JP7501433B2 - Exhaust Gas Purification Device - Google Patents

Description

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

The exhaust gas purification device for diesel engines is equipped with purification processing components such as a particulate matter removal filter (usually called a diesel particulate filter, hereinafter also referred to as "DPF") that captures and removes particulate matter (PM) from exhaust gas. Here, since the DPF that purifies exhaust gas is a filter that captures particulate matter in exhaust gas, various technologies have been proposed for burning and incinerating the particulate matter in the DPF before the particulate matter accumulates and clogs, increasing exhaust resistance, thereby restoring the DPF's collection function.

For example, in the exhaust gas purification device for a diesel internal combustion engine described in Patent Document 1 below, when the piston is near the top dead center of compression during unloaded deceleration operation of the internal combustion engine, the main injection of fuel is not performed. Instead, the exhaust valve drive unit is driven by the engine brake operating unit to open the exhaust valve, and a post injection is performed at the same time. This allows compressed high-temperature air to be released into the exhaust passage, raising the temperature of the oxidation catalyst to 250°C or higher. In addition, the fuel (HC) mixed with the air can be oxidized by the oxidation catalyst, and the particulate matter (hereinafter also referred to as "PM") captured in the DPF can be oxidized and removed.

JP 2010-112280 A

However, the diesel internal combustion engine exhaust gas purification device described in Patent Document 1 requires the provision of an exhaust valve drive unit that changes the valve timing, which increases costs. In addition, there is a problem in that post-injection must be performed at the same time each time the exhaust valve is opened near the compression top dead center, which deteriorates fuel efficiency.

The present invention was conceived in consideration of these points, and aims to provide an exhaust gas purification device that can regenerate the collection function of the DPF during no-load deceleration operation and improve fuel efficiency.

In order to solve the above problems, the first aspect of the present invention includes an oxidation catalyst disposed in an exhaust gas passage of an internal combustion engine and oxidizing unburned fuel in the exhaust gas, a particulate matter removal filter disposed downstream of the oxidation catalyst and trapping particulate matter in the exhaust gas, a fuel addition device that adds fuel to the exhaust gas flowing into the oxidation catalyst, a deposition amount acquisition device that acquires the deposition amount of the particulate matter trapped in the particulate matter removal filter, a filter bed temperature acquisition device that acquires the bed temperature of the particulate matter removal filter, and a fuel addition device that, when the deposition amount of the particulate matter acquired via the deposition amount acquisition device becomes equal to or exceeds a predetermined deposition amount threshold, adds fuel to the particulate matter removal filter while the internal combustion engine is decelerating at no load. The exhaust gas purification device includes a fuel addition control device that controls the fuel addition to be performed in the exhaust gas via the fuel addition device, and a filter bed temperature determination device that determines whether or not the bed temperature of the particulate matter removal filter acquired via the filter bed temperature acquisition device has reached a filter activation temperature that oxidizes the particulate matter after fuel has been added to the exhaust gas via the fuel addition device. When it is determined via the filter bed temperature determination device that the bed temperature of the particulate matter removal filter has reached the filter activation temperature that oxidizes the particulate matter, the fuel addition control device controls the fuel addition device to stop adding fuel to the exhaust gas.

The second aspect of the present invention is an exhaust gas purification device according to the first aspect of the present invention, which is provided with an intake throttle valve disposed in the intake passage of the internal combustion engine to adjust the intake flow rate, and the fuel addition control device controls the intake throttle valve to reduce the opening degree when the fuel addition device stops adding fuel to the exhaust gas, thereby maintaining the bed temperature of the particulate matter removal filter at the filter activation temperature.

Next, the third invention of the present invention is an exhaust gas purification device according to the second invention, further comprising an upper limit temperature determination device that determines whether the bed temperature of the particulate matter removal filter acquired via the filter bed temperature acquisition device has reached the upper limit temperature of the filter activation temperature, and when it is determined via the upper limit temperature determination device that the bed temperature of the particulate matter removal filter has reached the upper limit temperature of the filter activation temperature, the fuel addition control device increases the opening of the intake throttle valve to control the bed temperature of the particulate matter removal filter to be maintained at the filter activation temperature, which is lower than the upper limit temperature.

Next, the fourth invention of the present invention is an exhaust gas purification device according to any one of the first to third inventions, which includes an oxidation catalyst bed temperature acquisition device that acquires the bed temperature of the oxidation catalyst, and a catalyst bed temperature determination device that determines whether the bed temperature of the oxidation catalyst acquired via the oxidation catalyst bed temperature acquisition device is a temperature lower than the catalytic activity temperature that oxidizes the unburned fuel in the exhaust gas, and the fuel addition control device controls the fuel addition device not to add fuel to the exhaust gas when it is determined via the catalyst bed temperature determination device that the bed temperature of the oxidation catalyst is a temperature lower than the catalytic activity temperature that oxidizes the unburned fuel in the exhaust gas.

Next, the fifth aspect of the present invention is an exhaust gas purification device according to any one of the second to fourth aspects, further comprising an idle operation determination device that determines whether the internal combustion engine has transitioned from the no-load deceleration operation to the idle operation, and the fuel addition control device, when it is determined via the idle operation determination device that the internal combustion engine has transitioned from the no-load deceleration operation to the idle operation, reduces the opening of the intake throttle valve to control the bed temperature of the particulate matter removal filter to be maintained at the filter activation temperature.

According to the first invention, when the amount of particulate matter deposited in the DPF becomes equal to or greater than a predetermined deposition amount threshold, fuel is added to the exhaust gas flowing into the oxidation catalyst via the fuel addition device during unloaded deceleration operation of the internal combustion engine, thereby raising the bed temperature of the DPF. Then, when the bed temperature of the DPF reaches the filter activation temperature (e.g., 500°C or higher) at which particulate matter is oxidized, the addition of fuel to the exhaust gas by the fuel addition device is stopped.

As a result, when the bed temperature of the DPF reaches the filter activation temperature under operating conditions during no-load deceleration of the internal combustion engine, oxidation of particulate matter accumulated in the DPF begins. Therefore, even if the fuel addition device stops adding fuel to the exhaust gas, the particulate matter continues to be oxidized and burned due to self-heating caused by the heat of oxidation reaction of the particulate matter, and the collection function of the DPF can be regenerated. In addition, when the bed temperature of the DPF reaches the filter activation temperature, the fuel addition device stops adding fuel to the exhaust gas, thereby improving fuel efficiency compared to conventional methods.

According to the second invention, when the fuel addition device stops adding fuel to the exhaust gas, the opening of the intake throttle valve is reduced, so the intake flow rate is reduced, and the flow rate of the exhaust gas flowing into the DPF can be reduced. As a result, the temperature drop of the DPF can be suppressed, the bed temperature of the DPF can be maintained at the filter activation temperature, and the oxidation incineration of the particulate matter accumulated in the DPF can be continued.

According to the third invention, when the bed temperature of the DPF reaches the upper limit temperature of the filter activation temperature (e.g., 700°C), the opening of the intake throttle valve is increased to control the bed temperature of the DPF to be maintained at a filter activation temperature lower than the upper limit temperature. This makes it possible to maintain the bed temperature of the DPF at a filter activation temperature lower than the upper limit temperature, suppressing deterioration of the DPF and extending its life.

