JP7372899B2 - diesel engine - Google Patents

Description

The present invention relates to a diesel engine, and more particularly, to a diesel engine that can regenerate a DPF even during no-load and/or light-load operation.

Conventionally, in a diesel engine, when the conditions for starting DPF regeneration are met due to PM accumulation, post-injection control is started after activation of DOC, and the exhaust gas is regenerated by DPF through catalytic combustion of post-injected fuel in DOC. There is one in which the temperature is raised to a high temperature and the PM deposited on the DPF is incinerated (for example, see Patent Document 1).

Japanese Patent Application Publication No. 2010-151058 (see Figures 1 and 2)

<<Problem>> There is a possibility that the DPF cannot be regenerated during no-load or light-load operation.
In the conventional engine mentioned above, the opening of the intake throttle valve is reduced when DPF regeneration begins, but this alone has a low efficiency in raising the temperature of the exhaust gas, and the DOC is not activated during no-load or light-load operation when the exhaust temperature is low. , there is a possibility that post-injection cannot be performed and the DPF cannot be regenerated.

An object of the present invention is to provide a diesel engine that can regenerate the DPF even during no-load and/or light-load operation.

The configuration of the present invention is as follows.
As illustrated in FIG. 1, a fuel injection device (3) that injects fuel (2) into a combustion chamber (1), a DOC (12) disposed in an exhaust path (4), and an exhaust gas of the DOC (12) The DPF (7) located downstream, the exhaust throttle valve (5) located downstream of the DPF (7), the opening degree of the exhaust throttle valve (5), and the fuel of the fuel injection device (3). Equipped with an electronic control device (8) for controlling injection,
As illustrated in FIG. 2, it is configured to perform regeneration processing of the DPF (7),
In the regeneration process of the DPF (7), after the start condition (S1) for the regeneration process of the DPF (7) on which PM has accumulated is satisfied, the opening degree reduction control (S2) of the exhaust throttle valve (5) is performed, and the exhaust throttle valve (5) is ) becomes a predetermined after-injection permission temperature (TA) or higher, after-injection control is started (S5), and the combustion of the after-injected fuel causes the exhaust gas (9) to rise to a predetermined post-injection permission temperature (TP) or higher. Post-injection control is started (S7) after the temperature reaches the temperature, and the exhaust gas (9) heated by the catalytic combustion of the post-injected fuel in the downstream DOC (6) illustrated in Fig. 1 is deposited on the DPF (7). It is configured so that the PM is incinerated,
As illustrated in FIG. 1, the DOC (12) includes an upstream DOC (17) and a downstream DOC (6) disposed on the exhaust downstream side of the upstream DOC (17),
As illustrated in FIG. 4, the upstream DOC (17) is configured to perform catalyst function recovery processing,
In the catalytic function recovery process of the upstream DOC (17), the start conditions (S13) for the catalytic function recovery process of the upstream DOC (17) whose function has deteriorated based on the accumulation of unburned deposits consisting of unburned fuel and PM are set. After this is established, the opening degree reduction control (S15) of the exhaust throttle valve (5) is performed, and after the temperature of the exhaust gas (9) reaches a predetermined after-injection permission temperature (TA) or higher, the after-injection control is started (S18). After the exhaust gas (9) reaches a temperature equal to or higher than the predetermined post-injection permission temperature (TP) due to the combustion of the after-injected fuel, post-injection control is started (S18-3), and the post-injected fuel is heated by the combustion heat of the after-injected fuel. is combusted, and unburned deposits deposited on the upstream DOC (17) are vaporized or incinerated by the heat of the heated exhaust gas (9),
When the number of regeneration processes for the DPF (6) reaches a predetermined catalytic function recovery process start determination value (ISJ), the start condition (S13) for the catalytic function recovery process for the upstream DOC (17) is satisfied. A diesel engine characterized by:

The present invention has the following effects.
<<Effect 1>> The DPF (7) can be regenerated even during no-load and/or light-load operation.
In this engine, as illustrated in FIG. 2, when the start condition (S1) for the regeneration process of the DPF (7) is satisfied, the back pressure increases due to the decrease in the opening of the exhaust throttle valve (5), and the after-sales Since combustion of the injected fuel occurs, the temperature increase efficiency of the exhaust gas (9) is higher than in the case of intake throttling, and even during no-load and/or light-load operation when the exhaust temperature is low, the downstream DOC (as shown in FIG. 1) 6) is activated and the DPF (7) can be regenerated in post-injection.

[Effect 2] Engine output can be increased.
In this engine, the temperature of the exhaust gas (9) rises due to the combustion of the after-injected fuel, so the degree of reduction in the opening of the exhaust throttle valve (5) illustrated in FIG. 1 is small, and output loss due to back pressure is small. Can increase engine output.

<<Effect 3>> The reduced catalytic function of DOC (12) can be restored when DPF (7) is regenerated.
In this engine, even if unburned deposits consisting of unburned fuel and PM accumulate on the DOC (12) due to continuous no-load and/or light-load operation with low exhaust temperature, the catalytic function is reduced. As illustrated in FIG. 2, when the start condition (S1) for the regeneration process of the DPF (7) is satisfied, the exhaust gas (9) is raised by reducing the opening of the exhaust throttle valve (5) or by after-injection. When heated, unburned deposits are vaporized or burned, and the degraded catalytic function of the DOC (12) illustrated in FIG. 1 can be restored during regeneration of the DPF (7). Furthermore, since there is no unburned deposits that cause white smoke, the generation of white smoke is also suppressed.

