WO2013027546A1

WO2013027546A1 - Exhaust gas purification device

Info

Publication number: WO2013027546A1
Application number: PCT/JP2012/069546
Authority: WO
Inventors: 琢石川; 河合　健二; 松下　智彦
Original assignee: 株式会社豊田自動織機; トヨタ自動車株式会社
Priority date: 2011-08-22
Filing date: 2012-08-01
Publication date: 2013-02-28
Also published as: TW201315891A; JP2013044238A

Abstract

An exhaust gas purification device (1) has an exhaust pipe (7), a filter (4), and a regeneration mechanism. The filter (4) is provided in the exhaust pipe (7) and collects particulates included in exhaust gas. The regeneration mechanism removes particulates accumulated on the filter (4). The regeneration mechanism has an unburned fuel adding device (3), an upstream side exhaust gas temperature detector (5a), a flow detector (2), and a control unit (6). The unburned fuel adding device (3) adds an unburned fuel to exhaust gas at the upstream of the filter (4). The upstream side exhaust gas temperature detector (5a) detects the temperature of the exhaust gas. The flow detector (2) detects an airflow quantity supplied to an engine (10). The control unit (6) determines a lower limit temperature threshold value according to the airflow quantity obtained from the opening degrees of the flow detector (2) and an EGR valve (19). When the temperature obtained from the temperature of the exhaust gas obtained by the upstream side exhaust gas temperature detector (5a) is higher than the lower limit temperature threshold value, the control unit (6) further controls the unburned fuel adding device (3) and adds the unburned fuel to the exhaust gas.

Description

Exhaust gas purification device

The present invention relates to an exhaust gas purification device for purifying exhaust gas of an engine.

The exhaust gas purification device has, for example, an exhaust pipe, a filter that is provided in the exhaust pipe and collects particulate matter contained in the exhaust gas, and a regeneration mechanism that removes particulate matter accumulated on the filter. The regeneration mechanism includes an unburned fuel adder that adds unburned fuel to the exhaust gas, and burns particulate matter deposited on the filter with the unburned fuel. The regeneration mechanism described in Japanese Patent Application Laid-Open No. 2007-321614 has a NOx catalyst provided on the upstream side of the filter and a control unit that estimates the catalyst bed temperature from the exhaust gas temperature. The control unit determines an upper limit flow rate threshold of the air amount according to the estimated catalyst bed temperature, and reduces the amount of unburned fuel to be added when the intake air amount of the engine is larger than the upper limit flow rate threshold. Control the adder. This suppresses that unburned fuel is discharged without being sufficiently oxidized.

The regeneration mechanism described in Japanese Patent Application Laid-Open No. 2005-83252 has a NOx catalyst provided on the upstream side of the filter and a control unit that calculates the total intake amount from the time of engine startup. The control unit regenerates the exhaust gas purification device by adding the unburned fuel by controlling the unburned fuel adder when the total intake amount is larger than the reference value when other regeneration conditions are satisfied, and there is little Do not add unburned fuel. As a result, when the total intake air amount is large, the exhaust gas takes a large amount of heat away from the filter when the particulate matter burns, so that the filter can be prevented from exceeding the high temperature limit. When the total amount of intake air is small, the amount of exhaust gas carrying away heat from the filter is small, so that it is possible to avoid exceeding the high temperature limit by not adding unburned fuel and not regenerating the filter. Thus, it can be suppressed that the purification function of the filter is deteriorated by exceeding the high temperature limit.

There has been a need for an exhaust gas purification device that can regenerate the filter more efficiently.

According to one characteristic, the present invention includes an exhaust pipe, a filter, and a regeneration mechanism. The filter is provided in the exhaust pipe and collects particulate matter contained in the exhaust gas. The regeneration mechanism removes particulate matter deposited on the filter. The regeneration mechanism includes an unburned fuel adder, an exhaust gas temperature detector, an air flow rate detector, and a control unit. The unburned fuel adder adds unburned fuel to the exhaust gas upstream of the filter. The exhaust gas temperature detector detects the temperature of the exhaust gas. The air flow rate detector detects an air flow rate supplied to the engine or an air flow rate discharged from the engine. The control unit determines the lower limit temperature threshold based on the air flow rate obtained from the air flow rate detector. Further, the control unit controls the unburned fuel adder to add the unburned fuel to the exhaust gas when the temperature of the exhaust gas obtained from the exhaust gas temperature detector is higher than the lower limit temperature threshold.

