JP5621322B2 - Exhaust gas purification system - Google Patents

Description

  The present invention relates to an exhaust gas purification system that collects PM in exhaust gas of a diesel engine.

  PM (Particulate Matter) in exhaust gas of diesel engine is collected by DPF (Diesel Particulate Filter), for example, a kind of filter called DPD (Diesel Particulate Defuser), and the amount of PM discharged to the outside is collected. Reduction exhaust gas purification systems (hereinafter referred to as DPF systems) have been developed.

  A DPF system using a DPF is provided in the middle of an exhaust pipe in the same way as other exhaust gas purification systems (for example, an SCR (Selective Catalytic Reduction) system), purifies exhaust gas and discharges it into the atmosphere. Yes (see, for example, Patent Document 1).

As this DPF system, there is a continuous regeneration type DPF system in which a DOC (Diesel Oxidation Catalyst) is provided on the upstream side of the DPF and a CSF (Catalyzed Soot Filter) is provided on the downstream side of the DPF. The DPF system is obtained by utilizing the fact that oxidation of PM by NO ₂ is relatively performed at low temperature by the upstream DOC generate NO ₂ from the NO and O ₂ contained in the exhaust gas, in the NO ₂ The PM trapped in the downstream CSF is oxidized and removed as CO ₂ to perform DPF regeneration.

However, even in such a DPF system, when the exhaust gas temperature is low, the DOC is not activated, so the generation of NO ₂ is not promoted, and the PM cannot be oxidized to perform the DPF regeneration. Accumulation on the CSF continues and clogging of the CSF proceeds.

  In response to the clogging of the CSF, when the PM accumulation amount exceeds a predetermined amount, the exhaust gas temperature is forcibly raised to a target temperature (for example, about 500 ° C. to 600 ° C.) and collected by the DPF. Forcible combustion removal of the PM is performed.

  Since the PM accumulation amount is proportional to the output value of the differential pressure sensor that measures the differential pressure of the exhaust gas before and after the DPF, when the output value of the differential pressure sensor exceeds a predetermined differential pressure, the ECU (Engine Control Unit) Assuming that the accumulation amount exceeds a predetermined amount, the DPF warning lamp (DPF lamp) provided in the cabin is turned on, and then the ECU automatically starts DPF regeneration while the vehicle is running (automatic regeneration). Alternatively, the driver who stops the vehicle after the DPF lamp is lit presses the regeneration execution switch to start the DPF regeneration (manual regeneration).

  Note that the filter clogging may be detected based on the travel distance in addition to the differential pressure of the exhaust gas before and after the DPF. In this case, when the travel distance exceeds a predetermined distance, DPF regeneration is started automatically or manually as described above.

  When the DPF regeneration is started, the ECU controls the fuel injection, the exhaust throttle, and the exhaust brake valve to raise the exhaust gas temperature, and when the DOC catalyst activation temperature is reached, the post injection is started. The added fuel is oxidized (i.e., combusted) on the DOC, the temperature of the exhaust gas flowing downstream from the DOC is further increased (e.g., to about 500 to 600 [deg.] C.), and PM deposited on the CSF is oxidized.

Japanese Patent No. 4175281

  In the case of manual regeneration performed by stopping the vehicle, exhaust gas temperature control and DPF regeneration processing are performed stably. However, in the case of automatic regeneration performed while the vehicle is traveling, depending on the traveling pattern of the vehicle, Since the fuel injection amount changes sequentially, the temperature rise control of the exhaust gas becomes unstable.

  At this time, if the exhaust gas temperature decrease due to low-speed operation or deceleration and the exhaust gas temperature increase due to rapid acceleration are repeated, there will be a concern about melting of the DPF due to an excessive increase in the exhaust gas temperature.

  Also, due to insufficient combustion of PM due to the exhaust gas temperature decrease, a long processing time is required to complete the regeneration of the DPF, fuel used for increasing the exhaust gas temperature is increased, and there is a concern that the fuel consumption may deteriorate. The

  Furthermore, if the above unstable DPF regeneration process is repeated, the temperature and flow rate of the exhaust gas become uneven, and PM clogging occurs in the DOC upstream DOC. If DPF regeneration is performed in this state, the amount of exhaust gas flowing to the CSF in the shadow is reduced, so that the CSF is not sufficiently heated, and the PM combustion efficiency during DPF regeneration processing is significantly reduced. become.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust gas purification system that can reliably remove PM accumulated in a DPF without remaining unburned without causing a DPF melting loss or a deterioration in fuel consumption during the DPF regeneration process.