<<Effect 4>> The regeneration efficiency of the DPF (7) is high.
In this engine, during the regeneration process of the DPF (7), the temperature on the upstream side of the exhaust gas of the exhaust throttle valve (5) increases due to the exhaust throttle of the exhaust throttle valve (5), and the temperature of the DPF (7) also increases. DPF (7) has high regeneration efficiency.
<<Effect 5>> When the DPF (7) is regenerated, the decreased catalyst function of the downstream DOC (6) can be recovered.
In this engine, due to no load and/or continued operation, unburned deposits consisting of unburned fuel and PM accumulate in the downstream DOC (6), reducing the catalytic function of the downstream DOC (6). Even in the case where the start condition (S1) for the regeneration process of the DPF (7) is satisfied, as illustrated in FIG. As the exhaust gas (9) undergoes catalytic combustion in the DOC (17) and the temperature of the exhaust gas (9) rises significantly, the unburned deposits are quickly vaporized or combusted, and when the DPF (7) is regenerated, the downstream DOC (6) illustrated in FIG. can restore the reduced catalytic function of
<<Effect 6>> The degraded catalytic function of the upstream DOC (17) is recovered before the DPF (7) is regenerated, making it difficult for the catalytic function to deteriorate further.
In this engine, due to continuous no-load and/or light-load operation with low exhaust temperature, unburned deposits consisting of unburned fuel and PM accumulate on the upstream DOC (17) illustrated in FIG. Even when the exhaust throttle valve (5) illustrated in FIG. The temperature of the exhaust gas (9) rises due to the reduction in the opening of the DPF (9) and the combustion of after-injection and post-injection. The decreased catalytic function of DOC (17) is restored, and the deterioration of the catalytic function is difficult to progress.
《Effect 7》 It is possible to eliminate unnecessary exhaust throttling, after-injection, and post-injection.
With this engine, catalyst function recovery processing can be started in situations where there is a high probability that the catalyst function of the upstream DOC (17) has deteriorated due to unburned deposits, eliminating wasteful exhaust throttling, after-injection, and post-injection. I can do it.

1 is a schematic diagram of a diesel engine according to an embodiment of the present invention. 2 is a flowchart of a DPF regeneration process of the engine in FIG. 1. FIG. 2 is a flowchart of catalyst function recovery processing for the downstream DOC of the engine in FIG. 1. FIG. 2 is a flowchart of catalyst function recovery processing for the upstream DOC of the engine in FIG. 1. FIG.

1 to 4 are diagrams illustrating a diesel engine according to an embodiment of the present invention. In this embodiment, a common rail type vertical in-line multi-cylinder diesel engine will be explained.

The configuration of this engine is as follows.
As shown in Figure 1, the installation direction of the crankshaft (21) is the front-rear direction, the side where the flywheel (22) is placed is the rear side, the opposite side is the front side, and the engine width direction perpendicular to the front-rear direction is the lateral direction. shall be.
As shown in FIG. 1, this engine has an intake manifold (24) assembled on one side of the cylinder head (23), and an exhaust manifold (25) assembled on the other side of the cylinder head (23). It is equipped with
As shown in FIG. 1, this engine is equipped with an electronic control device (8).
The electronic control unit (8) is an engine ECU. Engine ECU is an abbreviation for electronic control unit, and is a microcomputer.

As shown in FIG. 1, this engine is equipped with an exhaust system.
The exhaust system includes an exhaust manifold (25), an exhaust turbine (26a) of a supercharger (26) connected to the exhaust manifold (25), and exhaust gas led out from an exhaust outlet (26b) of the exhaust turbine (26a). It is provided with a lead-out passage (26c).

As shown in FIG. 1, this engine is equipped with an intake device.
The intake device includes a compressor (26d) of the supercharger (26), an intake flow rate sensor (16) provided upstream of the intake inlet (26e) of the compressor (26d), and a supercharger (26d) of the compressor (26d). An intercooler (28) disposed between the air outlet (26f) and the intake manifold (24), an intake throttle valve (11) disposed between the intercooler (28) and the intake manifold (24), and an exhaust It includes an EGR cooler (30) disposed between the manifold (25) and the intake manifold (24), and an EGR valve (31) disposed between the EGR cooler (30) and the intake manifold (24). EGR is an abbreviation for exhaust gas recirculation.
The intake throttle valve (11) and the EGR valve (31) are both electrically operated on-off valves, and are electrically connected to a power source (29) via an electronic control device (8). The intake air flow rate sensor (16) includes an intake air temperature sensor and is electrically connected to the electronic control unit (8). The power source (29) is a battery.

As shown in FIG. 1, this engine is equipped with a common rail type fuel injection device (3).
This fuel injection device (3) includes a fuel injection valve (34) provided in each combustion chamber (1), a common rail (35) that accumulates pressure of fuel injected from the fuel injection valve (34), and a common rail (35). The engine is equipped with a fuel supply pump (37) that pumps fuel from the fuel tank (36).
The fuel injection valve (34) is equipped with an electromagnetic on-off valve, and the fuel supply pump (37) is equipped with an electric pressure regulating valve, which are electrically connected to a power source (29) via an electronic control device (8). ing.

As shown in FIG. 1, this engine is equipped with a speed governor.
The speed governor includes an accelerator sensor (39) that detects the setting position of an accelerator lever (38) that sets a target engine speed, and an actual engine speed sensor (40) that detects the actual engine speed. The sensors (39) (40) are electrically connected to the electronic control unit (8).

As shown in FIG. 1, this engine is equipped with a starter.
The starting device includes a starter motor (41) and a key switch (42), and the starter motor (41) and key switch (42) are electrically connected to a power source (29) via an electronic control device (8). has been done. The key switch (42) has an OFF position, an ON position, and a start position.

The electronic control device (8) is configured to perform the following operational control.
The fuel injection amount and injection timing from the fuel injection valve (34) are set so as to reduce the rotation speed deviation between the target engine speed and the actual engine speed, thereby reducing engine speed fluctuations due to load fluctuations.
The openings of the intake throttle valve (11) and EGR valve (31) are adjusted according to the engine speed, load, intake air amount, and intake air temperature to adjust the intake air amount and EGR rate.
When the key switch (42) is turned to the start position, the starter motor (41) is driven to start the engine. When the key switch (42) is turned to the ON position, the engine operating state is maintained by energizing each part of the engine from the power supply (29), and when the key switch (42) is turned to the OFF position, the fuel injection valve Fuel injection from (34) is stopped and the engine is stopped.

This engine is equipped with an exhaust treatment device.
As shown in FIG. 1, the exhaust treatment device includes a fuel injection device (3) that injects fuel (2) into a combustion chamber (1), a DOC (12) disposed in an exhaust path (4), and a DOC ( The DPF (7) located on the exhaust downstream side of the DPF (7), the exhaust throttle valve (5) located on the exhaust downstream side of the DPF (7), the opening degree of the exhaust throttle valve (5), and the fuel injection device ( It is equipped with an electronic control device (8) that controls the fuel injection in step 3).

In this engine, during the regeneration process of the DPF (7), the temperature on the upstream side of the exhaust gas of the exhaust throttle valve (5) increases due to the exhaust throttle of the exhaust throttle valve (5), and the temperature of the DPF (7) also increases. DPF (7) has high regeneration efficiency.