As a result of sincerity research, the present inventor has found that when the wall temperature of the exhaust pipe is lower than a predetermined temperature, for example, when the temperature is lower than the boiling point of the unburned fuel, the unburned fuel may accumulate in the exhaust pipe wall as a liquid. I realized that there was. The inventor has also noted that the higher the flow rate of exhaust gas (air) flowing through the exhaust pipe, the closer the wall temperature of the exhaust pipe becomes to the temperature of the exhaust gas detected by the exhaust gas temperature detector. That is, as the flow rate of the exhaust gas flowing through the exhaust pipe increases, the amount of the exhaust gas that touches the wall of the exhaust pipe increases, and the amount of heat transferred from the exhaust gas to the wall of the exhaust pipe increases. Therefore, as the flow rate of the exhaust gas flowing through the exhaust pipe increases, the wall temperature of the exhaust pipe approaches the temperature of the exhaust gas, and the wall temperature of the exhaust pipe increases. On the other hand, when the flow rate of the exhaust gas is small, the exhaust gas mainly passes through the center of the exhaust pipe, and the amount of the exhaust gas that touches the wall of the exhaust pipe decreases. The difference becomes larger.

According to the present invention, the unburned fuel is added when the condition that the wall temperature of the exhaust pipe reaches a predetermined temperature or more is satisfied. That is, the wall temperature of the exhaust pipe changes not only according to the temperature of the exhaust gas but also according to the flow rate of the exhaust gas, that is, the air flow rate. On the other hand, the control unit determines a lower limit temperature threshold value as a temperature corresponding to the air flow rate, compares the lower limit temperature threshold value with a temperature related to the exhaust gas temperature, and determines whether or not to add unburned fuel. Therefore, unburned fuel can be added when the wall temperature of the exhaust pipe becomes equal to or higher than a predetermined temperature. Moreover, since unburned fuel is added according to an air flow rate, the area | region which can add unburned fuel can be made wider compared with the form which does not judge whether unburned fuel is added irrespective of an air flow rate. Therefore, the regeneration time for burning the particulate matter can be extended, and the filter can be effectively regenerated. Further, unburned fuel can be prevented from accumulating in the exhaust pipe, and waste of fuel consumption is reduced.

It is a block diagram of the engine carrying an exhaust-gas purification apparatus. It is a flow volume-temperature diagram which shows a minimum temperature threshold value. It is a flowchart of filter reproduction | regeneration. It is another flowchart of filter reproduction. It is a figure which shows filter reproduction | regeneration and accumulated PM amount at the time of vehicle travel.

One embodiment of the present invention will be described with reference to FIGS. An engine 10 shown in FIG. 1 is a diesel engine having an exhaust gas purification device 1. The engine 10 includes a plurality of (for example, four) cylinders 11, an intake pipe 8, and an exhaust pipe 7.

As shown in FIG. 1, the intake pipe 8 branches from one inlet and communicates with each cylinder 11. The intake pipe 8 takes in fresh air (air) from the inlet and supplies it to each cylinder 11. A flow rate detector 2 is provided in the intake pipe 8. The flow rate detector 2 is an air flow meter, measures the flow rate of fresh air introduced from the intake pipe 8 into the engine 10, and transmits the air flow rate information to the control unit 6 as a detection signal. An intake throttle valve 16 is provided downstream of the flow rate detector 2. The opening degree of the intake throttle valve 16 is transmitted to the control unit 6 by the throttle valve sensor 17 and controlled by a control signal from the control unit 6 via the throttle valve sensor 17. The intake pipe 8 branches downstream of the intake throttle valve 16 and is connected to each cylinder 11.

Each cylinder 11 has a cylinder 11a and a piston 11b that moves in the cylinder 11a as shown in FIG. A fuel injector 13 is provided in the cylinder 11. The fuel injector 13 is connected to the fuel pump 14 via the common rail 15. The fuel pump 14 is controlled by the control unit 6 to pump fuel from the fuel tank 12 and supply it to the fuel injector 13. The fuel injector 13 is controlled by the control unit 6 to supply fuel to the combustion chamber in the cylinder 11.

