matter (for example, soot) in the exhaust is disposed in the middle of the exhaust pipe 5. An oxidation catalyst 10a having oxidation ability is disposed upstream in the exhaust purification apparatus 10, and a first filter 10b that collects particulate matter (for example, soot) in the exhaust is disposed downstream. . A second filter 11 having a smaller capacity than the first filter 10 b and housed in the exhaust pipe 5 is disposed on the exhaust pipe 5 downstream of the exhaust purification device 10.

  A fuel injection valve 14 for supplying fuel as a reducing agent to the oxidation catalyst 10a of the exhaust purification device 10 is disposed on the exhaust pipe 5 upstream of the exhaust purification device 10 during the regeneration process of the first filter 10b. Has been. The fuel injected from the fuel addition valve 14 is introduced into the oxidation catalyst 10a together with the exhaust from the internal combustion engine 1, and causes an oxidation reaction in the oxidation catalyst 10a. As a result, the temperature of the exhaust discharged from the oxidation catalyst 10a increases.

The first filter 10b and the second filter 11 in this embodiment are a wall flow type particulate filter made of a porous base material, an oxidation catalyst typified by platinum (Pt), potassium (K) and cesium (Cs). A NOx occlusion agent represented by the above is supported. However, the first filter 10b and the second filter 11 may not necessarily carry a NOx storage agent. For example, a separate NOx catalyst may be provided in the exhaust pipe 5 independently.

  Further, from the exhaust pipe 5 in this embodiment, the bypass pipe 6 is branched upstream of the exhaust purification device 10. At the branch point from the exhaust pipe 5 to the bypass pipe 6, the upstream exhaust pipe 5 is connected. A switching valve 15 is provided for selecting whether to introduce the exhaust gas flowing into the bypass pipe 6 or the exhaust gas purification device 10. The bypass pipe 6 joins the exhaust pipe 4 on the downstream side of the exhaust purification catalyst 10, in other words, on the downstream side of the first filter 10b.

  That is, by operating the switching valve 15 and allowing the exhaust pipe 5 to flow as it is to the exhaust discharged from the internal combustion engine 1, the first filter 10b and the second filter 11 can be passed. Similarly, by passing the bypass pipe 6 through the exhaust discharged from the internal combustion engine 1, the first filter 10b can be bypassed and only the second filter 11 can be passed. The switching valve 15 functions as switching means in the present embodiment.

  Further, an upstream side exhaust pressure sensor 13 for detecting the exhaust pressure upstream of the first filter 10b is provided in the exhaust pipe 5 upstream of the switching valve 15. In addition, a downstream side exhaust pressure sensor 18 that detects the exhaust pressure downstream of the second filter 11 is provided in the exhaust pipe 5 on the downstream side of the second filter 11. Further, a first exhaust temperature sensor 12 for detecting the temperature of the exhaust gas introduced into the exhaust gas purification device 10 or the first filter 10 b is provided in the exhaust pipe 5 immediately upstream of the exhaust gas purification device 10, and the second filter 11. A second exhaust temperature sensor 17 for detecting the temperature of the exhaust gas introduced into the second filter 11 is provided immediately upstream.

The internal combustion engine 1 configured as described above and its exhaust system are provided with an electronic control unit (ECU) 20 for controlling the internal combustion engine 1 and the exhaust system. The ECU 20 controls the operating state of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's request, and also includes an exhaust purification system including the exhaust purification device 10 and the second filter 11 of the internal combustion engine 1. It is a unit that performs such control.

  The ECU 20 includes an upstream exhaust pressure sensor 13 and a downstream exhaust pressure sensor in this embodiment, in addition to sensors related to control of the operating state of the internal combustion engine 1 such as an air flow meter, a crank position sensor, and an accelerator position sensor (not shown). 18, a first exhaust temperature sensor 12, a second exhaust temperature sensor 17, and the like are connected via electrical wiring, and an output signal is input to the ECU 20. On the other hand, a fuel injection valve (not shown) in the internal combustion engine 1 is connected to the ECU 20 via an electrical wiring, and the switching valve 15 and the fuel addition valve 14 in the present embodiment are connected via an electrical wiring. It is controlled by the ECU 20.