According to the fourth invention, when it is determined that the bed temperature of the oxidation catalyst is lower than the catalytic activation temperature at which unburned fuel in the exhaust gas is oxidized, fuel is not added to the exhaust gas by the fuel addition device. This makes it possible to prevent exhaust gas containing unburned fuel (especially HC components) that is not oxidized by the oxidation catalyst from being discharged into the atmosphere.

According to the fifth invention, when the internal combustion engine transitions from no-load deceleration operation to idle operation, the opening of the intake throttle valve is reduced to maintain the bed temperature of the DPF at the filter activation temperature. This allows the oxidation and incineration of particulate matter deposited in the DPF, which began during no-load deceleration operation of the internal combustion engine, to continue even when the engine transitions to idle operation, and the collection function of the DPF can be regenerated. In addition, when the bed temperature of the DPF reaches the filter activation temperature, the fuel addition device stops adding fuel to the exhaust gas even during idle operation, thereby improving fuel efficiency compared to conventional systems.

1 is a diagram illustrating an example of the configuration of an internal combustion engine to which an exhaust gas purification device according to an embodiment of the present invention is applied. 5 is a main flowchart showing an example of a filter regeneration process for regenerating a DPF, which is executed by a control device according to the present embodiment. 3 is a sub-flowchart showing a sub-process of the “PM accumulation state acquisition process” shown in FIG. 2 . 3 is a first sub-flowchart showing a sub-process of the "DPF regeneration process during deceleration" shown in FIG. 2; 3 is a second sub-flowchart showing the sub-processing of the "DPF regeneration process during deceleration" shown in FIG. 2; 5 is a sub-flowchart showing a sub-process of the “fuel addition amount acquisition process” shown in FIG. 4 . 5 is a sub-flowchart showing a sub-process of the "intake throttle valve adjustment process" shown in FIG. 4; FIG. 4 is a diagram showing an example of the relationship between the purification rate and the bed temperature of an oxidation catalyst. FIG. 4 is a diagram showing an example of a map for determining a fuel addition amount of an oxidation catalyst (DOC); FIG. 4 is a diagram showing an example of a map showing the relationship between the bed temperature of the DPF and the PM combustion speed. 4 is a timing chart showing an example of an operating state of an internal combustion engine and a regeneration state of a DPF. 13 is a third sub-flowchart showing a part of the sub-processing of the "DPF regeneration process during deceleration" according to the alternative first embodiment.

The following is a detailed description of an embodiment of an exhaust gas purification device according to the present invention, with reference to the drawings. First, the schematic configuration of the exhaust gas purification device 1 will be described with reference to FIG. 1. As shown in FIG. 1, the exhaust gas purification device 1 is composed of an internal combustion engine 10, a control device (ECU: Electronic Control Unit) 50, an intake flow detection device 31, an intake throttle valve 32, a rotation detection device 34, a vehicle speed detection device 37, a fuel addition valve 28, an exhaust gas purification unit 41, and the like.

The internal combustion engine 10 is, for example, a diesel engine. In the following description, the DPF 43 corresponds to a diesel particulate filter. In addition, a selective reduction catalyst that is disposed in the exhaust passage downstream of the DPF 43 and that neutralizes nitrogen oxides (NOx) and the like are not described.

As shown in FIG. 1, an exhaust gas purification unit 41 is provided in the exhaust passage (exhaust gas passage) 12 of an internal combustion engine 10. Inside the exhaust gas purification unit 41, from the upstream side, an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 42 and a DPF 43 are provided. The exhaust gas purification unit 41 constitutes an exhaust gas passage and removes harmful substances contained in the exhaust gas as the exhaust gas passes from the upstream side to the downstream side. Here, the internal combustion engine 10 is highly efficient and has excellent durability, but it emits harmful substances such as particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC) together with the exhaust gas.

The oxidation catalyst (DOC) 42 is made of a ceramic cellular cylinder formed into a cylindrical shape or the like, with numerous through holes formed in the axial direction, and with a precious metal such as platinum (Pt) supported on the inner surface. The oxidation catalyst (DOC) 42 oxidizes and removes carbon monoxide (CO), hydrocarbons (HC), etc. contained in the exhaust gas by passing the exhaust gas through the numerous through holes at a catalytic activation temperature (for example, a temperature of about 200°C to 250°C or higher), and also oxidizes unburned fuel in the exhaust gas, raising the exhaust gas temperature.

The DPF 43 is formed into a cylindrical shape or the like from a porous member made of a ceramic material or the like, forming a honeycomb-structured cellular cylinder with many small holes in the axial direction, and the ends of each small hole are blocked by a sealing material, alternating between adjacent small holes. The DPF 43 captures particulate matter (PM) by passing exhaust gas flowing into each small hole from the upstream side through the porous material, and allows only the exhaust gas to flow downstream through the adjacent small hole.

The DPF 43 may support a precious metal such as platinum (Pt) on the inner surface of each small hole. During the DPF regeneration process (filter regeneration process) described below, this precious metal may oxidize unburned fuel in the exhaust gas and raise the exhaust gas temperature. The amount of precious metal supported on the DPF 43 may be set to be less than the amount of precious metal supported on the oxidation catalyst (DOC) 42.

A fuel addition valve 28 and an exhaust temperature detection device 36A (e.g., an exhaust temperature sensor) (upstream exhaust temperature detection device) are provided upstream of the oxidation catalyst (DOC) 42 (upstream of the exhaust gas purification unit 41). The fuel addition valve 28 injects fuel to react with the exhaust gas in the oxidation catalyst (DOC) 42 and raise the temperature of the exhaust gas when performing a filter regeneration process (see FIG. 2) for regenerating the DPF 43 on which particulates have accumulated (when burning and incinerating particulate matter (PM)). The fuel addition valve 28 is driven by a control signal from the control device 50.

In addition, downstream of the oxidation catalyst (DOC) 42 and upstream of the DPF 43, an exhaust temperature detection device 36B (e.g., an exhaust temperature sensor) (intermediate exhaust temperature detection device) is provided. Downstream of the DPF 43, an exhaust temperature detection device 36C (e.g., an exhaust temperature sensor) (downstream exhaust temperature detection device) is provided. In addition, a differential pressure sensor 35 is provided in the exhaust gas purification unit 41, downstream of the oxidation catalyst (DOC) 42 and upstream of the DPF 43, to detect the differential pressure (pressure difference) between the exhaust pipe pressure and the exhaust pipe pressure downstream of the DPF 43.

The control device (ECU: Electronic Control Unit) 50 is a well-known device equipped with a CPU, RAM, ROM, timer, EEPROM, and a backup RAM (not shown). The CPU executes various calculation processes based on various programs and maps stored in the ROM and EEPROM. The RAM also temporarily stores the results of calculations by the CPU and data input from each detection device, and the EEPROM stores, for example, data that should be saved when the internal combustion engine 10 is stopped.

The EEPROM also includes a fuel addition amount map storage unit 501 and a PM combustion speed map storage unit 502. The fuel addition amount map storage unit 501 stores a fuel addition amount map M2 (see FIG. 9) used when determining the amount of fuel added to the oxidation catalyst (DOC) 42, as described below. The PM combustion speed map storage unit 502 stores a PM combustion speed map M3 (see FIG. 10) that stores the bed temperature of the DPF 43 and the PM combustion speed in association with each other, as described below.