Each of the above elements will be explained.
The combustion chamber (1) shown in FIG. 1 is formed within a cylinder. Fuel (2) is light oil. The exhaust throttle valve (5) is an electric on-off valve, and is electrically connected to a power source (29) via an electronic control device (8). DOC is an abbreviation for diesel oxidation catalyst, which is a through-flow type in which oxidation catalyst components such as platinum and palladium are supported on a ceramic honeycomb carrier. ) to oxidize. DPF is an abbreviation for diesel particulate filter, and is a wall flow type in which the entrances and exits of adjacent cells of a ceramic honeycomb are alternately blocked, and traps PM in the exhaust gas (9). PM is an abbreviation for particulate matter.
The DPF (12) includes an upstream DOC (17) and a downstream DOC (6) on the exhaust downstream side of the upstream DOC (17).
The upstream DOC (17) is housed in an upstream DOC case (4b) located midway through the exhaust route (4), and the downstream DOC (6) and DPF (7) are located midway through the exhaust route (4). The exhaust treatment case (4a) is housed on the upstream and downstream sides of the exhaust treatment case (4a), respectively.

This DPF system captures PM in the exhaust gas (9) with the DPF (7), and oxidizes NO (nitric oxide) in the exhaust gas (9) with the downstream DOC ( ₆ ). Nitrogen) is used to continuously oxidize and burn the PM accumulated in the DPF (7) at a relatively low temperature, and at the same time, the unburned fuel supplied to the exhaust gas (9) by the post injection of the common rail fuel injection device (3) is Catalytic combustion is performed in the downstream DOC (6), and the PM deposited on the DPF (7) is burned at a relatively high temperature to regenerate the DPF (7).

This exhaust treatment device has the following configuration for regenerating the DPF (7).
As shown in FIG. 2, when the start condition (S1) for the regeneration process of the DPF (7) on which PM has accumulated is satisfied, the opening degree reduction control (S2) of the exhaust throttle valve (5) is then performed, When the temperature of the exhaust gas (9) reaches or exceeds the predetermined after-injection permission temperature (TA), after-injection control is then started (S5), and the exhaust gas (9) is directed to the predetermined post by combustion of the after-injected fuel. If the temperature reaches or exceeds the injection permission temperature (TP), post-injection control is then started (S7), and the temperature is raised by catalytic combustion of the post-injected fuel in the downstream DOC (6) shown in Figure 1. The exhaust (9) is configured to incinerate PM accumulated on the DPF (7).

This engine has the following advantages:
As shown in Fig. 2, after the start condition (S1) for the regeneration process of the DPF (7) is satisfied, the back pressure increases due to the decrease in the opening of the exhaust throttle valve (5) and the combustion of the after-injected fuel occurs. Compared to the case of throttling, the temperature increase efficiency of the exhaust gas (9) is higher, and even during no-load and/or light-load operation when the exhaust gas temperature is low, the downstream DOC (6) shown in Figure 1 is activated and post injection is performed. , DPF(7) can be regenerated.

In addition, in this engine, the temperature of the exhaust gas (9) rises due to the combustion of after-injected fuel, so the degree of reduction in the opening of the exhaust throttle valve (5) shown in Figure 1 is small, and output loss due to back pressure is small. , the engine output can be increased.

In this engine, due to continuous no-load and/or light-load operation with low exhaust temperature, unburned deposits consisting of unburned fuel and PM accumulate in the downstream DOC (6), reducing its catalytic function. Even in this case, as shown in Fig. 2, if the start condition (S1) for the regeneration process of the DPF (7) is satisfied, the exhaust gas (9) is The temperature rises, unburned deposits are vaporized or burned, and the degraded catalytic function of the downstream DOC (6) shown in FIG. 1 can be restored during DPF (7) regeneration.

Each element in the case of regeneration of the DPF (7) will be explained.
As shown in FIG. 2, the start condition (S1) for the regeneration process of the DPF (7) is such that the estimated amount of PM accumulated in the DPF (7) (APM) is the start determination value for the regeneration process of the DPF (7) ( RSJ) or higher. The PM accumulation amount estimate (APM) may be estimated by the PM accumulation amount estimate calculation device (32) based on the differential pressure (ΔP) between the entrance and exit of the DPF (7) shown in FIG. 1, for example. be. The PM accumulation amount estimated value calculation device (32) is constituted by a calculation section of the electronic control device (8).

Types of injection performed from the fuel injection device (3) during one combustion cycle include blur injection (pilot injection), main injection, after injection, and post injection.
In a four-stroke engine, one combustion cycle consists of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke.
The blur injection (pilot injection) is an injection for suppressing the ignition delay of the main injected fuel, and is started during the intake stroke or the compression stroke.
Main injection is the main injection for obtaining output, and is started before compression top dead center.
The after injection is an injection for raising the temperature of the exhaust gas (9), and is started during the expansion stroke after the main injection.
The post injection is an injection to raise the temperature of the exhaust gas (9), and is started during the expansion stroke after the after injection. Post injection may be initiated during the exhaust stroke.

In the case of the DPF (7) regeneration process shown in FIG. 2, the after injection is set as follows.
The after-injection permission temperature (TA) is set at 150°C or higher and 700°C or lower.
In the after injection control, the exhaust temperature (T1) on the inlet side of the downstream DOC (6) shown in Fig. 1 is maintained at 400°C or more and 700°C or less (preferably 450°C or more and 500°C or less). It is set as follows.

The after-injection permission temperature (TA) is a judgment temperature for the outlet side exhaust temperature (T0) of the upstream DOC (17) detected by the upstream DOC outlet side exhaust temperature sensor (19). ) is detected by an upstream DOC outlet exhaust temperature sensor (19), and is controlled by adjusting the injection timing and fuel injection amount by an electronic control device (8).
The inlet exhaust temperature (T1) of the downstream DOC (6) is detected by the inlet exhaust temperature sensor (43) of the downstream DOC (6), and the injection timing and fuel injection amount are adjusted by the electronic control unit (8). controlled by
The inlet exhaust temperature (T1) of the downstream DOC (6) may be estimated from the valve upstream exhaust temperature (T0) detected by the valve upstream exhaust temperature sensor (19).

The after-injection permission temperature (TA) is preferably 150°C or more and less than 250°C, more preferably 150°C or more and less than 200°C.
The reason why the after-injection permission temperature (TA) may be as low as about 150°C is as follows.
In other words, when the exhaust pressure on the upstream side of the exhaust throttle valve (5) is set to 80 kPa or more and 120 kPa or less in gauge pressure (181.32 kPa or more and 221.23 kPa or less in absolute pressure), the exhaust pressure This is because the upstream DOC (17) is activated even at a temperature as low as 150°C, which is approximately twice the atmospheric pressure of 101.32 kPa, and an oxidation reaction (catalytic combustion) of the after-injected fuel occurs in the upstream DOC (17). be.