  The ECU 20 includes a CPU, a ROM, a RAM, and the like. The ROM stores a program for performing various controls of the internal combustion engine 1 and a map storing data. One of the programs stored in the ROM of the ECU 20 is also a regeneration processing routine (not described) for regenerating the particulate matter collecting ability of the first filter 10b and a filter control routine in this embodiment, which will be described later. It is. Further, in the present embodiment, it is used when deriving the accumulation amount of the particulate matter for the first filter 10b and the second filter 11 from the output of the upstream exhaust pressure sensor 13 and the output of the downstream exhaust pressure sensor 18. Maps are also stored in the ROM of the ECU 20.

Here, in the internal combustion engine 1 and its exhaust system shown in FIG. 1, particulate matter is deposited on the first filter 10 b and the second filter 11 from the output signals of the upstream exhaust pressure sensor 13 and the downstream exhaust pressure sensor 18. A method for deriving the quantity will be described. Here, first, when the exhaust gas from the internal combustion engine 1 passes through the exhaust gas purification device 10 and the second filter 11, the output signal of the upstream side exhaust pressure sensor 13 and the downstream side exhaust pressure sensor 18. An output signal is detected, and a difference ΔPF between the output signal of the upstream side exhaust pressure sensor 13 and the output signal of the downstream side exhaust pressure sensor 18 in that case is calculated. This ΔPF corresponds to the differential pressure when the first filter is selected in the present embodiment. ΔPF corresponds to a differential pressure obtained by adding a differential pressure ΔP1 before and after the first filter 10b and a differential pressure ΔP2 before and after the second filter 11. Here, at the same time, the exhaust flow rate GaF at the time when the output signal of the upstream side exhaust pressure sensor 13 and the output signal of the downstream side exhaust pressure sensor 18 are detected is obtained from the output of the air flow meter, and the exhaust temperature TF is changed to the first exhaust temperature sensor 12. From the output of.

  Then, the output signal of the upstream side exhaust pressure sensor 13 and the output signal of the downstream side exhaust pressure sensor 18 when the switching valve 15 is operated to bypass the first filter 10 b to the exhaust gas from the internal combustion engine 1. And the difference ΔPB between the output signal of the upstream side exhaust pressure sensor 13 and the output signal of the downstream side exhaust pressure sensor 18 in that case is calculated. Here, the output signal of the upstream side exhaust pressure sensor 13 and the output signal of the downstream side exhaust pressure sensor 18 when the first filter 10b is bypassed to the exhaust gas from the internal combustion engine 1 are actually switched for a short time. 15 may be detected by bypassing the first filter 10b to the exhaust gas from the internal combustion engine 1, or in the past, the switching valve 15 is operated to bypass the first filter 10b to the exhaust gas from the internal combustion engine 1. The value of ΔPB at the time of detection may be stored in the ROM of the ECU 20 and read out. This ΔPB corresponds to the differential pressure when the bypass passage is selected in this embodiment. ΔPB corresponds to the differential pressure ΔP2 before and after the second filter 11. Here, at the same time, the exhaust flow rate GaB at the time when the output signal of the upstream side exhaust pressure sensor 13 and the output signal of the downstream side exhaust pressure sensor 18 are detected is determined from the output of the air flow meter, and the exhaust temperature TB is determined as the second exhaust temperature sensor. Obtained from 17 outputs. Here, in the past, when reading the value of ΔPB when the switching valve 15 is operated and the exhaust from the internal combustion engine 1 is detected by bypassing the first filter 10b, the values of GaB and TB are similarly read. Alternatively, the value at the time of detection of the output signal of the upstream side exhaust pressure sensor 13 and the output signal of the downstream side exhaust pressure sensor 18 may be read from the ROM of the ECU 20.