The exhaust pipe 7 has an exhaust gas upstream pipe 7a, a first storage pipe 7b, a second storage pipe 7c, and an exhaust gas downstream pipe 7d as shown in FIG. The exhaust gas upstream pipe 7a extends and collects from each cylinder 11 and is connected to the first storage pipe 7b. The first storage pipe 7b has a larger diameter than the exhaust gas upstream pipe 7a and extends from the exhaust gas upstream pipe 7a. The second storage tube 7c has a larger diameter than the first storage tube 7b and extends from the first storage tube 7b. The exhaust gas downstream pipe 7d has a smaller diameter than the second storage pipe 7c and extends from the second storage pipe 7c. An outlet for discharging the exhaust gas to the atmosphere is formed at the end of the exhaust gas downstream pipe 7d.

As shown in FIG. 1, the exhaust gas purification apparatus 1 has a filter 4 and a regeneration mechanism. The filter (DPF: Diesel Particular Filter) 4 is formed of ceramic, stainless steel or the like. The filter 4 is stored in the second storage tube 7c. The filter 4 allows passage of exhaust gas and captures particulate matter (PM) from the exhaust gas passing therethrough.

The regeneration mechanism is a mechanism for continuously regenerating the filter 4 and includes an oxidation catalyst 9 and an unburned fuel adder 3 as shown in FIG. The oxidation catalyst 9 is stored in the first storage pipe 7 b upstream of the filter 4. The oxidation catalyst 9 allows the exhaust gas to pass through and makes the nitrogen oxide (NOx) in the passing exhaust gas more nitrogen dioxide (NO2). The oxidation catalyst 9 generates nitrogen dioxide at a predetermined temperature (for example, about 250 to 300 ° C.). Since nitrogen dioxide has a strong oxidizing action, the particulate matter deposited on the filter 4 is oxidized and removed (combusted) at a relatively low temperature (for example, about 200 ° C.).

The unburned fuel adder 3 is provided in the exhaust gas upstream pipe 7a upstream of the oxidation catalyst 9, as shown in FIG. The unburned fuel adder 3 has a control valve connected to the fuel pump 14 and controlled by the control unit 6. When the control valve of the unburned fuel adder 3 is opened, unburned fuel is added from the fuel pump 14 to the exhaust gas in the exhaust pipe 7. The unburned fuel burns particulate matter deposited on the filter 4 in an atmosphere rich in nitrogen dioxide. Thereby, the filter 4 is continuously regenerated.

The exhaust pipe 7 is provided with an upstream exhaust gas temperature detector 5a, a downstream exhaust gas temperature detector 5b, and an A / F sensor 22, as shown in FIG. The upstream side exhaust gas temperature detector 5a is a temperature sensor and is provided in the first storage pipe 7b. The downstream exhaust gas temperature detector 5b is a temperature sensor and is provided in the second storage pipe 7c.

The upstream exhaust gas temperature detector 5 a detects the gas temperature of the exhaust gas upstream of the oxidation catalyst 9 and transmits the exhaust gas temperature information to the control unit 6 as a detection signal. The downstream exhaust gas temperature detector 5 b detects the gas temperature of the exhaust gas downstream of the filter 4 and transmits the exhaust gas temperature information to the control unit 6 as a detection signal. The A / F sensor 22 is provided in the exhaust gas downstream pipe 7d. The A / F sensor 22 detects the air-fuel ratio (the air mass divided by the fuel mass) and transmits the air-fuel ratio information to the control unit 6 as a detection signal.

The engine 10 is provided with an EGR (exhaust gas recirculation) system as shown in FIG. The EGR system has an EGR pipe 18 and an EGR valve 19. The EGR pipe 18 communicates the exhaust pipe 7 and the intake pipe 8 and returns a part of the exhaust gas discharged to the exhaust pipe 7 to the intake pipe 8. The EGR valve 19 is controlled by the control unit 6 to adjust the opening, and adjusts the gas flow rate circulated by the EGR pipe 18. The control unit 6 detects the air flow rate based on the opening amounts of the flow rate detector 2 and the EGR valve 19.

The control unit (ECU) 6 has a ROM for storing programs and data, a CPU for performing various processes, a RAM for storing processing results of the CPU, and an input / output port for exchanging information with the outside. A rotational speed detector 20, an accelerator sensor 21, a throttle valve sensor 17, and the like are connected to the input port.