The exhaust temperature detector 36A (upstream exhaust temperature detector) outputs a detection signal corresponding to the temperature of the exhaust gas in the exhaust pipe upstream of the oxidation catalyst (DOC) 42 to the control device 50. The exhaust temperature detector 36B (intermediate exhaust temperature detector) outputs a detection signal corresponding to the temperature of the exhaust gas flowing downstream of the oxidation catalyst (DOC) 42 and upstream of the DPF 43 to the control device 50. The exhaust temperature detector 36C (downstream exhaust temperature detector) outputs a detection signal corresponding to the temperature of the exhaust gas downstream of the DPF 43 to the control device 50. The differential pressure sensor 35 outputs a detection signal corresponding to the differential pressure between the exhaust pressure (corresponding to the exhaust pipe pressure) downstream of the oxidation catalyst (DOC) 42 and upstream of the DPF 43 and the exhaust pipe pressure downstream of the DPF 43 to the control device 50.

An intake flow rate detection device 31 (e.g., an air flow meter) is provided on the inlet side of the intake passage 11 of the internal combustion engine 10 to detect the intake flow rate filtered by the air cleaner 30. The intake flow rate detection device 31 outputs a detection signal corresponding to the flow rate of air taken in by the internal combustion engine 10 to the control device 50. An intake throttle valve 32 is disposed in the intake passage 11 downstream of the air cleaner 30. The intake throttle valve 32 can adjust the opening of the intake passage 11 based on a control signal from the control device 50 to adjust the intake flow rate.

The accelerator opening detection device 33 (e.g., an accelerator opening sensor) outputs a detection signal corresponding to the opening of the accelerator operated by the driver (i.e., the load required by the driver) to the control device 50. The rotation detection device 34 (e.g., a rotation sensor) provided in the internal combustion engine 10 outputs a detection signal corresponding to, for example, the rotation speed of the crankshaft of the internal combustion engine 10 (i.e., the engine speed) to the control device 50. The vehicle speed detection device 37 (e.g., a vehicle speed sensor) is provided on the wheels of the vehicle or a drive shaft that rotates integrally with the wheels, and outputs a detection signal corresponding to the vehicle speed to the control device 50.

The control device 50 receives the detection signals of the intake air flow rate detection device 31 (e.g., an air flow meter) provided in the intake passage 11, the detection signals of the accelerator opening detection device 33, the detection signals of the rotation detection device 34, and the detection signals of the vehicle speed detection device 37. The control device 50 also receives the detection signals of the exhaust temperature detection devices 36A, 36B, and 36C described above, and the detection signal of the differential pressure sensor 35.

The control device 50 can then detect the operating state of the internal combustion engine 10 based on these input detection signals. The control device 50 also outputs control signals to control the amount of fuel injected from each injector 14A-14D into the cylinder of the internal combustion engine 10 and the amount of fuel injected from the fuel addition valve 28 in response to the detected operating state of the internal combustion engine 10 and a request from the driver based on the detection signal from the accelerator opening detection device 33.

The control device 50 also calculates the fuel consumption per second (g/s) injected from each injector 14A-14D at predetermined intervals (e.g., about 10 msec-100 msec) and stores it in chronological order in the RAM. The control device 50 also calculates the intake air flow rate GA from the detection signal input from the intake air flow rate detection device 31 at predetermined intervals (e.g., about 10 msec-100 msec) and stores it in chronological order in the RAM. The control device 50 also calculates the actual differential pressure ΔP from the detection signal input from the differential pressure sensor 35 at predetermined intervals (e.g., about 10 msec-100 msec) and stores it in chronological order in the RAM.

When the bed temperature of the oxidation catalyst (DOC) 42 reaches the catalyst activation temperature (e.g., about 200°C to 250°C), the fuel injected into the exhaust gas from the fuel addition valve 28 undergoes an oxidation reaction with the oxygen remaining in the exhaust gas due to the precious metal supported on the oxidation catalyst (DOC) 42, and burns, causing the exhaust gas temperature to rise due to the heat generated. Then, the bed temperature of the DPF 43 rises due to this high-temperature exhaust gas, and when it reaches the filter activation temperature (e.g., 500°C or higher), oxidation (combustion) of the particulate matter (PM) accumulated in the DPF 43 begins.

Then, as described below, after stopping the addition of fuel from the fuel addition valve 28, the control device 50 reduces the opening of the intake throttle valve 32 (for example, closes the intake throttle valve 32) to maintain the bed temperature of the DPF 43 at the filter activation temperature. This allows the control device 50 to oxidize (burn) and remove the particulate matter (PM) accumulated in the DPF 43, and to recover (regenerate) the collection function of the DPF 43, which collects particulate matter (PM) in the exhaust gas (this is known as filter regeneration processing).

[Filter regeneration process]
Next, an example of a filter regeneration process in which the control device 50 oxidizes (burns) and removes particulate matter (PM) trapped in the DPF 43 in the exhaust gas purification device 1 configured as above will be described with reference to Figures 2 to 11. The control device 50 repeatedly executes the process procedure shown in the flowchart of Figure 2 at predetermined time intervals (e.g., intervals of several tens to several hundreds of milliseconds) while the internal combustion engine 10 is in operation.

As shown in FIG. 2, first, in step S11, the control device 50 executes a sub-process of the "PM accumulation state acquisition process" and then proceeds to the process of step S12. The "PM accumulation state acquisition process" is a process for calculating the accumulation amount (PM accumulation amount) of particulate matter (PM) that is trapped in the DPF 43 during a predetermined time interval (e.g., an interval of several tens to several hundreds of msec), i.e., that accumulates in the DPF 43, and acquiring the accumulation state of the particulate matter (PM).

In step S12, the control device 50 executes the sub-processing of the "DPF regeneration process during deceleration" and then terminates the process. The "DPF regeneration process during deceleration" is a process that removes particulate matter (PM) trapped in the DPF 43 by oxidizing (burning) it during a predetermined time interval (e.g., an interval of several tens to several hundreds of milliseconds) during unloaded deceleration operation of the internal combustion engine 10.

[PM Accumulation State Acquisition Process]
Here, the details of the sub-process of the "PM accumulation state acquisition process" will be described with reference to Fig. 3. As shown in Fig. 3, first, in step S111, the control device 50 reads the deceleration DPF regeneration flag from the EEPROM and determines whether it is set to "OFF". The deceleration DPF regeneration flag indicates that the particulate matter (PM) accumulated in the DPF 43 has reached a regeneration start threshold C1 (accumulation amount threshold) (e.g., about 50 g) and that the DPF 43 needs to be regenerated to recover the collection function during the no-load deceleration operation of the internal combustion engine 10. The deceleration DPF regeneration flag is set to "OFF" and stored in the EEPROM when the vehicle is shipped from the factory.

If it is determined that the deceleration DPF regeneration flag is set to "ON" (S111: NO), the control device 50 ends the sub-processing, returns to the main flowchart, and proceeds to the sub-processing of step S12. On the other hand, if it is determined that the deceleration DPF regeneration flag is set to "OFF" (S111: YES), the control device 50 proceeds to the processing of step S112.