  Here, the amount of particulate matter deposited on the first filter 10b and the second filter 11 is derived from the values of ΔPB and ΔPF. Before that, generally the differential pressure between the exhaust pressure before and after the filter is the exhaust pressure. Since it is known that it is influenced by each condition such as the flow rate, the exhaust temperature, and the exhaust passage resistance, the value of ΔPB is corrected so as to match the above conditions when ΔPF is detected.

  Specifically, the values of ΔGa = GaF−GaB and ΔT = TF−TB, which are the differences between the conditions when ΔPB is detected and when ΔPF is detected, are calculated. A difference ΔW of the exhaust passage resistance due to the difference between whether the exhaust from the engine 1 passes through the first filter 10b or the bypass pipe 6 is calculated. Since this ΔW is determined by the shape of the exhaust pipe 5 and the bypass pipe 6, it may be calculated in advance and stored in the ROM of the ECU 20.

  Here, a map storing the relationship between the values of ΔPB, ΔGa, ΔT, and ΔW and ΔPB ′ that is a correction value of ΔPB is created in advance. Then, the value of ΔPB ′ corresponding to the values of ΔPB, ΔGa, ΔT, and ΔW obtained by the above calculation is read from the map so that the value of ΔPB matches the above-mentioned conditions when ΔPF is detected. A corrected value ΔPB ′ is calculated.

The values of the differential pressure ΔP1 before and after the first filter 10b and the differential pressure ΔP2 before and after the second filter 11 under the condition when ΔPF is detected can be obtained as follows.
ΔP1 = ΔPF−ΔPB ′ (1)
ΔP2 = ΔPB '(2)

  Furthermore, from the map obtained by experimentally determining and storing the relationship between the exhaust flow rate Ga, the exhaust temperature T, the differential pressure ΔP between the exhaust pressure before and after the filter, and the amount A of particulate matter deposited on the filter, ΔP1, By reading the values of the deposition amounts A1 and A2 corresponding to ΔP2, the deposition amount A1 of the particulate matter on the first filter 10b and the deposition amount A2 of the particulate matter on the second filter 11 can be finally derived. it can.

  In the above, when calculating the value of ΔPB ′ by correcting the value of ΔPB, the value of ΔPB ′ is calculated from the map storing the relationship between the values of ΔPB, ΔGa, ΔT, and ΔW and ΔPB ′. Calculated by reading. However, without using a map, a conversion equation for converting the value of ΔPB into a value of ΔPB ′ using the values of ΔGa, ΔT, and ΔW is created, and the ECU 20 calculates the value of ΔPB by calculating the conversion equation. From this, the value of ΔPB ′ may be calculated.

  In the following description, it is assumed that the amount of particulate matter deposited on the first filter 10b and the amount of particulate matter deposited on the second filter 11 are derived by the above method. Further, the upstream exhaust pressure sensor 13 and the downstream exhaust pressure sensor 18 described above constitute a differential pressure detecting means in the present embodiment.

  Next, regeneration processing in the internal combustion engine 1 and filter control at that time will be described. In the internal combustion engine 1, as described above, exhaust gas purification is performed by collecting particulate matter in the exhaust gas by the first filter 10b. However, when the amount of the particulate matter collected in the first filter 10b increases, the first filter 10b is clogged. As a result, the back pressure of the internal combustion engine 1 may increase, and the operation performance may deteriorate. is there.

  Therefore, in the internal combustion engine 1, the particulate matter in the first filter 10b is oxidized and removed every predetermined period or when it is detected that a prescribed amount of particulate matter has been collected in the first filter 10b. Playback processing is performed. In addition, the above-mentioned predetermined period is a period as a threshold that is considered that the increase in the back pressure of the first filter 10b affects the driving performance when the execution interval of the regeneration process of the first filter 10b becomes longer than that, The above-mentioned predetermined amount is the amount of particulate matter as a threshold that is considered to increase the back pressure of the first filter 10b when the amount of particulate matter collected by the first filter 10b is increased. .