In after-injection, the after-injected fuel that has started to be injected into the combustion chamber (1) during the expansion stroke is combusted by the heat of the exhaust gas (9), even when the temperature of the exhaust gas (9) is low during no-load or low-load operation. , the exhaust gas (9) is heated to a temperature at which the unburned deposits deposited on the downstream DOC (6) are vaporized or incinerated, and the catalytic function of the downstream DOC (6), which has been degraded by the unburned deposits, is restored. At the same time, the downstream DOC (6) is activated.

In the case of the DPF (7) regeneration process shown in FIG. 2, the post injection is set as follows.
The post-injection permission temperature (TP) is set at 200°C or higher and 700°C or lower.
The post-injection permission temperature (TP) is set to a higher temperature than the after-injection permission temperature (TA).
In post-injection control, the exhaust temperature (T1) on the inlet side of the downstream DOC (6) is maintained at 400°C or more and below 700°C, and the exhaust temperature (T2) on the inlet side of the DPF (7) is maintained at 550°C. It is set to be maintained at a temperature above 700°C and below 700°C. In particular, it is desirable to set the exhaust temperature (T2) on the inlet side of the DPF (7) to 700° C. or lower in order to prevent abnormal combustion of accumulated PM.
The post injection permission temperature (TP) is a judgment temperature for the outlet side exhaust temperature (T0) of the upstream DOC (17) detected by the upstream DOC outlet side exhaust temperature sensor (19), ) is detected by an upstream DOC outlet exhaust temperature sensor (19), and is controlled by adjusting the injection timing and fuel injection amount by an electronic control device (8).
The exhaust temperature (T2) on the inlet side of the DPF (7) is detected by the DPF inlet side exhaust temperature sensor (27), and is controlled by adjusting the injection timing and fuel injection amount by the electronic control device (8).
Note that if the exhaust temperature (T3) on the outlet side of the DPF (7) detected by the exhaust gas temperature sensor (33) on the DPF outlet side exceeds the predetermined upper limit temperature, the control of the electronic control unit (8) After-injection and post-injection are stopped in an emergency.
In post-injection, post-injected fuel, which is injected into the combustion chamber during the expansion stroke or exhaust stroke, undergoes catalytic combustion in the downstream DOC (6), raising the temperature of the exhaust gas (9) and reducing the PM accumulated in the DPF (7). will be incinerated and removed.

As shown in FIG. 1, this engine is equipped with an intake throttle valve (11) disposed in an intake path (10), and its opening degree is controlled by an electronic control device (8). In the DPF (7) regeneration process shown in FIG. 3 or the downstream DOC (6) catalytic function recovery process shown in FIG. After the start condition (13) of the catalyst function recovery process in 6) is satisfied, the opening degree reduction control (S2) (S15) of the exhaust throttle valve (5) is performed, and the opening degree of the intake throttle valve (11) is It is configured such that reduction control (S2) (S15) is performed.
Therefore, in this engine, intake throttling is performed together with exhaust throttling, so that the efficiency of raising the temperature of the exhaust gas (9) is increased by reducing the amount of intake air.

In this engine, as shown in FIG. 2 or 3, after the opening degree reduction control (S2) (S15) of the exhaust throttle valve (5) is performed, the exhaust pressure (P3) on the upstream side of the valve reaches a predetermined pressure upper limit value. (Pmax), the opening degree increasing control (S4-2) (S17-2) of the exhaust throttle valve (5) is performed thereafter.
Therefore, in this engine, an excessive increase in the exhaust pressure (P3) on the upstream side of the valve is suppressed, so that the exhaust throttle valve (5) and its upstream parts are less likely to malfunction due to this pressurization.
The pressure upper limit value (Pmax) is determined based on the specifications of the exhaust throttle valve (5), EGR valve (31), supercharger (26), etc. shown in FIG. 1, or the airtightness of the piping of the exhaust path (4).
The exhaust throttle valve (5) is arranged in the middle of the exhaust path (4).
The upper limit pressure value (Pmax) is preferably 80 kPa or more and 120 kPa or less in gauge pressure, and more preferably 100 kPa.
The valve upstream exhaust pressure (P3) is detected by a valve upstream exhaust pressure sensor (44) disposed between the DPF (7) and the exhaust throttle valve (5). The exhaust downstream side of the exhaust throttle valve (5) is at atmospheric pressure. Atmospheric pressure is detected by an atmospheric pressure sensor (14).
The valve upstream exhaust pressure (P3) may be calculated by calculation.

In this engine, as shown in FIG. 1, the DOC (12) includes an upstream DOC (17) and a downstream DOC (6) disposed on the exhaust downstream side of the upstream DOC (17).
In this engine, due to no load and/or continued operation, unburned deposits consisting of unburned fuel and PM accumulate in the downstream DOC (6), reducing the catalytic function of the downstream DOC (6). Even in this case, as shown in FIG. 2, if the start condition (S1) for the regeneration process of the DPF (7) is satisfied, the after-injection or post-injection fuel will be transferred to the upstream DOC by the subsequent after-injection or post-injection. (17) undergoes catalytic combustion and the temperature of the exhaust gas (9) rises significantly, so unburned deposits quickly vaporize or burn, resulting in a decrease in the downstream DOC (6) shown in Figure 1 when the DPF (7) is regenerated. The catalytic function can be restored.
The upstream DOC (17) is housed in an upstream DOC case (4b) placed in the middle of the exhaust path (4). The upstream DOC outlet exhaust temperature sensor (19) is arranged at the exhaust outlet of the upstream DOC (17).

In this engine, as shown in Fig. 1, the upstream DOC (17) and downstream DOC (6) are of a flow-through type in which a catalyst component is supported on a honeycomb carrier through which exhaust gas (9) passes through the cells. An oxidation catalyst is used.
For this reason, in this engine, as shown in Figure 1, flow-through type oxidation catalysts are used in the upstream DOC (17) and downstream DOC (6), so the output loss due to back pressure is small and the engine Can increase output.

In this engine, as shown in FIG. 1, the diameter of the upstream DOC (17) is smaller than the diameter of the downstream DOC (6).
Therefore, in the engine, the passage speed of the exhaust gas (9) passing through the cells of the upstream DOC (17) is faster than the passage speed of the exhaust gas (9) passing through the cells of the downstream DOC (6). Unburned deposits consisting of unburned fuel and PM are difficult to accumulate on the upstream DOC (17).