The present invention has been made in order to solve the above-mentioned problems. A DPF comprising an oxidation catalyst and a filter for collecting PM in exhaust gas is connected to an exhaust pipe of a diesel engine, and the amount of PM in the DPF is When the exhaust gas temperature reaches a certain amount or more, the exhaust gas temperature is regenerated by performing temperature rise control so as to maintain the initial regeneration target temperature and the final regeneration target temperature higher than the initial regeneration target temperature, and the initial regeneration target temperature the set final reproduction target temperature of the first predetermined temperature lower PM combustion determination temperature for each playback during playback, the exhaust gas temperature, after playing keeping the initial playback target temperature, keeping the final regeneration target temperature and, and at the beginning of the exhaust gas purification system determines that plays when the exhaust gas temperature is high is made to PM combustion determination temperature and the final PM combustion determination temperature, the oxidation catalyst It is an exhaust gas purification system, characterized in that a target temperature changing means Ru raising the final reproduction target temperature when it is determined that M is burned remains.

With respect to the initial playback target temperature and said final regeneration target temperature, the second predetermined temperature higher post-injection allows the upper limit temperature was set respectively, during playback, the exhaust gas temperature is greater than the initial and final post-injection possible upper limit temperature When the post-injection is stopped and PM is determined to remain unburned in the oxidation catalyst, the final regeneration target temperature is increased , and the second predetermined temperature of the post-injection upper limit temperature with respect to the increased final regeneration target temperature May be made smaller.

The target temperature changing means may increase the final regeneration target temperature and increase the first predetermined temperature when it is determined that PM remains unburned in the oxidation catalyst .

The DPF may be composed of DOC and CSF, and the final regeneration target temperature may be set to be equal to or higher than the initial post-injectable upper limit temperature .

The final post-injectable upper limit temperature may be set to be equal to or lower than a melting temperature of the DPF.

  According to the exhaust gas purification system of the present invention, it is possible to regenerate the DPF without causing unburned PM without causing the DPF melting damage or the deterioration of the fuel consumption during the DPF regeneration.

It is a system diagram which shows the structure of a DPF system. It is explanatory drawing of the exhaust-gas purification system which concerns on embodiment of this invention. It is explanatory drawing which concerns on other embodiment of this invention. It is explanatory drawing of a normal exhaust gas purification system.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a system diagram showing a DPF system.

  In FIG. 1, an intake manifold 11 and an exhaust manifold 12 of a diesel engine 10 are respectively connected to a compressor 14 and a turbine 15 of a supercharger (turbocharger) 13, and air from the upstream intake pipe 16 a is boosted by the compressor 14. Then, the air is cooled through the intercooler 17 of the downstream side intake pipe 16b and supplied to the diesel engine 10 from the intake manifold 11 via the intake throttle (intake throttle valve) 18, and the exhaust gas from the diesel engine 10 passes through the turbine 15. After driving, the exhaust pipe 20 is exhausted.

The upstream intake pipe 16a is provided with a MAF (Mass Air Flow) sensor 19 for measuring the intake air amount. The MAF sensor 19 controls the opening of the intake throttle 18 to adjust the intake air amount. Further, the exhaust pipe 20 and the suction tubes 16a returns a part of exhaust gas to the intake system of the diesel engine 10, EGR pipe 21 for reducing NO _X by raising the temperature during the combustion is connected, An EGR cooler 22 and an EGR valve 23 are connected to the EGR pipe 21.

  An exhaust brake valve 24, a DPF 25, an exhaust throttle (exhaust throttle valve) 26, and a silencer 27 are connected to the exhaust pipe 20. The DPF 25 includes a DOC 28 made of an active catalyst that oxidizes unburned fuel and a CSF 29 that collects PM in the exhaust gas.

  Before and after the DOC 28, exhaust gas temperature sensors 30a and 30b used for determining whether or not post injection is possible, post injection amount, and completion of DPF regeneration are provided. Further, in order to estimate the PM accumulation amount of the CSF 29, a differential pressure sensor 31 that measures the differential pressure of exhaust before and after the CSF 29 is provided.

  The output values of these sensors are input to an ECU 32 that performs overall control of the operation of the diesel engine 10 and also performs DPF regeneration, and the control signal output from the ECU 32 causes the fuel injector 33 of the diesel engine 10 and the exhaust gas to be exhausted. The throttle 26, the exhaust brake valve 24, the EGR valve 23 and the like are controlled.