  In this regeneration process, fuel as a reducing agent is supplied from the fuel addition valve 14 to the oxidation catalyst 10a. As a result, an oxidation reaction of fuel occurs in the oxidation catalyst 10a, and the temperature of the exhaust gas discharged from the oxidation catalyst 10a rises. Then, the temperature of the first filter 10b also rises, and when the temperature of the first filter 10b becomes equal to or higher than the ignition temperature of the particulate matter, the oxidation reaction of the particulate matter is started in the first filter 10b. As a result, the particulate matter in the first filter 10b can be oxidized and removed. In this case, it is a premise that the switching valve 15 selects a flow path in which exhaust from the internal combustion engine 1 does not bypass the first filter 10b.

In the regeneration process of the first filter 10b, oxygen continues to be supplied to the first filter 10b even after the start of the oxidation reaction of the particulate matter in the first filter 10b. Therefore, the oxidation reaction of the particulate matter occurs in the first filter 10b. Promoted. In this case, when the temperature of the exhaust gas from the internal combustion engine 1 rises due to the operating state of the internal combustion engine 1 becoming a high load and high rotation speed, the temperature of the first filter 10b becomes higher than the allowable temperature, and the first filter 10b. May be predicted to be OT. Here, the allowable temperature is a temperature as a threshold value at which the first filter 10b, the oxidation catalyst supported on the first filter 10b, the NOx storage agent, and the like may become abnormally hot.

  Here, the greater the amount of particulate matter deposited on the first filter 10b, the higher the temperature of the first filter 10b, and the higher the engine load and the higher engine speed, the more the first filter 10b becomes. It has been found that it becomes easier to OT. Therefore, in the present embodiment, the relationship between the amount of particulate matter deposited on the first filter 10b, the temperature of the first filter 10b, the operating state of the internal combustion engine 1, and the presence or absence of the possibility of OT is mapped beforehand. Then, the accumulation amount of the particulate matter in the first filter 10b derived by the above-described method from the output signals of the upstream side exhaust pressure sensor 13 and the downstream side exhaust pressure sensor 18, and the output of the second exhaust temperature sensor are estimated. The presence / absence of OT possibility corresponding to the temperature of one filter 10b and the operating state of the internal combustion engine 1 detected from a crank position sensor and an accelerator position sensor (not shown) is read from the map, and the result is considered as OT possibility. If OT occurs, it may be predicted that OT will occur.

  In this embodiment, when it is predicted that OT of the first filter 10b will occur according to the above prediction procedure, the bypass valve 6 is allowed to pass through the exhaust from the internal combustion engine 1 by operating the switching valve 15. Thus, by bypassing the first filter 10b, the supply of oxygen to the first filter 10b is stopped, and the temperature of the first filter 10b is lowered.

  Here, in the present embodiment, as described above, in order to suppress the OT of the first filter 10b, the exhaust gas from the internal combustion engine 1 is not allowed to pass through the first filter 10b but is passed through the bypass pipe 6. The particulate matter in the exhaust gas is collected by the second filter 11. As a result, it is possible to suppress the deterioration of the emission even during the period when the exhaust gas from the internal combustion engine 1 bypasses the first filter 10b.

  Further, in this embodiment, if the period for bypassing the first filter 10b to the exhaust gas from the internal combustion engine 1 is prolonged, the amount of particulate matter deposited on the second filter 11 may increase and exceed the allowable deposition amount. The allowable accumulation amount is a threshold at which the second filter 11 may be clogged with particulate matter and the back pressure upstream of the second filter 11 may increase, which may affect the operating state of the internal combustion engine 1. The amount of deposition as. This amount is experimentally determined in advance. The amount of particulate matter deposited on the second filter 11 is also derived from the output signals of the upstream exhaust pressure sensor 13 and the downstream exhaust pressure sensor 18 by the method described above.

  When the amount of particulate matter deposited on the second filter 11 exceeds the allowable accumulation amount, the bypass of the first filter 10b of the exhaust from the internal combustion engine 1 is canceled and the exhaust from the internal combustion engine 1 is discharged. The first filter 10b is passed. Thereby, the back pressure rise upstream of the 2nd filter 11 is avoided.