In this engine, as shown in FIG. 1, the cell density (over the entire area) of the upstream DOC (17) is formed to be larger than the cell density of the downstream DOC (6).
Therefore, in this engine, as shown in FIG. 1, the passage speed of the exhaust gas (9) passing through the cells of the upstream DOC (17) is lower than that of the exhaust gas (9) passing through the cells of the downstream DOC (6). Since the speed is faster than the passing speed, unburned deposits consisting of unburned fuel and PM are difficult to accumulate on the upstream DOC (17).

As shown in FIG. 3, this exhaust treatment device is configured to perform catalytic function recovery processing of the downstream DOC (6), and in the catalytic function recovery processing of the downstream DOC (6), After the start condition (S13) for the catalyst function recovery process of the downstream DOC (6) whose function has deteriorated due to the accumulation of unburned deposits consisting of After the exhaust gas (9) reaches a temperature equal to or higher than the predetermined after-injection permission temperature (TA), after-injection control is started (S18), and the exhaust gas (9), whose temperature has risen due to combustion of the after-injected fuel, is It is configured such that unburned deposits deposited on the DOC (6) are vaporized or incinerated.

In this engine, even if the DPF (7) is not being regenerated, the exhaust throttle valve (5) is opened after the start condition (S13) for catalyst function recovery of the downstream DOC (6) is satisfied, as shown in Fig. 3. Due to temperature reduction and after injection, the temperature of the exhaust gas (9) rises, unburned deposits are vaporized or burned, and the degraded catalytic function of the downstream DOC (6) shown in Figure 1 is restored before the DPF (7) is regenerated. This makes it difficult for the catalyst function to deteriorate. Furthermore, since there is no unburned deposits that cause white smoke, the generation of white smoke is also suppressed.

As shown in FIG. 3, the start condition (S13) of the catalyst function recovery process of the downstream DOC (6) is such that the cumulative value (tL) of the no-load and light-load operating time is the start determination of the predetermined catalyst function recovery process. This is established when the value is greater than or equal to the value (ISJ). The integrated value (tL) of the operation time for no-load and light-load operation is based on the fact that the outlet side exhaust temperature (T0) of the upstream DOC (17) is below the judgment temperature (LJ) for no-load and light-load operation. , is calculated by the driving time integration device (18) shown in FIG. The operating time integration device (18) is composed of a calculation section of an electronic control device (8).

In the case of the catalyst function recovery process of the downstream DOC (6) shown in FIG. 3, the after injection is set as follows.
The after-injection permission temperature (TA) is set at 150°C or higher and 700°C or lower.
In the after injection control, the exhaust temperature (T1) on the inlet side of the downstream DOC (6) shown in Fig. 1 is maintained at 180°C or more and 700°C or less (preferably 250°C or more and 300°C or less). It is set as follows. (
In after-injection, the after-injected fuel injected into the combustion chamber during the expansion stroke is combusted by the heat of the exhaust gas (9), and even when the temperature of the exhaust gas (9) is low during no-load or low-load operation, the exhaust gas (9) The temperature is raised to a temperature at which the unburned deposits deposited on the downstream DOC (6) are vaporized or incinerated, and the catalytic function of the downstream DOC (6), which has decreased due to the unburned deposits, is restored and the decline in catalytic function is reduced. Difficult to proceed.

The after-injection permission temperature (TA) is preferably 150°C or more and less than 250°C, more preferably 150°C or more and less than 200°C.
The reason why the after-injection permission temperature (TA) may be as low as about 150°C is as follows.
In other words, when the exhaust pressure on the upstream side of the exhaust throttle valve (5) is set to 80 kPa or more and 120 kPa or less in gauge pressure (181.32 kPa or more and 221.23 kPa or less in absolute pressure), the exhaust pressure This is because the upstream DOC (17) is activated even at a temperature as low as 150°C, which is approximately twice the atmospheric pressure of 101.32 kPa, and an oxidation reaction (catalytic combustion) of the after-injected fuel occurs in the upstream DOC (17). be.

As shown in FIG. 1, this engine is equipped with an operating time accumulating device (18) for accumulating operating time during no-load and/or light-load operation, and as shown in FIG. When the cumulative value (tL) of operating time reaches a predetermined catalyst function recovery process start judgment value (ISJ), the start condition (S13) for the catalyst function recovery process of the downstream DOC (6) is satisfied. It is composed of
Therefore, in this engine, improvement of the catalytic function can be started at a time when there is a high probability that the catalytic function of the downstream DOC (6) will deteriorate, so that unnecessary exhaust throttling and after-injection can be eliminated.

As shown in FIG. 4, the upstream DOC (17) is configured to perform a catalyst function recovery process, and in the upstream DOC (17) catalyst function recovery process, unburned deposits consisting of unburned fuel and PM are removed. After the start condition (S13) for the catalyst function recovery process of the upstream DOC (17) whose function has deteriorated due to the accumulation of After the temperature reaches the predetermined after-injection permission temperature (TA) or higher, after-injection control is started (S18), and the temperature of the exhaust (9) due to combustion of the after-injection fuel reaches the predetermined post-injection permission temperature (TP) or higher. After that, post injection control is started (S18-3), the post injection fuel is combusted by the combustion heat of the after injection fuel, and the heat of the heated exhaust gas (9) shown in FIG. ) is configured so that unburned deposits accumulated in the combustion chamber are vaporized or incinerated.

In this engine, due to continuous no-load and/or light-load operation with low exhaust temperature, unburned deposits consisting of unburned fuel and PM accumulate in the upstream DOC (17) shown in Figure 1, and its catalytic function is impaired. Even if the opening degree of the exhaust throttle valve (5) shown in FIG. 1 is lowered, if the start condition (S13) for catalyst function recovery of the upstream DOC (17) is satisfied as shown in FIG. The temperature of the exhaust gas (9) rises due to combustion during reduction, after-injection, and post-injection, and the unburned deposits are vaporized or burned by the heat of this exhaust gas (9), and the upstream DOC (17) is heated before the DPF (7) is regenerated. ) The decreased catalytic function is recovered, and the deterioration of the catalytic function is difficult to progress. Therefore, the DPF (7) can be regenerated even when no-load and/or light-load operation continues. Furthermore, since there is no unburned deposits that cause white smoke, the generation of white smoke is also suppressed.