  In order to operate the diesel engine 10, the ECU 32 includes information such as the accelerator opening from the accelerator position sensor, the engine speed from the rotation speed sensor, the vehicle speed from the vehicle speed sensor 34, the temperature of the engine cooling water, and the like. Information is also entered.

  The ECU 32 also includes a DPF warning light 35a for manual regeneration provided in the cabin, a DPF warning light 35b for automatic regeneration, a regeneration execution switch 36 for the driver to perform manual regeneration, and a diesel engine 10. A check engine lamp 37 and the like that are lit to notify the user when a malfunction occurs are connected and controlled.

  In this system, the air passes through the MAF sensor 19 in the upstream side intake pipe 16a, is pressurized by the compressor 14 of the supercharger 13, is cooled through the intercooler 17 in the downstream side intake pipe 16b, and is taken in the intake throttle 18 And enters the cylinder of the diesel engine 10 from the intake manifold 11.

  On the other hand, the exhaust gas generated in the cylinder passes through the exhaust manifold 12, drives the turbine 15, is purified by the exhaust gas purification system including the DPF 25 and the SCR device, is silenced by the silencer 27, and is discharged into the atmosphere. . A part of the exhaust gas is cooled by the EGR cooler 22, the amount thereof is adjusted by the EGR valve 23, and circulated to the intake manifold 11.

The exhaust gas contains PM, and this PM is collected by the DPF 25. In the DPF 25, NO in the exhaust gas is oxidized to NO ₂ by the DOC 28 at all times, and the PM collected in the downstream CSF 29 is oxidized to CO ₂ with this NO ₂ to remove the PM from the CSF 29. In other words, so-called DPF regeneration is continuously performed.

  However, when the exhaust gas temperature is low, the temperature of the DOC 28 is lowered and is not activated, so that the oxidation reaction of NO is not promoted and PM cannot be oxidized to perform DPF regeneration. As a result, the filter clogging continues.

  For this clogging of the filter, the exhaust gas temperature is forcibly raised when the PM accumulation amount exceeds a predetermined amount, and the PM collected in the CSF 29 is forcibly burned and removed. Is called.

  Since the PM accumulation amount is proportional to the output value of the differential pressure sensor 31, when the output value of the differential pressure sensor 31 exceeds a predetermined threshold, the ECU 32 detects clogging of the filter, and the ECU 32 automatically detects the DPF. Regeneration is performed, or the DPF warning lamp 35a is turned on, and the driver is prompted to perform DPF regeneration by pressing the regeneration execution switch 36.

  In addition to the output value of the differential pressure sensor 31, the start time of DPF regeneration is determined by whether or not the travel distance calculated based on the vehicle speed measured by the vehicle speed sensor 34 exceeds a predetermined distance (distance threshold). You may do it.

  When the regeneration process is started, the ECU 32 determines a vehicle state from input signals (for example, engine speed, vehicle speed, exhaust gas temperature, etc.), and the ECU 32 causes the fuel injector 33, the diesel engine 10, and the exhaust brake valve 24 to be used. Then, the EGR valve 23 and the intake throttle 18 are controlled, and the exhaust gas temperature detected by the temperature sensor 30a is raised until the temperature at which the DOC 28 is activated.

  When the DOC 28 is activated, post injection is started, and the exhaust gas temperature detected by the temperature sensor 30b is further raised to the regeneration target temperature. The ECU 32 feeds back the exhaust gas temperature and adjusts the post injection amount by PID control.

  At this time, the regeneration target temperature is set in two stages (for example, about 500 ° C. and about 600 ° C.) in the early stage of the regeneration process and late in the regeneration process, and is controlled by the ECU 32 so that the exhaust gas is maintained at each target temperature for a predetermined time. In the initial stage of DPF regeneration in which a large amount of PM remains, the target temperature is set low to prevent the CSF 29 from being melted due to the combustion of PM and melting the CSF 29. In the latter stage of DPF regeneration, when the amount of combustion is reduced, the target temperature is set high so that PM is burned efficiently.

  Thereafter, the ECU 32 returns the fuel injector 33 to normal injection, returns the engine speed of the diesel engine 10 to a normal idle state or running state, opens the exhaust throttle 26, returns the EGR valve 23 to normal (open), The intake throttle 18 is returned to normal (open). As a result, the exhaust gas temperature decreases, and the regeneration process ends.