  However, in this case, the supply of oxygen to the first filter 10b is restarted, so that there is a possibility that the first filter 10b is OT again. Therefore, in the present embodiment, when the bypass of the first filter 10b of the exhaust gas from the internal combustion engine 1 is cancelled, the first filter temperature lowering control for lowering the temperature of the first filter 10b is also performed. Specifically, the first filter temperature reduction control is introduced into the first filter 10b by increasing the engine speed of the internal combustion engine 1 without affecting the speed of the vehicle on which the internal combustion engine 1 is mounted. This is realized by increasing the amount of exhausted air and increasing the amount of heat removed from the first filter 10b by the exhaust.

Note that the particulate matter deposited on the second filter 11 at this stage can be oxidized and removed by the exhaust gas discharged from the first filter 10b during the subsequent regeneration process of the first filter 10b.

  As described above, in this embodiment, when the amount of particulate matter deposited on the second filter becomes equal to or greater than the allowable amount of accumulation, the switching valve 15 is operated after the first filter temperature lowering control is performed. The first filter 10b is passed through the exhaust gas from the internal combustion engine 1. Therefore, an increase in back pressure upstream of the second filter 11 can be suppressed, and at the same time, OT in the first filter 10b can be suppressed.

FIG. 2 is a flowchart showing a filter control routine in this embodiment.
This routine is a program stored in the ROM of the ECU 20, and is repeatedly executed by the ECU 20 at predetermined intervals during the operation of the internal combustion engine 1.

  When this routine is executed, it is first determined in S101 whether the first filter 10b is being regenerated. Specifically, during the execution of a regeneration process routine (not described) that is performed when performing the regeneration process, the regeneration process flag is set to “1”, and the value of the regeneration process flag is set to ECU 20 in S101. It may be determined whether or not the reproduction process is in progress.

  If it is determined that the first filter 10b is not being regenerated, the process proceeds to S110. In S110, output signals of the upstream exhaust pressure sensor 13 and the downstream exhaust pressure sensor 18 are acquired, and a difference ΔPF between these output signals is calculated. When the processing of S110 ends, this routine is ended as it is. Here, the reason why ΔPF is calculated is that it is desirable to use the latest value of ΔPF in order to determine the necessity of regeneration processing for the first filter 10b in a regeneration processing routine (not shown).

  On the other hand, if it is determined in S101 that the first filter 10b is being regenerated, the process proceeds to S102.

  In S102, the output signals of the upstream exhaust pressure sensor 13 and the downstream exhaust pressure sensor 18 are acquired, and the differences ΔPF and ΔPB between the output signals are calculated. Here, when calculating the value of ΔPB, the switching valve 15 allows the exhaust from the internal combustion engine 1 to pass through the bypass pipe 6 for a short period, and the upstream side exhaust pressure sensor 13 and the downstream side exhaust pressure in that period. The value of ΔPB is calculated from the output signal of the sensor 18. This is because it is desirable to use the latest ΔPB value in the following processing in this routine.

  Next, in S103, it is determined whether or not the first filter 10b may be OT. Specifically, the temperature of the first filter 10b and the operating state of the internal combustion engine 1 are acquired. Further, the amount A1 of particulate matter deposited on the first filter 10b is derived from the values of ΔPF and ΔPB acquired in S102 using the method described above. And the possibility of OT of the 1st filter 10b is derived | led-out by reading the presence or absence of the OT possibility of the 1st filter 10b corresponding to those values from the map produced previously. The process of S103 in this routine constitutes an excessive temperature rise prediction unit in the present embodiment.

  Here, if it is determined that there is no possibility that the first filter 10b will be OT, it can be determined that the exhaust from the internal combustion engine 1 does not need to bypass the first filter 10b, so that this routine is immediately terminated. To do. On the other hand, if it is determined that the first filter 10b may be OTed, the process proceeds to S104.

In S <b> 104, the switching valve 15 is actuated to allow the exhaust from the internal combustion engine 1 to bypass the first filter 10 b and pass the bypass pipe 6. In addition, this
Exhaust gas from the internal combustion engine 1 begins to pass through the second filter 11.