Rotational speed detector 20 has a position sensor that is provided in the vicinity of the crankshaft and detects the rotational position of the crankshaft, and detects the rotational speed of the crankshaft. The rotational speed detector 20 transmits the rotational speed information of the crankshaft to the control unit 6 as a detection signal. The accelerator sensor 21 is provided in the vicinity of the accelerator pedal and detects the amount by which the accelerator pedal is depressed. The accelerator sensor 21 transmits accelerator pedal information corresponding to the amount of movement of the accelerator pedal to the control unit 6 as a detection signal.

The control unit 6 receives a signal from each device connected to the input port, and based on the received signal, the throttle valve sensor 17, the fuel injector 13, the fuel pump 14, and the unburned fuel adder connected to the output port. 3. Control the EGR valve 19 and the like.

The ROM of the control unit 6 stores a lower limit temperature threshold map used when executing filter regeneration. The lower limit temperature threshold map is used for acquiring the lower limit temperature threshold used by the control unit 6 when determining whether or not unburned fuel is added to the exhaust gas. The lower limit temperature threshold is a temperature at which the unburned fuel can be prevented from becoming liquid and collecting in the exhaust pipe 7 when the exhaust gas contacts the wall of the exhaust pipe 7.

The wall temperature of the exhaust pipe 7 depends on the exhaust gas temperature and the exhaust gas flow rate. The wall temperature of the exhaust pipe 7 and the temperature of the exhaust gas usually have a difference, and the difference differs depending on the exhaust gas flow rate (air flow rate). That is, when the flow rate of the exhaust gas is small, the amount of the exhaust gas that contacts the wall of the exhaust pipe 7 is small, and the amount of energy for heat exchange is small. Therefore, the difference between the wall temperature of the exhaust pipe 7 and the temperature of the exhaust gas is large, and the wall temperature of the exhaust pipe 7 is lowered. On the other hand, when the flow rate of the exhaust gas is large, the amount of exhaust gas coming into contact with the wall of the exhaust pipe 7 is large, and the amount of energy for heat exchange is large. Therefore, the difference between the wall temperature of the exhaust pipe 7 and the temperature of the exhaust gas is reduced, and the wall temperature of the exhaust pipe 7 is increased.

In order to increase the wall temperature of the exhaust pipe 7 to a predetermined level or higher, the exhaust gas temperature may be relatively low when the exhaust gas flow rate (air flow rate) is large. On the other hand, when the flow rate of the exhaust gas is small, the temperature of the exhaust gas needs to be relatively high. As shown in FIG. 2, in order to set the wall temperature of the exhaust pipe 7 to the temperature line 26 or higher, it is necessary to set the temperature of the exhaust gas to a region above the exhaust gas threshold temperature line 24 (PM regeneration addition possible region 25). There is.

As shown in FIG. 2, the exhaust gas threshold temperature line 24 has a wider area where PM regeneration can be added as the air flow rate increases. In the PM regeneration addition possible region 25 on the upper side of the exhaust gas threshold temperature line 24, when unburned fuel is added, the fuel does not accumulate in the exhaust pipe 7, or the amount that accumulates is very small. On the other hand, in the lower region of the exhaust gas threshold temperature line 24, when unburned fuel is added to the exhaust gas, the unburned fuel tends to accumulate in the exhaust pipe 7.

The lower limit temperature threshold map is a map corresponding to FIG. The control unit 6 determines the exhaust gas threshold temperature, which is the lower limit temperature threshold, from the air flow rate using the lower limit temperature threshold map. When the exhaust gas temperature is higher than the exhaust gas threshold temperature, that is, in the PM regeneration addition possible region 25 shown in FIG. 2, the control unit 6 controls the unburned fuel adder 3 to add the unburned fuel to the exhaust gas. When the exhaust gas temperature is lower than the exhaust gas threshold temperature, the unburned fuel adder 3 is controlled so that the unburned fuel is not added to the exhaust gas. Thus, the unburned fuel can be added to the exhaust gas in a temperature range that does not accumulate in the exhaust pipe 7 and in a wide range. As a result, the accumulation of unburned fuel in the exhaust pipe 7 can be suppressed, and the generation of white smoke that can be generated when the accumulated unburned fuel is ejected into the atmosphere can be suppressed.