  Compared with manual regeneration that is performed while the vehicle is stopped, in automatic regeneration that is performed automatically while the vehicle is running, the DPF 25 is subjected to repeated acceleration / deceleration depending on the vehicle traveling pattern during the DPF regeneration process, that is, traffic congestion. The exhaust gas supplied to the engine (temperature, flow rate, etc.) changes, the exhaust gas temperature rises insufficiently, and the time required to complete the regeneration process and the post-injection amount become longer, and the fuel efficiency of the vehicle There is a problem that damages.

  In addition, when the temperature of the exhaust gas is close to the target temperature rise and the engine shifts from a low load state to a high load state, the exhaust gas flow rate or post-injection amount suddenly increases and the exhaust gas overheats. Then, there is a concern that the DPF 25 is melted.

Therefore, in the normal exhaust gas purification system, the PM combustion determination temperature T _PM lower than the regeneration target temperature T by the first predetermined temperature or the second predetermined temperature higher post-injectable upper limit temperature _TL is set as the target temperature. It is set to be linked.

Hereinafter, an exhaust gas purification system in which the regeneration target temperature is set in two stages of the initial regeneration target temperature T _1Y1 and the normal final regeneration target temperature T _2Y2 will be described in detail.

As shown in FIG. 4, when the regeneration target temperature is set in two stages (for example, about 500 ° C. and about 600 ° C.) of the initial regeneration target temperature T _1Y1 and the normal final regeneration target temperature T _2Y2 , the initial regeneration target temperature is set. PM combustion determination temperatures T _PMY1 and T _PMY2 lower than the first predetermined temperature (A ° C.) and the second predetermined temperature (B ° C.) higher than the temperature T _1Y1 and the normal final regeneration target temperature T _2Y2 , respectively. T _LY1 and T _LY2 are set in conjunction with the target temperature.

The PM combustion determination temperature T _PM is a temperature at which it can be guaranteed at least that PM is burning, and the post-injectable upper limit temperature T _L is a temperature at which the DPF 25 can be guaranteed at least to be not melted by experiment. Thereby, the first predetermined temperature (A ° C.) and the second predetermined temperature (B ° C.) are determined.

  Furthermore, a predetermined upper limit is set for the post-injection amount that can be used for one regeneration process, the fuel used for the post-injection is accumulated until the completion of the regeneration process, and the post-injection amount accumulated in the ECU 32 is the upper limit. When the value is exceeded, it is determined that the reproduction has failed, and the reproduction process is interrupted.

During AutoPlay, ECU 32, when the temperature T _G of the exhaust gases from the signal input is determined to be in the above PM combustion determination temperature T _PM, the time (hereinafter it is assumed that PM is burned, reproduction It is adapted to integrate the time of), also when the temperature T _G of the exhaust gases is above the post-injection allows the upper limit temperature T _L is adapted to immediately stop the post injection in order to prevent the erosion of the DPF 25.

ECU32 playback time (i.e., the integrated value of exhaust gas temperature T _G is the PM combustion determination temperature T _PM over a certain time) when has reached a predetermined value (e.g., 2 to 5 minutes), the amount of PM accumulated in the DPF25 _Assuming that it has been removed to a certain amount or less, the temperature rise target temperature of the exhaust gas is changed from the initial regeneration target temperature T _1Y1 to the normal final regeneration target temperature T _2Y2 .

  Thereafter, when the regeneration time reaches a predetermined value (for example, 3 to 10 minutes), the ECU 32 detects the completion of the DPF regeneration process.

  By the way, when the vehicle state changes during the regeneration process (for example, when the vehicle starts and stops repeatedly), the temperature and flow rate of the exhaust gas become non-uniform and PM remains unburned on the DOC 28. PM clogging may occur.

  In this case, if the DPF regeneration is performed with the DOC 28 being clogged, the amount of exhaust gas flowing to the CSF 29 that is behind it is reduced, the CSF 29 is not sufficiently heated, and the PM of the DPF regeneration process is reduced. There is a concern that PM may remain unburned after the end of regeneration due to a decrease in combustion efficiency, or generation of white smoke or deterioration of fuel consumption due to the need for regeneration time.