  Next, proceeding to S105, the output signals of the upstream side exhaust pressure sensor 13 and the downstream side exhaust pressure sensor 18 are acquired, and the value of the difference ΔPB between these output signals is calculated. Furthermore, the amount A2 of particulate matter deposited on the second filter 11 is derived using the method described above. When the process of S105 ends, the process proceeds to S106.

  In S106, it is determined whether or not the deposition amount A2 of the particulate matter on the second filter 11 is greater than or equal to the allowable deposition amount. Here, when it is determined that the particulate matter deposition amount A2 on the second filter 11 is smaller than the allowable deposition amount, it is still possible to continue bypassing the first filter 10b to the exhaust from the internal combustion engine 1. Since it can be determined that there is, the process proceeds to S107.

  In S107, it is determined again whether the first filter 10b may be OT. The details of this process are the same as S103. Here, when it is determined that there is a possibility that the first filter 10b may be OT, it is determined that it is still necessary to keep the first filter 10b bypassed to the exhaust gas from the internal combustion engine 1. Return to processing. Then, in S107, these processes are repeatedly executed until it is determined that there is no possibility that the first filter 10b is OT. On the other hand, if it is determined in S107 that the first filter 10b is not likely to OT, it is determined that the first filter 10b may be allowed to pass through the exhaust gas from the internal combustion engine 1. move on. In addition, the process of S107 in this routine comprises the excessive temperature rise prediction means in a present Example similarly to the process of S103.

  Here, returning to the description of S106, if it is determined in S106 that the deposition amount A2 of the particulate matter on the second filter 11 is equal to or larger than the allowable deposition amount, the exhaust from the internal combustion engine 1 is further increased. If the first filter 10b continues to be bypassed, it is determined that the back pressure on the upstream side of the second filter 11 is increased, which may affect the operation performance of the internal combustion engine 1. Therefore, the process proceeds to S111.

  In S111, the first filter temperature reduction control is performed. Specifically, the engine speed of the internal combustion engine 1 is increased so as not to increase the vehicle speed of the vehicle on which the internal combustion engine 1 is mounted. This increases the amount of exhaust gas introduced into the first filter 10b. As a result, the amount of heat removed from the first filter 10b increases, and the temperature of the first filter 10b can be lowered. When the process of S111 ends, the process proceeds to S108. In addition, the process of S111 in this routine comprises the 1st filter temperature fall means in a present Example.

  In S108, the switching valve 15 is actuated to pass the first filter 10b through the exhaust from the internal combustion engine 1, and the bypass of the first filter 10b is released. Thereby, the deposition of the particulate matter on the second filter 11 is stopped. When the process of S108 ends, the process proceeds to S109.

  In S109, output signals from the upstream exhaust pressure sensor 13 and the downstream exhaust pressure sensor 18 are acquired, and a difference ΔPF between these output signals is calculated. Here, the reason why ΔPF is calculated is that it is desirable to use the latest value of ΔPF in order to determine the necessity of regeneration processing for the first filter 10b in a regeneration processing routine (not shown). When the process of S109 is completed, this routine is temporarily ended.

As described above, in the present embodiment, when it is determined that the first filter 10b may be OT during the regeneration process of the first filter 10b, the first filter 10b is discharged into the exhaust gas of the internal combustion engine 1. The particulate matter in the bypassed exhaust gas is collected by the second filter 11 provided separately from the first filter 10b. Therefore, the first
It is possible to achieve both suppression of OT of the filter 10b and suppression of deterioration of emission during a period in which the exhaust gas of the internal combustion engine 1 bypasses the first filter 10b.

  Further, in this embodiment, when the amount of particulate matter accumulated in the second filter 11 exceeds an allowable value, the first filter temperature lowering control for lowering the temperature of the first filter 10b is performed and the exhaust gas is discharged. The bypass will be released. Therefore, it is possible to suppress the deterioration of the operating performance of the internal combustion engine 1 due to the increase of the back pressure upstream of the second filter 11, and it is possible to suppress the OT of the first filter 10b.