In step S112, the control device 50 acquires the operating state of the internal combustion engine 10, such as the engine speed and engine load (fuel injection amount), from detection signals from the accelerator opening detection device 33, the rotation detection device 34, etc., and stores them in RAM, and then proceeds to the processing of step S113. In step S113, the control device 50 calculates the amount of particulate matter (PM) deposited in the DPF 43 at a predetermined time interval (e.g., an interval of several tens to several hundreds of msec) based on a map (not shown) showing the relationship between the operating state of the internal combustion engine 10 and the amount of particulate matter (PM) deposited per unit time, and proceeds to the processing of step S114.

In step S114, the control device 50 reads the cumulative PM deposition amount PMS from the EEPROM, adds the particulate matter (PM) deposition amount (hereinafter also referred to as "PM deposition amount") calculated in step S113 to this cumulative PM deposition amount PMS, stores it again in the EEPROM, and then proceeds to processing in step S115.

In step S115, the control device 50 calculates the differential pressure ΔP between the upstream exhaust pressure and the downstream exhaust pressure of the DPF 43 based on the detection signal input from the differential pressure sensor 35, and then proceeds to processing in step S116. In step S116, the control device 50 calculates the PM deposition amount PMD trapped in the DPF 43 based on a map (not shown) showing the relationship between the differential pressure ΔP and the PM deposition amount (PM deposition amount PMD) deposited in the DPF 43, stores it in RAM, and then proceeds to processing in step S117.

In step S117, the control device 50 reads the cumulative PM accumulation amount PMS from the EEPROM and reads the PM accumulation amount PMD from the RAM. The control device 50 also reads the regeneration start threshold C1 (accumulation amount threshold), which is the upper limit of the amount of PM accumulated in the DPF 43, from the EEPROM. The control device 50 then determines whether or not one of the cumulative PM accumulation amount PMS or the PM accumulation amount PMD has become equal to or greater than the regeneration start threshold C1, that is, whether or not the amount of PM accumulation in the DPF 43 has reached its upper limit.

If it is determined that the cumulative PM accumulation amount PMS and the PM accumulation amount PMD are less than the regeneration start threshold C1, that is, if it is determined that the PM accumulation amount in the DPF 43 has not reached the upper limit value (S117: NO), the control device 50 ends the sub-processing, returns to the main flowchart, and proceeds to the sub-processing of step S12.

On the other hand, if it is determined that either the accumulated PM accumulation amount PMS or the PM accumulation amount PMD is equal to or greater than the regeneration start threshold C1, that is, if it is determined that the PM accumulation amount in the DPF 43 has reached the upper limit (S117: YES), the control device 50 proceeds to processing in step S118. In step S118, the control device 50 stores the larger of the accumulated PM accumulation amount PMS and the PM accumulation amount PMD in the EEPROM as the PM accumulation amount P1 accumulated in the DPF 43, and then proceeds to processing in step S119. The control device 50 may also store the average value of the accumulated PM accumulation amount PMS and the PM accumulation amount PMD in the EEPROM as the PM accumulation amount P1 accumulated in the DPF 43.

In step S119, the control device 50 reads the deceleration DPF regeneration flag from the EEPROM, sets it to "ON" and stores it again in the EEPROM, then ends the sub-processing, returns to the main flowchart, and proceeds to the sub-processing of step S12.

The control device 50 may execute only one of the above steps S112 to S114 and the above steps S115 to S116. In other words, it may acquire only one of the accumulated PM deposition amount PMS or the PM deposition amount PMD, and in step S117, determine whether or not it has reached the regeneration start threshold C1 or more, that is, whether or not the PM deposition amount in the DPF 43 has reached the upper limit value. In this case, in step S118, the acquired accumulated PM deposition amount PMS or PM deposition amount PMD may be stored in the EEPROM as the PM deposition amount P1. This can improve the processing speed of the control device 50.

[DPF regeneration process during deceleration]
Next, the details of the sub-process of the "DPF regeneration process during deceleration" will be described with reference to Figures 4 to 10. As shown in Figures 4 and 5, first, in step S211, the control device 50 reads the deceleration DPF regeneration flag from the EEPROM and determines whether it is set to "ON". If it is determined that the deceleration DPF regeneration flag is set to "OFF" (S211: NO), the control device 50 determines that the PM accumulation amount in the DPF 43 has not reached the upper limit value, ends the sub-process, returns to the main flowchart, and ends the filter regeneration process.

On the other hand, if it is determined that the deceleration DPF regeneration flag is set to "ON" (S211: YES), the control device 50 proceeds to processing in step S212. In step S212, the control device 50 determines whether the internal combustion engine 10 is in a no-load deceleration operation.

Specifically, the control device 50 detects the accelerator opening based on the detection signal input from the accelerator opening detection device 33 and stores it in the RAM. The control device 50 also detects the vehicle speed based on the detection signal input from the vehicle speed detection device 37 and stores it in the RAM. Next, the control device 50 reads the accelerator opening and vehicle speed from the RAM and determines whether the accelerator opening is "0", that is, whether the driver is not depressing the accelerator pedal, and whether the vehicle speed is equal to or greater than the vehicle speed threshold value V1 (e.g., 2 km/h). The vehicle speed threshold value V1 (e.g., 2 km/h) is stored in advance in the EEPROM.

If it is determined that the internal combustion engine 10 is not in unloaded deceleration operation (S212: NO), the control device 50 reads the deceleration flag from the RAM, sets it to "OFF" and stores it again in the RAM, then ends the sub-processing, returns to the main flowchart, and ends the filter regeneration process. Specifically, if the accelerator opening is not "0", that is, if the driver is depressing the accelerator pedal, the control device 50 determines that the internal combustion engine 10 is in normal operation (S212: NO). Also, if the accelerator opening is "0" and the vehicle speed is slower than the vehicle speed threshold V1 (e.g., 2 km/h), the control device 50 determines that the vehicle is about to stop and that the unloaded deceleration operation of the internal combustion engine 10 has ended (S212: NO).

On the other hand, if it is determined that the internal combustion engine 10 is in unloaded deceleration operation (S212: YES), the control device 50 reads the deceleration flag from the RAM, sets it to "ON", stores it again in the RAM, and then proceeds to the processing of step S213. Specifically, if the accelerator opening is "0" and the vehicle speed is equal to or greater than the vehicle speed threshold V1 (e.g., 2 km/h), the control device 50 determines that the internal combustion engine 10 is in unloaded deceleration operation (S212: YES). The deceleration flag is set to "OFF" and stored in the RAM when the control device 50 is started.

In step S213, the control device 50 detects the exhaust gas temperature T2 upstream of the DPF 43 and the exhaust gas temperature T3 downstream of the DPF 43 based on the detection signals from the exhaust temperature detection devices 36B and 36C, and stores them in the RAM. The control device 50 then calculates the bed temperature of the DPF 43 based on a temperature map MP1 (not shown) that associates the exhaust gas temperatures T2 and T3 with the bed temperature of the DPF 43, and stores them in the RAM. Next, the control device 50 determines whether the bed temperature of the DPF 43 is at a filter activation temperature (e.g., 500°C to 700°C) at which particulate matter (PM) is oxidized (burned), that is, whether the temperature has been raised to the filter activation temperature.