In this engine, the temperature of the exhaust gas (9) shown in Fig. 1 rises due to the combustion of after-injected fuel, so the degree of reduction in the opening of the exhaust throttle valve (5) is small, and output loss due to back pressure is small. Can increase output.

As shown in FIG. 1, this engine is equipped with an operating time accumulating device (18) for accumulating operating time during no-load and/or light-load operation, and as shown in FIG. When the cumulative value (tL) of the operating time reaches a predetermined catalyst function recovery process start judgment value (ISJ), the start condition (S13) for the catalyst function recovery process of the upstream DOC (17) is satisfied. It is composed of
Therefore, in this engine, the catalyst function recovery process can be started in a situation where there is a high probability that the catalyst function of the upstream DOC (17) has deteriorated as shown in Figure 1, eliminating unnecessary exhaust throttling, after-injection, and post-injection. be able to.

The start condition (S13) for the catalyst function recovery process of the upstream DOC (17) shown in FIG. (ISJ), the valve upstream exhaust pressure (P3) shown in Figure 1 and the number of regeneration processes of the DPF (7) shown in Figure 1 reach the predetermined catalyst function recovery process start judgment value. It may also be set to hold true when the condition is reached.
In any case, with this engine, the catalyst function recovery process can be started under conditions where there is a high probability that the catalyst function of the upstream DOC (17) has deteriorated due to unburned deposits, thereby eliminating wasteful exhaust throttling and after-injection. Post injection can be eliminated.
When the regeneration process of the DPF (7) is set as the start condition (S13), the electronic control unit (8) counts the number of regeneration processes, and when the count of regeneration processes reaches a predetermined value (for example, 5 times). In this case, the start condition (S13) is satisfied, and when the catalyst function recovery process is completed, the count number of the regeneration process is reset to 0.

In the case of the regeneration process of the DPF (7) shown in Fig. 2, the exhaust gas temperature (T2) on the inlet side of the DPF (7) is higher than in the case of the catalyst function recovery process of the upstream DOC (17) shown in Fig. 4. It is set to be.
In this engine, when the DPF (7) is regenerated, the exhaust temperature (T2) on the inlet side of the DPF (7) increases, so that the DPF (7) can be regenerated reliably.

In the case of the DPF (7) regeneration process shown in Figure 2, the injection amount of after-injection fuel is set to be smaller than in the case of the catalyst function recovery process of the upstream DOC (17) shown in Figure 4. There is.
In this engine, in the case of DPF (7) regeneration processing, the amount of after-injected fuel injected is small, so the combustion heat and the post-injected fuel combusted by the combustion heat are also small, and much of the post-injected fuel is upstream. It passes through the side DOC (17) and undergoes catalytic combustion in the downstream DOC (6), increasing the exhaust temperature (T2) on the inlet side of the DPF (7). Therefore, the DPF (7) can be regenerated reliably.
In addition, in the case of the catalyst function recovery process of the upstream DOC (17), since there is a lot of after-injected fuel, the combustion heat causes a lot of the post-injected fuel to burn on the upstream side of the upstream DOC (17). Unburned deposits deposited on the upstream DOC (17) are vaporized or incinerated by the heat of combustion. Therefore, the catalytic function of the upstream DOC (17) can be reliably restored.

In the case of the DPF (7) regeneration process shown in Figure 2, the injection amount of post-injected fuel is set to be larger than in the case of the upstream DOC (17) catalyst function recovery process shown in Figure 4. There is.
In this engine, in the case of DPF (7) regeneration processing, since the amount of post-injected fuel is large, much of the post-injected fuel passes through the upstream DOC (17) shown in Fig. 1 and the downstream DOC (6). ), catalytic combustion occurs, and the exhaust temperature (T2) on the inlet side of the DPF (7) increases. Therefore, the DPF (7) can be regenerated reliably.

In this engine, the flow of regeneration processing of the DPF (7) by the electronic control unit (8) shown in FIG. 1 is as follows.
As shown in FIG. 2, in step (S1), it is determined whether the start condition for the regeneration process of the DPF (7) is satisfied. Specifically, it is determined whether the estimated PM accumulation amount (APM) of the DPF (7) has reached a value equal to or greater than the regeneration process start determination value (RSJ) of the DPF (7). The PM accumulation amount estimated value (APM) of the DPF (7) is calculated by the PM accumulation amount estimated value calculation device (32) based on the differential pressure (ΔP) between the entrance and exit of the DPF (7) shown in FIG. The PM accumulation amount estimated value calculation device (32) is constituted by a calculation section of the electronic control device (8). The estimated PM accumulation amount (APM) of the DPF (7) may be calculated by a method other than calculation using the differential pressure (ΔP).
As shown in FIG. 2, the determination in step (S1) is repeated until the determination is positive, and if the determination is positive, the process proceeds to step (S2).

As shown in FIG. 2, in step (S2), the opening degree reduction control of the intake throttle valve (11) and the opening degree reduction control of the exhaust throttle valve (5) are performed, and the process proceeds to step (S3).
The opening reduction control of the intake throttle valve (11) and the exhaust throttle valve (5) in step (S2) is performed by an actuator (11a) that drives the intake throttle valve (11) and an actuator that drives the exhaust throttle valve (5). (5a) is controlled by the electronic control device (8).

As shown in FIG. 2, in step (S3), it is determined whether the valve upstream exhaust pressure (P3) is equal to or lower than the pressure upper limit value (Pmax), and if the determination is affirmative, step (S4-1 ).
In step (S4-1), it is determined whether the outlet side exhaust temperature (T0) of the upstream side DOC (17) is equal to or higher than the after injection permission temperature (TA), and if the determination is affirmative, step (S5 ).
In step (S5), after-injection control is started, and the process proceeds to step (S6).
If the determination in step (S3) is negative, the process proceeds to step (S4-2), where the opening degree increase control of the exhaust throttle valve (5) is performed, and the process proceeds to step (S4-1).
The opening degree increase control of the exhaust throttle valve (5) in step (S4-2) is performed by the electronic control device (8) controlling the actuator (5a) that drives the exhaust throttle valve (5).
If the determination in step (S4-1) is negative, the process returns to step (S3).

In step (S6), it is determined whether the outlet side exhaust temperature (T0) of the upstream DOC (17) is equal to or higher than the post injection permission temperature (TP). The determination in step (S6) is repeated until it is affirmed, and when the determination is affirmed, the process proceeds to step (S7).
In step (S7), post injection control is started, and the process proceeds to step (S8).