  In addition, in the present embodiment, the difference between the exhaust pressures before and after the first filter 10b and the second filter 11 is detected by the two exhaust pressure sensors, the upstream exhaust pressure sensor 13 and the downstream exhaust pressure sensor 18. The pressure is calculated, and the amount of particulate matter deposited on each of the first filter 10b and the second filter 11 is derived. Therefore, the number of exhaust pressure sensors can be reduced, and the cost of the exhaust purification system can be reduced.

It is the figure which showed schematic structure of the internal combustion engine which concerns on the Example of this invention, its exhaust system, and a control system. It is a flowchart which shows the filter control routine which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 5 ... Exhaust pipe 6 ... Bypass pipe 10 ... Exhaust gas purification device 10a ... Oxidation catalyst 10b ... 1st filter 11 ... 2nd filter 12 ... 1st DESCRIPTION OF SYMBOLS 1 Exhaust temperature sensor 13 ... Upstream exhaust pressure sensor 14 ... Fuel addition valve 15 ... Switching valve 17 ... 2nd exhaust temperature sensor 18 ... Downstream exhaust pressure sensor 20 ... ECU

Claims (4)

The particulate matter collecting ability is regenerated by a regeneration process that is provided in the exhaust passage of the internal combustion engine and collects particulate matter in the exhaust gas passing through the exhaust passage and oxidizes and removes the collected particulate matter. One filter,
One end is connected to the upstream side of the first filter in the exhaust passage, the other end is connected to the downstream side of the first filter in the exhaust passage, and the exhaust is discharged from the internal combustion engine to the filter. Bypass passage for bypassing,
Switching means for selecting whether to pass the first filter or the bypass passage through the exhaust gas flowing upstream of the first filter in the exhaust passage;
In the regeneration process, an excessive temperature rise prediction unit that predicts that the temperature of the first filter becomes higher than a predetermined allowable temperature, and
When the temperature of the first filter is predicted to be higher than the allowable temperature by the excessive temperature rise prediction means, the exhaust gas flowing through the upstream side of the first filter in the exhaust passage by the switching means. An exhaust purification system of an internal combustion engine selected to pass through the bypass passage,
A second filter that is provided on the downstream side of the connection portion of the exhaust passage with the other end of the bypass passage and collects particulate matter in the exhaust gas that passes through the bypass passage;
Further comprising first filter temperature lowering means for lowering the temperature of the first filter by increasing the amount of exhaust passing through the first filter in the exhaust passage;
During the period when the switching means is selected to pass the bypass passage through the exhaust gas flowing upstream of the first filter in the exhaust passage, the particulate matter in the exhaust gas passing through the bypass passage is When the amount of particulate matter collected by the second filter and collected by the second filter reaches a predetermined allowable deposition amount, the first filter temperature lowering means causes the first filter temperature lowering means to An exhaust gas purification system for an internal combustion engine, wherein the temperature of one filter is lowered and the first filter is selected to pass through the exhaust gas flowing upstream of the first filter in the exhaust passage by the switching means. system.   The exhaust purification system for an internal combustion engine according to claim 1, wherein a filter capacity of the second filter is smaller than a filter capacity of the first filter. Differential pressure detecting means for detecting a differential pressure between an exhaust pressure upstream of a connection portion with the one end of the bypass passage in the exhaust passage and an exhaust pressure downstream of the second filter in the exhaust passage. Further comprising
From the differential pressure at the time of bypass passage selection detected by the differential pressure detection means when the switching means is selected to pass the bypass passage through the exhaust gas flowing upstream of the first filter in the exhaust passage, 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein an accumulation amount of the particulate matter collected by the second filter on the second filter is derived.   The first filter selection differential pressure detected by the differential pressure detection means when the switching means is selected to pass the first filter through the exhaust gas flowing upstream of the first filter in the exhaust passage. The accumulation amount of the particulate matter collected by the first filter on the first filter is derived based on a difference between the pressure difference and the differential pressure when the bypass passage is selected. An exhaust purification system for an internal combustion engine.

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