If the bed temperature of the DPF 43 is not the filter activation temperature (e.g., 500°C to 700°C) at which particulate matter (PM) is oxidized (burned), that is, if it is determined that the temperature is lower than the filter activation temperature (S213: NO), the control device 50 proceeds to the process of step S214. The temperature map MP1 (not shown) is obtained by CAE (Computer Aided Engineering) analysis or experiment, and is stored in advance in the EEPROM. The filter activation temperature is also obtained by experiment and is stored in advance in the EEPROM.

In step S214, the control device 50 detects the exhaust gas temperature T1 upstream of the oxidation catalyst 42 and the exhaust gas temperature T2 downstream of the oxidation catalyst 42 based on the detection signals from the exhaust temperature detection devices 36A and 36B, and stores them in the RAM. The control device 50 then calculates the bed temperature of the oxidation catalyst 42 based on a temperature map MP2 (not shown) that associates the exhaust gas temperatures T1 and T2 with the bed temperature of the oxidation catalyst 42, and stores them in the RAM.

Then, the control device 50 determines whether the bed temperature of the oxidation catalyst 42 is at the catalyst activation temperature (e.g., a temperature of 150°C to 180°C or higher) at which the unburned fuel in the exhaust gas is oxidized (burned). The temperature map MP2 (not shown) is obtained by CAE (Computer Aided Engineering) analysis or experiment, and is stored in advance in the EEPROM. The catalyst activation temperature is also obtained by experiment and is stored in advance in the EEPROM.

If the bed temperature of the oxidation catalyst 42 is not the catalyst activation temperature (for example, a temperature of 150°C to 180°C or higher) at which the unburned fuel in the exhaust gas is oxidized (burned), that is, if it is determined that the temperature is lower than the catalyst activation temperature (S214: NO), the control device 50 ends the sub-processing, returns to the main flowchart, and ends the filter regeneration process. As a result, if the bed temperature of the oxidation catalyst 42 is lower than the catalyst activation temperature, fuel is not added to the exhaust gas by the fuel addition valve 28. This makes it possible to prevent exhaust gas containing unburned fuel (particularly HC components) that is not oxidized by the oxidation catalyst 42 from being discharged into the atmosphere.

On the other hand, if it is determined that the bed temperature of the oxidation catalyst 42 is at the catalyst activation temperature (e.g., a temperature of 150°C to 180°C or higher) at which unburned fuel in the exhaust gas is oxidized (burned) (S214: YES), the control device 50 proceeds to processing in step S215. In step S215, the control device 50 executes a sub-process of "fuel addition amount acquisition processing" (see FIG. 6), and then proceeds to processing in step S216. The sub-process of "fuel addition amount acquisition processing" is a process for acquiring the amount of fuel to be added (supplied) from the fuel addition valve 28 to the exhaust gas.

[Fuel addition amount acquisition process]
Here, the sub-processing of the "fuel addition amount acquisition process" will be described with reference to Figures 6, 8, and 9. As shown in Figure 6, first, in step S311, the control device 50 reads out the bed temperature of the oxidation catalyst 42 calculated in step S214 from the RAM. Then, the control device 50 obtains the purification rate [%] corresponding to the bed temperature of the oxidation catalyst 42 using a two-dimensional map M1 shown in Figure 8, which is indicated by a solid line 61 that corresponds to the relationship between the bed temperature of the oxidation catalyst (DOC) 42 and the purification rate (the proportion of hydrocarbons (HC) or carbon monoxide (CO) oxidized), stores it in the RAM, and then proceeds to the process of step S312.

For example, as shown in FIG. 8, the purification rate corresponding to the bed temperature TC1 of the oxidation catalyst 42 (e.g., 150°C to 180°C) is about 10%. Also, the purification rate corresponding to the bed temperature TC2 of the oxidation catalyst 42 (e.g., 200°C to 250°C) is about 90%.

In step S312, the control device 50 calculates the intake air flow rate GA [g/sec] from the detection signal input from the intake air flow rate detection device 31, stores it in RAM as the exhaust gas flow rate [g/sec], and then proceeds to processing in step S313. The control device 50 may also obtain the fuel injection amount instructed to each injector 14A-14D up to a predetermined time ago (e.g., 1 second) from the present, and store the sum of this and the intake air flow rate GA in RAM as the exhaust gas flow rate [g/sec].

In step S313, the control device 50 reads from the RAM the current purification rate [%] of the oxidation catalyst 42 obtained in step S311 and the current exhaust gas amount [g/sec] obtained in step S312. Then, using the fuel addition amount map M2 of the oxidation catalyst 42 shown in Figure 9, the control device 50 calculates the fuel addition amount [ ^mm3 /sec] corresponding to the current purification rate [%] of the oxidation catalyst 42 and the current exhaust gas flow rate [g/sec] and stores them in the RAM, then ends the sub-processing, returns to the sub-processing of "DPF regeneration process during deceleration", and proceeds to the process of step S216.

As shown in Fig. 4, in step S216, the control device 50 reads out from the RAM the amount of fuel added [ ^mm3 /sec] calculated in step S313. The control device 50 then multiplies this amount of fuel added [ ^mm3 /sec] by the interval at which the process shown in Fig. 2 is started (for example, 10 msec if the process is started at 10 msec intervals), calculates the amount of fuel added [mm3], and adds (injects) the calculated amount of fuel added [ ^mm3 ] into the exhaust gas via the fuel addition valve 28, and then proceeds to the process of step S217.

In step S217, the control device 50 reads from the EEPROM the exhaust fuel addition flag, which indicates that fuel is being added (injected) into the exhaust gas via the fuel addition valve 28, sets the exhaust fuel addition flag to "ON" and stores it in the EEPROM again, then ends the sub-processing, returns to the main flowchart, and ends the filter regeneration process. Note that the exhaust fuel addition flag is set to "OFF" and stored in the EEPROM when the vehicle is shipped from the factory.

On the other hand, if it is determined in step S213 that the bed temperature of the DPF 43 is at the filter activation temperature (e.g., 500°C to 700°C) at which particulate matter (PM) is oxidized (burned), that is, that the temperature has risen to the filter activation temperature (S213: YES), the control device 50 proceeds to the process of step S218. In step S218, the control device 50 reads the exhaust fuel addition flag from the EEPROM and determines whether the exhaust fuel addition flag is set to "ON" or not, that is, whether fuel is being added (injected) into the exhaust gas via the fuel addition valve 28 or not.

If it is determined that the exhaust fuel addition flag is set to "OFF" (S218: NO), the control device 50 determines that the addition (injection) of fuel into the exhaust gas via the fuel addition valve 28 has stopped, and proceeds to the processing of step S221 described below. On the other hand, if it is determined that the exhaust fuel addition flag is set to "ON" (S218: YES), the control device 50 determines that the addition (injection) of fuel into the exhaust gas via the fuel addition valve 28 is being performed, and proceeds to the processing of step S219.

In step S219, the control device 50 stops the addition (injection) of fuel into the exhaust gas via the fuel addition valve 28, and then proceeds to the process of step S220. In step S220, the control device 50 reads the exhaust fuel addition flag from the EEPROM, sets it to "OFF", stores it in the EEPROM again, and then proceeds to the process of step S221. In step S221, the control device 50 executes the sub-processing of "intake throttle valve adjustment processing" (see FIG. 7), and then proceeds to the process of step S222. The sub-processing of "intake throttle valve adjustment processing" is a process for setting the opening degree of the intake throttle valve 32 so as to maintain the bed temperature of the PDF 43 at the filter activation temperature (e.g., 500°C to 700°C).