In step (S8), it is determined whether the conditions for ending the regeneration process of the DPF (7) are satisfied. Specifically, the termination condition is that the estimated PM accumulation amount (APM) of the DPF (7) becomes a value equal to or less than the end determination value (REJ) of the regeneration process of the DPF (7), and in step (S8) , it is determined whether this termination condition is affirmed.
The determination in step (S8) is repeated until the determination is affirmative, and if the determination is affirmative, the process proceeds to step (S9).
In step (S9), the post injection control is ended, and the after injection control is also ended, and the process proceeds to step (S10).
In step (S10), the intake throttle valve (11) is reset to fully open, and the exhaust throttle valve (5) is also reset to fully open, and the process returns to step (S1).

The PM accumulation amount estimate (APM) of the DPF (7) in step (S8) is calculated by the PM accumulation amount estimate calculation device (32) based on the differential pressure (ΔP) between the entrance and exit of the DPF (7). be done.
The conditions for terminating the regeneration process of the DPF (7) in step (S8) are such that the exhaust temperature (T2) on the inlet side of the DPF (7) shown in FIG. It may be something you did.

In this engine, the flow of catalyst function recovery processing of the downstream DOC (6) by the electronic control unit (8) shown in FIG. 1 is as follows.
As shown in FIG. 3, in step (S11), it is determined whether the outlet side exhaust temperature (T0) of the upstream DOC (17) has become a value equal to or lower than the determination temperature (LJ) for no-load and light-load operation. be done. The determination in step (S11) is repeated until the determination is affirmed, and when the determination is affirmed, the process proceeds to step (S12).
In step (S11), it may be determined whether the inlet side exhaust temperature (T1) of the downstream DOC (6) has become a value equal to or lower than the no-load or light-load operation determination temperature (LJ).
In step (S12), the no-load and light-load operating times are integrated, and the process proceeds to step (S13).
In step (S13), it is determined whether or not conditions for starting the catalyst function recovery process are satisfied. Specifically, it is determined whether the cumulative value (tL) of the no-load and light-load operation times has become a value equal to or greater than the catalyst function recovery processing start determination value (ISJ), and if the determination is affirmative, The process proceeds to step (S14). If the determination in step (S13) is negative, the process returns to step (S11).

In step (S14), the integrated value (tL) of the no-load and light-load operation times integrated in step (S12) is reset to 0, the integration of the catalyst function recovery processing time to be performed after the fact is started, and step ( Proceed to S15).
In step (S15), the opening degree reduction control of the intake throttle valve (11) and the opening degree reduction control of the exhaust throttle valve (5) are performed, and the process proceeds to step (S16).
The opening reduction control of the intake throttle valve (11) and the exhaust throttle valve (5) in step (S15) is performed in the same manner as in step (S2).

In step (S16), it is determined whether the valve upstream exhaust pressure (P3) is equal to or lower than the pressure upper limit value (Pmax), and if the determination is affirmative, the process proceeds to step (S17-1).
In step (S17-1), it is determined whether the outlet side exhaust temperature (T0) of the upstream side DOC (17) is equal to or higher than the after injection permission temperature (TA), and if the determination is affirmative, step (S18 ).
In step (S18), after-injection control is started, and the process proceeds to step (S19).
If the determination in step (S16) is negative, the process proceeds to step (S17-2), where the opening degree increase control of the exhaust throttle valve (5) is performed, and the process proceeds to step (S17-1).
The opening degree reduction control of the exhaust throttle valve (5) in step (S17-1) is performed in the same manner as in step (S4-2).
If the determination at step (S17-1) is negative, the process returns to step (S16).

In step (S19), it is determined whether the conditions for ending the catalyst function recovery process are satisfied. Specifically, the termination condition is that the integrated value (tI) of the catalyst function recovery processing time becomes a value equal to or greater than the termination determination value (IEJ) of the catalyst function recovery process, and in step (S19), this termination condition is determined. It is determined whether the conditions are satisfied or not.
The determination in step (S19) is repeated until the determination is affirmative, and if the determination is affirmative, the process proceeds to step (S20).
In step (S20), after-injection control is ended, and the process proceeds to step (S21).
In step (S21), the intake throttle valve (11) is reset to full open, and the exhaust throttle valve (5) is also reset to full open. ) is reset to 0, and the process returns to step (S11). Note that the reset of the integrated value (tL) of the no-load and light-load operation times in the upper stage of step (S14) to 0 may also be performed in step (S21) instead of step (S14).

In this engine, the flow of the catalyst function recovery process for the upstream DOC (17) by the electronic control unit (8) shown in FIG. 4 is almost the same as the flow of the catalyst function recovery process for the downstream DOC (6) shown in FIG. We are doing so.
The difference from the flow in FIG. 3 is that step (S18-2) and step (S18-3) are set after step (S18), and step (S20) is set after step (S19) instead of step (S20). The point is that a similar step (S20') is set.
That is, when after-injection control is started in step (S18), the process proceeds to step (S18-2).
In step (S18-2), it is determined whether the outlet side exhaust temperature (T0) of the upstream DOC (17) is equal to or higher than the post injection permission temperature (TP). The determination in step (S18-2) is repeated until it is affirmed, and if the determination is affirmed, the process proceeds to step (S18-3).
In step (S18-3), post injection control is started, and the process proceeds to step (S19).
If it is determined in step (S19) that the conditions for ending the catalyst function recovery process are satisfied, the process proceeds to step (S20').
In step (S20'), the post injection control and after injection control are ended, and the process proceeds to step (S21).

Each of the processes shown in FIGS. 2 to 4 is executed independently and not simultaneously. If any process is started, no other process will be started until that process is finished. Further, the catalytic function recovery process of the downstream DOC (6) in FIG. 3 and the catalytic function recovery process of the upstream DOC (17) in FIG. 4 may be performed alternately, or once the former and once the latter. It may be performed alternately multiple times (eg, 2 or 3 times), or the former multiple times (eg, 2 or 3 times) and the latter once may be performed alternately.

Note that the upstream exhaust pressure of the exhaust throttle valve (5) in the above embodiment is actually measured with an exhaust pressure sensor and also calculated, and based on the difference, it is determined whether there is a failure of the exhaust throttle valve (5) or the exhaust path (4). ), or omit the downstream DOC (6), or perform post-injection with the injection pipe injector placed at the exhaust inlet of the exhaust downstream DOC (6). A modification of the form is also possible. When the downstream DOC (6) is omitted, a DPF (7) with a DOC function is used, and the injection pipe injector is placed on the exhaust inlet side of the DPF (7) with a DOC function. When the downstream DOC (6) is omitted, the inlet exhaust temperature (T2) of the DPF (7) with the DOC function is used in place of the inlet exhaust temperature (T1) of the downstream DOC (6).