The process for regenerating the filter 4 will be described with reference to FIG. First, when it is determined that the filter needs to be regenerated based on the output of a differential pressure sensor (not shown) that measures the differential pressure across the filter 4, the control unit 6 starts the process of regenerating the filter 4.

The control unit 6 obtains the exhaust gas temperature based on the transmission signal of the upstream side exhaust gas temperature detector 5a (step S1). The control unit 6 obtains the air flow rate based on the transmission signals from the flow rate detector 2 and the EGR valve 19 (step S2). The control unit 6 obtains the exhaust gas temperature threshold from the air flow rate using the lower limit temperature threshold map (step S3). Next, the control unit 6 determines whether or not the temperature of the exhaust gas is higher than an exhaust gas temperature threshold value (step S4).

When the control unit 6 determines in step S4 that the temperature of the exhaust gas is higher than the exhaust gas temperature threshold, the control unit 6 permits the addition of PM regeneration (step S5). Then, the unburned fuel adder 3 is controlled so that the value of the downstream side exhaust gas temperature detector 5b falls within a predetermined range, and unburned fuel is added to the exhaust gas in the exhaust pipe 7 for a certain period (step). S6) Return to step 1.

On the other hand, when the control unit 6 determines that the temperature of the exhaust gas is lower than the exhaust gas temperature threshold in step S4, the control unit 6 prohibits the PM regeneration addition and closes the control valve of the unburned fuel adder 3. . Thereby, unburned fuel is not added to the exhaust gas in the exhaust pipe 7 (step S7). Then, the process returns to step S1.

Steps S1 to S7 are repeated until playback is completed. When the control unit 6 determines that the process of regenerating the filter 4 is completed (PM regeneration end) by the output of the differential pressure sensor as a result of the addition of unburned fuel in step S6, the process proceeds to step S8 and this process is terminated. To do.

The process for regenerating the filter 4 may be the process shown in FIG. 4 instead of FIG. In the process of FIG. 4, when the control unit 6 first determines that the filter needs to be regenerated based on the output of a differential pressure sensor (not shown) that measures the pressure difference across the filter 4, the control unit 6 regenerates the filter 4. Start the process.

The control unit 6 obtains the exhaust gas temperature from the transmission signal of the upstream side exhaust gas temperature detector 5a (step S11). The control unit 6 obtains the air flow rate from the transmission signals of the flow rate detector 2 and the EGR valve 19 (step S12). The control unit 6 estimates the wall temperature of the exhaust pipe 7 from the exhaust gas temperature and the air flow rate (step S13). The wall temperature is determined by using a calculation formula or a map from the exhaust gas temperature and the air flow rate, for example.

Next, the control unit 6 obtains the wall temperature threshold value as the lower limit temperature threshold value using the wall temperature threshold value map (step S14). The wall temperature threshold value map is stored in the ROM of the control unit 6 as a map determined in advance from, for example, the rotational speed detector 20, the accelerator sensor 21, the vehicle speed, and the like. The control unit 6 obtains the wall temperature threshold using the wall temperature threshold map. Next, the control unit 6 determines whether or not the estimated wall temperature of the exhaust pipe 7 is higher than the wall temperature threshold (step S15).

When the control unit 6 determines that the wall temperature of the exhaust pipe 7 estimated in step S15 is higher than the wall temperature threshold, the control unit 6 permits PM regeneration addition (step S16). Then, the unburned fuel adder 3 is controlled to add the unburned fuel to the exhaust gas for a certain period so that the value of the downstream side exhaust gas temperature detector 5b falls within a predetermined range (step S17), and step S11. Return to.

When the control unit 6 determines that the wall temperature of the exhaust pipe 7 estimated in step S15 is lower than the wall temperature threshold, the control unit 6 prohibits PM regeneration addition and closes the control valve of the unburned fuel adder 3. . Thereby, unburned fuel is not added to exhaust gas (step S17). Then, the process returns to step S11.

Steps S11 to S18 are repeated until the reproduction is completed. If the control unit 6 determines that the process of regenerating the filter 4 is completed (PM regeneration end) by the output of the differential pressure sensor as a result of the addition of unburned fuel in step S17, the process proceeds to step S19, and this process is terminated. .