[Intake throttle valve adjustment process]
Here, the sub-processing of the "intake throttle valve adjustment process" will be described with reference to Fig. 7. As shown in Fig. 7, first, in step S411, the control device 50 reads out the bed temperature of the DPF 43 acquired in step S213 from the RAM, and determines whether the bed temperature of the DPF 43 has reached the upper limit temperature of the filter activation temperature (e.g., 695°C to 700°C). The upper limit temperature of the filter activation temperature (e.g., 695°C to 700°C) is acquired by experiment and stored in advance in the EEPROM.

If it is determined that the bed temperature of the DPF 43 has not reached the upper limit temperature of the filter activation temperature (e.g., 695°C to 700°C) (S411: NO), the control device 50 proceeds to the process of step S412. In step S412, the control device 50 reduces the opening of the intake throttle valve 32, for example, closes the intake throttle valve 32, and sets the flow rate to only the amount of intake air necessary to maintain the oxidation (combustion) of particulate matter (PM) accumulated in the DPF 43, and then ends the sub-processing, returns to the sub-processing of "DPF regeneration process during deceleration", and proceeds to the process of step S222.

The control device 50 can thus control the bed temperature of the DPF 43 to be maintained at the filter activation temperature (e.g., 500°C to 700°C) by self-heating due to oxidation (combustion) of particulate matter (PM) accumulated in the DPF 43, while suppressing a decrease in the bed temperature of the DPF 43. As a result, the bed temperature of the DPF 43 can be maintained at the filter activation temperature by suppressing a decrease in the temperature of the DPF 43, and the oxidation incineration of the particulate matter (PM) accumulated in the DPF 43 can be continued.

On the other hand, if it is determined that the bed temperature of the DPF 43 has reached the upper limit temperature of the filter activation temperature (e.g., 695°C to 700°C) (S411: YES), the control device 50 proceeds to processing in step S413. In step S413, the control device 50 increases the opening of the intake throttle valve 32 to increase the intake flow rate, and then ends the sub-processing, returns to the sub-processing of "DPF regeneration processing during deceleration," and proceeds to processing in step S222.

By this, the control device 50 can increase the exhaust gas flow rate through the DPF 43 and maintain the bed temperature of the DPF 43 at a filter activation temperature that is lower than the upper limit temperature of the filter activation temperature (e.g., 695°C to 700°C). As a result, the control device 50 can continue the oxidative incineration of particulate matter (PM) accumulated in the DPF 43, and can suppress deterioration of the DPF 43 and extend its life.

As shown in FIG. 4, in step S222, the control device 50 detects the exhaust gas temperature T2 upstream of the DPF 43 and the exhaust gas temperature T3 downstream of the DPF 43 based on the detection signals from the exhaust temperature detection devices 36B and 36C, and stores them in RAM. The control device 50 then calculates the bed temperature TP1 of the DPF 43 based on a temperature map MP1 (not shown) that associates the exhaust gas temperatures T2 and T3 with the bed temperature of the DPF 43, stores it in RAM, and then proceeds to the processing of step S223.

In step S223, the control device 50 calculates the PM combustion speed corresponding to the bed temperature TP1 of the DPF 43 calculated in step S222 using a PM combustion speed map M3 shown in FIG. 10, which corresponds to the relationship between the bed temperature of the DPF 43 and the combustion speed of particulate matter (PM) (hereinafter referred to as "PM combustion speed"). After storing the PM combustion speed in RAM, the control device 50 proceeds to the processing of step S224. The PM combustion speed map M3 is previously obtained by CAE (Computer Aided Engineering) analysis or experiment, and is previously stored in the EEPROM as a map or a formula.

In step S224, since the PM combustion rate is the amount of particulate matter (PM) burned per unit volume and per unit time in the DPF 43, the control device 50 reads the PM combustion rate corresponding to the bed temperature TP1 of the DPF 43 from the RAM and reads the volume of the DPF 43 from the EEPROM. The control device 50 then multiplies the PM combustion rate by the volume of the DPF 43 by the interval at which the process shown in FIG. 2 is started (for example, 10 msec when started at 10 msec intervals) to calculate the amount of particulate matter (PM) burned in the DPF 43 and stores the result in the RAM.

Next, the control device 50 reads out the amount of PM accumulated in the DPF 43, P1, from the EEPROM. The control device 50 then subtracts the amount of particulate matter (PM) burned in the DPF 43 from this amount of PM accumulated, P1, stores the amount in the EEPROM again, and then proceeds to the process of step S225.

As shown in FIG. 5, in step S225, the control device 50 reads the amount P1 of PM accumulated in the DPF 43 from the EEPROM and determines whether this amount P1 of PM accumulation is equal to or less than the "regeneration end threshold C2". In other words, the control device 50 determines whether almost all of the particulate matter (PM) in the DPF 43 has been oxidized and incinerated (combusted). The regeneration end threshold C2 is obtained by CAE (Computer Aided Engineering) analysis or experimentation and is stored in advance in the EEPROM.

If it is determined that the PM accumulation amount P1 is greater than the regeneration end threshold C2 (S225: NO), the control device 50 determines that almost all of the particulate matter (PM) in the DPF 43 has not been oxidized and incinerated (combusted), ends the sub-processing, returns to the main flowchart, and ends the filter regeneration process.

On the other hand, if it is determined that the PM accumulation amount P1 is equal to or less than the regeneration end threshold C2 (S225: YES), the control device 50 determines that almost all of the particulate matter (PM) in the DPF 43 has been oxidized and incinerated (combusted), and proceeds to the process of step S226. In step S226, the control device 50 opens the intake throttle valve 32 to increase the intake flow rate, sets the bed temperature of the DPF 43 to be lower than the filter activation temperature, and then proceeds to the process of step S227.

That is, the control device 50 sets the oxidation (combustion) of particulate matter (PM) accumulated in the DPF 43 to stop, and then proceeds to the process of step S227. In step S227, the control device 50 reads the deceleration DPF regeneration flag from the EEPROM, sets this deceleration DPF regeneration flag to "OFF", stores it again in the EEPROM, and then ends the sub-processing, returns to the main flowchart, and ends the filter regeneration process.

Here, an example of the operating state of the internal combustion engine 10 and the regeneration state of the DPF 43 when the control device 50 executes a filter regeneration process (see FIG. 2) that removes particulate matter (PM) trapped in the DPF 43 by oxidizing (burning) it will be described with reference to FIG. 11. As shown in FIG. 11, if the amount of PM accumulated in the DPF 43 becomes equal to or greater than the regeneration start threshold C1 at time TM1, the deceleration DPF regeneration flag is set to "ON" (S117 to S119).