(1) Combustion chamber, (2) Fuel, (3) Fuel injection device, (4) Exhaust path, (5) Exhaust throttle valve, (6) Downstream DOC, (7) DPF, (8)...Electronic control unit, (9)...Exhaust, (10)...Intake path, (11)...Intake throttle valve, (12)...DOC, (17)...Upstream DOC, (18)...Operating time integration device, (S1)...starting conditions for DPF regeneration processing, (S2)...exhaust throttle valve opening reduction control, (S4-2)...exhaust throttle valve opening increase control, (S5)...after injection control. Start, (S7)...Post injection control starts, (S20)...Post injection control starts, (T0)...Outlet side exhaust temperature of upstream DOC, (TA)...After injection permission temperature, (TP)...Post injection Permitted temperature, (P3)...Valve upstream exhaust pressure, (Pmax)...Pressure upper limit value.

Claims (8)

A fuel injection device (3) that injects fuel (2) into the combustion chamber (1), a DOC (12) placed in the exhaust path (4), and a DPF (12) placed on the exhaust downstream side of the DOC (12). 7), an exhaust throttle valve (5) disposed on the exhaust downstream side of the DPF (7), and an electronic control device ( 8),
It is configured to perform regeneration processing of the DPF (7),
In the regeneration process of the DPF (7), after the start condition (S1) for the regeneration process of the DPF (7) on which PM has accumulated is satisfied, the opening degree reduction control (S2) of the exhaust throttle valve (5) is performed, and the exhaust throttle valve (5) is ) becomes a predetermined after-injection permission temperature (TA) or higher, after-injection control is started (S5), and the combustion of the after-injected fuel causes the exhaust gas (9) to rise to a predetermined post-injection permission temperature (TP) or higher. After the temperature has reached the temperature, post injection control is started (S7), and the PM accumulated in the DPF (7) is incinerated by the exhaust gas (9) heated by catalytic combustion of the post-injected fuel in the downstream DOC (6). configured to
The DOC (12) includes an upstream DOC (17) and a downstream DOC (6) disposed on the exhaust downstream side of the upstream DOC (17),
The upstream DOC (17) is configured to perform catalyst function recovery processing ,
In the catalytic function recovery process of the upstream DOC (17), the start conditions (S13) for the catalytic function recovery process of the upstream DOC (17) whose function has deteriorated based on the accumulation of unburned deposits consisting of unburned fuel and PM are set. After this is established, the opening degree reduction control (S15) of the exhaust throttle valve (5) is performed, and after the temperature of the exhaust gas (9) reaches a predetermined after-injection permission temperature (TA) or higher, the after-injection control is started (S18). After the exhaust gas (9) reaches a temperature equal to or higher than the predetermined post-injection permission temperature (TP) due to the combustion of the after-injected fuel, post-injection control is started (S18-3), and the post-injected fuel is heated by the combustion heat of the after-injected fuel. is combusted, and unburned deposits deposited on the upstream DOC (17) are vaporized or incinerated by the heat of the heated exhaust gas (9),
When the number of regeneration processes for the DPF (6) reaches a predetermined catalytic function recovery process start determination value (ISJ), the start condition (S13) for the catalytic function recovery process for the upstream DOC (17) is satisfied. A diesel engine characterized by: The diesel engine according to claim 1 ,
Equipped with an operation time accumulation device (18) for accumulating operation time of no-load and/or light-load operation,
When the cumulative value (tL) of no-load and/or light-load operation time reaches a predetermined catalyst function recovery process start judgment value (ISJ), the catalyst function recovery process of the upstream DOC (17) is started. A diesel engine characterized in that it is configured so that condition (S13) is satisfied. In the diesel engine according to claim 1 or claim 2 ,
When the valve upstream exhaust pressure (P3) reaches a predetermined catalytic function recovery process start determination value, the upstream side DOC (17) is configured so that the catalytic function recovery process start condition (S13) is satisfied. A diesel engine that is characterized by: The diesel engine according to any one of claims 1 to 3 ,
The intake throttle valve (11) is arranged in the intake path (10), and the opening degree thereof is controlled by an electronic control device (8).
In the DPF (7) regeneration process, after the DPF (7) regeneration process start condition (S1) is satisfied, the exhaust throttle valve (5) is controlled to reduce the opening degree (S2), and the intake throttle valve (11) is ) A diesel engine characterized in that it is configured to perform opening reduction control (S2). The diesel engine according to any one of claims 1 to 4 ,
In the DPF (7) regeneration process, the opening degree reduction control (S2) of the exhaust throttle valve (5) is performed, and when the valve upstream exhaust pressure (P3) exceeds a predetermined pressure upper limit value (Pmax), A diesel engine characterized in that the exhaust throttle valve (5) is then controlled to increase the opening degree (S4-2). The diesel engine according to any one of claims 1 to 5 ,
The upstream DOC (17) and the downstream DOC (6) use a flow-through type oxidation catalyst in which a catalyst component is supported on a honeycomb carrier through which the exhaust gas (9) passes through the cells. Diesel engine. The diesel engine according to any one of claims 1 to 6 ,
The downstream DOC (6) is configured to perform catalyst function recovery processing,
In the catalytic function recovery process of the downstream DOC (6), the start conditions (S13) for the catalytic function recovery process of the downstream DOC (6) whose function has deteriorated due to the accumulation of unburned deposits consisting of unburned fuel and PM are set. After this is established, the opening degree reduction control (S15) of the exhaust throttle valve (5) is performed, and after the temperature of the exhaust gas (9) reaches a predetermined after-injection permission temperature (TA) or higher, the after-injection control is started (S18). . A diesel engine characterized in that the exhaust gas (9) heated by combustion of after-injected fuel vaporizes or incinerates unburned deposits deposited on the downstream DOC (6). The diesel engine according to claim 7 ,
Equipped with an operation time accumulation device (18) for accumulating operation time of no-load and/or light-load operation,
When the cumulative value (tL) of no-load and/or light-load operation time reaches a predetermined catalyst function recovery process start judgment value (ISJ), the catalyst function recovery process of the downstream DOC (6) is started. A diesel engine characterized in that it is configured so that condition (S13) is satisfied.

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