FIG. 5 shows the results of comparison of the regeneration of the filter 4 according to the present embodiment and the regeneration of the filter 4 according to the comparative embodiment. In this embodiment, as shown in FIG. 2, the filter 4 is regenerated by lowering the lower limit temperature threshold as the air flow rate increases. In the comparative mode, the lower limit temperature threshold is not a high temperature as shown by the temperature line 27 in FIG. 2, and even if the air flow rate is small, a relatively high temperature is set so that the amount of unburned fuel collected in the exhaust pipe 7 is small. To make it constant.

FIG. 5 shows a regeneration state when the vehicle is driven with a large air flow rate by the engine 10 and the temperature of the exhaust gas changes. In this embodiment, the regeneration process of the filter 4 is performed in the region 31. On the other hand, in the comparative example, the regeneration process of the filter 4 is performed in the region 32. The particulate matter deposited on the filter 4 decreased in proportion to the regeneration processing time, and decreased according to the line 33 in FIG. 5 in this embodiment, and decreased according to the line 34 in the comparative embodiment. Therefore, this embodiment can finish the regeneration of the particulate matter deposited on the filter 4 earlier than the comparative embodiment.

As described above, the exhaust gas purification apparatus 1 includes the exhaust pipe 7, the filter 4, and the regeneration mechanism as shown in FIG. The filter 4 is provided in the exhaust pipe 7 and collects particulate matter contained in the exhaust gas. The regeneration mechanism removes the particulate matter deposited on the filter 4. The regeneration mechanism includes an unburned fuel adder 3, an exhaust gas temperature detector (upstream exhaust gas temperature detector 5 a), a flow rate detector 2, and a control unit 6. The unburned fuel adder 3 adds unburned fuel to the exhaust gas upstream of the filter 4. The exhaust gas temperature detector detects the temperature of the exhaust gas. The flow rate detector 2 detects the flow rate of air supplied to the engine 10. The control unit 6 determines a lower limit temperature threshold value based on the air flow rate obtained from the opening amounts of the flow rate detector 2 and the EGR valve 19. Further, the control unit 6 controls the unburned fuel adder 3 to add unburned fuel to the exhaust gas when the temperature obtained from the temperature of the exhaust gas obtained from the exhaust gas temperature detector is higher than the lower limit temperature threshold. .

When the wall temperature of the exhaust pipe 7 is lower than a predetermined temperature, for example, when the temperature of the exhaust pipe 7 is lower than the boiling point of the unburned fuel, the inventor may store the unburned fuel in a liquid state on the wall of the exhaust pipe 7. Noticed. The inventor has also noted that the wall temperature of the exhaust pipe 7 approaches the temperature of the exhaust gas as the flow rate of the exhaust gas (air) flowing through the exhaust pipe 7 increases. That is, as the flow rate of the exhaust gas flowing through the exhaust pipe 7 increases, the amount of exhaust gas that touches the wall of the exhaust pipe 7 increases, and the amount of heat transferred from the exhaust gas to the wall of the exhaust pipe 7 increases. Therefore, as the flow rate of the exhaust gas flowing through the exhaust pipe 7 increases, the wall temperature of the exhaust pipe 7 approaches the temperature of the exhaust gas, and the wall temperature of the exhaust pipe 7 increases. On the other hand, when the flow rate of the exhaust gas is small, the exhaust gas mainly passes through the central portion of the exhaust pipe 7 and the amount of the exhaust gas that touches the wall of the exhaust pipe 7 decreases, so the wall temperature of the exhaust pipe 7 and the exhaust gas The difference from the temperature increases.

According to this embodiment, the unburned fuel is added when the condition that the wall temperature of the exhaust pipe 7 is equal to or higher than a predetermined value is satisfied. That is, the wall temperature of the exhaust pipe 7 changes not only according to the temperature of the exhaust gas but also according to the flow rate of the exhaust gas, that is, the air flow rate. On the other hand, the control unit 6 determines a lower limit temperature threshold value as a temperature corresponding to the air flow rate, compares the lower limit temperature threshold value with a temperature related to the exhaust gas temperature, and determines whether or not to add unburned fuel. . Therefore, unburned fuel can be added when the wall temperature of the exhaust pipe 7 becomes a predetermined temperature or higher. Moreover, since unburned fuel is added according to an air flow rate, the area | region which can add unburned fuel can be made wider compared with the form which does not judge whether unburned fuel is added irrespective of an air flow rate. Therefore, the time for burning the particulate matter can be extended, and the filter 4 can be effectively regenerated. Further, unburned fuel can be prevented from accumulating in the exhaust pipe 7, and waste of fuel consumption can be reduced by terminating regeneration earlier.