In order to suppress or eliminate the PM of the DOC 28, the final regeneration target temperature in the regeneration process is increased by a predetermined value (for example, about 20 to 50 ° C.) from the normal final regeneration target temperature T _2Y2 , thereby generating the heat generated by the DOC 28 itself. It has been found that the object surface temperature of the DOC 28 can be raised to suppress or eliminate the PM of the DOC 28, but in the conventional way of thinking, in conjunction with the final regeneration target temperature T _2Y2 to be changed The PM combustion determination temperature T _PMY2 and the post- _injectable upper limit temperature T _LY2 rise. In particular, even if the post-injectable upper limit temperature T _LY2 is higher than the temperature at which the DPF 25 may melt, the ECU 32 performs post-injection. May continue to run.

_Further, regarding the PM combustion determination temperature T _PMY2 , if the DOC 28 is in a healthy state (that is, a state where PM clogging has not occurred), no PM combustion residue is generated in the CSF 29 without raising the temperature. _TPMY2 is good.

Therefore, in the exhaust gas purification system according to the present embodiment, as shown in FIG.
With raising the normal final regeneration target temperature T _2X2, it has a target temperature changing means increases the first predetermined temperature A, so that you can change the PM combustion determination temperature T _PMX2 separately with changes in the final regeneration target temperature T _3X2 To be.

_{Alternatively} , the final regeneration target temperature T _3X2 is raised, the second predetermined temperature B is decreased, and the post- _injectable upper limit temperature T _LX2 can be individually changed as the final regeneration target temperature T _3X2 rises.

Alternatively, previously set at the time of normal initial playback target temperature T _1X1 and normal final reproduction target temperature T _2X2 from PM combustion determination temperature T _PMX1, T _PMX2 the post-injection allows the upper limit temperature T _LX1, T _LX2 respectively, final reproduction Only the target temperature T _3X2 may be changed individually.

Further, as shown in FIG. 3, the PM combustion determination temperatures T _PMX1 and T _PMX3 and the post- _injectable upper limit temperatures T _LX1 and T _LX3 are respectively determined from the initial normal regeneration target temperature T _1X1 and the normal final regeneration target temperature T _{2X3 in advance} . The final regeneration target temperature T _3X3 may be set so as to gradually increase from a predetermined value (for example, about 600 ° C.) after the regeneration target temperature is changed.

  The present invention does not specifically limit the target temperature changing means, and the regeneration target temperature may be changed from a changeover switch provided in the ECU 32, and a control system mounted on the ECU 32 automatically changes the regeneration target temperature. You may be able to.

The exhaust gas purification system according to the present embodiment, without worrying about the melting of fuel economy or DPF 25, change the final regeneration target temperature T _3X2, T _3X3, will be able to play the remaining without DPF 25 burn the PM.

  Next, returning to FIG. 2, the operation of the present invention will be described below.

Given in the exhaust gas purification system of the present invention, when the remaining burning DOC28 and CSF29 of PM in the automatic reproduction of the normal mode occurs, a final regeneration target temperature T _3X2 during automatic playback, the normal final reproduction target temperature T _2X2 It is changed so as to increase by a value α (for example, about 20 to 50 ° C.).

The timing for changing the final regeneration target temperature T _3X2 is not particularly specified, and without making the ECU 32 detect the PM unburned residue, a model of the PM that is likely to remain after DPF regeneration is obtained through experiments, and the final regeneration target temperature is determined. T _3X2 may be changed in advance, and the regeneration process may be performed constantly at the changed final regeneration target temperature T _3X2 .

Alternatively, by using a signal input to the ECU 32, PM remaining unburned is detected from the number of travel patterns in which PM may accumulate on the DOC 28, the temperature difference and pressure difference of the exhaust gas around the DPF 25, and the like. change the final regeneration target temperature T _3X2 only in AutoPlay, after the DPF25 is regenerated without remaining unburned PM may be adapted to return to the normal final reproduction target temperature T _2X2 at.

  As in the normal regeneration system, when the ECU 32 detects that the amount of PM collected in the DPF 25 exceeds a predetermined value, the DPF regeneration process is started.

When the exhaust gas temperature T _G reaches the catalyst activation temperature of DOC28, post injection to increase the temperature it is performed exhaust gas to the regeneration target temperature (e.g., 500 ° C. or so).

When the ECU 32 detects that the PM accumulated in the CSF 29 is removed to a predetermined amount or less during the initial regeneration process, that is, when the regeneration time reaches a predetermined time, the ECU 32 detects the exhaust gas temperature T _G. the is the initial playback target temperature T _1X2, to further raising the temperature to the final regeneration target temperature T _3X2 that have changed to the high temperature side.