Then, at time TM2, the accelerator opening becomes "0", the fuel injection amount becomes "0", and the vehicle speed is equal to or greater than the vehicle speed threshold V1 (e.g., 2 km/h), so the vehicle is in unloaded deceleration operation and the deceleration flag is set to "ON" (S212: YES). Also, because the bed temperature of the DPF 43 is lower than the filter activation temperature (e.g., 500°C to 700°C) and the bed temperature of the oxidation catalyst is equal to or greater than the catalyst activation temperature (e.g., 150°C to 180°C), the control device 50 adds (injects) fuel into the exhaust gas via the fuel addition valve 28, sets the exhaust fuel addition flag to "ON", and stores this in the EEPROM (S213: NO to S217).

After that, at time TM3, the control device 50 stops adding (injecting) fuel into the exhaust gas via the fuel addition valve 28 because the bed temperature of the DPF 43 has reached the filter activation temperature (e.g., 500°C), and then sets the exhaust fuel addition flag to "OFF" and stores it in the EEPROM (S213: YES to S220). In addition, the control device 50 closes the opening of the intake throttle valve 32, so that the exhaust gas flow rate into the DPF 43 becomes almost "0", and oxidation (combustion) of particulate matter (PM) continues, and the bed temperature of the DPF 43 is maintained at the filter activation temperature (e.g., 500°C to 700°C) by self-heating (S221).

Then, at time TM4, the amount of PM accumulated in the DPF 43, P1, becomes equal to or less than the "regeneration end threshold C2", meaning that almost all of the particulate matter (PM) in the DPF 43 is oxidized and incinerated (combusted). As a result, the control device 50 opens the intake throttle valve 32 to increase the intake flow rate, sets the bed temperature of the DPF 43 lower than the filter activation temperature, and then sets the deceleration DPF regeneration flag to "OFF" and stores it in the EEPROM (S225: YES to S227). Thereafter, when the vehicle speed becomes approximately "0", the control device 50 sets the deceleration flag to "OFF" and stores it in the RAM.

Here, the fuel addition valve 28 functions as an example of a fuel addition device. The control device 50 functions as an example of a deposition amount acquisition device, a fuel addition control device, a filter bed temperature determination device, an upper limit temperature determination device, a catalyst bed temperature determination device, and an idle operation determination device. The control device 50 and each of the exhaust temperature detection devices 36B, 36C constitute an example of a filter bed temperature acquisition device. The control device 50 and each of the exhaust temperature detection devices 36A, 36B constitute an example of an oxidation catalyst bed temperature acquisition device.

As described above in detail, in the exhaust gas purification device 1 according to this embodiment, when the amount of particulate matter (PM) deposited in the DPF 43 becomes equal to or greater than the regeneration start threshold C1 (deposition amount threshold), the control device 50 adds fuel to the exhaust gas flowing into the oxidation catalyst 42 via the fuel addition valve 28 during unloaded deceleration operation of the internal combustion engine 10 to raise the bed temperature of the DPF 43. Then, when the bed temperature of the DPF 43 reaches the filter activation temperature (e.g., 500°C to 700°C) at which the particulate matter (PM) is oxidized (burned), the addition of fuel to the exhaust gas by the fuel addition valve 28 is stopped.

As a result, when the bed temperature of the DPF 43 reaches the filter activation temperature under the operating conditions during no-load deceleration operation of the internal combustion engine 10, oxidation of the particulate matter (PM) deposited in the DPF 43 begins. Therefore, even if the addition of fuel to the exhaust gas by the fuel addition valve 28 is stopped, the oxidation and incineration (combustion and incineration) of the deposited particulate matter (PM) continues due to self-heating caused by the heat of oxidation reaction of the particulate matter (PM), and the collection function of the DPF 43 can be restored. In addition, when the bed temperature of the DPF 43 reaches the filter activation temperature (for example, 500°C to 700°C), the addition of fuel to the exhaust gas by the fuel addition valve 28 is stopped, so that fuel efficiency can be improved compared to the conventional method.

In addition, when the addition of fuel to the exhaust gas by the fuel addition valve 28 is stopped, the opening of the intake throttle valve 32 is reduced (for example, the intake throttle valve 32 is closed), so the intake flow rate is reduced and the flow rate of the exhaust gas flowing into the DPF 43 can be reduced. As a result, the control device 50 can suppress a decrease in the temperature of the DPF 43 and maintain the bed temperature of the DPF 43 at the filter activation temperature, and can continue the oxidation incineration (combustion incineration) of particulate matter (PM) accumulated in the DPF 43.

In addition, when the bed temperature of the DPF 43 reaches the upper limit of the filter activation temperature (e.g., 700°C), the opening of the intake throttle valve 32 is increased to control the bed temperature of the DPF 43 to be maintained at a filter activation temperature (e.g., 500°C to 695°C) lower than the upper limit. This allows the control device 50 to continue the oxidation and incineration of particulate matter (PM) accumulated in the DPF 43, and to maintain the bed temperature of the DPF 43 at a filter activation temperature lower than the upper limit, thereby suppressing deterioration of the DPF 43 and extending its life.

In addition, when the control device 50 determines that the bed temperature of the oxidation catalyst 42 is lower than the catalyst activation temperature (e.g., 150°C to 180°C) at which unburned fuel in the exhaust gas is oxidized, the control device 50 does not add fuel to the exhaust gas through the fuel addition valve 28. This makes it possible to prevent exhaust gas containing unburned fuel (especially HC components) that is not oxidized (burned) by the oxidation catalyst 42 from being discharged into the atmosphere.

The numerical values used in the description of the above embodiment are merely examples and are not limited to these numerical values. Furthermore, terms such as greater than or equal to (≧), less than or equal to (≦), greater than (>), less than (<), etc. may or may not include an equal sign.

The exhaust gas purification device of the present invention is not limited to the configuration, structure, appearance, shape, processing procedure, etc. described in the above embodiment, and various modifications, improvements, additions, and deletions are possible without changing the gist of the present invention. In the following description, the same reference numerals as those of the internal combustion engine 10, etc., according to the above embodiment in Figures 1 to 11 indicate the same or equivalent parts as those of the internal combustion engine 10, etc., according to the above embodiment.

[Another First Embodiment]
(A) For example, as shown in Fig. 12, in the control device 50 according to another first embodiment, when it is determined in step S212 of the sub-processing of the "DPF regeneration process during deceleration" that the internal combustion engine 10 is in no-load deceleration operation (S212: YES), the control device 50 proceeds to the process of step S213. On the other hand, when it is determined that the internal combustion engine 10 is not in no-load deceleration operation (S212: NO), the control device 50 may proceed to the process of step S311.

In step S311, the control device 50 may determine whether the internal combustion engine 10 is idling. Specifically, the control device 50 detects the accelerator opening based on the detection signal input from the accelerator opening detection device 33 and stores it in the RAM. The control device 50 also detects the vehicle speed based on the detection signal input from the vehicle speed detection device 37 and stores it in the RAM. The control device 50 also detects the engine speed based on the detection signal input from the rotation detection device 34 and stores it in the RAM.

Next, the control device 50 reads the accelerator opening, vehicle speed, and engine speed from the RAM, and determines whether the accelerator opening is "0", that is, the driver is not stepping on the accelerator pedal, the vehicle speed is slower than the vehicle speed threshold V1 (e.g., 2 km/h), and the engine speed is equal to or lower than the engine speed threshold N1 (e.g., 800 rpm). The vehicle speed threshold V1 (e.g., 2 km/h) and engine speed threshold N1 (e.g., 800 rpm) are stored in advance in the EEPROM.