The regeneration of the filter 4 of this embodiment is performed in consideration of the wall temperature of the exhaust pipe 7 in order to avoid unburned fuel from accumulating in the exhaust pipe 7. However, the filter 4 is regenerated using the temperature of the exhaust gas without directly detecting the wall temperature of the exhaust pipe 7. Therefore, without using a sensor that is not easily mounted on the wall of the exhaust pipe 7, regeneration can be performed in consideration of the wall temperature of the exhaust pipe 7 using the temperature of the exhaust gas.

The control unit 6 has a control to decrease the lower limit temperature threshold as the air flow rate increases. Therefore, unburned fuel can be added corresponding to the wall temperature of the exhaust pipe 7. That is, the wall temperature of the exhaust pipe 7 becomes closer to the temperature of the exhaust gas as the air flow rate increases. Conversely, the exhaust gas temperature or the like necessary for setting the wall temperature of the exhaust pipe 7 to be equal to or higher than a predetermined temperature decreases as the air flow rate increases. Therefore, unburned fuel can be added in a wide area | region by using a minimum temperature threshold value.

The control unit 6 stores a map for determining the exhaust gas temperature threshold as the lower limit temperature threshold. The control unit 6 adds the unburned fuel to the exhaust gas when the temperature of the exhaust gas obtained from the upstream side exhaust gas temperature detector 5a is higher than the exhaust gas temperature threshold (see FIG. 3). Therefore, the control unit 6 determines whether or not unburned fuel can be added based on the temperature of the exhaust gas.

As shown in FIG. 4, the control unit 6 estimates the wall temperature of the exhaust pipe 7 from the air flow rate obtained from the flow rate detector 2 and the EGR valve 19 and the exhaust gas temperature obtained from the upstream side exhaust gas temperature detector 5a. To do. The control unit 6 determines a wall temperature threshold value as a lower limit temperature threshold value from conditions other than the estimated wall temperature of the exhaust pipe 7 and the air flow rate. When the estimated wall temperature of the exhaust pipe 7 is higher than the wall temperature threshold, the control unit 6 controls the unburned fuel adder 3 to add unburned fuel to the exhaust gas. Therefore, the control unit 6 determines whether or not unburned fuel can be added based on the wall temperature of the exhaust pipe 7.

The flow rate detector 2 uses an air flow meter that detects the flow rate of fresh air supplied to the engine 10. Accordingly, the air flow rate is directly measured by an air flow meter.

As shown in FIG. 1, the exhaust pipe 7 has a portion having a different diameter downstream of the unburned fuel adder 3. For example, the exhaust gas upstream pipe 7a, the first storage pipe 7b, the second storage pipe 7c, and the exhaust gas downstream pipe 7d have mutually different diameters. In the portions having different diameters, a portion where the flow of the exhaust gas is slow tends to occur, and there is a high possibility that the unburned fuel will accumulate as a liquid in the portion where the flow is slow. On the other hand, in this embodiment, the unburned fuel is added in consideration of the wall temperature of the exhaust pipe 7 so that the unburned fuel does not accumulate as a liquid.

Although the embodiments of the present invention have been described with reference to the above structure, it will be apparent to those skilled in the art that many substitutions, improvements, and changes can be made without departing from the object of the present invention. Accordingly, aspects of the invention may include all alterations, modifications, and changes that do not depart from the spirit and scope of the appended claims. For example, the form of the present invention is not limited to the special structure, and can be modified as follows.

The exhaust gas purification device 1 may have an air flow meter that detects the flow rate of air supplied to the engine as the flow rate detector 2 as in the above embodiment. Instead of this, the exhaust gas purification apparatus 1 may have an air flow meter that detects the flow rate of air discharged from the engine upstream of the unburned fuel adder 3.