In the present embodiment, when the regeneration time reaches a predetermined time (that is, when the integrated value of the time when the exhaust gas temperature T _G is equal to or higher than the PM combustion determination temperature T _PM exceeds a predetermined value), The ECU 32 detects that the PM has been removed to a certain amount or less. For example, the PM accumulation amount estimated from the differential pressure before and after the DPF 25 before starting the regeneration process is calculated as PM. may be as found by subtracting an integration value of the difference between the combustion determination temperature T _PM and the exhaust gas temperature T _G, also DPF25 is to estimate the like temperature difference and a pressure difference of the exhaust gas before and after Also good.

  By changing the target temperature of the final regeneration process to a higher temperature than usual, the exhaust gas is sufficiently heated on the downstream side of the DOC 28 where PM is deposited, and remains unburned in the CSF 29 in the initial regeneration process. PM can be burned without burning.

  In addition, since the DOC 28 is also maintained at a higher temperature than normal, it is possible to burn and remove PM unburned residue deposited on the DOC 28.

At this time, the PM combustion determination temperature T _PMX2 and the post-injection possible upper limit temperature T _LX2 can be changed separately from the changed final regeneration target temperature T _3X2 , so the post necessary for completion of the regeneration process The injection amount and the possibility of melting of the DPF 25 can be reduced.

As described above, in the exhaust gas purification system of the present invention, the vehicle running pattern is changed sequentially, in DPF25 as unstable regeneration process is repeated, the final reproduction target temperature T _3X2 normal final regeneration target temperature by raising than T _2X2, it is possible to rest without removing burn the PM deposited on DOC28 and CSF29.

Further, since it changes the final reproduction target PM combustion determination independently of the temperature T _3X2 temperature T _PMX2 and post-injection allows the upper limit temperature T _LX2 which is changed to the high temperature side, reducing the fuel consumed until the reproduction processing is completed In addition, it is possible to prevent the DPF 25 from being melted due to excessive temperature rise of the exhaust gas.

The present invention is not particularly limited and a final regeneration target temperature T _3X2 and PM combustion determination temperature T _PMX2 and post-injection allows the upper limit temperature T _PMX2, can of course be suitably modified within the scope of the present invention .

28 DOC (oxidation catalyst)
T regeneration target temperature A first predetermined temperature T _PM PM combustion judgment temperature _TG exhaust gas temperature

Claims (5)

When a DPF consisting of an oxidation catalyst and a filter that collects PM in exhaust gas is connected to the exhaust pipe of the diesel engine, when the PM amount of the DPF exceeds a certain amount, the exhaust gas temperature is set to the initial regeneration target temperature. and its initial playback with the target temperature to play performed in warm-up control to keep the high final regeneration target temperature than the initial playback target temperature and the final reproduction first predetermined temperature lower PM combustion determination for the target temperature Each temperature is set and during regeneration, the exhaust gas temperature is maintained at the initial regeneration target temperature and then regenerated, and then is maintained at the final regeneration target temperature for regeneration, and the initial PM combustion determination temperature and the final PM combustion determination temperature are set. said final regeneration target temperature when a play when the high exhaust gas temperature in the exhaust gas purification system to determine that performed, it is determined that the PM is burned remain in the oxidation catalyst for An exhaust gas purification system characterized in that it has a target temperature changing means Ru is increased. With respect to the initial playback target temperature and said final regeneration target temperature, the second predetermined temperature higher post-injection allows the upper limit temperature was set respectively, during playback, the exhaust gas temperature is greater than the initial and final post-injection possible upper limit temperature When the post-injection is stopped and PM is determined to remain unburned in the oxidation catalyst, the final regeneration target temperature is increased , and the second predetermined temperature of the post-injection upper limit temperature with respect to the increased final regeneration target temperature The exhaust gas purification system according to claim 1, wherein The exhaust gas purification system according to claim 1 or 2, wherein the target temperature changing means increases the final regeneration target temperature and increases the first predetermined temperature when it is determined that PM remains unburned in the oxidation catalyst. . The exhaust gas purification system according to claim 2 or 3 , wherein the DPF includes DOC and CSF, and the final regeneration target temperature is set to be equal to or higher than the initial post-injectable upper limit temperature . The exhaust gas purification system according to claim 2 , wherein the final post-injectable upper limit temperature is set to be equal to or lower than a melting temperature of the DPF.

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