If it is determined that the internal combustion engine 10 is not idling (S311: NO), the control device 50 may read the deceleration flag from the RAM, set it to "OFF", store it again in the RAM, and then end the sub-processing, return to the main flowchart, and end the filter regeneration process. Specifically, if the accelerator opening is not "0" and the engine speed is higher than the engine speed threshold N1, that is, the driver is about to depress the accelerator pedal and start moving, the control device 50 determines that the idling operation of the internal combustion engine 10 has ended (S311: NO). Also, if the accelerator opening is not "0", that is, the driver is depressing the accelerator pedal, the control device 50 determines that the internal combustion engine 10 is in normal operation (S311: NO).

On the other hand, if it is determined that the internal combustion engine 10 is idling (S311: YES), the control device 50 may read the deceleration flag from the RAM, set it to "ON", store it again in the RAM, and then proceed to the processing of step S213. Specifically, if the accelerator opening is "0", the vehicle speed is slower than the vehicle speed threshold V1 (e.g., 2 km/h), and the engine speed is equal to or lower than the engine speed threshold N1 (e.g., 800 rpm), the control device 50 determines that the internal combustion engine 10 is idling (S311: YES). The deceleration flag is set to "OFF" and stored in the RAM when the control device 50 is started.

As described above, in the control device 50 according to the first embodiment, when the internal combustion engine 10 transitions from unloaded deceleration operation to idle operation, the opening of the intake throttle valve 32 is reduced (for example, the intake throttle valve 32 is closed) to maintain the bed temperature of the DPF 43 at the filter activation temperature (for example, 500°C to 700°C). This allows the oxidation and incineration (combustion and incineration) of particulate matter (PM) deposited in the DPF 43, which was started during unloaded deceleration operation of the internal combustion engine 10, to continue even when the engine transitions to idle operation, and the collection function of the DPF 43 can be regenerated. In addition, when the bed temperature of the DPF 43 reaches the filter activation temperature, the addition of fuel to the exhaust gas by the fuel addition valve 28 is stopped even during idle operation, thereby improving fuel efficiency more than before.

(B) For example, in the above embodiment, in the processing of step S216, the control device 50 adds (supplies) unburned fuel to the exhaust gas via the fuel addition valve 28, but it is also possible to supply unburned fuel to the exhaust gas by so-called post-injection via each injector 14A-14D.

1 exhaust gas purification device 10 internal combustion engine 11 intake passage 12 exhaust passage (exhaust gas passage)
28 Fuel addition valve 31 Intake flow rate detection device 32 Intake throttle valve 33 Accelerator opening detection device 34 Revolution detection device 35 Differential pressure sensor 36A to 36C Exhaust temperature detection device 37 Vehicle speed detection device 41 Exhaust gas purification unit 42 Oxidation catalyst (DOC)
43 Particulate matter removal filter (DPF)
50 Control device

Claims (3)

an oxidation catalyst disposed in an exhaust gas passage of the internal combustion engine and configured to oxidize unburned fuel in the exhaust gas;
a particulate matter removal filter disposed downstream of the oxidation catalyst and configured to collect particulate matter in the exhaust gas;
a fuel addition device that adds fuel to the exhaust gas flowing into the oxidation catalyst;
an accumulation amount acquisition device that acquires an accumulation amount of the particulate matter trapped in the particulate matter removal filter;
a filter bed temperature acquisition device for acquiring a bed temperature of the particulate matter removal filter;
a fuel addition control device that, when the deposition amount of the particulate matter acquired via the deposition amount acquisition device becomes equal to or greater than a predetermined deposition amount threshold, starts a deceleration DPF regeneration process for oxidizing and incinerating the particulate matter trapped in the particulate matter removal filter by controlling fuel to be added to the exhaust gas via the fuel addition device during a no-load deceleration operation of the internal combustion engine, and executes the deceleration DPF regeneration process until the deposition amount becomes equal to or less than a regeneration end threshold during the no-load deceleration operation;
a filter bed temperature determination device that determines whether or not the bed temperature of the particulate matter removal filter acquired through the filter bed temperature acquisition device has reached a filter activation temperature at which the particulate matter is oxidized after fuel is added to the exhaust gas through the fuel addition device;
Equipped with
The fuel addition control device, during the execution of the deceleration DPF regeneration process,
when it is determined via the filter bed temperature determination device that the bed temperature of the particulate matter removal filter has not reached a filter activation temperature at which the particulate matter is oxidized, control is performed so that the fuel addition device adds fuel to the exhaust gas;
when it is determined via the filter bed temperature determination device that the bed temperature of the particulate matter removal filter has reached a filter activation temperature at which the particulate matter is oxidized, control is performed so as to stop the addition of fuel to the exhaust gas by the fuel addition device;
an intake throttle valve arranged in an intake passage of the internal combustion engine to adjust the flow rate of intake air;
The fuel addition control device, during the execution of the deceleration DPF regeneration process,
when the addition of fuel to the exhaust gas by the fuel addition device is stopped, the opening of the intake throttle valve is decreased to reduce the flow rate of the exhaust gas, thereby controlling the bed temperature of the particulate matter removal filter to be maintained at the filter activation temperature;
the internal combustion engine is a diesel engine,
an idle operation determination device that determines whether the internal combustion engine has transitioned from the no-load deceleration operation to an idle operation,
The fuel addition control device starts the deceleration DPF regeneration process during the no-load deceleration operation, and then
When it is determined via the idle operation determination device that the internal combustion engine has transitioned from the no-load deceleration operation to the idle operation, the deceleration DPF regeneration process that was started during the no-load deceleration operation is continued without being stopped, and the opening of the intake throttle valve is reduced to reduce the flow rate of exhaust gas , thereby controlling the bed temperature of the particulate matter removal filter to be maintained at the filter activation temperature.
Exhaust gas purification device. The exhaust gas purification device according to claim 1,
an upper limit temperature determination device that determines whether or not the bed temperature of the particulate matter removal filter acquired via the filter bed temperature acquisition device has reached an upper limit temperature of the filter activation temperature;
The fuel addition control device, during the execution of the deceleration DPF regeneration process,
When it is determined via the upper limit temperature determination device that the bed temperature of the particulate matter removal filter has reached the upper limit temperature of the filter activation temperature, the opening degree of the intake throttle valve is increased to control the bed temperature of the particulate matter removal filter to be maintained at the filter activation temperature which is lower than the upper limit temperature.
Exhaust gas purification device. The exhaust gas purification device according to claim 1 or 2,
An oxidation catalyst bed temperature acquisition device for acquiring a bed temperature of the oxidation catalyst;
a catalyst bed temperature determination device that determines whether the bed temperature of the oxidation catalyst acquired via the oxidation catalyst bed temperature acquisition device is a temperature lower than a catalyst activation temperature at which unburned fuel in the exhaust gas is oxidized;
Equipped with
The fuel addition control device, during the execution of the deceleration DPF regeneration process,
When it is determined via the catalyst bed temperature determination device that the bed temperature of the oxidation catalyst is lower than a catalyst activation temperature at which unburned fuel in the exhaust gas is oxidized, control is performed so that the fuel addition device does not add fuel to the exhaust gas.
Exhaust gas purification device.

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