The exhaust gas purifying apparatus 1 may use a temperature sensor and a supercharging pressure sensor instead of the flow rate detector 2 and the EGR valve 19 that detect the air flow rate. The temperature sensor is provided upstream of the cylinder 11 and detects the temperature of the intake air. The supercharging pressure sensor is provided upstream of the cylinder 11 and detects the pressure upstream of the cylinder 11 pressurized by a supercharger (not shown). The temperature sensor and the supercharging pressure sensor transmit detection information to the control unit 6 as a detection signal. The control unit 6 calculates the air flow rate from the pressure, the temperature, and the engine speed. The engine speed is obtained from the rotational speed from the rotational speed detector 20.

The exhaust gas purification device 1 may use an A / F sensor 22 as the flow rate detector 2 that detects the air flow rate. That is, the A / F sensor 22 obtains the air-fuel ratio. A fuel injection amount injected into the cylinder 11 by the fuel injector 13 is obtained. The control unit 6 may calculate the air flow rate from the air-fuel ratio and the fuel injection amount.

The unburned fuel adder 3 may add unburned fuel into the exhaust gas of the exhaust pipe 7 as shown in FIG. Instead, the unburned fuel adder 3 may post-inject unburned fuel into the cylinder 11 after the combustion stroke.

The exhaust gas temperature detector (upstream exhaust gas temperature detector 5a) may be provided on the second storage pipe 7c of the exhaust pipe 7 or on the upstream side of the filter 4 as shown in FIG. Instead, an exhaust gas temperature detector may be provided in another place of the exhaust pipe 7.

The control unit 6 may perform the following control in addition to the above control. That is, the control unit 6 determines whether or not the heat removal due to the exhaust gas is greater than the temperature rise of the filter 4 due to the addition of unburned fuel. For example, the control unit 6 makes the determination from the detection value of the downstream side exhaust gas temperature detector 5b. When it is determined that heat removal is large, the control unit 6 stops adding unburned fuel.

The regeneration mechanism of the exhaust gas purification device 1 may burn the particulate matter deposited on the filter 4 in an atmosphere rich in nitrogen dioxide or burn in an oxygen atmosphere.

Claims

An exhaust gas purification device for an engine,
An exhaust pipe, a filter provided in the exhaust pipe for collecting particulate matter contained in the exhaust gas, and a regeneration mechanism for removing the particulate matter deposited on the filter,
The regeneration mechanism includes an unburned fuel adder for adding unburned fuel to the exhaust gas upstream of the filter, an exhaust gas temperature detector for detecting the temperature of the exhaust gas, and an air flow rate supplied to the engine Or an air flow detector for detecting an air flow discharged from the engine, and a lower limit temperature threshold value determined based on the air flow obtained from the air flow detector and the exhaust obtained from the exhaust gas temperature detector An exhaust gas purification apparatus comprising: a control unit that controls the unburned fuel adder to add the unburned fuel to the exhaust gas when a gas temperature is higher than the lower limit temperature threshold.
The exhaust gas purification apparatus according to claim 1, further comprising an oxidation catalyst disposed between the unburned fuel adder and the filter.
The exhaust gas purification device according to claim 1 or 2,
The exhaust gas purification apparatus, wherein the control unit decreases the lower limit temperature threshold as the air flow rate increases.
The exhaust gas purifying device according to any one of claims 1 to 3,
The control unit stores a map for determining an exhaust gas temperature threshold as the lower limit temperature threshold, and adds the unburned fuel to the exhaust gas when the temperature of the exhaust gas is higher than the exhaust gas temperature threshold. Exhaust gas purifier.
The exhaust gas purifying device according to any one of claims 1 to 3,
The control unit estimates the wall temperature of the exhaust pipe from the air flow rate and the exhaust gas temperature, determines a wall temperature threshold value from a map including conditions other than the estimated wall temperature of the exhaust pipe and the air flow rate, An exhaust gas purification device that adds the unburned fuel to the exhaust gas when the estimated wall temperature of the exhaust pipe is higher than the wall temperature threshold.
The exhaust gas purifying device according to any one of claims 1 to 5,
The air flow detector is supplied to an air flow meter that detects a flow rate of fresh air supplied to the engine, an A / F sensor that detects a ratio of air and fuel contained in the exhaust gas, and a cylinder of the engine. An exhaust gas purification apparatus using one of supercharging pressure sensors for detecting the pressure of air.